Cholangiocyte Biology and Cystic Fibrosis Liver Disease

• ABSTRACT
• CFTR IS A CAMP-ACTIVATED CL^- CHANNEL
• CFTR CONTRIBUTES TO DUCTULAR BILE FORMATION
• CFTR REGULATES OTHER PROTEINS
• LUMENAL FACTORS REGULATE BILIARY SECRETION
• PATHOGENESIS OF CF LIVER DISEASE
• Mucins
• Stellate Cell Activation
• Toxic Bile Acids
• CFTR MUTATIONS
• RISK FACTORS FOR THE DEVELOPMENT OF LIVER DISEASE
• Male Sex
• Meconium Ileus
• Histocompatibility Antigen Type
• Other Liver Diseases
• PREVALENCE OF CF LIVER DISEASE
• CLINICAL FEATURES
• Hepatic Steatosis
• Hepatic Congestion
• Neonatal Cholestasis
• Focal Biliary Cirrhosis
• Multilobular Cirrhosis
• Biliary Tract Disease
• DIAGNOSIS
• Physical Examination
• Biochemical Evaluation
• Ultrasonography
• Scintigraphy
• Upper Intestinal Endoscopy and Endoscopic Retrograde Cholangiography
• Liver Biopsy
• Potential Biochemical Markers of CF Liver Disease
• TREATMENT
• Ursodeoxycholic Acid
• Taurine
• Nutrition
• Management of Complications of Cirrhosis
• Liver Transplantation
• FUTURE THERAPIES
• ACKNOWLEDGMENTS
• ABBREVIATIONS
• WEBSITES
• REFERENCES

ABSTRACT

Cystic fibrosis (CF) is one of the most common inherited diseases in the white population. The disease results from mutations in the gene for the cystic fibrosis transmembrane conductance regulator (CFTR). How this gene defect leads to the clinical manifestations of the disease, however, is not entirely clear. CFTR functions as a Cl^- channel in the apical membrane of most secretory epithelia, including biliary epithelial cells, or cholangiocytes. In cholangiocytes, CFTR appears to be an important determinant of biliary secretion and bile flow. Additionally, recent evidence suggests that CFTR regulates other membrane transporters, channels, and proteins. Improving life expectancy has led to an increasing recognition of hepatobiliary complications from CF. The true prevalence of CF liver disease is unknown, but may affect up to 17-25% of CF patients. Clinical manifestations include hepatic steatosis, neonatal cholestasis, focal nodular cirrhosis, multilobular cirrhosis, and biliary tract complications. Why only a subset of CF patients develops severe liver disease and others with the same genotype do not is one of the many scientific curiosities of this disease. This review focuses on the function of CFTR in cholangiocytes with emphasis on ductular bile formation as well as the clinical consequences of abnormal CFTR, namely CF-associated liver disease. Data on the pathogenesis, prevalence, clinical course, and treatment of CF liver disease will be reviewed.

Cystic fibrosis (CF) is an autosomal-recessive disorder characterized by epithelial electrolyte transport abnormalities, elevated sweat chloride concentrations, and, in a majority of patients, pancreatic insufficiency and chronic lung disease. It is the most common potentially fatal genetic disorder in the white population, affecting 1 in 2,400-3,500 live births.[1] [2] This corresponds to a carrier frequency of ∼5% in the white population (CF Mutation Database). This high carrier frequency in a lethal genetic disease suggests the possibility of a survival advantage for heterozygotes. In fact, it has been suggested that the absent or unresponsive Cl^- channel associated with CFTR mutations may have protected infants during epidemics of cholera, which causes secretory diarrhea through toxin-mediated, cyclic adenosine monophosphate (cAMP)-dependent activation of Cl^- channels. The cftr -/- mouse has been shown to be resistant to the effects of cholera infection, providing some evidence for this theory.[3]

Although involvement of the liver and biliary tract has been recognized as a complication of CF since Anderson's initial description in 1938,[4] the clinical significance of hepatobiliary disease in CF has not been well characterized. Recently, with improved life expectancy, which now exceeds 30 years in the majority of patients,[5] CF associated hepatobiliary disease is being recognized and characterized more thoroughly. In fact, liver disease is now one of the major causes of death in CF.[6] Clinical identification of CF-associated liver disease has been difficult because, although it is progressive, liver involvement is often asymptomatic until the appearance of end-stage complications. Thus, early diagnosis and therapeutic intervention has not been possible. In recent years, advances in our understanding of the function of CFTR in bile duct epithelia have provided a stronger scientific basis for the pathogenesis of the disease, leading to insights concerning potentially novel therapeutic approaches.

CFTR IS A CAMP-ACTIVATED CL^- CHANNEL

Although CF was first described by Anderson in 1938,[4] and DiSant'Agnese described the abnormal sweat electrolytes (that still serve as the basis for diagnosis of the disease) in 1958[7] it was the discovery of the CF gene in 1989 by Riordan and colleagues[8] that permitted critical breakthroughs in the understanding of CF pathogenesis. The gene, located on the long arm of chromosome 7, contains 250,000 base pairs with 27 exons and encodes a polypeptide product of 1,480 amino acids known as the cystic fibrosis transmembrane conductance regulator (CFTR). The protein product of the CF gene belongs to a family of transmembrane proteins known as adenosine triphosphate (ATP)-binding cassette (ABC) proteins, which all contain transmembrane sequences and hydrolize ATP for activation. CFTR contains two domains, capable of spanning the membrane six times, separated by regulatory cytoplasmic domains consisting of two consensus nucleotide binding folds (NBF) with an intervening segment rich in phosphorylation sites assumed to be a regulatory domain. It is now well established that CFTR functions as a cAMP-dependent chloride channel in the apical membrane of secretory epithelia. CFTR-associated Cl^- channels have a small unitary conductance of 3-8 picosiemens and a linear current-voltage relationship.[9] [10] Under normal conditions, cAMP-dependent protein kinase A (PKA) phosphorylates CFTR, causing channel opening and efflux of Cl^- ions. In human liver, CFTR is expressed on the apical membrane of bile duct cells (cholangiocytes) and gallbladder epithelia, but is not expressed in hepatocytes or other cells of the liver.[11] Additionally, secretin, a potent stimulator of biliary secretion, activates a Cl^- conductance with electrophysiologic properties similar to those of CFTR.[12] These findings suggest an important role of CFTR in ductular fluid secretion and bile formation.

CFTR CONTRIBUTES TO DUCTULAR BILE FORMATION

Bile formation is initiated at the hepatocyte canalicular membrane through the transport of bile acids, other organic and inorganic solutes, electrolytes, and water. Bile leaving the canalicular space enters an extensive network of intrahepatic ducts. Cholangiocytes make an important contribution to the volume and composition of bile through absorption and secretion of fluid and electrolytes. In fact, ductular secretion may account for ∼40% of bile flow in humans.[13] Studies in isolated cholangiocytes have recently elucidated the basic mechanisms involved in constitutive and stimulated Cl^- and HCO₃ ^- transport in biliary epithelium (Fig. [1]).[14] [15] Basolateral Cl^- uptake involves a bumetanide-sensitive Na⁺/K⁺/2Cl^- cotransporter, whereas apical Cl^- efflux is mainly mediated by a cAMP-activated Cl^- channel that is encoded by CFTR.[16] Stimulation of cholangiocyte basolateral receptors by the hormone secretin results in increased intracellular concentration of cAMP,[17] opening of Cl^- channels,[12] and stimulation of Cl^-/ HCO₃ ^- exchange.[14] [18] Bile duct secretion is associated with a net flux of Cl^- and HCO₃ ^- into the lumen and generation of a lumen negative potential, consistent with a role for electrogenic Cl^- transport.[19] [20] Additionally, a small conductance K⁺ channel has been identified in cholangiocytes and may play a role in maintaining a membrane potential difference necessary for transepithelial secretion.[21] The findings that (a) CFTR is localized to the apical membrane of cholangiocytes and (b) secretin-activated Cl^- channels have properties analogous to CFTR support a working model that postulates an important role for CFTR Cl^- channels in the regulation of ductular secretion.[11] [18] According to this model, opening of Cl^- channels in the apical membrane leads to efflux of Cl^- and generation of a lumen-negative potential, which favors movement of Na⁺ into the bile duct lumen through a paracellular pathway and water via water-selective channels known as aquaporins.[22] [23] [24] The change in apical Cl^- gradient facilitates HCO₃ ^- extrusion via Cl^-/HCO₃ ^- exchange, providing biliary alkalinization. Thus, bile undergoes increasing dilution and alkalinization as it traverses the bile duct.

Alternatively, HCO₃ ^- could enter the lumen through a conductive pathway or through Cl^- channels.[25] [26] In fact, there is some evidence in other epithelia that HCO₃ ^- transport may be independent of transmembrane Cl^- gradients. In pancreatic duct cells, for instance, which also express apical CFTR, secretin-induced HCO₃ ^- secretion may occur even in the absence of luminal Cl^-.[27] In this epithelia, depolarization of the cell membrane through cAMP-dependent Cl^- secretion facilitates entry of HCO₃ ^- through basolateral membrane Na⁺/HCO₃ ^- electrogenically driven cotransporters, and apical secretion of HCO₃ ^- occurs through a conductive pathway, independent of the Cl^-/HCO₃ ^- exchanger.[28] [29] Additionally, there is recent evidence that in CF epithelia with some retained Cl^- secretion (associated with minor CFTR mutations), HCO₃ ^- transport is still significantly impaired, suggesting that HCO₃ ^- transport may be a primary problem, not necessarily secondary to abnormal Cl^- efflux, in CF.[30] The role of CFTR in the regulation of Cl^- and HCO₃ ^- transport and as a mediator of biliary secretion is an ongoing subject of investigation.

In addition to CFTR, cholangiocytes express several other Cl^- channels, including a G-protein- activated Cl^- channel,[31] a Ca²⁺/calmodulin-dependent Cl^- channel,[16] [32] and an osmosensitive Cl^- channel.[33] [34] However, their regulation and contribution to biliary secretion is largely unknown at the present time. It is attractive to speculate however, that these alternate Cl^- conductances may partly compensate for the CF secretory defect in the liver and may serve to suggest alternate strategies to bypass the Cl^- secretory defect associated with CF. In fact, in the cftr -/- mouse model, increased expression of Ca²⁺-activated Cl^- channels in tracheal epithelial cells is associated with mild pulmonary disease.[35] Exploring the pathways involved in the regulation of these alternate Cl^- channels therefore has become an exciting area of investigation.

CFTR REGULATES OTHER PROTEINS

There is a wealth of recent evidence to suggest that, in addition to its role as a Cl^- channel, CFTR, as the name implies, also functions as a regulator of other membrane proteins and channels. This was first suggested by the observation that, in addition to abnormal Cl^- and HCO₃ ^- transport, CF tissues display other transport abnormalities, including increased Na⁺ absorption, increased Ca²⁺-activated Cl^- secretion, and defective regulation of outwardly rectified Cl^- channels.[36] [37] [38] Expression of wild-type CFTR not only corrects the cAMP-dependent Cl^- conductance, but leads to normalization of Na⁺ channel activity and outwardly rectified Cl^- channel regulation.[39] [40] [41] These and other observations suggest that CFTR is multifunctional, serving as both an ion channel and as a channel regulatory protein. Additionally, CFTR has been shown to regulate glutathione transport,[42] [43] mucin secretion,[44] water transport through water-permeable channels,[22] [45] [46] and ATP permeability[47] in other secretory epithelia. How CFTR regulates these other membrane proteins is presently unknown, but the finding that CFTR contains specific sequences that bind integral membrane proteins and cytoskeletal elements raises the possibility of ``membrane regulatory complexes'' in the apical domain of epithelial cells. Recent studies demonstrate that the carboxy tail of CFTR binds to proteins that possess binding modules referred to as PDZ (for PSD-95, discs large, ZO-1) domains. These domains promote homotypic or heterotypic protein-protein interactions. Such interactions can facilitate the clustering of ion channels within microdomains at the cell surface. Several PDZ domain-containing proteins have been shown to bind to CFTR, including Ezrin-radixin-moesin (ERM)-binding phosphoprotein 50 (EBP50) and NHE3 kinase A regulatory protein (E3KARP).[48] Both of these proteins are expressed in cholangiocytes and may represent a means of linking CFTR to other integral membrane proteins and, hence, may be important regulators of ductular bile formation.[49] In fact, overexpression of the PDZ-1 domain of EBP50 decreases endogenous cAMP Cl^- channel activity in a cholangiocyte cell line, suggesting that this protein-protein interaction has direct regulatory effects on Cl^- secretion.[49] Conceivably, CFTR, through PDZ domain interactions, could form a macromolecular signaling complex and engage in interactions with a wide variety of transporters and signaling molecules to regulate cellular events. Understanding the nature of these interactions is an area for future investigation and may serve as the basis for novel therapies for CF.

LUMENAL FACTORS REGULATE BILIARY SECRETION

As previously discussed, cholangiocyte secretion is regulated in part by agonists, such as secretin, acting via basolateral receptors. Recently, however, constituents of bile, such as bile acids and ATP, have been shown to modulate cholangiocyte secretion in isolated cells in culture.[33] [50] [51] This exciting finding suggests that factors released by hepatocytes into bile may serve as signals coordinating the separate hepatic and biliary components of secretion, a process termed hepatobiliary coupling.

Cholangiocytes express transporters for bile acids on the apical membrane (Fig. [1]).[52] Recent evidence in the rat cholangiocytes demonstrates the presence of an apical Na⁺-dependent bile acid transporter (ASBT) similar to the ileal bile acid transporter and capable of transporting conjugated bile acids.[52] Additionally, bile acid uptake stimulates cholangiocyte secretion in isolated cells,[51] suggesting a mechanism by which lumenal bile acids may modulate ductular secretion. This provides further evidence for the cholehepatic shunt hypothesis proposed by Hofmann et al.,[53] [54] and may help to explain the hypercholeresis, out of proportion to bile salt pool enrichment alone, observed with bile acid therapy.[55] In fact, taurocholate feeding in rats results in cholangiocyte proliferation and increases in secretion.[56]

Recent studies have identified extracellular ATP as an important autocrine/paracrine signal that regulates diverse cellular processes by binding to one or more purinergic receptors in the plasma membrane of target cells. Several lines of evidence provide indirect support for ATP as a signaling molecule involved in hepatobiliary coupling and the regulation of biliary secretion. First, ATP is released by primary human hepatocytes,[57] as well as model liver and biliary cell lines.[58] [59] It is present in mammalian bile in concentrations (>100 nM) sufficient to activate purinergic receptors.[60] Second, receptor binding increases Cl^- efflux rates of isolated cholangiocytes.[33] [50] Third, similar mechanisms have been shown to be operative in airway cells where stimulation of apical purinergic receptors elicit potent secretory responses.[61] Such receptors are present in cholangiocytes,[62] and receptor binding results in increases in intracellular Ca²⁺ concentration and Cl^- secretion (Fig. [1]).[33] [50] Although both hepatocytes and cholangiocytes are capable of the regulated release of ATP, the molecular identity of the ATP channel/transporter is presently unknown. There has been evidence both for[63] and against[64] CFTR as an ATP-permeable channel. Recent studies suggest that CFTR may regulate, but is distinct from, an ATP-permeable pathway.[47] [65] In fact, in CFTR -/- cells, extracellular ATP has been shown to elicit large increases in Cl^- secretion, suggesting that purinergic signaling activates non-CFTR Cl^- channels and may be a potential site for stimulation of secretion in order to bypass the Cl^- secretory defect associated with CF.[61] [66] [67] [68] These findings have led to recent therapeutic trials of purinergic analogues in patients with CF. Aerosolized uridine 5' triphosphate (UTP) has been shown to increase mucociliary clearance in patients with CF.[69] The role of purinergic signaling in the regulation of normal bile flow, as well as a therapeutic agent in CF, requires further study.

In summary, CFTR is a cAMP-dependent Cl^- channel expressed on the apical membrane of cholangiocytes that contributes to ductular secretion. However, the possible role of other membrane Cl^- channels is yet to be determined. Intriguing studies have established that CFTR, in addition to its role as a Cl^- channel, is in fact a ``transmembrane regulator'' modulating other membrane permeability pathways. Further study of CFTR function and regulation may help to elucidate the mechanisms of cholangiocyte function and bile formation. The remainder of this review will focus on the hepatobiliary effects of abnormal CFTR function, namely, CF-associated liver disease.

PATHOGENESIS OF CF LIVER DISEASE

Studies directly assessing the effects of mutated CFTR in cholangiocytes are lacking, and the pathophysiology underlying the development of CF-associated liver disease is still only speculative. Presumably, CF-associated liver disease is the result of impaired secretory function of the biliary epithelium resulting in thickened, inspissated secretions in the bile ductules, which may cause obstruction and progress to the development of portal fibrosis, bridging, and eventually cirrhosis (Fig. [2]). Multiple factors may contribute to the abnormal viscosity and decreased bile flow, including defective Cl^- and HCO₃ ^- transport, altered Na⁺ reabsorption, impaired mucin secretion, and increased glycine-conjugated bile acids. In a model proposed by Sokol and Durie, bile duct plugging may lead to stellate cell activation, collagen deposition, fibrosis, and ultimately cirrhosis.[70] Altered mucin secretion, stellate cell activation, and accumulation of toxic bile acids have all been proposed as potential factors contributing to liver injury in CF as described below.

Mucins

Abnormalities in mucin secretion may increase bile viscosity in CF patients. Secretion of chondroitin sulfate was shown to be markedly increased in CF biliary epithelium in vitro.[71] In fact, accumulation of eosinophilic material in bile ductules is one of the earliest histologic features found in infants and children with CF.[72] Conversely, secretion of mucins was shown to be increased in gallbladder cells overexpressing normal CFTR,[44] suggesting that CFTR regulates constitutive mucin secretion. This is in contrast to an additional study that did not find any evidence for a link between mucin secretion and CFTR activity in primary mouse gallbladder epithelial cells.[73] The definitive role of mucins in both normal and impaired bile flow, and their potential role in CF liver disease, is yet to be determined.

Stellate Cell Activation

Because progressive fibrosis is a hallmark of CF liver disease, it is reasonable to implicate stellate cell activation as a contributor to the liver lesion in CF. Stellate cell activation and collagen deposition may be stimulated in several ways, as proposed by Sokol and Durie,[70] including, (a) direct cholangiocyte injury[74] with subsequent release of cytokines and growth factors[75]; (b) secondary hepatocyte injury, which also may lead to the release of proinflammatory cytokines, growth factors, and lipid peroxide products; and (c) ongoing inflammation, which leads to recruitment of other cells that generate cytokines responsible for stellate cell recruitment and activation. This process begins focally in the liver near or at the area of the portal triad, and therefore is termed focal biliary cirrhosis. As the fibrogenic process proceeds, bridging fibrosis develops, ultimately leading to multilobular cirrhosis.

Toxic Bile Acids

Retention of hydrophobic bile acids may be responsible for cell membrane injury at the hepatocellular level. Oxidative injury to the liver cell membrane may occur through increased free radical production favored by decreased lipid-soluble antioxidant activity reported in patients with CF.[76] The possible role of hepatic steatosis, so common in the CF liver, in terms of providing increased substrate for lipid peroxidation has not been examined. Both retention of hydrophobic bile acids and the presence of increased hepatocellular lipid have been associated with altered mitochondrial respiration and stimulation of the mitochondrial membrane permeability transition that is a key process in cellular apoptosis and necrosis.[77] Antioxidants counteract these effects on the mitochondrial membrane[77] and suggest an important role for oxidative stress in bile acid-induced hepatocyte injury[78] and steatohepatitis.[79]

CFTR MUTATIONS

There are now over 998 recognized mutations of the CFTR gene (CF Mutation Database). The most common mutation, ΔF508, results from a base pair deletion in exon 10, causing a deletion of phenylalanine at position 508 in the first NBF region on the CFTR protein, resulting in defective trafficking of CFTR to the apical membrane.[8] The absence of functional CFTR protein on the apical membrane results in deficient cAMP-induced Cl^- channel activity. This mutation accounts for ∼66% of the chromosome mutations in CF patients worldwide (CF Mutation Database); it is most common in patients of northern European (70-80%) or southern European (50%) background. The various CFTR gene mutations are classified into five classes according to their effect on the fate or function of the CFTR protein (Fig. [3]).[80] Class I mutations cause impairment of CFTR messenger RNA production; class II mutations result in defective processing or trafficking of CFTR protein to the apical membrane (the ΔF508 mutation is of this type); class III mutations are associated with defective regulation of CFTR, which locates correctly to the apical membrane, but does not respond to cAMP agonists; class IV mutations demonstrate some residual Cl^- conductance, but at a significantly decreased amplitude; and class V mutations lead to abnormal splicing of CFTR with a partial reduction in the number of functioning Cl^- channels. Recent data from the European Epidemiologic Registry of Cystic Fibrosis (ERCF), which performed genotype analysis in 8,963 patients with CF, provide useful information regarding the frequency of these mutations in the European population.[81] Although a significant proportion of mutations were unknown, the known mutations identified were classified according to type. Class II mutation (severe mutation) homozygotes accounted for 56% of all mutations and comprised the largest group. Class II/III mutation compound heterozygotes comprised 2.9% of the genotypes, and class IV/any (mild mutations) accounted for 2% of the mutations. Class I, III, and IV homozygotes and class IV/any heterozygotes each accounted for less than 1% of the mutations reported. Patients with pancreatic insufficiency and more severe disease generally have two severe mutations. In contrast, patients with preserved pancreatic function, who generally have milder disease in general, carry at least one mild mutation.

Although specific gene mutations (genotype) have been associated with the severity of pancreatic involvement, there is no correlation between specific genotype and clinically detectable liver disease in patients with CF.[82] [83] [84] However, there appears to be an overall lower frequency of liver disease in pancreatic sufficient patients with CF.[85] Because all patients with CF have abnormal CFTR in the biliary tree, it is unclear why significant liver disease does not develop in all patients. Because patients with CF and identical CFTR mutations exhibit variable onset and severity of liver disease, it is postulated that there are other modifying genetic or environmental factors that determine whether clinically significant hepatobiliary involvement will occur.

RISK FACTORS FOR THE DEVELOPMENT OF LIVER DISEASE

Male Sex

A preponderance of male patients has been described in all age groups of patients with CF and liver disease.[6] [86] [87] However, it is unclear if this is a true risk factor for the development of liver disease or represents an over-representation of males given the reported survival advantage.

Meconium Ileus

Several studies have suggested that a history of meconium ileus as an infant is a risk factor for the subsequent development of liver disease. Maurage et al.[88] reported this risk factor to be present in 50% of patients with CF-associated cirrhosis and 14% of those without. Colombo et al.[82] described a frequency of meconium ileus of 35% in patients with liver disease, but only 12% in patients without liver disease. In a recent review they reported an approximate 6-fold increase in the development of liver disease in those infants with a history of meconium ileus.[82] [89] However, other studies have failed to find such an association[90] and the majority of patients with CF and significant liver disease do not have a history of meconium ileus.

Histocompatibility Antigen Type

Several studies have shown an association between certain histocompatibility antigens (HLA) and susceptibility for liver disease in CF. A higher frequency of HLA-DQw6 has been reported in British CF patients with liver disease as compared to those without liver disease.[91] [92] Duthie et al. found that the HLA haplotype B7-DR15-DQ6 was associated with an increased risk of chronic liver disease in male patients with CF.[93] These findings suggest a possible immune contribution to the pathogenesis of hepatobiliary injury in CF; alternatively, another susceptibility gene linked with specific haplotypes lies at or near the HLA-DQ locus.

Other Liver Diseases

Further investigation into the possible association of modifier genes in the development of CF liver disease has led to the investigation of other genetic diseases known to cause liver disease. Perhaps patients with CF who develop significant liver disease are heterozygote carriers of another chromosomal mutation for common genetic liver diseases that render the liver more susceptible to injury in the presence of abnormal CFTR function. Hemochromatosis is one of the most common genetic liver diseases in the white population. However, in one preliminary study, no increased frequency of heterozygote carriers for this genetic disease could be found in patients with CF liver disease or meconium ileus.[94] Another commonly inherited genetic disease known to cause liver disease in a subset of patients is α₁-antitrypsin deficiency. Preliminary data suggest an increase in frequency of heterozygote carriers for the α1-antitrypsin mutation allele among CF patients with liver disease compared with those without (personal communication, Dr. Kenneth Friedman, University of North Carolina, Chapel Hill, NC). Larger studies in other populations are required for validation of this interesting observation. Other genes involved in bile acid or phospholipid transport (e.g., BSEP, MDR3, FIC-1, cMOAT) will need to be examined in this regard.

PREVALENCE OF CF LIVER DISEASE

Prevalence and incidence figures for liver disease in CF patients are not clearly defined. This is primarily due to the fact that there are no sensitive and specific markers for the diagnosis of CF-associated liver disease. Additionally, defining clinically significant liver disease in CF patients is problematic, because many patients, even with cirrhosis, are well compensated and asymptomatic. No universally accepted definition of ``CF liver disease'' has been established, so diagnostic criteria vary markedly between studies. The literature contains three sources of prevalence data: (a) the CF Foundation National CF registry from U.S. CF centers, (b) retrospective reviews from single-center experience, and (c) prospective studies.

Data from the CF Foundation National CF Registry from U.S. centers, which relies on voluntary reporting, reported elevated liver enzymes in 6.4% and liver cirrhosis in 2.3% of the 21,588 CF patients seen in 113 CF centers during 1999.[6] These figures are in sharp contrast with the findings that hepatic disease was the second most common cause of death after pulmonary decompensation, suggesting a significant underestimation of the true prevalence of liver disease.

Retrospective analyses of clinical records report prevalence figures between 4.2%[86] and 7%.[87] These studies have also reported a slight predominance in males. Additionally, clinically apparent liver disease peaked in adolescence, with a subsequent decrease during the third decade of life. This is probably a reflection that those patients with longer longevity probably have milder CFTR mutations. In another retrospective review of 233 patients (>15 years of age) with CF, 24% were found to have hepatomegaly or persistently abnormal liver blood tests.[95] Data obtained from autopsy studies, however, indicate a progressive increase in prevalence with age, from 10% in infants to 72% in adults.[72] [96]

Few prospective studies have documented the prevalence of hepatobiliary involvement in CF. In two prospective studies of children with CF in North America, investigators evaluated changes in concentrations of serum liver enzymes. Sokol et al. studied a series of 99 infants in Colorado, identified by newborn screening for the first 8 years of life, and found that overall, 27% of alkaline phosphatase values and 38% of AST levels were above the upper limit of normal for age.[97] Kovesi et al. evaluated the correlation of CFTR mutations to the prevalence of abnormal AST and alkaline phosphatase levels in 526 patients with CF in Ontario, Canada.[98] Abnormal AST or alkaline phosphatase was present in 46% of patients homozygous for ΔF508 compared with 20% of patients with mild mutations and pancreatic sufficiency. In both studies, most patients had elevations less than 1.5 times the upper limit of normal. Although the absolute frequencies of abnormal liver enzymes differed in these two studies, it is apparent that slight elevations of serum liver enzymes are common in patients with CF.

Lindblad et al. recently reported on a population of 124 CF patients followed over a 15-year period.[99] More than 50% had abnormal liver enzymes during infancy, however the majority of these early elevations subsequently normalized. Approximately 25% of children over 4 years of age had biochemical markers of liver disease during the study period. In about 10% of patients, cirrhosis or advanced fibrosis was confirmed at biopsy. Severe liver disease developed mainly during or before puberty. No specific risk factors for the development of liver disease were identified. These findings are similar to those of Colombo et al., who prospectively evaluated a cohort of 183 CF patients followed over a 3-year period in Milan, Italy.[82] Thirty percent of patients had hepatomegaly, 5.8% had splenomegaly, and 16.9% had abnormal serum liver enzymes. Liver disease (defined as hepatomegaly, persistent elevation of at least two liver enzymes, and abnormal ultrasonographic features of the liver) was present in 17% of patients. In a prospective study of 153 patients with CF (4-19 years of age) in New South Wales, Australia, Gaskin et al. found that 30% of patients had hepatomegaly, 9% had elevated liver enzymes without hepatomegaly, and 13% were judged to have multilobular cirrhosis by clinical, biochemical, and imaging criteria.[100] Although the criteria to define liver disease in these three prospective studies are different, the results are similar. Therefore, the best current estimate for clinically significant liver disease in children with CF is 13-25%. However the presence of hepatomegaly in 30% of patients in these studies suggests that the incidence of significant portal and biliary fibrosis may be higher.

CLINICAL FEATURES

The most common presentation of liver disease in CF is the finding of hepatomegaly on routine physical examination that may or may not be associated with abnormalities of liver biochemistry. This is often asymptomatic, and other signs of chronic liver disease such as jaundice, palmar erythema, and spider hemangiomas are rarely present. Jaundice is generally limited to patients presenting with neonatal cholestasis or in those with end-stage multilobular cirrhosis. Unfortunately, the liver disease in CF may progress silently, only manifesting with complications of end-stage liver disease and portal hypertension. In fact, variceal bleeding may occur in patients with normal or only mild biochemical abnormalities.[91] In a retrospective study, spanning a 26-year period, of 44 children with CF and cirrhosis, esophageal varices developed in 86%, and 50% experienced significant gastrointestinal bleeding.[101] Liver failure occurred in 36% of patients. Distinct hepatic manifestations of CF have been described, including hepatic steatosis, hepatic congestion, neonatal cholestasis, focal biliary cirrhosis, and multilobular cirrhosis (Table [1]).

Hepatic Steatosis

Steatosis, or ``fatty liver,'' is characterized by fat infiltration of hepatic parenchymal cells. Clinically, it is suggested by a large, but soft liver upon palpation. Computed tomography may reveal a liver with fat density. Hepatic steatosis is prominent, seen in 60% of liver biopsy specimens and autopsy reports.[102] Although apparently common in CF, steatosis has not been correlated with outcome, and there are no data to suggest that this lesion progresses to the more serious focal biliary cirrhosis or multilobular cirrhosis. The cause of steatosis is unknown, but has been associated with malnutrition and deficiencies of essential fatty acids, carnitine, and choline. Diabetes and ethanol use have been reported as contributing factors. It also has been suggested that steatosis may result from the effect of circulating cytokines on hepatic fatty acid oxidation or mitochondrial function. In some patients with malnutrition, optimizing nutritional status, correcting trace element and mineral deficiencies, and complying with enzyme replacement therapy programs is associated with resolution of steatosis. Overall, steatosis appears to be a benign condition in CF without any proven relationship to the subsequent development of cirrhosis. However, the current interest in the role of nonalcoholic steatohepatitis as a cause of cirrhosis in adults may change this in the future.

Hepatic Congestion

Although not due to abnormal biliary CFTR function, hepatic congestion may be seen in CF patients secondary to right heart failure in the context of poor cardiopulmonary function. Clinically it is suggested by the presence of hepatomegaly associated with cor pulmonale and dilated hepatic veins on imaging studies. Serum aminotransferases are usually only mildly elevated, but serum bilirubin elevation and mild elevation of prothrombin time may be present. Treatment consists of therapy to optimize cardiopulmonary function and avoid hypoxia.

Neonatal Cholestasis

There are several reports of prolonged neonatal cholestasis in infants with CF.[103] [104] Roy et al. noted that 35% of infants with CF manifested hepatomegaly or cholestasis in the first months of life.[105] This is consistent with findings at autopsy, which revealed histologic evidence of cholestasis in 38% of patients under 3 years of age with CF.[72] However, more recent data indicate that only 2% of CF infants display significant clinical cholestasis, perhaps due to improved care of infants with meconium ileus.[106] Some studies have demonstrated an association between neonatal cholestasis and meconium ileus,[88] but others have not.[86] It is apparent that coexistent factors, including abdominal surgery, parenteral nutrition, and sepsis, may contribute to prolonged cholestasis. The natural history of neonatal cholestasis and ultimate prognosis of infants with this finding is unknown. Although previous studies have suggested an increased risk for the development of cirrhosis in patients with a history of cholestasis, Gaskin et al. demonstrated no apparent difference in the subsequent development of significant liver disease between those with or without a history of neonatal cholestasis.[100] Management first entails the exclusion of other causes of neonatal cholestasis, including biliary atresia and metabolic and infectious liver diseases. Treatment involves optimizing nutritional status (weaning from parenteral nutrition if possible) and choleretic therapy with ursodeoxycholic acid (UDCA), which will be described below.

Focal Biliary Cirrhosis

This lesion, characterized by scattered areas of portal fibrosis, cholestasis, and bile duct proliferation suggestive of bile duct obstruction, is considered pathonogmonic of CF.[107] [108] Often eosinophilic material can be seen plugging and obstructing dilated ductules. Both clinical and autopsy studies indicate an increasing incidence of this lesion with increasing age, and focal biliary cirrhosis may progress into the more severe multilobular cirrhosis with portal hypertension or liver failure.[109] The prevalence of focal biliary cirrhosis can only be estimated by autopsy series, because the lesion is usually clinically silent and may be present with normal serum liver enzymes. The disease was identified after death in 10% of infants who died in the first 3 months of life, in 27% who died after 1 year,[72] and in 72% of adults.[96] As previously discussed, it remains unclear why some patients with focal biliary cirrhosis progress to the more severe multilobular cirrhosis, but the presence of polymorphisms of another unknown modifier gene has been suggested. Treatment of focal biliary cirrhosis is primarily by UDCA therapy, but there are presently no definitive data that this treatment will halt the progression to cirrhosis.

Multilobular Cirrhosis

Multilobular cirrhosis was first described by Craig and di Sant'Agnese.[102] [109] Histologically, there is extensive portal fibrosis, with broad bands of fibrosis extending between portal areas, but often with intervening areas of preserved hepatic parenchymal tissue. Clinically, a firm, hard, and multilobulated liver upon examination suggests the diagnosis. Signs of portal hypertension (splenomegaly, dilated abdominal vasculature, ascites) may or may not be present. A prospective study of CF patients found a prevalence of multilobular cirrhosis of 7%.[87] The majority of patients identified with this lesion were under 14 years of age. However, other prospective studies have suggested prevalence rates as high as 13-17%[82] [100] and an autopsy study of adult patients with CF demonstrated cirrhosis in 20%.[96] Patients with multilobular cirrhosis are at risk from complications from portal hypertension and hepatic synthetic failure, both of which are unpredictable in terms of their onset and progression.[107] Portal hypertension may lead to the development of esophageal or gastric varices presenting with hematemesis, melena, or iron-deficiency anemia. Ascites, splenomegaly, hypersplenism, encephalopathy, fatigue, and coagulopathy occur later in the course as cirrhosis decompensates. Hepatic synthetic failure is a late finding and a primary indication for liver transplantation. Impaired bile flow may enhance fat malabsorption and cause increased diarrhea, weight loss, and fat-soluble vitamin deficiencies.[110] Treatment at this advanced stage of liver disease is primarily supportive and aimed at reducing the risk of complications from portal hypertension and malnutrition.

Biliary Tract Disease

Biliary abnormalities are common in CF. Microgallbladder is present in 20-30% of patients.[105] [111] Although CFTR is found in gallbladder epithelium, it is unclear how defects in this protein result in gallbladder atrophy. Microgallbladder appears to be a benign condition without clinical sequelae. Cholelithiasis and cholecystitis are found in 1-10%[6] [87] [98]; however, symptoms have been reported to occur in less than 4% of cases, with an age-related trend for symptomatic gallbladder disease.[112] Calcium bilirubinate is the main component of identified gallstones[113] and they are insensitive to dissolution by bile acid therapy.[114] Common bile duct stenosis is a rare complication of CF, occurring in less than 1% of patients.[95] Sclerosing cholangitis, has been described in association with CF, but the diagnostic endoscopic retrograde cholangiopancreatography (ERCP) findings may be misleading in the face of inspissated biliary secretions, and the true incidence therefore is unknown. Cholangiocarcinoma has rarely been observed in patients with CF but must be considered in the adult with new onset of biliary obstruction, or worsening jaundice, abdominal pain, or weight loss.[115]

DIAGNOSIS

In the past, liver disease was usually identified due to complications of portal hypertension or end-stage liver failure. Today, asymptomatic hepatomegaly or elevated serum liver enzymes obtained as part of screening tests, are the typical scenarios for suspected liver disease. Persistent hepatomegaly, splenomegaly, a hard liver on palpation, persistently elevated liver enzymes, complications of portal hypertension, or abnormal liver histology all establish the presence of significant liver involvement.

Physical Examination

Physical examination remains the standard for detecting and following the progression of liver disease in CF. Hepatomegaly is the most important finding to suggest the presence of liver disease. Attention should be directed to the liver span, as well as the texture and consistency of the liver edge. The onset of splenomegaly in patients with suspected liver disease should alert the clinician to the possible development of portal hypertension. A thorough examination for other peripheral signs of liver disease (spider nevi, palmar erythema, jaundice, edema) should be performed.

Biochemical Evaluation

Evaluation for liver function and injury should include serum aspartate aminotransferase (AST), alanine aminotransferase (ALT), total and direct bilirubin, alkaline phosphatase, gamma-glutamyl transferase (GGT), total protein, albumin, prothrombin time, blood ammonia, cholesterol, and glucose. Serum liver enzyme analysis should be performed on a yearly basis as recommended by the CF Foundation Hepatobiliary Disease consensus guidelines.[70] It should be noted that none of these tests measures or correlates with the degree of hepatic fibrosis, and patients may have cirrhosis with completely normal serum liver enzymes. Nevertheless, if any of these values is over 1.5 times the upper limit of normal for age, it has been recommended that the test should be repeated at shorter intervals (3-6 months).[70] Because fluctuations in the values of these tests are common in CF, only persistently elevated results should be investigated more completely. Thus, if levels remain elevated for more than 6 months, without another explanation for the elevation, they are indicative of probable clinically significant liver involvement. Tests of hepatic synthetic function should then be obtained. It should be noted that in one series, elevated ALT and GGT had only 52% and 50% sensitivity and 77% and 74% specificity, respectively, as predictors of significant hepatic fibrosis in patients with CF who underwent liver biopsy.[116] In most surveys, 20-30% of patients with CF have elevation of at least one of these liver blood tests at a single point in time. Therefore, these tests should be used to screen for those patients who need a more complete evaluation, rather than to diagnose clinically significant liver disease. Other causes of acute elevation of aminotransferases (infectious hepatitis, drugs, toxins, autoimmune hepatitis, metabolic diseases, gallstones, etc.) should be excluded.

Ultrasonography

Ultrasonography of the liver and biliary tract and hepatic vasculature provides useful information and should be performed in all patients in whom CF liver disease is suspected. Ultrasonography is most helpful in detecting the presence of extrahepatic biliary tract disease such as gallstones, common bile duct stones, and bile duct dilation. Doppler ultrasonography can detect dilatation and flow patterns of hepatic vasculature. Dilated hepatic veins suggest that increased right heart pressure (secondary to pulmonary disease or cor pulmonale) may be contributing to hepatomegaly. Decreased or reversal of portal venous flow suggests the presence of portal hypertension. The test is less useful for the detection and quantification of hepatic fibrosis or cirrhosis because periportal steatosis can appear sonographically similar to focal fibrosis in the liver, both lesions being common in CF. However, others have reported a scoring system based on ultrasonographic findings to correlate with clinical and biochemical markers of liver disease.[117] An additional study by Patriquin et al., in 195 children with CF, revealed ultrasonographic abnormalities in 38 (19%), of whom 63% had abnormal liver enzyme levels.[118] The most specific ultrasonographic abnormality relating to elevated liver enzymes were those that suggested portal hypertension. However, findings at ultrasonography may be subjective and operator dependent, and clearly larger studies in other centers are needed to validate these findings to determine the accuracy of ultrasonography to predict the predominant liver lesion present.

Scintigraphy

Hepatobiliary scintigraphy (iminodiacetic acid [IDA] derivatives) has limited clinical utility compared with ultrasonography. Radiolabeled Tc-IDA derivatives administered intravenously are taken up by hepatocytes, excreted into the canaliculus and bile ducts, stored in the gallbladder, and excreted in the duodenum. Information regarding extrahepatic biliary tract obstruction, abnormal gallbladder function, and common bile duct stenosis can be determined.[119] Scintigraphy may be helpful in the evaluation of cholecystitis by demonstrating the absence of gallbladder filling characteristic of this condition. It has been suggested that scintigraphy may be of value in the initiation and monitoring of the therapeutic response to ursodeoxycholic acid (UDCA)[120] [121]; however, this has not been validated in controlled clinical trials.

Upper Intestinal Endoscopy and Endoscopic Retrograde Cholangiography

Upper intestinal endoscopy is most useful in detecting the presence of esophageal varices and portal hypertensive gastropathy. ERCP is an invasive procedure and is not used for diagnostic or screening purposes in patients with CF. It remains the investigation of choice for distal stenosis of the common bile duct, sclerosing cholangitis, and choledocholithiasis. Magnetic resonance imaging cholangiography is a noninvasive technique that may prove useful in evaluating the extrahepatic biliary tree and gallbladder,[122] but its utility in CF has yet to be determined.

Liver Biopsy

Liver biopsy may be useful for determining whether steatosis or focal biliary cirrhosis is the predominant type of liver lesion, for determining the extent of portal fibrosis or cirrhosis, and for excluding other lesions. However, not all clinicians think that liver biopsy is indicated in investigating liver disease in CF, because there is no definitive therapy. Additionally, there is the recognized risk of sampling error due to the heterogenous distribution of liver lesions.

Potential Biochemical Markers of CF Liver Disease

Given the difficulty in the diagnosis and assessment of severity of CF liver disease, investigators have sought sensitive and specific tests for diagnosis and screening of CF liver disease. New and potentially useful tests have been proposed, including high molecular mass alkaline phosphatase,[123] serum glutathione S-transferase B1,[124] and serum markers of fibrogenesis, including collagen VI[125] and prolyl hydroxylase.[126] However, the diagnostic value of these serum markers in predicting CF liver disease needs to be confirmed. Other tests of hepatic function, including galactose and caffeine clearance, also have been studied. Galactose clearance, an indirect measure of hepatic blood flow and hepatocyte functional mass, has been investigated in a small number of patients with CF, and results suggest that abnormalities may correlate with the presence of hepatic fibrosis.[127] Conversely, studies of caffeine clearance, as a measure of hepatic function, have not shown this test to be useful for the detection of liver disease in CF patients.[127] [128]

TREATMENT

After liver disease has been diagnosed it should be determined whether the liver abnormalities are most likely caused by hepatic steatosis, hepatic congestion, focal biliary cirrhosis, or multilobular cirrhosis. The evaluation and treatment of steatosis and hepatic congestion has previously been discussed.

Ursodeoxycholic Acid

No therapy has yet been shown to alter the course of progression to cirrhosis in CF; however, UDCA has been shown to improve bile flow and biochemical parameters of liver injury in CF. UDCA may have several mechanisms of action, including improving bile acid-dependent bile flow,[121] displacement of toxic hydrophobic bile acids that accumulate in the cholestatic liver,[129] a direct cytoprotective effect,[129] [130] [131] stimulation of biliary bicarbonate[129] and Ca²⁺-activated Cl^- secretion,[132] and direct immunomodulatory effects.[133] Prospective clinical trials of UDCA in pediatric patients with CF liver disease at doses of 10-20 mg/kg/day for 6-12 months have shown significant improvement in ALT, alkaline phosphatase, and GGT[134] [135] [136] [137] and demonstrated that these effects persist even after 2 years of treatment.[135] A double-blind, multicenter trial demonstrated improved biochemical and clinical parameters after 1 year of treatment with UDCA (15 mg/kg/day).[134] Several studies have reported a dose-response for UDCA in CF liver disease with maximal effect at a dose of 20 mg/kg/day, concluding that higher doses of UDCA may be necessary in CF compared with other forms of cholestasis.[136] [138] In addition to improvement of liver blood tests in CF liver disease, radionuclide hepatobiliary scintigraphy documented improved hepatobiliary excretory function and presumably bile secretion after treatment with 15-20 mg/kg/day of UDCA for 10-12 months.[121] In a 2-year, uncontrolled study, UDCA therapy improved the liver histology, with less inflammation and bile duct proliferation, in 7 of 10 patients with CF-related liver disease.[139] Lastly, UDCA may improve the nutritional status of patients with CF-related liver disease, including increases in serum essential fatty acid,[140] retinol,[140] and vitamin E levels.[141] Despite the improved biochemical, biliary excretory, and perhaps histologic data, it remains to be seen whether UDCA alters the natural course of liver disease in patients with CF. Although there is a need for long-term pediatric studies, the Cystic Fibrosis Foundation Hepatobiliary Disease Consensus Group recommended that it is prudent to use UDCA in CF patients with evidence of liver disease.[70]

Taurine

Taurine has been suggested as an adjunctive therapy in liver disease, because patients with CF are commonly deficient in taurine as a result of bile acid malabsorption. Treatment with unconjugated UDCA may increase the requirement for taurine needed for bile acid conjugation, and taurine conjugates of bile acids are better micellar solubilizing agents than the glycine conjugates.[134] However, a study by Colombo et al. showed no significant effect of taurine supplementation on liver blood test results or fecal fat excretion in patients with CF liver disease treated with UDCA or placebo.[134]

Nutrition

An important component of the management of liver disease in CF is maintenance of a normal nutritional state. Infants with significant cholestasis may need formulas containing medium-chain triglyceride (MCT) to promote intestinal absorption of dietary lipid. Protein intake should not be restricted in children with CF unless decompensated hepatic failure with encephalopathy is present. Patients with CF may require energy intake that exceeds recommendations by 20-40%, due to the increased caloric expenditure from chronic lung disease and the increased oxygen consumption associated with cholestasis.[142] Monitoring fat-soluble vitamin status is even more important in the presence of liver disease[76] than in the patient with CF who has pancreatic insufficiency alone.[143]

Management of Complications of Cirrhosis

The development of portal hypertension is a predictable complication of cirrhosis. Severe portal hypertension and variceal bleeding may require sclerotherapy or ligation during acute episodes of gastrointestinal bleeding. Surgical portosystemic shunt[144] and transjugular portosystemic shunt (TIPS)[145] may be indicated for the management of portal hypertension in these patients, particularly if they are not candidates for liver transplantation. Prophylactic treatment to avoid bleeding is indicated in various forms of liver cirrhosis.[146] However, the efficacy of β-blocker therapy has not been carefully evaluated in CF because of the possible adverse effects of β blockers on airway reactivity. Treatment of variceal bleeding by repeated injection sclerotherapy has not always been effective in patients with CF.[147] In a series by Debray et al., injection sclerotherapy did not prevent recurrence of bleeding in five of seven children treated.[101] In contrast, elective surgical portosystemic shunt was successfully performed in patients with preserved liver function and without severe pulmonary disease, allowing prolonged survival of up to 15 years.[101] Finally, TIPS can be used as a short-term method for portal decompression in patients awaiting liver transplantation or who are not candidates for transplantation.[145]

Liver Transplantation

Liver transplantation should be offered to those patients with life-threatening complications of portal hypertension or severe functional impairment and who have adequate pulmonary function, good compliance with care, and no other contraindications. Liver transplantation in CF patients results in a 1-year survival of approximately 75-80%.[108] [148] Special attention to pulmonary conditions should be provided, with intensive care beginning in the pretransplant period. Experience with combined lung and liver transplantation is limited, but has been performed in CF patients.[149] [150]

FUTURE THERAPIES

New pharmacologic treatments targeted toward specific CFTR mutant proteins are being studied. Although the results are promising, most have been performed in cell models, and the application to in vivo therapeutic treatment regimens has yet to be determined. Theoretically, therapies to correct the defects associated with the specific classes of CFTR mutations may be effective. For example, class I mutations, associated with a premature stop signal and therefore no functional CFTR protein, can be corrected by certain aminogylcoside antibiotics that cause the aberrant stop signal to be skipped.[151] Bronchial epithelial cells expressing premature stop mutations in CFTR demonstrated restoration of full-length CFTR when treated with aminoglycosides in culture.[152] Class II mutations (e.g., ΔF508) result in an unstable protein that does not traffic to the apical membrane correctly. The protein can potentially be restored to a normal pathway by manipulation of chaperone protein/CFTR interactions. This has been accomplished in vitro by the use of chemical chaperones or drugs such as butyrate, that affect gene regulation and modulation of protein folding.[153] A preliminary study in CF patients demonstrated partial restoration of chloride transport in nasal epithelium after 1 week of treatment with phenylbutyrate.[154] Another class of compounds, the α₁-adenosine receptor antagonists, also has been shown to restore the normal trafficking of ΔF508-CFTR to the cell membrane.[155] Class III mutations result in CFTR with reduced Cl^- secretory capacity, which can be augmented by the drug genistein, a flavonoid compound and tyrosine kinase inhibitor.[156] [157] Milrinone, a phosphodiesterase inhibitor, can partially restore the decreased Cl^- conductance associated with the class IV mutations.[158] Partial restoration of Cl^- transport by milrinone has been demonstrated both in vitro and in the mouse nasal mucosa.[159] At the present time all of these approaches still require further significant development. Their potential application to the treatment of the hepatobiliary complications of CF has not been studied.

An exciting possible treatment of hepatobiliary disease in CF is the use of somatic gene transfer. Successful insertion of normal CFTR into normal and CF bile duct cell lines in culture has been achieved[160] and has been performed experimentally by retrograde infusion into the biliary tree of the rat.[161] It remains to be seen whether this approach can alter bile flow adequately to prevent the development of hepatobiliary lesions and cirrhosis associated with CF. Strategies for clinically feasible approaches for gene transfer to the biliary tree (e.g., appropriate vector development) must be developed before clinical application of this novel approach to therapy.

Understanding the basic mechanisms involved in cholangiocyte transport and biliary secretion may suggest other areas of intervention to modulate bile flow. Indeed, the apical membrane of cholangiocytes contains several other Cl^- channels, which at least in single cell studies have a larger unitary conductance than CFTR itself. Understanding the regulation of these alternate channels may provide strategies to bypass the Cl^- secretory defect associated with CF. The finding that luminal agents, such as bile acids and ATP, may regulate biliary secretion is exciting and suggests that secretagogues targeted to the biliary lumen may offer another potential therapeutic option. In clinical trials, aerosilized UTP has been shown to decrease mucus plugging and improve ciliary function when applied to the airways of patients with CF.[69]

Understanding the molecular and cellular basis of liver injury and cirrhosis in CF may lead to new treatment strategies to prevent ongoing cellular injury and interrupt the fibrogenic process.[162] [163] Current results of antioxidant treatment in experimental models of oxidative liver injury appear promising[164] [165]; however, there is no direct clinical evidence to support this therapy. A number of antifibrogenic agents are in the development phase and may prove to be beneficial in the future.

In conclusion, our knowledge of CFTR structure, function, and regulation continues to increase at a rapid rate. In the future this knowledge will hopefully translate into therapeutic strategies for the successful prevention and treatment of CF liver disease.

ACKNOWLEDGMENTS

We extend special thanks to Drs. J. Gregory Fitz for his thoughtful review of the manuscript. This work was supported by the Pediatric General Clinical Research Center (NIH Grant RR 00069), the Children's Hospital Research Institute, The American Gastroenterologic Association and the American Digestive Health Foundation, and the Children's Digestive Health and Nutrition Foundation.

ABBREVIATIONS

ABC ATP-binding cassette

ALT alanine aminotransferase

AST aspartate aminotransferase

CF cystic fibrosis

CFTR cystic fibrosis transmembrane conductance

regulator

GGT gamma-glutamyl transferase.

NBF nucleotide binding fold

UDCA Ursodeoxycholic acid

WEBSITES

1. www.cff.org. The Cystic Fibrosis Foundation.

2. www.genet.sickkids.on.ca/cftr. The CFTR Mutation Database. An updated list of the described mutations in CFTR. Compiled by the Cystic Fibrosis Genetic Analysis Consortium. Run by Dr. Lap-Chee Tsui, Department of Genetics, The Hospital for Sick Children, Toronto, Canada.

REFERENCES

• 1 Dodge J A, Morison S, Lewis P A. Incidence, population, and survival of cystic fibrosis in the UK, 1968-95. UK Cystic Fibrosis Survey Management Committee.  Arch Dis Child . 1997;  77 493-496
  CrossrefPubMedSearch in Google Scholar
• 2 Kosorok M R, Wei W H, Farrell P M. The incidence of cystic fibrosis.  Stat Med . 1996;  15 449-462
  CrossrefPubMedSearch in Google Scholar
• 3 Gabriel S E, Brigman K N, Koller B H. Cystic fibrosis heterozygote resistance to cholera toxin in the cystic fibrosis mouse model.  Science . 1994;  266 107-109
  CrossrefPubMedSearch in Google Scholar
• 4 Anderson J. Cystic fibrosis of the pancreas and its relation to celiac disease.  Am J Dis Child . 2001;  56 344-399
  PubMedSearch in Google Scholar
• 5 Fitzsimmons S C. The changing epidemiology of cystic fibrosis.  J Peds . 1993;  122 1-9
  PubMedSearch in Google Scholar
• 6 Cystic Fibrosis Foundation, Patient Registry 1999 Annual Data Report. Bethesda, MD, September 2000
• 7 DiSant'Agnese P, Darling R. Abnormal electrolyte composition of sweat in cystic fibrosis of the pancreas.  Pediatrics . 1953;  12 549-563
  PubMedSearch in Google Scholar
• 8 Riordan J R, Rommens J M, Kerem B-S. Identification of the cystic fibrosis gene: cloning and characterization of complementary DNA.  Science . 1989;  245 1066-1073
  CrossrefPubMedSearch in Google Scholar
• 9 Anderson M P, Gregory R J, Thompson S. Demonstration that CFTR is a chloride channel by alteration of its anion selectivity.  Science . 1991;  253 202-205
  CrossrefPubMedSearch in Google Scholar
• 10 Fuller C M, Benos D J. CFTR! Am J Physiol .  1992;  263 C267-C286
  PubMedSearch in Google Scholar
• 11 Cohn J A, Strong T A, Picciotto M A. Localization of CFTR in human bile duct epithelial cells.  Gastroenterology . 1993;  105 1857-1864
  CrossrefPubMedSearch in Google Scholar
• 12 McGill J, Gettys T W, Basavappa S. Secretin activates Cl channels in bile duct epithelial cells through a cAMP-dependent mechanism.  Am J Physiol . 1994;  266 G731-G736
  PubMedSearch in Google Scholar
• 13 Nathanson M H, Boyer J L. Mechanisms and regulation of bile secretion.  Hepatology . 1991;  14 551-566
  CrossrefPubMedSearch in Google Scholar
• 14 Strazzabosco M, Mennone A, Boyer J L. Intracellular pH regulation in isolated rat bile duct epithelial cells.  J Clin Invest . 1991;  87 1503-1512
  CrossrefPubMedSearch in Google Scholar
• 15 Roberts S K, Kuntz S M, Gores G. Regulation of bicarbonate-dependent ductular bile secretion assessed by lumenal micropuncture of isolated rodent intrahepatic bile ducts.  Proc Nat Acad Sci USA . 1993;  90 9080-9084
  PubMedSearch in Google Scholar
• 16 Fitz J G, Basavappa S, McGill J. Regulation of membrane chloride currents in rat bile duct epithelial cells.  J Clin Invest . 1993;  91 319-328
  PubMedSearch in Google Scholar
• 17 Levine R A, Hall R C. Cyclic AMP in secretin choleresis. Evidence for a regulatory role in man and baboons but not in dogs.  Gastroenterology . 1976;  70 537-544
  PubMedSearch in Google Scholar
• 18 Alvaro D, Cho W K, Mennone A. Effect of secretin on intracellular pH regulation in isolated rat bile duct epithelial cells.  J Clin Invest . 1993;  92 1314-1325
  PubMedSearch in Google Scholar
• 19 Chenderovitch J. Secretory function of the rabbit common bile duct.  Am J Physiol . 1972;  223 695-706
  PubMedSearch in Google Scholar
• 20 London C D, Diamond J M, Brooks F P. Electrical potential differences in the biliary tree.  Biochim Biophys Acta . 1968;  150 509-517
  PubMedSearch in Google Scholar
• 21 Basavappa S, Middleton J P, Mangel A. Cl^- transport in human biliary cell lines.  Gastroenterology . 1993;  104 1796-1805
  PubMedSearch in Google Scholar
• 22 Roberts S K, Yano M, Ueno Y. Cholangiocytes express the aquaporin CHIP and transport water via a channel-mediated mechanism.  Proc Nat Acad Sci USA . 1994;  91 13009-13013
  PubMedSearch in Google Scholar
• 23 Marinelli R A, Pham L, Agre P. Secretin promotes osmotic water transport in rat cholangiocytes by increasing aquaporin-1 water channels in plasma membrane. Evidence for secretin-induced vesicular translocation of aquaporin-1.  J Biol Chem . 1997;  272 12984-12988
  CrossrefPubMedSearch in Google Scholar
• 24 Marinelli R A, Pham L D, Tietz P S. Expression of aquaporin-4 water channels in rat cholangiocytes.  Hepatology . 2000;  31 1313-1317
  CrossrefPubMedSearch in Google Scholar
• 25 Gray M A, Pollard C E, Harris A. Anion selectivity and block of the small-conductance chloride channel on pancreatic duct cells.  Am J Physiol . 1990;  259 C752-C761
  PubMedSearch in Google Scholar
• 26 Kunzelmann K, Gerlach L, Frobe U, Greger R. Bicarbonate permeability of epithelial chloride channels.  Pfluegers Arch . 1991;  417 616-621
  CrossrefPubMedSearch in Google Scholar
• 27 Ishiguro H, Steward M C, Wilson R W. Bicarbonate secretion in interlobular ducts from guinea-pig pancreas.  J Physiol . 1996;  495(Part 1) 179-191
  PubMedSearch in Google Scholar
• 28 Soleimani M, Aronson P S. Ionic mechanisms of Na⁺/HCO₃ cotransport in rabbit renal basolateral membrane vesicles.  J Biol Chem . 1989;  264 18302-18308
  PubMedSearch in Google Scholar
• 29 O'Reilly C M, Winpenny J P, Argent B E. Cystic fibrosis transmembrane conductance regulator currents in guinea pig pancreatic duct cells: inhibition by bicarbonate ions.  Gastroenterology . 2000;  118 1187-1196
  PubMedSearch in Google Scholar
• 30 Choi J Y, Muallem D, Kiselyov K. Aberrant CFTR-dependent HCO₃ ^- transport in mutations associated with cystic fibrosis.  Nature . 2001;  410 94-97
  CrossrefPubMedSearch in Google Scholar
• 31 McGill J, Gettys T W, Basavappa S. GTP-binding proteins regulate high conductance anion channels in rat bile duct epithelial cells.  J Membr Biol . 1993;  133 253-261
  PubMedSearch in Google Scholar
• 32 Schlenker T, Fitz J G. Calcium-activated chloride channels in a human biliary cell line: regulation by calcium/ calmodulin-dependent protein kinase.  Am J Physiol . 1996;  271 G304-G310
  PubMedSearch in Google Scholar
• 33 Roman R M, Feranchak A P, Salter K D. Endogenous ATP regulates Cl^- secretion in cultured human and rat biliary epithelial cells.  Am J Physiol . 1999;  276 G1391-G1400
  PubMedSearch in Google Scholar
• 34 Roman R M, Wang Y, Fitz J G. Regulation of cell volume in a human biliary cell line: calcium-dependent activation of K⁺ and Cl^- currents.  Am J Physiol . 1996;  271 G239-G248
  PubMedSearch in Google Scholar
• 35 Clarke L L, Grubb B R, Yankaskas J. Relationship of a non-cystic fibrosis transmembrane conductance regulator-mediated chloride conductance to organ-level disease in cftr(-/-) mice.  Proc Nat Acad Sci USA . 1994;  91 479-483
  PubMedSearch in Google Scholar
• 36 Chinet T C, Fullton J M, Yankaskas J R. Mechanism of sodium hyperabsorption in cultured cystic fibrosis nasal epithelium: a patch-clamp study.  Am J Physiol . 1994;  266(Part 1) C1061-C1068
  PubMedSearch in Google Scholar
• 37 Gabriel S, Clarke L L, Boucher R C. CFTR and outward rectifying chloride channels are distinct proteins with a regulatory relationship.  Nature . 1993;  363 263-266
  CrossrefPubMedSearch in Google Scholar
• 38 Grubb B R, Vick R N, Boucher R C. Hyperabsorption of Na⁺ and raised Ca(2+)-mediated Cl^- secretion in nasal epithelia of CF mice.  Am J Physiol . 1994;  266(Part 1) C1478-C1483
  PubMedSearch in Google Scholar
• 39 Egan M, Flotte T, Afione S. Defective regulation of outwardly rectifying Cl^- channels by protein kinase A corrected by insertion of CFTR.  Nature . 1992;  358 581-584
  CrossrefPubMedSearch in Google Scholar
• 40 Schwiebert E M, Egan M E, Hwang T-H. CFTR regulates outwardly rectifying chloride channels through an autocrine mechanism involving ATP.  Cell . 1995;  81 1063-1073
  CrossrefPubMedSearch in Google Scholar
• 41 Hyde S C, Gill D R, Higgins C F. Correction of the ion transport defect in cystic fibrosis transgenic mice by gene therapy.  Nature . 1993;  362 250-255
  CrossrefPubMedSearch in Google Scholar
• 42 Gao L, Kim K J, Yankaskas J R. Abnormal glutathione transport in cystic fibrosis airway epithelia.  Am J Physiol . 1999;  277(Part 1) L113-L118
  PubMedSearch in Google Scholar
• 43 Linsdell P, Hanrahan J W. Glutathione permeability of CFTR.  Am J Physiol . 1998;  275 C323-C326
  PubMedSearch in Google Scholar
• 44 Kuver R, Ramesh N, Lau S. Constitutive mucin secretion linked to CFTR expression.  Biochem Biophys Res Commun . 1994;  203 1457-1462
  CrossrefPubMedSearch in Google Scholar
• 45 Schreiber R, Nitschke R, Greger R. The cystic fibrosis transmembrane conductance regulator activates aquaporin 3 in airway epithelial cells.  J Biol Chem . 1999;  274 11811-11816
  CrossrefPubMedSearch in Google Scholar
• 46 Schreiber R, Pavenstadt H, Greger R. Aquaporin 3 cloned from Xenopus laevis is regulated by the cystic fibrosis transmembrane conductance regulator.  FEBS Lett . 2000;  475 291-295
  CrossrefPubMedSearch in Google Scholar
• 47 Braunstein G M, Roman R M, Clancy J P. Cystic fibrosis transmembrane conductance regulator facilitates ATP release by stimulating a separate ATP release channel for autocrine control of cell volume regulation.  J Biol Chem . 2001;  276 6621-6630
  CrossrefPubMedSearch in Google Scholar
• 48 Short D B, Trotter K W, Reczek D. An apical PDZ protein anchors the cystic fibrosis transmembrane conductance regulator to the cytoskeleton.  J Biol Chem . 1998;  273 19797-19801
  CrossrefPubMedSearch in Google Scholar
• 49 Fouassier L, Duan C Y, Feranchak A P. Ezrin-radixin-moesin-binding phosphoprotein 50 is expressed at the apical membrane of rat liver epithelia.  Hepatology . 2001;  33 166-176
  CrossrefPubMedSearch in Google Scholar
• 50 McGill J, Basavappa S, Shimokura G H. Adenosine triphosphate activates ion permeabilities in biliary epithelial cells.  Gastroenterology . 1994;  107 236-243
  PubMedSearch in Google Scholar
• 51 Alpini G, Glaser S, Robertson W. Bile acids stimulate proliferative and secretory events in large but not small cholangiocytes.  Am J Physiol . 1997;  273(Part 1) G518-G529
  PubMedSearch in Google Scholar
• 52 Lazaridis K N, Pham L, Tietz P S. Rat cholangiocytes absorb bile acids at their apical domain via the ileal sodium-dependent bile acid transporter.  J Clin Invest . 1997;  100 2714-2721
  PubMedSearch in Google Scholar
• 53 Hofmann A F. Bile acids. In: Arias IM, ed. The Liver: Biology and Pathobiology New York: Raven, 1994: 677-718
  Search in Google Scholar
• 54 Yoon Y B, Hagey L R, Hofmann A F. Effect of side chain shortening on the physiologic properties of bile acids: hepatic transport and effect on biliary secretion of 23-Norursodeoxycholate in rodents.  Gastroenterology . 1986;  90 837-852
  PubMedSearch in Google Scholar
• 55 Palmer R, Gurantz D, Hofmann A F. Hypercholeresis induced by norchenodeoxycholate in biliary fistula rodent.  Am J Physiol . 1987;  252 G219-G228
  PubMedSearch in Google Scholar
• 56 Alpini G, Glaser S S, Ueno Y. Bile acid feeding induces cholangiocyte proliferation and secretion: evidence for bile acid-regulated ductal secretion.  Gastroenterology . 1999;  116 179-186
  CrossrefPubMedSearch in Google Scholar
• 57 Feranchak A P, Fitz J G, Roman R M. Volume-sensitive purinergic signaling in human hepatocytes.  J Hepatol . 2000;  33 174-182
  CrossrefPubMedSearch in Google Scholar
• 58 Roman R M, Wang Y, Lidofsky S D. Hepatocellular ATP-binding cassette protein expression enhances ATP release and autocrine regulation of cell volume.  J Biol Chem . 1997;  272 21970-21976
  CrossrefPubMedSearch in Google Scholar
• 59 Feranchak A P, Roman R M, Doctor R B. The lipid products of phosphoinositide 3-kinase contribute to regulation of cholangiocyte ATP and chloride transport.  J Biol Chem . 1999;  274 30979-30986
  CrossrefPubMedSearch in Google Scholar
• 60 Chari R S, Schutz S M, Haebig J A. Adenosine nucleotides in bile.  Am J Physiol . 1996;  270 G246-G252
  PubMedSearch in Google Scholar
• 61 Knowles M R, Clarke L L, Boucher R C. Activation by extracellular nucleotides of chloride secretion in the airway epithelia of patients with cystic fibrosis.  N Engl J Med . 1991;  325 533-538
  PubMedSearch in Google Scholar
• 62 Schlenker T, Romac J MJ, Sharara A. Regulation of biliary secretion through apical purinergic receptors in cultured rat cholangiocytes.  Am J Physiol . 1997;  273 G1108-G1117
  PubMedSearch in Google Scholar
• 63 Reisin I L, Prat A G, Abraham E H. The cystic fibrosis transmembrane conductance regulator is a dual ATP and chloride channel.  J Biol Chem . 1994;  269 20584-20591
  PubMedSearch in Google Scholar
• 64 Al-Awqati Q. Regulation of ion channels by ABC transporters that secrete ATP.  Science . 1995;  269 805-806
  PubMedSearch in Google Scholar
• 65 Pasyk E A, Foskett J K. Cystic fibrosis transmembrane conductance regulator-associated ATP and adenosine 3′-phosphate 5′-phosphosulfate channels in endoplasmic reticulum and plasma membranes.  J Biol Chem . 1997;  272 7746-7751
  CrossrefPubMedSearch in Google Scholar
• 66 Parr C E, Sullivan D M, Paradiso A M. Cloning and expression of a human P2u nucleotide receptor, a target for cystic fibrosis pharmacotherapy.  Proc Nat Acad Sci USA . 1994;  91 3275-3279
  PubMedSearch in Google Scholar
• 67 Chan H C, Cheung W T, Leung P. Purinergic regulation of anion secretion by cystic fibrosis pancreatic duct cells.  Am J Physiol . 1996;  271 C469-C477
  PubMedSearch in Google Scholar
• 68 Taylor A L, Schwiebert L M, Smith J J. Epithelial P2x purinergic receptor channel expression and function.  J Clin Invest . 1999;  104 875-884
  PubMedSearch in Google Scholar
• 69 Bennett W D, Olivier K N, Zeman K L. Effect of uridine 5′-triphosphate plus amiloride on mucociliary clearance in adult cystic fibrosis.  Am J Respir Crit Care Med . 1996;  153(Part 1) 1796-1801
  PubMedSearch in Google Scholar
• 70 Sokol R J, Durie P R. Recommendations for management of liver and biliary tract disease in cystic fibrosis. Cystic Fibrosis Foundation Hepatobiliary Disease Consensus Group.  J Pediatr Gastroenterol Nutr . 1999;  28(Suppl 1) 1-13
  PubMedSearch in Google Scholar
• 71 Bhaskar K R, Turner B S, Grubman S A. Dysregulation of proteoglycan production by intrahepatic biliary epithelial cells bearing defective (delta-f508) cystic fibrosis transmembrane conductance regulator.  Hepatology . 1998;  27 7-14
  CrossrefPubMedSearch in Google Scholar
• 72 Oppenheimer E H, Esterly J R. Hepatic changes in young infants with cystic fibrosis: possible relation to focal biliary cirrhosis.  J Pediatr . 1975;  86 683-689
  CrossrefPubMedSearch in Google Scholar
• 73 Peters R H, French P J, van Doorninck H J. CFTR expression and mucin secretion in cultured mouse gallbladder epithelial cells.  Am J Physiol . 1996;  271(Part 1) G1074-G1083
  PubMedSearch in Google Scholar
• 74 Lindblad A, Hultcrantz R, Strandvik B. Bile-duct destruction and collagen deposition: a prominent ultrastructural feature of the liver in cystic fibrosis.  Hepatology . 1992;  16 372-381
  PubMedSearch in Google Scholar
• 75 Malizia G, Brunt E M, Peters M G. Growth factor and procollagen type I gene expression in human liver disease.  Gastroenterology . 1995;  108 145-156
  PubMedSearch in Google Scholar
• 76 Sokol R J. Fat-soluble vitamins and their importance in patients with cholestatic liver diseases.  Gastroenterol Clin North Am . 1994;  23 673-705
  PubMedSearch in Google Scholar
• 77 Sokol R J, Straka M S, Dahl R. Role of oxidant stress in the permeability transition induced in rat hepatic mitochondria by hydrophobic bile acids.  Pediatr Res . 2001;  49 519-531
  PubMedSearch in Google Scholar
• 78 Yerushalmi B, Dahl R, Devereaux M W. Bile acid-induced rat hepatocyte apoptosis is inhibited by antioxidants and blockers of the mitochondrial permeability transition.  Hepatology . 2001;  33 616-626
  CrossrefPubMedSearch in Google Scholar
• 79 Pessayre D, Berson A, Fromenty B. Mitochondria in steatohepatitis.  Semin Liver Dis . 2001;  21 57-69
  Thieme ConnectPubMedSearch in Google Scholar
• 80 Wilschanski M, Zielenski J, Markiewicz D. Correlation of sweat chloride concentration with classes of the cystic fibrosis transmembrane conductance regulator gene mutations.  J Pediatr . 1995;  127 705-710
  CrossrefPubMedSearch in Google Scholar
• 81 Koch C, Cuppens H, Rainisio M. European Epidemiologic Registry of Cystic Fibrosis (ERCF): comparison of major disease manifestations between patients with different classes of mutations.  Pediatr Pulmonol . 2001;  31 1-12
  CrossrefPubMedSearch in Google Scholar
• 82 Colombo C, Apostolo M G, Ferrari M. Analysis of risk factors for the development of liver disease associated with cystic fibrosis.  J Pediatr . 1994;  124 393-399
  PubMedSearch in Google Scholar
• 83 De Arce M, O'Brien S, Hegarty J. Deletion delta F508 and clinical expression of cystic fibrosis-related liver disease.  Clin Genet . 1992;  42 271-272
  PubMedSearch in Google Scholar
• 84 Duthie A, Doherty D G, Williams C. Genotype analysis for delta F508, G551D and R553X mutations in children and young adults with cystic fibrosis with and without chronic liver disease.  Hepatology . 1992;  15 660-664
  PubMedSearch in Google Scholar
• 85 Augarten A, Kerem B S, Yahav Y. Mild cystic fibrosis and normal or borderline sweat test in patients with the 3849 + 10 kb C → T mutation.  Lancet . 1993;  342 25-26
  CrossrefPubMedSearch in Google Scholar
• 86 Scott-Jupp R, Lama M, Tanner M S. Prevalence of liver disease in cystic fibrosis.  Arch Dis Child . 1991;  66 698-701
  PubMedSearch in Google Scholar
• 87 Feigelson J, Anagnostopoulos C, Poquet M. Liver cirrhosis in cystic fibrosis-therapeutic implications and long term follow up.  Arch Dis Child . 1993;  68 653-657
  PubMedSearch in Google Scholar
• 88 Maurage C, Lenaerts C, Weber A. Meconium ileus and its equivalent as a risk factor for the development of cirrhosis: an autopsy study in cystic fibrosis.  J Pediatr Gastroenterol Nutr . 1989;  9 17-20
  PubMedSearch in Google Scholar
• 89 Colombo C, Battezzati P M, Strazzabosco M. Liver and biliary problems in cystic fibrosis.  Semin Liver Dis . 1998;  18 227-235
  PubMedSearch in Google Scholar
• 90 Lindblad A, Strandvik B, Hjelte L. Incidence of liver disease in patients with cystic fibrosis and meconium ileus.  J Pediatr . 1995;  126 155-156
  PubMedSearch in Google Scholar
• 91 Tanner M S, Taylor C J. Liver disease in cystic fibrosis.  Arch Dis Child . 1995;  72 281-284
  PubMedSearch in Google Scholar
• 92 Williams S G, Westaby D, Tanner M S. Liver and biliary problems in cystic fibrosis.  Br Med Bull . 1992;  48 877-892
  PubMedSearch in Google Scholar
• 93 Duthie A, Doherty D G, Donaldson P T. The major histocompatibility complex influences the development of chronic liver disease in male children and young adults with cystic fibrosis.  J Hepatol . 1995;  23 532-537
  CrossrefPubMedSearch in Google Scholar
• 94 Rohlfs E M, Shaheen N J, Silverman L M. Is the hemochromatosis gene a modifier locus for cystic fibrosis?.  Genet Test . 1998;  2 85-88
  PubMedSearch in Google Scholar
• 95 Nagel R A, Westaby D, Javaid A. Liver disease and bile duct abnormalities in adults with cystic fibrosis.  Lancet . 1989;  2 1422-1425
  PubMedSearch in Google Scholar
• 96 Vawter G F, Shwachman H. Cystic fibrosis in adults: an autopsy study.  Pathol Annu . 1979;  14(Part 2) 357-382
  PubMedSearch in Google Scholar
• 97 Sokol R J, Carroll N M, Narkewicz M R, Wagener J S, Accurso F J. Liver blood tests during the first decade of life in children with cystic fibrosis identified by newborn screening.  Pediatr Pulm . 1994;  10 275
  PubMedSearch in Google Scholar
• 98 Kovesi T, Corey M, Tsui L-C. The association between liver disease and mutations of the cystic fibrosis gene.  Pediatr Pulm . 1992;  8 244
  PubMedSearch in Google Scholar
• 99 Lindblad A, Glaumann H, Strandvik B. Natural history of liver disease in cystic fibrosis.  Hepatology . 1999;  30 1151-1158
  CrossrefPubMedSearch in Google Scholar
• 100 Gaskin K J, Waters D LM, Howman-Giles R. Liver disease and common bile duct stenosis in cystic fibrosis.  N Engl J Med . 1988;  318 340-346
  PubMedSearch in Google Scholar
• 101 Debray D, Lykavieris P, Gauthier F. Outcome of cystic fibrosis-associated liver cirrhosis: management of portal hypertension.  J Hepatol . 1999;  31 77-83
  CrossrefPubMedSearch in Google Scholar
• 102 Craig J M. The pathological changes in the liver in cystic fibrosis of the pancreas.  Am J Dis Child . 1957;  93 357-369
  PubMedSearch in Google Scholar
• 103 Vlaman H B, France N E, Wallis P G. Prolonged neonatal jaundice in cystic fibrosis.  Arch Dis Child . 1971;  46 805-809
  PubMedSearch in Google Scholar
• 104 Shapira R, Hadzic N, Francavilla R. Retrospective review of cystic fibrosis presenting as infantile liver disease.  Arch Dis Child . 1999;  81 125-128
  CrossrefPubMedSearch in Google Scholar
• 105 Roy C C, Weber A M, Morin C L. Hepatobiliary disease in cystic fibrosis: a survey of current issues and concepts.  J Pediatr Gastroenterol Nutr . 1982;  1 469-478
  PubMedSearch in Google Scholar
• 106 Lykavieris P, Bernard O, Hadchouel M. Neonatal cholestasis as the presenting feature in cystic fibrosis.  Arch Dis Child . 1996;  75 67-70
  CrossrefPubMedSearch in Google Scholar
• 107 Colombo C, Crosignani A, Battezzati P M. Liver involvement in cystic fibrosis.  J Hepatol . 1999;  31 946-954
  CrossrefPubMedSearch in Google Scholar
• 108 Mack D R, Traystman M D, Colombo J L. Clinical denouement and mutation analysis of patients with cystic fibrosis undergoing liver transplantation for biliary cirrhosis.  J Pediatr . 1995;  127 881-887
  PubMedSearch in Google Scholar
• 109 di Sant'Agnese A P, Blanc W A. A distinctive type of biliary cirrhosis of the liver associated with cystic fibrosis of the pancreas.  Pediatrics . 1956;  18 387-409
  PubMedSearch in Google Scholar
• 110 Feranchak A P, Sontag M K, Wagener J S. Prospective, long-term study of fat-soluble vitamin status in children with cystic fibrosis identified by newborn screen.  J Pediatr . 1999;  135 601-610
  CrossrefPubMedSearch in Google Scholar
• 111 Willi U V, Reddish J M, Teele R L. Cystic fibrosis: its characteristic appearance on abdominal sonography.  AJR . 1980;  134 1005-1010
  PubMedSearch in Google Scholar
• 112 Stern R C, Rothstein F C, Doershuk C F. Treatment and prognosis of symptomatic gallbladder disease in patients with cystic fibrosis.  J Pediatr Gastroenterol Nutr . 1986;  5 35-40
  PubMedSearch in Google Scholar
• 113 Angelico M, Gandin C, Canuzzi P. Gallstones in cystic fibrosis: a critical reappraisal.  Hepatology . 1991;  14 768-775
  CrossrefPubMedSearch in Google Scholar
• 114 Colombo C, Bertolini E, Assaisso M L. Failure of ursodeoxycholic acid to dissolve radiolucent gallstones in patients with cystic fibrosis.  Acta Paediatr . 1993;  82 562-565
  CrossrefPubMedSearch in Google Scholar
• 115 Neglia J P, Fitzsimmons S C, Maisonneuve P. The risk of cancer among patients with cystic fibrosis. Cystic Fibrosis and Cancer Study Group.  N Engl J Med . 1995;  332 494-499
  CrossrefPubMedSearch in Google Scholar
• 116 Potter C J, Fishbein M, Hammond S. Can the histologic changes of cystic fibrosis-associated hepatobiliary disease be predicted by clinical criteria?.  J Pediatr Gastroenterol Nutr . 1997;  25 32-36
  CrossrefPubMedSearch in Google Scholar
• 117 Williams S G, Evanson J E, Barrett N. An ultrasound scoring system for the diagnosis of liver disease in cystic fibrosis.  J Hepatol . 1995;  22 513-521
  CrossrefPubMedSearch in Google Scholar
• 118 Patriquin H, Lenaerts C, Smith L. Liver disease in children with cystic fibrosis: US-biochemical comparison in 195 patients.  Radiology . 1999;  211 229-232
  CrossrefPubMedSearch in Google Scholar
• 119 Dogan A S, Conway J J, Lloyd-Still J D. Hepatobiliary scintigraphy in children with cystic fibrosis and liver disease.  J Nucl Med . 1994;  35 432-435
  PubMedSearch in Google Scholar
• 120 O'Connor P J, Southern K W, Bowler I M. The role of hepatobiliary scintigraphy in cystic fibrosis.  Hepatology . 1996;  23 281-287
  PubMedSearch in Google Scholar
• 121 Colombo C, Castellani M R, Balistreri W F. Scintigraphic documentation of an improvement in hepatobiliary excretory function after treatment with ursodeoxycholic acid in patients with cystic fibrosis and associated liver disease.  Hepatology . 1992;  15 677-684
  PubMedSearch in Google Scholar
• 122 Hubbard A M, Meyer J S, Mahboubi S. Diagnosis of liver disease in children: value of MR angiography.  AJR . 1992;  159 617-621
  PubMedSearch in Google Scholar
• 123 Schoenau E, Boeswald W, Wanner R. High-molecular-mass (``biliary'') isoenzyme of alkaline phosphatase and the diagnosis of liver dysfunction in cystic fibrosis.  Clin Chem . 1989;  35 1888-1890
  PubMedSearch in Google Scholar
• 124 Rattenbury J M, Taylor C J, Heath P K. Serum glutathione S-transferase B1 activity as an index of liver function in cystic fibrosis.  J Clin Pathol . 1995;  48 771-774
  PubMedSearch in Google Scholar
• 125 Gerling B, Becker M, Staab D. Prediction of liver fibrosis according to serum collagen VI level in children with cystic fibrosis.  N Engl J Med . 1997;  336 1611-1612
  CrossrefPubMedSearch in Google Scholar
• 126 Leonardi S, Giambusso F, Sciuto C. Are serum type III procollagen and prolyl hydroxylase useful as noninvasive markers of liver disease in patients with cystic fibrosis?.  J Pediatr Gastroenterol Nutr . 1998;  27 603-605
  CrossrefPubMedSearch in Google Scholar
• 127 Narkewicz M R, Smith D, Gregory C. Effect of ursodeoxycholic acid therapy on hepatic function in children with intrahepatic cholestatic liver disease.  J Pediatr Gastroenterol Nutr . 1998;  26 49-55
  CrossrefPubMedSearch in Google Scholar
• 128 Bianchetti M G, Kraemer R, Passweg J. Use of salivary levels to predict clearance of caffeine in patients with cystic fibrosis.  J Pediatr Gastroenterol Nutr . 1988;  7 688-693
  PubMedSearch in Google Scholar
• 129 Heuman D M. Hepatoprotective properties of ursodeoxycholic acid.  Gastroenterology . 1993;  104 1865-1870
  PubMedSearch in Google Scholar
• 130 Erlinger S, Dumont M. Influence of UDCA on bile secretion. In: Paumgartner G, Stiehl A, Barbara L, et al., eds. Strategies for the Treatment of Hepatobiliary Disease Dordrecht, The Netherlands: Kluwer Academic, 1990: 35-42
  Search in Google Scholar
• 131 Botla R, Spivey J R, Aguilar H. Ursodeoxycholate (UDCA) inhibits the mitochondrial membrane permeability transition induced by glycochenodeoxycholate: a mechanism of UDCA cytoprotection.  J Pharmacol Exp Ther . 1995;  272 930-938
  PubMedSearch in Google Scholar
• 132 Shimokura G H, McGill J, Schlenker T. Ursodeoxycholate increases cytosolic calcium concentration and activates Cl^- currents in a biliary cell line.  Gastroenterology . 1995;  109 965-972
  PubMedSearch in Google Scholar
• 133 Calmus Y, Gane P, Rouger P. Hepatic expression of class I and class II major histocompatibility complex molecules in primary biliary cirrhosis: effect of ursodeoxycholic acid.  Hepatology . 1990;  11 12-15
  CrossrefPubMedSearch in Google Scholar
• 134 Colombo C, Battezzati P M, Podda M. Ursodeoxycholic acid for liver disease associated with cystic fibrosis: a double-blind multicenter trial.  Hepatology . 1996;  23 1484-1490
  PubMedSearch in Google Scholar
• 135 Cotting J, Lentze M J, Reichen J. Effects of ursodeoxycholic acid treatment on nutrition and liver function in patients with cystic fibrosis and longstanding cholestasis.  Gut . 1990;  31 918-921
  PubMedSearch in Google Scholar
• 136 Colombo C, Setchell K D, Podda M. Effects of ursodeoxycholic acid therapy for liver disease associated with cystic fibrosis.  J Pediatr . 1990;  117 482-489
  PubMedSearch in Google Scholar
• 137 Galabert C, Montet J C, Lengrand D. Effects of ursodeoxycholic acid on liver function in patients with cystic fibrosis and chronic cholestasis.  J Pediatr . 1992;  121 138-141
  PubMedSearch in Google Scholar
• 138 van de Meeberg C P, Houwen R H, Sinaasappel M. Low-dose versus high-dose ursodeoxycholic acid in cystic fibrosis-related cholestatic liver disease. Results of a randomized study with 1-year follow-up.  Scand J Gastroenterol . 1997;  32 369-373
  PubMedSearch in Google Scholar
• 139 Lindblad A, Glaumann H, Strandvik B. A two-year prospective study of the effect of ursodeoxycholic acid on urinary bile acid excretion and liver morphology in cystic fibrosis-associated liver disease.  Hepatology . 1998;  27 166-174
  CrossrefPubMedSearch in Google Scholar
• 140 Lepage G, Paradis K, Lacaille F. Ursodeoxycholic acid improves the hepatic metabolism of essential fatty acids and retinol in children with cystic fibrosis.  J Pediatr . 1997;  130 52-58
  PubMedSearch in Google Scholar
• 141 Thomas P S, Bellamy M, Geddes D. Malabsorption of vitamin E in cystic fibrosis improved after ursodeoxycholic acid.  Lancet . 1995;  346 1230-1231
  PubMedSearch in Google Scholar
• 142 Pierro A, Koletzko B, Carnielli V. Resting energy expenditure is increased in infants and children with extrahepatic biliary atresia.  J Pediatr Surg . 1989;  24 534-538
  PubMedSearch in Google Scholar
• 143 Ramsey B W, Farrell P M, Pencharz P. Nutritional assessment and management in cystic fibrosis: a consensus report. The Consensus Committee.  Am J Clin Nutr . 1992;  55 108-116
  PubMedSearch in Google Scholar
• 144 Schuster S R, Shwachman H, Toyama W M. The management of portal hypertension in cystic fibrosis.  J Pediatr Surg . 1977;  12 201-206
  PubMedSearch in Google Scholar
• 145 Berger K J, Schreiber R A, Tchervenkov J. Decompression of portal hypertension in a child with cystic fibrosis after transjugular intrahepatic portosystemic shunt placement.  J Pediatr Gastroenterol Nutr . 1994;  19 322-325
  PubMedSearch in Google Scholar
• 146 Sanyal A J, Purdum III P P, Luketic V A. Bleeding gastroesophageal varices.  Semin Liver Dis . 1993;  13 328-342
  PubMedSearch in Google Scholar
• 147 Stringer M D, Price J F, Mowat A P. Liver cirrhosis in cystic fibrosis.  Arch Dis Child . 1993;  69 407
  PubMedSearch in Google Scholar
• 148 Noble-Jamieson G, Valente J, Barnes N D. Liver transplantation for hepatic cirrhosis in cystic fibrosis.  Arch Dis Child . 1994;  71 349-352
  PubMedSearch in Google Scholar
• 149 Couetil J P, Houssin D P, Soubrane O. Combined lung and liver transplantation in patients with cystic fibrosis. A 4 1/2-year experience.  J Thorac Cardiovasc Surg . 1995;  110 1415-1422
  PubMedSearch in Google Scholar
• 150 Dennis C M, McNeil K D, Dunning J. Heart-lung-liver transplantation.  J Heart Lung Transplant . 1996;  15 536-538
  PubMedSearch in Google Scholar
• 151 Palmer E, Wilhelm J M, Sherman F. Phenotypic suppression of nonsense mutants in yeast by aminoglycoside antibiotics.  Nature . 1979;  277 148-150
  PubMedSearch in Google Scholar
• 152 Bedwell D M, Kaenjak A, Benos D J. Suppression of a CFTR premature stop mutation in a bronchial epithelial cell line.  Nat Med . 1997;  3 1280-1284
  CrossrefPubMedSearch in Google Scholar
• 153 Rubenstein R C, Egan M E, Zeitlin P L. In vitro pharmacologic restoration of CFTR-mediated chloride transport with sodium 4-phenylbutyrate in cystic fibrosis epithelial cells containing delta F508-CFTR.  J Clin Invest . 1997;  100 2457-2465
  PubMedSearch in Google Scholar
• 154 Rubenstein R C, Zeitlin P L. A pilot clinical trial of oral sodium 4-phenylbutyrate (Buphenyl) in deltaF508-homozygous cystic fibrosis patients: partial restoration of nasal epithelial CFTR function.  Am J Respir Crit Care Med . 1998;  157 484-490
  PubMedSearch in Google Scholar
• 155 Eidelman O, Guay-Broder C, van Galen J P. A1 adenosine-receptor antagonists activate chloride efflux from cystic fibrosis cells.  Proc Natl Acad Sci USA . 1992;  89 5562-5566
  PubMedSearch in Google Scholar
• 156 Illek B, Yankaskas J, Machen T E. cAMP and genistein stimulate HCO₃ ^- conductance through CFTR in human airway epithelia.  Am J Physiol . 1997;  272 L752-L761
  PubMedSearch in Google Scholar
• 157 Illek B, Zhang L, Lewis N C. Defective function of the cystic fibrosis-causing missense mutation G551D is recovered by genistein.  Am J Physiol . 1999;  277(Part 1) C833-C839
  PubMedSearch in Google Scholar
• 158 Kelley T J, Al Nakkash L, Cotton C U. Activation of endogenous deltaF508 cystic fibrosis transmembrane conductance regulator by phosphodiesterase inhibition.  J Clin Invest . 1996;  98 513-520
  PubMedSearch in Google Scholar
• 159 Kelley T J, Thomas K, Milgram L J. In vivo activation of the cystic fibrosis transmembrane conductance regulator mutant deltaF508 in murine nasal epithelium.  Proc Natl Acad Sci USA . 1997;  94 2604-2608
  CrossrefPubMedSearch in Google Scholar
• 160 Grubman S A, Fang S L, Mulberg A E. Correction of the cystic fibrosis defect by gene complementation in human intrahepatic biliary cell lines.  Gastroenterology . 1995;  108 584-592
  PubMedSearch in Google Scholar
• 161 Yang Y, Raper S E, Cohn J A. An approach for treating the hepatobiliary disease of cystic fibrosis by somatic gene transfer.  Proc Nat Acad Sci USA . 1993;  90 4601-4605
  PubMedSearch in Google Scholar
• 162 Friedman S L. Molecular mechanisms of hepatic fibrosis and principles of therapy.  J Gastroenterol . 1997;  32 424-430
  PubMedSearch in Google Scholar
• 163 Friedman S L. Molecular regulation of hepatic fibrosis, an integrated cellular response to tissue injury.  J Biol Chem . 2000;  275 2247-2250
  CrossrefPubMedSearch in Google Scholar
• 164 Britton R S, Bacon B R. Role of free radicals in liver diseases and hepatic fibrosis.  Hepatogastroenterology . 1994;  41 343-348
  PubMedSearch in Google Scholar
• 165 Zhang M, Song G, Minuk G Y. Effects of hepatic stimulator substance, herbal medicine, selenium/vitamin E, and ciprofloxacin on cirrhosis in the rat.  Gastroenterology . 1996;  110 1150-1155
  PubMedSearch in Google Scholar

REFERENCES

• 1 Dodge J A, Morison S, Lewis P A. Incidence, population, and survival of cystic fibrosis in the UK, 1968-95. UK Cystic Fibrosis Survey Management Committee.  Arch Dis Child . 1997;  77 493-496
  CrossrefPubMedSearch in Google Scholar
• 2 Kosorok M R, Wei W H, Farrell P M. The incidence of cystic fibrosis.  Stat Med . 1996;  15 449-462
  CrossrefPubMedSearch in Google Scholar
• 3 Gabriel S E, Brigman K N, Koller B H. Cystic fibrosis heterozygote resistance to cholera toxin in the cystic fibrosis mouse model.  Science . 1994;  266 107-109
  CrossrefPubMedSearch in Google Scholar
• 4 Anderson J. Cystic fibrosis of the pancreas and its relation to celiac disease.  Am J Dis Child . 2001;  56 344-399
  PubMedSearch in Google Scholar
• 5 Fitzsimmons S C. The changing epidemiology of cystic fibrosis.  J Peds . 1993;  122 1-9
  PubMedSearch in Google Scholar
• 6 Cystic Fibrosis Foundation, Patient Registry 1999 Annual Data Report. Bethesda, MD, September 2000
• 7 DiSant'Agnese P, Darling R. Abnormal electrolyte composition of sweat in cystic fibrosis of the pancreas.  Pediatrics . 1953;  12 549-563
  PubMedSearch in Google Scholar
• 8 Riordan J R, Rommens J M, Kerem B-S. Identification of the cystic fibrosis gene: cloning and characterization of complementary DNA.  Science . 1989;  245 1066-1073
  CrossrefPubMedSearch in Google Scholar
• 9 Anderson M P, Gregory R J, Thompson S. Demonstration that CFTR is a chloride channel by alteration of its anion selectivity.  Science . 1991;  253 202-205
  CrossrefPubMedSearch in Google Scholar
• 10 Fuller C M, Benos D J. CFTR! Am J Physiol .  1992;  263 C267-C286
  PubMedSearch in Google Scholar
• 11 Cohn J A, Strong T A, Picciotto M A. Localization of CFTR in human bile duct epithelial cells.  Gastroenterology . 1993;  105 1857-1864
  CrossrefPubMedSearch in Google Scholar
• 12 McGill J, Gettys T W, Basavappa S. Secretin activates Cl channels in bile duct epithelial cells through a cAMP-dependent mechanism.  Am J Physiol . 1994;  266 G731-G736
  PubMedSearch in Google Scholar
• 13 Nathanson M H, Boyer J L. Mechanisms and regulation of bile secretion.  Hepatology . 1991;  14 551-566
  CrossrefPubMedSearch in Google Scholar
• 14 Strazzabosco M, Mennone A, Boyer J L. Intracellular pH regulation in isolated rat bile duct epithelial cells.  J Clin Invest . 1991;  87 1503-1512
  CrossrefPubMedSearch in Google Scholar
• 15 Roberts S K, Kuntz S M, Gores G. Regulation of bicarbonate-dependent ductular bile secretion assessed by lumenal micropuncture of isolated rodent intrahepatic bile ducts.  Proc Nat Acad Sci USA . 1993;  90 9080-9084
  PubMedSearch in Google Scholar
• 16 Fitz J G, Basavappa S, McGill J. Regulation of membrane chloride currents in rat bile duct epithelial cells.  J Clin Invest . 1993;  91 319-328
  PubMedSearch in Google Scholar
• 17 Levine R A, Hall R C. Cyclic AMP in secretin choleresis. Evidence for a regulatory role in man and baboons but not in dogs.  Gastroenterology . 1976;  70 537-544
  PubMedSearch in Google Scholar
• 18 Alvaro D, Cho W K, Mennone A. Effect of secretin on intracellular pH regulation in isolated rat bile duct epithelial cells.  J Clin Invest . 1993;  92 1314-1325
  PubMedSearch in Google Scholar
• 19 Chenderovitch J. Secretory function of the rabbit common bile duct.  Am J Physiol . 1972;  223 695-706
  PubMedSearch in Google Scholar
• 20 London C D, Diamond J M, Brooks F P. Electrical potential differences in the biliary tree.  Biochim Biophys Acta . 1968;  150 509-517
  PubMedSearch in Google Scholar
• 21 Basavappa S, Middleton J P, Mangel A. Cl^- transport in human biliary cell lines.  Gastroenterology . 1993;  104 1796-1805
  PubMedSearch in Google Scholar
• 22 Roberts S K, Yano M, Ueno Y. Cholangiocytes express the aquaporin CHIP and transport water via a channel-mediated mechanism.  Proc Nat Acad Sci USA . 1994;  91 13009-13013
  PubMedSearch in Google Scholar
• 23 Marinelli R A, Pham L, Agre P. Secretin promotes osmotic water transport in rat cholangiocytes by increasing aquaporin-1 water channels in plasma membrane. Evidence for secretin-induced vesicular translocation of aquaporin-1.  J Biol Chem . 1997;  272 12984-12988
  CrossrefPubMedSearch in Google Scholar
• 24 Marinelli R A, Pham L D, Tietz P S. Expression of aquaporin-4 water channels in rat cholangiocytes.  Hepatology . 2000;  31 1313-1317
  CrossrefPubMedSearch in Google Scholar
• 25 Gray M A, Pollard C E, Harris A. Anion selectivity and block of the small-conductance chloride channel on pancreatic duct cells.  Am J Physiol . 1990;  259 C752-C761
  PubMedSearch in Google Scholar
• 26 Kunzelmann K, Gerlach L, Frobe U, Greger R. Bicarbonate permeability of epithelial chloride channels.  Pfluegers Arch . 1991;  417 616-621
  CrossrefPubMedSearch in Google Scholar
• 27 Ishiguro H, Steward M C, Wilson R W. Bicarbonate secretion in interlobular ducts from guinea-pig pancreas.  J Physiol . 1996;  495(Part 1) 179-191
  PubMedSearch in Google Scholar
• 28 Soleimani M, Aronson P S. Ionic mechanisms of Na⁺/HCO₃ cotransport in rabbit renal basolateral membrane vesicles.  J Biol Chem . 1989;  264 18302-18308
  PubMedSearch in Google Scholar
• 29 O'Reilly C M, Winpenny J P, Argent B E. Cystic fibrosis transmembrane conductance regulator currents in guinea pig pancreatic duct cells: inhibition by bicarbonate ions.  Gastroenterology . 2000;  118 1187-1196
  PubMedSearch in Google Scholar
• 30 Choi J Y, Muallem D, Kiselyov K. Aberrant CFTR-dependent HCO₃ ^- transport in mutations associated with cystic fibrosis.  Nature . 2001;  410 94-97
  CrossrefPubMedSearch in Google Scholar
• 31 McGill J, Gettys T W, Basavappa S. GTP-binding proteins regulate high conductance anion channels in rat bile duct epithelial cells.  J Membr Biol . 1993;  133 253-261
  PubMedSearch in Google Scholar
• 32 Schlenker T, Fitz J G. Calcium-activated chloride channels in a human biliary cell line: regulation by calcium/ calmodulin-dependent protein kinase.  Am J Physiol . 1996;  271 G304-G310
  PubMedSearch in Google Scholar
• 33 Roman R M, Feranchak A P, Salter K D. Endogenous ATP regulates Cl^- secretion in cultured human and rat biliary epithelial cells.  Am J Physiol . 1999;  276 G1391-G1400
  PubMedSearch in Google Scholar
• 34 Roman R M, Wang Y, Fitz J G. Regulation of cell volume in a human biliary cell line: calcium-dependent activation of K⁺ and Cl^- currents.  Am J Physiol . 1996;  271 G239-G248
  PubMedSearch in Google Scholar
• 35 Clarke L L, Grubb B R, Yankaskas J. Relationship of a non-cystic fibrosis transmembrane conductance regulator-mediated chloride conductance to organ-level disease in cftr(-/-) mice.  Proc Nat Acad Sci USA . 1994;  91 479-483
  PubMedSearch in Google Scholar
• 36 Chinet T C, Fullton J M, Yankaskas J R. Mechanism of sodium hyperabsorption in cultured cystic fibrosis nasal epithelium: a patch-clamp study.  Am J Physiol . 1994;  266(Part 1) C1061-C1068
  PubMedSearch in Google Scholar
• 37 Gabriel S, Clarke L L, Boucher R C. CFTR and outward rectifying chloride channels are distinct proteins with a regulatory relationship.  Nature . 1993;  363 263-266
  CrossrefPubMedSearch in Google Scholar
• 38 Grubb B R, Vick R N, Boucher R C. Hyperabsorption of Na⁺ and raised Ca(2+)-mediated Cl^- secretion in nasal epithelia of CF mice.  Am J Physiol . 1994;  266(Part 1) C1478-C1483
  PubMedSearch in Google Scholar
• 39 Egan M, Flotte T, Afione S. Defective regulation of outwardly rectifying Cl^- channels by protein kinase A corrected by insertion of CFTR.  Nature . 1992;  358 581-584
  CrossrefPubMedSearch in Google Scholar
• 40 Schwiebert E M, Egan M E, Hwang T-H. CFTR regulates outwardly rectifying chloride channels through an autocrine mechanism involving ATP.  Cell . 1995;  81 1063-1073
  CrossrefPubMedSearch in Google Scholar
• 41 Hyde S C, Gill D R, Higgins C F. Correction of the ion transport defect in cystic fibrosis transgenic mice by gene therapy.  Nature . 1993;  362 250-255
  CrossrefPubMedSearch in Google Scholar
• 42 Gao L, Kim K J, Yankaskas J R. Abnormal glutathione transport in cystic fibrosis airway epithelia.  Am J Physiol . 1999;  277(Part 1) L113-L118
  PubMedSearch in Google Scholar
• 43 Linsdell P, Hanrahan J W. Glutathione permeability of CFTR.  Am J Physiol . 1998;  275 C323-C326
  PubMedSearch in Google Scholar
• 44 Kuver R, Ramesh N, Lau S. Constitutive mucin secretion linked to CFTR expression.  Biochem Biophys Res Commun . 1994;  203 1457-1462
  CrossrefPubMedSearch in Google Scholar
• 45 Schreiber R, Nitschke R, Greger R. The cystic fibrosis transmembrane conductance regulator activates aquaporin 3 in airway epithelial cells.  J Biol Chem . 1999;  274 11811-11816
  CrossrefPubMedSearch in Google Scholar
• 46 Schreiber R, Pavenstadt H, Greger R. Aquaporin 3 cloned from Xenopus laevis is regulated by the cystic fibrosis transmembrane conductance regulator.  FEBS Lett . 2000;  475 291-295
  CrossrefPubMedSearch in Google Scholar
• 47 Braunstein G M, Roman R M, Clancy J P. Cystic fibrosis transmembrane conductance regulator facilitates ATP release by stimulating a separate ATP release channel for autocrine control of cell volume regulation.  J Biol Chem . 2001;  276 6621-6630
  CrossrefPubMedSearch in Google Scholar
• 48 Short D B, Trotter K W, Reczek D. An apical PDZ protein anchors the cystic fibrosis transmembrane conductance regulator to the cytoskeleton.  J Biol Chem . 1998;  273 19797-19801
  CrossrefPubMedSearch in Google Scholar
• 49 Fouassier L, Duan C Y, Feranchak A P. Ezrin-radixin-moesin-binding phosphoprotein 50 is expressed at the apical membrane of rat liver epithelia.  Hepatology . 2001;  33 166-176
  CrossrefPubMedSearch in Google Scholar
• 50 McGill J, Basavappa S, Shimokura G H. Adenosine triphosphate activates ion permeabilities in biliary epithelial cells.  Gastroenterology . 1994;  107 236-243
  PubMedSearch in Google Scholar
• 51 Alpini G, Glaser S, Robertson W. Bile acids stimulate proliferative and secretory events in large but not small cholangiocytes.  Am J Physiol . 1997;  273(Part 1) G518-G529
  PubMedSearch in Google Scholar
• 52 Lazaridis K N, Pham L, Tietz P S. Rat cholangiocytes absorb bile acids at their apical domain via the ileal sodium-dependent bile acid transporter.  J Clin Invest . 1997;  100 2714-2721
  PubMedSearch in Google Scholar
• 53 Hofmann A F. Bile acids. In: Arias IM, ed. The Liver: Biology and Pathobiology New York: Raven, 1994: 677-718
  Search in Google Scholar
• 54 Yoon Y B, Hagey L R, Hofmann A F. Effect of side chain shortening on the physiologic properties of bile acids: hepatic transport and effect on biliary secretion of 23-Norursodeoxycholate in rodents.  Gastroenterology . 1986;  90 837-852
  PubMedSearch in Google Scholar
• 55 Palmer R, Gurantz D, Hofmann A F. Hypercholeresis induced by norchenodeoxycholate in biliary fistula rodent.  Am J Physiol . 1987;  252 G219-G228
  PubMedSearch in Google Scholar
• 56 Alpini G, Glaser S S, Ueno Y. Bile acid feeding induces cholangiocyte proliferation and secretion: evidence for bile acid-regulated ductal secretion.  Gastroenterology . 1999;  116 179-186
  CrossrefPubMedSearch in Google Scholar
• 57 Feranchak A P, Fitz J G, Roman R M. Volume-sensitive purinergic signaling in human hepatocytes.  J Hepatol . 2000;  33 174-182
  CrossrefPubMedSearch in Google Scholar
• 58 Roman R M, Wang Y, Lidofsky S D. Hepatocellular ATP-binding cassette protein expression enhances ATP release and autocrine regulation of cell volume.  J Biol Chem . 1997;  272 21970-21976
  CrossrefPubMedSearch in Google Scholar
• 59 Feranchak A P, Roman R M, Doctor R B. The lipid products of phosphoinositide 3-kinase contribute to regulation of cholangiocyte ATP and chloride transport.  J Biol Chem . 1999;  274 30979-30986
  CrossrefPubMedSearch in Google Scholar
• 60 Chari R S, Schutz S M, Haebig J A. Adenosine nucleotides in bile.  Am J Physiol . 1996;  270 G246-G252
  PubMedSearch in Google Scholar
• 61 Knowles M R, Clarke L L, Boucher R C. Activation by extracellular nucleotides of chloride secretion in the airway epithelia of patients with cystic fibrosis.  N Engl J Med . 1991;  325 533-538
  PubMedSearch in Google Scholar
• 62 Schlenker T, Romac J MJ, Sharara A. Regulation of biliary secretion through apical purinergic receptors in cultured rat cholangiocytes.  Am J Physiol . 1997;  273 G1108-G1117
  PubMedSearch in Google Scholar
• 63 Reisin I L, Prat A G, Abraham E H. The cystic fibrosis transmembrane conductance regulator is a dual ATP and chloride channel.  J Biol Chem . 1994;  269 20584-20591
  PubMedSearch in Google Scholar
• 64 Al-Awqati Q. Regulation of ion channels by ABC transporters that secrete ATP.  Science . 1995;  269 805-806
  PubMedSearch in Google Scholar
• 65 Pasyk E A, Foskett J K. Cystic fibrosis transmembrane conductance regulator-associated ATP and adenosine 3′-phosphate 5′-phosphosulfate channels in endoplasmic reticulum and plasma membranes.  J Biol Chem . 1997;  272 7746-7751
  CrossrefPubMedSearch in Google Scholar
• 66 Parr C E, Sullivan D M, Paradiso A M. Cloning and expression of a human P2u nucleotide receptor, a target for cystic fibrosis pharmacotherapy.  Proc Nat Acad Sci USA . 1994;  91 3275-3279
  PubMedSearch in Google Scholar
• 67 Chan H C, Cheung W T, Leung P. Purinergic regulation of anion secretion by cystic fibrosis pancreatic duct cells.  Am J Physiol . 1996;  271 C469-C477
  PubMedSearch in Google Scholar
• 68 Taylor A L, Schwiebert L M, Smith J J. Epithelial P2x purinergic receptor channel expression and function.  J Clin Invest . 1999;  104 875-884
  PubMedSearch in Google Scholar
• 69 Bennett W D, Olivier K N, Zeman K L. Effect of uridine 5′-triphosphate plus amiloride on mucociliary clearance in adult cystic fibrosis.  Am J Respir Crit Care Med . 1996;  153(Part 1) 1796-1801
  PubMedSearch in Google Scholar
• 70 Sokol R J, Durie P R. Recommendations for management of liver and biliary tract disease in cystic fibrosis. Cystic Fibrosis Foundation Hepatobiliary Disease Consensus Group.  J Pediatr Gastroenterol Nutr . 1999;  28(Suppl 1) 1-13
  PubMedSearch in Google Scholar
• 71 Bhaskar K R, Turner B S, Grubman S A. Dysregulation of proteoglycan production by intrahepatic biliary epithelial cells bearing defective (delta-f508) cystic fibrosis transmembrane conductance regulator.  Hepatology . 1998;  27 7-14
  CrossrefPubMedSearch in Google Scholar
• 72 Oppenheimer E H, Esterly J R. Hepatic changes in young infants with cystic fibrosis: possible relation to focal biliary cirrhosis.  J Pediatr . 1975;  86 683-689
  CrossrefPubMedSearch in Google Scholar
• 73 Peters R H, French P J, van Doorninck H J. CFTR expression and mucin secretion in cultured mouse gallbladder epithelial cells.  Am J Physiol . 1996;  271(Part 1) G1074-G1083
  PubMedSearch in Google Scholar
• 74 Lindblad A, Hultcrantz R, Strandvik B. Bile-duct destruction and collagen deposition: a prominent ultrastructural feature of the liver in cystic fibrosis.  Hepatology . 1992;  16 372-381
  PubMedSearch in Google Scholar
• 75 Malizia G, Brunt E M, Peters M G. Growth factor and procollagen type I gene expression in human liver disease.  Gastroenterology . 1995;  108 145-156
  PubMedSearch in Google Scholar
• 76 Sokol R J. Fat-soluble vitamins and their importance in patients with cholestatic liver diseases.  Gastroenterol Clin North Am . 1994;  23 673-705
  PubMedSearch in Google Scholar
• 77 Sokol R J, Straka M S, Dahl R. Role of oxidant stress in the permeability transition induced in rat hepatic mitochondria by hydrophobic bile acids.  Pediatr Res . 2001;  49 519-531
  PubMedSearch in Google Scholar
• 78 Yerushalmi B, Dahl R, Devereaux M W. Bile acid-induced rat hepatocyte apoptosis is inhibited by antioxidants and blockers of the mitochondrial permeability transition.  Hepatology . 2001;  33 616-626
  CrossrefPubMedSearch in Google Scholar
• 79 Pessayre D, Berson A, Fromenty B. Mitochondria in steatohepatitis.  Semin Liver Dis . 2001;  21 57-69
  Thieme ConnectPubMedSearch in Google Scholar
• 80 Wilschanski M, Zielenski J, Markiewicz D. Correlation of sweat chloride concentration with classes of the cystic fibrosis transmembrane conductance regulator gene mutations.  J Pediatr . 1995;  127 705-710
  CrossrefPubMedSearch in Google Scholar
• 81 Koch C, Cuppens H, Rainisio M. European Epidemiologic Registry of Cystic Fibrosis (ERCF): comparison of major disease manifestations between patients with different classes of mutations.  Pediatr Pulmonol . 2001;  31 1-12
  CrossrefPubMedSearch in Google Scholar
• 82 Colombo C, Apostolo M G, Ferrari M. Analysis of risk factors for the development of liver disease associated with cystic fibrosis.  J Pediatr . 1994;  124 393-399
  PubMedSearch in Google Scholar
• 83 De Arce M, O'Brien S, Hegarty J. Deletion delta F508 and clinical expression of cystic fibrosis-related liver disease.  Clin Genet . 1992;  42 271-272
  PubMedSearch in Google Scholar
• 84 Duthie A, Doherty D G, Williams C. Genotype analysis for delta F508, G551D and R553X mutations in children and young adults with cystic fibrosis with and without chronic liver disease.  Hepatology . 1992;  15 660-664
  PubMedSearch in Google Scholar
• 85 Augarten A, Kerem B S, Yahav Y. Mild cystic fibrosis and normal or borderline sweat test in patients with the 3849 + 10 kb C → T mutation.  Lancet . 1993;  342 25-26
  CrossrefPubMedSearch in Google Scholar
• 86 Scott-Jupp R, Lama M, Tanner M S. Prevalence of liver disease in cystic fibrosis.  Arch Dis Child . 1991;  66 698-701
  PubMedSearch in Google Scholar
• 87 Feigelson J, Anagnostopoulos C, Poquet M. Liver cirrhosis in cystic fibrosis-therapeutic implications and long term follow up.  Arch Dis Child . 1993;  68 653-657
  PubMedSearch in Google Scholar
• 88 Maurage C, Lenaerts C, Weber A. Meconium ileus and its equivalent as a risk factor for the development of cirrhosis: an autopsy study in cystic fibrosis.  J Pediatr Gastroenterol Nutr . 1989;  9 17-20
  PubMedSearch in Google Scholar
• 89 Colombo C, Battezzati P M, Strazzabosco M. Liver and biliary problems in cystic fibrosis.  Semin Liver Dis . 1998;  18 227-235
  PubMedSearch in Google Scholar
• 90 Lindblad A, Strandvik B, Hjelte L. Incidence of liver disease in patients with cystic fibrosis and meconium ileus.  J Pediatr . 1995;  126 155-156
  PubMedSearch in Google Scholar
• 91 Tanner M S, Taylor C J. Liver disease in cystic fibrosis.  Arch Dis Child . 1995;  72 281-284
  PubMedSearch in Google Scholar
• 92 Williams S G, Westaby D, Tanner M S. Liver and biliary problems in cystic fibrosis.  Br Med Bull . 1992;  48 877-892
  PubMedSearch in Google Scholar
• 93 Duthie A, Doherty D G, Donaldson P T. The major histocompatibility complex influences the development of chronic liver disease in male children and young adults with cystic fibrosis.  J Hepatol . 1995;  23 532-537
  CrossrefPubMedSearch in Google Scholar
• 94 Rohlfs E M, Shaheen N J, Silverman L M. Is the hemochromatosis gene a modifier locus for cystic fibrosis?.  Genet Test . 1998;  2 85-88
  PubMedSearch in Google Scholar
• 95 Nagel R A, Westaby D, Javaid A. Liver disease and bile duct abnormalities in adults with cystic fibrosis.  Lancet . 1989;  2 1422-1425
  PubMedSearch in Google Scholar
• 96 Vawter G F, Shwachman H. Cystic fibrosis in adults: an autopsy study.  Pathol Annu . 1979;  14(Part 2) 357-382
  PubMedSearch in Google Scholar
• 97 Sokol R J, Carroll N M, Narkewicz M R, Wagener J S, Accurso F J. Liver blood tests during the first decade of life in children with cystic fibrosis identified by newborn screening.  Pediatr Pulm . 1994;  10 275
  PubMedSearch in Google Scholar
• 98 Kovesi T, Corey M, Tsui L-C. The association between liver disease and mutations of the cystic fibrosis gene.  Pediatr Pulm . 1992;  8 244
  PubMedSearch in Google Scholar
• 99 Lindblad A, Glaumann H, Strandvik B. Natural history of liver disease in cystic fibrosis.  Hepatology . 1999;  30 1151-1158
  CrossrefPubMedSearch in Google Scholar
• 100 Gaskin K J, Waters D LM, Howman-Giles R. Liver disease and common bile duct stenosis in cystic fibrosis.  N Engl J Med . 1988;  318 340-346
  PubMedSearch in Google Scholar
• 101 Debray D, Lykavieris P, Gauthier F. Outcome of cystic fibrosis-associated liver cirrhosis: management of portal hypertension.  J Hepatol . 1999;  31 77-83
  CrossrefPubMedSearch in Google Scholar
• 102 Craig J M. The pathological changes in the liver in cystic fibrosis of the pancreas.  Am J Dis Child . 1957;  93 357-369
  PubMedSearch in Google Scholar
• 103 Vlaman H B, France N E, Wallis P G. Prolonged neonatal jaundice in cystic fibrosis.  Arch Dis Child . 1971;  46 805-809
  PubMedSearch in Google Scholar
• 104 Shapira R, Hadzic N, Francavilla R. Retrospective review of cystic fibrosis presenting as infantile liver disease.  Arch Dis Child . 1999;  81 125-128
  CrossrefPubMedSearch in Google Scholar
• 105 Roy C C, Weber A M, Morin C L. Hepatobiliary disease in cystic fibrosis: a survey of current issues and concepts.  J Pediatr Gastroenterol Nutr . 1982;  1 469-478
  PubMedSearch in Google Scholar
• 106 Lykavieris P, Bernard O, Hadchouel M. Neonatal cholestasis as the presenting feature in cystic fibrosis.  Arch Dis Child . 1996;  75 67-70
  CrossrefPubMedSearch in Google Scholar
• 107 Colombo C, Crosignani A, Battezzati P M. Liver involvement in cystic fibrosis.  J Hepatol . 1999;  31 946-954
  CrossrefPubMedSearch in Google Scholar
• 108 Mack D R, Traystman M D, Colombo J L. Clinical denouement and mutation analysis of patients with cystic fibrosis undergoing liver transplantation for biliary cirrhosis.  J Pediatr . 1995;  127 881-887
  PubMedSearch in Google Scholar
• 109 di Sant'Agnese A P, Blanc W A. A distinctive type of biliary cirrhosis of the liver associated with cystic fibrosis of the pancreas.  Pediatrics . 1956;  18 387-409
  PubMedSearch in Google Scholar
• 110 Feranchak A P, Sontag M K, Wagener J S. Prospective, long-term study of fat-soluble vitamin status in children with cystic fibrosis identified by newborn screen.  J Pediatr . 1999;  135 601-610
  CrossrefPubMedSearch in Google Scholar
• 111 Willi U V, Reddish J M, Teele R L. Cystic fibrosis: its characteristic appearance on abdominal sonography.  AJR . 1980;  134 1005-1010
  PubMedSearch in Google Scholar
• 112 Stern R C, Rothstein F C, Doershuk C F. Treatment and prognosis of symptomatic gallbladder disease in patients with cystic fibrosis.  J Pediatr Gastroenterol Nutr . 1986;  5 35-40
  PubMedSearch in Google Scholar
• 113 Angelico M, Gandin C, Canuzzi P. Gallstones in cystic fibrosis: a critical reappraisal.  Hepatology . 1991;  14 768-775
  CrossrefPubMedSearch in Google Scholar
• 114 Colombo C, Bertolini E, Assaisso M L. Failure of ursodeoxycholic acid to dissolve radiolucent gallstones in patients with cystic fibrosis.  Acta Paediatr . 1993;  82 562-565
  CrossrefPubMedSearch in Google Scholar
• 115 Neglia J P, Fitzsimmons S C, Maisonneuve P. The risk of cancer among patients with cystic fibrosis. Cystic Fibrosis and Cancer Study Group.  N Engl J Med . 1995;  332 494-499
  CrossrefPubMedSearch in Google Scholar
• 116 Potter C J, Fishbein M, Hammond S. Can the histologic changes of cystic fibrosis-associated hepatobiliary disease be predicted by clinical criteria?.  J Pediatr Gastroenterol Nutr . 1997;  25 32-36
  CrossrefPubMedSearch in Google Scholar
• 117 Williams S G, Evanson J E, Barrett N. An ultrasound scoring system for the diagnosis of liver disease in cystic fibrosis.  J Hepatol . 1995;  22 513-521
  CrossrefPubMedSearch in Google Scholar
• 118 Patriquin H, Lenaerts C, Smith L. Liver disease in children with cystic fibrosis: US-biochemical comparison in 195 patients.  Radiology . 1999;  211 229-232
  CrossrefPubMedSearch in Google Scholar
• 119 Dogan A S, Conway J J, Lloyd-Still J D. Hepatobiliary scintigraphy in children with cystic fibrosis and liver disease.  J Nucl Med . 1994;  35 432-435
  PubMedSearch in Google Scholar
• 120 O'Connor P J, Southern K W, Bowler I M. The role of hepatobiliary scintigraphy in cystic fibrosis.  Hepatology . 1996;  23 281-287
  PubMedSearch in Google Scholar
• 121 Colombo C, Castellani M R, Balistreri W F. Scintigraphic documentation of an improvement in hepatobiliary excretory function after treatment with ursodeoxycholic acid in patients with cystic fibrosis and associated liver disease.  Hepatology . 1992;  15 677-684
  PubMedSearch in Google Scholar
• 122 Hubbard A M, Meyer J S, Mahboubi S. Diagnosis of liver disease in children: value of MR angiography.  AJR . 1992;  159 617-621
  PubMedSearch in Google Scholar
• 123 Schoenau E, Boeswald W, Wanner R. High-molecular-mass (``biliary'') isoenzyme of alkaline phosphatase and the diagnosis of liver dysfunction in cystic fibrosis.  Clin Chem . 1989;  35 1888-1890
  PubMedSearch in Google Scholar
• 124 Rattenbury J M, Taylor C J, Heath P K. Serum glutathione S-transferase B1 activity as an index of liver function in cystic fibrosis.  J Clin Pathol . 1995;  48 771-774
  PubMedSearch in Google Scholar
• 125 Gerling B, Becker M, Staab D. Prediction of liver fibrosis according to serum collagen VI level in children with cystic fibrosis.  N Engl J Med . 1997;  336 1611-1612
  CrossrefPubMedSearch in Google Scholar
• 126 Leonardi S, Giambusso F, Sciuto C. Are serum type III procollagen and prolyl hydroxylase useful as noninvasive markers of liver disease in patients with cystic fibrosis?.  J Pediatr Gastroenterol Nutr . 1998;  27 603-605
  CrossrefPubMedSearch in Google Scholar
• 127 Narkewicz M R, Smith D, Gregory C. Effect of ursodeoxycholic acid therapy on hepatic function in children with intrahepatic cholestatic liver disease.  J Pediatr Gastroenterol Nutr . 1998;  26 49-55
  CrossrefPubMedSearch in Google Scholar
• 128 Bianchetti M G, Kraemer R, Passweg J. Use of salivary levels to predict clearance of caffeine in patients with cystic fibrosis.  J Pediatr Gastroenterol Nutr . 1988;  7 688-693
  PubMedSearch in Google Scholar
• 129 Heuman D M. Hepatoprotective properties of ursodeoxycholic acid.  Gastroenterology . 1993;  104 1865-1870
  PubMedSearch in Google Scholar
• 130 Erlinger S, Dumont M. Influence of UDCA on bile secretion. In: Paumgartner G, Stiehl A, Barbara L, et al., eds. Strategies for the Treatment of Hepatobiliary Disease Dordrecht, The Netherlands: Kluwer Academic, 1990: 35-42
  Search in Google Scholar
• 131 Botla R, Spivey J R, Aguilar H. Ursodeoxycholate (UDCA) inhibits the mitochondrial membrane permeability transition induced by glycochenodeoxycholate: a mechanism of UDCA cytoprotection.  J Pharmacol Exp Ther . 1995;  272 930-938
  PubMedSearch in Google Scholar
• 132 Shimokura G H, McGill J, Schlenker T. Ursodeoxycholate increases cytosolic calcium concentration and activates Cl^- currents in a biliary cell line.  Gastroenterology . 1995;  109 965-972
  PubMedSearch in Google Scholar
• 133 Calmus Y, Gane P, Rouger P. Hepatic expression of class I and class II major histocompatibility complex molecules in primary biliary cirrhosis: effect of ursodeoxycholic acid.  Hepatology . 1990;  11 12-15
  CrossrefPubMedSearch in Google Scholar
• 134 Colombo C, Battezzati P M, Podda M. Ursodeoxycholic acid for liver disease associated with cystic fibrosis: a double-blind multicenter trial.  Hepatology . 1996;  23 1484-1490
  PubMedSearch in Google Scholar
• 135 Cotting J, Lentze M J, Reichen J. Effects of ursodeoxycholic acid treatment on nutrition and liver function in patients with cystic fibrosis and longstanding cholestasis.  Gut . 1990;  31 918-921
  PubMedSearch in Google Scholar
• 136 Colombo C, Setchell K D, Podda M. Effects of ursodeoxycholic acid therapy for liver disease associated with cystic fibrosis.  J Pediatr . 1990;  117 482-489
  PubMedSearch in Google Scholar
• 137 Galabert C, Montet J C, Lengrand D. Effects of ursodeoxycholic acid on liver function in patients with cystic fibrosis and chronic cholestasis.  J Pediatr . 1992;  121 138-141
  PubMedSearch in Google Scholar
• 138 van de Meeberg C P, Houwen R H, Sinaasappel M. Low-dose versus high-dose ursodeoxycholic acid in cystic fibrosis-related cholestatic liver disease. Results of a randomized study with 1-year follow-up.  Scand J Gastroenterol . 1997;  32 369-373
  PubMedSearch in Google Scholar
• 139 Lindblad A, Glaumann H, Strandvik B. A two-year prospective study of the effect of ursodeoxycholic acid on urinary bile acid excretion and liver morphology in cystic fibrosis-associated liver disease.  Hepatology . 1998;  27 166-174
  CrossrefPubMedSearch in Google Scholar
• 140 Lepage G, Paradis K, Lacaille F. Ursodeoxycholic acid improves the hepatic metabolism of essential fatty acids and retinol in children with cystic fibrosis.  J Pediatr . 1997;  130 52-58
  PubMedSearch in Google Scholar
• 141 Thomas P S, Bellamy M, Geddes D. Malabsorption of vitamin E in cystic fibrosis improved after ursodeoxycholic acid.  Lancet . 1995;  346 1230-1231
  PubMedSearch in Google Scholar
• 142 Pierro A, Koletzko B, Carnielli V. Resting energy expenditure is increased in infants and children with extrahepatic biliary atresia.  J Pediatr Surg . 1989;  24 534-538
  PubMedSearch in Google Scholar
• 143 Ramsey B W, Farrell P M, Pencharz P. Nutritional assessment and management in cystic fibrosis: a consensus report. The Consensus Committee.  Am J Clin Nutr . 1992;  55 108-116
  PubMedSearch in Google Scholar
• 144 Schuster S R, Shwachman H, Toyama W M. The management of portal hypertension in cystic fibrosis.  J Pediatr Surg . 1977;  12 201-206
  PubMedSearch in Google Scholar
• 145 Berger K J, Schreiber R A, Tchervenkov J. Decompression of portal hypertension in a child with cystic fibrosis after transjugular intrahepatic portosystemic shunt placement.  J Pediatr Gastroenterol Nutr . 1994;  19 322-325
  PubMedSearch in Google Scholar
• 146 Sanyal A J, Purdum III P P, Luketic V A. Bleeding gastroesophageal varices.  Semin Liver Dis . 1993;  13 328-342
  PubMedSearch in Google Scholar
• 147 Stringer M D, Price J F, Mowat A P. Liver cirrhosis in cystic fibrosis.  Arch Dis Child . 1993;  69 407
  PubMedSearch in Google Scholar
• 148 Noble-Jamieson G, Valente J, Barnes N D. Liver transplantation for hepatic cirrhosis in cystic fibrosis.  Arch Dis Child . 1994;  71 349-352
  PubMedSearch in Google Scholar
• 149 Couetil J P, Houssin D P, Soubrane O. Combined lung and liver transplantation in patients with cystic fibrosis. A 4 1/2-year experience.  J Thorac Cardiovasc Surg . 1995;  110 1415-1422
  PubMedSearch in Google Scholar
• 150 Dennis C M, McNeil K D, Dunning J. Heart-lung-liver transplantation.  J Heart Lung Transplant . 1996;  15 536-538
  PubMedSearch in Google Scholar
• 151 Palmer E, Wilhelm J M, Sherman F. Phenotypic suppression of nonsense mutants in yeast by aminoglycoside antibiotics.  Nature . 1979;  277 148-150
  PubMedSearch in Google Scholar
• 152 Bedwell D M, Kaenjak A, Benos D J. Suppression of a CFTR premature stop mutation in a bronchial epithelial cell line.  Nat Med . 1997;  3 1280-1284
  CrossrefPubMedSearch in Google Scholar
• 153 Rubenstein R C, Egan M E, Zeitlin P L. In vitro pharmacologic restoration of CFTR-mediated chloride transport with sodium 4-phenylbutyrate in cystic fibrosis epithelial cells containing delta F508-CFTR.  J Clin Invest . 1997;  100 2457-2465
  PubMedSearch in Google Scholar
• 154 Rubenstein R C, Zeitlin P L. A pilot clinical trial of oral sodium 4-phenylbutyrate (Buphenyl) in deltaF508-homozygous cystic fibrosis patients: partial restoration of nasal epithelial CFTR function.  Am J Respir Crit Care Med . 1998;  157 484-490
  PubMedSearch in Google Scholar
• 155 Eidelman O, Guay-Broder C, van Galen J P. A1 adenosine-receptor antagonists activate chloride efflux from cystic fibrosis cells.  Proc Natl Acad Sci USA . 1992;  89 5562-5566
  PubMedSearch in Google Scholar
• 156 Illek B, Yankaskas J, Machen T E. cAMP and genistein stimulate HCO₃ ^- conductance through CFTR in human airway epithelia.  Am J Physiol . 1997;  272 L752-L761
  PubMedSearch in Google Scholar
• 157 Illek B, Zhang L, Lewis N C. Defective function of the cystic fibrosis-causing missense mutation G551D is recovered by genistein.  Am J Physiol . 1999;  277(Part 1) C833-C839
  PubMedSearch in Google Scholar
• 158 Kelley T J, Al Nakkash L, Cotton C U. Activation of endogenous deltaF508 cystic fibrosis transmembrane conductance regulator by phosphodiesterase inhibition.  J Clin Invest . 1996;  98 513-520
  PubMedSearch in Google Scholar
• 159 Kelley T J, Thomas K, Milgram L J. In vivo activation of the cystic fibrosis transmembrane conductance regulator mutant deltaF508 in murine nasal epithelium.  Proc Natl Acad Sci USA . 1997;  94 2604-2608
  CrossrefPubMedSearch in Google Scholar
• 160 Grubman S A, Fang S L, Mulberg A E. Correction of the cystic fibrosis defect by gene complementation in human intrahepatic biliary cell lines.  Gastroenterology . 1995;  108 584-592
  PubMedSearch in Google Scholar
• 161 Yang Y, Raper S E, Cohn J A. An approach for treating the hepatobiliary disease of cystic fibrosis by somatic gene transfer.  Proc Nat Acad Sci USA . 1993;  90 4601-4605
  PubMedSearch in Google Scholar
• 162 Friedman S L. Molecular mechanisms of hepatic fibrosis and principles of therapy.  J Gastroenterol . 1997;  32 424-430
  PubMedSearch in Google Scholar
• 163 Friedman S L. Molecular regulation of hepatic fibrosis, an integrated cellular response to tissue injury.  J Biol Chem . 2000;  275 2247-2250
  CrossrefPubMedSearch in Google Scholar
• 164 Britton R S, Bacon B R. Role of free radicals in liver diseases and hepatic fibrosis.  Hepatogastroenterology . 1994;  41 343-348
  PubMedSearch in Google Scholar
• 165 Zhang M, Song G, Minuk G Y. Effects of hepatic stimulator substance, herbal medicine, selenium/vitamin E, and ciprofloxacin on cirrhosis in the rat.  Gastroenterology . 1996;  110 1150-1155
  PubMedSearch in Google Scholar