The Skin-Lightening Effects of Artocarpin on UVB-Induced Pigmentation

• Abstract
• Materials and Methods
• References

Abstract

This study was conducted to evaluate the effects of the prenylated flavonol artocarpin from the heartwood of Artocarpus incisus on ultraviolet (UV)-induced hyperpigmentation of guinea pig skin. An efficient lightening effect was observed following topical application of artocarpin to UV-stimulated hyperpigmented dorsal skins of brownish guinea pigs.

Melanin pigment is a heterogeneous biopolymer formed from various intermediate products derived from dopaquinone; it is synthesized within melanocytes in the epidermis. The perceived color of skin and hair is determined by the ratio of eumelanins (brown and black pigments) to pheomelanins (amber and orange pigments), and in part on blood within the dermis. The balance in skin hue is regulated by many factors [1]. Exposure of skin to ultraviolet (UV) radiation, particularly in the ultraviolet-B (UVB) wavelengths, upregulates the synthesis of melanocyte tyrosinase, resulting in increased melanogenesis and thus tanning. Pharmacologic inhibitors of tyrosinase or other melanogenic pathway targets may serve as topical de novo inhibitors of melanogenesis, resulting in a skin-lightening effect [2]. The perceived uses of skin-lightening products vary among cultures and races around the world. Therefore, the intended uses range from genuine therapeutics for skin diseases to vanity-based, beauty-enhancing products [3]. In Japan, several products containing arbutin [4], kojic acid [5], or other substances are available to the public as cosmeceuticals. In our continuing search for melanin biosynthesis inhibitors from woody species, the crude methanol extract of the heartwood of Artocarpus incisus L. f. (Moraceae) showed inhibitory activity on mushroom tyrosinase and, after being subjected to further fractionation, yielded isolates of several potent tyrosinase inhibitors (2). A main component in the extract, artocarpin [6-(3-methyl-1-butenyl)-5,2′,4′-trihydroxy-3-isoprenyl-7-methoxyflavone], showed distinct skin-lightening effects on the UVB-induced hyperpigmented dorsal skin of brownish guinea pigs. This was surprising because this component showed no inhibitory activity on mushroom tyrosinase [2].[*]

Representative results of the lightening effect of artocarpin, kojic acid, and arbutin on UVB-induced hyperpigmentation at 0, 8, 22, and 29 days are shown in Fig. [1]. ΔL* values, which indicate the degree of pigmentation before and after up to 35 days of daily topical applications of artocarpin, kojic acid, or arbutin, are shown in Fig. [2]. The ΔL* values of the 10 guinea pig skins treated with artocarpin only (4.1 ± 0.64 at 29 days) were significantly lower than those of the base-solution-treated skins (6.1 ± 0.56 at 29 days) (Fig. [2]). The skin color of the artocarpin-treated skins became lighter than that of the control (Fig. [1] b - d). Furthermore, kojic acid and arbutin each appeared to produce only a slight lightening effect, and this effect was not significantly different from that of the control treatment (Figs. [1], [2]). It should be noted that kojic acid and arbutin have each been reported to show skin whitening effects [4], [5]. It is not easy to relate our data precisely to those of earlier reports because of differences in test methods (e. g., the dosage of UV radiation, the applied concentration, and so on).

 In in vitro experiments, inhibition of mushroom tyrosinase activity by artocarpin was not observed [2], suggesting that the mechanism of the pigment-reducing effect of artocarpin may exclude the inhibition of tyrosinase activity. However, it should be noted that the mushroom tyrosinase differs somewhat from those from other sources [3].

It was considered that artocarpin would be a good candidate for medicines and cosmetics used to treat sun-exposure pigmentation or pigmented skin disorders such as melasma, if safety is guaranteed. Additional studies on the skin-lightening mechanism of artocarpin and on the relationship between artocarpin’s structure and its lightening activity are in progress.

Materials and Methods

All chemicals used were of reagent grade (>98 %). Artocarpin was isolated previously [6] and its purity was confirmed by HPLC. UVB-induced hyperpigmentation was elicited on the backs of brownish guinea pigs (male, 9-week-old, 471 - 551 g, KYUDO Co., Ltd., Japan) using a modification of the method of Yokota et al. [7]. The guinea pigs were gently tethered without anesthesia, and four separate areas (2.2 cm × 2.2 cm) on the back of each animal were exposed to UVB radiation (Toshiba FL40S·BLB, Japan). The total energy dose of UVB was 1350 mJ/cm² per exposure. Groups of 10 animals were used in each experiment. The animals were exposed to UVB radiation once a day for three days. Then, a 0.25-M sample solution (base solution: propylene glycol/ethanol = 1/6) was topically applied daily to the irradiated areas (20 μl/cm²) five times per week for five successive weeks, while the base solution without the sample was applied to other areas as a control. Once every week from the beginning of sample application, the degree of pigmentation was assessed as the absolute value of ΔL*, calculated by the L* value (brightness index) measured with a chromameter (CR-200, Minolta, Japan), as follows: ΔL* = L* (at each day measured) - L* (at day 0). An increase in the absolute value of ΔL* indicates UVB-induced pigmentation of the skin. Kojic acid [5] and arbutin [4] were each used to compare with artocarpin. Differences between mean values were assessed for statistical significance by using the paired Student’s t-test.

References

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Kuniyoshi Shimizu, PhD

Laboratory of Systematic Forest and Forest Products Science

Department of Forestry and Forest Products Sciences

Faculty of Agriculture

Kyushu University

6-10-1 Hakozaki, Higashi-ku

Fukuoka, 812-8581

Japan

Phone: +81-92-642-2991

Fax: +81-92-642-3078, +81-92-642-2990

Email: shimizu@agr.kyushu-u.ac.jp

References

• 1 Hearing V J, Tsukamoto K. Enzymatic control of pigmentation in mammals.  FASEB Journal. 1991;  5 2902-9
  PubMedSearch in Google Scholar
• 2 Shimizu K, Kondo R, Sakai K, Lee S -H, Sato H. The inhibitory components from Artocarpus incisus on melanin biosynthesis.  Planta Medica. 1998;  64 408-12
  PubMedSearch in Google Scholar
• 3 Dooley T P. Topical skin depigmentation agents: current products and discovery of novel inhibitors of melanogenesis.  Journal of Dermatological Treatment. 1997;  8 275-9
  PubMedSearch in Google Scholar
• 4 Sugai T. Clinical effects of arbutin in patients with chloasma (in Japanese).  Hifu (Skin Research). 1992;  34 522-9
  PubMedSearch in Google Scholar
• 5 Mishima Y, Ohyama Y, Shibata T, Seto H, Hatae S. Inhibitory of kojic acid on melanogenesis and its therapeutic effect for various human hyper-pigmentation disorders (in Japanese).  Hifu (Skin Research). 1994;  36 134-50
  PubMedSearch in Google Scholar
• 6 Sato M, Fujiwara S, Tsuchiya H, Fujii T, Iinuma M, Tosa H, Ohkawa Y. Flavones with antibacterial activity against cariogenic bacteria.  Journal of Ethnopharmacology. 1996;  54 171-6
  CrossrefPubMedSearch in Google Scholar
• 7 Yokota T, Nishio H, Kubota Y, Mizoguchi M. The inhibitory effect of glabridin from licorice extracts on melanogenesis and inflammation.  Pigment Cell Research. 1998;  11 355-61
  CrossrefPubMedSearch in Google Scholar

Kuniyoshi Shimizu, PhD

Laboratory of Systematic Forest and Forest Products Science

Department of Forestry and Forest Products Sciences

Faculty of Agriculture

Kyushu University

6-10-1 Hakozaki, Higashi-ku

Fukuoka, 812-8581

Japan

Phone: +81-92-642-2991

Fax: +81-92-642-3078, +81-92-642-2990

Email: shimizu@agr.kyushu-u.ac.jp