Natural,semisynthetic and synthetic tyrosinase inhibitors

Tyrosinase plays a pivotal role in the synthesis of melanin pigment synthesis on skin utilizing tyrosine as a substrate. Melanin is responsible for the protection against harmful ultraviolet irradiation, which can cause significant pathological conditions, such as skin cancers. However, it can also create esthetic problems when accumulated as hyperpigmented spots. Various skin-whitening ingredients which inhibit tyrosinase activity have been identified. Some of them, especially ones with natural product origins, possess phenolic moiety and have been employed in cosmetic products. Semi-synthetic and synthetic inhibitors have also been developed under inspiration of the natural inhibitors yet some of which have no phenolic groups. In this review, tyrosinase inhibitors with natural, semi-synthetic and synthetic origins are listed up with their structures, activities and characteristics. Further, a recent report on the adverse effect of a natural melanin synthesis inhibitor which was included in skin-whitening cosmetics is also briefly discussed.     

Stoichiometry of interaction between soluble (—)-dopa melanin and enantiomers of ephedrine by NMR spectroscopy

Synthetic soluble (—)-dopa melanin was prepared in deuteriated buffer, pH 8, by autooxidation of the precursor. At 6 mM of the precursor, the incorporation was over 90%. The changes in the line width measurements of N-CH₃ protons of enantiomers of ephedrine in the soluble melanin were quantified by NMR spectroscopy. The dissociation constants of (—)-1R,2S-ephedrine, (+)-1S,2R-ephedrine, (—)-1R,2R-ψ-ephedrine, and (+)-1S,2S-ψ-ephedrine were 11.7, 4.20, 3.60, and 4.80 mM, respectively. Since the concentration of (—)-dopa was known and since the conversion of (—)-dopa to indole units of melanin was considered as 1:1, the stoichiometry of the interaction between the drug and the indole unit was calculated. Based on the dissociation constants of the enantiomers, it appears that up to four molecules of (—)-ephedrine can interact with one indole unit of the melanin, while such a ratio for other isomers appear to be 2:1. The preference by indole units of melanin is stereoselective. © 1992 Wiley-Liss, Inc.     

Suppressive effect of spinach extract on the formation of melanin in B16 mouse melanoma cells

A non-dialyzable extract of fresh spinach leaves exhibited a strong antioxidant activity towards oxidation of linoleic acid and suppressed the melanin formation of a mouse melanoma cell line, B16 melanoma 4A5, without any significant effect on the proliferation of cells.     

Short Communication: Effect of manganese on polysaccharide production and cellular pigmentation in the fungus Aureobasidium pullulans

Manganese supplementation resulted in higher polysaccharide levels and reduced cellular pigmentation by more than 8- or 17-fold after growth for 7d of the fungus Aureobasidium pullulans ATCC 42023 on sucrose or corn syrup, respectively, as a carbon source. The melanin content of the polysaccharide elaborated by ATCC 42023 cells also decreased if MnCl2 was added to the medium. The pullulan content of the polysaccharide synthesized by ATCC 42023 on sucrose was found to increase with increasing levels of manganese, whereas it was lower during growth on corn syrup if manganese was present.     

The effects of parasitic water mite larvae (Arrenurus spp.) on zygopteran imagoes (Odonata)

Arrenurus larvae, ectoparasitic on zygopteran imagoes, attach to the host's cuticle and tear it to obtain the host's tissue fluids. Within the host's epidermis, each larval mite produces a feeding device, the stylostome, a narrow gelatinous resilient blind sac. Heavy mite infestation brings about several wounds in close proximity, accompanied by loss of more or less extensive areas of the epidermis. Despite wound repair by congregating hemocytes, local lack of epidermis seems to enfeeble the host, presumably owing to desiccation. Heavily mite-loaded zygopterans have lost the typical agility and are easily caught. A mite-induced mortality seems to exist in zygopteran populations; the infestation contributes to reduced longevity. The study of formation and decline of the arrenurid stylostome in zygopterans renders it possible to trace cellular defence reactions under natural conditions. Most stylostomes seem to thwart the ability of the host to recognize them as foreign bodies. The host's defence appears as a two-step reaction: (1) initial hemolymph clotting and deposition of melanin associated with aggregating hemocytes at the penetration site, (2) occasional subsequent melanization and cellular encapsulation of the stylostome.     

Selection of malignant melanoma variant cell lines for ovary colonization

Murine melanoma line B16-F1, which shows some specificity for metastatic organ colonization of lung but rarely metastasizes to ovary, was used to select variant cell lines with increased preference for experimental ovary metastasis. Ovary-colonizing melanoma cell lines were sequentially selected in syngeneic C57BL/6 mice by repeated intravenous administration and surgical recovery of ovarian melanoma tumors for tissue culture. After ten selections for experimental ovary metastasis, line B16-010 was established which formed experimental metastatic ovary tumors in almost every test animal. In tissue culture B16–010 cells grew in circular in circular colonies with rounded, smooth cell peripheries compared to B16-F1 cells which were flatter, grew in irregular patterns, and exhibited long cellular projections. Ovary-selected B16 lines contained less melainin pigment (B16-010 < B16-05 < B16-01 ? B16-F1) compared to the parental melanoma line. Together with previous cloning and selection data, these results are consistent with the preexistence of highly malignant cells in the parental tumor population that possess the ability to metastasize to specific organs.     

Establishment of a mouse model for post‐inflammatory hyperpigmentation

Post‐inflammatory hyperpigmentation (PIH) is a common cutaneous condition that can cause a disfigured appearance. However, the pathophysiology of PIH remains poorly understood, at least in part, because an appropriate animal model for research has not been established. In order to analyze the pathomechanism of PIH, we successfully induced PIH in a hairless version of transgenic mice (hk14‐SCF Tg/HRM) that have a human‐type epidermis containing melanin by repeated hapten application of 2,4‐dinitrofluorobenzene. Histopathologic observation showed epidermal hyperplasia, predominant infiltrations of inflammatory cells, and melanin‐containing cells in the dermis just after elicitation of the atopic dermatitis‐like condition. At week 2, the findings were similar to the characteristics of PIH, that is, an increase of melanin without spongiosis or liquid degeneration in the epidermis and an increase in dermal melanophages. Dynamic analysis of melanin showed that the melanin in the dermis remained for a longer duration than in the epidermis. Furthermore, immunohistochemical staining revealed that the majority of cells containing melanin were positive for the anti‐CD68 antibody, but negative for the anti‐F4/80 antibody. These data suggest that novel treatments of PIH should be targeted against macrophages and should eventually lead to the development of new treatment modalities.