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Int. J. Mol. Sci. 2018, 19(2), 552;

Biochemical Mechanism of Rhododendrol-Induced Leukoderma

Department of Chemistry, Fujita Health University School of Health Sciences, 1-98 Dengakugakubo, Kutsukake-cho, Toyoake, Aichi 470-1192, Japan
Author to whom correspondence should be addressed.
Received: 30 January 2018 / Revised: 9 February 2018 / Accepted: 10 February 2018 / Published: 12 February 2018
(This article belongs to the Special Issue Melanins and Melanogenesis: From Nature to Applications)
PDF [1389 KB, uploaded 12 February 2018]


RS-4-(4-hydroxyphenyl)-2-butanol (rhododendrol (RD))—a skin-whitening ingredient—was reported to induce leukoderma in some consumers. We have examined the biochemical basis of the RD-induced leukoderma by elucidating the metabolic fate of RD in the course of tyrosinase-catalyzed oxidation. We found that the oxidation of racemic RD by mushroom tyrosinase rapidly produces RD-quinone, which gives rise to secondary quinone products. Subsequently, we confirmed that human tyrosinase is able to oxidize both enantiomers of RD. We then showed that B16 cells exposed to RD produce high levels of RD-pheomelanin and protein-SH adducts of RD-quinone. Our recent studies showed that RD-eumelanin—an oxidation product of RD—exhibits a potent pro-oxidant activity that is enhanced by ultraviolet-A radiation. In this review, we summarize our biochemical findings on the tyrosinase-dependent metabolism of RD and related studies by other research groups. The results suggest two major mechanisms of cytotoxicity to melanocytes. One is the cytotoxicity of RD-quinone through binding with sulfhydryl proteins that leads to the inactivation of sulfhydryl enzymes and protein denaturation that leads to endoplasmic reticulum stress. The other mechanism is the pro-oxidant activity of RD-derived melanins that leads to oxidative stress resulting from the depletion of antioxidants and the generation of reactive oxygen radicals. View Full-Text
Keywords: rhododendrol; 4-(4-hydroxyphenyl)-2-butanol; whitening agent: tyrosinase; melanocyte toxicity; sulfhydryl group; glutathione; cysteine; ultraviolet A; reactive oxygen species rhododendrol; 4-(4-hydroxyphenyl)-2-butanol; whitening agent: tyrosinase; melanocyte toxicity; sulfhydryl group; glutathione; cysteine; ultraviolet A; reactive oxygen species

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Ito, S.; Wakamatsu, K. Biochemical Mechanism of Rhododendrol-Induced Leukoderma. Int. J. Mol. Sci. 2018, 19, 552.

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