Rhododendrol, a depigmentation-inducing phenolic compound, exerts melanocyte cytotoxicity via a tyrosinase-dependent mechanism

Pigment Cell Melanoma Res. 2014 Sep;27(5):754-63. doi: 10.1111/pcmr.12269. Epub 2014 Jun 26.


Rhododendrol, an inhibitor of melanin synthesis developed for lightening/whitening cosmetics, was recently reported to induce a depigmentary disorder principally at the sites of repeated chemical contact. Rhododendrol competitively inhibited mushroom tyrosinase and served as a good substrate, while it also showed cytotoxicity against cultured human melanocytes at high concentrations sufficient for inhibiting tyrosinase. The cytotoxicity was abolished by phenylthiourea, a chelator of the copper ions at the active site, and by specific knockdown of tyrosinase with siRNA. Hence, the cytotoxicity appeared to be triggered by the enzymatic conversion of rhododendrol to active product(s). No reactive oxygen species were detected in the treated melanocytes, but up-regulation of the CCAAT-enhancer-binding protein homologous protein gene responsible for apoptosis and/or autophagy and caspase-3 activation were found to be tyrosinase dependent. These results suggest that a tyrosinase-dependent accumulation of ER stress and/or activation of the apoptotic pathway may contribute to the melanocyte cytotoxicity.

Keywords: ER stress; chemical leukoderma; cytotoxicity; depigmentation; rhododendrol; tyrosinase; vitiligo.

MeSH terms

  • Agaricales / enzymology
  • Apoptosis
  • Butanols / chemistry
  • Butanols / toxicity*
  • Caspase 3 / metabolism
  • Catalytic Domain
  • Cell Survival
  • Cells, Cultured
  • Chelating Agents / chemistry
  • Copper / chemistry
  • Endoplasmic Reticulum Stress
  • Enhancer Elements, Genetic
  • Enzyme-Linked Immunosorbent Assay
  • Gene Expression Profiling
  • Gene Expression Regulation
  • Humans
  • Hypopigmentation / chemically induced
  • Inhibitory Concentration 50
  • Interleukin-8
  • Melanocytes / cytology
  • Melanocytes / drug effects
  • Monophenol Monooxygenase / antagonists & inhibitors
  • Monophenol Monooxygenase / chemistry
  • Monophenol Monooxygenase / metabolism*
  • Phenylthiourea / chemistry
  • Pigmentation / drug effects*
  • RNA, Small Interfering / metabolism
  • Reactive Oxygen Species / metabolism
  • Skin Lightening Preparations / chemistry
  • Skin Lightening Preparations / toxicity*
  • Up-Regulation
  • Vitiligo / drug therapy


  • Butanols
  • Chelating Agents
  • Interleukin-8
  • RNA, Small Interfering
  • Reactive Oxygen Species
  • Skin Lightening Preparations
  • rhododendrol
  • Phenylthiourea
  • Copper
  • Monophenol Monooxygenase
  • Caspase 3