The cytotoxicity and apoptosis induced by 4-tertiary butylphenol in human melanocytes are independent of tyrosinase activity

Abstract

It has been known for several decades that cutaneous depigmentation, i.e., contact/occupational vitiligo, can be caused by some phenolic derivatives that have a similar structure to tyrosine. Among these phenolic depigmenting agents, 4-tertiary butylphenol is the most potent. The cutaneous depigmentation induced by phenolic derivatives results from the loss of functional melanocytes. Tyrosinase is a melanocyte specific copper-containing enzyme that catalyzes the conversion of the amino acid tyrosine, through a complex series of intermediates, to melanin. In this study we tested the hypothesis that the cytotoxicity induced by 4-tertiary butylphenol is mediated by tyrosinase and occurs via an apoptotic process. Melanocyte cultures derived from African-American and Caucasian donors exhibiting a 3-fold difference in tyrosinase activity and 14-fold difference in melanin content demonstrate comparable concentration-dependent sensitivity to 4-tertiary butylphenol. In addition, cultures of dermal fibroblasts and epidermal keratinocytes exhibited similar and reduced sensitivity, respectively, to 4-tertiary butylphenol compared with autologous melanocytes. Two melanoma cell lines, one melanotic and one amelanotic lacking the expression of both tyrosinase protein and activity, when transfected with the tyrosinase cDNA, exhibited no alteration in its sensitivity to 4-tertiary butylphenol. These data suggest that 4-tertiary butylphenol cytotoxicity is not mediated via tyrosinase. Melanocytes treated with 4-tertiary butylphenol, however, did exhibit plasma membrane blebbing, DNA fragmentation, and phosphatidylserine relocalization indicating that 4-tertiary butylphenol induced melanocyte destruction occurs by an apoptotic process.