Skin care cosmetics frequently contain whitening or lightening agents. The present study aimed to establish in vitro
methods for predicting chemical leukoderma caused by whitening agents in cosmetics. The risks of chemical leukoderma were predicted based on percutaneous absorption rates, toxic concentrations, and toxicity mechanisms. Thus, in vitro
skin permeation rate and cytotoxic concentrations of whitening agents were studied using excised skin and cultured B16 melanoma cells. Pigment cell toxicity was observed using transmission electron microscopy (TEM). The levels of hydroxyl radical (∙OH) were measured and the location of ∙OH generation sites were determined in cultured B16 melanoma cells. Pigment cells cultured under conditions with high tyrosinase activity developed cytotoxicity when exposed to compounds known to cause leukoderma, while those cultured under conditions with low tyrosinase activity did not. Phenolic compounds that cause leukoderma were applied to the pigment cells at the concentration absorbed percutaneously under conditions with high tyrosinase activity. Cells that were observed using TEM demonstrated a large number of vacuolar degenerations in intracellular melanosomes after treatment with phenolic compounds that are known to cause leukoderma. Hydroxyl radical generation during the tyrosinase reaction was examined, as the whitening agents that inhibit tyrosinase activity serve as tyrosinase substrates. Only phenolic compounds that cause leukoderma generated high amounts of hydroxyl radicals. Thus, the hydroxyl radical is a melanocyte-specific toxin that disrupts tyrosinase-containing melanosomes. Whitening agents that generate high amounts of hydroxyl radicals may cause leukoderma. The in vitro
method being reported here can predict the potential of a drug to cause leukoderma and whether the use of a specific whitening agent poses a risk.
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