Relationship between tyrosinase inhibitory action and oxidation-reduction potential of cosmetic whitening ingredients and phenol derivatives.

The oxidation-reduction potentials of cosmetic raw materials, showing tyrosinase inhibitory action, and phenolic compounds structurally similar to L-tyrosine were determined by cyclic voltammetry. The voltammograms obtained could be classified into 4 patterns (patterns 1-4). Pattern 1, characterized by oxidation and reduction peaks as a pair, was observed with catechol, hydroquinone or phenol, and pattern 2 exhibiting another oxidation peak in addition to oxidation and reduction peaks as a pair was found with arbutin, kojic acid, resorcinol, methyl p-hydroxybenzoate and L-tyrosine as the substrate of tyrosinase. Pattern 3 with an independent oxidation peak only was expressed by L-ascorbic acid, and pattern 4 with a reduction peak only at high potentials, by hinokitiol. The tyrosinase inhibitory activity of these compounds was also evaluated using the 50% inhibitory concentration (IC50) and the inhibition constant (Ki) as parameters. Hinokitiol, classified as pattern 4, showed the highest inhibitory activity (lowest IC50 and Ki). Hydroquinone showing the second highest activity belonged to pattern 1, which also included compounds showing no inhibition of tyrosinase activity. The inhibitory activity of compounds exhibiting pattern 2 was relatively low with Ki values being in the order of 10(-4) M. Although there was no consistent relationship between oxidation-reduction potentials and tyrosinase inhibitory action, the voltammetry data can be used as an additional index to establish the relationship between the structure and the tyrosine inhibitory activity.