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 tyros inase inhibitory action, and phenolic compounds structurally similar to L-t yrosine were determined by cyclic voltammetry. The voltammograms obtained c ould be classified into 4 patterns (patterns 1-4). Pattern 1, characterized by oxidation and reduction peaks as a pair, was observed with catechol, hy droquinone or phenol, and pattern 2 exhibiting another oxidation peak in ad dition to oxidation and reduction peaks as a pair was found with arbutin, k ojic acid, resorcinol, methyl p-hydroxybenzoate and L-tyrosine as the subst rate of tyrosinase. Pattern 3 with an independent oxidation peak only was e xpressed by L-ascorbic acid, and pattern 4 with a reduction peak only at hi gh potentials, by hinokitiol. The tyrosinase inhibitory activity of these c ompounds was also evaluated using the 50% inhibitory concentration (IC50) a nd the inhibition constant (Ki) as parameters. Hinokitiol, classified as pa ttern 4, showed the highest inhibitory activity (lowest IC50 and Ki). Hydro quinone showing the second highest activity belonged to pattern 1, which al so included compounds showing no inhibition of tyrosinase activity The inhi bitory activity of compounds exhibiting pattern 2 was relatively low with K i values being in the order of 10(-4) M. Although there was no consistent r elationship between oxidation-reduction potentials and tyrosinase inhibitor y action, the voltammetry data can be used as an additional index to establ ish the relationship between the structure and the tyrosine inhibitory acti vity.