Short-sequence oligopeptides with inhibitory activity against mushroom and human tyrosinase

Cutaneous hyperpigmentation is a common disorder due to excess melanin production by the enzyme Tyrosinase. The gold standard for treatment is hydroquinone (HQ), which reduces pigmentation through its toxicity to melanocytes rather than via Tyrosinase inhibition. We screened an internal library for oligopeptides that inhibited both mushroom and human Tyrosinase but showed no cytotoxicity to human melanocytes. We identified two highly active inhibitory sequences, P3 and P4, of 8- and 10-amino-acid-length, respectively. Mushroom Tyrosinase inhibition was dose-dependent with IC(50) (half-maximal inhibitory concentration) values of 123 and 40 microM, respectively, compared with 680 microM for HQ. Other oligopeptides showed weaker or no inhibitory activity. Kinetic studies showed that P3 and P4 are competitive inhibitors of mushroom Tyrosinase. At 100 microM, P3 and P4 inhibited human Tyrosinase by 25-35%. This inhibition partially depended on whether L-dopa or L-tyrosine was the substrate, suggesting that Tyrosinase may contain contains two distinct catalytic sites. Treatment of melanocytes with 100 microM P3 or P4 for 7 days led to a 27 or 43% reduction in melanin content. This inhibition was independent of cell proliferation and cytotoxic effects. Our data suggest that peptide-mediated inhibition of melanogenesis is due to reduction in Tyrosinase activity.