An extract of Melia toosendan attenuates endothelin-1-stimulated pigmentation in human epidermal equivalents through the interruption of PKC activity within melanocytes

Abstract

To elucidate the effects of redox balance regulation on epidermal pigmentation, we used an antioxidant-rich extract of the herb Melia toosendan (dried mature fruits) to assess its effect on endothelin-1 (EDN1)-stimulated pigmentation in human epidermal equivalents and analyzed its biological mechanism of action. Addition of the Melia toosendan extract elicited a marked depigmenting effect on EDN1-stimulated pigmentation after 14 days of treatment, which was accompanied by a significant decrease in eumelanin content. Real-time RT-PCR and Western blotting revealed that the EDN1-stimulated expression of melanocyte-specific proteins (including tyrosinase) was significantly suppressed at the gene and protein levels by the extract. Signaling analysis with specific inhibitors and immunoblots revealed that in melanoma cells treated with the extract, there was a marked deficiency in the EDN1-stimulated phosphorylation of Raf-1, MEK, ERK, MITF and CREB. Since all those proteins are downstream phosphorylation targets of PKC activity, these findings indicate that the Melia toosendan extract attenuates the EDN1-stimulated pigmentation by preferentially inhibiting PKC activity within melanocytes.