Abrogating effect of a xanthophyll carotenoid astaxanthin on the stem cell factor-induced stimulation of human epidermal pigmentation

Abstract

We established a model for the stem cell factor (SCF)-associated stimulation of human epidermal equivalent (HEE) pigmentation. The addition of SCF (at 5nM) gradually stimulated the visible pigmentation of HEEs over 14days of treatment. A time course study using real-time RT-PCR and western blotting analysis demonstrated that the expression of all melanocyte-specific genes and proteins examined was gradually up-regulated over 7-10days of treatment with SCF. The addition of astaxanthin (Ax) at concentrations of 1, 4, or 8μM markedly abolished the SCF- but not the endothelin (EDN)1-elicited increase in visible pigmentation over 14days in a dose-dependent manner, with almost complete inhibition at 8μM. While no degeneration of the epidermal tissue was visible at day 14 by HE staining, melanin deposition throughout the epidermis was markedly reduced in the Ax-treated HEEs at day 14 compared to untreated controls. Ax significantly reduced the eumelanin content of HEEs to the non-SCF-stimulated level at concentrations of 4 or 8μM compared with untreated controls. Real-time RT-PCR and western blotting of Ax-treated HEEs revealed that the SCF-stimulated expression of tyrosinase (TYR), TYR-related protein-1 (TYRP1), and Pmel17, as well as microphthalmia-associated transcription factor (MITF), is significantly suppressed by Ax at the transcriptional and translational levels. Studies using cultured normal human melanocytes revealed that pre-treatment with Ax interrupts the SCF- but not the EDN1-induced stimulation of TYR activity, and there was no direct inhibitory effect of Ax on TYR activity in vitro. These findings indicate that Ax attenuates SCF-stimulated pigmentation by directly interrupting SCF-associated intracellular signaling linkages through increased expression of MITF, which leads to the stimulated expression of melanogenic genes and proteins in a reactive oxygen species depletion-independent mechanism.