Pimecrolimus increases the melanogenesis and migration of melanocytes in vitro

Vitiligo is an intriguing depigmentary disorder and is notoriously difficult to be treated. The ultimate goal of vitiligo treatment is to replenish the lost melanocytes by immigration from hair follicle and to restore the normal function of melanogenesis by residual melanocytes. There are two types of topical calcineurin inhibitors called tacrolimus and pimecrolimus, and are recommended as the first-line treatments in vitiligo. Although pimecrolimus is efficacious for the repigmentation of vitiligo, its intrinsic mechanisms have never been investigated in vitro. This research aimed to study the ability of pimecrolimus on stimulating melanogenesis, melanocyte migration and MITF (microphthalmia associated transcription factor) protein expression. Results showed that pimecrolimus at the dosages of 1, 10, 10² nM were neither mitogenic nor cytotoxic to melanocytes. The addition of pimecrolimus at 10, 10² and 10³ nM significantly increased intracellular tyrosinase activity, which was consistent with the elevated content of melanin content at the same concentrations. The peak effect was seen at 72 h in response to 10² nM pimecrolimus. Results of the wound scratch assay and Transwell assays indicate that pimecrolimus is effective in facilitating melanocyte migration on a collagen IV-coated surface. In addition, MITF protein yield reached the highest by pimecrolimus at 10² nM. In brief, pimecrolimus enhances melanin synthesis as well as promotes migration of melanocytes directly, possibly via their effects on MITF protein expression.