The pigmentary activities of the neurohormone, melatonin, have long fascinated dermatologists. Yet, cell culture reports are contradictory, and it remains unclear how melatonin alters melanocyte physiology in human epidermis. Thus, we have asked in healthy, organ-cultured, full-thickness human eyelid skin whether melatonin stimulates/inhibits melanin production by epidermal melanocytes that operate within their natural skin habitat. By assessing melanin content, tyrosinase activity in situ, melanocyte number, proliferation, and dendricity (gp100/Ki-67 IF), we show here that, after 3 days of organ culture, 200ug/mL melatonin initially reduces the epidermal melanin content, but without affecting tyrosinase activity or melanocyte proliferation/number (no significant changes seen for 100ug/mL). However, after 6 days of culture, 100ug/mL melatonin increases epidermal melanin content, the melanized epidermal area, and melanocyte dendricity, while inhibiting tyrosinase activity in situ. At this time, 200ug/mL melatonin has no effect on epidermal melanin content or melanocyte dendricity yet continues to inhibit tyrosinase activity. Unexpectedly, it stimulates epidermal melanocyte and keratinocyte proliferation in situ. Thus, melatonin’s effects on human epidermal melanocytes ex vivo are complex, concentration- and time-dependent, possibly reflecting gradual changes in skin level of potent melatonin metabolites. That melanin production does not correlate with intraepidermal tyrosinase activity suggests tyrosinase-independent pigmentary effects of melatonin. Our ex vivo data raise the question whether short-term pulse therapy with high-dose melatonin may help to lighten hyperpigmented human skin lesions, while lower-dose long-term therapy could restimulate melanogenesis, and increase the pool and activity of epidermal melanocytes in hypopigmented lesions.

ESDR527 - Long-term melatonin treatment stimulates melanin production as well as melanocyte dendricity and proliferation in human epidermis ex vivo

The scientific meeting of the European Society for Dermatological Research (ESDR) is held yearly, usually in September. With an international attendance of more than 1000 skin scientists from around the globe, the four-day event includes short oral presentations from peer-reviewed abstracts, keynote lectures from international experts, sponsored symposia, satellite programs, educational events as well as an important focus on posters, networking and building collaborations amongst scientists. For more information about this year’s meeting visit our website.