NLE(4)DPHE(7)ALPHA-MELANOCYTE-STIMULATING HORMONE INCREASES THE EUMELANIN-PHEOMELANIN RATIO IN CULTURED HUMAN MELANOCYTES

In mammals, melanin exists in two chemically distinct forms: the red-yellow phaeomelanin and the brown-black eumelanin. Although administration of the pigmentary hormone cu-melanocyte-stimulating hormone (alpha MSH) and its synthetic analogue Nle(4)DPhe(7) alpha MSH induces skin darkening in man, the increases in melanogenesis in cultured human melanocytes in response to these peptides are relatively small. However, it is possible that MSH affects the eumelanin:phaeomelanin ratio rather than total cellular melanin. Thus, this study examined the specific effects of Nle(4)DPhe(7) alpha MSH on the two melanins in cultured human melanocytes, quantifying eumelanin and phaeomelanin by high performance liquid chromatography. Nle(4)DPhe(7) alpha MSH induced significant increases in the eumelanin content of these cells while having lesser and varied effects on the levels of phaeomelanin. As a consequence, the eumelanin:phaeomelanin ratio was increased in every culture. These results demonstrate that Nle(4)DPbe(7) alpha MSH affects melanin type in human melanocytes and suggest a possible mechanism bp which this peptide induces skin darkening in man.