Melanogenesis in cultured melanocytes can be substantially influenced by l-tyrosine and l-cysteine

We investigated the effect of varying concentration of l-tyrosine and l- cysteine in culture medium on melanin production by human skin melanocytes (skin phototype II/III). In addition to the analyses of dopa oxidase activity and total melanin, pheomelanin production in the cells was assessed by high- performance liquid chromatography determinations of pheomelanin degradation products, 3-aminotyrosine and 4-amino-3-hydroxyphenylalanine. As another marker for pheomelanin, melanosomal sulfur was determined by the use of X- ray microanalysis. With varying concentration of both amine acids, profound changes in the pigmentation patterns of the melanocytes were observed. A high concentration of l-tyrosine (0.2 mM) was always connected with increased pigmentation. In combination with a low l-cysteine content we saw an increase in tyrosinase activity and the highest melanin content. At high concentrations of both l-tyrosine and l-cysteine, the melanocytes showed reduced tyrosinase activity and they produced notably more pheomelanin. In case of the pheomelanin measurements by high-performance liquid chromatography and the sulfur detection with X-ray microanalysis, strongly increased concentrations were found when cells were maintained in high l- tyrosine medium as compared with those grown with low l-tyrosine. This was especially true for the combination with low l-cysteine showing that the l- tyrosine content of the medium strongly influences not only the eumelanin but also the pheomelanin production in the cultured melanocyte. It can be concluded that variations in the concentrations of l-tyrosine and l-cysteine in culture medium can be used to regulate the melanogenetic phenotype under in vitro conditions.