Effect of L - tyrosine on Proliferation and Melanization in Cultured Normal Human Melanocytes

Lee, Mu Hyoung; Kim, Jin Hwan; Park, Jai Kyung; Haw, Choong Rim

Abstract

BACKGROUND: The biosynthesis of melanin is initiated by the enzymatic oxidation of L-tyrosine to L-dopa by tyrosinase. Some precursors of melanin are cytotoxic, and melanoma cells are killed as a risk of exposare to excess tyrosine or dopa in the culture medium. However, there have been few observations of the effects of L-tyrosine on cultured normal human melanocyte.
OBJECTIVE
In order to investigate whether exogenous tyrosine induces cytotoxicity in cultured normal human melanocytes as in melanoma cells, we examined the effects of L-tyrosine on proliferation and melanization in normal human melanocytes.
METHODS
A melanocyte culture was produced with a modified TIC medium. L-tyrosine was added to the culture medium, 100, 200, 400, and 800uM. After 2 days of incubation, the proliferation was measured by methylthiazol tetrazolium(MTT) assay and sulforhodamine B(SRB) assay. The melanin contenis were also measured by the modified Whittaker's method.
RESULTS
On MTT assay, the proliferation of melanocytes had been stirnulated significantly (p< 0.05) in all L-tyrosine added groups. On SRB assay, the proliferation of melanocytes had heen stimulated significantly (p<005) in 200, 400, 800uM of L-tyrosine added groups. The melanin contents had increased in all L-tyrosine added groups, and had increased significantly (p<0.05) in 400uM of L-tyrosine added group.
CONCLUSION
L-tyrosine is not toxic to normal melanocytes, It stimulates the proliferation and melnization of cultured normal human melanocytes.