Ultrastructural study of a black insulinoma

Arbutin increases the pigmentation of cultured human melanocytes through mechanisms other than the induction of tyrosinase activity

We assessed the effects of arbutin on the pigmentation of cultured normal human melanocytes. As indicated by a cell-blotting assay, arbutin at concentrations in the range of 0.5-8 mM increased the pigmentation of the cultured melanocytes, while kojic acid at concentrations in the range of 0.5-4 mM decreased the pigmentation. The pigmentation-augmenting effect of arbutin was further confirmed by the results of a cell-pelleting assay, the traditional method of assessment. Treatment of the cells with arbutin increased the melanin content of the cells and the protein content as well. On the other hand, the tyrosinase activity in the cells was reduced by arbutin treatment. The levels of transcription of tyrosinase and tyrosinase related protein-1 genes were not affected by arbutin treatment as indicated by a semi-quantitative reverse transcription-polymerase chain reaction assay. These results demonstrate that arbutin promotes an increase in pigmentation of cultured human melanocytes that is not mediated by augmented tyrosinase activity.