Asian J Beauty Cosmetol. 2014; 12(6): 891-897.

Evaluation of Effect of Kojic acid by a Novel Flow Cytometric Method in Human Epidermal Melanocyte/keratinocyte Co-culture System

Kojic acid is a fungal metabolite widely used in medicinal and cosmetic formulations as a skin whitening agent. The activity of kojic acid is known to arise primarily from suppressing tyrosinase activity. Although kojic acid is effective in treating hyperpigmentation disorders in human clinical studies, it only shows weak antimelanogenic activity in mono-cultured human primary melanocytes, suggesting that there exists another pharmacological mechanism for in vivo activity of kojic acid. In the present study, we used primary human epidermal melanocytes and keratinocytes co-culture system to elucidate the mechanisms of skin whitening activity of kojic acid. We used a newly developed flow cytometric method to analyze the counts of live melanocytes and keratinocytes separately. When cultured without kojic acid, the proliferation of melanocytes co-cultured with keratinocytes was greatly enhanced compared to that of mono-cultured melanocytes. On the other hand, we found that kojic acid significantly reduced the proliferation of both melanocytes and keratinocytes at 100~200 μM in co-culture system, although kojic acid did not reduce the proliferation of mono-cultured melanocytes nor mono-cultured keratinocytes at the same concentration. These results suggest that kojic acid might suppress the expression of some growth factors produced by melanocytes or keratinocytes in co-culture system, resulting in reduced proliferation of melanocytes. In summary, the mechanisms of the clinical skin whitening activity of kojic acid might include the suppression of melanocyte proliferation as well as the already known activity of tyrosinase suppression. It suggests that a cross-talk between melanocytes and keratinocytes is indispensable to the pharmacological mechanisms of clinically effective dermatological drugs.

Keywords : Kojic acid, Flow cytometry, Melanocyte, Keratinocyte, Co-culture