Arbutin

Arbutin is a hydroquinone glycoside, however the hydroquinone moiety is not solely responsible for the de-pigmentating actions of arbutin. It acts as a competitive inhibitor of tyrosinase enzyme by acting on the L-tyrosine binding site to suppress melanogenesis and mediate its de-pigmenting actions on human skin. Tyrosinase is an enzyme involved in the regulation of rate-limiting steps during the synthesis of melanin; it regulates the conversion of L-tyrosine into L-dopa, and subsequent conversion of L-dopa to L-dopaquinone. Via inhibition of tyrosinase activity in a concentration-dependent manner, arbutin attenuates the production of melanin in melanocytes. While most studies suggest that arbutin has negligible effect on the tyrosinase mRNA expression, a study assessing the effect of arbutin on melanocyte differentiation inducement system using ES cells propose that arbutin may also downregulate the expression of tyrosinase in addition to its inhibitory action on the enzyme. The contradictory findings across studies may be due to previous studies using terminally-differentiated melanocytes and melanoma cells.