Kinobeon A as a potent tyrosinase inhibitor from cell culture of safflower: in vitro comparisons of kinobeon A with other putative inhibitors

Kinobeon A is produced from cell cultures of the medicinal plant, safflower. Mushroom tyrosinase activity was inhibited in a concentration-dependent manner when treated with kinobeon A using L-tyrosine or L-3,4-dihydroxyphenylalannine (L-DOPA) as substrates. IC50 values were 22 microM (substrate: L-tyrosine) and 27 microM (L-DOPA). Inhibition of human tyrosinase activity also increased with increasing concentrations of kinobeon A using L-DOPA as the substrate, with an IC50 value of 2.5 microM. Kinobeon A was a more potent competitive inhibitor than kojic acid, arbutin or L-ascorbic acid for both mushroom and human tyrosinase as determined from Lineweaver-Burk plots. These results suggested that kinobeon A could be a potent natural tyrosinase inhibitor.