Abstract
Scutellaria baicalensis Georgi root is traditionally used as a Chinese herbal medicine that has anti-pyretic and anti-inflammatory properties. In addition to these traditional uses, recent studies have shown that S. baicalensis has a lightening effect on skin pigmentation. The identity of the active ingredient responsible for its skin pigmentation-lightening effect or its mechanism of action is still unclear. This study reports three major findings: (1) S. baicalensis exhibits the highest inhibitory activity against melanogenesis among the 137 species of herbal plants tested; (2) an O-methylated flavone, wogonin, was identified as the active component of S. baicalensis that inhibits melanogenesis; and (3) the microphthalmia-associated transcription factor (MITF), is the probable target of wogonin to induce melanogenesis suppression. In addition, we found that wogonin inhibits the intracellular transport of melanosomes in melanocytes, suggesting that wogonin has bi-functional effects in terms of depigmentation. Several wogonin analogs and other major flavones present in S. baicalensis failed to inhibit intracellular trafficking of melanosomes, highlighting the unique effect of wogonin. Moreover, wogonin specifically decreases the concentration of the melanophilin (MLPH) protein but not that of other actin-based melanosome-transport-related molecules. Our findings reveal the potential applicability of S. baicalensis, which comprises wogonin and other flavones, in skin lightening and treating hyperpigmentation.