Effects of baicalein and wogonin isolated from Scutellaria baicalensis roots on skin damage in acute UVB-irradiated hairless mice

Solar ultraviolet (UV) radiation causes skin damage including increases in skin thickness, edema, and flush. In this study, we examined the effects of two main flavonoids (wogonin and baicalein) isolated from the roots of Scutellaria baicalensis, a traditional remedy for allergic inflammatory diseases long used in China and Japan, on acute UVB irradiation-induced skin damage in hairless mice. Baicalein and wogonin (10 or 50 mg/kg) were administered orally twice daily for 14 consecutive days. The UVB irradiation was performed at a dose of 200 mJ/cm2 on days 7 and 8 of the treatment with the two main flavonoids. Baicalein, and wogonin prevented the increases in skin thickness and the levels of matrix metalloproteinase (MMP)-9, and vascular endothelial growth factor (VEGF) induced by the irradiation. Wogonin reduced the levels of cyclooxygenase (COX)-2 and hypoxia inducible factor (HIF)-1α in UVB-treated HaCaT cells. These findings suggest that wogonin inhibits irradiation-induced skin damage by suppressing increases in the levels of MMP-9, and VEGF through the inhibition of COX-2 and HIF-1α expression. Baicalein inhibited COX-2 and NF-κB/p65 expression, but stimulated HIF-1α expression. Therefore, its inhibitory action is likely due to the expression of MMP-9 and VEGF through the suppression of COX-2 and NF-κB/p65 expression. Furthermore, the inhibitory effects of baicalein on UVB-irradiated hyperplasia of skin epidermis may be due to the stimulation of HIF-1α expression.