Effect of an extract of the root of Scutellaria baicalensis and its flavonoids on aflatoxin B1 oxidizing cytochrome P450 enzymes

The inhibition of aflatoxin B-1 (AFB(1)) metabolism by a water extract of the root of Scutellaria boicalensis and its flavonoids was examined in liver microsomes, AFB(1) is known to be metabolized to aflatoxin M-1 (AFM(1)), aflatoxin Q(1) (AFQ(1)), and AFB(1)-8,9-epoxide (AFBO). The water extract potently inhibited the production of AFM(1) by cytochrome P450 (CYP)1A1/2 and slightly reduced AFBO formation by CYP1A1/2, CYP2B1, CYP2C11 and CYP3A1/2 in TCDD-treated rat liver microsomes. IC50 values for AFM(1) and AFBO formation were 6.8 and 122.4 mug/ml, respectively. Wogonin showed the highest inhibitory activity towards AFM, formation among the flavonoids isolated from the extract. On the other hand, the extract had no effects on the formation of AFBO and AFQ(1) in human liver microsomes, and on the activities of CYP2B1, CYP2C11 and C/P3A1/2 which were detected by hydroxylation patterns of testosterone. These results demonstrated that the extract of the Foot of Scutellaria baicalensis has a specific inhibitory effect on CYP1A1/2 among CYP enzymes involved in AFB(1) metabolism by rat and human microsomes.