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 baicalensis 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. IC 50 values for AFM 1 and AFBO formation were 6.8 and 122.4μg/ml, respectively. Wogonin showed the highest inhibitory activity towards AFM 1 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 CYP3A1/2 which were detected by hydroxylation patterns of testosterone. These results demonstrated that the extract of the root of Scutellaria baicalensis has a specific inhibitory effect on CYP1A1/2 among CYP enzymes involved in AFB 1 metabolism by rat and human microsomes.