St. John's wort extract induces CYP3A and CYP2E1 in the Swiss Webster mouse

This investigation was designed to determine the ability of St. John's wort (SJW), a readily available antidepressant, to induce various hepatic drug metabolizing enzymes. SJW (140 or 280 mg/kg/day) was administered to male Swiss Webster mice for 1, 2, or 3 weeks. Enzymatic activity was analyzed in hepatic microsomes for all of the following drug metabolizing enzymes: CYP3A, CYP1A, CYP2E1, and UDP-glucuronosyltransferase (UDPGT). The catalytic activity of CYP1A was unchanged from control following any dose or duration of SJW, while both CYP3A and CYP2E1 catalytic activities were increased 2-fold by both SJW concentrations but only following 3 weeks of administration. Results from Western immunoblotting studies supported the changes in catalytic activity, as protein levels for CYP2E1 and CYP3A were increased (2.5-fold and 6-fold, respectively) following 3 weeks of SJW administration. Additionally, the catalytic activity of the conjugation enzyme UDPGT was unchanged from control following all SJW treatments. These results indicate that in the mouse moderate doses of SJW cause an increase in the catalytic activity and polypeptide levels of CYP2E1 and CYP3A but only following 21 days of administration, while the catalytic activity of CYP1A and UDPGT activity remain unaffected.