Differential effects of Saint John's Wort (hypericum perforatum) on the urinary excretion of D-glucaric acid and 6beta-hydroxycortisol in healthy volunteers.

OBJECTIVE

We investigated the effects of treatment with Saint John's wort (hypericum perforatum) extract on the urinary excretion of D-glucaric acid, 6beta-hydroxycortisol, and free cortisol in order to assess the effect of this extract on the activity of hepatic xenobiotic metabolizing enzymes.

METHODS

Forty-eight healthy volunteers (25 male and 23 female) received a daily dose of 1800 mg hypericum extract for 14 days. Urinary excretion of D-glucaric acid, 6beta-hydroxycortisol, and free cortisol was measured in 24-h urine samples on the day preceding the initiation of hypericum treatment and after 14 days of treatment. D-Glucaric acid was measured enzymatically. Cortisol and 6beta-hydroxycortisol were quantified using high-performance liquid chromatography with ultraviolet detection.

RESULTS

Urinary excretion of D-glucaric acid was unaffected after a 14-day treatment with Saint John's wort extract (26.7 micromol/day vs 27.7 micromol/day; 95% confidence interval of the difference: -1.9 to 3.8). The urinary excretion of 6beta-hydroxycortisol increased from a mean baseline value of 254 microg/day to 369 microg/day (P<0.0001) indicating induction of CYP3A. While the excretion of free cortisol was unaltered, the ratio of 6beta-hydroxycortisol to free cortisol changed significantly from 9.9 at baseline to 14.3 (95% confidence interval of the difference: 2.3-6.5) after Saint John's wort treatment.

CONCLUSIONS

High-dose treatment with Saint John's wort extract induced CYP3A activity in healthy volunteers as evidenced by increased 6beta-hydroxycortisol excretion. This enzyme induction most likely contributes to the decreased bioavailability observed upon co-administration of various drugs with Saint John's wort extract. The D-glucuronic acid pathway appeared unaffected by Saint John's wort.