Endocrinology of St. John’s Wort extract

Trials of antidepressant medications for smoking cessation have had mixed results. We conducted a double-blind, placebo-controlled trial of a sustained-release form of bupropion for smoking cessation. We excluded smokers with current depression, but not those with a history of major depression. The 615 subjects were randomly assigned to receive placebo or bupropion at a dose of 100, 150, or 300 mg per day for seven weeks. The target quitting date (or "target quit date") was one week after the beginning of treatment. Brief counseling was provided at base line, weekly during treatment, and at 8, 12, 26, and 52 weeks. Self-reported abstinence was confirmed by a carbon monoxide concentration in expired air of 10 ppm or less. At the end of seven weeks of treatment, the rates of smoking cessation as confirmed by carbon monoxide measurements were 19.0 percent in the placebo group, 28.8 percent in the 100-mg group, 38.6 percent in the 150-mg group, and 44.2 percent in the 300-mg group (P<0.001). At one year the respective rates were 12.4 percent, 19.6 percent, 22.9 percent, and 23.1 percent. The rates for the 150-mg group (P=0.02) and the 300-mg group (P=0.01) -- but not the 100-mg group (P=0.09) -- were significantly better than those for the placebo group. Among the subjects who were continuously abstinent through the end of treatment, the mean absolute weight gain was inversely associated with the dose (a gain of 2.9 kg in the placebo group, 2.3 kg in 100-mg and 150-mg groups, and 1.5 kg in the 300-mg group; P= 0.02). No effects of treatment were observed on depression scores as measured serially by the Beck Depression Inventory. Thirty-seven subjects stopped treatment prematurely because of adverse events; the frequency was similar among all groups. A sustained-release form of bupropion was effective for smoking cessation and was accompanied by reduced weight gain and minimal side effects. Many participants in all groups were smoking at one year.

St John's Wort (hypericum perforatum) is an herbal medicine that is frequently used for therapy of mild depression. Recently, St John's Wort was reported to substantially decrease blood/plasma concentrations and efficacy of cyclosporine (INN, ciclosporin), indinavir, and digoxin. In this study we investigated the mechanisms of these St John's Wort-induced drug interactions. In a preclinical study, the administration of St John's Wort extract to rats during 14 days resulted in a 3.8-fold increase of intestinal P-glycoprotein/Mdrl expression and in a 2.5-fold increase in hepatic CYP3A2 expression (Western blot analyses). In a clinical study, the administration of St John's Wort extract to 8 healthy male volunteers during 14 days resulted in an 18% decrease of digoxin exposure after a single digoxin dose (0.5 mg), in 1.4- and 1.5-fold increased expressions of duodenal P-glycoprotein/MDR1 and CYP3A4, respectively, and in a 1.4-fold increase in the functional activity of hepatic CYP3A4 (14C-erythromycin breath test). These results indicate direct inducing effects of St John's Wort on intestinal P-glycoprotein/MDR1 (in rats and humans), hepatic CYP3A2 (in rats), and intestinal and hepatic CYP3A4 (in humans). Therefore the results provide a mechanistic explanation for the previously observed drug interactions in patients and support the importance of intestinal P-glycoprotein/MDR1 in addition to intestinal and hepatic CYP3A4 for overall drug absorption and disposition in humans.

Hydroalcoholic hypericum extract inhibits the synaptosomal uptake of serotonin, norepinephrine, and dopamine with about similar affinities and leads to a significant down-regulation of cortical beta-adrenoceptors and 5-HT2-receptors after subchronic treatment of rats. While neither hypericine nor kaempferol did show any reuptake inhibiting properties, hyperforin was identified as the unspecific reuptake inhibitor of hypericum extracts with half-maximal inhibitory concentrations for the three synaptosomal uptake systems mentioned above between 80 and 200 nmol/l. Moreover, a hyperforin-enriched (38%) CO2 extract also leads to a significant beta-receptor down-regulation after subchronic treatment. The data suggest hyperforin as the active principle of hypericum extracts in biochemical models of antidepressant activity.