St. John's wort formulations induce rat CYP3A23-3A1 independent of their hyperforin content .

The pregnane X receptor (PXR) is a ligand activated regulator of cytochrome P450 (CYP)3A enzymes. Among the ligands of human PXR is hyperforin, a constituent of St John's wort (SJW) extracts and potent inducer of human CYP3A4. It was the aim of this study to compare the effect of hyperforin and SJW formulations controlled for its content on CYP3A23-3A1 in rats. Hyperiplant was used as it contains a high hyperforin content and Rebalance because it is controlled for a low hyperforin content. analysis revealed a weak hyperforin-rPXR binding affinity, which was further supported in cell-based reporter gene assays showing no hyperforin-mediated reporter activation in presence of rPXR. However, cellular exposure to Hyperiplant and Rebalance transactivated the CYP3A-reporter 3.8 fold and 2.8 fold, respectively, and they induced mRNA expression in rat hepatoma cells compared to control 48-fold and 18-fold, respectively. In Wistar rats treated for 10 days with 400 mg/kg of Hyperiplant we observed 1.8-times the mRNA expression, a 2.6-fold higher CYP3A23-3A1 protein amount and a 1.6-fold increase in activity compared to control. For Rebalance we only observed a 1.8-fold hepatic increase of CYP3A23-3A1 protein compared to control animals. Even though there are differing effects on r/CYP3A23-3A1 in rat liver reflecting the hyperforin content of the SJW extracts, the modulation is most likely not linked to an interaction of hyperforin with rPXR. Treatment with St John's wort (SJW) has been reported to affect CYP3A expression and activity in rats. Our comparative study further supports this finding but shows that the PXR-ligand hyperforin is not the driving force for changes in rat CYP3A23-3A1 expression and function and Importantly, CYP3A induction mimics findings in humans but our results suggest that another so far unknown constituent of SJW is responsible for the expression and function modifying effects in rat liver.