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. In silico 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 Cyp3a23-3a1 mRNA expression in rat hepatoma cells compared with 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 Cyp3a23-3a1 mRNA expression, a 2.6-fold higher CYP3A23-3A1 protein amount, and a 1.6-fold increase in activity compared with controls. For Rebalance we only observed a 1.8-fold hepatic increase of CYP3A23-3A1 protein compared with control animals. Even though there are differing effects on rCyp3a23-3a1/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. SIGNIFICANCE STATEMENT: 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 pregnane X receptor-ligand hyperforin is not the driving force for changes in rat CYP3A23-3A1 expression and function in vivo and in vitro. 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.

Simultaneous quantification of atorvastatin, erlotinib and OSI-420 in rat serum and liver microsomes using a novel liquid chromatography-mass spectrometry method.

Erlotinib is an epidermal growth factor receptor tyrosine kinase inhibitor used in the treatment of cancer. Atorvastatin is a statin commonly applied to treat hypercholesterolemia. In humans, both compounds are metabolized by CYP3A4 and are transported by OATP2B1, ABCB1 and ABCG2. We aimed to generate and validate a bioanalytical method for simultaneous determination of atorvastatin, erlotinib and its major metabolite OSI-420 applicable to biological samples. Quantification of erlotinib, OSI-420, and atorvastatin was achieved with an Agilent high-performance liquid chromatography system 1100/1200 coupled to a triple quadrupole G6410B. The method involved separation over the column Kinetex C8 (100 × 3 mm, 2.6 µm) using 2 mM ammonium acetate (pH 4.0) and acetonitrile as eluent. The method was assessed for selectivity, accuracy, recovery, matrix effect, and stability over a range from 1 to 4,000 ng/mL according to the respective guidelines. We applied the bioanalytical method to quantify the formation of OSI-420 in liver microsomes isolated from male and female Wistar rats. The optimized experiment revealed slower formation in microsomes of female compared to male rats, in which we observed lower amounts of CYP3A1 by Western blot analysis. Moreover, the presence of atorvastatin inhibited the CYP3A-mediated metabolism of erlotinib. Serum obtained from a drug-drug interaction study performed in male rats was also analyzed using the validated method. Non-compartmental pharmacokinetic analysis revealed a lower clearance of erlotinib when atorvastatin was co-administered. However, for atorvastatin we observed a lower systemic exposure in presence of erlotinib. In summary, we report a method to detect OSI-420, erlotinib and atorvastatin applicable to samples from ex vivo and in vivo studies.