stilbenes and carbamazepine-epoxide

Carbamazepine (CBZ), an antiepileptic with narrow therapeutic window, is a substrate of CYP 3A which metabolizes CBZ to carbamazepine-10,11-epoxide (CBZE), an active metabolite. This study investigated the acute and chronic effects of Polygonum cuspidatum (PC), a resveratrol-rich nutraceutical, on the pharmacokinetics of CBZ in rats and the underlying mechanisms. Rats were orally administered CBZ (200 mg/kg) alone and coadministered with a single dose and the 7th dose of PC (2 g/kg) in a crossover design. The concentrations of CBZ and CBZE in serum and various tissues were determined by HPLC method. The results showed that PC significantly increased the AUC(0-t) of CBZ and CBZE, whereas the formation rate of CBZE was decreased. Tissue analysis showed that the concentrations of CBZ and CBZE in brain, liver and kidney were significantly increased by PC. Cell studies indicated that the efflux function of MRP 2 was inhibited by the serum metabolites of PC. In conclusion, PC markedly increased the systemic exposure and brain concentration of CBZ and CBZE through inhibiting the activities of CYP 3A and MRP 2.

Topics: Administration, Oral; Animals; Anticonvulsants; Area Under Curve; Brain; Carbamazepine; Chromatography, High Pressure Liquid; Cross-Over Studies; Cytochrome P-450 CYP3A; Cytochrome P-450 CYP3A Inhibitors; Fallopia japonica; Herb-Drug Interactions; Kidney; Liver; Male; Multidrug Resistance-Associated Protein 2; Multidrug Resistance-Associated Proteins; Plant Extracts; Rats; Rats, Sprague-Dawley; Resveratrol; Stilbenes; Tissue Distribution

Microsomal epoxide hydrolase (HYL1) is a single-gene enzyme responsible for the hydrolysis of epoxides derived from the oxidative metabolism of xenobiotics. Variation in HYL1, therefore, may be an important determinant of drug toxicity. We have investigated HYL1 enzyme kinetics in six different species including man, for which a liver bank genotyped for polymorphisms in exons 3 and 4 of the HYL1 gene was used. Activity was measured by radiochromatography with high specific activity radiolabeled substrates, cis-stilbene oxide (CSO) and carbamazepine 10,11-epoxide (CBZ-E). In addition, naphthalene was used to investigate the hydrolysis of an epoxide (naphthalene 1,2-epoxide [N-E] generated in situ. There was marked species variation in enzyme activity that was substrate dependent. CSO was rapidly hydrolyzed by microsomes from all species, the rank order of specific activity being human > rabbit > dog > rat > hamster > mouse. In contrast, hydrolysis of CBZ-E was only observed with human liver microsomes. CBZ-E was only a weak (IC50 = 1 mM) inhibitor of CSO hydrolysis. The hydrolysis of N-E, determined as the diol-to-total metabolite ratio, was human > rabbit > dog > hamster > mouse > rat. Intraspecies variation in man was 4-fold, 7-fold and 2-fold for CSO, CBZ-E and N-E, respectively: none of this variation could be directly accounted for by the HYL1 polymorphisms in exons 3 and 4. These data emphasize the need for careful toxicokinetic evaluation of species used in the safety evaluation of compounds likely to form epoxide intermediates in vivo.

Topics: Adult; Animals; Carbamazepine; Cricetinae; Cytochrome P-450 Enzyme System; Dogs; Epoxide Hydrolases; Exons; Female; Humans; Kinetics; Male; Mice; Microsomes, Liver; Middle Aged; Naphthalenes; Polymorphism, Genetic; Rabbits; Rats; Species Specificity; Stilbenes