Role of Cyp2e1 in Deramciclane Metabolism

Abstract

ABSTRACT:The aim of our study was to identify the form(s) of cytochrome P450 responsible for the metabolism of deramciclane, a new anxiolytic drug candidate. The main routes of biotransformation in hepatic microsomes were side chain modification (N-demethylation or total side chain cleavage) and hydroxylation at several points of the molecule. Although several cytochrome P450 forms were involved in the metabolism, the role of CYP2E1 should be emphasized, since it catalyzed almost all steps. Production of deramciclane metabolites was significantly inhibited by diethyldithiocarbamate and was elevated in liver microsomes of isoniazid-treated rats. Furthermore, cDNA-expressed rat CYP2E1 generated the metabolites formed by side chain modification and hydroxylation. Neither deramciclane nor its primary metabolite, N-desmethyl deramciclane were able to influence directly the activity of CYP2E1. However, during the biotransformation, one or more metabolites must have been formed which were potent inhibitors of CYP2E1.Variability in drug response is often due to interindividual differences in drug metabolism. A patient's individual response to a drug depends on the activities of drug-metabolizing enzymes that determine the fate and elimination of the drug from the body. One of the reasons for variable drug metabolism is the polymorphic expression of these enzymes, mainly cytochromes P450 (P450s). Although poor metabolizers often have a low frequency in the population, being a poor metabolizer can cause severe side effects if a drug is metabolized through a polymorphic enzyme, particularly if it is the only pathway of the elimination (Tamási et al., 2003). Another aspect of interindividual variation involves enzyme induction and inhibition (Rendic and Di Carlo, 1997;Maurel, 1998). Not only drugs, but smoking, alcohol consumption, or foodstuffs can act as inducers or inhibitors of drug-metabolizing enzymes. Environmental influences (including drug interactions) and clinical consequences can be predicted from the identification of the enzyme(s) responsible for the metabolic steps. The procedures to determine the P450 form(s) involved in drug metabolism can use P450 form-selective inhibitors as well as microsomes containing cDNA-expressed P450 proteins (Ono et al., 1996).Deramciclane, developed by EGIS Pharmaceuticals Ltd. (Budapest, Hungary), is a new non-benzodiazepine-type anxiolytic agent that is more effective than diazepam or chlordiazepoxide (Gacsályi et al., 1988;Berényi et al., 1990). Its anticonvulsant activity is exerted via inhibition of synaptosomal ␥-aminobutyric acid uptake (Kovács et al., 1989). Our previous work (Monostory et al., 2005) identified the structures of the metabolites formed during the biotransformation of deramciclane in rat, mouse, rabbit, dog, and human primary hepatocytes. Deramciclane underwent side chain modification and oxidation at several positions of the molecule. The side chain modification led to the formation of N-desmethyl deramciclane and phenylborneol. The oxidation of deramcicla...

The Role of Analytical Chemistry in the Safety of Drug Therapy

“…8.15) [251]. Radio-HPLC detectors are standard accessories in laboratories dealing with metabolic research.…”

“…15 Radio-HPLC chromatogram of deramciclan and its metabolites in incubation media with human and rat liver microsomes. Reproduced with permission from Ref [251],. Reproduced with permission from Ref [251],.…”

Effects of cytochrome P450 (CYP) inducers and inhibitors on ondansetron pharmacokinetics in rats: involvement of hepatic CYP2D subfamily and 3A1/2 in ondansetron metabolism

“…The maximum velocity (V max ) and the apparent Michaelis-Menten constant (K m ; the concentration at which the rate is one half of the V max ) for the disappearance of ondansetron were determined after incubating the above microsomal fraction (equivalent to 0.5 mg protein), a 50-mL aliquot of distilled water containing the final ondansetron concentrations of 0.05, 0.1, 0.2, 0.5, 1, 2, and 5 mM as free ondansetron, a 5-mL aliquot of methanol containing 3 mM quinine or 50 mM troleandomycin (Monostory et al 2005), and a 50-mL aliquot of 0.1 M phosphate buffer (pH 7.4) containing 1 mM NADPH in a final volume of 0.5 mL by adding 0.1 M phosphate buffer (pH 7.4) in a water-bath shaker (37°C, 500 oscillationsmin −1 ). For the studies on the mechanism-based inhibitor (troleandomycin) and controls, the hepatic microsomes and NADPH were preincubated for 15 min, and 20 units of catalase were added to prevent auto-inactivation of CYP isozymes during preincubation of microsomes with NADPH (Huskey et al 1995).…”