Inhibition of zaleplon metabolism by cimetidine in the human liver : in vitro studies with subcellular fractions and precision-cut liver slices
article
The effect of cimetidine on the metabolism of zaleplon (ZAL) in human liver subcellular fractions and precision-cut liver slices was investigated. 2. ZAL was metabolized to a number of products including 5-oxo-ZAL (M2), which is known to be formed by aldehyde oxidase, N-desethyl-ZAL (DZAL), which is known to be formed by CYP3A forms, and N-desethyl-5-oxo-ZAL (M1). 3. Human liver microsomes catalysed the NADPH-dependent metabolism of ZAL to DZAL. Kinetic analysis of three microsomal preparations revealed mean (±SEM) S<sub>50</sub> and V<sub>max</sub> of 310±24 μM and 920±274 pmol/min/mg protein, respectively. 4. Human liver cytosol preparations catalysed the metabolism of ZAL to M2. Kinetic analysis of three cytosol preparations revealed mean (±SEM), K<sub>m</sub> and V<sub>max</sub> of 124±14 μM and 564±143 pmol/min/mg protein, respectively. 5. Cimetidine inhibited ZAL metabolism to DZAL in liver microsomes and to M2 in the liver cytosol. With a ZAL substrate concentration of 62 μM, the calculated mean (±SEM, n=3) IC<sub>50</sub> were 596±103 and 231±23 μM for DZAL and M2 formation, respectively. Kinetic analysis revealed that cimetidine was a competitive inhibitor of M2 formation in liver cytosol with a mean (±SEM, n=3) K<sub>i</sub> of 155±16 μM. 6. Freshly cut human liver slices metabolized ZAL to a number of products including M1, M2 and DZAL. 7. Cimetidine inhibited ZAL metabolism in liver slices to M1 and M2, but not to DZAL. Kinetic analysis revealed that cimetidine was a competitive inhibitor of M2 formation in liver slices with an average (n = 2 preparations) K<sub>i</sub> of 506 μM. 8. The results demonstrate that cimetidine can inhibit both the CYP3A and aldehyde oxidase pathways of ZAL metabolism in the human liver. Cimetidine appears to be a more potent inhibitor of aldehyde oxidase than of CYP3A forms and hence in vivo is likely to have a more marked effect on ZAL metabolism to M2 than on DZAL formation. 9. The results also demonstrate that precision-cut liver slices may be a useful model system for in vitro drug-interaction studies. Chemicals/CAS: Acetamides; Cimetidine, 51481-61-9; Enzyme Inhibitors; Hypnotics and Sedatives; Pyrimidines; zaleplon, 151319-34-5
Topics
Aldehyde oxidaseCimetidineCytochrome P450 3AReduced nicotinamide adenine dinucleotide phosphateZaleplonCell fractionationDrug inhibitionDrug metabolismHumanHuman cellHuman tissueIn vitro studyLiver metabolismLiver microsomeLiver sliceAcetamidesCimetidineCytosolDose-Response Relationship, DrugDrug InteractionsEnzyme InhibitorsHumansHypnotics and SedativesInhibitory Concentration 50KineticsLiverModels, ChemicalPyrimidinesSubcellular FractionsStaphylococcus phage 3A
TNO Identifier
42186
Source
Xenobiotica, 32(10), pp. 849-862.
Pages
849-862
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