TY - JOUR T1 - Selective time- and NADPH-dependent inhibition of human CYP2E1 by Clomethiazole JF - Drug Metabolism and Disposition JO - Drug Metab Dispos DO - 10.1124/dmd.116.070193 SP - dmd.116.070193 AU - David M. Stresser AU - Elke S Perloff AU - Andrew K Mason AU - Andrew P Blanchard AU - Shangara S Dehal AU - Timothy P Creegan AU - Ritu Singh AU - Eric T Gangl Y1 - 2016/01/01 UR - http://dmd.aspetjournals.org/content/early/2016/05/05/dmd.116.070193.abstract N2 - The sedative clomethiazole (CMZ) has been used in Europe since the mid-1960s to treat insomnia and alcoholism. It has been previously demonstrated to reversibly inhibit human CYP2E1 in vitro and decrease CYP2E1-mediated elimination of chlorzoxazone in clinical studies. We have investigated the selectivity of CMZ inhibition of CYP2E1 in pooled human liver microsomes (HLM). In a reversible inhibition assay of the major drug-metabolizing cytochrome P450 isoforms, CYP2A6 and CYP2E1 exhibited IC50 values of 24 μM and 42 μM, respectively with all other isoforms tested exhibiting values > 300 μM. However, when CMZ was preincubated with NADPH and liver microsomal protein for 30 min prior to combining with probe substrates, more potent inhibition was observed for CYP2E1 and CYP2B6, but not CYP2A6 or other P450 isoforms. The substantial increase in potency of CYP2E1 inhibition upon preincubation enables the use of CMZ to investigate the role of human CYP2E1 in xenobiotic metabolism that may provide advantages over other chemical inhibitors of CYP2E1. The KI and kinact values obtained with HLM-catalyzed 6-hydroxylation of chlorzoxazone were found to be 40 μM and 0.35 min-1, respectively and similar to values obtained with recombinant CYP2E1 (41 μM, 0.32 min-1). The KI and kinact values along with other parameters were used in a mechanistic static model to explain published observations of profound inhibition of CYP2E1 in vivo in the absence of detectable CMZ in volunteers ER -