title: Unchanged cytochrome P450 3A (CYP3A) expression and metabolism of midazolam, triazolam, and dexamethasone in mdr(-/-) mouse liver microsomes.
abstract: P-Glycoprotein (P-gp) and cytochrome P450 3A (CYP3A) share common substrates and expression properties, but the relationship of mdrl deficiency to CYP3A-mediated metabolism and protein expression is not established. The in vitro kinetic parameters of CYP3A-mediated metabolism of midazolam (MDZ), triazolam (TRZ), and dexamethasone (DEX) were studied in liver microsomes from three mrdrla(-/-) mice, one mdrla/b(-/-) mouse, and mdrla/b(+/+) controls. The kinetic profiles of CYP3A-mediated MDZ 4-hydroxylation were not significantly different between mdrl-deficient animals and controls. Overall mean (+/- SEM, N = 8) values were: Vmax, 0.74+/-0.05 nmol/min/mg protein; Km, 28.2+/-2.7 microM; and estimated intrinsic clearance, 0.026+/-0.003 mL/min/mg protein. Likewise, rates of formation of alpha-OH- and 4-OH-TRZ (from 500 microM TRZ), and of DEX metabolites sensitive to ketoconazole inhibition, M1 and M5 (from 20 microM DEX), did not differ between mdrl-deficient and control animals. Immunoquantified microsomal CYP3A protein levels in mdrla(-/-), mdrla/b(-/-), and mdrla/b(+/+) mice were not different, with overall mean immunoreactive protein levels of 2.68+/-0.09 pmol/microg protein. Although CYP3A and P-gp share aspects of activity and expression, disruption of the mdrl genes does not affect CYP3A-mediated metabolism or protein expression in the mouse.
authors.affiliation: Department of Pharmacology and Experimental Therapeutics, Tufts University School of Medicine, New England Medical Center Hospital, Boston, MA 02111, USA.
authors.forename: M D
authors.initials: MD
authors.lastname: Perloff
authors.forename: L L
authors.initials: LL
authors.lastname: von Moltke
authors.forename: M M
authors.initials: MM
authors.lastname: Cotreau
authors.forename: D J
authors.initials: DJ
authors.lastname: Greenblatt
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000235:genetics / Q000378:metabolism; D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases; D001711:Biotransformation; D015153:Blotting, Western; D051544:Cytochrome P-450 CYP3A; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis* / Q000235:genetics; D003907:Dexamethasone / Q000378:metabolism*; D051379:Mice; D008862:Microsomes, Liver / Q000378:metabolism*; D008874:Midazolam / Q000378:metabolism*; D010089:Oxidoreductases, N-Demethylating / Q000096:biosynthesis* / Q000235:genetics; D014229:Triazolam / Q000378:metabolism*
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D014229:Triazolam; D003907:Dexamethasone; D003577:Cytochrome P-450 Enzyme System; D001189:Aryl Hydrocarbon Hydroxylases; D051544:Cytochrome P-450 CYP3A; D010089:Oxidoreductases, N-Demethylating; D008874:Midazolam