PT  - JOURNAL ARTICLE
AU  - Perloff, Michael D.
AU  - von Moltke, Lisa L.
AU  - Court, Michael H.
AU  - Kotegawa, Tsutomu
AU  - Shader, Richard I.
AU  - Greenblatt, David J.
TI  - Midazolam and Triazolam Biotransformation in Mouse and Human Liver Microsomes: Relative Contribution of CYP3A and CYP2C Isoforms
DP  - 2000 Feb 01
TA  - Journal of Pharmacology and Experimental Therapeutics
PG  - 618--628
VI  - 292
IP  - 2
4099  - http://jpet.aspetjournals.org/content/292/2/618.short
4100  - http://jpet.aspetjournals.org/content/292/2/618.full
SO  - J Pharmacol Exp Ther2000 Feb 01; 292
AB  - Midazolam (MDZ) and triazolam (TRZ) hydroxylation, reactions considered to be cytochrome P-4503A (CYP3A)-mediated in humans, were examined in mouse and human liver microsomes. In both species, α- and 4-hydroxy metabolites were the principal products. Western blotting with anti-CYP3A1 antibody detected a single band of immunoreactive protein in both human and mouse samples: 0.45 ± 0.12 and 2.02 ± 0.24 pmol/mg protein (mean ± S.E., n = 3), respectively. Ketoconazole potently inhibited MDZ and TRZ metabolite formation in human liver microsomes (IC50 range, 0.038–0.049 μM). Ketoconazole also inhibited the formation of both TRZ metabolites and of 4-OH-MDZ formation in mouse liver microsomes (IC50 range, 0.0076–0.025 μM). However, ketoconazole (10 μM) did not produce 50% inhibition of α-OH-MDZ formation in mouse liver microsomes. Anti-CYP3A1 antibodies produced concentration-dependent inhibition of MDZ and TRZ metabolite formation in human liver microsomes and of TRZ metabolite and 4-OH-MDZ formation in mouse liver microsomes to less than 20% of control values but reduced α-OH-MDZ formation to only 66% of control values in mouse liver microsomes. Anti-CYP2C11 antibodies inhibited α-OH-MDZ metabolite formation in a concentration-dependent manner to 58% of control values in mouse liver microsomes but did not inhibit 4-OH-MDZ formation. Thus, TRZ hydroxylation appears to be CYP3A specific in mice and humans. α-Hydroxylation of MDZ has a major CYP2C component in addition to CYP3A in mice, demonstrating that metabolic profiles of drugs in animals cannot be assumed to reflect human metabolic patterns, even with closely related substrates. The American Society for Pharmacology and Experimental Therapeutics