RT Journal Article
SR Electronic
T1 Comparative Metabolic Capabilities of CYP3A4, CYP3A5, and CYP3A7
JF Drug Metabolism and Disposition
JO Drug Metab Dispos
FD American Society for Pharmacology and Experimental Therapeutics
SP 883
OP 891
DO 10.1124/dmd.30.8.883
VO 30
IS 8
A1 Williams, J. Andrew
A1 Ring, Barbara J.
A1 Cantrell, Varon E.
A1 Jones, David R.
A1 Eckstein, James
A1 Ruterbories, Kenneth
A1 Hamman, Mitchell A.
A1 Hall, Stephen D.
A1 Wrighton, Steven A.
YR 2002
UL http://dmd.aspetjournals.org/content/30/8/883.abstract
AB The human cytochromes P450 (P450) CYP3A contribute to the biotransformation of 50% of oxidatively metabolized drugs. The predominant hepatic form is CYP3A4, but recent evidence indicates that CYP3A5 contributes more significantly to the total liver CYP3A than was originally thought. CYP3A7 is the major fetal form and is rarely expressed in adults. To compare the metabolic capabilities of CYP3A forms for 10 substrates, incubations were performed using a consistent molar ratio (1:7:9) of recombinant CYP3A, P450 reductase, and cytochrome b5. A wide range of substrate concentrations was examined to determine the best fit to kinetic models for metabolite formation. In general, Km orS50 values for the substrates were 3 to 4 times lower for CYP3A4 than for CYP3A5 or CYP3A7. For a more direct comparison of these P450 forms, clearance to the metabolites was determined as a linear relationship of rate of metabolite formation for the lowest substrate concentrations examined. The clearance for 1′-hydroxy midazolam formation at low substrate concentrations was similar for CYP3A4 and CYP3A5. For CYP3A5 versus CYP3A4, clearance values at low substrate concentrations were 2 to 20 times lower for the other biotransformations. The clearance values for CYP3A7-catalyzed metabolite formation at low substrate concentrations were substantially lower than for CYP3A4 or CYP3A5, except for clarithromycin, 4-OH triazolam, and N-desmethyl diltiazem (CYP3A5 ≈ CYP3A7). The CYP3A forms demonstrated regioselective differences in some of the biotransformations. These results demonstrate an equal or reduced metabolic capability for CYP3A5 compared with CYP3A4 and a significantly lower capability for CYP3A7. The American Society for Pharmacology and Experimental Therapeutics