Digging Deeper into CYP3A Testosterone Metabolism: Kinetic, Regioselectivity, and Stereoselectivity Differences between CYP3A4/5 and CYP3A7.

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Kandel SE, Han LW, Mao Q, Lampe JN

Digging Deeper into CYP3A Testosterone Metabolism: Kinetic, Regioselectivity, and Stereoselectivity Differences between CYP3A4/5 and CYP3A7.

Drug Metab Dispos. 2017 Dec;45(12):1266-1275. doi: 10.1124/dmd.117.078055. Epub 2017 Oct 6.

PubMed ID

28986474 [ View in PubMed

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Abstract

The metabolism of testosterone to 6beta-hydroxytestosterone (6beta-OH-T) is a commonly used assay to evaluate human CYP3A enzyme activities. However, previous reports have indicated that CYP3A7 also produces 2alpha-hydroxytestosterone (2alpha-OH-T) and that a 2alpha-OH-T/6beta-OH-T ratio may be a unique endogenous biomarker of the activity of the enzyme. Until now, the full metabolite and kinetic profile for testosterone hydroxylation by CYP3A7 has not been fully examined. To this end, we performed a complete kinetic analysis of the 6beta-OH-T, 2alpha-OH-T, and 2beta-hydroxytestosterone metabolites for recombinant Supersome CYP3A4, CYP3A5, and CYP3A7 enzymes and monitored metabolism in fetal and adult human liver microsomes for comparison. In general, a decrease in the velocity of the reaction was observed between CYP3A4 and the two other enzymes, with CYP3A7 showing the lowest metabolic capacity. Interestingly, we found that the 2alpha-OH-T/6beta-OH-T ratio varied with substrate concentration when testosterone was incubated with CYP3A7, suggesting that this ratio would likely not function well as a biomarker for CYP3A7 activity. In silico docking studies revealed at least two different binding modes for testosterone between CYP3A4 and CYP3A7. In CYP3A4, the most energetically favorable docking mode places testosterone in a position with the methyl groups directed toward the heme iron, which is more favorable for oxidation at C6beta, whereas for CYP3A7 the testosterone methyl groups are positioned away from the heme, which is more favorable for an oxidation event at C2alpha In conclusion, our data indicate an alternative binding mode for testosterone in CYP3A7 that favors the 2alpha-hydroxylation, suggesting significant structural differences in its active site compared with CYP3A4/5.

DrugBank Data that Cites this Article

Drug Enzymes

Drug	Enzyme	Kind	Organism	Pharmacological Action	Actions
Testosterone	Cytochrome P450 3A4	Protein	Humans	Unknown	Substrate Inducer	Details