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Acta Pharmacol Sin. 2001 Feb;22(2):148-54.

Role of cytochrome P450 in estradiol metabolism in vitro.

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1
Pharmacogenetics Research Institute, Hunan Medical University, Changsha 410 078, China.

Abstract

AIM:

Catechol estrogens and 16alpha-hydroxy estrogen are important metabolites that cause carcinogenesis. This study was aimed to stud y the role of cytochrome P450 in estradiol metabolism.

METHODS:

The estradiol metabolites were determined with HPLC-ECD. Correlation of estradiol metabolites production between cytochrome P450 activity, the inhibitory effect of specific inhibitors and enzyme catalyzing kinetics were studied in cDNA-expressed P450 or human liver microsomes.

RESULT:

CYP1A2, CYP3A4, and CYP2C9 catalyze the estradiol 2-hydroxylation. CYP2C9, CYP2C19, and CYP2C8 have high activity in catalyzing 17beta-hydroxy dehydrogenation in cDNA expressed P450, but CYP1A2 is the most important enzyme in catalyzing estradiol 2-hydroxylation. Using furafyllin and troleandomycin to inhibit CYP1A2 and CYP3A4 in liver microsomes, it was found that the 2-hydroxylation had been inhibited about the same amount. This result suggests that in human liver microsomes CYP1A2 and CYP3A4 play an important role in 2-hydroxy estradiol formation. At low substrate concentration, 17beta -hydroxy dehydrogenation dominated the estradiol metabolism, but at high substrate concentration, 2-hydroxylation exceeded 17beta-hydroxy dehydrogenation to become the important mechanism.

CONCLUSION:

CYP1A2 and CYP3A4 are two important enzymes catalyzing the main estradiol 2-hydroxylation metabolism pathway at high substrate concentrations. 17beta-hydroxy dehydrogenation is the main metabolism pathway at low concentrations, and CYP2C9, CYP2C19, and CYP2C8 may have high catalyzing activity.

PMID:
11741520
[Indexed for MEDLINE]
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