Variability of CYP3A7 expression in human fetal liver.

Abstract

Fetal liver CYP3A7 plays an important role in placental estriol synthesis during pregnancy, yet little is known concerning the extent or consequences of variability in expression. The purpose of this investigation was to characterize the variability in CYP3A7 expression using several phenotypic measures in a panel of 54 fetal livers ranging in age from 76 days to 32 weeks gestation. CYP3A7 mRNA expression was measured using quantitative polymerase chain reaction, whereas immunoreactive CYP3A7 was determined using an affinity-purified antipeptide antibody. Variability in catalytic activity was evaluated using testosterone and dehydroepiandrosterone (DHEA) as substrates. Across the entire panel, CYP3A7 was the most abundant CYP3A mRNA species present and varied 634-fold from 151 to 95,700 transcripts/ng total RNA, corrected for 18S ribosomal RNA. CYP3A4 expression was minimal based on mRNA expression (1000-fold lower than CYP3A7) and the ratio of testosterone 2alpha- (T2alphaH) to 6beta- (T6betaH) hydroxylation. T2alphaH and T6betaH were highly correlated (r(2) = 0.859), and the correlation increased (r(2) = 0.974) in livers with CYP3A5*3/*3 genotypes implying that the same enzyme (CYP3A7) generated both products. Overall, T2alphaH and DHEA16alphaH activities varied 175- and 250-fold, respectively. A subset of five samples had extremely low mRNA, protein, and catalytic activity, possibly due to pathology affecting fetal viability (anencephaly, porencephaly). In the remaining samples, T2alphaH activity varied 6.7-fold (358 +/- 142, range 97 to 643 pmol/min/mg) and DHEA16alphaH activity varied 6.2-fold (8.07 +/- 2.87, range 2.41 to 14.9 nmol/min/mg). Observed variability in CYP3A7 activity was not related to CYP3A7*2, and alternative regulatory mechanisms require further investigation.

• Authors: J Steven Leeder, Roger Gaedigk, Kenda A Marcucci, Andrea Gaedigk, Carrie A Vyhlidal, Bradley P Schindel, Robin E Pearce
• Journal: The Journal of pharmacology and experimental therapeutics (J Pharmacol Exp Ther) Vol. 314 Issue 2 Pg. 626-35 (Aug 2005) ISSN: 0022-3565 [Print] United States
• PMID: 15845858 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, U.S. Gov't, P.H.S.)

Chemical References

• Testosterone
• Dehydroepiandrosterone
• RNA
• DNA
• Cytochrome P-450 Enzyme System
• Aryl Hydrocarbon Hydroxylases
• CYP3A protein, human
• CYP3A5 protein, human
• CYP3A7 protein, human
• Cytochrome P-450 CYP3A
• CYP3A4 protein, human

Topics

• Adult
• Aryl Hydrocarbon Hydroxylases (biosynthesis, immunology)
• Biotransformation
• Catalysis
• Chromatography, High Pressure Liquid
• Cytochrome P-450 CYP3A
• Cytochrome P-450 Enzyme System (genetics, metabolism)
• DNA (genetics, isolation & purification)
• Dehydroepiandrosterone (metabolism)
• Female
• Gene Expression Regulation, Enzymologic (physiology)
• Genotype
• Humans
• Hydroxylation
• Immunohistochemistry
• Liver (embryology, enzymology)
• Male
• Microsomes, Liver (enzymology)
• Pregnancy
• RNA (biosynthesis, genetics)
• Reverse Transcriptase Polymerase Chain Reaction
• Testosterone (metabolism)