Insulin differentially affects xenobiotic-enhanced, cytochrome P-450 (CYP)2E1, CYP2B, CYP3A, and CYP4A expression in primary cultured rat hepatocytes.
Uncontrolled diabetes results in enhanced expression of cytochrome P-450 (CYP)2E1, CYP2B, CYP3A, and CYP4A. Because of the simultaneous and confounding metabolic and hormonal changes that occur in vivo as a consequence of diabetes, primary cultured rat hepatocytes provide an excellent model system for examination of the effects of insulin on P-450 expression and on xenobiotic-mediated P-450 expression. In the present study, we examined the effects of insulin on pyridine-, phenobarbital-, and ciprofibrate-mediated expression of CYP2E1, CYP2B, CYP3A, and CYP4A in primary cultured rat hepatocytes. Pyridine addition to primary rat hepatocytes cultured in the presence of 1 nM insulin or in the absence of insulin resulted in a 3.5-fold and 3-fold enhancement in CYP2E1 protein expression, respectively, in the absence of any pyridine-mediated increase in mRNA expression. In contrast, hepatocytes cultured in the standard concentration of 1 microM insulin resulted in only a 2-fold increase in protein expression. Thus, the fold-induction of CYP2E1 protein in response to pyridine was 1.5- to 1.8-fold greater in either the absence of insulin or in the presence of 1 nM insulin, respectively, than that monitored in the presence of 1 microM insulin. To examine whether insulin effects on xenobiotic-mediated CYP2E1 expression were selective, insulin effects on xenobiotic-mediated expression of transcriptionally regulated CYP2B, CYP3A, and CYP4A were examined. Pyridine- or phenobarbital-mediated induction of CYP2B mRNA and protein expression in hepatocytes was suppressed by as much as 80% at lower insulin levels (0 and 1 nM), relative to the level monitored in the presence of 1 microM insulin. Omitting insulin from the medium resulted in a 50% decrease in CYP3A mRNA levels in response to phenobarbital treatment and a 30% decrease in CYP4A mRNA levels in response to ciprofibrate treatment, relative to the level obtained in response to these treatments in the presence of 1 microM insulin. The results of this study demonstrate that decreasing the insulin level in the primary hepatocyte culture medium enhanced xenobiotic-mediated CYP2E1 expression, whereas lower insulin levels suppressed xenobiotic-mediated CYP2B, CYP3A, and CYP4A expression in this cell culture system.
Woodcroft
K J
KJ
Institute of Chemical Toxicology, Wayne State University, Detroit, Michigan, USA.
Novak
R F
RF
D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases; D015152:Blotting, Northern; D002478:Cells, Cultured; D002995:Clofibric Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D019392:Cytochrome P-450 CYP2E1 / Q000096:biosynthesis; D051544:Cytochrome P-450 CYP3A; D042926:Cytochrome P-450 CYP4A; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis*; D004790:Enzyme Induction; D058607:Fibric Acids; D007328:Insulin / Q000494:pharmacology / Q000502:physiology*; D008099:Liver / Q000166:cytology / Q000187:drug effects / Q000201:enzymology*; D008297:Male; D006899:Mixed Function Oxygenases / Q000096:biosynthesis; D010089:Oxidoreductases, N-Demethylating / Q000096:biosynthesis; D010634:Phenobarbital / Q000494:pharmacology; D011725:Pyridines / Q000494:pharmacology; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D017207:Rats, Sprague-Dawley; D015262:Xenobiotics / Q000494:pharmacology*
D058607:Fibric Acids; D007328:Insulin; D011725:Pyridines; D012333:RNA, Messenger; D015262:Xenobiotics; D002995:Clofibric Acid; D003577:Cytochrome P-450 Enzyme System; D006899:Mixed Function Oxygenases; D019392:Cytochrome P-450 CYP2E1; D001189:Aryl Hydrocarbon Hydroxylases; D051544:Cytochrome P-450 CYP3A; D042926:Cytochrome P-450 CYP4A; D010089:Oxidoreductases, N-Demethylating; C019304:ciprofibrate; C023666:pyridine; D010634:Phenobarbital