title: Enhanced expression of rat hepatic CYP2B1/2B2 and 2E1 by pyridine: differential induction kinetics and molecular basis of expression.
abstract: Expression of the cytochrome P450 (CYP) 2B subfamily in rat and rabbit hepatic tissues after pyridine (PY) treatment has been examined, and the molecular basis for enhanced 2B1/2B2 expression has been determined. P450 expression was monitored using metabolic activity, sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblot analyses, and the identity of the proteins was confirmed through N-terminus microsequence analysis. PY caused a dose-dependent elevation of hepatic CYP2B1/B2B levels in rats, which ranged from 4- to 22-fold over the dosing regimen of 100 to 400 mg PY/kg/day, for 3 days, respectively. PY at low dose failed to induce CYP2B in rabbit hepatic tissue, suggesting a species-dependent response in 2B expression. Anti-2B1 IgG addition to PY-induced microsomes inhibited benzphetamine N-demethylase activity by only approximately 15%, in sharp contrast to the approximately 73% inhibition observed for phenobarbital-induced microsomes, suggesting the induction of other form(s) of P450 having benzphetamine N-demethylase activity. Northern blot analysis revealed that PY treatment increased 2B1 and 2B2 poly(A)+ RNA levels approximately 69- and approximately 34-fold, respectively, whereas the 2E1 poly(A)+ RNA levels failed to increase. The results of this study show that PY induces CYP2B1/2B2 and that induction is species-dependent and kinetically distinguishable from 2E1 induction. Moreover, 2B1/2B2 induction occurs as a result of elevated mRNA levels associated with either transcriptional activation or mRNA stabilization, and it differs from the mechanism of hepatic 2E1 induction by PY.
authors.affiliation: Institute of Chemical Toxicology, Wayne State University, Detroit, Michigan.
authors.forename: H
authors.initials: H
authors.lastname: Kim
authors.forename: D
authors.initials: D
authors.lastname: Putt
authors.forename: S
authors.initials: S
authors.lastname: Reddy
authors.forename: P F
authors.initials: PF
authors.lastname: Hollenberg
authors.forename: R F
authors.initials: RF
authors.lastname: Novak
mesh_terms: D000818:Animals; D001483:Base Sequence; D019362:Cytochrome P-450 CYP2B1; D019392:Cytochrome P-450 CYP2E1; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis* / Q000235:genetics* / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004790:Enzyme Induction; D015870:Gene Expression / Q000187:drug effects*; D007700:Kinetics; D008099:Liver / Q000187:drug effects / Q000201:enzymology*; D008297:Male; D008969:Molecular Sequence Data; D010088:Oxidoreductases / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism; D010089:Oxidoreductases, N-Demethylating / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism; D011725:Pyridines / Q000494:pharmacology*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011817:Rabbits; D051381:Rats; D017207:Rats, Sprague-Dawley; D013045:Species Specificity
chemical_list: D011725:Pyridines; D012333:RNA, Messenger; D003577:Cytochrome P-450 Enzyme System; D010088:Oxidoreductases; D019392:Cytochrome P-450 CYP2E1; D019362:Cytochrome P-450 CYP2B1; D010089:Oxidoreductases, N-Demethylating; C023666:pyridine