title: Augmentation of 3-methylcholanthrene-induced bioactivation in the human hepatoma cell line HepG2 by the calcium channel blocker nicardipine.
abstract: The abilities of the dihydropyridine calcium channel blocker nicardipine (Nic) to induce cytochrome P450 1 family enzymes (CYP1s) and to enhance the 3-methylcholanthrene (MC)-mediated induction of CYP1s and formation of MC-DNA adduct were examined in the human hepatoma cell line HepG2. The results from real time RT-PCR analysis demonstrated that Nic could induce CYP1 mRNAs and enhance the MC-mediated induction of the CYP1 mRNAs. The luciferase-reporter gene assay using the HepG2-A10 cell line, which has been previously established for the screening of aryl hydrocarbon receptor (AhR) activators, also indicated the augmentation of MC-mediated activation of AhR (induction of luciferase) by Nic, although Nic showed limited capacity for the activation of AhR. Furthermore, the results from the Western blot analysis of CYP1s, the enzyme activity assay, and the assay for MC-DNA adduct formation indicated that Nic could enhance the MC-mediated induction of CYP1s, especially CYP1A1. Furthermore, the intracellular accumulation level of [(3)H]MC after treatment of HepG2 cells with [(3)H]MC significantly increased in the presence of Nic. The present findings demonstrate that Nic can enhance the MC-mediated induction of CYP1s, especially CYP1A1, and the formation of MC-DNA adduct in HepG2 cells. Furthermore, the augmentation of the MC-mediated bioactivation by Nic is demonstrated to occur mainly through an increase in intracellular accumulation of MC.
authors.affiliation: Department of Molecular Toxicology, School of Pharmaceutical Sciences, University of Shizuoka, Shizuoka, Japan.
authors.forename: Takuomi
authors.initials: T
authors.lastname: Hosaka
authors.forename: Masashi
authors.initials: M
authors.lastname: Sekimoto
authors.forename: Kiyomitsu
authors.initials: K
authors.lastname: Nemoto
authors.forename: Masakuni
authors.initials: M
authors.lastname: Degawa
mesh_terms: D001189:Aryl Hydrocarbon Hydroxylases; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D006528:Carcinoma, Hepatocellular / Q000201:enzymology*; D045744:Cell Line, Tumor; D019363:Cytochrome P-450 CYP1A1 / Q000235:genetics; D019388:Cytochrome P-450 CYP1A2 / Q000235:genetics; D065633:Cytochrome P-450 CYP1B1; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics; D004790:Enzyme Induction / Q000187:drug effects; D006801:Humans; D008113:Liver Neoplasms / Q000201:enzymology*; D008748:Methylcholanthrene / Q000494:pharmacology*; D009529:Nicardipine / Q000494:pharmacology*
chemical_list: D002121:Calcium Channel Blockers; D008748:Methylcholanthrene; D003577:Cytochrome P-450 Enzyme System; D009529:Nicardipine; D001189:Aryl Hydrocarbon Hydroxylases; C504573:CYP1A2 protein, human; C585496:CYP1B1 protein, human; D019363:Cytochrome P-450 CYP1A1; D019388:Cytochrome P-450 CYP1A2; D065633:Cytochrome P-450 CYP1B1