title: The role of human CYP2C8 and CYP2C9 variants in pioglitazone metabolism in vitro.
abstract: The cytochrome P450 enzyme CYP2C8 appears to have a major role in pioglitazone metabolism. The present study was conducted to further clarify the role of individual CYPs and of the CYP2C8/9 polymorphisms in the primary metabolism of pioglitazone in vitro. Pioglitazone (2-400 microM) was incubated with isolated cytochrome P450 enzymes or human liver microsomes, some of them carrying either the CYP2C8*3/*3 genotype (and also the CYP2C9*2/*2 genotype) or the CYP2C8*1/*1 genotype (five samples each). The formation of the primary pioglitazone metabolite M-IV was monitored by HPLC. Enzyme kinetics were estimated assuming a single binding site. Mean intrinsic clearance of pioglitazone to the metabolite M-IV was highest for CYP2C8 and CYP1A2 with 58 pmol M-IV/min/nmol CYP P450/microM pioglitazone each, 53 for CYP2D6*1, 40 for CYP2C19*1, and 34 for CYP2C9*2, respectively. CYP2A6, CYP2B6, CYP2C9*1, CYP2C9*3, CYP2E1, CYP3A4 and CYP3A5 did not form quantifiable amounts of M-IV. CYP2C8*1/*1 microsomes (25 +/- 4 pmol M-IV/min/mg protein/muM pioglitazone) showed lower intrinsic clearance of pioglitazone than CYP2C8*3/*3 microsomes (35 +/- 9, p = 0.04). In all samples, metabolite formation showed substrate inhibition, while pioglitazone did not inhibit CYP2C8-mediated paclitaxel metabolism. CYP2C8, CYP1A2 and CYP2D6 are major CYPs forming M-IV in vitro. The higher activity of CYP2C8*3/CYP2C9*2 microsomes may result from a contribution of CYP2C9*2, or from differences in CYP2C8 expression. The evidence for substrate-specific inhibitory effects of pioglitazone on CYP2C-mediated metabolism needs to be tested in further studies.
authors.affiliation: Department of Pharmacology, University of Cologne, Cologne, Germany.
authors.forename: Eugen
authors.initials: E
authors.lastname: Muschler
authors.forename: Jawahar
authors.initials: J
authors.lastname: Lal
authors.forename: Alexander
authors.initials: A
authors.lastname: Jetter
authors.forename: Anke
authors.initials: A
authors.lastname: Rattay
authors.forename: Ulrich
authors.initials: U
authors.lastname: Zanger
authors.forename: Gregor
authors.initials: G
authors.lastname: Zadoyan
authors.forename: Uwe
authors.initials: U
authors.lastname: Fuhr
authors.forename: Julia
authors.initials: J
authors.lastname: Kirchheiner
mesh_terms: D001189:Aryl Hydrocarbon Hydroxylases / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism; D065727:Cytochrome P-450 CYP2C8; D065729:Cytochrome P-450 CYP2C9; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism; D006801:Humans; D007004:Hypoglycemic Agents / Q000378:metabolism*; D007527:Isoenzymes / Q000235:genetics; D007700:Kinetics; D008862:Microsomes, Liver / Q000201:enzymology / Q000378:metabolism; D017239:Paclitaxel / Q000378:metabolism; D000077205:Pioglitazone; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000378:metabolism; D045162:Thiazolidinediones / Q000378:metabolism*
chemical_list: D007004:Hypoglycemic Agents; D007527:Isoenzymes; D011994:Recombinant Proteins; D045162:Thiazolidinediones; D003577:Cytochrome P-450 Enzyme System; C450260:CYP2C9 protein, human; D065729:Cytochrome P-450 CYP2C9; D001189:Aryl Hydrocarbon Hydroxylases; C450259:CYP2C8 protein, human; D065727:Cytochrome P-450 CYP2C8; D017239:Paclitaxel; D000077205:Pioglitazone