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The Role of Human CYP2C8 and CYP2C9 Variants in Pioglitazone Metabolism In Vitro
Author(s) -
Muschler Eugen,
Lal Jawahar,
Jetter Alexander,
Rattay Anke,
Zanger Ulrich,
Zadoyan Gregor,
Fuhr Uwe,
Kirchheiner Julia
Publication year - 2009
Publication title -
basic and clinical pharmacology and toxicology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.805
H-Index - 90
eISSN - 1742-7843
pISSN - 1742-7835
DOI - 10.1111/j.1742-7843.2009.00457.x
Subject(s) - pioglitazone , cyp2c8 , cyp2c9 , in vitro , pharmacology , metabolism , chemistry , biology , biochemistry , cytochrome p450 , endocrinology , type 2 diabetes , diabetes mellitus
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 μM) 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/μM 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/μM 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.