Abstract
We recently proposed a possible stereoselective activation by lansoprazole of CYP2C9-catalyzed tolbutamide hydroxylation, as well as stereoselective inhibition of several cytochrome P450 (P450) isoforms. This study evaluated the effects of lansoprazole enantiomers on CYP2C9 activity in vitro, using several probe substrates. For tolbutamide 4-methylhydroxylation and phenytoin 4-hydroxylation, R-lansoprazole was an activator (140 and 550% of control at 100 μM R-lansoprazole, EC50 values of 19.9 and 30.2 μM, respectively). R-Lansoprazole-mediated activation of the formation of 4-hydroxyphenytoin was also seen with recombinant human CYP2C9. R-Lansoprazole increased the Michaelis-Menten-derived Vmax of phenytoin 4-hydroxylation from 0.024 to 0.121 pmol/min/pmol P450, and lowered its Km from 20.5 to 15.0 μM, suggesting that R-lansoprazole activates CYP2C9-mediated phenytoin metabolism without displacing phenytoin from the active site. Kinetic parameters were also estimated using the two-site binding equation, with α values <1 and β values >1, indicative of activation. Additionally, phenytoin at 10 to 200 μM had no reciprocal effect on the hydroxylation of R-lansoprazole. Meanwhile, R-lansoprazole had no activation effect on diclofenac and S-warfarin metabolism in the incubation study using both recombinant CYP2C9 and human liver microsomes. These substrate-dependent activation effects suggest that phenytoin has a different binding orientation compared with diclofenac and S-warfarin. Overall, these results suggest that R-lansoprazole activates CYP2C9 in a stereospecific and substrate-specific manner, possibly by binding within the active site and inducing positive cooperativity. This is the first report to describe stereoselective activation of this cytochrome P450 isoform.
Footnotes
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This work was supported by a grant from the Ministry of Science and Technology, Korea (National Research Laboratory Program).
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Article, publication date, and citation information can be found at http://dmd.aspetjournals.org.
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doi:10.1124/dmd.104.001438.
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ABBREVIATIONS: P450, cytochrome P450; HPLC, high-performance liquid chromatography.
- Received July 12, 2004.
- Accepted November 5, 2004.
- The American Society for Pharmacology and Experimental Therapeutics
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