Inter-individual variation in the pharmacokinetics and thereby pharmacodynamics of many therapeutic agents are possibly caused by genetic polymorphisms of drug metabolizing enzymes including cytochrome P450 2C9 (CYP2C9), CYP2C19 and CYP2D6. A series of clinical studies on the CYP2C19 genotype and the pharmacokinetics and pharmacodynamics of three proton pump inhibitors (PPIs), omeprazole, lansoprazole and rabeprazole, were conducted to establish the individualized pharmacotherapy based on the CYP2C19 genotyping. [1][2][3][4][5] The subjects were classified into homo extensive metabolizers, hetero extensive metabolizers and poor metabolizers according to the CYP2C19 genotype diagnosed. The findings were summarized as follows: 1) plasma concentrations of omeprazole and lansoprazole after single oral administration were defined by the CYP2C19 genotype, whereas rabeprazole was not, 2) the CYP2C19 genotype-dependency of lansoprazole was weaker than omeprazole, and 3) hetero extensive metabolizers could be included with homo extensive metabolizers to be extensive metabolizers. There were several in vitro studies reporting that CYP2C19 and CYP3A4 were responsible for the metabolism of 3 PPIs, however, little information is available for their relative contributions on total metabolism, 6-10) that would be adequate to explain that the CYP2C19 genotypedependent pharmacokinetics was more marked for omeprazole than the other two. Herein, to validate further the difference among 3 PPIs in CYP2C19 genotype-dependency on the phenotype, a comparative in vitro study on the metabolism of 3 PPIs was conducted using human liver microsomes and newly developed anti-human CYP antibodies.
MATERIALS AND METHODS
MaterialsOmeprazole and its two primary metabolites, 5-hydroxyomeprazole and omeprazole sulfone, were obtained from AstraZeneca Ltd. (Osaka, Japan). Lansoprazole and its two primary metabolites, 5-hydroxylansoprazole and lansoprazole sulfone, were obtained from Takeda Pharmaceutical Co. (Osaka, Japan). The internal standard for rabeprazole (IS735), rabeprazole and its two primary metabolites, thioether rabeprazole and rabeprazole sulfone, were obtained from Eisai Co. (Tokyo, Japan). All other chemicals were of reagent grade and obtained commercially. Six lots of human liver microsomes (Table 1) were purchased from KAC Co. Ltd. (Kyoto, Japan). Anti-human CYP antibodies raised against bacterial expressed recombinant human CYP2C19 and CYP3A4 (referred to as anti-CYP2C19 and anti-CYP3A4 antibodies, respectively) were prepared in rabbits according to the method of Kaminsky et al. 11) Cross reactivity of antibodies raised against CYP2C19 and 3A4 were checked by means of ELISA. Anti-CYP2C19 antibody recognized CYP2C19 and slightly cross reacted with CYP2C9, but did not react with CYP1A2, 2D6, 2E1 and 3A4. Under the condition employed in the present study, cross reaction between CYP2C9 and anti-CYP2C19 antibody is minimized. On the other hand, anti-CYP3A4 antibody recognized CYP3A4, but did not react with CYP1A2, 2C9, 2C19, 2D6 and 2E...
