Studies on the urinary assay of CYP-mediated endogenous corticosteroid metabolites with a LC-MS method

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Interindividual variability of the drug metabolizing enzyme activity is associated with those of drug responses and adverse drug reactions. Recent advances in molecular biology have made it possible to account for a part of interindividual variability of important drug metabolizing enzymes, particularly cytochrome P-450s (CYPs) in the light of pharmacogenomics. Nevertheless, it has also become evident that a large interindividual variability still exists in subjects or patients having none of the previously known loss-of-function SNPs in the respective CYP isoforms. Thus, there is a surge of interest to reappraise for assessing CYP isoform activity as phenotype individually. We have previously reported that in vivo CYP3A4 activity may be assessed by urinary excretion of 6β-hydroxycortisol, a CYP3A4 metabolite of adrenal cortisol, or its metabolic ratio of cortisol. In order to extend this idea to other steroid hormones which are thought to be metabolized by different CYP isoforms, we aimed to establish a comprehensive assay method using HPLC-UV and LC-MS. We have established a simultaneous assay method for urinary 2- and 4-hydroxyestradiol and 17-hydroxyprogesterone, of which metabolism are associated with CYP1A2 and CYP2C19, respectively, with an HPLC-UV method as a preliminary study. We found that there is a large interindividual variability in the urinary excretion of those sex steroid metabolites, indicating that there is a good chance to measure interindividual variability of the these CYP activities. Then, we advanced our study to establish a LC-MS method. We consider that this method would be useful for a population study where a large number of clinical samples are to be assayed.