Characterization of the in vitro glucuronidation of flurbiprofen enantiomers

To investigate the glucuronidation of the R- and S-enantiomers of the nonsteroidal antiinflammatory drug, flurbiprofen, by liver microsomes of several mammals, including humans, a new and reliable HPLC method for the separation and quantification of the corresponding diastereoisomeric glucuronides has been developed. Interspecies comparison revealed that the glucuronidation of flurbiprofen was highly efficient with liver microsomes of humans, monkeys, rats, and guinea pigs (in decreasing ranking order). Gunn rats, which present a genetic defect in the bilirubin UDP-glucuronosyltransferase (UGT) isoforms, were still able to glucuronidate the drug. The R-enantiomer was glucuronidated faster than the S-form by liver microsomes of rats and humans. Although the KM of glucuronidation of R- and S-enantiomers by rat liver UGT were in same order of magnitude (apparent KM 0.52 and 0.57 mM, respectively), the apparent Vmax's were significantly different (9.34 and 5.48 nmol/min.mg of protein). Regardless of the enantiomer considered, the glucuronidation of flurbiprofen was strongly increased up to 5-fold by treatment of rats with phenobarbital and, at a lower extent, by 3-methylcholanthrene. In contrast, the treatment of rats with ciprofibrate markedly decreased the activity. Glucuronidation of R-flurbiprofen was more enhanced by phenobarbital than that of the S-antipode. Each flurbiprofen enantiomer could weakly inhibit the glucuronidation of its antipode in a noncompetitive way. The apparent Ki was 0.51 mM with R-flurbiprofen as a substrate, and 0.37 mM with S-enantiomer. On the other hand, the rat liver UGT2B1 isoform, stably expressed in V79 cells, could glucuronidate flurbiprofen in an appreciable amount.(ABSTRACT TRUNCATED AT 250 WORDS)