Effect of gonadectomy and hormones on sex differences in ketoprofen enantiomer glucuronidation and renal excretion of formed glucuronides in the rat.

PURPOSE: To investigate the sex hormone dependency of phase II metabolism using S-ketoprofen (S-KT) urinary excretion (sigmaXu) as a marker in the rat. METHODS: The effect of surgical gonadectomy, with or without concomitant estradiol or testosterone treatment, on the sigmaXu of glucuronidated S-KT was studied in male and female rats. Hepatic and renal glucuronidation of KT enantiomers was also determined using microsomal preparations from these animals. RESULTS: A controlling effect of testosterone was demonstrated by a rapid increase in sigmaXu of glucuronidated S-KT in castrated males (27.9 +/- 9.0%) compared to control males (7.2 +/- 3.9%). This approximated control female excretion (40.5 +/- 11.6%). Treatment of ovarectomized females with testosterone resulted in a steady reduction in sigmaXu of glucuronidated S-KT with time (13.4 +/- 5.4% at end point). Hepatic glucuronidation of S-KT by male rat liver microsomes was significantly higher than that of female, whereas renal glucuronidation of S-KT by female rat kidney microsomes was significantly higher than that of male. Significant correlations were found between hepatic (r = -0.78) or renal (r = 0.83) glucuronidation and sigmaXu of glucuronidated S-KT. CONCLUSIONS: Urinary excretion of S-KT-GC is sex hormone-dependent. This metabolite may have utility as a marker or probe for sex hormone-dependent studies of phase II metabolism.

Human cytochromes P450 mediating phenacetin O-deethylation in vitro: validation of the high affinity component as an index of CYP1A2 activity.

Phenacetin O-deethylation, widely used as an index reaction for cytochrome P450 1A2 (CYP1A2) activity, displays biphasic kinetics in human liver microsomes. CYP1A2 has been identified as contributing to the high affinity component, but is not verified as the sole contributor to the high affinity phase. In addition, the human CYP isoforms accounting for the low affinity phase have not been identified. We have used heterologously expressed human CYP isoforms to identify, kinetically characterize, and predict the relative contribution of the major human liver CYP isoforms mediating phenacetin O-deethylation. CYP1A2 (Km 31 microM) is the only high affinity phenacetin O-deethylase in human liver microsomes, while CYPs 2A6 (Km 4098 microM), 2C9 (Km 566 microM), 2C19 (Km 656 microM), 2D6 (Km 1021 microM), and 2E1 (Km 1257 microM) all contribute to the low affinity phase of the reaction. Considering the relative abundance of the various CYPs in human liver, CYP1A2 accounts for 86% of net reaction velocity at a substrate concentration of 100 microM, while CYP2C9 becomes the primary phenacetin O-deethylase at substrate concentrations of 865 microM and higher and accounts for 31% of the net Vmax of the reaction. Predictions from kinetic studies on heterologously expressed CYPs are consistent with chemical inhibition studies on human liver microsomes with sulfaphenazole and alpha-naphthoflavone that suggest a greater role for CYP2C9, and a smaller role for CYP1A2, at higher substrate concentrations. Thus CYP1A2 is the only high affinity human liver phenacetin O-deethylase, thereby validating the use of the high affinity component as an index of CYP1A2 activity in human liver microsomes.