Increase in urinary excretion of 6 beta-hydroxycortisol in common marmosets as a marker of hepatic CYP3A induction

The ratio of urinary 6 beta-hydroxycortisol (6 beta-OHF) to free cortisol ( F), i.e., the 6 beta-OHF/F ratio, has been reported to be a specific marker for human CYP3A induction by in vivo studies of human subjects. In the dev elopment of drugs, it is quite beneficial to predict human CYP3A induction in preclinical safety studies using urine samples from experimental animals . We examined the 6 beta-OHF/F ratio in urine of common marmosets administe red with rifampicin, a potent inducer of CYP3A. to evaluate the usefulness of common marmosets for the prediction of CYP3A induction. Rifampicin was o rally administered to three groups of four male common marmosets at doses o f 0, 10, and 20 mg/kg per day for 4 days. Amounts of 6 beta-OHF and F in ur ine samples were determined by means of high-performance liquid chromatogra phy (HPLC) during the experimental period. One day after the 4th dosing, an imals were killed, and P450 contents and P450-catalyzed, 7-alkoxycoumarin O -dealkylase (ACD) activities in the liver were measured. Western blot analy sis of liver microsomes was also performed using anti-rat P450 (CYP1A1, 2B1 /2, 3A, and 4A) antibodies. The results indicated elevations in the 6 beta- OHF/F ratios that were dependent on both the dosing period and dose levels adopted. The ratios on day 4 reached 4.7- and 5.3-fold the pre-administrati on values in the 10 and 20 mg/kg per day groups, respectively. P450 content s and ACD activities were also elevated in all of the groups. Western blot analysis showed specific increases in the protein which cross-reacts with a nti-rat CYP3A antibody in all of the groups. Furthermore, the 6 beta-OHF/F ratio was well correlated with the CYP3A contents in liver (r = 0.906). The se results indicated that increase in urinary excretion of 6 beta-OHF is a specific marker of the induction of hepatic CYP3A in common marmosets just as in humans. Consequently, the present study suggested that human CYP3A in duction elicited by chemical agents call be predicted in common marmosets b y measuring the urinary excretion of 6P-OHF.