Induction of Liver and Intestinal Cytochrome P450 (CYP) Enzymes in Male and Female Cynomolgus Monkey
Male and female Cynomolgus monkeys were dosed orally (by nasogastric intubation) once daily for four days with saline (vehicle control), β-naphthoflavone (BNF, 50 mg/kg/day), phenobarbital (PB, 25 mg/kg/day), rifampin (RIF, 25 mg/kg/day), pyrazole (200 mg/kg/day) or omeprazole (OMP, 50 mg/kg/day). Microsomal samples from liver and intestine were analyzed for total cytochrome P450 content, cytochrome b5 content, NADPH-cytochrome c reductase activity, 7-ethoxyresorufin O-dealkylation (CYP1A1/2), testosterone 16α-hydroxylation and testosterone 16β-hydroxylation (CYP2B17), 4-nitrophenol hydroxylase (CYP2E1), testosterone 2α-hydroxylation and testosterone 6β-hydroxylation (CYP3A8). CYP mRNA levels in liver were determined for CYP1A1, 1A2, 2A24, 2B6, 2C8, 2C43, 2C75, 2E1, 3A8 and 4A11 by RT-PCR. Given the amount of data collected on this project, the primary focus will be CYP mRNA data.
Treatment of monkeys with BNF caused significant increases in liver CYP1A1 and CYP1A2 mRNA levels, and little or no increase (< 4-fold) in the mRNA levels of the other enzymes examined. Omeprazole caused increases in liver CYP1A1 and 1A2 mRNA levels, but as a CYP1A mRNA inducer OMP was less effective than BNF. Treatment with BNF caused an increase in CYP1A1 mRNA levels (66- and 240-fold in males and females) and CYP1A2 mRNA levels (51- and 1600-fold in males and females). Treatment with OMP caused an increase in CYP1A1 mRNA levels (2.2- and 5.8-fold in males and females) and CYP1A2 mRNA levels (14.9- and 173-fold in males and females). Similarly, BNF and OMP caused increases in liver microsomal CYP1A1/2 activity. Treatment with BNF caused significant increases in CYP1A activity in both liver and intestine. The increase in liver CYP1A activity by BNF was similar between male and female monkeys (11- and 9.4-fold, respectively) whereas induction of intestinal CYP1A activity by BNF was much lower in male than female monkeys (2.7- and 19-fold, respectively). Though to a smaller extent compared to BNF, OMP also caused increases in microsomal CYP1A1/2 activity (3.7- and 4.3-fold in the liver) and (1.5 and 4.3-fold in intestine) for male and female monkeys, respectively. Treatment with PB caused a large increase in liver CYP2B6 mRNA levels (21.6- and 52.5-fold in males and females, respectively), and caused less pronounced increases in CYP2A24 (5.6- and 7.3-fold), 2C8 (7.3- and 6.5-fold), 2C43 (6.4- and 5.7-fold), 2C75 (6.2- and 7.0-fold), and 3A8 (2.6- and 6.0-fold) mRNA levels in males and females, respectively. PB also caused an increase in liver microsomal CYP2B17 and CYP3A8 activity (3.2- and 2.2-fold, respectively). Rifampin treatment caused an increase in liver CYP2B6 (3.6- and 8.2-fold), 2C8 (8.2- and 7.5-fold), 2C43 (6.9- and 8.1-fold), 2C75 (6.7- and 8.6-fold) and 3A8 (5.9- and 5.8-fold) mRNA levels in males and females, respectively. Except for a small increase (3.5-fold in CYP2B6 and 2.7-fold in CYP4A mRNA levels), pyrazole did not cause an increase in the liver mRNA levels of any of the CYP enzymes examined. Results from this study indicate that BNF and OMP are in vivo inducers of CYP1A1 and CYP1A2 in monkeys, while PB and rifampin are inducers of CYP2B, 2C and CYP3A enzymes.