Induction of intestinal cytochrome P450 (CYP3A) by rifampicin in beagle dogs

Both male and female beagle dogs (four dogs/sex) were orally treated with r ifampicin (Rif) at the dose of 10 mg/kg/day for 7 days and an additional ei ght dogs (four dogs/sex) were used as a control. The inducible effect of Ri f on intestinal cytochrome P450, especially CYP3A enzyme, was investigated by measuring microsomal testosterone 6 beta -hydroxylation (6 beta -OHT) ac tivity, immunoblot and ELISA analysis. In male dogs, microsomal 6 beta -OHT activity in the duodenum, upper, middle and lower part of the jejunum and the ileum of the control was 229, 204, 194, 129 and 57 pmol/min/mg protein, while the activity of the Rif-treated dogs significantly increased to 456, 486, 430, 192 and 138 pmol/min/mg protein, respectively. The activity of i ntestinal 6 beta -OHT in the control and Rif-treated female dogs showed alm ost similar levels to those observed in the corresponding male dogs. The ac tivity of intestinal 6 beta -OHT in both control and Rif-treated dogs was s pecifically inhibited by anti-CYP3A12 antiserum. The apparent K-m value for 6 beta -OHT activity in all sections of the small intestine was comparable with that in the liver, and no significant changes: were observed in betwe en control and Rif-treated dogs. In both control and Rif-treated dogs, immu noblotting of intestinal microsomes with anti-CYP3A12 antiserum produced a band indistinguishable from that of purified CYP3A12 or of immunoreactive C YP3A12 in liver microsomes. A significant increase in intestinal CYP3A cont ent by Rif treatment was quantitatively verified by the ELISA analysis and the magnitude of its increase correlated well with that of 6 beta -OHT acti vity elevation. Furthermore, the results of immunohistochemistry using the anti-CYP3A12 antiserum indicated that CYP3A protein was specifically distri buted in epithelial cells throughout the small intestine and appealed to he predominant at the apical side of villus cells. These results demonstrate that Rif induces not only hepatic CYP3A12 but also intestinal CYP3A in dogs . (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.