A study of the expression of the xenobiotic-metabolising cytochrome P450 proteins and of testosterone metabolism in bovine liver

The expression of xenobiotic-metabolising cytochrome P450 proteins in the l iver of cattle was determined using substrate probes and immunologically by Western blot analysis. Compared to the rat, cattle displayed much higher c oumarin 7-hydroxylase (CYP2A) and ethoxyresorufin O-deethylase (CYP1) activ ity but, in contrast, it exhibited much lower debrisoquine 4-hydroxylase (C YP2D) and lauric acid hydroxylase activities (CYP4A). The ethoxyresorufin O -deethylase activity was markedly inhibited by furafylline and alpha -napht hoflavone, and coumarin 7-hydroxylase by 8-methoxypsoralen. Immunoblot anal ysis employing antibodies to rat CYP1A1 recognised two immunorelated protei ns in bovine liver whose expression appeared to be higher compared with rat . Kinetic studies indicated that a single enzyme is likely to be responsibl e for the O-deethylation of 7-ethoxyresorufin in bovine liver. When bovine microsomes were probed with antibodies to rat CYP2A2, a single protein was detected in cattle liver. Kinetic analysis followed by construction of Eadi e-Hofstee plots indicated that more than one enzyme contributes to the 7-hy droxylation of coumarin. Immunoblot analysis employing antibodies to human CYP2D6 and rat CYP4A1 revealed in both cases a single, poorly expressed imm unoreacting band in bovine microsomes. Similar immunoblot studies detected proteins in cattle liver immunorelated to the CYP2B, CYP2C, CYP2E, and CYP3 A subfamilies. Bovine microsomes metabolised testosterone but, in contrast to the rat, failed to produce 2 alpha- and 16 alpha -hydroxytestosterone. O n the other hand, bovine microsomes produced levels of another hydroxylated metabolite, possibly 12-hydroxytestosterone. In conclusion, results emanat ing from this study indicate the presence of proteins in the cattle liver b elonging to all the xenobiotic-metabolising families of cytochrome P450. (C ) 2001 Elsevier Science Inc. All rights reserved.