RT Journal Article
SR Electronic
T1 In Vivo and in Vitro Induction of Cytochrome P450 Enzymes in Beagle Dogs
JF Drug Metabolism and Disposition
JO Drug Metab Dispos
FD American Society for Pharmacology and Experimental Therapeutics
SP 1206
OP 1213
DO 10.1124/dmd.30.11.1206
VO 30
IS 11
A1 Richard A. Graham
A1 April Downey
A1 Dan Mudra
A1 Linda Krueger
A1 Kathy Carroll
A1 Christopher Chengelis
A1 Ajay Madan
A1 Andrew Parkinson
YR 2002
UL http://dmd.aspetjournals.org/content/30/11/1206.abstract
AB The aim of this study was to determine the in vitro and in vivo effects of several prototypical inducers, namely β-naphthoflavone, 3-methylcholanthrene, phenobarbital, isoniazid, rifampin, and clofibric acid, on the expression of cytochrome P450 (P450) enzymes in beagle dogs. For the in vitro induction study, primary cultures of dog hepatocytes were treated with enzyme inducers for 3 days, after which microsomes were prepared and analyzed for P450 activities. For the in vivo induction study, male and female beagle dogs were treated with enzyme inducers for 4 days (with the exception of phenobarbital, which was given for 14 days), after which the livers were removed and microsomal P450 activities were determined ex vivo. Treatment of male beagle dog hepatocyte cultures (n = 3) with β-naphthoflavone or 3-methlychloranthrene resulted in up to a 75-fold increase in microsomal 7-ethoxyresorufin O-dealkylase (CYP1A1/2) activity, whereas in vivo treatment of male and female beagle dogs with β-naphthoflavone followed by ex vivo analysis resulted in up to a 24-fold increase. Phenobarbital caused a 13-fold increase in 7-benzyloxyresorufin O-dealkylase (CYP2B11) activity in vitro and up to a 9.9-fold increase in vivo. Isoniazid had little or no effect on 4-nitrophenol hydroxylase activity in vitro. Rifampin caused a 13-fold induction of testosterone 6β-hydroxylase (CYP3A12) activity in vitro and up to a 4.5-fold increase in vivo. Treatment of dogs in vivo or dog hepatocytes in vitro with clofibric acid appeared to have no effect on CYP4A activity as determined by the 12-hydroxylation of lauric acid. In general, the absolute rates (picomoles per minute per milligram of microsomal protein) of P450 reactions catalyzed by microsomes from cultured hepatocytes (i.e., in vitro rates) were considerably lower than those catalyzed by microsomes from dog liver (i.e., ex vivo rates). These results suggest that beagle dogs have CYP1A, CYP2B, CYP2E, and CYP3A enzymes and that the induction profile resembles the profile observed in humans more than in rats. The American Society for Pharmacology and Experimental Therapeutics