Cytochrome P450-dependent drug oxidation activities in liver microsomes of various animal species including rats, guinea pigs, dogs, monkeys, and humans

Abstract

Levels of cytochrome P450 (P450 or CYP) proteins immunoreactive to antibodies raised against human CYP1A2, 2A6, 2C9, 2E1, and 3A4, monkey CYP2B17, and rat CYP2D1 were determined in liver microsomes of rats, guinea pigs, dogs, monkeys, and humans. We also examined several drug oxidation activities catalyzed by liver microsomes of these animal species using eleven P450 substrates such as phenacetin, coumarin, pentoxyresorufin, phenytoin, S-mephenytoin, bufuralol, aniline, benzphetamine, ethylmorphine, erythromycin, and nifedipine; the activities were compared with the levels of individual P450 enzymes. Monkey liver P450 proteins were found to have relatively similar immunochemical properties by immunoblotting analysis to the human enzymes, which belong to the same P450 gene families. Mean catalytic activities (on basis of mg microsomal protein) of P450-dependent drug oxidations with eleven substrates were higher in liver microsomes of monkeys than of humans, except that humans showed much higher activities for aniline p-hydroxylation than those catalyzed by monkeys. However, when the catalytic activities of liver microsomes of monkeys and humans were compared on the basis of nmol of P450, both species gave relatively similar rates towards the oxidation of phenacetin, coumarin, pentoxyresorufin, phenytoin, mephenytoin, benzphetamine, ethylmorphine, erythromycin, and nifedipine, while the aniline p-hydroxylation was higher and bufuralol 1'-hydroxylation was lower in humans than monkeys. On the other hand, the immunochemical properties of P450 proteins and the activities of P450-dependent drug oxidation reactions in dogs, guinea pigs, and rats were somewhat different from those of monkeys and humans; the differences in these animal species varied with the P450 enzymes examined and the substrates used. The results presented in this study provide useful information towards species-related differences in susceptibilities of various animal species regarding actions and toxicities of drugs and xenobiotic chemicals.

Species Differences in the Pharmacokinetic Parameters of Cytochrome P450 Probe Substrates between Experimental Animals, such as Mice, Rats, Dogs, Monkeys, and Microminipigs, and Humans

“…Therefore, species differences in CYP activities, which have been reported in a number of studies, need to be clarified between experimental animals and humans. Humans and rodents, such as mice and rats, generally exhibit greater species differences in CYP activities; however, rodents have frequently been used as animal models in drug discovery [4][5][6][7][8][9][10][11]. On the other hand, Bogaards et al [12] reported that CYP1A activity in mouse microsomes and CYP3A activity in mouse and rat microsomes were similar to those in human microsomes [12].…”

“…Although dogs are frequently used as non-rodent species in nonclinical studies, information concerning the canine CYP system is more limited. The hepatic metabolism of specific human CYP2C substrates, such as tolbutamide, warfarin, and (S)-mephenytoin, is known to be impaired more in dogs than in humans [13], whereas metabolism studies using liver microsomes demonstrated that the metabolism of human CYP2D substrates, such as bufuralol and dextromethorphan, was similar in humans and dogs [10,11,14]. Monkeys were originally considered to have pharmacokinetic properties similar to those of humans due to genetic similarities, however, previous studies showed that the bioavailability (BA) of some drugs including human CYP3A substrates was markedly lower in monkeys than in humans [7,[15][16][17][18][19][20].…”

Issues Related to the Use of Canines in Toxicologic Pathology—Issues With Pharmacokinetics and Metabolism

“…The amount of CYP450 enzyme per mg of liver protein is similar in dogs and humans, but less than that of rats, monkeys, and guinea pigs (59). The overall content of CYP450 in the liver, however, is not predictive of a species' ability to metabolize any single compound.…”

“…Comparisons of the sequence of canine isoforms with homologues of other species have shown a high degree of amino acid sequence identity, (6) but the similarities in sequence have not always predicted similarities in enzymatic characteristics. In an effort to better understand the metabolic profile of the canine CYP450s, numerous studies have been conducted comparing the activity and specificity of dog CYP450 isozymes with those of other species (6,8,56,59). An overarching conclusion in many of these studies is that there are significant differences in the metabolic activities of dog CYP450s when compared with other species.…”

“…It is possible that substrates that are metabolized by one CYP450 enzyme in humans or rats are, in dogs, metabolized by several. In addition, the specificity of non-canine inhibitory antibodies against unique canine CYP450s is also not well established (59). For example, human CYP450 3A4 antibodies were unable to inhibit the in vitro metabolism by recombinant canine CYP3A12 of disopyramide (67), while inhibition of disopyramide was successfully achieved with antibodies generated to CYP3A12.…”