Liver microsomal cytochrome P450 3A-dependent drug oxidation activities in individual dogs

Drug oxidations are mediated mainly by cytochromes P450 (P450s or CYPs). CYP3As are an important P450 subfamily and include liver-specific CYP3A12 and intestine-specific CYP3A98 in dogs. Individual differences in drug oxidation activities were investigated, including correlations with immunoreactive CYP3A protein intensities and CYP3A mRNA expression levels in liver microsomes.Pooled and individual dog liver microsomes showed activities toward nifedipine, midazolam, alprazolam, and estradiol, but the levels of catalytic activities varied approximately twofold among the individual dogs. One dog harbored a CYP1A2 variant causing protein deletion, but showed higher activities than the other dogs toward nifedipine oxidation, midazolam 1'-hydroxylation, alprazolam 4-hydroxylation, estradiol 16α-hydroxylation activities, and caffeine C₈-hydroxylation; the latter is used as a reference reaction for CYP1A.In individual dog liver microsomes, the intensities of the immunochemical bands with anti-human CYP3A4 and anti-rat CYP3A2 antibodies along with CYP3A12 and CYP3A26 mRNA expression levels showed good correlations (p < 0.05) with nifedipine oxidation, midazolam 1'- and 4-hydroxylation, alprazolam 1'- and 4-hydroxylation, and estradiol 16α-hydroxylation activities.These results suggest that the oxidation activities of dog liver microsomes toward nifedipine and other typical CYP3A-catalyzed drugs exhibit approximately twofold individual differences and were predominantly mediated by liver-specific CYP3A12 in the dogs.

2-Oxidation, 3-methyl hydroxylation, and 6-hydroxylation of skatole, a contributor to the odour of boar-tainted pork meat, mediated by porcine liver microsomal cytochromes P450 1A2, 2A19, 2E1, and 3A22

The 2-oxidation, 3-methyl hydroxylation, and 6-hydroxylation of skatole (a contributor to boar taint) mediated by minipig liver microsomes and recombinant P450 enzymes expressed in bacterial membranes were investigated.At low substrate concentrations of 10 µM, the formation rates of indole-3-carbinol, 6-hydroxyskatole, and the sum of 3-methyloxindole, indole-3-carbinol, and 6-hydroxyskatole in male minipig liver microsomes were significantly lower than those in female minipig liver microsomes.Compensatory 3-methyloxindole and indole-3-carbinol formation in minipig liver microsomes, which lack 6-hydroxyskatole formation in males, was mediated partly by liver microsomal P450 1A2 and P450 1A2/2E1, respectively. These enzymes were suppressed by typical P450 inhibitors in female minipig liver microsomes.Among the 14 pig P450 forms evaluated, P450 2A19 was the dominant form mediating 3-methyloxindole, indole-3-carbinol, and 6-hydroxyskatole formation from skatole at substrate concentrations of 100 µM. Positive cooperativity was observed in 3-methyloxindole formation from skatole mediated by male minipig liver microsomes and by pig P450 3A22 with Hill coefficients of 1.2-1.5.These results suggest high skatole 2-oxidation, 3-methyl hydroxylation, and 6-hydroxylation activities of pig P450 2A19 and compensatory skatole oxidations mediated by pig P450 1A2, 2E1, or 3A22 in male minipig liver microsomes.

Novel cytochrome P450 2C94 (CYP2C94) functionally metabolizes diclofenac and omeprazole in dogs

Cytochromes P450 (P450s or CYPs) are important drug-metabolizing enzymes. Because dogs are frequently used in drug metabolism studies, knowledge of dog CYP2C enzymes is essential because, in humans, these enzymes are abundant and play major roles in liver and intestine. The present study identified and characterized novel dog CYP2C94 along with previously identified dog CYP2C21 and CYP2C41. Dog CYP2C21, CYP2C41, and CYP2C94 cDNAs, respectively, contained open reading frames of 490, 489, and 496 amino acids and shared high sequence identities (70%, 75%, and 58%) with human CYP2Cs. Dog CYP2C94 mRNA was preferentially expressed in liver, just as dog CYP2C21 and CYP2C41 mRNAs were. In dog liver, CYP2C21 mRNA was the most abundant, followed by CYP2C94 and CYP2C41 mRNAs. Moreover, the hepatic expressions of all three dog CYP2C mRNAs varied in four individual dogs, two of which did not express CYP2C41 mRNA. The three dog CYP2C genes had similar gene structures, and CYP2C94, although located on the same chromosome, was in a genomic region far from the gene cluster containing CYP2C21 and CYP2C41 Metabolic assays with recombinant proteins showed that dog CYP2C94, along with CYP2C21 and CYP2C41, efficiently catalyzed oxidations of diclofenac, warfarin, and/or omeprazole, indicating that dog CYP2C94 is a functional enzyme. Novel dog CYP2C94 is expressed abundantly in liver and encodes a functional enzyme that metabolizes human CYP2C substrates; it is, therefore, likely responsible for drug clearances in dogs. Significance Statement Novel dog cytochrome P450 2C94 (CYP2C94) was identified and characterized, along with dog CYP2C21 and CYP2C41. Dog CYP2C94, isolated from liver, had 58% sequence identity and a close phylogenetic relationship with its human homologs and was expressed in liver at the mRNA level. Dog CYP2C94 (and CYP2C21 and CYP2C41) catalyzed oxidations of diclofenac and omeprazole, human CYP2C9 and CYP2C19 substrates, respectively, but CYP2C41 also hydroxylated warfarin. CYP2C94 is, therefore, a functional drug-metabolizing enzyme likely responsible for drug clearances in dogs.

A comprehensive analysis of six forms of cytochrome P450 2C (CYP2C) in pigs

Pigs are an important species used in drug metabolism studies; however, the cytochromes P450 (P450s or CYPs) have not been fully investigated in pigs.In this study, pig CYP2C32, CYP2C33, CYP2C34, CYP2C36, CYP2C42, and CYP2C49 cDNAs were isolated and found to contain open reading frames of 490 or 494 amino acids that shared 64-82% sequence identity with human CYP2C8/9/18/19.Pig CYP2C genes formed a gene cluster in a genomic region that corresponded to that of the human CYP2C cluster; an additional gene cluster was formed by pig CYP2C33a and CYP2C33b distant from the first cluster but located in the same chromosome.Among the tissues analysed, these pig CYP2C mRNAs were preferentially expressed in liver, small intestine, and/or kidney; pig CYP2C49, CYP2C32, CYP2C34, and CYP2C33 mRNAs were the most abundant CYP2C mRNAs in liver, jejunum, ileum, and kidney, respectively.Metabolic assays showed that pig CYP2C proteins (heterologously expressed in Escherichia coli) metabolised typical human CYP2C substrates diclofenac, warfarin, and/or omeprazole.The results suggest that these pig CYP2Cs are functional enzymes able to metabolise human CYP2C substrates in liver and small intestine, just as human CYP2Cs do.