Functional expression and comparative characterization of four feline P450 cytochromes using fluorescent substrates

The profile of urinary lipid metabolites in cats with bacterial cystitis

Bacterial cystitis is one of the feline lower urinary tract diseases (FLUTDs). Polyunsaturated fatty acids, such as arachidonic acid (ARA), docosahexaenoic acid (DHA), and eicosapentaenoic acid (EPA), are oxidized into various lipid mediators that modulate inflammation. Since the profile of lipid metabolites excreted in urine is useful for assessing inflammatory body conditions, we analyzed 126 types of urinary lipid metabolites in cats with bacterial cystitis. Using LC-MS/MS, we found that the levels of 11 metabolites were higher in the urine of cystitis cats than in the urine of healthy cats. In detail, the urinary levels of ARA, EPA, and DHA and eight of their metabolites were increased in cystitis cats. Focusing on the lipid oxidation pathway, the urinary levels of four cyclooxygenase-, three lipoxygenase-, and one cytochrome p450-dependent oxidated metabolites were increased in bacterial cystitis. These urinary lipid profiles can provide some insight into the pathology and future diagnosis of bacterial cystitis.

Metabolism and pharmacokinetics of pharmaceuticals in cats (Felix sylvestris catus) and implications for the risk assessment of feed additives and contaminants

In animal health risk assessment, hazard characterisation of feed additives has been often using the default uncertainty factor (UF) of 100 to translate a no-observed-adverse-effect level in test species (rat, mouse, dog, rabbit) to a 'safe' level of chronic exposure in farm and companion animal species. Historically, both 10-fold factors have been further divided to include chemical-specific data in both dimensions when available. For cats (Felis Sylvestris catus), an extra default UF of 5 is applied due to the species' deficiency in particularly glucuronidation and glycine conjugation. This paper aims to assess the scientific basis and validity of the UF for inter-species differences in kinetics (4.0) and the extra UF applied for cats through a comparison of kinetic parameters between rats and cats for 30 substrates of phase I and phase II metabolism. When the parent compound undergoes glucuronidation the default factor of 4.0 is exceeded, with exceptions for zidovudine and S-carprofen. Compounds that were mainly renally excreted did not exceed the 4.0-fold default. Mixed results were obtained for chemicals which are metabolised by CYP3A in rats. When chemicals were administered intravenously the 4.0-fold default was not exceeded with the exception of clomipramine, lidocaine and alfentanil. The differences seen after oral administration might be due to differences in first-pass metabolism and bioavailability. Further work is needed to further characterise phase I, phase II enzymes and transporters in cats to support the development of databases and in silico models to support hazard characterisation of chemicals particularly for feed additives.

The profile of urinary lipid metabolites in cats

Polyunsaturated fatty acids including arachidonic acid (AA), docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), are converted to lipid mediators by oxidation. Unlike other mammals, cats cannot synthesize AA. Since their lipid metabolic features remain unknown, we qualitatively analyzed 118 types of urinary lipid metabolites in healthy neutered cats. Using LC-MS, we found 26 lipid metabolites in urines of all individuals. In detail, 20 AA-, 5 EPA- and 1 DHA-derived lipid mediators were detected. Focusing on oxidative pathway, 17 cyclooxygenase-metabolites and 5 metabolites produced by non-enzymatic pathway were detected. Of interest, few lipoxygenase- or cytochrome P450-metabolites were excreted. Thus, AA-derived cyclooxygenase-metabolites mainly composed the urinary lipid metabolites in cats.

Tissue distribution and characterization of feline cytochrome P450 genes related to polychlorinated biphenyl exposure

Cats have been known to be extremely sensitive to chemical exposures. To understand these model species' sensitivity to chemicals and their toxicities, the expression profiles of xenobiotic-metabolizing enzymes should be studied. Unfortunately, the characterization of cytochrome P450 (CYP), the dominant enzyme in phase I metabolism, in cats has not extensively been studied. Polychlorinated biphenyls (PCBs) are known as CYP inducers in animals, but the information regarding the PCB-induced CYP expression in cats is limited. Therefore, in the present study, we aimed to elucidate the mRNA expression of the CYP1-CYP3 families in the cat tissues and to investigate the CYP mRNA expression related to PCB exposure. In cats, the greatest abundance of CYP1-CYP3 (CYP1A2, CYP2A13, CYP2C41, CYP2D6, CYP2E1, CYP2E2, CYP2F2, CYP2F5, CYP2J2, CYP2U1, and CYP3A132) was expressed in the liver, but some extrahepatic isozymes were found in the kidney (CYP1A1), heart (CYP1B1), lung (CYP2B11 and CYP2S1) and small intestine (CYP3A131). In cats, CYP1A1, CYP1A2 and CYP1B1 were significantly upregulated in the liver as well as in several tissues exposed to PCBs, indicating that these CYPs were distinctly induced by PCBs. The strong correlations between 3,3',4,4'-tetrachlorobiphenyl (CB77) and CYP1A1 and CYP1B1 mRNA expressions were noted, demonstrating that CB77 could be a potent CYP1 inducer. In addition, these CYP isoforms could play an essential role in the PCBs biotransformation, particularly 3-4 Cl-PCBs, because a high hydroxylated metabolite level of 3-4 Cl-OH-PCBs was observed in the liver.

Genetic diversity of cytochrome P450 2A with different metabolic activities in domestic cats

Knowledge of genetic polymorphisms of cytochrome P450 (CYP), the most important xenobiotic metabolizing enzyme, is very limited in cats. Preliminarily, we investigated genetic polymorphisms in CYP2A13, one of the major CYP isoforms in the liver and lung. Four synonymous and three non-synonymous polymorphic variants were identified in feline CYP2A13 in domestic cats in Japan, without an obvious major type. Metabolic parameters, Km and Vmax, of coumarin hydroxylation of CYP2A13 were shown to range within two times for the identified non-synonymous polymorphic variants by using heterologous coexpression system in Escherichia coli. The results confirmed the polymorphic nature of CYP2A13 as a basis for effective application of medicines and prevention of adverse reactions in treatment of domestic cats.

Genetic diversity of cytochrome P450 1A2 with different metabolic activities in domestic cats

Knowledge of genetic polymorphisms of metabolizing enzymes of medical drugs and xenobiotics including cytochrome P450 (CYP) is very limited in cats. We investigated polymorphisms in CYP1A2, one of the major CYP isoforms in the feline liver. Wild-type and three non-synonymous polymorphic variants, but no synonymous variant, were identified in feline CYP1A2 in 50 alleles of domestic cats in Japan. Metabolic parameters, Km and Vmax, of ethoxyresorufin hydroxylation by CYP1A2 were shown to range within two times for identified non-synonymous variants by using a heterologous coexpression system. The results confirmed the polymorphic nature of CYP1A2 as a basis for effective application of medicines and prevention of adverse reactions in the treatment of domestic cats as well as for hereditary disorders.

Genetic diversity of cytochrome P450 3A with different metabolic activity in domestic cats

Knowledge on genetic polymorphisms of metabolising enzymes including cytochrome P450 (CYP) is very limited in cats. We investigated polymorphisms in CYP3A131, one of the major CYP isoforms in the feline liver and small intestine. Eight non-synonymous variants and one synonymous variant of feline CYP3A131 were identified in 29 cats. A major non-synonymous type was not observed. Metabolic parameters (Km and Vmax) of dibenzylfluorescein hydroxylation were ranged within about 2 times for the identified non-synonymous variants by using a heterologous coexpression system of CYP3A131 and feline cytochrome P450 reductase in Escherichia coli. The results confirmed the polymorphic nature of CYP3A131 as a basis for effective application of medicines and prevention of adverse reactions in the treatment of domestic cats.

Identification and quantification of domestic feline cytochrome P450 transcriptome across multiple tissues

Understanding of cytochrome P450 (CYP) isoform distribution and function in the domestic feline is limited. Only a few studies have defined individual CYP isoforms across metabolically relevant tissues, hampering the ability to predict drug metabolism and potential drug-drug interactions. Using RNA sequencing (RNA-seq), transcriptomes from the 99 Lives Cat Genome Sequencing Initiative databank combined with experimentally acquired whole transcriptome sequencing of healthy, adult male (n = 2) and female (n = 2) domestic felines, expression of 42 CYP isoforms were identified in 20 different tissues. Thirty-seven of these isoforms had not been previously reported in cats. Depending on the tissue, three to twenty-nine CYP isoform transcripts were expressed. The feline genome annotations did not differentiate CYP2E1 and 2E2 genes, demonstrating poor annotation for this gene using the reference genome. As the majority of the sequences are based on automated pipelines, complete cDNA sequences for translation into CYP protein sequences could not be determined. This study is the first to identify and characterize 37 additional CYP isoforms in feline tissues, increasing the number of identified CYP from the previously reported seven isoforms to 42 across 20 tissues.

Limited expression of functional cytochrome p450 2c subtypes in the liver and small intestine of domestic cats

1. Compared to information for herbivores and omnivores, knowledge on xenobiotic metabolism in carnivores is limited. The cytochrome P450 2C (CYP2C) subfamily is recognized as one of the most important CYP groups in human and dog. We identified and characterized CYP2C isoforms and variants in cat, which is an obligate carnivore. 2. Quantitative RT-PCR and immunoblot analyses were carried out to evaluate the expression of CYP2C in the liver and small intestine. A functional CYP2C isoform was heterologously expressed in yeast microsomes to determine the enzymatic activity. 3. Cat had two CYP2C genes, 21 and 41, in the genome; however, CYP2C21P was a pseudogene that had many stop codons. Three splicing variants of CYP2C41 were identified (v1-v3), but only one of them (v1) showed a complete deduced amino acid sequence as CYP2C protein. Transcripts of feline CYP2C41v1 were detected but the amounts were negligible or very small in the liver and small intestine. Immunoreactivity to an antihuman CYP2C antibody was confirmed in the recombinant feline CYP2C41v1 but not in the feline liver. 4. Recombinant feline CYP2C41v1 metabolized several substrates, including dibenzylfluorescein that is specific to human CYP2C. 5. The results suggest a limited role of functional CYP2C isoforms in xenobiotic metabolism in cat.