CYP1D1, pseudogenized in human, is expressed and encodes a functional drug-metabolizing enzyme in cynomolgus monkey

Novel Cytochrome P450 2C119 Enzymes in Cynomolgus and Rhesus Macaques Metabolize Progesterone, Diclofenac, and Omeprazole

Cynomolgus and rhesus macaques are used in drug metabolism studies due to their evolutionary and phylogenetic closeness to humans. Cytochromes P450 (P450s or CYPs), including the CYP2C family enzyme, are important endogenous and exogenous substrate-metabolizing enzymes and play major roles in drug metabolism. In cynomolgus and rhesus macaques, six CYP2Cs have been identified and characterized, namely, CYP2C8, CYP2C9, CYP2C18, CYP2C19, CYP2C76, and CYP2C93. In this study, CYP2C119, a new CYP2C, was identified and characterized in cynomolgus and rhesus macaques. Cynomolgus and rhesus CYP2C119 contained open reading frames of 489 amino acids with high sequence identities to human CYP2C8 and to cynomolgus and rhesus CYP2C8. Phylogenetic analysis showed that cynomolgus and rhesus CYP2C119 were closely related to cynomolgus and rhesus CYP2C8. In cynomolgus and rhesus genomes, CYP2C genes, including CYP2C119, form a cluster. Among the tissues analyzed, cynomolgus CYP2C119 mRNA was predominantly expressed in liver. Hepatic expressions of CYP2C119 mRNA in four cynomolgus and two rhesus macaques varied, with no expression in one rhesus macaque. Among the CYP2C mRNAs, CYP2C119 mRNA was expressed less abundantly than CYP2C8, CYP2C9, CYP2C19, and CYP2C76 mRNAs but more abundantly than CYP2C18 mRNA. Recombinant cynomolgus and rhesus CYP2C119 catalyzed progesterone 16α-, 17α-, and 21-hydroxylation and diclofenac and omeprazole oxidations, indicating that CYP2C119 is a functional enzyme. Therefore, the novel CYP2C119 gene, expressed in macaque liver, encodes a functional enzyme that metabolizes human CYP2C substrates and is likely responsible for drug clearances. SIGNIFICANCE STATEMENT: Cytochrome P450 2C119 was found in cynomolgus and rhesus macaques, in addition to the known P450 2C8, 2C9, 2C18, 2C19, 2C76, and 2C93. Cynomolgus and rhesus CYP2C119 contain open reading frames of 489 amino acids with high sequence identity to human CYP2C8. Cynomolgus CYP2C119 mRNA is predominantly expressed in the liver. Recombinant CYP2C119 catalyzed progesterone hydroxylation and diclofenac and omeprazole oxidations. Therefore, the novel CYP2C119 gene expressed in the macaque liver encodes a functional enzyme that metabolizes human CYP2C substrates.

Novel cytochrome P450 1 (CYP1) genes in tree shrews are expressed and encode functional drug-metabolizing enzymes

Tree shrews (Tupaia belangeri) are a non-rodent primate-like species sometimes used for biomedical research involving hepatitis virus infections and toxicology. Genome analysis has indicated similarities between tree shrews and humans in the numbers of cytochromes P450 (P450 or CYP), which constitute a family of important drug-metabolizing enzymes; however, P450s have not been fully investigated in tree shrews. In this study, we identified CYP1A1, CYP1A2, CYP1B1, and CYP1D1 cDNAs from tree shrew liver and compared their characteristics with dog, pig, and human CYP1As. The deduced amino acid sequences of tree shrew CYP1s were highly identical (82-87 %) to human CYP1s. In tree shrews, CYP1A1 and CYP1A2 mRNAs were preferentially expressed in liver, whereas CYP1D1 mRNA was preferentially expressed in kidney and lung. In contrast, CYP1B1 mRNA was expressed in various tissues, with the most abundant expression in spleen. Among the tree shrew CYP1 mRNAs, CYP1A2 mRNA was most abundant in liver, and CYP1B1 mRNA was most abundant in kidney, small intestine, and lung. All tree shrew CYP1 proteins heterologously expressed in Escherichia coli catalyzed caffeine and estradiol in a similar manner to tree shrew liver microsomes and human, dog, and pig CYP1 proteins. These results suggest that tree shrew CYP1A1, CYP1A2, CYP1B1, and CYP1D1 genes, different form human pseudogene CYP1D1P, are expressed in liver, small intestine, lung, and/or kidney and encode functional drug-metabolizing enzymes important in toxicology.

Polymorphic cytochromes P450 in non-human primates

Cynomolgus macaques (Macaca fascicularis, an Old World monkey) are widely used in drug development because of their genetic and physiological similarities to humans, and this trend has continued with the use of common marmosets (Callithrix jacchus, a New World monkey). Information on the major drug-metabolizing cytochrome P450 (CYP, P450) enzymes of these primate species indicates that multiple forms of their P450 enzymes have generally similar substrate selectivities to those of human P450 enzymes; however, some differences in isoform, activity, and substrate specificity account for limited species differences in drug oxidative metabolism. This review provides information on the P450 enzymes of cynomolgus macaques and marmosets, including cDNA, tissue expression, substrate specificity, and genetic variants, along with age differences and induction. Typical examples of important P450s to be considered in drug metabolism studies include cynomolgus CYP2C19, which is expressed abundantly in liver and metabolizes numerous drugs. Moreover, genetic variants of cynomolgus CYP2C19 affect the individual pharmacokinetic data of drugs such as R-warfarin. These findings provide a foundation for understanding each P450 enzyme and the individual pharmacokinetic and toxicological results in cynomolgus macaques and marmosets as preclinical models. In addition, the effects of induction on some drug clearances mediated by P450 enzymes are also described. In summary, this review describes genetic and acquired individual differences in cynomolgus and marmoset P450 enzymes involved in drug oxidation that may be associated with pharmacological and/or toxicological effects.

Recent advances in computational metabolite structure predictions and altered metabolic pathways assessment to inform drug development processes

Many drug candidates fail during preclinical and clinical trials due to variable or unexpected metabolism which may lead to variability in drug efficacy or adverse drug reactions. The drug metabolism field aims to address this important issue from many angles which range from the study of drug-drug interactions, pharmacogenomics, computational metabolic modeling, and others. This manuscript aims to provide brief but comprehensive manuscript summaries highlighting the conclusions and scientific importance of seven exceptional manuscripts published in recent years within the field of drug metabolism. Two main topics within the field are reviewed: novel computational metabolic modeling approaches which provide complex outputs beyond site of metabolism predictions, and experimental approaches designed to discern the impacts of interindividual variability and species differences on drug metabolism. The computational approaches discussed provide novel outputs in metabolite structure and formation likelihood and/or extend beyond the saturated field of drug phase I metabolism, while the experimental metabolic pathways assessments aim to highlight the impacts of genetic polymorphisms and clinical animal model metabolic differences on human metabolism and subsequent health outcomes.

Topically instilled caffeine selectively alters emmetropizing responses in infant rhesus monkeys

Oral administration of the adenosine receptor (ADOR) antagonist, 7-methylxanthine (7-MX), reduces both form-deprivation and lens-induced myopia in mammalian animal models. We investigated whether topically instilled caffeine, another non-selective ADOR antagonist, retards vision-induced axial elongation in monkeys. Beginning at 24 days of age, a 1.4% caffeine solution was instilled in both eyes of 14 rhesus monkeys twice each day until the age of 135 days. Concurrent with the caffeine regimen, the monkeys were fitted with helmets that held either -3 D (-3D/pl caffeine, n = 8) or +3 D spectacle lenses (+3D/pl caffeine, n = 6) in front of their lens-treated eyes and zero-powered lenses in front of their fellow-control eyes. Refractive errors and ocular dimensions were measured at baseline and periodically throughout the lens-rearing period. Control data were obtained from 8 vehicle-treated animals also reared with monocular -3 D spectacles (-3D/pl vehicle). In addition, historical comparison data were available for otherwise untreated lens-reared controls (-3D/pl controls, n = 20; +3D/pl controls, n = 9) and 41 normal monkeys. The vehicle controls and the untreated lens-reared controls consistently developed compensating axial anisometropias (-3D/pl vehicle = -1.44 ± 1.04 D; -3D/pl controls = -1.85 ± 1.20 D; +3D/pl controls = +1.92 ± 0.56 D). The caffeine regime did not interfere with hyperopic compensation in response to +3 D of anisometropia (+1.93 ± 0.82 D), however, it reduced the likelihood that animals would compensate for -3 D of anisometropia (+0.58 ± 1.82 D). The caffeine regimen also promoted hyperopic shifts in both the lens-treated and fellow-control eyes; 26 of the 28 caffeine-treated eyes became more hyperopic than the median normal monkey (mean (±SD) relative hyperopia = +2.27 ± 1.65 D; range = +0.31 to +6.37 D). The effects of topical caffeine on refractive development, which were qualitatively similar to those produced by oral administration of 7-MX, indicate that ADOR antagonists have potential in treatment strategies for preventing and/or reducing myopia progression.

Molecular characterization of UDP-glucuronosyltransferases 3A and 8A in cynomolgus macaques

UDP-glucuronosyltransferases (UGTs) are drug-metabolizing enzymes essential for the metabolism of endogenous substrates and xenobiotics. The cynomolgus macaque is a nonhuman primate species widely used in drug metabolism studies. The molecular characteristics of UGTs have been extensively investigated in humans, but they remain to be elucidated in cynomolgus macaques. In this study, cynomolgus macaque UGT3A1, UGT3A2, and UGT8A1 cDNAs were isolated and characterized. Amino acid sequences deduced from cynomolgus UGT3A1, UGT3A2, and UGT8A1 cDNAs were highly identical with their human orthologs (93, 96, and 99%, respectively) and were closely clustered in a phylogenetic tree. In the genome, cynomolgus UGT3A and UGT8A genes were located in the regions corresponding to those of their human orthologs. Among the 10 tissue types analyzed, expression of cynomolgus UGT3A1 and UGT3A2 mRNAs was detected in liver, kidney, and testis; the UGT3A1 and UGT3A2 mRNAs were most abundant in liver and testis, respectively. Cynomolgus UGT8A1 was most abundantly expressed in kidney, followed by brain, jejunum, and testis. These results suggest that cynomolgus UGT3As and UGT8A1 have molecular similarities to their human orthologs.

Interleukin-1β and tumor necrosis factor-α affect cytochrome P450 expression in cynomolgus macaque hepatocytes

The cynomolgus macaque, partly due to its evolutionary closeness to humans, is an important nonhuman primate species used in drug metabolism studies. In humans, expressions of cytochromes P450 (P450s), including the important drug-metabolizing enzyme P450 3A4, are affected by various cytokines. However, this phenomenon has not been fully investigated in cynomolgus macaques. In this study, the effects of cytokines on P450 expression were investigated using the quantitative polymerase chain reaction to evaluate mRNA expression. Hepatocytes from cynomolgus macaques were treated with lipopolysaccharide and various cytokines, including interleukin (IL)-1β, IL-2, IL-6, interferon-γ, and tumor necrosis factor-α, and the expression levels of 11 P450s were compared with those of solvent-treated controls. Tumor necrosis factor-α significantly decreased cynomolgus P450 2C8 and 2C76 mRNA expression in multiple lots of cynomolgus hepatocytes investigated. IL-1β significantly decreased cynomolgus P450 1A1, 2C8, 2C19, and 2C76 mRNA expression, but increased P450 3A5 mRNA expression in multiple lots of hepatocytes. Moreover, P450 1A1-and 2C19-mediated drug oxidations were significantly and dose-dependently suppressed by IL-1β, under the present limited conditions. These results suggest that cytokines can influence hepatic P450 mRNA expression levels in cynomolgus macaques, just as cytokines are reported to affect P450 expression in humans.

mRNA levels of drug-metabolizing enzymes in 11 brain regions of cynomolgus macaques

The cynomolgus macaque is an important nonhuman primate species in drug metabolism studies, in part because of its evolutionary closeness to humans. Cytochromes P450 (P450s) have been investigated in the major drug-metabolizing organs, i.e., the liver and small intestine, but have not been fully investigated in the brain. However, recent investigations have indicated possible important roles for P450s in the brain. In this study, by using the quantitative polymerase chain reaction, we measured the mRNA levels of 38 cynomolgus drug-metabolizing enzymes, including 19 P450s, 10 UDP-glycosyltransferases, and 9 other enzymes, in 11 brain regions. Among these drug-metabolizing enzymes, expression of 32 enzyme mRNAs were detected in one or more brain regions, indicating their possible roles in the brain. Further investigation of metabolic activities would facilitate better understanding of the importance of these enzymes in the brain.

The marmoset cytochrome P450 superfamily: Sequence/phylogenetic analyses, genomic structure, and catalytic function

The common marmoset (Callithrix jacchus) is a New World monkey that has attracted much attention as a potentially useful primate model for preclinical testing. A total of 36 marmoset cytochrome P450 (P450) isoforms in the P450 1-51 subfamilies have been identified and characterized by the application of genome analysis and molecular functional characterization. In this mini-review, we provide an overview of the genomic structures, sequence identities, and substrate selectivities of marmoset P450s compared with those of human P450s. Based on the sequence identity, phylogeny, and genomic organization of marmoset P450s, orthologous relationships were established between human and marmoset P450s. Twenty-four members of the marmoset P450 1A, 2A, 2B, 2C, 2D, 2E, 3A, 4A, and 4F subfamilies shared high degrees of homology in terms of cDNA (>89%) and amino acid sequences (>85%) with the corresponding human P450s; P450 2C76 was among the exceptions. Phylogenetic analysis using amino acid sequences revealed that marmoset P450s in the P450 1-51 families were located in the same clades as their human and macaque P450 homologs. This finding underlines the evolutionary closeness of marmoset P450s to their human and macaque homologs. Most marmoset P450 1-4 enzymes catalyzed the typical drug-metabolizing reactions of the corresponding human P450 homologs, except for some differences of P450 2A6 and 2B6. Consequently, it appears that the substrate specificities of enzymes in the P450 1-4 families are generally similar in marmosets and humans. The information presented here supports a better understanding of the functional characteristics of marmoset P450s and their similarities and differences with human P450s. It is hoped that this mini-review will facilitate the successful use of marmosets as primate models in drug metabolism and pharmacokinetic studies.

Expression levels of microRNAs that are potential cytochrome P450 regulators in cynomolgus macaques

1. Although the cynomolgus macaque is an important non-human primate species used in drug metabolism studies, cynomolgus macaque microRNA expressions have not been fully investigated.2. The expressions of 11 cynomolgus microRNAs, all orthologues of P450 regulators in humans, were measured by quantitative polymerase chain reaction in adrenal gland, brain, heart, jejunum, kidney, liver, ovary, testis and uterus. mfa-miR-122 and mfa-miR-192, potentially important biomarkers for liver toxicity, were also analyzed.3. Several cynomolgus microRNAs showed preferential tissue expressions: mfa-miR-1 in heart, mfa-miR-122 in liver and mfa-miR-21 and mfa-miR-192 in jejunum. The remaining nine microRNAs had more ubiquitous expressions. All 13 cynomolgus microRNAs were expressed in liver. Among the 10 animals investigated, inter-individual microRNA expression levels in liver varied from 1.5- to 5.3-fold. mfa-miR-18b was the most variable microRNA. Sex differences in expression levels were <2.0-fold, and the difference was only significant for mfa-miR-29 [1.6-fold difference (p < .05)]. Six cynomolgus microRNAs (mfa-miR-18b, mfa-miR-27a, mfa-miR-132, mfa-miR-27b, mfa-miR-122 and mfa-miR-29) were significantly correlated with P450 mRNAs: mfa-miR-18b and mfa-miR-27a were each correlated with seven P450 mRNAs.4. Expression of these cynomolgus microRNAs in liver might indicate their possible roles in this tissue, and further investigation will clarify their involvement in P450 regulation.

Cytochrome P450 1A1, 2C9, 2C19, and 3A4 Polymorphisms Account for Interindividual Variability of Toxicological Drug Metabolism in Cynomolgus Macaques

Cytochromes P450 (P450s) and their genetic variants in humans are important drug-metabolizing enzymes partly accounting for interindividual variations in drug metabolism and toxicity. However, these genetic variants in P450s have not been fully investigated in cynomolgus macaques, a nonhuman primate species widely used in toxicological studies. In this study, genetic variants found in cynomolgus CYP1A1, CYP2C9 (formerly CYP2C43), CYP2C19 (CYP2C75), and CYP3A4 (CYP3A8) were assessed on functional importance. Resequencing of CYP1A1 in cynomolgus macaques found 18 nonsynonymous variants, of which M121I and V382I were located in SRSs, domains potentially important for P450 function. By further analyzing these two variants, V382I was significantly associated with lower drug-metabolizing activities in the liver for the heterozygotes than the wild types. Similarly, the heterozygotes or homozygotes of CYP2C9 variants (A82V and H344R) and CYP2C19 variant (A490V) showed significantly lower drug-metabolizing activities in the liver than the wild types. Moreover, the homozygotes of CYP3A4 variant (S437N) showed significantly higher activities than the wild type in the liver. Kinetic analyses using recombinant proteins revealed that CYP2C9 variants (A82V and H344R) showed substantially lower  K_s values than the wild type, although CYP1A1 variant (V382I) showed kinetic parameters similar to the wild type. Likewise, CYP2C19 variant (A490V) showed substantially a lower  V_max/ K_m value than the wild type, whereas CYP3A4 variant (S437N) showed a higher V_max/ K_m value than the wild type. These results suggest the toxicologically functional importance of CYP2C9 variants (A82V and H344R), CYP2C19 variant (A490V), and CYP3A4 variant (S437N) for hepatic drug metabolism in cynomolgus macaques.

Molecular and Functional Characterization of N-Acetyltransferases NAT1 and NAT2 in Cynomolgus Macaque

Arylamine N-acetyltransferases (NATs) are drug-metabolizing enzymes essential for the metabolism of endogenous substrates and xenobiotics, and their molecular characteristics have been extensively investigated in humans, but not in cynomolgus macaques, nonhuman primate species important for drug metabolism studies. In this study, cynomolgus NAT1 and NAT2 cDNAs were isolated from livers. NAT1 and NAT2 were characterized by molecular analyses and drug-metabolizing assays. A total of 9 transcript variants were found for cynomolgus NAT1, similar to human NAT1, and contained 1-4 exons with the coding region largely conserved with human NAT1. Genomic organization was similar between cynomolgus macaques and humans. Cynomolgus NAT1 and NAT2 amino acid sequences showed high sequence homology (95% and 89%, respectively) and showed close relationships with human NAT1 and NAT2 in a phylogenetic tree. Cynomolgus NAT2 mRNA was predominantly expressed in liver among the 10 different tissues analyzed, followed by kidney and jejunum. In contrast, cynomolgus NAT1 mRNA showed more ubiquitous expression with relatively more abundant expression in liver, kidney, and jejunum, along with testis. Metabolic assays using recombinant proteins showed that cynomolgus NAT1 and NAT2 metabolized human NAT substrates, including p-aminobenzoic acid, sulfamethazine, isoniazid, and 2-aminofluorene. Interestingly, p-aminobenzoic acid and isoniazid were largely metabolized by NAT1 and NAT2, respectively, in cynomolgus macaques and humans; sulfamethazine, a human NAT2 substrate, was metabolized by both NAT enzymes in cynomolgus macaques. These results suggest molecular and enzymatic similarities of NAT1 and NAT2 between cynomolgus macaques and humans, despite some small differences in substrate specificity of the enzymes.

Computational Identification of the Paralogs and Orthologs of Human Cytochrome P450 Superfamily and the Implication in Drug Discovery

The human cytochrome P450 (CYP) superfamily consisting of 57 functional genes is the most important group of Phase I drug metabolizing enzymes that oxidize a large number of xenobiotics and endogenous compounds, including therapeutic drugs and environmental toxicants. The CYP superfamily has been shown to expand itself through gene duplication, and some of them become pseudogenes due to gene mutations. Orthologs and paralogs are homologous genes resulting from speciation or duplication, respectively. To explore the evolutionary and functional relationships of human CYPs, we conducted this bioinformatic study to identify their corresponding paralogs, homologs, and orthologs. The functional implications and implications in drug discovery and evolutionary biology were then discussed. GeneCards and Ensembl were used to identify the paralogs of human CYPs. We have used a panel of online databases to identify the orthologs of human CYP genes: NCBI, Ensembl Compara, GeneCards, OMA ("Orthologous MAtrix") Browser, PATHER, TreeFam, EggNOG, and Roundup. The results show that each human CYP has various numbers of paralogs and orthologs using GeneCards and Ensembl. For example, the paralogs of CYP2A6 include CYP2A7, 2A13, 2B6, 2C8, 2C9, 2C18, 2C19, 2D6, 2E1, 2F1, 2J2, 2R1, 2S1, 2U1, and 2W1; CYP11A1 has 6 paralogs including CYP11B1, 11B2, 24A1, 27A1, 27B1, and 27C1; CYP51A1 has only three paralogs: CYP26A1, 26B1, and 26C1; while CYP20A1 has no paralog. The majority of human CYPs are well conserved from plants, amphibians, fishes, or mammals to humans due to their important functions in physiology and xenobiotic disposition. The data from different approaches are also cross-validated and validated when experimental data are available. These findings facilitate our understanding of the evolutionary relationships and functional implications of the human CYP superfamily in drug discovery.

Immunochemical detection of cytochrome P450 enzymes in small intestine microsomes of male and female untreated juvenile cynomolgus monkeys

The expression of small intestinal cytochromes P450 (P450s) has not been systematically measured in cynomolgus monkeys, which are widely used in preclinical drug studies to predict pharmacokinetics and toxicity in humans: therefore, P450 content of small intestine was quantified in 35 cynomolgus monkeys by immunoblotting using 11 selective antibodies. CYP2D, CYP2J2, CYP3A4 and CYP3A5 were detected in all 35 animals, while CYP1A and CYP2C9/19 were detected in 31 and 17 animals, respectively. CYP2C9 and CYP2C19 were detected with the same antibody. CYP1D, CYP2A, CYP2B6, CYP2C76 and CYP2E1 were not detected in any of the 35 animals examined. On analysis of pooled microsomes (35 animals), CYP3A (3A4+3A5) was most abundant (79% of total immunoquantified CYP1-3 proteins), followed by CYP2J2 (13%), CYP2C9/19 (4%), CYP1A (3%) and CYP2D (0.4%). On the analysis of individual microsome samples, each P450 content varied 2-to-6-fold between animals, and no sex differences were observed in any P450 content. These findings should help to increase the understanding of drug metabolism, especially the first-pass effect, in cynomolgus monkey small intestines.

Monkey liver cytochrome P450 2C9 is involved in caffeine 7-N-demethylation to form theophylline

Caffeine (1,3,7-trimethylxanthine) is a phenotyping substrate for human cytochrome P450 1A2. 3-N-Demethylation of caffeine is the main human metabolic pathway, whereas monkeys extensively mediate the 7-N-demethylation of caffeine to form pharmacological active theophylline. Roles of monkey P450 enzymes in theophylline formation from caffeine were investigated using individual monkey liver microsomes and 14 recombinantly expressed monkey P450 enzymes, and the results were compared with those for human P450 enzymes. Caffeine 7-N-demethylation activity in microsomes from 20 monkey livers was not strongly inhibited by α-naphthoflavone, quinidine or ketoconazole, and was roughly correlated with diclofenac 4'-hydroxylation activities. Monkey P450 2C9 had the highest activity for caffeine 7-N-demethylation. Kinetic analysis revealed that monkey P450 2C9 had a high Vmax/Km value for caffeine 7-N-demethylation, comparable to low Km value for monkey liver microsomes. Caffeine could dock favorably with monkey P450 2C9 modeled for 7-N-demethylation and with human P450 1A2 for 3-N-demethylation. The primary metabolite theophylline was oxidized to 8-hydroxytheophylline in similar ways by liver microsomes and by recombinant P450s in both humans and monkeys. These results collectively suggest a high activity for monkey liver P450 2C9 toward caffeine 7-N-demethylation, whereas, in humans, P450 1A2-mediated caffeine 3-N-demethylation is dominant.

Cytochrome P450 metabolic activities in the small intestine of cynomolgus macaques bred in Cambodia, China, and Indonesia

Cynomolgus macaques, used in drug metabolism studies due to their evolutionary closeness to humans, are mainly bred in Asian countries, including Cambodia, China, and Indonesia. Cytochromes P450 (P450s) are important drug-metabolizing enzymes, present in the liver and small intestine, major drug metabolizing organs. Previously, our investigation did not find statistically significant differences in hepatic P450 metabolic activities measured in cynomolgus macaques bred in Cambodia (MacfaCAM) and China (MacfaCHN). In the present study, P450 metabolic activity was investigated in the small intestine of MacfaCAM and MacfaCHN, and cynomolgus macaques bred in Indonesia (MacfaIDN) using P450 substrates, including 7-ethoxyresorufin, coumarin, bupropion, paclitaxel, diclofenac, S-mephenytoin, bufuralol, chlorzoxazone, and testosterone. The results indicated that P450 metabolic activity of the small intestine was not statistically significantly different (<2.0-fold) in MacfaCAM, MacfaCHN, and MacfaIDN. In addition, statistically significant sex differences were not observed (<2.0-fold) in any P450 metabolic activity in MacfaCAM as supported by mRNA expression results. These results suggest that P450 metabolic activity of the small intestine does not significantly differ statistically among MacfaCAM, MacfaCHN, and MacfaIDN.

Monkey liver cytochrome P450 2C19 is involved in R- and S-warfarin 7-hydroxylation

Cynomolgus monkeys are widely used as primate models in preclinical studies. However, some differences are occasionally seen between monkeys and humans in the activities of cytochrome P450 enzymes. R- and S-warfarin are model substrates for stereoselective oxidation in humans. In this current research, the activities of monkey liver microsomes and 14 recombinantly expressed monkey cytochrome P450 enzymes were analyzed with respect to R- and S-warfarin 6- and 7-hydroxylation. Monkey liver microsomes efficiently mediated both R- and S-warfarin 7-hydroxylation, in contrast to human liver microsomes, which preferentially catalyzed S-warfarin 7-hydroxylation. R-Warfarin 7-hydroxylation activities in monkey liver microsomes were not inhibited by α-naphthoflavone or ketoconazole, and were roughly correlated with P450 2C19 levels and flurbiprofen 4-hydroxylation activities in microsomes from 20 monkey livers. In contrast, S-warfarin 7-hydroxylation activities were not correlated with the four marker drug oxidation activities used. Among the 14 recombinantly expressed monkey P450 enzymes tested, P450 2C19 had the highest activities for R- and S-warfarin 7-hydroxylations. Monkey P450 3A4 and 3A5 slowly mediated R- and S-warfarin 6-hydroxylations. Kinetic analysis revealed that monkey P450 2C19 had high V(max) and low K(m) values for R-warfarin 7-hydroxylation, comparable to those for monkey liver microsomes. Monkey P450 2C19 also mediated S-warfarin 7-hydroxylation with V(max) and V(max)/K(m) values comparable to those for recombinant human P450 2C9. R-warfarin could dock favorably into monkey P450 2C19 modeled. These results collectively suggest high activities for monkey liver P450 2C19 toward R- and S-warfarin 6- and 7-hydroxylation in contrast to the saturation kinetics of human P450 2C9-mediated S-warfarin 7-hydroxylation.

Cytochrome P450 (CYP) in fish

Cytochrome P450 (CYP) enzymes are members of the hemoprotein superfamily, and are involved in the mono-oxygenation reactions of a wide range of endogenous and exogenous compounds in mammals and plants. Characterization of CYP genes in fish has been carried out intensively over the last 20 years. In Japanese pufferfish (Takifugu rubripes), 54 genes encoding P450s have been identified. Across all species of fish, 137 genes encoding P450s have been identified. These genes are classified into 18 CYP families: namely, CYP1, CYP2, CYP3, CYP4, CYP5, CYP7, CYP8, CYP11, CYP17, CYP19, CYP20, CYP21, CYP24, CYP26, CYP27, CYP39, CYP46 and CYP51.We pinpointed eight CYP families: namely, CYP1, CYP2, CYP3, CYP4, CYP11, CYP17, CYP19 and CYP26 in this review because these CYP families are studied in detail. Studies of fish P450s have provided insights into the regulation of P450 genes by environmental stresses including water pollution. In this review, we present an overview of the CYP families in fish.

Induction of cytochrome P450 family 1 mRNAs and activities in a cell line from the frog Xenopus laevis

Cytochrome P450 family 1 (CYP1) includes four subfamilies of enzymes: CYP1A, CYP1B, CYP1C, and CYP1D. In many vertebrates, CYP1A, 1B, and 1C expression is induced by agonists of the aryl hydrocarbon receptor, including toxic contaminants such as chlorinated dioxins, coplanar chlorinated biphenyls, and polynuclear aromatic hydrocarbons. Assessed at the level of mRNA, protein, or enzyme activity, CYP1s (especially CYP1As) represent potent and popular biomarkers of contaminant exposure in aquatic vertebrates. Alkylated resorufins are synthetic substrates used to detect, quantify, and describe catalytic activities of cytochrome P450s. The ability to oxidize specific resorufin-based substrates can distinguish the catalytic activities of individual CYP1s. Xenopus laevis, the African clawed frog, is the most widely employed amphibian model in aquatic toxicology, yet the number, inducibility, and activities of CYP1s have not been systematically characterized in this species. Here we report the cloning of cDNAs encoding two new CYP1 family members, X. laevis CYP1B and CYP1C, along with an integrated assessment of the induction of alkyloxyuresorufin-O-dealkylase (AROD) activities and mRNA expression of four known X. laevis CYP1s: CYP1A6, CYP1A7, CYP1B, and CYP1C. Using XLK-WG, an X. laevis kidney epithelial cell line, we determined that EROD (ethoxyresorufin substrate) and MROD (methoxyresorufin) were both induced 3000- to 5000-fold following 2,3,7,8 tetrachlorodibenzo-p-dioxin (TCDD) exposure up to 250 nM, while BROD (benzyloxyresorufin) and PROD (pentyloxyresorufin) activity was not detectable regardless of TCDD treatment. TCDD induced CYP1A6 and CYP1A7 mRNAs by 2-3 orders of magnitude, while CYP1B and CYP1C were unchanged. The more potent AHR agonist, FICZ (6-formylindolo[3,2-b]carbazole), induced CYP1B up to 10-fold at concentrations between 0.1 and 250 nM, while CYP1C induction was less than 3-fold. CYP1B mRNA showed the highest constitutive mRNA expression, 5- to 75-fold greater than the other CYP1 transcripts. Taken together, these results suggest that CYP1A6 and CYP1A7 perform the bulk of EROD and MROD activities we observed in these cells. The ability of each X. laevis CYP1 to catalyze oxidation of individual resorufin substrates remains to be determined. Correlating CYP1 mRNA and induced AROD activity is a significant step toward clarifying the biochemical meaning of these biomarkers and the roles of CYP1 enzymes in X. laevis. The cell culture approach represents an important complement to the long standing use of frog embryos and tadpoles in toxicological studies, providing a well suited model system for determining the molecular mechanisms underlying the regulation of these important biomarkers of contaminant exposure.

Functional screening of cytochrome P450 activity and uncoupling by capillary electrophoresis

Cytochrome P450s (CYPs) are functionally diverse monooxygenases responsible for oxidation of endogenous and xenobiotic compounds. The function of nonmammalian CYPs are largely unknown and tools for characterization limited. CYPs critical for xenobiotic metabolism are prone to catalytic cycle uncoupling resulting in reactive oxygen species (ROS) generation that is highly dependent on the specific CYP isoform and substrate interaction. This study describes the rapid assessment of the activity and coupling efficiency of CYPs using capillary electrophoresis with UV detection. The coupling efficiency of five zebrafish (Danio rerio) CYP1 isoforms with a series of fluorogenic substrate probes was determined by the rate of NADP(+) formation and compared with fluorescent product turnover rates. In most cases, NADP(+) formation significantly overestimated CYP1 catalytic activity for substrate O-dealkylation suggesting uncoupling. ROS production was confirmed by elevated hydrogen peroxide generation in poorly coupled reactions. Reactions with β-estradiol confirmed that CYP1A, 1C1, and 1C2 have greater catalytic activity and coupling efficiency; CYP1B1 and 1D1 had coupling efficiencies under 4%. This work highlights the wide disparity in uncoupling induced by unproductive substrate binding among different CYP isoforms.

Expression profile of hepatic genes in cynomolgus macaques bred in Cambodia, China, and Indonesia: implications for cytochrome P450 genes

Cynomolgus macaques, frequently used in drug metabolism studies, are bred mainly in the countries of Asia; however, comparative studies of drug metabolism between cynomolgus macaques bred in these countries have not been conducted. In this study, hepatic gene expression profiles of cynomolgus macaques bred in Cambodia (mfCAM), China (mfCHN), and Indonesia (mfIDN) were analyzed. Microarray analysis revealed that expression of most hepatic genes, including drug-metabolizing enzyme genes, was not substantially different between mfCAM, mfCHN, and mfIDN; only 1.1% and 3.0% of all the gene probes detected differential expression (>2.5-fold) in mfCAM compared with mfCHN and mfIDN, respectively. Quantitative polymerase chain reaction showed that the expression levels of 14 cytochromes P450 (P450s) important for drug metabolism did not differ (>2.5-fold) in mfCAM, mfCHN, and mfIDN, validating the microarray data. In contrast, expression of CYP2B6 and CYP3A4 differed (>2.5-fold, p < 0.05) between cynomolgus (mfCAM, mfCHN, or mfIDN) and rhesus macaques, indicating greater differences in expression of P450 genes between the two lineages. Moreover, metabolic activities measured using 14 P450 substrates did not differ substantially (<1.5-fold) between mfCAM and mfCHN. These results suggest that gene expression profiles, including drug-metabolizing enzyme genes such as P450 genes, are similar in mfCAM, mfCHN, and mfIDN.

Cytochrome p450 1 genes in birds: evolutionary relationships and transcription profiles in chicken and Japanese quail embryos

Background

Cytochrome P450 1 (CYP1) genes are biomarkers for aryl hydrocarbon receptor (AHR) agonists and may be involved in some of their toxic effects. CYP1s other than the CYP1As are poorly studied in birds. Here we characterize avian CYP1B and CYP1C genes and the expression of the identified CYP1 genes and AHR1, comparing basal and induced levels in chicken and quail embryos.

Methodology/Principal Findings

We cloned cDNAs of chicken CYP1C1 and quail CYP1B1 and AHR1. CYP1Cs occur in several bird genomes, but we found no CYP1C gene in quail. The CYP1C genomic region is highly conserved among vertebrates. This region also shares some synteny with the CYP1B region, consistent with CYP1B and CYP1C genes deriving from duplication of a common ancestor gene. Real-time RT-PCR analyses revealed similar tissue distribution patterns for CYP1A4, CYP1A5, CYP1B1, and AHR1 mRNA in chicken and quail embryos, with the highest basal expression of the CYP1As in liver, and of CYP1B1 in eye, brain, and heart. Chicken CYP1C1 mRNA levels were appreciable in eye and heart but relatively low in other organs. Basal transcript levels of the CYP1As were higher in quail than in chicken, while CYP1B1 levels were similar in the two species. 3,3′,4,5,5′-Pentachlorobiphenyl induced all CYP1s in chicken; in quail a 1000-fold higher dose induced the CYP1As, but not CYP1B1.

Conclusions/Significance

The apparent absence of CYP1C1 in quail, and weak expression and induction of CYP1C1 in chicken suggest that CYP1Cs have diminishing roles in tetrapods; similar tissue expression suggests that such roles may be met by CYP1B1. Tissue distribution of CYP1B and CYP1C transcripts in birds resembles that previously found in zebrafish, suggesting that these genes serve similar functions in diverse vertebrates. Determining CYP1 catalytic functions in different species should indicate the evolving roles of these duplicated genes in physiological and toxicological processes.

CpG site degeneration triggered by the loss of functional constraint created a highly polymorphic macaque drug-metabolizing gene, CYP1A2

Background

Elucidating the pattern of evolutionary changes in drug-metabolizing genes is an important subject not only for evolutionary but for biomedical research. We investigated the pattern of divergence and polymorphisms of macaque CYP1A1 and CYP1A2 genes, which are major drug-metabolizing genes in humans. In humans, CYP1A2 is specifically expressed in livers while CYP1A1 has a wider gene expression pattern in extrahepatic tissues. In contrast, macaque CYP1A2 is expressed at a much lower level than CYP1A1 in livers. Interestingly, a previous study has shown that Macaca fascicularis CYP1A2 harbored unusually high genetic diversity within species. Genomic regions showing high genetic diversity within species is occasionally interpreted as a result of balancing selection, where natural selection maintains highly diverged alleles with different functions. Nevertheless many other forces could create such signatures.

Results

We found that the CYP1A1/2 gene copy number and orientation has been highly conserved among mammalian genomes. The signature of gene conversion between CYP1A1 and CYP1A2 was detected, but the last gene conversion event in the simian primate lineage occurred before the Catarrhini-Platyrrhini divergence. The high genetic diversity of macaque CYP1A2 therefore cannot be explained by gene conversion between CYP1A1 and CYP1A2. By surveying CYP1A2 polymorphisms in total 91 M. fascicularis and M. mulatta, we found several null alleles segregating in these species, indicating functional constraint on CYP1A2 in macaques may have weakened after the divergence between humans and macaques. We propose that the high genetic diversity in macaque CYP1A2 is partly due to the degeneration of CpG sites, which had been maintained at a high level by purifying selection, and the rapid degeneration process was initiated by the loss of functional constraint on macaque CYP1A2.

Conclusions

Our findings show that the highly polymorphic CYP1A2 gene in macaques has not been created by balancing selection but by the burst of CpG site degeneration after loss of functional constraint. Because the functional importance of CYP1A1/2 genes is different between humans and macaques, we have to be cautious in extrapolating a drug-testing data using substrates metabolized by CYP1A genes from macaques to humans, despite of their somewhat overlapping substrate specificity.

Immunochemical detection of cytochrome P450 enzymes in liver microsomes of 27 cynomolgus monkeys

The cynomolgus monkey is widely used as a primate model in preclinical studies because of its evolutionary closeness to humans. Despite their importance in drug metabolism, the content of each cytochrome P450 (P450) enzyme has not been systematically determined in cynomolgus monkey livers. In this study, liver microsomes of 27 cynomolgus monkeys were analyzed by immunoblotting using selective P450 antibodies. The specificity of each antibody was confirmed by analyzing the cross-reactivity against 19 CYP1-3 subfamily enzymes using recombinant proteins. CYP2A, CYP2B6, CYP2C9/19, CYP2C76, CYP2D, CYP2E, CYP3A4, and CYP3A5 were detected in all 27 animals. In contrast, CYP1A, CYP1D, and CYP2J were below detectable levels in all liver samples. The average content of each P450 showed that among the P450s analyzed CYP3A (3A4 and 3A5) was the most abundant (40% of total immunoquantified P450), followed by CYP2A (25%), CYP2C (14%), CYP2B6 (13%), CYP2E1 (11%), and CYP2D (3%). No apparent sex differences were found for any P450. Interanimal variations ranged from 2.6-fold (CYP3A) to 11-fold (CYP2C9/19), and most P450s (CYP2A, CYP2D, CYP2E, CYP3A4, and CYP3A5) varied 3- to 4-fold. To examine the correlations of P450 content with enzyme activities, metabolic assays were performed in 27 cynomolgus monkey livers using 7-ethoxyresorufin, coumarin, pentoxyresorufin, flurbiprofen, bufuralol, dextromethorphan, and midazolam. CYP2D and CYP3A4 contents were significantly correlated with typical reactions of human CYP2D (bufuralol 1'-hydroxylation and dextromethorphan O-deethylation) and CYP3A (midazolam 1'-hydroxylation and 4-hydroxylation). The results presented in this study provide useful information for drug metabolism studies using cynomolgus monkeys.

Expression of cytochromes p450 in fetal, infant, and juvenile liver of cynomolgus macaques

Preclinical data of fetal, infant, and juvenile animals are important for the prediction of drug toxicity in fetuses and children. However, expression of drug-metabolizing enzymes, including cytochromes P450 (CYPs), have not been fully investigated in fetal, infant, or juvenile liver of the cynomolgus macaque, an animal species important for preclinical studies. In this study, hepatic expression of 20 cynomolgus macaque CYPs (mfCYPs) in the CYP1-4 subfamilies that are relevant to drug metabolism was measured in fetuses, infants, and juveniles using DNA microarrays. Expression of most mfCYPs, including those moderately or abundantly expressed in postnatal livers such as mfCYP2A23, mfCYP2A24, mfCYP2B6, mfCYP2C9, mfCYP2C19, mfCYP2C76, mfCYP2D17, mfCYP2E1 mfCYP3A4, and mfCYP3A5, was much less abundant in fetal livers, but increased substantially after birth. In contrast, expression of mfCYP2C8 in fetal livers was not substantially different from postnatal livers. Since human CYP3A7 is expressed more abundantly in fetal livers than in adult livers, mfCYP3A7, an ortholog of human CYP3A7, was analyzed by quantitative polymerase chain reaction. Expression of mfCYP3A7 in fetal livers was much lower than that in postnatal livers, and greatly increased after birth, unlike the expression of human CYP3A7. These results indicate that expression of most mfCYPs examined was low in fetal livers, but increased greatly in postnatal livers, with a few exceptions such as mfCYP2C8.

Structural features of cytochrome P450 1A associated with the absence of EROD activity in liver of the loricariid catfish Pterygoplichthys sp

The Amazon catfish genus Pterygoplichthys (Loricariidae, Siluriformes) is closely related to the loricariid genus Hypostomus, in which at least two species lack detectable ethoxyresorufin-O-deethylase (EROD) activity, typically catalyzed by cytochrome P450 1 (CYP1) enzymes. Pterygoplichthys sp. liver microsomes also lacked EROD, as well as activity with other substituted resorufins, but aryl hydrocarbon receptor agonists induced hepatic CYP1A mRNA and protein suggesting structural/functional differences in Pterygoplichthys CYP1s from those in other vertebrates. Comparing the sequences of CYP1As of Pterygoplichthys sp. and of two phylogenetically related siluriform species that do catalyze EROD (Ancistrus sp., Loricariidae and Corydoras sp., Callichthyidae) showed that these three proteins share amino acids at 17 positions that are not shared by any fish in a set of 24 other species. Pterygoplichthys and Ancistrus (the loricariids) have an additional 22 amino acid substitutions in common that are not shared by Corydoras or by other fish species. Pterygoplichthys has six exclusive amino acid substitutions. Molecular docking and dynamics simulations indicate that Pterygoplichthys CYP1A has a weak affinity for ER, which binds infrequently in a productive orientation, and in a less stable conformation than in CYP1As of species that catalyze EROD. ER also binds with the carbonyl moiety proximal to the heme iron. Pterygoplichthys CYP1A has amino acid substitutions that reduce the frequency of correctly oriented ER in the AS preventing the detection of EROD activity. The results indicate that loricariid CYP1As may have a peculiar substrate selectivity that differs from CYP1As of most vertebrate.

Cytochrome P450 1A, 1B, and 1C mRNA induction patterns in three-spined stickleback exposed to a transient and a persistent inducer

Cytochrome P450 1 (CYP1) mRNA induction patterns in three-spined stickleback (Gasterosteus aculeatus) were explored for use in environmental monitoring of aryl hydrocarbon receptor (AHR) agonists. The cDNAs of stickleback CYP1A, CYP1B1, CYP1C1, and CYP1C2 were cloned and their basal and induced expression patterns were determined in the brain, gill, liver and kidney. Also, their induction time courses were compared after waterborne exposure to a transient (indigo) or a persistent (3,3',4,4',5-pentacholorbiphenyl PCB 126) AHR agonist. The cloned stickleback CYP1s exhibited a high amino acid sequence identity compared with their zebrafish orthologs and their constitutive tissue distribution patterns largely agreed with those reported in other species. PCB 126 (100 nM) induced different CYP1 expression patterns in the four tissues, suggesting tissue-specific regulation. Both indigo (1 nM) and PCB 126 (10 nM) induced a strong CYP1 expression in gills. However, while PCB 126 gave rise to a high and persistent induction in gills and liver, induction by indigo was transient in both organs. The number of putative dioxin response elements found in each CYP1 gene promoter roughly reflected the induction levels of the genes. The high responsiveness of CYP1A, CYP1B1, and CYP1C1 observed in several organs suggests that three-spined stickleback is suitable for monitoring of pollution with AHR agonists.