Identification of cytochrome P450 2C18 and 2C76 in tree shrews: P450 2C18 effectively oxidizes typical human P450 2C9/2C19 chiral substrates warfarin and omeprazole with less stereoselectivity

Cytochromes P450 (P450s or CYPs), especially the CYP2C family, are important drug-metabolizing enzymes that play major roles in drug metabolism. Tree shrews, a non-rodent primate-like species, are used in various fields of biomedical research, notably hepatitis virus infection; however, its drug-metabolizing enzymes have not been fully investigated. In this study, tree shrew CYP2C18, CYP2C76a, CYP2C76b, and CYP2C76c cDNAs were identified and contained open reading frames of 489 or 490 amino acids with high sequence identities (70-78 %) to human CYP2Cs. Tree shrew CYP2C76a, CYP2C76b, and CYP2C76c showed higher sequence identities (79-80 %) to cynomolgus CYP2C76 and were not orthologous to any human CYP2C. Phylogenetic analysis revealed that tree shrew CYP2C18 and CYP2C76s were closely related to rat CYP2Cs and cynomolgus CYP2C76, respectively. Tree shrew CYP2C genes formed a gene cluster similar to human CYP2C genes. All four tree shrew CYP2C mRNAs showed predominant expressions in liver, among the tissue types examined; expression of CYP2C18 mRNA was also detected in small intestine. In liver, CYP2C18 mRNA was the most abundant among the tree shrew CYP2C mRNAs. In metabolic assays using human CYP2C substrates, all tree shrew CYP2Cs showed metabolic activities toward diclofenac, R,S-omeprazole, paclitaxel, and R,S-warfarin, with the activity of CYP2C18 exceeding that of the other CYP2Cs. Moreover, tree shrew CYP2C76 enzymes metabolized progesterone more efficiently than human, cynomolgus, or marmoset CYP2Cs. Therefore, these novel tree shrew CYP2Cs are expressed abundantly in liver, encode functional enzymes that metabolize human CYP2C substrates, and are likely responsible for drug clearances.

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.

Safety Issues of Herb-Warfarin Interactions

Warfarin is a popular anticoagulant with high global demand. However, studies have underlined serious safety issues when warfarin is consumed concomitantly with herbs or its formulations. This review aimed to highlight the mechanisms behind herb-warfarin interactions while laying special emphasis on its PKPD interactions and evidence on Herb-Warfarin Interaction (HWI) with regards to three different scenarios, such as when warfarin is consumed with herbs, taken as foods or prescribed as medicine, or when used in special situations. A targeted literature methodology involving different scientific databases was adopted for acquiring information on the subject of HWIs. Results of the present study revealed some of the fatal consequences of HWI, including post-operative bleeding, thrombosis, subarachnoid hemorrhage, and subdural hematomas occurring as a result of interactions between warfarin and herbs or commonly associated food products from Hypericum perforatum, Zingiber officinale, Vaccinium oxycoccos, Citrus paradisi, and Punica granatum. In terms of PK-PD parameters, herbs, such as Coptis chinensis Franch. and Phellodendron amurense Rupr., were found to compete with warfarin for binding with plasma proteins, leading to an increase in free warfarin levels in the bloodstream, resulting in its augmented antithrombic effect. Besides, HWIs were also found to decrease International Normalised Ratio (INR) levels following the consumption of Persea americana or avocado. Therefore, there is an urgent need for an up-to-date interaction database to educate patients and healthcare providers on these interactions, besides promoting the adoption of novel technologies, such as natural language processing, by healthcare professionals to guide them in making informed decisions to avoid HWIs.

Chronic Toxoplasma infection affects gene expression of drug-metabolizing enzymes in mouse liver

Toxoplasma gondii is an intracellular protozoan parasite causing toxoplasmosis, an infectious disease affecting warm-blooded vertebrates worldwide. Many drug-metabolizing enzymes are located in the liver, a major organ of drug metabolism, and their function can be affected by pathogen infection.Using next-generation sequencing (RNA-seq) and quantitative polymerase chain reaction (qPCR), changes in the hepatic expressions of drug-metabolizing enzymes were analysed in mice chronically infected with T. gondii. The analysis found that, among drug-metabolizing enzymes, 22 genes were upregulated and 28 genes were downregulated (≥1.5-fold); of these 5 and 17 genes, respectively, were cytochromes P450 (Cyp or P450).Subsequent qPCR analysis showed that six P450 genes were upregulated significantly (≥1.5-fold, p < 0.05), namely, Cyp1b1, Cyp2c29, Cyp2c65, Cyp2d9, Cyp2d12, and Cyp3a59, whereas nine P450 genes were downregulated significantly (≥1.5-fold, p < 0.05), namely, Cyp2c38, Cyp2c39, Cyp2c44, Cyp2c69, Cyp2d40, Cyp2e1, Cyp3a11, Cyp3a41, and Cyp3a44.Moreover, metabolic assays in infected mouse liver using typical P450 substrates revealed that midazolam 1'-hydroxylation and testosterone 2-hydroxylation activities decreased significantly (≥1.5-fold, p < 0.05), whereas testosterone 16-hydroxylation activity increased significantly (≥1.5-fold, p < 0.05).Chronic Toxoplasma infection affects drug metabolism, at least partly, by altering the gene expressions of drug-metabolizing enzymes, including P450s.

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.

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.

Human total clearance values and volumes of distribution of typical human cytochrome P450 2C9/19 substrates predicted by single-species allometric scaling using pharmacokinetic data sets from common marmosets genotyped for P450 2C19

Common marmosets (Callithrix jacchus) are small non-human primates that genetically lack cytochrome P450 2C9 (CYP2C9). Polymorphic marmoset CYP2C19 compensates by mediating oxidations of typical human CYP2C9/19 substrates.Twenty-four probe substrates were intravenously administered in combinations to marmosets assigned to extensive or poor metaboliser (PM) groups by CYP2C19 genotyping. Eliminations from plasma of cilomilast, phenytoin, repaglinide, tolbutamide, and S-warfarin in the CYP2C19 PM group were significantly slow; these drugs are known substrates of human CYP2C8/9/19.Human total clearance values and volumes of distribution of the 24 test compounds were extrapolated using single-species allometric scaling with experimental data from marmosets and found to be mostly comparable with the reported values.Human total clearance values and volumes of distribution of 15 of the 24 test compounds similarly extrapolated using reported data sets from cynomolgus or rhesus monkeys were comparable to the present predicted results, especially to those based on data from PM marmosets.These results suggest that single-species allometric scaling using marmosets, being small, has advantages over multiple-species-based allometry and could be applicable for pharmacokinetic predictions at the discovery stage of drug development.

Different Roles of Human Cytochrome P450 2C9 and 3A Enzymes in Diclofenac 4'- and 5-Hydroxylations Mediated by Metabolically Inactivated Human Hepatocytes in Previously Transplanted Chimeric Mice

To investigate the respective roles of cytochromes P450 2C9 and 3A in drug oxidation in human livers, the in vivo pharmacokinetics of S-warfarin and diclofenac were analyzed after intravenous administrations in chimeric mice that had been transplanted with human hepatocytes. P450 2C9 was metabolically inactivated in the humanized mice by orally pretreating them with tienilic acid. After intravenous administration of S-warfarin, a significant difference in the concentration-time profiles of the primary metabolite 7-hydroxywarfarin between untreated mice and mice treated with tienilic acid was observed. In contrast, there were no apparent differences in the profiles for S-warfarin between the treated and untreated groups. The mean values of the maximum concentrations (C_max) and the areas under the plasma concentration versus time curves (AUC_infinity) for 7-hydroxywarfarin were significantly lower (22 and 16% of the untreated values, respectively) in the treated group. This presumably resulted from suppressed P450 2C9 activity in the primary oxidative metabolism in vivo in the treated group. After diclofenac administration, plasma levels of diclofenac, 5-hydroxydiclofenac, and diclofenac acylglucuronide were roughly similar in pretreated and untreated mice. However, the mean C_max and AUC_infinity values for 4'-hydroxydiclofenac were significantly lower (38 and 53% of the untreated group, respectively) in the treated group. The reported value of ∼0.8 for the fraction of S-warfarin metabolized to 7-hydroxywarfarin mediated by P450 2C9 in in vitro systems was similar to the value implied by the present humanized-liver mouse model pretreated with tienilic acid in which the AUC of 7-hydroxywarfarin was reduced by 84%. In contrast, the fractions of diclofenac metabolized to 4'-hydroxydiclofenac in in vitro and in vivo experiments were inconsistent. These results suggested that humanized-liver mice orally treated with tienilic acid might constitute an in vivo model for metabolically inactivated P450 2C9 in human hepatocytes transplanted into chimeric mice. Moreover, diclofenac, a typical in vitro P450 2C9 probe substrate, was cleared differently in vitro and in humanized-liver mice in vivo.

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.

Survey of Drug Oxidation Activities in Hepatic and Intestinal Microsomes of Individual Common Marmosets, a New Nonhuman Primate Animal Model

BACKGROUND

Common marmosets (Callithrix jacchus) are potentially useful nonhuman primate models for preclinical studies. Information for major drug-metabolizing cytochrome P450 (P450) enzymes is now available that supports the use of this primate species as an animal model for drug development. Here, we collect and provide an overview of information on the activities of common marmoset hepatic and intestinal microsomes with respect to 28 typical human P450 probe oxidations.

RESULTS

Marmoset P450 2D6/8-dependent R-metoprolol O-demethylation activities in hepatic microsomes were significantly correlated with those of midazolam 1'- and 4-hydroxylations, testosterone 6β-hydroxylation, and progesterone 6β-hydroxylation, which are probe reactions for marmoset P450 3A4/5/90. In marmosets, the oxidation activities of hepatic microsomes and intestinal microsomes were roughly comparable for midazolam and terfenadine. Overall, multiple forms of marmoset P450 enzymes in livers and intestines had generally similar substrate recognition functionalities to those of human and/or cynomolgus monkey P450 enzymes.

CONCLUSION

The marmoset could be a model animal for humans with respect to the first-pass extraction of terfenadine and related substrates. These findings provide a foundation for understanding individual pharmacokinetic and toxicological results in nonhuman primates as preclinical models and will help to further support understanding of the molecular mechanisms of human P450 function.

Effects of aging and rifampicin pretreatment on the pharmacokinetics of human cytochrome P450 probes caffeine, warfarin, omeprazole, metoprolol and midazolam in common marmosets genotyped for cytochrome P450 2C19

1. The pharmacokinetics were investigated for human cytochrome P450 probes after single intravenous and oral administrations of 0.20 and 1.0 mg/kg, respectively, of caffeine, warfarin, omeprazole, metoprolol and midazolam to aged (10-14 years old, n = 4) or rifampicin-treated/young (3 years old, n = 3) male common marmosets all genotyped as heterozygous for a cytochrome P450 2C19 variant. 2. Slopes of the plasma concentration-time curves after intravenous administration of warfarin and midazolam were slightly, but significantly (two-way analysis of variance), decreased in aged marmosets compared with young marmosets. The mean hepatic clearances determined by in silico fitting for individual pharmacokinetic models of warfarin and midazolam in the aged group were, respectively, 23% and 56% smaller than those for the young group. 3. Significantly enhanced plasma clearances of caffeine, warfarin, omeprazole and midazolam were evident in young marmosets pretreated with rifampicin (25 mg/kg daily for 4 days). Two- to three-fold increases in hepatic intrinsic clearance values were observed in the individual pharmacokinetic models. 4. The in vivo dispositions of multiple simultaneously administered drugs in old, young and P450-enzyme-induced marmosets were elucidated. The results suggest that common marmosets could be experimental models for aged, induced or polymorphic P450 enzymes in P450-dependent drug metabolism studies.

Differences in Toxicological and Pharmacological Responses Mediated by Polymorphic Cytochromes P450 and Related Drug-Metabolizing Enzymes

Research over the past 30 years has elucidated the roles of polymorphic human liver cytochrome P450 (P450) enzymes associated with toxicological and/or pharmacological actions. Thalidomide exerts its various pharmacological and toxic actions in primates through multiple mechanisms, including nonspecific modification of many protein networks after bioactivation by autoinduced human P450 enzymes. To overcome species differences between rodents, currently, nonhuman primates and/or mouse models with transplanted human hepatocytes are used. Interindividual variability of P450-dependent drug clearances in cynomolgus monkeys and common marmosets is partly accounted for by polymorphic P450 variants and/or aging, just as it is in humans with increased prevalence of polypharmacy. Genotyping of P450 genes in nonhuman primates would be beneficial before and/or after drug metabolism and toxicity testing and evaluation as well in humans. Genome-wide association studies in humans have been rapidly advanced; however, unique whole-gene deletion of P450 2A6 was subsequently developed to cover nicotine-related lung cancer risk study. Regarding polypharmacy, toxicological research should generally be aimed at identifying the risk of adverse drug events following specific potential drug exposures by examining single or multiple metabolic pathways involving single or multiple drug-metabolizing enzymes. Current and next-generation research of drug metabolism and disposition resulting in drug toxicity would be addressed under advanced knowledge of polymorphic and age-related intra- and/or interspecies differences of drug-metabolizing enzymes. In the near future, humanized animal models combining transplanted hepatocytes and a humanized immune system may be available to study human immune reactions caused by human-type drug metabolites. Such sophisticated models should provide preclinical predictions of human drug metabolism and potential toxicity.

The impact of CYP4F2, ABCB1, and GGCX polymorphisms on bleeding episodes associated with acenocoumarol in Russian patients with atrial fibrillation

BACKGROUND

Oral anticoagulants are commonly used to treat patients with thromboembolic pathology. Genetic variations could influence personal response to anticoagulant drugs. Acenocoumarol (AC) is a vitamin K antagonist used in anticoagulant therapy and as a prophylaxis measure in Europe. In this study, we assessed the effect of CYP4F2 rs2108622, ABCB1, and GGCX polymorphisms on the safety profile and regime dosing of AC in patients with nonvalvular atrial fibrillation.

METHODS

Fifty patients aged 40-70 years were included. All patients received AC in the dose of 1-6 mg daily with a target international normalized ratio of 2.0-3.0. Genotyping for polymorphism markers C3435T for the ABCB1 gene, rs2108622 for the CYP4F2 gene, and rs11676382 for the GGCX gene were designed using polymerase chain reaction and restriction fragment length polymorphism. Statistical analysis was performed using the Fisher exact test and the Mann-Whitney U test.

RESULTS

We found that CYP4F2 rs2108622 CT carriers required a higher AC dose than CC (p=0.0366), and CT and TT carriers required a higher AC dose than CC (p=0.0314).

CONCLUSIONS

We found that ABCB1 CT and TT genotypes are associated with a higher risk of bleeding. No influence of ABCB1 and GGCX polymorphisms on the doses of AC was established. CYP4F2 could still be a genetic factor responsible for the personal variability of AC metabolism.