Drug-oxidizing and conjugating non-cytochrome P450 (non-P450) enzymes in cynomolgus monkeys and common marmosets as preclinical models for humans

Role of carboxylesterase and arylacetamide deacetylase in drug metabolism, physiology, and pathology

Carboxylesterases (CES1 and CES2) and arylacetamide deacetylase (AADAC), which are expressed primarily in the liver and/or gastrointestinal tract, hydrolyze drugs containing ester and amide bonds in their chemical structure. These enzymes often catalyze the conversion of prodrugs, including the COVID-19 drugs remdesivir and molnupiravir, to their pharmacologically active forms. Information on the substrate specificity and inhibitory properties of these enzymes, which would be useful for drug development and toxicity avoidance, has accumulated. Recently,in vitroandin vivostudies have shown that these enzymes are involved not only in drug hydrolysis but also in lipid metabolism. CES1 and CES2 are capable of hydrolyzing triacylglycerol, and the deletion of their orthologous genes in mice has been associated with impaired lipid metabolism and hepatic steatosis. Adeno-associated virus-mediated human CES overexpression decreases hepatic triacylglycerol levels and increases fatty acid oxidation in mice. It has also been shown that overexpression of CES enzymes or AADAC in cultured cells suppresses the intracellular accumulation of triacylglycerol. Recent reports indicate that AADAC can be up- or downregulated in tumors of various organs, and its varied expression is associated with poor prognosis in patients with cancer. Thus, CES and AADAC not only determine drug efficacy and toxicity but are also involved in pathophysiology. This review summarizes recent findings on the roles of CES and AADAC in drug metabolism, physiology, and pathology.

Transcript abundance of hepatic drug-metabolizing enzymes in two dog breeds compared with 14 species including humans

Drug-metabolizing enzymes are important in drug development and therapy, but have not been fully identified and characterized in many species, lines, and breeds. Liver transcriptomic data were analyzed for phase I cytochromes P450, flavin-containing monooxygenases, and carboxylesterases and phase II UDP-glucuronosyltransferases, sulfotransferases, and glutathione S-transferases. Comparisons with a variety of species (humans, rhesus macaques, African green monkeys, baboons, common marmosets, cattle, sheep, pigs, cats, dogs, rabbits, tree shrews, rats, mice, and chickens) revealed both general similarities and differences in the transcript abundances of drug-metabolizing enzymes. Similarly, Beagle and Shiba dogs were examined by next-generation sequencing (RNA-seq). Consequently, no substantial differences in transcript abundance were noted in different breeds of pigs and dogs and in different lines of mice and rats. Therefore, the expression profiles of hepatic drug-metabolizing enzyme transcripts appear to be similar in Shiba and Beagle dogs and pig breeds and the rat and mouse lines analyzed, although some differences were found in other species.

A variety of cytochrome P450 enzymes and flavin-containing monooxygenases in dogs and pigs commonly used as preclinical animal models

Drug oxygenation is mainly mediated by cytochromes P450 (P450s, CYPs) and flavin-containing monooxygenases (FMOs). Polymorphic variants of P450s and FMOs are known to influence drug metabolism.　Species differences exist in terms of drug metabolism and can be important when determining the contributions of individual enzymes. The success of research into drug-metabolizing enzymes and their impacts on drug discovery and development has been remarkable. Dogs and pigs are often used as preclinical animal models. This research update provides information on P450 and FMO enzymes in dogs and pigs and makes comparisons with their human enzymes. Newly identified dog CYP3A98, a testosterone 6β- and estradiol 16α-hydroxylase, is abundantly expressed in small intestine and is likely the major CYP3A enzyme in small intestine, whereas dog CYP3A12 is the major CYP3A enzyme in liver. The roles of recently identified dog CYP2J2 and pig CYP2J33/34/35 were investigated. FMOs have been characterized in humans and several other species including dogs and pigs. P450 and FMO family members have been characterized also in cynomolgus macaques and common marmosets. P450s have industrial applications and have been the focus of attention of many pharmaceutical companies. The techniques used to investigate the roles of P450/FMO enzymes in drug oxidation and clinical treatments have not yet reached maturity and require further development. The findings summarized here provide a foundation for understanding individual pharmacokinetic and toxicological results in dogs and pigs as preclinical models and will help to further support understanding of the molecular mechanisms of human P450/FMO functionality.

Non-cytochrome P450 enzyme aldehyde oxidase is involved in the oxidative metabolic pathway of diquat and its detoxification effect

Diquat (DQ) poisoning has garnered attention in recent years, primarily due to the rising incidence of cases worldwide, coupled with the absence of a viable antidote for its treatment. Despite the fact that diquat monopyridone (DQ-M) has been identified as a significant metabolite of DQ, the enzyme responsible for its formation remains unknown. In this study, we have identified aldehyde oxidase (AOX) as a vital enzyme involved in DQ oxidative metabolism. The metabolism of DQ to DQ-M was significantly inhibited by AOX inhibitors including raloxifene and hydralazine. The source of oxygen incorporated into DQ-M was proved to be from water through a H218O incubation experiment which further corroborated DQ-M formation via AOX metabolism. The product of DQ-M in vitro generated by fresh rat tissues co-incubation was consistent with its AOX expression. The result of the molecular docking analysis of DQ and AOX protein showed that DQ is capable of binding to AOX. Furthermore, the cytotoxicity of DQ was significantly higher than DQ-M at the same concentration tested in six cell types. This work is the first to uncover the involvement of aldehyde oxidase, a non-cytochrome P450 enzyme, in the oxidative metabolic pathway of diquat, thus providing a potential target for the development of detoxification treatment.

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.

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.

Species Specificity and Selection of Models for Drug Oxidations Mediated by Polymorphic Human Enzymes

Many drug oxygenations are mainly mediated by polymorphic cytochromes P450 (P450s) and also by flavin-containing monooxygenases (FMOs). More than 50 years of research on P450/FMO-mediated drug oxygenations have clarified their catalytic roles. The natural product coumarin causes hepatotoxicity in rats via the reactive coumarin 3,4-epoxide, a reaction catalyzed by P450 1A2; however, coumarin undergoes rapid 7-hydroxylation by polymorphic P450 2A6 in humans. The primary oxidation product of the teratogen thalidomide in rats is deactivated 5'-hydroxythalidomide plus sulfate and glucuronide conjugates; however, similar 5'-hydroxythalidomide and 5-hydroxythalidomide are formed in rabbits in vivo. Thalidomide causes human P450 3A enzyme induction in liver (and placenta) and is also activated in vitro and in vivo by P450 3A through the primary human metabolite 5-hydroxythalidomide (leading to conjugation with glutathione/nonspecific proteins). Species differences exist in terms of drug metabolism in rodents and humans, and such differences can be very important when determining the contributions of individual enzymes. The approaches used for investigating the roles of human P450 and FMO enzymes in understanding drug oxidations and clinical therapy have not yet reached maturity and still require further development. SIGNIFICANCE STATEMENT: Drug oxidations in animals and humans mediated by P450s and FMOs are important for understanding the pharmacological properties of drugs, such as the species-dependent teratogenicity of the reactive metabolites of thalidomide and the metabolism of food-derived odorous trimethylamine to non-odorous (but proatherogenic) trimethylamine N-oxide. Recognized differences exist in terms of drug metabolism between rodents, non-human primates, and humans, and such differences are important when determining individual liver enzyme contributions with substrates in in vitro and in vivo systems.

Recent insights into oxidative metabolism of quercetin: catabolic profiles, degradation pathways, catalyzing metalloenzymes and molecular mechanisms

Quercetin is the most abundant polyphenolic flavonoid (flavonol subclass) in vegetal foods and medicinal plants. This dietary chemopreventive agent has drawn significant interest for its multiple beneficial health effects ("polypharmacology") largely associated with the well-documented antioxidant properties. However, controversies exist in the literature due to its dual anti-/pro-oxidant character, poor stability/bioavailability but multifaceted bioactivities, leaving much confusion as to its exact roles in vivo. Increasing evidence indicates that a prior oxidation of quercetin to generate an array of chemical diverse products with redox-active/electrophilic moieties is emerging as a new linkage to its versatile actions. The present review aims to provide a comprehensive overview of the oxidative conversion of quercetin by systematically analyzing the current quercetin-related knowledge, with a particular focus on the complete spectrum of metabolite products, the enzymes involved in the catabolism and the underlying molecular mechanisms. Herein we review and compare the oxidation pathways, protein structures and catalytic patterns of the related metalloenzymes (phenol oxidases, heme enzymes and specially quercetinases), aiming for a deeper mechanistic understanding of the unusual biotransformation behaviors of quercetin and its seemingly controversial biological functions.

The Common Marmoset-Biomedical Research Animal Model Applications and Common Spontaneous Diseases

Marmosets are becoming more utilized in biomedical research due to multiple advantages including (1) a nonhuman primate of a smaller size with less cost for housing, (2) physiologic similarities to humans, (3) translatable hepatic metabolism, (4) higher numbers of litters per year, (5) genome is sequenced, molecular reagents are available, (6) immunologically similar to humans, (7) transgenic marmosets with germline transmission have been produced, and (8) are naturally occurring hematopoietic chimeras. With more use of marmosets, disease surveillance over a wide range of ages of marmosets has been performed. This has led to a better understanding of the disease management of spontaneous diseases that can occur in colonies. Knowledge of clinical signs and histologic lesions can assist in maximizing the colony's health, allowing for improved outcomes in translational studies within biomedical research. Here, we describe some basic husbandry, biology, common spontaneous diseases, and animal model applications for the common marmoset in biomedical research.