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

Molecular and Functional Characterization of N-Acetyltransferases in Common Marmosets and Pigs

Arylamine N-acetyltransferases (NATs) are drug-metabolizing enzymes that are essential for the metabolism of endogenous substrates and xenobiotics. The molecular characteristics of NATs have been extensively investigated in humans but remain to be investigated in common marmosets and pigs, animal species that are often used in drug metabolism studies. In this study, marmoset NAT1 and pig NAT1 cDNAs were isolated from liver samples and were characterized by molecular analyses and drug-metabolism assays. These NAT genes were intronless and formed gene clusters with one other NAT gene in the genome, just as human NAT genes do. Marmoset NAT1 and pig NAT1 amino acid sequences showed high sequence identities (94% and 85%, respectively) to human NAT1. Phylogenetic analysis indicated that marmoset NAT1 and pig NAT1 were more closely clustered with human NATs than with rat or mouse NATs. Marmoset NAT1 and pig NAT1 mRNAs were expressed in all the tissue types analyzed, with the expression levels being highest in the small intestine. Metabolic assays using recombinant proteins found that marmoset NAT1 and pig NAT1 metabolized human NAT substrates p-aminobenzoic acid, 2-aminofluorene, sulfamethazine, and isoniazid. Marmoset NAT1 and pig NAT1 substantially acetylated p-aminobenzoic acid and 2-aminofluorene relevant human NAT1, but their activities were lower toward sulfamethazine and isoniazid than those of the relevant human NAT2. Therefore, marmoset and pig NATs are functional enzymes with molecular similarities to human NAT1, but their substrate specificities, while similar to human NAT1, differ somewhat from human NAT2. SIGNIFICANCE STATEMENT: Marmoset N-acetyltransferase NAT1 and pig NAT1 were identified and showed high sequence identities to human NAT1. These NAT mRNAs were expressed in various tissues. Marmoset and pig NAT1s acetylated typical human NAT substrates, although their substrate specificities differed somewhat from human NAT2. Marmoset NAT1 and pig NAT1 have similarities with human NAT1 in terms of molecular and enzymatic characteristics.

Plasma lipidomics analysis reveals altered lipids signature in patients with osteonecrosis of the femoral head

INTRODUCTION

Although studies have established a link between lipid metabolism disorder and osteonecrosis of the femoral head (ONFH), the characteristics of the circulating lipidome signature of ONFH have not yet been investigated and need to be explored.

OBJECTIVES

We aimed to explore the plasma lipidome signatures in patients with ONFH, and to identify specific lipid biomarkers of ONFH.

METHODS

In this study, a comprehensive detection and analysis of plasma lipidomics was conducted in clinical human cohort, including 32 healthy normal control (NC) subjects and 91 ONFH patients in different subgroups [alcohol-induced ONFH (AONFH), steroid-induced ONFH (SONFH), and traumatic-induced ONFH (TONFH)] or at different disease stages (stage I, II, III and IV of ONFH) using ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS).

RESULTS

Overall, the plasma lipidome profile differs between ONFH and NC samples. Lipidome signature including 22 common differentially expressed lipids (DELs) in all three subgroups (variable importance in projection > 1, P < 0.05, fold change > 1.5 or < 0.67, compared to the NC group) was identified. Besides, the subtype-specific lipidome profiles for each ONFH subgroup were also analyzed. Generally, the AONFH subgroup has the largest number of DELs, and the plasma levels of triacylglycerol lipid compounds increased obviously in the AONFH samples. In the subgroup of SONFH, the relative abundance of lipid 4-Aminobenzoic acid increased significantly with changes in the expression of several of its interactive genes. We have identified that 9 stage-positive and 2 stage-negative lipids may function as novel biomarkers predicting the progression of ONFH.

CONCLUSION

Our study presents an overview of the phenotype-related plasma lipidome signature of patients with ONFH. The results will provide insight into the mechanisms underlying the metabolism of lipids in the pathogenesis and progression of ONFH and help identify novel lipids biomarkers or disease diagnosis and treatment targets.

De Novo Biosynthesis and Whole-Cell Catalytic Production of 2-Acetamidophenol in Escherichia coli

2-Acetamidophenol (AAP) is an aromatic product with promising activities in agricultural applications and medical research. At present, AAP is synthesized by chemical methods from nonrenewable fossil fuel resources, which cause environmental pollution and the reaction conditions are harsh. In this study, we constructed the artificial biosynthetic pathway of AAP with five different expressed proteins in Escherichia coli for the first time. By introducing the hydrogen peroxide degrading enzyme catalase and improving cell tolerance to toxic intermediates or products, the yield of AAP reached 33.54 mg/L using shaking-flask culture. The best-engineered strain could produce 568.57 mg/L AAP by fed-batch fermentation from glucose and precursor (2-aminophenol, 2-AP) addition. Furthermore, a one-pot whole-cell cascade biocatalytic pathway to AAP and analogues was developed and optimized. This method can efficiently produce 1.8 g/L AAP using the methyl anthranilate hydrolysis product as the substrate. This study provides not only the de novo artificial biosynthetic pathway of AAP in E. coli but also a promising sustainable and efficient strategy to enable the synthesis of AAP on a gram scale.

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

Many drug oxidations and conjugations are mediated by a variety of cytochromes P450 (P450) and non-P450 enzymes in humans and non-human primates. These non-P450 enzymes include aldehyde oxidases (AOX), carboxylesterases (CES), flavin-containing monooxygenases (FMO), glutathione S-transferases (GST), arylamine N-acetyltransferases (NAT),sulfotransferases (SULT), and uridine 5'-diphospho-glucuronosyltransferases (UGT) and their substrates include both endobiotics and xenobiotics. Cynomolgus macaques (Macaca fascicularis, an Old-World monkey) are widely used in preclinical studies because of their genetic and physiological similarities to humans. However, many reports have indicated the usefulness of common marmosets (Callithrix jacchus, a New World monkey) as an alternative non-human primate model. Although knowledge of the drug-metabolizing properties of non-P450 enzymes in non-human primates is relatively limited, new research has started to provide an insight into the molecular characteristics of these enzymes in cynomolgus macaques and common marmosets. This mini-review provides collective information on the isoforms of non-P450 enzymes AOX, CES, FMO, GST, NAT, SULT, and UGT and their enzymatic profiles in cynomolgus macaques and common marmosets. In general, these non-P450 cynomolgus macaque and marmoset enzymes have high sequence identities and similar substrate recognitions to their human counterparts. However, these enzymes also exhibit some limited differences in function between species, just as P450 enzymes do, possibly due to small structural differences in amino acid residues. The findings summarized here provide a foundation for understanding the molecular mechanisms of polymorphic non-P450 enzymes and should contribute to the successful application of non-human primates as model animals for humans.

Functional variability of rhesus macaque (Macaca mulatta) NAT2 gene for drug-metabolising arylamine N-acetyltransferase 2

Human NAT2 is a polymorphic pharmacogene encoding for N-acetyltransferase 2, a hepatic enzyme active towards arylamine and arylhydrazine drugs, including the anti-tubercular antibiotic isoniazid. The isoenzyme also modulates susceptibility to chemical carcinogenesis, particularly of the bladder. Human NAT2 represents an ideal model for anthropological investigations into the demographic adaptation of worldwide populations to their xenobiotic environment. Its sequence appears to be subject to positive selection pressures that are population-specific and may be attributed to gene-environment interactions directly associated with exogenous chemical challenges. However, recent evidence suggests that the same evolutionary pattern may not be observed in other primates. Here, we report NAT2 polymorphism in 25 rhesus macaques (Macaca mulatta) and compare the frequencies and functional characteristics of 12 variants. Seven non-synonymous single nucleotide variations (SNVs) were identified, including one nonsense mutation. The missense SNVs were demonstrated to affect enzymatic function in a substrate-dependent manner, albeit more moderately than certain NAT1 SNVs recently characterised in the same cohort. Haplotypic and functional variability of NAT2 was comparable to that previously observed for NAT1 in the same population sample, suggesting that the two paralogues may have evolved under similar selective pressures in the rhesus macaque. This is different to the population variability distribution pattern reported for humans and chimpanzees. Recorded SNVs were also different from those found in other primates. The study contributes to further understanding of NAT2 functional polymorphism in the rhesus macaque, a non-human primate model used in biomedicine and pharmacology, indicating variability in xenobiotic acetylation that could affect drug metabolism.

Genetic variants of aldehyde oxidase (AOX) 1 in cynomolgus and rhesus macaques

The cynomolgus macaque is a non-human primate species widely used in drug metabolism studies. Despite the importance of genetic polymorphisms in cytosolic aldehyde oxidase (AOX) 1 in humans, genetic variants have not been investigated in cynomolgus or rhesus macaques.Genetic variants in AOX1 were identified and allele frequencies were assessed using the genomes of 24 cynomolgus and 8 rhesus macaques. The analysis identified 38 non-synonymous variants, some of which were unique to cynomolgus macaques (bred in Cambodia, Indochina, or Indonesia) or rhesus macaques, whereas many variants were shared by the two lineages.Among the variants observed at relatively high frequencies, eight were selected for functional analysis. Recombinant P605L and V1338I AOX1 variants showed substantially lower phthalazine and carbazeran oxidation activities than the wild-type AOX1 protein.In liver cytosolic fractions from cynomolgus and rhesus macaques genotyped for P605L and V1338I AOX1, groups of cytosolic fractions with P605L and/or V1338I AOX1 variants showed significantly lower phthalazine and carbazeran oxidation activities than the wild type.These results indicate that AOX1 is polymorphic in cynomolgus and rhesus macaques, just as it is in humans. Further investigation is needed to reveal the functional significance of these AOX1 variants in drug metabolism.

Utility of Common Marmoset (Callithrix jacchus) Embryonic Stem Cells in Liver Disease Modeling, Tissue Engineering and Drug Metabolism

The incidence of liver disease is increasing significantly worldwide and, as a result, there is a pressing need to develop new technologies and applications for end-stage liver diseases. For many of them, orthotopic liver transplantation is the only viable therapeutic option. Stem cells that are capable of differentiating into all liver cell types and could closely mimic human liver disease are extremely valuable for disease modeling, tissue regeneration and repair, and for drug metabolism studies to develop novel therapeutic treatments. Despite the extensive research efforts, positive results from rodent models have not translated meaningfully into realistic preclinical models and therapies. The common marmoset Callithrix jacchus has emerged as a viable non-human primate model to study various human diseases because of its distinct features and close physiologic, genetic and metabolic similarities to humans. C. jacchus embryonic stem cells (cjESC) and recently generated cjESC-derived hepatocyte-like cells (cjESC-HLCs) could fill the gaps in disease modeling, liver regeneration and metabolic studies. They are extremely useful for cell therapy to regenerate and repair damaged liver tissues in vivo as they could efficiently engraft into the liver parenchyma. For in vitro studies, they would be advantageous for drug design and metabolism in developing novel drugs and cell-based therapies. Specifically, they express both phase I and II metabolic enzymes that share similar substrate specificities, inhibition and induction characteristics, and drug metabolism as their human counterparts. In addition, cjESCs and cjESC-HLCs are advantageous for investigations on emerging research areas, including blastocyst complementation to generate entire livers, and bioengineering of discarded livers to regenerate whole livers for transplantation.

Genetic variants of N-acetyltransferases 1 and 2 (NAT1 and NAT2) in cynomolgus and rhesus macaques

In humans, polymorphic N-acetyltransferases NAT1 and NAT2 are important enzymes that metabolize endogenous and exogenous compounds, including drugs. These enzymes exhibit considerable inter-individual variability in humans. The cynomolgus macaque is a nonhuman primate species that is widely used in drug metabolism studies. NAT1/2 in these macaques have molecular and enzymatic similarities to their human orthologs; however, genetic polymorphisms in NAT1/2 have not been fully investigated in this species. In this study, the resequencing of NAT1 and NAT2 in 114 cynomolgus macaques and 19 rhesus macaques found 15 non-synonymous variants for NAT1 and 11 non-synonymous variants and 1 insertion/deletion variant for NAT2. Nine (60%) and five (33%) NAT1 variants and seven (67%) and three (25%) NAT2 variants were unique to cynomolgus and rhesus macaques, respectively. Functional characterization of the mutant enzymes was carried out using cynomolgus NAT1 and NAT2 proteins heterologously expressed in Escherichia coli. Compared with wild-type NAT1, the D122N NAT1 variant showed substantially lower acetylation activities toward p-aminobenzoic acid but had higher acetylation activities toward isoniazid. Moreover, liver cytosolic fractions from cynomolgus macaques homozygous for T98A NAT2 showed significantly lower acetylation activities toward isoniazid than wild-type NAT2; similar results were obtained for recombinant T98A NAT2. Interestingly, all the rhesus macaques analyzed were homozygous for T98A. These findings indicate that polymorphic NAT1/2 variants in cynomolgus and rhesus macaques, especially the T98A NAT2 variant, could account for the inter-animal and/or inter-lineage variabilities of NAT-dependent drug metabolism in macaques.

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.

Population variability of rhesus macaque (Macaca mulatta) NAT1 gene for arylamine N-acetyltransferase 1: Functional effects and comparison with human

Human NAT1 gene for N-acetyltransferase 1 modulates xenobiotic metabolism of arylamine drugs and mutagens. Beyond pharmacogenetics, NAT1 is also relevant to breast cancer. The population history of human NAT1 suggests evolution through purifying selection, but it is unclear whether this pattern is evident in other primate lineages where population studies are scarce. We report NAT1 polymorphism in 25 rhesus macaques (Macaca mulatta) and describe the haplotypic and functional characteristics of 12 variants. Seven non-synonymous single nucleotide variations (SNVs) were identified and experimentally demonstrated to compromise enzyme function, mainly through destabilization of NAT1 protein and consequent activity loss. One non-synonymous SNV (c.560G > A, p.Arg187Gln) has also been characterized for human NAT1 with similar effects. Population haplotypic and functional variability of rhesus NAT1 was considerably higher than previously reported for its human orthologue, suggesting different environmental pressures in the two lineages. Known functional elements downstream of human NAT1 were also differentiated in rhesus macaque and other primates. Xenobiotic metabolizing enzymes play roles beyond mere protection from exogenous chemicals. Therefore, any link to disease, particularly carcinogenesis, may be via modulation of xenobiotic mutagenicity or more subtle interference with cell physiology. Comparative analyses add the evolutionary dimension to such investigations, assessing functional conservation/diversification among primates.

Overview of the Components of Cardiac Metabolism

Metabolism in organs other than the liver and kidneys may play a significant role in how a specific organ responds to chemicals. The heart has metabolic capability for energy production and homeostasis. This homeostatic machinery can also process xenobiotics. Cardiac metabolism includes the expression of numerous organic anion transporters, organic cation transporters, organic carnitine (zwitterion) transporters, and ATP-binding cassette transporters. Expression and distribution of the transporters within the heart may vary, depending on the patient's age, disease, endocrine status, and various other factors. Several cytochrome P450 (P450) enzyme classes have been identified within the heart. The P450 hydroxylases and epoxygenases within the heart produce hydroxyeicosatetraneoic acids and epoxyeicosatrienoic acids, metabolites of arachidonic acid, which are critical in regulating homeostatic processes of the heart. The susceptibility of the cardiac P450 system to induction and inhibition from exogenous materials is an area of expanding knowledge, as are the metabolic processes of glucuronidation and sulfation in the heart. The susceptibility of various transcription factors and signaling pathways of the heart to disruption by xenobiotics is not fully characterized but is an area with implications for disruption of normal postnatal development, as well as modulation of adult cardiac health. There are knowledge gaps in the timelines of physiologic maturation and deterioration of cardiac metabolism. Cross-species characterization of cardiac-specific metabolism is needed for nonclinical work of optimum translational value to predict possible adverse effects, identify sensitive developmental windows for the design and conduct of informative nonclinical and clinical studies, and explore the possibilities of organ-specific therapeutics.