Arylamine N-acetyltransferases: From Structure to Function

Differential expression of NAT1 pharmacogene in hormone receptor positive vs. negative female breast tumors may affect drug treatment

Studies have reported overexpression of NAT1 gene for xenobiotic metabolizing arylamine N -acetyltransferase type 1 in estrogen receptor positive breast tumors, and this association has been linked to patient chemoresistance and response to tamoxifen. We probed the expression of NAT1 , using quantitative reverse transcription PCR to screen clinically characterized breast cancer tissue cDNA arrays. Primers detecting all NAT1 alternative transcripts were used, and the protocol and results are reported according to consensus guidelines. The clinical information about 166 tumor samples screened is provided, including tumor stage, estrogen and progesterone receptor status and HER2 expression. NAT1 was found to be significantly ( P  < 0.001) upregulated in hormone receptor positive vs. negative tumors. No correlation was apparent between NAT1 and tumor stage or HER2 expression. Our findings demonstrate a strong correlation between the expression of NAT1 and steroid hormone receptors in breast tumors, supporting its possible utility as a pharmacogenetic biomarker or drug target. Of the two polymorphic NAT genes, NAT1 is the one primarily expressed in breast tissue, and is subjected to regulation by two differential promoters and more than one polyadenylation signal. Hormonal factors may enhance NAT1 gene expression at the transcriptional or epigenetic level, and tamoxifen has additionally been shown to inhibit NAT1 enzymatic activity. The outcome of tamoxifen treatment is also more favorable in patients with NAT1 overexpressing tumors. The study adds to the growing body of evidence implicating NAT1 in breast cancer and its pharmacological treatment.

Function and expression of N-acetyltransferases 1 and 2 are altered in lymphocytes in type 2 diabetes and obesity

The cytosolic enzymes N-Acetyl Transferases 1 and 2 (NATs) transfer an acetyl group from acetyl-CoA to a xenobiotic substrate. NATs are regulated at the genetic and epigenetic levels by deacetylase enzymes such as sirtuins. The enzymatic expression of NAT1, NAT2, and SIRT1 was evaluated by flow cytometry, as well as the enzymatic activity of NATs by cell culture and HPLC analysis. Six SNPs were determined through genotyping. T2D patients (n = 29) and healthy subjects (n = 25) with a median age of 57 and 50, respectively, were recruited. An increased enzyme expression and a diminished NAT2 enzymatic activity were found in cells of T2D patients compared to the control group, while NAT1 was negatively correlated with body fat percentage and BMI. In contrast, Sirtuin inhibition increased NAT2 activity, while Sirtuin agonism decreased its activity in both groups. The analysis of NAT2 SNPs showed a higher frequency of rapid acetylation haplotypes in T2D patients compared to the control group, possibly associated as a risk factor for diabetes. The enzymatic expression of CD3+NAT2+ cells was higher in the rapid acetylators group compared to the slow acetylators group. The levels and activity of NAT1 were associated with total cholesterol and triglycerides. Meanwhile, CD3+NAT2+ cells and NAT2 activity levels were associated with HbA1c and glucose levels. The results indicate that NAT2 could be involved in metabolic processes related to the development of T2D, due to its association with glucose levels, HbA1c, and the altered SIRT-NAT axis. NAT1 may be involved with dyslipidaemias in people who are overweight or obese.

The landscape of very important pharmacogenes variants and potential clinical relevance in the Chinese Jingpo population: a comparative study with worldwide populations

BACKGROUND

Pharmacogenomics is a facet of personalized medicine that explores how genetic variants affect drug metabolism and adverse drug reactions. Therefore, this study aims to detect distinct pharmacogenomic variations among the Jingpo population and explore their clinical correlation with drug metabolism and toxicity.

METHODS

Agena MassARRAY Assay was used to genotype 57 VIP variants in 28 genes from 159 unrelated Jingpo participants. Subsequently, the chi-squared test and Bonferroni's statistical tests were utilized to conduct a comparative analysis of genotypes and allele frequencies between the Jingpo population and the other 26 populations from the 1000 Genome Project.

RESULTS

We discovered that the KHV (Kinh in Ho ChiMinh City, Vietnam), CHS (Southern Han Chi-nese, China) and JPT (Japanese in Tokyo, Japan) exhibited the smallest differences from the Jingpo with only 4 variants, while ESN (Esan in Nigeria) exhibited the largest differences with 30 variants. Besides, a total of six considerably different loci (rs4291 in ACE, rs20417 in PTGS2, rs1801280 and rs1799929 in NAT2, rs2115819 in ALOX5, rs1065852 in CYP2D6, p < 3.37 × 10-5) were identified in this study. According to PharmGKB, rs20417 (PTGS2), rs4291 (ACE), rs2115819 (ALOX5) and rs1065852 (CYP2D6) were found to be associated with the metabolism efficiency of non-steroidal anti-inflammatory drugs (NSAIDs), aspirin, montelukast and tamoxifen, respectively. Meanwhile, rs1801280 and rs1799929 (NAT2) were found to be related to drug poisoning with slow acetylation.

CONCLUSION

Our study unveils distinct pharmacogenomic variants in the Jingpo population and discovers their association with the metabolic efficiency of NSAIDs, montelukast, and tamoxifen.

The Arylamine N-Acetyltransferases as Therapeutic Targets in Metabolic Diseases Associated with Mitochondrial Dysfunction

In humans, there are two arylamine N-acetyltransferase genes that encode functional enzymes (NAT1 and NAT2) as well as one pseudogene, all of which are located together on chromosome 8. Although they were first identified by their role in the acetylation of drugs and other xenobiotics, recent studies have shown strong associations for both enzymes in a variety of diseases, including cancer, cardiovascular disease, and diabetes. There is growing evidence that this association may be causal. Consistently, NAT1 and NAT2 are shown to be required for healthy mitochondria. This review discusses the current literature on the role of both NAT1 and NAT2 in mitochondrial bioenergetics. It will attempt to relate our understanding of the evolution of the two genes with biologic function and then present evidence that several major metabolic diseases are influenced by NAT1 and NAT2. Finally, it will discuss current and future approaches to inhibit or enhance NAT1 and NAT2 activity/expression using small-molecule drugs. SIGNIFICANCE STATEMENT: The arylamine N-acetyltransferases (NATs) NAT1 and NAT2 share common features in their associations with mitochondrial bioenergetics. This review discusses mitochondrial function as it relates to health and disease, and the importance of NAT in mitochondrial function and dysfunction. It also compares NAT1 and NAT2 to highlight their functional similarities and differences. Both NAT1 and NAT2 are potential drug targets for diseases where mitochondrial dysfunction is a hallmark of onset and progression.

Investigation of N-Acetyltransferase 2-Mediated Drug Interactions of Amifampridine: In Vitro and In Vivo Evidence of Drug Interactions with Acetaminophen

Amifampridine is a drug used for the treatment of Lambert-Eaton myasthenic syndrome (LEMS) and was approved by the Food and Drug Administration (FDA) of the United States (US) in 2018. It is mainly metabolized by N-acetyltransferase 2 (NAT2); however, investigations of NAT2-mediated drug interactions with amifampridine have rarely been reported. In this study, we investigated the effects of acetaminophen, a NAT2 inhibitor, on the pharmacokinetics of amifampridine using in vitro and in vivo systems. Acetaminophen strongly inhibits the formation of 3-N-acetylamifmapridine from amifampridine in the rat liver S9 fraction in a mixed inhibitory manner. When rats were pretreated with acetaminophen (100 mg/kg), the systemic exposure to amifampridine significantly increased and the ratio of the area under the plasma concentration-time curve for 3-N-acetylamifampridine to amifampridine (AUC_m/AUC_p) decreased, likely due to the inhibition of NAT2 by acetaminophen. The urinary excretion and the amount of amifampridine distributed to the tissues also increased after acetaminophen administration, whereas the renal clearance and tissue partition coefficient (K_p) values in most tissues remained unchanged. Collectively, co-administration of acetaminophen with amifampridine may lead to relevant drug interactions; thus, care should be taken during co-administration.

Rats with Long-Term Cholestasis Have a Decreased Cytosolic but Maintained Mitochondrial Hepatic CoA Pool

Previous studies showed that rats with long-term bile duct ligation have reduced coenzyme A stores per g of liver but maintained mitochondrial CoA stores. Based on these observations, we determined the CoA pool in the liver homogenate, liver mitochondria, and liver cytosol of rats with bile duct ligation for 4 weeks (BDL rats, n = 9) and sham-operated control rats (CON rats, n = 5). In addition, we tested the cytosolic and mitochondrial CoA pools by assessing the metabolism of sulfamethoxazole and benzoate in vivo and of palmitate in vitro. The hepatic total CoA content was lower in BDL than CON rats (mean ± SEM; 128 ± 5 vs. 210 ± 9 nmol/g), affecting all subfractions equally (free CoA (CoASH), short- and long-chain acyl-CoA). In BDL rats, the hepatic mitochondrial CoA pool was maintained, and the cytosolic pool was reduced (23.0 ± 0.9 vs. 84.6 ± 3.7 nmol/g liver; CoA subfractions were affected equally). The urinary excretion of hippurate after i.p. benzoate administration (measuring mitochondrial benzoate activation) was reduced in BDL rats (23.0 ± 0.9 vs. 48.6 ± 3.7% of dose/24 h), whereas the urinary elimination of N-acetylsulfamethoxazole after i.p. sulfamethoxazole administration (measuring the cytosolic acetyl-CoA pool) was maintained (36.6 ± 3.0 vs. 35.1 ± 2.5% of dose/24 h BDL vs. CON rats). Palmitate activation was impaired in the liver homogenate of BDL rats but the cytosolic CoASH concentration was not limiting. In conclusion, BDL rats have reduced hepatocellular cytosolic CoA stores, but this reduction does not limit sulfamethoxazole N-acetylation or palmitate activation. The hepatocellular mitochondrial CoA pool is maintained in BDL rats. Impaired hippurate formation in BDL rats is explained best by mitochondrial dysfunction.

Integrative omics-analysis of lipid metabolism regulation by peroxisome proliferator-activated receptor a and b agonists in male Atlantic cod

Lipid metabolism is essential in maintaining energy homeostasis in multicellular organisms. In vertebrates, the peroxisome proliferator-activated receptors (PPARs, NR1C) regulate the expression of many genes involved in these processes. Atlantic cod (Gadus morhua) is an important fish species in the North Atlantic ecosystem and in human nutrition, with a highly fatty liver. Here we study the involvement of Atlantic cod Ppar a and b subtypes in systemic regulation of lipid metabolism using two model agonists after in vivo exposure. WY-14,643, a specific PPARA ligand in mammals, activated cod Ppara1 and Ppara2 in vitro. In vivo, WY-14,643 caused a shift in lipid transport both at transcriptional and translational level in cod. However, WY-14,643 induced fewer genes in the fatty acid beta-oxidation pathway compared to that observed in rodents. Although GW501516 serves as a specific PPARB/D ligand in mammals, this compound activated cod Ppara1 and Ppara2 as well as Pparb in vitro. In vivo, it further induced transcription of Ppar target genes and caused changes in lipid composition of liver and plasma. The integrative approach provide a foundation for understanding how Ppars are engaged in regulating lipid metabolism in Atlantic cod physiology. We have shown that WY-14,643 and GW501516 activate Atlantic cod Ppara and Pparb, affect genes in lipid metabolism pathways, and induce changes in the lipid composition in plasma and liver microsomal membranes. Particularly, the combined transcriptomic, proteomics and lipidomics analyses revealed that effects of WY-14,643 on lipid metabolism are similar to what is known in mammalian studies, suggesting conservation of Ppara functions in mediating lipid metabolic processes in fish. The alterations in the lipid profiles observed after Ppar agonist exposure suggest that other chemicals with similar Ppar receptor affinities may cause disturbances in the lipid regulation of fish. Model organism: Atlantic cod (Gadus morhua). LSID: urn:lsid:zoobank.org:act:389BE401-2718-4CF2-BBAE-2E13A97A5E7B. COL Identifier: 6K72F.

The rs1801280 SNP is associated with non-small cell lung carcinoma by exhibiting a highly deleterious effect on N-acetyltransferase 2

PURPOSE

N-acetyltransferase 2 is an enzyme that is involved in the detoxification of carcinogens in the human body, so any damage to this protein may lead to the emergence of several metabolic dysfunctions. This work was conducted to determine the association between NAT2 polymorphism and non-small cell lung carcinoma (NSCLC) that is increasingly reported in the Iraqi population.

METHODS

PCR sequencing was conducted to assess the possible association between genetic variants and NSCLC. Several in silico tools were implemented to investigate the effect of the observed SNPs on the structure, function, and stability of the altered NAT2.

RESULTS

Five SNPS of NAT2 (rs1208, rs1041983, rs1799929, rs1799930, and rs1801280) were identified in high frequencies in the amplified fragment. These SNPs showed variable distributions of haplotypes between cases and controls. No significant association of rs1208, rs1041983, rs1799929, and rs1799930 with NSCLC was shown in the investigated population. In contrast, rs1801280: CC genotype showed a highly significant (P = 0.009) association with the NSCLC, and individuals with this genotype had 2.19 more chances for developing NSCLC (OR 2.19; Cl_95% 1.21-3.94). Association analysis of rs1801280 SNP distribution among the investigated patients showed that patients with CC genotype showed a significant (P = 0.02, OR 2.65) association with family history, which entailed a high hereditary possibility of this genotype among Iraqi patients. It was predicted that this SNP showed high damaging effects on the activity of NAT2 enzyme, with various deleterious outcomes on enzyme structure, function, and stability.

CONCLUSION

Data indicated that rs1801280 SNP exerted a tight association with NSCLC since individuals with CC genotype exhibited the most damaging effects on the NAT2 that may be behind the low acetylation rates of this enzyme in patients with NSCLC.

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.

Recent advancements in enzyme engineering via site-specific incorporation of unnatural amino acids

With increased attention to excellent biocatalysts, evolving methods based on nature or unnatural amino acid (UAAs) mutagenesis have become an important part of enzyme engineering. The emergence of powerful method through expanding the genetic code allows to incorporate UAAs with unique chemical functionalities into proteins, endowing proteins with more structural and functional features. To date, over 200 diverse UAAs have been incorporated site-specifically into proteins via this methodology and many of them have been widely exploited in the field of enzyme engineering, making this genetic code expansion approach possible to be a promising tool for modulating the properties of enzymes. In this context, we focus on how this robust method to specifically incorporate UAAs into proteins and summarize their applications in enzyme engineering for tuning and expanding the functional properties of enzymes. Meanwhile, we aim to discuss how the benefits can be achieved by using the genetically encoded UAAs. We hope that this method will become an integral part of the field of enzyme engineering in the future.

[N-aсetyltransferase (NAT2) gene polymorphism and gene network analysis]

To search for new targets of therapy, it is necessary to reconstruct the gene network of the disease, and identify the interaction of genes, proteins, and drug compounds. Using the online bioinformatics tools we have analyzed the current data set related to the metabolism of xenobiotics, mediated by the N-acetyltransferase 2 (NAT2) gene. The study of allelic polymorphism of the NAT2 gene has a prognostic value, allowing to determine the risk of a number of oncological diseases, the degree of increased risk due to smoking and exposure to chemical carcinogens, including drugs. The aim of this study was to determine the frequencies of two important "slow" variants of the NAT2 gene (NAT2*5, rs1801280 and NAT2*7, rs1799931), which significantly affected the rate of xenobiotic acetylation among the indigenous Nenets population of Northern Siberia. The obtained frequencies of polymorphic variants among the Nenets occupy an intermediate value between those for Europeans and Asians, which might indicate specific features of adaptation. We present a model of the distribution of two polymorphic variants of the NAT2 gene involved in the biotransformation of xenobiotics to study the characteristics of their metabolism in the indigenous inhabitants of Yamal.

Biochemical Characterization of Arylamine N-acetyltransferases From Vibrio vulnificus

Vibrio vulnificus is a zoonotic bacterium that is capable of causing highly lethal diseases in humans; this pathogen is responsible for 95% of all seafood-related deaths in the United States. Arylamine N-acetyltransferases (NAT, E.C. 2.3.1.5) is a major family of xenobiotic-metabolizing enzymes that can biotransform aromatic amine chemicals. In this research, to evaluate the effect of NAT on acetyl group transformation in arylamine antibiotics, we first used sequence alignment to study the structure of V. vulnificus NAT [(VIBVN)NAT]. The nat gene encodes a protein of 260 amino acids, which has an approximate molecular mass of 30 kDa. Then we purified recombinant (VIBVN)NAT and determined the enzyme activity by PNPA and DTNB methods. The DTNB method indicates that this prokaryotic NAT has a particular substrate specificity towards aromatic substrates. However, (VIBVN)NAT lost most of its activity after treatment with high concentrations of urea and H₂O₂. In addition, we also explored the stability of the enzyme at different temperatures and pH values. In analyzing the influence of metal ions, the enzyme activity was significantly inhibited by Zn²⁺ and Cu²⁺. The kinetic parameters K_m and V_max were determined using hydralazine, isoniazid, 4-amino salicylic acid, and 4-chloro-3-methylaniline as substrates, and the T_m, T_agg and size distribution of (VIBVN)NAT were observed. In particular, a molecular docking study on the structure of (VIBVN)NAT was conducted to understand its biochemical traits. These results showed that (VIBVN)NAT could acetylate various aromatic amine substrates and contribute to arylamine antibiotic resistance in V. vulnificus.

PtmC Catalyzes the Final Step of Thioplatensimycin, Thioplatencin, and Thioplatensilin Biosynthesis and Expands the Scope of Arylamine N-Acetyltransferases

The members of the arylamine N-acetyltransferase (NAT) family of enzymes are important for their many roles in xenobiotic detoxification in bacteria and humans. However, very little is known about their roles outside of detoxification or their specificities for acyl donors larger than acetyl-CoA. Herein, we report the detailed study of PtmC, an unusual NAT homologue encoded in the biosynthetic gene cluster for thioplatensimycin, thioplatencin, and a newly reported scaffold, thioplatensilin, thioacid-containing diterpenoids and highly potent inhibitors of bacterial and mammalian fatty acid synthases. As the final enzyme of the pathway, PtmC is responsible for the selection of a thioacid arylamine over its cognate carboxylic acid and coupling to at least three large, 17-carbon ketolide-CoA substrates. Therefore, this study uses a combined approach of enzymology and molecular modeling to reveal how PtmC has evolved from the canonical NAT scaffold into a key part of a natural combinatorial biosynthetic pathway. Additionally, genome mining has revealed the presence of other related NATs located within natural product biosynthetic gene clusters. Thus, findings from this study are expected to expand our knowledge of how enzymes evolve for expanded substrate diversity and enable additional predictions about the activities of NATs involved in natural product biosynthesis and xenobiotic detoxification.

Case Study 10: A Case to Investigate Acetyl Transferase Kinetics

Major routes of metabolism for marketed drugs are predominately driven by enzyme families such as cytochromes P450 and UDP-glucuronosyltransferases. Less studied conjugative enzymes, like N-acetyltransferases (NATs), are commonly associated with detoxification pathways. However, in the clinic, the high occurrence of NAT polymorphism that leads to slow and fast acetylator phenotypes in patient populations has been linked to toxicity for a multitude of drugs. A key example of this is the observed clinical toxicity in patients who exhibit the slow acetylator phenotype and were treated with isoniazid. Toxicity in patients has led to detailed characterization of the two NAT isoforms and their polymorphic genotypes. Investigation in recombinant enzymes, genotyped hepatocytes, and in vivo transgenic models coupled with acetylator status-driven clinical studies have helped understand the role of NATs in drug development, clinical study design and outcomes, and potential roles in human disease models. The selected case studies herein document NAT enzyme kinetics to explore substrate overlap from two human isoforms, preclinical species considerations, and clinical genotype population concerns.

Moonlighting in drug metabolism

Drug metabolizing enzymes catalyze the biotransformation of many of drugs and chemicals. The drug metabolizing enzymes are distributed among several evolutionary families and catalyze a range of detoxication reactions, including oxidation/reduction, conjugative, and hydrolytic reactions that serve to detoxify potentially toxic compounds. This detoxication function requires that drug metabolizing enzymes exhibit substrate promiscuity. In addition to their catalytic functions, many drug metabolizing enzymes possess functions unrelated to or in addition to catalysis. Such proteins are termed 'moonlighting proteins' and are defined as proteins with multiple biochemical or biophysical functions that reside in a single protein. This review discusses the diverse moonlighting functions of drug metabolizing enzymes and the roles they play in physiological functions relating to reproduction, vision, cell signaling, cancer, and transport. Further research will likely reveal new examples of moonlighting functions of drug metabolizing enzymes.

Parameterization of Microsomal and Cytosolic Scaling Factors: Methodological and Biological Considerations for Scalar Derivation and Validation

Mathematical models that can predict the kinetics of compounds have been increasingly adopted for drug development and risk assessment. Data for these models may be generated from in vitro experimental systems containing enzymes contributing to metabolic clearance, such as subcellular tissue fractions including microsomes and cytosol. Extrapolation from these systems is facilitated by common scaling factors, known as microsomal protein per gram (MPPG) and cytosolic protein per gram (CPPG). Historically, parameterization of MPPG and CPPG has employed the use of recovery factors, commonly benchmarked to cytochromes P450 which work well in some contexts, but could be problematic for other enzymes. Here, we propose absolute quantification of protein content and supplementary assays to evaluate microsomal/cytosolic purity that should be employed. Examples include calculation of microsomal latency by mannose-6-phosphatase activity and immunoblotting of subcellular fractions with fraction-specific markers. Further considerations include tissue source, as disease states can affect enzyme expression and activity, and the methodology used for scalar parameterization. Regional- and organ-specific expression of enzymes, in addition to differences in organ physiology, is another important consideration. Because most efforts have focused on the liver that is, for the most part, homogeneous, derived scalars may not capture the heterogeneity of other major tissues contributing to xenobiotic metabolism including the kidneys and small intestine. Better understanding of these scalars, and how to appropriately derive them from extrahepatic tissues can provide support to the inferences made with physiologically based pharmacokinetic modeling, increase its accuracy in characterizing in vivo drug pharmacokinetics, and improve confidence in go-no-go decisions for clinical trials.

Studying polymorphic variants of the NAT2 gene (NAT2*5 and NAT2*7) in Nenets populations of Northern Siberia

Background

N-acetyltransferase 2 plays a crucial role in the metabolism of a wide range of xenobiotics, including many drugs, carcinogens, and other chemicals in the human environment. The article presents for the first time data on the frequency of two important “slow” variants of NAT2 gene (NAT2*5, rs1801280 and NAT2*7, rs1799931), which significantly affect the rate of xenobiotics acetylation, among representatives of indigenous populations of Forest and Tundra Nenets in Northern Siberia. The aim of this study was to identify the frequencies of these variants and compare them with frequencies in other ethnic populations.

Results

NAT2*5 (T341C) genotyping revealed frequencies of 28,0% and 38,6% for Tundra and Forest Nenets, respectively. The frequencies of NAT2*7 (G857A) variant were 9,8% and 8,2% for Tundra and Forest Nenets, respectively. Polymorphic variants frequencies for Nenets are intermediate between those in populations of Europeans and Asians. These results can probably be explained by the presence of both European and Asian components in Nenets gene pools.

Conclusions

The results of this study expand the knowledge of NAT2 polymorphism in world populations. These data may also help assess the genetic predisposition of Nenets to multifactorial diseases associated with polymorphism in the NAT2 gene and, in general, contribute to the development of personalized medicine in reference to native people of Siberia.

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.

NAT1 genetic variation increases asthma risk in children with secondhand smoke exposure

OBJECTIVE

We previously reported that children exposed to secondhand smoke (SHS) that carried variants in the NAT1 gene had over two-fold higher hair cotinine levels. Our objective was to determine if NAT1 polymorphisms confer increased risk for developing asthma in children exposed to SHS.

METHODS

White participants in the Cincinnati Childhood Allergy and Air Pollution Study (n = 359) were genotyped for 10 NAT1 variants. Smoke exposure was defined by hair cotinine and parental report. Asthma was objectively assessed by spirometry and methacholine challenge. Findings were replicated in the Genomic Control Cohort (n = 638).

RESULTS

Significant associations between 5 NAT1 variants and asthma were observed in the CCAAPS exposed group compared to none in the unexposed group. There was a significant interaction between NAT1 rs13253389 and rs4921581 with smoke exposure (p = 0.02, p = 0.01) and hair cotinine level (p = 0.048, p = 0.042). Children wildtype for rs4921581 had increasing asthma risk with increasing hair cotinine level, whereas those carrying the NAT1 minor allele had an increased risk of asthma regardless of cotinine level. In the GCC, 13 NAT1 variants were associated with asthma in the smoke-exposed group, compared to 0 in the unexposed group, demonstrating gene-level replication.

CONCLUSIONS

Variation in the NAT1 gene modifies asthma risk in children exposed to secondhand-smoke. To our knowledge, this is the first report of a gene-environment interaction between NAT1 variants, smoke exposure, cotinine levels, and pediatric asthma. NAT1 genotype may have clinical utility as a biomarker of increased asthma risk in children exposed to smoke.

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.

Circulating miRNA-1290 as a potential biomarker for response to chemoradiotherapy and prognosis of patients with advanced oral squamous cell carcinoma: A single-center retrospective study

MicroRNAs are a class of small, endogenous, noncoding 18- to 24-nucleotide-long RNAs that can regulate multiple processes related to cancer progression. However, their clinical value in patients with oral squamous cell carcinoma has not yet been fully explored. Therefore, the aim of this study was to investigate the clinical significance of circulating microRNAs in oral squamous cell carcinoma patients. The expression levels of circulating miR-1246 and miR-1290 in healthy volunteers and oral squamous cell carcinoma patients were examined by quantitative real-time polymerase chain reaction. The expression levels of both microRNAs in the radioresistant oral squamous cell carcinoma cell line (SAS-R) and the parent cell line (SAS) and in the conditioned medium obtained from these cell lines were also examined by quantitative real-time polymerase chain reaction. In addition, the correlations between circulating microRNA status and various clinicopathological features in 55 oral squamous cell carcinoma patients with locally advanced oral squamous cell carcinoma who underwent surgery following 5-fluorouracil-based chemoradiotherapy were examined. The expression level of miR-1290 was significantly lower in the plasma of oral squamous cell carcinoma patients than in that of healthy volunteers (p < 0.01). The expression levels of microRNAs in the conditioned medium and in the cells varied from cell to cell. In the clinicopathological analyses, the frequency of patients with low miR-1290 levels was significantly higher among cases with lower pathological differentiation and among those with a poor pathological response for preoperative chemoradiotherapy (p = 0.030 each). Furthermore, Cox regression analysis based on the 5-year overall survival and disease-free survival revealed that miR-1290 status was a significant prognostic factor for patients with oral squamous cell carcinoma (hazard ratio = 0.169, p = 0.008, and hazard ratio = 0.186, p = 0.008, respectively). Circulating miR-1290 status could be a valuable biomarker for predicting the clinical response to chemoradiotherapy as well as overall survival in patients with oral squamous cell carcinoma.

Phylogenetic origins for severe acetaminophen toxicity in snake species compared to other vertebrate taxa

While it has been known for a while that some snake species are extremely sensitive to acetaminophen, the underlying mechanism for this toxicity has not been reported. To investigate if essential detoxification enzymes are missing in snake species that are responsible for biotransformation of acetaminophen in other vertebrate species, livers were collected from a variety of snake species, together with samples from alligator, snapping turtle, cat, rat, and cattle. Subcellular fractions were analyzed for enzymatic activities of phenol-type sulfotransferase and UDP‑glucuronosyltransferase, total glutathione S‑transferase, and N‑acetyltransferase. The results showed that none of the snake species, together with the cat samples, had any phenol-type glucuronidation activity, and that this activity was much lower in alligator and turtle samples than in the mammalian species. Combined with the lack of N‑acetyltransferase activity in snakes and cats, this would explain the accumulation of the aminophenol metabolite, which induces methemoglobinemia and subsequent suffocation of snakes and cats after acetaminophen exposure. While previous investigations have concluded that in cats the gene for the phenol-type glucuronosyltransferase isoform has turned into a pseudogene because of several point mutations, evaluation of genomic information for snake species revealed that they have only 2 genes that may code for glucuronosyltransferase isoforms. Similarity of these genes with mammalian genes is <50%, and suggests that the expressed enzymes may act on other types of substrates than aromatic amines. This indicates that the extreme sensitivity for acetaminophen in snakes is based on a different phylogenetic origin than the sensitivity observed in cats.

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.

Allosteric regulation of arylamine N-acetyltransferase 1 by adenosine triphosphate

In the present study, a screen of adenosine analogs as potential modulators of arylamine-N-acetyltransferase 1 activity identified ATP as an inhibitor within its range of physiological concentrations. Kinetically, ATP was a non-competitive inhibitor with respect to the acetyl acceptor but a competitive inhibitor with respect to the acetyl donor (acetyl-coenzyme A). In silico modelling predicted that ATP bound within the active site cleft arranged with the triphosphate group in close proximity to arginine 127. Since lysine 100 has previously been implicated in the binding of acetyl-coenzyme A to the enzyme, this amino acid was mutated to either an arginine or a glutamine. Both substitutions significantly changed the affinity of ATP for the enzyme, as well as the nature of the interaction to one with a large Hill coefficient (>3). Under these conditions, ATP was a strong allosteric modulator of arylamine-N-acetyltransferase 1 activity. Western blot analysis identified lysine 100 as a site of post-translational modification by acetylation. The results suggest that acetylation of lysine 100 converts arylamine-N-acetyltransferase 1 into a switch modulated by ATP. This observation provides important understanding of the molecular regulation of NAT1 activity and may reveal possible insight into the endogenous role of the enzyme.

Human Enzymes for Organic Synthesis

Human enzymes have been widely studied in various disciplines. The number of reactions taking place in the human body is vast, and so is the number of potential catalysts for synthesis. Herein, we focus on the application of human enzymes that catalyze chemical reactions in course of the metabolism of drugs and xenobiotics. Some of these reactions have been explored on the preparative scale. The major field of application of human enzymes is currently drug development, where they are applied for the synthesis of drug metabolites.

Subcellular Protein Labeling by a Spatially Restricted Arylamine N-Acetyltransferase

Mapping proteins at a specific subcellular location is essential to gaining detailed insight on local protein dynamics. We have developed an enzymatic strategy to label proteins on a subcellular level using arylamine N-acetyltransferase (NAT). The NAT enzyme activates an arylhydroxamic acid functionality into a nitrenium ion that reacts fast, covalently, and under neutral conditions with nucleophilic residues of neighboring proteins. The electron density on the aromatic ring proved important for probe activation as strong labeling was only observed with an arylhydroxamic acid bearing an electron donating substituent. We further demonstrate that, using this electron rich arylhydroxamic acid, clear labeling was achieved on a subcellular level in living cells that were transfected with a genetically targeted NAT to the nucleus or the cytosol.

A pilot study of the modulation of sirtuins on arylamine N-acetyltransferase 1 and 2 enzymatic activity

Arylamine N-acetyltransferase (NAT; E.C. 2.3.1.5) enzymes are responsible for the biotransformation of several arylamine and hydrazine drugs by acetylation. In this process, the acetyl group transferred to the acceptor substrate produces NAT deacetylation and, in consequence, it is susceptible of degradation. Sirtuins are protein deacetylases, dependent on nicotine adenine dinucleotide, which perform post-translational modifications on cytosolic proteins. To explore possible sirtuin participation in the enzymatic activity of arylamine NATs, the expression levels of NAT1, NAT2, SIRT1 and SIRT6 in peripheral blood mononuclear cells (PBMC) from healthy subjects were examined by flow cytometry and Western blot. The in situ activity of the sirtuins on NAT enzymatic activity was analyzed by HPLC, in the presence or absence of an agonist (resveratrol) and inhibitor (nicotinamide) of sirtuins. We detected a higher percentage of positive cells for NAT2 in comparison with NAT1, and higher numbers of SIRT1+ cells compared to SIRT6 in lymphocytes. In situ NAT2 activity in the presence of NAM inhibitors was higher than in the presence of its substrate, but not in the presence of resveratrol. In contrast, the activity of NAT1 was not affected by sirtuins. These results showed that NAT2 activity might be modified by sirtuins.

Altered cellular metabolism of HepG2 cells caused by microcystin-LR

This study aimed to evaluate the possible effects of microcystin-LR (MC-LR) exposure on the metabolism and drug resistance of human hepatocellular carcinoma (HepG2) cells. For this purpose, we first conducted an experiment to make sure that MC-LR could penetrate the HepG2 cell membrane effectively. The transcriptional levels of phase I (such as CYP2E1, CYP3A4, and CYP26B1) and phase II (such as EPHX1, SULTs, and GSTM) enzymes and export pump genes (such as MRP1 and MDR1) were altered by MC-LR-exposure for 24 h, indicating that MC-LR treatment may destabilize the metabolism of HepG2 cells. Further research showed that the CYP inducers omeprazole, ethanol, and rifampicin inhibited cell viability, in particular, ethanol, a CYP2E1 inducer, induced ROS generation, lipid peroxidation, and apoptosis in HepG2 cells treated with MC-LR. The CYP2E1 inhibitor chlormethiazole inhibited ROS generation, mitochondrial membrane potential loss, caspase-3 activity, and cytotoxicity caused by MC-LR. Meanwhile, the results also showed that co-incubation with the ROS scavenger l-ascorbic acid and MC-LR decreased ROS levels and effectively prevented apoptosis. These findings provide an interesting mechanistic explanation of cellular metabolism associated with MC-LR, i.e., MC-LR-exposure exerted toxicity on HepG2 cells and induced apoptosis of HepG2 cells via promoting CYP2E1 expression and inducing excessive ROS in HepG2 cells.

Association between NAT2 polymorphisms and the risk of schizophrenia in a Northern Chinese Han population

The gene that encodes N-acetyltransferase 2 (NAT2), an enzyme that plays a crucial role in the metabolism of many drugs and xenobiotics, is located on chromosome 8p22, one of the most convictive susceptibility loci of schizophrenia. NAT2 genetic polymorphisms lead to various enzyme acetylation phenotypes. In the present study, six selected NAT2 exonic single nucleotide polymorphisms were genotyped in an independent case-control sample of a Northern Chinese Han population to verify the possible association between NAT2 and schizophrenia. Three (rs1801280T/341C, rs1799930/G590A, and rs1208/A803G) of the six single nucleotide polymorphisms showed significant allele frequency differences between the case and the control groups after rigorous Bonferroni correction. One protective fast-acetylation haplotype (NAT2*4) and two risk slow acetylation haplotypes (NAT2*5B and NAT2*6A) were discovered to be associated with schizophrenia. Our results indicate that NAT2 may be a susceptibility gene for schizophrenia in this Chinese Han population, and the risk haplotypes might cause the impairment of NAT2 in metabolizing neurotoxic substances.

Xenobiotic-metabolizing enzymes in Bacillus anthracis: molecular and functional analysis of a truncated arylamine N-acetyltransferase isozyme

BACKGROUND AND PURPOSE

The arylamine N-acetyltransferases (NATs) are xenobiotic-metabolizing enzymes that play an important role in the detoxification and/or bioactivation of arylamine drugs and xenobiotics. In bacteria, NATs may contribute to the resistance against antibiotics such as isoniazid or sulfamides through their acetylation, which makes this enzyme family a possible drug target. Bacillus anthracis, a bacterial species of clinical significance, expresses three NAT isozymes with distinct structural and enzymatic properties, including an inactive isozyme ((BACAN)NAT3). (BACAN)NAT3 features both a non-canonical Glu residue in its catalytic triad and a truncated C-terminus domain. However, the role these unusual characteristics play in the lack of activity of the (BACAN)NAT3 isozyme remains unclear.

EXPERIMENTAL APPROACH

Protein engineering, recombinant expression, enzymatic analyses with aromatic amine substrates and phylogenetic analysis approaches were conducted.

KEY RESULTS

The deletion of guanine 580 (G580) in the nat3 gene was shown to be responsible for the expression of a truncated (BACAN)NAT3 isozyme. Artificial re-introduction of G580 in the nat3 gene led to a functional enzyme able to acetylate several arylamine drugs displaying structural characteristics comparable with its functional Bacillus cereus homologue ((BACCR)NAT3). Phylogenetic analysis of the nat3 gene in the B. cereus group further indicated that nat3 may constitute a pseudogene of the B. anthracis species.

CONCLUSION AND IMPLICATIONS

The existence of NATs with distinct properties and evolution in Bacillus species may account for their adaptation to their diverse chemical environments. A better understanding of these isozymes is of importance for their possible use as drug targets.

LINKED ARTICLES

This article is part of a themed section on Drug Metabolism and Antibiotic Resistance in Micro-organisms. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.14/issuetoc.

NAT2 polymorphisms and risk for Parkinson's disease: a systematic review and meta-analysis

INTRODUCTION

Several studies suggested a possible association between certain polymorphisms in the N-acetyl-transferase 2 (NAT2) gene (which encodes a very important enzyme involved in xenobiotic metabolism) and the risk for Parkinson's disease (PD). As the results of studies on this issue are controversial, we conducted a systematic review and a meta-analysis of eligible studies on this putative association.

AREAS COVERED

The authors revised the relationship between NAT2 polymorphisms and the risk of developing PD using several databases, and performed a meta-analysis using the software Meta-Disc1.1.1. In addition heterogeneity between studies was analyzed. A description of studies regarding gene-gene interactions and gene-environmental interactions involving NAT2 polymorphisms is also made.

EXPERT OPINION

Despite several recent meta-analyses showing an association between several polymorphisms in genes related with detoxification mechanisms such as cytochrome P4502D6 (CYP2D6), and glutathione transferases M1 and T1 (GSTM1, and GSTT1), data on NAT2 gene polymorphisms obtained from the current meta-analysis do not support a major association with PD risk, except in Asian populations. However, data from many studies are incomplete and therefore insufficient data exists to draw definitive conclusions. Several studies suggesting gene-gene and gene-environmental factors involving NAT2 gene in PD risk await confirmation.

Evaluation of a New Molecular Entity as a Victim of Metabolic Drug-Drug Interactions-an Industry Perspective

Under the guidance of the International Consortium for Innovation and Quality in Pharmaceutical Development (IQ), scientists from 20 pharmaceutical companies formed a Victim Drug-Drug Interactions Working Group. This working group has conducted a review of the literature and the practices of each company on the approaches to clearance pathway identification (fCL), estimation of fractional contribution of metabolizing enzyme toward metabolism (fm), along with modeling and simulation-aided strategy in predicting the victim drug-drug interaction (DDI) liability due to modulation of drug metabolizing enzymes. Presented in this perspective are the recommendations from this working group on: 1) strategic and experimental approaches to identify fCL and fm, 2) whether those assessments may be quantitative for certain enzymes (e.g., cytochrome P450, P450, and limited uridine diphosphoglucuronosyltransferase, UGT enzymes) or qualitative (for most of other drug metabolism enzymes), and the impact due to the lack of quantitative information on the latter. Multiple decision trees are presented with stepwise approaches to identify specific enzymes that are involved in the metabolism of a given drug and to aid the prediction and risk assessment of drug as a victim in DDI. Modeling and simulation approaches are also discussed to better predict DDI risk in humans. Variability and parameter sensitivity analysis were emphasized when applying modeling and simulation to capture the differences within the population used and to characterize the parameters that have the most influence on the prediction outcome.

The Discovery of Novel Biomarkers Improves Breast Cancer Intrinsic Subtype Prediction and Reconciles the Labels in the METABRIC Data Set

BACKGROUND

The prediction of breast cancer intrinsic subtypes has been introduced as a valuable strategy to determine patient diagnosis and prognosis, and therapy response. The PAM50 method, based on the expression levels of 50 genes, uses a single sample predictor model to assign subtype labels to samples. Intrinsic errors reported within this assay demonstrate the challenge of identifying and understanding the breast cancer groups. In this study, we aim to: a) identify novel biomarkers for subtype individuation by exploring the competence of a newly proposed method named CM1 score, and b) apply an ensemble learning, as opposed to the use of a single classifier, for sample subtype assignment. The overarching objective is to improve class prediction.

METHODS AND FINDINGS

The microarray transcriptome data sets used in this study are: the METABRIC breast cancer data recorded for over 2000 patients, and the public integrated source from ROCK database with 1570 samples. We first computed the CM1 score to identify the probes with highly discriminative patterns of expression across samples of each intrinsic subtype. We further assessed the ability of 42 selected probes on assigning correct subtype labels using 24 different classifiers from the Weka software suite. For comparison, the same method was applied on the list of 50 genes from the PAM50 method.

CONCLUSIONS

The CM1 score portrayed 30 novel biomarkers for predicting breast cancer subtypes, with the confirmation of the role of 12 well-established genes. Intrinsic subtypes assigned using the CM1 list and the ensemble of classifiers are more consistent and homogeneous than the original PAM50 labels. The new subtypes show accurate distributions of current clinical markers ER, PR and HER2, and survival curves in the METABRIC and ROCK data sets. Remarkably, the paradoxical attribution of the original labels reinforces the limitations of employing a single sample classifiers to predict breast cancer intrinsic subtypes.

N-acetyltransferase 1 polymorphism increases cotinine levels in Caucasian children exposed to secondhand smoke: the CCAAPS birth cohort

Cotinine is a proxy for secondhand smoke (SHS) exposure. Genetic variation along nicotine and cotinine metabolic pathways may alter the internal cotinine dose, leading to misinterpretations of exposure-health outcome associations. Caucasian children with available SHS exposure and hair cotinine data were genotyped for metabolism-related genes. SHS-exposed children had 2.4-fold higher hair cotinine (0.14±0.22 ng mg(-1)) than unexposed children (0.06±0.05 ng mg(-1), P<0.001). SHS-exposed children carrying the NAT1 minor allele had twofold higher hair cotinine (0.18 ng mg(-1) for heterozygotes and 0.17 ng mg(-1) for homozygotes) compared with major allele homozygotes (0.09 ng mg(-1), P=0.0009), even after adjustment for SHS dose. These findings support that NAT1 has a role in the metabolic pathway of nicotine/cotinine and/or their metabolites. The increased cotinine levels observed for those carrying the minor allele may lead to SHS exposure misclassification in studies utilizing cotinine as a biomarker. Additional studies are required to identify functional single-nucleotide polymorphism(s) (SNP(s)) in NAT1 and elucidate the biological consequences of the mutation(s).

Identification and validation of N-acetyltransferase 2 as an insulin sensitivity gene

Decreased insulin sensitivity, also referred to as insulin resistance (IR), is a fundamental abnormality in patients with type 2 diabetes and a risk factor for cardiovascular disease. While IR predisposition is heritable, the genetic basis remains largely unknown. The GENEticS of Insulin Sensitivity consortium conducted a genome-wide association study (GWAS) for direct measures of insulin sensitivity, such as euglycemic clamp or insulin suppression test, in 2,764 European individuals, with replication in an additional 2,860 individuals. The presence of a nonsynonymous variant of N-acetyltransferase 2 (NAT2) [rs1208 (803A>G, K268R)] was strongly associated with decreased insulin sensitivity that was independent of BMI. The rs1208 "A" allele was nominally associated with IR-related traits, including increased fasting glucose, hemoglobin A1C, total and LDL cholesterol, triglycerides, and coronary artery disease. NAT2 acetylates arylamine and hydrazine drugs and carcinogens, but predicted acetylator NAT2 phenotypes were not associated with insulin sensitivity. In a murine adipocyte cell line, silencing of NAT2 ortholog Nat1 decreased insulin-mediated glucose uptake, increased basal and isoproterenol-stimulated lipolysis, and decreased adipocyte differentiation, while Nat1 overexpression produced opposite effects. Nat1-deficient mice had elevations in fasting blood glucose, insulin, and triglycerides and decreased insulin sensitivity, as measured by glucose and insulin tolerance tests, with intermediate effects in Nat1 heterozygote mice. Our results support a role for NAT2 in insulin sensitivity.

Different phenotypes of the NAT2 gene influences hydralazine antihypertensive response in patients with resistant hypertension

AIM

Hydralazine, a vasodilator used in resistant hypertension (RH) treatment is metabolized by an acetylation reaction mediated by N-acetyltransferase 2, the activity of which depends on NAT2 polymorphisms. Our aim was to evaluate whether different acetylation phenotypes influenced the antihypertensive effect of hydralazine in patients with RH.

PATIENTS & METHODS

DNA samples from 169 RH patients using hydralazine were genotyped by sequencing the NAT2 coding region, and acetylation phenotypes were defined.

RESULTS

Sixty-five patients (38.5%) were intermediate, 60 (35.5%) slow and 21 (12.4%) fast acetylators. Twenty-three (13.6%) patients were indeterminate. Upon association analysis, only slow acetylators had significant blood pressure reductions after hydralazine use, with mean 24-h systolic and diastolic blood pressure reductions of 9.2 and 5.5 mmHg. Four patients presented hydralazine adverse effects resulting in drug withdrawal, three of them were slow acetylators.

CONCLUSION

The slow acetylation phenotype, determined by polymorphisms within NAT2, influenced both the antihypertensive and adverse effects of hydralazine in RH.

The role of lysine(100) in the binding of acetylcoenzyme A to human arylamine N-acetyltransferase 1: implications for other acetyltransferases

The arylamine N-acetyltransferases (NATs) catalyze the acetylation of aromatic and heterocyclic amines as well as hydrazines. All proteins in this family of enzymes utilize acetyl coenzyme A (AcCoA) as an acetyl donor, which initially binds to the enzyme and transfers an acetyl group to an active site cysteine. Here, we have investigated the role of a highly conserved amino acid (Lys(100)) in the enzymatic activity of human NAT1. Mutation of Lys(100) to either a glutamine or a leucine significantly increased the Ka for AcCoA without changing the Kb for the acetyl acceptor p-aminobenzoic acid. In addition, substrate inhibition was more marked with the mutant enzymes. Steady state kinetic analyzes suggested that mutation of Lys(100) to either leucine or glutamine resulted in a less stable enzyme-cofactor complex, which was not seen with a positively charged arginine at this position. When p-nitrophenylacetate was used as acetyl donor, no differences were seen between the wild-type and mutant enzymes because p-nitrophenylacetate is too small to interact with Lys(100) when bound to the active site. Using 3'-dephospho-AcCoA as the acetyl donor, kinetic data confirmed that Ly(100) interacts with the 3'-phosphoanion to stabilize the enzyme-cofactor complex. Mutation of Lys(100) decreases the affinity of AcCoA for the protein and increases the rate of CoA release. Crystal structures of several other unrelated acetyltransferases show a lysine or arginine residue within 3Å of the 3'-phosphoanion of AcCoA, suggesting that this mechanism for stabilizing the complex by the formation of a salt bridge may be widely applicable in nature.

Insight into cofactor recognition in arylamine N-acetyltransferase enzymes: structure of Mesorhizobium loti arylamine N-acetyltransferase in complex with coenzyme A

Arylamine N-acetyltransferases (NATs) are xenobiotic metabolizing enzymes that catalyze the acetyl-CoA-dependent acetylation of arylamines. To better understand the mode of binding of the cofactor by this family of enzymes, the structure of Mesorhizobium loti NAT1 [(RHILO)NAT1] was determined in complex with CoA. The F42W mutant of (RHILO)NAT1 was used as it is well expressed in Escherichia coli and displays enzymatic properties similar to those of the wild type. The apo and holo structures of (RHILO)NAT1 F42W were solved at 1.8 and 2 Å resolution, respectively. As observed in the Mycobacterium marinum NAT1-CoA complex, in (RHILO)NAT1 CoA binding induces slight structural rearrangements that are mostly confined to certain residues of its `P-loop'. Importantly, it was found that the mode of binding of CoA is highly similar to that of M. marinum NAT1 but different from the modes reported for Bacillus anthracis NAT1 and Homo sapiens NAT2. Therefore, in contrast to previous data, this study shows that different orthologous NATs can bind their cofactors in a similar way, suggesting that the mode of binding CoA in this family of enzymes is less diverse than previously thought. Moreover, it supports the notion that the presence of the `mammalian/eukaryotic insertion loop' in certain NAT enzymes impacts the mode of binding CoA by imposing structural constraints.

Exploring the substrate-assisted acetylation mechanism by UDP-linked sugar N-acetyltransferase from QM/MM calculations: the role of residue Asn84 and the effects of starting geometries

Based on the QM/MM calculation, we revised the proposed mechanism ofN-acetyltransferase and explore the role of Asn84 and the effects of starting geometries.

Arylamine N-acetyltransferases: from drug metabolism and pharmacogenetics to drug discovery

Arylamine N-acetyltransferases (NATs) are polymorphic drug-metabolizing enzymes, acetylating arylamine carcinogens and drugs including hydralazine and sulphonamides. The slow NAT phenotype increases susceptibility to hydralazine and isoniazid toxicity and to occupational bladder cancer. The two polymorphic human NAT loci show linkage disequilibrium. All mammalian Nat genes have an intronless open reading frame and non-coding exons. The human gene products NAT1 and NAT2 have distinct substrate specificities: NAT2 acetylates hydralazine and human NAT1 acetylates p-aminosalicylate (p-AS) and the folate catabolite para-aminobenzoylglutamate (p-abaglu). Human NAT2 is mainly in liver and gut. Human NAT1 and its murine homologue are in many adult tissues and in early embryos. Human NAT1 is strongly expressed in oestrogen receptor-positive breast cancer and may contribute to folate and acetyl CoA homeostasis. NAT enzymes act through a catalytic triad of Cys, His and Asp with the architecture of the active site-modulating specificity. Polymorphisms may cause unfolded protein. The C-terminus helps bind acetyl CoA and differs among NATs including prokaryotic homologues. NAT in Salmonella typhimurium supports carcinogen activation and NAT in mycobacteria metabolizes isoniazid with polymorphism a minor factor in isoniazid resistance. Importantly, nat is in a gene cluster essential for Mycobacterium tuberculosis survival inside macrophages. NAT inhibitors are a starting point for novel anti-tuberculosis drugs. Human NAT1-specific inhibitors may act in biomarker detection in breast cancer and in cancer therapy. NAT inhibitors for co-administration with 5-aminosalicylate (5-AS) in inflammatory bowel disease has prompted ongoing investigations of azoreductases in gut bacteria which release 5-AS from prodrugs including balsalazide.

Immunohistochemical determination of the miR-1290 target arylamine N-acetyltransferase 1 (NAT1) as a prognostic biomarker in breast cancer

Background

There are many molecular differences between estrogen receptor α (ERα)-positive and ER-negative breast cancers. Recent analyses have shown that the former can be divided into two subtypes, luminal A and luminal B. These differ in response to endocrine therapy and chemotherapy, and in prognosis. In a previous study, we found that microRNA (miR)-1290 that was significantly down-regulated in luminal A tumors and its potential target arylamine N-acetyltransferase 1 (NAT1). The aim of the present study was to determine whether NAT1 is a bona fide target of miR-1290, and to investigate the impact of NAT1 on breast cancer prognosis.

Methods

Luciferase reporter assays were employed to validate NAT1 as a putative miR-1290 target gene. Expression of NAT1, ERα, progesterone receptor (PgR) and HER2 was analyzed in 394 breast cancer samples by immunohistochemistry.

Results

NAT1 was confirmed to be a direct target of miR-1290. Levels of expression of NAT1 were positively correlated with those of ERα (P < 0.0001) and PgR (P < 0.0001), but negatively correlated with both tumor grade and size (P < 0.0001). Kaplan-Meier analysis showed that the presence of NAT1 was significantly associated with increased overall survival (OS) (P = 0.0416) in these patients. Similarly, significant associations of NAT1 with disease-free survival (DFS) (P = 0.0048) and OS (P = 0.0055) in those patients who received adjuvant endocrine therapy with tamoxifen (n = 176) were found. Moreover, NAT1 was also significantly associated with increased DFS (P = 0.0025) and OS (P = 0.0007) in the subset of lymph node-positive patients (n = 147). Univariate and multivariate analyses showed significant associations between levels of NAT1 and DFS (P = 0.0005 and 0.019, respectively).

Conclusions

We report that miR-1290 directly targets the NAT1 3′-UTR and that NAT1 protein expression is correlated with improved OS of breast cancer patients. NAT1 is a possible prognostic biomarker for lymph node-positive breast cancer. Thus, miR-1290 and its target NAT1 are associated with important characteristics of breast cancer.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2407-14-990) contains supplementary material, which is available to authorized users.

Differences between murine arylamine N-acetyltransferase type 1 and human arylamine N-acetyltransferase type 2 defined by substrate specificity and inhibitor binding

Background

The mouse has three arylamine N-acetyltransferase genes, (MOUSE)Nat1, (MOUSE)Nat2 and (MOUSE)Nat3. These are believed to correspond to (HUMAN)NAT1, (HUMAN)NAT2 and NATP in humans. (MOUSE)Nat3 encodes an enzyme with poor activity and human NATP is a pseudogene. (MOUSE)Nat2 is orthologous to (HUMAN)NAT1 and their corresponding proteins are functionally similar, but the relationship between (MOUSE)Nat1 and (HUMAN)NAT2 is less clear-cut.

Methods

To determine whether the (MOUSE)NAT1 and (HUMAN)NAT2 enzymes are functionally equivalent, we expressed and purified (MOUSE)NAT1*1 and analysed its substrate specificity using a panel of arylamines and hydrazines. To understand how specific residues contribute to substrate selectivity, three site-directed mutants of (MOUSE)NAT2*1 were prepared: these were (MOUSE)NAT2_F125S, (MOUSE)NAT2_R127G and (MOUSE)NAT2_R127L. All three exhibited diminished activity towards “(MOUSE)NAT2-specific” arylamines but were more active against hydrazines than (MOUSE)NAT1*1. The inhibitory and colorimetric properties of a selective naphthoquinone inhibitor of (HUMAN)NAT1 and (MOUSE)NAT2 were investigated.

Results

Comparing (MOUSE)NAT1*1 with other mammalian NAT enzymes demonstrated that the substrate profiles of (MOUSE)NAT1 and (HUMAN)NAT2 are less similar than previously believed. Three key residues (F125, R127 and Y129) in (HUMAN)NAT1*4 and (MOUSE)NAT2*1 were required for enzyme inhibition and the associated colour change on naphthoquinone binding. In silico modelling of selective ligands into the appropriate NAT active sites further implicated these residues in substrate and inhibitor specificity in mouse and human NAT isoenzymes.

Conclusions

Three non-catalytic residues within (HUMAN)NAT1*4 (F125, R127 and Y129) contribute both to substrate recognition and inhibitor binding by participating in distinctive intermolecular interactions and maintaining the steric conformation of the catalytic pocket. These active site residues contribute to the definition of substrate and inhibitor selectivity, an understanding of which is essential for facilitating the design of second generation (HUMAN)NAT1-selective inhibitors for diagnostic, prognostic and therapeutic purposes. In particular, since the expression of (HUMAN)NAT1 is related to the development and progression of oestrogen-receptor-positive breast cancer, these structure-based tools will facilitate the ongoing design of candidate compounds for use in (HUMAN)NAT1-positive breast tumours.

Electronic supplementary material

The online version of this article (doi:10.1186/2050-6511-15-68) contains supplementary material, which is available to authorized users.

Structural and functional characterization of an arylamineN-acetyltransferase from the pathogenMycobacterium abscessus: differences from other mycobacterial isoforms and implications for selective inhibition

Mycobacterium abscessusis the most pathogenic rapid-growing mycobacterium and is one of the most resistant organisms to chemotherapeutic agents. However, structural and functional studies ofM. abscessusproteins that could modify/inactivate antibiotics remain nonexistent. Here, the structural and functional characterization of an arylamineN-acetyltransferase (NAT) fromM. abscessus[(MYCAB)NAT1] are reported. This novel prokaryotic NAT displays significantN-acetyltransferase activity towards aromatic substrates, including antibiotics such as isoniazid andp-aminosalicylate. The enzyme is endogenously expressed and functional in both the rough and smoothM. abscessusmorphotypes. The crystal structure of (MYCAB)NAT1 at 1.8 Å resolution reveals that it is more closely related toNocardia farcinicaNAT than to mycobacterial isoforms. In particular, structural and physicochemical differences from other mycobacterial NATs were found in the active site. Peculiarities of (MYCAB)NAT1 were further supported by kinetic and docking studies showing that the enzyme was poorly inhibited by the piperidinol inhibitor of mycobacterial NATs. This study describes the first structure of an antibiotic-modifying enzyme fromM. abscessusand provides bases to better understand the substrate/inhibitor-binding specificities among mycobacterial NATs and to identify/optimize specific inhibitors. These data should also contribute to the understanding of the mechanisms that are responsible for the pathogenicity and extensive chemotherapeutic resistance ofM. abscessus.

Arylamine N-acetyltransferases: a structural perspective

Arylamine N-acetyltransferase (NAT) plays an important role in metabolism and detoxification of many compounds including drugs and environmental carcinogens through chemical modification of the amine group with an acetyl group. Recent studies have suggested that NATs are also involved in cancer cell growth and inhibition of the enzymes may be a potential target for cancer chemotherapy. Three-dimensional (3D) structures are available for NATs from both prokaryotes and eukaryotes. These structures provide valuable insights into the acetylation mechanism, features of the active site and the structural determinants that govern substrate/inhibitor-binding specificity. Such insights allow a more precise understanding of the structure-activity relationships for NAT substrates and inhibitors. Furthermore, the structural elucidation of NATs has generated powerful tools in the design of small molecule inhibitors that should alleviate cancer, based on the important role of the enzyme in cancer biology.