Human acetyltransferase polymorphisms

John N, Zaidi F, Doyle F, Fasullo M. High-throughput screening of the Saccharomyces cerevisiae genome for 2-amino-3-methylimidazo [4,5-f] quinoline resistance identifies colon cancer-associated genes

Heterocyclic aromatic amines (HAAs) are potent carcinogenic agents found in charred meats and cigarette smoke. However, few eukaryotic resistance genes have been identified. We used Saccharomyces cerevisiae (budding yeast) to identify genes that confer resistance to 2-amino-3-methylimidazo[4,5-f] quinoline (IQ). CYP1A2 and NAT2 activate IQ to become a mutagenic nitrenium compound. Deletion libraries expressing human CYP1A2 and NAT2 or no human genes were exposed to either 400 or 800 µM IQ for 5 or 10 generations. DNA barcodes were sequenced using the Illumina HiSeq 2500 platform and statistical significance was determined for exactly matched barcodes. We identified 424 ORFs, including 337 genes of known function, in duplicate screens of the "humanized" collection for IQ resistance; resistance was further validated for a select group of 51 genes by growth curves, competitive growth, or trypan blue assays. Screens of the library not expressing human genes identified 143 ORFs conferring resistance to IQ per se. Ribosomal protein and protein modification genes were identified as IQ resistance genes in both the original and "humanized" libraries, while nitrogen metabolism, DNA repair, and growth control genes were also prominent in the "humanized" library. Protein complexes identified included the casein kinase 2 (CK2) and histone chaperone (HIR) complex. Among DNA Repair and checkpoint genes, we identified those that function in postreplication repair (RAD18, UBC13, REV7), base excision repair (NTG1), and checkpoint signaling (CHK1, PSY2). These studies underscore the role of ribosomal protein genes in conferring IQ resistance, and illuminate DNA repair pathways for conferring resistance to activated IQ.

N-acetyltransferase 2 genetic polymorphism modifies genotoxic and oxidative damage from new psychoactive substances

The use of new psychoactive substances (NPS) as drugs of abuse is common and increasingly popular, particularly among youth and neglected communities. Recent studies have reported acute toxic effects from these chemicals; however, their long-term toxicity is unknown. Genetic differences between individuals likely affect the toxicity risk. Arylamine N-acetyltransferase 2 (NAT2) capacity differs among individuals due to genetic inheritance. The goal of the present study is to investigate the gene-environment interaction between NAT2 polymorphism and toxicity after exposure to these chemicals. We measured N-acetylation by human NAT1 and NAT2 and found that N-acetylation of NPS is carried out exclusively by NAT2. Differences in N-acetylation between NAT2*4 (reference allele) and NAT2*5B (common variant allele) were highly significant (p < 0.0001). Using DNA repair-deficient genetically engineered Chinese hamster ovary (CHO cells), expressing human CYP1A2 and either NAT2*4 or NAT2*5B, we measured the induction of DNA double-strand breaks ([Formula: see text]H2Ax) following treatment of the CHO cells with increasing concentrations of NPS. The induction of [Formula: see text]H2Ax showed a NAT2 allele-dependent response, higher in the NAT2*4 vs NAT2*5B alleles (p < 0.05). Induction of oxidative stress (ROS/RNS) was evaluated; we observed NAT2 allele-dependent response for all compounds in concentrations as low as 10 [Formula: see text]M, where NAT2*4 showed increased ROS/RNS vs NAT2*5B (p < 0.05). In summary, NPS are N-acetylated by NAT2 at rates higher in cells expressing NAT2*4 than NAT2*5B. Exposure to psychoactive chemicals results in genotoxic and oxidative damage that is modified by the NAT2 genetic polymorphism.

Enhanced cytotoxicity of a novel family of ATPase inhibitors in colorectal cancer cells with high NAT2 activity

Loss of heterozygosity (LOH) is a hallmark feature of cancer genomes that reduces allelic variation, thereby creating tumor specific vulnerabilities which could be exploited for therapeutic purposes. We previously reported that loss of drug metabolic arylamine N-acetyltransferase 2 (NAT2) activity following LOH at 8p22 could be targeted for collateral lethality anticancer therapy in colorectal cancer (CRC). Here, we report a novel compound CBK034026C that exhibits specific toxicity towards CRC cells with high NAT2 activity. Connectivity Map analysis revealed that CBK034026C elicited a response pattern related to ATPase inhibitors. Similar to ouabain, a potent inhibitor of the Na⁺/K⁺-ATPase, CBK034026C activated the Nf-kB pathway. Further metabolomic profiling revealed downregulation of pathways associated with antioxidant defense and mitochondrial metabolism in CRC cells with high NAT2 activity, thereby weakening the protective response to oxidative stress induced by CBK034026C. The identification of a small molecule targeting metabolic vulnerabilities caused by NAT2 activity provides novel avenues for development of anticancer agents.

Xenobiotic transport and metabolism in the human brain

Organisms have metabolic pathways responsible for eliminating endogenous and exogenous toxicants. Generally, we associate the liver par excellence as the organ in charge of detoxifying the body; however, this process occurs in all tissues, including the brain. Due to the presence of the blood-brain barrier (BBB) and the blood-cerebrospinal fluid barrier (BCSFB), the Central Nervous System (CNS) is considered a partially isolated organ, but similar to other organs, the CNS possess xenobiotic transporters and metabolic pathways associated with the elimination of xenobiotic agents. In this review, we describe the different systems related to the detoxification of xenobiotics in the CNS, providing examples in which their association with neurodegenerative processes is suspected. The CNS detoxifying systems include carrier-mediated, active efflux and receptor-mediated transport, and detoxifying systems that include phase I and phase II enzymes, as well as those enzymes in charge of neutralizing compounds such as electrophilic agents, reactive oxygen species (ROS), and free radicals, which are products of the bioactivation of xenobiotics. Moreover, we discuss the differential expression of these systems in different regions of the CNS, showing the different detoxifying needs and the composition of each region in terms of the cell type, neurotransmitter content, and the accumulation of xenobiotics and/or reactive compounds.

Association of NAT2 genetic polymorphism with the efficacy of Neurotropin® for the enhancement of aggrecan gene expression in nucleus pulposus cells: a pilot study

Background

Intervertebral disc degeneration, one of the major causes of low-back pain, results from altered biosynthesis/turnover of extracellular matrix in the disc. Previously, we reported that the analgesic drug Neurotropin® (NTP) had an anabolic effect on glycosaminoglycan synthesis in cultured nucleus pulposus (NP) cells via the stimulation of chondroitin sulfate N-acetylgalactosaminyltransferase 1. However, its effect on the aggrecan core protein was not significantly detected, because of the data variance. A microarray analysis suggested that the effect of NTP on aggrecan was correlated with N-acetyltransferase 2 (NAT2), a drug-metabolizing enzyme. Specific NAT2 alleles are known to correlate with rapid, intermediate, and slow acetylation activities and side effects of various drugs. We investigated the association between the efficacy of NTP on aggrecan expression and the NAT2 genotype in cell donors.

Methods

NP cells were isolated from intervertebral disc tissues donated by 31 Japanese patients (28–68 years) who underwent discectomy. NTP was added to the primary cell cultures and its effect on the aggrecan mRNA was analyzed using real-time quantitative PCR. To assess acetylator status, genotyping was performed based on the inferred NAT2 haplotypes of five common single-nucleotide polymorphisms using allele-specific PCR.

Results

The phenotype frequencies of NAT2 in the patients were 0%, 42.0%, and 58.0% for slow, intermediate, and rapid acetylators, respectively. The proportions of responders to NTP treatment (aggrecan upregulation, ≥ 1.1-fold) in the intermediate and rapid acetylators were 76.9% and 38.9%, respectively. The odds ratio of the comparison of the intermediate acetylator status between responders and nonresponders was 5.2 (95% CI 1.06–26.0, P = 0.036), and regarding the 19 male patients, this was 14.0 (95% CI 1.54–127.2, P = 0.012). In the 12 females, the effect was not correlated with NAT2 phenotype but seemed to become weaker along with aging.

Conclusions

An intermediate acetylator status significantly favored the efficacy of NTP treatment to enhance aggrecan production in NP cells. In males, this tendency was detected with higher significance. This study provides suggestive data of the association between NAT2 variants and the efficacy of NTP treatment. Given the small sample size, results should be further confirmed.

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.

Defining eligible patients for allele-selective chemotherapies targeting NAT2 in colorectal cancer

Therapies targeting somatic bystander genetic events represent a new avenue for cancer treatment. We recently identified a subset of colorectal cancer (CRC) patients who are heterozygous for a wild-type and a low activity allele (NAT2*6) but lack the wild-type allele in their tumors due to loss of heterozygosity (LOH) at 8p22. These tumors were sensitive to treatment with a cytotoxic substrate of NAT2 (6-(4-aminophenyl)-N-(3,4,5-trimethoxyphenyl)pyrazin-2-amine, APA), and pointed to NAT2 loss being a therapeutically exploitable vulnerability of CRC tumors. To better estimate the total number of treatable CRC patients, we here determined whether tumor cells retaining also other NAT2 low activity variants after LOH respond to APA treatment. The prevalent low activity alleles NAT2*5 and NAT2*14, but not NAT2*7, were found to be low metabolizers with high sensitivity to APA. By analysis of two different CRC patient cohorts, we detected heterozygosity for NAT2 alleles targetable by APA, along with allelic imbalances pointing to LOH, in ~ 24% of tumors. Finally, to haplotype the NAT2 locus in tumor and patient-matched normal samples in a clinical setting, we develop and demonstrate a long-read sequencing based assay. In total, > 79.000 CRC patients per year fulfil genetic criteria for high sensitivity to a NAT2 LOH therapy and their eligibility can be assessed by clinical sequencing.

Association of slow acetylator genotype of N-acetyltransferase 2 with Parkinson's disease in south Indian population

AIM

Parkinson's Disease (PD) is a neurodegenerative disorder with predisposing genetic and environmental factors. The present study was undertaken to elucidate the possible association of NAT2 gene polymorphism in PD patients from south India.

METHODS

Using previously validated PCR-RFLP assays, we genotyped 105 PD subjects and 101 healthy controls for N-acetyl transferase (NAT2) gene polymorphism.

RESULTS

We observed a significantly elevated frequencies of NAT2 *5/6 (OR = 4.21; p < 0.029) and *5/7 (OR = 2.73; p < 0.025) genotypes and NAT2*5 (OR = 1.83; p < 0.039) allele among PD cases showing susceptible associations. The age at onset analysis revealed a significant association of NAT2 *4/6 (OR = 4.62; p < 0.05) genotype with early onset PD (EOPD). A positive association with early onset disease was observed for *5/7 (OR = 3.88; p < 0.075) genotype, however without statistical significance. Whereas, in late onset PD (LOPD) cases, significant susceptible association was observed for NAT2 *5/7 (OR = 5.27; p < 0.029) genotype. We observed a highly significant protective association of NAT2 *4/6 (OR = 0.27; p < 0.012) genotype and NAT2 *4 (OR = 0.52; p < 0.027) allele with LOPD. The acetylator status phenotype analysis have revealed a higher risk for, 'NAT2 slow acetylator' in both overall PD (OR = 2.39; p < 0.002) and LOPD (OR = 2.88; p < 0.007). However, 'NAT2 intermediate acetylator' with a lower risk in both overall PD (OR = 0.47; p < 0.011) and LOPD (OR = 0.36; p < 0.007) cases revealed protective associations.

CONCLUSIONS

Thus, our results revealed the possible susceptible association of NAT2 slow acetylator in PD pathogenesis in south Indian population.

Unexpected Acetylation of Endogenous Aliphatic Amines by Arylamine N-Acetyltransferase NAT2

N-Acetyltransferases play critical roles in the deactivation and clearance of xenobiotics, including clinical drugs. NAT2 has been classified as an arylamine N-acetyltransferase that mainly converts aromatic amines, hydroxylamines, and hydrazines. Herein, we demonstrate that the human arylamine N-acetyltransferase NAT2 also acetylates aliphatic endogenous amines. Metabolomic analysis and chemical synthesis revealed increased intracellular concentrations of mono- and diacetylated spermidine in human cell lines expressing the rapid compared to the slow acetylator NAT2 phenotype. The regioselective N8 -acetylation of monoacetylated spermidine by NAT2 answers the long-standing question of the source of diacetylspermidine. We also identified selective acetylation of structurally diverse alkylamine-containing drugs by NAT2, which may contribute to variations in patient responses. The results demonstrate a previously unknown functionality and potential regulatory role for NAT2, and we suggest that this enzyme should be considered for re-classification.

Associations Between Glutathione-S-Transferase Genotypes and Bronchial Hyperreactivity Patients With Di-isocyanate Induced Asthma. A Follow-Up Study

Introduction: Di-isocyanates TDI (toluene di-isocyanate), MDI (diphenylmethane di-isocyanate), and HDI (hexamethylene di-isocyanate) are the most common chemicals causing occupational asthma. Di-isocyanate inhalation has been reported to induce oxidative stress via reactive oxygen and nitrogen species leading to tissue injury. Glutathione transferases (GSTs) and N-acetyltransferases (NATs) are detoxifying enzymes whose general function is to inactivate electrophilic substances. The most important genes regulating these enzymes, i.e., GSTM1, GSTP1, GSTT1, NAT1, and NAT2 have polymorphic variants resulting in enhanced or lowered enzyme activities. Since inability to detoxify harmful oxidants can lead to inflammatory processes involving activation of bronchoconstrictive mechanisms, we studied whether the altered GST and NAT genotypes were associated with bronchial hyperreactivity (BHR) in patients with di-isocyanate exposure related occupational asthma, irrespective of cessation of di-isocyanate exposure, and adequacy of asthma treatment.

Methods: Polymerase chain reaction (PCR) based methods were used to analyze nine common polymorphisms in GSTM1, GSTM3, GSTP1, GSTT1, NAT1, and NAT2 genes in 108 patients with diagnosed occupational di-isocyanate-induced asthma. The genotype data were compared with spirometric lung function and BHR status at diagnosis and in the follow-up examination on average 11 years (range 1–22 years) after the asthma diagnosis. Serum IgE and IL13 levels were also assessed in the follow-up phase.

Results: An association between BHR and GSTP1 slow activity (Val105/Val105) genotype was demonstrated in the subjects at the follow-up phase but not at the diagnosis phase. Moreover, the patients with the GSTP1 slow activity genotype exhibited characteristics of Th-2 type immune response more often compared to those with the unaltered GSTP1 gene. Interestingly, all 10 patients with the GSTP1 slow activity genotype had both the GSTM3 slow activity genotype and the unaltered GSTT1 gene.

Discussion: The results suggest associations of the low activity variants of the GSTP1 gene with BHR. The fact that these associations came up only at the follow-up phase when the subjects were not any more exposed to di-isocyanates, and used asthma medication, suggest that medication and environmental factors influence the presentation of these associations. However, due to the exploratory character of the study and relatively small study size, the findings remain to be confirmed in future studies with larger sample sizes.

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.

Determination of Arylamine N-Acetyltransferase 2 Acetylation Genotype by PCR and Phenotyping Using Dapsone Through High-Pressure Liquid Chromatography Assay: A Gender Wise Study

The main aim of the study was to establish the acetylation status of local population of Pakistan by N-acetyltransferase 2 (NAT2) enzyme and to find out the concordance between phenotypic and genotypic methods for the determination of NAT2 acetylation. Gender-wise comparison of selected healthy male and female volunteers aged greater than 18 years was also conducted to see the effect of sex on NAT2 acetylation. Phenotypically, the rate of acetylation was determined by high-pressure liquid chromatography with dapsone (DDS) probe drug, while genotypically, NAT2 acetylation was determined by using specific primers for NAT2 variant alleles (M1, M2, and M3) amplified in separate polymerase chain reactions. High-pressure liquid chromatography results indicated 64% of the male volunteers to be fast acetylators while 36% were slow acetylators, while ratio of fast and slow acetylators for female was found to be 66% and 34%, respectively. Genotypically, the ratio of fast and slow for male was 60% and 40% and for female was 66% and 34%, respectively. The distribution of 3 NAT2 variant alleles was found in invariable number. For male volunteers, the highest frequency distribution showed by M2 allele was 56%, while for M1 and M3 the frequency was 32% and 12%, respectively, and for female volunteers highest frequency (51%) was shown by the M2 variant allele while lowest frequency (18%) was shown by M3 allele. There was the 94% concordance between the DDS phenotype and genotype. Gender effect on the acetylation was found to be nonsignificant (P > .05). Therefore, it is concluded that NAT2 acetylation rate can be used to check in vivo acetylation status with dapsone as probe drug. It is concluded that NAT2 acetylation rate was unaffected by gender and can be used to check in vivo acetylation status with dapsone as probe drug, which is inexpensive and less time-consuming.

Functional expression of human arylamine N-acetyltransferase NAT1*10 and NAT1*11 alleles: a mini review

The arylamine N-acetyltransferase (NAT) nomenclature committee assigns functional phenotypes for human arylamine N-acetyltransferase 1 (NAT1) alleles in those instances in which the committee determined a consensus has been achieved in the scientific literature. In the most recent nomenclature update, the committee announced that functional phenotypes for NAT1*10 and NAT1*11 alleles were not provided owing to a lack of consensus. Phenotypic inconsistencies observed among various studies for NAT1*10 and NAT1*11 may be owing to variable allelic expression among different tissues, the limitations of the genotyping assays (which mostly relied on techniques not involving direct DNA sequencing), the differences in recombinant protein expression systems used (bacteria, yeast, and mammalian cell lines) and/or the known inherent instability of human NAT1 protein, which requires very careful handling of native and recombinant cell lysates. Three recent studies provide consistent evidence of the mechanistic basis underlying the functional phenotype of NAT1*10 and NAT1*11 as 'increased-activity' alleles. Some NAT1 variants (e.g. NAT1*14, NAT1*17, and NAT1*22) may be designated as 'decreased-activity' alleles and other NAT1 variants (e.g. NAT1*15 and NAT1*19) may be designated as 'no-activity' alleles compared with the NAT1*4 reference allele. We propose that phenotypic designations as 'rapid' and 'slow' acetylator should be discontinued for NAT1 alleles, although these designations remain very appropriate for NAT2 alleles.

Association between NAT2 polymorphisms and acute leukemia risk: A meta-analysis

BACKGROUND

N-acetyl-transferase 2 (NAT2) polymorphisms have been demonstrated to be associated with acute leukemia (AL); however, the results remain controversial. The present meta-analysis was performed to provide more precise results.

METHODS

Pubmed, Embase, Cochrane Library, China National Knowledge Infrastructure, and Wanfang databases were used to identify eligible studies. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated to evaluate the strength of the association between NAT2 polymorphisms and AL risk.

RESULTS

Increased risk was found under both heterozygous (OR 1.24, 95% CI 1.02-1.51) and recessive model (OR 1.28, 95% CI 1.06-1.55) for rs1801280. The slow acetylator phenotype (OR 1.22, 95% CI 1.07-1.40) also increased AL risk. Subgroup analysis demonstrated that rs1801280 increased AL risk under the recessive model (OR 1.14, 95% CI 0.93-1.41) in Caucasian population and the co-dominant (OR 1.77, 95% CI 1.40-2.23), homozygous (OR 3.06, 95% CI 1.88-4.99), dominant (OR 2.22, 95% CI 1.56-3.17), recessive model (OR 2.06, 95% CI 1.35-3.16) in the Mixed populations. Association between rs1799929 and decreased AL risk was found in the co-dominant (OR 0.82, 95% CI 0.70-0.97), homozygous (OR 0.65, 95% CI 0.46-0.93), heterozygous (OR 0.71, 95% CI 0.51-1.00), and the recessive model (OR 0.68, 95% CI 0.49-0.94) in the Caucasian group. As for rs1799931, the same effects were found in the co-dominant (OR 0.68, 95% CI 0.49-0.94) and the dominant model (OR 0.68, 95% CI 0.48-0.97) in the mixed group.

CONCLUSION

rs1801280 and the slow acetylator phenotype are risk factors for AL.

Xenobiotica-metabolizing enzymes in the skin of rat, mouse, pig, guinea pig, man, and in human skin models

Studies on the metabolic fate of medical drugs, skin care products, cosmetics and other chemicals intentionally or accidently applied to the human skin have become increasingly important in order to ascertain pharmacological effectiveness and to avoid toxicities. The use of freshly excised human skin for experimental investigations meets with ethical and practical limitations. Hence information on xenobiotic-metabolizing enzymes (XME) in the experimental systems available for pertinent studies compared with native human skin has become crucial. This review collects available information of which—taken with great caution because of the still very limited data—the most salient points are: in the skin of all animal species and skin-derived in vitro systems considered in this review cytochrome P450 (CYP)-dependent monooxygenase activities (largely responsible for initiating xenobiotica metabolism in the organ which provides most of the xenobiotica metabolism of the mammalian organism, the liver) are very low to undetectable. Quite likely other oxidative enzymes [e.g. flavin monooxygenase, COX (cooxidation by prostaglandin synthase)] will turn out to be much more important for the oxidative xenobiotic metabolism in the skin. Moreover, conjugating enzyme activities such as glutathione transferases and glucuronosyltransferases are much higher than the oxidative CYP activities. Since these conjugating enzymes are predominantly detoxifying, the skin appears to be predominantly protected against CYP-generated reactive metabolites. The following recommendations for the use of experimental animal species or human skin in vitro models may tentatively be derived from the information available to date: for dermal absorption and for skin irritation esterase activity is of special importance which in pig skin, some human cell lines and reconstructed skin models appears reasonably close to native human skin. With respect to genotoxicity and sensitization reactive-metabolite-reducing XME in primary human keratinocytes and several reconstructed human skin models appear reasonably close to human skin. For a more detailed delineation and discussion of the severe limitations see the Conclusions section in the end of this review.

Retrospective analysis of estrogen receptor 1 and N‑acetyltransferase gene expression in normal breast tissue, primary breast tumors, and established breast cancer cell lines

The expression levels of estrogen receptor 1 (ESR1), arylamine N‑acetyltransferase 1 (NAT1), and arylamine N‑acetyltransferase 2 (NAT2) are implicated in breast cancer; however, their co-expression profiles in normal breast tissue, primary breast tumors and established breast cancer cell lines are undefined. NAT1 expression is widely reported to be associated with ESR1 expression and is frequently investigated in breast cancer etiology. Furthermore, the NAT2 phenotype has been reported to modify breast cancer risk in molecular epidemiological association studies. Understanding the relationships between the expression levels of these genes is essential to understand their role in breast cancer etiology and treatment. In the present study, NAT1, NAT2 and ESR1 expression data were accessed from repositories of RNA‑Seq data covering 57 breast cancer cell lines, 1,043 primary breast tumors and 99 normal breast tissues. The relationships between gene expression, and between NAT1 activity and RNA expression in breast cancer cell lines were evaluated using non-parametric statistical analyses. Differences in gene expression in each dataset, as well as gene expression differences in normal breast tissue compared to primary breast tumors, and stratification by estrogen receptor status were determined. NAT1 and NAT2 mRNA expression were detected in normal and primary breast tumor tissues; NAT1 expression was much higher than NAT2. NAT1 and ESR1 expression were strongly associated, whereas NAT2 and ESR1 expression were not. Although NAT1 and NAT2 expression were associated, the magnitude was moderate. NAT1, NAT2, and ESR1 expression were increased in primary breast tumor tissue compared with normal breast tissue; however, the magnitude and significance of the differences were lower for NAT2. Analysis of NAT1, NAT2, and ESR1 expression in normal and primary breast tissues and breast cancer cell lines suggested that NAT1 and NAT2 expression are regulated by distinctive mechanisms, whereas NAT1 and ESR1 expression may have overlapping regulation. Defining these relationships is important for future investigations into breast cancer prevention.

A framework and case studies for evaluation of enzyme ontogeny in children's health risk evaluation

Knowledge of the ontogeny of Phase I and Phase II metabolizing enzymes may be used to inform children's vulnerability based upon likely differences in internal dose from xenobiotic exposure. This might provide a qualitative assessment of toxicokinetic (TK) variability and uncertainty pertinent to early lifestages and help scope a more quantitative physiologically based toxicokinetic (PBTK) assessment. Although much is known regarding the ontogeny of metabolizing systems, this is not commonly utilized in scoping and problem formulation stage of human health risk evaluation. A framework is proposed for introducing this information into problem formulation which combines data on enzyme ontogeny and chemical-specific TK to explore potential child/adult differences in internal dose and whether such metabolic differences may be important factors in risk evaluation. The framework is illustrated with five case study chemicals, including some which are data rich and provide proof of concept, while others are data poor. Case studies for toluene and chlorpyrifos indicate potentially important child/adult TK differences while scoping for acetaminophen suggests enzyme ontogeny is unlikely to increase early-life risks. Scoping for trichloroethylene and aromatic amines indicates numerous ways that enzyme ontogeny may affect internal dose which necessitates further evaluation. PBTK modeling is a critical and feasible next step to further evaluate child-adult differences in internal dose for a number of these chemicals.

Catalytic properties and heat stabilities of novel recombinant human N-acetyltransferase 2 allozymes support existence of genetic heterogeneity within the slow acetylator phenotype

Human N-acetyltransferase 2 (NAT2) catalyzes the N-acetylation of numerous aromatic amine drugs such as sulfamethazine (SMZ) and hydrazine drugs such as isoniazid (INH). NAT2 also catalyzes the N-acetylation of aromatic amine carcinogens such as 2-aminofluorene and the O- and N,O-acetylation of aromatic amine and heterocyclic amine metabolites. Genetic polymorphism in NAT2 modifies drug efficacy and toxicity as well as cancer risk. Acetyltransferase catalytic activities and heat stability associated with six novel NAT2 haplotypes (NAT2*6C, NAT2*14C, NAT2*14D, NAT2*14E, NAT2*17, and NAT2*18) were compared with that of the reference NAT2*4 haplotype following recombinant expression in Escherichia coli. N-acetyltransferase activities towards SMZ and INH were significantly (p < 0.0001) lower when catalyzed by the novel recombinant human NAT2 allozymes compared to NAT2 4. SMZ and INH N-acetyltransferase activities catalyzed by NAT2 14C and NAT2 14D were significantly lower (p < 0.001) than catalyzed by NAT2 6C and NAT2 14E. N-Acetylation catalyzed by recombinant human NAT2 17 was over several hundred-fold lower than by recombinant NAT2 4 precluding measurement of its kinetic or heat inactivation constants. Similar results were observed for the O-acetylation of N-hydroxy-2-aminofluorene and N-hydroxy-2-amino-1-methyl-6-phenylimidazo [4,5-b] pyridine and the intramolecular N,O-acetylation of N-hydroxy-N-acetyl-2-aminofluorene. The apparent V _max of the novel recombinant NAT2 allozymes NAT2 6C, NAT2 14C, NAT2 14D, and NAT2 14E towards AF, 4-aminobiphenyl (ABP), and 3,2'-dimethyl-4-aminobiphenyl (DMABP) were each significantly (p < 0.001) lower while their apparent K _m values did not differ significantly (p > 0.05) from recombinant NAT2 4. The apparent V _max catalyzed by NAT2 14C and NAT2 14D were significantly lower (p < 0.05) than the apparent V _max catalyzed by NAT2 6C and NAT2 14E towards AF, ABP, and DMABP. Heat inactivation rate constants for recombinant human NAT2 14C, 14D, 14E, and 18 were significantly (p < 0.05) higher than NAT2 4. These results provide further evidence of genetic heterogeneity within the NAT2 slow acetylator phenotype.

Role of the N-acetylation polymorphism in solithromycin metabolism

AIM

Solithromycin is a new macrolide antibiotic for the potential treatment of bacterial pneumonia.

MATERIALS & METHODS

Solithromycin N-acetylation by human NAT1 and NAT2 was investigated following recombinant expression in yeast and in cryopreserved human hepatocytes from rapid, intermediate and slow acetylators.

RESULTS

Solithromycin exhibited over twofold higher affinity for recombinant human NAT2 than NAT1. Apparent maximum velocities for the N-acetylation of solithromycin catalyzed by the NAT2 allozyme associated with rapid acetylators were significantly (p < 0.01) higher than by the NAT2 allozymes associated with slow acetylators. Robust gene dose responses (rapid>intermediate>slow acetylators) were exhibited in cryopreserved human hepatocytes in situ following incubation with 100 μM solithromycin.

CONCLUSION

Solithromycin is N-acetylated by human NAT1 and NAT2 and the role of the NAT2 acetylation polymorphism on solithromycin metabolism may be concentration dependent.

Determining the Potential of Aromatic Amines to Induce Cancer of the Urinary Bladder

Aromatic amines have been associated with the induction of cancer of the urinary bladder. Commercial production started over 100 years ago in Europe, with the synthesis of a mauve pigment from aniline. The discovery of other pigments by combining aniline with various chemicals initiated the aniline dye industry. By the turn of the century, a correlation between working in the dyestuff industry and the development of bladder cancer was established. Initially thought to be the result of exposure to aniline, various investigators identified benzidine, beta-naphthylamine, and 4-aminobipheny 1 as the causative agents. Evaluations of various aromatic amines in rats, mice, guinea pigs, rabbits, dogs, and monkeys showed significant species differences, with the dog and monkey being the most sensitive species. Several laboratories related these species differences to differences in the respective routes by which the various species metabolized aromatic amines. Excellent correspondence was shown between metabolic activation of benzidine, 4-aminobiphenyl, and beta-naphthylamine in dogs and primates and the induction of bladder cancer. Rodents were shown to be unresponsive to human bladder carcinogens. The need to use data developed in the most sensitive species, the dog, is essential to accurately predict the carcinogenic potential of aromatic amines.

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.

N-Acetyltransferase 2 (NAT2) polymorphism as a risk modifier of susceptibility to pediatric acute lymphoblastic leukemia

N-Acetyltransferases (NAT) have been known to modify the risk to a variety of solid tumors. However, the role of NAT2 polymorphism in risk susceptibility to childhood acute lymphoblastic leukemia (ALL) is still not well known. We performed a case-control study to determine if the common NAT2 polymorphisms play a role in altering susceptibility to pediatric ALL. DNA of 92 pediatric ALL patients and 312 healthy controls was analyzed for the NAT2 polymorphisms using the PCR-RFLP method. The wild-type NAT2*4 was encountered in 8.6 % of patients versus 11.8 % of controls (P = 0.23). The rapid acetylators NAT2*12 803A>G, AG, GG, and AG/GG were overrepresented in controls (P = 0.0001; odds ratio (OR) 0.22, 0.19, and 0.21 respectively). NAT2*5D 341T>C and NAT2*11A 481C>T were of comparable frequencies. For their combination, NAT2*5A, a slow acetylator, both TCTT and CCCT were overrepresented in patients (P < 0.001; OR 15.8 and 17.9 respectively). NAT2*5B (803A>G, 341T>C, 481C>T) was overrepresented in controls (P < 0.001; OR 0.12). Apparently, 803A>G ameliorated the combined effect of 341T>C and 481C>T. A similar effect was obtained with NAT2*5C (341T>A, 803A>G) (P < 0.0001; OR 0.11). For slow acetylator NAT2*7A 857G>A, GA and GA/AA were overrepresented in patients (P = 0.009 and 0.01; OR 2.74 and 2.72 respectively). NAT2*13 282C>T, NAT2*6B 590G>A, and NAT2*14A 191G>A were of comparable frequencies. NAT2 282C>A in combination with NAT2 857G>A (NAT2*7B) showed a synergistic effect in patients versus controls (P < 0.0001; OR 3.51). In conclusion, NAT2 gene polymorphism(s) with slow acetylator phenotype is generally associated with the risk of development of ALL in children.

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.

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.

Xenobiotic-metabolizing enzymes in the skin of rat, mouse, pig, guinea pig, man, and in human skin models

The exposure of the skin to medical drugs, skin care products, cosmetics, and other chemicals renders information on xenobiotic-metabolizing enzymes (XME) in the skin highly interesting. Since the use of freshly excised human skin for experimental investigations meets with ethical and practical limitations, information on XME in models comes in the focus including non-human mammalian species and in vitro skin models. This review attempts to summarize the information available in the open scientific literature on XME in the skin of human, rat, mouse, guinea pig, and pig as well as human primary skin cells, human cell lines, and reconstructed human skin models. The most salient outcome is that much more research on cutaneous XME is needed for solid metabolism-dependent efficacy and safety predictions, and the cutaneous metabolism comparisons have to be viewed with caution. Keeping this fully in mind at least with respect to some cutaneous XME, some models may tentatively be considered to approximate reasonable closeness to human skin. For dermal absorption and for skin irritation among many contributing XME, esterase activity is of special importance, which in pig skin, some human cell lines, and reconstructed skin models appears reasonably close to human skin. With respect to genotoxicity and sensitization, activating XME are not yet judgeable, but reactive metabolite-reducing XME in primary human keratinocytes and several reconstructed human skin models appear reasonably close to human skin. For a more detailed delineation and discussion of the severe limitations see the “Overview and Conclusions” section in the end of this review.

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.

Polymorphism p.Val231Ile alters substrate selectivity of drug-metabolizing arylamine N-acetyltransferase 2 (NAT2) isoenzyme of rhesus macaque and human

Arylamine N-acetyltransferases (NATs) are polymorphic enzymes mediating the biotransformation of arylamine/arylhydrazine xenobiotics, including pharmaceuticals and environmental carcinogens. The NAT1 and NAT2 genes, and their many polymorphic variants, have been thoroughly studied in humans by pharmacogeneticists and cancer epidemiologists. However, little is known about the function of NAT homologues in other primate species, including disease models. Here, we perform a comparative functional investigation of the NAT2 homologues of the rhesus macaque and human. We further dissect the functional impact of a previously described rhesus NAT2 gene polymorphism, causing substitution of valine by isoleucine at amino acid position 231. Gene constructs of rhesus and human NAT2, bearing or lacking non-synonymous polymorphism c.691G>A (p.Val231Ile), were expressed in Escherichia coli for comparative enzymatic analysis against various NAT1- and NAT2-selective substrates. The results suggest that the p.Val231Ile polymorphism does not compromise the stability or overall enzymatic activity of NAT2. However, substitution of Val231 by the bulkier isoleucine appears to alter enzyme substrate selectivity by decreasing the affinity towards NAT2 substrates and increasing the affinity towards NAT1 substrates. The experimental observations are supported by in silico modelling localizing polymorphic residue 231 close to amino acid loop 125-129, which forms part of the substrate binding pocket wall and determines the substrate binding preferences of the NAT isoenzymes. The p.Val231Ile polymorphism is the first natural polymorphism demonstrated to affect NAT substrate selectivity via this particular mechanism. The study is also the first to thoroughly characterize the properties of a polymorphic NAT isoenzyme in a non-human primate model.

Xenobiotic metabolism capacities of human skin in comparison with a 3D-epidermis model and keratinocyte-based cell culture as in vitro alternatives for chemical testing: phase II enzymes

The 7th Amendment to the EU Cosmetics Directive prohibits the use of animals in cosmetic testing for certain endpoints, such as genotoxicity. Therefore, skin in vitro models have to replace chemical testing in vivo. However, the metabolic competence neither of human skin nor of alternative in vitro models has so far been fully characterized, although skin is the first-pass organ for accidentally or purposely (cosmetics and pharmaceuticals) applied chemicals. Thus, there is an urgent need to understand the xenobiotic-metabolizing capacities of human skin and to compare these activities to models developed to replace animal testing. We have measured the activity of the phase II enzymes glutathione S-transferase, UDP-glucuronosyltransferase and N-acetyltransferase in ex vivo human skin, the 3D epidermal model EpiDerm 200 (EPI-200), immortalized keratinocyte-based cell lines (HaCaT and NCTC 2544) and primary normal human epidermal keratinocytes. We show that all three phase II enzymes are present and highly active in skin as compared to phase I. Human skin, therefore, represents a more detoxifying than activating organ. This work systematically compares the activities of three important phase II enzymes in four different in vitro models directly to human skin. We conclude from our studies that 3D epidermal models, like the EPI-200 employed here, are superior over monolayer cultures in mimicking human skin xenobiotic metabolism and thus better suited for dermatotoxicity testing.

Genetic polymorphism of NAT2 metabolizing enzymes on phenytoin pharmacokinetics in Indian epileptic patients developing toxicity

OBJECTIVE

To investigate the effects of NAT2 metabolizing enzymes on the pharmacokinetics of antiepileptic drug phenytoin in the epileptic patients showing toxicity.

METHODS

Fifty epileptic individuals who had developed toxicity to phenytoin and 50 control epileptic subjects who had not developed toxicity to phenytoin were genotyped for NAT2 (NAT2*5A, NAT2*5C, NAT2*7, NAT2*6) polymorphisms by polymerase chain reaction-restriction fragment length polymorphisms (PCR-RFLP method). Phenytoin plasma levels were analyzed by reversed phase HPLC method and pharmacokinetic parameters such as area under the concentration curve (AUC), maximum concentration (C(max)), time to C(max) (t(max)) and half-life (t(1/2)) were estimated by noncompartmental analysis using PK Solutions® software.

RESULTS

The NAT2 polymorphism was seen to be in Hardy-Weinberg equilibrium and showed significant genotypic as well as allelic association with phenytoin toxicity for NAT2*5A (481C>T) and NAT2*5C (803A>G). Pharmacokinetic parameters for phenytoin in toxicity group of poor metabolizers showed a longer elimination half-life of a drug (t(1/2) = 35.3 h) and less clearance rate (CL = 468 mL/h) compared to intermediate metabolizers (t(1/2) = 33.2 h, CL = 674 mL/h) and extensive metabolizer (t(1/2) = 20.7 h, CL = 977 mL/h) in NAT2*5A polymorphism.

CONCLUSION

Our findings suggest that the NAT2*5A genetic polymorphisms plays a significant role in the steady-state concentrations of phenytoin and thereby have impact on toxicity in epileptic patients.

Accuracy of various human NAT2 SNP genotyping panels to infer rapid, intermediate and slow acetylator phenotypes

AIM

Humans exhibit genetic polymorphism in NAT2 resulting in rapid, intermediate and slow acetylator phenotypes. Over 65 NAT2 variants possessing one or more SNPs in the 870-bp NAT2 coding region have been reported. The seven most frequent SNPs are rs1801279 (191G>A), rs1041983 (282C>T), rs1801280 (341T>C), rs1799929 (481C>T), rs1799930 (590G>A), rs1208 (803A>G) and rs1799931 (857G>A). The majority of studies investigate the NAT2 genotype assay for three SNPs: 481C>T, 590G>A and 857G>A. A tag-SNP (rs1495741) recently identified in a genome-wide association study has also been proposed as a biomarker for the NAT2 phenotype.

MATERIALS & METHODS

Sulfamethazine N-acetyltransferase catalytic activities were measured in cryopreserved human hepatocytes from a convenience sample of individuals in the USA with an ethnic frequency similar to the 2010 US population census. These activities were segregated by the tag-SNP rs1495741 and each of the seven SNPs described above. We assessed the accuracy of the tag-SNP and various two-, three-, four- and seven-SNP genotyping panels for their ability to accurately infer NAT2 phenotype.

RESULTS

The accuracy of the various NAT2 SNP genotype panels to infer NAT2 phenotype were as follows: seven-SNP: 98.4%; tag-SNP: 77.7%; two-SNP: 96.1%; three-SNP: 92.2%; and four-SNP: 98.4%.

CONCLUSION

A NAT2 four-SNP genotype panel of rs1801279 (191G>A), rs1801280 (341T>C), rs1799930 (590G>A) and rs1799931 (857G>A) infers NAT2 acetylator phenotype with high accuracy, and is recommended over the tag-, two-, three- and (for economy of scale) the seven-SNP genotyping panels, particularly in populations of non-European ancestry.

Effects of single nucleotide polymorphisms on human N-acetyltransferase 2 structure and dynamics by molecular dynamics simulation

Background

Arylamine N-acetyltransferase 2 (NAT2) is an important catalytic enzyme that metabolizes the carcinogenic arylamines, hydrazine drugs and chemicals. This enzyme is highly polymorphic in different human populations. Several polymorphisms of NAT2, including the single amino acid substitutions R64Q, I114T, D122N, L137F, Q145P, R197Q, and G286E, are classified as slow acetylators, whereas the wild-type NAT2 is classified as a fast acetylator. The slow acetylators are often associated with drug toxicity and efficacy as well as cancer susceptibility. The biological functions of these 7 mutations have previously been characterized, but the structural basis behind the reduced catalytic activity and reduced protein level is not clear.

Methodology/Principal Findings

We performed multiple molecular dynamics simulations of these mutants as well as NAT2 to investigate the structural and dynamical effects throughout the protein structure, specifically the catalytic triad, cofactor binding site, and the substrate binding pocket. None of these mutations induced unfolding; instead, their effects were confined to the inter-domain, domain 3 and 17-residue insert region, where the flexibility was significantly reduced relative to the wild-type. Structural effects of these mutations propagate through space and cause a change in catalytic triad conformation, cofactor binding site, substrate binding pocket size/shape and electrostatic potential.

Conclusions/Significance

Our results showed that the dynamical properties of all the mutant structures, especially in inter-domain, domain 3 and 17-residue insert region were affected in the same manner. Similarly, the electrostatic potential of all the mutants were altered and also the functionally important regions such as catalytic triad, cofactor binding site, and substrate binding pocket adopted different orientation and/or conformation relative to the wild-type that may affect the functions of the mutants. Overall, our study may provide the structural basis for reduced catalytic activity and protein level, as was experimentally observed for these polymorphisms.

Functional effects of genetic polymorphisms in the N-acetyltransferase 1 coding and 3' untranslated regions

BACKGROUND

The functional effects of N-acetyltransferase 1 (NAT1) polymorphisms and haplotypes are poorly understood, compromising the validity of associations reported with diseases, including birth defects and numerous cancers.

METHODS

We investigated the effects of genetic polymorphisms within the NAT1 coding region and the 3'-untranslated region (3'-UTR) and their associated haplotypes on N- and O-acetyltransferase catalytic activities, and NAT1 mRNA and protein levels following recombinant expression in COS-1 cells.

RESULTS

1088T>A (rs1057126; 3'-UTR) and 1095C>A (rs15561; 3'-UTR) each slightly reduced NAT1 catalytic activity and NAT1 mRNA and protein levels. A 9-bp (TAATAATAA) deletion between nucleotides 1065 and 1090 (3'-UTR) reduced NAT1 catalytic activity and NAT1 mRNA and protein levels. In contrast, a 445G>A (rs4987076; V149I), 459G>A (rs4986990; T153T), and 640T>G (rs4986783; S214A) coding region haplotype present in NAT1*11 increased NAT1 catalytic activity and NAT1 protein, but not NAT1 mRNA levels. A combination of the 9-bp (TAATAATAA) deletion and the 445G>A, 459G>A, and 640T>G coding region haplotypes, both present in NAT1*11, appeared to neutralize the opposing effects on NAT1 protein and catalytic activity, resulting in levels of NAT1 protein and catalytic activity that did not differ significantly from the NAT1*4 reference.

CONCLUSIONS

Because 1095C>A (3'-UTR) is the sole polymorphism present in NAT1*3, our data suggest that NAT1*3 is not functionally equivalent to the NAT1*4 reference. Furthermore, our findings provide biologic support for reported associations of 1088T>A and 1095C>A polymorphisms with birth defects.

Gene-diet interaction on cancer risk in epidemiological studies

Genetic factors clearly play a role in carcinogenesis, but migrant studies provide unequivocal evidence that environmental factors are critical in defining cancer risk. Therefore, one may expect that the lower availability of substrate for biochemical reactions leads to more genetic changes in enzyme function; for example, most studies have indicated the variant MTHFR genotype 677TT is related to biomarkers, such as homocysteine concentrations or global DNA methylation particularly in a low folate diet. The modification of a phenotype related to a genotype, particularly by dietary habits, could support the notion that some of inconsistencies in findings from molecular epidemiologic studies could be due to differences in the populations studied and unaccounted underlying characteristics mediating the relationship between genetic polymorphisms and the actual phenotypes. Given the evidence that diet can modify cancer risk, gene-diet interactions in cancer etiology would be anticipated. However, much of the evidence in this area comes from observational epidemiology, which limits the causal inference. Thus, the investigation of these interactions is essential to gain a full understanding of the impact of genetic variation on health outcomes. This report reviews current approaches to gene-diet interactions in epidemiological studies. Characteristics of gene and dietary factors are divided into four categories: one carbon metabolism-related gene polymorphisms and dietary factors including folate, vitamin B group and methionines; oxidative stress-related gene polymorphisms and antioxidant nutrients including vegetable and fruit intake; carcinogen-metabolizing gene polymorphisms and meat intake including heterocyclic amins and polycyclic aromatic hydrocarbon; and other gene-diet interactive effect on cancer.

Polymorphisms in NAT2 gene and atherosclerosis in an Algerian population

BACKGROUND AND AIMS

The etiology of atherosclerosis is multifactorial. Genetic and environmental factors are involved in the development of atherosclerosis. Human arylamine N-acetyltransferase 2 (NAT2) is an important metabolizing enzyme that exhibits genetic polymorphisms and modifies individual response and/or toxicity to many xenobiotics. We undertook this study to investigate the NAT2 polymorphisms in patients with atherosclerosis.

METHODS

Genotyping for NAT2 alleles was performed using polymerase chain reaction-restriction fragment-length polymorphism (PCR-RFLP) in 285 Algerian patients with atherosclerosis and 286 controls.

RESULTS

There was no association between NAT2 polymorphisms and atherosclerosis risk. However, the haplotype NAT2(*)5F decreased susceptibility to the disease (p = 0.005, OR = 0.55, 95% CI = 0.37-0.84). The frequency of the slow acetylator phenotype was approximately 50% in both cases and controls.

CONCLUSIONS

These results suggest that NAT2 polymorphisms may not be involved in the pathogenesis of atherosclerosis.

Caffeine, selected metabolic gene variants, and risk for neural tube defects

BACKGROUND

Investigations of maternal caffeine intake and neural tube defects (NTDs) have not considered genetic influences. Caffeine metabolism gene effects were examined in the National Birth Defects Prevention Study.

METHODS

Average daily caffeine was summed from self-reported coffee, tea, soda, and chocolate intake for mothers of 768 NTD cases, and 4143 controls delivered from 1997 to 2002. A subset of 306 NTD and 669 control infants and their parents were genotyped for CYP1A2*1F, NAT2 481C>T, and NAT2 590G>A. CYP1A2*1F was classified by fast or slow oxidation status, and NAT2 variants were categorized into rapid or slow acetylation status. Case-control logistic regression analyses, family-based transmission/disequilibrium tests and log-linear analyses, and hybrid log-linear analyses were conducted to produce odds ratios (ORs) or relative risks (RRs) and 95% confidence intervals (CIs) for caffeine intake and maternal and infant gene variants, and to examine interaction effects.

RESULTS

NTDs were independently associated with infant slow NAT2 acetylator status (RR, 2.00; 95% CI, 1.10-3.64) and maternal CYP1A2*1F fast oxidation status (OR, 1.49; 95% CI, 1.10-2.03). Mothers who consumed caffeine, oxidized CYP1A2*1F quickly, and acetylized NAT2 slowly had a nonsignificantly elevated estimated risk for an NTD-affected pregnancy (OR, 3.10; 95% CI, 0.86-11.21). Multiplicative interaction effects were observed between maternal caffeine and infant CYP1A2*1F fast oxidizer status (p(interaction) = 0.03).

CONCLUSIONS

The association identified between maternal CYP1A2*1F fast oxidation status and NTDs should be examined further in the context of the other substrates of CYP1A2. Maternal caffeine and its metabolites may be associated with increased risk for NTD-affected pregnancies in genetically susceptible subgroups.

N-acetyltransferase SNPs: emerging concepts serve as a paradigm for understanding complexities of personalized medicine

Arylamine N-acetyltransferase 1 and 2 exhibit single nucleotide polymorphisms in human populations that modify drug and carcinogen metabolism. This paper updates the identity, location and functional effects of these single nucleotide polymorphisms and then follows with emerging concepts for understanding why pharmacogenetic findings may not be replicated consistently. Using this paradigm as an example, laboratory-based mechanistic analyses can reveal complexities such that genetic polymorphisms become biologically and medically relevant when confounding factors are more fully understood and considered. As medical care moves to a more personalized approach, the implications of these confounding factors will be important in understanding the complexities of personalized medicine.

Para-phenylenediamine and allergic sensitization: risk modification by N-acetyltransferase 1 and 2 genotypes

BACKGROUND

Para-phenylenediamine (PPD) is a common contact sensitizer causing allergic contact dermatitis, a major skin problem. As PPD may need activation to become immunogenic, the balance between activation and/or detoxification processes may influence an individual's susceptibility. PPD is acetylated and the metabolites do not activate dendritic-like cells and T cells of PPD-sensitized individuals.

OBJECTIVES

To investigate whether PPD can be acetylated in vitro by the two N-acetyltransferases 1 (NAT1) and 2 (NAT2). Based on the assumption that N-acetylation by NAT1 or NAT2 is a detoxification reaction with respect to sensitization, we examined whether NAT1 and NAT2 genotypes are different between PPD-sensitized individuals and matched controls.

METHODS

Genotyping for NAT1 and NAT2 polymorphisms was performed in 147 PPD-sensitized individuals and 200 age- and gender-matched controls. Results Both PPD and monoacetyl-PPD were N-acetylated in vitro by recombinant human NAT1 and to a lesser extent by NAT2. Genotyping for NAT1*3, NAT1*4, NAT1*10, NAT1*11 and NAT1*14 showed that genotypes containing the rapid acetylator NAT1*10 allele were under-represented in PPD-sensitized cases (adjusted odds ratio 0.72, 95% confidence interval 0.45-1.16). For NAT2, NAT2*4, NAT2*5AB, NAT2*5C, NAT2*6A and NAT2*7B alleles were genotyped. Individuals homozygous for the rapid acetylator allele NAT2*4 were under-represented in cases compared with controls (4.3% vs. 9.4%), but this trend was not significant.

CONCLUSIONS

With respect to data indicating that NAT1 but not NAT2 is present in human skin, we conclude that NAT1 genotypes containing the rapid acetylator NAT1*10 allele are potentially associated with reduced susceptibility to PPD sensitization.

Association of Genetic Polymorphisms ofN-Acetyltransferase 2 and Susceptibility to Esophageal Cancer in North Indian Population

Esophageal cancer is multifactorial disease involving environmental and genetic risk factors. Tobacco smoke and alcohol are strong environmental risk factors. N-acetyltransferase 2 (NAT2) is known to metabolize heterocyclic amine carcinogens in tobacco smoke. The purpose of this study was to determine whether genetic polymorphism in the NAT2 and their interaction with environmental factors influence the susceptibility for esophageal cancer. For our study, 126 patients and 164 controls were genotyped for NAT2 2 * 5, 2 * 6 and 2 * 7 polymorphisms using PCR-RFLP method. In a case-control study, NAT2 slow acetylator genotype was not significantly associated with risk of esophageal cancer (OR 1.3, 95%CI = 0.78-2.2, P = 0.28). There was significant linkage disequilibrium between 2 * 5-2 * 6 and 2 * 5-2*7 (P < 0.05). Using expectation maximization algorithm, 6 haplotypes were obtained but none of them revealed any significant contribution to disease susceptibility. In case only analysis, the smokers with rapid acetylator were at slightly higher risk of esophageal cancer (OR 1.3, 95%CI = 0.62-3.0, P = 0.43) which was not statistically significant. NAT2 slow or fast genotypes did not affect the risk of esophageal cancer in patients with alcohol consumption or occupational exposure. These results suggest that NAT2 acetylator genotypes did not influence the susceptibility to esophageal cancer. NAT2 polymorphism did not significantly modulate the cancer risk after interaction with environmental factors like tobacco, alcohol or occupational exposure.