Structural Analysis of the Genes for Human Arylamine N-Acetyltransferases and Characterisation of Alternative Transcripts

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.

Precision Medicine Strategies to Improve Isoniazid Therapy in Patients with Tuberculosis

Due to interindividual variability in drug metabolism and pharmacokinetics, traditional isoniazid fixed-dose regimens may lead to suboptimal or toxic isoniazid concentrations in the plasma of patients with tuberculosis, contributing to adverse drug reactions, therapeutic failure, or the development of drug resistance. Achieving precision therapy for isoniazid requires a multifaceted approach that could integrate various clinical and genomic factors to tailor the isoniazid dose to individual patient characteristics. This includes leveraging molecular diagnostics to perform the comprehensive profiling of host pharmacogenomics to determine how it affects isoniazid metabolism, such as its metabolism by N-acetyltransferase 2 (NAT2), and studying drug-resistant mutations in the Mycobacterium tuberculosis genome for enabling targeted therapy selection. Several other molecular signatures identified from the host pharmacogenomics as well as other omics-based approaches such as gut microbiome, epigenomic, proteomic, metabolomic, and lipidomic approaches have provided mechanistic explanations for isoniazid pharmacokinetic variability and/or adverse drug reactions and thereby may facilitate precision therapy of isoniazid, though further validations in larger and diverse populations with tuberculosis are required for clinical applications. Therapeutic drug monitoring and population pharmacokinetic approaches allow for the adjustment of isoniazid dosages based on patient-specific pharmacokinetic profiles, optimizing drug exposure while minimizing toxicity and the risk of resistance. Current evidence has shown that with the integration of the host pharmacogenomics-particularly NAT2 and Mycobacterium tuberculosis genomics data along with isoniazid pharmacokinetic concentrations in the blood and patient factors such as anthropometric measurements, comorbidities, and type and timing of food administered-precision therapy approaches in isoniazid therapy can be tailored to the specific characteristics of both the host and the pathogen for improving tuberculosis treatment outcomes.

Genetic Variants and Drug Efficacy in Tuberculosis: A Step toward Personalized Therapy

Tuberculosis (TB) continues to be a major infectious disease affecting individuals worldwide. Current TB treatment strategy recommends the standard short-course chemotherapy regimen containing first-line drug, i.e., isoniazid, rifampicin, pyrazinamide, and ethambutol to treat patients suffering from drug-susceptible TB. Although Mycobacterium tuberculosis, the causing agent, is susceptible to drugs, some patients do not respond to the treatment or treatment may result in serious adverse reactions. Many studies revealed that anti-TB drug-related toxicity is associated with genetic variations, and these variations may also influence attaining maximum drug concentration. Thus, inter-individual diversities play a characteristic role by influencing the genes involved in drug metabolism pathways. The development of pharmacogenomics could bring a revolution in the field of treatment, and the understanding of germline variants may give rise to optimized targeted treatments and refine the response to standard therapy. In this review, we briefly introduced the field of pharmacogenomics with the evolution in genetics and discussed the pharmacogenetic impact of genetic variations on genes involved in the activities, such as anti-TB drug transportation, metabolism, and gene regulation.

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.

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.

Dietary effects of Sideritis scardica "mountain tea" on human in vivo activities of xenobiotic metabolizing enzymes in healthy subjects

Sideritis scardica(S. scardica) is an endemic plant of the Balkan Peninsula traditionally used as herbal tea for inflammation and gastric disorders. Aqueous herbal extracts may affect the activity of Phase I and II enzymes involved in xenobiotic metabolism. The purpose of the present study was to determine whether S. scardica decoction alters the activity of CYP1A2, CYP2A6, XO, NAT2 and UGT1A1/1A6 enzymes in humans. Fourteen healthy subjects consumed S. scardica decoction for six days. Enzyme phenotyping was assessed in saliva and urine using caffeine and paracetamol metabolite ratios as follows: CYP1A2: 17X/137X (saliva) and (AFMU+1U+1X)/17U, CYP2A6: 17U/(17U + 17X), XO: 1U/(1U+1X), NAT2: AFMU/(AFMU+1U+1X) and UGT1A1/1A6: glucuronidated/total paracetamol (urine). After S. scardica intake, CYP1A2 index was reduced by ∼16% and ∼8% in saliva (before: 0.54 ± 0.18, after: 0.46 ± 0.09; p = 0.08) and urine (before: 3.59 ± 0.52, after: 3.67 ± 0.78; p = 0.12), respectively. CYP2A6 index was significantly reduced only in males (before: 0.76 ± 0.08, after: 0.67 ± 0.07; p = 0.004), suggesting sexual dimorphism in CYP2A6 inhibition. There was no effect of Sideritis scardica treatment on XO, NAT2 or UGT1A1/1A6 indices. Usual consumption of the aerial parts of S. scardica decoction is unlikely to result in herb-drug interactions involving the enzymes studied, with the exception of potential herb-CYP2A6 substrate interaction in males.

Comparative analysis of xenobiotic metabolising N-acetyltransferases from ten non-human primates as in vitro models of human homologues

Xenobiotic metabolising N-acetyltransferases (NATs) perform biotransformation of drugs and carcinogens. Human NAT1 is associated with endogenous metabolic pathways of cells and is a candidate drug target for cancer. Human NAT2 is a well-characterised polymorphic xenobiotic metabolising enzyme, modulating susceptibility to drug-induced toxicity. Human NATs are difficult to express to high purification yields, complicating large-scale production for high-throughput screens or use in sophisticated enzymology assays and crystallography. We undertake comparative functional investigation of the NAT homologues of ten non-human primates, to characterise their properties and evaluate their suitability as models of human NATs. Considering the amount of generated recombinant protein, the enzymatic activity and thermal stability, the NAT homologues of non-human primates are demonstrated to be a much more effective resource for in vitro studies compared with human NATs. Certain NAT homologues are proposed as better models, such as the NAT1 of macaques Macaca mulatta and M. sylvanus, the NAT2 of Erythrocebus patas, and both NAT proteins of the gibbon Nomascus gabriellae which show highest homology to human NATs. This comparative investigation will facilitate in vitro screens towards discovery and optimisation of candidate pharmaceutical compounds for human NAT isoenzymes, while enabling better understanding of NAT function and evolution in primates.

Oral anti-diabetic agents for women with established diabetes/impaired glucose tolerance or previous gestational diabetes planning pregnancy, or pregnant women with pre-existing diabetes

BACKGROUND

While most guidance recommends the use of insulin in women whose pregnancies are affected by pre-existing diabetes, oral anti-diabetic agents may be more acceptable to women. The effects of these oral anti-diabetic agents on maternal and infant health outcomes need to be established in pregnant women with pre-existing diabetes or impaired glucose tolerance, as well as in women with previous gestational diabetes mellitus preconceptionally or during a subsequent pregnancy. This review is an update of a review that was first published in 2010.

OBJECTIVES

To investigate the effects of oral anti-diabetic agents in women with established diabetes, impaired glucose tolerance or previous gestational diabetes who are planning a pregnancy, or pregnant women with pre-existing diabetes, on maternal and infant health. The use of oral anti-diabetic agents for the management of gestational diabetes in a current pregnancy is evaluated in a separate Cochrane Review.

SEARCH METHODS

We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (31 October 2016) and reference lists of retrieved studies.

SELECTION CRITERIA

Randomised controlled trials (RCTs) and quasi-RCTs assessing the effects of oral anti-diabetic agents in women with established diabetes, impaired glucose tolerance or previous gestational diabetes who were planning a pregnancy, or pregnant women with pre-existing diabetes. Cluster-RCTs were eligible for inclusion, but none were identified.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed study eligibility, extracted data and assessed the risk of bias of the included RCTs. Review authors checked the data for accuracy, and assessed the quality of the evidence using the GRADE approach.

MAIN RESULTS

We identified six RCTs (707 women), eligible for inclusion in this updated review, however, three RCTs had mixed populations (that is, they included pregnant women with gestational diabetes) and did not report data separately for the relevant subset of women for this review. Therefore we have only included outcome data from three RCTs; data were available for 241 women and their infants. The three RCTs all compared an oral anti-diabetic agent (metformin) with insulin. The women in the RCTs that contributed data had type 2 diabetes diagnosed before or during their pregnancy. Overall, the RCTs were judged to be at varying risk of bias. We assessed the quality of the evidence for selected important outcomes using GRADE; the evidence was low- or very low-quality, due to downgrading because of design limitations (risk of bias) and imprecise effect estimates (for many outcomes only one or two RCTs contributed data).For our primary outcomes there was no clear difference between metformin and insulin groups for pre-eclampsia (risk ratio (RR) 0.63, 95% confidence interval (CI) 0.33 to 1.20; RCTs = 2; participants = 227; very low-quality evidence) although in one RCT women receiving metformin were less likely to have pregnancy-induced hypertension (RR 0.58, 95% CI 0.37 to 0.91; RCTs = 1; participants = 206; low-quality evidence). Women receiving metformin were less likely to have a caesarean section compared with those receiving insulin (RR 0.73, 95% CI 0.61 to 0.88; RCTs = 3; participants = 241; low-quality evidence). In one RCT there was no clear difference between groups for large-for-gestational-age infants (RR 1.12, 95% CI 0.73 to 1.72; RCTs = 1; participants = 206; very low-quality evidence). There were no perinatal deaths in two RCTs (very low-quality evidence). Neonatal mortality or morbidity composite outcome and childhood/adulthood neurosensory disability were not reported.For other secondary outcomes we assessed using GRADE, there were no clear differences between metformin and insulin groups for induction of labour (RR 1.42, 95% CI 0.62 to 3.28; RCTs = 2; participants = 35; very low-quality evidence), though infant hypoglycaemia was reduced in the metformin group (RR 0.34, 95% CI 0.18 to 0.62; RCTs = 3; infants = 241; very low-quality evidence). Perineal trauma, maternal postnatal depression and postnatal weight retention, and childhood/adulthood adiposity and diabetes were not reported.

AUTHORS' CONCLUSIONS

There are insufficient RCT data to evaluate the use of oral anti-diabetic agents in women with established diabetes, impaired glucose tolerance or previous gestational diabetes who are planning a pregnancy, or in pregnant women with pre-existing diabetes. Low to very low-quality evidence suggests possible reductions in pregnancy-induced hypertension, caesarean section birth and neonatal hypoglycaemia with metformin compared with insulin for women with type 2 diabetes diagnosed before or during their pregnancy, and no clear differences in pre-eclampsia, induction of labour and babies that are large-for-gestational age. Further high-quality RCTs that compare any combination of oral anti-diabetic agent, insulin and dietary and lifestyle advice for these women are needed. Future RCTs could be powered to evaluate effects on short- and long-term clinical outcomes; such RCTs could attempt to collect and report on the standard outcomes suggested in this review. We have identified three ongoing studies and four are awaiting classification. We will consider these when this review is updated.

Arylamine N-acetyltransferase 1 in situ N-acetylation on CD3+ peripheral blood mononuclear cells correlate with NATb mRNA and NAT1 haplotype

Human arylamine N-acetyltransferase 1 (NAT1) is responsible for the activation and elimination of xenobiotic compounds and carcinogens. Genetic polymorphisms in NAT1 modify both drug efficacy and toxicity. Previous studies have suggested a role for NAT1 in the development of several diseases. The aim of the present study was to evaluate NAT1 protein expression and in situ N-acetylation capacity in peripheral blood mononuclear cells (PBMC), as well as their possible associations with the expression of NAT1 transcript and NAT1 genotype. We report NAT1 protein, mRNA levels, and N-acetylation in situ activity for PBMC obtained from healthy donors. NAT1-specific protein expression was higher in CD3+ cells than other major immune cell subtypes (CD19 or CD56 cells). N-acetylation of pABA varied markedly among the PBMC of participants, but correlated very significantly with levels of NAT1 transcripts. NAT1*4 subjects showed significantly (p = 0.017) higher apparent pABA V _max of 71.3 ± 3.7 versus the NAT1*14B subjects apparent V _max of 58.5 ± 2.5 nmoles Ac-pABA/24 h/million cells. Levels of pABA N-acetylation activity at each concentration of substrate evaluated also significantly correlated with NAT1 mRNA levels for all samples (p < 0.0001). This highly significant correlation was maintained for samples with the NAT1*4 (p = 0.002) and NAT1*14B haplotypes (p = 0.0106). These results provide the first documentation that NAT1-catalyzed N-acetylation in PBMC is higher in T cell than in other immune cell subtypes and that individual variation in N-acetylation capacity is dependent upon NAT1 mRNA and NAT1 haplotype.

Metformin, the aspirin of the 21st century: its role in gestational diabetes mellitus, prevention of preeclampsia and cancer, and the promotion of longevity

Metformin is everywhere. Originally introduced in clinical practice as an antidiabetic agent, its role as a therapeutic agent is expanding to include treatment of prediabetes mellitus, gestational diabetes mellitus, and polycystic ovarian disease; more recently, experimental studies and observations in randomized clinical trials suggest that metformin could have a place in the treatment or prevention of preeclampsia. This article provides a brief overview of the history of metformin in the treatment of diabetes mellitus and reviews the results of metaanalyses of metformin in gestational diabetes mellitus as well as the treatment of obese, non-diabetic, pregnant women to prevent macrosomia. We highlight the results of a randomized clinical trial in which metformin administration in early pregnancy did not reduce the frequency of large-for-gestational-age infants (the primary endpoint) but did decrease the frequency of preeclampsia (a secondary endpoint). The mechanisms by which metformin may prevent preeclampsia include a reduction in the production of antiangiogenic factors (soluble vascular endothelial growth factor receptor-1 and soluble endoglin) and the improvement of endothelial dysfunction, probably through an effect on the mitochondria. Another potential mechanism whereby metformin may play a role in the prevention of preeclampsia is its ability to modify cellular homeostasis and energy disposition, mediated by rapamycin, a mechanistic target. Metformin has a molecular weight of 129 Daltons and therefore readily crosses the placenta. There is considerable evidence to suggest that this agent is safe during pregnancy. New literature on the role of metformin as a chemotherapeutic adjuvant in the prevention of cancer and in prolonging life and protecting against aging is reviewed briefly. Herein, we discuss the mechanisms of action and potential benefits of metformin.

Ocular non-P450 oxidative, reductive, hydrolytic, and conjugative drug metabolizing enzymes

Metabolism in the eye for any species, laboratory animals or human, is gaining rapid interest as pharmaceutical scientists aim to treat a wide range of so-called incurable ocular diseases. Over a period of decades, reports of metabolic activity toward various drugs and biochemical markers have emerged in select ocular tissues of animals and humans. Ocular cytochrome P450 (P450) enzymes and transporters have been recently reviewed. However, there is a dearth of collated information on non-P450 drug metabolizing enzymes in eyes of various preclinical species and humans in health and disease. In an effort to complement ocular P450s and transporters, which have been well reviewed in the literature, this review is aimed at presenting collective information on non-P450 oxidative, hydrolytic, and conjugative ocular drug metabolizing enzymes. Herein, we also present a list of xenobiotics or drugs that have been reported to be metabolized in the eye.

Congenic rats with higher arylamine N-acetyltransferase 2 activity exhibit greater carcinogen-induced mammary tumor susceptibility independent of carcinogen metabolism

Background

Recent investigations suggest role(s) of human arylamine N-acetyltransferase 1 (NAT1) in breast cancer. Rat NAT2 is orthologous to human NAT1 and the gene products are functional homologs. We conducted in vivo studies using F344.WKY-Nat2^rapid/slow rats, congenic at rat Nat2 for high (rapid) and low (slow) arylamine N-acetyltransferase activity, to assess a possible role for rat NAT2 in mammary tumor susceptibility.

Methods

Mammary carcinogens, methylnitrosourea (MNU) and 7,12-dimethylbenzanthracene (DMBA) neither of which is metabolized by N-acetyltransferase, were administered to assess mammary tumors. MNU was administered at 3 or 8 weeks of age. DMBA was administered at 8 weeks of age. NAT2 enzymatic activity and endogenous acetyl-coenzyme A (AcCoA) levels were measured in tissue samples and embryonic fibroblasts isolated from the congenic rats.

Results

Tumor latency was shorter in rapid NAT2 rats compared to slow NAT2 rats, with statistical significance for MNU administered at 3 and 8 weeks of age (p = 0.009 and 0.050, respectively). Tumor multiplicity and incidence were higher in rapid NAT2 rats compared to slow NAT2 rats administered MNU or DMBA at 8 weeks of age (MNU, p = 0.050 and 0.035; DMBA, p = 0.004 and 0.027, respectively). Recombinant rat rapid-NAT2, as well as tissue samples and embryonic fibroblasts derived from rapid NAT2 rats, catalyzed p-aminobenzoic acid N-acetyl transfer and folate-dependent acetyl-coenzyme A (AcCoA) hydrolysis at higher rates than those derived from rat slow-NAT2. Embryonic fibroblasts isolated from rapid NAT2 rats displayed lower levels of cellular AcCoA than slow NAT2 rats (p < 0.01).

Conclusions

A novel role for rat NAT2 in mammary cancer was discovered unrelated to carcinogen metabolism, suggesting a role for human NAT1 in breast cancer.

Variation in NAT2 acetylation phenotypes is associated with differences in food-producing subsistence modes and ecoregions in Africa

Background

Dietary changes associated to shifts in subsistence strategies during human evolution may have induced new selective pressures on phenotypes, as currently held for lactase persistence. Similar hypotheses exist for arylamine N-acetyltransferase 2 (NAT2) mediated acetylation capacity, a well-known pharmacogenetic trait with wide inter-individual variation explained by polymorphisms in the NAT2 gene. The environmental causative factor (if any) driving its evolution is as yet unknown, but significant differences in prevalence of acetylation phenotypes are found between hunter-gatherer and food-producing populations, both in sub-Saharan Africa and worldwide, and between agriculturalists and pastoralists in Central Asia. These two subsistence strategies also prevail among sympatric populations of the African Sahel, but knowledge on NAT2 variation among African pastoral nomads was up to now very scarce. Here we addressed the hypothesis of different selective pressures associated to the agriculturalist or pastoralist lifestyles having acted on the evolution of NAT2 by sequencing the gene in 287 individuals from five pastoralist and one agriculturalist Sahelian populations.

Results

We show that the significant NAT2 genetic structure of African populations is mainly due to frequency differences of three major haplotypes, two of which are categorized as decreased function alleles (NAT2*5B and NAT2*6A), particularly common in populations living in arid environments, and one fast allele (NAT2*12A), more frequently detected in populations living in tropical humid environments. This genetic structure does associate more strongly with a classification of populations according to ecoregions than to subsistence strategies, mainly because most Sahelian and East African populations display little to no genetic differentiation between them, although both regions hold nomadic or semi-nomadic pastoralist and sedentary agriculturalist communities. Furthermore, we found significantly higher predicted proportions of slow acetylators in pastoralists than in agriculturalists, but also among food-producing populations living in the Sahelian and dry savanna zones than in those living in humid environments, irrespective of their mode of subsistence.

Conclusion

Our results suggest a possible independent influence of both the dietary habits associated with subsistence modes and the chemical environment associated with climatic zones and biomes on the evolution of NAT2 diversity in sub-Saharan African populations.

Electronic supplementary material

The online version of this article (doi:10.1186/s12862-015-0543-6) contains supplementary material, which is available to authorized users.

Folate-Dependent Hydrolysis of Acetyl-Coenzyme A by Recombinant Human and Rodent Arylamine N-Acetyltransferases

Arylamine N-acetyltransferases (NATs) are drug and xenobiotic metabolizing enzymes that catalyze the N-acetylation of arylamines and hydrazines and the O-acetylation of N-hydroxy-arylamines. Recently, studies report that human NAT1 and mouse Nat2 hydrolyze acetyl-coenzyme A (AcCoA) into acetate and coenzyme A in a folate-dependent fashion, a previously unknown function. In this study, our goal was to confirm these findings and determine the apparent Michaelis-Menten kinetic constants (Vmax and Km) of the folate-dependent AcCoA hydrolysis for human NAT1/NAT2, and the rodent analogs rat Nat1/Nat2, mouse Nat1/Nat2, and hamster Nat1/Nat2. We also compared apparent Vmax values for AcCoA hydrolysis and N-acetylation of the substrate para-aminobenzoic acid (PABA). Human NAT1 and its rodent analogs rat Nat2, mouse Nat2 and hamster Nat2 catalyzed AcCoA hydrolysis in a folate-dependent manner. Rates of AcCoA hydrolysis were between 0.25 - 1% of the rates for N-acetylation of PABA catalyzed by human NAT1 and its rodent orthologs. In contrast to human NAT1, human NAT2 and its rodent analogs rat Nat1, mouse Nat1, and hamster Nat1 did not hydrolyze AcCoA in a folate-dependent manner. These results are consistent with the possibility that human NAT1 and its rodent analogs regulate endogenous AcCoA levels.

Homologues of xenobiotic metabolizing N-acetyltransferases in plant-associated fungi: Novel functions for an old enzyme family

Plant-pathogenic fungi and their hosts engage in chemical warfare, attacking each other with toxic products of secondary metabolism and defending themselves via an arsenal of xenobiotic metabolizing enzymes. One such enzyme is homologous to arylamine N-acetyltransferase (NAT) and has been identified in Fusarium infecting cereal plants as responsible for detoxification of host defence compound 2-benzoxazolinone. Here we investigate functional diversification of NAT enzymes in crop-compromising species of Fusarium and Aspergillus, identifying three groups of homologues: Isoenzymes of the first group are found in all species and catalyse reactions with acetyl-CoA or propionyl-CoA. The second group is restricted to the plant pathogens and is active with malonyl-CoA in Fusarium species infecting cereals. The third group generates minimal activity with acyl-CoA compounds that bind non-selectively to the proteins. We propose that fungal NAT isoenzymes may have evolved to perform diverse functions, potentially relevant to pathogen fitness, acetyl-CoA/propionyl-CoA intracellular balance and secondary metabolism.

Gene-environment interactions in esophageal cancer

Esophageal cancer (EC) is one of the most common malignancies in low- and medium-income countries and represents a disease of public health importance because of its poor prognosis and high mortality rate in these regions. The striking variation in the prevalence of EC among different ethnic groups suggests a significant contribution of population-specific environmental and dietary factors to susceptibility to the disease. Although individuals within a demarcated geographical area are exposed to the same environment and share similar dietary habits, not all of them will develop the disease; thus genetic susceptibility to environmental risk factors may play a key role in the development of EC. A wide range of xenobiotic-metabolizing enzymes are responsible for the metabolism of carcinogens introduced via the diet or inhaled from the environment. Such dietary or environmental carcinogens can bind to DNA, resulting in mutations that may lead to carcinogenesis. Genes involved in the biosynthesis of these enzymes are all subject to genetic polymorphisms that can lead to altered expression or activity of the encoded proteins. Genetic polymorphisms may, therefore, act as molecular biomarkers that can provide important predictive information about carcinogenesis. The aim of this review is to discuss our current knowledge on the genetic risk factors associated with the development of EC in different populations; it addresses mainly the topics of genetic polymorphisms, gene-environment interactions, and carcinogenesis. We have reviewed the published data on genetic polymorphisms of enzymes involved in the metabolism of xenobiotics and discuss some of the potential gene-environment interactions underlying esophageal carcinogenesis. The main enzymes discussed in this review are the glutathione S-transferases (GSTs), N-acetyltransferases (NATs), cytochrome P450s (CYPs), sulfotransferases (SULTs), UDP-glucuronosyltransferases (UGTs), and epoxide hydrolases (EHs), all of which have key roles in the detoxification of environmental and dietary carcinogens. Finally, we discuss recent advances in the study of genetic polymorphisms associated with EC risk, specifically with regard to genome-wide association studies, and examine possible challenges of case-control studies that need to be addressed to better understand the interaction between genetic and environmental factors in esophageal carcinogenesis.

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.

Recent advances in the diagnosis and management of gestational diabetes

Gestational diabetes is a condition which is seen in 7% of pregnancies and have potential risks for both mother and fetus. Despite its importance, there is not any golden standard approaches to the diagnosis and management of the disease. The aim of this review was to investigate the advances in the diagnosis and management of gestational diabetes in recent years.

Water-soluble mmp-9 inhibitor prodrug generates active metabolites that cross the blood-brain barrier

MMP-9 plays a detrimental role in the pathology of several neurological diseases and, thus, represents an important target for intervention. The water-soluble prodrug ND-478 is hydrolyzed to the active MMP-9 inhibitor ND-322, which in turn is N-acetylated to the even more potent metabolite ND-364. We used a sensitive bioanalytical method based on ultraperformance liquid chromatography with multiple-reaction monitoring detection to measure levels of ND-478, ND-322, and ND-364 in plasma and brain after administration of ND-478 and the metabolites. ND-478 did not cross the blood-brain barrier, as was expected; however the active metabolites ND-322 and ND-364 distributed to the brain. The active compound after administration of either ND-478 or ND-322 is likely ND-364. ND-322 is N-acetylated in both brain and liver, but it is so metabolized preferentially in liver. Since N-acetyltransferases involved in the metabolism of ND-322 to ND-364 are polymorphic, direct administration of the N-acetylated ND-364 would achieve the requisite therapeutic levels in the brain.

NAT2 sequence polymorphisms and acetylation profiles in Indians

BACKGROUND

NAT2, a broad-spectrum drug-metabolizing gene, is of high pharmacogenetic interest. Based on seven different mutations in the NAT2 gene, an individual can either be categorized as a slow or fast acetylator.

MATERIALS & METHODS

In order to characterize acetylation profiles of Indians, where data are poorly available, we sequenced the 873 bp NAT2 coding region in 250 Indians, covering the whole of India including three tribes.

RESULTS

Altogether, 35 NAT2 alleles forming two acetylator phenotypes (distributed almost in equal proportion in India) were found; while the alleles determining slow acetylators were highly differentiated, the fast acetylator alleles were less in number but highly frequent.

CONCLUSION

Interestingly, distribution of two different acetylation phenotypes correlated well with historical dietary pattern in India. The neighbor-joining phylogenetic tree based on NAT2 gene polymorphisms in worldwide humans revealed genetic affinities among populations with similar acetylation phenotypes, which also placed Indians and Africans together in a single cluster.

Evaluation of polymorphisms in the sulfonamide detoxification genes NAT2, CYB5A, and CYB5R3 in patients with sulfonamide hypersensitivity

OBJECTIVE

To determine whether polymorphisms in the sulfonamide detoxification genes, CYB5A (encoding cytochrome b(5)), CYB5R3 (encoding cytochrome b(5) reductase), or NAT2 (encoding N-acetyltransferase 2) were over-represented in patients with delayed sulfonamide drug hypersensitivity, compared with control patients who tolerated a therapeutic course of trimethoprim-sulfamethoxazole without adverse event.

METHODS

DNA from 99 nonimmunocompromised patients with sulfonamide hypersensitivity who were identified from the Personalized Medicine Research Project at the Marshfield Clinic, and from 99 age-matched, race-matched, and sex-matched drug-tolerant controls, were genotyped for four CYB5A and five CYB5R3 polymorphisms, and for all coding NAT2 SNPs.

RESULTS

CYB5A and CYB5R3 SNPs were found at low allele frequencies (<3-4%), which did not differ between hypersensitive and tolerant patients. NAT2 allele and haplotype frequencies, as well as inferred NAT2 phenotypes, also did not differ between groups (60 vs. 59% slow acetylators). Finally, no difference in NAT2 status was found in a subset of patients with more severe hypersensitivity signs (drug reaction with eosinophilia and systemic symptoms) compared with tolerant patients.

CONCLUSION

We found no evidence of a substantial involvement of these nine CYB5A or CYB5R3 polymorphisms in sulfonamide hypersensitivity risk, although minor effects cannot be completely ruled out. Despite careful medical record review and full resequencing of the NAT2 coding region, we found no association of NAT2 coding alleles with sulfonamide hypersensitivity (predominantly cutaneous eruptions) in this adult Caucasian population.

Glucocorticoid receptor-mediated transcriptional regulation of N-acetyltransferase 1 gene through distal promoter

Human arylamine N-acetyltransferase 1, (HUMAN)NAT1, is a phase II xenobiotic-metabolizing enzyme that plays an important role in drug and carcinogen biotransformation and cancer development. Its gene expression has been shown to be regulated by environmental factors. The purpose of the current study is to determine the involvement of nuclear receptors in transcriptional regulation of (HUMAN)NAT1 gene. We show that among the nuclear receptors examined, including the glucocorticoid receptor, retinoid acid receptor-related orphan receptor alpha, constitutive androstane receptor, pregnane X receptor, aryl hydrocarbon receptor, and retinoic acid receptor, the glucocorticoid receptor plays a dominant role in regulating (HUMAN)NAT1 gene expression through distal promoter (P3). The involvement of the glucocorticoid receptor in transcription regulation of (HUMAN)NAT1 gene expression was demonstrated by dexamethasone treatment, reporter assay using plasmid-containing 3 kbp of 5'-end region of promoter 3, and treatment of anti-glucocorticoid RU486 in primary culture of human hepatocytes and transfected HepG2 cells. In addition, translation inhibition did not affect dexamethasone-induced gene expression through P3, suggesting that dexamethasone effect is directly mediated by glucocorticoid receptor activation. Furthermore, deletion analysis revealed the presence of multiple responsive elements within the 3 kbp fragment of P3. Transfection assays in mice using hydrodynamics-based procedure and reporter gene assay in a mouse cell line revealed that glucocorticoid-induced NAT gene expression is species dependent. Dexamethasone treatment of transfected mice and mouse cell line decreased (MOUSE)Nat2 gene expression, (HUMAN)NAT1 homologue. These results suggest that glucocorticoids serve as a modulator for (HUMAN)NAT1 gene expression via the P3-containing 5'-flanking region.

mRNA transcript diversity creates new opportunities for pharmacological intervention

Most protein coding genes generate multiple RNA transcripts through alternative splicing, variable 3' and 5'UTRs, and RNA editing. Although drug design typically targets the main transcript, alternative transcripts can have profound physiological effects, encoding proteins with distinct functions or regulatory properties. Formation of these alternative transcripts is tissue-selective and context-dependent, creating opportunities for more effective and targeted therapies with reduced adverse effects. Moreover, genetic variation can tilt the balance of alternative versus constitutive transcripts or generate aberrant transcripts that contribute to disease risk. In addition, environmental factors and drugs modulate RNA splicing, affording new opportunities for the treatment of splicing disorders. For example, therapies targeting specific mRNA transcripts with splice-site-directed oligonucleotides that correct aberrant splicing are already in clinical trials for genetic disorders such as Duchenne muscular dystrophy. High-throughput sequencing technologies facilitate discovery of novel RNA transcripts and protein isoforms, applications ranging from neuromuscular disorders to cancer. Consideration of a gene's transcript diversity should become an integral part of drug design, development, and therapy.

Human N-acetyltransferase 1 *10 and *11 alleles increase protein expression through distinct mechanisms and associate with sulfamethoxazole-induced hypersensitivity

OBJECTIVES

N-acetyltransferase 1 (NAT1) metabolizes drugs and environmental carcinogens. NAT1 alleles *10 and *11 have been proposed to alter protein level or enzyme activity compared with wild-type NAT1 *4 and to confer cancer risk, through uncertain pathways. This study characterizes regulatory polymorphisms and underlying mechanisms of NAT1 expression.

METHODS

We measured allelic NAT1 mRNA expression and translation, as a function of multiple transcription start sites, alternative splicing, and three 3'-polyadenylation sites in human livers (one of which was discovered in this study), B lymphocytes, and transfected cells. In a clinical study of 469 patients with HIV/AIDS treated with the NAT1/NAT2 substrate sulfamethoxazole (SMX), associations were tested between SMX-induced hypersensitivity and NAT1 *10 and *11 genotypes, together with known NAT2 polymorphisms.

RESULTS

NAT1 *10 and *11 were determined to act as common regulatory alleles accounting for most NAT1 expression variability, both leading to increased translation into active protein. NAT1 *11 (2.4% minor allele frequency) affected 3'-polyadenylation site usage, thereby increasing formation of NAT1 mRNA with intermediate length 3'-untranslated region (major isoform) at the expense of the short isoform, resulting in more efficient protein translation. NAT1 *10 (19% minor allele frequency) increased translation efficiency without affecting 3'-untranslated region polyadenylation site usage. Livers and B-lymphocytes with *11/*4 and *10/*10 genotypes displayed higher NAT1 immunoreactivity and NAT1 enzyme activity than the reference genotype *4/*4. Patients who carry *10/*10 and *11/*4 (fast NAT1 acetylators) were less likely to develop hypersensitivity to SMX, but this was observed only in individuals who are also carrying a slow NAT2 acetylator genotype.

CONCLUSION

NAT1 *10 and *11 significantly increase NAT1 protein level/enzyme activity, enabling the classification of carriers into reference and rapid acetylators. Rapid NAT1 acetylator status seems to protect against SMX toxicity by compensating for slow NAT2 acetylator status.

Functional analysis of arylamine N-acetyltransferase 1 (NAT1) NAT1*10 haplotypes in a complete NATb mRNA construct

N-acetyltransferase 1 (NAT1) catalyzes N-acetylation of arylamines as well as the O-acetylation of N-hydroxylated arylamines. O-acetylation leads to the formation of electrophilic intermediates that result in DNA adducts and mutations. NAT1*10 is the most common variant haplotype and is associated with increased risk for numerous cancers. NAT1 is transcribed from a major promoter, NATb, and an alternative promoter, NATa, resulting in messenger RNAs (mRNAs) with distinct 5'-untranslated regions (UTRs). To best mimic in vivo metabolism and the effect of NAT1*10 polymorphisms on polyadenylation usage, pcDNA5/Flp recombination target plasmid constructs were prepared for transfection of full-length human mRNAs including the 5'-UTR derived from NATb, the open reading frame and 888 nucleotides of the 3'-UTR. Following stable transfection of NAT1*4, NAT1*10 and an additional NAT1*10 variant (termed NAT1*10B) into nucleotide excision repair-deficient Chinese hamster ovary cells, N- and O-acetyltransferase activity (in vitro and in situ), mRNA and protein expression were higher in cells transfected with NAT1*10 and NAT1*10B than in cells transfected with NAT1*4 (P < 0.05). Consistent with NAT1 expression and activity, cytotoxicity and hypoxanthine phosphoribosyl transferase mutants following 4-aminobiphenyl exposures were higher in NAT1*10 than in NAT1*4 transfected cells. Ribonuclease protection assays showed no difference between NAT1*4 and NAT1*10. However, protection of one probe by NAT1*10B was not observed with NAT1*4 or NAT1*10, suggesting additional mechanisms that regulate NAT1*10B. The higher mutants in cells transfected with NAT1*10 and NAT1*10B are consistent with an increased cancer risk for individuals possessing NAT1*10 haplotypes.

Characterization of genetic variation and natural selection at the arylamine N-acetyltransferase genes in global human populations

Functional variability at the arylamine N-acetyltransferase genes is associated with drug response in humans and may have been adaptive in the past owing to selection pressure from diet and exposure to toxins during human evolution.

AIMS

We have characterized nucleotide variation at the NAT1 and NAT2 genes, and at the NATP1 pseudogene in global human populations, including many previously under-represented African populations, in order to identify potential functional variants and to understand the role that natural selection has played in shaping variation at these loci in globally diverse populations.

MATERIALS & METHODS

We have resequenced approximately 2800 bp for each of the NAT1 and NAT2 gene regions, as well as the pseudogene NATP1, in 197 African and 132 nonAfrican individuals.

RESULTS & CONCLUSION

We observe a signature of balancing selection maintaining variation in the 3'-UTR of NAT1, suggesting that these variants may play a functional role that is currently undefined. In addition, we observed high levels of nonsynonymous functional variation at the NAT2 locus that differs amongst ethnically diverse populations.

NATb/NAT1*4 promotes greater arylamine N-acetyltransferase 1 mediated DNA adducts and mutations than NATa/NAT1*4 following exposure to 4-aminobiphenyl

N-acetyltransferase 1 (NAT1) is a phase II metabolic enzyme responsible for the biotransformation of aromatic and heterocyclic amine carcinogens such as 4-aminobiphenyl (ABP). NAT1 catalyzes N-acetylation of arylamines as well as the O-acetylation of N-hydroxylated arylamines. O-acetylation leads to the formation of electrophilic intermediates that result in DNA adducts and mutations. NAT1 is transcribed from a major promoter, NATb, and an alternative promoter, NATa, resulting in mRNAs with distinct 5'-untranslated regions (UTR). NATa mRNA is expressed primarily in the kidney, liver, trachea, and lung while NATb mRNA has been detected in all tissues studied. To determine if differences in 5'-UTR have functional effect upon NAT1 activity and DNA adducts or mutations following exposure to ABP, pcDNA5/FRT plasmid constructs were prepared for transfection of full-length human mRNAs including the 5'-UTR derived from NATa or NATb, the open reading frame, and 888 nucleotides of the 3'-UTR. Following stable transfection of NATb/NAT1*4 or NATa/NAT1*4 into nucleotide excision repair (NER) deficient Chinese hamster ovary cells, N-acetyltransferase activity (in vitro and in situ), mRNA, and protein expression were higher in NATb/NAT1*4 than NATa/NAT1*4 transfected cells (P < 0.05). Consistent with NAT1 expression and activity, ABP-induced DNA adducts and hypoxanthine phosphoribosyl transferase mutants were significantly higher (P < 0.05) in NATb/NAT1*4 than in NATa/NAT1*4 transfected cells following exposure to ABP. These differences observed between NATa and NATb suggest that the 5'-UTRs are differentially regulated.

Characterization, comparative genomics, and evolutionary inferences of a human drug metabolizing (NAT2) gene

Aim

The present-day genetic architecture of a species bears much significance to its closely related species. In recent availability of whole genome sequence data for closely related species, it is possible to detect genetic similarities/differences in specific lineages and infer the role of evolutionary forces in bringing such similarities/differences. In this respect, NAT2 gene, responsible for drug metabolism, is conserved across a few taxa and, thus, comparative genomic studies could be useful for better pharmacogenetic realization.

Methods

DNA sequences of human NAT2 gene were retrieved from NCBI and characterized. Comparative and evolutionary analyses were performed with sequences from four mammalian taxa and one avian taxon with different statistical algorithms.

Results

The observed genetic architecture of NAT2 gene was different across the taxa. Phylogenetic inferences revealed that human and chimpanzee are diverged recently and fowl was found to be diverged from rest of the taxa significantly. Also, gene length, microsatellites, Ka/Ks, secondary structure, and distribution of CpG islands were observed across taxa.

Conclusions

The detail architecture of NAT2 gene and its evolutionary history in different taxa show relationships with other taxa. Future population-based study in NAT2 would unravel the correlation between nucleotide changes and differential ability of drug metabolization in humans.

Oral anti-diabetic agents for women with pre-existing diabetes mellitus/impaired glucose tolerance or previous gestational diabetes mellitus

BACKGROUND

While most guidelines recommend the use of insulin in women whose pregnancies are affected by pre-existing diabetes, oral agents have obvious benefits for patient acceptability and adherence. It is necessary, however, to assess the effects of these anti-diabetic agents on maternal and infant health outcomes. Additionally, women with previous gestational diabetes mellitus are increasingly found to be predisposed to impaired glucose tolerance and, despite the potential need for intervention for these women, there has been little evidence about the use of oral anti-diabetic agents by these women pre-conceptionally or during a subsequent pregnancy.

OBJECTIVES

To investigate the effect of oral anti-diabetic agents in women with pre-existing diabetes mellitus, impaired glucose tolerance or previous gestational diabetes planning a pregnancy or pregnant women with diabetes mellitus on maternal and infant health.The use of oral antidiabetic agents for management of gestational diabetes in a current pregnancy is evaluated in a separate Cochrane review.

SEARCH STRATEGY

We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (March 2010).

SELECTION CRITERIA

We included randomised and quasi-randomised trials.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed trial eligibility for inclusion.

MAIN RESULTS

We identified 13 trials published as 25 papers using the Cochrane Pregnancy and Childbirth group literature search, and an additional ongoing trial. We have not included any trials in the review. One trial is awaiting assessment and we have excluded twelve trials because they evaluated treatment of women with gestational diabetes or women with polycystic ovary syndrome, were not randomised controlled trials or data were not available.

AUTHORS' CONCLUSIONS

Little randomised evidence is available evaluating the use of oral anti-diabetic agents in women with diabetes mellitus, impaired glucose tolerance, previous gestational diabetes mellitus planning a pregnancy or pregnant women with pre-existing diabetes mellitus. Large trials comparing any combination of oral anti-diabetic agent, insulin and dietary and lifestyle advice in these women, reporting on maternal and infant health outcomes, glycaemic control, women's views on the intervention and long-term health outcomes for mother and child, are required to guide clinical practice.

Interethnic diversity of NAT2 polymorphisms in Brazilian admixed populations

Background

N-acetyltransferase type 2 (Nat2) is a phase II drug- metabolizing enzyme that plays a key role in the bioactivation of aromatic and heterocyclic amines. Its relevance in drug metabolism and disease susceptibility remains a central theme for pharmacogenetic research, mainly because of its genetic variability among human populations. In fact, the evolutionary and ethnic-specific SNPs on the NAT2 gene remain a focus for the potential discoveries in personalized drug therapy and genetic markers of diseases. Despite the wide characterization of NAT2 SNPs frequency in established ethnic groups, little data are available for highly admixed populations. In this context, five common NAT2 SNPs (G191A, C481T, G590A, A803G and G857A) were investigated in a highly admixed population comprised of Afro-Brazilians, Whites, and Amerindians in northeastern Brazil. Thus, we sought to determine whether the distribution of NAT2 polymorphism is different among these three ethnic groups.

Results

Overall, there were no statistically significant differences in the distribution of NAT2 polymorphism when Afro-Brazilian and White groups were compared. Even the allele frequency of 191A, relatively common in African descendents, was not different between the Afro-Brazilian and White groups. However, allele and genotype frequencies of G590A were significantly higher in the Amerindian group than either in the Afro-Brazilian or White groups. Interestingly, a haplotype block between G590A and A803G was verified exclusively among Amerindians.

Conclusions

Our results indicate that ethnic admixture might contribute to a particular pattern of genetic diversity in the NAT2 gene and also offer new insights for the investigation of possible new NAT2 gene-environment effects in admixed populations.

Histone deacetylase inhibitors increase human arylamine N-acetyltransferase-1 expression in human tumor cells

Arylamine N-acetyltransferase-1 (NAT1) has been associated with disorders involving folate metabolism, such as spina bifida, as well as numerous human cancers. As a result, the transcriptional and post-transcriptional regulation of NAT1 activity has been extensively studied. However, little work has been reported on the epigenetic control of NAT1 expression. Here, we demonstrate that the histone deacetylase inhibitor trichostatin A (TSA) increases NAT1 activity in human cancer cells by increasing transcription from the proximal promoter NATb. A specific Sp1 binding site was identified as essential for optimal induction of NAT1 by TSA. However, TSA did not increase the expression of Sp1 in HeLa cells. Instead, TSA increased the acetylation of histones associated with the NATb promoter. This allowed recruitment of Sp1 to the promoter along with acetylated histones. We propose that NAT1 transcription is partially repressed by the local chromatin condensation in the vicinity of NATb and that histone deacetylase inhibition leads to up-regulation of NAT1 expression via a direct change in chromatin conformation.

Sequence analysis of NAT2 gene in Brazilians: identification of undescribed single nucleotide polymorphisms and molecular modeling of the N-acetyltransferase 2 protein structure

N-Acetyltransferase 2 (NAT2) metabolizes a variety of xenobiotics that includes many drugs, chemicals and carcinogens. This enzyme is genetically variable in human populations and polymorphisms in the NAT2 gene have been associated with drug toxicity and efficacy as well as cancer susceptibility. Here, we have focused on the identification of NAT2 variants in Brazilian individuals from two different regions, Rio de Janeiro and Goiás, by direct sequencing, and on the characterization of new haplotypes after cloning and re-sequencing. Upon analysis of DNA samples from 404 individuals, six new SNPs (c.29T>C, c.152G>T, c.203G>A, c.228C>T, c.458C>T and c.600A>G) and seven new NAT2 alleles were identified with different frequencies in Rio de Janeiro and Goiás. All new SNPs were found as singletons (observed only once in 808 genes) and were confirmed by three independent technical replicates. Molecular modeling and structural analysis suggested that p.Gly51Val variant may have an important effect on substrate recognition by NAT2. We also observed that amino acid change p.Cys68Tyr would affect acetylating activity due to the resulting geometric restrictions and incompatibility of the functional group in the Tyr side chain with the admitted chemical mechanism for catalysis by NATs. Moreover, other variants, such like p.Thr153Ile, p.Thr193Met, p.Pro228Leu and p.Val280Met, may lead to the presence of hydrophobic residues on NAT2 surface involved in protein aggregation and/or targeted degradation. Finally, the new alleles NAT2*6H and NAT2*5N, which showed the highest frequency in the Brazilian populations considered in this study, may code for a slow activity. Functional studies are needed to clarify the mechanisms by which new SNPs interfere with acetylation.

Characterisation of CpG methylation in the upstream control region of mouse Nat2: evidence for a gene-environment interaction in a polymorphic gene implicated in folate metabolism

Human arylamine N-acetyltransferase 1 (NAT1), a polymorphic xenobiotic metabolising enzyme, has been investigated in relation to susceptibility and prognosis in certain types of cancer. Both human NAT1 and its murine equivalent NAT2 have previously been shown to play roles in the catabolism of folate, which is required for the synthesis of S-adenosylmethionine, the methyl donor for cellular methylation reactions. We have tested whether the expression of mouse Nat2 is subject to epigenetic regulation, specifically CpG methylation in the promoter region, by determining levels of 5-methylcytosine by bisulphite sequencing and methylation-specific PCR. Under normal conditions, methylation levels of the Nat2 promoter were low, and varied in different tissues. However, CpG methylation was significantly increased by dietary folate supplementation, and increased methylation corresponded to decreased use of the core promoter. Functional deletion of the Nat2 gene gave rise to a significant increase in Nat2 methylation, extending our previous observations that folate catabolism is decreased in Nat2 null mice. Mouse NAT2 is likely to influence epigenetic gene control, particularly of its own locus, and this is consistent with recent evidence associating aberrant mouse Nat2/human NAT1 gene expression with certain developmental malformations and cancers.

N-acetyltransferase 1 and 2 gene sequence variants and risk of head and neck cancer

Polymorphisms that alter the function of genes involved in the activation or detoxification of carcinogenic compounds can influence an individuals risk of developing cancer. Polymorphic changes modulating the acetylation capacity of the N-acetyltransferase (NAT) genes have been implicated in the risk of developing cancer. In this study the role of genetically determined individual NAT1 and NAT2 genotypes, haplotypes and haplotype combinations in the predisposition to head and neck cancer was investigated. Polymorphic regions of the NAT1 and NAT2 genes were analyzed in patients with head and neck cancer and healthy individuals by polymerase chain reaction-restriction fragment length polymorphism. Distribution of the genotypes, allele frequencies, diplotypes and haplotypes and correlation with clinical characteristics were evaluated. No association was observed between the NAT1*3, NAT1*10, NAT1*11, NAT2*5 and NAT2*6 genotypes and risk of head and neck cancer. The NAT2*7 slow genotype was associated with reduced risk of disease. A significant association was observed between the fast acetylator NAT2*4/NAT1*10 diplotype and risk of head and neck cancer. Combined haplotypes harboring the T1088A and C1095A variants characterizing the NAT1*10 allele were associated with increased risk. Our results suggest that NAT1 and NAT2 gene combinations may influence the risk of developing head and neck cancer.

Update on the pharmacogenetics of NATs: structural considerations

The arylamine N-acetyltransferase (NAT) genes encode enzymes that catalyze the N-acetylation of aromatic amines and hydrazines and the O-acetylation of heterocyclic amines. These genes, which play a key role in cellular homeostasis as well as in gene-environment interactions, are subject to marked pharmacogenetic variation, and different combinations of SNPs in the human NAT genes lead to different acetylation phenotypes. Our understanding of the consequences of pharmacogenetic variability in NATs has recently been enhanced by structural studies showing that effects on protein folding, aggregation and turnover, as well as direct changes in active site topology, are involved. These developments pave the way for a better understanding of the role played by NATs in maintaining cellular homeostasis. In addition, the NATs represent a model for studying fundamental processes associated with protein folding and pharmacogenomic effects mediated by inheritance in human populations across a polymorphic region of the genome.

ArylamineN-Acetyltransferases: What We Learn from Genes and Genomes

Arylamine N-acetyltransferases (NATs) are phase II xenobiotic metabolizing enzymes, catalyzing acetyl-CoA-dependent N- and O-acetylation reactions. All NATs have a conserved cysteine protease-like Cys-His-Asp catalytic triad inside their active site cleft. Other residues determine substrate specificity, while the C-terminus may control hydrolysis of acetyl-CoA during acetyltransfer. Prokaryotic NAT-like coding sequences are found in >30 bacterial genomes, including representatives of Actinobacteria, Firmicutes and Proteobacteria. Of special interest are the nat genes of TB-causing Mycobacteria, since their protein products inactivate the anti-tubercular drug isoniazid. Targeted inactivation of mycobacterial nat leads to impaired mycolic acid synthesis, cell wall damage and growth retardation. In eukaryotes, genes for NAT are found in the genomes of certain fungi and all examined vertebrates, with the exception of canids. Humans have two NAT isoenzymes, encoded by highly polymorphic genes on chromosome 8p22. Syntenic regions in rodent genomes harbour two Nat loci, which are functionally equivalent to the human NAT genes, as well as an adjacent third locus with no known function. Vertebrate genes for NAT invariably have a complex structure, with one or more non-coding exons located upstream of a single, intronless coding region. Ubiquitously expressed transcripts of human NAT1 and its orthologue, murine Nat2, are initiated from promoters with conserved Sp1 elements. However, in humans, additional tissue-specific NAT transcripts may be expressed from alternative promoters and subjected to differential splicing. Laboratory animals have been widely used as models to study the effects of NAT polymorphism. Recently generated knockout mice have normal phenotypes, suggesting no crucial endogenous role for NAT. However, these strains will be useful for understanding the involvement of NAT in carcinogenesis, an area extensively investigated by epidemiologists, often with ambiguous results.

Influence of genetic factors on toluene diisocyanate-related symptoms: evidence from a cross-sectional study

BACKGROUND

Toluene diisocyanate (TDI) is a highly reactive compound used in the production of, e.g., polyurethane foams and paints. TDI is known to cause respiratory symptoms and diseases. Because TDI causes symptoms in only a fraction of exposed workers, genetic factors may play a key role in disease susceptibility.

METHODS

Workers (N = 132) exposed to TDI and a non-exposed group (N = 114) were analyzed for genotype (metabolising genes: CYP1A1*2A, CYP1A1*2B, GSTM1*O, GSTM3*B, GSTP1 I105V, GSTP1 A114V, GSTT1*O, MPO -463, NAT1*3, *4, *10, *11, *14, *15, NAT2*5, *6, *7, SULT1A1 R213H; immune-related genes: CCL5 -403, HLA-DQB1*05, TNF -308, TNF -863) and symptoms of the eyes, upper and lower airways (based on structured interviews).

RESULTS

For three polymorphisms: CYP1A1*2A, CYP1A1*2B, and TNF -308 there was a pattern consistent with interaction between genotype and TDI exposure status for the majority of symptoms investigated, although it did reach statistical significance only for some symptoms: among TDI-exposed workers, the CYP1A1 variant carriers had increased risk (CYP1A1*2A and eye symptoms: variant carriers OR 2.0 95% CI 0.68-6.1, p-value for interaction 0.048; CYP1A1*2B and wheeze: IV carriers OR = 12, 1.4-110, p-value for interaction 0.057). TDI-exposed individuals with TNF-308 A were protected against the majority of symptoms, but it did not reach statistical significance. In the non-exposed group, however, TNF -308 A carriers showed higher risk of the majority of symptoms (eye symptoms: variant carriers OR = 2.8, 1.1-7.1, p-value for interaction 0.12; dry cough OR = 2.2, 0.69-7.2, p-value for interaction 0.036). Individuals with SULT1A1 213H had reduced risk both in the exposed and non-exposed groups. Other polymorphisms, showed associations to certain symptoms: among TDI-exposed,NAT1*10 carriers had a higher risk of eye symptoms and CCL5 -403 AG+AA as well as HLA-DQB1 *05 carriers displayed increased risk of symptoms of the lower airways. GSTM1, GSTM3 and GSTP1 only displayed effects on symptoms of the lower airways in the non-exposed group.

CONCLUSION

Specific gene-TDI interactions for symptoms of the eyes and lower airways appear to exist. The results suggest different mechanisms for TDI- and non-TDI-related symptoms of the eyes and lower airways.

Sequence variants of NAT1 and NAT2 and other xenometabolic genes and risk of lung and aerodigestive tract cancers in Central Europe

Tobacco smoke contains an extensive cocktail of highly carcinogenic chemicals. Individuals with a slower elimination rate of the chemicals in tobacco smoke may have increased exposure to their carcinogenic properties compared with those with a faster rate. Polymorphisms that alter the function of the genes involved in the activation or the detoxification of the chemical carcinogens in tobacco smoke can potentially influence an individual's risk of developing a tobacco-related cancer. To test this hypothesis, we have genotyped polymorphisms in 16 genes involved in metabolism of chemical carcinogens in a Central and Eastern European case-control study comprising 2,250 lung cases, 811 upper aerodigestive cancer (UADT) cases, and 2,704 controls. The N-acetyltransferase (NAT) genes were the most implicated in risk, with the NAT1*10 haplotype showing an inverse association in lung cancer, in both heterozygote carriers [odds ratio (OR), 0.81; 95% confidence interval (95% CI), 0.70-0.93] and homozygote carriers (OR, 0.70; 95% CI, 0.48-1.01), suggesting a genotype dose response (P < 0.001). In UADT cancer, a similar inverse association was noted in NAT1*10 although only in heterozygotes (OR, 0.78; 95%CI, 0.65-0.95). In NAT2, when considering the individuals inferred acetylator phenotypes based on their NAT2 diplotype, "slow" acetylators compared with intermediate or fast acetylators showed no association with risk. None of the other 14 genes provided robust evidence of an association for either lung or UADT cancer. We therefore conclude that, of the genetic variation studied, NAT1 gene was the most likely candidate to influence the risk of developing a tobacco-related cancer.

Genetic profile of the arylamine N-acetyltransferase 2 coding gene among individuals from two different regions of Brazil

Arylamine N-acetyltranferase 2 is the main enzyme responsible for the isoniazid metabolization into hepatotoxic intermediates and the degree of hepatotoxicity severity has been attributed to genetic variability in the NAT2 gene. The main goal of this study was to describe the genetic profile of the NAT2 gene in individuals from two different regions of Brazil: Rio de Janeiro and Goiás States. Therefore, after preparation of DNA samples from 404 individuals, genotyping of the coding region of NAT2 was performed by direct PCR sequencing. Thirteen previously described SNPs were detected in these Brazilian populations, from which seven: 191 G>A; 282 C>T; 341 T>C; 481 C>T; 590 G>A; 803 A>G and 857 G>A are the most frequent in other populations. The presence of so-called ethnic-specific SNPs in our population is in accordance with the Brazilians' multiple ancestry. Upon allele and genotype analysis, the most frequent NAT2 alleles were respectively NAT2*5B (33%), NAT2*6A (26%) and NAT2*4 (20%) being NAT2*5/*5 the more prevalent genotype (31.7%). These results clearly demonstrate the predominance in the studied Brazilian groups of NAT2 alleles associated with slow over the fast and intermediate acetylator genotypes. Additionally, in Rio de Janeiro, a significantly higher frequency of intermediate acetylation status was found when compared to Goiás (42.5% versus 25%) (p=0.05), demonstrating that different regions of a country with a population characterized by a multi-ethnic ancestry may present a large degree of variability in NAT2 allelic frequencies. This finding has implications in the determination of nationwide policies for use of appropriate anti-TB drugs.

Epidemiology of carcinogen metabolism genes and risk of squamous cell carcinoma of the head and neck

The risk association between tobacco and alcohol use with squamous cell carcinoma of the head and neck (SCCHN) is well recognized. However, clearly not all individuals who smoke or drink develop SCCHN. Individual genetic susceptibility differences in carcinogen-metabolizing enzyme function, mutagen sensitivity, apoptosis, and chromosomal aberrations either alone or in combination have been theorized to modify the risk of SCCHN. Nearly all carcinogens and procarcinogens require activation by metabolizing enzymes. Similarly, detoxifying enzymes exist and deactivate carcinogens as well as their intermediate by-products. Together these enzymes are termed xenobiotic-metabolizing enzymes; genetic polymorphisms of these enzymes can modify an individual's response to carcinogens and hence the carcinogenic potential of such exposures. In this review, we explore the available evidence in recent literature regarding the risk association between SCCHN and various xenobiotic-metabolizing enzymes, including cytochrome P450s, glutathione S-transferases, N-acetyltransferases, NAD(P)H:quinone oxidoreductase 1, alcohol dehydrogenase, and aldehyde dehydrogenase.