Placental expression of arylamine N-acetyltransferases: evidence for linkage disequilibrium between NAT1*10 and NAT2*4 alleles of the two human arylamine N-acetyltransferase loci NAT1 and NAT2

Alteration of the risk of pre-oral cancer and cancer in North Indian population by NAT1 and NAT2 polymorphisms genotypes and haplotypes

PURPOSE

The risk of oral cancer is strongly related to consumption of tobacco, smoking and drinking alcohol. N-acetyl transferases 1,2 are phase II metabolic enzymes, metabolize aryl and heterocyclic amines which are present in tobacco. NAT2 slows acetylator phenotype and the genotype is related to reduced ability to detoxify these xenobiotic that are carcinogenic to tissues. The aim of our study to determine the risk of oral cancer as well as oral precancerous lesions in North Indian population with polymorphisms in these two N-acetyl transferases 1,2 genes.

MATERIALS AND METHODS

A total of 250 patients with pre oral cancer, oral cancer and 250 healthy volunteers were genotypes for the NAT1 and NAT2 gene polymorphisms. Genotypes were identified by PCR and RFLP. Genotype frequencies were evaluated by Chi-square test and risk of disease was estimated by Odds ratio (OR) with 95% confidence interval.

RESULT

Our results showed that individuals with CT and TT genotypes of NAT1 C > T polymorphism were significantly lower risk of oral diseases (p value = 0.02, OR = 0.60 and p value = 0.04, OR = 0.58, respectively). For NAT2 C > T polymorphism, the TT genotype significantly increased the risk of OSMF (Oral Sub mucous Fibrosis) and Leukoplakia (p value = 0.001, OR = 4.16; p value = 0.002, OR = 4.38, respectively). In contrary, the CC genotype for NAT2 T > C polymorphism increased the risk of OSMF (p value = 0.01, OR = 3.00, 95% CI = 1.31-6.86).

CONCLUSION

Our study concludes that the NAT1 polymorphism shows protective association with oral diseases and NAT2 polymorphism and haplotypes also influence the susceptibility to oral diseases in North Indian population subjects.

Effect of N-Acetyltransferase 2 Genotype on the Pharmacokinetics of Hydralazine During Pregnancy

Hydralazine, an antihypertensive agent used during pregnancy, undergoes N-acetylation primarily via N-acetyltransferase 2 (NAT2) to form 3-methyl-1,2,4-triazolo[3,4-a]phthalazine (MTP). To characterize the steady-state pharmacokinetics (PK) of hydralazine during pregnancy and evaluate the effects of NAT2 genotype on hydralazine and MTP PK during pregnancy, 12 pregnant subjects received oral hydralazine (5-25 mg every 6 hours) in mid- (n = 5) and/or late pregnancy (n = 8). Serial blood samples were collected over 1 dosing interval, and steady-state noncompartmental PK parameters were estimated. Subjects were classified as either (rapid acetylators, n = 6) or slow acetylators (SAs, n = 6) based on NAT2 genotype. During pregnancy, when compared with the SA group, the RA group had faster weight-adjusted hydralazine apparent oral clearance (70.0 ± 13.6 vs 20.1 ± 6.9 L/h, P < .05), lower dose-normalized area under the concentration-time curve (AUC; 1.5 ± 0.8 vs 5.9 ± 3.7 ng·h/mL, P < .05), lower dose-normalized peak concentrations (0.77 ± 0.51 vs 4.04 ± 3.18 ng/mL, P < .05), and larger weight-adjusted apparent oral volume of distribution (302 ± 112 vs 116 ± 45 L/kg, P < .05). Furthermore, the MTP/hydralazine AUC ratio was ∼10-fold higher in the RA group (78 ± 30 vs 8 ± 3, P < .05) than in the SA group. No gestational age or dose-dependent effects were observed, possibly because of the small sample size. This study describes for the first time, the PK of oral hydralazine and its metabolite, MTP, during pregnancy, and confirmed that the PK of oral hydralazine is NAT2 genotype dependent during pregnancy.

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.

NAT1 genotypic and phenotypic contribution to urinary bladder cancer risk: a systematic review and meta-analysis

N-acetyltransferase 1 (NAT1), a polymorphic Phase II enzyme, plays an essential role in metabolizing heterocyclic and aromatic amines, which are implicated in urinary bladder cancer (BCa). This systematic review investigates a possible association between the different NAT1 genetic polymorphisms and BCa risk. Medline, PubMed, EMBASE, Scopus, Web of Science, OpenGrey, and BASE databases were searched to identify eligible studies. The random-effect model was used to calculate pooled effects estimates. Statistical heterogeneity was tested with Chi-square and I². Twenty case-control studies, including 5606 cases and 6620 controls, met the inclusion criteria. Pooled odds ratios (OR) analyses showed a statistically significant difference in NAT1*10 versus non-NAT1*10 acetylators in the total sample (OR: 0.87; 95% CI: 0.79-0.96) but was borderline among Caucasians (OR: 0.88 with 95% CI: 0.77-1.01). No statistically significant differences in BCa risk were found for: NAT1*10 versus NAT1*4 wild type (OR: 0.97; 95% CI: 0.78-1.19), NAT1 'Fast' versus 'Normal' acetylators (OR: 1.03; 95% CI: 0.84-1.27), and NAT1 'Slow' versus 'Fast' (OR: 2.32; 95% CI: 0.93-5.84) or 'Slow' versus 'Normal' acetylators (OR: 1.84; 95% CI: 0.92-3.68). When stratifying by smoking status, no statistically significant differences in BCa risk were found for NAT1*10 versus non-NAT1*10 acetylators among the different subgroups. Our study suggests a modest protective role for NAT1*10 and a possible risk contributory role for slow acetylation genotypes in BCa risk. Further research is recommended to confirm these associations.

ArylamineN-acetyltransferase 2 Expression in the Developing Heart

Murine arylamine N-acetyltransferase 2 (NAT2) is expressed in the developing heart and in the neural tube at the time of closure. Classically described as a xenobiotic metabolizing enzyme, there is increasing evidence for a distinct biological role for murine NAT2. We have characterized the expression of arylamine N-acetyltransferase 2 during cardiogenesis, mapping its expression in vivo, using a lacZ insertion deletion, and also in vitro, by measuring NAT2 enzyme activity. These findings show that cardiac Nat2 expression is both temporally and spatially regulated during development. In neonatal mice, cardiac Nat2 expression is most extensive in the central fibrous body and is evident in the atrioventricular valves and the valves of the great vessels. Whereas Nat2 expression is not detected in ventricular myocardial cells, Nat2 is strongly expressed in scattered cells in the region of the sinus node, the epicardium of the right atrial appendage, and in the pulmonary artery. Expression of active NAT2 protein is maximal when the developing heart attains the adult circulation pattern and moves from metabolizing glucose to fatty acids. NAT2 acetylating activity in cardiac tissue from Nat2−/-and Nat2+/-mice indicates a lack of compensating acetylating activity either from other acetylating enzymes or by NAT2 encoded by the wild-type Nat2 allele in Nat2+/-heterozygotes. The temporal and spatial control of murine Nat2 expression points to an endogenous role distinct from xenobiotic metabolism and indicates that Nat2 expression may be useful as a marker in cardiac development.

NAT1 and NAT2 genetic polymorphisms and environmental exposure as risk factors for oesophageal squamous cell carcinoma: a case-control study

Background

Tobacco smoking and red meat consumption are some of the known risk factors associated with the development of oesophageal cancer. N-acetytransferases (NAT1 and NAT2) play a key role in metabolism of carcinogenic arylamines present in tobacco smoke and overcooked red meat. We hypothesized that NAT1 and NAT2 genetic polymorphisms may influence the risk of oesophageal cancer upon exposure to environmental carcinogens.

Methods

Single nucleotide polymorphisms (SNPs) in the NAT1 and NAT2 genes were investigated by genotyping 732 cases and 768 healthy individuals from two South African populations to deduce the acetylator phenotype (slow, intermediate or rapid) from the combination of the genotyped SNPs.

Results

The 341 CC genotype (rs1801280) was significantly associated with a reduced risk for oesophageal cancer in the Mixed Ancestry population (OR = 0.31; 95% CI 0.11-0.87). The NAT2 slow/intermediate acetylator status significantly increased the risk among cigarette smokers in the Black population (OR = 2.76; 95% CI 1.69-4.52), as well as among alcohol drinkers in the Mixed Ancestry population (OR = 2.77; 95% CI 1.38-5.58). Similarly, the NAT1 slow/intermediate acetylator status was a risk factor for tobacco smokers in the Black population (OR = 3.41; 95% CI 1.95-5.96) and for alcohol drinkers in the Mixed Ancestry population (OR = 3.41; 95% CI 1.70-6.81). In a case-only analysis, frequent red meat consumption was associated with a significantly increased cancer risk for NAT2 slow/intermediate acetylators in the Mixed Ancestry population (OR = 3.55; 95% CI 1.29-9.82; P = 0.019), whereas daily white meat intake was associated with an increased risk among NAT1 slow/intermediate acetylators in the Black population (OR = 1.82; 95% CI 1.09-3.04; P = 0.023).

Conclusions

Our findings indicate that N-acetylation polymorphisms may modify the association between environmental risk factors and oesophageal cancer risk and that N-acetyltransferases may play a key role in detoxification of carcinogens. Prevention strategies in lifestyle and dietary habits may reduce the incidence of oesophageal cancer in high-risk populations.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-015-1105-4) contains supplementary material, which is available to authorized users.

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.

Association of NAT1 and NAT2 genes with nonsyndromic cleft lip and palate

Nonsyndromic cleft lip and palate (NSCLP) is a common congenital deformity, often associated with environmental risk factors, including alcohol, smoking, drugs and radiation exposure. N-acetyltransferase (NAT)1 and NAT2 genes are involved in the detoxification and metabolic activation of numerous drugs and chemicals. The aim of the present study was to investigate whether genetic variations in these two genes and gene‑gene interactions are associated with NSCLP. We investigated eight NAT1 tag single nucleotide polymorphisms (SNPs) and five NAT2 tag SNPs, selected from HapMap data. These SNPs were examined for associations with NSCLP in 204 patients and 226 controls. Strong evidence of an association with NSCLP was identified for rs4921580 in the NAT1 gene, and haplotype analysis supported these findings. We also found a significant difference between NSCLP and control groups for rs1041983 in the NAT2 gene. The results of gene‑gene interaction analyses also indicated that the combination of rs4921580 (Cg+gg) x rs1041983 (Ct+tt) increased the risk of NSCLP. Thus, the present study provides evidence for the role of NAT1 and NAT2 variations in NSCLP, and indicates that interactions between the NAT1 and NAT2 genes may be important in susceptibility to NSCLP.

A meta-analysis of the NAT1 and NAT2 polymorphisms and prostate cancer: a huge review

Studies revealing conflicting results on the role of NAT1 or NAT2 phenotypes on prostate cancer risk led us to perform a meta-analysis to investigate the association of these polymorphisms and prostate cancer risk. The meta-analysis included six studies with NAT1 genotyping (610 prostate cancer cases and 713 controls), and 10 studies with NAT2 genotyping (1,253 cases and 1,722 controls). The fixed effects odds ratio was 0.96 [95% confidence interval (95% CI): 0.75, 1.21; I(2) = 32.9%, P for heterogeneity = 0.189] for the NAT1 genotype, and the random effects odds ratio was 1.10 (95% CI: 0.87, 1.39; I(2) = 49.1%, P for heterogeneity = 0.039) for the NAT2 genotype. For NAT2 polymorphism, a statistically significant association between NAT2 polymorphism and prostate cancer appeared in Asians, but not in Caucasians. In conclusion, the NAT1 or NAT2 phenotypes detoxify carcinogens and their reactive intermediates are unlikely to be the cause of PCa development.

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.

Expression of N-acetyltransferase in monocyte-derived dendritic cells

Dendritic cells (DCs) are known to internalize, process, and present low-molecular-weight chemicals to T cells in the course of the sensitization and elicitation phase of allergic contact dermatitis. Thus, DCs may be involved in metabolic activation and detoxification of haptens and thereby influence the quantity of immunogens inducing sensitization. Recently, the cytochrome P-450 enzymes expressed in monocyte-derived dendritic cells (MoDCs) were characterized. In the present study, N-acetyltransferase 1 and 2 (NAT-1 and -2) mRNA expression and N-acetylation capacities of these cells were investigated. Monocytes from healthy donors were incubated with granulocyte-monocyte colony-stimulating factor (GM-CSF) and interleukin (IL)-4 for 6 d and the resulting immature MoDCs were characterized by flow cytometry. Total RNA from MoDCs was isolated, reverse transcribed, and polymerase chain reaction (PCR) for NAT-1 and NAT-2 mRNA was performed. Data showed the presence of mRNA for NAT-1 (9 of 10 donors) and NAT-2 (8 of 10 donors) in these cells. NAT-1 enzyme activities were achieved through acetylation of para-aminobenzoic acid (PABA) by MoDC cell lysates and activities varied between 23.4 and 26.6 nmol/mg/min. In addition, complete cell acetylation of para-phenylenediamine (PPD), estimated via analysis of monoacetyl-PPD (MAPPD) and diacetyl-PPD (DAPPD) in cell culture supernatants, confirmed that in vitro generated MoDCs (4 of 6 donors) express metabolic active N-acetyltransferase (NAT-1). In the case of PPD, our results emphasize that N-acetylation status may influence the amounts of immunogens available for sensitization to PPD.

ArylamineN-acetyltransferases

Arylamine N-acetyltransferases (NATs), known as drug- and carcinogen-metabolising enzymes, have had historic roles in cellular metabolism, carcinogenesis and pharmacogenetics, including epidemiological studies of disease susceptibility. NAT research in the past 5 years builds on that history and additionally paves the way for establishing the following new concepts in biology and opportunities in drug discovery: i) NAT polymorphisms can be used as tools in molecular anthropology to study human evolution; ii) tracing NAT protein synthesis and degradation within cells is providing insight into protein folding in cell biology; iii) studies on control of NAT gene expression may help to understand the increase in the human NAT isoenzyme, NAT1, in breast cancer; iv) a NAT homologue in mycobacteria plays an essential role in cell-wall synthesis and mycobacterial survival inside host macrophage, thus identifying a novel biochemical pathway; v) transgenic mice, with genetic modifications of all Nat genes, provide in vivo tools for drug metabolism; and vi) structures of NAT isoenzymes provide essential in silico tools for drug discovery.

Phase I and Phase II Enzyme Polymorphisms and Childhood Cancer

Childhood cancers continue to be challenging clinical entities whose etiology, demographic characteristics, clinical progression, treatment efficacy, and outcomes remain incompletely understood. Research suggests that multiple environmental and genetic factors may play crucial roles in the pathophysiology of many of these malignancies. Recent attention has been directed to the role of carcinogen metabolizing enzymes in the etiology and progression of cancer in both adults and children due to their multitude of polymorphic variants and their intimate interaction with environmental factors. In particular, xenobiotic metabolizing enzymes (XME), which are intimately involved in the activation and deactivation of many environmental carcinogens, have become an area of significant interest. Traditionally, these enzymes have been classified into either phase I or phase II enzymes depending on their substrates, activity, and occasionally based on their sequence in the metabolic pathways, and have been demonstrated to have numerous polymorphic variants. Phase I enzymes predominantly consist of cytochrome enzymes responsible for mixed function oxidase activity, whereas phase II enzymes are frequently conjugation reactions necessary for drug metabolism or the further metabolism of phase I enzyme products. Current research has discovered numerous interactions between polymorphisms in these enzymes and changes in cancer susceptibility, treatment efficacy, and clinical outcomes in childhood cancer. Furthermore, studies of polymorphisms in these enzymes have demonstrated to have synergistic/antagonistic interactions with other XME polymorphisms and demonstrate variable influences on disease pathophysiology depending on the patient's ethnic background and environmental milieu. Continuing research on the role of polymorphisms in phase I and phase II enzymes will likely further elucidate the intimate role of these polymorphisms with environmental factors in the etiology of childhood cancer.

N-Acetyltransferase and sulfotransferase activity in human prostate: potential for carcinogen activation

BACKGROUND

N-Acetyltransferases (NATs) and sulfotransferases (SULTs) are key phase II metabolizing enzymes that can be involved both in the detoxification and in the activation of many human promutagens and procarcinogens.

METHODS AND RESULTS

We investigated the expression of NATs and SULTs in human prostate and tested their role in the activation the N-hydroxy (N-OH) metabolite of 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), a dietary carcinogen, to form DNA adducts. Western blotting showed detectable levels of NAT1, SULT1A1 and SULT1A3 with marked inter-individual variation. NAT2 and other SULT enzymes were not detectable. NAT1 was localized by immunohistochemistry to the cytoplasm of epithelial cells. The presence of acetyl Co-enzyme A (acetyl CoA) and 3'-phosphoadenosine-5'-phosphosulfate (PAPS), NAT and SULT cofactors, respectively, significantly increased the level of DNA adducts, detected by P-postlabelling analysis, in calf thymus DNA incubated with N-OH-IQ and prostate cytosolic fractions. The enhancement in the level of DNA adducts in the presence of PAPS correlated with the level of SULT1A1 protein. A single prostate cytosol with the SULT1A1*2/*2 genotype produced less DNA adducts than cytosols with the *1/*2 and *1/*1 genotypes. No significant correlation was observed between NAT1 protein level and the formation of DNA adducts, even in the presence of acetyl CoA.

CONCLUSIONS

In conclusion, we demonstrated that NAT1, SULT1A1 and SULT1A3 are present in human prostate and that both enzyme classes significantly contribute to the activation of N-hydroxylated heterocyclic amines to DNA-damaging species in this tissue. Variation in expression levels, in combination with dietary and/or environmental exposure to carcinogens, could be influential in determining individual susceptibility to prostate cancer.

Effect of NAT1 and NAT2 genetic polymorphisms on colorectal cancer risk associated with exposure to tobacco smoke and meat consumption

N-Acetyltransferases 1 and 2 (NAT1 and NAT2), both being highly polymorphic, are involved in the metabolism of aromatic and heterocyclic aromatic amines present in cigarette smoke and red meat cooked by high-temperature cooking techniques. We investigated the effect of differences in acetylation capacity, determined by NAT1 and NAT2 genotypes, on colorectal cancer risk associated with exposure to tobacco smoke or red meat consumption. In this population-based case-control study in Germany, 505 patients with incident colorectal cancer and 604 age- and sex-matched control individuals with genotyping data and detailed risk factor information were included. Genotyping of NAT1 and NAT2 genetic polymorphisms was done using a fluorescence-based melting curve analysis method. The association between genotypes, environmental exposures, and colorectal cancer risk was estimated using multivariate logistic regression. Colorectal cancer risk associated with active smoking was elevated after accumulation of 30(+) pack-years of smoking [odds ratio (OR), 1.4; 95% confidence interval (95% CI), 0.9-2.2] but not significantly modified by either NAT1 or NAT2 genotype. Exposure to environmental tobacco smoke was associated with an increased risk for colorectal cancer only among NAT2 fast acetylators (OR, 2.6; 95% CI, 1.1-5.9 for exposure in childhood and adulthood). Frequent consumption of red meat significantly increased colorectal cancer risk for the group comprising all NAT2 fast acetylators or carriers of the NAT1*10 allele (OR, 2.6; 95% CI, 1.1-6.1) but not among those with "slow" NAT1 and NAT2 genotypes. Our findings indicate that NAT1 and NAT2 genotypes may contribute jointly to individual susceptibility and that heterocyclic aromatic amines may play an important role in colorectal cancer associated with red meat and possibly also exposure to environmental tobacco smoke.

Cumulative genetic defects in carcinogen metabolism may increase breast cancer risk (The Netherlands)

Variants in the metabolic genes NAT1, NAT2, GSTM1 or GSTT1, may cause differences in individual detoxifying capacity of possible carcinogens. We examined the cumulative effect of putative at risk genotypes on breast cancer risk and we examined the extent to which these polymorphisms modify the association between smoking and breast cancer. A case cohort study was conducted in the DOM cohort with 676 breast cancer cases and a random sample of 669 individuals. No effect of the NAT1, NAT2 or GSTM1 genotypes on breast cancer risk was observed. However, women with GSTT1 null genotype had a 30% increased breast cancer risk compared to women with GSTT1 present (RR = 1.30 (95% confidence interval (CI) 1.04-1.64)). Smoking did not influence breast cancer risk nor did genetic variations in NAT1, NAT2 or GSTM1 in combination with smoking. Compared to women who never smoked with GSTT1 present, women with GSTT1 null genotype and who formerly smoked showed an increased breast cancer risk (RR = 2.55 (95% CI 1.10-5.90)), but current smokers who smoked 20 cigarettes or more per day did not (RR = 1.06 (95% CI 0.51-2.18)). Increasing numbers of putative at risk genotypes increased breast cancer risk in a dose dependent manner (p for trend 0.01). The risk was more than doubled in women with all four risk genotypes, RR = 2.45 (95% CI 1.24-4.86), compared to women with zero putative at risk genotypes. In conclusion, the results of this study suggest that presence of three or more putative at risk genotypes increases breast cancer risk.

Polymorphisms of cytochrome P4501A2 and N-acetyltransferase genes, smoking, and risk of pancreatic cancer

To test the hypothesis that genetic variation in the metabolism of tobacco carcinogens, such as aromatic amines (AA) and heterocyclic amines (HCA), contributes to pancreatic cancer, we have examined genetic polymorphisms of three key enzymes, i.e. cytochrome P450 1A2 (CYP1A2) and N-acetyltransferase 1 and 2 (NAT1 and NAT2), in a hospital-based case-control study of 365 patients with pancreatic adenocarcinoma and 379 frequency-matched healthy controls. Genotypes were determined using PCR-restriction fragment length polymorphism (RFLP) and Taqman methods. Smoking information was collected by personal interview. Adjusted odds ratio (AOR) and 95% confidence interval (CI) was estimated by unconditional multivariate logistic regression analysis. We found that the NAT1 'rapid' alleles were associated with a 1.5-fold increased risk of pancreatic cancer (95% CI: 1.0-2.1) with adjustment of potential confounders. This effect was more prominent among never smokers (AOR: 2.4, 95% CI: 1.4-4.3) and females (AOR: 1.8, 95% CI: 1.0-3.1). Some genotypes were significantly associated with increased risk for pancreatic cancer among smokers, especially heavy smokers (<20 pack years). For example, heavy smokers with the CYP1A2*1D (T-2467delT) delT, CYP1A2*1F(A-163C) C allele, NAT1 'rapid' or NAT2 'slow' alleles had an AOR (95% CI) of 1.4 (0.7-2.3), 1.9 (1.1-3.4), 3.0 (1.6-5.4) and 1.5 (0.8-2.6), respectively, compared with never smokers carrying the non-at-risk alleles. These effects were more prominent in females than in males. The corresponding AOR (95% CI) was 3.1 (1.0-8.0), 3.8 (1.5-10.1), 4.5 (1.6-12.7) and 2.0 (0.8-5.1) for females versus 1.0 (0.4-1.9), 1.1 (0.5-2.4), 2.1 (1.0-4.6) and 1.1 (0.5-2.6) for males. A significant synergistic effect of CYP1A2*1F C allele and NAT1"rapid" alleles on the risk for pancreatic cancer was also detected among never smokers (AOR: 2.9, 95% CI: 1.2-6.9) and among females (AOR: 2.5, 95% CI: 1.1-5.7). These data suggest that polymorphisms of the CYP1A2 and NAT1 genes modify the risk of pancreatic cancer.

The impact of genetic factors on the incidence of multiple primary tumors (MPT) of the head and neck

One of the most troublesome failures in head and neck tumors treatment is the incidence of multiple primary tumors (MPT). The aim of the study was to identity the genetic factors associated with the predisposition of second cancer occurrence. The polymorphisms of genes involved in carcinogen metabolic activation (CYP1A1, CYP2E1), detoxication (GSTM1, GSTT1, GSTM3, NAT2,) and DNA repair (XPD /A35931C-exon 23 and C22541A-exon 6/, XRCC1 /G28152A-exon 10 and C26304T-exon 6/, XRCC3/C18067T/) were studied by PCR-based techniques to analyze genotypes and allele distribution in 84 patients with MPT correlated with 182 subjects with a single tumor of head and neck and 143 cancer-free male volunteers recruited from healthy smokers. Out of 11 polymorphisms examined significant differences between studied groups in CYP1A1, GSTM1, NAT2 genes, but not at the CYP2E1, GSTT1, GSTM3, XPD (exon 23 and 6), XRCC1 (exon 10 and 6) and XRCC3 were established. Further, the coexistence of some genotypes/alleles associated with a higher cancer risk, so called 'risk genotypes' was established as an added genetic factor to MPT development. The interpretation of our data indicates that the same group of low-penetration genes is involved in the development of single and multiple primary head and neck cancer but their association with MPT is significantly stronger.

Screening and characterizing human NAT2 variants

Acetyl CoA:arylamine N-acetyltransferase (NAT; E.C. 2.3.1.5) enzymes play a key role in the metabolic activation of aromatic amine and nitroaromatic mutagens to electrophilic reactive intermediates. We have developed a system in which the activation of mutagens by recombinant human NAT2, expressed in Escherichia coli, can be detected by the appearance of Lac+ revertants. The mutagenesis assay is based on the reversion of an E. coli lacZ frameshift allele; the host strain for the assay is devoid of endogenous NAT activity and a plasmid vector is used for expression of human NAT2. A high-throughput version of the assay facilitates rapid screening of pools of NAT2 variants generated (for example) by random mutagenesis. Along with the methods for these assays, we present selected results of a screening effort in which mutations along the length of the NAT2 sequence have been examined. Homology modeling and simulated annealing have been used to analyze the potential effects of these mutations on structural integrity and substrate binding.

Generation and analysis of mice with a targeted disruption of the arylamine N-acetyltransferase type 2 gene

Arylamine N-acetyltransferases (NATs) are polymorphic xenobiotic metabolising enzymes, linked to cancer susceptibility in a variety of tissues. In humans and in mice there are multiple NAT isoforms. To identify whether the different isoforms represent inbuilt redundancy or whether they have unique roles, we have generated mice with a null allele of Nat2 by gene targeting. This mouse line conclusively demonstrates that the different isoforms have distinct functions with no compensatory expression in the Nat2 null animals of the other isoforms. In addition, we have used the transgenic line to show the pattern of Nat2 expression during development. Although Nat2 is not essential for embryonic development, it has a widespread tissue distribution from at least embryonic day 9.5. This mouse line now paves the way for the teratological role of Nat2 to be tested.

NAT gene polymorphisms and susceptibility to Alzheimer's disease: identification of a novel NAT1 allelic variant

BACKGROUND

Alzheimer's disease is multifactorial, having environmental, toxicological and genetic risk factors. Impaired folate and homocysteine metabolism has been hypothesised to increase risk. In addition to its xenobiotic-metabolising capacity, human arylamine N-acetyltransferase type-1 (NAT1) acetylates the folate catabolite para-aminobenzoylglutamate and is implicated in folate metabolism. The purpose of this study was to determine whether polymorphisms in the human NAT genes influence susceptibility to Alzheimer's disease.

METHODS

Elderly individuals with and without Alzheimer's disease were genotyped at the polymorphic NAT1 (147 cases; 111 controls) and NAT2 (45 cases; 63 controls) loci by polymerase chain reaction-restriction fragment length polymorphism, and the genotype and allele frequencies were compared using the chi-squared test.

RESULTS

Although a trend towards fast NAT2 acetylator-associated Alzheimer's disease susceptibility was indicated and the NAT1*10/1*10 genotype was observed only in cases of Alzheimer's disease (6/147, 4.1%), no significant difference in the frequency of NAT2 (p = 0.835) or NAT1 (p = 0.371) genotypes was observed between cases and controls. In addition, a novel NAT1 variant, NAT1*11B, was identified.

CONCLUSIONS

These results suggest that genetic polymorphisms in NAT1 and NAT2 do not influence susceptibility to Alzheimer's disease, although the increase in frequency of the NAT1*10 allele in Alzheimer's disease is worthy of further investigation. Due to its similarity with the NAT1*11A allele, NAT1*11B is likely to encode an enzyme with reduced NAT1 activity.

NAT2 slow acetylation and GSTM1 null genotypes may increase postmenopausal breast cancer risk in long-term smoking women

N-acetyltransferase (NAT) 1 and 2 and glutathione S-transferase (GST) M1 and T1 are phase II enzymes that are important for activation and detoxification of carcinogenic heterocyclic and aromatic amines, as present in cigarette smoke. We studied whether genetic polymorphisms in these genes modifies the relationship between smoking and breast cancer. A nested case-control study was conducted among participants in a Dutch prospective cohort. Breast cancer cases (n=229) and controls (n=264) were frequency-matched on age, menopausal status and residence. Compared to never smoking, smoking 20 cigarettes or more per day increased breast cancer risk statistically significant only in postmenopausal women [odds ratio (OR)=2.17; 95% confidence interval (CI) 1.04-4.51]. Neither NAT1 slow genotype, or GSTT1 null genotype, alone or in combination with smoking, affected breast cancer risk. However, compared to individuals with rapid NAT2 genotype, women with the very slow acetylator genotype (NAT2*5), who smoked for 20 years showed an increased breast cancer risk (OR=2.29; 95% CI 1.06-4.95). Similarly, the presence of GSTM1 null genotype combined with high levels of cigarette smoking (OR=3.00; 95% CI 1.46-6.15) or long duration (OR=2.53; 95% CI 1.24-5.16), increased rates of breast cancer. The combined effect of GSTM1 null genotype and smoking high doses was most pronounced in postmenopausal women (OR=6.78; 95% CI 2.31-19.89). In conclusion, our results provide support for the view that women who smoke and who have a genetically determined reduced inactivation of carcinogens (GSTM1 null genotype or slow NAT2 genotype (especially very slow NAT2 genotype)) are at increased risk of breast cancer.

Prenatal expression of N-acetyltransferases in C57Bl/6 mice

Exposure to carcinogens such as 4-aminobiphenyl (4ABP), found in tobacco smoke and other combustion products, results in the formation of detectable levels of 4ABP-hemoglobin adducts in cord blood and 4ABP-DNA adducts in conceptal tissue. The presence of these adducts requires that the parent compound undergo biotransformation. When exposure occurs in utero, the maternal, placental and conceptal tissues are all possible sites for the formation of DNA-reactive products. One step in the activation of 4ABP is catalyzed by N-acetyltransferases (NAT). The expression of NAT was evaluated in gestational day (GD) 10-18 conceptal tissues from C57Bl/6 mice. There was a quantitative increase in NAT1 and NAT2 mRNAs with increasing gestational age that was also reflected in age-related changes in functional protein measured as 4ABP-NAT activity. The ability to acetylate 4ABP increased from GD10 to 18 and was lower in conceptal tissue than in adult liver. The potential toxicologic significance of prenatal NAT expression was assessed by formation of 4ABP-DNA adducts. At GD 15 and 18, 4ABP-DNA adducts were detected by immunohistochemistry 24 h following a single oral dose of 120 mg 4ABP/kg. Based on nuclear fluorescence, conceptual 4ABP-DNA adducts were present at similar levels at GD15 and 18. Levels of 4ABP-DNA adducts were significantly higher in maternal liver compared with the conceptus. Results from this study show that both NAT genes were expressed prenatally and that functional enzymes were present. These data support the possible in situ generation of reactive products by the conceptus. The relative contributions of maternal activation of 4ABP and that by the conceptus remain to be determined.

The pharmacogenetics of NAT: structural aspects

Arylamine N-acetyltransferases (NATs) catalyze the transfer of an acetyl group from acetyl-CoA to arylhydrazines and to arylamine drugs and carcinogens or to their N-hydroxylated metabolites. NAT plays an important role in detoxification and metabolic activation of xenobiotics and was first identified as the enzyme responsible for inactivation of the antitubercular drug isoniazid, an arylhydrazine. The rate of inactivation was polymorphically distributed in the population: the first example of interindividual pharmacogenetic variation. Polymorphism in NAT activity is primarily due to single nucleotide polymorphisms (SNPs) in the coding region of NAT genes. NAT enzymes are widely distributed in eukaryotes and genome sequences have revealed many homologous members of this enzyme family in prokaryotes. The structures of S almonella typhimurium and Mycobacterium smegmatis NATs have been determined, revealing a unique fold in which a catalytic triad (Cys-His-Asp) forms the active site. Determination of prokaryotic and eukaryotic NAT structures could lead to a better understanding of their role in xenobiotics and endogenous metabolism.

Association of prostate cancer with rapid N-acetyltransferase 1 (NAT1*10) in combination with slow N-acetyltransferase 2 acetylator genotypes in a pilot case-control study

N-acetyltransferase-1 (NAT1) and N-acetyltransferase-2 (NAT2) are important in the metabolism of aromatic and heterocyclic amine carcinogens that induce prostate tumors in the rat. We investigated the association of genetic polymorphisms in NAT1 and NAT2, alone and in combination, with human prostate cancer. Incident prostate cancer cases and controls in a hospital-based case-control study were frequency-matched for age, race, and referral pattern. The frequency of slow acetylator NAT1 genotypes (NAT1*14, *15, *17) was 5.8% in controls but absent in cases. In contrast, in comparison with all other NAT1 genotypes the putative rapid acetylator NAT1 genotype (NAT1*10) was significantly higher in prostate cancer cases than controls (OR, 2.17; 95% CI, 1.08-4.33; P = 0.03). Combinations of NAT1*10 with NAT2 slow acetylator genotypes (OR, 5.08; 95% CI, 1.56-16.5; P = 0.008) or with NAT2 very slow (homozygous NAT2*5) acetylator genotypes (OR, 7.50; 95% CI, 1.55-15.4; P = 0.016) further increased prostate cancer risk. The results of this small pilot study suggest increased susceptibility to prostate cancer for subjects with combinations of NAT1*10 and slow (particularly very slow) NAT2 acetylator genotypes. This finding should be investigated further in larger cohorts and in other ethnic populations.

N-Acetyltransferases, sulfotransferases and heterocyclic amine activation in the breast

Heterocyclic amines are mammary carcinogens in rats and their N-hydroxy metabolites are substrates for subsequent metabolic activation by N-acetyltransferases (NAT) and sulfotransferases (SULT) in man. We investigated the expression of these enzymes in human breast tissue and the relationship between NAT genotype and NAT mRNA expression or enzyme activity. Immunohistochemical staining of sections of breast tissue identified expression of NAT1 and NAT2 protein in human mammary epithelial cells, but not in the stroma. We also measured the formation of DNA adducts of the heterocyclic amines 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine in calf thymus DNA after incubation of their promutagenic N-hydroxy metabolites with mammary cytosols prepared from reduction mammoplasty tissue. Experimental observations gained from use of enzyme cofactors and NAT and/or SULT inhibitors on cytosolic enzyme activity, recombinant NAT1 activity and heterocyclic amine-DNA adduct formation suggest that both NAT1 and SULT1A enzymes contribute significantly to the activation of N-hydroxylated heterocyclic amines in mammary tissue. NAT1 mRNA transcript levels were found to be two- to three-fold higher than mRNA transcripts of the NAT2 gene in reduction mammoplasty tissue and mammary epithelial cells. NAT1-specific p-aminobenzoic acid acetylation activity, but not NAT2-specific sulfamethazine acetylation activity, was detectable in mammary cytosols. There was no association apparent between NAT genotype and the levels of NAT mRNA or NAT enzyme activity, or between NAT1 genotype and IQ-DNA adduct formation mediated by mammary cytosols. Western blot analysis of mammary cytosolic protein showed detectable levels of SULT1A1 and SULT1A3.

Arylamine N-acetyltransferases - of mice, men and microorganisms

Arylamine N-acetyltransferases (NATs) catalyse the transfer of an acetyl group from acetyl CoA to the terminal nitrogen of hydrazine and arylamine drugs and carcinogens. These enzymes are polymorphic and have an important place in the history of pharmacogenetics, being first identified as responsible for the polymorphic inactivation of the anti-tubercular drug isoniazid. NAT has recently been identified within Mycobacterium tuberculosis itself and is an important candidate for modulating the response of mycobacteria to isoniazid. The first three-dimensional structure of the unique NAT family shows the active-site cysteine to be aligned with conserved histidine and aspartate residues to form a catalytic triad, thus providing an activation mechanism for transfer of the acetyl group from acetyl CoA to cysteine. The unique fold could allow different members of the NAT family to play a variety of roles in endogenous and xenobiotic metabolism.

Relevance of N-acetyltransferase 1 and 2 (NAT1, NAT2) genetic polymorphisms in non-small cell lung cancer susceptibility

The highly polymorphic N-acetyltransferases (NAT1 and NAT2) are involved in both activation and inactivation reactions of numerous carcinogens, such as tobacco derived aromatic amines. The potential effect of the NAT genotypes in individual susceptibility to lung cancer was examined in a hospital based case-control study consisting of 392 Caucasian lung cancer patients [152 adenocarcinomas, 173 squamous cell carcinomas (SCC) and 67 other primary lung tumours] and 351 controls. In addition to the wild-type allele NAT1*4, seven variant NAT1 alleles (NAT1*3, *10, *11, *14, *15, *17 and *22) were analysed. A new method based on the LightCycler (Roche Diagnostics Inc.) technology was applied for the detection of the polymorphic NAT1 sites at nt 1088 and nt 1095. The NAT2 polymorphic sites at nt 481, 590, 803 and 857 were detected by polymerase chain reaction-restriction fragment length polymorphism or LightCycler. Multivariate logistic regression analyses were performed taking into account levels of smoking, age, gender and occupational exposure. An increased risk for adenocarcinoma among the NAT1 putative fast acetylators [odds ratio (OR) 1.92 (1.16-3.16)] was found but could not be detected for SCC or the total case group. NAT2 genotypes alone appeared not to modify individual lung cancer risk, however, individuals with combined NAT1 fast and NAT2 slow genotype had significantly elevated adenocarcinoma risk [OR 2.22 (1.03-4.81)] compared to persons with other genotype combinations. These data clearly show the importance of separating different histological lung tumour subtypes in studies on genetic susceptibility factors and implicate the NAT1*10 allele as a risk factor for adenocarcinoma.

Placental arylamine N-acetyltransferase type 1: potential contributory source of urinary folate catabolite p-acetamidobenzoylglutamate during pregnancy

Human arylamine N-acetyltransferase type 1 (NAT1), better known as a drug-metabolising enzyme, has been proposed to acetylate the folate catabolite p-aminobenzoylglutamate (p-abaglu) to N-acetamidobenzoylglutamate (ap-abaglu) which is a major urinary folate catabolite. Using mass spectroscopic analysis, we demonstrate the formation of ap-abaglu by recombinant human NAT1 and human placental homogenates. Using density gradient centrifugation the placental enzymic activity which acetylates p-aba and the placental enzymic activity acetylating p-abaglu both have an S(20,w) value of 3.25 S. This is the expected value for a monomer of human NAT1 (33 kDa). The specific NAT1 inhibitor 5-iodosalicylate inhibits acetylation of both p-aba and p-abaglu catalysed by either recombinant human NAT1 or placental samples as the source of enzyme. These data demonstrate that NAT1 is the major placental enzyme involved in acetylating p-abaglu.

DNA adducts of 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) in fetal tissues of patas monkeys after transplacental exposure

Transplacental genotoxicity of the heterocyclic amine food-derived mutagen/carcinogen 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) has been investigated by (32)P-postlabeling assay for IQ-DNA adducts in maternal liver, placenta, and several fetal tissues of patas monkeys, after exposure to 15, 35, or 50 mg/kg IQ near the end of gestation or to the highest dose in the first or second trimester. Dose-dependent adduct formation occurred in all tissues, with the highest levels occurring in maternal liver. Adduct amounts were similar among fetal tissues and placenta, except for lower levels in fetal brain and slightly more adducts in fetal liver. Adducts in placenta, fetal liver, lung, kidney, skin, and adrenal gland, but not in maternal liver or fetal brain, increased significantly as gestation progressed. Pretreatment with phenobarbital, which induces CYP enzymes that detoxify IQ, decreased adducts in maternal liver and possibly placenta, but not in fetal tissues. The CYP inducer beta-naphthoflavone caused a significant increase in IQ-DNA adducts in fetal lungs. Regression analysis suggested that IQ activation in maternal and fetal liver and possibly placenta contributed to adduct formation in fetal tissues; adducts in placenta and/or fetal liver were strong predictors for those in most fetal tissues. The results indicate that exposure of pregnant primates to IQ results in DNA adduct formation in most fetal tissues, especially late in gestation; that upregulation of maternal detoxification does not provide fetal protection; and that adducts in placenta indicate adduct levels in fetal tissues.

N-acetyltransferase 1 and 2 polymorphisms in para-substituted arylamine-induced contact allergy

Sensitization to arylamines such as p-phenylenediamine is frequently diagnosed in patients with allergic contact dermatitis. Reactive metabolites of p-phenylenediamine might be produced in the skin by O-acetylation of N-hydroxylamines catalysed by local N-acetyltransferases (NATs). In this study, we tested whether genetic polymorphisms of NATs, which are known to affect enzyme activity, may influence the susceptibility to para-substituted arylamine-induced contact eczema. Using polymerase chain reaction and restriction enzyme analysis, the distribution of polymorphisms of NAT1 and NAT2 was investigated in 88 patients sensitized to para-substituted aryl compounds and 123 healthy controls. NAT2 rapid acetylators, i.e. carriers of the NAT2*4 wild-type allele, were more common in the contact allergy (44%) than in the healthy control group [30%; P = 0.042, odds ratio 1.9 (95% confidence interval, CI 1. 05-3.27)]. Slow acetylators carrying the NAT2*5b/2*6a genotype were significantly less frequent among patients [13% vs. 38% in controls; P = 0.009, odds ratio 0.39 (95% CI 0.19-0.78)]. The carriage rate of the NAT1*10 allele, which is supposed to encode for a rapid NAT1 phenotype, was not significantly different between patients and controls [43% vs. 36%; odds ratio 1.5 (95% CI 0.88-2.68)]. Interactions between NAT2*4 and NAT1*10 were suggested by the increased frequency of the NAT2*4/NAT1*10 haplotype in patients (27%) compared with controls [15%; P = 0.039, odds ratio 2.1 (95% CI 1.04-4.04)]. As the NAT1 and NAT2 encoding genes are located in close proximity on chromosome 8p22, the latter finding could at least partly be due to genetic linkage. In fact, a linkage disequilibrium between NAT2*4 and NAT1*10 was observed in the contact allergy (P = 0.0025) and in the control group (P = 0.042). Our data indicate an association between the NAT2*4/NAT1*10 haplotype and contact sensitization to para-substituted aryl compounds. Therefore, acetylation may either enhance contact sensitization or NAT2*4 and NAT1*10 might be linked to an unknown susceptibility factor.

N-Acetyltransferase genetics and their role in predisposition to aromatic and heterocyclic amine-induced carcinogenesis

N-Acetyltransferases (EC 2.3.1.5) are important in both the activation and deactivation of aromatic and heterocyclic amine carcinogens. Two N-acetyltransferase isozymes (NAT1 and NAT2) encoded by NAT1 and NAT2, respectively, have been identified. Both NAT1 and NAT2 exhibit genetic polymorphisms, and recent investigations have increased our understanding of the relationship between genotype and phenotype. Several studies have shown a role for NAT1 and NAT2 acetylation polymorphisms in cancer risk in human populations, but the findings have been inconsistent. These findings may relate to variability in carcinogen exposures and to differences in acetylator genotype/phenotype determinations.

Genetic polymorphisms in human xenobiotica metabolizing enzymes as susceptibility factors in toxic response

Biotransformation plays an important role in the carcinogenic activity and organ specificity of environmental carcinogens. Large interindividual variation in the biotransformation has been reported, and genetic polymorphisms in some xenobiotica metabolizing enzymes can in part explain some of these differences. The concentration of the ultimate carcinogen, that will react with DNA, is determined by the rate of activation and detoxification. Individuals with a decreased rate of detoxification, i.e., lacking the glutathione S-transferase M1 gene, have a slightly higher level of bulky carcinogen-DNA adduct in some tissues, and do also have an increased level of chromosomal aberrations. In addition, the genotype may also influence the type of mutations, e.g., in tumor suppressor gene, transversion being predominant in the GSTM1 null group. People with slow N-acetyltransferase activity do generally have a higher adduct level of aromatic amines in bladder tissues. Genetic polymorphism in either CYP1A1 or glutathione S-transferase is linked to an increased risk of smoking related cancers, while N-acetyltransferase activity is related to cancers in which aromatic amines are the main risk factor. Combination of the high risk genotypes for activating and detoxification enzymes, e.g., CYP1A MspI/GSTM1 null is not only associated with an increased risk of cancer development, but also an increased level of markers of the biological active dose and early markers of effect. Additional studies on the role of genetic variants of xenobiotica metabolizing enzymes and combinations thereof at relevant low levels of exposure are important in order to establish guidance values for toxic compounds.

N-Acetyltransferase polymorphism and human cancer risk

Because of the important role ofN-acetyltransferase (NAT) enzymes in both metabolic activation and detoxification of certain precarcinogens, such as homo-and heterocyclic arylamines, extensive research in the past has focused on the relationship between the distribution of different variants of these enzymes and cancer susceptibility. In this context, we examined the relationship between the acetylator type of two NAT isozymes (NAT1 and NAT2) and cancer risk. It was shown that any independent overall association of those diseases with acetylation for eitherNATl orNAT2 is likely to be weak at most. Besides individual genetic profile, differences in the degree of exposure to environmental precarcinogens should also be considered. It was suggested that smoking and red meat intake were associated with bothNATl andNAT2 genotype in the carcinogenesis. A gene-gene interaction, even linkage betweenNATl andNAT2 may also exist.

Arylamine N-acetyltransferase type 2 (NAT2), chromosome 8 aneuploidy, and identification of a novel NAT1 cosmid clone: an investigation in bladder cancer by interphase FISH

Two genes (arylamine N-acetyltransferase types 1 and 2, NAT1 and NAT2), which are known to metabolize bladder carcinogens, are located on chromosome band 8p22. Alterations in chromosome 8, including deletions of 8p, occur frequently in many epithelium-derived tumors. In this study, fluorescence in situ hybridization (FISH) was used for study of the relationship between chromosome 8 deletions in the region of NAT1 and NAT2 and grade and stage of tumor in bladder cancer. Cells from 52 bladder tumors were examined by dual-labeling FISH with a centromere 8-specific probe and a cosmid probe for NAT2. A more limited number were examined for loss with both the NAT2 probe and a newly constructed NAT1-specific cosmid. Loss of NAT2 was found in 6/52 patients in more than 30% of cells, and in 10/52 in 10%-30% of cells examined. Six samples also showed loss of NAT1, indicating that the region of deletion spans at least the distance of the two genes. No obvious correlation between loss of NAT genes with grade and stage of tumor was evident. Interestingly, 17/52 (32%) tumors showed an increased copy number of chromosome 8, with tumors of low stage showing relatively smaller increases of chromosome 8. Loss of 8p22 and genetic instability involving chromosome 8 indicate that this chromosome is important in bladder cancer and that NAT genes will act as important genetic landmarks in defining deletions in this disease. Genes Chromosomes Cancer 25:376-383, 1999.