The NAT2* slow acetylator genotype is associated with bladder cancer in Taiwanese, but not in the Black Foot Disease endemic area population

N-acetyltransferase 2 polymorphism is associated with bladder cancer risk: An updated meta-analysis based on 54 case-control studies

OBJECTIVE

N-acetyltransferase 2 (NAT2) polymorphism could participate in the metabolism of carcinogens through regulating the activity of a series of critical enzymes. However, the effects of NAT2 polymorphism on bladder cancer (BCa) risk were still inconclusive. In order to illustrate whether NAT2 polymorphism may influence the susceptibility to BCa, we conducted this updated meta-analysis.

MATERIALS AND METHODS

Databases including PubMed, Medline, Embase, Web of Science, Cochrane Library, and China National Knowledge Infrastructure(CNKI) were systematically retrieved and we applied MetaGenyo to perform final meta-analysis. Odds ratios (ORs) as well as 95% confidence intervals (CIs) were calculated and Bonferroni method was applied to correct the P-value for multiple comparisons. The registration of this study protocol is at PROSPERO and ID is CRD42019133957.

RESULTS

Ultimately, 54 case-control studies were identified for final meta-analysis (13343 BCa cases and 18,586 controls). Overall analysis indicated that the slow genotype in NAT2 polymorphism was obviously associated with BCa risk (P_Bonferroni < 0.001). Subgroup analyses demonstrated that significant risk with the slow genotype was observed in Caucasians, Asians, smokers, non-exposed individuals, high grade bladder cancer (HGBC) patients and muscle-invasive bladder cancer (MIBC) patients. In addition, the intermediate NAT2 genotype was revealed to increase the BCa risk of Asians and transitional cell carcinoma (TCC) patients. However, no correlation was identified in Africans with the NAT2 polymorphism.

CONCLUSIONS

The slow NAT2 genotype was identified to be the risk genotype for BCa. The intermediate genotype could serve as the candidate risk genotype. The gene-smoking interaction with NAT2 polymorphism might accelerate the tumor progression.

Synergism between the N-acetyltransferase 2 gene and oxidant exposure increases the risk of idiopathic male infertility

N-acetyltransferase (NAT2) is a phase-II xenobiotic-metabolizing enzyme participating in the detoxification of toxic arylamines, aromatic amines and hydrazines. The present study was designed to investigate whether two common single-nucleotide polymorphisms (SNP) of the NAT2 gene (481C>T, rs1799929; 590G>A, rs1799930) are associated with susceptibility to idiopathic male infertility and to assess if the risk is modified by oxidant and antioxidant exposures. A total 430 DNA samples (203 infertile patients and 227 fertile men) were genotyped for the polymorphisms by PCR and restriction fragment length polymorphism. No association was found between the NAT2 polymorphisms and idiopathic male infertility. However, gene-environment interaction analysis revealed that a low-acetylation genotype, 590GA, was significantly associated with increased disease risk in men who had environmental risk factors such as cigarette smoking (OR 1.71, 95% CI 1.02-2.87, P = 0.042), alcohol abuse (OR 2.14, 95% CI 1.08-4.27, P = 0.029) and low fruit/vegetable intake (OR 1.68, 95% CI 1.01-2.79, P = 0.04). This pilot study found, as far as is known for the first time, that the polymorphism 590G>A of NAT2 is a novel genetic marker for susceptibility to idiopathic male infertility, but the risk is potentiated by exposure to various environmental oxidants.

Rapid and intermediate N-acetylators are less susceptible to oxidative damage among 4,4'-methylenebis(2-chloroaniline) (MBOCA)-exposed workers

OBJECTIVES

In this study, we explored the association between a marker of oxidative stress, 8-hydroxydeoxyguanosine (8-OHdG), and genetic polymorphism of the carcinogen-metabolizing enzyme N-acetyltransferase 2 (NAT2) among 4,4'-methylenebis(2-chloroaniline) (MBOCA)-exposed workers.

METHODS

The study population was recruited from four MBOCA-producing factories, and included 57 MBOCA-exposed workers and 101 unexposed control workers. Personal characteristics were collected by questionnaire. Plasma 8-OHdG levels were measured by LC/MS/MS. NAT2 alleles were measured by polymerase chain reaction-based restriction fragment length polymorphism (PCR-RFLP).

RESULTS

NAT2 polymorphism influenced the plasma 8-OHdG levels of MBOCA-exposed workers, but not of non-exposed workers. No difference between exposed and control groups was found for the crude 8-OHdG levels among rapid, intermediate, and slow acetylators. After adjusting for gender, age, smoking, and alcohol consumption habit, the 8-OHdG concentration in the MBOCA-exposed workers was 0.18pg/ml (95% CI -1.80 to -0.12) lower than the control group among rapid and intermediate acetylators. However, the difference between exposed and control groups was not significant for slow acetylators.

CONCLUSION

Gene-environment interactions could play a role in the carcinogenesis of occupational MBOCA exposure. We suggest that the impact of the NAT2 acetylator status is low, if at all, on the generation of the oxidative stress marker 8-OHdG in the investigated exposed group.

SLC39A2 and FSIP1 polymorphisms as potential modifiers of arsenic-related bladder cancer

Arsenic is a carcinogen that contaminates drinking water worldwide. Accumulating evidence suggests that both exposure and genetic factors may influence susceptibility to arsenic-induced malignancies. We sought to identify novel susceptibility loci for arsenic-related bladder cancer in a US population with low to moderate drinking water levels of arsenic. We first screened a subset of bladder cancer cases using a panel of approximately 10,000 non-synonymous single nucleotide polymorphisms (SNPs). Top ranking hits on the SNP array then were considered for further analysis in our population-based case-control study (n = 832 cases and 1,191 controls). SNPs in the fibrous sheath interacting protein 1 (FSIP1) gene (rs10152640) and the solute carrier family 39, member 2 (SLC39A2) in the ZIP gene family of metal transporters (rs2234636) were detected as potential hits in the initial scan and validated in the full case-control study. The adjusted odds ratio (OR) for the FSIP1 polymorphism was 2.57 [95% confidence interval (CI) 1.13, 5.85] for heterozygote variants (AG) and 12.20 (95% CI 2.51, 59.30) for homozygote variants (GG) compared to homozygote wild types (AA) in the high arsenic group (greater than the 90th percentile), and unrelated in the low arsenic group (equal to or below the 90th percentile) (P for interaction = 0.002). For the SLC39A2 polymorphism, the adjusted ORs were 2.96 (95% CI 1.23, 7.15) and 2.91 (95% CI 1.00, 8.52) for heterozygote (TC) and homozygote (CC) variants compared to homozygote wild types (TT), respectively, and close to one in the low arsenic group (P for interaction = 0.03). Our findings suggest novel variants that may influence risk of arsenic-associated bladder cancer and those who may be at greatest risk from this widespread exposure.

NAT2 fast acetylator genotypes are associated with an increased risk for lung cancer with wildtype epidermal growth factor receptors in Taiwan

Identifying the risk factors responsible for lung cancer especially for nonsmokers is critical for both its prevention and treatment. Studies have linked the polymorphisms in N-acetyltransferases (NAT2), a key enzyme for metabolism of hydrocarbons, with lung cancer in Asian female nonsmokers. Since a high percentage of lung adenocarcinoma in Asian female nonsmokers contains activating hotspot mutations in epidermal growth factor receptors (EGFR), we hypothesized that NAT2 polymorphisms might represent a risk factor in lung cancer with EGFR mutations. We studied NAT polymorphisms in 117 nonsmall cell lung cancer (NSCLC) patients and in 119 healthy controls and EGFR hotspot mutations in exons 18-21 in 100 of the 117 patients using polymerase chain reactions. NAT2 fast acetylator genotypes were significantly associated with patients with lung cancer (P = 0.04, odds ratio (OR): 1.90, 95% confidence interval (CI): 1.02-3.57). Further analyses revealed that NAT2 fast acetylator genotypes were significantly associated with NSCLC with wildtype EGFR (P = 0.008, OR: 3.16, 95% CI: 1.31-7.63), but not with those with EGFR mutations (P = 0.40). Therefore, NAT2 fast acetylator genotypes are a potential risk factor especially for lung cancer with wildtype EGFR.

N-acetyltransferase 2 genetic polymorphism: effects of carcinogen and haplotype on urinary bladder cancer risk

A role for the N-acetyltransferase 2 (NAT2) genetic polymorphism in cancer risk has been the subject of numerous studies. Although comprehensive reviews of the NAT2 acetylation polymorphism have been published elsewhere, the objective of this paper is to briefly highlight some important features of the NAT2 acetylation polymorphism that are not universally accepted to better understand the role of NAT2 polymorphism in carcinogenic risk assessment. NAT2 slow acetylator phenotype(s) infer a consistent and robust increase in urinary bladder cancer risk following exposures to aromatic amine carcinogens. However, identification of specific carcinogens is important as the effect of NAT2 polymorphism on urinary bladder cancer differs dramatically between monoarylamines and diarylamines. Misclassifications of carcinogen exposure and NAT2 genotype/phenotype confound evidence for a real biological effect. Functional understanding of the effects of NAT2 genetic polymorphisms on metabolism and genotoxicity, tissue-specific expression and the elucidation of the molecular mechanisms responsible are critical for the interpretation of previous and future human molecular epidemiology investigations into the role of NAT2 polymorphism on cancer risk. Although associations have been reported for various cancers, this paper focuses on urinary bladder cancer, a cancer in which a role for NAT2 polymorphism was first proposed and for which evidence is accumulating that the effect is biologically significant with important public health implications.

Bayesian synthesis of epidemiological evidence with different combinations of exposure groups: application to a gene–gene–environment interaction

Meta-analysis to investigate the joint effect of multiple factors in the aetiology of a disease is of increasing importance in epidemiology. This task is often challenging in practice, because studies typically concentrate on studying the effect of only one exposure, sometimes may report the interaction between two exposures, but rarely address more complex interactions that involve more than two exposures. In this paper, we develop a meta-analysis framework that combines estimates from studies of multiple exposures. A key development is an approach to combining results from studies that report information on any subset or combination of the full set of exposures. The model requires assumptions to be made about the prevalence of the specific exposures. We discuss several possible model specifications and prior distributions, including information internal and external to the meta-analysis data set, and using fixed-effect and random-effects meta-analysis assumptions. The methodology is implemented in an original meta-analysis of studies relating the risk of bladder cancer to two N-acetyltransferase genes, NAT1 and NAT2, and smoking status.

NAT2 slow acetylation and bladder cancer in workers exposed to benzidine

This study expands a previous study of NAT2 polymorphisms and bladder cancer in male subjects occupationally exposed only to benzidine. The combined analysis of 68 cases and 107 controls from a cohort of production workers in China exposed to benzidine included 30 new cases and 67 controls not previously studied. NAT2 enzymatic activity phenotype was characterized by measuring urinary caffeine metabolite ratios. PCR-based methods identified genotypes for NAT2, NAT1 and GSTM1. NAT2 phenotype and genotype data were consistent. A protective association was observed for the slow NAT2 genotype (bladder cancer OR = 0.3; 95% CI = 0.1 = 1.0) after adjustment for cumulative benzidine exposure and lifetime smoking. Individuals carrying NAT1wt/*10 and NAT1*10/*10 showed higher relative risks of bladder cancer (OR = 2.8, 95% CI = 0.8-10.1 and OR = 2.2, 95% CI = 0.6-8.3, respectively). No association was found between GSTM1 null and bladder cancer. A metaanalysis risk estimate of case-control studies of NAT2 acetylation and bladder cancer in Asian populations without occupational arylamine exposures showed an increased risk for slow acetylators. The lower limit of the confidence interval (OR = 1.4; 95% CI = 1.0-2.0) approximated the upper confidence interval for the estimate obtained in our analysis. These results support the earlier finding of a protective association between slow acetylation and bladder cancer in benzidine-exposed workers, in contrast to its established link as a risk factor for bladder cancer in people exposed to 2-naphthylamine and 4-aminobiphenyl. Study findings suggest the existence of key differences in the metabolism of mono- and diarylamines.

Bladder cancer: epidemiology, diagnosis, and management

PURPOSE

The purpose of this article is to present an overview of the epidemiology diagnosis, and management of bladder cancer, with a focus on the early stage of this disease.

OVERVIEW

English-language articles published between 1990 and 2000, as well as selected abstracts published in non-English languages before 1990, were reviewed. Epidemiologic data clearly indicate that bladder cancer is much more common in men, White persons, and the elderly. Cigarette smoking appears to be the most significant environmental risk factor. Screening for the disease is currently not standard in the United States or Canada. Potential tests include urine cytology, hematuria dipstick, and the urinary biomarkers. Diagnosis is made most often on the basis of the findings of cystoscopy, tumor biopsy, and urine cytology. Transurethral resection (TUR) of the tumor is generally the first-line treatment for superficial disease. Cystectomy is the "gold standard" treatment for invasive disease in many countries, although trimodality therapy (TUR, radiation, systemic chemotherapy) has shown promise as a bladder-preserving strategy. Intravesical therapy is effective for preventing disease recurrence, although its role in slowing disease progression is uncertain. Chemotherapy and radiation also can be used with cystectomy to treat or prevent pelvic recurrence of invasive disease or to prolong life in patients with metastatic disease.

CLINICAL IMPLICATIONS

Bladder cancer is a commonly occurring disease. Prevention efforts must focus on the avoidance or cessation of cigarette smoking and on public education relating to known environmental risk factors. Patient and disease factors must be considered in making treatment decisions and determining prognosis. Careful follow-up after treatment is essential. It is hoped that ongoing research on potential tumor markers and tumor-specific therapies ultimately will result in improved clinical outcomes for patients with this malignancy.

The enhanced bladder cancer susceptibility of NAT2 slow acetylators towards aromatic amines: a review considering ethnic differences

Human bladder cancer may be caused by exposure to aromatic amines. The polymorphic enzyme N-acetyltransferase 2 (NAT2) is involved in the metabolism of these compounds. Two classical studies on chemical workers in Europe, exposed in the past to aromatic amines like benzidine, unambiguously showed that the slow acetylator status is a genetic risk factor for arylamine-induced bladder cancer. In the former benzidine industry in Huddington, Great Britain, 22 of 23 exposed cases with bladder cancer, but only 57% of 95 local controls without bladder cancer were of the slow acetylator phenotype. In Leverkusen, Germany, 82% of 92 benzidine-exposed chemical workers with bladder cancer were of the slow acetylator phenotype, whereas only 48% of 331 chemical workers who had worked at that plant were of the slow acetylator phenotype. This is in line with several smaller studies, which also show an over-representation of the slow acetylator status in formerly arylamine-exposed subjects with bladder cancer. Some of these studies included also subjects that were exposed to aromatic amines by having applied dyes, paints and varnishes. These European findings are in contrast to a large study on Chinese workers occupationally exposed to aromatic amines. In this study, only five of 38 bladder cancer cases occupationally exposed to arylamines were of the slow acetylator genotype. This is much lower than the ratio of slow acetylators to the general population in China. This points to different mechanisms of susceptibility for bladder cancer upon exposure to aromatic amines between European (Caucasian) and Chinese populations.

The cellular metabolism and systemic toxicity of arsenic

Although it has been known for decades that humans and many other species convert inorganic arsenic to mono- and dimethylated metabolites, relatively little attention has been given to the biological effects of these methylated products. It has been widely held that inorganic arsenicals were the species that accounted for the toxic and carcinogenic effects of this metalloid and that methylation was properly regarded as a mechanism for detoxification of arsenic. Elucidation of the metabolic pathway for arsenic has changed our understanding of the significance of methylation. Both methylated and dimethylated arsenicals that contain arsenic in the trivalent oxidation state have been identified as intermediates in the metabolic pathway. These compounds have been detected in human cells cultured in the presence of inorganic arsenic and in urine of individuals who were chronically exposed to inorganic arsenic. Methylated and dimethylated arsenicals that contain arsenic in the trivalent oxidation state are more cytotoxic, more genotoxic, and more potent inhibitors of the activities of some enzymes than are inorganic arsenicals that contain arsenic in the trivalent oxidation state. Hence, it is reasonable to describe the methylation of arsenic as a pathway for its activation, not as a mode of detoxification. This review summarizes the current knowledge of the processes that control the formation and fate of the methylated metabolites of arsenic and of the biological effects of these compounds. Given the considerable interest in the dose-response relationships for arsenic as a toxin and a carcinogen, understanding the metabolism of arsenic may be critical to assessing the risk associated with chronic exposure to this element.

N-acetyltransferase 2 and bladder cancer: an overview and consideration of the evidence for gene-environment interaction

Genetic polymorphism of the carcinogen metabolizing enzyme N-acetyl transferase 2 (NAT2) may influence susceptibility to bladder cancers related to smoking or to occupational exposure to arylamine carcinogens. This article reviews the results of 21 published case-control studies of NAT2 polymorphism and bladder-cancer risk, with a total of 2700 cases and 3426 controls. The published evidence suggests that NAT2 slow acetylator phenotype or genotype may be associated with a small increase in bladder cancer risk. However, given the possibility of selective publication of results from studies that found an excess risk, the current evidence is not sufficient to conclude that there is a real increase in risk. Only five of the 21 studies reported results separately for the effect of NAT2 on bladder cancer risk in smokers and non-smokers. Although the results suggest that the effect may be greater in smokers than in non-smokers, the possibility of publication bias makes these results difficult to interpret. There was insufficient evidence to assess the joint effect of NAT2 and occupational exposure to arylamines on bladder cancer risk. Even if estimates of the effect of NAT2 from published data are correct, studies with around 3000-5000 cases will be needed to confirm them.

NAT2 slow acetylation and bladder cancer risk: a meta-analysis of 22 case-control studies conducted in the general population

The NAT2 gene is involved in phase II detoxification of aromatic monoamines, a class of known bladder carcinogens. Certain allelic combinations result in the slow acetylation phenotype, which is thought to increase bladder cancer risk. We conducted a meta-analysis of all identifiable published case-control studies conducted in the general population that had examined the relationship of acetylation status and bladder cancer risk (22 studies, 2496 cases, 3340 controls). Using meta-analysis techniques that employed weighting based on individual-study variation, slow acetylators had an approximately 40% increase in risk compared with rapid acetylators [odds ratio (OR) 1.4, 95% confidence interval (CI) 1.2-1.6]. Statistical tests indicated, however, that pooling of all studies, or of studies conducted in Caucasian populations, hid potentially important heterogeneity in the individual study results, and suggested that the relationship of NAT2 slow acetylation and bladder cancer risk might differ by geographical region. Studies conducted in Asia generated a summary OR of 2.1 (CI 1.2-3.8), in Europe, a summary OR of 1.4 (CI 1.2-1.6), and in the USA, a summary OR of 0.9 (CI 0.7-1.3). Among European studies, the relationship between NAT2 slow acetylation and bladder cancer risk did not differ by method used to assess acetylation status (older drug-based phenotyping methods: 10 studies, OR 1.5, CI 1.2-1.8; more recent NAT2 genotyping methods: four studies, OR 1.4, CI 1.1-1.7). Our results suggest that in most populations studied to date, NAT2 slow acetylation status is associated with a modest increase in bladder cancer risk.