Increased genotype frequency of N-acetyltransferase 2 slow acetylation in patients with rheumatoid arthritis

NAT2 Gene Polymorphisms in Turkish Patients with Psoriasis Vulgaris

Psoriasis is a common, chronic, and autoimmune skin disease. Factors that play a role in etiopathogenesis of psoriasis include internal factors such as genetic susceptibility and immunological factors and external factors such as stress, infection, trauma, drug, and environmental compounds. N-acetyltransferase 2 (NAT2) is a xenobiotic enzyme that is involved in the metabolism of drugs, environmental toxins, and carcinogens. In this study, we aimed to demonstrate whether the variations in the NAT2 gene lead to a predisposition to psoriasis by affecting the enzyme's ability to metabolize drugs and environmental components or not. Three polymorphisms (rs1799929, rs1799930, and rs1799931) in NAT2 gene were genotyped and compared by real-time PCR method in 260 psoriasis vulgaris patients and 200 healthy controls. There was no difference in the genotype distributions and allele frequencies of polymorphisms between psoriasis vulgaris patients and controls. When the effects of polymorphisms on the clinical features of the disease, such as onset age and severity, are assessed, it has been found that rs1799930 and rs1799929 are, respectively, associated with early onset age and severity of the disease. In conclusion, rs1799929, rs1799930, and rs1799931 polymorphisms of the NAT-2 gene do not appear to be a risk factor for the development of psoriasis. Conversely, they may have an effect on either more severe or early onset cases of the disease.

Arylamine N-acetyltransferase polymorphisms in Han Chinese patients with ankylosing spondylitis and their correlation to the adverse drug reactions to sulfasalazine

BACKGROUND

Polymorphisms of Arylamine N-acetyltransferase (NAT) that contribute to diverse susceptibilities of some autoimmune diseases are also linked to the metabolism of several drugs including sulfasalazine (SSZ). The aim of this study was to investigate the distribution of NAT polymorphisms in Han Chinese patients with ankylosing spondylitis (AS) and their correlation to sulfasalazine-induced adverse drug reactions (ADRs).

METHODS

Arylamine N-acetyltransferase 1 (NAT1) and arylamine N-acetyltransferase 2 (NAT2) genotypes were determined in 266 AS patients who received SSZ treatment and 280 healthy controls. The correlation between NAT polymorphisms and SSZ-induced ADRs was analyzed.

RESULTS

The co-occurrence frequency of NAT2 fast acetylator genotype and NAT1*10/NAT1*10 genotype was lower in AS patients than in controls. No positive correlations were detected between NAT polymorphisms and AS clinical features. The prevalence of SSZ-induced ADRs and drug withdrawal was 9.4% and 7.1%, respectively. The frequencies of overall ADRs, dose-related ADRs, and termination of drug treatment because of intolerance were higher in the NAT2 slow acetylator genotype carriers than in the fast-type carriers and in those with co-existence of NAT1 and NAT2 slow acetylator genotypes. Furthermore, the ADRs emerged earlier in the AS cases carrying both NAT1 and NAT2 slow acetylator genotypes.

CONCLUSIONS

The prevalence of co-occurring NAT2 fast acetylator genotype and NAT1*10/NAT1*10 genotype was lower in AS patients than in controls. The NAT2 slow acetylator genotype and co-existing NAT1 and NAT2 slow acetylator genotypes appear to be associated with higher risks of SSZ-induced ADRs.

Impact of interactions of cigarette smoking with NAT2 polymorphisms on rheumatoid arthritis risk in African Americans

OBJECTIVE

To examine whether polymorphisms in genes coding for drug-metabolizing enzymes (DMEs) have an impact on rheumatoid arthritis (RA) risk due to cigarette smoking in African Americans.

METHODS

Smoking status was evaluated in African American patients with RA compared with non-RA controls, with smoking exposure categorized as heavy smoker (≥10 pack-years) versus never smoker/<10 pack-years. Individuals were genotyped for a homozygous deletion polymorphism in the M1 gene loci of glutathione S-transferase (GSTM1-null) in addition to tagging single-nucleotide polymorphisms (SNPs) in N-acetyltransferase 1 (NAT1), NAT2, and epoxide hydrolase 1 (EPXH1). Associations of these genotypes with RA risk were examined using logistic regression, and gene-smoking interactions were assessed.

RESULTS

There were no significant associations of any DME genotype with RA. After adjustment for multiple comparisons, there were significant additive interactions between heavy smoking and the NAT2 SNPs rs9987109 (P(additive) = 0.000003) and rs1208 (P(additive) = 0.00001); the attributable proportion due to interaction ranged from 0.61 to 0.67. None of the multiplicative gene-smoking interactions examined remained significant with regard to overall disease risk, after adjustment for multiple testing. There was no evidence of significant gene-smoking interactions in analyses of GSTM1-null, NAT1, or EPXH1. DME gene-smoking interactions were similar when cases were limited to those patients who were positive for anti-citrullinated protein antibodies.

CONCLUSION

Among African Americans, RA risk imposed by heavy smoking appears to be mediated in part by genetic variation in NAT2. While further studies are needed to elucidate the mechanisms underpinning these interactions, these SNPs appear to identify African American smokers at a much higher risk for RA, in whom the relative risk is at least 2-fold higher when compared to nonsmokers lacking these risk alleles.

N-acetyltransferase-2 genotypes among patients with rheumatoid arthritis attending Jordan University Hospital

AIM

To determine the frequency of major N-acetyltransferase (NAT2) alleles and genotypes among Jordanian patients with rheumatoid arthritis (RA).

METHODS

The study was approved by the IRB of the Jordan University Hospital. An informed consent was signed by every patient. DNA samples from 150 healthy volunteers and 108 patients with RA were analyzed by polymerase chain reaction followed by a restriction fragment length polymorphism assay (PCR-RFLP) to determine the frequency of four major alleles: NAT2*4, NAT2*5, NAT2*6, and NAT2*7.

RESULTS

The most prevalent genotypes are those that encode the slow acetylation phenotype. About 59.3% of the patients with RA carried the slow, 33.3% the intermediate, and 7.4% the fast-encoding genotypes. The frequency of NAT2 alleles was 0.241 (95% confidence interval [CI] 0.184-0.298) for NAT2*4, 0.449 (95% CI 0.383-0.515) for NAT2*5, 0.273 (95% CI 0.214-0.332) for NAT2*6, and 0.037 (95% CI 0.012-0.062) for NAT2*7 allele. The overall frequency of the slow acetylation genotype in patients with RA is similar to that in healthy Jordanian volunteers. However, the NAT2*5/7 genotype was found in seven patients (6.5%) with RA and was absent in Jordanian volunteers, and the z test revealed that the difference was statistically significant. This genotype constituted 10.9% of the genotypes encoding slow acetylation.

CONCLUSION

The overall acetylator genotype in RA is similar to that in healthy volunteers. The overall slow acetylator genotypes do not seem to be a genetic risk factor for RA among Jordanians. However, the NAT2*5/7 genotype seems to be related to RA. The nature of this relationship needs further clarification.

The role of N-acetyltransferase 2 polymorphism in the etiopathogenesis of inflammatory bowel disease

BACKGROUND AND PURPOSE

Inflammatory bowel disease (IBD) consists of ulcerative colitis (UC) and Crohn's disease (CD), which are complex genetic disorders resulting from the interplay between several genetic and environmental risk factors. The arylamine N-acetyltransferase 2 (NAT2) enzyme detoxifies a wide spectrum of naturally occurring xenobiotics including carcinogens and drugs. Acetylation catalyzed by NAT2 is an important process in metabolic activation of arylamines to electrophilic intermediates that initiate carcinogenesis. The aim of our study was to determine whether there is any association between the susceptibility to inflammatory bowel disease among the variations of NAT2 genotypes.

METHODS

This study was carried out in 80 patients with IBD. The control group consisted of 100 healthy volunteers. The most common mutations found in the Caucasian population are at the positions 481T, 803G, 590A and 857A on the NAT2 gene. This was determined using the polymerase chain reaction-restriction fragment length polymorphism method with DNA extracted from peripheral blood.

RESULTS

Risk of IBD development was 3.86 for the carriers of the NAT2*5/NAT2*7 genotype and 2.53 for the carriers with NAT2*6/NAT2*7, but it was not statistically significant. A statistically significant correlation between the NAT2*7 allele prevalence and the risk for developing IBD was found (OR = 5.8; P = 0.005).

CONCLUSIONS

Higher prevalence of the NAT2*7 allele in patients with IBD and the obtained OR values could suggest that this mutation has the effect of increasing IBD development. Future studies are needed to confirm our assumptions on larger group of patients.

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.

Correlation between N-acetyltransferase 2 gene polymorphisms and genetic susceptibility to inflammatory bowel disease

AIM: To investigate the correlation between N-acetyltransferase 2 (NAT2) gene polymorphisms and genetic susceptibility to inflammatory bowel disease (IBD).

METHODS: One hundred and nineteen patients with IBD and 120 controls were recruited in this study. The wild-type allele (NAT2 4) and three variant alleles (NAT2 5B, 6A and 7B) of NAT2 were determined with the polymerase chain reaction restriction fragment length polymorphism method.

RESULTS: In IBD cases, the frequency of NAT2 4, NAT2 5B, NAT2 6A, NAT2 7B was 55.9%, 6.7%, 23.5% and 13.9%, respectively. No statistically significant difference was found in the frequencies between the IBD patients and controls. The frequency of rapid genotype and intermediate genotype and slow genotype in IBD patients was 35.3%, 41.2% and 23.5%, respectively. No statistically significant difference was found between the IBD patients and controls.

CONCLUSION: There is no correlation between genetic polymorphisms of NAT2 and IBD.

Association of PTPN22 single nucleotide polymorphism with rheumatoid arthritis but not with allergic asthma

PTPN22 gene encodes a lymphoid tyrosine phosphatase (LYP), an important negative regulator of T-cell responses. The 1858C>T (Arg620Trp) single nucleotide polymorphism (rs2476601) was found associated with autoimmune diseases, including rheumatoid arthritis (RA). Allergic diseases are similar to autoimmune diseases, by an exaggerated immune response to an antigen (allergen in this case) normally not invoking such response in healthy individuals. We investigated whether polymorphism 1858C>T in PTPN22 gene is associated with susceptibility to allergic asthma and RA in a Polish population. PTPN22 was genotyped in 173 patients with RA, in 198 patients with allergic asthma, and in 543 controls using PCR-RFLP. The patients with RA differed from healthy controls in frequencies of PTPN22 1858C>T alleles (P=0.0004; odds ratio (OR), 1.8; 95% CI, 1.33-2.55) and genotypes (P=0.0009). Strong associations of 1858T allele with RA limited to joints (0.21 vs 0.12, P=0.0002; OR, 2.1; 95% CI, 1.44-3.00), with erosive disease (0.20 vs 0.12, P=0.0003; OR, 1.92; 95% CI, 1.34-2.71), with a lack of rheumatoid factor (RF; 0.23 vs 0.12, P=0.0008; OR, 2.29; 95% CI, 1.44-3.63), and weak association with the presence of RF (0.17 vs 0.12, P=0.02; OR, 1.6; 95% CI, 1.10-2.40) in comparison with healthy controls were observed. Very strong association of 1858T allele (P<0.0001; OR, 2.72; 95% CI, 1.9-3.9) and T phenotype (P<0001; OR, 3.2; 95% CI, 2.1-4.9) with antibodies to cyclic citrullinated peptide (CCP) was found. When patients with allergic asthma were typed for PTPN22 1858C>T polymorphism, no difference with control was found. Subdivision of patients into those with mild, moderate, or severe asthma did not reveal any associations. In conclusion, we confirmed associations between several clinical manifestations of RA and PTPN22 1858T allele. However, no association with 1858C>T polymorphism was found for susceptibility to allergic asthma or for severity of the disease.

N-acetyltransferase 2 slow acetylator genotype associated with adverse effects of sulphasalazine in the treatment of inflammatory bowel disease

AIM

N-acetyltransferase 2 (NAT2) is an important enzyme catalyzing N-acetylation of sulfasalazine (SASP). The aim of the present study was to investigate associations of the genotypes of NAT2 with inflammatory bowel disease (IBD), and with adverse effects of SASP, which is used as the first-line treatment of IBD.

PATIENTS AND METHODS

The wildtype allele (NAT2*4) and three variant alleles (NAT2*5B, NAT2*6A and NAT*7B) of the NAT2 gene were determined in 101 patients with IBD (84 patients with ulcerative colitis and 17 patients with Crohn's disease) and 109 healthy controls by the polymerase chain reaction-restriction fragment length polymorphism method. Sixty-eight patients with IBD treated with SASP were followed, and their adverse reactions were recorded.

RESULTS

Eleven patients (16%) experienced adverse effects from SASP, including nine cases of sulfapyridine (SP) dose-related adverse effects and two cases of hypersensitivity (skin rash). Patients with the slow acetylator genotypes without the NAT2*4 allele experienced adverse effects more frequently (36%) than those with the fast acetylator genotypes with at least one NAT2*4 allele (11%), but the results were not significantly different (OR of 0.26, 95% CI 0.065 to 1.004; P=0.051). However, those with the slow acetylator genotypes experienced more SP dose-related adverse effects than those with the fast acetylator genotypes (36% versus 8%, OR of 0.17, 95% CI 0.039 to 0.749; P=0.019).

CONCLUSIONS

The NAT2 gene polymorphism was not associated with susceptibility to IBD in Chinese populations, but the NAT2 slow acetylator genotypes were significantly associated with SP dose-related adverse effects of SASP in the treatment of IBD.

A cross-sectional study of self-reported chemical-related sensitivity is associated with gene variants of drug-metabolizing enzymes

BACKGROUND

N-acetyltransferases (NAT) and glutathione S-transferases (GST) are involved in the metabolism of several ubiquitous chemical substances leading to the activation and detoxification of carcinogenic heterocyclic and aromatic amines. Since polymorphisms within these genes are described to influence the metabolism of ubiquitous chemicals, we conducted the present study to determine if individuals with self-reported chemical-related sensitivity differed from controls without self-reported chemical-related sensitivity with regard to the distribution of genotype frequencies of NAT2, GSTM1, GSTT1, and GSTP1 polymorphisms.

METHODS

Out of 800 subjects who answered a questionnaire of ten items with regard to their severity of chemical sensitivity 521 unrelated individuals agreed to participate in the study. Subsequently, genetic variants of the NAT2, GSTM1, GSTT1, and GSTP1 genes were analyzed.

RESULTS

The results show significant differences between individuals with and without self-reported chemical-related sensitivity with regard to the distribution of NAT2, GSTM1, and GSTT1 gene variants. Cases with self-reported chemical-related sensitivity were significantly more frequently NAT2 slow acetylators (controlled OR = 1.81, 95% CI = 1.27-2.59, P = 0.001). GSTM1 and GSTT1 genes were significantly more often homozygously deleted in those individuals reporting sensitivity to chemicals compared to controls (GSTM1: controlled OR 2.08, 95% CI = 1.46-2.96, P = 0.0001; GSTT1: controlled OR = 2.80, 95% CI = 1.65-4.75, P = 0.0001). Effects for GSTP1 gene variants were observed in conjunction with GSTM1, GSTT1 and NAT2 gene.

CONCLUSION

The results from our study population show that individuals being slow acetylators and/or harbouring a homozygous GSTM1 and/or GSTT1 deletion reported chemical-related hypersensitivity more frequently.

Arylamine N-acetyltransferase gene polymorphisms: markers for atopic asthma, serum IgE and blood eosinophil counts

INTRODUCTION

Polymorphisms in N-acetyltransferase 2 (NAT2), present on chromosome 8p22, are responsible for the N-acetylation variants, which segregate human populations into rapid, intermediate and slow acetylators and influence the susceptibility towards atopic disorders. We have undertaken a study of the North Indian population to screen for various NAT2 polymorphisms and to investigate their association with atopic asthma and related phenotypes.

METHODS

First, to establish linkage of the 8p22 region with asthma, 158 families were recruited from North India. Next, a total of 219 unrelated atopic asthmatics and 210 unrelated healthy controls were recruited for case-control disease association studies.

RESULTS

A suggestive linkage was observed with microsatellite marker D8S549, 2.6 MB upstream of NAT2. By sequencing the DNA of 40 individuals, the T111C, G191A, A434C and C759T single nucleotide polymorphisms (SNPs) in NAT2 were found to be nonpolymorphic in our population and a pattern of strong linkage disequilibrium was observed among the T341C, C481T and A803G polymorphisms. Thus, a total of 429 individuals were genotyped for the C481T and unlinked C282T polymorphisms. The C481T polymorphism was found to be significantly associated with asthma in our case-control studies at the genotype level (Armitage p = 0.00027). C481T also showed a marginal association with serum total IgE (TsIgE) (p = 0.022). Furthermore, percent blood eosinophil counts were found to be significantly higher in patients carrying the 481T allele (p = 0.0037). Significant association was also detected with respect to the C282T polymorphism and TsIgE (p = 0.008). Moreover, C_T was found to be an important risk (p = 0.001), while C_C was a major protective haplotype (p = 0.0005). The associations remained significant after Bonferroni correction for multiple testing.

CONCLUSION

In summary, the genetic variants of the NAT2 gene do not seem to affect asthma alone, but act as modulators of asthma-related traits, such as serum IgE and blood eosinophil counts, and therefore could serve as genetic markers.

Pharmacogenetics/pharmacogenomics and antirheumatic drugs in rheumatology

Genomic medicine has raised many expectations with regard to individualized therapies. Drug response is a complex function of many genes interacting with environmental and behavioral factors. In addition, poor prescribing, interactions between drugs and an incomplete understanding of the metabolism of many drugs, which are administered simultaneously to treat concomitant morbidities, are leading causes of the occurrence of adverse drug reactions in chronic non-inflammatory and autoimmune rheumatic diseases. Symptomatic non-steroidal anti-inflammatory drugs, as well as disease-modifying drugs, are complicated by drop-outs (poor patient compliance) in a large percentage of patients. Even though intensive and careful monitoring is always clearly advisable, preliminary data suggest that typing of genes controlling the effects, metabolism and response of drugs might be of clinical utility to define the ‘at-risk’ genotype.

Lack of association between arylamine N-acetyltransferase 2 (NAT2) polymorphism and systemic sclerosis

OBJECTIVES

It has been shown that exposure to some environmental toxins may induce scleroderma-like illness in predisposed individuals, but the etiopathogenesis of the idiopathic form of systemic sclerosis (SSc) remains obscure. The genetic background of this illness has been confirmed in multiple studies. We investigated whether patients with SSc differ from healthy subjects with regard to the enzymatic activity of polymorphic N-acetyltransferase 2 (NAT2).

METHODS

The study was carried out in 39 patients with SSc; 15 fulfilled the criteria of diffuse SSc (dSSc) and 24 of limited SSc (lSSc); an ethnically matched control group consisted of 100 healthy volunteers. Acetylation phenotype was estimated using the isoniazid as a model drug. The most common mutations in the Caucasian population at positions 481T, 803G, 590A and 857A on the NAT2 gene were determined using the polymerase chain reaction-restriction fragment length polymorphism method with deoxyribonucleic acid (DNA) extracted from peripheral blood.

RESULTS

In the group of patients with SSc, the frequency of fast acetylator genotypes was 38.5% (95% CI 23.4-55.4), while that for the genotypes coding slow acetylator status was 51.3% (95% CI 34.8-67.6). There was a strong correlation between NAT2 phenotype and NAT2 genotype with a concordance of 97%. We did not observe a preponderance of slow acetylators among patients with SSc and in two subsets of SSc. With the sample size analyzed in the present study, there is a 90% probability of detecting significant differences in distribution of slow, fast, and intermediate phenotypes between patients with SSc and controls, there is a difference of at least 30.3, 28.7 and 21.9% in the distribution of these phenotypes in the general population, respectively.

CONCLUSION

Acetylator status does not seem to be the significant factor in the development of SSc in patients with both subsets of this autoimmune disease, but further studies are required to confirm this conclusion.

N-acetyltransferase 2 genotype-related efficacy of sulfasalazine in patients with rheumatoid arthritis

PURPOSE

For the individual optimization of drug therapy with sulfasalazine (SASP), we studied the influence of the N-acetyltransferase 2 (NAT2) genotype on the pharmacokinetics, efficacy, and incidence of adverse reactions of SASP in patients.

METHODS

Ninety-six rheumatoid arthritis (RA) patients were treated or had been treated with 0.5 and/or 1.0 g/day of SASP. The wild-type allele (NAT2*4) and three variant alleles (NAT2*5B, *6A, and *7B) of NAT2 were determined by the polymerase chain reaction-restriction fragment length polymorphism method. Plasma concentrations of SASP and its two metabolites, sulfapyridine (SP) and N-acetylsulfapyridine (AcSP), were estimated by HPLC. Therapeutic efficacy and incidence of adverse reactions were also monitored as recommended by the American College of Rheumatology.

RESULTS

Patients were classified into three groups by NAT2 genotyping: Rapid Type (homozygote for NAT2*4), Intermediate Type (heterozygote for NAT2*4 and variant alleles), and Slow Type (homozygote for variant alleles). There was no clear difference in the genotype frequencies between RA patients and healthy subjects. NAT2 genotypes significantly affected both the plasma concentration ratios of SP to AcSP (SP/AcSP) and the efficacy of SASP (p < 0.05). Adverse reactions to SASP were found in 26 (27.1%) out of 96 patients, and there was no difference among the three genotype groups.

CONCLUSIONS

NAT2 gene polymorphism is related to the plasma SP/AcSP ratio and the efficacy of SASP.