Correlation between N-acetyltransferase activity and NAT2 genotype in Chinese males

Drug-Induced Liver Injury in the Elderly: Consensus Statements and Recommendations from the IQ-DILI Initiative

The elderly demographic is the fastest-growing segment of the world's population and is projected to exceed 1.5 billion people by 2050. With multimorbidity, polypharmacy, susceptibility to drug-drug interactions, and frailty as distinct risk factors, elderly patients are especially vulnerable to developing potentially life-threatening safety events such as serious forms of drug-induced liver injury (DILI). It has been a longstanding shortcoming that elderly individuals are often a vulnerable population underrepresented in clinical trials. As such, an improved understanding of DILI in the elderly is a high-priority, unmet need. This challenge is underscored by recent documents put forward by the U.S. Food and Drug Administration (FDA) and European Medicines Agency (EMA) that encourage data collection in the elderly and recommend improved practices that will facilitate a more inclusive approach. To establish what is already known about DILI in the elderly and pinpoint key gaps of knowledge in this arena, a working definition of "elderly" is required that accounts for both chronologic and biologic ages and varying states of frailty. In addition, it is critical to characterize the biological role of aging on liver function, as well as the different epidemiological factors such as polypharmacy and inappropriate prescribing that are common practices. While data may not show that elderly people are more susceptible to DILI, DILI due to specific drugs might be more common in this population. Improved characterization of DILI in the elderly may enhance diagnostic and prognostic capabilities and improve the way in which liver safety is monitored during clinical trials. This summary of the published literature provides a framework to understand and evaluate the risk of DILI in the elderly. Consensus statements and recommendations can help to optimize medical care and catalyze collaborations between academic clinicians, drug manufacturers, and regulatory scientists to enable the generation of high-quality research data relevant to the elderly population.

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

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

Genetic heterogeneity among slow acetylator N-acetyltransferase 2 phenotypes in cryopreserved human hepatocytes

Genetic polymorphisms in human N-acetyltransferase 2 (NAT2) modify the metabolism of numerous drugs and carcinogens. These genetic polymorphisms modify both drug efficacy and toxicity and cancer risk associated with carcinogen exposure. Previous studies have suggested phenotypic heterogeneity among different NAT2 slow acetylator genotypes. NAT2 phenotype was investigated in vitro and in situ in samples of human hepatocytes obtained from various NAT2 slow and intermediate NAT2 acetylator genotypes. NAT2 gene dose response (NAT2*5B/*5B > NAT2*5B/*6A > NAT2*6A/*6A) was observed towards the N-acetylation of the NAT2-specific drug sulfamethazine by human hepatocytes both in vitro and in situ. N-acetylation of 4-aminobiphenyl, an arylamine carcinogen substrate for both N-acetyltransferase 1 and NAT2, showed the same trend both in vitro and in situ although the differences were not significant (p > 0.05). The N-acetylation of the N-acetyltransferase 1-specific substrate p-aminobenzoic acid did not follow this trend. In comparisons of NAT2 intermediate acetylator genotypes, differences in N-acetylation between NAT2*4/*5B and NAT2*4/*6B hepatocytes were not observed in vitro or in situ towards any of these substrates. These results further support phenotypic heterogeneity among NAT2 slow acetylator genotypes, consistent with differential risks of drug failure or toxicity and cancer associated with carcinogen exposure.

Methemoglobinemia induced by trimethoprim-sulfamethoxazole in a patient with systemic lupus erythematosus

We herein report a case of methemoglobinemia induced by trimethoprim-sulfamethoxazole (TMP/SMX). A 41-year-old woman with systemic lupus erythematosus (SLE) received TMP/SMX for prophylaxis of pneumocystis pneumonia (PCP) on the 7th day of hospitalization. She suddenly developed dyspnea and cyanosis on the 9th day of hospitalization. The level of oxygen saturation (SaO2) decreased, and the concentration of methemoglobin (MetHb) in the blood was elevated. We diagnosed the patient with methemoglobinemia induced by TMP/SMX. Methemoglobinemia should be considered in cases of sudden dyspnea following TMP/SMX administration.

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Population differences in major functional polymorphisms of pharmacokinetics/pharmacodynamics-related genes in Eastern Asians and Europeans: implications in the clinical trials for novel drug development

Drug lag, recently discussed extensively in Japan, can be divided into two phases: clinical development time and application review time. The former factor is still an important problem that might be improved by promoting multi-regional clinical trials and considering the results from other similar populations with Japanese, such as Koreans and Chinese. In this review, we compare the allelic or genotype frequencies of 30 relatively common functional alleles mainly between Eastern Asians and Europeans as well as among 3 major populations in Eastern Asian countries, Japan, Korea, and China, in 12 pharmacokinetics (PK)/pharmacodynamics (PD)-related genes; CYP2C9 (*2 and *3), CYP2C19 (*2, *3 and *17), 13 CYP2D6 haplotypes including *4, *5 and *10, CYP3A5 (*3), UGT1A1 (*28 and *6), NAT2 (*5, *6 and *7), GSTM1 and GSTT1 null genotypes, SLCO1B1 521T>C, ABCG2 421C>A, and HLA-A*31:01 and HLA-B*58:01. In this review, differences in allele frequencies (AFs) or genotype frequencies (GFs) less than 0.1 (in the cases of highest AF (GF) ≥0.1) or less than 0.05 (in the cases of lowest AF (GF) <0.1) were regarded as similar. Between Eastern Asians and Europeans, AFs (or GFs) are regarded as being different for many alleles such as CYP2C9 (*2), CYP2C19 (*2, *3 and *17), CYP2D6 (*4 and *10), CYP3A5 (*3), UGT1A1 (*28 and *6), NAT2 (*5*7), GSTT1 null and ABCG2 421C>A. Among the 3 Eastern Asian populations, however, only AFs of CYP2C19*3, CYP2D6*10, HLA-A*31:01 and HLA-B*58:01 are regarded as dissimilar. For CYP2C19*3, the total functional impact on CYP2C19 could be small if the frequencies of the two null alleles CYP2C19*2 and *3 are combined. Regarding CYP2D6*10, frequency difference over 0.1 is observed only between Japanese and Chinese (0.147). Although environmental factors should be considered for PK/PD differences, we could propose that among Japan, Korea, and China, genetic differences are very small for the analyzed common PK-related gene polymorphisms. On the other hand, AFs of the two HLA alleles important for cutaneous adverse drug reactions are diverse even among Eastern Asians and thus should be taken into account.

Estimating N-acetyltransferase metabolic activity and pharmacokinetic parameters of isoniazid from genotypes in Chinese subjects

BACKGROUND

To establish quantitative relationship between metabolic activity of N-acetyltransferase (NAT2) and single nucleotide polymorphisms (SNPs), and estimate pharmacokinetic parameters of isoniazid (INH) on the basis of NAT2 alleles in Chinese subjects.

METHODS

Concentrations of INH and acetylisoniazid in plasma of 24 subjects were measured 0-14 h after oral administration of INH. Pharmacokinetic parameters were simulated. NAT2 alleles were determined by a reversed dot blot method. Correlation between various NAT2 SNPs and metabolic ratio (MR) or INH pharmacokinetic parameters was studied by multiple linear regression analysis.

RESULTS

There was quantitative relationship between various NAT2 alleles and MR of sulphadimidine (r(2)=0.836, P<0.0001). The pharmacokinetic parameters such as k, C(max), AUC, Cl of INH and C(max), AUC of AcINH can be calculated by NAT2 variant patterns. There was good correlation between observed and calculated data (r(2)>0.75, P<0.0001) except for C(max) of INH (r(2)=0.35, P=0.021). The 95% confidence intervals for prediction error ranged from -3.3%-5.6% for k to -10.5%-37.0% for C(max) of INH.

CONCLUSION

NAT2 genotypes can be used to predict pharmacokinetic parameters of INH. It may be useful in the rational use of INH.

Effects of dietary factors and the NAT2 acetylator status on gastric cancer in Koreans

Environmental dietary carcinogens and genetic polymorphisms in metabolic enzymes have been reported to be the risk factors for gastric cancer. This study was undertaken to investigate the effects of the diet, the N-acetyltransferase (NAT) 2 acetylation status and their interaction on gastric cancer risk. The study population consisted of 471 gastric cancer patients and 471 age- and sex-matched control subjects. NAT2 genotypes were identified using single-nucleotide primer extension reaction methods. Thirty-one alleles related to 12 polymorphism sites were assayed in this study. Significantly increased odds ratios were observed in former smokers (OR = 2.39, 95% CI = 1.57-3.62), heavy drinkers (OR = 1.28, 95% CI = 1.06-1.55) and individuals who eat well-done meat (OR = 1.24, 95% CI = 1.09-1.41). The odds ratios (95% CI) for high intake of kimchi, stews and soybean paste were 3.27 (2.44-4.37), 1.96 (1.50-2.58) and 1.63 (1.24-2.14), respectively. The NAT2 genotype alone was not associated with gastric cancer risk. A significant gene-environment interaction was observed between environmental carcinogens and NAT2 genotypes. The odds ratios for kimchi, stews and soybean paste were higher in slow/intermediate acetylators than in rapid acetylators. The odds ratios for slow/intermediate acetylators were 2.28 (95% CI: 1.29-4.04) for light smokers and 3.42 (95% CI: 2.06-5.68) for well-done meat intake. The NAT2 acetylator genotype may be an important modifier of the effects of environmental factors on gastric cancer risk.

An Interethnic Comparison of Polymorphisms of the Genes Encoding Drug-Metabolizing Enzymes and Drug Transporters: Experience in Singapore

Much of the interindividual variability in drug response is attributable to the presence of single nucleotide polymorphisms (SNPs) in genes encoding drug-metabolizing enzymes and drug transporters. In recent years, we have investigated the polymorphisms in a number of genes encoding phase I and II drug-metabolizing enzymes including CYPIA1, CYP3A4, CYP3A5, GSTM1, NAT2, UGT1A1, and TPMT and drug transporter (MDR1) in three distinct Asian populations in Singapore, namely the Chinese, Malays, and Indians. Significant differences in the frequencies of common alleles encoding these proteins have been observed among these three ethnic groups. For example, the frequency of the variant A2455G polymorphism of CYP1A1 was 28% in Chinese and 31% in Malays, but only 18% in Indians. CYP3A4*4 was detected in two of 110 Chinese subjects, but absent in Indians and Malays. Many Chinese and Malays (61-63%) were homozygous for the GSTM1*0 null genotype compared with 33% of Indians. The frequency of the UGTIA1*28 allele was highest in the Indian population (35%) compared to similar frequencies that were found in the Chinese (16%) and Malay (19%) populations. More importantly, our experience over the years has shown that the pharmacogenetics of these drug-metabolizing enzymes and MDR1 in the Asian populations are different from these in the Caucasian and African populations. For example, the CYP3A4*1B allele, which contains an A-290G substitution in the promoter region of CYP3A4, is absent in all three Asian populations of Singapore studied, but occurs in more than 54% of Africans and 5% of Caucasians. There were no difference in genotype and allelic variant frequencies in exon 12 of MDR1 between the Chinese, Malay, and Indian populations. When compared with other ethnic groups, the distribution of the wild-type C allele in exon 12 in the Malays (34.2%) and Indians (32.8%) was relatively high and similar to the Japanese (38.55%) and Caucasians (41%) but different from African-Americans (15%). The frequency of wild-type TT genotype in Asians (43.5% to 52.1%) and Japanese (61.5%) was much higher than those found in Caucasians (13.3%). All the proteins we studied represent the primary hepatic or extrahepatic enzymes, and their polymorphic expression may be implicated in disease risk and the disposition of drugs or endogenous substances. As such, dose requirements of certain drugs may not be optimal for Asian populations, and a second look at the factors responsible for this difference is necessary.

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.

Genetic polymorphisms of drug-metabolizing enzymes and the susceptibility to antituberculosis drug-induced liver injury

Three first-line antituberculosis drugs, isoniazid, rifampicin and pyrazinamide, may induce liver injury, especially isoniazid. This antituberculosis drug-induced liver injury ranges from a mild to severe form, and the associated mortality cases are not rare. The major drug-metabolizing enzyme of isoniazid is N-acetyltransferase. Other possible enzymes are CYP2E1 and glutathione S-transferase. There is evidence that polymorphisms of the genes that encode these enzymes may influence the activity of the corresponding drug-metabolizing enzymes. Recent studies demonstrated that these genetic polymorphisms may be associated with the susceptibility to antituberculosis drug-induced liver injury. The proposed risk-associated genotypes are NAT2 slow acetylator (without wild-type NAT2*4 allele), CYP2E1 *1A/*1A (homozygous wild type) and homozygous null GSTM1 genotype. Although the available data in the field are still limited and warrants further confirmation in different ethnic populations with larger sample sizes, it still cast some light on the application of these pharmacogenetic or pharmacogenomic approaches to prevent grave antituberculosis drug-induced liver injury in the near future.

The influence of various genotypes on the metabolic activity of NAT2 in a Chinese population

AIM

To determine the phenotype and genotype of NAT2 in a Chinese population and study the influence of various NAT2 genotypes on the NAT2 activity.

METHODS

A reverse dot blot method was used to detect the genotype of NAT2 in 120 healthy Chinese subjects. All subjects were given a single dose of 500 mg sulphadimidine (SM(2)). The plasma concentration of SM(2) and acetyl-SM(2) (AcSM(2)) 6 h after administration was determined. Molar metabolic ratio (MR) was calculated by the ratio of AcSM(2) to AcSM(2)+SM(2).

RESULTS

Totals of 53 (44.2%), 47 (39.2%) and 20 (16.7%) subjects were homozygotes for wild type (wt/wt), heterozygotes for mutant (m/wt) and homozygotes for mutant (m/m), respectively. The MR of 120 subjects was 0.714+/-0.237. Twenty subjects (16.7%) were classified as poor metabolizers. All subjects in the m/m group were poor metabolizers. The MRs of the wt/wt, m/wt and m/m groups were 0.886+/-0.060, 0.719+/-0.089 and 0.246+/-0.105 (P<0.001), respectively. There was a significant difference between different NAT2 m/wt genotypes (P<0.001) and m/m genotypes (P<0.001). MR correlated well with NAT2 genotypes (r=0.947).

CONCLUSION

Various NAT2 genotypes have a significant impact on the metabolic activity of NAT2 in Chinese people.

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.

NAT2*5/*5 genotype (341T>C) is a potential risk factor for schistosomiasis-associated bladder cancer in Egyptians

Arylamine N-acetyl transferase (NAT2) displays extensive genetic polymorphisms that affect the rates of acetylation of drugs and genotoxic compounds such as amine carcinogens. To investigate whether the slow acetylator genotype is a risk factor for development of bladder cancer following schistosomal infection of the urinary tract, the authors determined the frequencies of 3 common polymorphisms in the NAT2 gene (341T>C, 590G>A, and 282C>T), which are associated with impaired acetylation activity, in control subjects (n=61; mean age 34.3+/-9.2 years) and in schistosomiasis-associated bladder cancer patients (n=55; 52+/-10.9 years) from the Egyptian population. Genotyping was carried out using rapid cycle PCR on the LightCycler, and subjects were assigned to a slow, intermediate, or rapid acetylator phenotype on the basis of the genotypes. The frequencies of the mutant alleles observed in the controls from the present study were similar to those reported previously for both the Egyptian population and other Arab populations. Patients showed a higher prevalence (78.2%) of slow acetylator phenotype than controls (67.2%), but this did not reach statistical significance (P=0.19). However, there were significantly more individuals who were carriers of 2 mutant 341T>C alleles (NAT2*5/*5 genotype) in the patient group compared with controls (odds ratio 2.6, CI 1.02-6.67, P=0.026). The alloenzyme encoded by this allele has been shown to display a large reduction in its catalytic activity. In conclusion, these data suggest that the NAT2*5/*5 genotype is a potential risk factor for development of urinary bladder cancer in patients with prior schistosomiasis infection.

N-acetyl-transferase phenotype and risk for preeclampsia

OBJECTIVE

This study was undertaken to determine whether the N-acetyltransferase (NAT) phenotype contributes to the susceptibility for the development of preeclampsia.

STUDY DESIGN

The NAT acetylator status was determined by measuring urinary caffeine metabolites in 134 nonpregnant women with a history of preeclampsia and in 109 control women with uncomplicated pregnancy. The chi(2) and logistic regression analyses were used for statistical evaluation of differences in acetylator status.

RESULTS

Significantly more fast acetylators were found among the women with a history of preeclampsia (46.3%) than among the controls (25.4%). Fast acetylators showed an odds ratio of 2.5 (95% CI 1.4-4.3) for preeclampsia. No differences in the acetylator status were found between women with a history of preeclampsia only and those with the HELLP syndrome as well.

CONCLUSION

The fast NAT acetylator status, which may result in altered NAT detoxification capacity, is associated with preeclampsia.

Toward individualized pharmaceutical care of East Asians: the value of genetic testing for polymorphisms in drug-metabolizing genes

Research into the relationship between genetics and drug response has focused on polymorphisms in genes that encode drug-metabolizing enzymes, particularly the genes of cytochrome P450 superfamily 2, which affect the clearance of the anticoagulant warfarin, proton pump inhibitors, tricyclic antidepressants, and many other clinically relevant drugs. Much of this work has targeted East Asians, a genetically distinguishable and populous group. Researchers have identified polymorphisms that inactivate gene function, compared polymorphism frequencies in East-Asian and Caucasian populations, and determined the effects on the pharmacokinetic parameters of drugs. Detection in an individual of polymorphisms known to inactivate a drug-metabolizing enzyme is predictive of poor metabolism of drugs processed by that pathway, which itself may be predictive of an atypical drug response. Genetic tests can be used to screen for individuals with poor metabolizer phenotypes, with the ultimate goal of predicting the clinical effects of drugs.

Arylamine N-acetyltransferase 2 slow acetylator polymorphisms in unrelated Iranian individuals

OBJECTIVE

To determine the frequency of mutations at the polymorphic gene coding for arylamine N-acetyltransferase 2 (NAT2, EC 2.3.1.5) and NAT2 genotypes associated with slow acetylation in healthy Iranian individuals.

METHODS

The polymorphisms in the NAT2 gene from 88 unrelated healthy subjects (48 men/40 women) from the general Tehran population were discriminated using polymerase chain reaction (PCR) with allele-specific primers (341 C > T) and PCR-restriction fragment length polymorphism analysis (481 C > T, 590 G > A, and 857 G > A).

RESULTS

Frequencies of the studied polymorphisms showed the most common alleles to be NAT2*4 (0.43) and NAT2*5, 481 C > T (0.32), followed by NAT2*6 (0.19) and NAT2*7 (0.06), previously referred to as WT, M1, M2, and M3, respectively. The most prevalent genotypes were NAT2*4/*5 [(31.8%; 95% confidence interval (CI): 29-34%] and *4/*4 (18.2%; 95% CI: 16-21%). When grouped according to the expected phenotypical effects, the resulting genotypes revealed the significant prevalence of the subjects with slow (32.9%) and intermediate (48.9%) acetylation status compared with wild-type rapid (18.2%) acetylators (P < 0.01).

CONCLUSIONS

The overall allele pattern and acetylator status distribution in Iranians displayed the considerable prevalence of "slow acetylators" over "rapid acetylators," similar to those of Caucasians except for a minor difference observed in the frequency of the NAT2*7 allele. Nucleic acid testing for common NAT2 mutations might be a potentially useful tool for an accurate phenotype interpretation and identification of Iranian individuals at risk.

Polymorphism of the N-acetyltransferase 2 gene, red meat intake, and the susceptibility of hepatocellular carcinoma

OBJECTIVE

Carcinogenic aromatic amines, derived from cooked meat, are activated or inactivated by hepatic N-acetyltransferase (NAT). The aim of this study was to evaluate the relationship of NAT2 genetic polymorphisms with hepatocellular carcinoma (HCC), with special reference to the interaction of dietary habits.

METHODS

Peripheral white blood cell DNA from 185 HCC patients and 185 matched controls were genotyped for NAT2 by a polymerase chain reaction-restriction fragment length polymorphism method. All the subjects studied were chronic viral hepatitis B or C carriers with liver cirrhosis. Dietary habits of the subjects were assessed using a semiquantitative food frequency questionnaire.

RESULTS

There was no association between the susceptibility of HCC and the overall NAT2 genotypes. However, in rapid acetylators (with two wild type NAT2*4 alleles), there was a trend of increased HCC risk from low to intermediate and high red meat intake (OR = 1, 2.66, 3.89; p(trend) = 0.016), even when adjusted for family history of HCC and habitual alcohol drinking. The interaction between red meat intake and the NAT2*4 acetylator status for an increased risk of HCC was significant (p = 0.007).

CONCLUSIONS

Polymorphisms of the NAT2 gene may confer different susceptibilities to the effect of red meat intake on HCC. In rapid acetylators with chronic viral hepatitis-related cirrhosis, red meat intake may play a role in hepatocarcinogenesis.

Arylamine N-acetyltransferases and drug response

Arylamine N-acetyltransferases (NATs) play an important role in the interaction of competing metabolic pathways determining the fate of and response to xenobiotics as therapeutic drugs, occupational chemicals and carcinogenic substances. Individual susceptibility for drug response and possible adverse drug reactions are modulated by the genetic predisposition (manifested for example, by polymorphisms) and the phenotype of these enzymes. For all drugs metabolized by NATs, the impact of different in vivo enzyme activities is reviewed with regard to therapeutic use, prevention of side effects and possible indications for risk assessment by phenotyping and/or genotyping. As genes of NATs are susceptibility genes for multifactorial adverse effects and xenobiotic-related diseases, risk prediction can only be made possible by taking the complexity of events into consideration.

Polymorphism of the N-acetyltransferase 2 gene as a susceptibility risk factor for antituberculosis drug-induced hepatitis

Antituberculosis drug-induced hepatitis is one of the most prevalent drug-induced liver injuries. Isoniazid is the major drug incriminated in this hepatotoxicity. Isoniazid is mainly metabolized to hepatotoxic intermediates by N-acetyltransferase (NAT). However, the association of polymorphic NAT acetylator status and antituberculosis drug-induced hepatitis is debatable. To determine whether acetylator status is a risk factor for antituberculosis drug-induced hepatitis, we genotyped NAT2 in 224 incident tuberculosis patients who received antituberculosis treatment. Antituberculosis drug-induced hepatitis was diagnosed based on a positive isoniazid rechallenge test and exclusion of viral hepatitis. Acetylator status was determined by genotyping NAT2 in patients using a polymerase chain reaction with restriction fragment length polymorphism. Univariate analysis and logistic regression analysis were used to evaluate the risk factors of isoniazid-induced hepatitis. Thirty-three patients (14.7%) were diagnosed with antituberculosis drug-induced hepatitis. Slow acetylators had a higher risk of hepatotoxicity than rapid acetylators (26.4% vs. 11.1%, P =.013). Among patients with hepatotoxicity, slow acetylators had significantly higher serum aminotransferase levels than rapid acetylators. Logistic regression showed that slow-acetylator status (odds ratio [OR], 3.66; 95% CI, 1.58-8.49; P =.003) and age (OR, 1.09; 95% CI, 1.04-1.14; P <.001) were the only 2 independent risk factors for antituberculosis drug-induced hepatitis. In conclusion, slow-acetylator status of NAT2 is a significant susceptibility risk factor for antituberculosis drug-induced hepatitis. Additionally, slow acetylators are prone to develop more severe hepatotoxicity than rapid acetylators. Regular monitoring of serum aminotransferase levels is mandatory in patients receiving antituberculosis treatment, especially in slow acetylators.

Validity of an ELISA for N-acetyltransferase-2 (NAT2) phenotyping

A competitive antigen ELISA was previously developed for NAT2 phenotyping, using caffeine as the probe drug. The ELISA phenotypes by measuring the ratio of 5-acetamido-6-amino-3-methyluracil (AAMU) and 1-methylxanthine (1X) after transformation of 5-acetamido-6-formylamino-3-methyluracil (AFMU) to AAMU, in contrast to capillary electrophoresis high-pressure liquid chromatography (HPLC) which phenotype by measuring the AFMU/1X ratio. The ELISA phenotyping was previously determined in 30 samples and correlated well with phenotypes determined by capillary electrophoresis (29/30). The correlation was extended with the standard HPLC methodology by expanding the data set by 146 in order to test the validity of the ELISA methodology. The correlation with HPLC in this larger sample size was 96%; whereas the correlation between the two methods for determination of 1X was high (r(2)=0.90), that for determination of AAMU by ELISA and AFMU by HPLC was low (r(2)=0.53). The poor correlation between the two methodologies could not be attributed to the age of urine samples, nor to a significant decomposition of AFMU in the body prior to collection of the urine sample. The addition of a simple caffeine metabolite extraction method, originally developed for HPLC analysis of metabolites, to the ELISA phenotyping protocol produced a methodology with absolute correlation to the standard HPLC method.

Prediction of metabolic activity from genotype: the gene-dose effect of N-acetyltransferase

Metabolic activity of the polymorphic N-acetyltransferase (NAT2) is determined by the mutation pattern of the NAT2 gene. This results in interindividual differences in the metabolic capacity (the phenotype), with continuous distribution of the activities rather than qualitative distinction between rapid and slow acetylators. To determine whether the phenotype might be predicted solely from the mutation pattern of NAT2, quantitative relationships were calculated between mutation patterns of the NAT2 gene and the phenotype of NAT2 assessed either in vitro or in vivo. Healthy volunteers were examined for the velocity at which they metabolized sulfamethazine, and human liver cytosols were measured for NAT2 enzymatic activity, obtaining in vivo and in vitro metabolic phenotype, respectively. Typing of the NAT2 gene was performed by polymerase chain reaction, restriction fragment length analysis, or allele-specific polymerase chain reaction. Multiple linear regression analysis provided quantitative relationships between allelic pattern and the NAT2 activities measured in vivo and in vitro. Estimates showed the influence of particular allelic configurations on enzyme activity in vitro and the extent of acetylation of the probe drug in vivo, resulting in a strict gene-dose effect. Comparison of in vitro results with in vivo phenotyping figures showed a high degree of correspondence, indicating that the one is the reflection of the other.

Formulation of a neutral solution of ciprofloxacin upon complexation with aluminum

Clear solutions of 0.5 and 1.0% ciprofloxacin (CF) of pH 7.2 were prepared by the addition of aluminum chloride hexahydrate (AlCl3.6H2O) in the molar proportion CF:AlCl3.6H2O (3:1). Minimum inhibitory concentrations (MIC) of these solutions were the same as an equimolar solution of CF.HCl. Solutions exhibited good physical, chemical and microbiological stability and satisfactorily overcame an ocular irritation test on rabbits.

Update: genetic polymorphism of drug metabolizing enzymes in humans

The cytochrome P450 (P450 or CYP) monooxygenases, CYP2D6, CYP2C19, CYP2E1 and CYP2C9, and non-P450 monooxygenases, N-acetyltransferase, thioprine methyltransferases and dihydropyrimidine dehydrogenase, all display polymorphism. CYP2D6 and CYP2C19 have been studied extensively and, despite their low abundance in the liver, they have been found to catalyse the metabolism of many drugs. CYP2D6 has many allelic variants, whereas CYP2C19 has only two. Most variants are translated into inactive, truncated proteins or fail to express protein. There is, as yet, no clear information about CYP2E1 polymorphism. In addition, genetic differences in certain foreign-compound metabolizing enzymes, such as Phase II enzymes, have been shown to be associated with an increased risk of developing environmentally and occupationally related diseases such as cancer. When two drugs that are substrates of a polymorphic CYP enzyme are administered concomitantly during drug therapy, each will compete for that enzyme and competitively inhibit the metabolism of the other substrate. This can result in toxicity. Patients who are poor metabolizers (PMs), extensive metabolizers (EMs) and ultrarapid metabolizers (URMs) can be identified. Having such information will help in determining the appropriate dosage of certain drugs when treating patients with an inherited abnormality of a drug-metabolizing enzyme. In view of the remarkable progress in this particular field, it is to be expected that more genetic polymorphisms will be discovered in the near future.

Review of the genetics of renal disease

The results of many of human studies indicate that the genetics of the more common forms of renal disease are quite complex. There are indications that human renal disease may be both polygenic and heterogenic. There are several approaches. Some researchers studying small populations are collecting larger numbers of families with multiple affected individuals. Others are employing discordant sib-pair analysis. Also, trios (individual with renal disease and that individual's parents) have been suggested as a means of collecting larger numbers of people with renal disease. Another population of interest is the group susceptible to nephrotoxicity. At common doses of nephrotoxic drugs and common levels of exposure to environmental and occupational nephrotoxic substances, only a portion of those similarly exposed develop significant renal damage. This subset of individuals may have a genetic susceptibility to renal damage caused by toxic agents.

Genetic polymorphisms of human N-acetyltransferase, cytochrome P450, glutathione-S-transferase, and epoxide hydrolase enzymes: relevance to xenobiotic metabolism and toxicity

In this review, an overview is presented of the current knowledge of genetic polymorphisms of four of the most important enzyme families involved in the metabolism of xenobiotics, that is, the N-acetyltransferase (NAT), cytochrome P450 (P450), glutathione-S-transferase (GST), and microsomal epoxide hydrolase (mEH) enzymes. The emphasis is on two main topics, the molecular genetics of the polymorphisms and the consequences for xenobiotic metabolism and toxicity. Studies are described in which wild-type and mutant alleles of biotransformation enzymes have been expressed in heterologous systems to study the molecular genetics and the metabolism and pharmacological or toxicological effects of xenobiotics. Furthermore, studies are described that have investigated the effects of genetic polymorphisms of biotransformation enzymes on the metabolism of drugs in humans and on the metabolism of genotoxic compounds in vivo as well. The effects of the polymorphisms are highly dependent on the enzyme systems involved and the compounds being metabolized. Several polymorphisms are described that also clearly influence the metabolism and effects of drugs and toxic compounds, in vivo in humans. Future perspectives in studies on genetic polymorphisms of biotransformation enzymes are also discussed. It is concluded that genetic polymorphisms of biotransformation enzymes are in a number of cases a major factor involved in the interindividual variability in xenobiotic metabolism and toxicity. This may lead to interindividual variability in efficacy of drugs and disease susceptibility.

Genotyping of the polymorphic N-acetyltransferase (NAT2) and loss of heterozygosity in bladder cancer patients

Acetylation is one of the major routes in metabolism and detoxification of a large number of drugs, chemicals and carcinogens. Slow acetylators are said to be more susceptible to developing bladder cancer and because of investigations about tumor risk based on phenotyping procedures, it was our aim to study the distribution of allelic constellations of the N-acetyltransferase (NAT2) by genotyping patients with bladder cancer. We analysed NAT2 gene of blood and tumor DNA from 60 patients with primary bladder cancer and DNA of blood samples from 154 healthy individuals. Using ASO-PCR/RFLP techniques we identified 70% of patients with bladder cancer (n = 42) to be slow acetylators while genotyping of controls resulted in 61% with slow acetylators (n = 94). In addition, dividing bladder cancer patients in males and females the genotype NAT2*5B/NAT2*6A occured with much higher frequencies in males (OR = 4, 95%); CI = 1.8-8.9). Furthermore, investigating bladder cancer tissues we could detect loss of heterozygosity (LOH) in slow and rapid acetylator genotypes. In eleven out of 60 tumor samples (18.3%) we observed allelic loss at the NAT2 locus while in control DNA of blood from the same patients both alleles were still detectable.

A simplified assay for the arylamine N-acetyltransferase 2 polymorphism validated by phenotyping with isoniazid

Human arylamine N-acetyltransferase (NAT) activity is determined by two distinct genes, NAT1 and NAT2, and the classical acetylation polymorphism in NAT2 has been associated with a variety of disorders, including lupus erythematosus and arylamine induced cancers. Over 50% of the white population exhibit a slow acetylator phenotype. The genetic basis of the defect has been identified and several DNA based assays are available for genotyping studies. We present here a simplified, rapid PCR based assay for the identification of the major slow acetylator genotypes and validate it using isoniazid as probe drug. This assay was 100% predictive of phenotype. The three genotypes (homozygous mutated, heterozygous, and homozygous rapid) corresponded to a trimodal distribution of Ac-INH/INH metabolic ratios (slow, intermediate, and rapid) without overlapping.

Genetic polymorphisms in human drug-metabolizing enzymes: potential uses of reverse genetics to identify genes of toxicological relevance

The human mind was engaged with fundamental questions on the nature of heredity long before the study of genetics became a scientific discipline. Many traits, such as height, eye color, blood pressure, or cancer susceptibility, have been known to run in families, although the genes or combination of genes that underlie these observable characteristics remain unknown in most cases. Differences in susceptibility to environmental agents in humans are likewise determined by variations in genetic background--genetic polymorphisms. In this article, we review the current status of studies on human polymorphisms in drug-metabolizing enzymes and discuss various approaches to the analysis of genetic polymorphisms. We expect that in the near future, novel methods in genetic analysis of human populations will be likely to play a key role in the identification of genes of toxicological relevance.

The impact of interindividual variation in NAT2 activity on benzidine urinary metabolites and urothelial DNA adducts in exposed workers

Several epidemiologic studies indicate that NAT2-related slow N-acetylation increases bladder cancer risk among workers exposed to aromatic amines, presumably because N-acetylation is important for the detoxification of these compounds. Previously, we showed that NAT2 polymorphisms did not influence bladder cancer risk among Chinese workers exposed exclusively to benzidine (BZ), suggesting that NAT2 N-acetylation is not a critical detoxifying pathway for this aromatic amine. To evaluate the biologic plausibility of this finding, we carried out a cross-sectional study of 33 workers exposed to BZ and 15 unexposed controls in Ahmedabad, India, to evaluate the presence of BZ-related DNA adducts in exfoliated urothelial cells, the excretion pattern of BZ metabolites, and the impact of NAT2 activity on these outcomes. Four DNA adducts were significantly elevated in exposed workers compared to controls; of these, the predominant adduct cochromatographed with a synthetic N-(3'- phosphodeoxyguanosin-8-yl)-N'-acetylbenzidine standard and was the only adduct that was significantly associated with total BZ urinary metabolites (r = 0.68, P < 0.0001). To our knowledge this is the first report to show that BZ forms DNA adducts in exfoliated urothelial cells of exposed humans and that the predominant adduct formed is N-acetylated, supporting the concept that monofunctional acetylation is an activation, rather than a detoxification, step for BZ. However, because almost all BZ-related metabolites measured in the urine of exposed workers were acetylated among slow, as well as rapid, acetylators (mean +/- SD 95 +/- 1.9% vs. 97 +/- 1.6%, respectively) and NAT2 activity did not affect the levels of any DNA adduct measured, it is unlikely that interindividual variation in NAT2 function is relevant for BZ-associated bladder carcinogenesis.

Determination and allelic allocation of seven nucleotide transitions within the arylamine N-acetyltransferase gene in the Polish population

The frequency of various genotypes of arylamine N-acetyltransferase (NAT2) was investigated in 248 Polish unrelated children. Allele-specific polymerase chain reaction (PCR) was applied for mutation at 341 nucleotide (nt) of NAT2 coding sequence and PCR/restriction fragment length polymorphism for the other mutations. Genotypes coded for slow acetylation in 62.9% (56.6% to 68.9%). The frequency of specific NAT2 alleles was *4 (wild-type), 22.0%; *5A (341C, 481T), 5.2%; *5B (341C, 481T, 803G), 33.1%; *5C (341C, 803G), 6.0%; *6A (282T, 590A), 30.0%; *7B (282T, 857A), 3.4%; and *12A (803G), 0.2%. No mutations were found at 191, 434, and 845 nt. By a molecular-genetic procedure, genotypes *4/*6A were confirmed not to mask *6B/*13 (590A/282T). *6B and *13 were absent in a composite sample representative of 826 alleles (95% confidence limits, 0% to 0.45%). Five cases of genotype-phenotype discrepancy were sequenced and their mutation allocation confirmed; 21 further genotypes were confirmed by sequencing. This first evaluation of NAT2 genes among a Slavic population should provide a basis for clinical and epidemiologic investigations of NAT2 in the Polish population.