NAT2 fast acetylator genotype is associated with an increased risk of colorectal cancer in Taiwan

Heterocyclic Amines Disrupt Lipid Homeostasis in Cryopreserved Human Hepatocytes

Metabolic dysfunction associated-steatotic liver disease (MASLD)/metabolic dysfunction-associated steatohepatitis (MASH) is the liver manifestation of metabolic syndrome, which is characterized by insulin resistance, hyperglycemia, hypertension, dyslipidemia, and/or obesity. Environmental pollutant exposure has been recently identified as a risk factor for developing MASH. Heterocyclic amines (HCAs) are mutagens generated when cooking meat at high temperatures or until well-done. Recent epidemiological studies reported that dietary HCA exposure may be linked to insulin resistance and type II diabetes, and we recently reported that HCAs induce insulin resistance and glucose production in human hepatocytes. However, no previous studies have examined the effects of HCAs on hepatic lipid homeostasis. In the present study, we assessed the effects of two common HCAs, MeIQx (2-amino-3, 8-dimethylimidazo [4, 5-f] quinoxaline) and PhIP (2-amino-1-methyl-6-phenylimidazo[4, 5-b] pyridine), on lipid homeostasis in cryopreserved human hepatocytes. Exposure to a single concentration of 25 μM MeIQx or PhIP in human hepatocytes led to dysregulation of lipid homeostasis, typified by significant increases in lipid droplets and triglycerides. PhIP significantly increased expression of lipid droplet-associated genes, PNPLA3 and HSD17B13, and both HCAs significantly increased PLIN2. Exposure to MeIQx or PhIP also significantly increased expression of several key genes involved in lipid synthesis, transport and metabolism, including FASN, DGAT2, CPT1A, SCD, and CD36. Furthermore, both MeIQx and PhIP significantly increased intracellular cholesterol and decreased expression of PON1 which is involved in cholesterol efflux. Taken together, these results suggest that HCAs dysregulate lipid production, metabolism, and storage. The current study demonstrates, for the first time, that HCA exposure may lead to fat accumulation in hepatocytes, which may contribute to hepatic insulin resistance and MASH.

GSTT1/GSTM1 Genotype and Anti-Tuberculosis Drug-Induced Hepatotoxicity in Peruvian Patients

In Peru, 24,581 people were diagnosed with tuberculosis (TB) in 2020. Although TB treatments are effective, 3.4-13% are associated with significant adverse drug reactions (ADRs), with drug-induced liver injury (DILI) considered the most predominant. Among the first-line antituberculosis drugs, isoniazid (INH) is the main drug responsible for the appearance of DILI. In the liver, INH is metabolized by the enzymes N-acetyltransferase-2 (NAT2), cytochrome P450 2E1 (CYP2E1), and glutathione S-transferase (GST) with two isoforms, GSTT1 and GSTM1. Based on previous studies, we hypothesized that interactions between the GSTT1 and GSTM1 null genotypes induce DILI in TB patients. In this cross-sectional study of 377 participants who completed their anti-TB treatment, we genotyped by revealing the presence or absence of 215- and 480-bp bands of GSTM1 and GSTT1, respectively. We found that the prevalence of the GSTM1 genotype was 52.79% and 47.21% for presence and null, respectively, and for GSTT1 it was 69.76% and 30.24% for presence and null, respectively. Neither genotype was prevalent in the patients who developed DILI (n = 16). We did not confirm our hypothesis; however, we found that the combination of GSTM1 present genotype, GSTT1 null genotype, fast NAT2 acetylators, and CYP2E1 c1/c1 genotype had a significant risk for the development of ADR (OR 11; p = 0.017; 95% CI: (0.54-186.35)). We propose that the presence of the GSTM1 present genotype, GSTT1 null genotype, fast NAT2 acetylators, and CYP2E1 c1/c1 genotype in the Peruvian population could be considered a risk factor for the development of ADR due to therapeutic drug intake.

N-acetyltransferase 2 polymorphism and acetylation profiles in Buginese ethnics of Indonesia

BACKGROUND

N-acetyltransferase 2 (NAT2) is a key enzyme involved in the phase II metabolism of aromatic amines and heterocyclic aromatic amines present in a wide range of xenobiotics. The aim of this study was to investigate the NAT2 polymorphism in the Buginese ethnic group of Indonesia to determine the frequency of NAT2 alleles in this population.

RESULTS

We found six haplotypes consisting of six single-nucleotide polymorphisms and 12 NAT2 genotype variations. NAT2*6A haplotype (42%) showed the highest frequency, followed by NAT2*4 (33%), NAT2*7B (15%), NAT2*5B (5%), NAT2*12A (3%), and NAT2*13 (2%). In terms of phenotypes, the Buginese population comprised 18% rapid acetylators, 40% intermediate acetylators, and 42% slow acetylators.

CONCLUSION

We confirmed the high-frequency slow acetylator phenotype in the Buginese population. The NAT2*6A/*6A genotype was the most frequent slow acetylator genotype, followed by NAT2*6A/*7B. The pattern of NAT2 alleles of Buginese is similar to Southeast Asian populations but not Northeast Asian populations. However, the slow acetylator frequencies in the Buginese population were higher than those in Northeast Asian populations and lower than those in Caucasians and some American populations.

N-acetyltransferase polymorphism and risk of colorectal adenoma and cancer: a pooled analysis of variations from 59 studies

BACKGROUND

There have been an increasing number of studies with evidence suggesting that the N-acetyltransferase 1 (NAT1) and N-acetyltransferase 2 (NAT2) genotypes may be implicated in the development of colorectal cancer (CRC) and colorectal adenoma (CRA). So far the published data on this association has remained controversial, however. We performed a meta-analysis of case-cohort and case-control studies using a subset of the published data, with an aim to derive a better understanding of the underlying relationship.

METHODS/PRINCIPAL FINDINGS

A literature search was performed using Medline database for relevant studies published through October 31, 2011. A total of 39 publications were selected for this meta-analysis, including 11,724 cases and 16,215 controls for CRC, and 3,701 cases and 5,149 controls for CRA. In our pooled analysis of all these studies, the results of our meta-analysis suggested that the NAT1 genotype was not significantly associated with an elevated CRC risk (OR 0.99, 95% CI 0.91-1.07). We also found that individuals with the rapid NAT2 genotype did have an elevated risk of CRC (OR 1.07, 95% CI 1.01-1.13). There was no evidence for an association between the NAT1 and 2 rapid genotype and an elevated CRA risk (NAT1: OR 1.14, 95% CI 0.99-1.29; NAT2: OR 0.94, 95% CI 0.86-1.03).

CONCLUSION

This meta-analysis suggests that individuals with NAT2 genotype had an elevated risk of CRC. There was no evidence for the association between NAT1 and 2 rapid genotype and CRA risk.

Absence of association between N-acetyltransferase 2 acetylator status and colorectal cancer susceptibility: based on evidence from 40 studies

BACKGROUND AND OBJECTIVES

N-Acetyltransferase (NAT) 2 is an important enzyme involved in the metabolism of different xenobiotics, including potential carcinogens, whose phenotypes were reported to be related to individual susceptibility to colorectal cancer (CRC). However, the results remain conflicting. To assess the relationship between NAT2 phenotypes and CRC risk, we performed this meta-analysis.

METHODS

A comprehensive literature search was conducted to identify all case-control or cohort studies of NAT2 acetylator status on the susceptibility of CRC by searching of PubMed and EMBASE, up to May 20, 2011. Crude odds ratios (ORs) with 95% confidence intervals (CIs) were used to assess the association.

RESULTS

A total of over 40,000 subjects from 40 published literatures were identified by searching the databases. No significantly elevated CRC risk in individuals with NAT2 slow acetylators compared with fast acetylators was found when all studies pooled (OR = 0.95, 95% CI: 0.87-1.04, I(2) = 52.6%). While three studies contributed to the source of heterogeneity were removed, there was still null result observed (OR = 0.96, 95% CI: 0.90-1.03, P = 0.17 for heterogeneity, I(2) = 17.8%). In addition, we failed to detect any associations in the stratified analyses by race, sex, source of controls, smoking status, genotyping methods or tumor localization. No publication bias was observed in this study.

CONCLUSIONS

This meta-analysis suggests that the NAT2 phenotypes may not be associated with colorectal cancer development.

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.

N-Acetyltransferase 2 genetic polymorphisms and risk of colorectal cancer

AIM: To investigate the possible association between meat intake, cigarette smoking and N-acetyltransferase 2 (NAT2) genetic polymorphisms on colorectal cancer (CRC) risk.

METHODS: Patients with CRC were matched for gender and age to healthy controls. Meat intake and cigarette smoking were assessed using a specific frequency questionnaire. DNA was extracted from peripheral blood and the genotypes of the polymorphism were assessed by polymerase chain reaction-restriction fragment length polymorphism. Five NAT2 alleles were studied (WT, M1, M2, M3 and M4) using specific digestion enzymes.

RESULTS: A total of 147 patients with colorectal cancer (76 women and 90 men with colon cancer) and 212 controls were studied. The mean age of the two groups was 62 years. More than half the subjects (59.8% in the case group and 51.9% in the control group) were NAT2 slow acetylators. The odds ratio for colorectal cancer was 1.38 (95% CI: 0.90-2.12) in slow acetylators. Although the number of women was small (n = 76 in the case group), the cancer risk was found to be lower in intermediate (W/Mx) acetylators [odds ratio (OR): 0.55, 95% confidence interval (95% CI): 0.29-1.02]. This difference was not observed in men (OR: 0.56, 95% CI: 0.16-2.00). Among NAT2 fast acetylators (W/W or W/Mx), meat consumption more than 3 times a week increased the risk of colorectal cancer (OR: 2.05, 95% CI: 1.01-4.16). In contrast, cigarette smoking increased the risk of CRC among slow acetylators (OR: 1.97, 95% CI: 1.02-3.79).

CONCLUSION: The risk of CRC was higher among fast acetylators who reported a higher meat intake. Slow NAT2 acetylation was associated with an increased risk of CRC.

Gender-related differences in response to mutagens and carcinogens

The incidences of many cancers can be very different in men and women. Besides differences in exposures to putative causative agents, it is plausible that both genetic and epigenetic effects play roles in these differences. In addition, gender-specific lifestyle and behavioural factors may modulate the effects of exposure to genotoxins. This commentary focuses on several aspects of gender-related differences in responses to mutagens and carcinogens, including sensitivity to chromosome damage, the contribution of genotypic variation and the role of DNA methylation. It is concluded that the reasons for gender differences in cancer susceptibility remain largely unknown in many cases, and the subject deserves more attention and study.

NAT2 fast acetylator genotype and MGMT promoter methylation may contribute to gender difference in K-RAS mutation occurrence in Taiwanese colorectal cancer

A recent study conducted by our group showed that the NAT2 fast acetylator genotype is associated with an increasing risk for the development of colorectal cancer (CRC), especially for females. We therefore examined whether a higher risk of CRC in females with the NAT2 fast acetylator genotype was associated with the occurrence of K-RAS mutation, and to further verify whether MGMT promoter methylation was linked to the occurrence of K-RAS mutation in patients with the NAT2 fast acetylator genotype. Herein, 151 CRC cases were examined for NAT2 genetic polymorphisms and MGMT promoter methylation by PCR-RFLP and methylation-specific PCR (MSP). The results of this study show that the NAT2 fast acetylator genotype is associated with the occurrence of K-RAS mutation in female cases (OR = 4.820, 95% CI = 1.113-20.873), but not associated with MGMT promoter methylation. Surprisingly, MGMT promoter methylation significantly deepens the impact of NAT2 fast acetylation on K-RAS mutation in the female cases (OR = 5.129, 95% CI = 1.092-24.105). In conclusion, Taiwanese women with the NAT2 fast acetylator genotype may exhibit a higher risk of CRC with increased occurrence of K-RAS mutation. Detection of NAT2 genotypes and MGMT promoter methylation may be useful in the risk assessment for CRC in Taiwanese women.

Genetic polymorphism in N-Acetyltransferase (NAT): Population distribution of NAT1 and NAT2 activity

N-Acetyltransferases (NAT) are key enzymes in the conjugation of certain drugs and other xenobiotics with an arylamine structure. Polymorphisms in NAT2 have long been recognized to modulate toxicity produced by the anti-tubercular drug isoniazid, with molecular epidemiologic studies suggesting a link between acetylator phenotype and increased risk for bladder cancer. Recent evidence indicates that the other major NAT isozyme, NAT1, is also polymorphic. The current analysis characterizes the main polymorphisms in both NAT2 and NAT1 in terms of their effect on enzyme activity and frequency in the population. Multiple NAT2 alleles (NAT2*5, *6, *7, and *14) have substantially decreased acetylation activity and are common in Caucasians and populations of African descent. In these groups, most individuals carry at least one copy of a slow acetylator allele, and less than 10% are homozygous for the wild type (fast acetylator) trait. Incorporation of these data into a Monte Carlo modeling framework led to a population distribution of NAT2 activity that was bimodal and associated with considerable variability in each population assessed. The ratio of the median to the first percentile of NAT2 activity ranged from 7 in Caucasians to 18 in the Chinese population. This variability indicates the need for more quantitative approaches (e.g., physiologically based pharmacokinetic [PBPK] modeling) to assess the full distribution of internal dose and adverse responses to aromatic amines and other NAT2 substrates. Polymorphisms in NAT1 are generally associated with relatively minor effects on acetylation function, with Monte Carlo analysis indicating less interindividual variability than seen in NAT2 analysis.

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.

Polymorphisms of promoter and coding regions of the arylamine N-acetyltransferase 2 (NAT2) gene in the Indonesian population: proposal for a new nomenclature

Polymorphisms of arylamine N-acetyltransferase 2 (NAT2) are reportedly associated with the risk of drug toxicities and development of various diseases. The present study examined NAT2 polymorphisms in both promoter and coding regions in the Indonesian population using PCR direct sequencing. The promoter and coding regions of NAT2 displayed 23 polymorphisms/variations, including eight new ones. Seven haplotypes in the promoter region and six haplotypes in the coding region were inferred. The haplotypes in promoter and coding regions showed limited combinations, and 13 combined haplotypes were inferred. The most frequent haplotypes were U1 (38.9%), U2 (33.5%) in the promoter region and NAT2*4 (37.3%), NAT2*6A (36.8%) in the coding region. When converted to predicted phenotypes, the studied population comprised 65.4% rapid acetylators and 35.6% slow acetylators according to bimodal distribution. According to trimodal distribution, frequencies of predicted phenotypes were 13.6, 50.8 and 35.6% for rapid, intermediate and slow acetylators, respectively. Frequencies of NAT2 alleles for the Indonesian population resembled those of other Southeast Asian populations. We also propose a new NAT2 nomenclature composed of haplotypes in the promoter region and conventional NAT2 haplotypes in the coding region, symbolized by NAT2*4.U1, NAT2*4.U2, NAT2*4.U3, NAT2*4.U5, NAT2*4.U6, NAT2*4.U7, NAT2*6A.U1, NAT2*7B.U2, NAT2*7B.U3, NAT2*5B.U1, NAT2*5B.U4, NAT2*12A.U4 and NAT2*13.U1.