Phenotype of the most common "slow acetylator" arylamine N-acetyltransferase 1 genetic variant (NAT1*14B) is substrate-dependent

Effects of dose and human N-acetyltransferase 1 genetic polymorphism in benzidine metabolism and genotoxicity

Benzidine undergoes N-acetylation and following CYP1A2-catalyzed N-hydroxylation undergoes O-acetylation catalyzed by N-acetyltransferase 1 (NAT1). Benzidine exposure is associated with urinary bladder cancer but the effect of NAT1 genetic polymorphism on individual risk remains unclear. We used Chinese hamster ovary (CHO) cells transfected with human CYP1A2 and NAT1*4 allele (reference) or NAT1*14B (variant) to investigate the effects of dose and NAT1 polymorphism on benzidine metabolism and genotoxicity. Rates of benzidine N-acetylation in vitro were higher in CHO cells transfected with NAT1*4 compared to NAT1*14B. CHO cells transfected with NAT1*14B exhibited greater N-acetylation rates in situ than cells transfected with NAT1*4 at low doses of benzidine expected with environmental exposures but not at higher doses. NAT1*14B exhibited over tenfold lower apparent KM which resulted in higher intrinsic clearance for benzidine N-acetylation compared to CHO cells transfected with NAT1*4. Benzidine-induced hypoxanthine phosphoribosyl transferase (HPRT) mutations were higher in CHO cells transfected with NAT1*14B than with NAT1*4 (p < 0.001). Benzidine caused concentration-dependent increase in γ-H2AX signal (indicative of DNA double-strand breaks) in CHO cells transfected with NAT1*4 or NAT1*14B. CHO cells transfected with NAT1*14B exhibited significantly higher level of DNA damage than with NAT1*4 (p < 0.0001). Benzidine-induced ROS did not differ significantly (p > 0.05) between CHO cells transfected with NAT1*4 or NAT1*14B except at 50 μM. Levels of benzidine-induced DNA damage and reactive oxygen species (ROS) showed strong dose-dependent correlation. Our findings support human studies associating NAT1*14B with increased incidence or severity of urinary bladder cancer in workers exposed to benzidine.

N-acetyltransferase 2 genetic polymorphism modifies genotoxic and oxidative damage from new psychoactive substances

The use of new psychoactive substances (NPS) as drugs of abuse is common and increasingly popular, particularly among youth and neglected communities. Recent studies have reported acute toxic effects from these chemicals; however, their long-term toxicity is unknown. Genetic differences between individuals likely affect the toxicity risk. Arylamine N-acetyltransferase 2 (NAT2) capacity differs among individuals due to genetic inheritance. The goal of the present study is to investigate the gene-environment interaction between NAT2 polymorphism and toxicity after exposure to these chemicals. We measured N-acetylation by human NAT1 and NAT2 and found that N-acetylation of NPS is carried out exclusively by NAT2. Differences in N-acetylation between NAT2*4 (reference allele) and NAT2*5B (common variant allele) were highly significant (p < 0.0001). Using DNA repair-deficient genetically engineered Chinese hamster ovary (CHO cells), expressing human CYP1A2 and either NAT2*4 or NAT2*5B, we measured the induction of DNA double-strand breaks ([Formula: see text]H2Ax) following treatment of the CHO cells with increasing concentrations of NPS. The induction of [Formula: see text]H2Ax showed a NAT2 allele-dependent response, higher in the NAT2*4 vs NAT2*5B alleles (p < 0.05). Induction of oxidative stress (ROS/RNS) was evaluated; we observed NAT2 allele-dependent response for all compounds in concentrations as low as 10 [Formula: see text]M, where NAT2*4 showed increased ROS/RNS vs NAT2*5B (p < 0.05). In summary, NPS are N-acetylated by NAT2 at rates higher in cells expressing NAT2*4 than NAT2*5B. Exposure to psychoactive chemicals results in genotoxic and oxidative damage that is modified by the NAT2 genetic polymorphism.

Acetyl coenzyme A kinetic studies on N-acetylation of environmental carcinogens by human N-acetyltransferase 1 and its NAT1*14B variant

N-acetyltransferase 1 (NAT1) is a xenobiotic metabolizing enzyme that uses acetyl coenzyme A (AcCoA) as a cofactor for N-acetylation of many carcinogens including aromatic amines and alkylanilines. NAT1 is characterized by single nucleotide polymorphisms (SNPs) that may modulate affinity towards AcCoA. In the current study, we used Chinese hamster ovary (CHO) cells stably transfected with human NAT1*4 (reference allele) or NAT1*14B (variant allele) to measure AcCoA kinetic parameters for N-acetyltransferase activity measurements towards p-aminobenzoic acid (PABA), 4-aminobiphenyl (4-ABP), β-naphthylamine (BNA), benzidine and 3,4-dimethylaniline (3,4-DMA). Our results showed higher N-acetylation rates for each substrate catalyzed by NAT1*4 compared to NAT1*14B. NAT1*4 exhibited higher affinity to AcCoA when catalyzing the N-acetylation of BNA and benzidine compared to NAT1*14B. The results of the current study provide further insights into differences in carcinogen metabolism among individuals possessing the NAT1*14B haplotype.

The role of arylamine N-acetyltransferases in chronic degenerative diseases: Their possible function in the immune system

Since their discovery, arylamine N-acetyltransferases 1 and 2 (NAT1 and NAT2, respectively) have been associated with the metabolism of xenobiotics. NAT2 is the main factor in the therapeutic success of tuberculosis treatment due to its role in the biotransformation of isoniazid. However, researchers have started to investigate the possible participation of NAT1 and NAT2 (NATs) in carcinogenesis, although the mechanisms have not been elucidated fully. NATs enzymatic activity is essential in some types of cancer, such as breast cancer and acute lymphoblastic leukemia. Whether NAT1 and/or NAT2 participate in insulin resistance level in diabetes mellitus or in the immune system remains to be explored. Therefore, it is clear that its role in cell physiology has more implications than just metabolizing compounds.

560G>A (rs4986782) (R187Q) Single Nucleotide Polymorphism in Arylamine N-Acetyltransferase 1 Increases Affinity for the Aromatic Amine Carcinogens 4-Aminobiphenyl and N-Hydroxy-4-Aminobiphenyl: Implications for Cancer Risk Assessment

Human arylamine N-acetyltransferase 1 (NAT1) catalyzes the N-acetylation of arylamine carcinogens such as 4-aminobiphenyl (ABP), and following N-hydroxylation, the O-acetylation of N-hydroxy-arylamine carcinogens such as N-hydroxy-ABP (N-OH-ABP). Genetic polymorphisms in NAT1 are linked to cancer susceptibility following exposures. The effects of individual single nucleotide polymorphisms (SNPs) in the NAT1 coding exon on Michaelis-Menten kinetic constants was assessed for ABP N-acetyltransferase and N-OH-ABP O-acetyltransferase activity following transfection of human NAT1 into COS-1 cells (SV40-transformed African green monkey kidney cells). NAT1 coding region SNPs 97C > T (rs56318881) (R33stop), 190C > T (rs56379106) (R64W), 559C > T (rs5030839) (R187stop) and 752A > T (rs56172717) (D251V) reduced ABP N- acetyltransferase and N-OH-ABP O-acetyltransferase activity below detection. 21T > G (rs4986992) (synonymous), 402T > C (rs146727732) (synonymous), 445G > A (rs4987076) (V149I), 613A > G (rs72554609) (M205V) and 640T > G (rs4986783) (S241A) did not significantly affect Vmax for ABP N-acetyltransferase or N-OH-ABP O-acetyltransferase. 781G > A (rs72554610) (E261K), and 787A > G (rs72554611) (I263V) slightly reduced ABP N-acetyltransferase and N-OH-ABP O-acetyltransferase activities whereas 560G > A (rs4986782) (R187Q) substantially and significantly reduced them. 560G > A (rs4986782) (R187Q) significantly reduced the apparent Km for ABP and N-OH-ABP a finding that was not observed with any of the other NAT1 SNPs tested. These findings suggest that the role of the 560G > A (rs4986782) (R187Q) SNP cancer risk assessment may be modified by exposure level to aromatic amine carcinogens such as ABP.

Identification and characterization of potent, selective, and efficacious inhibitors of human arylamine N-acetyltransferase 1

Arylamine N-acetyltransferase 1 (NAT1) plays a pivotal role in the metabolism of carcinogens and is a drug target for cancer prevention and/or treatment. A protein-ligand virtual screening of 2 million chemicals was ranked for predicted binding affinity towards the inhibition of human NAT1. Sixty of the five hundred top-ranked compounds were tested experimentally for inhibition of recombinant human NAT1 and N-acetyltransferase 2 (NAT2). The most promising compound 9,10-dihydro-9,10-dioxo-1,2-anthracenediyl diethyl ester (compound 10) was found to be a potent and selective NAT1 inhibitor with an in vitro IC₅₀ of 0.75 µM. Two structural analogs of this compound were selective but less potent for inhibition of NAT1 whereas a third structural analog 1,2-dihydroxyanthraquinone (a compound 10 hydrolysis product also known as Alizarin) showed comparable potency and efficacy for human NAT1 inhibition. Compound 10 inhibited N-acetylation of the arylamine carcinogen 4-aminobiphenyl (ABP) both in vitro and in DNA repair-deficient Chinese hamster ovary (CHO) cells in situ stably expressing human NAT1 and CYP1A1. Compound 10 and Alizarin effectively inhibited NAT1 in cryopreserved human hepatocytes whereas inhibition of NAT2 was not observed. Compound 10 caused concentration-dependent reductions in DNA adduct formation and DNA double-strand breaks following metabolism of aromatic amine carcinogens beta-naphthylamine and/or ABP in CHO cells. Compound 10 inhibited proliferation and invasion in human breast cancer cells and showed selectivity towards tumorigenic versus non-tumorigenic cells. In conclusion, our study identifies potent, selective, and efficacious inhibitors of human NAT1. Alizarin's ability to inhibit NAT1 could reduce breast cancer metastasis particularly to bone.

Case Study 10: A Case to Investigate Acetyl Transferase Kinetics

Major routes of metabolism for marketed drugs are predominately driven by enzyme families such as cytochromes P450 and UDP-glucuronosyltransferases. Less studied conjugative enzymes, like N-acetyltransferases (NATs), are commonly associated with detoxification pathways. However, in the clinic, the high occurrence of NAT polymorphism that leads to slow and fast acetylator phenotypes in patient populations has been linked to toxicity for a multitude of drugs. A key example of this is the observed clinical toxicity in patients who exhibit the slow acetylator phenotype and were treated with isoniazid. Toxicity in patients has led to detailed characterization of the two NAT isoforms and their polymorphic genotypes. Investigation in recombinant enzymes, genotyped hepatocytes, and in vivo transgenic models coupled with acetylator status-driven clinical studies have helped understand the role of NATs in drug development, clinical study design and outcomes, and potential roles in human disease models. The selected case studies herein document NAT enzyme kinetics to explore substrate overlap from two human isoforms, preclinical species considerations, and clinical genotype population concerns.

Acetylation of putative arylamine and alkylaniline carcinogens in immortalized human fibroblasts transfected with rapid and slow acetylator N-acetyltransferase 2 haplotypes

Exposure to alkylanilines found in tobacco smoke and indoor air is associated with risk of bladder cancer. Genetic factors significantly influence the metabolism of arylamine carcinogens and the toxicological outcomes that result from exposure. We utilized nucleotide excision repair (NER)-deficient immortalized human fibroblasts to examine the effects of human N-acetyltransferase 1 (NAT1), CYP1A2, and common rapid (NAT2*4) and slow (NAT2*5B or NAT2*7B) acetylator human N-acetyltransferase 2 (NAT2) haplotypes on environmental arylamine and alkylaniline metabolism. We constructed SV40-transformed human fibroblast cells that stably express human NAT2 alleles (NAT2*4, NAT2*5B, or NAT2*7B) and human CYP1A2. Human NAT1 and NAT2 apparent kinetic constants were determined following recombinant expression of human NAT1 and NAT2 in yeast for the arylamines benzidine, 4-aminobiphenyl (ABP), and 2-aminofluorene (2-AF), and the alkylanilines 2,5-dimethylaniline (DMA), 3,4-DMA, 3,5-DMA, 2-6-DMA, and 3-ethylaniline (EA) compared with those of the prototype NAT1-selective substrate p-aminobenzoic acid and NAT2-selective substrate sulfamethazine. Benzidine, 3,4-DMA, and 2-AF were preferential human NAT1 substrates, while 3,5-DMA, 2,5-DMA, 3-EA, and ABP were preferential human NAT2 substrates. Neither recombinant human NAT1 or NAT2 catalyzed the N-acetylation of 2,6-DMA. Among the alkylanilines, N-acetylation of 3,5-DMA was substantially higher in human fibroblasts stably expressing NAT2*4 versus NAT2*5B and NAT2*7B. The results provide important insight into the role of the NAT2 acetylator polymorphism (in the presence of competing NAT1 and CYP1A2-catalyzed N-acetylation and N-hydroxylation) on the metabolism of putative alkyaniline carcinogens. The N-acetylation of two alkylanilines associated with urinary bladder cancer (3-EA and 3,5-DMA) was modified by NAT2 acetylator polymorphism.

Arylamine N-acetyltransferase 1 in situ N-acetylation on CD3+ peripheral blood mononuclear cells correlate with NATb mRNA and NAT1 haplotype

Human arylamine N-acetyltransferase 1 (NAT1) is responsible for the activation and elimination of xenobiotic compounds and carcinogens. Genetic polymorphisms in NAT1 modify both drug efficacy and toxicity. Previous studies have suggested a role for NAT1 in the development of several diseases. The aim of the present study was to evaluate NAT1 protein expression and in situ N-acetylation capacity in peripheral blood mononuclear cells (PBMC), as well as their possible associations with the expression of NAT1 transcript and NAT1 genotype. We report NAT1 protein, mRNA levels, and N-acetylation in situ activity for PBMC obtained from healthy donors. NAT1-specific protein expression was higher in CD3+ cells than other major immune cell subtypes (CD19 or CD56 cells). N-acetylation of pABA varied markedly among the PBMC of participants, but correlated very significantly with levels of NAT1 transcripts. NAT1*4 subjects showed significantly (p = 0.017) higher apparent pABA V _max of 71.3 ± 3.7 versus the NAT1*14B subjects apparent V _max of 58.5 ± 2.5 nmoles Ac-pABA/24 h/million cells. Levels of pABA N-acetylation activity at each concentration of substrate evaluated also significantly correlated with NAT1 mRNA levels for all samples (p < 0.0001). This highly significant correlation was maintained for samples with the NAT1*4 (p = 0.002) and NAT1*14B haplotypes (p = 0.0106). These results provide the first documentation that NAT1-catalyzed N-acetylation in PBMC is higher in T cell than in other immune cell subtypes and that individual variation in N-acetylation capacity is dependent upon NAT1 mRNA and NAT1 haplotype.

Congenic rats with higher arylamine N-acetyltransferase 2 activity exhibit greater carcinogen-induced mammary tumor susceptibility independent of carcinogen metabolism

Background

Recent investigations suggest role(s) of human arylamine N-acetyltransferase 1 (NAT1) in breast cancer. Rat NAT2 is orthologous to human NAT1 and the gene products are functional homologs. We conducted in vivo studies using F344.WKY-Nat2^rapid/slow rats, congenic at rat Nat2 for high (rapid) and low (slow) arylamine N-acetyltransferase activity, to assess a possible role for rat NAT2 in mammary tumor susceptibility.

Methods

Mammary carcinogens, methylnitrosourea (MNU) and 7,12-dimethylbenzanthracene (DMBA) neither of which is metabolized by N-acetyltransferase, were administered to assess mammary tumors. MNU was administered at 3 or 8 weeks of age. DMBA was administered at 8 weeks of age. NAT2 enzymatic activity and endogenous acetyl-coenzyme A (AcCoA) levels were measured in tissue samples and embryonic fibroblasts isolated from the congenic rats.

Results

Tumor latency was shorter in rapid NAT2 rats compared to slow NAT2 rats, with statistical significance for MNU administered at 3 and 8 weeks of age (p = 0.009 and 0.050, respectively). Tumor multiplicity and incidence were higher in rapid NAT2 rats compared to slow NAT2 rats administered MNU or DMBA at 8 weeks of age (MNU, p = 0.050 and 0.035; DMBA, p = 0.004 and 0.027, respectively). Recombinant rat rapid-NAT2, as well as tissue samples and embryonic fibroblasts derived from rapid NAT2 rats, catalyzed p-aminobenzoic acid N-acetyl transfer and folate-dependent acetyl-coenzyme A (AcCoA) hydrolysis at higher rates than those derived from rat slow-NAT2. Embryonic fibroblasts isolated from rapid NAT2 rats displayed lower levels of cellular AcCoA than slow NAT2 rats (p < 0.01).

Conclusions

A novel role for rat NAT2 in mammary cancer was discovered unrelated to carcinogen metabolism, suggesting a role for human NAT1 in breast cancer.

Evidence for extensive pleiotropy among pharmacogenes

AIM

We sought to identify potential pleiotropy involving pharmacogenes.

METHODS

We tested 184 functional variants in 34 pharmacogenes for associations using a custom grouping of International Classification and Disease, Ninth Revision billing codes extracted from deidentified electronic health records of 6892 patients.

RESULTS

We replicated several associations including ABCG2 (rs2231142) and gout (p = 1.73 × 10(-7); odds ratio [OR]: 1.73; 95% CI: 1.40-2.12); and SLCO1B1 (rs4149056) and jaundice (p = 2.50 × 10(-4); OR: 1.67; 95% CI: 1.27-2.20).

CONCLUSION

In this systematic screen for phenotypic associations with functional variants, several novel genotype-phenotype combinations also achieved phenome-wide significance, including SLC15A2 rs1143672 and renal osteodystrophy (p = 2.67 × 10(-) (6); OR: 0.61; 95% CI: 0.49-0.75).

Arylamine N-acetyltransferases: from drug metabolism and pharmacogenetics to drug discovery

Arylamine N-acetyltransferases (NATs) are polymorphic drug-metabolizing enzymes, acetylating arylamine carcinogens and drugs including hydralazine and sulphonamides. The slow NAT phenotype increases susceptibility to hydralazine and isoniazid toxicity and to occupational bladder cancer. The two polymorphic human NAT loci show linkage disequilibrium. All mammalian Nat genes have an intronless open reading frame and non-coding exons. The human gene products NAT1 and NAT2 have distinct substrate specificities: NAT2 acetylates hydralazine and human NAT1 acetylates p-aminosalicylate (p-AS) and the folate catabolite para-aminobenzoylglutamate (p-abaglu). Human NAT2 is mainly in liver and gut. Human NAT1 and its murine homologue are in many adult tissues and in early embryos. Human NAT1 is strongly expressed in oestrogen receptor-positive breast cancer and may contribute to folate and acetyl CoA homeostasis. NAT enzymes act through a catalytic triad of Cys, His and Asp with the architecture of the active site-modulating specificity. Polymorphisms may cause unfolded protein. The C-terminus helps bind acetyl CoA and differs among NATs including prokaryotic homologues. NAT in Salmonella typhimurium supports carcinogen activation and NAT in mycobacteria metabolizes isoniazid with polymorphism a minor factor in isoniazid resistance. Importantly, nat is in a gene cluster essential for Mycobacterium tuberculosis survival inside macrophages. NAT inhibitors are a starting point for novel anti-tuberculosis drugs. Human NAT1-specific inhibitors may act in biomarker detection in breast cancer and in cancer therapy. NAT inhibitors for co-administration with 5-aminosalicylate (5-AS) in inflammatory bowel disease has prompted ongoing investigations of azoreductases in gut bacteria which release 5-AS from prodrugs including balsalazide.

Toxicogenetic profile and cancer risk in Lebanese

An increasing number of genetic polymorphisms in drug-metabolizing enzymes (DME) were identified among different ethnic groups. Some of these polymorphisms are associated with an increased cancer risk, while others remain equivocal. However, there is sufficient evidence that these associations become significant in populations overexposed to environmental carcinogens. Hence, genetic differences in expression activity of both Phase I and Phase II enzymes may affect cancer risk in exposed populations. In Lebanon, there has been a marked rise in reported cancer incidence since the 1990s. There are also indicators of exposure to unusually high levels of environmental pollutants and carcinogens in the country. This review considers this high cancer incidence by exploring a potential gene-environment model based on available DME polymorphism prevalence, and their impact on bladder, colorectal, prostate, breast, and lung cancer in the Lebanese population. The examined DME include glutathione S-transferases (GST), N-acetyltransferases (NAT), and cytochromes P-450 (CYP). Data suggest that these DME influence bladder cancer risk in the Lebanese population. Evidence indicates that identification of a gene-environment interaction model may help in defining future research priorities and preventive cancer control strategies in this country, particularly for breast and lung cancer.