The effect of the rs1799931 G857A (G286E) polymorphism on N-acetyltransferase 2-mediated carcinogen metabolism and genotoxicity differs with heterocyclic amine exposure

Human N-acetyltransferase 2 (NAT2) is subject to genetic polymorphism in human populations. In addition to the reference NAT2*4 allele, two genetic variant alleles (NAT2*5B and NAT2*7B) are common in Europe and Asia, respectively. NAT2*5B possesses a signature rs1801280 T341C (I114T) single-nucleotide polymorphism (SNP), whereas NAT2*7B possesses a signature rs1799931 G857A (G286E) SNP. NAT2 alleles possessing the T341C (I114T) or G857A (G286E) SNP were recombinant expressed in yeast and tested for capacity to catalyze the O-acetylation of the N-hydroxy metabolites of heterocyclic amines (HCAs). The T341C (I114T) SNP reduced the O-acetylation of N-hydroxy-2-amino-3-methylimidazo [4,5-f] quinoline (N-OH-IQ), N-hydroxy-2-amino-3,8-dimethylimidazo [4,5-f] quinoxaline (N-OH-MeIQx) and N-hydroxy- 2-amino-1-methyl-6-phenylimidazo[4,5-b] pyridine (N-OH-PhIP), whereas the G857A (G286E) SNP reduced the O-acetylation of N-OH-IQ and N-OH-MeIQx but not N-OH-PhIP. The G857A (G286E) SNP significantly (p < 0.05) reduced apparent Km toward N-OH-PhIP but did not significantly (p > 0.05) affect apparent Vmax. Cultures of DNA repair-deficient Chinese hamster ovary (CHO) cells transfected with human CYP1A2 and NAT2*4, NAT2*5B or NAT2*7B alleles were incubated with various concentrations of IQ, MeIQx or PhIP and double-stranded DNA damage and reactive oxygen species (ROS) were measured. Transfection with human CYP1A2 did not significantly (p > 0.05) increase HCA-induced DNA damage and ROS over un-transfected cells. Additional transfection with NAT2*4, NAT2*5B or NAT2*7B allele increased both DNA damage and ROS. The magnitude of the increases was both NAT2 allele- and substrate-dependent showing the same pattern as observed for the O-acetylation of the N-hydroxylated HCAs suggesting that both are mediated via NAT2-catalyzed O-acetylation. The results document the role of NAT2 and its genetic polymorphism on the O-acetylation and genotoxicity of HCAs.

N -acetyltransferase 2 haplotype modifies risks for both dyslipidemia and urinary bladder cancer

A novel haplotype in N -acetyltransferase 2 ( NAT2 ) composed of seven non-coding variants (rs1495741, rs4921913, rs4921914, rs4921915, rs146812806, rs35246381, and rs35570672) has been linked to dyslipidemia by multiple, independent genome-wide association studies. The haplotype is located approximately 14 kb downstream of NAT2-coding region (ch8:18,272,377-18,272,881; GRCh38/hg38) and represents a non-coding, intergenic haplotype. Interestingly, the same dyslipidemia NAT2 haplotype is also linked to urinary bladder cancer risk. Dyslipidemia risk alleles are associated with rapid acetylator phenotype, whereas bladder cancer risk alleles are associated with slow acetylator, suggesting that the level of systemic NAT2 activity modifies the risk of these pathologies. We speculate that rs1495741 (and its associated haplotype) belongs to a distal regulatory element of human NAT2 gene (e.g., enhancer or silencer), and the genetic variation at the newly discovered haplotype results in a differential level of NAT2 gene expression. Understanding how this NAT2 haplotype contributes to not only urinary bladder cancer but also to dyslipidemia will ultimately help devise strategies to identify and protect susceptible individuals.

Induction of glucose production by heterocyclic amines is dependent on N-acetyltransferase 2 genetic polymorphism in cryopreserved human hepatocytes

Heterocyclic amines (HCAs) are mutagenic compounds found in cooked meat. Recent epidemiological studies reported significant associations between dietary HCA exposure and insulin resistance and type II diabetes, and we recently reported that HCAs induce insulin resistance and glucose production in human hepatocytes. It is well known that HCAs require hepatic bioactivation by cytochrome P450 1A2 (CYP1A2) and N-acetyltransferase 2 (NAT2). NAT2 expresses a well-defined genetic polymorphism in humans that, depending on the combination of NAT2 alleles, correlates to rapid, intermediate, or slow acetylator phenotype that exhibits differential metabolism of aromatic amines and HCAs. No previous studies have examined the role of NAT2 genetic polymorphism in the context of HCA-mediated induction of glucose production. In the present study, we assessed the effect of three HCAs commonly found in cooked meat (2-amino-3,4-dimethylimidazo[4,5-f]quinoline [MeIQ], 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline [MeIQx], and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine [PhIP]) on glucose production in cryopreserved human hepatocytes with slow, intermediate, or rapid NAT2 acetylator phenotype. HCA treatment did not affect glucose production in slow NAT2 acetylator hepatocytes, while a slight increase in glucose production was observed in intermediate NAT2 acetylators treated with MeIQ or MeIQx. However, significant increases in glucose production were observed in rapid NAT2 acetylators following each HCA. The current findings suggest that individuals who are rapid NAT2 acetylators may be at a greater risk of developing hyperglycemia and insulin resistance following dietary exposure to HCAs.

Upregulation of cytidine deaminase in NAT1 knockout breast cancer cells

PURPOSE

Arylamine N-acetyltransferase 1 (NAT1), a phase II metabolic enzyme, is frequently upregulated in breast cancer. Inhibition or depletion of NAT1 leads to growth retardation in breast cancer cells in vitro and in vivo. A previous metabolomics study of MDA-MB-231 breast cancer cells suggests that NAT1 deletion leads to a defect in de novo pyrimidine biosynthesis. In the present study, we observed that NAT1 deletion results in upregulation of cytidine deaminase (CDA), which is involved in the pyrimidine salvage pathway, in multiple breast cancer cell lines (MDA-MB-231, MCF-7 and ZR-75-1). We hypothesized that NAT1 KO MDA-MB-231 cells show differential sensitivity to drugs that either inhibit cellular pyrimidine homeostasis or are metabolized by CDA.

METHODS

The cells were treated with (1) inhibitors of dihydroorotate dehydrogenase or CDA (e.g., teriflunomide and tetrahydrouridine); (2) pyrimidine/nucleoside analogs (e.g., gemcitabine and 5-azacytidine); and (3) naturally occurring, modified cytidines (e.g., 5-formyl-2'-deoxycytidine; 5fdC).

RESULTS

Although NAT1 KO cells failed to show differential sensitivity to nucleoside analogs that are metabolized by CDA, they were markedly more sensitive to 5fdC which induces DNA damage in the presence of high CDA activity. Co-treatment with 5fdC and a CDA inhibitor, tetrahydrouridine, abrogated the increase in 5fdC cytotoxicity in NAT1 KO cells, suggesting that the increased sensitivity of NAT1 KO cells to 5fdC is dependent on their increased CDA activity.

CONCLUSIONS

The present findings suggest a novel therapeutic strategy to treat breast cancer with elevated NAT1 expression. For instance, NAT1 inhibition may be combined with cytotoxic nucleosides (e.g., 5fdC) for breast cancer treatment.

Heterocyclic amines reduce insulin-induced AKT phosphorylation and induce gluconeogenic gene expression in human hepatocytes

Heterocyclic amines (HCAs) are well-known for their mutagenic properties. One of the major routes of human exposure is through consumption of cooked meat, as certain cooking methods favor formation of HCAs. Recent epidemiological studies reported significant associations between dietary HCA exposure and insulin resistance and type II diabetes. However, no previous studies have examined if HCAs, independent of meat consumption, contributes to pathogenesis of insulin resistance or metabolic disease. In the present study, we have assessed the effect of three HCAs commonly found in cooked meat (2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline [MeIQ], 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline [MeIQx], and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine [PhIP]) on insulin signaling and glucose production. HepG2 or cryopreserved human hepatocytes were treated with 0-50 μM of MeIQ, MeIQx, or PhIP for 3 days. Treatment of HepG2 cells and hepatocytes with MeIQ and MeIQx resulted in a significant reduction in insulin-induced AKT phosphorylation, suggesting that HCA exposure decreases hepatic insulin signaling. HCA treatment also led to significant increases in expression of gluconeogenic genes, G6PC and PCK1, in both HepG2 and cryopreserved human hepatocytes. Additionally, the level of phosphorylated FOXO1, a transcriptional regulator of gluconeogenesis, was significantly reduced by HCA treatment in hepatocytes. Importantly, HCA treatment of human hepatocytes led to increases in extracellular glucose level in the presence of gluconeogenic substrates, suggesting that HCAs induce hepatic glucose production. The current findings suggest that HCAs induce insulin resistance and promote hepatic glucose production in human hepatocytes. This implicates that exposure to HCAs may lead to the development of type II diabetes or metabolic syndrome.

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.

Effect of N-acetyltransferase 2 genetic polymorphism on 4,4'-methylenebis(2-chloroaniline)-induced genotoxicity and oxidative stress

4,4'-Methylenebis(2-chloroaniline) or MOCA is an aromatic amine used primarily in polyurethane and rubber industry. MOCA has been linked to hepatomas in animal studies while limited epidemiologic studies reported the association of exposure to MOCA and urinary bladder and breast cancer. We investigated MOCA-induced genotoxicity and oxidative stress in DNA repair-deficient Chinese hamster ovary (CHO) cells stably transfected with human metabolizing enzymes CYP1A2 and N-acetyltransferase 2 (NAT2) variants as well as in rapid, intermediate, and slow NAT2 acetylator cryopreserved human hepatocytes. N-acetylation of MOCA was highest in UV5/1A2/NAT2*4 followed by UV5/1A2/NAT2*7B and UV5/1A2/NAT2*5B CHO cells. Human hepatocytes showed a NAT2 genotype-dependent response with highest N-acetylation in rapid acetylators followed by intermediate and slow acetylators. MOCA induced higher levels of mutagenesis and DNA damage in UV5/1A2/NAT2*7B compared to UV5/1A2/NAT2*4 and UV5/1A2/NAT2*5B cells (p < 0.0001). MOCA also induced higher levels of oxidative stress in UV5/1A2/NAT2*7B cells. MOCA caused concentration-dependent increase in DNA damage in cryopreserved human hepatocytes (linear trend p < 0.001) which was NAT2 genotype dependent i.e., highest in rapid acetylators, lower in intermediate acetylators, and lowest in slow acetylators (p < 0.0001). Our findings show that N-acetylation and genotoxicity of MOCA is NAT2 genotype dependent and suggest that individuals possessing NAT2*7B are at higher risk to MOCA-induced mutagenicity. DNA damage, and oxidative stress. They confirm significant differences in genotoxicity between the NAT2*5B and NAT2*7B alleles, both of which are associated with slow acetylator phenotype.

Non-coding and intergenic genetic variants of human arylamine N-acetyltransferase 2 (NAT2) gene are associated with differential plasma lipid and cholesterol levels and cardiometabolic disorders

Arylamine N-acetyltransferase 2 (NAT2) is a phase II metabolic enzyme, best known for metabolism of aromatic amines and hydrazines. Genetic variants occurring in the NAT2 coding region have been well-defined and are known to affect the enzyme activity or protein stability. Individuals can be categorized into rapid, intermediate, and slow acetylator phenotypes that significantly alter their ability to metabolize arylamines, including drugs (e.g., isoniazid) and carcinogens (e.g., 4-aminobiphenyl). However, functional studies on non-coding or intergenic variants of NAT2 are lacking. Multiple, independent genome wide association studies (GWAS) have reported that non-coding or intergenic variants of NAT2 are associated with elevated plasma lipid and cholesterol levels, as well as cardiometabolic disorders, suggesting a novel cellular role of NAT2 in lipid and cholesterol homeostasis. The current review highlights and summarizes GWAS reports that are relevant to this association. We also present a new finding that seven, non-coding, intergenic NAT2 variants (i.e., rs4921913, rs4921914, rs4921915, rs146812806, rs35246381, rs35570672, and rs1495741), which have been associated with plasma lipid and cholesterol levels, are in linkage disequilibrium with one another, and thus form a novel haplotype. The dyslipidemia risk alleles of non-coding NAT2 variants are associated with rapid NAT2 acetylator phenotype, suggesting that differential systemic NAT2 activity might be a risk factor for developing dyslipidemia. The current review also discusses the findings of recent reports that are supportive of the role of NAT2 in lipid or cholesterol synthesis and transport. In summary, we review data suggesting that human NAT2 is a novel genetic factor that influences plasma lipid and cholesterol levels and alters the risk of cardiometabolic disorders. The proposed novel role of NAT2 merits further investigations.

Stable Isotope Tracing Reveals an Altered Fate of Glucose in N-Acetyltransferase 1 Knockout Breast Cancer Cells

Breast cancer is one of the leading causes of cancer death. Recent studies found that arylamine N-acetyltransferase 1 (NAT1) is frequently upregulated in breast cancer, further suggesting NAT1 could be a potential therapeutic target for breast cancer. Previous publications have established that NAT1 knockout (KO) in breast cancer cell lines leads to growth reduction both in vitro and in vivo and metabolic changes. These reports suggest that NAT1 contributes to the energy metabolism of breast cancer cells. Proteomic analysis and non-targeted metabolomics suggested that NAT1 KO may change the fate of glucose as it relates to the TCA/KREB cycle of the mitochondria of breast cancer cells. In this current study, we used [U-13C]-glucose stable isotope resolved metabolomics to determine the effect of NAT1 KO on the metabolic profile of MDA-MB-231 breast cancer cells. We incubated breast cancer cells (MDA-MB-231 cells) and NAT1 Crispr KO cells (KO#2 and KO#5) with [U-13C]-glucose for 24 h. Tracer incubation polar metabolites from the cells were extracted and analyzed by 2DLC-MS, and metabolite differences were compared between the parental and NAT1 KO cells. Differences consistent between the two KO cells were considered changes due to the loss of NAT1. The data revealed decreases in the 13C enrichment of TCA/Krebs cycle intermediates in NAT1 KO cells compared to the MDA-MB-231 cells. Specifically, 13C-labeled citrate, isocitrate, a-ketoglutarate, fumarate, and malate were all decreased in NAT1 KO cells. We also detected increased 13C-labeled L-lactate levels in the NAT1 KO cells and decreased 13C enrichment in some nucleotides. Pathway analysis showed that arginine biosynthesis, alanine, aspartate and glutamate metabolism, and the TCA cycle were most affected. These data provide additional evidence supporting the impacts of NAT1 knockout on cellular energy metabolism. The data suggest that NAT1 expression is important for the proper functioning of mitochondria and the flux of glucose through the TCA/Krebs cycle in breast cancer cells. The metabolism changes in the fate of glucose in NAT1 KO breast cancer cells offer more insight into the role of NAT1 in energy metabolism and the growth of breast cancer cells. These data provide additional evidence that NAT1 may be a useful therapeutic target for breast cancer.

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.

Association between cigarette smoking and ovarian reserve among women seeking fertility care

INTRODUCTION

This study examined the association of smoking with ovarian reserve in a cross-sectional study of 207 women enrolled in the Louisville Tobacco Smoke Exposure, Genetic Susceptibility, and Infertility (LOUSSI) Study and assessed effect modification by NAT2 acetylator phenotype.

METHODS

Information on current smoking status was collected using a structured questionnaire and confirmed by cotinine assay. Serum anti-Müllerian hormone (AMH) levels were used to assess ovarian reserve. Diminished ovarian reserve (DOR) was defined as AMH <1ng/mL. Single nucleotide polymorphisms in the NAT2 gene, which metabolizes toxins found in cigarette smoke, were analyzed to determine NAT2 acetylator status. Linear and logistic regression were used to determine the effects of smoking on ovarian reserve and evaluate effect modification by NAT2. Regression analyses were stratified by polycystic ovary syndrome (PCOS) status and adjusted for age.

RESULTS

Current smoking status, either passive or active as measured by urinary cotinine assay, was not significantly associated with DOR. For dose-response assessed using self-report, the odds of DOR increased significantly for every additional cigarette currently smoked (Odds ratio, OR:1.08; 95% confidence interval, 95%CI:1.01-1.15); additionally, every 1 pack-year increase in lifetime exposure was associated with an increased odds of DOR among women without PCOS (OR: 1.08 95%CI: 0.99-1.18). These trends appear to be driven by the heavy or long-term smokers. Effect modification by NAT2 genotype was not established.

CONCLUSION

A history of heavy smoking may indicate increased risk of diminished ovarian reserve.

N-acetyltransferase 2 acetylator genotype-dependent N-acetylation and toxicity of the arylamine carcinogen β-naphthylamine in cryopreserved human hepatocytes

We used cryopreserved human hepatocytes that express rapid, intermediate, and slow acetylator N-acetyltransferase 2 (NAT2) genotypes to measure the N-acetylation of β-naphthylamine (BNA) which is one of the aromatic amines found in cigarette smoke including E-cigarettes. We investigated the role of NAT2 genetic polymorphism in genotoxicity and oxidative stress induced by BNA. In vitro BNA NAT2 activities in rapid acetylators was 1.6 and 3.5-fold higher than intermediate (p < 0.01) and slow acetylators (p < 0.0001). BNA N-acetylation in situ was 3 to 4- fold higher in rapid acetylators than slow acetylators, following incubation with 10 and 100 µM BNA (p < 0.01). DNA damage was two to threefold higher in the rapid versus slow acetylators (p < 0.0001) and 2.5-fold higher in intermediate versus slow acetylators following BNA treatment at 100 and 1000 μM, ROS/RNS level was the highest in rapid acetylators followed by intermediate and then slow acetylators (p < 0.0001). Our findings show that the N-acetylation of BNA is NAT2 genotype dependent in cryopreserved human hepatocytes and our data further document an important role for NAT2 genetic polymorphism in modifying BNA-induced genotoxicity and oxidative damage.

Transcriptional Regulation of Human Arylamine N-Acetyltransferase 2 Gene by Glucose and Insulin in Liver Cancer Cell Lines

Arylamine N-acetyltransferase 2 (NAT2) is well-known for its role in phase II metabolism of xenobiotics and drugs. More recently, genome wide association studies and murine models implicated NAT2 in regulation of insulin sensitivity and plasma lipid levels. However, the mechanism remains unknown. Transcript levels of human NAT2 varied dynamically in HepG2 (hepatocellular) cells, depending on the nutrient status of the culture media. Culturing the cells in the presence of glucose induced NAT2 mRNA expression as well as its N-acetyltransferase activity significantly. In addition, insulin or acetate treatment also significantly induced NAT2 mRNA. We examined and compared the glucose- and acetate-dependent changes in NAT2 expression to those of genes involved in glucose and lipid metabolism, including FABP1, CPT1A, ACACA, SCD, CD36, FASN, ACLY, G6PC, and PCK1. Genes that are involved in fatty acid transport and lipogenesis, such as FABP1 and CD36, shared a similar pattern of expression with NAT2. In silico analysis of genes co-expressed with NAT2 revealed an enrichment of biological processes involved in lipid and cholesterol biosynthesis and transport. Among these, A1CF (APOBEC1 complementation factor) showed the highest correlation with NAT2 in terms of its expression in normal human tissues. The current study shows, for the first time, that human NAT2 is transcriptionally regulated by glucose and insulin in liver cancer cell lines and that the gene expression pattern of NAT2 is similar to that of genes involved in lipid metabolism and transport.

Differences in β-naphthylamine metabolism and toxicity in Chinese hamster ovary cell lines transfected with human CYP1A2 and NAT2*4, NAT2*5B or NAT2*7B N-acetyltransferase 2 haplotypes

β-naphthylamine (BNA) is an important aromatic amine carcinogen. Current exposures derive primarily from cigarette smoking including e-cigarettes. Occupational and environmental exposure to BNA is associated with urinary bladder cancer which is the fourth most frequent cancer in the United States. N-acetyltransferase 2 (NAT2) is an important metabolizing enzyme for aromatic amines. Previous studies investigated mutagenicity and genotoxicity of BNA in bacteria and in rabbit or rat hepatocytes. However, the effects of human NAT2 genetic polymorphism on N-acetylation and genotoxicity induced by BNA still need to be clarified. We used nucleotide excision repair-deficient Chinese hamster ovary (CHO) cells that were stably transfected with human CYP1A2 and NAT2 alleles: NAT2*4 (reference allele), NAT2*5B (variant slow acetylator allele common in Europe) or NAT2*7B (variant slow acetylator allele common in Asia). BNA N-acetylation was measured both in vitro and in situ via high-performance liquid chromatography (HPLC). Hypoxanthine phosphoribosyl transferase (HPRT) mutations, double-strand DNA breaks, and reactive oxygen species (ROS) were measured as indices of toxicity. NAT2*4 cells showed significantly higher BNA N-acetylation rates followed by NAT2*7B and NAT2*5B. BNA caused concentration-dependent increases in DNA damage and ROS levels. NAT2*7B showed significantly higher levels of HPRT mutants, DNA damage and ROS than NAT2*5B (p < 0.001, p < 0.0001, p < 0.0001 respectively) although both are slow alleles. Our findings suggest that BNA N-acetylation and toxicity are modified by NAT2 polymorphism. Furthermore, they confirm heterogeneity among slow acetylator alleles for BNA metabolism and toxicity supporting differential risk for individuals carrying NAT2*7B allele.

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.

Dataset for proteomic analysis of arylamine N-acetyltransferase 1 knockout MDA-MB-231 breast cancer cells

Arylamine N-acetyltransferase 1 (NAT1) is frequently upregulated in breast cancer. An unbiased analysis of proteomes of parental MDA-MB-231 breast cancer cells and two separate NAT1 knockout (KO) cell lines were performed. Among 4,890 proteins identified, 737 and 651 proteins were found significantly (p < 0.01) upregulated and downregulated, respectively, in NAT1 KO cells, compared to the parental cells. Each set of proteins was analyzed to identify Gene Ontology biological processes, molecular functions, and cellular components that were enriched in the set. Among the proteins upregulated in NAT1 KO cells, processes associated with MHC major histocompatibility complex I-mediated antigen presentation were significantly enriched. Multiple processes involved in mitochondrial functions were collectively downregulated in NAT1 KO cells, including multiple subunits of mitochondrial ATP synthase (Complex V of the electron transport chain). This was accompanied by a reduction in cell cycle-associated proteins and an increase in pro-apoptotic pathways in NAT1 KO cells. The current dataset contains additional representations of the biological processes and components that are differentially enriched in NAT1 KO MDA-MB-231 cells and will serve as a basis for generating novel hypotheses regarding the role of NAT1 in breast cancer. Data are available via ProteomeXchange with identifier PXD035953.

Hexavalent chromium increases the metabolism and genotoxicity of aromatic amine carcinogens 4-aminobiphenyl and β-naphthylamine in immortalized human lung epithelial cells

Humans are exposed to carcinogenic chemicals via occupational and environmental exposures. Common chemicals of concern that can occur in exposures together are aromatic amines (e.g., 4-aminobiphenyl [4-ABP] and β-naphthylamine [BNA]) and hexavalent chromium (Cr[VI]). Arylamine N-acetyltransferases 1 and 2 (NAT1 and NAT2) are key to the metabolism of aromatic amines and their genotoxicity. The effects of Cr(VI) on the metabolism of aromatic amines remains unknown as well as how it may affect their ensuing toxicity. The objective of the research presented here is to investigate the effects of Cr(VI) on the metabolism and genotoxicity of 4-ABP and BNA in immortalized human lung epithelial cells (BEP2D) expressing NAT1 and NAT2. Exposure to Cr(VI) for 48 h increased NAT1 activity (linear regression analysis: P < 0.0001) as measured by N-acetylation of para-aminobenzoic acid (PABA) in BEP2D cells but not NAT2 N-acetylation of sulfamethazine, which are prototypic NAT1 and NAT2 substrates respectively. Cr(VI) also increased the N-acetylation of 4-ABP and BNA. In BEP2D cells the N-acetylation of 4-ABP (1-3 μM) exhibited a dose-dependent increase (linear regression analysis: P < 0.05) following co-incubation with 0-3 μM Cr(VI). In BEP2D cells, incubation with Cr(VI) caused dose-dependent increases (linear regression analysis: P < 0.01) in expression of CYP1A1 protein and catalytic activity. For genotoxicity, BEP2D cells were exposed to 4-ABP or BNA with/without Cr(VI) for 48 h. We observed dose-dependent increases (linear regression analysis: P < 0.01) in phospho-γH2AX protein expression for combined treatment of 4-ABP or BNA with Cr(VI). Further using a CYP1A1 inhibitor (α-naphthoflavone) and NAT1 siRNA, we found that CYP1A1 inhibition did not reduce the increased N-acetylation or genotoxicity of BNA by Cr(VI), while NAT1 inhibition did reduce increases in BNA N-acetylation and genotoxicity by Cr(VI). We conclude that during co-exposure of aromatic amines and Cr(VI) in human lung cells, Cr(VI) increased NAT1 activity contributing to increased 4-ABP and BNA genotoxicity.

Proteomic analysis of arylamine N-acetyltransferase 1 knockout breast cancer cells: Implications in immune evasion and mitochondrial biogenesis

Previous studies have shown that inhibition or depletion of N-acetyltransferase 1 (NAT1) in breast cancer cell lines leads to growth retardation both in vitro and in vivo, suggesting that NAT1 contributes to rapid growth of breast cancer cells. To understand molecular and cellular processes that NAT1 contributes to and generate novel hypotheses in regard to NAT1's role in breast cancer, we performed an unbiased analysis of proteomes of parental MDA-MB-231 breast cancer cells and two separate NAT1 knockout (KO) cell lines. Among 4890 proteins identified, 737 proteins were found significantly (p < 0.01) upregulated, and 651 proteins were significantly (p < 0.01) downregulated in both NAT1 KO cell lines. We performed enrichment analyses to identify Gene Ontology biological processes, molecular functions, and cellular components that were enriched in each data set. Among the proteins upregulated in NAT1 KO cells, pathways associated with MHC (major histocompatibility complex) I-mediated antigen presentation were significantly enriched. This raises an interesting and new hypothesis that upregulation of NAT1 in breast cancer cells may aid them evade immune detection. Multiple pathways involved in mitochondrial functions were collectively downregulated in NAT1 KO cells, including multiple subunits of mitochondrial ATP synthase (Complex V of the electron transport chain). This was accompanied by a reduction in cell cycle-associated proteins and an increase in pro-apoptotic pathways in NAT1 KO cells, consistent with reported observations that NAT1 KO cells exhibit a slower growth rate both in vitro and in vivo. Thus, mitochondrial dysfunction in NAT1 KO cells likely contributes to growth retardation.

Abstract 4037: The effects of n-acetyltransferase 1 gene knockout on the cytotoxicity of pyrimidine biosynthesis inhibitors in human breast cancer cells

Arylamine N-acetyltransferase 1 (NAT1), a polymorphic drug metabolism enzyme, is often upregulated in breast cancer cells. To develop novel hypotheses on how NAT1 contributes to breast cancer development and progression, NAT1 knockout (KO) cell lines (KO2 and KO5) were created from MDA-MB-231 using CRISPR/Cas9 technology. According to our proteomics and RNA sequencing analyses, NAT1 KO cells have increased cytidine deaminase (CDA), a player in the pyrimidine salvage pathway. Metabolomics data showed NAT1 KO cells had defects in the de novo pyrimidine pathway, which can explain the upregulation of the salvage pathway. Pyrimidine de novo synthesis and salvage pathways are essential for DNA and RNA synthesis and cell growth.We hypothesize that NAT1 plays a key role in maintaining pyrimidine biosynthesis in breast cancer cells, and hence, exhibit increased sensitivity to some of chemotherapeutic drugs that depends on pyrimidine metabolic pathways for their cytotoxicity.

Parental, KO2, and KO5 MDA-MB-231 breast cancer cell lines were treated with several different classes of drugs: CDA inhibitors: Tetrahydrouridine and zebularine; pyrimidine biosynthesis inhibitors teriflunomide and leflunomide; DNA damaging agent doxorubicin; and cytidine analogues 5-hydroxymethyl-2’-deoxycytidine, 5’-formyl-2’-deoxycytidine, and 5’-deoxy-5-fluoropyridine at varying concentrations for 4 days. Cell viability was assessed by Alamarblue assay. Differences between cell lines were assessed for statistical significance by two-way ANOVA.

The results were as follows Tetrahydrouridine: No statistically significant difference in cell viability between parental and NAT1 KOs except at 200 µM p= 0.0002Zebularine: Statistically significant difference between parental and NAT1 KOs at concentrations above 60 µM at p &lt; 0.0001Teriflunomide: Statistically significant difference between parental and NAT1 KOs between 20 and 60 µM at p &lt; 0.0001Leflunomide: No statistically significant difference between parental and NAT1 KOs except at 200 µM at p = 0.00065’- Formyl- 2'- Deoxycytidine: Statistically significant difference between parental and NAT1 KOs above 12 µM at p = 0.0042Doxorubicin: No statistically significant difference between parental and NAT1 KOs 5-Hydroxymethyl-2’-deoxycytidine: No statistically significant difference between parental and NAT15’-Deoxy-5-fluorocytidine: No statistically significant difference between parental and NAT1 KOs

Whereas the results with many of the drugs were inconsistent with our initial hypothesis, it is possible that the NAT1 KO cells are more resistant to CDA or pyrimidine biosynthesis inhibitors because of the upregulation of CDA. Understanding the pharmacogenomic similarities in Tetrahydrouridine, zebularine and teriflunomide’s may help develop a new hypothesis.

Citation Format: Afi Henriette Tagnedji, Kyung U. Hong, David W. Hein. The effects of n-acetyltransferase 1 gene knockout on the cytotoxicity of pyrimidine biosynthesis inhibitors in human breast cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 4037.

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.

Expression of arylamine N-acetyltransferase 2 activity in immortalized human bronchial epithelial cells

Lung cancer is the leading cause of cancer deaths in the United States with high incidence in tobacco smokers. Arylamine N-acetyltransferase 2 (NAT2) is a xenobiotic enzyme that catalyzes both N- and O-acetylation of carcinogens present in tobacco smoke and contributes towards the genotoxicity of these carcinogens. NAT2 allelic variants result in slow, intermediate, and rapid acetylation phenotypes. A recent meta-analysis reported NAT2 non-rapid (slow and intermediate) phenotypes had a significantly increased risk of lung cancer. NAT2 activity in humans is thought to be restricted to liver and gastrointestinal tract, and no studies to our knowledge have reported the expression of NAT2 activity in immortalized human lung epithelial cells. Given the importance of NAT2 in cancer and inhalation of various carcinogens directly into the lungs, we investigated NAT2 activity in human lung epithelial cells. Both NAT1 and NAT2 protein were detected by "in-cell" Western. Arylamine N-acetyltransferase activity was determined with selective substrates for NAT1 (p-aminobenzoic acid; PABA) and NAT2 (sulfamethazine; SMZ) in the presence and absence of a selective NAT1 inhibitor. PABA N-acetylation (NAT1 activity) in cell protein lysates was abolished in the presence of 25 μM of NAT1 inhibitor whereas SMZ N-acetylation (NAT2) was unaffected. Incubation with the NAT1 inhibitor partially reduced the N-acetylation of β-naphthylamine and the O-acetylation of N-hydroxy-4-aminobiphenyl consistent with catalysis by both NAT1 and NAT2. Immortalized human lung epithelial cells exhibited dose-dependent N-acetylation of 4-ABP with an apparent K_M of 24.4 ± 5.1 μM. These data establish that NAT2 is expressed and functional in immortalized human lung epithelial cells and will help us further our understanding of NAT2 in lung cancer.

Human N-Acetyltransferase 1 and 2 Differ in Affinity Towards Acetyl-Coenzyme A Cofactor and N-Hydroxy-Arylamine Carcinogens

Arylamine N-acetyltransferases catalyze the transfer of acetyl groups from the endogenous cofactor acetyl coenzyme A (AcCoA) to arylamine (N-acetylation) and N-hydroxy-arylamine (O-acetylation) acceptors. Humans express two arylamine N-acetyltransferase isozymes (NAT1 and NAT2) which catalyze both N- and O-acetylation but differ in genetic regulation, substrate selectivity, and expression in human tissues. We investigated recombinant human NAT1 and NAT2 expressed in an Escherichia coli JM105 and Schizosaccharomyces pombe expression systems as well as in Chinese hamster ovary (CHO) cells to assess the relative affinity of AcCoA for human NAT1 and NAT2. NAT1 and NAT2 affinity for AcCoA was higher for recombinant human NAT1 than NAT2 when catalyzing N-acetylation of aromatic amine carcinogens 2-aminofluroene (AF), 4-aminobiphenyl (ABP), and β-naphthylamine (BNA) and the metabolic activation of N-hydroxy-2-aminofluorene (N-OH-AF) and N-hydroxy-4-aminobiphenyl (N-OH-ABP) via O-acetylation. These results suggest that AcCoA level may influence differential rates of arylamine carcinogen metabolism catalyzed by NAT1 and NAT2 in human tissues. Affinity was higher for NAT2 than for NAT1 using N-OH-AF and N-OH-ABP as substrate consistent with a larger active site for NAT2. In conclusion, following recombinant expression in bacteria, yeast, and CHO cells, we report significant differences in affinity between human NAT1 and NAT2 for its required co-factor AcCoA, as well as for N-hydroxy-arylamines activated via O-acetylation. The findings provide important information to understand the relative contribution of human NAT1 vs NAT2 towards N-acetylation and O-acetylation reactions in human hepatic and extrahepatic tissues.

Arylamine N-Acetyltransferase 1 Activity is Regulated by the Protein Acetylation Status

Arylamine N-acetyltransferase 1 (NAT1) is a drug metabolizing enzyme that influences cancer cell proliferation and survival, especially in breast cancer. Lysine-acetylation is an important Post-Translational Modification (PTM) in the regulation of diverse cellular processes. Histone deacetylases (HDACs) and Sirtuins (SIRT) may have an important role on the NAT1 acetylation status, affecting its catalytic capacity and having an impact on the downstream functions of this protein. The aim of the present work is to investigate the acetylation status of NAT1 in human breast cancer. Breast cancer cell lines MDA-MB-231 (ER-, PR-, HER2-) and ZR-75-1 (estrogen receptor+, PR+, HER2+) were cultured in the presence of HDAC inhibitors (SAHA, TSA) or Sirtuin inhibitors (AGK2, EX527, Sirtinol). Under these conditions, NAT1 protein and gene expression as well as enzymatic activity were quantified. Acetylation of NAT1 protein was evaluated following an immunoprecipitation protocol and acetyl-Lysine quantification. Sirt1 and Sirt2 knockdown were performed and NAT1 protein and NAT1 mRNA expression and catalytic activity were quantified. The treatment of MDA-MB-231 or ZR-75-1 cells with increasing HDAC inhibitors resulted in 2 to 15-fold upregulation in NAT1 message expression. Finally, the catalytic activity of NAT1 in the presence of HDAC inhibition increased 2-fold. Conversely, the inhibition of Sirtuin activity did not cause significant changes in NAT1 message but produced a significant decrease in NAT1 catalytic activity. NAT1 acetylation was higher in the cells treated with HDAC inhibitors, as well as Sirtuin inhibitors. Finally, silencing of Sirt1 and Sirt2 genes by siRNA transient knockdown of each or both genes resulted in reduction of NAT1 protein expression and catalytic activity. The use of HDAC and Sirtuin inhibitors has been demonstrated as a promising powerful therapeutic alternative in various cancers. These inhibitors can significantly attenuate tumor burden by limiting tumor growth and metastasis. These compounds can also induce DNA damage, cell cycle arrest, apoptosis, and autophagy to promote cancer cell death. Several studies have shown that NAT1 is upregulated in cancer cells. The results of the present study show that the acetylation status of NAT1 is an important factor that might have a relevant role in the progression of cancer.

Deletion of arylamine N-acetyltransferase 1 in MDA-MB-231 human breast cancer cells reduces primary and secondary tumor growth in vivo with no significant effects on metastasis

Arylamine N-acetyltransferase 1 (NAT1) is frequently upregulated in breast cancer. Previous studies showed that inhibition or depletion of NAT1 in breast cancer cells diminishes anchorage-independent growth in culture, suggesting that NAT1 contributes to breast cancer growth and metastasis. To further investigate the contribution of NAT1 to growth and cell invasive/migratory behavior, we subjected parental and NAT1 knockout (KO) breast cancer cell lines (MDA-MB-231, MCF-7, and ZR-75-1) to multiple assays. The rate of cell growth in suspension was not consistently decreased in NAT1 KO cells across the cell lines tested. Similarly, cell migration and invasion assays failed to produce reproducible differences between the parental and NAT1 KO cells. To overcome the limitations of in vitro assays, we tested parental and NAT1 KO cells in vivo in a xenograft model by injecting cells into the flank of immunocompromised mice. NAT1 KO MDA-MB-231 cells produced primary tumors smaller than those formed by parental cells, which was contributed by an increased rate of apoptosis in KO cells. The frequency of lung metastasis, however, was not altered in NAT1 KO cells. When the primary tumors of the parental and NAT1 KO cells were allowed to grow to a pre-determined size or delivered directly via tail vein, the number and size of metastatic foci in the lung did not differ between the parental and NAT1 KO cells. In conclusion, NAT1 contributes to primary and secondary tumor growth in vivo in MDA-MB-231 breast cancer cells but does not appear to affect its metastatic potential.

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.

Human Arylamine N-Acetyltransferase 1 (NAT1) Knockout in MDA-MB-231 Breast Cancer Cell Lines Leads to Transcription of NAT2

Many cancers, including breast cancer, have shown differential expression of human arylamine N-acetyltransferase 1 (NAT1). The exact effect this differential expression has on disease risk and progression remains unclear. While NAT1 is classically defined as a xenobiotic metabolizing enzyme, other functions and roles in endogenous metabolism have recently been described providing additional impetus for investigating the effects of varying levels of NAT1 on global gene expression. Our objective is to further evaluate the role of NAT1 in breast cancer by determining the effect of NAT1 overexpression, knockdown, and knockout on global gene expression in MDA-MB-231 cell lines. RNA-seq was utilized to interrogate differential gene expression (genes correlated with NAT1 activity) across three biological replicates of previously constructed and characterized MDA-MB-231 breast cancer cell lines expressing parental (Scrambled), increased (Up), decreased (Down, CRISPR 2–12), or knockout (CRISPR 2–19, CRISPR 5–50) levels of NAT1. 3,889 genes were significantly associated with the NAT1 N-acetylation activity of the cell lines (adjusted p ≤ 0.05); of those 3,889 genes, 1,756 were positively associated with NAT1 N-acetylation activity and 2,133 were negatively associated with NAT1 N-acetylation activity. An enrichment of genes involved in cell adhesion was observed. Additionally, human arylamine N-acetyltransferase 2 (NAT2) transcripts were observed in the complete NAT1 knockout cell lines (CRISPR 2–19 and CRISPR 5–50). This study provides further evidence that NAT1 functions as more than just a drug metabolizing enzyme given the observation that differences in NAT1 activity have significant impacts on global gene expression. Additionally, our data suggests the knockout of NAT1 results in transcription of its isozyme NAT2.

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 acetylation polymorphisms: paradigm for pharmacogenomic-guided therapy- a focused review

INTRODUCTION

The N-acetylation polymorphism has been the subject of comprehensive reviews describing the role of arylamine N-acetyltransferase 2 (NAT2) in the metabolism of numerous aromatic amine and hydrazine drugs.

AREAS COVERED

We describe and review data that more clearly defines the effects of NAT2 haplotypes and genotypes on the expression of acetylator phenotype towards selected drugs within human hepatocytes in vitro, within human hepatocyte cultures in situ, and clinical measures such as bioavailability, plasma metabolic ratios of parent to N-acetyl metabolite, elimination rate constants and plasma half-life, and/or clearance determinations in human subjects. We review several drugs (isoniazid, hydralazine, sulfamethazine, amifampridine, procainamide, sulfasalazine, amonafide and metamizole) for which NAT2 phenotype-guided therapy may be important. The value of pharmacogenomics-guided isoniazid therapy for the prevention and treatment of tuberculosis is presented as a paradigm for NAT2 phenotype-dependent dosing strategies.

EXPERT OPINION

Studies in human subjects and cryopreserved human hepatocytes show evidence for rapid, intermediate and slow acetylator phenotypes, with further data suggesting genetic heterogeneity within the slow acetylator phenotype. Incorporation of more robust NAT2 genotype/phenotypes relationships, including genetic heterogeneity within the slow acetylator phenotype, should lead to further advancements in both health outcomes and cost benefit for prevention and treatment of tuberculosis.

Acetylator Genotype-Dependent Dyslipidemia in Rats Congenic for N-Acetyltransferase 2

Recent reports suggest that arylamine N-acetyltransferases (NAT1 and/or NAT2) serve important roles in regulation of energy utility and insulin sensitivity. We investigated the interaction between diet (control vs. high-fat diet) and acetylator phenotype (rapid vs. slow) using previously established congenic rat lines (in F344 background) that exhibit rapid or slow Nat2 (orthologous to human NAT1) acetylator genotypes. Male and female rats of each genotype were fed control or high-fat (Western-style) diet for 26 weeks. We then examined diet- and acetylator genotype-dependent changes in body and liver weights, systemic glucose tolerance, insulin sensitivity, and plasma lipid profile. Male and female rats on the high fat diet weighed approximately 10% more than rats on the control diet and the percentage liver to body weight was consistently higher in rapid than slow acetylator rats. Rapid acetylator rats were more prone to develop dyslipidemia overall (i.e., higher triglyceride; higher LDL; and lower HDL), compared to slow acetylator rats. Total cholesterol (TC)-to-HDL ratios were significantly higher and HDL-to-LDL ratios were significantly lower in rapid acetylator rats. Our data suggest that rats with rapid systemic Nat2 (NAT1 in humans) genotype exhibited higher dyslipidemia conferring risk for metabolic syndrome and cardiovascular dysfunction.

CRISPR/Cas9 knockout of human arylamine N-acetyltransferase 1 in MDA-MB-231 breast cancer cells suggests a role in cellular metabolism

Human arylamine N-acetyltransferase 1 (NAT1), present in all tissues, is classically described as a phase-II xenobiotic metabolizing enzyme but can also catalyze the hydrolysis of acetyl-Coenzyme A (acetyl-CoA) in the absence of an arylamine substrate using folate as a cofactor. NAT1 activity varies inter-individually and has been shown to be overexpressed in estrogen receptor-positive (ER+) breast cancers. NAT1 has also been implicated in breast cancer progression however the exact role of NAT1 remains unknown. The objective of this study was to evaluate the effect of varying levels of NAT1 N-acetylation activity in MDA-MB-231 breast cancer cells on global cellular metabolism and to probe for unknown endogenous NAT1 substrates. Global, untargeted metabolomics was conducted via ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) on MDA-MB-231 breast cancer cell lines constructed with siRNA and CRISPR/Cas9 technologies to vary only in NAT1 N-acetylation activity. Many metabolites were differentially abundant in NAT1-modified cell lines compared to the Scrambled parental cell line. N-acetylasparagine and N-acetylputrescine abundances were strongly positively correlated (r = 0.986 and r = 0.944, respectively) with NAT1 N-acetylation activity whereas saccharopine abundance was strongly inversely correlated (r = −0.876). Two of the most striking observations were a reduction in de novo pyrimidine biosynthesis and defective β-oxidation of fatty acids in the absence of NAT1. We have shown that NAT1 expression differentially affects cellular metabolism dependent on the level of expression. Our results support the hypothesis that NAT1 is not just a xenobiotic metabolizing enzyme and may have a role in endogenous cellular metabolism.

Role of Human N-Acetyltransferase 2 Genetic Polymorphism on Aromatic Amine Carcinogen-Induced DNA Damage and Mutagenicity in a Chinese Hamster Ovary Cell Mutation Assay

Carcinogenic aromatic amines such as 4-aminobiphenyl (ABP) and 2-aminofluorene (AF) require metabolic activation to form electrophilic intermediates that mutate DNA leading to carcinogenesis. Bioactivation of these carcinogens includes N-hydroxylation catalyzed by CYP1A2 followed by O-acetylation catalyzed by arylamine N-acetyltransferase 2 (NAT2). To better understand the role of NAT2 genetic polymorphism in ABP- and AF-induced mutagenesis and DNA damage, nucleotide excision repair-deficient (UV5) Chinese hamster ovary (CHO) cells were stably transfected with human CYP1A2 and either NAT2*4 (rapid acetylator) or NAT2*5B (slow acetylator) alleles. ABP and AF both caused significantly (P < 0.001) greater mutagenesis measured at the hypoxanthine phosphoribosyl transferase (hprt) locus in the UV5/CYP1A2/NAT2*4 acetylator cell line compared to the UV5, UV5/CYP1A2, and UV5/CYP1A2/NAT2*5B cell lines. ABP- and AF-induced hprt mutant cDNAs were sequenced and over 80% of the single-base substitutions were at G:C base pairs. DNA damage also was quantified by γH2AX in-cell western assays and by identification and quantification of the two predominant DNA adducts, N-(deoxyguanosin-8-yl)-4-aminobiphenyl (dG-C8-ABP) and N-(deoxyguanosin-8-yl)-2-aminofluorene (dG-C8-AF) by liquid chromatography-mass spectrometry. DNA damage and adduct levels were dose-dependent, correlated highly with levels of hprt mutants, and were significantly (P < 0.0001) greater in the UV5/CYP1A2/NAT2*4 rapid acetylator cell line following treatment with ABP or AF as compared to all other cell lines. Our findings provide further clarity on the importance of O-acetylation in CHO mutagenesis assays for aromatic amines. They provide evidence that NAT2 genetic polymorphism modifies aromatic amine-induced DNA damage and mutagenesis that should be considered in human risk assessments following aromatic amine exposures. Environ. Mol. Mutagen. 61:235-245, 2020. © 2019 Wiley Periodicals, Inc.

Knockout of human arylamine N-acetyltransferase 1 (NAT1) in MDA-MB-231 breast cancer cells leads to increased reserve capacity, maximum mitochondrial capacity, and glycolytic reserve capacity

Human arylamine N-acetyltransferase 1 (NAT1) is a phase II xenobiotic metabolizing enzyme found in almost all tissues. NAT1 can also hydrolyze acetyl-coenzyme A (acetyl-CoA) in the absence of an arylamine substrate. Expression of NAT1 varies between individuals and is elevated in several cancers including estrogen receptor positive (ER+) breast cancers. To date, however, the exact mechanism by which NAT1 expression affects mitochondrial bioenergetics in breast cancer cells has not been described. To further evaluate the role of NAT1 in energy metabolism MDA-MB-231 breast cancer cells with parental, increased, and knockout levels of NAT1 activity were compared for bioenergetics profile. Basal oxygen consumption rate (OCR) and extracellular acidification rate (ECAR) were measured followed by programmed sequential injection of Oligomycin (ATP synthase inhibitor), FCCP (ETC uncoupler), Antimycin A (Complex III inhibitor), and Rotenone (Complex I inhibitor) to evaluate mitochondrial bioenergetics. Compared to the cell lines with parental NAT1 activity, NAT1 knockout MDA-MB-231 cell lines exhibited significant differences in bioenergetics profile, while those with increased NAT1 did not. Significant increases in reserve capacity, maximum mitochondrial capacity, and glycolytic reserve capacity were observed in NAT1 knockout MDA-MB-231 cell lines compared to those with parental and increased NAT1 activity. These data indicate that NAT1 knockout in MDA-MB-231 breast cancer cells may enhance adaptation to stress by increasing plasticity in response to energy demand.

Retrospective analysis of estrogen receptor 1 and N‑acetyltransferase gene expression in normal breast tissue, primary breast tumors, and established breast cancer cell lines

The expression levels of estrogen receptor 1 (ESR1), arylamine N‑acetyltransferase 1 (NAT1), and arylamine N‑acetyltransferase 2 (NAT2) are implicated in breast cancer; however, their co-expression profiles in normal breast tissue, primary breast tumors and established breast cancer cell lines are undefined. NAT1 expression is widely reported to be associated with ESR1 expression and is frequently investigated in breast cancer etiology. Furthermore, the NAT2 phenotype has been reported to modify breast cancer risk in molecular epidemiological association studies. Understanding the relationships between the expression levels of these genes is essential to understand their role in breast cancer etiology and treatment. In the present study, NAT1, NAT2 and ESR1 expression data were accessed from repositories of RNA‑Seq data covering 57 breast cancer cell lines, 1,043 primary breast tumors and 99 normal breast tissues. The relationships between gene expression, and between NAT1 activity and RNA expression in breast cancer cell lines were evaluated using non-parametric statistical analyses. Differences in gene expression in each dataset, as well as gene expression differences in normal breast tissue compared to primary breast tumors, and stratification by estrogen receptor status were determined. NAT1 and NAT2 mRNA expression were detected in normal and primary breast tumor tissues; NAT1 expression was much higher than NAT2. NAT1 and ESR1 expression were strongly associated, whereas NAT2 and ESR1 expression were not. Although NAT1 and NAT2 expression were associated, the magnitude was moderate. NAT1, NAT2, and ESR1 expression were increased in primary breast tumor tissue compared with normal breast tissue; however, the magnitude and significance of the differences were lower for NAT2. Analysis of NAT1, NAT2, and ESR1 expression in normal and primary breast tissues and breast cancer cell lines suggested that NAT1 and NAT2 expression are regulated by distinctive mechanisms, whereas NAT1 and ESR1 expression may have overlapping regulation. Defining these relationships is important for future investigations into breast cancer prevention.

Genetic and small molecule inhibition of arylamine N-acetyltransferase 1 reduces anchorage-independent growth in human breast cancer cell line MDA-MB-231

Arylamine N-acetyltransferase 1 (NAT1) expression is reported to affect proliferation, invasiveness, and growth of cancer cells. MDA-MB-231 breast cancer cells were engineered such that NAT1 expression was elevated or suppressed, or treated with a small molecule inhibitor of NAT1. The MDA-MB-231 human breast cancer cell lines were engineered with a scrambled shRNA, a NAT1 specific shRNA or a NAT1 overexpression cassette stably integrated into a single flippase recognition target (FRT) site facilitating incorporation of these different genetic elements into the same genomic location. NAT1-specific shRNA reduced NAT1 activity in vitro by 39%, increased endogenous acetyl coenzyme A levels by 35%, and reduced anchorage-independent growth (sevenfold) without significant effects on cell morphology, growth rates, anchorage-dependent colony formation, or invasiveness compared to the scrambled shRNA cell line. Despite 12-fold overexpression of NAT1 activity in the NAT1 overexpression cassette transfected MDA-MB-231 cell line, doubling time, anchorage-dependent cell growth, anchorage-independent cell growth, and relative invasiveness were not changed significantly when compared to the scrambled shRNA cell line. A small molecule (5E)-[5-(4-hydroxy-3,5-diiodobenzylidene)-2-thioxo-1,3-thiazolidin-4-one (5-HDST) was 25-fold more selective towards the inhibition of recombinant human NAT1 than N-acetyltransferase 2. Incubation of MDA-MB-231 cell line with 5-HDST resulted in 60% reduction in NAT1 activity and significant decreases in cell growth, anchorage-dependent growth, and anchorage-independent growth. In summary, inhibition of NAT1 activity by either shRNA or 5-HDST reduced anchorage-independent growth in the MDA-MB-231 human breast cancer cell line. These findings suggest that human NAT1 could serve as a target for the prevention and/or treatment of breast cancer.

Design and Success of a 21st Century Cancer Education Program at the University of Louisville

Cancer incidence, morbidity, and mortality in the Commonwealth of Kentucky are among the highest in the nation. The University of Louisville was the recipient of a National Cancer Institute (NCI)-funded cancer education program grant in 1975 under the leadership of Dr. Norbert Burzynski. A new and totally redesigned performance-based University of Louisville Cancer Education Program was funded by NCI in 2011 to recruit and motivate outstanding undergraduate and health professional students to pursue further training and careers in cancer research. Here, we describe the strategy, design, methods, implementation, and accomplishments of our twenty-first century performance-based cancer education program. Our program will meet or exceed all of its 5-year performance goals, including the total number students (n = 156) and under-represented minorities (n = 53) who successfully completed the program under the mentorship of cancer research-intensive faculty members of the James Graham Brown Cancer Center (JGBCC). The mentored research program is complemented with professional development and enhancement activities, including cancer research seminars presented by faculty members actively engaged in research centered on the diagnosis, treatment or prevention of cancer, creation of individual career development plans, exploration of cancer research careers, and acquisition of professionalism skills. Student interests towards cancer research significantly increased after completion of the program compared to baseline (P = 0.02). Based on quantitative and qualitative analysis of various components of the curricula, the trainees favor practical, engaging, and interactive activities aligned within professional career goals and objectives. For instance, the trainees prefer two 30-min small group discussions on "Navigating Careers in Cancer Research" with faculty, professional students, and program alumni. Future updates to the program include new activities that capitalize on the cross-disciplinary background of our mentors and trainees as well as a team-based approach to professional development. Our cancer education program will continue to enhance the professional development of the next generation of cancer scientists and clinicians.

High N-Acetyltransferase 1 Expression Is Associated with Estrogen Receptor Expression in Breast Tumors, but Is not Under Direct Regulation by Estradiol, 5α-androstane-3β,17β-Diol, or Dihydrotestosterone in Breast Cancer Cells

N-acetyltransferase 1 (NAT1) is an enzyme that metabolizes carcinogens, which suggests a potential role in breast carcinogenesis. High NAT1 expression in breast tumors is associated with estrogen receptor α (ERα+) and the luminal subtype. We report that NAT1 mRNA transcript, protein, and enzyme activity were higher in human breast tumors with high expression of ERα/ESR1 compared with normal breast tissue. There was a strong correlation between NATb promoter and NAT1 protein expression/enzyme activity. High NAT1 expression in tumors was not the result of adipocytes, as evidenced by low perilipin (PLIN) expression. ESR1, NAT1, and XBP1 expression were associated in tumor biopsies. Direct regulation of NAT1 transcription by estradiol (E₂) was investigated in ERα (+) MCF-7 and T47D breast cancer cells. E₂ did not increase NAT1 transcript expression but increased progesterone receptor expression in a dose-dependent manner. Likewise, NAT1 transcript levels were not increased by dihydrotestosterone (DHT) or 5α-androstane-3β, (3β-adiol) 17β-diol. Dithiothreitol increased levels of the activated, spliced XBP1 in ERα (+) MCF-7 and T47D breast cancer cells but did not affect NAT1 or ESR1 expression. We conclude that NAT1 expression is not directly regulated by E₂, DHT, 3β-adiol, or dithiothreitol despite high NAT1 and ESR1 expression in luminal A breast cancer cells, suggesting that ESR1, XBP1, and NAT1 expression may share a common transcriptional network arising from the luminal epithelium associated with better survival in breast cancer. Clusters of high-expression genes, including NAT1, in breast tumors might serve as potential targets for novel therapeutic drug development.

Role of N-acetyltransferase 2 acetylation polymorphism in 4, 4'-methylene bis (2-chloroaniline) biotransformation

Arylamine N-acetyltransferase 1 (NAT1) and 2 (NAT2) catalyze the acetylation of arylamine carcinogens. Single nucleotide polymorphisms in the NAT2 coding exon present in NAT2 haplotypes encode allozymes with reduced N-acetyltransferase activity towards the N-acetylation of arylamine carcinogens and the O-acetylation of their N-hydroxylated metabolites. NAT2 acetylator phenotype modifies urinary bladder cancer risk following exposures to arylamine carcinogens such as 4-aminobiphenyl. 4, 4'-methylene bis (2-chloroaniline) (MOCA) is a Group 1 carcinogen for which a role of the NAT2 acetylation polymorphism on cancer risk is unknown. We investigated the role of NAT2 and the genetic acetylation polymorphism on both MOCA N-acetylation and N-hydroxy-MOCA O-acetylation. MOCA N-acetylation exhibited a robust gene dose response in rabbit liver cytosol and in cryopreserved human hepatocytes derived from individuals of rapid, intermediate and slow acetylator NAT2 genotype. MOCA exhibited about 4-fold higher affinity for recombinant human NAT2 than NAT1. Recombinant human NAT2*4 (reference) and 15 variant recombinant human NAT2 allozymes catalyzed both the N-acetylation of MOCA and the O-acetylation of N-hydroxy-MOCA. Human NAT2 5, NAT2 6, NAT2 7 and NAT2 14 allozymes catalyzed MOCA N-acetylation and N-hydroxy-O-acetylation at rates much lower than the reference NAT2 4 allozyme. In conclusion, our results show that NAT2 acetylator genotype has an important role in MOCA metabolism and suggest that risk assessments related to MOCA exposures consider accounting for NAT2 acetylator phenotype in the analysis.

N-Acetyltransferase 2 Genotype-Dependent N-Acetylation of Hydralazine in Human Hepatocytes

Hydralazine is used in the treatment of essential hypertension and is under investigation for epigenetic therapy in the treatment of neoplastic and renal diseases. N-acetyltransferase (NAT) 2 exhibits a common genetic polymorphism in human populations. After recombinant expression in yeast, human NAT2 exhibited an apparent Lineweaver-Burk constant (K-_m) value (20.1 ± 8.8 μM) for hydralazine over 20-fold lower than the apparent K-_m value (456 ± 57 μM) for recombinant human NAT1 (P = 0.0016). The apparent V_max value for recombinant human NAT1 (72.2 ± 17.9 nmol acetylated/min/mg protein) was significantly (P = 0.0245) lower than recombinant human NAT2 (153 ± 15 nmol acetylated/min/mg protein), reflecting 50-fold higher clearance for recombinant human NAT2. Hydralazine NAT activities exhibited a robust acetylator gene dose response in cryopreserved human hepatocytes both in vitro and in situ. Hydralazine NAT activities in vitro differed significantly with respect to NAT2 genotype at 1000 (P = 0.0319), 100 (P = 0.002), and 10 μM hydralazine (P = 0.0029). Hydralazine NAT activities differed significantly (P < 0.001) among slow acetylator hepatocytes, (NAT2*5B/*5B > NAT2*5B/*6A > NAT2*6A/*6A). The in situ hydralazine N-acetylation rates differed significantly with respect to NAT2 genotype after incubation with 10 (P = 0.002) or 100 µM (P = 0.0015) hydralazine and were higher after incubation with 100 μM (10-fold) than with 10 μM (4.5-fold) hydralazine. Our results clearly document NAT2 genotype-dependent N-acetylation of hydralazine in human hepatocytes, suggesting that hydralazine efficacy and safety could be improved by NAT2 genotype-dependent dosing strategies.

Arylamine N-acetyltransferase 2 genotype-dependent N-acetylation of isoniazid in cryopreserved human hepatocytes

Cryopreserved human hepatocytes were used to investigate the role of arylamine N-acetyltransferase 2 (NAT2; EC 2.3.1.5) polymorphism on the N-acetylation of isoniazid (INH). NAT2 genotype was determined by Taqman allelic discrimination assay and INH N-acetylation was measured by high performance liquid chromatography. INH N-acetylation rates in vitro exhibited a robust and highly significant (P<0.005) NAT2 phenotype-dependent metabolism. N-acetylation rates in situ were INH concentration- and time-dependent. Following incubation for 24 h with 12.5 or 100 µmol/L INH, acetyl-INH concentrations varied significantly (P = 0.0023 and P = 0.0002) across cryopreserved human hepatocytes samples from rapid, intermediate, and slow acetylators, respectively. The clear association between NAT2 genotype and phenotype supports use of NAT2 genotype to guide INH dosing strategies in the treatment and prevention of tuberculosis.

Rabbit N-acetyltransferase 2 genotyping method to investigate role of acetylation polymorphism on N- and O-acetylation of aromatic and heterocyclic amine carcinogens

The rabbit was the initial animal model to investigate the acetylation polymorphism expressed in humans. Use of the rabbit model is compromised by lack of a rapid non-invasive method for determining acetylator phenotype. Slow acetylator phenotype in the rabbit results from deletion of the N-acetyltransferase 2 (NAT2) gene. A relatively quick and non-invasive method for identifying the gene deletion was developed and acetylator phenotypes confirmed by measurement of N- and O-acetyltransferase activities in hepatic cytosols. Rabbit liver cytosols catalyzed the N-acetylation of sulfamethazine (p = 0.0014), benzidine (p = 0.0257), 4-aminobiphenyl (p = 0.0012), and the O-acetylation of N-hydroxy-2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (N-OH-PhIP; p = 0.002) at rates significantly higher in rabbits possessing NAT2 gene than rabbits with NAT2 gene deleted. In contrast, hepatic cytosols catalyzed the N-acetylation of p-aminobenzoic acid (an N-acetyltransferase 1 selective substrate) at rates that did not differ significantly (p > 0.05) between rabbits positive and negative for NAT2. The new NAT2 genotyping method facilitates use of the rabbit model to investigate the role of acetylator polymorphism in the metabolism of aromatic and heterocyclic amine drugs and carcinogens.

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.

Daily Rhythm in Plasma N-acetyltryptamine

Normal physiology undergoes 24-h changes in function that include daily rhythms in circulating hormones, most notably melatonin and cortical steroids. This study focused on N-acetyltryptamine, a little-studied melatonin receptor mixed agonist-antagonist and the likely evolutionary precursor of melatonin. The central issue addressed was whether N-acetyltryptamine is physiologically present in the circulation. N-acetyltryptamine was detected by LC-MS/MS in daytime plasma of 3 different mammals in subnanomolar levels (mean ± SEM: rat, 0.29 ± 0.05 nM, n = 5; rhesus macaque, 0.54 ± 0.24 nM, n = 4; human, 0.03 ± 0.01 nM, n = 32). Analysis of 24-h blood collections from rhesus macaques revealed a nocturnal increase in plasma N-acetyltryptamine (p < 0.001), which varied from 2- to 15-fold over daytime levels among the 4 animals studied. Related RNA sequencing studies indicated that the transcript encoding the tryptamine acetylating enzyme arylalkylamine N-acetyltransferase (AANAT) is expressed at similar levels in the rhesus pineal gland and retina, thereby indicating that either tissue could contribute to circulating N-acetyltryptamine. The evidence that N-acetyltryptamine is a physiological component of mammalian blood and exhibits a daily rhythm, together with known effects as a melatonin receptor mixed agonist-antagonist, shifts the status of N-acetyltryptamine from pharmacological tool to candidate for a physiological role. This provides a new opportunity to extend our understanding of 24-h biology.

Role of the N-acetylation polymorphism in solithromycin metabolism

AIM

Solithromycin is a new macrolide antibiotic for the potential treatment of bacterial pneumonia.

MATERIALS & METHODS

Solithromycin N-acetylation by human NAT1 and NAT2 was investigated following recombinant expression in yeast and in cryopreserved human hepatocytes from rapid, intermediate and slow acetylators.

RESULTS

Solithromycin exhibited over twofold higher affinity for recombinant human NAT2 than NAT1. Apparent maximum velocities for the N-acetylation of solithromycin catalyzed by the NAT2 allozyme associated with rapid acetylators were significantly (p < 0.01) higher than by the NAT2 allozymes associated with slow acetylators. Robust gene dose responses (rapid>intermediate>slow acetylators) were exhibited in cryopreserved human hepatocytes in situ following incubation with 100 μM solithromycin.

CONCLUSION

Solithromycin is N-acetylated by human NAT1 and NAT2 and the role of the NAT2 acetylation polymorphism on solithromycin metabolism may be concentration dependent.

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.

Untargeted polar metabolomics of transformed MDA-MB-231 breast cancer cells expressing varying levels of human arylamine N-acetyltransferase 1

INTRODUCTION

Human arylamine N-acetyltransferase 1 (NAT1) is a phase II xenobiotic metabolizing enzyme found in almost all tissues. Expression of NAT1 is elevated in several cancers including breast cancer. However, the exact mechanism by which NAT1 expression affects cancer risk and progression remains unclear.

OBJECTIVE

This study explored polar metabolome differences between MDA-MB-231 breast cancer cells expressing varying levels of NAT1 activity using an untargeted approach.

METHODS

Three MDA-MB-231 breast adenocarcinoma cell lines that stably express wild-type, increased, and decreased levels of human NAT1 were investigated for differences in polar metabolic profile using a comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry (GC×GC-TOF MS) system.

RESULTS

Increased levels of human NAT1 in the transformed cell lines resulted in a statistically significant decreased abundance of the metabolite palmitoleic acid (q = 0.0006), when compared to normal and decreased levels of human NAT1. The fatty acid synthesis pathway utilizes acetyl coenzyme A (acetyl-CoA) in the first two reactions of the pathway and eventually leads to the synthesis of palmitoleic acid.

CONCLUSION

These data suggest a link between increased levels of NAT1 activity and decreased flux of acetyl-CoA through this portion of the fatty acid synthesis pathway.

Evaluation of Oxidative Stress Response Related Genetic Variants, Pro-oxidants, Antioxidants and Prostate Cancer

Background

Oxidative stress and detoxification mechanisms have been commonly studied in Prostate Cancer (PCa) due to their function in the detoxification of potentially damaging reactive oxygen species (ROS) and carcinogens. However, findings have been either inconsistent or inconclusive. These mixed findings may, in part, relate to failure to consider interactions among oxidative stress response related genetic variants along with pro- and antioxidant factors.

Methods

We examined the effects of 33 genetic and 26 environmental oxidative stress and defense factors on PCa risk and disease aggressiveness among 2,286 men from the Cancer Genetic Markers of Susceptibility project (1,175 cases, 1,111 controls). Single and joint effects were analyzed using a comprehensive statistical approach involving logistic regression, multi-dimensionality reduction, and entropy graphs.

Results

Inheritance of one CYP2C8 rs7909236 T or two SOD2 rs2758331 A alleles was linked to a 1.3- and 1.4-fold increase in risk of developing PCa, respectively (p-value = 0.006–0.013). Carriers of CYP1B1 rs1800440GG, CYP2C8 rs1058932TC and, NAT2 (rs1208GG, rs1390358CC, rs7832071TT) genotypes were associated with a 1.3 to 2.2-fold increase in aggressive PCa [p-value = 0.04–0.001, FDR 0.088–0.939]. We observed a 23% reduction in aggressive disease linked to inheritance of one or more NAT2 rs4646247 A alleles (p = 0.04, FDR = 0.405). Only three NAT2 sequence variants remained significant after adjusting for multiple hypotheses testing, namely NAT2 rs1208, rs1390358, and rs7832071. Lastly, there were no significant gene-environment or gene-gene interactions associated with PCa outcomes.

Conclusions

Variations in genes involved in oxidative stress and defense pathways may modify PCa. Our findings do not firmly support the role of oxidative stress genetic variants combined with lifestyle/environmental factors as modifiers of PCa and disease progression. However, additional multi-center studies poised to pool genetic and environmental data are needed to make strong conclusions.