Metabolic activation of aromatic and heterocyclic N-hydroxyarylamines by wild-type and mutant recombinant human NAT1 and NAT2 acetyltransferases

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.

Nuclear DNA and Mitochondrial Damage of the Cooked Meat Carcinogen 2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine in Human Neuroblastoma Cells

Animal fat and iron-rich diets are risk factors for Parkinson's disease (PD). The heterocyclic aromatic amines (HAAs) harman and norharman are neurotoxicants formed in many foods and beverages, including cooked meats, suggesting a role for red meat in PD. The structurally related carcinogenic HAAs 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), 2-amino-3,8-dimethylmidazo[4,5-f]quinoxaline (MeIQx), and 2-amino-9H-pyrido[2,3-b]indole (AαC) also form in cooked meats. We investigated the cytotoxicity, DNA-damaging potential, and mitochondrial damage of HAAs and their genotoxic HONH-HAA metabolites in galactose-dependent SH-SY5Y cells, a human neuroblastoma cell line relevant for PD-related neurotoxicity. All HAAs and HONH-HAAs induced weak toxicity except HONH-PhIP, which was 1000-fold more potent than the other chemicals. HONH-PhIP DNA adduct formation occurred at 300-fold higher levels than adducts formed with HONH-MeIQx and HONH-AαC, assuming similar cellular uptake rates. PhIP-DNA adduct levels occurred at concentrations as low as 1 nM and were threefold or higher and more persistent in mitochondrial DNA than nuclear DNA. N-Acetyltransferases (NATs), sulfotransferases, and kinases catalyzed PhIP-DNA binding and converted HONH-PhIP to highly reactive ester intermediates. DNA binding assays with cytosolic, mitochondrial, and nuclear fractions of SH-SY5Y fortified with cofactors revealed that cytosolic AcCoA-dependent enzymes, including NAT1, mainly carried out HONH-PhIP bioactivation to form N-acetoxy-PhIP, which binds to DNA. Furthermore, HONH-PHIP and N-acetoxy-PhIP inhibited mitochondrial complex-I, -II, and -III activities in isolated SH-SY5Y mitochondria. Mitochondrial respiratory chain complex dysfunction and DNA damage are major mechanisms in PD pathogenesis. Our data support the possible role of PhIP in PD etiology.

Colon Transcriptomics Reveals Sex-Dependent Metabolic Signatures in Response to 2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine Treatment in C57BL/6N Mice

Diets high in red meats, particularly meats cooked at high temperature, increase the risk of colon cancer due to a production of heterocyclic aromatic amines (HAAs). Of the identified HAAs, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) is the most mass abundant colon carcinogen in charred meat or fish. Here, we comprehensively examined sex-dependent colon transcriptome signatures in response to PhIP treatment to identify biological discrepancies. Eight-week-old male and female C57BL/6N mice were intraperitoneally injected with PhIP (10 mg/kg of body weight) and colon tissues were harvested 24 h after PhIP injection, followed by colon transcriptomics analysis. A list of differentially expressed genes (DEGs) was utilized for computational bioinformatic analyses. Specifically, overrepresentation test using the Protein Analysis Through Evolutionary Relationships tool was carried out to annotate sex-dependent changes in transcriptome signatures after PhIP treatment. Additionally, the most significantly affected canonical pathways by PhIP treatment were predicted using the Ingenuity Pathway Analysis. As results, male and female mice presented different metabolic signatures in the colon transcriptome. In the male mice, oxidative phosphorylation in the mitochondrial respiratory chain was the pathway impacted the most; this might be due to a shortage of ATP for DNA repair. On the other hand, the female mice showed concurrent activation of lipolysis and adipogenesis. The present study provides the foundational information for future studies of PhIP effects on underlying sex-dependent mechanisms.

Gut microbial beta-glucuronidase and glycerol/diol dehydratase activity contribute to dietary heterocyclic amine biotransformation

BACKGROUND

Consuming red and processed meat has been associated with an increased risk of colorectal cancer (CRC), which is partly attributed to exposure to carcinogens such as heterocyclic amines (HCA) formed during cooking and preservation processes. The interaction of gut microbes and HCA can result in altered bioactivities and it has been shown previously that human gut microbiota can transform mutagenic HCA to a glycerol conjugate with reduced mutagenic potential. However, the major form of HCA in the colon are glucuronides (HCA-G) and it is not known whether these metabolites, via stepwise microbial hydrolysis and acrolein conjugation, are viable precursors for glycerol conjugated metabolites. We hypothesized that such a process could be concurrently catalyzed by bacterial beta-glucuronidase (B-GUS) and glycerol/diol dehydratase (GDH) activity. We therefore investigated how the HCA-G PhIP-N2-β-D-glucuronide (PhIP-G), a representative liver metabolite of PhIP (2-Amino-1-methyl-6-phenylimidazo [4,5-b] pyridine), which is the most abundant carcinogenic HCA in well-cooked meat, is transformed by enzymatic activity of human gut microbial representatives of the phyla Firmicutes, Bacteroidetes, and Proteobacteria.

RESULTS

We employed a combination of growth and enzymatic assays, and a bioanalysis approach combined with metagenomics. B-GUS of Faecalibacterium prausnitzii converted PhIP-G to PhIP and GDH of Flavonifractor plautii, Blautia obeum, Eubacterium hallii, and Lactobacillus reuteri converted PhIP to PhIP-M1 in the presence of glycerol. In addition, B-GUS- and GDH-positive bacteria cooperatively converted PhIP-G to PhIP-M1. A screen of genes encoding B-GUS and GDH was performed for fecal microbiome data from healthy individuals (n = 103) and from CRC patients (n = 53), which revealed a decrease in abundance of taxa with confirmed GDH and HCA transformation activity in CRC patients.

CONCLUSIONS

This study for the first time demonstrates that gut microbes mediate the stepwise transformation of PhIP-G to PhIP-M1 via the intermediate production of PhIP. Findings from this study suggest that targeted manipulation with gut microbes bearing specific functions, or dietary glycerol supplementation might modify gut microbial activity to reduce HCA-induced CRC risk.

Metabolic Activation of the Cooked Meat Carcinogen 2-Amino-1-Methyl-6-Phenylimidazo[4,5-b]Pyridine in Human Prostate

2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), an heterocyclic aromatic amine (HAA) formed in cooked meat, is a rodent and possible human prostate carcinogen. Recently, we identified DNA adducts of PhIP in the genome of prostate cancer patients, but adducts of 2-amino-3, 8-dimethylmidazo[4,5-f]quinoxaline (MeIQx) and 2-amino-9 H-pyrido[2,3-b]indole (AαC), other prominent HAAs formed in cooked meats, were not detected. We have investigated the bioactivation of HAAs by Phase I and II enzymes in the human prostate (LNCaP) cell line using cytotoxicity and DNA adducts as endpoints. PhIP, MeIQx, and 2-amino-3-methylimidazo[4,5-f]quinoline, another HAA found in cooked meats, were poorly bioactivated and not toxic. The synthetic genotoxic N-hydroxylated-HAAs were also assayed in LNCaP cells with Phase II enzyme inhibitors. Notably, 2-hydroxy-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (HONH-PhIP), but not other HONH-HAAs, induced cytotoxicity. Moreover, PhIP-DNA adduct formation was 20-fold greater than adducts formed with other HONH-HAAs. Pretreatment of LNCaP cells with mefenamic acid, a specific inhibitor of sulfotransferase (SULT1A1), decreased PhIP-DNA adducts by 25%, whereas (Z)-5-(2'-hydroxybenzylidene)-2-thioxothiazolidin-4-one and pentachlorophenol, inhibitors of SULTs and N-acetyltransferases (NATs), decreased the PhIP-DNA adduct levels by 75%. NATs in cytosolic fractions of LNCaP cells and human prostate catalyzed DNA binding of HONH-PhIP by up to 100-fold greater levels than for SULT and kinase activities. Recombinant NAT2 is catalytically superior to recombinant NAT1 in the bioactivation of HONH-PhIP; however, the extremely low levels of NAT2 activity in prostate suggest that NAT1 may be the major isoform involved in PhIP-DNA damage. Thus, the high susceptibility of LNCaP cells recapitulates the DNA-damaging effect of HONH-PhIP in rodent and human prostate.

Gut Microbial Transformation of the Dietary Imidazoquinoxaline Mutagen MelQx Reduces Its Cytotoxic and Mutagenic Potency

The diverse community of microbes present in the human gut has emerged as an important factor for cancer risk, potentially by altering exposure to chemical carcinogens. In the present study, human gut bacteria were tested for their capacity to transform the carcinogenic heterocyclic amine 2-Amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MelQx). Eubacterium hallii, Lactobacillus reuteri, and Lactobacillus rossiae were able to convert MelQx to a new microbial metabolite characterized on the basis of high-resolution mass spectrometry and NMR as 9-hydroxyl-2,7-dimethyl-7,9,10,11-tetrahydropyrimido[2′,1′:2,3]imidazo[4,5-f]quinoxaline (MelQx-M1), resulting from conjugation with activated glycerol. Acrolein derived from the decomposition of 3-hydroxypropionaldehyde, which is the product of bacterial glycerol/diol dehydratase activity, was identified as the active compound responsible for the formation of MelQx-M1. A complex human gut microbial community obtained from invitro continuous intestinal fermentation was found to also transform MelQx to MelQx-M1. MelQx-M1 had slightly reduced cytotoxic potency toward human colon epithelial cells invitro, and diminished mutagenic potential toward bacteria after metabolic activation. As bacterially derived acrolein also transformed 2 other HCAs, namely 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine and 2-amino-3-methylimidazo[4,5-f]quinoline, these results generalize the capacity of gut microbiota to detoxify HCAs in the gut, potentially modulating cancer risk.

Catalytic properties and heat stabilities of novel recombinant human N-acetyltransferase 2 allozymes support existence of genetic heterogeneity within the slow acetylator phenotype

Human N-acetyltransferase 2 (NAT2) catalyzes the N-acetylation of numerous aromatic amine drugs such as sulfamethazine (SMZ) and hydrazine drugs such as isoniazid (INH). NAT2 also catalyzes the N-acetylation of aromatic amine carcinogens such as 2-aminofluorene and the O- and N,O-acetylation of aromatic amine and heterocyclic amine metabolites. Genetic polymorphism in NAT2 modifies drug efficacy and toxicity as well as cancer risk. Acetyltransferase catalytic activities and heat stability associated with six novel NAT2 haplotypes (NAT2*6C, NAT2*14C, NAT2*14D, NAT2*14E, NAT2*17, and NAT2*18) were compared with that of the reference NAT2*4 haplotype following recombinant expression in Escherichia coli. N-acetyltransferase activities towards SMZ and INH were significantly (p < 0.0001) lower when catalyzed by the novel recombinant human NAT2 allozymes compared to NAT2 4. SMZ and INH N-acetyltransferase activities catalyzed by NAT2 14C and NAT2 14D were significantly lower (p < 0.001) than catalyzed by NAT2 6C and NAT2 14E. N-Acetylation catalyzed by recombinant human NAT2 17 was over several hundred-fold lower than by recombinant NAT2 4 precluding measurement of its kinetic or heat inactivation constants. Similar results were observed for the O-acetylation of N-hydroxy-2-aminofluorene and N-hydroxy-2-amino-1-methyl-6-phenylimidazo [4,5-b] pyridine and the intramolecular N,O-acetylation of N-hydroxy-N-acetyl-2-aminofluorene. The apparent V _max of the novel recombinant NAT2 allozymes NAT2 6C, NAT2 14C, NAT2 14D, and NAT2 14E towards AF, 4-aminobiphenyl (ABP), and 3,2'-dimethyl-4-aminobiphenyl (DMABP) were each significantly (p < 0.001) lower while their apparent K _m values did not differ significantly (p > 0.05) from recombinant NAT2 4. The apparent V _max catalyzed by NAT2 14C and NAT2 14D were significantly lower (p < 0.05) than the apparent V _max catalyzed by NAT2 6C and NAT2 14E towards AF, ABP, and DMABP. Heat inactivation rate constants for recombinant human NAT2 14C, 14D, 14E, and 18 were significantly (p < 0.05) higher than NAT2 4. These results provide further evidence of genetic heterogeneity within the NAT2 slow acetylator phenotype.

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.

2-amino-1-methyl-6-phenylimidazo(4,5-b) pyridine (PhIP) induces gene expression changes in JAK/STAT and MAPK pathways related to inflammation, diabetes and cancer

Background

2-amino-1-methyl-6-phenylimidazo(4,5-b)pyridine (PhIP), a heterocyclic aromatic amine (HCA) formed in meat that is cooked at high temperatures and then ingested, can potentially be retained in human adipose tissues.

Methods

To determine if PhIP is bioactive in the adipocyte, we exposed a human adipocyte cell line,HepG2 and Caco-2 cells to low dose PhIP. Uptake and retention of PhIP was determined and cytotoxicity was assessed by the TUNEL assay. Relative expression of PhIP-activating genes (CYP1A1, CYP1A2, SULT1A1 and UGT1A1) was determined by RT-PCR and global expression changes were also examined.

Results

The percent retention of 0.1 μCi [¹⁴C]-PhIP over a 24 h period was significantly higher in the adipocyte than the HepG2 (p = 0.0001) and Caco-2 (p = 0.0007) cell lines. Cytotoxicity rates were 14.4 and 2.6 % higher compared to controls in Caco-2 and HepG2 cells (p < 0.001 and 0.054, respectively); no significant differences were detected in adipocyte cells (p = 0.18). Caco-2 and HepG2 cells, respectively, had significantly higher basal expression of CYP1A1 (p = 0.001, p = 0.003), SULT1A1 (p = 0.04, p < 0.001) and UGT1A1 (p < 0.001, p = 0.01) compared to the adipocyte. Exposure to 5nM PhIP did not significantly induce expression of these genes in any of the cell lines. Global gene expression analysis of mature adipocytes exposed to 5nM PhIP for 72 h resulted in statistically significant changes in 8 genes (ANGPTL2, CD14, CIDEA, EGR1, FOS, IGFBP5, PALM and PSAT1). Gene-gene interaction and pathway analysis indicates that PhIP modulates genes controlled by the STAT3 transcriptional factor and initiates leptin signaling via the JAK/STAT and MAPK pathway cascades. Early growth response 1 (EGR1) and prostaglandin synthase 2 (COX-2) were down-regulated via c-Fos, while insulin binding protein 5 (IBP5) was up regulated. Expression of transcription factors (ANGPTL2, HP, LEP, SAA1, SAA2), genes related to inflammation (SAA1, LEP), diabetes (IGFBP5) and cancer risk (SAA2) were also elevated upon exposure to 5 nM PhIP..

Conclusions

PhIP mediates gene expression changes within the adipocyte, and the pathways most affected are related to cancer and other chronic diseases. Further studies are needed on the relationship between dietary carcinogens such as PhIP with cancer, obesity and diabetes.

Electronic supplementary material

The online version of this article (doi:10.1186/s12986-016-0111-0) contains supplementary material, which is available to authorized users.

Phenethyl isothiocyanate and indole-3-carbinol from cruciferous vegetables, but not furanocoumarins from apiaceous vegetables, reduced PhIP-induced DNA adducts in Wistar rats

SCOPE

We previously showed that apiaceous but not cruciferous vegetables reduced DNA adducts formed by 2-amino-1-methyl-6-phenylimidazo[4, 5-b]pyridine (PhIP) in rats. Here, we report the effects of the putative chemopreventive phytochemicals from these vegetables on PhIP metabolism and DNA adduct formation.

METHODS AND RESULTS

Rats received three supplemented diets: P + I (phenethyl isothiocyanate and indole-3-carbinol), furanocoumarins (FC, 5-methoxypsoralen, 8-methoxypsoralen, and isopimpinellin), and combination (P + I and FC). Phytochemical supplementation matched the levels in vegetables fed in our previous study. After 6 days, rats were injected with PhIP (10 mg/kg body wt) and killed after 24-h urine collection. Compared to the control, P + I increased activity of hepatic cytochrome P450 (CYP) 1A1 (10.1-fold), CYP1A2 (3.62-fold), and sulfotransferase 1A1 (2.70-fold). The combination diet also increased CYP1A1 and CYP1A2 activity. Urinary metabolomics revealed that PhIP metabolite profiles generally agreed with biotransformation enzyme activities. P + I and combination diets reduced PhIP-DNA adducts by 43.5 and 24.1%, respectively, whereas FC had no effect on adducts, compared to the control diet.

CONCLUSION

Effects of phytochemicals on metabolic outcomes and markers of carcinogenesis might differ from fresh vegetables, thus limiting the inferences that one can draw from the effects of purified phytochemicals on the health benefits of the vegetables from which they derive.

Gene-diet interactions in exposure to heterocyclic aromatic amines and bulky DNA adduct levels in blood leukocytes

Heterocyclic aromatic amines (HAAs), carcinogens produced in meat when cooked at high temperatures, are an emerging biologic explanation for the meat-colorectal cancer relationship. HAAs form DNA adducts; left unrepaired, adducts can induce mutations, which may initiate/promote carcinogenesis. The purpose of this research was to investigate the relationship between dietary HAAs, genetic susceptibility and bulky DNA adduct levels. Least squares regression was used to examine the relationship between dietary HAA exposure and bulky DNA adduct levels in blood measured using (32)P-postlabeling among 99 healthy volunteers. Gene-diet interactions between dietary HAAs and genetic factors relevant to the biotransformation of HAAs and DNA repair were also examined. No main effects of dietary HAAs on bulky DNA adduct levels was found. However, those with the putative NAT1 rapid acetylator phenotype had lower adduct levels than those with the slow acetylator phenotype (P = 0.02). Furthermore, having five or more 'at-risk' genotypes was associated with higher bulky DNA adduct levels (P = 0.03). Gene-diet interactions were observed between NAT1 polymorphisms and dietary HAAs (P < 0.05); among the slow acetylator phenotype, higher intakes of HAAs were associated with an increase in DNA adduct levels compared to lower intakes. This study provides evidence of a biologic relationship between dietary HAAs, genetic susceptibility and bulky DNA adduct formation. However, the lack of a strong main effect of HAAs suggests that dietary HAAs are not a large contributor to bulky DNA adducts in this population; future studies should consider relevant gene-diet interactions to clarify the role of HAAs in carcinogenesis.

N-Acetyltransferase 2 (NAT2) polymorphism as a risk modifier of susceptibility to pediatric acute lymphoblastic leukemia

N-Acetyltransferases (NAT) have been known to modify the risk to a variety of solid tumors. However, the role of NAT2 polymorphism in risk susceptibility to childhood acute lymphoblastic leukemia (ALL) is still not well known. We performed a case-control study to determine if the common NAT2 polymorphisms play a role in altering susceptibility to pediatric ALL. DNA of 92 pediatric ALL patients and 312 healthy controls was analyzed for the NAT2 polymorphisms using the PCR-RFLP method. The wild-type NAT2*4 was encountered in 8.6 % of patients versus 11.8 % of controls (P = 0.23). The rapid acetylators NAT2*12 803A>G, AG, GG, and AG/GG were overrepresented in controls (P = 0.0001; odds ratio (OR) 0.22, 0.19, and 0.21 respectively). NAT2*5D 341T>C and NAT2*11A 481C>T were of comparable frequencies. For their combination, NAT2*5A, a slow acetylator, both TCTT and CCCT were overrepresented in patients (P < 0.001; OR 15.8 and 17.9 respectively). NAT2*5B (803A>G, 341T>C, 481C>T) was overrepresented in controls (P < 0.001; OR 0.12). Apparently, 803A>G ameliorated the combined effect of 341T>C and 481C>T. A similar effect was obtained with NAT2*5C (341T>A, 803A>G) (P < 0.0001; OR 0.11). For slow acetylator NAT2*7A 857G>A, GA and GA/AA were overrepresented in patients (P = 0.009 and 0.01; OR 2.74 and 2.72 respectively). NAT2*13 282C>T, NAT2*6B 590G>A, and NAT2*14A 191G>A were of comparable frequencies. NAT2 282C>A in combination with NAT2 857G>A (NAT2*7B) showed a synergistic effect in patients versus controls (P < 0.0001; OR 3.51). In conclusion, NAT2 gene polymorphism(s) with slow acetylator phenotype is generally associated with the risk of development of ALL in children.

Apiaceous vegetable consumption decreases PhIP-induced DNA adducts and increases methylated PhIP metabolites in the urine metabolome in rats

BACKGROUND

Heterocyclic aromatic amines, such as 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), are carcinogenic compounds produced during heating of protein-containing foods. Apiaceous vegetables inhibit PhIP-activating enzymes, whereas cruciferous vegetables induce both PhIP-activating and -detoxifying enzymes.

OBJECTIVE

We investigated the effects of these vegetables, either alone or combined, on PhIP metabolism and colonic DNA adduct formation in rats.

METHODS

Male Wistar rats were fed cruciferous vegetables (21%, wt:wt), apiaceous vegetables (21%, wt:wt), or a combination of both vegetables (10.5% wt:wt of each). Negative and positive control groups were fed an AIN-93G diet. After 6 d, all groups received an intraperitoneal injection of PhIP (10 mg · kg body weight(-1)) except for the negative control group, which received only vehicle. Urine was collected for 24 h after the injection for LC-tandem mass spectrometry metabolomic analyses. On day 7, rats were killed and tissues processed.

RESULTS

Compared with the positive control, cruciferous vegetables increased the activity of hepatic PhIP-activating enzymes [39.5% and 45.1% for cytochrome P450 (CYP) 1A1 (P = 0.0006) and CYP1A2 (P < 0.0001), respectively] and of uridine 5'-diphospho-glucuronosyltransferase 1A (PhIP-detoxifying) by 24.5% (P = 0.0267). Apiaceous vegetables did not inhibit PhIP-activating enzymes, yet reduced colonic PhIP-DNA adducts by 20.4% (P = 0.0496). Metabolomic analyses indicated that apiaceous vegetables increased the relative abundance of urinary methylated PhIP metabolites. The sum of these methylated metabolites inversely correlated with colonic PhIP-DNA adducts (r = -0.43, P = 0.01). We detected a novel methylated urinary PhIP metabolite and demonstrated that methylated metabolites are produced in the human liver S9 fraction.

CONCLUSIONS

Apiaceous vegetables did not inhibit the activity of PhIP-activating enzymes in rats, suggesting that the reduction in PhIP-DNA adducts may involve other pathways. Further investigation of the importance of PhIP methylation in carcinogen metabolism is warranted, given the inverse correlation of methylated PhIP metabolites with a biomarker of carcinogenesis and the detection of a novel methylated PhIP metabolite.

Polymorphisms in the human cytochrome P450 and arylamine N-acetyltransferase: susceptibility to head and neck cancers

The occurrence of head and neck cancer (HNC) is associated with smoking and alcohol drinking. Tobacco smoking exposes smokers to a series of carcinogenic chemicals. Cytochrome P450 enzymes (CYP450s), such as CYP1A1, CYP1B1, and CYP2D6, usually metabolize carcinogens to their inactive derivatives, but they occasionally convert the chemicals to more potent carcinogens. In addition, via CYP450 (CYP2E1) oxidase, alcohol is metabolized to acetaldehyde, a highly toxic compound, which plays an important role in carcinogenesis. Furthermore, two N-acetyltransferase isozymes (NATs), NAT1 and NAT2, are polymorphic and catalyze both N-acetylation and O-acetylation of aromatic and heterocyclic amine carcinogens. Genetic polymorphisms are associated with a number of enzymes involved in the metabolism of carcinogens important in the induction of HNC. It has been suggested that such polymorphisms may be linked to cancer susceptibility. In this paper, we select four cytochrome P450 enzymes (CYP1A1, CYP1BA1, CYP2D6, and CYP2E1), and two N-acetyltransferase isozymes (NAT1 and NAT2) in order to summarize and analyze findings from the literature related to HNC risk by focusing on (i) the interaction between these genes and the environment, (ii) the impact of genetic defect on protein activity and/or expression, and (iii) the eventual involvement of race in such associations.

Arylarnine N-acetyltransferase as a potential biornarker in bladder cancer: fluorescent in situ hybridization and irnmunohistochernistry studies

Abstract Arylamine N-acetyltransferase isoenzymes NAT1 and NAT2 are encoded at two polymorphic loci on human chromosome 8p22. The two loci have previously been identified using chimeric Yeast Artificial Chromosome (YAC) clones encoding either NAT1 or NAT2 as probes for metaphase chromosomes using fluorescent in situ hybridization. The 8p22 region has been demonstrated to be deleted in highly invasive bladder tumours and since NAT isoenzymes participate in the metabolism of arylamine bladder carcinogens, it is important to determine whether NAT1 and NAT2 gene loci are included in the region of deletion. We describe here the application of a cosmid clone for NAT2 as a biomarker for Fluorescent In Situ Hybridization (FISH) on interphase nuclei of exfoliated bladder cells. We also describe a 70kb probe for NAT1 which is a candidate for a suitable biomarker for use in similar FISH studies. lmmunohistochemical staining of bladder tumour sections with a polyclonal anti-peptide antibody specific for the NATl isoenzyme as a biomarker for NAT1 protein expression is also shown.

Differential response of flat and polypoid colitis-associated colorectal neoplasias to chemopreventive agents and heterocyclic amines

Individuals with ulcerative colitis face an increased risk of developing colorectal cancer and would benefit from early chemopreventive intervention. Results from preclinical studies in the mouse model of dextran sulfate sodium-induced colitis demonstrate that flat and polypoid colitis-associated dysplasias arise via distinct genetic pathways, impacted by the allelic status of p53. Furthermore, flat and polypoid dysplasias vary in their response to induction by the heterocyclic amine 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) and inhibition by 5-aminosalicylic acid, a common therapy for the maintenance of colitis patients. These data suggest that use of combination therapy is essential for the optimal inhibition of colitis-associated colorectal cancer.

Variable NAT1 enzyme activity in long-term cultured human HaCaT keratinocytes

Since animal testing should be avoided whenever possible, the development of in vitro tests for predicting the effect of chemicals becomes a major field. This rise of in vitro test systems led to an increased requirement for well-characterized continuously growing cell lines. Monitoring of the cells during test and routine culture is necessary to gain relevant and reproducible results. In the present study, the influence of passaging under constant culture conditions on the human keratinocyte cell line HaCaT was investigated. Data demonstrated that growth rate rose with increasing passages. Doubling times of the cells were decreased to 24 ± 0.6 h in the late passages (12-16), in comparison to 36.2 ± 1.5 h in the early passages (2-8). These data were confirmed by a fall in mRNA expression levels of keratin 1 and transglutaminase 1 within the passages. Furthermore, the activities of the xenobiotic metabolizing phase II enzyme N-acetyltransferase 1 (NAT1) were higher in the late passages compared to the early passages. These results are contrary to an expected decrease in enzyme activity and proliferation rate induced by replicative senescence or cell aging. Data also indicate that routine culture might result in significant changes in proliferation and phase II metabolism. These findings reinforce the necessity of a strict characterization and knowledge of regulation of in vitro systems, as well as the need for new biomarkers, in order to use cells for the development and evaluation of reproducible in vitro test systems.

Metabolism and biomarkers of heterocyclic aromatic amines in molecular epidemiology studies: lessons learned from aromatic amines

Aromatic amines and heterocyclic aromatic amines (HAAs) are structurally related classes of carcinogens that are formed during the combustion of tobacco or during the high-temperature cooking of meats. Both classes of procarcinogens undergo metabolic activation by N-hydroxylation of the exocyclic amine group to produce a common proposed intermediate, the arylnitrenium ion, which is the critical metabolite implicated in toxicity and DNA damage. However, the biochemistry and chemical properties of these compounds are distinct, and different biomarkers of aromatic amines and HAAs have been developed for human biomonitoring studies. Hemoglobin adducts have been extensively used as biomarkers to monitor occupational and environmental exposures to a number of aromatic amines; however, HAAs do not form hemoglobin adducts at appreciable levels, and other biomarkers have been sought. A number of epidemiologic studies that have investigated dietary consumption of well-done meat in relation to various tumor sites reported a positive association between cancer risk and well-done meat consumption, although some studies have shown no associations between well-done meat and cancer risk. A major limiting factor in most epidemiological studies is the uncertainty in quantitative estimates of chronic exposure to HAAs, and thus, the association of HAAs formed in cooked meat and cancer risk has been difficult to establish. There is a critical need to establish long-term biomarkers of HAAs that can be implemented in molecular epidemioIogy studies. In this review, we highlight and contrast the biochemistry of several prototypical carcinogenic aromatic amines and HAAs to which humans are chronically exposed. The biochemical properties and the impact of polymorphisms of the major xenobiotic-metabolizing enzymes on the biological effects of these chemicals are examined. Lastly, the analytical approaches that have been successfully employed to biomonitor aromatic amines and HAAs, and emerging biomarkers of HAAs that may be implemented in molecular epidemiology studies are discussed.

NAT2 polymorphism and gastric cancer susceptibility: a meta-analysis

BACKGROUND AND AIMS

N-acetyltransferase 2 (NAT2) is a polymorphic enzyme that plays an important role in the metabolism of various potential carcinogens. NAT2 can be subdivided into rapid and slow acetylation phenotype according to the different genotypes. Studies investigating the association between NAT2 polymorphisms and gastric cancer risk in humans showed conflicting results. The aim of this study was to conduct a meta-analysis assessing the association of NAT2 acetylation phenotype with risk of gastric cancer.

METHODS

Relevant studies were identified through a search of Embase, ISI Web of Knowledge, Medline and Chinese Biomedicine Database until January 2010. A meta-analysis was conducted to quantitatively summarize association of NAT2 acetylation phenotype with GC susceptibility.

RESULTS

Thirteen studies were included in the present meta-analysis, which described a total of 2,391 gastric cancer cases and 3,237 controls. The combined ORs for NAT2 slow or rapid acetylator and gastric cancer risk were 1.05 (95% CI 0.810-1.35) and 0.96 (95% CI 0.74-1.23), respectively. When stratifying for race and Lauren's classification, results also showed no significant association in genotype distribution between gastric cancer and control.

CONCLUSIONS

No association is found between NAT2 acetylation status and gastric cancer risk in this meta-analysis.

Differences between human slow N-acetyltransferase 2 alleles in levels of 4-aminobiphenyl-induced DNA adducts and mutations

Aromatic amines such as 4-aminobiphenyl (ABP) require biotransformation to exert their carcinogenic effects. Genetic polymorphisms in biotransformation enzymes such as N-acetyltransferase 2 (NAT2) may modify cancer risk following exposure. Nucleotide excision repair-deficient Chinese hamster ovary (CHO) cells stably transfected with human cytochrome P4501A1 (CYP1A1) and a single copy of either NAT2*4 (rapid acetylator), NAT2*5B (common Caucasian slow acetylator), or NAT2*7B (common Asian slow acetylator) alleles (haplotypes) were treated with ABP to test the effect of NAT2 polymorphisms on DNA adduct formation and mutagenesis. ABP N-acetyltransferase catalytic activities were detectable only in cell lines transfected with NAT2 and were highest in cells transfected with NAT2*4, lower in cells transfected with NAT2*7B, and lowest in cells transfected with NAT2*5B. Following ABP treatment, N-(deoxyguanosin-8-yl)-4-aminobiphenyl (dG-C8-ABP) was the primary adduct formed. Cells transfected with both CYP1A1 and NAT2*4 showed the highest concentration-dependent cytotoxicity, hypoxanthine phosphoribosyl transferase (hprt) mutants, and dG-C8-ABP adducts. Cells transfected with CYP1A1 and NAT2*7B showed lower levels of cytotoxicity, hprt mutagenesis, and dG-C8-ABP adducts. Cells transfected with CYP1A1 only or cells transfected with both CYP1A1 and NAT2*5B did not induce cytotoxicity, hprt mutagenesis or dG-C8-ABP adducts. ABP-DNA adduct levels correlated very highly (r>0.96) with ABP-induced hprt mutant levels following each treatment. The results of the present study suggest that investigations of NAT2 genotype or phenotype associations with disease or toxicity could be more precise and reproducible if heterogeneity within the "slow" NAT2 acetylator phenotype is considered and incorporated into the study design.

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

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

N-acetyltransferase SNPs: emerging concepts serve as a paradigm for understanding complexities of personalized medicine

Arylamine N-acetyltransferase 1 and 2 exhibit single nucleotide polymorphisms in human populations that modify drug and carcinogen metabolism. This paper updates the identity, location and functional effects of these single nucleotide polymorphisms and then follows with emerging concepts for understanding why pharmacogenetic findings may not be replicated consistently. Using this paradigm as an example, laboratory-based mechanistic analyses can reveal complexities such that genetic polymorphisms become biologically and medically relevant when confounding factors are more fully understood and considered. As medical care moves to a more personalized approach, the implications of these confounding factors will be important in understanding the complexities of personalized medicine.

Arylamine N-acetyltransferases: a new inhibitor of apoptosis in HepG2 cells

OBJECTIVE

To explore how arylamine N-acetyltransferases (NATs) is related to cell apoptosis.

METHODS

NAT activity in apoptotic HepG2 cells was measured using high performance liquid chromatography (HPLC); the apoptosis rate of HepG2 cells acted upon by an NAT inhibitor was measured using flow cytometry.

RESULTS

NAT activity was lowered in apoptotic HepG2 cells; apoptosis rate induced by camptothecin (CAM) increased after inhibition of NAT activity in HepG2 cells.

CONCLUSION

NAT can inhibit apoptosis in HepG2 cells.

N-acetyltransferase 1 in colon and rectal cancer cases from an industrialized area

Colon and rectal cancers are both associated with genetic as well as nutritional, occupational, and environmental factors. Aromatic amines and heterocyclic amines are established colorectal carcinogens. The polymorphic enzyme N-acetyltransferase 1 (NAT1) contributes to heterocyclic amine metabolism in the human colon. Thereby, NAT1 may influence the risk for development of colorectal cancer. The distribution of NAT1 genotypes was determined in 107 colon cancer cases, 77 rectal cancer cases, and 185 controls (suffering from nonmalignant diseases) by standard methods. In addition, possible occupational and nonoccupational risk factors were determined by a personal interview. Cancer cases and controls were derived from an area of former coal, iron, and steel industries, which is known for elevated colon cancer mortality. The proportions of NAT1*4/*4 genotype were 72% in controls, 75% in rectal cancer cases, and 72% in colon cancer cases. The proportions of the NAT1*4/*10 genotype were 17.8% in controls, 12.9% in rectal cancer cases, and 14% in colon cancer cases. Combinations of the determined NAT1 alleles *3/*3, *3/*10, *4/*3, *4/*11, *10/*10 and *11/*11 contributed to 10.2% of the genotypes in controls, 12.1% in rectal cancer cases, and 14% in colon cancer cases. In contrast to another study on healthy German volunteers, the NAT1*4/*4 genotype (wild type) is overrepresented. This might be due to the variation in the proportion of NAT1 alleles in the general population. The present study does not support a relevant impact of the NAT1 genotype on colorectal cancer risk development in the study area.

Divergence of cofactor recognition across evolution: coenzyme A binding in a prokaryotic arylamine N-acetyltransferase

Arylamine N-acetyltransferase (NAT) enzymes are widespread in nature. They serve to acetylate xenobiotics and/or endogenous substrates using acetyl coenzyme A (CoA) as a cofactor. Conservation of the architecture of the NAT enzyme family from mammals to bacteria has been demonstrated by a series of prokaryotic NAT structures, together with the recently reported structure of human NAT1. We report here the cloning, purification, kinetic characterisation and crystallographic structure determination of NAT from Mycobacterium marinum, a close relative of the pathogenic Mycobacterium tuberculosis. We have also determined the structure of M. marinum NAT in complex with CoA, shedding the first light on cofactor recognition in prokaryotic NATs. Surprisingly, the principal CoA recognition site in M. marinum NAT is located some 30 A from the site of CoA recognition in the recently deposited structure of human NAT2 bound to CoA. The structure explains the Ping-Pong Bi-Bi reaction mechanism of NAT enzymes and suggests mechanisms by which the acetylated enzyme intermediate may be protected. Recognition of CoA in a much wider groove in prokaryotic NATs suggests that this subfamily may accommodate larger substrates than is the case for human NATs and may assist in the identification of potential endogenous substrates. It also suggests the cofactor-binding site as a unique subsite to target in drug design directed against NAT in mycobacteria.

Reconstruction of N-acetyltransferase 2 haplotypes using PHASE

The genotyping of N-acetyltransferase 2 (NAT2) by PCR/RFLP methods yields in a considerable percentage ambiguous results. To resolve this methodical problem a statistical approach was applied. PHASE v2.1.1, a statistical program for haplotype reconstruction was used to estimate haplotype pairs from NAT2 genotyping data, obtained by the analysis of seven single nucleotide polymorphisms relevant for Caucasians. In 1,011 out of 2,921 (35%) subjects the haplotype pairs were clearcut by the PCR/RFLP data only. For the majority of the data the applied method resulted in a multiplicity (2-4) of possible haplotype pairs. Haplotype reconstruction using PHASE v2.1.1 cleared this ambiguity in all cases but one, where an alternative haplotype pair was considered with a probability of 0.029. The estimation of the NAT2 haplotype is important because the assignment of the NAT2 alleles *12A, *12B, *12C or *13 to the rapid or slow NAT2 genotype has been discussed controversially. A clear assignment is indispensable in surveys of human bladder cancer caused by aromatic amine exposures. In conclusion, PHASE v2.1.1 software allowed an unambiguous haplotype reconstruction in 2,920 of 2,921 cases (>99.9%).

2-amino-1-methyl-6-phenylimidazo [4,5-b] pyridine-induced DNA adducts and genotoxicity in chinese hamster ovary (CHO) cells expressing human CYP1A2 and rapid or slow acetylator N-acetyltransferase 2

Heterocyclic amine carcinogens such as 2-amino-1-methyl-6-phenylimidazo [4,5-b] pyridine (PhIP) are present in diet and cigarette smoke. Bioactivation in humans includes N-hydroxylation catalyzed by cytochrome P4501A2 possibly followed by O-acetylation catalyzed by N-acetyltransferase 2 (NAT2). Nucleotide excision repair-deficient Chinese hamster ovary (CHO) cells were stably transfected with human CYP1A2 and either NAT2*4 (rapid acetylator) or NAT2*5B (slow acetylator) alleles. CYP1A2 and NAT2 catalytic activities were undetectable in untransfected CHO cell lines. CYP1A2 catalytic activity levels did not differ significantly (P > 0.05) among the CYP1A2-transfected cell lines. Cells transfected with NAT2*4 had significantly higher levels of N-acetyltransferase (P = 0.0001) and N-hydroxy-PhIP O-acetyltransferase (P = 0.0170) catalytic activity than cells transfected with NAT2*5B. PhIP caused dose-dependent decreases in cell survival and significant (P < 0.001) increases in mutagenesis measured at the hypoxanthine phosphoribosyl transferase (hprt) locus in all the CYP1A2-transfected cell lines. Transfection with NAT2*4 or NAT2*5B did not further increase hprt mutagenesis. PhIP-induced hprt mutant cDNAs were sequenced, and 80% of the mutations were single base substitutions at G:C base pairs. dG-C8-PhIP DNA adduct levels were dose-dependent in the order: untransfected < transfected with CYP1A2 < transfected with CYP1A2 and NAT2*5B < transfected with CYP1A2 and NAT2*4. Following incubation with 1.2 microM PhIP, DNA adduct levels were significantly (P < 0.05) higher in CHO cells transfected with CYP1A2/NAT2*4 versus CYP1A2/NAT2*5B. These results strongly support an activation role for CYP1A2 in PhIP-induced mutagenesis and DNA damage and suggest a modest effect of human NAT2 and its genetic polymorphism on PhIP DNA adduct levels.

Enhanced glutathione S-transferase expression in 2-hydroxyamino-1-methyl-6-phenylimidazo[4,5-b]pyridine-resistant IEC-18 cells

In the present study we show that repeated exposure of the rat intestinal epithelial cell line IEC-18 to 2-hydroxyamino-1-methyl-6-phenylimidazo[4,5-b]pyridine (N-OH-PhIP), from a toxicological point of view the most relevant phase-1 metabolite of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP, the main heterocyclic aromatic amine present in processed meat), led to the selection of N-OH-PhIP-resistant IEC-18 cells. This phenomenon was accompanied by a fivefold increase in total glutathione S-transferase (GST) activity, measured with the broad-spectrum substrate 1-chloro-2,4-dinitrobenzene, in the N-OH-PhIP-resistant IEC-18 cells. Furthermore, a Western blotting analysis revealed that the expression of GST subunits A1, A3, A4, M1 and P1 was enhanced in the N-OH-PhIP-resistant IEC-18 cells.

Effects of single nucleotide polymorphisms in human N-acetyltransferase 2 on metabolic activation (O-acetylation) of heterocyclic amine carcinogens

N-Acetyltransferase 2 (NAT2) catalyzes the O-acetylation of N-hydroxy heterocyclic amines such as 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) to DNA binding metabolites that initiate mutagenesis and carcinogenesis. NAT2 acetylator phenotype is associated with increased cancer risk. Single nucleotide polymorphisms (SNPs) have been identified in the NAT2 coding region. Although the effects of these SNPs on N-acetyltransferase activity have been reported, very little is known regarding their effects on O-acetylation activity. To investigate the functional consequences of SNPs in the NAT2 coding region on the O-acetylation of N-hydroxy heterocyclic amines, reference NAT2*4 and NAT2 variant alleles possessing one were cloned and expressed in yeast (Schizosaccaromyces pombe). T111C, C282T, C481T, C759T, and A803G (K268R) SNPs did not significantly (p > 0.05) modify O-acetylation catalysis with N--OH--PhIP or N--OH--MeIQx. C190T (R64W), G191A (R64Q), T341C (I114T), A434C (E145P), G590A (R197Q) and A845C (K282T) significantly (p < 0.01) reduced the O-acetylation of both N--OH--PhIP and N--OH--MeIQx, whereas G857A (G286E) significantly (p < 0.05) decreased catalytic activity towards the O-acetylation of N--OH--MeIQx but not N--OH--PhIP. These results have important implications towards the interpretation of molecular epidemiological studies of NAT2 genotype and cancer risk.

Genetic variation in N-acetyltransferase 1 (NAT1) and 2 (NAT2) and risk of non-Hodgkin lymphoma

Animal studies suggest that lymphomagenesis can be induced by exposure to carcinogenic aromatic and heterocyclic amines found in diet, cigarette smoke and the environment, but human epidemiologic investigations of these exogenous exposures have yielded conflicting results. As part of our evaluation of the role of aromatic and heterocyclic amines, which are metabolized by N-acetyltransferase (NAT) enzymes, in the etiology of non-Hodgkin lymphoma (NHL), we examined NHL risk in relation to genetic variation in NAT1 and NAT2 and exposure to cigarette smoke and dietary heterocyclic amines and mutagens. We genotyped 10 common single nucleotide polymorphisms (SNPs) in NAT1 and NAT2 among 1136 cases and 922 controls from a population-based case-control study in four geographical areas of the USA. Relative risk of NHL for NAT1 and NAT2 genotypes, NAT2 acetylation phenotype, and exposure to cigarette smoke and dietary heterocyclic amines and mutagens was estimated using odds ratios (ORs) and 95% confidence intervals (CIs) derived from unconditional logistic regression models. We observed increased risk of NHL among individuals with the NAT1*10/*10 genotype compared with individuals with other NAT1 genotypes (OR = 1.60, 95% CI = 1.04-2.46, P = 0.03). We also observed increased NHL risk in a dose-dependent model among NAT2 intermediate- and rapid-acetylators compared with slow-acetylators, although only the trend was statistically significant (intermediate: OR = 1.18, 95% CI = 0.97-1.44, P = 0.1; rapid: OR = 1.43, 95% CI = 0.97-2.14, P = 0.07; P for linear trend = 0.03). Compared with non-smokers, NHL risk estimates for current cigarette smoking were increased only among NAT2 intermediate/rapid-acetylators (OR = 2.44, 95% CI = 1.15-5.20, P = 0.02). Our data provide evidence that NAT1 and NAT2 genotypes are associated with NHL risk and support a contributory role for carcinogenic aromatic and/or heterocyclic amines in the multi-factorial etiology of NHL.

N-Acetyltransferase and sulfotransferase activity in human prostate: potential for carcinogen activation

BACKGROUND

N-Acetyltransferases (NATs) and sulfotransferases (SULTs) are key phase II metabolizing enzymes that can be involved both in the detoxification and in the activation of many human promutagens and procarcinogens.

METHODS AND RESULTS

We investigated the expression of NATs and SULTs in human prostate and tested their role in the activation the N-hydroxy (N-OH) metabolite of 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), a dietary carcinogen, to form DNA adducts. Western blotting showed detectable levels of NAT1, SULT1A1 and SULT1A3 with marked inter-individual variation. NAT2 and other SULT enzymes were not detectable. NAT1 was localized by immunohistochemistry to the cytoplasm of epithelial cells. The presence of acetyl Co-enzyme A (acetyl CoA) and 3'-phosphoadenosine-5'-phosphosulfate (PAPS), NAT and SULT cofactors, respectively, significantly increased the level of DNA adducts, detected by P-postlabelling analysis, in calf thymus DNA incubated with N-OH-IQ and prostate cytosolic fractions. The enhancement in the level of DNA adducts in the presence of PAPS correlated with the level of SULT1A1 protein. A single prostate cytosol with the SULT1A1*2/*2 genotype produced less DNA adducts than cytosols with the *1/*2 and *1/*1 genotypes. No significant correlation was observed between NAT1 protein level and the formation of DNA adducts, even in the presence of acetyl CoA.

CONCLUSIONS

In conclusion, we demonstrated that NAT1, SULT1A1 and SULT1A3 are present in human prostate and that both enzyme classes significantly contribute to the activation of N-hydroxylated heterocyclic amines to DNA-damaging species in this tissue. Variation in expression levels, in combination with dietary and/or environmental exposure to carcinogens, could be influential in determining individual susceptibility to prostate cancer.

Effect of NAT1 and NAT2 genetic polymorphisms on colorectal cancer risk associated with exposure to tobacco smoke and meat consumption

N-Acetyltransferases 1 and 2 (NAT1 and NAT2), both being highly polymorphic, are involved in the metabolism of aromatic and heterocyclic aromatic amines present in cigarette smoke and red meat cooked by high-temperature cooking techniques. We investigated the effect of differences in acetylation capacity, determined by NAT1 and NAT2 genotypes, on colorectal cancer risk associated with exposure to tobacco smoke or red meat consumption. In this population-based case-control study in Germany, 505 patients with incident colorectal cancer and 604 age- and sex-matched control individuals with genotyping data and detailed risk factor information were included. Genotyping of NAT1 and NAT2 genetic polymorphisms was done using a fluorescence-based melting curve analysis method. The association between genotypes, environmental exposures, and colorectal cancer risk was estimated using multivariate logistic regression. Colorectal cancer risk associated with active smoking was elevated after accumulation of 30(+) pack-years of smoking [odds ratio (OR), 1.4; 95% confidence interval (95% CI), 0.9-2.2] but not significantly modified by either NAT1 or NAT2 genotype. Exposure to environmental tobacco smoke was associated with an increased risk for colorectal cancer only among NAT2 fast acetylators (OR, 2.6; 95% CI, 1.1-5.9 for exposure in childhood and adulthood). Frequent consumption of red meat significantly increased colorectal cancer risk for the group comprising all NAT2 fast acetylators or carriers of the NAT1*10 allele (OR, 2.6; 95% CI, 1.1-6.1) but not among those with "slow" NAT1 and NAT2 genotypes. Our findings indicate that NAT1 and NAT2 genotypes may contribute jointly to individual susceptibility and that heterocyclic aromatic amines may play an important role in colorectal cancer associated with red meat and possibly also exposure to environmental tobacco smoke.

N-acetyltransferase 2 phenotype may be associated with susceptibility to age-related cataract

Free radicals and oxidative damage play roles in aging and age-related ocular diseases such as cataracts, so defensive mechanisms become important factors for protection. Because N-acetylation is involved in a wide variety of detoxification processes, this study was conducted to examine the relationship between the acetylator phenotypes and genotypes in a group of patients with age-related cataract. Sixty-one cases of age-related cataract and 104 controls were included in this study. Blood was collected in EDTA-containing tubes, and genomic DNA was extracted from the white blood cells by high pure PCR template preparation kit. Genotyping of NAT2 polymorphisms were detected by using a LightCycler-NAT2 mutation detection kit in real-time PCR. There was a significant difference in the distribution of the NAT2*6A acetylator phenotype between cases and the controls. The odds ratio of cataract for the NAT2*6A slow phenotype was 3.8 (95% CI = 1.08 to 13.11, p = 0.032) compared with the fast type. Our results suggest that slow acetylators are at higher risk of developing age-related cataracts than fast acetylators. As NAT2 is an important xenobiotic-metabolizing enzyme and theoretically xenobiotics such as ultraviolet B radiation, smoking, and alcohol use may induce cataract formation, NAT2 gene polymorphisms may be associated with genetic susceptibility of cataract.

N-acetyltransferase 2 gene polymorphism in patients with colorectal carcinoma

The acetylation polymorphism is a common inherited variation in human drug and carcinogen metabolism. Because N- acetyltransferase (NAT2) is important for the detoxification and/or bioactivation of drugs and carcinogens, polymorphisms of this gene have important implications in therapeutics of and susceptibility to cancer. In this study, NAT2 genotype (NAT2*5A (C(481)T), NAT2*6A (G(590)A), NAT2*7A/B (G(857)A)) and NAT2*14A (G(191)A) and phenotype were determined in 125 patients with colorectal carcinoma and 82 healthy control in Mersin, a city located in the southern region of Turkey. Isolation of the subjects' DNA was performed by using a highly purified PCR template preparation kit/(Roche Diagnostics cat. no: 1 796 828) and the NAT2 polymorphism was detected using real-time PCR (Roche Diagnostics, GmbH, Mannheim, Germany). According to this study high protein intake is associated with the increased risk for the development of colon cancer (OR = 1.73; 95% CI, 1.10-3.07). Although only NAT2*14A fast type was associated with increased risk in patients with colorectal carcinoma (OR = 3.03; 95% CI, 1.56-5.86), when a high protein diet was considered, NAT2*7A/B fast genotype was also found to be associated with an increased risk (OR = 2.06, 95% CI for NAT2*7A/B, 1.10-3.86; OR = 2.65; 95% CI, 1.29-5.46 for NAT2*14A). Smoking status did not differ between the control and patient groups. Our data suggest that exposure to carcinogens through consumption of a high-protein diet may increase the risk of colorectal carcinoma only in genetically-susceptible individuals.

Inhibitory effects of polyphenolic compounds on human arylamine N-acetyltransferase 1 and 2

Arylamine N-acetyltransferases (NAT) are important enzymes involved in the metabolic activation of aromatic and heterocyclic amines and inhibitors of NAT enzymes may be valuable as chemopreventive agents. Phytochemicals including cinnamic acid derivatives, various classes of flavonoids and coumarins were tested for the inhibitory activity on NAT1 and NAT2 from human liver and the human cholangiocarcinoma cell line: KMBC cells. Assays were performed using p-aminobenzoic acid and sulfamethazine as selective substrates for NAT1 and NAT2, respectively. NAT1 and NAT2 activities were present in liver cytosol. However, the KMBC cells showed only NAT1 activity. There was a marked difference in the ability of the test chemicals to inhibit NAT1 and NAT2. Caffeic acid, ferulic acid, gallic acid and EGCG inhibited NAT1 but not NAT2, whereas scopuletin and curcumin inhibited NAT2 but not NAT1. Quercetin, kaemferol and other flavonoids, except epicatechin and silymarin, inhibited both enzymes. The kinetics of inhibition of NAT1 by caffeic acid, EGCG and quercetin were of the non-competitive type, whereas that of NAT2 by quercetin, curcumin and kaemferol was also of the non-competitive type. The most potent inhibitor was quercetin, which has the inhibitory constants for NAT1 and NAT2 of 48.6 +/- 17.3 and 10.0 +/- 1.8 microM, respectively.

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

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

Acetylation genotype and the genetic susceptibility to prostate cancer in a southern European population

BACKGROUND

Epidemiologic studies have suggested that environmental factors and diet are important risk factors in the pathogenesis of prostate cancer. The N-acetyltransferases (NAT) are important enzymes in activation and inactivation of various carcinogens, including those found in well-cooked meat and cigarette smoke.

METHODS

We analyzed DNA samples from 146 prostate cancer patients and 174 healthy men. We used PCR-RFLP method to analyze NAT 1 and NAT 2 polymorphisms.

RESULTS

We did not find statistically significant differences in NAT 1 genotypes frequencies between prostate cancer patients and control group. We observed an association of the slow acetylator genotype, NAT 2*6/NAT2*6 with prostate cancer protection (P=0.017; OR=0.31, 95% CI 0.11--0.84). Multivariate logistic regression analysis confirmed this association (0.030; OR=0.32, 95% CI 0.12--0.89).

CONCLUSIONS

Our results indicate a role of NAT2 polymorphisms in the carcinogenic pathway of prostate cancer, specifically in a population of Southern Europe.

Aplastic Anemia in a Professional Musician Exposed to Instrument Polish

Chemicals are known to cause toxin-induced aplastic anemia. However, some chemicals documented in only a few cases to possess only a possibility of toxic potential may also be responsible for the development of aplastic anemia. This report presents a case of a string musician with bone marrow failure. The patient used a certain type of polish (komalak) to shine his musical instrument and did this frequently. He presented with nasal bleeding, and a workup on admission revealed pancytopenia. Aplastic anemia was diagnosed on the basis of bone marrow histology results. An analysis for gene polymorphism related to the metabolic detoxification enzymes glutathione S-transferase and N-acetyltransferase 2 indicated that the patient was genetically susceptible to developing toxicity. This case suggests that frequent use of this polish may cause a toxic effect that leads to bone marrow failure. Musicians should be made aware of the risks associated with these types of chemicals.

The T341C (Ile114Thr) polymorphism of N-acetyltransferase 2 yields slow acetylator phenotype by enhanced protein degradation

OBJECTIVES

Human N-acetyltransferase 2 (NAT2) plays a significant role in the clearance and biotransformation of many drugs and carcinogens. A TC (Ile114Thr) single nucleotide polymorphism (SNP) of NAT2 is commonly found in slow acetylators, leading to altered drug response and toxicity and possibly cancer susceptibility from carcinogens. The objective of this study was to investigate the mechanism by which this SNP causes slow acetylator phenotype.

METHODS

A cDNA expression system was used to compare the NAT2*4 reference allele with an identical one possessing the TC SNP in COS-1 cells. The recombinant human NAT2 enzymes were compared in regard to catalytic activity, kinetic parameters, thermostability, immunoreactive protein level, mRNA level and in-vivo protein degradation.

RESULTS

The TC (Ile114Thr) SNP significantly reduced enzyme activity without changing the apparent kinetic parameters Km and Vmax (normalized for NAT2 protein), indicating that Ile114Thr did not change substrate or cofactor binding affinities or catalytic efficiency. Furthermore, no significant difference in NAT2 mRNA level was observed, indicating no impairment of transcription. The TC (Ile114Thr) SNP did not alter thermostability of NAT2 at either 37 or 50 degrees C. However, this SNP significantly reduced cytosolic NAT2 immunoreactive protein through enhanced protein degradation.

CONCLUSION

This is the first report indicating that protein degradation is an important mechanism of human NAT2 slow acetylator phenotype.

NAT2 slow acetylator genotype as an important modifier of breast cancer risk

N-acetyltransferase 2 (NAT2) is a polymorphic enzyme participating in the metabolism of numerous pharmaceutical drugs and carcinogens found in tobacco smoke and diet. The NAT2 gene is highly polymorphic and several different allelic variants exist that determine the acetylator phenotype. In the course of our case-control study, we developed a new method based on fluorogenic allele-specific probes for analyzing the C282T and T341C polymorphisms of the NAT2 gene in 483 Finnish breast cancer patients and 482 healthy population controls. The slow NAT2 acetylation capacity-associated genotypes posed a somewhat increased overall breast cancer risk (odds ratio [OR], 1.32; 95% confidence interval [CI], 1.01-1.73). This association was found to be confined to the advanced (stage III or IV) breast cancer (OR, 2.60; 95% CI, 1.29-5.24). When stratified by smoking habits, women who had smoked <5 pack-years and carried a NAT2 slow acetylator genotype were at a 2.6-fold (OR, 2.55; 95% CI, 1.01-6.48) risk of breast cancer. Moreover, women with the NAT2 slow acetylator genotype and low body mass index (BMI) (<25.4 kg/m2) were at somewhat increased risk of this malignancy (OR, 1.60; 95% CI, 1.07-2.39). Our results therefore suggest that NAT2 slow acetylator genotype may be an important modifier of environmentally induced breast cancer risk in Finnish women.

D-amino acid N-acetyltransferase of Saccharomyces cerevisiae: a close homologue of histone acetyltransferase Hpa2p acting exclusively on free D-amino acids

D-Amino acid N-acetyltransferase is a unique enzyme of Saccharomyces cerevisiae acting specifically on D-amino acids. The enzyme was found to be encoded by HPA3, a putative histone/protein acetyl transferase gene, and we purified its gene product, Hpa3p, from recombinant Escherichia coli cells. Hpa3p shares 49% sequence identity and 81% sequence similarity with a histone acetyltransferase, Hpa2p, of S. cerevisiae. Hpa3p acts on a wide range of D-amino acids but shows extremely low activity toward histone. However, Hpa2p does not act on any of the free amino acids except L-lysine and D-lysine. Kinetic analyses suggest that Hpa3p catalyzes the N-acetylation of D-amino acids through an ordered bi-bi mechanism, in which acetyl-CoA is the first substrate to be bound and CoA is the last product to be liberated.

Chemopreventive drug treatment in subjects with genetic predisposition to cancer: prescriber liability and healthcare disparities

Advancements in pharmacogenomics and chemoprevention promise to reduce cancer incidence and mortality, but utilization will undoubtedly be accompanied with ethical and legal issues that largely remain unexplored or discussed. As pharmacogenomic information is assessed more comprehensively and inexpensively, it will influence decisions regarding when and to whom chemoprevention therapy will be initiated. Pharmacogenomics will change the manner in which the liability system will perceive and analyse risks. Management of the risks related to chemopreventive treatment will differ from traditional disease management. Knowledge about cancer susceptibility will need to consider environmental factors as they relate to healthcare disparities.

The effects of genetic variation in N-acetyltransferases on 4-aminobiphenyl genotoxicity in mouse liver

Inbred, congenic and transgenic strains of mice were characterized for acetylation of p-aminobenzoic (PABA) and the carcinogen 4-aminobiphenyl (4ABP). C57Bl/6 mice have the NAT2*8 allele, A/J mice have NAT2*9 and congenic B6.A mice have NAT2*9 on the C57Bl/6 background. The first transgenic strain with human NAT1, the functional equivalent of murine NAT2, was also tested. The murine NAT2*9 allele correlated with a slow phenotype measured with the murine NAT2 selective substrate PABA. The two strains having this allele also had a lower capacity to acetylate 4ABP. A line with five copies of the human NAT1 transgene was bred for at least five generations with either C57Bl/6 or A/J mice. There was no significant change in PABA NAT activity on the C57Bl/6 background but a 2.5-fold increase was seen in hNAT1:A/J compared with A/J. The effect of variation in NATs on 4ABP genotoxicity was assessed in these strains. Twenty-four hours after exposure to a single oral dose of 120 mg 4ABP/kg, hepatic 4ABP-DNA adducts were detected by immunofluoresence in all strains. Nuclear fluorescence intensities (mean+/-S.D.) were 41.1+/-3.6 for C57Bl/6, 37.9+/-1.11 for A/J and 36.3+/-2.44 for B6.A. There was no correlation between murine NAT2 alleles and 4ABP-DNA adduct levels. Similar results were seen with the transgenic strains. The data indicate that the range of variation present in these strains of mice was insufficient to alter susceptibility to 4ABP genotoxicity. The impact of these relatively modest differences in the acetylation of the activation of 4ABP may be masked by other competing biotransformation reactions since 4ABP is a substrate for both NAT1 and NAT2. Mouse models with variation in both isoforms are needed to adequately assess the role of variation in NATs in susceptibility to 4ABP genotoxicity.

NAT2 slow acetylation and GSTM1 null genotypes may increase postmenopausal breast cancer risk in long-term smoking women

N-acetyltransferase (NAT) 1 and 2 and glutathione S-transferase (GST) M1 and T1 are phase II enzymes that are important for activation and detoxification of carcinogenic heterocyclic and aromatic amines, as present in cigarette smoke. We studied whether genetic polymorphisms in these genes modifies the relationship between smoking and breast cancer. A nested case-control study was conducted among participants in a Dutch prospective cohort. Breast cancer cases (n=229) and controls (n=264) were frequency-matched on age, menopausal status and residence. Compared to never smoking, smoking 20 cigarettes or more per day increased breast cancer risk statistically significant only in postmenopausal women [odds ratio (OR)=2.17; 95% confidence interval (CI) 1.04-4.51]. Neither NAT1 slow genotype, or GSTT1 null genotype, alone or in combination with smoking, affected breast cancer risk. However, compared to individuals with rapid NAT2 genotype, women with the very slow acetylator genotype (NAT2*5), who smoked for 20 years showed an increased breast cancer risk (OR=2.29; 95% CI 1.06-4.95). Similarly, the presence of GSTM1 null genotype combined with high levels of cigarette smoking (OR=3.00; 95% CI 1.46-6.15) or long duration (OR=2.53; 95% CI 1.24-5.16), increased rates of breast cancer. The combined effect of GSTM1 null genotype and smoking high doses was most pronounced in postmenopausal women (OR=6.78; 95% CI 2.31-19.89). In conclusion, our results provide support for the view that women who smoke and who have a genetically determined reduced inactivation of carcinogens (GSTM1 null genotype or slow NAT2 genotype (especially very slow NAT2 genotype)) are at increased risk of breast cancer.

NMR investigation of the catalytic mechanism of arylamine N-acetyltransferase from Salmonella typhimurium

Arylamine N-acetyltransferases (NAT) are a family of enzymes found in both eucaryotes and procaryotes, which catalyse the N-acetylation of a range of arylamine and hydrazine drugs and carcinogenic arylamines, using acetyl Coenzyme A as a cofactor. Here we describe a nuclear magnetic resonance (NMR) investigation of the interaction of substrates with Salmonella typhimurium NAT. For solution NMR investigations, pure recombinant NAT from S. typhimurium was used at up to 0.1 mM. We demonstrate that a hydrazine substrate, isoniazid (INH), binds to the protein in the absence of the cofactor, acetyl CoA, and thereby suggest that even though the catalysis may follow a ping-pong pathway, ligand-enzyme interactions can occur in the absence of acetyl CoA.