Single nucleotide polymorphisms, metabolic activation and environmental carcinogenesis: why molecular epidemiologists should think about enzyme expression

Association of Single Nucleotide Polymorphisms (SNPs) in Genes Encoding for Folate Metabolising Enzymes with Glioma and Meningioma in Indian Population

Background:

The association of primary brain tumors with Single Nucleotide polymorphisms (SNPs) in genes of folate metabolising enzymes have been reported to vary among different ethnic population. Here, we have studied the association of SNPs of folate metabolizing genes with the primary brain tumors (glioma and meningioma) in North Indian population.

Methods:

SNPs of genes coding for folate metabolizing enzymes was carried out in 288 study population from North India [Glioma (n=108), Meningioma (n=76) and healthy-control (n=104)]. The allele-specific polymerase chain reaction (ARMS-PCR) was used to analyse the SNP A1298C of the MTHFR (Methylenetetrahydrofolate-reductase) and the SNP A66G of the methionine synthase reductase (MTRR) genes. The PCR-RLFP (Restriction Fragment Length Polymorphism) was used to analyse the SNP C677T of the Methylene tetrahydrofolate-reductase and the SNP A2756G of the methionine-synthase (MTR) genes. Serum homocysteine, vitamin B₁₂ and folate levels were evaluated in controls/patients serum using Chemiluminescence immunoassay and the levels were correlated with SNPs genotype.

Results:

The CC genotype of MTHFR A1298C was observed to have reduced risk of having meningioma than AA genotype (odd ratio=0.62, 95%CI 0.32-0.97, p=0.03). Similarly, the AG genotype of MTRR A66G showed reduced risk of glioma than AA genotype (odd ratio=0.56, 95%CI 0.32-0.97, p=0.039). Furthermore, in patients with AA genotype of MTR A2756G and CT genotype of MTHFR C677T showed higher serum homocysteine level than GG genotype (8.6 µmol/L, p=0.048) and CC genotype (11.2µmol/L, p=0.039) respectively.

Conclusion:

Our findings provide an insight into the risk association of SNPs in MTHFR A1298C and MTRR A66G genes with glioma/meningioma patients. Further studies are needed to evaluate their clinical implications.

Molecular epidemiology of acute leukemia in children: causal model, interaction of three factors-susceptibility, environmental exposure and vulnerability period

Acute leukemias have a huge morphological, cytogenetic and molecular heterogeneity and genetic polymorphisms associated with susceptibility. Every leukemia presents causal factors associated with the development of the disease. Particularly, when three factors are present, they result in the development of acute leukemia. These phenomena are susceptibility, environmental exposure and a period that, for this model, has been called the period of vulnerability. This framework shows how the concepts of molecular epidemiology have established a reference from which it is more feasible to identify the environmental factors associated with the development of leukemia in children. Subsequently, the arguments show that only susceptible children are likely to develop leukemia once exposed to an environmental factor. For additional exposure, if the child is not susceptible to leukemia, the disease does not develop. In addition, this exposure should occur during a time window when hematopoietic cells and their environment are more vulnerable to such interaction, causing the development of leukemia. This model seeks to predict the time when the leukemia develops and attempts to give a context in which the causality of childhood leukemia should be studied. This information can influence and reduce the risk of a child developing leukemia.

CYP2S1 depletion enhances colorectal cell proliferation is associated with PGE2-mediated activation of β-catenin signaling

Colorectal epithelial cancer is one of the most common cancers in the world and its 5-year survival rate is still relatively low. Cytochrome P450 (CYP) enzymes in epithelial cells lining the alimentary tract play an important role in the oxidative metabolism of a wide range of xenobiotics, including (pro-)carcinogens and endogenous compounds. Although CYP2S1, a member of CYP family, strongly expressed in many extrahepatic tissues, the role of CYP2S1 in cancer remains unclear. To investigate whether CYP2S1 involves in colorectal carcinogenesis, cell proliferation was analyzed in HCT116 cells depleted of CYP2S1 using small hairpin interfering RNA. Our data show that CYP2S1 knockdown promotes cell proliferation through increasing the level of endogenous prostaglandin E2(PGE2). PGE2, in turn, reduces phosphorylation of β-catenin and activates β-catenin signaling, which contributes to the cell proliferation. Furthermore, CYP2S1 knockdown increase tumor growth in xenograft mouse model. In brief, these results demonstrate that CYP2S1 regulates colorectal cancer growth through associated with PGE2-mediated activation of β-catenin signaling.

Phenanthrene metabolism in smokers: use of a two-step diagnostic plot approach to identify subjects with extensive metabolic activation

Polycyclic aromatic hydrocarbons (PAHs) in cigarette smoke are among the most likely causes of lung cancer. PAHs require metabolic activation to initiate the carcinogenic process. Phenanthrene (Phe), a noncarcinogenic PAH, was used as a surrogate of benzo[α]pyrene and related PAHs to study the metabolic activation of PAHs in smokers. A dose of 10 μg of deuterated Phe ([D₁₀]Phe) was administered to 25 healthy smokers in a crossover design, either as an oral solution or by smoking cigarettes containing [D₁₀]Phe. Phe was deuterated to avoid interference from environmental Phe. Intensive blood and urine sampling was performed to quantitate the formation of deuterated r-1,t-2,3,c-4-tetrahydroxy-1,2,3,4-tetrahydrophenanthrene ([D₁₀]PheT), a biomarker of the diol epoxide metabolic activation pathway. In both the oral and smoking arms approximately 6% of the dose was metabolically converted to diol epoxides, with a large intersubject variability in the formation of [D₁₀]PheT observed. Two diagnostic plots were developed to identify subjects with large systemic exposure and significant lung contribution to metabolic activation. The combination of the two plots led to the identification of subjects with substantial local exposure. These subjects produced, in one single pass of [D₁₀]Phe through the lung, a [D₁₀]PheT exposure equivalent to the systemic exposure of a typical subject and may be an indicator of lung cancer susceptibility. Polymorphisms in PAH-metabolizing genes of the 25 subjects were also investigated. The integration of phenotyping and genotyping results indicated that GSTM1-null subjects produced approximately 2-fold more [D₁₀]PheT than did GSTM1-positive subjects.

Gene expression in the mammary gland tissue of female Fischer 344 and Lewis rats after magnetic field exposure (50 Hz, 100 μT) for 2 weeks

PURPOSE

The issue of whether exposure to environmental power-frequency magnetic fields (MF) has impact on breast cancer development still remains equivocal. Previously, we observed rat strain differences in the MF response of breast tissue, so that the genetic background plays a role in MF effects. The present experiment aimed to elucidate candidate genes involved in MF effects by comparison of MF-susceptible Fischer 344 (F344) rats and MF-insensitive Lewis rats.

MATERIALS AND METHODS

Female F344 and Lewis rats were exposed to MF (50 Hz, 100 μT) for two weeks, and a whole genome microarray analysis in the mammary gland tissue was performed.

RESULTS

A remarkably decreased α-amylase gene expression, decreases in carbonic anhydrase 6 and lactoperoxidase, both relevant for pH regulation, and an increased gene expression of cystatin E/M, a tumor suppressor, were observed in MF-exposed F344, but not in Lewis rats.

CONCLUSION

The MF-exposed F344 breast tissue showed alterations in gene expression, which were absent in Lewis and may therefore be involved in the MF-susceptibility of F344. Notably α-amylase might serve as a promising target to study MF effects, because first experiments indicate that MF exposure alters the functionality of this enzyme in breast tissue.

Tumor spectrum in lynch syndrome, DNA mismatch repair system and endogenous carcinogens

Inactivation of Mismatch Repair genes in Lynch Syndrome, caused by inherited mutations, decreases the ability to repair DNA errors throughout life. This deficit may allow the development of any tumor type. Nevertheless, the Syndrome develops a specific tumor spectrum associated with the disease. We think that such spectrum of tumors would be related to the action of certain endogenous carcinogens such as bile acids and estrogens that aggravate the inherited defect.

SULT1A1 Arg213His polymorphism, smoked meat, and breast cancer risk: a case-control study and meta-analysis

SULT1A1 is involved in both detoxification of estrogens and bioactivation of carcinogens in smoked meat. SULT1A1 Arg213His polymorphism's effect on breast cancer risk is still unclear. We recruited 400 case-control pairs to investigate the association between SULT1A1 genotypes and breast cancer risk, and the combined effect of SULT1A1 polymorphism and daily intake of smoked meat. Participants were questioned about their dietary habits and other risk factors, and their SULT1A1 genotypes were determined. Adjusted odds ratios (aORs) and 95% confidence intervals (CIs) were estimated by multivariable unconditional logistic regression. We also performed a meta-analysis of relevant published studies to test these associations. In the case-control study, no significant associations were observed between SULT1A1 polymorphism and breast cancer risk. In the meta-analysis, SULT1A1 His/His genotype slightly increased risk among both overall and postmenopausal women (OR(pooled-overall)=1.12, 95% CI: 1.02-1.24; OR(pooled-post)=1.17, 95% CI: 1.03-1.32). A larger positive association was observed in Asian populations (OR(pooled-Asian)=2.01, 95% CI: 1.24-3.26). In our case-control study, high energy-adjusted daily intake of smoked meat was significantly associated with breast cancer risk in overall, pre- and postmenopausal women (aORs: 2.31-3.13, OR 95% CIs exclude 1). High smoked meat intake interacted positively with the His variant allele (all γ>1). These results correlated with those of the meta-analysis (γ(pooled-overall)=1.27). The SULT1A1 His/His genotype may increase the risk of breast cancer among Asian women, and dietary exposure to heterocyclic amines and polycyclic aromatic hydrocarbons, along with the SULT1A1 His/His variant genotype, may synergistically increase the risk of breast cancer.

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.

SULT1A1 R213H polymorphism and breast cancer risk: a meta-analysis based on 8,454 cases and 11,800 controls

The SULT1A1 R213H polymorphism is suggested to be implicated in the development and progression of breast cancer. However, the published findings are inconsistent. We therefore performed a meta-analysis of 8,454 breast cancer cases and 11,800 controls from 14 published case-control studies. We used odds ratios (ORs) with 95% confidence intervals (CIs) to assess the strength of the association of the R213H polymorphism with breast cancer risk. Overall, our results suggested that there is no significant relationship between SULT1A1 R213H polymorphism and the risk of breast cancer. However, further ethnic population analysis revealed a significantly increased risk of breast cancer for HH allele carriers among Asians (for HH vs. RR: OR = 2.27, 95% CI = 1.11-4.63, P (heterogeneity) = 0.63; for the recessive model: OR = 2.03, 95% CI = 1.00-4.41, P (heterogeneity) = 0.62). Taken together, this meta-analysis suggests that the SULT1A1 R213H may be a low-penetrant risk factor for developing breast cancer in Asian population.

Aromatic DNA adducts and polymorphisms in metabolic genes in healthy adults: findings from the EPIC-Spain cohort

Aromatic compounds such as polycyclic aromatic hydrocarbons, arylamines and heterocyclic amines require metabolic activation to form metabolites able to bind to DNA, a process mediated by polymorphic enzymes. We measured aromatic DNA adducts in white blood cells by the (32)P-post-labelling assay in a sample of 296 healthy adults (147 men and 149 women) from five regions of Spain. We also analyzed functional polymorphisms in the metabolic genes CYP1A1, CYP1A2, EPHX1, GSTM1, GSTT1, NAT2 and SULT1A1. A significant increased level of DNA aromatic adducts was found related to the fast oxidation-hydrolysis phenotype defined by the polymorphism I462V in CYP1A1, the allele A in IVS1-154C>A of CYP1A2 and the combination Tyrosine-Arginine for Y113H and H139R of EPHX1. Geometric means (adducts per 10(-9) normal nucleotides) were 2.17, 4.04 and 6.30 for slow, normal and fast phenotypes, respectively (P-trend = 0.01). Slow acetylation by NAT2 was associated with a significant decrease in adduct level; subjects with slow alleles *5A and *7A/B had in average 1.56 x 10(-9)adducts, as compared with 5.60 for those with normal NAT2 activity (P-value = 0.01). No association was seen with polymorphisms of other metabolic genes such as GSTM1, GSTT1 or SULT1A1. We concluded that the metabolic pathways of oxidation, hydrolysis and acetylation are relevant to the formation of bulky DNA adducts. This could suggest a potential involvement of aromatic compounds in the formation of such adducts; however, given lack of specificity of the post-labeling assay, a firm conclusion cannot be drawn.

ATSDR evaluation of health effects of benzene and relevance to public health

As part of its mandate, the Agency for Toxic Substances and Disease Registry (ATSDR) prepares toxicological profiles on hazardous chemicals found at Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) National Priorities List (NPL) sites that have the greatest public health impact. These profiles comprehensively summarize toxicological and environmental information. This article constitutes the release of portions of the Toxicological Profile for Benzene. The primary purpose of this article is to provide public health officials, physicians, toxicologists, and other interested individuals and groups with an overall perspective on the toxicology of benzene. It contains descriptions and evaluations of toxicological studies and epidemiological investigations and provides conclusions, where possible, on the relevance of toxicity and toxicokinetic data to public health.

Red meat intake, doneness, polymorphisms in genes that encode carcinogen-metabolizing enzymes, and colorectal cancer risk

Colorectal cancer literature regarding the interaction between polymorphisms in carcinogen-metabolizing enzymes and red meat intake/doneness is inconsistent. A case-control study was conducted to evaluate the interaction between red meat consumption, doneness, and polymorphisms in carcinogen-metabolizing enzymes. Colorectal cancer cases diagnosed 1997 to 2000, ages 20 to 74 years, were identified through the population-based Ontario Cancer Registry and recruited by the Ontario Family Colorectal Cancer Registry. Controls were sex-matched and age group-matched random sample of Ontario population. Epidemiologic and food questionnaires were completed by 1,095 cases and 1,890 controls; blood was provided by 842 and 1,251, respectively. Multivariate logistic regression was used to obtain adjusted odds ratio (OR) estimates. Increased red meat intake was associated with increased colorectal cancer risk [OR (> 5 versus < or = 2 servings/wk), 1.67 (1.36-2.05)]. Colorectal cancer risk also increased significantly with well-done meat intake [OR (> 2 servings/wk well-done versus < or = 2 servings/wk rare-regular), 1.57 (1.27-1.93)]. We evaluated interactions between genetic variants in 15 enzymes involved in the metabolism of carcinogens in overcooked meat (cytochrome P450, glutathione S-transferase, UDP-glucuronosyltransferases, SULT, NAT, mEH, and AHR). CYP2C9 and NAT2 variants were associated with colorectal cancer risk. Red meat intake was associated with increased colorectal cancer risk regardless of genotypes; however, CYP1B1 combined variant and SULT1A1-638G>A variant significantly modified the association between red meat doneness intake and colorectal cancer risk. In conclusion, well-done red meat intake was associated with an increased risk of colorectal cancer regardless of carcinogen-metabolizing genotype, although our data suggest that persons with CYP1B1 and SULT1A1 variants had the highest colorectal cancer risk.

Genetic polymorphisms and benzene metabolism in humans exposed to a wide range of air concentrations

Using generalized linear models with natural-spline smoothing functions, we detected effects of specific xenobiotic metabolizing genes and gene-environment interactions on levels of benzene metabolites in 250 benzene-exposed and 136 control workers in Tianjin, China (for all individuals, the median exposure was 0.512 p.p.m. and the 10th and 90th percentiles were 0.002 and 6.40 p.p.m., respectively). We investigated five urinary metabolites (E,E-muconic acid, S-phenylmercapturic acid, phenol, catechol, and hydroquinone) and nine polymorphisms in seven genes coding for key enzymes in benzene metabolism in humans {cytochrome P450 2E1 [CYP2E1, rs2031920], NAD(P)H: quinone oxidoreductase [NQO1, rs1800566 and rs4986998], microsomal epoxide hydrolase [EPHX1, rs1051740 and rs2234922], glutathione-S-transferases [GSTT1, GSTM1 and GSTP1(rs947894)] and myeloperoxidase [MPO, rs2333227]}. After adjusting for covariates, including sex, age, and smoking status, NQO1*2 (rs1800566) affected all five metabolites, CYP2E1 (rs2031920) affected most metabolites but not catechol, EPHX1 (rs1051740 or rs2234922) affected catechol and S-phenylmercapturic acid, and GSTT1 and GSTM1 affected S-phenylmercapturic acid. Significant interactions were also detected between benzene exposure and all four genes and between smoking status and NQO1*2 and EPHX1 (rs1051740). No significant effects were detected for GSTP1 or MPO. Results generally support prior associations between benzene hematotoxicity and specific gene mutations, confirm earlier evidence that GSTT1 affects production of S-phenylmercapturic acid, and provide additional evidence that genetic polymorphisms in NQO1*2, CYP2E1, and EPHX1 (rs1051740 or rs2234922) affect metabolism of benzene in the human liver.

Genetic variability in CYP3A4 and CYP3A5 in primary liver, gastric and colorectal cancer patients

Background

Drug-metabolizing enzymes play a role in chemical carcinogenesis through enzymatic activation of procarcinogens to biologically reactive metabolites. The role of gene polymorphisms of several cytochrome P450 enzymes in digestive cancer risk has been extensively investigated. However, the drug-metabolizing enzymes with the broader substrate specificity, CYP3A4 and CYP3A5, have not been analyzed so far. This study aims to examine associations between common CYP3A4 and CYP3A5 polymorphisms and digestive cancer risk.

Methods

CYP3A4 and CYP3A5 genotypes were determined in 574 individuals including 178 patients with primary liver cancer, 82 patients with gastric cancer, 151 patients with colorectal cancer, and 163 healthy individuals.

Results

The variant allele frequencies for patients with liver cancer, gastric cancer, colorectal cancer and healthy controls, respectively, were: CYP3A4*1B, 4.8 % (95% C.I. 2.6–7.0), 3.7 % (0.8–6.6) 4.3% (2.0–6.6) and 4.3% (2.1–6.5); CYP3A5*3, 91.8 % (93.0–97.4), 95.7% (92.6–98.8), 91.7% (88.6–94.8) and 90.8% (87.7–93.9). The association between CYP3A4*1B and CYP3A5*3 variant alleles did not significantly differ among patients and controls. No differences in genotypes, allele frequencies, or association between variant alleles were observed with regard to gender, age at diagnosis, tumour site or stage.

Conclusion

Common polymorphisms on CYP3A4 and CYP3A5 genes do not modify the risk of developing digestive cancers in Western Europe.

Identification of N-acetyltransferase 2 (NAT2) transcription start sites and quantitation of NAT2-specific mRNA in human tissues

Human N-acetyltransferase 2 (NAT2) genetic polymorphism is associated with drug toxicity and/or carcinogenesis in various tissues. Knowledge of NAT2 gene structure and expression is critical for understanding these associations. Previous findings suggest that human NAT2 expression is highest in liver and gut but expressed at functional levels in other tissues. A sensitive and specific TaqMan reverse transcriptase-polymerase chain reaction (RT-PCR) assay with intron-spanning primers was developed and used, together with a second TaqMan RT-PCR assay based on amplification of a NAT2 open reading frame (ORF) exon segment, to measure NAT2 mRNA in 29 different human tissues. Cap-dependent amplification of mRNA 5' termini and review of public database information were done to more precisely define the NAT2 promoter(s) and to validate the quantitative RT-PCR assay design. The great majority (40/41) of NAT2 liver cDNAs had 5' termini between 8682 and 8752 nucleotides upstream of the NAT2 ORF exon, and 34 of 40 5' termini were at the -8711 and -8716 adenines. All 59 NAT2 cDNAs with 5' termini in this vicinity, including 40 of the liver isolates and 19 cDNAs in public databases from liver and other sources, showed direct splicing to the ORF exon, with no other noncoding exon detected. NAT2 mRNA was highest in liver, small intestine, and colon and was readily detected in most other tissues, albeit at much lower levels. NAT2 expression in diverse human tissues provides further mechanistic support underlying associations between NAT2 genetic polymorphism, drug toxicity, and/or chemical carcinogenesis.

Xenobiotic-metabolizing enzymes involved in activation and detoxification of carcinogenic polycyclic aromatic hydrocarbons

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental carcinogens and metabolized by a variety of xenobiotic-metabolizing enzymes such as cytochrome P450 (P450 or CYP), epoxide hydrolase, glutathione transferase, UDP-glucuronosyltransferase, sulfotransferase, NAD(P)H quinone oxidoreductase 1, and aldo-keto reductase. These enzymes mainly participate in the conversion of PAHs to more polar and water-soluble metabolites, and the resultant metabolites are readily excreted from the body. However, during the course of metabolism, a variety of unstable and reactive intermediates of PAHs are formed, and these metabolites attack DNA, causing cell toxicity and transformation. P450s and epoxide hydrolase convert PAHs to proximate carcinogenic metabolites, PAH-diols, and these products are further metabolized by P450s to ultimate carcinogenic metabolites, PAH diol-epoxides, or by aldo-keto reductase to reactive PAH o-quinones. PAHs are also activated by P450 and peroxidases to reactive radical cations that bind covalently to DNA. The oxygenated and reactive metabolites of PAHs are usually converted to more polar and detoxified products by phase II enzymes. Inter-individual differences exist in levels of expression and catalytic activities of a variety of enzymes that activate and/or detoxify PAHs in various organs of humans and these phenomena are thought to be critical in understanding the basis of individual differences in response to PAHs. Factors affecting such variations include induction and inhibition of enzymes by diverse chemicals and, more importantly, genetic polymorphisms of enzymes in humans.

Tissue distribution of N-acetyltransferase 1 and 2 catalyzing the N-acetylation of 4-aminobiphenyl and O-acetylation of N-hydroxy-4-aminobiphenyl in the congenic rapid and slow acetylator Syrian hamster

N-acetyltransferase 1 (NAT1) and 2 (NAT2) enzymes catalyzing both deactivation (N-acetylation) and activation (O-acetylation) of arylamine carcinogens such as 4-aminobiphenyl (ABP) were investigated in a Syrian hamster model congenic at the NAT2 locus. NAT2 catalytic activities (measured with p-aminobenzoic acid) were significantly (P < 0.001) higher in rapid than slow acetylators in all tissues (except heart and prostate where activity was undetectable in slow acetylators). NAT1 catalytic activities (measured with sulfamethazine) were low but detectable in most tissues tested and did not differ significantly between rapid and slow acetylators. ABP N-acetyltransferase activity was detected in all tissues of rapid acetylators but was below the limit of detection in all tissues of slow acetylators except liver where it was about 15-fold lower than rapid acetylators. ABP N-acetyltransferase activities correlated with NAT2 activities (r2 = 0.871; P < 0.0001) but not with NAT1 activities (r2 = 0.132; P > 0.05). Levels of N-hydroxy-ABP O-acetyltransferase activities were significantly (P < 0.05) higher in rapid than slow acetylator cytosols for many but not all tissues. The N-hydroxy-ABP O-acetyltransferase activities correlated with ABP N-acetyltransferase activities (r2 = 0.695; P < 0.0001) and NAT2 activities (r2 = 0.521, P < 0.0001) but not with NAT1 activities (r2 = 0.115; P > 0.05). The results suggest widespread tissue distribution of both NAT1 and NAT2, which catalyzes both N- and O-acetylation. These conclusions are important for interpretation of molecular epidemiological investigations into the role of N-acetyltransferase polymorphisms in various diseases including cancer.

Bioactivation of 3-aminobenzanthrone, a human metabolite of the environmental pollutant 3-nitrobenzanthrone: evidence for DNA adduct formation mediated by cytochrome P450 enzymes and peroxidases

3-Nitrobenzanthrone (3-NBA) is a suspected human carcinogen found in diesel exhaust and ambient air pollution. The main metabolite of 3-NBA, 3-aminobenzanthrone (3-ABA), was detected in the urine of salt mining workers occupationally exposed to diesel emissions. We evaluated the role of hepatic cytochrome P450 (CYP) enzymes in the activation of 3-ABA in vivo by treating hepatic cytochrome P450 oxidoreductase (POR)-null mice and wild-type littermates intraperitoneally with 0.2 and 2mg/kg body weight of 3-ABA. Hepatic POR-null mice lack POR-mediated CYP enzyme activity in the liver. Using the (32)P-postlabelling method, multiple 3-ABA-derived DNA adducts were observed in liver DNA from wild-type mice, qualitatively similar to those formed in incubations using human hepatic microsomes. The adduct pattern was also similar to those formed by the nitroaromatic counterpart 3-NBA and which derive from reductive metabolites of 3-NBA bound to purine bases in DNA. DNA binding by 3-ABA in the livers of the null mice was undetectable at the lower dose and substantially reduced (by up to 80%), relative to wild-type mice, at the higher dose. These data indicate that POR-mediated CYP enzyme activities are important for the oxidative activation of 3-ABA in livers, confirming recent results indicating that CYP1A1 and -1A2 are mainly responsible for the metabolic activation of 3-ABA in human hepatic microsomes. No difference in DNA binding was found in kidney and bladder between null and wild-type mice, suggesting that cells in these extrahepatic organs have the metabolic capacity to oxidize 3-ABA to species forming the same 3-ABA-derived DNA adducts, independently from the CYP-mediated oxidation in the liver. We determined that different model peroxidases are able to catalyse DNA adduct formation by 3-ABA in vitro. Horseradish peroxidase (HRP), lactoperoxidase (LPO), myeloperoxidase (MPO), and prostaglandin H synthase (PHS) were all effective in activating 3-ABA in vitro, forming DNA adducts qualitatively similar to those formed in vivo in mice treated with 3-ABA and to those found in DNA reacted with N-hydroxy-3-aminobenzanthrone (N-OH-ABA). Collectively, these results suggest that both CYPs and peroxidases may play an important role in metabolizing 3-ABA to reactive DNA adduct forming species.

Molecular mechanism of genotoxicity of the environmental pollutant 3-nitrobenzanthrone

3-Nitrobenzanthrone (3-NBA) is a suspected human carcinogen identified in diesel exhaust and air pollution. This article reviews the results of our laboratories showing which of the phase I and II enzymes are responsible for 3-NBA genotoxicity, participating in activation of 3-NBA and its human metabolite, 3-aminobenzanthrone (3-ABA), to species generating DNA adducts. Among the phase I enzymes, the most of the activation of 3-NBA in vitro is attributable to cytosolic NAD(P)H:quinone oxidoreductase (NQO1), while N,O-acetyltransferase (NAT), NAT2, followed by NAT1, sulfotransferase (SULT), SULT1A1 and, to a lesser extent, SULT1A2 are the major phase II enzymes activating 3- NBA. To evaluate the importance of hepatic cytosolic enzymes in relation to microsomal NADPH:cytochrome P450 (CYP) oxidoreductase (POR) in the activation of 3-NBA in vivo, we treated hepatic POR-null and wild-type C57BL/6 mice with 3-NBA or 3-ABA. The results indicate that 3-NBA is predominantly activated by cytosolic nitroreductases such as NQO1 rather than microsomal POR. In the case of 3-ABA, CYP1A1/2 enzymes are essential for the oxidative activation of 3-ABA in liver. However, cells in the extrahepatic organs have the metabolic capacity to activate 3-ABA to form DNA adducts, independently from CYP-mediated oxidation in the liver. Peroxidases such as prostaglandin H synthase, lactoperoxidase, myeloperoxidase, abundant in several extrahepatic tissues, generate DNA adducts, which are formed in vivo by 3-ABA or 3-NBA. The results suggest that both CYPs and peroxidases may play an important role in metabolism of 3-ABA to reactive species forming DNA adducts, participating in genotoxicity of this compound and its parental counterpart, 3-NBA.

Genetic polymorphism in the sulfotransferase SULT1A1 gene in cancer

Cytosolic sulfotransferases are enzymes that catalyze the conjugation of sulfate groups to a variety of xenobiotic and endogenous substrates. A mutation in the SULT1A1 gene has been associated with decreased sulfotransferase activity. We studied 125 cancer patients and 100 healthy controls from Brazil matched by age and gender. The objective of this study was to assess the impact of the SULT1A1 polymorphism on sulfotransferase activity in a population of cancer patients. Both heterozygous and homozygous individuals for the mutant allele had significantly decreased sulfotransferase enzymatic activity. This decrease was more significant in cancer patients. The frequency of the SULT1A1( *)2 allele was increased in the myeloma group (odds ratio=0.53). These data suggest a functional role for the SULT1A1 gene polymorphism in cancer.

After Helsinki: a multidisciplinary review of the relationship between asbestos exposure and lung cancer, with emphasis on studies published during 1997-2004

Despite an extensive literature, the relationship between asbestos exposure and lung cancer remains the subject of controversy, related to the fact that most asbestos-associated lung cancers occur in those who are also cigarette smokers: because smoking represents the strongest identifiable lung cancer risk factor among many others, and lung cancer is not uncommon across industrialised societies, analysis of the combined (synergistic) effects of smoking and asbestos on lung cancer risk is a more complex exercise than the relationship between asbestos inhalation and mesothelioma. As a follow-on from previous reviews of prevailing evidence, this review critically evaluates more recent studies on this relationship--concentrating on those published between 1997 and 2004--including lung cancer to mesothelioma ratios, the interactive effects of cigarette smoke and asbestos in combination, and the cumulative exposure model for lung cancer induction as set forth in The Helsinki Criteria and The AWARD Criteria (as opposed to the asbestosis-->cancer model), together with discussion of differential genetic susceptibility/resistance factors for lung carcinogenesis by both cigarette smoke and asbestos. The authors conclude that: (i) the prevailing evidence strongly supports the cumulative exposure model; (ii) the criteria for probabilistic attribution of lung cancer to mixed asbestos exposures as a consequence of the production and end-use of asbestos-containing products such as insulation and asbestos-cement building materials--as embodied in The Helsinki and AWARD Criteria--conform to, and are further consolidated by, the new evidence discussed in this review; (iii) different attribution criteria (e.g., greater cumulative exposures) are appropriate for chrysotile mining/milling and perhaps for other chrysotile-only exposures, such as friction products manufacture, than for amphibole-only exposures or mixed asbestos exposures; and (iv) emerging evidence on genetic susceptibility/resistance factors for lung cancer risk as a consequence of cigarette smoking, and potentially also asbestos exposure, suggests that genotypic variation may represent an additional confounding factor potentially affecting the strength of association and hence the probability of causal contribution in the individual subject, but at present there is insufficient evidence to draw any meaningful conclusions concerning variation in asbestos-mediated lung cancer risk relative to such resistance/susceptibility factors.

Personalized diagnostic and therapeutic strategies in oncology

In our lifetimes we hope to see the genome transform diagnosis and facilitate individualized management of cancer. In the foreseeable future, cancer genomes and transcriptomes will be identified and cataloged, and pathway-specific therapies will continue to be developed. Population-wide databases will be used to assist physicians in guiding patients to the appropriate therapy for their tumor. Already there are early outstanding examples of the successful application of genetic and genomic data to guide cancer therapy. However, truly tailored therapeutics in oncology will require genomic analyses of an individual's tumor as well as a more comprehensive assessment of their genetic background, health, and environment exposures in order to determine the risk of disease, the dose requirements for drugs, and the likelihood of response. Tumor genomics will eventually result in a comprehensive description of cellular processes critical to cancer growth for subsequent therapeutic impact. While there will be significant technical and societal challenges to overcome, the integration of personalized medicine into clinical practice is anticipated by clinicians, expected by patients, and represents the likely future of oncology.

Cytochrome p450 2E1 polymorphisms and the risk of gastric cardia cancer

AIM: Genetic polymorphisms of drug-metabolizing enzymes have recently been shown to affect susceptibility to chemical carcinogenesis. Cytochrome P450 2E1 (CYP2E1) enzyme catalyzes the metabolism of many procarcinogens, such as N-nitrosamines and related compounds. The gene coding for this enzyme is polymorphic and thus may play a role in gastric cardia cancer (GCC) etiology. In this hospital-based case-control study, we evaluate the relationship between genetic polymorphisms of CYP2E1 and the risk of GCC.

METHODS: The study subjects comprised 159 histologically confirmed GCC cases identified via hospital cancer registry and surgical records at five hospitals in Fuzhou, Fujian Province, China, between April and November 2001. Controls were 192 patients admitted to the same hospitals for nonmalignant conditions. The genotypes of CYP2E1 were detected by a PCR-based RFLP assay. The odds ratios were estimated by logistic regression analyses and were adjusted for potential confounding factors.

RESULTS: The distribution of three genotypes of CYP2E1 in GCC cases and controls was significantly different (χ² = 16.04, P<0.01). The frequency of the CYP2E1 (c1/c1) genotype in GCC cases and controls was 60.4% and 40.1%, respectively. The CYP2E1 (c1/c1) genotype was associated with an increased risk for GCC (the adjusted (OR) was 2.37, 95% confidence interval (CI): 1.52-3.70). Subjects who carried the CYP2E1 (c1/c1) genotype and were habitual smokers were at a significantly higher risk of developing GCC (OR = 4.68, 95%CI: 2.19-10.04) compared with those who had the CYP2E1 (c1/c2 or c2/c2) genotype and did not smoke.

CONCLUSION: These results suggest that the CYP2E1 genotype may influence individual susceptibility to development of GCC, and that the risk increases significantly in smokers.

Biomarkers of genetic susceptibility to cancer: applications to epidemiological studies

Cancer is a multifactorial disease in which both environmental and genetic factors play a role. Biological markers have been perceived as a great improvement in terms of understanding the biological mechanisms of the association between a risk factor and cancer. Genetic markers have been used very extensively in epidemiological studies, mainly with the purpose of identifying high-risk subjects because of their genetic make-up. This review describes some of the issues concerned with the use of genetic susceptibility markers in epidemiology, such as the interaction between genetic and environmental factors. Some aspects of study design are also discussed.

MPO and SOD2 polymorphisms, gender, and the risk of non-small cell lung carcinoma

Manganese superoxide dismutase (SOD2) and myeloperoxidase (MPO) are polymorphic enzymes involved in reactive oxidative species metabolism. In this case-control study (830 non-small cell lung carcinoma (NSCLC) patients; 1119 controls) we evaluated whether the MPO -G463A polymorphism (associated with a novel estrogen receptor binding site) modifies the association between the SOD2 Ala16Val polymorphism and NSCLC risk differently by gender. For women carrying the MPO variant genotypes, the adjusted odds ratio of the SOD2 polymorphism (Val/Val vs. Ala/Ala) was 3.26 (95% CI, 1.55-6.83). No associations were found in men or in women carrying the MPO GG wildtype genotype.

Development of a food database of nitrosamines, heterocyclic amines, and polycyclic aromatic hydrocarbons

Some nitrosocompounds that are formed during food preservation, as well as polycyclic aromatic hydrocarbons (PAH) and heterocyclic amines (HA) formed during cooking, may have carcinogenic activity. An accurate assessment of dietary intake of such compounds is difficult, mainly because they are not naturally present in foods, and they are not included in standard food composition tables. Our objective was to develop a food composition database of nitrates, nitrites, nitrosamines, HA, and PAH. We conducted a literature search on the food content of these compounds using the Medline and EMBASE databases. We gathered the following information: 1) Food information: name, cooking methods, preservation methods, cooking doneness, temperature, and time; 2) compound information: type, quantity, value type, analytic method, and sampling methods; and 3) publication information: year, author, and country. We developed a table that includes 207 food items with information concerning the concentration of nitrites, nitrates, and nitrosamines, 297 food items with information about HA concentration and 313 food items with information about PAH. The database is based on 139 references from 23 different countries. It is arranged according to compounds and food groups to facilitate its practical use. The potential limitations are due to the quality of the information we could obtain through Medline and EMBASE databases. This database will allow investigators to quantify dietary exposure to several potential carcinogens, and to analyze their relation to the risk of cancer.

Sulfotransferase 1A1 (SULT1A1) polymorphism and breast cancer risk in Chinese women

BACKGROUND

Sulfonation catalyzed by sulfotransferase enzymes plays an important role in chemical defense mechanisms against various xenobiotics but also bioactivates carcinogens. A major human sulfotransferase, SULT1A1, catalyzes the sulfation of a variety of phenolic and estrogenic compounds. A functional polymorphism of the SULT1A1 gene has been implicated in a decreased activity and thermostability when the wild-type arginine (Arg) at codon 213 is substituted by a histidine (His).

METHODS

We investigated the association between the His allele and the risk breast cancer in 213 cases and 430 matched controls in Chinese women, and the interaction between His allele and endogenous estrogen and dietary mutagens exposure factors were also determined by use of logistic regression analysis.

RESULTS

There was no significant difference in genotypes between the cancer patients and control populations. However, the frequency of the His allele in cases (13.6%) were significant higher than that in controls (9.5%), P = 0.03. Compared with women carrying the Arg/Arg genotype, the adjusted odds ratio (OR) of Arg/His was 1.48 (95% CI = 0.59-3.31) and His/His was 2.28 (95% CI = 0.69-9.58), P trend was 0.04. The adjusted OR of Arg/His + His/His was 2.60 (95% CI = 1.12-6.05). His allele strengthen the effect of endogenous estrogen exposure with interaction index r > 1, and weaken the effect of heterocyclic amines and polycyclic aromatic hydrocarbons derived from dietary with interaction index r > 1, both were multiplicative interaction model.

CONCLUSIONS

Our findings suggest that the SULT1A1 His allele was positively associated with the risk of breast cancer in Chinese women. And there was interaction between SULT1A1 polymorphism and related exposure factors.

Environmental tobacco smoke in the workplace: markers of exposure, polymorphic enzymes and implications for disease state

Studies focusing directly on tobacco smoke have tended to center on the differences in effect between smokers and non-smokers and many hundreds of such studies have been performed. In this review, we examine the current literature specifically concerning workplace exposure to environmental tobacco smoke (ETS) and its impact on individuals, particularly non-smokers and never smokers. The paper deals with quantifying and minimizing ETS exposures in a working environment, the effect of polymorphisms and other genetic factors that influence health outcomes after exposure to ETS and the association of occupational ETS exposure to disease-specific biomarkers.

Interactions between genetic polymorphism of cytochrome P450-1B1, sulfotransferase 1A1, catechol-o-methyltransferase and tobacco exposure in breast cancer risk

Genetic polymorphisms of enzymes involved in the metabolism of xenobiotics and estrogens might play a role in breast carcinogenesis related to environmental exposures. In a case-only study on 282 women with breast cancer, we studied the interaction effects (ORi) between smoking habits and the gene polymorphisms of Cytochrome P450 1B1 (Val432Leu CYP1B1), Phenol-sulfotransferase 1A1 (Arg213His SULT1A1) and Catechol-O-methyltransferase (Val158Met COMT). The smokers carrying the Val CYP1B1 allele associated with a high hydroxylation activity had a higher risk of breast cancer than never smokers with the Leu/Leu genotype (ORi=2.32, 95%CI: 1.00-5.38). Also, the smokers carrying the His SULT1A1 allele associated with a low sulfation activity had a 2-fold excess risk compared to never smokers carrying Arg/Arg SULT1A1 common genotype (ORi= 2.55, 95%CI: 1.21-5.36). The His SULT1A1 allele increased the risk only in premenopausal patients. The Met COMT allele with a lower methylation activity than Val COMT did not modify the risk among smokers. The excess risk due to joint effect could result from a higher exposure to activated tobacco-compounds for women homo/heterozygous for the Val CYP1B1 allele. Also, a lower sulfation of the tobacco carcinogens among women with His SULT1A1 could increase exposure to genotoxic compounds. Alternatively, the Val CYP1B1 or His SULT1A1 allele with modified ability to metabolize estrogens could increase the level of genotoxic catechol estrogen (i.e., 4-hydroxy-estradiol) among smokers. Our study showed that gene polymorphisms of CYP1B1 and SULT1A1 induce an individual susceptibility to breast cancer among current smokers.

Cloning, expression, and mutation analysis of NOR1, a novel human gene down-regulated in HNE1 nasopharyngeal carcinoma cell line

PURPOSE

To investigate cloning, expression, and mutation analysis of the putative candidate tumor suppressor gene related with nasopharyngeal carcinoma (NPC).

METHODS

We studied the expression profiles in the NPC cell line HNE(1) with the normal nasopharyngeal epithelial cell as control by using cDNA array representing 11,000 cDNA clusters. EST W95442 was found down-regulated in HNE(1). Subsequently, the corresponding gene sequence including this EST was established by cDNA cloning and the RACE (rapid amplification of cDNA end) procedure. The expression pattern of this gene was examined by using Northern blot analysis in various human tissues. Furthermore, we screened the mutations of the coding sequence of the gene using reverse transcription-polymerase chain reaction and single-strand conformation polymorphisms (RT-PCR-SSCP) as well as direct sequencing analysis.

RESULTS

A novel gene (GenBank accession No. AF462348) was cloned and named NOR(1) standing for oxidored-nitro domain-containing protein 1 (Human Gene Nomenclature Committee-approved symbol). Northern blot analysis revealed that the NOR(1) gene had two transcripts (1.2 kb, 1.6 kb), and expressed ubiquitously in human tissues. Moreover, a Glu58Gly mutation in the exon 1 of NOR(1) was detected in two of 25 NPC biopsies.

CONCLUSIONS

We cloned a novel gene NOR(1), and the Glu58Gly polymorphism of NOR(1) may be involved in the development and/or progression of NPC suggesting that NOR(1) could be a candidate tumor repressor gene related with NPC.

Oxidative stress has a role in malignant transformation in Barrett's oesophagus

Mechanisms underlying the development of oesophageal adenocarcinoma are poorly understood. To discover the role of oxidative stress and radical scavenger capacity in the malignant transformation of Barrett's oesophagus, we measured myeloperoxidase activity, superoxide dismutase activity, glutathione content and total aromatic DNA adducts. Mucosal specimens came from 52 patients in 6 groups: symptomatic gastro-oesophageal reflux disease (GORD) without and with endoscopic oesophagitis, Barrett's epithelium without and with dysplasia, adenocarcinoma in the oesophagus and controls. In the GORD-oesophagitis-metaplasia-dysplasia-adenocarcinoma sequence, glutathione content was progressively lower and myeloperoxidase activity higher than in controls, plateauing at Barrett's epithelium without dysplasia. Only in Barrett's epithelium with dysplasia was SOD activity significantly increased. In all patient groups, DNA adduct levels were significantly higher than the control level. Though these levels between patient groups did not differ significantly, the level was highest in Barrett's epithelium without dysplasia and progressively lower in Barrett's with dysplasia and adenocarcinoma. Pooled data showed a negative correlation between glutathione content and DNA adducts (-0.28, p = 0.05). Simultaneous formation of DNA adducts, increased myeloperoxidase-related oxidative stress, decreased antioxidant capacity (glutathione content) and the negative correlation between glutathione content and DNA adducts in the GORD-oesophagitis-metaplasia-dysplasia-adenocarcinoma sequence of Barrett's oesophagus indicate a role in the pathogenesis and malignant transformation related to oxidative stress.

Biologic damage resulting from exposure to tobacco smoke and from radon: implication for preventive interventions

Cigarette smoking and residential radon are, respectively, the first and second leading cause of lung cancer in the United States today. Of the approximately 157 000 lung deaths occurring in 2000, approximately 90% can be attributed to cigarette smoking and 30% of the lung cancer deaths among non-smokers can be attributed to residential radon exposure. Although dwarfed by cigarette related lung cancer, lung cancer among lifetime non-smokers is a leading cause of death in the United States, and many other countries, accounting for approximately 16 000 deaths per year in the US. Laboratory studies and epidemiological investigations, particularly those conducted in the past decade, are yielding evidence that tobacco smoke and radon may share important elements of lung cancer's pathologic mechanism(s). Lung cancer prevention among smokers, ex-smokers and lifetime nonsmokers can be enhanced as we learn more about the etiologic mechanism(s) of lung cancer resulting from these and other exposures including diet, non-malignant respiratory diseases, occupational exposures, and susceptibility-gene. In this article we review both laboratory and epidemiologic data that gives insight into the biologic damage done to the lung from these exposures.

Biomonitoring of arylamines and nitroarenes

Arylamines and nitroarenes are very important intermediates in the industrial manufacture of dyes, pesticides and plastics, and are significant environmental pollutants. The metabolic steps of N-oxidation and nitroreduction to yield N-hydroxyarylamines are crucial for the toxic properties of arylamines and nitroarenes. Nitroarenes are reduced by microorganisms in the gut or by nitroreductases and aldehyde dehydrogenase in hepatocytes to nitrosoarenes and N-hydroxyarylamines. N-Hydroxyarylamines can be further metabolized to N-sulphonyloxyarylamines, N-acetoxyarylamines or N-hydroxyarylamine N-glucuronide. These highly reactive intermediates are responsible for the genotoxic and cytotoxic effects of this class of compounds. N-Hydroxyarylamines can form adducts with DNA, tissue proteins, and the blood proteins albumin and haemoglobin in a dose-dependent manner. DNA and protein adducts have been used to biomonitor humans exposed to such compounds. All these steps are dependent on enzymes, which are present in polymorphic forms. This article reviews the metabolism of arylamines and nitroarenes and the biomonitoring studies performed in animals and humans exposed to these substances.

Association of the myeloperoxidase -463G-->A polymorphism with development of atrophy in Helicobacter pylori-infected gastritis

OBJECTIVES

Although the host factors governing clinical outcomes subsequent to Helicobacter pylori infection have not yet been defined, it has been generally perceived that the development of the atrophic gastritis is determined more by host-related factors than by bacterial factors. It is very important to define the host factors controlling the pathway to atrophic gastritis, which is the precursor of gastric cancer. H. pylori infection is characterized by extensive infiltration of neutrophils. Myeloperoxidase in neutrophils amplifies the oxidative potential of hydrogen peroxides that induce gastric mucosal damage, and thus myeloperoxidase is suspected to play a role in H. pylori-induced gastric injury. The aim of this study was to elucidate the association of host myeloperoxidase genetic polymorphism with atrophic gastritis upon H. pylori infection.

METHODS

Biopsy specimens taken from the gastric mucosa were examined histologically using the updated Sydney System in 127 Korean patients. The polymerase chain reaction-restriction fragment length polymorphism assay was used to characterize myeloperoxidase genotypes.

RESULTS

The distributions of myeloperoxidase genotypes in Korea were 81.9% for myeloperoxidase (G/G) and 18.1% for myeloperoxidase (G/A). No myeloperoxidase (A/A) genotype was observed in 127 patients studied. The degree of active inflammation increased with the increase in H. pylori colonization. A strong positive correlation between the levels of neutrophil infiltration and gastric atrophy was found in the myeloperoxidase (G/G) genotype but not in myeloperoxidase (G/A).

CONCLUSIONS

These results suggest that myeloperoxidase genotype is a critical determinant in the pathogenesis of atrophic gastritis subsequent to H. pylori infection. More work is needed to clarify the functional relevance of myeloperoxidase genetic polymorphisms to gastric cell injury.

NAD(P)H:quinone oxidoreductase (NQO1) polymorphism, exposure to benzene, and predisposition to disease: a HuGE review

NAD(P)H:quinone oxidoreductase (NQO1) catalyzes the two- or four-electron reduction of numerous endogenous and environmental quinones (e.g., the vitamin E alpha-tocopherol quinone, menadione, benzene quinones). In laboratory animals treated with various environmental chemicals, inhibition of NQO1 metabolism has long been known to increase the risk of toxicity or cancer. Currently, there are 22 reported single-nucleotide polymorphisms (SNPs) in the NQO1 gene. Compared with the human consensus (reference, "wild-type") NQO1*1 allele coding for normal NQO1 enzyme and activity, the NQO1*2 allele encodes a nonsynonymous mutation (P187S) that has negligible NQO1 activity. The NQO1*2 allelic frequency ranges between 0.22 (Caucasian) and 0.45 (Asian) in various ethnic populations. A large epidemiologic investigation of a benzene-exposed population has shown that NQO1*2 homozygotes exhibit as much as a 7-fold greater risk of bone marrow toxicity, leading to diseases such as aplastic anemia and leukemia. The extent of the contribution of polymorphisms in other genes involved in the metabolism of benzene and related compounds-such as the P450 2E1 (CYP2E1), myeloperoxidase (MPO), glutathione-S-transferase (GSTM1, GSTT1), microsomal epoxide hydrolase (EPHX1), and other genes-should also be considered. However, it now seems clear that a lowered or absent NQO1 activity can increase one's risk of bone marrow toxicity, after environmental exposure to benzene and benzene-like compounds. In cancer patients, the NQO1*2 allele appears to be associated with increased risk of chemotherapy-related myeloid leukemia. Many other epidemiological studies, attempting to find an association between the NQO1 polymorphism and one or another human disease, have now begun to appear in the medical literature.

Mutagens in human breast lipid and milk: the search for environmental agents that initiate breast cancer

Epidemiological studies indicate the involvement of environmental factors in the etiology of breast cancer, but have not provided clear indications of the nature of the agents responsible. Several environmental carcinogens are known to induce mammary tumors in rodents, and the abundance of adipose tissue in the human breast suggests that the epithelial cells, from which breast tumors commonly arise, could be exposed to lipid-soluble carcinogens sequestered by the adipose tissue. In this report we review our studies in which we have examined human mammary lipid, obtained from elective reduction mammoplasties from healthy donors, and human milk from healthy mothers, for the presence of components with genotoxic activity in several in vitro assays. A significant proportion of lipid extracts induced mutations in bacteria and micronuclei in mammalian cells. They also caused DNA damage, detected as single-strand breaks in the alkaline single-cell gel electrophoresis (comet) assay, in both the MCL-5 cell line and in primary cultures of human mammary epithelial cells. Genotoxic activity was also found in a significant proportion of extracts of human breast milk. Viable cells recovered from milk samples showed evidence of DNA damage and were susceptible to comet formation by genotoxic agents in vitro. Genotoxic activity was found to be less prevalent in milk samples from countries of lower breast cancer incidence (the Far East) compared with that in samples from the UK. The agents responsible for the activity in milk appear to be moderately polar lipophilic compounds and of low molecular weight. Identification of these agents and their sources may hold clues to the origins of breast cancer.

N-Acetyltransferases, sulfotransferases and heterocyclic amine activation in the breast

Heterocyclic amines are mammary carcinogens in rats and their N-hydroxy metabolites are substrates for subsequent metabolic activation by N-acetyltransferases (NAT) and sulfotransferases (SULT) in man. We investigated the expression of these enzymes in human breast tissue and the relationship between NAT genotype and NAT mRNA expression or enzyme activity. Immunohistochemical staining of sections of breast tissue identified expression of NAT1 and NAT2 protein in human mammary epithelial cells, but not in the stroma. We also measured the formation of DNA adducts of the heterocyclic amines 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine in calf thymus DNA after incubation of their promutagenic N-hydroxy metabolites with mammary cytosols prepared from reduction mammoplasty tissue. Experimental observations gained from use of enzyme cofactors and NAT and/or SULT inhibitors on cytosolic enzyme activity, recombinant NAT1 activity and heterocyclic amine-DNA adduct formation suggest that both NAT1 and SULT1A enzymes contribute significantly to the activation of N-hydroxylated heterocyclic amines in mammary tissue. NAT1 mRNA transcript levels were found to be two- to three-fold higher than mRNA transcripts of the NAT2 gene in reduction mammoplasty tissue and mammary epithelial cells. NAT1-specific p-aminobenzoic acid acetylation activity, but not NAT2-specific sulfamethazine acetylation activity, was detectable in mammary cytosols. There was no association apparent between NAT genotype and the levels of NAT mRNA or NAT enzyme activity, or between NAT1 genotype and IQ-DNA adduct formation mediated by mammary cytosols. Western blot analysis of mammary cytosolic protein showed detectable levels of SULT1A1 and SULT1A3.

Cancer genetics

Cancer genetics has for many years focused on mutational events that have their primary effect within the cancer cell. Recently that focus has widened, with evidence of the importance of epigenetic events and of cellular interactions in cancer development. The role of common genetic variation in determining the range of individual susceptibility within the population is increasingly recognized, and will be addressed using information from the Human Genome Project. These new research directions will highlight determinants of cancer that lie outside the cancer cell, suggest new targets for intervention, and inform the design of strategies for prevention in groups at increased risk.