N-Nitroso compounds in the diet

Role of dietary mutagens in cancer and atherosclerosis

PURPOSE OF REVIEW

To provide an updated summary of dietary mutagens and their potential role in the etiology of cancer and atherosclerosis.

RECENT FINDINGS

Compelling evidence supports an accumulation of somatic mutations during carcinogenesis, leading to the activation of oncogenes or inactivation of tumor suppressor genes or both. There is also suggestive evidence that mutation provides an early event in atherosclerosis. Genome-wide association studies (GWAS) identify genes associated with familial cancers and atherosclerosis, but genes involved in sporadic events are less well characterized. Many dietary components are mutagenic, including natural dietary components, mutagens generated during cooking and processing of food or through contamination. Molecular epidemiology associates specific mutagens with specific types of cancer. Although chromosome mutations may provide a risk biomarker for atherosclerosis, they are not necessarily causal.

SUMMARY

Association studies, supported by molecular epidemiology, provide evidence that certain dietary mutagens, including aflatoxin B1, aristolochic acid and benzo[a]pyrene, are causal in some human cancers. Similar studies have correlated the level of oxidative DNA damage, DNA adducts and clastogenesis in arterial smooth muscle cells with atherogenic risk factors described through traditional epidemiology. However, establishing whether or not dietary mutagens lead to mutations that are causal in atherosclerosis remains a challenge for the newer genomic technologies.

Meat and cancer

An increasing literature associates high intake of meat, especially red meat and processed meat with an increased risk of cancers, especially colorectal cancer. There is evidence that this risk may not be a function of meat per se, but may reflect high-fat intake, and/or carcinogens generated through various cooking and processing methods. The cancer risk may be modulated by certain genotypes. Cancers associated with high meat consumption may be reduced by the addition of anticarcinogens in the diet, especially at the same time as meat preparation or meat consumption, or modification of food preparation methods. Meat contains potential anticarcinogens, including omega-3 polyunsaturated fatty acids, and conjugated linoleic acid (CLA). Red meat, in particular, is an important source of micronutrients with anticancer properties, including selenium, vitamin B6 and B12, and vitamin D. Adjusting the balance between meat and other dietary components may be critical to protecting against potential cancer risks.

Cancer incidence in British vegetarians

Background:

Few prospective studies have examined cancer incidence among vegetarians.

Methods:

We studied 61 566 British men and women, comprising 32 403 meat eaters, 8562 non-meat eaters who did eat fish (‘fish eaters’) and 20 601 vegetarians. After an average follow-up of 12.2 years, there were 3350 incident cancers of which 2204 were among meat eaters, 317 among fish eaters and 829 among vegetarians. Relative risks (RRs) were estimated by Cox regression, stratified by sex and recruitment protocol and adjusted for age, smoking, alcohol, body mass index, physical activity level and, for women only, parity and oral contraceptive use.

Results:

There was significant heterogeneity in cancer risk between groups for the following four cancer sites: stomach cancer, RRs (compared with meat eaters) of 0.29 (95% CI: 0.07–1.20) in fish eaters and 0.36 (0.16–0.78) in vegetarians, P for heterogeneity=0.007; ovarian cancer, RRs of 0.37 (0.18–0.77) in fish eaters and 0.69 (0.45–1.07) in vegetarians, P for heterogeneity=0.007; bladder cancer, RRs of 0.81 (0.36–1.81) in fish eaters and 0.47 (0.25–0.89) in vegetarians, P for heterogeneity=0.05; and cancers of the lymphatic and haematopoietic tissues, RRs of 0.85 (0.56–1.29) in fish eaters and 0.55 (0.39–0.78) in vegetarians, P for heterogeneity=0.002. The RRs for all malignant neoplasms were 0.82 (0.73–0.93) in fish eaters and 0.88 (0.81–0.96) in vegetarians (P for heterogeneity=0.001).

Conclusion:

The incidence of some cancers may be lower in fish eaters and vegetarians than in meat eaters.

Development of estimates of dietary nitrates, nitrites, and nitrosamines for use with the Short Willet Food Frequency Questionnaire

BACKGROUND

Studies have suggested that nitrates, nitrites, and nitrosamines have an etiologic role in adverse pregnancy outcomes and chronic diseases such as cancer. Although an extensive body of literature exists on estimates of these compounds in foods, the extant data varies in quality, quantified estimates, and relevance.

METHODS

We developed estimates of nitrates, nitrites, and nitrosamines for food items listed in the Short Willet Food Frequency Questionnaire (WFFQ) as adapted for use in the National Birth Defects Prevention Study. Multiple reference databases were searched for published literature reflecting nitrate, nitrite, and nitrosamine values in foods. Relevant published literature was reviewed; only publications reporting results for items listed on the WFFQ were selected for inclusion. The references selected were prioritized according to relevance to the U.S. population.

RESULTS

Based on our estimates, vegetable products contain the highest levels of nitrate, contributing as much as 189 mg/serving. Meat and bean products contain the highest levels of nitrites with values up to 1.84 mg/serving. Alcohol, meat and dairy products contain the highest values of nitrosamines with a maximum value of 0.531 microg/serving. The estimates of dietary nitrates, nitrites, and nitrosamines generated in this study are based on the published values currently available.

CONCLUSION

To our knowledge, these are the only estimates specifically designed for use with the adapted WFFQ and generated to represent food items available to the U.S. population. The estimates provided may be useful in other research studies, specifically in those exploring the relation between exposure to these compounds in foods and adverse health outcomes.

Human exposure to selected animal neurocarcinogens: a biomarker-based assessment and implications for brain tumor epidemiology

This review is based on the proceedings from the Second Lebow Conference, held in Chicago in 2007. The conference concentrated on developing a framework for innovative studies in the epidemiology of environmental exposures, focusing specifically on the potential relationship with brain tumors. Researchers with different perspectives, including toxicology, pharmacokinetics, and epidemiological exposure assessment, exchanged information and ideas on the use of biomarkers of exposure in molecular epidemiology studies and summarized the current knowledge on methods and approaches for biomarker-based exposure assessment. This report presents the state of science regarding biomarker-based exposure assessment of the four most common neurocarcinogens: acrylamide, 1,3-butadiene, N-nitroso compounds, and polycyclic aromatic hydrocarbons. Importantly, these chemicals are also carcinogenic in other organs; therefore, this discussion is useful for environmental epidemiologists studying all cancer types.

Intakes of red meat, processed meat, and meat mutagens increase lung cancer risk

Red and processed meat intake may increase lung cancer risk. However, the epidemiologic evidence is inconsistent and few studies have evaluated the role of meat mutagens formed during high cooking temperatures. We investigated the association of red meat, processed meat, and meat mutagen intake with lung cancer risk in Environment And Genetics in Lung cancer Etiology, a population-based case-control study. Primary lung cancer cases (n = 2,101) were recruited from 13 hospitals within the Lombardy region of Italy examining approximately 80% of the cases from the area. Noncancer population controls (n = 2,120), matched to cases on gender, residence, and age, were randomly selected from the same catchment area. Diet was assessed in 1,903 cases and 2,073 controls and used in conjunction with a meat mutagen database to estimate intake of heterocyclic amines (HCA) and benzo(a)pyrene (BaP). Multivariable odds ratios (OR) and 95% confidence intervals (95% CI) for sex-specific tertiles of intake were calculated using unconditional logistic regression. Red and processed meat were positively associated with lung cancer risk (highest-versus-lowest tertile: OR, 1.8; 95% CI, 1.5-2.2; P trend < 0.001 and OR, 1.7; 95% CI, 1.4-2.1; P trend < 0.001, respectively); the risks were strongest among never smokers (OR, 2.4; 95% CI, 1.4-4.0; P trend = 0.001 and OR, 2.5; 95% CI, 1.5-4.2; P trend = 0.001, respectively). HCAs and BaP were significantly associated with increased risk of lung cancer. When separated by histology, significant positive associations for both meat groups were restricted to adenocarcinoma and squamous cell carcinoma but not small cell carcinoma of the lung. In summary, red meat, processed meat, and meat mutagens were independently associated with increased risk of lung cancer.

Determinants of whether or not mixtures of disinfection by-products are similar

Reactive chemicals have been used to disinfect drinking waters for over a century. In the 1970s, it was first observed that the reaction of these chemicals with the natural organic matter (NOM) in source waters results in the production of variable, complex mixtures of disinfection by-products (DBP). Because limited toxicological and epidemiological data are available to assess potential human health risks from complex DBP mixture exposures, methods are needed to determine when health effects data on a specific DBP mixture may be used as a surrogate for evaluating another environmental DBP mixture of interest. Before risk assessors attempt such efforts, a set of criteria needs to be in place to determine whether two or more DBP mixtures are similar in composition and toxicological potential. This study broadly characterizes the chemical and toxicological measures that may be used to evaluate similarities among DBP mixtures. Variables are discussed that affect qualitative and quantitative shifts in the types of DBP that are formed, including disinfectants used, their reactions with NOM and with bromide/iodide, pH, temperature, time, and changes in the water distribution system. The known toxicological activities of DBP mixtures and important single DBPs are also presented in light of their potential for producing similar toxicity. While DBP exposures are associated with a number of health effects, this study focuses on (1) mutagenic activity of DBP mixtures, (2) DBP cancer epidemiology, and (3) toxicology studies to evaluate similarity among DBP mixtures. Data suggest that further chemical characterization of DBP mixtures and more systematic study of DBP toxicology will improve the quality and usefulness of similarity criteria.

Mechanisms of nitrosamine-mediated neurodegeneration: potential relevance to sporadic Alzheimer's disease

Streptozotocin (STZ) is a nitrosamine-related compound that causes Alzheimer's disease (AD)-type neurodegeneration with cognitive impairment, brain insulin resistance, and brain insulin deficiency. Nitrosamines and STZ mediate their adverse effects by causing DNA damage, oxidative stress, lipid peroxidation, pro-inflammatory cytokine activation, and cell death, all of which occur in AD. We tested the hypothesis that exposure to N-nitrosodiethylamine (NDEA), which is widely present in processed/preserved foods, causes AD-type molecular and biochemical abnormalities in central nervous system (CNS) neurons. NDEA treatment of cultured post-mitotic rat CNS neurons (48 h) produced dose-dependent impairments in ATP production and mitochondrial function, and increased levels of 8-hydroxy-2'-deoxyguanosine, 4-hydroxy-2-nonenal, phospho-tau, amyloid-beta protein precursor-amyloid-beta (A beta PP-A beta), and ubiquitin immunoreactivity. These effects were associated with decreased expression of insulin, insulin-like growth factor (IGF)-I, and IGF-II receptors, and choline acetyltransferase. Nitrosamine exposure causes neurodegeneration with a number of molecular and biochemical features of AD including impairments in energy metabolism, insulin/IGF signaling mechanisms, and acetylcholine homeostasis, together with increased levels of oxidative stress, DNA damage, and A beta PP-A beta immunoreactivity. These results suggest that environmental exposures and food contaminants may play critical roles in the pathogenesis of sporadic AD.

Dietary intake of meat and meat-derived heterocyclic aromatic amines and their correlation with DNA adducts in female breast tissue

It was the aim of this study to examine the association of the consumption of meat in general, meat prepared by different cooking methods and the dietary intake of heterocyclic aromatic amines (HCA) with the level of DNA adducts in the breast tissue of women undergoing reduction mammoplasty. Dietary intake of meat and HCA were assessed via questionnaire in 44 women undergoing reduction mammoplasty. DNA adduct analysis in breast tissue was performed by (32)P-postlabelling analysis. Spearman rank correlation coefficients (r) were calculated to examine the association of meat consumption and dietary HCA intake with tissue DNA adduct levels. A median DNA adduct level of 18.45 (interquartile range 12.81-25.65) per 10(9) nucleotides in breast tissue was observed; median HCA intake was 40.43 ng/day (interquartile range 19.55-102.33 ng/day). Total HCA intake (r = 0.33, P = 0.03), consumption of fried meat (r = 0.39, P = 0.01), beef (r = 0.32, P = 0.03) and processed meat (r = 0.51, P = 0.0004) were statistically significantly correlated with the level of DNA adducts in breast tissue. The detected DNA adducts could not be confirmed to be specific HCA-derived DNA adducts by comparison with external standards, using the (32)P-postlabelling assay. We observed strong correlations of dietary HCA intake and consumption of fried and processed meat with DNA adduct levels in breast tissue of 44 women. Since the detected DNA adducts were not necessarily specific only for HCA, it is possible that HCA intake is a surrogate of other genotoxic substances, such as polycyclic aromatic hydrocarbons, in meat prepared at high temperatures.

Potential role of tryptophan derivatives in stress responses characterized by the generation of reactive oxygen and nitrogen species

To face physicochemical and biological stresses, living organisms evolved endogenous chemical responses based on gas exchange with the atmosphere and on formation of nitric oxide (NO(*)) and oxygen derivatives. The combination of these species generates a complex network of variable extension in space and time, characterized by the nature and level of the reactive oxygen (ROS) and nitrogen species (RNS) and of their organic and inorganic scavengers. Among the latter, this review focusses on natural 3-substituted indolic structures. Tryptophan-derived indoles are unsensitive to NO(*), oxygen and superoxide anion (O(2)(*-)), but react directly with other ROS/RNS giving various derivatives, most of which have been characterized. Though the detection of some products like kynurenine and nitroderivatives can be performed in vitro and in vivo, it is more difficult for others, e.g., 1-nitroso-indolic compounds. In vitro chemical studies only reveal the strong likelihood of their in vivo generation and biological effects can be a sign of their transient formation. Knowing that 1-nitrosoindoles are NO donors and nitrosating agents indicating they can thus act both as mutagens and protectors, the necessity for a thorough evaluation of indole-containing drugs in accordance with the level of the oxidative stress in a given pathology is highlighted.

Irradiated Chinese Rugao ham: Changes in volatile N-nitrosamine, biogenic amine and residual nitrite during ripening and post-ripening

N-nitrosamines, biogenic amines and residual nitrite are harmful substances and often present in cured meat. The effects of gamma-irradiation (γ-irradiation) on these chemicals in dry-cured Chinese Rugao ham during ripening and post-ripening were investigated. Rugao hams were irradiated at a dose of 5kGy before ripening and were then ripened in an aging loft. Although γ-irradiation degraded tyramine, putrescine and spermine, on the other hand, it promoted the formation of spermidine, phenylethylamine, cadaverine and tryptamine. Residual nitrite was significantly reduced by γ-irradiation. N-nitrosodimethylamine (NDMA), N-nitrosodiethylamine (NDEA) and N-nitrosopyrrolidine (NPYR) were found in Chinese Rugao ham during ripening and post-ripening but could be degraded with γ-irradiation. The results suggest that γ-irradiation may be a potential decontamination measure for certain chemical compounds found in dry-cured meat.

Os nitritos são importantes na gênese do adenocarcinoma associado ao esôfago de Barrett?

RACIONAL: O esôfago de Barrett é complicação do refluxo gastroesofágico e predispõe ao surgimento do adenocarcinoma, sendo que vários fatores têm sido relacionados à sua etiopatogenia. OBJETIVO: Analisar o modelo experimental de refluxo duodenogastroesofágico e a ingestão de solução de nitrito de sódio na gênese do adenocarcinoma associado ao esôfago de Barrett. MÉTODOS: Sessenta ratos machos Wistar foram divididos em quatro grupos, com 20 animais controles não operados (10 animais ingeriram somente água e 10 água mais solução de nitrito de sódio) e 40 animais submetidos à anastomose duodenogastroesofágica látero-lateral (20 animais ingeriram somente água e 20 animais ingeriram água mais solução de nitrito de sódio). A ocorrência de esofagite, metaplasia, displasia, esôfago de Barrett e adenocarcinoma associado foram analisados. A classificação de Viena para displasia e adenocarcinoma foi empregada na análise dos resultados. RESULTADOS: Após 42 semanas de observação, nos animais operados sem ingestão de nitritos o esôfago de Barrett foi registrado em 26,3% (5/19), enquanto no grupo operado associado à ingestão de nitritos, foi encontrado em 72,3% (13/18) dos animais, sendo que neste grupo também foi encontrado seis adenocarcinomas (33,3%). Nenhum animal não operado apresentou o esôfago de Barrett. As categorias 2, 3 e 5 da classificação de Viena somente foram encontradas nos animais operados que ingeriram nitrito de sódio (66,7%). CONCLUSÃO: A ingestão de nitrito de sódio associado ao refluxo duodenogastroesofágico têm importante participação na gênese do adenocarcinoma associado ao esôfago de Barrett.

Nutrition and Mutagenesis

Diet-related mutagenesis plays an etiologic role in chronic diseases, including cardiovascular disease and cancer. Many dietary mutagens are DNA reactive, leading to distinct spectra of base-pair substitution mutations and structural chromosome changes. Examples include aflatoxin B1, ochratoxin A, ptaquiloside, various pyrrolizidine alkaloids, heterocyclic amines including 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine, and polycyclic aromatic hydrocarbons such as benzo[a]pyrene. However, endogenously or exogenously formed reactive species, inhibitors of topoisomerase II enzymes (e.g., flavonoids), of DNA repair (e.g., caffeine), or of the mitotic spindle (possibly acrylamide), also cause mutations, including structural chromosome changes and copy number variants. Genomic instability also results from inadequate nutrient intake (e.g., folate and selenium). Antimutagens include vitamin C, carotenoids, chlorophyllin, dietary fibers, and plant polyphenols acting through various mechanisms. Polymorphisms in genes for nutrient uptake, metabolism, and excretion will affect dietary intake in determining individual risk of disease development. Human studies utilizing nutrigenomic/nutrigenetic technologies will be essential to quantifying and overcoming diet-related mutagenesis.

Processed meat and colorectal cancer: a review of epidemiologic and experimental evidence

Processed meat intake may be involved in the etiology of colorectal cancer, a major cause of death in affluent countries. The epidemiologic studies published to date conclude that the excess risk in the highest category of processed meat-eaters is comprised between 20% and 50% compared with non-eaters. In addition, the excess risk per gram of intake is clearly higher than that of fresh red meat. Several hypotheses, which are mainly based on studies carried out on red meat, may explain why processed meat intake is linked to cancer risk. Those that have been tested experimentally are (i) that high-fat diets could promote carcinogenesis via insulin resistance or fecal bile acids; (ii) that cooking meat at a high temperature forms carcinogenic heterocyclic amines and polycyclic aromatic hydrocarbons; (iii) that carcinogenic N-nitroso compounds are formed in meat and endogenously; (iv) that heme iron in red meat can promote carcinogenesis because it increases cell proliferation in the mucosa, through lipoperoxidation and/or cytotoxicity of fecal water. Nitrosation might increase the toxicity of heme in cured products. Solving this puzzle is a challenge that would permit to reduce cancer load by changing the processes rather than by banning processed meat.

Human germline and somatic cells have similar TP53 and Kirsten-RAS gene single base mutation frequencies

Understanding the risk of offspring inheriting rare mutations, and the frequencies at which these mutations are present in germ cells can be explored with direct analysis of human semen samples. The present work utilized the ultrasensitive PCR/RE/LCR mutation assay to detect, identify and determine the prevalence single base substitution mutations in the TP53 and KRAS genes in human sperm. Four disease-associated base sites in the TP53 and KRAS genes, three of which are known to be heritable to live, term offspring, were studied in sperm from eleven human semen specimens. Eight of the specimens (73%) displayed single base substitution mutations, and 30% of all base sites tested were found to harbor mutations ranging in prevalence from 1 x 10(-6) to 1 x 10(-5) wild type sperm. These germ cell single base substitution mutation frequencies are very similar to somatic tissue TP53 and KRAS mutation frequencies. Equivalent single base mutation frequencies in both germ and somatic cells suggest that there is no unusual selection or mutation protective process operating premeiotically in the germline, and that a selection bias at the level of sperm viability, conception, early cleavage, implantation, and/or embryogenesis operates to exclude the majority of these TP53 mutations and all of the activating KRAS mutations.

Associations between beer, wine, and liquor consumption and lung cancer risk: a meta-analysis

OBJECTIVE

Epidemiologic studies suggest that the effect on lung cancer risk may be different for beer, wine, and liquor. We conducted dose-specific meta-analyses and dose-response meta-regression to summarize findings from the current literature on the association between consumption of beer, wine, or liquor and lung cancer risk.

RESULTS

Average beer consumption of one drink or greater per day was associated with an increased risk of lung cancer [relative risk (RR), 1.23; 95% confidence interval (95% CI), 1.06-1.41]. This association was observed in both men and women, although it was only significant in men. A J-shaped dose-response curve was suggested for beer intake. An inverse association was observed for both average wine consumption of less than one drink per day (RR, 0.77; 95% CI, 0.59-1.00) and one drink or greater per day (RR, 0.78; 95% CI, 0.60-1.02) in the drinking range incurred in the source studies. Average liquor consumption of one drink or greater per day was found to be associated with increased risk in men (RR, 1.33; 95% CI, 1.10-1.62). No association was observed for liquor drinking in women. The presence of heterogeneity between studies was detected. Study design, country, gender, adjustment factors, and lung cancer histologic type were not significant predictors of the heterogeneity.

CONCLUSIONS

The results from this meta-analysis suggest that high consumption of beer and liquors may be associated with increased lung cancer risk, whereas modest wine consumption may be inversely associated with risk. More research with improved control of confounding is needed to confirm these findings and to establish the dose-response relationship, particularly risk at high consumption levels.

Rapid reduction of N-nitrosamine disinfection byproducts in water with hydrogen and porous nickel catalysts

There is a need for new technologies to rapidly and economically treatwater contaminated with N-nitrosodimethylamine (NDMA) and related compounds because of their high toxicity and recent detection in drinking water sources as a consequence of industrial releases and chlorine disinfection of wastewater effluent Treatment of N-nitrosamines with H2 in conjunction with a high surface area porous nickel material, a model nonprecious metal catalyst, has been evaluated. Experiments show that NDMA is reduced rapidly and catalytically to dimethylamine and N2 (e.g., t1/2 = 1.5 min for 500 mg/L catalyst and PH2 = 1 atm), and kinetic trends are consistent with a surface-mediated mechanism involving scission of the N-nitrosamine N-N bond and subsequent reactions with adsorbed atomic hydrogen. The metal-loading-normalized pseudo-first-order rate constant (77.9 +/- 13.1 L g(Ni)(-1) h(-1)) exceeds values reported for Pd-based catalysts. Several related N-nitrosamines react at rates similar to those of NDMA, indicating a weak dependence on structure. The reaction rates for NDMA reduction are not significantly affected by changing pH, and the presence of high concentrations of many common water constituents (Na+, Ca2+, Mg2+, Cl-, SO4(2-), HCO(3-), and NOM) exerts only a small effect on reaction rates. Nitrate is also reduced by the Ni catalyst, and high nitrate concentrations competitively inhibit the reduction of NDMA. (Bi)sulfide poisons the catalyst by strong chemisorption to the Ni surface. Cost-normalized rate constants for the Ni catalyst are highly favorable compared to Pd-based catalysts, indicating that, with further development, Ni-based catalysts may become attractive alternatives to precious metal catalysts.

Prospective study of cured meats consumption and risk of chronic obstructive pulmonary disease in men

Cured meats are high in nitrites. Nitrites generate reactive nitrogen species that may cause damage to the lung. The objective is to assess the relation between frequent consumption of cured meats and the risk of newly diagnosed chronic obstructive pulmonary disease (COPD). Between 1986 and 1998, the authors identified 111 self-reported cases of newly diagnosed COPD among 42,915 men from the Health Professionals Follow-up Study. The cumulative average intake of cured meats consumption (processed meats, bacon, hot dogs) was calculated from food frequency questionnaires administrated in 1986, 1990, and 1994 and divided according to servings per week (never/almost never, <1 serving/week, 1-3 servings/week, 4-6 servings/week, at least once/day). After adjustment for age, smoking status, pack-years, pack-years squared, energy intake, race/ethnicity, US region, body mass index, and physical activity, the consumption of cured meats was positively associated with the risk of newly diagnosed COPD (for highest vs. lowest intake: relative risk = 2.64, 95% confidence interval: 1.39, 5.00; p(trend) = 0.002). In contrast to these findings, the consumption of cured meats was not associated with the risk of adult-onset asthma. These data suggest that cured meat may worsen the adverse effects of smoking on risk of COPD.

Meat consumption and cancer risk

The authors review the key studies on the association between meat intake and cancer risk, including a new prospective cohort study by Amanda Cross and colleagues published inPLoS Medicine.

Current incidence of N-nitrosodimethylamine in beers worldwide

A range of beers (n = 138) from 42 countries were analysed for the presence of N-nitrosodimethylamine (NDMA) using a chemiluminescence technique with a limit of quantification of 0.1 microg L(-1). The overwhelming majority of samples (79%) did not contain detectable NDMA, and only three samples exceeded 0.5 microg L(-1). No association was found between NDMA content and beer strength, type or geographical origin. It was noted that water can be a potential source of NDMA in beverages.

Acetylation and nitrosation of ciprofloxacin by environmental strains of mycobacteria

To determine the ability of environmental bacteria to metabolize the frequently prescribed fluoroquinolone drug ciprofloxacin, eight Mycobacterium spp. cultures were grown for 4 days in a medium containing sorbitol and yeast extract with 100 mg x L(-1) ciprofloxacin. After the cultures had been centrifuged and the supernatants extracted with ethyl acetate, two metabolites were purified by using high-performance liquid chromatography. They were identified with liquid chromatography/electrospray ionization mass spectrometry and proton nuclear magnetic resonance spectroscopy. Ciprofloxacin was transformed to both N-acetylciprofloxacin (2.5%-5.5% of the total peak area at 280 nm) and N-nitrosociprofloxacin (6.0%-8.0% of the peak area) by Mycobacterium gilvum PYR-GCK and Mycobacterium sp. PYR100 but it was transformed only to N-acetylciprofloxacin by Mycobacterium frederiksbergense FAn9, M. gilvum ATCC 43909, M. gilvum BB1, Mycobacterium smegmatis mc2155, Mycobacterium sp. 7E1B1W, and Mycobacterium sp. RJGII-135. The results suggest that biotransformation may serve as a ciprofloxacin resistance mechanism for these bacteria.

Carcinogenic food contaminants

A large number of scientific studies and reviews have addressed the potential for dietary components to influence the risk of developing cancer. One topic of particular interest has been the impact of food contaminants. Two complementary programs, among others, have reviewed and synthesized information on the carcinogenic potential of food contaminants and judged the degree of evidence linking different food contaminants to the risk of cancer in humans. These programs, the International Agency for Research on Cancer's IARC Monographs on the Evaluation of Carcinogenic Risks to Humans and the US National Toxicology Program's Report of Carcinogens have reviewed hundreds of chemicals, mixtures, and natural products and then graded the cancer risk posed to humans. Contaminants with the highest level of evidence include aflatoxin, alcoholic beverages, 2,3,7,8-tetracholordibenzo-p-dioxin. Agents with a moderate level of evidence include acetaldehyde, polycyclic aromatic hydrocarbons, some nitrosamines, and yerba mate. Agents with a low level of evidence include bracken fern, fumonsin B(1), ochratoxin, and others. This review presents a summary of the evidence for the carcinogenicity of these and other agents and the ranks provided by two important assessment programs.

Involvement of Escherichia coli DNA polymerase IV in tolerance of cytotoxic alkylating DNA lesions in vivo

Escherichia coli PolIV, a DNA polymerase capable of catalyzing synthesis past replication-blocking DNA lesions, belongs to the most ubiquitous branch of Y-family DNA polymerases. The goal of this study is to identify spontaneous DNA damage that is bypassed specifically and accurately by PolIV in vivo. We increased the amount of spontaneous DNA lesions using mutants deficient for different DNA repair pathways and measured mutation frequency in PolIV-proficient and -deficient backgrounds. We found that PolIV performs an error-free bypass of DNA damage that accumulates in the alkA tag genetic background. This result indicates that PolIV is involved in the error-free bypass of cytotoxic alkylating DNA lesions. When the amount of cytotoxic alkylating DNA lesions is increased by the treatment with chemical alkylating agents, PolIV is required for survival in an alkA tag-proficient genetic background as well. Our study, together with the reported involvement of the mammalian PolIV homolog, Polkappa, in similar activity, indicates that Y-family DNA polymerases from the DinB branch can be added to the list of evolutionarily conserved molecular mechanisms that counteract cytotoxic effects of DNA alkylation. This activity is of major biological relevance because alkylating agents are continuously produced endogenously in all living cells and are also present in the environment.

Analysis of nitrosamines by capillary electrospray-high-field asymmetric waveform ion mobility spectrometry-MS with programmed compensation voltage

Emerging disinfection by-products (DBPs) in drinking water are an important public health concern. Certain DBPs, such as nitrosamines, are probable carcinogens, and exposure to halogenated DBPs may lead to birth defects. It is difficult to obtain complete separation of nitrosamines by chromatographic techniques. Thus we explored high-field asymmetric waveform ion mobility spectrometry (FAIMS) as an alternative separation technique for the characterization of individual DBPs in a complex matrix. We first used ESI-FAIMS-MS to separate four nitrosamines: N-nitrosodi-n-butylamine (NDBA), N-nitrosodi-n-propylamine (NDPA), N-nitrosopiperidine (NPip), and N-nitrosodiethylamine (NDEA) in the compensation voltage (CV) spectra. The optimal CVs with a fixed dispersion voltage of -4000 V were found to be -1.2 V (NDBA), 2.7 V (NDPA), 7.5 V (NPip) and 10.1 V (NDEA). In addition, FAIMS-MS effectively reduced the chemical noise and dramatically improved the LODs by as much as tenfold compared to the conventional ESI-MS technique. To further improve sensitivity, an on-line CE system was used in combination with FAIMS-MS to take advantage of the higher ionization efficiency. The calibration curves for the four nitrosamines were linear over a range of 5 ng/mL to 1000 ng/mL with an r(2 )value of 0.9929 to 0.9992. To increase sample throughput, a multiple-injection strategy was developed, in which the CV values were preprogrammed so that the FAIMS device allowed different nitrosamines to pass through at selected time windows. The potential application of the proposed method was demonstrated for the analysis of drinking water samples spiked with nitrosamines.

Meat and dairy consumption and subsequent risk of prostate cancer in a US cohort study

OBJECTIVE

To evaluate the association of meat and dairy food consumption with subsequent risk of prostate cancer.

METHODS

In 1989, 3,892 men 35+ years old, who participated in CLUE II study of Washington County, MD, completed an abbreviated Block food frequency questionnaire. Intake of meat and dairy related foods was calculated using consumption frequency and portion size. Incident prostate cancer cases (n = 199) were ascertained through October 2004. Cox proportional hazards regression was used to calculate hazard ratios (HR) of total and advanced (SEER states three and four; n = 54) prostate cancer and 95% confidence intervals (CI) adjusted for age, BMI at age 21, and intake of energy, saturated fat, and tomato products.

RESULTS

Intakes of total mean (HR = 0.90, 95% CI 0.60-1.33, comparing highest to lowest tertile) and red meat (HR = 0.87, 95% CI 0.59-1.32) were not statistically significantly associated with prostate cancer. However, processed meat consumption was associated with a non-statistically significant higher risk of total (5+ vs. < or =1 servings/week: HR = 2.24; 95% CI 0.90-5.59) prostate cancer. There was no association across tertiles of dairy or calcium with total prostate cancer, although compared tp < or =1 servings/week consumption of 5+ servings/week of dairy foods was associated with an increased risk of prostate cancer (HR = 1.65, 98% CI 1.02-2.66).

CONCLUSION

Overall, consumption of processed meat, but not total meat or red meat, was associated with a possible increased risk of total prostate cancer in this prospective study. Higher intake of dairy foods but not calcium was positively associated with prostate cancer. Further investigation into the mechanisms by which processed meat and dairy consumption might increase the risk of prostate cancer is suggested.

Prospective study of intake of fruit, vegetables, and carotenoids and the risk of adult glioma

BACKGROUND

Nutrients in dietary fruit and vegetables have been hypothesized to lower the risk of glioma by reducing the endogenous formation of N-nitroso compounds. Studies examining fruit and vegetable consumption and brain tumors have relied on case-control study designs, with one exception, and results have been inconsistent.

OBJECTIVE

We prospectively examined the relation between consumption of fruit and vegetables (and specifically carotenoids) and the risk of glioma among men and women in 3 large US cohort studies: the Health Professionals Follow-Up Study (HPFS), the Nurses' Health Study I (NHS I), and NHS II.

DESIGN

Dietary intake was assessed by food-frequency questionnaires obtained at baseline and updated every 4 y through 2002 (HPFS and NHS I) or 2003 (NHS II). We identified 296 incident adult gliomas during 3 669 589 person-years of follow-up. Cox proportional hazard models were used to estimate incidence rate ratios (RR) and 95% CIs between intake of fruit, vegetables, and carotenoids and glioma risk, with adjustment for age and total caloric intake.

RESULTS

Updated average consumption of total fruit and vegetables was not significantly associated with glioma risk in the men and women (pooled multivariate RR in a comparison of the highest with the lowest quintile: 1.12; 95% CI: 0.74, 1.69). Other fruit and vegetable subgroups, individual fruit and vegetables, and 5 major carotenoids were not significantly associated with risk of glioma.

CONCLUSION

Our findings suggest that fruit, vegetable, and carotenoid consumption is not likely associated strongly with the risk of adult glioma.

N-Nitrosation of Amines by NO2 and NO: A Theoretical Study

Gas-phase nitrosation of amines implies a nonionic pathway different from the nitrosonium nitrosation via acidification of nitrite. Electronic structure calculations discussed in this work suggest a free radical mechanism, in which NO2 abstracts a hydrogen atom from the nitrogen in primary and secondary amines to form an intermediate complex of an aminyl radical and nitrous acid. The aminyl radical intermediate is then quenched by nitric oxide, leading to the formation of nitrosamine. High-level calculations (CBS-QB3) show that alkyl substitutions on amines can activate the H-abstraction reaction. Thus, while H-abstraction from NH3 was found to exhibit a reaction barrier (DeltaH) of 106 kJ/mol, similar calculations indicate that the corresponding barriers decrease to 72 and 45 kJ/mol for methylamine and dimethylamine, respectively. Heterocyclic secondary amines have also been investigated in a similar manner. The five-membered-ring (5-m-r) amine appears to be the most reactive: pyrrolidine (DeltaH=30 kJ/mol), azetidine (DeltaH=44 kJ/mol), piperidine (DeltaH=44 kJ/mol), and aziridine (DeltaH=74 kJ/mol). The reaction barrier for 1H-pyrrole, an aromatic 5-m-r secondary amine, was found to be 59 kJ/mol. The origin of the high activity for the 5-m-r alkylamine stems from a hydrogen-bond-like interaction between the aminyl radical and the nascent nitrous acid molecule. This theoretical study suggests that, in the presence of nitrogen oxides, the gas-phase nitrosation of secondary amines is feasible.

Dietary intake of different types and characteristics of processed meat which might be associated with cancer risk – results from the 24-hour diet recalls in the European Prospective Investigation into Cancer and Nutrition (EPIC)

Objective

There is increasing evidence for a significant effect of processed meat (PM) intake on cancer risk. However, refined knowledge on how components of this heterogeneous food group are associated with cancer risk is still missing. Here, actual data on the intake of PM subcategories is given; within a food-based approach we considered preservation methods, cooking methods and nutrient content for stratification, in order to address most of the aetiologically relevant hypotheses.

Design and setting

Standardised computerised 24-hour diet recall interviews were collected within the framework of the European Prospective Investigation into Cancer and Nutrition (EPIC), a prospective cohort study in 27 centres across 10 European countries.

Subjects

Subjects were 22 924 women and 13 031 men aged 35–74 years.

Results

Except for the so-called ‘health-conscious’ cohort in the UK, energy-adjusted total PM intake ranged between 11.1 and 47.9 g day−1 in women and 18.8 and 88.5 g day−1 in men. Ham, salami-type sausages and heated sausages contributed most to the overall PM intake. The intake of cured (addition of nitrate/nitrite) PM was highest in the German, Dutch and northern European EPIC centres, with up to 68.8 g day−1 in men. The same was true for smoked PM (up to 51.8 g day−1). However, due to the different manufacturing practice, the highest average intake of NaNO2 through PM consumption was found for the Spanish centres (5.4 mg day−1 in men) as compared with German and British centres. Spanish centres also showed the highest intake of NaCl-rich types of PM; most cholesterol- and iron-rich PM was consumed in central and northern European centres. Possibly hazardous cooking methods were more often used for PM preparation in central and northern European centres.

Conclusions

We applied a food-based categorisation of PM that addresses aetiologically relevant mechanisms for cancer development and found distinct differences in dietary intake of these categories of PM across European cohorts. This predisposes EPIC to further investigate the role of PM in cancer aetiology.

Parental alcohol consumption and childhood cancers: a review

The etiology of childhood cancers remains generally unknown. Given that the metabolites of alcohol are likely carcinogens and that leukemia, the most frequent childhood cancer, can arise in utero, the study of alcohol consumption as a potential risk factor for the development of childhood cancer is justified. This article summarizes the epidemiological evidence on the association between parental exposure to alcohol and the risk of childhood cancers. To do this, a thorough search of the literature from 1960 to 2003 using the PubMed database was carried out. It yielded 33 case-control studies published between 1982 and 2003, including 13 studies that considered paternal exposure in the preconceptional period. In 10 of the 33 studies at least 1 statistically significant risk increase was reported in relation with parental alcohol consumption; in 7 of these studies the increase was related to maternal consumption, whereas in 3 studies, it was related to paternal consumption. The cancers most often found associated with parental drinking were leukemia, brain tumors, and neuroblastoma. A few studies also reported a protective effect with maternal exposure at modest levels. Inconsistencies in the results and the low risks reported do not suggest an association between childhood cancer and parental consumption of alcohol. However, before reaching any definitive conclusions, methodological issues need to be addressed in future studies, as well as the role of genetic susceptibility. Moreover, subtypes of specific cancers need to be studied separately.

Genotoxic and carcinogenic risk to humans of drug-nitrite interaction products

The large majority of N-nitroso compounds (NOC) have been found to produce genotoxic effects and to cause tumor development in laboratory animals; four NOC have been classified by the International Agency for Research on Cancer (IARC) as probably and another 15 as possibly carcinogenic to humans. A considerable fraction of drugs are theoretically nitrosatable due to the presence of amine, amide or other groups which by reacting with nitrite in the gastric environment, or even in other sites, can give rise to the formation of NOC, and in some cases other reactive species. This review provides a synthesis of information on the chemistry of NOC formation, the carcinogenic activity of NOC in animals and humans and the inhibitors of nitrosation reactions. It contains information on the drugs which have been tested for the formation of NOC by reaction with nitrite and the genotoxic-carcinogenic effects of their nitrosation products. In an extensive search we have found that 182 drugs, representing a wide variety of chemical structures and therapeutic activities, were examined in various experimental conditions for their ability to react with nitrite, and 173 (95%) of them were found to form NOC or other reactive species. Moreover, 136 drugs were examined in short-term genotoxicity tests and/or in long-term carcinogenesis assays, either in combination with nitrite or using their nitrosation product, in order to establish whether they produce genotoxic and carcinogenic effects; 112 (82.4%) of them have been found to give at least one positive response. The problem of endogenous drug nitrosation is largely unrecognized. Only a small fraction of theoretically nitrosatable drugs have been examined for the possible formation of genotoxic-carcinogenic NOC, guidelines for genotoxicity testing of pharmaceuticals do not indicate the need of performing the appropriate tests, and patients are not informed that the drug-nitrite interaction and the consequent risk can be reduced to a large extent by consuming the nitrosatable drug with ascorbic acid.

Transformation of the antibacterial agent norfloxacin by environmental mycobacteria

Because fluoroquinolone antimicrobial agents may be released into the environment, the potential for environmental bacteria to biotransform these drugs was investigated. Eight Mycobacterium sp. cultures in a sorbitol-yeast extract medium were dosed with 100 microg ml(-1) of norfloxacin and incubated for 7 days. The MICs of norfloxacin for these strains, tested by an agar dilution method, were 1.6 to 25 microg ml(-1). Cultures were extracted with ethyl acetate, and potential metabolites in the extracts were purified by high-performance liquid chromatography. The metabolites were identified using mass spectrometry and nuclear magnetic resonance spectroscopy. N-Acetylnorfloxacin (5 to 50% of the total absorbance at 280 nm) was produced by the eight Mycobacterium strains. N-Nitrosonorfloxacin (5 to 30% of the total absorbance) was also produced by Mycobacterium sp. strain PYR100 and Mycobacterium gilvum PYR-GCK. The MICs of N-nitrosonorfloxacin and N-acetylnorfloxacin were 2- to 38- and 4- to 1,000-fold higher, respectively, than those of norfloxacin for several different bacteria, including the two strains that produced both metabolites. Although N-nitrosonorfloxacin had less antibacterial activity, nitrosamines are potentially carcinogenic. The biotransformation of fluoroquinolones by mycobacteria may serve as a resistance mechanism.

Meat intake and bladder cancer risk in 2 prospective cohort studies

BACKGROUND

Nitrosamines, which are known bladder carcinogens, or their precursors are found in certain meat items, and concentrations of these compounds are especially high in bacon. Only 3 cohort studies, all with <100 case subjects, have examined the relation between meat intake and bladder cancer, and few studies have examined the relation of different meat types with bladder cancer.

OBJECTIVE

The aim was to examine the association between specific meat items and bladder cancer in 2 large prospective studies.

DESIGN

We analyzed data from 2 cohorts with up to 22 y of follow-up and 808 incident bladder cancer cases. Detailed data on meat were obtained from multiple food-frequency questionnaires administered over time. Multivariate relative risks (RRs) and 95% CIs were estimated by using Cox proportional hazards models with control for potential confounders, including detailed smoking history.

RESULTS

Men and women with a high intake of bacon (>/=5 servings/wk) had an elevated risk of bladder cancer compared with those who never ate bacon (multivariate RR = 1.59; 95% CI = 1.06, 2.37), although the overall association was not statistically significant (P for trend = 0.06). However, the association with bacon was stronger and became statistically significant after the removal of individuals who indicated having "greatly" changed their red meat (men) or bacon (women) intake during the 10 y before baseline (multivariate RR = 2.10; 95% CI = 1.24, 3.55; P for trend = 0.006). A positive association was also detected for intake of chicken without skin, but not for chicken with skin or for other meats, including processed meats, hot dogs, and hamburgers.

CONCLUSIONS

In these 2 cohorts combined, frequent consumption of bacon was associated with an elevated risk of bladder cancer. Other studies with data on specific meat items are necessary to confirm our findings.

A prospective study of dietary patterns, meat intake and the risk of gestational diabetes mellitus

AIMS/HYPOTHESIS

The aim of this study was to prospectively examine whether dietary patterns are related to risk of gestational diabetes mellitus (GDM).

METHODS

This prospective cohort study included 13,110 women who were free of cardiovascular disease, cancer, type 2 diabetes and history of GDM. Subjects completed a validated semi-quantitative food frequency questionnaire in 1991, and reported at least one singleton pregnancy between 1992 and 1998 in the Nurses' Health Study II. Two major dietary patterns (i.e. 'prudent' and 'Western') were identified through factor analysis. The prudent pattern was characterised by a high intake of fruit, green leafy vegetables, poultry and fish, whereas the Western pattern was characterised by high intake of red meat, processed meat, refined grain products, sweets, French fries and pizza.

RESULTS

We documented 758 incident cases of GDM. After adjustment for age, parity, pre-pregnancy BMI and other covariates, the relative risk (RR) of GDM, comparing the highest with the lowest quintile of the Western pattern scores, was 1.63 (95% CI 1.20-2.21; p (trend)=0.001), whereas the RR comparing the lowest with the highest quintile of the prudent pattern scores was 1.39 (95% CI 1.08-1.80; p (trend)=0.018). The RR for each increment of one serving/day was 1.61 (95% CI 1.25-2.07) for red meat and 1.64 (95% CI 1.13-2.38) for processed meat.

CONCLUSIONS/INTERPRETATION

These findings suggest that pre-pregnancy dietary patterns may affect women's risk of developing GDM. A diet high in red and processed meat was associated with a significantly elevated risk.

Protective effects of isothiocyanates towards N-nitrosamine-induced DNA damage in the single-cell gel electrophoresis (SCGE)/HepG2 assay

The aim of this study was to investigate the protective effect of isothiocyanates towards N-nitrosamine-induced DNA damage in the single-cell gel electrophoresis (SCGE)/HepG2 assay. None of the isothiocyanates (ITCs) concentrations tested in the presence or absence of formamidopyrimidine-DNA glycosylase (Fpg) caused DNA damage per se. Combined treatments of HepG2 cells with phenethyl isothiocyanate (PEITC), allyl isothiocyanate (AITC) or indol-3-carbinol (I3C) and N-nitrosopyrrolidine (NPYR) or N-nitrosodimethylamine (NDMA) reduced the genotoxic effects of the N-nitrosamines in a dose-dependent manner. The protective effect of the three ITCs tested was higher towards NPYR-induced oxidative DNA damage than against NDMA. The greatest protective effect towards NPYR-induced oxidative DNA damage was shown by I3C (1 microM, 79%) and by PEITC (1 microM, 67%) and I3C (1 microM, 61%) towards NDMA (in presence of Fpg enzyme). However, in absence of Fpg enzyme, AITC (1 microM, 72%) exerted the most drastic reduction towards NPYR-induced oxidative DNA damage, and PEITC (1 microM, 55%) towards NDMA. Our results indicate that ITCs protect human-derived cells against the DNA damaging effect of NPYR and NDMA, two carcinogenic compounds that occur in the environment.

Polymorphisms in O 6-methylguanine DNA methyltransferase and breast cancer risk

OBJECTIVE

Endogenous and exogenous estrogens influence breast cancer risk by interacting with estrogen receptor (ER). The O-methylguanine DNA methyltransferase (MGMT) gene has a dual role in repairing alkylation damage and in inhibiting ER-mediated cell proliferation. We assessed the two MGMT polymorphisms, Leu84Phe and Ile143Val, with breast cancer risk. We also evaluated the potential interactions between the two polymorphisms and estrogen-related risk factors and cigarette smoking on breast cancer risk.

METHODS

We conducted a nested case-control study within the Nurses' Health Study (1311 cases, 1760 controls).

RESULTS

Compared with the 84Leu/Leu genotype, the Phe/Phe genotype had a multivariate odds ratio (OR) of 1.68 (95% confidence interval (CI), 0.98-2.88). This positive association was magnified among postmenopausal women with body mass index>25 (OR, 3.01; 95% CI, 1.30-6.94), those in the highest tertile of pre-diagnostic plasma endogenous estradiol levels (Phe carriers versus non-carriers, OR, 2.42; 95% CI, 1.49-3.94), non-current postmenopausal hormone users (OR, 2.60; 95% CI, 1.19-5.64), and possibly estrogen receptor-positive cases (OR, 1.82; 95% CI, 0.99-3.35). We did not observe a main effect of the Ile143Val polymorphism or its interactions with these factors. No interaction was observed between either of the polymorphisms and cigarette smoking on breast cancer risk.

CONCLUSIONS

These data suggest that the Leu84Phe polymorphism affect the capacity of MGMT to inhibit estrogen receptor-mediated cell proliferation and is associated with breast cancer risk.

O6-Methylguanine-DNA Methyltransferase Leu84Phe and Ile143Val Polymorphisms and Risk of Colorectal Cancer in the Nurses’ Health Study and Physicians’ Health Study (United States)

OBJECTIVE

O6-methylguanine-DNA methyltransferase (MGMT) removes mutagenic adducts from the O6-position of guanine in DNA. Unrepaired O6-methylguanines result in G:C to A:T transitions in mutated K-ras and p53 in colorectal tumors. Two non-synonymous MGMT coding region variants, Leu84Phe and Ile143Val, lie in close proximity to the reactive 145Cys residue and to a conserved estrogen receptor interacting helix.

METHODS

We assessed the association between the MGMT Leu84Phe and Ile143Val polymorphisms and risk of colorectal cancer in two nested case-control studies: one each in the Nurses' Health Study (NHS) and the Physicians' Health Study (PHS) cohorts.

RESULTS

Among 197 female cases and 2,500 controls from the NHS, the variant 143Val allele was significantly associated with reduced risk of colorectal cancer [odds ratio (OR) = 0.52, 95% confidence interval (CI) 0.33-0.80]. In women, statistically significant gene-environment interactions were found between the Leu84Phe polymorphism and alcohol intake (P = 0.03), BMI (P = 0.04) and postmenopausal hormone use (P = 0.03). The Leu84Phe and Ile143Val polymorphisms were not significantly associated with risk of colorectal cancer among 271 male cases and 451 controls from the PHS.

CONCLUSIONS

Our results suggest that the common Leu84Phe and Ile143Val polymorphisms in MGMT influence risk of colorectal cancer in women possibly through modulating estrogen receptor-dependent transcriptional activation, which has previously been shown to occur in response to DNA alkylation damage.

Evaluation of occupational exposure to N-nitrosamines in a rubber-manufacturing industry

OBJECTIVE

We sought to determine volatile N-nitrosamines levels in the air of a rubber-manufacturing industry and to measure urinary N-nitrosamines concentrations in exposed workers.

METHODS

Personal monitoring of 34 workers was performed by sampling nine airborne N-nitrosamines in four factories that manufactured rubber drive belts for automotive engines. Urinary N-nitrosamine levels were determined in all workers and in a control group of 26 subjects. Analyses were conducted by capillary gas chromatography-thermal energy analyzer.

RESULTS

Airborne and urinary N-nitrosamines levels were very low and, in most cases, below the limit of detection (0.06 microg/m and 0.1 microg/L, respectively).

CONCLUSIONS

Although airborne and urinary N-nitrosamines levels were found to be very low, exposed workers should still be monitored constantly because some of these substances are known to be genotoxic and carcinogenic.

Kinetics and Mechanisms of the Reactions of Hydroxyl Radicals and Hydrated Electrons with Nitrosamines and Nitramines in Water

Absolute rate constants for hydroxyl radical, *OH, and hydrated electron, e(aq)(-), reactions with low-molecular-weight nitrosamines and nitramines in water at room temperature were measured using the techniques of electron pulse radiolysis and transient absorption spectroscopy. The bimolecular rate constants obtained, k (M(-1) s(-1)), for e(aq)(-) and *OH reactions, respectively, were as follows: methylethylnitrosamine, (1.67 +/- 0.06) x 10(10) and (4.95 +/- 0.21) x 10(8); diethylnitrosamine, (1.61 +/- 0.06) x 10(10) and (6.99 +/- 0.28) x 10(8); dimethylnitramine, (1.91 +/- 0.07) x 10(10) and (5.44 +/- 0.20) x 10(8); methylethylnitramine, (1.83 +/- 0.15) x 10(10) and (7.60 +/- 0.43) x 10(8); and diethylnitramine, (1.76 +/- 0.07) x 10(10) and (8.67 +/- 0.48) x 10(8), respectively. MNP/DMPO spin-trapping experiments demonstrated that hydroxyl radical reaction with these compounds occurs by hydrogen atom abstraction from an alkyl group, while the reaction of the hydrated electron was to form a transient radical anion. The latter adduct formation implies that the excess electron could subsequently be transferred to regenerate the parent chemical, which would significantly reduce the effectiveness of any free-radical-based remediation effort on nitrosamine/nitramine-contaminated waters.

Circulating NO Pool in Humans

Nitric oxide (NO) generated from L-arginine by NO synthases in the endothelium and in other cells plays a central role in several aspects of vascular biology and has been linked to many regulatory functions in mammalian cells. Whereas for a long time the signaling actions of NO in the vasculature have been thought to be short-lived as a result of the rapid reaction of NO with hemoglobin, recent studies changed the biochemical thinking of NO. NO is not anymore the paracrine agent with only local effects, but, like a hormone, it disseminates throughout the body. Thus, a circulating pool of NO exists, opening new considerable pharmacological and therapeutical avenues in the diagnosis and therapy of cardiovascular diseases. In this review we briefly discuss the major routes of NO metabolism and transport in the mammalian circulation, considering plasma, red blood cell and tissue compartments separately, with a special focus on the implication of the circulating NO pool in clinical research.

Nitrites, nitrates and N-nitrosoamines in Estonian cured meat products: intake by Estonian children and adolescents

The contents of nitrate, nitrite and N-nitrosoamines in commercial cured meat products on the Estonian market were determined for 2000-01 and 2003-04 as part of the Estonian food safety monitoring programme and the Estonian Science Foundation grant research activities. The maximum permitted levels of residual nitrites and nitrates were not exceeded in the samples analysed. However, a great variation in the content of nitrate, nitrite and N-nitrosoamines was found for all the products. The concentrations of these compounds in domestic cured meat products showed a decrease from year to year. The mean intake of nitrate, nitrite and N-nitrosoamines by Estonian children (n=346) from cured meat products was calculated on the basis of individual intake data. The mean daily intake of nitrates was 1.7 mg, that of nitrites was 0.83 mg and that of N-nitrosoamines was 0.073 microg. In the 2000-01 study, the calculated nitrite intake exceeded the acceptable daily intake by up to 140% for 1-6-year-old children and up to 105% in 2003-04.

A review: dietary and endogenously formed N-nitroso compounds and risk of childhood brain tumors

Maternal dietary exposure to N-nitroso compounds (NOC) or to their precursors during pregnancy has been associated with risk of childhood brain tumors. Cured meat is one source of exposure to dietary NOC and their precursors. Most epidemiological studies that have examined the role of maternal consumption of cured meats during pregnancy have found a significant positive association between maternal intake of cured meat and the risk of childhood brain tumor (CBT). NOC consist of two main groups, N-nitrosamines and N-nitrosamides. The carcinogenicity profiles of NOC suggest that N-nitrosamides rather than N-nitrosamines are the compounds that may be associated with CBT and that they should be investigated more closely in epidemiological studies. We present a review of the chemical and carcinogenic properties of NOC in connection with the findings of case-control studies. This approach may be helpful in determining the essential information that must be collected in future epidemiological studies on CBT.