Assessment of the risk of formation of carcinogenic N-nitroso compounds from dietary precursors in the stomach

Nitrosamines crisis in pharmaceuticals - Insights on toxicological implications, root causes and risk assessment: A systematic review

The presence of N-nitroso compounds, particularly N-nitrosamines, in pharmaceutical products has raised global safety concerns due to their significant genotoxic and mutagenic effects. This systematic review investigates their toxicity in active pharmaceutical ingredients (APIs), drug products, and pharmaceutical excipients, along with novel analytical strategies for detection, root cause analysis, reformulation strategies, and regulatory guidelines for nitrosamines. This review emphasizes the molecular toxicity of N-nitroso compounds, focusing on genotoxic, mutagenic, carcinogenic, and other physiological effects. Additionally, it addresses the ongoing nitrosamine crisis, the development of nitrosamine-free products, and the importance of sensitive detection methods and precise risk evaluation. This comprehensive overview will aid molecular biologists, analytical scientists, formulation scientists in research and development sector, and researchers involved in management of nitrosamine-induced toxicity and promoting safer pharmaceutical products.

Modified NAP test: A simple and Responsive Nitrosating Methodology for Risk Evaluation of NDSRIs

N-Nitroso compounds have been listed as one of the cohorts of concern as per ICH M7. In recent years, the regulatory focus has shifted from common nitrosamines to nitroso-impurities of drug products. Thus, the detection and quantification of unacceptable levels of nitrosamine drug substance-related impurities are of great concern for analytical scientists during drug development. Moreover, risk assessment of nitrosamines is also an essential part of the regulatory filling. For risk assessment, the Nitrosation Assay Procedure suggested by WHO expert group in 1978 is being followed. However, it could not be adopted by the pharmaceutical industries due to the limitation of drug solubility and artefact formation in the test conditions. In this work, we have optimized an alternative nitrosation test to investigate the likelihood of direct nitrosation. The technique is simple, where the drug solubilized in an organic solvent is incubated at 37°C with a nitrosating agent named tertiary butyl nitrite in a 1:10 molar ratio. LC-UV/MS-based chromatographic method was developed to separate drug substances and respective nitrosamine impurities using the C18 analytical column. The methodology was successfully tested on five drugs with varying structural chemistry. The procedure is straightforward, effective, and quick for the nitrosation of secondary amines. This modified nitrosation test and WHO prescribed nitrosation test have been compared and found that the modified methodology is more effective and time-saving.

Groundwater characterization and non-carcinogenic and carcinogenic health risk assessment of nitrate exposure in the Mahanadi River Basin of India

Agriculture is the mainstay of India's economy and chemical fertilizers have been extensively used to meet increasing demands. Anthropogenic interventions at the soil surface, especially the application of nitrogenous fertilizers in agricultural fields, provide essential nutrients but become major pollutant sources in terrestrial ecosystems and aquatic environments. Groundwater samples from phreatic aquifers of the Mahanadi River Basin, Chhattisgarh, India, showed that the Ca²⁺-Mg²⁺-HCO₃^- freshwater type dominates, followed by the Ca²⁺-Mg²⁺-Cl- and Na⁺-HCO₃^- types. Increasing trends in the ionic ratios of (NO₃-+Cl-)/HCO₃- over TDS and of NO₃-/Cl- over Cl- indicated the significant impact of anthropogenic pollution on groundwater contamination. Deterministic and probabilistic approaches were used to assess the non-carcinogenic and carcinogenic health risks of nitrate to children and adults. Both approaches produced the same results and indicated children were more prone to non-carcinogenic health risk than adults. An excess gastric cancer risk (ER) exposure model showed that approximately 42% of the groundwater samples had a non-negligible ER (1.00 × 10^-4 to 1.00 × 10^-5). Sensitivity analysis indicated groundwater nitrate concentration, ingestion rate, and the percentage of nitrite from nitrate were the most significant variables in determining HI and ER. It is suggested to adopt proper management of control policies for reducing the elevated groundwater nitrate concentration in the present study area.

Dietary N-Nitroso Compounds and Risk of Hepatocellular Carcinoma: A USA-Based Study

BACKGROUND AND AIMS

N-nitroso compounds (NOCs) are among the most potent dietary carcinogens. N-nitrosodiethylamine (NDEA), N-nitrosodimethylamine (NDMA), and N-nitrosopiperidine (NPIP) are abundant in foods and carcinogenic to the liver. We investigated the relationship between dietary NOCs and HCC risk.

APPROACH AND RESULTS

In this large, hospital-based, case-control study of 827 pathologically or radiologically confirmed HCC cases and 1,013 controls, NOC intake was calculated by linking food frequency questionnaire-derived dietary data with a comprehensive NOC concentration database. Multivariable-adjusted ORs and 95% CIs of HCC by quartiles of NOC consumption were estimated using logistic regression models, with the lowest quartile as the referent. We further investigated joint effects of consuming the highest quartile of NOCs that were associated with increased HCC risk and hepatitis, diabetes, or alcohol drinking on HCC risk. After adjustment for confounding factors, higher intake of NDEA from plant sources (ORQ4 vs. Q1  = 1.58; 95% CI = 1.03-2.41), NDMA from plant sources (ORQ4 vs. Q1  = 1.54; 95% CI = 1.01-2.34), and NPIP (ORQ4 vs. Q1  = 2.52; 95% CI = 1.62-3.94) was associated with increased HCC risk. No association was observed for nitrate or total NOC intake and HCC risk. Higher consumption of HCC-inducing NOCs and positive hepatitis virus status jointly increased the risk of developing HCC.

CONCLUSIONS

In conclusion, though some of our findings may indicate the presence of reverse causation owing to lower meat intake among cases with chronic liver diseases before HCC diagnosis, the potent dietary HCC carcinogens, NDEA, NDMA, and NPIP, and their enhanced carcinogenic effects among chronic carriers of hepatitis virus warrant further prospective investigation.

Association of a Tobacco-specific Nitrosamine Carcinogen with Urinary Cotinine, Urinary Sodium Excretion, and Total Energy Intake in Adolescents and Children

This study investigated the association of a tobacco-specific nitrosamine carcinogen, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) with urinary cotinine (uCot), urinary sodium (uNa) excretion, systolic blood pressure (sBP), and total energy intake in adolescents and children in relation to the subjects' age. A total of 790 subjects aged 6-19 years were evaluated. NNAL, uCot, corrected NNAL (cNNAL), the NNAL/uCot ratio, uNa, sBP, and nutrient intake were measured. A strong association between uCot and cNNAL was observed in children who were 11 years of age (r=0.881, P<0.001); however, no significant association was noted in adolescents who were 19 years of age. The uNa level was significantly higher (133.9 mmol/L vs. 107.8 mmol/L, P<0.001) and sBP was significantly lower (105.3 mmHg vs. 110.6 mmHg, P=0.012) in adolescents with elevated NNAL than in those without elevated NNAL. NNAL was significantly higher in subjects with increased uNa excretion than in those without increased uNa excretion. NNAL was positively correlated with uNa (r=0.183, P<0.001) and negatively correlated with sBP (r=-0.142, P<0.001). Non-smokers with elevated NNAL/uCot ratios had significantly lower total energy intake than those without elevated NNAL/uCot ratios (1729.0 kcal/day vs. 1911.0 kcal/day, P=0.008). The relationship between NNAL and uCot varied according to the subjects' age. NNAL seems to play a role in decreasing sBP by enhancing uNa excretion. Insufficient nutrient intake may contribute to endogenous formation of NNAL in non-smoking adolescents and children.

Nitrates/Nitrites in Food-Risk for Nitrosative Stress and Benefits

In the context of impact on human health, nitrite/nitrate and related nitrogen species such as nitric oxide (NO) are a matter of increasing scientific controversy. An increase in the content of reactive nitrogen species may result in nitrosative stress-a deleterious process, which can be an important mediator of damage to cell structures, including lipids, membranes, proteins and DNA. Nitrates and nitrites are widespread in the environment and occur naturally in foods of plant origin as a part of the nitrogen cycle. Additionally, these compounds are used as additives to improve food quality and protect against microbial contamination and chemical changes. Some vegetables such as raw spinach, beets, celery and lettuce are considered to contain high concentrations of nitrates. Due to the high consumption of vegetables, they have been identified as the primary source of nitrates in the human diet. Processed meats are another source of nitrites in our diet because the meat industry uses nitrates/nitrites as additives in the meat curing process. Although the vast majority of consumed nitrates and nitrites come from natural vegetables and fruits rather than food additives, there is currently a great deal of consumer pressure for the production of meat products free of or with reduced quantities of these compounds. This is because, for years, the cancer risks of nitrates/nitrites have been considered, since they potentially convert into the nitrosamines that have carcinogenic effects. This has resulted in the development and rapid expansion of meat products processed with plant-derived nitrates as nitrite alternatives in meat products. On the other hand, recently, these two ions have been discussed as essential nutrients which allow nitric oxide production and thus help cardiovascular health. Thus, this manuscript reviews the main sources of dietary exposure to nitrates and nitrites, metabolism of nitrites/nitrates, and health concerns related to dietary nitrites/nitrates, with particular emphasis on the effect on nitrosative stress, the role of nitrites/nitrates in meat products and alternatives to these additives used in meat products.

Evaluation of carcinogenic risks related to nitrate exposure in drinking water in Iran

Nitrate is one of the most important contaminants that can release into the environment predominantly as a result of anthropogenic processes. Excessive intake of nitrates may increase the risk of certain types of cancer. The aim of this study was to investigate the concentration of nitrate in drinking water and its health to people in Iran. This cross-sectional study has performed in 2019. Nitrate concentrations in drinking water supplies were obtained from peer-reviewed publications. Monte Carlo stimulations and mathematical models were used to determine the excess cancer risk. Risk level for assessing the carcinogen risk was 10⁻⁵ (1 per 100,000 persons). Nitrate concentrations and cancer risk related to nitrate were classified by GIS software. According to the obtained results, the drinking water supplies of Tehran, Mashhad (Khorasan Razavi), Zahedan (Sistan and Baluchestan), Shiraz (Fars), Qom, Ardabil and Ahwaz (Khuzestan) have higher nitrate concentrations than the limit recommended by WHO and Institute of Standards and industrial Research of Iran (ISIRI). The estimated cancer risks for the provinces of Tehran, Mashhad (Khorasan Razavi), Zahedan (Sistan and Baluchestan), Shiraz (Fars), Qom, Ardabil and Ahwaz (Khuzestan) were in the no negligible range set by the Health Canada and WHO. The majority of Iran provinces that have impermissible level of nitrate in drinking water supplies had a significant association between cancer prevalence and nitrate exposure.

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The findings demonstrated that carcinogen risk values of nitrate exposure through drinking water was 0.001%.

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Results showed that Tehran, Mashhad (Khorasan Razavi), Zahedan (Sistan and Baluchestan), Shiraz (Fars), Qom, Ardabil and Ahwaz (Khuzestan) are more exposed to additional cancer risk related to nitrosamine.

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The results of this study is considered as the comprehensive report that indicate the association between gastrointestinal cancer and nitrate exposure through drinking water.

Dietary protein source and butyrylated high-amylose maize starch included in a high-protein diet determines the urinary metabolome of rats

Intake of red and processed meat increases the risk of colorectal cancer (CRC), whereas dairy product consumption and the intake of dietary fibre are negatively associated with this risk. We investigated the effect of (i) low-protein diets with either whey or cooked meat (beef) as the protein source and (ii) high-protein diets with cooked meat (beef) either without or with the inclusion of 10% butyrylated high-amylose maize starch (HAMSB), on the urinary metabolome of rats. Urine samples from rats were analysed using untargeted LC-MS metabolomics. The level and source of the dietary protein affected the urinary excretion of numerous metabolites indicating that several metabolic pathways were changed. The inclusion of HAMSB in a high-protein diet caused significant alterations in the excretion of several metabolites. HAMSB reduced urinary excretion of potentially harmful metabolites resulting from a high level of meat consumption.

Presence of the Carcinogen N'-Nitrosonornicotine in Saliva of E-cigarette Users

Many harmful constituents are present in e-cigarettes at much lower levels than in cigarette smoke, and the results of analysis of urinary biomarkers in e-cigarette users are consistent with these findings. However, understanding the health effects of chronic exposures to e-cigarette aerosols may require thinking beyond these comparisons. In this study, we investigated the endogenous formation of the tobacco-specific oral and esophageal carcinogen N'-nitrosonornicotine (NNN) in e-cigarette users. Salivary NNN, nornicotine, and nicotine as well as urinary tobacco biomarkers, including total NNN, were analyzed in 20 e-cigarette users, 20 smokers, and 19 nonsmokers. Nornicotine and NNN levels in e-cigarettes used by the study participants were also analyzed. The mean of NNN in saliva of e-cigarette users was 14.6 (±23.1) pg/mL, ranging from nonquantifiable (below the limit of quantitation, LOQ) to 76.0 pg/mL. In smokers, salivary NNN ranged from below LOQ to 739 pg/mL, with 80% of smokers having salivary NNN in the range of levels found in e-cigarette users. Consistent with a previous report, very low levels of urinary total NNN were present in only 5 out of 20 e-cigarette users (ranging from 0.001 to 0.01 pmol/mL urine). Only trace levels of NNN were found in e-cigarette liquids. Together, our findings demonstrate that NNN is formed endogenously in e-cigarette users. While the overall exposure to NNN in e-cigarette users is dramatically lower than in smokers, the known carcinogenic potency of NNN warrants further investigations into the potential consequences of its endogenous formation. Salivary NNN, rather than urinary total NNN, which accounts for only 1-3% of the NNN dose, should be used to monitor e-cigarette users' exposure to this carcinogen.

Nicotine levels and presence of selected tobacco-derived toxins in tobacco flavoured electronic cigarette refill liquids

BACKGROUND

Some electronic cigarette (EC) liquids of tobacco flavour contain extracts of cured tobacco leaves produced by a process of solvent extraction and steeping. These are commonly called Natural Extract of Tobacco (NET) liquids. The purpose of the study was to evaluate nicotine levels and the presence of tobacco-derived toxins in tobacco-flavoured conventional and NET liquids.

METHODS

Twenty-one samples (10 conventional and 11 NET liquids) were obtained from the US and Greek market. Nicotine levels were measured and compared with labelled values. The levels of tobacco-derived chemicals were compared with literature data on tobacco products.

RESULTS

Twelve samples had nicotine levels within 10% of the labelled value. Inconsistency ranged from -21% to 22.1%, with no difference observed between conventional and NET liquids. Tobacco-specific nitrosamines (TSNAs) were present in all samples at ng/mL levels. Nitrates were present almost exclusively in NET liquids. Acetaldehyde was present predominantly in conventional liquids while formaldehyde was detected in almost all EC liquids at trace levels. Phenols were present in trace amounts, mostly in NET liquids. Total TSNAs and nitrate, which are derived from the tobacco plant, were present at levels 200-300 times lower in 1 mL of NET liquids compared to 1 gram of tobacco products.

CONCLUSIONS

NET liquids contained higher levels of phenols and nitrates, but lower levels of acetaldehyde compared to conventional EC liquids. The lower levels of tobacco-derived toxins found in NET liquids compared to tobacco products indicate that the extraction process used to make these products did not transfer a significant amount of toxins to the NET. Overall, all EC liquids contained far lower (by 2-3 orders of magnitude) levels of the tobacco-derived toxins compared to tobacco products.

Probiotic lactic acid bacteria detoxify N-nitrosodimethylamine

Humans can be exposed to N-nitroso compounds (NOCs) due to many environmental sources, as well as endogenous formation. The main nitrosamine found in food products and also synthesised in vivo by intestinal microbiota is N-nitrosodimethylamine (NDMA). It can cause cancer of the stomach, kidney and colon. The effect of four probiotic Lactobacillus strains on NDMA was studied under different culture conditions (24 h in MRS, 168 h in modified MRS N, and 168 h in phosphate buffer). HPLC and GC-TEA methods were used for NDMA determination in supernatants. The influence of lactic acid bacteria on NDMA genotoxicity was investigated by means of the comet assay. Additionally, the effect of NDMA (2-100 µg ml⁻¹) on the growth and survival of the probiotic strains was studied. The results indicate that the bacteria decreased NDMA concentration by up to 50%, depending on the culture conditions, time of incubation, NDMA concentration, pH and bacterial strain. Lb. brevis 0945 lowered the concentration and genotoxicity of NDMA most effectively by up to 50%. This could be due to either adsorption or metabolism. The growth and survival of the bacteria was not affected by any of the tested NDMA concentrations.

Nornicotine nitrosation in saliva and its relation to endogenous synthesis of N'-nitrosonornicotine in humans

INTRODUCTION

We recently reported that certain amounts of the carcinogen N'-nitrosonornicotine (NNN) can be formed endogenously from nicotine and/or nornicotine in some users of oral nicotine replacement therapy products. Although the acidic environment of the stomach creates the most favorable conditions for nitrosation, this reaction could also occur in the oral cavity in the presence of bacteria that catalyze nitrosation at neutral pH.

METHODS

To test the hypothesis that endogenous formation of NNN could occur in the oral cavity, we investigated nitrosation of nicotine and nornicotine in human saliva. To specifically identify NNN as derived from precursors added to saliva, we incubated saliva samples with [pyridine-D(4)]nicotine and [pyridine-D(4)]nornicotine, with and without the addition of nitrite, and subsequently analyzed [pyridine-D(4)]NNN by liquid chromatography-tandem mass spectrometry.

RESULTS

Consistent with kinetic studies on nicotine and nornicotine nitrosation, incubation of saliva with [pyridine-D(4)]nornicotine alone produced detectable amounts of [pyridine-D(4)]NNN, whereas only traces of [pyridine-D(4)]NNN were found in samples incubated with [pyridine-D(4)]nicotine and sodium nitrite. Incubation of saliva samples from 10 nonsmoking volunteers with [pyridine-D(4)]nornicotine resulted in the formation of [pyridine-D(4)]NNN in 8 samples, with yields ranging from 0.003% to 0.051% of the added alkaloid.

CONCLUSION

Our results demonstrate that NNN can be formed from nornicotine in human saliva without deliberate addition of any other substance. Therefore, nornicotine, as present in tobacco or in nicotine replacement products, is a carcinogen precursor.

QSAR study of liver specificity of carcinogenicity of N-nitroso compounds

The quantitative structure-activity relationship (QSAR) of N-nitroso compounds (NOCs) for rat liver was developed by a topological sub-structural molecular-descriptors (TOPS-MODE) approach to predict non-liver-carcinogenic and liver-carcinogenic N-nitroso compounds based on a data set of 108 NOCs. Three descriptors calculated solely from the molecular structures of the compounds were selected by enhanced replacement method (ERM) and were weighted, respectively, with atomic weight, bond dipole moments and Abraham solute descriptor partition between water and aqueous solvent systems to indicate the importance of their roles in liver specificity. A detailed discussion on these three descriptors was carried out, and the contributions of different fragments to rat-liver specificity and the interactions among fragments were analyzed. Such results can offer some useful theoretical references for understanding the chemical structural and biological factors related to the liver-specific biological activity of NOCs.

Occurrence and source of nitrosamines and secondary amines in groundwater and its adjacent Jialu River basin, China

The presence of mutagenic and carcinogenic nitrosamines in groundwater is of great concern. In this study, eight nitrosamines including N-nitrosodimethylamine (NDMA), N-nitrosodiethylamine (NDEA), N-nitrosomethylethylamine (NMEA), N-nitrosopyrrolidine (NPYR), N-nitrosomorpholine (NMOR), N-nitrosopiperidine (NPIP), N-nitrosodi-n-propylamine (NDPA), and N-nitrosodi-n-butylamine (NDBA) and corresponding secondary amines were investigated in shallow groundwater, river water, and wastewater samples collected from the Jialu River basin. The total concentrations of nitrosamines and secondary amines in groundwater were ND-101.1 ng/L and 0.36-4.38 μg/L, respectively. NDMA and its secondary amine DMA (44.7%/40.1%) were the predominant compounds in groundwater, followed by NDEA/DEA (21.7%/29.3%) and NDBA/DBA (26.4%/27.4%). Relatively high concentrations of these six compounds were also observed in river water that was influenced by the direct discharge of industrial and domestic wastewater. Using acesulfame as a quantitative population marker, the contribution of domestic sources to the concentrations of nitrosamines and secondary amines was 39-85% in downstream reaches of the Jialu River, and that of industrial sources was estimated to be 65-98% in other sites of the area. Both on-site leakage of domestic and industrial wastewater and leaching from river water would contribute to the occurrence of target pollutants in groundwater. The target pollutants posed a cancer risk of 4.12 × 10(-5) to the local populations due to the direct usage of groundwater as potable water.

Evidence for endogenous formation of N'-nitrosonornicotine in some long-term nicotine patch users

INTRODUCTION

Nitrosation of nicotine or its metabolites in the human body could lead to formation of the 2 carcinogenic tobacco-specific nitrosamines-N'-nitrosonornicotine (NNN) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK).

METHODS

We investigated the possibility of endogenous formation of NNN in people who had stopped smoking and used the 21-mg nicotine patch for 6 months. We quantified urinary biomarkers of exposure to NNN-the sum of NNN and its pyridine-N-glucuronide, referred to as total NNN. Also measured were NNK metabolites-the sum of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) and its N- and O-glucuronides, referred to as total NNAL.

RESULTS

The average decline of urinary total NNN was less drastic than that of total NNAL: 22% of baseline total NNN and 7.3% of baseline total NNAL were detected in urine 24 weeks after smoking cessation and patch use (p = .02). The average ratio of total NNN to total NNAL in the same urine samples increased from 0.14 in baseline urine to 0.38 after 24 weeks of nicotine patch use.

DISCUSSION

Overall, these results demonstrate that endogenous formation of NNN may occur in nicotine patch users. However, the levels of urinary total NNN during patch use were generally extremely low. Moreover, in 10 of 20 subjects analyzed here, the rate of decline in total NNN was similar to that in total NNAL, indicating that endogenous formation of NNN is virtually nonexistent in these subjects. Supplementation with ascorbic acid could be a simple approach to block possible NNN formation in nicotine patch users.

New and traditional smokeless tobacco: comparison of toxicant and carcinogen levels

Declining cigarette use and spreading bans on smoking in public places in the United States are encouraging the U.S. cigarette industry to turn to another tobacco category, smokeless tobacco products. Currently, a number of new brands are being test marketed, including Taboka, Marlboro Snus, Camel Snus, and Skoal Dry. We report here levels of tobacco-specific nitrosamines (TSNAs), alkaloids, anions, polycyclic aromatic hydrocarbons (PAH), and volatile aldehydes in these products, and compare them to the most popular traditional moist snuff brands. Total TSNAs averaged 1.97 microg/g dry weight tobacco in Taboka, Marlboro Snus, and Camel Snus, 4.54 microg/g tobacco in Skoal Dry, and 7.42 microg/g tobacco in traditional brands. The amounts of unprotonated nicotine averaged 0.961 mg/g tobacco in Taboka, Marlboro Snus, and Skoal Dry, 7.22 mg/g tobacco in Camel Snus, and 7.57 mg/g tobacco in traditional brands. Levels of minor tobacco alkaloids were relatively high in Taboka, Marlboro Snus, and Skoal Dry, as compared to other products analyzed here. Levels of nitrite and nitrate in new U.S. smokeless tobacco products and the Swedish snus General were lower than those in the other products. Remarkably high levels of chloride and some PAH were observed in the traditional moist snuff. Crotonaldehyde levels were about five times higher in Taboka and Marlboro Snus than in traditional products. The large variation in the levels of some toxicants and carcinogens analyzed here indicates that more effort is required from the U.S. tobacco industry to further reduce their amounts in new and traditional smokeless tobacco products.

Consumption of different types of meat and the risk of renal cancer: meta-analysis of case-control studies

BACKGROUND

Kidney cancers account for almost 2% of all cancers worldwide, with 150,000 new cases and 78,000 deaths from the disease occurring annually. An increase in the incidence of kidney neoplasm in western countries was noticed in the past few years. Between 1988 and 1992, the incidence of renal cancer per 100,000 person-year among males in USA, Norway, and France was 34.1, 9.00, and 16.10, respectively. Among females in the same countries, it was 5.70, 5.00, and 7.30, respectively. Although several individual case-control studies examined the association of meat intake and renal cancer risk, the results were inconsistent because of the insufficient statistical power of the individual studies. Therefore, the following meta-analysis was designed to help in clarifying the association.

METHODS

Electronic search of MEDLINE, OVID, and PUBMED databases which have articles published between (1966 and 2006) was conducted to select studies for this meta-analysis.

STATISTICAL ANALYSIS

Fixed and random-effects meta-analytical techniques were used to estimate the overall association between meat consumption and kidney cancer.

RESULTS

Thirteen case-control studies were found. This meta-analysis supported a positive relationship between meat consumption and risk of renal cancer. Summary results indicated that there was from 20% to 22% higher risk of renal cancer among those in the highest relative to the lowest category of poultry and processed meat consumption. Consumption of all meat and red meat was associated with 27% and 30% higher risk, respectively. The increased risks were statistically significant.

CONCLUSIONS

Increased consumption of all meat, red meat, poultry, and processed meat is associated with an increase risk of kidney cancer. Reduction of meat consumption is an important approach to decreasing the incidence of kidney cancer in the general population.

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.

Epidemiology of brain tumors in childhood--a review

Malignant brain tumors are the leading cause of cancer death among children and the second most common type of pediatric cancer. Despite several decades of epidemiologic investigation, the etiology of childhood brain tumors (CBT) is still largely unknown. A few genetic syndromes and ionizing radiation are established risk factors. Many environmental exposures and infectious agents have been suspected of playing a role in the development of CBT. This review, based on a search of the medical literature through August 2003, summarizes the epidemiologic evidence to date. The types of exposures discussed include ionizing radiation, N-nitroso compounds (NOC), pesticides, tobacco smoke, electromagnetic frequencies (EMF), infectious agents, medications, and parental occupational exposures. We have chosen to focus on perinatal exposures and review some of the recent evidence indicating that such exposures may play a significant role in the causation of CBT. The scientific community is rapidly learning more about the molecular mechanisms by which carcinogenesis occurs and how the brain develops. We believe that advances in genetic and molecular biologic technology, including improved histologic subtyping of tumors, will be of huge importance in the future of epidemiologic research and will lead to a more comprehensive understanding of CBT etiology. We discuss some of the early findings using these technologies.

Intragastric formation and modulation of N-nitrosodimethylamine in a dynamic in vitro gastrointestinal model under human physiological conditions

Human exposure to carcinogenic N-alkylnitrosamines can occur exogenously via food consumption or endogenously by formation of these compounds through nitrosation of amine precursors. Information on the intragastric formation of NDMA from complex mixtures of precursors and inhibitors in humans is not available. In this study the formation of N-nitrosodimethylamine (NDMA) has been quantitatively analysed in a dynamic in vitro gastrointestinal model, in which gastric conditions can be modulated and closely simulates the physiological situation in humans. Substantial amounts of NDMA were produced when nitrite and dimethylamine or codfish were simultaneously introduced into the model. However, humans are gradually exposed to nitrite by the intake of nitrate-containing food. Nitrate secreted in saliva is converted to nitrite by oral bacteria. To mimic the human exposure to nitrite in a realistic way, nitrite was gradually added into the gastric compartment, simulating the swallowing of nitrite containing oral fluid after the intake of nitrate at the level of 0.1-10 times the ADI. Under these conditions, the cumulative amounts of NDMA formed were 2.3-422 microg NDMA and 1.8-42.7 microg NDMA at a rapid and slow gastric pH decrease, respectively. Beside codfish, various fish species and batches in combination with nitrite, simulating the intake of for times the ADI of nitrate, were investigated. Herring, pollack and plaice were also able to induce NDMA formation. Mackerel, salmon and pike perch did not result in increased NDMA formation. Furthermore, the effect of nitrosation modulators on NDMA formation was investigated. Thiocyanate (2 mM) increased NDMA formation, but the increase was not statistically significant. In contrast, orange jus and tea effectively, but not totally, reduced the amount of NDMA formed in the gastric compartment. These experiments show that (1). the dynamic in vitro gastrointestinal model is an appropriate tool for mechanistic studies on the intragastric formation of nitrosamines, and (2). that the results obtained with this model are helpful in evaluating human cancer risk for the combined intake of codfish-like fish species and nitrate-containing vegetables.

Health Implications of Exposure to Environmental Nitrogenous Compounds

All living systems need nitrogen for the production of complex organic molecules, such as proteins, nucleic acids, vitamins, hormones and enzymes. Due to the intense use of synthetic nitrogen fertilisers and livestock manure in modern day agriculture, food (particularly vegetables) and drinking water may contain higher concentrations of nitrate than in the past. The mean intake of nitrate per person in Europe is about 50-140 mg/day and in the US about 40-100 mg/day. In the proximal small intestine, nitrate is rapidly and almost completely absorbed (bioavailability at least 92%). In humans, approximately, 25% of the nitrate ingested is secreted in saliva, where some 20% (about 5-8% of the nitrate intake) is converted to nitrite by commensal bacteria. The nitrite so formed is then absorbed primarily in the small intestine. Nitrate may also be synthesised endogenously from nitric oxide (especially in case of inflammation), which reacts to form nitrite. Normal healthy adults excrete in the urine approximately 62 mg nitrate ion/day from endogenous synthesis. Thus, when nitrate intake is low and there are no additional exogenous sources (e.g. gastrointestinal infections), the endogenous production of nitrate is more important than exogenous sources. Nitrate itself is generally regarded nontoxic. Toxicity is usually the result of the conversion of nitrate into the more toxic nitrite. There are two major toxicological concerns regarding nitrite. First, nitrite may induce methaemoglobinaemia, which can result in tissue hypoxia, and possibly death. Secondly, nitrite may interact with secondary or N-alkyl-amides to form N-nitroso carcinogens. However, epidemiological investigations and human toxicological studies have not shown an unequivocal relationship between nitrate intake and the risk of cancer. The Joint Expert Committee of the Food and Agriculture Organization of the United Nations/World Health Organization (JECFA) and the European Commission's Scientific Committee on Food have set an acceptable daily intake (ADI) for nitrate of 0-3.7 mg nitrate ion/kg bodyweight; this appears to be safe for healthy neonates, children and adults. The same is also true of the US Environmental Protection Agency (EPA) Reference Dose (RfD) for nitrate of 1.6 mg nitrate nitrogen/kg bodyweight per day (equivalent to about 7.0 mg nitrate ion/kg bodyweight per day). This opinion is supported by a recent human volunteer study in which a single dose of nitrite, equivalent to 15-20 times the ADI for nitrate, led to only mild methaemoglobinaemia (up to 12.2%), without other serious adverse effects. The JECFA has proposed an ADI for nitrite of 0-0.07 mg nitrite ion/kg bodyweight and the EPA has set an RfD of 0.1 mg nitrite nitrogen/kg bodyweight per day (equivalent to 0.33 mg nitrite ion/kg bodyweight per day). These values are again supported by human volunteer studies.

Associação entre fatores da dieta e tumores de cérebro em adultos: uma revisão da literatura

Desenvolveu-se uma revisão da literatura científica publicada entre 1986 e 1999, sobre a associação entre fatores da dieta e os tumores de cérebro em adultos, com o objetivo de descrever as associações observadas e discutir os aspectos metodológicos que possam influenciar os resultados observados. De um modo geral, os estudos revisados parecem apontar na direção de uma associação moderada entre os fatores da dieta e os tumores de cérebro; há evidências de que o consumo de compostos N-nitroso possa favorecer o desenvolvimento desses tumores, e de que o consumo de vegetais e frutas pode ter papel na sua inibição. A participação dos respondentes substitutos nos estudos analisados, pode ter introduzido viés de memória nas informações levantadas e contribuído para a inconsistência dos achados. As investigações epidemiológicas sobre a associação da dieta com estes tumores devem considerar a análise de outros fatores alimentares, além dos compostos N-nitroso. É necessário precisar os períodos de exposição que devem ser investigados e contar com criteriosa metodologia, de modo a prevenir a ocorrência de tendenciosidades relacionadas com a seleção dos controles e minimizar os efeitos do viés de memória.

Fluorometric determination of N-nitroso-N-methylurea with nicotinamide and acetophenone

A fluorometric method for the determination of N-nitroso-N-methylurea (NMU) has been developed. It is based on the N-methylation reaction of nicotinamide with NMU and a subsequent condensation reaction with acetophenone, followed by an acid treatment to form a fluorescent 2,7-naphthyridine derivative. This method enabled the determination of NMU in the range 0.05 - 2 nmol/200 microl with a relative standard deviation of ca. 3%. It was applied to the determination of NMU formed from a precursor N-methylurea (MU) under simulated gastric conditions containing nitrite and thiocyanate ions at pH 3.0 in the presence of fresh orange juice and milk. NMU was extracted by an Extrelut 20 column and then determined. The mean recoveries of NMU added to the simulated gastric juice containing water, orange juice and milk were 86.5, 85.1 and 69.8%, respectively. The amounts of NMU formed from MU were found to decrease to below 25% in the presence of orange juice and milk.

Chemopreventive effects of S-methylcysteine on rat hepatocarcinogenesis induced by concurrent administration of sodium nitrite and morpholine

The aim of the present study was to examine the chemopreventive efficacy of S-methylcysteine (SMC) on rat hepatocarcinogenesis induced by concurrent administration of sodium nitrite (NaNO(2)) and morpholine (Mor) using a medium-term rat liver carcinogenesis bioassay (Ito test). Administration of SMC caused significant reduction in the areas of glutathione S-transferase placental form positive foci along with a significant decrease of hepatocyte 5-bromo-2'-deoxyuridine (BrdU) labeling indices. These results demonstrated potent chemopreventive effects of SMC against hepatocarcinogenesis due to concurrent administration of Mor and NaNO(2). SMC could thus be an effective chemopreventive agent for decreasing the risk of carcinogenicity from environmental precursors of N-nitroso compounds.

Excretion of volatile nitrosamines in a rural population in relation to food and drinking water consumption

Urinary excretion of volatile nitrosamines was assessed in 59 non-smokers living in a rural county of Québec, Canada. Water and food intakes were measured by means of a 24-hour recall. Nitrates were analyzed in the tap water of all participants (geometric mean=2.0 mg nitrate-N/L) and dietary intakes of nitrate and vitamins C and E were estimated via a validated Canadian food database. Urine was collected over the same 24-hour period and analyzed for nitrates by hydrazine reduction and for volatile nitrosamines by gas-chromatography/mass spectrometry. N-Nitrosopiperidine (NPIP) was found in urine samples from 52 of the 59 subjects. Geometric mean of NPIP urinary excretion was 67 ng/day and maximum value was 1045 ng/day. No other volatile nitrosamine was detected. There was a correlation between urinary nitrate excretion and total nitrate intake (r=0.71, P < 0.001). However, no relationship was found between urinary NPIP excretion and either nitrate excretion, dietary or water nitrate intakes. NPIP excretion was significantly correlated to coffee intake (r=0.40, P=0.002) and this relation was not modified by vitamin intake. We conclude that nitrate intake is not related to nitrosamine excretion in this rural population. The influence of coffee consumption on NPIP excretion deserves further attention.

Evaluation of fecal mutagenicity and colorectal cancer risk

Colorectal cancer is one of the most common internal malignancies in Western society. The cause of this disease appears to be multifactorial and involves genetic as well as environmental aspects. The human colon is continuously exposed to a complex mixture of compounds, which is either of direct dietary origin or the result of digestive, microbial and excretory processes. In order to establish the mutagenic burden of the colorectal mucosa, analysis of specific compounds in feces is usually preferred. Alternatively, the mutagenic potency of fecal extracts has been determined, but the interpretation of these more integrative measurements is hampered by methodological shortcomings. In this review, we focus on exposure of the large bowel to five different classes of fecal mutagens that have previously been related to colorectal cancer risk. These include heterocyclic aromatic amines (HCA) and polycyclic aromatic hydrocarbons (PAH), two exogenous factors that are predominantly ingested as pyrolysis products present in food and (partially) excreted in the feces. Additionally, we discuss N-nitroso-compounds, fecapentaenes and bile acids, all fecal constituents (mainly) of endogenous origin. The mutagenic and carcinogenic potency of the above mentioned compounds as well as their presence in feces, proposed mode of action and potential role in the initiation and promotion of human colorectal cancer are discussed. The combined results from in vitro and in vivo research unequivocally demonstrate that these classes of compounds comprise potent mutagens that induce many different forms of genetic damage and that particularly bile acids and fecapentaenes may also affect the carcinogenic process by epigenetic mechanisms. Large inter-individual differences in levels of exposures have been reported, including those in a range where considerable genetic damage can be expected based on evidence from animal studies. Particularly, however, exposure profiles of PAH and N-nitroso compounds (NOC) have to be more accurately established to come to a risk evaluation. Moreover, lack of human studies and inconsistency between epidemiological data make it impossible to describe colorectal cancer risk as a result of specific exposures in quantitative terms, or even to indicate the relative importance of the mutagens discussed. Particularly, the polymorphisms of genes involved in the metabolism of heterocyclic amines are important determinants of carcinogenic risk. However, the present knowledge of gene-environment interactions with regard to colorectal cancer risk is rather limited. We expect that the introduction of DNA chip technology in colorectal cancer epidemiology will offer new opportunities to identify combinations of exposures and genetic polymorphisms that relate to increased cancer risk. This knowledge will enable us to improve epidemiological study design and statistical power in future research.

Concurrent administration of fish meal and sodium nitrite does not promote renal carcinogenesis in rats after initiation with N-ethyl-N-hydroxyethylnitrosamine

The modifying effects of concurrent administration of fish meal and sodium nitrite on the development of renal tumors after initiation with N-ethyl-N-hydroxyethylnitrosamine (EHEN) were investigated. A total of 120 male 6-week-old Wistar rats were divided into six groups. Groups 1-3 (30 animals each) were given 1000 ppm EHEN in their drinking water for 3 weeks as an initiation treatment for renal cancer induction and thereafter fed respective diets containing 64, 32, and 8% (original concentration in the basal diet) fish meal, and simultaneously given 0.12% sodium nitrite in the drinking water for 33 weeks. Groups 4-6 (ten animals each) were similarly treated without the prior application of EHEN. At the end of the 37th experimental week, all surviving animals were autopsied and examined histopathologically for the existence of renal proliferative lesions. The incidences of dysplastic lesions, adenomas or adenocarcinomas of the kidney were not significantly different among groups 1-3. No renal proliferative lesions were found in groups 4-6. Chronic nephropathy was slightly but significantly enhanced in the 64 and 32% fish meal-treated groups as compared with group 3. Our results suggest that concurrent administration of fish meal and sodium nitrite does not affect the post-initiation phase of EHEN-induced renal carcinogenesis in the rat.

Renal carcinogenicity of concurrently administered fish meal and sodium nitrite in F344 rats

The effects of long-term concurrent administration of powdered fish meal and sodium nitrite were examined in F344 rats. A total of 600, 6-week-old rats were divided into 6 male and 6 female groups, each consisting of 50 animals. Rats in groups 1-3 and 7-9 were respectively fed diets supplemented with 64%, 32% and 8% (basal diet) fish meal, and simultaneously given 0.12% sodium nitrite in their drinking water. Groups 4-6 and 10-12 were respectively given 64%, 32% and 8% fish meal and tap water. At the 104th week, all surviving animals were killed and examined histopathologically. Treatment with fish meal dose-dependently increased the incidences and multiplicities of atypical tubules, adenomas and renal cell carcinomas in sodium nitrite-treated males. Females were less susceptible than males for renal tumor induction. In males given the 64% fish meal diet alone, the incidence and multiplicity of atypical tubules were also significantly increased as compared with the 8% fish meal alone case. Nephropathy was apparent in fish meal-treated groups in a clear dose-dependent manner, irrespective of the sodium nitrite treatment, and was more prominent in males than in females. Dimethylnitrosamine was found in the stomach contents after 4-week treatment with 64% fish meal plus 0.12% sodium nitrite, at a level twice that in the 8% fish meal plus 0.12% sodium nitrite group. The results clearly indicate that concurrent administration of fish meal and sodium nitrite induces renal epithelial tumors. Further studies are required to elucidate how nephropathy and nitrosamines produced in stomach contents may contribute to the observed renal tumor induction.

Digestive System 1

This chapter deals with the digestive system. The major and minor salivary glands and their secretions also represent and integral part of the protective mechanism of the oral cavity, and derangement of saliva production may lead to loss of integrity of the oral mucosa. Drug-induced abnormalities of taste sensation are also well-described phenomena occurring in man although human studies are necessary for the detection of these effects. Inflammation of the oral cavity may involve the buccal mucosa, the gingiva (gingivitis), the tongue (glossitis), and the peridontal tissues (peridontitis). Therapeutic agents can induce inflammatory lesions in the tongue. Moreover, a protective layer of mucus, a visco-elastic material containing high molecular weight glycoproteins produced by the major and minor salivary glands, covers the stratified squamous mucosa of the oral cavity. Salivary secretions also possess digestive enzyme activity although in herbivores and carnivores, it is usually low in contrast to high digestive enzyme activity in omnivorous species.

Oxygen and nitrogen are pro-carcinogens. Damage to DNA by reactive oxygen, chlorine and nitrogen species: measurement, mechanism and the effects of nutrition

Humans are exposed to many carcinogens, but the most significant may be the reactive species derived from metabolism of oxygen and nitrogen. Nitric oxide seems unlikely to damage DNA directly, but nitrous acid produces deamination and peroxynitrite leads to both deamination and nitration. Scavenging of reactive nitrogen species generated in the stomach may be an important role of flavonoids, flavonoids and other plant-derived phenolic compounds. Different reactive oxygen species produce different patterns of damage to DNA bases, e.g., such patterns have been used to implicate hydroxyl radical as the ultimate agent in H(2)O(2)-induced DNA damage. Levels of steady-state DNA damage in vivo are consistent with the concept that such damage is a major contributor to the age-related development of cancer and so such damage can be used as a biomarker to study the effects of diet or dietary supplements on risk of cancer development, provided that reliable assays are available. Methodological questions addressed in this article include the validity of measuring 8-hydroxydeoxyguanosine (8OHdG) in cellular DNA or in urine as a biomarker of DNA damage, the extent of artifact formation during analysis of oxidative DNA damage by gas chromatography-mass spectrometry and the levels of oxidative damage in mitochondrial DNA.

Formation of nitrosamines during consumption of nitrate- and amine-rich foods, and the influence of the use of mouthwashes

We studied the formation of carcinogenic nitrosamines during consumption of food rich in nitrate and amines, and its possible inhibition by use of an antibacterial mouthwash. Twelve volunteers were fed a diet containing the high-nitrate vegetables lettuce or spinach during two periods of four consecutive days, in combination with fish products containing high levels of amines as nitrosatable precursors. During the two periods, the subjects used an antibacterial mouthwash containing chlorhexidine or a control mouthwash without antibacterial activity. Twenty-four-hour urine samples were collected after consumption of the meals, and saliva samples were collected 1 h after each meal. The nitrate and nitrite contents of the urine and saliva samples were determined by spectrophotometry (for nitrite) and HPLC (for nitrate). The concentrations of volatile nitrosamines in the urine samples were determined by gas chromatography-mass spectrometry. Significant increases in mean urinary nitrate levels (from 59 to 135 mg/24 h) and in mean salivary nitrate levels (from 10 to 56 microg/ml) and salivary nitrite levels (from 2 to 11 microg/ml) were observed during the consumption of food rich in nitrate and amines, as well as a significant increase in the mean urinary excretion of total examined volatile nitrosamines (from 2 to 7 nmol/24 h) and of N-nitrosodimethylamine (from 1.2 to 2.9 nmol/24 h). Use of the antibacterial mouthwash resulted in a decrease in mean salivary nitrite levels from 16 to 3 microg/ml and a decrease in mean urinary excretion of N-nitrosomorpholine (from 7.0 to 0.3 nmol/24 h). For the whole data set, significant correlations were observed between nitrate intake in food and urinary nitrate (p = 0.01; r2 = 0.07) and between urinary nitrate and urinary N-nitrosodimethylamine (p = 0.002; r2 = 0.11). In conclusion, consumption of a diet rich in nitrate and amines increases the risk of formation of carcinogenic nitrosamines. Use of an antibacterial mouthwash containing chlorhexidine can result in inhibition of nitrosamine formation.

Analysis of the in vivo nitrosation capacity of the larvae used in the wing somatic mutation and recombination test of Drosophila melanogaster

The in vivo nitrosation capacity of third-instar larvae of Drosophila melanogaster was assessed using the wing somatic mutation and recombination test (SMART). Larvate derived from two different crosses, the standard cross (ST) and the high bioactivation cross (HB) both involving the recessive wing cell markers multiple wing hairs (mwh) and flare (flr3), were used. The HB cross is characterised by an increased cytochrome P450-dependent bioactivation capacity for promutagens and procarcinogens. The larvae were treated either with methyl urea, sodium nitrite or its combination. N-Nitrosomethylurea was used as a positive control. The wings of the resulting flies were analysed for the occurrence of mutant spots produced by various types of mutational events or by mitotic recombination. Methyl urea is negative in the ST and the HB cross, whereas sodium nitrite is weakly genotoxic in both crosses. However, the combination of both compounds produces highly increased frequencies of mutations and recombinations predominantly in the HB cross. The genotoxic effects produced by the combined treatments were considerably increased when mashed potatoes or an agar-yeast medium were used for the treatment instead of the standard instant medium. Treatment of larvae with the mixture resulting from the in vitro reaction of nitrosation precursors also resulted in high frequencies of induced spots comparable to those recorded with the potent genotoxin N-nitrosomethylurea. Further experiments showed that the genotoxic effect resulting from the in vivo exposure to nitrosation precursors can be reduced by co-treatment with catechin, a known nitrosation inhibitor. The present study demonstrates that the wing spot test is well suited for the determination of genotoxicity produced by in vivo nitrosation processes and for the study of their modulation by individual compounds or dietary complex mixtures.

Carcinogenicity of methylurea or morpholine in combination with sodium nitrite in rat multi-organ carcinogenesis bioassay

For carcinogenic risk assessment of combinations of N-nitroso precursors in man, the effects of feeding methylurea (MU) or morpholine (Mor) plus sodium nitrite (NaNO2) were investigated using a multi-organ carcinogenesis model. In experiment 1, to initiate multiple organs, groups of 10 or 20 male F344 rats were treated with 6 carcinogens targeting different organs. Starting a week after completion of this initiation phase, animals were given 0.1% MU or 0.5% Mor in their food and/or 0.15% NaNO2 in their drinking water for 23 weeks. The induction of tumors and/or preneoplastic lesions in the forestomach and esophagus was significantly increased in the group receiving MU plus NaNO2. The numbers and areas of liver glutathione S-transferase placental form (GST-P)-positive foci were significantly elevated with MU or Mor plus NaNO2. Experiment 2 was conducted to assess formation of N-nitroso compounds in the stomach, and to detect DNA adduct generation in target organs by immunohistochemical staining. Groups of 5 or 14 animals were starved overnight, then given 0.4% MU or 2.0% Mor in the diet, or basal diet alone for 1 h. Then NaNO2 or distilled water was given intragastrically. The mean gastric N-methyl-N-nitrosourea yield in the MU plus NaNO2 group was 7700 micrograms at 2 h after combined administration. The mean N-nitrosomorpholine yield in the group given Mor plus NaNO2 was 6720 micrograms. Immunohistochemically, N7-methyldeoxyguanosine-positive nuclei were evident in the forestomach epithelium at 8 h after the combination treatment with MU plus NaNO2.

Rapid gas chromatographic profiling and screening of biologically active amines

An efficient method is described for the simultaneous determination of 57 amines including volatile aliphatic amines, nonvolatile polyamines and catecholamines present in aqueous samples. The method is based on two-phase isobutyloxycarbonylation (isoBOC) with a pH shift. In 1.0 M phosphate buffer at pH 7.5, phenolic hydroxyl groups were allowed to react with isobutyl chloroformate in the dichloromethane phase, and subsequently pH of the aqueous phase was increased to 12.0 for the reaction of basic amino functions. The resulting N(O)-isoBOC amines were recovered by solid-phase extraction using Chromosorb P in normal phase partition mode, with subsequent tert.- butyldimethylsilylation of the remaining hydroxyl groups for gas chromatographic analysis. Using this combined procedure, linear responses were obtained in the concentration range of 0.2-12 ppm, with correlation coefficients varying from 0.945 to 0.999 for most of the amines studied except for 5-methoxytryptamine (0.864). Temperature-programmed retention index (I) sets as measured on DB-5 and DB-17 dual-capillary columns of different polarity were characteristic of each amine and thus, useful in the screening for amines by computer I matching. When applied to saliva samples, the present method allowed rapid screening for each spiked amine and unspiked polyamines such as 1,3-diaminopropane, putrescine, cadaverine and spermidine.

Generation of an endogenous DNA-methylating agent by nitrosation in Escherichia coli

Escherichia coli ada ogt mutants, which are totally deficient in O6-methylguanine-DNA methyltransferases, have an increased spontaneous mutation rate. This phenotype is particularly evident in starving cells and suggests the generation of an endogenous DNA alkylating agent under this growth condition. We have found that in wild-type cells, the level of the inducible Ada protein is 20-fold higher in stationary-phase and starving cells than in rapidly growing cells, thus enhancing the defense of these cells against DNA damage. The increased level of Ada in stationary cells is dependent on RpoS, a stationary-phase-specific sigma subunit of RNA polymerase. We have also identified a potential source of the mutagenic agent. Nitrosation of amides and related compounds can generate directly acting methylating agents and can be catalyzed by bacteria] enzymes. E. coli moa mutants, which are defective in the synthesis of a molybdopterin cofactor required by several reductases, are deficient in nitrosation activity. It is reported here that a moa mutant shows reduced generation of a mutagenic methylating agent from methylamine (or methylurea) and nitrite added to agar plates. Moreover, a moa mutation eliminates much of the spontaneous mutagenesis in ada ogt mutants. These observations indicate that the major endogenous mutagen is not S-adenosylmethionine but arises by bacterially catalyzed nitrosation.

Response of human keratinocytes to extremely low concentrations of N-methyl-N'-nitro-N-nitrosoguanidine

Since alkylating agents are widely present in the environment and constitute a continuous challenge to genome integrity, cells and organisms have developed defense mechanisms to remove such lesions. We monitored the response of human keratinocytes to a very low concentration of a methylating agent, namely 2.5 nM N-methyl-N'-nitro- N-nitrosoguanidine (MNNG). The effect of a 60-min exposure of quiescent cells to 2.5 nM MNNG was studied in terms of DNA integrity, poly(ADP-ribose) metabolism, clonogenic survival and DNA synthesis. We observed two waves of DNA strand break formation and resealing. Interestingly, the amount of DNA strand breaks in exposed cells was lower than in unexposed control cells. This phenomenon was also observed when cells were exposed to MNNG in the presence of a protein synthesis inhibitor, or when they were maintained on ice during the treatment. A dose of 2.5 nM MNNG stimulated poly(ADP-ribose) turnover, reduced the intracellular NAD+ content, stimulated DNA synthesis and caused a remarkable increase in clonogenic survival. Thus, the cellular responses to extremely low concentrations of MNNG differ sharply from those observed at higher doses of this carcinogen. We conclude that the very low dose response cannot be extrapolated from usual dose-response analyses.

The etiology of bladder cancer--are there any new clues or predictors of behavior?

It is well documented that the etiology of bladder cancer involves environmental factors. Most chemical carcinogens probably affect the urothelial cells via their presence in the urine. As an important cofactor, cell proliferative activity may be increased by urinary bladder infection, irritation by bladder stones or through the action of a variety of endogenously produced direct acting chemicals or agents. Among the known causative factors, avoidable major ones are occupational exposure to certain chemicals such as benzidine and 4-aminobiphenyl, cigarette smoking and bilharzial infection, which could be eradicated by a combination of praziquantel, antihelminth therapy, education and improvements in social welfare. An anticarcinogenic drug, cyclophosphamide, used as an immunosuppressive agent also seems to be associated with a high risk of idiopathic induction of bladder cancer and physicians should therefore pay particular attention to its diverse effects when considering its prescription. In contrast to the above, the consumption of coffee and tea including artificial sweeteners is now thought unlikely to be major risk. So far there is no good biochemical tool to predict individual exposure to bladder carcinogens/or relative risk of bladder cancer development. However, acetylation capacity can be applied to assess susceptibility to carcinogenic amines in people exposed in their working environment. Progress in molecular biological analysis will hopefully bring to light etiology-specific DNA damage in the bladder tumors and prove useful for prediction of tumor behavior in the near future.

The role of chemical, physical, or viral exposures and health factors in neurocarcinogenesis: implications for epidemiologic studies of brain tumors

This review highlights some future prospects and implications for epidemiologic research on the etiology of nervous system tumors. It reviews some points regarding physiology of the nervous system, in connection with mechanisms of neurocarcinogenesis, and experimental studies in animals. The results of epidemiologic studies are summarized in the light of the biological and experimental observations. The following aspects are particularly emphasized: (i) higher susceptibility of the developing nervous system to neurocarcinogenic agents (in the fetus and after birth); (ii) possible implications of knowledge about mechanisms of neurocarcinogenesis regarding crossing of the blood-brain barrier, activation of oncogenes and inactivation of anti-oncogenes, relationship between chemical structure and neurocarcinogenic action; (iii) necessity of further investigation concerning the occurrence of nitrosoureas and their precursors in the environment, and the potential role of nitroso compounds in the development of human brain tumors; (iv) lack of information about promoting or inhibiting neurocarcinogenic effects, and co-carcinogenesis--among others, interaction between X-irradiation and exposure to neurocarcinogenic nitrosoureas; (v) need for studying the potential neurocarcinogenic risk of polyomaviruses BKV, JCV, and SV40 to humans.

N-nitroso compounds in two nitrosated food products in southwest Korea

Gastric cancer is the commonest malignant neoplasm in Southwest Korea. The possibility of carcinogenic dietary factors led to the investigation of exposure to N-nitroso compound precursors among residents of the City of Chonju and of two outlying rural townships in North Cholla Province. Two traditional and widely consumed home-prepared food products, salted pickled cabbage (kimchi) and salted seafood sauce (chut-kal) were analysed (a) for nitrite, nitrate, total secondary amines and pH in these food products prior to nitrite incubation and (b) for volatile nitrosamines and total N-nitroso compounds before and after incubation with nitrite in simulated human stomach conditions. Nitrate levels were significantly higher in kimchi (median 1550 mg/kg) than in chut-kal (median 140 mg/kg) (P < 0.001). Secondary amine levels in non-nitrosated samples of kimchi (median 5.5 mg/kg) were significantly lower than secondary amine levels in non-nitrosated chut-kal (median 56 mg/kg) (P = < 0.001). Analyses of nitrite-incubated kimchi revealed high levels of total N-nitroso compounds (median 1173 micrograms/kg); the increase with nitrosation was significant (P = 0.001). The concentration of N-nitroso compounds in nitrite-incubated kimchi was significantly greater than that found in nitrite-incubated chut-kal (P = 0.015). The combination of high levels of nitrate in the kimchi, the demonstration of high levels of total N-nitroso compounds in this food after nitrosation, and the volume of kimchi consumed in the traditional diet suggest that salted pickled cabbage may play a role in gastric carcinogenesis in Southwest Korea.

Dietary factors and the risk of glioma in adults: results of a case-control study in Melbourne, Australia

In a population-based case-control study of 416 incident gliomas in adults carried out in Melbourne, Australia, between 1987 and 1991, 409 age-sex-matched case-control pairs (243 male and 166 female) had adequate data available to examine associations between the dietary intake of N-nitroso compounds, N-nitroso precursors, other nutrients including N-nitroso inhibitors, and the risk of glioma. Dietary intakes were based on the reported frequency of consumption of 59 food items. Increased odds ratio (OR) were observed in males who consumed high levels of bacon, corned meats, apples, melons and oil. OR less than unity were observed in men consuming cabbage and cola drinks, and in women who consumed wholegrain bread, pasta, corned meat, bananas, cauliflower, brocoli, cola drinks and nuts. Generally, N-nitroso associations were greater in men and micronutrient associations were greater in women. Elevated OR in men, but not women, were associated with the intake of N-nitroso dimethylamine (NDMA), retinol and vitamin E. The intake of nitrate (largely of vegetable origin) was protective in women but not in men. When analyzed using multiple logistic regression, the association with NDMA intake in males was not modified by dietary micronutrient intakes. In females, beta carotene alone, though not directly associated with risk, modified the effect of NDMA. On balance, this study added only limited support to the N-nitroso hypothesis of glial carcinogenesis.

Nitrate, nitrite and N-nitroso compounds

A risk assessment has been made on nitrate, nitrite and N-nitroso compounds encountered in the human diet. Vegetables constitute a major source of nitrate providing over 85% of the average daily human dietary intake. Nitrite and N-nitroso compounds present in the diet contribute relatively small amounts to the body burden and the major source of these biologically reactive compounds is derived from the bacterial and mammalian metabolism of ingested nitrate. Additionally, endogenous synthesis provides an important source contributing to the body burden of nitrate. Data from animal toxicological studies, human effects and epidemiological surveys have been reviewed and evaluated. It is concluded that there is no firm scientific evidence at present to recommend drastic reductions beyond the average levels of nitrate encountered in vegetables grown in keeping with good agricultural practice. Recommendations have also been made for further animal and human studies to be carried out to elucidate the potential risks to man from ingested nitrate.

High-performance liquid chromatographic determination of N-nitroso-N-alkylureas by pre-column fluorescence derivatization and application to blood analysis

A method for the derivatization and separation of N-nitroso-N-alkylureas [alkyl = methyl (NMU), ethyl (NEU), and n-butyl (NBU)] has been developed. Fluorescent derivatives were formed with sodium sulphide, taurine and o-phthalaldehyde and separated by reversed-phase high-performance liquid chromatography. The limits of detection of standard NMU, NEU and NBU were 0.25, 0.8 and 1.5 pmol/200 microliters, respectively. The method was applied to the determination of NMU in blood after extraction with acetonitrile in the presence of calcium chloride. NBU was used as the internal standard. The recovery of NMU from blood was ca. 95%, and the limit of detection was 10 pmol/400 microliters blood. NMU levels in rabbit blood following a single oral administration were also measured.