N-Nitroso compounds in the diet

In vitro DNA adduct profiling to mechanistically link red meat consumption to colon cancer promotion

Colorectal cancer (CRC) is the third most common cancer type in the world. Epidemiological research has demonstrated that both red and processed meat consumption significantly contribute to CRC risk. In this study, red meat toxicity was investigated by means of simulated gastrointestinal conditions, malondialdehyde (MDA) analysis and UHPLC-(HR)MS(/MS) based DNA adductomics. Since dairy products with high calcium content are associated with a decreased CRC-risk, the possible CRC-protective effects of calcium were assessed as well. The obtained results confirmed the earlier reported finding that heme-rich meat stimulates lipid peroxidation and O⁶-carboxymethylguanine (O⁶-CMG) DNA adduct formation during digestion. Calcium carbonate (CaCO₃) supplementation resulted in both toxic and anti-toxic effects; i.e. stimulation of O⁶-CMG production, but reduction of MDA formation. DNA adductome mapping of meat digests revealed a significant interindividual variability. The observed DNA adduct profile also differed according to the digested meat type, uncovering different putative DNA adducts that seem to be associated with digestion of beef or chicken with or without supplemented CaCO₃. Formamidopyrimidine-adenine was found to be discriminative for meat digests without added CaCO₃, carboxyethylcytosine was significantly higher in beef digests and methoxymethylcytosine (or its hydroxyethylcytosine isomer) was found to be lower in meat digests supplemented with CaCO₃. These results demonstrate that DNA adduct formation may be involved in the pathway that links red meat digestion to CRC promotion. In addition, the possible CRC-protective attributes of calcium through anti-oxidant actions could be documented.

Diet-related DNA adduct formation in relation to carcinogenesis

The human diet contributes significantly to the initiation and promotion of carcinogenesis. It has become clear that the human diet contains several groups of natural foodborne chemicals that are at least in part responsible for the genotoxic, mutagenic, and carcinogenic potential of certain foodstuffs. Electrophilic chemicals are prone to attack nucleophilic sites in DNA, resulting in the formation of altered nucleobases, also known as DNA adducts. Since DNA adduct formation is believed to signal the onset of chemically induced carcinogenesis, the DNA adduct-inducing potential of certain foodstuffs has been investigated to gain more insight into diet-related pathways of carcinogenesis. Many studies have investigated diet-related DNA adduct formation. This review summarizes work on known or suspected dietary carcinogens and the role of DNA adduct formation in hypothesized carcinogenesis pathways.

Long-Term Stability of Volatile Nitrosamines in Human Urine

Volatile nitrosamines (VNAs) are established teratogens and carcinogens in animals and classified as probable (group 2A) and possible (group 2B) carcinogens in humans by the IARC. High levels of VNAs have been detected in tobacco products and in both mainstream and sidestream smoke. VNA exposure may lead to lipid peroxidation and oxidative stress (e.g., inflammation), chronic diseases (e.g., diabetes) and neurodegenerative diseases (e.g., Alzheimer's disease). To conduct epidemiological studies on the effects of VNA exposure, short-term and long-term stabilities of VNAs in the urine matrix are needed. In this report, the stability of six VNAs (N-nitrosodimethylamine, N-nitrosomethylethylamine, N-nitrosodiethylamine, N-nitrosopiperidine, N-nitrosopyrrolidine and N-nitrosomorpholine) in human urine is analyzed for the first time using in vitro blank urine pools fortified with a standard mixture of all six VNAs. Over a 24-day period, analytes were monitored in samples stored at ∼20°C (collection temperature), 4-10°C (transit temperature) and -20 and -70°C (long-term storage temperatures). All six analytes were stable for 24 days at all temperatures (n = 15). The analytes were then analyzed over a longer time period at -70°C; all analytes were stable for up to 1 year (n = 62). A subset of 44 samples was prepared as a single batch and stored at -20°C, the temperature at which prepared samples are stored. These prepared samples were run in duplicate weekly over 10 weeks, and all six analytes were stable over the entire period (n = 22).

A New Automated Method and Sample Data Flow for Analysis of Volatile Nitrosamines in Human Urine

Volatile nitrosamines (VNAs) are a group of compounds classified as probable (group 2A) and possible (group 2B) carcinogens in humans. Along with certain foods and contaminated drinking water, VNAs are detected at high levels in tobacco products and in both mainstream and sidestream smoke. Our laboratory monitors six urinary VNAs-N-nitrosodimethylamine (NDMA), N-nitrosomethylethylamine (NMEA), N-nitrosodiethylamine (NDEA), N-nitrosopiperidine (NPIP), N-nitrosopyrrolidine (NPYR), and N-nitrosomorpholine (NMOR)-using isotope dilution GC-MS/MS (QQQ) for large population studies such as the National Health and Nutrition Examination Survey (NHANES). In this paper, we report for the first time a new automated sample preparation method to more efficiently quantitate these VNAs. Automation is done using Hamilton STAR^™ and Caliper Staccato^™ workstations. This new automated method reduces sample preparation time from 4 hours to 2.5 hours while maintaining precision (inter-run CV < 10%) and accuracy (85% - 111%). More importantly this method increases sample throughput while maintaining a low limit of detection (<10 pg/mL) for all analytes. A streamlined sample data flow was created in parallel to the automated method, in which samples can be tracked from receiving to final LIMs output with minimal human intervention, further minimizing human error in the sample preparation process. This new automated method and the sample data flow are currently applied in bio-monitoring of VNAs in the US non-institutionalized population NHANES 2013-2014 cycle.

Processed meat: the real villain?

Meat is a food rich in protein, minerals such as iron and zinc as well as a variety of vitamins, in particular B vitamins. However, the content of cholesterol and saturated fat is higher than in some other food groups. Processed meat is defined as products usually made of red meat that are cured, salted or smoked (e.g. ham or bacon) in order to improve the durability of the food and/or to improve colour and taste, and often contain a high amount of minced fatty tissue (e.g. sausages). Hence, high consumption of processed foods may lead to an increased intake of saturated fats, cholesterol, salt, nitrite, haem iron, polycyclic aromatic hydrocarbons, and, depending upon the chosen food preparation method, also heterocyclic amines. Several large cohort studies have shown that a high consumption of processed (red) meat is related to increased overall and cause-specific mortality. A meta-analysis of nine cohort studies observed a higher mortality among high consumers of processed red meat (relative risk (RR) = 1·23; 95 % CI 1·17, 1·28, top v. bottom consumption category), but not unprocessed red meat (RR = 1·10; 95 % CI 0·98, 1·22). Similar associations were reported in a second meta-analysis. All studies argue that plausible mechanisms are available linking processed meat consumption and risk of chronic diseases such as CVD, diabetes mellitus or some types of cancer. However, the results of meta-analyses do show some degree of heterogeneity between studies, and it has to be taken into account that individuals with low red or processed meat consumption tend to have a healthier lifestyle in general. Hence, substantial residual confounding cannot be excluded. Information from other types of studies in man is needed to support a causal role of processed meat in the aetiology of chronic diseases, e.g. studies using the Mendelian randomisation approach.

Consumption of meat is associated with higher fasting glucose and insulin concentrations regardless of glucose and insulin genetic risk scores: a meta-analysis of 50,345 Caucasians

BACKGROUND

Recent studies suggest that meat intake is associated with diabetes-related phenotypes. However, whether the associations of meat intake and glucose and insulin homeostasis are modified by genes related to glucose and insulin is unknown.

OBJECTIVE

We investigated the associations of meat intake and the interaction of meat with genotype on fasting glucose and insulin concentrations in Caucasians free of diabetes mellitus.

DESIGN

Fourteen studies that are part of the Cohorts for Heart and Aging Research in Genomic Epidemiology consortium participated in the analysis. Data were provided for up to 50,345 participants. Using linear regression within studies and a fixed-effects meta-analysis across studies, we examined 1) the associations of processed meat and unprocessed red meat intake with fasting glucose and insulin concentrations; and 2) the interactions of processed meat and unprocessed red meat with genetic risk score related to fasting glucose or insulin resistance on fasting glucose and insulin concentrations.

RESULTS

Processed meat was associated with higher fasting glucose, and unprocessed red meat was associated with both higher fasting glucose and fasting insulin concentrations after adjustment for potential confounders [not including body mass index (BMI)]. For every additional 50-g serving of processed meat per day, fasting glucose was 0.021 mmol/L (95% CI: 0.011, 0.030 mmol/L) higher. Every additional 100-g serving of unprocessed red meat per day was associated with a 0.037-mmol/L (95% CI: 0.023, 0.051-mmol/L) higher fasting glucose concentration and a 0.049-ln-pmol/L (95% CI: 0.035, 0.063-ln-pmol/L) higher fasting insulin concentration. After additional adjustment for BMI, observed associations were attenuated and no longer statistically significant. The association of processed meat and fasting insulin did not reach statistical significance after correction for multiple comparisons. Observed associations were not modified by genetic loci known to influence fasting glucose or insulin resistance.

CONCLUSION

The association of higher fasting glucose and insulin concentrations with meat consumption was not modified by an index of glucose- and insulin-related single-nucleotide polymorphisms. Six of the participating studies are registered at clinicaltrials.gov as NCT0000513 (Atherosclerosis Risk in Communities), NCT00149435 (Cardiovascular Health Study), NCT00005136 (Family Heart Study), NCT00005121 (Framingham Heart Study), NCT00083369 (Genetics of Lipid Lowering Drugs and Diet Network), and NCT00005487 (Multi-Ethnic Study of Atherosclerosis).

Chromium (VI) potentiates the DNA adducts (O(6)-methylguanine) formation of N-nitrosodimethylamine in rat: implication on carcinogenic risk

Chromium (VI) [Cr(VI)] and nitrosamines such as N-nitrosodimethylamine (NDMA) exist commonly in the environment. To evaluate the potential influence of Cr(VI) co-exposure on the carcinogenic risk of NDMA, Female Wistar rats were treated with various concentrations of Cr(VI) and/or NDMA via drinking water for 15days and the DNA adducts (O(6)-methylguanine, O(6)-MeG) of NDMA in liver tissue was used as a bioindicator. The results showed that Cr(VI) synergistically enhanced the O(6)-MeG formation, which could lead to an increase in DNA damage and carcinogenic potential. Although Cr(VI) did not alter the CYP 2E1 enzyme activity, it decreased GSH content, which would be an potential mechanism for the potentiated O(6)-MeG formation by Cr(VI) co-exposure. These results would contribute to the development of quantitative risk assessment of NDMA or even for a group of nitrosamines under environmental mixture exposure.

N-Methyl-N-nitrosourea as a mammary carcinogenic agent

The administration of chemical carcinogens is one of the most commonly used methods to induce tumors in several organs in laboratory animals in order to study oncologic diseases of humans. The carcinogen agent N-methyl-N-nitrosourea (MNU) is the oldest member of the nitroso compounds that has the ability to alkylate DNA. MNU is classified as a complete, potent, and direct alkylating compound. Depending on the animals' species and strain, dose, route, and age at the administration, MNU may induce tumors' development in several organs. The aim of this manuscript was to review MNU as a carcinogenic agent, taking into account that this carcinogen agent has been frequently used in experimental protocols to study the carcinogenesis in several tissues, namely breast, ovary, uterus, prostate, liver, spleen, kidney, stomach, small intestine, colon, hematopoietic system, lung, skin, retina, and urinary bladder. In this paper, we also reviewed the experimental conditions to the chemical induction of tumors in different organs with this carcinogen agent, with a special emphasis in the mammary carcinogenesis.

Plant-Based and Plant-Rich Diet Patterns during Gestation: Beneficial Effects and Possible Shortcomings

Environmental and lifestyle factors are known to play an important role during gestation, determining newborns' health status and influencing their risk of being subject to certain noncommunicable diseases later in life. In particular, maternal nutritional patterns characterized by a low intake of plant-derived foods could increase the risk of gestation-related issues, such as preeclampsia and pregravid obesity, increase genotoxicant susceptibility, and contribute to the onset of pediatric diseases. In particular, the risk of pediatric wheeze, diabetes, neural tube defects, orofacial clefts, and some pediatric tumors seems to be reduced by maternal intake of adequate amounts of vegetables, fruits, and selected antioxidants. Nevertheless, plant-based diets, like any other diet, if improperly balanced, could be deficient in some specific nutrients that are particularly relevant during gestation, such as n-3 (ω-3) fatty acids, vitamin B-12, iron, zinc, and iodine, possibly affecting the offspring's health state. Here we review the scientific literature in this field, focusing specifically on observational studies in humans, and highlight protective effects elicited by maternal diets enriched in plant-derived foods and possible issues related to maternal plant-based diets.

High resolution mass spectrometry based profiling of diet-related deoxyribonucleic acid adducts

Exposure of DNA to endo- and exogenous DNA binding chemicals can result in the formation of DNA adducts and is believed to be the first step in chemically induced carcinogenesis. DNA adductomics is a relatively new field of research which studies the formation of known and unknown DNA adducts in DNA due to exposure to genotoxic chemicals. In this study, a new UHPLC-HRMS(/MS)-based DNA adduct detection method was developed and validated. Four targeted DNA adducts, which all have been linked to dietary genotoxicity, were included in the described method; O(6)-methylguanine (O(6)-MeG), O(6)-carboxymethylguanine (O(6)-CMG), pyrimidopurinone (M1G) and methylhydroxypropanoguanine (CroG). As a supplementary tool for DNA adductomics, a DNA adduct database, which currently contains 123 different diet-related DNA adducts, was constructed. By means of the newly developed method and database, all 4 targeted DNA adducts and 32 untargeted DNA adducts could be detected in different DNA samples. The obtained results clearly demonstrate the merit of the described method for both targeted and untargeted DNA adduct detection in vitro and in vivo, whilst the diet-related DNA adduct database can distinctly facilitate data interpretation.

Impact of O6-methylguanine-DNA methyltransferase expression on the drug resistance of clear cell renal cell carcinoma

OBJECTIVE

The deoxyribonucleic acid-repair protein O(6)-methylguanine-deoxyribonucleic acid methyltransferase is a major determinant of resistance of cells to various alkylating drugs. Its expression profile is different in different cancer types. Here, we studied the expression and function of O(6)-methylguanine-deoxyribonucleic acid methyltransferase in clear cell renal cell carcinoma.

METHODS

The expression of O(6)-methylguanine-deoxyribonucleic acid methyltransferase was evaluated in clear cell renal cell carcinoma tissues and cell lines by quantitative real-time polymerase chain reaction and immunohistochemistry. The relationship between O(6)-methylguanine-deoxyribonucleic acid methyltransferase expression and clinicopathological characteristics was analyzed. To further investigate the function of O(6)-methylguanine-deoxyribonucleic acid methyltransferase in clear cell renal cell carcinoma resistance to alkylating agents, siRNA targeting O(6)-methylguanine-deoxyribonucleic acid methyltransferase were used to silence the O(6)-methylguanine-deoxyribonucleic acid methyltransferase expression.

RESULTS

We found that O(6)-methylguanine-deoxyribonucleic acid methyltransferase is over-expressed in clear cell renal cell carcinoma tissues and cell lines. O(6)-methylguanine-deoxyribonucleic acid methyltransferase expression is related with tumor progression in clear cell renal cell carcinoma patients. Up-regulation of O(6)-methylguanine-deoxyribonucleic acid methyltransferase plays a critical role in primary resistance to alkylating agents.

CONCLUSIONS

The overexpression of O(6)-methylguanine-deoxyribonucleic acid methyltransferase contributes to resistance of clear cell renal cell carcinoma to standard chemotherapy. Our results have significance for understanding a new pathway of the development of drug resistance of clear cell renal cell carcinoma.

A survey of nitrate and nitrite concentrations in conventional and organic-labeled raw vegetables at retail

A national survey of the nitrate ( NO3(-)) and nitrite ( NO2(-)) concentrations in raw and highly consumed vegetables available at retail in the United States was conducted. A total of 194 samples of fresh broccoli, cabbage, celery, lettuce, and spinach categorized as conventional or organic by label were collected from 5 major cities in different geographic regions of the United States and analyzed to determine NO3(-) and NO2(-) concentrations. There were no differences in the mean NO2(-) values of conventional compared with organic vegetables taken from the 5 metropolitan areas. However, significant differences in mean pairwise comparisons between some conventional and organic vegetables for NO3(-) content were observed. The mean NO2(-) concentration of both conventional and organic vegetables ranged between 0.1 and 1.2 mg/kg of fresh weight (FW) with the exception of conventional spinach that contained 8.0 mg/kg FW. Mean NO3(-) contents of conventional broccoli, cabbage, celery, lettuce, and spinach were 394, 418, 1496, 851, and 2797 mg/kg FW, respectively, while their organic-labeled counterparts averaged 204, 552, 912, 844, and 1318 mg/kg FW. In most cases, organic vegetables were numerically lower in NO3(-) content than their conventional counterparts. Based on survey results, the finding that low NO3(-) levels were observed in some organic vegetables in different cities may warrant further study to determine if true differences exist, due to production practices, seasonal differences, and the magnitudes of those differences. Furthermore, the geographic differences in NO3(-) content of vegetables may flaw estimates of daily NO2(-) and NO3(-) exposure.

Transnitrosation of non-mutagenic N-nitrosoproline forms mutagenic N-nitroso-N-methylurea

N-Nitroso-N-methylurea (NMU) is a potent carcinogen and suspected as a cause of human cancer. In this study, mutagenic NMU was detected by HPLC after the transnitrosation of non-mutagenic N-nitrosoproline (NP) to N-methylurea in the presence of thiourea (TU) under acidic conditions. The structure of NMU was confirmed by comparing (1)H NMR and IR spectra with that of authentic NMU after fractionation by column chromatography. Furthermore, a fraction containing NMU formed by transnitrosation was mutagenic in Salmonella typhimurium TA1535. NMU was formed in the reaction of NP and N-methylurea in the presence of 1,1,3,3-tetramethylthiourea (TTU) or 1,3-dimethylthiourea in place of TU as an accelerator. The reaction rate constants (k) for NMU formation were correlated with their nucleophilicity of sulfur atom in thioureas. The N-methylurea concentration did not affect the NMU formation, whereas the rate of NMU formation correlated linearly with concentrations of NP, TTU and oxonium ion. The observed kinetics suggests a mechanism by which the nitroso group was transferred directly from the protonated NP to the thiourea then to N-methylurea to form NMU. The rate-determining step was the formation of the complex with the protonated NP and thiourea.

Dose-dependent effect of N'-Nitrosodiethylamine on hepatic architecture, RBC rheology and polypeptide repertoire in Wistar rats

N'-Nitrosodiethylamine (NDEA) is an effective hepatotoxicant, carcinogen and mutagen. NDEA-induced hepatic necrosis, through metabolic activation by CYP2E1, is an extensively used experimental model. In the present study, we analysed the dose- and time-dependent effect of NDEA on hepatic damage, RBC rheology and proteomic profile in male Wistar rats. The rats, 5-6 weeks old, were divided into four groups: Group-1 served as control and received normal saline, Group-2 received a single dose of 200 mg/kg body weight NDEA intraperitoneally (i.p.) and the animals were sacrificed after one week; the rats of Group-3 received a single dose of 100 mg/kg body weight NDEA and were sacrificed after one week; Group-4 received 100 mg/kg body weight/wk NDEA for two weeks and were then sacrificed. Various biochemical parameters such as ALT, AST, ALP and bilirubin were determined. Further, RBC rheology, histopathology (H&E staining) of liver biopsies and polypeptide profiling (SDS-PAGE) in sera and liver sections were also carried out both in control and NDEA treated groups. Our results showed a significant increase in all the biochemical parameters of the liver function test (p<0.05). In NDEA treated categories dacryocytes (tear drop cells), schistocytes (fragmented cells), codocytes (target cells), acanthocytes (spur cells) and ovalocytes (oval cells) were observed. H & E stained liver biopsies treated with NDEA showed abnormal liver architecture with severe haemorrhage, neutrophilic infiltration and dysplastic hepatocytes manifested in a dose-dependent manner. Software analysis of SDS-PAGE of control and NDEA treated rat sera and liver revealed qualitative and quantitative differences in polypeptide composition. Based on the presence/absence, polypeptides were classified in three different categories: (1) house-keeping, present in all the groups investigated; (2) novel, present in either control or NDEA treated group at any given time; (3) differential expression, showing quantitative differences. Our study indicates a dose and time-dependent hepatocellular damage and proteome profile which is likely due to NDEA-mediated oxidative stress in rats.

Red Meat and Colorectal Cancer

Colorectal cancer (CRC) is the third most common cancer in men and the second in women worldwide. More than half of cases occur in more developed countries. The consumption of red meat (beef, pork, lamb, veal, mutton) is high in developed countries and accumulated evidence until today demonstrated a convincing association between the intake of red meat and especially processed meat and CRC risk. In this review, meta-analyses of prospective epidemiological studies addressed to this association, observed link of some subtypes of red meat with CRC risk, potential carcinogenic compounds, their mechanisms and actual recommendations of international guidelines are presented.

A facile fabrication of copper particle-decorated novel graphene flower composites for enhanced detecting of nitrite

A novel 3D porous flower-like reduced graphene oxide (f-RGO) was explored as the support material for the Cu particles on glassy carbon electrode (Cu/f-RGO/GCE) for detecting nitrite.

Antioxidant effect of lycopene-enriched tomato paste on N-nitrosodiethylamine-induced oxidative stress in rats

Lycopene is a carotenoid pigment produced by vegetables and fruits, with tomatoes and their processed products being the most abundant sources. A high number of conjugated dienes make lycopene a powerful radical scavenger. Its antioxidant properties are considered to be primarily involved in many beneficial health effects. The present study was designed to assess the protective effect of lycopene-enriched tomato paste against N-nitrosodiethylamine (NDEA)-induced oxidative stress in rats. Forty-eight male Wistar rats were divided randomly into six groups. Four groups were treated with tomato paste, per os, for 28 days in doses which were equivalent to 0.5 (groups II and V) and 2.5 mg/kg b.w./day of lycopene (groups III and VI). Rats from groups IV-VI were given intraperitoneally a single dose of NDEA, 150 mg/kg b.w. Group I (control) was given distilled water. Pretreatment with tomato paste protected the antioxidant enzymes: superoxide dismutase, catalase and glutathione reductase. Their activity was recovered by 32-97 %, as compared to NDEA-treated rats. Microsomal lipid peroxidation in the liver was decreased in rats pretreated with a lower dose of tomato paste by 28 %, as compared to animals given NDEA alone. Pretreatment with tomato paste caused a decrease in plasma concentration of protein carbonyls, even below the control level, in rats given NDEA. Moreover, a 10 % reduction of DNA damage in leucocytes caused by NDEA was observed. The tomato paste tested was able to suppress NDEA-induced oxidative stress in rats.

Expression of selected proteins of the extrinsic and intrinsic pathways of apoptosis in human leukocytes exposed to N-nitrosodimethylamine

N-nitrosodimethylamine (NDMA) is a xenobiotic widespread in human environment capable of regulating the lifespan of immune cells. In this study, we examined the roles of the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)/death receptor 5 (DR5) complex and the Fas molecule in the induction of the extrinsic apoptosis pathway in human neutrophils (polymorphonuclear neutrophils (PMNs)) and peripheral blood mononuclear cells (PBMCs) exposed to NDMA. Also we assessed these proteins ability to trigger the intrinsic apoptosis pathway in those cells. For this purpose, we examined the expression of Fas-associated protein with death domain, truncated Bid (tBid) proteins, and apoptogenic factors such as apoptosis-inducing factor, Smac/Diablo, Omi/HtrA2, and caspase-3 as an indication of accomplished apoptosis phenomenon. PMNs and PBMCs were isolated from whole blood by density gradient centrifugation using Polymorphrep. Apoptotic cells were assessed with flow cytometry using a ready-made kit. The expression of proapoptotic molecules was investigated by Western blot analysis of PMNs and PBMCs treated with NDMA and/or rhTRAIL. The obtained results confirm the proapoptotic effects of NDMA on the examined human leukocytes and indicate an active participation of the TRAIL/DR5 complex and Fas protein in the process of apoptosis. Moreover, the research revealed distinct mechanisms of intrinsic apoptosis pathway activation between PMNs and PBMCs exposed to NDMA, as confirmed by the different levels of tBid, Smac/Diablo, Omi/HtrA2, and caspase-3 expression in those cells.

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.

Novel study on N-nitrosamines as risk factors of cardiovascular diseases

Millions of people are exposed daily to N-nitrosamines from different environmental sources. The present study aims at investigating the role of N-nitrosamines in the alteration of homocysteine, lipid profile, oxidative stress, paraoxonase activity, antioxidant enzymes, and free radicals which are important risk factors for CVD. In addition, biomarkers of cardiovascular diseases such as creatine kinase MB activity (CK-MB) and lactate dehydrogenase (LDH) as well as protein expression of both glutathione peroxidase and glutathione S-transferase π isozyme were assayed after treatment of rats with 0.2 mg/kg body weight of N-nitrosodibutylamine (NDBA), N-nitrosoethylbutylamine (NEBA), N-nitrosobutylpropylamine (NBPA), N-nitrosodiethylamine (NDEA), N-nitrosodimethylamine (NDMA), and N-nitrosodiphenylamine (NDPA) as a daily dose for two weeks. LDL levels, paraoxonase activity, reduced glutathione levels, and glutathione reductase activities were increased, whereas HDL levels decreased after treatment of rats with most of N-nitrosamines compared to control group. Moreover, levels of free radicals and catalase activity increased, whereas protein expression of both glutathione peroxidase and glutathione S-transferase decreased after treatment of rats with some N-nitrosamines. The data showed that most N-nitrosamines increased CK-MB and LDH activities. It is concluded that N-nitrosamines increased levels of free radicals, and decreased the activity of antioxidant enzymes which may consequently increase the incidence of CVDs.

Usual dietary intake among female breast cancer survivors is not significantly different from women with no cancer history: results of the National Health and Nutrition Examination Survey, 2003-2006

Dietary intake is a modifiable behavior that may reduce the risk of recurrence and death among breast cancer survivors. Cancer survivors are encouraged to consume a diet rich in fruit, vegetables, and whole grains and limit red meat, processed meat, and alcohol intake. Using data from the National Health and Nutrition Examination Survey (2003-2006), this study examined whether breast cancer survivors and women with no history of cancer differed in the distribution of usual intake of foods included in the dietary recommendations for preventing cancer and recurrences. Participants completed one or two 24-hour dietary recalls. The food groups included in this analysis were whole fruit; total vegetables; dark green and orange vegetables; whole grains; red meat; processed meat; alcohol; and calories from solid fat, alcohol, and added sugar. The National Cancer Institute Method was used to estimate the distribution of usual intake and to compare breast cancer survivors (n=102) to noncancer respondents (n=2,684). Using age and cancer survivor as covariates, subgroup estimates of usual intake were constructed. No significant group differences were found, except that survivors reported a greater intake of whole grains. More than 90% of both groups did not meet recommendations for fruits, vegetables, and whole grains; 75.4% and 70.2%, respectively, consumed less than the red meat recommendation; and <10% of either group met the recommendation for percent energy from solid fat, alcohol, and added sugar. The diet of breast cancer survivors was not significantly different from women with no history of cancer.

Fish intake and ovarian cancer risk: a meta-analysis of 15 case-control and cohort studies

Background

Previous epidemiological studies have shown that fish consumption may modify the risk of ovarian cancer. However, these studies yielded controversial results. The present meta-analysis was undertaken to evaluate the relationship between fish intake and ovarian cancer risk.

Methods

A literature search was carried out using Pubmed, Embase, and Cochrane Library Central database for all relevant studies up to August 2013. We pooled the relative risks (RR) from individual studies using fixed-effect or random-effect model, and carried out heterogeneity and publication bias analyses.

Results

A total of 15 (ten case–control, and five cohort) studies were included in the present meta-analysis, representing data for 889,033 female subjects and 6,087 ovarian cancer cases. We found that total fish intake was not significantly associated with the risk of ovarian cancer among cohort studies (RR = 1.04 95% CI [0.89, 1.22]) as well as case–control studies (RR = 0.90, 95% CI [0.73,1.12]). There was no evidence of publication bias as suggested by Begg's test (P = 0.55) and Egger's test(P = 0.29).

Conclusions

The present meta-analysis showed that total fish consumption was not significantly associated with the risk of ovarian cancer. Further analysis on different fish species and food preparation methods should be conducted in future studies.

Reactive oxygen species mediate Epstein-Barr virus reactivation by N-methyl-N'-nitro-N-nitrosoguanidine

N-nitroso compounds (NOCs) and Epstein-Barr virus (EBV) reactivation have been suggested to play a role in the development of nasopharyngeal carcinoma (NPC). Although chemicals have been shown to be a risk factor contributing to the carcinogenesis of NPC, the underlying mechanism is not fully understood. We demonstrated recently that N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) enhances the genomic instability and tumorigenicity of NPC cells via induction of EBV reactivation. However, the mechanisms that trigger EBV reactivation from latency remain unclear. Here, we address the role of ROS in induction of EBV reactivation under MNNG treatment. EBV reactivation was induced in over 70% of EBV-positive NA cells and the promoter of Rta (Rp) was activated after MNNG treatment. Inhibitor experiments revealed ATM, p38 MAPK and JNK were activated by ROS and involved in MNNG-induced EBV reactivation. Significantly, ROS scavengers N-acetyl-L-cysteine (NAC), catalase and reduced glutathione inhibited EBV reactivation under MNNG and H₂O₂ treatment, suggesting ROS mediate EBV reactivation. The p53 was essential for EBV reactivation and the Rp activation by MNNG. Moreover, the p53 was phosphorylated, translocated into nucleus, and bound to Rp following ROS stimulation. The results suggest ROS play an important role in initiation of EBV reactivation by MNNG through a p53-dependent mechanism. Our findings demonstrate novel signaling mechanisms used by NOCs to induce EBV reactivation and provide a novel insight into NOCs link the EBV reactivation in the contribution to the development of NPC. Notably, this study indicates that antioxidants might be effective for inhibiting N-nitroso compound-induced EBV reactivation and therefore could be promising preventive and therapeutic agents for EBV reactivation-associated malignancies.

O6-methylguanine-DNA methyltransferase in the defense against N-nitroso compounds and colorectal cancer

Colorectal cancer (CRC) is among the leading causes of cancer death worldwide, involving multiple dietary and non-dietary risk factors. A growing body of evidence suggests that N-nitroso compounds (NOC) play a pivotal role in the etiology of CRC. NOC are present in food and are also formed endogenously in the large intestine. Upon metabolic activation and also spontaneously, they form electrophilic species that methylate the DNA, producing N-methylated purines and O(6)-methylguanine, the latter of which bears high mutagenic and carcinogenic potential. Methylated DNA bases are removed by base excision repair initiated by the alkyladenine-DNA glycosylase, the family of AlkB homologs proteins, and the suicide enzyme O(6)-methylguanine-DNA methyltransferase (MGMT), which is the main focus of this review. We present animal models with a deficiency of MGMT that display a tremendously enhanced sensitivity toward alkylation-induced colorectal carcinogenesis, highlighting its role in the protection against the cytotoxic and mutagenic effects of alkylating agents. In line with these studies, MGMT was linked to the formation of human sporadic CRC. Colorectal tumors and precursor lesions frequently display epigenetic inactivation of MGMT resulting from promoter hypermethylation, which is tightly associated with the occurrence of G:C to A:T transition mutations in the KRAS oncogene. We also discuss clinical data, which identified the MGMT status of CRC patients as promising parameter for the treatment of metastasized CRC using alkylating anticancer drugs such as temozolomide.

Prenatal exposure to nitrosatable drugs, vitamin C, and risk of selected birth defects

Nitrosatable drugs, such as secondary or tertiary amines and amides react with nitrite in an acidic environment to form N-nitroso compounds, teratogens in animal models. Vitamin C is a known nitrosation inhibitor.

METHODS

Using data from the National Birth Defects Prevention Study, we assessed nitrosatable drug exposure and vitamin C intake during the first trimester among 11,606 case-mothers of infants with oral clefts, limb deficiencies (LDs), or congenital heart defects and 6807 control-mothers of infants without major birth defects during 1997-2005. Daily intake of vitamin C was estimated from maternal interviews that elicited information about supplement use and dietary intake.

RESULTS

With no reported use of nitrosatable drugs as the referent group, a lower odds ratio (OR) was observed for transverse LDs among births to mothers exposed to secondary amine drugs and daily vitamin C supplementation (adjusted odds ratio [aOR] 1.2, 95% confidence interval [CI] 0.83-1.8) compared with women taking these drugs and no supplementation (aOR 2.7, 95% CI 1.5-4.6). The OR for longitudinal LDs associated with secondary amine exposure was lower with daily dietary vitamin C intake ≥85 mg (aOR 1.2, 95% CI 0.68-2.0) compared with <85 mg (aOR 1.9, 95% CI 1.2-3.1). Daily vitamin C supplementation in combination with higher dietary vitamin C intake reduced associations between nitrosatable drug exposures and limb deficiencies and atrial septal defects not otherwise specified.

CONCLUSION

Prenatal dietary and vitamin C supplement intake may diminish the association between nitrosatable drug exposure during pregnancy and selected birth defects.

Non-viral factors contributing to hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a major cause of cancer death worldwide, accounting for over half a million deaths per year. The geographic pattern of HCC incidence is parallel to exposure to viral etiologic factors. Its incidence is increasing, ranging between 3% and 9% annually depending on the geographical location, and variability in the incidence rates correspond closely to the prevalence and pattern of the primary etiologic factors. Chronic infections with hepatitis B viruses or hepatitis C viruses have both been recognized as human liver carcinogens with a combined attributable fraction of at least 75% of all HCC cases. Multiple non-viral factors have been implicated in the development of HCC. Increased body mass index and diabetes with subsequent development of non-alcoholic steatohepatitis represent significant risk factors for HCC. Other non-viral causes of HCC include iron overload syndromes, alcohol use, tobacco, oral contraceptive, aflatoxin, pesticides exposure and betel quid chewing, a prevalent habit in the developing world. Wilson disease, α-1 antitrypsin deficiency, Porphyrias, autoimmune hepatitis, Schistosoma japonicum associated with positive hepatitis B surface antigen, and thorotrast-ray are also contributing hepatocellualar carcinoma. In addition, primary biliary cirrhosis, congestive liver disease and family history of liver cancer increase the risk of HCC incident. In conclusion, clarification of relevant non-viral causes of HCC will help to focus clinicians on those risk factors that are modifiable. The multilevel preventative approach will hopefully lead to a reduction in incidence of non-viral HCC, and a decrease in the patient morbidity and mortality as well as the societal economic burden associated with HCC.

Non-viral factors contributing to hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a major cause of cancer death worldwide, accounting for over half a million deaths per year. The geographic pattern of HCC incidence is parallel to exposure to viral etiologic factors. Its incidence is increasing, ranging between 3% and 9% annually depending on the geographical location, and variability in the incidence rates correspond closely to the prevalence and pattern of the primary etiologic factors. Chronic infections with hepatitis B viruses or hepatitis C viruses have both been recognized as human liver carcinogens with a combined attributable fraction of at least 75% of all HCC cases. Multiple non-viral factors have been implicated in the development of HCC. Increased body mass index and diabetes with subsequent development of non-alcoholic steatohepatitis represent significant risk factors for HCC. Other non-viral causes of HCC include iron overload syndromes, alcohol use, tobacco, oral contraceptive, aflatoxin, pesticides exposure and betel quid chewing, a prevalent habit in the developing world. Wilson disease, α-1 antitrypsin deficiency, Porphyrias, autoimmune hepatitis, Schistosoma japonicum associated with positive hepatitis B surface antigen, and thorotrast-ray are also contributing hepatocellualar carcinoma. In addition, primary biliary cirrhosis, congestive liver disease and family history of liver cancer increase the risk of HCC incident. In conclusion, clarification of relevant non-viral causes of HCC will help to focus clinicians on those risk factors that are modifiable. The multilevel preventative approach will hopefully lead to a reduction in incidence of non-viral HCC, and a decrease in the patient morbidity and mortality as well as the societal economic burden associated with HCC.

Influence of various cooking methods on the concentrations of volatile N-nitrosamines and biogenic amines in dry-cured sausages

N-nitrosamines, biogenic amines, and residual nitrites are harmful substances and are often present in cured meats. The effects of different cooking methods (boiling, pan-frying, deep-frying, and microwave) were investigated on their contents in dry-cured sausage. The various N-nitrosamines were isolated by a steam distillation method and analyzed by gas chromatography mass spectrometry (GC-MS). The biogenic amines were determined after extraction with perchloric acid as dansyl derivatives by high-performance liquid chromatography (HPLC) method. The results showed that initial dry-cured raw sausage contained 5.31 μg/kg of total N-nitrosamines. Cooking by deep-frying or pan-frying resulted in products having the highest (P < 0.05) contents, compared with boiling or microwave treatments, which were not different from the raw. Although frying increased the content of N-nitrosodimethylamine (NDMA), N-nitrosodiethylamine (NDEA), and N-nitrosopyrrolidine (NPYR), it decreased the contents of histamine and cadaverine. Boiling and microwave treatments decreased the total biogenic amines significantly (P < 0.05). Residual nitrite was significantly reduced by cooking treatments. The results suggest that boiling and microwave treatments were more suitable methods for cured meat.

Meat consumption, diabetes, and its complications

Several prospective studies have reported that risk of type 2 diabetes (T2DM) is elevated in meat consumers, especially when processed meats are consumed. Elevated risks of coronary heart disease (CHD) and stroke in meat consumers have also been reported. In this overview, the evidence regarding meat consumption and the risk of diabetes, both type 1 diabetes (T1DM) and T2DM and their macro- and microvascular complications, is reviewed. For T2DM, we performed a new meta-analysis including publications up to October 2012. For T1DM, only a few studies have reported increased risks for meat consumers or for high intake of saturated fatty acids and nitrates and nitrites. For T2DM, CHD, and stroke, the evidence is strongest. Per 100 g of total meat, the pooled relative risk (RR) for T2DM is 1.15 (95 % CI 1.07-1.24), for (unprocessed) red meat 1.13 (95 % CI 1.03-1.23), and for poultry 1.04 (95 % CI 0.99-1.33); per 50 g of processed meat, the pooled RR is 1.32 (95 % CI 1.19-1.48). Hence, the strongest association regarding T2DM is observed for processed (red) meat. A similar observation has been made for CHD. For stroke, however, a recent meta-analysis shows moderately elevated risks for meat consumers, for processed as well as for fresh meats. For the microvascular complications of diabetes, few prospective data were available, but suggestions for elevated risks can be derived from findings on hyperglycemia and hypertension. The results are discussed in the light of the typical nutrients and other compounds present in meat--that is, saturated and trans fatty acids, dietary cholesterol, protein and amino acids, heme-iron, sodium, nitrites and nitrosamines, and advanced glycation end products. In light of these findings, a diet moderate to low in red meat, unprocessed and lean, and prepared at moderate temperatures is probably the best choice from the public health point of view.

A meta-analysis of alcohol consumption and the risk of brain tumours

BACKGROUND

Alcohol is capable of traversing the blood-brain barrier and is thus a possible risk factor for brain cancer. Several epidemiological studies have been published on the issue, a number of those during recent years, with inconsistent findings.

MATERIALS AND METHODS

We performed a systematic literature search in the Medline and EMBASE databases. We found a total of 19 studies providing risk estimates for total alcohol or specific alcoholic beverages. Pooled estimates of the relative risks (RR) and 95% confidence intervals (CI) were calculated using random-effects models.

RESULTS

The pooled RR of brain cancer for alcohol drinkers versus non-drinkers was 0.97 (95% CI 0.82-1.15; based on 12 studies). Moderate (<2 drinks/day) and heavy alcohol drinkers had RRs of 1.01 (95% CI 0.81-1.25) and 1.35 (95% CI 0.85-2.15), respectively. With reference to specific alcoholic beverages, the RRs were 1.01 (95% CI 0.70-1.48) for wine, 0.96 (95% CI 0.82-1.12) for beer, and 1.20 (95% CI 1.01-1.42) for spirit consumption. The RRs for drinkers versus non-drinkers were 0.93 (95% CI 0.81-1.07) for glioma and 0.71 (95% CI 0.45-1.12) for meningioma.

CONCLUSIONS

Alcohol drinking does not appear to be associated with adult brain cancer, though a potential effect of high doses deserves further study.

Intestinal formation of N-nitroso compounds in the pig cecum model

N-Nitroso compounds (NOC) are a group of compounds including N-nitrosamines and N-nitrosamides, which are well-known for their carcinogenic, mutagenic, and teratogenic properties. Humans can be exposed to NOC through the diet and environmentally, or NOC can be formed endogenously in the stomach and intestine. In the intestine, the formation of NOC is supposed to be afforded by the gut microbiota. In this study, the formation of the N-nitrosamines, N-nitrosomorpholine (NMOR) and N-nitrosopyrrolidine (NPYR), and the N-nitrosamides, N-nitrosomethylurea (NMU) and N-nitrosoethylurea (NEU), was investigated in the pig cecum model after the incubation of the corresponding precursor amine or amide with nitrite or nitrate. Following the incubation with nitrate, the formation of NMOR, NPYR, NMU, and NEU was detectable with the microbiota being responsible for the reduction of nitrate to nitrite. After the incubation of nitrite a chemical formation of NOC was shown.

Consumption of dairy and meat in relation to breast cancer risk in the Black Women's Health Study

PURPOSE

Dairy and meat consumption may impact breast cancer risk through modification of hormones (e.g., estrogen), through specific nutrients (e.g., vitamin D), or through products formed in processing/cooking (e.g., heterocyclic amines). Results relating meat and dairy intake to breast cancer risk have been conflicting. Thus, we examined the risk of breast cancer in relation to intake of dairy and meat in a large prospective cohort study.

METHODS

In the Black Women's Health Study, 1,268 incident breast cancer cases were identified among 52,062 women during 12 years of follow-up. Multivariable (MV) relative risks (RRs) and 95 % confidence intervals (CIs) were calculated using Cox proportional hazards models.

RESULTS

Null associations were observed for total milk (MV RR = 1.05, 95 % CI 0.74-1.46 comparing ≥1,000-0 g/week) and total meat (MV RR = 1.04, 95 % CI 0.85-1.28 comparing ≥1,000 < 400 g/week) intake and risk of breast cancer. Associations with intakes of specific types of dairy, specific types of meat, and dietary calcium and vitamin D were also null. The associations were not modified by reproductive (e.g., parity) or lifestyle factors (e.g., smoking). Associations with estrogen receptor (ER) positive (+), ER negative (-), progesterone receptor (PR) +, PR-, ER+/PR+, and ER-/PR- breast cancer were generally null.

CONCLUSIONS

This analysis of African-American women provides little support for associations of dairy and meat intake with breast cancer risk.

Association between dietary meat consumption and incident type 2 diabetes: the EPIC-InterAct study

AIMS/HYPOTHESIS

A diet rich in meat has been reported to contribute to the risk of type 2 diabetes. The present study aims to investigate the association between meat consumption and incident type 2 diabetes in the EPIC-InterAct study, a large prospective case-cohort study nested within the European Prospective Investigation into Cancer and Nutrition (EPIC) study.

METHODS

During 11.7 years of follow-up, 12,403 incident cases of type 2 diabetes were identified among 340,234 adults from eight European countries. A centre-stratified random subsample of 16,835 individuals was selected in order to perform a case-cohort design. Prentice-weighted Cox regression analyses were used to estimate HR and 95% CI for incident diabetes according to meat consumption.

RESULTS

Overall, multivariate analyses showed significant positive associations with incident type 2 diabetes for increasing consumption of total meat (50 g increments: HR 1.08; 95% CI 1.05, 1.12), red meat (HR 1.08; 95% CI 1.03, 1.13) and processed meat (HR 1.12; 95% CI 1.05, 1.19), and a borderline positive association with meat iron intake. Effect modifications by sex and class of BMI were observed. In men, the results of the overall analyses were confirmed. In women, the association with total and red meat persisted, although attenuated, while an association with poultry consumption also emerged (HR 1.20; 95% CI 1.07, 1.34). These associations were not evident among obese participants.

CONCLUSIONS/INTERPRETATION

This prospective study confirms a positive association between high consumption of total and red meat and incident type 2 diabetes in a large cohort of European adults.

Can methanolic extract of Nigella sativa seed affect glyco-regulatory enzymes in experimental hepatocellular carcinoma?

BACKGROUND AND AIM

To investigate the possible modulating role of "Nigella sativa" (NS), a plant commonly used in Egyptian traditional medicine, on premalignant perturbations in three glycol-regulatory enzymes in an experimental rat model of hepatocellular carcinoma (HCC).

METHODS

Thirty-six (36) male albino rats were divided into four groups (n = 9). Group 1 served as a normal control, group 2 was treated with methanolic extract of Nigella sativa (MENS) (1 g/kg/day, orally) for 14 weeks, group 3 received a single intraperitoneal dose of diethyl nitrosamine (DENA) (200 mg/kg), followed 2 weeks later by a subcutaneous injection of carbon tetrachloride (CCl(4), 3 ml/kg/week/6 weeks) and group IV was treated with MENS for 2 weeks prior to administration of the carcinogenic combination (DENA + CCl(4), as in group 3) until the end of the experiment. The total period of the experiment was 14 weeks.

RESULTS

In the DENA + CCl(4)-treated group, there was a significant increase in the relative liver weight, serum alpha fetoprotein level and the activities of hexokinase, glyceraldehyde phosphate dehydrogenase and glucose 6 phosphate dehydrogenase in both the serum and liver homogenate; this was accompanied by a subsequent decrease in body weight. Pre-treatment with MENS significantly maintained these parameters close to the normal condition.

CONCLUSION

Based on these results, we conclude that MENS has a chemo-preventive effect against the progression into liver malignancy through its modulation of the energy metabolic pathways (i.e. glycolysis) that may be involved in hepatocarcinogenesis.