N-Nitroso compounds in the diet

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

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

Beer constituents as potential cancer chemopreventive agents

Beer is a complex alcoholic beverage made from barley (malt), hop, water and yeast. Phenolic constituents of beer are derived from malt (70-80%) and hop (20-30%). Structural classes include simple phenols, benzoic- and cinnamic acid derivatives, coumarins, catechins, di-, tri- and oligomeric proanthocyanidins, (prenylated) chalcones and flavonoids as well as alpha- and iso-alpha-acids derived from hop. Compounds belonging to different structural classes have distinct profiles of biological activity in in vitro test systems, and in combination might lead to enhanced effects. Scientific evidence has accumulated over the past 10 years pointing to the cancer preventive potential of selected hop-derived beer constituents, i.e., prenylflavonoids including xanthohumol and isoxanthohumol, and hop bitter acids. Chemopreventive activities observed with these compounds relevant to inhibition of carcinogenesis at the initiation, promotion and progression phases, as well as results from in vivo studies on metabolism, bioavailability and efficacy are summarised in this review.

Maternal hair dye use and risk of neuroblastoma in offspring*

OBJECTIVE

Studies have suggested an association between maternal hair dye use and elevated risk of childhood cancer, including neuroblastoma. We analyzed data from a large case-control study to investigate the relationship between maternal hair dye use around pregnancy and risk of neuroblastoma in offspring.

METHODS

Cases were children with neuroblastoma diagnosed between 1992 and 1994 at hospitals in the United States and Canada participating in the Children's Cancer Group or the Pediatric Oncology Group. Random-digit dialing was used to identify one matched control for each case. Information on hair dye use was gathered from telephone interviews of 538 case and 504 control mothers.

RESULTS

Use of any hair dye in the month before and/or during pregnancy was associated with a moderately increased risk of neuroblastoma (adjusted odds ratio (OR) = 1.6; 95% confidence interval (CI) = 1.2-2.2). Temporary hair dye use (OR = 2.0, CI = 1.1-3.7) was more strongly associated with neuroblastoma than use of permanent hair dye (OR = 1.4, CI = 1.0-2.0).

CONCLUSION

Although the results of this study provide evidence of an association between maternal hair dye use and neuroblastoma, further research is necessary to evaluate effects by method of hair dye application, color, and chemical composition.

Mammary glands of sexually immature rats are more susceptible than those of mature rats to the carcinogenic, lethal, and mutagenic effects ofN-nitroso-N-methylurea

Knowing that the prepubertal period is a time of enhanced susceptibility for radiation-induced human breast cancer, we used the Fischer 344 rat model to explore the age-differential susceptibility of the mammary gland to the carcinogenic, lethal, and mutagenic effects of two structurally diverse chemical carcinogens, N-nitroso-N-methylurea (NMU), and 7,12-dimethylbenz(a)anthracene (DMBA). Mammary carcinoma incidences and multiplicities were significantly greater in immature than mature NMU-treated rats while mammary carcinoma incidences and multiplicities were significantly lower in immature than mature DMBA-treated rats. The survival of mammary clonogens of mature NMU-treated rats in limiting dilution transplantation assays was greater than that of the survival of mammary clonogens of immature NMU-treated rats. No differences were found in the survival of mammary cells from immature and mature rats exposed to DMBA. Although there were no mutation spectra differences, mammary epithelial cells of immature NMU-treated rats had greater mutation frequencies than those of mature NMU-treated rats. Together these results support the hypothesis that the mammary gland of immature rats is more susceptible to the carcinogenic, lethal, and mutagenic effects of alkylating agents represented by NMU in a carcinogen-class-specific manner. Further, the results suggest the importance of mechanistic and epidemiological studies of the susceptibility of the prepubertal breast to specific carcinogens such as alkylating agents.

Methylguanine methyltransferase activity deficiency in immature rat mammary epithelial cells parallels increased carcinogenic susceptibility

The prepubertal breast is more susceptible than the mature breast to the carcinogenic effects of ionizing radiation, and potentially to cigarette smoke and alkylating chemotherapeutics. Mammary epithelial cells (MECs) from sexually immature (3-week (wk)-old) Fischer 344 rats were more sensitive than mature (8-wk-old) rats to the carcinogenic, lethal, and mutagenic effects of N-nitroso-N-methylurea (NMU). The work reported here was undertaken to better define this age-specific susceptibility of the mammary gland to NMU. Using the alkaline comet assay, it was found that MECs from immature but not mature rats displayed an increase in single-strand DNA breaks or alkali-labile lesions 2 h following NMU treatment. Hoechst staining indicated apoptosis was not responsible for the increase. Inhibition of methylguanine methyltransferase (MGMT) did not affect immature MECs but caused mature MECs to recapitulate the immature response to NMU. Direct measurement of MGMT activity revealed that immature MECs are significantly deficient in MGMT activity relative to mature MECs. MECs had the lowest MGMT activity of all organs tested. Immature kidneys, which preferentially developed nephroblastomas after NMU treatment, also displayed significantly lower MGMT activity than mature kidneys. These results suggest that age-related differences in MGMT activity may play a significant role in age-differential susceptibility to rat mammary gland and kidney carcinogenesis, and argue the importance of extending these studies to humans. They also provide a mechanistic basis for studying, as potentially initiating events in breast cancer, exposures of prepubertal girls to alkylating agents, to which humans are exposed in cigarette smoke, the diet, and as chemotherapy.

Epoxide hydrolase and CYP2C9 polymorphisms, cigarette smoking, and risk of colorectal carcinoma in the Nurses' Health Study and the Physicians' Health Study

Microsomal epoxide hydrolase (mEH) and cytochrome P450 2C9 (CYP2C9) are involved in the bioactivation and detoxification of polycyclic aromatic hydrocarbons (PAHs) derived from tobacco smoke. Two coding-region mEH variants (Tyr113His, His139Arg) and CYP2C9 variants (Arg144Cys, Ile359Leu) have been described and affect enzyme specific activity. We investigated these polymorphisms and tested interactions with smoking in relationship to risk of colorectal carcinoma in two case-control studies nested in the Nurses' Health Study (NHS) and Physicians' Health Study (PHS) cohorts. mEH Tyr113His and His139Arg polymorphisms were not associated with the risk of cancer among 197 incident cases and 490 controls from the NHS. Among 273 incident cases and 453 controls from the PHS, carrying one or two copies of the 'rapid' 139Arg allele was associated with a significantly reduced risk of colorectal cancer (OR=0.70, 95% CI 0.49--0.99) when compared with His139 wild-type individuals. Risk of colorectal cancer was significantly reduced among men carrying the CYP2C9 *1/*2 genotype (OR=0.62, 95% CI 0.42--0.92) or at least one CYP2C9 variant allele (OR=0.72, 95% CI 0.52--1.00) when compared with *1/*1 wild-type individuals. For women, carrying at least one variant CYP2C9 allele was inversely associated with the risk of colorectal cancer (OR=0.85, 95% CI, 0.57--1.27) when compared with *1/*1 wild-type individuals. No statistically significant genotype-smoking or gene-gene interactions were found in this study. Our results indicate that individuals exposed to tobacco carcinogens were at increased risk of colorectal cancer and that overall risk is related to mEH and CYP2C9 genotype, although the results were not consistent between men and women.

A prospective study of red meat consumption and type 2 diabetes in middle-aged and elderly women: the women's health study

OBJECTIVE

The aim of this study was to prospectively assess the relation between red meat intake and incidence of type 2 diabetes.

RESEARCH DESIGN AND METHODS

Over an average of 8.8 years, we evaluated 37,309 participants in the Women's Health Study aged >/=45 years who were free of cardiovascular disease, cancer, and type 2 diabetes and completed validated semiquantitative food frequency questionnaires in 1993.

RESULTS

During 326,876 person-years of follow-up, we documented 1,558 incident cases of type 2 diabetes. After adjusting for age, BMI, total energy intake, exercise, alcohol intake, cigarette smoking, and family history of diabetes, we found positive associations between intakes of red meat and processed meat and risk of type 2 diabetes. Comparing women in the highest quintile with those in the lowest quintile, the multivariate-adjusted relative risks (RRs) of type 2 diabetes were 1.28 for red meat (95% CI 1.07-1.53, P < 0.001 for trend) and 1.23 for processed meat intake (1.05-1.45, P = 0.001 for trend). Furthermore, the significantly increased diabetes risk appeared to be most pronounced for frequent consumption of total processed meat (RR 1.43, 95% CI 1.17-1.75 for >/=5/week vs. <1/month, P < 0.001 for trend) and two major subtypes, which were bacon (1.21, 1.06-1.39 for >/=2/week vs. <1/week, P = 0.004 for trend) and hot dogs (1.28, 1.09-1.50 for >/=2/week vs. <1/week, P = 0.003 for trend). These results remained significant after further adjustment for intakes of dietary fiber, magnesium, glycemic load, and total fat. Intakes of total cholesterol, animal protein, and heme iron were also significantly associated with a higher risk of type 2 diabetes.

CONCLUSIONS

Our data indicate that higher consumption of total red meat, especially various processed meats, may increase risk of developing type 2 diabetes in women.

Current problems of food intake in young women in Japan: Their influence on female reproductive function

Accumulating evidence suggests that food customs are associated with quality of life in women of the reproductive age. In Japan, dietary limitation for cosmetic purposes, skipping food intake, intake of processed foods and the shift from Japanese to Westernized style food have increased among young women. These changes in food habits can cause inadequate intake of calories, micronutrients, unsaturated fat, phytestrogens and fiber as well as increasing environmental toxins. Furthermore, these food habits increase risk as a result of intake of food additives, anti-oxidants, processing agents and sweeteners, which have been demonstrated to be harmful to human health. These factors are speculated to not only influence the present lifestyle, but also to induce gynecologic disorders such as dysmenorrhea and irregular menstruation. The adverse effects of these dietary habits on pregnancy outcome and carcinogenesis of breast and ovarian cancers have also been demonstrated. In addition, latent development of organic diseases such as endometriosis, which are accompanied by dysmenorrhea, is a concern under the current nutritional environment in young women. Thus, it is an urgent issue to evaluate the present situation of eating habits in young Japanese women and estimate the influence of these habits on the quality of life including reproductive functions. (Reprod Med Biol 2004; 3: 107-114).

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

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

Nutrition and carcinogenesis

Traditional views of nutritional carcinogenesis depend on the identification of exogenous carcinogens as major risk factors. As our understanding evolves, it is clear that the pattern of events involves not only exogenous carcinogens, but also metabolic processes and endogenous and exogenous anticarcinogens. The process is modulated by the immune system, and genetics plays a significant role. New monitoring methods provide much-needed tools for providing proof of involvement of various factors at the level of human populations.

Dietary cancer and prevention using antimutagens

Many of the cancers common in the Western world, including colon, prostate and breast cancers, are thought to relate to dietary habits. Of the known risk factors, many will act through increasing the probability of mutation. Recognised dietary mutagens include cooked meat compounds, N-nitroso compounds and fungal toxins, while high meat and saturated fat consumption, increasing rates of obesity, and regular consumption of alcohol and tobacco are all dietary trends that could indirectly enhance the probability of mutation. However, there are significant difficulties in implementing and sustaining major dietary changes necessary to reduce the population's intake of dietary mutagens. Dietary antimutagens may provide a means of slowing progression toward cancer, and be more acceptable to the population. Consideration of genetic mechanisms in cancer development suggest several distinct targets for intervention. Strategies that reduce mutagen uptake may be the most simple intervention, and the one least likely to result in undesirable side effects. Certain (but not all) types of dietary fibres appear to reduce mutation through this mechanism, as may certain probiotics and large planar molecules such as chlorophyllin. Antioxidants have been suggested to scavenge free radicals, and prevent their interactions with cellular DNA. Small molecule dietary antioxidants include ascorbic acid, Vitamin E, glutathione, various polyphenols and carotenoids. We found a statistically significant relationship between colon cancer incidence and soil selenium status across different regions of New Zealand. Additionally, a study of middle-aged men suggested that blood selenium levels lower than 100 ng/ml were inadequate for repair or surveillance of oxidative (and other) DNA damage. We suggest that selenium will be an important antimutagen, at least in New Zealand, possibly through antioxidant effects associated with selenium's role in enzymes associated with endogenous repair of DNA damage. Modulation of xenobiotic metabolizing enzymes is well recognised as cancer-protective, and is a property of various flavonoids and a number of sulfur-containing compounds. Many fruits and vegetables contain compounds that will protect against mutation and cancer by several mechanisms. For example, kiwifruit has antioxidant effects and may also affect DNA repair enzymes. Dietary folate may be a key factor in maintenance of methylation status, while enhanced overall levels of vitamins and minerals may retard the development of genomic instability. The combination of each of these factors could provide a sustainable intervention that might usefully delay the development of cancer in New Zealand and other populations. Although there are a range of potentially antimutagenic fruits, vegetables and cereals available to these populations, current intake is generally below the level necessary to protect from dietary or endogenous mutagens. Dietary supplementation may provide an alternative approach.

Free radical destruction of N-nitrosodimethylamine in water

Absolute rate constants for the reactions of the hydroxyl radical, hydrated electron, and hydrogen atom with N-nitrosodimethylamine (NDMA) in water at room temperature have been determined using electron pulse radiolysis and transient absorption spectroscopy (*OH and e- aq) and EPR free induction decay attenuation (*H) measurements. Specific values of (4.30 +/- 0.12) x 10(8), (1.41 +/- 0.02) x 10(10), and (2.01 +/- 0.03) x 10(8) M(-1) s(-1) were measured, respectively. DMPO spin-trapping experiments demonstrated that the hydroxyl radical reaction with NDMA occurs by hydrogen atom abstraction from a methyl group, and the rate constant for the subsequent reaction of this radical transient with dissolved oxygen was measured as (5.3 +/- 0.6) x 10(6) M(-1) s(-1). This relatively slow rate constant implies that regeneration of the parent nitrosoamine from the oxidized transient could occur in natural waters containing dissolved organic compounds. The reaction of the hydrated electron with NDMA was to form a transient adduct anion, which could subsequently transfer this excess electron to regenerate the parent chemical. Such regeneration reactions would significantly reduce the effectiveness of any applied advanced oxidation technology remediation effort on NDMA-contaminated natural waters.

Circulating NO pool: assessment of nitrite and nitroso species in blood and tissues

The formation of nitric oxide (NO) has been linked to many regulatory functions in mammalian cells. With the appreciation that NO-mediated nitrosation reactions are involved in cell signaling and pathology there is a need to elucidate and better characterize the different biochemical pathways of NO in vivo. Despite significant methodological advances over the years one major obstacle in assessing the significance of nitrosated species and other NO-related metabolites remains: their reliable measurement in complex biological matrices. In this review we briefly discuss the major routes of NO metabolism and transport in the mammalian circulation, considering plasma, red blood cell, and tissue compartments separately. In addition, we attempt to give a recommendation as to the most appropriate analytical technique and sample processing procedures for the reliable quantification of either species.

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.

Infrequent microsatellite instability in liver fluke infection-associated intrahepatic cholangiocarcinomas from Thailand

The liver fluke infection-associated intrahepatic cholangiocarcinoma (ICC) is a major liver cancer in Northeast Thailand. The molecular basis of this ICC is poorly understood. To address possible roles of the DNA mismatch repair (MMR) system in ICC carcinogenesis, a fluorescence-labeling PCR/laser scanning technique with high sensitivity was employed to analyze genomic instability in the nuclear DNA (nDNA) and mitochondrial DNA (mtDNA) in 24 fresh and 13 formalin-fixed, paraffin-embedded tissues of ICC and their corresponding normal parts. Microsatellite instability (MSI) was assessed in nDNA, using 12 highly polymorphic loci including 5 Bethesda markers. These loci were mainly related to major MMR genes, hMSH2 and hMLH1. Also 3 (C)n and/or (C)n(A)n repeat instability at 1 noncoding region in the displacement-loop (D-loop) and 2 coding sequences in NADH dehydrogenase subunit 1 and subunit 5 gene in mtDNA were analyzed. MSI was only detected in 1 (2.7%), 6 (16.7%), 1 (2.9%), 1 (2.9%) or 2 (6.3%) out of 37, 36, 35, 35 or 32 cases at BAT-25, D2S123, D3S1611, D11S904 or D17S250, respectively. LOH was found at D3S1298, D3S1561, D5S346 and TP53 in 4 (18.2%) out of 22, 2 (18.2%) out of 11, 6 (33.3%) out of 18 and 3 (12.5%) out of 24 informative cases, respectively. In mtDNA, none except a single case out of the 37 (2.7%) exhibited repeat sequence instability in the D-loop. We conclude that the liver fluke infection-associated ICC in Thailand is classified as low frequency MSI or microsatellite stable type and that DNA MMR system, through hMSH2 and hMLH1 gene mutations, does not play a major role in its carcinogenesis.

Processed meat intake and incidence of Type 2 diabetes in younger and middle-aged women

AIM/HYPOTHESIS

The aim of this study was to investigate the association between processed and other meat intake and incidence of Type 2 diabetes in a large cohort of women.

METHODS

Incident cases of Type 2 diabetes were identified during 8 years of follow-up in a prospective cohort study of 91246 U.S. women aged 26 to 46 years and being free of diabetes and other major chronic diseases at baseline in 1991.

RESULTS

We identified 741 incident cases of confirmed Type 2 diabetes during 716276 person-years of follow-up. The relative risk adjusted for potential non-dietary confounders was 1.91 (95% CI: 1.42-2.57) in women consuming processed meat five times or more a week compared with those consuming processed meat less than once a week ( p<0.001 for trend). Further adjustment for intakes of magnesium, cereal fibre, glycaemic index, and caffeine or for a Western dietary pattern did not appreciably change the results and associations remained strong after further adjustment for fatty acid and cholesterol intake. Frequent consumption of bacon, hot dogs, and sausage was each associated with an increased risk of diabetes. While total red meat (beef or lamb as main dish, pork as main dish, hamburger, beef, pork or lamb as sandwich or mixed dish) intake was associated with an increased risk of diabetes, this association was attenuated after adjustment for magnesium, cereal fiber, glycaemic index, and caffeine (relative risk: 1.44; 95% CI: 0.92-2.24).

CONCLUSION/INTERPRETATION

Our data suggest that diets high in processed meats could increase the risk for developing Type 2 diabetes.

Cancer prevention and therapy: strategies and problems

During the next years, molecular diagnostic science and the pharmaceutical industry will face increasing demand for personalized medicine. Therapeutic treatments should be tailored to the needs of individual patient. Patients will inquire for information about potential tumor detection at an early stage when disease can be more likely to be arrested or cured with specific regimens of drug therapy. To respond to this demand, science and industry need to modulate therapeutic approaches to the continuous development of cancer. Now more than ever, it is necessary to fill the knowledge hiatus between the "beginning" and the "end" of cancer development, i.e we need to critically analyze the extensive multi-step process of cancer development that still remains poorly understood.

Effect of modified atmosphere packaging and irradiation in combination on content of nitrosamines in cooked pork sausage

The effect of modified atmosphere packaging and irradiation in combination on nitrosodimethylamine (NDMA) and nitrosopyrrolidine (NPYR) levels in pork sausage was studied. Emulsion-type cooked pork sausage was manufactured and packaged in aerobic, CO2 (100%), N2 (100%), and CO2/N2 (25%/75%) environments, respectively, and irradiated at 0, 5, 10, and 20 kGy with gamma irradiation. The nitrosamine contents were significantly reduced by irradiation, and the reduction of nitrosamines was more extensive with modified atmosphere packaging than with aerobic packaging. The correlation coefficient between irradiation dose and nitrosamine content indicated that irradiation can reduce the levels of nitrosamines. The combination of irradiation and modified atmosphere packaging is effective in enhancing the chemical safety of sausage by reducing nitrosamines, if present, as well as enhancing the microbial safety of cooked pork sausage.

Use of human liver S9 in the Ames test: assay of three procarcinogens using human S9 derived from multiple donors

The purpose of the present study was to examine the inter-individual variation in the mutagenicity of chemicals using a variety of human S9 fractions. For this purpose, three procarcinogens, 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), benzo[a]pyrene (BP), and dimethylnitrosamine (DMN), were selected for the Ames test and their mutagenicity was examined using human liver S9 fractions prepared from 18 different donors and one pooled liver S9 fraction prepared from 15 different donors. In addition, rat S9 fraction prepared from male rats pretreated with phenobarbital and 5,6-benzoflavone (PB/BF) was used as reference in order to examine the mutagenic differences between human and rat (PB/BF) S9 fractions. The data demonstrate a large inter-individual diversity in the mutagenic response to procarcinogens. The mutagenicity of IQ and BP in the presence of a human liver S9 fraction (lot HLS-014) was equal to that observed in the presence of rat (PB/BF) S9 fraction. The mutagenicity of IQ and BP in the presence of a pooled human liver S9 fraction was lower (90 and 95%, respectively) than that observed in the presence of rat (PB/BF) S9. On the contrary, the mutagenicity of DMN in the presence of either a selected human liver S9 fraction (lot HLS-014) or pooled fraction was 8-fold higher than that found in the presence of rat (PB/BF) S9 fraction. Human liver S9 fraction (lot HLS-014) had one of the highest cytochrome P450 enzyme activities among the 18 different donors and higher than the pooled human liver S9 fraction. These results suggest that the use of both selected human liver S9 fractions with high metabolic activity (e.g., lot HLS-014 as used in this study) and a pooled S9 fraction with moderate metabolic activity could be used as a means to evaluate the inter-individual variability in mutagenic response to chemicals and to confirm positive responses from studies completed with rodent S9.

Inhibitory effect of chlorophyllin on the frequency of micronuclei induced by sodium nitrite in mice

In this report the potency of chlorophyllin (CHL) was evaluated to prevent two types of damage produced by nitrite in mice: the increase of micronucleated polychromatic erythrocytes (MNPE) and the bone marrow toxicity, measured as the index of polychromatic erythrocytes/normochromatic erythrocytes (PE/NE). The study was done in eight groups of male mice. The first three groups were administered orally for 4 days with sodium nitrite (10, 15 and 20 mg/kg), the daily administration with nitrite was followed by an intraperitoneal administration of CHL (4 mg/kg), three more groups were administered with the same amounts of nitrite, a seventh group of mice was treated with distilled water while another was treated with CHL (4 mg/kg). Our study produced two main results: (a) no bone marrow injury was induced by any of the tested chemicals, as indicated with the PE/NE index, and (b) CHL protected (as high as 44%) the MNPE produced in nitrite treated mice.

Cytotoxic and genotoxic effects of megazol, an anti-Chagas' disease drug, assessed by different short-term tests

Cyto- and genotoxicity induced by drugs can limit the dose and duration of treatment, can adversely affect patient quality of life, and may be life-threatening. Two drugs are currently being used for treatment of the acute phase of Chagas' disease and both have serious undesirable effects. In this research, cyto- and genotoxic activity of the nitroimidazole-tiadiazole derivative CL 64855 2-amino-5-(1-methyl-5-nitro-2-imidazolyl)-1,3,4-thiadiazole (megazol), a promising alternative drug, was evaluated in vitro with different short-term tests: (a) induction of recombination events and mutation in the yeast Saccharomyces cerevisiae D7 strain, with and without induction of cytochrome P-450; DNA damage (single and double strand breaks, alkali-labile sites, etc.) by the Comet assay in different mammalian cells. S. cerevisiae did not show a significant increase of mutant and recombinant event frequency, both with and without cytochrome P-450. On the other hand, the cytochrome complex appeared to detoxify the drug with respect to cytotoxicity. Results in rat and mouse fresh leukocytes showed a dose-response relation of drug-induced DNA damage. Findings in treated VERO cells suggested a complex treatment time-DNA damage relationship and the possible induction of repair mechanisms. Furthermore, bleomycin effects were increased in rat cells by simultaneous administration of megazol. Megazol shows different biological activity in relation to cellular types and experimental conditions (with or without cytochrome P-450, short/long time of exposure, with or without other genotoxins), thus suggesting a modulation of effectiveness by different physiological/biochemical conditions of cells. The findings could be useful to evaluate new megazol-derived compounds and to assess the risks/benefits relationship for each drug.

Concomitant presence of N-nitroso and S-nitroso proteins in human plasma

Nitric oxide (NO)-mediated nitrosation reactions are involved in cell signaling and pathology. Recent efforts have focused on elucidating the role of S-nitrosothiols (RSNO) in different biological systems, including human plasma, where they are believed to represent a transport and buffer system that controls intercellular NO exchange. Although RSNOs have been implicated in cardiovascular disease processes, it is yet unclear what their true physiological concentration is, whether a change in plasma concentration is causally related to the underlying pathology or purely epiphenomenological, and to what extent other nitrosyl adducts may be formed under the same conditions. Therefore, using gas phase chemiluminescence and liquid chromatography we sought to quantify the basal plasma levels of NO-related metabolites in 18 healthy volunteers. We find that in addition to the oxidative products of NO metabolism, nitrite (0.20 +/- 0.02 micromol/l nitrite) and nitrate (14.4 +/- 1.7 micromol/l), on average human plasma contains an approximately 5-fold higher concentration of N-nitroso species (32.3 +/- 5.0 nmol/l) than RSNOs (7.2 +/- 1.1 nmol/l). Both N- and S-nitroso moieties appear to be associated with the albumin fraction. This is the first report on the constitutive presence of a high-molecular-weight N-nitroso compound in the human circulation, raising the question as to its origin and potential physiological role. Our findings may not only have important implications for the transport of NO in vivo, but also for cardiovascular disease diagnostics and the risk assessment of nitrosamine-related carcinogenesis in man.

Oxidation of biological systems: oxidative stress phenomena, antioxidants, redox reactions, and methods for their quantification

Reactive oxygen species (ROS) and other radicals are involved in a variety of biological phenomena, such as mutation, carcinogenesis, degenerative and other diseases, inflammation, aging, and development. ROS are well recognized for playing a dual role as deleterious and beneficial species. The objectives of this review are to describe oxidative stress phenomena, terminology, definitions, and basic chemical characteristics of the species involved; examine the biological targets susceptible to oxidation and the defense mechanisms of the organism against these reactive metabolites; and analyze methodologies, including immunohistochemical markers, used in toxicological pathology in the visualization of oxidative stress phenomena. Direct detection of ROS and other free radicals is difficult, because these molecules are short-lived and highly reactive in a nonspecific manner. Ongoing oxidative damage is, thus, generally analyzed by measurement of secondary products including derivatives of amino acids, nuclei acids, and lipid peroxidation. Attention has been focused on electrochemical methods based on voltammetry measurements for evaluating the total reducing power of biological fluids and tissues. This approach can function as a tool to assess the antioxidant-reducing profile of a biological site and follow changes in pathological situations. This review thus includes different topics essential for understanding oxidative stress phenomena and provides tools for those intending to conduct study and research in this field.

Meat consumption, cancer risk and population groups within New Zealand

In comparison with other OECD countries with good cancer registries, New Zealand has the highest mortality rate of colon cancer, second highest of breast cancer and third highest of prostate cancer. A possible association with heterocyclic amine consumption has been suggested for each of these cancers. Studies of locally cooked meat suggest that the main contributors to heterocyclic amines in the New Zealand diet would be well-cooked beef, chicken and pork. Well-cooked beef steak, and the specific heterocyclic amine, IFP, showed a weak positive correlation with prostate cancer risk in the New Zealand population, but no studies thus far have considered the role of meat cooking practices or heterocyclic amines in the development of other cancers. The Maori and Pacific Island people, despite a superficially similar diet, have a substantially lower incidence of colon cancer than people of Caucasian origin. These differences are particularly intriguing in view of a report that a very high percentage of these people have a fast acetylator phenotype-a factor suggested to augment the effect of well-cooked red meat in other populations. The three population groups are known to differ in their preferences for meat type (including processed meats), and there are anecdotal suggestions that they may differ in preferred cooking methods. More detailed population studies are warranted to establish the role of meat, meat processing, cooking methods and the interaction with food plants and/or with genotype and phenotype in New Zealand.

Monitoring of nitrite and N-nitrosamine levels in irradiated pork sausage

Residual nitrite and N-nitrosamine levels were monitored on irradiated emulsion-type cooked pork sausage in aerobic or vacuum packaging states during storage. The sausage was irradiated at 0, 5, 10, and 20 kGy and stored at 4 degrees C for 4 weeks. The residual nitrite levels were significantly reduced by gamma irradiation (P < 0.05), whereas the vacuum packaging was more effective for nitrite reduction than aerobic packaging during storage. N-nitrosodimethylamine (NDMA) and N-nitrosopyrrolidine (NPYR) levels were significantly reduced in the vacuum packaged sausage irradiated with 20 kGy after 4 weeks. Reduction of NPYR in aerobically packaged sausage was also found after 4 weeks by irradiating with a 5-kGy or higher dose. NDMA reduction was shown in vacuum packaging and irradiation at 20 kGy. Gamma irradiation was effective in reducing the residual nitrite all throughout storage and N-nitrosamines in sausage after storage.

Detecting rare mutations associated with cancer risk

For more than a decade, investigators have been searching for a means of determining the risk of individuals developing cancer by detecting rare oncogenic mutations. The accumulation of mutations and the clonal evolvement of tumors provide opportunities for monitoring disease development and intervening prior to the presentation of clinical symptoms, or determining the risk of disease relapse during remission. A number of techniques, mostly polymerase chain reaction (PCR)-based, have been developed that enable the detection of rare oncogenic mutations within the range of 10(-2) to 10(-4) wild-type cells. Only a handful of procedures enable the detection of intragenic single base mutations at one mutant in 10-6 or better. These ultra-sensitive mutation detection techniques have produced some interesting results regarding single base mutation spectra and frequencies in p53, Harvey-ras, N-ras, and other reporter genes and DNA sequences in human tissues. Although there is evidence that some individuals may harbor cells or clones expressing genomic instability, the connection with the processes of carcinogenesis is still tenuous. There remains a need for rigorous epidemiological studies employing these ultra-sensitive mutation detection procedures. Since genomic instability is considered key to tumor development, the relevance of the detection of hypermutable clones in individuals is discussed in the context of cancer risk.

Mechanisms by which garlic and allyl sulfur compounds suppress carcinogen bioactivation. Garlic and carcinogenesis

Overall, a host of studies provides compelling evidence that garlic and its organic allyl sulfur components are effective inhibitors of the cancer process. These studies reveal that the benefits of garlic are not limited to a specific species, to a particular tissue, or to a specific carcinogen. Several mechanisms are likely to account for this protection. Notable among these is a depression in nitrosamine formation and a reduction in carcinogen bioactivation. The benefits provided by garlic must be viewed as part of the entire diet, since several dietary constituents can influence the degree of protection. More than one compound is responsible for the anticancer properties associated with garlic. Future research should focus on how genetic variability and daily environmental factors influence the anticancer benefits attributed to garlic and its allyl sulfur components.

Dietary fat and meat intake in relation to risk of type 2 diabetes in men

OBJECTIVE

To examine dietary fat and meat intake in relation to risk of type 2 diabetes.

RESEARCH DESIGN AND METHODS

We prospectively followed 42,504 male participants of the Health Professionals Follow-Up Study who were aged 40-75 years and free of diagnosed diabetes, cardiovascular disease, and cancer in 1986. Diet was assessed by a validated food frequency questionnaire and updated in 1990 and 1994. During 12 years of follow-up, we ascertained 1,321 incident cases of type 2 diabetes.

RESULTS

Intakes of total fat (multivariate RR for extreme quintiles 1.27, CI 1.04-1.55, P for trend=0.02) and saturated fat (1.34, 1.09-1.66, P for trend=0.01) were associated with a higher risk of type 2 diabetes. However, these associations disappeared after additional adjustment for BMI (total fat RR 0.97, CI 0.79-1.18; saturated fat 0.97, 0.79-1.20). Intakes of oleic acid, trans-fat, long-chain n-3 fat, and alpha-linolenic acid were not associated with diabetes risk after multivariate adjustment. Linoleic acid was associated with a lower risk of type 2 diabetes in men <65 years of age (RR 0.74, CI 0.60-0.92, P for trend=0.01) and in men with a BMI <25 kg/m(2) (0.53, 0.33-0.85, P for trend=0.006) but not in older and obese men. Frequent consumption of processed meat was associated with a higher risk for type 2 diabetes (RR 1.46, CI 1.14-1.86 for > or = 5/week vs. <1/month, P for trend <0.0001).

CONCLUSIONS

Total and saturated fat intake were associated with a higher risk of type 2 diabetes, but these associations were not independent of BMI. Frequent consumption of processed meats may increase risk of type 2 diabetes.

Mutagenic activity and mutational specificity of antiprotozoal drugs with and without nitrite treatment

We examined the mutagenic activities of six antiprotozoal drugs (three diaminopyrimidine compounds [pyrimethamine, diaveridine, and trimethoprim] and three 8-aminoquinoline derivatives [primaquine, pentaquine, and pamaquine]) in Escherichia coli WP2uvrA/pKM101 and Salmonella typhimurium TA100 and TA98 with and without nitrite treatment. The diaminopyrimidine compounds showed no mutagenic activity under any condition in any strain. The 8-aminoquinoline derivatives after nitrite treatment at 5-20 mM for 5 min at pH 3, on the contrary, showed clear mutagenicity in TA100 and WP2uvrA/pKM101 in the presence and absence of S9 mix. We concluded that 8-aminoquinoline derivatives became mutagenic following nitrite treatment. In the Lac(+) reversion assay with E. coli WP3101P-WP3106P, these nitrite-treated compounds induced G:C --> A:T transitions and G:C --> T:A transversions in the absence of S9 mix. On the other hand, A:T --> T:A transversions were induced only in the presence of S9 mix, suggesting a different kind of products may be responsible for the mutagenicity.

Dietary protective and risk factors for esophageal and stomach cancers in a low-epidemic area for stomach cancer in Jiangsu Province, China: comparison with those in a high-epidemic area

Comparative epidemiological studies with ecological and case-control approaches in high- and low-epidemic areas of China have provided us with much evidence with regard to risk and benefit in the environment. To clarify how dietary factors are involved in esophageal and stomach cancer development, we performed a case-control study in a low-epidemic area, and compared the findings with those obtained earlier for a high-epidemic area for stomach cancer in the same Jiangsu Province, China. We recruited 199 and 187 cases with esophageal and stomach cancers, respectively, and 333 population-based common controls. Odds ratios (ORs) for esophageal and stomach cancers were calculated with adjustment for potential confounding factors, using an unconditional logistic model. Current and former smoking elevated the OR for esophageal cancer, along with high intake of pickled vegetables and broiled meat, while decreased ORs were observed for frequently consumed raw vegetables and garlic. With regard to stomach cancer, ORs were increased with frequent consumption of salty fish, leftover gruel, and broiled meat, and lowered by snap bean consumption. The present risk factors were common to the previously obtained results in the high-epidemic area, and similarly distributed in each general population. While more protective factors were observed in the high-epidemic area, their penetrance was much greater in the low-epidemic area. The present study thus suggests that frequent vegetable and garlic consumption contributes to low mortality rates for esophageal and stomach cancers in a low-epidemic area, counteracting similar exposure levels for risk factors as in the high-epidemic area.

Role of plant polyphenols in genomic stability

Polyphenols are a large and diverse class of compounds, many of which occur naturally in a range of food plants. The flavonoids are the largest and best-studied group of these. A range of plant polyphenols are either being actively developed or currently sold as dietary supplements and/or herbal remedies. Although, these compounds play no known role in nutrition (non-nutrients), many of them have properties including antioxidant, anti-mutagenic, anti-oestrogenic, anti-carcinogenic and anti-inflammatory effects that might potentially be beneficial in preventing disease and protecting the stability of the genome. However not all polyphenols and not all actions of individual polyphenols are necessarily beneficial. Some have mutagenic and/or pro-oxidant effects, as well as interfering with essential biochemical pathways including topoisomerase enzyme activities, prostanoid biosynthesis and signal transduction. There is a very large amount of in vitro data available, but far fewer animal studies, and these are not necessarily predictive of human effects because of differences in bacterial and hepatic metabolism of polyphenols between species. Epidemiological studies suggest that high green tea consumption in the Japanese population and moderate red wine consumption in the French population may be beneficial for heart disease and cancer, and these effects may relate to specific polyphenols. A small number of adequately controlled human intervention studies suggest that some, but not all polyphenol extracts or high polyphenol diets may lead to transitory changes in the antioxidative capacity of plasma in humans. However, none of these studies have adequately considered long-term effects on DNA or the chromosome and unequivocally associated these with polyphenol uptake. Furthermore, clinical trials have required intravenously administered polyphenols at concentrations around 1400mg/m(2) before effects are seen. These plasma concentrations are unlikely to be achieved using the dietary supplements currently available. More focused human studies are necessary before recommending specific polyphenolic supplements at specific doses in the human population.

A historical perspective on garlic and cancer

Epidemiological and laboratory studies provide insight into the anticarcinogenic potential of garlic and its constituent compounds. Both water- and lipid-soluble allyl sulfur compounds are effective in blocking a myriad of chemically induced tumors. Part of the protection from these compounds probably relates to a block in nitrosamine formation and metabolism. However, blockage in the initiation and promotion phases of the carcinogenicity of various compounds, including polycyclic hydrocarbons, provide evidence that garlic and its constituents can alter several phase I and II enzymes. Their ability to block experimentally induced tumors in a variety of sites including skin, mammary and colon, suggests a general mechanism of action. Changes in DNA repair and in immunocompetence may also account for some of this protection. Some, but not all, allyl sulfur compounds can also effectively retard tumor proliferation and induce apoptosis. Changes in cellular thiol and phosphorylation stains may account for some of these antitumorigenic properties. The anticarcinogenic potential of garlic can be influenced by several dietary components including specific fatty acids, selenium, and vitamin A. Since garlic and its constituents can suppress carcinogen formation, carcinogen bioactivation, and tumor proliferation it is imperative that biomarkers be established to identify which individuals might benefit most and what intakes can occur with ill consequences.

Coexposure to ethanol with N-nitrosodimethylamine or 4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone during lactation of rats: marked increase in O(6)-methylguanine-DNA adducts in maternal mammary gland and in suckling lung and kidney

Use of alcoholic beverages increases risk of cancer at several target sites, including the breast. Of several possible mechanisms for this effect, competitive inhibition by ethanol of hepatic clearance of nitrosamines, resulting in increased dose delivery to posthepatic tissues, gives the quantitatively most pronounced enhancement. We investigated whether this effect would pertain to the mammary gland, and to ethanol and nitrosamines delivered translactationally to sucklings. Ethanol (1.6 g/kg) was administered by gavage to nursing Sprague-Dawley rats 10 min before 5 mg/kg N-nitrosodimethylamine (NDMA) or 50 mg/kg 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK); treatment was on postnatal days 1, 7, or 14. Tissues taken 4 h later for analysis of O(6)-methylguanine in DNA were liver, blood, and mammary glands from the mothers, and liver, lung, kidney, and blood from the sucklings. Ethanol cotreatment resulted in a marked, 10-fold increase in O(6)-methylguanine adducts from NDMA in mammary gland, as well as smaller but significant increases in this tissue from NNK and in maternal blood cells from both chemicals; adducts in maternal liver decreased slightly. In the sucklings, ethanol cotreatment also lowered adducts in liver after NDMA or NNK treatment. After NDMA, adducts were also detected in suckling lung and kidney and were increased five- to 10-fold after ethanol coexposure. Adducts from either chemical, with or without ethanol, decreased markedly in all suckling tissues with development from postnatal day 1 to day 14. Thus ethanol coexposure with nitrosamines increases O(6)-methylguanine DNA adducts in mammary gland and strongly influences adduct formation in suckling tissues after translactational delivery.

Mutagenicity of nitrosamines in methyltransferase-deficient strains of Salmonella typhimurium coexpressing human cytochrome P450 2E1 and reductase

Although dialkylnitrosamines are environmentally significant carcinogens, the use of short-term bioassays to assess the mutagenic potential of these compounds is problematic. The Ames test, a mutagenicity assay based on the reversion of Salmonella typhimurium histidine auxotrophs, is the most widely used bioassay in genetic toxicology, but the traditional Ames tester strains are largely insensitive to dialkylnitrosamine mutagenicity. We have constructed two mutagenicity tester strains that co-express full-length human cytochrome P450 2E1 and P450 reductase in S. typhimurium lacking ogt and ada methyltransferases (YG7104ER, ogt- and YG7108ER, ogt-, ada-). These new strains are susceptible to dialkylnitrosamine mutagenicity in the absence of an exogenous metabolic activating system (S9 fraction). Mutagenicity is dependent upon the coexpression of P450 2E1 with P450 reductase and is similar to or greater than that obtained with the parental strains in the presence of S9 fraction from ethanol-induced rat liver. These strains were also sensitive to nitrosamines with longer alkyl side chains including diethylnitrosamine, dipropylnitrosamine and dibutylnitrosamine. Mutagenicity decreased with alkyl chain length, consistent with the stringency of the ada-encoded enzyme for methyl and ethyl DNA adducts. These new strains may prove useful in the evaluation of nitrosamine contamination of food and environmental samples.

Endogenous N-nitroso compounds, and their precursors, present in bacon, do not initiate or promote aberrant crypt foci in the colon of rats

Processed meat intake is associated with increased risk of colorectal cancer. This association may be explained by the endogenous formation of N-nitroso compounds (NOC). The hypothesis that meat intake can increase fecal NOC levels and colon carcinogenesis was tested in 175 Fischer 344 rats. Initiation was assessed by the number of aberrant crypt foci (ACF) in the colon of rats 45 days after the start of a high-fat bacon-based diet. Promotion was assessed by the multiplicity of ACF (crypts per ACF) in rats given experimental diets for 100 days starting 7 days after an azoxymethane injection. Three promotion studies were done, each in 5 groups of 10 rats, whose diets contained 7%, 14%, or 28% fat. Tested meats were bacon, pork, chicken, and beef. Fecal and dietary NOC were assayed by thermal energy analysis. Results show that feces from rats fed bacon-based diets contained 10-20 times more NOC than feces from control rats fed a casein-based diet (all p < 0.0001 in 4 studies). In bacon-fed rats, the amount of NOC input (diet) and output (feces) was similar. Rats fed a diet based on beef, pork, or chicken meat had less fecal NOC than controls (most p < 0.01). No ACF were detected in the colon of bacon-fed uninitiated rats. After azoxymethane injection, unprocessed but cooked meat-based diets did not change the number of ACF or the ACF multiplicity compared with control rats. In contrast, the bacon-based diet consistently reduced the number of large ACF per rat and the ACF multiplicity in the three promotion studies by 12%, 17%, and 20% (all p < 0.01). Results suggest that NOC from dietary bacon would not enhance colon carcinogenesis in rats.