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PubMed1977

Correlation of animal brain tumor models with human neuro-oncology.

The paper reviews the histopathology and cytopathology of a number of experimental animal brain tumor models to determine their relevance to human neuro-oncology. The models discussed include brain tumors produced by local implants of carcinogenic hydrocarbons and by the administration of resorptive N-nitroso compounds, some of the cell lines derived from the latter, tumors resulting from the intracerebral inoculation of oncogenic viruses, and the differentiating neuroepithelial component of a transplantable mouse teratoma. The structural and biochemical criteria that can be applied for the identification of the various stages of neuronal and glial cell maturation are highly precise. They reveal a wide diversity of tumor cell types that are now available in experimental neuro-oncogenesis.

Animals↗
PubMed1984

Catalysis and inhibition of N-nitrosation reactions.

A number of factors that can lead to an acceleration or inhibition of N-nitrosation reactions may play an important role in the formation of N-nitroso compounds in foods and other environmental samples and in the body. The anion thiocyanate is a particularly effective catalyst for nitrosamine formation. It occurs in normal human saliva, but at higher concentrations in the saliva of smokers. Although nitrosation reactions are accelerated in the normal manner with increasing temperature, rate enhancements are also observed in frozen systems, a phenomenon that may be important in frozen foods. Surfactants that form micellar aggregates can accelerate the nitrosation of hydrophobic amines. This may be important in foods in view of the presence of components such as lecithin, or in the body in view of the occurrence of bile acid micelles. Nitrosation reactions may also be accelerated in the presence of certain carbonyl compounds, thiols and nitrosophenols. A number of compounds readily convert nitrosating agents into innocuous products and hence inhibit nitrosation reactions. If reductones such as ascorbic acid are present, they may react much faster with nitrous acid than amines and therefore effectively scavenge the nitrosating agent. Rapid reaction of polyhydroxyphenols with nitrous acid is another example of how endogenous or exogenous nitrosation reactions may be inhibited. Many microorganisms can influence nitrosation reactions by converting nitrate to nitrite, a reaction that can take place in foods, but which is particularly important in the body.

Ascorbic Acid↗
PubMed1998

Maternal diet during pregnancy and risk of brain tumors in children.

Nine studies of childhood brain tumors and maternal diet during pregnancy have focused on foods related to the N-nitroso-compound(NOC) hypothesis. An association between frequent consumption of cured meat by pregnant women and increased risk is a consistent finding in most of the studies. The data on fruit and vegetable consumption are less consistent, but suggest decreased risk. Studies that assess all aspects of maternal diet during pregnancy are needed to determine whether the observed associations remain after adjustment for other aspects of diet. Such comprehensive studies also may elucidate other dietary factors that affect the risk of brain tumors in children.

Brain Neoplasms↗
PubMed1981

[Carcinogenesis of gastric cancer with special reference to etiological aspects (author's transl)].

The article discusses possible etiological factors for the carcinogenesis of stomach tumours. Apart from genetic factors, stomach carcinogenesis may be attributed to the exposure of the stomach to carcinogenic substances taken in with the food, such as pyrrolysis products of certain amino acids, N-nitroso compounds or disturbances of the physiological function of the stomach, for example pathological reflux after stomach operations. The frequency of stomach cancer could not be related to occupational exposure. Geographic pathology has shown that people coming from high risk areas (e.g. Japan) adapt to the risk pattern of the host country when they emigrate (e.g. to the United States, where there is only a low risk for stomach cancer). Therefore, it is assumed that several factors play a role in the etiology of stomach cancer.

Age Factors↗
PubMed1978

[Carcinogens in food (author's transl)].

There is no evidence at present that certain chemicals are responsible for certain human cancers (with the exception of aflatoxin, which is the most suspect agent in the development of primary liver cancer in some districts of Africa and in Thailand). A number of chemicals which are carcinogenic to animals are present in human food. Any chemical which induces tumours in animals should be considered as a potential human carcinogen. But special studies must be undertaken before the role played by these substances in the development of human cancer can be definitely evaluated. First priority should be given to polycyclic aromatic hydrocarbons and N-nitroso compounds by reason of their general distribution in the human environment and their high efficiency in animal experiments. An appropriate approach to such studies would be the establishment of correlations between cancer morbidity data and the data on levels of these chemicals in special environments and, if possible, their total intake. This approach has proved fruitful in the aflatoxin intake studies carried out in countries where liver cancer is endemic. The IARC is currently carrying out a study of this kind in areas of high oesophageal cancer morbidity in Iran and in the north of France.

Carcinogens↗
PubMed2001

Synergistic interaction between Helicobacter pylori gastritis and diet in gastric cancer.

Infection with Helicobacter pylori increases the risk of gastric cancer. One possible mechanism is the higher likelihood of malignant transformation due to inflammatory responses in the epithelium. An alternative explanation is that these inflammatory responses induce chronic gastritis associated with decreased acidity in the stomach, which in turn increases the endogenous formation of carcinogenic N-nitroso compounds. Inflammatory responses seem to trigger two different causal pathways: one for the diffuse type of gastric cancer and the other for the intestinal type. The striking geographic variability in intestinal gastric cancer can be explained by the synergistic interaction between H. pylori infection and dietary factors, such as intake of salt and ascorbic acid. Screening and eradication of this organism, together with appropriate dietary modifications, offer promise in countries with a high prevalence of H. pylori infection and high risk of gastric cancer, but the safety of such interventions needs to be ensured.

Diet↗
PubMed1997

[Investigation on nitrosamines in the diets of the inhabitants of high-risk area for esophageal cancer in the southern China and analysis of the correlation factors].

Nan'ao County in Guangdong Province was an esophageal cancer high-risk area in the southern China. Of the suspected etiological factors in the environment, N-nitrosamines and their precursors have been received the most attention. 55 samples of the diets ingested by the inhabitants were collected and tested for volatile N-nitroso compounds and for their precursors by GC-TEA. Five kinds of N-nitrosamines (NDMA, NDEA, NPYR, NPIP and NMBzA) were detected in the samples. The average level of them was 312.0 micrograms/kg(median). The day intake of the nitrosamines was 286.5 micrograms/head/day. By the computerized stepwise regression analysis and curve fitting, we studied the correlation among the nitrosamines, the precursors and the major food items. It demonstrated that a relatively high content of volatile N-nitrosamines was present in the diets collected in the area.

Carcinogens↗
PubMed1975

Carcinogenesis of laryngeal carcinoma.

Experimental models have been developed for the induction of carcinoma of the larynx and for the study of its pathogenesis. The hamster has been the animal of choice. Polynuclear hydrocarbons, administered intratracheally, induce mostly squamous cell carcinomas. Diethylnitrosamine given systemically induces papillary tumors; some other N-nitroso-compounds given topically or systemically also induce laryngeal tumors, including carcinomas. Cigarette smoke inhalation induces preneoplastic and early neoplastic lesions of the larynx, including some invasive carcinomas. In vivo and in vitro methods have been developed for the morphological and biochemical study of target tissues in respiratory epithelial carcinogenesis to identify critical pathogenetic steps and their inhibition. These methods are now applicable to the in vitro study of human laryngeal epithelium and its susceptibility to cancer induction and prevention.

Animals↗
PubMed2003

Electrochemical assay of human haemoglobin S-nitrosylation by nitrosocysteine.

Oxyhaemoglobin (oxyHb) and methaemoglobin (metHb) react with S-nitrosocysteine (CysNO) to form nitroso derivatives. We test this reaction with a new method for evaluating transnitrosation reaction. The assay exploits an amperometric sensor developed in our laboratory. The results we obtain are in good agreement with those reported by others, although at much higher sensitivity, indicating the suitability of the method for examining high-mass nitroso compounds. The S-nitrosylation of oxyHb at a CysNO/haem ratio of 1 : 1 is about 5% in 60 min. In the same experimental conditions, the nitrosylation of met-Hb reaches 25%. OxyHb and metHb derivatize by 50% in 60 min upon using a CysNO/haem ratio of 10 : 1. The oxidation of haem iron occurs at ratios of haem/CysNO of 1 : 5 or higher. We conclude that CysNO transfers NO(+) both to metHb and oxyHb. We propose that NO transfer in RBC may occur through transnitrosation reactions between high and low-mass nitrosothiols.

Cysteine↗
PubMed1989

An exploratory case-control study of brain tumors in children.

An exploratory case-control study of childhood brain tumors was conducted in southern Ontario between 1977 and 1983, on 74 cases and 138 age- and sex-matched population controls. A significantly elevated risk (perhaps due to early case symptoms) was seen for skull X-rays at least 5 years prior to diagnosis, and for head or neck injuries which required medical attention. However, no evidence of an increased risk appeared for exposure to sick pets or to pesticides, maternal or paternal history of smoking, and various birth characteristics or antenatal exposure of the child, though these have previously been reported to be associated with childhood brain tumors. With respect to the hypothesis that N-nitroso compounds may be involved in the etiology of childhood brain tumors, most exposures of this type were not associated with risk, though a significant positive association was seen for consumption of beer by the mother during pregnancy, and a significant negative association was seen with consumption of fruit juice by the child. Other findings in the present study include an association with developmental problems relating to height and weight and with certain socioeconomic characteristics of the mother. Further investigation of these results in future studies is warranted.

Adolescent↗
PubMed1980

Inhibitory agents and chemical and mechanisms in the dihalomethane-mediated nitrosation of amines with solid nitrite.

Methylene chloride and certain other dihaloalkanes react efficiently with dissolved secondary amines and, in presence of insoluble sodium nitrite, yield N-nitroso compounds. Mechanistic studies indicate that the intermediates in the nitrosation mixture include the formaldiminium ion, the amine hydrochloride and the diaminomethane (aminal). They also indicate that the formaldiminium ion is by far the most reactive toward sodium nitrite, which probably reacts with the former by nucleophilic attack. Ascorbic acid, ascorbyl palmitate, dehydroascorbic acid, potassium iodide and potassium carbonate inhibited the reaction, whereas alpha-tocopherol, Trolox and sodium ascorbate were found to be ineffective. Ascorbic acid reacted with the secondary amine in a complex fashion. The mode of inhibition probably does not involve reduction of the solid nitrite.

Chemical Phenomena↗
PubMed1986

[Combined laboratory/epidemiological studies on endogenous nitrosation and human cancer].

Endogenous formation of carcinogenic N-nitroso compounds has been suspected of being associated with an increased risk for cancer of the stomach, esophagus and bladder, but no convincing epidemiological evidence has been presented. For these reasons, a new, non-invasive method for quantitative estimation of endogenous nitrosation in humans has been developed on the basis of the findings that certain non-carcinogenic N-nitrosamino acids such as N-nitrosproline are excreted unchanged almost quantitatively in the urine. Some results from the application of this method to clinical and epidemiological studies to evaluate the role of endogenous nitrosation in human cancer are presented.

Animals↗
PubMed1996

Epidemiology of gastric cancer.

The incidence of gastric cancer varies widely by country and population, with higher rates among the lower socioeconomic groups. Although the most common cause of cancer death in the United States in 1930, its incidence has decreased dramatically during the past 60 years. Most populations show a 2-1 ratio for male to female gastric cancer cases, and a higher incidence rate among United States blacks than whites. Although rates have generally decreased, there has been a dramatic increase in the incidence of gastric cancer in the cardia. Diet has been the most studied risk factor for gastric cancer. Of particular interest have been N-nitroso compounds derived from the consumption of preserved, smoked, and cured foods. An inverse association with the consumption of fruits and vegetables has also been consistently demonstrated, though the specific nutrient(s) that this represents has been unclear, although ascorbate and beta-carotene have been intensively studied. Among nondietary factors, substantial evidence has accumulated for an increased risk with Helicobacter pylori infection. Other exposures which have been fairly consistently associated with gastric cancer include cigarette smoking, partial gastrectomy, radiation exposure, family history, pernicious anemia, blood group A, certain occupational exposures, and Epstein-Barr virus.

Age Factors↗
PubMed1986

Mutagenicities of nitrosated carboline derivatives.

Food-borne amines have been considered as the potential precursors of endogenous carcinogenic N-nitroso compounds in humans. A compound which yields a direct mutagen after nitrite treatment was isolated from soy sauce and was identified as 1-methyl-1,2,3,4-tetrahydro-2-carboline-3-carboxylic acid (MTCA) (Wakabayashi, et al., 1983). The mutagenicities of other carboline derivatives such as harman, norharman, harmaline, harmalol, harmine, and harmol were studied. Like MTCA, the nitrosated carboline derivatives showed higher mutagenic activity as compared to their corresponding parent compounds. The demethylated analogue of MTCA, 1,2,3,4-tetrahydro-2-carboline-3-carboxylic acid was synthesized and its nitrosated products were shown to be mutagenic to Salmonella typhimurium TA 100 and TA 98. The potent mutagen Trp-P-2 is a typical 3-carboline derivative. The mutagenicity of Trp-P-2 was suppressed remarkably after nitrosation. Several 3-carboline derivatives also showed the similar property. Nitrosation of MTCA gave several derivatives which were isolated and showed direct mutagenicity to Salmonella typhimurium TA 98. Further characterization of these new carboline derivatives is in progress.

Carbolines↗
PubMed1989

Mechanisms of endogenous nitrosation.

Endogenous formation of N-nitroso compounds has been demonstrated in both humans and experimental animals. The extent of this process has been estimated by measurement of urinary N-nitrosoproline and has been shown to be modulated by dietary precursors and inhibitors. It is now also recognized that other (non-gastric) pathways of endogenous nitrosation, including those catalysed by bacteria and mammalian cells, may exist. The mammalian cell catalysed pathway utilizes arginine as a precursor for the nitrosating agent and may occur in macrophages or endothelial cells. The estimated contribution of this pathway to normal basal endogenous nitrosation is approximately 20 nmol of N-nitrosoproline/day.

Animals↗
PubMed1993

Biomarkers of individual susceptibility to carcinogens: application for biological monitoring.

In order to develop new markers of individual susceptibility to various human carcinogens, we studied some parameters of formation and metabolism of carcinogens, as well as DNA adducts formation and DNA repair in animals and humans. Following an i.p. administration of benzo(a)pyrene (BP) to the rats, levels of urinary excretion of BP-7,8-diol correlated with tumour latency. A high correlation was found between excretion of this metabolite and BP-DNA adducts level in the liver. Healthy smokers excreted higher quantities of BP-7,8-diol, than smoking lung cancer patients, thus confirming the suggestion on existence of cancer-prone phenotype. N-nitroso compounds formed most efficiently in stomach juice of children with superficial gastritis who therefore could be at high risk of stomach cancer. N-ethyl-N'-nitro-N-nitrosoguanidine induced stomach cancer earlier in monkeys with a low level of DNA repair enzyme, O6-alkylguanine-DNA alkyltransferase (AGT) in gastric mucosa. Overall, these markers can be helpful in predicting individual susceptibility to carcinogens.

Adult↗
PubMedDate not supplied

Toxicity, immunosuppressive effects and carcinogenic potential of volatile nitrites: possible relationship to Kaposi's sarcoma.

Volatile nitrite in the form of amyl nitrite was used for 100 years for the treatment of angina pectoris. In spite of recognized toxicity, its use in this form was considered safe. During the 1960s prescriptions were not required for purchase of amyl nitrite (called poppers) and its use for recreational purposes became popular. With reinstatement of the prescription requirement in 1969, non-medicinal, street-variety volatile nitrites were made commercially available in the form of mixtures of impure butyl and isobutyl nitrite; some of these preparations also included amyl nitrite. These products have been found to be profoundly immunosuppressive for human lymphocytes in vitro, and their by-products when metabolized into N-nitroso compounds have been known to be highly carcinogenic in many animal species. Recreational use of inhaled volatile nitrites is prevalent among male homosexuals and the compounds have been suspected as possible cofactors in Kaposi's sarcoma associated with the Acquired Immune Deficiency Syndrome (AIDS). This association could be explained by nitrite-induced vasodilation of rectal mucosal vessels providing a port of entry for a transmissible agent, by direct immunosuppression of the host allowing expression of a potentially oncogenic virus by co-carcinogenic effects of by-products by themselves or in conjunction with other putative cofactors such as cytomegalovirus. Nitrites should continue to be considered as a possible cofactor in the etiology of Kaposi's Sarcoma among male homosexuals and possibly those with other manifestations of AIDS.

Amyl Nitrite↗
PubMed1993

Inhibition of nitrosation.

Humans are exposed through ingestion or inhalation to preformed N-nitroso compounds (NOC) in the environment and through the endogenous nitrosation of amino precursors in the body. Activated macrophages and bacterial strains isolated from human infections can enzymatically produce nitrosating agents and NOC from precursors at neutral pH. As a consequence, endogenous nitrosation may occur at various sites of the body, such as the oral cavity, stomach, urinary bladder, and at other sites of infection or inflammation. Numerous substances to which humans are exposed have been identified and shown to inhibit formation of NOC. Such inhibitors include vitamins C and E, certain phenolic compounds, and complex mixtures such as fruit and vegetable juices or other plant extracts. Nitrosation inhibitors normally destroy the nitrosating agents and, thus, act as competitors for the amino compound that serves as substrate for the nitrosating species. Independently, epidemiological studies have already established that fresh fruits and vegetables that are sources of vitamin C, other vitamins, and polyphenols have a protective effect against cancers at various sites and in particular gastric cancer. This article briefly reviews (a) the chemistry of NOC formation and inhibition; (b) the studies in experimental animals that showed that inhibition of endogenous NOC synthesis leads to a reduction of toxic, mutagenic, and carcinogenic effects; (c) recent studies in humans where the degree of inhibition of endogenous NOC synthesis was directly quantified; and (d) the possible contribution of nitrosation inhibitors to human cancer prevention.

Animals↗