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.

Childhood brain tumors and exposure to tobacco smoke

Brain tumors are the second most common cancer in children after leukemia, yet the etiology of childhood brain tumors remains unknown. Tobacco smoke contains several dozen compounds that are known to be carcinogens. Among these are N-nitroso compound precursors, principally tobacco-specific nitrosamines. Although smoking has not been identified as a significant risk factor for the development of brain tumors in adults, fetuses and infants have incompletely formed blood-brain barriers that may allow the passage of carcinogenic tobacco metabolites into the central nervous system and initiate the formation of neural tumors. In this review, we present data from case-control and cohort studies published between 1971 and 1995 that examined the relationship between parental smoking during pregnancy and childhood brain tumors (CBTs). The majority of these studies found little association between CBTs and maternal smoking before or during pregnancy or between CBTs and maternal exposure to passive smoke during pregnancy.

Systemic effects of S-nitroso-glutathione in the human following intravenous infusion

Nitric oxide (NO) is a potent vasodilator and inhibitor of platelet aggregation. At present the clinical use of NO donors as inhibitors of platelet activation is limited by their concomitant hypotensive effect. The new NO donor S-nitroso-glutathione (GSNO) has a significant antiplatelet effect at doses that cause only a small decrease in blood pressure in rats. We have examined the antiplatelet and vasodilator properties of this nitrosothiol following systemic intravenous infusion in the human. GSNO was administered intravenously to 10 normal females of reproductive age noting changes in blood pressure, pulse and reported side effects. Ex vivo platelet aggregation to ADP was then performed in a platelet-ionized calcium lumiaggregometer on blood samples taken both before and after the infusions. Side effects such as headache or palpitations occurred only in two subjects at the highest infusion rate of 250 micrograms min-1. Blood pressure and pulse did not vary significantly during the study. Ex vivo platelet aggregation in response to ADP was significantly reduced by the infusion. These results suggest that GSNO is a more potent inhibitor of platelet activation than it is a vasodilator and therefore potentially represents a more clinically useful NO donor than has so far been available where an anti-thrombotic effect is required.

Potential genotoxicity of chronically elevated nitric oxide: a review

Several human cancers are associated with chronic bacterial, viral and parasitic infections. Nitric oxide, which is a short-lived free radical produced by many types of cells for a number of important physiological functions, is elevated in these infections. Long-term exposure to elevated NO. in cells could have potential genotoxic effects on hosts. There are at least three mechanisms by which intracellular elevated NO. could exert genotoxic affects after reacting with O2. These include formation of carcinogenic N-nitroso compounds, direct deamination of DNA bases, and oxidation of DNA after formation of peroxynitrite and/or hydroxyl radicals. One or more of these mechanisms could, theoretically, explain why chronic infection increases the risk of certain cancers.

Maternal exposure to N-nitrosatable drugs as a risk factor for childhood brain tumours

BACKGROUND

Animal models suggest that compounds containing a nitrosyl group (N-nitroso compounds (NNO)) can act as potent transplacental carcinogens. Many common drug formulations have the potential to undergo nitrosation in vivo. The association between maternal use of nitrosatable drugs during pregnancy and development of brain tumours in the offspring was examined in a SEER-based case-control study.

METHODS

Maternal exposure to nitrosatable drugs during pregnancy was compared among 361 childhood brain tumour cases and 1083 matched controls recruited through random-digit dialing.

RESULTS

There was no increase in risk observed for childhood brain tumours overall (OR = 1.15; 95% CI: 0.69-1.94) or for astrocytomas individually (OR = 1.16; 95% CI: 0.50-2.69). A slight elevation in risk was noted for medulloblastomas (OR = 1.47; 95% CI: 0.28-7.62) and 'other' tumours (OR = 1.27; 95% CI: 0.56-2.86), however, both estimates were based on small numbers.

CONCLUSIONS

Our findings suggest that no increased risk of childhood brain tumours was associated with maternal exposure to nitrosatable drugs. The study results should be viewed with caution given the imprecision of the point estimates as well as the lack of data on specific timing and dosage of exposure and degree of nitrosatability of drugs taken.

[Pathogenesis of stomach carcinoma--significance of nitrates, N-nitroso compounds, nutritional factors and Helicobacter pylori-induced chronic active and chronic atrophic gastritis]

Epidemiological data on gastric cancer, time trends and histological classification are reviewed. Known models on gastric carcinogenesis including the pathogenetic importance of nitrates and N-nitroso compounds and protective effects of dietary components are discussed and recent evidence on Helicobacter pylori (Hp) induced chronic active gastritis, its progression to chronic atrophic gastritis and its role in gastric carcinogenesis is summarized. Epidemiological, clinical and pathological support for a causal relationship of Hp and gastric carcinoma is included in a new multistep model on aetiopathogenesis of gastric cancer. The follow-up of patients at risk as well as the question of cancer prevention by Hp eradication are mentioned.

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

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

Nitrate, nitrite and N-nitroso compounds

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

Risk factors for astrocytic glioma and primitive neuroectodermal tumor of the brain in young children: a report from the Children's Cancer Group

We conducted a matched case-control study to investigate risk factors for the two most common types of brain tumors in children, astrocytic glioma and primitive neuroectodermal tumor (PNET). Since the study focused on gestational exposures, we restricted it to young children because these exposures would be expected to act early in life. Parents of 155 astrocytic glioma cases, 166 PNET cases, and controls identified by random digit dialing completed telephone interviews. Few associations occurred with the hypothesized risk factors, which were gestational exposure to alcohol, hair coloring products, farms, and substances containing N-nitroso compounds (passive smoking, makeup, incense, new cars, pacifiers, baby bottles, beer). Of the products studied that contain N-nitroso compounds, only beer was associated with a significantly increased risk of either tumor type [odds ratio (OR) for PNET = 4.0; 95% confidence interval (CI), 1.1-22.1; P = 0.04]. Elevated ORs for PNET were observed for farm residence of the mother during the pregnancy (OR = 3.7; 95% CI, 0.8-23.9; P = 0.06) and of the child for at least a year (OR = 5.0; 95% CI, 1.1-46.8; P = 0.04). Significant associations with astrocytoma were observed for mother's use of kerosene (OR = 8.9; 95% CI, 1.1-71.1; P = 0.04) and birth by Caesarean section (OR = 1.8; 95% CI, 1.1-3.2; P = 0.03). History of miscarriage was associated with a lower risk of PNET (OR = 0.5; 95% CI, 0.3-0.9; P = 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)

Urinary markers for exposures to alkylating or nitrosating agents

Investigation of urinary markers as indices of endogenous nitrosation and of gastric cancer etiology has been a major focus of our work. As part of this effort, studies have been carried out on a Colombian population at high risk for gastric cancer. In this group, nitrosoproline excretion was highly correlated with nitrate excretion in the subpopulation with advanced gastric pathology, but not in control subpopulations with more normal stomachs. Neither urinary 7-methylguanine nor 3-methyladenine was strongly related to gastric pathology or to urinary nitrate or nitrosoproline levels. More recently, as evidence has accumulated concerning the importance of nitric oxide as a cellular messenger, we have begun research toward developing markers for the presence of nitric oxide and for endogenous nitrosation via this compound. Nitric oxide is formed from arginine by activated endothelial cells as a messenger for vasodilation. We have shown that prolonged exercise leads to increased urinary nitrate and that when 15N-arginine is ingested by humans, 15N-nitrate levels increase in 24-hr urine collections. Nitrosohydroxyethylglycine and 3-nitrotyrosine were evaluated as indices for the formation of N-nitrosomorpholine and for the nitration of protein, respectively, under experimental conditions (e.g., immunostimulation) expected to enhance nitric oxide formation. Nitrotyrosine has not proved useful as a biomarker for nitration/nitrosation reactions in immunostimulated rats. Immunostimulation of rats following administration of morpholine led to increases in urinary nitrate and nitrosohydroxyethylglycine. This procedure, however, would not be appropriate for humans due to the toxicity of morpholine and the carcinogenicity of N-nitrosomorpholine.

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.