Geographic association between urinary excretion of N-nitroso compounds and oesophageal cancer mortality in China

Calcium, magnesium, and nitrate in drinking water and gastric cancer mortality

The possible association between the risk of gastric cancer and the levels of calcium, magnesium, and nitrate in drinking water from municipal supplies was investigated in a matched case-control study in Taiwan. Records of gastric cancer deaths among eligible residents in Taiwan from 1987 through 1991 were obtained from the Bureau of Vital Statistics of the Taiwan Provincial Department of Health. Controls were deaths from other causes and were pair-matched to the cases by sex, year-of-birth, and year-of-death. Each matched control was selected randomly from the set of possible controls for each case. Data on calcium, magnesium, and nitrate levels in drinking water throughout Taiwan were obtained from the Taiwan Water Supply Corporation. The municipality of residence of the cases and controls was assumed to be the source of the subject's calcium, magnesium, and nitrate exposure via drinking water. The subjects were divided into tertiles according to the levels of calcium, magnesium, and nitrate in their drinking water. The results of the present study show that there is a significant positive association between drinking water nitrate exposure and gastric cancer mortality. The present study also suggests that there was a significant protective effect of calcium intake from drinking water on the risk of gastric cancer. Magnesium also exerts a protective effect against gastric cancer, but only for the group with the highest levels.

Glucose modulates hemodynamic, metabolic, and inflammatory responses to lipopolysaccharide in rabbits

Glucose is important for vascular and immunocompetent cell functions. We hypothesized that modifications in glucose metabolism (normal feeding, 24-h fasting, glucose loading) may influence the hemodynamic, metabolic, and inflammatory responses to lipopolysaccharide administration (LPS; 600 micrograms/kg iv) in rabbits. Aortic (ABFV), hepatic artery (HABFV), and portal vein blood flow velocities (PVBFV) (pulsed Doppler), plasma tumor necrosis factor (TNF) and nitrites were measured. Fasting depleted hepatic glycogen content, and intraportal glucose load (2 g/kg) partially restored it. LPS induced a similar hypotension (-20%, P < 0.05) in three groups of animals. In fed animals, systemic vasoconstriction occurred with low ABFV and PVBFV (-40%, P < 0.05), together with lactacidemia and hyperglycemia. In fasted animals, ABFV and PVBFV were maintained, without metabolic acidosis or hyperglycemia. Glucose loading induced hemodynamic and metabolic patterns comparable to those observed in fed animals, although significantly more severe. TNF release was amplified fourfold by glucose loading, with no impact on nitrite levels. In conclusion, glucose metabolism interferes with hemodynamic, metabolic, and inflammatory responses to LPS.

Identification of cytokeratin subspecies altered in rat experimental esophageal tumors by subtractive cloning

By using the subtractive hybridization method, two complementary DNA clones differently expressed in rat normal esophageal epithelium and squamous cell carcinoma induced by administration of precursors of N-nitrososarcosine ethyl ester were isolated. A rat homologue of the human 50-kDa type I cytokeratin 14 was cloned for the first time and shown to be expressed preferentially in squamous cell papillomas and carcinomas, whereas it was weakly expressed or absent in normal squamous epithelial cells and in hyperplastic lesions. A rat homologue of the mouse 57-kDa type II cytokeratin showed strong expression in both normal and tumor tissues. These results are well consistent with the reported alteration of keratin subspecies in human esophageal cancers, therefore, encouraging us to use this experimental system as a model for human esophageal carcinogenesis.

Nitrate contamination of drinking water: relationship with HPRT variant frequency in lymphocyte DNA and urinary excretion of N-nitrosamines

We studied peripheral lymphocyte HPRT variant frequency and endogenous nitrosation in human populations exposed to various nitrate levels in their drinking water. Four test populations of women volunteers were compared. Low and medium tap water nitrate exposure groups (14 and 21 subjects) were using public water supplies with nitrate levels of 0.02 and 17.5 mg/l, respectively. Medium and high well water nitrate exposure groups (6 and 9 subjects) were using private water wells with mean nitrate levels of 25 and 135 mg/l, respectively. Higher nitrate intake by drinking water consumption resulted in a dose-dependent increase in 24-hr urinary nitrate excretion and in increased salivary nitrate and nitrite levels. The mean log variant frequency of peripheral lymphocytes was significantly higher in the medium well water exposure group than in the low and medium tap water exposure groups. An inverse correlation between peripheral lymphocyte labeling index and nitrate concentration of drinking water was observed. Analysis of N-nitrosamine in the urine of 22 subjects by gas chromatography-mass spectrometry revealed the presence of N-nitrosopyrrolidine in 18 subjects. Analysis of the mutagenicity of well water samples showed that a small number of the well water samples were mutagenic in the Ames Salmonella typhimurium test after concentration over XAD-2 resin. In conclusion, consumption of drinking water, especially well water, with high nitrate levels can imply a genotoxic risk for humans as indicated by increased HPRT variant frequencies and by endogenous formation of carcinogenic N-nitroso compounds from nitrate-derived nitrite.

Nutrition and esophageal cancer

Epidemiologic evidence on the relation between nutrition and esophageal cancer is reviewed. Results from ecologic, case-control, cohort, and intervention studies are included. Most of the findings pertain more to squamous cell carcinoma than adenocarcinoma of the esophagus. The protective effect of fruit and vegetable consumption is supported by a large body of evidence, especially from case-control studies. The effects of food groups and nutrients other than fruits and vegetables also have been examined, but the overall evidence is less convincing. Recent intervention studies in high incidence areas in China indicate that micronutrient supplements may have a modest effect in reducing risk, but the generalizability of this result is uncertain. Hot drinks are likely to increase the risk of esophageal cancer. On the other hand, the role of tea drinking, especially the use of green tea, remains to be defined better.

Ascorbic acid and gastrointestinal cancer

A literature review was made to critically evaluate the ability of ascorbic acid to modulate the incidence of gastrointestinal cancer. A comparison of preclinical, clinical, and epidemiological studies indicated that evidence for ascorbic acid as an inhibitor of carcinogenesis is stronger with regard to gastric cancer and weaker with regard to esophageal and colon/rectal cancer. Insufficient evidence currently exists regarding the oral cavity and the use of ascorbic acid in precancerous conditions such as polyposis and leukoplakia.

Role of N-nitroso compounds (NOC) and N-nitrosation in etiology of gastric, esophageal, nasopharyngeal and bladder cancer and contribution to cancer of known exposures to NOC

The questions of whether and how N-nitroso compounds (NOC) may be inducing cancer in humans are discussed. The principal subjects covered include nitrite-derived alkylating agents that are not NOC, reasons for the wide tissue specificity of carcinogenesis by NOC, the acute toxicity of nitrosamines in humans, mechanisms of in vivo formation of NOC by chemical and bacterial nitrosation in the stomach and via nitric oxide (NO) formation during inflammation, studies on nitrite esters, use of the nitrosoproline test to follow human gastric nitrosation, correlations of nitrate in food and water with in vivo nitrosation and the inhibition of gastric nitrosation by vitamin C and polyphenols. Evidence that specific cancers are caused by NOC is reviewed for cancer of the stomach, esophagus, nasopharynx, urinary bladder in bilharzia and colon. I review the occurrence of nitrosamines in tobacco products, nitrite-cured meat (which might be linked with childhood leukemia and brain cancer) and other foods, and in drugs and industrial situations. Finally, I discuss clues from mutations in ras and p53 genes in human tumors about whether NOC are etiologic agents and draw some general conclusions.

Historical origins of current concepts of carcinogenesis

The first attempts to understand the causes of cancer were based on generalizations of what might now be termed a "holistic" nature, and hereditary influences were recognized at an early stage; these views survive principally through a supposed positive connection between psychological factors such as stress and diminished ability to combat the progressive development of tumors through some form of immunologically mediated rejection of potentially cancerous cells. While evidence for immunosurveillance is generally accepted, it is now widely regarded as almost wholly confined to instances where tumor viruses are involved as causative agents. The earliest theorists drew an analogy between the processes of carcinogenesis and of evolution; the cancer cells acquired the ability to outstrip their normal counterparts in their capacity for proliferation. This was even before evolution had been interpreted as involving a continuous succession of mutations. Evidence was already to hand before the end of the 18th century that exogenous agents, notably soot, a product of the "industrial revolution," could cause skin cancer. Somewhat over 100 years later, another industrial innovation, the manufacture of synthetic dyestuffs, implicated specific chemical compounds that could act systemically to cause bladder cancer. Meanwhile, the 19th century saw the establishment of the fundamentals of modern medical science; of particular relevance to cancer was the demonstration that it involved abnormalities in the process of cell division. The commencement of the 20th century was marked by a rediscovery of the concept of mutation; and it was proposed that cancer originated through uncontrolled division of somatically mutated cells. At around this time, two further important exogenous causative agents were discovered: X-rays and tumor viruses. In the late 1920s, x-radiation became the first established exogenous cause of mutagenesis. The discoverer of this phenomenon, H. J. Muller, suggested that while mutation in a single cell was the primary causative mechanism in carcinogenesis, its generally observed logarithmic increase in incidence with age reflected a "multihit" process, and that multiple successive mutations were required in the progeny of the original mutants. He also recognized that the rate of proliferation of potentially cancerous cells would markedly influence the probability of their subsequent mutation. These considerations are essentially the foundation of the generally accepted view of carcinogenesis that now seems unlikely to be superseded. However, this acceptance did not come about unopposed. The analogy between carcinogenesis and evolution was disliked by many biologists because it embodied the concept that cancer was an inevitable consequence of our evolutionary origins.(ABSTRACT TRUNCATED AT 400 WORDS)