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.

Endogenously formed N-nitroso compounds and nitrosating agents in human cancer etiology

Humans are exposed to preformed N-nitroso compounds (NOC), but also to a wide range of precursors and nitrosating agents which can react in vivo to form potentially carcinogenic NOC and diazo compounds. Nitrite, nitrate and nitrosating agents can also be synthesized endogenously in enzymic reactions mediated by bacteria, activated macrophages and neutrophils. The latter two cell types generate, via the enzyme nitric oxide synthase, the nitric oxide radical that is involved in cytotoxicity, and is believed to be involved in formation of carcinogenic nitrosamines, DNA base deamination and oxidative damage. Thus endogenous NOC formation, DNA damage and gene mutations in humans could occur at various sites of the body such as the stomach and chronically infected or inflamed organs. Sensitive procedures to estimate the exposure of humans to NOC have been developed and applied in ecological and cross-sectional studies. These have shown that inhabitants of high-risk areas for stomach and esophageal cancer, patients with urinary tract infections (at risk for bladder cancer) and Thai subjects infected with liver fluke (at risk for cholangiocarcinoma) had significantly higher exposure to endogenous NOC. Clinical studies have examined the model of stomach carcinogenesis based on intragastric nitrosation, but the precise roles of bacterial overgrowth and of Helicobacter pylori infection in NOC synthesis and/or inducing oxidative stress in stomach mucosa remain to be clarified. Together these results support the role of NOC and other nitrite-derived mutagens in human cancer etiology, in particular when exposure starts early in life and persists over a long period.(ABSTRACT TRUNCATED AT 250 WORDS)

Pickled vegetables in the aetiology of oesophageal cancer in Hong Kong Chinese

Oesophageal cancer is common in Chinese populations, but individual-based epidemiological studies have provided little explanation. A case control study with 400 cases and 1598 controls (800 hospital and 798 general practice) was conducted among Hong Kong Chinese. In multivariate analyses, statistically significant effects on risk were detected for several potentially preventable exposures with high attributable risks (ARs). These included preference for consuming drinks or soups at high temperature (AR = 14%), infrequent consumption of green leafy vegetables (AR = 15%) and citrus fruits (AR = 26%), ingestion of pickled vegetables (AR = 29%), tobacco smoking (AR = 44%), and alcohol drinking (AR = 48%). On the assumption of multiplicative risk, the combined AR due to these exposures was 89%. This is the first case control study to show an association between pickled vegetable consumption and oesophageal cancer risk. The finding considerably strengthens the evidence for carcinogenicity of N-nitroso compounds in man and helps to explain the very high risk among Chinese.

Risk factors for tumors of the brain and meninges: results from the Adelaide Adult Brain Tumor Study

A population-based case-control study of incident primary brain tumors in adults was carried out in Adelaide, Australia in the period 1987 through 1990. It included 110 subjects with newly diagnosed primary glioma, 60 subjects with meningioma and 417 controls selected from the Australian Electoral Roll and frequency-matched to cases for age (within 2 years), sex and postal code. Some interesting new associations were found: (1) an increased risk of glioma in women who reported working with cathode-ray tubes (relative risk = 4.1, 95% confidence interval: 1.3-13.2); (2) a decreased risk of glioma in those with a history of allergic diseases (relative risk = 0.5, 95% confidence interval: 0.3-0.9); and (3) an increased risk of meningioma in those exposed to passive smoking from a spouse, especially amongst females (relative risk = 2.7, 95% confidence interval: 1.2-6.1). A pooled analysis of the multi-center group of studies to which the present study belongs should allow more confident claims concerning risk factors for brain tumors.

Effect of 1-methyl-2-nitrosoimidazole on intracellular thiols and calcium levels in Chinese hamster ovary cells

The cellular reduction of 2-nitroimidazoles under hypoxic conditions can lead to cell killing. One of the postulated toxic intermediates is the two-electron reduction product, the nitrosoimidazole. 1-Methyl-2-nitrosoimidazole (INO) was used as a model to study the reactivity of 2-nitrosoimidazoles with sulfhydryls. INO reacted within minutes with bovine serum albumin (BSA) in a stoichiometric fashion as measured by the loss of its characteristic absorption at 360 nm. It appeared to react specifically with the SH group of BSA as demonstrated by the loss of 5,5'-dithiobis-2- nitrobenzoic acid (DTNB) reactive groups and by the loss of INO reactivity if BSA was previously reacted with DTNB. INO also depleted glutathione (GSH) and protein sulfhydryls (Pr-SH) in Chinese hamster ovary (CHO) cells in a concentration-dependent fashion. INO at 25 microM, a non-toxic concentration in terms of cell colony-forming ability, depleted GSH to 10-20% of control levels within 5 min after treatment. Pr-SH were depleted more slowly to 60% of control levels. GSH recovered to near control levels over 3-4 hr but Pr-SH remained depressed. The recovery of GSH was blocked by buthionine sulfoximine (BSO), suggesting that the recovery was due to de novo synthesis of GSH. At a toxic concentration of INO (45 microM), GSH was again depleted to 10-20% and Pr-SH to 50% of control levels. No recovery of either was observed up to 4 hr. The effect of this extensive oxidative stress on intracellular calcium (Ca2+i) levels was monitored using 1-[2-amino-5-(6-carboxyindole-2-yl)-phenoxyl]-2- (2'-amino-5'-methylphenoxy)-ethane-N,N,N',N'-tetraacetic acid pentaacetoxy methylester (INDO-1 AM). At toxic concentrations of INO, Ca2+i increased in a sustained, non-physiological manner starting at approximately 60 min after the addition of INO. No increase in Ca2+i was observed when cells were treated with nontoxic concentrations of INO. INO toxicity may be modulated by an uncontrolled influx of Ca2+ which can trigger the activation of cellular enzymes and lead to cell death.

Induction of chromosome breaks and sister chromatid exchanges in patients with Hodgkin's disease by two combination chemotherapy regimens of different leukemogenic potential

The success of various combination chemotherapies in the treatment of cancer is compromised by their potential to cause secondary leukemia. Previous studies have suggested that the alkylating agents used in some regimens are the major etiological factor in these leukemias. In this study, we compared the abilities of two standard regimens used in the treatment of Hodgkin's disease to cause chromosome breaks and sister chromatid exchanges, the two most common types of chromosomal damage induced by alkylating agents. These regimens are MOPP [mechlorethamine-vincristine (Oncovin)-procarbazine-prednisone] and CVPP-ABDIC [cyclophosphamide-vinblastine-procarbazine-prednisone-doxorubicin (Adriamycin)-bleomycin-dacarbazine-1-(2-chloroethyl)-3-cyclohexyl-1- nitrosourea]. Our study demonstrated that (a) levels of spontaneous chromosome breaks and sister chromatid exchanges were low in untreated Hodgkin's disease patients; (b) significantly higher levels of these damages were induced in patients receiving eight cycles of CVPP-ABDIC, as compared with their pretreatment levels; (c) significantly elevated levels of sister chromatid exchanges, but not chromosome breaks, were induced in patients receiving two cycles of MOPP; and (d) no differences in the effect of these two regimens on cell cycle kinetics were observed. Although MOPP therapy has been reported to have higher rates of secondary leukemia than CVPP-ABDIC, our studies show that eight cycles of CVPP-ABDIC are more potent than two cycles of MOPP in inducing chromosome damage in patients during treatments.

Nitrosatable drug exposure during pregnancy and adverse pregnancy outcome

Recent investigations have suggested that drugs that are amines can undergo endogenous or exogenous nitrosation reactions to form N-nitroso compounds. These compounds have been extensively characterized in animal models as carcinogens, mutagens and teratogens. In order to examine the possible effects of exposure to nitrosatable drugs during gestation on pregnancy outcome, data were utilized from the Collaborative Perinatal Project of the National Institute of Neurological and Communicative Disorders and Stroke. Pregnancy outcomes for 6061 pregnancies in which the mother ingested a drug known to undergo nitrosation were compared with 6921 randomly sampled pregnancies without such exposure. The major outcome factors of interest were birth defects, fetal, neonatal and infant death and birthweight. Our findings suggest that no significant increases in risk of fetal, neonatal and infant death or low birthweight were associated with nitrosatable drug exposure during pregnancy. However, the risk of a tumour in the offspring of exposed mothers was increased (relative risk, RR = 2.29; 95% Cl 0.99-5.26). Increases in relative risk of major malformations was also observed and this increase was greater when exposure during the first four months of pregnancy was examined separately (RR = 1.33; 1.11-1.58). There were specific individual malformations that were observed to have increased relative risks (for example: eye malformations, hydrocephaly, craniosynostosis and meningomyelocoele/meningocoele) but interpretation was difficult due to multiple comparisons and some of these observations were associated with wide confidence intervals. These types of adverse pregnancy outcomes were consistent with animal study outcomes.

A case-control study of risk factors for hepatoblastoma. A report from the Childrens Cancer Study Group

Parents of 75 children with hepatoblastoma, registered with the Childrens Cancer Study Group, and 75 age-matched controls, who had been identified through random digit dialing were interviewed. No evidence was found to support the primary study hypotheses relating to hepatitis infection, maternal estrogen exposure, alcohol consumption, smoking, or potential sources of nitrosamines. Case mothers were more likely to report occupational exposure to metals (odds ratio [OR] = 8.0, P = 0.01), petroleum products (OR = 3.7, P = 0.03), and paints or pigments (OR = 3.7, P = 0.05). Metal exposures were commonly to welding or soldering fumes, and most occurred daily, before and during the index pregnancy. Petroleum product exposures were predominantly to lubricating oils or protective greases. The only significant paternal exposure was to metals (OR = 3.0, P = 0.01) and the risk with exposure to petroleum products was marginally significant (OR = 1.9, P = 0.06). These findings provide further evidence that occupational exposures may increase the risk of cancer in offspring.

[Surveillance of health status in an agrarian environment: proposal for a method. 1. Epidemiological data]

In order to evaluate the risk of the exposure of the pesticides and N-nitroso compounds in the agricultural environment not only farm-hands have to be considered but also their families. So it is necessary to prepare survey methodologies to examine the state of health of all individuals who are exposed to same kind of risk (pesticides and nitroso compounds), even if in different ways and intensity. We have therefore chosen four farms situated on the same territory which cultivate vegetables. Three, of these farms, made wide use of pesticides and fertilizers, the fourth one was used as a "control farm" because it did not employ any chemicals. For every farm data about the neighbouring territory, the climate, the kind of cultivation, the pesticides and other employed chemicals were collected. Every subject (in all 25) residing in the farm was interviewed with a standard questionnaire about personal data, the duties performed on the farm, the way in which chemicals were used, their medical history as well as the life style. Samples of blood were drawn periodically in different seasons, over a two year period, to determine both nitrosoamine (NA) and the enzymes which reveal hepatic damage: Alkaline phosphatase (ALP), Leucinoaminopeptidase (LAP), Gamma-glutamyltransferase (GGT) and Acetylcholinesterase (Ach). We have observed that: a. the most frequent pathologies concern skin (16% of the people) and liver (12% of the people), which are favourite targets for agricultural chemicals though the serum enzymes did not show any important change; b. 8% of the subjects had acute pesticide poisoning; we therefore observed neither particular precautionary safety measures, nor a particular knowledge of acute and chronic toxic effects depending on the use of pesticides. So we suggest: 1) that the Sanitary Authorities control the state of health not only of the farm-hands but also of their families, if exposed to risk; this can be realized through the strict collaboration of the Occupational Physician and the Family doctor; 2) capillary action of health education regarding agricultural risks; 3) to increase research to find more sensitive and efficient biological indicators in order to evaluate the hazards of agricultural chemicals.

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.

[The problem of carcinogenic N-nitroso compounds--30 years old]

For 30 years a correlation between N-nitroso compounds and cancer in man has been suspected. Investigations of nitrate and nitrite in food and human gastric cancer were performed all over the world. Literature on nitrosamines and nitrosamides is abundant, but it is impossible to make a realistic assessment of the danger of N-nitroso compounds and their precursors for man. Restriction of unnecessary intake of nitrate through drinking water and food is in any case an important task of hygiene.

Chronic atrophic gastritis and risk of N-nitroso compounds carcinogenesis

Chronic atrophic gastritis is considered a precancerous condition for carcinoma of the stomach. To evaluate the correlation between progressive alterations in the mucosa and gastric juice microenvironmental factors, retained involved on N-nitroso compounds carcinogenesis, detailed analyses of biochemical and microbiological parameters such as pH, total viable counts (TVC), nitrate reductase positive bacterial counts (NRPBC), nitrite (NO2-) and thiocyanate (SNC-) levels, were carried out on 56 fasting gastric juices samples obtained at endoscopy from 28 patients with chronic atrophic gastritis (CAG), 14 with gastric cancers (GC), and 14 normal controls (NC). The mean values of pH, nitrite, TVC, and NRPBC were significantly lower in the juices of NC than in those of CAG and GC patients. Furthermore, the mean levels of the same parameters were higher in GC than in CAG juices. No significant difference was found in the three groups for SCN- level which principally resulted influenced by smoke habit. The 28 patients with CAG were subdivided into two groups (Group A = Diffuse chronic atrophic gastritis--DCAG; Group B = Multifocal chronic atrophic gastritis--MCAG) according to the involvement of gastric corpus and fundus besides antrum by a process of mucosal atrophy. The mean levels of pH, nitrite, TVC, and NRPBC were significantly higher in MCAG than in normal controls but statistically lower in reference to DCAG and cancers. In these two groups no difference was found for the same variables. The percentage of contaminated juices was higher for DCAG and cancers in respect to MCAG but no difference was found between DCAG and neoplastic stomachs. The results of this study suggest that the DCAG could be considered as the chronic atrophic gastritis type more exposed to the risk of N-nitroso compounds carcinogenesis.

Assessment of the risks associated with the use of chemical carcinogens in biomedical research

Estimates of occupational exposure to chemical carcinogens in biomedical research based on environmental monitoring data, efficiency of containment devices, and accident data suggest that workers may be exposed to a few tenths of a microgram of these carcinogens per work day. Environmental exposure to carcinogenic polycyclic aromatic hydrocarbons and N-nitroso compounds exceeds one microgram per day. Because occupational exposure to chemical carcinogens in the laboratory can be readily controlled and because environmental exposure appears to be greater than the occupational exposure that does occur, the relative risk of occupational exposure does not seem to constitute a major health problem.

[Promoting effect of Roussin red methyl ester (RRME) in the pickled vegetables in Linxian County on the forestomach epithelium of mice]

The promoting effect of Roussin red methyl ester (RRME) identified and isolated in the pickled vegetables from Linxian county, a high incidence area of esophageal cancer, was studied in mice. In the mice fed on RRME alone, no pathological lesions were detected in the esophagus and forestomach. Other mice, intubated with N-methyl-N-benzyl-nitrosamine (NMBzA) for 3 times, were then given gastric doses of RRME. 8 out of 36 mice were found to have papilloma of the forestomach, the incidence of papilloma was 22.2%. By histological examination, 51.7% of grade II precancerous lesions in the epithelium of forestomach was found. One other group of mice was intubated with NMBzA only for 3 times, then followed until the end of experiment. 3 out of 21 mice were found to have papilloma of the forestomach, an incidence of 14.3%. 21.1% of grade II precancerous lesions was found in the epithelium of forestomach. The experimental results show that RRME appears to have a promoting effect on the process of tumorigenesis initiated by NMBzA in the forestomach of mice. The promoting effect of RRME on the multisteps of the development of esophageal cancer in Linxian county is discussed.

Volatile nitrites. Use and adverse effects related to the current epidemic of the acquired immune deficiency syndrome

Early reports of the acquired immune deficiency syndrome (AIDS) in homosexual men suggested that the cause might be related to homosexual life-style practices, including use of recreational drugs. Inhalation of volatile nitrites is a possible contributing factor in AIDS because their pharmacologic properties lead to toxicity. Metabolism of N-nitroso compounds produces mutagens, teratogens, and potent carcinogens in 39 different animal species, and volatile nitrites have deleterious effects on human lymphocytes in vitro and in vivo. In relation to the current AIDS epidemic, the timing of production and sales of volatile nitrites for recreational use is the only new life-style factor that might answer the question "why AIDS now?" Prevalence of nitrite use among male homosexuals is very high, and almost every reported case of Kaposi's sarcoma during the past three years includes a history of prior nitrite use. The age of the group of patients in whom Kaposi's sarcoma and AIDS are developing is consistent with a cohort initially exposed seven to 10 years ago. Cessation of nitrite use could reduce the epidemic.

Genotoxicity of N-nitrosothiazolidine in microbial and hepatocellular test systems

The genotoxicity of N-nitrosothiazolidine was studied in a microbial system and in a hepatocellular system. The compound showed positive responses in both tests, exhibiting weak mutagenicity at the lowest level tested (1 mg/plate) in the rec assay in Bacillus subtilis, and inducing statistically significant levels of DNA repair in primary hepatocyte cultures at concentrations ranging from 2 X 10(-4) to 2 X 10(-3) M.