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PubMed1980

Exposure assessment to preformed environmental N-nitroso compounds from the point of view of our own studies.

The largest human exposure to N-nitrosamines is in the industrial section. Leather tanners are exposed to N-nitrosodimethylamine at levels up to 47 microgram/m3, corresponding to 440 microgram/person/day. Workers in the curing area of tire factories are exposed to N-nitrosomorpholine at levels up to 27 microgram/m3, corresponding to a intake of 250 microgram/person/day. These industrial exposures are considerably greater than exposure via foodstuffs, beer, cosmetics, cutting fluids and herbicides.

Air Pollutants↗
PubMedDate not supplied

[N-nitroso compounds in the food products in regions with a high stomach cancer morbidity].

The content of cancerogenous N-nitrosamines (NA) was examined in food marketed in the regions with the increased gastric carcinoma incidence. The food was analyzed by means of the fluorescent technique. Some of food products, such as lard, corned beef, dried mushrooms were found to be contaminated with volatile NA, while vegetable and milk products contained negligible amounts of NA or did not contain them at all.

Animals↗
PubMed1980

Occupational exposure to N-nitroso compounds.

N-Nitrosodiphenylamine is used as an additive in the rubber industry. This N-nitrosamine has not been associated with carcinogenic effects in laboratory animals. However, it can serve as a powerful transnitrosation agent, reacting with amines present in the rubber mixture to form other N-nitrosamines; e.g., N-nitrosodibutylamine from di-n-butylamine and N-nitrosodimethylamine from tetramethylthiuram disulfide. Di-n-butylamine and tetramethylthiuram disulfide are both used as additives in the rubber industry.

Air Pollutants↗
PubMed1976

Carcinogenic effects of different nitroso-compounds in Chinese hamsters. II. N-nitrosomorpholine and N-nitrosopiperidine.

A total of 320 Chinese hamsters (Cricetulus griseus) (CH) were subcutaneously (s.c.) treated with 1/5, 1/10, or 1/20 LD50 of N-nitrosomorpholine (NM) or N-nitrosopiperidine (NP). In the CH, NM and NP both produced up to a 100% rate of papillomas of the cheek pouch, tongue, pharynx, esophagus and forestomach. Occasionally squamous cell carcinomas also developed in these organs. A high rate of hepatomas was realized by NP.

Animals↗
PubMed1977

Mechanism of alkylation by N-nitroso compounds: detection of rearranged alcohol in the microsomal metabolism of N-nitrosodi-n-propylamine and base-catalyzed decomposition of N-n-propyl-N-nitrosourea.

Metabolism of N-nitrosodi-n-propylamine by an isolated rat liver microsomal fraction yielded 17% isopropanol and 83% n-propanol (expressed as a percentage of total propanol formed). Base-catalyzed decomposition of N-n-propyl-N-nitrosourea yielded 39% isopropanol and 61% n-propanol. The values provide evidence for involvement of carbocations in both of these reactions.

Alcohols↗
PubMed1977

[Development of tumors in Unio pictorum bivalve mollusks under the influence of N-nitroso compounds].

Diethyl- and dimethylnitrosamines dissolved in tank water in doses of 200-400 ppm induced neoplasms of the digestive gland (basophilic cell neoplasms) in 16 of 95 and in 6 of 17 molusco which survived to the time of appearance of the first tumour (38-39 days), and also neoplasms of the hemopoietic system (lymphatic leukemia) in 7 and 1 molluscs, chiefly in combination with tumours of the digestive gland. Methylnitrosoguanidine induced only inflammatory changes at the site of injections. It is of expedience to use the molluscs as a biological indicator of the hydrosphere pollution with chemical carcinogens.

Animals↗
PubMed1981

Cimetidine is unlikely to increase formation of intragastric N-nitroso-compounds in patients taking a normal diet.

Studies in fasting subjects have suggested that cimetidine therapy might lead to nocturnal hypochlorhydria, allowing bacterial overgrowth and the production of intragastric carcinogens. This hypothesis was investigated in normal subjects taking full-dose and maintenance cimetidine with food. Nocturnal hypochlorhydria wa rarely found and the incidence of bacterial overgrowth was correspondingly low; gastric-juice nitrite concentrations were rarely raised. These findings suggest that long term treatment with cimetidine is unlikely to promote gastric cancer as a result of bacterial metabolic activity.

Bacteria↗
PubMed1987

Endogenous formation of N-nitroso compounds: a current perspective.

Exposure of people to nitrosating agents occurs through multiple pathways, ranging from nitrogen dioxide reactions in the lung to acid-catalysed nitrosation in the stomach to nitrosation mediated by macrophages or bacteria. The use of N-nitrosoproline (NPRO) as an index of endogenous nitrosation has proved to be especially valuable for some of these pathways but may not be universally indicative. Since the development of the NPRO test by Ohshima and Bartsch in 1981, several forms of the test have been used for different purposes. This paper examines some of the issues related to endogenous nitrosation and NPRO and attempts to view the immediate future.

Bacteria↗
PubMedDate not supplied

Effect of cooking on availability and in vitro nitrosation of precursors of volatile N-nitroso compounds in seafood.

Aqueous extracts of uncooked and cooked samples of squid and shrimp, characterized by their high amine content, were exposed to nitrate. The samples were cooked following traditional Italian recipes: stewing, grilling and deep-frying for squid; boiling, grilling and deep-frying for shrimp. Incubation of the aqueous extracts with nitrite in acidic medium yielded appreciable amounts of N-nitrosodimethylamine. Ascorbic acid and alpha-tocopherol were effective in preventing nitrosation of seafood amines only in the presence of molar excesses of these vitamins. An attempt at modulating nitrosation through the use of food ingredients naturally rich in vitamin C was unsuccessful.

Animals↗
PubMed1984

Nitrosating properties of bis-methylthio-diiron-tetranitrosyl (Roussin's red methyl ester), a nitroso compound isolated from pickled vegetables consumed in northern China.

Bis-methylthio-diiron-tetranitrosyl (Roussin's red methyl ester, RRME), recently identified in pickled vegetables consumed in a high incidence area of oesophageal cancer in Northern China, was examined for its activity as a nitrosating agent in vivo and in vitro. Freshly synthesized RRME nitrosated secondary amines (morpholine and pyrrolidine) slowly in the presence of air; it failed to nitrosate these amines under strictly anaerobic conditions. In experiments in rats, a fresh sample of RRME was found to be a weak nitrosating agent, whereas partially decomposed RRME showed a strong nitrosating activity comparable to that of nitrite. Possible mechanisms for nitrosation by RRME are discussed.

Animals↗
PubMed2001

Characteristics and use as spin trapping agent of a beta-phosphorylated nitroso compound, DEPNP.

2-(Diethylphosphonate)-nitrosopropane (DEPNP), prepared by oxidation of the corresponding aminophosphonate, was found to essentially exist as monomer in both water and organic solvents. The mechanisms of its degradation under 80 degrees C heating or visible light exposure were studied by EPR spectroscopy: its decomposition gave rise to paramagnetic by-products, which have been identified as DEPNP/.C(CH(3) )(2) [P(O)(OC(2) H(5) )(2) ] and DEPNP/.P(O)(OC(2) H(5) )(2) spin adducts. Despite this drawback, DEPNP was successfully used as spin trapping agents to scavenge various carbon - and phosphorus-centred free radicals both in aqueous and organic media, giving rise to intense EPR spectra characteristic of the species trapped.

Electron Spin Resonance Spectroscopy↗
PubMed1978

The use of short-term tests to measure the preventive action of reducing agents on formation and activation of carcinogenic nitroso compounds.

The effect of reducing agents on the nitrosation of methylguanidine (MG) and on the in vitro activation of dimethylnitrosamine (DMN) was examined by measuring DNA-repair synthesis (unscheduled incorporation of [3h]TdR), shifts in alkaline sucrose gradients, frequency of chromosome aberrations, and clone-forming capacity of cultured human fibroblasts. The reducing agents examined were sodium ascorbate, cysteine, cysteamine, and propyl gallate. Since the short-term bioassays used can be quantitated, it has become relatively easy to detect the inhibitory action of reducing compounds on the nitrosation reaction of MG and metabolic activation (with S-9 preparation) of the precarcinogen DMN, to measure their effective dose range, and to establish the most effective ratios between inhibitory agent and reactant. The results indicate that DNA-repair synthesis is a suitable short-term test for studying the numerous combinations and premutations between several carcinogenic or non-carcinogenic agents, and for estimating the capacity of inhibitory agents to affect formation and activation of chemical carcinogens.

Adolescent↗
PubMed1985

Enzymatic inactivation of N-nitroso compounds in murine blood plasma.

Murine blood plasma rapidly inactivates nitrosamides and nitrosocarbamates but not nitrosoureas. The mechanism of this inactivation in murine blood plasma has been investigated. The vast majority of activity (greater than 97%) was inhibited by serine hydroxylase inhibitors. Also, 92% of the activity was inhibited by bis(p-nitrophenyl)phosphate, a selective inhibitor of carboxylesterases. Decomposition products formed after blood plasma action on N-ethyl-N-nitrosoacetamide or N-methyl-N-nitrosoethylcarbamate were separated and identified by gas chromatography. The products formed were consistent with a hydrolytic cleavage of the amidic bond. These observations are consistent with the idea that the major active factor(s) in plasma is a carboxylesterase(s).

Animals↗
PubMed1988

Effect of carcinogenic nitroso compounds on rat kidney proximal tubule NAD levels.

An exposure of proximal tubules to alkylating nitrosamines is not necessary to deplete their NAD levels. Further work is needed to test if the poly(ADP-ribose) transferase induction theory accounts for the observed depletion of intracellular NAD. Also the viability of proximal tubule cells in the conditions of the study must be determined. Phosphate uptake by BBM vesicles prepared from chilled proximal tubules compared to those from proximal tubules incubated at 37 degrees C is a useful model for examining the role of intracellular NAD in renal Na+ gradient-dependent Pi transport. More experiments are required to assess the significance of changes in Pi-uptake by BBM vesicles induced by depletion of proximal tubule NAD content.

Animals↗
PubMed1980

Formation of N-nitroso compounds of the pesticides atrazine, simazine and carbaryl with nitrogen oxides.

The nitrosation of atrazine, simazine and carbaryl by nitrogen oxides was investigated in model experiments. Pure pesticides and their corresponding formulations were exposed, as dry powders and as aqueous suspensions, to defined concentrations of NOx (1000, 100, 10 and 1 ppm) in a reaction chamber. Nitrosated pesticides were determined by HPLC-TEA. Generally, the amount of nitrosation increased with the reaction time. At high NOx concentrations (1000 and 100 ppm), nitrosation approached saturation. For atrazine and simazine, further reaction with nitrogen oxides might occur. Nitrosation rates of dry powdered pesticides were inversely proportional to grain size and to air moisture content. Nitrosation of aqueous pesticide suspensions by nitrogen oxides was strongly inhibited at pH values higher than 5.

Atrazine↗
PubMed1978

Mutagenicity and cytotoxicity of congeners of two classes of nitroso compounds in Chinese hamster ovary cells.

The induction of mutation by certain nitrosamidines and nitrosamides has been quantitated utilizing the hypoxanthine--guanine phosphoribosyl transferase (HGPRT) locus in Chinese hamster ovary cells. Dose--response relationships for cytotoxicity and mutagenicity are presented for N-methyl-N-nitrosourea (MNU), N-ethyl-N-nitrosourea (ENU), N-butyl-N-nitrosourea (BNU), N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), and N-ethyl-N'-nitro-N-nitrosoguanidine (ENNG). Based on the concentration of each agent required to kill 90% of the cells, the following order of cytotoxicity was observed: MNNG greater than ENNG greater than MNU greater than ENU greater than BNU. This is the same order of potency as observed for mutation induction per unit concentration of mutagen.

Cell Line↗
PubMed1983

Biological activity of benzylating N-nitroso compounds. Models of activated N-nitrosomethylbenzylamine.

Unsymmetrically substituted N-nitrosomethylbenzylamine is an oesophageal carcinogen with potential methylating and benzylating properties. Whereas the methylating activity of the compound has been investigated, little is known of its potential benzylating properties. In order to elucidate the biological consequences of benzylation, related model compounds which are presumed benzylating agents were synthesized and tested for mutagenicity. N-nitrosobenzylurea and its structural analogue N-nitroso-p-methylbenzylurea were direct acting mutagens in Salmonella typhimurium TA 98. Activity was also present in TA 1535, but it was less pronounced. N-nitroso-alpha-acetoxybenzyl-benzylamine was equally mutagenic in S. typhimurium TA and TA 1535. N-nitroso-acetoxymethyl-benzylamine and N-nitrosoacetoxy-methyl-p-methylbenzylamine are two model compounds which may decompose by hydrolysis or through esterases to yield intermediates also though to arise after alpha-C hydroxylation of the methyl group of the parent nitrosamines. These compounds needed additional activation by enzymes present in the post-mitochondrial supernatant of rat liver. They were distinctly mutagenic in TA 98. Furthermore, all compounds also caused the induction of phage lambda in a qualitative assay with Escherichia coli Br 513. Thus, benzylation of DNA clearly results in a biological consequence. These findings are supportive of the theory that if enzymic attack occurs on the methyl group of N-nitrosomethylbenzylamine, benzylation may also contribute to the overall biological activity of the compound.

Animals↗
PubMed1980

Dose-response studies and 'no-effect-levels' of N-nitroso compounds: some general aspects.

One major problem in the evaluation of potential carcinogenic food additives and contaminants is that of thresholds or, better, of 'no-adverse-effect-levels'. Arguments in favor of the postulated 'irreversibility' of carcinogenic effects are based on dose-response studies, single dose and multigeneration experiments as well as on the concept of somatic mutation as the first step in carcinogenesis with subsequent transmittance of induced defects during cell replication. The problem of extrapolation of results of animal experiments using high doses to low exposure and low incidences in man is not yet solved satisfactorily. Possible practical consequences include zero tolerance, acceptable thresholds at low risk and safety factors. Acceptable intakes should never be considered constants but should be changeable as soon as new facts in regard to the safety evaluation are available.

Animals↗