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PubMed1977

Effects of nine N-nitroso compounds on the specific radioactivity of liver proteins after injection of [14C]leucine into rats.

We compared the effect of nine N-nitroso compounds, given by gavage to adult rats, on specific radioactivity of the trichloroacetic acid-precipitable liver proteins, 1 hr after the injection of [14C]leucine. The specific radioactivity was decreased by dimethylnitrosamine, diethylnitrosamine, methyl-n-butylnitrosamine, and nitrosomorpholine 5 to 10 hr after their administration; was increased by nitrosopiperidine, dinitrosopiperazine, and methylnitrosourea 5 to 24 hr after gavage; and was unaffected by nitrososarcosine and nitrosodihydrouracil. With dimethylnitrosamine, specific radioactivity was decreased by 10 but not 5 mg/kg. In control rats and rats given injections of either of two nitrosamines, protein specific radioactivity at 60 min after the [14C]leucine injection was 76 to 87% of that at 30 min, indicating some degradation of the proteins at 60 min. The liver:blood ratio of [14C]cycloleucine concentration was unaffected by four nitrosamines, indicating no effect on leucine transport. The effect of the nine compounds was examined on total pool size of free leucine in the liver, at times close to those for the maximum specific radioactivity effect. For these data, we calculated "corrected specific radioactivity," adjusted for changes in pool size. This adjustment is only a first approximation since, for example, the free leucine pool is not uniform with respect to protein synthesis. The four N-nitroso compounds that decreased specific radioactivity also decreased corrected specific radioactivity, even though they enlarged the leucine pool. Of the remaining compounds, two enlarged the leucine pool and three increased corrected specific radioactivity. For all nine compounds, the decrease in specific and correlated with the ability to cause acute liver necrosis. When nitrosodihydrouracil was excluded, the decrease in specific and corrected specific radioactivity was significantly correlated with the reported liver carcinogenicity.

Animals↗

PubMed1990

Nitrate, nitrite, and N-nitroso compounds in Finnish foods and the estimation of the dietary intakes.

An estimate of the dietary intakes of nitrite, nitrate and N-nitroso compounds is presented, based on the analytical data supplied by the Finnish Food Quality Control. Figures on the food consumption of the Finnish population, taken from a national dietary survey, and food consumption of 1768 children and adolescents over a 48-h recall period were used. The mean daily dietary nitrate intakes were estimated to be about 55 mg for the total population and for children and adolescents. The mean nitrite intakes were 1.88 mg for the total population and 1.07 mg for children and adolescents. The intake of N-nitroso compounds (NDMA) was estimated to be 0.08 micrograms for the total population and 0.02 micrograms for children. Nitrates were found to originate mainly from vegetables (80%), nitrites from meat products (97%) and nitrosamines mostly from fish products and beer. A comparison of the estimate of dietary intake of with ADI values indicated that the nitrite intake of the total population was 23% and by children 39% of ADI. The average weight was approximately 60 kg for adults and 20 kg for children. When measured average weight (39 kg) was used, and the nitrite intake was found to be 28% of ADI. Nitrate intakes from food additives were 2.5% and 1.4% of the ADI value, respectively. When the total nitrate intake from various food sources was compared with the ADI (which is given only for food additives), the estimated nitrate intake of the total population was 25% and that of children 28% of the ADI value.

Adolescent↗

PubMed1996

Effects of low dose mixtures of four N-nitroso compounds on hepatic foci development in the rat.

Potential synergism between four N-nitroso compounds (nitrosomorpholine, nitrosodimethylamine, nitrosodiethanolamine, nitroso-oxazolidine) in rat liver carcinogenesis was examined in the medium-term bioassay. Male F344 rats were initially given diethylnitrosamine (DEN, 200 mg/kg, ip) and beginning 2 weeks later received test chemicals for 6 weeks individually at a full or 1/4 dose of that proven to be carcinogenic individually or in combination. All animals were subjected to partial hepatectomy at week 3 and killed at week 8. Induction of immunohistochemically-demonstrated glutathione S-transferase placental form (GST-P) positive foci was evaluated. The numbers and size of GST-P positive foci were significantly higher than the control levels by the treatment with each nitrosamine at full (1/1) and one quarter doses (1/4), excepting nitrosodiethanolamine and by combination of the four chemicals at 1/4 and 1/16. Because the dose-response curves were considered non-linear for most nitrosamines, synergistic effects were not apparent for the 1/4 mixture. Interestingly, however, the values for rats treated with these four chemicals in combination at the 1/4 dose level were almost the same as the average of four individual treatments at the full dose, and those for the 1/16 dose mixture were almost the same as the average of 1/4 individual treatment groups. These results indicate that these nitrosamines worked additively, rather than synergistically, in rat liver carcinogenesis.

Animals↗

PubMed1986

DNA adducts by N-nitroso compounds.

Some unsolved problems in DNA alkylation by N-nitroso compounds are discussed in this overview. Does O6 alkylation of guanine represent the initiating event exclusively or are O4 alkylation of thymidine and phosphate triester formation also involved in the initiating process? Does the formation of rearranged DNA alkylation products by longer chained alkylnitroso compounds have any significance for the carcinogenic effects of these compounds? The concept of hard and soft acids and bases (HSAB principle) as a qualitative model can predict the changes in the DNA alkylation pattern by branched carbenium ions.

Alkylation↗

PubMed1985

N-Nitroso compounds and human cancer. A molecular epidemiologic approach.

N-Nitroso compounds are known to be potent animal carcinogens. However, evidence of their effect on human cancers is inconclusive, and further investigations are needed. A mathematical model to create indices of nitrate, nitrite, and N-nitrosamine exposures, both exogenous and endogenous, is described in this paper. Estimation of the endogenous formation is based on the current knowledge of biochemistry and chemical kinetics of these compounds. The model can be applied to analyze data regarding the dietary history and use of tobacco products and alcoholic beverages obtained from epidemiologic questionnaires. Exposure levels of study and control subjects to these compounds can then be compared by conventional epidemiologic methods. This is an approach toward the combination of conventional epidemiologic methods and laboratory findings to study disease etiology.

Adult↗

PubMed1976

[Carcinogenicity of N-nitroso compounds].

The toxic, carcinogenic and mutagenic effects of N-nitroso compounds are briefly discussed with reference to recent reviews. These adverse biological effects are discussed in relation to the necessity of metabolic activation by microsomal enzymes for the nitrosamins but not for the nitrosamides.

Amides↗

PubMed1987

The role of various food products in the formation of N-nitroso compounds under acidic conditions.

The effect of lettuce cultivars on the nitrosation rate of proline was investigated. The lettuce was analysed for the presence of phenolic compounds. Lettuce and/or fish was incubated with nitrite under acidic conditions, and the incubation mixtures were investigated for the presence of N-nitroso compounds and mutagenic activity. Both volatile N-nitrosamines and mutagenic nonvolatile N-nitrosamines were detected. The formation of mutagenic N-nitroso compounds was also studied in selected cheese products after treatment with nitrite under acidic conditions. No direct relationship was observed between the total N-nitroso content of the samples and the corresponding mutagenicity. The ability of cheese to inhibit the direct mutagenicity occurring in fava beans after treatment with nitrite under acidic conditions was investigated. The antimutagenic factor, possibly casein, in cheese was not extractable with different solvents.

Animals↗

PubMed1987

An investigation of apparent total N-nitroso compounds in beer.

The concentration of apparent total N-nitroso compounds (ATNC) in beer has been investigated using a group-selective procedure based on chemical denitrosation with hydrogen bromide and chemiluminescence detection of the released nitric oxide. In a survey of samples of 40 brands of beer and lager, detectable levels of ATNC were present in 17 samples at concentrations of 20-100 micrograms N-NO/kg in 11 and 100-500 micrograms N-NO/kg in six. To determine the origin of ATNC in beer the production of a commercial batch was examined in detail. ATNC levels were below the detection limit in the sweet wort (aqueous extract of malt), bitter wort (malt extract boiled with hops) and also at the start of fermentation, but during the course of fermentation the concentration of ATNC increased appreciably and that of inorganic nitrate decreased; detectable, though transitory, levels of inorganic nitrite were observed. None of the brewing ingredients contained sufficiently high enough levels of ATNC to account for the concentration of these compounds present in the beer after fermentation. These findings suggest that the presence of detectable levels of ATNC in some beers is a result of N-nitrosation reactions occurring in the fermenting wort with the nitrosating species derived from reduction of nitrate, due probably to the presence of microbial species with nitrate reductase activity.

Beer↗

PubMed2002

[Exposure level of total N-nitroso compounds in residents of high-and low-risk areas for esophageal cancer in southern].

OBJECTIVE: To assess the exposure level of total N-nitroso compounds (TNOCs) in the residents of high- and low-risk areas for esophageal cancer in southern China. METHODS: Samples of duplicate plate diets and 12 hr overnight urine were collected from 120 male adults in each of the 2 areas, a high-risk area (Nanao county) and a low-risk area (Lufeng county) for esophageal cancer. The 240 male healthy subjects (35 - 64 years old) were selected by a 3-stage random cluster sampling procedure. Levels of TNOC, N-nitrosamino acids (NAAs) and volatile N-nitroso compounds (VNOC) in the samples were measured by Thermo Energy Analyzer. RESULTS: The detectable rate (95%) of diet TNOC, daily dietary TNOC intake (4.25 +/- 0.84) micromol/day, 12-hr urinary TNOC excretion levels (1.76 +/- 0.23 ng/12 h) and daily dietary intake of VNOC (266 +/- 31.2 microg/day) in the high-risk area were all significantly higher than those of the low-risk area. Oesophageal cancer mortality rates were positively and significantly associated with daily dietary TNOC intake and 12-hr urinary TNOC excretion. Urinary NAAs excretion levels were not different in the two areas. CONCLUSION: The results suggest that TNOCs may be implicated in the etiology of esophageal cancer in southern China.

Adult↗

PubMed1992

Selective mutation of codons 204 and 213 of the p53 gene in rat tumors induced by alkylating N-nitroso compounds.

Kidney and esophageal tumors induced by alkylating N-nitroso compounds in rats contain a high incidence (75-100%) of G----A transition mutations in the p53 gene. These are almost selectively (89%) located in the first base of codon 204 and the second base of 213, leading to amino acid substitutions Glu----Lys and Arg----Gln, respectively. In contrast to human neoplasms, a considerable fraction of rat kidney and esophageal tumors carries multiple p53 mutations. All nephroblastomas induced by transplacental exposure to N-nitrosoethylurea and 56% of esophageal tumors induced by N-nitrosomethylurea showed double mutations in codons 204 and 213 of exon 6. The selective targeting of p53 codons by alkylating nitrosamines may provide a basis for molecular epidemiological studies on this class of chemical carcinogens.

Acylation↗

PubMed1986

Effects of vitamins C and E on N-nitroso compound formation, carcinogenesis, and cancer.

The properties of N-nitroso compounds (NNC) and of vitamins C and E are briefly described. The author reviews the ability of vitamins C and E to inhibit NNC formation in chemical systems, in nitrite-preserved meat, in experimental animals and in humans. Dietary vitamins C and E both produced 30% to 60% inhibitions in most carcinogenesis experiments employing preformed carcinogens. Vitamin C reversed transformation in an in vitro system. Carcinogenicity tests of the vitamins are reviewed (vitamin C can promote bladder carcinogenesis). Intake of fresh fruits and vegetables (which contain vitamin C) is negatively correlated with cancer of the stomach, esophagus, larynx, mouth and cervix. For gastric and esophageal cancer, there is evidence that this association is due to an inhibition of in vivo NNC formation. Vitamin C is apparently not a useful treatment for cancer. The author supports the recommendation that fresh fruit and vegetable intake be increased to lower the risk of cancer.

Animals↗

PubMedDate not supplied

Reactions of nitrate and nitrite in foods with special reference to the determination of N-nitroso compounds.

The stabilities of nitrate and nitrite in food systems and their reactions in such matrices are reviewed. Particular reference is made to reactions with haem proteins, smoke components and amines in foods, and the chemistry of formation of N-nitroso compounds from food components is discussed. Finally, the methodology available for determination of both volatile and non-volatile N-nitroso compounds is addressed.

Catalysis↗

PubMed2004

[NO-release ability and DNA-damage activity of aromatic N-nitroso compounds].

To develop a new nitric oxide-donor (NO-donor) that is useful for chemical and biochemical research, we synthesized several aromatic N-nitroso compounds including 1-[N-nitroso-N-(4-tolyl)carbamoyl] piperidine-4-carboxylic acid (1f) and phenyl(2-pyridyl)-N-nitrosamines, which spontaneously generate NO at ambient temperature. Thermal decomposition of these compounds was run under mild conditions. Gaseous NO released from them was quantified by means of the Griess reaction using a specially designed apparatus in which NO2- is generated from NO. The structure of products arose from the radical cleavage of N-NO bond was clarified by chemical and spectral studies. Generation of NO from the N-nitroso compounds was also confirmed by ESR spectroscopy. The action of these NO-releasing compounds against DNA was examined. When the pBR 322 DNA was treated with 1f at 37 degrees C for 3 h, the DNA single-strand breaks was 31% for 1 mM of 1f. The denitrosated compound and sodium nitrite did not show any effective DNA-cleaving activity. On the other hand, aromatic N-nitrosamines induced weak DNA-cleaving activity under the same condition.

DNA Damage↗

PubMed1994

Spin trapping of methyl radicals by the acyl nitroso compound Ph--C(= O)NO formed in the photochemical reaction between benzohydroxamic acid, dimethyl sulfoxide and hydrogen peroxide. An EPR study.

By the use of EPR spectroscopy, it has been shown that acyl nitroso compounds can act as spin traps for short-lived radicals with the formation of acyl aminoxyl radicals. The reaction was studied for the system benzohydroxamic acid [Ph--C(= O)N(H)]-dimethyl sulfoxide-hydrogen peroxide. The acyl aminoxyl radicals appeared almost immediately when the reaction mixture was irradiated in situ in the EPR cavity with UV light. The trapping reaction involved two photochemical reactions, i.e. the oxidation of the hydroxamic acid to the acyl nitroso compound Ph--C(= O)NO, and the formation of methyl radicals from dimethyl sulfoxide. The EPR spectra are superpositions of the spectra of two species of acyl aminoxyl radicals, i.e. the radicals Ph--C(= O)N(O.)H formed by oxidation of the parent benzohydroxamic acid, and the radical Ph--C(= O)N(O.)CH3, formed by trapping of methyl radicals.

Dimethyl Sulfoxide↗

PubMed1984

Recent studies on N-nitroso compounds as possible etiological factors in oesophageal cancer.

Possible etiological factors involved in oesophageal cancer in various parts of the world and in certain provinces in Northern China are summarized. Evidence is accumulating that N-nitroso compounds and their precursors are involved in the disease in Northern China, as shown in a recent study: excretion of urinary N-nitrosamino acids by inhabitants living in a high- (Linxian) and in a low-risk area (Fanxian) for oesophageal cancer was compared. Linxian subjects excreted significantly more nitrate and nitrosamino acids (N-nitrosoproline, N-nitrosothiazolidine-4-carboxylic acid, N-nitrososarcosine) than those in Fanxian. When Linxian subjects were given 100 mg vitamin C three times a day (after each meal) together with proline, the level of urinary N-nitrosamino acids was reduced to that found in Fanxian. Thus, vitamin C, an efficient inhibitor of endogenous nitrosation, should now be examined in intervention trials in subjects in whom endogenous formation of N-nitroso compounds is elevated.

Africa↗

PubMed1981

Animal Species in which N-nitroso compounds induce cancer.

In reviews on the carcinogenicity of N-nitroso compounds (NC) the number of animal species in which these compounds induce cancer is understated. In recent years additional species have been used in experiments. Tumours have been induced by NC in 39 species which belong to 36 genera, 25 families, 17 orders and five class of animals. The names of these taxa are presented in Latin and the common names of species are given in English, French and German. The carcinogenic action of eight NC in various species is tabulated.

Animals↗

PubMed1988

The occurrence of preformed N-nitroso compounds in food samples from a high risk area of esophageal cancer in Kashmir, India.

Several commonly used raw foodstuffs from a high risk esophageal cancer region in Kashmir (India) were analysed for the presence of N-nitroso compounds. The food items were selected on the basis of their frequent consumption with particular emphasis on the preserved foods (dried, pickled and smoked) and those which are unique to the region. Nine out of 11 food items were found to contain low concentrations of N-nitrosodimethylamine (NDMA), N-nitrosopyrrolidine (NPYR), N-nitrososarcosine (NSAR), N-nitrosoproline (NPRO) and N-nitrosothaizolidine-4-carboxylic acid (NTCA). The preliminary survey shows a widespread contamination of N-nitroso compounds in raw foodstuffs from Kashmir.

Esophageal Neoplasms↗

PubMed1994

[N-nitroso-compounds of pickles in the areas with high incidence of digestive cancers and their mutagenic effects].

Contents of N-nitroso-compounds and their precursors in pickles preserved by local residents living in the areas with high incidence of digestive cancers in Jiangsu Province, and micronucleus test in animals taking-in pickles were determined. Results showed nitrite was detected in pickles ranging 0.010 to 0.450g/kg, with 37.5% of them exceeding the national hygienic criterium of 0.030 g/kg set for meat products, and N-nitroso-compounds were detected in 95% of the samples ranging 0.02 to 110.50 micrograms/kg. N-nitrosodimethylamine (NDMA) and N-nitrosodiethylamine (NDEA) in pickles averaged 31.98 and 34.02 micrograms/kg, respectively. Micronucleus frequencies in bone marrow of mice induced by NDMA and NDEA in pickles were 6.92/1000 and 6.17/1000, respectively, with a significant difference as compared with control animals (F = 34.43, P < 0.01), indicating apparently mutagenic effects.

Animals↗