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PubMed1988

An ESR study of nonenzymatic reactions of nitroso compounds with biological reducing agents.

The nonenzymatic reduction of nitrosobenzene (I), 2-nitroso-1-naphthol (II) and 2-nitroso-1-naphthol-4-sulfonic acid (III) with reducing agents such as NADPH, L-cysteine and N-acetyl-L-cysteine led to the formation of the corresponding hydronitroxide radicals, as confirmed with ESR spectroscopy. In addition to these radicals, a novel hydronitroxide radical, which was conjugated with GSH at the 4-position, was observed in the reaction of II or III with GSH. The formation of a hydronitroxide conjugated with GSH still retains the radical structure with its related redox chemistry. In this case, the formation of a GSH conjugate does not lead to the formation of chemically less reactive species.

Acetylcysteine↗
PubMed1977

N-nitroso compounds: their chemical and in vivo formation and possible importance as environmental carcinogens.

Brief reviews are presented on the occurrence of N-nitroso (NNO) compounds, the chemistry and kinetics of NNO compound formation from nitrite and amines or amides, the in vivo formation of these compounds (as detected by tumor induction) on feeding nitrite with amines or amides to rodents, and the carcinogenicity for rats of some new nitrosamides. The possible human hazard caused by exposure to specific readily nitrosated compounds is reviewed. Whether NNO compounds might be causing human cancer of various organs (e.g., pancreatic, nasopharyngeal, and esophageal cancer) is discussed. Some of our results in [3H]thymidine incorporation in the rat esophageal epithelium are presented. Nitrosamines that cause esophageal cancer in rats were found to inhibit [3H]thymidine incorporation, both in vivo and in vitro, when esophagi were incubated with nitrosamines. With reference to the hypothesis that human gastric cancer is caused by nitrosamides (e.g., nitrosoureas), certain correlations were examined between gastric cancer and environmental exposure to nitrate, nitrite, and nitrosatable amides. In studies from our laboratory, dried, salted fish, which was treated with excess nitrite at pH 1 and then "denitrosated" at pH O, yielded 16 mg methylurae/kh fish, possibly derived from methylguanidine.

Animals↗
PubMed1976

Air-water and ether-water distribution of N-nitroso compounds: implications for laboratory safety, analytic methodology, and carcinogenicity for the rat esophagus, nose, and liver.

The air-water distribution ratio K1, ether-water distribution ratio K2, and solubility in water were measured for 17 nitrosamines, 3 nitrosamides, and 1 nitrosocyanamide. For K1, air was analysed either by UV absorption of ethanol extracts or by gas chromatography. K1 at 37 degrees C varied from less than 2 X 10(-6) to 4.5 X 10(-3), with 11 compounds showing K1 greater than 10(-4). A literature analysis provided data on the carcinogenicity of these N-nitroso (NNO) compounds toward the esophagus, nose, and liver of the rat. This compilation of data on physical properties and carcinogenicity of NNO compounds was then analysed in terms of: a) safety of workers handling either solutions of volatile NNO compounds or animals treated with these compounds, b) analytic methdology, and c) possible correlations between K1-, K2-, and solubility-characteristics, and carcinogenicity. Overall correlations were not observed. However, within each of five chemical groups, K1 and K2 tended to be associated positively with esophageal and nasal carcinogenicity and negatively with hepatic carcinogenicity. Water solubility showed the opposite associations.

Air↗
PubMed1988

Inhibitory effects of para-aminobenzoic acid on the formation and mutagenicity of N-nitroso compounds.

Naturally occurring para-aminobenzoic acid (PABA) inhibited the formation of N-methyl-N-nitrosourea (MNU) from a nitrosation mixture of N-methylurea and nitrite at pH 3. The suppressive effect of PABA on the formation of MNU is higher than that of ascorbic acid. The presence of the MNU was assayed by its mutagenicity in a higher plant, Arabidopsis thaliana. In addition, PABA markedly reduced the mutagenicity of N-methyl-N'-nitro-N-nitrosoguanidine in A.thaliana, but had no or only a low inhibitory effect on the mutagenicity of preformed MNU and on the promutagen N-nitrosodimethylamine.

4-Aminobenzoic Acid↗