Endogenous nitrosation

Ohshima, H., Friesen, M., Brouet, I., and Bartsch, H. (1990). Nitrotyrosine as a new marker for endogenous nitrosation and nitratit)n of proteins. Food Chem. Toxicol. 28, 647-652. 

Nitrate or nitrite (ingested) under conditions that result in endogenous nitrosation Exposure circumstances 14797-55-8 and 14797-65-0 20A34... 

Endogenous nitrosation is a process that is involved with the formation of DMNA and other nitrosamines in human body, with or without the involvement of microbial activity. The reaction can take place in different parts of the human body. Since a strong correlation appears between the exposure of humans to endogenously formed N-nitroso compounds and the induction of cancer [57], extensive studies have been in progress in recent years. 

Bartsch, H., Ohshima, H. Pignatelli, B. 1988 Inhibitors of endogenous nitrosation. Mechanisms and implications in human cancer prevention. Mutation Res. 202, 307-324. 

Oshima, H., and Bartsch, H., 1981, Quantitative estimation of endogenous nitrosation in humans by monitoring N-nitroso-proline excreted in the urine. Cancer Res. 41 3658-3662. 

The bacterial formation of nitrite led to the assumption that toxic nitrosamines can arise endogenously by the nitrosation of amines (cf. 9.8.2). This danger has been overestimated. Endogenous nitrosation was described as practically insignificant in the nutrition report as early as 1996. 

A correlation may be established between the concentration of oxidized lipids and the TEARS value, expressed as MDA equivalents, in uM units. Correction is due in some cases for the interference by dyes or other factors. For example, the presence of anthocyanins in red cabbage leaves or turbiditjf causes overestimation of lipid hydroperoxides in plant tissue by the TEARS method. TEARS was used to assert the level of endogenous peroxides in hypo- and hyperthyroidism, both conditions being characterized by low lipid and lipoprotein plasma levels and enhanced oxidative metabolism . In a procedure for determination of TEARS in edible oils, the sample is placed in a centrifuge at 12000 g before measuring at 532 nm (e = 1.56 x 10 M cm ) . A usual procedure for determination of TEARS in certain complex matrices involves steam distillation of the aldehydes responsible for the value, instead of extraction. In nitrite-cured meats, excess nitrite may cause nitrosation of MDA, thus interfering with distillation. To avoid this interference sulfanilamide is added, which is converted to a diazonium salt and... 

Nitrosation of thiols to form lutrosothiols as a result of endogenous NO synthesis can occur for both small molecules such as glutathione and large molecules, especially the... 

Chronic hyperglycemia induces numerous alterations in the vasculature that accelerate the atherosclerotic process. Several major mechanisms contribute to the pathological alterations in blood vessels in diabetes, including 1) the nonenzymatic glyco-sylation of proteins and lipids, which form advanced glycation endproducts (AGEs) that can interfere with their normal function and 2) the induction of oxidative and nitrosative stress, as well as exacerbation of proinflammatory responses (50). These abnormalities lead to impaired endogenous platelet inhibition and platelet activation, which could result in arterial thrombosis, and consequently myocardial infarction and stroke (51). 

Methylating agents can be generated by chemical ni-trosation of endogenous metabolites. For example, methylamine produced by the decomposition of organic matter can condense with carbamyl phosphate, a precursor of pyrimidines, to form methylurea, which in turn can be nitrosated to yield methylnitrosourea (MNU). Such nitrosation reactions can be catalyzed by bacterial enzymes (35). 

Taverna P, Sedgwick B. Generation of an endogenous DNA-methylating agent by nitrosation in Escherichia coli. J. Bacteriol. 1996 178 5105-5111. 

In principle, then, ascorbic acid appears to have considerable importance as an inhibitor of in vivo nitrosation of ingested or biosynthesized amines via endogenous nitrite. However, this potential is far from realized. The reaction conditions actually encountered in living organisms are complex and varied and—perhaps more importantly—the in vitro interactions among ascorbic acid, nitrite, and amines are not straightforward. 

The nitrous acid generated in foods at low pH values, from endogenous or added nitrites, decomposes easily to yield the nitrosating agents nitrous anhydrate and nitrosonium ion ... 

Bioavailability from Environmental Media. No studies were located regarding the bioavailability of NDMA from environmental media. Since NDMA has been detected in ambient air, water and soil (ppb levels), it is important to determine if NDMA can be absorbed by humans from environmental samples. It must be noted that NDMA has been found in trace amounts in some foods and beverages and that endogenous formation of NDMA has been found to occur from the nitrosation of amines in the gastrointestinal tract. An... 

How are the nitrosoamines formed in a living organism Apart from the possibility that nitrogen oxides are taken up from the environment, endogenic ways of forming enzymatic nitrosating agents are likely to be in operation, as work of en-... 

Ohshima H, Bartsch H. Quantitative estimation of endogenous N-nitrosation in humans by monitoring N-nitrosoprolme in urine. Methods Enzymol 1999 301 40-49. 

DNICs have been reported to react with low molecular thiols or protein thiols to yield S-nitrosothiols. Further, DNIC may nitrosate endogenous secondary amines with the formation of nitrosamines [68]. In biological systems, therefore, transnitro-sylation by DNIC would be in competition with nitrosation. This is consistent with findings of Ueno et al. [65] that the efficiency of transnitrosylation of Fe-DTC by DNICs is lower in the liver, a thiol-rich organ, than in the kidney. 

Because of the enormous volume of reports of studies on nitrosamines, many of the recent reviews are focused on a narrow topic endogenous N-nitrosation [5], bacterial mutagenesis by nitrosamines [6], occurrence of nitrosamines in foodstuffs, and dietary exposure to nitrosamines [7,8,9], environmental exposure to preformed nitroso compounds [10], and the levels of both N-nitroso compounds and their precursors in the human environment [11]. While bacterially mediated N-nitrosation has been reviewed as a part of endogenous N-nitrosation [6], there have been no comprehensive reviews on the production and degradation of DMNA in various environments, that are closely associated with microbial processes. 

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