Nitrosamines (or more formally N-Nitrosamines) are organic compounds of the chemical structure R2N−N=O, where R is usually an alkyl group. They feature a nitroso group (NO+) bonded to a deprotonated amine. Most nitrosamines are carcinogenic in animals. There is no conclusive epidemiological evidence that nitrosamines are carcinogenic in humans. 
The organic chemistry of nitrosamines is well developed with regard to their syntheses, their structures, and their reactions. They usually are produced by the reaction of nitrous acid (HNO2) and secondary amines.
- HONO + R2NH → R2N-NO + H2O
The nitrous acid usually arises from protonation of nitrite. This synthesis method is relevant to the generation of nitrosamines under some biological conditions.
With regards to structure, the C2N2O core of nitrosamines is planar, as established by X-ray crystallography. The N-N and N-O distances are 132 and 126 pm, respectively in dimethylnitrosamine, one of the simplest members of a large class of N-nitrosamines
Nitrosamines are not directly carcinogenic. Metabolic activation is required to convert them to the alkylating agents that modify bases in DNA, inducing mutations. The specific alkylating agents vary with the nitrosamine, but all are proposed to feature alkyldiazonium centers.
History and occurrenceEdit
In 1956, two British scientists, John Barnes and Peter Magee, reported that a simple member of the large class of N-nitrosamines, dimethylnitrosamine, produced liver tumours in rats. Subsequent studies showed that approximately 90% of the 300 nitrosamines tested were carcinogenic in a wide variety of animals.
A common way ordinary consumers are exposed to nitrosamines is through tobacco use and cigarette smoke. Tobacco-specific nitrosamines also can be found in American dip snuff, chewing tobacco, and to a much lesser degree, snus (127.9 ppm for American dip snuff compared to 2.8 ppm in Swedish snuff or snus).
Nitrosamines are produced by the reaction of nitrites and secondary amines. Nitrites are used as food preservatives, e.g. cured meats. Secondary amines arise by the degradation of proteins (food).
Adverse reaction with dimethylamineEdit
During the 1970s, an elevated frequency of liver cancer was found in Norwegian farm animals after the farm animals had been fed on herring meal that was preserved using sodium nitrite. The sodium nitrite had reacted with dimethylamine in the fish and produced dimethylnitrosamine, which was determined to be carcinogenic during the studies of the 1950s.
Opposing reactions with ascorbic acidEdit
Endogenous nitrosamine formation can be affected by ascorbic acid, either inhibiting its formation or increasing its formation, depending upon whether ascorbic acid is consumed in conjunction with it as opposed to the effect being reversed by factors related to dietary fat consumed at the same time.
In the case of formation of carcinogenic nitrosamines in the stomach from dietary nitrite (used as a processed meat preservative), ascorbic acid markedly decreases nitrosamine formation in the absence of fat in the meal, through inhibition. However, when 10% of the meal is fat, the effect is reversed, such that ascorbic acid then markedly increases nitrosamine formation. A yeast study has shown that N-nitrosamines can perturb amino acid metabolism and mitochondrial function.
|Substance name||CAS number||Synonyms||Molecular formula||Physical appearance||Carcinogenity category|
|N-Nitrosonornicotine||16543-55-8||NNN||C9H11N3O||Light yellow low-melting solid|
|4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone||64091-91-4||NNK, 4′-(nitrosomethylamino)-1-(3-pyridyl)-1-butanone||C10H15N3O2||Light yellow oil|
|N-Nitrosodimethylamine||62-75-9||Dimethylnitrosamine, N,N-dimethylnitrosamine, NDMA, DMN||C2H6N2O||Yellow liquid||EPA-B2; IARC-2A; OSHA carcinogen; TLV-A3|
|N-Nitrosodiethylamine||55-18-5||Diethylnitrosamide, diethylnitrosamine, N,N-diethylnitrosamine, N-ethyl-N-nitrosoethanamine, diethylnitrosamine, DANA, DENA, DEN, NDEA||C4H10N2O||Yellow liquid||EPA-B2; IARC-2A|
|N-Nitrosoanatabine||71267-22-6||NAT||C10H11N3O||Clear yellow-to-orange oil||IARC-3|
- Altkofer, Werner; Braune, Stefan; Ellendt, Kathi; Kettl-Grömminger, Margit; Steiner, Gabriele (2005). "Migration of nitrosamines from rubber products - are balloons and condoms harmful to the human health?". Molecular Nutrition & Food Research. 49 (3): 235–238. doi:10.1002/mnfr.200400050. PMID 15672455.
- Proctor, Robert N. (2012). Golden Holocaust: Origins of the Cigarette Catastrophe and the Case for Abolition. Berkeley: University of California Press. ISBN 9780520950436. OCLC 784884555.
- Beard, Jessica C.; Swager, Timothy M. (21 January 2021). "An Organic Chemist's Guide to N-Nitrosamines: Their Structure, Reactivity, and Role as Contaminants". The Journal of Organic Chemistry. 86 (3): 2037–2057. doi:10.1021/acs.joc.0c02774. PMID 33474939.
- Yang, Chung S.; Yoo, Jeong-Sook H.; Ishizaki, Hiroyuki; Hong, Junyan (1990). "Cytochrome P450IIe1: Roles in Nitrosamine Metabolism and Mechanisms of Regulation". Drug Metabolism Reviews. 22 (2–3): 147–159. doi:10.3109/03602539009041082. PMID 2272285.
- Jakszyn, Paula; Gonzalez, Carlos. "Nitrosamine and related food intake and gastric and oesophageal cancer risk: A systematic review of the epidemiological evidence". NCBI. Retrieved 6 September 2021.
- Tricker, A.R.; Preussmann, R. (1991). "Carcinogenic N-Nitrosamines in the Diet: Occurrence, Formation, Mechanisms and Carcinogenic Potential". Mutation Research/Genetic Toxicology. 259 (3–4): 277–289. doi:10.1016/0165-1218(91)90123-4. PMID 2017213.
- Anselme, Jean-Pierre (1979). "The Organic Chemistry of N-Nitrosamines: A Brief Review". N-Nitrosamines. ACS Symposium Series. 101. pp. 1–12. doi:10.1021/bk-1979-0101.ch001. ISBN 0-8412-0503-5.
- Vogel, A. I. (1962). Practical Organic Chemistry (3rd ed.). Impression. p. 1074.
- Krebs, Bernt; Mandt, Jürgen (1975). "Kristallstruktur des N-Nitrosodimethylamins". Chemische Berichte. 108 (4): 1130–1137. doi:10.1002/cber.19751080419.
- Hecht, Stephen S. (1998). "Biochemistry, Biology, and Carcinogenicity of Tobacco-Specific N-Nitrosamines". Chemical Research in Toxicology. 11 (6): 559–603. doi:10.1021/tx980005y. PMID 9625726.
- Advances in Agronomy. Academic Press. 2013-01-08. p. 159. ISBN 978-0-12-407798-0.
- Gregory N. Connolly; Howard Saxner (August 21, 2001). "Informational Update Research on Tobacco Specific Nitrosamines (TSNAs) in Oral Snuff and a Request to Tobacco Manufacturers to Voluntarily Set Tolerance Limits For TSNAs in Oral Snuff". Cite journal requires
- Honikel, Karl-Otto (2008). "The use and control of nitrate and nitrite for the processing of meat products". Meat Science. 78 (1–2): 68–76. doi:10.1016/j.meatsci.2007.05.030. PMID 22062097.
- Jakszyn, P; Gonzalez, CA (2006). "Nitrosamine and related food intake and gastric and oesophageal cancer risk: A systematic review of the epidemiological evidence". World Journal of Gastroenterology. 12 (27): 4296–4303. doi:10.3748/wjg.v12.i27.4296. PMC 4087738. PMID 16865769.
- Joyce I. Boye; Yves Arcand (2012-01-10). Green Technologies in Food Production and Processing. Springer Science & Business Media. p. 573. ISBN 978-1-4614-1586-2.
- Tannenbaum SR, Wishnok JS, Leaf CD (1991). "Inhibition of nitrosamine formation by ascorbic acid". The American Journal of Clinical Nutrition. 53 (1 Suppl): 247S–250S. Bibcode:1987NYASA.498..354T. doi:10.1111/j.1749-6632.1987.tb23774.x. PMID 1985394. S2CID 41045030. Retrieved 2015-06-06.
Evidence now exists that ascorbic acid is a limiting factor in nitrosation reactions in people.
- Combet, E.; Paterson, S; Iijima, K; Winter, J; Mullen, W; Crozier, A; Preston, T; McColl, K. E. (2007). "Fat transforms ascorbic acid from inhibiting to promoting acid-catalysed N-nitrosation". Gut. 56 (12): 1678–1684. doi:10.1136/gut.2007.128587. PMC 2095705. PMID 17785370.
- Combet, E; El Mesmari, A; Preston, T; Crozier, A; McColl, K. E. (2010). "Dietary phenolic acids and ascorbic acid: Influence on acid-catalyzed nitrosative chemistry in the presence and absence of lipids". Free Radical Biology and Medicine. 48 (6): 763–771. doi:10.1016/j.freeradbiomed.2009.12.011. PMID 20026204.
- Ogbede, J.U., Giaever, G. & Nislow, C. A genome-wide portrait of pervasive drug contaminants. Sci Rep 11, 12487 (2021). https://doi.org/10.1038/s41598-021-91792-1
- Hecht, Steven S.; Borukhova, Anna; Carmella, Steven G. "Tobacco specific nitrosamines" Chapter 7; of "Nicotine safety and toxicity" Society for Research on Nicotine and Tobacco; 1998 - 203 pages