Helicobacter pylori does not mediate the formation of carcinogenic N-nitrosamines |
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Authors: | Vermeer I T M Gerrits M M Moonen E J C Engels L G J B Dallinga J W Kleinjans J C S van Maanen J M S Kuipers E J Kusters J G |
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Institution: | Department of Health Risk Analysis and Toxicology, Maastricht University, PO Box 616, 6200 MD, Maastricht, the Netherlands;;Department Medical Microbiology, Vrije Universiteit, Amsterdam, the Netherlands;;Department of Gastroenterology and Hepatology, Academic Hospital Dijkzigt, Rotterdam, the Netherlands;;Department of Gastroenterology, Maasland Hospital Sittard, The Netherlands |
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Abstract: | Background. Both N‐nitroso compounds and colonization with Helicobacter pylori represent known risk‐factors for the development of gastric cancer. Endogenous formation of N‐nitroso compounds is thought to occur predominantly in acidic environments such as the stomach. At neutral pH, bacteria can catalyze the formation of N‐nitroso compounds. Based on experiments with a noncarcinogenic N‐nitroso compound as end product, and using only a single H. pylori strain, it was recently reported that H. pylori only displays a low nitrosation capacity. As H. pylori is a highly diverse bacterial species, it is reasonable to question the generality of this finding. In this study, several genetically distinct H. pylori strains are tested for their capacity to form carcinogenic N‐nitrosamines. Materials and Methods. Bacteria were grown in the presence of 0–1000 µM morpholine and nitrite (in a 1 : 1 molar ratio), at pH 7, 5 and 3. Results. Incubation of Neisseria cinerea (positive control) with 500 µM morpholine and 500 µM nitrite, resulted in a significant increase in formation of N‐nitrosomorpholine, but there was no significant induction of N‐nitrosomorpholine formation by any of the H. pylori strains, at any of the three pH conditions. Conclusion. H. pylori does not induce formation of the carcinogenic N‐nitrosomorpholine in vitro. The previously reported weak nitrosation capacity of H. pylori is not sufficient to nitrosate the more difficultly nitrosatable morpholine. This probably also holds true for other secondary amines. These results imply that the increased incidence of gastric cancer formation that is associated with gastric colonization by H. pylori is unlikely to result from the direct induced formation of carcinogenic nitrosamines by H. pylori. However, this has to be further confirmed in in vivo studies. |
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Keywords: | Helicobacter pylori carcinogenic N-nitrosamines nitrosation capacity |
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