O 6-alkylguanine adducts, e.g., have been identified as the main premutagenic lesion and cause GC-AT transition mutations ( Mirvish, 1995). NOC can be divided into two main subclasses, nitrosamines and nitrosamides ( Preussmann and Eisenbrand, 1984), which are both capable of inducing alkylating DNA damage by formation of a highly reactive diazonium ion ( Mirvish, 1995 Tricker and Preussmann, 1991). Although a direct link with human carcinogenicity is still lacking, NOCs have been suggested to play a role in the development of several types of cancers, including those of the brain, head and neck, gastric, and colorectal cancer ( Knekt et al., 1999 Lijinsky, 1992). NOCs have been found in the environment and certain types of food, such as beer, fish, and nitrite-preserved meat ( Tricker and Preussmann, 1991), but can also be formed endogenously by nitrosation of dietary precursors, a process that occurs predominantly in the gastrointestinal tract ( Kuhnle et al., 2007 Mirvish, 1995 Sen et al., 2000). Department of Health and Human Services, 2005). N-nitroso compounds (NOCs) have long been known to be mutagenic in bacterial mutagenicity studies and carcinogenic in test animals ( Lijinsky, 1992), which has lead to the classification of dozens of NOC as potential human carcinogen ( U.S.
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Nitrosamines, nitrosamides, N-nitroso compounds, free radicals, toxicogenomics, colon carcinogenesis INTRODUCTION These findings suggest that following NOC exposure in Caco-2 cells, ROS formation plays an important role in deregulation of gene expression patterns that may be relevant for the process of chemical carcinogenesis in the human colon, in addition to the role of DNA alkylation. By associating gene expression patterns with ROS formation, several cellular processes responding to nitrosamine exposure were identified, including apoptosis, cell cycle blockage, DNA repair, and oxidative stress. N-methyl-N′-nitro-N-nitrosoguanidine did not cause radical formation at genotoxic concentrations, but at increased exposure levels, both ROS and NCR formation was observed. N-methyl-N-nitrosourea exposure resulted in a small ROS signal, and formation of nitrogen-centered radicals (NCRs), also stimulated by Caco-2 cells. Nitrosamines caused formation of reactive oxygen species (ROS) and carbon-centered radicals, which was further stimulated in the presence of Caco-2 cells. Cells were exposed to nitrosamides (N-methyl-N′-nitro-N-nitrosoguanidine and N-methyl-N-nitrosourea) or nitrosamines (N-nitrosodiethylamine, N-nitrosodimethylamine, N-nitrosopiperidine, and N-nitrosopyrrolidine). Using electron spin resonance spectroscopy, we investigated the radical-generating properties of genotoxic NOC concentrations in human colon adenocarcinoma cells (Caco-2). Because it was previously demonstrated that nitrosamines and nitrosamides, representing two classes of NOC, induce distinct gene expression effects in colon cells that are particularly related to oxidative stress, we hypothesized that different radical mechanisms are involved.
Streamlined deployment wizard for fast and easy rollout of custom installations everything from workgroups to entire sites.N-nitroso compounds (NOCs) may be implicated in human colon carcinogenesis, but the toxicological mechanisms involved have not been elucidated. Secure documents with passwords and certificates.
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