Metabolism and Carcinogenicity of Heterocyclic Amines

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DESCRIPTION (provided by applicant): Colorectal cancer is one of the leading causes of cancer deaths in the United States. Both cooked red meat intake and chronic inflammation/infection play a role in the etiology of colon cancer. During the cooking process, genotoxic heterocyclic amines (HCAs), i.e., 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), are formed which can initiate colon cancer. Colorectal carcinoma incidence in patients with inflammatory bowel disease is 20-fold higher and occurs 20 years earlier than the general population. Findings in patients are paralleled in animal models with persistent severe inflammation in the colonic mucosa thought to cause development of colorectal cancer. Dextran sulfate sodium (DSS)-induced colitis is an animal model for studying both inflammation and colitis-associated neoplasia. Reactive nitrogen oxygen species (RNOS), components of the inflammatory response, contribute to deleterious effects of inflammation. RNOS catalyze nitrosation, oxidation, and nitration reactions. However, the influence of RNOS on HCA carcinogenicity has not been evaluated. Such an evaluation is essential to understanding the strong association between cooked red meat intake and chronic infection/inflammation in colon cancer. Because we recently demonstrated RNOS transformation of IQ to an N-nitroso product N-NO-IQ), which forms DNA adducts and is mutagenic, we hypothesize that RNOS derived from the inflammatory response react with HCAs forming N-nitroso products that initiate colon cancer. Critical to testing this hypothesis is the identification and measurement of N-nitroso products in animals and cells responding to inflammatory stimuli; the demonstration that N-nitroso products are genotoxic and that HCA-induced colon cancer is increased in DSS-treated mice. The following specific aims will test our hypothesis: 1. Investigate HCA transformation by RNOS; 2. Determine reactivity and potential genotoxicity of HCAs and their RNOS-derived N-nitroso products; 3. Evaluate formation and metabolism of N-NO-IQ and its products by in vitro cellular systems, using inflammatory models; 4. Assess formation and metabolism of N-NO-IQ in mice with DSS-induced colitis; 5. Determine effect of DSS-induced colitis inflammation) in IQ carcinogenicity. The long-term goal is to understand the role of RNOS on HCA carcinogenesis.