We propose that N-nitroso compounds (NOC) in colon contents are a significant cause of colon cancer and that NOC formation in the gastrointestinal tract (GIT) and their carcinogenic action in colon can be inhibited by chemopreventive agents. Experiments in Aims 1-3 will use Swiss mice that receive semipurified diet and are treated for 7 days. On day 7, 24-h feces or GIT sections will be analyzed for NOC by our standard method.
Aim 1 : We found that feeding 1% sodium nitrite in drinking water increased fecal NOC excretion 15 times. We will study effect of successively lower levels of nitrite on fecal NOC output, determine NOC in different GIT sections when nitrite is fed or not fed; study effect of nitrate on fecal NOC; study effect of acid suppressant omeprazole on gastric and fecal NOC in mice fed or not fed nitrite; feed nitrite with frankfurters to find out whether nitrite reacts with frankfurter-derived NOC precursors (NOCP); and feed 1, 2 and 4% hemin in diet with nitrite.
Aim 2 : Because ascorbate inhibits acid-catalyzed gastric nitrosation, we will test reduction of fecal NOC level on feeding 3 ascorbate doses in diet with nitrite in water, and test 1 ascorbate dose given alone or with nitrite plus """"""""hemin, nitrite plus frankfurters or frankfurters alone.
Aim 3 : We will test inhibition by ascorbate and 5 dietary polyphenols of the chemical nitrosation of frankfurter-derived NOCP to give NOC, and study effect of polyphenols, given in diet to mice with and without nitrite in drinking water, on fecal NOC excretion.
Aim 4 : NOC produced from partially purified NOCP in frankfurters were directly mutagenic in Salmonella typhimurium TA-100. We will conduct similar tests on NOC derived from purified fecal NOCP from rats fed commercial diet.
Aim 5 : We will test NOC derived from frankfurter-derived NOCP for ability to induce colonic tumors when fed to A/J mice receiving a Western diet for > 6 weeks. At 15 or 30 weeks after beginning treatment, colons will be evaluated for aberrant crypt foci and tumors. Other mice will be evaluated similarly after treatment with azoxymethane or with NOC obtained from NCOP from rat feces. Overall results will indicate how fecal NOC levels are controlled and can be reduced, and whether fecal NOC can induce colon cancer. ? ? ?
