Detection of endogenous DNA adducts, O6‐carboxymethyl‐2′‐deoxyguanosine and 3‐ethanesulfonic acid‐2′‐deoxycytidine, in the rat stomach after duodenal reflux

The endogenous DNA adducts O6-carboxymethyl-deoxyguanosine (O6-CM-dG) and 3-ethanesulfonic acid-deoxycytidine (3-ESA-dC) are produced from N-nitroso bile acid conjugates, such as N-nitrosoglycocholic acid (NO-GCA) and N-nitrosotaurocholic acid (NO-TCA), respectively. Formation of these DNA adducts in vivo was here analyzed by 32P-postlabeling in the glandular stomach of rats subjected to duodenal content reflux surgery. In this model, all duodenal contents, including bile acid conjugates, flow back from the jejunum into the gastric corpus. The levels of O6-CM-dG found at 4 and 8 weeks after surgery were 40.9 ± 9.4 and 56.3 ± 3.2 per 108 nucleotides, respectively, whereas the sham operation groups had values of 5.8 ± 2.3 and 5.9 ± 0.5 per 108 nucleotides. Moreover, adduct spots corresponding to 3-ESA-dC were detected in both duodenal reflux and sham operation groups and levels in the duodenal reflux groups were around four-fold elevated at 11.2 ± 1.0 and 8.9 ± 1.0 per 108 nucleotides after 4 and 8 weeks, respectively. When the duodenal reflux animals were treated with a nitrite trapping agent, thiazolidine- 4-carboxylic acid (thioproline, TPRO), the levels of O6-CM-dG and 3-ESA-dC were reduced to the same levels as in the sham operation animals. These observations suggest that NO-TCA and NO-GCA are formed by nitrosation of glycocholic acid and taurocholic acid, respectively, and these nitroso compounds produce DNA adducts in the glandular stomach of rats subjected to duodenal content reflux surgery. (Cancer Sci 2008; 99: 1741–1746)