Basal level of DNA single strand breaks and oxidative damage in freshly isolated nuclei from colon mucosa in a rat genetic model of colon carcinogenesis

Apc-mutated Pirc rats are a model of colon carcinogenesis as they spontaneously develop large and small intestinal tumors. The Apc gene is mutated in Familial Adenomatous Polyposis and in the majority of sporadic colon cancers. There are evidences that Pirc rats have a reduced ability to counteract the damaging effects of oxidant xenobiotics, which could contribute to spontaneous carcinogenesis (Femia et al., 2016). The purpose of this study was to verify whether the basal level of DNA damage in the colon mucosa of Pirc and wild-type rats are different. Nuclei were obtained from medial and proximal scraped colon mucosa by homogenization (Luceri et al., 2008), and run through the basic and oxidation-sensitive (fpg) comet assay. The results show no significant difference between Pirc and wild-type animals in the mean level of single strand breaks and fpg sites in either proximal or medial colon mucosa. However, analyzing the results by classes of damage, the frequency of class 4 nuclei (the most damaged) resulted to be significantly higher in Pirc mucosa. In the proximal mucosa, the effect was significant for SSBs only, whereas in medial mucosa it resulted to be significant for the sum of SSBs and fpg sites. These data indicate that a subset of cells in the colon mucosa of Pirc rats show excessive levels of DNA damage compared to the wild-type counterpart: further studies will define the relevance of this subset for colon carcinogenesis in Apc-mutated mucosa.