Attenuation of DNA base oxidation in post-surgery colorectal stage III patients at subsequent follow-ups

DNA damage caused by oxidative reactions plays a crucial role in the pathogenesis of colorectal cancer (CRC). In a previous cross-sectional study, CRC patients diagnosed with regional disease (stage III) exhibited a higher level of DNA base oxidation in peripheral blood mononuclear cells (PBMCs) 2-9 months post-surgery compared to those with localized disease (stage I-II). To further explore this observation over time, the present study aimed to investigate DNA base oxidation in CRC patients with localized versus regional disease 6 and 12 months after the initial measurements. The present study included patients enrolled in the randomized controlled trial Norwegian Dietary Guidelines and Colorectal Cancer Survival (CRC-NORDIET). The standard comet assay, modified with the lesion-specific enzyme formamidopyrimidine DNA glycosylase (Fpg), was applied to measure DNA base oxidation in PBMCs at the 6- and 12-month follow-ups. Of the 255 patients assessed at baseline, 156 were included at the 6-month follow-up, with 89 of these patients included in the 12-month follow-up. In contrast to our observation at baseline, there were no significant differences in the levels of DNA base oxidation between patients diagnosed with localized disease and those with regional involvement at the 6- and 12-month follow-up visits (P = 0.81 and P = 0.09, respectively). Patients with stage III disease exhibited a significant decrease in the levels of DNA base oxidation from baseline to 6 months (P < 0.01) and baseline to 12 months (P = 0.03), but no significant difference from 6 to 12 months (P = 0.80). In conclusion, the initially elevated levels of DNA base oxidation in PBMCs, observed 2-9 months post-surgery in patients diagnosed with regional disease (stage III), subsequently decreased to levels comparable to patients with localized disease (stage I-II) at the 6- and 12-month follow-ups.