Variations in systemic biomarkers of oxidative/nitrosative stress and DNA damage before and during the consequent two cycles of chemotherapy in breast cancer patients

Background: Previous studies have suggested the importance of redox regulation in carcinogenesis. The aim of this study was to evaluate the prognostic role of altered redox homeostasis and oxidative DNA damage in patients with breast carcinoma before and during two cycles of chemotherapy. Methods: This study included 30 patients whose serum samples were obtained on admission before treatment, and after the first and second cycles of chemotherapy, and 20 controls. We investigated serum total antioxidant status (TAS), thiobarbituric acid reacting substances (TBARS), total nitrite/nitrate (NOx), nitrotyrosine (NT), and 8-hydroxydeoxyguanosine (8-OHdG), as well as antioxidant enzyme activities, such as glutathione peroxidase (GPx), glutathione reductase (GRx). Results: TBARS, NOx, NT and 8-OHdG concentrations were significantly increased, while antioxidant enzyme activities and TAS were significantly decreased in patients when compared to controls. A concurrent increase in TBARS, NOx, NT, and 8-OHdG and a decrease in antioxidant enzyme activities and TAS were also seen after chemotherapy. No difference was observed in the second cycle of chemotherapy when compared with the first course. Conclusions: In conclusion, decreased activities of these antioxidant enzymes and low TAS concentrations observed in our study might be due to the depletion of the antioxidant defense system to combat the free radical storm produced by chemotherapy. We suggest that the increased 8-OHdG and other oxidative/nitrosative stress products that we have measured in breast cancer patients may be prognostic risk factors for the magnitude of oxidation in serum. Clin Chem Lab Med 2010;48:1487-95.