Status of antioxidant enzyme: glutathione peroxidase and total polyphenol level in plasma of Tunisian patients suffering from colorectal and gastric cancer: interaction with clinical outcome.

In our case-control study, we measure the antioxidant status by dosing enzymes involved in oxidant stress in plasma of patients with colorectal and gastric cancer, and in the second step, we investigate the impact of chemotherapy before and after surgery on plasma antioxidant status and polyphenols in patients. Blood serum was collected from patients with stomach and colorectal cancer before conventional treatment, and glutathione peroxidase (GSHPX) enzyme activities and total polyphenols were determined by spectrophotometric methods. In our study, we found a significant decrease in glutathione peroxidase activity in plasma of patients compared with controls (P = 0.