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 = 0.02), although we did not find a significant association between total
polyphenols and 2,2'-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) or
ABTS in plasma of colorectal and
stomach cancer compared with control; furthermore, we observed no significant difference in the average plasma
polyphenols in patients treated with
chemotherapy before and after surgery. We have shown the decrease in GSHPX activity in plasma of cases with colorectal and
gastric cancer, and this decrease reflects that the oxidative stress is associated with
tumor tract and related to oxidative metabolism; however, no association was found between total
polyphenols and
ABTS in our study.