The role of oxidative stress (OS) in cancer is a matter of great interest due to the implication of reactive oxygen species (ROS) and their oxidation products in the initiation of tumorigenesis, its progression, and metastatic dissemination. Great efforts have been made to identify the mechanisms of ROS-induced carcinogenesis; however, the validation of OS byproducts as potential tumor markers (TMs) remains to be established. This interventional study included a total of 80 colorectal cancer (CRC) patients and 60 controls. By measuring reduced glutathione (GSH), its oxidized form (GSSG), and the glutathione redox state in terms of the GSSG/GSH ratio in the serum of CRC patients, we identified significant changes as compared to healthy subjects. These findings are compatible with the effectiveness of glutathione as a TM. The thiol redox state showed a significant increase towards oxidation in the CRC group and correlated significantly with both the tumor state and the clinical evolution. The sensitivity and specificity of serum glutathione levels are far above those of the classical TMs CEA and CA19.9. We conclude that the GSSG/GSH ratio is a simple assay which could be validated as a novel clinical TM for the diagnosis and monitoring of CRC.

Oxidative stress (OS) and inflammation are known to play an important role in chronic diseases, including cancer, and specifically colorectal cancer (CRC). The main objective of this study was to explore the diagnostic potential of OS markers in patients with CRC, which may translate into an early diagnosis of the disease. To do this, we compared results with those in a group of healthy controls and assessed whether there were significant differences. In addition, we explored possible correlations with the presence of tumors and tumor stage, with anemia and with inflammatory markers used in clinical practice. The study included 80 patients with CRC and 60 healthy controls. The following OS markers were analyzed: catalase (CAT), reduced glutathione (GSH) and oxidized glutathione (GSSG) in serum; and 8-oxo-7,8-dihydro-2′-deoxyguanosine (8-oxodG) and F2-isoprotanes in urine (F2-IsoPs). Tumor markers (CEA and CA 19.9), anemia markers (hemoglobin, hematocrit and medium corpuscular volume) and inflammatory markers (leukocytes, neutrophils, N/L index, platelets, fibrinogen, C-reactive protein, CRP and IL-6) were also determined. Comparison of means between patients and controls revealed highly significant differences for all OS markers, with an increase in the prooxidant markers GSSG, GSSG/GSH ratio, 8-oxodG and F2-IsoPs, and a decrease in the antioxidant markers CAT and GSH. Tumor and inflammatory markers (except CRP) correlated positively with GSSG, GSSG/GSH ratio, 8-oxodG and F2-IsoPs, and negatively with CAT and GSH. In view of the results obtained, OS markers may constitute a useful tool for the early diagnosis of CRC patients.

Oxidative stress (OS) and inflammation have been related to colorectal cancer (CRC), but the influence of the Mediterranean diet (MD) on these parameters is unknown. Therefore, the aim of this study was to determine the association between adherence to the MD and markers of OS and DNA damage in CRC patients and to study the influence of adherence to the MD on metabolic and tumor-related factors. This prospective observational study included a total of 80 patients diagnosed with CRC. Adherence to the MD was estimated by the 14-item Mediterranean Diet Adherence Screener (MEDAS) questionnaire. The levels of OS markers (catalase, glutathione peroxidase, and glutathione system in serum; 8-oxo-7′8-dihydro-2′-deoxyguanosine and F2-isoprotanes in urine) and tumor and metabolic factors were determined. A total of 51.2% of our CRC patients showed a high adherence to the MD. These patients presented decreased levels of 8-oxodG, increased GPX and HDL–cholesterol levels, and a downward trend in the GSSG/GSH ratio with respect to patients with low adherence to the MD. In addition, a high adherence to the MD was associated with a lower histological grade of the tumor and a lower presence of synchronous adenomas. We conclude that a high adherence to the MD has a protective role against metabolic and oxidative DNA damage and improves antioxidant systems in CRC patients.