The Effectiveness of Glutathione Redox Status as a Possible Tumor Marker in Colorectal Cancer

Abstract

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.

Keywords: GSH; GSSG; GSSG/GSH redox state; colorectal cancer; oxidative stress; tumor markers.

Figure 1

Tumor markers of controls and colorectal cancer (CRC) patients. (a) CEA and (b) CA 19.9. * p-value adjusted by age and body mass index (* p < 0.05; ** p < 0.01); Data are expressed as the mean ± standard error of the mean. CEA: carcinoembryonic antigen (normal value: <5 ng/mL); CA 19.9: carbohydrate antigen 19.9 (normal value: <37 U/mL).

Figure 2

Levels of serum reduced glutathione (a), oxidized glutathione (b), and percentage ratio GSSG/GSH (c) in controls and CRC patients. p-value adjusted by age and body mass index (*** p < 0.001). GSH: reduced glutathione; GSSG: oxidized glutathione. Data are expressed as box and whiskers.

Figure 3

Reduced (a) and oxidized (b) glutathione levels and GSSG/GSH% ratio (c) grouped by tumor stages. Data are expressed as box and whiskers (stage 0, n = 44; stage 1, n = 26: stage 2, n = 9). Values with different superscript letters (a, b) were significantly different when the 3 groups were compared by one-way ANOVA followed by a Student–Newman-Keuls post hoc test. GSH: reduced glutathione; GSSG: oxidized glutathione.

Figure 4

Time course evolution of serum glutathione levels after treatment of colorectal cancer (CRC) patients and controls. (a) Reduced glutathione (GSH); (b) oxidized glutathione (GSSG); (c) GSSG/GSH ratio. Data are expressed as box and whiskers. Values with different superscript letters (a–d) were significantly different when the evolutionary times of the CRC group were compared by repeated measures one-way ANOVA followed by a Student–Newman–Keuls post hoc test. * p < 0.05; ** p < 0.01 when control and CRC groups were compared with an unpaired Student’s t test.

Figure 5

Receiver operating characteristic (ROC) curves for the analyzed markers. (A) Reduced glutathione (GSH); (B): CEA, CA 19.9, oxidized glutathione (GSSG), and the GSSG/GSH ratio.