The association of plasma homocysteine and cysteine with antioxidant enzyme activities in patients with colorectal polyps and colorectal cancer

Abstract

Colorectal polyps are considered to be precursors of colorectal cancer, especially of adenomatous polyps. Cysteine is synthesized by the transsulfuration pathway of homocysteine, and further contributed to glutathione. Although increased homocysteine has been shown to be associated with the development of colorectal polyps and carcinogenesis, the role of cysteine is not cleared. The purpose of this study was to investigate the association of plasma homocysteine and cysteine with glutathione‐dependent antioxidant enzymes [i.e., glutathione peroxidase (GPx) and glutathione S‐transferase (GST)] in patients with colorectal polyps or colorectal cancer. 70 subjects with adenomatous polyps, 40 subjects with hyperplastic polyps and 168 patients with colorectal cancer were recruited. Fasting plasma homocysteine and cysteine concentrations in patients with colorectal cancer were significantly higher than subjects with adenomatous and hyperplastic polyps. There was no significant association of homocysteine with GPx and GST activities in all subjects. However, cysteine significantly correlated with GPx and GST after adjusting for age, gender, serum creatinine and smoking in subjects with adenomatous and hyperplastic polyps. Higher cysteine rather than homocysteine is an important contributing factor in the elevation of GPx and GST activities in subjects with colorectal polyps.