RESUMO
BACKGROUND & AIMS: Increased homocysteine concentration and oxidative stress and decreased antioxidant capacities are thought to affect carcinogenesis. However, the associations of homocysteine, cysteine, pyridoxal 5'-phosphate (PLP) and folate with oxidative stress and antioxidant capacities in patients with colorectal cancer are unclear. The purpose of this study was to determine the associations of homocysteine, cysteine, PLP and folate with oxidative stress indicators and antioxidant capacities, and to further analyze their relationships with respect to risk for colorectal cancer. METHODS: One hundred and sixty-eight subjects with colorectal cancer (cases) and 188 healthy subjects (controls) were recruited. RESULTS: There were no significant associations of homocysteine, cysteine and folate with oxidative stress indicators and antioxidant capacities in cases; however, PLP positively correlated with glutathione S-transferase activities after adjusting for potential confounders in cases. Subjects with higher plasma homocysteine concentration exhibited significantly increased risk of colorectal cancer with or without adjustment for potential confounders. The associations of cysteine, PLP and folate with the risk of colorectal cancer were not observed when potential confounders were adjusted. CONCLUSIONS: Increased homocysteine was strongly associated with the risk of colorectal cancer independently of oxidative stress indicators and antioxidant capacities. However, cysteine, PLP and folate were not found to be related to oxidative stress, antioxidant capacities and the risk of colorectal cancer.