| Summary: | 碩士 === 中山醫學大學 === 營養學研究所 === 101 === High homocysteine plays an important role in the progression of colorectal cancer. However the association of transsulfuration of homocysteine metabolism with related nutrients, antioxidant enzyme activities and the risk of colorectal cancer are unclear. During the transsulfuration, homocysteine is irreversibly sulfoconjugated to serine conversion to cystathionine and then cysteine by the pyridoxal 5’-phosphat (PLP) dependent enzymes. Cysteine is an important contributor to glutathione synthesis, which is a key buffer of glutathione S-transferase (GST) and glutathione peroxidase (GPx). There two enzymes involve a fundamental role in protecting the cell from oxidative damage and cellular detoxification. The purpose of this case-control study was to examine the effects of homocysteine, cysteine and vitamin B-6 status on oxidative stress, antioxidant capacities and the risk of developing colorectal cancer. One hundred and sixty-eight patients with colorectal cancer (cases), and 188 healthy participants (controls) were recreated from Taichung Veterans General Hospital, Taichung, Taiwan. Fasting blood samples were drawn to measure homocysteine, cysteine, vitamin B-6 status (plasma PLP), oxidative stress indicators, antioxidant capacities, glutathione and glutathione - dependent enzyme activities patients with colorectal cancer had significantly higher levels of homocysteine, cysteine, glutathione and oxidized low-density lipoprotein (ox-LDL), but had significantly lower levels of GST and GPx when compared to healthy participants. There were no significant differences in plasma PLP and antioxidant capacities between patients with colorectal cancer and healthy participants. After adjusting for confounders, homocysteine and cysteine had no effects on oxidative stress indicators, total antioxidant capacity (TAC), glutathione and glutathione - dependent enzyme activities in patients with colorectal cancer. However, high PLP levels would increase GST activities in patients with colorectal cancer. Logistic regression analysis revealed that high homocysteine levels significantly increased the risk of colorectal cancer (OR,1.25, p<0.001). Homocysteine and cysteine did not affect oxidative stress and antioxidant capacities in patients with colorectal cancer; however, higher homocysteine is an independent contributing factor to increase the risk of colorectal cancer.
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