The free radical-mediated oxidations of biologic molecules, membranes, and tissues are now accepted to be related with cancer, aging and other variety of pathologic events. Natural de- fence mechanisms against oxygen free radical damage include superoxide dismutase(SOD) which converts superoxide to H,Ocatalase, and glutathion peraxidase which decomposes H202. Many studies have been made on the activities of antioxidant enzymes in tumor. To evaluate the relationship between GI cancer and antioxidant enzyme, we measured SOD and catalase in tissues from cancer patients. The following relations of specific activities in tissues from cancer and normal were found: catalase 60.31+- 8.05 U/mg protein to 60.84 +- 11.93 U/mg protein in stomach cancer patients, 67.52 +- 9.9l U/mg protein to 65.16+- 2.69 U/mg protein in rectal cancer patients(P > 0.05): Cutn SOD 1.53+-0.38 U/mg protein to 1.49+-0.49U/mg protein in stomach cancer patients 1.88+-0.09U/mg protein to 1.89+-0.20 U/mg protein in rectal cancer patients(P>0.05): Mn SOD 0.32 +- 0.10 U/mg protein to 0.50+-0.08 U/mg protein in stomach cancer patients 0.26+-0.05 U/mg protein to 0.36+ 0.05 U/mg protein to 0.36+-0.05 U/mg protein in rectal cancer patients(P<0.01). In Dot-blot, Cutn SOD mRNA densities were not changed in cancer tissues compaired with normal tissues, but, Mn SOD mRNA densities were decreased in cancer tissues compaired with normal tissues. In conclusion, decrease of Mn SOD activities results from decrease of Mn SOD mRNA in GI cancer patients.
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