The activity of the peroxide-metabolizing system in human colon carcinoma.

The major parameters of the peroxide-metabolizing system were investigated in eight human colon carcinoma excisions and compared with apparently non-neoplastic colon tissue from the same patients. The mean malondialdehyde level as an index of lipid peroxidation was 147 pmol/mg protein in carcinoma compared to 40 pmol/mg in healthy tissue. The following relations of specific activities in carcinoma and healthy tissue were found: superoxide dismutase 3.9 micrograms/mg protein (carcinoma): 2.4 micrograms/mg (healthy), glutathione peroxidase 23 mU/mg:10 mU/mg; GSH-transferase 38 mU/mg:25 mU/mg; catalase 2.3 mK/mg:4.1 mK/mg. The mean selenium concentration in carcinoma was 36 ng/mg protein compared to 24 ng/mg. The difference between carcinoma and normal tissue showed an overall-significance of p < 0.002 for the whole set of data. No significant differences were found in GSH levels (12.6 nmol/mg protein in carcinoma: 9.4 nmol/mg in normal colon), GSSG levels (0.6 nmol/mg:0.7 nmol/mg) and in the protein content (70 +/- 23.5 mg/g wet tissue: 66 +/- 20 mg/g). It is concluded that the enhanced lipid peroxidation in tumor tissue may be due to peroxisomally generated H2O2 in conjunction with a lowered catalase activity.