Superoxide dismutase level in human erythrocytes and its clinical application to the patients with cancers and thyroidal dysfunctions.

The activity, content and true specific activity of superoxide dismutase (SOD) were determined for human erythrocytes of 105 normal healthy subjects. At the same time the activities of erythrocyte SOD are also determined in patients with lung cancer, lymphoma, leukemia and thyroidal dysfunctions. The mean SOD activity of healthy subjects assayed by the method of inhibition of xanthine autoxidation was 11.0 X 10(3) units/g of hemoglobin (Hb). The mean SOD content of healthy subjects assayed by an immunodiffusion method was 456 micrograms/g of Hb. Both the activity and the content of SOD showed normal distributions, while no significant variations in regard to sex and age were detected. A high positive correlation between the activity and the content of SOD was observed in normal healthy subjects (r = 0.77, p less than 0.001). True specific activity was calculated from the levels of activity and content of SOD. The mean true specific activity of SOD in human erythrocytes was 23.7 units/micrograms of SOD. There was no significant difference in true specific activity among age groups. The activity of erythrocyte SOD was determined in 38 patients with lung cancer (n = 15), malignant lymphoma (n = 11) and acute myeloid leukemia (n = 12). Patients with malignant lymphoma and acute myeloid leukemia showed a significant decrease in enzyme activity (p less than 0.01) while the patients with lung cancer (9 squamous cell carcinomas and 6 small cell carcinomas) showed a normal value of SOD activity. Furthermore, patients with malignant lymphoma and acute myeloid leukemia who were in remission and were not being treated with anticancer drugs also showed a significant decrease in SOD activity. These observations therefore indicate that a low level of erythrocyte SOD activity is related to cancer and that degree of the activities varies with the type of cancer. A total of 18 determinations of erythrocyte SOD activity were made on 16 patients with thyroidal dysfunction. Patients with hyperthyroidism showed a significant increase in SOD activity (p less than 0.01), while patients with hypothyroidism showed the same SOD activity as those of healthy subjects. A significantly high positive correlation was found between erythrocyte SOD activity and the level of thyroxine in serum (r = 0.60, p less than 0.01). The author suggests therefore that erythrocyte SOD activity has a close relationship to the state of the thyroid hormones.