Total lipid peroxidation and antioxidant activity were studied in pulmonary and mediastinal malignant and benign neoplasms. In malignant tumors total lipid peroxidation increased and antioxidant activity decreased; the intensity of these shifts depended on histological characteristics and degree of malignancy: the most pronounced changes were observed in thymoma and adenocarcinoma tissues and minimum changes were found in bronchoalveolar carcinoma tissue.

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In vitro effects of folic acid (10(-5), 10(-4), and 10(-3)M) on activities of gamma-glutamyltransferase and glutathione reductase, the enzymes involved in glutathione metabolism, were studied in tissue samples obtained after surgical treatment of the lungs and thymus. Folic acid did not change gamma-glutamyltransferase activity in lung cancer tissue, but in thymoma tissue this substance in a concentration of 10(-3)M inhibited it by 16%. Folic acid had no effects on glutathione reductase activity in benign tumors and normal lung and thymus tissues, but increased this activity in thymoma and lung cancer tissues. Activation of glutathione reductase was probably related to binding of folic acid in the allosteric center of the enzyme, which probably induced conformational changes in the catalytic center, acceleration of electron transport from NADPH(2) to oxidized glutathione via flavin adenine nucleotide, and intense production of reduced glutathione.