DYNAMICS OF ANTIOXIDANT ENZYME ACTIVITY IN THE THYMUS OF WHITE RATS DURING INDUCED CARCINOGENESIS

Abstract

Introduction. Oncological diseases remain one of the leading causes of mortality worldwide. Oxidative stress is one of the key factors in the initiation and progression of the neoplastic process. The thymus, as the central organ of T-lymphopoiesis, is susceptible to alterations in oxidative status, and investigating antioxidant enzyme activity in this organ as an indicator of the systemic response to tumor development is of considerable relevance. The Aim of the Study to determine the changes in SOD and CAT activity in the thymus of intact white rats and in animals with an N,N-dimethylhydrazine-induced carcinogenesis model. Research Methods. The study was performed on 98 white male outbred rats. The animals were divided into groups: I – intact animals; II – animals in which colorectal cancer was induced by injections of N,N‑dimethylhydrazine hydrochloride. The induction period lasted 210 days, and the animals were euthanized every 30 days to monitor the dynamics of changes (7 study time points). The activity of superoxide dismutase in thymus homogenates was assessed by the ability of the enzyme to inhibit the reduction of nitroblue tetrazolium. Catalase activity was evaluated spectrophotometrically based on the capacity of hydrogen peroxide to decompose into water and oxygen and to form a stable yellow complex with ammonium molybdate. Statistical analysis of the obtained results was performed using an independent two-sample two-tailed Student’s t-test and one-way analysis of variance (ANOVA) followed by Tukey’s post-hoc test. Results and Discussion. In thymus homogenates from intact rats, a gradual decrease in SOD and CAT activity was observed, which mostly did not reach statistical significance between consecutive time points. Still, it showed a significant reduction relative to baseline at later stages of the experiment. Under N, N-dimethylhydrazine-induced carcinogenesis, early adaptive fluctuations in superoxide dismutase activity were observed, followed by progressive suppression, reaching 43,55 % on day 210. Catalase showed greater sensitivity to the carcinogen: a significant decrease in its activity was observed as early as day 120, with a maximum suppression of 39,79 % at the final stage of the experiment. Conclusions. The development of the neoplastic process is accompanied by a profound imbalance in the enzymatic component of the thymic antioxidant system, manifested by depletion of SOD and, particularly, CAT, which may exacerbate oxidative stress and impair the thymus’s immunoregulatory function during progressive carcinogenesis.