CAT and cancer: In tumortissues, ROS accumulation is higher compared to healthycells, partly due to reduced activity of antioxidant defense systems. Enzymes such as catalase, glutathione peroxidases,and peroxiredoxins, which normally detoxify H2O2, are less active in cancer cells. Similarly, Leishmania species possess antioxidant defense mechanisms,but their system differs significantly from that of mammals.