CAT and chronic obstructive pulmonary disease: The expression and activity of antioxidant enzymes such as Manganese Superoxide Dismutase (MnSOD), Catalase (Cat), and Glutathione-S-Transferase (GST) have been found deranged during COPD [21, 22], and a positive correlation between the deficiency of antioxidant status and the severity of COPD exacerbations was reported [23].