CAT and Alzheimer disease: Other classical markers of oxidative stress in plasma of early stage AD patients include thiobarbituric acid reactive substances (TBARS) as an index of lipid peroxidation, protein carbonyl content as an index of protein oxidation, the enzymatic activities of GPx, catalase (CAT), and superoxide dismutase (SOD) as well as the plasma levels of total glutathione (reduced GSH plus oxidized glutathione (GSSG) [122].