Superoxide dismutase, catalase and glutathione peroxidase in SHR kidney: effect of antioxidant-rich diet

Background and objective Earlier studies have shown increased production of reactive oxygen species (ROS) and upregulation of ROS-generating enzyme, nicotinamide adenine dinucleotide (phosphate) oxidase, in the kidney of spontaneously hypertensive rats (SHR). This study aimed to examine the activities and protein abundance of the main antioxidant enzymes [i.e. superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPX)] in the kidney of SHR fed a regular or an antioxidant-rich diet. Methods Pregnant SHR and their offspring were fed either a regular diet or an antioxidant-rich diet (alpha-tocopherol, ascorbic acid, zinc and selenium) and observed for 6 months. Wistar-Kyoto (WKY) rats fed a regular or antioxidant-fortified diet served as controls. Results The untreated SHR showed severe hypertension and significant increases in plasma hydrogen peroxide and renal tissue nitrotyrosine abundance, indicating the presence of oxidative/nitrosative stress. Despite oxidative stress, Cu Zn SOD, CAT and GPX activities were unchanged in the cortex and medulla of untreated SHR. Immunodetectable Mn SOD was reduced in the medulla and elevated in the cortex, whereas, Cu Zn SOD protein was unchanged in the cortex and reduced in the medulla. By contrast CAT protein abundance was increased in both cortex and medulla while GPX protein was elevated in the cortex and unchanged in the medulla. Comparison of protein abundance and activities of the antioxidant enzymes revealed significant discordance in the untreated SHR. Lifelong antioxidant therapy diminished the severity of hypertension, improved oxidative stress and ameliorated or reversed abnormalities of antioxidant enzyme expressions and activities. By contrast, antioxidant therapy had no effect on the measured parameters in the WKY rat controls. Conclusions Oxidative stress in SHR was associated with a lack of coordinate upregulation of the antioxidant enzymes and discordance between their protein abundance and enzymatic activity. These findings suggest an impaired antioxidant defense system and the presence of functionally abnormal enzymes in the SHR kidney. Lifelong antioxidant therapy improved expression, activity and activity-to-mass relationship of the measured enzymes. The latter suggests oxidative and nitrosative modification of these molecules in the SHR kidney.