Enhanced Nitric Oxide Inactivation and Protein Nitration by Reactive Oxygen Species in Renal Insufficiency

Abstract

Abstract-Chronic renal failure (CRF) is associated with oxidative stress which promotes production of reactive carbonyl compounds and lipoperoxides leading to the accumulation of advanced glycation and lipoxidation end products. Reactive oxygen species (ROS) avidly reacts with nitric oxide (NO) producing cytotoxic reactive nitrogen species capable of nitrating proteins and damaging other molecules. This study tested the hypothesis that CRF results in enhanced ROS-mediated NO inactivation and protein nitration which can be ameliorated with antioxidant therapy. Male Sprague Dawley rats were randomized to CRF (5/6 nephrectomy) and sham-operated controls and fed either a regular diet (vitamin E, 40 U/Kg food) or an antioxidant-fortified diet (vitamin E, 5000 U/Kg food) for 6 weeks. Blood pressure, plasma malondialdehyde (MDA), tissue NO synthase (NOS) isoforms, tissue nitrotyrosine (the footprint of NO interaction with ROS), and vascular tissue NO production were determined. CRF resulted in marked elevations of blood pressure, plasma MDA, and tissue nitrotyrosine abundance, but did not change plasma L-arginine level. This was coupled with depressed vascular tissue NO production and reduced immunodetectable NOS proteins in the vascular, renal, and cardiac tissues. Antioxidant therapy ameliorated the CRF-induced hypertension, improved vascular tissue NO production, lowered tissue nitrotyrosine burden, and reversed downregulations of NOS isoforms. In contrast, antioxidant therapy had no effects in the controls. CRF is associated with oxidative stress which promotes NO inactivation by ROS leading to functional NO deficiency, hypertension, and widespread accumulation of protein nitration products. Amelioration of oxidative stress by high-dose vitamin E enhances NO availability, improves hypertension, lowers protein nitration products, and increases NOS expression and vascular NO production in CRF animals. Key Words: uremia Ⅲ nitric oxide synthase Ⅲ hypertension, renal Ⅲ oxidative stress Ⅲ oxygen O xidative stress occurs when generation of the reactive oxygen species (ROS) exceeds the natural antioxidant capacity of the organism. In the presence of oxidative stress, uncontained ROS attack, denature, or modify lipids, proteins, carbohydrates, DNA, and other molecules. Oxidative stress is a known feature of chronic renal failure (CRF), and its presence is evidenced by the reported elevation of lipid peroxidation product, malondialdehyde, depressed antioxidant capacity, and impaired antioxidant enzyme activities in the plasma and erythrocytes of CRF patients and animals. [1][2][3][4][5][6][7] Increased ROS activity results in the nonenzymatic production of reactive carbonyl compounds and lipoperoxides which, in turn, react with and modify structural and functional proteins leading to formation of advanced glycation end products (AGE) and advanced lipoxidation end products (ALE). 8,9 Accumulation of these products is thought to contribute to the cardiovascular and other complications of CRF. The present study extends the prev...

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