Vascular Effects of the Human Extracellular Superoxide Dismutase R213G Variant

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Abstract
Background— Extracellular superoxide dismutase (ECSOD) is a major extracellular antioxidant enzyme. We have demonstrated that vascular effects of ECSOD require an intact heparin-binding domain. A common genetic variant with a substitution in the heparin-binding domain (ECSOD R213G ) was reported recently to be associated with ischemic heart disease. The goal of this study was to examine vascular effects of ECSOD R213G . Methods and Results— A recombinant adenovirus (Ad) that expresses ECSOD R213G was constructed. ECSOD R213G and ECSOD proteins bound to collagen type I in vitro, but binding to aorta ex vivo was 10-fold greater with ECSOD than ECSOD R213G . Three days after intravenous injection of AdECSOD R213G or AdECSOD in spontaneously hypertensive rats (SHR), immunostaining demonstrated binding of ECSOD to carotid arteries and kidneys but minimal binding of ECSOD R213G . Binding to aorta and carotid artery was 2.5- to 3-fold greater with ECSOD than ECSOD R213G by immunoblotting. Arterial pressure was significantly reduced by AdECSOD but not by AdECSOD R213G . Responses to acetylcholine and basal levels of nitric oxide in carotid arteries were impaired in SHR compared with normotensive Wistar-Kyoto rats and were improved after AdECSOD but not AdECSOD R213G . Levels of superoxide and nitrotyrosine in aorta were higher in SHR than Wistar-Kyoto rats and were greatly reduced after AdECSOD but not AdECSOD R213G . Conclusions— In contrast to ECSOD, ECSOD R213G has no significant protective effect on arterial pressure, vascular function, or vascular levels of oxidative stress in SHR. These findings may provide a mechanistic basis for association studies that suggest that human beings carrying ECSOD R213G are predisposed to vascular diseases.