Vascular bound recombinant extracellular superoxide dismutase type C protects against the detrimental effects of superoxide radicals on endothelium-dependent arterial relaxation.

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Abstract
Extracellular superoxide dismutase type C (EC-SOD C) is a secretory SOD isoenzyme that, in vivo, is bound to heparan sulfate proteoglycans in the glycocalyx of various cell types (e.g., endothelial cells) and in the connective tissue matrix. The aim of this study was to investigate the efficacy of vascular bound EC-SOD C in protecting arterial relaxation mediated by endothelium-derived relaxing factor (EDRF) against the inhibitory effects of superoxide radicals. For comparison, the effect of CuZn SOD was also studied. This SOD isoenzyme lacks affinity toward heparan sulfate and does not bind to cell surfaces. Rings from rabbit aorta were mounted in an organ bath and acetylcholine-induced endothelium-dependent relaxation was then studied in preparations precontracted with phenylephrine. Pyrogallol (10(-4) M), used to generate superoxide radicals, reduced the maximal relaxant effect of acetylcholine from about 65% to 25%. When present in the buffer throughout the experiment, CuZn SOD and EC-SOD C caused a concentration-dependent prevention of the pyrogallol effect on EDRF-mediated relaxation, with a half-maximal effect at about 100 units/ml (KO2 assay). In a second set of experiments, the arterial rings were preincubated with 8,000 units/ml CuZn SOD (50 micrograms/ml) or EC-SOD C (69 micrograms/ml) during 30 minutes, followed by washing, before the effect of pyrogallol on EDRF-mediated relaxation was studied in SOD-free buffer.(ABSTRACT TRUNCATED AT 250 WORDS)