Peroxidase Properties of Extracellular Superoxide Dismutase

Abstract

Objective-The cytosolic form of Cu/Zn-containing superoxide dismutase (SOD1) has peroxidase activity, with H 2 O 2 used as a substrate to oxidize other molecules. We examined peroxidase properties of the extracellular form of SOD (SOD3), a major isoform of SOD in the vessel wall, by using recombinant SOD3 and an in vivo model of atherosclerosis. Methods and Results-In the presence of HCO 3 Ϫ , SOD3 reacted with H 2 O 2 to produce a hydroxyl radical adduct of the spin trap 5-diethoxyphosphoryl-5methyl-1-pyrroline N-oxide (DEMPO). SOD1 and SOD3 were inactivated by H 2 O 2 in a dose-and time-dependent fashion, and this was prevented by physiological levels of uric acid. To examine the in vivo role of uric acid on SOD1 and SOD3, control and apolipoprotein E-deficient (ApoE Ϫ/Ϫ ) mice were treated with oxonic acid, which inhibits urate metabolism. This treatment increased plasma levels of uric acid in control and ApoE Ϫ/Ϫ mice by Ϸ3-fold. Although increasing uric acid levels did not alter aortic SOD1 and SOD3 protein expression, aortic SOD1 and SOD3 activities were increased by 2-to 3-fold in aortas from ApoE Ϫ/Ϫ mice but not in aortas from control mice. Conclusions-These studies show that SOD1 and SOD3 are partially inactivated in atherosclerotic vessels of ApoE See page 1367Extracellular SOD (SOD3) is also a Cu/Zu-containing SOD that shares Ϸ50% sequence homology with SOD1 within its catalytic region. 7 Compared with the x-ray crystallography structure data for SOD1, 8 all ligands to the copper and zinc atoms can be identified in SOD3, as can the cysteines forming the intramolecular disulfide bond. 7 Thus, these findings suggest that the conformation of the active copper-binding site of SOD3 may resemble the active site of SOD1. The rate constants for dismutation of O 2 ⅐Ϫ by SOD1 and SOD3 are similar, and both enzymes are inhibited by cyanide, azide, and diethyldithiocarbamate. 9 Because SOD3 constitutes 30% to 50% of the total SOD in vascular tissues 10 and is localized in the extracellular space, it would be of considerable importance to determine whether SOD3 also has peroxidase activity and to determine which small molecule reductants can preserve its dismutase activity.Although peroxidase properties of SOD1 have been studied extensively in vitro, evidence is lacking to prove that either SOD1 or SOD3 activities are affected by H 2 O 2 in vivo. In the present study, we sought to determine whether SOD3 has peroxidase activities that are similar to those of SOD1 and to examine small molecules that might prevent the inactivation of SOD3 by using recombinant SOD3 expressed in Pichia pastoris. In these experiments, we found that physiological levels of uric acid completely prevented the inactivation of SOD1 and SOD3 by H 2 O 2 . In additional experiments, we provide evidence for peroxidase activity of SOD1 and SOD3 in vivo, by showing that these enzymes seem to be partially inactivated in the aortas of apolipoprotein E-deficient (ApoE Ϫ/Ϫ ) mice and that the activity of these

Sex-dependent changes in the pulmonary vasoconstriction potential of newborn rats following short-term oxygen exposure

“…This finding, in conjunction with the hyperoxia-induced increase in lung H 2 O 2 observed solely in females, strongly suggests that the reduced thromboxanemediated force development in the pulmonary arteries reflects dismutation of the excess superoxide by SOD. Despite the published evidence that H 2 O 2 can inactivate SOD3 (27), our data on hyperoxia-exposed female pups suggest otherwise. This apparent discrepancy might be related to the fact that although the lung H 2 O 2 content was increased, the levels measured in the present experiments are significantly lower than those required for SOD inactivation, as previously reported (27).…”

“…Despite the published evidence that H 2 O 2 can inactivate SOD3 (27), our data on hyperoxia-exposed female pups suggest otherwise. This apparent discrepancy might be related to the fact that although the lung H 2 O 2 content was increased, the levels measured in the present experiments are significantly lower than those required for SOD inactivation, as previously reported (27).…”

Everything we always wanted to know about furosemide but were afraid to ask

“…This finding could indicate compensation of the oxidative stress caused by CVD and CKD (111). The antioxidant activity of uric acid could be mediated by increasing the activity of SOD1 and SOD3 (62). Others have suggested that uric acid only functions as an antioxidant in the extracellular space, and indeed a reciprocal relationship has been demonstrated between uric acid and NO level in serum (79).…”

Redox Control of Renal Function and Hypertension

“…(eNOS) uncoupling and endothelial dysfunction (121,145). Although elevated levels of uric acid may confer protective antioxidant effects on the vasculature and the kidneys, the correlation with cardiovascular disease risk is not readily apparent (145).…”