Polyethylene glycol-conjugated superoxide dismutase fails to augment brain superoxide dismutase activity in piglets

We studied the effect of intravenously administered polyethylene glycol-conjugated superoxide dismutase (8,000 units/kg) on brain su peroxide dismutase activity in 441-2-week-old piglets in the absence and presence of global cerebral ischemia and reperfusion. Four groups (n=6 each) of piglets not exposed to ischemia were studied. Enzyme administration increased plasma superoxide dismutase activity from <5 to 142±8 units/ml (mean±SEM) without increasing brain activity (e.g., activities in the caudate were 7.9±0.5 and 8.1 ±0.4 units/mg protein) for up to 2 hours following administration. Four additional groups (n=5 each) of piglets were given either enzyme or polyethylene glycol 5 minutes prior to 10 minutes of global cerebral ischemia induced by aortic cross-clamping followed by either 5 or 45 minutes of reperfusion. Enzyme administration increased plasma superoxide dismutase activity from <5 to 144±5 units/ml but failed to increase brain activity even after 45 minutes of reperfusion (e.g., activities in the caudate were 8.5±03 and 8.6±0.6 units/mg protein). We conclude that intravenous polyethylene glycol-conjugated superoxide dismutase does not increase superoxide dismutase activity in the brain despite global ischemia and reperfusion.