Superoxide anion production during reperfusion is reduced by an antineutrophil antibody after prolonged cerebral ischemia

Neutrophils may be involved in the pathophysiology of reperfusion injury following cerebral ischemia. One potential mechanism of reperfusion injury by neutrophils is through production of the superoxide anion. We hypothesized that, due to progressive endothelial damage during ischemia, neutrophil activation would be more prominent after longer periods of ischemia prior to reperfusion. Thus, neutrophils would contribute more to pathological processes such as superoxide anion formation after longer than after shorter periods of ischemia. A reversible middle cerebral artery occlusion model in rats was employed and superoxide anion concentration was measured with a cytochrome c coated electrode placed on the cortical penumbral region. Occlusion times were varied from 60 min to 2 h, and neutrophils were inhibited with an antiCD18 antibody administered prior to occlusion. Neutrophil accumulation and reduction with antibody treatment was confirmed immunohistochemically. Superoxide anion (O2*-) concentration was detected during the hours following 60 min of occlusion, and increased further with 2 h of occlusion. Treatment with the antiCD18 antibody had no effect on O2*- concentration during reperfusion in the 60-90 min occlusion groups, but O2*- concentration was significantly lower in the antiCD18 antibody treated group than in the control group during reperfusion after 120 min of ischemia. The antibody also reduced cortical neutrophil accumulation in the 120 min ischemia group. These results indicate for the first time that superoxide production by neutrophils becomes more important with longer periods of ischemia, and other quantitatively less important sources of superoxide predominate with shorter periods of ischemia. This phenomenon may explain some of the variation seen between different models of ischemia with different durations of ischemia when targeting reactive oxygen species, and supports an approach to combination therapy to extend the therapeutic window and reduce the deleterious effects of reperfusion.