SUPEROXIDE AND HYDROGEN-PEROXIDE INDUCE CD18-MEDIATED ADHESION IN THEPOSTISCHEMIC HEART

A burst of endothelial derived oxidants including hydrogen peroxide (H 2O2) and superoxide (. O-2(-)) occurs on reperfusion of ischemic tissu es that directly causes injury; however, it is not known if this also triggers further injury due to subsequent leukocyte adhesion and adhes ion molecule expression. Therefore, studies were performed in an isola ted heart model developed to enable study of the role of isolated cell ular and humoral factors in the mechanism of postischemic injury. Isol ated rat hearts were, subjected to 20 min of 37 degrees C-global ische mia followed by reperfusion with polymorphonuclear leukocytes (PMNs) a nd plasma in the presence or absence of superoxide dismutase (SOD), 20 0 U/ml, or catalase, 500 U/ml. Measurements of contractile function, c oronary flow, high-energy phosphates, free radical generation, and PMN accumulation were performed. Adhesion molecule expression was measure d on the surface of effluent PMNs by fluorescence flow cytometry and w ithin the tissue using immunohistochemistry. SOD or catalase treatment resulted in 2- to 3-fold higher recoveries of contractile function, c oronary flow, and high energy phosphates. EPR spin trapping measuremen ts demonstrated that SOD totally quenched the free radical generation observed upon reperfusion while catalase prevented the formation of hy droxyl and alkyl radicals derived from superoxide. SOD or catalase tre atment decreased PMN accumulation in the reperfused heart and prevente d the marked upregulation of CD18 expression seen after reperfusion. T hese experiments demonstrate that in addition to their direct antioxid ative actions, SOD and catalase each decrease PMN adhesion and CD18 ex pression resulting in marked suppression of PMN-mediated injury in the postischemic heart. Thus, endothelial derived H2O2 and . O-2(-) furth er amplify postischemic injury by triggering CD18 expression on the su rface of PMNs leading to increased PMN adhesion within the heart.