ROLE OF GRANULOCYTES IN ENDOTHELIAL INJURY IN CORONARY HEART-DISEASE IN HUMANS

Recent studies suggest that granulocytes (PMNs) play a role in the pathogenesis of acute and chronic myocardial ischemia and extension of myocardial injury. A positive correlation was also found between leukocyte count and severity of coronary artery disease. Rabbit derived antiserum dependent-reduction of circulating PMNs in the dog or using monoclonal antibody anti-CD11b/CD18 of PMNs resulted in smaller myocardial infarcts. Granulocytes can release a variety of mediators tissue injury and synergize with these different mediators and other cells resulting in amplification of neutrophil stimulation and rising to additional products with enhanced endothelial injury. This paper reviews "in vivo" studies that have been instrumental in demonstrating this role of granulocytes as a mediator of myocardial ischemia. Experience in humans shows the modification of PMNs function in angina and during myocardial ischemia, and data from our group demonstrated that their aggregability is increased in the coronary sinus of patients with angiographically documented coronary disease. Upon re-perfusion PMNs accumulate and produce an inflammatory response resulting in endothelial injury. Free radicals formed during ischemia or re-perfusion produce deleterious effects on cell membranes, endothelial cell and myocardium. On the other hand the PMNs activation occurring during coronary angioplasty (PTCA) by the release of proteolytic enzymes and the generation of oxygen-free radicals, may aggravate the endothelial damage induced by PTCA and further stimulate platelets having potential implications in subsequent development of restenosis. An other aspect of PMNs function is related to leukotriene C4 release; the vasoconstrictor effect of this leukotriene on coronary arteries is synergistic with that induced by platelet-released thromboxane A2, as well as the decrease in coronary flow produced by the combination of both substances is greater than the sum of changes caused by the two eicosanoids separately administered. The potential role of leukocytes, oxygen radicals, leukotrienes and granulocyte enzymes in pathophysiology of myocardial injury due to a regional ischemia and reperfusion is an area of intense investigation. Experimental and clinical studies to elucidate these events should not only provide insights into acute and chronic pathologic tissue damage, but may also lead to the identification of important new targets of pharmacologic intervention.