Albumin Mildly Oxidized by the Myeloperoxidase Product Hypochlorous Acid Strongly Activates Platelets and Monocytes Via CD36

Abstract number: P0495

Brodde¹ MF, Volf² I, Jurk¹ K, Kehrel¹ BE

¹¹Universityhospital Münster, Dept of Anaesthesiology and Intensive Care, Exp. and Clin Haemostasis, Muenster, Germany ¹¹Universityhospital Münster, Dept of Anaesthesiology and Intensive Care, Exp. and Clin Haemostasis, Muenster, Germany ²²Medical University Vienna, Dept of Physiology, Vienna, Austria

Objectives:  Inflammatory pathways promote thrombosis. Two large studies, one from Europe one from the states, came to the conclusion that measurement of plasma/serum myeloperoxidase (MPO) predicts the early risk of myocardial infarction in patients with chest pain. A unique activity of MPO is its ability to generate hypochlorous acid (HOCl). HOCl-modified proteins accumulate in culprit lesions at ruptured or eroded sites of coronary atheroma. The effect of HOCl-modified proteins on platelets and monocytes were measured.

Methods:  Flowcytometric analysis of platelet and monocyte function, monocyte transmigration assay, mouse animal models for macrophage homing into atherosclerotic plaques in a defined region of the aortic valve region and for thrombus formation, Biacore.

Results:  Proteins (several tested) mildly oxidised by HOCl are very strong activators of platelets as well as monocytes. HOCl-modified albumin induced in pathologic relevant concentrations platelet adhesion to collagen and to subendothelial matrix. It induced on its own full granule secretion, strong aggregation, procoagulant activity and microparticle formation as well as local thrombus formation in mice, when given together with LPS. These effects were PI3-kinase dependent. HOCl-modified albumin induced a significant increase in monocyte transmigration through an endothelial monolayer and oxidative burst in leukocytes. After application of HOCl-modified protein into the peritoneum of ApoE deficient mice, mimicking local inflammation, a significant increase in macrophage invasion into the atherosclerotic plaques was observed. HOCL-modified protein bind with high affinity to CD36 and two of our monoclonal antibodies inhibited all effects of HOCl-mod. proteins on platelets. Platelets from a CD36 deficient donor were not activated by HOCl-mod. protein.

Conclusion:  These findings might help to explain the cause of acute thrombotic events in atherosclerosis responsible for myocardial infarction and ischemic stroke.