Atherosclerosis 213 (2010) 129–134 Contents lists available at ScienceDirect Atherosclerosis journal homepage: www.elsevier.com/locate/atherosclerosis Hypochlorite-oxidized LDL induces intraplatelet ROS formation and surface exposure of CD40L—A prominent role of CD36 Alice Assinger a , Franz Koller b , Werner Schmid a , Maria Zellner a , Elisabeth Koller a , Ivo Volf a,∗ a Institute of Physiology, Center for Physiology & Pharmacology, Medical University of Vienna, Schwarzspanierstr. 17, A-1090 Vienna, Austria b Department of Biochemistry, Max F. Perutz Laboratories, University of Vienna, Dr. Bohrgasse 9, A-1030 Vienna, Austria article info Article history: Received 20 May 2010 Received in revised form 5 July 2010 Accepted 15 July 2010 Available online 22 July 2010 Key words: OxLDL Oxidative stress Platelet function Inflammation CD40 ligand CD36 abstract Objective: OxLDL represents a central player in atherogenesis and has been shown to activate human blood platelets. In light of the pivotal role of CD40L in inflammation, it was the aim of this work to clarify if platelet-activating effects of oxidized LDL result in surface exposure and liberation of CD40L and to explore the role of platelet scavenger receptor CD36 in this process. Methods: Binding and functional studies were performed with hypochlorite-oxidized LDL in absence and presence of (potential) competitors in normal and CD36-deficient human platelets. To determine functional effects of hypochlorite-oxidized LDL on human platelets, formation of reactive oxygen species, intraplatelet calcium, CD40L and CD62P as well as platelet aggregation were quantified. Results: Addition of OxLDL to resting human platelets results in intracellular calcium flux, platelet aggre- gation and surface expression of CD62P. OxLDL triggers the formation of intracellular reactive oxygen species and surface exposure of CD40L, with both being sensitive to the NADPH oxidase inhibitor apoc- ynin. In CD36-deficient human platelets, functional effects as well as high affinity binding of hypochlorite- oxidized LDL appears to be significantly reduced compared with platelets positive for CD36. Conclusions: Our results prove a prominent – however, not exclusive – role of CD36 in platelet binding of hypochlorite-oxidized LDL. CD36 appears to be the major receptor responsible for hypochlorite-oxidized LDL-induced platelet activation that accumulates in the release of CD40L. As platelets represent the major source of CD40L, our findings emphasize an important pro-inflammatory role of platelets, especially in conditions of oxidative stress. © 2010 Elsevier Ireland Ltd. All rights reserved. 1. Introduction Atherosclerosis, resulting in cardiovascular disease and its (athero)thrombotic consequences is clearly the major source of morbidity and mortality in the Western world. As thrombotic events are responsible for the lethal con- sequences of atherosclerosis, the central importance of blood platelets and other elements of the hemostatic/thrombotic system to this disease is apparent and has been recognized for many years. Nevertheless, current literature provides compelling evidence that it is not only the final stages of atherosclerosis where platelets and their activation state are involved in. Since the mere existence of certain risk factors can result in platelet activation and – in turn – stimulated platelets causally ∗ Corresponding author. Tel.: +43 1 4277/62121, fax: +43 1 4277/9621. E-mail address: ivo.volf@meduniwien.ac.at (I. Volf). trigger the onset of inflammatory reactions, cell proliferation and immune responses [1,2], platelets play a prominent role in the ini- tiation and development of atherosclerosis. While a number of risk factors have been identified, high plasma concentrations of low density lipoprotein (LDL) seem to play a key role in the development of atherosclerosis. Furthermore, a large body of evidence supports the view that oxidative stress is closely related to atherogenesis. Today, it is gen- erally accepted that LDL gains its (full) atherogenic potential upon oxidative modification (for review, see literature [3]) and the in vivo occurrence of oxidized LDL (OxLDL) has been confirmed both in atherosclerotic lesions as well as in plasma (reviewed in literature [4,5]). Since atherosclerosis represents an inflammatory disease, the resulting pro-oxidative environment (further) favors the formation of oxidized LDL. Consequently, results of several studies were able to show that distinct markers of inflamma- tion and oxidative stress (among them myeloperoxidase and CD40 ligand) are associated with and even predictive for both 0021-9150/$ – see front matter © 2010 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.atherosclerosis.2010.07.018