Oxidation of C-reactive protein by hypochlorous acid leads to the formation of potent platelet activator

We examined the structural and functional consequences of oxidative modification of C-reactive protein (CRP) by hypochlorous acid (HOCI), which can be generated in vivo via the myeloperoxidase/H2O2/Cl- system. HOCI exposure resulted in the oxidation and chlorination of CRP amino acid residues, leading to protein unfolding, greater surface hydrophobicity and the formation of aggregates. After treatment of isolated platelets with 50 mu g/ml HOCI-CRP, the modified CRP significantly stimulated platelet activation (over 10-fold increase in the fraction of CD62-positive platelets compared to controls, P<0.008), enhanced deposition of platelets onto immobilized fibrinogen (two-fold rise in platelet adhesion compared to controls, P<0.0001), and induced platelet aggregation by up to 79.5%. The ability of HOCI-CRP to interact with several platelet receptors (TLR-4, GPIIbIIIa) and plasma proteins (C1q, IgG) strongly indicates that HOCl-modification leads to structural changes of CRP resulting in the formation of new ligand binding sites, which is characteristic of the monomeric form of CRP exerting pro-inflammatory effects on a variety of cells. Overall, the oxidation of native CRP by HOCI seems to represent an alternative mechanism of CRP modification, by which CRP reveals its pro-inflammatory and pro-thrombotic properties, and as such, it might be of causal relevance in the pathogenesis of atherosclerosis. (C) 2017 Elsevier B.V. All rights reserved.