Cholesterol crystals induce coagulation activation in a complement-dependent manner

Cholesterol crystals (CC) are a hallmark of atherosclerotic plaques and have recently been found to be potent activators of the complement system and promote inflammation. In the present study we focused on the ability of CC to induce activation of the coagulation system. This might be of relevance during atherosclerotic plaque disruption, where released CC into blood could potentially be involved in the thrombotic events. To study the effects of CC on coagulation we used a lepirudin-based human whole blood model and cholesterol crystals. Our data showed for the first time that CC induced coagulation activation as revealed by increased prothrombin fragment 1.2 (PTF 1.2), a cleavage product from thrombin generation. Further on, CC stimulated monocyte tissue factor (TF) expression and TF mRNA synthesis, thus pointing to the involvement of the extrinsic pathway. This was further confirmed by inhibitory experiments showing that antibodies against TF reduced the PTF1.2 formation with approximately 90%, while we could not detect inhibition by factor XII blockage (intrinsic pathway) using corn trypsin inhibitor. The coagulation activation induced by CC thus mainly occurs through monocyte TF expression. Since the coagulation and complement systems cross-talk closely, we further determined if the complement system could be involved in the coagulation activation. Inhibition of complement at the level of complement C3 (Compstatin CP40) or C5 (Eculizumab) suppressed the CC-induced increases of PTF1.2 (83% and 90%) and monocyte TF expression (99% and 92%), thus demonstrating that the coagulation activation in response to CC is complement mediated. In conclusion, these data are the first to show that activation of coagulation by CC is dependent on complement. Thus, complement inhibitions should be regarded as a potential treatment strategy during atherosclerotic plaque disruptions.