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, thus promoting inflammation. In the present study we have utilized the lepirudin-based whole blood model to investigate the ability of CC to induce coagulation by measuring prothrombin fragment 1.2 (PTF 1.2), monocyte tissue factor (TF) expression, and TF mRNA. Coagulation pathway activation by CC was investigated by inhibiting TF or factor XII, initiating factors in the TF and contact pathways, respectively. Furthermore, the role of complement activation was studied with the use of inhibitors of complement factors C3 and C5. Following CC stimulation, increased TF mRNA was observed after 1 hour, increased monocyte TF expression was observed after 2 hours, and increased plasma levels of PTF1.2 was observed after 4 hours, suggesting that CC might be directly involved in the thrombotic events following atherosclerotic plaque disruption. Inhibiting TF abolished PTF1.2 induction by CC, while inhibiting factor XII with corn trypsin inhibitor (CTI) had no effect, demonstrating that coagulation activation by CC occurs through monocyte TF activation. Inhibition of complement at the level of C3 or C5 effectively suppressed the CC-induced increases in PTF1.2 and TF, strongly suggesting that the coagulation activation in response to CC is complement mediated. Using blood from a C5 deficient patient we further confirmed the involvement of C5. Preliminary data using whole blood from obese patients before and after weight reduction showed that the coagulation activation by CC is reduced after 8 weeks calorie restriction, emphasizing that dietary restriction could be beneficial.