Systemic lupus erythematosus (SLE) is a chronic inflammatory disorder with a high prevalence of cardiovascular disease due to accelerated atherosclerosis, as well as an increased risk of venous thromboembolism. Many of these clinical features have been attributed to the high prevalence of autoantibodies that are directed against phospholipid-bound antigens and that induce prothrombotic effects and disturb endothelial cell function. We conducted a case-control study in a cohort of female patients with SLE and in age-matched and sex-matched normal individuals. Patients had significantly higher levels of plasma inflammatory markers, but their overall coagulation status assessed by prothrombin fragment 1 + 2 and D-dimer plasma levels was not different from controls. Resistance against activated protein C (APC), assessed by a thrombin generation-based as well as an activated partial thromboplastin time-based method, however, was increased in patients. This defect was neither due to factor V Leiden carriership or to the use of oral contraceptives. This acquired form of APC resistance was due to proinflammatory changes associated with lower plasma levels of free protein S. In conclusion, acquired APC resistance may be an important determinant of the risk of thrombosis in patients with SLE, probably due to an active cross-talk between inflammation and coagulation systems.

Tissue factor (TF) is a transmembrane protein, which is essential for initiation of the coagulation cascade. TF has been reported to play an important role in the progression of endotoxin (lipopolysaccharide, LPS)-mediated endotoxemia, being induced in numerous tissues, such as kidney, spleen and lung. We developed and validated a rabbit anti-murine TF peptide antiserum to localize TF protein in a murine sepsis model. TF protein distribution was compared to localization of TF mRNA and fibrin deposits, the ultimate resultant of procoagulant TF activity. Evident LPS mediated TF mRNA induction was observed in the tubular area at the cortico-medullar junction in the kidney, and TF activity was increased after 6 hours of endotoxemia. In the spleen, however, TF mRNA was induced in the interfollicular region upon LPS injection, corresponding to increased TF protein in the same area. The clusters of TF-protein positive cells in the spleen are predominantly granulocytes, but no TF mRNA expression was observed within these cells. Based on these observations and the presence of TF-protein positive granulocytes after splenectomy, we hypothesize that granulocytes take-up TF for transport to other locations in order to initiate fibrin formation or to induce pro-inflammatory gene expression upon interaction with factor VIIa.

Recent human studies reveal that hyperglycemia induces procoagulant and antifibrinolytic effects in blood that may contribute to a greater risk of arterial thrombosis, but the direct relationship between high blood glucose levels and thrombosis has not yet been investigated. We performed a number of experiments to clarify whether hyperglycemia was causally related to arterial thrombosis and whether the combined stimulus of hyperglycemia and inflammation would enhance the thrombotic effect. In a model of ferric-chloride-induced carotid artery thrombosis, hyperglycemia did not influence the time to occlusion in mice pretreated with streptozotocin, but the rate of thrombus formation was accelerated. This effect was associated with increased thrombin generation and could not be explained by changes in vessel-wall tissue factor activity. The prothrombotic effect of hyperglycemia was assessed in a separate experiment, showing that collagen/thrombin-induced platelet procoagulant activity was increased in hyperglycemic mice. The effect of inflammation was studied by injecting a low dose of endotoxin that caused a systemic inflammatory state after 24 h (increased plasma levels of tumor necrosis factor alpha, interleukin-6 and monocyte chemotactic protein 1 in diabetic and nondiabetic mice) associated with a mild delay in thrombus formation. This reduced rate of thrombus formation was attenuated by hyperglycemia. Together, these data establish a discrete but clear contribution of hyperglycemia in experimental arterial thrombosis.