Risk of Recurrent Venous Thromboembolism Reduced by High Density Lipoproteins.

Venous thrombosis is clinically distinct from arterial thrombosis, with notable differences in thrombus appearance, pathogenic mechanisms, and therapeutic approaches. High-density lipoprotein (HDL) protects against arterial atherothrombosis, but it is not known if HDL protects against recurrent venous thromboembolism. We hypothesized that HDL protects against recurrent venous thrombosis because of its multiple antithrombotic and anti-inflammatory actions. These protective activities include down-regulation of thrombin generation by acting as an anticoagulant cofactor for activated protein C/protein S, enhancement of protective endothelial nitric oxide synthase activity, reduction of leukocyte adhesion to endothelium, and anti-apoptotic effects on endothelium. To test our hypothesis, we prospectively studied 772 patients who had a first episode of spontaneous venous thromboembolism. During an average follow-up observation period of 48 months we recorded the end point of objectively documented, symptomatic recurrent venous thromboembolism. Patients with a genetic deficiency of a plasma coagulation inhibitor deficiency, with a lupus anticoagulant, or with cancer as well as those who required long-term antithrombotic treatment or were on statin therapy were excluded. The relationship between plasma lipoprotein parameters and recurrence of venous thrombosis was evaluated. Plasma apolipoproteins AI and B were measured by immunoassays for all subjects. Using NMR, we determined the levels of ten major lipoprotein subclasses in plasma for 99 patients with venous thrombosis recurrence and for 297 matched patients without recurrence. Recurrent venous thromboembolism developed in 100 of the 772 patients (12.8%). Patients with recurrence compared to those without recurrence had lower mean (±SD) plasma levels of apolipoprotein AI (1.12±0.22 vs. 1.23±0.27 mg/ml, P<0.001) but similar apolipoprotein B levels. The relative risk of recurrence was 0.87 (95% CI, 0.80 to 0.94) for each increase of 0.1 mg/ml in plasma apolipoprotein AI. For patients with apolipoprotein AI above the 67^th percentile of the study population values compared with those with lower levels, the relative risk of recurrence was 0.51 (95% CI 0.32–0.83). Comparisons of plasma lipoprotein particle levels from subjects with recurrence versus those without recurrence gave similar results showing that HDL particle concentrations were lower in subjects with recurrence. Patients with high levels of apolipoprotein AI, HDL-cholesterol, and large HDL particles had decreased risk of recurrent venous thromboembolism. In summary, these novel findings that HDL appears to protect against recurrent venous thrombosis may have implications for testing HDL parameters to predict risk and may imply that lipid-altering drugs that increase HDL might reduce the risk for first or recurrent venous thrombotic events.