OC 08.2 - High-Density Lipoprotein prevents Microvascular Thrombosis in two Mouse Models of Thrombotic Microangiopathy

Background: We have shown through a variety of methods that high-density lipoprotein (HDL) efficiently prevents the self-association of VWF. Self-associated VWF strands and fibers can reach enormous lengths and are very efficient in capturing platelets. In vitro, the extent to which HDL prevented self-association correlated with the reduction in platelet coverage. In a mouse model of thrombotic microangiopathy induced by VWF infusion into ADAMTS13-deficient mice, HDL attenuated the thrombocytopenia induced by VWF challenge.

Aims: Here, we examined by intravital microscopy the effect of HDL on microvascular thrombosis.

Methods: Microvascular thrombosis was induced in two ways: 1) by the stimulation of mesenteric venules with calcium ionophore; or 2) by infusion of high doses of recombinant human VWF (rVWF) and imaging arterioles and venules of the cremaster muscle. Both sets of experiments used ADAMTS13-deficient mice.

Results: In the ionophore-induced thrombosis model, control mice evinced robust platelet adhesion and platelet string formation and embolization. Time to thrombus resolution was much longer (about 15 min) than in wild-type mice ( < 5 min). In ADAMTS13-deficient mice pretreated with 100 mg/kg HDL, the thrombotic response was largely prevented, with only occasional single platelets adhering. The differences with the untreated mice in number of large thrombi and time to resolution were both statistically significant. In the VWF challenge model, rVWF infusion into ADAMTS13-deficient mice was soon followed by adhesion of platelets to endothelium-associated VWF fibers, forming long strings on the walls of arterioles and venules. Many microvessels obstructed completely. The effect persisted over the 90 min of monitoring. By contrast, KO mice pretreated with 100 mg/kg HDL demonstrated markedly less platelet adhesion and string formation; vessel occlusion was almost completely prevented (see figures).

Conclusion(s): These data show a biologically significant effect of HDL in preventing VWF-mediated small vessel occlusion and suggest that this effect can be exploited clinically to treat thrombotic microangiopathies.