Thrombin Inhibition Prevents Against Severe Atherosclerosis Progression in Prothrombotic Mice

Besides its well-known role in initiation and propagation of thrombus formation, thrombin may have multiple pro-atherogenic actions.

Pharmacologic thrombin inhibition attenuates the onset and progression of atherosclerosis and favors plaque stability in hypercoagulable mice prone to aggressive atherosclerosis development.

Hypercoagulability in TM^Pro/Pro:ApoE^−/− mice resulted in severe atherosclerotic burden formation compared to ApoE^−/− mice (389.1*10³ μm² vs. 187.0*10³ μm², p<0.0005). Pro-coagulant mice showed larger necrotic cores, decreased plaque collagen content, vast stenosis (up to 90%) and enhanced outward remodeling. Hypercoagulability markedly increased systemic and vascular inflammation, represented by significantly higher CXCL1, MCP-1 and G-CSF plasma levels, pronounced neutrophilia, enhanced Ly6G+ cells arrest to carotid plaques, increased neutrophil recruitment (IHC/Intravital Microscopy), massive intraplaque hemorrhage and spontaneous plaque ruptures. Genetically diminished prothrombin levels (FII^-/WT:ApoE^−/− mice) caused a significant decrease in atherosclerosis (72.5*10³ μm² vs. 128.4*10³ μm², p<0.01) with a pronounced stable phenotype with less/smaller necrotic cores, thicker fibrous caps and abundant collagen and vascular smooth muscle cell content. Ly6G⁺ cell intraplaque recruitment was reduced and white blood cell counts and IL-6 levels (3.8±1.66 vs. 8.8±5.34 pg/mL, p<0.05) were diminished compared to control mice. Remarkably, administration of the oral direct thrombin inhibitor Dabigatran etexilate or the anticoagulant activated protein C (APC) in TM^Pro/Pro:ApoE^−/− mice reduced lesions formation by > 80%, suppressed leukocyte recruitment, enhanced plaque stability, whereas numerous pro-inflammatory cytokines were diminished to levels comparable to non-atherosclerotic mice.

These data establish a pivotal role for thrombin generation in controlling the level of inflammation related to atherosclerosis development in ApoE^−/− mice. The potential clinical impact of long term administration of novel classes of anticoagulants on atherosclerosis merits further study.

Weiler:BloodCenter of Wisconsin: Patents & Royalties. van Ryn:Boehringer Ingelheim Pharma GmbH & Co KG: Employment.