Abstract 521: The Thrombotic Potential of the Endothelium Is Regulated by Hemodynamic Flow

Abstract

BACKGROUND: Vascular wall mechanisms underlying human arterial and venous thrombosis are still evolving. TNFα and other cytokines have been shown to be potent mediators of endothelial cell-derived tissue factor in vitro, which mediates fibrin deposition in the vascular wall. Circulating levels of TNFα detected in humans with cardiovascular disease are approximately 0.05 ng/ml. METHODS: Human endothelial cells were co-cultured with or without smooth muscle cells in the presence or absence of human-derived, region-specific hemodynamics. Endothelial cells were exposed to TNFα at various concentrations and incubated in human, platelet-free-plasma supplemented by Alexa 488-labeled fibrinogen. Conversion of A488-fibrinogen to A488-fibrin and deposition on the endothelium was quantified by confocal microscopy. RESULTS: In static cultures, samples treated with 1ng/ml TNFα demonstrated minimal fibrin deposition whereas samples treated with 10ng/ml or 20ng/ml exhibited dense fibrin networks (1.17e5 vs. 2.69e7 vs. 3.61e7 mean fluorescence intensity, respectively). Fibrin deposition was tissue factor-dependent. In contrast, endothelial/smooth muscle cell co-cultures primed with inflammatory-prone hemodynamics derived from the internal carotid sinus and 0.05ng/ml TNFα deposited a dense fibrin network (1.9e7 mean fluorescence intensity). Identical experiments in which only endothelial cells were cultured yielded similar results demonstrating the result is hemodynamic-specific and not a consequence of the presence of smooth muscle cells. CONCLUSIONS: Hemodynamic priming of endothelial cells in vitro shifts the dose-dependent fibrin deposition response to TNFα into a more human physiological range, two orders of magnitude below that required to induce fibrin deposition in static endothelial cell cultures. Similar approaches can be used to investigate the differential mechanisms underlying vascular wall-mediated venous and arterial thrombosis.