Low anticoagulant heparin blocks thrombin-induced endothelial permeability in a PAR-dependent manner.

[heparin-induced thrombocytopenia]

Acute lung injury and acute respiratory distress syndrome are accompanied by thrombin activation and fibrin deposition that enhance lung inflammation , activate endothelial cells and disrupt lung paracellular permeability . Heparin possesses anti-inflammatory properties but its clinical use is limited by hemorrhage and heparin induced thrombocytopenia . We studied the effects of heparin and low anticoagulant 2 -O , 3 -O desulfated heparin (ODSH ) on thrombin-induced increases in paracellular permeability of cultured human pulmonary endothelial cells (ECs ). Pretreatment with heparin or ODSH blocked thrombin-induced decrease in the EC transendothelial electrical resistance (TER ), attenuated thrombin-stimulated paracellular gap formation and actin cytoskeletal rearrangement . Our data demonstrated that heparin and ODSH had inhibitory effects on thrombin-induced RhoA activation and intracellular calcium elevation . Thrombin-stimulated phosphorylation of the cytoskeletal regulatory proteins , myosin light chain and ezrin /radixin /moesin was also reduced . In these effects , low anticoagulant ODSH was more potent than heparin . Heparin or ODSH alone produced decreases in the EC TER that were abolished by siRNA-mediated depletion of the thrombin receptor , PAR-1 . We also demonstrated that , in contrast to heparin , ODSH did not possess thrombin-binding activity . Results suggest that heparin and low anticoagulant ODSH can interfere with thrombin-activated signaling .