Transforming growth factor beta-1 released from platelets contributes to hypercoagulability in veno-occlusive disease following hematopoetic stem cell transplantation

Background: Hepatic veno-occlusive disease (VOD) is one of the most disastrous complications after allogeneic hematopoetic stem cell transplantation (HSCT). Thrombocytopenia with refractoriness to platelet transfusions suggests an increased platelet consumption in these patients. Interactions between platelets and endothelial cells might contribute to the hypercoagulable state at the sinusoidal endothelium as a central mechanism in the pathogenesis of VOD. Study design: The influence of activated platelets on cultured human endothelial cells was investigated in vitro. We focused on the release of plasminogen activator inhibitor-1 (PAI-1) from endothelial cells which has earlier been found to be significantly elevated in plasma of VOD patients. Endothelial cells isolated from human umbilical cords (HUVEC) were incubated with activated platelets. The release of PAI-1 in the presence or absence of specific antibodies was determined by ELISA technique. Tissue factor (TF) expression on endothelial cells was observed by flowcytometric analysis. Results: HUVEC incubated with activated platelets were found to release significantly more PAI-1 compared to untreated cultures. The endothelial PAI-1-secretion after incubation of HUVEC with activated platelets was completely inhibited by an IgG monoclonal antibody against human transforming growth factor beta-1 (TGF beta-1). In contrast, PAI-1 production was not suppressed after inhibition of HUVEC-platelet-interaction by an IgG monoclonal antibody against CD154 (CD40L) expressed on the surface of activated platelets. An increased release of PAI-1 and an increased expression of tissue factor (TF) on the endothelial cell surface were observed after stimulation with TGF beta-1. Conclusion: TGF beta-1 released from activated platelets contributes to the hemostatic imbalance at the sinusoidal endothelium in patients with hepatic VOD by increase of endothelial cell PAI-1 production and TF expression. As a potent profibrotic cytokine, TGF beta-1 might further be involved in phlebosclerosis and sinusoidal fibrosis occurring in VOD.