The role of circulating thrombospondin-1 in patients with precapillary pulmonary hypertension

Background: The vasoconstrictive protein TSP-1 is released from endothelial cells upon increased shear stress and hypoxia. Both conditions are prevalent in pulmonary hypertension (PH). TSP-1 damages the local microcirculation by disrupting pathways, which are essential for specific medical therapeutics. Furthermore, TSP-1 induces excessive fibrosis and smooth muscle proliferation - a common finding in advanced PH - via TGF-beta and might promote disease progression. The prognostic impact of circulating TSP-1, influence on hemodynamic parameters and interaction with other biomarkers in patients with PH is incompletely understood. This study examines prospectively circulating TSP-1 in association with hemodynamic parameters, clinical variables and mortality. Methods: Circulating TSP-1 was measured prospectively in 93 patients with precapillary PH undergoing right heart catheterization and in 19 subjects without PH. TSP-1 levels were determined by ELISA and examined in the context of hemodynamic variables. For evaluation of survival, patients were monitored for adverse events on a 3-monthly basis and contacted at the end of the study after 5 years. In addition, levels of big-endothelin and humoral cofactors of TSP-1 release were measured. Results: Patients with PH had significantly increased TSP-1 levels compared to controls without PH (1114 +/- 136 ng/mL vs. 82.1 +/- 15.8 ng/mL, p < 0.05). Levels were correlated with mean pulmonary artery pressure (PAPm, r = -0.58, p < 0.001) and pulmonary vascular resistance (PVR, r = 0.33, p = 0.002). Survivors had lower TSP-levels as non-survivors and all cause mortality associated with TSP-1 plasma levels above 2051 ng/mL (p = 0.0002, HR 1.49). Conclusions: High plasma levels of TSP-1 are associated with increased PAPm, increased PVR and decreased survival. Due to its interaction with therapeutic pathways, studies are warranted to clarify the impact of TSP-1 on of specific medications for PH.