View Abstract

A4382 - Free Heme-Mediated Endothelial Barrier Dysfunction Contributes to the Development of Pulmonary Hypertension
Author Block: R. Rafikov1, A. Srivastava2, A. A. Desai3, P. Langlais1, E. Zemskov4, L. Mandarino1, O. Rafikova1; 1Medicine, University of Arizona, Tucson, AZ, United States, 2University of Arizona, Tucson, AZ, United States, 3Medicine/Cardiology, University of Arizona, Tucson, AZ, United States, 4Department of Medicine, University of Arizona, Tucson, AZ, United States.
Rationale: There is a significant prevalence of Pulmonary Hypertension (PH) in patients with hemolytic anemias resulting in 160,000-400,000 fold higher frequency of PH compared to a general population. However, the mechanistic role of hemolysis in severely increased PH prevalence in hemolytic patients and, more importantly, in PH development is poorly understood. In the present study, the effect of free hemoglobin (Hb) and its degradation product, free heme, are explored as the possible contributors to the hemolysis related effects in PH development. We hypothesized that hemolysis contributes to PH pathogenesis via endothelial barrier dysfunction with resulting perivascular edema and inflammation.
Methods: Plasma samples from patients with and without pulmonary arterial hypertension (both confirmed by right heart catheterization) were used to measure free Hb and its correlation with the severity of PH. A sugen (50mg/kg) /hypoxia (3wks) /normoxia (2wks) rat model was used to elucidate the role of free Hb/heme pathways in PH. Human lung microvascular endothelial cells (HLMVECs) were utilized to study heme-mediated endothelial barrier effects.
Results: Our data indicate that PH patients have increased levels of free Hb in plasma that correlate with disease severity and progression. There is also a significant accumulation of free Hb and depletion of haptoglobin in the sugen/hypoxia rat model. In rats, perivascular edema was observed during first two weeks of PH concomitant with increased infiltration of inflammatory cells. In the cell culture model of HLMVECs, we found that not hemoglobin but free heme-induced endothelial permeability via activation of the p38/HSP27 signaling pathway. Indeed, the rat model also exhibited an increased activation of p38/HSP27 during the initial phase of PH. Surprisingly, despite the increased levels of hemolysis and heme-mediated signaling; there was no heme oxygenase-1 activation. This can be explained by observed destabilization of HIF1a during the first two weeks of PAH regardless of hypoxic conditions. We found that heme-
mediated effects on endothelium, at least in part, depend on Heme Carrier Protein 1 (HCP-1) and pharmacological inhibition of HCP-1 by sulfasalazine reduced barrier disruptive potential of the heme. Sulfasalazine administration to sugen/hypoxia rats results in attenuation of PH by a reduction in vascular remodeling in the lungs as well as decreasing right heart hypertrophy.
Conclusions: Our data suggest that hemolysis plays a significant role in PH pathobiology and attenuation of heme-mediated signaling pathways could be the important therapeutic approach.