Increased levels of soluble ICAM‐1 in the plasma of sickle cell patients are reversed by hydroxyurea

Phosphatidylserine (PS)-positive erythrocytes adhere to endothelium and subendothelial matrix components. While thrombospondin mediates these interactions, it is unknown whether PSassociated erythrocyte-endothelial adhesion occurs in the absence of plasma ligands. Using ionophore-treated PSexpressing control HbAA erythrocytes, we demonstrate that PS-positive erythrocytes adhered to human lung microendothelial cells in the absence of plasma ligands, that this adhesion was enhanced following endothelial activation with IL-1␣, TNF-␣, LPS, hypoxia, and heme, and that this adhesive interaction was selective to erythrocyte PS. We next explored whether microendothelial cells express an adhesion receptor that recognizes cell surface-expressed PS (PSR) similar to that expressed on activated macrophages. We demonstrate constitutive expression of both PSR mRNA and protein that were up-regulated in a time-dependent manner following endothelial activation. While minimal PSR expression was noted on unstimulated cells, endothelial activation up-regulated PSR surface expression. In antibody-blocking studies, using PSpositive erythrocytes generated either artificially via ionophore treatment of control erythrocytes or from patients with sickle cell disease, we demonstrate that PSR was functional, supporting PSmediated erythrocyte adhesion to activated endothelium. Our results demonstrate the existence of a novel functional adhesion receptor for PS on the microendothelium that is up-regulated by such pathologically relevant agonists as hypoxia, cytokines, and heme. IntroductionThe anionic phospholipid phosphatidylserine (PS), present exclusively in the inner leaflet of the plasma membrane of a normal cell, is externalized following cell activation with both physiologic and pathologic stimuli such as activation of blood platelets resulting from vessel wall injury and cells that are undergoing apoptosis. 1,2 PS exposure on the red cell surface occurs in patients with various hemolytic anemias 3-9 activating numerous pathobiologic processes, of which one is red cell-endothelial cell adhesion. 10,11 The mechanism(s) underlying this PS-mediated adhesion process is not well defined. Interaction of PS with immobilized subendothelial matrix thrombospondin has been documented. 10 In addition, soluble thrombospondin-mediated adhesion of PS-positive erythrocytes to endothelium can occur via the constitutively expressed endothelial vitronectin receptor (VnR). 10 Whether PS-related erythrocyte adhesion to endothelium can occur in the absence of plasma ligands is not known. In the present study, we explore this possibility, and hypothesize that endothelial cells express novel adhesion receptor(s) that can interact directly with PS-positive erythrocytes in the absence of plasma ligands. One such candidate is a receptor that recognizes cell surface-expressed membrane-associated phosphatidylserine, referred hitherto as the phosphatidylserine receptor or PSR, originally described by Fadok et al on the surface of activated macrophages that recogni...

Section: Discussionmentioning

confidence: 99%

Microvascular endothelial cells express a phosphatidylserine receptor: a functionally active receptor for phosphatidylserine-positive erythrocytes

Setty

Betal

2008

“…Some in vitro and animal studies suggest that hydroxyurea increases endothelial intracellular adhesion molecule-1 (ICAM-1) expression, 10 which could enhance parasite adhesion to endothelium, 11 and also increases tumor necrosis factor a levels, 12 both of which are associated with increased malaria severity and death. 13 Other studies have challenged these findings, 14,15 but definitive human data are lacking. If hydroxyurea induces effects that shift the clinical course in SCA from uncomplicated to severe malaria, this could increase mortality despite benefits for the underlying SCA.…”

Section: Introductionmentioning

confidence: 99%

Novel use Of Hydroxyurea in an African Region with Malaria (NOHARM): a trial for children with sickle cell anemia

Opoka

Ndugwa

Latham

et al. 2017

116

122

“…Plasma free hemoglobin and heme both have proinflammatory and pro-oxidant effects on endothelial cells and are associated with increased expression of endothelial cell adhesion molecules such as intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule (VCAM-1), and E-selectin. 9,12,[26][27][28][29] NO, in contrast, inhibits the expression of the same endothelial cell adhesion molecules. 9 Normally, the plasma proteins haptoglobin and hemopexin, which bind hemoglobin and heme, respectively, are protective against the potentially damaging effects of intravascular hemolysis.…”

Section: Introductionmentioning

confidence: 99%

Vascular dysfunction in a murine model of severe hemolysis

Frei

Guo

Jones

et al. 2008

Spectrin is the backbone of the erythroid cytoskeleton; sph/sph mice have severe hereditary spherocytosis (HS) because of a mutation in the murine erythroid ␣-spectrin gene. sph/sph mice have a high incidence of thrombosis and infarction in multiple tissues, suggesting significant vascular dysfunction. In the current study, we provide evidence for both pulmonary and systemic vascular dysfunction in sph/sph mice. We found increased levels of soluble cell adhesion molecules in sph/ sph mice, suggesting activation of the vascular endothelium. We hypothesized that plasma hemoglobin released by intravascular hemolysis initiates endothelial injury through nitric oxide (NO) scavenging and oxidative damage. Likewise, electron paramagnetic resonance spectroscopy showed that plasma hemoglobin is much greater in sph/sph mice. Moreover, plasma from sph/sph mice had significantly higher oxidative potential. Finally, xanthine oxidase, a potent superoxide generator, is decreased in subpopulations of liver hepatocytes and increased on liver endothelium in sph/sph mice. These results indicate that vasoregulation is abnormal, and NO-based vasoregulatory mechanisms particularly impaired, in sph/sph mice. Together, these data indicate that sph/sph mice with severe HS have increased plasma hemoglobin and NO scavenging capacity, likely contributing to aberrant vasoregulation and initiating oxidative damage. (Blood. 2008;112:398-405) IntroductionThe membrane skeleton, a multiprotein complex located just beneath the plasma membrane, provides the red blood cells (RBCs) with the mechanical strength and deformability required to withstand the high shear forces of the microcapillaries. Spectrin, a tetramer composed of ␣-and ␤-subunits, is the backbone of the erythroid membrane skeleton and is tethered to the membrane at 2 positions. Disruption of either spectrin or proteins involved in tethering spectrin to the RBC plasma membrane can result in the hemolytic anemia known as hereditary spherocytosis (HS) in both humans and mice. [1][2][3] We have shown that sph/sph mice have severe autosomal recessive HS because of a spontaneous single-base deletion in the murine erythroid ␣-spectrin gene, Spna1. 4 Although heterozygous (sph/ϩ) mice are phenotypically normal, the sph/sph RBC is extremely fragile, resulting in an RBC life span of approximately 1 day (normal is 48 days). 5 As a consequence, sph/sph mice have a very severe hemolytic anemia, with hematocrit values of 0.15 to 0.20 and compensatory reticulocytosis of 90% to 95%. 5 As a result of the severe hemolysis, sph/sph mice with severe HS develop multiorgan pathology in kidney, heart, liver, and spleen. 6,7 In addition, sph/sph mice develop thrombosis and infarction in multiple tissues, 6-8 suggesting significant vascular dysfunction.Recent studies of patients with hemolytic anemia have indicated that the incidence of pulmonary hypertension, as indicated by increased tricuspid regurgitant jet velocity (Ն 3.0 m/sec), is relatively high in patients with sickle cell disease (SCD), thalassemia,...