Severe sickle cell anemia is associated with increased plasma levels of TNF‐R1 and VCAM‐1

Abstract

b b-thalassemias are characterized by an imbalance of globin chains with an excess of a-chains which precipitates in erythroid precursors and red blood cells (RBCs) leading to inefficient erythropoiesis. The severity of the disease correlates with the amount of unpaired achains. Our goal was to develop a simple test for evaluation of the free a-hemoglobin pool present in RBC lysates. Alpha-Hemoglobin Stabilizing Protein (AHSP), the chaperone of a-Hb, was used to trap excess aHb. A recombinant GST-AHSP fusion protein was bound to an affinity micro-column and then incubated with hemolysates of patients. After washing, the a-Hb was quantified by spectrophotometry in the elution fraction. This assay was applied to 54 patients: 28 without apparent Hb disorder, 20 b-thalassemic and 6 a-thalassemic. The average value of free a-Hb pool was 93 ± 21 ppm (ng of free a-Hb per mg of Hb subunits) in patients without Hb disorder, while it varies from 119 to 1,756 ppm, in b-thalassemic patients and correlated with genotype. In contrast, the value of the free a-Hb pool was decreased in a-thalassemic patients (65 ± 26 ppm). This assay may help to characterize b-thalassemia phenotypes and to follow the evolution of the globin chain imbalance (a/b+c ratio) in response to treatment.b-thalassemias (b-thal) are inherited autosomal diseases characterized by a decreased or abolished b-globin chain biosynthesis [1]. During the transition of g to b globin expression in the first year of life, the clinical severity is mainly related to the ratio a/b1g which indicates the level of chain disequilibrium. b-thal are generally classified as minor, intermediate, or major phenotype, and encompass a wide clinical spectrum ranging from asymptomatic carriers to forms that can be lethal in the absence of extensive treatment. Different factors can modulate the severity of this disease [2] such as the magnitude of the decrease of the b globin synthesis, for example hemoglobin E (Hb E b26Glu?Lys) [3], or with the co-inheritance of (i) an a-thalassemia (a-thal) [4], (ii) a triplicated a-globin gene [5] or (iii) a low but variable residual capacity of g globin production which can have the phenotype of a hereditary persistence of fetal Hb (Hb F a 2 g 2 ) [6].The imbalance between a and non a-globin (g1d1b) synthesis was established by radioactive in vitro biosynthesis of globin chains from reticulocytes or of bone marrow of b-thalassemic patients [7][8][9][10]. This imbalance leads to an excess of highly unstable free a-hemoglobin (a-Hb), precipitating on the cell membrane and acting as active oxidants causing apoptosis and inefficient erythropoiesis [1,11]. The severity of b-thal is directly correlated with the degree of imbalance as quantified by the amount of unbound a-globin chain [12]. Many studies have shown that one observes a soluble a chain fraction present in the cytosolic RBC and an insoluble a chain fraction in the membrane of b-thalassemic erythrocytes [13,14]. Because of technical difficulties and the burden of using radioactive materials, ...

VLA‐4 blockade by natalizumab inhibits sickle reticulocyte and leucocyte adhesion during simulated blood flow

“…Deformable ssRBC and sickle reticulocytes are critical to adhesion-based pathology in SCD (Hebbel et al, 1980a;Smith & La Celle, 1986;Barabino et al, 1987;Joneckis et al, 1993). Endothelial activation in SCD up-regulates a number of adhesion molecules on endothelium and as soluble proteins in circulation including vascular cell adhesion molecule 1 (VCAM-1), intercellular adhesion molecule 1 (ICAM-1), Pselectin, E-selectin and von Willebrand factor among others Turhan et al, 2002;Chang et al, 2010;Dworkis et al, 2011;Kanavaki et al, 2012). Endothelial activation in SCD up-regulates a number of adhesion molecules on endothelium and as soluble proteins in circulation including vascular cell adhesion molecule 1 (VCAM-1), intercellular adhesion molecule 1 (ICAM-1), Pselectin, E-selectin and von Willebrand factor among others Turhan et al, 2002;Chang et al, 2010;Dworkis et al, 2011;Kanavaki et al, 2012).…”

Applications of high-throughput DNA sequencing to benign hematology

“…To address the former, many GWAS have been performed, attempting to identify common variants contributing to complex disease. [52][53][54][55][56] These studies have revealed that in most complex diseases, common variants explain only a small fraction of genetic risk.…”

<i>ARFGEF2</i> Knockdown Enhances TNF-<i>α</i> Induced Endothelial Expression of the Cell Adhesion Molecules <i>VCAM1</i> and <i>ICAM1</i>

“…Recently, we reported a genetic association between SCA disease severity and single nucleotide polymerphisms (SNPs) in ARFGEF2 as well as demonstrated elevated TNF-R1 and VCAM-1 levels in the serum of subjects with severe SCA compared to those with less severe disease [7]. Together with the observation that ARFGEF2 modulates VCAM1 and ICAM1 expression, this suggests that genetic polymorphisms in ARFGEF2 may alter either its function or expression level in the endothelium.…”

“…Pulmonary vascular disease, particularly the acute chest syndrome and pulmonary hypertension, are among the most common causes of morbidity and mortality in SCA and pulmonary hypertension, in particular, is reflective of disease severity. [5,6] Recently, we reported genetic associations between SCA severity and single nucleotide polymorphisms (SNPs) in the ADP-ribosylation guanine nucleotide exchange factor-2 (ARFGEF2), a gene involved in release of tumor necrosis factor-α (TNF-α) receptor-1 (TNF-R1) from endothelial cells, and reported elevated plasma levels of both soluble TNF-R1 and soluble vascular cell adhesion molecule-1 (VCAM1, VCAM-1) in subjects with more severe SCA [3,7].…”