α‐ and β‐haemoglobin chain induced changes in normal erythrocyte deformability: comparison to β thalassaemia intermedia and Hb H disease

Abstract

The alpha- and beta-thalassaemias are characterized by decreased erythrocyte deformability. To determine what effects excess alpha- and beta-haemoglobin (globin) chains have on cellular and membrane deformability, purified haem-containing alpha- and beta-chains were entrapped within normal erythrocytes. Entrapment of purified alpha-chains in normal erythrocytes resulted in a significant decrease in cellular and membrane deformability similar to that observed in beta-thalassaemia intermedia. The decreased deformability was correlated with alpha-chain membrane deposition, an alteration in membrane proteins and a decrease in membrane reactive thiol groups. These changes in membrane and cellular deformability were time dependent and closely correlated with membrane alpha-chain deposition. The membrane changes and the loss of membrane deformability appeared to account for the loss of cellular deformability in the alpha-chain loaded cells. While both beta-chain loaded and Hb H erythrocytes demonstrated a significant loss of cellular deformability, this loss was less pronounced than in the alpha-chain loaded and beta-thalassaemic cells and may arise from either the increased intracellular viscosity of the beta-chain loaded cells or to the smaller amount of membrane bound globin. In summary, these studies demonstrate that alteration of cellular and membrane deformability occurs very rapidly and as a direct consequence of the autoxidation and membrane binding of the unpaired globin chains.

Microfluidic analysis of cellular deformability of normal and oxidatively damaged red blood cells

“…To accomplish these functions, the approximately 8 mm diameter RBC must traverse capillaries that are as small as 2-2.5 mm in diameter and splenic interendothelial clefts that are only 0.5-1.0 mm in diameter [1][2][3][4][5]. Successful transit of these anatomical structures is dependent upon the deformability of the RBC.…”

“…Cellular deformability is a function of its surface to volume ratio, cytoplasmic viscosity, and membrane viscoelasticity [6][7][8][9][10]. Biological, pharmacological or biochemical changes that affect any of these variables can contribute to loss of cellular deformability and the premature clearance of the RBC via capillary or splenic sequestration, phagocytosis or intravascular lysis [3,[11][12][13][14][15][16]. If sufficient RBC are lost, anemia and tissue hypoxia will result.…”

“…Altered cellular deformability is a component of multiple clinically significant red cell abnormalities and hemoglobinopathies such as Sickle Cell Disease (SCD) or bThalassemia [3,[16][17][18][19][20][21][22][23]. In SCD, the inter-chain hydrophobic interactions and polymerization of the deoxygenated hemoglobin impairs deformability as well as promotes microocclusions via vasculature adhesion and blockage [18].…”

“…In b-Thalassemia, the unpaired and unstable a-hemoglobin chains generate reactive oxygen species damaging cytoskeletal proteins and oxidizing lipids and also tightly adhere to the membrane leading to a reduction in cellular deformability. The loss of deformability is further compounded by the decreased surface area to volume ratio of the microcytic red cells [3,17,22]. Experimentally, the aforementioned red cell damage can be modeled by exposing them to oxidants such as phenazine methosulphate (PMS) [3,15,17,24,25].…”

“…To understand the pathophysiology of disease, previous investigators have used techniques such as ektacytometry and the cell transit analyzer to measure cellular deformability [3,[26][27][28][29][30][31][32][33]. Ektacytometry measures deformability by subjecting RBC suspended in a viscous solution to rotational shear stress such that the normal cells form ellipsoids.…”