Intracellular polymerization of sickle hemoglobin. Effects of cell heterogeneity.

Abstract

A B S T R A C T To determine the extent to which the broad distribution in intracellular hemoglobin concentrations found in sickle erythrocytes affects the extent of intracellular polymerization of hemoglobin S, we have fractionated these cells by density using discontinuous Stractan gradients. The amount of polymer formed in the subpopulations was experimentally measured as a function of oxygen saturation using '3C nuclear magnetic resonance spectroscopy. The results for each subpopulation are in very good agreement with the theoretical predictions based on the current thermodynamic description for hemoglobin S gelation. We further demonstrate that the erythrocyte density profile for a single individual with sickle cell anemia can be used with the theory to predict the amount of polymer in unfractionated cells. We find that heterogeneity in intracellular hemoglobin concentration causes the critical oxygen saturation for formation of polymer to shift from 84 to >90%; polymer is formed predominantly in the dense cells at the very high oxygen saturation values. The existence of polymer at arterial oxygen saturation values has significance for understanding the pathophysiology of sickle cell anemia.

Alpha thalassemia changes erythrocyte heterogeneity in sickle cell disease.

“…Compared with normal individuals, the broader distribution results in a larger value for the 60% density transition (R60) and an increase in the proportion of dense cells which is all but absent in normal individuals (35,36). Since these parameters are little influenced by the increased reticulocyte production, they presumably reflect an accelerated increase in cell density beyond normal cell aging (26) due to the cycles of intracellular polymerization (8,9).…”

“…Corpuscular hemoglobin concentration (CHC)' (2,3) and corpuscular hemoglobin composition (4,5) are the principal factors which determine the extent of intracellular polymerization. Several studies on sickle cell disease have detailed the tremendous heterogeneity in these parameters such as reflected in the heterogeneous density distribution (6)(7)(8)(9), in hemoglobin F levels (10)(11)(12) and in hemoglobin F-containing cells (13)(14). While chemical and biophysical processes associated with polymerization of hemoglobin S have been extensively studied (15), the precise relationship between polymer formation and disease manifestation is unknown.…”

Intravascular hemolysis and the pathophysiology of sickle cell disease

“…Damage to circulating erythrocytes occurs with wide diversity amongst individuals (1). This heterogeneity arises from differences in intrinsic characteristics of sickle erythrocytes, like heterocellular fetal hemoglobin (HbF) distribution, HbS concentration (2), hydration, and density (3,4), and the cell's environmental transitions from macro-to microcirculation, laminar to turbulent flow, normoxia to hypoxia, isotonic to hypertonic environment, and acidotic to alkalotic milieu. Multiple components contribute to sickle hemoglobinopathy pathophysiology, including primary components arising from HbS polymerization and secondary components that are downstream effects of the HbS polymer.…”

Nitrite Reductase Activity of Hemoglobin S (Sickle) Provides Insight into Contributions of Heme Redox Potential Versus Ligand Affinity

“…When HbS concentration exceeds its solubility threshold deoxygenation induces polymerization of HbS tetramers, rigidifying and ultimately deforming red blood cells (34). Polymerization of HbS is affected primarily by Hb concentration and composition (relative amounts of HbS, HbF, and HbA forms), but is also modulated by pH, temperature, phosphate concentration, and ligand pressure (35)(36)(37). Interestingly, non-polymerized solution-phase HbS follows the same equilibrium ligand-binding curve as HbA (38) and demonstrates similar ligand-binding kinetics (39 -41).…”