The effect of cell hydration on the deformability of normal and sickle erythrocytes

A preliminary study of phosphodiesterases and adenylyl cyclase signaling pathway on red blood cell deformability of sickle cell patients

Sickle cell disease (SCD) is an inherited hemoglobinopathy characterized by chronic anemia, intravascular hemolysis, and the occurrence of vaso-occlusive crises due to the mechanical obstruction of the microcirculation by poorly deformable red blood cells (RBCs). RBC deformability is a key factor in the pathogenesis of SCD, and is affected by various factors. In this study, we investigated the effects of adenylyl cyclase (AC) signaling pathway modulation and different phosphodiesterase (PDE) modulatory molecules on the deformability and mechanical stress responses of RBC from SCD patients (HbSS genotype) by applying 5 Pa shear stress with an ektacytometer (LORRCA). We evaluated RBC deformability before and after the application of shear stress. AC stimulation with Forskolin had distinct effects on RBC deformability depending on the application of 5 Pa shear stress. RBC deformability was increased by Forskolin before shear stress application but decreased after 5 Pa shear stress. AC inhibition with SQ22536 and protein kinase A (PKA) inhibition with H89 increased RBC deformability before and after the shear stress application. Non-selective PDE inhibition with Pentoxifylline increased RBC deformability. However, modulation of the different PDE types had distinct effects on RBC deformability, with PDE1 inhibition by Vinpocetine increasing deformability while PDE4 inhibition by Rolipram decreased RBC deformability after the shear stress application. The effects of the drugs varied greatly between patients suggesting some could benefit from one drug while others not. Developing drugs targeting the AC signaling pathway could have clinical applications for SCD, but more researches with larger patient cohorts are needed to identify the differences in the responses of sickle RBCs.

The Gardos effect drives erythrocyte senescence and leads to Lu/BCAM and CD44 adhesion molecule activation

Senescence of erythrocytes is characterized by a series of changes that precede their removal from the circulation, including loss of red cell hydration, membrane shedding, loss of deformability, phosphatidyl serine exposure, reduced membrane sialic acid content, and adhesion molecule activation. Little is known about the mechanisms that initiate these changes nor is it known whether they are interrelated. In this study, we show that Ca2+-dependent K+ efflux (the Gardos effect) drives erythrocyte senescence. We found that increased intracellular Ca2+ activates the Gardos channel, leading to shedding of glycophorin-C (GPC)-containing vesicles. This results in a loss of erythrocyte deformability but also in a marked loss of membrane sialic acid content. We found that GPC-derived sialic acid residues suppress activity of both Lutheran/basal cell adhesion molecule (Lu/BCAM) and CD44 by the formation of a complex on the erythrocyte membrane, and Gardos channel-mediated shedding of GPC results in Lu/BCAM and CD44 activation. This phenomenon was observed as erythrocytes aged and on erythrocytes that were otherwise prone to clearance from the circulation, such as sickle erythrocytes, erythrocytes stored for transfusion, or artificially dehydrated erythrocytes. These novel findings provide a unifying concept on erythrocyte senescence in health and disease through initiation of the Gardos effect.

Dietary supplementation with docosahexanoic acid (DHA) increases red blood cell membrane flexibility in mice with sickle cell disease

Humans and mice with sickle cell disease (SCD) have rigid red blood cells (RBCs). Omega-3 fatty acids, such as docosahexanoic acid (DHA), may influence RBC deformability via incorporation into the RBC membrane. In this study, sickle cell (SS) mice were fed natural ingredient rodent diets supplemented with 3% DHA (DHA diet) or a control diet matched in total fat (CTRL diet). After 8weeks of feeding, we examined the RBCs for: 1) stiffness, as measured by atomic force microscopy; 2) deformability, as measured by ektacytometry; and 3) percent irreversibly sickled RBCs on peripheral blood smears. Using atomic force microscopy, it is found that stiffness is increased and deformability decreased in RBCs from SS mice fed CTRL diet compared to wild-type mice. In contrast, RBCs from SS mice fed DHA diet had markedly decreased stiffness and increased deformability compared to RBCs from SS mice fed CTRL diet. Furthermore, examination of peripheral blood smears revealed less irreversibly sickled RBCs in SS mice fed DHA diet as compared to CTRL diet. In summary, our findings indicate that DHA supplementation improves RBC flexibility and reduces irreversibly sickled cells by 40% in SS mice. These results point to potential therapeutic benefits of dietary omega-3 fatty acids in SCD.

Optical measurement of biomechanical properties of individual erythrocytes from a sickle cell patient

Sickle cell disease (SCD) is characterized by the abnormal deformation of red blood cells (RBCs) in the deoxygenated condition, as their elongated shape leads to compromised circulation. The pathophysiology of SCD is influenced by both the biomechanical properties of RBCs and their hemodynamic properties in the microvasculature. A major challenge in the study of SCD involves accurate characterization of the biomechanical properties of individual RBCs with minimum sample perturbation. Here we report the biomechanical properties of individual RBCs from a SCD patient using a non-invasive laser interferometric technique. We optically measure the dynamic membrane fluctuations of RBCs. The measurements are analyzed with a previously validated membrane model to retrieve key mechanical properties of the cells: bending modulus; shear modulus; area expansion modulus; and cytoplasmic viscosity. We find that high cytoplasmic viscosity at ambient oxygen concentration is principally responsible for the significantly decreased dynamic membrane fluctuations in RBCs with SCD, and that the mechanical properties of the membrane cortex of irreversibly sickled cells (ISCs) are different from those of the other types of RBCs in SCD.

Effects of a single sickling event on the mechanical fragility of sickle cell trait erythrocytes

Hemolysis contributes to the pathology associated with sickle cell disease. However, the mechanism of hemolysis or relative contribution of sickling due to hemoglobin (Hb) polymerization vs. oxidative damage remains unknown. Earlier studies aimed at deciphering the relative importance of these two mechanisms have been complicated by the fact that sickle red cells (SS) have already been affected by multiple rounds of sickling and oxidative damage before they are collected. In our study, we examine the mechanical fragility of sickle cell trait cells, which do not sickle in vivo, but can be made to do so in vitro. Thus, our novel approach explores the effects of sickle Hb polymerization on cells that have never been sickled before. We find that the mechanical fragility of these cells increases dramatically after a single sickling event, suggesting that a substantial amount of hemolysis in vivo probably occurs in polymer-containing cells.

Transfusion Management in Sickle Cell Disease

Sickle cell disease (SCD) is the most commonly inherited hemoglobinopathy in the United States. Blood transfusion is a critical part of the multidisciplinary approach necessary in the management of SCD; however, blood transfusions are not without complications. The successful use of transfusion as a treatment strategy in SCD requires the critical review and knowledge of transfusion methods, generally accepted indications, clinical situations in which transfusion generally is not considered, the selection of blood products, and strategies to prevent transfusion-related complications.

Optical tweezers for measuring red blood cell elasticity: application to the study of drug response in sickle cell disease

The deformability of erythrocytes is a critical determinant of blood flow in microcirculation. By capturing red blood cells (RBC) with optical tweezers and dragging them through a viscous fluid we were able to measure their overall elasticity. We measured, and compared, the RBC deformability of 15 homozygous patients (HbSS) including five patients taking hydroxyurea (HU) for at least 6 months (HbSS/HU), 10 subjects with sickle cell trait (HbAS) and 35 normal controls. Our results showed that the RBC deformability was significantly lower in haemoglobin S (HbS) subjects (HbSS and HbAS), except for HbSS/HU cells, whose deformability was similar to the normal controls. Our data showed that the laser optical tweezers technique is able to detect differences in HbS RBC from subjects taking HU, and to differentiate RBC from normal controls and HbAS, indicating that this is a very sensitive method and can be applied for detection of drug-response in sickle cell disease.

Cation transport and volume regulation in sickle red blood cells

Cellular dehydration is one of several pathological features of the sickle cell. Cation depletion is quite severe in certain populations of sickle cells and contributes to the rheological dysfunction that is the root cause of vascular occlusion in this disease. The mechanism of dehydration of sickle cells in vivo has not been ascertained, but three transport pathways may play important roles in this process. These include the deoxygenation-induced pathway that permits passive K+ loss and entry of Na+ and Ca2+; the K(+)-Cl- cotransport pathway, activated by acidification or cell swelling; and the Ca(2+)-activated K+ channel, or Gardos pathway, presumably activated by deoxygenation-induced Ca2+ influx. Recent evidence suggests that these pathways may interact in vivo. Heterogeneity exists among sickle cells as to the rate at which they become dense, suggesting that other factors may affect the activity or interactions of these pathways. Understanding the mechanism of dehydration of sickle cells may provide opportunities for pharmacological manipulation of cell volume to mitigate some of the symptoms of sickle cell disease.

Technological advances in blood rheology

The science of blood rheology (study of the flow and deformability of blood) is of increasing practical importance to the investigation of blood disorders. In diagnostic laboratories, rheological tests such as the erythrocyte sedimentation rate, zeta sedimentation ratio, and plasma viscosity are used to monitor patients with an acute-phase response of greater than 24 h duration. In sickle-cell anemia, new methods for measuring erythrocyte deformability can be used to investigate the pathogenesis of vaso-occlusion, to test potential anti-sickling drugs, and to monitor drug efficacy in clinical trials. Genetic defects in the structure of the red cell membrane can have rheological consequences, monitoring of which may be useful for diagnosis. Rheological analysis of red cells infected by Plasmodium falciparum has indicated that their abnormal flow behavior may be an important pathological factor in malaria. Finally, the flow behavior of white blood cells, particularly neutrophils, is also important, as these cells, once activated, have the potential to occlude microvessels. The authors have reviewed the laboratory methodology and clinical applications that have led to recent advances in these aspects of blood rheology.

Mean corpuscular hemoglobin concentration and cell deformability

A prominent characteristic of sickle cells is the presence of a subpopulation of severely dehydrated cells. Apart from its effect on the rate and extent of Hb S polymerization at low oxygen tension, dehydration has adverse effects on deformability of oxygenated sickle cells. In general, the degree of deformability defect induced by cellular dehydration measured in vitro depends on the method used to measure deformability. Methods in which the extent or rate of cellular deformation are measured are especially sensitive to intracellular Hb concentration, whereas filtration methods are more sensitive to cell size. Studies of naturally occurring cellular dehydration in red cell disorders other than sickle cell disease have indicated that red cells can tolerate dehydration and a substantial increase in intracellular viscosity much more readily than a loss of deformability that results from loss of surface area or increase in cell volume. Further, the major clinical problems in sickle cell disease, involving occlusion of small vessels, do not correlate with the proportion of poorly deformable, dehydrated cells. Thus, the direct rheologic effects of cellular dehydration in sickle cell disease are probably much less important than the effects of MCHC on the kinetics of Hb S polymerization.

Effect of polymerization tendency on haematological, rheological and clinical parameters in sickle cell anaemia

The polymerization tendency of sickle haemoglobin was estimated as a function of oxygen saturation in 30 patients with homozygous sickle cell anaemia. The deformability of their erythrocytes was also measured, by initial-flow-rate filtration at 37 degrees C through pores of 5 microns diameter, and clinical severity was assessed using a visual analogue scale. By means of partial correlation analysis, it was found that correlations between haematological, rheological, and clinical parameters in sickle cell anaemia could be explained on the basis of an association of each variable with polymerization tendency. Patients with the greatest tendency to form polymer had the least deformable erythrocytes and perceived their disease to be more severe as judged by the visual analogue scale. Polymer formation also appeared to be a determinant of the number of dense cells which, in turn, determine haemolytic rate and erythrocyte deformability.

Stimulation of K-C1 cotransport in rat red cells by a hemolytic anemia-producing metabolite of dapsone

Dapsone, a sulfone compound used in the treatment of leprosy and, more recently, Pneumocystis carinii pneumonia, produces as a major side effect a hemolytic anemia. This anemia is characterized by oxidation of hemoglobin to methemoglobin and increased splenic uptake of red blood cells. Using a rat model, Grossman and Jollow (J. Pharmacol. Exp. Ther. 244: 118-125, 1988) found that dapsone hydroxylamine (DDS-NOH), a dapsone metabolite, is responsible for its hemolytic effect in vivo. DDS-NOH also promotes hemoglobin binding to SH groups on rat red cell membrane proteins (Budinsky et al., FASEB J. 2: A801, 1988). Since the binding of hemoglobin and other reagents (e.g., N-ethylmaleimide) to membrane SH groups has been associated with increased K transport in red blood cells, we examined the effect of DDS-NOH on K efflux from rat red blood cells in vitro. Cells shrink when exposed to DDS-NOH (100 microM) in media with plasma-like ionic composition. This shrinkage is prevented if extracellular K is raised to 110 mM or if intra- and extracellular Cl are replaced by methylsulfate (MeSO4), suggesting involvement of a K-Cl cotransport pathway. Indeed, 100 microM DDS-NOH produces a 4- to 5-fold increase in K efflux in cells containing Cl but less than a 2-fold increase in cells containing MeSO4. This stimulatory effect is specific for K; Na efflux is slightly inhibited by 100 microM DDS-NOH. The concentrations of DDS-NOH required for half-maximal stimulation of Cl-dependent K efflux (53 microM) is similar to its half-maximal hemolytic concentration in rats (approximately 100 microM). Furthermore, the stimulation of Cl-dependent K efflux by DDS-NOH is greater than 80% reversed by subsequent treatment of the cells with dithiothreitol, suggesting involvement of SH groups. Our results indicate that DDS-NOH exposure stimulates an apparent K-Cl cotransport in rat red blood cells, resulting in cell shrinkage under physiological ionic conditions. Since shrinkage of red blood cells renders them less deformable (Mohandas et al., J. Clin. Invest. 66: 563-573, 1980), this suggests a pathophysiological mechanism whereby DDS-NOH exposure in vivo could promote increased splenic uptake of red blood cells and hemolytic anemia.

Oxpentifylline and cetiedil citrate improve deformability of dehydrated sickle cells

Erythrocytes from 14 patients with homozygous sickle cell anaemia were treated with the calcium ionophore A23187 to induce loss of cellular potassium and water. The dehydrated cells showed a decrease in filterability (loss of deformability) through pores of 5 micron diameter. Oxpentifylline and cetiedil citrate, which preserve erythrocyte cation and water content, had a significant (p less than 0.01) protective effect against loss of deformability at a concentration of 1 mumol/l. Oxpentifylline showed no adverse effect on the rheology, morphology, or haemolysis of sickle cells at concentrations up to 500 mumol/l. Drugs that act on the erythrocyte membrane to maintain cell hydration are of potential rheological benefit in sickle cell anaemia.

Rheology of the sickle cell disorders

The sickling process causes secondary changes in cell shape, size, cation and water content, and membrane structure that contribute to the impairment of intrinsic cell deformability (Figure 2). This rheological defect is partially compensated by a low haematocrit, which moderates the rise in whole-blood viscosity, and by a rise in cardiac output which increases capillary flow velocity (Berger and King, 1982). A delicate balance exists between these mechanisms and any local disturbance of this balance by pathological changes in factors extrinsic to the sickle cell (Figure 2) can precipitate vaso-occlusion. There is still considerable controversy over the site (arteriolar, capillary, or venular) of vaso-occlusion, the type of sickle cell (reversibly sickled or irreversibly sickled) that is primarily involved, and the relative importance of extra-erythrocytic precipitating factors such as stasis, hypoxia, hyperosmolality, acidosis, alteration in temperature, acute-phase rise in plasma proteins and leukocytes, prothrombotic changes in coagulation factors and platelets, and adhesion of blood cells to vascular endothelium (Figure 2). A low-grade hypercoagulable state has been described in patients with SS (Leichtman and Brewer, 1978; Richardson et al, 1979) which may be related to the procoagulant effect of the shift of phosphatidyl serine to the outer lipid bilayer of the sickle cell (Chiu et al, 1981; Franck et al, 1985). Platelets appear to accumulate at sites of vaso-occlusion (Siegel et al, 1985) and their migration to the vessel wall may be enhanced by the presence of poorly deformable erythrocytes (Aarts et al, 1984). Endothelial cell damage in the arterial or venous circulation may also contribute (Klug et al, 1982). Thus vaso-occlusion appears to result from a complex interaction between blood cells, plasma proteins and endothelium and any one of several precipitating factors may disturb the fragile steady state and cause a painful crisis. The study of sickle cells by rheological methods has considerable potential for investigating the pathophysiology of vaso-occlusive episodes in the SCD and for monitoring, both in vitro and ex vivo, the efficacy of antisickling compounds. Because of the multiple intrinsic and extrinsic factors that contribute to the rheological defect, it is not yet known which of these should be the primary target for an antisickling agent. In-vitro rheological studies in which different metabolic stresses can be applied to intact sickle cells in the presence of a putative antisickling drug should help to answer this question.(ABSTRACT TRUNCATED AT 400 WORDS)

Red blood cell phagocytosis and lysis following oxidative damage by phenylhydrazine

Red blood cells exposed in vitro to phenylhydrazine acquired Heinz bodies, bound autologous IgG and were then phagocytized when incubated with autologus mononuclear phagocytes. In vivo, phenylhdyrazine administered to rabbits, caused the appearance of high plasma hemoglobin levels and hemoglobinuria as well as Heinz body formations and IgG binding to erythrocytes. This suggests that while in vitro the main mechanism of red cell removal seems to be phagocytoses, in vivo both intravascular hemolysis and phagocytosis are active processes. Preliminary biochemical studies on phenylhydrazine-exposed erythrocytes showed that together with the well-known appearance of Heinz bodies, methemoglobin and a drop in reduced glutathione, this drug also causes ATP depletion. This is initially concomitant with the appearance of ADP and AMP and subsequently hypoxantine. Thus, irreversible ATP depletion may contribute to the genesis of the hemolytic process observed in vivo.

Passive sodium and potassium movements in sickle erythrocytes

Deoxygenation causes an increase in passive Na and K movements across the membrane of the sickle erythrocyte. Some investigators find that these ion movements are accompanied by cell dehydration, while others find no evidence for cell water loss with sickling. Because gelation of hemoglobin S would be enhanced by cell water loss, we reinvestigated Na and K movements in sickle cells to define further the role that ion movements might play in the pathogenesis of sickling. With deoxygenation, we found that sickle cells gained Na and lost K without losing cell water. These net ion movements were not seen in control red blood cells. For sickle cells, deoxygenation also increased passive unidirectional influxes of Na and K, effects not observed when control red blood cells were deoxygenated. The deoxygenation-induced passive influxes of Na and K in sickle cells were not diminished by anion substitution or by the addition of the diuretic furosemide. We also found differences in passive Na and K fluxes between oxygenated sickle cells and normal red blood cells. The addition of furosemide or replacement of Cl with NO3 or SCN, maneuvers that largely reduced passive Na and K movements in oxygenated normal cells, had no effect on Na and K movements in oxygenated sickle cells. These findings militate against the idea that solute and water loss occur as a consequence of deoxygenation but do indicate that there are acquired membrane abnormalities in sickle red blood cells.

A further characterization of the selective K movements observed in human red blood cells following acetylphenylhydrazine exposure

Following brief exposure to acetylphenylhydrazine, the potassium permeability of the human erythrocyte membrane is selectively augmented. While a similar increase in potassium permeability results from the intracellular accumulation of calcium (the Gardos phenomenon), we have found a number of features that allow these two pathways to be distinguished from one another. The acetylphenylhydrazine pathway does not require calcium for its activation, and can be seen even in the presence of a molar excess of the calcium chelator EGTA. The transmembrane potassium movement via this channel has a specific requirement for the anion chloride, and it can be inhibited by furosemide. The potassium that moves through the Gardos pathway, on the other hand, can be accompanied by any permeant anion, and is inhibitable by quinidine or cetiedil. Thus, acetylphenylhydrazine exposure seems to promote K + Cl cotransport, whereas the Gardos pathway represents a potassium conductive channel. While full demonstration of both these pathways requires harsh in vitro manipulation, the large electrochemical potassium gradient favoring the movement of this cation out from the erythrocyte suggests that even a partial activation of either pathway could cause intracellular dehydration and thus contribute importantly to the pathophysiology of in vivo red cell destruction.