Shapes and shape changes in vitro in normal red blood cells

Structural changes in hemoglobin and glycation

Hemoglobin (Hb) is a hemeprotein found inside erythrocytes and is crucial in transporting oxygen and carbon dioxide in our bodies. In erythrocytes (Ery), the main energy source is glucose metabolized through glycolysis. However, a fraction of Hb can undergo glycation, in which a free amine group from the protein spontaneously binds to the carbonyl of glucose in the bloodstream, resulting in the formation of glycated hemoglobin (HbA1c), widely used as a marker for diabetes. Glycation leads to structural and conformational changes, compromising the function of proteins, and is intensified in the event of hyperglycemia. The main changes in Hb include structural alterations to the heme group, compromising its main function (oxygen transport). In addition, amyloid aggregates can form, which are strongly related to diabetic complications and neurodegenerative diseases. Therefore, this chapter discusses in vitro protocols for producing glycated Hb, as well as the main techniques and biophysical assays used to assess changes in the protein's structure before and after the glycation process. This more complete understanding of the effects of glycation on Hb is fundamental for understanding the complications associated with hyperglycemia and for developing more effective prevention and treatment strategies.

Molecular Study on Twin Cohort with Discordant Birth Weight

The increased rate of twinning has pointed out newer challenges in clinical practices related to gestational complications, intrauterine growth restriction, perinatal mortality, and comorbidities. As a twin pregnancy progresses, the increased demand for oxygen supply can easily disrupt the redox homeostasis balance and further impose a greater challenge for the developing fetuses. A substantial birth-weight difference acts as an indicator of a deficit in oxygenation or blood flow to one of the fetuses, which might be related to a low bioavailable nitric oxide level. Therefore, in this study, we focused on networks involved in the adjustment of oxygen supply, like the activation of inducible and endothelial nitric oxide synthase (NOS3) along with free radical and lipid peroxide formation in mature twin pairs with high birth-weight differences. The selected parameters were followed by immunofluorescence staining, fluorescence-activated cell sorting analysis, and biochemical measurements in the umbilical cord vessels and fetal red blood cells. Based on our data set, it is clear that the lower-weight siblings are markedly exposed to persistent intrauterine hypoxic conditions, which are connected to a decreased level in NOS3 activation. Furthermore, the increased level of peroxynitrite aggravates lipid peroxidation and induces morphological and functional damage and loss in redox homeostasis.

Effect of naproxen on the model lipid membrane formed on the water-chitosan subphase

Non steroidal anti-inflammatory drugs (NSAIDs) are those of the most common over the counter (OTC) medications widely used by millions of people every day. Unfortunately, despite their popularity those drugs can cause serious side effects in the digestive system (ulcers, bleeding, and pain). These inconveniences are caused by the changes in the structures of the outer phospholipid layers of gastric mucus and mucosa. As a result the H⁺ ions from the stomach acid can pass easily through these natural protective barriers and damage the epithelial cells which causes ulcers and bleeding. Chitosan as a polysaccharide known for its unique biocompatibility, drug delivery possibilities and wound healing effect has been chosen to examine if it can induce the reduction of undesirable effects of naproxen. This paper focuses on the interactions of the naproxen with a model biological membrane with and without the presence of chitosan. Applying the Langmuir technique coupled with the surface potential measurements and the Brewster angle microscope imaging allowed to characterize successfully examined systems in terms of the monolayer compressibility, thickness, stability, electric properties and morphology. The results proved that the presence of naproxen alters the mechanical and electrical properties of the model membrane depending on its surface pressure. Moreover, the addition of chitosan to the lipid-drug system causes significant changes in the properties of the layer, i.e. a reduction of its compressibility, thickness and morphology modification. Nevertheless, chitosan suppresses some changes induced by naproxen such as alteration of the apparent dipole moment and film stability.

Effects of osmolality and solutes on the morphology of red blood cells according to three-dimensional refractive index tomography

Phosphate-buffered saline (PBS) and Alsever's solution (AS) are frequently used as media in blood-related studies, while 0.9% normal saline (NS) is frequently used in transfusion medicine. Despite the frequent use, the effects of these solutions on the shape and volume of red blood cells (RBCs) have not been reported. We collected blood samples from five healthy adults and used three-dimensional refractive index tomography to investigate the changes in the morphology of RBCs caused by changes in osmolality and solutes at the single-cell level. After diluting 2 μL of RBCs 200-fold with each solution (PBS, AS, and 0.9% NS), 40 randomly selected RBCs were microscopically observed. RBC shape was measured considering sphericity, which is a dimensionless quantity ranging from 0 (flat) to 1 (spherical). RBCs in plasma or AS showed a biconcave shape with a small sphericity, whereas those in 0.9% NS or PBS showed a spherical shape with a large sphericity. Moreover, we confirmed that sodium chloride alone could not elicit the biconcave shape of RBCs, which could be maintained only in the presence of an osmotic pressure-maintaining substance, such as glucose or mannitol. Although 0.9% NS solution is one of the most commonly used fluids in hematology and transfusion medicine, RBCs in 0.9% NS or PBS are not biconcave. Therefore, as the debate on the use of NS continues, future clinical studies or applications should consider the effect of glucose or mannitol on the shape of RBCs.

Morphometry and Stiffness of Red Blood Cells—Signatures of Neurodegenerative Diseases and Aging

Human red blood cells (RBCs) are unique cells with the remarkable ability to deform, which is crucial for their oxygen transport function, and which can be significantly altered under pathophysiological conditions. Here we performed ultrastructural analysis of RBCs as a peripheral cell model, looking for specific signatures of the neurodegenerative pathologies (NDDs)—Parkinson’s disease (PD), amyotrophic lateral sclerosis (ALS) and Alzheimer’s disease (AD), utilizing atomic force (AFM) and conventional optical (OM) microscopy. We found significant differences in the morphology and stiffness of RBCs isolated from patients with the selected NDDs and those from healthy individuals. Neurodegenerative pathologies’ RBCs are characterized by a reduced abundance of biconcave discoid shape, lower surface roughness and a higher Young’s modulus, compared to healthy cells. Although reduced, the biconcave is still the predominant shape in ALS and AD cells, while the morphology of PD is dominated by crenate cells. The features of RBCs underwent a marked aging-induced transformation, which followed different aging pathways for NDDs and normal healthy states. It was found that the diameter, height and volume of the different cell shape types have different values for NDDs and healthy cells. Common and specific morphological signatures of the NDDs were identified.

Surface property induced morphological alterations of human erythrocytes

Microscopic investigations of any abnormality associated with erythrocyte/red blood cell morphology constitute an important segment of the age-old peripheral smear test. Though the test is conducted on a glass slide, the effect of glass and similar other solid substrates on erythrocyte morphology remained majorly unexplored. In the first of its kind investigation, we have outlined the effect of varying the substrate surface potential on erythrocyte morphology. Such a substrate induced phenomenon has been quantified for two distinctly different drying configurations (droplets and film) upon systematically varying the cell concentration. Experimental results and supporting theoretical analysis unambiguously show the surface potential of the solid substrate to be the most influential parameter in the process of morphological alteration. The findings of the present investigation may be utilized to formulate an error-free protocol for the baseline peripheral smear test of hematological diagnosis.

Atomic force microscopy: From red blood cells to immunohaematology

Atomic force microscopy (AFM) offers complementary imaging modes that can provide morphological and structural details of red blood cells (RBCs), and characterize interactions between specific biomolecules and RBC surface antigen. This review describes the applications of AFM in determining RBC health by the observation of cell morphology, elasticity and surface roughness. Measurement of interaction forces between plasma proteins and antibodies against RBC surface antigen using the AFM also brought new information to the immunohaematology field. With constant improvisation of the AFM in resolution and imaging time, the reaction of RBC to changes in the physico-chemistry of its environment and the presence of RBC surface antigen specific-biomolecules is achievable.

Changes in hemoglobin-oxygen affinity with shape variations of red blood cells

Shape variations of red blood cells (RBCs) are known to occur upon exposure to various drugs or under diseased conditions. The commonly observed discocytic RBCs can be transformed to echinocytic or stomatocytic shape under such conditions. Raman spectra of the three major shape variations, namely discocyte, echinocyte, and stomatocyte, of RBCs were studied while subjecting the cells to oxygenated and deoxygenated conditions. Analysis of the recorded spectra suggests an increased level of hemoglobin (Hb)-oxygen affinity for the echinocytes. Also, some level of Hb degradation could be noticed for the deoxygenated echinocytes. The effects may arise from a reduced level of intracellular adenosine triphosphate in echinocytic cells and an increased fraction of submembrane Hb.

Biconcave shape of human red-blood-cell ghosts relies on density differences between the rim and dimple of the ghost's plasma membrane

The shape of the human red blood cell is known to be a biconcave disk. It is evident from a variety of theoretical work that known physical properties of the membrane, such as its bending energy and elasticity, can explain the red-blood-cell biconcave shape as well as other shapes that red blood cells assume. But these analyses do not provide information on the underlying molecular causes. This paper describes experiments that attempt to identify some of the underlying determinates of cell shape. To this end, red-blood-cell ghosts were made by hypotonic hemolysis and then reconstituted such that they were smooth spheres in hypo-osmotic solutions and smooth biconcave discs in iso-osmotic solutions. The spherical ghosts were centrifuged onto a coated coverslip upon which they adhered. When the attached spheres were changed to biconcave discs by flushing with an iso-osmotic solution, the ghosts were observed to be mainly oriented in a flat alignment on the coverslip. This was interpreted to mean that, during centrifugation, the spherical ghosts were oriented by a dense band in its equatorial plane, parallel to the centrifugal field. This appears to be evidence that the difference in the densities between the rim and the dimple regions of red blood cells and their ghosts may be responsible for their biconcave shape.

Morphological and functional alteration of erythrocyte ghosts and giant unilamellar vesicles caused by Vipera latifi venom

Snake bites are an endemic public health problem in Iran, both in rural and urban area. Viper venom as a hemolytic biochemical "cocktail" of toxins, primarily cause to the systemic alteration of blood cells. In the sixties and seventies, human erythrocytes were extensively studied, but the mechanical and chemical stresses commonly exerted on red blood cells continue to attract interest of scientists for the study of membrane structure and function. Here, we monitor the effect of Vipera latifi venom on human erythrocytes ghost membranes using phase contrast and fluorescent microscopy and changes in ATPase activity under snake venom influence in vitro. The ion pumps [Na⁺,K⁺]-ATPase and (Ca²⁺+Mg²⁺)-ATPase plays a pivotal role in the active transport of certain cations and maintenance of intracellular electrolyte homeostasis. We also describe the interaction of Vipera latifi (VL) venom with giant unilamellar vesicles (GUVs) composed of the native phospholipid mixtures visualized by the membrane fluorescence probe, ANS, used to assess the state of membrane and specifically mark the phospholipid domains.

Structure and function in native and pathological erythrocytes: a quantitative view from the nanoscale

The red blood cells (RBCs) are among the most simple and less expensive cells to purify; for this reason and for their physiological relevance, they have been extensively studied with a variety of techniques. The picture that results is that these cells have several peculiarities including extreme mechanical performances, relatively simple architecture, biological relevance and predictable behavior that make them a perfect laboratory of testing for novel techniques, methodologies and ideas. These include the re-evaluation of old concepts, such as the relationship between structure and function (which is one of the guideline of this report) but considered at the cellular level. The studies reported on this paper, indeed, exploit the full potential of an high resolution quantitative microscopy such as the atomic force microscopy (AFM) to investigate different aspect of the erythrocytes' life, death and interaction with the environment. Indeed, the erythrocytes have a special relationship with the environment that is able to deeply influence their morphology as consequence of alteration of their biochemical or biophysical status. In this context the conditions under which the erythrocytes can be considered as biochemically programmable systems have been investigated by analyzing different environmentally induced alteration of the cell's morphology and comparing the results with naturally occurring pathological morphologies. This class of studies takes great advantage by the additional consideration of the nanomechanical properties of the cells. These latter are particularly important for the cell functionality and are shown to be of practical usefulness to discriminate and partition environmental effects charging different cellular structure (e.g. membrane or membrane-skeleton). Moreover, the development of novel morphological parameter can be important to push the level of investigation on the RBCs' status towards the molecular level. In particular, we describe the introduction and use of the plasma membrane roughness as a morphometric parameter of simple derivation from the AFM images and that results sensitive to the structural integrity of the cells' membrane-skeleton. This offer a remarkable opportunity to investigate the relationship between structure and function in normal and pathological cells by using a morphometric parameter that probes the cell surface at the nanoscale level. At last, a complex but physio-pathologically important phenomenon such as the erythrocytes aging was considered. To properly analyze the many variation that the cells experience during the whole aging path we used all the parameters that the AFM can provides: quantitative imaging, analysis of the membrane roughness and local measure of the nanomechanical properties analyzed together with biochemical parameter such as the ATP content. The picture that emerged is that the aging path is triggered by the ATP intracellular concentration that influence the membrane-skeleton structure and the support exerted on the plasma membrane. The consequences of the membrane-skeleton involvement can be monitored by AFM and showed the occurrence of peculiar morphologies and morphological defects that appear in the very place where the membrane-skeleton contact with the membrane became loose. As a whole, the collected data enable to describe the entire phenomenon as a sequence of morphological intermediates following one another along the aging path.

Protective effect of PEGylation against poly(amidoamine) dendrimer-induced hemolysis of human red blood cells

Poly(amidoamine) (PAMAM) dendrimers are widely used in medical applications. However, dendrimers bearing positively charged surface groups are prone to destabilize cell membrane and cause cell lysis. The lytic effect of dendrimers on red blood cells (RBCs) namely hemolysis is extremely dangerous when administered in vivo. To diminish the hematologic toxicity, we modified PAMAM dendrimers with poly(ethylene glycol) (PEG) of three molecular weights (2k, 5k, and 20k). The protective effect of PEGylation against PAMAM dendrimer-induced hemolysis was studied. RBCs morphology and surface structure were analyzed by optical microscopy (OM) and atomic force microscopy (AFM). The results indicated that PAMAM and PEG-2k modified dendrimers induced hemolysis at 0.1 and 0.5 mg/mL respectively, whereas PEG-5k and PEG-20k modified dendrimers showed no significant difference in hemolysis compared with control even at 5 mg/mL. OM and AFM investigation indicated PAMAM and PEG-2k modified dendrimers caused RBCs aggregation and lysis. However, no changes were observed in the overall shape of RBCs treated with PEG-5k and PEG-20k modified dendrimers. The surface roughness of RBCs treated with PEGylated dendrimers were far lower than that of RBCs treated with PAMAM dendrimers. This study demonstrated that hemocompatibility of PAMAM dendrimers could be greatly enhanced by PEGylation.

Erythrocyte-shape evolution recorded with fast-measurement NMR diffusion-diffraction

PURPOSE

To monitor red blood cell (RBC) shape evolution by (1)H(2)O diffusion-diffraction NMR in time steps comparable to those required for the acquisition of a (31)P NMR spectrum; thus, to correlate RBC mean diameter with ATP concentration after poisoning with NaF.

MATERIALS AND METHODS

Pulsed-field gradient-stimulated echo (PFGSTE) diffusion experiments were recorded on (1)H(2)O in RBC suspensions. Under conditions of restricted diffusion, q-space experiments report on mean RBC diameter. To decrease experiment time, the phase cycling of radiofrequency (RF) pulses was cut to two transients by using unbalanced pairs of gradient pulses. Data processing used a recent digital filter. Differential interference contrast (DIC) light microscopy also recorded shape changes. (31)P NMR spectroscopy gave estimates of mean ATP concentration.

RESULTS

NaF caused RBC-shape evolution from discocytes, through various forms of echinocytes, to spherocytes, over approximately 6 h and approximately 10 h at 37 degrees C and 25 degrees C, respectively. ATP declined to approximately 0.5 its normal concentration before the first stage of discocyte transformation; the concentration was 0.0 after approximately 1.5 h and 3.0 h, respectively, at the two temperatures.

CONCLUSION

RBC shape was readily monitored by NMR with a temporal resolution that was useful for correlations with both DIC microscopy and (31)P NMR spectra.

Roughness of the plasma membrane as an independent morphological parameter to study RBCs: a quantitative atomic force microscopy investigation

A novel approach to the study of RBCs based on the collection of three-dimensional high-resolution AFM images and on the measure of the surface roughness of their plasma membrane is presented. The dependence of the roughness from several parameters of the imaging was investigated and a general rule for a trustful analysis and comparison has been suggested. The roughness of RBCs is a morphology-related parameter which has been shown to be characteristic of the single cells composing a sample, but independent of the overall geometric shape (discocyte or spherocyte) of the erythrocytes, thus providing extra-information with respect to a conventional morphology study. The use of the average roughness value as a label of a whole sample was tested on different kinds of samples. Analyzed data revealed that the quantitative roughness value does not change after treatment of RBCs with various commonly used fixation and staining methods while a drastic decrease occurs when studying cells with membrane-skeletal alteration both naturally occurring or artificially induced by chemical treatments. The present method provides a quantitative and powerful tool for a novel approach to the study of erythrocytes structure through an ultrastructural morphological analysis with the potential to give information, in a non-invasive way, on the RBCs function.

Modeling normal and altered human erythrocyte shapes by a new parametric equation: Application to the calculation of induced transmembrane potentials

We present simple parametric equations in terms of Jacobi elliptic functions that provide a realistic model of abnormal variations in size which maintain the biconcave shape of a normal erythrocyte (anisocytosis) and abnormal variations in shape which maintain the original volume of the erythrocyte (poikilocytosis), as well as continuous deformations from the normal to the altered shapes. We illustrate our results with parameterizations of microcytes, macrocytes, and stomatocytes, and we apply these parameterizations to the numerical calculation of the induced transmembrane voltage in microcytes, macrocytes, and stomatocytes exposed to an external electromagnetic field of 1800 MHz.

Effect of tetracaine chlorhydrate on the mechanical properties of the erythrocyte membrane

Pharmacologically active agents that locate in the cell membrane are useful tools to investigate the interactions taking place between its molecular components. In the present work, the effect of tetracaine chlorhydrate (Tc) on the membrane mechanical properties of intact and desialated erythrocytes was studied. Our results evince the complex interaction between the drug and the membrane structures. The effect of Tc on erythrocyte shape suggests that this drug locates in the inner hemilayer of the lipid bilayer. Since Tc also modifies osmotic fragility and mechanical properties ascribed to the cytoskeleton, it can be inferred that the lipid bilayer has an effect on the rheology of the membrane, in a direct or indirect way, in this case through the close interaction with the structural proteins. Moreover, our results support the hypothesis of a second localization of the drug in the membrane, i.e., as monovalent cations intercalated among the glycocalix sialic endings, where it generates an effect superimposed on that produced from its typical site in the lipid bilayer.

Quasi-elastic light scattering from large anisotropic particles: application to the red blood cells

The usefulness of dynamic light scattering measurements for the determination of particle size and shape in suspensions of biological objects is well established. However, when the particle sizes are larger than the wavelength of the incident light, so that structural information on the scattering particles can be made available, the analysis of the correlation function of the scattered light requires a careful examination, owing to the problem involved in its theoretical description. In this note, dynamic light scattering techniques were employed for the determination of the size of human normal erythrocytes in physiological saline solution (isotonic solution) with the aim to discuss in detail the different effects that contribute to the scattered light intensity distribution and to evidentiate how correct information can be made available only when the anisotropic contribution to the translational diffusion coefficient of the erythrocyte cells is properly taken into account. In the case of erythrocytes, this effect produces deviation of the order of 8-10% in the evaluation of the cell size (the cell diameter and cell thickness) that can be accounted for by an appropriate dependence upon time of the autocorrelation function. Once the electric field autocorrelation function, where the intraparticle correlation function contains the correction for the anisotropic contribution, is considered, reasonable agreement was obtained between the data deduced from light scattering methods and those from scanning electron microscope pictures.

Pathways involved in trifluoperazine-, dibucaine- and praziquantel-induced hemolysis

This work elucidates differences in the hemolytic pathway developed by the antipsychotic trifluoperazine (TFP), the local anesthetic dibucaine (DBC) and the antihelminthic praziquantel (PZQ). Their partition coefficients (P) were measured at pH 7.4 between n-octanol, microsomes, liposomes, erythrocyte ghosts and n-octanol/water. The effective drug:lipid molar ratios for the onset of membrane solubilization (ReSAT) and complete hemolysis (ReSOL) were calculated from the experimental P values and compared with a classical surface-active compound treatment Lichtenberg, D. Biochim. Biophys. Acta 821 (1985) 470-478[. The contribution of charged/uncharged forms of TFP and DBC for the hemolytic activity was also analyzed. In all cases the hemolytic phenomena could be related to the monomeric drug insertion into the membrane. Only for TFP at isosmotic condition lysis occurs at concentrations beyond the CMC of the drug, indicating that micellization facilitates TFP hemolytic effect, while DBC and PZQ reach a real membrane saturation at their monomeric form.

Shapes of bilayer vesicles with membrane embedded molecules

The interdependence of the lateral distribution of molecules which are embedded in a membrane (such as integral membrane proteins) and the shape of a cell with no internal structure (such as phospholipid vesicles or mammalian erythrocytes) has been studied. The coupling of the lateral distribution of the molecules and the cell shape is introduced by considering that the energy of the membrane embedded molecule at a given site of the membrane depends on the curvature of the membrane at that site. Direct interactions between embedded molecules are not considered. A simple expression for the interaction of the membrane embedded molecule with the local membrane curvature is proposed. Starting from this interaction, the consistently related expressions for the free energy and for the distribution function of the embedded molecules are derived. The equilibrium cell shape and the corresponding lateral distribution of the membrane embedded molecules are determined by minimization of the membrane free energy which includes the free energy of the membrane embedded molecules and the membrane elastic energy. The resulting inhomogeneous distribution of the membrane embedded molecules affects the cell shape in a nontrivial manner. In particular, it is shown that the shape corresponding to the absolute energy minimum at given cell volume and membrane area may be elliptically non-axisymmetric, in contrast to the case of a laterally homogeneous membrane where it is axisymmetric.

The effects of palmitate on human erythrocyte membrane potential and osmotic stability

To evaluate the mechanism(s) of erythrocyte stabilization in hypotonic medium by free fatty acids, we have studied the effect of palmitic acid and its derivatives on human erythrocyte membrane electrochemical properties, osmotic stability and fluidity. Palmitic acid increased the membrane potential to the highest extent as compared with its derivatives. The membrane potential was equal to -11.0 +/- 1.7 mV in the absence and -23.3 +/- 3.2 mV in the presence of 400 mumol 1(-1) of palmitic acid, -15.3 +/- 2.2 mV in the presence of 400 mumol 1(-1) of methyl ester of palmitic acid and -14.2 +/- 1.8 mV in the presence of 400 mumol 1(-1) of lauric aldehyde. We propose that free fatty acids, containing the charged carboxylic end group, in contrast to the corresponding esters or aldehydes, can act as ionophores. At the same time, the osmotic stabilization of erythrocytes by palmitic acid and its derivatives was higher in sodium-containing as compared with potassium-containing media and did not correlate with the effect of these compounds on the membrane potential. We suggest that protective potassium leakage does not play a main role in erythrocyte osmotic stabilization by free fatty acids. Possibly this stabilization is due to the structural rearrangement of the whole membrane.

Do band 3 protein conformational changes mediate shape changes of human erythrocytes?

The bilayer-couple model predicts a reversible membrane crenation for an increasing ratio of external to internal monolayer area. This was comprehensively proven. However, individual erythrocytes may undergo dramatic shape changes within seconds when the suspension medium is changed. In contrast, under physiological conditions with no addition of membrane active compounds, active phospholipid translocation and passive flip-flops are comparatively slow. We propose that conformational changes of the anion-exchange protein, band 3, may rapidly alter the monolayer area ratio. Band 3 occupies about 10% of the total membrane area of human erythrocytes. Under physiological conditions, its conformers are asymmetrically distributed with about 90% of the transport sites facing the cytoplasm. This distribution is altered when external conformations are recruited by changing the transmembranous Cl- gradient, the external pH, or by the application of inhibitors. In experiments, recruitment by low ionic strength caused a rapid, temporary formation of echinocytes. This suspension effect could also be found at high ionic concentrations, when Cl- was replaced by SO4(2-). Inhibitors known to recruit the external band 3 conformation, like DIDS, SITS and flufenamic acid, are echinocytogenic. For inhibitors not recruiting a certain conformation, e.g. phenylglyoxal and niflumic acid, no shape effect was found. Since band 3 ensures a fast equilibrium of internal and external anions these ions are usually distributed according to the transmembrane potential (TMP). In the literature, a correlation of TMP and band 3 conformation, as well as a correlation of TMP and red cell shape, is described. In the proposed model, low external Cl- concentrations, inhibitors, or a negative TMP may recruit the transport sit outwards.(ABSTRACT TRUNCATED AT 250 WORDS)

Exercise, training and red blood cell turnover

Endurance training can lead to what has been termed 'sports anaemia'. Although under normal conditions, red blood cells (RBCs) have a lifespan of about 120 days, the rate of aging may increase during intensive training. However, RBC deficiency is rare in athletes, and sports anaemia is probably due to an expanded plasma volume. Cycling, running and swimming have been shown to cause RBC damage. While most investigators measure indices of haemolysis (for example, plasma haemoglobin or haptoglobin), RBC removal is normally an extravascular process that does not involve haemolysis. Attention is now turning to cellular indices (such as antioxidant depletion, or protein or lipid damage) that may be more indicative of exercise-induced damage. RBCs are vulnerable to oxidative damage because of their continuous exposure to oxygen and their high concentrations of polyunsaturated fatty acids and haem iron. As oxidative stress may be proportional to oxygen uptake, it is not surprising that antioxidants in muscle, liver and RBCs can be depleted during exercise. Oxidative damage to RBCs can also perturb ionic homeostasis and facilitate cellular dehydration. These changes impair RBC deformability which can, in turn, impede the passage of RBCs through the microcirculation. This may lead to hypoxia in working muscle during single episodes of exercise and possibly an increased rate of RBC destruction with long term exercise. Providing RBC destruction does not exceed the rate of RBC production, no detrimental effect to athletic performance should occur. An increased rate of RBC turnover may be advantageous because young cells are more efficient in transporting oxygen. Because most techniques examine the RBC population as a whole, more sophisticated methods which analyse cells individually are required to determine the mechanisms involved in exercise-induced damage of RBCs.

Computer simulation of a model network for the erythrocyte cytoskeleton

The geometry and mechanical properties of the human erythrocyte membrane cytoskeleton are investigated by a computer simulation in which the cytoskeleton is represented by a network of polymer chains. Four elastic moduli as well as the area and thickness are predicted for the chain network as a function of temperature and the number of segments in each chain. Comparisons are made with mean field arguments to examine the importance of steric interactions in determining network properties. Applied to the red blood cell, the simulation predicts that in the bilayer plane the membrane cytoskeleton has a shear modulus of 10 +/- 2 x 10(-6) J/m2 and an areal compression modulus of 17 +/- 2 x 10(-6) J/m2. The volume compression modulus and the transverse Young's modulus of the cytoskeleton are predicted to be 1.2 +/- 0.1 x 10(3) J/m3 and 2.0 +/- 0.1 x 10(3) J/m3, respectively. Elements of the cytoskeleton are predicted to have a mean displacement from the bilayer plane of 15 nm. The simulation agrees with some, but not all, of the shear modulus measurements. The other predicted moduli have not been measured.

Band 3 antagonists, p-azidobenzylphlorizin and DIDS, mediate erythrocyte shape and flexibility changes as characterized by digital image morphometry and microfiltration

Two nonpenetrating membrane probes, p-azidobenzylphlorizin (p-AzBPhz) and 4,4'-diisothiocyano-2,2'-stilbene disulfonate (DIDS), have been shown in earlier studies to induce dose-dependent changes in red blood cell (RBC) shape and volume at the same low concentrations that inhibit anion transport. In the present work, these ligand-induced morphology and rheology changes were studied using video digital image morphometry (VDIM) and microfiltration techniques. The results of these experiments corroborate our earlier investigation. RBCs were filmed using a Nomarski optics microscope with video camera attachment and cell size and shape changes were computer analyzed using VDIM. Low microM p-AzBPhz or DIDS levels caused collapse of the cell's biconcave structure and cell flattening occurred within 1-2 sec after drug exposure. Higher doses of either agent converted cells to a new steady-state in which a concurrent limited increase in erythrocyte volume and blunt membrane protrusions were produced. These changes were reversed in less than 2 sec by washing the drug from the membrane. Both ligands increased the deformability of RBCs in a dose-dependent manner as determined by filtration through Nuclepore polycarbonate filters (3 microns pore diameter). The improvement in deformability of drug-treated sickle cells was much more dramatic than for normal cells at low p-AzBPhz concentrations. These results support our earlier conclusions that the ligands, through a common interaction with band 3, induce volume-associated cytoskeletal alterations which lead to changes in morphology and flexibility.

pH-induced denaturation of spectrin changes the interaction of membrane proteins in erythrocyte ghosts. Biochemical and electron microscopic evidence

The influence of different buffer pH values on the properties of spectrin in erythrocyte ghosts and on isolated spectrin was investigated. Ultrastructural findings and the results of biochemical studies show that denaturation and aggregation of spectrin molecules rather than disulfide crosslinking are responsible for the precipitation of spectrin in acidic buffer. Since hemolysis in hypotonic buffer at pH 6.0 yields ghosts with spicules and microvesicles, the structure of spectrin in intact cells might also be changed and lead to the clustering of transmembrane proteins and the aggregation of components of the cytoplasmic network.

Response of the 23Na-NMR double-quantum filtered signal to changes in Na+ ion concentration in model biological solutions and human erythrocytes

Double quantum filtered (DQF) 23Na-NMR signals were evaluated as a function of [Na+] at constant temperature in two model systems (bovine serum albumin (BSA) and Ficoll 400) and in human red blood cells (RBCs). In model systems, the ratio of double quantum filtered to single quantum (SQ) signal intensities was independent of [Na+], even over a wide range of Na+/K+ ratios. Varying the DQF preparation time affected only the DQF signal intensity. In contrast, in human red blood cells (RBCs) the shape and phase of the DQF intracellular Na+ signal (Na+in) varied as a function of preparation time. Similar observations in cartilage [Eliav, U., Shinar, H. and Navon, G. (1992) J. Magn. Reson. 28, 223-229] have been attributed to the generation of a second- and a third-rank tensor by the DQF pulse sequence, resulting from Na+ ion ordering. By using a DQF sequence which isolates the second-rank tensor only, this component was found to originate from the intracellular Na+ ion pool in human RBCs, as well as from interactions of Na+ ions with the extracellular face of the plasma membrane. The residual quadrupolar splitting for the signal originating from the former environment was shown to be less than the SQ linewidth, explaining its absence in SQ spectra, and this was confirmed by two-dimensional DQF 23Na-NMR experiments. By isolating the contribution from the third-rank tensor exclusively, the ratio of DQF:SQ signal intensities for Na+in in human RBCs was shown to be constant over a 4-fold change in [Na+in] produced by addition of an ionophore (nystatin). This indicates that such changes in physiological state do not alter the efficiency of DQF signal generation in human RBCs.

Divalent cation binding to erythrocyte spectrin

Erythrocyte spectrin dimers and separated alpha- and beta-spectrin chains bound 45Ca2+ after electrophoresis on native or sodium dodecyl sulfate-polyacrylamide gels, blotting, and 45Ca2+ overlay. Flow dialysis and equilibrium dialysis revealed two binding components: high-affinity, Ca(2+)-specific sites with kd = 4 x 10(-7) M and n = 100 +/- 20 per dimer and a low-affinity (millimolar) divalent cation component. Whereas brain spectrin had only four high-affinity sites [Wallis, C. J., Wenegieme, E. F., & Babitch, J. A. (1992) J. Biol. Chem. 267, 4333-4337], erythrocyte spectrin had 25-fold more sites per dimer. In addition to possibly modifying spectrin interactions with calcium-dependent protease and actin, as suggested by previous work on the interaction of Ca2+ with brain spectrin, the approximately two high-affinity sites per repeating segment of erythrocyte spectrin appear to stabilize a folded conformation of repeat structures indicated by an entropy increase upon binding. These data support the hypothesis that divalent cation binding to erythrocyte spectrin has become specialized to stabilize the membrane skeletal network and the cell, making them flexible but resistant to shear under the stressful conditions of blood circulation.

Structural organisation of band 3 in Melanesian ovalocytes

The diffusional freedom of human erythrocyte band 3 (anion exchanger 1) has been measured in membranes from normocytic and ovalocytic erythrocytes. A dramatic reorganisation of band 3 in the ovalocyte membranes is indicated by a markedly restricted rotational mobility. Extraction of spectrin from erythrocyte membranes had no effect on normocyte band 3 mobility, but partially relieved the restrictions on ovalocyte band 3 mobility. Further removal of ankyrin and band 4.2 resulted in an increase in the rotational mobility of both ovalocyte and normocyte band 3 to similar levels. The results suggest that the molecular basis of the unusual shape and decreased deformability of ovalocytes resides in an altered interaction of band 3 with one or more of the peripheral proteins. We present a model which illustrates a possible role for band 3 aggregation in controlling erythrocyte deformability.