Erythrocyte Membrane Alterations in β -Thalassaemia

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

Microfluidic analysis of blood has potential clinical value for determining normal and abnormal erythrocyte deformability. To determine if a microfluidic device could reliably measure intra- and inter-personal variations of normal and oxidized human red blood cell (RBC), venous blood samples were collected from repeat donors over time. RBC deformability was defined by the cortical tension (pN/µm), as determined from the threshold pressure required to deform RBC through 2-2.5 μm funnel-shaped constrictions. Oxidized RBC were prepared by treatment with phenazine methosulphate (PMS; 50 µM). Analysis of the control and oxidized RBC demonstrated that the microfluidic device could clearly differentiate between normal and mildly oxidized (20.13 ± 1.47 versus 27.51 ± 3.64 pN/µm) RBC. In vivo murine studies further established that the PMS-mediated loss of deformability correlated with premature clearance. Deformability variation within an individual over three independent samplings (over 21 days) demonstrated minimal changes in the mean pN/µm. Moreover, inter-individual variation in mean control RBC deformability was similarly small (range: 19.37-21.40 pN/µm). In contrast, PMS-oxidized cells demonstrated a greater inter-individual range (range: 25.97-29.90 pN/µm) reflecting the differential oxidant sensitivity of an individual's RBC. Importantly, similar deformability profiles (mean and distribution width; 20.49 ± 1.67 pN/µm) were obtained from whole blood via finger prick sampling. These studies demonstrated that a low cost microfluidic device could be used to reproducibly discriminate between normal and oxidized RBC. Advanced microfluidic devices could be of clinical value in analyzing populations for hemoglobinopathies or in evaluating donor RBC products post-storage to assess transfusion suitability.

Na, K ATPase ?3 subunit (CD298): association with ? subunit and expression on peripheral blood cells

Beta3 subunit is described as one of the Na, K ATPase subunits. Recently, we generated a monoclonal antibody (mAb), termed P-3E10. This mAb was shown to react with the Na, K ATPase beta3 subunit or CD298. By immunofluorescence analysis using mAb P-3E10, it was found that all peripheral blood leukocytes express Na, K ATPase beta3. The presence of beta3 subunit on leukocytes is not in a quantitative polymorphic manner. Upon phytohemagglutinin or phorbol myristate acetate activation, the expression level of the Na, K ATPase beta3 subunit on activated peripheral blood mononuclear cells was not altered in comparison with those of unstimulated cells. Red blood cells (RBCs) of healthy donors showed negative reactivity with mAb P-3E10. However, more than 80% of thalassemic RBCs showed positive reactivity. By immunoprecipitation, moreover, a protein band of 55-65 kDa was precipitated from normal RBC membrane using mAb P-3E10. These results evidenced that the beta3 subunit of Na, K ATPase is expressed on RBC membrane but the epitope recognized by mAb P-3E10 is hidden in normal RBCs. Furthermore, we showed the association of beta3 subunit and alpha subunit of Na, K ATPase. This information is important for further understanding of the functional roles of this molecule.

Redox imbalance, macrocytosis, and RBC homeostasis

The erythrocyte represents a major component of the antioxidant capacity of the blood through the enzymes contained in the cell, the glutathione system, and the low-molecular-weight antioxidants of the erythrocyte membrane. A further major red blood cell contribution is in regenerating consumed redox equivalents via the oxidative pentose phosphate pathway and glutathione reductase. Moreover, its extracellular antioxidant capacity, its mobility, and the existence of reducing equivalents far in excess of its normal requirements make erythrocytes function as an effective oxidative sink in the organism. That is why red blood cell metabolism and homeostasis strongly affect the antioxidant properties of the whole body. Conversely, the relation between macrocytosis and oxidative stress has not been fully delineated. Reviewing the mechanisms involved in red blood cell homeostasis in cases of redox imbalance is crucial in identification of factors that could potentially improve erythrocyte survival and defense against oxidant damage.

Effect of coenzyme Q10 as an antioxidant in beta-thalassemia/Hb E patients

Thalassemia is a group of genetic disorders resulting from different mutations in the globin gene complex and leading to an imbalance in globin synthesis. Unmatched globin chains are less stable and susceptible to oxidation. Patients with beta-thalassemia/HbE are prone to increased oxidative stress as indicated by increased lipid peroxidation product, malondialdehyde (MDA), partly because of the presence of iron in the form of heme and hemichromes released from excess globin chains and excess iron deposition in various tissues. The level of antioxidant such as glutathione is markedly decreased while activities of antioxidant enzymes including superoxide dismutase (SOD), catalase, and glutathione peroxidase (GSH-Px) are increased. We have recently found that the levels of coenzyme Q(10) (CoQ(10)) are also very low in thalassemia. We therefore evaluated the oxidative stress and the antioxidants in these patients before and after supplementation with 100 mg CoQ(10) daily for 6 months. The results showed that the plasma level of CoQ(10) significantly increased and the oxidative stress decreased as the level of MDA declined. The administration of CoQ(10) led to significant improvement of biochemical parameters of antioxidant enzymes. The antioxidant supplementation will be beneficial for thalassemia patients as adjunct therapy to increase their quality of life.

Oral supplements of vitamin E improve measures of oxidative stress in plasma and reduce oxidative damage to LDL and erythrocytes in beta-thalassemia intermedia patients

Fifteen beta-thalassemia intermedia patients, not requiring chronic transfusional therapy, were monitored in order to check their antioxidant status, and the lipid oxidation products in plasma, LDL, and erythrocytes before and during a 9-month oral treatment with 600 mg/day vitamin E. The low level of vitamin E, and high level of malondialdehyde in plasma clearly tended to normalize after three months (P < .001), and were quite similar to control after six months. The abnormally low level of vitamin E in LDL and the four times higher than control basal level of conjugated dienes (LDL-CD), were not modified after three months of treatment. Significant changes of LDL-VE (P < .05) and of the basal LDL-CD (P < .001) were evident after six months. LDL-VE was within the normal range after nine months, whereas LDL-CD still appeared twice as higher than control. Plasma vitamin A, ascorbate, beta-carotene, and lycopene increased markedly at the end of the trial (P < .005). The level of vitamin E in red blood cells was normalized after six months of supplementation. A decrease of the baseline value of conjugated dienes was observed after nine months, although it remained 1.4-fold higher than control. The RBC count and hematocrit appeared higher at the end of the trial (P < .05 and P < .001, respectively). The hemoglobin value did not show variations. A shift to normal of the resistance of erythrocytes to osmotic lysis was observed. Our findings provide evidence that an oral treatment with vitamin E improves the antioxidant/oxidant balance in plasma, LDL particles, and red blood cells, and counteracts lipid peroxidation processes in beta-thalassemia intermedia patients.

Impairment of Plasmodium falciparum Growth in Thalassemic Red Blood Cells: Further Evidence by Using Biotin Labeling and Flow Cytometry

Certain red blood cell (RBC) disorders, including thalassemia, have been associated with an innate protection against malaria infection. However, many in vitro correlative studies have been inconclusive. To better understand the relationship between human RBCs with thalassemia hemoglobinopathies and susceptibility to in vitro infection, we used an in vitro coculture system that involved biotin labeling and flow cytometry to study the ability of normal and variant RBC populations in supporting the growth of Plasmodium falciparum malaria parasites. Results showed that both normal and thalassemic RBCs were susceptible to P falciparum invasion, but the parasite multiplication rates were significantly reduced in the thalassemic RBC populations. The growth inhibition was especially marked in RBCs from -thalassemia patients (both -thalassemia1/-thalassemia2 and -thalassemia1 heterozygote). Our observations support the contention that thalassemia confers protection against malaria and may explain why it is more prevalent in malaria endemic areas.

Impairment of Plasmodium falciparum Growth in Thalassemic Red Blood Cells: Further Evidence by Using Biotin Labeling and Flow Cytometry

Certain red blood cell (RBC) disorders, including thalassemia, have been associated with an innate protection against malaria infection. However, many in vitro correlative studies have been inconclusive. To better understand the relationship between human RBCs with thalassemia hemoglobinopathies and susceptibility to in vitro infection, we used an in vitro coculture system that involved biotin labeling and flow cytometry to study the ability of normal and variant RBC populations in supporting the growth of Plasmodium falciparum malaria parasites. Results showed that both normal and thalassemic RBCs were susceptible to P falciparum invasion, but the parasite multiplication rates were significantly reduced in the thalassemic RBC populations. The growth inhibition was especially marked in RBCs from -thalassemia patients (both -thalassemia1/-thalassemia2 and -thalassemia1 heterozygote). Our observations support the contention that thalassemia confers protection against malaria and may explain why it is more prevalent in malaria endemic areas.

Pathophysiology of thalassaemia

Most of the major clinical manifestations of the beta-thalassaemias can be related to the deleterious effects of imbalanced globin chain synthesis on erythroid maturation and red cell survival. The destruction of red cell progenitors and their progeny results from an extremely complex series of mechanisms all related to the presence of excess alpha-globin chain production. These include mechanical damage, interference with cell division and oxidative destruction of both organelles and components of the red cell membrane. The unequal distribution of gamma-globin chains between different precursors, and the intense selection of those with relatively higher levels of gamma chain production, lead to an extremely heterogeneous cell population in the peripheral blood. Iron overload, due to increased gastrointestinal absorption and blood transfusion is the major cause of tissue damage, morbidity and death.

Thalassaemia trait, red blood cell age and oxidant stress: effects on Plasmodium falciparum growth and sensitivity to artemisinin

Knowledge of innate mechanisms of protection against malaria could be used to bolster the existing limited treatments. Oxidant stress may play a role in the protective mechanism and the effect of red blood cell (RBC) age has recently been recognized. This study investigated the role of oxidant stress in the protection against malaria in thalassaemic trait RBC (alpha and beta) using an experimental approach which controlled for cell age. 'Young', 'intermediate' and 'old' RBC obtained by Percoll fractionation and whole blood were used to set up malaria cultures. Antioxidants (vitamin E and dithiothreitol) and pro-oxidants (riboflavin, menadione and artemisinin) were added to modulate oxidant stress effect. Antioxidants improved parasite growth. The degree of improvement was significantly greater with increasing RBC age (P < 0.0001), and relatively greater in thalassaemic RBC (P < 0.0001). Pro-oxidants had a parasiticidal effect. With the exception of the 'old' RBC fraction, the median inhibitory concentration (IC50) for riboflavin and menadione was significantly higher in normal RBC. In contrast, the IC50 for artemisinin was significantly higher in 'old' thalassaemic RBC but was similar in the 'young' and 'intermediate' fractions and whole blood. These findings suggest that oxidant stress plays a role in mediating the protection against malaria in thalassaemic RBC. Vitamin E and other antioxidant supplementation could feasibly exacerbate clinical malaria. Conversely, pro-oxidant agents could act as useful adjuvants to therapy. It is important to confirm the reduced sensitivity to artemisinin in 'old' thalassaemic trait RBC, as such an effect may promote selective pressure for the emergence of resistant parasite strains with widespread use of artemisinin.

Invasion and growth of Plasmodium falciparum is inhibited in fractionated thalassaemic erythrocytes

Epidemiological and clinical studies have indicated that the thalassaemias may confer protection against malaria. The study reported here investigated this protective effect in vitro, using a new approach which controls for the potential effect of red cell size and age on the virulence of the parasite. A Percoll density gradient method was used to separate alpha- and beta-thalassaemic trait, haemoglobin H and normal red blood cells (RBC) into fractions of different density. Correlations between RBC density, age and size in fractions of all genotypes were established using red cell creatine as an index of cell age. The development of Plasmodium falciparum over 3 erythrocytic cycles (144 h) in whole blood as well as fractionated samples was monitored by slide microscopy and flow cytometry. A significantly reduced rate of parasite invasion and growth was demonstrated in RBC from all thalassaemic genotypes tested. Poor reinvasion rates were noted in the second and third cycles. Increased duration of culture and red cell age also had a greater negative impact on parasite growth in thalassaemic RBC. This poor growth rate was also associated with the arrest of parasite growth at the schizont stage (schizont maturation arrest) and the accumulation of abnormal, trophozoite/schizont stage parasites in the older thalassaemic RBC fractions. These findings suggest a defect in the number and viability of merozoites generated by parasites growing in thalassaemic RBC. Age related factors such as oxidant stress may play a key role in mediating this kind of protective mechanism and deserve further investigation.

Copper-specific damage in human erythrocytes exposed to oxidative stress

Ascorbate and complexes of Cu(II) and Fe(III) are capable of generating significant levels of oxygen free radicals. Exposure of erythrocytes to such oxidative stress leads to increased levels of methemoglobin and extensive changes in cell morphology. Cu(II) per mole is much more effective than Fe(III). However, isolated hemoglobin is oxidized more rapidly and completely by Fe(III)- than by Cu(II)-complexes. Both Fe(III) and Cu(II) are capable of inhibiting a number of the key enzymes of erythrocyte metabolism. The mechanism for the enhanced activity of Cu(II) has not been previously established. Using intact erythrocytes and hemolysates we demonstrate that Cu(II)-, but not Fe(III)-complexes in the presence of ascorbate block NADH-methemoglobin reductase. Complexes of Cu(II) alone are not inhibitory. The relative inability of Fe(III)-complexes and ascorbate to cause methemoglobin accumulation is not owing to Fe(III) association with the membrane, or its failure to enter the erythrocytes. The toxicity of Cu(II) and ascorbate appears to be a result of site-specific oxidative damage of erythrocyte NADH-methemoglobin reductase and the enzyme's subsequent inability to reduce the oxidized hemoglobin.

Increased susceptibility of microcytic red blood cells to in vitro oxidative stress

Oxidative damage to erythrocytes in thalassaemia has been related to generation of free radicals by an excess of denaturated alpha- or beta-globin chains, intracellular iron overload and low concentration of normal haemoglobin (HGB). Two good indicators of such oxidative damage are the high red blood cell (RBC) malonyldialdehyde (MDA) production detected following exogenous oxidant stress and the decrease of pyrimidine 5'-nucleotidase (P5N), the most sensitive enzyme to SH-group damage in vivo. Conflicting data, however, have so far accumulated in the literature concerning differences in oxidative damage between the different forms of thalassaemia and iron deficiency anaemia (IDA). In the present study, oxidative susceptibility, as defined by the production of MDA in vitro and antioxidant capacity, as measured by the activity of RBC glutathione peroxidase (GPx), superoxide dismutase (SOD) and by reduced glutathione (GSH), have been studied in microcytic RBCs from patients with beta-thalassaemia trait, Spanish (delta beta) zero-thalassaemia heterozygotes (delta beta-thalassaemia trait) and iron deficiency anaemia (IDA). The results are consistent with the existence of significant differences in the severity and pattern of oxidative stress susceptibility between beta-thalassaemia trait (increased MDA production and higher SOD and GPx activities) and the other two forms of microcytosis (delta beta thalassaemia trait and IDA). Furthermore, the finding of normal P5' N activity in delta beta thalassaemia trait, gives further support to the less intense peroxidative environment of RBCs in this form of thalassaemia when compared to beta-thalassaemia trait, characterized by acquired RBC P5' N deficiency due to oxidative damage.

In vivo metabolic studies of glucose, ATP and 2,3-DPG in beta-thalassaemia intermedia, heterozygous beta-thalassaemic and normal erythrocytes: 13C and 31P MRS studies

13C and 31P magnetic resonance spectroscopy was used to characterize the in vivo kinetics of glucose metabolism and intracellular ATP and 2,3-DPG concentrations in erythrocytes obtained from beta-thalassaemia intermedia, heterozygous beta-thalassaemic and normal individuals and maintained in suspension. Except for an upfield chemical shift in the 2P and 3P resonance of 2,3-DPG in the thalassaemia intermedia erythrocytes, the 31P spectra were comparable between all three blood types, showing similar concentrations of ATP (from 4.5 to 5.2 mumol/g Hb) and 2,3-DPG (from 17.2 to 19.7 mumol/g Hb). However, the profile of glucose metabolism was quite different in beta-thalassaemia intermedia erythrocytes, whereas glucose was consumed at a rate of 0.089 +/- 0.035 fmol/cell/h, significantly higher than that of normal (0.032 +/- 0.018 fmol/cell/h; P = 0.01) and heterozygous (0.025 +/- 0.004 fmol/cell/h; P = 0.01) erythrocytes. This near 3-fold faster rate of glucose metabolism in the thalassaemia intermedia erythrocytes could not be accounted for by any increase in glucose flux via the Embden-Meyerhof pathway, since no significant difference in 3-13C-lactate synthesis was observed among the three blood types (in units of fmol/cell/h, normal, 0.021 +/- 0.013; heterozygous, 0.021 +/- 0.006; beta-thalassaemia intermedia 0.045 +/- 0.025). These results reflect an accelerated rate of glucose metabolism in thalassaemia intermedia erythrocytes because the contribution of reticulocytes to this altered pattern of metabolism could be excluded. As the only other route of glucose metabolism in erythrocytes is the pentose phosphate pathway (PPP), these results indicate that the PPP is more active in beta-thalassaemia intermedia erythrocytes, perhaps as a consequence of their elevated intracellular oxidative state.

The membrane defect in hereditary stomatocytosis

Hereditary stomatocytosis and allied conditions represent a series of diseases in which abnormal movements of univalent cations across the plasma membrane play an important part in cellular disease. The primary problem lies not in the active transporters but in the basal permeability of the membrane, which is always increased, and the extent of the increase correlates with the cellular dysfunction. A number of structural abnormalities have been described in these membranes, but the most consistent and convincing is the deficiency of a hitherto uncharacterized integral membrane protein of molecular weight 31 kDa in the severe, 'overhydrated' form of the disease. The true function of this protein remains enigmatic, but its deficiency in this condition indicates that it may have a role in the regulation of cation transport.

Laboratory diagnosis of hemoglobinopathies

Diagnostic tests for most common hemoglobinopathies and recent advances in structural analysis of variant hemoglobins are reviewed. Routine and newly introduced methods that apply to the diagnosis of sickle cell anemia, thalassemia and the hemoglobin E disorders are presented. A brief description of the clinical course for each of these disorders is given, and potential pitfalls in diagnosis are discussed. Application of high-performance liquid chromatography and various mass spectrometric techniques (electrospray ionization mass spectrometry, liquid secondary ion mass spectrometry, and tandem mass spectrometry) for evaluation of hemoglobinopathy is presented.

Erythrophagocytosis in malaria: Host defence or menace to the macrophage?

Macrophages in the host's bloodstream and tissue serve as a first line of defence during infection with Plasmodium. While the killing effect of these cells on parasites has been investigated extensively, relatively little is known about the phagocytosis of infected red blood cells. In this article, Paolo Arese and Franca Turrini have joined Hagai Ginsburg to address the perplexing relationships between the macrophage and the malaria-infected red blood cell. They suggest that the same molecular mechanisms that normally operate to remove senescent or damaged red blood cells also operate during malaria, although the parasite may indirectly cause the destruction of macrophages.

Fate of alpha-hemoglobin chains and erythrocyte defects in beta-thalassemia

The fate of alpha-hemoglobin chains and the cause of membrane protein defects in thalassemic erythrocytes have been studied in: (1) human beta-thalassemia syndromes, (2) mouse beta-thalassemia, and (3) normal human erythrocytes loaded with purified alpha-hemoglobin chains. The similarity and differences observed in these three systems underline the importance of insoluble alpha chains and the direct relationship between the amount of these chains and the membrane protein defects. Indeed, in addition to the alpha/non-alpha ratio of globin chain synthesis, the proteolysis and instability of alpha chains are major factors in modulating the cellular defects.

Differences in the pathophysiology of hemolysis of alpha- and beta-thalassemic red blood cells

The basic pathology in all forms of thalassemia results from the presence of excess unstable globin chains within the pathological RBC, but the pattern and rate of their precipitation is different. Consequently, their effects on the RBC membrane components are not the same and may account for the different rheological properties that have been found. It is possible that the damage incurred by excess beta chains in Hb H disease is primarily due to the direct interaction of the large inclusions with some cytoskeletal proteins such as spectrin, ankyrin, and band 3. In beta-thalassemia, where excess unstable alpha chains have already precipitated in young erythroblasts, the main damage might be caused by an excess of free oxygen radicals, which affect in particular protein 4.1. A search for additional changes and for potential differences in the membrane and cellular properties between the different thalassemic syndromes is warranted in order to understand better the different clinical expression in the various types of the disease. Moreover, when there is a better elucidation of the mechanisms by which the RBC are destroyed, one may look for possible ways and means to prevent these changes, with a consequent extension of the current short life span of the affected RBC.

Spectrin modifications in a heterozygous case of both hereditary elliptocytosis and beta-thalassemia

The clinical and hematological parameters of a patient described here, who inherited the genes of both hereditary elliptocytosis (HE) and beta-thalassemia, seem to reflect a mutual enhancement of the two diseases. The coexistence of the two pathologies is probably also responsible for the observed changes in spectrin: the appearance of an extra spectrin band between tetramers and dimers on denaturing gel electrophoresis and the metabolic-dependent reduction in spectrin amount. It is assumed that the instability of the skeletal network that results from the HE pathology caused increased exposure of the spectrin molecule to oxidative damage that usually occurs in thalassemic red cells. The products of such oxidation may have led to abnormal spectrin associations which finally resulted in the above changes.

Unstable hemoglobins

About 70 variants of Hb A with associated hemolytic disorders have been reported during the past 30 years. I have classified them according to four grades of severity of chronic hemolysis. Acute episodes of severe hemolysis may be seen in all classes. In addition, some 80 variants without overt hemolysis have given positive results with in vitro hemoglobin instability tests. The stereochemical bases for instability can be conjectured in most cases, although few unstable hemoglobins have actually been studied by X-ray crystallography. The mechanisms for denaturation of normal Hb A and its acceleration in unstable hemoglobins were proposed some 15 years ago. The alterations of membrane lipids and proteins leading to red cell senescence and the relevance of hemoglobin denaturation to this process are presently being investigated. Several "hyperunstable" variants are clinically silent, or equivalent to a thalassemia, probably because of very efficient degradation of the abnormal chains.

Oxidative damage to human red cells induced by copper and iron complexes in the presence of ascorbate

The role of trace metals in the generation of free radical mediated oxidative stress in normal human red cells was studied. Ascorbate and either soluble complexes of Cu(II) or Fe(III) provoked changes in red cell morphology, alteration in the polypeptide pattern of membrane proteins, and significant increases in methemoglobin. Neither ascorbate nor the metal complexes alone caused significant changes to the cells. The rate of methemoglobin formation was a function of ascorbate and metal concentrations, and the chemical nature of the chelate. Cu(II) was about 10-times more effective than Fe(III) in the formation of methemoglobin. Several metals were tested for their ability to compete with Cu(II) and Fe(III). Only zinc caused a significant inhibition of methemoglobin formation by Fe(III)-fructose. These observations suggest that site-specific as well as general free radical damage is induced by redox metals when the metals are either bound to membrane proteins or to macromolecules in the cytoplasm. The Cu(II) and Fe(III) function in two catalytic capacities: (1) oxidation of ascorbate by O2 to yield H2O2, and (2) generation of hydroxyl radicals from H2O2 in a Fenton reaction. These mechanisms are different from the known damage to red cells caused by the binding of Fe(III) or Cu(II) to the thiol groups of glucose-6-phosphate dehydrogenase. Our system may be a useful model for understanding the mechanisms for oxidative damage associated with thalassemia and other congenital hemolytic anemias.

Alteration in protein kinase C activity and subcellular distribution in sickle erythrocytes

In agreement with previous data, membrane protein phosphorylation was found to be altered in intact sickle cells (SS) relative to intact normal erythrocytes (AA). Similar changes were observed in their isolated membranes. The involvement of protein kinase C (PKC) in this process was investigated. The membrane PKC content in SS cells, measured by [3H]phorbol ester binding, was about 6-times higher than in AA cells. In addition, the activity of the enzyme, measured by histone phosphorylation was also found to be increased in SS cell membranes but decreased in their cytosol compared to the activity in AA cell membranes and cytosol. The increase in membrane PKC activity was observed mostly in the light fraction of SS cells, fractionated by density gradient, whereas the decrease in cytosolic activity was only observed in the dense fraction. PKC activity, measured in cells from the blood of reticulocyte-rich patients, exhibited an increase in both membranes and cytosol, thus explaining some of the effects observed in the SS cell light fraction, which is enriched in reticulocytes. The increase in PKC activity in the membranes of SS cells is partly explained by their young age but the loss of PKC activity in their cytosol, particularly in that of the dense fraction, seems to be specific to SS erythrocytes. The relative decrease in membrane PKC activity between the dense and the light fractions of SS cells might be related to oxidative inactivation of the enzyme.

Cation transport in oxidant-stressed human erythrocytes: heightened N-ethylmaleimide activation of passive K+ influx after mild peroxidation

Normal and chronically dehydrated (hereditary xerocytosis) human red cells were subjected to mild peroxidative treatment (315 microM hydrogen peroxide (H2O2), 15 min) in the presence of azide. The subsequent expression of passive (ouabain-resistant) K+ transport activities was analyzed by measurement of 86Rb+ influx. Peroxidation of normal red cells did not affect basal K+ transport activity, but the increment in K+ influx elicited by 0.5 mM N-ethylmaleimide (NEM) was increased 3-fold. The enhanced K+ influx was chloride-dependent, but only partially inhibited by 0.1 mM furosemide. Stimulated activity declined progressively after NEM activation, but could be restored by a second NEM treatment. Prior conversion of hemoglobin to the carbonmonoxy form abolished the response to peroxide, while 200 microM butylated hydroxytoluene (BHT) exerted only partial inhibition, suggesting that the effect of H2O2 requires interaction of activated, unstable hemoglobin species with the membrane, but that lipid peroxidation is not sufficient. Peroxidation following NEM treatment also enhanced NEM activation, indicating that enhancement does not require altered NEM reactions with stimulatory or inhibitory sites. Passive K+ transport in hereditary xerocytosis red cells was not activated by NEM, with or without H2O2 pretreatment. The results demonstrate that modest peroxidative damage to red cells can heighten the activation of a transport system that is thought to be capable of mediating net K+ efflux and volume reduction in cells that express it. Models are proposed in which the effects of NEM, H2O2, cell swelling and other factors are mediated by conformational changes in a postulated subpopulation of anion channel (Band 3) molecules that bind the K+ transporter.

The distribution and aggregatability of intramembrane particles in phenylhydrazine-treated human erythrocytes

Freeze-fracture analysis of phenylhydrazine-treated, unfixed human erythrocytes showed a random distribution of intramembrane particles both over membrane-bound Heinz-bodies and in the intervening areas when examined after fast freezing in liquid propane. The same results was obtained when unfixed, glycerinated red cells were frozen in liquid Freon. In contrast to previously published data (Low et al. (1985) Science 227, 531-533) these results indicate that binding of Heinz-bodies to the red cell membrane cannot cause morphologically detectable clustering of Band 3 in phenylhydrazine-treated red cells. Over numerous Heinz-bodies a decreased Acridine orange-induced particle aggregation was observed. The phenomenon of the oxidant-induced red cell fluorescence is described.

Modulation of iron-mediated oxidant damage in erythrocytes by cellular energy levels

In this work we have investigated the effects of iron-induced oxidative stress on erythrocytes and their membranes, the importance of haemoglobin oxidation and of the maintenance of the metabolic properties of the cells. The results show that by maintaining the energy requirements of the erythrocyte, methaemoglobin production is minimised under conditions of iron-stress. However, in this situation, the membranes of the erythrocytes become more susceptible to the oxidative damage and increased lipid peroxidation ensues.

Clinical disorders of the red cell membrane skeleton

The lipid bilayer of the adult red cell is supported on its inner surface by a complex arrangement of proteins known as the membrane skeleton. This filamentous network, a major component of which is a multifunctional protein called spectrin, has an essential role in determining the shape, structural integrity, and deformability of the red cell. A significant achievement of modern biochemistry and hematology has been the elucidation of the organization of the components of the membrane skeleton and their relationship to other membrane proteins and lipids. This article reviews current concepts of membrane skeleton structure and function and emphasizes recent advances which have been made in characterizing and classifying molecular defects of the skeleton which manifest clinically with changes in the shape and stability of the red cell. The pathobiology of hereditary skeletal defects associated with hereditary spherocytosis (HS), hereditary elliptocytosis (HE), and hereditary pyropoikilocytosis (HPP) are comprehensively discussed. Secondary defects of the membrane skeleton occurring in glucose-6-phosphate dehydrogenase deficiency and sickle cell anemia are also briefly considered.

Erythrophagocytosis in vivo in sickle cell anemia

Recent observations that the sickle RBC are excessively susceptible to phagocytosis by macrophages in vitro prompted me to look for evidence of in vivo erythrophagocytosis (Ep) in patients with sickle cell anemia (SS). Freshly prepared smears of unmanipulated blood of 27 patients with SS in steady state were examined for Ep by a 500-cell differential white blood cell (WBC) count performed in duplicate. Ten of 27 (37%) SS patients showed Ep (1-6/1,000 WBC or 1-10/100 monocytes). By contrast, no Ep was found in similarly prepared blood smears of 25 normal adult controls and nine splenectomized subjects. The mean hemotocrit value of the Ep(+) SS patients was significantly lower than that of the Ep(-) patients (21.0 +/- 1.7% vs 24.0 +/- 2.7% p less than 0.01). Considering the rarity of spontaneous Ep in unmanipulated blood from normal subjects and the relative insensitivity of the method used, the finding of Ep in over one third of SS patients indicates a significant membrane injury of the sickle RBC and serves to validate the in vitro observations. The possible role of the "senescence" mechanism in the induction of Ep is discussed.