Altered membrane structure and surface potential in homozygous hemoglobin C erythrocytes

Elucidating the binding properties of methemoglobin in red blood cell to cyanide, hydrosulfide, and azide ions using artificial red blood cell

Methemoglobin (metHb), the oxidized form of hemoglobin, lacks the ability of reversible oxygen binding; however, it has a high binding affinity to toxic substances such as cyanide, hydrosulfide, and azide. This innate property of metHb offers the clinical option to treat patients poisoned with these toxins, by oxidizing the endogenous hemoglobin in the red blood cells (RBCs). The binding properties of naked metHb (isolated from RBC) with these toxins has been studied; however, the binding behaviors of metHb under the intracellular conditions of RBC are unclear because of the difficulty in detecting metHb status changes in RBC. This study aimed to elucidate the binding properties of metHb in RBC under physiological and poisoned conditions using artificial RBC, which was hemoglobin encapsulated in a liposome. The mimic-circumstances of metHb in RBC (metHb-V) was prepared by oxidizing the hemoglobin in artificial RBC. Spectroscopic analysis indicated that the metHb in metHb-V exhibited a binding behavior different from that of naked metHb, depending on the toxic substance: When the pH decreased, (i) the cyanide binding affinity of metHb-V remained unchanged, but that of naked metHb decreased (ii) the hydrosulfide binding affinity was increased in metHb-V but was decreased in naked metHb. (iii) Azide binding was increased in metHb-V, which was similar to that in naked metHb, irrespective of the pH change. Thus, the binding behavior of intracellular metHb in the RBC with cyanide, hydrosulfide, and azide under physiological and pathological conditions were partly elucidated using the oxidized artificial RBC.

Pharmaceutical stability of methemoglobin-albumin cluster as an antidote for hydrogen sulfide poisoning after one-year storage in freeze-dried form

Long-term stability during storage is an important requirement for pharmaceutical preparations. The methemoglobin (metHb)-albumin cluster, in which bovine metHb is covalently enveloped with an average of three human albumin molecules, is a promising antidote for hydrogen sulfide (H2S) poisoning. In this study, we investigated the pharmaceutical stability of metHb-albumin cluster after storage for one year in solution and as freeze-dried powder. The lyophilized powder of metHb-albumin cluster stored for one year was readily reconstituted in sterile water for injection, yielding a homogeneous brown solution. Physicochemical measurements revealed that the overall structure of the metHb-albumin cluster was still maintained after preservation. Results of the pharmacological study showed that 100 % of the H2S-poisoned mice survived after treatment with the reconstituted solution of metHb-albumin cluster powder. Furthermore, the solution did not cause any toxic reactions. The antidotal efficacy of metHb-albumin cluster for H2S poisoning was preserved in freeze-dried powder form for at least one year.

The Effect of Molecular Hydrogen on Functional States of Erythrocytes in Rats with Simulated Chronic Heart Failure

Molecular hydrogen has an anti-inflammatory and cardioprotective effect, which is associated with its antioxidant properties. Erythrocytes are subjected to oxidative stress in pathologies of the cardiovascular system, which is the cause of a violation of the gas transport function of blood and microcirculation. Therefore, our aim was to investigate the effects of H₂ inhalation on the functional states of red blood cells (RBCs) in chronic heart failure (CHF) in rats. The markers of lipid peroxidation, antioxidant capacity, electrophoretic mobility of erythrocytes (EPM), aggregation, levels of adenosine triphosphate (ATP) and 2,3-diphosphoglyceric acid (2,3-DPG), hematological parameters were estimated in RBCs. An increase in EPM and a decrease in the level of aggregation were observed in groups with multiple and single H₂ application. The orientation of lipoperoxidation processes in erythrocytes was combined with the dynamics of changes in oxidative processes in blood plasma, it was observed with both single and multiple exposures, although the severity of the changes was greater with multiple H₂ inhalations. Probably, the antioxidant effects of molecular hydrogen mediate its metabolic action. Based on these data, we conclude the use of H₂ improves microcirculation and oxygen transport function of blood and can be effective in the treatment of CHF.

Syk Kinase Inhibitors Synergize with Artemisinins by Enhancing Oxidative Stress in Plasmodium falciparum-Parasitized Erythrocytes

Although artemisinin-based combination therapies (ACTs) treat Plasmodium falciparum malaria effectively throughout most of the world, the recent expansion of ACT-resistant strains in some countries of the Greater Mekong Subregion (GMS) further increased the interest in improving the effectiveness of treatment and counteracting resistance. Recognizing that (1) partially denatured hemoglobin containing reactive iron (hemichromes) is generated in parasitized red blood cells (pRBC) by oxidative stress, (2) redox-active hemichromes have the potential to enhance oxidative stress triggered by the parasite and the activation of artemisinin to its pharmaceutically active form, and (3) Syk kinase inhibitors block the release of membrane microparticles containing hemichromes, we hypothesized that increasing hemichrome content in parasitized erythrocytes through the inhibition of Syk kinase might trigger a virtuous cycle involving the activation of artemisinin, the enhancement of oxidative stress elicited by activated artemisinin, and a further increase in hemichrome production. We demonstrate here that artemisinin indeed augments oxidative stress within parasitized RBCs and that Syk kinase inhibitors further increase iron-dependent oxidative stress, synergizing with artemisinin in killing the parasite. We then demonstrate that Syk kinase inhibitors achieve this oxidative enhancement by preventing parasite-induced release of erythrocyte-derived microparticles containing redox-active hemichromes. We also observe that Syk kinase inhibitors do not promote oxidative toxicity to healthy RBCs as they do not produce appreciable amounts of hemichromes. Since some Syk kinase inhibitors can be taken daily with minimal side effects, we propose that Syk kinase inhibitors could evidently contribute to the potentiation of ACTs.

Predictive Model for Delivery Efficiency: Erythrocyte Membrane-Camouflaged Magnetofluorescent Nanocarriers Study

Delivery efficiencies of theranostic nanoparticles (NPs) based on passive tumor targeting strongly depend either on their blood circulation time or on appropriate modulations of the tumor microenvironment. Therefore, predicting the NP delivery efficiency before and after a tumor microenvironment modulation is highly desirable. Here, we present a new erythrocyte membrane-camouflaged magnetofluorescent nanocarrier (MMFn) with long blood circulation time (92 h) and high delivery efficiency (10% ID for Ehrlich murine tumor model). MMFns owe their magnetic and fluorescent properties to the incorporation of manganese ferrite nanoparticles (MnFe₂O₄ NPs) and IR-780 (a lipophilic indocyanine fluorescent dye), respectively, to their erythrocyte membrane-derived camouflage. MMFn composition, morphology, and size, as well as optical absorption, zeta potential, and fluorescent, magnetic, and magnetothermal properties, are thoroughly examined in vitro. We then present an analytical pharmacokinetic (PK) model capable of predicting the delivery efficiency (DE) and the time of peak tumor uptake (t_max), as well as changes in DE and t_max due to modulations of the tumor microenvironment, for potentially any nanocarrier. Experimental PK data sets (blood and tumor amounts of MMFns) are simultaneously fit to the model equations using the PK modeling software Monolix. We then validate our model analytical solutions with the numerical solutions provided by Monolix. We also demonstrate how our a priori nonmechanistic model for passive targeting relates to a previously reported mechanistic model for active targeting. All in vivo PK studies, as well as in vivo and ex vivo biodistribution studies, were conducted using two noninvasive techniques, namely, fluorescence molecular tomography (FMT) and alternating current biosusceptometry (ACB). Finally, histopathology corroborates our PK and biodistribution results.

Physicochemical Aspects of the Plasmodium chabaudi-Infected Erythrocyte

Membrane electrochemical potential is a feature of the molecular profile of the cell membrane and the two-dimensional arrangement of its charge-bearing molecules. Plasmodium species, the causative agents of malaria, are intracellular parasites that remodel host erythrocytes by expressing their own proteins on erythrocyte membranes. Although various aspects of the modifications made to the host erythrocyte membrane have been extensively studied in some human Plasmodium species (such as Plasmodium falciparum), details of the structural and molecular biological modifications made to host erythrocytes by nonhuman Plasmodium parasites have not been studied. We employed zeta potential analysis of erythrocytes parasitized by P. chabaudi, a nonhuman Plasmodium parasite. From these measurements, we found that the surface potential shift was more negative for P. chabaudi-infected erythrocytes than for P. falciparum-infected erythrocytes. However, electron microscopic analysis of the surface of P. chabaudi-infected erythrocytes did not reveal any modifications as compared with nonparasitized erythrocytes. These results suggest that differences in the membrane modifications found herein represent unique attributes related to the pathogenesis profiles of the two different malaria parasite species in different host animals and that these features have been acquired through parasite adaptations acquired over long evolutionary time periods.

Inward cholesterol gradient of the membrane system in P. falciparum-infected erythrocytes involves a dilution effect from parasite-produced lipids

Plasmodium falciparum (Pf) infection remodels the human erythrocyte with new membrane systems, including a modified host erythrocyte membrane (EM), a parasitophorous vacuole membrane (PVM), a tubulovesicular network (TVN), and Maurer's clefts (MC). Here we report on the relative cholesterol contents of these membranes in parasitized normal (HbAA) and hemoglobin S-containing (HbAS, HbAS) erythrocytes. Results from fluorescence lifetime imaging microscopy (FLIM) experiments with a cholesterol-sensitive fluorophore show that membrane cholesterol levels in parasitized erythrocytes (pRBC) decrease inwardly from the EM, to the MC/TVN, to the PVM, and finally to the parasite membrane (PM). Cholesterol depletion of pRBC by methyl-β-cyclodextrin treatment caused a collapse of this gradient. Lipid and cholesterol exchange data suggest that the cholesterol gradient involves a dilution effect from non-sterol lipids produced by the parasite. FLIM signals from the PVM or PM showed little or no difference between parasitized HbAA vs HbS-containing erythrocytes that differed in lipid content, suggesting that malaria parasites may regulate the cholesterol contents of the PVM and PM independently of levels in the host cell membrane. Cholesterol levels may affect raft structures and the membrane trafficking and sorting functions that support Pf survival in HbAA, HbAS and HbSS erythrocytes.

Membrane rafts of the human red blood cell

The cell type of election for the study of cell membranes, the mammalian non-nucleated erythrocyte, has been scarcely considered in the research of membrane rafts of the plasma membrane. However, detergent-resistant-membranes (DRM) were actually first described in human erythrocytes, as a fraction resisting solubilization by the nonionic detergent Triton X-100. These DRMs were insoluble entities of high density, easily pelleted by centrifugation, as opposed to the now accepted concept of lipid raft-like membrane fractions as material floating in low-density regions of sucrose gradients. The present article reviews the available literature on membrane rafts/DRMs in human erythrocytes from an historical point of view, describing the experiments that provided the solution to the above described discrepancy and suggesting possible avenue of research in the field of membrane rafts that, moving from the most studied model of living cell membrane, the erythrocyte's, could be relevant also for other cell types.

Structural modifications induced by the switch from an endogenous bis-histidyl to an exogenous cyanomet hexa-coordination in a tetrameric haemoglobin

Two EPR- and structurally-distinct bis-histidyl conformers of the ferric haemoglobin from Trematomus bernacchii react differently with CN⁻

Dynamic Light Scattering Based Microelectrophoresis: Main Prospects and Limitations

Microelectrophoresis based on the dynamic light scattering (DLS) effect has been a major tool for assessing and controlling the conditions for stability of colloidal systems. However, both the DLS methods for characterization of the hydrodynamic size of dispersed submicron particles and the theory behind the electrokinetic phenomena are associated with fundamental and practical approximations that limit their sensitivity and information output. Some of these fundamental limitations, including the spherical approximation of DLS measurements and an inability of microelectrophoretic analyses of colloidal systems to detect discrete charges and differ between differently charged particle surfaces due to rotational diffusion and particle orientation averaging, are revisited in this work. Along with that, the main prospects of these two analytical methods are mentioned. A detailed review of the role of zeta potential in processes of biochemical nature is given too. It is argued that although zeta potential has been used as one of the main parameters in controlling the stability of colloidal dispersions, its application potentials are much broader. Manipulating surface charges of interacting species in designing complex soft matter morphologies using the concept of zeta potential, intensively investigated recently, is given as one of the examples. Branching out from the field of colloid chemistry, DLS and zeta potential analyses are now increasingly finding application in drug delivery, biotechnologies, physical chemistry of nanoscale phenomena and other research fields that stand on the frontier of the contemporary science. Coupling the DLS-based microelectrophoretic systems with complementary characterization methods is mentioned as one of the prosperous paths for increasing the information output of these two analytical techniques.

Erythrocyte membranes convert monomeric ferriprotoporphyrin IX to β-hematin in acidic environment at malarial fever temperature

Hemozoin production makes it possible for intraerythrocytic malaria parasites to digest massive quantities of hemoglobin but still avoid potential ferriprotoporphyrin IX (FP) toxicity, which they cannot decompose further. Some antimalarial drugs, such as chloroquine, work by inhibiting this production, forcing the parasite to starve to death. As part of the efforts to identify possible biological mechanisms of FP polymerization, we have used normal human erythrocyte membranes as a model, to promote β-hematin (β-h) synthesis. Hemin in 35% aqueous dimethyl sulfoxide (DMSO) was reacted with isolated erythrocyte membranes and incubated overnight in sodium acetate buffer, pH 4.8, at 41°C. Infrared spectroscopy and electron microscopy showed that β-h was produced. Hemin in 10% was less effective as the substrate than when it was in 35% DMSO. A high malarial temperature seemed to be necessary, because FP polymerization was less at 37°C than at 41°C. Production was partially inhibited by chloroquine. These observations are of interest because other investigators have reported that membrane lipids mediated FP polymerization, but whole membranes were ineffective. On the other hand, our hypothesis is that the transport vesicles (TV) in malaria parasites could provide the receptor for FP and the lipids that promote hemozoin formation. Erythrocyte membranes may not be directly involved, but Plasmodium species transport hemoglobin in membrane-bound TV into food vacuoles, where hemoglobin catabolism is completed and hemozoin crystals are stored.

Modifications in erythrocyte membrane zeta potential by Plasmodium falciparum infection

The zeta potential (ZP) is an electrochemical property of cell surfaces that is determined by the net electrical charge of molecules exposed at the surface of cell membranes. Membrane proteins contribute to the total net electrical charge of cell surfaces and can alter ZP through variation in their copy number and changes in their intermolecular interactions. Plasmodium falciparum extensively remodels its host red blood cell (RBC) membrane by placing 'knob'-like structures at the cell surface. Using an electrophoretic mobility assay, we found that the mean ZP of human RBCs was -15.7 mV. In RBCs infected with P. falciparum trophozoites ('iRBCs'), the mean ZP was significantly lower (-14.6 mV, p<0.001). Removal of sialic acid from the cell surface by neuraminidase treatment significantly decreased the ZP of both RBCs (-6.06 mV) and iRBCs (-4.64 mV). Parasite-induced changes in ZP varied by P. falciparum clone and the presence of knobs on the iRBC surface. Variations in ZP values were accompanied by altered binding of iRBCs to human microvascular endothelial cells (MVECs). These data suggest that parasite-derived knob proteins contribute to the ZP of iRBCs, and that electrostatic and hydrophobic interactions between iRBC and MVEC membranes are involved in cytoadherence.

Occurrence and formation of endogenous histidine hexa-coordination in cold-adapted hemoglobins

Spectroscopic and crystallographic evidence of endogenous (His) ligation at the sixth coordination site of the heme iron has been reported for monomeric, dimeric, and tetrameric hemoglobins (Hbs) in both ferrous (hemochrome) and ferric (hemichrome) oxidation states. In particular, the ferric bis- histidyl adduct represents a common accessible ordered state for the β chains of all tetrameric Hbs isolated from Antarctic and sub-Antarctic fish. Indeed, the crystal structures of known tetrameric Hbs in the bis-His state are characterized by a different binding state of the α and β chains. An overall analysis of the bis-histidyl adduct of globin structures deposited in the Protein Data Bank reveals a marked difference between hemichromes in tetrameric Hbs compared to monomeric/dimeric Hbs. Herein, we review the structural, spectroscopic and stability features of hemichromes in tetrameric Antarctic fish Hbs. The role of bis-histidyl adducts is also addressed in a more evolutionary context alongside the concept of its potential physiological role.

Influence of haemoglobins S and C on predominantly asymptomatic Plasmodium infections in northern Ghana

The haemoglobin (Hb) variants HbS and HbC protect against severe malaria. Yet, the influence particularly of HbC on asymptomatic or mild Plasmodium infection is not well established. In a dry season cross-sectional survey among 2108 children aged 0.5-9 years in the Northern Region of Ghana, Plasmodium species and density, as well as Hb, were analysed with respect to Hb genotypes. HbAC occurred in 19.7% and HbAS in 7.4% (HbSC, 0.8%; HbCC, 0.8%; HbSS, 0.3%). Overall, 56% of the children had microscopically visible parasitaemia. By PCR, P. falciparum, P. malariae, and P. ovale were present in 74.5%, 9.7%, and 5.5%, respectively. Febrile parasitaemia was rare (2.8%) but anaemia (Hb<11g/dL) frequent (59.3%). Children with HbAA and HbAC showed virtually identical malariometric parameters. In contrast, children with HbAS had significantly less parasitaemia, lower parasite densities, and a higher proportion of submicroscopic P. falciparum infection. Remarkably, in children with HbCC, P. malariae infection occurred in 37.5% (adjusted odds ratio (aOR), 5.8; 95% CI, 1.8-18.8) and P. ovale in 18.8% (aOR, 3.61; 95% CI, 0.97-13.5). In this population with predominantly asymptomatic Plasmodium infection, HbAC shows no discernible effect on malaria-related parameters. Homozygous HbC, in contrast, confers an increased risk of P. malariae infection which conceivably may modulate falciparum malaria.

Irreversible AE1 tyrosine phosphorylation leads to membrane vesiculation in G6PD deficient red cells

BACKGROUND

While G6PD deficiency is one of the major causes of acute hemolytic anemia, the membrane changes leading to red cell lysis have not been extensively studied. New findings concerning the mechanisms of G6PD deficient red cell destruction may facilitate our understanding of the large individual variations in susceptibility to pro-oxidant compounds and aid the prediction of the hemolytic activity of new drugs.

METHODOLOGY/PRINCIPAL FINDINGS

Our results show that treatment of G6PD deficient red cells with diamide (0.25 mM) or divicine (0.5 mM) causes: (1) an increase in the oxidation and tyrosine phosphorylation of AE1; (2) progressive recruitment of phosphorylated AE1 in large membrane complexes which also contain hemichromes; (3) parallel red cell lysis and a massive release of vesicles containing hemichromes. We have observed that inhibition of AE1 phosphorylation by Syk kinase inhibitors prevented its clustering and the membrane vesiculation while increases in AE1 phosphorylation by tyrosine phosphatase inhibitors increased both red cell lysis and vesiculation rates. In control RBCs we observed only transient AE1 phosphorylation.

CONCLUSIONS/SIGNIFICANCE

Collectively, our findings indicate that persistent tyrosine phosphorylation produces extensive membrane destabilization leading to the loss of vesicles which contain hemichromes. The proposed mechanism of hemolysis may be applied to other hemolytic diseases characterized by the accumulation of hemoglobin denaturation products.

Dynamic light scattering and zeta potential of colloidal mixtures of amelogenin and hydroxyapatite in calcium and phosphate rich ionic milieus

The concept of zeta-potential has been used for more than a century as a basic parameter in controlling the stability of colloidal suspensions, irrespective of the nature of their particulate ingredients--organic or inorganic. There are prospects that self-assembly of peptide species and the protein-mineral interactions related to biomineralization may be controlled using this fundamental physicochemical parameter. In this study, we have analysed the particle size and zeta-potential of the full-length recombinant human amelogenin (rH174), the main protein of the developing enamel matrix, in the presence of calcium and phosphate ions and hydroxyapatite (HAP) particles. As calcium and phosphate salts are introduced to rH174 sols in increments, zeta-potential of the rH174 nanospheres is more affected by negatively charged ions, suggesting their tendency to locate within the double charge layer. Phosphate ions have a more pronounced effect on both the zeta-potential and aggregation propensity of rH174 nanospheres compared to calcium ions. The isoelectric point of amelogenin was independent on the ionic strength of the solution and the concentration of calcium and/or phosphate ions. Whereas rH174 shows a higher affinity for phosphate than for calcium, HAP attracts both of these ions to the shear plane of the double layer. The parallel size and zeta-potential analysis of HAP and rH174 colloidal mixtures indicated that at pH 7.4, despite both HAP and rH174 particles being negatively charged, rH174 adsorbs well onto HAP particles. The process is slower at pH 7.4 than at pH 4.5 when the HAP surface is negatively charged and the rH174 nanosphere carries an overall positive charge. The results presented hereby demonstrate that electrostatic interactions can affect the kinetics of the adsorption of rH174 onto HAP.