A description of the holes in human erythrocyte membrane ghosts

Molecular thermodynamic modeling of a bilayer perforation in mixed catanionic surfactant systems

An interplay between electrostatics and deformation of surfactant tails is responsible for the spontaneous formation of pores in self-assembled bilayers.

Fighting microbial infections: A lesson from amphibian skin-derived esculentin-1 peptides

Due to the growing emergence of resistance to commercially available antibiotics/antimycotics in virtually all clinical microbial pathogens, the discovery of alternative anti-infective agents, is greatly needed. Gene-encoded antimicrobial peptides (AMPs) hold promise as novel therapeutics. In particular, amphibian skin is one of the richest storehouses of AMPs, especially that of the genus Rana, with esculentins-1 being among the longest (46 amino acids) AMPs found in nature to date. Here, we report on the recently discovered in vitro and in vivo activities and mechanism of action of two derivatives of the N-terminal part of esculentin-1a and -1b peptides, primarily against two relevant opportunistic microorganisms causing a large number of life-threatening infections worldwide; i.e. the Gram-negative bacterium Pseudomonas aeruginosa and the yeast Candida albicans. Because of distinct advantages compared to several mammalian AMPs, the two selected frog skin AMP-derivatives represent attractive candidates for the development of new antimicrobial compounds with expanded properties, for both human and veterinary medicine.

Flavonoids in Microheterogeneous Media, Relationship between Their Relative Location and Their Reactivity towards Singlet Oxygen

In this work, the relationship between the molecular structure of three flavonoids (kaempferol, quercetin and morin), their relative location in microheterogeneous media (liposomes and erythrocyte membranes) and their reactivity against singlet oxygen was studied. The changes observed in membrane fluidity induced by the presence of these flavonoids and the influence of their lipophilicity/hydrophilicity on the antioxidant activity in lipid membranes were evaluated by means of fluorescent probes such as Laurdan and diphenylhexatriene (DPH). The small differences observed for the value of generalized polarization of Laurdan (GP) curves in function of the concentration of flavonoids, indicate that these three compounds promote similar alterations in liposomes and erythrocyte membranes. In addition, these compounds do not produce changes in fluorescence anisotropy of DPH, discarding their location in deeper regions of the lipid bilayer. The determined chemical reactivity sequence is similar in all the studied media (kaempferol < quercetin < morin). Morin is approximately 10 times more reactive than quercetin and 20 to 30 times greater than kaempferol, depending on the medium.

Dynamic morphology and cytoskeletal protein changes during spontaneous inside-out vesiculation of red blood cell membranes

Vesicle preparations from cell plasma membranes, red blood cells in particular, are extensively used in transport and enzymic studies and in the fields of drug delivery and drug-transport interactions. Here we investigated the role of spectrin–actin, the main components of the red cell cortical cytoskeleton, in a particular mechanism of vesicle generation found to be relevant to the egress process of Plasmodium falciparum merozoites from infected red blood cells. Plasma membranes from red blood cells lysed in ice-cold media of low ionic strength and free of divalent cations spontaneously and rapidly vesiculate upon incubation at 37 °C rendering high yields of inside-out vesicles. We tested the working hypothesis that the dynamic shape transformations resulted from changes in spectrin–actin configuration within a disintegrating cytoskeletal mesh. We showed that cytoskeletal-free membranes behave like a two-dimensional fluid lacking shape control, that spectrin–actin remain attached to vesiculating membranes for as long as spontaneous movement persists, that most of the spectrin–actin detachment occurs terminally at the time of vesicle sealing and that naked membrane patches increasingly appear during vesiculation. These results support the proposed role of spectrin–actin in spontaneous vesiculation. The implications of these results to membrane dynamics and to the mechanism of merozoite egress are discussed.

Mitochondrial toxin betulinic acid induces in vitro eryptosis in human red blood cells through membrane permeabilization

Betulinic acid (BA), a compound isolated from the bark of white birch (Betula pubescens), was reported to induce apoptosis in many types of cancer through mitochondrial dysfunction with low side effects in normal cells. Because of these features, BA is regarded as a potential anti-cancer agent. However, the effect of BA on the induction of cell death in human erythrocytes remains unknown. Given that BA is a mitochondrial toxin and mitochondria are the central cell death regulator, we hypothesized that BA is unable to elicit apoptosis (also known as eryptosis or erythroptosis) in human erythrocytes devoid of mitochondria. This study therefore tried to determine the in vitro effect of BA on the induction of eryptosis/erythroptosis. Contrary to our prediction, BA caused phosphatidylserine externalization, increase in cellular Ca(2+) ion concentration ([Ca(2+)]i) and eryptosis/erythroptosis in human erythrocytes with a lethal dose larger than that in cancer lines. Mechanistically, the rise of [Ca(2+)]i seems not to be the only key mediator in the BA-mediated eryptosis/erythroptosis because depletion of external Ca(2+) and use of Ca(2+) channels blockers could not eliminate the BA's effect. Also, BA was able to elicit discocyte-echinocyte transformation and release calcein from the RBC ghosts in a way similar to digitonin through membrane permeabilization. Collectively, we report here for the first time that BA induced eryptosis/erythroptosis in human erythrocytes through Ca(2+) loading and membrane permeabilization.

pH-dependent disruption of Escherichia coli ATCC 25922 and model membranes by the human antimicrobial peptides hepcidin 20 and 25

The human hepcidin 25 (hep-25) and its isoform hepcidin 20 (hep-20) are histidine-containing, cystein rich, β-sheet structured peptides endowed with antimicrobial activity. We previously reported that, similar to other histidine-containing peptides, the microbicidal effects of hep-25 and hep-20 are highly enhanced at acidic pH. In the present study, we investigated whether pH influences the mode of action of hep-25 and hep-20 on Escherichia coli American Type Culture Collection 25922 and model membranes. A striking release of β-galactosidase by hepcidin-treated E. coli was observed at pH 5.0, whereas no inner membrane permeabilization capacity was seen at pH 7.4, even at bactericidal concentrations. Similar results were obtained by flow cytometry when assessing the internalization of propidium iodide by hepcidin-treated E. coli. Scanning electron microscope imaging revealed that both peptides induced the formation of numerous blebs on the surface of bacterial cells at acidic pH but not at neutral pH. Moreover, a phospholipid/polydiacetylene colourimetric vesicle assay revealed a more evident membrane damaging effect at pH 5.0 than at pH 7.4. The leakage of entrapped dextrans of increasing molecular size from liposomes was also assessed at pH 7.4. Consistent with the lack of β-galactosidase release from whole E. coli observed at such a pH value, evident leakage of only the smallest 4-kDa dextran (and not of dextrans of 20 or 70 kDa) was observed, indicating a poor ability of hepcidin peptides to permeabilize liposome vesicles at pH 7.4. Altogether, the data obtained in the present study using different approaches strongly suggest that the ability of hepcidins to perturb bacterial membranes is markedly pH-dependent.

Development of a radial ventricular assist device using numerical predictions and experimental haemolysis

The objective of this study was to demonstrate the potential of Computational Fluid Dynamics (CFD) simulations in predicting the levels of haemolysis in ventricular assist devices (VADs). Three different prototypes of a radial flow VAD have been examined experimentally and computationally using CFD modelling to assess device haemolysis. Numerical computations of the flow field were computed using a CFD model developed with the use of the commercial software Ansys CFX 13 and a set of custom haemolysis analysis tools. Experimental values for the Normalised Index of Haemolysis (NIH) have been calculated as 0.020 g/100 L, 0.014 g/100 L and 0.0042 g/100 L for the three designs. Numerical analysis predicts an NIH of 0.021 g/100 L, 0.017 g/100 L and 0.0057 g/100 L, respectively. The actual differences between experimental and numerical results vary between 0.0012 and 0.003 g/100 L, with a variation of 5% for Pump 1 and slightly larger percentage differences for the other pumps. The work detailed herein demonstrates how CFD simulation and, more importantly, the numerical prediction of haemolysis may be used as an effective tool in order to help the designers of VADs manage the flow paths within pumps resulting in a less haemolytic device.

Improving the endosomal escape of cell-penetrating peptides and their cargos: strategies and challenges

Cell penetrating peptides (CPPs) can deliver cell-impermeable therapeutic cargos into cells. In particular, CPP-cargo conjugates tend to accumulate inside cells by endocytosis. However, they often remain trapped inside endocytic organelles and fail to reach the cytosolic space of cells efficiently. In this review, the evidence for CPP-mediated endosomal escape is discussed. In addition, several strategies that have been utilized to enhance the endosomal escape of CPP-cargos are described. The recent development of branched systems that display multiple copies of a CPP is presented. The use of viral or synthetic peptides that can disrupt the endosomal membrane upon activation by the low pH of endosomes is also discussed. Finally, we survey how CPPs labeled with chromophores can be used in combination with light to stimulate endosomal lysis. The mechanisms and challenges associated with these intracellular delivery methodologies are discussed.

Engineering erythrocytes to be erythrosensors: first steps

Molecules can be loaded into mammalian erythrocytes through a reversible lysis pore that forms in the membrane when placed in hypotonic media, the result being resealed red cell ghosts. Many studies on the sidedness of transport processes have utilized this approach. In addition, red cell ghosts encapsulated with enzymes have been used in patients to treat specific enzyme deficiencies, particularly when the substrate can cross the red cell membrane. Our long-term goal is to put fluorescent sensors inside erythrocytes, return the loaded red cell ghosts to the animal or patient, and then monitor the fluorescence non-invasively to follow changes in plasma analyte concentration. In this paper, we present a novel dialysis method for making the red cell ghosts. In addition, we present a theoretical analysis showing that it is not necessary that every loaded red cell ghost has the same dye concentration. Finally we discuss the constraints on the optimal affinity for the sensor/analyte interaction.

Electrostatic self-energy of a partially formed spherical shell in salt solution: application to stability of tethered and fluid shells as models for viruses and vesicles

We investigate the electrostatics of a partially formed, charged spherical shell in a salt solution. We solve the problem numerically at the Poisson-Boltzmann level and analytically in the Debye-Hückel regime. From the results on energetics of partially formed shells we examine the stability of tethered (crystalline) and fluid shells toward rupture. We delineate different regimes of stability, where, for fluid shells, we also include the effects of bending elasticity of the shells. Our analysis shows how charging of the shell induces its instability toward rupture but also provides insight regarding growth of charged shells.

Modeling of the endosomolytic activity of HA2-TAT peptides with red blood cells and ghosts

HA2-TAT is a peptide-based delivery agent that combines the pH-sensitive HA2 fusion peptide from influenza and the cell-penetrating peptide TAT from HIV. This chimeric peptide is engineered to induce the cellular uptake of macromolecules into endosomes via the TAT moiety and to respond to the acidifying lumen of endosomes to cause membrane leakage and release of macromolecules into cells via the HA2 moiety. The question of how HA2 and TAT affect the properties of one another remains, however, unanswered, and the behavior of the peptide inside endosomes is mostly uncharacterized. To address these issues, the binding and membrane leakage activity of a glutamic acid-enriched analogue E5-TAT was assessed with red blood cells and giant unilamellar vesicles as membrane models for endosomes. Hemolysis and microscopy assays reveal that E5-TAT binds to membranes in a pH-dependent manner and causes membrane leakage by inducing the formation of pores through which macromolecules can escape. The TAT moiety contributes to this activity by causing a shift in the pH response of E5 and by binding to negatively charged phospholipids. On the other hand, TAT binding to glycosaminoglycans reduces the lytic activity of E5-TAT. Addition of TAT to the C-terminus of E5 can therefore either increase or inhibit the activity of E5 depending on the cellular components present at the membrane. Taken together, these results suggest a model for the endosomolytic activity of the peptide and provide the basis for the molecular design of future delivery agents.

Band 3 (AE1, SLC4A1)-mediated transport of stilbenedisulfonates. III: Role of solute and protein structure in proton-activated stilbenedisulfonate influx

DBDS (4,4'-dibenzamido-2,2'-stilbenedisulfonate) influx into magnesium resealed ghosts (MRSG) occurs over the anion/proton co-transport pH range (pK approximately 5.0). Here, factors are studied which may influence the pH dependence of DBDS transport. Accumulation of various stilbenedisulfonate (SD) molecules was studied and found to be correlated with the hydrophobicity of the R-groups (Hansch factor), not protonation of the sulfonates. The role of proton binding to glutamate 681 was found not to be part of the rate-limiting step in DBDS uptake by MRSG. Finally, the pH dependence of changes in quaternary structure/conformational state was investigated using an assay involving photo-crosslinking of band 3 subunits in the presence of DASD (4,4'-diazido-2,2'-stilbenedisulfonate). Lowering the pH promoted intersubunit crosslinking by DASD, with a pK value of 4.75+/-1.0. This value is comparable to the pK for DBDS binding to the "second" class of sites on control band 3 (pK = 5.01+/-0.16), and to DBDS influx into control MRSG (pK values between 4.57+/-0.15 and 4.7+/-0.1). Susceptibility to photo-crosslinking was reversed by raising the pH prior to initiation of the reaction. Significantly, no photo-crosslinking was observed between pH 6.0 and 8.0, where band 3 subunits are known to exist as stable dimers and tetramers. We conclude that intersubunit photo-crosslinking does not simply involve random collision between photo-activated DASD and band 3. Rather, proton binding to band 3 either alters the conformation at the interface between subunits of pre-existing tetramers, or it promotes self-association of stable dimers to a "novel" tetrameric conformational state.

Mechanical cell injury

The tissues of the body are continually subjected to mechanical stimulation by external forces, such as gravity, and internally generated forces, such as the pumping of blood or muscle contraction. Within a physiological range, the forces elicit adaptive responses acutely (to rapidly alter function) and chronically (to remodel tissue structure to optimize load-bearing capabilities). When the forces exceed certain thresholds, injury results. To understand the mechanisms of mechanical injury at the cellular level, we must analyze the structural response of the cell to various modes of deformation and examine the biological consequences of the structural alterations caused by the trauma. This chapter reviews the mechanics of cell membrane deformation and failure. Evidence for the strain-rate-dependent, transient disruption of cell membranes, or mechanoporation, is presented for a variety of cell types. The complex interactions between the structural damage and the biological sequelae are illustrated using clinically relevant forms of cell injury. Finally, novel therapeutic approaches targeting membrane integrity are described.

Dielectric dispersion of erythrocyte ghosts

The underlying mechanism of the low-frequency dielectric dispersion, called the alpha dispersion, of osmotically lysed erythrocytes (erythrocyte ghosts) has remained open since its finding [H. P. Schwan and E. L. Carstensen, Science 125, 985 (1957)]. The alpha dispersion is peculiar to erythrocyte ghosts and has never been observed for intact erythrocytes. Numerical calculation based on interfacial polarization revealed that the alpha dispersion is due to the presence of a hole of about 30 nm in radius in the plasma membrane.

Effects of HPE-101, a skin penetration enhancer, on human erythrocyte membranes

The primary aim of this study was to investigate the skin permeation-enhancing mechanism of HPE-101 using erythrocyte ghost cells prepared from human whole blood as a biomembrane model. The extent of hemolysis of erythrocytes induced by HPE-101 was measured using a spectrophotometer at 540nm. The effect of HPE-101 on lipid fluidity was examined by observing the change of intramolecular excimer formation and fluorescence polarization using an intramolecular probe (1,3-bis(pyrene) propane) and a lipid probe (1,6-diphenyl 1,3,5-hexatriene), respectively. Hemolysis of erythrocytes was observed at 0.01mM and completed at 1.0mM of HPE-101. The fluorescence polarization of the ghost membrane decreased with the addition of HPE-101, whereas the intramolecular excimer formation increased. HPE-101 thus enhanced the rotational mobility and the lateral diffusion, thereby decreasing the microviscosity of ghost membranes, implying that HPE-101 increases the lipid fluidity of ghost membranes. Therefore, HPE-101 seems to cause an increase in fluidity of the lipid bilayers in the stratum corneum of the skin, resulting in the reduction of diffusion resistance.

Model of creation and evolution of stable electropores for DNA delivery

Electroporation, in which electric pulses create transient pores in the cell membrane, is becoming an important technique for gene therapy. To enable entry of supercoiled DNA into cells, the pores should have sufficiently large radii (>10 nm), remain open long enough for the DNA chain to enter the cell (milliseconds), and should not cause membrane rupture. This study presents a model that can predict such macropores. The distinctive features of this model are the coupling of individual pores through membrane tension and the electrical force on the pores, which is applicable to pores of any size. The model is used to explore the process of pore creation and evolution and to determine the number and size of pores as a function of the pulse magnitude and duration. Next, our electroporation model is combined with a heuristic model of DNA uptake and used to predict the dependence of DNA uptake on pulsing parameters. Finally, the model is used to examine the mechanism of a two-pulse protocol, which was proposed specifically for gene delivery. The comparison between experimental results and the model suggests that this model is well-suited for the investigation of electroporation-mediated DNA delivery.

Shape transformation and burst of giant POPC unilamellar liposomes modulated by non-ionic detergent C12E8

We studied spontaneous shape transformations and burst of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine (POPC) vesicles with exogeneously added non-ionic detergent octaethylene-glycol dodecylether C(12)E(8). The addition of C(12)E(8) increased the speed of the vesicle shape transformation, so that we were able to study for the first time the complete sequence of POPC vesicle shapes starting from initial spherical vesicle with long thin tubular protrusion to final shape with invagination(s). The average mean curvature of the vesicle membrane continuously decreases during this process. The shape of the invaginations is usually spherical, however also non-spherical shapes of invaginations were observed. C(12)E(8) increases amplitudes of the fluctuations of the vesicle membrane. At higher concentrations in the membrane, C(12)E(8) induces the membrane leakage and burst of the vesicles.

The endomembrane requirement for cell surface repair

The capacity to reseal a plasma membrane disruption rapidly is required for cell survival in many physiological environments. Intracellular membrane (endomembrane) is thought to play a central role in the rapid resealing response. We here directly compare the resealing response of a cell that lacks endomembrane, the red blood cell, with that of several nucleated cells possessing an abundant endomembrane compartment. RBC membrane disruptions inflicted by a mode-locked Ti:sapphire laser, even those initially smaller than hemoglobin, failed to reseal rapidly. By contrast, much larger laser-induced disruptions made in sea urchin eggs, fibroblasts, and neurons exhibited rapid, Ca(2+)-dependent resealing. We conclude that rapid resealing is not mediated by simple physiochemical mechanisms; endomembrane is required.

New insights into regulation of erythrocyte shape

Two ideas explain the mechanism of shape regulation: the lipid bilayer coupled theory and the protein network scaffold theory. Recently, several important articles have been published on the former theory. However, many phenomena argue against the theory, including behavior of ghosts and triton shells, various types of manipulation of proteins, and fixation of the shape by the addition of large reagents outside the cell. Moreover, hereditary spherocytosis shows normal, uneven distribution of phospholipids, and hereditary and artificial defects of a membrane protein show spherocytes or elliptocytes. The liquid state of the lipid layer does not seem to support the shape or mechanical characteristics. On the other hand, all of these phenomena argue for the protein network scaffold theory. Characteristics of each protein and interactions among proteins are now being clarified, but this theory and the author's own ideas still lack decisive evidence.

Coping with the inevitable: how cells repair a torn surface membrane

Disruption of the cell plasma membrane is a commonplace occurrence in many mechanically challenging, biological environments. 'Resealing' is the emergency response required for cell survival. Resealing is triggered by Ca2+ entering through the disruption; this causes vesicles present in cytoplasm underlying the disruption site to fuse rapidly with one another (homotypically) and also with the adjacent plasma membrane (heterotypically/exocytotically). The large vesicular products of homotypic fusion are added as a reparative 'patch' across the disruption, when its resealing requires membrane replacement. The simultaneous activation of the local cytoskeleton supports these membrane fusion events. Resealing is clearly a complex and dynamic cell adaptation, and, as we emphasize here, may be an evolutionarily primitive one that arose shortly after the ancestral eukaryote lost its protective cell wall.

Cytoplasmic molecular delivery with shock waves: importance of impulse

Cell permeabilization using shock waves may be a way of introducing macromolecules and small polar molecules into the cytoplasm, and may have applications in gene therapy and anticancer drug delivery. The pressure profile of a shock wave indicates its energy content, and shock-wave propagation in tissue is associated with cellular displacement, leading to the development of cell deformation. In the present study, three different shock-wave sources were investigated; argon fluoride excimer laser, ruby laser, and shock tube. The duration of the pressure pulse of the shock tube was 100 times longer than the lasers. The uptake of two fluorophores, calcein (molecular weight: 622) and fluorescein isothiocyanate-dextran (molecular weight: 71,600), into HL-60 human promyelocytic leukemia cells was investigated. The intracellular fluorescence was measured by a spectrofluorometer, and the cells were examined by confocal fluorescence microscopy. A single shock wave generated by the shock tube delivered both fluorophores into approximately 50% of the cells (p < 0.01), whereas shock waves from the lasers did not. The cell survival fraction was >0.95. Confocal microscopy showed that, in the case of calcein, there was a uniform fluorescence throughout the cell, whereas, in the case of FITC-dextran, the fluorescence was sometimes in the nucleus and at other times not. We conclude that the impulse of the shock wave (i.e., the pressure integrated over time), rather than the peak pressure, was a dominant factor for causing fluorophore uptake into living cells, and that shock waves might have changed the permeability of the nuclear membrane and transferred molecules directly into the nucleus.

Characteristics of the osmotically induced membrane rupture

The phenomenon of reciprocating mechanical oscillations of electrofused erythrocytes was used to investigate the mechanical characteristics of ruptures induced in erythrocyte membranes by colloid osmotic pressure. The rupture characteristics follow an exponentially decaying time function. Time constants determined for opening times of ruptures decreased from 5.5 ms at 10 degrees C to 3.8 ms and 2.0 ms at 40 degrees C for the first and the last observable rupture, respectively. Evidence is given that the diameter of the membrane rupture exceeds the size of a haemoglobin molecule. With repetitive membrane rupturing, the ability of the membrane bilayer and associated structures to heal decreases, owing to the reduced ability to withstand pressure gradients. This change allows oscillating doublets to be classified according to one of three groups: group A showing no development in response to swell times, group B showing a continuous decrease in response to swell times, and group C showing a spontaneous decrease in response to swell times. These results suggest that oscillations cease as a result of defects of membrane healing. Calculations of respective temperature ranges are in agreement with temperature ranges for spectrin denaturation. Thus, conclusions obtained from this study suggest that the spectrin network plays a key role in membrane healing processes after mechanical membrane rupture.

Sonoporation of erythrocytes by lithotripter shockwaves in vitro

Sonoporation of red blood cells was examined in relation to cavitation-induced hemolysis. FITC-dextran at 580,000 MW was added to suspensions of canine erythrocytes and the mixture was exposed to lithotripter shockwaves. Exposure at 5% or 50% hematocrit in PBS or 50% in plasma yielded not only hemolysis but also FITC-dextran uptake in surviving cells. Hemolysis increased with increasing numbers of shockwaves. The numbers of cells with fluorescent dextran uptake remained roughly constant for 250-1000 shockwaves, but this represented an increasing percentage of the surviving cells. In addition, fluorescent microspheres formed spontaneously in samples with hemolysis. An air bubble was needed in the chamber to obtain substantial effects, implicating the cavitation mechanism. The exposure-response trends could be modeled by simple theory for random interaction of the cells with bubbles.

Mechanism of the enhancement effect of n-octyl-beta-D-thioglucoside on the transdermal penetration of fluorescein isothiocyanate-labeled dextrans and the molecular weight dependence of water-soluble penetrants through stripped skin

To clarify the mechanism of the enhancing effect of n-octyl-beta-D-thioglucoside (OTG), which acts as a potent enhancer for skin penetration of peptides and water-soluble penetrants, the in vitro penetration of macromolecules [fluorescein isothiocyanate-labeled dextrans (FTIC-dextrans)] was evaluated with hairless rat skin and stripped skin. The FITC-dextrans (MW, 4400, 9600, and 69,000 Da, referred to as FD-4, FD-10, and FD-70, respectively) penetrated more easily in the presence of OTG (1.5%), with high fluxes equivalent to those through stripped skin. This result indicated that the enhancement effect of OTG on the penetration of macromolecules through the stratum corneum was extensive, and the barrier function of the corneum was nearly eliminated by the OTG treatment. OTG significantly solubilized the stratum corneum proteins and ceramides during the initial time stage. Scanning electron microscopic observations demonstrated that OTG treatment dramatically changed the cell membrane (i.e., exfoliation of cell membranes and dissociation of adherent cornified cells), suggesting a significant disturbance of the cohesive laminae and barrier functions. The extent of dissociation of cell membranes increased with treatment time, without significant changes in the cell junctions. These results clarify that the enhancement mechanism of OTG was different from that of laurocapram and other lipophilic enhancers. The permeability of polar solutes with differing molecular sizes (MW, 180-69,000 Da) through stripped skin was size dependent (r = 0.997, p < 0.001). However, the viable epidermis and dermis restricted the penetration of macromolecules, such as FD-70.

Superoxide-mediated lysis of erythrocytes: the role of colloid-osmotic forces

Although superoxide anions are a well-known mediator of cytotoxicity, their mechanism of target cell lysis is not clearly understood. In the present study we have used an exogenous source of superoxide to study erythrocyte cytolysis. RBC lysis was studied in buffers containing the cations Li+, Na+, K+, Rb+, and Cs+; superoxide anions were produced and available in these buffers. During this model superoxide-dependent cytolytic process, erythrocytes underwent a shape change from biconcave disk to sphere as shown by scanning electron microscopy. Soret band transmitted light microscopy has confirmed this shape change and shown that it precedes cytosolic oxidation. This evidence is consistent with a colloid-osmotic type lytic mechanism. Erythrocyte lysis was studied by 51Cr-release and light scattering methods. Superoxide-mediated target cytolysis was characterized by: 1) a sigmoidal dose-response curve and 2) a lag time in cytolysis after superoxide addition in kinetic light scattering experiments. The efficacy of cytolysis followed the rank order Cs+ > Rb+ > Na+, Li+ > sucrose = raffinose, which provides additional support for a colloid-osmotic lytic mechanism. Furthermore, the rank order potency correlates with the cations' hydration numbers. We suggest that oxidative events trigger the formation of colloid-osmotic pores approximately 1 nm in diameter.

Effect of intra-erythrocytic magnesium ions on invasion by Plasmodium falciparum

Exclusion of magnesium ions from resealed ghosts or their extraction from intact human red cells by means of an ionophore results in a reversible drop in susceptibility to invasion by Plasmodium falciparum merozoites in vitro. Resealed ghosts, containing magnesium-ATP and diluted cytosol, are invaded with high efficiency only when the original hypotonic lysis is carried out in the presence of magnesium ions. This effect is not related to the loss of membrane-associated constituents when magnesium ions are absent. Ghosts containing calcium ions, together with the protective agent, flunarizine, were essentially resistant to invasion; this effect is again at least partially reversible. A possible explanation of these phenomena is that entry of the merozoite may be inhibited by breakdown of the host cell phospholipid asymmetry, with the appearance of aminophospholipids at the outer cell surface.

Involvement of cytoskeletal proteins in the barrier function of the human erythrocyte membrane. III. Permeability of spectrin-depleted inside-out membrane vesicles to hydrophilic nonelectrolytes. Formation of leaks by chemical or enzymatic modification of membrane proteins

Spectrin-depleted inside-out vesicles (IOV's) prepared from human erythrocyte membranes were characterized in terms of size, ground permeability to hydrophilic nonelectrolytes and their sensitivity to modification by SH reagents, DIDS and trypsin. IOV's proved to have the same permeability of their lipid domain to erythritol as native erythrocytes, in contrast to resealed ghosts (Klonk, S. and Deuticke, B. (1992) Biochim. Biophys. Acta 1106, 126-136 (Part I in this series)), which have a residual leak. On the other hand, IOV's have a slightly elevated permeability for mannitol and sucrose, nonelectrolytes which are almost (mannitol) or fully (sucrose) impermeant in the native membrane. These increased fluxes, which have a high activation energy and can be stimulated by phloretin, are, however, also much smaller than the corresponding leak fluxes observed in resealed ghosts. In view of these differences, formation of IOV's can be concluded to go along with partial annealing of barrier defects persisting in the erythrocyte membrane after preparation of resealed ghosts. Oxidation of SH groups of the IOV membrane by diamide produces an enhancement of permeability for hydrophilic nonelectrolytes which is much less pronounced than that induced by a similar treatment of erythrocytes or ghosts (Klonk, S. and Deuticke, B. (1992) Biochim. Biophys. Acta 1106, 126-136 (Part I in this series)). Moreover, proteolytic treatment of the vesicle membrane, although leading to a marked digestion of integral membrane proteins, only induces a minor, saturating increase of permeability, much lower than that in trypsinized resealed ghosts (Klonk, S. and Deuticke, B. (1992) Biochim. Biophys. Acta 1106, 137-142 (Part II of this series)). Since absence of the cytoskeletal proteins, spectrin and actin, is the major difference between IOV's and resealed ghosts, these results may be taken as further evidence for a dependence of the barrier properties of the erythrocyte membrane bilayer domain on its interaction with cytoskeletal elements. In contrast, these barrier properties seem to be rather insensitive to perturbations of integral proteins.

Involvement of cytoskeletal proteins in the barrier function of the human erythrocyte membrane. II. Formation of membrane leaks in ghost membranes after limited proteolysis of skeletal proteins by trypsin

Limited proteolysis of human erythrocyte ghost membranes by low levels of trypsin (10-240 ng/ml) added bilaterally at 0 degrees C together with the proteinase inhibitor, phenylmethylsulfonyl fluoride (PMSF) before resealing at 37 degrees C leads to a graded digestion of spectrin and ankyrin and the disappearance of band 4.1 protein, while band 3 is cleaved only to a very low extent. These alterations are accompanied by an increase of membrane permeability of the resealed ghosts to hydrophilic nonelectrolytes (erythritol to sucrose), taken to reflect impaired resealing. Moreover, the membrane begins to vesiculate. Shedding of vesicles during the efflux measurements can not be responsible for the increased release of test solutes, since the ghosts do not loose hemoglobin and discriminate the nonelectrolytes according to their size. Moreover, the vesiculation site itself does not seem to act as the leak site, since ghosts prepared from erythrocytes pretreated with a carbodiimide which induces membrane rigidification still exhibit a pronounced protein degradation and vesiculation while the permeability enhancement induced by trypsination is markedly suppressed. The trypsin-induced leak has the properties of an aqueous pore as indicated, besides size selectivity, by its inhibition by phloretin and the very low activation energy. In analogy with concepts developed in the preceding paper (Klonk, S. and Deuticke, B. (1992) Biochim. Biophys. Acta 1106, 126-136 (Part I in this series)) the impaired resealing after limited proteolysis is assumed to be related to a perturbation of interactions of membrane skeletal elements with themselves and/or with the bilayer domain constituting the permeability barrier.

Involvement of cytoskeletal proteins in the barrier function of the human erythrocyte membrane. I. Impairment of resealing and formation of aqueous pores in the ghost membrane after modification of SH groups

Resealed human erythrocyte ghosts prepared by a two-step procedure were shown to have small residual barrier defects with the properties of aqueous pores, such as size discrimination of hydrophilic nonelectrolytes (erythritol to sucrose), indicative of an apparent pore radius of about 0.7 nm, and a low activation energy (about 12-20 kJ/mol (mannitol, sucrose)) of the leak fluxes. As in other cases (Deuticke et al. (1991) Biochim. Biophys. Acta 1067, 111-122) these leak fluxes can be inhibited by phloretin. Treatment of such resealed ghosts with the mild SH oxidizing agent, diamide, induces additional membrane leaks to the same extent and with the same properties as in native erythrocytes (Deuticke et al. (1983) Biochim. Biophys. Acta 731, 196-210), including reversibility of the leak by SH reducing agents, inhibition by phloretin and stimulation by alkanols. In contrast, resealed ghosts prepared either from diamide-treated erythrocytes or by adding diamide to the 'open' membranes prior to reconstitution of high ionic strength and raising the temperature, exhibit a state of greater leakiness. This leakiness is somewhat different in its origin from the former class of leaks, since it can also be produced by N-ethylmaleimide, which is essentially ineffective when added to the membrane in its 'tight' state. The leaks induced in the 'open' state of the membrane, which can be regarded as a consequence of an impaired resealing, are nevertheless reversible by reducing agents added after resealing and are comparable in many, but not all their characteristics to leaks induced in the 'tight' state of the membrane. Resealing in the presence of the isothiocyanostilbenes DIDS or SITS mimicks the leak forming effect of diamide by modifying a small population of SH groups, while amino groups seem not to be involved. The findings indicate and substantiate an important role of the redox state of membrane skeletal protein sulfhydryls in the maintenance and the re-establishment of the barrier function of the erythrocyte membrane.

The inhibition of ATP-dependent shape change of human erythrocyte ghosts correlates with an inhibition of Mg(2+)-ATPase activity by fluoride and aluminofluoride complexes

The vanadate-sensitive Mg(2+)-dependent ATPase activity of the human erythrocyte ghost is believed to be involved in the shape change events that convert echinocytic ghosts to smoothed forms (biconcave discs and stomatocytes). At physiological salt concentration, pH 7.4, 2 mM ATP, 5 mM Mg2+ and 1 mM EGTA, the Mg(2+)-ATPase activity of ghosts was inhibited strongly by millimolar concentrations of sodium fluoride: I50 = 1.31 +/- 0.23 mM (mean +/- S.D.; n = 12). The addition of aluminium chloride to 15 microM reduced the concentration of NaF required for 50% inhibition to 0.76 +/- 0.21 mM (n = 10). Aluminium alone had only a small inhibitory effect on the ATPase activity (13 +/- 9%; n = 10). Desferrioxamine, a strong chelator of tervalent aluminium ion, failed to reverse the inhibition by fluoride and reversed the inhibition in the presence of aluminium and fluoride back to those values obtained with fluoride alone. Of several metal salts tested only beryllium sulfate was able to replace aluminium as an effective inhibitor in the presence of fluoride. Inhibition of the Mg(2+)-ATPase activity by fluoride and the aluminofluoride complexes correlated with an inhibition of the rate of MgATP-dependent change in red cell ghost shape from echinocytes to smoothed forms. All gross morphological changes of the smoothing process were affected, including the production of discocytes, stomatocytes and endocyctic vesicles.

Maintenance and mobility of hemoglobin and water within the human erythrocyte after detergent disruption of the plasma membrane

Is an intact plasma membrane responsible for keeping hemoglobin and water within the human erythrocyte? If not, what is responsible? How free is Hb to move about within the erythrocyte? To answer these questions erythrocytes were taken for phase contrast microscopy, transmission electron microscopy (TEM), determination of water-holding capacity, and proton NMR studies both before and after membrane disruption with a nonionic detergent (Brij 58). Addition of 0.2% Brij to a D2O saline solution of hemoglobin (Hb) caused particles of Hb to appear and to aggregate. This aggregation of Hb caused the amplitude of the Hb proton NMR spectra to decrease. Thus, the less mobile the Hb the lower the Hb proton spectra amplitude. Erythrocytes washed in D2O saline showed proton NMR spectra of relatively low amplitude. Addition of Brij (0.2%) to these erythrocytes caused increased Hb mobility within these erythrocytes. The TEM of fixed and thin-sectioned erythrocytes treated with Brij showed disruption of the plasma membrane of all erythrocytes regardless of whether or not they had lost Hb. Brij-permeabilized erythrocytes washed in D2O saline or in a D2O K buffer maintained a higher heavy water-holding capacity upon centrifugation as compared to nonpermeabilized erythrocytes. The TEM of Brij-treated and washed erythrocyte "shells" revealed a continuous submembrane lamina but no other evidence of cytoskeletal elements. The water-holding capacity of the erythrocyte can be accounted for by the water-holding capacity of hemoglobin. The evidence favors a relatively immobile state of Hb and of water in the erythrocyte that is not immediately dependent on an intact plasma membrane but is attributed to interactions between Hb molecules and the submembrane lamina.

Kinetic analysis of the free-radical-induced lipid peroxidation in human erythrocyte membranes: evaluation of potential antioxidants using cis-parinaric acid to monitor peroxidation

cis-Parinaric acid (PnA), cis-trans-trans-cis-9, 11, 13, 15-octadecatetraenoic acid, is fluorescent (epsilon = 74,000 at 324 nm) when partitioned into a lipid environment and the fluorescence is destroyed upon reaction with free radicals. It has been used to monitor semiquantitatively free-radical-induced lipid peroxidation in human erythrocyte membranes. We have applied this assay to the quantitative evaluation of potential antioxidants. The kinetics of the reaction of PnA with free radicals were measured in erythrocyte ghosts. After initiation of free radical generation by cumene hydroperoxide and cupric ion, a steady-state rate of fluorescence decay is rapidly established. In the steady state the oxidation of PnA and, hence, the loss of fluorescence is a first-order process. In the presence of antioxidants, such as vitamin E, the rate constant of fluorescence loss decreases, thereby indicating that the antioxidant decreases the steady-state concentration of free radicals. By adding various concentrations of potential antioxidants, pseudo-first-order rate constants [k1] which measure the reactivity of antioxidants with free radicals were determined. Results show that, when incorporated into erythrocyte membranes, U-78, 517f, a vitamin E analog, is a potent free radical scavenger, being approximately 50% as effective as vitamin E and 10-15 times more potent than the aminosteroids evaluated (see Table 1).

A simple spectroscopic method for studying erythrocyte ghost resealing

A novel spectroscopic method is described for following the kinetics of resealing of hemolysed erythrocyte ghosts. The procedure is based on the broadening of the EPR spectrum of nitroxyl radicals by paramagnetic ions. The method is used to study the effect of Ca2+, Mg2+ and dimethonium ion on the kinetics of resealing.

A 35Cl and 37Cl NMR study of chloride binding to the erythrocyte anion transport protein

Band 3, the erythrocyte anion transport protein, mediates the one-for-one exchange of bicarbonate and chloride ions across the membrane and consequently plays an important role in respiration. Binding to the protein forms the first step in the translocation of the chloride across the membrane. 35Cl and 37Cl NMR relaxation measurements at various field strengths were used to study chloride binding to the protein in the presence and absence of the transport inhibitor 4,4'-dinitrostilbene-2,2'-disulfonate. Significant differences occurred in the NMR relaxation rates depending on whether the inhibitor was present or not. The results indicate that the rate of chloride association and dissociation at each external binding site occurs on a time scale of less than or equal to 5 microseconds. This implies that the transmembrane flux is not limited by the rate of chloride binding to the external chloride binding site of band 3. The rotational correlation-time of chloride bound to band 3 was found to be greater than 20 ns with a quadrupole coupling constant of approximately 2 MHz.

Degradation of erythrocyte glycophorin results in increased membrane bound hemoglobin

Degradation of glycophorin by trypsin in intact red cells results in an increase in hemoglobin bound to the membrane. Incubation of resealed ghosts made from these cells demonstrated that the hemoglobin was bound to the intracellular membrane surface. We found that treatment of hemoglobin with KCNO inhibited the ability of hemoglobin to bind to the membrane. Addition of KCNO to intact cells followed by trypsin treatment abolished the additional membrane-bound hemoglobin, indicating that the bound hemoglobin resulted from increased Band 3 binding. Treatment of intact cells with neuraminidase also resulted in increased membrane-bound Hb, which correlated with the amount of sialic acid released. Scatchard analysis revealed that enzyme treatment increased the affinity of hemoglobin for the high affinity Band 3 binding site, while KCNO treatment abolished this binding. Taken together, these studies demonstrate that extracellular proteolytic degradation of glycophorin by proteases similar to those released by cells of the reticuloendothelial system results in an increased ability of hemoglobin to bind to Band 3.

Mechanism of hemolysis of red blood cell mediated by ethanol

The effects of ethanol on hemolysis of human red blood cells (RBCs) were studied at 21 +/- 1 degrees C in the saline buffer (138 mM NaCl, 6.1 mM Na2HPO4, 1.4 mM NaH2PO4, 5 mM glucose and pH 7.4). The hemolysis process for ethanol-treated RBCs was preceded by the leakage of the small cation K+ from the cells indicating the colloid-osmotic nature of lysis. Since the extent of membrane lesion increased with an increasing ethanol concentration, osmotic protection experiments by using solutes varying in size were carried out to estimate the diameter of the pore. Quantitative analysis of the data by considering the effect of molecular seiving of the protectants with different sizes indicated that ethanol induced formation of membrane pores with a diameter of approximately 13 A. There was no detectable release of membrane fragments as assayed by the acetylcholinesterase activity, but the membrane structures were significantly perturbed, presumably at the membrane cytoskeletal protein, as evidenced by the altered rheological properties of RBC in the presence of ethanol. It is suggested that the creation of membrane pores might involve in the deranged cytoskeletal network of ethanol-treated RBC.

Low concentrations of macromolecular solutes significantly affect electrofusion yield in erythrocyte ghosts

Electrofusion yields in rabbit erythrocyte ghosts containing various amounts of hemoglobin, bovine serum albumin, or dextran at low concentrations were measured as a function of pulse field strength and pulse decay half-time. The presence of any of the macromolecules in low concentrations caused fusion yields to be significantly higher than when the ghosts were white (i.e., containing only buffer). The fusion yield enhancement was also critically dependent on the parameters of the electric field pulse. The fusion yield was also significantly affected by small changes in the concentration of hemoglobin when it was present outside the ghost membranes in the suspension buffer.

The retention of entrapped molecules within erythrocyte ghosts during cryopreservation

In view of the interest in erythrocyte ghosts and carrier erythrocytes as potential drug delivery systems, this work was undertaken to determine conditions facilitating the retention of entrapped molecules during cryopreservation. Upon freeze-thaw treatment intact erythrocytes and erythrocyte ghosts displayed different damage profiles with respect to cryoprotectant concentration. Non-penetrating cryoprotectants showed optimum protection of intact cells at 0.4-0.5 M; this optimum was not observed with ghosts, in which damage decreased with concentration up to 1.0 M. The concentration optimum for intact cells was not abolished by oxidative or reductive treatments suggesting that its absence in ghosts is not due to altered protein-protein or protein-lipid interactions. The extent of freeze-thaw damage to ghosts was influenced by the qualitative ionic composition of a cryoprotectant-free suspending medium, with 10-12% haemolysis observed in the presence of Li+ and Mg2+ but greater than 60% for Na+, Cs+, K+ and NH4+ with increasing loss following that order. The release on freezing of entrapped haemoglobin, insulin and sucrose was found to be inversely proportional to their molecular weights.

States of stability/lysis in human fetal and adults red blood cells

In human red blood cells from umbilical cord (NRBC) and from adult (ARBC) blood we measured: (i) the equilibrium distribution (medium/cells) for haemoglobin as a function of medium osmolality (osmotic fragility curve) and (ii) the rate of haemoglobin loss to a hypotonic medium of fixed osmolality. From the analysis of the osmotic (cumulative) fragility curve, a subpopulation of high resistance (young?) cells was individualized only in samples from cord blood. The differences presented in the rate of haemoglobin loss between samples of umbilical cord and adult's blood point to distinct cell surface restrictions (cytoskeleton and/or plasma membrane phospholipid) to haemoglobin leak in both cells. Uniformly distributed (among all cells in both samples) differences could explain the distinct rates of haemoglobin loss. However, marked differences restricted to only a subpopulation of cord blood cells could also explain these results.