Drug-induced erythrocyte membrane internalization

Cell-based carrier for targeted hitchhiking delivery

Drug delivery systems aim at improving drug transport efficiency and therapeutic efficacy by rational design, and current research on conventional delivery systems brings new developments for disease treatment. Recently, studies on cell-based drug delivery systems are rapidly emerging, which shows great advantages in comparison to conventional drug delivery system. The system uses cells as carriers to delivery conventional drugs or nanomedicines and shows good biocompatibility and enhanced targeting efficiency, beneficial from self component and its physiological function. The construction methodology of cell-based carrier determines the effect on the physiological functions of transporting cell and affects its clinical application. There are different strategies to prepare cell-based carrier, such as direct internalization or surface conjugation of drugs or drug loaded materials. Thus, it is necessary to fully understand the advantages and disadvantages of different strategies for constructing cell-based carrier and then to seek the appropriate construction methodology for achieving better therapeutic results based on disease characterization. We here summarize the application of different types of cell-based carriers reported in recent years and further discuss their applications in disease therapy and the dilemmas faced in clinical translation. We hope that this summary can accelerate the process of clinical translation by promoting the technology development of cell-based carrier.

Role of Spectrin in Endocytosis

Cytoskeletal spectrin is found in (non)erythroid cells. Eukaryotic endocytosis takes place for internalizing cargos from extracellular milieu. The role of spectrin in endocytosis still remains poorly understood. Here, I summarize current knowledge of spectrin function, spectrin-based cytoskeleton and endocytosis of erythrocytes, and highlight how spectrin contributes to endocytosis and working models in different types of cells. From an evolutionary viewpoint, I discuss spectrin and endocytosis in a range of organisms, particularly in plants and yeast where spectrin is absent. Together, the role of spectrin in endocytosis is related to its post-translational modification, movement/rearrangement, elimination (by proteases) and meshwork fencing.

In vivo nano-biosensing element of red blood cell-mediated delivery

Biosensors based on nanotechnology are developing rapidly and are widely applied in many fields including biomedicine, environmental monitoring, national defense and analytical chemistry, and have achieved vital positions in these fields. Novel nano-materials are intensively developed and manufactured for potential biosensing and theranostic applications while lacking comprehensive assessment of their potential health risks. The integration of diagnostic in vivo biosensors and the DDSs for delivery of therapeutic drugs holds an enormous potential in next-generation theranostic platforms. Controllable, precise, and safe delivery of diagnostic biosensing devices and therapeutic agents to the target tissues, organs, or cells is an important determinant in developing advanced nanobiosensor-based theranostic platforms. Particularly, inspired by the comprehensive biological investigations on the red blood cells (RBCs), advanced strategies of RBC-mediated in vivo delivery have been developed rapidly and are currently in different stages of transforming from research and design to pre-clinical and clinical investigations. In this review, the RBC-mediated delivery of in vivo nanobiosensors for applications of bio-imaging at the single-cell level, advanced medical diagnostics, and analytical detection of biomolecules and cellular activities are presented. A comprehensive perspective of the technical framework of the state-of-the-art RBC-mediated delivery systems is explained in detail to inspire the design and implementation of advanced nanobiosensor-based theranostic platforms taking advantage of RBC-delivery modalities.

Erythrocytes as Carriers: From Drug Delivery to Biosensors

Drug delivery using natural biological carriers, especially erythrocytes, is a rapidly developing field. Such erythrocytes can act as carriers that prolong the drug's action due to its gradual release from the carrier; as bioreactors with encapsulated enzymes performing the necessary reactions, while remaining inaccessible to the immune system and plasma proteases; or as a tool for targeted drug delivery to target organs, primarily to cells of the reticuloendothelial system, liver and spleen. To date, erythrocytes have been studied as carriers for a wide range of drugs, such as enzymes, antibiotics, anti-inflammatory, antiviral drugs, etc., and for diagnostic purposes (e.g. magnetic resonance imaging). The review focuses only on drugs loaded inside erythrocytes, defines the main lines of research for erythrocytes with bioactive substances, as well as the advantages and limitations of their application. Particular attention is paid to in vivo studies, opening-up the potential for the clinical use of drugs encapsulated into erythrocytes.

Host Cytoskeleton Remodeling throughout the Blood Stages of Plasmodium falciparum

The asexual intraerythrocytic development of Plasmodium falciparum, causing the most severe form of human malaria, is marked by extensive host cell remodeling. Throughout the processes of invasion, intracellular development, and egress, the erythrocyte membrane skeleton is remodeled by the parasite as required for each specific developmental stage. The remodeling is facilitated by a plethora of exported parasite proteins, and the erythrocyte membrane skeleton is the interface of most of the observed interactions between the parasite and host cell proteins. Host cell remodeling has been extensively described and there is a vast body of information on protein export or the description of parasite-induced structures such as Maurer's clefts or knobs on the host cell surface. Here we specifically review the molecular level of each host cell-remodeling step at each stage of the intraerythrocytic development of P. falciparum We describe key events, such as invasion, knob formation, and egress, and identify the interactions between exported parasite proteins and the host cell cytoskeleton. We discuss each remodeling step with respect to time and specific requirement of the developing parasite to explain host cell remodeling in a stage-specific manner. Thus, we highlight the interaction with the host membrane skeleton as a key event in parasite survival.

Platelet-Microcapsule Hybrids Leverage Contractile Force for Targeted Delivery of Hemostatic Agents

We report a cell-mediated, targeted drug delivery system utilizing polyelectrolyte multilayer capsules that hybridize with the patient's own platelets upon intravenous administration. The hybridized platelets function as the sensor and actuator for targeted drug delivery and controlled release in our system. These capsules are biochemically and mechanically tuned to enable platelet adhesion and capsule rupture upon platelet activation and contraction, enabling the targeted and controlled "burst" release of an encapsulated biotherapeutic. As platelets are the "first responders" in the blood clot formation process, this platelet-hybridized system is ideal for the targeted delivery of clot-augmenting biotherapeutics wherein immediate therapeutic efficacy is required. As proof-of-concept, we tailored this system to deliver the pro-clotting biotherapeutic factor VIII for hemophilia A patients that have developed inhibitory antifactor VIII antibodies. The polyelectrolyte multilayer capsules physically shield the encapsulated factor VIII from the patient's inhibitors during circulation, preserving its bioactivity until it is delivered at the target site via platelet contractile force. Using an in vitro microfluidic vascular injury model with factor VIII-inhibited blood, we demonstrate a 3.8× increase in induced fibrin formation using capsules loaded with factor VIII at a concentration an order of magnitude lower than that used in systemic delivery. We further demonstrate that clot formation occurs 18 min faster when factor VIII loaded capsules are used compared to systemic delivery at the same concentration. Because platelets are integral in the pathophysiology of thrombotic disorders, cancer, and innate immunity, this paradigm-shifting smart drug delivery system can be similarly applied to these diseases.

Plasmodium falciparum ligand binding to erythrocytes induce alterations in deformability essential for invasion

The most lethal form of malaria in humans is caused by Plasmodium falciparum. These parasites invade erythrocytes, a complex process involving multiple ligand-receptor interactions. The parasite makes initial contact with the erythrocyte followed by dramatic deformations linked to the function of the Erythrocyte binding antigen family and P. falciparum reticulocyte binding-like families. We show EBA-175 mediates substantial changes in the deformability of erythrocytes by binding to glycophorin A and activating a phosphorylation cascade that includes erythrocyte cytoskeletal proteins resulting in changes in the viscoelastic properties of the host cell. TRPM7 kinase inhibitors FTY720 and waixenicin A block the changes in the deformability of erythrocytes and inhibit merozoite invasion by directly inhibiting the phosphorylation cascade. Therefore, binding of P. falciparum parasites to the erythrocyte directly activate a signaling pathway through a phosphorylation cascade and this alters the viscoelastic properties of the host membrane conditioning it for successful invasion.

Erythrocyte encapsulated l-asparaginase (GRASPA) in acute leukemia

l-asparaginase, an enzyme originally derived from Escherichia coli, represents a major drug in the treatment of acute lymphoblastic leukemia. However, the occurrence of major adverse effects often leads to early withdrawal of the enzyme. Main side effects include immune-allergic reactions, coagulopathy, pancreatitis and hepatic disorders. Novel asparaginase formulations and alternative sources have been developed to address this issue, but the results were not totally satisfactory. l-asparaginase loaded red blood cells (RBCs; GRASPA) represent a new asparaginase presentation with reduced immunological adverse reactions. RBCs protect l-asparaginase, enhance its half-life and reduce the occurrence of adverse events. We reviewed the history, biology and clinical experiences with l-asparaginase, and the characteristics and first clinical experiences with GRASPA in the treatment of acute leukemia.

Microscopy and Microanalysis of Blood in a Snake Head Fish, Channa gachua Exposed to Environmental Pollution

Conventional and highly sophisticated analytical methods (Cyria et al., 1989; Massar et al., 2012a) were used to analyze micro-structural and micro-analytical aspects of the blood of snake head fish, Channa gachua, exposed to municipal wastes and city garbage. Red (RBC) and white blood cell (WBC) counts and hemhemoglobin content were found to be higher in pollution affected fish as compared with control. Scanning electron microscopy revealed the occurrence of abnormal erythrocytes such as crenated cells, echinocytes, lobopodial projections, membrane internalization, spherocytes, ruptured cells, contracted cells, depression, and uneven elongation of erythrocyte membranes in fish inhabiting the polluted sites. Energy-dispersive X-ray spectroscopy (EDS) revealed the presence of silicon and lead in the RBCs of pollution affected fish. Significance of the study includes the highly sophisticated analytical approach, which revealed the aforementioned micro-structural abnormalities.

Design strategies and applications of circulating cell-mediated drug delivery systems

Drug delivery systems, particularly nanomaterial-based drug delivery systems, possess a tremendous amount of potential to improve diagnostic and therapeutic effects of drugs. Controlled drug delivery targeted to a specific disease is designed to significantly improve the pharmaceutical effects of drugs and reduce their side effects. Unfortunately, only a few targeted drug delivery systems can achieve high targeting efficiency after intravenous injection, even with the development of numerous surface markers and targeting modalities. Thus, alternative drug and nanomedicine targeting approaches are desired. Circulating cells, such as erythrocytes, leukocytes, and stem cells, present innate disease sensing and homing properties. Hence, using living cells as drug delivery carriers has gained increasing interest in recent years. This review highlights the recent advances in the design of cell-mediated drug delivery systems and targeting mechanisms. The approaches of drug encapsulation/conjugation to cell-carriers, cell-mediated targeting mechanisms, and the methods of controlled drug release are elaborated here. Cell-based "live" targeting and delivery could be used to facilitate a more specific, robust, and smart payload distribution for the next-generation drug delivery systems.

Erythrocyte-inspired delivery systems

Herein recent progress in developing red blood cell (RBC)-inspired delivery systems is reviewed, with an emphasis on how our growing understanding of fundamental biological properties of natural RBCs has been applied in the design and engineering of these delivery systems. Specifically, progress achieved in developing carrier RBCs, a class of delivery vehicles engineered by directly loading natural RBCs with therapeutic agents, will be reviewed. Then alternative approaches to engineering synthetic vehicles through mimicking the mechanobiological and chemico-biological properties of natural RBCs will be considered. The synthesis and application of RBC membrane-derived vesicles, of which the natural RBC membranes are collected and directly utilized to prepare drug carriers, will then be discussed. Finally, a recent approach in engineering RBC membrane-camouflaged nanoparticle systems that combine advantages of natural RBCs and synthetic biomaterials will be highlighted. These developments indicate that RBC-inspired delivery systems will result in next-generation nanomedicine with extensive medical applications.

L-Asparaginase encapsulated intact erythrocytes for treatment of acute lymphoblastic leukemia (ALL)

As a primary drug for the treatment of acute lymphoblastic leukemia (ALL), encapsulation of L-asparaginase (ASNase) into red blood cells (RBC) has been popular to circumvent immunogenicity from the exogenous protein. Unlike existing methods that perturbs RBC membranes, we introduce a novel method of RBC-incorporation of proteins using the membrane-translocating low molecular weight protamine (LMWP). Confocal study of fluorescence-labeled LMWP-ovalbumin, as a model protein conjugate, has shown significant fluorescence inside RBCs. Surface morphology by scanning electron microscopy of the RBCs loaded with LMWP-ASNase was indistinguishable with normal RBCs. These drug loaded RBCs also closely resembled the profile of the native erythrocytes in terms of osmotic fragility, oxygen dissociation and hematological parameters. The in vivo half-life of enzyme activity after administering 8 units of RBC/LMWP-ASNase in DBA/2 mice was prolonged to 4.5+/-0.5 days whereas that of RBCs loaded with ASNase via a hypotonic method was 2.4+/-0.7 days. Furthermore, the mean survival time of DBA/2 mice bearing mouse lymphoma cell L5178Y was improved by approximately 44% compared to the saline control group after treatment with the RBC loaded enzymes. From these data, an innovative, novel method for encapsulating proteins into intact and fully functional erythrocytes was established for potential treatment of ALL.

Structural determinants of antimicrobial and antiplasmodial activity and selectivity in histidine-rich amphipathic cationic peptides

Designed histidine-rich amphipathic cationic peptides, such as LAH4, have enhanced membrane disruption and antibiotic properties when the peptide adopts an alignment parallel to the membrane surface. Although this was previously achieved by lowering the pH, here we have designed a new generation of histidine-rich peptides that adopt a surface alignment at neutral pH. In vitro, this new generation of peptides are powerful antibiotics in terms of the concentrations required for antibiotic activity; the spectrum of target bacteria, fungi, and parasites; and the speed with which they kill. Further modifications to the peptides, including the addition of more hydrophobic residues at the N terminus, the inclusion of a helix-breaking proline residue or using D-amino acids as building blocks, modulated the biophysical properties of the peptides and led to substantial changes in toxicity to human and parasite cells but had only a minimal effect on the antibacterial and antifungal activity. Using a range of biophysical methods, in particular solid-state NMR, we show that the peptides are highly efficient at disrupting the anionic lipid component of model membranes. However, we also show that effective pore formation in such model membranes may be related to, but is not essential for, high antimicrobial activity by cationic amphipathic helical peptides. The information in this study comprises a new layer of detail in the understanding of the action of cationic helical antimicrobial peptides and shows that rational design is capable of producing potentially therapeutic membrane active peptides with properties tailored to their function.

Drug, enzyme and peptide delivery using erythrocytes as carriers

Erythrocytes are potential biocompatible vectors for different bioactive substances, including drugs. These can be used successfully as biological carriers of drugs, enzymes and peptides. There are currently diverse methods that permit drug encapsulation in erythrocytes with an appropriate yield. The methods most commonly employed are based on a high-haematocrit dialysis procedure, mainly hypo-osmotic dialysis. Erythrocytes loaded with drugs and other substances allow for different release rates to be obtained. Encapsulation in erythrocytes significantly changes the pharmacokinetic properties of drugs in both animals and humans, enhancing liver and spleen uptake and targeting the reticulo-endothelial system (RES). Amongst other applications, erythrocytes have been used for drug-targeting the RES with aminoglycoside antibiotics; the selective transport to certain organs and tissues of certain antineoplastic drugs, such as methotrexate, doxorubicine, etoposide, carboplatin, etc.; the encapsulation of angiotensin-converting enzyme (ACE) inhibitors, systemic corticosteroids, the encapsulation of new prodrugs with increased duration of action, etc. Erythrocytes are also attractive systems in the sense of their potential ability to deliver proteins and therapeutic peptides. Thus, erythrocytes have been used for the transport of enzymes destined for the correction of metabolic alterations as l-asparaginase, alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (AlDH) among others. Erythrocytes have been used successfully as carriers of anti-HIV peptides, such as AZT, nucleoside analogues, antisense oligonucleotides, antineoplastic peptides, erythropoietin, interleukin 3, etc. Amongst other applications, mention may be made of paramagnetic erythrocytes, encapsulation of MRI contrast agents or the study of the metabolism of the red cell. Although erythrocytes have been applied with different uses in human medicine, their deployment is still very limited due to difficulties involving storage, its exposure to contamination and the absence of a validated industrial procedure for its preparation.

Receptor-mediated targeted drug or toxin delivery

The new approach to the treatment of cancer or to immunomodulation is drug targeting. Cellular uptake of drugs bound to a targeting carrier or to a targetable polymeric carrier is mostly restricted to receptor-mediated endocytosis. Factors that influence the efficiency of receptor-mediated uptake of targeted drug conjugate are the affinity of the targeting moieties, the affinity and nature of the target antigen, density of the target antigen, the epitope of the target antigen, the type of cell target, the rate of endocytosis, the route of internalization of the ligand-receptor complex, the ability of the drug or toxin to release from its targeted carrier, the ability of the drug or toxin to escape from a vesicular compartment into the cytosol, the affinity of the carrier to the drug and the concentration of the carrier. Targeted chemotherapy is also significantly influenced by the antigenic modulation and/or immunoselection of tumor cells. The binding of drug (toxin) to targetable polymeric carrier considerably decreases unwanted side toxicity.

Phospholipids in animal eukaryotic membranes: transverse asymmetry and movement

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Spontaneous endocytosis in human neonatal and adult red blood cells: comparison to drug-induced endocytosis and to receptor-mediated endocytosis

Neonatal RBC contain many more spontaneous endocytic vacuoles than do adult RBC. It is not known if this difference is a result of an increase in production of vacuoles in the neonatal RBC (as is the case in drug-induced endocytosis), or is the result of a less effective neonatal macrophagic "pitting" process. Using an in vitro model of spontaneous endocytosis, we compared the rate and quantity of vacuoles and the shape of cord and adult RBC containing pits, visible by interference contrast microscopy (Nomarski method). The mechanism of the spontaneous endocytosis was explored using different inhibitors: sodium vanadate an inhibitor of ATPases, sodium fluoride which inhibits the generation of ATP and sodium cyanide a potent inhibitor of oxidative phosphorylation. We then compared spontaneous endocytosis with two other forms of RBC endocytosis: drug-induced endocytosis and receptor-mediated endocytosis. Spontaneous endocytosis is in fact increased in neonatal RBC initially but the increase in number of RBC containing pits after 144 hr of incubation is almost the same in adult RBC and neonatal RBC. Comparing spontaneous endocytosis with drug-induced endocytosis, it appears that their mechanisms are different in that spontaneous endocytosis is not preceded by stomatocytic shape change and is not inhibited by sodium vanadate or sodium fluoride as is the case for drug-induced endocytosis. Spontaneous endocytosis is different than transferrin receptor-mediated endocytosis because it occurs in many RBC, not only in the motile R1 reticulocytes and is not inhibited by sodium cyanide as is receptor-mediated endocytosis. Thus spontaneous endocytosis appears to be different than drug-induced endocytosis and transferrin receptor-mediated endocytosis. The increase in spontaneous endocytosis in cord RBC seen in vivo is probably a consequence of an immaturity of the neonatal macrophage pitting process.

Amphiphile-induced antihaemolysis is not causally related to shape changes and vesiculation

A wide variety of structurally different antihaemolytic amphiphiles were tested for their ability to induce exovesiculation (acetylcholinesterase (AChE) release, transmission electron microscopic (TEM) studies), endovesiculation (fluorescein isothiocyanate conjugated dextran (FITC-dextran) internalization, TEM studies) and shape changes in human erythrocytes at concentrations where they exert maximum protection against hypotonic haemolysis. The results show that vesiculation is a common phenomenon induced by amphiphiles in erythrocytes. Sphero-echinocytogenic amphiphiles induced exovesiculation, whereas stomatocytogenic amphiphiles induced endovesiculation. The antihaemolytic potency of the amphiphiles was not related to their ability to induce exo- or endovesiculation, or to the type or extent of shape changes induced, and it could not be ascribed to any molecular feature of the amphiphiles or to their charge. It is proposed that amphiphiles, when intercalated into the lipid bilayer of the membrane, rapidly induce rearrangements within the bilayer and that these rearrangements are associated with an increase in the permeability of the membrane; it is suggested that a rapid efflux of ions decreases the difference in osmotic pressure between cell interior and hypotonic buffer, thereby protecting cells from being lysed.

Vesiculation induced by amphiphiles in erythrocytes

The ability of shape-transforming cationic, anionic, zwitterionic, and nonionic amphiphiles to induce vesiculation in human erythrocytes was studied. At concentrations where they exhibit maximum protection against hypotonic haemolysis (CAHmax) echinocytogenic amphiphiles induced a rapid release of exovesicles. Following 5 min of incubation, the vesicle release (acetylcholinesterase release) amounted from 4% (sodium alkyl sulphates) to 13% (zwittergents) of the total acetylcholinesterase activity of the erythrocytes. At concentrations corresponding to CAH50 the vesicle release was less than 15% of that released at CAHmax. The size and the appearance of the vesicles varied with the type of amphiphile. Stomatocytogenic amphiphiles which do not pass the erythrocytes through echinocytic stages, did not induce release of exovesicles. Electron and fluorescence microscopic observations of erythrocytes treated with stomatocytogenic amphiphiles strongly indicated that an endovesiculation had occurred. Amphiphiles which pass the erythrocytes through echinocytic stages before stomatocytic shapes are attained, induced a release of both exo- and endovesicles.

Lysosomal movements during heterophagy and autophagy: with special reference to nematolysosome and wrapping lysosome

Recent studies on lysosomal movements during heterophagy and autophagy performed in our laboratory for the past several years were reviewed; methods for the investigation of lysosomes and the cytoskeleton in these studies mainly involved electron microscopic cytochemistry. Lysosomal movements during heterophagy were observed in cultured rat alveolar macrophages taking up horseradish peroxidase (HRP) and rat peroxidase-antiperoxidase (PAP) by fluid-phase pinocytosis and adsorptive pinocytosis, respectively. A characteristic lysosomal change which was induced by the pinocytosis was the appearance of long, threadlike lysosomes (nematolysosomes) in the cytoplasm. The effects of actin filament destabilizer and antimicrotubular drug on lysosomal changes revealed that the appearance of nematolysosomes was dependent on the presence of both actin filaments and microtubules. The close morphological relationship between lysosomes and cytoskeletal elements, such as actin filaments and microtubules in the alveolar macrophages, supports the participation of the cytoskeletal system in the regulatory mechanism of lysosomal movements. In the study of the lysosomal wrapping mechanism (LWM), which is one type of lysosomal movement that occurs during autophagy, it was found that the occurrence of LWM was dependent on energy--namely, the supply of ATP--and on the presence of actin filaments. However, deconstruction of microtubules induced or favored the occurrence of LWM. It is conceivable that the LWM is also related to the cytoskeletal system. We conclude that intracellular dynamics of lysosomes during heterophagy and autophagy are largely a consequence of complicated modulation by the cytoskeletal system.

Physiologic formation of intracellular vesicles in mature erythrocytes

The ability of mature erythrocytes to spontaneously form intracellular vesicles has been implied from clinical studies but has not been examined experimentally. An in vitro model was developed to demonstrate whether mature erythrocytes are capable of spontaneously forming intracellular vesicles. Normal human erythrocytes were incubated in vitro at 37 degrees C for 144 hr in a synthetic medium. During the course of these incubations, approximately 4% of erythrocytes developed intracellular vesicles which were quantitated by using interference contrast microscopy. Electron microscopic studies confirmed the intracellular nature of these vesicles. Incubation of erythrocytes in autologous plasma produced similar results. The rate of vesicle acquisition in vivo was measured by quantitating erythrocyte vesicles immediately prior to and following splenectomy. The rates of vesicle acquisition in vivo and in vitro were comparable. This in vitro model confirms the ability of mature erythrocytes to spontaneously form intracellular vesicles and strongly supports the concept that this is a physiologic process.

Influence of chlorpromazine on the transverse mobility of phospholipids in the human erythrocyte membrane: relation to shape changes

The influence of chlorpromazine (CPZ) on the transverse mobility of spin-labeled phospholipids incorporated into human erythrocytes was investigated by electron spin resonance. The very slow transverse diffusion of phosphatidylcholine, as well as the absence of transverse mobility of sphingomyelin were not modified even by sublytic concentrations (approximately equal to 1 mM) of CPZ. On the other hand, the rapid outside-inside translocation of the aminophospholipids (Seigneuret and Devaux (1984) Proc. Natl. Acad. Sci. USA 81, 3751-3755), was slightly hindered in CPZ containing membranes. If the spin-labeled aminolipids were incorporated in erythrocytes and allowed to flip to the inner monolayer before CPZ addition, a fraction of the spin labels (10-15%) flipped back instantaneously from the inner to the outer leaflet, upon incubation with CPZ. Similar experiments carried out with spin-labeled phosphatidylcholine and spin-labeled sphingomyelin showed that a fraction of the spin-labeled choline derivatives flip instantaneously to the inner leaflet if CPZ was added after the spin labels. Addition of lysophosphatidylcholine had no effect on the spin-labeled phospholipid redistribution nor on their transmembrane mobility. We interpret the immediate effect of CPZ addition as being due to a reorganization of the bilayer accompanying the rapid CPZ membrane penetration, phenomenon which is independent of the CPZ effect on the steady-state activity of the 'aminophospholipid translocase', the latter effect being probably a direct CPZ-protein interaction. By comparison of the time course of phosphatidylserine transverse diffusion in control discocyte cells and in CPZ-induced stomatocytes, we infer that the difference in cell shape is not a major factor in the regulation of the active inward transport of aminophospholipids in human erythrocytes.

Endovesiculation of human erythrocytes exposed to sphingomyelinase C: a possible explanation for the enzyme-resistant pool of sphingomyelin

When human erythrocytes are treated with Staphylococcus aureus sphingomyelinase C at 37 degrees C they become susceptible to cold lysis and appear to endovesiculate. Endovesiculation has been confirmed by showing that in parallel with sphingomyelin breakdown, the cells accumulate [3H]inulin or [14C]sucrose (without losing intracellular K+) and also experience a loss of cell-surface acetylcholinesterase activity into a latent intracellular pool which can be revealed by treatment with detergent. On the basis of these observations it can be calculated that endovesicles account for about 2-4% of cell volume and about 25% of total cell surface. Pretreatment of cells with bee venom phospholipase A2 completely blocked sphingomyelinase-induced endovesiculation but this effect was related to a concomitant decrease in sphingomyelin breakdown which was reduced by about 90%. These results indicate that the pool of sphingomyelin which is not susceptible to attack by sphingomyelinase C (about 15% of total sphingomyelin) may be resistant because of membrane internalisation and not because it originally resides in the inner leaflet of the plasma membrane.

Drug-induced endocytosis and entrapment in red cells and ghosts

Induction of endocytosis in intact human RBC can be achieved by treating RBC in vitro with several classes of amphipathic cations. Perhaps 1-2% of the 90 fl volume of the red cell will then consist of any material suspended or dissolved in the bulk supernatant medium. This amount could be increased if the material in question also binds selectively to the outer surface of the red cell's plasma membrane. Such a red cell, now rendered spherostomatocytic if reinjected into the circulation, would be removed by the monocytes-macrophages concentrated in spleen and to a lesser extent in liver, lymph nodes, and bone marrow. Conceivably, one could deliver a significant amount of drug or other agent to monocytes-macrophages in these sites. Endocytosis can also be induced in white ghosts and the resulting vacuoles are not accessible to small molecules. The targeting of white ghosts has not been subjected to extensive study but such ghosts containing material included in their endocytic vacuoles could be used to deliver agents to the recipient's monocyte-macrophage system.

Decreased membrane deformability in Melanesian ovalocytes from Papua New Guinea

We examined the ability of Melanesian ovalocytes from Papua New Guinea to be deformed in order to probe the resistance of these cells to invasion by several species of malaria parasite. We found ovalocytes were refractile to drug-induced endocytosis, that they formed abnormal rouleaux, showed reduced deformability when aspirated into 0.6-micron diameter pores in polycarbonate sieves, and failed to crenate when mounted under a glass coverslip. No substantial differences were found between normocytes and ovalocytes in their initial rate of filtration through 4.5-micron pore polycarbonate sieves, their membrane fluidity as measured by the rate of depolarization of fluorescent probes or the rate of extraction of cytoskeletal proteins in low ionic strength buffers. We conclude that the resistance of ovalocytes to undergo localized deformation might be significant in explaining the resistance of these cells to invasion by malarial merozoites.

Drug-induced stomatocytosis and anemia during consolidation chemotherapy of childhood acute leukemia

In a group of 23 children with acute leukemia, all but one of whom had entered complete remission, retrospective analysis of hematological profiles demonstrated that administration of consolidation chemotherapy, with a combination of cytosine arabinoside (Ara-C) and 6-thioguanine (TG), was associated with a fall in the erythrocyte concentration in peripheral blood, the rate of which was at least as fast as would have occurred with total marrow ablation and consequent red cell aplasia. In the absence of profound myelosuppression or detectable hemorrhage, drug-induced erythrocytotoxicity was suspected, prompting in vitro studies of erythrocytes from children with acute leukemia and normal adults. At therapeutic concentration, Ara-C and TG, individually and in combination, produced significant stomatocytosis in samples from both groups. Since phenothiazines are stomatocytogenic and are administered as anti-emetics in conjunction with cancer chemotherapy, chlorpromazine was investigated in parallel studies that demonstrated stomatocytosis at therapeutic concentration, but no consistent interaction with the effects of Ara-C and TG in this regard. These observations suggest a possible pathogenetic mechanism for the development of anemia resulting from drug-induced erythrocytotoxicity.

Alteration of membrane phospholipid bilayer organization in human erythrocytes during drug-induced endocytosis

Our plan was to evaluate the potentially important role of phospholipids in erythrocyte shape alterations by determining if their orientation was altered during endocytosis. Stomatocytosis and endocytosis were induced in normal intact human erythrocytes by incubation with three agents: primaquine, vinblastine, and chlorpromazine, each of which has its own requirements and time course for producing endocytosis. The organization of the phospholipid bilayer was assessed by measuring the extent of degradation of phophatidylcholine (PC), phophatidylethanolamine (PE), phosphatidylserine (PS), and sphingomyelin (SM) produced by exposure of erythrocytes to a nonpenetrating protease-free phospholipase A2 alone or in combination with a purified sphingomyelinase as well. The induction of stomatocytosis did not change this orientation. However, correlating with the onset of endocytosis but not its extent, there was an increase in PE degradation, which could be detected regularly only by use of phospholipase A2 alone. Use of the combination of phospholipase A2 and sphingomyelinase showed that the extent and course of endocytosis was paralleled by an apparent movement of PC and SM from the outer to the inner half of the lipid bilayer. Since no further PE was hydrolyzed and because no PS was ever degraded, this inward movement of PC and SM did not represent the establishment of complete symmetry in the membrane. By adjusting the experimental design it was possible to implicate the endocytic process, and not insertion of drug in the membrane, as the cause of the alterations in phospholipid organization seen. Our findings indicate that the phospholipid orientation is very closely involved in the endocytosis process and that specific states of phospholipid asymmetry may be related to identifiable membrane events.

Cytosolic protein binding to band-3 protein inhibits endocytosis of isolated human erythrocyte membranes

Recent studies of haemoglobin binding to the cytoplasmic side of the erythrocyte membrane have shown that the predominant high-affinity interaction occurs with the major integral membrane protein known as band-3 protein and that this interaction may occur within the intact erythrocyte in a manner regulated by cell pH. We report here that haemoglobin and glyceraldehyde 3-phosphate dehydrogenase binding to band-3 protein in isolated membranes can inhibit endocytosis during vesiculation in vitro. The specificity of this effect was demonstrated by showing that myoglobin, which has an affinity for the membrane fully one to two orders of magnitude lower than that for haemoglobin, does not inhibit endocytosis.

Purification of a water-soluble Mg2+-ATPase from human erythrocyte membranes

A water-soluble Mg2+-ATPase previously reported (White, M.D. and Ralston, G.B. (1976) Biochim. Biophys. Acta 436, 567-576) has been purified from human erythrocyte membranes. The purified enzyme has a molecular weight of 575 000; the apparent minimum molecular weight was 100 000, corresponding to a soluble protein of the component 3 region. The Km value for ATP was 1 mM and apparent Km for Mg2+ was 3.6 mM. By means of histochemical activity staining in acrylamide gels it was shown that the purified ATPase preparation could be inhibited by Cd2+ and Zn2+ salts, p-chloromercuribenzoate and N-ethylmaleimide, known inhibitors of membrane endocytosis.

Inhibition of malaria parasite invasion into erythrocytes pretreated with membrane-active drugs

Normal rhesus monkey erythrocytes were incubated with various membrane-active drugs (for 1 h at 37 degrees C) and after thorough washing, were exposed to infection with Plasmodium knowlesi in an invitro cultivation system. The ability of merozoites to infect with drug-pretreated erythrocytes was assessed both by counting the number of infected cells and by measuring the incorporation of [3H]isoleucine into parasite protein. Marked inhibition of invasion was observed with vinblastine and colchicine, at concentrations greater than 5 x 10(-4) M, respectively. At similar concentrations, cytochalasin B or amantadine had no apparent effect. The addition of 10(-3) M 3',5'-cAMP to the medium during the incubation in the presence of colchicine or vinblastine partially decreased the inhibitory effects. The effects of colchicine and vinblastine on parasite invasion may be correlated with a reversible alteration in erythrocyte conformation (spherocytosis) which occurs at similar drug concentrations to those above and which can be relieved by simultaneous incubation with cAMP. A possible mechanism of action is proposed.

Desacetyl vinblastine amide sulfate induced ineffective erythropoiesis

Ineffective erythropoiesis occurred during desacetyl vinblastine amide sulfate (VDS) therapy of a patient with metastatic Ewing's sarcoma. The peripheral blood was characterized by anisocytosis, poikilocytosis and reticulocytopenia. Bone marrow showed megaloblastic red cell hyperplasia with nuclear fragmentation, binuclearity and abnormal metaphases. Radioiron incorporation into red cells was markedly decreased. Electron microscopy showed red cell surface changes previously called ropalocytosis. Normal erythropoiesis promptly resumed when VDS treatment was withheld. Although less common than leukopenia, red cell abnormalities are part of the spectrum of vinca alkaloid toxicity.

Endocytosis in adenosine triphosphate-depleted erythrocytes

The extent of membrane invagination or endocytosis in intact erythrocytes was quantified by measuring the loss of acetylcholinesterase activity. Primaquine-induced endocytosis was completely inhibited in ATP-depleted cells. However, chlorpromazine and vinblastine were capable of inducing membrane invagination in depleted cells. With both drugs, the loss of enzyme activity was less than that measured in fresh cells. We conclude that drug-induced endocytosis is not necessarily an energy-dependent process.

The effects of vinblastine on acinar cells of the exorbital lacrimal gland of the rat

The effects of vinblastine treatment on acinar cells of the rat exorbital lacrimal gland were studied by electron microscopy. Experimental animals of both sexes were given single intraperitoneal injections of (1) vinblastine (4 mg/kg body weight) at 1 to 24 h before sacrifice; (2) pilocarpine (20 mg/kg b.w.) for 1 h; or (3) vinblastine for 1 h followed by pilocarpine for 1 h. Vinblastine treatment caused a number of changes including autophagocytosis, formation of intracisternal granules, and alteration of secretory granules. These changes varied in extent and onset between male and female rats. In addition, the Golgi apparatus was reduced in size and dispersed throughout the cytoplasm. Mitotic figures were commonly observed. Moreover, vinblastine inhibited the pilocarpine-stimulated degranulation of the acinar cells. In view of the known anti-microtubular action of vinblastine, these results suggest that microtubules are involved in various aspects of the transport, packaging, and secretion of exportable proteins in the lacrimal gland. Additionally, autophagocytosis and alteration of secretory granules may partially result from the interaction of vinblastine with membranes.

A microtechnique for measuring red cell osmotic fragility of infants

Chloramphenicol (D-threo-2-dichloroacetamido-1-p-nitrophenylpropane-1,3-diol) added to blood samples did not alter the observed shift in the red cell osmotic fragility curves as the samples were aged in vitro for 24 hours at 37 degrees C. Nor was the normal rate of loss of 2,3-diphosphoglycerate, ATP, or glutathione from the red cells affected by the presence of chloramphenicol over the same period. Consequently, this bacteriostatic agent can be added to blood samples taken under non-sterile conditions, such as from the heel of an infant, in order to preserve them from the effects of microbial contamination. In this way red cell osmotic fragility results can be obtained on non-sterile samples after their incubation at 37 degrees C for 24 hours. A miniaturisation of the standard osmotic fragility procedure is described, which allows results to be produced from the small, non-sterile samples obtained by heel-prick of infants.

Studies of erythrocyte membrane loss produced by amphipathic drugs and in vitro storage

Four amphipathic drugs, primaquine, propranolol, chlorpromazine and tetracaine, were used to cause endocytosis in glucose-depleted red cells, and the relative reduction of membrane surfaces was measured by the toluidine blue (TB) method. The TB measurements correlated well with the observed electron microscopic alterations. In vitro blood storage studies indicated loss of cell membrane during storage correlated with decreasing uptake of TB by the red cells. Regeneration of cellular ATP with adenosine did not always restore TB uptake by the cells. Loss of red blood cell membrane either by exocytosis or endocytosis may occur during normal in vivo or in vitro ageing, and may be increased in pathological states or by the action of drugs.

Evaluation of toluidine blue for measuring erythrocyte membrane loss during in vivo ageing

A simple method using a cationic dye, toluidine blue (TB), to quantify changes of red cell membrane area has been developed and tested for its validity. After incubating a glucose-depleted red cell suspension with a fixed quantity of TB at 37 degrees C for 10 min, the remaining TB was measured spectrophotometrically at 640 nm. Using this technique, we were able to show differences in TB uptake by populations of young and old red cells. The exact mechanism for TB uptake by the red cells is not clear. Treatment of the cells with bromelin, papain and trypsin reduced the uptake of TB, but neuraminidase and ficin had little or no effect. No inhibition of TB removal by red cells was observed using heparin, D-glucose, glucuronic acid, or N-acetylglucosamine.