On the mechanism of vesicle release from ATP-depleted human red blood cells

Anti-Cancer Role and Therapeutic Potential of Extracellular Vesicles

Cell-cell communication is an important mechanism in biological processes. Extracellular vesicles (EVs), also referred to as exosomes, microvesicles, and prostasomes, are microvesicles secreted by a variety of cells. EVs are nanometer-scale vesicles composed of a lipid bilayer and contain biological functional molecules, such as microRNAs (miRNAs), mRNAs, and proteins. In this review, "EVs" is used as a comprehensive term for vesicles that are secreted from cells. EV research has been developing over the last four decades. Many studies have suggested that EVs play a crucial role in cell-cell communication. Importantly, EVs contribute to cancer malignancy mechanisms such as carcinogenesis, proliferation, angiogenesis, metastasis, and escape from the immune system. EVs derived from cancer cells and their microenvironments are diverse, change in nature depending on the condition. As EVs are thought to be secreted into body fluids, they have the potential to serve as diagnostic markers for liquid biopsy. In addition, cells can encapsulate functional molecules in EVs. Hence, the characteristics of EVs make them suitable for use in drug delivery systems and novel cancer treatments. In this review, the potential of EVs as anti-cancer therapeutics is discussed.

Mechanisms tagging senescent red blood cells for clearance in healthy humans

This review focuses on the analysis and evaluation of the diverse senescence markers suggested to prime red blood cells (RBC) for clearance in humans. These tags develop in the course of biochemical and structural alterations accompanying RBC aging, as the decrease of activities of multiple enzymes, the gradual accumulation of oxidative damage, the loss of membrane in form of microvesicles, the redistribution of ions and alterations in cell volume, density, and deformability. The actual tags represent the penultimate galactosyl residues, revealed by desialylation of glycophorins, or the aggregates of the anion exchanger (band 3 protein) to which anti-galactose antibodies bind in the first and anti-band 3 naturally occurring antibodies (NAbs) in the second case. While anti-band 3 NAbs bind to the carbohydrate-free portion of band 3 aggregates in healthy humans, induced anti-lactoferrin antibodies bind to the carbohydrate-containing portion of band 3 and along with anti-band 3 NAbs may accelerated clearance of senescent RBC in patients with anti-neutrophil cytoplasmic antibodies (ANCA). Exoplasmically accessible phosphatidylserine (PS) and the alterations in the interplay between CD47 on RBC and its receptor on macrophages, signal regulatory protein alpha (SIRPalpha protein), were also reported to induce erythrocyte clearance. We discuss the relevance of each mechanism and analyze the strength of the data.

The how and why of exocytic vesicles

The purpose of this review is to draw the attention of general readers to the importance of cellular exocytic vesiculation as a normal mechanism of development and subsequent adjustment to changing conditions, focusing on red cell (RBC) vesiculation. Recent studies have emphasized the possible role of these microparticles as diagnostic and investigative tools. RBCs lose membrane, both in vivo and during ex vivo storage, by the blebbing of microvesicles from the tips of echinocytic spicules. Microvesicles shed by RBCs in vivo are rapidly removed by the reticuloendothelial system. During storage, this loss of membrane contributes to the storage lesion and the accumulation of the microvesicles are believed to be thrombogenic and thus to be clinically important.

Iron release, membrane protein oxidation and erythrocyte ageing

The aerobic incubation of erythrocytes in phosphate buffer for 24-60 h (a model of rapid in vitro ageing) induced progressive iron release and methemoglobin formation. Membrane proteins showed electrophoretic alterations and increase in carbonyl groups (as documented by IR spectroscopy). None of these phenomena were seen when the erythrocytes were incubated under anaerobic conditions. The membranes from aerobically incubated cells bound a much higher amount of autologous IgG than those from anaerobically incubated ones, suggesting that the aerobic incubation gives rise to the senescent antigen. The addition of ferrozine during the aerobic incubation prevented both the IgG binding and the protein alterations seen in the IR spectra, suggesting an intracellular chelation of the released iron by ferrozine.

Effect of red cell age on vesiculation in vitro

Microvesiculation of RBC occurs in vivo and during in vitro storage. Vesiculation of young and old populations of RBC was measured under blood bank conditions. The RBC in whole units of blood were divided by density into two approximately equal fractions in a closed system. After storage for 35 d the haemoglobin-containing vesicles were quantitatively recovered. Quantitation of protein, cholesterol and phospholipids showed significantly larger amounts in the vesicles shed by the younger RBC. Otherwise vesicles shed by the two populations of RBC did not differ.

Re-evaluation of the structural integrity of red-cell glycoproteins during aging in vivo and nutrient deprivation

Results presented in this paper show that removal of white-cell contaminations from human red blood cells by filtration through cellulose [Beutler, West & Blume (1976) J. Lab. Clin. Med. 88, 328-333] is a necessity whenever red cells are incubated at elevated temperatures or haemolysed after density separation. Omission of this precaution results in proteolysis of sialoglycoproteins in membranes from less-dense (young), but not dense (old), subpopulations. This proteolytic damage occurs during haemolysis of the cytoplasmic domain of glycophorin. A different type of proteolysis occurs if white-cell-contaminated red cells are incubated in the absence of glucose at elevated temperatures. Red cells release sialoglycopeptides. This process is stimulated by Ca2+ ions and is accompanied by the release of vesicles that differ from spectrin-free vesicles [Lutz, Liu & Palek (1977) J. Cell Biol. 73, 548-560]. This sialoglycopeptide release is dependent on white-cell contamination and is not required for the release of spectrin-free vesicles.

Concanavalin A-agglutinability of membrane-skeleton-free vesicles and aged cellular remnants derived from human erythrocytes. Is the membrane skeleton required for agglutination?

Vesicles and cell remnants have been obtained by aging of erythrocytes in vitro. The vesicles lacking the membrane skeletal proteins and the remnants known to possess a rigid skeleton have been used to assess the role of membrane skeletal proteins in the process of Con A (concanavalin A)-mediated agglutination of erythrocytes. Both the vesicles and the remnants were found to bind Con A at the same density as did intact cells. The vesicles, isolated from normal as well as from the Con A-agglutinable trypsin- and Pronase-treated cells, failed to agglutinate with Con A. They were, however, well agglutinated by WGA (wheat-germ agglutinin) and RCA [Ricinus communis (castor bean) agglutinin], indicating that the vesicles are not defective in agglutination. Large, cytoskeleton-free, vesicles prepared by another procedure also gave the same results. The aged remnants from trypsin- and Pronase-treated erythrocytes showed significantly decreased agglutination with Con A, but were agglutinated as well as the fresh cells by WGA and RCA. The agglutination with Con A is thus abolished when the membrane skeleton is absent, and reduced when it is rigid, suggesting that the skeleton may play an important role in the agglutination of erythrocytes by Con A.

Effects of chlorpromazine and other calmodulin antagonists on phosphatidylcholine-induced vesiculation of platelet plasma membranes

Dilauroylglycerophosphocholine (C12:0PC)-induced vesiculation of platelet plasma membranes (Kobayashi, T., Okamoto, H., Yamada, J.-I., Setaka, M. and Kwan, T. (1984) Biochim. Biophys. Acta 778, 210-218; Kobayashi, T., Yamada, J.-I., Satoh, N., Setaka, M. and Kwan, T. (1985) Biochim. Biophys. Acta 817, 307-312) was inhibited by chlorpromazine. Preincubation of platelets with chlorpromazine was required for inhibition but incorporation of chlorpromazine into C12:0PC liposomes was not necessary for it, indicating that the observed inhibition of vesiculation was mainly due to the effect of chlorpromazine on platelets and not that on liposomes. The change in platelet membrane fluidity caused by chlorpromazine was not the cause of inhibition of vesiculation. The inhibition of vesiculation by various other calmodulin antagonists was also observed. The inhibitory activities of these calmodulin antagonists and chlorpromazine correspond very well to their abilities to bind to calmodulin. N-(6-Aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7) inhibited vesiculation but a structural analogue of it, N-(6-aminohexyl)-1-naphthalenesulfonamide (W-5), had no inhibitory activity. These results suggest the involvement of calmodulin in membrane vesiculation.

The influence of cellular ATP levels on dimyristoylphosphatidylcholine-induced release of vesicles from human erythrocytes

Release of membrane vesicles from human erythrocytes was induced by modulation of red cell ATP levels, by incubation of erythrocytes with sonicated dimyristoylphosphatidylcholine (DMPC) suspensions, or by a sequential combination of both procedures. When red blood cell ATP levels were decreased prior to incubation with DMPC, the lag-time between addition of the lipid and beginning of vesiculation was reduced. Furthermore, the rate of vesicle release itself was accelerated. Experiments carried out with a rapid ATP depletion technique showed that the onset of vesiculation and the release were most evidently accelerated in those cases where echinocytes had been formed prior to the addition of DMPC. The results suggest that red blood cells with reduced cellular ATP levels or an altered cell shape are more susceptible to a further perturbation of the membrane by addition of exogenous DMPC.

Changes in morphology and in polyphosphoinositide turnover of human erythrocytes after cholesterol depletion

Human erythrocytes were cholesterol-depleted (5-25%) by incubation with phosphatidylcholine vesicles in media containing Ca2+ at different concentrations (0, 28 nM, 5 microM or 1 mM). After removal of the vesicles, the cells were reincubated with [32P]phosphate in the same media. Control (incubated in buffer alone) and cholesterol-maintained erythrocytes (incubated with cholesterol/phosphatidylcholine vesicles) were treated similarly. Cholesterol depletion induced the conversion of the cells into stomatocytes III and spherostomatocytes and decreased the turnover rate of phosphatidylinositol phosphate and of phosphatidylinositol bisphosphate. None of these effects were observed in cholesterol-maintained cells. In cholesterol-depleted cells, they occurred without changes in the ATP specific activity or in the polyphosphoinositide concentrations. Moreover, these modifications of shape and of lipid metabolism were proportional to the extent of the cholesterol depletion and were independent of the external Ca2+ concentration. In contrast, other effects of cholesterol depletion, a decrease in the turnover rate of phosphatidic acid, a decrease in diacylglycerol and in phosphatidic acid concentrations were dependent on the external Ca2+ concentration. Thus it appears that the shape change was not correlated with a change in the concentrations of these phospholipids or of diacylglycerol and therefore cannot be explained by a bilayer couple mechanism involving these phospholipids. However, the spherostomatocytic transformation was correlated with the decrease in the turnover rate of the polyphosphoinositides, but not with the turnover rate of phosphatidic acid, suggesting a role for the turnover of the polyphosphoinositides in the maintenance of the erythrocyte shape.

Erythrocyte membrane vesiculation and changes in membrane composition during storage in citrate-phosphate-dextrose-adenine-1

Serial studies were made of the membranes of the erythrocytes and the vesicles shed during storage of blood in polyvinyl chloride containers for 35 days in citrate-phosphate-dextrose-adenine anticoagulant. Special precautions were taken to eliminate artifacts created by contaminating leukocytes, platelets and red blood cell ghosts. A total of 15.6% of the cholesterol and 5.2% of the phospholipids of the membranes was lost with no gross change in the gel electrophoretic patterns. The quantity of vesicles found in the supernatant plasma increased during storage and their membranes were characterized by the absence of spectrin, ankyrin, and periodic acid Schiff bands 2 and 3. The ratio of lipids to protein in the vesicles increased as they accumulated perhaps reflecting a rearrangement of the erythrocyte membrane constituents during prolonged maintenance at 4 degrees C.

Binding of autologous IgG to human red blood cells before and after ATP-depletion. Selective exposure of binding sites (autoantigens) on spectrin-free vesicles

Binding of autologous IgG to fresh, ATP-depleted red blood cells as well as to spectrin-free vesicles was studied by a non-equilibrium binding assay using 125I-iodinated protein A from Staphylococcus aureus. IgG binding was 14-times higher to spectrin-free vesicles than to ATP-maintaining red blood cells and 4-times higher than to ATP-depleted erythrocytes from which these vesicles were released. Protein A binding to vesicles that were released from washed and nutrient-deprived erythrocytes, was dependent on added autologous IgG. However, spectrin-free vesicles that were spontaneously released from erythrocytes conserved in whole blood, bound similar amounts of protein A with or without added autologous IgG (0.45-0.55 ng/micrograms band 3 protein). These findings demonstrate that opsonization of spectrin-free vesicles by autologous IgG occurs not only in the test tube, but also under blood blank conditions. The binding characteristics of IgG to spectrin-free vesicles are indicative of a natural autoantibody rather than an unspecific binding of autologous IgG. The preferential binding of IgG to spectrin-free vesicles implies a selective exposure of corresponding autoantigens in membrane regions that have lost cytoskeletal anchorage and bud off.

Isolation and characterization of large (0.5 - 1.0 micron) cytoskeleton-free vesicles from human and rabbit erythrocytes

Large (0.5 - 1.0 micron) cytoskeleton-free vesicles were obtained, by 'budding', from fresh human and rabbit erythrocytes incubated at 45 degrees C and titrated with EDTA and CaCl2. This process occurs without hemolysis. The isolated vesicles maintain their cytoplasmic integrity and normal membrane orientation, and are resistant to hemolysis over the pH range 5.0 - 11.0 and temperature range 4-50 degrees C. The only membrane proteins detected in vesicles from human erythrocytes were band 3 region polypeptides and bands PAS-1, PAS-2 and PAS-3. Vesicles obtained from rabbit erythrocytes were similarly simple. Because of their size and stability these vesicles are amenable to both kinetic and quantitative analysis using the same experimental techniques employed in studies of synthetic lipid membranes. The results obtained in this study indicate that these vesicles are essentially markedly simplified biological cells, and thus may be useful as a biologically relevant model membrane system for examining the molecular interactions which occur within, across and between cell membranes.

Microvesiculation and sphingomyelinase activation in chicken erythrocytes treated with ionophore A23187 and Ca2+

Treatment of chicken erythrocytes with ionophore A23187 and Ca2+ leads to the disappearance of the marginal band of microtubules and to a release of the constraints which normally maintain the nucleus in a central position in the cells. The consequent close apposition of the nucleus to the plasma membrane may allow nuclear-plasma membrane fusion to occur and subsequently results in the release of microvesicles from the hybrid surface membrane. The remnant cells are spherical, and have nuclei which appear to be partly exocytosed. Concomitant with these morphological changes, there is a breakdown of 20-30% of the total cell sphingomyelin by an endogenous sphingomyelinase which does not require Ca2+ and which releases phosphorylcholine only into the cell interior. It is suggested that the pool of sphingomyelin which is broken down as a consequence of Ca2+ entry into the cells is present in the nuclear membrane and that it becomes available to the plasma membrane sphingomyelinase as a result of the close apposition of nucleus and plasma membrane induced by Ca2+.