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

[Acquired Stomatocytosis in Hyperosmolar Hyperglycemic Derangement]

Acquired Stomatocytosis in Hyperosmolar Hyperglycemic Derangement Abstract. In the context of a suicidally motivated suspension of insulin therapy, a massive hyperosmolar hyperglycemic derailment occurred in pancreoprivic diabetes mellitus most likely due to aethyltoxicity. In the blood picture differentiation stomatocytes could be detected, the development of which will be discussed in more detail below.

Phenothiazine-derived antipsychotic drugs inhibit dynamin and clathrin-mediated endocytosis

Chlorpromazine is a phenothiazine-derived antipsychotic drug (APD) that inhibits clathrin-mediated endocytosis (CME) in cells by an unknown mechanism. We examined whether its action and that of other APDs might be mediated by the GTPase activity of dynamin. Eight of eight phenothiazine-derived APDs inhibited dynamin I (dynI) in the 2-12 µm range, the most potent being trifluoperazine (IC50 2.6 ± 0.7 µm). They also inhibited dynamin II (dynII) at similar concentrations. Typical and atypical APDs not based on the phenothiazine scaffold were 8- to 10-fold less potent (haloperidol and clozapine) or were inactive (droperidol, olanzapine and risperidone). Kinetic analysis showed that phenothiazine-derived APDs were lipid competitive, while haloperidol was uncompetitive with lipid. Accordingly, phenothiazine-derived APDs inhibited dynI GTPase activity stimulated by lipids but not by various SH3 domains. All dynamin-active APDs also inhibited transferrin (Tfn) CME in cells at related potencies. Structure-activity relationships (SAR) revealed dynamin inhibition to be conferred by a substituent group containing a terminal tertiary amino group at the N2 position. Chlorpromazine was previously proposed to target AP-2 recruitment in the formation of clathrin-coated vesicles (CCV). However, neither chlorpromazine nor thioridazine affected AP-2 interaction with amphiphysin or clathrin. Super-resolution microscopy revealed that chlorpromazine blocks neither clathrin recruitment by AP-2, nor AP-2 recruitment, showing that CME inhibition occurs downstream of CCV formation. Overall, potent dynamin inhibition is a shared characteristic of phenothiazine-derived APDs, but not other typical or atypical APDs, and the data indicate that dynamin is their likely in-cell target in endocytosis.

Alterations of red cell membrane properties in neuroacanthocytosis

Neuroacanthocytosis (NA) refers to a group of heterogenous, rare genetic disorders, namely chorea acanthocytosis (ChAc), McLeod syndrome (MLS), Huntington’s disease-like 2 (HDL2) and pantothenate kinase associated neurodegeneration (PKAN), that mainly affect the basal ganglia and are associated with similar neurological symptoms. PKAN is also assigned to a group of rare neurodegenerative diseases, known as NBIA (neurodegeneration with brain iron accumulation), associated with iron accumulation in the basal ganglia and progressive movement disorder. Acanthocytosis, the occurrence of misshaped erythrocytes with thorny protrusions, is frequently observed in ChAc and MLS patients but less prevalent in PKAN (about 10%) and HDL2 patients. The pathological factors that lead to the formation of the acanthocytic red blood cell shape are currently unknown. The aim of this study was to determine whether NA/NBIA acanthocytes differ in their functionality from normal erythrocytes. Several flow-cytometry-based assays were applied to test the physiological responses of the plasma membrane, namely drug-induced endocytosis, phosphatidylserine exposure and calcium uptake upon treatment with lysophosphatidic acid. ChAc red cell samples clearly showed a reduced response in drug-induced endovesiculation, lysophosphatidic acid-induced phosphatidylserine exposure, and calcium uptake. Impaired responses were also observed in acanthocyte-positive NBIA (PKAN) red cells but not in patient cells without shape abnormalities. These data suggest an “acanthocytic state” of the red cell where alterations in functional and interdependent membrane properties arise together with an acanthocytic cell shape. Further elucidation of the aberrant molecular mechanisms that cause this acanthocytic state may possibly help to evaluate the pathological pathways leading to neurodegeneration.

Stimulation of erythrocyte phosphatidylserine exposure by chlorpromazine

Side effects of treatment with chlorpromazine include anaemia which could result from decreased formation or accelerated clearance of circulating erythrocytes. Recently, a novel mechanism leading to erythrocyte clearance has been disclosed. Osmotic shock, oxidative stress and glucose deprivation lead to activation of cation channels, Ca(2+) entry, activation of a Ca(2+)-sensitive erythrocyte scramblase and subsequent exposure of phosphatidylserine at the erythrocyte surface. As macrophages are equipped with phosphatidylserine receptors, they bind, engulf and degrade phosphatidylserine exposing cells. The present experiments have been performed to explore whether chlorpromazine triggers phosphatidylserine exposure of erythrocytes. The phosphatidylserine exposure was estimated from annexin binding as determined in fluorescence activated cell sort (FACS) analysis. A 24 h exposure to glucose-free medium decreased cytosolic ATP levels, decreased cellular levels of reduced glutathione (GSH) and increased annexin binding. The effect on annexin binding and ATP but not on GSH was significantly enhanced in the presence of chlorpromazine (10 microM). Higher concentrations of chlorpromazine (40 microM) increased cytosolic Ca(2+) activity. Osmotic shock and Cl(-) removal similarly increased annexin binding, effects again being enhanced in the presence of chlorpromazine. In conclusion, the present observations point to a novel side effect of chlorpromazine, i.e. increased sensitivity of erythrocytes to glucose deprivation. The effect could well contribute to the known anaemia observed in the treatment with this antipsychotic drug.

Improved preservation of human red blood cells by lyophilization

The lyophilization of human red blood cells has important implications for blood transfusion in clinical medicine. In this study, sugars, human serum albumin, polyvinylpyrrolidone, and dimethyl sulfoxide were used as protective reagents for the lyophilization of red blood cells. Freezing temperature, shelf temperature, and the rehydration conditions were optimized. The results showed that extracellular disaccharides, especially trehalose, did not increase the recovery of hemoglobin. However, when the concentration of human serum albumin was higher than 25%, it had a considerable protective effect on the recovery of lyophilized red blood cells; the cellular hemoglobin recovery was over 70%, which was significantly higher than that in the group without human serum albumin (P<0.01). As the concentration of polyvinylpyrrolidone was increased, the extent of vitrification also increased. But when the concentration of polyvinylpyrrolidone was over 40%, the resulting concentration of free hemoglobin was over 1g/L, which was significantly higher than that with 40% (P<0.01). When lyophilization was carried out after freezing at different temperatures, the recovery of cells and hemoglobin was 70-80% and there were no significant differences among the five groups. When the shelf temperature was higher than -30 degrees C, the samples were partly collapsed, but when the shelf temperature was lower than -30 degrees C, the recovery of cells in the -40 and -45 degrees C groups was significantly higher than in the -30 and -35 degrees C groups (P<0.05). The recovery of cells and hemoglobin after lyophilization and rehydration in solutions containing low concentrations of polymers was over 80%, which is significantly higher than the other groups (P<0.01). In addition, when the temperature was higher than 25 degrees C, the concentration of free hemoglobin was significantly lower than it was at 4 degrees C (P<0.01). In conclusion, our study showed the lyophilization of red blood cells is feasible. Disaccharides have no protective effect on lyophilized cells when they are only extracellular and extensive vitrification may be not beneficial. Although the recovery of cells after lyophilization and rehydration by our method was over 70%, the ultrastructure of the cells may be compromised and some hemolysis does still exist. Further research is required.

Facilitated phosphatidylcholine flip-flop across erythrocyte membranes using low molecular weight synthetic translocases

The transmembrane distribution of phospholipids plays an important regulatory role in human erythrocytes. Membrane-bound translocase enzymes maintain an asymmetric phospholipid distribution across the membrane monolayers by promoting transmembrane diffusion or flip-flop. Mechanistic understanding of the flip-flop process is weak at the molecular level. Recently, we discovered that amide and sulfonamide derivatives of tris(aminoethyl)amine facilitate phospholipid flip-flop across vesicle membranes; that is, they act as low molecular weight, synthetic translocases. In this report, NMR evidence is provided that suggests that the synthetic translocases work by forming a hydrogen-bonded complex with the phosphocholine headgroup which decreases headgroup polarity and promotes diffusion across the lipophilic interior of the membrane. Also cell morphology and fluorescence probe methods are used to show that these synthetic translocases facilitate phosphatidylcholine flip-flop across erythrocyte membranes. Addition of a small amount of dilauroylphosphatidylcholine to erythrocytes produces echinocyte morphology which takes days to revert back to the original discocyte shape. The rate of return is significantly accelerated by the presence of the synthetic translocases. The synthetic translocases facilitate inward-translocation (flip) of the fluorescent phosphatidylcholine probe, 1-palmitoyl-2-(N-[7-nitrobenz-2-oxa-1,3-diazol-4-yl]aminohexanoyl)-sn-glycero-3-phosphocholine (PC-NBD).

Multidrug resistance protein 1 regulates lipid asymmetry in erythrocyte membranes

The role of multidrug resistance protein 1 (MRP1) in the maintenance of transbilayer lipid asymmetry in the erythrocyte membrane was investigated. The transbilayer distribution of endogenous phospholipids and [(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]hexanoyl (NBD)-labelled lipid analogues was compared in the absence and the presence of inhibitors of MRP1. At equilibrium the transbilayer distribution of the NBD analogues (in the absence of MRP1 inhibitors) was very similar to that of the endogenous lipids. Inhibition of MRP1 by verapamil or indomethacin resulted in a shift in the amount of probe that was internalized: approx. 50% of NBD-labelled phosphatidylcholine (PtdCho) and 9% of NBD-sphingomyelin (NBD-Spm) were no longer extractable by BSA in cells treated with inhibitor, in comparison with 25% and 3% for control cells respectively. To verify whether inhibition of MRP1 also affected the distribution of the endogenous phospholipids, phospholipase A2 and sphingomyelinase were used to assess the amount of each of the various lipid classes present in the membrane outer leaflet. No shift in phospholipid distribution was observed after 5 h of incubation with verapamil or indomethacin. However, after 48 h of incubation with these inhibitors, significantly smaller amounts of PtdCho and Spm were present in the outer membrane leaflet. No appreciable change was observed in the distribution of phosphatidylethanolamine or phosphatidylserine. Decreased hydrolysis of PtdCho and Spm was not due to endovesicle formation, as revealed by electron microscopy. This is the first report to show that MRP1 has a role in the maintenance of the outwards orientation of endogenous choline-containing phospholipids in the erythrocyte membrane.

Amphiphile-induced phosphatidylserine exposure in human erythrocytes

Nonionic and anionic water-soluble amphiphiles were shown to increase strongly the binding of fluorescein isothiocyanate-conjugated annexin V (FITC-annexin V) in human erythrocytes pretreated with the aminophospholipid translocase (APLT) inhibitor n-ethylmaleimide (NEM). At high sublytic amphiphile-concentrations the binding of FITC-annexin V, monitored in a flow cytometer, was time- and temperature-dependent and occurred heterogeneously in the cell population, with 43-81% of cells being stained above background following incubation for 60 minutes at 37 degrees C. The increased FITC-annexin V binding apparently indicates an increased flop rate of phosphatidylserine (PS) to the outer membrane leaflet. When the NEM-pretreatment was omitted, the FITC-annexin V binding was markedly, but not completely, reduced. In erythrocytes incubated with a zwitter-ionic amphiphile, a small increase in FITC-annexin V binding was detected, while cationic amphiphiles did not induce an increased FITC-annexin V binding. The potency of amphiphiles to induce PS exposure was not related to the type of shape alteration or vesiculation induced. Our results indicate a significant role of the charge status of a membrane intercalated amphiphile for its capability to induce PS exposure.

Drug-induced transmembrane lipid scrambling in erythrocytes and in liposomes requires the presence of polyanionic phospholipids

The asymmetric transmembrane distribution of phospholipids between the two bilayer halves of erythrocyte can be modified upon addition of cationic amphiphilic drugs, such as chlorpromazine or verapamil. We studied this phenomenon in erythrocytes and in lipid vesicles using spin-labelled analogues of the endogenous phospholipids. The extent of the rapid disappearance of the analogues from the erythrocyte outer leaflet depended on the concentration of the drug. Up to 40% of spin-labelled sphingomyelin moved to the inner erythrocyte leaflet in 10 min in the presence of 1.5 mm chlorpromazine. Verapamil or vinblastine gave similar results. On the other hand, the inside-outside movement of the aminophospholipid analogues was less evident, and did not exceed 10%. This apparent discrepancy between inward and outward movements could result from the formation of an endovesicle which is known to occur upon drug addition at high concentration. A fraction of lipids would be trapped in the intravesicular leaflet, corresponding to the cell outer leaflet, and be inaccessible both from the cytoplasm and the extracellular medium. In cells submitted to a metabolic depletion of cellular ATP the intensity of the scrambling induced by the amphipaths was drastically lowered. We attribute this effect to the important reduction of the membrane content in phosphatidylinositol-4,5-bisphosphate (PIP2). The involvement of the latter lipid in triggering scrambling was partly confirmed by experiments carried out with artificial membranes. Indeed, in large unilamellar vesicles PIP2 is required in order to obtain a rapid redistribution of phospholipids between the two leaflets upon addition of drugs. However, the extent of phospholipid redistribution was limited to 15-20%. This redistribution was also induced when the vesicle membrane contained di-anionic phospholipids (phosphatidylinositol-4-monophosphate or diphosphatidylglycerol), but did not occur when it contained mono-anionic phospholipids (phosphatidylserine or phosphatidylinositol). Some drugs such as methochlorpromazine, active in artificial membranes, were ineffective in erythrocyte membranes, probably because they could not cross the membrane and reach PIP2 molecules at the cytoplasmic leaflet.

Phospholipids in animal eukaryotic membranes: transverse asymmetry and movement

Images

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.

Modulation of human erythrocyte shape and fatty acids by diet

A semi-synthetic diet (Vivonex) was administered via nasogastric tube to three cystic fibrosis patients with pancreatic exocrine deficiency for 14 days to gain weight. Dietary essential fatty acids were provided as safflower oil, which constituted 1.3% of total calories. Plasma and red blood cells were analyzed for the content and composition of lipids at the start of the diet and at days 7 and 14 of the dietary period, and the results were correlated with the morphology of the cells. Feeding Vivonex to the patients led to an essential fatty acid deficiency, which was manifested in a 50% decrease in the linoleic acid content of the phosphatidylcholine of plasma and red blood cells at days 7 and 14 and in a 20% decrease in the linoleic acid content of red cell phosphatidylethanolamine at day 14. There was no significant alteration in the levels or composition of the other phospholipid classes and in the free cholesterol/phospholipid ratio. The decrease in the linoleic acid content of the erythrocytes was accompanied by a dramatic increase in the proportion of cells as echinocytes. We conclude that restricted linoleic acid availability in cystic fibrosis patients causes a change in red blood cell shape either directly by decreasing the linoleoylphosphatidylcholine content of the membrane or indirectly by affecting enzyme activity.

Effect of hydrogen peroxide exposure on normal human erythrocyte deformability, morphology, surface characteristics, and spectrin-hemoglobin cross-linking

To further define the conditions for forming spectrin-hemoglobin cross-linking in human erythrocyte membranes and to examine its possible effects on membrane function, we incubated normal human erythrocytes for up to 3 h in concentrations of H2O2, varying from 45 to 180 microM, in an azide phosphate buffer, pH 7.4. The chemical changes observed indicated that methemoglobin formation occurred early and at a low concentration (45 microM). Morphologic changes characterized by increased echinocyte formation occurred in a dose-dependent fashion. In addition, decreased cell deformability commensurate with increased membrane rigidity was found. Finally, an increase in cell recognition as determined by monocyte phagocytosis and adherence in vitro, as well as decreased phosphatidylcholine accessibility to bee venom phospholipase A2, was found in H2O2-treated erythrocytes compared with controls. Both of these latter changes were closely correlated with the extent of spectrin-hemoglobin cross-linking. In addition to these protein-mediated interactions, lipid peroxidation also occurred after H2O2 exposure, as shown by generation of fluorescent amino propene derivatives. The addition of the antioxidant, butylated hydroxytoluene, decreased the fluorescent derivatives, but did not prevent the effects on membrane function. This suggests that lipid peroxidation, though present, was not necessary for the membrane changes found. In contrast, spectrin-hemoglobin aggregation and the alterations in membrane function were completely prevented by prior exposure of the erythrocytes to carbon monoxide.

Lipid organization in erythrocyte membrane microvesicles

The aminophospholipids of microvesicles released from human erythrocytes on storage or prepared from erythrocyte ghosts by shearing under pressure are susceptible to the action of 2,4,6-trinitrobenzenesulphonic acid. The aminophospholipids of the former vesicles are also susceptible to attack by phospholipase A2. Under the same conditions, the aminophospholipids of erythrocytes undergo little reaction. This suggests that the phospholipids in microvesicle membranes are more randomly distributed than those in erythrocyte membranes. Measurements have also been made of the ability of filipin to react with the cholesterol of sealed and unsealed erythrocyte ghosts and of microvesicles prepared from them. From the initial rates of reaction, it was concluded that there is no preferential transfer of cholesterol molecules from one side of the bilayer to the other during the formation of the microvesicles.