Membrane transport in resealed haemoglobin-containing human erythrocyte 'ghosts' prepared by a dialysis procedure

Temperature-induced shape transformation of carrier erythrocytes

Erythrocytes have been proposed as cellular carriers for enzymes and drugs for protected delivery, slow release, or targeting to specific organs. Several studies have established the heterogeneity of resealed carrier erythrocytes concerning various characteristics, including morphology. Carrier erythrocytes were prepared by hypo-osmotic dialysis and consecutive iso-osmotic resealing at different temperatures, and the morphology of these cells was studied by scanning electron microscopy. Different cell shapes could be prepared by temperature variations during resealing or incubation. All intermediate shapes of echinocytosis were observed at low temperatures or with depleted energy supply but could be reversed to biconcave discocytes. Resealing at 4 degrees C resulted in highest percentage of echinocytes III, spherocytes, and leaky cells. Spontaneous resealing of 20% of the cells was obtained at high lysis temperatures. Combining low temperatures for lysis and high temperatures for resealing and sufficient energy supply are advantageous for highest recovery of biconcave discocytes. Shape of the erythrocyte, is the result of divergent forces, and temperature during resealing was found to be an important factor.

Plasma separator for encapsulating fluorescent probe in erythrocytes

Using a plasma separator, it is possible to wash large volumes of whole blood free of plasma proteins in short periods. The novelty, however, is that the same apparatus can be used to reversibly hemolyze and reseal the red blood cells (RBCs) using hypotonic and hypertonic dialysates, respectively. This technique was assessed using the fluorescent exogenous agent uranin (fluorescein sodium). Results indicate that the encapsulation of the RBCs can be completed in under 2 h. The encapsulation efficiency of the RBCs was approximately 80% with a RBC recovery rate of 75%.

Laboratory-scale finned-rotor impeller for dialysis

Dialysis of blood and other fluids may be accomplished using semi-permeable membranes. Most commonly used are the commercially available hollow-fibre dialysers, which have large priming volumes, an important consideration especially when laboratory techniques are being developed. With dialysis tubing (DT), however, priming volumes are readily controlled. To ensure adequate mass transfer, mixing of both dialysate and DT content is necessary. An impeller-based dialyser which consists of two open-boxed finned rotors facilitates both dialysate and DT content mixing. The operation of this device relies on the difference in hydrodynamic forces acting on opposite ends of the rotors, causing rotation in the vertical plane. This laboratory device was assessed via mass-transfer trials in which saline and washed-packed erythrocytes were dialysed against hypo- and hypertonic dialysate, allowing estimation of the DT's overall mass-transfer coefficient. Experimental correlation between the angular speeds of the impeller's rotation in the horizontal plane omega H and finned rotors' rotation in the vertical plane omega V were also established. Results indicate that the osmolality of the DT's content follows an exponential decay, and that omega V is strongly dependent on both omega H and the submergence depth of the impeller.

Osmotic fragility of drug carrier erythrocytes

Erythrocytes have been proposed as biogradable cellular carriers for drugs. Potentials of this therapeutic approach are organ-specific targeting, protection and prolonged in vivo function of the encapsulated drugs. Previous studies demonstrated the advantage of a hypo-osmotic dialysis procedure for macromolecule loading resulting in cells that are closely similar to normal erythrocytes. Osmotic fragility of unloaded and loaded "carrier" erythrocytes was studied both in respect of shelf-life and in vivo survival. Sudden haemolysis which is characteristic for normal erythrocytes was never obtained with carrier erythrocytes. Haemolysis appeared at all osmotic pressures and increased stepwise indicating the existence of various cell populations. However, the majority of cells were haemolysed at lower values of the osmotic fragility curve. Osmotic fragility was highly increased when cytotoxic chemotherapeutics were encapsulated, and these cells appeared as spherocytes using scanning electron microscopy. Osmotic fragility proved to be a simple but reliable method for the in vitro evaluation of carrier erythrocytes and the effect of the encapsulated substances.

Properties of red cell ghost preparations susceptible to invasion by malaria parasites

Experimental procedures are described that lead to the formation of sealed red cell ghosts capable of efficient invasion by malaria parasites. Both human and monkey cells have been studied with respect to invasion by Plasmodium falciparum and P. knowlesi respectively. Resealed ghosts containing about half the normal concentration of haemoglobin are prepared by osmotic lysis and resealing at a haematocrit of 70%. When examined in the scanning electron microscope, populations of these ghosts contain few echinocytes, but have an abundance of stomatocytic forms. When undiluted haemolysate is substituted for the aqueous saline diluent, in which the cells are suspended for lysis and resealing, discocytes result, with a morphology very similar to that of the original cells. Invasion is somewhat, but not dramatically higher for this material. An investigation of the effect of intracellular potassium concentration revealed that this had no major effect on invasion. A small increase in invasion resulted from addition of 50 or 100 mg/ml of albumin to the medium in which the cells were resealed, but intra-erythrocytic protein content per se is evidently not a major factor in determining the efficiency of invasion. Augmentation of the cytoplasmic ATP concentration during lysis and resealing increased the level of parasitaemia significantly, and the parasites in these ghosts developed normally and gave rise to viable merozoites. It was found that albumin at certain concentrations passed freely into the lysed cells and reached equilibrium with that in the external medium. By contrast, the high molecular weight solute Blue Dextran 2000 was completely excluded from the lysed cells.

Inhibition of malarial invasion of red cells by chemical and immunochemical linking of spectrin molecules

The invasion of resealed human red cell ghosts by Plasmodium falciparum, and those from monkey cells by P. knowlesi, was strongly inhibited by anti-spectrin antibodies introduced into their cytoplasm. Univalent F(ab)1 fragments gave no such effect, but a combination of these fragments and goat anti-rabbit immunoglobulin, to restore bifunctionality, caused perceptible inhibition of invasion. Disulphide cross-links introduced between spectrin molecules in intact red cells by the membrane-permeant oxidizing agent, diamide, again led to inhibition of invasion. This effect was largely reversed by reduction of the cross-links. Gel electrophoresis was used to confirm that cross-linking was essentially confined to spectrin, and that extended covalent networks were not formed. It follows that local formation of bridges, whether by antibodies or oxidation of thiol groups, functions by inhibiting a local rearrangement of the cytoskeleton that forms a step in the invasion process.

A cytoplasmic requirement of red cells for invasion by malarial parasites

Human red cells, when lysed by dialysis at high haematocrit against a medium of low ionic strength and then dialysed back to physiological saline at 37 degrees C, give rise to resealed ghosts that are invaded with high efficiency by Plasmodium falciparum parasites. When the haematocrit is reduced, a critical concentration is reached, such that the resealed ghosts no longer support invasion. This indicates that a constituent of the cytoplasm becomes diluted to a concentration below a critical level. This constituent is evidently ATP, for when extraneous ATP is added to the diluent and the dialysate, the susceptibility to invasion is fully restored. This does not occur when the non-hydrolysable analogue, adenylyl-imidodiphosphate (AMP-PNP) is substituted for ATP, whereas the hydrolysable ATP analogue, adenosine-5'-O-(3-thiotriphosphate) (ATP-gamma-S), which can be utilised by kinases, can partly replace ATP. Stimulation of invasion by the addition of 2,3-diphosphoglycerate was also associated with a perceptible rise in ATP concentration. The invasion process does not appear to involve intracellular calcium, for EGTA introduced into the resealed ghost has no detectable effect. Moreover, vanadate in the medium does not appreciably inhibit invasion, and it is thus unlikely that the requirement for ATP is linked to the activity of membrane ion-pump enzymes. An inhibitor of phosphorylation, adenosine, introduced into the cells at high concentration, causes significant inhibition of invasion. The results suggest that ATP is required for maintaining the turnover of phosphoryl groups of membrane-associated proteins, such as spectrin. A basic scheme for the mechanism of the invasion process is suggested. In addition to the effect of ATP, it is also shown that with greater dilution, and in the presence of ATP, there is an abrupt loss of susceptibility to invasion. It is inferred that this is due to the dilution of another essential cytoplasmic constituent to below a critical concentration. This second constituent has not yet been identified.

Measurement of arginine transport in human erythrocytes using their intrinsic arginase activity: implications for the treatment of familial hyperargininemia

A procedure making use of the intracellular arginase activity has been developed for measuring the transport of arginine across the human erythrocyte membrane. (1) The arginine translocation is carrier mediated with simple Michaelis-Menten kinetics, showing one high affinity, low capacity transport system characterized by a half saturation constant KT of 0.177 +/- 0.036 mmol/1, and a maximum velocity VT of 0.332 +/- 0.068 mumol X h-1 X ml-1 cells. (2) Competition experiments with lysine, ornithine and leucine indicated that the arginine transport system in specific for dibasic amino acids. (3) The value calculated for the intracellular arginine concentration agreed well with the values obtained by independent methods. (4) The low arginine transport rate of human erythrocytes can explain the failure to lower the hyperargininemia in familial hyperargininemia by blood transfusion with normal arginase-containing erythrocytes.

Entry of malaria parasites into resealed ghosts of human and simian erythrocytes

Whereas "white' ghosts, conventionally prepared by hypotonic lysis and washing are resistant to invasion by malaria parasites, cells lysed at high haematocrit and resealed without separating the membranes from the cytosol are invaded with high efficiency (not less than one-third the frequency of intact cells). Similar results were obtained with human and monkey cells, exposed respectively to Plasmodium falciparum and P. knowlesi. Microspectrophotometry of individual cells was used to ascertain the the susceptibility to invasion of lysed, resealed cells was not related to its haemoglobin content.

Short term changes of glycosylated haemoglobins during glucose administration in healthy and diabetic subjects

Haemoglobin A1 (Hb A1) is becoming a routine parameter for monitoring diabetic metabolism. Although widely used, the kinetic relationship between glucose concentration and Hb A1 value is not clarified yet. In vivo biosynthesis of Hb A1 was studied in 30 patients during an oral glucose tolerance test. Ten diabetics received an i.v. injection of 0.5 g glucose/kg, 20 healthy students and infusion of 1.0 g and 1.5 g glucose/kg and hour for 6h, and six volunteers 2.0 g/kg and hour. A parallel increase and decrease of serum glucose levels and Hb A1 could be demonstrated beginning a few minutes after administration of glucose. These acute changes of Hb A1 are closely related to fluctuation of serum glucose probably representing the formation and dissociation of the labile aldimine-linkage between haemoglobin and glucose. Severe hyperglycaemia of 6 h duration is not sufficient to cause an elevation of stable glycohaemoglobin.

Organic-acid transport in resealed haemoglobin-containing human erythrocyte 'ghosts'

The transport of organic acids across the membrane of resealed haemoglobin-containing erythrocyte 'ghosts' prepared by a dialysis technique has been studied. The present work forms part of studies directed towards the use of erythrocyte cellular carriers in enzyme-replacement therapy of inherited metabolic diseases. Oxalic acid, glycollic acid and glyoxylic acid were taken as representative of aliphatic acids of low molecular mass and benzoic and cinnamic acids as representative of unsubstituted aromatic acids. These selected acids are important in the diseases with which the present work is concerned. Comparison of influx and efflux transport characteristics showed that erythrocyte 'ghosts' retain transport properties closely similar to those of normal erythrocytes. Rapid transport was observed with all organic acids studied and there was a linear relationship between initial amount of influx and external concentration of aliphatic acid. Saturation of the transport system was not observed up to 1 mM external concentration, and the presence of plasma in the external medium had no effect on transport characteristics. Transport in intact erythrocytes and prepared erythrocyte 'ghosts' from patients with hyperoxaluria was also studied.

In vivo life span of resealed rabbit erythrocyte 'ghosts'

Resealed erythrocyte 'ghosts' have been proposed as biodegradable in vivo carriers for exogenous enzymes in the therapy of inherited metabolic diseases. Extended animal studies are essential prior to clinical application. The survival of rabbit erythrocyte 'ghosts' has been studied to find a suitable animal model. In vitro experiments have shown that incorporation of macromolecules into rabbit erythrocyte 'ghosts' is much lower than into human erythrocyte 'ghosts'. This could be related to the continuous cell destruction during 'ghost' preparation procedures. Rapid destruction of 'ghosts' in the circulation was obtained in all experiments particularly in the first minutes and hours. Cells surviving this initial period showed a longer life span and kinetics of further cell destruction followed a logarithmic function similar to that of normal erythrocytes. The experimental use of rabbits appears limited to studies where rapid uptake of the enzyme is required and other animal models must be studied when prolonged survival of the erythrocyte 'ghosts' is required, e.g., as the site of substrate degradation in the circulation.