An erythrocyte encapsulator dialyzer used in preparing large quantities of erythrocyte ghosts and encapsulation of a pesticide in erythrocyte ghosts

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.

Resealed Erythrocytes as Drug Carriers and Its Therapeutic Applications

In this pharma innovative world, there are more than 30 drug delivery systems. Today's due to lacking the target specificity, the present scenario about drug delivery is emphasizing towards targeted drug delivery systems. Erythrocytes are the most common type of blood cells travel thousands of miles from wide to narrow pathways to deliver oxygen, drugs and nutrient during their lifetime. Red blood cells have strong and targeted potential carrier capabilities for varieties of drugs. Drug-loaded carrier erythrocytes or resealed erythrocytes are promising for various passive and active targeting. Resealed erythrocyte have advantage over several drug carrier models like biocompatibility, biodegradability without toxic products, inert intracellular environment, entrapping potential for a variety of chemicals, protection of the organism against toxic effects of the drug, able to circulate throughout the body, ideal zero-order drug-release kinetics, no undesired immune response against encapsulated drug etc. Resealed erythrocytes are rapidly taken up by macrophages of the Reticuloendothelial System (RES) of the liver, lung, and spleen of the body and hence drugs also. Resealed erythrocytes method of drugs delivery is secure and effective for drugs targeting specially for a longer period of time. This chapter will explain the different method of drug loading for resealed erythrocytes, their characterization, and applications in various therapies and associated health benefits.

Biomembranes from slaughterhouse blood erythrocytes as prolonged release systems for dexamethasone sodium phosphate

The present study investigated preparation of bovine and porcine erythrocyte membranes from slaughterhouse blood as bio-derived materials for delivery of dexamethasone-sodium phosphate (DexP). The obtained biomembranes, i.e., ghosts were characterized in vitro in terms of morphological properties, loading parameters, and release behavior. For the last two, an UHPLC/-HESI-MS/MS based analytical procedure for absolute drug identification and quantification was developed. The results revealed that loading of DexP into both type of ghosts was directly proportional to the increase of drug concentration in the incubation medium, while incubation at 37°C had statistically significant effect on loaded amount of DexP (P < 0.05). The encapsulation efficiency was about fivefold higher in porcine compared to bovine ghosts. Insight into ghosts' surface morphology by field emission-scanning electron microscopy and atomic force microscopy confirmed that besides inevitable effects of osmosis, DexP inclusion itself had no observable additional effect on the morphology of the ghosts carriers. DexP release profiles were dependent on erythrocyte ghost type and amount of residual hemoglobin. However, sustained DexP release was achieved and shown over 3 days from porcine ghosts and 5 days from bovine erythrocyte ghosts. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:1046-1055, 2016.

Recent advancements in erythrocytes, platelets, and albumin as delivery systems

In the past few years, nanomaterial-based drug delivery systems have been applied to enhance the efficacy of therapeutics and to alleviate negative effects through the controlled delivery of targeting and releasing agents. However, few drug carriers can achieve high targeting efficacy, even when targeting modalities and surface markers are introduced. Immunological problems have also limited their wide applications. Biological drug delivery systems, such as erythrocytes, platelets, and albumin, have been extensively investigated because of their unique properties. In this review, erythrocytes, platelets, and albumin are described as efficient drug delivery systems. Their properties, applications, advantages, and limitations in disease treatment are explained. This review confirms that these systems can be used to facilitate a specific, biocompatible, and smart drug delivery.

Erythrocytes-based synthetic delivery systems: transition from conventional to novel engineering strategies

INTRODUCTION

Erythrocytes (red blood cells [RBCs]) and artificial or synthetic delivery systems such as liposomes, nanoparticles (NPs) are the most investigated carrier systems. Herein, progress made from conventional approach of using RBC as delivery systems to novel approach of using synthetic delivery systems based on RBC properties will be reviewed.

AREAS COVERED

We aim to highlight both conventional and novel approaches of using RBCs as potential carrier system. Conventional approaches which include two main strategies are: i) directly loading therapeutic moieties in RBCs; and ii) coupling them with RBCs whereas novel approaches exploit structural, mechanical and biological properties of RBCs to design synthetic delivery systems through various engineering strategies. Initial attempts included coupling of antibodies to liposomes to specifically target RBCs. Knowledge obtained from several studies led to the development of RBC membrane derived liposomes (nanoerythrosomes), inspiring future application of RBC or its structural features in other attractive delivery systems (hydrogels, filomicelles, microcapsules, micro- and NPs) for even greater potential.

EXPERT OPINION

In conclusion, this review dwells upon comparative analysis of various conventional and novel engineering strategies in developing RBC based drug delivery systems, diversifying their applications in arena of drug delivery. Regardless of the challenges in front of us, RBC based delivery systems offer an exciting approach of exploiting biological entities in a multitude of medical applications.

Nano-intercalated organophosphorus-hydrolyzing enzymes in organophosphorus antagonism

A dendritic poly(2-alkyloxazoline)-based polymer was studied as a new carrier system for the organophosphorus-hydrolyzing recombinant enzymes, organophosphorus acid anhydrolase and organophosphorus hydrolase. Paraoxon (PO) and diisopropylfluorophosphate (DFP) were used as model organophosphorus compounds. Changes in plasma cholinesterase activity were monitored. The cholinesterase activity was proportional to the concentrations of DFP or PO. Plasma cholinesterase activity was higher in animals receiving enzyme and oxime before the organophosphates than in the oxime-only pretreated groups. These studies suggest that cholinesterase activity can serve as an indicator for the in vivo protection by the nano-intercalated organophosphorus acid anhydrolase or organophosphorus hydrolase against organophosphorus intoxications. These studies represent a practical application of polymeric nano-delivery systems as enzyme carriers in drug antidotal therapy.

Engineering erythrocytes to be erythrosensors: first steps

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

Evaluation of hepatotropic targeting properties of allogenic and xenogenic erythrocyte ghosts in normal and liver-injured rats

BACKGROUND/AIMS

Haemoglobin-depleted erythrocyte ghosts have been recommended as vesicle carriers of drugs with hepatotropic properties. However, the influence of liver injury on ghost elimination and targeting has not been reported so far.

METHODS

Human and rat ghosts were prepared and loaded with model substances, and the basic parameters were characterized. Ghosts were injected intravenously into rats with acute, subacute and chronic liver injuries. Elimination from circulation, organ distribution and cellular targeting was measured. The uptake of ghosts by liver macrophages/Kupffer cells was determined in cell culture.

RESULTS

Ghosts are strong hepatotropic carriers with a recovery of 90% in normal liver. Kupffer cells are the almost exclusive target cell type. Hepatotropic properties remain in rats with chronic liver diseases, but are reduced by 60-70% in acute liver damage as a result of decline of phagocytosis of macrophages/Kupffer cells. Although the uptake of ghosts per gram liver tissue in chronic liver injury was also reduced by about 40%, the increase of liver mass and of macrophages/Kupffer cells compensated for the reduced phagocytotic activity. In subacute injury, the uptake per gram liver tissue was only moderately reduced.

CONCLUSION

Drug targeting with ghosts might be feasible in chronic and subacute liver injuries, e.g. fibrogenesis and tumours, because the content of ingested ghosts is released by Kupffer cells into the micro-environment, providing the uptake by and pharmacological effects on adjacent cells.

The mouse immune response to carrier erythrocyte entrapped antigens

This study investigated the potential of a single administration of carrier erythrocyte entrapped antigen to elicit humoral responses in the Balb/c mouse. Humoral responses to primary immunizations of erythrocyte encapsulated antigens were compared with those obtained with adjuvanted antigen administered via the subcutaneous route. Ig isotype responses to primary immunizations of erythrocyte entrapped antigen and subcutaneous antigen were compared to responses observed in mice that subsequently received booster immunizations with un-entrapped antigen. This study demonstrates that a single administration of antigen-loaded carrier erythrocytes is able to elicit humoral immune responses comparable or superior to those obtained via the adjuvanted subcutaneous vaccination route. The IgG isotype profiles demonstrate that the erythrocyte entrapment of antigens is another mechanism by which the Th responses to antigens maybe modulated.

Encapsulation of PEG-urease/PEG-AlaDH enzyme system in erythrocyte

No intravenously injectable enzyme preparate containing urease as an alternetive to hemodialysis, hemoperfusion and CAPD systems in patients having chronic renal failure has been encountered in literature. In this study, it has been aimed to convert blood urea to alanine by using PEG-urease/PEG-AlaDH enzyme pair encapsulated within living erythrocyte. In this system, urea is decomposed into NH3 and HCO3- and the ammonia released is converted into alanine by reacting pyruvate under the catalytic action of alaninedehydrogenase. The production of pyruvate and NADH by erythrocyte required in the second stage of the reaction will make the process a feasible and ceaseless one. The success of the system will enable the renal patients with diabetes mellitus. Urease and AlaDH were covalently immobilized on activated PEG. PEG-urease/PEG-AlaDH were encapsulated in erythrocyte (1/1)(v/v) by using slow dialysis methods. The activity of enzyme system, encapsulation yield and hemogram analysis were determined for each sample.

Evaluation of hypotonic preswelling method for encapsulation of enalaprilat in intact human erythrocytes

The hypotonic preswelling method for encapsulation of drugs in intact human erythrocytes was evaluated using enalaprilat as a model peptide-like drug. Several process variables, including volume, concentration, pH, and method of addition of drug solution, type of erythrocyte-suspending medium, temperature, initial packed density of erythrocytes, and individual process steps, were exploited with respect to their effects on the loading parameters (i.e., loaded amount, efficiency of entrapment, and cell recovery). In addition, the probable mechanism by which the erythrocytes were loaded by enalaprilat at the point of lysis was shown to be a simple concentration gradient-based diffusion through membrane openings occurring on hemolysis. Finally, the adopted method was validated, and the results showed a considerable degree of reproducibility and recovery for the entire loading procedure.

In vitro studies on sterically stabilized liposomes (SL) as enzyme carriers in organophosphorus (OP) antagonism

This study describes a new approach for organophosphorous (OP) antidotal treatment by encapsulating an OP hydrolyzing enzyme, OPA anhydrolase (OPAA), within sterically stabilized liposomes. The recombinant OPAA enzyme was derived from Alteromonas strain JD6. It has broad substrate specificity to a wide range of OP compounds: DFP and the nerve agents, soman and sarin. Liposomes encapsulating OPAA (SL)* were made by mechanical dispersion method. Hydrolysis of DFP by (SL)* was measured by following an increase of fluoride ion concentration using a fluoride ion selective electrode. OPAA entrapped in the carrier liposomes rapidly hydrolyze DFP, with the rate of DFP hydrolysis directly proportional to the amount of (SL)* added to the solution. Liposomal carriers containing no enzyme did not hydrolyze DFP. The reaction was linear and the rate of hydrolysis was first order in the substrate. This enzyme carrier system serves as a biodegradable protective environment for the recombinant OP-metabolizing enzyme, OPAA, resulting in prolongation of enzymatic concentration in the body. These studies suggest that the protection of OP intoxication can be strikingly enhanced by adding OPAA encapsulated within (SL)* to pralidoxime and atropine.

Antagonism of paraoxon intoxication by recombinant phosphotriesterase encapsulated within sterically stabilized liposomes

This investigation effort is focused on increasing organophosphate (OP) degradation by phosphotriesterase to antagonize OP intoxication. For these studies, sterically stabilized liposomes encapsulating recombinant phosphotriesterase were employed. This enzyme was obtained from Flavobacterium sp. and was expressed in Escherichia coli. It has a broad substrate specificity, which includes parathion, paraoxon, soman, sarin, diisopropylfluorophosphate, and other organophosphorous compounds. Paraoxon is rapidly hydrolyzed by phosphotriesterase to the less toxic 4-nitrophenol and diethylphosphate. This enzyme was isolated and purified over 1600-fold and subsequently encapsulated within sterically stabilized liposomes (SL). The properties of this encapsulated phosphotriesterase were investigated. When these liposomes containing phosphotriesterase were incubated with paraoxon, it readily degraded the paraoxon. Hydrolysis of paraoxon did not occur when these sterically stabilized liposomes contained no phosphotriesterase. These sterically stabilized liposomes (SL) containing phosphotriesterases (SL)* were employed as a carrier model to antagonize the toxic effects of paraoxon by hydrolyzing it to the less toxic 4-nitrophenol and diethylphosphate. This enzyme-SL complex (SL)* was administered intravenously to mice either alone or in combination with pralidoxime (2-PAM) and/or atropine intraperitoneally. These results indicate that this carrier model system provides a striking enhanced protective effects against the lethal effects of paraoxon. Moreover when these carrier liposomes were administered with 2-PAM and/or atropine, a dramatic enhanced protection was observed.

Magnetically responsive diclofenac sodium-loaded erythrocytes: preparation and in vitro characterization

Diclofenac sodium-bearing magnetic erythrocytes were prepared using a preswell technique. The optimum loading of drug and magnetite achieved were 63-73 and 12-18 per cent, respectively. Drug-loaded erythrocytes and drug-loaded magnetic erythrocytes were characterized for in vitro drug and haemoglobin release, magnetic responsiveness, osmotic fragility, turbulence shock, morphology and percentage cell recovery. The drug-loaded magnetic erythrocytes were found less resistant to osmotic and turbulence shock when compared with the normal and drug-loaded erythrocytes. However, in optimum concentration erythrocytes tolerated drug and coated magnetite appreciably. The drug-loaded magnetic erythrocytes responded effectively for an external magnetic field of 8.0 kOe. The study suggested the potentiality of diclofenac sodium-loaded magnetic erythrocytes, for active delivery of drug to painful inflamed joints.

In vivo studies on rhodanese encapsulation in mouse carrier erythrocytes

Resealed erythrocytes containing sodium thiosulfate and rhodanese (CRBC) are being employed as a new approach in the antagonism of cyanide intoxication. In earlier in vitro studies, the behavior of red blood cells containing rhodanese and sodium thiosulfate was investigated with regard to their properties and their capability of metabolizing cyanide to thiocyanate. The present studies are concerned with the properties of these rhodanese-containing carrier erythrocytes in the intact animal. These carrier erythrocytes were administered intravenously and the survival of the encapsulated enzyme was compared with the administration (iv) of free exogenous enzyme. Also, the amount of leakage of the encapsulated rhodanese from the red blood cell was determined. The survival of the carrier red blood cell. prepared by hypotonic dialysis, was found to be characterized by a biphasic curve. There was an initial rapid loss of approximately 40 to 50% of the carrier cells with a t1/2 = 2.5 hr. Subsequently the remaining resealed annealed carrier erythrocytes persisted in the vascular system with a t1/2 = 8.5 days. When free exogenous rhodanese was administered directly into the vascular system, it was rapidly eliminated with a t1/2 = 53 min. Red blood cells containing sodium thiosulfate and rhodanese apparently are effective in vivo in the biotransformation of cyanide. In animals pretreated with encapsulated rhodanese and sodium thiosulfate, blood cyanide concentrations are appreciably decreased with a concomitant increase in thiocyanate ion, a metabolite of cyanide. When erythrocytes, which contained no rhodanese or sodium thiosulfate, were subjected to hypotonic dialysis, cyanide was not metabolized to any appreciable extent. Furthermore, carrier erythrocytes containing rhodanese and sodium thiosulfate were found to increase the protection against the lethal effects of cyanide by approximately twofold. The ability of these carrier erythrocytes alone to metabolize cyanide and to antagonize the lethal effects of cyanide reflects the potential of this new antidotal approach in the antagonism of chemical toxicants.

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.

Hypoosmotic dialysis and ultrafiltration technique for preparation of mammalian hemoglobin: a comparison of three species

Dialysis of human, bovine, and ovine red blood cells using a hypotonic solution and a commercial kidney dialysis unit, followed by ultrafiltration through 0.1 micron pore hollow-fibers provides an easily managed method for isolation of lipid-free hemoglobin (LFHB). High performance liquid chromatography (HPLC) analysis of hemoglobin indicated 99% protein purity. SDS polyacrylamide gel electrophoresis analysis demonstrated that LFHB migrates as a single band. Processing one-half liter of packed red blood cells requires approximately 10 hours and resulting in an average of 93% hemoglobin recovery.

Interaction of T-2 toxin with bovine carrier erythrocytes: effects on cell lysis, permeability, and entrapment

Hemolysis, morphological changes, binding, and effect on encapsulation of exogenous substances were used as a basis to study the interaction of the trichothecene mycotoxin, T-2 toxin, with erythrocytes. T-2 toxin did not cause hemolysis of bovine erythrocytes but readily hemolyzed rat erythrocytes. T-2 toxin interaction with bovine erythrocytes was minimal because T-2 toxin did not bind appreciably to the erythrocytes. Entrapment of T-2 toxin in carrier erythrocytes was independent of toxin concentration, and interaction of T-2 toxin with erythrocytes did not affect the entrapment of the markers sucrose or inulin. T-2 toxin rapidly diffuses from carrier erythrocytes with less than 20% remaining after 4 hr of incubation. Cross-linking of the erythrocyte membrane with glutaraldehyde prevents T-2 toxin efflux from carrier erythrocytes.

A continuous-flow high-yield process for preparation of lipid-free hemoglobin

Hypotonic hollow-fiber dialysis of bovine red blood cells followed by ultrafiltration through 0.1-micron pore hollow fibers provides a simple method for isolation of lipid-free hemoglobin. Hemoglobin (Hb) isolated by comparative techniques were all contaminated with membrane stroma. HPLC analysis of Hb revealed a protein peak of 99.6% purity and sodium dodecylsulfate-polyacrylamide gel electrophoresis analysis revealed a single band. The process requires hypoosmotic dialysis of bovine RBC to a final 160-180 mosmol/kg osmotic pressure. Additional reduction in osmotic pressure causes irreversible cell lysis which leads to lipid contamination of the Hb. Processing of 1/2 liter of packed red blood cells requires 4-5 h, resulting in an average of 90% hemoglobin recovery.

Encapsulation of thiosulfate: cyanide sulfurtransferase by mouse erythrocytes

Murine carrier erythrocytes, prepared by hypotonic dialysis, were employed in the encapsulation of several compounds including [14C]sucrose, [3H]inulin, and bovine thiosulfate:cyanide sulfurtransferase (rhodanese), a mitochondrial enzyme which converts cyanide to thiocyanate. Approximately 30% of the added [14C]sucrose, [3H]inulin, and rhodanese was encapsulated by predialyzed erythrocytes, and a decrease in the mean corpuscular volume and mean corpuscular hemoglobin was observed. In the encapsulation of rhodanese a recovery of 95% of the erythrocytes was achieved and an 85% equilibrium was established. The addition of potassium cyanide (50 mM) to intact, rhodanese-loaded erythrocytes containing sodium thiosulfate resulted in its metabolism to thiocyanate. These results establish the potential use of erythrocytes as biodegradable drug carrier in drug antagonism.

Preparation of ovine carrier erythrocytes: their action and survival

Conditions for preparation of and the stability of carrier-red blood cells (C-RBC) are described for sheep RBC. The average percentage entrapment of 14C-sucrose was greater than 35% with 65% recovery of the cells. Cells prepared by dialysis encapsulation are morphologically similar to sheep RBC, although smaller in size than normal sheep RBC. C-RBC have a 28-day half-life in vivo and are stable in vitro for 24 hr at 37 degrees C. C-RBC are more resistant to osmotic stress than are normal sheep erythrocytes.

Immunospecific vesicle targeting facilitates fusion with selected cell populations

Antibody-directed targeting of vesicles to cells dramatically enhances polyethylene glycol-mediated fusion and microinjection. Sealed erythrocyte ghosts or liposomes, containing fluorescent bovine serum albumin, were targeted to murine spleen and thymus cells, and to lymphocyte and monocyte cell lines. In all cases, targeted cell populations showed substantial levels of microinjection, whereas populations treated with the fusogen in the absence of targeting were not significantly microinjected. Attachment of vesicles to selected cells was achieved by first labelling the cells with biotin-modified antibody and then treating them with avidin-coupled sealed ghosts or liposomes. Another approach to the promotion of selective fusion aims to alter the cell recognition properties of Sendai virus so that its fusogenic activity may be redirected to specific cellular targets. The agglutination and fusion of red cells by UV-inactivated Sendai virus were completely blocked by low concentrations of a Fab preparation of a monoclonal antibody against the viral haemagglutinin (HN) sites. Agglutination and fusion activity were restored in the presence of Fab-anti-HN by providing an alternative recognition system, namely, when the virus had been coupled with biotin and the red cells with avidin. Methods for facilitating microinjection by specifically directing vesicles to target cells may be particularly useful in overcoming barriers to the transfer of genes into lymphocytes by standard transfection techniques.

Encapsulation of drugs in intact erythrocytes: an intravenous delivery system

A number of drugs and the plasma antiprotease alpha 1-antitrypsin has been encapsulated in intact erythrocytes after hypotonic swelling, using a technique designed to preserve the viability of the cells. By labelling the cells with fluorescein isothiocyanate it has been shown that the cells survive exceptionally well when returned to the animal's circulation. Cell survival has been demonstrated in the rat, rabbit and guinea-pig. With encapsulation of cortisol-21-phosphate and methotrexate it was found that blood levels of the drug were maintained for a longer period than when the free drug was administered. Cortisol-21-phosphate was hydrolysed enzymatically by acid phosphatase located primarily in the erythrocyte membrane. An in vitro test involving the interaction or erythrocytes with phagocytes was developed to determine the viability or erythrocytes after being subjected to the encapsulation process. Preparations which did not interact with phagocytes survived when returned to the animal's circulation. The encapsulation procedure increased the fragility of the cell membrane compared to that of normal cells as measured by the leakage of haemoglobin after thermal treatment but it was found that encapsulated cortisol-21-phosphate in cells actually stabilized the membrane. The electrical charge on the membrane of encapsulating cells was the same as that of the normal cells. The charge on reformed ghosts was lower than that of normal cells. Reformed ghosts were rapidly removed when introduced into the circulation. The encapsulation procedure and its possible applications are discussed.

Hepatic pharmacokinetics of glutaraldehyde-treated methotrexate-loaded carrier erythrocytes in dogs

Methotrexate-loaded glutaraldehyde-treated canine carrier erythrocytes were used to deliver a 1.6-mg/kg dosage of drug. About 90% of the drug-loaded cells disappeared from circulation within 1 h. Approximately 11 mg of drug reached the liver, and a substantial portion of the methotrexate entered the enterohepatic bile salt circulation. Biochemical tests of liver function, such as alkaline phosphatase and serum glutamine pyruvate transaminase, indicated mild hepatocellular necrosis which was attributed to the action of methotrexate on the hepatocytes. Bilirubin levels were unchanged during and following drug treatment. The plasma half-life of the drug was extended 2.4-fold in the first 24 h following injection.