Carrier erythrocytes

Characterization of carrier erythrocytes for biosensing applications

Erythrocyte abundance, mobility, and carrying capacity make them attractive as a platform for blood analyte sensing as well as for drug delivery. Sensor-loaded erythrocytes, dubbed erythrosensors, could be reinfused into the bloodstream, excited noninvasively through the skin, and used to provide measurement of analyte levels in the bloodstream. Several techniques to load erythrocytes, thus creating carrier erythrocytes, exist. However, their cellular characteristics remain largely unstudied. Changes in cellular characteristics lead to removal from the bloodstream. We hypothesize that erythrosensors need to maintain native erythrocytes’ (NEs) characteristics to serve as a long-term sensing platform. Here, we investigate two loading techniques and the properties of the resulting erythrosensors. For loading, hypotonic dilution requires a hypotonic solution while electroporation relies on electrical pulses to perforate the erythrocyte membrane. We analyze the resulting erythrosensor signal, size, morphology, and hemoglobin content. Although the resulting erythrosensors exhibit morphological changes, their size was comparable with NEs. The hypotonic dilution technique was found to load erythrosensors much more efficiently than electroporation, and the sensors were loaded throughout the volume of the erythrosensors. Finally, both techniques resulted in significant loss of hemoglobin. This study points to the need for continued development of loading techniques that better preserve NE characteristics.

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.

Red blood cells and polyelectrolyte multilayer capsules: natural carriers versus polymer-based drug delivery vehicles

INTRODUCTION

Red blood cells (RBCs) and lipid-based carriers on the one hand and polymeric capsules on the other hand represent two of the most widely used carriers in drug delivery. Each class of these carriers has its own set of properties, specificity and advantages. Thorough comparative studies of such systems are reported here for the first time.

AREAS COVERED

In this review, RBCs are described in comparison with synthetic polymeric drug delivery vehicles using polyelectrolyte multilayer capsules as an example. Lipid-based composition of the shell in the former case is particularly attractive due to their inherent biocompatibility and flexibility of the carriers. On the other hand, synthetic approaches to fabrication of polyelectrolyte multilayer capsules permit manipulation of the permeability of their shell as well as tuning their composition, mechanical properties, release methods and targeting.

EXPERT OPINION

In conclusion, properties of RBCs and polyelectrolyte multilayer capsules are reported here highlighting similarities and differences in their preparation and applications. In addition, their advantages and disadvantages are discussed.

Encapsulation of FITC to monitor extracellular pH: a step towards the development of red blood cells as circulating blood analyte biosensors

A need exists for a long-term, minimally-invasive system to monitor blood analytes. For certain analytes, such as glucose in the case of diabetics, a continuous system would help reduce complications. Current methods suffer significant drawbacks, such as low patient compliance for the finger stick test or short lifetime (i.e., 3-7 days) and required calibrations for continuous glucose monitors. Red blood cells (RBCs) are potential biocompatible carriers of sensing assays for long-term monitoring. We demonstrate that RBCs can be loaded with an analyte-sensitive fluorescent dye. In the current study, FITC, a pH-sensitive fluorescent dye, is encapsulated within resealed red cell ghosts. Intracellular FITC reports on extracellular pH: fluorescence intensity increases as extracellular pH increases because the RBC rapidly equilibrates to the pH of the external environment through the chloride-bicarbonate exchanger. The resealed ghost sensors exhibit an excellent ability to reversibly track pH over the physiological pH range with a resolution down to 0.014 pH unit. Dye loading efficiency varies from 30% to 80%. Although complete loading is ideal, it is not necessary, as the fluorescence signal is an integration of all resealed ghosts within the excitation volume. The resealed ghosts could serve as a long-term (>1 to 2 months), continuous, circulating biosensor for the management of diseases, such as diabetes.

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.

Delivery to macrophages and toxic action of etoposide carried in mouse red blood cells

Erythrocytes could be used as physiological carriers of active compounds. Several substances can be loaded into erythrocytes by hypotonic dialysis methods. Furthermore, carrier erythrocyte membrane can be chemically modified in order to promote increased arrival of the loaded compound to macrophages. In this work, we have prepared erythrocytes loaded with etoposide. We found conditions to obtain high etoposide encapsulation yields with minor alteration of some cell parameters of these carrier erythrocytes. Etoposide loaded into erythrocytes is mainly localised in the cytoplasmic compartment. Membrane modification of etoposide-loaded erythrocytes with band 3 crosslinkers produces an increased incorporation of the drug into macrophages mainly by phagocytosis process. The toxic effect of etoposide conveyed in these carrier erythrocytes determined as DNA fragmentation in macrophages was higher than that shown by free etoposide added at the same concentration in the culture medium to macrophages. These results seem to indicate the usefulness of this model to deliver this anti-tumour compound to macrophages, which might be useful in therapy.

In vivo survival of selected murine carrier red blood cells after separation by density gradients or aqueous polymer two-phase systems

In order to explore possibilities of using erythrocytes as carrier systems for delivery of pharmacological agents, we have studied the in vivo survival of murine carrier red blood cell populations enriched in young or old cells. Hypotonic-isotonic dialysis has been used to modify the cells as carrier systems and Percoll/albumin density gradients or counter-current distribution in aqueous polymer two-phase systems to separate them according to age. Hypotonic-isotonic dialysis produces a decrease in the red blood cell populations in vivo survival rate (from 9.5 to 7.8 days). Among the cells modified as carriers, the enriched young red blood cell populations show a higher in vivo survival (half-life 6.5-7.4 days) than populations made up of predominantly old red blood cells (half-life 4.7-6.2 days). Half-life of young or old circulating red blood cells was approximately one day longer when these cells were separated by counter-current distribution rather than by Percoll density gradients. Based on these results, hypotonic-isotonic dialysis of whole and enriched young or old red blood cell populations, with higher or lower survival rates, can be considered as a useful tool for modification of these cells as carriers. The final outcome of such changes can be translated into better control of plasma drug delivery during therapy.

In vitro study of alcohol dehydrogenase and acetaldehyde dehydrogenase encapsulated into human erythrocytes by an electroporation procedure

The optimal conditions for electroporated/resealed loading of alcohol dehydrogenase (ADH) and/or acetaldehyde dehydrogenase (ALDH) into human erythrocytes were established prior to the study, with the following characteristics: 300 V, 1 ms pulse time, eight pulses every 15 min and 1 h resealing at 37 degreesC. High encapsulation yield and carrier cell recoveries were achieved. Cell volumes increase while hemoglobin contents decrease; in consequence a decrease in cell hemoglobin concentration was observed. A lower hypotonic resistance of loading erythrocytes (throughout osmotic fragility curves) and unaltered oxygen transport capability (as given by oxygen equilibrium curves) were observed. The stability against time (up to 168 h-7 days) of encapsulated individual enzymes, either ADH- or ALDH-red blood cells (RBCs), was studied at 4 degreesC and 37 degreesC, in comparison with that of free enzyme solutions. Both enzymes were released from carrier RBCs to the incubation medium. The stability of carrier RBCs was studied under similar conditions. Non-significant variations in hematological parameters were observed. However, the hemoglobin derivative forms showed modifications. The continuous degradation of ethanol by ADH-RBCs and coencapsulated ADH- and ALDH-RBCs, as a function of time (up to 70 h) suggests the use of these carrier RBCs as agents for complete metabolization of ethanol. The mentioned properties bare the possibility of using ADH and ALDH as carrier systems in in vivo situations.

In vivo behaviour of rat band 3 cross-linked carrier erythrocytes

Rat band 3 cross-linked carrier erythrocytes have been prepared. Iodinated carbonic anhydrase has been encapsulated into rat erythrocytes. Then, carrier erythrocytes were labeled with 51chromium. Eventually, these doubly labeled rat RBCs were treated with a band 3 cross-linking reagent, namely bis(sulfosuccinimidyl)suberate (BS3). 51Chromium labeling and 125I CA showed to have cytosolic localization in cross-linked carrier erythrocytes. Estimation of the band 3 cross-linking induced by BS3 on rat carrier erythrocytes has been done rendering values around 25% of band 3 monomer reduction. BS3-cross-linked carrier erythrocytes when injected into rats are mainly targeted to liver as shown by chromium labeling localization. Also, encapsulated CA radioactivity carried by cross-linked carrier rat erythrocytes when injected into rats is localized predominantly in liver as shown by in vivo experiments. Accordingly, cross-linked carrier erythrocytes are highly recognized by peritoneal macrophages as detected by in vitro analyses of macrophage recognition. Thus, our data revealed a targeting of carrier rat erythrocytes induced by cross-linking of band 3 protein by BS3. These results support claims in favor of this animal model as a feasible system to analyze cross-linked carrier erythrocytes survival and targeting as well as the in vivo efficacy of targeting of loaded compounds to liver.

Oxygenation capacity of hypotonized and crosslinked rat erythrocytes

Rat erythrocytes subjected to hypotonic-isotonic dialysis, or crosslinking with bifunctional reagents (glutaraldehyde and dimethyl suberimidate hydrochloride) show a high percentage of methemoglobin and decreased oxyhemoglobin content which implies a low oxygen carrying capacity. Such modified cells maintain reversible oxygen binding properties although, they present a high hemoglobin oxygen affinity (low P50) and a diminished cooperativity in binding oxygen to hemoglobin (low n). These results suggest a reduced capacity of liberating oxygen to tissues under low PO2. Changes produced in erythrocytes can not be restored even in the presence of energy (ATP), reduced glutathione and 2,3-bisphosphoglyceric acid during the dialysis process or after crosslinking/permeabilizing treatment.

In vitro properties and organ uptake of rat band 3 cross-linked erythrocytes

Chemical conditions for cross-linking rat erythrocytes with bis(sulfosuccinimidyl)suberate (BS3) and 3,3' dithiobis(sulfosuccinimidyl propionate) (DTSSP) have been studied. These two cross-linking reagents seem to react with band 3 proteins in rat erythrocyte membrane. Two different conditions have been assayed using different cell/cross-linker concentration ratios. Similar cell volumes were observed in cross-linked rat erythrocytes compared to rat control erythrocytes. Cell yields after cross-linking account for about 65% when a high ratio of cell-to-cross-linker was used. Slightly lower cell yields (about 62%) were obtained when this ratio was reduced. Estimation of band 3 cross-linking by gel electrophoresis revealed a level of cross-linking of around 45% and 50% at the different conditions used. In vivo behavior of these modified rat erythrocytes revealed that they do not circulate, showing a predominant localization in the liver. This effect is evident from the concentration (5 mM BS3 or DTSSP) used. Based on these results, BS3 and DTSSP can be considered as useful tools to cross-link rat erythrocyte band 3 and to target rat erythrocytes to the liver.

Targeting of mouse erythrocytes by band 3 crosslinkers

Chemical conditions of crosslinking mouse erythrocytes with BS3 and DTSSP have been studied. These two crosslinking reagents seem to react with band 3 protein in mouse erythrocytes membrane. Extent of crosslinking is dependent on the concentration of the reagent used. Similar cell volumes were observed in crosslinked erythrocytes with respect to control erythrocytes. In vivo behaviour of these modified erythrocytes revealed prominent targeting of crosslinked erythrocytes to liver. This effect is clearly evident when concentrations of 5 mM BS3 or DTSSP were used and can be dependent of reagent concentration. Consequently, from our results BS3 and DTSSP can be considered as very useful tools to control and modulate targeting of crosslinked erythrocytes.

A single partitioning step in aqueous polymer two-phase systems reduces hypotonized rat erythrocyte heterogeneity

Rat carrier erythrocytes prepared by hypotonic dialysis (80 mOsm/kg) are a heterogeneous cell population that can be fractionated into two well-defined cell subpopulations by a single partition step, in charge-sensitive dextran-poly(ethylene glycol) aqueous two-phase systems. One subpopulation (65% of total cells) has a decreased cell surface charge and is partitioned at the interface in a single step and then fractionated by counter-current distribution as a low-G subpopulation. The other subpopulation (35% of total cells) has charge surface properties more like those of the untreated control rat erythrocytes. These last cells are partitioned in the top phase in a single step and then fractionated by counter-current distribution as a high-G subpopulation. Partitioning is more effective in reducing cell heterogeneity in hypotonized rat erythrocyte populations than is density separation in Ficoll-paque which only separates a small less dense cell subpopulation (5% of total cells), with the most fragile cells, from a larger and more dense cell subpopulation (95% of total cells), with a mixture of fragile and normal cells. This simple cell separation procedure quickly reduces carrier erythrocyte heterogeneity in a single partitioning step so it can be used to prepare cells for in vivo studies.

Heterogeneity of hypotonically loaded rat erythrocyte populations as detected by counter-current distribution in aqueous polymer two-phase systems

Carrier rat erythrocytes loaded with exogenous substances ([125I] carbonic anhydrase) by hypotonic-isotonic dialysis become heterogeneous cell populations that can be fractionated using the counter-current distribution (CCD) technique. Two well-defined low- and high-partition ratio, G, subpopulations are obtained in charge-sensitive dextran-polyethylene glycol two-phase systems. The low-G subpopulation, which contains the most fragile and surface-altered cells, as deduced from their osmotic fragility curves and partition behaviour, respectively, presents a high amount of exogenous substance incorporated (134.6 cpm/10(6) cells). The high-G subpopulation, that contains cells similar to the control or isotonically dialyzed cells presents a lower amount of exogenous substance incorporated (69.8 cpm/10(6) cells). Cells in this high-G subpopulation seem to be fractionated, like the controls, according to ageing as suggested by the decline of the pyruvate kinase specific activity from the left- to the right-hand side of the CCD profile.

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.

Antagonism of cyanide intoxication with murine carrier erythrocytes containing bovine rhodanese and sodium thiosulfate

Murine carrier erythrocytes containing bovine rhodanese and sodium thiosulfate are being explored as a new approach to antagonize the lethal effects of potassium cyanide in mice. Prior studies indicated that these carrier erythrocytes persist in the vascular system for the same length of time as normal erythrocytes and can enhance metabolism of cyanide to thiocyanate. The present studies demonstrate the ability of these carrier red blood cells containing rhodanese and thiosulfate to antagonize the lethal effects of cyanide either alone or in various combinations with sodium nitrite and/or sodium thiosulfate. Potency ratios are compared in groups of mice treated with sodium nitrite, sodium thiosulfate, and carrier erythrocytes containing rhodanese and sodium thiosulfate either alone or in various combinations prior to the administration of potassium cyanide. These results indicate that the administration of carrier erythrocytes containing rhodanese and thiosulfate alone can provide significant protection against the lethal effects of cyanide. These carrier erythrocytes potentiate the antidotal effect of sodium thiosulfate alone or the combination of sodium nitrite and sodium thiosulfate. The mechanisms of cyanide antagonism by these carrier erythrocytes and their broader conceptual significance to the antagonism of other chemical toxicants are discussed.

Preparation and in vitro characterization of a magnetically responsive ibuprofen-loaded erythrocytes carrier

The erythrocytes were loaded with ibuprofen and magnetite (ferrofluids) using the pre-swell technique. Various process variables including drug concentration, magnetite concentration, sonication of ferrofluids that could affect the loading of drug and magnetite were optimized. The loaded erythrocytes were characterized for in vitro drug efflux, haemoglobin release, morphology, osmotic fragility, turbulence shock, in vitro magnetic responsiveness and percentage cell recovery. In optimum concentration erythrocytes could tolerate ibuprofen as no appreciable detrimental effects were noticed on cell morphology, osmotic fragility, and turbulence shock, when compared with normal erythrocytes. However, magnetite showed some detrimental effect on erythrocytes. A drug release profile from the cellular system was observed to follow approximate zero-order kinetics. The loaded cells effectively responded for an external magnetic field of 8.0 KOe.

Carrier erythrocytes from white-tailed deer: morphology, osmotic fragility and survival of circulating sickled erythrocytes

Carrier erythrocytes are used to disseminate drugs in the circulatory system of animals. Carrier erythrocytes prepared from white-tailed deer (Odocoileus virginianus) do not circulate well in vivo. Although carrier cells were prepared from sickle and non-sickle cells with no apparent differences, their 24-hour survival was only 10 per cent. Osmotic fragility of carrier cells was increased over that of normal deer erythrocytes. Unlike erythrocytes from other ruminants, deer carrier erythrocytes are extremely fragile. Scanning electron micrographs of deer erythrocytes (sickle or non-sickle) in different stages of carrier cell preparation revealed no morphological differences. These data suggest that carrier cells from deer would not be amenable for use in long-term dissemination of drugs.

Antagonism of the lethal effects of cyanide with resealed erythrocytes containing rhodanese and thiosulfate

A new concept has been presented for the antagonism of cyanide and possibly other chemical toxicants. Until now, only a half dozen truly specific "antidotes" were known. There are many other "antidotes" which merely prevent the absorption or enhance the elimination of a toxic compound rather than specifically destroying the substance to prevent its toxic effect. This new approach has considerable conceptual significance in toxicology, as it suggests the encapsulating other enzymes to degrade various other chemical toxicants. There are many chemical toxicants for which there are no specific antidotes, and the conceptual approach of employing erythrocyte-encapsulated enzyme provides an innovative, specific approach to antagonize the toxic and lethal effects of these chemicals.

Properties of hypotonized, crosslinked and crosslinked- permeabilized rat erythrocytes as potential carrier systems

The osmotic fragility curves of isotonic rat RBCs, studied at pH 8 to avoid the Hb insolubility, are similar to those in humans at pH 7.4. Hypotonized rat RBCs, either directly or dialysed (0-24 h), are more hemolysis-resistant than isotonic rat RBCs. The discocyte-stomatocyte-spherocyte transformation can be observed with scanning electron microscopy. Protein crosslinking with dimethyl suberimidate can stabilize RBCs. The crosslinking level (60%), the cellular yield (80%), the mechanical and hemolytic resistance and the protective effect of enzyme activities, were studied in crosslinked or crosslinked- permeabilized RBCs after digitonin treatment. The normal discocytic shape of RBCs under scanning electron microscopy becomes stomatocytic in crosslinked and crosslinked- permeabilized RBCs with an erosioned surface.

Red blood cells augment transport of reactive metabolites of monocrotaline from liver to lung in isolated and tandem liver and lung preparations

Monocrotaline (MCT) is a pyrrolizidine alkaloid that causes pulmonary hypertension in rats by mechanisms which remain largely unknown. MCT is thought to be activated in the liver to a reactive intermediate that is transported to the lung where it causes endothelial injury. Our previous pharmacokinetic work demonstrated significant sequestration of radioactivity in red blood cells (RBCs) of rats treated with [14C]MCT. To determine whether this RBC sequestration might be important in the transport of reactive MCT metabolites, we compared the effect of inclusion of RBCs in the perfusion buffer on the extent of covalent binding of [14C]MCT to rat lungs in tandem liver-lung preparations. The potential effect of RBCs in stabilizing reactive intermediates was evaluated by preperfusion of isolated liver preparations with [14C]MCT with and without RBCs, separation and washing of the RBC fraction, and subsequent (90 min later) perfusion of washed RBCs or buffer alone in isolated perfused lungs. Covalent binding to lung tissues was determined by exhaustive methanol/chloroform extractions of unbound label from homogenized lung tissue followed by scintillation counting of residual 14C. Covalent binding was expressed as picomole MCT molecular weight equivalents/mg protein. Comparison of the relative capability of these isolated organ preparations for conversion of MCT to polar metabolites was done by extraction and HPLC analysis of perfusate at the end of the experiment. Isolated livers converted 65-85% of MCT to polar metabolites compared with less than 5% conversion in the isolated lungs. Inclusion of RBCs in the buffer of tandem lung liver preparations perfused with 400 microM [14C]MCT increased the covalent binding to the lung from 97 +/- 25 (buffer alone) to 182 +/- 36 (buffer + RBC) pmol/mg protein. At the end of these perfusions, RBCs contained 1552 +/- 429 pmol/mg hemoglobin of which 333 +/- 98 pmol/mg hemoglobin resisted exhaustive solvent extraction. After 90 min at room temperature, buffer with 400 microM [14C]MCT preperfused in isolated livers resulted in covalent binding to isolated perfused lung of 0.8 +/- 0.4 pmol/mg protein while washed RBCs isolated from buffer of similar liver preperfusions preparations resulted in 53 +/- 7 pmol/mg protein bound to lung. Control groups perfused with 400 microM [14C]MCT in buffer or buffer + RBCs through isolated lungs only resulted in covalent binding of 2 +/- 1 or 1 +/- 0.6 pmol/mg protein respectively. We conclude: (1) RBCs significantly augment the transport of lung reactive MCT metabolites from the liver to the lung.(ABSTRACT TRUNCATED AT 400 WORDS)

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.

Enhanced antitumor activity of adriamycin by encapsulation in mouse erythrocytes targeted to liver and lungs

Adriamycin was encapsulated within human and murine (B6D2F1 female mice) erythrocytes using a procedure based on hypotonic hemolysis followed by isotonic resealing and reannealing. Following drug encapsulation the murine erythrocytes were treated with glutaraldehyde to obtain: a) control of Adriamycin efflux from loaded erythrocytes, b) appropriate hepatic and pulmonary targeting of the in vivo re-infused cells. The antitumor effect of equivalent amounts of bolus (i.v.) administered Adriamycin, 1) free, 2) encapsulated within erythrocytes, 3) encapsulated within glutaraldehyde-treated erythrocytes, was compared using an in vivo model of metastasis based on selective hepatic and pulmonary dissemination of intrasplenically injected L1210 cells in B6D2F1 mice. The therapeutic index (TI) of Adriamycin encapsulated within glutaraldehyde-treated erythrocytes increased by more than two-fold over that of the free drug.

Species-specific hemolysis of erythrocytes by T-2 toxin

The tricothecene mycotoxin, T-2 toxin interacts differently with mammalian erythrocytes. Pig, man, rabbit, guinea pig, horse, dog, rat, and mouse erythrocytes are all lysed to a varying degree by T-2 toxin. But cow, sheep, goat, buffalo, and deer erythrocytes are all resistant to hemolysis by T-2 toxin. Since erythrocytes from ruminant animals contain little or no phosphatidylcholine, perhaps the presence of phosphatidylcholine in the membrane is required for the hemolytic action of T-2 toxin. Sheep erythrocytes were used to encapsulate T-2 toxin further confirming the resistance of erythrocytes from animals with ruminant physiology to T-2 toxin lysis.

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.