Preparation of ovine carrier erythrocytes: their action and survival

Novel engineering: Biomimicking erythrocyte as a revolutionary platform for drugs and vaccines delivery

Over the years, extensive studies on erythrocytes, also known as red blood cells (RBCs), as a mechanism for drug delivery, have been explored mainly because the cell itself is the most abundant and has astonishing properties such as a long life span of 100-120 days, low immunogenicity, good biocompatibility, and flexibility. There are various types of RBC-based systems for drug delivery, including those that are genetically engineered, non-genetically engineered RBCs, as well as employing erythrocyte as nanocarriers for drug loading. Although promising, these systems are still in an early development stage. In this review, we aimed to highlight the development of biomimicking RBC-based drug and vaccine delivery systems, as well as the loading methods with illustrative examples. Drug-erythrocyte associations will also be discussed and highlighted in this review. We have highlighted the possibility of exploiting erythrocytes for the sustained delivery of drugs and vaccines, encapsulation of these biological agents within the erythrocyte or coupling to the surface of carrier erythrocytes, and provided insights on genetically- and non-genetically engineered erythrocytes-based strategies. Erythrocytes have been known as effective cellular carriers for therapeutic moieties for several years. Herein, we outline various loading methods that can be used to reap the benefits of these natural carriers. It has been shown that drugs and vaccines can be delivered via erythrocytes but it is important to select appropriate methods for increasing the drug encapsulated or conjugated on the surface of the erythrocyte membrane. The outlined examples will guide the selection of the most effective method as well as the impact of using erythrocytes as delivery systems for drugs and vaccines.

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.

Encapsulation of glutamine synthetase in mouse erythrocytes: a new procedure for ammonia detoxification

There are a number of pathological situations in which ammonia levels increase leading to hyperammonemia, which may cause neurological alterations and can lead to coma and death. Currently, there are no efficient treatments allowing rapid and sustained decrease of ammonia levels in these situations. A way to increase ammonia detoxification would be to increase its incorporation in glutamine by glutamine synthetase. The aim of this work was to develop a procedure to encapsulate glutamine synthetase in mouse erythrocytes and to assess whether administration of these erythrocytes containing glutamine synthetase (GS) reduce ammonia levels in hyperammonemic mice. The procedure developed allowed the encapsulation of 3 +/- 0.25 IU of GS / mL of erythrocytes with a 70% cell recovery. Most metabolites, including ATP, remained unaltered in glutamine synthetase-loaded erythrocytes (named ammocytes by us) compared with native erythrocytes. The glutamine synthetase-loaded ammocytes injected in mice survived and retained essentially all of their glutamine synthetase activity for at least 48 h in vivo. Injection of these ammocytes into hyperammonemic mice reduced ammonia levels in the blood by about 50%. The results reported indicate that ammocytes are able to keep their integrity, normal energy metabolism, the inserted glutamine synthetase activity, and can be useful to reduce ammonia levels in hyperammonemic situations.

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.

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.

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.