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.Pharmaceutics 2020, 12, 276 2 of 44 property of RBCs allows to load them with biologically active substances of different molecular weights. For these reasons, erythrocytes are promising biocompatible cells for drug delivery.The methods for incorporating various substances into red blood cells differ in the way that substances penetrate the cells. The cause of permeability may be the pores' formation in the cell membrane due to a physical exposure (high voltage electric pulse [10,11] or ultrasound [12]). Drug molecules can also enter the RBCs by endocytosis in the presence of certain chemical compounds (for example, primaquine [13], vinblastine, chlorpromazine, hydrocortisone or tetracaine [14,15]), or using the cell-penetrating peptides bounded to the compound that should be encapsulated [16]. However, the most popular are different variants of osmotic methods.In some cases, RBCs are first exposed to a hyperosmotic pulse of a low molecular weight substance that penetrates very well through the cell membrane (for example, dimethyl sulfoxide (DMSO) [17,18] or glucose [19,20]). After washing the cells, which decreases the external concentration of these compounds and creates a gradient of their concentration between both sides of the RBC membrane, the target drug is introduced into the external volume. Water with this drug begins to enter into the cells to decrease the osmotic pressure there. The process ends when the gradient of DMSO or glucose disappears. The pores close and part of the drug remains into RBCs. Other, the most popular of the osmotic methods are hypoosmotic. These methods are based on creating a hypotonic environment around RBCs, which causes swelling of the cells and opening pores in the cellular membrane, through which therapeutic compounds can penetrate RBCs. Then, a hypertonic solution is introduced into the cell suspension. The pores close, the cells restore their original size, trapping the drug molecules inside the cell. Osmotic methods are divided into severa...
Background. L-asparaginase is an enzyme, widely used in the therapy of acute lymphoblastic leukemia in children and adults, but its use is limited due to a wide range of side effects and anaphylactic reactions. L-asparaginase loaded into erythrocytes can solve these problems. This enzyme is protected from the immune system and plasma proteases due to erythrocyte membrane, but continues to work inside the cell because its membrane is permeable to L-asparagine. Thus, the half-life of the drug increases and anaphylactic reactions reduce. The encapsulation of L-asparaginase into erythrocytes can be performed by various osmotic methods. Each of them is characterized by the amount of encapsulated enzyme, the cell yield, as well as by the quality indices of the survived erythrocytes. An important parameter of each method is the possibility to provide sterility of this dosage form for the clinical use.The aim of the study was the comparing of three osmotic methods of L-asparaginase encapsulation into erythrocytes (hypo-osmotic lysis, dialysis and flow dialysis) to select the most promising method for clinical use.Materials and methods. A suspension of erythrocytes of healthy donors (hematocrit 60–70%) was mixed with L-asparaginase from E. сoli. The procedures of hypotonic reversible lysis, dialysis in dialysis bags, or flow dialysis using pediatric dialyzers were performed. The physiological osmolality was restored in suspensions after the procedure by the addition of a hypertonic solution, and they were incubated for 30 min at 37 °C. Then the cells were washed in isotonic phosphate-buffered saline with pH 7.4. Activity of L-asparaginase, volume, hematocrit, hematological indices and osmotic cell fragility of erythrocytes were measured in the suspensions of erythrocytes before and after the enzyme encapsulation procedure.Results. An optimal osmolality of the hypotonic buffer for each method was selected and was equal to 90–110 mOsm/kg. The yields of encapsulation were 4.2 ± 2.0, 6.0 ± 2.3 and 16.2 ± 2.2 % for hypotonic lysis, dialysis and flow dialysis, respectively. The hematological indices of the obtained erythrocyte-carriers differed from the corresponding parameters of the initial erythrocytes, but did not differ significantly for different methods.Conclusion. Comparative investigation of mentioned above parameters allowed choosing the method of flow dialysis as the most promising for clinical use.
The limitations of the efficiency of ammonium-neutralizing erythrocyte-bioreactors based on glutamate dehydrogenase and alanine aminotransferase reactions were analyzed using a mathematical model. At low pyruvate concentrations in the external medium (below about 0.3 mM), the main limiting factor is the rate of pyruvate influx into the erythrocyte from the outside, and at higher concentrations, it is the disappearance of a steady state in glycolysis if the rate of ammonium processing is higher than the critical value (about 12 mM/h). This rate corresponds to different values of glutamate dehydrogenase activity at different concentrations of pyruvate in plasma. Oxidation of reduced nicotinamide adenine dinucleotide phosphate (NADPH) by glutamate dehydrogenase decreases the fraction of NADPH in the constant pool of nicotinamide adenine dinucleotide phosphates (NADP + NADPH). This, in turn, activates the pentose phosphate pathway, where NADP reduces to NADPH. Due to the increase in flux through the pentose phosphate pathway, stabilization of the ATP concentration becomes impossible; its value increases until almost the entire pool of adenylates transforms into the ATP form. As the pool of adenylates is constant, the ADP concentration decreases dramatically. This slows the pyruvate kinase reaction, leading to the disappearance of the steady state in glycolysis.
Excessive ammonium blood concentration causes many serious neurological complications. The medications currently used are not very effective. To remove ammonium from the blood, erythrocyte-bioreactors containing enzymes that processing ammonium have been proposed. The most promising bioreactor contained co-encapsulated glutamate dehydrogenase (GDH) and alanine aminotransferase (ALT). However, a low encapsulation of a commonly used bovine liver GDH (due to high aggregation), makes clinical use of such bioreactors impossible. In this study, new bioreactors containing ALT and non-aggregating GDH at higher loading were first produced using the flow dialysis method and the new bacterial GDH enzyme from Proteus sp. The efficacy of these erythrocyte-bioreactors and their properties (hemolysis, osmotic fragility, intracellular and extracellular activity of included enzymes, erythrocyte indices, and filterability) were studied and compared with native cells during 1-week storage. The ammonium removal rate in vitro by such erythrocyte-bioreactors increased linearly with an increase in encapsulated GDH activity. Alanine in vitro increased in accordance with ammonium consumption, which indicated the joint functioning of both included enzymes. Thus, novel bioreactors for ammonium removal containing GDH from Proteus sp. are promising for clinical use, since they have a more efficient GDH encapsulation and their properties are not inferior to previously obtained erythrocyte-bioreactors.
The review is devoted to one of the main regulatory enzymes of glycolysis in erythrocytes – pyruvate kinase, a deficiency of which is often the cause of hereditary nonspherocytic hemolytic anemia. The article presents data on the structure and function of pyruvate kinase and the currently known mutations of coding this enzyme gene. Authors analyzed associations between various genetic types and impaired enzyme function and the severity of the hemoly sis.
Drug delivery using natural biological carriers, especially erythrocytes, is a rapidly developing field. Erythrocytes can act as carriers with the gradual release of a pharmacological agent, as bioreactors with encapsulated enzymes, or as a tool for targeted delivery of drugs to target organs especially tissue macrophages, liver and spleen. To date, red blood cells have been studied as carriers for a wide range of drug compounds, such as enzymes, antibiotics, anti-inflammatory, antiviral drugs, etc. The review is devoted to the advantages of erythrocytes as carriers for the delivery of drugs loaded into the erythrocyte, or related to its surface, and defines the main directions of research on erythrocytes carriers of biologically active substances. Particular attention is paid to in vivo studies that reveal the potential of carrier erythrocytes for clinical use.
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