Review on Resealed Erythrocyte
Sarika V. Khandbahale, Saudagar R. B.
Department of Quality Assurance Technique, R.G. Sapkal College of Pharmacy, Anjaneri, Nashik
Erythrocytes, also known as red blood cells, and have been extensively studied for their potential carrier capabilities for the delivery of drugs. Such drug-loaded carrier erythrocytes are prepared simply by collecting blood samples from the organism of interest, separating erythrocytes from plasma, entrapping drug in the erythrocytes, and resealing the resultant cellular carriers, these carriers are called resealed erythrocytes. Among the various carriers used for targeting drugs to various body tissues, the cellular carriers meet several criteria desirable in clinical applications, among the most important being biocompatibility of carrier and its degradation products. Carrier erythrocytes, resealed erythrocytes loaded by a drug or other therapeutic agents, have been exploited extensively in recent years for both temporally and spatially controlled delivery of a wide variety of drugs and other bioactive agents owing to their remarkable degree of biocompatibility, biodegradability and a series of other potential advantages. Leucocytes, platelets, erythrocytes, nano erythrocytes, hepatocytes, and fibroblast etc. have been proposed as cellular carrier systems. Among these, the erythrocytes have been the most investigated and have found to possess greater potential in drug delivery. In this review article, the potential applications of erythrocytes in drug delivery have been reviewed with a particular stress on the studies and laboratory experiences on successful erythrocyte loading and characterization of the different classes of biopharmaceuticals.
Blood contains different type of cells like erythrocytes (RBC), leucocytes (WBC) and platelets, among them erythrocytes are the most interesting carrier and possess great potential in drug delivery due to their ability to circulate throughout the body, zero order kinetics, reproducibility and ease of preparation. Primary aim for the development of this drug delivery system is to maximize therapeutic performance, reducing undesirable side effects of drug as well as increase patient compliance.
Erythrocytes, the most abundant cells in the human body, have potential carrier capabilities for the delivery of drugs. Erythrocytes are biocompatible, biodegradable, possess very long circulation half-lives and can be loaded with a variety of chemically and biologically active compounds using various chemical and physical methods. Most of the resealed erythrocytes used as drug carriers are rapidly taken up from blood by macrophages of reticuloendothelial system (RES), which is present in liver, lung, and spleen of the body . The aim of the present review is to focus on the various features, drug loading technology and biomedical application of resealed erythrocytes.
Red blood cells (also referred to as erythrocytes) are the most common type of blood cells and the vertebrate organism's principal means of delivering oxygen (O2) to the body tissues via the blood flow through the circulatory system. The cells develop in the bone marrow and circulate for about 100–120 days in the body before their components are recycled by macrophages. Each circulation takes about 20 seconds. Approximately a quarter of the cells in the human body are red blood cells.
Resealed Erythrocytes (2)
Such drug-loaded carrier erythrocytes are prepared simply by collecting blood samples from the organism of interest, separating erythrocytes from plasma, entrapping drug in the erythrocytes, and resealing the resultant cellular carriers8. Hence, these carriers are called resealed erythrocytes. The overall process is based on the response of these cells under osmotic conditions. Upon reinjection, the drug-loaded erythrocytes serve as slow circulating depots and target the drugs to a reticuloendothelial system( RES).
Morphology and Physiology of Erythrocytes :(5,8)
Erythrocytes (Fig1) are the most abundant cells in the human body (~5.4million cells/mm3 blood in healthy male and ~4.8 million cells in a healthy female). These cells were described in human blood samples by Dutch Scientist Lee Van Hock in 1674. In the 19th century, Hope Seyler identified hemoglobin and its crucial role in oxygen delivery to various parts of the body. Erythrocytes are biconcave discs with an average diameter of 7.8μm, a thickness of 2.5μm in periphery, 1μm in the centre, and a volume of 85–91μm3.8 The red blood cell membrane is dynamic, semi permeable components of the cell associated with energy metabolism in the maintenance of the permeability characteristic of the cell of various cations (Na+,K+) and anions (Cl‐, HCO3‐).
The flexible, biconcave shape enables erythrocytes to squeeze through narrow capillaries, which may be only 3m wide. Mature erythrocytes are quite simple in structure. They lack a nucleus and other organelles. Their plasma membrane encloses hemoglobin, a heme‐containing protein that is responsible for O2–CO2 binding inside the erythrocytes. The main role of erythrocytes is the transport of O2 from the lungs to tissues and the CO2 produced in tissues back to lungs. Thus, erythrocytes are a highly specialized O2 carrier system in the body. Because a nucleus is absent, all the intracellular space is available for O2 transport. Also, because mitochondria are absent and because energy is generated an aerobically in erythrocytes, these cells do not consume any of the oxygen they are carrying. Erythrocytes live only about 120 days because of wear and tear on their plasma membranes as they squeeze through the narrow blood capillaries. The process of erythrocyte formation within the body is known as erythropoiesis. In a mature human being, erythrocytes are produced in red bone marrow under the regulation of a hemopoietic hormone called erythropoietin
Isolation of Erythrocyte: (5)
Source: Erythrocytes may be prepared as carriers from blood taken from human beings and from different animal species including erythrocytes of mice, cattle, pigs, dogs, sheep, goats, monkeys, chicken, rats and rabbits. To isolate erythrocytes, the blood is collected in heparinised tubes by venipuncture. Freshly collected blood is centrifuged in a refrigerated centrifuge and washed in order to obtain erythrocyte. The washed cells are suspended in buffer (e.g. acid‐citrate‐dextrose buffer) at various haematocrit values as desired.
Fig. 1: Erythrocytes(5)
Advantages(8, 3, 4,5)
1. Biocompatible, particularly when autologous cells are used hence no possibility of triggered immune response.
2. Biodegradability with no generation of toxic product.
3. Considerable uniform size and shape of carrier.
4. Relatively inert intracellular environment can be encapsulated in a small volume of cells.
5. Isolation is easy and large amount of drug can be loaded.
6. Prevention of degradation of the loaded drug from inactivation by endogenous chemical.
7. Entrapment of wide variety of chemicals can be possible.
8. Entrapment of drug can be possible without chemical modification of the substance to be entrapped.
9. Possible to maintain steady-state plasma concentration, decrease fluctuation in concentration.
10. Protection of the organism against toxic effect of drug.
11. Targeting to the organ of the RES.
12. Ideal zero-order drug release kinetic.
13. Prolong the systemic activity of drug by residing for a longer time in the body.
14. Attainment of steady state plasma concentration with possibility of zero order drug release kinetics.
15. Modification of pharmacokinetics and Pharmacodynamics parameters of drug.
16. Significant decrease in side effects.
17. Large quantities of drug that can be encapsulated within a small volume of cells ensure dose sufficiency.
18. Ability to target the organs of RES.
1. They have a limited potential as carrier to non-phagocyte target tissue.
2. Possibility of clumping of cells and dose dumping may be there.
3. Rapid leakage of certain encapsulated material from the loaded erythrocytes.
4. Several molecules may alter the physiology of erythrocytes.
Requirement for Encapsulation:(2,4)
1. Variety of biologically active substance (5000-60,000dalton) can be entrapped in erythrocytes.
2. Non-polar molecule may be entrapped in erythrocytes in salts.Example: tetracycline HCl salt can be appreciably entrapped in bovine RBC.
3. Generally, molecule should be Polar & Non polar molecule also been entrapped.
4. Hydrophobic molecules can be entrapped in erythrocyte by absorbing over other molecules.
5. Once encapsulated charged molecule are retained longer than uncharged molecule. The size of molecule entrapped is a significant factor when the molecule is smaller than sucrose and larger than B-galactosidase.
Factors which Considering Resealed Erythrocytes as Carrier:(3)
1. Its shape and size to permit the passage through the capillaries.
2. Its specific physico-chemical properties by which a prerequisite site can be recognized.
3. Its biocompatible and minimum toxicity character.
4. Its degradation product, after release of the drug at the target site, should be biocompatible.
5. Low leaching/leakage of drug should take place before target site is reached.
6. Its drug released pattern in a controlled manner.
7. High drug loading efficiency for broad spectrum of drugs with different properties.
8. Physico-chemical compatibility with the drug.
9. The carrier system should have an appreciable stability during storage.
Erythrocytes can be used as Carriers in two Ways (4, 6)
1. Targeting Particular Tissue/Organ:
For targeting, only the erythrocyte membrane is used. This is obtained by splitting the cell in hypotonic solution and after introducing the drug into the cells, allowing them to reseal into spheres. Such erythrocytes are called Red cell ghosts.
2. For Continuous or Prolonged Release of Drugs:
Alternatively, erythrocytes can be used as a continuous or prolonged release system, which provide prolonged drug action. There are different methods for encapsulation of drugs within erythrocytes. They remain in the circulation for prolonged periods of time (up to 120 days) and release the entrapped drug at a slow and steady rate.
Methods of Drug Loading of in Erythrocytes:(2, 3, 5, 7)
In general, the potential use of erythrocytes depends on their ability to encapsulate exogenous enzymes or other substances into erythrocytes. Several methods can be used to load drugs or other bioactive compounds in erythrocytes, including physical (e.g., electrical pulse method), osmosis –based systems and chemical methods (e.g., chemical perturbation of the erythrocytes membrane). Irrespective of the method used, the optimal characteristics for the successful entrapment of the compound requires the drug to have a considerable degree of water solubility, resistance against degradation within erythrocytes, lack of physical or chemical interaction with erythrocytes membrane, an well-defined pharmacokinetic and Pharmacodynamics properties. The following methods are used for entrapment of therapeutic agent into erythrocytes:
Hypo- osmosis lysis method:
In this process, the intracellular and extracellular solute of erythrocytes is exchange by osmotic lysis and resealing .The drug present will be encapsulated within the RBCs by this process.
A. Hypotonic dilution:
It was the first method investigated for the encapsulation of chemicals into erythrocytes and is simplest and fastest (Fig 2).17 In this method, a volume of packed erythrocytes is diluted with 2‐20 volumes of aqueous solution of a drug. The solution tonicity is then restored by adding a hypertonic buffer. The resultant mixture is then centrifuged, the supernatant is discarded and the pellet is washed with isotonic buffer solution. These cell are rapidly phagocytosed by RES macrophages and hence can be used for targeting RES organ.
Fig. 2: Hypotonic dilution
B. Hypotonic Dialysis method:
This method was first reported by Klibansky in 1959 and was used in 1977 by Deloach, Ihler and Dale for loading enzymes and lipids. In the process, an isotonic, buffered suspension of erythrocytes with a haematocrit value of 70–80 is prepared and placed in a conventional dialysis tube immersed in 10–20 volumes of a hypotonic buffer. The medium is agitated slowly for 2 h. The tonicity of the dialysis tube is restored by directly adding a calculated amount of a hypertonic buffer to the surrounding medium or by replacing the surrounding medium by isotonic buffer. The drug to be loaded can be added by either dissolving the drug in isotonic cell suspending buffer inside a dialysis bag at the beginning of the experiment or by adding the drug to a dialysis bag after the stirring is complete.
C. Hypotonic preswell technique:
This method was investigated by Rechsteiner in 1975 and was modified by Jenner et al. for drug loading. This method based on the principle of first swelling the erythrocytes without lysis by placing them in slightly hypotonic solution. The swollen cells are recovered by centrifugation at low speed. Then, relatively small volumes of aqueous drug solution are added to the point of lysis. The slow swelling of cells results in good retention of the cytoplasmic constituents and hence good survival in vivo. This method is simpler and faster than other methods, causing minimum damage to cells. Drugs encapsulated in erythrocytes using this method include propranolol , asparginase, cyclophosphamide, cortisol-21-phosphate, 1-antitrypsin, methotrexate insulin, metronidazole, levothyroxine, enalaprilat and isoniazid.
D. Isotonic osmotic lysis method:
This method was reported by Schrier et al in 1975. This method, also known as the osmotic pulse method, involves isotonic haemolysis that is achieved by physical or chemical means. The isotonic solutions may or may not be isotonic. If erythrocytes are incubated in solutions of a substance with high membrane permeability, the solute will diffuse into the cells because of the concentration gradient. This process is followed by an influx of water to maintain osmotic equilibrium. Chemicals such as urea solution, polyethylene glycol, and ammonium chloride have been used for isotonic haemolysis. However, this method also is not immune to changes in membrane structure composition. In 1987, Franco et al. developed a method that involved suspending erythrocytes in an isotonic solution of dimethyl sulfoxide (DMSO). The suspension was diluted with an isotonic-buffered drug solution. After the cells were separated, they were sealed at 37oC.
E. Isotonic Osmotic Lysis:
This method is also known as osmotic pulse method. In which isotonic haemolysis is achieved by physical or chemical means. If erythrocytes are incubated in solutions of a substance with high membrane permeability, the solute will diffuse into the cells because of the concentration gradient. This process is followed by an influx of water to maintain osmotic equilibrium.
F. Chemical perturbation of the membrane:
This method is based on the fact that erythrocyte when exposed to certain chemicals like polyene antibiotic such as amphotericin B, halothane etc. and the membrane permeability of erythrocyte increases. The main drawback of this method is that it induces irreversible changes in the cell membrane and hence are not very popular.
G. Electro-insertion or Electro encapsulation method:
In 1973, Zimmermann tried an electrical pulse method to encapsulate bioactive molecules. Also known as electroporation, the method is based on the observation that electrical shock brings about irreversible changes in an erythrocyte membrane. This method is also called as electroporation. In this method erythrocyte membrane is open by a dielectric breakdown; subsequently the pore of erythrocyte can be resealed by incubation at 370C in an isotonic medium. The various chemical encapsulated into the erythrocytes are primaquin and related 8- amino quinolone, vinblastine chlorpromazine and related phenothiazine, propranolol, tetracaine and vitamin A.
Fig. 3: Electro encapsulation
H. Entrapment by Endocytosis:
Endocytosis involves the addition of one volume of washed packed erythrocytes to nine volumes of buffer containing 2.5 mM ATP, 2.5 mM MgCl2, and 1mM CaCl2, followed by incubation for 2 min at room temperature. The pores created by this method are resealed by using 154 mM of NaCl and incubation at 370C for 2 min. The entrapment of material occurs by endocytosis. The vesicle membrane separates endocytosed material from cytoplasm thus protecting it from the erythrocytes and vice-versa.
Fig. 4: Entrapment by endocytosis
I. Lipid fusion method:
The lipid vesicles containing a drug can be directly fuse to human erythrocytes, which lead to an exchange with a lipid 161 entrapped drug. The methods are useful for entrapping inositol monophosphate to improve the oxygen carrying capacity of cells and entrapment efficiency of this method is very low (~1%).
J. Loading by electric cell fusion:
This method involves the initial loading of drug molecules into erythrocyte ghosts followed by adhesion of these cells to target cells. The fusion is accentuated by the application of an electric pulse, which causes the release of an entrapped molecule. An example of this method is loading a cell-specific monoclonal antibody into an erythrocyte ghost. An antibody against a specific surface protein of target cells can be chemically cross-linked to drug-loaded cells that would direct these cells to desired cells.
K. Use of red cell loader:
Novel method was developed for entrapment of non-diffusible drugs into erythrocytes. They developed a piece of equipment called a “red cell loader”. With as little as 50 ml of a blood sample, different biologically active compounds were entrapped into erythrocytes within a period of 2 h at room temperature under blood banking conditions. The process is based on two sequential hypotonic dilutions of washed erythrocytes followed by concentration with a hem filter and an isotonic resealing of the cells. There was 30% drug loading with 35–50% cell recovery. The processed erythrocytes had normal survival in vivo. The same cells could be used for targeting by improving their recognition by tissue macrophages.
Store encapsulated preparation without loss of integrity when suspended in hank's balanced salt solution [HBSS] at 40C for two weeks. Use of group 'O' [universal donor] cells and by using the preswell or dialysis technique, batches of blood for transfusion. Standard blood bag may be used for both encapsulation and storage.
Evaluation of Resealed Erythrocyte: (4-7)
After loading of therapeutic agent on erythrocytes, the carrier cells are exposed to physical, cellular as well as biological evaluations.
1. Shape and Surface Morphology:
The morphology of erythrocytes decides their life span after administration. The morphological characterization of erythrocytes is undertaken by comparison with untreated erythrocytes using either transmission (TEM) or Scanning electron microscopy (SEM). Other methods like phase contrast microscopy can also be used.
2. Drug Content:
Drug content of the cells determines the entrapment efficiency of the method used. The process involves deproteinization of packed loaded cells (0.5 mL) with 2.0 mL acetonitrile and centrifugation at 2500 rpm for 10 min. The clear supernatant is analyzed for the drug content.
3. Cell Counting and Cell Recovery:
This involves counting the number of red blood cells per unit volume of whole blood, usually by using automated machine it is determined by counting the no. of intact cells per cubic mm of packed erythrocytes before and after loading the drug.
4. Turbulence Fragility:
It is determined by the passage of cell suspension through needles with smaller internal diameter (e.g., 30 gauges) or vigorously shaking the cell suspension. In both cases, haemoglobin and drug released after the procedure are determined. The turbulent fragility of resealed cells is found to be higher.
5. Drug Release:
The drug loading may produce sustained release of the drug that influences the pharmacokinetic behavior in vivo of he loaded erythrocytes. In vitro leakage of the drug from loaded erythrocytes is tested using autologous plasma or an isosmotic buffer at 370C with a haematocrit adjusted between 0.5% and 50%. The supernatant is removed at previously programmed time intervals and replaced by an equal volume of autologous plasma or buffer. Some authors recommended performing in vitro release studies from loaded erythrocytes using a dialysis bag.
6. Erythrocyte Sedimentation Rate (ESR):
It is an estimate of the suspension stability of RBC in plasma and is related to the number and size of the red cells and to relative concentration of plasma protein, especially fibrinogen and α, β globulins. This test is performed by determining the rate of sedimentation of blood cells in a standard tube. Normal blood ESR is 0 to 15 mm/hr. higher rate is indication of active but obscure disease processes.
7. Osmotic Fragility:
This test of resealed erythrocytes is an indicator of the possible changes in cell membrane integrity and the resistance of these cells to osmotic pressure of the suspension medium. The test is carried out by suspending cells in media of varying sodium chloride concentration and determining the haemoglobin released. In most cases, osmotic fragility of resealed cells is higher than that of normal cells.
8. Determination of Entrapped Magnetite:
Atomic absorption spectroscopic method is reported for determination of the concentration of particular metal in the sample. The HCl is added to a fixed amount of magnetite bearing erythrocytes and content are heated at 600C for 2 hours, then 20 %w/v trichloro acetic acid is added and supernatant obtained after centrifugation is used to determine magnetite concentration using atomic absorption spectroscopy.
9. Haemoglobin Release:
The content of haemoglobin of the erythrocytes may be diminished by the alterations in the permeability of the membrane of the red blood cells during the encapsulation procedure. Furthermore, the relationship between the rate of haemoglobin and rate of drug release of the substance encapsulated from the erythrocytes. The haemoglobin leakage is tested using a red cell suspension by recording absorbance of supernatant at 540nm on a spectrophotometer.
10. Cell Counting and Cell Recovery:
This involves counting the number of red blood cells per unit volume of whole blood, usually by using automated machine. Red blood cell recovery may be calculated on the basis of the differences in the haematocrit and the volume of the suspension of erythrocytes before and after loading. The goal is to minimize the loss during the encapsulation procedure to maximize recovery.
11. In Vitro Stability:
The stability of the loaded erythrocytes is assessed by means of the incubation of the cells in the autologous plasma or in an isoosmotic buffer, setting haematocrit between 0.5% and 5% at temperatures of 40C and 370C.
12. In-Vitro Drug Release and Hb Content:
The cell suspensions (5% haematocrit in PBS) are stored at 40C in ambered colour glass container. Periodically clear supernatant are drawn using a hypodermic syringe equipped with 0.45 are filter, deproteined using methanol and were estimated far drug content. The supernatant of each sample after centrifugation collected and assayed, % Hb release may be calculated using formula % Hb release=A540 of sample-A540 of background A540 of 100% Hb.
13. Osmotic Shock:
For osmotic shock study, erythrocytes suspension (1 ml 10% hct) was diluted with distilled water (5 ml) and centrifuge at 300 rpm for 15 minutes. The supernant was estimated for % haemoglobin release analytically.
Resealed erythrocyte can also be characterized by cell sizes, mean cell volume, energy metabolism, lipid composition, membrane fluidity, rheological properties, and density gradient separation.
Application of Resealed Erythrocytes::(5, 7, 8)
Resealed erythrocytes have several possible applications in various fields of human and veterinary medicine. Such cells could be used as circulating carriers to disseminate a drug within a prolonged period of time in circulation or in target-specific organs, including the liver, spleen, and lymph nodes. A majority of the drug delivery studies using drug-loaded erythrocytes are in the preclinical phase. In a few clinical studies, successful results were obtained.
In Vitro Application:
Carrier RBCs have proved to be useful for a variety of in vitro tests. For in vitro phagocytosis cells have been used to facilitate the uptake of enzymes by phagolysosomes. An inside to this study showed that enzymes content within carrier RBC could be visualized with the help of cytochemical technique. The most frequent in vitro application of RBC mediated microinjection. A protein or nucleic acid to be injected into eukaryotic cells by fusion process. Similarly, when antibody molecules are introduced using erythrocytic carrier system, they immediately diffuse throughout the cytoplasm. Antibody RBC auto injected into living cells have been used to confirm the site of action of fragment of diphtheria toxin. In-vitro tests include utilization of erythrocytes carrier to introduce ribosomes inactivating proteins into cells by fusion technique.
In Vivo Applications:
This includes the following
1. Slow drug release:
Erythrocytes have been used as circulating depots for the sustained delivery of antineoplastic, antiparasitics, veterinary antiamoebics, vitamins, steroids, antibiotics, and cardiovascular drugs.
2. Drug Targeting:
Ideally, drug delivery should be site‐specific and target oriented to exhibit maximal therapeutic index with minimum adverse effects. Resealed erythrocytes can act as drug carriers and targeting tools as well. They can be used to target RES organs as well as non RES organs. Targeting RES organs: Surface modified erythrocytes are used to target organs of mononuclear phagocytic systems/ reticuloendothelial system because the changes in membrane are recognized by macrophages (table3).
The various approaches used include:
· Surface modification with antibodies (coating of loaded erythrocytes by anti‐Rh or other types of antibodies)
· Surface modification with glutaraldehyde.
· Surface modification with sulfhydryl
· Surface chemical crosslinking
· Surface modification with carbohydrates such as sialic acid.
3. Liver Targeting /Enzyme deficiency/replacement therapy:
Many metabolic disorders related to deficient or missing enzymes can be treated by injecting these enzymes. However, the problems of exogenous enzyme therapy include a shorter circulation half-life of enzymes, allergic reactions, and toxic manifestations. These problems can be successfully overcome by administering the enzymes as resealed erythrocytes. The enzymes used include -glycosidase, -glucoronidase, -galactosidase. The disease caused by an accumulation of glucocerebrosides in the liver and spleen can be treated by glucocerebrosidase- loaded erythrocytes.
4. Treatment of parasitic disease:
The ability of resealed erythrocytes to selectively accumulate with in RES organs make them useful tool during the delivery of anti-parasitic agents. Parasitic diseases that involve harboring parasites in The RES organs can be successfully controlled by this method. Results were favourable in studies involving animal models for erythrocytes loaded with anti-malarial, anti leishmanial and anti-amoebic drugs.
5. Treatment of hepatic tumours:
Hepatic tumours are one of the most prevalent types of cancer. Antineoplastic drugs such as methotrexate, bleomycin, asparginase, and Adriamycin have been successfully delivered by erythrocytes. Agents such as daunorubicin diffuse rapidly from the cells upon loading and hence pose a problem. This problem can be overcome by covalently linking daunorubicin to the erythrocyte membrane using gluteraldehyde or cisaconitic acid as a spacer. The resealed erythrocytes loaded with carboplatin show localization in liver.
6. Removal toxic agents:
Cannon et al. reported inhibition of cyanide intoxication with murine carrier erythrocyte containing bovine rhodanase and sodium thiosulphate. Antagonization of organophosphorus intoxication by released erythrocyte containing a recombinate phosphodiestrase also has been reported.
7. Delivery of antiviral drugs:
Several reports have been cited in the literature about antiviral agents entrapped in resealed erythrocytes for effective delivery and targeting. Because most antiviral drugs are nucleotides or nucleoside analogs, their entrapment and exit through the membrane needs careful consideration.
8. Enzyme therapy:
Enzyme therapy offers considerable promise for the long term treatment of inherited metabolic diseases. For enzyme therapy the selected carrier must have a long circulatory life, although specific ultimate uptake would also be advantageous. For all these, purposes and as a more general carrier of the other therapeutic agents, the erythrocytes offer the greatest potential, being a natural carrier of endogeneous substrates, non-toxic, non-immunogenic, biodegradable and easy to obtain.
9. Removal of RES iron overloads:
Desferrioxamine-loaded erythrocytes have been used to treat excess iron accumulated because of multiple transfusions to thalassemia patients. Targeting this drug to the RES is very beneficial because the aged erythrocytes are destroyed in RES organs, which results in an accumulation of iron in these organs.
10. Targeting Non RES:
Erythrocytes loaded with drugs have also been used to target organs outside the RES The various approaches for targeting non‐RES organs include:
· Entrapment of paramagnetic particles along with the drug.
· Entrapment of photosensitive material.
· Use of ultrasound waves.
· Antibody attachment to erythrocytes membrane to get specificity of action.
· Other approaches include fusion with liposome, lectin pre-treatment of resealed cell etc.
Route of Administration:(5)
Intra peritoneal injection reported that survival of cells in circulation was equivalent to the cells administered by i.e. injection .They reported that 25% of resealed cell remained in circulation for 14 days they also proposed this method of injection as a method for extra vascular targeting of RBCs to peritoneal macrophages. Subcutaneous route for slow release of entrapped agents. They reported that the loaded cell released encapsulated molecules at the injection site.
These are specially engineered vesicular systems that are chemically cross-linked to human erythrocytes’ support upon which a lipid bilayer is coated. This process is achieved by modifying a reverse-phase evaporation technique. These vesicles have been proposed as useful encapsulation systems for macromolecular drugs.
These are prepared by extrusion of erythrocyte ghosts to produce small vesicles with an average diameter of 100 nm. Daunorubicin was covalently conjugated to nanoerythrosomes using gluteraldehyde spacer. This complex was more active than free daunorubicin alone, both in vitro and in vivo.
The resealed erythrocytes showed promising drug carrier characteristics. Due to the several potential advantages over other, this drug loaded erythrocytes seems to be a promising delivery system for the controlled and site specific delivery of therapeutic agents. The preparation of resealed erythrocytes is very easy and can be easily characterized by different available techniques. However, the concept needs further research and optimization to become a routine drug delivery system. The targeted release of therapeutic agents is among the most attractive applications of erythrocytes carrier which can be extended for the delivery of biopharmaceuticals. Thus the potential of this delivery system need to be explored for management of diseases.
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Received on 15.11.2016 Accepted on 18.12.2016
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