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

Impaired Enzymatic Antioxidant Defense in Erythrocytes of Rats with Ammonia-Induced Encephalopathy: Role of NMDA Receptors

Hepatic encephalopathy (HE), a neuropsychiatric disorder developing in patients with severe hepatic dysfunction, has been known for more than a century. However, pathogenetic mechanisms of cerebral dysfunction associated with liver disease are still poorly understood. There is a consensus that the primary cause of HE is accumulation of ammonia in the brain as a result of impaired liver detoxification capacity or the portosystemic shunt. Current evidence suggests that ammonia toxicity is mediated by hyperactivation of glutamate receptors, mainly N-methyl-D-aspartate receptors (NMDARs), and affects brain aerobic metabolism, which provides energy for multiple specific functions and neuronal viability. Recent reports on the presence of functional NMDARs in erythrocytes and the data on the deviations of blood parameters from their normal ranges indicate impaired hemodynamics and reduced oxygen-carrying capacity of erythrocytes in most patients with HE, thus suggesting a relationship between erythrocyte damage and cerebral dysfunction. In order to understand how hyperammonemia (HA)-induced disturbances in the energy metabolism in the brain (which needs a constant supply of large amounts of oxygen in the blood) lead to encephalopathy, it is necessary to reveal ammonia-induced impairments in the energy metabolism and antioxidant defense system of erythrocytes and to explore a potential role of ammonia in reduced brain oxygenation. To identify the said missing link, the activities of antioxidant enzymes and concentrations of reduced glutathione (GSH), oxidized glutathione (GSSG), and H2O2 were measured in the erythrocytes of rats with HA that were injected with the noncompetitive NMDAR antagonist MK-801. We found that in rats with HA, ammonia was accumulated in erythrocytes (cells lacking ammonia removal enzymes), which made them more susceptible to the prooxidant environment created during oxidative stress. This effect was completely or partially inhibited by MK-801. The data obtained might help to identify the risk factors in cognitive disorders and facilitate prediction of unfavorable outcomes of hypoperfusion in patients with a blood elevated ammonia concentration.

Preclinical and clinical developments in enzyme-loaded red blood cells: an update

INTRODUCTION

We have previously described the preclinical developments in enzyme-loaded red blood cells to be used in the treatment of several rare diseases, as well as in chronic conditions.

AREA COVERED

Since our previous publication we have seen further progress in the previously discussed approaches and, interestingly enough, in additional new studies that further strengthen the idea that red blood cell-based therapeutics may have unique advantages over conventional enzyme replacement therapies in terms of efficacy and safety. Here we highlight these investigations and compare, when possible, the reported results versus the current therapeutic approaches.

EXPERT OPINION

The continuous increase in the number of new potential applications and the progress from the encapsulation of a single enzyme to the engineering of an entire metabolic pathway open the field to unexpected developments and confirm the role of red blood cells as cellular bioreactors that can be conveniently manipulated to acquire useful therapeutic metabolic abilities. Positioning of these new approaches versus newly approved drugs is essential for the successful transition of this technology from the preclinical to the clinical stage and hopefully to final approval.

Prediction of Oscillations in Glycolysis in Ethanol-Consuming Erythrocyte-Bioreactors

A mathematical model of energy metabolism in erythrocyte-bioreactors loaded with alcohol dehydrogenase and acetaldehyde dehydrogenase was constructed and analyzed. Such erythrocytes can convert ethanol to acetate using intracellular NAD and can therefore be used to treat alcohol intoxication. Analysis of the model revealed that the rate of ethanol consumption by the erythrocyte-bioreactors increases proportionally to the activity of incorporated ethanol-consuming enzymes until their activity reaches a specific threshold level. When the ethanol-consuming enzyme activity exceeds this threshold, the steady state in the model becomes unstable and the model switches to an oscillation mode caused by the competition between glyceraldehyde phosphate dehydrogenase and ethanol-consuming enzymes for NAD. The amplitude and period of metabolite oscillations first increase with the increase in the activity of the encapsulated enzymes. A further increase in these activities leads to a loss of the glycolysis steady state, and a permanent accumulation of glycolytic intermediates. The oscillation mode and the loss of the steady state can lead to the osmotic destruction of erythrocyte-bioreactors due to an accumulation of intracellular metabolites. Our results demonstrate that the interaction of enzymes encapsulated in erythrocyte-bioreactors with erythrocyte metabolism should be taken into account in order to achieve the optimal efficacy of these bioreactors.

Red Blood Cell Inspired Strategies for Drug Delivery: Emerging Concepts and New Advances

In the past five decades, red blood cells (RBCs) have been extensively explored as drug delivery systems due to their distinguishing potential in modulating the pharmacokinetic, pharmacodynamics, and biological activity of carried payloads. The extensive interests in RBC-mediated drug delivery technologies are in part derived from RBCs' unique biological features such as long circulation time, wide access to many tissues in the body, and low immunogenicity. Owing to these outstanding properties, a large body of efforts have led to the development of various RBC-inspired strategies to enable precise drug delivery with enhanced therapeutic efficacy and reduced off-target toxicity. In this review, we discuss emerging concepts and new advances in such RBC-inspired strategies, including native RBCs, ghost RBCs, RBC-mimetic nanoparticles, and RBC-derived extracellular vesicles, for drug delivery.

Ammonium removal by erythrocyte-bioreactors based on glutamate dehydrogenase from Proteus sp. jointly with porcine heart alanine aminotransferase

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.

Is NMDA-Receptor-Mediated Oxidative Stress in Mitochondria of Peripheral Tissues the Essential Factor in the Pathogenesis of Hepatic Encephalopathy?

Background: Hepatic encephalopathy (HE) is a neuropsychiatric syndrome of increased ammonia-mediated brain dysfunction caused by impaired hepatic detoxification or when the blood bypasses the liver. Ammonia-activated signal transduction pathways of hyperactivated NMDA receptors (NMDAR) are shown to trigger a cascade of pathological reactions in the brain, leading to oxidative stress. NMDARs outside the brain are widely distributed in peripheral tissues, including the liver, heart, pancreas, and erythrocytes. To determine the contribution of these receptors to ammonia-induced oxidative stress in peripheral tissues, it is relevant to investigate if there are any ammonia-related changes in antioxidant enzymes and free radical formation and whether blockade of NMDARs prevents these changes. Methods: Hyperammonemia was induced in rats by ammonium acetate injection. Oxidative stress was measured as changes in antioxidant enzyme activities and O2•− and H2O2 production by mitochondria isolated from the tissues and cells mentioned above. The effects of the NMDAR antagonist MK-801 on oxidative stress markers and on tissue ammonia levels were evaluated. Results: Increased ammonia levels in erythrocytes and mitochondria isolated from the liver, pancreas, and heart of hyperammonemic rats are shown to cause tissue-specific oxidative stress, which is prevented completely (or partially in erythrocyte) by MK-801. Conclusions: These results support the view that the pathogenesis of HE is multifactorial and that ammonia-induced multiorgan oxidative stress-mediated by activation of NMDAR is an integral part of the disease and, therefore, the toxic effects of ammonia in НЕ may be more global than initially expected.

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.

Theoretical Analysis of the Built-in Metabolic Pathway Effect on the Metabolism of Erythrocyte-Bioreactors That Neutralize Ammonium

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.

Preclinical developments of enzyme-loaded red blood cells

INTRODUCTION

Therapeutic enzymes are currently used in the treatment of several diseases. In most cases, the benefits are limited due to poor in vivo stability, immunogenicity, and drug-induced inactivating antibodies. A partial solution to the problem is obtained by masking the therapeutic protein by chemical modifications. Unfortunately, this is not a satisfactory solution because frequent adverse events, including anaphylaxis, can arise.

AREA COVERED

Among the delivery systems, we focused on red blood cells for the delivery of therapeutic enzymes. Erythrocytes possess a long circulation time, a reduced immunogenicity, there is no need of chemical modifications and the encapsulated enzyme remains active because it is protected by the cell membrane. Here we discuss some representative applications of the preclinical developments of the field. Some of these are currently in clinic, others are approaching the clinic and others are illustrative of the development process. The selected examples are not always the most recent, but they are the most useful for a comparative approach.

EXPERT OPINION

The results discussed confirm the central role that red blood cells can play in the treatment of several conditions and suggest the benefit in using a natural cellular carrier in terms of pharmacokinetic, biodistribution, safety, and efficacy.

A Look into Liver Mitochondrial Dysfunction as a Hallmark in Progression of Brain Energy Crisis and Development of Neurologic Symptoms in Hepatic Encephalopathy

BACKGROUND

The relationship between liver disease and neuropathology in hepatic encephalopathy is well known, but the genesis of encephalopathy in liver failure is yet to be elucidated. Conceptually, the main cause of hepatic encephalopathy is the accumulation of brain ammonia due to impaired liver detoxification function or occurrence of portosystemic shunt. Yet, as well as taking up toxic ammonia, the liver also produces vital metabolites that ensure normal cerebral function. Given this, for insight into how perturbations in the metabolic capacity of the liver may be related to brain pathology, it is crucial to understand the extent of ammonia-related changes in the hepatic metabolism that provides respiratory fuel for the brain, a deficiency of which can give rise to encephalopathy.

METHODS

Hepatic encephalopathy was induced in starved rats by injection of ammonium acetate. Ammonia-induced toxicity was evaluated by plasma and freeze-clamped liver and brain energy metabolites, and mitochondrial, cytoplasmic, and microsomal gluconeogenic enzymes, including mitochondrial ketogenic enzymes. Parameters of oxidative phosphorylation were recorded polarographically with a Clark-type electrode, while other measures were determined with standard fluorometric enzymatic methods.

RESULTS

Progressive impairment of liver mitochondrial respiration in the initial stage of ammonia-induced hepatotoxicity and the subsequent energy crisis due to decreased ATP synthesis lead to cessation of gluconeogenesis and ketogenesis. Reduction in glucose and ketone body supply to the brain is a terminal event in liver toxicity, preceding the development of coma.

CONCLUSIONS

Our study provides a framework to further explore the relationship between hepatic dysfunction and progression of brain energy crisis in hepatic encephalopathy.

Erythrocytes as Carriers of Therapeutic Enzymes

Therapeutic enzymes are administered for the treatment of a wide variety of diseases. They exert their effects through binding with a high affinity and specificity to disease-causing substrates to catalyze their conversion to a non-noxious product, to induce an advantageous physiological change. However, the metabolic and clinical efficacies of parenterally or intramuscularly administered therapeutic enzymes are very often limited by short circulatory half-lives and hypersensitive and immunogenic reactions. Over the past five decades, the erythrocyte carrier has been extensively studied as a strategy for overcoming these limitations and increasing therapeutic efficacy. This review examines the rationale for the different therapeutic strategies that have been applied to erythrocyte-mediated enzyme therapy. These strategies include their application as circulating bioreactors, targeting the monocyte-macrophage system, the coupling of enzymes to the surface of the erythrocyte and the engineering of CD34+ hematopoietic precursor cells for the expression of therapeutic enzymes. An overview of the diverse biomedical applications for which they have been investigated is also provided, including the detoxification of exogenous chemicals, thrombolytic therapy, enzyme replacement therapy for metabolic diseases and antitumor therapy.

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.

Erythrocytes as bioreactors to decrease excess ammonium concentration in blood

Increased blood ammonium concentrations cause neurological complications. Existing drugs are not always sufficiently effective. Alternatively, erythrocytes-bioreactors (EBRs) loaded with enzymes utilizing ammonium, were suggested for ammonium removal from blood. However all they worked only for a short period of time. The reasons for this were not investigated. In this study, EBR mathematical models were developed and analysed based on the reactions of glycolysis and different enzymes utilizing ammonium, which showed that the efficiency and duration of EBRs' functioning could be limited due to low permeability of the cell membrane for some key substrates and products. A new enzyme system including glutamate dehydrogenase and alanine aminotransferase was proposed and realised experimentally, which was not limited by cell membrane permeability for glutamate and α-ketoglutarate due to creating metabolic pathway where these metabolites were produced and consumed cyclically. New bioreactors removed ammonium in vitro at the rate of 1.5 mmol/h × lRBCs (for human bioreactors) and in vivo in a model of hyperammoniemia in mice at the rate of 2.0 mmol/h × lRBCs (for mouse bioreactors), which correlated with model calculations. Experimental studies proved the proposed mathematical models are correct. Mathematical simulation of erythrocyte-bioreactors opens new opportunities for analysing the efficiency of any enzyme included in erythrocytes.

Metabolic Abnormalities of Erythrocytes as a Risk Factor for Alzheimer's Disease

Alzheimer's disease (AD) is a slowly progressive, neurodegenerative disorder of uncertain etiology. According to the amyloid cascade hypothesis, accumulation of non-soluble amyloid β peptides (Aβ) in the Central Nervous System (CNS) is the primary cause initiating a pathogenic cascade leading to the complex multilayered pathology and clinical manifestation of the disease. It is, therefore, not surprising that the search for mechanisms underlying cognitive changes observed in AD has focused exclusively on the brain and Aβ-inducing synaptic and dendritic loss, oxidative stress, and neuronal death. However, since Aβ depositions were found in normal non-demented elderly people and in many other pathological conditions, the amyloid cascade hypothesis was modified to claim that intraneuronal accumulation of soluble Aβ oligomers, rather than monomer or insoluble amyloid fibrils, is the first step of a fatal cascade in AD. Since a characteristic reduction of cerebral perfusion and energy metabolism occurs in patients with AD it is suggested that capillary distortions commonly found in AD brain elicit hemodynamic changes that alter the delivery and transport of essential nutrients, particularly glucose and oxygen to neuronal and glial cells. Another important factor in tissue oxygenation is the ability of erythrocytes (red blood cells, RBC) to transport and deliver oxygen to tissues, which are first of all dependent on the RBC antioxidant and energy metabolism, which finally regulates the oxygen affinity of hemoglobin. In the present review, we consider the possibility that metabolic and antioxidant defense alterations in the circulating erythrocyte population can influence oxygen delivery to the brain, and that these changes might be a primary mechanism triggering the glucose metabolism disturbance resulting in neurobiological changes observed in the AD brain, possibly related to impaired cognitive function. We also discuss the possibility of using erythrocyte biochemical aberrations as potential tools that will help identify a risk factor for AD.

Rapid Elimination of Blood Alcohol Using Erythrocytes: Mathematical Modeling and In Vitro Study

Erythrocytes (RBCs) loaded with alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALD) can metabolize plasma ethanol and acetaldehyde but with low efficiency. We investigated the rate-limiting factors in ethanol oxidation by these enzymes loaded into RBCs. Mathematical modeling and in vitro experiments on human RBCs loaded simultaneously with ADH and ALD (by hypoosmotic dialysis) were performed. The simulation showed that the rate of nicotinamide-adenine dinucleotide (NAD⁺) generation in RBC glycolysis, but not the activities of the loaded enzymes, is the rate-limiting step in external ethanol oxidation. The rate of oxidation could be increased if RBCs are supplemented by NAD⁺ and pyruvate. Our experimental data verified this theoretical conclusion. RBCs loaded with the complete system of ADH, ALD, NAD⁺, and pyruvate metabolized ethanol 20–40 times faster than reported in previous studies. The one-step procedure of hypoosmotic dialysis is the optimal method to encapsulate ADH and ALD in RBCs after cell recovery, encapsulation yield, osmotic resistance, and RBC-indexes. Consequently, transfusion of the RBCs loaded with the complete metabolic system, including ADH, ALD, pyruvate, and NAD⁺ in the patients with alcohol intoxication, may be a promising method for rapid detoxification of blood alcohol based on metabolism.

Erythrocyte-mediated delivery of recombinant enzymes

The possibility to clone, express and purify recombinant enzymes have originated the opportunity to dispose of a virtually infinite array of proteins that could be used in the clinics to treat several inherited and acquired pathological conditions. However, the direct administration of these recombinant proteins faces some intrinsic difficulties, such as degradation by circulating proteases and/or inactivation by the patient immune system. The use of drug delivery systems may overcome these limitations. Concerning recombinant enzyme therapy, the present review will mainly focus on the exploitation of erythrocytes as a carrier system for enzymes removing potentially noxious metabolites from the circulation, either as limiting treatment strategy for auxotrophic tumours or as a detoxing approach for some intoxication type inherited metabolic disorders. Moreover, the possibility of using RBCs as a potential delivering system addressing the enzymes to the monocyte-macrophages of reticular endothelial system for the treatment of diseases associated with this cell lineage, e.g. lysosome storage diseases, will be briefly discussed.

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.

Hyperammonemia Is Associated with Increasing Severity of Both Liver Cirrhosis and Hepatic Encephalopathy

Background. Hyperammonemia resulting from chronic liver disease (CLD) can potentially challenge and damage any organ system of the body, particularly the brain. However, there is still some controversy regarding the diagnostic or prognostic values of serum ammonia in patients with over hepatic encephalopathy, especially in the setting of acute-on-chronic or chronic liver failure. Moreover, the association of serum ammonia with worsening Child-Pugh grade of liver cirrhosis has not been studied. Objective. This study was conducted to solve the controversy regarding the association between hyperammonemia and cirrhosis, especially hepatic encephalopathy in chronically failed liver. Material and Methods. In this study, 171 cirrhotic patients had their serum ammonia measured and analyzed by SPSS version 16. Chi-squared test and one-way ANOVA were applied. Results. The study had 110 male and 61 female participants. The mean age of all the participants in years was 42.33 ± 7.60. The mean duration (years) of CLD was 10.15 ± 3.53 while the mean Child-Pugh (CP) score was 8.84 ± 3.30. Chronic viral hepatitis alone was responsible for 71.3% of the cases. Moreover, 86.5% of participants had hepatic encephalopathy (HE). The frequency of hyperammonemia was 67.3%, more frequent in males (N = 81, z-score = 2.4, and P < 0.05) than in females (N = 34, z-score = 2.4, and P < 0.05), and had a statistically significant relationship with increasing CP grade of cirrhosis (χ²(2) = 27.46, P < 0.001, Phi = 0.40, and P < 0.001). Furthermore, serum ammonia level was higher in patients with hepatic encephalopathy than in those without it; P < 0.001. Conclusion. Hyperammonemia is associated with both increasing Child-Pugh grade of liver cirrhosis and hepatic encephalopathy.

Carrier erythrocytes: recent advances, present status, current trends and future horizons

INTRODUCTION

Carrier erythrocytes, thanks to their main advantages, including biocompatibility, biodegradability, immunocompatibility, simple and well-known structure and physiology, availability for sampling and versatility in loading and use, have been studied as cellular carriers for delivery of drugs and other bioactive agents for more than three decades. Based on this body of knowledge and recent advances in this field, and with the help of novel multidisciplinary sciences and technologies, it seems that this field is becoming renowned and experiencing an outstanding turning point in its developmental history.

AREAS COVERED

In this trendy and timely review, following a short historical review of the story of erythrocytes from oxygen delivery to drug delivery and evaluation of the present status of these biocarriers, recent advances and current experimental, technological and clinical trends, as well as future horizons, and, in particular, translation-prone strategies, are going to be discussed in detail.

EXPERT OPINION

Despite the challenging developmental history of carrier erythrocytes, they now stand closer to clinical use and market entrance due to their unique advantages in drug delivery, proven by recently reported success stories in late-stage clinical trials and progresses made in biotechnology, nanotechnology and biomaterials fields. Translation-prone approaches, like in vivo loading of circulating erythrocytes or semiautomatic loading of erythrocytes, and more realistic study designs by focusing on clinical needs that have not been responded to or erythrocyte biology/fate-inspired study design are among the main trends being focused on by pioneer research groups active in this field of drug delivery.

Global initiative for interdisciplinary approach to improve innovative clinical research and treatment outcomes in geriatrics: biological cell-based targeted drug delivery systems for geriatrics

At the intersection of the late 20(th) century and early 21(st) century, a worldwide challenge began to emerge--how can the quality of life be improved for a steadily increasing elderly population. It is well known that elderly patients show increased susceptibility to infections and a higher incidence of co-morbidity rates. Older adults frequently demonstrate pharmacokinetic and pharmacodynamic changes promoting adverse drug reactions and complications. Analysis of world literature and practical observations indicate that new approaches are required in gerontology and geriatric medicine due to recent significant advances in biomedical science. Global interdisciplinary approaches to improve medical science and medical care services for growing elderly population are indicated. This global, interdisciplinary initiative should integrate select, tangible clinical results achieved in leading research centers and universities that are applicable in the field of geriatrics and helpful to geriatricians. Among past scientific and clinically significant study results in the field of biomedicine, one must consider targeted drug delivery systems (DDS), which are designed to minimize drug side effects, increase the efficacy of drugs, and prolong and target drug interactions with particular pathological foci in sick patients. Many review articles focus on various methods of drug encapsulation and pharmacokinetics, but not on developing clinical modalities. This article attempts to further the discussion with researchers and clinicians from various fields, as well as to encourage comprehensive and elderly patient-oriented research focused on clinical implementation of DDS, especially erythrocyte-based DDS.

Argocytes containing enzyme nanoparticles reduce toxic concentrations of arginine in the blood

A method for incorporation of arginase nanoparticles into mouse erythrocytes has been developed and the possibility of reducing blood arginine concentration in animals with experimental hyperargininemia with arginase-loaded erythrocytes (argocytes) has been studied. Argocyte infusion to animals with hyperargininemia led to a rapid decrease in blood arginine concentration within 1 h and this effect of argocytes persisted for at least 4 h. This was paralleled by an increase in plasma concentrations of urea and ornithine. Hence, plasma arginine is hydrolyzed by arginase incorporated into argocytes; argocytes are functionally active and can serve as a defense system in pathological hyperargininemia, while the method developed by us can be regarded as a new nanobiotechnology for medicine and veterinary.

International seminar on the red blood cells as vehicles for drugs

The first human transfusion was performed by the pioneer Dr Jean-Baptiste Denis in France in 1667 and now, three centuries later, around 50 millions blood units are transfused every year, saving millions of lives. Today, there is a new application for red blood cells (RBCs) in cellular therapy: the effective use of erythrocytes as vehicles for chemical or biological drugs. Using this approach, the therapeutic index of RBC-entrapped molecules can be significantly improved with increased efficacy and reduced side effects. This cell-based medicinal product can be manufactured at an industrial scale and is now used in the clinic for different therapeutic applications. A seminar dedicated to this field of research, debating on this inventive formulation for drugs, was held in Lyon (France) on 28 January 2011. Drs KC Gunter and Y Godfrin co-chaired the meeting and international experts working on the encapsulation of drugs within erythrocytes met to exchange knowledge on the topic ‘The Red Blood Cells as Vehicles for Drugs’. The meeting was composed of oral presentations providing the latest knowledge and experience on the preclinical and clinical applications of this technology. This Meeting Highlights article presents the most relevant messages given by the speakers and is a joint effort by international experts who share an interest in studying erythrocyte as a drug delivery vehicle. The aim is to provide an overview of the applications, particularly for clinical use, of this innovative formulation. Indeed, due to the intrinsic properties of erythrocytes, their use as a drug carrier is one of the most promising drug delivery systems investigated in recent decades. Of the different methods developed to encapsulate therapeutic agents into RBCs [,,] the most widely used method is the lysis of the RBCs under tightly controlled hypotonic conditions in the presence of the drug to be encapsulated, followed by resealing and annealing under normotonic conditions (Figure 1). This results in uniform encapsulation of the material into the cells and a final product with good stability, reproducibility and viability. This process, which has now been developed to an industrial scale, is the technique chosen by the majority of the experts presenting their work in this seminar (by R Franco).

Drug delivery by red blood cells: vascular carriers designed by mother nature

IMPORTANCE OF THE FIELD

Vascular delivery of several classes of therapeutic agents may benefit from carriage by red blood cells (RBC), for example, drugs that require delivery into phagocytic cells and those that must act within the vascular lumen. The fact that several protocols of infusion of RBC-encapsulated drugs are now being explored in patients illustrates a high biomedical importance for the field. AREAS COVERED BY THIS REVIEW: Two strategies for RBC drug delivery are discussed: encapsulation into isolated RBC ex vivo followed by infusion in compatible recipients and coupling therapeutics to the surface of RBC. Studies of pharmacokinetics and effects in animal models and in human studies of diverse therapeutic enzymes, antibiotics and other drugs encapsulated in RBC are described and critically analyzed. Coupling to RBC surface of compounds regulating immune response and complement, affinity ligands, polyethylene glycol alleviating immune response to donor RBC and fibrinolytic plasminogen activators are described. Also described is a new, translation-prone approach for RBC drug delivery by injection of therapeutics conjugated with fragments of antibodies providing safe anchoring of cargoes to circulating RBC, without need for ex vivo modification and infusion of RBC.

WHAT THE READER WILL GAIN

Readers will gain historical perspective, current status, challenges and perspectives of medical applications of RBC for drug delivery.

TAKE HOME MESSAGE

RBC represent naturally designed carriers for intravascular drug delivery, characterized by unique longevity in the bloodstream, biocompatibility and safe physiological mechanisms for metabolism. New approaches for encapsulating drugs into RBC and coupling to RBC surface provide promising avenues for safe and widely useful improvement of drug delivery in the vascular system.

Specific and pronounced impacts of lisinopril and lisinopril plus simvastatin on erythrocyte antioxidant enzymes

Angiotensin-converting enzyme inhibitors are effective at reducing blood pressure, whereas statins decrease plasma cholesterol impeding atherosclerosis. It is hypothesized that these medications may improve blood pressure and serum cholesterol by modifying the antioxidative status and energy metabolism of erythrocytes. In this study, the effects of 2 treatments are compared: lisinopril alone versus lisinopril + simvastatin, on erythrocyte antioxidant and energy metabolic enzymes. Patients with atherosclerosis and moderate hypertension are randomly assigned to receive lisinopril 10 to 20 mg/d or lisinopril 10 to 20 mg/d plus simvastatin 20 mg/d for 24 weeks. Higher catalase activity and lower glutathione peroxidase activity are observed in 94% to 100% patients from both groups after 12 and 24 weeks of treatment. Superoxide dismutase activity is increased significantly only after 24 weeks. No changes of glutathione reductase, lactate dehydrogenase, and phosphofructokinase activities are found under any conditions indicated. Both treatments decrease systolic and diastolic blood pressure equally. Only lisinopril + simvastatin treatment decreases plasma total cholesterol and low-density lipoprotein cholesterol. The results show for the first time that lisinopril monotherapy and combined lisinopril + simvastatin therapy exhibit specific and pronounced effects on antioxidant and energy metabolic enzyme activities in erythrocytes of hypertensive patients.