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

Building Synthetic Biosensors Using Red Blood Cell Proteins

As the use of engineered cell therapies expands from pioneering efforts in cancer immunotherapy to other applications, an attractive but less explored approach is the use of engineered red blood cells (RBCs). Compared to other cells, RBCs have a very long circulation time and reside in the blood compartment, so they could be ideally suited for applications as sentinel cells that enable in situ sensing and diagnostics. However, we largely lack tools for converting RBCs into biosensors. A unique challenge is that RBCs remodel their membranes during maturation, shedding many membrane components, suggesting that an RBC-specific approach may be needed. Toward addressing this need, here we develop a biosensing architecture built on RBC membrane proteins that are retained through erythropoiesis. This biosensor employs a mechanism in which extracellular ligand binding is transduced into intracellular reconstitution of a split output protein (including either a fluorophore or an enzyme). By comparatively evaluating a range of biosensor architectures, linker types, scaffold choices, and output signals, we identify biosensor designs and design features that confer substantial ligand-induced signal in vitro. Finally, we demonstrate that erythroid precursor cells engineered with our RBC-protein biosensors function in vivo. This study establishes a foundation for developing RBC-based biosensors that could ultimately address unmet needs including noninvasive monitoring of physiological signals for a range of diagnostic applications.

Building synthetic biosensors using red blood cell proteins

As the use of engineered cell therapies expands from pioneering efforts in cancer immunotherapy to other applications, an attractive but less explored approach is the use of engineered red blood cells (RBCs). Compared to other cells, RBCs have a very long circulation time and reside in the blood compartment, so they could be ideally suited for applications as sentinel cells that enable in situ sensing and diagnostics. However, we largely lack tools for converting RBCs into biosensors. A unique challenge is that RBCs remodel their membranes during maturation, shedding many membrane components, suggesting that an RBC-specific approach may be needed. Towards addressing this need, here we develop a biosensing architecture built on RBC membrane proteins that are retained through erythropoiesis. This biosensor employs a mechanism in which extracellular ligand binding is transduced into intracellular reconstitution of a split output protein (including either a fluorophore or an enzyme). By comparatively evaluating a range of biosensor architectures, linker types, scaffold choices, and output signals, we identify biosensor designs and design features that confer substantial ligand-induced signal in vitro. Finally, we demonstrate that erythroid precursor cells engineered with our RBC protein biosensors function in vivo. This study establishes a foundation for developing RBC-based biosensors that could ultimately address unmet needs including non-invasive monitoring of physiological signals for a range of diagnostic applications.

Red blood cells: The metamorphosis of a neglected carrier into the natural mothership for artificial nanocarriers

Drug delivery research pursues many types of carriers including proteins and other macromolecules, natural and synthetic polymeric structures, nanocarriers of diverse compositions and cells. In particular, liposomes and lipid nanoparticles represent arguably the most advanced and popular human-made nanocarriers, already in multiple clinical applications. On the other hand, red blood cells (RBCs) represent attractive natural carriers for the vascular route, featuring at least two distinct compartments for loading pharmacological cargoes, namely inner space enclosed by the plasma membrane and the outer surface of this membrane. Historically, studies of liposomal drug delivery systems (DDS) astronomically outnumbered and surpassed the RBC-based DDS. Nevertheless, these two types of carriers have different profile of advantages and disadvantages. Recent studies showed that RBC-based drug carriers indeed may feature unique pharmacokinetic and biodistribution characteristics favorably changing benefit/risk ratio of some cargo agents. Furthermore, RBC carriage cardinally alters behavior and effect of nanocarriers in the bloodstream, so called RBC hitchhiking (RBC-HH). This article represents an attempt for the comparative analysis of liposomal vs RBC drug delivery, culminating with design of hybrid DDSs enabling mutual collaborative advantages such as RBC-HH and camouflaging nanoparticles by RBC membrane. Finally, we discuss the key current challenges faced by these and other RBC-based DDSs including the issue of potential unintended and adverse effect and contingency measures to ameliorate this and other concerns.

Erythrocytes as Carriers for Drug Delivery in Blood Transfusion and Beyond

Red blood cells (RBCs) are innate carriers that can also be engineered to improve the pharmacokinetics and pharmacodynamics of many drugs, particularly biotherapeutics. Successful loading of drugs, both internally and on the external surface of RBCs, has been demonstrated for many drugs including anti-inflammatory, antimicrobial, and antithrombotic agents. Methods for internal loading of drugs within RBCs are now entering clinical use. Although internal loading can result in membrane disruption that may compromise biocompatibility, surface loading using either affinity or chemical ligands offers a diverse set of approaches for the production of RBC drug carriers. A wide range of surface determinants is potentially available for this approach, although there remains a need to characterize the effects of coupling agents to these surface proteins. Somewhat surprisingly, recent data also suggest that red cell-mediated delivery may confer tolerogenic immune effects. Questions remaining before widespread application of these technologies include determining the optimal loading protocol, source of RBCs, and production logistics, as well as addressing regulatory hurdles. Red blood cell drug carriers, after many decades of progress, are now poised to enter the clinic and broaden the potential application of RBCs in blood transfusion.

Delivery of drugs bound to erythrocytes: new avenues for an old intravascular carrier

For several decades, researchers have used erythrocytes for drug delivery of a wide variety of therapeutics in order to improve their pharmacokinetics, biodistribution, controlled release and pharmacodynamics. Approaches include encapsulation of drugs within erythrocytes, as well as coupling of drugs onto the red cell surface. This review focuses on the latter approach, and examines the delivery of red blood cell (RBC)-surface-bound anti-inflammatory, anti-thrombotic and anti-microbial agents, as well as RBC carriage of nanoparticles. Herein, we discuss the progress that has been made in surface loading approaches, and address in depth the issues relevant to surface loading of RBC, including intrinsic features of erythrocyte membranes, immune considerations, potential surface targets and techniques for the production of affinity ligands.

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.

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.

Aqueous polymer two-phase systems: effective tools for plasma membrane proteomics

Plasma membranes (PMs) are of particular importance for all living cells. They form a selectively permeable barrier to the environment. Many essential tasks of PMs are carried out by their proteinaceous components, including molecular transport, cell-cell interactions, and signal transduction. Due to the key role of these proteins for cellular function, they take center-stage in basic and applied research. A major problem towards in-depth identification and characterization of PM proteins by modern proteomic approaches is their low abundance and immense heterogeneity in different cells. Highly selective and efficient purification protocols are hence essential to any PM proteome analysis. An effective tool for preparative isolation of PMs is partitioning in aqueous polymer two-phase systems. In two-phase systems, membranes are separated according to differences in surface properties rather than size and density. Despite their rare application to the fractionation of animal tissues and cells, they represent an attractive alternative to conventional fractionation protocols. Here, we review the principles of partitioning using aqueous polymer two-phase systems and compare aqueous polymer two-phase systems with other methods currently used for the isolation of PMs.

Factors associated with the performance of carrier erythrocytes obtained by hypotonic dialysis

Carrier erythrocytes containing drugs, enzymes or peptides can be used as a delivery system that allows changes in the kinetic behaviour and selective biodistribution of the substances encapsulated. Hypotonic dialysis is the method most commonly used in the preparation of carrier erythrocytes, but many factors affect the yield and characteristics of the ghost erythrocytes obtained using this method. This review analyses the factors that affect the performance of carrier erythrocytes prepared by hypotonic dialysis. Factors such as the composition and osmolality range of the hypotonic buffer used, the duration of the hypotonic dialysis, temperature, the volume ratio between the erythrocyte suspension and the dialysis buffer, the inclusion in the process of an annealing phase, the composition and osmolality of the resealing buffer, and the conditions under which the final washing of the erythrocytes is carried out may all affect the morphological properties and the later in vivo behaviour of the ghost erythrocytes obtained. Changes in the yield of the encapsulation process, the in vitro drug or enzyme controlled delivery, the pharmacokinetic properties or the in vivo tissue targeting may be modified depending on the conditions under which the preparation of carrier erythrocytes by hypotonic dialysis is carried out. Chemical alterations to the membrane of carrier erythrocytes obtained by hypotonic dialysis with substances such as glutaraldehyde, band 3 cross-linking reagents, trypsin or NHS-biotin, among others, may affect the release rate of the substances encapsulated and may increase the uptake of cells by macrophages both in vitro and in vivo.

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.

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.

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.