Engineering erythrocytes to be erythrosensors: first steps

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.

Phototheranostics Using Erythrocyte-Based Particles

There has been a recent increase in the development of delivery systems based on red blood cells (RBCs) for light-mediated imaging and therapeutic applications. These constructs are able to take advantage of the immune evasion properties of the RBC, while the addition of an optical cargo allows the particles to be activated by light for a number of promising applications. Here, we review some of the common fabrication methods to engineer these constructs. We also present some of the current light-based applications with potential for clinical translation, and offer some insight into future directions in this exciting field.

Chronicles of Nanoerythrosomes: An Erythrocyte-Based Biomimetic Smart Drug Delivery System as a Therapeutic and Diagnostic Tool in Cancer Therapy

Recently, drug delivery using natural biological carriers has emerged as one of the most widely investigated topics of research. Erythrocytes, or red blood cells, can act as potential carriers for a wide variety of drugs, including anticancer, antibacterial, antiviral, and anti-inflammatory, along with various proteins, peptides, enzymes, and other macromolecules. The red blood cell-based nanocarrier systems, also called nanoerythrosomes, are nanovesicles poised with extraordinary features such as long blood circulation times, the ability to escape immune system, the ability to release the drug gradually, the protection of drugs from various endogenous factors, targeted and specified delivery of drugs, as well as possessing both therapeutic and diagnostic applications in various fields of biomedical sciences. Their journey over the last two decades is escalating with fast pace, ranging from in vivo to preclinical and clinical studies by encapsulating a number of drugs into these carriers. Being biomimetic nanoparticles, they have enhanced the stability profile of drugs and their excellent site-specific targeting ability makes them potential carrier systems in the diagnosis and therapy of wide variety of tumors including gliomas, lung cancers, breast cancers, colon cancers, gastric cancers, and other solid tumors. This review focuses on the most recent advancements in the field of nanoerythrosomes, as an excellent and promising nanoplatform for the novel drug delivery of various drugs particularly antineoplastic drugs along with their potential as a promising diagnostic tool for the identification of different tumors.

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.

Characterization of carrier erythrocytes for biosensing applications

Erythrocyte abundance, mobility, and carrying capacity make them attractive as a platform for blood analyte sensing as well as for drug delivery. Sensor-loaded erythrocytes, dubbed erythrosensors, could be reinfused into the bloodstream, excited noninvasively through the skin, and used to provide measurement of analyte levels in the bloodstream. Several techniques to load erythrocytes, thus creating carrier erythrocytes, exist. However, their cellular characteristics remain largely unstudied. Changes in cellular characteristics lead to removal from the bloodstream. We hypothesize that erythrosensors need to maintain native erythrocytes’ (NEs) characteristics to serve as a long-term sensing platform. Here, we investigate two loading techniques and the properties of the resulting erythrosensors. For loading, hypotonic dilution requires a hypotonic solution while electroporation relies on electrical pulses to perforate the erythrocyte membrane. We analyze the resulting erythrosensor signal, size, morphology, and hemoglobin content. Although the resulting erythrosensors exhibit morphological changes, their size was comparable with NEs. The hypotonic dilution technique was found to load erythrosensors much more efficiently than electroporation, and the sensors were loaded throughout the volume of the erythrosensors. Finally, both techniques resulted in significant loss of hemoglobin. This study points to the need for continued development of loading techniques that better preserve NE characteristics.

Optical properties of biomimetic probes engineered from erythrocytes

Light-activated theranostic materials offer a potential platform for optical imaging and phototherapeutic applications. We have engineered constructs derived from erythrocytes, which can be doped with the FDA-approved near infrared (NIR) chromophore, indocyanine green (ICG). We refer to these constructs as NIR erythrocyte-mimicking transducers (NETs). Herein, we investigated the effects of changing the NETs mean diameter from micron- (≈4 μm) to nano- (≈90 nm) scale, and the ICG concentration utilized in the fabrication of NETs from 5 to 20 μM on the resulting absorption and scattering characteristics of the NETs. Our approach consisted of integrating sphere-based measurements of light transmittance and reflectance, and subsequent utilization of these measurements in an inverse adding-doubling algorithm to estimate the absorption (μ _a) and reduced scattering (μ _s') coefficients of these NETs. For a given NETs diameter, values of μ _a increased over the approximate spectral band of 630-860 nm with increasing ICG concentration. Micron-sized NETs produced the highest peak value of μ _a when using ICG concentrations of 10 and 20 μM, and showed increased values of μ _s' as compared to nano-sized NETs. Spectral profiles of μ _s' for these NETs showed a trend consistent with Mie scattering behavior for spherical objects. For all NETs investigated, changing the ICG concentration minimally affected the scattering characteristics. A Monte Carlo-based model of light distribution showed that the presence of these NETs enhanced the fluence levels within simulated blood vessels. These results provide important data towards determining the appropriate light dosimetry parameters for an intended light-based biomedical application of NETs.

Towards a Novel Spatially-Resolved Hemolysis Detection Method Using a Fluorescent Indicator and Loaded Ghost Cells: Proof-of-Principle

It is of the utmost importance to reduce flow-induced hemolysis in devices such as heart-valve prostheses and blood pumps. Thus, in vitro measurements of hemolysis are performed in order to optimize their design in this regard. However, with existing measurement methods, hemolysis can only be assessed as an integrated value over the complete test-circuit. Currently, there are no spatially-resolved in vitro hemolysis measurement techniques known to the authors that would allow for a determination of the critical regions within a device. In this study, a novel spatially-resolved measurement principle is proposed. Ghost cells (i.e. erythrocytes with a lower hemoglobin concentration) were loaded with a calcium-dicitrato complex, and a fluorescent calcium indicator was suspended in the extracellular medium. Calcium and indicator are separated until the cell membrane ruptures (i.e. hemolysis occurs). In the moment of hemolysis, the two compounds bind to each other and emit a fluorescent signal that can be recorded and spatially-resolved in a setup very similar to a standard Particle Image Velocimetry measurement. A proof-of-principle experiment was performed by intentionally inducing hemolysis in a flow-model with a surfactant. The surfactant-induced hemolysis demonstrated a clear increase of the fluorescent signal compared to that of a negative reference. Furthermore, the signal was spatially restricted to the area of hemolysis. Although further challenges need to be addressed, a successful proof-of-principle for novel spatially-resolved hemolysis detection is presented. This method can contribute to better design optimization of devices with respect to flow-induced hemolysis.

Erythrocyte-derived photo-theranostic agents: hybrid nano-vesicles containing indocyanine green for near infrared imaging and therapeutic applications

Development of theranostic nano-constructs may enable diagnosis and treatment of diseases at high spatial resolution. Some key requirements for clinical translation of such constructs are that they must be non-toxic, non-immunogenic, biodegradable, with extended circulating lifetime. Cell-based structures, particularly those derived from erythrocytes, are promising candidate carrier systems to satisfy these requirements. One particular type of theranostic materials utilize light-sensitive agents that once photo-activated can provide diagnostic imaging capability, and elicit therapeutic effects. Here we demonstrate the first successful engineering of hybrid nano-scale constructs derived from membranes of hemoglobin-depleted erythrocytes that encapsulate the near infrared chromophore, indocyanine green. We show the utility of the constructs as photo-theranostic agents in fluorescence imaging and photothermal destruction of human cells. These erythrocyte-mimicking nano-structures can be derived autologously, and may have broad applications in personal nanomedicine ranging from imaging and photo-destruction of cancerous tissues to vascular abnormalities, and longitudinal evaluations of therapeutic interventions.