O2 release from Hb vesicles evaluated using an artificial, narrow O2-permeable tube: comparison with RBCs and acellular Hbs

Nanomaterial-related hemoglobin-based oxygen carriers, with emphasis on liposome and nano-capsules, for biomedical applications: current status and future perspectives

Oxygen is necessary for life and plays a key pivotal in maintaining normal physiological functions and treat of diseases. Hemoglobin-based oxygen carriers (HBOCs) have been studied and developed as a replacement for red blood cells (RBCs) in oxygen transport due to their similar oxygen-carrying capacities. However, applications of HBOCs are hindered by vasoactivity, oxidative toxicity, and a relatively short circulatory half-life. With advancements in nanotechnology, Hb encapsulation, absorption, bioconjugation, entrapment, and attachment to nanomaterials have been used to prepare nanomaterial-related HBOCs to address these challenges and pend their application in several biomedical and therapeutic contexts. This review focuses on the progress of this class of nanomaterial-related HBOCs in the fields of hemorrhagic shock, ischemic stroke, cancer, and wound healing, and speculates on future research directions. The advancements in nanomaterial-related HBOCs are expected to lead significant breakthroughs in blood substitutes, enabling their widespread use in the treatment of clinical diseases.

Artificial red blood cells increase large vessel wall damage and decrease surrounding dermal tissue damage in a rabbit auricle model after subsequent flashlamp-pumped pulsed-dye laser treatment

Artificial red blood cells (i.e. hemoglobin [Hb] vesicles [Hb-Vs]) function effectively as photosensitizers in flashlamp-pumped pulsed-dye laser (PDL) treatment for port-wine stains in animal models. Hb-Vs deliver more Hb to the vicinity of the endothelial cells. Both Hb-Vs and red blood cells absorb the laser energy and generate heat, supporting the removal of very small blood vessels and deeper subcutaneous blood vessels with PDL irradiation in in vivo experiments. Here, we analyzed the photosensitizing effect of Hb-Vs in PDL irradiation on large blood vessels and surrounding soft tissues. We histopathologically analyzed markers of damage to the large vessels and surrounding dermal tissue in a rabbit auricle model following PDL irradiation alone or subsequent to the addition of intravenous Hb-V injection. Markers were graded on a five-point scale and statistically compared. The changes in laser light absorption and reflection in a human skin model caused by the administration of Hb-Vs were evaluated using Monte Carlo light-scattering programs. Histological markers of damage to blood vessels were significantly greater in Hb-V-injected arteries and veins measuring 1-3 mm in diameter as compared with the controls. However, Hb-V injection significantly reduced PDL-induced necrosis and hemorrhage in the surrounding tissues. During computer simulation, photon absorption increased within the vessel layer and decreased around the layer. Intravenous Hb-Vs increase the extent of damage in larger vessel walls but significantly reduce damage to the surrounding skin after subsequent PDL irradiation. These beneficial effects are the result of improving vessel selectivity by Hb-Vs in vessels. Hb-V administration prior to PDL irradiation therapy could mechanically improve the outcomes and safety profiles of port-wine stain treatment protocols.

Exhaustive-exercise-induced oxidative stress alteration of erythrocyte oxygen release capacity

The aim of the present study was to explore the effect of exhaustive running exercise in the oxygen release capacity of rat erythrocytes. Rats were divided into sedentary control, moderate running exercise, and exhaustive running exercise groups. The thermodynamic and kinetic properties of the erythrocyte oxygen release process of the different groups were tested. We also determined the degree of band-3 oxidation and phosphorylation, anion transport activity, and carbonic anhydrase isoform II activity. Biochemical studies suggested that exhaustive running significantly increased oxidative injury parameters in thiobarbituric acid reactive substances and methaemoglobin levels. Furthermore, exhaustive running significantly decreased anion transport activity and carbonic anhydrase isoform II activity. Thermodynamic analysis indicated that erythrocytes oxygen release ability also significantly increased due to elevated 2,3-DPG level after exhaustive running. Kinetic analysis indicated that exhaustive running resulted in significantly decreased T50 value. We presented evidence that exhaustive running remarkably impacted thermodynamic and kinetic properties of RBC oxygen release. In addition, changes in 2,3-DPG levels and band-3 oxidation and phosphorylation could be the driving force for exhaustive-running-induced alterations in erythrocyte oxygen release thermodynamic and kinetic properties.

The Use of Hemoglobin Vesicles for Delivering Medicinal Gas for the Treatment of Intractable Disorders

Bioactive gaseous molecules, such as oxygen (O₂) and carbon monoxide (CO), are essential elements for most living organisms to maintain their homeostasis and biological activities. An accumulating body of evidence suggests that such molecules can be used in clinics as a medical gas in the treatment of various intractable disorders. Recent developments in hemoglobin-encapsulated liposomes, namely hemoglobin vesicles (HbV), possess great potential for retaining O₂ and CO and could lead to strategies for the development of novel pharmacological agents as medical gas donors. HbV with either O₂ or CO bound to it has been demonstrated to have therapeutic potential for treating certain intractable disorders and has the possibility to serve as diagnostic and augmenting product by virtue of unique physicochemical characteristics of HbV. The present review provides an overview of the present status of the use of O₂- or CO-binding HbV in experimental animal models of intractable disorders and discusses prospective clinical applications of HbV as a medical gas donor.

Artificial Red Blood Cells as Potential Photosensitizers in Dye Laser Treatment Against Port-Wine Stains

We suggest a novel method that uses artificial blood cells (hemoglobin vesicles, Hb-Vs) as photosensitizers in dye laser treatment (at 595-nm wavelength) for port-wine stains (i.e., capillary malformations presenting as red birthmarks) based on the results of animal experiments. As compared with human red blood cells, Hb-Vs have the same absorbance of 595 nm wavelength light and produce the same level of heat following dye laser irradiation. Small sized Hb-Vs (250 nm) distribute in the plasma phase in blood and tend to flow in the marginal zone of microvessels. Intravenous injections of Hb-Vs caused the dilatation of microvessels, and dye laser treatment with Hb-Vs destroyed the vessel wall effectively. Following the intravenous injection of Hb-Vs, the microvessels contained more Hb that absorbed laser photons and produced heat. This extra Hb tended to flow near the endothelial cells, which were the target of the laser treatment. These attributes of Hb-Vs will potentially contribute to enhancing the efficacy of dye laser treatment for port-wine stains. Hemoglobin is a type of porphyrin. Thus, our proposed treatment may have aspects of photodynamic therapy using porphyrin that leads to a cytotoxicity effect by active oxygen.

In vitro kinetics of oxygen transport in erythrocyte suspension or unmodified hemoglobin solution from human and other animals

Oxygen transport behavior in erythrocyte suspension or in hemoglobin solution was studied as a potential therapeutic model for the clinical treatment of blood loss, and this can also provide physiological data with which to evaluate blood substitutes. In the present project, we examined the in vitro kinetics of hemoglobin binding to and releasing oxygen, to provide detailed oxygen-flux measurements for unmodified hemoglobin solutions and erythrocyte suspensions in human, as well as other vertebrates. An in vitro method was used, based on a widely used artificial system, with the oxygen saturation level being detected in real time. Results from this study indicated that the kinetic curves of human erythrocyte suspensions and hemoglobin solutions were either S-shaped or hyperbolic, respectively. Based on these curves, the significance of T50 emerged in our investigation, where T50 is defined as the time needed for 50% hemoglobin to be saturated with oxygen, and reflects the efficiency with which hemoglobin carries oxygen. This parameter may be used to diagnose blood diseases, and could be a standard for evaluating blood substitutes. In this study, we also compared the T50 of 4 species of vertebrates, and found that it shows a distinct efficiency of oxygen binding related to species, and potentially reveals the evolutionary function of hemoglobin and its possible adaptation to the environment.

Simple method for preparing poly(ethylene glycol)-surface-conjugated liposome-encapsulated hemoglobins: physicochemical properties, long-term storage stability, and their reactions with O2, CO, and NO

During the last few decades, liposome-encapsulated hemoglobin (LEH) dispersions have been investigated for use as red blood cell (RBC) substitutes. However, the process for formulating LEHs is cumbersome, and the composition of the lipid mixture is often complex. This work investigates a simple approach to formulating LEHs from a simple lipid mixture composed of high-phase-transition lipid distearoylphosphatidylcholine (DSPC) and cholesterol. To improve the circulation half-life and colloidal state of LEHs, the surfaces of unmodified LEHs were conjugated with poly(ethylene glycol) (PEG-LEHs). The results of this work show that PEG-LEH dispersions exhibited average diameters ranging from 166 to 195 nm that were colloidally stable for 4 to 5 months, hemoglobin (Hb) concentrations ranging from 9.6 to 14 g/dL, methemoglobin levels of less than 1%, oxygen affinities (i.e., P(50) values) ranging from 20 to 23 mm Hg, and cooperativity coefficients ranging from 1.4 to 2.2. The reactions of PEG-LEHs with physiologically important ligands, such as oxygen (O(2)), carbon monoxide (CO), and nitric oxide (NO), were also measured. It was observed that PEG-LEHs and RBCs exhibited retarded gaseous ligand binding/release kinetics compared to that of acellular Hb's. This result provides important insight into the pivotal role that the intracellular diffusion barrier plays in the transport of gases into and out of these structures. Collectively, our results demonstrate that the PEG-LEH dispersions prepared in this study show good potential as an RBC substitute.

Hemoglobin encapsulation in vesicles retards NO and CO binding and O2 release when perfused through narrow gas-permeable tubes

Intravenous administration of cell-free Hb induces vasoconstriction and circulatory disorders, presumably because of the intrinsic affinities to endogenous nitric oxide (NO) and carbon monoxide (CO) as vasorelaxation factors and because of the facilitated O2 release that might induce autoregulatory vasoconstriction. We examined these gas reactions when Hb-containing solutions of four kinds were perfused through artificial narrow tubes at a practical Hb concentration (10 g/dl). Purified Hb solution, polymerized bovine Hb (PolyBHb), encapsulated Hb [Hb-vesicles (HbV), 279 nm], and red blood cells (RBCs) were perfused through a gas-permeable narrow tube (25 μm inner diameter) at 1 mm/s centerline velocity. The level of reactions was determined microscopically based on the visible-light absorption spectrum of Hb. When the tube was immersed in NO and CO atmospheres, both NO binding and CO binding of deoxygenated Hb (deoxy-Hb) and PolyBHb in the tube was faster than those of HbV and RBCs, and HbV and RBCs showed almost identical binding rates. When the tube was immersed in a N2 atmosphere, oxygenated Hb and PolyBHb showed much faster O2 release than did HbV and RBCs. PolyBHb showed a faster reaction than Hb because of the lower O2 affinity of PolyBHb than Hb. The diffusion process of the particles was simulated using Navier-Stokes and Maxwell-Stefan equations. Results clarified that small Hb (6 nm) diffuses laterally and mixes rapidly. However, the large-dimension HbV shows no such rapid diffusion. The purely physicochemical differences in diffusivity of the particles and the resulting reactivity with gas molecules are one factor inducing biological vasoconstriction of Hb-based oxygen carriers.

Peculiar flow patterns of RBCs suspended in viscous fluids and perfused through a narrow tube (25 μm)

Red blood cells (RBCs) generally deform to adopt a parachute-like, torpedo-like, or other configuration to align and flow through a capillary that is narrower than their major axis. As described herein, even in a narrow tube (25 μm) with diameter much larger than that of a capillary, flowing RBCs at 1 mm/s align axially and deform to a paraboloid shape in a viscous Newtonian fluid (505 kDa dextran medium) with viscosity of 23.4–57.1 mPa·s. A high-speed digital camera image showed that the silhouette of the tip of RBCs fits a parabola, unlike the shape of RBCs in capillaries, because of the longer distance of the RBC-free layer between the tube wall and the RBC surface (∼8.8 μm). However, when RBCs are suspended in a “non-Newtonian” viscous fluid (liposome-40 kDa dextran medium) with a shear-thinning profile, they migrate toward the tube wall to avoid the axial lining, as “near-wall-excess,” which is usually observed for platelets. This migration results from the presence of flocculated liposomes at the tube center. In contrast, such near-wall excess was not observed when RBCs were suspended in a nearly Newtonian liposome-albumin medium. Such unusual flow patterns of RBCs would be explainable by the principle; a larger particle tends to flow near the centerline, and a small one tends to go to the wall to flow with least resistance. However, we visualized for the first time the complete axial aligning and near-wall excess of RBCs in the noncapillary size tube in some extreme conditions.

Haemoglobin-vesicles as artificial oxygen carriers: present situation and future visions

During the long history of development of haemoglobin (Hb)-based O2 carriers (HBOCs), many side effects of Hb molecules have become apparent. They imply the physiological importance of the cellular structure of red blood cells. Hb-vesicles (HbV) are artificial O2 carriers that encapsulate concentrated Hb solution with a thin lipid membrane. We have overcome the intrinsic issues of the suspension of HbV as a molecular assembly, such as stability for storage and in blood circulation, blood compatibility and prompt degradation in the reticuloendothelial system. Animal tests clarified the efficacy of HbV as a transfusion alternative and the possibility for other clinical applications. The results of ongoing HbV research make us confident in advancing further development of HbV, with the expectation of its eventual realization.

Effect of hemoglobin vesicle, a cellular-type artificial oxygen carrier, on middle cerebral artery occlusion- and arachidonic acid-induced stroke models in rats

Hemoglobin vesicle (HbV), which is also called liposome-encapsulated hemoglobin, functions as a hemoglobin-based oxygen carrier and is expected to be utilized in emergency situations including hemorrhagic shock and several kinds of ischemic diseases. In the present study, we evaluated the efficacy of HbV for improving stroke-related symptoms induced by middle cerebral artery (MCA) occlusion/reperfusion and an intra-internal carotid arterial injection of arachidonic acid (AA) in rats. When HbV (10 mL/kg, i.v.) was administered to rats immediately after the MCA occlusion, it reduced the cerebral infarct volumes of the cortex and total of the cortex plus sub-cortex significantly as compared with saline as a vehicle. In AA-induced stroke model, HbV (10 mL/kg, i.v.) improved the motor dysfunction score and inhibited the increase in cerebral water content suggesting it could suppress cerebral edema. These results strongly suggest that HbV would provide a novel beneficial option for the treatment of stroke, especially acute ischemic stroke.

Dependence of acetylcholine and ADP dilation of pial arterioles on heme oxygenase after transfusion of cell-free polymeric hemoglobin

Polymers of cell-free hemoglobin have been designed for clinical use as oxygen carriers, but limited information is available regarding their effects on vascular regulation. We tested the hypothesis that the contribution of heme oxygenase (HO) to acetylcholine-evoked dilation of pial arterioles is upregulated 2 days after polymeric hemoglobin transfusion. Dilator responses to acetylcholine measured by intravital microscopy in anesthetized cats were blocked by superfusion of the HO inhibitor tin protoporphyrin-IX (SnPPIX) in a group that had undergone exchange transfusion with hemoglobin 2 days earlier but not in surgical sham and albumin-transfused groups. However, immunoblots from cortical brain homogenates did not reveal changes in expression of the inducible isoform HO1 or the constitutive isoform HO2 in the hemoglobin-transfused group. To test whether the inhibitory effect of SnPPIX was present acutely after hemoglobin transfusion, responses were measured within an hour of completion of the exchange transfusion. In control and albumin-transfused groups, acetylcholine responses were unaffected by SnPPIX but were blocked by addition of the nitric oxide synthase inhibitor N(omega)-nitro-l-arginine (l-NNA) to the superfusate. In hemoglobin-transfused groups, the acetylcholine response was blocked by either SnPPIX or l-NNA alone. The effect of another HO inhibitor, chromium mesoporphyrin (CrMP), was tested on ADP, another endothelial-dependent dilator, in anesthetized rats. Pial arteriolar dilation to ADP was unaffected by CrMP in controls but was attenuated 62% by CrMP in rats transfused with hemoglobin. It is concluded that 1) polymeric hemoglobin transfusion acutely upregulates the contribution of HO to acetylcholine-induced dilation of pial arterioles in cats, 2) this upregulation persists 2 days after transfusion when 95% of the hemoglobin is cleared from the circulation, and 3) this acute upregulation of HO signaling is ubiquitous in that similar effects were observed with a different endothelial-dependent agonist (i.e., ADP) in a another species (rat).

Oxygen release from low and normal P50 Hb vesicles in transiently occluded arterioles of the hamster window model

A phospholipid vesicle encapsulating Hb [Hb vesicle (HbV)] has been developed as a transfusion alternative. One characteristic of HbV is that the O(2) affinity [Po(2) at which Hb is 50% saturated (P(50))] of Hb can be easily regulated by the amount of the coencapsulated allosteric effector pyridoxal 5'-phosphate. In this study, we prepared two HbVs with different P(50)s (8 and 29 mmHg, termed HbV(8) and HbV(29), respectively) and observed their O(2)-releasing behavior from an occluded arteriole in a hamster skinfold window model. Conscious hamsters received HbV(8) or HbV(29) at a dose rate of 7 ml/kg. In the microscopic view, an arteriole (diameter: 53.0 +/- 6.6 mum) was occluded transcutaneously by a glass pipette on a manipulator, and the reduction of the intra-arteriolar Po(2) 100 mum down from the occlusion was measured by the phosphorescence quenching of preinfused Pd-porphyrin. The baseline arteriolar Po(2) (50-52 mmHg) decreased to about 5 mmHg for all the groups. Occlusion after HbV(8) infusion showed a slightly slower rate of Po(2) reduction compared with that after HbV(29) infusion. The arteriolar O(2) content was calculated at each reducing Po(2) in combination with the O(2) equilibrium curves of HbVs, and it was clarified that HbV(8) showed a significantly slower rate of O(2) release compared with HbV(29) and was a primary source of O(2) (maximum fraction, 0.55) overwhelming red blood cells when the Po(2) was reduced (e.g., <10 mmHg) despite a small dosage of HbV. This result supports the possible utilization of Hb-based O(2) carriers with lower P(50) for oxygenation of ischemic tissues.