Poly(2-ethyl-2-oxazoline)-Conjugated Hemoglobins as a Red Blood Cell Substitute

Hemoglobin wrapped covalently with poly(2-ethyl-2-oxazoline)s (POx-Hb) is characterized physicochemically and physiologically as an artificial O2 carrier for use as a red blood cell (RBC) substitute. The POx-Hb is generated by linkage of porcine Hb surface-lysines to a sulfhydryl terminus of the POx derivative, with the average binding number of the polymers ascertained as 6. The POx-Hb shows moderately higher colloid osmotic activity and O2 affinity than the naked Hb. Human adult HbA conjugated with POx also possesses equivalent features and O2 binding properties. The POx-Hb solution exhibits good hemocompatibility, with no influence on the functions of platelets, granulocytes, and monocytes. Its circulation half-life in rats is 14 times longer than that of naked Hb. Hemorrhagic shock in rats is relieved sufficiently by infusion of the POx-Hb solution, as revealed by improvements of circulatory parameters. Serum biochemistry tests and histopathological observations indicate no acute toxicity or abnormality in the related organs. All results indicate that POx-Hb represents an attractive alternative for RBCs and a useful O2 therapeutic reagent in transfusion medicine.

Engineering tyrosine residues into hemoglobin enhances heme reduction, decreases oxidative stress and increases vascular retention of a hemoglobin based blood substitute

Hemoglobin (Hb)-based oxygen carriers (HBOC) are modified extracellular proteins, designed to replace or augment the oxygen-carrying capacity of erythrocytes. However, clinical results have generally been disappointing due to adverse side effects, in part linked to the intrinsic oxidative toxicity of Hb. Previously a redox-active tyrosine residue was engineered into the Hb β subunit (βF41Y) to facilitate electron transfer between endogenous antioxidants such as ascorbate and the oxidative ferryl heme species, converting the highly oxidizing ferryl species into the less reactive ferric (met) form. We inserted different single tyrosine mutations into the α and β subunits of Hb to determine if this effect of βF41Y was unique. Every mutation that was inserted within electron transfer range of the protein surface and the heme increased the rate of ferryl reduction. However, surprisingly, three of the mutations (βT84Y, αL91Y and βF85Y) also increased the rate of ascorbate reduction of ferric(met) Hb to ferrous(oxy) Hb. The rate enhancement was most evident at ascorbate concentrations equivalent to that found in plasma (< 100 μM), suggesting that it might be of benefit in decreasing oxidative stress in vivo. The most promising mutant (βT84Y) was stable with no increase in autoxidation or heme loss. A decrease in membrane damage following Hb addition to HEK cells correlated with the ability of βT84Y to maintain the protein in its oxygenated form. When PEGylated and injected into mice, βT84Y was shown to have an increased vascular half time compared to wild type PEGylated Hb. βT84Y represents a new class of mutations with the ability to enhance reduction of both ferryl and ferric Hb, and thus has potential to decrease adverse side effects as one component of a final HBOC product.

Hemoglobin-Based Oxygen Carrier (HBOC) Development in Trauma: Previous Regulatory Challenges, Lessons Learned, and a Path Forward

Historically, hemoglobin-based oxygen carriers (HBOCs) were being developed as "blood substitutes," despite their transient circulatory half-life (~ 24 h) vs. transfused red blood cells (RBCs). More recently, HBOC commercial development focused on "oxygen therapeutic" indications to provide a temporary oxygenation bridge until medical or surgical interventions (including RBC transfusion, if required) can be initiated. This included the early trauma trials with HemAssist ^® (BAXTER), Hemopure ^® (BIOPURE) and PolyHeme ^® (NORTHFIELD) for resuscitating hypotensive shock. These trials all failed due to safety concerns (e.g., cardiac events, mortality) and certain protocol design limitations. In 2008 the Food and Drug Administration (FDA) put all HBOC trials in the US on clinical hold due to the unfavorable benefit:risk profile demonstrated by various HBOCs in different clinical studies in a meta-analysis published by Natanson et al. (2008). During standard resuscitation in trauma, organ dysfunction and failure can occur due to ischemia in critical tissues, which can be detected by the degree of lactic acidosis. SANGART'S Phase 2 trauma program with MP4OX therefore added lactate >5 mmol/L as an inclusion criterion to enroll patients who had lost sufficient blood to cause a tissue oxygen debt. This was key to the successful conduct of their Phase 2 program (ex-US, from 2009 to 2012) to evaluate MP4OX as an adjunct to standard fluid resuscitation and transfusion of RBCs. In 2013, SANGART shared their Phase 2b results with the FDA, and succeeded in getting the FDA to agree that a planned Phase 2c higher dose comparison study of MP4OX in trauma could include clinical sites in the US. Unfortunately, SANGART failed to secure new funding and was forced to terminate development and operations in Dec 2013, even though a regulatory path forward with FDA approval to proceed in trauma had been achieved.

Influence of Molecular Structure on O2-Binding Properties and Blood Circulation of Hemoglobin‒Albumin Clusters

A hemoglobin wrapped covalently by three human serum albumins, a Hb-HSA3 cluster, is an artificial O2-carrier with the potential to function as a red blood cell substitute. This paper describes the synthesis and O2-binding properties of new hemoglobin‒albumin clusters (i) bearing four HSA units at the periphery (Hb-HSA4, large-size variant) and (ii) containing an intramolecularly crosslinked Hb in the center (XLHb-HSA3, high O2-affinity variant). Dynamic light scattering measurements revealed that the Hb-HSA4 diameter is greater than that of either Hb-HSA3 or XLHb-HSA3. The XLHb-HSA3 showed moderately high O2-affinity compared to the others because of the chemical linkage between the Cys-93(β) residues in Hb. Furthermore, the blood circulation behavior of 125I-labeled clusters was investigated by assay of blood retention and tissue distribution after intravenous administration into anesthetized rats. The XLHb-HSA3 was metabolized faster than Hb-HSA3 and Hb-HSA4. Results suggest that the molecular structure of the protein cluster is a factor that can influence in vivo circulation behavior.

Novel Nanodimension artificial red blood cells that act as O2 and CO2 carrier with enhanced antioxidant activity: PLA-PEG nanoencapsulated PolySFHb-superoxide dismutase-catalase-carbonic anhydrase

Poly(ethylene glycol)-Poly(lactic acid) block-copolymer (PEG-PLA) was prepared and characterized using Fourier transform infrared spectrophotometer (FTIR). Glutaraldehyde was used to crosslink stroma-free hemoglobin (SFHb), superoxide dismutase (SOD), catalase (CAT), and carbonic anhydrase (CA) into a soluble complex of PolySFHb-SOD-CAT-CA. PEG-PLA was then used to nanoencapsulated PolySFHb-SOD-CAT-CA by oil in water emulsification. This resulted in the formation of PLA-PEG-PolySFHb-SOD-CAT-CA nanocapsules that have enhanced antioxidant activity and that can transport both O2 and CO2. These are homogeneous particles with an average diameter of 100 nm with good dispersion and core shell structure, high entrapment efficiency (EE%), and nanocapsule percent recovery. A lethal hemorrhagic shock model in rats was used to evaluate the therapeutic effect of the PLA-PEG-PolySFHb-SOD-CAT-CA nanocapsules. Infusion of this preparation resulted in the lowering of the elevated tissue PCO2 and also recovery of the mean arterial pressure (MAP).

Interpretation of hemolysis tests following administration of a second-generation hemoglobin-based oxygen carrier

Hemoglobin released into the circulation during hemolysis or therapy with chemically modified hemoglobins, exert oxidative and NO-scavenging toxic effects. Pyridoxalated hemoglobin polyoxyethylene conjugate (PHP) is one of the second-generation hemoglobin-based oxygen carriers (HBOCs). We wanted to investigate the metabolism of PHP with a special focus on its consequences for interpreting hemolysis-related diagnostic parameters in PHP-treated patients. Clinical samples were analyzed from 3 patients, who received PHP (as part of the PHOENIX phase III trial) for treatment of catecholamine-resistant distributive shock. In contrast to expectations, clearance of PHP by hemopexin, instead of haptoglobin was documented by increased hemolysis indices, absence of decreased haptoglobin values, presence of free PHP-hemoglobin and exhausted hemopexin concentrations. The present case report is important for both clinicians and laboratorians since it nicely illustrates that a hemolytic aspect of plasma is not necessarely synonymous with hemolysis. A hemolytic aspect of plasma or serum (high hemolysis index) in combination with normal or increased haptoglobin values should draw the attention; additional determination of lactate dehydrogenase and hemopexin may then be useful to distinguish the condition from in vitro hemolysis and to monitor the in vivo elimination of the heme compounds.

Molecular controls of the oxygenation and redox reactions of hemoglobin

SIGNIFICANCE

The broad classes of O(2)-binding proteins known as hemoglobins (Hbs) carry out oxygenation and redox functions that allow organisms with significantly different physiological demands to exist in a wide range of environments. This is aided by allosteric controls that modulate the protein's redox reactions as well as its O(2)-binding functions.

RECENT ADVANCES

The controls of Hb's redox reactions can differ appreciably from the molecular controls for Hb oxygenation and come into play in elegant mechanisms for dealing with nitrosative stress, in the malarial resistance conferred by sickle cell Hb, and in the as-yet unsuccessful designs for safe and effective blood substitutes.

CRITICAL ISSUES

An important basic principle in consideration of Hb's redox reactions is the distinction between kinetic and thermodynamic reaction control. Clarification of these modes of control is critical to gaining an increased understanding of Hb-mediated oxidative processes and oxidative toxicity in vivo.

FUTURE DIRECTIONS

This review addresses emerging concepts and some unresolved questions regarding the interplay between the oxygenation and oxidation reactions of structurally diverse Hbs, both within red blood cells and under acellular conditions. Developing methods that control Hb-mediated oxidative toxicity will be critical to the future development of Hb-based blood substitutes.

Challenges of the movement of catalytic micromotors in blood

Catalytic microjet bubble-propelled engines have attracted a large amount of interest for their potential applications in biomedicine, environmental sciences and natural resources discovery. One of the current efforts in this field is focused on the search of biocompatible fuels. However, only a minimal amount of effort has been made to assess the challenges facing the movement of such devices in a real world environment, especially with regards to the components of blood and their interactions with the catalytic microjets. Herein, we will show the limitations on the movement of catalytic microengines prepared via the rolled-up, as well as the templated-electrochemical deposition method, in an artificial blood sample, due to the presence of two main components of animal blood: the cellular component (red blood cells in this study) and serum. We will show that the motion of catalytic microjets is only possible in highly diluted dispersions of the red blood cells and serum. This finding has a profound implication on the development of the whole field, where the components found in real environments have to be considered carefully, and issues arising from the presence of such components have to be resolved prior to deploying these devices in real world applications.

From artificial red blood cells, oxygen carriers, and oxygen therapeutics to artificial cells, nanomedicine, and beyond

The first experimental artificial red blood cells have all three major functions of red blood cells (rbc). However, the first practical one is a simple polyhemoglobin (PolyHb) that only has an oxygen-carrying function. This is now in routine clinical use in South Africa and Russia. An oxygen carrier with antioxidant functions, PolyHb-catalase-superoxide dismutase, can fulfill two of the three functions of rbc. Even more complete is one with all three functions of rbc in the form of PolyHb-catalase-superoxide dismutase-carbonic anhydrase. The most advanced ones are nanodimension artificial rbc with either PEG-lipid membrane or PEG-PLA polymer membrane. Extensions into oxygen therapeutics include a PolyHb-tyrosinase that suppresses the growth of melanoma in a mice model. Another is a PolyHb-fibrinogen that is an oxygen carrier with platelet-like function. Research has now extended well beyond the original research on artificial rbc into many areas of artificial cells. These include nanoparticles, nanotubules, lipid vesicles, liposomes, polymer-tethered lipid vesicles, polymersomes, microcapsules, bioencapsulation, nanocapules, macroencapsulation, synthetic cells, and others. These are being used in nanotechnology, nanomedicine, regenerative medicine, enzyme/gene therapy, cell/stem cell therapy, biotechnology, drug delivery, hemoperfusion, nanosensers, and even by some groups in agriculture, industry, aquatic culture, nanocomputers, and nanorobotics.

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.

Acellular Invertebrate Hemoglobins as Model Therapeutic Oxygen Carriers: Unique Redox Potentials

Natural acellular polymeric hemoglobins (Hb) provide oxygen transport and delivery within many terrestrial and marine invertebrate organisms. It has been our premise that these natural acellular Hbs may serve as models of therapeutic hemoglobin-based oxygen carriers (HBOC). Our attention has focused on the acellular Hb from the terrestrial invertebrate, Lumbricus terrestris (Lt), which possesses a unique hierarchical structure and a unique ability to function extracellularly without oxidative damage. Lumbricus Hb and Arenicola Hb are resistant to autoxidation, chemical oxidation by potassium ferricyanide, and have little or no capacity to transfer electrons to Fe(+3)-complexes at 37 degrees C. An understanding of how these invertebrate acellular oxygen carriers maintain their structural integrity and redox stability in vivo is vital for the design of a safe and effective red cell substitute. We report here a positive redox potential for these giant hemoglobins that may lie at the basis for its resistance to oxidation.

Understanding the Fundamentals of Perfluorocarbons and Perfluorocarbon Emulsions Relevant toIn VivoOxygen Delivery

The unique behavior of perfluorocarbons (PFCs), including their high oxygen dissolving capacity, hydrophobic and lipophobic character, and extreme inertness, derive directly, in a predictable manner, from the electronic structure and spatial requirements of the fluorine atom. Their low water solubility is key to the prolonged in vivo persistence of the now commercially available injectable microbubbles that serve as contrast agents for diagnostic ultrasound imaging. Oxygent, a stable, small-sized emulsion of a slightly lipophilic, rapidly excreted PFC, perfluorooctyl bromide (perflubron), has been engineered. Significant oxygen delivery has been established in animal models and through Phase II and III human clinical trials. However, an inappropriate testing protocol and the lack of funding led to temporary suspension of the trials.

Mathematical model of NO and O2 transport in an arteriole facilitated by hemoglobin based O2 carriers

The increasing demand for donated human blood has spurred research to develop hemoglobin-based O(2) carriers (HBOCs) that can be used as red blood cell (RBC) substitutes. However, in vivo studies of acellular HBOCs have shown an increase in mean arterial pressure following transfusion that has been attributed to the HBOC's ability to scavenge NO (an important vasodilator that is synthesized by endothelial cells in the blood vessel wall that signals neighboring smooth muscle cells to relax). In this study, a mathematical model was developed to describe NO and O(2) transport in an arteriole containing a mixture of acellular HBOCs and RBCs. The acellular HBOCs studied in this work possessed a wide range of O(2) affinities, O(2) dissociation rate constants and NO reactivities in order to evaluate their effect on O(2) tension and NO concentration in the arteriole tissue region. By focusing on the concentration of NO that is localized in the arteriole smooth muscle cell region, the model can predict the vasopressor response of HBOCs. The results of this study confirmed that acellular HBOCs scavenge large amounts of NO from the entire arteriole (approximately 50% or more NO compared to RBCs only). A recombinant Hb, rHb3011, displayed the least NO reactivity and consequently left the most NO remaining in the arteriole. The NO concentration in the arteriole with respect to the other HBOCs studied was proportional to their NO reactivity. Therefore, the results of this study demonstrate that NO scavenging is an unavoidable consequence of transfusing HBOCs. To prevent or reduce vasodilatation, we suggest administration of NO by either inhaling NO or transfusing nitrite into the blood stream followed by transfusion of HBOC.

A noninvasive method for measuring the oxygen binding-releasing capacity of hemoglobin-loaded polymeric nanoparticles as oxygen carrier

Based on the strong penetration capacity of near infrared lights (NIRs) and different absorption of oxyhemoglobin and deoxyhemoglobin in NIRs region, a novel noninvasive method, with the aid of an airproof-equilibrium apparatus, was developed to determine the oxygen binding-releasing capacity, including oxygen dissociation curve (ODC) and P(50), of the hemoglobin-loaded polymeric nanoparticles (HbP) in this study. The measured ODC of the PLA-PEG HbP was very close to that of the native hemoglobin, and the corresponding P(50) (26.1 mmHg) was also near to the native precursor protein (27.3 mmHg), indicative of the validity of the method proposed. To further verify the method proposed, the oxygen binding-releasing capacity of the HbPs prepared by PCL, PCL-PEG, PLA were also investigated with human blood as control. These results indicated that the method developed here enabled accurate and noninvasive determination of the oxygen binding-releasing capacity of the biodegradable polymeric oxygen carriers.

Thermodynamic approach to oxygen delivery in vivo by natural and artificial oxygen carriers

Oxygen is a toxic gas, still indispensable to aerobic life. This paper explores how normal physiology uses the physico-chemical and thermodynamic characteristics of oxygen for transforming a toxic gas into a non toxic indispensable metabolite. Plasma oxygen concentration is in the range of 10(-5) M, insufficient to sustain metabolism. Oxygen carriers, present in blood, release oxygen into plasma, thereby replacing consumed oxygen and buffering PO(2) near their P(50). They are the natural cell-bound carriers, like hemoglobin inside red cells, myoglobin inside myocytes, and artificial cell-free hemoglobin-based oxygen carriers (HBOC) dissolved in plasma. Metabolic oxygen replacement can be defined as cell-bound and cell-free delivery. Cell-bound delivery is retarded by the slow diffusion of oxygen in plasma and interstitial fluids. The 40% hematocrit of normal blood compensates for the delay, coping with the fast oxygen consumption by mitochondria. Facilitated oxygen diffusion by HBOCs corrects for the slow diffusion, making cell-free delivery relatively independent from P(50). At all oxygen affinities, HBOCs produce hyperoxygenations that are compensated by vasoconstrictions. There is a strict direct correlation between the rate of oxygen replacement and hemoglobin content of blood. The free energy loss of the gradient adds a relevant regulation of tissues oxygenation. Oxygen is retained intravascularly by the limited permeability to gases of vessel walls.

[Study on mass transfer behavior of hemoglobin-based nanocapsule surface]

Three dimensional structure of the surface is an important factor that influences the mass transfer behavior of hemoglobin-based nanocapsule surface. In this paper, the modified double emulsion method was used to fabricate the blood substitute of hemoglobin-based nanocapsules, and with the use of different molecular weight of PEG as probes, the effects of different technical conditions (such as primary emulsion, double emulsion, polymer, solvent, et al) in the processing on the three dimensional structure of the nanocapsule surface were investigated in details. Researches indicated that the water-soluable solvent, such as ethyl acetate and acetone could effectively modulate the pore size of the nanocapsule surface. With the increasing of the ratio of water-soluble solvent, the pore size of the nanocapsules firstly increased and then decreased. The increasing of the extra-water volume, the prolongation of the solvent evaporation time, and the improvement of the stirring speed resulted in a bigger pore size, but the increasing of the solvent volume and PEG polymer could reduce the pore size of nanocapsule surface.

Targeted O2 delivery by blood substitutes: in vitro arteriolar simulations of first- and second-generation products

The O(2) transport from mixtures of commercially produced hemoglobin-based O(2) carriers (HBOCs) and red blood cells (RBCs) flowing through arteriolar-sized (25-mum) conduits is simulated. A generalized treatment of extraluminal O(2) transport processes is used to reflect variations in physiological conditions, such as increased O(2) consumption. Of the HBOCs considered, polymerized bovine hemoglobin (PolyBvHb, p50=54 mmHg), tetrameric cross-linked human hemoglobin (alphaalphaHb, p50=33 mmHg), and PEGylated human hemoglobin (MP4, p50=5 mmHg), only MP4 does not increase O(2) extraction ratios when compared to RBC suspensions alone. A reduction in arteriolar O(2) extraction is likely to be beneficial for HBOCs by preventing O(2)-induced vasoactivity and maximizing the supply of O(2) available to the capillaries. Results from in vivo HBOC transfusion experiments cannot be predicted by the model, unless PolyBvHb has a significant decrease in extraluminal O(2) transport resistance as compared to MP4. This result is consistent with the literature that shows arteriolar O(2) consumption to increase with intravascular pO(2).

How to evaluate blood substitutes for endothelial cell toxicity

The most common and widely transplanted tissue worldwide is blood. But concerns about safety and adequacy of blood transfusion have fostered 20 years of research into blood substitutes such as oxygen carriers based on modified hemoglobin (Hb). Chemically modified or genetically engineered Hb developed as oxygen therapeutics are designed to restore blood volume and to correct oxygen deficit due to ischemia in a variety of clinical settings. Uncontrolled oxidative reactions mediated by large amounts of cell-free Hb and their reactions with various oxidant/antioxidant and cell signalling systems emerge as an important pathway of toxicity. Hemoglobin can react with oxygen and NO, leading to the production of reactive oxygen or nitrogen species. Inside the bloodstream, oxidized Hb and ROS/RNS are in direct contact with endothelial cells (EC). Thus, chain reactions may trigger molecular and cellular biology, causing oxidative stress-related pathologies. This editorial presents an overview of interactions between Hb (modified or not) and EC. We also propose a wide range of techniques and methods to assess oxidative stress and inflammation responses of EC after exposure to Hb. This editorial can serve as a guide to evaluate in vitro toxicity of new Hb molecules.

Effects of PEG-PLA-nano artificial cells containing hemoglobin on kidney function and renal histology in rats

This study is to investigate the long-term effects of PEG-PLA nano artificial cells containing hemoglobin (NanoRBC) on renal function and renal histology after 1/3 blood volume top loading in rats. The experimental rats received one of the following infusions: NanoRBC in Ringer lactate, Ringer lactate, stroma-free hemoglobin (SFHB), polyhemoglobin (PolyHb), autologous rat whole blood (rat RBC). Blood samples were taken before infusions and on days 1, 7 and 21 after infusions for biochemistry analysis. Rats were sacrificed on day 21 after infusions and kidneys were excised for histology examination. Infusion of SFHB induced significant decrease in renal function damage evidenced by elevated serum urea, creatinine and uric acid throughout the 21 days. Kidney histology in SFHb infusion group revealed focal tubular necrosis and intraluminal cellular debris in the proximal tubules, whereas the glomeruli were not observed damaged. In all the other groups, NanoRBC, PolyHb, Ringer lactate and rat RBC, there were no abnormalities in renal biochemistry or histology. In conclusion, injection of NanoRBC did not have adverse effects on renal function nor renal histology.

Recombinant hemoglobins as artificial oxygen carriers

This paper describes the approaches we have taken to construct a) mutant hemoglobins with different oxygen affinities, and b) mutant hemoglobins and myoglobins that polymerize to high molecular weight aggregates in an effort to prevent extravasation and the associated vasoactivity. In vivo testing indicates that exchange transfusion of polymeric hemoglobins in mice does not result in vasoactivity and that polymeric hemoglobins are effective oxygen carriers to ischemic tissues irrespective of their oxygen affinity and cooperativity.

Numerical simulation of oxygen delivery to muscle tissue in the presence of hemoglobin-based oxygen carriers

This work represents a culmination of research on oxygen transport to muscle tissue, which takes into account oxygen transport due to convection, diffusion, and the kinetics of simultaneous reactions between oxygen and hemoglobin and myoglobin. The effect of adding hemoglobin-based oxygen carriers (HBOCs) to the plasma layer of blood in a single capillary surrounded by muscle tissue based on the geometry of the Krogh tissue cylinder is examined for a range of HBOC oxygen affinity, HBOC concentration, capillary inlet oxygen tension (pO(2)), and hematocrit. The full capillary length of the hamster retractor muscle was modeled under resting (V(max) = 1.57 x 10(-4) mLO(2) mL(-1) s(-1), cell velocity (v(c)) = 0.015 cm/s) and working (V(max) = 1.57 x 10(-3) mLO(2) mL(-1) s(-1), v(c) = 0.075 cm/s) conditions. Two spacings between the red blood cell (RBC) and the capillary wall were examined, corresponding to a capillary with and without an endothelial surface layer. Simulations led to the following conclusions, which lend physiological insight into oxygen transport to muscle tissue in the presence of HBOCs: (1) The reaction kinetics between oxygen and myoglobin in the tissue region, oxygen and HBOCs in the plasma, and oxygen and RBCs in the capillary lumen should not be neglected. (2) Simulation results yielded new insight into possible mechanisms of oxygen transport in the presence of HBOCs. (3) HBOCs may act as a source or sink for oxygen in the capillary and may compete with RBCs for oxygen. (4) HBOCs return oxygen delivery to muscle tissue to normal for varying degrees of hypoxia (inlet capillary pO(2) < 30 mmHg) and anemia (hematocrit < 46%) for the hamster model.

Cerebral oxygen delivery by liposome-encapsulated hemoglobin: a positron-emission tomographic evaluation in a rat model of hemorrhagic shock

Liposome-encapsulated Hb (LEH) is being developed as an artificially assembled, low-toxicity, and spatially isolated Hb-based oxygen carrier (HBOC). Standard methods of evaluating oxygen carriers are based on surrogate indicators of physiology in animal models of shock. Assessment of actual delivery of oxygen by HBOCs and resultant improvement in oxygen metabolism at the tissue level has been a technical challenge. In this work, we report our findings from 15O-positron emission tomographic (15O-PET) evaluation of LEH in a rat model of 40% hypovolemic shock. In vitro studies showed that PEGylated LEH formulation containing approximately 7.5% Hb and consisting of neutral lipids (distearoylphosphatidylcholine:cholesterol:alpha-tocopherol, 51.4:46.4:2.2) efficiently picks up 15O-labeled oxygen gas. The final preparation of LEH contained 5% human serum albumin to provide oncotic pressure. Cerebral PET images of anesthetized rats inhaling 15O-labeled O2 gas showed efficient oxygen-carrying and delivery capacity of LEH formulation. From the PET images, we determined cerebral metabolic rate of oxygen (CMR(O2)) as a direct indicator of oxygen-carrying capacity of LEH as well as oxygen delivery and metabolism in rat brain. Compared with control fluids [saline and 5% human serum albumin (HSA)], LEH significantly improved CMR(O2) to approximately 80% of baseline level. Saline and HSA resuscitation could not improve hypovolemia-induced decrease in CMR(O2). On the other hand, resuscitation of shed blood was the most efficient in restoring oxygen metabolism. The results suggest that 15O-PET technology can be successfully employed to evaluate potential oxygen carriers and blood substitutes and that LEH resuscitation in hemorrhage enhances oxygen delivery to the cerebral tissue and improves oxygen metabolism in brain.

O2-Binding Albumin Thin Films: Solid Membranes of Poly(ethylene glycol)-Conjugated Human Serum Albumin Incorporating Iron Porphyrin

Poly(ethylene glycol) (PEG)-conjugated human serum albumin (HSA) incorporating the tetrakis(alpha,alpha,alpha,alpha-o-amidophenyl)porphinatoiron(II) derivative (FeP) [PEG(HSA-FeP)] is a unique plasma protein-based O2 carrier as a red blood cell substitute. The aqueous solution of PEG(HSA-FeP) [mw of PEG: 2-kDa (PEG2) or 5-kDa (PEG5)] was evaporated on a glass surface to produce a red-colored solid membrane. Scanning electron microscopy observations revealed that the PEG2(HSA-FeP) membrane consisted of two parts: (i) a surface layer made of a fibrous component (10 microm thickness), and (ii) a bottom layer of an amorphous phase (5 microm thickness). The condensed solution provided a thick membrane (70 microm), which also has the amorphous bottom layer. On the other hand, the PEG5(HSA-FeP) produced homogeneous membrane made of the fibrous component. The FeP active sites in the solid membrane formed very stable O2-adduct complexes at 37 degrees C with a half-lifetime of 40 h. The O2-binding affinity of the PEG2(HSA-FeP) membrane (P1/2 = 40 Torr, 25 degrees C) was 4-fold lower than that in aqueous solution, which is kinetically due to the low association rate constant. The membrane was soluble again in water and organic solvents (ethanol and chloroform) without deformation of the secondary structure of the protein. The addition of hyaluronic acid gave a free-standing flexible thin film, and it can also bind and release O2 as well. These O2-carrying albumin membranes with a micrometer-thickness would be of significant medical importance for a variety of clinical treatments.

First-generation blood substitutes: what have we learned? Biochemical and physiological perspectives

Chemically modified or recombinant hemoglobin (Hb)-based oxygen carriers (HBOCs) have been developed as oxygen therapeutics or 'blood substitutes' for use in a variety of clinical settings. Oxidative and nitrosative reactions of acellular Hb can limit the effectiveness and compromise the safety of HBOCs. The reactions between Hb and biologically relevant redox active molecules may also perturb redox sensitive signaling pathways. In recent years, systematic in vitro and in vivo structural and functional evaluation of several HBOCs has been carried out and, in some cases, delineated the 'structural' origin of their toxicity. This enables potential protective strategies against Hb-mediated side reactions to be rationally suggested. Here the authors provide an overview of their research experiences, novel insights into the molecular basis of toxicities of these products and some lessons learned.

[Blood substitutes: state of the art and technical setbacks and why we are still disappointed]

Volume loading solutions used therapeutically (albumin, dextrans, modified gelatins and hydroxylstarches) are simple plasma substitutes and cannot ensure oxygen transport. The search for erythrocyte substitutes initially seemed utopian, but this goal is now within our reach, in the form of hemoglobin-based oxygen carriers (HBOC) for example. The clinical development of HBOC has been slowed by adverse effects, including an increase in arterial pressure due to the vasoconstrictive effect of cell-free hemoglobin in plasma, haemoprotein autoxidation leading to methemoglobin formation, and free radical generation that creates oxidative stress.

New strategy of platelet substitutes for enhancing platelet aggregation at high shear rates: cooperative effects of a mixed system of fibrinogen γ-chain dodecapeptide- or glycoprotein Ibα-conjugated latex beads under flow conditions

To construct platelet substitutes that have hemostatic properties over a wide range of shear rates, we used fibrinogen gamma-chain carboxy-terminal sequence HHLGGAKQAGDV (H12), which recognizes activated platelets at low shear rates, and a recombinant water-soluble moiety of the platelet glycoprotein (rGPIbalpha), which recognizes von Willebrand factor at high shear rates. Three kinds of samples were prepared for this purpose: H12-conjugated latex beads (H12-latex beads), rGPIbalpha-latex beads, and H12/rGPIbalpha-latex beads. These samples were evaluated in thrombocytopenia-imitation blood at various flow conditions. Based on ADP-induced platelet aggregation studies, the H12-latex beads significantly enhanced platelet aggregation via H12 binding with GPIIb/IIIa activated on the surface of activated platelets, whereas the rGPIbalpha-latex beads did not support platelet aggregation. In the case of the H12/rGPIbalpha-latex beads, the function of H12 was suppressed by steric hindrance from the larger rGPIbalpha bound to the latex bead. A mixture of the H12-latex beads and the rGPIbalpha-latex beads adhered to a collagen surface over a wide range of shear rates. In particular, at high shear rates, a cooperative effect was observed in the enhancement of platelet thrombus formation compared with H12-latex beads or rGPIbalpha-latex beads alone. We propose that a mixed system of H12- and rGPIbalpha-conjugated nanoparticles is a more effective platelet substitute than each of the beads used alone and has enhanced platelet aggregation properties.

Hemoglobin-based oxygen carriers in trauma care: scientific rationale for the US multicenter prehosptial trial

BACKGROUND

The greatest need for blood substitutes worldwide is in patients with unanticipated acute blood loss, and trauma is the most likely scenario. The blood substitutes reaching advanced clinical trials today are red blood cell (RBC) substitutes derived from hemoglobin. The hemoglobin-based oxygen carriers (HBOCs) tested currently in advanced clinical trials are polymerized hemoglobin solutions.

METHODS

In the USA, the standard approach to restoring oxygen delivery for hemorrhagic shock has been crystalloid administration to expand intravascular volume, followed by stored RBCs for critical anemia. Allogeneic RBCs, however, may have adverse immunoinflammatory effects that increase the risk of postinjury multiple organ failure (MOF). Phase II in hospital clinical trials, as well as in vitro and in vivo work, suggest that resuscitation with an HBOC--in lieu of stored RBCs--attenuates the systemic inflammatory response invoked in the pathogenesis of MOF. Specifically, an HBOC has been shown to obviate stored RBC-provoked polymorphonuclear neutrophil (PMN) priming, endothelial activation, and systemic release of interleukins (IL) 6, 8, and 10. In a 2-event rodent study of shock-induced PMN-mediated acute respiratory distress syndrome (ARDS), the simulated prehospital administration of an HBOC markedly attenuated lung injury.

RESULTS

Based on this background and work by others, we have initiated a US multicenter prehospital trial in which severely injured patients with major blood loss [systolic blood pressure (SBP)<or=90 mmHg] are randomized to initial field resuscitation with crystalloid versus HBOC. During the hospital phase, the control group is further resuscitated with stored RBCs whereas the study group receives HBOC (up to 6 units) in the first 12 hours. The primary study endpoint is decreased 30-day mortality, and secondary endpoints include reductions in administration of allogeneic RBCs and uncrossmatched RBCs; avoiding circulating hemoglobin levels<5 g/dl; and decreased ARDS and MOF.

CONCLUSIONS

To date, >500 injured patients have been enrolled in this multicenter trial, and the final interim analyses support the original target of 720.

Preparation of hemoglobin-loaded nano-sized particles with porous structure as oxygen carriers

Hb (hemoglobin)-loaded particles (HbP) encapsulated by a biodegradable polymer used as oxygen carrier were prepared. A modified double emulsion and solvent diffusion/evaporation method was adopted. All experiments were performed based on two types of biodegradable polymers, poly(epsilon-caprolactone) (PCL) and poly(epsilon-caprolactone-ethylene glycol) (PCL-PEG). The biodistribution and the survival time in blood of the particles were investigated in a mouse model. Encapsulation efficiency and pore-connecting efficiency were evaluated by a novel sulfocyanate potassium method. The influence of process parameters on the particle size and pore-connecting efficiency (PCE%) of nanoparticles have been discussed. The prepared conditions: solvent, external aqueous phase, pressure were discussed. The system utilizing dichloromethane (DCM)/ethyl acetate (EA) as a solvent with an unsaturated external aqueous phase yielded the highest encapsulation efficiency (87.35%) with a small mean particle size (153 nm). The formation of porous channels was attributed to the diffusion of solvent. The PCE% was more sensitive to the rate of solvent diffusion that was obviously affected by the preparation temperature. The PCE% reached 87.47% when PCL-PEG was employed at 25 degrees C. P(50) of HbP was 27 mmHg, which does not seem to be greatly affected by the encapsulation procedure. In vivo, following intravenous injection of 6-coumarin labeled HbP, the major organ accumulating Hb-loaded particles was the liver. The half-life of nano-sized PCL HbP was 3.1 times as long as the micro-sized PCL HbP. Also, Nano-sized as well as a PEGylated surface on HbP is beneficial for prolonged blood residence (7.2 fold increase).

Electrophoretic, size-exclusion high-performance liquid chromatography and liquid chromatography-electrospray ionization ion trap mass spectrometric detection of hemoglobin-based oxygen carriers

Hemoglobin-based oxygen carriers (HBOCs) are blood substitutes based on hemoglobin of either bovine or human origin and they can potentially be misused in elite sports to improve endurance performance. Recently, three methods have been proposed in doping control analysis to allow HBOCs screening and identification by application of electrophoresis, size-exclusion chromatography coupled with HPLC and LC coupled with tandem mass spectrometry (LC/MSMS). In view of the Athens 2004 Olympic Games, modifications were introduced in order to increase the specificity of these methods. The sample preparation protocols of the electrophoretic and SEC-HPLC methods were modified with the introduction of sequential ultra filtration steps to remove all heme containing material below 100 kDa, thus leaving only HBOCs material for analysis. Furthermore, a modification of the LC/MSMS methodology was introduced to allow full scan MS-MS spectra of peptide segments arising from the tryptic digestion of bovine HBOCs. These relatively simple methodological modifications have major impact, as far as time and cost effectiveness is concerned in doping control procedures, because they provide a useful tool in order to identify which suspect samples from the initial visual screening are due to hemolysis and exclude them from further analysis.

MICROVASCULAR PERSPECTIVE OF OXYGEN-CARRYING AND -NONCARRYING BLOOD SUBSTITUTES

The development of an alternative to natural blood has evolved from the initial goal of replicating blood properties to the current objective of formulating a fluid that can be used to replace blood while preserving microvascular function and delivering oxygen. The properties of this fluid are counterintuitive and different from blood because it has high viscosity, oxygen affinity, and a low oxygen carrier concentration when compared with blood. The optimal oxygen carrier devised presently is poly-ethylene-conjugated human hemoglobin, a material demonstrated to be vasoinactive and void of the toxicities present in previous hemoglobin formulations. A feature of this material is that it is effective in small quantities, and therefore amplifies the equivalent supply of blood derived from blood donations.

Modification of leech behavior following foraging for artificial blood

In this study we examined whether the foraging for artificial blood affected the behavioral responsiveness of leeches to electrical stimulation of the body wall. After foraging for artificial blood, electrical stimulation of the posterior end of the leech significantly increased the percentage of stimulation trials that elicited locomotory activity--swimming and crawling--compared to the behaviors elicited when leeches did not forage or foraged for normal saline. On the other hand, shortening always dominated the behavioral profile of the leech to anterior stimulation even after foraging for artificial blood. In intact anterior end-isolated nerve cord preparations, we also found that application of artificial blood to the intact anterior end was sufficient to modify motor responsiveness to DP nerve stimulation. Full strength artificial blood had an overall negative effect on the likelihood of DP nerve stimulation initiating swimming and on the average length of elicited swim episodes compared to when pond water surrounded the anterior end. Application of a 10% solution of artificial blood to the anterior end led to an increase in the likelihood of DP nerve stimulation eliciting swimming.

Arenicola marina extracellular hemoglobin: a new promising blood substitute

The need to develop a blood substitute is now urgent because of the increasing concern over Europe's BSE outbreak and the worldwide HIV/AIDS epidemic, which have cut blood supplies. Extracellular soluble hemoglobin has long been studied for its possible use as a safe and effective alternative to blood transfusion, but this has met with little success. Clinical trials have revealed undesirable side effects-oxidative damage and vasoconstriction-that hamper the application of cell-free hemoglobin as a blood substitute. We have addressed these problems and have found a new promising extracellular blood substitute: the natural giant extracellular polymeric hemoglobin of the polychaete annelid Arenicola marina. Here we show that it is less likely to cause immunogenic response; its functional and structural properties should prevent the side effects often associated with the administration of extracellular hemoglobin. Moreover, its intrinsic properties are of interest for other therapeutic applications often associated with hemorrhagic shock (ischemia reperfusion, treatment of septic shock and for organ preservation prior to transplantation). Moreover, using natural hemoglobin is particularly useful since recombinant DNA techniques could be used to express the protein in large quantities.

Structural and functional characteristics of erythrocyte membranes and their correction with perftoran

We studied the effect of single intravenous injection of perftoran on the intensity of the initial stages of lipid peroxidation and structural and functional characteristics of erythrocyte membranes (cell model). Perftoran slightly activated the initial stages of lipid peroxidation and optimized structural and functional characteristics of erythrocyte membranes.

Hemostatic effects of fibrinogen gamma-chain dodecapeptide-conjugated polymerized albumin particles in vitro and in vivo

BACKGROUND

Prototypes of platelet (PLT) substitutes have been studied and the focus was on a dodecapeptide, HHLGGAKQAGDV (H12), which is a fibrinogen gamma-chain carboxy-terminal sequence (gamma 400-411) and exists only in the fibrinogen domain.

STUDY DESIGN AND METHODS

H12 was conjugated to the surface of polymerized albumin particles (polyAlb) as biocompatible and biodegradable particles with a mean diameter of 260 +/- 60 nm, and the hemostatic ability of H12-conjugated polyAlb (H12-polyAlb) under flow conditions and thrombocytopenic rats have been studied.

RESULTS

H12-polyAlb enhanced the in vitro thrombus formation of activated PLTs on a collagen-immobilized plate when exposed to the flowing thrombocytopenic imitation blood. Furthermore, the analysis of the tail bleeding time of rats that were made thrombocytopenic by busulfan injection showed that H12-polyAlb had a hemostatic effect. Based on the bleeding time and the amount injected, the hemostatic capacity of 20 H12-polyAlb was estimated to correspond to that of one PLT.

CONCLUSION

These results were important first steps toward the development of PLT substitutes and indicated that H12-polyAlb may be a suitable candidate for an alternative to human PLT concentrates transfused into thrombocytopenic patients in the future.

Liposome-encapsulated actin–hemoglobin (LEAcHb) artificial blood substitutes

A new approach to enhance the circulation persistence of liposomes has been applied to develop liposome-encapsulated actin-hemoglobin (LEAcHb) dispersions as potential blood substitutes by introducing an actin matrix into the liposome aqueous core. Asymmetric flow field-flow fractionation coupled with multi-angle static light scattering was used to study the shape, size distribution, and encapsulation efficiency of liposome-encapsulated hemoglobin (LEHb) and LEAcHb dispersions. By polymerizing monomeric actin into filamentous actin inside the liposome aqueous core, LEAcHb particles transformed into a disk-like shape. We studied the effect of an encapsulated actin matrix on the size distribution, hemoglobin (Hb) encapsulation efficiency, oxygen affinity, and methemoglobin (MetHb) level of LEAcHb dispersions, and compared them with plain LEHb dispersions (without actin). LEHb, and LEAcHb dispersions extruded through 400 nm membranes were injected into rats and it was observed that LEAcHb dispersions with 1mg/mL of actin enhanced the circulatory half-life versus LEHb dispersions. The circulatory characteristics of empty PEGylated and non-PEGylated actin-containing liposomes (without Hb) were studied as controls for the LEHb and LEAcHb dispersions in this paper, which displayed maximum circulatory half-lives greater than 72 h. Taken together the results of this study supports our hypothesis that a lipid membrane supported by an underlying actin matrix will extend the circulatory half-life of LEHb dispersions.

Role of nitric oxide scavenging in vascular response to cell-free hemoglobin transfusion

Modified Hb solutions have been developed as O(2) carrier transfusion fluids, but of concern is the possibility that increased scavenging of nitric oxide (NO) within the plasma will alter vascular reactivity even if the Hb does not readily extravasate. The effect of decreasing hematocrit from approximately 30% to 18% by an exchange transfusion of a 6% sebacyl cross-linked tetrameric Hb solution on the diameter of pial arterioles possessing tight endothelial junctions was examined through a cranial window in anesthetized cats with and without a NO synthase (NOS) inhibitor. Superfusion of a NOS inhibitor decreased diameter, and subsequent Hb transfusion produced additional constriction that was not different from Hb transfusion alone but was different from the dilation observed by exchange transfusion of an albumin solution after NOS inhibition. In contrast, abluminal application of the cross-linked Hb produced constriction that was attenuated by the NOS inhibitor. Neither abluminal nor intraluminal cross-linked Hb interfered with pial arteriolar dilation to cromakalim, an activator of ATP-sensitive potassium channels. Pial vascular reactivity to hypocapnia and hypercapnia was unaffected by Hb transfusion. Microsphere-determined regional blood flow indicated selective decreases in perfusion after Hb transfusion in the kidney, small intestine, and neurohypophysis, which does not have tight endothelial junctions. Administration of a NOS inhibitor to reduce the basal level of NO available for scavenging before Hb transfusion prevented further decreases in blood flow to these regions compared with NOS inhibition alone. In contrast, blood flow to skeletal and left ventricular muscle increased, and cerebral blood flow was unchanged after Hb transfusion. This cross-linked Hb tetramer is known to appear in renal lymph but not in urine. We conclude that cell-free tetrameric Hb does not scavenge sufficient NO in the plasma space to significantly affect baseline tone in vascular beds with tight endothelial junctions but does produce substantial constriction in beds with porous endothelium. The data support increasing the molecular size of Hb by polymerization or conjugation to limit extravasation in all vascular beds to preserve normal vascular reactivity.

Targeted O2 delivery by low-p50 hemoglobin: a new basis for hemoglobin-based oxygen carriers

We have proposed new criteria for a successful cell-free, hemoglobin-based O2 carrier. These include increased molecular radius, increased viscosity, increased oncotic pressure, and reduced p50. A new molecule, MalPEG-Hb, formulated at 4.2g/dL in lactated Ringer's solution (MP4), has been produced according to these new criteria. MP4 has a p50 of 5-6 mm Hg, oncotic pressure of 49mm Hg and viscosity of 2.2cPs. After 50% exchange transfusion with MP4, rats survive a 60% controlled hemorrhage in spite of total hemoglobin of 7.8 g/dL and plasma hemoglobin concentration of 1.6 g/dL. This model results in 50% mortality in control animals and 100% mortality in animals exchange-transfused with either crosslinked or polymerized hemoglobin. Oxygen supply to tissue was measured directly in the hamster skinfold model, in which O2 release in precapillary and capillary vessels can be quantified. The data demonstrate that the effectiveness of MP4 results from its ability to conserve O2 in precapillary vessels and release O2 in capillaries, thereby "targeting" O2 to hypoxic tissue. Preservation of functional capillary density and prevention of vasoconstriction further contribute to the effectiveness of this new formulation.

Oxygen transport by low and normal oxygen affinity hemoglobin vesicles in extreme hemodilution

The oxygen transport capacity of phospholipid vesicles encapsulating purified Hb (HbV) produced with a Po2at which Hb is 50% saturated (P 50 ) of 8 (HbV8) and 29 mmHg (HbV29) was investigated in the hamster chamber window model by using microvascular measurements to determine oxygen delivery during extreme hemodilution. Two isovolemic hemodilution steps were performed with 5% recombinant albumin (rHSA) until Hct was 35% of baseline. Isovolemic exchange was continued using HbV suspended in rHSA solution to a total [Hb] of 5.7 g/dl in blood. P50was modified by coencapsulating pyridoxal 5′-phosphate. Final Hct was 11% for the HbV groups, with a plasma [Hb] of 2.1 ± 0.1 g/dl after exchange with HbV8or HbV29. A reference group was hemodiluted to Hct 11% with only rHSA. All groups showed stable blood pressure and heart rate. Arterial oxygen tensions were significantly higher than baseline for the HbV groups and the rHSA group and significantly lower for the HbV groups compared with the rHSA group. Blood pressure was significantly higher for the HbV8group compared with the HbV29group. Arteriolar and venular blood flows were significantly higher than baseline for the HbV groups. Microvascular oxygen delivery and extraction were similar for the HbV groups but lower for the rHSA group ( P < 0.05). Venular and tissue Po2were statistically higher for the HbV8vs. the HbV29and rHSA groups ( P < 0.05). Improved tissue Po2is obtained when red blood cells deliver oxygen in combination with a high- rather than low-affinity oxygen carrier.

Mechanisms for vasoconstriction and decreased blood flow following intravenous administration of cell-free native hemoglobin solutions

Acellular free hemoglobin-based oxygen carriers (HBOC) are being developed as red cell substitutes. However, following intravenous administration of some HBOC, decreased systemic blood flow and decreased functional capillary density have been observed. In isolated blood vessels, hemoglobin (Hb) in solution free of erythrocyte membranes has been shown to elicit vascular contraction. Therefore, the decreased blood flow and functional capillary density may be due to inherent vasoactive property of native Hb. There are two plausible mechanisms for the Hb-mediated vasoconstriction: nitrosylation of heme-irons and S-nitrosation of reactive beta-chain cysteines (Cys93beta). In this study, we investigated whether Hb Cys93beta thiols play a role in Hb-mediated vascular contraction using functional bioassays with isolated rat thoracic aorta. To better define the roles of globin thiols and heme-iron, Hbs modified at the heme-iron and/or Cys93beta sites were prepared and their vasoactivities tested. In addition, vasoactivities of natural heme proteins with heme and/or cysteine sites unavailable for NO reaction were also examined.

20-HETE-mediated vasoconstriction by hemoglobin-O2 carrier in Sprague-Dawley but not Wistar rats

Hypothetically either decreased nitric oxide (NO) or increased O(2) could initiate 20-HETE-mediated vasoconstriction associated with hemoglobin-based blood substitutes (HBOC). To test this hypothesis, we infused Tm-Hb, an HBOC with low O(2) affinity, into isoflurane-anesthetized Wistar (W) and Sprague-Dawley (SD) rats after exchanging 20% of their blood with Ringer lactate. For comparison we infused an equal amount of BSA or BSA with N(G)-nitro-L-arginine methyl ester (BSA + NAME). Tm-Hb increased blood pressure (BP) and renal vascular resistance (RVR) equally in W and SD rats. Renal blood flow (RBF; Doppler ultrasound) decreased. BSA decreased RVR and raised glomerular filtration rate. BSA + NAME raised BP, RVR, and GFR. HET0016, an inhibitor of 20-HETE production, blunted BP and RVR responses to Tm-Hb and BSA+NAME in SD but not W rats. Arterial O(2) content with BSA was lower than with Tm-Hb but O(2) delivery was 60% higher with BSA because of higher RBF. BSA raised Po(2) (Oxylite) in cortex and medulla and reduced RVR. Tm-Hb decreased Po(2) and increased RVR. Switching rats from breathing air to 100% O(2) raised intrarenal Po(2) two- to threefold and increased BP and RVR. HET0016 did not alter hyperoxic responses. In conclusion, 20-HETE contributes to vasoconstriction by Tm-Hb in SD but not in W rats, and increased 20-HETE activity results primarily from decreased NO.

Artificial Oxygen Carriers as Red Blood Cell Substitutes: A Selected Review and Current Status

Two distinct approaches are being explored in red blood cell substitute (RCS) development: hemoglobin-based oxygen carriers (HBOCs) and perfluorocarbon-based oxygen carriers (PFBOCs). HBOCs are based on intra- and/or intermolecularly "engineered" human or animal hemoglobins (Hbs), optimized for O2 delivery and longer intravascular circulation. Some are currently being evaluated in Phase II/III clinical studies. PFBOCs are aqueous emulsions of perfluorocarbon derivatives that dissolve relatively large amounts of O2. A PFBOC based on a 60% (wt/vol) emulsion of perfluorooctyl bromide has been evaluated in Phase II/III clinical trials. Although current PFBOC products generally require patients to breathe O2 enriched air, they render certain advantages since they are totally synthetic. This article provides a short review of the basic principles, approaches, and current status of RCS development. Results of preclinical and clinical studies including recent Phase II/III clinical studies are discussed.

Hemoglobin-based Red Blood Cell Substitutes

Polyhemoglobin is already well into the final stages of clinical trials in humans with one approved for routine clinical use in South Africa. Conjugated hemoglobin is also in ongoing clinical trials. Meanwhile, recombinant Hb has been modified to modulate the effects of nitric oxide. Other systems contain antioxidant enzymes for those clinical applications that may have potential problems related to ischemia-reperfusion injuries. Other developments are based on hemoglobin-lipid vesicles and also the use of nanotechnology and biodegradable copolymers to prepare nanodimension artificial red blood cells containing hemoglobin and complex enzyme systems.

Chemically modified porcine hemoglobins and their biological properties

Hemoglobin cross-linked with small molecular modifiers turns out to be more stable. Modifications of proteins with polyethylene glycol (PEG) have been proven to enlarge the molecular size of proteins, to prolong their retention time in the circulation as well as blunt immune reactions. In the present study, the optimal conditions for porcine hemoglobin (pHb) modification with bis (3, 5-dibromosalicyl) fumarate (DBBF) and PEG were evaluated. The derivative of DBBF cross-linked pHb (DBBF-pHb) showed improved oxygen affinity and the ability to resist the dissociation of the alpha2beta2 tetramer compared with the natural protein. DBBF-pHb was then bound to the activated PEG. The results indicated that the pHb modified with DBBF and PEG had more stable tetrameric conformation with a molecular weight of 107000. Their oxygen half-saturation pressure (P50) is around 3.33 kPa, which approximates the physiological P50 of human red blood cells. Both routine and reinforced immunizing methods were adopted to study the immunogenicity of modified products and the results showed that the products had very low immunogenicity evaluated by enzyme-linked immunoadsordent assay (ELISA). Somewhat beneficial effects were shown in the treatment of hemorrhagic shock where modified hemoglobin solutions were used as resuscitation fluids in the hemorrhagic shock Sprague-Dawley (SD) rats model.

No scavenging and the hypertensive effect of hemoglobin-based blood substitutes

The major pathway for nitric oxide scavenging in red cells involves the direct reaction of the gas with HbO2 to form nitrate and the ferric form of the protein, metHb. Because both atoms of O2 are incorporated into nitrate, this process is called NO dioxygenation (NOD). The NOD reaction involves an initial, very rapid bimolecular addition of NO to bound O2 to form a transient Fe(III)-peroxynitrite complex, which can be observed spectrally at alkaline pH. This intermediate rapidly isomerizes at pH 7 (t1/2 <== 1 ms) to metHb and NO3-, which is nontoxic and readily transported out of red cells and excreted. The rate of NO consumption by intracellular HbO2 during normal blood flow is limited by diffusion up to and into the red cells and is too slow to interfere significantly with vasoregulation. In contrast, extracellular HbO2 is highly vasoconstrictive, and the resultant hypertension is a significant side effect of most hemoglobin-based blood substitutes. The major cause of this blood pressure effect seems to be the high rate of NO dioxygenation by cell-free HbO2, which can extravasate into the vessel walls and interfere directly with NO signaling between endothelial and smooth muscle cells. This interpretation is supported by a strong linear correlation between the magnitude of the blood pressure effect caused by infusion of cross-linked recombinant hemoglobin tetramers in vivo and the rate of NO dioxygenation by these proteins measured in vitro.

Blood on tap. Part 1. History in the making

Emergency services around the United States are about to become part of the front lines in the race to bring to market the first blood substitute with oxygen-carrying capabilities. Take a look inside the high-tech world of biopharmaceuticals and the innovative pioneers who are chasing after a scientific holy grail; a synthetic substitute for blood. In the process, they have made and lost fortunes, advanced our understanding of the nature of blood and launched one of the biggest ethical controversies in modern medical history. As phase three clinical trials move to the prehospital arena, biotechnology firms are staking everything on the notion that they're about to change the way we treat trauma patients. They may be right.

Oxygen therapeutics: can we tame haemoglobin?

Chemically modified or genetically engineered haemoglobins (Hbs) developed as oxygen therapeutics (often termed 'blood substitutes') are designed to correct oxygen deficit due to ischaemia in a variety of clinical settings. These modifications are intended to stabilize Hb outside its natural environment--red blood cells--in a functional tetrameric and/or polymeric form. Uncontrolled haem-mediated oxidative reactions of cell-free Hb and its reactions with various oxidant/antioxidant and cell signalling systems have emerged as an important pathway of toxicity. Current protective strategies designed to produce safe Hb-based products are focused on controlling or suppressing the 'radical' nature of Hb while retaining its oxygen-carrying function.

Exchange transfusion with entirely synthetic red-cell substitute albumin-heme into rats: Physiological responses and blood biochemical tests

Recombinant human serum albumin (rHSA) incorporating 2-[8-[N-(2-methylimidazolyl)]octanoyloxymethyl]-5,10,15,20-[tetrakis[alpha,alpha,alpha,alpha-o-(1-methylcyclohexanoyl)amino]phenyl]porphinatoiron(II) [albumin-heme (rHSA-heme)] is an artificial hemoprotein which has the capability to transport O(2) in vitro and in vivo. A 20% exchange transfusion with rHSA-heme into anesthetized rats has been performed to evaluate its clinical safety by monitoring the circulation parameters and blood parameters for 6 h after the infusion. Time course changes in all parameters essentially showed the same features as those of the control group (without infusion) and rHSA group (with administration of the same amount of rHSA). Blood biochemical tests of the withdrawn plasma at 6 h after the exchange transfusion have also been carried out. No significant difference was found between the rHSA-heme and rHSA groups, suggesting the initial clinical safety of this entirely synthetic O(2)-carrier as a red-cell substitute.

Function of fibrinogen γ-chain dodecapeptide-conjugated latex beads under flow

In order to perform a fundamental study of platelet substitutes, novel particles that bound to activated platelets were prepared using two oligopeptides conjugated to latex beads. The oligopeptides were CHHLGGAKQAGDV (H12), which is a fibrinogen gamma-chain carboxy-terminal sequence (gamma 400-411), and CGGRGDF (RGD), which contains a fibrinogen alpha-chain sequence (alpha 95-98 RGDF). Both peptides contained an additional amino-terminal cysteine to enable conjugation. Human serum albumin was adsorbed onto the surface of latex beads (average diameter 1microm) and pyridyldisulfide groups were chemically introduced into the adsorbed protein. H12 or RGD peptides were then chemically linked to the modified surface protein via disulfide linkages. H12- or RGD-conjugated latex beads prepared in this way enhanced the in vitro thrombus formation of activated platelets on collagen-immobilized plates under flowing thrombocytopenic-imitation blood. Based on the result of flow cytometric analyses of agglutination, PAC-1 binding, antiP-selectin antibody binding, and annexin V binding, the H12-conjugated latex beads showed minimal interaction with non-activated platelets. These results indicate the excellent potential of H12-conjugated particles as a candidate for a platelet substitute.

Abnormal glycosylation of red cell membrane band 3 in the congenital disorder of glycosylation Ig

A description is provided of the clinical presentation in an infant of the recently described congenital disorder of glycosylation type Ig, and the changes affecting glycosylation of red cell membrane band 3, the anion exchanger. It has been shown that the condition stems from a homozygous mutation within the human ortholog of yeast ALG12 gene, which encodes a dolichol-P-mannose:Man7GlcNAc2-PP-dolichol alpha,1-6 mannosyltransferase of the endoplasmic reticulum. The clinical phenotype included prominent central and peripheral manifestations in the CNS. Although the infant studied had no anemia, band 3 abnormally separated into two fractions upon electrophoresis. The chemical composition of the glycans of both fractions was analyzed in detail. The fraction with low electrophoretic mobility was moderately hypoglycosylated (by 27%) and its mannose content was normal. The fraction with high electrophoretic mobility was deeply carbohydrate deficient (by 64%) and had 1 mol mannose in excess but only three residues of N-acetylglucosamine. Glycophorin A was hypoglycosylated with respect to O-linked glycans. Glycosphingolipids of red cells were normal. We suggest that the incomplete biosynthesis of the N-linked glycan of band 3 was largely caused by the persistence of the 3-linked mannose residue on the 6-mannose arm of the trimannosyl moiety of the glycoprotein. It is remarkable that the changes recorded in band 3 have no clinical consequences. Band 3 alteration might serve as an additional indicator (some serum N-glycoproteins of hepatic origin are also indicative) of the congenital disorder of glycosylation type Ig.

Future generations of red blood cell substitutes

Polyhaemoglobins (PolyHb) and perfluorochemicals are in advanced phase III clinical trials and conjugated haemoglobins in phase II clinical trial. New recombinant human haemoglobin with no vasoactivity is being developed. A soluble macromolecule of PolyHb-catalase-superoxide dismutase is being studied as an oxygen carrier with antioxidant properties. New artificial red blood cells that are more like RBC are being developed. One is based on haemoglobin lipid vesicles. A more recent one is based on nano-dimension artificial red blood cells containing haemoglobin and RBC enzymes with membrane formed from composite copolymer of polyethylene glycol-polylactic acid. Their circulation time is double that of PolyHb.