Superoxide dismutase targets NO from GSNO to Cysbeta93 of oxyhemoglobin in concentrated but not dilute solutions of the protein

The role of hemoglobin (Hb) in transmitting the vasodilatory property of NO throughout the vascular system is of much current interest. NO exchange between Hb and low-molecular-weight nitrosothiols such as S-nitrosoglutathione (GSNO) has been speculated and reported in vitro. Previously, we reported that NO delivery from GSNO to Cysbeta93 of human oxyHb is prevented in the presence of the Cu chelators, neocuproine, and DTPA.(1) In the present work, 5 mM solutions of commercial human Hb were found by ICP-MS to contain approximately 20 microM Cu and Zn, suggesting the presence of Cu,Zn-superoxide dismutase (CuZnSOD), which was confirmed by Western blotting. SOD activity measurements were consistent with the presence of approximately 20 microM CuZnSOD monomer in 5 mM Hb solutions, which is the physiological concentrations of these proteins in the red blood cell. Incubation of 3.75 mM oxyHb (15 mM heme; 7.5 mM Cysbeta93) with 3.75 or 7.5 mM GSNO gave rise to 50% or 100% S-nitrosation, respectively, of Cysbeta93 as monitored by FTIR nu(SH) absorption, whereas excess GSNO over Cysbeta93 converted oxyHb to metHb due to the reaction, oxyHb + NO<==>metHb + NO(3)(-). Removal of CuZnSOD by anion-exchange chromatography yielded an oxyHb sample that was unreactive toward GSNO, and replacement with bovine CuZnSOD restored reactivity. Addition of 1 microM GSNO (Cysbeta93/GSNO = 1) to solutions diluted 10(4)-fold from physiological concentrations of oxyHb and CuZnSOD resulted largely in metHb formation. Thus, this work reports the following key findings: CuZnSOD is an efficient catalyst of NO transfer between GSNO and Cysbeta93 of oxyHb; metHb is not detected in oxyHb/GSNO incubates containing close to the physiological concentration (5 mM) of Hb and CuZnSOD when the Cysbeta93/GSNO molar ratio is 0.5 to 1.0, but metHb is detected when the total Hb concentration is low micromolar. These results suggest that erythrocyte CuZnSOD may play a critical role in preserving the biological activity of NO by targeting it from GSNO to Cysbeta93 of oxyHb rather than to its oxyheme.     

Modulation of oxygen-carrying capacity of artificial red cells

The oxygen-carrying capacity of artificial red cells (ARC), which were prepared by encapsulating hemoglobin (Hb) into polymerized lipid vesicles, has been investigated in detail. It was found that the effects of inositol hexaphosphate (IHP) on the oxygen affinity of stromafree Hb and ARC are quite different. By co-encapsulating IHP at a IHP:Hb molar ratio of 1.0, the oxygen affinity of the encapsulated Hb in ARC was decreased to such an extent that P₅₀ was about 60–65 mmHg, and only about 70–80% of the encapsulated Hb could be oxygenated at an oxygen partial pressure (Po₂) of about 100 mmHg. As pyridoxal 5-phosphate (PLP) and chloride ions were coencapsulated instead of IHP, P₅₀ and the Hill coefficient of the obtained ARC were adjusted to 25–30 mmHg and 2.5–2.8 respectively. The oxygen-transporting efficiency of PLP-modulated ARC was similar to or better than that of red blood cells.     

Encapsulation of Hb into unsaturated lipid vesicles and γ-ray polymerization

A carbonyl hemoglobin (HbCO) solution was stirred with a mixed powder of polymerizable 1,2-bis(2,4-octadecadienoyl)-sn-glycero-3-phosphocholine (DODPC), cholesterol and stearic acid (7/7/2 by mol). The mixture was extruded through polycarbonate membrane filters (final pore size = 0.2 μm Ø). The average diameter of the resulting vesicles was 203 ± 39 nm. The [Hb]/[Lipid] ratio (the weight ratio of Hb in vesicle to lipid) increased with the Hb concentration, and decreased with the NaCl concentration. A maximum [Hb]/[lipid] ratio was observed at pH 6.9, which was the same as the isoelectric point of Hb. The vesicles were stabilized by γ-irradiation (⁶⁰Co) because the bilayer lipids bound each other to yield polyphospholipids. Denaturation of Hb by γ-irradiation was not detected. These polyphospholipid vesicles encapsulating Hb were stable even against the freeze–thaw cycles and the freeze-drying procedure.     

Low‐Fouling Electrosprayed Hemoglobin Nanoparticles with Antioxidant Protection as Promising Oxygen Carriers

Despite all the attempts to create advanced hemoglobin (Hb)‐based oxygen carriers (HBOCs) employing an encapsulation platform, major challenges including attaining a high Hb loading and long circulation times still need to be overcome. Herein, the fabrication, for the first time, of nanoparticles fully made of Hb (Hb‐NPs) employing the electrospray technique is reported. The Hb‐NPs are then coated by antioxidant and self‐polymerized poly(dopamine) (PDA) to minimize the conversion of Hb into nonfunctional methemoglobin (metHb). The PDA shell is further functionalized with poly(ethylene glycol) (PEG) to achieve stealth properties. The results demonstrate that the as‐prepared Hb‐NPs are hemo‐ and biocompatible while offering antioxidant protection and decreasing the formation of metHb. Additionally, decoration with PEG results in decreased protein adsorption onto the Hb‐NPs surface, suggesting a prolonged retention time within the body. Finally, the Hb‐NPs also preserve the reversible oxygen‐binding and releasing properties of Hb. All in all, within this study, a novel HBOCs with high Hb content is fabricated and its potential as an artificial blood substitute is evaluated.     

Formation of nitrosothiols by the reaction of different forms of hemoglobin with (tetranitrosyl)bis(pyrimidin-2-ylthio)diiron

The reaction of hemoglobin (Hb), oxyhemoglobin (HbO₂), and methemoglobin (metHb) with the tetranitrosyl iron complex of the fu₂-S type [Fe₂(SC₄H₃N₂)₂(NO)₄] (1) was studied. The reaction results in the nitrosylation of the free SH group of 93-β-cysteine in these forms of hemoglobin. The change in the Hb, HbO₂, and metHb concentrations was monitored by spectrophotometry, recording the difference absorption spectra of the experimental systems with these forms of hemoglobin and the buffer containing complex 1 in the same concentration. The absorption spectra were processed to obtain the components using the MATHCAD method. The nitrosothiol concentration was determined by the Saville reaction. In a protic medium containing 3.3% DMSO, complex 1 spontaneously generates NO due to hydrolysis (k = 3.7 · 10^-4 s^-1). Oxyhemoglobin reacts with evolved NO to form metHb. Complex 1 reduces metHb with a high rate to yield Hb (k = 6.7 · 10^-3 s^-1) followed by the formation of HbNO (k = 6.5 · 10^-3 s^-1). Oxidized complex 1 yields NO with a higher rate than the starting complex does. The reaction of HbO₂ and metHb (0.02 mmo1 L^-1) with complex 1 affords nitrosothiols in micromolar concentration during 5 min, and no nitrosothiol is formed in the case of Hb.     

Stable preservation of hemoglobin vesicles as a blood substitute

Long‐term preservation of hemoglobin (Hb) vesicles, the so‐called artificial red cell (ARC), in dry powder was studied. Carbonylhemoglobin (COHb) was encapsulated in the vesicle of 1,2‐bis(2,4‐octadecadienoyl)‐sn‐glycero‐3‐phosphocholine (DODPC) and the polymerizable membrane components were polymerized by γ‐ray irradiation. The obtained ARC suspension was then freeze‐dried in the presence of sucrose. The factors influencing the shelf‐life of the freeze‐dried ARC, such as sucrose concentration, moisture and storage temperature, were elucidated. After storage in the dry state for more than one year, the oxygen‐carrying capacity was recovered by rehydration of the freeze‐dried ARC with distilled water and substitution of the carbon monoxide ligand with oxygen. Copyright © 1999 John Wiley & Sons, Ltd.     

Evaluation of human hemoglobin vesicle as an oxygen carrier: recovery from hemorrhagic shock in rabbits

The Neo Red Cell (NRC), an artificial oxygen carrier, has been developed and evaluated for its oxygen‐transporting capacity, hemodynamics and safety in experimental animals. Stroma‐free hemoglobin prepared from outdated human red blood cells was encapsulated in liposome capsules together with inositol hexaphosphate as an allosteric effector, coenzyme and substrates for reducing metHb formation. The NRCs were coated with polyethylene glycol bounded to phosphatidylethanolamine (PEG‐PE) as a surface modifier to prevent aggregation of NRC in plasma and to prolong the circulation time in the blood stream. The formation of metHb formation was reduced from 1%/hr to 0.5%/hr by incorporating a metHb reduction system into NRC. The efficacy of the NRC in tissue oxygenation and recovery from anemia was examined in rabbits which had been made severely anemic by drawing 85% of their blood and replacing it with NRC. All the animals infused with NRC recovered to pre‐anemic conditions within 6–8 hr and survived until they were sacrificed, 6 months after the exchange transfusion. Our observations suggest that NRCs constitute an efficient oxygen carrier not having serious adverse effects and associated with low metHb formation in vivo and during storage. Copyright © 2000 John Wiley & Sons, Ltd.     

The Reactivity of Polymersome Encapsulated Hemoglobin with Physiologically Important Gaseous Ligands: Oxygen, Carbon Monoxide and Nitric Oxide

Two distinct preparations of amphiphilic diblock copolymer vesicles (i.e. polymersomes), composed of (poly(ethylene oxide)-poly(butadiene)) (PEO-PBD), with molecular weights of 1.8 kDa and 10.4 kDa, offering different hydrophobic membrane thicknesses, were used to encapsulate the oxygen (O(2)) storage and transport protein hemoglobin (Hb) for possible application as a red blood cell (RBC) substitute. Key biophysical properties as well as the kinetics of polymersome encapsulated Hb (PEH) interaction with physiologically important gaseous ligands (O(2), carbon monoxide and nitric oxide) were measured as a function of the hydrophobic membrane thickness of the PEH particle. Taken together, the results of this work show that PEHs exhibit biophysical properties and retarded ligand binding/release kinetics (compared to cell-free Hb), which are similar to the behavior of RBCs. Therefore, PEHs have the potential to serve as safe and efficacious RBC substitutes for use in transfusion medicine.     

Characteristics and function of human hemoglobin vesicles as an oxygen carrier

A liposome‐encapsulated human hemoglobin (Neo Red Cell, (NRC) has been developed and evaluated as an artificial oxygen carrier. The NRC is a liposome‐encapsulated highly concentrated (>45%) stroma‐free human hemoglobin with inositol hexaphosphate (IHP as an allosteric effector), a coenzyme and substrates for reducing methemoglobin (metHb). The NRC's surface was coated with polyethylene glycol to prevent aggregation in plasma and to prolong their retention time in the blood stream. The oxygen binding behavior of the NRC in vitro was investigated and it was found that it effectively transports oxygen in vivo as an oxygen carrier. The oxygen binding behavior and kinetics were studied by the stopped‐flow method and the oxygen binding curve of the NRC was determined. The oxygen binding speed and binding coefficient (K_on) of NRC, washed human red blood cells (WRBC) and stroma‐free human hemoglobin (SFHb) were measured by stopped‐flow method. The oxygen binding speed of SFHb was the highest, while that of RBC was the lowest and that of NRC was intermediate. The oxygen binding of NRC ended within 60 msec when deoxy‐NRC was mixed with oxygen. The K_on of NRC was 2.9 × 10⁵, 10 times faster than that of RBC. The oxygen binding curve and P₅₀O₂ of NRC that contained various IHP concentrations were measured. The oxygen‐binding curve of the NRC sequentially shifted to the right as the IHP content was increased. Exchange transfusion of 70% was carried out for rats with NRC containing various concentrations of IHP and of Hb, and investigated the optimum concentration of NRC in vivo. The lactate value after exchange transfusion was three times higher than before exchange transfusion, when rats were subjected to exchange transfused with NRC that did not contain IHP. But the increase of lactate was suppressed when rats were transfused with NRC that contained IHP. When the Hb concentration of NRC was 5 and 6%, exchange transfused rats recovered to normality just like rats transfused with RBC. Copyright © 2000 John Wiley & Sons, Ltd.     

Encapsulation of Hemoglobin Using Condensation Reaction of Butylcyanoacetate with Formaldehyde

Summary: Hemoglobin (Hb)-encapsulating particles have been prepared in a single step by condensation reaction of butylcyanoacetate (BCNA) with formaldehyde (FA) in Hb aqueous solution. Dimethylamine was used as a base catalyst and then the reaction was performed in 0.1 M HEPES buffer (pH 7.4) at room temperature. Particle composition analysis by extraction indicated that the particles consisted of PBCNA, HEPES and Hb. The content of Hb loaded into the particles monotonously increased with increasing initial Hb concentrations. Almost all Hb molecules in aqueous solution could be recovered as particles. In addition, the encapsulated Hb maintained the oxygen-carrying capacity similar to native Hb. These results indicate that condensation reaction of BCNA with FA can provide the assembly of Hb molecules in aqueous solution.     

Attachment and phospholipase A2-induced lysis of phospholipid bilayer vesicles to plasma-polymerized maleic anhydride/SiO2 multilayers

This article describes a method by which intact vesicles can be chemically attached to hydrolyzed maleic anhydride films covalently bound to plasma-polymerized SiO2 on Au substrates. Surface plasmon field-enhanced fluorescence spectroscopy (SPFS) combined with surface plasmon resonance spectroscopy (SPR) was used to monitor the activation of plasma-deposited maleic anhydride (pp-MA) film with EDC/NHS and the subsequent coupling of lipid vesicles. The vesicles were formed from a mixture of phosphatidylcholine and phosphatidylethanolamine lipids, with a water-soluble fluorophore encapsulated within. Vesicle attachment was measured in real time on plasma films formed under different pulse conditions (plasma duty cycle). Optimum vesicle attachment was observed on the pp-MA films containing the highest density of maleic anhydride groups. Phospholipase A2 was used to lyse the surface-bound vesicles and to release the encapsulated fluorophore.     

Small‐Angle Neutron Scattering (SANS) Study of Magneto‐Vesicles

Small‐angle neutron scattering from magneto‐vesicles (MVs) prepared by extrusion was studied. Contrast variation allowed the determination of structure and sizes of the vesicles and the encapsulated magnetic nanoparticles, respectively. The results from MVs synthesized with a 0.3% volume fraction of citrate‐coated magnetic nanoparticles are compared to those of similarly prepared vesicles of the neutral lipid 1,2‐Dioleoyl‐sn‐Glycero‐3‐Phosphocholine (DOPC) (without magnetic particles), and magnetic particles not encapsulated in vesicles. It is observed that the bilayers of the as‐prepared MVs, and the encapsulated nanoparticles retain their structural properties, highlighting the suitability of the MVs for applications.     

Quantification of changes in oxygen release from red blood cells as a function of age based on magnetic susceptibility measurements

This study extends the in vitro understanding of the RBC storage lesion by serially analyzing the RBC's magneophoretic mobility, a property dependent on the content and oxygenation or oxidation state of hemoglobin (Hb) iron, during storage. Four prestorage leukoreduced, AS-5 preserved RBC units were stored between 1 and 6 °C for 42 days. Weekly starting on storage day 7, each unit was sampled, divided into 3 aliquots, each subjected to different reactions: one aliquot was exposed to room air to produce oxyhemoglobin (oxyHb), another aliquot was mixed with sodium nitrite to produce methemoglobin (metHb), while the third aliquot was desaturated of oxygen (deoxyhemoglobin, deoxyHb) using nitrogen gas. These aliquots were placed into a cell tracking velocimetry (CTV) apparatus which measured both the settling velocity (u(s)) of the RBCs as well as their magnetically induced velocity (u(m)). The u(m)/u(s) ratio depends on the oxygenation state of the hemoglobin and the quantity of iron within the RBC. The RBC density was measured by percoll centrifugation. There was a significant reduction in the u(m)/u(s) ratio for the deoxyHb RBC aliquot as storage time elapsed, with a smaller but still significant reduction in the u(m)/u(s) ratio for the metHb aliquot. The average RBC density decreased very slightly during storage, as determined by the percoll centrifugation technique, although the average settling velocity (another measure of cell density) seemed to fluctuate during storage. The decrease in magnetophoretic mobility of the deoxyHb portion is explicable either by Hb's increased affinity for oxygen during storage, or else a loss of iron from the cells.     

A novel composite: layered double hydroxides encapsulated in vesicles

We report a novel composite: layered double hydroxides (LDHs) encapsulated in vesicles. It was found that positively charged Mg3Al-LDH nanoparticles can induce the spontaneous formation of vesicles in a mixture of a zwitterionic surfactant, dodecyl betaine (C12BE), and an anionic surfactant, sodium bis(2-ethylhexyl) sulfosuccinate (AOT), and importantly, we obtain simultaneously a novel composite of Mg3Al-LDH encapsulated in vesicles. The obtained composite is very stable and expected to be potentially used in drug delivery and gene therapy.     

Controlled microfluidic encapsulation of cells, proteins, and microbeads in lipid vesicles

Cells have been encapsulated inside lipid vesicles by using a new microfluidic lipid vesicle formulation technique. Lipid vesicles are formulated within minutes without using toxic lipid solvents. The encapsulation efficiency inside the vesicles is controlled by the microfluidic flows. Green fluorescent proteins (GFP), carcinoma cells, and bead encapsulated vesicles have mean diameters of 27.2 mum, 62.4 mum, and 55.9 mum, respectively. The variations of vesicle sizes are approximately 20% for the GFP and cell encapsulated vesicles and approximately 10% for the bead encapsulated vesicles.     

Artificial red cells with crosslinked hemoglobin membranes

Artificial cells containing concentrated hemoglobin (Hb) solution were prepared by interfacial polymerization of Hb with glutaraldehyde (GA) in liquid membrane capsules (LMC). A solution containing 30% of Hb was emulsified in mineral oil as red cell-size microdroplets, and this emulsion was dispersed in an aqueous phase containing glutaraldehyde to form LMC. The LMC were semipermeable templates that held the microdroplets of Hb in suspension while GA diffused through the oil to the microdroplet surfaces. The GA crosslinked Hb at the surface of each microdroplet to form an artificial red-cell membrane encapsulating Hb solution. A water-soluble surfactant was used to eject the cells from the LMC and suspend them in saline. Several surfactants were evaluated. Cell size was controlled by agitation speed during preparation of the original emulsion. Cells of 2.52 = ±1.69 μm were prepared. The encapsulated Hb retained capacity to bind and release O₂. The cells had aP ₅₀ of 8.9 torr (1200 Pa) and a capacity of 0.55 cc O₂/g of total Hb, indicating that the crosslinked portion of the Hb did not contribute to O₂ transport.     

Interactions of Hemoglobin with Vesicles and Tubes Formed from Mixtures of Histidine-Derived Bolaamphiphile and Conventional Surfactants

The interactions between protein and surfactant aggregates have been the subject of intensive studies due to their potential applications in biological systems. Here we report the interactions of hemoglobin (Hb) with vesicles and tube-like aggregates formed from mixtures of a histidine-derived bolaamphiphile and a cconventional surfactant dodecyltrimethylammonium bromide (DTAB). This study was performed using a combination of UV–vis spectroscopy, steady and synchronous fluorescence spectroscopy, circular dichroism, and microcalorimetry measurements. The secondary structure of the protein is disturbed, and then the partially unfolded protein is capable of penetrating the vesicles and tube-like aggregates, this is mainly the result of hydrogen bonding and hydrophobic interactions between Hb and the H₂D/DTAB aggregates. The polar portion of the unfolded protein chains is near to the polar head of the amphiphile in the aggregate’s membrane. Hb is converted to hemichrome in the vesicles, and the heme monomer is solubilized in tube-like aggregates after escaping from the hydrophobic cavity of Hb.     

Supramolecular core-shell nanosilica@liposome nanocapsules for drug delivery

The fabrication of core-shell structural nanosilica@liposome nanocapsules as a drug delivery vehicle is reported. SiO(2) nanoparticles are encapsulated within liposomes by a W/O/W emulsion approach to form supramolecular assemblies with a core of colloidal particles enveloped by a lipid bilayer shell. A nanosilica core provides charge compensation and architectural support for the lipid bilayer, which significantly improves their physical stability. A preliminary application of these core-shell nanocapsules for hemoglobin (Hb) delivery is described. Through the H-bonding interaction between the hydroxyl groups on nanosilicas and the amino nitrogens of Hb, Hb-SiO(2) nanocomplexes in which the saturated adsorption amount of Hb on SiO(2) is 0.47 g g(-1) are coated with lipids to generate core-shell Hb-SiO(2)@liposome nanocapsules with mean diameters of 60-500 nm and Hb encapsulation efficiency of 48.4-87.9%. Hb-SiO(2)@liposome supramolecular nanovehicles create a mode of delivery that stabilizes the encapsulated Hb and achieves long-lasting release, thereby improving the efficacy of the drug. Compared with liposome-encapsulated Hb and Hb-loaded SiO(2) particles, such core-shell nanovehicles show substantially enhanced release performance of Hb in vitro. This finding opens up a new window of liposome-based formulations as drug delivery nanovehicles for widespread pharmaceutical applications.     

Hollow giant lipid vesicles prepared by coaxially electrospraying solutions of phospholipid and degradable polyelectrolyte

Hollow giant lipid vesicles were prepared in a single step by coaxially electrospraying separate solutions of phospholipid and a degradable polyelectrolyte. We synthesized a hydrolytically degradable cationic polyelectrolyte, poly(β-amino esters) (PBAE), and employed it as a degradable microgel template to form giant vesicles. Droplets of the phospholipid solution and the degradable polyelectrolyte solution were electrosprayed from coaxial double needles into a receiving solution. The PBAE formed a microgel by crosslinking with multivalent anions in the receiving solution, and the phospholipids formed bilayers on the microgel. Hollow giant lipid vesicles were successfully obtained and the mean diameters were 7.6 μm (C.V. 58 %). Substrates (calcein, dextran, and polymeric microparticles) were successfully encapsulated in the giant vesicles. Microscopic observations of microparticle mobility inside a giant vesicle indicated the fluidity of its aqueous interior. Investigations using fluorescently labeled PBAE also suggested the degradation of PBAE, and the release of fluorescent PBAE fragments from the encapsulated microgel, to form hollow giant lipid vesicles.     

Melting characteristics of fat present on the surface of industrial spray-dried dairy powders

The melting characteristics of the fat present on the surface (surface free-fat) of two industrial spray-dried dairy powders (cream powder and whole milk powder) were investigated in comparison with those of other milk fat fractions present in the powder, such as free-fat from the interior of the powder particle (inner free-fat) and encapsulated fat. The melting characteristics of the milk fat fractions were studied by fatty acid composition, melting profile and solid fat content profile. The results indicated that all milk fat fractions including surface free-fat contained various triglycerides with melting points ranging from -40 to +40 degrees C. However, some fractionation was observed among the different milk fat fractions. The free-fat fractions (surface free-fat and inner free-fat) had a greater proportion of high-melting triglyceride species than the encapsulated fat. Furthermore, the high-melting triglyceride species present in the free-fat fractions were slightly accumulated at the surface of powder. This phenomenon was observed in both cream powder and whole milk powder and its effect on wetting time was established. This indicates that manipulation of the surface fat content during drying operation may hold the key to functionality improvement.