Future prospects for artificial blood

Progress toward synthetic cells

The complexity of even the simplest known life forms makes efforts to synthesize living cells from inanimate components seem like a daunting task. However, recent progress toward the creation of synthetic cells, ranging from simple protocells to artificial cells approaching the complexity of bacteria, suggests that the synthesis of life is now a realistic goal. Protocell research, fueled by advances in the biophysics of primitive membranes and the chemistry of nucleic acid replication, is providing new insights into the origin of cellular life. Parallel efforts to construct more complex artificial cells, incorporating translational machinery and protein enzymes, are providing information about the requirements for protein-based life. We discuss recent advances and remaining challenges in the synthesis of artificial cells, the possibility of creating new forms of life distinct from existing biology, and the promise of this research for gaining a deeper understanding of the nature of living systems.

Receptor mediated binding of avidin to polymer covered liposomes

Fluoresence technique involving a receptor-mediated fluorescence increase of bodipy-labeled avidin upon binding to biotinylated lipids has been used to investigate the steric barrier effect of submicellar concentrations of poly(ethylene glycol)-phospholipids (PE-PEG(2000) and PE-PEG(5000)) incorporated into pure DPPC liposomes as well as PE-PEG(5000) incorporated into DPPC liposomes containing 20 mol% cholesterol. It is found that the incorporation of PE-PEG lipopolymers into DPPC lipid bilayers lowers the receptor-mediated adhesion of avidin to the biotinylated liposomes. The most pronounced screening effect is observed at surface densities corresponding to the mushroom conformation of the polymer. Furthermore, the results show that the steric baric effect induced by the surface-grafted polymers becomes stronger when the length of the polymer chain increases. In addition it is found that cholesterol improves the barrier effect of PE-PEG(5000) at low lipopolymer concentrations while no effect is observed at higher concentrations. The results reveal that both the surface density and the polymer length of the PE-PEG lipopolymers play a major role for the accessibility of avidin to biotin surface receptors. However, none of the lipopolymers were capable of completely preventing avidin from reaching the surface bound ligands. Cholesterol only affected the barrier effect at lipopolymer concentrations below the mushroom to brush transition. Consequently, from a steric stabilization viewpoint there is no rationale for incorporating cholesterol into liposomes when the PE-PEG lipopolymer concentration exceeds the mushroom to brush transition. The results presented in this study are of importance in relation to a deeper understanding of the interaction of liposome degrading enzymes and proteins with polymer covered liposomes as well as for the receptor-based targeting and interaction of liposomes with cell surface receptors.

Microencapsulated Saccharomyces cerevisiae column bioreactor for potential use in renal failure uremia

A novel bioreactor containing viable APA microencapsulated yeast cells was designed. Rat plasma was used for perfusion. Yeast cell loading and perfusion flow rate were studied to maximize urea removal. An increase in column loading from 25% to 100%, increased urea removal from 5.67 ± 1.34% to 30.45 ± 0.48%. An increase in flow rate from low to high, increased urea removal from 30.46% to 40.4%. At 100% column loading and high flow rate, the creatinine and phosphate concentrations decreased by 22% and 10%, respectively, while ammonia concentrations increased by 58.9% (p < 0.05). Our in-vitro perfusion study demonstrates that microencapsulated yeast cells can remove urea efficiently.

Polymer/hemoglobin assemblies: biodegradable oxygen carriers for artificial red blood cells

In routine clinical procedures, blood transfusion is now suffering from the defects of the blood products, like cross-matching, short storage time and virus infection. Various blood substitutes have been designed by researchers through continual efforts. With recent progress in nanotechnology, new types of artificial red blood cells with cellular structure are available. This article aims to describe some artificial red blood cells which encapsulate or conjugate hemoglobin molecules through various approaches, especially the nanoscale self-assembly technique, to mitigate the adverse effects of free hemoglobin molecules. These types of artificial red blood cell systems, which make use of biodegradable polymers as matrix materials, show advantages over the traditional types.

Molecular Aspects of the High Oxygen Afinity of Non-Hypertensive Hexa Pegylated Hemoglobin, [(SP-PEG5K)6-Hb]

The development of hexaPEGylated Hb, (SP-PEG5K)(6)-Hb, using the newly designed thiolation-mediated maleimide chemistry based PEGylation, has validated the concept that engineering 'plasma volume expander' -like properties to Hb neutralizes its vasoactivity. The high O(2) affinity of hexaPEGylated Hb has been attributed to the two PEG-5K chains on its two Cys-93(beta) residues. In an attempt to map the influence of the additional four PEG-5K chains of HexaPEGylated Hb on the O(2) affinity, we have now investigated the influence of PEGylation of the surface amino groups alone on the subunit interface interactions and O(2) affinity of Hb using rHb(betaC93A). The molecular radius of PEGylated rHb(betaC93A) was slightly smaller than that of (SP-PEG5K)(6)-Hb, and the overall site-selectivity of PEGylation in the PEGylated rHb(betaC93A) at Lys-residues was comparable to that of (SP-PEG5K)(6)-Hb. Proton NMR studies have shown that the conjugation of the protein with PEG-5K does not have any significant influence on its subunit interface interactions. Surprisingly, the influence of PEGylation on the O(2) affinity and Bohr effect of HbA and rHb(betaC93A) is also nearly the same. Apparently, conjugation of PEG-chains to Lys residues of Hb by the thiolation mediated PEGylation induces unique changes in the structure of the hydration shell of Hb (layer of tightly bound water molecules), which, in turn, induces constraints in its R to T conformational transition to favor the more hydrated R-state.

CURRENT PERCEIVED RISKS OF TRANSFUSION IN THE UK AND RELEVANCE TO THE FUTURE ACCEPTANCE OF BLOOD SUBSTITUTES

Data has been gathered on the perception of risk associated with blood donation and transfusion (including the use of so-called blood substitutes) by UK general practitioners (GPs), anaesthetists, healthcare journalists and blood donors of both genders. A questionnaire survey was conducted from March-July 2000 involving (i) GPs (n = 88), (ii) anaesthetists (n = 143), (iii)journalists (n = 20), and (iv) blood donors (n = 250). Respondents rated (scale of 1-7) the general risk of blood transfusion and the risk of infection associated with blood transfusion and donation. Respondents were asked through free response questions to identify the risks they most associated with blood transfusion and the infections associated with blood transfusion and donation. They were also asked to indicate their preference for their own blood, compared to donor blood or a blood substitute and to make a choice between donated blood or a blood substitute. The percentage of respondents who preferred to receive their own blood, compared to donor blood or a suitable substitute, was 73-94%. When required to choose between donor blood or a blood substitute, there were significant (P < 0.05) differences between sample groups: anaesthetists and GPs preferred to receive a blood substitute (52-59%), whereas blood donors and journalists preferred donated blood (74-93%). These findings have clear implications for the future development and implementation of modern transfusion options, including the use and acceptability of blood substitutes as alternatives to donor blood.

Long-circulation of hemoglobin-loaded polymeric nanoparticles as oxygen carriers with modulated surface charges

The aim of this study was to investigate the effects of the surface charges on the in vitro macrophage cellular uptake and in vivo blood clearance and biodistribution of the hemoglobin-loaded polymeric nanoparticles (HbPNPs). The surface charges of the HbPNPs fabricated from mPEG-PLA-mPEG were modulated with cationized cetyltrimethylammonium bromide (CTAB) and anionized sodium dodecyl sulphate (SDS), respectively. In vitro macrophage cellular uptake and in vivo biodistribution of the coumarin 6-labeled HbPNPs with different electric charges were investigated, and the half-lives in the circulation were pharmacokinetically analyzed. The particle sizes of the HbPNPs were all below 200 nm with a narrow size distribution and high encapsulation efficiency (>84%). And the zeta-potentials of the untreated, cationized and anionized HbPNPs in phosphate buffered sodium chloride solution (PBS) were -12.3, +3.28 and -25.4 mV, respectively. The HbPNPs did not occur significant aggregation or sedimentation, even after 5 days. Compared with the untreated HbPNPs, 1-fold decrease/increase of the uptake percentage associated with the cationized/anionized HbPNPs was observed. In vivo experiment demonstrated that the calculated half-life of the cationized HbPNPs was 10.991 h, 8-fold longer than that of the untreated HbPNPs (1.198 h). But the anionized HbPNPs displayed opposite effect. Furthermore, the cationized HbPNPs mainly accumulated in the liver, lung and spleen after 48 h injection. MTT results showed that the HbPNPs with different surface charges all exhibited slight toxicity. These results demonstrated that the CTAB-modulated HbPNPs with low positive charge and suitable size have a promising potential as a long-circulating oxygen carrier system with desirable biocompatibility and biofunctionality.

A solid-phase adsorption method for PEGylation of human serum albumin and staphylokinase: preparation, purification and biochemical characterization

A solid-phase adsorption method was developed to circumvent the disadvantage of the conventional liquid-phase PEGylation, i.e. the heterogeneity of the PEGylated products. The model proteins, human serum albumin (HSA) and staphylokinase (SAK), were adsorbed on the ion exchange chromatography media, followed by PEGylation with succinimidyl carbonate (SC)-mPEG5K and salt elution. Since PEGylation with SC-PEG5K alters the positive charge of the proteins, Q-Sepharose Big Beads and DEAE Sepharose Fast Flow were used for adsorption of HSA and SAK, respectively. Size exclusion chromatography and SDS-PAGE studies demonstrated that solid-phase PEGylation of proteins generate monoPEGylated proteins with the yield of 35-47%. Circular dichroism and intrinsic fluorescence studies showed that solid-phase PEGylation led to little conformational change of the proteins. Solid-phase PEGylation resulted in 35% loss in the biological activity of SAK, which is lower than the liquid-phase PEGylation (70%).

Hemoglobin conjugated with a Band 3 N-terminus derived peptide as an oxygen carrier

A peptide composed of 9 amino acids, 7 residues from N-terminus of human erythrocytic Band 3 protein (AcMEELQDD) followed by cysteine and glutamic acids, was conjugated to hemoglobin (Hb) serving as an allosteric effector for oxygen release. The activated polyethylene glycol (PEG), maleimide-PEG-N-hydroxysuccinimidyl, was used to crosslink Hb with the peptide. The putative conjugation site on Hb for effective enhancement of oxygen release was characterized as Lys-beta95 by liquid chromatography-tandem mass spectrometry. In addition, the conjugated peptide causes a rightward shift of the oxygen dissociation curve as compared to that of its parent Hb when the degree of oxygen saturation is higher than 50%. Furthermore, this conjugated peptide remains effective on lowering Hb's oxygen affinity after Hb polymerization by another PEG crosslinker. The allosteric properties of the peptide-conjugated Hb may provide a new aspect of Hb-based oxygen carriers.

Transport advances in disposable bioreactors for liver tissue engineering

Acute liver failure (ALF) is a devastating diagnosis with an overall survival of approximately 60%. Liver transplantation is the therapy of choice for ALF patients but is limited by the scarce availability of donor organs. The prognosis of ALF patients may improve if essential liver functions are restored during liver failure by means of auxiliary methods because liver tissue has the capability to regenerate and heal. Bioartificial liver (BAL) approaches use liver tissue or cells to provide ALF patients with liver-specific metabolism and synthesis products necessary to relieve some of the symptoms and to promote liver tissue regeneration. The most promising BAL treatments are based on the culture of tissue engineered (TE) liver constructs, with mature liver cells or cells that may differentiate into hepatocytes to perform liver-specific functions, in disposable continuous-flow bioreactors. In fact, adult hepatocytes perform all essential liver functions. Clinical evaluations of the proposed BALs show that they are safe but have not clearly proven the efficacy of treatment as compared to standard supportive treatments. Ambiguous clinical results, the time loss of cellular activity during treatment, and the presence of a necrotic core in the cell compartment of many bioreactors suggest that improvement of transport of nutrients, and metabolic wastes and products to or from the cells in the bioreactor is critical for the development of therapeutically effective BALs. In this chapter, advanced strategies that have been proposed over to improve mass transport in the bioreactors at the core of a BAL for the treatment of ALF patients are reviewed.

Autoxidation of the site-specifically PEGylated hemoglobins: role of the PEG chains and the sites of PEGylation in the autoxidation

The PEGylated hemoglobin (Hb) has been evaluated as a potential blood substitute. In an attempt to understand the autoxidation of the PEGylated Hb, we have studied the autoxidation of the PEGylated Hb site-specifically modified at Cys-93(beta) or at Val-1(beta). PEGylation of Hb at Cys-93(beta) perturbed the heme environment and increased the autoxidation rate of Hb, which is at a higher level than that caused by PEGylation at Val-1(beta). The perturbation of the heme environment of Hb is attributed to the maleimide modification at Cys-93(beta) and not due to conjugation of the PEG chains. However, the PEG chains enhance the autoxidation and the H 2O 2 mediated oxidation of Hb. Accordingly, the PEG chains are assumed to increase the water molecules in the hydration layer of Hb and enhance the autoxidation by promoting the nucleophilic attack of heme. The autoxidation rate of the PEGylated Hb does not show an inverse correlation with the oxygen affinity. The H 2O 2 mediated structural loss and the heme loss of Hb are increased by maleimide modification at Cys-93(beta) and further decreased by conjugation of the PEG chains. The autoxidation of the PEGylated Hbs is attenuated significantly in the plasma, possibly due to the presence of the antioxidant species in the plasma. This result is consistent with the recent suggestion that there is no direct correlation between the in vitro and in vivo autoxidation of the PEGylated Hb. Therefore, the pattern of PEGylation can be manipulated for the design of the PEGylated Hb with minimal autoxidation.

Cellular-scale hydrodynamics

Microfluidic tools are providing many new insights into the chemical, physical and physicochemical responses of cells. Both suspension-level and single-cell measurements have been studied. We review our studies of these kinds of problems for red blood cells with particular focus on the shapes of individual cells in confined geometries, the development and use of a 'differential manometer' for evaluating the mechanical response of individual cells or other objects flowing in confined geometries, and the cross-streamline drift of cells that pass through a constriction. In particular, we show how fluid mechanical effects on suspended cells can be studied systematically in small devices, and how these features can be exploited to develop methods for characterizing physicochemical responses and possibly for the diagnosis of cellular-scale changes to environmental factors.

Polyethylene glycol improves conjugation of bovine hemoglobin and human serum albumin in a controlled ratio

Direct conjugation of bovine hemoglobin (Hb) and human serum albumin (HSA) with glutaraldehyde would result in a complex mixture of dimers Hb-Hb, Hb-HSA, HSA-HSA and other oligomers. To obtain a high yield of target Hb-HSA, modulation of the reaction environment was carried out. It was found that polyethylene glycol (PEG), a hydrophilic polymer, could improve the yield of Hb-HSA conjugate. The degree of improvement depended on the molecular weight and concentration of PEG. Under optimum condition of 9% (w/v) of PEG 4000, the reaction proceeded in a controlled mode with conversion yield of starting proteins to Hb-HSA increasing from 6% to 30%. The purity was about 88% of the total conjugates. Furthermore, the impurities were mainly tetrameric molecules of two Hb-HSA conjugates. The improvement could be attributed to the "micro-compartment" created by addition of polyethylene glycol, which brings HSA and Hb close together, thus increasing the chance of conjugation between the two molecules.

Stroma-free hemoglobin from bovine blood

Isolation and purification of bovine hemoglobin (HbBv) was carried out after reaction of whole blood with carbon monoxide. Washing/centrifugation steps were used to eliminate leukocytes, platelets, and plasma proteins. Hypotonic media and ultrasound radiation were used to lyse red blood cells. Lyse by ultrasound was shown to lead to solutions at the highest concentrations in HbBv, and the least concentrations in major phospholipids contaminants. Additional purification procedures were performed to remove membrane proteins and phospholipids. In the first case, proteins were denatured by thermal treatment, and filtered. To eliminate phospholipids, liquid chromatography was used with strong anion exchangers. Purity of HbBv was evaluated by normal phase high performance liquid chromatography (HPLC), electrophoresis, and size-exclusion HPLC.

Non-hypertensive tetraPEGylated canine haemoglobin: correlation between PEGylation, O2 affinity and tissue oxygenation

TetraPEGylated canine Hb, [SP (succinimidophenyl)-PEG5K]4-canine-Hb, with PEGylation at its four reactive cysteine residues (a111 and b93) has been prepared and characterized. The hydrodynamic volume and the molecular radius of (SP-PEG5K)4-canine-Hb are intermediate to those of di- and hexaPEGylated human Hb as expected. However, the COP (colloidal osmotic pressure) of tetraPEGylated canine Hb is closer to that of hexaPEGylated human Hb than to that of diPEGylated human Hb. The O2 affinity of tetraPEGylated canine Hb is higher than that of canine Hb and comparable with that of hexaPEGylated Hb. The O2 affinity of tetraPEGylated canine Hb is not responsive to the presence of DPG (diphosphoglycerate) or chloride, but it retains almost full response to L-35, an allosteric effector that interacts at the aa-end of the central cavity. The tetraPEGylated canine Hb is vasoinactive in hamster in 10% top load infusion studies. It is also essentially non-hypertensive in an extreme exchange haemodilution protocol in hamster just as di- and hexaPEGylated human Hb. The O2 delivery by tetraPEGylated canine Hb is comparable with that of hexaPEGylated Hb but not as efficient as diPEGylated Hb. These results demonstrate that PEGylation-induced solution properties of PEG [poly(ethylene glycol)]-Hb conjugates are dictated by the level and chemistry of PEGylation and the interplay of these plays a critical role in tissue oxygenation. The studies imply the need to establish the right level (and/or pattern) of PEGylation and O2 affinity of Hb-PEG adducts in designing O2-carrying plasma volume expanders, and this remains the primary challenge in the design of PEGylated Hb as blood substitutes.

Influence of intramolecular cross-links on the molecular, structural and functional properties of PEGylated haemoglobin

The influence of intramolecular cross-links on the molecular, structural and functional properties of PEGylated {PEG [poly(ethylene glycol)]-conjugated} haemoglobin has been investigated. The sites and the extent of PEGylation of haemoglobin by reductive alkylation are not influenced by the presence of an alphaalpha-fumaryl cross-link at Lys-99(alpha). The propylated hexaPEGylated cross-linked haemoglobin, (propyl-PEG5K)(6)-alphaalpha-Hb, exhibits a larger molecular radius and lower colloidal osmotic pressure than propylated hexaPEGylated non-cross-linked haemoglobin, (propyl-PEG5K)(6)-Hb. Perturbation of the haem microenvironment and the alpha1beta2 interface by PEGylation of haemoglobin is reduced by intramolecular cross-linking. Sedimentation velocity analysis established that PEGylation destabilizes the tetrameric structure of haemoglobin. (Propyl-PEG5K)(6)-Hb and (propyl-PEG5K)(6)-alphaalpha-Hb sediment as stable dimeric and tetrameric molecules, respectively. The betabeta-succinimidophenyl PEG-2000 cross-link at Cys-93(beta) outside the central cavity also influences the molecular properties of haemoglobin, comparable to that by the alphaalpha-fumaryl cross-link within the central cavity. However, the influence of the two cross-links on the oxygen affinity of PEGylated haemoglobin are very distinct, indicating that the high oxygen affinity of PEGylated haemoglobin is not a direct consequence of the dissociation of the haemoglobin tetramers into dimers. alphaalpha-Fumaryl cross-linking is preferred to modulate both oxygen affinity and molecular properties of PEGylated haemoglobin, and cross-linking outside the central cavity could only modulate molecular properties of PEGylated haemoglobin. It is suggested that PEGylation induces a hydrodynamic drag on haemoglobin and this plays a role in the microcirculatory properties of PEGylated haemoglobin.

Extension Arm Facilitated PEGylation of Hemoglobin: Correlation of the Properties with the Extent of PEGylation

Human hemoglobin (Hb) conjugated with six copies of PEG-5K is nonhypertensive. The hexaPEGylated Hb exhibits molecular size homogeneity in spite of the chemical heterogeneity with respect to the sites of conjugation (Manjula et al., 2005). In the present study, Hb conjugated with an average of 4, 6, 8 and 10 copies of PEG-5K chains have been generated using the extension arm facilitated PEGylation protocol. Except for the tetraPEGylated Hb, all the other products exhibit molecular size homogeneity. The molecular, colligative and functional properties of PEG-Hb conjugates have been correlated with the extent of PEGylation. The results imply that six copies of PEG-5K chains are accommodated on Hb without significant crowding on the molecular surface. As more copies of PEG-5K chains are conjugated to form octa and deca PEGylated Hb, the PEG-chains conjugated appear to undergo transition from a mushroom (compact) to a brush-like conformation (extended conformation) with a concomitant decrease in the propensity of the molecule to transition from oxy to deoxy conformation in the presence of allosteric effectors. The viscosity and the colloidal osmotic pressure of Hb increase with the number of the PEG-chains conjugated in an exponential fashion. The composition of the PEGylated Hb generated appears to be controlled by (i) high reactivity of thiol groups of the extension arms on Hb with maleimide-PEG, (ii) increase in the viscosity of the reaction mixture as the level of PEGylation increases and (iii) increased resistance induced by the PEG-shell of PEGylated Hb to accommodate more PEG-chains as the level of PEGylation increases. Potential implications of extent of PEGylation on the oxygen delivery by PEG-Hb conjugate in vivo have been discussed.

Influence of the chemistry of conjugation of poly(ethylene glycol) to Hb on the oxygen-binding and solution properties of the PEG-Hb conjugate

Our recent studies on PEG-Hb [poly(ethylene glycol)-Hb] conjugates generated by thiolation-mediated maleimide-chemistry based PEGylation demonstrated that the vasoactivity of the PEG-Hb conjugates is a function of the configuration of the PEG chains on the surface of the protein and is independent of the PEG/protein-mass ratio [Manjula, A. G. Tsai, Intaglietta, H.-C. Tsai, Ho, Smith, Perumalsamy, Kanika, Friedman and Acharya (2005) Protein J. 24, 133-146]. A Hb conjugated with six PEG5k chains (SP-PEG5k)6-Hb, was vasoinactive. In an attempt to understand whether the chemistry of conjugation of PEG to Hb has any influence on the modulation of its functional and solution properties, we have now generated a new hexaPEGylated-Hb, (propyl-PEG5k)6-Hb, by reductive alkylation chemistry. CD (circular dichroism) spectral measurements indicated that the overall secondary structure of Hb is not adversely influenced upon PEGylation. (Propyl-PEG5k)6-Hb exhibited an increased O2 affinity with decreased co-operativity and decreased modulation by allosteric effectors comparable with that of (SP-PEG5k)6-Hb, although its Cys-93(b) is not derivatized as in the latter. On a molecular mass basis, PEG linked to Hb by reductive alkylation increased its COP (colloidal osmotic pressure) more efficiently than when linked by thiolation-mediated maleimide-chemistry. These results demonstrate that the functional properties of PEG-Hb conjugates may be a direct consequence of surface decoration of Hb with PEG, but are independent of the site (pattern) and/or the chemistry of PEGylation. However the solution properties of PEGylated Hb are influenced by the site (pattern) and/or the chemistry of PEGylation and the presence or absence of an 'extension arm' between the conjugating site of Hb and the PEG chain.

Stability of liposome encapsulated hemoglobin dispersions

The demand for artificial blood substitutes in cases of elective surgeries, trauma, and civilian mass catastrophes increases every day. However, few studies have been done to characterize the mechanical stability of blood substitutes, especially liposome encapsulated hemoglobin (LEHb) dispersions. In this work, the stability of LEHb dispersions was investigated by fitting Jung et al.'s liposome size distribution model to experimentally measured LEHb size distributions [6] (produced via extrusion) using asymmetric flow field-flow fractionation coupled with multi-angle static light scattering. The effective bending constant (KB) and radius of curvature (R0) of each liposome dispersion were regressed from the size distribution fits. The model was found to be in agreement with the size distributions of LEHbs extruded through 400, 200 and 100 nm pore diameter membranes, but not in agreement with LEHbs extruded through 80 and 50 nm pore diameter membranes. Although the magnitude of KB fluctuated, we deduced a general trend for KB to decrease with decreasing pore diameter, and increasing initial Hb concentration. LEHbs extruded through 400nm pore diameter membranes were stabilized by the spontaneous curvature effect, while those extruded through 80 and 50 nm pore diameter membranes were mostly stabilized by thermal undulations, regardless of the initial Hb concentration. For LEHb dispersions extruded through 200 and 100 nm pore diameter membranes, there was a transition of stabilization mechanism from spontaneous curvature to thermal undulations with increasing initial Hb concentration. Taken together, these results suggest that moderate Hb encapsulation might actually impart better mechanical stability to LEHb dispersions extruded through 200 and 100 nm pore diameter membranes.

A novel hemoglobin-based blood substitute protects against myocardial reperfusion injury

HBOC-201 (Biopure; Cambridge, MA) is a glutaraldehyde-polymerized bovine hemoglobin (Hb) solution that is stroma free, has lower viscosity than blood, and promotes O(2) unloading. We investigated the effects of HBOC-201 in a canine model of myocardial ischemia-reperfusion injury. Dogs were anesthetized and subjected to 90 min of regional myocardial ischemia and 270 min of reperfusion. HBOC-201 or 0.9% saline vehicle equivalent to 10% total blood volume was infused 30 min before myocardial ischemia. Hemodynamic data and peripheral blood samples were taken at baseline, 1 h of myocardial ischemia, and 1, 2, and 4 h of reperfusion. At 270 min of reperfusion, the area at risk (AAR) per left ventricle and the area of infarction (Inf) per AAR were determined. The myocardial AARs in the two study groups were similar. In addition, myocardial blood flow (as measured by radioactive microspheres) in the ischemic zone was similar between the vehicle and HBOC-201 groups. HBOC-201-infused dogs demonstrated a significant (P < 0.01) 56% reduction in Inf/AAR. Analysis of blood samples taken at 4 h of reperfusion showed a significant (P < 0.05) reduction in creatine kinase MB isoform for the HBOC-201 group. Histological analysis of the myocardium demonstrated significant (P < 0.01) reductions in neutrophil infiltration in the HBOC-201 group. These data indicate that treatment with HBOC-201 before myocardial ischemia-reperfusion reduces the extent of myocardial inflammation and ischemia-reperfusion injury in the canine myocardium.

Artificial Cell Therapy: New Strategies for the Therapeutic Delivery of Live Bacteria

There has been rapid growth in research regarding the use of live bacterial cells for therapeutic purposes. The recognition that these cells can be genetically engineered to synthesize products that have therapeutic potential has generated considerable interest and excitement among clinicians and health professionals. It is expected that a wide range of disease modifying substrates such as enzymes, hormones, antibodies, vaccines, and other genetic products will be used successfully and will impact upon health care substantially. However, a major limitation in the use of these bacterial cells is the complexity of delivering them to the correct target tissues. Oral delivery of live cells, lyophilized cells, and immobilized cells has been attempted but with limited success. Primarily, this is because bacterial cells are incapable of surviving passage through the gastrointestinal tract. In many occasions, when given orally, these cells have been found to provoke immunogenic responses that are undesirable. Recent studies show that these problems can be overcome by delivering live bacterial cells, such as genetically engineered cells, using artificial cell microcapsules. This review summarizes recent advances in the therapeutic use of live bacterial cells for therapy, discusses the principles of using artificial cells for the oral delivery of bacterial cells, outlines methods for preparing suitable artificial cells for this purpose, addresses potentials and limitations for their application in therapy, and provides insight for the future direction of this emergent and highly prospective technology.

Artificial cell bioencapsulation in macro, micro, nano, and molecular dimensions: keynote lecture

Artificial cells now ranges from macro-dimensions, to micron-dimensions, to nano-dimensions, and to molecular dimensions. Those in the macro-dimensions are suitable for use in the bioencapsulation of cells, tissues, microorganisms, and bioreactants. Those in the micron-dimensions are suitable for the bioencapsulation of enzymes, microorganisms, peptides, drugs, vaccine, and other materials. Those in the nano-dimension are being used for blood substitutes and carriers for enzymes, peptides, drugs, etc. Those in the molecular-dimensions are used as blood substitutes, crosslinked enzymes etc.

Artificial Cells for Cell and Organ Replacements

The artificial cell is a Canadian invention (Chang, Science, 1964). This principle is being actively investigated for use in cell and organ replacements. The earliest routine clinical use of artificial cells is in the form of coated activated charcoal for hemoperfusion for use in the removal of drugs, and toxins and waste in uremia and liver failure. Encapsulated cells are being studied for the treatment of diabetes, liver failure, and kidney failure, and the use of encapsulated genetically-engineered cells is being investigated for gene therapy. Blood substitutes based on modified hemoglobin are already in Phase III clinical trials in patients, with as much as 20 units being infused into each patient during trauma surgery. Artificial cells containing enzymes are being developed for clinical trial in hereditary enzyme deficiency diseases and other diseases. The artificial cell is also being investigated for drug delivery and for other uses in biotechnology, chemical engineering, and medicine.

Hemoglobin-based oxygen carrier provides heterogeneous microvascular oxygenation in heart and gut after hemorrhage in pigs

BACKGROUND

In this study, the hypothesis was tested that resuscitation with hemoglobin-based oxygen carriers (HBOCs) affects the oxygenation of the microcirculation differently between and within organs. To this end, we tested the influence of the volume of an HBOC on the microcirculatory oxygenation of the heart and the gut serosa and mucosa in a porcine model of hemorrhage.

METHODS

In anesthetized open-chested pigs (n = 24), a controlled hemorrhage (30 mL/kg over 1 hour) was followed by resuscitation with 10, 20, or 30 mL/kg diaspirin-crosslinked hemoglobin (DCLHb) or isovolemic resuscitation with 30 mL/kg of a 6% hydroxyethyl starch solution (HAES). Measurements included systemic and regional hemodynamic and oxygenation parameters. Microvascular oxygen pressures (microPO2) of the epicardium and the serosa and mucosa of the ileum were measured simultaneously by the palladium-porphyrin phosphorescence technique. Measurements were obtained up to 120 minutes after resuscitation.

RESULTS

After hemorrhage, a low volume of DCLHb restored both cardiac and intestinal microPO2. Resuscitation of gut microPO2 with a low volume of DCLHb was as effective as isovolemic resuscitation with HAES. Higher volumes of DCLHb did not restore cardiac microPO2, as did isovolemic resuscitation with HAES, but increased gut microPO2 to hyperoxic values, dose-dependently. Effects were similar for the serosal and mucosal microPo2. In contrast to a sustained hypertensive effect after resuscitation with DCLHb, effects of DCLHb on regional oxygenation and hemodynamics were transient.

CONCLUSION

This study showed that a low volume of DCLHb was effective in resuscitation of the microcirculatory oxygenation of the heart and gut back to control levels. Increasing the volume of DCLHb did not cause an additional increase in heart microPO2, but caused hyperoxic microvascular values in the gut to be attained. It is concluded that microcirculatory monitoring in this way elucidates the regional behavior of oxygen transport to the tissue by HBOCs, whereas systemic variables were ineffective in describing their response.

Doping with Artificial Oxygen Carriers

There is a long history of science seeking to develop artificial substitutes for body parts damaged by disease or trauma. While defective teeth and limbs are commonly replaced by imitations without major loss of functionality, the development of a substitute for red blood cells has proved elusive. There is a permanent shortage of donor blood in western societies. Nevertheless, despite whole blood transfusions carrying measurable risks due to immunogenicity and the transmission of blood-borne infectious diseases, red blood cells are still relatively inexpensive, well tolerated and widely available. Researchers seeking to develop products that are able to meet and perhaps exceed these criteria have responded to this difficult challenge by adopting many different approaches. Work has focussed on two classes of substances: modified haemoglobin solutions and perfluorocarbon emulsions. Other approaches include the creation of artificial red cells, where haemoglobin and supporting enzyme systems are encapsulated into liposomes. Haemoglobin is ideally suited to oxygen transport when encased by the red cell membrane; however, once removed, it rapidly dissociates into dimers and is cleared by the kidney. Therefore, it must be stabilised before it can be safely re-infused into humans. Modifications concomitantly alter the vascular half-life, oxygen affinity and hypertensive characteristics of raw haemoglobin, which can be sourced from outdated blood stores, genetically-engineered Escherichia coli or even bovine herds. In contrast, perfluorocarbons are entirely synthetic molecules that are capable of dissolving oxygen but biologically inert. Since they dissolve rather than bind oxygen, their capacity to serve as a blood substitute is determined principally by the oxygen pressure gradients in the lung and at the target tissue. Blood substitutes have important potential areas of clinical application including red cell replacement during surgery, emergency resuscitation of traumatic blood loss, oxygen therapeutic applications in radiography (oxygenation of tumour cells is beneficial to the effect of certain chemotherapeutic agents), other medical applications such as organ preservation, and finally to meet the requirements of patients who cannot receive donor blood because of religious beliefs. Given the elite athlete's historical propensity to experiment with novel doping strategies, it is likely that the burgeoning field of artificial oxygen carriers has already attracted their attention. Scientific data concerning the performance benefits associated with blood substitutes are virtually nonexistent; however, international sporting federations have been commendably proactive in adding this category to their banned substance lists. The current situation is vulnerable to exploitation by immoral athletes since there is still no accepted methodology to test for the presence of artificial oxygen carriers.

Drugs for increasing oxygen and their potential use in doping: a review

Blood oxygenation is a fundamental factor in optimising muscular activity. Enhancement of oxygen delivery to tissues is associated with a substantial improvement in athletic performance, particularly in endurance sports. Progress in medical research has led to the identification of new chemicals for the treatment of severe anaemia. Effective and promising molecules have been created and sometimes used for doping purposes. The aim of this review is to present methods, and drugs, known to be (or that might be) used by athletes to increase oxygen transport in an attempt to improve endurance capacity. These methods and drugs include: (i) blood transfusion; (ii) endogenous stimulation of red blood cell production at altitude, or using hypoxic rooms, erythropoietins (EPOs), EPO gene therapy or EPO mimetics; (iii) allosteric effectors of haemoglobin; and (iv) blood substitutes such as modified haemoglobin solutions and perfluorochemicals. Often, new chemicals are used before safety tests have been completed and athletes are taking great health risks. Such new chemicals have also created the need for new instrumental strategies in doping control laboratories, but not all of these chemicals are detectable. Further progress in analytical research is necessary.

Artificial cells for replacement of metabolic organ functions

Artificial cells are being actively investigated for use in the replacement of cell and organ functions, especially related to metabolic functions. The earliest routine clinical use of artificial cells is in the form of coated activated charcoal for hemoperfusion. Implantation of encapsulated cells are being studied for the treatment of diabetes, liver failure, kidney failure and the use of encapsulated genetically engineered cells for gene therapy. Blood substitutes based on modified hemoglobin are already in Phase III clinical trials in patients with as much as 20 units infused into each patient during trauma surgery. Artificial cells containing enzymes are being developed for clinical trial in hereditary enzyme deficiency diseases and other diseases. Artificial cell is also being investigated for drug delivery and for other uses in biotechnology, chemical engineering and medicine.

A solid phase adsorption method for preparation of bovine serum albumin-bovine hemoglobin conjugate

A solid phase adsorption method was proposed to prepare well-defined bovine serum albumin-bovine hemoglobin (Hb) conjugate. After adsorption by the solid phase, Q Sepharose Fast Flow media, bovine serum albumin (BSA) molecules were allowed to react with glutaraldehyde. The spacing out of BSA molecules on the solid phase was assumed to limit polymerization of BSA molecules, except some molecules bound closely on the solid phase resulting in minor dimer formation. Following the elution procedure, the activated monomeric BSA was separated from the dimers by gel filtration chromatography on Superdex 200 and then reacted with bovine Hb at 4 degrees C and pH 9.5. The 1:1 (BSA:Hb) conjugate was obtained with the yield of 64%. The P(50) values of the conjugates, prepared under anaerobic and aerobic conditions, were 19.1 and 14.2 mmHg, respectively. The dependence of the P(50) on chloride ions for the conjugate was slightly diminished, presumably due to covalent attachment of BSA to bovine Hb.

Beyond EPO

The objective of this review is to examine newer compounds coming on the market capable of boosting red blood cell concentration and thus improving aerobic activities in particular. Erythropoietin (EPO) has been used extensively in the past by the athletic community in this role. Its main disadvantages are the side effects due to increased viscosity, and the recent development of a blood test for drug testing methods. Two new methods of increasing red blood cell concentration for use in medicine are hemoglobin oxygen carriers and perfluorocarbons, each having a different structure, but which allow oxygen to be delivered to the tissues. Hemoglobin oxygen carriers physically alter the hemoglobin molecule by several methods so that complications such as renal toxicity are obviated. Perfluorocarbons belong to a group of synthetic compounds containing hydrocarbons to which fluorine is added. Evidence is available to suggest that athletes are already adapting these newer molecules for their benefit.

Preparation of well-defined bovine polyhemoglobin based on dimethyl adipimidate and glutaraldebyde cross-linkage

A well-defined bovine polyhemoglobin was prepared by dimethyl adipimidate (DMA) and glutaraldehyde double cross-linkage method. DMA was used to block some amino groups of hemoglobin, followed by further polymerization with glutaraldehyde. The amino modification degree of hemoglobin was 32% when DMA reacted with hemoglobin at the molar ratio of 200. The bovine polyhemoglobin with narrow molecular weight distribution (mainly 128 kDa) was obtained when glutaraldehyde reacted with DMA-modified hemoglobin. The P(50) and the Hill coefficient for DMA-modified hemoglobin were 19.4 mm Hg and 2.28, respectively, while those for the bovine polyhemoglobin were 15.1 mm Hg and 1.70, respectively. The number of Bohr protons released for DMA-modified hemoglobin and the polyhemoglobin was 0.86 and 0.56 H/tetramer, respectively.

Artificial cells: prospects for biotechnology

A variety of techniques can now be used to alter the genome of a cell. Although these techniques are very powerful, they have limitations related to cost and efficiency of scale. Artificial cells designed for specific applications combine properties of biological systems such as nanoscale efficiency, self-organization and adaptability at relatively low cost. Individual components needed for such structures have already been developed, and now the main challenge is to integrate them in functional microscopic compartments. It will then become possible to design and construct communities of artificial cells that can perform different tasks related to therapeutic and diagnostic applications.

Redox cycling of diaspirin cross-linked hemoglobin induces G2/M arrest and apoptosis in cultured endothelial cells

It is hypothesized that oxidative reactions of hemoglobin driven by reactive oxygen species in the vasculature lead to endothelial cell injury or death. Bovine aortic endothelial cells were incubated with diaspirin cross-linked hemoglobin (DBBF-Hb), developed as a hemoglobin-based oxygen carrier, and hydrogen peroxide (H(2)O(2)), generated by the glucose oxidase system. The low steady flux of H(2)O(2) oxidizes the ferrous form of DBBF-Hb and drives the redox cycling of ferric and ferryl DBBF-Hb. Cells underwent rounding, swelling and detachment, and accumulated in the G2/M phase of the cell cycle. G2/M arrest preceded the onset of apoptosis as determined by increases in phosphatidylserine (PS) externalization and sub-G1 events. Redox cycling of unmodified hemoglobin also led to G2/M arrest and apoptosis. The rate and extent of DBBF-Hb oxidation correlated with the onset and extent of G2/M arrest and apoptosis and induced significant decreases in soluble reduced thiols. Earlier depletion of glutathione by pretreatment with buthionine sulfoximine rendered cells more susceptible to G2/M arrest and apoptosis. The caspase inhibitor, z-VAD-fmk, had no effect on the induction of G2/M arrest but completely inhibited the subsequent increases in PS externalization and sub-G1 events. Catalase inhibited DBBF-Hb oxidation, the loss of thiols, and the onset of G2/M arrest and apoptosis. These data support a causative role for the ferric-ferryl redox cycle in the development of endothelial cell injury.

Beneficial effects of Pluronic F-68 and artificial oxygen carriers on the post-thaw recovery of cryopreserved plant cells

The storage of prokaryotic and eukaryotic cells at ultra-low temperature in liquid nitrogen (-196 degrees C) is a procedure that has assumed an increasingly important role in underpinning many aspects of biotechnology. For eukaryotic cells, the transition from a cryopreserved state to physiologically normal temperatures and oxygen tensions, induces respiratory imbalances that may stimulate the production of toxic oxygen radicals causing impaired cellular functions. Novel treatments, that focus specifically on enhancing oxygen delivery to cells, are important in maximising post-thaw recovery. Recently, several approaches have been evaluated with suspension cultured plant cells as a model, yet biotechnologically-important, totipotent eukaryotic cell system. Such treatments include non-ionic surfactants, primarily Pluronic F-68, and artificial oxygen carriers, the latter based on inert perfluorochemical liquids or chemically-modifed haemoglobin, as supplements to culture medium used during the post-thaw recovery phase of cell growth. When used either alone or in combination, such novel treatments stimulate significantly the post-thaw viability and biomass production of cultured plant cells. Many of these technologies will be exploitable in cryopreservation protocols for eukaryotic cells in general.

O-raffinose-polymerised haemoglobin. A biochemical and pharmacological profile of an oxygen carrier

Haemoglobin-based oxygen carriers (HBOCs) represent an interesting class of blood substitutes which are undergoing advanced clinical trials. The therapeutic goal of these compounds is to avoid or reduce blood transfusion in different surgical and medical situations of acute haemoglobin deficiency. Their main advantages include availability in large volumes, storage for prolonged periods, rapid administration (without typing and cross matching) and sterilisation by pasteurisation. Their main known disadvantages are reduced circulation half-life, haemodynamic and gastrointestinal perturbations, probably related to nitric oxide (NO) scavenging, free radical induction, and alterations of biochemical and haematological parameters (increases in liver enzymes levels, platelet aggregation). Cell-free o-raffinose cross-linked and oligomerised human haemoglobin (O-r-poly-Hb) (Hemolink, Hemosol, Canada) is a modified haemoglobin with molecular weight ranging from 32- > 500 kDa. Its affinity for oxygen appears lower than normal blood and an n (Hill coefficient) value of about 1 indicates a very low degree of co-operativity. Probably related to the low O2 affinity value and to the high molecular weight, O-r-poly-Hb has been shown to induce lesser haemodynamic perturbations than other first generation modified haemoglobins. This HBOC is in Phase III clinical trials in cardiac and orthopaedic surgery for perioperative haemodilution, at doses from 25 g (250 ml)-100 g (1000 ml).

Interactions of hemoglobin with hydrogen peroxide alters thiol levels and course of endothelial cell death

We investigated cellular injury and death induced by ultrapure human Hb (HbA(0)) and its diaspirin cross-linked derivative DBBF-Hb in normal and glutathione (GSH)-depleted bovine aortic endothelial cells subjected to hydrogen peroxide (H(2)O(2)). HbA(0) underwent extensive degradation and heme loss, whereas DBBF-Hb persisted longer in its ferryl (Fe(4+)) form. The formation of ferryl HbA(0) or ferryl DBBF-Hb was associated with a significant decrease in endothelial cell GSH compared with the addition of H(2)O(2) or Hbs alone. This effect was inhibited by catalase, but not by superoxide dismutase or deferoxamine mesylate. The presence of HbA(0) and DBBF-Hb reduced H(2)O(2)-induced apoptosis, as measured by cell morphology, annexin V binding assay, and caspase inhibition, consistent with the ability to consume H(2)O(2) in an enzyme-like fashion. However, the pattern of cell death and injury produced by HbA(0) and DBBF-Hb appeared to be distinctly different among proteins as well as among cells with and without GSH. These findings may have important implications for the use of cell-free Hb as oxygen therapeutics in patients with coexisting pathologies who may lack antioxidant protective mechanisms.