Pilot scale production and characterization of next generation high molecular weight and tense quaternary state polymerized human hemoglobin

Polymerized human hemoglobin (PolyhHb) is being studied as a possible red blood cell (RBC) substitute for use in scenarios where blood is not available. While the oxygen (O2 ) carrying capacity of PolyhHb makes it appealing as an O2 therapeutic, the commercial PolyhHb PolyHeme® (Northfield Laboratories Inc.) was never approved for clinical use due to the presence of large quantities of low molecular weight (LMW) polymeric hemoglobin (Hb) species (<500 kDa), which have been shown to elicit vasoconstriction, systemic hypertension, and oxidative tissue injury in vivo. Previous bench-top scale studies in our lab demonstrated the ability to synthesize and purify PolyhHb using a two-stage tangential flow filtration purification process to remove almost all undesirable Hb species (>0.2 µm and <500 kDa) in the material, to create a product that should be safer for transfusion. Therefore, to enable future large animal studies and eventual human clinical trials, PolyhHb synthesis and purification processes need to be scaled up to the pilot scale. Hence in this study, we describe the pilot scale synthesis and purification of PolyhHb. Characterization of pilot scale PolyhHb showed that PolyhHb could be successfully produced to yield biophysical properties conducive for its use as an RBC substitute. Size exclusion high performance liquid chromatography showed that pilot scale PolyhHb yielded a high molecular weight Hb polymer containing a small percentage of LMW Hb species (<500 kDa). Additionally, the auto-oxidation rate of pilot scale PolyhHb was even lower than that of previous generations of PolyhHb. Taken together, these results demonstrate that PolyhHb has the ability to be seamlessly manufactured at the pilot scale to enable future large animal studies and clinical trials.

Mixtures of tense and relaxed state polymerized human hemoglobin regulate oxygen affinity and tissue construct oxygenation

Pure tense (T) and relaxed (R) quaternary state polymerized human hemoglobins (PolyhHbs) were synthesized and their biophysical properties characterized, along with mixtures of T- and R-state PolyhHbs. It was observed that the oxygen affinity of PolyhHb mixtures varied linearly with T-state mole fraction. Computational analysis of PolyhHb facilitated oxygenation of a single fiber in a hepatic hollow fiber (HF) bioreactor was performed to evaluate the oxygenation potential of T- and R-state PolyhHb mixtures. PolyhHb mixtures with T-state mole fractions greater than 50% resulted in hypoxic and hyperoxic zones occupying less than 5% of the total extra capillary space (ECS). Under these conditions, the ratio of the pericentral volume to the perivenous volume in the ECS doubled as the T-state mole fraction increased from 50 to 100%. These results show the effect of varying the T/R-state PolyhHb mole fraction on oxygenation of tissue-engineered constructs and their potential to oxygenate tissues.

Investigation of receptor binding and functional characteristics of hemopressin(1-7)

The orally active, α-hemoglobin derived hemopressin (PVNFKFLSH, Hp(1-9)) and its truncated (PVNFKFL, Hp(1-7) and PVNFKF, Hp(1-6)) and extended ((R)VDPVNFKFLSH, VD-Hp(1-9) and RVD-Hp(1-9)) derivatives have been postulated to be the endogenous peptide ligands of the cannabinoid receptor type 1 (CB1). In an attempt to create a versatile peptidic research tool for the direct study of the CB1 receptor-peptide ligand interactions, Hp(1-7) was radiolabeled and in vitro characterized in rat and CB1 knockout mouse brain membrane homogenates. In saturation and competition radioligand binding studies, [(3)H]Hp(1-7) labeled membrane receptors with high densities and displayed specific binding to a receptor protein, but seemingly not to the cannabinoid type 1, in comparison the results with the prototypic JWH-018, AM251, rimonabant, Hp(1-9) and RVD-Hp(1-9) (pepcan 12) ligands in both rat brain and CB1 knockout mouse brain homogenates. Furthermore, functional [(35)S]GTP γS binding studies revealed that Hp(1-7) and Hp(1-9) only weakly activated G-proteins in both brain membrane homogenates. Based on our findings and the latest literature data, we assume that the Hp(1-7) peptide fragment may be an allosteric ligand or indirect regulator of the endocannabinoid system rather than an endogenous ligand of the CB1 receptor.

Identification and quantification of a new family of peptide endocannabinoids (Pepcans) showing negative allosteric modulation at CB1 receptors

The α-hemoglobin-derived dodecapeptide RVD-hemopressin (RVDPVNFKLLSH) has been proposed to be an endogenous agonist for the cannabinoid receptor type 1 (CB(1)). To study this peptide, we have raised mAbs against its C-terminal part. Using an immunoaffinity mass spectrometry approach, a whole family of N-terminally extended peptides in addition to RVD-Hpα were identified in rodent brain extracts and human and mouse plasma. We designated these peptides Pepcan-12 (RVDPVNFKLLSH) to Pepcan-23 (SALSDLHAHKLRVDPVNFKLLSH), referring to peptide length. The most abundant Pepcans found in the brain were tested for CB(1) receptor binding. In the classical radioligand displacement assay, Pepcan-12 was the most efficacious ligand but only partially displaced both [(3)H]CP55,940 and [(3)H]WIN55,212-2. The data were fitted with the allosteric ternary complex model, revealing a cooperativity factor value α < 1, thus indicating a negative allosteric modulation. Dissociation kinetic studies of [(3)H]CP55,940 in the absence and presence of Pepcan-12 confirmed these results by showing increased dissociation rate constants induced by Pepcan-12. A fluorescently labeled Pepcan-12 analog was synthesized to investigate the binding to CB(1) receptors. Competition binding studies revealed K(i) values of several Pepcans in the nanomolar range. Accordingly, using competitive ELISA, we found low nanomolar concentrations of Pepcans in human plasma and ∼100 pmol/g in mouse brain. Surprisingly, Pepcan-12 exhibited potent negative allosteric modulation of the orthosteric agonist-induced cAMP accumulation, [(35)S]GTPγS binding, and CB(1) receptor internalization. Pepcans are the first endogenous allosteric modulators identified for CB(1) receptors. Given their abundance in the brain, Pepcans could play an important physiological role in modulating endocannabinoid signaling.

Site-selective glycosylation of hemoglobin with variable molecular weight oligosaccharides: potential alternative to PEGylation

Poly(ethylene glycol) (PEG) conjugation (i.e., PEGylation) is a commonly used strategy to increase the circulatory half-life of therapeutic proteins and colloids; however, few viable alternatives exist to replicate its functions. Herein, we report a method for the rapid site-selective glycosylation of proteins with variously sized carbohydrates, up to a molecular weight (MW) of 10,000, thus serving as a potential alternative for PEGylation. More importantly, the method developed has two unique features. First, traditional protecting group strategies that typically accompany the modification of the carbohydrate fragments are circumvented, allowing for the facile site-selective glycosylation of a desired protein with variously sized glycans. Second, the methodology employed is not limited by oligosaccharide size; consequently, glycans of MW similar to that of PEG, used in the PEGylation of therapeutic proteins, can be employed. To demonstrate the usefulness of this technology, hemoglobin (Hb) was site-selectively glycosylated with a series of carbohydrates of increasing MW (from 504 to ∼10,000). Hb was selected on the basis of the vast wealth of biochemical and biophysical knowledge present in the literature and because of its use as a precursor in the synthesis/formulation of artificial red blood cell substitutes. Following the successful site-selective glycosylation of Hb, the impact of increasing the glycan MW on Hb's biophysical properties was investigated in vitro.

Synthesis of a Hemoglobin Polymer Containing Antioxidant Enzymes Using Complementary Chemistry of Maleimides and Sulfhydryls

To increase the overall size of hemoglobin (Hb), we developed a novel system of polymerization based on the complementary chemistry between sulfhydryls and maleimides. The maleimides were introduced onto the protein through N-(-maleimidobutyryloxy) succinimide, while the sulfhydryls were added using 2-iminothiolane hydrochloride (Trauts reagent). Resulting polymers showed SDS-PAGE bands with molecular weights as high as 96 kDa. Size exclusion chromatography has demonstrated species with molecular weight > 700 kDa. The flexibility of the sulfhydryl-maleimide chemistry has also allowed insertion of two antioxidant enzymes, catalase (Cat) and superoxide dismutase (SOD), into the Hb polymer. Cat was incorporated into the heavier fractions of the polymer, while SOD was found throughout the molecular weight range.

Evolution of Artificial Cells Using Nanobiotechnology of Hemoglobin Based RBC Blood Substitute as an Example

The original artificial red blood cells have evolved into oxygen carriers in the form of polyhemoglobin and conjugated hemoglobin. Clinical conditions requiring only oxygen carriers are responding well to these types of oxygen carriers without the need for a complete artificial red blood cell. For those conditions requiring more than just oxygen carriers, new generations of polyhemoglobin containing antioxidant enzymes are being developed. Though a complete artificial red blood cell comparable to red blood cell is still a dream, development in lipid membrane artificial red blood cells and biodegradable polymeric nano artificial red blood cells are steps towards this possibility. The many years of neglect on basic research in the area of blood substitutes have resulted in the lack of important basic knowledge needed for the rapid development of blood substitutes suitable for clinical use. This is further hampered by the mistaken conception that blood substitute is a single entity. We need to look at blood substitutes as consisting of progressively more complicated entities, e.g. oxygen carriers, oxygen carriers with antioxidant activity, and complete red blood cell substitutes. Each of these entities is not applicable to all clinical conditions, but is suitable for specific applications.

Enhanced Molecular Volume of Conservatively Pegylated Hb: (SP-PEG5K)6-HbA is Non-Hypertensive

Recent studies have suggested that the "pressor effect" of acellular Hb is a consequence of perturbation of the macro-and microcirculatory system in multiple ways, and that PEGylation is an effective approach for controlling the same. In an attempt to confirm this concept, a new and simple thiolation mediated, maleimide chemistry-based conservative PEGylation protocol has been developed to conjugate multiple copies of PEG-chains to Hb. This approach combines the high reactivity of maleimides towards thiols with the propensity of iminothiolane to derivatize the epsilon-amino groups of proteins into reactive thiol groups, with conservation of their positive charge. One of the PEGylated products, namely (SP-PEG5K)6-HbA, that carries on an average six copies of PEG5000 chains per Hb, is non-hypertensive in hamster top load and in rat 50% exchange transfusion models. This hexa-PEGylated-Hb has (i) a hydrodynamic volume corresponding to that of an oligomerized Hb of 256kDa, (ii) a molecular radius of approximately 6.8 nm, (iii) high oxygen affinity, (iv) lowered Bohr effect, and (v) increased viscosity and colloidal osmotic pressure. These properties of (SP-PEG5K)6-HbA are consistent with the emerging new paradigms for the design of Hb based oxygen carriers and confirm the concept that the "pressor effect" of Hb is a multifactorial event. The thiolation mediated maleimide chemistry-based PEGylation protocol described here for the generation of (SP-PEG5K)6-Hb is simple, highly efficient, and is carried out under oxy conditions. The results demonstrate that a non-hypertensive PEG-Hb can be generated by conjugation of a lower number of PEG chains than previously reported.

Nanobiotechnology for hemoglobin-based blood substitutes

Nanobiotechnology is the assembling of biological molecules into nanodimension complexes. This has been used for the preparation of polyhemoglobin formed by the assembling of hemoglobin molecules into a soluble nanodimension complex. New generations of this approach include the nanobiotechnological assembly of hemoglobin, catalase, and superoxide dismutase into a soluble nanodimension complex. This acts as an oxygen carrier and an antioxidant for those conditions with potential for ischemiareperfusion injuries. Another recent novel approach is the assembling of hemoglobin and fibrinogen into a soluble nanodimension polyhemoglobin-fibrinogen complex that acts as an oxygen carrier with platelet-like activity. This is potentially useful in cases of extensive blood loss requiring massive replacement using blood substitutes, resulting in the need for the replacement of platelets and clotting factors. A further step is the preparation of nanodimension artificial red blood cells that contain hemoglobin and all the enzymes present in red blood cells.

[Study of polymerizing hemoglobin on cation exchange chromatography]

Poly-hemoglobin is the active component of hemoglobin-based blood substitutes. The excess reactivity of glutaraldehyde with hemoglobin in solution leads to poly-hemoglobin of a wide molecular weight distribution and a high average molecular weight. A new polymerization method has been tested to decrease the molecular weight distribution and the average molecular weight. The poly-hemoglobin with lower degree of modification (polymerization) was found enriched on the cation exchange columns and further polymerized with glutaraldehyde. The poly-hemoglobin of narrower molecular weight distribution has been prepared in this way.

Hemoglobin protein hollow shells fabricated through covalent layer-by-layer technique

Hemoglobin (Hb) protein microcapsules held together by cross-linker, glutaraldehyde (GA), were successfully fabricated by covalent layer-by-layer (LbL) technique. The Schiff base reaction occurred on the colloid templates between the aldehyde groups of GA and free amino sites of Hb results in the formation of GA/Hb microcapsules after the removal of the templates. The structure of obtained monodisperse protein microcapsule was characterized by transmission electron microscopy (TEM) and confocal laser scanning microscopy (CLSM). The UV-Vis spectra measurements demonstrate the existence of Hb in the assembled capsules. Cyclic voltammetry (CV) and potential-controlled amperometric measurements (I-t curve) confirm that hemoglobin microcapsules after fabrication remain their heme electroactivity. Moreover, direct electron transfer process from protein to electrode surface was performed to detect the heme electrochemistry without using any mediator or promoter. The experiments of fluorescence recovery after photobleaching (FRAP) by CLSM demonstrate that the hemoglobin protein microcapsules have an improved permeability comparing to the conventional polyelectrolyte microcapsules.

High O2 affinity hemoglobin-based oxygen carriers synthesized via polymerization of hemoglobin with ring-opened 2-chloroethyl-β-D-fructopyranoside and 1-o-octyl-β-D-glucopyranoside

Second generation hemoglobin-based O(2) carriers (HBOCs) are being developed with high O(2) affinity (low P(50)) in order to suppress vasoconstriction elicited by over-oxygenating tissues, a problem associated with low O(2) affinity first generation HBOCs. Our group has previously investigated the polymerization of hemoglobin (Hb) with dialdehydes as a strategy for engineering high O(2) affinity HBOCs. In this study, two novel reactive dialdehydes were synthesized by ring-opening 2-chloroethyl-beta-D-fructopyranoside (2-CEFP) and 1-o-octyl-beta-D-glucopyranoside (1-OGP) at the 1,2-diol position, respectively, to yield novel Hb polymerizing reagents. High-affinity polymerized HBOCs were synthesized by reacting R-state bovine hemoglobin (bHb) with ring-opened 2-CEFP and 1-OGP at cross-linker to bHb molar ratios ranging from 10:1 to 30:1. The resulting polymerized bovine HBOCs (bHBOCs) displayed P(50)s ranging from 7 to 18 mmHg, cooperativities ranging from 0.8 to 1.4, and methemoglobin (metHb) levels ranging from 3% to 10%. The cross-linking reaction also stabilized the third stepwise Adair coefficient for bHbs reacted with ring-opened 1-OGP at cross-linker to bHb molar ratios of 20:1 and 30:1 and for bHbs reacted with ring-opened 2-CEFP at molar ratios of 30:1. Additionally, the number-averaged molecular weight, M(n), of each polymerized bHBOC was larger compared to bHb. Molecular weight distributions leaning towards larger molecular weight bHBOCs were obtained by increasing the cross-linker to bHb molar ratio. Taken together, the results of this study have identified novel Hb polymerization reagents that are easy to synthesize, and that are capable of yielding bHBOCs with higher O(2) affinities and weight-averaged molecular weights compared to bHb.

Microencapsulation of hemoglobin in chitosan-coated alginate microspheres prepared by emulsification/internal gelation

Chitosan-coated alginate microspheres prepared by emulsification/internal gelation were chosen as carriers for a model protein, hemoglobin (Hb), owing to nontoxicity of the polymers and mild conditions of the method. The influence of process variables related to the emulsification step and microsphere recovering and formulation variables, such as alginate gelation and chitosan coating, on the size distribution and encapsulation efficiency was studied. The effect of microsphere coating as well its drying procedure on the Hb release profile was also evaluated. Chitosan coating was applied by either a continuous microencapsulation procedure or a 2-stage coating process. Microspheres with a mean diameter of less than 30 microm and an encapsulation efficiency above 90% were obtained. Calcium alginate cross-linking was optimized by using an acid/CaCO(3) molar ratio of 2.5, and microsphere-recovery with acetate buffer led to higher encapsulation efficiency. Hb release in gastric fluid was minimal for air-dried microspheres. Coating effect revealed a total release of 27% for 2-stage coated wet microspheres, while other formulations showed an Hb release above 50%. Lyophilized microspheres behaved similar to wet microspheres, although a higher total protein release was obtained with 2-stage coating. At pH 6.8, uncoated microspheres dissolved in less than 1 hour; however, Hb release from air-dried microspheres was incomplete. Chitosan coating decreased the release rate of Hb, but an incomplete release was obtained. The 2-stage coated microspheres showed no burst effect, whereas the 1-stage coated microspheres permitted a higher protein release.

Photopolymerization of Bovine Hemoglobin Entrapped Nanoscale Hydrogel Particles within Liposomal Reactors for Use as an Artificial Blood Substitute

Lipogel particles encapsulating bovine hemoglobin (BHb) were synthesized via photopolymerization of poly(N-isopropylacrylamide) (pNIPA) and poly(acrylamide) (pAAm) monomers within liposomal reactors. Nanoscale hydrogel particles (NHPs) encapsulating bovine hemoglobin, which represent a hybrid between acellular and cellular hemoglobin based oxygen carriers, were formed upon solubilization of the lipid bilayer of lipogel particles encapsulating BHb. Lipogels and NHPs encapsulating BHb constitute a new class of blood substitute that prevents both dissociation of hemoglobin (Hb) and in vivo exposure of acellular Hb, while allowing oxygen transport through the polymer matrix. pNIPA and pAAm particles encapsulating BHb displayed oxygen affinities ranging from 9.9 +/- 1.9 to 14.4 +/- 0.1 mmHg for lipogels, methemoglobin levels ranging from 9.3 +/- 3.7% to 26.0 +/- 5.0% for lipogels and NHPs, and encapsulation efficiencies ranging from 34.2 +/- 3.4% to 97.4 +/- 15.8% for lipogels and NHPs. Interestingly, the methemoglobin level of pNIPA particles was reduced 61% by coencapsulating the reducing agent, N-acetylcysteine. Fractionation and light scattering results showed that lipogels and NHPs were spherical and exhibited narrow size distributions. The colloidal osmotic pressure of pNIPA and pAAm lipogels ranged from 3.71 +/- 0.02 to 206.87 +/- 0.42 mmHg, depending on UV-irradiation time, type of buffer, and polymer composition. These results demonstrate that hemoglobin can be encapsulated within hydrogel based particles for use as an artificial blood substitute.

In vitro and in vivo enzyme studies of polyhemoglobin-tyrosinase

Melanoma is now the fifth most common type of cancer in North America. At present, there is no optimal treatment for this cancer. However, the lowering of the tyrosine level can inhibit the growth of melanoma. Unfortunately, this diet restriction cannot be humanly tolerated and causes vomiting, nausea, and severe body weight loss. To prevent these problems, we are studying a new approach involving the preparation intermolecularly crosslinked hemoglobin and tyrosinase for intravenous injection. In this article we describe the method of preparation and the structural and functional properties of polyhemoglobin-tyrosinase. We evaluate the effects of varying glutaraldehyde ratio, crosslinking time, and enzyme concentration on the enzyme activity of polyhemoglobin-tyrosinase. We also optimize the molecular weight distribution of polyhemoglobin-tyrosinase. The stability of polyhemoglobin-tyrosinase at 37 degrees C is much more stable when compared to noncrosslinked tyrosinase solution. Animal studies show that a higher degree of polymerization correlates with a longer circulation time of polyhemoglobin-tyrosinase, and the optimal crosslinking time is 24 hours. One intravenous injection of polyhemoglobin-tyrosinase lowers the plasma tyrosine to about 10% of its original level within one hour.

PolyHeme. Northfield Laboratories

Northfield is developing PolyHeme, a solution of polymerized hemoglobin, as a potential blood substitute for use following surgery and trauma.

Kinetic-controlled hydrolysis of Leu-Val-Val-hemorphin-7 catalyzed by angiotensin-converting enzyme from rat brain

Leu-Val-Val-hemorphin-7 (LVV-H7, LVVYPWTQRY), an opioid peptide, was found to be hydrolyzed sequentially by rat brain angiotensin-converting enzyme (ACE) in three steps through dipeptidyl carboxypeptidase activity. The kinetic constants evaluated were in order of: k(1) (0.19 min(-1))>>k(2) (0.0008 min(-1)) approximately k(3) (0.0006 min(-1)) in 10 mM NaCl at pH 7.5 giving rise to LVV-H5 almost quantitatively. The decapeptide was noted to be hydrolyzed 164- and 346-fold more efficiently than angiotensin I (Ang I) in k(cat) and kcat/Km values, respectively, at their optimal conditions. The kinetic-controlled preferential action of the brain enzyme on LVV-H7 is suggestive of its multiple roles in vivo.

Continuous production of a peptidic fraction containing the intermediate opioid peptide LVV-haemorphin-7 (LVVh-7) by peptic hydrolysis of bovine haemoglobin in a continuous membrane reactor

Peptic hydrolysis of native bovine haemoglobin at pH 3 yields the LVV-haemorphin-7 (Leu-Val-Val-Tyr-Pro-Trp-Thr-Gln-Arg-Phe; LVVh-7) opioid peptide corresponding to the residues-31-40 fragment of the beta-chain of haemoglobin. This peptide is intermediate in the course of batch hydrolysis and is rapidly degraded. Indeed, it shows an optimum at 3% degree of hydrolysis (i.e. 2 min of reaction time). The hydrolysis was carried out in a continuous membrane reactor with a space time (ratio of the flux to the reactor volume) set to 2 min (corresponding to optimum LVVh-7 production). This process allows the continuous production of a constant fraction of intermediate peptides containing LVVh-7 for 48 min.

[Change in spectral properties of nitrosohemoglobin induced by UV light]

The effect of UV radiation on the spectral characteristics of human nitrosohemoglobin in a wide dose range (151-4530 J/m2) was studied. It was shown that the irradiation of hemoprotein solutions with low doses of UV light (151-453 J/m2) led to local conformational rearrangements of the iron porphyrin moiety of the molecule. The apoprotein exhibited a high photostability under the conditions of the experiment. High doses of UV radiation (1359-4530 J/m2) induced the accumulation of methemoglobin in the protein sample. A scheme of the photoinduced formation of methemoglobin was elaborated.

MP4, a new nonvasoactive PEG-Hb conjugate

BACKGROUND

Vasoconstriction has been an obstacle to clinical development of Hb-based O2 carriers. It is proposed that this limitation can be overcome by increasing molecular size and oxygen affinity.

STUDY DESIGN AND METHODS

Surface-modified Hb (MP4) was designed, whose properties are consistent with the theory that cell-free Hb engages autoregulatory vasoconstrictive responses to Hb diffusion in the plasma space ("facilitated diffusion"). Human Hb was modified by reaction first with 2-iminothiolane to add sulfhydryl groups and then with monofunctional maleimide- activated 5-kDa PEG.

RESULTS

MP4 was found to have a molecular weight of 90 kDa, a molecular radius increased relative to native Hb (9.3 +/- 1.4 vs. 3.2 nm), high oxygen affinity (p50 approximately 5-6 mmHg), and a Bohr effect approximately half that of native human Hb (-0.24Deltalogp50/DeltapH). At 4.2 g per dL in Ringer's lactate, its viscosity was 2.5 cP, and its oncotic pressure was 50 mmHg. The t50 of 14C-MP4 in rats was approximately 24 hours. No significant elevation in mean arterial pressure was observed.

CONCLUSION

MP4 appears to be free of a pressor effect, a major limitation to the development of a safe and effective RBC substitutes in the past.

Molecular engineering of proteins with predefined function. Part I: Design of a hemoglobin-based oxygen carrier

Molecular engineering refers to a collection of complex, computer-based methods used to study molecular structures and properties. These methods include ones for determining properties as well as for accessing prior knowledge about them. Applying these methods, one can generate, manipulate and calculate the energy involved with the three-dimensional conformation of a given molecule. These computational tools were utilized in this study, to design cross-linking reagents for cell-free Hb, for the purpose of O(2)-carriers development. Hb, when removed from the red blood cell, misses some of its functional characteristics required. Yet, these characteristics can be rebuilt into the Hb molecule by appropriate chemical modifications. These modifications have been devised to prevent dimer formation, increase the retention time in circulation, and decrease the high oxygen affinity of free Hb. The reagent reported in this study, namely, oxidized-NAD (o-NAD), has been designed to fulfill both criteria of retention time and oxygen affinity, in a single package. Feasibility of the cross-linking reaction of o-NAD with Hb was assessed by studying the docking process of o-NAD within the 2,3-DPG pocket of Hb. In this study, we provide an insight into how the overall factors involved with the potential energy calculations contribute to the hydrogen bonding network, formed within the complex. Conformational search analysis has shown a high proximity, of functional moieties on the Hb molecule, to reactive groups on the o-NAD molecule suggested. This is an important step in the design and later synthesis of O(2)-carrying materials to be used as blood substitutes.

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.

Intersubunit circular permutation of human hemoglobin

For many years, human hemoglobin (Hb) isolated from erythrocytes has been investigated as a potential oxygen delivery therapeutic. Advantages with respect to the need for blood typing were balanced with various undesirable properties of cell-free Hb, including cost, overall oxygen affinity, alterations in cooperativity, and ready dissociation into toxic dimeric species. The use of total gene synthesis has resulted in very high levels of functional human Hb expression in Escherichia coli, but there remains a desire for effecting the crosslinking of the hemoglobin tetramer and providing for ready means for increasing the globular molecular weight. In this communication, we report a novel method for linking alpha chains. By circularly permuting one alpha sequence, the second alpha chain in the Hb tetramer can be linked with glycine residues to form 2 bridges across the central cavity. The second alpha chain thus presents its amino and carboxyl termini on a solvent exposed surface, providing for additional polymerization of oxygen-carrying subunits or attachment of any other peptide-based therapeutic.

Oxygenation properties of human erythrocytes containing exclusively alpha-nitrosyl hemoglobin: a promising blood transfusant candidate

We have prepared human erythrocytes that contain exclusively alpha-nitrosyl hemoglobin (Hb), i.e., alpha(Fe-NO)2beta(Fe-O2)2, by incorporating nitric oxide (NO) into erythrocytes in a well-controlled nitrosylation process. The amount of alpha(Fe-NO) corresponding to 50% of the total heme content of the erythrocytes and exclusive binding of NO to alpha-subunits of intraerythrocytic Hb were confirmed by EPR. Oxygenation experiments on the intraerythrocytic alpha-nitrosyl Hb over a wide range of pH showed that: (1) the oxygen affinity of cell-free and intraerythrocytic alpha-nitrosyl Hbs were much lower than native Hb in their respective environments; (2) the oxygenation characteristics of the intraerythrocytic alpha-nitrosyl Hb in the acidic range was similar to that of the cell-free alpha-nitrosyl Hb in the presence of 2,3-diphosphoglycerate; and (3) the apparent Bohr effect in the intraerythrocytic alpha-nitrosyl Hb was dramatically diminished. This can be due to a restricted variation in intraerythrocytic pH in the alkaline region and the presence and/or production of endogenous 2,3-diphosphoglycerate. By comparing oxygen saturation characteristics, it was found that the intraerythrocytic alpha-nitrosyl Hb, despite its halved oxygen carrying capacity, could deliver more oxygen than DPG-depleted erythrocytes under similar experimental conditions. This makes alpha-nitrosyl Hb-containing erythrocytes a promising candidate for blood transfusant.

Attenuation of hypothermia-induced platelet activation and platelet adhesion to artificial surfaces in vitro by modification of hemoglobin to carry S-nitric oxide and polyethylene glycol

Hypothermic cardiopulmonary bypass alters platelet function and hypothermia is associated with postoperative myocardial ischemia. Thrombogenic surfaces such as extracorporeal circuits, vascular graft materials, and components of atherosclerotic plaque induce activation of platelets. The effects of human hemoglobin (Hb) covalently modified to carry S-nitric oxide (NO) functional groups (SNO-Hb), polyethylene glycol (PEG-Hb), and SNO-PEG-Hb on platelet activation were studied. Platelet activation was assessed by cytometric analysis of GPIIb-IIIa activation and P-selectin expression at hypothermic condition (22 degrees C) after stimulation with Hb derivatives. Platelet adhesion and aggregation were measured in a parallel glass plate chamber coated with unmodified Hb, SNO-Hb, PEG-Hb, SNO-PEG-Hb, and collagen. Platelet binding of antibodies to GPIIb-IIIa and P-selectin was significantly enhanced by hypothermic condition and by unmodified Hb. There was significantly less platelet binding of antibodies to GPIIb-IIIa and P-selectin with SNO-Hb, PEG-Hb, and SNO-PEG-Hb compared with unmodified Hb. There was significantly less platelet attachment, adhesion, and aggregation on the SNO-Hb, PEG-Hb and SNO-PEG-Hb coated surfaces compared with unmodified Hb-coated and -uncoated surfaces. SNO-Hb, PEG-Hb, and SNO-PEG-Hb induced less platelet activation at hypothermic temperature, and induced less platelet adhesion and aggregation on thrombogenic surfaces compared with unmodified Hb. The inhibitory effect may be derived from antiadhesive properties of Hb, antiplatelet actions of NO, and molecular barrier action of PEG.

Synthesis and physicochemical characterization of a series of hemoglobin-based oxygen carriers: objective comparison between cellular and acellular types

A series of hemoglobin (Hb)-based O(2) carriers, acellular and cellular types, were synthesized and their physicochemical characteristics were compared. The acellular type includes intramolecularly cross-linked Hb (XLHb), polyoxyethylene (POE)-conjugated pyridoxalated Hb (POE-PLP-Hb), hydroxyethylstarch-conjugated Hb (HES-XLHb), and glutaraldehyde-polymerized XLHb (Poly-XLHb). The cellular type is Hb-vesicles (HbV) of which the surface is modified with POE (POE-HbV). Their particle diameters are 7 +/- 2, 22 +/- 2, 47 +/- 17, 68 +/- 24, and 224 +/- 76 nm, respectively, thus all the materials penetrate across membrane filters with 0.4 microm pore size, though only the POE-HbV cannot penetrate across the filter with 0.2 microm pore size. These characteristics of permeability are important to consider an optimal particle size in microcirculation in vivo. POE-PLP-Hb ([Hb] = 5 g/dL) showed viscosity of 6.1 cP at 332 s(-1) and colloid osmotic pressure (COP) of 70.2 Torr, which are beyond the physiological conditions (human blood, viscosity = 3-4 cP, COP = ca. 25 Torr). XLHb and Poly-XLHb showed viscosities of 1.0 and 1.5 cp, respectively, which are significantly lower than that of blood. COP of POE-HbV is regulated to 20 Torr in 5% human serum albumin (HSA). HES-XLHb and POE-HbV/HSA showed comparable viscosity with human blood. Microscopic observation of human red blood cells (RBC) after mixing blood with POE-PLP-Hb or HES-XLHb disclosed aggregates of RBC, a kind of sludge, indicating a strong interaction with RBC, which is anticipated to modify peripheral blood flow in vivo. On the other hand, XLHb and POE-HbV showed no rouleaux or aggregates of RBC. The acellular Hbs (P(50) = 14-32 Torr) have their specific O(2) affinities determined by their structures, while that of the cellular POE-HbV is regulated by coencapsulating an appropriate amount of an allosteric effector (e.g., P(50) = 18, 32 Torr). These differences in physicochemical characteristics between the acellular and cellular types indicate the advantages of the cellular type from the physiological points of view.

The reaction of deoxy-sickle cell hemoglobin with hydroxyurea

In addition to its capacity to increase fetal hemoglobin levels, other mechanisms are implicated in hydroxyurea's ability to provide beneficial effects to patients with sickle cell disease. We hypothesize that the reaction of hemoglobin with hydroxyurea may play a role. It is shown that hydroxyurea reacts with deoxy-sickle cell hemoglobin (Hb) to form methemoglobin (metHb) and nitrosyl hemoglobin (HbNO). The products of the reaction as well as the kinetics are followed by absorption spectroscopy and electron paramagnetic resonance (EPR) spectroscopy. Analysis of the kinetics shows that the reaction can be approximated by a pseudo-first order rate constant of 3.7x10(-4) (1/(s.M)) for the disappearance of deoxy-sickle cell hemoglobin. Further analysis shows that HbNO is formed at an observed average rate of 5.25x10(-5) (1/s), three to four times slower than the rate of formation of metHb. EPR spectroscopy is used to show that the formation of HbNO involves the specific transfer of NO from the NHOH group of hydroxyurea. The potential importance of this reaction is discussed in the context of metHb and HbNO being able to increase the delay time for sickle cell hemoglobin polymerization and HbNO's vasodilating capabilities through conversion to S-nitrosohemoglobin.

Zinc-substituted hemoglobins: alpha- and beta-chain differences monitored by high-resolution emission spectroscopy

The absorption and emission properties of hybrid Zn-substituted human hemoglobin (Hb) were used to monitor differences in interaction between the porphyrin and the polypeptide chain for the two subunits. Although alpha-substituted (alpha-ZnHb), beta-substituted (beta-ZnHb), or totally substituted Hb all show optical properties characteristic of Zn porphyrins, the spectra are also indicative of specific interactions between the polypeptide chain and the porphyrin. The Q0,0 absorption band of alpha-ZnHb at 5 K shows a splitting of approximately 300 cm-1, comparable to the largest split ever reported for a heme protein. This value is approximately 140 cm-1 for beta-ZnHb. The possible origin of the split is discussed in terms of the local electric field imposed by the amino acids of the respective heme pockets, different configurations of the porphyrin, and/or influences of the liganding histidine. The Zn derivatives show quasiline spectra under fluorescence line narrowing conditions, and the resolved excitation spectrum reveals differences in the vibrational levels of the Zn porphyrin in the two subunits. Broad underlying emission in the fluorescence line-narrowed emission spectrum can be accounted for, in part, by the existence of the two closely spaced electronic origins and also by the extent of phonon coupling between the porphyrin and the protein matrix.

Absence of hemoprotein-associated free radical events following oxidant challenge of crosslinked hemoglobin-superoxide dismutase catalase

Crosslinking hemoglobin with superoxide dismutase and catalase (PolyHb-SOD-CAT) helps to limit free radical reactivity of modified hemoglobin red blood cell substitutes. In the present study, in vitro oxidant challenge experiments were performed with exogenous hydrogen peroxide (H2O2) and xanthine oxidase-derived superoxide (O2.-). PolyHb-SOD-CAT was compared to PolyHb for the presence of secondary hemoprotein-free radical events. PolyHb-SOD-CAT prevents ferrylhemoglobin formation, measured as Na2S-induced absorbance at 620 nm. Similarly, PolyHb-SOD-CAT inhibited ferrozine-detectable iron release at high oxidant-heme ratios. The formation of oxygen radicals, monitored by salicylate hydroxylation, was prevented at high oxidant-heme ratios with PolyHb-SOD-CAT. The peroxidation of liposomal membranes was also inhibited in PolyHb-SOD-CAT mixtures subject to oxidant challenge. These results show that PolyHb-SOD-CAT prevents secondary hemoprotein-associated free radical events. This new type of modified hemoglobin oxygen carrier with antioxidant activity may reduce the potential toxicity of hemoglobin-based substitutes in certain applications, especially during reperfusion of ischemic tissues.

Synthesis, physico-chemical and biological properties of crosslinked modified hemoglobin

Polymer aspects of polycondensation of pyridoxylated hemoglobin with glutaraldehyde have been considered. On the basis of the investigation of reaction kinetics, the mechanism of chemical crosslinking of hemoglobin molecules into oligohemoglobin is proposed. Owing to the statistical character of the reaction, the resulting macromolecules are polydisperse with respect to the degree of modification of hemoglobin amino groups, and size of oligohemoglobin molecules. The formation of hemoglobin oligomers was studied by varying the following reaction conditions: pH, the components ratio, and their concentrations. It is shown that the net electric charge of the oligohemoglobin molecule depends on the terminating agents. However, these agents have no effect on the electrophoretic mobility of erythrocytes in oligohemoglobin solutions. The efficiency of oxygen transport of these solutions is close to that of human blood erythrocytes. Oligohemoglobin circulation in the blood of animals after intravenous infusion leads to rapid removal of low molecular weight fractions from blood and to the accumulation of high molecular weight fractions in plasma. The period of half-release of oligohemoglobin from the organism is 14-16 h.

Applications of site-specific chemical modification in the manufacture of biopharmaceuticals: I. An overview

The chemical modification of proteins has long been a useful approach to elucidating structure-function relationships. Recently, these same chemistries have been finding application in the preparation of proteins for both diagnostic and therapeutic use. These applications include alterations to introduce new properties, such as improved stability, or new traits, such as drug binding and transport, that take advantage of both broad and narrow ranges of selectivity. Site-specific chemical modification of proteins, when combined with the powerful advantages of site-specific mutagenesis, can yield protein agents superior to those generated by either approach alone.

Protein engineering strategies for designing more stable hemoglobin-based blood substitutes

Over the past five years our laboratory has been using rational, comparative, and random combinatorial mutagenesis strategies to optimize the alpha and beta subunits of recombinant human hemoglobin (Hb) for efficient O2 transport, greater stability, and minimum interference with vascular activity. In each approach, mammalian myoglobin (Mb) has been used as a prototype to develop experimental methodologies and to study the stereochemical mechanisms that govern O2 affinity, discrimination against CO, rates of ligand binding, auto- and chemically induced oxidation, resistance to hemin loss, and stability to globin denaturation. Multiple replacements in the distal portion of the heme pocket have been designed rationally to lower oxygen affinity and at the same time inhibit oxidative side reactions. The P50 values are adjusted by altering electrostatic and steric interactions between the bound ligand and residues at the Leu(B10), His(E7), and Va(E11) positions. Large apolar residues (Leu, Phe, Trp) at the B10 and E11 positions inhibit NO-induced and autooxidation in both myoglobin and hemoglobin by excluding oxidants and proton donors from the immediate vicinity of the bound ligand. Similar strategies appear to have evolved in a number of animal myoglobins and hemoglobins which have unusual amino acids at the E7, B10, and E11 positions. Random combinatorial mutagenesis techniques have been developed to insert new amino acid combinations near the bound ligand in sperm whale Mb. The objective is to obtain "unnatural" distal pocket structures that enhance O2 transport and resistance to oxidation by alternative mechanisms.

Cross-linking hemoglobin by design: lessons from using molecular clamps

The development of a red cell substitute by chemical modification of hemoglobin has been approached as a systematic, iterative process. Acyl phosphate methyl esters were designed as anionic electrophiles to permit selective acylation of amino groups in the cationic site of hemoglobin which binds polyanions. Kinetic studies with systematically substituted acyl phosphates and amines show that the reaction is controlled by a reversible addition step followed by an irreversible elimination step. Acyl phosphate methyl esters which are derivatives of rigid dicarboxylic acids introduce cross-links in human hemoglobin between amino groups in the beta subunits (epsilon-NH2-Lys-82, alpha-NH2-Val-1) and permit correlation of oxygen binding properties with cross-link structure. The data suggest that the cross-link maintains cooperativity while reducing overall oxygen affinity by lowering the affinity of the R form for oxygen rather than by perturbing the R,T equilibrium of native hemoglobin. Materials produced from deoxyhemoglobin with a cross-link between positions 1 and 82 of the two beta units have appropriate oxygen affinity for red cell substitutes. The use of a trifunctional cross-linker, trimesyl tris(methyl phosphate) selectively produces hemoglobin with the desired 1-82 connection in good yield. The reagent is readily prepared and the properties of this chemically modified hemoglobin are suitable for trial as a red cell substitute, closely resembling those of optimized materials produced by recombinant technology. Further work is producing new chemicals and providing structural information.

A potential blood substitute from carboxylic dextran and oxyhemoglobin. I. Preparation, purification and characterization

Human adult hemoglobin (Hb) from peripheral venous blood was covalently linked, under its oxygenated form, to a dextran polymeric effector to yield conjugates with low oxygen affinity. The polymeric effector was synthesized by directly coupling benzene tetracarboxylic anhydride to dextran (MW approximately 10,000) under mild conditions. The reaction parameters were chosen so that the resulting polymeric derivative was only very little cross-linked and possessed benzene tricarboxylate site concentrations lesser than 1 site for 10 glucose units, as it was found that for higher concentrations the polymer exhibited anticlotting properties. The reaction between oxyHb and the polymer (dex-BTC) was carried out in water in the presence of a water-soluble carbodiimide (EDCI). By optimization of the reaction conditions, a dextran-Hb conjugate with a P50 of 21 torr (37 degrees C, 50mM Bis-tris buffer pH 7.4, 0.14M NaCl, 40 mM glucose) and a potential O2 release of 0.30 ml/g Hb between oxygen partial pressures of 100 and 40 torr, was obtained. The viscosity and oncotic pressure of a solution containing about 6% of conjugated Hb were respectively 1.8 cSt (37 degrees C) and 28 torr (25 degrees C). This solution could be stored frozen at -20 degrees C for a long time, without modification of its properties.

Preparation and characterization of crosslinked and polymerized hemoglobin solutions

In 1982 we synthesized 2-Nor-2-formylpyridoxal 5'-phosphate (NFPLP) and subsequently showed that coupling of the beta chains of hemoglobin (Hb) by this organic phosphate compound according to Benesch et al. (1) lowers the oxygen affinity and prolongs the retention time in the circulation of rats and rabbits with a factor 3 by prevention of excretion via the kidneys. Optimal conditions for the purification of HbNFPLP either by ion-exchange chromatography or by heat treatment were established with recoveries of 70% and 85%, respectively. By extrapolation from the data in rats and rabbits a half life of about 8 hours can be expected in the circulation of humans. However, under some conditions a further prolongation is required. The aim of further modification of HbNFPLP was to achieve a retention time of about 24 hours. Polymerization with glutaraldehyde to polyHbNFPLP resulted in a mixture of polymers of different size. We determined the optimal degree of polymerization with respect to the effects on vascular retention time, oncotic activity, viscosity and oxygen affinity. Depending on the degree of polymerization we found in rats a 5- to 7- fold increase in vascular half-life compared to native Hb. The change in oxygen affinity was found to be independent of the polymer size (P50 = 18-22 mmHg). A limiting factor for polymerization is the increase in viscosity, which was dramatic when large polymers (greater than 300 kD) were present in the preparation.(ABSTRACT TRUNCATED AT 250 WORDS)

Stabilized hemoglobins as acellular resuscitative fluids

This study reports some recent work dealing with the stabilization of the tetramers of hemoglobin. It is shown that by using a variety of diacids, it is possible to increase the P50 above that of stroma free hemoglobin. In order to lengthen the retention times in the circulatory system, the stabilized hemoglobins were complexed with both hydroxyethyl starch polymers and polyol tetronic polymers. The resulting hemoglobin-polymer compounds were then freeze-dried. It was possible to reconstitute the powder by the addition of physiological saline when needed. The methods presented here appear to be appear to be as effective as using pyridoxal phosphate but at a fraction of the cost.

Stabilities and properties of multilinked hemoglobins

Crosslinking of both human and dog hemoglobin has been done with a variety of reagents to produce singly, doubly and multiply crosslinked hemoglobins. Succinate and glutarate diaspirins did not crosslink deoxy human hemoglobin in good yield, in contrast to the fumarate analog (DBSF). Deoxy dog Hb did not react well with DBSF, but oxy dog Hb did react, giving crosslinked tetramers as well as dimers on SDS electrophoresis. Crosslinking with a short, rigid reagent (difluorodinitrobenzene) resulted in a similar product for both oxy and deoxy hemoglobin that had high stability and oxygen affinity. The trilinker, tris-chloroethylamine, produced a more stable product than the corresponding crosslinker, bis-chloroethylamine. Double crosslinking oxy Hb with DBSF and dimethylpimelimidate or with DBSF followed by deoxygenation and recrosslinking with DBSF gave products with higher denaturation temperatures. The diaspirin double crosslinked product had high oxygen affinity.

Hemoglobin tetramers stabilized with polyaspirins

Organic acids activated by esterification with 3,5-dibromosalicylate react preferentially either with the beta 82 lysines or the alpha 99 lysines of hemoglobin. The versatility and site specificity of these polysapirins and the usage of both human and bovine hemoglobins allowed the construction of a family of oxygen carriers with various P50 ranging from 10 to 50 mmHg. These derivatives are obtained in pure homogeneous form by column chromatography. They are stabilized tetramers where the dissociation into dimers is inhibited. The latest addition is Tri-(3,5,dibromosalicyl)-benzenetricarboxylate, which crosslinks both human and bovine hemoglobin across the beta subunits, decreasing the oxygen affinity of both proteins. The crosslinked hemoglobins have a normal Bohr effect, more expanded in the alkaline region, and are sensitive to chlorides but not to polyphosphates. Solutions of stabilized tetramers, infused into rats or cats up to 25-50% blood replacement, do not produce altered renal and cardiac function. In the cat isovolemic hemodilution increases cerebral flow in controls treated with albumin solutions, when an oxygen carrier is used the cerebral flow remains normal.