Bovine hemoglobin cross-linked through the beta chains: functional and structural aspects

Alternatives to Transfusion

OBJECTIVES

We discuss two main categories of blood substitutes: perfluorocarbons and hemoglobin-based oxygen carriers.

METHODS

We provide a review of the notable products developed in both categories and include their attributes as well as their setbacks.

RESULTS

We contribute a case report tothe growing literature of the successful use of Sanguinate.

CONCLUSIONS

We find that artificial oxygen carriers are an attractive field of research because of the practical limitations and the multitude of potential complications that surround human blood transfusions.

Physical properties of hemoglobin-poly(acrylamide) hydrogel-based oxygen carriers: effect of reaction pH

This work examines the physical properties of bovine hemoglobin (BHb) chemically cross-linked to a pH responsive polymer (poly(acrylamide)) with the goal of taking advantage of the polymer's pH sensitivity to generate low-P50 oxygen carriers for application in physiological conditions characterized by deviations from normal pH. BHb-hydrogel-based oxygen carriers encapsulating 10-16 g/dL BHb displayed P50s < 10 mmHg when encapsulated inside of liposomes (i.e. Hb-LGs) and <15 mmHg in the absence of a lipid bilayer (i.e. Hb-NHPs), when synthesized at pHs less than normal physiological pH. The results of this work suggest that synthesis of Hb-LGs/Hb-NHPs under different pH conditions affect the ionization of BHb and the flexibility of the polymer chains to which BHb is chemically cross-linked. The degree of BHb cross-linking to the polymer matrix and the chain flexibility of the polymer influences the oxygen affinity and cooperativity of the oxygen carrier by influencing how easy it is for the Hb molecule to change conformations between the R and T states. The magnitude of the zeta potential of Hb-LGs and Hb-NHPs was shown to be within the range of stored red blood cells and within the range of limited flocculation. Taken together, this work describes the preparation and characterization of oxygen carriers with increased oxygen affinities compared to those of red blood cells.

Unique Tryptic Peptides Specific for Bovine and Human Hemoglobin in the Detection and Confirmation of Hemoglobin-Based Oxygen Carriers

Hemoglobin-based oxygen carriers (HBOCs) of bovine hemoglobin (Hb) or human Hb origin were developed for replacement or augmentation of blood during transfusion and have the potential to increase oxygen-carrying capacity of circulating blood and thus improve tissue oxygen delivery. Due to their potential for increasing oxygen-carrying capacity of circulating blood, they are excellent candidates for abuse in human and equine athletes. To deter athletes from blood doping with HBOCs such as Hemopure and Oxyglobin (OXY), a method for detection, confirmation, quantification, and distinguishing of HBOCs from native hemoglobin in test samples is needed. The purpose of this study was to identify unique peptides specific for bovine Hb and human Hb that are useful in the detection and confirmation of HBOCs in test samples. The LC-MS chromatographic peak profiles of tryptic digests from OXY, bovine Hb, human Hb, and equine Hb were compared, and unique tryptic peptides specific for bovine Hb, human Hb, and equine Hb were identified. The peptides specific for bovine Hb and OXY are related to bovine Hb alpha chain residues 69-90 and beta chain residues 40-58. The peptides specific for human Hb are related to human Hb alpha chain residues 63-91 and beta chain residues 42-60 and 68-83. The amino acid sequences of these unique tryptic peptides were confirmed by their characteristic MS/MS spectra. MS/MS spectra, b-ion series and y-ion series, and LC retention time of the tryptic peptides are essential pieces of information for the unequivocal identification, detection, and confirmation of HBOCs. The results of this study provide useful and defensible data on identification, detection, and confirmation of HBOCs of bovine Hb or human Hb origin. In addition, in-ESI-source fragmentation of tryptic peptides was observed in this study. The fragmentation was undesired since it decreased intensities of the trypic peptide ions, but it was helpful to elucidating sequences of the tryptic peptides thanks to the fragment peptide ions produced from the fragmentation.

Regioselective covalent modification of hemoglobin in search of antisickling agents

Although the molecular defect in sickle hemoglobin that produces sickle cell disease has been known for decades, there is still no effective drug treatment that acts on hemoglobin itself. In this work, a series of diversely substituted isothiocyanates (R-NCS) were examined for their regioselective reaction with hemoglobin in an attempt to alter the solubility properties of sickle hemoglobin. Electrospray mass spectrometry, molecular modeling, X-ray crystallography, and conventional protein chemistry were used to study this regioselectivity and the resulting increase in solubility of the modified hemoglobin. Depending on the attached R-group, the isothiocyanates were found to react either with the Cysbeta93 or the N-terminal amine of the alpha-chain. One of the most effective compounds in the series, 2-(N,N-dimethylamino)ethyl isothiocyanate, selectively reacts with the thiol of Cysbeta93 which, in conjunction with the cationic group, was seen to perturb the local hemoglobin structure. This modified HbS shows an approximately 30% increase in solubility for the fully deoxygenated state, along with a significant increase in oxygen affinity. This compound and a related analogue appear to readily traverse the erythrocyte membrane. A discussion of the relation of these structural changes to inhibition of gelation is presented. The dual activities of increasing HbS oxygen affinity and directly inhibiting deoxy HbS polymerization, in conjunction with facile membrane traversal, suggest that these cationic isothiocyanates show substantial promise as lead compounds for development of therapeutic agents for sickle cell disease.

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.

Polar bear hemoglobin and human Hb A0: same 2,3-diphosphoglycerate binding site but asymmetry of the binding?

Polar bear (Ursus maritimus) hemoglobin (Hb) shows a low response to 2,3-diphosphoglycerate (2,3-DPG), compared to human Hb A0, even though these proteins have the same 2,3-DPG-binding site. In addition, polar bear Hb shows a high response to chloride and an alkaline Bohr effect (deltalog P50/deltapH) that is significantly greater than that of human Hb A0. The difference in sequence Pro (Hb A0)-->Gly (polar bear Hb) at position A2 in the A helix seems to be critical for reduced binding of 2,3-DPG. Our results also show that the A2 position may influence not only the flexibility of the A helix, but that differences in flexibility of the first turn of the A helix may affect the unloading of oxygen for the intrinsic ligand affinities of the alpha and beta chains. However, preferential binding to either chain can only take place if there is appreciable asymmetric binding of the phosphoric effector. Regarding this point, 31P NMR data suggest a loss of symmetry of the 2,3-DPG-binding site in the deoxyHb-2,3-DPG complex.

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.

Effects of glutaraldehyde polymerization on oxygen transport and redox properties of bovine hemoglobin

Crosslinking of bovine Hb (HbBv) with glutaraldehyde produces a mixture of low oxygen affinity (P(50)) tetrameric and polymeric Hb species (PolyHbBv). Under physiological conditions the P(50) of HbBv and PolyHbBv were 27 and 35 mmHg, respectively. The dependence of the P(50) on pH and chloride ions and the cooperativity (n(50)) of the protein were diminished as a result of glutaraldehyde modification. Rapid kinetic studies showed greater overall rates of oxygen dissociation (k(off)) with little or no change in the association of CO (k(on)) to the modified protein. The rate of nitric oxide (NO)-induced oxidation of the PolyHbBv was slightly lower than that of HbBv. Autoxidation rate of PolyHbBv was 1.4 times faster than that of HbBv. The reaction of hydrogen peroxide (H2O2) with the ferrous (Fe(2+)) and ferric (Fe(3+)) forms of the proteins led to the formation of a more stable ferrylHb (Fe(4+)) in the case of PolyHbBv. Glutaraldehyde polymerization of HbBv alters its normal allosteric mechanisms, autoxidation kinetics and other related redox properties, which may compromise its function and cause greater toxicity when used as an oxygen transport fluid.

2,3-DPG-Hb complex: a hypothesis for an asymmetric binding

This study was undertaken to test the symmetry of 2,3-diphosphoglycerate (2,3-DPG) binding site in hemoglobin (Hb). From Arnone's study [A. Arnone, Nature (London) 237 (1972) 146] the 2,3-DPG binding site is located at the top of the cavity, that runs through the center of the deoxy-Hb molecule. However, it is possible that this symmetry reported by Arnone, for crystals of 2,3-DPG-Hb complex, might not be conserved in solution. In this paper, we report the 31P nuclear magnetic resonances of the 2,3-DPG interaction with Hb. The 2,3-DPG chemical shifts of the P2 and P3 resonance are both pH- and hemoglobin-dependent [protein from man, polar bear (Ursus maritimus), Arctic fox (Alopex lagopus) and bovine]. 2,3-DPG binds tightly to deoxyhemoglobin and weakly, nevertheless significantly, to oxyhemoglobin. In particular, our results suggest similar spatial position of the binding site of 2,3-DPG in both forms of Hb in solutions. However, the most unexpected result was the apparent loss of symmetry in the binding site, which might correlate with the ability of the hemoglobin to modulate its functional behavior. The different interactions of the phosphate groups indicate small differences in the quaternary structure of the different deoxy forms of hemoglobin. Given the above structural perturbation an asymmetric binding in the complex could justify, at least in part, different physiological properties of Hb. Regardless, functionally relevant effects of 2,3-DPG seem to be measured and best elucidated through solution studies.

Anionic binding site and 2,3-DPG effect in bovine hemoglobin

It is generally believed that bovine hemoglobin (BvHb) interacts weakly with 2,3-diphosphoglycerate (2,3-DPG) in a chloride-free media and not at all in the presence of physiological concentrations of chloride (100 mM). This lack of interaction has raised several questions at both structural and evolutionary levels. Results obtained in this study via 31P nuclear magnetic resonance (NMR) show that, even in the presence of 100 mM chloride ions, 2,3-DPG does, in fact, interact with bovine deoxy-Hb. This spectroscopic observation has been confirmed by oxygen binding experiments, which have also shown that, under certain conditions, chloride and 2,3-DPG may display a synergistic effect in modifying the oxygen affinity of bovine hemoglobin. It could be that this synergistic effect has its structural basis in a conformational modification induced by 2,3-DPG, possibly causing extra chloride anions to approach the positive charges which constitute the anion binding site. Another possibility, not necessarily an alternative, is the additional chloride binding site recently identified [Fronticelli, C., Sanna, M. T., Perez-Alvarado, G. C., Karavitis, M., Lu, A.-L., and Brinnigar, W. S. (1995) J. Biol. Chem 270, 30588-30592] involving lysine beta76 that in bovine Hb substitutes for the alanine residue present in human hemoglobin. All of these findings are in agreement with the very low enthalpy of oxygenation that characterizes bovine Hb when both chloride and 2,3-DPG are present in concomitance. The results reported here clearly show that bovine hemoglobin does react with 2, 3-DPG and is functionally affected by this organic phosphate. Hence, the very low intraerythrocytic concentration of 2,3-DPG (0.5 mM) in adult bovine red blood cells is the result of metabolic adaptation which cannot be explained solely by the different amino acid sequence at the level of the 2,3-DPG binding site.

Analysis of protein aggregates by combination of cross-linking reactions and chromatographic separations

Chemical cross-linking provides a method that covalently bridges near-neighbour associations within proteins and protein aggregates. Combined with chromatographic separations and protein-chemical methods, it may be used to localize and to investigate three-dimensional relations as present under natural conditions. This paper reviews the chemistry and application of cross-linking reagents and the development of combination experimental approaches in view of chromatographic separations and cross-linking reactions. Investigations of homooligomeric and heterooligomeric protein associations as well as conformational analysis are presented.