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

The Long-Acting Serine Protease Inhibitor mPEG-SPA-MDSPI16 Alleviates LPS-Induced Acute Lung Injury

Anti-inflammatory drugs have become the second-largest class of common drugs after anti-infective drugs in animal clinical care worldwide and are often combined with other drugs to treat fever and viral diseases caused by various factors. In our previous study, a novel serine protease inhibitor-encoding gene (MDSPI16) with improved anti-inflammatory activity was selected from a constructed suppressive subducted hybridization library of housefly larvae. This protein could easily induce an immune response in animals and had a short half-life, which limited its wide application in the clinic. Thus, in this study, mPEG-succinimidyl propionate (mPEG-SPA, Mw = 5 kDa) was used to molecularly modify the MDSPI16 protein, and the modified product mPEG-SPA-MDSPI16, which strongly inhibited elastase production, was purified. It had good stability and safety, low immunogenicity, and a long half-life, and the IC50 for elastase was 86 nM. mPEG-SPA-MDSPI16 effectively inhibited the expression of neutrophil elastase and decreased ROS levels. Moreover, mPEG-SPA-MDSPI16 exerted anti-inflammatory effects by inhibiting activation of the NF-κB signaling pathway and the MAPK signaling pathway in neutrophils. It also exerted therapeutic effects on a lipopolysaccharide (LPS)-induced acute lung injury (ALI) mouse model. In summary, mPEG-SPA-MDSPI16 is a novel anti-inflammatory protein modified with PEG that has the advantages of safety, nontoxicity, improved stability, and strong anti-inflammatory activity in vivo and in vitro and is expected to become an effective anti-inflammatory drug.

Structural order of water molecules around polyrotaxane including PEG, α-cyclodextrin, and α-lipoic acid linker on gold surface by molecular dynamics simulations

In materials science, water plays an important part, especially at the molecular level. It shows various properties when sorbed onto surfaces of polymers. The structure of the molecular water ensemble in the vicinity of the polymers is under discussion. In this study, we used molecular dynamics methods to analyze the structure of water in the vicinity of the polymer polyrotaxane (PR), composed of α-cyclodextrins (α-CDs), a poly(ethylene glycol) (PEG) axial chain, and α-lipoic acid linkers, at various temperatures. The distribution of water around the functional groups, hydrogen bond network, and tetrahedral order were analyzed to classify the various types of water around the polymer. We found that the tetrahedral order of water had a strained relationship from the XES experiment. Four water regions were separated from each other in the vicinity of 1 to 5 Å around PR. The intermediate and non-freezing water were formed due to the interaction between water molecules and the functional groups, such as hydroxyl, ether, and ester.

Structural Stability and Biophysical Properties of the Mega-Protein Erythrocruorin Are Regulated by Polyethylene Glycol Surface Coverage

A wide variety of hemoglobin-based oxygen carriers (HBOCs) have been designed for use as red blood cell (RBC) substitutes in transfusion medicine, ex vivo organ perfusion, oxygen delivery to hypoxic tissues, and a myriad of other applications. However, hemoglobin (Hb) derived from annelids (erythrocruorins [Ecs]) comprise a natural class of HBOC, since they are larger in size (30 nm in diameter) and contain more heme groups per molecule (144 heme groups) compared to human Hb (hHb; 5 nm in diameter and 4 heme groups). The larger size of Ec compared to hHb reduces tissue extravasation from the vascular space, thus, reducing vasoconstriction, systemic hypertension, and tissue oxidative injury when used as an RBC substitute. In addition, prior research has shown that Ecs possess slower auto-oxidation rates than hHb at physiological temperature, thus, making them attractive candidates for use as RBC substitutes. Unfortunately, it was also observed that Ecs have a much lower circulatory half-life in vivo compared to other HBOCs. Hence, conjugating polyethylene glycol (PEG) to the surface of Ec was proposed as a simple strategy to increase Ec circulatory half-life. Therefore, in order to inform future in vivo studies with PEGylated Ec, we decided to investigate the structural stability and biophysical properties of variable PEG surface coverage on Ec compared to native Ec. We observed an increase in PEG-Ec diameter and molecular weight (MW) and changes to the quaternary structure, secondary structure, and surface hydrophobicity after PEGylation. There was also an increase in oxygen binding affinity, reduction in oxygen offloading rate, and increase in auto-oxidation rate for increasing PEGylation ratios. Weak dissociation of Ec was also observed after dense PEGylation caused by steric repulsion of the conjugated PEG chains. Hence, we determined an optimum Ec PEGylation ratio that resulted in a substantial size and MW increase along with preservation of oxygen binding properties. In future studies, these materials will be tested in animal models to evaluate pharmacodynamics, pharmacokinetics, tissue oxygenation, microcirculatory responses, and overall safety.

Conjugation of Hemoglobin and Mannan Markedly Improves the Immunogenicity of Domain III of the Zika Virus E Protein: Structural and Immunological Study

Zika virus (ZIKV) leads to congenital microcephaly and anomalies and severe neurological diseases such as Guillain-Barre syndrome. Safe and effective vaccines are necessitated to deal with these severe health threats. As an ideal antigen, the domain III of the envelope protein (EDIII) of ZIKV can evoke potent neutralizing antibodies without any antibody-dependent enhancement (ADE) effect. However, EDIII necessitates to be formulated with an antigen delivery system or adjuvants to improve its immunogenicity. Hemoglobin (Hb) regulates inflammation, cytokine levels, and activate macrophage. Mannan is a polysaccharide of the fungal cell wall with an immunomodulatory activity. In this study, EDIII was conjugated with Hb and mannan, using the disulfide bond as the linker. Hb and mannan both functioned as the adjuvants. Conjugation of Hb and mannan acted as the delivery system for EDIII. The structure of EDIII was essentially maintained upon conjugation of Hb and mannan. The intracellular release of EDIII from the conjugate (HM-EDIII-2) was achieved by reduction of the glutathione-sensitive disulfide bond. As compared with EDIII, HM-EDIII-2 elicited high EDIII-specific IgG titers and high levels of Th1-type cytokines (IFN-γ and IL-2) and Th2-type cytokines (IL-5 and IL-10), along with no apparent toxicity to the organs. Moreover, the pharmacokinetic study revealed a prolonged serum exposure of HM-EDIII-2 to the immune cells. Thus, HM-EDIII-2 could boost a strong humoral and cellular immune response to EDIII. Our study was expected to provide the feasibility necessary to develop a robust and potentially safe ZIKV vaccine.

Polymer Nanoparticles and Nanomotors Modified by DNA/RNA Aptamers and Antibodies in Targeted Therapy of Cancer

Polymer nanoparticles and nano/micromotors are novel nanostructures that are of increased interest especially in the diagnosis and therapy of cancer. These structures are modified by antibodies or nucleic acid aptamers and can recognize the cancer markers at the membrane of the cancer cells or in the intracellular side. They can serve as a cargo for targeted transport of drugs or nucleic acids in chemo- immuno- or gene therapy. The various mechanisms, such as enzyme, ultrasound, magnetic, electrical, or light, served as a driving force for nano/micromotors, allowing their transport into the cells. This review is focused on the recent achievements in the development of polymer nanoparticles and nano/micromotors modified by antibodies and nucleic acid aptamers. The methods of preparation of polymer nanoparticles, their structure and properties are provided together with those for synthesis and the application of nano/micromotors. The various mechanisms of the driving of nano/micromotors such as chemical, light, ultrasound, electric and magnetic fields are explained. The targeting drug delivery is based on the modification of nanostructures by receptors such as nucleic acid aptamers and antibodies. Special focus is therefore on the method of selection aptamers for recognition cancer markers as well as on the comparison of the properties of nucleic acid aptamers and antibodies. The methods of immobilization of aptamers at the nanoparticles and nano/micromotors are provided. Examples of applications of polymer nanoparticles and nano/micromotors in targeted delivery and in controlled drug release are presented. The future perspectives of biomimetic nanostructures in personalized nanomedicine are also discussed.

Laser Techniques on Acoustically Levitated Droplets

This work reports the results of an experimental study where laser techniques are applied to acoustically levitated droplets of trehalose aqueous solutions in order to perform spectroscopic analyses as a function of concentration and to test the theoretical diameter law. The study of such systems is important in order to better understand the behaviour of trehalose-synthesizing extremophiles that live in extreme environments. In particular, it will be shown how acoustic levitation, combined with optical spectroscopic instruments allows to explore a wide concentration range and to test the validity of the diameter law as a function of levitation lag time, i.e. the D2 vs t law. On this purpose a direct diameter monitoring by a video camera and a laser pointer was first performed; then the diameter was also evaluated by an indirect measure through an OH/CH band area ratio analysis of collected Raman and Infrared spectra. It clearly emerges that D2 vs t follows a linear trend for about 20 minutes, reaching then a plateau at longer time. This result shows how trehalose is able to avoid total water evaporation, this property being essential for the surviving of organisms under extreme environmental conditions.

Preparation of artificial red cell and its application on alleviation of tumor hypoxia

Hemoglobin-based oxygen carriers were developed as an alternative for blood transfusion. However, the research progress for their further clinic applications was slow in recent several years. Hypoxia is found in most solid tumors, which is responsible for the tumor formation, increased metastasis, drug resistance during therapeutic process as well as poor patient survival. In this work, novel hemoglobin (Hb) loaded nanoliposomes, as artificial red cells for oxygen delivery, were optimized by screening various types of phospholipids and analyzing different mole ratio of phospholipid to cholesterol. The nanoliposomes presented a high encapsulating efficiency to hemoglobin and also significantly enhanced its stability. The obtained hemoglobin loaded nanoliposome (HLL) could be lyophilized for long term storage. HLL did not cause significant cell death in the concentration range of 0-100μg equivalent Hb/mL under normoxia and hypoxia incubation conditions, suggesting the low cytotoxicity and high biocompatibility of HLL. Importantly, HLL could efficiently accumulate into subcutaneous and deep orthotopic tumors, inducing a significant decrease of hypoxia-inducible factors 1α subunits (HIF-1α) in the tumors and remarkably reduced expression of vascular endothelial growth factor (VEGF). The study of acute and chronic toxicity indicated that HLL did not induce obvious damage to main organs of mice after intravenous injections with total Hb dose of 120mg/kg. We presented a promising method for relieving the hypoxia degree in solid tumors and down-regulating HIF-1α protein by directly delivering oxygen into tumors, which will be very helpful for subsequent cancer therapy.

"Inside-Out" PEGylation of Bovine β-Cross-Linked Hemoglobin

The development of a blood substitute is urgent due to blood shortages and potential communicable diseases. A novel method, inside-out PEGylation, has been used here to conjugate a multiarm maleimide-PEG (Mal-PEG) to β-cross-linked (βXL-Hb) hemoglobin (Hb) tetramers through the Cys β93 residues. This method produces a polymer with a single PEG backbone that is surrounded by multiple proteins, rather than coating a single protein with multiple PEG chains. Electrophoresis under denaturing conditions showed a large molecular weight species. Gel filtration chromatography and analytical ultracentrifugation determined the most prevalent species had three βXL-Hb to one Mal-PEG. Thermal denaturation studies showed that the cross-linked and PEGylated species were more stable than native Hb. Cross-linking under oxy-conditions produced a high oxygen affinity Hb species (P₅₀  = 9.18 Torr), but the oxygen affinity was not significantly altered by PEGylation (P₅₀  = 9.67 Torr). Inside-out PEGylation can be used to produce a hemoglobin-based oxygen carrier and potentially for other multiprotein complexes.

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

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

PEGylated recombinant human interferon-ω as a long-acting antiviral agent: structure, antiviral activity and pharmacokinetics

Recombinant human interferon-ω (rhIFN-ω) exhibits a potent antiviral activity. Because of poor pharmacokinetics (PK) of rhIFN-ω, frequent dosing of rhIFN-ω is necessitated to achieve the sustained antiviral efficacy. PEGylation can efficiently improve the PK of rhIFN-ω while substantially decrease its bioactivity. The structure, antiviral activity and PK of the PEGylated rhIFN-ω were measured to establish their relationship with PEGylation sites, polyethylene glycol (PEG) mass and PEG structure. Accordingly, N-terminus and the lysine residues were selected as the PEGylation sites. PEGs with Mw of 20kDa and 40kDa were used to investigate the effect of PEG mass. Linear and branched PEGs were used to investigate the effect of PEG structure. PEGylation decreased the antiviral activity of rhIFN-ω and improved its PK. The PEGylation sites determine the bioactivity of the PEGylated rhIFN-ω and the conjugated PEG mass determines the PK. N-terminally PEGylated rhIFN-ω with 40kDa linear PEG maintains 21.7% of the rhIFN-ω antiviral activity with a half-life of 139.6h. Thus, N-terminally PEGylated rhIFN-ω with linear 40kDa PEG is a potential antiviral agent for long-acting treatment of the viral diseases.

PEGylation of αα-Hb using succinimidyl propionic acid PEG 5K: Conjugation chemistry and PEG shell structure dictate respectively the oxygen affinity and resuscitation fluid like properties of PEG αα-Hbs

PEGylation of intramolecularly crosslinked Hb has been studied here to overcome the limitation of dissociation of Hb tetramers. New hexa and deca PEGylated low oxygen affinity PEG-ααHbs have been generated. Influence of PEG conjugation chemistry and the PEG shell structure on the functional properties as well as PEGylation induced plasma expander like properties of the protein has been delineated. The results have established that in the design of PEG-Hbs as oxygen therapeutics, the influence of conjugation chemistry and the PEG shell structure on the oxygen affinity of Hb needs to be optimized independently besides optimizing the PEG shell structure for inducing resuscitation fluid like properties.

Enhanced nitrite reductase activity associated with the haptoglobin complexed hemoglobin dimer: functional and antioxidative implications

The presence of acellular hemoglobin (Hb) within the circulation is generally viewed as a pathological state that can result in toxic consequences. Haptoglobin (Hp), a globular protein found in the plasma, binds with high avidity the αβ dimers derived from the dissociation of Hb tetramer and thus helps clear free Hb. More recently there have been compelling indications that the redox properties of the Hp bound dimer (Hb-Hp) may play a more active role in controlling toxicity by limiting the potential tissue damage caused by propagation of the free-radicals generated within the heme containing globin chains. The present study further examines the potential protective effect of Hp through its impact on the production of nitric oxide (NO) from nitrite through nitrite reductase activity of the Hp bound αβ Hb dimer. The presented results show that the Hb dimer in the Hb-Hp complex has oxygen binding, CO recombination and spectroscopic properties consistent with an Hb species having properties similar to but not exactly the same as the R quaternary state of the Hb tetramer. Consistent with these observations is the finding that the initial nitrite reductase rate for Hb-Hp is approximately ten times that of HbA under the same conditions. These results in conjunction with the earlier redox properties of the Hb-Hp are discussed in terms of limiting the pathophysiological consequences of acellular Hb in the circulation.

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.

Hexa-thiocarbamoyl phenyl PEG5K Hb: vasoactivity and structure: influence of rigidity of the conjugation linkage on the PEGylation induced plasma expander-like solution properties of PEG-Hb adducts

A new hexaPEGylated hemoglobin, (TCP-PEG5K)(6)-Hb (TCP, thiocarbamoyl phenyl) has been developed using PEG-phenyl-isothiocyanate and its vasoactivity and structure has been investigated. Of the six PEG5K chains of (TCP-PEG5K)(6)-Hb, 4 are conjugated to the alpha-amino groups of Hb, and the other 2 chains are distributed on epsilon-amino groups, identified as Lys-40(alpha) (approximately 45%), Lys-56(alpha) (approximately 25%), and Lys-8(beta) (approximately 24%). The studies with hamster infused with a bolus of a 4 gm % solution of (TCP-PEG5K)(6)-Hb equivalent to 10% of their blood volume have established that this new hexaPEGylated Hb is vasoinactive. The viscosity and the colloidal osmotic pressure of (TCP-PEG5K)(6)-Hb at 4% is 1.9 cP and 69.7 mmHg, respectively. The molecular radius of (TCP-PEG5K)(6)-Hb is about 4.6 nm and is significantly smaller than hexaPEGylated Hbs developed using other direct and extension arm facilitated PEGylation platform. The presence of an outside the central cavity intramolecular crosslink, succinimidophenyl-PEG2K between Cys-93(beta, beta') in (TCP-PEG5K)(6)-betabeta-Hb strongly impacts its solution properties. These patterns of influence suggest that the inter-dimeric interactions in (TCP-PEG5K)(6)-Hb is weakened just as with other direct PEGylation platforms, and (SP-PEG5K)(6)-Hb generated by EAF-PEGylation is unique in not inducing this effect. A comparison of the properties of hexaPEGylated Hbs establishes that rigidity of the conjugation linkage between PEG and Hb plays a significant influence on the resultant dictating solution properties and/structure/conformation of PEG-Hb adduct.

Site-selective glycosylation of hemoglobin on Cys beta93

In this work, we describe the synthesis and characterization of a novel glycosylated hemoglobin (Hb) with high oxygen affinity as a potential Hb-based oxygen carrier. Site-selective glycosylation of bovine Hb was achieved by conjugating a lactose derivative to Cys 93 on the beta subunit of Hb. LC-MS analysis indicates that the reaction was quantitative, with no unmodified Hb present in the reaction product. The glycosylation site was identified by chymotrypsin digestion of the glycosylated bovine Hb followed with LC-MS/MS and from the X-ray crystal structure of the glycosylated Hb. The chemical conjugation of the lactose derivative at Cys beta93 yields an oxygen carrier with a high oxygen affinity (P(50) of 4.94 mmHg) and low cooperativity coefficient (n) of 1.20. Asymmetric flow field-flow fractionation (AFFFF) coupled with multiangle static light scattering (MASLS) was used to measure the absolute molecular weight of the glycosylated Hb. AFFFF-MASLS analysis indicates that glycosylation of Hb significantly altered the alpha(2)beta(2)-alphabeta equilibrium compared to native Hb. Subsequent X-ray analysis of the glycosylated Hb crystal showed that the covalently linked lactose derivative is sandwiched between the beta(1) and alpha(2) (and hence by symmetry the beta(2) and alpha(1)) subunits of the tetramer, and the interaction between the saccharide and amino acid residues located at the interface is apparently stabilized by hydrogen bonding interactions. The resultant structural analysis of the glycosylated Hb helps to explain the shift in the alpha(2)beta(2)-alphabeta equilibrium in terms of the hydrogen bonding interactions at the beta(1)alpha(2)/beta(2)alpha(1) interface. Taken together, all of these results indicate that it is feasible to site-specifically glycosylate Hb. This work has great potential in developing an oxygen carrier with defined chemistry that can target oxygen delivery to low pO(2) tissues and organs.

PEGylation of Val-1(alpha) destabilizes the tetrameric structure of hemoglobin

A hexaPEGylated hemoglobin (Hb), (Propyl-PEG5K)(6)-Hb, is essentially in alphabeta dimers (Hu et al. (2007) Biochem. J. 402, 143-151). In order to provide a biochemical insight into the tetramer-dimer dissociation of this PEGylated Hb, we prepared and characterized two PEGylated Hbs site-specifically modified at Val-1(alpha) and at Val-1(beta), respectively. PEGylation at Val-1(alpha) and at Val-1(beta) increase the tetramer-dimer dissociation constant (K(d)) of Hb by 2 and 1 order of magnitude, respectively. Accordingly, the sites of PEGylation can determine the tetramer stability of the PEGylated Hb. In order to determine the role of the polyethylene glycol (PEG) chains on the tetramer stability of Hb, we prepared a propylated Hb site-specifically modified at Val-1(alpha). Interestingly, site-specific propylation of Hb at Val-l(alpha) stabilizes the Hb tetramer by 1 order of magnitude. Therefore, conjugation of the PEG chains at Val-1(alpha) can greatly destabilize the tetramer stability of Hb. On the structural aspects, the PEG chains conjugated at Va-1(alpha) unfavorably alter the heme environment and quaternary structure and destabilize the alpha1beta2 interface of Hb. On the functional aspects, the PEG chains conjugated at Val-1(alpha) decrease the Hill coefficient, the Bohr effect of Hb and the sensitization to the presence of the allosteric effectors. In contrast, PEGylation of Hb at Val-1(beta) gives rise to less pronounced structural alteration and different functional change.

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.

Role of extension arm in PEG-Hb conjugates on the stability of the tetramer: non-conservative EAF maleimide thio-PEG mediated PEGylation

PEGylation induced increase in colloidal osmotic pressure (COP) of Hb, one of the unique molecular properties of PEG-Hb conjugates, facilitates the neutralization of the vasoconstrictive activity of acellular Hb is a function of chemistry of conjugation of PEG-chains. The dependence of COP with the chemistry is a consequence of PEGylation induced weakening of interdimeric interactions. The conservative Extension Arm Facilitated (EAF) PEGylation exerts least influence on lowering the tetramer stability as compared to direct PEGylation. We have now designed a new, non-conservative EAF PEGylation that uses acylation chemistry to introduce the extension arm onto proteins to delineate the role of the extension arm and of the charge at the site of attachment in PEG-Hb conjugate on tetramer stability. The non-conservative EAF PEGylation does not lower the tetramer stability just as the non-conservative direct PEGylation of Hb. The impact of the extension arm in PEGylated Hb in terms of their structure and potential significance of higher tetramer stability of PEG-Hb conjugates generated by EAF-PEGylation in the in vivo toxicity and in the design of oxygen carrying plasma expander has been discussed.

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.

Molecular dynamics studies of polyethylene oxide and polyethylene glycol: hydrodynamic radius and shape anisotropy

A revision (C35r) to the CHARMM ether force field is shown to reproduce experimentally observed conformational populations of dimethoxyethane. Molecular dynamics simulations of 9, 18, 27, and 36-mers of polyethylene oxide (PEO) and 27-mers of polyethylene glycol (PEG) in water based on C35r yield a persistence length lambda = 3.7 A, in quantitative agreement with experimentally obtained values of 3.7 A for PEO and 3.8 A for PEG; agreement with experimental values for hydrodynamic radii of comparably sized PEG is also excellent. The exponent upsilon relating the radius of gyration and molecular weight (R(g) proportional, variantM(w)(upsilon)) of PEO from the simulations equals 0.515 +/- 0.023, consistent with experimental observations that low molecular weight PEG behaves as an ideal chain. The shape anisotropy of hydrated PEO is 2.59:1.44:1.00. The dimension of the middle length for each of the polymers nearly equals the hydrodynamic radius R(h)obtained from diffusion measurements in solution. This explains the correspondence of R(h) and R(p), the pore radius of membrane channels: a polymer such as PEG diffuses with its long axis parallel to the membrane channel, and passes through the channel without substantial distortion.

Combining the influence of two low O2 affinity-inducing chemical modifications of the central cavity of hemoglobin

HexaPEGylated hemoglobin (Hb), a non-hypertensive Hb, exhibits high O2 affinity, which makes it difficult for it to deliver the desired levels of oxygen to tissues. The PEGylation of very low O2 affinity Hbs is now contemplated as the strategy to generate PEGylated Hbs with intermediate levels of O2 affinity. Toward this goal, a doubly modified Hb with very low O2 affinity has been generated. The amino terminal of the beta-chain of HbA is modified by 2-hydroxy, 3-phospho propylation first to generate a low oxygen affinity Hb, HPPr-HbA. The oxygen affinity of this Hb is insensitive to DPG and IHP. Molecular modeling studies indicated potential interactions between the covalently linked phosphate group and Lys-82 of the trans beta-chain. To further modulate the oxygen affinity of Hb, the alpha alpha-fumaryl cross-bridge has been introduced into HPPr-HbA in the mid central cavity. The doubly modified HbA (alpha alpha-fumaryl-HPPr-HbA) exhibits an O2 affinity lower than that of either of the singly modified Hbs, with a partial additivity of the two modifications. The geminate recombination and the visible resonance Raman spectra of the photoproduct of alpha alpha-fumaryl-HPPr-HbA also reflect a degree of additive influence of each of these modifications. The two modifications induced a synergistic influence on the chemical reactivity of Cys-93(beta). It is suggested that the doubly modified Hb has accessed the low affinity T-state that is non-responsive to effectors. The doubly modified Hb is considered as a potential candidate for generating PEGylated Hbs with an O2 affinity comparable to that of erythrocytes for developing blood substitutes.