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 novel single sensor hemoglobin domain from the thermophilic cyanobacteria Thermosynechococcus elongatus BP-1 exhibits higher pH but lower thermal stability compared to globins from mesophilic organisms

Thermosynechococcus elongatus-BP1 belongs to the class of photoautotrophic cyanobacterial organisms. The presence of chlorophyll a, carotenoids, and phycocyanobilin are the characteristics that categorize T. elongatus as a photosynthetic organism. Here, we report the structural and spectroscopic characteristics of novel hemoglobin (Hb) Synel Hb from T.elongatus, synonymous with Thermosynechococcus vestitus BP-1. The X-ray crystal structure (2.15 Å) of Synel Hb suggests the presence of a globin domain with a pre-A helix similar to the sensor domain (S) family of Hbs. The rich hydrophobic core accommodates heme in a penta-coordinated state and readily binds an extraneous ligand(imidazole). The absorption and circular dichroic spectral analysis of Synel Hb reiteratedthat the heme is in Fe^III+ state with a predominantly α-helical structure similar to myoglobin. Synel Hb displays higher resistance to structural perturbations induced via external stresses like pH and guanidium hydrochloride, which is comparable to Synechocystis Hb. However, Synel Hb exhibited lower thermal stability compared to mesophilic hemoglobins. Overall, the data is suggestive of the structural sturdiness of Synel Hb, which probably corroborates its origin in extreme thermophilic conditions. The stable globin provides scope for further investigation and may lead to new insights with scope for engineering stability in hemoglobin-based oxygen carriers.

Molecular Simulations of PEGylated Biomolecules, Liposomes, and Nanoparticles for Drug Delivery Applications

Since the first polyethylene glycol (PEG)ylated protein was approved by the FDA in 1990, PEGylation has been successfully applied to develop drug delivery systems through experiments, but these experimental results are not always easy to interpret at the atomic level because of the limited resolution of experimental techniques. To determine the optimal size, structure, and density of PEG for drug delivery, the structure and dynamics of PEGylated drug carriers need to be understood close to the atomic scale, as can be done using molecular dynamics simulations, assuming that these simulations can be validated by successful comparisons to experiments. Starting with the development of all-atom and coarse-grained PEG models in 1990s, PEGylated drug carriers have been widely simulated. In particular, recent advances in computer performance and simulation methodologies have allowed for molecular simulations of large complexes of PEGylated drug carriers interacting with other molecules such as anticancer drugs, plasma proteins, membranes, and receptors, which makes it possible to interpret experimental observations at a nearly atomistic resolution, as well as help in the rational design of drug delivery systems for applications in nanomedicine. Here, simulation studies on the following PEGylated drug topics will be reviewed: proteins and peptides, liposomes, and nanoparticles such as dendrimers and carbon nanotubes.

Determination of extinction coefficients of human hemoglobin in various redox states

The role of hemoglobin (Hb) redox forms in tissue and organ toxicities remain ambiguous despite the well-documented contribution of Hb redox reactivity to cellular and subcellular oxidative changes. Moreover, several recent studies, in which Hb toxicity were investigated, have shown conflicting outcomes. Uncertainties over the potential role of these species may in part be due to the protein preparation method of choice, the use of published extinction coefficients and the lack of suitable controls for Hb oxidation and heme loss. Highly purified and well characterized redox forms of human Hb were used in this study and the extinction coefficients of each Hb species (ferrous/oxy, ferric/met and ferryl) were determined. A new set of equations were established to improve accuracy in determining the transient ferryl Hb species. Additionally, heme concentrations in solutions and in human plasma were determined using a novel reversed phase HPLC method in conjugation with our photometric measurements. The use of more accurate redox-specific extinction coefficients and method calculations will be an invaluable tool for both in vitro and in vivo experiments aimed at determining the role of Hb-mediated vascular pathology in hemolytic anemias and when Hb is used as oxygen therapeutics.

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.

Packing density of the PEG-shell in PEG-albumins: PEGylation induced viscosity and COP are inverse correlate of packing density

PEG-Alb represents a new class of low viscogenic plasma expanders that achieve super perfusion in vivo by mimicking the vasodilatory influence of high viscogenic plasma expanders. PEGylation-engineered structure of PEG albumin can be envisaged as a deformable molecular domain around the rigid central protein core. The correlation between the structure of PEG-shell in terms of packing of the PEG inside the PEG shell and PEGylation induced plasma expander (PE)-like properties of albumin has been investigated as a function of the number and length of the PEG-chain. The increase in molecular radius of albumin on PEGylation is non-linear as a function of the number of PEG chains conjugated. The packing density of PEG within the PEG-shell is an inverse correlate of PEG-chain size; i.e. the shorter chains pack more compactly than the longer ones. The PEGylation induced increase in the viscosity and COP of albumin is an exponential correlation of the number of ethylene oxide units (-CH(2)-CH(2)-O-) conjugated and is also a function of the PEG-chain length. At equivalence of PEG mass conjugated, the viscosity and COP of PEG-albumin adducts correlate inversely with packing density of PEG. All PEGylated albumins are not equivalent on the basis of total PEG mass conjugated. Accordingly, the structure of PEG albumin and its solution properties can be engineered to optimize a given total PEG mass for the application of PEG albumin as a resuscitation fluid. The extension arms minimize the influence of PEG shell on the structure of the protein core. We speculate that EAF-PEGylation is a preferable platform for PEGylation of protein therapeutics and is expected to generate products with better therapeutic efficacy.

Effects of a combination hemoglobin based oxygen carrier-hypertonic saline solution on oxygen transport in the treatment of traumatic shock

BACKGROUND

Logistics complicate fluid resuscitation of traumatic shock on the battlefield. Traumatic shock can result in oxygen debt (O(2)D) accumulation that is fatal. However, the ability of fluid strategies to repay O(2)D are not commonly reported. This pilot study examined various resuscitation fluids, including a combination of PEGylated bovine hemoglobin and hypertonic saline (AfterShock™) on their ability to repay O(2)D in traumatic shock.

METHODS

41 anesthetized swine underwent hemorrhage to an O(2)D of 80 mL/kg. Animals received one of the following: 500 mL whole blood, 500 mL AfterShock™, 500 mL hypertonic (7.2%) saline, 250 mL hypertonic (7.2%) saline, 500 mL Hetastarch (6%), or 500 mL lactated Ringer's. Oxygen transport variables (O(2)D, oxygen consumption, oxygen delivery, central venous hemoglobin oxygen saturation, oxygen extraction ratios), lactate clearance, and survival were monitored for 3h after treatment. Data were analyzed using mixed-model ANOVA and comparisons were made to the performance of whole blood.

RESULTS

Only animals receiving AfterShock™, 500 mL hypertonic saline, and 500 mL Hetastarch survived to 180 min. While not statistically significant AfterShock™ demonstrated trends in improving the repayment of O(2)D and in improving oxygen transport variables despite having lower levels of global oxygen delivery compared to whole blood, Hetastarch and 500 mL hypertonic saline groups.

CONCLUSION

Use of 500 mL AfterShock™, 500 mL of 7.2% saline or 500 mL of Hetastarch resulted in improved short-term survival. While not statistically significant, AfterShock™ demonstrated trends in improving O(2)D. These findings may have implications for designing resuscitation fluids for combat casualty care.

Tissue oxidative metabolism after extreme hemodilution with PEG-conjugated hemoglobin

NADH-localized fluorometry was used as a noninvasive technique to monitor changes in the energy state of intact tissue (muscle and connective tissue), without anesthesia, as a function of blood plasma O(2)-carrying capacity in the hamster window chamber model. Acute moderate isovolemic hemodilution was induced by two isovolemic hemodilution steps: in the first step, 6% 70-kDa dextran (Dex70) was used to induce an acute anemic state (18% Hct); in the second step, exchange transfusion of polyethylene glycol (PEG) maleimide-conjugated Hb (4 g/dl, PEG-Hb) or Dex70 (6 g/dl) was used to reduce erythrocytes to 75% of baseline (11% Hct). PEG-Hb had six copies of PEG (5 kDa) conjugated to each human Hb (0.48 g PEG/g Hb) through extension arm-facilitated chemistry. Systemic parameters, microvascular perfusion, functional capillary density, intravascular and interstitial Po(2), and intracellular NADH fluorescence were monitored. Mean arterial blood pressure after extreme hemodilution was statistically significantly reduced for Dex70 compared with PEG-Hb. The presence of PEG-Hb in the circulation maintained positive acid-base balance. While microvascular blood flows were not different, functional capillary density was significantly higher for PEG-Hb than Dex70. Arteriolar Po(2) was higher in the presence of PEG-Hb than Dex70, but tissue and venular Po(2) were not different. Cellular energy metabolism (intracellular O(2)) in the tissues was improved with PEG-Hb. Moderate hemodilution to 18% Hct (6.4 g Hb/dl) brings tissue O(2) delivery to the verge of inadequacy. Extreme hemodilution to 11% Hct (3.7 g Hb/dl) produces tissue anoxia, and high-O(2)-affinity PEG-Hb (Po(2) at which blood is 50% saturated with O(2) = 4 Torr, 1.1 g Hb/dl) only partially decreases anaerobic metabolism without increasing tissue Po(2).