Comparison of PEG-modified albumin and hemoglobin in extreme hemodilution in the rat.
ABSTRACT We have reported a new polyethylene glycol (PEG)-modified, hemoglobin-based O2 carrier (MP4) with novel properties, including a large molecular excluded volume and low PO2 necessary to obtain 50% O2 (approximately 6 Torr). To evaluate the ability of MP4 to transport O2, we compared it with PEG-modified albumin (MPA) using the identical chemistry of attachment of PEG chains. The resulting solutions were well matched with respect to all physical properties except that MP4 is an O2 carrier, whereas MPA is not. An additional solution, 10% pentastarch, was matched with the PEG-modified proteins with regard to oncotic activity and viscosity but does not contain PEG. The model used to evaluate O2 transport was continuous exchange transfusion in the rat until the hematocrit was virtually unmeasurable. Objective end points included survival and the onset of anaerobic metabolism, signaled by acid-base derangement and accumulation of lactic acid. Continuous exchange transfusion of 2.5 blood volumes in rats (n=5 in each treatment group) was carried out over 60 min, such that the final hematocrit was between 0 and 5% in all animals. Animals were observed for an additional 70 min, when survivors were killed. Overall survival for the MP4 animals was 100%; no animal that received either pentastarch or MPA survived. The hematocrit at which lactic acid began to rise was approximately 14.8% in both pentastarch and MPA animals and 7.4% in the animals that received MP4. In all groups, the total hemoglobin was approximately 5 g/dl at this point. We conclude that, despite its low PO2 necessary to obtain 50% O2, MP4 effectively substitutes for red blood cell hemoglobin in its ability to oxygenate tissues in extreme hemodilution.
Article: Sites of modification of hemospan, a poly(ethylene glycol)-modified human hemoglobin for use as an oxygen therapeutic.[show abstract] [hide abstract]
ABSTRACT: Hemospan is an acellular hemoglobin-based oxygen therapeutic in clinical trials in Europe and the United States. The product is prepared by site-specific conjugation of maleimide-activated poly(ethylene) glycol (PEG, MW approximately 5500) to human oxyhemoglobin through maleimidation reactions either (1) directly to reactive Cys thiols or (2) at surface Lys groups following thiolation using 2-iminothiolane. The thiolation/maleimidation reactions lead to the addition of approximately 8 PEGs per hemoglobin tetramer. Identification of PEG modified globins by SDS-PAGE and MALDI-TOF reveals a small percentage of protein migrating at the position for unmodified globin chains and the remaining as separate bands representing globin chains conjugated with 1 to 4 PEGs per chain. Identification of PEG modification sites on individual alpha and beta globins was made using reverse-phase HPLC, showing a series of alpha globins conjugated with 0 to 3 PEGs and a series of beta globins conjugated with 0 to 4 PEGs per globin. Mass analysis of tryptic peptides from hemoglobin thiolated and maleimidated with N-ethyl maleimide showed the same potential sites of modification regardless of thiolation reaction ratio, with seven sites identified on beta globins at beta8, beta17, beta59, beta66, beta93, beta95, and beta132 and three sites identified on alpha globins at alpha7, alpha16, and alpha40.Bioconjugate Chemistry 11/2008; 19(11):2163-70. · 4.93 Impact Factor
Article: Survival time in severe hemorrhagic shock after perioperative hemodilution is longer with PEG-conjugated human serum albumin than with HES 130/0.4: a microvascular perspective.[show abstract] [hide abstract]
ABSTRACT: Preoperative hemodilution is an established practice that is applied to reduce surgical blood loss. It has been proposed that polyethylene glycol (PEG) surface decorated proteins such as PEG-conjugated human serum albumin may be used as non-oxygen-carrying plasma expanders. The purpose of this study was to determine whether there is any difference in survival time after severe hemorrhagic shock following extreme hemodilution using a conventional hydroxyethyl starch (HES)-based plasma expander or PEG-albumin. Experiments were performed using the hamster skinfold window preparation. Human serum albumin that was surface decorated with PEG was compared with Voluven 6% (Fresenius Kabi, Austria; a starch solution that is of low molecular weight and has a low degree of substitution; HES). These plasma expanders were used for a 50% (blood volume) exchange transfusion to simulate preoperative hemodilution. Exchange transfusion was followed by a 60% (blood volume) hemorrhage to reproduce a severe surgical bleed over a 1 hour period. Observation of the animal was continued for another hour during the shock phase. The PEG-albumin group exhibited significantly greater survival rate than did the HES group, in which none of the animals survived the hemorrhage phase of the experiment. Among the treatment groups there were no changes in mean arterial pressure and heart rate from baseline after hemodilution. Both groups experienced gradual increases in arterial oxygen tension and disturbance in acid-base balance, but this response was more pronounced in the HES group during the shock period. Mean arterial pressure remained elevated after the initial hemorrhage period in the PEG-albumin group but not in the HES group. Maintenance of a greater mean arterial pressure during the initial stages of hemorrhage is proposed to be in part due to the improved volume expansion with PEG-albumin, as indicated by the significant decrease in systemic hematocrit compared with the HES group. PEG-albumin treatment yielded higher functional capillary density during the initial stages of hemorrhage as compared with HES treatment. The ability of PEG-albumin to prolong maintenance of microvascular function better than HES is a finding that would be significant in a clinical setting involving preoperative blood management and extreme blood loss.Critical care (London, England) 02/2008; 12(2):R54. · 4.61 Impact Factor