Hemoglobin-Based O2Carrier O2Affinity and Capillary Inlet pO2Are Important Factors That Influence O2Transport in a Capillary

Facile fabrication of poly(glycidyl methacrylate)-b-polystyrene functional fibers under a shear field and immobilization of hemoglobin

PGMA-b-PS fibers were fabricated under a shear field for immobilization of bovine hemoglobin which has potential applications in blood substitutes.

A bovine hemoglobin-based oxygen carrier as pump prime for cardiopulmonary bypass: reduced systemic lactic acidosis and improved cerebral oxygen metabolism during low flow in a porcine model

OBJECTIVES

Cerebral ischemia can occur during cardiopulmonary bypass, especially during low flow. HBOC-201 (OPK Biotech, Cambridge, Mass) is a hemoglobin-based oxygen-carrying solution that enhances oxygen delivery. This project evaluated the benefits on total body and cerebral oxygen delivery and consumption using HBOC-201 during cardiopulmonary bypass.

METHODS

Twelve immature swine were assigned to one of 2 groups. One group used HBOC-201 in pump prime, and the other used donor porcine blood. Cardiopulmonary bypass was initiated and then flow was serially decreased from 100% to 75%, to 50%, and then back to full flow. At each interval, (15)O positron emission tomographic analysis was performed, and blood was collected. Total body and cerebral oxygen delivery and consumption were calculated. Statistical analysis was performed with a Tukey-Kramer adjusted P value based on a repeated measures linear model on log-transformed data.

RESULTS

Total and plasma hemoglobin levels were higher in the HBOC-201 group. Oxygen delivery and consumption were not statistically different but did tend to be higher in the HBOC-201 group. Mixed venous saturation was lower in the HBOC-201 group but not significant. Mild metabolic acidosis with increased lactate levels developed in the blood group. Mean cerebral blood flow decreased in both groups when total flow was 50%. In the HBOC-201 group cerebral oxygen metabolism was maintained.

CONCLUSIONS

The addition of HBOC-201 for cardiopulmonary bypass appears to improve oxygen use and minimize anaerobic metabolism. Cerebral oxygen use was preserved in the HBOC-201 group, even during decrease in blood flow. These findings support the reported improved oxygen-unloading properties of HBOC-201 and might provide a benefit during cardiopulmonary bypass.

Hemoglobin conjugates with antioxidant enzymes (hemoglobin-superoxide dismutase-catalase) via poly(ethylene glycol) crosslinker for protection of pancreatic beta RINm5F cells in hypoxia

A low p50 hemoglobin (Hb) (p50 indicates O(2) tension at which Hb is half-saturated)-based oxygen carrier conjugated to antioxidant enzymes via dicarboxymethylated poly(ethylene glycol) (PEG) linker may have the beneficial effect in protecting pancreatic beta cells from severe hypoxia at transplantation sites. In this study, the oxygen dissociation curves, Hill plots, Bohr Effect, and oxygen content of Hb conjugates were measured. The protective effect due to incubation of Hb-conjugates (Hb/PEG molar ratio 1:10) with pancreatic beta cells (RINm5F) against hypoxia (6%, 3%, and 1% oxygen) was evaluated by an MTT assay and confocal microscopy. Quantitatively, Hb conjugates with antioxidant enzymes offered statistically significant protection (p<0.01, increased viability ∼80%) from hypoxia compared to control cells in 1% oxygen environment. Confocal images also showed that the low p50 Hb conjugates with antioxidants protected RINm5F cells from hypoxia.

Blood gas analysis and cooximetry in retired racing Greyhounds

OBJECTIVE

The purposes of this study were to evaluate the oxygen affinity of hemoglobin (Hb) in healthy retired racing Greyhounds via cooximetry, and to establish reference intervals for blood gases and cooximetry in this breed.

DESIGN

Prospective clinical study.

SETTING

University Teaching Hospital.

ANIMALS

Fifty-seven Greyhounds and 30 non-Greyhound dogs.

INTERVENTIONS

Venous blood samples were collected from the jugular vein and placed into heparinized tubes. The samples were analyzed within 30 minutes of collection using a blood gas analyzer equipped with a cooximeter.

MEASUREMENTS AND MAIN RESULTS

Greyhounds had significantly higher pH, PO(2) , oxygen saturation, oxyhemoglobin, total Hb, oxygen content, and oxygen capacity and significantly lower deoxyhemoglobin and P(50) when compared with non-Greyhound dogs.

CONCLUSION

These findings support the fact that this breed is able to carry a higher concentration of total oxygen in the blood. As reported previously, this breed also has lower P(50) and, therefore, high oxygen affinity. In light of recent findings suggesting that in certain tissues a high affinity for oxygen is beneficial, this adaptation may be of benefit during strenuous exercise.

Mathematical model of NO and O2 transport in an arteriole facilitated by hemoglobin based O2 carriers

The increasing demand for donated human blood has spurred research to develop hemoglobin-based O(2) carriers (HBOCs) that can be used as red blood cell (RBC) substitutes. However, in vivo studies of acellular HBOCs have shown an increase in mean arterial pressure following transfusion that has been attributed to the HBOC's ability to scavenge NO (an important vasodilator that is synthesized by endothelial cells in the blood vessel wall that signals neighboring smooth muscle cells to relax). In this study, a mathematical model was developed to describe NO and O(2) transport in an arteriole containing a mixture of acellular HBOCs and RBCs. The acellular HBOCs studied in this work possessed a wide range of O(2) affinities, O(2) dissociation rate constants and NO reactivities in order to evaluate their effect on O(2) tension and NO concentration in the arteriole tissue region. By focusing on the concentration of NO that is localized in the arteriole smooth muscle cell region, the model can predict the vasopressor response of HBOCs. The results of this study confirmed that acellular HBOCs scavenge large amounts of NO from the entire arteriole (approximately 50% or more NO compared to RBCs only). A recombinant Hb, rHb3011, displayed the least NO reactivity and consequently left the most NO remaining in the arteriole. The NO concentration in the arteriole with respect to the other HBOCs studied was proportional to their NO reactivity. Therefore, the results of this study demonstrate that NO scavenging is an unavoidable consequence of transfusing HBOCs. To prevent or reduce vasodilatation, we suggest administration of NO by either inhaling NO or transfusing nitrite into the blood stream followed by transfusion of HBOC.

Modern cross-linking strategies for synthesizing acellular hemoglobin-based oxygen carriers

Unmodified cell-free hemoglobin (Hb) is structurally unstable when transfused into the blood stream (Valeri et al., Artif Cells Blood Substit Immobil Biotechnol. 2000;28:451-475; Chan et al., Toxicol Pathol. 2000;28:635-642; Eike, Dissertation, 2005; Eike and Palmer, Biotechnol Prog. 2004;20:946-952). This review examines some of the latest chemical strategies used over the last 5 years to intra- and intermolecularly cross-link Hb, thereby stabilizing its quaternary structure. Therefore, this work will address the following aspects: (1) site-specific chemical modifications of Hb and (2) non-site-specific chemical modifications of Hb, including, but not limited to, PolyHeme, Hemopure, Oxyglobin, and SOD-Hb. Current strategies for synthesizing PEGylated Hb is outside the scope of this review and will not be discussed herein. For a more thorough review of PEGylated Hb, the reader is directed to the following works: Cabrales and Friedman, Transfus Alternatives in Transfus Med. 2007;9:281-293 and Winslow, Biochim Biophys Acta, 2008;1784(10):1382-1386.

Tangential flow filtration of hemoglobin

Bovine and human hemoglobin (bHb and hHb, respectively) was purified from bovine and human red blood cells via tangential flow filtration (TFF) in four successive stages. TFF is a fast and simple method to purify Hb from RBCs using filtration through hollow fiber (HF) membranes. Most of the Hb was retained in stage III (100 kDa HF membrane) and displayed methemoglobin levels less than 1%, yielding final concentrations of 318 and 300 mg/mL for bHb and hHb, respectively. Purified Hb exhibited much lower endotoxin levels than their respective RBCs. The purity of Hb was initially assessed via SDS-PAGE, and showed tiny impurity bands for the stage III retentate. The oxygen affinity (P(50)) and cooperativity coefficient (n) were regressed from the measured oxygen-RBC/Hb equilibrium curves of RBCs and purified Hb. These results suggest that TFF yielded oxygen affinities of bHb and hHb that are comparable to values in the literature. LC-MS was used to measure the molecular weight of the alpha (alpha) and beta (beta) globin chains of purified Hb. No impurity peaks were present in the HPLC chromatograms of purified Hb. The mass of the molecular ions corresponding to the alpha and beta globin chains agreed well with the calculated theoretical mass of the alpha- and beta- globin chains. Taken together, our results demonstrate that HPLC-grade Hb can be generated via TFF. In general, this method can be more broadly applied to purify Hb from any source of RBCs. This work is significant, since it outlines a simple method for generating Hb for synthesis and/or formulation of Hb-based oxygen carriers.

Targeted O2 delivery by blood substitutes: in vitro arteriolar simulations of first- and second-generation products

The O(2) transport from mixtures of commercially produced hemoglobin-based O(2) carriers (HBOCs) and red blood cells (RBCs) flowing through arteriolar-sized (25-mum) conduits is simulated. A generalized treatment of extraluminal O(2) transport processes is used to reflect variations in physiological conditions, such as increased O(2) consumption. Of the HBOCs considered, polymerized bovine hemoglobin (PolyBvHb, p50=54 mmHg), tetrameric cross-linked human hemoglobin (alphaalphaHb, p50=33 mmHg), and PEGylated human hemoglobin (MP4, p50=5 mmHg), only MP4 does not increase O(2) extraction ratios when compared to RBC suspensions alone. A reduction in arteriolar O(2) extraction is likely to be beneficial for HBOCs by preventing O(2)-induced vasoactivity and maximizing the supply of O(2) available to the capillaries. Results from in vivo HBOC transfusion experiments cannot be predicted by the model, unless PolyBvHb has a significant decrease in extraluminal O(2) transport resistance as compared to MP4. This result is consistent with the literature that shows arteriolar O(2) consumption to increase with intravascular pO(2).