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ABSTRACT: A vasodilatory hemoglobin (Hb)-based O(2) carrier (HBOC) has been developed by surface conjugation polyethylene glycol to tetrameric human Hb (MP4, Sangart, San Diego). Because the NO-binding kinetics of MP4 are similar to vasoconstrictive HBOCs, we propose that the decoupling of NO scavenging from vascular response is a consequence of MP4's high O(2) affinity (p50 = 5 mmHg) and unique surface chemistry. The release of ATP from erythrocytes is vasodilatory and the application of a high O(2) affinity HBOC minimizes ATP interference with intravascular ATP signaling. A second potential mechanism of action for MP4 involves the surface conjugation of polyethylene glycol (PEG) to tetrameric human Hb. It has been shown that the addition of unconjugated high molecular weight (Mw) PEG to cultured lung endothelial cells causes an immediate and significant reduction in endothelial permeability; an effect opposite to that of endothelial agonists such as cell-free Hb. It appears that some of the benefits of the PEG-endothelium interaction are carried onto molecules such as PEGylated Hb and PEGylated albumin, as demonstrated by favorable hemodynamic responses in vivo. PEGylation of ß93 cysteine residues, as in MP4, has also been reported to increase the nitrite reductase activity of Hb and enhance conversion of endogenous nitrite to bioactive NO.
Advances in experimental medicine and biology 01/2011; 701:85-90. · 1.09 Impact Factor
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ABSTRACT: The red blood cell (RBC) has been proposed as an O(2) sensor through a direct link between the desaturation of intracellular hemoglobin (Hb) and ATP release, leading to vasodilation. We hypothesized that the addition of cell-free Hb to the extracellular space provides a supplementary O(2) source that reduces RBC desaturation and, consequently, ATP release. In this study, the saturation of RBC suspensions was lowered by additions of deoxygenated hemoglobin-based oxygen carrier (HBOC) and then assayed for extracellular ATP. When an acellular human Hb intramolecularly cross-linked between alpha subunits (alphaalphaHb, p50 = 33 mmHg) was added to the red cell suspension, ATP production was significantly less than that in the presence of a lower p50 HBOC (Hb cross-linked between beta subunits, betabetaHb, p50 = 8 mmHg). These results provide a potential mechanism for the O(2) affinity of HBOCs to interfere with a vasodilatory signal.
Biophysical chemistry 09/2009; 144(3):119-22. · 2.28 Impact Factor
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ABSTRACT: The delivery of oxygen to tissue by cell-free carriers eliminates intraluminal barriers associated with red blood cells. This is important in arterioles, since arteriolar tone controls capillary perfusion. We describe a mathematical model for O(2) transport by hemoglobin solutions and red blood cells flowing through arteriolar-sized tubes to optimize values of p50, Hill number, hemoglobin molecular diffusivity and concentration. Oxygen release is evaluated by including an extra-luminal resistance term to reflect tissue oxygen consumption. For low consumption (i.e., high resistance to O(2) release) a hemoglobin solution with p50=15 mmHg, n=1, D(HBO2)=3 x 10(-7) cm(2)/s delivers O(2) at a rate similar to that of red blood cells. For high consumption, the p50 must be decreased to 5 mmHg. The model predicts that regardless of size, hemoglobin solutions with higher p50 will present excess O(2) to arteriolar walls. Oversupply of O(2) to arteriolar walls may cause constriction and paradoxically reduced capillary perfusion.
Biophysical Chemistry 07/2007; 128(1):63-74. · 2.20 Impact Factor
