Hemoglobin–Oxygen Equilibrium Curves Measured during Enzymatic Oxygen Consumption

Vandegriff, Kim D.; Rohlfs, Ronald J.; Magde, Michael D.; Winslow, Robert M.

doi:10.1006/abio.1997.2487

Cited by 31 publications

(22 citation statements)

References 27 publications

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“…Colloid oncotic pressure was measured with the use of a colloid osmometer (model 4420, Wescor; Logan, UT) (34). O 2 equilibrium curves of MP4 and of freshly collected hamster red blood cells were measured as described previously (37) in 100 mM phosphate buffer, pH 7.4. In the case of PolyBvHb, the published equilibrium curve (19) was digitized.…”

Section: Methodsmentioning

confidence: 99%

Targeted O₂delivery by low-P₅₀hemoglobin: a new basis for O₂therapeutics

Tsai¹,

Vandegriff²,

Intaglietta³

et al. 2003

American Journal of Physiology-Heart and Circulatory Physiology

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135

179

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To assess O2 delivery to tissue by a new surface-modified, polyethylene glycol-conjugated human hemoglobin [MP4; PO2 at 50% saturation of hemoglobin (P50); 5.4 mmHg], we studied microcirculatory hemodynamics and O2 release in golden Syrian hamsters hemodiluted with MP4 or polymerized bovine hemoglobin (PolyBvHb; P50 54.2 mmHg). Comparisons were made with the animals' hemodiluted blood with a non-O2 carrying plasma expander with similar solution properties (Dextran-70). Systemic hemodynamics (arterial blood pressure and heart rate) and acid-base parameters were not correlated with microhemodynamics (arteriolar and venular diameter, red blood cell velocity, and flow). Microscopic measurements of PO2 and the O2 equilibrium curves permitted analysis of O2 release in precapillary and capillary vessels by red blood cells and plasma hemoglobin separately. No significant differences between the groups of animals with respect to arteriolar diameter, flow, or flow velocity were observed, but the functional capillary density was significantly higher in the MP4-treated animals (67%) compared with PolyBvHbtreated animals (37%; P Ͻ 0.05) or dextran-treated animals (53%). In the PolyBvHb-treated animals, predominant O2 release (both red blood cells and plasma hemoglobin) occurred in precapillary vessels, whereas in MP4 animals most of the O2 was released from both red blood cells and plasma hemoglobin in capillaries. Base excess correlated directly with capillary O2 release but not systemic O2 content or total O2 release. Higher O2 extraction of both red blood cell and plasma hemoglobin in capillaries represents a new mechanism of action of cell-free hemoglobin. High O2 affinity appears to be an important property for cell-free hemoglobin solutions. blood substitutes; microcirculation; polyethylene glycol ARTERIOLAR VASOCONSTRICTION limits tissue perfusion by some early-generation hemoglobin-based O 2 carriers, increasing vascular resistance, which may be manifest as systemic hypertension, offsetting potential efficacy (40). Although the mechanism of vasoactivity has been disputed, one popular explanation is that nitric oxide (NO) is scavenged by cell-free hemoglobin (9), either directly in the lumen of the vessel or in the interstitial space after extravasation. We observed, however, that derivatized hemoglobins with different hypertensive effects have nearly identical NO binding constants (26). An alternative (or additional) mechanism is the involvement of autoregulation, by which vasoconstriction results from an oversupply of O 2 to vascular walls, particularly in arterioles, which regulate the entry of blood into capillary networks (23). An O 2 oversupply would result from facilitated diffusion of O 2 as oxyhemoglobin in plasma. Oxyhemoglobin diffusion is a function of molecular size, viscosity, and O 2 affinity, and manipulation of these three parameters offers strategies for potentially overcoming autoregulatory vasoconstriction. We explored these ideas in an artificial capillary system and concluded that the O 2 deliver...

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Section: Methodsmentioning

confidence: 99%

Targeted O₂delivery by low-P₅₀hemoglobin: a new basis for O₂therapeutics

Tsai¹,

Vandegriff²,

Intaglietta³

et al. 2003

American Journal of Physiology-Heart and Circulatory Physiology

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135

179

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“…In all cases, the blood oxygen content was determined by using the oxygen dissociation curves corresponding to each of the oxygencarrying blood components to calculate the oxygen content at the measured blood PO 2. Data on oxygen saturation were obtained as previously described (30). In this analysis, microvascular Hct was corrected according to the findings of Lipowsky and Firrell (11).…”

Section: Methodsmentioning

confidence: 99%

Microvascular Po₂during extreme hemodilution with hemoglobin site specifically PEGylated at Cys-93(β) in hamster window chamber

Cabrales

Kanika

Manjula

et al. 2004

American Journal of Physiology-Heart and Circulatory Physiology

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Intaglietta. Microvascular PO 2 during extreme hemodilution with hemoglobin site specifically PEGylated at Cys-93(␤) in hamster window chamber. Am J Physiol Heart Circ Physiol 287: H1609 -H1617, 2004. First published June 10, 2004 10.1152/ajpheart.00146.2004.-The oxygen transport capacity of nonhypertensive polyethylene glycol (PEG)-conjugated hemoglobin solutions were investigated in the hamster chamber window model. Microvascular measurements were made to determine oxygen delivery in conditions of extreme hemodilution [hematocrit (Hct) 11%]. Two isovolemic hemodilution steps were performed with a 6% Dextran 70 (70-kDa molecular mass) plasma expander until Hct was 35% of control. Isovolemic blood volume exchange was continued using two surface-modified PEGylated hemoglobins (P5K2, P 50 ϭ 8.6, and P10K2, P50 ϭ 8.3; P50 is the hemoglobin PO2 corresponding to its 50% oxygen saturation) until Hct was 11%. P5K2 and P10K2 are PEG-conjugated hemoglobins that maintain most of the hemoglobin allosteric properties and have a cooperativity index of n ϭ 2.2. The effects of these molecular solutions were compared with those obtained in a previous study using MP4, a PEG-modified hemoglobin whose P 50 was 5.4 and cooperativity was 1.2 (Tsai et al., Am J Physiol Heart Circ Physiol 285: H1411-H1419, 2003). Tissue oxygen levels were higher after P5K2 (7.0 Ϯ 2.5 mmHg) and P10K2 (6.3 Ϯ 2.3 mmHg) versus MP4 (1.7 Ϯ 0.5 mmHg) or the nonoxygen carrier Dextran 70 (1.3 Ϯ 1.2 mmHg). Microvascular oxygen delivery was higher after P5K2 and P10K2 (2.22 and 2.34 ml O 2/dl blood) compared with MP4 (1.41 ml O2/dl blood) or Dextran 70 (0.90 ml O2/dl blood); however, all these values were lower than control (7.42 ml O2/dl blood). The total hemoglobin in blood was similar in all cases; therefore, the improvement in tissue PO 2 and oxygen delivery appears to be due to the increased cooperativity of the new molecules.surface-modified hemoglobin; functional capillary density; oxygencarrying capacity; blood substitutes; tissue oxygen delivery; hemoglobin cooperativity THE DEVELOPMENT of blood substitutes [oxygen-carrying plasma expanders (OCPEs)] has traditionally focused on devising fluids whose transport properties are equivalent to those of blood. This requires using an oxygen carrier that provides an oxygen transport capacity and release properties similar to those of erythrocytes, a task for which hemoglobin (Hb) placed inside the red blood cell (RBC) is ideally suited.

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“…Measurement of Oxygen Equilibrium Curves-Hemoglobin-oxygen equilibrium curves were measured as described by Vandegriff et al (13). Hemoglobin solutions (0.1 M bis-Tris propane, 0.1 M Cl Ϫ , pH 7.4) were rapidly deoxygenated using the protocatechuic acid/protocatechuic acid 3,4-dioxygenase system (14).…”

Section: Methodsmentioning

confidence: 99%

“…(25). Oxygen equilibrium binding parameters (p 50 , n 50 ) were measured in 0.1 M bis-Tris propane, 0.1 M Cl Ϫ , pH 7.4, 37°C by the method described in Vandegriff et al (13). The errors represent the standard error of the mean.…”

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confidence: 99%

Arterial Blood Pressure Responses to Cell-free Hemoglobin Solutions and the Reaction with Nitric Oxide

Rohlfs

Bruner

Chiu

et al. 1998

Journal of Biological Chemistry

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214

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Changes in mean arterial pressure were monitored in rats following 50% isovolemic exchange transfusion with solutions of chemically modified hemoglobins. Blood pressure responses fall into three categories: 1) an immediate and sustained increase, 2) an immediate yet transient increase, or 3) no significant change either during or subsequent to exchange transfusion. The reactivities of these hemoglobins with nitric monoxide ( ⅐ NO) were measured to test the hypothesis that different blood pressure responses to these solutions result from differences in ⅐ NO scavenging reactions. All hemoglobins studied exhibited a value of 30 M ؊1 s ؊1 for both ⅐ NO bimolecular association rate constants and the rate constants for ⅐ NO-induced oxidation in vitro. Only the ⅐ NO dissociation rate constants and, thus, the equilibrium dissociation constants varied. Values of equilibrium dissociation constants ranged from 2 to 14 pM and varied inversely with vasopressor response. Hemoglobin solutions that exhibited either transient or no significant increase in blood pressure showed tighter ⅐ NO binding affinities than hemoglobin solutions that exhibited sustained increases. These results suggest that blood pressure increases observed upon exchange transfusion with cell-free hemoglobin solutions can not be the result of ⅐ NO scavenging reactions at the heme, but rather must be due to alternative physiologic mechanisms.Control of blood pressure and resistance to blood flow is achieved by a dynamic constriction and relaxation of smooth muscle tissue which surrounds all blood vessels except capillaries. Vascular smooth muscle tension is continually adjusted by a complex system that causes either vasoconstriction or vasodilation, depending on metabolic need (1). Research performed over the last decade has established that endotheliumderived nitric oxide ( ⅐ NO) 1 can cause vasodilation. ⅐ NO is produced by endothelial cells that lie between the intravascular space and the surrounding smooth muscle. Among the findings was the demonstration that ⅐ NO donors (e.g. nitroprusside, nitroglycerin) lead to vasorelaxation through activation of guanylate cyclase, whereas inhibitors of ⅐ NO synthesis (e.g. N Gmonomethyl-L-arginine) or scavengers (e.g. hemoglobin) cause vasoconstriction (for reviews, see Refs. 2 and 3).Since cell-free hemoglobin is being developed as a red cell substitute (4), reactions between hemoglobin and ⅐ NO are of potential importance in maintenance of microvascular blood flow and O 2 delivery. Despite the wide variation that exists in the physical properties (O 2 affinity, molecular mass, and solution properties) of different cell-free hemoglobins, it appears vasoconstriction is a feature common to many hemoglobin solutions (for reviews, see Refs. 2, 3, and 5). It is tempting to conclude that ⅐ NO scavenging is the principal, if not sole mechanism for vasoconstriction associated with cell-free hemoglobin. However, it is well established that multiple factors contribute to the physiological control of vascular smooth muscle to...

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Hemoglobin–Oxygen Equilibrium Curves Measured during Enzymatic Oxygen Consumption

Cited by 31 publications

References 27 publications

Targeted O₂delivery by low-P₅₀hemoglobin: a new basis for O₂therapeutics

Targeted O₂delivery by low-P₅₀hemoglobin: a new basis for O₂therapeutics

Microvascular Po₂during extreme hemodilution with hemoglobin site specifically PEGylated at Cys-93(β) in hamster window chamber

Arterial Blood Pressure Responses to Cell-free Hemoglobin Solutions and the Reaction with Nitric Oxide

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Hemoglobin–Oxygen Equilibrium Curves Measured during Enzymatic Oxygen Consumption

Cited by 31 publications

References 27 publications

Targeted O2delivery by low-P50hemoglobin: a new basis for O2therapeutics

Targeted O2delivery by low-P50hemoglobin: a new basis for O2therapeutics

Microvascular Po2during extreme hemodilution with hemoglobin site specifically PEGylated at Cys-93(β) in hamster window chamber

Arterial Blood Pressure Responses to Cell-free Hemoglobin Solutions and the Reaction with Nitric Oxide

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Targeted O₂delivery by low-P₅₀hemoglobin: a new basis for O₂therapeutics

Targeted O₂delivery by low-P₅₀hemoglobin: a new basis for O₂therapeutics

Microvascular Po₂during extreme hemodilution with hemoglobin site specifically PEGylated at Cys-93(β) in hamster window chamber