Vascular response to infusions of a nonextravasating hemoglobin polymer

Abstract

The clinical utility of cross-linked tetrameric hemoglobin solutions is limited by peripheral vasoconstriction thought to be due to scavenging of nitric oxide. In addition, transfusion of crude preparations of hemoglobin polymers can cause arterial hypertension. We tested the hypothesis that eliminating low-molecular-weight components from the polymer solution would prevent extravasation and its associated pressor response. A zero-link polymer of bovine hemoglobin was developed without chemical linkers left between the tetramers. Transfusion of unprocessed preparations of these polymers in rats resulted in appearance of the polymer in the renal hilar lymph. However, eliminating the low-molecular-weight components with a 300-kDa diafiltration resulted in an average hydrodynamic radius of 250 A and in undetectable levels of polymer in hilar lymph. Exchange transfusion in anesthetized rats and cats and in awake cats produced no increase in arterial pressure. In anesthetized cats, exchange transfusion with an albumin solution reduced hematocrit from 30 to 18%, increased cerebral blood flow, and dilated pial arterioles. In contrast, reducing hematocrit by transfusing the diafiltered polymer did not increase cerebral blood flow as pial arterioles constricted. These results are consistent with the hypothesis that the increase in arterial pressure associated with cell-free hemoglobin transfusion depends on hemoglobin extravasation. Constriction observed in the cerebrovascular bed with a nonextravasating hemoglobin polymer at low hematocrit is presumably a regulatory response to prevent overoxygenation at low blood viscosity.

The potential of Angeli's salt to decrease nitric oxide scavenging by plasma hemoglobin

“…Three mechanisms contribute to reduced NO scavenging by RBCs [46]. : (1) the rate of the reaction is largely limited by external diffusion of NO through the plasma to the surface of the RBC [44], especially due to the presence of a red cell free zone adjacent to the vessel walls where NO is made [37][38][39]; (2) NO diffusion is partially blocked by a physical barrier across the RBC membrane [40,43,47]; and (3) RBC-encapsulated Hb is efficiently compartmentalized in the lumen; it does not extravasate into the endothelium and interstitium [44,[48][49][50][51][52].…”

Insensitivity of cerebral oxygen transport to oxygen affinity of hemoglobin-based oxygen carriers

“…As mentioned, Hb-Zerolink is a large polymer (average MW∼25 MDa) that does not extravasate into renal lymph and does not produce arterial hypertension [1]. In each case, the decrease in hematocrit was accompanied by very little change in arterial oxygen content and CBF (Fig.…”

“…Polymerization of Hb bovine has been described [1]. In essence, the surface caboxyl groups were activated by treatment with 1-ethyl-3-3(dimethyl-amino-propyl)carbodiimmide to form pseudopeptide bonds with the amino residues on the surface of adjacent molecules.…”

“…A major problem encountered in the development of hemoglobin-based oxygen carriers (HBOCs) was the occurrence of systemic vasoconstriction (which leads to arterial hypertension) that follows infusion of cell-free Hb solutions. It has been clearly demonstrated that a factor that contributes to this phenomenon is the scavenging of nitric oxide (NO) by the Hb molecules extravasating through the endothelium [1]. To prevent Hb extravasation, Hb molecules were subjected to chemical modifications by introducing intramolecular crosslinks to prevent the dissociation of tetrameric Hb molecules into dimers.…”

Quantitative assessment of hemoglobin-induced endothelial barrier dysfunction

“…They concluded that 1) vasoconstriction is mediated by arteriole autoregulation by local oxygen tension, and 2) differences in the extravasation rates of HBOC may affect the magnitude of NO scavenging and, therefore, the degree of vasoconstriction. In support of this notion, Matheson et al (25) and Sakai et al (31) demonstrated that the hypertensive response was inversely related to the size of the HBOC, suggesting that extravasation rates are clinically important. Our data extend these observations by demonstrating that HBOCs increase endothelial permeability; therefore, HBOC extravasation rates may actually increase over time, thus altering the magnitude of NO scavenging.…”