[The oxygen transporting capability of neo red cells (NRC) evaluated under total cardiopulmonary bypass]

Use of hemoglobin vesicles during cardiopulmonary bypass priming prevents neurocognitive decline in rats

BACKGROUND

Homologous blood use is considered to be the gold standard for cardiopulmonary bypass (CPB) priming in infants despite exposure of the patient to potential cellular and humoral antigens. However, the use of hemoglobin vesicles (HbVs), artificial oxygen carriers that encapsulate a concentrated hemoglobin solution within phospholipid bilayer membranes, for CPB priming may prevent neurocognitive decline in infants. The goal of this study was to determine whether HbV use offsets hemodilution caused by patient/priming volume-mismatched CPB and thereby prevents the development of postoperative neurocognitive deficits.

METHODS AND RESULTS

CPB was established in 28 male Sprague-Dawley rats (age, 14 to 16 weeks; weight, 450 grams) after cannulation of the tail artery and right atrium. The animals were randomly assigned to 1 of 3 groups: sham surgery (n=9), HbV (-) prime (n=10), or HbV (+) prime (n=9). CPB was conducted for 90 minutes at 200 mL/kg per minute. The hematocrit during CPB was 10.0+/-1.2% in the HbV (+) prime group and 9.9+/-1.3% in the HbV (-) prime group (P=not significant). Learning and memory function were evaluated using 2 different maze tests (Maze-1 and Maze-2, in which the arrival times to the target were measured on the first, third, fifth, and seventh postoperative days). Learning and memory function were significantly better in the HbV (+) prime group than in the HbV (-) prime group (Maze-1, P=0.012; Maze-2, P=0.042); there was no difference between the HbV (+) prime and the sham surgery group.

CONCLUSIONS

The use of HbV for CPB priming may serve as a substitute for homologous blood to prevent the unacceptable hemodilution and contribute to maintenance of intact neurocognitive function.

A novel hemoglobin-adenosine-glutathione based blood substitute: evaluation of its effects on human blood ex vivo

Chemically modified hemoglobin (Hb) solutions are under current investigation as potential red cell substitutes. Researchers at Texas Tech University have developed a novel free Hb based blood substitute product. This blood substitute is composed of purified bovine Hb cross-linked intramolecularly with o-adenosine-5'-triphosphate and intermolecularly with o-adenosine, and conjugated with reduced glutathione (GSH). In this study, we compared the effects of our novel blood substitute and unmodified (U) Hb, by using allogenic plasma as the control, on human blood components: red blood cells (RBCs), platelets, monocytes (Mo), and low-density lipoproteins (LDLs). The pro-oxidant potential of both Hb solutions on RBCs was examined by the measurement of osmotic and mechanical fragility, conjugated dienes (CD), lipid hydroperoxides (LOOH), thiobarbituric acid reactants (TBAR-S), isoprostanes (8-iso PGF2alpha) and intracellular GSH. The oxidative modification of LDLs was assessed by CD, LOOH, and TBAR-S, and the degree of apolipoprotein (apo) B cross-linking. The effects of Hb on platelets have been studied by monitoring their responses to the aggregation agonists: collagen, ADP, epinephrine, and arachidonic acid. Monocytes were cultured with Hb solutions or plasma and tested for TNF-alpha and IL-1beta release, then examined by electron microscopy. Results indicate that native UHb initiates oxidative stress of many blood components and aggravates inflammatory responses of Mo. It also caused an increase in RBC osmotic and mechanical fragility (p < 0.001). While the level of GSH was slightly changed, the lipid peroxidation of RBC increased (p < 0.001). UHb was found to be a stimulator of 8-iso PGF2alpha synthesis, a potent modulator of LDLs, and an effective potentiator of agonist induced platelet aggregation. Contrarily, our novel blood substitute did not seem to induce oxidative stress nor to increase Mo inflammatory reactions. The osmotic and mechanical fragility of RBCs was similar to that of the control. Such modified Hb failed to alter LDLs, increase the production of 8-iso PGF2alpha, but markedly inhibited platelet aggregation. The effect of this novel blood substitute can be linked with the cytoprotective and anti-inflammatory properties of adenosine, which is used as a cross-linker and surface modifier, and a modification procedure that lowers the hemoglobin pro-oxidant potential.