Editorial

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.

Reduction of hydroxyl radical generation in a rat hindlimb model of ischemia-reperfusion injury using crosslinked hemoglobin-superoxide dismutase-catalase

The effects of PolyHb (intermolecularly crosslinked hemoglobin) and PolyHb-SOD-CAT (intermolecularly crosslinked hemoglobin, superoxide dismutase and catalase) on the production of hydroxyl radical was studied using a rat hindlimb model of ischemia-reperfusion. Hydroxyl radical generation was assessed by an indirect assay based on the hydroxylation of 4-hydroxybenzoate. The hydroxylation product, 3,4 dihydroxybenzoate (3,4 DHBA), was analyzed by high performance liquid chromatography and electrochemical detection. The identification of 3,4 DHBA was confirmed by analysis of authentic standard and an in vitro hydroxyl radical generation system. Ischemia was induced in both hindlimbs by ligation of the infrarenal aorta. After a 4hr ischemic period, hindlimbs were simultaneously perfused with PolyHb-SOD-CAT (5 g/dl) into one limb and PolyHb (5 g/dl) into the other limb via femoral arterial catheters. Each perfusate also contained the hydroxyl radical trap, 4-hydroxbenzoate (5 mM). Femoral venous effluents were analyzed for the presence of the 3,4 DHBA. Data indicates that greater 3,4 DHBA production occurs during PolyHb perfusion as compared to PolyHb-SOD-CAT. These preliminary results show that perfusion with PolyHb-SOD-CAT may alleviate oxidative stress in a model of ischemia-reperfusion.

Modified hemoglobin solution, with desired pharmacological properties, does not activate nuclear transcription factor NF-kappa B in human vascular endothelial cells

The aim of the present study was to evaluate the role of hemoglobin (Hb) and the contribution of chemically modified Hb solutions on the activation of nuclear transcription factor. NF-kappa B, and propagation of oxidative stress within human vascular endothelial cells. The activation of an oxidative stress-sensitive NF-kappa B can be linked with the propagation of an inflammatory state via rapid induction of genes for several pro-inflammatory mediators. Human coronary artery endothelial cells (HCAEC) were cultured on glass coverslips or cell culture plates to confluence. Then, the cells were incubated for up to 18 hours with endothelial basal medium (EBM) supplemented with 5% FBS and test agents in a concentration of 0.1 and 0.2 mmol: 1) unmodified bovine Hb (UHb): 2) modified Hb solution polymerized with glutaraldehyde (GLUT-Hb), and 3) a novel modified Hb solution (Hb-PP-GSH) prepared according to our patented procedure (U.S. Patent No. 5,439,882). The positive control for the NF-kappa B activation study included a treatment of the cells with: I) endotoxin: IL-1; TNF; and H2O2. Results indicate that Hb's pro-oxidant potential was influenced by the type of chemical modification procedure. The GLUT-Hb autoxidation rate, peroxidase-like activity and reactivity with H2O2/ferryl species formation were higher as compared to UHb, by 15%, 35% and 30%, respectively. However, pro-oxidant potential of Hb-PP-GSH was significantly lower than that of UHb (by 22%, 12% and 28%, respectively). The extent of oxidative stress of the HCAECs was found to be the Hb modification-type and concentration dependent. Although the highest endothelial lipid peroxidation and the largest depletion of intracellular GSH was associated with 0.2 mmol of GLUT-Hb, the Hb-PP-GSH did not produce significant changes when compared to the control cells. The UHb generated a moderate oxidative stress to the endothelium. The immunofluorescent and EMSA results indicate a correlation between the type of Hb chemical modification and the induction of NF-kappa B nuclear translocation. We found that GLUT-Hb rapidly activated NF-kappa B and induced nuclear translocation. Treatment of the cells with an increasing amount of UHb leads to the partial nuclear induction of NF-kappa B. However, Hb-PP-GSH did not activate NF-kappa B directly. In this study, the positive control cells treated with endotoxin, IL-1 or TNF demonstrated full nuclear translocations, whereas H2O2 caused only partial induction. In conclusion, nuclear translocation of NF-kappa B by Hb solutions might be dependent on Hb's pro-oxidant potential and extent of Hb-mediated endothelial oxidative stress. Besides the low oxidative potential of Hb-PP-GSH, the observed lack of NF-kappa B activation by this Hb solution can be also related to the anti-inflammatory properties of adenosine which is used in our novel modification procedure. In this study, only the Hb-PP-GSH, cross-linked intramolecularly with o-adenosine triphosphate and intermolecularly with o-adenosine, and combined with reduced glutathiore, was shown to be non-toxic to the endothelium and promises to be an effective free-Hb based blood substitute.