Generation of free oxygen radicals and the toxicity of hemoglobin solutions

Mechanisms of soft tissue and protein preservation in Tyrannosaurus rex

The idea that original soft tissue structures and the native structural proteins comprising them can persist across geological time is controversial, in part because rigorous and testable mechanisms that can occur under natural conditions, resulting in such preservation, have not been well defined. Here, we evaluate two non-enzymatic structural protein crosslinking mechanisms, Fenton chemistry and glycation, for their possible contribution to the preservation of blood vessel structures recovered from the cortical bone of a Tyrannosaurus rex (USNM 555000 [formerly, MOR 555]). We demonstrate the endogeneity of the fossil vessel tissues, as well as the presence of type I collagen in the outermost vessel layers, using imaging, diffraction, spectroscopy, and immunohistochemistry. Then, we use data derived from synchrotron FTIR studies of the T. rex vessels to analyse their crosslink character, with comparison against two non-enzymatic Fenton chemistry- and glycation-treated extant chicken samples. We also provide supporting X-ray microprobe analyses of the chemical state of these fossil tissues to support our conclusion that non-enzymatic crosslinking pathways likely contributed to stabilizing, and thus preserving, these T. rex vessels. Finally, we propose that these stabilizing crosslinks could play a crucial role in the preservation of other microvascular tissues in skeletal elements from the Mesozoic.

Peroxisome proliferator-activated receptor γ (PPARγ): A master gatekeeper in CNS injury and repair

Peroxisome proliferator-activated receptor γ (PPARγ) is a widely expressed ligand-modulated transcription factor that governs the expression of genes involved in inflammation, redox equilibrium, trophic factor production, insulin sensitivity, and the metabolism of lipids and glucose. Synthetic PPARγ agonists (e.g. thiazolidinediones) are used to treat Type II diabetes and have the potential to limit the risk of developing brain injuries such as stroke by mitigating the influence of comorbidities. If brain injury develops, PPARγ serves as a master gatekeeper of cytoprotective stress responses, improving the chances of cellular survival and recovery of homeostatic equilibrium. In the acute injury phase, PPARγ directly restricts tissue damage by inhibiting the NFκB pathway to mitigate inflammation and stimulating the Nrf2/ARE axis to neutralize oxidative stress. During the chronic phase of acute brain injuries, PPARγ activation in injured cells culminates in the repair of gray and white matter, preservation of the blood-brain barrier, reconstruction of the neurovascular unit, resolution of inflammation, and long-term functional recovery. Thus, PPARγ lies at the apex of cell fate decisions and exerts profound effects on the chronic progression of acute injury conditions. Here, we review the therapeutic potential of PPARγ in stroke and brain trauma and highlight the novel role of PPARγ in long-term tissue repair. We describe its structure and function and identify the genes that it targets. PPARγ regulation of inflammation, metabolism, cell fate (proliferation/differentiation/maturation/survival), and many other processes also has relevance to other neurological diseases. Therefore, PPARγ is an attractive target for therapies against a number of progressive neurological disorders.

A role for iron and oxygen chemistry in preserving soft tissues, cells and molecules from deep time

The persistence of original soft tissues in Mesozoic fossil bone is not explained by current chemical degradation models. We identified iron particles (goethite-αFeO(OH)) associated with soft tissues recovered from two Mesozoic dinosaurs, using transmission electron microscopy, electron energy loss spectroscopy, micro-X-ray diffraction and Fe micro-X-ray absorption near-edge structure. Iron chelators increased fossil tissue immunoreactivity to multiple antibodies dramatically, suggesting a role for iron in both preserving and masking proteins in fossil tissues. Haemoglobin (HB) increased tissue stability more than 200-fold, from approximately 3 days to more than two years at room temperature (25°C) in an ostrich blood vessel model developed to test post-mortem 'tissue fixation' by cross-linking or peroxidation. HB-induced solution hypoxia coupled with iron chelation enhances preservation as follows: HB + O2 > HB - O2 > -O2 >> +O2. The well-known O2/haeme interactions in the chemistry of life, such as respiration and bioenergetics, are complemented by O2/haeme interactions in the preservation of fossil soft tissues.

Evaluation of Angiotensin Converting Enzyme (ACE)-Like Activity of Acellular Hemoglobin

Despite the tremendous progress in research on hemoglobin (Hb) cellular and molecular responses, the current understanding of Hb's overall intrinsic toxicity is still limited. The complete mechanism of Hb-induced vasoconstriction has not yet been established, particularly the involvement of the renin-angiotensin system (RAS). Some studies emphasized that Hb may augment the vascular responsiveness to angiotensin (Ang)-II. It was also reported that Hb, as well as Ang-II, influences the synthesis of 8-iso prostaglandin F2 alpha, which has an impact on renal flow and possibly RAS. Hb in the presence of H(2)O(2) gains enzymatic activity. Thus, it is possible that Hb directly and/or indirectly can activate RAS. In this study, we monitored the effect of ferrous- and ferryl-Hb, and H(2)O(2) alone, on conversion of Ang-I to its active metabolites. The structural and immunological identity of the resulting products were evaluated by reversed phase C-18 HPLC and ELISA, respectively. Additionally, ACE-like activity of Hbs was measured spectrophotometrically by determining their ability to react with the ACE substrate, the synthetic tripeptide N-[3-(2-furyl)acryloyl]-L-phenylalanylglycylglycine. Results indicate that while ferrous-Hb can serve as a receptor for Ang-I, its ferryl form possesses ACE-like activity, being able to convert, within minutes, Ang-I to Ang-II, Ang-III, Ang-IV, Ang (1-7) and other unresolved fragments. H(2)O(2) itself had a very limited hydrolyzing effect on Ang-I. Based on this study, it can be concluded that ACE-like activity of Hb with rapid formation of active angiotensins may be a contributor to the still unexplained vasoconstrictive response observed immediately after Hb administration.

Control of oxidative reactions of hemoglobin in the design of blood substitutes: role of the ascorbate-glutathione antioxidant system

Uncontrolled oxidative reactions of hemoglobin (Hb) are still the main unresolved problem for Hb-based blood substitute developers. Spontaneous oxidation of acellular ferrous Hb into a nonfunctional ferric Hb generates superoxide anion. Hydrogen peroxide, formed after superoxide anion dismutation, may react with ferrous/ferric Hb to produce toxic ferryl Hb, fluorescent heme degradation products, and/or protein-based free radicals. In the presence of free iron released from heme, superoxide anion and hydrogen peroxide might react via the Haber-Weiss and Fenton reactions to generate the hydroxyl radical. These highly reactive oxygen and heme species may not only be involved in shifting the cellular redox balance to the oxidized state that facilitates signal transduction and pro-inflammatory gene expression, but could also be involved in cellular and organ injury, and generation of vasoactive compounds such as isoprostanes and angiotensins. It is believed that these toxic species may be formed after administration of Hb-based blood substitutes, particularly in ischemic patients with a diminished ability to control oxidative reactions. Although varieties of antioxidant strategies have been suggested, this in vitro study examined the ability of the ascorbate-glutathione antioxidant system in preventing Hb oxidation and formation of its ferryl intermediate. The results suggest that although ascorbate is effective in reducing the formation of ferryl Hb, glutathione protects heme against excessive oxidation. Ascorbate without glutathione failed to protect the red blood cell membranes against Hb/hydrogen peroxide-mediated peroxidation. This study provides evidence that the ascorbate-glutathione antioxidant system is essential in attenuation of the pro-oxidant potential of redox active acellular Hbs, and superior to either ascorbate or glutathione alone.

Role of Free Hemoglobin in 8-Iso Prostaglandin F2-Alpha Synthesis in Chronic Renal Failure and Its Impact on CD163-Hb Scavenger Receptor and on Coronary Artery Endothelium

Free hemoglobin (Hb) during autoxidation increases 8-iso-prostaglandin-F2-alpha (8-isoprostane) formation in vitro. Because 8-isoprostane and plasma Hb are elevated in chronic renal failure (CRF), we evaluated the role of Hb in this isoprostane synthesis in vivo. By monitoring correlations between Hb, haptoglobin (Hp), CD163-Hb-scavenger receptor, and 8-isoprostane that is known to induce CD163 shedding, we examined whether 8-isoprostane blocks Hb catabolism in CRF. Additionally, by studying the effect of 8-isoprostane on human coronary artery endothelium (HCAEC) in vitro and its impact on intercellular adhesion molecule-1 (ICAM-1) in vivo, we tested its role in promotion of cardiovascular events in CRF. Twenty-two never-dialyzed CRF patients and 18 control patients were screened for renal function, plasma and urine 8-isoprostane, and plasma Hb, Hp, thiobarbituric-acid-reactants (TBARS), C-reactive-protein (CRP), and soluble (s) ICAM-1 and sCD163. HCAEC exposed to 8-isoprostane were tested for ICAM-1 and apoptosis. In CRF, urine 8-isoprostane was significantly elevated and correlated with free-Hb and TBARS. The increased free-Hb, Hp, and sCD163 in CRF suggested 8-isoprostane-mediated suppression of Hb catabolism through CD163 receptor shedding. 8-Isoprostane enhanced ICAM-1 expression and apoptosis in HCAEC. CRF patients showed elevated sICAM-1. In conclusion, free-Hb, via 8-isoprostane, paradoxically blocks its own catabolism. Free-Hb and/or 8-isoprostane may intensify cardiovascular events in CRF.

Effects of Diaspirin Crosslinked Hemoglobin (DCLHb) on microcirculation and local tissue pO2 of striated skin muscle following resuscitation from hemorrhagic shock

The hemoglobin based oxygen carrier (HBOC) Diaspirin Crosslinked Hemoglobin (DCLHb) has been developed to substitute not only the blood volume, but also to restore the oxygen-carrying properties of blood during hemorrhagic shock. However, it has been suggested that HBOCs may enhance the formation of free oxygen radicals through the release of free iron ions via the Haber-Weiss reaction. The aim of this study was to investigate the effects of DCLHb on the microcirculation, leukocyte-endothelial cell interaction and local tissue oxygenation in striated skin muscle of Syrian golden hamsters during and after resuscitation from hemorrhagic shock. In particular we focused on the local tissue oxygenation after resuscitation with DCLHb (hemoglobin content 10 g%) compared to resuscitation using autologous blood diluted to a hemoglobin content of 10 g%. Hemorrhagic shock was induced for 45 minutes by bleeding the animals at a rate of 33 ml/kg BW maintaining a mean arterial pressure of 30 +/- 5 mmHg. Animals were resuscitated either with 33 ml/kg BW 6% Dextran-60.000 or with 10 g% DCLHb. The control group received shed blood diluted with Ringers to a hemoglobin content of 10 g%. Intravital microscopy was used for investigation of the microcirculatory parameters and a multiwire platinum surface electrode for measurement of local tissue pO2 in striated skin muscle in the dorsal skinfold chamber of Syrian golden hamsters. Resuscitation from hemorrhagic shock with 10 g% AUB revealed significant increase of leukocytes rolling in postcapillary venules at 30 to 120 minutes after resuscitation compared to baseline values. DCLHb turned out to reduce the number of firmly adherent leukocytes after resuscitation compared to 10 g% AUB. Microvascular permeability as an indicator for functional endothelial integrity revealed no significant differences between the groups. DCLHb and 10 g% AUB led to a significant increase in local tissue oxygenation after resuscitation from hemorrhagic shock. However, 10 g% AUB turned out to be most effective to restore the local tissue pO2 compared to Dx-60. Our findings indicate that DCLHb restores microvascular perfusion after critical hemorrhagic shock as efficient as Dx-60 and 10 g% AUB. The absence of enhanced leukocyte-endothelium interaction after resuscitation with DCLHb implies that this HBOC does not exacerbate formation of oxygen free radicals during reperfusion. DCLHb effectively increases local tissue pO2 after resuscitation from hemorrhagic shock; however, not as effectively as 10 g% AUB.

Oxygen radical formation does not have an impact in the treatment of severe acute experimental pancreatitis using free cellular hemoglobin

AIM: Microcirculatory dysfunction and free oxygen radicals are important factors in the pathogenesis of severe acute pancreatitis. Additional oxygen delivery might enhance lipid peroxidation but may also improve pancreatic microcirculation. This study assesses the effect of free cellular bovine hemoglobin on the formation of oxygen radicals and microcirculation in a rodent model of severe acute pancreatitis.

METHODS: Fifteen minutes after induction of acute pancreatitis Wistar rats received either 0.8 mL bovine hemoglobin (HBOC-200), hydroxyethyl starch (HES) or 2.4 mL of normal saline to ensure normovolemic substitution. After 6 h of examination the pancreas was excised and rapidly processed for indirect measurement of lipid peroxidation products malondialdehyde (MDA) and reduced glutathione (GSH) in pancreatic tissue.

RESULTS: The single application of HBOC-200 improved pancreatic microcirculation and reduced histopathological tissue damage significantly. Tissue concentration of MDA did not differ between the groups. Also no differences in GSH levels were detected.

CONCLUSION: Though the single application of HBOC-200 and HES improve pancreatic microcirculation, no differences in lipid peroxidation products were detected. The beneficial effect of additional oxygen supply (HBOC-200) does not lead to enhanced lipid peroxidation.

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.

Cell-free hemoglobin preserves renal function during normothermic ischemia

INTRODUCTION

The purpose of this study is to determine whether an infusion of polymerized hemoglobin solution is capable of suppressing the tubular damage and loss of renal function normally seen during a clinically relevant period of warm ischemia.

METHODS

Male rats (350-450 g) were randomized to treatment with control (5% human serum albumin, HSA, n = 6) or test solution (9% polymerized hemoglobin, PHB, n = 6). Following a right nephrectomy, the left renal artery was perfused with 4 ml of HSA or PHB at 37 degreesC. The left renal artery was temporarily occluded for 50 min. At 72 h, creatinine (Cr), blood urea nitrogen (BUN), and percentage hemoglobin (Hb) were measured and the kidney was removed. Stained kidney sections were graded for ischemic injury (0-4, 0 = normal and 4 = necrosis of the proximal tubule). All results were expressed as means +/- SEM and statistical analysis was performed by t test.

RESULTS

Treatment with PHB resulted in lower Cr (1.2 +/- 0.23 mg/dl vs 3.26 +/- 0.60 mg/dl, P < 0.01) and BUN (60.5 +/- 12.7 mg/dl vs 151 +/- 20.2 mg/dl, P < 0.01) at 72 h compared to HSA controls. Total hemoglobin was not significantly different at 72 h. The weight of all treated kidneys increased; however, the increase was significantly less in the PHB-treated group (34 +/- 9.1% vs 70 +/- 7. 4%, P < 0.01). PHB-treated kidneys had less evidence of histologic damage compared to those in the HSA group (0.75 +/- 0.11 vs 2.50 +/- 0.64, P < 0.05).

CONCLUSIONS

During normothermic renal ischemia, renal artery infusion of PHB resulted in preservation of renal function and histologic architecture. PHB solutions may be useful in preserving organ function during prolonged periods of in vivo ischemia.

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.

Expression of adhesion molecules and von Willebrand factor in human coronary artery endothelial cells incubated with differently modified hemoglobin solutions

Previous studies have established a linkage between free Hb molecules and the production of inflammatory mediators by the reticuloendothelial cells. An important aspect of the endothelial response to the inflammatory stimuli is the expression of adhesion molecules on the luminal surface. Therefore, the present study was designed to investigate the effects of various free-Hb based oxygen carrying solutions on the intracellular adhesion molecule-1 (ICAM-1), the vascular cell adhesion molecule-1 (VCAM-1) and also von Willebrand factor (vWF) expression by human endothelium. Human coronary artery endothelial cells (HCAEC) were cultured on glass coverslips until they reached confluence, then incubated for 18 hours with endothelial basal medium (EBM) supplemented with 5% FBS and a 0.1 mmol or 0.2 mmol of the bovine Hb solutions: 1) pure unmodified bovine Hb (UHb); 2) modified bovine Hb solution (Hb-PP-GSH) prepared according to our newly developed procedure (U.S. Patent No. 5,439,882); and 3) modified bovine Hb solution polymerized with glutaraldehyde (GLUT-Hb). The HCAECs were also incubated with EBM (negative control) and EBM containing bacterial endotoxins in a concentration of 50 EU/ml (positive control). After treatment, cells were exposed to primary antibodies; anti-human ICAM-1, anti-human VCAM-1 or anti-human vWF, and consequently to the secondary antibody (fluorescein isothiocyanate-conjugated F(ab)2). Immunofluorescence analysis revealed different expressions of ICAM-1 and VCAM-1 on the surface membranes of variously treated cells. Although negative control cells had an undetectable level of adhesion molecules, the positive control cells, activated by endotoxin, exhibited high immunoreactivity for ICAM-1 and VCAM-1. The Hb's treated cells demonstrated differing degrees of activation. An insignificant expression of ICAM-1 was observed in HCAEC, following treatment with a 0.1 or 0.2 mmol of Hb-PP-GSH and 0.1 mmol of UHb. Cell treated with 0.2 mmol of UHb and both concentrations of GLUT-Hb demonstrated a massive expression of this adhesion molecule. A similar effects was observed during induction of VCAM-1. While a lack of expression was noted with both concentrations of Hb-PP-GSH and 0.1 mmol of UHb, the GLUT-Hb stimulated significant VCAM-1 induction at all tested concentrations. Immunofluorescence analysis confirmed the expression of vWF uniformly in HCAEC from the different experimental groups. The data suggest, vWF expression was unaffected by all but the GLUT-Hb treatment. In conclusion, the Hb stimulatory activity toward ICAM-1 and VCAM-1 inductions were related with the type of Hb chemical modification method. Although modification of Hb with glutaraldehyde potentiates adhesion molecules expression, our novel Hb modification procedure, which comprises intramolecular cross-linking with o-adenosine triphosphate and intermolecular with o-adenosine, and combined with reduced glutathione, apparently prevents these inflammatory events.

Hemoglobin-induced contraction of pig pulmonary veins

The effects of hemoglobin Ao (HbAo), alpha alpha cross-linked hemoglobin (alpha alphaHb), cyanomet alpha alpha cross-linked hemoglobin (cyanomet alpha alphaHb), and human serum albumin (HSA) were compared under basal conditions and during relaxation with acetylcholine (ACh), sodium nitroprusside (SNP), and papaverine (PAP) in porcine pulmonary veins. Isometric tension changes were recorded in isolated rings (3 to 4 mm) that were suspended in Krebs solution bubbled with 95% O2/5% CO2. Increasing concentrations of HbAo and alpha alphaHb (10(-9) - 3 x 10(-6) mol/L) caused concentration-dependent increases in tension that reached a maximum of 4.20 +/- 0.3 gm and 3.78 +/- 0.6 gm, respectively. Cyanomet alpha alphaHb and HSA (10(-9) - 3 x 10(-6) mol/L) did not cause significant increases in tension. The maximum responses to HbAo and alpha alphaHb were significantly increased during relaxation with ACh and SNP but not with PAP. In contrast, SNP (10(-4) mol/L) and PAP (10(-5) mol/L), but not ACh, reversed contractions induced by HbAo and alpha alphaHb. These studies support the concept that hemoglobin-induced vascular contraction is primarily mediated by inactivation of the vasodilator nitric oxide in vitro. We suggest that this mechanism is common to acellular hemoglobins in which the ligand binding site is unimpaired and in which the heme iron is in the ferrous (+2) state.

Inhibition of endothelium-dependent relaxation by hemoglobin in rabbit aortic strips: comparison between acellular hemoglobin derivatives and cellular hemoglobins

Hemoglobin (Hb)-based artificial oxygen carriers are supposed to induce vasoconstriction through the inactivation of endothelium-derived relaxing factor (EDRF). We examined the vasoconstrictive activity of acellular Hb and cellular Hb solutions in rabbit aortic strips. Unmodified Hb, pyridoxalated Hb, bovine unmodified Hb, haptoglobin-Hb complex (Hp-Hb), and polyoxyethylene glycol-conjugated Hb (PEG-Hb) were used as acellular Hbs having different molecular masses. Cellular Hbs included liposome-encapsulated Hb and red blood cells (RBC). In the first experiment, Hb (10 ng/ml to 1 mg/ml) was cumulatively added to the tissues in which steady-state relaxation was evoked by acetylcholine (ACh) after precontraction induced by phenylephrine. Although all Hb solutions induced a dose-dependent reversal of ACh-induced relaxation, the most potent vasoconstrictive effect was noted with acellular Hbs, and their contractile activities were almost the same independent of molecular mass. On the other hand, liposome-Hb and RBC showed reduced potencies in this order. These results indicate the importance of cellularity as the major factor determining Hb-related EDRF inactivation. In another experiment, the tissues were exposed to Hb at 0.01, 0.1, or 1 mg/ml for 30 min and ACh-induced relaxation was recorded after the complete removal of Hb in an organ bath chamber. Exposure to unmodified Hb at > 0.1-mg/ml concentrations significantly reduced the ACh-induced relaxation, whereas the relaxation was not affected by PEG-Hb, Hp-Hb, liposome-Hb, or RBC. These results suggest that unmodified Hb might be persistently associated with tissues and thereby inhibit ACh-induced relaxation. From these findings, we propose two attributes of Hb-related inhibition of endothelium-dependent relaxation: Acellular Hbs inhibit EDRF more efficiently in the luminal space than cellular Hbs, and unmodified Hb can also inhibit it adluminally and/or adventitially.

Effects of bacterial endotoxin on human cross-linked and native hemoglobins

Previous investigations have demonstrated that hemoglobin (Hb) is a binding protein for bacterial endotoxin (lipopolysaccharide, LPS) and that the structure and biological activity of LPS are altered in the presence of Hb. In the present study, the influence of LPS on the structure of native human HbA0 and covalently cross-linked Hb (alpha alpha Hb) was studied by analyzing the absorption and circular dichroic spectra of Hb in the wavelength region of 200-650 nm. Incubation of oxyHb with each of several LPSs resulted in a decrease in the intensity of the major Soret band at 414 nm with a shift in the maximum peak to 410 nm, decreases in the intensities of the major visible region peaks at 541 and 577 nm, and the appearance of increased absorbance in the visible region in the range of 630 nm. The resultant spectra are characteristic of methemoglobin formation. These spectral changes were time-dependent and LPS-concentration-dependent. Production of methemoglobin was prominent with chemically modified, partially deacetylated rough LPS, and was observed to a lesser extent both with native, complete rough and with native smooth LPSs. The influence of LPS on the absorption spectrum of methemoglobin also was directly tested. The conversion of methemoglobin to hemichrome in the presence of LPS was demonstrated and was shown to be reversible. Analysis of circular dichroic spectra of Hb demonstrated LPS-induced spectral changes in the visible and Soret regions consistent with the production of a substantial quantity of metHb, but did not demonstrate any alteration in the far-UV region (210-240 nm). Moreover, Hb oxygen affinity was only slightly altered after incubation with any of several LPSs. In conclusion, analyses of absorption and circular dichroic spectra reveal the potential of LPS to produce a facilitated oxidation of both alpha alpha-cross-linked human Hb and native human HbA0, without substantial changes in the secondary structure of the globin.

Diaspirin crosslinked hemoglobin (DCLHb): absence of increased free radical generation following administration in a rabbit model of renal ischemia and reperfusion

In control rabbits, a renal ischemia of 60 min followed by 10 min of reperfusion resulted in an enhanced free radical production in cortical tissue, as assessed by a significant decrease of free glutathione (42%), protein-bound GSH (17%), and vitamin E (49%). In contrast, catalase or glutathione peroxidase activities were not affected by these experimental conditions. Free radical production in this model was also measured directly using electron spin resonance (ESR) spectroscopy associated with a PBN (alpha-phenyl N-tert-butyl-nitrone) spin trap agent in the venous blood arising from the ischemic kidney. The signal consisted of a triplet of doublets. In contrast, no signal could be detected in control blood samples taken prior to inducing ischemia. The burst of free radical production occurred in the early phase after restoration of flow in the kidneys rendered ischemic, as evidenced by a signal of weak intensity which generally appeared within the third minute after reperfusion and progressively increased to form a well-defined asymmetric signal following 10 min of reperfusion. The precise nature of free radicals trapped by the PBN agent remains, however, to be elucidated, but analysis of the coupling constants (aN = 14.5-15 G; a beta H = 2.5-3 G) and asymmetry of the central doublets suggests that the ESR signal may arise from a nitorxy-radical adduct resulting from the spin trapping by PBN of both oxygen- or carbon-centered radicals of lipid origin. As evidenced by both direct and indirect measurements, exchange of rabbit blood immediately after inducing renal ischemia with 30 ml/kg of Diaspirin Crosslinked Hemoglobin (7.5 g/dl in lactated electrolyte) or human serum albumin (7.5 g/dl in lactated electrolyte) did not exacerbate free radical production mediated by an ischemia reperfusion phenomenon, a typical situation found in a resuscitation setting.

The autoxidation of alpha alpha cross-linked hemoglobin: a possible role in the oxidative stress to endothelium

The aim of the present study was to investigate the role of hemoglobin autoxidation in the induction of endothelial heme oxygenase (HO), an inducible "stress" protein which is responsible for heme catabolism. Porcine aortic endothelial cells were incubated for six hours in the presence of 60 microM unmodified hemoglobin (HbA0), hemoglobin cross-linked between the alpha chains with bis-(3,5-dibromosalicyl) fumarate (alpha alpha Hb) or cyanomet-alpha alpha-hemoglobin (CNmet alpha alpha Hb). Microsomal HO content increased 4.1-fold in the presence of alpha alpha Hb, 2.7-fold with HbA0 and 1.8-fold with CNmet alpha alpha Hb over the control value. The rates of methemoglobin formation exhibited a linear relationship over the time of incubation (r = 0.94) and the apparent rate constant was 1.8-fold higher for alpha alpha Hb (0.023 h-1) than HbA0 (0.013 h-1). In addition, a linear relationship was obtained by plotting the rates of autoxidation of hemoglobins versus the HO activity (r = 0.99). When cells were incubated with 100% methemoglobin, HO activity increased 5.0-fold and 4.7-fold for HbA0 and alpha alpha Hb, respectively. Intracellular heme concentration, measured after 24 hours of incubation, was also significantly greater in the presence of alpha alpha Hb (52.6% over baseline) compared to HbA0 (10.8%) and CNmet alpha alpha Hb (15.3%) groups (p < 0.05). However, lactate dehydrogenase (LDH) release, measured as an index of endothelial cell injury, increased in all the hemoglobins examined: alpha alpha Hb, 33.8 +/- 1.1 U/l; HbA0, 38.5 +/- 3.5 U/l; CNmet alpha alpha Hb, 41.9 +/- 4.0 U/l; (control group, 19.4 +/- 2.8 U/l). We conclude that: 1) the higher rate of oxidation of alpha alpha Hb renders the molecule more susceptible to induce endothelial oxidative stress (HO induction); 2) the accelerated methemoglobin formation is directly correlated to intracellular HO content and endothelial heme uptake; 3) persistent cell injury suggests that other factors besides heme release may contribute to the hemoglobin-mediated cytotoxicity.

Protective effect of selenium on hemoglobin mediated lipid peroxidation in vivo

The toxicity of hemoglobin (Hb) solutions is related, at least in part, to the generation of oxygen free radicals with consequent induction of lipid peroxidation. The present study was designed to examine whether selenium (Se) may prevent the oxidative damage observed after Hb administration. Three groups of rats were compared; (I) the negative control group receiving autotransfusion; (II) the positive control group with replacement of 40% total blood volume (TBV) with modified bovine Hb solution; and (III) the experimental group which received dietary supplemented selenium (Na2SeO3) in daily doses of 5 micrograms.kg body wt-1 in drinking water, 4 days before and 3 days after administration of Hb solution in the same volume as in group II. Three days after Hb injection, all animals were sacrificed. Oxidative stress was determined by measuring conjugated dienes (CD) and thiobarbituric acid reactants (MDA) in homogenates of the perfused liver, heart, lungs, kidney, brain and plasma. Additionally, the 45k x g supernatants of the organs homogenates and plasma were assayed for the antioxidant enzymes activity: superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px) and the intracellular level of reduced glutathione (GSH). Also, a measurement of nonprotein bound intracellular free iron (Fe) and tissue Se concentrations was performed. Simultaneously, injury dysfunction of vital organs was assessed by the measurement of plasma LDH, SGPT, creatinine, blood PaO2 and by histopathological studies. Results indicate that the exchange transfusion with Hb solution introduced significant increases in CD and MDA formation, particularly in the liver and heart tissues, and in plasma. While the values of the SOD and CAT in the liver and heart tissue were generally altered, the SOD/CAT ratio was also increased. After the Hb injection, activity of GSH-Px remained unchanged and was associated with significant depletion of GSH. The plasma levels of SGPT and LDH were increased, but the creatinine and PaO2 was similar to that of the control and corresponded with histopathological findings. The liver and heart intracellular free Fe was found to be higher than that of control. Treatment with Se was very effective in the prevention of oxidative damage introduced by Hb. Full protection from MDA formation was noted in liver tissue (p < 0.001). Also, plasma levels of MDA, SGPT and LDH were significantly decreased and appeared similar to that of the control group (I). Treatment with Se increased liver (p < 0.05) and plasma (p < 0.1) level of GSH-Px.(ABSTRACT TRUNCATED AT 400 WORDS)

Cytokines and PAF release from human monocytes and macrophages: effect of hemoglobin and contaminants

Monocytes [M] were isolated from venous blood of healthy volunteers and activated macrophage-leukocytes (Mø-L] were obtained from peritoneal fluid of patients with mild endometriosis. The M were incubated with pyrogen free CELLGRO culture medium [Control], and with 0.2 mM of [A] unmodified bovine hemoglobin (UHb), [B] Hb crosslinked to form polymers with M.W. < 400 kDa (LMWHb), [C] Hb crosslinked to form large polymers (< 1,020 kDa) (HMWHb), and Mø-L additionally with [D] UHb contaminated with endotoxin (Hb+E) (2.5 EU/mL), and [E] UHb contaminated with phospholipids (Hb+PLs). The Mø-L medium of incubation was tested for TNF alpha, IL-1 alpha, IL-6, GM-CSF and PAF after 6 and 24 hours, but M for TNF alpha and GM-CSF at 12, 24 and 36 hours. Mø-L were found more responsive than M colonies. The strongest reaction of Mø-L was to Hb+E, which produced levels of cytokines and PAF higher than Controls (p < 0.001). Hb+PLs induced smaller increases of TNF and IL-6, and a decrease in the levels of IL-1 and GM-CSF. However, the release of PAF was much greater with this Hb than with Hb+E. UHb caused an increase in TNF, as compared to control (p < 0.01). LMWHb generated a similar increase in TNF, but also a decrease in IL-1. Both polymerized Hb forms inhibited expression of GM-CSF. HMWHb induced high levels of TNF, IL-1 and PAF. UHb, LMWHb and HMWHb significantly increase levels of TNF in M cultures after 36 hours of incubation.

Reaction of human endothelial cells to bovine hemoglobin solutions and tumor necrosis factor

Human umbilical vein endothelial cells (HUVEC) were incubated for 24 hours with 0.1 mM or 0.3 mM of: [A] unmodified (U) Hb-FeIIO2; [B] UHb-FeIII; [C] UHb-FeIV-OH; [D] polymerized low molecular weight Hb (< 400 kDa); [E] polymerized high molecular weight Hb (< 1,020 kDa); [F] polymerized low molecular weight Hb + Endotoxin (2.5 EU/mL); [G] rTNF alpha 100 pg/mL; [H] rTNF alpha 400 pg/mL; [I] rTNF alpha 800 pg/mL. The medium of the incubation was tested for LDH (index of cell injury), and for cytokines GM-CSF and IL-1 alpha released by the cells. The data suggests that oxidation status of the iron in the Hb molecule and concentration of Hb play an important role in causing EC injury. The highest toxicity was observed when EC were incubated with 0.1 mM of UHb-FeIV-OH (ferryl-Hb) and no toxicity with 0.3 mM of Hb-FeIII (ferric-Hb). The direct stimulation of EC by Hb for the production of IL-1 was limited, related only to high molecular weight Hb polymers or to Hb+E, however GM-CSF expression was increased by almost all Hb forms. TNF induced dose-related injury (R2 = 0.986), and dose-related release of IL-1 (R2 = 0.977). A different EC reaction was observed on the release of GM-CSF. Intermediate levels of TNF (400 pg/mL) increased the expression of this cytokine, while high levels (800 pg/mL) blocked its release.

Acellular and cellular hemoglobin solutions as vasoconstrictive factor

The inhibitory effects of acellular and cellular hemoglobin (Hb) solutions on endothelium-dependent vasorelaxation were investigated in rabbit thoracic aortic strips. As acellular Hb solutions, 2,3-diphosphoglycerate (DPG)-depleted Hb and pyridoxylated Hb were examined. Cellular Hb solutions included washed human fresh red cells and liposome Hb encapsulated with pyridoxal-5'-phosphate (PLP). The tissues were precontracted with phenylephrine (PE), after which acetylcholine (ACh) was added to elicit a steady-state relaxation. Acellular Hb solutions cumulatively reversed ACh-induced relaxation, and these inhibitory effects reached a plateau at 10 micrograms/ml. Increasing oxygen affinity by pyridoxylation had little effect on this. In contrast, both red cells and liposome Hb solution showed moderate inhibitory effects, and they reached a plateau at 1 mg/ml. These findings indicate that acellular Hb solutions are more potent inhibitors than cellular Hb solutions by a factor of about 100, and that the encapsulation of Hb is a preferable method to mimic the red cell.

Generation and detection of hydroxyl radical in vivo in rat spinal cord by microdialysis administration of Fenton's reagents and microdialysis sampling

We developed a double microdialysis fiber technique to generate hydroxyl radicals (OH.) in rat spinal cord. H2O2 and FeCl2/EDTA were pumped through two parallel microdialysis fibers inserted into the spinal cord such that the reactants mix in the tissue to generate OH. by the Fenton reaction. Generated OH. was detected by administering phenylalanine through one fiber and measuring o-, m- and p-hydroxyphenylalanine in collected dialysates by high pressure liquid chromatography and fluorescence detection. The hydroxyphenylalanines are produced by OH. attacking the phenylalanine. OH. generation was also accomplished in in vitro experiments and the results were consistent with in vivo experiments. This novel method to generate and measure OH. radical in vivo overcomes difficulties in studying damage to tissue by short-lived OH.. Although developed to study the role of OH. in spinal cord injury, this method could be used to study other diseases involving OH. damage.

Cross-linked hemoglobin-superoxide dismutase-catalase scavenges oxygen-derived free radicals and prevents methemoglobin formation and iron release

In this study, we prepared PolyHb-SOD-catalase (intermolecularly cross-linked hemoglobin, superoxide dismutase (SOD), and catalase). We found that PolyHb-SOD-catalase is effective in scavenging oxygen-derived free radicals. In the xanthine/xanthine oxidase system, the initial rate of cytochrome c reduction was 2.13 +/- 0.26 nmoles cyt. c/min for PolyHb alone. PolyHb- SOD-catalase reduced this to 0.56 +/- 0.08 nmoles cyt. c/min because of its ability to eliminate superoxide (O2-). Addition of PolyHb to 200 microM of hydrogen peroxide (H2O2), changed the H2O2 level slightly to 192 +/- 0.4 microM. Addition of PolyHb-SOD-catalase, on the other hand, lower the level to 41 +/- 0.3 microM. Results also show that both effects were dependent on the concentration of SOD-catalase cross-linked with hemoglobin. Oxidative challenge with H2O2 resulted in minimal changes in the absorbance spectra of PolyHb-SOD-catalase. With PolyHb, there were spectral changes reflecting the formation of methemoglobin and heme degradation. Furthermore, the amount of iron released, after incubation with 250 microM H2O2, was 6.8 +/- 1.8 micrograms/dl for PolyHb-SOD-catalase and 76.6 +/- 1.0 micrograms/dl for PolyHb. These results show that cross-linked SOD-catalase prevents oxidative reactions involving the hemoglobin component of PolyHb-SOD-catalase.

The effects of alpha-alpha cross-linked hemoglobin on the feeding and locomotor activity of rats

The feeding and locomotor activities of rats were used as an assay for the potentially toxic effects of an oxygen-carrying blood substitute. Rats lived in individual cages where they could feed ad lib by pressing a lever once for each small food pellet, drink water, or run in a wheel; a 12-h light/dark cycle was continuously in effect. After being anesthetized and hemorrhaged one-third of their total blood volume, individual rats were resuscitated with one of the following fluids: their own shed blood (OB), bis(3,5-dibromosalicylfumarate) alpha-alpha cross-linked hemoglobin (HbXL), human serum albumin (HSA), or Ringer's lactate (RL). Rats in a fifth group were not resuscitated (NR). During the dark period on the day of hemorrhage, the food intake and running activity of rats in all groups decreased. Food intake and locomotor activity of rats in the HbXL, NR and OB groups were more suppressed than the HSA or RL groups. The food intake of rats in the HbXL and NR groups remained significantly more suppressed during the dark period of the first recovery day; running continued to be suppressed in the HbXL group on the first recovery day, but not the second recovery day. In an effort to determine the extent to which the rats in the HbXL group were impaired, an increasing number of lever presses was required for each food pellet beginning with recovery day number 3 for all treatment groups. As the ratio of presses per pellet was increased, food intake decreased and running increased for all groups; no differences between groups were significant.(ABSTRACT TRUNCATED AT 250 WORDS)