Peroxidase activity of hemoglobin towards ascorbate and urate: a synergistic protective strategy against toxicity of Hemoglobin-Based Oxygen Carriers (HBOC)

Carbon monoxide polyhemoglobin improves the therapeutic effect and relieves inflammation in the colon tissue of haemorrhagic shock/resuscitation rats

OBJECTIVE

The objective of this study was to test the therapeutic effect of carbon monoxide polyhemoglobin (polyCOHb) in haemorrhagic shock/resuscitation and its underlying mechanisms.

METHODS

48 rats were divided into two experimental parts, and 36 rats in the first experiment and 12 rats in the second experiment. In the first experimental part, 36 animals were randomly assigned to the following groups: hydroxyethyl starch group (HES group, n = 12), polyhemoglobin group (polyHb group, n = 12), and carbon monoxide polyhemoglobin group (polyCOHb group, n = 12). In the second experimental part, 12 animals were randomly assigned to the following groups: polyHb group (n = 6), and polyCOHb group (n = 6). Then the anaesthetised rats were haemorrhaged by withdrawing 50% of the animal's blood volume (BV), and resuscitated to the same volume of the animal's withdrawing BV with HES, polyHb, polyCOHb. In the first experimental part, the 72h survival rates of each groups animals were measured. In the second experimental part, the rats' mean arterial pressure (MAP), heart rate (HR), blood gas levels and other indicators were dynamically monitored in baseline, haemorrhagic shock (HS), at 0point resuscitation (RS 0h) and after 1 h resuscitation (RS 1h). The concentrations of malondialdehyde (MDA), superoxide dismutase (SOD), tumour necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6) were measured by ELISA kits in both groups of rats at RS 1h. Changes in pathological sections were examined by haematoxylin-eosin (HE) staining. Nuclear factor erythroid 2-related factor 2 (Nrf2) and haem oxygenase-1 (HO-1) levels were detected by immunohistochemical analysis, while myeloperoxidase (MPO) levels were detected by immunofluorescence. DHE staining was used to determine reactive oxygen species (ROS) levels.

RESULTS

The 72h survival rates of the polyHb and polyCOHb groups were 50.00% (6/12) and 58.33% (7/12) respectively, which were significantly higher than that of the 8.33% (1/12) in the HES group (p < 0.05). At RS 0h and RS 1h, the HbCO content of rats in the polyCOHb group (1.90 ± 0.21, 0.80 ± 0.21) g/L were higher than those in the polyHb group (0.40 ± 0.09, 0.50 ± 0.12)g/L (p < 0.05); At RS 1h, the MDA (41.47 ± 3.89 vs 34.17 ± 3.87 nmol/ml) in the plasma, Nrf2 and HO-1 content in the colon of rats in the polyCOHb group were lower than the polyHb group. And the SOD in the plasma (605.01 ± 24.46 vs 678.64 ± 36.37) U/mg and colon (115.72 ± 21.17 vs 156.70 ± 21.34) U/mg and the MPO content in the colon in the polyCOHb group were higher than the polyHb group (p < 0.05).

CONCLUSIONS

In these haemorrhagic shock/resuscitation models, both polyCOHb and polyHb show similar therapeutic effects, and polyCOHb has more effective effects in maintaining MAP, correcting acidosis, reducing inflammatory responses than that in polyHb.

Selective Attachment of Polyethylene Glycol to Hemerythrin for Potential Use in Blood Substitutes

Due to its ability to reversibly bind O₂, alongside a relatively low redox reactivity and a limited cytotoxicity, the oxygen-carrying protein hemerythrin has been considered as an alternative to hemoglobin in preparing blood substitutes. In order to increase the hydrodynamic volume and lower antigenicity, two site-directed variants, H82C and K92C, were engineered that contained a single cysteine residue on the surface of each hemerythrin octamer for the specific attachment of polyethylene glycol (PEG). A sulfhydryl-reactive PEGylation reagent with a 51.9 Å spacer arm was used for selective cysteine derivatization. The mutants were characterized by UV-vis spectroscopy, size-exclusion chromatography, oxygen affinity, and autooxidation rate measurements. The H82C variant showed altered oligomeric behavior compared to the wild-type and was unstable in the met form. The PEGylated K92C variant is reasonably stable, displays an oxygen affinity similar to that of the wild-type, and shows an increased rate of autoxidation; the latter disadvantage may be counteracted by further chemical modifications.

Polymerized human cord hemoglobin assisted with ascorbic acid as a red blood cell substitute alleviating oxidative stress for blood transfusion

Introduction: Blood transfusion is widely used in clinical settings, where considerable efforts have been devoted to develop red blood cell substitutes to overcome blood shortage and safety concerns. Among the several kinds of artificial oxygen carriers, hemoglobin-based oxygen carriers are promising due to their inherent good oxygen-binding and -loading properties. However, difficulties in prone to oxidation, production of oxidative stress, and injury in organs limited their clinical utility. In this work, we report a red blood cell substitute composed of polymerized human cord hemoglobin (PolyCHb) assisted with ascorbic acid (AA) that alleviates oxidative stress for blood transfusion. Methods: In this study, the in vitro impacts of AA on the PolyCHb were evaluated by testing the circular dichroism, methemoglobin (MetHb) contents and oxygen binding affinity before and after the addition of AA. In the in vivo study, guinea pigs were subjected to a 50% exchange transfusion with PolyCHb and AA co-administration, followed by the collection of blood, urine, and kidney samples. The hemoglobin contents of the urine samples were analyzed, and histopathologic changes, lipid peroxidation, DNA peroxidation, and heme catabolic markers in the kidneys were evaluated. Results: After treating with AA, there was no effect on the secondary structure and oxygen binding affinity of the PolyCHb, while the MetHb content was kept at 55%, which was much lower than that without AA treating. Moreover, the reduction of PolyCHbFe3+ was significantly promoted, and the content of MetHb could be reduced from 100% to 51% within 3 h. In vivo study results showed that PolyCHb assisted with AA inhibited the formation of hemoglobinuria, upgraded the total antioxidant capacity and downgraded the superoxide dismutase activity of kidney tissue, and lowered the expression of biomarkers for oxidative stress, e.g., malondialdehyde (ET vs ET+AA: 4.03±0.26 μmol/mg vs 1.83±0.16 μmol/mg), 4-hydroxy-2-nonenal (ET vs ET+AA: 0.98±0.07 vs 0.57±0.04), 8-hydroxy 2 deoxyguanosine(ET vs ET+AA: 14.81±1.58 ng/ml vs 10.91±1.36 ng/ml), heme oxygenase 1 (ET vs ET+AA: 1.51±0.08 vs 1.18±0.05) and ferritin (ET vs ET+AA: 1.75±0.09 vs 1.32±0.04). The kidney histopathology results also demonstrated that kidney tissue damage was effectively alleviated. Conclusion: In conclusion, these comprehensive results provide evidence for the potential role of AA in controlling oxidative stress and organ injury in the kidneys induced by PolyCHb, and suggest that PolyCHb assisted with AA has promising application for blood transfusion.

HBOC-301 in Porcine Kidney Normothermic Machine Perfusion and the Effect of Vitamin C on Methemoglobin Formation

Normothermic machine perfusion (NMP) of kidneys in combination with an optimized perfusate composition may increase donor organ preservation quality, especially in the case of marginal donor grafts. Optimization of currently employed perfusates is still a subject of present research. Due to the advantages of being cell-free, easy to store, and having minimal antigenicity, hemoglobin-based oxygen carriers, such as HBOC-301 (Oxyglobin^®, Hemoglobin Oxygen Therapeutics LLC, Souderton, PA, USA), offer an alternative to the commonly used perfusates based on packed red blood cells (pRBC). As previously described, using HBOC results in formation of methemoglobin (metHb) as an adverse effect, inducing hypoxic conditions during the perfusion. As a potential counterpart to metHb formation, the application of the antioxidant ascorbic acid (VitC) is of high interest. Therefore, this study was conducted in four experimental groups, to compare the effect of NMP with (1) HBOC or (3) pRBC, and additionally examine a beneficial effect of VitC in both groups (2) HBOC + VitC and (4) pRBC + VitC. All groups were subjected to NMP for 6 h at a pressure of 75 mmHg. Kidneys in the HBOC groups had a significantly lower renal blood flow and increasing intrarenal resistance, with reduced renal function in comparison to the pRBC groups, as demonstrated by significantly lower creatinine clearance and higher fractional sodium excretion rates. Clinical chemistry markers for tissue damage (LDH, lactate) were higher in the HBOC groups, whereas no significant histological differences were observed. Although the application of VitC decreased oxidative stress levels, it was not able to significantly increase the outcome parameters mentioned above in either group. This study demonstrated that HBOC-301 is inferior to pRBCs in our porcine kidney NMP model, independent of additional VitC administration. Oxidative stress and fragmentation of the hemoglobin polymers could be detected as a possible reason for these results, hence further research, focusing on the use of cell-free oxygen carriers that do not exhibit this complex of issues, is required.

From hemoglobin allostery to hemoglobin-based oxygen carriers

Hemoglobin (Hb) plays its vital role through structural and functional properties evolutionarily optimized to work within red blood cells, i.e., the tetrameric assembly, well-defined oxygen affinity, positive cooperativity, and heterotropic allosteric regulation by protons, chloride and 2,3-diphosphoglycerate. Outside red blood cells, the Hb tetramer dissociates into dimers, which exhibit high oxygen affinity and neither cooperativity nor allosteric regulation. They are prone to extravasate, thus scavenging endothelial NO and causing hypertension, and cause nephrotoxicity. In addition, they are more prone to autoxidation, generating radicals. The need to overcome the adverse effects associated with cell-free Hb has always been a major hurdle in the development of substitutes of allogeneic blood transfusions for all clinical situations where blood is unavailable or cannot be used due to, for example, religious objections. This class of therapeutics, indicated as hemoglobin-based oxygen carriers (HBOCs), is formed by genetically and/or chemically modified Hbs. Many efforts were devoted to the exploitation of the wealth of biochemical and biophysical information available on Hb structure, function, and dynamics to design safe HBOCs, overcoming the negative effects of free plasma Hb. Unfortunately, so far, no HBOC has been approved by FDA and EMA, except for compassionate use. However, the unmet clinical needs that triggered intensive investigations more than fifty years ago are still awaiting an answer. Recently, HBOCs "repositioning" has led to their successful application in organ perfusion fluids.

Translational research of hemoglobin vesicles as a transfusion alternative

Clinical situations arise in which blood for transfusion becomes scarce or unavailable. Considerable demand for a transfusion alternative persists because of various difficulties posed by blood donation and transfusion systems. Hemoglobin-vesicles (HbV) are artificial oxygen carriers being developed for use as a transfusion alternative. Just as biomembranes of red blood cells (RBCs) do, phospholipid vesicles (liposomes) for Hb encapsulation can protect the human body from toxic effects of molecular Hb. The main HbV component, Hb, is obtained from discarded human donated blood. Therefore, HbV can be categorized as a biologic agent targeting oxygen for peripheral tissues. The purification procedure strictly eliminates the possibility of viral contamination. It also removes all concomitant unstable enzymes present in RBC for utmost safety from infection. The deoxygenated HbVs, which are storable for over years at ambient temperature, can function as an alternative to blood transfusion for resuscitation from hemorrhagic shock and O₂ therapeutics. Moreover, a recent study clarified beneficial effects for anti-oxidation and anti-inflammation by carbon monoxide (CO)-bound HbVs. Autoxidation of HbV (HbO₂ → metHb + O₂-.) is unavoidable after intravenous administration. Co-injection of methylene blue can extract the intraerythrocytic glycolytic electron energy effectively and reduce metHb. Other phenothiazine dyes can also function as electron mediators to improve the functional life span of HbV. This review paper summarizes recent progress of the research and development of HbV, aimed at clinical applications.

Hemoglobins from Scapharca subcrenata (Bivalvia: Arcidae) likely play an bactericidal role through their peroxidase activity

Hemoglobin (Hb) is an iron-containing respiratory protein present in all vertebrates and some invertebrates. The blood clam Scapharca subcrenata is one of the few invertebrates that have Hb-containing red hemocytes. In this study, we purified Hb (Ss-Hb), including Ss-HbI and Ss-HbII, from S. subcrenata hemocytes using gel chromatography with a recovery rate of 70.71%, and then characterized their peroxidase activities. Both Ss-Hbs possessed peroxidase activity with high affinity to the substrates guaiacol and H₂O₂. Moreover, both Ss-Hbs had structural similarities, such as type b heme, proximal histidine (His), distal His, and heme pocket arginine (Arg), with other peroxidases. The optimal peroxidase activity of both Ss-Hbs was at pH 5 and 35 °C, but this was inhibited in the presence of Cu²⁺ and Fe²⁺. Ss-Hbs produced [Formula: see text] in the presence of H₂O₂. β-phenylethylamine, a substrate of peroxidase, increased the [Formula: see text] generation, while Cu²⁺, an inhibitor of peroxidase, inhibited this reaction. These results indicated that the peroxidase cycle of Ss-Hb was involved in the production of [Formula: see text] . A large amount of [Formula: see text] may be generated by the peroxidase cycle if the substrate is sufficient. During the incubation of Ss-Hbs with Bacillus subtilis, it was speculated that trace H₂O₂, probably from autoxidation of Ss-Hbs or generated by B. subtilis, started the peroxidase cycle of Ss-Hb. and produced a large amount of [Formula: see text] in the presence of sufficient substrate in the culture medium. It is therefore reasonable to assume that Ss-Hbs played an antibacterial role owing to their peroxidase activity, which produced [Formula: see text] .

Mechanisms of Toxicity and Modulation of Hemoglobin-based Oxygen Carriers

Several adverse events have been associated with the infusion of hemoglobin-based oxygen carriers (HBOCs), including transient hypertension, gastrointestinal, pancreatic/liver enzyme elevation, and cardiac/renal injury in humans. Although several mechanisms have been suggested, the basis of HBOC toxicity is still poorly understood. Scavenging of vascular endothelial nitric oxide (NO) and heme-mediated oxidative side reactions are thought to be the major causes of toxicity. However, based on more recent preclinical studies, oxidative pathways (driven by the heme prosthetic group) seem to play a more prominent role in the overall toxicity of free Hb or HBOCs. HBOCs display a diversity of physicochemical properties, including molecular size/cross-linking characteristics leading to differences in oxygen affinity, allosteric, redox properties, and even oxidative inactivation by protein/heme clearing mechanisms. These diverse characteristics can therefore be manipulated independently, leaving open the possibility of engineering a safe and effective HBOC. To date, several antioxidative strategies have been proposed to counteract the redox side reactions of current generation HBOCs.

Excess Ascorbate is a Chemical Stress Agent against Proteins and Cells

Excess ascorbate (as expected in intravenous treatment proposed for COVID-19 management, for example) oxidizes and/or degrades hemoglobin and albumin, as evidenced by UV-vis spectroscopy, gel electrophoresis, and mass spectrometry. It also degrades hemoglobin in intact blood or in isolated erythrocytes. The survival rates and metabolic activities of several leukocyte subsets implicated in the antiviral cellular immune response are also affected. Excess ascorbate is thus an unselective biological stress agent.

Redox states of hemoglobin determine left ventricle pressure recovery and activity of mitochondrial complex IV in hypoxic rat hearts

Cardiovascular effects were reported to occur in humans and in animal models during transfusion with hemoglobin (Hb)-based oxygen therapeutics. The effects of Hb's iron redox states on cardiac parameters during hypoxia/reoxygenation are however poorly defined. We hypothesize that acute exposures to ferric Hb during hypoxia leads to cardiomyocyte injury and an impaired left ventricular response accompanied by cardiac mitochondrial bioenergetic dysfunction. Recovery of left ventricular functions in an isolated rat heart Langendorff perfusion system was observed following perfusion with ferrous but not with ferric Hb. Ferric Hb induced the development of heart lesions, and impairment of the respiratory chain complex activity. Under normoxia, a sharp decline in cardiac parameters was observed following co-perfusion of low (20 μM) and high (100 μM) ascorbic acid (Asc) with ferrous Hb. This trend continued with ferric Hb co-perfusion, but only at the higher concentration of Asc. These observations suggest that perfusion of the hypoxic heart with ferric Hb increases oxidative stress thereby resulting in cardiac dysfunction. Intervention with Asc to reduce ferric Hb may offer a strategy to control Hb toxicity; however, timing of administration, and dosage of Asc may require individual optimization to target specific redox forms of Hb.

Engineering tyrosine residues into hemoglobin enhances heme reduction, decreases oxidative stress and increases vascular retention of a hemoglobin based blood substitute

Hemoglobin (Hb)-based oxygen carriers (HBOC) are modified extracellular proteins, designed to replace or augment the oxygen-carrying capacity of erythrocytes. However, clinical results have generally been disappointing due to adverse side effects, in part linked to the intrinsic oxidative toxicity of Hb. Previously a redox-active tyrosine residue was engineered into the Hb β subunit (βF41Y) to facilitate electron transfer between endogenous antioxidants such as ascorbate and the oxidative ferryl heme species, converting the highly oxidizing ferryl species into the less reactive ferric (met) form. We inserted different single tyrosine mutations into the α and β subunits of Hb to determine if this effect of βF41Y was unique. Every mutation that was inserted within electron transfer range of the protein surface and the heme increased the rate of ferryl reduction. However, surprisingly, three of the mutations (βT84Y, αL91Y and βF85Y) also increased the rate of ascorbate reduction of ferric(met) Hb to ferrous(oxy) Hb. The rate enhancement was most evident at ascorbate concentrations equivalent to that found in plasma (< 100 μM), suggesting that it might be of benefit in decreasing oxidative stress in vivo. The most promising mutant (βT84Y) was stable with no increase in autoxidation or heme loss. A decrease in membrane damage following Hb addition to HEK cells correlated with the ability of βT84Y to maintain the protein in its oxygenated form. When PEGylated and injected into mice, βT84Y was shown to have an increased vascular half time compared to wild type PEGylated Hb. βT84Y represents a new class of mutations with the ability to enhance reduction of both ferryl and ferric Hb, and thus has potential to decrease adverse side effects as one component of a final HBOC product.

Novel Redox Active Tyrosine Mutations Enhance the Regeneration of Functional Oxyhemoglobin from Methemoglobin: Implications for Design of Blood Substitutes

Heme mediated oxidative toxicity has been linked to adverse side effects in Hemoglobin Based Oxygen Carriers (HBOC), initiated by reactive ferryl (Fe^IV) iron and globin based free radical species. We recently showed that the addition of a redox active tyrosine residue in the beta subunit (βF41Y) of recombinant hemoglobin had the capability to decrease lipid peroxidation by facilitating the reduction of Fe^IV iron by plasma antioxidants such as ascorbate. In order to explore this functionality further we created a suite of tyrosine mutants designed to be accessible for both reductant access at the protein surface, yet close enough to the heme cofactor to enable efficient electron transfer to the Fe^IV. The residues chosen were: βF41Y; βK66Y; βF71Y; βT84Y; βF85Y; and βL96Y. As with βF41Y, all mutants significantly enhanced the rate of ferryl (Fe^IV) to ferric (Fe^III) reduction by ascorbate. However, surprisingly a subset of these mutations (βT84Y, and βF85Y) also enhanced the further reduction of ferric (Fe^III) to ferrous (Fe^II) heme, regenerating functional oxyhemoglobin. The largest increase was seen in βT84Y with the percentage of oxyhemoglobin formed from ferric hemoglobin in the presence of 100 μM ascorbate over a time period of 60 min increasing from 10% in βF41Y to over 50% in βT84Y. This increase was accompanied by an increased rate of ascorbate consumption. We conclude that the insertion of novel redox active tyrosine residues may be a useful component of any recombinant HBOC designed for longer functional activity without oxidative side effects.

The high affinity of small-molecule antioxidants for hemoglobin

Hemoglobin has previously been shown to display ascorbate peroxidase and urate peroxidase activity, with measurable Michaelis-Menten parameters that reveal a particularly low Km for ascorbate as well as for urate - lower than the respective in vivo concentrations of these antioxidants in blood. Also, direct detection of a hemoglobin-ascorbate interaction was possible by monitoring the 1H-NMR spectrum of ascorbate in the presence of hemoglobin. The relative difference in structures between ascorbate and urate may raise the question as to exactly what the defining structural features would be, for a substrate that binds to hemoglobin with high affinity. Reported here are Michaelis-Menten parameters for hemoglobin acting as peroxidase against a number of other substrates of varying structures - gallate, caffeate, rutin, 3-hydroxyflavone, 3,6-dihydroxyflavone, quercetin, epicatechin, luteolin - all with high affinities (some higher than those of physiologically-relevant redox partners of Hb - ascorbate and urate). Moreover, this high affinity appears general to animal hemoglobins. ¹H-NMR and ¹³C-NMR spectra reveal a general pattern wherein small hydrophilic antioxidants appear to all have their signals affected, presumably due to binding to hemoglobin. Fluorescence and calorimetry measurements confirm these conclusions. Docking calculations confirm the existence of binding sites on hemoglobin and on myoglobin for ascorbate as well as for other antioxidants. Support is found for involvement of Tyr42 in binding of three out of the four substrates investigated in the case of hemoglobin (including ascorbate and urate, as blood-contained relevant substrates), but also for Tyr145 (with urate and caffeate) and Tyr35 (with gallate).

Sources for developing new medicinal products: biochemical investigations on alcoholic extracts obtained from aerial parts of some Romanian Amaryllidaceae species

BACKGROUND

Although Galanthus nivalis L. (snowdrop) is known for the galanthamine content, used in the treatment of Alzheimer disease, the polyphenolic compounds of Amaryllidaceae species are less studied. Proper understanding of the polyphenolics in these extracts and of their antioxidant and antimicrobial properties may allow a reconsideration of their medicinal uses.

METHODS

The polyphenolic content of four selected Amaryllidaceae species harvested from Romania (Galanthus nivalis L., Narcissus pseudonarcissus L., N. poeticus L. and Leucojum vernum L.) was determined by spectrophotometric methods; the identification of phenolic compounds was performed by a HPLC-MS method, in order to establish their polyphenolic fingerprints. For the evaluation of the antioxidant potential the following methods were employed: DPPH radical scavenging, FRAP, hemoglobin ascorbate peroxidase activity inhibition (HAPX), inhibition of lipid peroxidation catalyzed by cytochrome c, and electron paramagnetic resonance (EPR) spectroscopy assays. Antimicrobial activity was assessed using the disc diffusion method.

RESULTS

Qualitative and quantitative analyses highlight important amount of polyphenols (over 15 mg/g); the main identified compounds are chlorogenic and p-coumaric acids in all species. Only G. nivalis shows antioxidant activity by all the used methods. G. nivalis and L. vernum strongly inhibits the growth of S. aureus, while N. poeticus shows a very good antifungal activity.

CONCLUSIONS

The results of this study provide a new approach to the properties and therapeutic uses of some Romanian widespread Amaryllidaceae species that could be considered sources of developing new medicinal products with anti anti-staphylococcal and antifungal activity.

Comparison of the oxidative reactivity of recombinant fetal and adult human hemoglobin: implications for the design of hemoglobin-based oxygen carriers

Hemoglobin (Hb)-based oxygen carriers (HBOCs) have been engineered to replace or augment the oxygen carrying capacity of erythrocytes. However, clinical results have generally been disappointing, in part due to the intrinsic oxidative toxicity of Hb. The most common HBOC starting material is adult human or bovine Hb. However, it has been suggested that fetal Hb may offer advantages due to decreased oxidative reactivity. Large-scale manufacturing of HBOC will likely and ultimately require recombinant sources of human proteins. We, therefore, directly compared the functional properties and oxidative reactivity of recombinant fetal (rHbF) and recombinant adult (rHbA) Hb. rHbA and rHbF produced similar yields of purified functional protein. No differences were seen in the two proteins in: autoxidation rate; the rate of hydrogen peroxide reaction; NO scavenging dioxygenase activity; and the NO producing nitrite reductase activity. The rHbF protein was: less damaged by low levels of hydrogen peroxide; less damaging when added to human umbilical vein endothelial cells (HUVEC) in the ferric form; and had a slower rate of intrinsic heme loss. The rHbA protein was: more readily reducible by plasma antioxidants such as ascorbate in both the reactive ferryl and ferric states; less readily damaged by lipid peroxides; and less damaging to phosphatidylcholine liposomes. In conclusion in terms of oxidative reactivity, there are advantages and disadvantages to the use of rHbA or rHbF as the basis for an effective HBOC.

Inflammation in sickle cell disease

The primary β-globin gene mutation that causes sickle cell disease (SCD) has significant pathophysiological consequences that result in hemolytic events and the induction of the inflammatory processes that ultimately lead to vaso-occlusion. In addition to their role in the initiation of the acute painful vaso-occlusive episodes that are characteristic of SCD, inflammatory processes are also key components of many of the complications of the disease including autosplenectomy, acute chest syndrome, pulmonary hypertension, leg ulcers, nephropathy and stroke. We, herein, discuss the events that trigger inflammation in the disease, as well as the mechanisms, inflammatory molecules and cells that propagate these inflammatory processes. Given the central role that inflammation plays in SCD pathophysiology, many of the therapeutic approaches currently under pre-clinical and clinical development for the treatment of SCD endeavor to counter aspects or specific molecules of these inflammatory processes and it is possible that, in the future, we will see anti-inflammatory drugs being used either together with, or in place of, hydroxyurea in those SCD patients for whom hematopoietic stem cell transplants and evolving gene therapies are not a viable option.

Haptoglobin and hemopexin inhibit vaso-occlusion and inflammation in murine sickle cell disease: Role of heme oxygenase-1 induction

During hemolysis, hemoglobin and heme released from red blood cells promote oxidative stress, inflammation and thrombosis. Plasma haptoglobin and hemopexin scavenge free hemoglobin and heme, respectively, but can be depleted in hemolytic states. Haptoglobin and hemopexin supplementation protect tissues, including the vasculature, liver and kidneys. It is widely assumed that these protective effects are due primarily to hemoglobin and heme clearance from the vasculature. However, this simple assumption does not account for the consequent cytoprotective adaptation seen in cells and organs. To further address the mechanism, we used a hyperhemolytic murine model (Townes-SS) of sickle cell disease to examine cellular responses to haptoglobin and hemopexin supplementation. A single infusion of haptoglobin or hemopexin (± equimolar hemoglobin) in SS-mice increased heme oxygenase-1 (HO-1) in the liver, kidney and skin several fold within 1 hour and decreased nuclear NF-ĸB phospho-p65, and vaso-occlusion for 48 hours after infusion. Plasma hemoglobin and heme levels were not significantly changed 1 hour after infusion of haptoglobin or hemopexin. Haptoglobin and hemopexin also inhibited hypoxia/reoxygenation and lipopolysaccharide-induced vaso-occlusion in SS-mice. Inhibition of HO-1 activity with tin protoporphyrin blocked the protections afforded by haptoglobin and hemopexin in SS-mice. The HO-1 reaction product carbon monoxide, fully restored the protection, in part by inhibiting Weibel-Palade body mobilization of P-selectin and von Willebrand factor to endothelial cell surfaces. Thus, the mechanism by which haptoglobin and hemopexin supplementation in hyperhemolytic SS-mice induces cytoprotective cellular responses is linked to increased HO-1 activity.

The Reaction of Oxy Hemoglobin with Nitrite: Mechanism, Antioxidant-Modulated Effect, and Implications for Blood Substitute Evaluation

The autocatalytic reaction between nitrite and the oxy form of globins involves free radicals. For myoglobin (Mb), an initial binding of nitrite to the iron-coordinated oxygen molecule was proposed; the resulting ferrous-peroxynitrate species was not detected, but its decay product, the high-valent ferryl form, was demonstrated in stopped-flow experiments. Reported here are the stopped flow spectra recorded upon mixing oxy Hb (native, as well as chemically-derivatized in the form of several candidates of blood substitutes) with a supraphysiological concentration of nitrite. The data may be fitted to a simple kinetic model involving a transient met-aqua form, in contrast to the ferryl detected in the case of Mb in a similar reaction sequence. These data are in line with a previous observation of a transient accumulation of ferryl Hb under auto-catalytic conditions at much lower concentrations of nitrite (Grubina, R. et al. J. Biol. Chem. 2007, 282, 12916). The simple model for fitting the stopped-flow data leaves a small part of the absorbance changes unaccounted for, unless a fourth species is invoked displaying features similar to the oxy and tentatively assigned as ferrous-peroxynitrate. Density functional theory (DFT) calculations support this latter assignment. The reaction allows for differentiating between the reactivities of various chemically modified hemoglobins, including candidates for blood substitutes. Polymerization of hemoglobin slows the nitrite-induced oxidation, in sharp contrast to oxidative-stress type reactions which are generally accelerated, not inhibited. Sheep hemoglobin is found to be distinctly more resistant to reaction with nitrite compared to bovine Hb, at large nitrite concentrations (stopped-flow experiments directly observing the oxy + nitrite reaction) as well as under auto-catalytic conditions. Copolymerization of Hb with bovine serum albumin (BSA) using glutaraldehyde leads to a distinct increase of the lag time compared to native Hb as well as to any other form of derivatization examined in the present study. The Hb-BSA copolymer also displays a slower initial reaction with nitrite under stopped-flow conditions, compared to native Hb.

Ascorbate protects the diheme enzyme, MauG, against self-inflicted oxidative damage by an unusual antioxidant mechanism

Ascorbate protects MauG from self-inactivation that occurs during the autoreduction of the reactive bis-FeIV state of its diheme cofactor. The mechanism of protection does not involve direct reaction with reactive oxygen species in solution. Instead, it binds to MauG and mitigates oxidative damage that occurs via internal transfer of electrons from amino acid residues within the protein to the high-valent hemes. The presence of ascorbate does not inhibit the natural catalytic reaction of MauG, which catalyzes oxidative post-translational modifications of a substrate protein that binds to the surface of MauG and is oxidized by the high-valent hemes via long-range electron transfer. Ascorbate was also shown to prolong the activity of a P107V MauG variant that is more prone to inactivation. A previously unknown ascorbate peroxidase activity of MauG was characterized with a kcat of 0.24 s−1 and a Km of 2.2 µM for ascorbate. A putative binding site for ascorbate was inferred from inspection of the crystal structure of MauG and comparison with the structure of soybean ascorbate peroxidase with bound ascorbate. The ascorbate bound to MauG was shown to accelerate the rates of both electron transfers to the hemes and proton transfers to hemes which occur during the multistep autoreduction to the diferric state which is accompanied by oxidative damage. A structural basis for these effects is inferred from the putative ascorbate-binding site. This could be a previously unrecognized mechanism by which ascorbate mitigates oxidative damage to heme-dependent enzymes and redox proteins in nature.

Oxidative pathways in the sickle cell and beyond

Polymerization of deoxy sickle cell hemoglobin (HbS) is well recognized as the primary event that triggers the classic cycles of sickling/unsickling of patients red blood cells (RBCs). RBCs are also subjected to continuous endogenous and exogenous oxidative onslaughts resulting in hemolytic rate increases which contribute to the evolution of vasculopathies associated with this disease. Compared to steady-state conditions, the occurrences of vaso-occlusive crises increase the levels of both RBC-derived microparticles as well as extracellular Hb in circulation. Common byproduct resulting from free Hb oxidation and from Hb-laden microparticles is heme (now recognized as damage associated molecular pattern (DAMP) molecule) which has been shown to initiate inflammatory responses. This review provides new insights into the interplay between microparticles, free Hb and heme focusing on Hb's pseudoperoxidative activity that drives RBC's cytosolic, membrane changes as well as oxidative toxicity towards the vascular system. Emerging antioxidative strategies that include the use of protein and heme scavengers in controlling Hb oxidative pathways are discussed.

Redox and Peroxidase Activities of the Hemoglobin Superfamily: Relevance to Health and Disease

SIGNIFICANCE

Erythrocyte hemoglobin (Hb) and myocyte myoglobin, although primarily oxygen-carrying proteins, have the capacity to do redox chemistry. Such redox activity in the wider family of globins now appears to have important associations with the mechanisms of cell stress response. In turn, an understanding of such mechanisms in vivo may have a potential in the understanding of cancer therapy resistance and neurodegenerative disorders such as Alzheimer's. Recent Advances: There has been an enhanced understanding of the redox chemistry of the globin superfamily in recent years, leading to advances in development of Hb-based blood substitutes and in hypotheses relating to specific disease mechanisms. Neuroglobin (Ngb) and cytoglobin (Cygb) have been linked to cell protection mechanisms against hypoxia and oxidative stress, with implications in the onset and progression of neurodegenerative diseases for Ngb and cancer for Cygb.

CRITICAL ISSUES

Despite advances in the understanding of redox chemistry of globins, the physiological roles of many of these proteins still remain ambiguous at best. Confusion over potential physiological roles may relate to multifunctional roles for globins, which may be modulated by surface-exposed cysteine pairs in some globins. Such roles may be critical in deciphering the relationships of these globins in human diseases.

FUTURE DIRECTIONS

Further studies are required to connect the considerable knowledge on the mechanisms of globin redox chemistry in vitro with the physiological and pathological roles of globins in vivo. In doing so, new therapies for neurodegenerative disorders and cancer therapy resistance may be targeted. Antioxid. Redox Signal. 26, 763-776.

Chlorite reactivity with myoglobin: Analogy with peroxide and nitrite chemistry?

Stopped-flow UV-vis data allow for the first time direct spectroscopic detection of a ferryl species during the reaction of met myoglobin (Mb) with chlorite, analogous to what is observed in the reaction with peroxides. Ferryl is also observed in the reaction of oxy Mb+chlorite. A pathway involving Fe-O-O-ClO₂ is explored by analogy with the Fe-O-O-NO and Fe-O-O-NO₂ previously proposed as intermediates in the reactions of oxy globins with nitric oxide and nitrite, respectively. However, Fe-O-O-ClO₂ is not detectable in these stopped-flow experiments and is in fact, unlike its nitrogenous congeners, predicted by density functional theory (DFT) to be impossible for a heme complex. Deoxy Mb reacts with chlorite faster than met - suggesting that, unlike with hydrogen peroxide (with which deoxy Mb reacts slower than met), binding of chlorite to the heme is not a rate-determining step (hence, most likely, an outer-sphere electron transfer mechanism); to correlate this, a Fe-O-Cl-O adduct was not observed experimentally for the met or for the deoxy reactions - even though prior DFT calculations suggest it to be feasible and detectable.

Hemoglobins Likely Function as Peroxidase in Blood Clam Tegillarca granosa Hemocytes

Hemoglobins are a group of respiratory proteins principally functioning in transport of oxygen and carbon dioxide in red blood cells of all vertebrates and some invertebrates. The blood clam T. granosa is one of the few invertebrates that have hemoglobin-containing red hemocytes. In the present research, the peroxidase activity of T. granosa hemoglobins (Tg-Hbs) was characterized and the associated mechanism of action was deciphered via structural comparison with other known peroxidases. We detected that purified Tg-Hbs catalyzed the oxidation of phenolic compounds in the presence of exogenous H₂O₂. Tg-Hbs peroxidase activity reached the maximum at pH 5 and 35°C and was inhibited by Fe²⁺, Cu²⁺, SDS, urea, and sodium azide. Tg-Hbs shared few similarities in amino acid sequence and overall structural characteristics with known peroxidases. However, the predicted structure at their heme pocket was highly similar to that of horseradish peroxidase (HRP) and myeloperoxidase (MPO). This research represented the first systemic characterization of hemoglobin as a peroxidase.

Copolymerization of recombinant Phascolopsis gouldii hemerythrin with human serum albumin for use in blood substitutes

Hemerythrin is an oxygen-carrying protein found in marine invertebrates and may be a promising alternative to hemoglobin for use in blood substitutes, primarily due to its negligible peroxidative toxicity. Previous studies have shown that glutaraldehyde-induced copolymerization of hemoglobin with bovine serum albumin increases the half-life of the active oxy form of hemoglobin (i.e. decreases the auto-oxidation rate). Here, we describe a protocol for glutaraldehyde copolymerization of Hr with human serum albumin and the dioxygen-binding properties of the co-polymerized products. The copolymerization with HSA results in alteration of hemerythrin's dioxygen-binding properties in directions that may be favorable for use in blood substitutes.

Achillea schurii Flowers: Chemical, Antioxidant, and Antimicrobial Investigations

This study aims to evaluate the phenolic profile, and antioxidant and antimicrobial activity of Achillea schurii Sch.-Bip., an endemic species from Romania that has not been investigated yet. The chromatographic profile of the phenolic components was obtained using the HPLC-MS method, while the total polyphenol, flavonoid, caffeic acid derivative contents were quantified using spectrophotometric methods. The antioxidant activity was evaluated using different methods: DPPH radical scavenging, hemoglobin ascorbate peroxidase activity inhibition (HAPX), inhibition of lipid peroxidation catalyzed by cytochrome c, and direct detection of plant-derived free radicals using electron paramagnetic resonance (EPR). The antimicrobial test was performed using the disk diffusion assay. The phenolic profile has revealed high amounts of isoquercitrin, rutin, luteolin, and apigenin. The A. schurii extract exhibited a good antioxidant capacity, and high phenolic contents (76.93 mg/g polyphenols, 18.61 mg/g flavonoids and 41.48 mg/g caffeic acid derivatives, respectively). The antimicrobial tests reveal a remarkable inhibitory activity against Listeria monocytogenes, Staphylococcus aureus, and Salmonella typhimurium. Considering the above, A. schurii may be deemed to offer good perspectives for pharmaceutical and industrial applications.

High Presence of Extracellular Hemoglobin in the Periventricular White Matter Following Preterm Intraventricular Hemorrhage

Severe cerebral intraventricular hemorrhage (IVH) in preterm infants continues to be a major clinical problem, occurring in about 15-20% of very preterm infants. In contrast to other brain lesions the incidence of IVH has not been reduced over the last decade, but actually slightly increased. Currently over 50% of surviving infants develop post-hemorrhagic ventricular dilatation and about 35% develop severe neurological impairment, mainly cerebral palsy and intellectual disability. To date there is no therapy available to prevent infants from developing either hydrocephalus or serious neurological disability. It is known that blood rapidly accumulates within the ventricles following IVH and this leads to disruption of normal anatomy and increased local pressure. However, the molecular mechanisms causing brain injury following IVH are incompletely understood. We propose that extracellular hemoglobin is central in the pathophysiology of periventricular white matter damage following IVH. Using a preterm rabbit pup model of IVH the distribution of extracellular hemoglobin was characterized at 72 h following hemorrhage. Evaluation of histology, histochemistry, hemoglobin immunolabeling and scanning electron microscopy revealed presence of extensive amounts of extracellular hemoglobin, i.e., not retained within erythrocytes, in the periventricular white matter, widely distributed throughout the brain. Furthermore, double immunolabeling together with the migration and differentiation markers polysialic acid neural cell adhesion molecule (PSA-NCAM) demonstrates that a significant proportion of the extracellular hemoglobin is distributed in areas of the periventricular white matter with high extracellular plasticity. In conclusion, these findings support that extracellular hemoglobin may contribute to the pathophysiological processes that cause irreversible damage to the immature brain following IVH.

High-Dose Polymerized Hemoglobin Fails to Alleviate Cardiac Ischemia/Reperfusion Injury due to Induction of Oxidative Damage in Coronary Artery

Objective. Ischemia/reperfusion (I/R) injury is an unavoidable event for patients in cardiac surgery under cardiopulmonary bypass (CPB). This study was designed to investigate whether glutaraldehyde-polymerized human placenta hemoglobin (PolyPHb), a hemoglobin-based oxygen carrier (HBOC), can protect heart against CPB-induced I/R injury or not and to elucidate the underlying mechanism. Methods and Results. A standard dog CPB model with 2-hour cardiac arrest and 2-hour reperfusion was established. The results demonstrated that a low-dose PolyPHb (0.1%, w/v) provided a significant protection on the I/R heart, whereas the high-dose PolyPHb (3%, w/v) did not exhibit cardioprotective effect, as evidenced by the impaired cardiac function, decreased myocardial oxygen utilization, and elevated enzymes release and pathological changes. Further study indicated that exposure of isolated coronary arteries or human umbilical vein endothelial cells (HUVECs) to a high-dose PolyPHb caused impaired endothelium-dependent relaxation, which was companied with increased reactive oxygen species (ROS) production, reduced superoxide dismutase (SOD) activity, and elevated malonaldehyde (MDA) formation. Consistent with the increased oxidative stress, the NAD(P)H oxidase activity and subunits expression, including gp91^phox, p47^phox, p67^phox, and Nox1, were greatly upregulated. Conclusion. The high-dose PolyPHb fails to protect heart from CPB-induced I/R injury, which was due to overproduction of NAD(P)H oxidase-induced ROS and resultant endothelial dysfunction.

Antioxidant activity evaluation involving hemoglobin-related free radical reactivity

Two methods for the measurement of antioxidant capacity are described: one based on a chronometric variation of a hemoglobin ascorbate peroxidase assay and the other based on electron paramagnetic resonance (EPR) spectra collected upon alkaline treatment of ethanolic samples. The involved chemical mechanisms are discussed, alongside the most important benefits and shortcomings; the assays offer new qualitative and quantitative information on samples of biological as well as synthetic origin.

Evaluation of antioxidant and antimicrobial activities and phenolic profile for Hyssopus officinalis, Ocimum basilicum and Teucrium chamaedrys

This study was designed to examine the in vitro antioxidant and antimicrobial activities and to characterize the polyphenolic composition of the ethanolic extracts of Hyssopus officinalis, Ocimum basilicum and Teucrium chamaedrys. Qualitative and quantitative analysis of the major phenolic compounds were conducted using high-performance liquid chromatography coupled to mass spectrometry (HPLC-MS). The total polyphenols, caffeic acid derivatives and flavonoids content was spectrophotometrically determined. The phenolic profile showed the presence of phenolic acid derivatives (caftaric, gentisic, caffeic, p-coumaric, chlorogenic and ferulic acids), flavonoid glycosides (rutin, isoquercitrin and quercitrin) and free flavonoid aglycons (luteolin, quercetin), in different concentrations. DPPH radical scavenging assay, Trolox equivalent antioxidant capacity (TEAC) method, hemoglobin ascorbate peroxidase activity inhibition (HAPX) assay, and electron paramagnetic resonance (EPR) radicals detection were employed, revealing several aspects of the antioxidant activities of these species. The antimicrobial tests were performed using the disk diffusion assay. These extracts contained a large amount of the polyphenolic compounds (77.72, 175.57, and 243.65 mg/g, respectively), and they showed a good antioxidant activity, as witnessed by a number of methods. T. chamaedrys had a high antimicrobial activity. Besides their antioxidant activity, the antimicrobial effect of these extracts confirms the biological activities of these herbal medicinal products.

Polyphenolic composition, antioxidant and antibacterial activities for two Romanian subspecies of Achillea distans Waldst. et Kit. ex Willd

The aim of this work was to study the chemical composition, antioxidant and antibacterial properties of Achillea distans Waldst. et Kit. subsp. distans and Achillea distans Waldst. et Kit. subsp. alpina Rochel, from the Rodna Mountains (Romania). The identification and quantification of major phenolic compounds was performed by a HPLC-MS method. The total polyphenolic and flavonoid content was determined spectrophotometrically. The antioxidant activity was evaluated using the DPPH bleaching method, trolox equivalent antioxidant capacity assay (TEAC), hemoglobin ascorbate peroxidase activity inhibition (HAPX) assay, and an Electron Paramagnetic Resonance (EPR) spectroscopy method. A data indicated that A. distans subsp. alpina extract has more antioxidant activity than A. distans subsp. distans extract. Luteolin, apigenin, quercetin, caffeic and chlorogenic acids were present in the two extracts of A. distans, but in different amounts. Three flavonoids were detected only in A. distans subsp. alpina. The polyphenol-richer A. distans subsp. alpina extract showed a higher antioxidant activity than A.distans subsp. distans extract. A.distans subsp. distans extract showed inhibitory activity for Gram-positive bacteria, as evaluated with four species. The quantitative and qualitative differences between the two subspecies of Achillea distans could be used as a potential taxonomic marker in order to distinguish the species.

Blood substitutes: evolution from noncarrying to oxygen- and gas-carrying fluids

The development of oxygen (O2)-carrying blood substitutes has evolved from the goal of replicating blood O2 transport properties to that of preserving microvascular and organ function, reducing the inherent or potential toxicity of the material used to carry O2, and treating pathologies initiated by anemia and hypoxia. Furthermore, the emphasis has shifted from blood replacement fluid to "O2 therapeutics" that restore tissue oxygenation to specific tissues regions. This review covers the different alternatives, potential and limitations of hemoglobin-based O2 carriers (HBOCs) and perfluorocarbon-based O2 carriers (PFCOCs), with emphasis on the physiologic conditions disturbed in the situation that they will be used. It describes how concepts learned from plasma expanders without O2-carrying capacity can be applied to maintain O2 delivery and summarizes the microvascular responses due to HBOCs and PFCOCs. This review also presents alternative applications of HBOCs and PFCOCs namely: 1) How HBOC O2 affinity can be engineered to target O2 delivery to hypoxic tissues; and 2) How the high gas solubility of PFCOCs provides new opportunities for carrying, dissolving, and delivering gases with biological activity. It is concluded that the development of current blood substitutes has amplified their applications horizon by devising therapeutic functions for O2 carriers requiring limited O2 delivery capacity restoration. Conversely, full, blood-like O2-carrying capacity reestablishment awaits the control of O2 carrier toxicity.

Examining and mitigating acellular hemoglobin vasoactivity

SIGNIFICANCE

There has been a striking advancement in our understanding of red cell substitutes over the past decade. Although regulatory oversight has influenced many aspects of product development in this period, those who have approached the demonstration of efficacy of red cell substitutes have failed to understand their implication at the level of the microcirculation, where blood interacts closely with tissue.

RECENT ADVANCES

The understanding of the adverse effects of acellular hemoglobin (Hb)-based oxygen carriers (HBOCs) has fortunately expanded from Hb-induced renal toxicity to a more complete list of biochemical mechanism. In addition, various unexpected adverse reactions were seen in early clinical studies. The effects of the presence of acellular Hb in plasma are relatively unique because of the convergence of mechanical and biochemical natures.

CRITICAL ISSUES

Controlling the variables using genetic engineering and chemical modification to change specific characteristics of the Hb molecule may allow for solving the complex multivariate problems of acellular Hb vasoactivity. HBOCs may never be rendered free of negative effects; however, quantifying the nature and extent of microvascular complications establishes a platform for designing new ameliorative therapies.

FUTURE DIRECTIONS

It is time to leave behind the study of vasoactivity and toxicity based on bench-top measurements of biochemical changes and those based solely on systemic parameters in vivo, and move to a more holistic analysis of the mechanisms creating the problems, complemented with meaningful studies of efficacy.

Amplification of antioxidant activity of haptoglobin(2-2)-hemoglobin at pathologic temperature and presence of antibiotics

It is clear that Haptoglobin binds to Hemoglobin strongly and irreversibly. This binding, protects body tissues against heme-mediated oxidative tissue damages via peroxidase activity of Haptoglobin-Hemoglobin complex. Peroxidase activity of Haptoglobin(2-2)-Hemoglobin complex was determined via measurement of following increase in absorption of produced tetraguaiacol as the second substrate of Haptoglobin-Hemoglobin complex by UV-Vis spectrophotometer at 470 nm and 42°C. The results are showing that peroxidase activity of Haptoglobin(2-2)-Hemoglobin complex is modulated by homotropic effect of hydrogen peroxide as the allosteric substrate. On the other hand, antioxidant activity of Haptoglobin(2-2)-Hemoglobin is increased via heterotropic effect of two antibiotics (especially ampicillin) on the peroxidase activity of the complex. The condition of pathologic temperature along with the administration of ampicillin and/or coamoxiclav is in favor of amplification in antioxidant activity of Haptoglobin(2-2)-Hemoglobin and combating against free radicals in individuals with Hp2-2 phenotype. Therefore, oxidative stress effects have been diminished in the population with this phenotype.

Anticancer and antimicrobial activities of some antioxidant-rich cameroonian medicinal plants

Traditional remedies have a long-standing history in Cameroon and continue to provide useful and applicable tools for treating ailments. Here, the anticancer, antimicrobial and antioxidant activities of ten antioxidant-rich Cameroonian medicinal plants and of some of their isolated compounds are evaluated.The plant extracts were prepared by maceration in organic solvents. Fractionation of plant extract was performed by column chromatography and the structures of isolated compounds (emodin, 3-geranyloxyemodin, 2-geranylemodin) were confirmed spectroscopically. The antioxidant activity (AOA) was determined using the 1,1-diphenyl-2-picrylhydrazyl (DPPH) bleaching method, the trolox equivalent antioxidant capacity (TEAC), and the hemoglobin ascorbate peroxidase activity inhibition (HAPX) assays. The anticancer activity was evaluated against A431 squamous epidermal carcinoma, WM35 melanoma, A2780 ovary carcinoma and cisplatin-resistant A2780cis cells, using a direct colorimetric assay. The total phenolic content in the extracts was determined spectrophotometrically by the Folin–Ciocalteu method. Rumex abyssinicus showed the best AOA among the three assays employed. The AOA of emodin was significantly higher than that of 3-geranyloxyemodin and 2-geranylemodin for both TEAC and HAPX methods. The lowest IC₅₀ values (i.e., highest cytotoxicity) were found for the extracts of Vismia laurentii, Psorospermum febrifugum, Pentadesma butyracea and Ficus asperifolia. The Ficus asperifolia and Psorospermum febrifugum extracts are selective against A2780cis ovary cells, a cell line which is resistant to the standard anticancer drug cisplatin. Emodin is more toxic compared to the whole extract, 3-geranyloxyemodin and 2-geranylemodin. Its selectivity against the platinum-resistant A2780cis cell line is highest. All of the extracts display antimicrobial activity, in some cases comparable to that of gentamycin.

Biocatalytic oxidation of phenolic compounds by bovine methemoglobin in the presence of H2O2: quantitative structure-activity relationships

In the present work, 13 p-substituted phenols with different functional groups have been systematically evaluated as metHb substrates by means of HPLC analysis. Non-hyperbolic kinetics were observed and Hill coefficients in the 0.37-1.00 range were obtained. The catalytic constants and the Hill coefficients were found to be quantitatively correlated with two independent variables: the energy level of the highest-occupied molecular orbital (E(HOMO)), which describes the intrinsic redox activity of the substrates and the pK(a)-values, which are related to substrate ionization. Oxygen evolution in the presence of each phenol derivative was also measured, and good correlation between peroxidase-like and catalase-like activities of the protein was observed. It is also shown that bovine metHb, although less active than other peroxidases, may represent a good alternative from an economical point of view for phenol removal processes. The equations here obtained may serve as a basis to further explore the potential use of metHb-mediated reactions in the treatment of phenols in wastewaters and to predict which phenol will be removed most efficiently under this treatment with satisfactory reliability.

Towards hemerythrin-based blood substitutes: comparative performance to hemoglobin on human leukocytes and umbilical vein endothelial cells

Hemerythrin is a dioxygen-carrying protein whose oxidative/nitrosative stress-related reactivity is lower than that of hemoglobin, which may warrant investigation of hemerythrin as raw material for artificial oxygen carriers ('blood substitutes'). We report here the first biological tests for hemerythrin and its chemical derivatives, comparing their performance with that of a representative competitor, glutaraldehyde-polymerized bovine hemoglobin. Hemerythrin (native or derivatized) exhibits a proliferative effect on human umbilical vein endothelial cell (HUVEC) cultures, as opposed to a slight inhibitory effect of hemoglobin. A similar positive effect is displayed on human lymphocytes by glutaraldehyde-polymerized hemerythrin, but not by native or polyethylene glycol-derivatized hemerythrin.

Ascorbate peroxidase activity of cytochrome c

The peroxidase-type reactivity of cytochrome c is proposed to play a role in free radical production and/or apoptosis. This study describes cytochrome c catalysis of peroxide consumption by ascorbate. Under conditions where the sixth coordination position at the cytochrome c heme iron becomes more accessible for exogenous ligands (by carboxymethylation, cardiolipin addition or by partial denaturation with guanidinium hydrochloride) this peroxidase activity is enhanced. A reaction intermediate is detected by stopped-flow UV-vis spectroscopy upon reaction of guanidine-treated cytochrome c with peroxide, which resembles the spectrum of globin Compound II species and is thus proposed to be a ferryl species. The ability of physiological levels of ascorbate (10-60 µM) to interact with this species may have implications for mechanisms of cell signalling or damage that are based on cytochrome c/peroxide interactions.

Haemoglobin-induced oxidative stress is associated with both endogenous peroxidase activity and H2O2 generation from polyunsaturated fatty acids

Patients with increased haemolytic haemoglobin (Hb) have 10-20-times greater incidence of cardiovascular mortality. The objective of this study was to evaluate the role of Hb peroxidase activity in LDL oxidation. The role of Hb in lipid peroxidation, H(2)O(2) generation and intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) was assessed using NaN(3), a peroxidase inhibitor, catalase, a H(2)O(2) decomposing enzyme and human umbilical vein endothelial cells (HUVECs), respectively. Hb induced H(2)O(2) production by reacting with LDL, linoleate and cell membrane lipid extracts. Hb-induced LDL oxidation was inhibited by NaN(3) and catalase. Furthermore, Hb stimulated ICAM-1 and VCAM-1 expression, which was inhibited by the antioxidant, probucol. Thus, the present study suggests that the peroxidase activity of Hb produces atherogenic, oxidized LDL and oxidized polyunsaturated fatty acids (PUFAs) in the cell membrane and reactive oxygen species (ROS) formation mediated Hb-induced ICAM-1 and VCAM-1 expression.

Derivatization of haemoglobin with periodate-generated reticulation agents: evaluation of oxidative reactivity for potential blood substitutes

Periodate modification of the sugar moiety in sugars, including adenosine triphosphate (ATP), has previously been employed in order to prepare dialdehyde-type reagents, which were then utilized in crosslinking reactions on haemoglobin, yielding polymerized material with useful dioxygen-binding properties and hence proposed as possible artificial oxygen carriers ('blood substitutes'). Here, the periodate protocol is shown to be applicable to a wider range of oxygen-containing compounds, illustrated by starch and polyethylene glycol. Derivatization protocols are described for haemoglobin with such periodate-treated crosslinking agents, and the dioxygen-binding properties and redox reactivities are investigated for the derivatized haemoglobins, with emphasis on pro-oxidative properties. There is a general tendency of the derivatization to result in higher autooxidation rates. The peroxide reactivity of the met (ferric) form is also affected by derivatization, as witnessed, among others, by varying yields of ferryl [Fe (IV)-oxo] and free radical generated. In cell, culture tests (human umbilical vein epithelial cells, HUVEC), the derivatization protocols show no toxic effect.

Structural and redox behavior of OxyVita, a zero-linked polymeric hemoglobin: comparison with natural acellular polymeric hemoglobins

A zero-linked polymeric hemoglobin (OxyVita Hb) has been developed for application as an acellular therapeutic hemoglobin-based-oxygen-carrier (HBOC). For effective and safe oxygen binding, transport and delivery, an HBOC must meet essential molecular requirements related to its structural integrity and redox stability. OxyVita is a super polymer possessing an average M.wt. of 17 x 10(6) Da. Structural integrity was determined by unfolding studies of OxyVita in the presence of increasing concentrations of urea. The unfolding midpoints (D(1/2)) of different preparations of OxyVita (solution and powder forms) were compared to Lumbricus Hb (LtHb) and Arenicola Hb (ArHb), natural acellular polymeric hemoglobins, which are serving as models for an effective and safe acellular HBOC. Reduction studies of OxyVita Hb using endogenous reducing agents were also investigated. Results from these studies indicate that: 1) OxyVita Hb exhibits greater resistance to conformational change than either LtHb or ArHb in the reduced (oxyHb) state; and 2) the reduction of met OxyVita Hb to oxyHb occurs slowly in the presence of either ascorbic acid (70% reduction in 560 min.) or beta-NADH (40% reduction in 90 min.). These studies provide consistent evidence that OxyVita Hb possesses physiochemical properties that exhibit structural integrity and redox behavior necessary for functioning as an effective and safe HBOC within clinical applications. These results are in agreement with observations made by other investigators as to the reduction in heme-loss of OxyVita Hb, essential for the reversible binding/release of molecular oxygen within the circulatory system.

The quaternary structure of tetrameric hemoglobin regulates the oxygen affinity of polymerized hemoglobin

This study focuses on the effect of the initial quaternary structure of bovine hemoglobin (Hb) on the physical properties of glutaraldehyde polymerized Hb (PolyHb) solutions. Tense (T) state PolyHb was synthesized by maintaining the pO(2) of Hb before and after polymerization at 0 mm Hg. In contrast, relaxed (R) state PolyHb was generated by maintaining the pO(2) of Hb before and after polymerization to >749 mm Hg. PolyHb solutions were characterized by measuring the pO(2), methemoglobin (metHb) level, molecular weight distribution, O(2) affinity and cooperativity coefficient. The metHb level of all PolyHb solutions was low (<2%). Analysis of the molecular weight distribution of PolyHb solutions indicates that in general, the molecular weight of PolyHb solutions increased with increasing cross-link density. T-state PolyHb solutions exhibited lower O(2) affinity compared to unmodified Hb, whereas R-state PolyHb solutions exhibited higher O(2) affinity compared to unmodified Hb. In addition, the polymerization reaction resulted in a significant decrease in cooperativity that was more pronounced at higher cross-link densities. All of these results were explained in terms of the quaternary structure of Hb. Taken together, our results yield more insight into the importance Hb's quaternary structure plays in defining the physical properties of glutaraldehyde PolyHb solutions. This information will be useful in designing optimized glutaraldehyde PolyHb oxygen carriers for various applications in transfusion medicine.

Redox reactivity in propolis: direct detection of free radicals in basic medium and interaction with hemoglobin

Propolis is one of many natural products with known antioxidant properties. The present work aims to investigate the intimate molecular-level mechanisms of this antioxidant reactivity. Electron paramagnetic resonance (EPR)-detectable free radical signals are described here for the first time in propolis extracts. The shape of these signals and the conditions in which they were obtained, point to polyphenolic flavonoids as the sites of the radicals. An inverse correlation between antioxidant capacity and free radical signal intensity is shown. The free radical reactivity of propolis is also illustrated by the effect it exerts on the biologically-relevant peroxide reactivity of hemoglobin. A new test of antioxidant ability in natural extracts such as propolis is proposed, based on modulation of the ascorbate peroxidase activity of hemoglobin (HAPX). Results of this test correlate well with those obtained via traditional methods such as those based on DPPH (2,2-diphenyl-1-picrylhydrazyl), or on ABTS (2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid).

Hemoglobin can attenuate hydrogen peroxide-induced oxidative stress by acting as an antioxidative peroxidase

Hemoglobin is considered a potentially toxic molecule when released from erythrocytes during hemolysis, inflammation, or tissue injury. The mechanisms of toxicity involve reduced nitric oxide bioavailability and oxidative processes both occurring at the heme prosthetic groups. When the endogenous oxidant H(2)O(2) reacts with Hb, transient radicals are generated during the peroxidative consumption of H(2)O(2). If not neutralized, these radicals can lead to tissue toxicity. The net biologic effect of extracellular Hb in an H(2)O(2)-rich environment will therefore be determined by the balance of H(2)O(2) decomposition (potential protective effect) and radical generation (potential damaging effect). Here we show that Hb can protect different cell types from H(2)O(2)-mediated cell death and the associated depletion of intracellular glutathione and ATP. Importantly, Hb blunts the transcriptional oxidative-stress response induced by H(2)O(2) in human vascular smooth muscle cells (VSMCs). Based on spectrophotometric and quantitative mass spectrometry analysis, we suggested a novel mechanism in which Hb redox-cycles H(2)O(2) and simultaneously internalizes the radical burden, with irreversible structural globin changes starting with specific amino acid oxidation involving the heme proximate betaCys93 and ultimately ending with protein precipitation. Our results suggest that complex interactions determine whether extracellular Hb, under certain circumstances, acts a protective or a damaging factor during peroxidative stress conditions.