Ascorbate removes key precursors to oxidative damage by cell-free haemoglobin in vitro and in vivo

Degree of PEGylatation of Lumbricus terrestris Hemoglobin Improves Microcirculatory Blood Flow but Increases the Rate of Auto-Oxidation

INTRODUCTION

The demand for red blood cells (RBCs) is on the rise due to the increasing diagnosis of chronic diseases such as sickle cell anemia, malaria, and thalassemia. Despite many commercial attempts, there are no U.S. FDA-approved artificial RBCs for use in humans. Existing RBC substitutes have employed various strategies to transport oxygen, extend the circulation time, and reduce organ toxicity, but none have replicated the natural protective mechanisms of RBCs, which prevent hemoglobin (Hb) dimerization and heme iron oxidation. Lumbricus terrestris (earthworm) erythrocruorin (LtEc) is a naturally occurring extracellular hemoglobin (Hb) with promising attributes: large molecular diameter (30 nm), high molecular weight (3.6 MDa), low auto-oxidation rate, and limited nitric oxide-scavenging properties. These characteristics make LtEc an ideal candidate as an RBC substitute. However, LtEc has a significant drawback, its short circulatory half-life. To address this issue, we explored thiol-mediated surface PEGylation of LtEc (PEG-LtEc) at varying polyethylene glycol (PEG) surface coverages. Increasing PEG surface coverage beyond 40% destabilizes LtEc into smaller subunits that are 1/12th the size of LtEc. Therefore, we evaluated two PEG surface coverage options: PEG-LtEc-0.2 (20% PEGylation) and PEG-LtEc-1.0 (100% PEGylation).

METHODS

We conducted experiments using golden Syrian hamsters with dorsal window chambers and catheters to assess the efficacy of these solutions. We measured microvascular parameters, organ function, cerebral blood flow, circulation time, mean arterial pressure, heart rate, and blood gases and performed histology to screen for toxicity.

CONCLUSION

Our findings indicate that both PEG-LtEc molecules offer significant benefits in restoring microvascular parameters, organ function, cerebral blood flow, and circulation time compared to LtEc alone. Notably, PEG-LtEc-1.0 showed superior microvascular perfusion, although it exhibited a higher rate of auto-oxidation compared to PEG-LtEc-0.2. These results underscore the advantages of PEGylation in terms of tissue perfusion and organ health while highlighting its limitations.

A Case study of polypharmacy-induced serotonin syndrome in a cancer patient

ABSTRACT

Polypharmacy in cancer care can be complex and detrimental, particularly among younger patients, who can be easily overlooked. This report showcases a 54-year-old woman with cancer, treated for dapsone-induced methemoglobinemia with methylene blue (MB), subsequently developing serotonin syndrome (SS) due to concurrent serotonin-active medications. This case highlights the critical impact of polypharmacy, emphasizing the necessity for acute care providers to diligently assess medication interactions, especially in emergencies. It underscores the importance of considering alternative treatments and the vigilant monitoring of symptoms indicative of adverse drug interactions to ensure patient safety and optimize outcomes in complex therapeutic scenarios.

Ascorbate protects human kidney organoids from damage induced by cell-free hemoglobin

Sepsis-associated acute kidney injury is associated with high morbidity and mortality in critically ill patients. Cell-free hemoglobin (CFH) is released into the circulation of patients with severe sepsis and the levels of CFH are independently associated with mortality. CFH treatment increased cytotoxicity in the human tubular epithelial cell line HK-2. To better model the intact kidney, we cultured human kidney organoids derived from induced pluripotent stem cells. We treated human kidney organoids grown using both three-dimensional and transwell protocols with CFH for 48 h. We found evidence for increased tubular toxicity, oxidative stress, mitochondrial fragmentation, endothelial cell injury and injury-associated transcripts compared to those of the untreated control group. To evaluate the protective effect of clinically available small molecules, we co-treated CFH-injured organoids with ascorbate (vitamin C) or acetaminophen for 48 h. We found significantly decreased toxicity, preservation of endothelial cells and reduced mitochondrial fragmentation in the group receiving ascorbate following CFH treatment. This study provides direct evidence that ascorbate or ascorbic acid protects human kidney cells from CFH-induced damage such as that in sepsis-associated acute kidney injury.

Changes in hemoglobin oxidation and band 3 during blood storage impact oxygen sensing and mitochondrial bioenergetic pathways in the human pulmonary arterial endothelial cell model

Red blood cells (RBCs) undergo metabolic, oxidative, and physiological changes during storage, collectively described as the "storage lesion." The impact of storage on oxygen homeostasis, following transfusion, is not fully understood. We show that RBC storage induces changes in oxygen binding that were linked to changes in oxygen sensing (hypoxia-inducible factor, HIF-1α) mechanisms and mitochondrial respiration in human pulmonary arterial endothelial cells (HPAECs). A decrease in oxygen affinity (P50) to approximately 20 from 30 mmHg was seen at the first week but remained unchanged for up to 42 days. This led to the suppression of HIF-1α in the first 3 weeks due to limited oxygen supplies by RBCs. Furthermore, membrane oxidative damage, band 3 alterations, and subsequent microparticle (MP) formation were also noted. Mass spectrometric analysis revealed the upregulation of transitional endoplasmic reticulum ATPase, essential for clearing ROS-damaged membrane proteins and the protein DDI1 homolog, a proteasomal shuttle chaperone. Band 3 complex proteins and superoxide dismutase were among the downregulated proteins. Mitochondrial oxygen consumption rates measured in HPAECs incubated with RBC-derived MPs (14-day and 42-day) showed a rise in maximal respiration. Intervention strategies that target intracellular hemoglobin (Hb)'s redox transitions and membrane changes may lead to the reestablishment of oxygen homeostasis in old RBCs.

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.

Oxidation reactions of cellular and acellular hemoglobins: Implications for human health

Oxygen reversibly binds to the redox active iron, a transition metal in human Hemoglobin (Hb), which subsequently undergoes oxidation in air. This process is akin to iron rusting in non-biological systems. This results in the formation of non-oxygen carrying methemoglobin (ferric) (Fe3+) and reactive oxygen species (ROS). In circulating red blood cells (RBCs), Hb remains largely in the ferrous functional form (HbF2+) throughout the RBC's lifespan due to the presence of effective enzymatic and non-enzymatic proteins that keep the levels of metHb to a minimum (1%-3%). In biological systems Hb is viewed as a Fenton reagent where oxidative toxicity is attributed to the formation of a highly reactive hydroxyl radical (OH•) generated by the reaction between Hb's iron (Fe2+) and hydrogen peroxide (H2O2). However, recent research on both cellular and acellular Hbs revealed that the protein engages in enzymatic-like activity when challenged with H2O2, resulting in the formation of a highly reactive ferryl heme (Fe4+) that can target other biological molecules before it self-destructs. Accumulating evidence from several in vitro and in vivo studies are summarized in this review to show that Hb's pseudoperoxidase activity is physiologically more dominant than the Fenton reaction and it plays a pivotal role in the pathophysiology of several blood disorders, storage lesions associated with old blood, and in the toxicity associated with the infusion of Hb-derived oxygen therapeutics.

Scalable production and complete biophysical characterization of poly(ethylene glycol) surface conjugated liposome encapsulated hemoglobin (PEG-LEH)

Particle encapsulated hemoglobin (Hb)-based oxygen (O2) carriers (HBOCs) have clear advantages over their acellular counterparts because of their larger molecular diameter and lack of vasoactivity upon transfusion. Poly(ethylene glycol) surface conjugated liposome encapsulated Hb (PEG-LEH) nanoparticles are considered a promising class of HBOC for use as a red blood cell (RBC) substitute. However, their widespread usage is limited by manufacturing processes which prevent material scale up. In this study, PEG-LEH nanoparticles were produced via a scalable and robust process using a high-pressure cell disruptor, and their biophysical properties were thoroughly characterized. Hb encapsulation, methemoglobin (metHb) level, O2-PEG-LEH equilibria, PEG-LEH gaseous (oxygen, carbon monoxide, nitric oxide) ligand binding/release kinetics, lipocrit, and long-term storage stability allowed us to examine their potential suitability and efficacy as an RBC replacement. Our results demonstrate that PEG-LEH nanoparticle suspensions manufactured via a high-pressure cell disruptor have Hb concentrations comparable to whole blood (~12 g/dL) and possess other desirable characteristics, which may permit their use as potential lifesaving O2 therapeutics.

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.

Efficacy and Safety of Parenteral High-Dose Vitamin C Therapy in Pediatric Patients: A Scoping Review

OBJECTIVES

Recently, several adult trials have investigated the potential benefit of high-dose vitamin C therapy in critically ill patients. In pediatric patients, little is known on the efficacy, safety, and risk of high-dose vitamin C therapy. We aimed to review the efficacy and potential harm associated with high-dose vitamin C treatment.

DATA SOURCES

We searched MEDLINE, EMBASE, Cochrane Library, and National Institute of Health Clinical Trials Register.

STUDY SELECTION

We included studies in neonatal and pediatric patients who received IV or intra-arterial high-dose vitamin C (ascorbic acid) defined as greater than or equal to 75 mg/kg/d.

DATA EXTRACTION

Two independent investigators screened articles and extracted data.

DATA SYNTHESIS

We found 1,364 articles, assessed 193 full texts for eligibility, and identified 12 eligible studies. These studies included 855 patients, with 194 receiving high-dose vitamin C. The age of patients who received high-dose vitamin C ranged from 2 hours after delivery to 8.4 years (median 2.4 yr), and the vitamin C dose ranged from 100 to 1,500 mg/kg/d (median 260.5 mg/kg/d). Four studies were double-blind randomized controlled trials, and no clinical efficacy outcome was reported in favor of or against vitamin C. Furthermore, no adverse event or signal of harm was reported with high-dose vitamin C.

CONCLUSIONS

In 12 studies with 194 children treated with parenteral high-dose vitamin C, there was no evidence of clinical efficacy or inferior clinical outcomes in double-blind randomized controlled trials, and no reported harmful effects. These findings justify further investigations of this treatment in children.

Glutaraldehyde-Polymerized Hemoglobin: In Search of Improved Performance as Oxygen Carrier in Hemorrhage Models

Hemoglobin- (Hb-) based oxygen carriers (HBOC) have for several decades been explored for treatment of hemorrhage. In our previous top-up tests, HBOC with lower in vitro prooxidant reactivity (incorporating a peroxidase or serum albumin to this end) showed a measurable but small improvement of oxidative stress-related parameters. Here, such HBOCs are tested in a hemorrhage set-up; ovine hemoglobin is also tested for the first time in such a setting, based on in vitro data showing its improved performance versus bovine Hb against oxidative and nitrosative stress agents. Indeed, ovine Hb performs better than bovine Hb in terms of survival rates, arterial tension, immunology, and histology. On the other hand, unlike in the top-up models, where the nonheme peroxidase rubrerythrin as well as bovine serum albumin copolymerized with Hb were shown to improve the performance of HBOC, in the present hemorrhage models rubrerythrin fails dramatically as HBOC ingredient (with a distinct immunological reaction), whereas serum albumin appears not feasible if its source is a different species (i.e., bovine serum albumin fares distinctly worse than rat serum albumin, in HBOC transfusions in rats). An effect of the matrix in which the HBOCs are dissolved (PBS versus gelofusine versus plasma) is noted.

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.

Increased formation of reactive oxygen species during tumor growth: Ex vivo low-temperature EPR and in vivo bioluminescence analyses

Previous studies have shown that reactive oxygen species (ROS) such as superoxide or hydrogen peroxide generated at low levels can exert a tumor-promoting role via a redox-signaling mechanism. Reports also suggest that both tumorigenesis and tumor growth are associated with enhanced ROS formation. However, whether ROS levels or ROS-derived oxidative marker levels increase during tumor growth remains unknown. In this study, in vivo bioluminescence imaging with a boronate-based pro-luciferin probe was used to assess ROS formation. Additionally, probe-free cryogenic electron paramagnetic resonance was used to quantify a characteristic aconitase [3Fe4S]⁺ center that arises in the tumor tissue of mouse xenografts from the reaction of the native [4Fe4S]²⁺ cluster with superoxide. Results indicated that tumor growth is accompanied by increased ROS formation, and revealed differences in oxidant formation in the inner and outer sections of tumor tissue, respectively, demonstrating redox heterogeneity. Studies using luciferin and pro-luciferin probes enabled the assessment of tumor size, ROS formation, and bioenergetic status (e.g., ATP) in luciferase-transfected mice tumor xenografts. Probe-free ex vivo low-temperature electron paramagnetic resonance can also be translated to clinical studies.

On the characteristic and stability of iron diet supplements

The iron diet supplements: AproFER 1000 and AproTHEM were subjected to various chemical, microbial and magnetic analysis. The microbial analysis revealed no presence of pathogenic bacteria in the studied products. No significant changes in iron content or forms (bivalent/trivalent) were observed in EPR analysis of supplements stored at different conditions for a long period of time. The chemical and magnetic analysis showed that both AproFER 1000 and AproTHEM contain a high concentration of bivalent iron so they can be used as an iron diet supplements.

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.

EPR detection of sulfanyl radical during sulfhemoglobin formation - Influence of catalase

Hemoglobin in its ferryl form oxidizes hydrogen sulfide and is transformed to sulfhemoglobin, where the sulfur is inserted covalently at the heme edge. Shown here is evidence that-as previously proposed by others-this process involves oxidation of hydrogen sulfide to a sulfanyl radical detectable by spin-trapping in electron paramagnetic resonance (EPR) spectroscopy. The yields and rates of formation of sulfhemoglobin as well as of the sulfanyl radical are affected by the same factors that affect the reactivity of hemoglobin ferryl, in bovine hemoglobin and in phytoglobins as well. A freely-diffusing sulfanyl radical is thus proposed to be involved in sulfhemoglobin formation. Catalase is shown to accelerate this process due to a previously described hydrogen sulfide oxidase activity, within which EPR evidence for sulfanyl generation is shown here for the first time. The reaction of preformed ferryl with hydrogen sulfide-in absence of hydrogen peroxide-is studied by stopped-flow at several pH values and explained in light of reactivity and redox potential control.

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.

Calculation of the required transfusion volume in anaemic Holstein calves

In bovine medicine, blood transfusion practice represents an emergency therapy where time is critical. The aim of this study was to develop a mathematical model to calculate the required blood for transfusion, using parameters which could be easily determined on the spot. Twenty Holstein calves were assigned to two groups depending on body weight (100.1 ± 3.1 kg and 151.1 ± 3.0 kg, respectively). All animals were subjected to an anaemia induction protocol in isovolaemic conditions in order to reduce the packed cell volume (PCV) by more than one third. Twenty-four hours later, each group received an auto-transfusion therapy. In order to find a valid constant for specific weight categories with high confidence interval in cattle, we calculated the value of constant 'CC' for each individual, using a formula described for carnivores as a basis. The value of the constant for the 100.1 ± 3.1 kg and 151.1 ± 3.0 kg groups was 80.6315 ± 1.1069 and 76.5294 ± 2.5640, respectively. The comparison between the two groups demonstrated significantly different mean values (P = 0.0002, by t-test) and, furthermore, significantly different values of the constant distributions (P = 0.0001, by the Kolmogorov-Smirnov test).

Nebulised recombinant activated factor VII (rFVIIa) does not attenuate the haemorrhagic effects of blast lung injury

Introduction

Primary blast lung injury causes intrapulmonary haemorrhage. A number of case reports have suggested the efficacy of recombinant activated factor VII (rFVIIa) in the treatment of diffuse alveolar haemorrhage from a range of medical causes, but its efficacy in blast lung is unknown. The aim of this study was to investigate whether nebulised rFVIIa attenuates the haemorrhagic effects of blast lung injury in an animal model.

Methods

Terminally anaesthetised rabbits subjected to blast lung injury were randomised to receive either rFVIIa or placebo via a nebuliser. The primary outcome was the level of blood iron–transferrin complex, a marker of the extent of blast lung injury, analysed using low temperature electron paramagnetic resonance spectroscopy.

Results

Blast exposure led to a significant fall in iron-bound transferrin in both groups of animals (p<0.001), which remained depressed during the study. There were no significant differences in iron–transferrin between the rFVIIa and placebo treatment groups over the duration of the study (p=0.081), and there was no trend towards elevated iron–transferrin in the rFVIIa-treated group once drug treatment had started. There was suggestive evidence of systemic absorption of rFVIIa given via the inhaled route.

Conclusion

A single dose of nebulised rFVIIa did not attenuate pulmonary haemorrhage in a rabbit model of blast lung injury. As there was some evidence of systemic absorption, the inhaled route does not avoid the concern about potential thromboembolic complications from administration of rFVIIa.

Preservation of myocardial contractility during acute hypoxia with OMX-CV, a novel oxygen delivery biotherapeutic

The heart exhibits the highest basal oxygen (O₂) consumption per tissue mass of any organ in the body and is uniquely dependent on aerobic metabolism to sustain contractile function. During acute hypoxic states, the body responds with a compensatory increase in cardiac output that further increases myocardial O₂ demand, predisposing the heart to ischemic stress and myocardial dysfunction. Here, we test the utility of a novel engineered protein derived from the heme-based nitric oxide (NO)/oxygen (H-NOX) family of bacterial proteins as an O₂ delivery biotherapeutic (Omniox-cardiovascular [OMX-CV]) for the hypoxic myocardium. Because of their unique binding characteristics, H-NOX–based variants effectively deliver O₂ to hypoxic tissues, but not those at physiologic O₂ tension. Additionally, H-NOX–based variants exhibit tunable binding that is specific for O₂ with subphysiologic reactivity towards NO, circumventing a significant toxicity exhibited by hemoglobin (Hb)-based O₂ carriers (HBOCs). Juvenile lambs were sedated, mechanically ventilated, and instrumented to measure cardiovascular parameters. Biventricular admittance catheters were inserted to perform pressure-volume (PV) analyses. Systemic hypoxia was induced by ventilation with 10% O₂. Following 15 minutes of hypoxia, the lambs were treated with OMX-CV (200 mg/kg IV) or vehicle. Acute hypoxia induced significant increases in heart rate (HR), pulmonary blood flow (PBF), and pulmonary vascular resistance (PVR) (p < 0.05). At 1 hour, vehicle-treated lambs exhibited severe hypoxia and a significant decrease in biventricular contractile function. However, in OMX-CV–treated animals, myocardial oxygenation was improved without negatively impacting systemic or PVR, and both right ventricle (RV) and left ventricle (LV) contractile function were maintained at pre-hypoxic baseline levels. These data suggest that OMX-CV is a promising and safe O₂ delivery biotherapeutic for the preservation of myocardial contractility in the setting of acute hypoxia.

While hemoglobin is the primary oxygen delivery molecule used to maintain tissue oxygenation in metazoans, many organisms have other heme-containing proteins that can bind oxygen and other diatomic gases. Here, we tested whether a member of the H-NOX family of heme-containing proteins found in the thermostable bacterium Thermoanaerobacter tengcongensis can be engineered to deliver oxygen to severely hypoxic tissues in large mammals. This class of molecules has the advantage of high oxygen affinity and minimal nitric oxide reactivity. We demonstrate that these molecules can effectively deliver oxygen to a lamb heart with induced severe hypoxia, without overexposing the animal to oxygen or triggering systemic vascular reactivity. These molecules thus represent a novel class of oxygen delivery biotherapeutics to specifically target hypoxic tissue beds without the toxicity concerns of hemoglobin-based oxygen carriers. As tissue hypoxia is a central feature of many disease processes, this therapeutic approach may have broad clinical applicability.

Low-Temperature EPR Spectroscopy as a Probe-Free Technique for Monitoring Oxidants Formed in Tumor Cells and Tissues: Implications in Drug Resistance and OXPHOS-Targeted Therapies

Oxidants formed from oxidative and nitrative metabolism include reactive oxygen species (ROS) such as superoxide, hydrogen peroxide/lipid hydroperoxides and reactive nitrogen species (RNS) (e.g., peroxynitrite [ONOO^-] and nitrogen dioxide), and reactive halogenated species (e.g., hypochlorous acid [HOCl]). Increasingly, ROS and RNS are implicated in tumorigenesis as well as tumor growth, progression, and metastasis. Recently, ROS were implicated in drug resistance, metabolic reprogramming, and T-cell metabolism in immunotherapy. Mostly, fluorescent probes have been used in cell culture systems. The identity of species is obtained by LC-MS analyses of diagnostic marker products. However, extrapolation of these assays to cancer xenografts is difficult if not impossible. Thus, development of a probe-free assay for monitoring and assessing oxidant formation in tumor cells and tumor xenografts is critical and timely. Here, we describe the use of ex vivo electron paramagnetic resonance (EPR) spectroscopy at cryogenic temperatures as a uniquely useful probe-free technique for assessing intracellular oxidation and oxidants via EPR signals from redox centers, particularly iron-sulfur clusters, in mitochondrial and cytosolic redox proteins. Examples of cancer cells subjected to inhibition of mitochondrial oxidative phosphorylation are presented. This ex vivo methodology can be readily extended to monitor oxidant formation in tumor tissues isolated from mice and humans.

Redox control and autoxidation of class 1, 2 and 3 phytoglobins from Arabidopsis thaliana

Despite a recent increase in interest towards phytoglobins and their importance in plants, much is still unknown regarding their biochemical/biophysical properties and physiological roles. The present study presents data on three recombinant Arabidopsis phytoglobins in terms of their UV-vis and Raman spectroscopic characteristics, redox state control, redox potentials and autoxidation rates. The latter are strongly influenced by pH for all three hemoglobins - (with a fundamental involvement of the distal histidine), as well as by added anion concentrations - suggesting either a process dominated by nucleophilic displacement of superoxide for AtHb2 or an inhibitory effect for AtHb1 and AtHb3. Reducing agents, such as ascorbate and glutathione, are found to either enhance- (presumably via direct electron transfer or via allosteric regulation) or prevent autoxidation. HbFe3+ reduction was possible in the presence of high (presumably not physiologically relevant) concentrations of NADH, glutathione and ascorbate, with differing behaviors for the three globins. The iron coordination sphere is found to affect the autoxidation, redox state interconversion and redox potentials in these three phytoglobins.

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).

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.

Severe acute haemolytic anaemia associated with severe methaemoglobinaemia in a G6PD-deficient man

Methaemoglobin is a form of haemoglobin in which the ferrous (Fe²⁺) ion contained in the iron-porphyrin complex of haem is oxidised to its ferric (Fe³⁺) state. Methaemoglobinaemia, the presence of methaemoglobin in the blood, is most commonly treated with methylene blue. However, methylene blue cannot be used in patients with glucose-6-phosphate dehydrogenase (G6PD) deficiency as it is ineffective in such patients and it can worsen G6PD deficiency haemolysis. We report the case of a 30-year-old man who presented with clinical features of G6PD deficiency-associated haemolysis and was found to have severe methaemoglobinaemia (35%). He was administered blood transfusions and intravenous ascorbic acid. His methaemoglobinaemia resolved within 24 hours. This case demonstrates the successful management of a patient with severe methaemoglobinaemia in the setting of G6PD deficiency haemolysis. Emergency physicians should be aware of the possible co-occurrence of severe methaemoglobinaemia in a patient with G6PD deficiency haemolysis.

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.

Oxidized Mutant Human Hemoglobins S and E Induce Oxidative Stress and Bioenergetic Dysfunction in Human Pulmonary Endothelial Cells

Cell free hemoglobin (Hb), becomes oxidized in the circulation during hemolytic episodes in sickle cell disease (SCD) or thalassemia and may potentially cause major complications that are damaging to the vascular system. Hemolytic anemias are commonly associated with pulmonary hypertension (PH) and often result from dysfunction of lung endothelial cells. The aim of this study was to determine the effect of different Hbs on cultured human lung endothelial function. Toward this goal, endothelial permeability, oxidative stress response parameters, glycolytic and mitochondrial bioenergetic functions were monitored in cultured human pulmonary arterial endothelial cells (HPAEC) following incubation with human adult Hb (HbA), and Hb isolated from patients with sickle cell Hb (HbS, βV6E) and HbE (βE26K) that commonly co-exist with β-thalassemia. These mutant Hbs are known for their distinct oxidative profiles. HPAEC treated with the ferrous forms of HbE, HbS for 24 h showed higher loss of endothelial monolayer integrity with concomitant rise in reactive oxygen radical production, lipid hydroperoxide formation and higher expressions of oxidative stress response proteins including heme oxygenase-1 (HO-1) accompanied by a rise in uncoupled mitochondrial respiration. Loss of membrane permeability was diminished in part by haptoglobin (Hp, protein scavenger), hemopexin (Hpx, heme scavenger) or ascorbate (reducing agent). To understand the role of Hb oxidation, HPAEC were exposed to ferric or ferryl states of the mutant Hbs. Ferryl forms of all proteins caused a significant damage to the endothelial monolayer integrity at a higher degree than their respective ferric Hbs. Ferryl forms of HbS and HbE also caused a loss of respiratory chain complex activities in isolated endothelial mitochondria and basal oxygen consumption in HPAEC. However, longer incubation with ferryl Hbs produced bioenergetic reprogramming including higher degree of uncoupled respiration and glycolytic rate. The data in this report collectively indicate that higher oxidation forms of HbS and HbE cause endothelial dysfunction through distinct damaging mechanisms involving mitochondrial bioenergetic function.

The influence of radiotherapy on ceruloplasmin and transferrin in whole blood of breast cancer patients

Ceruloplasmin and transferrin are proteins which play a potential role in the process of breast cancer development. These molecules contain Cu2+ (ceruloplasmin) or Fe3+ ions (transferrin) and thus constitute paramagnetic centers, which can be studied using electron paramagnetic resonance method. The aim of the study was to determine how paramagnetic centers in whole blood of breast cancer patients change under the influence of radiation therapy. Samples of whole blood were taken from 17 women with breast cancer treated with radiotherapy. The measurements were carried out at 170 K using X-band electron paramagnetic resonance (EPR) spectrometer Bruker EMX-10. Two distinct EPR lines, derived from high-spin Fe3+ in transferrin and Cu2+ from ceruloplasmin, were revealed in all frozen samples. The amplitude and integrated intensity of the EPR signal from Cu2+ in ceruloplasmin significantly decreased in all patients after the delivery of the radiation fraction. When comparing the integral intensity of the signal from Fe3+ in transferrin, three different situations were identified which are patient specific: a significant increase, an insignificant change, or a significant decrease after the irradiation. A decreased level of Cu2+ from ceruloplasmin in patients after radiotherapy means a low level of ceruloplasmin in the plasma or an increased content of reduced Cu+ ions. Differences in the integrated intensity of the EPR signal from transferrin translate directly into the amount of bound iron. The observed changes could indicate how well the organism fights against cancer and how easily it adapts to the situation of biochemical stress.

In vivo evaluation of hemerythrin-based oxygen carriers: Similarities with hemoglobin-based counterparts

We have previously proposed the annelid-derived protein, hemerythrin, as a viable replacement for hemoglobin in the synthesis of semi-synthetic oxygen carriers ("blood substitutes"). Here, we report the first in vivo tests for potential hemerythrin-based oxygen carriers (HrBOC), using a battery of experiments involving Wistar rats and previously tested on a series of hemoglobin-based oxygen carrier candidates (HBOC). At the concentrations tested, hemerythrin appears to behave similarly to hemoglobin - including, importantly, immunological effects. The antioxidant strategies based on albumin as well as based on rubrerythrin appear to offer observable physiological advantages.

Protective Role for Antioxidants in Acute Kidney Disease

Acute kidney injury causes significant morbidity and mortality in the community and clinic. Various pathologies, including renal and cardiovascular disease, traumatic injury/rhabdomyolysis, sepsis, and nephrotoxicity, that cause acute kidney injury (AKI), induce general or regional decreases in renal blood flow. The ensuing renal hypoxia and ischemia promotes the formation of reactive oxygen species (ROS) such as superoxide radical anions, peroxides, and hydroxyl radicals, that can oxidatively damage biomolecules and membranes, and affect organelle function and induce renal tubule cell injury, inflammation, and vascular dysfunction. Acute kidney injury is associated with increased oxidative damage, and various endogenous and synthetic antioxidants that mitigate source and derived oxidants are beneficial in cell-based and animal studies. However, the benefit of synthetic antioxidant supplementation in human acute kidney injury and renal disease remains to be realized. The endogenous low-molecular weight, non-proteinaceous antioxidant, ascorbate (vitamin C), is a promising therapeutic in human renal injury in critical illness and nephrotoxicity. Ascorbate may exert significant protection by reducing reactive oxygen species and renal oxidative damage via its antioxidant activity, and/or by its non-antioxidant functions in maintaining hydroxylase and monooxygenase enzymes, and endothelium and vascular function. Ascorbate supplementation may be particularly important in renal injury patients with low vitamin C status.

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.

Glutaraldehyde-polymerized hemoglobin and tempol (PolyHb-tempol) has superoxide dismutase activity that can attenuate oxidative stress on endothelial cells induced by superoxide anion

A Tempol compound with an amine group (4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl, NH₂-Tempol) was cross-linked to hemoglobin in a one-step polymerization reaction to produce a novel hemoglobin-based oxygen carrier (HBOC) designated PolyHb-Tempol. The reaction parameters, including the reaction time, pH, temperature, and ratio of reactants, were optimized, and the physiochemical properties of the resulting product were characterized. PolyHb-Tempol didn't show any toxicity towards endothelial cells. Furthermore, from observations of cell morphology and viability, PolyHb-Tempol showed a significant ability to inhibit or eliminate oxidative stress induced by superoxide free radicals. These results suggest that PolyHb-Tempol may potentially be suitable as an HBOC.

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.

Engineering tyrosine electron transfer pathways decreases oxidative toxicity in hemoglobin: implications for blood substitute design

Hemoglobin (Hb)-based oxygen carriers (HBOC) have been engineered to replace or augment the oxygen-carrying capacity of erythrocytes. However, clinical results have generally been disappointing due to adverse side effects linked to intrinsic heme-mediated oxidative toxicity and nitric oxide (NO) scavenging. Redox-active tyrosine residues can facilitate electron transfer between endogenous antioxidants and oxidative ferryl heme species. A suitable residue is present in the α-subunit (Y42) of Hb, but absent from the homologous position in the β-subunit (F41). We therefore replaced this residue with a tyrosine (βF41Y, Hb Mequon). The βF41Y mutation had no effect on the intrinsic rate of lipid peroxidation as measured by conjugated diene and singlet oxygen formation following the addition of ferric(met) Hb to liposomes. However, βF41Y significantly decreased these rates in the presence of physiological levels of ascorbate. Additionally, heme damage in the β-subunit following the addition of the lipid peroxide hydroperoxyoctadecadieoic acid was five-fold slower in βF41Y. NO bioavailability was enhanced in βF41Y by a combination of a 20% decrease in NO dioxygenase activity and a doubling of the rate of nitrite reductase activity. The intrinsic rate of heme loss from methemoglobin was doubled in the β-subunit, but unchanged in the α-subunit. We conclude that the addition of a redox-active tyrosine mutation in Hb able to transfer electrons from plasma antioxidants decreases heme-mediated oxidative reactivity and enhances NO bioavailability. This class of mutations has the potential to decrease adverse side effects as one component of a HBOC product.

Comparative In Vivo Effects of Hemoglobin-Based Oxygen Carriers (HBOC) with Varying Prooxidant and Physiological Reactivity

A series of hemoglobin-based oxygen carrier candidates (HBOC), previously noted for their differences in prooxidative and physiological reactivity, were compared in terms of the negative effects displayed upon injection in Wistar rats. At the concentrations tested, antioxidant strategies based on albumin as well as based on rubrerythrin appear to offer observable physiological advantages.

Pharmacokinetics and mechanisms of plasma removal of hemoglobin-based oxygen carriers

The circulatory persistence, distribution, and metabolism of hemoglobin-based oxygen carriers (HBOCs) is a major determinant of their safety and efficacy. In this communication, published data on the pharmacokinetics and routes of plasma elimination of HBOCs are summarized and evaluated. The circulating half-life of HBOCs is dose-dependent in both animals and humans. Half-life also increases with molecular weight in animals, at least up to the MDa range. The functional half-life of HBOCs is diminished by as much as 40% due to oxidation of the heme group relative to the overall rate of removal of hemoglobin (Hb) from plasma. Kidney excretion of HBOCs is greatly diminished compared to that of unmodified Hb, but the liver remains a primary site of catabolism. Both hepatocytes and Kupffer cells have been implicated in receptor-mediated HBOC uptake. Removal also occurs in the spleen and/or bone marrow and probably at dispersed sites in the endothelium as well. HBOCs extravasate into the lymph at a rate inversely proportional to their molecular weight and are taken up by monocyte/macrophage CD163 receptors, both as free Hb and in complexes with haptoglobin (Hp). The interactions with both Hp and the CD163 receptor are altered by Hb modification. However, monocyte/macrophage uptake may not be a quantitatively important route for the removal of clinically relevant doses of HBOCs. The relative contributions of different removal pathways have yet to be comprehensively determined, particularly in humans.

Nitrite binding to globins: linkage isomerism, EPR silence and reductive chemistry

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A DFT-derived barrier for nitrite linkage isomerism on heme center is reported.

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EPR spectra of nitrite adducts show evidence for linkage isomerism.

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The electronic structure of Fe(III)-nitrite heme is conformation-dependent.

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Certain conformations are inducive to EPR silence.

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Fe(II)-nitrite is undetectable on stopped-flow time scales.

The nitrite adducts of globins can potentially bind via O- or N- linkage to the heme iron. We have used EPR (electron paramagnetic resonance) and DFT (density functional theory) to explore these binding modes to myoglobin and hemoglobin. We demonstrate that the nitrite adducts of both globins have detectable EPR signals; we provide an explanation for the difficulty in detecting these EPR features, based on uniaxial state considerations. The EPR and DFT data show that both nitrite linkage isomers can be present at the same time and that the two isomers are readily interconvertible in solution. The millisecond-scale process of nitrite reduction by Hb is investigated in search of the elusive Fe(II)-nitrite adduct.

Methaemoglobinaemia in a G6PD-deficient child treated with rasburicase

A 5-year-old boy from the Congo, was admitted for hyperleucocytic acute lymphoblastic leukaemia, with a high risk of tumour lysis syndrome (TLS). He had splenomegaly and mediastinal lymphadenopathy on chest X-ray. We started steroids and hyperhydration with rasburicase to prevent TLS. Respiratory failure with mediastinal enlargement developed rapidly. A few hours after intensive care unit (ICU) admission, he was started on mechanical ventilation. Chemotherapy was started immediately given the strong suspicion of mediastinal compression. Low oxygen saturation with high partial arterial oxygen pressure persisted. Blood tests confirmed 20% methaemoglobinaemia and glucose-6-phosphate dehydrogenase (G6PD) deficiency. Allopurinol was substituted for rasburicase. The methaemoglobinaemia disappeared rapidly and he was discharged from the ICU after 72 h. In case of rasburicase use, a close clinical monitoring is mandatory, especially in populations where G6PD deficiency is highly prevalent. Methaemoglobinaemia must be suspected in case of low oxygen saturation when all other potential causes have been ruled out.

Involvement of ferryl in the reaction between nitrite and the oxy forms of globins

The reaction between nitrite and the oxy forms of globins has complex autocatalytic kinetics with several branching steps and evolves through chain reactions mediated by reactive species (including radicals) such as hydrogen peroxide, ferryl and nitrogen dioxide, starting with a lag phase, after which it proceeds onto an autocatalytic phase. Reported here are UV-Vis spectra collected upon stopped-flow mixing of myoglobin with a supraphysiological excess of nitrite. The best fit to the experimental data follows an A → B → C reaction scheme involving the formation of a short-lived intermediate identified as ferryl. This is consistent with a mechanism where nitrite binds to oxy myoglobin to generate an undetectable ferrous-peroxynitrate intermediate, whose decay leads to nitrate and ferryl. The ferryl is then reduced to met by the excess nitrite. DFT calculations reveal an essentially barrierless reaction between nitrite and the oxy heme, with a notable outer-sphere component; the resulting metastable ferrous-peroxynitrate adduct is found to feature a very low barrier towards nitrate liberation, with ferryl as a final product-in good agreement with experiment.

The influence of storage age on iron status, oxidative stress and antioxidant protection in paediatric packed cell units

BACKGROUND

Receipt of blood transfusions is associated with the major consequences of prematurity such as bronchopulmonary dysplasia. Transfusion-mediated (iron-induced) oxidative damage, coupled with the limited ability of the premature baby to deal with enhanced iron and oxidative load may contribute to this. Adverse effects of transfusion may be related to duration of storage. This study examined the influence of storage on iron and oxidative status in paediatric packed red blood cell units.

MATERIALS AND METHODS

Paediatric packed red blood cell units were sampled 3 days post-donation, then at 7 days and weekly until day 35. The extracellular medium was separated and the following measured: total iron concentration, total iron binding capacity, non-transferrin-bound iron, haemoglobin, total and reduced ascorbate, glutathione and malondialdehyde.

RESULTS

Measurable total and non-transferrin bound iron were present in the extracellular fluid of paediatric packs on day 3. Both parameters rose almost linearly to maximal values at 35 days. Haemoglobin and malondialdehyde levels rose gradually from day 3 to day 21, then more steeply to day 35. Ascorbate existed mainly in the oxidised form and fell rapidly towards the end of storage. Intracellular GSH fell throughout the period of storage. Strong correlations existed between biomarkers of oxidative damage and iron parameters.

DISCUSSION

These data suggest that iron released following the initial preparation of packed red blood cell units may derive from free radical-mediated oxidative damage to the red blood cells and haemoglobin, rather than from extracellular haemoglobin. Iron continues to be released during storage as antioxidant protection declines. A cycle of free radical-mediated damage may initiate and then further exacerbate iron release during storage which, in turn, may mediate further free radical-mediated cellular damage. The potential consequences to recipients of older stored blood may be significant.

Blood substitutes: why haven't we been more successful?

Persistent safety concerns have stalled the development of viable hemoglobin (Hb)-based oxygen carriers (HBOCs). HBOCs have several advantages over human blood, including availability, long-term storage, and lack of infectious risk. The basis of HBOC toxicity is poorly understood, however, several mechanisms have been suggested, including Hb extravasation across the blood vessel wall, scavenging of endothelial nitric oxide (NO), oversupply of oxygen, and heme-mediated oxidative side reactions. Although there are some in vitro and limited animal studies supporting these mechanisms, heme-mediated reactivity appears to provide an alternative path that can explain some of the observed pathophysiological changes. Moreover, recent mechanistic and animal studies support a role for globin and heme scavengers in controlling oxidative toxicity associated with Hb infusion.

Evaluation and management of acquired methemoglobinemia associated with topical benzocaine use

Benzocaine is a widely used topical oropharyngeal anesthetic and has been reported to cause methemoglobinemia. We discuss benzocaine-induced methemoglobinemia and review the causes, presentation, and management of this serious complication. Treatment with methylene blue will result in reversal of methemoglobinemia and clinical recovery in most cases but needs to be used at appropriate doses in carefully selected individuals. Physicians who perform procedures involving the application of benzocaine for topical anesthesia need to rapidly identify and treat methemoglobinemia to avoid significant associated morbidity and mortality.

Protein-based blood substitutes: recent attempts at controlling pro-oxidant reactivity with and beyond hemoglobin

Reviewed here are recent attempts to produce protein-based artificial oxygen carriers (“blood substitutes”). Most of these involve chemical or physical modifications on hemoglobin, although a recent line of research using hemerythrin instead of hemoglobin is also described. The focus is set on the extent to which these modifications alter the redox reactivity of the proteins, and on ways in which this can be done systematically and purposefully, within the framework of a working hypothesis where redox side-reactions hold an important role in the physiological outcome of experimental transfusions with artificial oxygen carriers.