The radical and redox chemistry of myoglobin and hemoglobin: from in vitro studies to human pathology

Association between acetaminophen administration and clinical outcomes in patients with sepsis admitted to the ICU: a retrospective cohort study

Background

Sepsis, affecting over 30 million people worldwide each year, is a key mortality risk factor in critically ill patients. There are significant regional discrepancies in its impact. Acetaminophen, a common over-the-counter drug, is often administered to control fever in suspected infection cases in intensive care units (ICUs). It is considered generally safe when used at therapeutic levels. Despite its widespread use, there's inconsistent research regarding its efficacy in sepsis management, which creates uncertainties for ICU doctors about its possible advantages or harm. To address this, we undertook a retrospective cohort study utilizing the MIMIC-IV database to examine the correlation between acetaminophen use and clinical outcomes in septic patients admitted to the ICU.

Methods

We gathered pertinent data on sepsis patients from the MIMIC-IV database. We used propensity score matching (PSM) to pair acetaminophen-treated patients with those who were not treated. We then used Cox Proportional Hazards models to examine the relationships between acetaminophen use and factors such as in-hospital mortality, 30-day mortality, hospital stay duration, and ICU stay length.

Results

The data analysis involved 22,633 sepsis patients. Post PSM, a total of 15,843 patients were matched; each patient not receiving acetaminophen treatment was paired with two patients who received it. There was a correlation between acetaminophen and a lower in-hospital mortality rate (HR 0.443; 95% CI 0.371-0.530; p < 0.001) along with 30-day mortality rate (HR 0.497; 95% CI 0.424-0.583; p < 0.001). Additionally, it correlated with a decrease in the duration of hospitalization [8.4 (5.0, 14.8) vs. 9.0 (5.1, 16.0), p < 0.001] and a shorter ICU stay [2.8 (1.5, 6.0) vs. 3.1 (1.7, 6.5); p < 0.05].

Conclusion

The use of acetaminophen may lower short-term mortality in critically ill patients with sepsis. To confirm this correlation, future research should involve multicenter randomized controlled trials.

Insights into the function of cytoglobin

Since its discovery in 2001, the function of cytoglobin has remained elusive. Through extensive in vitro and in vivo research, a range of potential physiological and pathological mechanisms has emerged for this multifunctional member of the hemoglobin family. Currently, over 200 research publications have examined different aspects of cytoglobin structure, redox chemistry and potential roles in cell signalling pathways. This research is wide ranging, but common themes have emerged throughout the research. This review examines the current structural, biochemical and in vivo knowledge of cytoglobin published over the past two decades. Radical scavenging, nitric oxide homeostasis, lipid binding and oxidation and the role of an intramolecular disulfide bond on the redox chemistry are examined, together with aspects and roles for Cygb in cancer progression and liver fibrosis.

Targeting Labile Iron-Mediated Ferroptosis Provides a Potential Therapeutic Strategy for Rhabdomyolysis-Induced Acute Kidney Injury

Acute kidney injury (AKI) is a global health problem that occurs in a variety of clinical settings. Despite some advances in supportive clinical care, no medicinal intervention has been demonstrated to reliably prevent AKI thus far. Therefore, it is highly necessary to investigate the pathophysiology and mechanisms involved in AKI for the discovery of therapeutics. In the current study, a robust change in the level of renal malondialdehyde (MDA) and 4-hydroxynonenal (4-HNE) and elevated renal iron levels were observed in murine rhabdomyolysis-induced AKI (RM-AKI), which supports a pathogenic role of labile iron-mediated ferroptosis and provides a chance to utilize iron chelation for RM-AKI prevention. Given that the existing small molecule-based iron chelators did not show promising preventative effects against RM-AKI, we further designed and synthesized a new hydroxypyridinone-based iron chelator to potently inhibit labile iron-mediated ferroptosis. Lead compound AKI-02 was identified, which remarkably protected renal proximal tubular epithelial cells from ferroptosis as well as showed excellent iron chelation ability. Moreover, administration of AKI-02 led to renal function recovery, a result that was substantiated by the decreased contents of BUN and creatinine, as well as the reduced labile iron level and improved histopathology. Thus, our studies highlighted that targeting labile iron-mediated ferroptosis could provide therapeutic benefits against RM-AKI.

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.

Inhibitory mechanisms of polyphenols on heme protein-mediated lipid oxidation in muscle food: New insights and advances

Lipid oxidation is a major cause of quality deterioration that decreases the shelf-life of muscle-based foods (red meat, poultry, and fish), in which heme proteins, particularly hemoglobin and myoglobin, are the primary pro-oxidants. Due to increasing consumer concerns over synthetic chemicals, extensive research has been carried out on natural antioxidants, especially plant polyphenols. The conventional opinion suggests that polyphenols inhibit lipid oxidation of muscle foods primarily owing to their strong hydrogen-donating and transition metal-chelating activities. Recent developments in analytical techniques (e.g., protein crystallography, nuclear magnetic resonance spectroscopy, fluorescence anisotropy, and molecular docking simulation) allow deeper understanding of the molecular interaction of polyphenols with heme proteins, phospholipid membrane, reactive oxygen species, and reactive carbonyl species; hence, novel hypotheses regarding their antioxidant mechanisms have been formulated. In this review, we summarize five direct and three indirect pathways by which polyphenols inhibit heme protein-mediated lipid oxidation in muscle foods. We also discuss the relation between chemical structures and functions of polyphenols as antioxidants.

Impact of glycoengineering and antidrug antibodies on the anticancer activity of a plant-made lectin-Fc fusion protein

Plants are an efficient production platform for manufacturing glycoengineered monoclonal antibodies and antibody-like molecules. Avaren-Fc (AvFc) is a lectin-Fc fusion protein or lectibody produced in Nicotiana benthamiana, which selectively recognizes cancer-associated high-mannose glycans. In this study, we report the generation of a glycovariant of AvFc that is devoid of plant glycans, including the core α1,3-fucose and β1,2-xylose residues. The successful removal of these glycans was confirmed by glycan analysis using HPLC. This variant, AvFc^ΔXF , has significantly higher affinity for Fc gamma receptors and induces higher levels of luciferase expression in an antibody-dependent cell-mediated cytotoxicity (ADCC) reporter assay against B16F10 murine melanoma cells without inducing apoptosis or inhibiting proliferation. In the B16F10 flank tumour mouse model, we found that systemic administration of AvFc^ΔXF , but not an aglycosylated AvFc variant lacking affinity for Fc receptors, significantly delayed the growth of tumours, suggesting that Fc-mediated effector functions were integral. AvFc^ΔXF treatment also significantly reduced lung metastasis of B16F10 upon intravenous challenge whereas a sugar-binding-deficient mutant failed to show efficacy. Lastly, we determined the impact of antidrug antibodies (ADAs) on drug activity in vivo by pretreating animals with AvFc^ΔXF before implanting tumours. Despite a significant ADA response induced by the pretreatment, we found that the activity of AvFc^ΔXF was unaffected by the presence of these antibodies. These results demonstrate that glycoengineering is a powerful strategy to enhance AvFc's antitumor activity.

Antiglycation and Antioxidant Effect of Nitroxyl towards Hemoglobin

Donors of nitroxyl and nitroxyl anion (HNO/NO⁻) are considered to be promising pharmacological treatments with a wide range of applications. Remarkable chemical properties allow nitroxyl to function as a classic antioxidant. We assume that HNO/NO⁻ can level down the non-enzymatic glycation of biomolecules. Since erythrocyte hemoglobin (Hb) is highly susceptible to non-enzymatic glycation, we studied the effect of a nitroxyl donor, Angeli’s salt, on Hb modification with methylglyoxal (MG) and organic peroxide―tert-butyl hydroperoxide (t-BOOH). Nitroxyl dose-dependently decreased the amount of protein carbonyls and advanced glycation end products (AGEs) that were formed in the case of Hb incubation with MG. Likewise, nitroxyl effectively protected Hb against oxidative modification with t-BOOH. It slowed down the destruction of heme, formation of carbonyl derivatives and inter-subunit cross-linking. The protective effect of nitroxyl on Hb in this system is primarily associated with nitrosylation of oxidized Hb and reduction of its ferryl form, which lowers the yield of free radical products. We suppose that the dual (antioxidant and antiglycation) effect of nitroxyl makes its application possible as part of an additional treatment strategy for oxidative and carbonyl stress-associated diseases.

The Role of Circadian Clock Genes in Critical Illness: The Potential Role of Translational Clock Gene Therapies for Targeting Inflammation, Mitochondrial Function, and Muscle Mass in Intensive Care

The Earth's 24-h planetary rotation, with predictable light and heat cycles, has driven profound evolutionary adaptation, with prominent impacts on physiological mechanisms important for surviving critical illness. Pathways of interest include inflammation, mitochondrial function, energy metabolism, hypoxic signaling, apoptosis, and defenses against reactive oxygen species. Regulation of these by the cellular circadian clock (BMAL-1 and its network) has an important influence on pulmonary inflammation; ventilator-associated lung injury; septic shock; brain injury, including vasospasm; and overall mortality in both animals and humans. Whether it is cytokines, the inflammasome, or mitochondrial biogenesis, circadian medicine represents exciting opportunities for translational therapy in intensive care, which is currently lacking. Circadian medicine also represents a link to metabolic determinants of outcome, such as diabetes and cardiovascular disease. More than ever, we are appreciating the problem of circadian desynchrony in intensive care. This review explores the rationale and evidence for the importance of the circadian clock in surviving critical illness.

Pseudoperoxidase activity, conformational stability, and aggregation propensity of the His98Tyr myoglobin variant: implications for the onset of myoglobinopathy

The autosomal dominant striated muscle disease myoglobinopathy is due to the single point mutation His98Tyr in human myoglobin (MB), the heme protein responsible for binding, storage, and controlled release of O₂ in striated muscle. In order to understand the molecular basis of this disease, a comprehensive biochemical and biophysical study on wt MB and the variant H98Y has been performed. Although only small differences exist between the active site architectures of the two proteins, the mutant (a) exhibits an increased reactivity toward hydrogen peroxide, (b) exhibits a higher tendency to form high‐molecular‐weight aggregates, and (c) is more prone to heme bleaching, possibly as a consequence of the observed H₂O₂‐induced formation of the Tyr98 radical close to the metal center. These effects add to the impaired oxygen binding capacity and faster heme dissociation of the H98Y variant compared with wt MB. As the above effects result from bond formation/cleavage events occurring at the distal and proximal heme sites, it appears that the molecular determinants of the disease are localized there. These findings set the basis for clarifying the onset of the cascade of chemical events that are responsible for the pathological symptoms of myoglobinopathy.

Paracetamol use and lowered risk of acute kidney injury in patients with rhabdomyolysis

BACKGROUND

Mortality with rhabdomyolysis-associated acute kidney injury can be as high as 80%. Experimental data from mouse models of rhabdomyolysis showed that paracetamol reduces the expected increase in serum creatinine level. We aimed to assess the association between paracetamol use and the need for starting renal replacement therapy (RRT).

METHODS

We conducted a propensity score-matched cohort study in Orléans Hospital, France (a 1136-bed, public, university-affiliated and teaching hospital). All patients with serum creatine phosphokinase (CK) level > 5000 IU/L between January 1st, 2008 and December 31st, 2017 were included. A propensity score was calculated for each included patient by using multivariable logistic regression and all available baseline characteristics. The main outcome was the incidence of RRT initiation from day 1 to day 28 in the propensity score-matched cohort between patients exposed and unexposed to paracetamol.

RESULTS

Over the study period, 1065 patients with at least one CK level measurement > 5000 IU/L were included; 40 (3.8%) had at least one RRT session. Among the 343 matched pairs, 10 (2.9%) exposed and 24 (7.0%) unexposed patients underwent RRT before day 28 (P = 0.021). Primary time-to-event analysis showed that exposure to paracetamol was significantly associated with reduced absolute risk of RRT: absolute risk difference = - 3.18% (95% CI - 5.23 to - 1.20, P = 0.001). All secondary analyses showed a significantly reduced absolute risk of RRT in patients exposed to paracetamol.

CONCLUSION

Our study showed a significant association between paracetamol exposure and reduced incidence of RRT among patients with rhabdomyolysis.

Haptoglobin administration into the subarachnoid space prevents hemoglobin-induced cerebral vasospasm

Delayed ischemic neurological deficit (DIND) is a major driver of adverse outcomes in patients with aneurysmal subarachnoid hemorrhage (aSAH), defining an unmet need for therapeutic development. Cell-free hemoglobin that is released from erythrocytes into the cerebrospinal fluid (CSF) is suggested to cause vasoconstriction and neuronal toxicity, and correlates with the occurrence of DIND. Cell-free hemoglobin in the CSF of patients with aSAH disrupted dilatory NO signaling ex vivo in cerebral arteries, which shifted vascular tone balance from dilation to constriction. We found that selective removal of hemoglobin from patient CSF with a haptoglobin-affinity column or its sequestration in a soluble hemoglobin-haptoglobin complex was sufficient to restore physiological vascular responses. In a sheep model, administration of haptoglobin into the CSF inhibited hemoglobin-induced cerebral vasospasm and preserved vascular NO signaling. We identified 2 pathways of hemoglobin delocalization from CSF into the brain parenchyma and into the NO-sensitive compartment of small cerebral arteries. Both pathways were critical for hemoglobin toxicity and were interrupted by the large hemoglobin-haptoglobin complex that inhibited spatial requirements for hemoglobin reactions with NO in tissues. Collectively, our data show that compartmentalization of hemoglobin by haptoglobin provides a novel framework for innovation aimed at reducing hemoglobin-driven neurological damage after subarachnoid bleeding.

Intraoperative Oxidative Damage and Delirium after Cardiac Surgery

BACKGROUND

Mechanisms of postoperative delirium remain poorly understood, limiting development of effective treatments. We tested the hypothesis that intraoperative oxidative damage is associated with delirium and neuronal injury and that disruption of the blood-brain barrier modifies these associations.

METHODS

In a prespecified cohort study of 400 cardiac surgery patients enrolled in a clinical trial of atorvastatin to reduce kidney injury and delirium, we measured plasma concentrations of F2-isoprostanes and isofurans using gas chromatography-mass spectrometry to quantify oxidative damage, ubiquitin carboxyl-terminal hydrolase isozyme L1 to quantify neuronal injury, and S100 calcium-binding protein B using enzyme-linked immunosorbent assays to quantify blood-brain barrier disruption before, during, and after surgery. We performed the Confusion Assessment Method for the Intensive Care Unit twice daily to diagnose delirium. We measured the independent associations between intraoperative F2-isoprostanes and isofurans and delirium (primary outcome) and postoperative ubiquitin carboxyl-terminal hydrolase isozyme L1 (secondary outcome), and we assessed if S100 calcium-binding protein B modified these associations.

RESULTS

Delirium occurred in 109 of 400 (27.3%) patients for a median (10th, 90th percentile) of 1.0 (0.5, 3.0) days. In the total cohort, plasma ubiquitin carboxyl-terminal hydrolase isozyme L1 concentration was 6.3 ng/ml (2.7, 14.9) at baseline and 12.4 ng/ml (7.9, 31.2) on postoperative day 1. F2-isoprostanes and isofurans increased throughout surgery, and the log-transformed sum of intraoperative F2-isoprostanes and isofurans was independently associated with increased odds of postoperative delirium (odds ratio, 3.70 [95% CI, 1.41 to 9.70]; P = 0.008) and with increased postoperative ubiquitin carboxyl-terminal hydrolase isozyme L1 (ratio of geometric means, 1.42 [1.11 to 1.81]; P = 0.005). The association between increased intraoperative F2-isoprostanes and isofurans and increased postoperative ubiquitin carboxyl-terminal hydrolase isozyme L1 was amplified in patients with elevated S100 calcium-binding protein B (P = 0.049).

CONCLUSIONS

Intraoperative oxidative damage was associated with increased postoperative delirium and neuronal injury, and the association between oxidative damage and neuronal injury was stronger among patients with increased blood-brain barrier disruption.

The Role of Circulating Cell-Free Hemoglobin in Sepsis-Associated Acute Kidney Injury

Sepsis is a heterogeneous clinical syndrome that is complicated commonly by acute kidney injury (sepsis-AKI). Currently, no approved pharmacologic therapies exist to either prevent sepsis-AKI or to treat sepsis-AKI once it occurs. A growing body of evidence supports a connection between red blood cell biology and sepsis-AKI. Increased levels of circulating cell-free hemoglobin (CFH) released from red blood cells during hemolysis are common during sepsis and can contribute to sepsis-AKI through several mechanisms including tubular obstruction, nitric oxide depletion, oxidative injury, and proinflammatory signaling. A number of potential pharmacologic therapies targeting CFH in sepsis have been identified including haptoglobin, hemopexin, and acetaminophen, and early phase clinical trials have suggested that acetaminophen may have beneficial effects on lipid peroxidation and kidney function in patients with sepsis. Bedside measurement of CFH levels may facilitate predictive enrichment for future clinical trials of CFH-targeted therapeutics. However, rapid and reliable bedside tests for plasma CFH will be required for such trials to move forward.

A Novel Possible Role for Met Hemoglobin as Carrier of Hydrogen Sulfide in the Blood

Significance: Along with other gasotransmitters nitric oxide (NO) and carbon monoxide, hydrogen sulfide (H₂S) has recently emerged as an important signaling molecule with a particularly complex metabolism. Endogenous H₂S reacts with multiple cellular targets, including protein ferric heme groups, to elicit physiological responses, such as regulation of local blood flow. Recent Advances: Recent in vitro evidence suggests that H₂S at low physiological concentrations is carried in the blood as bound to the small fraction of oxidized ferric hemoglobin (metHb). A relatively stable metHb-sulfide complex forms when H₂S and purified metHb react in vitro, with an affinity within the in vivo physiological range of sulfide in the blood. Formation and subsequent redox metabolism of metHb-sulfide complex have also been confirmed in isolated intact red blood cells (RBCs) containing enhanced metHb levels. Thus, H₂S may function as an endocrine signaling molecule and elicit responses at sites away from the site of production. In addition, metHb, considered as an inert or pathological hemoglobin derivative, may have a novel potential physiological role in the transport of H₂S in the blood. Critical Issues: The transport of H₂S in the blood mediated by metHb would represent an O₂-independent pH-dependent mechanism for the blood-mediated control of blood flow and as such it is critical to understand the in vivo significance of this transport. Future Directions: Major challenges must be resolved to understand how metHb may carry H₂S in the RBCs, in particular determination of metHb-sulfide levels in the blood and identification of targets in the vasculature.

Haptoglobin-2 variant increases susceptibility to acute respiratory distress syndrome during sepsis

Acute respiratory distress syndrome (ARDS) is an inflammatory lung disorder that frequently complicates critical illness and commonly occurs in sepsis. Although numerous clinical and environmental risk factors exist, not all patients with risk factors develop ARDS, raising the possibility of genetic underpinnings for ARDS susceptibility. We have previously reported that circulating cell-free hemoglobin (CFH) is elevated during sepsis, and higher levels predict worse outcomes. Excess CFH is rapidly scavenged by haptoglobin (Hp). A common HP genetic variant, HP2, is unique to humans and is common in many populations worldwide. HP2 haptoglobin has reduced ability to inhibit CFH-mediated inflammation and oxidative stress compared with the alternative HP1. We hypothesized that HP2 increases ARDS susceptibility during sepsis when plasma CFH levels are elevated. In a murine model of sepsis with elevated CFH, transgenic mice homozygous for Hp2 had increased lung inflammation, pulmonary vascular permeability, lung apoptosis, and mortality compared with wild-type mice. We then tested the clinical relevance of our findings in 496 septic critically ill adults, finding that HP2 increased ARDS susceptibility after controlling for clinical risk factors and plasma CFH. These observations identify HP2 as a potentially novel genetic ARDS risk factor during sepsis and may have important implications in the study and treatment of ARDS.

Catalase-Like Antioxidant Activity is Unaltered in Hypochlorous Acid Oxidized Horse Heart Myoglobin

Activated neutrophils release myeloperoxidase that produces the potent oxidant hypochlorous acid (HOCl). Exposure of the oxygen transport protein horse heart myoglobin (hhMb) to HOCl inhibits Iron III (Fe(III))-heme reduction by cytochrome b5 to oxygen-binding Iron II (Fe(II))Mb. Pathological concentrations of HOCl yielded myoglobin oxidation products of increased electrophoretic mobility and markedly different UV/Vis absorbance. Mass analysis indicated HOCl caused successive mass increases of 16 a.m.u., consistent serial addition of molecular oxygen to the protein. By contrast, parallel analysis of protein chlorination by quantitative mass spectrometry revealed a comparatively minor increase in the 3-chlorotyrosine/tyrosine ratio. Pre-treatment of hhMb with HOCl affected the peroxidase reaction between the hemoprotein and H₂O₂ as judged by a HOCl dose-dependent decrease in spin-trapped tyrosyl radical detected by electron paramagnetic resonance (EPR) spectroscopy and the rate constant of 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid (ABTS) oxidation. By contrast, Mb catalase-like antioxidant activity remained unchanged under the same conditions. Notably, HOCl-modification of Mb decreased the rate of ferric-to-ferrous Mb reduction by a cytochrome b5 reductase system. Taken together, these data indicate oxidizing HOCl promotes Mb oxidation but not chlorination and that oxidized Mb shows altered Mb peroxidase-like activity and diminished rates of one-electron reduction by cytochrome b5 reductase, possibly affecting oxygen storage and transport however, Mb-catalase-like antioxidant activity remains unchanged.

Affinity and Effect of Anticancer Drugs on the Redox Reactivity of Hemoglobin

Hemoglobin's redox reactivity is affected by anticancer drugs of the antitubulin class. Direct binding of these drugs to hemoglobin, with biomedically relevant affinities, is demonstrated. While this interaction is mostly allosteric, in the case of docetaxel, a direct redox reaction is also observed-correlating well with structural differences between the four compounds. A role for Tyr145 in this reactivity is proposed, in line with previous observations of the importance of this amino acid in the reactivity of Hb toward agents of oxidative stress. A susceptibility of vinorelbin (and to a lower extent of paclitaxel) toward peroxide and peroxidase is shown.

Tyrosyl radical in haemoglobin and haptoglobin-haemoglobin complex: how does haptoglobin make haemoglobin less toxic?

One of the difficulties in creating a blood substitute on the basis of human haemoglobin (Hb) is the toxic nature of Hb when it is outside the safe environment of the red blood cells. The plasma protein haptoglobin (Hp) takes care of the Hb physiologically leaked into the plasma – it binds Hb and makes it much less toxic while retaining the Hb's high oxygen transporting capacity. We used Electron Paramagnetic Resonance (EPR) spectroscopy to show that the protein bound radical induced by H₂O₂ in Hb and Hp-Hb complex is formed on the same tyrosine residue(s), but, in the complex, the radical is found in a more hydrophobic environment and decays slower than in unbound Hb, thus mitigating its oxidative capacity. The data obtained in this study might set new directions in engineering blood substitutes for transfusion that would have the oxygen transporting efficiency typical of Hb, but which would be non-toxic.

Protective Effect of Dinitrosyl Iron Complexes with Glutathione in Red Blood Cell Lysis Induced by Hypochlorous Acid

Hypochlorous acid (HOCl), one of the major precursors of free radicals in body cells and tissues, is endowed with strong prooxidant activity. In living systems, dinitrosyl iron complexes (DNIC) with glutathione ligands play the role of nitric oxide donors and possess a broad range of biological activities. At micromolar concentrations, DNIC effectively inhibit HOCl-induced lysis of red blood cells (RBCs) and manifest an ability to scavenge alkoxyl and alkylperoxyl radicals generated in the reaction of HOCl with tert-butyl hydroperoxide. DNIC proved to be more effective cytoprotective agents and organic free radical scavengers in comparison with reduced glutathione (GSH). At the same time, the kinetics of HOCl-induced oxidation of glutathione ligands in DNIC is slower than in the case of GSH. HOCl-induced oxidative conversions of thiolate ligands cause modification of DNIC, which manifests itself in inclusion of other ligands. It is suggested that the strong inhibiting effect of DNIC with glutathione on HOCl-induced lysis of RBCs is determined by their antioxidant and regulatory properties.

Myoglobin induces mitochondrial fusion, thereby inhibiting breast cancer cell proliferation

Myoglobin is a monomeric heme protein expressed ubiquitously in skeletal and cardiac muscle and is traditionally considered to function as an oxygen reservoir for mitochondria during hypoxia. It is now well established that low concentrations of myoglobin are aberrantly expressed in a significant proportion of breast cancer tumors. Despite being expressed only at low levels in these tumors, myoglobin is associated with attenuated tumor growth and a better prognosis in breast cancer patients, but the mechanism of this myoglobin-mediated protection against further cancer growth remains unclear. Herein, we report a signaling pathway by which myoglobin regulates mitochondrial dynamics and thereby decreases cell proliferation. We demonstrate in vitro that expression of human myoglobin in MDA-MB-231, MDA-MB-468, and MCF7 breast cancer cells induces mitochondrial hyperfusion by up-regulating mitofusins 1 and 2, the predominant catalysts of mitochondrial fusion. This hyperfusion causes cell cycle arrest and subsequent inhibition of cell proliferation. Mechanistically, increased mitofusin expression was due to myoglobin-dependent free-radical production, leading to the oxidation and degradation of the E3 ubiquitin ligase parkin. We recapitulated this pathway in a murine model in which myoglobin-expressing xenografts exhibited decreased tumor volume with increased mitofusin, markers of cell cycle arrest, and decreased parkin expression. Furthermore, in human triple-negative breast tumor tissues, mitofusin and myoglobin levels were positively correlated. Collectively, these results elucidate a new function for myoglobin as a modulator of mitochondrial dynamics and reveal a novel pathway by which myoglobin decreases breast cancer cell proliferation and tumor growth by up-regulating mitofusin levels.

Peroxidase Activity of Human Hemoproteins: Keeping the Fire under Control

The heme in the active center of peroxidases reacts with hydrogen peroxide to form highly reactive intermediates, which then oxidize simple substances called peroxidase substrates. Human peroxidases can be divided into two groups: (1) True peroxidases are enzymes whose main function is to generate free radicals in the peroxidase cycle and (pseudo)hypohalous acids in the halogenation cycle. The major true peroxidases are myeloperoxidase, eosinophil peroxidase and lactoperoxidase. (2) Pseudo-peroxidases perform various important functions in the body, but under the influence of external conditions they can display peroxidase-like activity. As oxidative intermediates, these peroxidases produce not only active heme compounds, but also protein-based tyrosyl radicals. Hemoglobin, myoglobin, cytochrome c/cardiolipin complexes and cytoglobin are considered as pseudo-peroxidases. Рeroxidases play an important role in innate immunity and in a number of physiologically important processes like apoptosis and cell signaling. Unfavorable excessive peroxidase activity is implicated in oxidative damage of cells and tissues, thereby initiating the variety of human diseases. Hence, regulation of peroxidase activity is of considerable importance. Since peroxidases differ in structure, properties and location, the mechanisms controlling peroxidase activity and the biological effects of peroxidase products are specific for each hemoprotein. This review summarizes the knowledge about the properties, activities, regulations and biological effects of true and pseudo-peroxidases in order to better understand the mechanisms underlying beneficial and adverse effects of this class of enzymes.

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.

Engineering oxidative stability in human hemoglobin based on the Hb providence (βK82D) mutation and genetic cross-linking

Previous work suggested that hemoglobin (Hb) tetramer formation slows autoxidation and hemin loss and that the naturally occurring mutant, Hb Providence (HbProv; βK82D), is much more resistant to degradation by H₂O₂ We have examined systematically the effects of genetic cross-linking of Hb tetramers with and without the HbProv mutation on autoxidation, hemin loss, and reactions with H₂O₂, using native HbA and various wild-type recombinant Hbs as controls. Genetically cross-linked Hb Presbyterian (βN108K) was also examined as an example of a low oxygen affinity tetramer. Our conclusions are: (a) at low concentrations, all the cross-linked tetramers show smaller rates of autoxidation and hemin loss than HbA, which can dissociate into much less stable dimers and (b) the HbProv βK82D mutation confers more resistance to degradation by H₂O₂, by markedly inhibiting oxidation of the β93 cysteine side chain, particularly in cross-linked tetramers and even in the presence of the destabilizing Hb Presbyterian mutation. These results show that cross-linking and the βK82D mutation do enhance the resistance of Hb to oxidative degradation, a critical element in the design of a safe and effective oxygen therapeutic.

Myoglobin and Polydopamine-Engineered Raman Nanoprobes for Detecting, Imaging, and Monitoring Reactive Oxygen Species in Biological Samples and Living Cells

Highly reliable detection, imaging, and monitoring of reactive oxygen species (ROS) are critical for understanding and studying the biological roles and pathogenesis of ROS. This study describes the design and synthesis of myoglobin and polydopamine-engineered surface-enhanced Raman scattering (MP-SERS) nanoprobes with strong, tunable SERS signals that allow for specifically detecting and imaging ROS sensitively and quantitatively. The study shows that a polydopamine nanolayer can facilitate the modification of Raman-active myoglobins and satellite Au nanoparticles (s-AuNPs) to a plasmonic core AuNP (c-AuNP) in a controllable manner and the generation of plasmonically coupled hot spots between a c-AuNP and s-AuNPs that can induce strong SERS signals. The six-coordinated Fe(III)-OH₂ of myoglobins in plasmonic hotspots is reacted with ROS (H₂ O₂ , •OH, and O₂^- ) to form Fe(IV)O. The characteristic Raman peaks of Fe(IV)O from the Fe-porphyrin is used to analyze and quantify ROS. This chemistry allows for these probes to detect ROS in solution and image ROS in cells in a highly designable, specific, and sensitive manner. This work shows that these MP-SERS probes allow for detecting and imaging ROS to differentiate cancerous cells from noncancerous cells. Importantly, for the first time, SERS-based monitoring of the autophagy process in living cells under starvation conditions is validated.

Can half-marathon affect overall health? The yin-yang of sport

Physical activity improves overall health and counteracts metabolic pathologies. Adipose tissue and bone are important key targets of exercise; the prevalence of diseases associated with suboptimal physical activity levels has increased in recent times as a result of lifestyle changes. Mesenchymal stem cells (MSCs) differentiation in either osteogenic or adipogenic lineage is regulated by many factors. Particularly, the expression of master genes such as RUNX2 and PPARγ2 is essential for MSC commitment to osteogenic or adipogenic differentiation, respectively. Besides various positive effects on health, some authors have reported stressful outcomes as a consequence of endurance in physical activity. We looked for further clues about MSCs differentiation and serum proteins modulation studying the effects of half marathon in runners by means of gene expression analyses and a proteomic approach. Our results demonstrated an increase in osteogenic commitment and a reduction in adipogenic commitment of MSCs. In addition, for the first time we have analyzed the proteomic profile changes in runners after half-marathon activity in order to survey the related systemic adjustments. The shotgun proteomic approach, performed through the immuno-depletion of the 14 most abundant serum proteins, allowed the identification of 23 modulated proteins after the half marathon. Interestingly, proteomic data showed the activation of both inflammatory response and detoxification process. Moreover, the involvement of pathways associated to immune response, lipid transport and coagulation, was elicited. Notably, positive and negative effects may be strictly linked. Data are available via ProteomeXchange with identifier PXD006704.

SIGNIFICANCE

We describe gene expression and proteomic studies aiming to an in-depth understanding of half-marathon effects on bone and adipogenic differentiation as well as biological phenomena involved in sport activity. We believe that this novel approach suggests the physical effects on overall health and show the different pathways involved during half marathon. Contents of the paper have not been published or submitted for publication elsewhere. The authors declare no conflict of interest.

Effective intermediate-spin iron in O2-transporting heme proteins

Proteins carrying an iron-porphyrin (heme) cofactor are essential for biological O2 management. The nature of Fe-O2 bonding in hemoproteins is debated for decades. We used energy-sampling and rapid-scan X-ray Kβ emission and K-edge absorption spectroscopy as well as quantum chemistry to determine molecular and electronic structures of unligated (deoxy), CO-inhibited (carboxy), and O2-bound (oxy) hemes in myoglobin (MB) and hemoglobin (HB) solutions and in porphyrin compounds at 20-260 K. Similar metrical and spectral features revealed analogous heme sites in MB and HB and the absence of low-spin (LS) to high-spin (HS) conversion. Amplitudes of Kβ main-line emission spectra were directly related to the formal unpaired Fe(d) spin count, indicating HS Fe(II) in deoxy and LS Fe(II) in carboxy. For oxy, two unpaired Fe(d) spins and, thus by definition, an intermediate-spin iron center, were revealed by our static and kinetic X-ray data, as supported by (time-dependent) density functional theory and complete-active-space self-consistent-field calculations. The emerging Fe-O2 bonding situation includes in essence a ferrous iron center, minor superoxide character of the noninnocent ligand, significant double-bond properties of the interaction, and three-center electron delocalization as in ozone. It resolves the apparently contradictory classical models of Pauling, Weiss, and McClure/Goddard into a unifying view of O2 bonding, tuned toward reversible oxygen transport.

Erythrocyte-heme proteins and STEMI: implications in prognosis

The role of erythrocytes in thrombus formation has been often neglected, but some studies have highlighted their active role in thrombotic events. Free-haemoglobin (Hb) has shown to induce oxidative-stress damage. Herein we have investigated the coordinated changes in heme-related proteins in patients with acute-coronary-syndromes (ACS), their association to ongoing thrombosis and their impact on patients' prognosis. The serum proteome of STEMI-patients (N=27) within the first 6h after event-onset and 3d after were compared to controls (N=60). Changes in heme-metabolism were characterized in a second STEMI-group by a dual proteomic approach analyzing in-vivo aspirated coronary thrombi at PCI (N=24) and the associated peripheral-blood changes (N=10). A third STEMI-group (N=132) was studied to analyze the impact of the observed changes in prognosis at 6-months-follow-up. The haptoglobin/hemopexin(Hpg/Hpx)-scavenging-system revealed a time-dependent response after STEMI with an early increase in Hpg circulating levels in the acute phase (P=0.01) and a late increase in Hpx levels 3d after (P=0.045). Beta-Hb content in coronary thrombi was directly correlated with systemic beta-Hb and Hpg (R=0.804,P=0.0029; R=0.859,P=0.0007) levels. The presence of a fully-occlusive thrombus was associated to higher circulating levels of beta-Hb (P=0.03) and unbound-Hpg (P=0.03). ELISA validation demonstrated a decreased survival rate at 6-months follow-up in STEMI-patients with lower Hpg plasma levels at admission (P=0.027). Our results show active Hb-release form erythrocytes in ACS. This release is followed by a systemic early increase in Hpg levels and a late increase in Hpx levels that can co-ordinately help to prevent systemic pro-oxidative effects. The Hb-scavenging ability of haptoglobin is related to patients' prognosis.

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.

There is blood in the water: hemolysis, hemoglobin, and heme in acute lung injury

The major role of red blood cells (RBCs) is to deliver oxygen and remove carbon dioxide within organisms through the unique properties of hemoglobin. Although beneficial within RBCs, when outside hemoglobin and its breakdown products (heme, iron) induce proinflammatory responses affecting various cellular responses. Although these effects are considered to be prominent in disorders with increased hemolysis, recent evidence suggests that this process may be active in nonhemolytic disorders such as acute lung injury/acute respiratory distress syndrome. This perspectives article focuses on data related to red cell products in nonhemolytic disorders and the potential to target these factors in acute lung injury/acute respiratory distress syndrome.

Effects of pharmacological ascorbate on hemoglobin-induced cancer cell proliferation

The high heme content in red meat is associated with an increased risk of developing cancer. Pharmacologic concentrations of ascorbate can specifically kill a wide range of cancer cells. In this study, the impact of ascorbate at pharmacologic concentrations on hemoglobin (Hb)-modulated human hepatoma HepG2 cell survival was investigated. It was found that HepG2 cells were proliferated by Hb (5-25μM), but killed by high pharmacologic concentrations of ascorbate (2-10mM). Although ascorbate at the low pharmacologic concentration (0.5mM) alone exhibited insignificant effect on cell viability, it effectively inhibited Hb (10μM)-induced cancer cell proliferation. The mechanism of this cytotoxicity was based on the production of extracellular H₂O₂ and involved transition iron. The influence of ascorbate on Hb-dependent redox reactions (i.e. the oxidative stability of Hb and its cytotoxic ferryl intermediate) was further investigated to illustrate the reaction mechanism of ascorbate toxicity, where H₂O₂ was generated in the reaction of ascorbate with Hb. Furthermore, circular dichroism demonstrated no significant change in the secondary structure of Hb after ascorbate addition and molecular docking revealed binding modes of ascorbate with Hb. These results demonstrated that ascorbate could possess anti-cancer activity through interfering in Hb-dependent redox reactions.

The role of red blood cells and cell-free hemoglobin in the pathogenesis of ARDS

The primary focus of research into the pathophysiology of the acute respiratory distress syndrome (ARDS) has been on the interaction between the lung, underlying causes of ARDS, and the role of white blood cells and platelets in contributing to lung injury. Given a lack of specific therapies for this common complication of critical illness, further insight into the pathophysiology of this syndrome is greatly needed to develop targeted interventions. The red blood cell (RBC) has been reported to undergo deleterious changes in critical illness and be present in the alveoli of patients with ARDS. Release of RBC contents is known to be injurious in other conditions but has only recently been studied in critical illness and ARDS. The contribution of the RBC to ARDS represents a new avenue of research that may produce new, targeted therapies for this deadly syndrome.

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.

Randomized, placebo-controlled trial of acetaminophen for the reduction of oxidative injury in severe sepsis: the Acetaminophen for the Reduction of Oxidative Injury in Severe Sepsis trial

OBJECTIVES

This trial evaluated the efficacy of acetaminophen in reducing oxidative injury, as measured by plasma F2-isoprostanes, in adult patients with severe sepsis and detectable plasma cell-free hemoglobin.

DESIGN

Single-center, randomized, double-blind, placebo-controlled phase II trial.

SETTING

Medical ICU in a tertiary, academic medical center.

PATIENTS

Critically ill patients 18 years old or older with severe sepsis and detectable plasma cell-free hemoglobin.

INTERVENTIONS

Patients were randomized 1:1 to enteral acetaminophen 1 g every 6 hours for 3 days (n = 18) or placebo (n = 22) with the same dosing schedule and duration.

MEASUREMENTS AND MAIN RESULTS

F2-Isoprostanes on study day 3, the primary outcome, did not differ between acetaminophen (30 pg/mL; interquartile range, 24-41) and placebo (36 pg/mL; interquartile range, 25-80; p = 0.35). However, F2-isoprostanes were significantly reduced on study day 2 in the acetaminophen group (24 pg/mL; interquartile range, 19-36) when compared with placebo (36 pg/mL; interquartile range, 23-55; p = 0.047). Creatinine on study day 3, a secondary outcome, was significantly lower in the acetaminophen group (1.0 mg/dL; interquartile range, 0.6-1.4) when compared with that in the placebo (1.3 mg/dL; interquartile range, 0.83-2.0; p = 0.039). There was no statistically significant difference in hospital mortality (acetaminophen 5.6% vs placebo 18.2%; p = 0.355) or adverse events (aspartate aminotransferase or alanine aminotransferase > 400; acetaminophen 9.5% vs placebo 4.3%; p = 0.599).

CONCLUSIONS

In adults with severe sepsis and detectable plasma cell-free hemoglobin, treatment with acetaminophen within 24 hours of ICU admission may reduce oxidative injury and improve renal function. Additional study is needed to confirm these findings and determine the effect of acetaminophen on patient-centered outcomes.

Cytoglobin ligand binding regulated by changing haem-co-ordination in response to intramolecular disulfide bond formation and lipid interaction

Cytoglobin (Cygb) is a hexa-co-ordinate haem protein from the globin superfamily with a physiological function that is unclear. We have previously reported that the haem co-ordination is changed in the presence of lipids, potentially transforming the redox properties of the protein and hence the function of Cygb in vivo. Recent research suggests that the protein can exist in a number of states depending on the integrity and position of disulfide bonds. In the present study, we show that the monomeric protein with an internal disulfide bond between the two cysteine residues Cys38 and Cys83, interacts with lipids to induce a change in haem co-ordination. The dimeric protein with intermolecular disulfide bonds and monomeric protein without an intramolecular disulfide bond does not exhibit these changes in haem co-ordination. Furthermore, monomeric Cygb with an intramolecular disulfide bond has significantly different properties, oxidizing lipid membranes and binding ligands more rapidly as compared with the other forms of the protein. The redox state of these cysteine residues in vivo is therefore highly significant and may be a mechanism to modulate the biochemical properties of the haem under conditions of stress.

Elevation of plasma cell-free hemoglobin in pulmonary arterial hypertension

BACKGROUND

Cell-free hemoglobin (CFH) is a potent nitric oxide scavenger associated with poor outcomes in several diseases. Pulmonary arterial hypertension (PAH) is characterized by reduced nitric oxide availability. We hypothesized that CFH would be elevated in PAH and would associate with hemodynamics and clinical outcomes.

METHODS

We measured CFH in 200 consecutively evaluated patients with PAH, 16 unaffected bone morphogenetic receptor protein type 2 (BMPR2) mutation carriers, 19 healthy subjects, and 29 patients with pulmonary venous hypertension (PVH). CFH values were tested for association with hemodynamics, time to hospitalization, and death.

RESULTS

CFH was elevated in patients with PAH and BMPR2 carriers compared with healthy subjects and patients with PVH (P ≤ .01 all comparisons). There were no differences in CFH across PAH subtypes. CFH modestly correlated with mean pulmonary artery pressure (ρ = 0.16, P = .03) and pulmonary vascular resistance (ρ = 0.21, P = .01) and inversely with cardiac index (ρ = -0.18, P = .02) in patients with PAH. CFH was not associated with hemodynamic response to nitric oxide or death. Patients with the highest CFH levels had increased risk of PAH-related hospitalization when adjusted for age, sex, and PAH cause (hazard ratio, 1.69; 95% CI ,1.08-2.66; P = .02).

CONCLUSIONS

CFH is elevated in patients with PAH and BMPR2 carriers compared with healthy subjects and patients with PVH. Elevated CFH levels are independently associated with an increased risk of hospitalization. Further study is required to understand the mechanism of CFH elevation and the potential pathologic contribution of CFH in PAH.

Perioperative intravenous acetaminophen attenuates lipid peroxidation in adults undergoing cardiopulmonary bypass: a randomized clinical trial

BACKGROUND

Cardiopulmonary bypass (CPB) lyses erythrocytes and induces lipid peroxidation, indicated by increasing plasma concentrations of free hemoglobin, F2-isoprostanes, and isofurans. Acetaminophen attenuates hemeprotein-mediated lipid peroxidation, reduces plasma and urine concentrations of F2-isoprostanes, and preserves kidney function in an animal model of rhabdomyolysis. Acetaminophen also attenuates plasma concentrations of isofurans in children undergoing CPB. The effect of acetaminophen on lipid peroxidation in adults has not been studied. This was a pilot study designed to test the hypothesis that acetaminophen attenuates lipid peroxidation in adults undergoing CPB and to generate data for a clinical trial aimed to reduce acute kidney injury following cardiac surgery.

METHODS AND RESULTS

In a prospective double-blind placebo-controlled clinical trial, sixty adult patients were randomized to receive intravenous acetaminophen or placebo starting prior to initiation of CPB and for every 6 hours for 4 doses. Acetaminophen concentrations measured 30 min into CPB and post-CPB were 11.9 ± 0.6 μg/mL (78.9 ± 3.9 μM) and 8.7 ± 0.3 μg/mL (57.6 ± 2.0 μM), respectively. Plasma free hemoglobin increased more than 15-fold during CPB, and haptoglobin decreased 73%, indicating hemolysis. Plasma and urinary markers of lipid peroxidation also increased during CPB but returned to baseline by the first postoperative day. Acetaminophen reduced plasma isofuran concentrations over the duration of the study (P = 0.05), and the intraoperative plasma isofuran concentrations that corresponded to peak hemolysis were attenuated in those subjects randomized to acetaminophen (P = 0.03). Perioperative acetaminophen did not affect plasma concentrations of F2-isoprostanes or urinary markers of lipid peroxidation.

CONCLUSIONS

Intravenous acetaminophen attenuates the increase in intraoperative plasma isofuran concentrations that occurs during CPB, while urinary markers were unaffected.

TRIAL REGISTRATION

ClinicalTrials.gov NCT01366976.

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.

In vitro heme and non-heme iron capture from hemoglobin, myoglobin and ferritin by bovine lactoferrin and implications for suppression of reactive oxygen species in vivo

Lactoferrin (Lf), present in colostrum and milk is a member of the transferrin family of iron-binding glyco-proteins, with stronger binding capacity to ferric iron than hemoglobin, myoglobin or transferrin. Unlike hemoglobin and myoglobin, iron-bound Lf is reasonably stable to gastric and duodenal digestive conditions. Unlike ferrous iron, ferric iron is not directly reactive with oxygen supporting the capacity of Lf capture of heme iron to suppress reactive oxygen species (ROS) production. We therefore hypothesized that bovine Lf could capture and thereby terminate the cycle of ROS production by heme iron. The transfer of heme iron from either intact or digested forms of hemoglobin and myoglobin and from intact ferritin was demonstrated by in vitro methods, monitoring Fe-saturation status of Lf by changes in absorptivity at 465 nm. The results are discussed in the context of new proposed opportunities for orally administered Lf to regulate oxidative damage associated with heme iron. In addition to potentially suppressing oxidative heme-iron-mediated tissue damage in the lumen, Lf is expected to also reverse the overload of ferritin-bound iron, that accompanies chronic inflammation and aging. These new proposed uses of Lf are additional to known host defense functions that include anti-microbial, anti-viral properties, immune and cancer cell growth regulation. The findings and interpretations presented require clinical substantiation and may support important additional protective and therapeutic uses for Lf in the future.

Phagocytic uptake of oxidized heme polymer is highly cytotoxic to macrophages

Apoptosis in macrophages is responsible for immune-depression and pathological effects during malaria. Phagocytosis of PRBC causes induction of apoptosis in macrophages through release of cytosolic factors from infected cells. Heme polymer or β-hematin causes dose-dependent death of macrophages with LC₅₀ of 132 µg/ml and 182 µg/ml respectively. The toxicity of hemin or heme polymer was amplified several folds in the presence of non-toxic concentration of methemoglobin. β-hematin uptake in macrophage through phagocytosis is crucial for enhanced toxicological effects in the presence of methemoglobin. Higher accumulation of β-hematin is observed in macrophages treated with β-hematin along with methemoglobin. Light and scanning electron microscopic observations further confirm accumulation of β-hematin with cellular toxicity. Toxicological potentiation of pro-oxidant molecules toward macrophages depends on generation of H₂O₂ and independent to release of free iron from pro-oxidant molecules. Methemoglobin oxidizes β-hematin to form oxidized β-hematin (βH*) through single electron transfer mechanism. Pre-treatment of reaction mixture with spin-trap Phenyl-N-t-butyl-nitrone dose-dependently reverses the β-hematin toxicity, indicates crucial role of βH* generation with the toxicological potentiation. Acridine orange/ethidium bromide staining and DNA fragmentation analysis indicate that macrophage follows an oxidative stress dependent apoptotic pathway to cause death. In summary, current work highlights mutual co-operation between methemoglobin and different pro-oxidant molecules to enhance toxicity towards macrophages. Hence, methemoglobin peroxidase activity can be probed for subduing cellular toxicity of pro-oxidant molecules and it may in-turn make up for host immune response against the malaria parasite.

Myoglobin and haemoglobin-mediated lipid oxidation in washed muscle: observations on crosslinking, ferryl formation, porphyrin degradation, and haemin loss rate

Reduced trout haemoglobin (Hb) is a mixture of oxy- and deoxy-Hb at pH 6.3. Addition of oxy/deoxyHb to washed muscle resulted in detectable ferryl Hb while adding bovine oxyHb, trout metHb, or bovine metHb did not. Trout metHb promoted lipid oxidation more rapidly than bovine metHb, attributable to lower haemin affinity in fish Hbs. Protoporphyrin IX degradation was prevalent during trout and bovine Hb-mediated lipid oxidation. Caffeic acid prevented porphyrin degradation and lipid oxidation. Crosslinked myoglobin (Mb) promoted lipid oxidation more effectively than metMb. Fish metMb released haemin more readily than mammalian metMb at pH 5.5. These studies suggest haemin dissociation from metHb causes formation of free radicals that degrade protoporphyrin and cause lipid oxidation, and appreciable quantities of deoxyHb are needed to generate ferryl Hb oxidant. Crosslinking appears to facilitate Mb-mediated lipid oxidation in washed muscle yet haemin release can occur from fish metMb at low pH.

Tyrosine can protect against oxidative stress through ferryl hemoglobin reduction

The toxic mechanism of hemoglobin (Hb) under oxidative stress is linked to the formations of highly cytotoxic ferryl species and subsequently heme-to-protein cross-linked derivative of Hb (Hb-X). In this study, we have examined the effects of free tyrosine and its analogues (3-chlorotyrosine, phenylalanine) on the stability of ferryl hemoglobin and the formation of Hb-X. The results showed that free tyrosine (not phenylalanine, 10-500 μM) was an efficient reducing agent of ferryl species and also effective at preventing the formation of cytotoxic Hb-X. Meanwhile, the dimeric tyrosine was formed as the oxidation product of tyrosine during Hb redox reaction. Compared with free tyrosine, 3-chlorotyrosine, an oxidation product of tyrosine and a proposed biomarker for hypochlorous acid (HOCl) in vivo, exhibited stronger antioxidant properties in Hb-induced oxidative stress, which was consistent with its more efficient ability in the reduction of ferryl species. These results showed that the presence of tyrosine and its derivative in vivo and vitro could ameliorate oxidative damage through ferryl heme reduction. The antioxidant ability, therefore, may provide new insights into the nutritional and physiological significance of free tyrosine with redox active heme proteins-related oxidative stress.