Oxidation of hemoglobin to methemoglobin in intact erythrocyte by a hydroperoxide induces formation of glutathionyl hemoglobin and binding of alpha-hemoglobin to membrane

Glutathionyl Hemoglobin and Its Emerging Role as a Clinical Biomarker of Chronic Oxidative Stress

Hemoglobin is one of the proteins that are more susceptible to S-glutathionylation and the levels of its modified form, glutathionyl hemoglobin (HbSSG), increase in several human pathological conditions. The scope of the present review is to provide knowledge about how hemoglobin is subjected to S-glutathionylation and how this modification affects its functionality. The different diseases that showed increased levels of HbSSG and the methods used for its quantification in clinical investigations will be also outlined. Since there is a growing need for precise and reliable methods for markers of oxidative stress in human blood, this review highlights how HbSSG is emerging more and more as a good indicator of severe oxidative stress but also as a key pathogenic factor in several diseases.

Rheological Abnormalities in Human Erythrocytes Subjected to Oxidative Inflammation

Erythrocytes are oxygen carriers and exposed to redox cycle in oxygenation and deoxygenation of hemoglobin. This indicates that circulating erythrocytes are vulnerable to the oxidative injury occurring under the imbalance of redox homeostasis. In this review article, two topics are presented concerning the human erythrocytes exposed to the oxidative inflammation including septic and sterile conditions. First, we demonstrate rheological derangement of erythrocytes subjected to acute oxidative injury caused by exogenous generators of reactive oxygen species (ROS). Erythrocyte filterability as whole-cell deformability has been estimated by the gravity-based nickel mesh filtration technique in our laboratory and was dramatically impaired in a time-dependent manner after starting exposure to the ROS generators, that is associated with concurrent progression of membrane protein degradation, phospholipid peroxidation, erythrocyte swelling, methemoglobin formation, and oxidative hemolysis. Second, we introduce an impairment of erythrocyte filterability confirmed quantitatively in diabetes mellitus and hypertension of animal models and patients under treatment. Among the cell geometry, internal viscosity, and membrane property as the three major determinants of erythrocyte deformability, erythrocyte membrane alteration is supposed to be the primary cause of this impairment in these lifestyle-related diseases associated with persistent oxidative inflammation. Excessive ROS trigger the inflammatory responses and reduce the erythrocyte membrane fluidity. Oxidative inflammation increasing erythrocyte membrane rigidity underlies the impaired systemic microcirculation, which is observed in diabetic and/or hypertensive patients. On the other hand, elevated internal viscosity caused by sickle hemoglobin polymerization is a primary cause of impaired erythrocyte filterability in sickle cell disease (SCD). However, oxidative inflammation is also involved in the pathophysiology of SCD. The physiologic level of ROS acts as signaling molecules for adaptation to oxidative environment, but the pathological level of ROS induces suicidal erythrocyte death (eryptosis). These findings provide further insight into the ROS-related pathophysiology of many clinical conditions.

The Redox Potential of the β-93-Cysteine Thiol Group in Human Hemoglobin Estimated from In Vitro Oxidant Challenge Experiments

Glutathionyl hemoglobin is a minor form of hemoglobin with intriguing properties. The measurement of the redox potential of its reactive β-⁹³-Cysteine is useful to improve understanding of the response of erythrocytes to transient and chronic conditions of oxidative stress, where the level of glutathionyl hemoglobin is increased. An independent literature experiment describes the recovery of human erythrocytes exposed to an oxidant burst by measuring glutathione, glutathione disulfide and glutathionyl hemoglobin in a two-hour period. This article calculates a value for the redox potential E₀ of the β-⁹³-Cysteine, considering the erythrocyte as a closed system at equilibrium described by the Nernst equation and using the measurements of the literature experiment. The obtained value of E₀ of −121 mV at pH 7.4 places hemoglobin as the most oxidizing thiol of the erythrocyte. By using as synthetic indicators of the concentrations the electrochemical potentials of the two main redox pairs in the erythrocytes, those of glutathione–glutathione disulfide and of glutathionyl–hemoglobin, the mechanism of the recovery phase can be hypothesized. Hemoglobin acts as the redox buffer that scavenges oxidized glutathione in the oxidative phase and releases it in the recovery phase, by acting as the substrate of the NAD(P)H-cofactored enzymes.

Brain Endothelial Erythrophagocytosis and Hemoglobin Transmigration Across Brain Endothelium: Implications for Pathogenesis of Cerebral Microbleeds

Peripheral endothelial cells are capable of erythrophagocytosis, but data on brain endothelial erythrophagocytosis are limited. We studied the relationship between brain endothelial erythrophagocytosis and cerebral microhemorrhage, the pathological substrate of MRI-demonstrable cerebral microbleeds. To demonstrate the erythrophagocytic capability of the brain endothelium, we studied the interactions between brain endothelial cells and red blood cells exposed to oxidative stress in vitro, and developed a new in vitro cerebral microbleeds model to study the subsequent passage of hemoglobin across the brain endothelial monolayer. Using multiple approaches, our results show marked brain endothelial erythrophagocytosis of red blood cells exposed to oxidative stress compared with control red blood cells in vitro. This brain endothelial erythrophagocytosis was accompanied by passage of hemoglobin across the brain endothelial monolayer with unaltered monolayer integrity. In vivo and confocal fluorescence microscopy studies confirmed the extravasation of RBC exposed to oxidative stress across brain endothelium. These findings, demonstrating erythrophagocytosis mediated by the brain endothelial monolayer and the subsequent passage of iron-rich hemoglobin in vitro and RBC in vivo, may have implications for elucidating mechanisms involved in the development of cerebral microbleeds that are not dependent on disruption of the microvasculature.

Mapping of hemoglobin in erythrocytes and erythrocyte ghosts using two photon excitation fluorescence microscopy

The present study describes utilization of two photon excitation fluorescence (2PE) microscopy for visualization of the hemoglobin in human and porcine erythrocytes and their empty membranes (i.e., ghosts). High-quality, label- and fixation-free visualization of hemoglobin was achieved at excitation wavelength 730 nm by detecting visible autofluorescence. Localization in the suspension and spatial distribution (i.e., mapping) of residual hemoglobin in erythrocyte ghosts has been resolved by 2PE. Prior to the 2PE mapping, the presence of residual hemoglobin in the bulk suspension of erythrocyte ghosts was confirmed by cyanmethemoglobin assay. 2PE analysis revealed that the distribution of hemoglobin in intact erythrocytes follows the cells’ shape. Two types of erythrocytes, human and porcine, characterized with discocyte and echinocyte morphology, respectively, showed significant differences in hemoglobin distribution. The 2PE images have revealed that despite an extensive washing out procedure after gradual hypotonic hemolysis, a certain amount of hemoglobin localized on the intracellular side always remains bound to the membrane and cannot be eliminated. The obtained results open the possibility to use 2PE microscopy to examine hemoglobin distribution in erythrocytes and estimate the purity level of erythrocyte ghosts in biotechnological processes.

Attenuation of oxidative hemolysis of human red blood cells by the natural phenolic compound, allylpyrocatechol

The protecting ability of the Piper betle leaves-derived phenol, allylpyrocatechol (APC) against AAPH-induced membrane damage of human red blood cells (RBCs) was investigated. Compared to control, AAPH (50 mM) treatment resulted in significant hemolysis (55%, p < 0.01), associated with increased malondialdehyde (MDA) (2.9-fold, p < 0.001) and methemoglobin (6.1-fold, p < 0.001) levels. The structural deformation due to membrane damage was confirmed from scanning electron microscopy (SEM) images and Heinz bodies formation, while the cell permeability was evident from the K(+) efflux (28.7%, p < 0.05) and increased intracellular Na(+) concentration (8%, p < 0.05). The membrane damage, due to the reduction of the cholesterol/phospholipids ratio and depletion (p < 0.001) of ATP, 2,3-DPG by ˜44-54% and Na(+)-K(+) ATPase activity (43.7%), indicated loss of RBC functionality. The adverse effects of AAPH on all these biochemical parameters and the resultant oxidative hemolysis of RBCs were significantly reduced by pretreating the cells with APC (7 μM) or α-tocopherol (50 μM) for 1 h, prior to incubation with AAPH.

Oxygenation properties and oxidation rates of mouse hemoglobins that differ in reactive cysteine content

House mice (genus Mus) harbor extensive allelic variation at two tandemly duplicated genes that encode the β-chain subunits of adult hemoglobin (Hb). Alternative haplotypes differ in the level of sequence divergence between the two β-globin gene duplicates: the Hbb(d) and Hbb(p) haplotypes harbor two structurally distinct β-globin genes, whereas the Hbb(s) haplotype harbors two β-globin duplicates that are identical in sequence. One especially salient difference between the s-type Hbs relative to the d- and p-type Hbs relates to the number of reactive β-chain cysteine residues. In addition to the highly conserved cysteine residue at β93, the d- and p-type Hbs contain an additional reactive cysteine residue at β13. To assess the functional consequences of allelic variation in β-globin cysteine content, we measured O(2)-binding properties and H(2)O(2)-induced oxidation rates of mono- and dicysteinyl β-Hbs from 4 different inbred strains of mice: C57BL/6J, BALB/cJ, MSM/Ms, and CAROLI/EiJ. The experiments revealed that purified Hbs from the various mouse strains did not exhibit substantial variation in O(2)-binding properties, but s-type Hb (which contains a single reactive β-chain cysteine residue) was far more readily oxidized to Fe(3+) metHb by H(2)O(2) than other mouse Hbs that contain two reactive β-chain cysteine residues. These results suggest that the possession of an additional reactive cysteine residue may protect against metHb formation under oxidizing conditions. The allelic differences in β-globin cysteine content could affect aspects of redox signaling and oxidative/nitrosative stress responses that are mediated by Hb-S-nitrosylation and Hb-S-glutathionylation pathways.

Determination of reduced nicotinamide adenine dinucleotide phosphate concentration using high-performance liquid chromatography with fluorescence detection: ratio of the reduced form as a biomarker of oxidative stress

Reduced nicotinamide adenine dinucleotide phosphate (NADPH) is the principal source of reducing power in numerous processes of physiological importance. We examined the influence of oxidative stress on the relative amounts of NADPH in human red blood cells (RBCs). To determine the homeostasis of the NADPH existing in the reduced form following oxidation, we developed an improved method for measurement of NADPH in human RBCs using high-performance liquid chromatography (HPLC). The present method with fluorescent detection is reproducible and selective than enzymatic cycling method and HPLC methods with spectrometric detection. The calibration curve is linear over the range of 0.1-5.0 muM with a correlation coefficient of 0.999. The within-run precision of the assays for total NADPH (NADPH+NADP(+)) and NADPH concentrations in human RBC were 2.4% and 8.6%, respectively (n=5). After the RBC suspension was exposed to tert-butyl hydroperoxide (t-BHP), which is scavenged by glutathione peroxidase (GPX) along with NADPH consumption, a significant decrease in the NADPH ratio [(NADPH/(NADPH+NADP(+))] was observed after a transient decrease and rapid recovery of the reduced form of glutathione. The marked decrease in the NADPH ratio induced by t-BHP exposure was observed in the absence of glucose. However, the NADPH ratio was not decreased by t-BHP exposure after pre-treatment with a glutathione reductase inhibitor. This method may be useful for the measurement of small amounts of NADPH from various biological sources.

Effects of aging on antioxidant response and phagocytosis in senescent erythrocytes

Red blood cell (RBC) aging is a complex process affected by immunological and biochemical parameters. In this work we studied the antioxidant response in RBC of different ages. We also investigated their interaction with peripheral blood monocytes. Anticoagulated blood samples from 19 O RhD+ volunteers' donors were processed. Young (Y) RBC and Senescent (Se) RBC were obtained by self-formed gradients of Percoll. The fractionation of the erythrocytes suspensions was demonstrated by statistically significant density-related changes in hematological determinations. Activities of glucose-6-phosphate dehydrogenase (G6PD), of soluble NADH-cytochrome b5 reductase (b5Rs) and membrane-bound b5R (b5Rm) were determined spectrophotometrically. The interaction between monocytes and different RBC suspensions was evaluated by the erythrophagocytosis assay. The G6PD and b5Rm activities in SeRBC were significantly lower than that observed in YRBC. No differences were found in the b5Rs of both groups. We observed an increased rate of erythrophagocytosis the SeRBC compared to YRBC. The decline in the activities of G6PD and b5Rm would indicate a decrease in the antioxidant response associated to RBC aging. These findings would signify that the oxidative changes of membrane occurring during the life span of the RBC might be relevant in the process of removal of SeRBC from the circulation.

Biopreservation of red blood cells--the struggle with hemoglobin oxidation

One of the least recognized causes of cellular damage during ex vivo preservation of red blood cells is oxidative injury to the hemoglobin. The latter has been associated with hemolysis through the release of toxic substances and oxidation of vital cell components. This review delineates some of the major pathways that link hemoglobin oxidation and cellular damage, and summarizes the incidence of red blood cell oxidative injury during hypothermic storage, cryopreservation and desiccation stress. Red blood cell hypothermic storage, despite its success, is not exempt from oxidative injury. Growing evidence portrays a time-dependant oxidative assault including formation of reactive oxygen species, attachment of denatured hemoglobin to membrane phospholipids and the release of hemoglobin-containing membrane microvesicles throughout storage. Similar symptoms have been observed in attempts to stabilize red blood cells in the dried state, in which methemoglobin levels of reconstituted red blood cells reached 50%. Factors affecting the rate of hemoglobin oxidation during red blood cell ex vivo storage include compromised antioxidant activity, high concentrations of glucose in the storage media and the presence of molecular oxygen. Hemoglobin oxidation largely dictates our ability to effectively preserve red blood cells. Understanding its origins along with investigating methods to minimize it can significantly improve the quality of our future blood products.

Detection of protein glutathionylation

Recent studies indicate that protein glutathionylation is an important regulatory mechanism. The develop-ment of redox proteomics techniques to identify proteins undergoing glutathionylation has a key role in defining the importance of this post-translational modification, although the available methods are not yet comparable to those for the study of other modifications like phosphorylation. We describe here methods that have been successfully employed to identify in vitro glutathionylated proteins.

Clotrimazole enhances lysis of human erythrocytes induced by t-BHP

Clotrimazole (CLT) is an antifungal and antimalarial agent also effective as a Gardos channel inhibitor. In addition, CLT possesses antitumor properties. Recent data provide evidence that CLT forms a complex with heme (hemin), which produces a more potent lytic effect than heme alone. This study addressed the effect of CLT on the lysis of normal human erythrocytes induced by tert-butyl hydroperoxide (t-BHP). For the first time, it was shown that 10 microM CLT significantly enhanced the lytic effect of t-BHP on erythrocytes in both Ca(2+)-containing and Ca(2+)-free media, suggesting that the effect is not related to Gardos channels. CLT did not affect the rate of free radical generation, the kinetics of GSH degradation, methemoglobin formation and TBARS generation; therefore, we concluded that CLT does not cause additional oxidative damage to erythrocytes treated with t-BHP. It is tempted to speculate that CLT enhances t-BHP-induced changes in erythrocyte volume and lysis largely by forming a complex with hemin released during hemoglobin oxidation in erythrocytes: the CLT-hemin complex destabilizes the cell membrane more potently than hemin alone. If so, the effect of CLT on cell membrane damage during free-radical oxidation may be used to increase the efficacy of antitumor therapy.

Protection of wheat bran feruloyl oligosaccharides against free radical-induced oxidative damage in normal human erythrocytes

The present work assessed the protective effect of water-soluble feruloyl oligosaccharides (FSH), ferulic acid ester of oligosaccharides from wheat bran, against in vitro oxidative damage of normal human erythrocytes induced by a water-soluble free radical initiator, 2,2'-azobis-2-amidinopropane dihydrochloride (AAPH). In the whole process of AAPH-initiated oxidation, hemolysis occurred quickly after the lag time. The rate of hemolysis is correlated dose-dependently with AAPH concentration. Significant decrease in reduced glutathione (GSH) levels of erythrocyte with concomitant enhancement in oxidized gluthione (GSSG) levels was noticed. It was also observed that lipid and protein peroxidation of erythrocytes induced by AAPH was significantly increased, and scanning electron microscopy observations showed that AAPH induced obvious morphological alteration in the erythrocytes from a smooth discoid to an echinocytic form. FSH suppressed depletion of GSH, lipid peroxidation, and methaemoglobin and protein carbonyl group formation of erythrocytes in concentration- and time-dependent manners, remarkably delayed AAPH-induced hemolysis. Morphological changes to erythrocyte caused by AAPH were effectively protected by FSH. It was also observed that FSH could work synergistically with endogenous antioxidants in erythrocytes. These results indicated that FSH efficiently protected normal human erythrocytes against oxidative stress, and they could be used as a potential source of natural antioxidants.

Methods for analysis of protein glutathionylation and their application to photosynthetic organisms

Protein S-glutathionylation, the reversible formation of a mixed-disulfide between glutathione and protein thiols, is involved in protection of protein cysteines from irreversible oxidation, but also in protein redox regulation. Recent studies have implicated S-glutathionylation as a cellular response to oxidative/nitrosative stress, likely playing an important role in signaling. Considering the potential importance of glutathionylation, a number of methods have been developed for identifying proteins undergoing glutathionylation. These methods, ranging from analysis of purified proteins in vitro to large-scale proteomic analyses in vivo, allowed identification of nearly 200 targets in mammals. By contrast, the number of known glutathionylated proteins is more limited in photosynthetic organisms, although they are severely exposed to oxidative stress. The aim of this review is to detail the methods available for identification and analysis of glutathionylated proteins in vivo and in vitro. The advantages and drawbacks of each technique will be discussed as well as their application to photosynthetic organisms. Furthermore, an overview of known glutathionylated proteins in photosynthetic organisms is provided and the physiological importance of this post-translational modification is discussed.

Molecular mechanisms and potential clinical significance of S-glutathionylation

Protein S-glutathionylation, the reversible binding of glutathione to protein thiols (PSH), is involved in protein redox regulation, storage of glutathione, and protection of PSH from irreversible oxidation. S-Glutathionylated protein (PSSG) can result from thiol/disulfide exchange between PSH and GSSG or PSSG; direct interaction between partially oxidized PSH and GSH; reactions between PSH and S-nitrosothiols, oxidized forms of GSH, or glutathione thiyl radical. Indeed, thiol/disulfide exchange is an unlikely intracellular mechanism for S-glutathionylation, because of the redox potential of most Cys residues and the GSSG export by most cells as a protective mechanism against oxidative stress. S-Glutathionylation can be reversed, following restoration of a reducing GSH/GSSG ratio, in an enzyme-dependent or -independent manner. Currently, definite evidence of protein S-glutathionylation has been clearly demonstrated in few human diseases. In aging human lenses, protein S-glutathionylation increases; during cataractogenesis, some of lens proteins, including alpha- and beta-crystallins, form both mixed disulfides and disulfide-cross-linked aggregates, which increase with cataract severity. The correlation of lens nuclear color and opalescence intensity with protein S-glutathionylation indicates that protein-thiol mixed disulfides may play an important role in cataractogenesis and development of brunescence in human lenses. Recently, specific PSSG have been identified in the inferior parietal lobule in Alzheimer's disease. However, much investigation is needed to clarify the actual involvement of protein S-glutathionylation in many human diseases.

Protein glutathionylation and oxidative stress

Liquid chromatography/electrospray ionization-mass spectrometry (LC/ESI-MS) demonstrated that glutathionyl hemoglobin (Hb) levels are increased in patients with diabetes, hyperlipidemia, uremia and Friedreich's ataxia. Glutathionylation of Hb is enhanced by oxidative stress. High performance liquid chromatography (HPLC) and matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF-MS) have also been developed for the quantification of glutathionyl Hb. Glutathionyl-lens proteins were detected in uremic patients and cataractous aged subjects. Glutathionylation of numerous enzymes is induced by oxidative stress, reduces their catalytic activities and may be involved in protection from the damaging effects of oxidative agents. Thioredoxin, glutaredoxin (thioltransferase) and protein disulfide isomerase are the key enzymes in controlling cellular oxidative stress that catalyze reduction of glutathionyl protein disulfide bonds. Thus, protein glutathionylation is closely associated with oxidative stress.

Interaction of Arsine with Hemoglobin in Arsine-Induced Hemolysis

The mechanism of arsine (AsH3) toxicity is not completely understood, but hemoglobin (Hb) has long been recognized as a necessary component of the overall mechanism of AsH3-induced hemolysis. In this study, the role of Hb in AsH3-induced hemolysis was investigated. The purpose was to determine whether exposure to AsH3 altered the structure of the heme or globin constituents of Hb. Arsine was incubated with isolated, human oxyhemoglobin (oxyHb) and carboxyhemoglobin (carboxyHb), and the release of heme and formation of AsH3-induced hemoglobin modifications were examined. Arsine increased the amount of heme released from oxyHb by 18%. When carboxyHb was incubated with AsH3, there was no change in heme release, suggesting that the sixth ligand position on the heme iron may be critical in the interaction with AsH3. Arsine-Hb interactions were studied by mass spectral analysis of heme, alpha-chain globin, and beta-chain globin. Arsine had no significant effect on the alpha- or beta-chain LCMS spectra in oxyHb and carboxyHb, but in oxyHb, arsine consistently increased the frequency of methyl acetate ion fragment (.CH2OOH, m/z = 59) loss from heme in the matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS) spectra. The formation of Hb-protein crosslinks was investigated by Western blotting using an anti-Hb antibody in isolated membranes from AsH3-treated erythrocytes, but no Hb-membrane adducts were found. These results suggest that the interaction between AsH3 and hemoglobin result in an increase in heme release which may contribute to the hemolytic mechanism of AsH3.

Rat, caprine, equine and bovine erythrocyte ghosts exposed to t-butyl hydroperoxide as a model to study lipid peroxidation using a chemiluminescence assay

The aim of the present study was to analyze the time-course of t-butyl hydroperoxide-induced changes in lipid peroxidation, fatty acid composition and chemiluminescence intensity in rat, caprine, equine and bovine erythrocyte ghosts. A relatively high content of arachidonic acid (C20:4 n6) and docosahexaenoic acid (C22:6 n3) was characteristic of the rat erythrocyte ghosts. The fatty acid composition of native erythrocyte ghosts obtained from caprine, equine and bovine was characterized by a high content of oleic acid (C18:1 n9) and a low content of the peroxidable polyunsaturated fatty acids (C20:4 n6 and C22:6 n3). The proportion of linoleic acid (C18:2 n6) was higher in equine and bovine compared to rat and caprine. Increase in lipid peroxidation in rat erythrocyte ghosts was maximal within 12 min of incubation, t-butyl hydroperoxide concentration dependent and was paralleled by a decrease in C18:2 n6, C20:4 n6 and C22:6 n3 and an increase in chemiluminescence formation. Polyunsaturated fatty acids (PUFAs) present in rat erythrocyte ghosts exhibit the highest sensitivity to oxidative damaged and their sensitivity increases as a power function of the number of double bonds per fatty acid molecule. Light emission in caprine, equine and bovine erythrocyte ghosts was very low, t-butyl hydroperoxide concentration-dependent but changes in fatty acid composition were not observed. The main conclusion of this work is that a low unsaturation degree of fatty acids in erythrocyte ghosts of caprine, equine and bovine prevent the lipid peroxidation on those membranes when they are incubated with t-butyl hydroperoxide.

Different types of glutathionylation of hemoglobin can exist in intact erythrocytes

Glutathionylation of hemoglobin (Hb) was studied by incubation of intact human erythrocytes with 1 mM tert-butylhydroperoxide (tBHP). Electrophoresis of the membranes showed a time dependent increase of membrane-bound Hb alpha chain until 10 min, and immunoblotting study showed that membrane-bound Hb alpha chain reacted with anti-glutathione antibody only after 10 min. Concomitant with the Hb alpha chain, membrane associated actin, spectrin, and glyceraldehyde 3-phosphate dehydrogenase reacted with the antibody. Cytosolic Hb of the control erythrocytes reacted with anti-glutathione antibody. Together with our previous paper, the present study indicates that at least three different types of glutathionylation of Hb can exist in erythrocytes. The first type is a mixed disulfide bond between reduced glutathione (GSH) and normal Hb. The second type is a disulfide bond between the cysteine 93 of metHb beta chain and oxidized glutathione (GSSG), and the third type is a disulfide bond between the other cysteine residues of metHb alpha chain and/or metHb beta chain and GSSG.