The Efficacy of Reducing Agents or Antioxidants in Blocking the Formation of Dense Cells and Irreversibly Sickled Cells In Vitro

Phenotypic analysis of erythrocytes in sickle cell disease using imaging flow cytometry

The morphology and other phenotypic characteristics of erythrocytes in sickle cell disease (SCD) have been analyzed for decades in patient evaluation. This involves a variety of techniques, including microscopic analysis of stained blood films, flow cytometry, and cell counting. Here, we analyzed SCD blood using imaging flow cytometry (IFC), a technology that combines flow cytometry and microscopy to enable simultaneous rapid-throughput analysis of cellular morphology and cell-surface markers. With IFC, we were able to automate quantification of poikilocytes from SCD blood. An important subpopulation of poikilocytes represented dense cells, although these could not be distinguished from other poikilocytes without first centrifuging the blood through density gradients. In addition, CD71-positive RBCs from SCD patients had two subpopulations: one with high CD71 expression and a puckered morphology and another with lower CD71 expression and biconcave morphology and presumably representing a later stage of differentiation. Some RBCs with puckered morphologies that were strongly positive for DAPI and CD49d were in fact nucleated RBCs. IFC identified more phosphatidylserine-expressing red cells in SCD than did conventional flow cytometry and these could also be divided into two subpopulations. One population had diffuse PS expression and appeared to be composed primarily of RBC ghosts; the other had lower overall PS expression present in intense, punctate dots overlying Howell-Jolly bodies. This study demonstrates that IFC can rapidly reveal and quantify RBC features in SCD that require numerous tedious methods to identify conventionally. Thus, IFC is likely to be a useful technique for evaluating and monitoring SCD.

Interleukin-1 receptor antagonism leads to improved anaemia in a murine model of sickle cell disease and is associated with reduced ex vivo platelet-mediated erythrocyte sickling

Sickle cell disease (SCD) is associated with haemolytic anaemia and secondary activation of leucocytes and platelets, which in turn may further exacerbate haemolysis. As cytokine signalling pathways may participate in this cycle, the present study investigated whether pharmacological blockade of the interleukin-1 receptor (IL-1R) would mitigate anaemia in a murine model of SCD. Within 2 weeks of treatment, reduced markers of haemolysis were observed in anakinra-treated mice compared to vehicle-treated mice. After 4 weeks of anakinra treatment, mice showed increased numbers of erythrocytes, haemoglobin, and haematocrit, along with reduced reticulocytes. Blood from anakinra-treated mice was less susceptible to ex vivo erythrocyte sickling and was resistant to exogenous IL-1β-mediated sickling. Supernatant generated from IL-1β-treated platelets was sufficient to promote erythrocyte sickling, an effect not observed with platelet supernatant generated from IL-1R^-/- mice. The sickling effect of IL-1β-treated platelet supernatant was inhibited by a transforming growth factor-β (TGF-β) neutralising antibody, nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibition, and superoxide scavengers, but replicated by recombinant TGF-β. In conclusion, pharmacological IL-1R antagonism leads to improved anaemia in a murine SCD model. IL-1β stimulation of platelets promotes erythrocyte sickling. This effect may be mediated by platelet-derived TGF-β-induced reactive oxygen species generation though erythrocyte NADPH oxidase.

Facile L-Glutamine delivery to erythrocytes via DOPC-DPPG mixed liposomes

Sickle cell disease (SCD) is a mortal erythrocyte-based disease which is hard to treat effectively. Development of a treatment method that can prevent deoxygenation of erythrocytes or reduce the oxidative stress of sickle erythrocytes is one of the important issues towards SCD. Among a wide variety of potential drug carriers, liposomes are advantageous and preferable with their easy preparation and biocompatibility. In this study, L-Glutamine (Gln) loaded liposomes were prepared with 1,2-Dioleoyl-sn-glycero-3-phosphocholine (DOPC) and 1,2-Dioleoyl-sn-glycero-3-phospho-rac-(1-glycerol) sodium salt (DPPG). Liposomes were characterized via zeta potential, size measurements, differential scanning calorimetry, Fourier Transform Infra-red Spectroscopy and they were visualized via transmission electron microscopy and scanning electron microscopy. Effect of the encapsulated amount of Gln was investigated by encapsulating Gln at three different concentrations (i.e0.20 mM, 40 mM and 60 mM). Drug encapsulation and release studies were implemented with high pressure liquid chromatography (HPLC). The encapsulation efficiency of Gln was determined to be the higher than the ones reported in the literature: 83.6%, 87.1% and 84.9% for 20 mM, 40 mM and 60 mM Gln, respectively. It was found that after 6 hours, liposomes loaded with 60 mM of Gln had released 45.7% of Gln. Optical microscopy images of the erythrocytes after 3 hours of incubation and haemolysis measurements proved that presence of liposomes did not cause any structural changes on the erythrocyte shape. Overall, it was concluded that L-Gln loaded PC/PG liposomes provide promising results in terms of developing a new drug delivery platform for SCD.

Effects of three months of treatment with vitamin E and N-acetyl cysteine on the oxidative balance in patients with transfusion-dependent β-thalassemia

Oxidative stress is a major mechanism contributing to the progression of β-thalassemia. To assess the effect of vitamin E and N-acetyl cysteine (NAC) as antioxidant agents on total oxidative stress (TOS) status and total antioxidant capacity (TAC) in patients with transfusion-dependent β-thalassemia (TDT). In this open-label randomized controlled trial, from May to August 2019, 78 eligible patients with TDT over the age of 18 were enrolled. All patients were registered at the Thalassemia Clinic of Shiraz University of Medical Sciences in Southern Iran. Patients were randomly allocated to the NAC group (10 mg/kg/day, orally), vitamin E group (10 U/kg/day, orally), and control group. The duration of the study was 3 months. The mean age of the participants was 28.5 ± 5.1 (range: 18-41) years. At the end of the study, TOS significantly decreased only in the vitamin E group (mean difference (MD), 95% confidence interval (CI): 0.27 (0.03-0.50), P = 0.026). TAC significantly decreased in both supplemented groups at the 3rd month of treatment (NAC group: MD (95% CI): 0.11 (0.04-0.18), P = 0.002 and vitamin E group: 0.09 (0.01-0.16), P = 0.022 respectively). Hemoglobin did not significantly change at the end of the study in each group (P > 0.05). Mild transient adverse events occurred in 4 patients of the NAC group and 5 patients of the vitamin E group with no need to discontinue the treatment. Vitamin E can be a safe and effective supplement in improving oxidative stress in patients with TDT. Moreover, it seems that a longer duration of using antioxidant supplements needs to make clinical hematologic improvement in TDT patients.

The Toxicity Effect of Echium amoenum on the Liver and Kidney of Mice

AIMS

The aim of this study was to investigate the toxic effect of Echium amoenum plants on the liver and kidney of the animal model.

BACKGROUND

Echium amoenum is one of the medicinal plants containing pyrrolizidine alkaloids with several properties which has widely consumed among different communities.

OBJECTIVE

The toxic effects of Echium amoenum on the liver and kidney were investigated in this study.

METHODS

Sixty mice were kept for 28 days under the appropriate laboratory conditions. Echium amoenum extract (25, 12.5, 50 mg / kg, ip.) was administered for 28 days. At the end of the experiment, blood samples were drawn and liver and kidneys were removed for evaluating hepatotoxicity and nephrotoxicity of extract. Additionally, experiments were conducted to assay the enzymatic and oxidative activities.

RESULTS

There was no significant difference in the levels of copper ion in the liver and kidneys among all groups. There was a significant difference in the levels of lipid peroxidation in the liver of treated groups versus the control group. The significant difference was not observed in the levels of glutathione of the liver of all groups. However, the levels of glutathione of the kidney significantly decreased in the treated groups versus the control group. There was no significant difference in the liver enzymes, including ALP, SGOT, and SGPT, between all groups. This indicates that damage increases with enhancing the time and concentrations of the extract. Biochemical analysis showed the creatinine and urea levels did not change in the treated groups versus the control group.

CONCLUSION

According to the present findings, it is suggested that Echium amoenum causes hepatotoxicity and nephrotoxicity effects in dose and time-dependent manner.

Pathophysiology and recent therapeutic insights of sickle cell disease

Sickle cell disease (SCD) is an autosomal recessive blood disorder which occurs due to point mutation in the β-globin chain of hemoglobin. Since the past decades, various therapies have been put forth, which are based on obstructing pathophysiological mechanisms of SCD including inhibition of Gardos channel and cation fluxes which in turn prevents sickle erythrocyte destruction and dehydration. The pharmacological approaches are based on the mechanism of reactivating γ-globin expression by utilizing fetal hemoglobin (HbF)-inducing drugs such as hydroxyurea. In SCD, gene therapy could be considered as a promising tool which involves modifying mutation at the gene-specific target by either promoting insertion or deletion of globins. Although there are various therapies emerged so far in the treatment of SCD, many of them have faced a major setback in most of developing countries in terms of cost, unavailability of expertise, and suitable donor. Therefore, in addition to pathophysiological aspects, this review will discuss new advancements and approaches made in the therapeutic domain of SCD including a viewpoint of modulating hemoglobin in SCD by the intervention of probiotics.

Emerging therapies in sickle cell disease

Despite sickle cell disease (SCD) being the most common and severe inherited condition worldwide, therapeutic options are limited. To date, hydroxyurea remains the main treatment option in SCD. However, in the last decade the numbers of interventional clinical trials focussing on therapies for SCD have increased significantly. Many new drugs with various pharmacological targets have emerged and, although the majority have failed to show benefit in clinical trials, some have produced encouraging results. It seems probable that more drugs will soon become available for the treatment of SCD. Furthermore, promising clinical trials with improved outcomes have recently changed the perspective of curative therapies in SCD. Nevertheless, the application of novel therapeutic agents and potential curative treatments will most likely be limited to high-income countries and, thus, will remain unavailable for the majority of people with SCD in the foreseeable future.

The Spectrinome: The Interactome of a Scaffold Protein Creating Nuclear and Cytoplasmic Connectivity and Function

We provide a review of Spectrin isoform function in the cytoplasm, the nucleus, the cell surface, and in intracellular signaling. We then discuss the importance of Spectrin’s E2/E3 chimeric ubiquitin conjugating and ligating activity in maintaining cellular homeostasis. Finally we present spectrin isoform subunit specific human diseases. We have created the Spectrinome, from the Human Proteome, Human Reactome and Human Atlas data and demonstrated how it can be a useful tool in visualizing and understanding spectrins myriad of cellular functions.

Impact statement

Spectrin was for the first 12 years after its discovery thought to be found only in erythrocytes. In 1981, Goodman and colleagues1found that spectrin-like molecules were ubiquitously found in non-erythroid cells leading to a great multitude of publications over the next thirty eight years. The discovery of multiple spectrin isoforms found associated with every cellular compartment, and representing 2-3% of cellular protein, has brought us to today’s understanding that spectrin is a scaffolding protein, with its own E2/E3 chimeric ubiquitin conjugating ligating activity that is involved in virtually every cellular function. We cover the history, localized functions of spectrin isoforms, human diseases caused by mutations, and provide the spectrinome: a useful tool for understanding the myriad of functions for one of the most important proteins in all eukaryotic cells.

The Effect of Antioxidants on the Properties of Red Blood Cells From Patients With Sickle Cell Anemia

Oxidative damage to red blood cells (RBCs) may contribute to pathogenesis of sickle cell anemia. Reducing the deleterious effects of oxidants by exposing RBCs to a number of antioxidants has been shown to have protective effects against lipid and protein peroxidation. We hypothesize that antioxidants may also have beneficial effects on the abnormal membrane permeability of sickle cells. Increased cation permeability of these cells encourages HbS polymerization by causing RBC dehydration and also leads to externalization of the prothrombotic aminophospholipid phosphatidylserine (PS). Three antioxidants with different mechanisms of action were investigated - dithiothreitol, N-acetylcysteine, and quercetin. All three were found to inhibit the main cation pathways responsible for dehydration - the deoxygenation-induced cation conductance (or Psickle), the Ca2+-activated K+ channel (or Gardos channel), and the K+-Cl- cotransporter. They also reduced Ca2+-induced PS exposure and hemolysis. Findings provide evidence for additional beneficial actions of antioxidants in maintenance of rheology and reducing vascular adhesion and further inform the rationale for their clinical use.

Advances in the Treatment of Sickle Cell Disease

Sickle cell disease (SCD) is a monogenic disorder that afflicts approximately 100,000 Americans and millions of people worldwide. It is characterized by hemolytic anemia, vaso-occlusive crises, relentless end-organ injury, and premature death. Currently, red blood cell transfusion and hydroxyurea are the major disease-modifying therapies available for SCD. Hematopoetic stem cell transplant is curative, but barriers to treatment are substantial and include a lack of suitable donors, immunologic transplant rejection, long-term adverse effects, prognostic uncertainty, and poor end-organ function, which is especially problematic for older patients. Gene therapy to correct the β^s point mutation is under investigation as another curative modality. Deeper insights into the pathophysiology of SCD have led to the development of novel agents that target cellular adhesion, inflammation, oxidant injury, platelets and/or coagulation, vascular tone, and hemoglobin polymerization. These agents are in preclinical and clinical trials. One such agent, L-glutamine, decreases red blood cell oxidant injury and is recently US Food and Drug Administration approved to prevent acute pain episodes of SCD in patients 5 years of age or older. The purpose of this review is to describe the currently established therapies, barriers to curative therapies, and novel therapeutic agents that can target sickle cell hemoglobin polymerization and/or its downstream sequelae. A PubMed search was conducted for articles published up to May 15, 2018, using the search terms sickle cell disease, novel treatments, hematopoietic stem cell transplantation, and gene therapy. Studies cited include case series, retrospective studies, prospective clinical trials, meta-analyses, online abstracts, and original reviews.

The Effect of Borage (Echium amoenum) on the Mouse Heart and Hematology Parameters

BACKGROUND

There has been considerable interest in the potential health benefits of borage. Little information is available regarding the safety of this plant. The purpose of this study was to evaluate the impact of borage on the mouse heart.

METHODS

Different amounts of borage extract were injected in mice. The mice were randomly divided into 4 groups including group1 (Control group without injection), group2, 3 and 4 that received 12.5 mg/kg, 25 mg/kg and 50 mg/kg respectively for 28 days. Oxidative stress parameters (lipid peroxidation, total glutathione groups assay and cupric assay) and biochemical (Creatine kinase activity and total cholesterol) and hematology parameters were evaluated. Furthermore, histopathology study was carried out on heart tissues.

RESULTS

We found that there was no significant difference in oxidative stress parameters and biochemical parameters between the control group and the groups that received different amounts of borage extract. There were also no changes in histopathology study. In blood parameters, the level of erythrocytes, hematocrit and hemoglobin decreased to 50mg/kg, whereas the level of MCH and MCV decreased in high doses.

CONCLUSION

This article suggested that borage did not cause significant damage to the heart tissue in mice model. In hematology factors, significant changes were observed in erythrocytes and related parameters. Therefore, hematotoxicity of consumption this plant should be considered at high doses.

Drugs for preventing red blood cell dehydration in people with sickle cell disease

BACKGROUND

Sickle cell disease is an inherited disorder of hemoglobin, resulting in abnormal red blood cells. These are rigid and may block blood vessels leading to acute painful crises and other complications. Recent research has focused on therapies to rehydrate the sickled cells by reducing the loss of water and ions from them. Little is known about the effectiveness and safety of such drugs. This is an updated version of a previously published review.

OBJECTIVES

To assess the relative risks and benefits of drugs to rehydrate sickled red blood cells.

SEARCH METHODS

We searched the Cochrane Cystic Fibrosis and Genetic Disorders Group's Haemoglobinopathies Trials Register. We also searched online trials registries for any ongoing trials (01 July 2018).Last search of the Group's Haemoglobinopathies Trials Register: 08 October 2018.

SELECTION CRITERIA

Randomized or quasi-randomized controlled trials of drugs to rehydrate sickled red blood cells compared to placebo or an alternative treatment.

DATA COLLECTION AND ANALYSIS

Both authors independently selected studies for inclusion, assessed study quality and extracted data.

MAIN RESULTS

Of the 51 studies identified, three met the inclusion criteria, including 524 people with sickle cell disease aged between 12 and 65 years of age. One study tested the effectiveness of zinc sulphate as compared to placebo and the remaining two assessed senicapoc versus placebo. No deaths were seen in any of the studies (low-quality evidence). The zinc sulphate study showed a significant reduction in painful crises (in a total of 145 participants) over one and a half years, mean difference -2.83 (95% confidence interval -3.51 to -2.15) (moderate-quality evidence). However, analysis was restricted due to limited statistical data. Changes to red blood cell parameters and blood counts were inconsistent (very low-quality evidence). No serious adverse events were noted in the study. The Phase II dose-finding study of senicapoc (a Gardos channel blocker) compared to placebo showed that the high dose senicapoc showed significant improvement in change in hemoglobin level, the number and proportion of dense red blood cells, red blood cell count and indices and hematocrit value (very low-quality evidence). The results with low-dose senicapoc were similar to the high-dose senicapoc group but of lesser magnitude. There was no difference in the frequency of painful crises between the three groups (low-quality evidence). A subsequent Phase III study of senicapoc was terminated early since there was no difference observed between the treatment and control groups in the primary end point of painful crises.

AUTHORS' CONCLUSIONS

While the results of zinc for reducing sickle-related crises are encouraging, larger and longer-term multicenter studies are needed to evaluate the effectiveness of this therapy for people with sickle cell disease.While the Phase II and the prematurely terminated phase III studies of senicapoc showed that the drug improved red blood cell survival (depending on dose), this did not lead to fewer painful crises.Given this is no longer an active area of research, this review will no longer be regularly updated.

Drugs for preventing red blood cell dehydration in people with sickle cell disease

BACKGROUND

Sickle cell disease is an inherited disorder of hemoglobin, resulting in abnormal red blood cells. These are rigid and may block blood vessels leading to acute painful crises and other complications. Recent research has focused on therapies to rehydrate the sickled cells by reducing the loss of water and ions from them. Little is known about the effectiveness and safety of such drugs. This is an updated version of a previously published review.

OBJECTIVES

To assess the relative risks and benefits of drugs to rehydrate sickled red blood cells.

SEARCH METHODS

We searched the Cochrane Cystic Fibrosis and Genetic Disorders Group's Haemoglobinopathies Trials Register.Last search of the Group's Trials Register: 28 November 2015.

SELECTION CRITERIA

Randomized or quasi-randomized controlled trials of drugs to rehydrate sickled red blood cells compared to placebo or an alternative treatment.

DATA COLLECTION AND ANALYSIS

Both authors independently selected studies for inclusion, assessed study quality and extracted data.

MAIN RESULTS

Of the 51 studies identified, three met the inclusion criteria. The first study tested the effectiveness of zinc sulphate to prevent sickle cell-related crises in a total of 145 participants and showed a significant reduction in painful crises over one and a half years, mean difference -2.83 (95% confidence interval -3.51 to -2.15). However, analysis was restricted due to limited statistical data. Changes to red cell parameters and blood counts were inconsistent. No serious adverse events were noted in the study.The second study was a Phase II dose-finding study of senicapoc (a Gardos channel blocker) compared to placebo. Compared to the placebo group the high dose senicapoc showed significant improvement in change in hemoglobin level, number and proportion of dense red blood cells, red blood cell count and indices and hematocrit. The results with low-dose senicapoc were similar to the high-dose senicapoc group but of lesser magnitude. There was no difference in the frequency of painful crises between the three groups. A subsequent Phase III study of senicapoc was terminated early since there was no difference observed between the treatment and control groups in the primary end point of painful crises.

AUTHORS' CONCLUSIONS

While the results of zinc for reducing sickle-related crises are encouraging, larger and longer-term multicenter studies are needed to evaluate the effectiveness of this therapy for people with sickle cell disease.While the Phase II and the prematurely terminated phase III studies of senicapoc showed that the drug improved red cell survival (depending on dose), this did not lead to fewer painful crises.We will continue to run searches to identify any potentially relevant trials; however, we do not plan to update other sections of the review until new trials are published.

Spectrin's chimeric E2/E3 enzymatic activity

In this minireview, we cover the discovery of the human erythrocyte α spectrin E2/E3 ubiquitin conjugating/ligating enzymatic activity and the specific cysteines involved. We then discuss the consequences when this activity is partially inhibited in sickle cell disease and the possibility that the same attenuation is occurring in multiple organ dysfunction syndrome. We finish by discussing the reasons for believing that nonerythroid α spectrin isoforms (I and II) also have this activity and the importance of testing this hypothesis. If correct, this would suggest that the nonerythroid spectrin isoforms play a major role in protein ubiquitination in all cell types. This would open new fields in experimental biology focused on uncovering the impact that this enzymatic activity has upon protein-protein interactions, protein turnover, cellular signaling, and many other functions impacted by spectrin, including DNA repair.

Potential utility of melatonin as an antioxidant therapy in the management of sickle cell anemia

This study aimed to assess antioxidant effects of melatonin treatment compared to N-acetylcysteine (NAC) and to their combination in a sickle cell suspension. Sickle erythrocytes were suspended in phosphate-buffered saline, pH 7.4, composing external control group. They were also suspended and incubated at 37°C either in the absence (experimental control group) or in the presence of NAC, melatonin and their combination at concentrations of 100 pm, 100 nm and 100 μm for 1 hr (treatment groups). The melatonin influences were evaluated by spectrophotometric [hemolysis degree, catalase (CAT), glutathione S-transferase (GST), glutathione peroxidase (GPx), glutathione reductase (GR), glucose-6-phosphate dehydrogenase (G6PDH), and superoxide dismutase (SOD) activities] and chromatographic methods [glutathione (GSH) and malondialdehyde (MDA) levels]. Incubation period was able to cause a rise about 64% on hemolysis degree as well as practically doubled the lipid peroxidation levels (P < 0.01). However, almost all antioxidants tested treatments neutralized this incubation effect observed in MDA levels. Among the antioxidant biomarkers evaluated, we observed a modulating effect of combined treatment on GPx and SOD activities (P < 0.01), which showed ~25% decrease in their activities. In addition, we found an antioxidant dose-dependent effect for melatonin on lipid peroxidation (r = -0.29; P = 0.03) and for combined antioxidant treatments also on MDA levels (r = -0.37; P = 0.01) and on SOD activity (r = -0.54; P < 0.01). Hence, these findings contribute with important insight that melatonin individually or in combination with NAC may be useful for sickle cell anemia management.

Oxidative stress in sickle cell disease: an overview of erythrocyte redox metabolism and current antioxidant therapeutic strategies

Erythrocytes have an environment of continuous pro-oxidant generation due to the presence of hemoglobin (Hb), which represents an additional and quantitatively significant source of superoxide (O2(-)) generation in biological systems. To counteract oxidative stress, erythrocytes have a self-sustaining antioxidant defense system. Thus, red blood cells uniquely function to protect Hb via a selective barrier allowing gaseous and other ligand transport as well as providing antioxidant protection not only to themselves but also to other tissues and organs in the body. Sickle hemoglobin molecules suffer repeated polymerization/depolymerization generating greater amounts of reactive oxygen species, which can lead to a cyclic cascade characterized by blood cell adhesion, hemolysis, vaso-occlusion, and ischemia-reperfusion injury. In other words, sickle cell disease is intimately linked to a pathophysiologic condition of multiple sources of pro-oxidant processes with consequent chronic and systemic oxidative stress. For this reason, newer therapeutic agents that can target oxidative stress may constitute a valuable means for preventing or delaying the development of organ complications.

The proteomics and interactomics of human erythrocytes

In this minireview, we focus on advances in our knowledge of the human erythrocyte proteome and interactome that have occurred since our seminal review on the topic published in 2007. As will be explained, the number of unique proteins has grown from 751 in 2007 to 2289 as of today. We describe how proteomics and interactomics tools have been used to probe critical protein changes in disorders impacting the blood. The primary example used is the work done on sickle cell disease where biomarkers of severity have been identified, protein changes in the erythrocyte membranes identified, pharmacoproteomic impact of hydroxyurea studied and interactomics used to identify erythrocyte protein changes that are predicted to have the greatest impact on protein interaction networks.

Erythrocyte NADPH oxidase activity modulated by Rac GTPases, PKC, and plasma cytokines contributes to oxidative stress in sickle cell disease

Chronic inflammation has emerged as an important pathogenic mechanism in sickle cell disease (SCD). One component of this inflammatory response is oxidant stress mediated by reactive oxygen species (ROS) generated by leukocytes, endothelial cells, plasma enzymes, and sickle red blood cells (RBC). Sickle RBC ROS generation has been attributed to sickle hemoglobin auto-oxidation and Fenton chemistry reactions catalyzed by denatured heme moieties bound to the RBC membrane. In this study, we demonstrate that a significant part of ROS production in sickle cells is mediated enzymatically by NADPH oxidase, which is regulated by protein kinase C, Rac GTPase, and intracellular Ca(2+) signaling within the sickle RBC. Moreover, plasma from patients with SCD and isolated cytokines, such as transforming growth factor β1 and endothelin-1, enhance RBC NADPH oxidase activity and increase ROS generation. ROS-mediated damage to RBC membrane components is known to contribute to erythrocyte rigidity and fragility in SCD. Erythrocyte ROS generation, hemolysis, vaso-occlusion, and the inflammatory response to tissue damage may therefore act in a positive-feedback loop to drive the pathophysiology of sickle cell disease. These findings suggest a novel pathogenic mechanism in SCD and may offer new therapeutic targets to counteract inflammation and RBC rigidity and fragility in SCD.

Drugs for preventing red blood cell dehydration in people with sickle cell disease

BACKGROUND

Sickle cell disease is an inherited disorder of hemoglobin, resulting in abnormal red blood cells. These are rigid and may block blood vessels leading to acute painful crises and other complications. Recent research has focused on therapies to rehydrate the sickled cells by reducing the loss of water and ions from them. Little is known about the effectiveness and safety of such drugs.

OBJECTIVES

To assess the relative risks and benefits of drugs to rehydrate sickled red blood cells.

SEARCH METHODS

We searched the Cochrane Cystic Fibrosis and Genetic Disorders Group's Haemoglobinopathies Trials Register.Last search of the Group's Trials Register: 25 October 2011.

SELECTION CRITERIA

Randomized or quasi-randomized controlled trials of drugs to rehydrate sickled red blood cells compared to placebo or an alternative treatment.

DATA COLLECTION AND ANALYSIS

Both authors independently selected studies for inclusion, assessed study quality and extracted data.

MAIN RESULTS

Of the 51 studies identified, three met the inclusion criteria. The first study tested the effectiveness of zinc sulphate to prevent sickle cell-related crises in a total of 145 participants and showed a significant reduction in painful crises over one and a half years, mean difference -2.83 (95% confidence interval -3.51 to -2.15). However, analysis was restricted due to limited statistical data. Changes to red cell parameters and blood counts were inconsistent. No serious adverse events were noted in the study.The second study was a Phase II dose-finding study of senicapoc (a Gardos channel blocker) compared to placebo. Compared to the placebo group the high dose senicapoc showed significant improvement in change in hemoglobin level, number and proportion of dense red blood cells, red blood cell count and indices and hematocrit. The results with low-dose senicapoc were similar to the high-dose senicapoc group but of lesser magnitude. There was no difference in the frequency of painful crises between the three groups. A subsequent Phase III study of senicapoc was terminated early since there was no difference observed between the treatment and control groups in the primary end point of painful crises.

AUTHORS' CONCLUSIONS

While the results of zinc for reducing sickle-related crises are encouraging, larger and longer-term multicenter studies are needed to evaluate the effectiveness of this therapy for people with sickle cell disease.While the Phase II and the prematurely terminated phase III studies of senicapoc showed that the drug improved red cell survival (depending on dose), this did not lead to fewer painful crises.

Altered phosphorylation of cytoskeleton proteins in sickle red blood cells: the role of protein kinase C, Rac GTPases, and reactive oxygen species

The small Rho GTPases Rac1 and Rac2 regulate actin structures and mediate reactive oxygen species (ROS) production via NADPH oxidase in a variety of cells. We have demonstrated that deficiency of Rac1 and Rac2 GTPases in mice disrupts the normal hexagonal organization of the RBC cytoskeleton and reduces erythrocyte deformability. This is associated with increased phosphorylation of adducin at Ser-724, (corresponding to Ser-726 in human erythrocytes), a domain target of protein kinase C (PKC). PKC phosphorylates adducin and leads to decreased F-actin capping and dissociation of spectrin from actin, implicating a significant role of such phosphorylation in cytoskeletal remodeling. We evaluated adducin phosphorylation in erythrocytes from patients with sickle cell disease and found it consistently increased at Ser-726. In addition, ROS concentration is elevated in sickle erythrocytes by 150-250% compared to erythrocytes from normal control individuals. Here, we review previous studies demonstrating that altered phosphorylation of erythrocyte cytoskeletal proteins and increased ROS production result in disruption of cytoskeleton stability in healthy and sickle cell erythrocytes. We discuss in particular the known and potential roles of protein kinase C and the Rac GTPases in these two processes.

Drugs for preventing red blood cell dehydration in people with sickle cell disease

BACKGROUND

Sickle cell disease is an inherited disorder of hemoglobin, resulting in abnormal red blood cells. These are rigid and may block blood vessels leading to acute painful crises and other complications. Recent research has focused on therapies to rehydrate the sickled cells by reducing the loss of water and ions from them. Little is known about the effectiveness and safety of such drugs.

OBJECTIVES

To assess the relative risks and benefits of drugs to rehydrate sickled red blood cells.

SEARCH STRATEGY

We searched the Cochrane Cystic Fibrosis and Genetic Disorders Group's Haemoglobinopathies Trials Register.Last search of the Group's Trials Register: 22 May 2009.

SELECTION CRITERIA

Randomized or quasi-randomized controlled trials of drugs to rehydrate sickled red blood cells compared to placebo or an alternative treatment.

DATA COLLECTION AND ANALYSIS

Both authors independently selected studies for inclusion, assessed study quality and extracted data.

MAIN RESULTS

Of the 47 studies identified, two met the inclusion criteria. The first study tested the effectiveness of zinc sulphate to prevent sickle cell-related crises in a total of 145 participants and showed a significant reduction in painful crises over one and a half years, mean difference -2.83 (95% confidence interval -3.51 to -2.15). However, analysis was restricted due to limited statistical data. Changes to red cell parameters and blood counts were inconsistent. No serious adverse events were noted in the study.The second study was a Phase II dose-finding study of senicapoc (Gardos channel blocker) compared to placebo. Compared to the placebo group the high dose senicapoc showed significant improvement in change in hemoglobin level, number and proportion of dense red blood cells, red blood cell count and indices and hematocrit. The results with low-dose senicapoc were similar to the high-dose senicapoc group but of lesser magnitude. There was no difference in the frequency of painful crises between the three groups. A subsequent Phase III study had to be stopped prematurely due to lack of reduction in the number of painful crisis.

AUTHORS' CONCLUSIONS

While the results of zinc for reducing sickle-related crises are encouraging, larger and longer-term multicentre studies are needed to evaluate the effectiveness of this therapy for people with sickle cell disease.Though the phase II study of senicapoc showed that the drug improved red cell survival, depending on dose, this did not lead to fewer painful crises; a subsequent phase III study was terminated prematurely for this reason.

Cysteine-iron promotes arginase activity by driving the Fenton reaction

Impairment of nitric oxide bioavailability secondary to increased arginase activity and overproduction of reactive oxygen species (ROS) is thought to be a major cause of vascular complications in sickle cell disease (SCD). However, the role of ROS in the induction of arginase activity is unknown. This study investigated whether the mechanism of arginase activation involves the ROS produced during oxidative stress. Our study reveals that cysteine-iron dose-dependently stimulated arginase activity with a corresponding increase in (.)OH radical formation. The ()OH radicals produced were significantly inhibited by salicylic acid derivatives and superoxide dismutase. Surprisingly, the inhibition of (.)OH radicals parallels the inhibition of arginase activity, thus suggesting the role of cysteine-iron in the stimulation of arginase via the Fenton reaction. This is the first evidence demonstrating the participation of (.)OH radicals in the stimulation of arginase activity, and thus provides novel avenues for therapeutic modalities in hemoglobinopathies and other inflammation-mediated diseases.

Drugs for preventing red blood cell dehydration in people with sickle cell disease

BACKGROUND

Sickle cell disease is an inherited disorder of haemoglobin, which results in abnormal red blood cells. These can deform and cause blockages in blood vessels, leading to acute crises such as pain; stroke and splenic sequestration; and chronic organ and tissue damage. Recently research has begun to focus on therapies which prevent the red blood cells deforming by reducing the loss of water and ions from the cells. However, little is known about the effectiveness and safety of such drugs.

OBJECTIVES

To assess the relative risks and benefits of drugs which aim to prevent sickle cell-related crises by reducing red blood cell dehydration.

SEARCH STRATEGY

We searched the Cochrane Cystic Fibrosis and Genetic Disorders Group's Haemoglobinopathies Trials Register which comprises of references identified from comprehensive electronic database searches and handsearches of relevant journals and abstract books of conference proceedings. Date of the most recent search of the Group's Haemoglobinopathies Trials Register: November 2006.

SELECTION CRITERIA

Randomised or quasi-randomised controlled trials of drugs which aim to prevent sickle cell crises by reducing red cell dehydration, compared to placebo or an alternative treatment.

DATA COLLECTION AND ANALYSIS

Both authors independently selected studies for inclusion, assessed study quality and extracted data from the included studies.

MAIN RESULTS

Of the 39 studies identified, one met the inclusion criteria. This study tested the effectiveness of zinc sulphate to prevent sickle cell-related crises in a total of 145 participants and showed a significant reduction in the total number of pain, haemolytic, aplastic and sequestration crises over one and a half years, WMD -2.83 (95% CI -3.51 to -2.15). However, our analysis was limited by non-reporting of standard deviations for some data. Changes to red cell parameters and blood counts were inconsistent. No serious adverse events were noted in the study.

AUTHORS' CONCLUSIONS

While the results of zinc for reducing sickle-related crises are encouraging, larger and longer-term multicentre studies over a number of years are needed to evaluate the effectiveness of this therapy for people with sickle cell disease.

Oxidation-induced calcium-dependent dehydration of normal human red blood cells

Phenazine-methosulphate (PMS) is a strong oxidant that induces reactive oxygen species (ROS) formation in cells. Though it has been shown that PMS increases the red blood cell (RBC) membrane permeability to K(+), the hypotheses on the mechanism of PMS-induced effects are contradictory and there are no data on volume changes induced by this oxidant. Therefore, the influence of the PMS + ascorbate oxidative system on the volume of normal human RBCs was studied. In a Ca(2 + )-containing medium, PMS + ascorbate caused dehydration (shrinking) of RBCs judged by: (1) changes in the density and osmotic resistance distributions of RBCs, and (2) a decrease in their low-angle scattering assessed by FACS analysis. The dehydration resulted from activation of the Gardos channels, was PMS and ascorbate concentration-dependent, was associated with broadening of the density and osmotic resistance distributions of the RBCs, and decreased in the presence of the taxifolin and rutin antioxidants. These findings contribute to a better understanding of the physiology and pathology of oxidatively-modified RBCs and may be of practical significance in estimating the antioxidant activity of various substances.

Conserved actin cysteine residues are oxidative stress sensors that can regulate cell death in yeast

Actin's functional complexity makes it a likely target of oxidative stress but also places it in a prime position to coordinate the response to oxidative stress. We have previously shown that the NADPH oxidoreductase Oye2p protects the actin cytoskeleton from oxidative stress. Here we demonstrate that the physiological consequence of actin oxidation is to accelerate cell death in yeast. Loss of Oye2p leads to reactive oxygen species accumulation, activation of the oxidative stress response, nuclear fragmentation and DNA degradation, and premature chronological aging of yeast cells. The oye2Delta phenotype can be completely suppressed by removing the potential for formation of the actin C285-C374 disulfide bond, the likely substrate of the Oye2p enzyme or by treating the cells with the clinically important reductant N-acetylcysteine. Because these two cysteines are coconserved in all actin isoforms, we theorize that we have uncovered a universal mechanism whereby actin helps to coordinate the cellular response to oxidative stress by both sensing and responding to oxidative load.

Decreased sensitivity of transformed 3T3-SV40 cells treated with N-acetylcysteine to bacterial invasion

Long-term treatment of transformed 3T3-SV40 mouse fibroblasts with antioxidant N-acetylcysteine decreased cell level of ROS and increased the concentration of reduced glutathione. Removal of N-acetylcysteine from the medium led to the appearance of well-expressed stress fibrils, virtually absent in control cells. In contrast to control cells, these cells were not invaded by apathogenic Escherichia coli A2 strain producing ECP32 protease specifically cleaving actin. Antioxidant N-acetylcysteine can cause partial reversion of transformed phenotype at the expense of a shift of cell redox balance in favor of reduced glutathione.

In vivo rates of erythrocyte glutathione synthesis in adults with sickle cell disease

Despite reports of lower GSH concentration in sickle cell disease (SCD), the in vivo kinetic mechanism(s) responsible for GSH deficiency is unknown. To determine whether suppressed synthesis was responsible for the lower erythrocyte GSH concentration, we used a primed intermittent infusion of [(2)H(2)]glycine to measure erythrocyte GSH synthesis in vivo in 23 individuals with homozygous beta(s) SCD and 8 healthy controls. Erythrocyte cysteine concentration, the rate-limiting precursor for GSH synthesis, plasma markers of oxidant damage, and dietary intakes of energy and protein were also measured. Compared with values of controls, SCD subjects had significantly lower erythrocyte GSH (P < 0.04) and cysteine concentrations (P < 0.004) but significantly faster fractional rates of GSH synthesis (P < 0.02). The absolute rates of GSH synthesis in SCD subjects compared with control subjects was greater by approximately 57% (P = 0.062). However, the concentrations of markers of oxidative damage, plasma derivatives of reactive oxygen metabolites, plasma nitrotyrosine, urinary isoprostane-to-creatinine ratio, and GSH-to-GSSG ratio, as well as dietary intakes of energy, protein, and GSH precursor amino acids, were not different between SCD subjects and controls. The findings of this study suggest that the lower erythrocyte GSH of SCD patients is not due to suppressed synthesis or impaired regeneration but rather to increased consumption. In addition, the lower erythrocyte cysteine concentration plus the faster rate of GSH synthesis strongly suggest that the endogenous cysteine supply is not sufficient to meet all anabolic demands; hence, cysteine may be a conditionally essential amino acid in individuals with SCD.

Alterations in erythrocyte membrane protein composition in advanced non-small cell lung cancer

Cancer can be associated with hematological complications related to red blood cell (RBC) function, whose physiological roles have now been expanded since it is now known that RBC are also signalling cells. The aim of this study was to explore the alterations occurring in the protein composition of RBC in advanced non-small cell lung cancer (NSCLC). Blood samples from 21 patients with advanced (stages III-IV) NSCLC (16 squamous cell carcinomas and 5 adenocarcinomas), and from 21 healthy volunteers were used. Samples from 6 randomly selected patients and 6 controls were used for the screening of erythrocyte ghost alterations by Differential Scanning Calorimetry (DSC). Samples from 15 patients and 15 controls, different from those used in the DSC measurements, were randomly selected for analysis of the expression of glycophorin (GP) species, band 3, and glycoproteins by SDS-PAGE and Western blotting or lectin enzyme immunoassays. Additionally, 5 patients with chronic obstructive pulmonary disease (COPD) were used as a control group representative of a benign inflammatory disease. Blood samples from the COPD patients were used to analyze the expression of GPs, band 3 and syaloglycoproteins. We observed the following in NSCLC: (a) changes in GP expression levels, mainly decreases in the GPA and GPC monomers, and in the GPAB dimers; (b) a decrease in the band 3 protein level, and (c) alterations in the expression of different sialoglycoproteins. RBC from the COPD patients also showed protein abnormalities, some of them, especially at the level of band 3 and the syaloglycoproteins, being similar to those in NSCLC.

Spectrin's E2/E3 ubiquitin conjugating/ligating activity is diminished in sickle cells

Erythrocyte spectrin contains E2/E3 ubiquitin conjugating/ligating activity in its alpha subunit. Ankyrin is a target of spectrin's E2/E3 ubiquitin conjugating/ligating activity in vitro and in vivo. We compare the ubiquitination levels of ankyrin mediated by control and sickle cell spectrin using a biotinylated ubiquitin cell-free assay. Sickle cell spectrin has diminished ability to transfer ubiquitin from an intermediate spectrin-ubiquitin thioester adduct (alpha' spectrin) to ankyrin, which may be due to glutathiolation of spectrin's E2 and/or E3 active site cysteines. There is also a diminished ability of the sickle cell ankyrin to serve as target of spectrin's E2/E3 activity, probably due to oxidative damage to ankyrin. A direct correlation exists between the alpha'/alpha spectrin ratio and spectrin's ability to ubiquitinate ankyrin. There is also an inverse correlation between severity of the disease and the alpha'/alpha spectrin ratio in SS erythrocytes. These results suggest that reduced spectrin E2/E3 activity is an important determinant of sickle cell severity.

Beneficial in vitro effect of N-acetyl-cysteine on oxidative stress and apoptosis

Chronic renal failure (CRF) is usually accompanied by abnormalities of both humoral and cellular immune response. The aim of the study was to investigate the influence of N-acetyl-cysteine (NAC) on intracellular oxidative stress and apoptosis rate of T lymphocytes in children with CRF. Twenty-two children (aged 4-16, mean 7.4) with CRF treated with dialysis were enrolled in the study. Intracellular reactive oxygen species (ROS) production was quantified by mean rhodamine 123 (RHO) fluorescence intensity with flow cytometry. Annexin V FITC was used for identifying apoptotic cells. Mean fluorescence intensity (MFI), which reflected intracellular oxidative stress in T lymphocytes, was increased in patients with CRF compared with the controls (CD3+: 31.58+/-11.58 vs 22.55+/-4.97, p = 0.043; CD3+CD4+: 32.50+/-8.59 vs 27.75+/-12.76, NS; CD3+CD8+: 32.10+/-11.85 vs 20.77+/- 4.89, p =0.012). Apoptotic T lymphocytes occurred more frequently in patients with CRF treated with hemodialysis (HD) (11.36+/-6.96%) than in the controls (6.14%+/-3.36%; p = 0.025). After 24 h incubation with NAC MFI and apoptosis rate decreased significantly in all subpopulations of lymphocytes. NAC, as a strong antioxidant, has a favorable effect on intracellular oxidative stress and apoptosis rate of T lymphocytes in patients with CRF. A decreased apoptosis rate may have positive effect on functional abnormalities of T cells already found in patients with CRF.

KCl cotransport mediates abnormal sulfhydryl-dependent volume regulation in sickle reticulocytes

KCl cotransport (KCC) activation by cell swelling and pH was compared in sickle (SS) and normal (AA) red blood cells (RBCs). KCC fluxes had the same relationship to mean corpuscular hemoglobin concentration (MCHC) in SS and AA RBCs when normalized to the maximal volume-stimulated (VSmax) flux (MCHC &lt; 270 g/L [27 g/dL]). Acid-stimulated (pH 6.9) KCC flux in SS RBCs was 60% to 70% of VSmax KCC versus 20% in AA RBCs. Density gradients were used to track changes in reticulocyte MCHC during KCC-mediated regulatory volume decrease (RVD). Swelling to MCHC of 260 g/L (26 g/dL) produced Cl-dependent RVD that resulted in higher MCHC in SS than AA reticulocytes. In acid pH, RVD was also greater in SS than AA reticulocytes. Sulfhydryl reduction by dithiothreitol (DTT) lowered VSmax KCC flux in AA and SS RBCs by one third but did not alter swelling-induced RVD. DTT lowered acid-activated KCC in SS RBCs by 50% and diminished acid-induced RVD in SS reticulocytes. Thus, swelling activation of KCC is normal in SS RBCs but KCC-mediated RVD produces higher MCHC in SS than AA reticulocytes. Acid activation of KCC is exaggerated in SS RBCs and causes dehydration in SS reticulocytes. KCC response to acid stimulation was mitigated by DTT, suggesting that it arises from sulfhydryl oxidation.

Flow cytometric analysis of the oxidative status of normal and thalassemic red blood cells

BACKGROUND

The oxidative status of cells has been shown to modulate various cell functions and be involved in physiological and pathological conditions, including hereditary chronic anemias, such as thalassemia. It is maintained by the balance between oxidants, such as reactive oxygen species (ROS), and antioxidants, such as reduced glutathione (GSH).

METHODS

We studied peripheral RBC derived from normal and thalassemic donors. Flow cytometric methods were used to measure (1) generation of ROS; (2) the content of reduced GSH; and (3) peroxidation of membrane lipids as an indication of membrane damage.

RESULTS

ROS and lipid peroxidation were found to be higher, and GSH lower, in thalassemic RBC compared with normal RBC, both at baseline as well as following oxidative stress, such as exposure to hydrogen peroxide. To simulate a state of iron overload, normal RBC were exposed to extracellular ferric ammonium citrate or hemin, or their Hb was denatured by phenylhydrazine. All these treatments increased ROS and lipid peroxidation and decreased GSH. These effects were reversed by N-acetyl cysteine, a known ROS scavenger.

CONCLUSIONS

Flow cytometry can be useful for measuring oxidative stress and its effects on RBC in various diseases and for studying various chemical agents as antioxidants.

Flow cytometric measurement of reactive oxygen species production by normal and thalassaemic red blood cells

Reactive oxygen species (ROS) contribute to the pathogenesis of several hereditary disorders of red blood cells (RBCs), including thalassaemia. We report here on a modified flow cytometric method for measuring ROS in normal and thalassaemic RBCs. RBCs were incubated with 0.4 mM 2',7'-dichlorofluorescin diacetate (DCFH-DA), then washed and further incubated either with or without 2 mM H2O2. Flow cytometric analysis showed that RBC fluorescence increased with time; it increased faster and reached higher intensity (by 10-30-fold) in H2O2-stimulated RBCs as compared to unstimulated RBCs. In both cases, the antioxidant N-acetyl-l-cysteine reduced fluorescence, confirming previous reports that DCFH fluorescence is mediated by ROS. While the fluorescence of unstimulated RBCs increased with time, probably because of exposure to atmospheric oxygen, in H2O2-stimulated RBCs fluorescence decreased after 30 min. The latter effect is most likely related to H2O2 decomposition by catalase as both sodium azide, an antimetabolite that inhibits catalase and low temperature increased the fluorescence of stimulated RBCs. Washing had a similar effect, suggesting that maintenance of the oxidised DCF requires a constant supply of ROS. We next studied RBCs of beta-thalassaemic patients. The results demonstrated a significantly higher ROS generation by stimulated and unstimulated thalassaemic RBCs compared to their normal counterparts. These results suggest that flow cytometry can be useful for measuring the ROS status of RBCs in various diseases and for studying chemical agents as antioxidants.

Drugs for preventing red blood cell dehydration in people with sickle cell disease

BACKGROUND

Sickle cell disease is an inherited disorder of haemoglobin, which results in abnormal red blood cells. These can deform and cause blockages in blood vessels, leading to acute crises such as pain, stroke and splenic sequestration, and chronic organ and tissue damage. Recently research has begun to focus on therapies which prevent the red blood cells deforming by reducing the loss of water and ions from the cells. However, little is known about the effectiveness and safety of such drugs.

OBJECTIVES

To assess the relative risks and benefits of drugs which aim to prevent sickle cell related crises by reducing red blood cell dehydration.

SEARCH STRATEGY

We searched the Cochrane Cystic Fibrosis and Genetic Disorders Group specialist register which comprises references identified from comprehensive electronic database searches, handsearching relevant journals and handsearching abstract books of conference proceedings. Date of the most recent search of the Group's specialised register: December 2001.

SELECTION CRITERIA

All those randomised or quasi-randomised controlled trials of drugs which aim to prevent sickle cell crises by reducing red cell dehydration, compared to placebo or an alternative treatment.

DATA COLLECTION AND ANALYSIS

Both reviewers independently selected trials for inclusion, assessed trial quality and extracted data from the included studies.

MAIN RESULTS

Of the 27 trials identified, two met the inclusion criteria. The two trials tested the effectiveness of zinc sulphate and piracetam to prevent sickle cell related crises in a total of 246 patients. A reduction in pain crises was shown in the piracetam study over one year (weighted mean difference (WMD) -1.9 (95% CI -3.01, -0.79)), although blood counts were not significantly changed. The zinc trial showed a significant reduction in the total number of pain, haemolytic, aplastic and sequestration crises over one and a half years (WMD -2.83 (95% CI -3.51, -2.15)), but our analysis was limited by non-reporting of standard deviations for some data. Changes to red cell parameters and blood counts were inconsistent. No serious adverse events were noted in either trial.

REVIEWER'S CONCLUSIONS

While the results of both zinc and piracetam for reducing sickle related crises are encouraging, larger, and/or longer term multicentre trials over a number of years are needed to evaluate the effectiveness of these therapies for patients with sickle cell disease.

Deoxygenation of sickle cells stimulates Syk tyrosine kinase and inhibits a membrane tyrosine phosphatase

Polymerization of hemoglobin S in sickle red cells, in deoxygenated conditions, is associated with K+ loss and cellular dehydration. It was previously reported that deoxygenation of sickle cells increases protein tyrosine kinase (PTK) activity and band 3 tyrosine phosphorylation and that PTK inhibitors reduce cell dehydration. Here, the study investigates which PTKs are involved and the mechanism of their activation. Deoxygenation of sickle cells induced a 2-fold increase in Syk activity, measured by autophosphorylation in immune complex assays, but had no effect on Lyn. Syk was not stimulated by deoxygenation of normal red cells, and stimulation was partly reversible on reoxygenation of sickle cells. Syk activation was independent of the increase in intracellular Ca++ and Mg2+ associated with deoxygenation. Lectins that promote glycophorin or band 3 aggregation did not activate Syk. In parallel to Syk stimulation, deoxygenation of sickle cells, but not of normal red cells, decreased the activity of both membrane-associated protein tyrosine phosphatase (PTPs) and membrane protein thiol content. In vitro pretreatment of Syk immune complexes with membrane PTP inhibited Syk autophosphorylation. It is suggested that Syk activation in vivo could be mediated by PTP inhibition, itself resulting from thiol oxidation, as PTPs are known to be inhibited by oxidants. Altogether these data indicate that Syk could be involved in the mechanisms leading to sickle cell dehydration.

Erythrocyte-active agents and treatment of sickle cell disease

The sickle hemoglobin (HbS)-containing erythrocyte and its membrane represent a logical target for sickle cell disease therapy. Several antisickling agents which interfere with HbS polymerization have been studied over the last 30 years, but none has overcome the challenge of delivering high concentrations inside the sickle red blood cell without toxicity. The sickle erythrocyte membrane has also been targeted for therapeutic developments. Prevention of sickle cell dehydration by use of specific blockers of ion transport pathways mediating potassium loss from the sickle erythrocyte has been shown to be a feasible strategy in vitro, in vivo in transgenic sickle mice, and in patients. Other approaches have focused on improving the hemorheology of sickle erythrocytes and reducing their abnormal adhesion to endothelial cells. These potential treatments could be used alone or in combination with other approved therapies, such as hydroxyurea.

Oxidative insult in sheep red blood cells induced by T-butyl hydroperoxide: the roles of glutathione and glutathione peroxidase

Three different types of red blood cells (RBC) were used: (i) RBC from sheep having genetically high GSH (ii) RBC from sheep with genetically low GSH and (iii) RBC from high-GSH sheep treated with CDNB to deplete GSH. Incubation of these RBC with t-butyl hydroperoxide (tBHP, 3 mM) for 10 min caused the formation of TBARS, oxidation of haemoglobin and degradation and aggregation of membrane proteins in RBC from low-GSH sheep and GSH-depleted RBC. By contrast, RBC from high-GSH sheep (normal RBC) did not show the degradation and aggregation of membrane proteins within the first 10 min. Dithiothreitol (DTT) was highly effective in preventing the tBHP-mediated oxidation of haemoglobin, the formation of TBARS and the degradation and aggregation of membrane proteins in both normal RBC and low-GSH RBC. However, DTT did not provide protection in GSH-depleted RBC or normal RBCs in the presence of 1.5 mM mercaptosuccinate (MCS), a potent inhibitor of GSH peroxidase (GSHPx). The ability of GSH to prevent the oxidation of haemoglobin and the degradation and aggregation of membrane proteins was abolished in the presence of MCS. These results indicate that the protective function of DTT involves a GSH-dependent mechanism. Both GSH and GSHPx play key roles in this enzymatic system. In the light of the complete protection of RBC against oxidation induced by tBHP in the presence of DTT or GSH, the GSH/GSHPx system appears to act directly as a tBHP scavenger. The activities of four well-known antioxidants, Butylated hydroxytoluene, ascorbate, alpha-tocopherol and desferrioxamine were also tested in this study to cast further light on the role of free radical scavenging in protection from tBHP mediated free radical insult.

Glutathione in disease

Altered glutathione metabolism in association with increased oxidative stress has been implicated in the pathogenesis of many diseases. However, whether strategies aimed at restoring glutathione concentration and homeostasis are effective in ameliorating or modifying the natural history of these states is unknown. In this review we discuss the pathogenic role for altered glutathione metabolism in such diseases as protein energy malnutrition, seizures, Alzheimer's disease, Parkinson's disease, sickle cell anaemia, chronic diseases associated with ageing and the infected state. In addition, we discuss the efficacy of glutathione precursors in restoring glutathione homeostasis both in vitro and in vivo.

N-Acetylcysteine counteracts erythrocyte alterations occurring in chronic obstructive pulmonary disease

A key role has been proposed for reactive oxygen species (ROS) in chronic obstructive pulmonary disease (COPD). Aim of the present work was to evaluate possible implications of ROS in the integrity and function of the cell type mainly involved in oxygen uptake and delivery to the peripheral tissues: the erythrocyte. Red blood cells (RBCs) were thus collected from blood samples from COPD patients. Furthermore, blood samples from the same patients treated with the antioxidizing drug of widespread use in such disease i.e., N-acetylcysteine (NAC), were also considered. Morphometric and analytical cytology studies were then conducted. We report herein that: (i) alterations of RBC ultrastructure were detectable in RBCs from COPD patients, that (ii) relevant changes of spectrin cytoskeleton and glycophorin expression were also found and that (iii) NAC treatment was capable of significantly counteracting these changes. These results are consistent with a reappraisal of the role of RBCs in this disease.

The Gardos channel is responsible for CDNB-induced dense sickle cell formation

The red blood cells (RBCs) derived from blood taken from homozygous sickle cell (SS) patients demonstrate densities that are inversely proportional to the intracellular reduced glutathione (GSH) content. Addition of 1 mM 1-chloro-2,4-dinitrobenzene (CDNB) to low-density sickle cells (LDSS), at 4 degrees C, results in a shift of LDSS erythrocytes to high-density sickle cells (HDSS), with corresponding decreases in GSH. We have previously demonstrated that this CDNB effect was due to increased K(+) leakage and that dense cell formation could be inhibited by clotrimazole (specific for the Gardos channel) but not DIOA (specific for the K(+)-Cl(-) co-transport system) at pH 7.4 (Shartava et al. Am. J. Hematol. 1999;62:19-24). Here we demonstrate that clotrimazole (10 microM) inhibits dense cell formation at pH 7.1 and 6.8, while DIOA (1 mM) has no effect. As pH 6.8 is the optimal pH for the K(+)-Cl(-) co-transport system, we can now reasonably conclude that damage to the Gardos channel is responsible for CDNB-induced dense cell formation.

N-acetylcysteine and clotrimazole inhibit sickle erythrocyte dehydration induced by 1-chloro-2,4-dinitrobenzene

Clotrimazole, a specific inhibitor of the Ca(2+) activated potassium (Gardos) channel, and the antioxidant N-acetylcysteine were found to inhibit the in vitro formation of high-density sickle cells induced by treatment with 1-chloro-2,4-dinitrobenzene (CDNB). The CDNB induced leakage of K(+) can be inhibited by treatment of SS erythrocytes with 20 mM N-acetylcysteine. We conclude that the effect of N-acetylcysteine in preventing K(+) efflux and formation of high-density sickle cells is related to its ability to protect the Gardos channel from oxidative damage caused by diminished levels of reduced glutathione. This effect is due to the ability of N-acetylcysteine to maintain an appropriate level of reduced glutathione and its direct antioxidant activity.