Metabolic indicators of oxidative stress correlate with haemichrome attachment to membrane, band 3 aggregation and erythrophagocytosis in beta-thalassaemia intermedia

Erythrocyte-enabled immunomodulation for vaccine delivery

Erythrocytes capture pathogens in circulation and present them to antigen-presenting cells (APCs) in the spleen. Senescent or apoptotic erythrocytes are physiologically eliminated by splenic APCs in a non-inflammatory manner as to not induce an immune reaction, while damaged erythrocytes tend to induce immune activation. The distinct characteristics of erythrocytes in their lifespan or different states inspire the design of targeting splenic APCs for vaccine delivery. Specifically, normal or damaged erythrocyte-driven immune targeting can induce antigen-specific immune activation, whereas senescent or apoptotic erythrocytes can be tailored to achieve antigen-specific immune tolerance. Recent studies have revealed the potential of erythrocyte-based vaccine delivery; however, there is still no in-depth review to describe the latest progress. This review summarizes the characteristics, different immune functions, and diverse vaccine delivery behaviors and biomedical applications of erythrocytes in different states. This review aims to contribute to the rational design and development of erythrocyte-based vaccine delivery systems for treating various infections, tumors, inflammatory diseases, and autoimmune diseases.

Effects of Visceralising Leishmania on the Spleen, Liver, and Bone Marrow: A Pathophysiological Perspective

The leishmaniases constitute a group of parasitic diseases caused by species of the protozoan genus Leishmania. In humans it can present different clinical manifestations and are usually classified as cutaneous, mucocutaneous, and visceral (VL). Although the full range of parasite—host interactions remains unclear, recent advances are improving our comprehension of VL pathophysiology. In this review we explore the differences in VL immunobiology between the liver and the spleen, leading to contrasting infection outcomes in the two organs, specifically clearance of the parasite in the liver and failure of the spleen to contain the infection. Based on parasite biology and the mammalian immune response, we describe how hypoxia-inducible factor 1 (HIF1) and the PI3K/Akt pathway function as major determinants of the observed immune failure. We also summarize existing knowledge on pancytopenia in VL, as a direct effect of the parasite on bone marrow health and regenerative capacity. Finally, we speculate on the possible effect that manipulation by the parasite of the PI3K/Akt/HIF1 axis may have on the myelodysplastic (MDS) features observed in VL.

The relationship between hyperbilirubinemia and the promoter region and first exon of UGT1A1 gene polymorphisms in Vietnamese newborns

BACKGROUND

To investigate the relationship between unexplained indirect hyperbilirubinemia of Vietnamese newborns and the polymorphism of the promoter TATA box and exon 1 of bilirubin uridine diphosphate glucuronosyltransferase (UGT1A1) gene.

METHODS

A total of 149 neonates were divided into the hyperbilirubinemia group (n = 99) and control group (n = 50). The gene polymorphisms of UGT1A1 gene in the two groups were detected by PCR and direct sequencing, which revealed the relationship between UGT1A1 polymorphism with neonatal hyperbilirubinemia of neonates. The types of UGT1A1 polymorphism in the hyperbilirubinemia group and the peak total serum bilirubin (PSB) levels with different genotypes were observed.

RESULTS

(1) (TA)7 insertion mutation, 211G>A, 189C>T, 190G>A, 378C>T and 686C>A were detected. (2) The allele frequency of 211G>A allele mutation was significantly different between the two groups (p < 0.05). (3) Logistic regression analysis showed that homozygosity and heterozygosity of 211G>A were both significantly associated with neonatal hyperbilirubinemia. (4) In the hyperbilirubinemia group, the peak total serum bilirubin level of 211G>A homozygous neonates was higher than that of the wild-type neonates (p < 0.05).

CONCLUSIONS

We noted that there was an association between neonates with unexplained indirect hyperbilirubinemia in Vietnam and the polymorphism of UGT1A1c.211G>A. In addition, the homozygous 211G>A polymorphism was related to the degree of hyperbilirubinemia.

IMPACT

Our article provided data on UGT1A1 polymorphism distribution in the Vietnamese population, which have not been reported yet. Our findings revealed that mutations in UGT1A1 gene are risk factors for unexplained hyperbilirubinemia in Vietnamese neonates. Our article will strengthen the cognition of neonatal jaundice at the genetic level in the pediatric field in Vietnam.

In Vivo Imaging with Genetically Encoded Redox Biosensors

Redox reactions are of high fundamental and practical interest since they are involved in both normal physiology and the pathogenesis of various diseases. However, this area of research has always been a relatively problematic field in the context of analytical approaches, mostly because of the unstable nature of the compounds that are measured. Genetically encoded sensors allow for the registration of highly reactive molecules in real-time mode and, therefore, they began a new era in redox biology. Their strongest points manifest most brightly in in vivo experiments and pave the way for the non-invasive investigation of biochemical pathways that proceed in organisms from different systematic groups. In the first part of the review, we briefly describe the redox sensors that were used in vivo as well as summarize the model systems to which they were applied. Next, we thoroughly discuss the biological results obtained in these studies in regard to animals, plants, as well as unicellular eukaryotes and prokaryotes. We hope that this work reflects the amazing power of this technology and can serve as a useful guide for biologists and chemists who work in the field of redox processes.

Non-oxidative band-3 clustering agents cause the externalization of phosphatidylserine on erythrocyte surfaces by a calcium-independent mechanism

Aging of red blood cells (RBCs) is associated with alteration in a wide range of RBC features, occurring each on its own timescale. A number of these changes are interrelated and initiate a cascade of biochemical and structural transformations, including band-3 clustering and phosphatidylserine (PS) externalization. Using specific band-3 clustering agents (acridine orange (AO) and ZnCl₂), we examined whether treatment of RBCs with these agents may affects PS externalization and whether this process is Ca²⁺-dependent. RBCs were isolated from the blood of eight healthy donors upon obtaining their informed consent. The suspension was supplemented with increasing concentrations of AO or ZnCl₂ (from 0.5 to 2.0 mM) and incubated at 25 °C for 60 min. To detect PS at the RBC surface, we used allophycocyanin-conjugated recombinant human Annexin V. We demonstrated, that treatment of RBCs with both clustering agents caused an elevation in the percent of cells positively labeled by Annexin-V (RBC^PS), and that this value was not dependent on the presence of calcium in the buffer: RBCs treated with AO in the presence of either EDTA, EGTA or calcium exhibited similar percentage of RBC^PS. Moreover, the active influx of Zn²⁺ into RBCs induced by their co-incubation with both ZnCl₂ and A23187 did not increase the percent of RBC^PS as compared to RBCs incubated with ZnCl₂ alone. Taken together, these results demonstrate that the band-3 clustering agents (AO or ZnCl₂) induce PS externalization in a Ca²⁺ independent manner, and we hereby suggest a possible scenario for this phenomenon.

What can we learn from ineffective erythropoiesis in thalassemia?

Erythropoiesis is a dynamic process regulated at multiple levels to balance proliferation, differentiation and survival of erythroid progenitors. Ineffective erythropoiesis is a key feature of various diseases, including β-thalassemia. The pathogenic mechanisms leading to ineffective erythropoiesis are complex and still not fully understood. Altered survival and decreased differentiation of erythroid progenitors are both critical processes contributing to reduced production of mature red blood cells. Recent studies have identified novel important players and provided major advances in the development of targeted therapeutic approaches. In this review, β-thalassemia is used as a paradigmatic example to describe our current knowledge on the mechanisms leading to ineffective erythropoiesis and novel treatments that may have the potential to improve the clinical phenotype of associated diseases in the future.

Red Blood Cell Function and Dysfunction: Redox Regulation, Nitric Oxide Metabolism, Anemia

SIGNIFICANCE

Recent clinical evidence identified anemia to be correlated with severe complications of cardiovascular disease (CVD) such as bleeding, thromboembolic events, stroke, hypertension, arrhythmias, and inflammation, particularly in elderly patients. The underlying mechanisms of these complications are largely unidentified. Recent Advances: Previously, red blood cells (RBCs) were considered exclusively as transporters of oxygen and nutrients to the tissues. More recent experimental evidence indicates that RBCs are important interorgan communication systems with additional functions, including participation in control of systemic nitric oxide metabolism, redox regulation, blood rheology, and viscosity. In this article, we aim to revise and discuss the potential impact of these noncanonical functions of RBCs and their dysfunction in the cardiovascular system and in anemia.

CRITICAL ISSUES

The mechanistic links between changes of RBC functional properties and cardiovascular complications related to anemia have not been untangled so far.

FUTURE DIRECTIONS

To allow a better understanding of the complications associated with anemia in CVD, basic and translational science studies should be focused on identifying the role of noncanonical functions of RBCs in the cardiovascular system and on defining intrinsic and/or systemic dysfunction of RBCs in anemia and its relationship to CVD both in animal models and clinical settings. Antioxid. Redox Signal. 26, 718-742.

Erythrocyte Catalase Activity in More Frequent Microcytic Hypochromic Anemia: Beta-Thalassemia Trait and Iron Deficiency Anemia

Most common microcytic hypochromic anemias are iron deficiency anemia (IDA) and β-thalassemia trait (BTT), in which oxidative stress (OxS) has an essential role. Catalase causes detoxification of H₂O₂ in cells, and it is an indispensable antioxidant enzyme. The study was designed to measure erythrocyte catalase activity (ECAT) in patients with IDA (10) or BTT (21), to relate it with thalassemia mutation type (β⁰ or β⁺) and to compare it with normal subjects (67). Ninety-eight individuals were analyzed since September 2013 to June 2014 in Tucumán, Argentina. Total blood count, hemoglobin electrophoresis at alkaline pH, HbA₂, catalase, and iron status were performed. β-thalassemic mutations were determined by real-time PCR. Normal range for ECAT was 70,0–130,0 MU/L. ECAT was increased in 14% (3/21) of BTT subjects and decreased in 40% (4/10) of those with IDA. No significant difference (p = 0,245) was shown between normal and BTT groups, while between IDA and normal groups the difference was proved to be significant (p = 0,000). In β⁰ and β⁺ groups, no significant difference (p = 0,359) was observed. An altered ECAT was detected in IDA and BTT. These results will help to clarify how the catalase activity works in these anemia types.

Antimalarial NADPH-Consuming Redox-Cyclers As Superior Glucose-6-Phosphate Dehydrogenase Deficiency Copycats

AIMS

Early phagocytosis of glucose-6-phosphate dehydrogenase (G6PD)-deficient erythrocytes parasitized by Plasmodium falciparum were shown to protect G6PD-deficient populations from severe malaria. Here, we investigated the mechanism of a novel antimalarial series, namely 3-[substituted-benzyl]-menadiones, to understand whether these NADPH-consuming redox-cyclers, which induce oxidative stress, mimic the natural protection of G6PD deficiency.

RESULTS

We demonstrated that the key benzoylmenadione metabolite of the lead compound acts as an efficient redox-cycler in NADPH-dependent methaemoglobin reduction, leading to the continuous formation of reactive oxygen species, ferrylhaemoglobin, and subsequent haemichrome precipitation. Structure-activity relationships evidenced that both drug metabolites and haemoglobin catabolites contribute to potentiate drug effects and inhibit parasite development. Disruption of redox homeostasis by the lead benzylmenadione was specifically induced in Plasmodium falciparum parasitized erythrocytes and not in non-infected cells, and was visualized via changes in the glutathione redox potential of living parasite cytosols. Furthermore, the redox-cycler shows additive and synergistic effects in combination with compounds affecting the NADPH flux in vivo.

INNOVATION

The lead benzylmenadione 1c is the first example of a novel redox-active agent that mimics the behavior of a falciparum parasite developing inside a G6PD-deficient red blood cell (RBC) giving rise to malaria protection, and it exerts specific additive effects that are inhibitory to parasite development, without harm for non-infected G6PD-sufficient or -deficient RBCs.

CONCLUSION

This strategy offers an innovative perspective for the development of future antimalarial drugs for G6PD-sufficient and -deficient populations.

The involvement of cation leaks in the storage lesion of red blood cells

Stored blood components are a critical life-saving tool provided to patients by health services worldwide. Red cells may be stored for up to 42 days, allowing for efficient blood bank inventory management, but with prolonged storage comes an unwanted side-effect known as the "storage lesion", which has been implicated in poorer patient outcomes. This lesion is comprised of a number of processes that are inter-dependent. Metabolic changes include a reduction in glycolysis and ATP production after the first week of storage. This leads to an accumulation of lactate and drop in pH. Longer term damage may be done by the consequent reduction in anti-oxidant enzymes, which contributes to protein and lipid oxidation via reactive oxygen species. The oxidative damage to the cytoskeleton and membrane is involved in increased vesiculation and loss of cation gradients across the membrane. The irreversible damage caused by extensive membrane loss via vesiculation alongside dehydration is likely to result in immediate splenic sequestration of these dense, spherocytic cells. Although often overlooked in the literature, the loss of the cation gradient in stored cells will be considered in more depth in this review as well as the possible effects it may have on other elements of the storage lesion. It has now become clear that blood donors can exhibit quite large variations in the properties of their red cells, including microvesicle production and the rate of cation leak. The implications for the quality of stored red cells from such donors is discussed.

Abnormal erythropoiesis and the pathophysiology of chronic anemia

Erythropoiesis, the bone marrow production of erythrocytes by the proliferation and differentiation of hematopoietic cells, replaces the daily loss of 1% of circulating erythrocytes that are senescent. This daily output increases dramatically with hemolysis or hemorrhage. When erythrocyte production rate of erythrocytes is less than the rate of loss, chronic anemia develops. Normal erythropoiesis and specific abnormalities of erythropoiesis that cause chronic anemia are considered during three periods of differentiation: a) multilineage and pre-erythropoietin-dependent hematopoietic progenitors, b) erythropoietin-dependent progenitor cells, and c) terminally differentiating erythroblasts. These erythropoietic abnormalities are discussed in terms of their pathophysiological effects on the bone marrow cells and the resultant changes that can be detected in the peripheral blood using a clinical laboratory test, the complete blood count.

Identifying term breast-fed infants at risk of significant hyperbilirubinemia

BACKGROUND

The aim of this study was to establish a model to identify term breast-fed infants who are at risk of developing significant neonatal hyperbilirubinemia.

METHODS

A prospective study was designed to investigate the effects of birth weight, mode of delivery, cephalohematoma, glucose-6-phosphate dehydrogenase (G6PD) deficiency, predischarge total serum bilirubin, variant uridine 5'diphospho-glucuronosyltransferase 1A1 (UGT1A1) gene, and hepatic solute carrier organic anion transporter 1B1 (SLCO1B1) gene on significant hyperbilirubinemia in term breast-fed neonates. Significant hyperbilirubinemia was defined as a bilirubin level exceeding the hour-specific phototherapy treatment threshold recommended by the American Academy of Pediatrics in 2004.

RESULTS

Of 240 exclusively breast-fed term neonates, 26 (10.8%) had significant hyperbilirubinemia. The predischarge total serum bilirubin on the third day (odds ratio (OR) = 2.63; 95% confidence interval (CI): 1.87-3.70; P < 0.001) and the variant UGT1A1 gene at nucleotide 211 (OR = 5.00; 95% CI: 1.08-23.03; P < 0.05) were significant risk factors. The area under the receiver operating characteristic (ROC) curve of the predictive probability was 0.964 (95% CI: 0.932-0.984; P < 0.0001).

CONCLUSION

Combining the total serum bilirubin on the third day and the variant UGT1A1 gene at nucleotide 211 can predict hyperbilirubinemia well in term breast-fed infants.

Oxidative stress and β-thalassemic erythroid cells behind the molecular defect

β-thalassemia is a worldwide distributed monogenic red cell disorder, characterized by the absence or reduced β-globin chain synthesis. Despite the extensive knowledge of the molecular defects causing β-thalassemia, less is known about the mechanisms responsible for the associated ineffective erythropoiesis and reduced red cell survival, which sustain anemia of β-thalassemia. The unbalance of alpha-gamma chain and the presence of pathological free iron promote a severe red cell membrane oxidative stress, which results in abnormal β-thalassemic red cell features. These cells are precociously removed by the macrophage system through two mechanisms: the removal of phosphatidylserine positive cells and through the natural occurring antibody produced against the abnormally clustered membrane protein band 3. In the present review we will discuss the changes in β-thalassemic red cell homeostasis related to the oxidative stress and its connection with production of microparticles and with malaria infection. The reactive oxygen species (ROS) are also involved in ineffective erythropoiesis of β-thalassemia through still partially known pathways. Novel cytoprotective systems such as ASHP, eIF2α, and peroxiredoxin-2 have been suggested to be important against ROS in β-thalassemic erythropoiesis. Finally, we will discuss the results of the major in vitro and in vivo studies with antioxidants in β-thalassemia.

Thalassemic erythrocytes release microparticles loaded with hemichromes by redox activation of p72Syk kinase

High counts of circulating microparticles, originated from the membrane of abnormal erythrocytes, have been associated with increased thrombotic risk in hemolytic disorders. Our studies indicate that in thalassemia intermedia patients the number of circulating microparticles correlates with the capability of the thalassemic erythrocytes to release microparticles. The microparticles are characteristically loaded with hemichromes formed by denatured α-chains. This finding was substantiated by the positive correlation observed in thalassemia intermedia patients between the amount of hemichromes measured in erythrocytes, their capability to release microparticles and the levels of plasma hemichromes. We observed that hemichromes, following their binding to the cytoplasmic domain of band 3, induce the formation of disulfide band 3 dimers that are subsequently phosphorylated by p72Syk kinase. Phosphorylation of oxidized band 3 appears to be relevant for the formation of large hemichromes/band 3 clusters that, in turn, induce local membrane instability and the release of microparticles. Proteomic analysis of microparticles released from thalassemia intermedia erythrocytes indicated that, besides hemichromes and clustered band 3, the microparticles contain a characteristic set of proteins that includes catalase, heat shock protein 70, peroxiredoxin 2 and carbonic anhydrase. High amounts of immunoglobulins and C3 have also been found to be associated with microparticles, accounting for their intense phagocytosis. The effect of p72Syk kinase inhibitors on the release of microparticles from thalassemia intermedia erythrocytes may indicate new perspectives for controlling the release of circulating microparticles in hemolytic anemias.

Glutathione is involved in the antimalarial action of chloroquine and its modulation affects drug sensitivity of human and murine species ofPlasmodium

Ferriprotoporphyrin IX (FP) is released inside the food vacuole of the malaria parasite during the digestion of host cell hemoglobin. FP is detoxified by its biomineralization to hemozoin. This process is effectively inhibited by chloroquine (CQ) and amodiaquine (AQ). Undegraded FP accumulates in the membrane fraction and inhibits enzymes of infected cells in parallel with parasite killing. FP is demonstrably degraded by reduced glutathione (GSH) in a radical-mediated mechanism. This degradation is inhibited by CQ and AQ in a competitive manner, thus explaining the ability of increased GSH levels in Plasmodium falciparum-infected cells to increase resistance to CQ and vice versa, and to render Plasmodium berghei that were selected for CQ resistance in vivo sensitive to the CQ when glutathione synthesis is inhibited. Some over-the-counter drugs that are known to reduce GSH in body tissues when used in excess were found to enhance the antimalarial action of CQ and AQ in mice infected either with P. berghei or Plasmodium vinckei. In contrast, N-acetyl-cysteine which is expected to increase the cellular levels of GSH, antagonized the action of CQ. These results suggest that some over-the-counter drugs can be used in combination with some antimalarials to which the parasite has become resistant.

Protein antioxidants in thalassemia

It is common knowledge that thalassemic patients are under significant oxidative stress. Chronic hemolysis, frequent blood transfusion, and increased intestinal absorption of iron are the main factors that result in iron overload with its subsequent pathophysiologic complications. Iron overload frequently associates with the generation of redox-reactive labile iron, which in turn promotes the production of other reactive oxygen species (ROS). If not neutralized, uncontrolled production of ROS often leads to damage of various intra- and extracellular components such as DNA, proteins, lipids, and small antioxidant molecules among others. A number of endogenous and exogenous defense mechanisms can neutralize and counteract the damaging effects of labile iron and the reactive substances associated with it. Endogenous antioxidant enzymes, such as superoxide dismutase, catalase, glutathione peroxidase, and ferroxidase, may directly or sequentially terminate the activities of ROS. Nonenzymatic endogenous defense mechanisms include metal binding proteins (ceruloplasmin, haptoglobin, albumin, and others) and endogenously produced free radical scavengers (glutathione (GSH), ubiquinols, and uric acid). Exogenous agents that are known to function as antioxidants (vitamins C and E, selenium, and zinc) are mostly diet-derived. In this review, we explore recent findings related to various antioxidative mechanisms operative in thalassemic patients with special emphasis on protein antioxidants.

Red blood cell clearance in inflammation

SUMMARY

Anemia is a frequently encountered problem in the critically ill patient. The inability to compensate for anemia includes several mechanisms, collectively referred to as anemia of inflammation: reduced production of erythropoietin, impaired bone marrow response to erythropoietin, reduced iron availability, and increased red blood cell (RBC) clearance. This review focuses on mechanisms of RBC clearance during inflammation. We state that phosphatidylserine (PS) expression in inflammation is mainly enhanced due to an increase in ceramide, caused by an increase in sphingomyelinase activity due to either platelet activating factor, tumor necrosis factor-α, or direct production by bacteria. Phagocytosis of RBCs during inflammation is mediated via RBC membrane protein band 3. Reduced deformability of RBCs seems an important feature in inflammation, also mediated by band 3 as well as by nitric oxide, reactive oxygen species, and sialic acid residues. Also, adherence of RBCs to the endothelium is increased during inflammation, most likely due to increased expression of endothelial adhesion molecules as well as PS on the RBC membrane, in combination with decreased capillary blood flow. Thereby, clearance of RBCs during inflammation shows similarities to clearance of senescent RBCs, but also has distinct entities, including increased adhesion to the endothelium.

Absence of JAK2V617F mutation in patients with beta-thalassemia major and thrombocytosis due to splenectomy

The report of Janus Kinase 2 (JAK2) mutations in myeloid malignancies with high frequency in myeloproliferative neoplasms has been well known since 2005. By monitoring allele burden, it is found that the expression of JAK2V617F mutation is increasing significantly from essential thrombocytosis to polycythemia vera. Furthermore, JAK2 abnormalities are reported in the majority of unexplained thrombotic episodes. Thalassemic syndromes are characterized by ineffective erythropoiesis and thrombocytosis, mainly due to splenectomy. The high incidence of thromboembolic events has led to the identification of a prothrombotic state in these patients. The contribution of JAK2 mutations to the hypercoagulable state of thalassemic patients is still unknown. Furthermore, the potential role of Janus Kinase mutations in hepcidin expression and consequently in ineffective erythropoiesis is still under investigation. This study was scheduled to determine whether the presence of JAK2V617F mutation in thalassemic patients is associated with thrombocytosis. We studied 20 patients DNA with beta-thalassemia for JAK2V617F mutation by using RG-PCR method. None of the patients were positive for this particular mutation. More studies are needed to prove the role of JAK2 in ineffective erythropoiesis, iron metabolism and thrombocytosis and to determine if using JAK2 inhibitors in thalassemic patients can be a potential therapeutic option.

Decreased blood catalase activity is not related to specific beta-thalassemia mutations in Hungary

INTRODUCTION

Thalassemia erythrocytes are exposed to oxidative stress especially to hydrogen peroxide, which is regulated with the enzyme catalase. The aim of this study was to examine blood catalase activity and the relationship of blood catalase and beta-thalassemia gene mutations.

METHODS

Blood catalase activity, hemoglobin, HbA(2) , HbF, and beta-globin gene mutations were determined in 43 Hungarian patients with beta-thalassemia trait.

RESULTS

Compared to controls, the beta-thalassemia trait patients showed a low mean (P < 0.001) of blood catalase (men: 84 ± 29 MU/L vs. sex-matched controls: 118 ± 18 MU/L and women: 74 ± 18 MU/L vs. 108 ± 114 MU/L) and a low mean of blood catalase-to-blood hemoglobin ratio (men: 0.72 ± 0.22 MU/g vs. 0.85 ± 0.12 MU/g, women: 0.77 ± 0.26 MU/g vs. 0.84 ± 0.11 MU/g). The HbA(2) determination showed high sensitivity and specificity for the detection of beta-thalassemia trait patients. Mutation analyses revealed 13 beta-thalassemia trait mutations, of which six have not been reported before in Hungarian beta-thalassemia trait patients. Each group of mutations revealed decreased (P < 0.01) mean of blood catalase and catalase-to-hemoglobin ratio. Acatalasemia mutations were not found in beta-thalassemia trait patients.

CONCLUSION

The decrease in blood catalase activity might be due to the damaging effects of free radicals on the catalase protein. Consequently, these beta-thalassemia trait patients may be relatively susceptible to damage caused by oxidative stress.

β-thalassemia: a model for elucidating the dynamic regulation of ineffective erythropoiesis and iron metabolism

β-thalassemia is a disease characterized by anemia and is associated with ineffective erythropoiesis and iron dysregulation resulting in iron overload. The peptide hormone hepcidin regulates iron metabolism, and insufficient hepcidin synthesis is responsible for iron overload in minimally transfused patients with this disease. Understanding the crosstalk between erythropoiesis and iron metabolism is an area of active investigation in which patients with and models of β-thalassemia have provided significant insight. The dependence of erythropoiesis on iron presupposes that iron demand for hemoglobin synthesis is involved in the regulation of iron metabolism. Major advances have been made in understanding iron availability for erythropoiesis and its dysregulation in β-thalassemia. In this review, we describe the clinical characteristics and current therapeutic standard in β-thalassemia, explore the definition of ineffective erythropoiesis, and discuss its role in hepcidin regulation. In preclinical experiments using interventions such as transferrin, hepcidin agonists, and JAK2 inhibitors, we provide evidence of potential new treatment alternatives that elucidate mechanisms by which expanded or ineffective erythropoiesis may regulate iron supply, distribution, and utilization in diseases such as β-thalassemia.

Increased oxidative stress and iron overload in Jordanian β-thalassemic children

β-Thalassemia (β-thal) is associated with abnormal synthesis of hemoglobin (Hb). Repeated blood transfusions in patients with β-thal major (β-TM) leads to an enhanced generation of reactive oxygen species (ROS), and subjects patients to peroxidative injury. We studied the antioxidant status and oxidative damage to children with β-thal in Jordan. Samples from 40 children with β-thal and 40 healthy controls were used. All children were under 13 years of age. Our results showed that plasma thiobarbituric acid reactive substances (TBARS) were elevated in β-thalassemic children compared to controls together with compensatory increase in superoxide dismutase (SOD) activity and decrease in catalase (CAT) activity. Elevated serum ferritin showed positive correlation with elevated liver enzyme levels except gamma glutamyl transferase (GGT), confirming liver involvement due to iron overload. Serum ferritin also showed a positive correlation with elevated TBARS and SOD, suggesting that iron overload is involved in the oxidative stress shown in cells.

Iron metabolism and ineffective erythropoiesis in beta-thalassemia mouse models

beta-thalassemia is a disease associated with decreased beta-globin production leading to anemia, ineffective erythropoiesis, and iron overload. New mechanisms associated with modulation of erythropoiesis and iron metabolism have recently been discovered in thalassemic mice, improving our understanding of the pathophysiology of this disease. These discoveries have the potential to be translated into clinically-relevant therapeutic options to reduce ineffective erythropoiesis and iron overload. A new generation of therapies based on limiting ineffective erythropoiesis, iron absorption, and the correction of iron maldistribution could be on the way, possibly complementing and improving the current standard of patient care.

Imbalanced globin chain synthesis determines erythroid cell pathology in thalassemic mice

BACKGROUND

beta-thalassemia occurs from the imbalanced globin chain synthesis due to the absence or inadequate beta-globin chain production. The excessive unbound alpha-globin chains precipitate in erythroid precursors and mature red blood cells leading to ineffective erythropoiesis and hemolysis.

DESIGN AND METHODS

In vitro globin chain synthesis in reticulocytes from different types of thalassemic mice was performed. The effect of imbalanced globin chain synthesis was assessed from changes of red blood cell properties including increased numbers of red blood cells vesicles and apoptotic red blood cells, increased reactive oxygen species and decreased red blood cell survival.

RESULTS

The alpha/beta-globin chain ratio in beta(IVSII-654)-thalassemic mice, 1.26+/-0.03, was significantly higher than that of wild type mice, 0.96+/-0.05. The thalassemic mice show abnormal hematologic data and defective red blood cell properties. These values were improved significantly in doubly heterozygous thalassemic mice harboring 4 copies of human beta(E)-globin transgene, with a more balanced globin chain synthesis, 0.92+/-0.05. Moreover, transgenic mice harboring 8 extra copies of the human beta(E)-globin transgene showed inversely imbalanced alpha/beta-globin synthesis ratio, 0.83+/-0.01, that resulted in a mild beta-thalassemia phenotype due to the excessive beta-globin chains. The degree of ineffective erythropoiesis also correlated with the degree of imbalanced globin chain synthesis. Bone marrow and splenic erythroid precursor cells of beta(IVSII-654)-thalassemic mice showed increased phosphatidylserine exposure in basophilic and polychromatophilic stages, which was restored to the normal level in doubly heterozygous mice.

CONCLUSIONS

Imbalanced alpha/beta-globin chain as a consequence of either reduction or enhancement of beta-globin chain synthesis can cause abnormal red blood cell properties in mouse models.

Erythrophagosomal haemolytic degradative pathway in rat brown adipocytes induced by hyperinsulinaemia: an ultrastructural study

The phagocytosis and degradation of erythrocytes were studied in brown adipose tissue of experimentally hyperinsulinaemic rats. We found that insulin induces intensive erythrophagocytosis by brown adipocytes and their degradation by haemolytic pathway. Ultrastuctural study revealed that haemolytic degradation of erythrophagosomes was characterized by progressive and uniform decrease of erythrocyte matrix density. At the beginning of the degradative process small, clear vesicles resembling primary lysosomes were visible inside the erythrophagosome. With time, the erythrocyte structure totally disappeared and transformed into a fine, granular material within the erythrophagosomal vacuole. Finally, the erythrocyte membrane detached from the phagosomal and clumped into the vacuolar space forming one or several small myelin-like figures. In conclusion, brown adipocytes are capable of performing intensive erythrophagocytic activity when brown adipose tissue is stimulated and blood flow is enhanced. The molecular basis for favouring a haemolytic instead of more common granular erythrophagosomal degradative pathway remains unknown.

Oxidative effects of gemfibrozil on anion influx and metabolism in normal and Beta-thalassemic erythrocytes: physiological implications

To further clarify some peculiar molecular mechanisms related to the physiology and pathophysiology of erythrocytes with respect to oxygen binding and release, metabolism and senescence, we investigated the oxidative effects of gemfibrozil in normal and beta-thalassemic red blood cells. Our results showed that the oxidative stress promoted by the drug, through a direct interaction with hemoglobin, may lead to activation of caspase 3, which in turn influences the band 3 anion flux and glucose metabolism. In a comparative context, we also evaluated the effect on band 3 and caspase 3 activation of orthovanadate (a phosphatase inhibitor) and t-butylhydroperoxide (a known oxidant). The results support the hypothesis that gemfibrozil influences band 3 function through several mechanisms of action, centered on oxidative stress, which induces significant alterations of glucose metabolism.

Naturally occurring anti-band 3 antibodies and red blood cell removal under physiological and pathological conditions

Naturally occurring antibodies (NAbs) directed to band 3 protein (major erythrocyte membrane protein) are involved in the clearance of red blood cell (RBC) at the end of their lifespan as well as in the removal of RBC in different hereditary haemolytic disorders and in malaria. In all cited situations RBC undergoes oxidative stress and hemichromes (haemoglobin degradation products) are formed. Hemichromes possess a strong affinity for band 3 cytoplasmic domain and, following their binding, lead to band 3 oxidation and clusterisation. Those band 3 clusters show increased affinity for NAbs which activate complement and finally trigger the phagocytosis of altered RBC. During intra-erythrocytic malaria parasite growth, NAbs begin to bind to RBC surface at early parasite development stages increasing their abundance in parallel with parasite development. Interestingly, a number of hereditary haemolytic disorders, known to exert a protective effect on malaria, tend to exacerbate this phenomenon leading to a more precocious and effective opsonization of diseased RBC infected by malaria parasites. The exact definition of band 3 neo-antigens and the mechanism of their surface exposure are still unclear. Also band 3 clusterisation is only superficially understood, new insights about band 3 phosphorylation by Src kinases suggest the presence of a complex regulatory pathway.

Physiologically important secondary modifications of red cell membrane in hereditary spherocytosis-evidence for in vivo oxidation and lipid rafts protein variations

Hereditary spherocytosis (HS) is a heterogeneous group of disorders. The abnormal red cell morphology (resulting in shortened cell survival) is due to a primary deficiency in spectrin, ankyrin-1, band 3 or protein 4.2. Secondary protein deficiencies are often observed and may be involved in the outcome of the disease. In the present study, we searched for secondary erythrocyte membrane protein alterations in HS, including the lipid raft associated proteins and the oxidative index. For this purpose, 12 patients with clinical and laboratory diagnosis of mild to typical HS were examined. Erythrocyte membrane ghosts and skeletons were subjected to SDS-PAGE and immunoblotting analysis using antibodies against red cell membrane proteins and DNP moiety, after 2,4-dinitrophenylhydrazine derivatization. Protein deficiencies, degradation, aggregation and enhanced binding of cytoplasmic components, band 8, hemoglobin and immunoglobulins G to the membrane as well as increased oxidative index, were found in the majority of the HS patients. Proportion of the membrane- and skeleton-bound globin was oxidized/denatured Hb or hemichromes and crosslinkings. Some HS membranes are deficient in lipid rafts proteins and contain sorcin. A context of these distortions is more pronounced in typical HS cases compared to the mild ones. Similar defects in thalassemia and senescent RBCs are dictated by increased oxidative stress and are positively correlated with perturbations in membrane properties. These data add some new insight in the field of HS pathophysiology and clinical variability.

Splenectomy: a strong risk factor for pulmonary hypertension in patients with thalassaemia

OBJECTIVE

To determine the association between splenectomy and pulmonary hypertension in patients with thalassaemia with anaemia.

DESIGN

Prospective cross-sectional study.

METHODS

68 patients with thalassaemia, who had a haemoglobin concentration of less than 100 g/l, were recruited into this study. Echocardiography was performed before clinical data were reviewed. Pulmonary artery pressure was estimated by measuring the systolic transtricuspid pressure gradient from tricuspid regurgitation and adding it to the right atrial pressure, which was estimated by the response of the inferior vena cava to inspiration. Pulmonary hypertension was defined as systolic pulmonary artery pressure > 35 mm Hg. History of splenectomy and other clinical data were compared between patients with and without pulmonary hypertension.

RESULTS

29 patients had pulmonary hypertension and 39 did not. Patients with pulmonary hypertension had significantly more nucleated red blood cells and higher platelet counts, and a higher prevalence of splenectomy (75.8% v 25.6%, odds ratio 9.1, 95% confidence interval 3.0 to 27.7). In multivariate analysis, splenectomy was the only factor significantly related to pulmonary hypertension.

CONCLUSION

Splenectomy is a strong risk factor for pulmonary hypertension in patients with thalassaemia.

H2O2 injury in beta thalassemic erythrocytes: protective role of catalase and the prooxidant effects of GSH

Redox-mediated injury is an important pathway in the destruction of beta thalassemic red blood cells (RBC). Because of the autoxidation of the unstable hemoglobin chains and subsequent release of globin free heme and iron, significant amounts of superoxide (O2-) and, more importantly, hydrogen peroxide (H2O2) are generated intracellularly. Hence, catabolism of H2O2 is crucial in preventing cellular injury. Removal of H2O2 is mediated via two primary pathways: GSH-dependent glutathione peroxidase or catalase. Importantly, both pathways are ultimately dependent on NADPH. In the absence of any exogenous oxidants, model thalassemic RBC demonstrated significantly decreased GSH levels (P < 0.001 at 20 h). Perhaps of greater pathophysiologic importance, however, was the finding that the model thalassemic RBC exhibited significantly (P < 0.001) decreased catalase activity. Following 20 h incubation at 37 degrees C only 61.5 +/- 2.9% of the initial catalase activity remained in the alpha-hemoglobin chain-loaded cells versus 104.6 +/- 4.5 and 108.2 +/- 3.2% in the control and control-resealed cells, respectively. The mechanism underlying the loss of both catalase activity and GSH appears to be the same in that both catabolic pathways require adequate NADPH levels. As shown in this study, model beta thalassemic cells are unable to maintain a normal ( approximately 1.0) NADPH/NADP(total) ratio and, after 20 h, the model beta thalassemic cells have a significantly (P < 0.001) lower ratio ( approximately 0.5) which is quite similar to a G6PD-deficient RBC. In support of these findings, direct inactivation of catalase gives rise to significantly increased oxidant damage. In contrast, GSH depletion is not closely associated with oxidant sensitivity. Indeed, the consumption of GSH noted in the thalassemic RBC may be via a prooxidant pathway as augmentation of cellular GSH levels actually enhances alpha-hemoglobin chain-mediated injury.

Band 3/complement-mediated recognition and removal of normally senescent and pathological human erythrocytes

Band 3 modifications that normally occur during physiological red blood cell (RBC) senescence in humans, and occasionally in pathological conditions are described in the context of their role in enhancing RBC recognition and phagocytic removal. Band 3 modifications are mostly due to oxidative insults that gradually accumulate during the RBC lifespan or impact massively in a shorter time period in pathological conditions. The oxidative insults that impact on the RBC, the protective mechanisms that counteract those damages and the phenotypic modifications that accumulate during the RBC lifespan are described. It is shown how specific oxidative as well as non-oxidative band 3 modifications enhance RBC membrane affinity for normally circulating anti-band 3 antibodies, and how membrane-bound anti-band 3 antibodies bring about a limited complement activation and membrane deposition of complement C3 fragments. The partially covalent complexes between anti-band 3 antibodies and complement C3 fragments are very powerful opsonins readily recognized by the CR1 complement receptor on the phagocyte. Band 3 modifications typically encountered in old RBCs have crystallized to a number of band 3-centered models of RBC senescence. One of those band 3-centered models, the so-called 'band 3/complement RBC removal model' first put up by Lutz et al. is discussed in more detail. Finally, it is shown how the genetic deficiency of glucose-6-phosphate dehydrogenase (G6PD) plus fava bean consumption, and a widespread RBC parasitic disease, P. falciparum malaria, may lead to massive and rapid destruction of RBCs by a mechanism comparable to a dramatic, time-compressed enhancement of normal RBC senescence.

Coagulation and Splenectomy: An Overview

Venous thromboembolic events, such as pulmonary embolism, deep venous thrombosis, and portal vein thrombosis, have been observed in adult thalassemia patients, mainly in beta-thalassemia intermedia. The clinical findings are consistent with the observation of several alterations that indicate a state of activation of the hemostatic mechanisms in thalassemias. These alterations have usually been related to high platelet counts due to splenectomy and/or liver dysfunction. In a retrospective study of a large cohort of adults with thalassemia, we found a larger prevalence of venous thromboembolic events in transfusion-independent patients with thalassemia intermedia (29%) than in regularly transfused patients with thalassemia major (2%); moreover, the higher prevalence occurred particularly in splenectomized thalassemia intermedia patients. More recently, a multicenter study involving 56 tertiary referral centers in 7 countries was planned to assess the magnitude of thrombotic risk in thalassemia patients. The total number of patients who had thrombotic events was 146 (1.65%) out of 8860, with a prevalence of 0.9% in thalassemia major and 4% in thalassemia intermedia. The highest prevalence was confirmed in splenectomized patients. The observation that thrombotic events are more frequent in beta-thalassemia patients who are not receiving regular transfusions (thalassemia intermedia or thalassemia major patients in less developed countries with limited transfusion resources) or in thalassemic patients who have undergone splenectomy strongly supports the procoagulant activity of circulating damaged red blood cells.

Frequencies of A(TA)7TAA, G71R, and G493R mutations of the UGT1A1 gene in the Malaysian population

BACKGROUND

Gilbert syndrome is caused by defects in the uridine diphosphate glucuronosyltransferase 1A1 (UGT1A1) gene. These mutations differ among different populations and many of them have been found to be genetic risk factors for the development of neonatal jaundice.

OBJECTIVES

The objective was to determine the frequencies of the following mutations in the UGT1A1 gene: A(TA)7TAA (the most common cause of Gilbert syndrome in Caucasians), G71R (more common in the Japanese and Taiwanese population), and G493R (described in a homozygous Malay woman with Crigler-Najjar syndrome type 2) in a group of Malaysian babies with hyperbilirubinemia and a group of normal controls.

METHODS

The GeneScan fragment analysis was used to detect the A(TA)7TAA variant. Mutation screening of both G71R and G493R was performed using denaturing high performance liquid chromatography.

RESULTS

Fourteen out of fifty-five neonates with hyperbilirubinemia (25%) carried the A(TA)7TAA mutation (10 heterozygous, 4 homozygous). Seven out of fifty controls (14%) carried this mutation (6 heterozygous, 1 homozygous). The allelic frequencies for hyperbilirubinemia and control patients were 16 and 8%, respectively (p=0.20). Heterozygosity for the G71R mutation was almost equal among both groups (5.5% for hyperbilirubinemia patients and 6.0% for controls; p=0.61). One subject (1.8%) in the hyperbilirubinemia group and none of the controls were heterozygous for the G493R mutation (p=0.476).

CONCLUSIONS

The A(TA)7TAA seems more common than the G71R and G493R mutations in the Malaysian population.

In vitro interactions of thallium with components of the glutathione-dependent antioxidant defence system

We investigated the hypothesis that thallium (Tl) interactions with the glutathione-dependent antioxidant defence system could contribute to the oxidative stress associated with Tl toxicity. Working in vitro with reduced glutathione (GSH), glutathione reductase (GR) or glutathione peroxidase (GPx) in solution, we studied the effects of Tl+ and Tl3+ (1-25 microM) on: (a) the amount of free GSH, investigating whether the metal binds to GSH and/or oxidizes it; (b) the activity of the enzyme GR, that catalyzes GSH regeneration; and (c) the enzyme GPx, that reduces hydroperoxide at expense of GSH oxidation. We found that, while Tl+ had no effect on GSH concentration, Tl3+ oxidized it. Both cations inhibited the reduction of GSSG by GR and the diaphorase activity of this enzyme. In addition, Tl3+ per se oxidized NADPH, the cofactor of GR. The effects of Tl on GPx activity depended on the metal charge: Tl+ inhibited GPx when cumene hydroperoxide (CuOOH) was the substrate, while Tl(3+)-mediated GPx inhibition occurred with both substrates. The present results show that Tl interacts with all the components of GSH/GSSG antioxidant defence system. Alterations of this protective pathway could be partially responsible for the oxidative stress associated with Tl toxicity.

Genetic factors related to unconjugated hyperbilirubinemia amongst adults

Some variations in the UDP-glucuronosyltransferase 1A1 (UGT1A1) gene are involved in the development of unconjugated hyperbilirubinemia. We hypothesize that other genetic factors may also be associated with this disease. A total of 227 adults with normal routine haematology and liver function (apart from bilirubin testing for which they revealed bilirubin > or = 25.7 micromol/l and unconjugated bilirubin/total bilirubin > or = 80%), and 235 sex- and age-matched controls, were recruited. All subjects were analysed for UGT1A1, glucose-6-phosphate dehydrogenase (G6PD) and organic anion transporter polypeptide 2 (OATP2) genotypes using polymerase chain reaction-restriction fragment length polymorphism. The results indicated that G6PD deficiency, variant UGT1A1 gene and variant OATP2 gene were risk factors for hyperbilirubinemia. The odds ratios (OR) (with 95% confidence interval) were 220.83 (34.68-1406.30), 73.61 (17.01-318.63), 45.15 (11.19-182.22), 15.46 (4.35-54.99) and 6.51 (1.83-23.09), respectively, for individuals featuring the common UGT1A1/OATP2 haplotypes homozygous/heterozygous, compound heterozygous/heterozygous, compound heterozygous/wild-type, heterozygous/heterozygous and heterozygous/wild-type variations amongst subjects with normal G6PD activity. Amongst the subjects with G6PD deficiency, the OR was 159.00 (24.57-1028.94) for individuals carrying variations in both UGT1A1 and OATP2 genes. The UGT1A1/OATP2 haplotypes homozygous/wild-type, homozygous/compound heterozygous and homozygous/homozygous for G6PD normal and variant/wild-type for G6PD deficient individuals were only observed in the case group, and not in the control group. Amongst hyperbilirubinemic adults, bilirubin values tended to parallel variation status of their haplotypes. Adults featuring certain haplotypes in UGT1A1, OATP2 and G6PD genes face a high risk of developing unconjugated hyperbilirubinemia.

Oxidant stress and haemolysis of the human erythrocyte

The erythrocyte is a highly specialised cell with a limited metabolic repertoire. As an oxygen shuttle, it must continue to perform this essential task while exposed to a wide range of environments on each vascular circuit, and to a variety of xenobiotics across its lifetime. During this time, it must continuously ward off oxidant stress on the haeme iron, the globin chain and on other essential cellular molecules. Haemolysis, the acceleration of the normal turnover of senescent erythrocytes, follows severe and irreversible oxidant injury. A detailed understanding of the molecular mechanisms underlying oxidant injury and its reversal, and of the clinical and laboratory features of haemolysis is important to the medical toxicologist. This review will also briefly review glucose-6-phosphate deficiency, a common but heterogeneous range of enzyme-deficient states, which impairs the ability of the erythrocyte to respond to oxidant injury.

Molecular genetics of unconjugated hyperbilirubinemia in Taiwanese

In bilirubin metabolism, increased destruction of erythrocytes, defect in the function of organic anion transporter polypeptide 2 (OATP2) or UDP-glucuronosyltransferase 1A1 (UGT1A1) may result in unconjugated hyperbilirubinemia. Although glucose-6-phosphate dehydrogenase (G6PD) deficiency is known to be associated with the development of neonatal hyperbilirubinemia, it was observed that in neonates severe hyperbilirubinemia caused by G6PD deficiency, without associated polymorphisms in the UGT1A1 or the OATP2 gene, was preventable. Variations at the nucleotide (nt) 388 of OATP2 gene and nt-211 of UGT1A1 gene, were found to be a risk factor for severe hyperbilirubinemia amongst Taiwanese neonates, respectively. G6PD deficiency, variations at nts 388 and 521 of OATP2 gene, and variations at nt-211 and in the promoter area of UGT1A1 gene were reported to be the risk factors for the occurrence of mild hyperbilirubinemia amongst Taiwanese adults. The status of the haplotypes of G6PD, OATP2, and UGT1A1 genes affected the odds ratio and the bilirubin levels in the hyperbilirubinemic subjects. Moreover, carriage of the variant-211 UGT1A1 allele, as well as UGT1A7*3 allele, was demonstrated to represent a risk factor for the development of, and a determinant for, metastases associated with Taiwanese colorectal-cancer patients. Further investigation is warranted to evaluate this phenomenon.

Experiences in the measurement of RBC-bound IgG as markers of cell age

An immunologically mediated pathway has been largely accepted to be one of the mechanisms involved in the clearance of senescent or prematurely damaged RBC. According to this pathway, RBC removal is mediated by binding of naturally occurring IgG to clustered integral membrane proteins, followed by complement deposition. The validation of an immunoenzymatic method for the detection of RBC-bound autologous IgG is presented. The use of RBC-bound IgG as an index related to red cell age was evaluated by measuring IgG binding in RBC treated with the clustering agent ZnCl2, in density fractionated RBC and in a selected group of patients expected to have an altered RBC life span. The immunoenzymatic method for IgG detection resulted to be reproducible (CV = 3.4%). IgG binding to in vitro clustered RBC was found to be enhanced to a very great extent, about 20 times higher with respect to untreated RBC. A slight but significant increase (about 1.8-fold) in membrane-bound IgG was observed in the highest density fraction of normal RBC, which constituted 1% of the total cells. A significantly greater number of RBC-bound IgG was measured in splenectomized beta-thalassemia intermedia patients and in subjects with secondary decreases in the C3 complement fraction concentration.

Malaria infection induces a conformational change in erythrocyte band 3 protein

Sequestration in the microvessels of the deep tissues is a signal characteristic of the human malaria Plasmodium falciparum. The adhesion of P. falciparum-infected cells to the post-capillary endothelial cells in various tissues contributes to both the pathology of the disease (i.e. organ infarcts and coma) and parasite survival (i.e. the microaerophilic environment favors plasmodial growth while avoiding passage through and destruction in the spleen). This report identifies a conformational change in a region of band 3 protein involved in the enhanced adhesiveness of P. falciparum-infected erythrocytes.

Mechanisms of band 3 oxidation and clustering in the phagocytosis of Plasmodium falciparum-infected erythrocytes

Erythrocytes (RBCs) opsonized by IgG and complement are prevalently recognized and phagocytosed by complement receptor CR1. This mechanism, effective in senescent and damaged RBCs seems to be operative in ring-parasitized RBCs, since infection by Plasmodium falciparum induces stage-dependent binding of auto-antibodies and activated C3 to the RBC membrane. Later, parasite forms are also recognized by non-opsonic receptors, such as scavenger receptor CD36. Malaria parasites induce the oxidative formation of hemichromes which are the trigger for the auto-antigen development. Band 3 protein is the most plausible candidate of the RBC auto-antigen, induced by hemichromes. Auto-antigens isolated from trophozoites were found only in a high-molecular-weight protein aggregates not present in the normal RBC. The immunocomplex was purified by protein-A affinity chromatography, purified proteins digested by trypsin and analyzed by MALDI-TOF. Peptide mapping showed that the main antigen consisted of band 3 protein aggregates that also contained hemichromes, IgGs, complement factor 3 (C3), and traces of spectrin and glycophorin but no parasite proteins. Two cysteines located in the band 3 cytoplasmic domain were found to be particularly reactive to oxidants and mediated band 3 covalent dimerization via disulfide bonds. Thus, parasites promote oxidative alterations in the membrane of the host which lead to exposure of antigenic sites recognized by anti-band 3 auto-antibodies. Formation of band 3 clusters appears to be mediated by cytoplasmic binding of hemichromes and also by direct band 3 oxidation, whereby clustered, oxidized and antigenic band 3 was underglycosylated.

Oxidative stress in malaria parasite-infected erythrocytes: host–parasite interactions

Experimenta naturae, like the glucose-6-phosphate dehydrogenase deficiency, indicate that malaria parasites are highly susceptible to alterations in the redox equilibrium. This offers a great potential for the development of urgently required novel chemotherapeutic strategies. However, the relationship between the redox status of malarial parasites and that of their host is complex. In this review article we summarise the presently available knowledge on sources and detoxification pathways of reactive oxygen species in malaria parasite-infected red cells, on clinical aspects of redox metabolism and redox-related mechanisms of drug action as well as future prospects for drug development. As delineated below, alterations in redox status contribute to disease manifestation including sequestration, cerebral pathology, anaemia, respiratory distress, and placental malaria. Studying haemoglobinopathies, like thalassemias and sickle cell disease, and other red cell defects that provide protection against malaria allows insights into this fine balance of redox interactions. The host immune response to malaria involves phagocytosis as well as the production of nitric oxide and oxygen radicals that form part of the host defence system and also contribute to the pathology of the disease. Haemoglobin degradation by the malarial parasite produces the redox active by-products, free haem and H(2)O(2), conferring oxidative insult on the host cell. However, the parasite also supplies antioxidant moieties to the host and possesses an efficient enzymatic antioxidant defence system including glutathione- and thioredoxin-dependent proteins. Mechanistic and structural work on these enzymes might provide a basis for targeting the parasite. Indeed, a number of currently used drugs, especially the endoperoxide antimalarials, appear to act by increasing oxidant stress, and novel drugs such as peroxidic compounds and anthroquinones are being developed.

Potentiation of the antimalarial action of chloroquine in rodent malaria by drugs known to reduce cellular glutathione levels

Ferriprotoporphyrin IX (FP) is released inside the food vacuole of the malaria parasite during the digestion of host cell hemoglobin. FP is detoxified by its biomineralization to hemozoin. This process is effectively inhibited by 4-aminoquinolines. As a result FP accumulates in the membrane fraction and associates with enzymes of infected cells in parallel with parasite killing. Free FP is degraded by reduced glutathione (GSH). This degradation is inhibited by chloroquine (CQ) and amodiaquine (AQ) but not by quinine (Q) or mefloquine (MQ). Increased GSH levels in Plasmodium falciparum-infected cells confer resistance to CQ and vice versa, and sensitize CQ-resistant Plasmodium berghei by inhibiting the synthesis of glutathione. Some drugs are known to reduce GSH in body tissues when used in excess, either due to their pro-oxidant activity or their ability to form conjugates with GSH. We show that acetaminophen, indomethacin and disulfiram were able to potentiate the antimalarial action of sub-curative doses of CQ and AQ in P. berghei- or Plasmodium vinckei petteri-infected mice, but not that of Q and MQ. In contrast, N-acetyl-cysteine which is expected to increase the cellular levels of GSH, antagonized the action of CQ. Although these results imply that alteration in GSH are involved, measurement of total glutathione either in uninfected or P. berghei-infected mice, treated with these drugs did not reveal major changes. In conclusion, experimental evidences provided in this study suggest that some off the counter drugs can be used in combination with some antimalarials to which the parasite has become resistant.

Defective organization of the erythroid cell membrane in a novel case of congenital anemia

In the present paper, we demonstrate the erythroid cell membrane unique properties in a previously characterized case of hemoglobin-H disease, associated with congenital dyserythropoietic anemia type-I features. In order to explain the patient's cell membrane distortions and the high affinity for the various intracellular inclusions, we studied its composition and structure in comparison to other anemic and non-anemic cases. Red cells from peripheral blood were fractionated into cellular, membrane and protein extracts. Membrane attached immunocomplexes were separated and collected by immunoprecipitation. The subcellular fractions were analyzed by SDS-PAGE electrophoresis and immunoblotted against a variety of erythroid-specific antibodies. The protein composition of the membrane was characterized by immunogold electron microscopy. In the membrane of the CDA-associated case, we identified sialic acid and protein deficiencies, formation of protein crosslinkings, excesses of bound globin and immunoglobulins and aberrant peptides. In contrast to the typical hemoglobin-H disease, the ghost-bound globin exhibited preferential attachment to the skeletal proteins than the band 3 and the skeleton-bound globin consisted not only of beta- but also of alpha-globin chains. Another hallmark, probably associated with the CDA defect, was the participation of glycophorins in the membrane-bound immunocomplexes and the pathological clustering of the latter in the membrane. This study strongly suggests that the result of the combinatorial effects on the diseased membrane created a unique profile, quite distinct from the one observed in several typical hemoglobinopathies. Our observations shed light into critical membrane alterations leading to hemolysis in the novel CDA-associated disease and probably into the CDA-I or CDA-I-like diseases.