Removal of erythrocyte membrane iron in vivo ameliorates the pathobiology of murine thalassemia

A randomized placebo-controlled clinical trial of oral green tea epigallocatechin 3-gallate on erythropoiesis and oxidative stress in transfusion-dependent β-thalassemia patients

β-Thalassemia patients suffer from ineffective erythropoiesis and increased red blood cell (RBC) hemolysis. Blood transfusion, erythropoietic enhancement, and antioxidant supplementation can ameliorate chronic anemia. Green tea extract (GTE) is comprised of catechin derivatives, of which epigallocatechin-3-gallate (EGCG) is the most abundant, presenting free-radical scavenging, iron-chelating, and erythropoiesis-protective effects. The present study aimed to evaluate the effects of GTE tablets on the primary outcome of erythropoiesis and oxidative stress parameters in transfusion-dependent β-thalassemia (TDT) patients. Twenty-seven TDT patients were randomly divided into placebo and GTE tablet (50 and 100 mg EGCG equivalent) groups and assigned to consume the product once daily for 60 days. Blood was collected for analysis of hematological, biochemical, and oxidative stress parameters. Accordingly, consumption of GTE tablets improved blood hemoglobin levels when compared with the placebo; however, there were more responders to the GTE tablets. Interestingly, amounts of nonheme iron in RBC membranes tended to decrease in both GTE tablet groups when compared with the placebo. Importantly, consumption of GTE tablets lowered plasma levels of erythroferrone (p < 0.05) and reduced bilirubin non-significantly and dose-independently. Thus, GTE tablets could improve RBC hemolysis and modulate erythropoiesis regulators in transfusion-dependent thalassemia patients.

A computational model to understand mouse iron physiology and disease

It is well known that iron is an essential element for life but is toxic when in excess or in certain forms. Accordingly there are many diseases that result directly from either lack or excess of iron. Yet many molecular and physiological aspects of iron regulation have only been discovered recently and others are still elusive. There is still no good quantitative and dynamic description of iron absorption, distribution, storage and mobilization that agrees with the wide array of phenotypes presented in several iron-related diseases. The present work addresses this issue by developing a mathematical model of iron distribution in mice calibrated with ferrokinetic data and subsequently validated against data from mouse models of iron disorders, such as hemochromatosis, β-thalassemia, atransferrinemia and anemia of inflammation. To adequately fit the ferrokinetic data required inclusion of the following mechanisms: a) transferrin-mediated iron delivery to tissues, b) induction of hepcidin by transferrin-bound iron, c) ferroportin-dependent iron export regulated by hepcidin, d) erythropoietin regulation of erythropoiesis, and e) liver uptake of NTBI. The utility of the model to simulate disease interventions was demonstrated by using it to investigate the outcome of different schedules of transferrin treatment in β-thalassemia.

Iron is an essential nutrient in almost all life forms. In humans and animals iron is used for respiration and for transporting oxygen inside red blood cells. But in excess iron can be toxic and therefore the body regulates its distribution and absortion through the action of hormones, which is not yet completely understood. Here we created a computational model of the regulation of iron distribution in the body of a mouse based on experimental data. The model can accurately simulate many iron diseases such as anemia, hemochromatosis, and thalassemia. This computational model is helpful to understand the basis of these diseases and plan therapies to address them.

Enhancing uniformity and overall quality of red cell concentrate with anaerobic storage

BACKGROUND

Recent research focused on understanding stored red blood cell (RBC) quality has demonstrated high variability in measures of RBC function and health across units. Studies have historically linked this high variability to variations in processing, storage method, and age. More recently, a large number of studies have focused on differences in donor demographics, donor iron sufficiency, and genetic predisposition of the donor to poor storage, particularly through mechanisms of accelerated oxidative damage. A study was undertaken to evaluate a potential additional source of unit to unit variation in stored RBC: the role of variable percent oxygen saturation (%SO₂) levels on blood quality parameters during storage.

MATERIALS AND METHODS

%SO₂ data from 492 LR-RBC/AS-3 units used for internal and external collaborative research was included in the analysis. Whole blood units were processed into red blood cells, AS-3 added, leucocyte reduced, in compliance with American Association of Blood Banks guidelines. LR-RBC/AS-3 products were subsequently analysed for %SO₂ levels within 3-24 hours of phlebotomy using a co-oximeter. Separately, to evaluate the impact of pre-storage as well as increasing levels of %SO₂ during storage, a pool-and-split study was performed. Four units of LR-RBC/AS-3 were split 6 ways; "as is" (control), hyperoxygenated to more than 90%, and four levels of pre-storage %SO₂. The units were periodically sampled up to 42 days and analysed for %SO₂, pCO₂, methaemoglobin, ATP, 2,3-BPG as well as with the metabolomics workflow.

RESULTS

The measured mean %SO₂ in LR-RBC/AS-3 within 24 hours of collection was 45.9±17.5% with (32.7-61.0 IQR). %SO₂ in all products increased to approximately 95-100% in three weeks. Measured blood quality parameters including ATP, % haemolysis, methaemoglobin, oxidised lipids, and GSH/GSSG indicated suppressed cellular metabolism and increased red cell degradation in response to higher %SO₂ levels.

DISCUSSION

The surprisingly high variability in starting %SO₂ levels, coupled with negative impacts of high oxygen saturation on red blood cell quality indicates that oxygen levels may be an important and under-appreciated source of unit-to-unit variability in RBC quality.

Physiology and pathophysiology of iron in hemoglobin-associated diseases

Iron overload and iron toxicity, whether because of increased absorption or iron loading from repeated transfusions, can be major causes of morbidity and mortality in a number of chronic anemias. Significant advances have been made in our understanding of iron homeostasis over the past decade. At the same time, advances in magnetic resonance imaging have allowed clinicians to monitor and quantify iron concentrations noninvasively in specific organs. Furthermore, effective iron chelators are now available, including preparations that can be taken orally. This has resulted in substantial improvement in mortality and morbidity for patients with severe chronic iron overload. This paper reviews the key points of iron homeostasis and attempts to place clinical observations in patients with transfusional iron overload in context with the current understanding of iron homeostasis in humans.

Heme oxygenase 1 is expressed in murine erythroid cells where it controls the level of regulatory heme

Heme is essential for the function of all aerobic cells. However, it can be toxic when it occurs in a non-protein-bound form; cells maintain a fine balance between heme synthesis and catabolism. The only physiological mechanism of heme degradation is by heme oxygenases (HOs). The heme-inducible isoform, HO-1, has been extensively studied in numerous nonerythroid cells, but virtually nothing is known about the expression and potential significance of HO-1 in developing red blood cells. We have demonstrated that HO-1 is present in erythroid cells and that its expression is upregulated during erythroid differentiation. Overexpression of HO-1 in erythroid cells impairs hemoglobin synthesis, whereas HO-1 absence enhances hemoglobinization in cultured erythroid cells. Based on these results, we conclude that HO-1 controls the regulatory heme pool at appropriate levels for any given stage of erythroid differentiation. In summary, our study brings to light the importance of HO-1 expression for erythroid development and expands our knowledge about the fine regulation of hemoglobin synthesis in erythroid cells. Our results indicate that HO-1 plays an important role as a coregulator of the erythroid differentiation process. Moreover, HO-1 expression must be tightly regulated during red blood cell development.

Proteomic analysis of ERK1/2-mediated human sickle red blood cell membrane protein phosphorylation

BACKGROUND

In sickle cell disease (SCD), the mitogen-activated protein kinase (MAPK) ERK1/2 is constitutively active and can be inducible by agonist-stimulation only in sickle but not in normal human red blood cells (RBCs). ERK1/2 is involved in activation of ICAM-4-mediated sickle RBC adhesion to the endothelium. However, other effects of the ERK1/2 activation in sickle RBCs leading to the complex SCD pathophysiology, such as alteration of RBC hemorheology are unknown.

RESULTS

To further characterize global ERK1/2-induced changes in membrane protein phosphorylation within human RBCs, a label-free quantitative phosphoproteomic analysis was applied to sickle and normal RBC membrane ghosts pre-treated with U0126, a specific inhibitor of MEK1/2, the upstream kinase of ERK1/2, in the presence or absence of recombinant active ERK2. Across eight unique treatment groups, 375 phosphopeptides from 155 phosphoproteins were quantified with an average technical coefficient of variation in peak intensity of 19.8%. Sickle RBC treatment with U0126 decreased thirty-six phosphopeptides from twenty-one phosphoproteins involved in regulation of not only RBC shape, flexibility, cell morphology maintenance and adhesion, but also glucose and glutamate transport, cAMP production, degradation of misfolded proteins and receptor ubiquitination. Glycophorin A was the most affected protein in sickle RBCs by this ERK1/2 pathway, which contained 12 unique phosphorylated peptides, suggesting that in addition to its effect on sickle RBC adhesion, increased glycophorin A phosphorylation via the ERK1/2 pathway may also affect glycophorin A interactions with band 3, which could result in decreases in both anion transport by band 3 and band 3 trafficking. The abundance of twelve of the thirty-six phosphopeptides were subsequently increased in normal RBCs co-incubated with recombinant ERK2 and therefore represent specific MEK1/2 phospho-inhibitory targets mediated via ERK2.

CONCLUSIONS

These findings expand upon the current model for the involvement of ERK1/2 signaling in RBCs. These findings also identify additional protein targets of this pathway other than the RBC adhesion molecule ICAM-4 and enhance the understanding of the mechanism of small molecule inhibitors of MEK/1/2/ERK1/2, which could be effective in ameliorating RBC hemorheology and adhesion, the hallmarks of SCD.

Quercetin-iron chelates are transported via glucose transporters

Flavonoids are well-known antioxidants and free radical scavengers. Their metal-binding activity suggests that they could be effective protective agents in pathological conditions caused by both extracellular and intracellular oxidative stress linked to metal overload. Quercetin is both a permeant ligand via glucose transport proteins (GLUTs) and a high-affinity inhibitor of GLUT-mediated glucose transport. Chelatable "free iron" at micromolar concentrations in body fluids is a catalyst of hydroxyl radical (OH(•)) production from hydrogen peroxide. A number of flavonoids, e.g., quercetin, luteolin, chrysin, and 3,6-dihydroxyflavone, have been demonstrated to chelate intracellular iron and suppress OH(•) radical production in Madin Darby canine kidney cells. The most effective chelation comes from the flavonone B ring catechol found in both quercetin and luteolin. We show here that quercetin concentrations of <1μM can facilitate chelatable iron shuttling via GLUT1 in either direction across the cell membrane. These siderophoric effects are inhibited by raised quercetin concentrations (>1μM) or GLUT inhibitors, e.g., phloretin or cytochalasin B, and iron efflux is enhanced by impermeant extracellular iron chelators, either desferrioxamine or rutin. This iron shuttling property of quercetin might be usefully harnessed in chelotherapy of iron-overload conditions.

Robust erythrophagocytosis leads to macrophage apoptosis via a hemin-mediated redox imbalance: role in hemolytic disorders

MP from the RES are responsible for the clearance of senescent RBC. Although the frequency of senescent RBC is low under steady-state conditions, it increases dramatically during hemolytic disorders, resulting in enhanced erythrophagocytosis. As erythrophagocytosis has been involved in MP dysfunction and as certain hemolytic disorders associate to MP apoptosis, a possible link between erythrophagocytosis and the viability of phagocytes was investigated herein. To mimic hemolytic disorders, two distinct in vitro models, artificially oxidized RBC and DSRBC, were chosen to study the erythrophagocytosis impact on the viability of J774A.1 MP. Although CRBC were weakly phagocytosed and did not affect MP viability significantly, erythrophagocytosis of oxidized RBC and DSRBC was robust and resulted in a sharp decrease of MP viability via apoptosis. Under these conditions, Hb-derived HE was shown to be involved in the induction of apoptosis. Moreover, oxidized RBC, DSRBC, and HE generated ROS species, which were responsible for the apoptosis of MP. Furthermore, HO-1, strongly induced in response to treatment with oxidized RBC, DSRBC, or HE, was shown to protect MP partially against apoptosis, suggesting that robust erythro-phagocytosis may exceed the detoxification capabilities of MP. Taken together, these results suggest that enhanced erythrophagocytosis associated to hemolytic disorders leads to MP apoptosis in vitro and may have critical implications for the control of malaria infection and for the exacerbated susceptibility to bacterial infections during hemolytic disorders.

A systems biology consideration of the vasculopathy of sickle cell anemia: the need for multi-modality chemo-prophylaxsis

Much of the morbidity and mortality of sickle cell anemia is accounted for by a chronic vasculopathy syndrome. There is currently no identified therapy, interventional or prophylactic, for this problem. For two reasons, development of an effective therapeutic approach will require a systems biology level perspective on the vascular pathobiology of sickle disease. In the first place, multiple biological processes contribute to the pathogenesis of vasculopathy: red cell sickling, inflammation and adhesion biology, coagulation activation, stasis, deficient bioavailability and excessive consumption of NO, excessive oxidation, and reperfusion injury physiology. The probable hierarchy of involvement of these disparate sub-biologies places inflammation caused by reperfusion injury physiology as the likely, proximate, linking pathophysiological factor. In the second place, most of these sub-biologies overlap with each other and, in any case, have multiple points of potential interaction and transactivation. Consequently, an approach modeled upon chemotherapy for cancer is needed. This would be a truly multi-modality approach that hopefully could be achieved via employment of relatively few drugs. It is proposed here that the specific combination of a statin with suberoylanilide hydroxamic acid would provide a suitable, broad, multi-modality approach to chemo-prophylaxis for sickle vasculopathy.

Current knowledge about the functional roles of phosphorylative changes of membrane proteins in normal and diseased red cells

With the advent of proteomic techniques the number of known post-translational modifications (PTMs) affecting red cell membrane proteins is rapidly growing but the understanding of their role under physiological and pathological conditions is incompletely established. The wide range of hereditary diseases affecting different red cell membrane functions and the membrane modifications induced by malaria parasite intracellular growth represent a unique opportunity to study PTMs in response to variable cellular stresses. In the present review, some of the major areas of interest in red cell membrane research have been considered as modifications of erythrocyte deformability and maintenance of the surface area, membrane transport alterations, and removal of diseased and senescent red cells. In all mentioned research areas the functional roles of PTMs are prevalently restricted to the phosphorylative changes of the more abundant membrane proteins. The insufficient information about the PTMs occurring in a large majority of the red membrane proteins and the general lack of mass spectrometry data evidence the need of new comprehensive, proteomic approaches to improve the understanding of the red cell membrane physiology.

Alternative treatment paradigm for thalassemia using iron chelators

OBJECTIVE

beta-thalassemia major, or Cooley's anemia, is a red blood cell disorder requiring lifelong blood transfusions for survival. Erythrocytes accumulate toxic iron at their membranes, triggering an oxidative cascade that leads to their premature destruction in high numbers. We hypothesized that removing this proximate iron compartment as a primary treatment, using standard and alternative orally active iron chelators, could prevent hastened red cell removal and, clinically, perhaps alleviate the need for transfusion.

MATERIALS AND METHODS

Iron chelators of the pyridoxal isonicotinoyl hydrazone family (pyridoxal isonicotinoyl hydrazone and its analog pyridoxal ortho-chlorobenzoyl hydrazone) were evaluated in addition to the present mainstay, desferrioxamine and deferiprone, in vitro and in vivo.

RESULTS

Treatment of human beta-thalassemic erythrocytes with chelators resulted in significant depletion of membrane-associated iron and reduction of oxidative stress, as evaluated by methemoglobin levels. When administered to beta-thalassemic mice, iron chelators mobilized erythrocyte membrane iron, reduced cellular oxidation, and prolonged erythrocyte half-life. The treated thalassemic mice also showed improved hematological abnormalities. Remarkably, a beneficial effect as early as the erythroid precursor stage was manifested by normalized proportions of mature vs immature reticulocytes. All four compounds were also found to mitigate iron accumulation in target organs, a critical determinant for patient survival. In this respect, pyridoxal ortho-chlorobenzoyl hydrazone displayed higher activity relative to other chelators tested, further diminishing iron in liver and spleen by up to approximately fivefold and twofold, respectively.

CONCLUSION

Our study demonstrates the ability of iron chelators to improve several of the fundamental pathological disturbances of thalassemia, and reveals their potential for clinical use in diminishing requirement for transfusion when administered early in disease development.

Extended storage of red blood cells under anaerobic conditions

BACKGROUND

Red blood cells (RBC) are subject to oxidative stress by reactive oxygen species during refrigerated storage. Near-complete removal of oxygen from red cells during storage should eliminate this contributor to the red cell 'storage lesion'. The in vitro effects of storing red cells under oxygen-depleted conditions for extended periods were investigated, and these were correlated with the observed recoveries after reinfusion.

STUDY DESIGN AND METHODS

Units of red cells, obtained after 'soft spin', were placed in a double volume of AS-3 additive solution and subdivided. Oxygen in the test units was depleted by repeated exposure to Ar gas (to O(2) saturation < 4%), and units were stored in anaerobic canisters for up to 15 weeks. Samples were taken weekly to monitor adenosine triphosphate (ATP), 2,3-diphosphoglycerate (2,3-DPG), cell-free haemoglobin, and vesicle production. In a parallel experiment, six units of red cells was depleted of oxygen in a similar manner, stored for 8, 9 and 10 weeks, and reinfused autologously to determine the 24 h post-transfusion recovery via (51)Cr/(99m)Tc radiolabelling. A similar study was also carried out using EAS61 additive solution, which by itself, had shown the ability to support 9-week storage, comparing biochemical profiles and in vivo recovery after aerobic vs. anaerobic storage.

RESULTS

Oxygen-depleted AS-3 units had significantly elevated ATP levels compared to controls. They also had significantly lower cell free haemoglobin and vesicle production when RBCs were stored for more than 9 weeks. An average of over 75% post-transfusion survival was observed after 9 weeks of anaerobic storage with less than 0.43% haemolysis. However, no further extension of storage was achieved with EAS61 additive.

CONCLUSION

Anaerobic conditions permit acceptable 9-week storage of RBCs using double-volume AS-3 additive solution. It did not synergize with the alkaline, 9-week additive, EAS61, to further lengthen the acceptable storage time. These studies indicate that anaerobic storage may allow reduction in the effect of the storage lesion, but suggest that other factors contribute to limitations of RBC storage as well.

Peroxidative stress and antioxidant enzymes in children with beta-thalassemia major

OBJECTIVE

Regular blood transfusions and secondary iron overload make thalassemic erythrocytes prone to peroxidative injury. Although some reports suggest endogenous free radical damage in thalassemia, there remains discrepancy in the status of antioxidant enzymes. The aim of this study was to evaluate the extent of lipid peroxidation and status of antioxidant enzyme in children with beta-thalassemia.

METHODS

Fifty transfusion-dependent beta-thalassemics were subjected to analysis of lipoperoxides as malondialdehyde (MDA), nitric oxide (NOx), superoxide dismutase (SOD), glutathione (GSH), and glutathione peroxidase (GPx) along with serum iron and ferritin, liver functions and uric acid. Plasma MDA was analyzed to indicate the oxidative parameters, whereas the erythrocyte SOD, GPx, and plasma NOx were measured to show the antioxidant status of the children. All these parameters in 30 non-anemic healthy controls attending the child health promotion clinic of hospital were also studied.

RESULTS

All the patients were iron overloaded. Markers of free radical injury such as MDA and antioxidant enzyme SOD and NOx levels were significantly elevated in thalassemic children while mean GPx levels were decreased in patients compared to controls (P < 0.001). All these markers significantly correlated with serum ferritin levels. There was no significant difference in levels of GSH measured but it correlated with serum iron levels.

CONCLUSION

Our study results suggest that iron overload causes peroxidative damage in beta-thalassemia and antioxidant systems try to compensate for reducing lipid peroxidation to lower tissue damage.

Labile plasma iron (LPI) as an indicator of chelatable plasma redox activity in iron-overloaded beta-thalassemia/HbE patients treated with an oral chelator

Persistent levels of plasma nontransferrin bound iron (NTBI) have been associated with tissue iron overload and toxicity. We characterized NTBI's susceptibility to deferoxamine (directly chelatable iron [DCI]) and redox activity (labile plasma iron [LPI]) during the course of long-term, continuous L1 (deferiprone) treatment of patients with hemoglobin E disease and beta-thalassemia (n = 17). In 97% of serum samples (n = 267), the LPI levels were more than 0.4 microM (mean +/- SEM, 3.1 +/- 0.2 microM) and the percent transferrin (Tf) saturation more than 85 (111 +/- 6), whereas only in 4% of sera were the LPI levels more than 0.4 microM for Tf saturation less than 85%. Daily administration of L1 (50 mg/kg) for 13 to 17 months caused both LPI and DCI to decrease from respective initial 5.1 +/- 0.5 and 5.4 +/- 0.6 microM to steady mean levels of 2.18 +/- 0.24 and 2.81 +/- 0.14 microM. The steady lowest levels of LPI and DCI were attained after 6 to 8 months, with a half time (t(1/2)) of 2 to 3 months. Serum ferritin and red cell membrane-associated iron followed a similar course but attained steady basal levels only after 10 to 12 months of continuous treatment, with a t(1/2) of 5 to 7 months. These studies indicate that LPI and DCI can serve as early indicators of iron overload and as measures for the effectiveness of iron chelation in reducing potentially toxic iron in the plasma.

The effects of intravenous iron treatment on oxidant stress and erythrocyte deformability in hemodialysis patients

BACKGROUND

It is well known that free iron causes oxidant stress to increase. However data concerning whether intravenously (I.V) administered iron in maintenance doses (10-20 mg) gives rise to increased oxidant stress and disturbed erythrocyte deformability (EDEF) in hemodialysis (HD) patients is lacking. In the present study, we aimed to evaluate and compare the effects of I.V iron on oxidant stress and EDEF.

PATIENTS AND METHODS

Thirteen HD patients (10 males, 3 females, mean age: 49.9 +/- 13.4 years), given I.V iron were included in the study. All patients were undergone three consecutive HD session. The first HD session was performed without iron administration (Group 1), whereas in the following sessions the same patients were given 20 mg (Group 2) and 100 mg (Group 3) iron III hydroxide sucrose (Venofer--Abdi Ibrahim) I.V at the end of the dialysis session. In study periods, 7 blood samples were drawn from each patient: before dialysis, at the end of the dialysis (just after the session), 15, 30, 60, 90 and 120 minutes after each dialysis session. However 15 minute samples were not drawn in the third group, since I.V iron was given by infusion in 30 minutes. EDEF and plasma malondialdehyde (MDA) were studied in all samples.

RESULTS

When the results of the session without iron were considered, bivariate correlation analysis did not reveal any correlation between MDA and EDEF. When the course of each parameter were considered separately, MDA levels 90 and 120 minutes after HD session were significantly higher than that of the before and just after the HD session (p < 0.05). Whereas EDEF in 60, 90 and 120 minutes after HD session was found to be worsened when compared to before and just after HD sessions' values (p < 0.05). When results of the session with 20 mg iron were considered, EDEF and MDA values were not found to be correlated and throughout the course. Although EDEF did not present any significant change, MDA levels 60, 90 and 120 minutes after HD session were found to be significantly higher than that of the 15 and 30 minutes after HD session (p < 0,05). When results of the session with 100 mg iron were considered, MDA levels 30, 60, 90 and 120 minutes after HD session were found to be significantly higher than that of the before and just after the HD sessions' (p < 0,05). EDEF in 90 and 120 minutes after HD session was improved and no correlation between MDA and EDEF was observed. When groups were compared with each other, plasma MDA levels in session with 100 mg iron at the beginning, at the end and 30 minutes after HD were significantly lower than that of the without iron group (p < 0.05). Similarly MDA levels in session with 100 mg iron at the beginning, at the end, 30 minutes and 120 minutes after HD were significantly lower than that of the 20 mg iron (p < 0.05). When EDEF values in sessions with 20 mg iron and without iron were considered, only values 60 and 90 minutes after dialysis were significantly improved in 20 mg iron group. The others were statistically similar.

CONCLUSION

In the present study, it was observed that I.V administered iron in 20 and 100 mg doses did not cause additional deteriorating effect on oxidant stress and EDEF was even improved by I.V iron.

Mechanisms leading to sustained reversion of beta-thalassemia in mice by doxycycline-controlled Epo delivery from muscles

Erythropoiesis has been considered as a potential treatment for beta-thalassemia. Although Epo secretion from genetically engineered muscles allowed long-term correction of the disease in the mouse, repeated injections of rHuEpo were disappointing in human patients. Whether different mechanisms operate in humans and mice or whether Epo exhibits different biological activity depending on the administration route is currently unknown. We provide evidence that mechanisms recruited over a 36-week follow-up in beta-thalassemic mice were similar to those acting during stress-induced erythropoiesis in humans. beta-Thalassemic mice were rendered steadily normocythemic by the intramuscular injection of a tetracycline-inducible AAV vector encoding mouse Epo. Doxycycline dosage was adapted to hematocrit. Circulating red blood cells essentially synthesized beta-minor globin, the mouse equivalent to human gamma-globin. Quantification of erythroid progenitors indicated a steady-state expansion of erythroid burst-forming units programmed for beta-minor globin synthesis and a hastening of their maturation to hemoglobin-synthesizing cells. We discuss hypotheses that could account for the failure to recruit this mechanism over the long term in beta-thalassemic patients and raise the possibility of Epo gene therapy trials to treat beta-thalassemia.

Heme-regulated eIF2alpha kinase (HRI) is required for translational regulation and survival of erythroid precursors in iron deficiency

Although the physiological role of tissue-specific translational control of gene expression in mammals has long been suspected on the basis of biochemical studies, direct evidence has been lacking. Here, we report on the targeted disruption of the gene encoding the heme-regulated eIF2alpha kinase (HRI) in mice. We establish that HRI, which is expressed predominantly in erythroid cells, regulates the synthesis of both alpha- and beta-globins in red blood cell (RBC) precursors by inhibiting the general translation initiation factor eIF2. This inhibition occurs when the intracellular concentration of heme declines, thereby preventing the synthesis of globin peptides in excess of heme. In iron-deficient HRI(-/-) mice, globins devoid of heme aggregated within the RBC and its precursors, resulting in a hyperchromic, normocytic anemia with decreased RBC counts, compensatory erythroid hyperplasia and accelerated apoptosis in bone marrow and spleen. Thus, HRI is a physiological regulator of gene expression and cell survival in the erythroid lineage.

betaMinor-globin messenger RNA accumulation in reticulocytes governs improved erythropoiesis in beta thalassemic mice after erythropoietin complementary DNA electrotransfer in muscles

Mechanisms governing the induction of effective erythropoiesis in response to erythropoietin (Epo) oversecretion have been investigated in beta thalassemic C57Bl/6(Hbbth) mice. Naked DNA encoding an expression vector for mouse Epo was introduced into skeletal muscles by electrotransfer. A transient increase of serum Epo concentrations with a proportional augmentation of hematocrit values was observed. Various parameters relevant to beta thalassemia were surveyed in blood samples taken before treatment, at the peak of Epo secretion, and when the phenotype reverted to anemia. We measured globin messenger RNA (mRNA) levels in reticulocytes by real-time quantitative polymerase chain reaction, globin chain synthesis levels, and several indicators of erythrocyte membrane quality, including bound alpha chains, bound immunoglobulins, main protein components, and iron compartmentalization. Data indicated that high serum Epo levels primarily affect betaminor-globin mRNA accumulation in reticulocytes. Other changes subsequent to intense Epo stimulation, like increased betaminor/alpha-globin chain synthesis ratio, reduced levels of alpha chains and immunoglobulins bound to membranes, improved spectrin/band 3 ratio, increased red blood cell survival, and improved erythropoiesis appeared as consequences of increased betaminor-globin mRNA levels. This conclusion is consistent with models postulating that intense Epo stimulation induces the expansion and differentiation of erythroid progenitors committed to fetal erythropoiesis. Although phenotypic correction was partial in mice, and comparable achievements will probably be more difficult to obtain in humans, naked DNA electrotransfer may provide a safe and low-cost method for reassessing the potentials of Epo as an inducer of fetal erythropoiesis reactivation in patients with beta thalassemia.

Reduced oxidative-stress response in red blood cells from p45NFE2-deficient mice

p45NF-E2 is a member of the cap 'n' collar (CNC)-basic leucine zipper family of transcriptional activators that is expressed at high levels in various types of blood cells. Mice deficient in p45NF-E2 that were generated by gene targeting have high mortality from bleeding resulting from severe thrombocytopenia. Surviving p45nf-e2(-/-) adults have mild anemia characterized by hypochromic red blood cells (RBCs), reticulocytosis, and splenomegaly. Erythroid abnormalities in p45nf-e2(-/-) animals were previously attributed to stress erythropoiesis caused by chronic bleeding and, possibly, ineffective erythropoiesis. Previous studies suggested that CNC factors might play essential roles in regulating expression of genes that protect cells against oxidative stress. In this study, we found that p45NF-E2-deficient RBCs have increased levels of reactive oxygen species and an increased susceptibility to oxidative-stress-induced damage. Deformability of p45NF-E2-deficient RBCs was markedly reduced with oxidative stress, and mutant cells had a reduced life span. One possible reason for increased sensitivity to oxidative stress is that catalase levels were reduced in mutant RBCs. These findings suggest a role for p45NF-E2 in the oxidative-stress response in RBCs and indicate that p45NF-E2 deficiency contributes to the anemia in p45nf-e2(-/-) mice. (Blood. 2001;97:2151-2158)

Antioxidant defense status of red blood cells of patients with beta-thalassemia and Ebeta-thalassemia

Anemia in beta-thalassemia is caused by a combination of ineffective erythropoiesis and premature hemolysis of RBC in the peripheral circulation. Excess of the alpha-globin chain present in beta-thalassemic RBC is mainly responsible for oxidative damage of erythrocyte membrane protein. The activities of glucose-6-phosphate dehydrogenase, glutathione reductase, glutathione peroxidase, and glutathione-S-transferase, and the catalytic activity of catalase and superoxide dismutase, and the concentrations of non-enzymic antioxidants such as reduced glutathione were measured to estimate the status of the antioxidant defense system in the erythrocytes for protection against oxidative stress. The extent of lipid peroxidation was also estimated in thalassemic erythrocytes. Significantly lower activities of reduced glutathione indicate the cell to be in a pro-oxidant state and decreased activity of catalase favors hydrogen peroxide-mediated lipid peroxidation in beta-thalassemic and Ebeta-thalassemic RBC.

Improvement of mouse beta-thalassemia by electrotransfer of erythropoietin cDNA

OBJECTIVE

A new intramuscular DNA electrotransfer method for erythropoietin (EPO) expression was evaluated in the natural mouse model of human beta-thalassemia (Hbb-thal1) in terms of its ability to reverse the anemia and improve the thalassemic features of erythrocytes.

MATERIALS AND METHODS

Intramuscular injection of small amounts of a plasmid encoding mouse EPO, immediately followed by controlled electric pulses, was used.

RESULTS

This procedure induced very high hematocrit levels in beta-thalassemic mice compared to nonelectrotransferred mice. The hematocrit increase was dose dependent, still increased 4 months after injection of plasmid DNA, and associated with a high transgenic EPO blood level in all mice (up to 2500 mU/mL of plasma). EPO gene electrotransfer not only led to a long-lasting and dose-dependent increase in the hematocrit but also to a 100% increase in the lifespan of erythrocytes of thalassemic mice. This was related to a nearly complete reestablishment of alpha/beta globin chain balance, as demonstrated by a marked decrease in unpaired alpha globin chain. Eight months after the first electrotransfer of pCMV-mEPO plasmid, reinjection of the same construct raised the hematocrit to a level close to that observed following the first electrotransfer.

CONCLUSION

This is the first description of the use of plasmid DNA to achieve long-term improvement in a mouse model of a human genetic disorder.

Modulation of transduced erythropoietin expression by iron

OBJECTIVE

Future prospects for gene therapy of chronic anemias involve expression of the erythropoietin transgene, which is regulated by oxygen tension. However, other factors such as cytokines or the iron load of erythropoietin-expressing cells can concomitantly modulate transgene expression, as shown for the expression of the endogenous erythropoietin gene in human cell lines and in animals. We tested the effects of iron overload or depletion on the expression of the mouse erythropoietin transgene (cDNA), driven by the hypoxia-regulated phosphoglycerate kinase 1 promoter.

MATERIALS AND METHODS

Retrovirally transduced mouse cells (C3H fibroblasts or C2C12 myoblasts) were cultured in normoxia (room air, O2: 21%) or hypoxia (O2: 1.5%) in the presence or absence of hemin (an iron donor) or deferiprone (an iron chelator), both of which easily enter the cell.

RESULTS

Hemin inhibited the hypoxia-induced expression of the transgene. In contrast, deferiprone enhanced the hypoxia-induced expression of the erythropoietin transgene and induced its expression in normoxia.

CONCLUSION

These results show that, in addition to oxygen partial pressure, the intracellular iron content is critical in the modulation of hypoxia-regulated erythropoietin transgene expression.

Transport of 14C-deferiprone in normal, thalassaemic and sickle red blood cells

The transport of deferiprone (L1) in normal (N), sickle (S) and thalassaemic (T) red blood cells (RBC) was determined by incubation with 14C-L1 at 37 degrees C. Following incubation with 0.5 mM 14C-L1 for 4 h, the intracellular concentration of L1 in T RBC was 3 times higher than was found extracellularly. In contrast, no concentration gradient across N and S RBC membranes was detected. Efflux studies showed that T RBC released only 17 +/- 2% of 14C-L1 into the extracellular space. We hypothesize that L1 accumulation in T RBC results from their high content of chelatable iron and formation of large, hydrophilic L1-Fe(III) complexes trapped within the cytosol.

Deferiprone therapy in homozygous human beta-thalassemia removes erythrocyte membrane free iron and reduces KCl cotransport activity

Deposition of free iron is a characteristic feature of beta-thalassemia (beta-thal) red blood cells believed to play an important role in the generation of oxidative injury to the cell membrane. Increased red blood cell KCI cotransport, reduced K content, and cell dehydration are also found in beta-thal red blood cells. It is not known, however, whether deposition of free iron plays a role in these membrane transport changes. To explore this issue, we studied-both in vitro and in vivo-the effect on KCI cotransport of removing red blood cell membrane free iron from beta-thal erythrocytes. Eleven patients with beta-thal major who underwent long-term transfusion and were treated with deferiprone (75 mg/kg/day) for 9 months participated in the study. Deferiprone therapy removed membrane free iron from beta-thal erythrocytes, which was followed by reduced KCI cotransport activity. The reduced KCI cotransport activity was accompanied by an increase in the red blood cell K content. These data suggest that the increased activity of KCI cotransport in beta-thal red blood cells is mediated by the deposition of membrane free iron, a mechanism that may be attenuated by deferiprone therapy.