Elastic hysteresis loop acts as cell deformability in erythrocyte aging.

The decrease in cellular deformability shows strong correlation with erythrocyte aging. Cell deformation can be divided into passive deformation and active deformation; however, the active deformation has been ignored in previous studies. In this work, Young's moduli of age-related erythrocytes were tested by atomic force microscopy. Furthermore, the deformation and passive and active deformation values were calculated by respective areas. Our results showed that erythrocytes in the densest fraction had the highest values of the Young's modulus, deformation, and active deformation, but the lowest values of passive deformation. Moreover, values of the deformation and active deformation both increased gradually with erythrocyte aging. The present data indicate that the elastic hysteresis loop between the approach and the retract curve could be regarded as erythrocyte deformability, and cellular deformability could be characterized by energy states. In addition, active deformation might be a crucial mechanical factor for clearing aged erythrocytes. This could provide an important information on erythrocyte biomechanics in the removal of aged cell.

Erythrocyte aging as a mechanism of anemia and a biomarker of device thrombosis in continuous-flow left ventricular assist devices.

BACKGROUND: Blood trauma caused by continuous-flow left ventricular assist devices (CF-LVADs) has been associated with device thrombosis and anemia. Accurate in vivo quantification of erythrocyte turnover and its contribution to CF-LVAD complications have yet to be elucidated. METHODS: We investigated the age (lifespan) of circulating erythrocytes in subjects with CF-LVAD. Erythrocyte lifespan is a quantitative indicator of in vivo erythrocyte turnover that can be accurately derived from measurement of the exhaled carbon monoxide (CO) level. Sixty non-smoking subjects were prospectively enrolled: 25 had a CF-LVAD without thrombosis; 10 had a CF-LVAD with thrombosis; and 25 were normal controls. End-tidal breath CO levels were measured and used to calculate erythrocyte lifespan. RESULTS: The mean erythrocyte lifespan was significantly shorter in CF-LVAD subjects with (29.7 ± 14.9 days) compared to those without (65.0 ± 17.3 days) device thrombosis (p < 0.0001). The lifespans in these 2 groups were significantly shorter compared with normal controls (96.0 ± 24.9 days, both p < 0.0001). A receiver operator curve demonstrated high sensitivity-specificity for use of erythrocyte lifespan to detect device thrombosis (AUC = 0.94). In addition, all CF-LVAD subjects had low hemoglobin (11.8 ± 2.0 g/dl), and their anemia was normochromic normocytic with elevated mean reticulocyte counts. Erythrocyte lifespan correlated significantly with mean corpuscular hemoglobin concentration (r = 0.56, p = 0.0005) and red cell distribution width (r = -0.65, p < 0.001), but not with reticulocyte count (r = 0.27, p = 0.32). CONCLUSIONS: Erythrocyte lifespan is substantially reduced in subjects with a CF-LVAD, which was more pronounced in the presence of device thrombosis. The etiology of anemia in CF-LVAD was primarily due to accelerated erythrocyte aging. Further studies are needed to determine whether erythrocyte lifespan could provide a practical means of detecting subtle pre-clinical thrombosis.

Understanding quasi-apoptosis of the most numerous enucleated components of blood needs detailed molecular autopsy.

Erythrocytes are the most numerous cells in human body and their function of oxygen transport is pivotal to human physiology. However, being enucleated, they are often referred to as a sac of molecules and their cellularity is challenged. Interestingly, their programmed death stands a testimony to their cell-hood. They are capable of self-execution after a defined life span by both cell-specific mechanism and that resembling the cytoplasmic events in apoptosis of nucleated cells. Since the execution process lacks the nuclear and mitochondrial events in apoptosis, it has been referred to as quasi-apoptosis or eryptosis. Several studies on molecular mechanisms underlying death of erythrocytes have been reported. The data has generated a non-cohesive sketch of the process. The lacunae in the present knowledge need to be filled to gain deeper insight into the mechanism of physiological ageing and death of erythrocytes, as well as the effect of age of organism on RBCs survival. This would entail how the most numerous cells in the human body die and enable a better understanding of signaling mechanisms of their senescence and premature eryptosis observed in individuals of advanced age.

Biomarkers defining the metabolic age of red blood cells during cold storage.

Metabolomic investigations of packed red blood cells (RBCs) stored under refrigerated conditions in saline adenine glucose mannitol (SAGM) additives have revealed the presence of 3 distinct metabolic phases, occurring on days 0-10, 10-18, and after day 18 of storage. Here we used receiving operating characteristics curve analysis to identify biomarkers that can differentiate between the 3 metabolic states. We first recruited 24 donors and analyzed 308 samples coming from RBC concentrates stored in SAGM and additive solution 3. We found that 8 extracellular compounds (lactic acid, nicotinamide, 5-oxoproline, xanthine, hypoxanthine, glucose, malic acid, and adenine) form the basis for an accurate classification/regression model and are able to differentiate among the metabolic phases. This model was then validated by analyzing an additional 49 samples obtained by preparing 7 new RBC concentrates in SAGM. Despite the technical variability associated with RBC processing strategies, verification of these markers was independently confirmed in 2 separate laboratories with different analytical setups and different sample sets. The 8 compounds proposed here highly correlate with the metabolic age of packed RBCs, and can be prospectively validated as biomarkers of the RBC metabolic lesion.

Glycated Hemoglobin, Plasma Glucose, and Erythrocyte Aging.

BACKGROUND: The relationship between HbA1c and blood glucose averages has been characterized many times, yet, a unifying, mechanistic description is still lacking. METHODS: We calculated the level of HbA1c from plasma glucose averages based solely on the in vivo rate of hemoglobin glycation, and the different turnover rates for erythrocytes of different ages. These calculations were then compared to the measured change of HbA1c due to changes in mean blood glucose (MBG), to complex models in the literature, and our own experiments. RESULTS: Analysis of data on erythrocyte ageing patterns revealed that 2 separate RBC turnover mechanisms seem to be present. We calculated the mean red blood cell (RBC) life span within individuals to lie between 60 and 95 days. Comparison of expected HbA1c levels to data taken from continuous glucose monitors and finger-stick MBG yielded good agreement (r = .87, P < .0001). Experiments on the change with time of HbA1c induced by a change of MBG were in excellent agreement with our calculations (r = .98, P < .0001). CONCLUSIONS: RBC turnover seems to be dominated by a constant rate of cell loss, and a mechanism that targets cells of a specific age. Average RBC life span is 80 ± 10.9 days. Of HbA1c change toward treatment goal value, 50% is reached in about 30 days. Many factors contribute to the ratio of glycated hemoglobin, yet we can make accurate estimations considering only the in vivo glycation constant, MBG, and the age distribution of erythrocytes.

Restoring the youth of aged red blood cells and extending their lifespan in circulation by remodelling membrane sialic acid.

Membrane sialic acid (SA) plays an important role in the survival of red blood cells (RBCs), the age-related reduction in SA content negatively impacts both the structure and function of these cells. We have therefore suggested that remodelling the SA in the membrane of aged cells would help recover cellular functions characteristic of young RBCs. We developed an effective method for the re-sialylation of aged RBCs by which the cells were incubated with SA in the presence of cytidine triphosphate (CTP) and α-2,3-sialytransferase. We found that RBCs could be re-sialylated if they had available SA-binding groups and after the re-sialylation, aged RBCs could restore their membrane SA to the level in young RBCs. Once the membrane SA was restored, the aged RBCs showed recovery of their biophysical and biochemical properties to similar levels as in young RBCs. Their life span in circulation was also extended to twofold. Our findings indicate that remodelling membrane SA not only helps restore the youth of aged RBCs, but also helps recover injured RBCs.

Triggers, inhibitors, mechanisms, and significance of eryptosis: the suicidal erythrocyte death.

Suicidal erythrocyte death or eryptosis is characterized by erythrocyte shrinkage, cell membrane blebbing, and cell membrane scrambling with phosphatidylserine translocation to the erythrocyte surface. Triggers of eryptosis include Ca(2+) entry, ceramide formation, stimulation of caspases, calpain activation, energy depletion, oxidative stress, and dysregulation of several kinases. Eryptosis is triggered by a wide variety of xenobiotics. It is inhibited by several xenobiotics and endogenous molecules including NO and erythropoietin. The susceptibility of erythrocytes to eryptosis increases with erythrocyte age. Phosphatidylserine exposing erythrocytes adhere to the vascular wall by binding to endothelial CXC-Motiv-Chemokin-16/Scavenger-receptor for phosphatidylserine and oxidized low density lipoprotein (CXCL16). Phosphatidylserine exposing erythrocytes are further engulfed by phagocytosing cells and are thus rapidly cleared from circulating blood. Eryptosis eliminates infected or defective erythrocytes thus counteracting parasitemia in malaria and preventing detrimental hemolysis of defective cells. Excessive eryptosis, however, may lead to anemia and may interfere with microcirculation. Enhanced eryptosis contributes to the pathophysiology of several clinical disorders including metabolic syndrome and diabetes, malignancy, cardiac and renal insufficiency, hemolytic uremic syndrome, sepsis, mycoplasma infection, malaria, iron deficiency, sickle cell anemia, thalassemia, glucose 6-phosphate dehydrogenase deficiency, and Wilson's disease. Facilitating or inhibiting eryptosis may be a therapeutic option in those disorders.

Molecular mechanisms of erythrocyte aging.

Anemia and hemorrhagic shock are leading causes of morbidity and mortality worldwide, and transfusion of human blood products is the ideal treatment for these conditions. As human erythrocytes age during storage in blood banks they undergo many biochemical and structural changes, termed the red blood cell 'storage lesion'. Specifically, ATP and pH levels decrease as metabolic end products, oxidative stress, cytokines, and cell-free hemoglobin increase. Also, membrane proteins and lipids undergo conformational and organizational changes that result in membrane loss, viscoelastic changes and microparticle formation. As a result, transfusion of aged blood is associated with a host of adverse consequences such as decreased tissue perfusion, increased risk of infection, and increased mortality. This review summarizes current research detailing the known parts of the erythrocyte storage lesion and their physiologic consequences.

An update on red blood cell storage lesions, as gleaned through biochemistry and omics technologies.

Red blood cell (RBC) aging in the blood bank is characterized by the accumulation of a significant number of biochemical and morphologic alterations. Recent mass spectrometry and electron microscopy studies have provided novel insights into the molecular changes underpinning the accumulation of storage lesions to RBCs in the blood bank. Biochemical lesions include altered cation homeostasis, reprogrammed energy, and redox metabolism, which result in the impairment of enzymatic activity and progressive depletion of high-energy phosphate compounds. These factors contribute to the progressive accumulation of oxidative stress, which in turn promotes oxidative lesions to proteins (carbonylation, fragmentation, hemoglobin glycation) and lipids (peroxidation). Biochemical lesions negatively affect RBC morphology, which is marked by progressive membrane blebbing and vesiculation. These storage lesions contribute to the altered physiology of long-stored RBCs and promote the rapid clearance of up to one-fourth of long-stored RBCs from the recipient's bloodstream after 24 hours from administration. While prospective clinical evidence is accumulating, from the present review it emerges that biochemical, morphologic, and omics profiles of stored RBCs have observable changes after approximately 14 days of storage. Future studies will assess whether these in vitro observations might have clinically meaningful effects.

Blood storage duration and morbidity and mortality in children undergoing cardiac surgery. A retrospective analysis.

BACKGROUND: Blood transfusion is frequently required in children undergoing cardiac surgery and is associated with altered postoperative outcome. This may be due to alterations in red blood cell properties related to the storage process. OBJECTIVE: To evaluate the effect of blood storage duration on postoperative morbidity and mortality in children undergoing cardiac surgery. DESIGN: A retrospective review of a paediatric cardiac surgery database. SETTING: Department of Anaesthesiology, Queen Fabiola Children's University Hospital, Brussels, Belgium. PARTICIPANTS: Children transfused with one or two units of blood in the perioperative period. INTERVENTIONS: None. MAIN OUTCOME MEASURES: Storage duration was used to allocate children to the Group 'Young' or the Group 'Old' (cut-off = 7 days). The primary endpoint was a composite based on the incidence of hospital mortality and/or the incidence of at least one organ failure. RESULTS: From 1014 children in the database, 570 were included in the final analysis. One hundred and eighteen patients were included in the Group 'Young' [median (interquartile range, IQR) storage duration 6 (5 to 7) days] and 452 in the Group 'Old' [storage duration 14 (11 to 19) days]. No difference was found in mortality, length of ICU stay, mechanical ventilation duration, postoperative infection and major organ dysfunction. Duration of storage used as a continuous variable did not influence the incidence of the composite endpoint when evaluated by univariate or multivariate logistic regression analyses. CONCLUSION: Red blood cell storage duration did not influence postoperative morbidity and mortality in paediatric cardiac surgery patients transfused with one or two units of blood.

Membrane peroxidation and methemoglobin formation are both necessary for band 3 clustering: mechanistic insights into human erythrocyte senescence.

Oxidative damage and clustering of band 3 in the membrane have been implicated in the removal of senescent human erythrocytes from the circulation at the end of their 120 day life span. However, the biochemical and mechanistic events leading to band 3 cluster formation have yet to be fully defined. Here we show that while neither membrane peroxidation nor methemoglobin (MetHb) formation on their own can induce band 3 clustering in the human erythrocytes, they can do so when acting in combination. We further show that binding of MetHb to the cytoplasmic domain of band 3 in peroxidized, but not in untreated, erythrocyte membranes induces cluster formation. Age-fractionated populations of erythrocytes from normal human blood, obtained by a density gradient procedure, have allowed us to examine a subpopulation, highly enriched in senescent cells. We have found that band 3 clustering is a feature of only this small fraction, amounting to ∼0.1% of total circulating erythrocytes. These senescent cells are characterized by an increased proportion of MetHb as a result of reduced nicotinamide adenine dinucleotide-dependent reductase activity and accumulated oxidative membrane damage. These findings have allowed us to establish that the combined effects of membrane peroxidation and MetHb formation are necessary for band 3 clustering, and this is a very late event in erythrocyte life. A plausible mechanism for the combined effects of membrane peroxidation and MetHb is proposed, involving high-affinity cooperative binding of MetHb to the cytoplasmic domain of oxidized band 3, probably because of its carbonylation, rather than other forms of oxidative damage. This modification leads to dissociation of ankyrin from band 3, allowing the tetrameric MetHb to cross-link the resulting freely diffusible band 3 dimers, with formation of clusters.

A semi-mechanistic red blood cell survival model provides some insight into red blood cell destruction mechanisms.

Most mathematical models developed for the survival of haematological cell populations, in particular red blood cells (RBCs), follow the principle of parsimony. They focus on the predominant destruction mechanism of age-related cell death (senescence) and do not account for within subject variability in the RBC lifespan. However, assessment of the underlying physiological destruction mechanisms can be of interest in pathological conditions that affect RBC survival, for example sickle cell anaemia or anaemia of chronic kidney disease. We have previously proposed a semi-mechanistic RBC survival model which accounts for four different types of RBC destruction mechanisms. In this work, it is shown that the proposed model in combination with informative RBC survival data is able to provide a deeper insight into RBC destruction mechanisms. The proposed model was applied in a non-linear mixed effect modelling framework to biotin derived RBC survival data available from literature. Three mechanisms were estimable based on the available data of twelve subjects, including random destruction, senescence and destruction due to delayed failure. It was possible to identify three subjects with a decreased RBC survival in the study population. These three subjects all showed differences in the contribution of the estimated destruction mechanisms: an increased random destruction, versus an accelerated senescence, versus a combination of both.

Population pharmacodynamic analysis of erythropoiesis in preterm infants for determining the anemia treatment potential of erythropoietin.

A population pharmacokinetics/pharmacodynamic (PK/PD) model was developed to describe changes in erythropoiesis as a function of plasma erythropoietin (EPO) concentration over the first 30 days of life in preterm infants who developed severe anemia requiring red blood cell (RBC) transfusion. Several covariates were tested as possible factors influencing the responsiveness to EPO. Discarded blood samples in 27 ventilated preterm infants born at 24-29 wk of gestation were used to construct plasma EPO, hemoglobin (Hb), and RBC concentration-time profiles. The amount of Hb removed for laboratory testing and that transfused throughout the study period were recorded. A population PK/PD model accounting for the dynamic Hb changes experienced by these infants was simultaneously fitted to plasma EPO, Hb, and RBC concentrations. A covariate analysis suggested that the erythropoietic efficacy of EPO is increased for preterm infants at later gestational ages. The PD analysis showed a sevenfold difference in maximum Hb production rate dependent on gestational age and indicated that preterm infants, when stimulated by EPO, have the capacity to produce additional Hb that may result in a decrease in RBC transfusions. The present model has utility in clinical trial simulations investigating the treatment potential of erythropoietic stimulating agents in the treatment of anemia of prematurity.

Effects of erythrocyte aging on nitric oxide and nitrite metabolism.

AIMS: Recent studies have suggested that in addition to oxygen transport, red blood cells (RBC) are key regulators of vascular function by both inhibiting and promoting nitric oxide (NO)-mediated vasodilation. Most studies assume that RBC are homogenous, but, in fact, they comprise cells of differing morphology and biochemical composition which are dependent on their age, parameters that control NO reactions. We tested the hypothesis that distinct RBC populations will have differential effects on NO signaling. RESULTS: Young and old RBC were separated by density gradient centrifugation. Consistent with previous reports, old RBC had decreased levels of surface N-acetyl neuraminic acid and increased oxygen binding affinities. Competition kinetic experiments showed that older RBCs scavenged NO∼2-fold faster compared with younger RBC, which translated to a more potent inhibition of both acetylcholine and NO-donor dependent vasodilation of isolated aortic rings. Moreover, nitrite oxidation kinetics was faster with older RBC compared with younger RBC; whereas no differences in nitrite-reduction kinetics were observed. This translated to increased inhibitory effect of older RBC to nitrite-dependent vasodilation under oxygenated and deoxygenated conditions. Finally, leukodepleted RBC storage also resulted in more dense RBC, which may contribute to the greater NO-inhibitory potential of stored RBC. INNOVATION: These results suggest that a key element in vascular NO-homeostasis mechanisms is the distribution of RBC ages across the physiological spectrum (0-120 days) and suggest a novel mechanism for inhibited NO bioavailability in diseases which are characterized by a shift to an older RBC phenotype. CONCLUSION: Older RBC inhibit NO bioavailability by increasing NO- and nitrite scavenging.

Anemia and transfusion after aneurysmal subarachnoid hemorrhage.

Anemia is common in patients with aneurysmal subarachnoid hemorrhage (SAH), but these patients have constituted only a small fraction of those studied in large trials of anemia and transfusion. Unlike other critically ill patients, those with SAH face a well-defined risk of vasospasm and cerebral ischemia in the weeks after their hemorrhage. The risk of ongoing ischemia may make them less able to tolerate anemia and more likely to benefit from blood transfusion. The available data show that anemia is associated with poor outcomes after SAH but that blood transfusion does not consistently improve physiological markers, and it may be associated with poor outcomes. Most of these data are observational in nature, although 1 recent study demonstrated the safety and feasibility of maintaining relatively high transfusion thresholds in patients with SAH. Larger, randomized trials are needed to determine at what levels of anemia patients with SAH might benefit from transfusion, the optimal timing of transfusion, and how to identify those patients who are most likely to benefit.

Transfusion-related biologic effects and free hemoglobin, heme, and iron.

BACKGROUND: Red blood cell (RBC) transfusion is common in intensive care unit (ICU) patients and is associated with complications that appear related to the duration of blood storage. We hypothesize that hemolysis of stored RBCs results in increases in the availability of non-heme-bound iron, which inhibits macrophage activation. STUDY DESIGN AND METHODS: RBCs were sampled at multiple time points to evaluate hemolysis and iron release. Activation of THP-1 monocytic cells was assessed in the presence of plasma from aged RBCs. Age of transfused blood in our pediatric intensive care unit (PICU) from 2001 to 2006 was analyzed to assess relevance to our patient population. RESULTS: Hemolysis increased significantly during storage time as demonstrated by increases in free heme and hemoglobin. While there was a trend toward elevated levels of non-heme-bound iron, this was not significant (p = 0.07). THP-1 cell activation was inhibited by exposures to both plasma and a ferric compound; the effect of plasma on macrophage activation was not reversed by the iron chelator desferroxamine. Thirty-one percent of our PICU patients received blood older than 2 weeks. CONCLUSION: Hemolysis products increased significantly over time in our stored RBCs. Ferric compounds and plasma from stored blood inhibit THP-1 cell activation. Plasma inhibition does not appear to be due primarily to increased iron. Further studies are needed to define the inhibitory effect of stored blood plasma on macrophage function. Complications related to blood storage are relevant to our PICU patients.

Calpain-1 knockout reveals broad effects on erythrocyte deformability and physiology.

Pharmacological inhibitors of cysteine proteases have provided useful insights into the regulation of calpain activity in erythrocytes. However, the precise biological function of calpain activity in erythrocytes remains poorly understood. Erythrocytes express calpain-1, an isoform regulated by calpastatin, the endogenous inhibitor of calpains. In the present study, we investigated the function of calpain-1 in mature erythrocytes using our calpain-1-null [KO (knockout)] mouse model. The calpain-1 gene deletion results in improved erythrocyte deformability without any measurable effect on erythrocyte lifespan in vivo. The calcium-induced sphero-echinocyte shape transition is compromised in the KO erythrocytes. Erythrocyte membrane proteins ankyrin, band 3, protein 4.1R, adducin and dematin are degraded in the calcium-loaded normal erythrocytes but not in the KO erythrocytes. In contrast, the integrity of spectrin and its state of phosphorylation are not affected in the calcium-loaded erythrocytes of either genotype. To assess the functional consequences of attenuated cytoskeletal remodelling in the KO erythrocytes, the activity of major membrane transporters was measured. The activity of the K+-Cl- co-transporter and the Gardos channel was significantly reduced in the KO erythrocytes. Similarly, the basal activity of the calcium pump was reduced in the absence of calmodulin in the KO erythrocyte membrane. Interestingly, the calmodulin-stimulated calcium pump activity was significantly elevated in the KO erythrocytes, implying a wider range of pump regulation by calcium and calmodulin. Taken together, and with the atomic force microscopy of the skeletal network, the results of the present study provide the first evidence for the physiological function of calpain-1 in erythrocytes with therapeutic implications for calcium imbalance pathologies such as sickle cell disease.

Modeling of red blood cell life-spans in hematologically normal populations.

Despite the impact of red blood cell (RBC) Life-spans in some disease areas such as diabetes or anemia of chronic kidney disease, there is no consensus on how to quantitatively best describe the process. Several models have been proposed to explain the elimination process of RBCs: random destruction process, homogeneous life-span model, or a series of 4-transit compartment model. The aim of this work was to explore the different models that have been proposed in literature, and modifications to those. The impact of choosing the right model on future outcomes prediction--in the above mentioned areas--was also investigated. Both data from indirect (clinical data) and direct life-span measurement (biotin-labeled data) methods were analyzed using non-linear mixed effects models. Analysis showed that: (1) predictions from non-steady state data will depend on the RBC model chosen; (2) the transit compartment model, which considers variation in life-span in the RBC population, better describes RBC survival data than the random destruction or homogenous life-span models; and (3) the additional incorporation of random destruction patterns, although improving the description of the RBC survival data, does not appear to provide a marked improvement when describing clinical data.

Physiologically aged red blood cells undergo erythrophagocytosis in vivo but not in vitro.

BACKGROUND: The lifespan of red blood cells is terminated when macrophages remove senescent red blood cells by erythrophagocytosis. This puts macrophages at the center of systemic iron recycling in addition to their functions in tissue remodeling and innate immunity. Thus far, erythrophagocytosis has been studied by evaluating phagocytosis of erythrocytes that were damaged to mimic senescence. These studies have demonstrated that acquisition of some specific individual senescence markers can trigger erythrophagocytosis by macrophages, but we hypothesized that the mechanism of erythrophagocytosis of such damaged erythrocytes might differ from erythrophagocytosis of physiologically aged erythrocytes. DESIGN AND METHODS: To test this hypothesis we generated an erythrocyte population highly enriched in senescent erythrocytes by a hypertransfusion procedure in mice. Various erythrocyte-aging signals were analyzed and erythrophagocytosis was evaluated in vivo and in vitro. RESULTS: The large cohort of senescent erythrocytes from hypertransfused mice carried numerous aging signals identical to those of senescent erythrocytes from control mice. Phagocytosis of fluorescently-labeled erythrocytes from hypertransfused mice injected into untreated mice was much higher than phagocytosis of labeled erythrocytes from control mice. However, neither erythrocytes from hypertransfused mice, nor those from control mice were phagocytosed in vitro by primary macrophage cultures, even though these cultures were able to phagocytose oxidatively damaged erythrocytes. CONCLUSIONS: The large senescent erythrocyte population found in hypertransfused mice mimics physiologically aged erythrocytes. For effective erythrophagocytosis of these senescent erythrocytes, macrophages depend on some features of the intact phagocytosing tissue for support.

Oxidative stress due to aluminum exposure induces eryptosis which is prevented by erythropoietin.

The widespread use of aluminum (Al) provides easy exposure of humans to the metal and its accumulation remains a potential problem. In vivo and in vitro assays have associated Al overload with anemia. To better understand the mechanisms by which Al affects human erythrocytes, morphological and biochemical changes were analyzed after long-term treatment using an in vitro model. The appearance of erythrocytes with abnormal shapes suggested metal interaction with cell surface, supported by the fact that high amounts of Al attached to cell membrane. Long-term incubation of human erythrocytes with Al induced signs of premature erythrocyte death (eryptosis), such as phosphatidylserine externalization, increased intracellular calcium, and band 3 degradation. Signs of oxidative stress, such as significant increase in reactive oxygen species in parallel with decrease in the amount of reduced glutathione, were also observed. These oxidative effects were completely prevented by the antioxidant N-acetylcysteine. Interestingly, erythrocytes were also protected from the prooxidative action of Al by the presence of erythropoietin (EPO). In conclusion, results provide evidence that chronic Al exposure may lead to biochemical and morphological alterations similar to those shown in eryptosis induced by oxidant compounds in human erythrocytes. The antieryptotic effect of EPO may contribute to enhance the knowledge of its physiological role on erythroid cells. Irrespective of the antioxidant mechanism, this property of EPO, shown in this model of Al exposure, let us suggest potential benefits by EPO treatment of patients with anemia associated to altered redox environment.