Enhanced susceptibility to suicidal death of erythrocytes from transgenic mice overexpressing erythropoietin

Erythroid Cells as Full Participants in the Tumor Microenvironment

The tumor microenvironment is an important factor that can determine the success or failure of antitumor therapy. Cells of hematopoietic origin are one of the most important mediators of the tumor-host interaction and, depending on the cell type and functional state, exert pro- or antitumor effects in the tumor microenvironment or in adjacent tissues. Erythroid cells can be full members of the tumor microenvironment and exhibit immunoregulatory properties. Tumor growth is accompanied by the need to obtain growth factors and oxygen, which stimulates the appearance of the foci of extramedullary erythropoiesis. Tumor cells create conditions to maintain the long-term proliferation and viability of erythroid cells. In turn, tumor erythroid cells have a number of mechanisms to suppress the antitumor immune response. This review considers current data on the existence of erythroid cells in the tumor microenvironment, formation of angiogenic clusters, and creation of optimal conditions for tumor growth. Despite being the most important life-support function of the body, erythroid cells support tumor growth and do not work against it. The study of various signaling mechanisms linking tumor growth with the mobilization of erythroid cells and the phenotypic and functional differences between erythroid cells of different origin allows us to identify potential targets for immunotherapy.

Role of Eryptosis in Hemorrhagic Stroke

Erythrocytes undergo certain morphological changes resembling apoptosis during senescence or in an abnormal state/site, which is termed eryptosis. This process is characterized by phosphatidylserine (PS) exposure, membrane blebbing, and cell shrinkage. Eryptotic erythrocytes are subsequently removed via macrophage-mediated efferocytosis. In hemorrhagic stroke (HS), blood within an artery rapidly bleeds into the brain tissue or the subarachnoid space, resulting in severe neurological deficits. A hypoxic, over-oxidative, and pro-inflammatory microenvironment in the hematoma leads to oxidative stress, hyperosmotic shock, energy depletion, and Cl^– removal in erythrocytes, which eventually triggers eryptosis. In addition, eryptosis following intracerebral hemorrhage favors hematoma clearance, which sheds light on a common mechanism of intrinsic phagocytosis. In this review, we summarized the canonical mechanisms of eryptosis and discussed its pathological conditions associated with HS. Understanding the role of eryptosis in HS may uncover additional potential interventions for further translational clinical research.

THE IN-VITRO STUDY OF NOVEL PHOSPHOLIPID MICELLES LOADED WITH AMPHOTERICIN B ON PLASMODIUM FALCIPARUM PROTOZOAN

Malaria is one of the most challenging parasitic infectious diseases in tropical and subtropical regions all over the world. The increasing drug resistance of plasmodium falciparum even makes the treatment procedure of malaria challenging and more problematic. Therefore, it is essential to develop new antimalarial drugs for effective treatments. In this study, the encapsulated amphotericin B (Constantinides et al.) in DSPC/DSPE-PEG2000 micelles was investigated as an antimalarial drug against P. falciparum 3D7 strain. The mean particle size, morphological and microstructural properties of drug-free and drug-loaded micelles prepared with amphotericin B were determined through DLS, FESEM, and TEM analysis. The synthesized phospholipid micelles containing AmB drug with a mean diameter of 115nm and a polydispersity index of 0.331. The TEM and SEM studies indicate the uniform and homogeneous morphology of the micelles. Drug encapsulation efficiency is 88.3%. The slow release of the micellar system shows the maximum drug release of 75.67% within 24h. This in vitro study was conducted on P. falciparum 3D7 to investigate the interactions between AmB micelles and P. falciparum parasites using different drug ratios. According to the findings, the IC₅₀ of free AmB is 4.834µg/mL, while the nano-diameter AmB has a significantly lower IC₅₀ of 2.394µg/mL. The results of this study suggest that the drug-loaded phospholipid micelles have significantly higher bioactivity and greater plasmodial properties compared to the direct application of AmB against P. falciparum. Moreover, according to the results of this study, the encapsulated AmB drugs are promising nanostructures for malaria treatment. Therefore the nanoencapsulation AmB showed promising application for malaria treatment.

Enhanced eryptosis contributes to anemia in lung cancer patients

Objectives

Anemia is a common complication of malignancy, which could result from either compromised erythropoiesis or decreased lifespan of circulating erythrocytes. Premature suicidal erythrocyte death, characterized by cell shrinkage and phosphatidylserine (PS) externalization, decreases erythrocyte lifespan and could thus cause anemia. Here, we explored whether accelerated eryptosis participates in the pathophysiology of anemia associated with lung cancer (LC) and its treatment.

Methods

Erythrocytes were drawn from healthy volunteers and LC patients with and without cytostatic treatment. PS exposure (annexin V-binding), cell volume (forward scatter), cytosolic Ca²⁺ (Fluo3 fluorescence), reactive oxygen species (ROS) production (DCFDA fluorescence) and ceramide formation (anti-ceramide antibody) were determined by flow cytometry.

Results

Hemoglobin concentration and hematocrit were significantly lower in LC patients as compared to healthy controls, even though reticulocyte number was higher in LC (3.0±0.6%) than in controls (1.4±0.2%). The percentage of PS-exposing erythrocytes was significantly higher in LC patients with (1.4±0.1%) and without (1.2±0.3%) cytostatic treatment as compared to healthy controls (0.6±0.1%). Erythrocyte ROS production and ceramide abundance, but not Fluo3 fluorescence, were significantly higher in freshly drawn erythrocytes from LC patients than in freshly drawn erythrocytes from healthy controls. PS exposure of erythrocytes drawn from healthy volunteers was significantly more pronounced following incubation in plasma from LC patients than following incubation in plasma from healthy controls.

Conclusion

Anemia in LC patients with and without cytostatic treatment is paralleled by increased eryptosis, which is triggered, at least in part, by increased oxidative stress and ceramide formation.

Eryptosis - the Neglected Cause of Anemia in End Stage Renal Disease

End stage renal disease (ESRD) invariably leads to anemia which has been mainly attributed to compromised release of erythropoietin from the defective kidneys with subsequent impairment of erythropoiesis. However, erythropoietin replacement only partially reverses anemia pointing to the involvement of additional mechanisms. As shown more recently, anemia of ESRD is indeed in large part a result of accelerated erythrocyte loss due to suicidal erythrocyte death or eryptosis, characterized by cell shrinkage and cell membrane scrambling with phosphatidylserine translocation to the cell surface. Phosphatidylserine exposing erythrocytes are bound to and engulfed by macrophages and are thus rapidly cleared from circulating blood. If the loss of erythrocytes cannot be fully compensated by enhanced erythropoiesis, stimulation of eryptosis leads to anemia. Eryptotic erythrocytes may further adhere to the vascular wall and thus impair microcirculation. Stimulators of eryptosis include complement, hyperosmotic shock, energy depletion, oxidative stress, and a wide variety of xenobiotics. Signaling involved in the stimulation of eryptosis includes increase of cytosolic Ca2+ activity, ceramide, caspases, calpain, p38 kinase, protein kinase C, Janus-activated kinase 3, casein kinase 1α, and cyclin-dependent kinase 4. Eryptosis is inhibited by AMP-activated kinase, p21-activated kinase 2, cGMP-dependent protein kinase, mitogen- and stress-activated kinase MSK1/2, and some illdefined tyrosine kinases. In ESRD eryptosis is stimulated at least in part by a plasma component, as it is triggered by exposure of erythrocytes from healthy individuals to plasma from ESRD patients. Several eryptosis-stimulating uremic toxins have been identified, such as vanadate, acrolein, methylglyoxal, indoxyl sulfate, indole-3-acetic acid and phosphate. Attempts to fully reverse anemia in ESRD with excessive stimulation of erythropoiesis enhances the number of circulating suicidal erythrocytes and bears the risk of interference with micocirculation, At least in theory, anemia in ESRD could preferably be treated with replacement of erythropoietin and additional inhibition of eryptosis thus avoiding eryptosis-induced impairment of microcirculation. A variety of eryptosis inhibitors have been identified, their efficacy in ESRD remains, however, to be shown.

Ceramide in the regulation of eryptosis, the suicidal erythrocyte death

Similar to apoptosis of nucleated cells, erythrocytes may undergo eryptosis, a suicidal death characterized by cell shrinkage and phospholipid scrambling of the cell membrane leading to phosphatidylserine exposure at the cell surface. As eryptotic erythrocytes are rapidly cleared from circulating blood, excessive eryptosis may lead to anemia. Moreover, eryptotic erythrocytes may adhere to the vascular wall and thus impede microcirculation. Stimulators of eryptosis include osmotic shock, oxidative stress and energy depletion. Mechanisms involved in the stimulation eryptosis include ceramide formation which may result from phospholipase A2 dependent formation of platelet activating factor (PAF) with PAF dependent stimulation of sphingomyelinases. Enhanced erythrocytic ceramide formation is observed in fever, sepsis, HUS, uremia, hepatic failure, and Wilson's disease. Enhanced eryptosis is further observed in iron deficiency, phosphate depletion, dehydration, malignancy, malaria, sickle-cell anemia, beta-thalassemia and glucose-6-phosphate dehydrogenase-deficiency. Moreover, eryptosis is triggered by osmotic shock and a wide variety of xenobiotics, which are again partially effective by enhancing ceramide abundance. Ceramide formation is inhibited by high concentrations of urea. As shown in Wilson's disease, pharmacological interference with ceramide formation may be a therapeutic option in the treatment of eryptosis inducing clinical disorders.

Enhanced suicidal erythrocyte death in acute cardiac failure

BACKGROUND

A common complication of acute cardiac failure (AHF) is anaemia, which negatively influences the clinical outcome. Causes of anaemia include enhanced eryptosis, a suicidal erythrocyte death characterized by cell shrinkage and cell membrane scrambling with phosphatidylserine translocation. Signalling triggering eryptosis include oxidative stress, increase of cytosolic Ca(2+) -activity ([Ca(2+) ]i ) and ceramide. The present study explored whether AHF is associated with accelerated eryptosis.

MATERIALS AND METHODS

Erythrocytes were drawn from healthy volunteers (n = 10) and patients hospitalized for AHF (n = 22). Phosphatidylserine exposure was estimated from annexin-V-binding, cell volume from forward scatter, [Ca(2+) ]i from Fluo3-fluorescence, ceramide abundance utilizing specific antibodies and reactive oxygen species (ROS) abundance from 2',7'-dichlorodihydrofluorescein diacetate (DCFDA) fluorescence, as determined by flow cytometry.

RESULTS

In AHF-patients, haemoglobin concentration (11·5 ± 0·5 g/dL), and haematocrit (35·6 ± 1·2%) were significantly lower than haemoglobin concentration (14·1 ± 0·4 g/dL), and haematocrit (40·1 ± 1·0%) in healthy volunteers, even though reticulocyte number was significantly higher in AHF patients (2·3 ± 0·3%) than in healthy volunteers (1·1 ± 0·2%). The percentage of erythrocytes exposing phosphatidylserine was significantly higher in AHF patients (1·8 ± 0·1%) than in healthy volunteers (1·2 ± 0·2%). The forward scatter was significantly lower and the ROS abundance significantly larger in AHF patients than in healthy volunteers. In erythrocytes drawn from healthy volunteers, phosphatidylserine and ROS abundance was increased to significantly higher values following a 24 h treatment with plasma from AHF patients than with plasma from healthy volunteers.

CONCLUSION

AHF leads to anaemia despite increased reticulocyte number and at least partially due to enhanced eryptosis. Underlying mechanisms include oxidative stress imposed by a plasma borne component.

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.

Piperlongumine-induced phosphatidylserine translocation in the erythrocyte membrane

BACKGROUND

Piperlongumine, a component of Piper longum fruit, is considered as a treatment for malignancy. It is effective by inducing apoptosis. Mechanisms involved in the apoptotic action of piperlongumine include oxidative stress and activation of p38 kinase. In analogy to apoptosis of nucleated cells, erythrocytes may undergo eryptosis, the suicidal death of erythrocytes characterized by cell shrinkage and cell membrane scrambling with phosphatidylserine-exposure at the erythrocyte surface. Signaling involved in eryptosis include increase of cytosolic Ca²⁺-activity ([Ca²⁺]i), formation of ceramide, oxidative stress and activation of p38 kinase.

METHODS

Cell volume was estimated from forward scatter, phosphatidylserine-exposure from annexin V binding, [Ca²⁺]i from Fluo3 fluorescence, reactive oxygen species from 2',7'-dichlorodihydrofluorescein-diacetate fluorescence, and ceramide abundance from binding of fluorescent antibodies in flow cytometry.

RESULTS

A 48 h exposure to piperlongumine (30 µM) was followed by significant decrease of forward scatter and increase of annexin-V-binding. Piperlongumine did not significantly modify [Ca²⁺]i and the effect was not dependent on presence of extracellular Ca²⁺. Piperlongumine significantly increased ROS formation and ceramide abundance.

CONCLUSIONS

Piperlongumine triggers cell membrane scrambling, an effect independent from entry of extracellular Ca²⁺ but at least partially due to ROS and ceramide formation.

Suicidal erythrocyte death in end-stage renal disease

Anemia in end-stage renal disease (ESRD) results mainly from erythropoietin and iron deficiency. Anemia could be confounded, however, by accelerated clearance of circulating erythrocytes because of premature suicidal erythrocyte death or eryptosis characterized by phosphatidylserine exposure at the erythrocyte surface. Triggers of eryptosis include increased cytosolic Ca(2+) concentration ([Ca(2+)]i), oxidative stress, and ceramide. The present study explored whether and how ESRD influences eryptosis. Blood was drawn from healthy volunteers (n = 20) as well as ESRD patients (n = 20) prior to and after hemodialysis. Phosphatidylserine exposure was estimated from annexin V binding, [Ca(2+)]i from Fluo3-fluorescence, reactive oxygen species (ROS) from 2',7'dichlorodihydrofluorescein fluorescence, and ceramide from fluorescein-isothiocyanate-conjugated antibody binding in flow cytometry. Measurements were made in erythrocytes from freshly drawn blood and in erythrocytes from healthy volunteers exposed in vitro for 24 h to plasma from healthy volunteers or ESRD patients prior to and following dialysis. The patients suffered from anemia (hemoglobin 10.1 ± 0.5 g/100 ml) despite 1.96 ± 0.34 % reticulocytes. The percentage of phosphatidylserine-exposing erythrocytes was significantly higher in ESRD patients (0.84 ± 0.09 %) than in healthy volunteers (0.43 ± 0.04 %) and was significantly increased immediately after dialysis (1.35 ± 0.13 %). The increase in phosphatidylserine exposure was paralleled by increase in [Ca(2+)]i, oxidative stress, and ceramide abundance. As compared to addition of plasma from healthy individuals, addition of predialytic but not of postdialytic plasma from ESRD patients increased phosphatidylserine exposure, [Ca(2+)]i, ROS, and ceramide abundance. In conclusion, both, dialyzable components of uremic plasma and dialysis procedure, trigger eryptosis at least in part by increasing erythrocyte [Ca(2+)]i, ROS, and ceramide formation.

KEY MESSAGES

Anemia in uremia results in part from eryptosis, the suicidal erythrocyte death. Eryptosis in uremia is triggered in part by a dialyzable plasma component. Eryptosis in uremia is further triggered by dialysis procedure. Eryptosis in uremia is in part due to increased cytosolic Ca(2+) concentration. Eryptosis in uremia is further due to oxidative stress and ceramide formation.

Decreased stability of erythroblastic islands in integrin β3-deficient mice

Erythroblasts proliferate and differentiate in hematopoietic organs within erythroblastic islands (EI) composed of erythropoietic progenitor cells attached to a central macrophage. This cellular interaction crucially involves the erythroid intercellular adhesion molecule-4 (ICAM-4) and αv integrin. Because integrins are biologically active as α/β heterodimers, we asked whether β3 could be a heterodimerization partner of αv integrin in EIs. To this end we compared stress erythropoiesis driven by two different mechanisms, namely that of integrin β3-deficient (β3(-/-)) mice that exhibit impaired hemostasis due to platelet dysfunction with that of systemically erythropoietin-overexpressing (tg6) mice. While compared to the respective wild type (wt) controls β3(-/-) mice had much less erythropoietic stimulation than tg6 mice β3(-/-) blood contained more erythrocytes of a lower maturity stage. Unexpectedly, membranes of peripheral erythrocytes from β3(-/-) mice (but not those from either wt control or from tg6 mice) contained calnexin, a chaperone that is normally completely lost during terminal differentiation of reticulocytes prior to their release into the circulation. In contrast to erythropoietin-overexpressing mice, the erythropoietic subpopulations representing orthochromatic erythroblasts and premature reticulocytes as well as the number of cells per EI were reduced in β3(-/-) bone marrow. In conclusion, absence of integrin β3 impairs adhesion of the latest erythroid developmental stage to the central macrophage of EIs resulting in preterm release of abnormally immature erythrocytes into the circulation.

The impact of erythrocyte age on eryptosis

Mature, circulating erythrocytes undergo senescence, which limits their life span to approximately 120 d. Upon injury, erythrocytes may undergo suicidal erythrocyte death or eryptosis, which may accelerate senescence and shorten their survival. Eryptosis is defined as cell shrinkage and exposure of phosphatidylserine at the cell surface. Triggers of eryptosis include oxidative stress. The present study addresses the impact of erythrocyte age on the relative susceptibility to eryptosis. Erythrocytes were separated into five fractions, based on age-associated differences in density and volume. Cell membrane scrambling was estimated from binding of annexin V to phosphatidylserine at the erythrocyte surface, the cell volume from forward scatter, and the Ca(2+) level from Fluo-3-dependent fluorescence. In addition, glutathione (GSH) concentrations were measured by an enzymatic/colourimetric method. After 48 h incubation in Ringer solution, Annexin V binding increased significantly with erythrocyte age. The differences were not accompanied by altered GSH concentrations, but were reversed by addition of the antioxidant N-acetyl-L-cysteine in vitro. Also, N-acetyl-L-cysteine significantly prolonged the half-life of circulating mouse erythrocytes in vivo. Thus, the susceptibility to eryptosis increases with the age of the erythrocytes, and this effect is at least partially due to enhanced sensitivity to oxidative stress.

Erythrocyte programmed cell death

Eryptosis, the suicidal death of erythrocytes, is characterised by cell shrinkage, membrane blebbing and cell membrane phospholipid scrambling with phosphatidylserine exposure at the cell surface. Phosphatidylserine-exposing erythrocytes are recognised by macrophages, which engulf and degrade the affected cells. Reported triggers of eryptosis include osmotic shock, oxidative stress, energy depletion, ceramide, prostaglandin E(2), platelet activating factor, hemolysin, listeriolysin, paclitaxel, chlorpromazine, cyclosporine, methylglyoxal, amyloid peptides, anandamide, Bay-5884, curcumin, valinomycin, aluminium, mercury, lead and copper. Diseases associated with accelerated eryptosis include sepsis, malaria, sickle-cell anemia, beta-thalassemia, glucose-6-phosphate dehydrogenase (G6PD)-deficiency, phosphate depletion, iron deficiency, hemolytic uremic syndrome and Wilsons disease. Eryptosis may be inhibited by erythropoietin, adenosine, catecholamines, nitric oxide (NO) and activation of G-kinase. Most triggers of eryptosis except oxidative stress are effective without activation of caspases. Their signalling involves formation of prostaglandin E(2) with subsequent activation of cation channels and Ca2+ entry and/or release of platelet activating factor (PAF) with subsequent activation of sphingomyelinase and formation of ceramide. Ca2+ and ceramide stimulate scrambling of the cell membrane. Ca2+ further activates Ca2+-sensitive K+ channels leading to cellular KCl loss and cell shrinkage and stimulates the protease calpain resulting in degradation of the cytoskeleton. Eryptosis allows defective erythrocytes to escape hemolysis. On the other hand, excessive eryptosis favours the development of anemia. Thus, a delicate balance between proeryptotic and antieryptotic mechanisms is required to maintain an adequate number of circulating erythrocytes and yet avoid noneryptotic death of injured erythrocytes.

Erythropoietin: elucidating new cellular targets that broaden therapeutic strategies

Given that erythropoietin (EPO) is no longer believed to have exclusive biological activity in the hematopoietic system, EPO is now considered to have applicability in a variety of nervous system disorders that can overlap with vascular disease, metabolic impairments, and immune system function. As a result, EPO may offer efficacy for a broad number of disorders that involve Alzheimer's disease, cardiac insufficiency, stroke, trauma, and diabetic complications. During a number of clinical conditions, EPO is robust and can prevent metabolic compromise, neuronal and vascular degeneration, and inflammatory cell activation. Yet, use of EPO is not without its considerations especially in light of frequent concerns that may compromise clinical care. Recent work has elucidated a number of novel cellular pathways governed by EPO that can open new avenues to avert deleterious effects of this agent and offer previously unrecognized perspectives for therapeutic strategies. Obtaining greater insight into the role of EPO in the nervous system and elucidating its unique cellular pathways may provide greater cellular viability not only in the nervous system but also throughout the body.

Erythropoietin and oxidative stress

Unmitigated oxidative stress can lead to diminished cellular longevity, accelerated aging, and accumulated toxic effects for an organism. Current investigations further suggest the significant disadvantages that can occur with cellular oxidative stress that can lead to clinical disability in a number of disorders, such as myocardial infarction, dementia, stroke, and diabetes. New therapeutic strategies are therefore sought that can be directed toward ameliorating the toxic effects of oxidative stress. Here we discuss the exciting potential of the growth factor and cytokine erythropoietin for the treatment of diseases such as cardiac ischemia, vascular injury, neurodegeneration, and diabetes through the modulation of cellular oxidative stress. Erythropoietin controls a variety of signal transduction pathways during oxidative stress that can involve Janus-tyrosine kinase 2, protein kinase B, signal transducer and activator of transcription pathways, Wnt proteins, mammalian forkhead transcription factors, caspases, and nuclear factor kappaB. Yet, the biological effects of erythropoietin may not always be beneficial and may be poor tolerated in a number of clinical scenarios, necessitating further basic and clinical investigations that emphasize the elucidation of the signal transduction pathways controlled by erythropoietin to direct both successful and safe clinical care.

Triple play: promoting neurovascular longevity with nicotinamide, WNT, and erythropoietin in diabetes mellitus

Oxidative stress is a principal pathway for the dysfunction and ultimate destruction of cells in the neuronal and vascular systems for several disease entities, not promoting the ravages of oxidative stress to any less of a degree than diabetes mellitus. Diabetes mellitus is increasing in incidence as a result of changes in human behavior that relate to diet and daily exercise and is predicted to affect almost 400 million individuals worldwide in another two decades. Furthermore, both type 1 and type 2 diabetes mellitus can lead to significant disability in the nervous and cardiovascular systems, such as cognitive loss and cardiac insufficiency. As a result, innovative strategies that directly target oxidative stress to preserve neuronal and vascular longevity could offer viable therapeutic options to diabetic patients in addition to more conventional treatments that are designed to control serum glucose levels. Here we discuss the novel application of nicotinamide, Wnt signaling, and erythropoietin that modulate cellular oxidative stress and offer significant promise for the prevention of diabetic complications in the nervous and vascular systems. Essential to this process is the precise focus upon diverse as well as common cellular pathways governed by nicotinamide, Wnt signaling, and erythropoietin to outline not only the potential benefits, but also the challenges and possible detriments of these therapies. In this way, new avenues of investigation can hopefully bypass toxic complications, or at the very least, avoid contraindications that may limit care and offer both safe and robust clinical treatment for patients.