Erythropoietin molecules to treat acute ischemic stroke: a translational dilemma!

The Effects of a Blood-Brain Barrier Penetrating Erythropoietin in a Mouse Model of Tauopathy

Erythropoietin (EPO), a hematopoietic neurotrophin, is a potential therapeutic for Alzheimer's disease (AD) but has limited blood-brain barrier (BBB) permeability. EPO fused to a chimeric transferrin receptor monoclonal antibody (cTfRMAb) enters the brain via TfR-mediated transcytosis across the BBB. We previously showed that cTfRMAb-EPO is protective in a mouse model of amyloidosis, but its effects on tauopathy are not known. Given that amyloid and tau pathology are characteristics of AD, the effects of cTfRMAb-EPO were studied in a tauopathy mouse model (PS19). Six-month-old PS19 mice were injected intraperitoneally with either saline (PS19-Saline; n = 9) or cTfRMAb-EPO (PS19-cTfRMAb-EPO, 10 mg/kg; n = 10); every two or three days on alternate weeks for 8 weeks. Age-matched, saline-treated, wildtype littermates (WT-Saline; n = 12) were injected using the same protocol. After 8 weeks, locomotion, hyperactivity, and anxiety were assessed via the open-field test, and brains were harvested and sectioned. Cerebral cortex, hippocampus, amygdala, and entorhinal cortex sections were analyzed for phospho-tau (AT8) and microgliosis (Iba1). Hippocampal cellular density (H&E) was also assessed. PS19-Saline mice were hyperactive and less anxious compared to WT-Saline mice, and these behavioral phenotypes were significantly reduced in the PS19-cTfRMAb-EPO mice compared to the PS19-Saline mice. cTfRMAb-EPO significantly reduced AT8 load by ≥50% in all of the brain regions analyzed and microgliosis in the entorhinal cortex and amygdala compared to the PS19-Saline mice. Hippocampal pyramidal and granule cell layer density did not differ significantly between the PS19-cTfRMAb-EPO and PS19-Saline mice. This proof-of-concept study demonstrates the therapeutic effects of the BBB-penetrating cTfRMAb-EPO in PS19 mice.

Erythropoietin in Critical Illness and Trauma

Erythropoietin (EPO) is a 34kD pleiotropic cytokine that was first identified as being essential for red blood cell (RBC) production. It is now recognized however that EPO is produced by many tissues. It plays a key role in the modulation of the response to injury, inflammation, and tissue hypoxia via the inhibition of apoptosis. Large clinical trials in the critically ill failed to demonstrate a role for EPO as an RBC transfusion sparing agent; however, improved clinical outcomes, attributable to EPO role in tissue protection are observed in critically ill trauma patients. Further research to confirm or refute these observations is required.

The Promises and Challenges of Erythropoietin for Treatment of Alzheimer's Disease

Alzheimer's disease (AD) is the most prevalent neurodegenerative disorder in the world, and intracellular neurofibrillary tangles and extracellular amyloid-beta protein deposits represent the major pathological hallmarks of the disease. Currently available treatments provide some symptomatic relief but fail to modify primary pathological processes that underlie the disease. Erythropoietin (EPO), a hematopoietic growth factor, acts primarily to stimulate erythroid cell production, and is clinically used to treat anemia. EPO has evolved as a therapeutic agent for neurodegeneration and has improved neurological outcomes and AD pathology in rodents. However, penetration of the blood-brain barrier (BBB) and negative hematopoietic effects are the two major challenges for the therapeutic development of EPO for chronic neurodegenerative diseases like AD. The transferrin receptors at the BBB, which are responsible for transporting transferrin-bound iron from the blood into the brain parenchyma, can be used to shuttle therapeutic molecules across the BBB. In this review, we discuss the role of EPO as a potential neurotherapeutic for AD, challenges associated with EPO development for AD, and targeting the BBB transferrin receptor for EPO brain delivery.

Anemia and stroke: Where do we stand?

Anemia seems to have a clear relationship with cerebrovascular events (CVEs), as there is a direct connection between central nervous system, blood supply, and tissue oxygen delivery. Anemia is considered a hyperkinetic state which disturbs endothelial adhesion molecule genes that may lead to thrombus formation. Furthermore, blood flow augmentation and turbulence may result in the migration of this thrombus, thus producing artery-to-artery embolism. It is for this reason that anemia is characterized as "the fifth cardiovascular risk factor." Anemia is consistently present in patients with acute stroke, ranging from 15% to 29%, while the mortality rate was significantly higher in patients suffering from anemia at the time of admission. Different types of anemia (sickle cell disease, beta thalassemia, iron deficiency anemia [IDA]) have been associated with increased cardiovascular and CVE risk. The relation between hemoglobin level and stroke would require further investigation. Unfortunately, treatment of anemia in cardiovascular and cerebrovascular disease still lacks clear targets and specific therapy has not developed. However, packed red blood cell transfusion is generally reserved for therapy in patients with CVEs. What is more, treatment of IDA prevents thrombosis and the occurrence of stroke; although iron levels should be checked, chronic administration favors thrombosis. Regarding erythropoietin (EPO), as there is lack of studies in anemic stroke patients, it would be desirable to utilize both neuroprotective and hematopoietic properties of EPO in anemic stroke patients. This review aims to clarify the poorly investigated and defined issues concerning the relation of anemia and CVEs.

HIF hydroxylase pathways in cardiovascular physiology and medicine

Hypoxia inducible factors (HIFs) are α/β heterodimeric transcription factors that direct multiple cellular and systemic responses in response to changes in oxygen availability. The oxygen sensitive signal is generated by a series of iron and 2-oxoglutarate-dependent dioxygenases that catalyze post-translational hydroxylation of specific prolyl and asparaginyl residues in HIFα subunits and thereby promote their destruction and inactivation in the presence of oxygen. In hypoxia, these processes are suppressed allowing HIF to activate a massive transcriptional cascade. Elucidation of these pathways has opened several new fields of cardiovascular research. Here, we review the role of HIF hydroxylase pathways in cardiac development and in cardiovascular control. We also consider the current status, opportunities, and challenges of therapeutic modulation of HIF hydroxylases in the therapy of cardiovascular disease.

Endogenous neurogenesis following ischaemic brain injury: insights for therapeutic strategies

Ischaemic stroke is among the most common yet most intractable types of central nervous system (CNS) injury in the adult human population. In the acute stages of disease, neurons in the ischaemic lesion rapidly die and other neuronal populations in the ischaemic penumbra are vulnerable to secondary injury. Multiple parallel approaches are being investigated to develop neuroprotective, reparative and regenerative strategies for the treatment of stroke. Accumulating evidence indicates that cerebral ischaemia initiates an endogenous regenerative response within the adult brain that potentiates adult neurogenesis from populations of neural stem and progenitor cells. A major research focus has been to understand the cellular and molecular mechanisms that underlie the potentiation of adult neurogenesis and to appreciate how interventions designed to modulate these processes could enhance neural regeneration in the post-ischaemic brain. In this review, we highlight recent advances over the last 5 years that help unravel the cellular and molecular mechanisms that potentiate endogenous neurogenesis following cerebral ischaemia and are dissecting the functional importance of this regenerative mechanism following brain injury. This article is part of a Directed Issue entitled: Regenerative Medicine: the challenge of translation.

Subventricular zone-derived oligodendrogenesis in injured neonatal white matter in mice enhanced by a nonerythropoietic erythropoietin derivative

Perinatal hypoxia-ischemia (HI) frequently causes white-matter injury, leading to severe neurological deficits and mortality, and only limited therapeutic options exist. The white matter of animal models and human patients with HI-induced brain injury contains increased numbers of oligodendrocyte progenitor cells (OPCs). However, the origin and fates of these OPCs and their potential to repair injured white matter remain unclear. Here, using cell-type- and region-specific genetic labeling methods in a mouse HI model, we characterized the Olig2-expressing OPCs. We found that after HI, Olig2+ cells increased in the posterior part of the subventricular zone (pSVZ) and migrated into the injured white matter. However, their oligodendrocytic differentiation efficiency was severely compromised compared with the OPCs in normal tissue, indicating the need for an intervention to promote their differentiation. Erythropoietin (EPO) treatment is a promising candidate, but it has detrimental effects that preclude its clinical use for brain injury. We found that long-term postinjury treatment with a nonerythropoietic derivative of EPO, asialo-erythropoietin, promoted the maturation of pSVZ-derived OPCs and the recovery of neurological function, without affecting hematopoiesis. These results demonstrate the limitation and potential of endogenous OPCs in the pSVZ as a therapeutic target for treating neonatal white-matter injury.

Brain ischemic injury in rodents: the protective effect of EPO

Animal models constitute an indispensable tool to investigate human pathology. Here we describe the procedure to induce permanent and transient cerebral ischemia in the mouse and the rat. The model of transient occlusion of the middle cerebral artery (MCA) is performed by the insertion of an occlusive filament until the origin of the MCA while the permanent occlusion described in the mice is performed by a distal electrocoagulation of the MCA. Those models allow evaluating the efficiency of therapeutic strategy of ischemia from tissular aspect to behavioral and cognitive impairment assessment. They were widely used in the literature to evaluate the efficiency of different drugs including the cytokines and especially erythropoietin (EPO) or its derivatives.

A cohort study of patients with anemia on admission and fatality after acute ischemic stroke

Reduced blood hemoglobin levels may impair oxygen delivery to the brain and hinder neurological improvement. We prospectively registered consecutively hospitalized Chinese patients with acute ischemic stroke within 24 hours of symptom onset to investigate whether anemia on admission influences case fatality and functional outcome of acute ischemic stroke at 12 months. Anemia was defined as a blood hemoglobin level of < 120 g/L for women, and < 130 g/L for men. We also performed a meta-analysis of the current cohort and previously published studies. We included 1176 patients, of whom 351 patients (29.8%) had anemia. Age (odds ratio [OR]=1.02, 95% confidence interval [CI]: 1.01-1.03), history of hemorrhagic stroke (OR=3.34, 95% CI: 1.17-9.56), alcohol consumption (OR=0.59, 95% CI: 0.38-0.92), and estimated glomerular filtration rate < 60 mL/minute per 1.73 m(2) (OR=1.34, 95% CI: 1.00-1.80) were the independent predictors of anemia. After adjustment for potential confounders, anemia on admission was shown to be an independent predictor of death at discharge and at 12 months (OR=1.66, 95% CI, 1.08-2.56; OR=1.56, 95% CI, 1.05-2.31). A meta-analysis of six included studies involving 3810 participants confirmed that anemia on admission was an independent predictor of death at the end of follow-up (OR=1.67, 95% CI, 1.25-2.08). Further studies are required to confirm these findings.