Passage of erythropoietic agents across the blood-brain barrier: a comparison of human and murine erythropoietin and the analog darbepoetin alfa

Tryptophan metabolism as a 'reflex' feature of neuroimmune communication: Sensor and effector functions for the indoleamine-2, 3-dioxygenase kynurenine pathway

Although the central nervous system (CNS) and immune system were regarded as independent entities, it is now clear that immune system cells can influence the CNS, and neuroglial activity influences the immune system. Despite the many clinical implications for this 'neuroimmune interface', its detailed operation at the molecular level remains unclear. This narrative review focuses on the metabolism of tryptophan along the kynurenine pathway, since its products have critical actions in both the nervous and immune systems, placing it in a unique position to influence neuroimmune communication. In particular, since the kynurenine pathway is activated by pro-inflammatory mediators, it is proposed that physical and psychological stressors are the stimuli of an organismal protective reflex, with kynurenine metabolites as the effector arm co-ordinating protective neural and immune system responses. After a brief review of the neuroimmune interface, the general perception of tryptophan metabolism along the kynurenine pathway is expanded to emphasize this environmentally driven perspective. The initial enzymes in the kynurenine pathway include indoleamine-2,3-dioxygenase (IDO1), which is induced by tissue damage, inflammatory mediators or microbial products, and tryptophan-2,3-dioxygenase (TDO), which is induced by stress-induced glucocorticoids. In the immune system, kynurenic acid modulates leucocyte differentiation, inflammatory balance and immune tolerance by activating aryl hydrocarbon receptors and modulates pain via the GPR35 protein. In the CNS, quinolinic acid activates N-methyl-D-aspartate (NMDA)-sensitive glutamate receptors, whereas kynurenic acid is an antagonist: the balance between glutamate, quinolinic acid and kynurenic acid is a significant regulator of CNS function and plasticity. The concept of kynurenine and its metabolites as mediators of a reflex coordinated protection against stress helps to understand the variety and breadth of their activity. It should also help to understand the pathological origin of some psychiatric and neurodegenerative diseases involving the immune system and CNS, facilitating the development of new pharmacological strategies for treatment.

Asialo-rhuEPO as a Potential Neuroprotectant for Ischemic Stroke Treatment

Neuroprotective drugs to protect the brain against cerebral ischemia and reperfusion (I/R) injury are urgently needed. Mammalian cell-produced recombinant human erythropoietin (rhuEPOM) has been demonstrated to have excellent neuroprotective functions in preclinical studies, but its neuroprotective properties could not be consistently translated in clinical trials. The clinical failure of rhuEPOM was thought to be mainly due to its erythropoietic activity-associated side effects. To exploit its tissue-protective property, various EPO derivatives with tissue-protective function only have been developed. Among them, asialo-rhuEPO, lacking terminal sialic acid residues, was shown to be neuroprotective but non-erythropoietic. Asialo-rhuEPO can be prepared by enzymatic removal of sialic acid residues from rhuEPOM (asialo-rhuEPOE) or by expressing human EPO gene in glycoengineered transgenic plants (asialo-rhuEPOP). Both types of asialo-rhuEPO, like rhuEPOM, displayed excellent neuroprotective effects by regulating multiple cellular pathways in cerebral I/R animal models. In this review, we describe the structure and properties of EPO and asialo-rhuEPO, summarize the progress on neuroprotective studies of asialo-rhuEPO and rhuEPOM, discuss potential reasons for the clinical failure of rhuEPOM with acute ischemic stroke patients, and advocate future studies needed to develop asialo-rhuEPO as a multimodal neuroprotectant for ischemic stroke treatment.

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.

An integrated cytokine and kynurenine network as the basis of neuroimmune communication

Two of the molecular families closely associated with mediating communication between the brain and immune system are cytokines and the kynurenine metabolites of tryptophan. Both groups regulate neuron and glial activity in the central nervous system (CNS) and leukocyte function in the immune system, although neither group alone completely explains neuroimmune function, disease occurrence or severity. This essay suggests that the two families perform complementary functions generating an integrated network. The kynurenine pathway determines overall neuronal excitability and plasticity by modulating glutamate receptors and GPR35 activity across the CNS, and regulates general features of immune cell status, surveillance and tolerance which often involves the Aryl Hydrocarbon Receptor (AHR). Equally, cytokines and chemokines define and regulate specific populations of neurons, glia or immune system leukocytes, generating more specific responses within restricted CNS regions or leukocyte populations. In addition, as there is a much larger variety of these compounds, their homing properties enable the superimposition of dynamic variations of cell activity upon local, spatially limited, cell populations. This would in principle allow the targeting of potential treatments to restricted regions of the CNS. The proposed synergistic interface of 'tonic' kynurenine pathway affecting baseline activity and the superimposed 'phasic' cytokine system would constitute an integrated network explaining some features of neuroimmune communication. The concept would broaden the scope for the development of new treatments for disorders involving both the CNS and immune systems, with safer and more effective agents targeted to specific CNS regions.

Recombinant human erythropoietin upregulates PPARγ through the PI3K/Akt pathway to protect neurons in rats subjected to oxidative stress

In vitro cell experiments have suggested that recombinant human erythropoietin (rhEPO) and peroxisome proliferator activated receptor γ (PPARγ) activation exert protective effects on neurons. This study observed the learning and memory ability, antioxidant capacity and the ratio of apoptotic cells after rhEPO intervention and investigated the relationship among rhEPO, PI3K/Akt and PPARγ in the anti-neural oxidative stress injury process in vivo. The results showed that rhEPO significantly improved the learning and memory abilities of rats subjected to oxidative stress, enhanced the antioxidant capacity of cells, and reduced neuronal apoptosis. Then, the PI3K/Akt and PPARγ pathways were inhibited, and TUNEL staining were used to observe the changes in the effect of rhEPO. After the PI3K/Akt and PPARγ pathways were inhibited, the effect of rhEPO on rats subjected to oxidative stress was significantly weakened, suggesting that both the PI3K/Akt and PPARγ pathways are involved in the process by which rhEPO protects neurons. Finally, Western blotting and immunofluorescence staining were used to observe the changes in PI3K/Akt and PPARγ signalling proteins in the neurons after the rhEPO intervention and to explore the relationship among the three. The results showed that rhEPO significantly increased the levels of the p-Akt and PPARγ proteins and the level of the PPARγ protein in the nucleus, indicating that the PI3K/Akt pathway was located upstream of and regulates PPARγ. In conclusion, this study suggested that rhEPO activates the PI3K/Akt to upregulate PPARγ, enhance the cellular antioxidant capacity, and protect neurons in rats subjected to oxidative stress.

Erythropoietin Use and the Risk of Stroke in Patients on Hemodialysis: A Retrospective Cohort Study in Taiwan

Background

Targeting higher hemoglobin levels with erythropoietin to treat anemia in patients with chronic kidney disease is associated with increased cardiovascular risk, including that of stroke. The risks of the subtypes of stroke, ischemic, hemorrhagic, and unspecified, following the administration of erythropoietin in patients with end‐stage renal disease receiving hemodialysis remain unclear.

Methods and results

Overall, 12 948 adult patients with end‐stage renal disease treated during 1999 to 2010 who had undergone hemodialysis were included. The study end points were the incidences of stroke and its subtypes. We used Cox proportional hazards regression models to estimate hazard ratios (HRs) of stroke and its subtypes in erythropoietin recipients compared with nonrecipients. Patients in the erythropoietin cohort did not have an increased risk of stroke compared with those in the nonerythropoietin cohort (adjusted HR, 1.03; 95% CI, 0.92–1.15). Compared with patients in the nonerythropoietin cohort, the risks of ischemic, hemorrhagic, or unspecified stroke were not higher in patients in the erythropoietin cohort (adjusted HRs, 1.08 [95% CI, 0.93–1.26], 0.96 [95% CI, 0.78–1.18], and 1.03 [95% CI, 0.80–1.32], respectively). Increased risks of stroke and its subtypes were not observed with even large annual defined daily doses of erythropoietin (>201).

Conclusions

Erythropoietin in patients receiving hemodialysis is not associated with increased risk of stroke or any of its subtypes.

Darbepoetin as a neuroprotective agent in mild neonatal encephalopathy: a randomized, placebo-controlled, feasibility trial

OBJECTIVE

To assess the feasibility and safety of one dose of Darbepoetin alpha (Darbe) administered to neonates ≥34 weeks with mild neonatal encephalopathy (NE).

METHODS

Randomized, masked, placebo-controlled study including neonates ≥34 weeks gestation with mild NE. Neonates were randomized to receive one dose of Darbe (10 μg/kg IV) or placebo. Clinical and laboratory maternal and newborn data were collected. The Bayley Scales of Infant and Toddler Development, third edition (Bayley-III) and a standardized neurological examination at 8-12 months of corrected age were assessed.

RESULTS

There were no differences in baseline characteristics of the 21 infants randomized (9 Darbe, 12 placebo). Adverse events were not reported at any time. Bayley-III scores were average in both Darbe and placebo groups.

CONCLUSION

This study demonstrates that a randomized, masked, placebo-controlled trial is safe and feasible. A large, randomized trial is warranted to assess the effect of Darbe in this population.

Novel erythropoietin-based therapeutic candidates with extra N-glycan sites that block hematopoiesis but preserve neuroplasticity

Neurological disorders affect millions of people causing behavior-cognitive disabilities. Nowadays they have no effective treatment. Human erythropoietin (hEPO) has been clinically used because of its neurotrophic and cytoprotective properties. However, the erythropoietic activity (EA) should be considered as a side effect. Some analogs like non-sialylated EPO, carbamylated EPO, or EPO peptides have been developed showing different weaknesses: erythropoiesis preservation, low stability, potential immunogenicity, or fast clearance. Herein, we used a novel strategy that blocks the EA but preserves hEPO neurobiological actions. N-glycoengineering was accomplished to add a new glycosylation site within the hEPO sequence responsible for its EA. hEPO-derivatives were produced by CHO.K1 cells, affinity-purified and functionally analyzed studying their in vitro and in vivo EA, their in vitro neuronal plasticity in hippocampal neurons and their neuroprotective action by rescuing hippocampal neurons from apoptosis. Muteins Mut 45_47 (K45 > N45 + N47 > T47), Mut 104 (S104 > N104), and Mut 151_153 (G151 > N151 + K153 > T153) lost their EA but preserved their neuroprotection activity and enhanced neuroplasticity more efficiently than hEPO. Interestingly, Mut 45_47 resulted in a promising candidate to explore as neurotherapeutic considering not only its biopotency but also its pharmacokinetic potential due to the hyperglycosylation.

Eliminating Fc N-Linked Glycosylation and Its Impact on Dosing Consideration for a Transferrin Receptor Antibody-Erythropoietin Fusion Protein in Mice

Erythropoietin (EPO), a hematopoietic growth factor and a promising therapy for Alzheimer's disease, has low permeability across the blood-brain barrier. The transferrin receptor antibody fused to EPO (TfRMAb-EPO) is a chimeric monoclonal antibody that ferries EPO into the brain via the transvascular route. However, TfRMAbs have Fc-effector function-related adverse effects including reticulocyte suppression. To overcome this, we recently developed an effectorless TfRMAb-EPO fusion protein, designated TfRMAb-N292G-EPO, by eliminating the Fc N-linked glycosylation site at position 292 of the antibody heavy chain. The mutant fusion protein showed enhanced plasma clearance and dramatically reduced plasma concentrations compared with the wild-type (WT) nonmutant fusion protein. This increased clearance of the aglycosylated TfRMAb is expected to increase the injection dose of the mutant fusion protein. To provide a basis for future therapeutic uses of this IgG-neurotrophin fusion protein, the current study aimed to characterize the pharmacokinetic profile of this effectorless TfRMAb-N292G-EPO at different doses following different routes of administration in the mouse. Adult C57BL/6J male mice were injected with a single dose (3, 6, 9, or 20 mg/kg; n = 3-6 per dose) of TfRMAb-N292G-EPO through either the subcutaneous (SQ) or intraperitoneal (IP) route. TfRMAb-N292G-EPO plasma concentrations were determined using an enzyme-linked immunosorbent assay. Mice were sacrificed 24 h after injection, and terminal blood was used for a complete blood count. Brain concentrations in the WT- and mutant fusion protein-treated mice were compared. We observed stark differences in the plasma pharmacokinetics of TfRMAb-N292G-EPO between the IP and SQ routes of administration. Dose escalation from 3 to 20 mg/kg increased the plasma C_max only 3.5-fold for the SQ route, compared with a 35-fold increase for the IP route. The plasma C_max was 15.0 ± 2.0, 21.3 ± 4.1, 21.3 ± 6.4, and 52.8 ± 27.9 ng/mL following SQ injection and 288 ± 47, 389 ± 154, 633 ± 194, and 10,066 ± 7059 ng/mL following IP injection for 3, 6, 9, and 20 mg/kg doses, respectively. The plasma C_max following the SQ route was therefore 19- to 190-fold lower than that following the IP route. This finding is consistent with a 31-fold higher apparent clearance following the SQ route compared with the IP route at the highest dose administered. The brain concentrations in the mice treated with a 3 mg/kg dose of the mutant fusion protein were lower than those in the nonmutant WT-treated mice. No reticulocyte suppression was observed at the 3 mg/kg SQ dose of TfRMAb-N292G-EPO. However, reticulocyte suppression increased with an increase in dose and area under the plasma concentration-time curve (AUC) for both the IP and SQ routes. Overall, elimination of Fc N-linked glycosylation, to mitigate TfRMAb effector function side effects, has a profound effect on the plasma exposure of TfRMAb-N292G-EPO at therapeutic as well as high doses (3-20 mg/kg). This effect is more pronounced following SQ injection. The low plasma concentrations of the mutant fusion protein following a 3 mg/kg dose resulted in negligible brain uptake. The beneficial rescue of reticulocyte reduction by the N292G mutation is a function of AUC and is negated at high doses of the N292G mutant.

Coping with hypoxemia: Could erythropoietin (EPO) be an adjuvant treatment of COVID-19?

A very recent epidemiological study provides preliminary evidence that living in habitats located at 2500 m above sea level (masl) might protect from the development of severe respiratory symptoms following infection with the novel SARS-CoV-2 virus. This epidemiological finding raises the question of whether physiological mechanisms underlying the acclimatization to high altitude identifies therapeutic targets for the effective treatment of severe acute respiratory syndrome pivotal to the reduction of global mortality during the COVID-19 pandemic. This article compares the symptoms of acute mountain sickness (AMS) with those of SARS-CoV-2 infection and explores overlapping patho-physiological mechanisms of the respiratory system including impaired oxygen transport, pulmonary gas exchange and brainstem circuits controlling respiration. In this context, we also discuss the potential impact of SARS-CoV-2 infection on oxygen sensing in the carotid body. Finally, since erythropoietin (EPO) is an effective prophylactic treatment for AMS, this article reviews the potential benefits of implementing FDA-approved erythropoietin-based (EPO) drug therapies to counteract a variety of acute respiratory and non-respiratory (e.g. excessive inflammation of vascular beds) symptoms of SARS-CoV-2 infection.

Protective impacts of erythropoietin on myelinization of oligodendrocytes and schwann cells in CNS and PNS following cuprizone-induced multiple sclerosis- histology, molecular, and functional studies

BACKGROUND

Multiple sclerosis (MS) is known as one of the chronic inflammatory diseases characterized by lesions in the central nervous system (CNS) and peripheral nervous system(PNS) resulting in serious cognitive or physical disabilities as well as neurological disorders. Thus, protective effects of erythropoietin(EPO) on myelinization of oligodendrocytes and schwann cells respectively in CNS and PNS following MS induced by cuprizone (CPZ) administration in young female mice.

METHODOLOGY

To meet the objectives of this study; a chow with 0.2 % CPZ was used to feed young female C57BL/6 J mice for six weeks. After three weeks, EPO (5000 IU/kg body weight) was administered via daily intra-peritoneal injection for simultaneous treatment of the mice. Measurement of latency and amplitude of the compound muscle action potential (CMAP) of gastrocnemius muscle was also performed every week during a six-week demyelination interval, and then examinations were fulfilled on the histological sections of the brain and sciatic nerve. Therefore, we focused on the removal of the sciatic and sciatic nerve specimens and analysis of the use of the stereological procedures, western blot, immuno-histochemistry, and gene expression.

RESULTS

According to the results of this study, MBP levels increased in oligodendrocytes (OLs) in the treated mice. Moreover, EPO could concurrently enhance motor coordination and muscle activity. Analysis showed the significant enhancement of the gene expression of MBP, MAG, and S100, as well as stereological variables in the treatment group in comparison with the cuprizone (CPZ) group.

CONCLUSION

Findings could help further understand the alleviation of the detrimental impacts of CPZ using the OLs that would be capable of increasing the level of S100, MAG, and MBP.

Hematologic safety of chronic brain-penetrating erythropoietin dosing in APP/PS1 mice

Introduction

Low blood-brain barrier (BBB) penetration and hematopoietic side effects limit the therapeutic development of erythropoietin (EPO) for Alzheimer's disease (AD). A fusion protein of EPO and a chimeric monoclonal antibody targeting the mouse transferrin receptor (cTfRMAb) has been engineered. The latter drives EPO into the brain via receptor-mediated transcytosis across the BBB and increases its peripheral clearance to reduce hematopoietic side effects of EPO. Our previous work shows the protective effects of this BBB-penetrating EPO in AD mice but hematologic effects have not been studied. Herein, we investigate the hematologic safety and therapeutic effects of chronic cTfRMAb-EPO dosing, in comparison to recombinant human EPO (rhu-EPO), in AD mice.

Methods

Male APPswe PSEN1dE9 (APP/PS1) mice (9.5 months) were treated with saline (n = 11), and equimolar doses of cTfRMAb-EPO (3 mg/kg, n = 7), or rhu-EPO (0.6 mg/kg, n = 9) 2 days/week subcutaneously for 6 weeks, compared to saline-treated wild-type mice (n = 10). At 6 weeks, exploration and memory were assessed, and mice were sacrificed at 8 weeks. Spleens were weighed, and brains were evaluated for amyloid beta (Aβ) load and synaptophysin. Blood was collected at 4, 6 and 8 weeks for a complete blood count and white blood cells differential.

Results

cTfRMAb-EPO transiently increased reticulocyte counts after 4 weeks, followed by normalization of reticulocytes at 6 and 8 weeks. rhu-EPO transiently increased red blood cell count, hemoglobin and hematocrit, and significantly decreased mean corpuscular volume and reticulocytes at 4 weeks, which remained low at 6 weeks. At 8 weeks, a significant decline in red blood cell indices was observed with rhu-EPO treatment. Exploration and cognitive deficits were significantly worse in APP/PS1-rhu-EPO mice. Both cTfRMAb-EPO and rhu-EPO decreased 6E10-positive brain Aβ load; however, cTfRMAb-EPO and not rhu-EPO selectively reduced brain Aβ_1-42 and elevated synaptophysin expression.

Discussion

Chronic treatment with cTfRMAb-EPO results in better hematologic safety, behavioral, and therapeutic indices compared with rhu-EPO, supporting the development of this BBB-penetrable EPO analog for AD.

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Chimeric monoclonal antibody against the mouse TfR (cTfRMAb)-erythropoietin (EPO) is a brain-penetrating IgG-EPO fusion protein.

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Chronic treatment with cTfRMAb-EPO does not alter hematology indices in APP/PS1 mice.

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Equimolar dose of recombinant human EPO significantly alters hematologic indices in APP/PS1 mice.

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Both cTfRMAb-EPO and recombinant human EPO reduce amyloid beta load in APP/PS1 mice.

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cTfRMAb-EPO selectively reduces amyloid beta (1–42) and increases synaptophysin in APP/PS1 mice.

Plasma Pharmacokinetics of High-Affinity Transferrin Receptor Antibody-Erythropoietin Fusion Protein is a Function of Effector Attenuation in Mice

Erythropoietin (EPO) is a potential therapeutic for Alzheimer's disease (AD); however, limited blood-brain barrier (BBB) penetration reduces its applicability as a CNS therapeutic. Antibodies against the BBB transferrin receptor (TfRMAbs) act as molecular Trojan horses for brain drug delivery, and a fusion protein of EPO and TfRMAb, designated TfRMAb-EPO, is protective in a mouse model of AD. TfRMAbs have Fc effector function side effects, and removal of the Fc N-linked glycosylation site by substituting Asn with Gly reduces the Fc effector function. However, the effect of such Fc mutations on the pharmacokinetics (PK) of plasma clearance of TfRMAb-based fusion proteins, such as TfRMAb-EPO, is unknown. To examine this, the plasma PK of TfRMAb-EPO (wild-type), which expresses the mouse IgG1 constant heavy chain region and includes the Asn residue at position 292, was compared to the mutant TfRMAb-N292G-EPO, in which the Asn residue at position 292 is mutated to Gly. Plasma PK was compared following IV, IP, and SQ administration for doses between 0.3 and 3 mg/kg in adult male C57 mice. The results show a profound increase in clearance (6- to 8-fold) of the TfRMAb-N292G-EPO compared with the wild-type TfRMAb-EPO following IV administration. The clearance of both the wild-type and mutant TfRMAb-EPO fusion proteins followed nonlinear PK, and a 10-fold increase in dose resulted in a 7- to 11-fold decrease in plasma clearance. Following IP and SQ administration, the C_max values of the TfRMAb-N292G-EPO mutant were profoundly (37- to 114-fold) reduced compared with the wild-type TfRMAb-EPO, owing to comparable increases in plasma clearance of the mutant fusion protein. The wild-type TfRMAb fusion protein was associated with reticulocyte suppression, and the N292G mutation mitigated this suppression of reticulocytes. Overall, the beneficial suppression of effector function via the N292G mutation may be offset by the deleterious effect this mutation has on the plasma levels of the TfRMAb-EPO fusion protein, especially following SQ administration, which is the preferred route of administration in humans for chronic neurodegenerative diseases including AD.

Erythropoietin and caffeine exert similar protective impact against neonatal intermittent hypoxia: Apnea of prematurity and sex dimorphism

Apnea of prematurity (AoP) is associated with severe and repeated episodes of arterial oxygen desaturation (intermittent hypoxia - IH), which in turn increases the number of apneas. So far, there is no data addressing whether IH leads to sex-specific respiratory consequences, neither if drugs targeting AoP are more effective in males or females. We used rat pups for investigating whether IH-mediated increase of apneas is sex-specific. We also tested whether caffeine (treatment of choice of AoP), erythropoietin (Epo - a neuroprotective factor and potent respiratory stimulant), and combination of both (caffeine+Epo) prevent the IH-mediated formation of apneas in a sex-dependent manner. Newborn rats exposed to IH (21% - 10% FIO₂-8 h a day - 10 cycles per hour) during postnatal days (P) 3-10 were used in this work. Animals were administered drug vehicle, Epo, caffeine and Epo + caffeine (daily from P3 to P10) gavage. At P10 the frequency of apneas at rest (as an index of respiratory dysfunction induced by IH), and respiratory parameters were measured by plethysmography. Our results showed that IH significantly increases the number of apneas in male but not in female rat pups. Moreover, caffeine and Epo in males similarly prevented the increase of apneas induced by IH, and the administration of both drugs together did not provide a cumulative beneficial effect. No impact of drugs was evidenced in females. Apart from apneas, IH increased the normoxic basal ventilation (ventilation at rest) of male animals, and treatments did not prevent such alteration. Besides, no IH- nor treatment-mediated modulation of basal ventilation was found in the basal ventilation of female animals. Analysis of the activity of pro- and antioxidative molecules revealed that IH induces oxidative stress in the brainstem of male and female animals and that all tested treatments similarly prevented such oxidative imbalance in pups of both sexes. We concluded that neonatal IH and the treatments tested to prevent its respiratory consequences are sex-specific. The mechanics associated with such prevention are directly linked with the prevention of oxidative stress and the maturation of the brain. These findings are relevant to understanding better the AoP disorder and for proposing Epo as a new therapeutical tool.

Erythropoietin and Friedreich Ataxia: Time for a Reappraisal?

Friedreich ataxia (FRDA) is a rare neurological disorder due to deficiency of the mitochondrial protein frataxin. Frataxin deficiency results in impaired mitochondrial function and iron deposition in affected tissues. Erythropoietin (EPO) is a cytokine which was mostly known as a key regulator of erythropoiesis until cumulative evidence showed additional neurotrophic and neuroprotective properties. These features offered the rationale for advancement of EPO in clinical trials in different neurological disorders in the past years, including FRDA. Several mechanisms of action of EPO may be beneficial in FRDA. First of all, EPO exposure results in frataxin upregulation in vitro and in vivo. By promoting erythropoiesis, EPO influences iron metabolism and induces shifts in iron pool which may ameliorate conditions of free iron excess and iron accumulation. Furthermore, EPO signaling is crucial for mitochondrial gene activation and mitochondrial biogenesis. Up to date nine clinical trials investigated the effects of EPO and derivatives in FRDA. The majority of these studies had a proof-of-concept design. Considering the natural history of FRDA, all of them were too short in duration and not powered for clinical changes. However, these studies addressed significant issues in the treatment with EPO, such as (1) the challenge of the dose finding, (2) stability of frataxin up-regulation, (3) continuous versus intermittent stimulation with EPO/regimen, or (4) tissue changes after EPO exposure in humans in vivo (muscle biopsy, brain imaging). Despite several clinical trials in the past, no treatment is available for the treatment of FRDA. Current lines of research focus on gene therapy, frataxin replacement strategies and on regulation of key metabolic checkpoints such as NrF2. Due to potential crosstalk with all these mechanisms, interventions on the EPO pathway still represent a valuable research field. The recent development of small EPO mimetics which maintain cytoprotective properties without erythropoietic action may open a new era in EPO research for the treatment of FRDA.

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.

Brain Penetrating Bifunctional Erythropoietin-Transferrin Receptor Antibody Fusion Protein for Alzheimer's Disease

Erythropoietin (EPO), a glycoprotein cytokine essential to hematopoiesis, has neuroprotective effects in rodent models of Alzheimer's disease (AD). However, high therapeutic doses or invasive routes of administration of EPO are required to achieve effective brain concentrations due to low blood-brain barrier (BBB) penetrability, and high EPO doses result in hematopoietic side effects. These obstacles can be overcome by engineering a BBB-penetrable analog of EPO, which is rapidly cleared from the blood, by fusing EPO to a chimeric monoclonal antibody targeting the transferrin receptor (cTfRMAb), which acts as a molecular Trojan horse to ferry the EPO into the brain via the transvascular route. In the current study, we investigated the effects of the BBB-penetrable analog of EPO on AD pathology in a double transgenic mouse model of AD. Five and a half month old male APPswe/PSEN1dE9 (APP/PS1) transgenic mice were treated with saline ( n = 10) or the BBB-penetrable EPO ( n = 10) 3 days/week intraperitoneally for 8 weeks, compared to same-aged C57BL/6J wild-type mice treated with saline ( n = 8) with identical regiment. At 9 weeks following treatment initiation, exploration and spatial memory were assessed with the open-field and Y-maze test, mice were sacrificed, and brains were evaluated for Aβ peptide load, synaptic loss, BBB disruption, microglial activation, and microhemorrhages. APP/PS1 mice treated with the BBB-penetrable cTfRMAb-EPO fusion protein had significantly lower cortical and hippocampal Aβ peptide number ( p < 0.05) and immune-positive area ( p < 0.05), a decrease in hippocampal synaptic loss ( p < 0.05) and cortical microglial activation ( p < 0.001), and improved spatial memory ( p < 0.05) compared with APP/PS1 saline controls. BBB-penetrating EPO was not associated with microhemorrhage development. The cTfRMAb-EPO fusion protein offers therapeutic benefits by targeting multiple targets of AD pathogenesis and progression (Aβ load, synaptic loss, microglial activation) and improving spatial memory in the APP/PS1 mouse model of AD.

Brain-derived erythropoietin protects from intermittent hypoxia-induced cardiorespiratory dysfunction and oxidative stress in mice

Study Objectives

Based on the fact that erythropoietin (Epo) administration in rodents protects against spatial learning and cognitive deficits induced by chronic intermittent hypoxia (CIH)-mediated oxidative damage, here we tested the hypothesis that Epo in the brain protects against cardiorespiratory disorders and oxidative stress induced by CIH in adult mice.

Methods

Adult control and transgenic mice overexpressing Epo in the brain only (Tg21) were exposed to CIH (21%-10% O2-10 cycles/hour-8 hours/day-7 days) or room air. After CIH exposure, we used the tail cuff method to measure arterial pressure, and whole-body plethysmography to assess the frequency of apneic episodes at rest, minute ventilation, and ventilatory responses to hypoxia and hypercapnia. Finally, the activity of pro-oxidant (XO-xanthine oxidase, and NADPH) and antioxidant (super oxide dismutase) enzymes was evaluated in the cerebral cortex and brainstem.

Results

Exposure of control mice to CIH significantly increased the heart rate and arterial pressure, the number of apneic events, and the ventilatory response to hypoxia and hypercapnia. Furthermore, CIH increased the ratio of pro-oxidant to antioxidant enzymes in cortex and brainstem tissues. Both physiological and molecular changes induced by CIH were prevented in transgenic Tg21 mice.

Conclusions

We conclude that the neuroprotective effect of Epo prevents oxidative damage in the brain and cardiorespiratory disorders induced by CIH. Considering that Epo is used in clinics to treat chronic kidney disease and stroke, our data show convincing evidence suggesting that Epo may be a promising alternative drug to treat sleep-disorder breathing.

Hypoxia and myelination deficits in the developing brain

Myelination is a complex and orderly process during brain development that is essential for normal motor, cognitive and sensory functions. Cellular and molecular interactions between myelin-forming oligodendrocytes and axons are required for normal myelination in the developing brain. Oligodendrocyte progenitor cells (OPCs) proliferate and differentiate into mature myelin-forming oligodendrocytes. In this connection, astrocytes and microglia are also involved in survival and proliferation of OPCs. Hypoxic insults during the perinatal period affect the normal development, differentiation and maturation of the OPCs or cause their death resulting in impaired myelination. Several factors such as augmented release of proinflammatory cytokines by activated microglia and astrocytes, extracellular accumulation of excess glutamate and increased levels of nitric oxide are some of the underlying factors for hypoxia induced damage to the OPCs. Additionally, hypoxia also leads to down-regulation of several genes involved in oligodendrocyte differentiation encoding proteolipid protein, platelet-derived growth factor receptor and myelin-associated glycoprotein in the developing brain. Furthermore, oligodendrocytes may also accumulate increased amounts of iron in hypoxic conditions that triggers endoplasmic reticulum stress, misfolding of proteins and generation of reactive oxygen species that ultimately would lead to myelination deficits. More in-depth studies to elucidate the pathophysiological mechanisms underlying the inability of oligodendrocytes to myelinate the developing brain in hypoxic insults are desirable to develop new therapeutic options or strategies for myelination deficits.

Neuroimmune Axes of the Blood-Brain Barriers and Blood-Brain Interfaces: Bases for Physiological Regulation, Disease States, and Pharmacological Interventions

Central nervous system (CNS) barriers predominantly mediate the immune-privileged status of the brain, and are also important regulators of neuroimmune communication. It is increasingly appreciated that communication between the brain and immune system contributes to physiologic processes, adaptive responses, and disease states. In this review, we discuss the highly specialized features of brain barriers that regulate neuroimmune communication in health and disease. In section I, we discuss the concept of immune privilege, provide working definitions of brain barriers, and outline the historical work that contributed to the understanding of CNS barrier functions. In section II, we discuss the unique anatomic, cellular, and molecular characteristics of the vascular blood-brain barrier (BBB), blood-cerebrospinal fluid barrier, and tanycytic barriers that confer their functions as neuroimmune interfaces. In section III, we consider BBB-mediated neuroimmune functions and interactions categorized as five neuroimmune axes: disruption, responses to immune stimuli, uptake and transport of immunoactive substances, immune cell trafficking, and secretions of immunoactive substances. In section IV, we discuss neuroimmune functions of CNS barriers in physiologic and disease states, as well as pharmacological interventions for CNS diseases. Throughout this review, we highlight many recent advances that have contributed to the modern understanding of CNS barriers and their interface functions.

Erythropoietin, a putative neurotransmitter during hypoxia, is produced in RVLM neurons and activates them in neonatal Wistar rats

Recent studies indicate that erythropoietin (EPO) is present in many areas of the brain and is active in the restoration of impaired neurons. In this study, we examined the presence of EPO and its role in bulbospinal neurons in the rostral ventrolateral medulla (RVLM). Hypoxia is often accompanied by a high blood pressure (BP). We hypothesized that EPO is produced in response to hypoxia in RVLM neurons and then activates them. To investigate whether RVLM neurons are sensitive to EPO, we examined the changes in the membrane potentials (MPs) of bulbospinal RVLM neurons using the whole cell patch-clamp technique during superfusion with EPO. A brainstem-spinal cord preparation was used for the experiments. EPO depolarized the RVLM neurons, and soluble erythropoietin receptor (SEPOR), an antagonist of EPO, hyperpolarized them. Furthermore, hypoxia-depolarized RVLM neurons were significantly hyperpolarized by SEPOR. In histological examinations, the EPO-depolarized RVLM neurons showed the presence of EPO receptor (EPOR). The RVLM neurons that possessed EPORs showed the presence of EPO and hypoxia-inducible factor (HIF)-2α. We also examined the levels of HIF-2α and EPO messenger RNA (mRNA) in the ventral sites of the medullas (containing RVLM areas) in response to hypoxia. The levels of HIF-2α and EPO mRNA in the hypoxia group were significantly greater than those in the control group. These results suggest that EPO is produced in response to hypoxia in RVLM neurons and causes a high BP via the stimulation of those neurons. EPO may be one of the neurotransmitters produced by RVLM neurons during hypoxia.

Erythropoietin mediates brain-vascular-kidney crosstalk and may be a treatment target for pulmonary and resistant essential hypertension

Organ crosstalk pathways represent the next frontier for target-mining in molecular medicine for existing syndromes. Pulmonary hypertension and resistant essential hypertension are syndromes that have been proven elusive in etiology, and frequently refractory to first-line management. Underlying crosstalk mechanisms, not yet considered in these treatments, may hinder outcomes or unlock novel treatments. This review focuses systematically on erythropoietin, a synthesizable molecule, as a mediator of brain-kidney crosstalk. Insights gained from this review will be applied to cardiovascular diseases in a clinician-directed fashion.

Erythropoietin signaling increases neurogenesis and oligodendrogenesis of endogenous neural stem cells following spinal cord injury both in vivo and in vitro

Erythropoietin (Epo) promotes functional recovery following spinal cord injury (SCI); however, the exact underlying mechanisms are yet to be determined. Although endogenous neural stem cells (NSCs) in the adult spinal cord are a therapeutic target in SCI models, the effect of Epo on this NSC population remains unknown. The present study investigated the effects of Epo on endogenous NSCs in the adult spinal cord both in vitro and in vivo. For the in vivo analyses, normal rats (Normal) and SCI contusion model rats (SCI) received either recombinant human Epo or saline treatment for 7 days (5,000 U/kg), and spinal cords were subsequently analyzed at 2, 8, and 14 days. For in vitro analyses, NSCs harvested from adult rat spinal cords were exposed to Epo (10 U/ml). A significant increase in β-tubulin⁺ new neurons (P<0.01) was observed at all three time points and O4⁺ new oligodendrocytes (P<0.05) at days 8 and 14 in the SCI+Epo group compared with the SCI+Saline group. This was concomitant with a prolonged activation of Epo signaling; however, no effect on NSCs proliferation was observed. Similar results were also obtained in vitro. Motor functional recovery was also noted at days 8 and 14 only in the Epo-treated SCI rats. Although the expression of Epo and EpoR significantly increased in Normal+Epo rats compared with Normal+Saline rats (P<0.05), the cell numbers and phenotype were comparable between the two groups. To the best of the author's knowledge, this is the first study to demonstrate that Epo signaling promotes both neurogenesis and oligodendrogenesis following SCI and that these may represent the underlying mechanisms for the functional recovery and therapeutic effects of Epo following SCI.

Transfection of primary brain capillary endothelial cells for protein synthesis and secretion of recombinant erythropoietin: a strategy to enable protein delivery to the brain

Treatment of chronic disorders affecting the central nervous system (CNS) is complicated by the inability of drugs to cross the blood-brain barrier (BBB). Non-viral gene therapy applied to brain capillary endothelial cells (BCECs) denotes a novel approach to overcome the restraints in this passage, as turning BCECs into recombinant protein factories by transfection could result in protein secretion further into the brain. The present study aims to investigate the possibility of transfecting primary rat brain endothelial cells (RBECs) for recombinant protein synthesis and secretion of the neuroprotective protein erythropoietin (EPO). We previously showed that 4% of RBECs with BBB properties can be transfected without disrupting the BBB integrity in vitro, but it can be questioned whether this is sufficient to enable protein secretion at therapeutic levels. The present study examined various transfection vectors, with regard to increasing the transfection efficiency without disrupting the BBB integrity. Lipofectamine 3000™ was the most potent vector compared to polyethylenimine (PEI) and Turbofect. When co-cultured with astrocytes, the genetically modified RBECs secreted recombinant EPO into the cell culture medium both luminally and abluminally, and despite lower levels of EPO reaching the abluminal chamber, the amount of recombinant EPO was sufficient to evolve a biological effect on astrocytes cultured at the abluminal side in terms of upregulated gene expression of brain-derived neurotropic factor (BDNF). In conclusion, non-viral gene therapy to RBECs leads to protein secretion and signifies a method for therapeutic proteins to target cells inside the CNS otherwise omitted due to the BBB.

Erythropoietin-Mediated Regulation of Central Respiratory Command

Erythropoietin (Epo) is a cytokine expressed throughout the body, including in the central nervous system where it can act as a breathing modulator in the central respiratory network. In vitro, Epo allows maintaining the activity of respiratory neurons during acute hypoxia, resulting in inhibition of the hypoxia-induced rhythm depression. In vivo, Epo action on the central respiratory command results in enhancement of the acute hypoxic ventilatory response, allowing a better oxygenation of the body by improvement of gases exchanges in the lungs. Importantly, this effect of Epo is age-dependent, being observed at adulthood and at both early and late postnatal ages, but not at middle postnatal ages, when an important setup of the central respiratory command occurs. Epo regulation of the central respiratory command involves at least two intracellular signaling pathways, PI3K-Akt and MEK-ERK pathways. However, the exact mechanism underlying the action of Epo on the central respiratory control remains to be deciphered, as well as the exact cell types and nuclei involved in this control. Epo-mediated effect on the central respiratory command is regulated by several factors, including hypoxia, sex hormones, and an endogen antagonist. Although more knowledge is needed before reaching the clinical trial step, Epo seems to be a promising therapeutic treatment, notably against newborn breathing disorders.

Population Pharmacokinetics of Darbepoetin in Infants Following Single Intravenous and Subcutaneous Dosing

Darbepoetin alfa (Darbe) is a hyperglycosylated analogue of recombinant human erythropoietin (Epo). The aim of this study was to develop a population pharmacokinetic model for Darbe following intravenous (i.v.) and subcutaneous (s.c.) administration to infants. Data from 2 infant clinical studies (a single i.v. dose study following a 4 μg/kg dose of Darbe, and a single s.c. dose study following 1 μg/kg or 4 μg/kg dose of Darbe) were combined and analyzed simultaneously using nonlinear mixed-effect modeling approach. Darbe population pharmacokinetics was well described by a 2-compartment model with first-order elimination. The covariate analysis identified significant impact of gender on clearance and bodyweight on volume of distribution. The clearance of Darbe was estimated to be 0.050 L/h/kg in male infants and 0.031 L/h/kg in female infants. The predicted population mean value of Vp is 0.84 L/kg, which is associated with the subject's bodyweight (p < 0.05). Following s.c. administration, the estimated absorption rate (i.e., ka) of Darbe was 0.062 L/h. The model provides a suitable starting point for the development of further pharmacokinetic-pharmacodynamic models in infants in a variety of disease settings. Because the covariate-pharmacokinetic parameter relationships were identified in only 22 infants, further investigation with larger sample size is warranted.

Efficient breathing at neonatal ages: A sex and Epo-dependent issue

During postnatal life, the respiratory control system undergoes intense development and is highly responsive to stimuli emerging from the environment. In fact, interruption of breathing prevents gas exchange and results in systemic hypoxia that, if prolonged, can lead to cardio-respiratory failure or sudden infant death. Moreover, in newborns and infants, respiratory disorders related to neural control dysfunction show significant sexual dimorphism with a higher prevalence in males. To this day, the therapeutic tools available to alleviate these respiratory disorders remain limited. Furthermore, the factors explaining the sexual dimorphism in newborns and during infancy remain unknown. Erythropoietin (Epo) was originally discovered as a cytokine able to increase the production of red blood cells upon conditions of reduced oxygen availability. We now know that Epo is a cytokine also secreted by neurons and astrocytes that protects the brain during trauma or hypoxic stress in a sex dependent manner. In this novel line of research, our previous studies demonstrated at adult ages that cerebral Epo acts as a respiratory stimulant in rodents and humans. These results provided a strong rationale for exploring the role of cerebral Epo in neuronal respiratory control during postnatal development. The objective of this review is to summarize our recent findings showing that cerebral Epo is a potent sex-specific respiratory stimulant at neonatal ages. Keeping in mind that Epo is routinely and safely administrated in newborn humans for anemia and neonatal asphyxia, we predict that our research provides the basis necessary to promote the clinical use of Epo against neonatal respiratory disorders related to neural control dysfunction.

Age-associated expression of erythropoietin and its receptor in rat spiral ganglion neurons and its association with neuronal apoptosis and hearing alterations

The present study aimed to determine the expression of erythropoietin (EPO) and the EPO receptor (EPOR) in spiral ganglion neurons (SGNs) in the inner ear of rats of various ages, and the associated neuronal apoptosis and hearing alterations. A total of 15 healthy rats (n=30 ears), were divided into three groups: i) A nominated infant group at post-natal day (PND) 12–14, ii) an adult group at PND 60 and iii) a 3-year postnatal aged group. Auditory brainstem response (ABR) measurements were performed on all rats. EPO and EPOR expression in the inner ear was detected by immunohistochemistry. In situ terminal deoxynucleotidyl transferase dUTP nick end labeling assays were performed to detect the apoptosis of SGNs. The average hearing thresholds of the ABR (decibels above normal hearing level) were 5.625±4.955 in the infant, 15.000±8.498 in the adult and 23.500±13.134 in the aged groups. Hearing thresholds for aged and adult rats increased significantly compared with infant rats. However, the difference in latencies of peak I was not significant (P>0.05). EPO in SGNs was detected during different developmental periods without significant alterations, but were reduced compared with Corti's organ or the stria vascularis. EPOR expression increased significantly from infant to adult stage, and this increased expression was maintained in the aged group. An age-associated increase in the apoptosis of SGNs was detected in all three groups (P=0.0347). The potential neuroprotective effects of EPO in SGNs may not be revealed during the aging process under natural conditions, and may be associated with spontaneous neuronal apoptosis and consequently, hearing diminution. However, the age-associated increase in EPOR in SGNs may exert a role in neuroprotection when necessary, for example in presbycusis.

Population Pharmacokinetics of Darbepoetin Alfa in Conjunction with Hypothermia for the Treatment of Neonatal Hypoxic-Ischemic Encephalopathy

AIM

The aim of this study was to determine the population pharmacokinetics of darbepoetin alfa in hypothermic neonates with hypoxic-ischemic encephalopathy treated with hypothermia.

METHODS

Neonates ≥36 weeks gestation and <12 h postpartum with moderate to severe hypoxic-ischemic encephalopathy who were undergoing hypothermia treatment were recruited in this randomized, multicenter, investigational, new drug pharmacokinetic study. Two intravenous darbepoetin alfa treatment groups were evaluated: 2 and 10 µg/kg. Serum erythropoietin concentrations were measured using an enzyme-linked immunosorbent assay. Monolix 4.3.1 was used to estimate darbepoetin alfa clearance and volume of distribution. Covariates tested included: birthweight, gestational age, postnatal age, postmenstrual age, sex, Sarnat score, and study site.

RESULTS

Darbepoetin alfa pharmacokinetics were well described by a one-compartment model with exponential error. Clearance and the volume of distribution were scaled by birthweight (centered on the mean) a priori. Additionally, gestational age (also centered on the mean) significantly affected darbepoetin alfa clearance. Clearance and volume of distribution were estimated as 0.0465 L/h (95% confidence interval 0.0392-0.0537) and 1.58 L (95% confidence interval 1.29-1.87), respectively.

CONCLUSIONS

A one-compartment model successfully described the pharmacokinetics of darbepoetin alfa among hypothermic neonates treated for hypoxic-ischemic encephalopathy. Clearance decreased with increasing gestational age.

Carbamylated erythropoietin enhances mice ventilatory responses to changes in O2 but not CO2 levels

Erythropoietin (EPO) has beneficial tissue-protective effects in several diseases but erythrocytosis may cause deleterious effects in EPO-treated patients. Thus carbamylated-EPO (C-EPO) and other derivatives retaining tissue-protective but lacking bone marrow-stimulating actions have been developed. Although EPO modulates ventilatory responses, the effects of C-EPO on ventilation have not been investigated. Here, basal breathing and respiratory chemoreflexes were measured by plethysmography after acute and chronic treatments with recombinant human C-EPO (rhC-EPO; 15,000 IU/kg during 5days) or saline (control group). Hematocrit, plasma and brainstem rhC-EPO levels were also quantified. Chronic rhC-EPO significantly elevated tissue rhC-EPO levels but not hematocrit. None of the drug regimen altered basal ventilation (normoxia). Chronic but not acute rhC-EPO enhanced hyperoxic ventilatory depression, and sustained the hypoxic ventilatory response mainly via a reduction of the roll-off phase. By contrast, rhC-EPO did not blunt the ventilatory response to hypercapnia. Thus, chronic C-EPO may be a promising therapy to improve breathing during hypoxia while minimizing adverse effects on cardiovascular function.

Polycythemia and high levels of erythropoietin in blood and brain blunt the hypercapnic ventilatory response in adult mice

Changes in arterial Po2, Pco2, and pH are the strongest stimuli sensed by peripheral and central chemoreceptors to adjust ventilation to the metabolic demand. Erythropoietin (Epo), the main regulator of red blood cell production, increases the hypoxic ventilatory response, an effect attributed to the presence of Epo receptors in both carotid bodies and key brainstem structures involved in integration of peripheral inputs and control of breathing. However, it is not known whether Epo also has an effect on the hypercapnic chemoreflex. In a first attempt to answer this question, we tested the hypothesis that Epo alters the ventilatory response to increased CO2 levels. Basal ventilation and hypercapnic ventilatory response (HCVR) were recorded from control mice and from two transgenic mouse lines constitutively expressing high levels of human Epo in brain only (Tg21) or in brain and plasma (Tg6), the latter leading to polycythemia. To tease apart the potential effects of polycythemia and levels of plasma Epo in the HCVR, control animals were injected with an Epo analog (Aranesp), and Tg6 mice were treated with the hemolytic agent phenylhydrazine after splenectomy. Ventilatory parameters measured by plethysmography in conscious mice were consistent with data from electrophysiological recordings in anesthetized animals and revealed a blunted HCVR in Tg6 mice. Polycythemia alone and increased levels of plasma Epo blunt the HCVR. In addition, Tg21 mice with an augmented level of cerebral Epo also had a decreased HCVR. We discuss the potential implications of these findings in several physiopathological conditions.

Therapies negating neuroinflammation after brain trauma

Traumatic brain injury (TBI) elicits a complex secondary injury response, with neuroinflammation as a crucial central component. Long thought to be solely a deleterious factor, the neuroinflammatory response has recently been shown to be far more intricate, with both beneficial and detrimental consequences depending on the timing, magnitude and specific immune composition of the response post-injury. Despite extensive preclinical and clinical research into mechanisms of secondary injury after TBI, no effective neuroprotective therapy has been identified, with potential candidates repeatedly proving disappointing in the clinic. The neuroinflammatory response offers a promising avenue for therapeutic targeting, aiming to quell the deleterious consequences without influencing its function in providing a neurotrophic environment supportive of repair. The present review firstly describes the findings of recent clinical trials that aimed to modulate inflammation as a means of neuroprotection. Secondly, we discuss promising multifunctional and single-target anti-inflammatory candidates either currently in trial, or with ample experimental evidence supporting clinical application. This article is part of a Special Issue entitled SI:Brain injury and recovery.

Antioxidant and antiapoptotic effects of darbepoetin-α against traumatic brain injury in rats

INTRODUCTION

In this study, we tried to determine whether darbepoetin-α would protect the brain from oxidative stress and apoptosis in a rat traumatic brain injury model.

MATERIAL AND METHODS

The animals were randomized into four groups; group 1 (sham), group 2 (trauma), group 3 (darbepoetin α), group 4 (methylprednisolone). In the sham group only the skin incision was performed. In all the other groups, a moderate traumatic brain injury modelwas applied.

RESULTS

Following trauma both glutathione peroxidase, superoxide dismutase levels decreased (p < 0.001 for both); darbepoetin-α increased the activity of both antioxidant enzymes (p = 0.001 and p < 0.001 respectively). Trauma caused significant elevation in the nitric oxide synthetase and xanthine oxidase levels (p < 0.001 for both). Administration of darbepoetin-α significantly decreased the levels of nitric oxide synthetase and xanthine oxidase (p < 0.001 for both). Also, trauma caused significant elevation in the nitric oxide levels (p < 0.001); darbepoetin-α administration caused statistically significant reduction in the nitric oxide levels (p < 0.001). On the other hand, malondialdehyde levels were increased following trauma (p < 0.001), and darbepoetin α significantly reduced the malondialdehyde levels (p < 0.001). Due to the elevated apoptotic activity following the injury, caspase-3 activity increased significantly. Darbepoetin-α treatment significantly inhibited apoptosis by lowering the caspase-3 activity (p < 0.001). In the darbepoetin group, histopathological score was lower than the trauma group (p = 0.016).

CONCLUSIONS

In this study, darbepoetin-α was shown to be at least as effective as methylprednisolone in protecting brain from oxidative stress, lipid peroxidation and apoptosis.

Darbepoetin administration to neonates undergoing cooling for encephalopathy: a safety and pharmacokinetic trial

BACKGROUND

Despite therapeutic hypothermia, neonates with encephalopathy (NE) have high rates of death or disability. Darbepoetin alfa (Darbe) has comparable biological activity to erythropoietin, but has extended circulating half-life (t(1/2)). Our aim was to determine Darbe safety and pharmacokinetics as adjunctive therapy to hypothermia.

STUDY DESIGN

Thirty infants (n = 10/arm) ≥36 wk gestation undergoing therapeutic hypothermia for NE were randomized to receive placebo, Darbe low dose (2 μg/kg), or high dose (10 μg/kg) given intravenously within 12 h of birth (first dose/hypothermia condition) and at 7 d (second dose/normothermia condition). Adverse events were documented for 1 mo. Serum samples were obtained to characterize Darbe pharmacokinetics.

RESULTS

Adverse events (hypotension, altered liver and renal function, seizures, and death) were similar to placebo and historical controls. Following the first Darbe dose at 2 and 10 μg/kg, t(1/2) was 24 and 32 h, and the area under the curve (AUC(inf)) was 26,555 and 180,886 h*mU/ml*, respectively. In addition, clearance was not significantly different between the doses (0.05 and 0.04 l/h). At 7 d, t(1/2) was 26 and 35 h, and AUC(inf) was 10,790 and 56,233 h*mU/ml*, respectively (*P < 0.01).

CONCLUSION

Darbe combined with hypothermia has similar safety profile to placebo with pharmacokinetics sufficient for weekly administration.

Erythropoietin in amyotrophic lateral sclerosis: a multicentre, randomised, double blind, placebo controlled, phase III study

OBJECTIVE

To assess the efficacy of recombinant human erythropoietin (rhEPO) in amyotrophic lateral sclerosis (ALS).

METHODS

Patients with probable laboratory-supported, probable or definite ALS were enrolled by 25 Italian centres and randomly assigned (1:1) to receive intravenous rhEPO 40,000 IU or placebo fortnightly as add-on treatment to riluzole 100 mg daily for 12 months. The primary composite outcome was survival, tracheotomy or >23 h non-invasive ventilation (NIV). Secondary outcomes were ALSFRS-R, slow vital capacity (sVC) and quality of life (ALSAQ-40) decline. Tolerability was evaluated analysing adverse events (AEs) causing withdrawal. The randomisation sequence was computer-generated by blocks, stratified by centre, disease severity (ALSFRS-R cut-off score of 33) and onset (spinal or bulbar). The main outcome analysis was performed in all randomised patients and by intention-to-treat for the entire population and patients stratified by severity and onset. The study is registered, EudraCT 2009-016066-91.

RESULTS

We randomly assigned 208 patients, of whom 5 (1 rhEPO and 4 placebo) withdrew consent and 3 (placebo) became ineligible (retinal thrombosis, respiratory insufficiency, SOD1 mutation) before receiving treatment; 103 receiving rhEPO and 97 placebo were eligible for analysis. At 12 months, the annualised rate of death (rhEPO 0.11, 95% CI 0.06 to 0.20; placebo: 0.08, CI 0.04 to 0.17), tracheotomy or >23 h NIV (rhEPO 0.16, CI 0.10 to 0.27; placebo 0.18, CI 0.11 to 0.30) did not differ between groups, also after stratification by onset and ALSFRS-R at baseline. Withdrawal due to AE was 16.5% in rhEPO and 8.3% in placebo. No differences were found for secondary outcomes.

CONCLUSIONS

RhEPO 40,000 IU fortnightly did not change the course of ALS.

Safety and angiogenic effects of systemic gene delivery of a modified erythropoietin

Erythropoietin (EPO) is critical for red blood cell production and is also an effective neuroprotective agent. However, it may also contribute to pathological angiogenesis. Here we investigate the angiogenic potential of EPO and a mutant form with attenuated erythropoietic activity, EPO-R76E, on primary human retinal microvascular endothelial cells (HRMEC) and in the adult retina. Assays of death, proliferation, and tube-formation were performed on HRMECs exposed to EPO, EPO-R76E, or media alone. Postnatal day 9 wild-type mice were injected intramuscularly with adeno-associated virus vectors expressing either enhanced green fluorescent protein or EpoR76E. At 3 months, levels of EPO-R76E in the eye were quantified, and the health of the retinal vasculature was assessed by fluorescein angiography and isolectin immunolabeling. Immunohistochemistry, histology, and electroretinogram assessments were performed as measures of retinal health. Neither EPO nor EPO-R76E induced proliferation or tube-formation in HRMEC under the conditions used. EPO-R76E decreased HRMEC death in a dose-dependent manner. Long-term systemic gene delivery of EPO-R76E was safe in terms of retinal vasculature, histology, and the electroretinogram in vivo. Our results show that EPO-R76E can block HRMEC death, consistent with its role in erythropoiesis and neuroprotection. In addition, long-term gene delivery of EPO-R76E is safe in the adult retina.

Targeted delivery of protein and gene medicines through the blood-brain barrier

The development of biologic drugs (recombinant proteins, therapeutic antibodies, peptides, nucleic acid therapeutics) as new treatments of brain disorders has been difficult, and a major reason is the lack of transport through the blood-brain barrier (BBB) of these large molecule pharmaceuticals. Biologic drugs can be re-engineered as brain-penetrating neuropharmaceuticals using BBB molecular Trojan horse technology. Certain peptidomimetic monoclonal antibodies that target endogenous receptors on the BBB, such as the insulin or transferrin receptor, enable the re-engineering of biologic drugs that cross the BBB.

Delivery of therapeutic peptides and proteins to the CNS

Peptides and proteins have potent effects on the brain after their peripheral administration, suggesting that they may be good substrates for the development of CNS therapeutics. Major hurdles to such development include their relation to the blood-brain barrier (BBB) and poor pharmacokinetics. Some peptides cross the BBB by transendothelial diffusion and others cross in the blood-to-brain direction by saturable transporters. Some regulatory proteins are also transported across the BBB and antibodies can enter the CNS via the extracellular pathways. Glycoproteins and some antibody fragments can be taken up and cross the BBB by mechanisms related to adsorptive endocytosis/transcytosis. Many peptides and proteins are transported out of the CNS by saturable efflux systems and enzymatic activity in the blood, CNS, or BBB are substantial barriers to others. Both influx and efflux transporters are altered by various substances and in disease states. Strategies that manipulate these interactions between the BBB and peptides and proteins provide many opportunities for the development of therapeutics. Such strategies include increasing transendothelial diffusion of small peptides, upregulation of saturable influx transporters with allosteric regulators and other posttranslational means, use of vectors and other Trojan horse strategies, inhibition of efflux transporters including with antisense molecules, and improvement in pharmacokinetic parameters to overcome short half-lives, tissue sequestration, and enzymatic degradation.

Agile delivery of protein therapeutics to CNS

A variety of therapeutic proteins have shown potential to treat central nervous system (CNS) disorders. Challenge to deliver these protein molecules to the brain is well known. Proteins administered through parenteral routes are often excluded from the brain because of their poor bioavailability and the existence of the blood-brain barrier (BBB). Barriers also exist to proteins administered through non-parenteral routes that bypass the BBB. Several strategies have shown promise in delivering proteins to the brain. This review, first, describes the physiology and pathology of the BBB that underscore the rationale and needs of each strategy to be applied. Second, major classes of protein therapeutics along with some key factors that affect their delivery outcomes are presented. Third, different routes of protein administration (parenteral, central intracerebroventricular and intraparenchymal, intranasal and intrathecal) are discussed along with key barriers to CNS delivery associated with each route. Finally, current delivery strategies involving chemical modification of proteins and use of particle-based carriers are overviewed using examples from literature and our own work. Whereas most of these studies are in the early stage, some provide proof of mechanism of increased protein delivery to the brain in relevant models of CNS diseases, while in few cases proof of concept had been attained in clinical studies. This review will be useful to broad audience of students, academicians and industry professionals who consider critical issues of protein delivery to the brain and aim developing and studying effective brain delivery systems for protein therapeutics.

The comparative effects of recombinant human erythropoietin and darbepoetin-alpha on cerebral vasospasm following experimental subarachnoid hemorrhage in the rabbit

BACKGROUND

Darbepoetin alpha is a hypersialylated analogue of erythropoietin effective for activating erythropoietin-receptors. This study investigated the vasodilator and neuroprotective effects of darbepoetin alpha on an experimental subarachnoid hemorrhage model and compared it with erythropoietin.

METHODS

Forty adult male New Zealand white rabbits were randomly divided into four groups of ten rabbits each: group 1 (control), group 2 (subarachnoid hemorrhage), group 3 (erythropoietin), and group 4 (darbepoetin alpha). Recombinant human erythropoietin was administered at a dose of 1,000 U/kg intraperitoneally after the induction of subarachnoid hemorrhage and continued every 8 h up to 72 h. Darbepoetin alpha was administered at a single intraperitoneal dose of 30 μg/kg. Animals were killed 72 h after subarachnoid hemorrhage. Basilar artery cross-sectional areas, arterial wall thicknesses, hippocampal degeneration scores and biochemical analyses were measured in all groups.

RESULTS

Both erythropoietin and darbepoetin alpha treatments were found to attenuate cerebral vasospasm and provide neuroprotection after subarachnoid hemorrhage in rabbits. Darbepoetin alpha revealed better morphometric and histopathological results than erythropoietin among experimental subarachnoid hemorrhage-induced vasospasm.

CONCLUSIONS

Our findings, for the first time, showed that darbepoetin alpha can prevent vasospasm and provides neuroprotection following experimental subarachnoid hemorrhage. Moreover, darbepoetin alpha showed better results when compared with erythropoietin.

Erythropoietin: powerful protection of ischemic and post-ischemic brain

Ischemic brain injury inflicted by stroke and cardiac arrest ranks among the leading causes of death and long-term disability in the United States. The brain consumes large amounts of metabolic substrates and oxygen to sustain its energy requirements. Consequently, the brain is exquisitely sensitive to interruptions in its blood supply, and suffers irreversible damage after 10-15 min of severe ischemia. Effective treatments to protect the brain from stroke and cardiac arrest have proven elusive, due to the complexities of the injury cascades ignited by ischemia and reperfusion. Although recombinant tissue plasminogen activator and therapeutic hypothermia have proven efficacious for stroke and cardiac arrest, respectively, these treatments are constrained by narrow therapeutic windows, potentially detrimental side-effects and the limited availability of hypothermia equipment. Mounting evidence demonstrates the cytokine hormone erythropoietin (EPO) to be a powerful neuroprotective agent and a potential adjuvant to established therapies. Classically, EPO originating primarily in the kidneys promotes erythrocyte production by suppressing apoptosis of proerythroid progenitors in bone marrow. However, the brain is capable of producing EPO, and EPO's membrane receptors and signaling components also are expressed in neurons and astrocytes. EPO activates signaling cascades that increase the brain's resistance to ischemia-reperfusion stress by stabilizing mitochondrial membranes, limiting formation of reactive oxygen and nitrogen intermediates, and suppressing pro-inflammatory cytokine production and neutrophil infiltration. Collectively, these mechanisms preserve functional brain tissue and, thus, improve neurocognitive recovery from brain ischemia. This article reviews the mechanisms mediating EPO-induced brain protection, critiques the clinical utility of exogenous EPO to preserve brain threatened by ischemic stroke and cardiac arrest, and discusses the prospects for induction of EPO production within the brain by the intermediary metabolite, pyruvate.

Enhancement of ventricular-subventricular zone-derived neurogenesis and oligodendrogenesis by erythropoietin and its derivatives

In the postnatal mammalian brain, stem cells in the ventricular-subventricular zone (V-SVZ) continuously generate neuronal and glial cells throughout life. Genetic labeling of cells of specific lineages have demonstrated that the V-SVZ is an important source of the neuroblasts and/or oligodendrocyte progenitor cells (OPCs) that migrate toward injured brain areas in response to several types of insult, including ischemia and demyelinating diseases. However, this spontaneous regeneration is insufficient for complete structural and functional restoration of the injured brain, so interventions to enhance these processes are sought for clinical applications. Erythropoietin (EPO), a clinically applied erythropoietic factor, is reported to have cytoprotective effects in various kinds of insult in the central nervous system. Moreover, recent studies suggest that EPO promotes the V-SVZ-derived neurogenesis and oligodendrogenesis. EPO increases the proliferation of progenitors in the V-SVZ and/or the migration and differentiation of their progenies in and around injured areas, depending on the dosage, timing, and duration of treatment, as well as the type of animal model used. On the other hand, EPO has undesirable side effects, including thrombotic complications. We recently demonstrated that a 2-week treatment with the EPO derivative asialo-EPO promotes the differentiation of V-SVZ-derived OPCs into myelin-forming mature oligodendrocytes in the injured white matter of neonatal mice without causing erythropoiesis. Here we present an overview of the multifaceted effects of EPO and its derivatives in the V-SVZ and discuss the possible applications of these molecules in regenerative medicine.

Long-term moderate dose exogenous erythropoietin treatment protects from intermittent hypoxia-induced spatial learning deficits and hippocampal oxidative stress in young rats

Exposure to intermittent hypoxia (IH) is associated with cognitive impairments and oxidative stress in brain regions involved in learning and memory. In earlier studies, erythropoietin (EPO) showed a neuroprotective effect in large doses. The aim of the present study was to explore the effect of smaller doses of EPO, such as those used in the treatment of anemia, on IH-induced cognitive deficits and hippocampal oxidative stress in young rats. The effect of concurrent EPO treatment (500 and 1,000 IU/kg/day ip) on spatial learning and memory deficits induced by long-term exposure to IH for 6 weeks was tested using the Morris water maze (MWM) test and the elevated plus maze (EPM) test. Moreover, the effect on hippocampal glutamate and oxidative stress were assessed. Exposure to IH induced a significant impairment of spatial learning and cognition of animals in both MWM and EPM performance parameters. Moreover, hippocampal glutamate and thiobarbituric acid reactive substances (TBARS) increased while antioxidant defenses (GSH and GSH-Px) decreased. EPO in the tested doses significantly reduced the IH-induced spatial learning deficits in both MWM and EPM tests and dose-dependently antagonized the effects of IH on hippocampal glutamate, TBARS, GSH levels, and GSH-Px activity. Treatment with EPO in moderate doses that used for anemia, concurrently with IH exposure can antagonize IH-induced spatial learning deficits and protect hippocampal neurons from IH-induced lipid peroxidation and oxidative stress-induced damage in young rats, possibly through multiple mechanisms involving a potential antioxidative effect.

Neuroplasticity and the next wave of antidepressant strategies

Depression is a common chronic psychiatric disorder that is also often co-morbid with numerous neurological and immune diseases. Accumulating evidence indicates that disturbances of neuroplasticity occur with depression, including reductions of hippocampal neurogenesis and cortical synaptogenesis. Improper trophic support stemming from stressor-induced reductions of growth factors, most notably brain derived neurotrophic factor (BDNF), likely drives such aberrant neuroplasticity. We posit that psychological and immune stressors can interact upon a vulnerable genetic background to promote depression by disturbing BDNF and neuroplastic processes. Furthermore, the chronic and commonly relapsing nature of depression is suggested to stem from "faulty wiring" of emotional circuits driven by neuroplastic aberrations. The present review considers depression in such terms and attempts to integrate the available evidence indicating that the efficacy of current and "next wave" antidepressant treatments, whether used alone or in combination, is at least partially tied to their ability to modulate neuroplasticity. We particularly focus on the N-methyl-D-aspartate (NMDA) antagonist, ketamine, which already has well documented rapid antidepressant effects, and the trophic cytokine, erythropoietin (EPO), which we propose as a potential adjunctive antidepressant agent.

High performance collection of cerebrospinal fluid in rats: evaluation of erythropoietin penetration after osmotic opening of the blood-brain barrier

An important issue to be considered when studying a new drug for treatment of central nervous system (CNS) diseases is its ability to cross the blood-brain barrier (BBB) and distribute throughout the brain. As cerebrospinal fluid (CSF) has demonstrated to be an invaluable reservoir to study CNS availability of therapeutic proteins, we have developed an improved method for CSF sampling from the cisterna magna of rats. The technique enables the simple and rapid collection of adequate quantities (50-75 μl) of blood-free CSF, rendering a high percentage of animal survival (99%) without clinic or neurological consequences. Its success in avoiding blood contamination of CSF lays in the use of a mixture of lidocaine/ephinephrine topically injected in the rat's suboccipital area and neck. Another relevant feature of the methodology is its low cost, since the puncture device can be easily assembled with cheap and available materials and, more importantly, neither expensive stereotaxic equipment nor frame is required. The present method is demonstrated by studying the CSF pharmacokinetics of recombinant human erythropoietin (rhEPO), a well-studied therapeutic candidate for neurological diseases. Moreover, we applied this technique to evaluate a strategy of osmotic disruption of the BBB to achieve a faster delivery of rhEPO into the CNS.