Effects of erythropoietin on intracellular calcium concentration of rat primary cortical neurons

Unravelling the potential neuroprotective facets of erythropoietin for the treatment of Alzheimer's disease

During the last three decades, recombinant DNA technology has produced a wide range of hematopoietic and neurotrophic growth factors, including erythropoietin (EPO), which has emerged as a promising protein drug in the treatment of several diseases. Cumulative studies have recently indicated the neuroprotective role of EPO in preclinical models of acute and chronic neurodegenerative disorders, including Alzheimer's disease (AD). AD is one of the most prevalent neurodegenerative illnesses in the elderly, characterized by the accumulation of extracellular amyloid-ß (Aß) plaques and intracellular neurofibrillary tangles (NFTs), which serve as the disease's two hallmarks. Unfortunately, AD lacks a successful treatment strategy due to its multifaceted and complex pathology. Various clinical studies, both in vitro and in vivo, have been conducted to identify the various mechanisms by which erythropoietin exerts its neuroprotective effects. The results of clinical trials in patients with AD are also promising. Herein, it is summarized and reviews all such studies demonstrating erythropoietin's potential therapeutic benefits as a pleiotropic neuroprotective agent in the treatment of Alzheimer's disease.

Ramipril Alleviates Oxaliplatin-Induced Acute Pain Syndrome in Mice

Oxaliplatin is a key drug for colorectal cancer that causes OXP-induced peripheral neuropathy, a dose-limiting effect characterized by cold and tactile hyperesthesia. The relationship between the sensory nervous system and modulation of the renin-angiotensin system has been described, focusing on pain and neurodegeneration in several animal models. We assessed the effect of the RAS modulator, ramipril, an angiotensin converting-enzyme inhibitor in a mouse model of OXP-induced acute pain syndrome. OXP was administered in Swiss mice at a cumulative dose of 15 mg/kg (3 x 5 mg/kg/3 days, i.p.). RAM was administered i.p. every day from 24 h before the first OXP injection until the end of the experiments. We evaluated OIAS development and treatment effects by sensorimotor tests, intraepidermal nerve fiber and dorsal root ganglia-neuron immunohistochemical analyses, and sciatic nerve ultrastructural analysis. OXP-treated mice showed tactile allodynia and cold hypersensitivity, without motor impairment and evidence of nerve degeneration. RAM prevented cold sensitivity and improved recovery of normal tactile sensitivity in OXP-treated mice. Our finding that RAM alleviates OXP-induced pain is a step towards evaluating its therapeutic potential in patients receiving OXP treatment.

Neuroprotective effects of EpoL against oxidative stress induced by soluble oligomers of Aβ peptide

Erythropoietin is a glycoproteic hormone that regulates hematopoiesis by acting on its specific receptor (EpoR). The expression of EpoR in the central nervous system (CNS) suggests a role for this hormone in the brain. Recently, we developed a new Epo variant without hematopoietic activity called EpoL, which showed marked neuroprotective effects against oxidative stress in brain ischemia related models. In this study, we have evaluated the neuroprotective effects of EpoL against oxidative stress induced by chronic treatment with Aβ. Our results show that EpoL was neuroprotective against Aβ-induced toxicity by a mechanism that implicates EpoR, reduction in reactive oxygen species, and reduction in astrogliosis. Furthermore, EpoL treatment improved calcium handling and SV2 levels. Interestingly, the neuroprotective effect of EpoL against oxidative stress induced by chronic Aβ treatment was achieved at a concentration 10 times lower than that of Epo. In conclusion, EpoL, a new variant of Epo without hematopoietic activity, is of potential interest for the treatment of diseases related to oxidative stress in the CNS such as Alzheimer disease.

Neuroprotective Effects of neuroEPO Using an In Vitro Model of Stroke

Erythropoietin (EPO) is a glycoprotein initially identified as a hormone synthesized and secreted by the kidney that regulates erythropoiesis. EPO, and a group of its derivatives, are being evaluated as possible neuroprotective agents in cerebral ischemia. The objective of this study, using an in vitro model, was to determine how neuroEPO—which is a variant of EPO with a low sialic acid content—protects neurons from the toxic action of glutamate. Primary neuronal cultures were obtained from the forebrains of Wistar rat embryos after 17 days of gestation. Excitotoxicity was induced after nine days of in vitro culture by treatment with a medium containing 100 µM glutamate for 15 min. After this time, a new medium containing 100 ng of neuroEPO/mL was added. Morphological cell change was assessed by phase-contrast microscopy. Oxidative stress was analysed by measuring antioxidant and oxidant activity. After 24 h, the treatment with 100 ng of neuroEPO/mL showed a significant (p < 0.01) decrease in mortality, compared to cells treated with glutamate alone. neuroEPO treatment decreased mortality and tended to reproduce the morphological characteristics of the control. The oxidative stress induced by glutamate is reduced after neuroEPO treatment. These results confirm that neuroEPO has a protective effect against neuronal damage induced by excitotoxicity, improving antioxidant activity in the neuron, and protecting it from oxidative stress.

Erythropoietin: Endogenous Protection of Ischemic Brain

The human brain requires uninterrupted delivery of blood-borne oxygen and nutrients to sustain its function. Focal ischemia, particularly, ischemic stroke, and global ischemia imposed by cardiac arrest disrupt the brain's fuel supply. The resultant ATP depletion initiates a complex injury cascade encompassing intracellular Ca²⁺ overload, glutamate excitotoxicity, oxido-nitrosative stress, extracellular matrix degradation, and inflammation, culminating in neuronal and astroglial necrosis and apoptosis, neurocognitive deficits, and even death. Unfortunately, brain ischemia has proven refractory to pharmacological intervention. Many promising treatments afforded brain protection in animal models of focal and global ischemia, but failed to improve survival and neurocognitive recovery of stroke and cardiac arrest patients in randomized clinical trials. The culprits are the blood-brain barrier (BBB) that limits transferral of medications to the brain parenchyma, and the sheer complexity of the injury cascade, which presents a daunting array of targets unlikely to respond to monotherapies. Erythropoietin is a powerful neuroprotectant capable of interrupting multiple aspects of the brain injury cascade. Preclinical research demonstrates erythropoietin's ability to suppress glutamate excitotoxicity and intracellular Ca²⁺ overload, dampen oxidative stress and inflammation, interrupt the apoptotic cascade, and preserve BBB integrity. However, the erythropoietin dosages required to traverse the BBB and achieve therapeutically effective concentrations in the brain parenchyma impose untoward side effects. Recent discoveries that hypoxia induces erythropoietin production within the brain and that neurons, astroglia, and cerebrovascular endothelium harbor membrane erythropoietin receptors, raise the exciting prospect of harnessing endogenous erythropoietin to protect the brain from the ravages of ischemia-reperfusion.

Erythropoietin alleviates hepatic insulin resistance via PPARγ-dependent AKT activation

Erythropoietin (EPO) has beneficial effects on glucose metabolism and insulin resistance. However, the mechanism underlying these effects has not yet been elucidated. This study aimed to investigate how EPO affects hepatic glucose metabolism. Here, we report that EPO administration promoted phosphatidylinositol 3-kinase (PI3K)/AKT pathway activation in palmitic acid (PA)-treated HepG2 cells and in the liver of high-fat diet (HFD)-fed mice, whereas adenovirus-mediated silencing of the erythropoietin receptor (EPOR) blocked EPO-induced AKT signalling in HepG2 cells. Importantly, a peroxisome proliferator-activated receptor γ (PPARγ) antagonist and PPARγ small interfering RNA (siRNA) abrogated the EPO-induced increase in p-AKT in HepG2 cells. Lentiviral vector-mediated hepatic PPARγ silencing in HFD-fed C57BL/6 mice impaired EPO-mediated increases in glucose tolerance, insulin sensitivity and hepatic AKT activation. Furthermore, EPO activated the AMP-activated protein kinase (AMPK)/sirtuin 1 (SIRT1) signalling pathway, and AMPKα and SIRT1 knockdown each attenuated the EPO-induced PPARγ expression and deacetylation and PPARγ-dependent AKT activation in HepG2 cells. In summary, these findings suggest that PPARγ is involved in EPO/EPOR-induced AKT activation, and targeting the PPARγ/AKT pathway via EPO may have therapeutic implications for hepatic insulin resistance and type 2 diabetes.

Neuroprotective effect of erythropoietin against pressure ulcer in a mouse model of small fiber neuropathy

An increased risk of skin pressure ulcers (PUs) is common in patients with sensory neuropathies, including those caused by diabetes mellitus. Recombinant human erythropoietin (rhEPO) has been shown to protect the skin against PUs developed in animal models of long-term diabetes. The aim of this work was to determine whether rhEPO could prevent PU formation in a mouse model of drug-inducedSFN. Functional SFN was induced by systemic injection of resiniferatoxin (RTX, 50 µg/kg, i.p.). RhEPO (3000 UI/kg, i.p.) was given the day before RTX injection and then every other day. Seven days after RTX administration, PUs were induced by applying two magnetic plates on the dorsal skin. RTX-treated mice expressed thermal and mechanical hypoalgesia and showed calcitonin gene-related peptide (CGRP) and substance P (SP) depletion without nerve degeneration or vascular dysfunction. RTX mice developed significantly larger stage 2 PUs than Vehicle mice. RhEPO prevented thermal and mechanical hypoalgesia and neuropeptide depletion in small nerve fibers. RhEPO increased hematocrit and altered endothelium-dependent vasodilatation without any effect on PU formation in Vehicle mice. The characteristics of PUs in RTX mice treated with rhEPO and Vehicle mice were found similar. In conclusion, RTX appeared to increased PU development through depletion of CGRP and SP in small nerve fibers, whereas systemic rhEPO treatment had beneficial effect on peptidergic nerve fibers and restored skin protective capacities against ischemic pressure. Our findings support the evaluation of rhEPO and/or its non-hematopoietic analogs in preventing to prevent PUs in patients with SFN.

The PI3K/Akt and ERK1/2 signaling pathways mediate the erythropoietin-modulated calcium influx in kainic acid-induced epilepsy

Erythropoietin (EPO) suppresses epileptogenesis and limits the neuronal damage associated with recurrent seizures, but the neurocellular mechanism is unclear. Dysregulation of intracellular calcium homeostasis is a key pathogenic event leading to the progression of epileptic activity, suggesting that EPO may suppress seizures by stabilizing intracellular calcium. In this study, we examined the effects of EPO on voltage-gated Ca(2+) influx in cultured rat hippocampal neurons and population spike (PS) amplitude in kainic acid (KA)-induced rats and the mechanisms responsible. KA injection markedly increased EPO and EPO receptor expression and the amplitude of PS in the hippocampal CA3 region, evoked by perforant pathway stimulation. Intracerebroventricular injection of exogenous rat recombinant EPO reversed KA-induced PS amplitude in the hippocampal CA3 region. Similarly, rat recombinant EPO pretreatment attenuates the increased voltage-gated calcium current's (I(Ca)) amplitude and density induced by KA in cultured hippocampal neurons. In contrast, transient transfection of rat EPO small interfering RNS (siRNA) further enhanced I(Ca) amplitude and density in the presence of KA, whereas a scrambled control siRNA had no effect. Further, EPO activates the PI3K and ERK1/2 pathways in cultured hippocampal neurons, and the PI3K/Akt inhibitor LY294002 and ERK1/2 inhibitor U0126 both blocked, at least in part, the suppressive effect of exogenous EPO on KA-induced calcium currents. This study indicates that both endogenous and exogenous EPO decrease KA-sensitive calcium influx and concomitant hyperexcitability in hippocampal neurons. The results also demonstrate that the PI3K/Akt and ERK1/2 signaling pathways mediate the EPO-modulated calcium influx in KA-induced epilepsy.

Carbamylated erythropoietin ameliorates hypoxia-induced cognitive and behavioral defects with the generation of choline acetyltransferase-positive neurons

Carbamylated erythropoietin (CEPO) is attracting widespread interest because of its neuroprotective effects without influencing erythropoiesis. Here we show that CEPO, unlike EPO, does not stimulate erythropoiesis. Both CEPO and EPO inhibit the death/apoptosis of neurons in the hypoxic model of primary neurons and induce neuron proliferation and differentiation in hypoxic mice. Hypoxic mice show apparent memory deficits at 3 and 30 days after hypoxia. The administration of CEPO/EPO significantly improves cognitive and behavioral defects after hypoxic insults. Further investigation shows that CEPO/EPO induces neuron proliferation and differentiation and promotes the generation of choline acetyltransferase (ChAT)(+) neurons in hypoxic mice. Phosphorylated AKT was colabeled with ChAT(+) neurons and coexpressed in bromodeoxyuridine-positive cells, suggesting that the PI3K/AKT pathway may play a pivotal role in CEPO/EPO-cholinergic neuron generation. These results reveal that CEPO/EPO ameliorates hypoxia-induced cognitive and behavioral defects possibly through the generation of ChAT-positive neurons.