Elsevier

Brain and Development

Volume 25, Issue 7, October 2003, Pages 494-498
Brain and Development

Erythropoietin exerts neuroprotective effect in neonatal rat model of hypoxic–ischemic brain injury

https://doi.org/10.1016/S0387-7604(03)00039-1Get rights and content

Abstract

Hypoxic–ischemic encephalopathy seen in survivors of perinatal asphyxia is a frequently encountered and a major clinical problem for which there is currently no effective treatment. Hematopoietic neuroprotective agents, such as erythropoietin (EPO) may rescue neurons from cell death in this setting. EPO is a cytokine hormone that has neuroprotective effect in vitro and in vivo. In this study, we evaluated the effect of posthypoxic EPO administration in an animal model of neonatal hypoxic–ischemic injury. Our results show that a single intracerebroventricular injection of EPO immediately after hypoxic–ischemic insult in neonatal rat model of hypoxic-ischemia reduced the extent of hypoxic–ischemic brain damage. The mean infarct volume assessed 7 days after hypoxia was significantly smaller in EPO-treated group than in the control group. These findings suggest that EPO may provide benefit after hypoxic–ischemic events in the developing brain, a major contributor to static encephalopathy and cerebral palsy.

Introduction

Perinatal asphyxia is an important cause of neonatal mortality and sequelae such as cerebral palsy, mental retardation, learning disability, and epilepsy [1], [2]. Although there is an increased understanding of some of the mechanisms that may underlie neonatal hypoxic–ischemic brain injury, there is currently no clinically utilized treatment for this common disorder. It is clear that destructive processes such as glutamate and nitric oxide (NO) neurotoxicity, free radical formation, calcium accumulation, and immune/inflammatory activation continue to damage the brain for many hours after oxygenation and circulation have been restored [1], [2]. Pharmacological agents which restore one or more of these processes may provide neuroprotection in this condition.

Erythropoietin (EPO) is a cytokine hormone produced by the kidney and the fetal liver [3]. Stimulation of erythropoiesis was thought to be the sole physiological function of EPO, but a different function in the central nervous system (CNS) has been proposed. Recently, it has been shown that cultured neurons express EPO receptor (EPOR) and astrocytes produce EPO [4], [5]. Expression of EPO and EPOR have been shown in the CNS of mice, rats, and primates [4], [6], [7]. EPO and its receptor are also present in the developing human brain as early as 5 weeks postconception [8], [9]. In vivo, EPO protects neurons from global and focal cerebral ischemia in animal models [10], [11], [12]. The mechanisms of neuroprotective action of EPO in these animal models of cerebral ischemia may involve reducing the NO overproduction that mediates glutamate toxicity and formation of free radicals also implicated in the pathophysiology of hypoxic–ischemic brain injury [1], [13]. In vitro findings support these assumptions. EPO has been shown to protect primary cultured neurons from N-methyl-d-aspartate (NMDA) receptor-mediated glutamate toxicity [5]. The presence of EPO in neuron cultures rescues the neurons from NO-induced death [11]. Because of these described effects, we hypothesized EPO would be neuroprotective in a well-characterized model of hypoxic–ischemic brain injury in neonatal rat.

Section snippets

Animals

This study was performed in accordance with the guidelines provided by the Experimental Animal Laboratory and approved by the Animal Care and Use Committee of the Dokuz Eylul University, School of Medicine. A modification of Levine preparation was used as a model for perinatal hypoxic–ischemic brain injury [14]. Dated, pregnant Wistar rats were housed in individual cages under standard conditions. Offspring, delivered vaginally, were reared with their dams until time of initial experimentation

Results

In the present study, EPO treatment diminished hypoxic–ischemic brain injury significantly as assessed by infarction volume determinations 1 week following the insult. Severe brain damage (infarction) was observed less frequently in rat pups treated with EPO (2/9) as compared with control group (5/9, 22.2, and 55.6%, respectively). However, this difference did not reach statistically significant level (P>0.05). Besides, morphometric analysis to determine any quantitative differences in the

Discussion

The present data indicate that EPO is an effective neuroprotective agent in this particular animal model when given after the end of hypoxic exposure. This post hoc neuroprotection has possible human therapeutic implications. Since most treatment of human perinatal asphyxia will have to be delivered after the insult, we investigated the neuroprotective potency of post hoc EPO in rat pups with hypoxic–ischemic brain injury.

The exact mechanisms responsible for the in vivo neuroprotective effects

Acknowledgements

This work was supported by a grant from Dokuz Eylül University Foundation.

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