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