Erythropoietin Protects Dopaminergic Neurons and Improves Neurobehavioral Outcomes in Juvenile Rats after Neonatal Hypoxia-Ischemia

Abstract

Brain injury as a result of hypoxia-ischemia remains a common cause of morbidity and mortality in neonates. No effective therapy is currently available. The hematopoietic cytokine erythropoietin (Epo) provides neuroprotection in many adult models of brain injury and is currently being investigated as a therapeutic agent for human stroke and spinal cord injury. We tested the hypothesis that recombinant Epo (rEpo) would improve neurobehavioral outcomes after neonatal hypoxic-ischemic brain injury. Postnatal day 7 rats underwent right common carotid artery occlusion followed by a 90-min exposure to 8% oxygen. Rats were subsequently treated with rEpo or placebo. Sensory neglect and apomorphine-induced rotation were measured at P27 and P28. Rats were killed at P30, blood was drawn, and the brains were perfusion-fixed for histology and immunohistochemistry. No differences in gross brain injury between rEpo and placebotreated rats were found. Neonatal rEpo treatment protected dopamine neurons as indicated by the preservation of tyrosine hydroxylase-positive cells in the substantia nigra pars compacta and ventral tegmental area. rEpo treatment also improved functional outcomes by reducing sensory neglect and preventing the rotational asymmetry seen in control animals. No differences in hematocrit, white blood cell counts, neutrophil counts, or platelet counts were measured. We observed that rEpo treatment protected mesencephalic dopamine neurons and reduced the degree of behavioral asymmetries at 4 wk of life. On the basis of these findings, we conclude that further studies investigating the safety and efficacy of high-dose rEpo as a neuroprotective strategy are indicated in neonatal models of hypoxic-ischemic brain injury. Abbreviations ADHD, attention-deficit/hyperactivity disorder DA, dopamine Epo, erythropoietin EpoR, erythropoietin receptor HI, hypoxia-ischemia P, postnatal day rEpo, recombinant Epo SNpc, substantia nigra pars compacta TH, tyrosine hydroxylase VTA, ventral tegmental area Perinatal exposure to hypoxia-ischemia (HI) produces brain injury that is a significant source of morbidity and mortality for preterm and term neonates. Neonatal HI exposure initiates a multifactorial cascade that can persist for days, producing injury to multiple brain regions with corresponding motor, behavioral, and cognitive impairments. Although there are currently no effective therapies to ameliorate hypoxic-ischemic brain injury, several useful rodent models of neonatal brain injury are available. Using 7-d-old (P7) rat pups, which are comparable to near-term humans in brain maturity (1), the technique entails unilateral ligation of the common carotid artery and subsequent exposure of the animals to hypoxia (Rice-Vannucci model) (2). This procedure produces permanent unilateral brain injury in multiple regions, with specific impact on the basal ganglia including decreases in striatal dopamine (DA) receptors and increases in striatal DA transporters (3,4). Disruption of dopaminergic neurotransmission is suspect for several de...

High-Dose Erythropoietin and Hypothermia for Hypoxic-Ischemic Encephalopathy: A Phase II Trial

“…[10][11][12][13][14][15] In a phase I trial of combined Epo treatment with hypothermia, we found that Epo (1000 U/kg given intravenously) provided the optimal plasma Epo levels consistent with animal studies of neuroprotection. 16 Although the study was not designed to evaluate efficacy, patients who received multiple high doses of Epo exhibited a lower rate of death or moderate/ severe disability at 22 months (4.5%) 17 than had been expected based on studies of infants with similar entry criteria who received hypothermia alone (44%-51%).…”

Erythropoietin and Oxidative Stress

“…In cells that involve the brain or the retina, EPO can prevent injury from hypoxic ischemia , Chong, et al, 2002b, Liu, et al, 2006, Meloni, et al, 2006, Wei, et al, 2006, Yu, et al, 2005, excitotoxicity (Montero, et al, 2007, Yamasaki, et al, 2005, infection (Kaiser, et al, 2006), free radical exposure , Chong, et al., 2003e, Yamasaki, et al, 2005, staurosporine (Pregi, et al, 2006), and dopaminergic cell injury (Demers, et al, 2005, McLeod, et al, 2006. In addition, administration of EPO also represents a viable option for the prevention of retinal cell injury during glaucoma (Tsai, et al, 2007).…”

“…Enhanced survival by EPO also extends to afford protection of the neurovascular unit during cerebral vascular disease (Demers, et al, 2005, Dzietko, et al, 2004, Wei, et al, 2006. In addition, EPO can protect sensitive hippocampal neurons from both focal and global ischemic brain injury (Keogh, et al, 2007, Wei, et al, 2006, Yu, et al, 2005, Zhang, et al, 2006.…”

“…EPO appears to be both necessary and sufficient to protect neurons from Aβ toxicity. Application of a blocking antibody of EPO, which can bind to EPO and block its biological activities in cells (Koshimura, et al, 1999), can otherwise negate the protective effects of EPO to increase neuronal hippocampal cell survival and prevent apoptotic injury during Aβ exposure (Chong, et al, 2005d).Enhanced survival by EPO also extends to afford protection of the neurovascular unit during cerebral vascular disease (Demers, et al, 2005, Dzietko, et al, 2004, Wei, et al, 2006. In addition, EPO can protect sensitive hippocampal neurons from both focal and global ischemic brain injury (Keogh, et al, 2007, Wei, et al, 2006, Yu, et al, 2005, Zhang, et al, 2006.…”

AAV9-mediated erythropoietin gene delivery into the brain protects nigral dopaminergic neurons in a rat model of Parkinson's disease

“…Accumulating evidence has shown that EPO protein and EPO receptors (EPORs) exist in CNS neurons. 1,2 EPO has been found to protect dopaminergic (DA) neurons from experimental insults and druginduced degeneration, 1,[3][4][5][6] suggesting its therapeutic potential for Parkinson's disease (PD). In our previous study with EPO protein infusions, although intrastriatal delivery was protective, systemic administration of EPO did not protect DA neurons from 6-hydroxydopamine (6-OHDA) toxicity in a rat model of PD.…”