New horizons for newborn brain protection: enhancing endogenous neuroprotection
Institute for Women's Health, University College London, London, UK
The Hatter Cardiovascular Institute, Institute of Cardiovascular Science, NIHR University College London Hospitals Biomedical Research Centre, University College London Hospital & Medical School, London, UK
Abstract
Intrapartum-related events are the third leading cause of childhood mortality worldwide and result in one million neurodisabled survivors each year. Infants exposed to a perinatal insult typically present with neonatal encephalopathy (NE). The contribution of pure hypoxia-ischaemia (HI) to NE has been debated; over the last decade, the sensitising effect of inflammation in the aetiology of NE and neurodisability is recognised. Therapeutic hypothermia is standard care for NE in high-income countries; however, its benefit in encephalopathic babies with sepsis or in those born following chorioamnionitis is unclear. It is now recognised that the phases of brain injury extend into a tertiary phase, which lasts for weeks to years after the initial insult and opens up new possibilities for therapy.
There has been a recent focus on understanding endogenous neuroprotection and how to boost it or to supplement its effectors therapeutically once damage to the brain has occurred as in NE. In this review, we focus on strategies that can augment the body's own endogenous neuroprotection. We discuss in particular remote ischaemic postconditioning whereby endogenous brain tolerance can be activated through hypoxia/reperfusion stimuli started immediately after the index hypoxic-ischaemic insult. Therapeutic hypothermia, melatonin, erythropoietin and cannabinoids are examples of ways we can supplement the endogenous response to HI to obtain its full neuroprotective potential. Achieving the correct balance of interventions at the correct time in relation to the nature and stage of injury will be a significant challenge in the next decade.
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Keywords: Neuroprotection, Post Conditioning, Neonatal encephalopathy, Birth asphyxia, Melatonin
Article notes
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Received 2014 Oct 23; Revised 2015 Jan 21; Accepted 2015 Jan 28; Issue date 2015 Nov.
Background
Intrapartum-related insults at full term such as hypoxia-ischaemia (HI) are the third leading cause of global child deaths.1 Each year, over 0.7 million affected newborns die and 1.15 million develop acute disordered brain function known as neonatal encephalopathy (NE).2 NE is the second commonest preventable cause of childhood neurodisability worldwide3 with profound psychosocial and economic consequences for families and society. Protecting the newborn brain from injury around the time of birth is a global health priority.4 5
Term newborn brain injury: causes, pathogenesis and management
NE is a descriptive term for neurological dysfunction in the newborn infant, manifested by symptoms including difficulty with initiating and maintaining respiration, depression of tone and reflexes, subnormal level of consciousness, poor feeding and seizures.6 NE has a complex and multifactorial aetiology. For over two decades, perinatal neuroprotection research has focused on pure hypoxic-ischaemic brain injury; however, accumulating preclinical7 8 and clinical9 evidences suggest the critical importance of the sensitising effect of inflammation.
The clinical signs of NE progress after a latent period of hours to days. This timing of the evolution of clinical signs is thought to reflect brain energy levels and the cascade of neurochemical processes responsible for brain injury. These are summarised in figure 1 and described in more detail below.
Acute HI
During the acute hypoxic-ischaemic insult, some cells undergo primary cell death, the magnitude of which will depend on the severity and duration of HI. In the absence of substrates (oxygen, glucose), the neuron's supply of high-energy metabolites such as ATP falls below a critical threshold. The Na+/K+ ATP-dependent pump begins to fail, neuronal depolarisation occurs and the synaptic cleft floods with glutamate, which activates the N-methyl-D-aspartate (NMDA) receptor. Toxic cytoplasmic Ca2+ concentrations arise through several mechanisms, including overactivation of glutamate receptors (NMDA, a-amino-3-hydroxy-5-methyl-4-isoxazolepropioinic acid (AMPA)), other channels and transporters, or through release from internal stores through physical damage to mitochondria and endoplasmic reticulum10; the increased Ca2+ triggers many downstream neurotoxic cascades. As well as generating an osmotic gradient that leads to oedema and lysis of cells, Ca2+ activates nitric oxide synthase, which in turn generates high levels of the toxic reactive oxygen species nitric oxide (NO•). At high concentrations, NO• reacts with superoxide (O•−) to produce peroxynitrite (ONOO−), which damages mitochondria via peroxidation and nitrosylation of membrane lipids. Consequently, mitochondrial dysfunction and membrane depolarisation develop with further release of O•− and decline in endogenous anti-oxidants such as glutathione. Ca2+ also triggers the activation of cytosolic phospholipases, which increase eicosanoid release leading to inflammation.
Latent phase
After reperfusion, the initial hypoxia-induced cytotoxic oedema and accumulation of excitatory amino acids partially resolve in 30–60 min, with apparent recovery of cerebral oxidative metabolism. It is thought that the neurotoxic cascade is largely inhibited during the latent phase, when there is endogenous inhibition of oxidative metabolism and increased tissue oxygenation.11 The ‘therapeutic window’ is believed to span this period. Much of our understanding of cerebral metabolism following HI has evolved through magnetic resonance spectroscopy (MRS) through which we have shown that latent phase duration is inversely related to insult severity.12 In the early recovery period (2–8 h after HI), MRS may provide an early marker of injury severity; an overshoot of phosphocreatine (PCr; donates phosphate to ADP to generate ATP) is associated with favourable outcome13 and raised cerebral lactate or inorganic phosphate (Pi) at 2 h is indicative of adverse outcome.14
Secondary phase
Both preclinical15 and baby studies16 using phosphorus-31 (31P) MRS have demonstrated the deterioration in cerebral oxidative metabolism 6–24 h after HI (termed secondary energy failure) (figure 1). Despite adequate oxygenation and circulation, PCr and nucleotide triphosphate (NTP—mainly ATP) fell and Pi increased. Low cerebral PCr/Pi, NTP/total mobile phosphates,16 17 increased brain lactate18 and an alkaline intracellular pH (pHi)19 in the first few days after birth were associated with neurodevelopmental impairment and increased mortality.
This secondary phase is marked by the onset of seizures, secondary cytotoxic oedema, accumulation of cytokines and mitochondrial failure (figure 1). Mitochondrial failure is a key step leading to delayed cell death. The degree of energy failure influences the type of neuronal death during early and delayed stages,20 21 and the degree of trophic support influences the angiogenesis and neurogenesis during the recovery phase after HI.
Tertiary phase
There is evidence that active pathological processes occur for weeks, months and years after a hypoxic-ischaemic insult; this has been termed tertiary brain injury.22 Indeed, a persisting cerebral lactic alkalosis has been observed using MRS over the first year after birth in those infants with adverse neurodevelopmental outcomes.18 Mechanisms of this persisting damage involve gliosis, persistent inflammatory receptor activation and epigenetic changes.
Endogenous neuroprotection
Brain damage and lasting functional impairment after NE are the results of a balance between injurious mechanisms (cell death, persistent inflammation) and endogenous protection (acute response, recovery, repair). Optimal therapy will demand exploitation of multiple pathways that prevent brain cell death and promote repair.23 Much neonatal neuroprotection research has emphasised immediate cytotoxic mechanisms; however, the brain also mounts a potent, though only partially successful, defensive response against many of the deleterious secondary mechanisms of injury.24 Therapies to boost the endogenous neuroprotective response are particularly attractive; they are less likely to disrupt physiological neurotransmission, so may offer more effective treatments with fewer unwanted side effects.
We discuss five interventions whose actions include the augmentation of the endogenous neuroprotective response. Birth asphyxiated babies have an endogenous cooling response;25 therapeutic hypothermia is already the standard clinical care for babies with moderate or severe NE. Remote ischaemic postconditioning (RIPostC) is a novel therapy, which has enormous promise as an intervention that harnesses the body's neuroprotective ‘conditioning’ mechanisms. Melatonin is known for its role in entraining the circadian rhythm;26 however, endogenous levels of melatonin increase after HI and exogenously administered melatonin confers brain protection.27 Endogenous endocannabinoids and erythropoietin (Epo), likewise increased following HI, also have a role in neuroprotection. There is expanding evidence to show that Epo confers protection that extends to the tertiary phase of injury, promoting repair.
Therapeutic hypothermia
Background
For over 50 years, it has been known that babies with birth depression have an endogenous cooling response.25 We observed this phenomenon in our pilot cooling study in a low-resource setting.28 After two decades of laboratory studies,29 30 clinical trials31 and endorsement from regulatory bodies (http://www.nice.org.uk/guidance/ipg347), therapeutic hypothermia is now standard clinical care for moderate-to-severe NE in the UK and high-income countries.5
Mechanism
Pathways underpinning hypothermic neuroprotection are covered in detail in recent reviews by Wassink et al32 and Edwards et al33 In brief, these pathways include a decrease in metabolic rate with parallel decreases in O2 consumption and CO2 production, reduced loss of high-energy phosphates during HI and during secondary cerebral energy failure, reduced excitotoxicity, reduced reactive oxygen species production, protein synthesis preservation, decreased oedema, modulation of the inflammatory cascade and a change in pro-apoptotic and anti-apoptotic signalling.34–36
Clinical application
In intensive care settings, clinical trials have included whole body cooling with core temperature reduced to 33.5°C for 72 h37 and selective head cooling with core temperatures reduced to 34.5°C.38 Some studies suggest less severe brain MRI findings in babies who have had whole body cooling versus selective head cooling; other studies suggest equal benefit from both cooling methods.39 40
There is clear evidence that therapeutic hypothermia as a therapy for moderate-to-severe NE reduces adverse outcome (mortality and neurodevelopmental disability) at 18 months of age (typical relative risk 0.75, 95% CI 0.68 to 0.83)31; this improvement persists into childhood41 and there is widespread benefit to society, individuals and the economy (UK >£125 million benefit).42 However, therapeutic hypothermia offers only an 11% reduction in risk of death or disability, from 58% to 47%.4 Moreover, effective cooling treatment requires a high level of neonatal intensive care support, which is not available in many lower resource settings. There is an urgent need to develop additional simple, safe and effective neuroprotective treatment strategies.
Caveats of hypothermia
Recently, therapeutic hypothermia has been shown to be ineffective and even harmful in the presence of infection/inflammation in adult clinical studies.43 In a preclinical neonatal rodent study, cooling was not neuroprotective in inflammation-sensitised HI.44 In a small prospective study of placental histology relative to MRI in babies, therapeutic hypothermia was less protective in babies whose placenta showed chorioamnionitis.45 We reported an unexpectedly high mortality in NE cases cooled to 33.5°C in a small pilot therapeutic hypothermia feasibility (not efficacy) study in sub-Saharan Africa28; this may have been related in part to higher rates of intercurrent infection/inflammation in affected infants.
Brain injury and hypothermia both alter immune responsiveness. Following HI, a bidirectional communication between the injured brain and the peripheral innate and adaptive immune system regulates the progression of both ischaemic pathology and tissue repair (for an in-depth review of the dualistic role of inflammation, see An et al,46). HI acutely triggers the release of cytokines and chemokines from neurons, astrocytes and microglia. These signals induce microglial activation, trigger further release of pro-inflammatory cytokines such as tumour necrosis factor α and interleukin 6 (IL-6) and recruit white blood cells (WBCs). The infiltration of macrophages is both detrimental in ischaemic injury and protective against haemorrhage. Similarly, while early elevation of circulating neutrophils after HI may augment brain injury,47 prolonged immunosuppression and T cell lymphopenia is associated with immune paralysis and worse outcome in animal models of stroke,48 traumatic brain injury49 and human adult stroke.50 Thus, inflammation following HI has both helpful and harmful effects, which may affect the response to neuroprotective treatments.
A key mechanism of action of therapeutic hypothermia is the inhibition of the pro-inflammatory cascade51; and hypothermia may therefore inhibit both protective and damaging responses.52 A recent study investigated the effect of therapeutic hypothermia on modulating the peripheral immune response over the first 72 h after birth in 65 infants with NE.53 Hypothermia lowered absolute neutrophil and lymphocyte counts compared with normothermic infants. In the hypothermic group, those patients who did not have a recovery of their WBC counts after rewarming had poor outcomes, whereas those who had better recovery of WBC counts had a better long-term outcome.53 This may indicate immune paralysis in the adverse outcome group. It is possible, therefore, that hypothermic immune suppression has a negative influence on infants with infection-sensitised brain injury. Several adult studies of hypothermia have found higher infection rates in cooled groups.54 This has not been shown in neonatal studies of hypothermia treatment; however, blood culture-positive neonatal sepsis rates are low (5–12%) and much larger trials would be needed to detect any increase. A better understanding is crucial for achieving optimal neuroprotection in NE.
Remote ischaemic postconditioning
Background
‘Conditioning’ describes an adaptive process of endogenous protection that occurs in all mammalian species, in which small, sublethal doses of a harmful agent protect an organism against a lethal dose of the same agent. Conditioning paradigms include toxins, substrate deprivation and infection/inflammation.24 One conditioning agent may also confer protection against a different insult.55 56
Ischaemic preconditioning describes brief non-lethal episodes of ischaemia that confer protection against subsequent cell-lethal ischaemia, as has been observed in clinical studies of transient ischaemic attack57 58 and angina.59 It is likely that contractions during labour also represent a preconditioning stimulus. Ischaemic postconditioning evolved from this concept60 61 and is defined as intermittent sublethal interruptions to blood flow after the cell-lethal ischaemia.62 Postconditioning is effective if performed on a non-vital organ, such as a limb, remote to the affected organ63—called remote ischaemic postconditioning (RIPostC). Use of a remote limb makes RIPostC a feasible clinical treatment strategy for NE.
Mechanism
RIPostC has been shown to protect the adult and neonatal brain in rodent models of stroke. The protective mechanisms of RIPostC are incompletely understood, but are thought to involve three intimately inter-related pathways initiated by the release of a number of endogenous autocoids (including adenosine, bradykinin, opioids) from the ischaemic skeletal muscle. These pathways are (i) the neuronal pathway; (ii) the humoral pathway and (iii) the systemic response (figure 2).64 Animal models have shown that interruption of any one of these pathways abrogates the neuroprotection conferred by RIPostC.
In brief, the neuronal pathway describes the autocoid-mediated stimulation of local afferent nerves that effect remote protection via efferent nerves, including the autonomic nervous system.65 66 Both limb ischaemia and efferent nerve activation trigger the release of a number of bloodborne protective factors that are transported in the circulation and mediate protection in the brain—the humoral pathway.67 68 The systemic pathway describes the impact of RIPostC throughout the body, including immune effects (such as reduced neutrophil activation) and reduced expression of apoptotic and inflammatory genes.69
Following remote ischaemic stimulus, these three pathways converge in the brain to increase cerebral blood flow, attenuate neuroinflammation and at a cellular level to activate pro-survival signalling cascades, including genetic and epigenetic modulation. Ultimately these processes protect mitochondrial integrity, reduce energy demands, increase cell survival and promote repair mechanisms70–72 (figure 2).
In neonatal73 and adult74 small animal models, RIPostC reduces infarct size in focal and global ischaemia. Moreover, these studies have shown an extended therapeutic window for the application of RIPostC following hypoxic-ischaemic brain injury63 and application of RIPostC up to 24 h after insult was associated with improved long-term motor outcomes.75
In our large animal (piglet) model of perinatal asphyxia, we found that four 10 min cycles of ischaemia/reperfusion of both lower limbs, starting immediately following resuscitation, provided protection in the white matter,76 with decreased cell death and inflammation. MRS data in our study showed that RIPostC mitigated the rise in white matter lactate/N-acetyl aspartate and increased whole-brain ATP, findings that predict better long-term outcome in clinical studies in human newborns.16 77
Hurdles to clear before clinical translation
RIPostC has been explored in clinical settings for conditions, including cardiac disease and stroke.78 A meta-analysis of 23 randomised clinical trials of limb conditioning in adults undergoing cardiac surgery found reduced incidence of myocardial infarction in the limb-conditioned groups, regardless of timing. A randomised control trial of RIPostC for children undergoing cardiac bypass also showed cardioprotection.79 In adult stroke, a recent study of 443 adults who underwent prehospital remote ischaemic perconditioning as an adjunct to thrombolysis for acute ischaemic stroke found a reduced risk of tissue infarction in the treatment group.80 In all studies, remote ischaemic conditioning was safe and well tolerated. However, another meta-analysis of remote ischaemic preconditioning in open cardiac surgery showed the cardioprotective effect was most marked in studies without full blinding, emphasising the need for further double-blind randomised studies.81
Clinical trials are needed to establish whether RIPostC is safe and protective in NE. It will be important to address the safety and reproducibility of inducing intermittent limb ischaemia, with and without concomitant cooling therapy. There remain difficult hurdles such as the dose–response of RIPostC (how many cycles and for how long achieves best protection and avoids any detrimental effects), the therapeutic time windows and the precise protective mechanisms.82
Melatonin
Background
Melatonin is a naturally occurring neuroendocrine molecule secreted in response to environmental light–dark cycles. Melatonin is both lipophilic and hydrophilic. It easily crosses biological membranes and acts via receptor-dependent and receptor-independent processes to modulate cell signalling and gene expression.83 84 While melatonin's key and probably best-known role is to regulate the body's multifarious circadian rhythms,26 it influences numerous physiological functions, including growth and development, reproduction and the immune response.
Endogenous melatonin is integral to normal neurodevelopment and protects the developing brain from injury.85–90 Maternal melatonin levels are raised in pregnancy91 92 and melatonin readily crosses the placenta and blood–brain barrier.93 94 Healthy term-born neonates have relatively low pineal melatonin production, which lacks diurnal variation for the first weeks of life.95 96 However, we observed a 6- to 15-fold increase in plasma melatonin following HI in our experimental model of perinatal HI27 and a similar response has also been observed in human stroke and in critically ill children,97 98 implying a role for melatonin in an endogenous protective response.
Mechanism
Acting via specific cell membrane and nuclear receptors, melatonin achieves powerful neuroprotective effect via anti-oxidant, anti-apoptotic and anti-inflammatory processes85–88 and by promoting neuronal and glial development.99–101 Developing brain tissue is highly susceptible to free radical damage102–104 and the potent free radical-scavenging properties of melatonin and its metabolites provide a fundamental neuroprotective mechanism.105–109 Additional indirect anti-oxidant effects of melatonin include upregulation of anti-oxidant enzymes94 and crucially the preservation of mitochondrial integrity.106 107 109 Numerous rodent and large animal studies have shown that melatonin reduces oxidative damage to cerebral lipids104 110–116 and notably ameliorates secondary cerebral energy failure27 and apoptosis.116–121
Further, melatonin's wide-ranging immune-modulating properties122 123 facilitate neuroprotection following HI.27 118 121 124 Importantly, melatonin is protective in lipopolysaccharide-sensitised HI.125 Given the evidence outlined above indicating therapeutic cooling may lack efficacy following infection-sensitised HI,44 45 melatonin may prove an effective immune-modulating neuroprotectant in such cases.
Clinical use and safety
Melatonin is an extremely safe neurotherapeutic. No study of antenatal or postnatal melatonin treatment has shown any serious side effects,126 nor were any serious adverse events identified in 3000 children taking melatonin for up to 6 years.127 In small neonatal clinical studies, melatonin improved outcomes in sepsis,128 prematurity129 and perinatal asphyxia.130 In our large animal model of perinatal asphyxia, we showed neuroprotective efficacy conferred by melatonin-augmented cooling when compared with cooling alone.27 In our study, melatonin 30 mg/kg (which is 100 times the dose administered for disordered sleep in children) administered to newborn piglets immediately after HI over 6 h did not alter any physiological variable.27 A study of 30 term infants with NE randomised to cooling alone or cooling plus oral melatonin (five daily doses of 10 mg/kg per day made up from melatonin tablets crushed and dissolved in distilled water) suggested improved neurological outcome at 6 months in the melatonin group.131 However, four patients in the hypothermia group had severe encephalopathy, whereas only two in the hypothermia/melatonin group had severe encephalopathy at birth; this may lend bias to the results in this small study. Further, the blood levels of melatonin on day 5 in the cooling group were 32.1+3.5 pg/mL, while in the melatonin/cooling group were 42.7+5.1 pg/mL; preclinical data suggest that significantly higher pharmacological levels of melatonin are needed for optimal protection and work is currently underway to determine the lowest effective dose of melatonin for neuroprotection. Nevertheless, phase I and II clinical studies of melatonin-augmented hypothermia for NE are keenly awaited. In 2011, melatonin was rated by an international group of leading perinatal neuroscientists as the most promising of 13 neuroprotectants nearing clinical translation.132
Cannabinoids
Background
Endocannabinoids are emerging as a potential neurotherapeutic for NE. The endocannabinoid system is a neuromodulatory system that participates in a wide range of physiological processes in mammals.133 This endogenous system consists of target receptors, endogenous ligands and the enzymes responsible for endocannabinoid biosynthesis, transport and degradation.134 135 Accumulating evidence indicates that endocannabinoids, like melatonin, are inherently involved in the normal development of the fetal central nervous system and its functions.136–141 Moreover, the levels of endocannabinoids, which are normally found at low concentrations in the brain, dramatically increase upon neuronal injury,136 142–144 suggesting that endocannabinoids provide an endogenous neuroprotective system.145
Mechanism
Endocannabinoids modulate the intensity and extension of neurotoxic processes146–150 and the inflammatory response151–155 and promote cell survival.156–161 Synthetic cannabinoid agonists have shown significant grey and white matter protection in animal studies of brain injury.162–167 In large animal models of perinatal asphyxia, cannabinoid WIN55212-2 administered immediately after HI protected mitochondrial injury and prevented apoptosis.162 163 Cannabidiol given immediately after HI reduced neuronal injury, cerebral haemodynamic impairment, brain oedema and seizures and restored motor and behavioural performance in the 72 h after HI.166 167 In rodent models of stroke, prolonged 7-day administration of cannabinoid WIN55212-2 started immediately after injury enhanced long-term neuronal and oligodendrocyte recovery and regeneration.164 165 Cannabinoids, however, achieve neuroprotection in part through hypothermia. For example, the cannabinoid agonist HU10 induced hypothermia in an experimental stroke model and was protective, but this benefit was completely abolished by rewarming animals to the temperature of the control group.168
Clinical use and safety
The main established clinical uses of cannabinoids are for chronic pain, for muscle spasms and as an appetite stimulant.169 170 Additionally, the synthetic cannabinoid dexanabinol is in a number of phase I clinical trials for primary and secondary solid tumours (http://www.clinicaltrials.gov). A previous phase III randomised controlled trial of 861 adult patients given dexanabinol as a neuroprotectant following traumatic brain injury showed that dexanabinol was safe but not efficacious.171 However, we did not identify any reported clinical studies of cannabinoids for stroke or perinatal brain injury, or studies where cannabinoids were combined with therapeutic hypothermia.
Reported side effects of cannabinoids have all been mild and transient, including sedation, anxiety, dizziness and nausea.169 170 Maas et al171 found no toxic cardiac, hepatic or renal effects in their study of dexanabinol for traumatic brain injury. However, cannabinoids have been shown to accumulate selectively in the brain and their clearance is relatively slow,169 thus preclinical pharmacokinetic studies would be imperative prior to clinical trials of cannabinoids for NE.
Erythropoietin (Epo)
Background
Epo is a pleiotropic cytokine with multiple roles in addition to that of a haemopoietic growth factor. As with melatonin and cannabinoids, the role of Epo in normal brain development and neuroprotection is becoming clear (for review see Rangarajan and Juul172). Epo receptors (EpoR) are located throughout the central nervous system on neurons,173 glia174 and endothelial cells;175 they participate in proliferation and differentiation of these cells176 and are upregulated following brain injury. In a similar way to the exaggerated hypoxic-ischaemic injury observed when the endogenous melatonin response is abolished in pinealectomised animals,177 the absence of endogenous Epo and EpoR augments ischaemic damage and impairs neuronal survival.178
Epo is a key component of the body's endogenous ‘conditioning’ response to injurious paradigms, including ischaemia. Hypoxic preconditioning occurs when Epo is expressed after brief hypoxia, reducing damage following a second insult.179 This effect can be replicated by treatment with exogenous Epo prior to HI.180 Preclinical and clinical studies have harnessed the conditioning and regenerative potential of Epo, which is now emerging as a promising neuroprotectant that promotes repair into the tertiary phase of NE.
Mechanism
Hypoxia and pro-inflammatory cytokines activate hypoxia-inducible factor to induce expression of Epo and EpoR. Following brain injury, Epo is anti-apoptotic,181 anti-oxidative182 and anti-inflammatory.183 However, a key role for Epo is repair; Epo binding stimulates neurogenesis, oligodendrogenesis and angiogenesis, all of which are upregulated following brain injury.184 185 Additionally, Epo increases neuronal and glial migration around the injured area via the secretion of matrix metalloproteinases.186 187 In animal studies of term and preterm perinatal HI, Epo treatment results in reduced brain volume loss and improved cognitive and motor outcomes188–190 and augments the neuroprotection conferred by cooling alone.191
Epo in clinical trials
Numerous animal studies of Epo for brain injuries, including stroke and perinatal HI, have shown that high-dose recombinant Epo and Epo-mimetics are safe and cross the blood–brain barrier, resulting in neuroprotection.192 Epo pharmacokinetics has been studied using doses from 250 U/kg to 2500 U/kg.193 Phase I/II studies in human preterm193 and term194 195 neonates, performed to establish feasibility, safety and appropriate dosing, have not identified any of the common side effects observed in adults (polycythaemia, thrombosis, hypertension). Epo-mimetics have been developed to improve neuroprotection without stimulating erythropoesis.196
Follow-up of 22 infants enrolled in a phase I clinical trial of Epo-augmented hypothermia (no comparison group) for treatment of NE found no deaths and only one infant with moderate–severe disability at age 2 years.197 A number of larger phase II/III studies of Epo safety and efficacy in neonatal populations are underway (reviewed in Rangarajan and Juul172). The optimal dose and regimen for human Epo neuroprotection is still not known; however, key points have been learnt from rodent studies such as the requirement for multiple injections and late 1 week dosing for maximal protection198; a study of 45 term infants comparing single-dose Epo alone on day 0 with 72 h therapeutic hypothermia alone for treatment of NE found superior protection in the hypothermia group.199 Further studies are needed to fully understand the specific role of Epo in the tertiary phase of brain injury and repair. Thus, the combined safety and efficacy of Epo administered alongside established and novel treatments that ameliorate secondary energy failure (cooling, melatonin) must be determined as key next steps in clinical translation.
Conclusion
Perinatal HI leading to NE sets up a cascade of processes that lead to an evolving brain injury, which includes a latent phase, secondary energy failure phase and tertiary brain injury phase. Coexisting infection/inflammation may exacerbate this injury. The brain mounts a potent, though only partially successful, defensive response against many of the deleterious secondary mechanisms of injury. Therapies that augment the endogenous neuroprotective response such as RIPostC are attractive but need further study to define optimal protocols. Part of the endogenous neuroprotective response is lowering of the core body temperature as well as increased melatonin, Epo and cannabinoid levels. Augmenting these endogenous responses have shown protection in preclinical studies and therapeutic hypothermia is now a routine therapy for moderate-to-severe NE. Clinical trials are now ongoing for Epo-augmented hypothermia. We anticipate that future newborn brain protection will comprise a tailored combination of therapies; the challenge will be to ensure the timing and dose of each neuroprotectant are appropriate for the phase of injury to ensure optimal and lasting protection.
Footnotes
Footnote Group
References
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References
- 1.Liu L, Oza S, Hogan D, et al. Global, regional, and national causes of child mortality in 2000-13, with projections to inform post-2015 priorities: an updated systematic analysis. Lancet 2015;385:430–40. 10.1016/S0140-6736(14)61698-6
- 2.Lee AC, Kozuki N, Blencowe H, et al. Intrapartum-related neonatal encephalopathy incidence and impairment at regional and global levels for 2010 with trends from 1990. Pediatr Res 2013;74(Suppl 1):50–72. 10.1038/pr.2013.206
- 3.Lawn JE, Blencowe H, Oza S, et al. Every Newborn: progress, priorities, and potential beyond survival. Lancet 2014;384:189–205. 10.1016/S0140-6736(14)60496-7
- 4.Edwards AD, Brocklehurst P, Gunn AJ, et al. Neurological outcomes at 18 months of age after moderate hypothermia for perinatal hypoxic ischaemic encephalopathy: synthesis and meta-analysis of trial data. BMJ 2010;340:c363 10.1136/bmj.c363
- 5.Roka A, Azzopardi D. Therapeutic hypothermia for neonatal hypoxic ischaemic encephalopathy. Early Hum Dev 2010;86:361–7. 10.1016/j.earlhumdev.2010.05.013
- 6.Nelson KB, Leviton A. How much of neonatal encephalopathy is due to birth asphyxia? Am J Dis Child 1991;145:1325–31. 10.1001/archpedi.1991.02160040098016
- 7.Eklind S, Mallard C, Leverin AL, et al. Bacterial endotoxin sensitizes the immature brain to hypoxic–ischaemic injury. Eur J Neurosci 2001;13:1101–16. 10.1046/j.0953-816x.2001.01474.x
- 8.Wang X, Stridh L, Li W, et al. Lipopolysaccharide sensitizes neonatal hypoxic-ischemic brain injury in a MyD88-dependent manner. J Immunol 2009;183:7471–7. 10.4049/jimmunol.0900762
- 9.Nelson KB, Willoughby RE. Infection, inflammation and the risk of cerebral palsy. Curr Opin Neurol 2000;13:133–9. 10.1097/00019052-200004000-00004
- 10.Szydlowska K, Tymianski M. Calcium, ischemia and excitotoxicity. Cell Calcium 2010;47:122–9. 10.1016/j.ceca.2010.01.003
- 11.Jensen EC, Bennet L, Hunter CJ, et al. Post-hypoxic hypoperfusion is associated with suppression of cerebral metabolism and increased tissue oxygenation in near-term fetal sheep. J Physiol 2006;572(Pt 1):131–9. 10.1113/jphysiol.2005.100768
- 12.Iwata O, Iwata S, Thornton JS, et al. “Therapeutic time window” duration decreases with increasing severity of cerebral hypoxia-ischaemia under normothermia and delayed hypothermia in newborn piglets. Brain Res 2007;1154:173–80. 10.1016/j.brainres.2007.03.083
- 13.Iwata O, Iwata S, Bainbridge A, et al. Supra- and sub-baseline phosphocreatine recovery in developing brain after transient hypoxia-ischaemia: relation to baseline energetics, insult severity and outcome. Brain 2008;131(Pt 8):2220–6. 10.1093/brain/awn150
- 14.Cady EB, Iwata O, Bainbridge A, et al. Phosphorus magnetic resonance spectroscopy 2 h after perinatal cerebral hypoxia-ischemia prognosticates outcome in the newborn piglet. J Neurochem 2008;107:1027–35. 10.1111/j.1471-4159.2008.05662.x
- 15.Lorek A, Takei Y, Cady EB, et al. Delayed (“secondary)” cerebral energy failure after acute hypoxia-ischemia in the newborn piglet: continuous 48-hour studies by phosphorus magnetic resonance spectroscopy. Pediatr Res 1994;36:699–706. 10.1203/00006450-199412000-00003
- 16.Azzopardi D, Wyatt JS, Cady EB, et al. Prognosis of newborn infants with hypoxic-ischemic brain injury assessed by phosphorus magnetic resonance spectroscopy. Pediatr Res 1989;25:445–51. 10.1203/00006450-198905000-00004
- 17.Martin E, Buchli R, Ritter S, et al. Diagnostic and prognostic value of cerebral 31P magnetic resonance spectroscopy in neonates with perinatal asphyxia. Pediatr Res 1996;40:749–58. 10.1203/00006450-199611000-00015
- 18.Robertson NJ, Cox IJ, Cowan FM, et al. Cerebral intracellular lactic alkalosis persisting months after neonatal encephalopathy measured by magnetic resonance spectroscopy. Pediatr Res 1999;46:287–96. 10.1203/00006450-199909000-00007
- 19.Robertson NJ, Cowan FM, Cox IJ, et al. Brain alkaline intracellular pH after neonatal encephalopathy. Ann Neurol 2002;52:732–42. 10.1002/ana.10365
- 20.Hagberg H, Mallard C, Rousset CI, et al. Mitochondria: hub of injury responses in the developing brain. Lancet Neurol 2014;13:217–32. 10.1016/S1474-4422(13)70261-8
- 21.Northington FJ, Chavez-Valdez R, Martin LJ. Neuronal cell death in neonatal hypoxia-ischemia. Ann Neurol 2011;69:743–58. 10.1002/ana.22419
- 22.Fleiss B, Gressens P. Tertiary mechanisms of brain damage: a new hope for treatment of cerebral palsy? Lancet Neurol 2012;11:556–66. 10.1016/S1474–4422(12)70058-3
- 23.Gonzalez FF, Ferriero DM. Therapeutics for neonatal brain injury. Pharmacol Ther 2008;120:43–53. 10.1016/j.pharmthera.2008.07.003
- 24.Dirnagl U, Simon RP, Hallenbeck JM. Ischemic tolerance and endogenous neuroprotection. Trends Neurosci 2003;26:248–54. 10.1016/S0166-2236(03)00071-7
- 25.Burnard ED, Cross KW. Rectal temperature in the newborn after birth asphyxia. BMJ 1958;2:1197–9. 10.1136/bmj.2.5106.1197
- 26.Reiter RJ, Tan D-X, Fuentes-Broto L. Melatonin: a multitasking molecule. Prog Brain Res 2010;181:127–51. 10.1016/s0079-6123(08)81008-4
- 27.Robertson NJ, Faulkner S, Fleiss B, et al. Melatonin augments hypothermic neuroprotection in a perinatal asphyxia model. Brain 2013;136(Pt 1):90–105. 10.1093/brain/aws285
- 28.Robertson NJ, Nakakeeto M, Hagmann C, et al. Therapeutic hypothermia for birth asphyxia in low-resource settings: a pilot randomised controlled trial. Lancet 2008;372:801–3. 10.1016/S0140-6736(08)61329-X
- 29.Bona E, Hagberg H, Loberg EM, et al. Protective effects of moderate hypothermia after neonatal hypoxia-ischemia: short- and long-term outcome. Pediatr Res 1998;43:738–45. 10.1203/00006450-199806000-00005
- 30.Thoresen M, Penrice J, Lorek A, et al. Mild hypothermia after severe transient hypoxia-ischemia ameliorates delayed cerebral energy failure in the newborn piglet. Pediatr Res 1995;37:667–70. 10.1203/00006450-199505000-00019
- 31.Jacobs SE, Berg M, Hunt R, et al. Cooling for newborns with hypoxic ischaemic encephalopathy. Cochrane Database Syst Rev 2013;1:CD003311 10.1002/14651858.CD003311.pub3
- 32.Wassink G, Gunn ER, Drury PP, et al. The mechanisms and treatment of asphyxial encephalopathy. Front Neurosci 2014;8:40 10.3389/fnins.2014.00040
- 33.Edwards AD, Azzopardi DV, Gunn AJ. Neonatal neural rescue: a clinical guide. Cambridge University Press, 2013.
- 34.Busto R, Globus MY, Dietrich WD, et al. Effect of mild hypothermia on ischemia-induced release of neurotransmitters and free fatty acids in rat brain. Stroke 1989;20:904–10. 10.1161/01.STR.20.7.904
- 35.Drury PP, Bennet L, Gunn AJ. Mechanisms of hypothermic neuroprotection. Semin Fetal Neonatal Med 2010;15:287–92. 10.1016/j.siny.2010.05.005
- 36.Yenari MA, Han HS. Neuroprotective mechanisms of hypothermia in brain ischaemia. Nat Rev Neurosci 2012;13:267–78.
- 37.Azzopardi DV, Strohm B, Edwards AD, et al. Moderate hypothermia to treat perinatal asphyxial encephalopathy. N Engl J Med 2009;361:1349–58. 10.1056/NEJMoa0900854
- 38.Gluckman PD, Wyatt JS, Azzopardi D, et al. Selective head cooling with mild systemic hypothermia after neonatal encephalopathy: multicentre randomised trial. Lancet 2005;365:663–70. 10.1016/S0140-6736(05)17946-X
- 39.Sarkar S, Donn SM, Bapuraj JR, et al. Distribution and severity of hypoxic-ischaemic lesions on brain MRI following therapeutic cooling: selective head versus whole body cooling. Archives of disease in childhood. Fetal Neonatal Ed 2012;97:F335–9. 10.1136/fetalneonatal-2011-300964
- 40.Tagin MA, Woolcott CG, Vincer MJ, et al. Hypothermia for neonatal hypoxic ischemic encephalopathy: an updated systematic review and meta-analysis. Arch Pediatr Adolesc Med 2012;166:558–66. 10.1001/archpediatrics.2011.1772
- 41.Shankaran S. Therapeutic hypothermia for neonatal encephalopathy. Curr Treat Options Neurol 2012;14:608–19. 10.1007/s11940-012-0200-y
- 42.Azzopardi D, Strohm B, Linsell L, et al. Implementation and conduct of therapeutic hypothermia for perinatal asphyxial encephalopathy in the UK–analysis of national data. PloS ONE 2012;7:e38504 10.1371/journal.pone.0038504
- 43.Mourvillier B, Tubach F, van de Beek D, et al. Induced hypothermia in severe bacterial meningitis: a randomized clinical trial. JAMA 2013;310:2174–83. 10.1001/jama.2013.280506
- 44.Osredkar D, Thoresen M, Maes E, et al. Hypothermia is not neuroprotective after infection-sensitized neonatal hypoxic-ischemic brain injury. Resuscitation 2014;85:567–72. 10.1016/j.resuscitation.2013.12.006
- 45.Wintermark P, Boyd T, Gregas MC, et al. Placental pathology in asphyxiated newborns meeting the criteria for therapeutic hypothermia. Am J Obstet Gynecol 2010;203:579 e1–9. 10.1016/j.ajog.2010.08.024
- 46.An C, Shi Y, Li P, et al. Molecular dialogs between the ischemic brain and the peripheral immune system: dualistic roles in injury and repair. Prog Neurobiol 2014;115:6–24. 10.1016/j.pneurobio.2013.12.002
- 47.Buck BH, Liebeskind DS, Saver JL, et al. Early neutrophilia is associated with volume of ischemic tissue in acute stroke. Stroke 2008;39:355–60. 10.1161/STROKEAHA.107.490128
- 48.Liesz A, Suri-Payer E, Veltkamp C, et al. Regulatory T cells are key cerebroprotective immunomodulators in acute experimental stroke. Nat Med 2009;15:192–9. 10.1038/nm.1927
- 49.Kline AE, Bolinger BD, Kochanek PM, et al. Acute systemic administration of interleukin-10 suppresses the beneficial effects of moderate hypothermia following traumatic brain injury in rats. Brain Res 2002;937:22–31. 10.1016/S0006-8993(02)02458-7
- 50.Klehmet J, Harms H, Richter M, et al. Stroke-induced immunodepression and post-stroke infections: lessons from the preventive antibacterial therapy in stroke trial. Neuroscience 2009;158:1184–93. 10.1016/j.neuroscience.2008.07.044
- 51.Kimura A, Sakurada S, Ohkuni H, et al. Moderate hypothermia delays proinflammatory cytokine production of human peripheral blood mononuclear cells. Crit Care Med 2002;30:1499–502. 10.1097/00003246-200207000-00017
- 52.Polderman KH. Hypothermia, immune suppression and SDD: can we have our cake and eat it? Crit Care 2011;15:144 10.1186/cc10080
- 53.Jenkins DD, Lee T, Chiuzan C, et al. Altered circulating leukocytes and their chemokines in a clinical trial of therapeutic hypothermia for neonatal hypoxic ischemic encephalopathy*. Pediatr Crit Care Med 2013;14:786–95. 10.1097/PCC.0b013e3182975cc9
- 54.Geurts M, Macleod MR, Kollmar R, et al. Therapeutic hypothermia and the risk of infection: a systematic review and meta-analysis. Crit Care Med 2014;42:231–42. 10.1097/CCM.0b013e3182a276e8
- 55.Lin HY, Huang CC, Chang KF. Lipopolysaccharide preconditioning reduces neuroinflammation against hypoxic ischemia and provides long-term outcome of neuroprotection in neonatal rat. Pediatr Res 2009;66:254–9. 10.1203/PDR.0b013e3181b0d336
- 56.McAuliffe JJ, Loepke AW, Miles L, et al. Desflurane, isoflurane, and sevoflurane provide limited neuroprotection against neonatal hypoxia-ischemia in a delayed preconditioning paradigm. Anesthesiology 2009;111:533–46. 10.1097/ALN.0b013e3181b060d3
- 57.Wegener S, Gottschalk B, Jovanovic V, et al. Transient ischemic attacks before ischemic stroke: preconditioning the human brain? A multicenter magnetic resonance imaging study. Stroke 2004;35:616–21. 10.1161/01.STR.0000115767.17923.6A
- 58.Weih M, Kallenberg K, Bergk A, et al. Attenuated stroke severity after prodromal TIA: a role for ischemic tolerance in the brain? Stroke 1999;30:1851–4. 10.1161/01.STR.30.9.1851
- 59.Rezkalla SH, Kloner RA. Ischemic preconditioning and preinfarction angina in the clinical arena. Nat Clin Pract Cardiovasc Med 2004;1:96–102. 10.1038/ncpcardio0047
- 60.Vinten-Johansen J, Zhao ZQ, Jiang R, et al. Myocardial protection in reperfusion with postconditioning. Expert Rev Cardiovasc Ther 2005;3:1035–45. 10.1586/14779072.3.6.1035
- 61.Zhao ZQ, Corvera JS, Halkos ME, et al. Inhibition of myocardial injury by ischemic postconditioning during reperfusion: comparison with ischemic preconditioning. Am J Physiol Heart Circ Physiol 2003;285:H579–88. 10.1152/ajpheart.01064.2002
- 62.Zhao ZQ, Vinten-Johansen J. Postconditioning: reduction of reperfusion-induced injury. Cardiovasc Res 2006;70:200–11. 10.1016/j.cardiores.2006.01.024
- 63.Ren C, Gao X, Niu G, et al. Delayed postconditioning protects against focal ischemic brain injury in rats. PloS ONE 2008;3:e3851 10.1371/journal.pone.0003851
- 64.Lim SY, Hausenloy DJ. Remote ischemic conditioning: from bench to bedside. Front Physiol 2012;3:27 10.3389/fphys.2012.00027
- 65.Malhotra S, Naggar I, Stewart M, et al. Neurogenic pathway mediated remote preconditioning protects the brain from transient focal ischemic injury. Brain Res 2011;1386:184–90. 10.1016/j.brainres.2011.02.032
- 66.Pignataro G, Esposito E, Sirabella R, et al. nNOS and p-ERK involvement in the neuroprotection exerted by remote postconditioning in rats subjected to transient middle cerebral artery occlusion. Neurobiol Dis 2013;54:105–14. 10.1016/j.nbd.2013.02.008
- 67.Denning GM, Ackermann LW, Barna TJ, et al. Proenkephalin expression and enkephalin release are widely observed in non-neuronal tissues. Peptides 2008;29:83–92. 10.1016/j.peptides.2007.11.004
- 68.Kanoria S, Jalan R, Seifalian AM, et al. Protocols and mechanisms for remote ischemic preconditioning: a novel method for reducing ischemia reperfusion injury. Transplantation 2007;84:445–58. 10.1097/01.tp.0000228235.55419.e8
- 69.Shimizu M, Saxena P, Konstantinov IE, et al. Remote ischemic preconditioning decreases adhesion and selectively modifies functional responses of human neutrophils. J Surg Res 2010;158:155–61. 10.1016/j.jss.2008.08.010
- 70.Mergenthaler P, Dirnagl U. Protective conditioning of the brain: expressway or roadblock? J Physiol 2011;589(Pt 17):4147–55. 10.1113/jphysiol.2011.209718
- 71.Saxena P, Newman MA, Shehatha JS, et al. Remote ischemic conditioning: evolution of the concept, mechanisms, and clinical application. J Card Surg 2010;25:127–34. 10.1111/j.1540-8191.2009.00820.x
- 72.Tapuria N, Kumar Y, Habib MM, et al. Remote ischemic preconditioning: a novel protective method from ischemia reperfusion injury–a review. J Surg Res 2008;150:304–30. 10.1016/j.jss.2007.12.747
- 73.Zhou Y, Fathali N, Lekic T, et al. Remote limb ischemic postconditioning protects against neonatal hypoxic-ischemic brain injury in rat pups by the opioid receptor/Akt pathway. Stroke 2011;42:439–44. 10.1161/STROKEAHA.110.592162
- 74.Liu X, Zhao S, Liu F, et al. Remote ischemic postconditioning alleviates cerebral ischemic injury by attenuating endoplasmic reticulum stress-mediated apoptosis. Transl Stroke Res 2014;5:692–700. 10.1007/s12975-014-0359-5
- 75.Drunalini Perera PN, Hu Q, Tang J, et al. Delayed remote ischemic postconditioning improves long term sensory motor deficits in a neonatal hypoxic ischemic rat model. PloS ONE 2014;9:e90258 10.1371/journal.pone.0090258
- 76.Ezzati M, Bainbridge A, Broad KD, et al. Limb remote ischemic post-conditioning protects cerebral white matter in a piglet model of perinatal asphyxia. PAS 2014;4118.305.
- 77.Thayyil S, Chandrasekaran M, Taylor A, et al. Cerebral magnetic resonance biomarkers in neonatal encephalopathy: a meta-analysis. Pediatrics 2010;125:e382–95. 10.1542/peds.2009-1046
- 78.Brevoord D, Kranke P, Kuijpers M, et al. Remote ischemic conditioning to protect against ischemia-reperfusion injury: a systematic review and meta-analysis. PloS ONE 2012;7:e42179 10.1371/journal.pone.0042179
- 79.Zhong H, Gao Z, Chen M, et al. Cardioprotective effect of remote ischemic postconditioning on children undergoing cardiac surgery: a randomized controlled trial. Paediatr Anaesth 2013;23:726–33. 10.1111/pan.12181
- 80.Hougaard KD, Hjort N, Zeidler D, et al. Remote ischemic perconditioning as an adjunct therapy to thrombolysis in patients with acute ischemic stroke: a randomized trial. Stroke 2014;45:159–67. 10.1161/STROKEAHA.113.001346
- 81.Pilcher JM, Young P, Weatherall M, et al. A systematic review and meta-analysis of the cardioprotective effects of remote ischaemic preconditioning in open cardiac surgery. J R Soc Med 2012;105:436–45. 10.1258/jrsm.2012.120049
- 82.Zhao H. Hurdles to clear before clinical translation of ischemic postconditioning against stroke. Transl Stroke Res 2013;4:63–70. 10.1007/s12975-012-0243-0
- 83.Reiter RJ, Tan DX, Manchester LC, et al. Medical implications of melatonin: receptor-mediated and receptor-independent actions. Adv Med Sci 2007;52:11–28.
- 84.Slominski RM, Reiter RJ, Schlabritz-Loutsevitch N, et al. Melatonin membrane receptors in peripheral tissues: distribution and functions. Mol Cell Endocrinol 2012;351:152–66. 10.1016/j.mce.2012.01.004
- 85.Acuna-Castroviejo D, Martin M, Macias M, et al. Melatonin, mitochondria, and cellular bioenergetics. J Pineal Res 2001;30:65–74. 10.1034/j.1600-079X.2001.300201.x
- 86.Cardinali DP, Pagano ES, Scacchi Bernasconi PA, et al. Melatonin and mitochondrial dysfunction in the central nervous system. Horm Behav 2013;63:322–30. 10.1016/j.yhbeh.2012.02.020
- 87.Jou MJ, Peng TI, Yu PZ, et al. Melatonin protects against common deletion of mitochondrial DNA-augmented mitochondrial oxidative stress and apoptosis. J Pineal Res 2007;43:389–403. 10.1111/j.1600-079X.2007.00490.x
- 88.Pandi-Perumal SR, BaHammam AS, Brown GM, et al. Melatonin antioxidative defense: therapeutical implications for aging and neurodegenerative processes. Neurotox Res 2013;23:267–300. 10.1007/s12640-012-9337-4
- 89.Sharma R, Ottenhof T, Rzeczkowska PA, et al. Epigenetic targets for melatonin: induction of histone H3 hyperacetylation and gene expression in C17.2 neural stem cells. J Pineal Res 2008;45:277–84. 10.1111/j.1600-079X.2008.00587.x
- 90.Thomas L, Purvis CC, Drew JE, et al. Melatonin receptors in human fetal brain: 2-[(125)I]iodomelatonin binding and MT1 gene expression. J Pineal Res 2002;33:218–24. 10.1034/j.1600-079X.2002.02921.x
- 91.Tamura H, Nakamura Y, Korkmaz A, et al. Melatonin and the ovary: physiological and pathophysiological implications. Fertil Steril 2009;92:328–43. 10.1016/j.fertnstert.2008.05.016
- 92.Tamura H, Nakamura Y, Terron MP, et al. Melatonin and pregnancy in the human. Reprod Toxicol 2008;25:291–303. 10.1016/j.reprotox.2008.03.005
- 93.Okatani Y, Okamoto K, Hayashi K, et al. Maternal-fetal transfer of melatonin in pregnant women near term. J Pineal Res 1998;25:129–34. 10.1111/j.1600-079X.1998.tb00550.x
- 94.Okatani Y, Wakatsuki A, Kaneda C. Melatonin increases activities of glutathione peroxidase and superoxide dismutase in fetal rat brain. J Pineal Res 2000;28:89–96. 10.1034/j.1600-079X.2001.280204.x
- 95.Ardura J, Gutierrez R, Andres J, et al. Emergence and evolution of the circadian rhythm of melatonin in children. Horm Res 2003;59:66–72. 10.1159/000068571
- 96.Kennaway DJ, Stamp GE, Goble FC. Development of melatonin production in infants and the impact of prematurity. J Clin Endocrinol Metab 1992;75:367–9. 10.1210/jcem.75.2.1639937
- 97.Marseglia L, Aversa S, Barberi I, et al. High endogenous melatonin levels in critically Ill children: a Pilot study. J Pediatr 2013;162:357–60. 10.1016/j.jpeds.2012.07.019
- 98.Seifman MA, Adamides AA, Nguyen PN, et al. Endogenous melatonin increases in cerebrospinal fluid of patients after severe traumatic brain injury and correlates with oxidative stress and metabolic disarray. Cereb Blood Flow Metab 2008;28:684–96. 10.1038/sj.jcbfm.9600603
- 99.Fu J, Zhao SD, Liu HJ, et al. Melatonin promotes proliferation and differentiation of neural stem cells subjected to hypoxia in vitro. J Pineal Res 2011;51:104–12. 10.1111/j.1600-079X.2011.00867.x
- 100.Husson I, Mesples B, Bac P, et al. Melatoninergic neuroprotection of the murine periventricular white matter against neonatal excitotoxic challenge. Ann Neurol 2002;51:82–92. 10.1002/ana.10072
- 101.Villapol S, Fau S, Renolleau S, et al. Melatonin promotes myelination by decreasing white matter inflammation after neonatal stroke. Pediatr Res 2011;69:51–5. 10.1203/PDR.0b013e3181fcb40b
- 102.Pearce W. Hypoxic regulation of the fetal cerebral circulation. J Appl Physiol 2006;100:731–8. 10.1152/japplphysiol.00990.2005
- 103.Vento M, Escobar J, Cernada M, et al. The use and misuse of oxygen during the neonatal period. Clin Perinatol 2012;39:165–76. 10.1016/j.clp.2011.12.014
- 104.Wakatsuki A, Okatani Y, Izumiya C, et al. Melatonin protects against ischemia and reperfusion-induced oxidative lipid and DNA damage in fetal rat brain. J Pineal Res 1999;26:147–52. 10.1111/j.1600-079X.1999.tb00576.x
- 105.Galano A, Tan DX, Reiter RJ. On the free radical scavenging activities of melatonin's metabolites, AFMK and AMK. J Pineal Res 2013;54:245–57. 10.1111/jpi.12010
- 106.Gilad E, Cuzzocrea S, Zingarelli B, et al. Melatonin is a scavenger of peroxynitrite. Life Sci 1997;60:PL169–74. 10.1016/S0024-3205(97)00008-8
- 107.Hardeland R, Tan DX, Reiter RJ. Kynuramines, metabolites of melatonin and other indoles: the resurrection of an almost forgotten class of biogenic amines. J Pineal Res 2009;47:109–26. 10.1111/j.1600-079X.2009.00701.x
- 108.Ressmeyer AR, Mayo JC, Zelosko V, et al. Antioxidant properties of the melatonin metabolite N1-acetyl-5-methoxykynuramine (AMK): scavenging of free radicals and prevention of protein destruction. Redox Rep 2003;8:205–13. 10.1179/135100003225002709
- 109.Tan DX, Manchester LC, Terron MP, et al. One molecule, many derivatives: a never-ending interaction of melatonin with reactive oxygen and nitrogen species? J Pineal Res 2007;42:28–42. 10.1111/j.1600-079X.2006.00407.x
- 110.Miller SL, Yan EB, Castillo-Melendez M, et al. Melatonin provides neuroprotection in the late-gestation fetal sheep brain in response to umbilical cord occlusion. Dev Neurosci 2005;27:200–10. 10.1159/000085993
- 111.Wakatsuki A, Izumiya C, Okatani Y, et al. Oxidative damage in fetal rat brain induced by ischemia and subsequent reperfusion. Relation to arachidonic acid peroxidation. Biol Neonate 1999;76:84–91. 10.1159/000014145
- 112.Wakatsuki A, Okatani Y, Shinohara K, et al. Melatonin protects against ischemia/reperfusion-induced oxidative damage to mitochondria in fetal rat brain. J Pineal Res 2001;31:167–72. 10.1034/j.1600-079x.2001.310211.x
- 113.Wakatsuki A, Okatani Y, Shinohara K, et al. Melatonin protects fetal rat brain against oxidative mitochondrial damage. J Pineal Res 2001;30:22–8. 10.1034/j.1600-079X.2001.300103.x
- 114.Watanabe K, Hamada F, Wakatsuki A, et al. Prophylactic administration of melatonin to the mother throughout pregnancy can protect against oxidative cerebral damage in neonatal rats. J Matern Fetal Neonatal Med 2012;25:1254–9. 10.3109/14767058.2011.636094
- 115.Watanabe K, Wakatsuki A, Shinohara K, et al. Maternally administered melatonin protects against ischemia and reperfusion-induced oxidative mitochondrial damage in premature fetal rat brain. J Pineal Res 2004;37:276–80. 10.1111/j.1600-079X.2004.00167.x
- 116.Yawno T, Castillo-Melendez M, Jenkin G, et al. Mechanisms of melatonin-induced protection in the brain of late gestation fetal sheep in response to hypoxia. Dev Neurosci 2012;34:543–51. 10.1159/000346323
- 117.Cetinkaya M, Alkan T, Ozyener F, et al. Possible neuroprotective effects of magnesium sulfate and melatonin as both pre- and post-treatment in a neonatal hypoxic-ischemic rat model. Neonatology 2011;99:302–10. 10.1159/000320643
- 118.Hutton LC, Abbass M, Dickinson H, et al. Neuroprotective properties of melatonin in a model of birth asphyxia in the spiny mouse (Acomys cahirinus). Dev Neurosci 2009;31:437–51. 10.1159/000232562
- 119.Kaur C, Sivakumar V, Ling EA. Melatonin protects periventricular white matter from damage due to hypoxia. J Pineal Res 2010;48:185–93. 10.1111/j.1600-079X.2009.00740.x
- 120.Ozyener F, Cetinkaya M, Alkan T, et al. Neuroprotective effects of melatonin administered alone or in combination with topiramate in neonatal hypoxic-ischemic rat model. Restor Neurol Neurosci 2012;30:435–44. 10.3233/RNN-2012-120217
- 121.Welin AK, Svedin P, Lapatto R, et al. Melatonin reduces inflammation and cell death in white matter in the mid-gestation fetal sheep following umbilical cord occlusion. Pediatr Res 2007;61:153–8. 10.1203/01.pdr.0000252546.20451.1a
- 122.Carrillo-Vico A, Lardone PJ, Fernandez-Santos JM, et al. Human lymphocyte-synthesized melatonin is involved in the regulation of the interleukin-2/interleukin-2 receptor system. J Clin Endocrinol Metab 2005;90:992–1000. 10.1210/jc.2004-1429
- 123.Srinivasan V, Pandi-Perumal SR, Spence DW, et al. Melatonin in septic shock: some recent concepts. J Crit Care 2010;25:656 e1–6. 10.1016/j.jcrc.2010.03.006
- 124.Balduini W, Carloni S, Perrone S, et al. The use of melatonin in hypoxic-ischemic brain damage: an experimental study. J Matern Fetal Neonatal Med 2012;25(Suppl 1):119–24. 10.3109/14767058.2012.663232
- 125.Wang X, Svedin P, Nie C, et al. N-acetylcysteine reduces lipopolysaccharide-sensitized hypoxic-ischemic brain injury. Ann Neurol 2007;61:263–71. 10.1002/ana.21066
- 126.Jahnke G, Marr M, Myers C, et al. Maternal and developmental toxicity evaluation of melatonin administered orally to pregnant Sprague-Dawley rats. Toxicol Sci 1999;50:271–9. 10.1093/toxsci/50.2.271
- 127.Buscemi N, Vandermeer B, Hooton N, et al. Efficacy and safety of exogenous melatonin for secondary sleep disorders and sleep disorders accompanying sleep restriction: meta-analysis. BMJ 2006;332:385–93. 10.1136/bmj.38731.532766.F6
- 128.Gitto E, Karbownik M, Reiter RJ, et al. Effects of melatonin treatment in septic newborns. Pediatr Res 2001;50:756–60. 10.1203/00006450-200112000-00021
- 129.Gitto E, Reiter RJ, Cordaro SP, et al. Oxidative and inflammatory parameters in respiratory distress syndrome of preterm newborns: beneficial effects of melatonin. Am J Perinatol 2004;21:209–16. 10.1055/s-2004-828610
- 130.Fulia F, Gitto E, Cuzzocrea S, et al. Increased levels of malondialdehyde and nitrite/nitrate in the blood of asphyxiated newborns: reduction by melatonin. J Pineal Res 2001;31:343–9. 10.1034/j.1600-079X.2001.310409.x
- 131.Aly H, Elmahdy H, El-Dib M, et al. Melatonin use for neuroprotection in perinatal asphyxia: a randomized controlled pilot study. J Perinatol 2014. doi: 10.1038/jp.2014.186. [Epub ahead of print] 10.1038/jp.2014.186
- 132.Robertson NJ, Tan S, Groenendaal F, et al. Which neuroprotective agents are ready for bench to bedside translation in the newborn infant? J Pediatr 2012;160:544–52 e4 10.1016/j.jpeds.2011.12.052
- 133.Pacher P, Batkai S, Kunos G. The endocannabinoid system as an emerging target of pharmacotherapy. Pharmacol Rev 2006;58:389–462. 10.1124/pr.58.3.2
- 134.Ahn K, McKinney MK, Cravatt BF. Enzymatic pathways that regulate endocannabinoid signaling in the nervous system. Chem Rev 2008;108:1687–707. 10.1021/cr0782067
- 135.Di Marzo V, Bisogno T, De Petrocellis L. Endocannabinoids and related compounds: walking back and forth between plant natural products and animal physiology. Chem Biol 2007;14:741–56. 10.1016/j.chembiol.2007.05.014
- 136.Berger C, Schmid PC, Schabitz WR, et al. Massive accumulation of N-acylethanolamines after stroke. Cell signalling in acute cerebral ischemia? J Neurochem 2004;88:1159–67.
- 137.Fernandez-Ruiz J, Berrendero F, Hernandez ML, et al. The endogenous cannabinoid system and brain development. Trends Neurosci 2000;23:14–20. 10.1016/S0166-2236(99)01491-5
- 138.Gaffuri AL, Ladarre D, Lenkei Z. Type-1 cannabinoid receptor signaling in neuronal development. Pharmacology 2012;90:19–39. 10.1159/000339075
- 139.Harkany T, Keimpema E, Barabas K, et al. Endocannabinoid functions controlling neuronal specification during brain development. Mol Cell Endocrinol 2008; 286(1–2 Suppl 1):S84–90. 10.1016/j.mce.2008.02.011
- 140.Mato S, Del Olmo E, Pazos A. Ontogenetic development of cannabinoid receptor expression and signal transduction functionality in the human brain. Eur J Neurosci 2003;17:1747–54. 10.1046/j.1460-9568.2003.02599.x
- 141.Paria BC, Dey SK. Ligand-receptor signaling with endocannabinoids in preimplantation embryo development and implantation. Chem Phys Lipids 2000;108:211–20. 10.1016/S0009-3084(00)00197-3
- 142.Hansen HH, Ikonomidou C, Bittigau P, et al. Accumulation of the anandamide precursor and other N-acylethanolamine phospholipids in infant rat models of in vivo necrotic and apoptotic neuronal death. J Neurochem 2001;76:39–46. 10.1046/j.1471-4159.2001.00006.x
- 143.Panikashvili D, Simeonidou C, Ben-Shabat S, et al. An endogenous cannabinoid (2-AG) is neuroprotective after brain injury. Nature 2001;413:527–31. 10.1038/35097089
- 144.Sugiura T, Yoshinaga N, Kondo S, et al. Generation of 2-arachidonoylglycerol, an endogenous cannabinoid receptor ligand, in picrotoxinin-administered rat brain. Biochem Biophys Res Commun 2000;271:654–8. 10.1006/bbrc.2000.2686
- 145.van der Stelt M, Di Marzo V. Cannabinoid receptors and their role in neuroprotection. Neuromolecular Med 2005;7:37–50. 10.1385/NMM:7:1-2:037
- 146.Freund TF, Katona I, Piomelli D. Role of endogenous cannabinoids in synaptic signaling. Physiol Rev 2003;83:1017–66. 10.1152/physrev.00004.2003
- 147.Kim SH, Won SJ, Mao XO, et al. Molecular mechanisms of cannabinoid protection from neuronal excitotoxicity. Mol Pharmacol 2006;69:691–6. 10.1124/mol.105.016428
- 148.Marsicano G, Goodenough S, Monory K, et al. CB1 cannabinoid receptors and on-demand defense against excitotoxicity. Science 2003;302:84–8. 10.1126/science.1088208
- 149.van der Stelt M, Veldhuis WB, Maccarrone M, et al. Acute neuronal injury, excitotoxicity, and the endocannabinoid system. Mol Neurobiol 2002;26:317–46. 10.1385/MN:26:2-3:317
- 150.Waksman Y, Olson JM, Carlisle SJ, et al. The central cannabinoid receptor (CB1) mediates inhibition of nitric oxide production by rat microglial cells. J Pharmacol Exp Ther 1999;288:1357–66.
- 151.Klein TW. Cannabinoid-based drugs as anti-inflammatory therapeutics. Nature Rev Immunol 2005;5:400–11. 10.1038/nri1602
- 152.Murikinati S, Juttler E, Keinert T, et al. Activation of cannabinoid 2 receptors protects against cerebral ischemia by inhibiting neutrophil recruitment. FASEB J 2010;24:788–98. 10.1096/fj.09-141275
- 153.Stella N. Endocannabinoid signaling in microglial cells. Neuropharmacology 2009;56(Suppl 1):244–53. 10.1016/j.neuropharm.2008.07.037
- 154.Tanasescu R, Constantinescu CS. Cannabinoids and the immune system: an overview. Immunobiology 2010;215:588–97. 10.1016/j.imbio.2009.12.005
- 155.Walter L, Stella N. Cannabinoids and neuroinflammation. Br J Pharmacol 2004;141:775–85. 10.1038/sj.bjp.0705667
- 156.Guzman M, Sanchez C, Galve-Roperh I. Control of the cell survival/death decision by cannabinoids. J Mol Med 2001;78:613–25. 10.1007/s001090000177
- 157.Guzman M, Sanchez C, Galve-Roperh I. Cannabinoids and cell fate. Pharmacol Ther 2002;95:175–84. 10.1016/S0163-7258(02)00256-5
- 158.Molina-Holgado E, Vela JM, Arevalo-Martin A, et al. Cannabinoids promote oligodendrocyte progenitor survival: involvement of cannabinoid receptors and phosphatidylinositol-3 kinase/Akt signaling. JNeurosci 2002;22:9742–53.
- 159.Ozaita A, Puighermanal E, Maldonado R. Regulation of PI3K/Akt/GSK-3 pathway by cannabinoids in the brain. J Neurochem 2007;102:1105–14. 10.1111/j.1471-4159.2007.04642.x
- 160.Ramirez SH, Hasko J, Skuba A, et al. Activation of cannabinoid receptor 2 attenuates leukocyte-endothelial cell interactions and blood-brain barrier dysfunction under inflammatory conditions. J Neurosci 2012;32:4004–16. 10.1523/JNEUROSCI.4628-11.2012
- 161.Viscomi MT, Oddi S, Latini L, et al. Selective CB2 receptor agonism protects central neurons from remote axotomy-induced apoptosis through the PI3K/Akt pathway. J Neurosci 2009;29:4564–70. 10.1523/JNEUROSCI.0786-09.2009
- 162.Alonso-Alconada D, Alvarez A, Alvarez FJ, et al. The cannabinoid WIN 55212-2 mitigates apoptosis and mitochondrial dysfunction after hypoxia ischemia. Neurochem Res 2012;37:161–70. 10.1007/s11064-011-0594-z
- 163.Alonso-Alconada D, Alvarez FJ, Alvarez A, et al. The cannabinoid receptor agonist WIN 55,212-2 reduces the initial cerebral damage after hypoxic-ischemic injury in fetal lambs. Brain Res 2010;1362:150–9. 10.1016/j.brainres.2010.09.050
- 164.Fernandez-Lopez D, Pazos MR, Tolon RM, et al. The cannabinoid agonist WIN55212 reduces brain damage in an in vivo model of hypoxic-ischemic encephalopathy in newborn rats. Pediatr Res 2007;62:255–60. 10.1203/PDR.0b013e318123fbb8
- 165.Fernandez-Lopez D, Pradillo JM, Garcia-Yebenes I, et al. The cannabinoid WIN55212-2 promotes neural repair after neonatal hypoxia-ischemia. Stroke 2010;41:2956–64. 10.1161/STROKEAHA.110.599357
- 166.Lafuente H, Alvarez FJ, Pazos MR, et al. Cannabidiol reduces brain damage and improves functional recovery after acute hypoxia-ischemia in newborn pigs. Pediatr Res 2011;70:272–7. 10.1203/PDR.0b013e3182276b11
- 167.Pazos MR, Mohammed N, Lafuente H, et al. Mechanisms of cannabidiol neuroprotection in hypoxic-ischemic newborn pigs: role of 5HT(1A) and CB2 receptors. Neuropharmacology 2013;71:282–91. 10.1016/j.neuropharm.2013.03.027
- 168.Leker RR, Gai N, Mechoulam R, et al. Drug-induced hypothermia reduces ischemic damage: effects of the cannabinoid HU-210. Stroke 2003;34:2000–6. 10.1161/01.STR.0000079817.68944.1E
- 169.Borgelt LM, Franson KL, Nussbaum AM, et al. The pharmacologic and clinical effects of medical cannabis. Pharmacotherapy 2013;33:195–209. 10.1002/phar.1187
- 170.Croxford JL. Therapeutic potential of cannabinoids in CNS disease. CNS Drugs 2003;17:179–202. 10.2165/00023210-200317030-00004
- 171.Maas AI, Murray G, Henney H III, et al. Efficacy and safety of dexanabinol in severe traumatic brain injury: results of a phase III randomised, placebo-controlled, clinical trial. Lancet Neurol 2006;5:38–45. 10.1016/S1474-4422(05)70253-2
- 172.Rangarajan V, Juul SE. Erythropoietin: emerging role of erythropoietin in neonatal neuroprotection. Pediatr Neurol 2014;51:481–8. 10.1016/j.pediatrneurol.2014.06.008
- 173.Morishita E, Masuda S, Nagao M, et al. Erythropoietin receptor is expressed in rat hippocampal and cerebral cortical neurons, and erythropoietin prevents in vitro glutamate-induced neuronal death. Neuroscience 1997;76:105–16. 10.1016/S0306-4522(96)00306-5
- 174.Nagai A, Nakagawa E, Choi HB, et al. Erythropoietin and erythropoietin receptors in human CNS neurons, astrocytes, microglia, and oligodendrocytes grown in culture. J Neuropathol Exp Neurol 2001;60:386–92.
- 175.Yamaji R, Okada T, Moriya M, et al. Brain capillary endothelial cells express two forms of erythropoietin receptor mRNA. Eur J Biochem 1996;239:494–500. 10.1111/j.1432-1033.1996.0494u.x
- 176.Marti HH, Bernaudin M, Petit E, et al. Neuroprotection and angiogenesis: dual role of erythropoietin in brain ischemia. News Physiol Sci 2000;15:225–9.
- 177.Kilic E, Ozdemir YG, Bolay H, et al. Pinealectomy aggravates and melatonin administration attenuates brain damage in focal ischemia. J Cereb Blood Flow Metab 1999;19:511–6. 10.1097/00004647-199905000-00005
- 178.Chen ZY, Asavaritikrai P, Prchal JT, et al. Endogenous erythropoietin signaling is required for normal neural progenitor cell proliferation. J Biol Chem 2007;282:25875–83. 10.1074/jbc.M701988200
- 179.Prass K, Scharff A, Ruscher K, et al. Hypoxia-induced stroke tolerance in the mouse is mediated by erythropoietin. Stroke 2003;34:1981–6. 10.1161/01.STR.0000080381.76409.B2
- 180.Ferriero DM. Protecting neurons. Epilepsia 2005;46(Suppl 7):45–51. 10.1111/j.1528-1167.2005.00302.x
- 181.Juul SE, Beyer RP, Bammler TK, et al. Microarray analysis of high-dose recombinant erythropoietin treatment of unilateral brain injury in neonatal mouse hippocampus. Pediatr Res 2009;65:485–92. 10.1203/PDR.0b013e31819d90c8
- 182.Maiese K, Chong ZZ, Hou J, et al. Erythropoietin and oxidative stress. Curr Neurovasc Res 2008;5:125–42. 10.2174/156720208784310231
- 183.Villa P, van Beek J, Larsen AK, et al. Reduced functional deficits, neuroinflammation, and secondary tissue damage after treatment of stroke by nonerythropoietic erythropoietin derivatives. Cereb Blood Flow Metab 2007;27:552–63. 10.1038/sj.jcbfm.9600370
- 184.Gonzalez FF, Larpthaveesarp A, McQuillen P, et al. Erythropoietin increases neurogenesis and oligodendrogliosis of subventricular zone precursor cells after neonatal stroke. Stroke 2013;44:753–8. 10.1161/STROKEAHA.111.000104
- 185.Xiong Y, Mahmood A, Meng Y, et al. Delayed administration of erythropoietin reducing hippocampal cell loss, enhancing angiogenesis and neurogenesis, and improving functional outcome following traumatic brain injury in rats: comparison of treatment with single and triple dose. J Neurosurg 2010;113:598–608. 10.3171/2009.9.JNS09844
- 186.Kaneko N, Kako E, Sawamoto K. Enhancement of ventricular-subventricular zone-derived neurogenesis and oligodendrogenesis by erythropoietin and its derivatives. Front Cell Neurosci 2013;7:235 10.3389/fncel.2013.00235
- 187.Wang L, Zhang ZG, Zhang RL, et al. Matrix metalloproteinase 2 (MMP2) and MMP9 secreted by erythropoietin-activated endothelial cells promote neural progenitor cell migration. J Neurosci 2006;26:5996–6003. 10.1523/JNEUROSCI.5380-05.2006
- 188.Fan X, Heijnen CJ, van der KM, et al. Beneficial effect of erythropoietin on sensorimotor function and white matter after hypoxia-ischemia in neonatal mice. Pediatr Res 2011;69:56–61. 10.1203/PDR.0b013e3181fcbef3
- 189.Gonzalez FF, Abel R, Almli CR, et al. Erythropoietin sustains cognitive function and brain volume after neonatal stroke. Dev Neurosci 2009;31:403–11. 10.1159/000232558
- 190.van de Looij Y, Chatagner A, Quairiaux C, et al. Multi-modal assessment of long-term erythropoietin treatment after neonatal hypoxic-ischemic injury in rat brain. PloS ONE 2014;9:e95643 10.1371/journal.pone.0095643
- 191.Traudt CM, McPherson RJ, Bauer LA, et al. Concurrent erythropoietin and hypothermia treatment improve outcomes in a term nonhuman primate model of perinatal asphyxia. Dev Neurosci 2013;35:491–503. 10.1159/000355460
- 192.McPherson RJ, Demers EJ, Juul SE. Safety of high-dose recombinant erythropoietin in a neonatal rat model. Neonatology 2007;91:36–43. 10.1159/000096969
- 193.Juul SE, McPherson RJ, Bauer LA, et al. A phase I/II trial of high-dose erythropoietin in extremely low birth weight infants: pharmacokinetics and safety. Pediatrics 2008;122:383–91. 10.1542/peds.2007-2711
- 194.Benders MJ, van der Aa NE, Roks M, et al. Feasibility and safety of erythropoietin for neuroprotection after perinatal arterial ischemic stroke. J Pediatr 2014;164:481–6 e1–2 10.1016/j.jpeds.2013.10.084
- 195.Wu YW, Bauer LA, Ballard RA, et al. Erythropoietin for neuroprotection in neonatal encephalopathy: safety and pharmacokinetics. Pediatrics 2012;130:683–91. 10.1542/peds.2012-0498
- 196.Sanchis-Gomar F, Perez-Quilis C, Lippi G. Erythropoietin receptor (EpoR) agonism is used to treat a wide range of disease. Mol Med 2013;19:62–4. 10.2119/molmed.2013.00025
- 197.Rogers EE, Bonifacio SL, Glass HC, et al. Erythropoietin and hypothermia for hypoxic-ischemic encephalopathy. Pediatr Neurol 2014;51:657–62. 10.1016/j.pediatrneurol.2014.08.010
- 198.Kellert BA, McPherson RJ, Juul SE. A comparison of high-dose recombinant erythropoietin treatment regimens in brain-injured neonatal rats. Pediatr Res 2007;61:451–5. 10.1203/pdr.0b013e3180332cec
- 199.El Shimi MS, Awad HA, Hassanein SM, et al. Single dose recombinant erythropoietin versus moderate hypothermia for neonatal hypoxic ischemic encephalopathy in low resource settings. J Matern Fetal Neonatal Med 2014;27:1295–300. 10.3109/14767058.2013.855894