Neonatal Hypoxia Ischaemia: Mechanisms, Models, and Therapeutic Challenges
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fncel-11-00078 May 4, 2017 Time: 20:34 # 1 REVIEW published: 08 May 2017 doi: 10.3389/fncel.2017.00078 Neonatal Hypoxia Ischaemia: Mechanisms, Models, and Therapeutic Challenges Lancelot J. Millar1*, Lei Shi1,2, Anna Hoerder-Suabedissen1 and Zoltán Molnár1 1 Molnár Group, Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, UK, 2 JNU-HKUST Joint Laboratory for Neuroscience and Innovative Drug Research, College of Pharmacy, Jinan University, Guangzhou, China Neonatal hypoxia-ischaemia (HI) is the most common cause of death and disability in human neonates, and is often associated with persistent motor, sensory, and cognitive impairment. Improved intensive care technology has increased survival without preventing neurological disorder, increasing morbidity throughout the adult population. Early preventative or neuroprotective interventions have the potential to rescue brain development in neonates, yet only one therapeutic intervention is currently licensed for use in developed countries. Recent investigations of the transient cortical layer known as subplate, especially regarding subplate’s secretory role, opens up a novel set of potential molecular modulators of neonatal HI injury. This review examines the biological mechanisms of human neonatal HI, discusses evidence for the relevance of subplate-secreted molecules to this condition, and evaluates available animal models. Neuroserpin, a neuronally released neuroprotective factor, is discussed as a case study for developing new potential pharmacological interventions for use post-ischaemic injury. Edited by: Daniela Tropea, Keywords: neonatal, hypoxia-ischemia, encephalopathy, subplate, neurodevelopment, neuroserpin, Trinity College, Dublin, Ireland neuroprotection Reviewed by: Alla B. Salmina, Krasnoyarsk State Medical University, INTRODUCTION: GLOBAL CLINICAL IMPACT OF NEONATAL Russia HYPOXIA ISCHAEMIA Gunnar Naulaers, KU Leuven, Belgium The clinical definition of neonatal HI injury is “asphyxia of the umbilical blood supply to the *Correspondence: human fetus occurring at 36 gestational weeks or later” (Perlman, 1997, 2006; Volpe, 2001, 2012; Lancelot J. Millar Shah P.S. et al., 2006). Neonatal HI is synonymous with hypoxic-ischaemic encephalopathy (HIE) [email protected] occurring in the term infant, where term is defined as 36 gestational weeks or later. This review addresses neonatal HI or HIE, any results concerning perinatal hypoxic-ischaemia injury will be Received: 31 October 2016 clearly indicated in the text. This disorder encompasses a large range of physiological origins Accepted: 07 March 2017 Published: 08 May 2017 Citation: Millar LJ, Shi L, Abbreviations: AMPA, alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid; BBB, blood brain barrier; CPR, Hoerder-Suabedissen A and cardiopulmonary resuscitation; CNS, central nervous system; CSF, cortico-spinal fluid; CSPG, chondroitin sulfate proteoglycan; CTGF, connective tissue growth factor; E(18), embryonic day (18); EM, electron microscopy; GABA, Molnár Z (2017) Neonatal Hypoxia g-aminobutyric acid; HI, hypoxia-ischaemia; HIF-1, hypoxia inducible factor 1; IL-1ß, interleukin-1ß; IL-6, interleukin-6; Ischaemia: Mechanisms, Models, IL-9, interleukin-9; LPS, lipopolysaccharide; MRI, magnetic resonance imaging; MRS, magnetic resonance spectroscopy; and Therapeutic Challenges. NMDA, N-methyl-D-aspartate; OGD, oxygen glucose deprivation; P(8), postnatal day (8); poly(I:C), polyinosinic- Front. Cell. Neurosci. 11:78. polycytidylic acid; rER, rough endoplasmic reticulum; TNF-a, tumour-necrosis factor-a; tPA, tissue plasminogen activator; doi: 10.3389/fncel.2017.00078 VEGF, vascular endothelial growth factor. Frontiers in Cellular Neuroscience| www.frontiersin.org 1 May 2017| Volume 11| Article 78 fncel-11-00078 May 4, 2017 Time: 20:34 # 2 Millar et al. Neonatal Hypoxia-ischaemia and Models and clinical outcomes (Volpe, 1995). The diagnostic criteria 1–18% of patients were identified as having severe sensorimotor for neonatal HI are based on a set of markers demonstrated or learning disorders by the age of 2–5 years, with only 50–60% to correlate with clinical outcome (Finer et al., 1981; Perlman, of patients reported as developmentally normal (Dilenge et al., 1997; Richer et al., 2001). These include: 5-min Apgar score 2001). This study covered a wide range of injury severities of less than 5 (Levene et al., 1986; Ruth and Raivio, 1988; and follow-up ages. Disorders included seizures, hearing and Laptook et al., 2009); need for delivery room intubation or CPR vision loss (Robertson and Finer, 1985), language disorders, (Richardson B.S. et al., 1996; Salhab et al., 2004a; Shalak and microcephaly, and muscle spasticity (Shankaran et al., 1991, Perlman, 2004; Kattwinkel et al., 2010); umbilical cord arterial pH 2012). Studies also report more severe neurological signs in less than 7.00 (Ruth and Raivio, 1988; Perlman and Risser, 1993; patients suffering severe HI compared to those with milder HI Robertson N.J. et al., 2002; Salhab et al., 2004b); and abnormal injury (Robertson and Finer, 1985). Yet, many individuals who neurological signs, such as hypotonic muscles or lack of sucking showed abnormal neurological signs at birth were normal at 2- reflex (Levene et al., 1986; Robertson et al., 1989; Richer et al., year follow-up (De Souza and Richards, 1978). Clinical features 2001). Electroencephalography (EEG) has also proved helpful as and outcomes of neonatal HI are summarized in Figure 1. a predictor of clinical outcome (reviewed in Walsh et al., 2011; Despite the high disability burden associated with surviving van Laerhoven et al., 2013). Amplitude-integrated EEG (aEEG) neonatal HI patients, there are very few preventative or protective in particular, a filtered time-compressed continuous one- or treatments available for infants suspected to have suffered two-channel read-out, has been demonstrated a reliable predictor an HI event. The only licensed treatment currently available in meta-analyses up to 5 years after birth (al Naqeeb et al., is hypothermia. This treatment involves subjecting either the 1999; Sinclair et al., 1999; Toet et al., 1999; Biagioni et al., 2001; infant’s whole body or head-only to temperatures of around Shah D.K. et al., 2006; Nash et al., 2011; Murray et al., 2016; 33◦C(Choi et al., 2012; Tagin et al., 2012). Hypothermia was Weeke et al., 2016), however, some report that aEEG remains less first demonstrated to improve survival in cases of cardiac arrest reliable than MRI, especially following hypothermia treatment (Bernard et al., 2002; Nikolov and Cunningham, 2003), and (Doyle et al., 2010; Weeke et al., 2016). The Thompson score, an has since been applied as a neuroprotective treatment in acute EEG measure of predictive neurodevelopment, is likely to remain neonatal HI injury patients (Gunn et al., 1997, 2005; Gunn and useful to clinicians (Thompson et al., 1997; Horn et al., 2016). Gunn, 1998; Shankaran et al., 2002, 2005; Eicher et al., 2005; This is by no means an exhaustive list of risk factors and signs of Gluckman et al., 2005; Jacobs et al., 2005, 2013; Shah et al., 2007; clinical concern that can occur during the early postnatal period Azzopardi et al., 2009; Shah, 2010). A recent meta-analysis found (Shalak and Perlman, 2004; Hagberg et al., 2015). that hypothermia carried out in over 1,200 infants reduced the Neonatal HI is the most common cause of death and disability rate of death and neurological handicaps at 18 months follow- in human neonates (Grow and Barks, 2002; Ferriero, 2004; Shalak up across all severity categories of neonatal HI injury (Tagin and Perlman, 2004), accounting for 23% of infant mortality et al., 2012). However, hypothermia alone is not sufficient to worldwide, and affecting 0.7–1.2 million infants annually (Lawn prevent all brain injury or neurological symptoms, highlighting et al., 2005; see Figure 1). In developed countries, incidence of HI the need for additional therapies to use in conjunction. Xenon gas injury has not decreased in the past two decades (Himmelmann administration is currently being trialed as an additive therapy et al., 2005; Vincer et al., 2006), remaining a significant cause alongside hypothermia (Hobbs et al., 2008; Thoresen et al., 2009; of fatality and disability. The frequency of motor and cognitive Johnston et al., 2011). There are currently no other licensed disorders linked to perinatal and early postnatal brain injury treatments available for neonatal HI. actually increased during the 1990s, and currently remains stable (Vincer et al., 2006; Robertson and Iwata, 2007; Wilson-Costello et al., 2007). Progress in assisted respiratory and intensive care technology has led to greater than 90% survival of infants born after gestational week 23 (Larroque et al., 2004; Fellman et al., 2010), perhaps accounting for the increased burden of disability within the population as mortality rates have decreased substantially. Amongst those who survive the initial injury, rates of disability remain high throughout life. Of patients surviving neonatal HI, 5–10% of infants demonstrate persistent motor deficits, and 20– 50% display sensory or cognitive abnormalities that persist to adolescence (Hack et al., 1992; Vohr et al., 2000; Volpe, 2001, 2012; Lee et al., 2013). A meta-analysis of seven studies including FIGURE 1 | Summary of Clinical Impact of Neonatal HI. This figures 386 infant patients investigated the average incidence of mortality summarizes the number of neonates affected by neonatal HI annually across