Elsevier

Experimental Neurology

Volume 252, February 2014, Pages 114-123
Experimental Neurology

Inhaled NO prevents hyperoxia-induced white matter damage in neonatal rats

https://doi.org/10.1016/j.expneurol.2013.11.025Get rights and content

Highlights

  • Postnatal hyperoxia induces injury on both developing brain and developing lung in neonatal rat.

  • Inhaled NO exposure attenuates white matter damage with significant behavioral impact.

  • Neuroprotective effects of inhaled NO appear unrelated to improvements in the histological markers of lung injury.

Abstract

White matter damage (WMD) and bronchopulmonary dysplasia (BPD) are the two main complications occurring in very preterm infants. Inhaled nitric oxide (iNO) has been proposed to promote alveolarization in the developing lung, and we have reported that iNO promotes myelination and induces neuroprotection in neonatal rats with excitotoxic brain damage. Our hypothesis is that, in addition to its pulmonary effects, iNO may be neuroprotective in rat pups exposed to hyperoxia. To test this hypothesis, we exposed rat pups to hyperoxia, and we assessed the impact of iNO on WMD and BPD.

Rat pups were exposed to either hyperoxia (80% FiO2) or to normoxia for 8 days. Both groups received iNO (5 ppm) or air. We assessed the neurological and pulmonary effects of iNO in hyperoxia-injured rat pups using histological, molecular and behavioral approaches.

iNO significantly attenuated the severity of hyperoxia-induced WMD induced in neonatal rats. Specifically, iNO decreased white matter inflammation, cell death, and enhanced the density of proliferating oligodendrocytes and oligodendroglial maturation. Furthermore, iNO triggered an early upregulation of P27kip1 and brain-derived growth factor (BDNF). Whereas hyperoxia disrupted early associative abilities, iNO treatment maintained learning scores to a level similar to that of control pups. In contrast to its marked neuroprotective effects, iNO induced only small and transient improvements of BPD.

These findings suggest that iNO exposure at low doses is specifically neuroprotective in an animal model combining injuries of the developing lung and brain that mimicked BPD and WMD in preterm infants.

Introduction

Bronchopulmonary dysplasia (BPD) and white matter damage (WMD) are the two most common complications of preterm birth. Their incidence reaches 20 to 40% of infants born below 28 weeks of gestation (Jobe, 2011, Volpe, 2009). Whereas advances in neonatal intensive care have resulted in a marked decrease in neonatal mortality, the incidence of both morbidities in these infants remains high. Several common risk factors, such as low gestational age, perinatal inflammation and excessive oxidative stress make more likely the devastating co-occurrence of BPD and WMD (Dammann et al., 2004). In addition, BPD increases the risk for cerebral palsy (CP), which is a common consequence of WMD in infants born prematurely. Among these common risk factors, an excessive release of free radicals induced by oxygen therapy in preterm neonates with respiratory distress was involved in the pathogenesis of WMD as well as BPD. Furthermore, recent experimental studies have supported that hyperoxia causes oxidative stress and triggers maturation-dependent cell death, maturation arrest of developing oligodendrocytes, and disruption of axon–oligodendrocyte integrity, all key features of WMD (Back et al., 2007, Gerstner et al., 2008, Ritter et al., 2013, Schmitz et al., 2011, Vottier et al., 2011). For these reasons, the design of therapeutic strategies that take into account both BPD and WMD is a highly relevant, to date poorly explored challenge.

In the present study, we focused on the therapeutic use of nitric oxide (NO) in neonates. NO is widely recognized as an important messenger and effector molecule in a variety of acute and chronic inflammation systems, and also as a mediator of vascular tone and tolerance to damage (Moncada et al., 1991, Toda and Okamura, 2003, Vaucher et al., 2000). Interestingly, NO is both a physiological mediator of the central nervous system and a key factor for lung angiogenesis and alveolarization, two developmental phenomena involved in BPD pathophysiology (Jobe, 2011, Yun et al., 1996). On the other hand, we have recently reported that inhaled NO (iNO) has several critical properties in the developing brain by promoting myelination and inducing neuroprotection against excitotoxic-induced brain injury and neonatal stroke (Charriaut-Marlangue et al., 2012, Charriaut-Marlangue et al., 2013, Olivier et al., 2010, Pansiot et al., 2010). Interestingly, similar results were reported in preclinical model of adult stroke (Terpolilli et al., 2012, Terpolilli et al., 2013). Thus, iNO appears to be a promising candidate for the prevention and/or the clinical management of WMD and BPD, but remains to be evaluated in an animal model mimicking simultaneously these two developmental diseases.

Here, we used a rat model of prolonged postnatal hyperoxia that induced BPD and WMD. We made the hypothesis that iNO, in addition to its potential effects on lung injury, may be neuroprotective in rat pups exposed to hyperoxia. The present results showed that iNO induces neuroprotection with a significant effect at both histopathological and behavioral levels, whereas it had only transient and mild effects on BPD.

Section snippets

Experimental protocol and gas exposure

This study was approved by the National Institute of Health and Medical Research and complied with the instructions of the Institutional Animal Care and Use Committees INSERM 676—Paris. The day before delivery, pregnant rats (Sprague–Dawley, Janvier S.A.S., Le Genest-St-Isle, France) were placed in a transparent Plexiglas chamber supplied with a gas mixture that either induced hyperoxia (FiO2 = 80 +/− 0.5%) until postnatal day (P)7 or maintained normoxia (FiO2 = 21 +/− 0.5%). Hyperoxia exposure of

Body, lung and brain phenotypes induced by postnatal hyperoxia

Postnatal hyperoxia resulted in a pronounced decrease in body weight at both P3 and P10 (Supplemental Table S3), as well as increased postnatal mortality rates overall (15.5% vs. 1% in controls, p < 0.001). Blood gas analyses performed showed that blood concentrations of pO2 and fraction of oxyhemoglobin (fO2Hb) were significantly elevated no longer than 1 h after the onset of hyperoxia exposure (Supplemental Fig. S1). Hyperoxic condition also induced a significant but transient increased in pCO2

Discussion

In this study, we developed an animal model that combines the two main complications associated with prematurity, BPD and WMD, which share several risk factors including low gestational age, inflammation and oxidative stress. Using this model, we demonstrated that iNO exposure during the first postnatal week significantly attenuated the main features of hyperoxia-induced WMD in neonatal rats and the devastating effects of hyperoxia on learning abilities.

Our animal model simultaneously displayed

Role of funding source

This study was financially supported by the Institut National Sur la Recherche Médicale (INSERM), the INSERM AVENIR Program and the Mairie de Paris. Ikaria Inc. partially supports the experimental research program of Prof. Olivier Baud and co-workers with respect to inhaled nitric oxide. However, Ikaria Inc. has taken part neither in the study design nor in the data analysis.

Acknowledgments

We are grateful to Mathias Schroijen for his help in cognitive assessment. This study has been supported by the Prime Brain project and de Spoelberch Foundation.

References (46)

  • P. Bonnin et al.

    Impact of intracranial blood-flow redistribution on stroke size during ischemia-reperfusion in 7-day-old rats

    J Neurosci Methods

    (2011 May 15)
  • C. Charriaut-Marlangue et al.

    Inhaled nitric oxide reduces brain damage by collateral recruitment in a neonatal stroke model

    Stroke

    (2012)
  • C. Charriaut-Marlangue et al.

    Nitric oxide signaling in the brain: A new target for inhaled nitric oxide?

    Ann. Neurol.

    (2013)
  • C.C. Chiueh

    Neuroprotective properties of nitric oxide

    Ann. N. Y. Acad. Sci.

    (1999)
  • F.S. Cole et al.

    NIH Consensus Development Conference statement: inhaled nitric-oxide therapy for premature infants

    Pediatrics

    (2011)
  • O. Dammann et al.

    Lung and brain damage in preterm newborns. Are they related? How? Why?

    Biol. Neonate

    (2004)
  • M.S. Dunnill

    Quantitative methods in the study of pulmonary pathology

    Thorax

    (1962)
  • J.L. Emery et al.

    The number of alveoli in the terminal respiratory unit of man during late intrauterine life and childhood

    Arch. Dis. Child.

    (1960)
  • R.H. Fontaine et al.

    Vulnerability of white matter towards antenatal hypoxia is linked to a species-dependent regulation of glutamate receptor subunits

    Proc. Natl. Acad. Sci. U. S. A.

    (2008)
  • B. Gerstner et al.

    Hyperoxia causes maturation-dependent cell death in the developing white matter

    J. Neurosci.

    (2008)
  • R.L. Haynes et al.

    Oxidative and nitrative injury in periventricular leukomalacia: a review

    Brain Pathol.

    (2005)
  • Z. Huang et al.

    Effects of cerebral ischemia in mice deficient in neuronal nitric oxide synthase

    Science

    (1994)
  • C. Ikonomidou et al.

    Neuronal death and oxidative stress in the developing brain

    Antioxid. Redox Signal.

    (2011)
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