Neuroprotective effect of inhaled nitric oxide on excitotoxic-induced brain damage in neonatal rat

Association between short-term air pollution exposure and traumatic intracranial hemorrhage: pilot evidence from Taiwan

Introduction

The detrimental effects of air pollution on the brain are well established. However, few studies have examined the effect of air pollution on traumatic brain injury (TBI). This pilot study evaluated the association between short-term air pollution exposure and traumatic intracranial hemorrhage (TIH).

Methods

Hospital data of patients with TBI following road traffic accidents were retrospectively collected from the electronic medical records at five trauma centers in Taiwan between 1 January and 31 December 2017. TIH was employed as an outcome measure. All road accident locations were geocoded, and air quality data were collected from the nearest monitoring stations. Air pollutants were entered into five multivariable models. A sensitivity analysis was performed on patients who are vulnerable to suffering TBI after road accidents, including motorcyclists, bicyclists, and pedestrians.

Results

Among 730 patients with TBI, 327 had TIH. The ages of ≥65 [odds ratio (OR), 3.24; 95% confidence interval (CI), 1.85-5.70], 45-64 (OR, 2.61; 95% CI, 1.64-4.15), and 25-44 (OR, 1.79; 95% CI, 1.13-2.84) years were identified as significant risk factors in the multivariable analysis. In the best-fit multivariable model, exposure to higher concentrations of particulate matter ≤ 2.5 μm in aerodynamic diameter (PM_2.5) was associated with an elevated TIH risk (OR, 1.50; 95% CI, 1.17-1.94). The concentration of nitrogen oxides (NO_X) did not increase the risk of TIH (OR, 0.45; 95% CI, 0.32-0.61). After categorizing the air pollution concentration according to quartile, the trend tests in the multivariate model showed that the concentrations of PM_2.5 and NO_X were significant (p = 0.017 and p < 0.001, respectively). There was a negative borderline significant association between temperature and TIH risk (OR, 0.75; 95% CI, 0.56-1.00, p = 0.05). Notably, the single-vehicle crash was a significant risk factor (OR, 2.11; 95% CI, 1.30-3.42) for TIH.

Discussion

High PM_2.5 concentrations and low temperatures are risk factors for TIH in patients with TBI. High NO_X concentrations are associated with a lower TIH risk.

Inhaled Nitric Oxide Promotes Angiogenesis in the Rodent Developing Brain

Inhaled nitric oxide (iNO) is a therapy used in neonates with pulmonary hypertension. Some evidence of its neuroprotective properties has been reported in both mature and immature brains subjected to injury. NO is a key mediator of the VEGF pathway, and angiogenesis may be involved in the reduced vulnerability to injury of white matter and the cortex conferred by iNO. Here, we report the effect of iNO on angiogenesis in the developing brain and its potential effectors. We found that iNO promotes angiogenesis in the developing white matter and cortex during a critical window in P14 rat pups. This shift in the developmental program of brain angiogenesis was not related to a regulation of NO synthases by exogenous NO exposure, nor the VEGF pathway or other angiogenic factors. The effects of iNO on brain angiogenesis were found to be mimicked by circulating nitrate/nitrite, suggesting that these carriers may play a role in transporting NO to the brain. Finally, our data show that the soluble guanylate cyclase/cGMP signaling pathway is likely to be involved in the pro-angiogenetic effect of iNO through thrombospondin-1, a glycoprotein of the extracellular matrix, inhibiting soluble guanylate cyclase through CD42 and CD36. In conclusion, this study provides new insights into the biological basis of the effect of iNO in the developing brain.

Capsaicin attenuates excitotoxic-induced neonatal brain injury and brain mast cell-mediated neuroinflammation in newborn rats

Excitotoxicity and neuroinflammation are key contributors to perinatal brain injuries. Capsaicin, an active ingredient of chili peppers, is a potent exogenous agonist for transient receptor potential vanilloid 1 receptors. Although the neuroprotective and anti-inflammatory effects of capsaicin are well-documented, its effects on excitotoxic-induced neonatal brain injury and neuroinflammation have not previously been investigated. The aim of this study was to investigate the effects of capsaicin on brain damage, brain mast cells, and inflammatory mediators in a model of ibotenate-induced excitotoxic brain injury in neonatal rats. P5 rat-pups were intraperitoneally injected with vehicle, 0.2-, 1-, and 5-mg/kg doses of capsaicin, or the NMDA (N-methyl-d-aspartate) receptor antagonist MK-801 (dizocilpine), 30 min before intracerebral injection of 10 μg ibotenate. The naive-control group received no substance administration. The rat pups were sacrificed one or five days after ibotenate injection. Levels of activin A and interleukin (IL)-1β, IL-6, and IL-10 in brain tissue were measured using the enzyme-linked immunosorbent assay method. Cortex and white matter thicknesses, white matter lesion size, and mast cells were evaluated in brain sections stained with cresyl-violet or toluidine-blue. Capsaicin improved ibotenate-induced white matter lesions and cerebral white and gray matter thicknesses in a dose-dependent manner. In addition, it suppressed the degranulation and increased number of brain mast cells induced by ibotenate. Capsaicin also reduced the excitotoxic-induced production of neuronal survival factor activin A and of the pro-inflammatory cytokines IL-1β, and IL-6 in brain tissue. However, IL-10 levels were not altered by the treatments. MK-801, as a positive control, reversed all these ibotenate-induced changes, further confirming the success of the model. Our findings provide, for the first time, evidence for the therapeutic effects of capsaicin against excitotoxic-induced neonatal brain injury and brain mast cell-mediated neuroinflammation. Capsaicin may therefore be a promising candidate in the prevention and/or reduction of neonatal brain damage.

NOS1 mutations cause hypogonadotropic hypogonadism with sensory and cognitive deficits that can be reversed in infantile mice

The nitric oxide (NO) signaling pathway in hypothalamic neurons plays a key role in the regulation of the secretion of gonadotropin-releasing hormone (GnRH), which is crucial for reproduction. We hypothesized that a disruption of neuronal NO synthase (NOS1) activity underlies some forms of hypogonadotropic hypogonadism. Whole-exome sequencing was performed on a cohort of 341 probands with congenital hypogonadotropic hypogonadism to identify ultrarare variants in NOS1. The activity of the identified NOS1 mutant proteins was assessed by their ability to promote nitrite and cGMP production in vitro. In addition, physiological and pharmacological characterization was carried out in a Nos1-deficient mouse model. We identified five heterozygous NOS1 loss-of-function mutations in six probands with congenital hypogonadotropic hypogonadism (2%), who displayed additional phenotypes including anosmia, hearing loss, and intellectual disability. NOS1 was found to be transiently expressed by GnRH neurons in the nose of both humans and mice, and Nos1 deficiency in mice resulted in dose-dependent defects in sexual maturation as well as in olfaction, hearing, and cognition. The pharmacological inhibition of NO production in postnatal mice revealed a critical time window during which Nos1 activity shaped minipuberty and sexual maturation. Inhaled NO treatment at minipuberty rescued both reproductive and behavioral phenotypes in Nos1-deficient mice. In summary, lack of NOS1 activity led to GnRH deficiency associated with sensory and intellectual comorbidities in humans and mice. NO treatment during minipuberty reversed deficits in sexual maturation, olfaction, and cognition in Nos1 mutant mice, suggesting a potential therapy for humans with NO deficiency.

Neuroprotective role of nitric oxide inhalation and nitrite in a Neonatal Rat Model of Hypoxic-Ischemic Injury

Background

There is evidence from various models of hypoxic-ischemic injury (HII) that nitric oxide (NO) is protective. We hypothesized that either inhaled NO (iNO) or nitrite would alleviate brain injury in neonatal HII via modulation of mitochondrial function.

Methods

We tested the effects of iNO and nitrite on the Rice-Vannucci model of HII in 7-day-old rats. Brain mitochondria were isolated for flow cytometry, aconitase activity, electron paramagnetic resonance, and Seahorse assays.

Results

Pretreatment of pups with iNO decreased survival in the Rice-Vannucci model of HII, while iNO administered post-insult did not. MRI analysis demonstrated that pre-HII iNO at 40 ppm and post-HII iNO at 20 ppm decreased the brain lesion sizes from 6.3±1.3% to 1.0±0.4% and 1.8±0.8%, respectively. Intraperitoneal nitrite at 0.165 μg/g improved neurobehavioral performance but was harmful at higher doses and had no effect on brain infarct size. NO reacted with complex IV at the heme a₃ site, decreased the oxidative stress of mitochondria challenged with anoxia and reoxygenation, and suppressed mitochondrial oxygen respiration.

Conclusions

This study suggests that iNO administered following neonatal HII may be neuroprotective, possibly via its modulation of mitochondrial function.

Nitric oxide and the brain. Part 1: Mechanisms of regulation, transport and effects on the developing brain

Apart from its known actions as a pulmonary vasodilator, nitric oxide (NO) is a key signal mediator in the neonatal brain. Despite the extensive use of NO for pulmonary artery hypertension (PAH), its actions in the setting of brain hypoxia and ischemia, which co-exists with PAH in 20-30% of affected infants, are not well established. This review focuses on the mechanisms of actions of NO covering the basic, translational, and clinical evidence of its neuroprotective and neurotoxic properties. In this first part, we present the physiology of transport and delivery of NO to the brain and the regulation of cerebrovascular and systemic circulation by NO, as well the role of NO in the development of the immature brain. IMPACT: NO can be transferred from the site of production to the site of action rapidly and affects the central nervous system. Inhaled NO (iNO), a commonly used medication, can have significant effects on the neonatal brain. NO regulates the cerebrovascular and systemic circulation and plays a role in the development of the immature brain. This review describes the properties of NO under physiologic conditions and under stress. The impact of this review is that it describes the effects of NO, especially regarding the vulnerable neonatal brain, and helps understand the conditions that could contribute to neurotoxicity or neuroprotection.

Nitric oxide and the brain. Part 2: Effects following neonatal brain injury-friend or foe?

Nitric oxide (NO) has critical roles in a wide variety of key biologic functions and has intricate transport mechanisms for delivery to key distal tissues under normal conditions. However, NO also plays important roles during disease processes, such as hypoxia-ischemia, asphyxia, neuro-inflammation, and retinopathy of prematurity. The effects of exogenous NO on the developing neonatal brain remain controversial. Inhaled NO (iNO) can be neuroprotective or toxic depending on a variety of factors, including cellular redox state, underlying disease processes, duration of treatment, and dose. This review identifies key gaps in knowledge that should prompt further investigation into the possible role of iNO as a therapeutic agent after injury to the brain. IMPACT: NO is a key signal mediator in the neonatal brain with neuroprotective and neurotoxic properties. iNO, a commonly used medication, has significant effects on the neonatal brain. Dosing, duration, and timing of administration of iNO can affect the developing brain. This review article summarizes the roles of NO in association with various disease processes that impact neonates, such as brain hypoxia-ischemia, asphyxia, retinopathy of prematurity, and neuroinflammation. The impact of this review is that it clearly describes gaps in knowledge, and makes the case for further, targeted studies in each of the identified areas.

eNOS-dependent S-nitrosylation of the NF-κB subunit p65 has neuroprotective effects

Cell death by glutamate excitotoxicity, mediated by N-methyl-D-aspartate (NMDA) receptors, negatively impacts brain function, including but not limited to hippocampal neurons. The NF-κB transcription factor (composed mainly of p65/p50 subunits) contributes to neuronal death in excitotoxicity, while its inhibition should improve cell survival. Using the biotin switch method, subcellular fractionation, immunofluorescence, and luciferase reporter assays, we found that NMDA-stimulated NF-κB activity selectively in hippocampal neurons, while endothelial nitric oxide synthase (eNOS), an enzyme expressed in neurons, is involved in the S-nitrosylation of p65 and consequent NF-κB inhibition in cerebrocortical, i.e., resistant neurons. The S-nitro proteomes of cortical and hippocampal neurons revealed that different biological processes are regulated by S-nitrosylation in susceptible and resistant neurons, bringing to light that protein S-nitrosylation is a ubiquitous post-translational modification, able to influence a variety of biological processes including the homeostatic inhibition of the NF-κB transcriptional activity in cortical neurons exposed to NMDA receptor overstimulation.

The Effects of Crinum asiaticum var. japonicum Baker Seeds on Neuroprotection and Antineuroinflammation in Neuronal Cell Lines

Crinum asiaticum var. japonicum Baker is a Korean herbal medicine that is traditionally prescribed for reducing fever and inflammation. In the present study, we investigated if the ethanol extract of C. asiaticum seeds (ECAS) influences the hallmarks of Alzheimer’s disease (AD) pathogenesis. ECAS markedly inhibited the activity of acetylcholinesterase (AChE). Concurrent treatment with hydrogen peroxide (H2O2) and ECAS significantly prevented the neuronal cell death by regulating phosphorylation of cyclic adenosine monophosphate response element-binding protein and p38 mitogen-activated protein kinase. ECAS revealed antineuroinflammatory effects by inhibiting nitric oxide production and suppressing inducible nitric oxide expression in lipopolysaccharide-stimulated BV-2 microglia. Furthermore, the high-performance liquid chromatographic analysis determined lycorine as a standard compound of ECAS. Our data suggest that ECAS has inhibitory effects on AD pathogenesis such as AChE activation, neuronal damage, and neuroinflammation.

Updates on Versatile Role of Putative Gasotransmitter Nitric Oxide: Culprit in Neurodegenerative Disease Pathology

Nitric oxide (NO) is a versatile gasotransmitter that contributes in a range of physiological and pathological mechanims depending on its cellular levels. An appropriate concentration of NO is essentially required for cellular physiology; however, its increased level triggers pathological mechanisms like altered cellular redox regulation, functional impairment of mitochondrion, and modifications in cellular proteins and DNA. Its increased levels also exhibit post-translational modifications in protein through S-nitrosylation of their thiol amino acids, which critically affect the cellular physiology. Along with such modifications, NO could also nitrosylate the endoplasmic reticulum (ER)-membrane located sensors of ER stress, which subsequently affect the cellular protein degradation capacity and lead to aggregation of misfolded/unfolded proteins. Since protein aggregation is one of the pathological hallmarks of neurodegenerative disease, NO should be taken into account during development of disease therapies. In this Review, we shed light on the diverse role of NO in both cellular physiology and pathology and discussed its involvement in various pathological events in the context of neurodegenerative diseases.

Clinical use of inhaled nitric oxide: Local and systemic applications

Upon the FDA approval for inhaled nitric oxide (iNO) in 1999 to treat persistent pulmonary hypertension in neonates, iNO has proven to be a beneficial therapeutic in multiple diseases. We aim to review applications of iNO that have modeled its protective and therapeutic attributes, as well as highlight preliminary studies that could allude to future avenues of use. Numerous publications have reported specific incidences where iNO therapy has proved advantageous, while some applications have potential after further validation. Establishing guidelines on dosing, duration, and defined clinical uses are crucial for the future of iNO. Delivery of iNO has been controlled by a sole distributor, and comes with high cost, and lack of portability. A shift in patents has allowed for new designs for iNO device synthesis, with many new developments of iNO medical devices that will likely change the future of iNO in a medical setting.

Modulation of Microglial Activation by Adenosine A2a Receptor in Animal Models of Perinatal Brain Injury

Neuroinflammation has a key role in the pathogenesis of perinatal brain injury. Caffeine, a nonspecific antagonist of adenosine receptors (ARs), is widely used to treat apnea of prematurity and has been linked to a decrease in the incidence of cerebral palsy in premature infants. The mechanisms explaining its neuroprotective effect have not yet been elucidated. The objective of this study was to characterize the expression of adenosine and ARs in two neonatal rat models of neuroinflammation and to determine the effect of A2aR blockade on microglial activation assessed through inflammatory cytokine gene expression. We have used two rat models of microglial activation: the gestational low protein diet (LPD) model, associated with chronic brain injury, and postnatal ibotenate intracerebral injections, responsible for acute excitotoxicity injury. Adenosine blood levels have been measured by Tandem Mass Spectrometry. The expression of ARs in vivo was assessed using qPCR and immunohistochemistry. In vivo models have been replicated in vitro on primary microglial cell cultures exposed to A2aR agonist CGS-21680 or antagonist SCH-58261. The effects of these treatments have been assessed on the M1/M2 cytokine expressions measured by RT-qPCR. LPD during pregnancy was associated with higher adenosine levels in pups at postnatal day 1 and 4. A2aR mRNA expression was significantly increased in both cortex and magnetically sorted microglial cells from LPD animals compared to controls. CD73 expression, responsible for extracellular production of brain adenosine, was significantly increased in LPD cortex and sorted microglia cells. Moreover, CD73 protein level was increased in ibotenate treated animals. In vitro experiments confirmed that LPD or control microglial cells exposed to ibotenate display an increased expression, at both protein and molecular levels, of A2aR and M1 markers (IL-1β, IL-6, iNOS, TNFα). This pro-inflammatory profile was significantly reduced by SCH-58261, which reduces M1 markers in both LPD and ibotenate-exposed cells, with no effect on control cells. In the same experimental conditions, a partial increased of M1 cytokines was observed in response to A2aR agonist CGS-21680. These results support the involvement of adenosine and particularly of its receptor A2aR in the regulation of microglia in two different animal models of neuroinflammation.

Intracarotid Sodium Nitroprusside on Fifth Post Ischemic Stroke Day in Middle Cerebral Artery Occlusion Rat Model

INTRODUCTION

Ischemic stroke at later stages (>4.5 hour) have very few treatment options left. In those cases Nitric Oxide (NO) may provide promising results. NO is active in signaling pathways. Sodium Nitroprusside (SNP), a NO donor was tested earlier in rat Middle Cerebral Artery Occlusion (MCAO) model in early stages (5-60 minutes) and found useful but in delayed stroke cases (60-120 minutes) found useless. This was due to local inducible Nitric Oxide Synthase Enzyme (iNOS) and superoxide (causes destructive effect) formation which was skipped.

AIM

To evaluate the effect of Intracarotid Sodium Nitroprusside (ICSNP) in MCAO rat model of ischemic stroke (I/R model) fifth post ischemic stroke day.

MATERIALS AND METHODS

A total of 24 Sprague Dawley rats, weighing 250 gm to 280 gm, at CDRI-Lucknow, India were used. Rats were divided in three groups. Group A (n=4) were taken as sham with standard procedure but without any injection on fifth day, Group B (n=8) as control with injection of saline on fifth day and Group C (n=12) received SNP at dose of 3 mcg/kg/minute given directly in internal carotid artery via External Carotid Artery (ECA) with a modified intraluminal stump technique as Ischemia/Reperfusion (I/R) in ipsilateral MCAO at intracarotid artery region as a single dose therapy on fifth day and then wound was closed. Waited for full recovery for two hours, then neurobehavioural assessment scores were noted. Thereafter, the brains were quickly removed and sliced at 2 mm intervals. Animals showing no sign of neurological deficit, were excluded from the study. Tested animals were compared with control animals for neurological deficit, percentage of infarction by 2,3,5-Triphenyl Tetrazolium Chloride (TTC) staining, nNOS expression and scores were summed up. The statistical analysis was done by Newman-Keuls test, Graph Pad prism (version.5.0) and p<0.05 was considered statistically significant.

RESULTS

ICSNP group (Group C) showed a good reduction in the cerebral infarction of 53.42% as compared to control (Group B). Group A mean change in Newman-Keuls test and Graph Pad prism (version.5.0) was showing increase of 1.44 points/6.55%, compared to Group B decrease of 0.7 points. A 60% decrease in ischemic zone noted in Group A.

CONCLUSION

The use of single dose ICSNP is beneficial (53.42%) in fifth post stroke day.

Pharmacological approaches to intervention in hypomyelinating and demyelinating white matter pathology

White matter disease afflicts both developing and mature central nervous systems. Both cell intrinsic and extrinsic dysregulation result in profound changes in cell survival, axonal metabolism and functional performance. Experimental models of developmental white matter (WM) injury and demyelination have not only delineated mechanisms of signaling and inflammation, but have also paved the way for the discovery of pharmacological approaches to intervention. These reagents have been shown to enhance protection of the mature oligodendrocyte cell, accelerate progenitor cell recruitment and/or differentiation, or attenuate pathological stimuli arising from the inflammatory response to injury. Here we highlight reports of studies in the CNS in which compounds, namely peptides, hormones, and small molecule agonists/antagonists, have been used in experimental animal models of demyelination and neonatal brain injury that affect aspects of excitotoxicity, oligodendrocyte development and survival, and progenitor cell function, and which have been demonstrated to attenuate damage and improve WM protection in experimental models of injury. The molecular targets of these agents include growth factor and neurotransmitter receptors, morphogens and their signaling components, nuclear receptors, as well as the processes of iron transport and actin binding. By surveying the current evidence in non-immune targets of both the immature and mature WM, we aim to better understand pharmacological approaches modulating endogenous oligodendroglia that show potential for success in the contexts of developmental and adult WM pathology. This article is part of the Special Issue entitled 'Oligodendrocytes in Health and Disease'.

Melatonin reduces excitotoxic blood-brain barrier breakdown in neonatal rats

The blood-brain barrier (BBB) is a complex structure that protects the central nervous system from peripheral insults. Understanding the molecular basis of BBB function and dysfunction holds significant potential for future strategies to prevent and treat neurological damage. The aim of our study was (1) to investigate BBB alterations following excitotoxicity and (2) to test the protective properties of melatonin. Ibotenate, a glutamate analog, was injected intracerebrally in postnatal day 5 (P5) rat pups to mimic excitotoxic injury. Animals were than randomly divided into two groups, one receiving intraperitoneal (i.p.) melatonin injections (5mg/kg), and the other phosphate buffer saline (PBS) injections. Pups were sacrificed 2, 4 and 18 h after ibotenate injection. We determined lesion size at 5 days by histology, the location and organization of tight junction (TJ) proteins by immunohistochemical studies, and BBB leakage by dextran extravasation. Expression levels of BBB genes (TJs, efflux transporters and detoxification enzymes) were determined in the cortex and choroid plexus by quantitative PCR. Dextran extravasation was seen 2h after the insult, suggesting a rapid BBB breakdown that was resolved by 4h. Extravasation was significantly reduced in melatonin-treated pups. Gene expression and immunohistochemical assays showed dynamic BBB modifications during the first 4h, partially prevented by melatonin. Lesion-size measurements confirmed white matter neuroprotection by melatonin. Our study is the first to evaluate BBB structure and function at a very early time point following excitotoxicity in neonates. Melatonin neuroprotects by preventing TJ modifications and BBB disruption at this early phase, before its previously demonstrated anti-inflammatory, antioxidant and axonal regrowth-promoting effects.

Impact of inhaled nitric oxide on white matter damage in growth-restricted neonatal rats

BACKGROUND

Fetal growth restriction is the second leading cause of perinatal morbidity and mortality, and neonates with intrauterine growth retardation (IUGR) have increased neurocognitive and neuropsychiatric morbidity. These neurocognitive impairments are mainly related to injury of the developing brain associated with IUGR. Growing evidence from preclinical models of brain injury in both adult and neonatal rodents supports the view that nitric oxide can promote neuroprotection.

METHODS

In a model of IUGR induced by protracted gestational hypoxia leading to diffuse white matter injury, we subjected neonatal rats to low dose (5 ppm) but long-lasting (7 d) exposure to inhaled NO (iNO). We used a combination of techniques, including immunohistochemistry, quantitative PCR, and cognitive assessment, to assess neuroprotection.

RESULTS

Antenatal hypoxia-induced IUGR was associated with severe neuroinflammation and delayed myelination. iNO exposure during the first postnatal week significantly attenuated cell death and microglial activation, enhanced oligodendroglial proliferation and finally improved myelination. Remarkably, iNO was associated with the specific upregulation of P27kip1, which initiates oligodendrocytic differentiation. Finally, iNO counteracted the deleterious effects of hypoxia on learning abilities.

CONCLUSION

This study provides new evidence that iNO could be effective in preventing brain damage and/or enhancing repair of the developing brain.

Nitric Oxide Pathway and Proliferation of Neural Progenitors in the Neonatal Rat

Several lines of evidence demonstrate that inhaled nitric oxide (iNO) not only acts locally on the pulmonary vasculature but also has remote effects on the mature and developing brain under basal or pathological conditions by modulating cerebral blood flow and microvascularization, white matter maturation, inflammation, and subsequent brain repair. Previously, consistent studies demonstrated that increased levels of guanosine 3',5' cyclic monophosphate (cGMP), the main effector of biological effect induced by nitric oxide (NO), significantly augment proliferation and neuronal differentiation of adult neural progenitor cells (NPCs). In the present study, we ask the question whether iNO could promote the proliferation of NPCs in the uninjured developing brain. We first reported that iNO exposure at a concentration of 20 ppm during the first 7 days of life was associated with a significant but transient elevation of brain cGMP concentration 2 h after the onset of iNO exposure and a subsequent increase in myelin content of the developing white matter at postnatal day (P) 10. Using BrDu labelling and colabelling with specific cell-type markers we found that iNO exposure of rat pups results in an increased NPC proliferation in several layers of the subventricular zone (SVZ) at both early (30 h) and late (P7) time points. These proliferating NPCs were found to be sustainably viable and subsequently differentiated into oligodendroglial cells in the developing white matter and cortex. We also found that NG2 immunoreactivity around vessel walls, labeling pericyte cells, was increased in NO-exposed rat pups in the periventricular SVZ. In conclusion, iNO appears to act on oligodendrocyte progenitor cells, leading to increased density of mature oligodendrocytes and myelin content in the immature rat brain.

The role of the nitric oxide pathway in brain injury and its treatment--from bench to bedside

Nitric oxide (NO) is a key signalling molecule in the regulation of cerebral blood flow. This review summarises current evidence regarding the role of NO in the regulation of cerebral blood flow at rest, under physiological conditions, and after brain injury, focusing on subarachnoid haemorrhage, traumatic brain injury, and ischaemic stroke and following cardiac arrest. We also review the role of NO in the response to hypoxic insult in the developing brain. NO depletion in ischaemic brain tissue plays a pivotal role in the development of subsequent morbidity and mortality through microcirculatory disturbance and disordered blood flow regulation. NO derived from endothelial nitric oxide synthase (eNOS) appears to have neuroprotective properties. However NO derived from inducible nitric oxide synthase (iNOS) may have neurotoxic effects. Cerebral NO donor agents, for example sodium nitrite, appear to replicate the effects of eNOS derived NO, and therefore have neuroprotective properties. This is true in both the adult and immature brain. We conclude that these agents should be further investigated as targeted pharmacotherapy to protect against secondary brain injury.

Impact of inhaled nitric oxide on the sulfatide profile of neonatal rat brain studied by TOF-SIMS imaging

Despite advances in neonatal intensive care leading to an increased survival rate in preterm infants, brain lesions and subsequent neurological handicaps following preterm birth remain a critical issue. To prevent brain injury and/or enhance repair, one of the most promising therapies investigated in preclinical models is inhaled nitric oxide (iNO). We have assessed the effect of this therapy on brain lipid content in air- and iNO-exposed rat pups by mass spectrometry imaging using a time-of-flight secondary ion mass spectrometry (TOF-SIMS) method. This technique was used to map the variations in lipid composition of the rat brain and, particularly, of the white matter. Triplicate analysis showed a significant increase of sulfatides (25%–50%) in the white matter on Day 10 of life in iNO-exposed animals from Day 0–7 of life. These robust, repeatable and semi-quantitative data demonstrate a potent effect of iNO at the molecular level.

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

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.

Two-year outcomes of a randomized controlled trial of inhaled nitric oxide in premature infants

BACKGROUND AND OBJECTIVES

The European Union Nitric Oxide trial was designed to assess the potential benefits of inhaled nitric oxide (iNO) compared with placebo in infants with respiratory failure. This follow-up study evaluated respiratory, neurodevelopmental, and other outcomes for infants entered into the European Union Nitric Oxide trial to age 2 years.

METHODS

In a multicenter, randomized, double-blind study, preterm infants born at <29 weeks' gestation with moderate respiratory failure were allocated to receive iNO (5 ppm) or placebo for 7 to 21 days. Subjects underwent assessments at 1 and 2 years corrected for prematurity.

RESULTS

At 36 weeks' postmenstrual age, 696 of 792 infants were alive; 4 in the iNO arm subsequently died before age 2 years compared with 7 in the control arm. We evaluated 95% of the survivors at 12 months and 90% at 2 years. In the iNO arm, 244 of 363 (67.2%) infants had survived without disability at age 2 years compared with 270 of 374 (72.2%) who received placebo (P = .094). Mean (SD) cognitive composite scores (Bayley Scales of Infant and Toddler Development, third edition) were 94 (13) in the iNO group and 95 (14) in the placebo group; in the iNO group, 19% scored <85 and 9.5% developed cerebral palsy compared with 13.3% and 9%, respectively. There were no significant differences in hospitalizations overall or due to respiratory illness in use of home oxygen therapy or respiratory medications, in growth, or in other health outcomes.

CONCLUSIONS

At 2 years of age, low-dose (5 ppm) iNO started early (<24 hours after birth) for a median of 20 days did not affect neurodevelopmental or other health outcomes.

Targeting gaseous molecules to protect against cerebral ischaemic injury: mechanisms and prospects

1. Ischaemic brain injury is a leading cause of death and disability in many countries. However, the pathological mechanisms underlying ischaemic brain injury, including oxidative stress, calcium overload, excitotoxicity and neuronal apoptosis, are perplexing and this makes it difficult to find effective novel drugs for the treatment of the condition. 2. Recently, gaseous molecules such as nitric oxide (NO), carbon monoxide (CO), hydrogen sulphide (H(2)S) and hydrogen (H(2)) have attracted considerable interest because of their physiological and pathophysiological roles in various body systems. Emerging evidence indicates that gaseous molecules are involved in the pathological processes of ischaemic brain damage. 3. In the present review, we summarize evidence regarding the involvement of gaseous molecules in ischaemic brain injury and discuss the therapeutic potential of targeting gaseous molecules. 4. Collectively, the available data suggest that the application of these biological gas molecules and their pharmacological regulators may be a potential therapeutic approach for the treatment of ischaemic brain injury.

Inhaled Nitric Oxide Reduces Brain Damage by Collateral Recruitment in a Neonatal Stroke Model

Background and Purpose—

We recently demonstrated that endogenous nitric oxide (NO) modulates collateral blood flow in a neonatal stroke model in rats. The inhalation of NO (iNO) has been found to be neuroprotective after ischemic brain damage in adults. Our objective was to examine whether iNO could modify cerebral blood flow during ischemia–reperfusion and reduce lesions in the developing brain.

Methods—

In vivo variations in cortical NO concentrations occurring after 20-ppm iNO exposure were analyzed using the voltammetric method in P7 rat pups. Inhaled NO-mediated blood flow velocities were measured by ultrasound imaging with sequential Doppler recordings in both internal carotid arteries and the basilar trunk under basal conditions and in a neonatal model of ischemia–reperfusion. The hemodynamic effects of iNO (5 to 80 ppm) were correlated with brain injury 48 hours after reperfusion.

Results—

Inhaled NO (20 ppm) significantly increased NO concentrations in the P7 rat cortex and compensated for the blockade of endogenous NO synthesis under normal conditions. Inhaled NO (20 ppm) during ischemia increased blood flow velocities and significantly reduced lesion volumes by 43% and cellular damage. In contrast, both 80 ppm iNO given during ischemia and 5 or 20 ppm iNO given 30 minutes after reperfusion were detrimental.

Conclusions—

Our findings strongly indicate that, with the appropriate timing, 20 ppm iNO can be transported into the P7 rat brain and mediated blood flow redistribution during ischemia leading to reduced infarct volume and cell injury.

Neuroprotective effects of the sigma-1 receptor ligand PRE-084 against excitotoxic perinatal brain injury in newborn mice

Excessive glutamate release followed by N-methyl-D-aspartate receptor (NMDAR) activation plays a crucial role in perinatal brain injury. We have previously shown that dextromethorphan, a low-affinity NMDAR antagonist with anti-inflammatory properties, is neuroprotective against neonatal excitotoxic brain injury. Of interest, dextromethorphan is also a sigma-1 receptor (σ1R) agonist. The pharmacologic class of σ1R agonists has yielded propitious results in various animal models of adult central nervous system pathology. In an established neonatal mouse model of excitotoxic brain injury, we evaluated the effect of the selective σ1R agonist 2-(4-morpholinethyl) 1-phenylcyclohexanecarboxylate (PRE-084). A single intraperitoneal injection of 0.1 μg/g (low dose) or 10 μg/g (high dose) bodyweight (bw) PRE-084, given 1h after the excitotoxic insult, significantly reduced lesion size in cortical gray matter 24 h and 120 h after the insult. Repetitive injections of 0.1 μg/g PRE-084 proved to be equally effective. PRE-084 treatment resulted in a decrease in cell death indicated by reduced TUNEL positivity and caspase-3 activation. Furthermore, it lowered the number of isolectin B4-positive, activated microglial cells. PRE-084 had no effect on developmental apoptosis in the undamaged brain. In vitro findings in primary hippocampal neurons suggest that PRE-084 treatment provides partial protection against glutamate induced morphological and functional changes. For excitotoxicity as playing a crucial role in the pathogenesis of perinatal brain injury, we demonstrate for the first time that systemic treatment with the highly selective σ1R agonist PRE-084 protects against NMDAR-mediated excitotoxic brain damage.

Antenatal insults modify newborn olfactory function by nitric oxide produced from neuronal nitric oxide synthase

Newborn feeding, maternal, bonding, growth and wellbeing depend upon intact odor recognition in the early postnatal period. Antenatal stress may affect postnatal odor recognition. We investigated the exact role of a neurotransmitter, nitric oxide (NO), in newborn olfactory function. We hypothesized that olfactory neuron activity depended on NO generated by neuronal NO synthase (NOS). Utilizing in vivo functional manganese enhanced MRI (MEMRI) in a rabbit model of cerebral palsy we had shown previously that in utero hypoxia-ischemia (H-I) at E22 (70% gestation) resulted in impaired postnatal response to odorants and poor feeding. With the same antenatal insult, we manipulated NO levels in the olfactory neuron in postnatal day 1 (P1) kits by administration of intranasal NO donors or a highly selective nNOS inhibitor. Olfactory function was quantitatively measured by the response to amyl acetate stimulation by MEMRI. The relevance of nNOS to normal olfactory development was confirmed by the increase of nNOS gene expression from fetal ages to P1 in olfactory epithelium and bulbs. In control kits, nNOS inhibition decreased NO production in the olfactory system and increased MEMRI slope enhancement. In H-I kits the MEMRI slope did not increase, implicating modification of endogenous NO-mediated olfactory function by the antenatal insult. NO donors as a source of exogenous NO did not significantly change function in either group. In conclusion, olfactory epithelium nNOS in newborn rabbits probably modulates olfactory signal transduction. Antenatal H-I injury remote from delivery may affect early functional development of the olfactory system by decreasing NO-dependent signal transduction.

Impact of prenatal ischemia on behavior, cognitive abilities and neuroanatomy in adult rats with white matter damage

Early brain damage, such as white matter damage (WMD), resulting from perinatal hypoxia-ischemia in preterm and low birth weight infants represents a high risk factor for mortality and chronic disabilities, including sensory, motor, behavioral and cognitive disorders. In previous studies, we developed a model of WMD based on prenatal ischemia (PI), induced by unilateral ligation of uterine artery at E17 in pregnant rats. We have shown that PI reproduced some of the main deficits observed in preterm infants, such as white and gray matter damage, myelination deficits, locomotor, sensorimotor, and short-term memory impairments, as well as related musculoskeletal and neuroanatomical histopathologies [1-3]. Here, we determined the deleterious impact of PI on several behavioral and cognitive abilities in adult rats, as well as on the neuroanatomical substratum in various related brain areas. Adult PI rats exhibited spontaneous exploratory and motor hyperactivity, deficits in information encoding, and deficits in short- and long-term object memory tasks, but no impairments in spatial learning or working memory in watermaze tasks. These results were in accordance with white matter injury and damage in the medial and lateral entorhinal cortices, as detected by axonal degeneration, astrogliosis and neuronal density. Although there was astrogliosis and axonal degeneration in the fornix, hippocampus and cingulate cortex, neuronal density in the hippocampus and cingulate cortex was not affected by PI. Levels of spontaneous hyperactivity, deficits in object memory tasks, neuronal density in the medial and lateral entorhinal cortices, and astrogliosis in the fornix correlated with birth weight in PI rats. Thus, this rodent model of WMD based on PI appears to recapitulate the main neurobehavioral and neuroanatomical human deficits often observed in preterm children with a perinatal history of ischemia.

Inhaled nitric oxide and neonatal brain damage: experimental and clinical evidences

Inhaled nitric oxide (iNO) has been used not only for pulmonary vasodilation in term neonates with hypoxemic respiratory failure, but also in preterm ones at risk of chronic lung disease (CLD) with variable results in prevention and treatment of CLD and/or brain injury. However, meta analysis of clinical trials does not support that iNO should be used routinely in preterm infants with hypoxic respiratory failure as it has no convincing long-term follow-up data to show its advantages in neurodevelopment. Investigation of extra-pulmonary effects of iNO through nitrosothiol hemoglobin-associated hypoxic vasodilation, as well as its intra- and extra-pulmonary anti-inflammation effect, would have biological and physiological potential in the management of the lung and brain injury of prematurity. The eligibility and safety of iNO in these premature infants at high risk of neurodevelopmental disability require more clinical and follow-up effort to test its pharmacological benefit over harm.

NO-dependent protective effect of VEGF against excitotoxicity on layer VI of the developing cerebral cortex

In industrialized countries, cerebral palsy affects 2.5‰ of preterm and term infants. At a neurochemical level, the massive release of glutamate constitutes a major process leading to excitotoxicity and neonatal brain lesions. Previous studies, conducted in the laboratory, revealed that, in (δ/δ)VEGF(A) transgenic mice, glutamate-induced brain lesions are exacerbated suggesting that VEGF(A) could play a protective action against excitotoxicity. Using a model of cultured cortical brain slices, the aim of the study was to characterize the central effects of VEGF against glutamate-induced excitotoxicity in neonates. Exposure of brain slices to glutamate induced a strong increase of necrotic cell death in the deep cortical layer VI and a decrease of apoptotic death in superficial layers II-IV. When administered alone, a 6-h treatment with VEGF(A) had no effect on both apoptotic and necrotic deaths. In contrast, VEGF(A) abolished the glutamate-induced necrosis observed in layer VI. While MEK and PI3-K inhibitors had no effect on the protective action of VEGF(A), L-NAME, a pan inhibitor of NOS, abrogated the effect of VEGF(A) and exacerbated the excitotoxic action of glutamate. Calcimetry experiments performed on brain slices revealed that VEGF(A) reduced the massive calcium influx induced by glutamate in layer VI and this effect was blocked by L-NAME. Neuroprotective effect of VEGF(A) was also blocked by LNIO and NPLA, two inhibitors of constitutive NOS, while AGH, an iNOS inhibitor, had no effect. Nitrite measurements, electron paramagnetic resonance spectroscopy and immunohistochemistry indicated that glutamate was a potent inducer of NO production via activation of nNOS in the cortical layer VI. In vivo administration of nNOS siRNA promoted excitotoxicity and mimicked the effects of L-NAME, LNIO and NPLA. A short-term glutamate treatment increased nNOS Ser1412 phosphorylation, while a long-term exposure inhibited nNOS/NR2B protein-protein interactions. Altogether, these findings indicate that, in deep cortical layers of mice neonates, glutamate stimulates nNOS activity. Contrasting with mature brain, NO production induced by high concentrations of glutamate is neuroprotective and is required for the anti-necrotic effect of VEGF(A).

Nitric oxide for the adjunctive treatment of severe malaria: hypothesis and rationale

We hypothesize that supplemental inhaled nitric oxide (iNO) will improve outcomes in children with severe malaria receiving standard antimalarial therapy. The rationale for the hypothesized efficacy of iNO rests on: (1) biological plausibility, based on known actions of NO in modulating endothelial activation; (2) pre-clinical efficacy data from animal models of experimental cerebral malaria; and (3) a human trial of the NO precursor l-arginine, which improved endothelial function in adults with severe malaria. iNO is an attractive new candidate for the adjunctive treatment of severe malaria, given its proven therapeutic efficacy in animal studies, track record of safety in clinical practice and numerous clinical trials, inexpensive manufacturing costs, and ease of administration in settings with limited healthcare infrastructure. We plan to test this hypothesis in a randomized controlled trial (ClinicalTrials.gov Identifier: NCT01255215).

Neuroanatomical, sensorimotor and cognitive deficits in adult rats with white matter injury following prenatal ischemia

Perinatal brain injury including white matter damage (WMD) is highly related to sensory, motor or cognitive impairments in humans born prematurely. Our aim was to examine the neuroanatomical, functional and behavioral changes in adult rats that experienced prenatal ischemia (PI), thereby inducing WMD. PI was induced by unilateral uterine artery ligation at E17 in pregnant rats. We assessed performances in gait, cognitive abilities and topographical organization of maps, and neuronal and glial density in primary motor and somatosensory cortices, the hippocampus and prefrontal cortex, as well as axonal degeneration and astrogliosis in white matter tracts. We found WMD in corpus callosum and brainstem, and associated with the hippocampus and somatosensory cortex, but not the motor cortex after PI. PI rats exhibited mild locomotor impairments associated with minor signs of spasticity. Motor map organization and neuronal density were normal in PI rats, contrasting with major somatosensory map disorganization, reduced neuronal density, and a marked reduction of inhibitory interneurons. PI rats exhibited spontaneous hyperactivity in open-field test and short-term memory deficits associated with abnormal neuronal density in related brain areas. Thus, this model reproduces in adult PI rats the main deficits observed in infants with a perinatal history of hypoxia-ischemia and WMD.

Nitric oxide counteracts the hyperoxia-induced proliferation and proinflammatory responses of mouse astrocytes

Preclinical studies in the premature baboon evaluating the efficacy and potential toxicity of inhaled nitric oxide indicated a significant effect on astrocyte area density, suggesting phenotypic and functional changes in astrocytes upon exposure to nitric oxide. However, the effects of nitric oxide and oxygen, the two major therapeutic gases utilized in neonatal intensive care, on astrocyte morphology and function remain vastly unknown. Herein, we report that exposure of mouse neonatal cortical astrocytes to hyperoxia results in a proinflammatory phenotype and increase in proliferation without significant changes in cellular morphology or levels of intermediate filament proteins. The proinflammatory phenotype was evident by a significant increase in cellular levels of cyclooxygenase-2 and a concomitant increase in prostaglandin E(2) secretion, a decline in the intracellular and secreted levels of apolipoprotein E, and a significant increase in the intracellular levels of clusterin. This proinflammatory phenotype was not evident upon simultaneous exposure to hyperoxia and nitric oxide. These results suggest that exposure to nitric oxide in the setting of hyperoxia confers unrecognized beneficial effects by suppressing astrocytic inflammation.

Learning to live with patency of the ductus arteriosus in preterm infants

Treatment of persistent patency of the ductus arteriosus in preterm infants remains heterogeneous and controversial. Routine early treatment to induce ductal closure is not beneficial, but the potential criteria for, timing of, methods for and benefits of later ductal closure have not been determined. Management strategies for infants awaiting spontaneous closure or meeting criteria for treatment may be based on pathophysiological considerations but require evaluation in clinical trials. Better diagnostic tools allowing the identification of infants who might benefit from ductal closure, supplemented by data from clinical trials confirming realization of that potential, are urgently needed.