Prenatal hypoxia-induced adaptation and neuroprotection that is inducible nitric oxide synthase-dependent

Glucocorticoid-Dependent Mechanisms of Brain Tolerance to Hypoxia

Adaptation of organisms to stressors is coordinated by the hypothalamic-pituitary-adrenal axis (HPA), which involves glucocorticoids (GCs) and glucocorticoid receptors (GRs). Although the effects of GCs are well characterized, their impact on brain adaptation to hypoxia/ischemia is still understudied. The brain is not only the most susceptible to hypoxic injury, but also vulnerable to GC-induced damage, which makes studying the mechanisms of brain hypoxic tolerance and resistance to stress-related elevation of GCs of great importance. Cross-talk between the molecular mechanisms activated in neuronal cells by hypoxia and GCs provides a platform for developing the most effective and safe means for prevention and treatment of hypoxia-induced brain damage, including hypoxic pre- and post-conditioning. Taking into account that hypoxia- and GC-induced reprogramming significantly affects the development of organisms during embryogenesis, studies of the effects of prenatal and neonatal hypoxia on health in later life are of particular interest. This mini review discusses the accumulated data on the dynamics of the HPA activation in injurious and non-injurious hypoxia, the role of the brain GRs in these processes, interaction of GCs and hypoxia-inducible factor HIF-1, as well as cross-talk between GC and hypoxic signaling. It also identifies underdeveloped areas and suggests directions for further prospective studies.

New insights on nitric oxide: Focus on animal models of schizophrenia

Schizophrenia is a devastating complex disorder characterised by a constellation of behavioral deficits with the underlying mechanisms not fully known. Nitric oxide (NO) has emerged as a key signaling molecule implicated in schizophrenia. Three nitric oxide sinthases (NOS), endothelial, neuronal, and inducible, release NO within the cell. Animal models of schizophrenia are grouped in four groups, neurovedelopmental, glutamatergic, dopaminergic and genetic. In this review, we aim to evaluate changes in NO levels in animal models of schizophrenia and the resulting long-lasting behavioral and neural consequences. In particular, NO levels are substantially modified, region-specific, in various neurodevelopmental models, e.g. bilateral excitotoxic lesion of the ventral hippocampus (nVHL), maternal immune activation and direct NO manipulations early in development, among others. In regards to glutamatergic models of schizophrenia, phencyclidine (PCP) administration increases NO levels in the prefrontal cortex (PFC) and ventral hippocampus. As far as genetic models are concerned, neuronal NOS knock-out mice display schizophrenia-related behaviors. Administration of NO donors can reverse schizophrenia-related behavioral deficits. While most modifications in NO are derived from neuronal NOS, recent evidence indicates that PCP treatment increases NO from the inducible NOS isoform. From a pharmacological perspective, treatment with various antipsychotics including clozapine, haloperidol and risperidone normalize NO levels in the PFC as well as improve behavioral deficits in nVHL rats. NO induced from the neuronal and inducible NOS is relevant to schizophrenia and warrants further research.

Attenuating oxygen-glucose deprivation-caused autophagosome accumulation may be involved in sevoflurane postconditioning-induced protection in human neuron-like cells

Application of the commonly used volatile anesthetic sevoflurane after brain ischemia (sevoflurane postconditioning) attenuates ischemic brain injury. It is not known whether autophagy plays a role in this sevoflurane postconditioning-induced neuroprotection. Human SH-SY5Y cells were induced to become neuron-like cells. These cells were subjected to 1 h oxygen-glucose deprivation (OGD) and then exposed to sevoflurane for 1 h. Chloroquine, an inhibitor of autolysosomes, rapamycin, an autophagy inducer, or 3-methyladenine (3-MA), an autophagy inhibitor, were incubated with cells during OGD and sevoflurane exposure. OGD and the subsequent simulated reperfusion increased lactate dehydrogenase (LDH) release from the cells. This increase was dose-dependent inhibited by sevoflurane postconditioning. OGD increased the ratio of microtubule-associated protein 1 light chain 3 (LC3) II to LC3I and the expression of beclin-1 and p62. These increases were attenuated by sevoflurane. Sevoflurane alone did not have any effects on the expression of p62, beclin-1 and the ratio of LC3II to LC3I. Sevoflurane also enhanced the co-location of autophagosomes and lysosomes. Chloroquine increased the ratio of LC3II to LC3I, p62 and LDH release in cells subjected to OGD. Sevoflurane postconditioning attenuated OGD-induced inactivation of Akt and mechanistic target of rapamycin (mTOR). Inducing autophagosome generation by rapamycin attenuated sevoflurane postconditioning-reduced LDH release. Inhibition of autophagosome generation by 3-MA decreased OGD-induced LDH release. These results suggest that OGD increase autophagosome accumulation via increased formation of autophagosomes and reduced autophagosome clearance and that attenuation of OGD-induced autophagosome accumulation may contribute to sevoflurane postconditioning-induced cell protection.

Role of Prenatal Hypoxia in Brain Development, Cognitive Functions, and Neurodegeneration

This review focuses on the role of prenatal hypoxia in the development of brain functions in the postnatal period and subsequent increased risk of neurodegenerative disorders in later life. Accumulating evidence suggests that prenatal hypoxia in critical periods of brain formation results in significant changes in development of cognitive functions at various stages of postnatal life which correlate with morphological changes in brain structures involved in learning and memory. Prenatal hypoxia also leads to a decrease in brain adaptive potential and plasticity due to the disturbance in the process of formation of new contacts between cells and propagation of neuronal stimuli, especially in the cortex and hippocampus. On the other hand, prenatal hypoxia has a significant impact on expression and processing of a variety of genes involved in normal brain function and their epigenetic regulation. This results in changes in the patterns of mRNA and protein expression and their post-translational modifications, including protein misfolding and clearance. Among proteins affected by prenatal hypoxia are a key enzyme of the cholinergic system-acetylcholinesterase, and the amyloid precursor protein (APP), both of which have important roles in brain function. Disruption of their expression and metabolism caused by prenatal hypoxia can also result, apart from early cognitive dysfunctions, in development of neurodegeneration in later life. Another group of enzymes affected by prenatal hypoxia are peptidases involved in catabolism of neuropeptides, including amyloid-β peptide (Aβ). The decrease in the activity of neprilysin and other amyloid-degrading enzymes observed after prenatal hypoxia could result over the years in an Aβ clearance deficit and accumulation of its toxic species which cause neuronal cell death and development of neurodegeneration. Applying various approaches to restore expression of neuronal genes disrupted by prenatal hypoxia during postnatal development opens an avenue for therapeutic compensation of cognitive dysfunctions and prevention of Aβ accumulation in the aging brain and the model of prenatal hypoxia in rodents can be used as a reliable tool for assessment of their efficacy.

Long-term functional outcomes and correlation with regional brain connectivity by MRI diffusion tractography metrics in a near-term rabbit model of intrauterine growth restriction

BACKGROUND

Intrauterine growth restriction (IUGR) affects 5-10% of all newborns and is associated with increased risk of memory, attention and anxiety problems in late childhood and adolescence. The neurostructural correlates of long-term abnormal neurodevelopment associated with IUGR are unknown. Thus, the aim of this study was to provide a comprehensive description of the long-term functional and neurostructural correlates of abnormal neurodevelopment associated with IUGR in a near-term rabbit model (delivered at 30 days of gestation) and evaluate the development of quantitative imaging biomarkers of abnormal neurodevelopment based on diffusion magnetic resonance imaging (MRI) parameters and connectivity.

METHODOLOGY

At +70 postnatal days, 10 cases and 11 controls were functionally evaluated with the Open Field Behavioral Test which evaluates anxiety and attention and the Object Recognition Task that evaluates short-term memory and attention. Subsequently, brains were collected, fixed and a high resolution MRI was performed. Differences in diffusion parameters were analyzed by means of voxel-based and connectivity analysis measuring the number of fibers reconstructed within anxiety, attention and short-term memory networks over the total fibers.

PRINCIPAL FINDINGS

The results of the neurobehavioral and cognitive assessment showed a significant higher degree of anxiety, attention and memory problems in cases compared to controls in most of the variables explored. Voxel-based analysis (VBA) revealed significant differences between groups in multiple brain regions mainly in grey matter structures, whereas connectivity analysis demonstrated lower ratios of fibers within the networks in cases, reaching the statistical significance only in the left hemisphere for both networks. Finally, VBA and connectivity results were also correlated with functional outcome.

CONCLUSIONS

The rabbit model used reproduced long-term functional impairments and their neurostructural correlates of abnormal neurodevelopment associated with IUGR. The description of the pattern of microstructural changes underlying functional defects may help to develop biomarkers based in diffusion MRI and connectivity analysis.

Prenatal hypoxia may aggravate the cognitive impairment and Alzheimer's disease neuropathology in APPSwe/PS1A246E transgenic mice

Most cases of Alzheimer's disease (AD) arise through interactions between genetic and environmental factors. It is believed that hypoxia is an important environmental factor influencing the development of AD. Our group has previously demonstrated that hypoxia increased β-amyloid (Aβ) generation in aged AD mice. Here, we further investigate the pathological role of prenatal hypoxia in AD. We exposed the pregnant APP(Swe)/PS1(A246E) transgenic mice to high-altitude hypoxia in a hypobaric chamber during days 7-20 of gestation. We found that prenatal hypoxic mice exhibited a remarkable deficit in spatial learning and memory and a significant decrease in synapses. We also documented a significantly higher level of amyloid precursor protein, lower level of the Aβ-degrading enzyme neprilysin, and increased Aβ accumulation in the brain of prenatal hypoxic mice. Finally, we demonstrated striking neuropathologic changes in prenatal hypoxic AD mice, showing increased phosphorylation of tau, decreased hypoxia-induced factor, and enhanced activation of astrocytes and microglia. These data suggest that although the characteristic features of AD appear later in life, hypoxemia in the prenatal stage may contribute to the pathogenesis of the disease, supporting the notion that environmental factors can trigger or aggravate AD.

Neurovascular protection by ischaemic tolerance: role of nitric oxide

Nitric oxide (NO) has emerged as a key mediator in the mechanisms of ischaemic tolerance induced by a wide variety of preconditioning stimuli. NO is involved in the brain protection that develops either early (minutes-hours) or late (days-weeks) after the preconditioning stimulus. However, the sources of NO and the mechanisms underlying the protective effects differ substantially. While in early preconditioning NO is produced by the endothelial and neuronal isoform of NO synthase, in delayed preconditioning NO is synthesized by the inducible or 'immunological' isoform of NO synthase. Furthermore, in early preconditioning, NO acts through the canonical cGMP pathway, possibly through protein kinase G and opening of mitochondrial K(ATP) channels. In late preconditioning, the protection is mediated by peroxynitrite formed by the reaction of NO with superoxide derived from the enzyme NADPH oxidase. The mechanisms by which peroxynitrite exerts its protective effect may include improvement of post-ischaemic cerebrovascular function, leading to enhancement of blood flow to the ischaemic territory, and expression of prosurvival genes resulting in cytoprotection. The evidence suggests that NO can engage highly effective and multifunctional prosurvival pathways, which could be exploited for the prevention and treatment of cerebrovascular pathologies.

Different effects of anoxia and hind-limb immobilization on sensorimotor development and cell numbers in the somatosensory cortex in rats

Cerebral palsy (CP) is a group of movement and posture disorders attributed to insults in the developing brain. In rats, CP-like motor deficits can be induced by early hind-limb sensorimotor restriction (SR; from postnatal days P2 to P28), associated or otherwise with perinatal anoxia (PA; on P0 and P1). In this study, we address the question of whether PA, early SR or a combination of both produces alterations to sensorimotor development. Developmental milestones (surface righting, cliff aversion, stability on an inclined surface, proprioceptive placing, auditory startle, eye opening) were assessed daily from P3 to P14. Motor skills (horizontal ladder and beam walking) were evaluated weekly (from P31 to P52). In addition, on P52, the thickness of the somatosensory (S1) and cerebellar cortices, and corpus callosum were measured, and the neuronal and glial cell numbers in S1 were counted. SR (with or without PA) significantly delayed the stability on an inclined surface and hastened the appearance of the placing reflex and impaired motor skills. No significant differences were found in the thickness measurements between the groups. Quantitative histology of S1 showed that PA, either alone or associated with SR, increased the number of glial cells, while SR alone reduced neuronal cell numbers. Finally, the combination of PA and SR increased the size of neuronal somata. We conclude that SR impairs the achievement of developmental milestones and motor skills. Moreover, both SR and PA induce histological alterations in the S1 cortex, which may contribute to sensorimotor deficits.

Family-based association study between NOS-I and -IIA polymorphisms and autism spectrum disorders in Korean trios

Autism spectrum disorder (ASD) is a complex neurodevelopmental disorder with a strong genetic component and environmental risk factors. Nitric oxide (NO), which is produced by nitric oxide synthase (NOS), may play a role in the development of ASD. We genotyped nine single nucleotide polymorphisms (SNPs) in the NOS-I gene and nine SNPs in the NOS-IIA gene and carried out the transmission disequilibrium test (TDT) and haplotype analysis in 151 Korean ASD trios. We found preferential transmission of the A allele of rs8068149 (P = 0.039) and G allele of rs1060826 (P = 0.035) of NOS-IIA in ASD and the haplotype analysis revealed that the two haplotypes had significant associations (P = 0.014 and 0.031, respectively). The behavioral subdomain score of failure to use nonverbal behaviors to regulate social interaction in Autism Diagnostic Interview-Revised (ADI-R) was significantly higher in subjects with the GG or AG allele in rs1060826 of NOS-IIA compared to those who had the AA allele (P = 0.027). These results provide significant but weak evidence for an association between NOS-IIA and ASD in the Korean population.

Free radical injury and blood-brain barrier permeability in hypoxic-ischemic encephalopathy

OBJECTIVES

The purpose of this work was to evaluate the extent of free radical injury in newborns with hypoxic ischemic encephalopathy by measuring plasma levels of malondialdehyde and nitric oxide and to assess the blood-brain barrier permeability by measuring the cerebrospinal fluid albumin/plasma albumin ratio.

METHODS

This prospective observational study was conducted over a period of 2 years at Sir Sundarlal Hospital, Banaras Hindu University. The study population consisted of 43 term neonates with perinatal asphyxia who subsequently developed hypoxic ischemic encephalopathy. Twenty normal gestational age- and gender-matched healthy infants without any perinatal asphyxia served as control subjects. Peripheral venous blood samples were analyzed for malondialdehyde, total plasma nitrates/nitrites, and albumin levels between 12 and 24 hours of life. To assess the blood-brain barrier permeability, the cerebrospinal fluid albumin/plasma albumin ratio was measured. Correlation among the levels of malondialdehyde, nitrates/nitrites, and blood-brain barrier permeability was calculated. Data were analyzed by using SPSS 10 software.

RESULTS

Plasma malondialdehyde and nitrate/nitrite levels were significantly higher in infants with hypoxic ischemic encephalopathy compared with control subjects. Although there was a progressive increment in plasma levels of malondialdehyde with increasing severity of hypoxic ischemic encephalopathy, the differences were not statistically significant. Plasma nitrate/nitrite levels were almost similar in all stages of hypoxic ischemic encephalopathy. Plasma albumin levels were comparable in infants with hypoxic ischemic encephalopathy and control subjects, whereas cerebrospinal fluid albumin levels and blood-brain barrier permeability were significantly higher in infants with hypoxic ischemic encephalopathy. Significant correlation was observed between plasma malondialdehyde and nitrate/nitrite levels with blood-brain barrier permeability.

CONCLUSIONS

Increased plasma levels of malondialdehyde and nitrates/nitrites are found to be associated with hypoxic ischemic encephalopathy, indicating the possible role of free radical injury in its causation. Increased blood-brain barrier permeability may be another contributory factor to the progression of the disease.

Prenatal hypoxia preconditioning improves hypoxic ventilatory response and reduces mortality in neonatal rats

OBJECTIVE

Severe hypoxia/ischemia is a major cause of neonatal cardiorespiratory dysfunction and mortality. We tested whether prenatal hypoxia preconditioning would augment hypoxic and hypercapnic ventilatory responses, and thereby reduce neonatal mortality.

METHODS

Pregnant rats at 19 days' gestation were exposed to six episodes of intermittent hypoxia (10-min of 15% O(2) followed by 10-min of normoxia/episode, PPC), or room air (CON) per day until delivery. The ventilatory responses to 1 min of 10% O(2) and 10% CO(2), and 5 min of 5% O(2) were performed in anesthetized pups. The conscious pups were exposed to 5% O(2) for approximately 105 min, and their mortality and dry/wet weight of the lung and brain were evaluated.

RESULTS

We found that augmented ventilatory responses to 1 min of 10% O(2) and 10% CO(2) were similar in the two groups (P>0.05). In contrast, 5 min of 5% O(2) initially caused a ventilatory peak response followed by a decline that was markedly diminished (35%, P=0.013) by PPC. PPC also significantly decreased neonatal mortality by 22% (P=0.044) as compared with CON.

CONCLUSION

We conclude that prenatal hypoxia preconditioning reduces neonatal mortality apparently by improving the severe hypoxic ventilatory response.

Lipopolysaccharide preconditioning induces robust protection against brain injury resulting from deep hypothermic circulatory arrest

OBJECTIVE

Delayed preconditioning genetically reprograms the response to ischemic injury. Subclinical bacterial lipopolysaccharide acts through preconditioning, powerfully protecting against experimental stroke. We investigated the potential for lipopolysaccharide to protect against brain injury related to cardiopulmonary bypass.

METHODS

Neonatal piglets were blindly and randomly preconditioned with lipopolysaccharide (n = 6) or saline (n = 6). Three days later, they experienced 2 hours of deep hypothermic circulatory arrest before being weaned and supported anesthetized for 20 hours in an intensive care setting. Controls included cardiopulmonary bypass without deep hypothermic circulatory arrest (n = 3) and no cardiopulmonary bypass (n = 3). Brain injury was quantified by light and fluorescent microscopy (Fluoro-Jade; Histo-Chem, Inc, Jefferson, Ark).

RESULTS

All animals were clinically indistinguishable before surgery. Perioperative and postoperative parameters between experimental groups were similar. No control animal scored falsely positive. Histologic scores were 0.33 +/- 0.21, 0.66 +/- 0.42, and 0.5 +/- 0.24 in the cortex, basal ganglia, and hippocampus, respectively, in the lipopolysaccharide-treated animals but significantly worse in all saline control animals (1.33 +/- 0.21, P < .01; 1.66 +/- 0.33, P = .09; and 6.0 +/- 1.5, P < .01). One lipopolysaccharide-treated brain was histologically indistinguishable from controls.

CONCLUSION

This is the first evidence that lipopolysaccharide can precondition against cardiopulmonary bypass-related injury. Because lipopolysaccharide preconditioning is a systemic phenomenon offering proven protection against myocardial, hepatic, and pulmonary injury, this technique offers enormous potential for protecting against systemic neonatal injury related to cardiopulmonary bypass.

Determinants of outcomes after head cooling for neonatal encephalopathy

OBJECTIVE

The goal of this study was to evaluate the role of factors that may determine the efficacy of treatment with delayed head cooling and mild systemic hypothermia for neonatal encephalopathy.

METHODS

A total of 218 term infants with moderate to severe neonatal encephalopathy plus abnormal amplitude-integrated electroencephalographic recordings, assigned randomly to head cooling for 72 hours, starting within 6 hours after birth (with the rectal temperature maintained at 34.5 +/- 0.5 degrees C), or conventional care, were studied. Death or severe disability at 18 months of age was assessed in a multicenter, randomized, controlled study (the CoolCap trial).

RESULTS

Treatment, lower encephalopathy grade, lower birth weight, greater amplitude-integrated electroencephalographic amplitude, absence of seizures, and higher Apgar score, but not gender or gestational age, were associated significantly with better outcomes. In a multivariate analysis, each of the individually predictive factors except for Apgar score remained predictive. There was a significant interaction between treatment and birth weight, categorized as > or =25th or <25th percentile for term, such that larger infants showed a lower frequency of favorable outcomes in the control group but greater improvement with cooling. For larger infants, the number needed to treat was 3.8. Pyrexia (> or =38 degrees C) in control infants was associated with adverse outcomes. Although there was a small correlation with birth weight, the adverse effect of greater birth weight in control infants remained significant after adjustment for pyrexia and severity of encephalopathy.

CONCLUSIONS

Outcomes after hypothermic treatment were strongly influenced by the severity of neonatal encephalopathy. The protective effect of hypothermia was greater in larger infants.

Moderate growth restriction: deleterious and protective effects on white matter damage

The role for growth restriction in the multifactorial pathophysiology of developing white-matter damage remains debated. We studied rat pups with prenatal growth restriction (GR) induced by unilateral ligation of the uterine artery. Pups with severe GR exhibited white-matter damage that persisted to adulthood [Olivier, P., Baud, O., Evrard, P., Gressens, P.,Verney, C., 2005. Prenatal ischemia and white matter damage in rats. J. Neuropathol. Exp. Neurol. 64, 998-1006]. Moderate GR was associated with diffuse white-matter lesions, microglial activation, and astrogliosis. Loss of pre-oligodendrocytes on postnatal day 7 was followed by a delay in myelination. Following a cortical excitotoxic insult on postnatal day 5, the size of the induced white-matter lesion was smaller in pups with moderate GR and larger in pups with severe GR, compared to normal pups. The increased pre-oligodendrocyte proliferation seen in the white matter of pups with moderate GR subjected to this "double-hit" injury may constitute a heretofore-undescribed neuroprotective mechanism of immature white matter.

Adaptation to hypoxia prevents disturbances in cerebral blood flow during neurodegenerative process

The rats with neurodegenerative brain disorder induced by administration of a toxic fragment of beta-amyloid demonstrate weakened endothelium-dependent dilation of cerebral vessels, which attested to impaired production of endothelial NO. At the same time, toxic beta-amyloid fragment induced the formation of NO depots in the walls of cerebral vessels, which indirectly attests to NO overproduction in the brain tissue. Preadaptation to hypoxia prevented endothelial dysfunction and improved the efficiency of NO storage. Our results suggest that adaptation to hypoxia protects the brain from various changes in NO production during neurodegenerative damage.

Ischemic preconditioning: a novel target for neuroprotective therapy

Ischemic preconditioning involves a brief exposure to ischemia in order to develop a tolerance to injurious effects of prolonged ischemia. The molecular mechanisms of neuroprotection that lead to ischemic tolerance are not yet completely understood. However, it seems that two distinct phases are involved. Firstly, a cellular defense function against ischemia may be developed by the mechanisms inherent to neurons such as posttranslational modification of proteins or expression of new proteins via a signal transduction system to the nucleus. Secondly, a stress response and synthesis of stress proteins (heat shock proteins) may be activated. These mechanisms are mediated by chaperones. The objective of ischemic preconditioning research is to identify the underlying endogenous protective cellular receptors and signaling cascades, with the long-term goal of allowing therapeutic augmentation of the endogenous protective mechanisms in cerebral ischemia and possibly development of new neuroprotective strategies for ischemic stroke treatment.