Glutamate signaling in the pathophysiology and therapy of prenatal insults

Serum Vitamin D status in full term neonates with severe perinatal depression

BACKGROUND

Severe perinatal depression is a significant cause of mortality and morbidity in neonates. Vitamin D levels were observed to be low in mothers and their neonates with hypoxic ischemic encephalopathy in some studies, owing to its neuroprotective properties.

OBJECTIVE

Primary objective was to compare vitamin D deficiency state in full term neonates with severe perinatal depression and healthy term controls. Secondary objectives were to determine sensitivity and specificity of serum 25(OH)D<12 ng/mL in predicting mortality, development of hypoxic ischemic encephalopathy, abnormal neurological examination at discharge, and developmental outcome at 12 weeks of age.

MATERIAL AND METHODS

Serum 25(OH)D levels in full term neonates with severe perinatal depression and healthy controls were compared.

RESULTS

Serum 25(OH)D levels in severe perinatal depression and controls (n = 55 each group) were significantly different (7.50 ± 3.53 ng/mL vs 20.23 ± 12.70 ng/mL). At cut-off of <  12 ng/mL, serum 25(OH)D could predict mortality with 100% sensitivity and 17% specificity and poor developmental outcomes with sensitivity of 100% and specificity of 50% .

CONCLUSION

Vitamin D deficiency status at birth can serve as an effective screening tool and poor prognostic markers in term neonates with severe perinatal depression.

Neonatal Anesthesia and Oxidative Stress

Neonatal anesthesia, while often essential for surgeries or imaging procedures, is accompanied by significant risks to redox balance in the brain due to the relatively weak antioxidant system in children. Oxidative stress is characterized by concentrations of reactive oxygen species (ROS) that are elevated beyond what can be accommodated by the antioxidant defense system. In neonatal anesthesia, this has been proposed to be a contributing factor to some of the negative consequences (e.g., learning deficits and behavioral abnormalities) that are associated with early anesthetic exposure. In order to assess the relationship between neonatal anesthesia and oxidative stress, we first review the mechanisms of action of common anesthetic agents, the key pathways that produce the majority of ROS, and the main antioxidants. We then explore the possible immediate, short-term, and long-term pathways of neonatal-anesthesia-induced oxidative stress. We review a large body of literature describing oxidative stress to be evident during and immediately following neonatal anesthesia. Moreover, our review suggests that the short-term pathway has a temporally limited effect on oxidative stress, while the long-term pathway can manifest years later due to the altered development of neurons and neurovascular interactions.

Autism Spectrum Disorder: Focus on Glutamatergic Neurotransmission

Disturbances in the glutamatergic system have been increasingly documented in several neuropsychiatric disorders, including autism spectrum disorder (ASD). Glutamate-centered theories of ASD are based on evidence from patient samples and postmortem studies, as well as from studies documenting abnormalities in glutamatergic gene expression and metabolic pathways, including changes in the gut microbiota glutamate metabolism in patients with ASD. In addition, preclinical studies on animal models have demonstrated glutamatergic neurotransmission deficits and altered expression of glutamate synaptic proteins. At present, there are no approved glutamatergic drugs for ASD, but several ongoing clinical trials are currently focusing on evaluating in autistic patients glutamatergic pharmaceuticals already approved for other conditions. In this review, we provide an overview of the literature concerning the role of glutamatergic neurotransmission in the pathophysiology of ASD and as a potential target for novel treatments.

Glutamate receptors in brain development

Brain development encompasses a number of processes including synaptogenesis, migration and synaptic plasticity. These activities are regulated by neurotransmitter receptors such as glutamate receptors. The development, activation and expression of these receptors vary during foetal and neonatal brain development. In this review, it has been shown that the stage or age of brain development, which correlates with the functional activities ongoing in the neonatal brain, determines the cellular distribution and the expression of glutamate receptors in the neonatal brain. Additionally, environmental factors including stress and alcohol may trigger the dysregulation of glutamate receptors during development. This deficit or dysregulation of glutamate receptors may result in developmental neuropathology, some of which may affect later development and normal functioning of the individual.

Linking acute symptomatic neonatal seizures, brain injury and outcome in preterm infants

Neonatal seizures (NS) are the most frequent sign of neurological dysfunction in newborn infants. With increased survival of preterm neonates, the current clinical focus has shifted from preventing death to improving long-term neurological outcome. In the context of acute symptomatic NS, the main negative prognostic factors include etiology, and severity of brain injury, but also prolonged seizures and especially status epilepticus. However, the reasons for the detrimental contribution of seizures to outcome are still unclear, and evidence has been collected both in favor of seizures being an epiphenomenon of brain injury and of independently contributing to further damage. In this narrative focused review, we will discuss both hypotheses, with special emphasis on data relating to preterm infants. We will also identify present controversies and possible future lines of research.

Hypoxic-Ischemic Encephalopathy and Mitochondrial Dysfunction: Facts, Unknowns, and Challenges

Significance: Hypoxic-ischemic events due to intrapartum complications represent the second cause of neonatal mortality and initiate an acute brain disorder known as hypoxic-ischemic encephalopathy (HIE). In HIE, the brain undergoes primary and secondary energy failure phases separated by a latent phase in which partial neuronal recovery is observed. A hypoxic-ischemic event leads to oxygen restriction causing ATP depletion, neuronal oxidative stress, and cell death. Mitochondrial dysfunction and enhanced oxidant formation in brain cells are characteristic phenomena associated with energy failure. Recent Advances: Mitochondrial sources of oxidants in neurons include complex I of the mitochondrial respiratory chain, as a key contributor to O₂^•- production via succinate by a reverse electron transport mechanism. The reaction of O₂^•- with nitric oxide (^•NO) yields peroxynitrite, a mitochondrial and cellular toxin. Quantitation of the redox state of cytochrome c oxidase, through broadband near-infrared spectroscopy, represents a promising monitoring approach to evaluate mitochondrial dysfunction in vivo in humans, in conjunction with the determination of cerebral oxygenation and their correlation with the severity of brain injury. Critical Issues: The energetic failure being a key phenomenon in HIE connected with the severity of the encephalopathy, measurement of mitochondrial dysfunction in vivo provides an approach to assess evolution, prognosis, and adequate therapies. Restoration of mitochondrial redox homeostasis constitutes a key therapeutic goal. Future Directions: While hypothermia is the only currently accepted therapy in clinical management to preserve mitochondrial function, other mitochondria-targeted and/or redox-based treatments are likely to synergize to ensure further efficacy.

[Disturbance of oligodendrocyte differentiation in schizophrenia in relation to main hypothesis of the disease]

Increasing evidence coming from neuroimaging, molecular genetic and post-mortem studies have implicated oligodendrocyte abnormalities and compromised myelin integrity in schizophrenia. Activity-dependent myelination in adult brain is considered to be an important mechanism of neural circuit's plasticity due to the presence of a large population of oligodendrocyte progenitor cells (OPC) in the adult CNS. Growing evidence for impairment of oligodendrocyte differentiation has been reported in the brain of schizophrenia subjects. OPC are very vulnerable inflammation, oxidative stress, and elevated glutamate levels leading to excitotoxicity. The mechanisms of prolonged suppression of oligodendrocyte differentiation caused by prenatal maternal infection or preterm birth are discussed in view of increased risk of schizophrenia, neurodevelopmental and inflammation hypotheses of the disease. The data that some neuroleptics stimulate OPC differentiation and ameliorate myelin alterations support the notion that impairment in the differentiation of OPCs contributes to oligodendrocyte abnormalities and to the pathophysiology of schizophrenia.

Potential protective role of endogenous glutamate-oxaloacetate transaminase against glutamate excitotoxicity in fetal hypoxic-ischaemic asphyxia

AIM

Fetal blood contains higher concentrations of glutamate-oxaloacetate transaminase (GOT; a blood enzyme able to metabolize glutamate) than maternal blood. The aim of this study was to determine the relationship between GOT and glutamate levels in arterial blood samples from umbilical cord in control newborn infants and newborn infants with hypoxic-ischaemic insult and/or symptoms of hypoxia-ischemia after delivery.

METHOD

A total of 46 newborn infants (28 females, 18 males) were prospectively included in the study. Twenty-three infants (18 females, five males) were included as control participants and 23 (10 females, 13 males) were included as newborn infants at risk of adverse neurological outcome (defined as umbilical blood with pH <7.1).

RESULTS

Analysis of glutamate concentration and GOT activity in umbilical blood samples showed that newborn infants with pH <7.1 had higher levels of glutamate (142.4 μmol/L [SD 61.4] vs 62.8 μmol/L [SD 25.5]; p<0.001) and GOT (83.1 U/L [SD 60.9] vs 34.9 U/L [SD 18.2]; p<0.001) compared to newborn infants without fetal distress. Analysis of Apgar scores and blood pH values (markers of perinatal distress) showed that conditions of severe distress were associated with higher glutamate and GOT levels.

INTERPRETATION

During fetal development, the ability of GOT to metabolize glutamate suggests that this enzyme can act as an endogenous protective mechanism in the control of glutamate homeostasis.

Environmental enrichment decreases asphyxia-induced neurobehavioral developmental delay in neonatal rats

Perinatal asphyxia during delivery produces long-term disability and represents a major problem in neonatal and pediatric care. Numerous neuroprotective approaches have been described to decrease the effects of perinatal asphyxia. Enriched environment is a popular strategy to counteract nervous system injuries. The aim of the present study was to investigate whether enriched environment is able to decrease the asphyxia-induced neurobehavioral developmental delay in neonatal rats. Asphyxia was induced in ready-to-deliver mothers by removing the pups by caesarian section after 15 min of asphyxia. Somatic and neurobehavioral development was tested daily and motor coordination weekly. Our results show that rats undergoing perinatal asphyxia had a marked developmental delay and worse performance in motor coordination tests. However, pups kept in enriched environment showed a decrease in the developmental delay observed in control asphyctic pups. Rats growing up in enriched environment did not show decrease in weight gain after the first week and the delay in reflex appearance was not as marked as in control rats. In addition, the development of motor coordination was not as strikingly delayed as in the control group. Short-term neurofunctional outcome are known to correlate with long-term deficits. Our results thus show that enriched environment could be a powerful strategy to decrease the deleterious developmental effects of perinatal asphyxia.

Propofol administration to the fetal-maternal unit reduces cardiac injury in late-preterm lambs subjected to severe prenatal asphyxia and cardiac arrest

BACKGROUND

Cardiac dysfunction is reported to occur after severe perinatal asphyxia. We hypothesized that anesthesia of the mother with propofol during emergency cesarean section (c-section) would result in less cardiac injury (troponin T) in preterm fetuses exposed to global severe asphyxia in utero than anesthesia with isoflurane. We tested whether propofol decreases the activity of proapoptotic caspase-3 by activating the antiapoptotic AKT kinase family and the signal transducer and activator of transcription-3 (STAT-3).

METHODS

Pregnant ewes were randomized to receive either propofol or isoflurane anesthesia. A total of 44 late-preterm lambs were subjected to in utero umbilical cord occlusion (UCO), resulting in asphyxia and cardiac arrest, or sham treatment. After emergency c-section, each fetus was resuscitated, mechanically ventilated, and supported under anesthesia for 8 h using the same anesthetic as the one received by its mother.

RESULTS

At 8 h after UCO, the fetuses whose mothers had received propofol anesthesia had lower plasma troponin T levels, and showed a trend toward a higher median left ventricular ejection fraction (LVEF) of 84% as compared with 74% for those whose mothers had received isoflurane. Postasphyxia activation of caspase-3 was lower in association with propofol anesthesia than with isoflurane. Postasphyxia levels of STAT-3 and the AKT kinase family rose 655% and 500%, respectively with the use of propofol anesthesia for the mother.

CONCLUSION

The use of propofol for maternal anesthesia results in less cardiac injury in late-preterm lambs subjected to asphyxia than the use of isoflurane anesthesia. The underlying mechanism may be activation of the antiapoptotic STAT-3 and AKT pathways.

PRAS40 is an integral regulatory component of erythropoietin mTOR signaling and cytoprotection

Emerging strategies that center upon the mammalian target of rapamycin (mTOR) signaling for neurodegenerative disorders may bring effective treatment for a number of difficult disease entities. Here we show that erythropoietin (EPO), a novel agent for nervous system disorders, prevents apoptotic SH-SY5Y cell injury in an oxidative stress model of oxygen-glucose deprivation through phosphatidylinositol-3-kinase (PI 3-K)/protein kinase B (Akt) dependent activation of mTOR signaling and phosphorylation of the downstream pathways of p70 ribosomal S6 kinase (p70S6K), eukaryotic initiation factor 4E-binding protein 1 (4EBP1), and proline rich Akt substrate 40 kDa (PRAS40). PRAS40 is an important regulatory component either alone or in conjunction with EPO signal transduction that can determine cell survival through apoptotic caspase 3 activation. EPO and the PI 3-K/Akt pathways control cell survival and mTOR activity through the inhibitory post-translational phosphorylation of PRAS40 that leads to subcellular binding of PRAS40 to the cytoplasmic docking protein 14-3-3. However, modulation and phosphorylation of PRAS40 is independent of other protective pathways of EPO that involve extracellular signal related kinase (ERK 1/2) and signal transducer and activator of transcription (STAT5). Our studies highlight EPO and PRAS40 signaling in the mTOR pathway as potential therapeutic strategies for development against degenerative disorders that lead to cell demise.

Glutamate receptors: the cause or cure in perinatal white matter injury?

Glutamate toxicity from hypoxia-ischaemia during the perinatal period causes white matter injury that can result in long-term motor and intellectual disability. Blocking ionotropic glutamate receptors (GluRs) has been shown to inhibit oligodendrocyte injury in vitro, but GluR antagonists have not yet proven helpful in clinical studies. The opposite approach of activating GluRs on developing oligodendrocytes shows promise in experimental studies on rodents as reported by Jartzie et al., in this issue. Group I metabotropic glutamate receptors (mGluRs) are expressed transiently on developing oligodendrocytes in humans during the perinatal period, and the blood-brain-barrier permeable agonist of group I mGluRs, 1-aminocyclopentane-trans-1,3-dicarboxylic acid (ACPD), reduces white matter damage significantly in a rat model of perinatal hypoxia-ischaemia. The results suggest drugs activating this class of GluRs could provide a new therapeutic approach for preventing cerebral palsy and other neurological consequences of diffuse white matter injury in premature infants.

Pathophysiology of perinatal asphyxia: can we predict and improve individual outcomes?

Perinatal asphyxia occurs still with great incidence whenever delivery is prolonged, despite improvements in perinatal care. After asphyxia, infants can suffer from short- to long-term neurological sequelae, their severity depend upon the extent of the insult, the metabolic imbalance during the re-oxygenation period and the developmental state of the affected regions. Significant progresses in understanding of perinatal asphyxia pathophysiology have achieved. However, predictive diagnostics and personalised therapeutic interventions are still under initial development. Now the emphasis is on early non-invasive diagnosis approach, as well as, in identifying new therapeutic targets to improve individual outcomes. In this review we discuss (i) specific biomarkers for early prediction of perinatal asphyxia outcome; (ii) short and long term sequelae; (iii) neurocircuitries involved; (iv) molecular pathways; (v) neuroinflammation systems; (vi) endogenous brain rescue systems, including activation of sentinel proteins and neurogenesis; and (vii) therapeutic targets for preventing or mitigating the effects produced by asphyxia.