Excitatory amino acids and magnesium sulfate in neonatal asphyxia

Neonatal magnesium sulphate for neuroprotection: A systematic review and meta-analysis

AIM

To review the evidence of the effects of neonatal magnesium sulphate for neuroprotection in perinatal asphyxia and hypoxic-ischaemic encephalopathy (HIE).

METHOD

This was a systematic review of randomized controlled trials (RCTs) (with meta-analysis) and non-RCTs assessing magnesium sulphate for treating perinatal asphyxia and HIE at 35 weeks or more gestation (primary outcomes: neonatal death and death or long-term major neurodevelopmental disability).

RESULTS

Twenty-five RCTs (2099 infants) and four non-RCTs (871 infants) were included, 23 in low- and middle-income countries (LMICs). In RCTs, reductions in neonatal death with magnesium sulphate versus placebo or no treatment (risk ratio [RR] = 0.68; 95% confidence interval [CI] = 0.53-0.86; 13 RCTs), and magnesium sulphate with melatonin versus melatonin alone (RR = 0.74; 95% CI = 0.58-0.95; one RCT) were observed. No difference in neonatal death was seen for magnesium sulphate with therapeutic hypothermia versus therapeutic hypothermia alone (RR = 0.66, 95% CI = 0.34-1.26; three RCTs), or magnesium sulphate versus phenobarbital (RR = 3.00; 95% CI = 0.86-10.46; one RCT). No reduction in death or long-term neurodevelopmental disability (RR = 0.52; 95% CI = 0.14-1.89; one RCT) but reductions in several short-term adverse outcomes were observed with magnesium sulphate. Evidence was low- to very-low certainty because of risk of bias and imprecision.

INTERPRETATION

Given the uncertainty of the current evidence, further robust neonatal magnesium sulphate research is justified. This may include high-quality studies to determine stand-alone effects in LMICs and effects with and after therapeutic hypothermia in high-income countries.

Outcomes of Neonates with Hypoxic-Ischemic Encephalopathy Treated with Magnesium Sulfate: A Systematic Review with Meta-analysis

OBJECTIVE

To assess magnesium sulfate (MgSO4) as a neuroprotective agent in hypoxic-ischemic encephalopathy.

STUDY DESIGN

For this systematic review, PubMed, EMBASE, the Cochrane Library, EMCARE, and MedNar were searched in November 2022 for randomized controlled trials (RCTs). Meta-analysis was conducted using Stata 16.0 and RevMan 5.3.

RESULTS

Twenty RCTs with a total sample size of 1485 were included, of which 16 were from settings where therapeutic hypothermia (TH) was not offered. Regarding MgSO4 in settings where TH was not offered, only 1 study evaluated composite outcome of death or disability at ≥18 months and reported such poor outcome in 8 of 14 control infants and 4 of 8 in the MgSO4 group. MgSO4 was not associated with mortality (RR, 0.86; 95% CI, 0.72-1.03; 13 RCTs) or hypotension (RR, 1.02; 95% CI, 0.88-1.18; 5 RCTs). Thirteen studies reported that MgSO4 improved in-hospital outcomes, such as reduced seizure burden and improved neurological status at discharge. MgSO4 reduced the risk of poor suck feeds (RR, 0.52; 95% CI, 0.40-0.68; 6RCTs) and abnormal electroencephalogram (RR, 0.64; 95% CI, 0.45-0.93; 5 RCTs). Certainty of evidence was moderate for mortality and low or very low for other outcomes. For studies with MgSO4 as an adjunct to TH, none reported on death or neurodevelopmental disability at ≥18 months. MgSO4 was not associated with mortality (RR, 0.65; 95% CI, 0.34-1.27; 3 RCTs) or hypotension (RR, 1.0; 95% CI, 0.71-1.40; 3 RCTs).

CONCLUSIONS

Evidence around long-term outcomes of MgSO4 when used with or without TH was scant. MgSO4 therapy may improve in-hospital neurological outcomes without affecting mortality in settings where TH is not offered. Well-designed RCTs for neuroprotection are needed, especially in low-resource settings.

TRIAL REGISTRATION

"Open Science Forum" (https://doi.org/10.17605/OSF.IO/FRM4D).

Magnesium Sulfate as an Adjunct to Therapeutic Hypothermia in the Management of Term Infants with Hypoxic-Ischemic Encephalopathy: A Randomized, Parallel-Group, Controlled Trial

OBJECTIVE

To evaluate whether magnesium sulfate and therapeutic hypothermia in combination decreases mortality and/or major neurodevelopmental disability at 1 y of age among term neonates with hypoxic-ischemic encephalopathy.

METHODS

A total of 134 term neonates were randomized to receive intravenous magnesium sulfate at a dose of 250 mg/kg (at 8 mg/kg/min) once daily for 3 d starting within 6 h after birth along with therapeutic hypothermia in the intervention group and therapeutic hypothermia alone in the comparator group. The primary outcome was the composite outcome of mortality and/or major neurodevelopmental disability (Developmental Assessment Scale for Indian Infants score < 70) at 1 y of age.

RESULTS

A total of 115 infants were included in the primary analysis. The composite primary outcome occurred in 14 (24%) infants in the intervention group and 19 (33%) infants in the comparator group, and the difference was not statistically significant (p = 0.30; relative risk 0.72; 95% confidence interval 0.40-1.30). The secondary outcomes including neonatal mortality, major neurodevelopmental disability at 1 y of age, neurological status at discharge, level of oxidative stress markers, and adverse effects including hypotension and respiratory depression requiring support were also comparable between the groups.

CONCLUSIONS

The combination of magnesium sulfate and therapeutic hypothermia did not improve the composite outcome of neonatal mortality and/or major neurodevelopmental disability at 1 y of age.

TRAIL REGISTRATION

Clinical Trials Registry of India (CTRI/2018/06/014594), prospectively registered.

Neurologic Disorders of the Foal

Neurologic disease of foals is a diagnostic and therapeutic challenge for veterinarians. Disease conditions such as neonatal encephalopathy are seen as well as developmental and congenital defects, bacterial infections, and trauma. Neonatal encephalopathy can be considered a "syndrome" with a variety of causes resulting in a similar clinical presentation. These causes can be categorized as maladaptation, hypoxic/ischemic encephalopathy, and metabolic abnormalities, all leading to signs of cerebral and brainstem disease. Spinal cord signs may occasionally be seen, but these signs are usually overshadowed by cerebral disease. Treatment in most cases involves supportive care and outcome is favorable in most cases.

Hypoxia, Oxidative Stress, and Inflammation: Three Faces of Neurodegenerative Diseases

The cerebral hypoxia-ischemia can induce a wide spectrum of biologic responses that include depolarization, excitotoxicity, oxidative stress, inflammation, and apoptosis, and result in neurodegeneration. Several adaptive and survival endogenous mechanisms can also be activated giving an opportunity for the affected cells to remain alive, waiting for helper signals that avoid apoptosis. These signals appear to help cells, depending on intensity, chronicity, and proximity to the central hypoxic area of the affected tissue. These mechanisms are present not only in a large list of brain pathologies affecting commonly older individuals, but also in other pathologies such as refractory epilepsies, encephalopathies, or brain trauma, where neurodegenerative features such as cognitive and/or motor deficits sequelae can be developed. The hypoxia inducible factor 1α (HIF-1α) is a master transcription factor driving a wide spectrum cellular response. HIF-1α may induce erythropoietin (EPO) receptor overexpression, which provides the therapeutic opportunity to administer pharmacological doses of EPO to rescue and/or repair affected brain tissue. Intranasal administration of EPO combined with other antioxidant and anti-inflammatory compounds could become an effective therapeutic alternative, to avoid and/or slow down neurodegenerative deterioration without producing adverse peripheral effects.

Acute symptomatic neonatal seizures, brain injury, and long-term outcome: The role of neuroprotective strategies

INTRODUCTION

Neonatal seizures are frequent but underdiagnosed manifestations of acute brain dysfunction and an important contributor to unfavorable outcomes. Etiology and severity of brain injury are the single strongest outcome determinants.

AREAS COVERED

The authors will discuss the prognostic role of acute symptomatic seizures versus brain injury and the main neuroprotective and neurorestorative strategies for full-term and preterm infants.

EXPERT OPINION

Prolonged acute symptomatic seizures likely contribute to long-term outcomes by independently adding further brain injury to initial insults. Correct timing and dosing of therapeutic interventions, depending on etiology and gestational ages, need careful evaluation. Although promising strategies are under study, the only standard of care is whole-body therapeutic hypothermia in full-term newborns with hypoxic-ischemic encephalopathy.

Potential attenuation of biochemical parameters and enzymatic functions in Cyprinus carpio fingerlings by Phenthoate 50 EC insecticide exposure

The risks of the health-associated problems of pesticide-exposed non-target organisms are ubiquitous, therefore an emerging concern to strike the balance between benefit and risk factors. In the present study, by elucidating multiple biomarkers, the effects of Phenthoate 50 EC on the acute toxicity tests and different pathophysiological changes of common carp (Cyprinus carpio) fingerlings were studied in time- and concentration-dependent manners. The LC₅₀ of Phenthoate 50 EC for the fish was 7.39 (6.716-8.076) ppm at 96 h. As an indicator of neurotoxicity, compared to the control group, significant (P < 0.01) reduction in brain acetylcholinesterase (AChE) activity was observed, whereas plasma glutamate-oxalacetate transaminase (PGOT) and plasma glutamate pyruvate transaminase (PGPT) activities were increased significantly (P < 0.01) at the doses of 2.22 and 3.69 ppm of Phenthoate 50 EC, respectively. Histopathological changes in the insecticide-treated fish liver suggested the hepatic tissue damages, while alteration of the blood, gills and kidney morphology; progressive decrease (P < 0.05) in the serum calcium levels; and significantly (P < 0.01) decreased blood glucose level at 2.22 and 3.69 or 5.17 ppm of Phenthoate 50 EC demonstrated the oxidative stress and requirement of the up-surging energy demands due to the exposure of this organophosphate chemical. These results advice the modulation caused by this widely used agrochemical on the physiology of aquatic fauna by changing the enzymatic and biochemical indices at cellular level.

Impact of perinatal hypoxia on the developing brain

Perinatal hypoxia is still one of the greatest threats to the newborn child, even in developed countries. However, there is a lack of works which summarize up-to-date information about that huge topic. Our review covers a broader spectrum of recent results from studies on mechanisms leading to hypoxia-induced injury. It also resumes possible primary causes and observed behavioral outcomes of perinatal hypoxia. In this review, we recognize two types of hypoxia, according to the localization of its primary cause: environmental and placental. Later we analyze possible pathways of prenatal hypoxia-induced injury including gene expression changes, glutaminergic excitatory damage (and a role of NMDA receptors in it), oxidative stress with ROS and RNS production, inflammation and apoptosis. Moreover, we focus on the impact of these pathophysiological changes on the structure and development of the brain, especially on its regions: corpus striatum and hippocampus. These brain changes of the offspring lead to impairments in their postnatal growth and sensorimotor development, and in their motor functions, activity, emotionality and learning ability in adulthood. Later we compare various animal models used to investigate the impact of prenatal and postnatal injury (hypoxic, ischemic or combinatory) on living organisms, and show their advantages and limitations.

Neuroprotection Strategies for Term Encephalopathy

Brain injury in the full-term and near-term neonates is a significant cause of mortality and long-term morbidity, resulting in injury patterns distinct from that seen in premature infants and older patients. Therapeutic hypothermia improves long-term outcomes for many of these infants, but there is a continued search for therapies to enhance the plasticity of the newborn brain, resulting in long-term repair. It is likely that a combination strategy utilizing both early and late interventions may have the most benefit, capitalizing on endogenous mechanisms triggered by hypoxia or ischemia. Optimizing care of these critically ill newborns in the acute setting is also vital for improving both short- and long-term outcomes.

Time and sex dependent effects of magnesium sulphate on post-asphyxial seizures in preterm fetal sheep

KEY POINTS

We evaluated the effect of magnesium sulphate (MgSO₄ ) on seizures induced by asphyxia in preterm fetal sheep. MgSO₄ did not prevent seizures, but significantly reduced the total duration, number of seizures, seizure amplitude and average seizure burden. Saline-asphyxia male fetuses had significantly more seizures than female fetuses, but male fetuses showed significantly greater reduction in seizures during MgSO₄ infusion than female fetuses. A circadian profile of seizure activity was observed in all fetuses, with peak seizures seen around 04.00-06.00 h on the first and second days after the end of asphyxia. This study is the first to demonstrate that MgSO₄ has utility as an anti-seizure agent after hypoxia-ischaemia. More information is needed about the mechanisms mediating the effect of MgSO₄ on seizures and sexual dimorphism, and the influence of circadian rhythms on seizure expression.

ABSTRACT

Seizures are common in newborns after asphyxia at birth and are often refractory to anti-seizure agents. Magnesium sulphate (MgSO₄ ) has anticonvulsant effects and is increasingly given to women in preterm labour for potential neuroprotection. There is limited information on its effects on perinatal seizures. We examined the hypothesis that MgSO₄ infusion would reduce fetal seizures after asphyxia in utero. Preterm fetal sheep at 0.7 gestation (104 days, term = 147 days) were given intravenous infusions of either saline (n = 14) or MgSO₄ (n = 12, 160 mg bolus + 48 mg h^-1 infusion over 48 h). Fetuses underwent umbilical cord occlusion (UCO) for 25 min, 24 h after the start of infusion. The start time for seizures did not differ between groups, but MgSO₄ significantly reduced the total number of seizures (P < 0.001), peak seizure amplitude (P < 0.05) and seizure burden (P < 0.005). Within the saline-asphyxia group, male fetuses had significantly more seizures than females (P < 0.05). Within the MgSO₄ -asphyxia group, although both sexes had fewer seizures than the saline-asphyxia group, the greatest effect of MgSO₄ was on male fetuses, with reduced numbers of seizures (P < 0.001) and seizure burden (P < 0.005). Only 1 out of 6 MgSO₄ males had seizures on the second day post-UCO compared to 5 out of 6 MgSO₄ female fetuses (P = 0.08). Finally, seizures showed a circadian profile with peak seizures between 04.00 and 06.00 h on the first and second day post-UCO. Collectively, these results suggest that MgSO₄ may have utility in treating perinatal seizures and has sexually dimorphic effects.

Neonatal hypoxic ischemic encephalopathy: an update on disease pathogenesis and treatment

INTRODUCTION

Hypoxic ischemic encephalopathy (HIE) is the most important reason for morbidity and mortality in term-born infants. Understanding pathophysiology of the brain damage is essential for the early detection of patients with high risk for HIE and development of strategies for their treatments. Areas covered: This review discusses pathophysiology of the neonatal HIE and its treatment options, including hypothermia, melatonin, allopurinol, topiramate, erythropoietin, N-acetylcyctein, magnesium sulphate and xenon. Expert commentary: Several clinical studies have been performed in order to decrease the risk of brain injury due to difficulties in the early diagnosis and treatment, and to develop strategies for better long-term outcomes. Although currently standard treatment methods include therapeutic hypothermia for neonates with moderate to severe HIE, new supportive options are needed to enhance neuroprotective effects of the hypothermia, which should aim to reduce production of the free radicals and to have anti-inflammatory and anti-apoptotic actions.

Lipid peroxides in the serum of asphyxiated neonates

OBJECTIVE

Lipid peroxides (LPOs) are released when free radicals react with unsaturated fatty acids in cell membranes during hypoxic ischemic insult in neonates. We aimed to assess LPO concentrations in the serum of asphyxiated and non-asphyxiated neonates and examine their correlation with the severity of asphyxia.

STUDY DESIGN

This prospective cross-sectional study was conducted on a group of asphyxiated neonates and controls. Serum LPO concentrations was measured by enzyme-linked immunosorbent assay at 4-6 h of life in all subjects. Encephalopathy was classified according to Sarnat's stages into mild, moderate and severe at 12-24 h of life. LPO was compared between groups and was correlated with severity of encephalopathy and mortality.

RESULTS

A total of 90 infants were enrolled; of them 45 had asphyxia. Serum LPO (nmol ml(-1)) was significantly greater in the asphyxia group (6.9±3.01 vs 1.78±1.09, P<0.001). It correlated positively with severity of encephalopathy (P<0.001) and negatively with Apgar score at 5 min (r=-0.532, P<0.001) and with initial blood gases pH (r=-0.664, P<0.001). LPO measured greater concentrations in infants who died compared with asphyxiated survivors (11.64±1.31 vs 6.18±2.48, P=0.0004).

CONCLUSION

LPO was increased and correlated with severity of asphyxia as well as with mortality. Further studies are warranted to examine whether it is only a marker for outcome or a contributor in the pathogenesis of hypoxic-ischemic brain injury.

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.

Magnesium is not consistently neuroprotective for perinatal hypoxia-ischemia in term-equivalent models in preclinical studies: a systematic review

There is an important unmet need to further improve the outcome of neonatal encephalopathy in term infants. Meta-analyses of large controlled trials now suggest that maternal magnesium sulfate (MgSO4) therapy is associated with a reduced risk of cerebral palsy and gross motor dysfunction after premature birth, but that it has no effect on death or disability. Because of this inconsistency, it remains controversial whether MgSO4 is clinically neuroprotective and, thus, it is unclear whether it would be appropriate to test MgSO4 for treatment of encephalopathy in term infants. We therefore systematically reviewed the preclinical evidence for neuroprotection with MgSO4 before or after hypoxic-ischemic encephalopathy (HIE) in term-equivalent perinatal and adult animals. The outcomes were highly inconsistent between studies. Although there were differences in dose and timing of administration, there was evidence that beneficial effects of MgSO4 were associated with confounding mild hypothermia and, strikingly, the studies that included rigorous maintenance of environmental temperature or body temperature consistently suggested a lack of effect. On balance, these preclinical studies suggest that peripherally administered MgSO4 is unlikely to be neuroprotective. Rigorous testing in translational animal models of perinatal HIE is needed before MgSO4 should be considered in clinical trials for encephalopathy in term infants.

Magnesium for newborns with hypoxic-ischemic encephalopathy: a systematic review and meta-analysis

OBJECTIVE

Magnesium may have a role in neuroprotection in neonatal hypoxic-ischemic encephalopathy (HIE). The objective of this study was to systematically review the efficacy and safety of postnatal magnesium therapy in newborns with HIE.

STUDY DESIGN

MEDLINE, EMBASE, CINAHL and CCRCT were searched for studies of magnesium for HIE. Randomized controlled trials that compared magnesium to control in newborns with HIE were selected. The primary outcome was a composite outcome of death or moderate-to-severe neurodevelopmental disability at 18 months. When appropriate, meta-analyses were conducted using random effects model and risk ratios (RRs) and 95% confidence intervals (CIs) were calculated.

RESULT

Five studies with sufficient quality were included. There was no difference in the primary outcome between the magnesium and the control groups (RR 0.81, 95% CI 0.36 to 1.84). There was significant reduction in the unfavorable short-term composite outcome (RR 0.48, 95% CI 0.30 to 0.77) but no difference in mortality (RR 1.39, 95% CI 0.85 to 2.27), seizures (RR 0.84, 95% CI 0.59 to 1.19) or hypotension (RR 1.28, 95% CI 0.69 to 2.38) between the magnesium and the control groups.

CONCLUSION

The improvement in short-term outcomes without significant increase in side effects indicate the need for further trials to determine if there are long-term benefits of magnesium and to confirm its safety. Mortality was statistically insignificant between the magnesium and the control groups. However, the trend toward increase in mortality in the magnesium group is a major clinical concern and should be monitored closely in future trials.

Baseline serum magnesium concentrations and neurodevelopmental outcomes of extremely low birth weight premature infants

AIM

To test the hypothesis that, in ELBW infants who did not receive antenatal MgSO4, lower baseline serum Mg is associated with poorer neurodevelopmental outcomes (NDO).

STUDY DESIGN

The study was conducted in two phases: phase 1-- retrospective, and phase 2--prospective.

SUBJECTS

Extremely low birth weight infants.

OUTCOME MEASURES

Mortality and adverse NDO were assessed in relation to initial serum Mg measured in the first 12 hours of age.

RESULTS

We studied 156 ELBW infants. In phase 1 (n=102): initial serum Mg (median [IQ range]) was greater in the infants who died compared to those who survived (1.7 [1.5-2.2] mg/dL vs. 1.6 [1.4-1.7] mg/dL, p=0.034). In phase 2 (n=54): initial serum Mg was greater in infants who died or had adverse NDO at 9 months when compared to those who survived with better NDO (1.7 [1.55-2.1] mg/dL vs. 1.5 [1.4-1.68] mg/dL, p=0.008). Using receiver operating characteristic (ROC) curve, increased Mg concentration in the first 12 hours>1.6 mg/dL was associated with unfavorable outcomes with sensitivity of 73%, specificity of 67%, and odds ratio of 5.5 (CI=1.2-24.8, p=0.037).

CONCLUSIONS

In a cohort of preterm infants without antenatal exposure to MgSO4, initial serum Mg concentrations associated positively with poor outcomes. Further studies are needed in ELBW infants with poor NDO to determine whether they have a dysfunctional transport system that prevents Mg from entering into cells, or they have an active process that excretes Mg extracellularly.

Neuroprotective therapies after perinatal hypoxic-ischemic brain injury

Hypoxic-ischemic (HI) brain injury is one of the main causes of disabilities in term-born infants. It is the result of a deprivation of oxygen and glucose in the neural tissue. As one of the most important causes of brain damage in the newborn period, the neonatal HI event is a devastating condition that can lead to long-term neurological deficits or even death. The pattern of this injury occurs in two phases, the first one is a primary energy failure related to the HI event and the second phase is an energy failure that takes place some hours later. Injuries that occur in response to these events are often manifested as severe cognitive and motor disturbances over time. Due to difficulties regarding the early diagnosis and treatment of HI injury, there is an increasing need to find effective therapies as new opportunities for the reduction of brain damage and its long term effects. Some of these therapies are focused on prevention of the production of reactive oxygen species, anti-inflammatory effects, anti-apoptotic interventions and in a later stage, the stimulation of neurotrophic properties in the neonatal brain which could be targeted to promote neuronal and oligodendrocyte regeneration.

Metabolic effects of perinatal asphyxia in the rat cerebral cortex

We reported previously that intrauterine asphyxia acutely affects the rat hippocampus. For this reason, the early effects of this injury were studied in the cerebral cortex, immediately after hysterectomy (acute condition) or following a recovery period at normoxia (recovery condition). Lactacidemia and glycemia were determined, as well as glycogen levels in the muscle, liver and cortex. Cortical tissue was also used to assay the ATP levels and glutamate uptake. Asphyxiated pups exhibited bluish coloring, loss of movement, sporadic gasping and hypertonia. However, the appearance of the controls and asphyxiated pups was similar at the end of the recovery period. Lactacidemia and glycemia were significantly increased by asphyxia in both the acute and recovery conditions. Concerning muscle and hepatic glycogen, the control group showed significantly higher levels than the asphyxic group in the acute condition and when compared with groups of the recovery period. In the recovery condition, the control and asphyxic groups showed similar glycogen levels. However, in the cortex, the control groups showed significantly higher glycogen levels than the asphyxic group, in both the acute and recovery conditions. In the cortical tissue, asphyxia reduced ATP levels by 70 % in the acute condition, but these levels increased significantly in asphyxic pups after the recovery period. Asphyxia did not affect glutamate transport in the cortex of both groups. Our results suggest that the cortex uses different energy resources to restore ATP after an asphyxia episode followed by a reperfusion period. This strategy could sustain the activity of essential energy-dependent mechanisms.

Relationship between glutamate, GOT and GPT levels in maternal and fetal blood: a potential mechanism for fetal neuroprotection

BACKGROUND

Excess glutamate in the brain is thought to be implicated in the pathophysiology of fetal anoxic brain injury, yet little is known about the mechanisms by which glutamate is regulated in the fetal brain. This study examines whether there are differences between maternal and fetal glutamate concentrations, and whether a correlation between them exists.

METHODS

10 ml of venous blood was extracted from 87 full-term (>37 weeks gestation) pregnant women in active labor. Immediately after delivery of the neonate, 10 ml of blood from the umbilical artery and vein was extracted. Samples were analyzed for levels of glutamate, glutamate-oxaloacetate transaminase (GOT), and glutamate pyruvate transaminase (GPT).

RESULTS

Fetal blood glutamate concentrations in both the umbilical artery and vein were found to be significantly higher than maternal blood (p<0.001). Similarly, fetal serum GOT levels in the umbilical artery and vein were found to be significantly higher than maternal GOT levels (p<0.001). The difference in GPT levels between maternal and fetal serum was not statistically significant. There was no difference in fetal glutamate, GOT or GPT between the umbilical artery and vein. There was an association observed between glutamate levels in maternal blood and glutamate levels in both venous (R=0.32, p<0.01) and arterial (R=0.33, p<0.05) fetal blood.

CONCLUSIONS

This study demonstrated that higher baseline concentrations of blood glutamate are present in fetal blood compared with maternal blood, and this was associated with elevated GOT, but not GPT levels. An association was observed between maternal and fetal blood glutamate levels.

Blood glutamate scavenging: insight into neuroprotection

Brain insults are characterized by a multitude of complex processes, of which glutamate release plays a major role. Deleterious excess of glutamate in the brain's extracellular fluids stimulates glutamate receptors, which in turn lead to cell swelling, apoptosis, and neuronal death. These exacerbate neurological outcome. Approaches aimed at antagonizing the astrocytic and glial glutamate receptors have failed to demonstrate clinical benefit. Alternatively, eliminating excess glutamate from brain interstitial fluids by making use of the naturally occurring brain-to-blood glutamate efflux has been shown to be effective in various animal studies. This is facilitated by gradient driven transport across brain capillary endothelial glutamate transporters. Blood glutamate scavengers enhance this naturally occurring mechanism by reducing the blood glutamate concentration, thus increasing the rate at which excess glutamate is cleared. Blood glutamate scavenging is achieved by several mechanisms including: catalyzation of the enzymatic process involved in glutamate metabolism, redistribution of glutamate into tissue, and acute stress response. Regardless of the mechanism involved, decreased blood glutamate concentration is associated with improved neurological outcome. This review focuses on the physiological, mechanistic and clinical roles of blood glutamate scavenging, particularly in the context of acute and chronic CNS injury. We discuss the details of brain-to-blood glutamate efflux, auto-regulation mechanisms of blood glutamate, natural and exogenous blood glutamate scavenging systems, and redistribution of glutamate. We then propose different applied methodologies to reduce blood and brain glutamate concentrations and discuss the neuroprotective role of blood glutamate scavenging.

Effects of acute perinatal asphyxia in the rat hippocampus

In the present work, we have used a rat animal model to study the early effects of intrauterine asphyxia occurring no later than 60 min following the cesarean-delivery procedure. Transitory hypertonia accompanied by altered posture was observed in asphyxiated pups, which also showed appreciably increased lactate values in plasma and hippocampal tissues. Despite this, there was no difference in terms of either cell viability or metabolic activities such as oxidation of lactate, glucose, and glycine in the hippocampus of those fetuses submitted to perinatal asphyxia with respect to normoxic animals. Moreover, a significant decrease in glutamate, but not GABA uptake was observed in the hippocampus of asphyctic pups. Since intense ATP signaling especially through P2X(7) purinergic receptors can lead to excitotoxicity, a feature which initiates neurotransmission failure in experimental paradigms relevant to ischemia, here we assessed the expression level of the P2X(7) receptor in the paradigm of perinatal asphyxia. A three-fold increase in P2X(7) protein was transiently observed in hippocampus immediately following asphyxia. Nevertheless, further studies are needed to delineate whether the P2X(7) receptor subtype is involved in the pathogenesis, contributing to ongoing brain injury after intrapartum asphyxia. In that case, new pharmacologic intervention strategies providing neuroprotection during the reperfusion phase of injury might be identified.

Neuroprotection in the newborn infant

Neonatal brain injury is an important cause of death and disability, with pathways of oxidant stress, inflammation, and excitotoxicity that lead to damage that progresses over a long period of time. Therapies have classically targeted individual pathways during early phases of injury, but more recent therapies such as growth factors may also enhance cell proliferation, differentiation, and migration over time. More recent evidence suggests combined therapy may optimize repair, decreasing cell injury while increasing newly born cells.

Neuroprotective strategies in excitotoxic brain injury: potential applications to the preterm brain

Neuronal and oligodendroglial cell death owing to increased glutamate levels plays an important role in the pathophysiology of hypoxic-, ischemic- and inflammation-mediated brain injury as well as in disorders such as epilepsy, Alzheimer’s, Parkinson’s or Huntington’s disease. In addition, excitotoxic brain injury is known to be a major contributing factor to brain injury in preterm infants. Excitotoxicity is characterized as excessive glutamatergic activation of postsynaptic receptors that consequently leads to cell injury and cell death. The major excitatory amino acid neurotransmitter is glutamate. Glutamate plays a key role in brain development, affecting progenitor cell differentiation, proliferation, migration and survival. In physiological conditions the presence of glutamate in the synapse is regulated by ATP-dependent glutamate transporters in neurons and glial cells, with astrocytes being responsible for a major part of glutamate uptake in the brain. In pathologic circumstances the function of the transporters is impaired, leading to glutamate accumulation in the synaptic cleft and in turn excessive activation of postsynaptic glutamate receptors with subsequent massive Ca2+ influx, activation of neuronal nitric oxide synthase, translocation of proapoptotic genes to the mitochondria, mitochondrial dysfunction, release of cytochrome C into the cytosol, activation of caspases and subsequent cell death. Based on the pathogenic concept of an overactivation of the excitatory pathways, glutamate receptors have been a longstanding therapeutic target for rational drug design. This article reviews the pathophysiology of excitotoxic brain injury in the example of preterm brain injury, as well as current research on therapeutic antiexcitotoxic strategies.

The chilling details: hypoxic-ischemic encephalopathy

Hypoxic-ischemic encephalopathy (HIE) is one of the most important complications found in the newborn period. It is the result of a deprivation of oxygen and glucose to the neural tissue, which may be the result of either hypoxemia or ischemia. Experimental animal research and clinical observations in humans have noted that the pattern of injury occurs in 2 phases. The first phase is a primary energy failure related to the insult, and then a second energy failure occurs some hours later. The combined effects of cellular energy failure, acidosis, glutamate release, intracellular accumulation of calcium, lipid peroxidation, and nitric oxide neurotoxicity destroy essential components of the cell, culminating in cell death. The clinical presentation depends on the severity, timing, and duration of the insult, with symptoms typically evolving over approximately 72 hours. Hypothermia strategies are aimed at targeting this narrow window of opportunity to ameliorate the brain injury.

Therapeutics for neonatal brain injury

Neonatal brain injury is an important cause of death and neurodevelopmental delay. Multiple pathways of oxidant stress, inflammation, and excitotoxicity lead to both early and late phases of cell damage and death. Therapies targeting these different pathways have shown potential in protecting the brain from ongoing injury. More recent therapies, such as growth factors, have demonstrated an ability to increase cell proliferation and repair over longer periods of time. Even though hypothermia, which decreases cerebral metabolism and possibly affects other mechanisms, may show some benefit in particular cases, no widely effective therapeutic interventions for human neonates exist. In this review, we summarize recent findings in neuroprotection and neurogenesis for the immature brain, including combination therapy to optimize repair.

Neuroprotective effect of long-term MgSO4 administration after cerebral hypoxia-ischemia in newborn rats is related to the severity of brain damage

Previous studies have shown contradictory results regarding magnesium-mediated neuroprotection in animal models of perinatal asphyxia. The aim of this study is to investigate the effects of MgSO(4) postasphyxial treatment on hypoxia-ischemia (HI)-induced brain injury in neonatal rats and the possibility that this effect is related to the severity of brain damage. Seven-day-old rats underwent unilateral carotid artery ligation followed by 1 or 2 hours of hypoxia (8% O(2)) and MgSO(4) administration. Adenosine triphosphate/phosphocreatine and glutamate/glutamine measurements and neuropathological evaluation of the hippocampus were used to assess the effects of HI and MgSO(4). HI caused time-dependent changes in energy stores, amino acid concentrations, and brain damage. Administration of MgSO(4) after 1 hour but not after 2 hours of hypoxia resulted in significant prevention of HI-induced brain injury. MgSO(4) administration results in a significant protection against moderate HI-induced brain damage, whereas it fails to offer a similar effect against severe brain damage.