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

Magnesium sulfate and risk of hypoxic-ischemic encephalopathy in a high-risk cohort

BACKGROUND

Hypoxic-ischemic encephalopathy contributes to morbidity and mortality among neonates ≥36 weeks of gestation. Evidence of preventative antenatal treatment is limited. Magnesium sulfate has neuroprotective properties among preterm fetuses. Hypertensive disorders of pregnancy are a risk factor for hypoxic-ischemic encephalopathy, and magnesium sulfate is recommended for maternal seizure prophylaxis among patients with preeclampsia with severe features.

OBJECTIVE

(1) Determine trends in the incidence of hypertensive disorders of pregnancy, antenatal magnesium sulfate, and hypoxic-ischemic encephalopathy; (2) evaluate the association between hypertensive disorders of pregnancy and hypoxic-ischemic encephalopathy; and (3) evaluate if, among patients with hypertensive disorders of pregnancy, the odds of hypoxic-ischemic encephalopathy is mitigated by receipt of antenatal magnesium sulfate.

STUDY DESIGN

We analyzed a prospective cohort of live births ≥36 weeks of gestation between 2012 and 2018 within the California Perinatal Quality Care Collaborative registry, linked with the California Department of Health Care Access and Information files. We used Cochran-Armitage tests to assess trends in hypertensive disorders, encephalopathy diagnoses, and magnesium sulfate utilization and compared demographic factors between patients with or without hypertensive disorders of pregnancy or treatment with magnesium sulfate. Hierarchical logistic regression models were built to explore if hypertensive disorders of pregnancy were associated with any severity and moderate/severe hypoxic-ischemic encephalopathy. Separate hierarchical logistic regression models were built among those with hypertensive disorders of pregnancy to evaluate the association of magnesium sulfate with hypoxic-ischemic encephalopathy.

RESULTS

Among 44,314 unique infants, the diagnosis of hypoxic-ischemic encephalopathy, maternal hypertensive disorders of pregnancy, and the use of magnesium sulfate increased over time. Compared with patients with hypertensive disorders of pregnancy alone, patients with hypertensive disorders treated with magnesium sulfate represented a high-risk population. They were more likely to be publicly insured, born between 36 and 38 weeks of gestation, be small for gestational age, have lower Apgar scores, require a higher level of resuscitation at delivery, have prolonged rupture of membranes, experience preterm labor and fetal distress, and undergo operative delivery (all P<.002). Hypertensive disorders of pregnancy were associated with hypoxic-ischemic encephalopathy (adjusted odds ratio, 1.26 [95% confidence interval, 1.13-1.40]; P<.001) and specifically moderate/severe hypoxic-ischemic encephalopathy (adjusted odds ratio, 1.26 [95% confidence interval, 1.11-1.42]; P<.001). Among patients with hypertensive disorders of pregnancy, treatment with magnesium sulfate was associated with 29% reduction in the odds of neonatal hypoxic-ischemic encephalopathy (adjusted odds ratio, 0.71 [95% confidence interval, 0.52-0.97]; P=.03) and a 37% reduction in the odds of moderate/severe neonatal hypoxic-ischemic encephalopathy (adjusted odds ratio, 0.63 [95% confidence interval, 0.42-0.94]; P=.03).

CONCLUSION

Hypertensive disorders of pregnancy are associated with hypoxic-ischemic encephalopathy and, specifically, moderate/severe disease. Among people with hypertensive disorders, receipt of antenatal magnesium sulfate is associated with a significant reduction in the odds of hypoxic-ischemic encephalopathy and moderate/severe disease in a neonatal cohort admitted to neonatal intensive care unit at ≥36 weeks of gestation. The findings of this observational study cannot prove causality and are intended to generate hypotheses for future clinical trials on magnesium sulfate in term infants.

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).

A systematic review of immune-based interventions for perinatal neuroprotection: closing the gap between animal studies and human trials

BACKGROUND

Perinatal infection/inflammation is associated with a high risk for neurological injury and neurodevelopmental impairment after birth. Despite a growing preclinical evidence base, anti-inflammatory interventions have not been established in clinical practice, partly because of the range of potential targets. We therefore systematically reviewed preclinical studies of immunomodulation to improve neurological outcomes in the perinatal brain and assessed their therapeutic potential.

METHODS

We reviewed relevant studies published from January 2012 to July 2023 using PubMed, Medline (OvidSP) and EMBASE databases. Studies were assessed for risk of bias using the SYRCLE risk of bias assessment tool (PROSPERO; registration number CRD42023395690).

RESULTS

Forty preclinical publications using 12 models of perinatal neuroinflammation were identified and divided into 59 individual studies. Twenty-seven anti-inflammatory agents in 19 categories were investigated. Forty-five (76%) of 59 studies reported neuroprotection, from all 19 categories of therapeutics. Notably, 10/10 (100%) studies investigating anti-interleukin (IL)-1 therapies reported improved outcome, whereas half of the studies using corticosteroids (5/10; 50%) reported no improvement or worse outcomes with treatment. Most studies (49/59, 83%) did not control core body temperature (a known potential confounder), and 25 of 59 studies (42%) did not report the sex of subjects. Many studies did not clearly state whether they controlled for potential study bias.

CONCLUSION

Anti-inflammatory therapies are promising candidates for treatment or even prevention of perinatal brain injury. Our analysis highlights key knowledge gaps and opportunities to improve preclinical study design that must be addressed to support clinical translation.

Neuroprotective Effects of Delayed TGF-β1 Receptor Antagonist Administration on Perinatal Hypoxic-Ischemic Brain Injury

Hypoxic-ischemic (HI) brain injury in neonatal encephalopathy triggers a wave of neuroinflammatory events attributed to causing the progressive degeneration and functional deficits seen weeks after the primary damage. The cellular processes mediating this prolonged neurodegeneration in HI injury are not sufficiently understood. Consequently, current therapies are not fully protective. In a recent study, we found significant improvements in neurologic outcomes when a small molecule antagonist for activin-like kinase 5 (ALK5), a transforming growth factor beta (TGF-β) receptor was used as a therapeutic in a rat model of moderate term HI. Here, we have extended those studies to a mouse preterm pup model of HI. For these studies, postnatal day 7 CD1 mice of both sexes were exposed to 35-40 min of HI. Beginning 3 days later, SB505124, the ALK5 receptor antagonist, was administered systemically through intraperitoneal injections performed every 12 h for 5 days. When evaluated 23 days later, SB505124-treated mice had ∼2.5-fold more hippocampal area and ∼2-fold more thalamic tissue. Approximately 90% of the ipsilateral hemisphere (ILH) was preserved in the SB505124-treated HI mice compared to the vehicle-treated HI mice, where the ILH was ∼60% of its normal size. SB505124 also preserved the subcortical white matter. SB505124 treatment preserved levels of aquaporin-4 and n-cadherin, key proteins associated with blood-brain barrier function. Importantly, SB505124 administration improved sensorimotor function as assessed by a battery of behavioral tests. Altogether, these data lend additional support to the conclusion that SB505124 is a candidate neuroprotective molecule that could be an effective treatment for HI-related encephalopathy in moderately injured preterm infants.

Magnesium sulphate reduces tertiary gliosis but does not improve EEG recovery or white or grey matter cell survival after asphyxia in preterm fetal sheep

Maternal magnesium sulphate (MgSO4 ) treatment is widely recommended before preterm birth for neuroprotection. However, this is controversial because there is limited evidence that MgSO4 provides long-term neuroprotection. Preterm fetal sheep (104 days gestation; term is 147 days) were assigned randomly to receive sham occlusion with saline infusion (n = 6) or i.v. infusion with MgSO4 (n = 7) or vehicle (saline, n = 6) from 24 h before hypoxia-ischaemia induced by umbilical cord occlusion until 24 h after occlusion. Sheep were killed after 21 days of recovery, for fetal brain histology. Functionally, MgSO4 did not improve long-term EEG recovery. Histologically, in the premotor cortex and striatum, MgSO4 infusion attenuated post-occlusion astrocytosis (GFAP+ ) and microgliosis but did not affect numbers of amoeboid microglia or improve neuronal survival. In the periventricular and intragyral white matter, MgSO4 was associated with fewer total (Olig-2+ ) oligodendrocytes compared with vehicle + occlusion. Numbers of mature (CC1+ ) oligodendrocytes were reduced to a similar extent in both occlusion groups compared with sham occlusion. In contrast, MgSO4 was associated with an intermediate improvement in myelin density in the intragyral and periventricular white matter tracts. In conclusion, a clinically comparable dose of MgSO4 was associated with moderate improvements in white and grey matter gliosis and myelin density but did not improve EEG maturation or neuronal or oligodendrocyte survival. KEY POINTS: Magnesium sulphate is widely recommended before preterm birth for neuroprotection; however, there is limited evidence that magnesium sulphate provides long-term neuroprotection. In preterm fetal sheep exposed to hypoxia-ischaemia (HI), MgSO4 was associated with attenuated astrocytosis and microgliosis in the premotor cortex and striatum but did not improve neuronal survival after recovery to term-equivalent age, 21 days after HI. Magnesium sulphate was associated with loss of total oligodendrocytes in the periventricular and intragyral white matter tracts, whereas mature, myelinating oligodendrocytes were reduced to a similar extent in both occlusion groups. In the same regions, MgSO4 was associated with an intermediate improvement in myelin density. Functionally, MgSO4 did not improve long-term recovery of EEG power, frequency or sleep stage cycling. A clinically comparable dose of MgSO4 was associated with moderate improvements in white and grey matter gliosis and myelin density but did not improve EEG maturation or neuronal or oligodendrocyte survival.

Midazolam Prevents the Adverse Outcome of Neonatal Asphyxia

OBJECTIVE

Birth asphyxia (BA) is the most frequent cause of neonatal death as well as central nervous system (CNS) injury. BA is often associated with neonatal seizures, which only poorly respond to anti-seizure medications and may contribute to the adverse neurodevelopmental outcome. Using a non-invasive rat model of BA, we have recently reported that the potent benzodiazepine, midazolam, prevents neonatal seizures in ~50% of rat pups. In addition to its anti-seizure effect, midazolam exerts anti-inflammatory actions, which is highly relevant for therapeutic intervention following BA. The 2 major aims of the present study were to examine (1) whether midazolam reduces the adverse outcome of BA, and (2) whether this effect is different in rats that did or did not exhibit neonatal seizures after drug treatment.

METHODS

Behavioral and cognitive tests were performed over 14 months after asphyxia, followed by immunohistochemical analyses.

RESULTS

All vehicle-treated rats had seizures after asphyxia and developed behavioral and cognitive abnormalities, neuroinflammation in gray and white matter, neurodegeneration in the hippocampus and thalamus, and hippocampal mossy fiber sprouting in subsequent months. Administration of midazolam (1 mg/kg i.p.) directly after asphyxia prevented post-asphyctic seizures in ~50% of the rats and resulted in the prevention or decrease of neuroinflammation and the behavioral, cognitive, and neurodegenerative consequences of asphyxia. Except for neurodegeneration in the thalamus, seizures did not seem to contribute to the adverse outcome of asphyxia.

INTERPRETATION

The disease-modifying effect of midazolam identified here strongly suggests that this drug provides a valuable option for improving the treatment and outcome of BA. ANN NEUROL 2023;93:226-243.

Hypothermia combined with neuroprotective adjuvants shortens the duration of hospitalization in infants with hypoxic ischemic encephalopathy: Meta-analysis

Objective: Therapeutic hypothermia (TH) is the current standard of care for neonatal hypoxic-ischemic encephalopathy (HIE), yet morbidity and mortality remain significant. Adjuvant neuroprotective agents have been suggested to augment hypothermic-mediated neuroprotection. This analysis aims to identify the classes of drugs that have been used in combination with hypothermia in the treatment of neonatal HIE and determine whether combination therapy is more efficacious than TH alone. Methods: A systematic search of PubMed, Embase and Medline from conception through December 2022 was conducted. Randomized- and quasi-randomized controlled trials, observational studies and retrospective studies evaluating HIE infants treated with combination therapy versus TH alone were selected. Primary reviewers extracted information on mortality, neurodevelopmental impairment and length of hospitalization for meta-analyses. Effect sizes were pooled using a random-effects model and measured as odds ratio (OR) or mean difference (MD) where applicable, and 95% confidence intervals (CI) were calculated. Risk of bias was assessed using the tool from the Cochrane Handbook for Systematic Reviews of Interventions. Results: The search strategy collected 519 studies, 16 of which met analysis inclusion criteria. HIE infants totaled 1,288 infants from included studies, 646 infants received some form of combination therapy, while 642 received TH alone. GABA receptor agonists, NMDA receptor antagonists, neurogenic and angiogenic agents, stem cells, glucocorticoids and antioxidants were identified as candidate adjuvants to TH that have been evaluated in clinical settings compared to TH alone. Length of hospitalization was significantly reduced in infants treated with combination therapy (MD -4.81, 95% CI [-8.42. to -1.19], p = .009) compared to those treated with TH alone. Risk of mortality and neurodevelopmental impairment did not differ between combination therapy and TH alone groups. Conclusion: Compared to the current standard of care, administration of neuroprotective adjuvants with TH reduced the duration of hospitalization but did not impact the risk of mortality or neurodevelopmental impairment in HIE infants. Meta-analysis was limited by a moderate risk of bias among included studies and small sample sizes. This analysis highlights the need for preclinical trials to conduct drug development studies in hypothermic settings to identify relevant molecular targets that may offer additive or synergistic neuroprotection to TH, and the need for larger powered clinical trials to determine the dose and timing of administration at which maximal clinical benefits are observed for adjuvant neuroprotectants.

[Developmental outcomes of very preterm and extremely preterm infants at the 12 months corrected age]

OBJECTIVE

To establish effect of Cortexin for development outcomes of preterm neonates born with low and extremely low body weight, with perinatal pyramidal tract (PT) damage.

MATERIAL AND METHODS

127 children born with very low body weight and extremely low body weight were examined. I group - 22 infant with damage to the PT, treating non-drug rehabilitation during the first year. II group - 59 infant with damage to the PT, treating non-drug rehabilitation and Cortexin during the first year. III control group - 46 infant without structural changes according DTI MRI. Neurodevelopmental outcomes was evaluated by using the INFANIB scale at the 12 months corrected age.

RESULTS

Significant differences were found between groups. The results showed that at the correct age of 12 months normal neurodevelopment occurred more often in two times in second group (1 group - 18.2%, 2 group - 40.7%, p<0.05). Almost of children from control group had normal psychomotor development (3 group - 93.5%). Cerebral palsy was noted significantly more often in the first group (1 group - 36.4%, 3 group - 13.6%, p<0.05).

CONCLUSIONS

DTI MRI has high prognostic value for very preterm and extremely preterm infants. In the same time, we can observe better development outcomes with damage to the PT in the group of children treating non-drug rehabilitation and Cortexin during the first year.

Assessing Creatine Supplementation for Neuroprotection against Perinatal Hypoxic-Ischaemic Encephalopathy: A Systematic Review of Perinatal and Adult Pre-Clinical Studies

There is an important unmet need to develop interventions that improve outcomes of hypoxic-ischaemic encephalopathy (HIE). Creatine has emerged as a promising neuroprotective agent. Our objective was to systematically evaluate the preclinical animal studies that used creatine for perinatal neuroprotection, and to identify knowledge gaps that need to be addressed before creatine can be considered for pragmatic clinical trials for HIE. Methods: We reviewed preclinical studies up to 20 September 2021 using PubMed, EMBASE and OVID MEDLINE databases. The SYRCLE risk of bias assessment tool was utilized. Results: Seventeen studies were identified. Dietary creatine was the most common administration route. Cerebral creatine loading was age-dependent with near term/term-equivalent studies reporting higher increases in creatine/phosphocreatine compared to adolescent-adult equivalent studies. Most studies did not control for sex, study long-term histological and functional outcomes, or test creatine post-HI. None of the perinatal studies that suggested benefit directly controlled core body temperature (a known confounder) and many did not clearly state controlling for potential study bias. Conclusion: Creatine is a promising neuroprotective intervention for HIE. However, this systematic review reveals key knowledge gaps and improvements to preclinical studies that must be addressed before creatine can be trailed for neuroprotection of the human fetus/neonate.

Interleukin-1 blockade attenuates white matter inflammation and oligodendrocyte loss after progressive systemic lipopolysaccharide exposure in near-term fetal sheep

Background

Increased systemic and tissue levels of interleukin (IL)-1β are associated with greater risk of impaired neurodevelopment after birth. In this study, we tested the hypothesis that systemic IL-1 receptor antagonist (Ra) administration would attenuate brain inflammation and injury in near-term fetal sheep exposed to lipopolysaccharide (LPS).

Methods

Chronically instrumented near-term fetal sheep at 0.85 of gestation were randomly assigned to saline infusion (control, n = 9), repeated LPS infusions (0 h = 300 ng, 24 h = 600 ng, 48 h = 1200 ng, n = 8) or repeated LPS plus IL-1Ra infusions (13 mg/kg infused over 4 h) started 1 h after each LPS infusion (n = 9). Sheep were euthanized 4 days after starting infusions for histology.

Results

LPS infusions increased circulating cytokines and were associated with electroencephalogram (EEG) suppression with transiently reduced mean arterial blood pressure, and increased carotid artery perfusion and fetal heart rate (P < 0.05 vs. control for all). In the periventricular and intragyral white matter, LPS-exposure increased IL-1β immunoreactivity, numbers of caspase 3+ cells and microglia, reduced astrocyte and olig-2+ oligodendrocyte survival but did not change numbers of mature CC1+ oligodendrocytes, myelin expression or numbers of neurons in the cortex and subcortical regions. IL-1Ra infusions reduced circulating cytokines and improved recovery of EEG activity and carotid artery perfusion. Histologically, IL-1Ra reduced microgliosis, IL-1β expression and caspase-3+ cells, and improved olig-2+ oligodendrocyte survival.

Conclusion

IL-1Ra improved EEG activity and markedly attenuated systemic inflammation, microgliosis and oligodendrocyte loss following LPS exposure in near-term fetal sheep. Further studies examining the long-term effects on brain maturation are now needed.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-021-02238-4.

Current Therapies for Neonatal Hypoxic-Ischaemic and Infection-Sensitised Hypoxic-Ischaemic Brain Damage

Neonatal hypoxic-ischaemic brain damage is a leading cause of child mortality and morbidity, including cerebral palsy, epilepsy, and cognitive disabilities. The majority of neonatal hypoxic-ischaemic cases arise as a result of impaired cerebral perfusion to the foetus attributed to uterine, placental, or umbilical cord compromise prior to or during delivery. Bacterial infection is a factor contributing to the damage and is recorded in more than half of preterm births. Exposure to infection exacerbates neuronal hypoxic-ischaemic damage thus leading to a phenomenon called infection-sensitised hypoxic-ischaemic brain injury. Models of neonatal hypoxia-ischaemia (HI) have been developed in different animals. Both human and animal studies show that the developmental stage and the severity of the HI insult affect the selective regional vulnerability of the brain to damage, as well as the subsequent clinical manifestations. Therapeutic hypothermia (TH) is the only clinically approved treatment for neonatal HI. However, the number of HI infants needed to treat with TH for one to be saved from death or disability at age of 18-22 months, is approximately 6-7, which highlights the need for additional or alternative treatments to replace TH or increase its efficiency. In this review we discuss the mechanisms of HI injury to the immature brain and the new experimental treatments studied for neonatal HI and infection-sensitised neonatal HI.

Fetal Neuroprotective Strategies: Therapeutic Agents and Their Underlying Synaptic Pathways

Synaptic signaling is integral for proper brain function. During fetal development, exposure to inflammation or mild hypoxic-ischemic insult may lead to synaptic changes and neurological damage that impairs future brain function. Preterm neonates are most susceptible to these deleterious outcomes. Evaluating clinically used and novel fetal neuroprotective measures is essential for expanding treatment options to mitigate the short and long-term consequences of fetal brain injury. Magnesium sulfate is a clinical fetal neuroprotective agent utilized in cases of imminent preterm birth. By blocking N-methyl-D-aspartate receptors, magnesium sulfate reduces glutamatergic signaling, which alters calcium influx, leading to a decrease in excitotoxicity. Emerging evidence suggests that melatonin and N-acetyl-L-cysteine (NAC) may also serve as novel putative fetal neuroprotective candidates. Melatonin has important anti-inflammatory and antioxidant properties and is a known mediator of synaptic plasticity and neuronal generation. While NAC acts as an antioxidant and a precursor to glutathione, it also modulates the glutamate system. Glutamate excitotoxicity and dysregulation can induce perinatal preterm brain injury through damage to maturing oligodendrocytes and neurons. The improved drug efficacy and delivery of the dendrimer-bound NAC conjugate provides an opportunity for enhanced pharmacological intervention. Here, we review recent literature on the synaptic pathways underlying these therapeutic strategies, discuss the current gaps in knowledge, and propose future directions for the field of fetal neuroprotective agents.

Preventing Brain Injury in the Preterm Infant-Current Controversies and Potential Therapies

Preterm birth is associated with a high risk of morbidity and mortality including brain damage and cerebral palsy. The development of brain injury in the preterm infant may be influenced by many factors including perinatal asphyxia, infection/inflammation, chronic hypoxia and exposure to treatments such as mechanical ventilation and corticosteroids. There are currently very limited treatment options available. In clinical trials, magnesium sulfate has been associated with a small, significant reduction in the risk of cerebral palsy and gross motor dysfunction in early childhood but no effect on the combined outcome of death or disability, and longer-term follow up to date has not shown improved neurological outcomes in school-age children. Recombinant erythropoietin has shown neuroprotective potential in preclinical studies but two large randomized trials, in extremely preterm infants, of treatment started within 24 or 48 h of birth showed no effect on the risk of severe neurodevelopmental impairment or death at 2 years of age. Preclinical studies have highlighted a number of promising neuroprotective treatments, such as therapeutic hypothermia, melatonin, human amnion epithelial cells, umbilical cord blood and vitamin D supplementation, which may be useful at reducing brain damage in preterm infants. Moreover, refinements of clinical care of preterm infants have the potential to influence later neurological outcomes, including the administration of antenatal and postnatal corticosteroids and more accurate identification and targeted treatment of seizures.

The Function of the NMDA Receptor in Hypoxic-Ischemic Encephalopathy

Hypoxic-ischemic encephalopathy (HIE) is one of the main forms of neonatal brain injury which could lead to neonatal disability or even cause neonatal death. Therefore, HIE strongly affects the health of newborns and brings heavy burden to the family and society. It has been well studied that N-methyl-D-aspartate (NMDA) receptors are involved in the excitotoxicity induced by hypoxia ischemia in adult brain. Recently, it has been shown that the NMDA receptor also plays important roles in HIE. In the present review, we made a summary of the molecular mechanism of NMDA receptor in the pathological process of HIE, focusing on the distinct role of GluN2A- and GluN2B-containing NMDA receptor subtypes and aiming to provide some insights into the clinical treatment and drug development of HIE.

Combination treatments with therapeutic hypothermia for hypoxic-ischemic neuroprotection

Therapeutic hypothermia is now proven to reduce death or disability in term and near-term born infants with moderate to severe hypoxic-ischemic encephalopathy. Nevertheless, many infants still survive with disability, despite treatment with hypothermia. Recent preclinical and clinical studies suggest that current protocols for therapeutic hypothermia are near-optimal. The obvious strategy, in addition to improving early initiation of therapeutic hypothermia after birth, is to combine hypothermia with other neuroprotective agents. We review evidence that the mechanisms of action of many promising agents overlap with the anti-excitotoxic, anti-apoptotic, and anti-inflammatory mechanisms of hypothermia, leading to a lack of benefit from combination treatment. Moreover, even apparently beneficial combinations have failed to translate in clinical trials. These considerations highlight the need for preclinical studies to test clinically realistic protocols of timing and duration of treatment, before committing to large randomized controlled trials.

Stem cell-based interventions for the prevention of morbidity and mortality following hypoxic-ischaemic encephalopathy in newborn infants

BACKGROUND

Hypoxic-ischaemic encephalopathy (HIE) is a leading cause of mortality and long-term neurological sequelae, affecting thousands of children worldwide. Current therapies to treat HIE are limited to cooling. Stem cell-based therapies offer a potential therapeutic approach to repair or regenerate injured brain tissue. These preclinical findings have now culminated in ongoing human neonatal trials.

OBJECTIVES

To determine the efficacy and safety of stem cell-based interventions for the treatment of hypoxic-ischaemic encephalopathy (HIE) in newborn infants.

SEARCH METHODS

We used the standard search strategy of Cochrane Neonatal to search the Cochrane Central Register of Controlled Trials (CENTRAL; 2020, Issue 5), MEDLINE via PubMed (1966 to 8 June 2020), Embase (1980 to 8 June 2020), and CINAHL (1982 to 8 June 2020). We also searched clinical trials databases, conference proceedings, and the reference lists of retrieved articles for randomised controlled trials and quasi-randomised trials.

SELECTION CRITERIA

Randomised controlled trials, quasi-randomised controlled trials and cluster trials comparing 1) stem cell-based interventions (any type) compared to control (placebo or no treatment); 2) use of mesenchymal stem/stromal cells (MSCs) of type (e.g. number of doses or passages) or source (e.g. autologous versus allogeneic, or bone marrow versus cord) versus MSCs of other type or source; 3) use of stem cell-based interventions other than MSCs of type (e.g. mononuclear cells, oligodendrocyte progenitor cells, neural stem cells, hematopoietic stem cells, and inducible pluripotent stem cells) or source (e.g. autologous versus allogeneic, or bone marrow versus cord) versus stem cell-based interventions other than MSCs of other type or source; or 4) MSCs versus stem cell-based interventions other than MSCs.

DATA COLLECTION AND ANALYSIS

For each of the included trials, two authors independently planned to extract data (e.g. number of participants, birth weight, gestational age, type and source of MSCs or other stem cell-based interventions) and assess the risk of bias (e.g. adequacy of randomisation, blinding, completeness of follow-up). The primary outcomes considered in this review are all-cause neonatal mortality, major neurodevelopmental disability, death or major neurodevelopmental disability assessed at 18 to 24 months of age. We planned to use the GRADE approach to assess the quality of evidence.

MAIN RESULTS

Our search strategy yielded 616 references. Two review authors independently assessed all references for inclusion. We did not find any completed studies for inclusion. Fifteen RCTs are currently registered and ongoing. We describe the three studies we excluded.

AUTHORS' CONCLUSIONS

There is currently no evidence from randomised trials that assesses the benefit or harms of stem cell-based interventions for the prevention of morbidity and mortality following hypoxic-ischaemic encephalopathy in newborn infants.

A randomized controlled trial on the use of magnesium sulfate and melatonin in neonatal hypoxic ischemic encephalopathy

BACKGROUND

Birth asphyxia is a leading case of neonatal morbidity and mortality especially in developing countries. Hypoxic-ischemic encephalopathy (HIE) attributed to asphyxia can be ameliorated with several remedies, although full recovery is currently not feasible. The aim of this trial on infants with HIE who are receiving melatonin therapy, is to assess the added effect of magnesium sulfate (MgSO4) on the expression of S100-B, a marker of brain injury.

METHODS

This study is a randomized controlled trial on neonates with moderate HIE (Sarnat grade II). Infants were randomized into 2 groups; group1 who received MgSO4 and melatonin; and group 2 who received melatonin only. Serum concentrations of S100-B were measured at baseline, and at days 2 and 6 of therapy.

RESULTS

The study included 60 neonates of them 30 infants in group 1 and 30 infants in group 2. S100-B did not differ between groups 1 and 2 at enrollment (median = 13.5 vs 13.2, p = 0.381). However, group 1 had lower concentrations of S100-B at 2 days (median = 8 vs 12, p = 0.001) and at 6 days (median = 3 vs 10.5, p < 0.001), respectively. Compared to baseline, S100-B decreased in in group 2 at day 6 (13.2 vs 10.5, p = 0.011) but did not decrease at day 2 (13.2 vs 12, p = 0.478).

CONCLUSIONS

MgSO4 may have an added effect for the reduction in brain injury in infants with HIE who are receiving melatonin.

A Systematic Review of Magnesium Sulfate for Perinatal Neuroprotection: What Have We Learnt From the Past Decade?

There is an important unmet need to improve long term outcomes of encephalopathy for preterm and term infants. Meta-analyses of large controlled trials suggest that maternal treatment with magnesium sulfate (MgSO₄) is associated with a reduced risk of cerebral palsy and gross motor dysfunction after premature birth. However, to date, follow up to school age has found an apparent lack of long-term clinical benefit. Because of this inconsistency, it remains controversial whether MgSO₄ offers sustained neuroprotection. We systematically reviewed preclinical and clinical studies reported from January 1 2010, to January 31 2020 to evaluate the most recent advances and knowledge gaps relating to the efficacy of MgSO₄ for the treatment of perinatal brain injury. The outcomes of MgSO₄ in preterm and term-equivalent animal models of perinatal encephalopathy were highly inconsistent between studies. None of the perinatal rodent studies that suggested benefit directly controlled body or brain temperature. The majority of the studies did not control for sex, study long term histological and functional outcomes or use pragmatic treatment regimens and many did not report controlling for potential study bias. Finally, most of the recent preterm or term human studies that tested the potential of MgSO₄ for perinatal neuroprotection were relatively underpowered, but nevertheless, suggest that any improvements in neurodevelopment were at best modest or absent. On balance, these data suggest that further rigorous testing in translational preclinical models of perinatal encephalopathy is essential to ensure safety and best regimens for optimal preterm neuroprotection, and before further clinical trials of MgSO₄ for perinatal encephalopathy at term are undertaken.

Pathophysiology of hypoxic-ischemic encephalopathy: a review of the past and a view on the future

Hypoxic-ischemic encephalopathy, also referred as HIE, is a type of brain injury or damage that is caused by a lack of oxygen to the brain during neonatal period. The incidence is approximately 1.5 cases per 1000 live births in developed countries. In low and middle-income countries, the incidence is much higher (10‒20 per 1000 live births). The treatment for neonatal HIE is hypothermia that is only partially effective (not more than 50% of the neonates treated achieve an improved outcome). HIE pathophysiology involves oxidative stress, mitochondrial energy production failure, glutaminergic excitotoxicity, and apoptosis. So, in the last years, many studies have focused on peptides that act somewhere in the pathway activated by severe anoxic injury leading to HIE. This review describes the pathophysiology of perinatal HIE and the mechanisms that could be the target of innovative HIE treatments.

Short-term effects of early initiation of magnesium infusion combined with cooling after hypoxia-ischemia in term piglets

BACKGROUND

Neuroprotection from therapeutic hypothermia (HT) is incomplete, therefore additional strategies are necessary to improve long-term outcomes. We assessed the neuroprotective efficacy of magnesium sulfate (MgSO₄) bolus and infusion over 48 h plus HT in a piglet model of term neonatal encephalopathy (NE).

METHODS

Fifteen newborn piglets were randomized following hypoxia-ischemia (HI) to: (i) MgSO₄ 180 mg/kg bolus and 8 mg/kg/h infusion with HT (Mg+HT) or (ii) HT and saline 0.5 ml/h (HT). Treatments were initiated 1 h post-HI; HT administered for 12 h (33.5 °C). HI was performed by transient carotid occlusion and inhalation of 6% O₂ for 20-25 min. Primary outcomes included aEEG, magnetic resonance spectroscopy (MRS) at 24, and 48 h, and immunohistochemistry.

RESULTS

MgSO₄ bolus and infusion was well tolerated (no hypotension) and doubled serum magnesium (0.72 vs 1.52 mmol/L) with modest (16%) rise in CSF. In Mg+HT compared to HT, there was overall reduced cell death (p = 0.01) and increased oligodendrocytes (p = 0.002). No improvement was seen on aEEG recovery (p = 0.084) or MRS (Lac/NAA; PCr/Pi; NTP/epp) (p > 0.05) at 48 h.

CONCLUSION

Doubling serum magnesium with HT was safe; however, the small incremental benefit of Mg+HT compared to HT is unlikely to translate into substantive long-term improvement. Such an incremental effect might justify further study of MgSO₄ in combination with multiple therapies.

Microglia in developing white matter and perinatal brain injury

Perinatal brain injury (PBI) to the developing white matter results in hypomyelination of axons and can cause long-term motor and cognitive deficits e.g. cerebral palsy. There are currently no approved therapies aimed at repairing the white matter following insult, underscoring the need to investigate the mechanisms underlying the pathogenesis of PBI. Microglia have been strongly implicated, but their function and heterogeneity in this context remain poorly understood, posing a barrier to the development of microglia-targeted therapies for white matter repair following PBI. In this review, we discuss the roles of microglia in normal white matter development and in PBI, and potential drug strategies to influence microglial responses in this setting.

Antenatal prevention of cerebral palsy and childhood disability: is the impossible possible?

This review covers our current knowledge of the causes of perinatal brain injury leading to cerebral palsy-like outcomes, and argues that much of this brain damage is preventable. We review the experimental evidence that there are treatments that can be safely administered to women in late pregnancy that decrease the likelihood and extent of perinatal brain damage that occurs because of acute and severe hypoxia that arises during some births, and the additional impact of chronic fetal hypoxia, infection, inflammation, growth restriction and preterm birth. We discuss the types of interventions required to ameliorate or even prevent apoptotic and necrotic cell death, and the vulnerability of all the major cell types in the brain (neurons, astrocytes, oligodendrocytes, microglia, cerebral vasculature) to hypoxia/ischaemia, and whether a pan-protective treatment given to the mother before birth is a realistic prospect.

Current and Emerging Therapies in the Management of Hypoxic Ischemic Encephalopathy in Neonates

Neonatal hypoxic ischemic encephalopathy (HIE) presents a significant clinical burden with its high mortality and morbidity rates globally. Therapeutic hypothermia (TH) is now standard of care for infants with moderate to severe HIE, but has not definitively changed outcomes in severe HIE. In this review, we discuss newer promising markers that may help the clinician identify severity of HIE. Therapies that are beneficial and agents that hold promise for neuroprotection are described, both for use either alone or as adjuncts to TH. These include endogenous pathway modifiers such as erythropoietin and analogues, melatonin, and remote ischemic post conditioning. Stem cells have therapeutic potential in this condition, as in many other neonatal conditions. Of the agents listed, only erythropoietin and analogues are currently being evaluated in large randomized controlled trials (RCTs). Exogenous therapies such as argon and xenon, allopurinol, monosialogangliosides, and magnesium sulfate continue to be investigated. The recognition of tertiary mechanisms of brain damage has opened up new research into therapies not only to attenuate brain damage but also to promote cell repair and regeneration in a developmentally disorganized brain long after the perinatal insult. These alternative modalities may be especially important in mild HIE and in areas of the world where there is limited access to expensive hypothermia equipment and services.

The fetus at the tipping point: modifying the outcome of fetal asphyxia

Brain injury around birth is associated with nearly half of all cases of cerebral palsy. Although brain injury is multifactorial, particularly after preterm birth, acute hypoxia-ischaemia is a major contributor to injury. It is now well established that the severity of injury after hypoxia-ischaemia is determined by a dynamic balance between injurious and protective processes. In addition, mothers who are at risk of premature delivery have high rates of diabetes and antepartum infection/inflammation and are almost universally given treatments such as antenatal glucocorticoids and magnesium sulphate to reduce the risk of death and complications after preterm birth. We review evidence that these common factors affect responses to fetal asphyxia, often in unexpected ways. For example, glucocorticoid exposure dramatically increases delayed cell loss after acute hypoxia-ischaemia, largely through secondary hyperglycaemia. This critical new information is important to understand the effects of clinical treatments of women whose fetuses are at risk of perinatal asphyxia.

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.

Pediatric brain repair from endogenous neural stem cells of the subventricular zone

There is great interest in the regenerative potential of the neural stem cells and progenitors that populate the germinal zones of the immature brain. Studies using animal models of pediatric brain injuries have provided a clearer understanding of the responses of these progenitors to injury. In this review, we have compared and contrasted the responses of the endogenous neural stem cells and progenitors of the subventricular zone in animal models of neonatal cerebral hypoxia-ischemia, neonatal stroke, congenital cardiac disease, and pediatric traumatic brain injury. We have reviewed the dynamic shifts that occur within this germinal zone with injury as well as changes in known signaling molecules that affect these progenitors. Importantly, we have summarized data on the extent to which cell replacement occurs in response to each of these injuries, opportunities available, and obstacles that will need to be overcome to improve neurological outcomes in survivors.

Examining the effect of MgSO4 on sharp wave transient activity in the hypoxic-ischemic fetal sheep model

Hypoxic-ischemic encephalopathy (HIE) due to lack of oxygen is a debilitating disorder experienced by a significant number of preterm infants during birth. Studies show that the brain undergoes different phases of injury following hypoxic insult, but the first 6-8 hours (known as a latent phase) are the key to treatment efficacy. Cerebral hypothermia is one known treatment, and for it to be effective it must be started during the latent phase and continued for several days. In order to determine the effectiveness of treatment it is important to pinpoint the time of insult. Monitoring of sharp wave transient activity in the hypoxic-ischemic (HI) electroencephalogram (EEG) could be a predictor for time of hypoxic insult. Due to practicality, it is optimal if this monitoring is performed automatically. Further, MgSO4 is a drug given to an increasing number of women in labor, due to its neuroprotective properties. This drug may influence transient activity in the HI fetal sheep EEG, leading to further complications in predicting hypoxic insult. This paper explores the effect of MgSO4 on sharp wave transient activity in the EEG of a HI fetal sheep. Demonstrated in this paper is the usage of a Wavelet-Type-II Fuzzy classifier to detect sharp wave transients during the latent phase of a control group fetal sheep and an MgSO4-treated fetal sheep. This detection was performed with an average overall performance of 93.21%±5.49 over 660 minutes of latent phase, post occlusion. There were no significant differences in number of sharp wave transients in the early- and mid-latent phases of injury for both fetal sheep. However, in the late-latent phase the MgSO4-treated fetal sheep had significantly fewer sharp wave transients than the control fetal sheep.

Management and investigation of neonatal encephalopathy: 2017 update

This review discusses an approach to determining the cause of neonatal encephalopathy, as well as current evidence on resuscitation and subsequent management of hypoxic-ischaemic encephalopathy (HIE). Encephalopathy in neonates can be due to varied aetiologies in addition to hypoxic-ischaemia. A combination of careful history, examination and the judicious use of investigations can help determine the cause. Over the last 7 years, infants with moderate to severe HIE have benefited from the introduction of routine therapeutic hypothermia; the number needed to treat for an additional beneficial outcome is 7 (95% CI 5 to 10). More recent research has focused on optimal resuscitation practices for babies with cardiorespiratory depression, such as delayed cord clamping after establishment of ventilation and resuscitation in air. Around a quarter of infants with asystole at 10 min after birth who are subsequently cooled have normal outcomes, suggesting that individualised decision making on stopping resuscitation is needed, based on access to intensive treatment unit and early cooling. The full benefit of cooling appears to have been exploited in our current treatment protocols of 72 hours at 33.5°C; deeper and longer cooling showed adverse outcome. The challenge over the next 5-10 years will be to assess which adjunct therapies are safe and optimise hypothermic brain protection in phase I and phase II trials. Optimal care may require tailoring treatments according to gender, genetic risk, injury severity and inflammatory status.

Magnesium sulfate reduces EEG activity but is not neuroprotective after asphyxia in preterm fetal sheep

Magnesium sulfate is now widely recommended for neuroprotection for preterm birth; however, this has been controversial because there is little evidence that magnesium sulfate is neuroprotective. Preterm fetal sheep (104 days gestation; term is 147 days) were randomly assigned to receive sham occlusion (n = 7), i.v. magnesium sulfate (n = 10) or saline (n = 8) starting 24 h before asphyxia until 24 h after asphyxia. Sheep were killed 72 h after asphyxia. Magnesium sulfate infusion reduced electroencephalograph power and fetal movements before asphyxia. Magnesium sulfate infusion did not affect electroencephalograph power during recovery, but was associated with marked reduction of the post-asphyxial seizure burden (mean ± SD: 34 ± 18 min vs. 107 ± 74 min, P < 0.05). Magnesium sulfate infusion did not affect subcortical neuronal loss. In the intragyral and periventricular white matter, magnesium sulfate was associated with reduced numbers of all (Olig-2+ve) oligodendrocytes in the intragyral (125 ± 23 vs. 163 ± 38 cells/field) and periventricular white matter (162 ± 39 vs. 209 ± 44 cells/field) compared to saline-treated controls ( P < 0.05), but no effect on microglial induction or astrogliosis. In conclusion, a clinically comparable dose of magnesium sulfate showed significant anticonvulsant effects after asphyxia in preterm fetal sheep, but did not reduce asphyxia-induced brain injury and exacerbated loss of oligodendrocytes.

Sex, drugs and rock and roll: tales from preterm fetal life

Premature fetuses and babies are at greater risk of mortality and morbidity than their term counterparts. The underlying causes are multifactorial, but include exposure to hypoxia. Immaturity of organs and their functional control may impair the physiological defence responses to hypoxia and the preterm fetal responses, or lack thereof, to moderate hypoxia appear to support this concept. However, as this review demonstrates, despite immaturity, the preterm fetus responds to asphyxia in a qualitatively similar manner to that seen at term. This highlights the importance in understanding metabolism versus homeostatic threat when assessing fetal responses to adverse challenges such as hypoxia. Data are presented to show that the preterm fetal adaptation to asphyxia is triphasic in nature. Phase one represents the rapid institution of maximal defences, designed to maintain blood pressure and central perfusion at the expense of peripheral organs. Phase two is one of adaptive compensation. Controlled reperfusion partially offsets peripheral tissue oxygen debt, while maintaining sufficient vasoconstriction to limit the fall in perfusion. Phase three is about decompensation. Strikingly, the preterm fetus generally performs better during phases two and three, and can survive for longer without injury. Paradoxically, however, the ability to survive can lead to longer exposure to hypotension and hypoperfusion and thus potentially greater injury. The effects of fetal sex, inflammation and drugs on the triphasic adaptations are reviewed. Finally, the review highlights the need for more comprehensive studies to understand the complexity of perinatal physiology if we are to develop effective strategies to improve preterm outcomes.

Role of Antioxidants in Neonatal Hypoxic-Ischemic Brain Injury: New Therapeutic Approaches

Hypoxic-ischemic brain damage is an alarming health and economic problem in spite of the advances in neonatal care. It can cause mortality or detrimental neurological disorders such as cerebral palsy, motor impairment and cognitive deficits in neonates. When hypoxia-ischemia occurs, a multi-faceted cascade of events starts out, which can eventually cause cell death. Lower levels of oxygen due to reduced blood supply increase the production of reactive oxygen species, which leads to oxidative stress, a higher concentration of free cytosolic calcium and impaired mitochondrial function, triggering the activation of apoptotic pathways, DNA fragmentation and cell death. The high incidence of this type of lesion in newborns can be partly attributed to the fact that the developing brain is particularly vulnerable to oxidative stress. Since antioxidants can safely interact with free radicals and terminate that chain reaction before vital molecules are damaged, exogenous antioxidant therapy may have the potential to diminish cellular damage caused by hypoxia-ischemia. In this review, we focus on the neuroprotective effects of antioxidant treatments against perinatal hypoxic-ischemic brain injury, in the light of the most recent advances.

Magnesium sulfate treatment for juvenile ferrets following induction of hydrocephalus with kaolin

Background

Previous work with 3-week hydrocephalic rats showed that white matter damage could be reduced by the calcium channel antagonist magnesium sulfate (MgSO₄). We hypothesized that MgSO₄ therapy would improve outcomes in ferrets with hydrocephalus induced with kaolin at 15 days.

Methods

MRI was performed at 29 days to assess ventricle size and stratify ferrets to treatment conditions. Beginning at 31 days age, they were treated daily for 14 days with MgSO₄ (9 mM/kg/day) or sham saline therapy, and then imaged again before sacrifice. Behavior was examined thrice weekly. Histological and biochemical ELISA and myelin enzyme activity assays were performed at 46 days age.

Results

Hydrocephalic ferrets exhibited some differences in weight and behavior between treatment groups. Those receiving MgSO₄ weighed less, were more lethargic, and displayed reduced activity compared to those receiving saline injections. Hydrocephalic ferrets developed ventriculomegaly, which was not modified by MgSO₄ treatment. Histological examination showed destruction of periventricular white matter. Glial fibrillary acidic protein content, myelin basic protein content, and myelin enzyme activity did not differ significantly between treatment groups.

Conclusion

The hydrocephalus-associated disturbances in juvenile ferret brains are not ameliorated by MgSO₄ treatment, and lethargy is a significant side effect.

Drugs for neuroprotection after birth asphyxia: Pharmacologic adjuncts to hypothermia

An adverse outcome is still encountered in 45% of full-term neonates with perinatal asphyxia who are treated with moderate hypothermia. At present pharmacologic therapies are developed to be added to hypothermia. In the present article, these potential neuroprotective interventions are described based on the molecular pathways set in motion during fetal hypoxia and following reoxygenation and reperfusion after birth. These pathways include excessive production of excitotoxins with subsequent over-stimulation of NMDA receptors and calcium influx in neuronal cells, excessive production of reactive oxygen and nitrogen species, activation of inflammation leading to inappropriate apoptosis, and loss of neurotrophic factors. Possibilities for pharmacologic combination therapy, where each drug will be administered based on the optimal point of time in the cascade of destructive molecular reactions, may further reduce brain damage due to perinatal asphyxia.

What can you do to protect the newborn brain?

PURPOSE OF REVIEW

Hypoxic-ischemic brain injury is a leading cause of mortality and morbidity in neonates. Treating such injury by interrupting the excitotoxic-oxidative cascade is of immense importance. This review will focus on novel techniques of neuroprotection and describe the latest advances in established therapeutic methods.

KEY FINDINGS

Although the primacy of therapeutic hypothermia in treating hypoxic-ischemic encephalopathy is well established, recent research establishes that the arbitrarily chosen regimen of cooling to 33°C for 72 h may indeed be the most appropriate method. The optimal duration of antenatal magnesium therapy for neuroprotection remains unsettled, though it is reassuring that even 12 h or less of magnesium therapy results in comparable neurological outcomes. Combining adjuvant therapies such as melatonin or erythropoietin with therapeutic hypothermia results in favorable neurological outcomes compared with hypothermia alone. Finally, stem cell-based therapies show considerable potential in preclinical studies.

SUMMARY

Significant advances have occurred in the management of neonatal brain injury. With establishment of the optimal temperature and duration of hypothermia, combinatory therapies using adjuncts hold the greatest promise. Promising preclinical approaches such as stem cell-based therapy and use of noble gases need to be confirmed with clinical trials.

Neuroprotective Strategies after Neonatal Hypoxic Ischemic Encephalopathy

Neonatal hypoxic ischemic encephalopathy (HIE) is a devastating disease that primarily causes neuronal and white matter injury and is among the leading cause of death among infants. Currently there are no well-established treatments; thus, it is important to understand the pathophysiology of the disease and elucidate complications that are creating a gap between basic science and clinical translation. In the development of neuroprotective strategies and translation of experimental results in HIE, there are many limitations and challenges to master based on an appropriate study design, drug delivery properties, dosage, and use in neonates. We will identify understudied targets after HIE, as well as neuroprotective molecules that bring hope to future treatments such as melatonin, topiramate, xenon, interferon-beta, stem cell transplantation. This review will also discuss some of the most recent trials being conducted in the clinical setting and evaluate what directions are needed in the future.

Neuroprotective agents for neonatal hypoxic-ischemic brain injury

Hypoxic-ischemic (H-I) brain injury in newborns is a major cause of morbidity and mortality that claims thousands of lives each year. In this review, we summarize the promising neuroprotective agents tested on animal models and pilot clinical studies of neonatal H-I brain injury according to the different phases of the disease. These agents target various phases of injury including the early phase of excitotoxicity, oxidative stress and apoptosis as well as late-phase inflammatory reaction and neural repair. We analyze the cell survival and cell death pathways modified by these agents in neonatal H-I brain injury. We aim to 'build a bridge' between animal trials of neuroprotective agents and potential candidate treatments for future clinical applications against H-I encephalopathy.

Magnesium sulphate and cardiovascular and cerebrovascular adaptations to asphyxia in preterm fetal sheep

Magnesium sulphate is a standard therapy for eclampsia in pregnancy and is widely recommended for perinatal neuroprotection during threatened preterm labour. MgSO4 is a vasodilator and negative inotrope. Therefore the aim of this study was to investigate the effect of MgSO4 on the cardiovascular and cerebrovascular responses of the preterm fetus to asphyxia. Fetal sheep were instrumented at 98 ± 1 days of gestation (term = 147 days). At 104 days, unanaesthetised fetuses were randomly assigned to receive an intravenous infusion of MgSO4 (n = 6) or saline (n = 9). At 105 days all fetuses underwent umbilical cord occlusion for 25 min. Before occlusion, MgSO4 treatment reduced heart rate and increased femoral blood flow (FBF) and vascular conductance compared to controls. During occlusion, carotid and femoral arterial conductance and blood flows were higher in MgSO4-treated fetuses than controls. After occlusion, fetal heart rate was lower and carotid and femoral arterial conductance and blood flows were higher in MgSO4-treated fetuses than controls. Femoral arterial waveform height and width were increased during MgSO4 infusion, consistent with increased stroke volume. MgSO4 did not alter the fetal neurophysiological or nuchal electromyographic responses to asphyxia. These data demonstrate that a clinically comparable dose of MgSO4 increased FBF and stroke volume without impairing mean arterial pressure (MAP) or carotid blood flow (CaBF) during and immediately after profound asphyxia. Thus, MgSO4 may increase perfusion of peripheral vascular beds during adverse perinatal events.

Beneficence and Nonmaleficence in Treating Neonatal Hypoxic-Ischemic Brain Injury

The successful clinical translation of therapeutic hypothermia offers the tantalizing possibility that further improvements in outcomes may be possible by combining cooling with other neuroprotective drugs. The challenge now is to select from a daunting range of potential treatments. The patient's best interest must be central to ethical decision making at all times. However, the beneficence or nonmaleficence of potential therapies is seldom clear for any individual patient at the time of testing new therapies. Clinical randomized controlled trials are generally acknowledged by the scientific community as the 'gold standard' for evaluating interventions in health care. Therefore, ethical trial design is of the utmost importance. This paper explores contrasting ethical perspectives on how to select new interventions to treat neonatal encephalopathy after perinatal hypoxia-ischemia.

A Critical Review of Models of Perinatal Infection

One of the central, unanswered questions in perinatology is why preterm infants continue to have such poor long-term neurodevelopmental, cognitive and learning outcomes, even though severe brain injury is now rare. There is now strong clinical evidence that one factor underlying disability may be infection, as well as nonspecific inflammation, during fetal and early postnatal life. In this review, we examine the experimental evidence linking both acute and chronic infection/inflammation with perinatal brain injury and consider key experimental determinants, including the microglia response, relative brain and immune maturity and the pattern of exposure to infection. We highlight the importance of the origin and derivation of the bacterial cell wall component lipopolysaccharide. Such experimental paradigms are essential to determine the precise time course of the inflammatory reaction and to design targeted neuroprotective strategies to protect the perinatal brain from infection and inflammation.