Experimental and clinical evidence of differential effects of magnesium sulfate on neuroprotection and angiogenesis in the fetal brain

Effects of MgSO4 Alone or Associated with 4-PBA on Behavior and White Matter Integrity in a Mouse Model of Cerebral Palsy: A Sex- and Time-Dependent Study

Cerebral palsy (CP) is defined as permanent disorders of movement and posture. Prematurity and hypoxia-ischemia (HI) are risk factors of CP, and boys display a greater vulnerability to develop CP. Magnesium sulfate (MgSO₄) is administered to mothers at risk of preterm delivery as a neuroprotective agent. However, its effectiveness is only partial at long term. To prolong MgSO₄ effects, it was combined with 4-phenylbutyrate (4-PBA). A mouse model of neonatal HI, generating lesions similar to those reported in preterms, was realized. At short term, at the behavioral and cellular levels, and in both sexes, the MgSO₄/4-PBA association did not alter the total prevention induced by MgSO₄ alone. At long term, the association extended the MgSO₄ preventive effects on HI-induced motor and cognitive deficits. This might be sustained by the promotion of oligodendrocyte precursor differentiation after HI at short term, which led to improvement of white matter integrity at long term. Interestingly, at long term, at a behavioral level, sex-dependent responses to HI were observed. This might partly be explained by early sex-dependent pathological processes that occur after HI. Indeed, at short term, apoptosis through mitochondrial pathways seemed to be activated in females but not in males, and only the MgSO₄/4-PBA association seemed to counter this apoptotic process.

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.

Effect of Neuroprotective Magnesium Sulfate Treatment on Brain Transcription Response to Hypoxia Ischemia in Neonate Mice

MgSO₄ is widely used in the prevention of preterm neurological disabilities but its modes of action remain poorly established. We used a co-hybridization approach using the transcriptome in 5-day old mice treated with a single dose of MgSO₄ (600 mg/kg), and/or exposed to hypoxia-ischemia (HI). The transcription of hundreds of genes was altered in all the groups. MgSO₄ mainly produced repressions culminating 6 h after injection. Bio-statistical analysis revealed the repression of synaptogenesis and axonal development. The putative targets of MgSO₄ were Mnk1 and Frm1. A behavioral study of adults did not detect lasting effects of neonatal MgSO₄ and precluded NMDA-receptor-mediated side effects. The effects of MgSO₄ plus HI exceeded the sum of the effects of separate treatments. MgSO₄ prior to HI reduced inflammation and the innate immune response probably as a result of cytokine inhibition (Ccl2, Ifng, interleukins). Conversely, MgSO₄ had little effect on HI-induced transcription by RNA-polymerase II. De novo MgSO₄-HI affected mitochondrial function through the repression of genes of oxidative phosphorylation and many NAD-dehydrogenases. It also likely reduced protein translation by the repression of many ribosomal proteins, essentially located in synapses. All these effects appeared under the putative regulatory MgSO₄ induction of the mTORC2 Rictor coding gene. Lasting effects through Sirt1 and Frm1 could account for this epigenetic footprint.

Short-Term Effect of MgSO4 on the Expression of NRG-ErbB, Dopamine, GABA, and Glutamate Systems in the Fetal Rat Brain

MgSO₄ has been used for the past two decades as neuroprotective treatment in a variety of preterm conditions. Despite the putative advantages of MgSO₄ as a neuroprotective agent in the preterm brain, the short- and long-term molecular function of MgSO₄ as a neuroprotective agent has not been fully elucidated. Neuregulin (NRG1)-ErbB4 signaling plays a critical role in embryonic brain development, in the biology of dopaminergic, GABAergic, and glutamatergic systems. We hypothesize that this pathway may be associated with the neuroprotective role of MgSO₄. The current study aims to investigate the ability of MgSO₄ to modulate the normal developing expression pattern of selected genes related to the NRG1-ErbB, dopaminergic, GABAergic, and glutamatergic systems. We demonstrate that overall short-term treatment of dam rats with MgSO₄ affects the expression of fetal brain NRG1, NRG3, ErbB4, GAD67, tyrosine hydroxylase (TH), dopamine D₂ and D₁ receptors, GluN1, and GluN2B. More specifically, the administration of MgSO₄ alters the expression of NRG-ErbB, GAD67, TH, and D2R at early gestation day 16 (GD16) regardless of the activation of the maternal immune system by lipopolysaccharide (LPS). Our data suggest that MgSO₄ treatment may affect the expression of major neuronal systems and pathways mostly at an early gestation day. These changes might be an initial clue (foundation stone) in the molecular mechanism that underlies the beneficial effect of MgSO₄ as a neuroprotective agent for the developmental brain.

A Case-Control Study of Essential and Toxic Trace Elements and Minerals in Hair of 0-4-Year-Old Children with Cerebral Palsy

The objective of the present study was to assess hair essential and toxic trace elements and minerals in children with cerebral palsy in relation to age of the examinees. A total of 70 children with cerebral palsy and 70 healthy controls aged 0-4 years old were enrolled in the present study. The examined children were also divided into two age groups of those younger and older than 2 years old. Hair trace element content was assessed using ICP-MS at NexION 300D (PerkinElmer, USA). The obtained data demonstrate that hair boron was more than 2-fold lower in CP children as compared with the control group. At the same time, hair Na, Se, and V levels were 21%, 12%, and 20% lower when compared with healthy controls, respectively. It is also notable that a 9% and 28% decrease in hair Fe and Li levels respectively were nearly significant. The observed alterations were more profound in a younger group of patients. No significant group difference in hair toxic metal and metalloid levels was observed between the general cohorts of children with and without CP. In regression models, only hair Al and Ca contents were significantly associated with the presence of cerebral palsy, whereas hair Mg, Na, Ni, and Se levels were characterized as significant negative predictors. The observed alteration in trace element metabolism may also provide an additional link between cerebral palsy, psychomotor delay, and certain diseases, including diabetes, epilepsy, and osteoporosis. However, further studies using other substrates (blood, urine) or biomarkers are required.

Antenatal Magnesium Sulfate and Preeclampsia Differentially Affect Neonatal Cerebral Oxygenation

INTRODUCTION

Magnesium sulfate (MgSO4) is frequently administered for maternal and fetal neuroprotection in preeclampsia (PE) and imminent preterm birth, respectively.

OBJECTIVE

To assess whether MgSO4 affects neonatal cerebral oxygenation, blood flow, and cerebral autoregulation (CAR) during the first postnatal days independently from PE.

METHODS

148 neonates <32 weeks gestational age were included. Cerebral fractional tissue oxygen extraction (cFTOE) was extracted from a daily 2-h period, during which peak systolic blood flow velocity (PSV) and resistance index (RI) of the pericallosal artery were obtained. The percent time of impaired CAR (correlation coefficient between mean arterial blood pressure and cerebral oxygen saturation >0.5) was determined. Linear mixed models were applied.

RESULTS

MgSO4 exposure was recorded in 77 neonates. Twenty-nine neonates were born following PE. MgSO4 independently lowered cFTOE (B: -0.026, 95% CI: -0.050 to 0.002, p < 0.05) but did not affect PSV and RI. PE was associated with a lower cFTOE (B: -0.041, 95% CI: -0.067 to -0.015, p < 0.05) and a tendency towards both lower PSV (B: -4.285, 95% CI: -9.067 to 0.497, p < 0.1) and more impaired CAR (B: 4.042, 95% CI: -0.028 to 8.112, p < 0.1), which seemed to be strongly mediated by fetal brain sparing. MgSO4 did not alter CAR.

CONCLUSIONS

In contrast to fetal brain sparing in PE, MgSO4 seems to lower cFTOE by lowering cerebral oxygen demands in preterm neonates without affecting the cerebrovasculature.

Magnesium Sulfate and Novel Therapies to Promote Neuroprotection

Cerebral palsy occurs more often in preterm than in term deliveries and is one of the major neurologic injuries seen in preterm infants. Magnesium sulfate has been found to reduce the risk of cerebral palsy in patients at risk of delivery before 32 weeks' gestational age. Multiple large clinical trials have shown this effect. The authors recommend magnesium sulfate bolus followed by continuous dosing of magnesium sulfate in those at risk of delivery before 32 weeks' gestation until delivery occurs or is no longer imminent. This article also discusses novel and emerging therapies for the prevention of cerebral palsy.

Use Profile of Magnesium Sulfate in Anesthesia in Brazil

Objectives: The use of magnesium sulfate in the perioperative period has several benefits, including analgesia, inhibition of the release of catecholamines and prevention of vasospasm. The aim of this survey was to provide an overview of the use of magnesium sulfate in anesthesia.

Method: This was a prospective descriptive cross-sectional study. An online questionnaire was sent to 9,869 Brazilian anesthesiologists and trainees. The questionnaire comprised closed questions mainly regarding the frequency, clinical effects, adverse events, and doses of magnesium sulfate used in anesthesia.

Results: Of the 954 doctors who responded to the survey, 337 (35.32%) reported using magnesium sulfate in anesthesia. The most commonly cited clinical effects for the use of magnesium sulfate in anesthesia were (n/%): postoperative analgesia (245/72.70%), reduction of anesthetic consumption (240/71.21%) and prevention and treatment of preeclampsia and seizures in eclampsia (220/65.28%). The most frequently reported adverse events were hypotension (187/55.48%), residual neuromuscular blockade (133/39.46%), hypermagnesemia (30/8.90%), and intravenous injection pain (26/7.71%). The intravenous doses of magnesium sulfate used in most general anesthesia inductions were between 30 and 40 mg.kg⁻¹.

Conclusions: Magnesium sulfate is an important adjuvant drug in the practice of anesthesia, with several clinical effects and a low incidence of adverse events when used at recommended doses.

Protection of brain development by antenatal magnesium sulphate for infants born preterm

Cerebral palsy (CP) remains the most significant neurological disorder associated with preterm birth. It disrupts quality of life and places huge cost burdens on society. Antenatal magnesium sulphate administration to females before 32 weeks' gestation has proven to be an effective intervention to reduce the rate of CP. In models of hypoxia, hypoxia-ischemia, inflammation, and excitotoxicity in various animal species, magnesium sulphate preconditioning decreased the resulting lesion sizes and inflammatory cytokine levels, prevented cell death, and improved long-term cognitive and motor behaviours. In humans, meta-analyses of five randomized controlled trials using magnesium sulphate as a neuroprotectant showed prevention of CP at 2 years. The benefit remained consistent regardless of gestational age, cause of preterm birth, and total dose received. Antenatal magnesium sulphate treatment is now recommended by the World Health Organization and by many obstetric societies. Its cost-effectiveness further justifies its widespread implementation. WHAT THIS PAPER ADDS: Neuroprotective effect of magnesium sulphate to reduce cerebral palsy in infants born preterm when administered to females at risk of imminent preterm birth. Neuroprotection regardless of gestational age, cause of preterm birth, and total dose. Antenatal magnesium sulphate treatment has good cost-effectiveness.

Impact of dosing schedule on uptake of neuroprotective magnesium sulfate

Background: Preterm delivery <32-week gestation is associated with significant neurodevelopmental morbidity ranging from mild delay to profound disability. Several randomized trials have shown that magnesium sulfate (MgSO₄) is an effective neuroprotectant, demonstrating reduced rates of cerebral palsy, death, and gross motor dysfunction for the neonate or infant. Dosing was not consistent among the major trials and the onus was placed on institutions by ACOG to develop and implement protocols with respect to MgSO₄ as a neuroprotectant. A recent study demonstrated that MgSO₄ exposure <12 h prior to delivery was associated with a decrease in CP compared to more remote exposure.Objective: To assess impact of dosing schedule on uptake of neuroprotective MgSO₄ in patients delivering <32 weeks gestational age.Study design: A retrospective cohort study of all deliveries occurring <32 weeks' gestation at a single academic center between March-December 2014 and March-December 2015 was conducted. Institutional policy shifted in 2015 from MgSO₄ bolus with continuous infusion based on the BEAM trial to a single bolus dose based on the PREMAG trial. Patients with preeclampsia, known fetal anomalies, and/or stillbirth were excluded from this analysis. Patients were identified through query of the Medical University of South Carolina Perinatal Information System (PINS) database with respect to whether or not they had received MgSO₄ within 12 h of delivery. Chi-squared analysis was performed to compare the overall rate of MgSO₄ exposure and MgSO₄ exposure <12 h prior to delivery between groups. Fisher's exact test was used to evaluate maternal, obstetric, and neonatal variables among those receiving MgSO₄ within 12 h of delivery in each cohort. Binary logistic regression analysis was performed to control for co-linear or potential confounding variables.Results: A total of 224 patients were identified, 115 delivered between March-December 2014 and 109 delivered between March-December 2015. With respect to MgSO₄ exposure prior to delivery, 27 (23.5%) received MgSO₄ in the 2014 cohort compared to 44 (40.4%) in the 2015 cohort (OR: 2.2, p < .01). Of those being exposed within 12 h of delivery, there were 16 (13.9%) maternal exposures in the 2014 cohort versus 28 (26.7%) in the 2015 cohort (OR: 2.15, p = .02). Of the 18 neonates delivered in 2014 there were four cases of grade III or IV intraventricular hemorrhage versus one case among the 36 neonates (2.7%) born in 2015 (0.04). This finding holds after controlling for race, preterm labor, gestational age, corticosteroid, birthweight, and indomethacin exposure.Conclusions: Dosing of neuroprotective MgSO₄ according to PREMAG trial specifications was associated with a significantly greater percentage of patients having received neuroprotective magnesium at any point prior to delivery or within the 12 h prior to delivery when compared to dosing according to BEAM trial specifications.

Time- and sex-dependent efficacy of magnesium sulfate to prevent behavioral impairments and cerebral damage in a mouse model of cerebral palsy

Cerebral lesions acquired in the perinatal period can induce cerebral palsy (CP), a multifactorial pathology leading to lifelong motor and cognitive deficits. Several risk factors, including perinatal hypoxia-ischemia (HI), can contribute to the emergence of CP in preterm infants. Currently, there is no international consensus on treatment strategies to reduce the risk of developing CP. A meta-analysis showed that magnesium sulfate (MgSO₄) administration to mothers at risk of preterm delivery reduces the risk of developing CP (Crowther et al., 2017). However, only a few studies have investigated the long-term effects of MgSO₄ and it is not known whether sex would influence MgSO₄ efficacy. In addition, the search for potential deleterious effects is essential to enable broad use of MgSO₄ in maternity wards. We used a mouse model of perinatal HI to study MgSO₄ effects until adolescence, focusing on cognitive and motor functions, and on some apoptosis and inflammation markers. Perinatal HI at postnatal day 5 (P(5)) induced (1) sensorimotor deficits in pups; (2) increase in caspase-3 activity 24 h after injury; (3) production of proinflammatory cytokines from 6 h to 5 days after injury; (4) behavioral and histological alterations in adolescent mice with considerable interindividual variability. MgSO₄ prevented sensorimotor alterations in pups, with the same efficacy in males and females. MgSO₄ displayed anti-apoptotic and anti-inflammatory effects without deleterious side effects. Perinatal HI led to motor coordination impairments in female adolescent mice and cognitive deficits in both sexes. MgSO₄ tended to prevent these motor and cognitive deficits only in females, while it prevented global brain tissue damage in both sexes. Moreover, interindividual and intersexual differences appeared regarding the lesion size and neuroprotection by MgSO₄ in a region-specific manner. These differences, the partial prevention of disorders, as well as the mismatch between histological and behavioral observations mimic clinical observations. This underlines that this perinatal HI model is suitable to further analyze the mechanisms of sex-dependent perinatal lesion susceptibility and MgSO₄ efficacy.

Fetal Neuroprotection by Magnesium Sulfate: From Translational Research to Clinical Application

Despite improvements in perinatal care, preterm birth still occurs regularly and the associated brain injury and adverse neurological outcomes remain a persistent challenge. Antenatal magnesium sulfate administration is an intervention with demonstrated neuroprotective effects for preterm births before 32 weeks of gestation (WG). Owing to its biological properties, including its action as an N-methyl-d-aspartate receptor blocker and its anti-inflammatory effects, magnesium is a good candidate for neuroprotection. In hypoxia models, including hypoxia-ischemia, inflammation, and excitotoxicity in various species (mice, rats, pigs), magnesium sulfate preconditioning decreased the induced lesions’ sizes and inflammatory cytokine levels, prevented cell death, and improved long-term behavior. In humans, some observational studies have demonstrated reduced risks of cerebral palsy after antenatal magnesium sulfate therapy. Meta-analyses of five randomized controlled trials using magnesium sulfate as a neuroprotectant showed amelioration of cerebral palsy at 2 years. A meta-analysis of individual participant data from these trials showed an equally strong decrease in cerebral palsy and the combined risk of fetal/infant death and cerebral palsy at 2 years. The benefit remained similar regardless of gestational age, cause of prematurity, and total dose received. These data support the use of a minimal dose (e.g., 4 g loading dose ± 1 g/h maintenance dose over 12 h) to avoid potential deleterious effects. Antenatal magnesium sulfate is now recommended by the World Health Organization and many pediatric and obstetrical societies, and it is requisite to maximize its administration among women at risk of preterm delivery before 32 WG.

Experimental and clinical evidence of differential effects of magnesium sulfate on neuroprotection and angiogenesis in the fetal brain

Clinical studies showed beneficial effects of magnesium sulfate regarding the risk of cerebral palsy. However, regimen protocols fluctuate worldwide and risks of adverse effects impacting the vascular system have been reported for human neonates, keeping open the question of the optimal dosing. Using clinically relevant concentrations and doses of magnesium sulfate, experiments consisted of characterizing, respectively, ex vivo and in vivo, the effects of magnesium sulfate on the nervous and vascular systems of mouse neonates by targeting neuroprotection, angiogenesis, and hemodynamic factors and in measuring, in human fetuses, the impact of a 4‐g neuroprotective loading dose of magnesium sulfate on brain hemodynamic parameters. Preclinical experiments using cultured cortical slices from mouse neonates showed that the lowest and highest tested concentrations of magnesium sulfate were equally potent to prevent excitotoxic‐induced cell death, cell edema, cell burst, and intracellular calcium increase, whereas no side effects were found regarding apoptosis. In contrast, in vivo data revealed that magnesium sulfate exerted dose‐dependent vascular effects on the fetal brain. In particular, it induced brain hypoperfusion, stabilization of Hif‐1α, long‐term upregulation of VEGF‐R2 expression, impaired endothelial viability, and altered cortical angiogenesis. Clinically, in contrast to 6‐g loading doses used in some protocols, a 4‐g bolus of magnesium sulfate did not altered fetal brain hemodynamic parameters. In conclusion, these data provide the first mechanistic evidence of double‐sword and dose‐dependent actions of magnesium sulfate on nervous and vascular systems. They strongly support the clinical use of neuroprotection protocols validated for the lowest (4‐g) loading dose of magnesium sulfate.