The Effect of Antenatal Betamethasone on White Matter Inflammation and Injury in Fetal Sheep and Ventilated Preterm Lambs

The synergistic effects of mechanical ventilation and intrauterine inflammation on cerebral inflammation in preterm fetal sheep

Background

Intrauterine inflammation and the requirement for mechanical ventilation independently increase the risk of perinatal brain injury and adverse neurodevelopmental outcomes. We aimed to investigate the effects of mechanical ventilation for 24 h, with and without prior exposure to intrauterine inflammation, on markers of brain inflammation and injury in the preterm sheep brain.

Methods

Chronically instrumented fetal sheep at ~115 days of gestation were randomly allocated to receive a single intratracheal dose of 1 mg lipopolysaccharide (LPS) or isovolumetric saline, then further randomly allocated 1 h after to receive mechanical ventilation with room air or no mechanical ventilation (unventilated control + saline [UVC, n = 7]; in utero mechanical ventilation + saline [VENT, n = 8], unventilated control + intratracheal LPS [UVC + LPS, n = 7]; in utero ventilation + intratracheal LPS [VENT + LPS, n = 7]). Serial fetal blood and plasma samples were collected throughout the experimental protocol for assessment of blood biochemistry and plasma interleukin (IL)-6 levels. After 24 h of mechanical ventilation, fetal brains were collected for RT-qPCR and immunohistochemical analyses.

Results

LPS exposure increased numbers of microglia and upregulated pro-inflammatory related genes within the cortical gray matter (GM) and subcortical white matter (SCWM) (pLPS  < 0.05). Mechanical ventilation alone increased astrocytic cell density in the periventricular white matter (PVWM) (pVENT  = 0.03) but had no effect on pro-inflammatory gene expression. The combination of ventilation and LPS increased plasma IL-6 levels (p < 0.02 vs. UVC and VENT groups), and exacerbated expression of pro-inflammatory-related genes (IL1β, TLR4, PTGS2, CXCL10) and microglial density (p < 0.05 vs. VENT).

Conclusion

This study demonstrates that 24 h of mechanical ventilation after exposure to intrauterine inflammation increased markers of systemic and brain inflammation and led to the upregulation of pro-inflammatory genes in the white matter. We conclude that 24 h of mechanical ventilation following intrauterine inflammation may precondition the preterm brain toward being more susceptible to inflammation-induced injury.

Characterisation of ciclesonide metabolism in human placentae across gestation

INTRODUCTION

Current clinical management of pregnancies at risk of preterm delivery includes maternal antenatal corticosteroid (ACS) treatment. ACS activate the glucocorticoid receptor (GR) in all fetal tissues, maturing the lungs at the cost of impaired brain development, creating a need for novel treatments. The prodrug ciclesonide (CIC) activates the GR only when converted to des-CIC by specific enzymes, including acetylcholinesterase (ACHE) and carboxylesterase 1 and 2 (CES1, CES2). Importantly, the human placenta expresses ACHE and CES, and could potentially produce des-CIC, resulting in systemic fetal exposure and GR activation in all fetal tissues. We therefore investigated CES gene expression and conversion of CIC to des-CIC in human placentae collected during the second trimester (Tri2), and at preterm and term birth.

METHODS

Differential expression analysis was performed in Tri2 (n = 27), preterm (n = 34), and term (n = 40) placentae using the DESeq2 R-package. Conversion of CIC to des-CIC was measured in a subset of placenta samples (Tri2 n = 7, preterm n = 26, term n = 20) using functional assays.

RESULTS

ACHE mRNA expression was higher in Tri2 male than preterm and term male placentae only, whereas CES1 mRNA expression was higher in Tri2 than preterm or term placentae of both sexes. Conversion of CIC to des-CIC did not differ between gestational ages.

DISCUSSION

Conversion of CIC to des-CIC by the human placenta may preclude its use as a novel GR-agonist in threatened preterm birth. In vivo studies are required to confirm the extent to which placental activation occurs after maternal treatment.

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.

Molecular mechanisms underlying adverse effects of dexamethasone and betamethasone in the developing cardiovascular system

Antenatal glucocorticoids accelerate fetal lung maturation and reduce mortality in preterm babies but can trigger adverse effects on the cardiovascular system. The mechanisms underlying off-target effects of the synthetic glucocorticoids mostly used, Dexamethasone (Dex) and Betamethasone (Beta), are unknown. We investigated effects of Dex and Beta on cardiovascular structure and function, and underlying molecular mechanism using the chicken embryo, an established model system to isolate effects of therapy on the developing heart and vasculature, independent of effects on the mother or placenta. Fertilized eggs were treated with Dex (0.1 mg kg-1 ), Beta (0.1 mg kg-1 ), or water vehicle (Control) on embryonic day 14 (E14, term = 21 days). At E19, biometry, cardiovascular function, stereological, and molecular analyses were determined. Both glucocorticoids promoted growth restriction, with Beta being more severe. Beta compared with Dex induced greater cardiac diastolic dysfunction and also impaired systolic function. While Dex triggered cardiomyocyte hypertrophy, Beta promoted a decrease in cardiomyocyte number. Molecular changes of Dex on the developing heart included oxidative stress, activation of p38, and cleaved caspase 3. In contrast, impaired GR downregulation, activation of p53, p16, and MKK3 coupled with CDK2 transcriptional repression linked the effects of Beta on cardiomyocyte senescence. Beta but not Dex impaired NO-dependent relaxation of peripheral resistance arteries. Beta diminished contractile responses to potassium and phenylephrine, but Dex enhanced peripheral constrictor reactivity to endothelin-1. We conclude that Dex and Beta have direct differential detrimental effects on the developing cardiovascular system.

Increased Prostaglandin E2 in Brainstem Respiratory Centers Is Associated With Inhibition of Breathing Movements in Fetal Sheep Exposed to Progressive Systemic Inflammation

Background

Preterm newborns commonly experience apnoeas after birth and require respiratory stimulants and support. Antenatal inflammation is a common antecedent of preterm birth and inflammatory mediators, particularly prostaglandin E2 (PGE₂), are associated with inhibition of vital brainstem respiratory centers. In this study, we tested the hypothesis that exposure to antenatal inflammation inhibits fetal breathing movements (FBMs) and increases inflammation and PGE₂ levels in brainstem respiratory centers, cerebrospinal fluid (CSF) and blood plasma.

Methods

Chronically instrumented late preterm fetal sheep at 0.85 of gestation were randomly assigned to receive repeated intravenous saline (n = 8) or lipopolysaccharide (LPS) infusions (experimental day 1 = 300 ng, day 2 = 600 ng, day 3 = 1200 ng, n = 8). Fetal breathing movements were recorded throughout the experimental period. Sheep were euthanized 4 days after starting infusions for assessment of brainstem respiratory center histology.

Results

LPS infusions increased circulating and cerebrospinal fluid PGE₂ levels, decreased arterial oxygen saturation, increased the partial pressure of carbon dioxide and lactate concentration, and decreased pH (p < 0.05 for all) compared to controls. LPS infusions caused transient reductions in the % of time fetuses spent breathing and the proportion of vigorous fetal breathing movements (P < 0.05 vs. control). LPS-exposure increased PGE₂ expression in the RTN/pFRG (P < 0.05 vs. control) but not the pBÖTC (P < 0.07 vs. control) of the brainstem. No significant changes in gene expression were observed for PGE₂ enzymes or caspase 3. LPS-exposure reduced the numbers of GFAP-immunoreactive astrocytes in the RTN/pFRG, NTS and XII of the brainstem (P < 0.05 vs. control for all) and increased microglial activation in the RTN/pFRG, preBÖTC, NTS, and XII brainstem respiratory centers (P < 0.05 vs. control for all).

Conclusion

Chronic LPS-exposure in late preterm fetal sheep increased PGE₂ levels within the brainstem, CSF and plasma, and was associated with inhibition of FBMs, astrocyte loss and microglial activation within the brainstem respiratory centers. Further studies are needed to determine whether the inflammation-induced increase in PGE₂ levels plays a key role in depressing respiratory drive in the perinatal period.

Respiratory Support of the Preterm Neonate: Lessons About Ventilation-Induced Brain Injury From Large Animal Models

Many preterm neonates require mechanical ventilation which increases the risk of cerebral inflammation and white matter injury in the immature brain. In this review, we discuss the links between ventilation and brain injury with a focus on the immediate period after birth, incorporating respiratory support in the delivery room and subsequent mechanical ventilation in the neonatal intensive care unit. This review collates insight from large animal models in which acute injurious ventilation and prolonged periods of ventilation have been used to create clinically relevant brain injury patterns. These models are valuable resources in investigating the pathophysiology of ventilation-induced brain injury and have important translational implications. We discuss the challenges of reconciling lung and brain maturation in commonly used large animal models. A comprehensive understanding of ventilation-induced brain injury is necessary to guide the way we care for preterm neonates, with the goal to improve their neurodevelopmental outcomes.

Brain inflammation and injury at 48 h is not altered by human amnion epithelial cells in ventilated preterm lambs

BACKGROUND

Mechanical ventilation of preterm neonates is associated with neuroinflammation and an increased risk of adverse neurological outcomes. Human amnion epithelial cells (hAECs) have anti-inflammatory and regenerative properties. We aimed to determine if intravenous administration of hAECs to preterm lambs would reduce neuroinflammation and injury at 2 days of age.

METHODS

Preterm lambs were delivered by cesarean section at 128-130 days' gestation (term is ~147 days) and either ventilated for 48 h or humanely killed at birth. Lambs received 3 mL surfactant (Curosurf) via endotracheal tube prior to delivery (either with or without 90 × 10⁶ hAECs) and 3 mL intravenous phosphate-buffered saline (with or without 90 × 10⁶ hAECs, consistent with intratracheal treatment) after birth.

RESULTS

Ventilation increased microglial activation, total oligodendrocyte cell number, cell proliferation and blood-brain barrier permeability (P < 0.05, PBS + ventilation and hAEC + ventilation vs. control), but did not affect numbers of immature and mature oligodendrocytes. Ventilation reduced astrocyte and neuron survival (P < 0.05, PBS + ventilation and hAEC + ventilation vs. control). hAEC administration did not alter markers of neuroinflammation or injury within the white or gray matter.

CONCLUSIONS

Mechanical ventilation for 48 h upregulated markers of neuroinflammation and injury in preterm lambs. Administration of hAECs did not affect markers of neuroinflammation or injury.

IMPACT

Mechanical ventilation of preterm lambs for 48 h, in a manner consistent with contemporary neonatal intensive care, causes neuroinflammation, neuronal loss and pathological changes in oligodendrocyte and astrocyte survival consistent with evolving neonatal brain injury.Intravenous administration of hAECs immediately after birth did not affect neonatal cardiorespiratory function and markers of neuroinflammation or injury.Reassuringly, our findings in a translational large animal model demonstrate that intravenous hAEC administration to the preterm neonate is safe.Considering that hAECs are being used in phase 1 trials for the treatment of BPD in preterm infants, with future trials planned for neonatal neuroprotection, we believe these observations are highly relevant.