Magnetic Resonance Imaging Correlates of White Matter Gliosis and Injury in Preterm Fetal Sheep Exposed to Progressive Systemic Inflammation.

Progressive fetal infection/inflammation is strongly associated with neural injury after preterm birth. We aimed to test the hypotheses that progressively developing fetal inflammation leads to neuroinflammation and impaired white matter development and that the histopathological changes can be detected using high-field diffusion tensor magnetic resonance imaging (MRI). Chronically instrumented preterm fetal sheep at 0.7 of gestation were randomly assigned to receive intravenous saline (control; n = 6) or a progressive infusion of lipopolysaccharide (LPS, 200 ng intravenous over 24 h then doubled every 24 h for 5 days to induce fetal inflammation, n = 7). Sheep were killed 10 days after starting the infusions, for histology and high-field diffusion tensor MRI. Progressive LPS infusion was associated with increased circulating interleukin (IL)-6 concentrations and moderate increases in carotid artery perfusion and the frequency of electroencephalogram (EEG) activity (p < 0.05 vs. control). In the periventricular white matter, fractional anisotropy (FA) was increased, and orientation dispersion index (ODI) was reduced (p < 0.05 vs. control for both). Histologically, in the same brain region, LPS infusion increased microglial activation and astrocyte numbers and reduced the total number of oligodendrocytes with no change in myelination or numbers of immature/mature oligodendrocytes. Numbers of astrocytes in the periventricular white matter were correlated with increased FA and reduced ODI signal intensities. Astrocyte coherence was associated with increased FA. Moderate astrogliosis, but not loss of total oligodendrocytes, after progressive fetal inflammation can be detected with high-field diffusion tensor MRI.

Tumor necrosis factor inhibition attenuates white matter gliosis after systemic inflammation in preterm fetal sheep.

BACKGROUND: Increased circulating levels of tumor necrosis factor (TNF) are associated with greater risk of impaired neurodevelopment after preterm birth. In this study, we tested the hypothesis that systemic TNF inhibition, using the soluble TNF receptor Etanercept, would attenuate neuroinflammation in preterm fetal sheep exposed to lipopolysaccharide (LPS). METHODS: Chronically instrumented preterm fetal sheep at 0.7 of gestation were randomly assigned to receive saline (control; n = 7), LPS infusion (100 ng/kg i.v. over 24 h then 250 ng/kg/24 h for 96 h plus 1 µg LPS boluses at 48, 72, and 96 h, to induce inflammation; n = 8) or LPS plus two i.v. infusions of Etanercept (2 doses, 5 mg/kg infused over 30 min, 48 h apart) started immediately before LPS-exposure (n = 8). Sheep were killed 10 days after starting infusions, for histology. RESULTS: LPS boluses were associated with increased circulating TNF, interleukin (IL)-6 and IL-10, electroencephalogram (EEG) suppression, hypotension, tachycardia, and increased carotid artery perfusion (P < 0.05 vs. control). In the periventricular and intragyral white matter, LPS exposure increased gliosis, TNF-positive cells, total oligodendrocytes, and cell proliferation (P < 0.05 vs control), but did not affect myelin expression or numbers of neurons in the cortex and subcortical regions. Etanercept delayed the rise in circulating IL-6, prolonged the increase in IL-10 (P < 0.05 vs. LPS), and attenuated EEG suppression, hypotension, and tachycardia after LPS boluses. Histologically, Etanercept normalized LPS-induced gliosis, and increase in TNF-positive cells, proliferation, and total oligodendrocytes. CONCLUSION: TNF inhibition markedly attenuated white matter gliosis but did not affect mature oligodendrocytes after prolonged systemic inflammation in preterm fetal sheep. Further studies of long-term brain maturation are now needed.

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.