Effects of Antenatal Melatonin Treatment on the Cerebral Vasculature in an Ovine Model of Fetal Growth Restriction

Abstract

Chronic moderate hypoxia, such as occurs in fetal growth restriction (FGR) during gestation, compromises the blood-brain barrier (BBB) and results in structural abnormalities of the cerebral vasculature. We have previously determined the neuroprotective and antioxidant effects of maternal administration of melatonin (MLT) on growth-restricted newborn lambs. The potential of maternal MLT therapy for the treatment of cerebrovascular dysfunction-associated developmental hypoxia has also been demonstrated in newborn lambs. We assessed whether MLT had an effect on the previously reported structural and cerebral vascular abnormalities in chronically hypoxic FGR lambs. Single umbilical-artery ligation surgery was performed in fetuses at approximately 105 days of gestation (term: 147 days) to induce placental insufficiency and FGR, and treatment with either saline or an MLT infusion (0.1 mg/kg) was started 4 h after surgery. Ewes delivered naturally at term and lambs were euthanased 24 h later. We found a significant reduction in the number of laminin-positive blood vessels within the subcortical and periventricular white matter (SCWM and PVWM) and the subventricular zone (SVZ) in FGR (p < 0.0005) and FGR + MLT brains (p < 0.0005 vs. controls), with no difference found between FGR and FGR + MLT animals. This was associated with a significant decrease in VEGF immunoreactivity in FGR and FGR + MLT brains versus controls (p < 0.0005; SCWM and PVWM) and in the SVZ in FGR brains versus controls (p < 0.005) and also with significantly lower levels of proliferating blood vessels versus controls (p < 0.0005). Glucose transporter-1 immunoreactivity (vascular endothelium) was decreased in FGR versus control lambs (p < 0.0005) in SCWM, PVWM, and the SVZ; it was significantly increased in FGR + MLT lambs compared with FGR lambs in SCWM and PVWM (p < 0.005) and even more markedly in the SVZ (p < 0.0005). FGR brains showed a 72% reduction in pericyte coverage versus control lambs and 68% versus FGR + MLT in PVWM. In SCWM, we found a 77 and 73% reduction compared with control and FGR + MLT lambs, respectively, while in the SVZ, we observed a 68% reduction versus controls and a 70% reduction in FGR versus FGR + MLT lambs. Astrocyte end-feet coverage in the SCWM showed a significant 24% reduction in FGR versus control levels, a 42% decrease within the PVWM, and a 35% decrease within the SVZ versus controls. MLT normalized astrocyte attachment to blood vessels, with no difference seen between controls and FGR + MLT animals in any of the brain regions examined. We also observed a decrease in albumin extravasation and microhemorrhage in controls and FGR + MLT brains versus FGR lambs. Our results demonstrate that umbilicoplacental insufficiency is associated with FGR-produced vascular changes in the white matter and SVZ of FGR newborn brains and that maternal MLT prevented disruption of the BBB by protecting perivascular cells essential for the maintenance of vascular homeostasis and stability.

Melatonin for prevention of placental malperfusion and fetal compromise associated with intrauterine inflammation‐induced oxidative stress in a mouse model

“…Our results are in agreement with past studies that used fetal sheep models from pregnancies complicated by fetal growth restriction. These past studies showed that antenatal treatment with melatonin could reduce oxidative stress to decrease neurodevelopmental deficits in newborn lambs and protect their cerebral vascular endothelium to maintain the blood‐brain barrier . Furthermore, other studies have shown that melatonin administration even after an ischemic insult to the fetus, such as following hypoxia‐ischemia or brief asphyxiation via cord occlusion, can provide neuroprotection for the fetus.…”

“…These past studies showed that antenatal treatment with melatonin could reduce oxidative stress to decrease neurodevelopmental deficits in newborn lambs and protect their cerebral vascular endothelium to maintain the blood-brain barrier. 44,45 Furthermore, other studies have shown that melatonin administration even after an ischemic insult to the fetus, such as following hypoxiaischemia 46 or brief asphyxiation via cord occlusion, 47 can provide neuroprotection for the fetus. Our results, along with these past studies, show the plausibility of using adjuvant melatonin for the prevention and/or partial treatment of fetal neurodevelopmental deficits induced by IUI.…”

Physiologically based cord clamping stabilises cardiac output and reduces cerebrovascular injury in asphyxiated near-term lambs

“…The similar findings in this study suggest that cerebrovascular injury results in increased vasoreactivity, ultimately reducing cerebral perfusion, as a protective effect to prevent increased injury. While the mechanism for this is unknown, it could be mediated by withdrawal of astrocyte end-feed from the blood vessel walls due to haemodynamic injury, resulting in cerebrovascular breakdown and increased leakage 34. However, more research is required to fully elucidate the cause of cerebrovascular dysfunction in this model.…”

Therapeutic potential to reduce brain injury in growth restricted newborns

“…Alterations in BBB composition have been reported in IUGR neonates (Castillo‐Melendez et al . , ). Decreased BBB integrity may result in an increased infiltration of systemic inflammatory mediators into the brain, further exacerbating the neuroinflammatory response.…”