Melatonin Provides Neuroprotection in the Late-Gestation Fetal Sheep Brain in Response to Umbilical Cord Occlusion

Abstract

Oxygen free radicals, including the highly toxic hydroxyl radical (^·OH), initiate lipid peroxidation and DNA/RNA fragmentation and damage cells. The pineal hormone melatonin is an antioxidant and powerful scavenger of ^·OH. We hypothesized that maternally administered melatonin could reduce ^·OH formation, lipid peroxidation, and DNA/RNA damage in the fetal brain in response to asphyxia. In 15 fetal sheep, extracellular ^·OH was measured by microdialysis in white and gray matter of the parasagittal cortex. In 10 fetuses, asphyxia was induced by umbilical cord occlusion for 10 min using an inflatable cuff – the ewes of these fetuses received either intravenous melatonin (1 mg bolus, then 1 mg/h for 2 h; n = 5) or vehicle (1% ethanol in saline; n = 5), and results were compared to fetuses with sham cord occlusion and vehicle-infused ewes (n = 5). Hypoxemia, acidemia, hypertension and bradycardia produced by cord occlusion was similar in the melatonin- and vehicle-treated groups. In the vehicle-treated group, cord occlusion resulted in a significant increase in ^·OH in gray matter at 8–9.5 h after occlusion (p < 0.05); in contrast, there was no ^·OH change in the melatonin-treated group. After cord occlusion, lipid peroxidation (4-hydroxynonenal immunoreactivity) found throughout the brain of vehicle-infused ewes was significantly less in the melatonin-infused group. Melatonin had no significant effect on the distribution of DNA/RNA fragmentation, as shown by 8-hydroxydeoxyguanosine immunoreactivity. Thus, brief asphyxia results in significant and delayed entry of ^·OH into the extracellular space of cortical gray matter in the fetal sheep brain, and melatonin given to the mother at the time of the insult abrogates this increase. Melatonin, in reducing O₂ free radical production, may be an effective neuroprotective treatment for the fetus.

Melatonin Reduces Inflammation and Cell Death in White Matter in the Mid-Gestation Fetal Sheep Following Umbilical Cord Occlusion

“…In these studies melatonin given at doses of more than 5 mg/kg, with treatment starting either before or during ischemia, showed maximum protection. In contrast, experiments in term fetal sheep did not find an effect of melatonin treatment on DNA/RNA fragmentation following umbilical cord occlusion, although the increase in hydroxyl radicals was prevented (19). However, these experiments differed from the present study with regard to several aspects; a lower melatonin dose (1 mg/kg) and shorter infusion period (2h) were used and the drug was administered to the mother rather than the fetus.…”

Antioxidant Therapies: A Potential Role in Perinatal Medicine

“…Therefore, not surprisingly, there is direct and indirect evidence that oxidative stress plays a central role in mediating developmental brain injury [16,19,23]. In late gestation fetal sheep, we have used umbilical cord occlusion to show that acute fetal asphyxia causes increased production of hydroxyl radical within the fetal brain, predominantly in the grey matter [24], and widespread upregulation of lipid peroxidation (4-HNE positive cells) in both the grey and white matter [25]. Our observations are supported by those of others where upregulation of free radicals and lipid peroxidation products within the brain following acute perinatal asphyxia has been shown to occur across a range of species and under varying experimental conditions [26,27,28].…”

Partial Neural Protection with Prophylactic Low-Dose Melatonin after Asphyxia in Preterm Fetal Sheep

“…In fetal sheep, Miller et al 11 showed that maternal prophylactic melatonin (1 mg total) given before 10-minute umbilical cord occlusion at term-equivalent was associated with reduced brain lipid peroxidation, neuronal death, microglial activation, and astrogliosis. 11,12 In preterm fetal sheep at 0.6 gestation (Term ¼ 147 days) fetal infusion of high-dose (20 mg/kg) …”