Neuroprotective effects of diazoxide against ischemia-reperfusion brain injury

Hypoxia-ischemia (HI) brain injury in the newborn is a leading cause of neonatal death and disability in the United States and worldwide. Currently, there are no effective therapies to ameliorate brain damage caused by HI. The studies presented herein were conducted to elucidate the molecular mechanisms involved in this type of injury in order to assist the development of novel therapies to combat newborn mortality and neurologic morbidity. Our central hypothesis was that HI-induced damage to the newborn brain is due to mitochondrial dysfunction and that the activation of mitochondrial ATP sensitive potassium channels (mK_ATP) using the mK_ATP opener-diazoxide may be neuroprotective against brain hypoxia-ischemia.; In order to investigate mitochondrial responses after HI, the first study was designed to isolate and characterize a pure preparation of mitochondria from 7-day old rat brain using Percoll gradient centrifugation. These studies revealed that damage to the mitochondria occurs as a result of cerebral ischemia-reperfusion in the neonatal rat brain.; The second study indicated that activation of mK_ATP channels in mitochondria with diazoxide conferred protection against HI in the neonatal rat. Administration of diazoxide 30 minutes prior to hypoxic-ischemic insult reduced total infarct volume by 20% in the newborn rat.; The third study indicated diazoxide could confer protection to astrocytes by in vitro analogues of HI, known as oxygen-glucose deprivation (OGD) and oxidative stress induced by hydrogen peroxide (H₂O ₂) toxicity. We found that three cycles of diazoxide administration prior to exposure to OGD or H₂O₂ toxicity produced concentration dependent reduction in cell death in rat primary astrocytes.; The fourth study using primary neuronal cultures indicated that the neuroprotective effect of diazoxide against OGD was not limited to astrocytes. Diazoxide completely abolished the OGD-induced cell death in primary neurons via mechanisms involving ROS.; The fifth study indicated that the opening of mK_ATP channels by diazoxide augmented Bcl-2 expression in both neurons and astrocytes. Bcl-2 localized to the biological membranes has multifunctional effects on the cell including mitochondrial prevention of permeability transition pore opening and cytochrome c release ultimately inhibiting apoptosis. (Abstract shortened by UMI.)...