Heme Oxygenase-1 Mediates Neuroprotection Conferred by Argon in Combination with Hypothermia in Neonatal Hypoxia–Ischemia Brain Injury

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Background:Hypoxic–ischemic encephalopathy is a major cause of mortality and disability in the newborn. The authors investigated the protective effects of argon combined with hypothermia on neonatal rat hypoxic–ischemic brain injury.Methods:In in vitro studies, rat cortical neuronal cell cultures were challenged by oxygen and glucose deprivation for 90 min and exposed to 70% Ar or N2 with 5% CO2 balanced with O2, at 33°C for 2 h. Neuronal phospho-Akt, heme oxygenase-1 and phospho-glycogen synthase kinase-3β expression, and cell death were assessed. In in vivo studies, neonatal rats were subjected to unilateral common carotid artery ligation followed by hypoxia (8% O2 balanced with N2 and CO2) for 90 min. They were exposed to 70% Ar or N2 balanced with oxygen at 33°, 35°, and 37°C for 2 h. Brain injury was assessed at 24 h or 4 weeks after treatment.Results:In in vitro studies, argon–hypothermia treatment increased phospho-Akt and heme oxygenase-1 expression and significantly reduced the phospho-glycogen synthase kinase-3β Tyr-216 expression, cytochrome C release, and cell death in oxygen–glucose deprivation–exposed cortical neurons. In in vivo studies, argon–hypothermia treatment decreased hypoxia/ischemia-induced brain infarct size (n = 10) and both caspase-3 and nuclear factor-κB activation in the cortex and hippocampus. It also reduced hippocampal astrocyte activation and proliferation. Inhibition of phosphoinositide-3-kinase (PI3K)/Akt pathway through LY294002 attenuated cerebral protection conferred by argon–hypothermia treatment (n = 8).Conclusion:Argon combined with hypothermia provides neuroprotection against cerebral hypoxia–ischemia damage in neonatal rats, which could serve as a new therapeutic strategy against hypoxic–ischemic encephalopathy.

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