Isoflurane Posttreatment Reduces Neonatal Hypoxic–Ischemic Brain Injury in Rats by the Sphingosine-1-Phosphate/Phosphatidylinositol-3-Kinase/Akt Pathway

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Abstract
Background and Purpose— Isoflurane, administered before or during cerebral ischemia, has been shown to exhibit neuroprotection in animal models of ischemic stroke. However, the underlying mechanism remains to be elucidated. In the present study, we determined whether isoflurane posttreatment provides neuroprotection after neonatal hypoxia–ischemia (HI) in rats and evaluated the role of the sphingosine-1-phosphate/phosphatidylinositol-3-kinase/Akt pathway in this volatile anesthetic-mediated neuroprotection. Methods— HI was induced in postnatal day 10 (P10) rat pups by unilateral carotid ligation and 2 hours of hypoxia. For treatment, 2% isoflurane was administered immediately after HI for 1 hour. As pharmacological interventions, the sphingosine-1-phosphate antagonist VPC23019, phosphatidylinositol-3-kinase inhibitor wortmannin, or opioid antagonist naloxone was administered before HI. Isoflurane posttreatment was evaluated for effects on infarct volume at 48 hours after HI and brain atrophy and neurological outcomes at 4 weeks after HI. The expression of phosphorylated Akt and cleaved caspase-3 was determined by Western blotting and immunofluorescence analysis. Results— Isoflurane posttreatment significantly reduced infarct volume at 48 hours after HI. VPC23019 or wortmannin abrogated the neuroprotective effect of isoflurane, whereas naloxone did not inhibit the isoflurane-induced neuroprotection. Isoflurane posttreatment significantly preserved phosphorylated Akt expression and decreased cleaved caspase-3 levels. These effects were reversed by VPC23019 and wortmannin, respectively. Isoflurane also confers long-term neuroprotective effects against brain atrophy and neurological deficits at 4 weeks after HI. Conclusions— Isoflurane posttreatment provides lasting neuroprotection against hypoxic–ischemic brain injury in neonatal rats. Activation of the sphingosine-1-phosphate/phosphatidylinositol-3-kinase/Akt pathway may play a key role in isoflurane posttreatment-induced neuroprotection.

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