Delta 2 ‐Specific Opioid Receptor Agonist and Hibernating Woodchuck Plasma Fraction Provide Ischemic Neuroprotection

Objectives:  The authors present evidence that the δ opioid receptor agonist Deltorphin‐D variant (Delt‐D var ) and hibernating woodchuck plasma (HWP), but not summer‐active woodchuck plasma (SAWP), can provide significant neuroprotection from focal ischemia in mice by a mechanism that relies in part on reducing nitric oxide (NO) release in ischemic tissue. Methods:  Cerebral ischemia was produced in wild‐type and NO synthase–deficient (NOS –/– ) mice by transient, 1‐hour middle cerebral artery occlusion (MCAO). Behavioral deficits were determined at 22 hours and infarct volume was assessed at 24 hours after MCAO. Mice were treated with saline or Delt‐D var at 2.0 and 4.0 mg/kg, or 200 μL of HWP or SAWP. NOS –/– mice were treated with either saline or Delt‐D var at 4.0 mg/kg. NO release was determined using an N9 microglial cell line pretreated with δ‐ or μ‐specific opioids and HWP or SAWP prior to activation with lipopolysaccharide and interferon‐γ. Nitrate in the medium was measured as an indicator of NO production. Results:  Infusion of Delt‐D var or HWP (but not SAWP) decreased infarct volume and improved behavioral deficits following 1 hour of MCAO and 24 hours of reperfusion. In NOS –/– mice, endothelial NOS +/+ is required to provide Delt‐D var –induced neuroprotection. Delt‐D var and HWP dose‐dependently decreased NO release in cell culture, while SAWP and other δ‐ and μ‐specific opioids did not. Conclusions:  Delt‐D var and HWP, but not SAWP, are effective neuroprotectant agents in a mouse model of transient MCAO. In cell culture, the mechanism of this ischemic neuroprotection may rely in part on their ability to block NO release.