Delta2-specific opioid receptor agonist and hibernating woodchuck plasma fraction provide ischemic neuroprotection

Objectives: The authors present evidence that the delta 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 mu L 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 delta- or mu-specific opioids and HWP or SAWP prior to activation with lipopolysaccharide and interferon-gamma. 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 delta- and mu-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.