Neuroprotective effect of selective kappa opioid receptor agonist is gender specific and linked to reduced neuronal nitric oxide

We have previously shown that treatment with selective kappa-opioid receptor agonist BRL 52537 hydrochloride [(±)-1-(3,4-dichlorophenyl) acetyl-2-(1-pyrrolidinyl) methylpiperidine] (1) has a long therapeutic window for providing ischemic neuroprotection and (2) attenuates ischemia-evoked nitric oxide (NO) production in vivo in rats. Neuronally derived NO has been shown to be deleterious in the male, but not in the female, rodent model of focal ischemic stroke. We sought to determine if the agent fails to protect ischemic brain when neuronal NO synthase (nNOS) is genetically deleted in male, but not female, mice. Halothane-anesthetized adult male and female nNOS null mutants (nNOS^-/-) and the genetically matched wildtype (WT) strain were subjected to transient (2 h) middle cerebral artery occlusion by the intraluminal filament technique. Vehicle or BRL 52537 treatment with continuous intravenous infusion was instituted at the onset of reperfusion and continued for 22 h. In WT male mice, infarct volumes measured at 72 h of reperfusion were robustly decreased with BRL 52537 treatment. In contrast, BRL 52537 did not decrease infarct volume in male nNOS^-/- mice. BRL 52537 had no effect in the WT or nNOS^-/- female mice. These data support that BRL 5253's mechanism of neuroprotection in vivo is through attenuation of nNOS activity and ischemia-evoked NO production. Neuroprotective effects of BRL 52537 are lost in the male when nNOS is not present; therefore, BRL 52537 likely acts upstream from NO generation and its subsequent neurotoxicity.