Summary: Aims: Neurologic impairment following ischemic injury complicates the quality of life for stroke survivors. Xenon (Xe) has favorable neuroprotective properties to modify stroke. Xe delivery is hampered by a lack of suitable administration strategies. We have developed Xe‐containing echogenic liposomes (Xe‐ELIP) for systemic Xe delivery. We investigated the time window for Xe‐ELIP therapeutic effect and the most efficacious dose for neuroprotection. Molecular mechanisms for Xe neuroprotection were investigated.Methods: Xenon‐containing echogenic liposomes were created by a previously developed pressurization‐freezing method. Following right middle cerebral artery occlusion (2 h), animals were treated with Xe‐ELIP at 2, 3, or 5 h to determine time window of therapeutic effect. The neuroprotectant dosage for optimal effect was evaluated 3 h after stroke onset. Expression of brain‐derived neurotrophic factor (BDNF), protein kinase B (Akt), and mitogen‐activated protein kinases (MAPK) was determined.Results: Xenon‐containing echogenic liposomes administration for up to 5 h after stroke onset reduced infract size. Treatment groups given 7 and 14 mg/kg of Xe‐ELIP reduced infarct size. Behavioral outcomes corresponded to changes in infarct volume. Xe‐ELIP treatment reduced ischemic neuronal cell death via activation of both MAPK and Akt. Elevated BDNF expression was shown following Xe‐ELIP delivery.Conclusion: This study demonstrates the therapeutic efficacy of Xe‐ELIP administered within 5 h after stroke onset with an optimal dosage range of 7–14 mg/kg for maximal neuroprotection.

Background—: Ischemia-related neurological injury is a primary cause of stroke disability. Studies have demonstrated that xenon (Xe) may have potential as an effective and nontoxic neuroprotectant. Xe delivery is, however, hampered by lack of suitable administration methods. We have developed a pressurization-freeze method to encapsulate Xe into echogenic liposomes (Xe-ELIP) and have modulated local gas release with transvascular ultrasound exposure. Methods and Results—: Fifteen microliters of Xe were encapsulated into each 1 mg of liposomes (70% Xe and 30% argon). Xe delivery from Xe-ELIP into cells and consequent neuroprotective effects were evaluated with oxygen/glucose-deprived and control neuronal cells in vitro. Xe-ELIP were administered into Sprague-Dawley rats intravenously or intra-arterially after right middle cerebral artery occlusion. One-megahertz low-amplitude (0.18 MPa) continuous wave ultrasound directed onto the internal carotid artery triggered Xe release from circulating Xe-ELIP. Effects of Xe delivery on ischemia-induced neurological injury and disability were evaluated. Xe-ELIP delivery to oxygen/glucose-deprived neuronal cells improved cell viability in vitro and resulted in a 48% infarct volume decrease in vivo. Intravenous Xe-ELIP administration in combination with the ultrasound directed onto the carotid artery enhanced local Xe release from circulating Xe-ELIP and demonstrated 75% infarct volume reduction. This was comparable to the effect after intra-arterial administration. Behavioral tests on limb placement and grid and beam walking correlated with infarct reduction. Conclusions—: This novel methodology may provide a noninvasive strategy for ultrasound-enhanced local therapeutic gas delivery for cerebral ischemia–related injury while minimizing systemic side effects.