BACKGROUND:
Ischemic stroke is the second most common cause of death worldwide and a major cause of disability. Intravenous (iv) tissue plasminogen activator (tPA) in combination with the neuroprotective gas, xenon (Xe), is a promising strategy for ischemic stroke treatment. However, Xe delivery by inhalation may reduce oxygen uptake and tPA activity. We have developed novel Xe-containing echogenic liposomes (Xe-ELIP). In this study, we investigated the therapeutic effect of Xe-ELIP in a rat embolic stroke model.
METHODS:
Xe-ELIP was prepared by the pressurized-freeze method. Thrombotic strokes were induced in male Sprague-Dawley rats (n=16) by injecting a 13mm long blood clot into the middle cerebral artery (MCA). In the treatment group, tPA (10mg/kg) was infused intravenously at 2 hours after the onset occlusion. Xe-ELIP was administrated into the common carotid artery just before iv tPA. Continuous wave ultrasound (1 MHz, 50% duty cycle, 0.5 W/cm
2
) was applied to trigger Xe release from ELIP during the 5 min of Xe-ELIP administration. Behavioral tests (limb placement, grid walking and beam walking) were conducted three days after the thrombotic stroke. Two mm-thick coronal brain sections were cut and stained with TTC to determine infarct size.
RESULTS:
The thrombotic stroke control group without any treatment exhibited the largest damage and infarct size (17±5% of the whole brain); tPA treatment reduced the damage and the infarct size to 5.2±0.4% of (p=0.025
vs
stroke). tPA treatment in combination with Xe-ELIP further reduced the infarct size to 1.5±0.4% (p=0.05
vs
tPA group) (
Fig
1a, 1b). Behavioral deficit correlated with the infarct volume reduction. Regional blood flow velocity monitored by a laser Doppler flow meter was the same in both tPA and tPA+Xe-ELIP treatment groups.
CONCLUSIONS:
This study has demonstrated a significant neuroprotective effect of ELIP-encapsulated xenon released by application of 1 MHz ultrasound. Xe-ELIP can be used in combination with tPA without affecting tPA thrombolytic activity.
In vitrothrombolytic efficacy of echogenic liposomes loaded with tissue plasminogen activator and octafluoropropane gas
