Delayed cerebral vasospasm following subarachnoid hemorrhage causes severe ischemic neurologic deficits leading to permanent neurologic dysfunction or death. Reduced intravascular and perivascular nitric oxide (NO) availability is a primary pathophysiology of cerebral vasospasm. In this study, we evaluated NO-loaded echogenic liposomes (NO-ELIP) for ultrasound-facilitated NO delivery to produce vasodilation for treatment of vasospasm following subarachnoid hemorrhage. We investigated the vasodilative effects of NO released from NO-ELIP both ex vivo and in vivo. Liposomes containing phospholipids and cholesterol were prepared, and NO was encapsulated. The encapsulation and release of NO from NO-ELIP were determined by the syringe/vacuum method and ultrasound imaging. The ex vivo vasodilative effect of NO-ELIP was investigated using rabbit carotid arteries. Arterial vasodilation was clearly observed with NO-ELIP exposed to Doppler ultrasound whereas there was little vasodilative effect without exposure to Doppler ultrasound in the presence of red blood cells. Penetration of NO into the arterial wall was determined by fluorescent microscopy. The vasodilative effects of intravenously administered NO-ELIP in vivo were determined in a rat subarachnoid hemorrhage model. NO-ELIP with ultrasound activation over the carotid artery demonstrated effective arterial vasodilation in vivo resulting in improved neurologic function. This novel methodology for ultrasound-controlled delivery of NO has the potential for therapeutic treatment of vasospasm following subarachnoid hemorrhage. This ultrasound-controlled release strategy provides a new avenue for targeted bioactive gas and therapeutic delivery for improved stroke treatment.
Keywords: liposomes; nitric oxide; subarachnoid hemorrhage; ultrasound; vasodilation; vasospasm.