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Microbubbles Improve Sonothrombolysis In Vitro and Decrease Hemorrhage In Vivo in a Rabbit Stroke Model

Brown, Aliza T. PhD*; Flores, Rene PhD*; Hamilton, Eric BS*; Roberson, Paula K. PhD; Borrelli, Michael J. PhD*; Culp, William C. MD*

doi: 10.1097/RLI.0b013e318200757a
Original Article

Introduction: Tissue plasminogen activator (tPA) is the thrombolytic standard of care for acute ischemic stroke, but intracerebral hemorrhage (ICH) remains a common and devastating complication. We investigated using ultrasound (US) and microbubble (MB) techniques to reduce required tPA doses and to decrease ICH.

Materials and Methods: Fresh blood clots (3–5 hours) were exposed in vitro to tPA (0.02 or 0.1 mg/mL) plus pulsed 1 MHz US (0.1 W/cm2), with or without 1.12 × 108/mL MBs (Definity or albumin/dextrose MBs [adMB]). Clot mass loss was measured to quantify thrombolysis. New Zealand white rabbits (n = 120) received one 3- to 5-hour clot angiographically delivered into the internal carotid artery. All had transcutaneous pulsed 1 MHz US (0.8 W/cm2) for 60 minutes and intravenous tPA (0.1–0.9 mg/kg) with or without Definity MBs (0.16 mL/mg/kg). After killing the animals, the brains were removed for histology 24 hours later.

Results: In vitro, MBs (Definity or adMB) increased US-induced clot loss significantly, with or without tPA (P < 0.0001). At 0 and 0.02 mg/mL, tPA clot loss was greater with adMBs compared with Definity (P ≤ 0.05). With MB, the tPA dose was reduced 5-fold with good efficacy. In vivo, both Definity MB and tPA groups had less infarct volume compared with controls at P < 0.0183 and P = 0.0003, respectively. Definity MB+tPA reduces infarct volume compared with controls (P < 0.0001), and ICH incidence outside of strokes was significantly lower (P = 0.005) compared with no MB. However, infarct volume in Definity MB versus tPA was not different at P = 0.19.

Conclusion: Combining tPAand MB yielded effective loss of clot with very low dose or even no dose tPA, and infarct volumes and ICH were reduced in acute strokes in rabbits. The ability of MBs to reduce tPA requirements may lead to lower rates of hemorrhage in human stroke treatment.

From the Departments of *Radiology and †Biostatistics, University of Arkansas for Medical Sciences, Little Rock, AR.

Received March 12, 2010; accepted for publication (after revision) August 28, 2010.

Supported from the National Institutes of Health, NIH R01HL82481 (to W.C.C.); and R01CA99178 (to M.J.B.).

Reprints: William C. Culp, MD, Department of Radiology, University of Arkansas for Medical Sciences, M1/269, 4301 West Markham St, Little Rock, AR 72205. E-mail:

© 2011 Lippincott Williams & Wilkins, Inc.