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Uses Blood Flow to Trigger tPA Release RESE ARCHERS ARE DE VELOPING A ME ANS TO QUICKLY DISSOLVE BLOOD CLOTS USING A DRUG«AND«DE VICE COMBINATION THAT AL SO REDUCES VA SCUL AR INJURY. THE TECHNIQUE FOR treating stroke is the work of scientists at the University of Massachusetts' New England Center for Stroke Research and Harvard's Wyss Institute. The technique uses nanopar- ticles coated with clot-dissolving tissue plasminogen activator (tPA) in conjunc- tion with a stent device commonly used in cardiac blockages to quickly restore blood fl ow in the brain. The stent creates a narrow opening through the clot to create shear force of blood fl ow, which activates the nanoparticles to release tPA at the site of the blockage. "The idea is that [the nanoparticles] travel around like a platelet as an aggre- gate, and they're coated with tPA," says Dona ld Ingber, M D, Ph D, Fou ndi ng Director at Wyss Institute for Biologically Inspired Engineering and Judah Folkman Professor of Vascular Biology at Harvard Medica l School. " When they see high shear stress, they break up ... and bind fi brin in the clot, and so we would con- centrate the drug right at the site where the clot was formed." The study, whose fi ndings were pub- lished recently in the journal Stroke, was conducted in clinica lly relevant large a nima ls a nd demonstrated t hat t he therapy is eœ cient in dissolving clots that are fully occluding brain blood vessels. REFINING PREVIOUS TECHNIQUES The technique enhances safety as well. " You don't ta ke the stent out — you don't drag it out, you re-sheath it into a micro-catheter," says Matthew Gounis, PhD, Associate Professor of Radiology at the University of Massachusetts Medical School and Director of the New England Center for Stroke Research. " You can safely pull the whole system out after t he clot is dissolved because of t his nanoparticle delivery system." Researchers found injury to the vessel was signifi cantly less using the combined approach than when a stent is pulled out during a stent-retriever thrombectomy. "When you pull out the clot with these stentrievers, not only do you get loca l injuries and secondary infl ammation, but you also break down the clot," says Ajay Wakhloo, MD, PhD, Fellow of the American Heart Association, Director of Neurointervention and Imaging, and Professor of Neurolog y, Neurosurgery a nd R a d iolog y at t he Un iversit y of Massachusetts Medical School. "What you see in about 10 to 15 percent of the patients is smaller particles of clot migrat- ing into the smaller vessels, and that may create further injury to the brain tissue." Dr. Gounis stresses that stent-retriever thrombectomy is a very e- ective tech- n ique, ca l li ng it t he si ng le g reatest advance in stroke treatment, but he notes that research is moving ever forward. "What we have learned from these data [is] that it's very important to rapidly get complete reperfusion of the ischemic brain," he says. "In our research, what we showed was a very high rate of obtaining complete angiographic reperfusion when the treatment was tailored appropri- ately — using roughly the equivalent of 20 milligrams of free tPA in combination with the stent." ■ Stroke Treatment BY HANNAH STUART SPECIAL CLINICAL SECTION: NEUROLOGY 2 2