Study identifies protein that shrinks brain lesions in stroke victims

July 28, 2011, 2:05 a.m.

Researchers at the Stanford School of Medicine published a study earlier this week in the Proceedings of the National Academy of Sciences that revealed alpha-B-crystallin, a naturally occurring protein, significantly shrank the size of stroke-induced lesions in the brains of laboratory mice and mitigated the destructiveness of the inflammatory response that follows the stroke.

The study, conducted by Dr. Gary Steinberg PhD. ’79 M.D. ‘80, director of Stanford’s Institute for Neuro-Innovation and Translational Neurosciences and neurology professor Dr. Lawrence Steinman, is a follow-up on an earlier study published in Nature in 2007 that showed how alpha-B-crystallin reduces brain damage caused by multiple sclerosis, a chronic autoimmune brain disease.

Alpha-B-crystallin is an important structural protein found in the eye’s lens. It is regularly produced in the heart. When other tissues undergo stress–for example, when a stroke deprives the brain of oxygen–this triggers alpha-B-crystallin production, the body’s natural defense to limit the inflammatory activity.

“The brain, when it’s injured, doesn’t roll over and play dead,” Steinman said. “It fights back by producing protective molecules; one of those molecules is alpha-B-crystallin. Since we’ve seen how the presence of alpha-B-crystallin plays an active role in the brain’s healing response to a stroke, we wanted to see if administering more of it could increase its effect.”

Senior authors Steinberg and Steinman, along with postdoctoral scholar Ahmet Arac and Sara Brownwell M.A. ’11 Ph.D. ’13, employed knockouts–mice bioengineered to lack the ability to produce alpha-b-crystallin–to investigate the level of efficacy the protein has in reducing stroke lesions.

“We temporarily blocked off one of the arteries,” Steinberg said. “We do it by opening the carotid artery, inserting a thread that’s about the size of the artery and temporarily block the blood flow to induce a stroke.”

There were two groups of mice: the knockouts and the wild types, mice that contained the gene to produce alpha-B-crystallin.

After inducing the strokes, the mice from both groups were monitored for up to a week, their recovery time measured with the use of a neurologic scale, which ranges from zero to 28. Zero is a full recovery and 28 is the lowest level of neurologic functioning.

“For seven categories, we score them from zero to four,” Steinberg said. “We test for lots of things. We test for body symmetry–is it asymmetric in that it’s favoring one side more than the other? We test for its gait–see if there’s any limping or staggering. We measure their ability to climb 45 degrees and also test circling behavior–whether or not it’s swaying–and whisker response.”

Twelve hours after the stroke, the wild types scored around 12 while the knockouts were at 14. The results, according to Steinberg, were not statistically significant. However, seven days later, the wild types scored around four while the knockouts scored around eight, a statistically significant difference that sheds light on the body’s natural recovery.

“The stroke evolves, but neurologic function actually improves,” Steinberg said. “This is because there’s some natural recovery the body performs. In this case, the wild types recovered quicker than the knockouts.”

The study presents a promising start to finding a drug that will treat not only the stroke but the post-stress inflammatory response. TPA, the current government-approved stroke drug, is limited in its effectiveness in that while it breaks up clots, it does not treat the inflammatory aftershock caused by dead tissue and toxins.

There is still much work to be done including further investigation into the efficacy and safety of alpha-B-crystallin administration before the protein can eventually be brought into clinical trials.

“We’d like to have [the experiment] reproduced and verified,” Steinberg said. “Some other questions we want to look at are whether or not there’s benefit from the protein after 24 hours as well as figuring out the level of dosage necessary to achieve efficacy. You’d be surprised how many therapeutic treatments, while successful in the lab, may not be successful in clinical trials.”

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