stroke model

(Image caption: Glyconanoparticles resulting from fullerene spheres chemically coupled to amino sugars. Credit: MPIKG)

Sweet nanoparticles target stroke

The majority of stroke occurs when the blood vessels that reach the brain are blocked by clots or fatty deposits which decrease the flow of blood towards its cells. It is then that an ischemic attack occurs, a pathology that leads to the degeneration of neurones, which can be fatal and not many drugs can treat.

Now, German and Swiss scientists have discovered that the combination of two substances help to reduce inflammation and the brain volume affected after a cerebrovascular accident. This is glucosamine, an amino sugar commonly used to treat arthritis and arthrosis; and certain derivatives of fullerenes, hollow and spherical structures formed by many carbon atoms.

Before now it was known that the fullerenes capture chemical radicals well which makes them act as neuroprotective agents, while the glucosamine brings down the inflammation.

What the researchers have done is chemically bond the two compounds to produce what is known as ‘glyconanoparticles’. These have subsequently been administered to laboratory rats which then had a cerebrovascular accident induced.

The results, published in the journal ‘Experimental Neurology’, conclude that this combination of fullerene derivatives and glucosamine reduces cell damage and inflammation after a stroke, according to the MRI scans of animal brains and the improvement of their neurological symptoms.

“Our study confirms that it is possible to couple fullerenes with sugars in order to combine their protective effects and in this way, to obtain new materials which may help to prevent and to treat Stroke,” says Guillermo Orts-Gil, a Spanish researcher at the Max-Planck Institute of Colloids and Interfaces (Germany) and co-author of the research.

“Although the present study was carried out on mice, the results indicate that these sweet buckyballs are potential new drugs for treating Stroke also in humans. However, this must be taken with caution, since what works in mice does not necessarily will work in the same way in humans,” declared Orts-Gil.

This work is the continuation of another previous piece of research, published last year in the journal ‘Nano Letters’, in which the researchers also confirmed that a protein called E-selectin, linked to the chain of events that occur during a stroke, is distributed throughout the brain and not only in the area where the stroke originates, as previously thought.

Targeted brain stimulation aids stroke recovery in mice

When investigators at the Stanford University School of Medicine applied light-driven stimulation to nerve cells in the brains of mice that had suffered strokes several days earlier, the mice showed significantly greater recovery in motor ability than mice that had experienced strokes but whose brains weren’t stimulated.

These findings, published online Aug. 18 in Proceedings of the National Academy of Sciences, could help identify important brain circuits involved in stroke recovery and usher in new clinical therapies for stroke, including the placement of electrical brain-stimulating devices similar to those used for treating Parkinson’s disease, chronic pain and epilepsy. The findings also highlight the neuroscientific strides made possible by a powerful research technique known as optogenetics.

Stroke, with 15 million new victims per year worldwide, is the planet’s second-largest cause of death, according to Gary Steinberg, MD, PhD, professor and chair of neurosurgery and the study’s senior author. In the United States, stroke is the largest single cause of neurologic disability, accounting for about 800,000 new cases each year — more than one per minute — and exacting an annual tab of about $75 billion in medical costs and lost productivity.

The only approved drug for stroke in the United States is an injectable medication called tissue plasminogen activator, or tPA. If infused within a few hours of the stroke, tPA can limit the extent of stroke damage. But no more than 5 percent of patients actually benefit from it, largely because by the time they arrive at a medical center the damage is already done. No pharmacological therapy has been shown to enhance recovery from stroke from that point on.

Enhancing recovery

But in this study — the first to use a light-driven stimulation technology called optogenetics to enhance stroke recovery in mice — the stimulations promoted recovery even when initiated five days after stroke occurred.

“In this study, we found that direct stimulation of a particular set of nerve cells in the brain — nerve cells in the motor cortex — was able to substantially enhance recovery,” said Steinberg, the Bernard and Ronni Lacroute-William Randolph Hearst Professor in Neurosurgery and Neurosciences.

About seven of every eight strokes are ischemic: They occur when a blood clot cuts off oxygen flow to one or another part of the brain, destroying tissue and leaving weakness, paralysis and sensory, cognitive and speech deficits in its wake. While some degree of recovery is possible — this varies greatly among patients depending on many factors, notably age — it’s seldom complete, and typically grinds to a halt by three months after the stroke has occurred.

Animal studies have indicated that electrical stimulation of the brain can improve recovery from stroke. However, “existing brain-stimulation techniques activate all cell types in the stimulation area, which not only makes it difficult to study but can cause unwanted side effects,” said the study’s lead author, Michelle Cheng, PhD, a research associate in Steinberg’s lab.

For the new study, the Stanford investigators deployed optogenetics, a technology pioneered by co-author Karl Deisseroth, MD, PhD, professor of psychiatry and behavioral sciences and of bioengineering. Optogenetics involves expressing a light-sensitive protein in specifically targeted brain cells. Upon exposure to light of the right wavelength, this light-sensitive protein is activated and causes the cell to fire.

Steinberg’s team selectively expressed this protein in the brain’s primary motor cortex, which is involved in regulating motor functions. Nerve cells within this cortical layer send outputs to many other brain regions, including its counterpart in the brain’s opposite hemisphere. Using an optical fiber implanted in that region, the researchers were able to stimulate the primary motor cortex near where the stroke had occurred, and then monitor biochemical changes and blood flow there as well as in other brain areas with which this region was in communication. “We wanted to find out whether activating these nerve cells alone can contribute to recovery,” Steinberg said.

Walking farther

By several behavioral, blood flow and biochemical measures, the answer two weeks later was a strong yes. On one test of motor coordination, balance and muscular strength, the mice had to walk the length of a horizontal beam rotating on its axis, like a rotisserie spit. Stroke-impaired mice whose primary motor cortex was optogenetically stimulated did significantly better in how far they could walk along the beam without falling off and in the speed of their transit, compared with their unstimulated counterparts.

The same treatment, applied to mice that had not suffered a stroke but whose brains had been similarly genetically altered and then stimulated just as stroke-affected mice’s brains were, had no effect on either the distance they travelled along the rotating beam before falling off or how fast they walked. This suggests it was stimulation-induced repair of stroke damage, not the stimulation itself, yielding the improved motor ability.

Stroke-affected mice whose brains were optogenetically stimulated also regained substantially more of their lost weight than unstimulated, stroke-affected mice. Furthermore, stimulated post-stroke mice showed enhanced blood flow in their brain compared with unstimulated post-stroke mice.

In addition, substances called growth factors, produced naturally in the brain, were more abundant in key regions on both sides of the brain in optogenetically stimulated, stroke-affected mice than in their unstimulated counterparts. Likewise, certain brain regions of these optogenetically stimulated, post-stroke mice showed increased levels of proteins associated with heightened ability of nerve cells to alter their structural features in response to experience — for example, practice and learning. (Optogenetic stimulation of the brains of non-stroke mice produced no such effects.)

Steinberg said his lab is following up to determine whether the improvement is sustained in the long term. “We’re also looking to see if optogenetically stimulating other brain regions after a stroke might be equally or more effective,” he said. “The goal is to identify the precise circuits that would be most amenable to interventions in the human brain, post-stroke, so that we can take this approach into clinical trials.”

‘Window of Recovery’ Can Reopen after Stroke

Using mice whose front paws were still partly disabled after an initial induced stroke, Johns Hopkins researchers report that inducing a second stroke nearby in their brains let them “rehab” the animals to successfully grab food pellets with those paws at pre-stroke efficiency.

The findings, described online Dec. 31, 2015, in Neurorehabilitation and Neural Repair, show that the “window of opportunity” for recovering motor function after a stroke isn’t permanently closed after brain damage from an earlier stroke and can reopen under certain conditions, in conjunction with rapid rehabilitation efforts.

(Image caption: A cross-section of a mouse brain with the initial stroke showing as a gray region on the right. The second stroke was given in the region on the left labeled AGm. Credit: Courtesy of Neurorehabilitation and Neural Repair)

The investigators strongly emphasize that their experiments do not and will never make a case for inducing strokes as a therapy in people with stroke disability. But they do suggest the mammalian brain may be far more “plastic” in such patients, and that safe and ethical ways might be found to better exploit that plasticity and reopen the recovery window for people who have never fully regained control of their motor movements.

“If we can better understand how to reopen or extend the optimal recovery period after a stroke, then we might indeed change how we treat patients for the better,” says Steven Zeiler, M.D., Ph.D., assistant professor of neurology at the Johns Hopkins University School of Medicine. “Our study adds new strong and convincing evidence that there is a sensitive period following stroke where it’s easiest to relearn motor movements — a topic that is still debated among stroke researchers.”

The new mouse experiments build on a previous study at Johns Hopkins, which found that the window of optimal recovery following a stroke in mice was within the first seven days, but this time period could be extended by giving mice the common antidepressant fluoxetine immediately after the stroke. The investigators suspected that the antidepressant increased the brain’s response to learning. Until now, however, the researchers say, there was no evidence that once the optimal period was over — with or without fluoxetine — the potential for recovery could be reopened.

For the new research, which did not involve the use of the antidepressant, the researchers — as in their first experiments — taught mice to reach through a slit in their cage with their front paw to grasp food pellets affixed to a bar, a task that four-legged animals don’t naturally perform.

Once the mice became efficient at the task — it took about 10 days of training — the researchers measured their individual success rates. On average, they found the mice successfully grabbed pellets just over 50 percent of the time.

The researchers then induced a stroke in the motor cortex of the mice’s brains, making them unable to perform the task. After waiting a week — well beyond the known “optimal” window during which rehab training will work — they put the mice through almost three weeks of task training, during which the mice successfully grabbed the pellets again, but only about 30 percent of the time.

For the next phase of the experiment, the scientists built on previous research and observations in mice that brain ischemia — the cutoff or reduction of oxygen to the brain during a stroke or other insult to the cortex — under certain conditions increased brain plasticity, the ability of the brain to compensate for injury and form new connections.

To that end, the scientists induced a second stroke in the lab mice either in the secondary motor cortex near the first stroke site or, for purposes of a control group, in the visual cortex, located far from the original site.

Instead of waiting days, the investigators began retraining these mice the next day and found that mice with the follow-up stroke in the motor cortex relearned to grasp the food pellets just as well as they did before the first stroke, with success more than 50 percent of the time.

Mice in the control group never did any better, even with extended training, suggesting that the motor cortex may be the only part of the brain with this type of “reopening” capability for motor movements, the investigators say.

Zeiler plans to investigate other ways to reopen the window of recovery and make use of the optimal recovery window. The lead investigator of the study, John Krakauer, M.D., M.A., professor of neurology, directs the Brain, Learning, Animation and Movement Lab, which uses basic science data, like that in this study, to develop new patient therapies. Currently, the lab is investigating the importance of early and intense rehabilitation in patients to enhance brain plasticity after stroke.

According to the Centers for Disease Control and Prevention, in the U.S., stroke is the No. 1 cause of disability and costs $34 billion each year in in health care, medications and missed days of work.