According to the World Health Organisation, 1.5 crore people suffer a stroke every year. Of these, fifty lakh end up permanently disabled and another 50 lakh million die. A stroke occurs when the brain does not get enough blood supply either due to a blood clot or due to the bursting of a blood vessel, which results in lack of oxygen and other nutrients in the brain. If not treated early, it can be life-threatening, but managing the complications of stroke can be difficult.
In a recent study published in the journal Nature Communications on 25 August 2020, it was found that after a stroke, if the existing blood is replaced by the blood of a healthy donor, the damage to the brain can be reduced significantly.
What happens after a stroke?
After a stroke occurs, the body’s immune system gets activated and starts sending messenger molecules across the blood-brain barrier. These molecules then deploy the immune cells to the damaged area. Most of the time, the first cells to arrive the site of damage are neutrophils, which increase the levels of an enzyme called MMP-9. The enzyme MMP-9 destroys the blood-brain barrier a little more so that more immune cells and signalling molecules can enter the brain. But in some cases, the body releases too many immune cells including the cytokines (inflammation-causing immune cells) into the blood. This results in a cytokine storm which damages the brain tissue surrounding the blood clot, ultimately resulting in more inflammation and brain damage.
The stroke study
In order to find the link between the brain and the blood, scientists from the West Virginia University conducted a study on a group of mice. The scientists simulated an ischemic stroke in these mice and cleared the stroke after 90 minutes. The scientists then divided the mice into two categories: one group went under blood replacement while the other one was a control group, so it didn’t get a blood replacement.
Six to seven hours after the stroke, the scientists replaced 250 to 500 microliters of the mice’s blood with blood from healthy donor mice, which accounts for 10 percent to 20 percent of a mouse’s total blood volume. After an hour, the scientists examined the amount of the blood-brain barrier degraded in the brain of the mice. The scientists further examined the amount of brain tissue damaged 24 hours after the treatment was given.
The results of the study showed that the mice who received healthy blood showed lesser ill effects and lesser cognitive defects as compared to the control mice. It was found that the amount of brain damage around the clot was reduced by 70 percent to 80 percent in the mice who got blood replacements.
Finding the ‘stroke clearing’ part in the blood
To confirm their findings, scientists also replaced the blood with that of other stroke-suffering mice but did not find any benefit. They concluded that healthy blood was the key element. After the fact was established that blood from a healthy donor can reduce the ill effects of stroke, the doctors were keen on finding the exact components of the blood that were responsible for this.
On further investigation, scientists found that the replaced blood weakens the immune response in the body of the mice. After the blood replacement, the authors measured the levels of leukocytes, neutrophils, monocytes, T cells and B cells that were circulating in the mice’s blood and they were found to be comparatively low. There were also low levels of chemokines, cytokines and MMP-9 in the blood and brain of the treated mice, which resulted in lesser degeneration of the blood-brain barrier.
Hope for the future
The scientists believe that by identifying the most important components in the healthy blood, it would be easy for the doctors to target these to either reduce or increase their levels in the blood of the mice. For instance, if the neutrophils were found to deteriorate the blood-brain barrier, they can be reduced in the blood after a stroke. Similarly, if there is any beneficial component, it can be increased.
More studies are to be done in different groups of mice before commencing the study in humans.
For more information, read our article on Stroke.
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