If something lodges in the blood vessels that feed the brain – say a blood clot, piece of bone marrow after a bone has been broken, or tissue debris from damaged tissue – the brain undergoes a loss of blood flow. Since the brain received its oxygen and nutrients from the bloodstream, blockage of the vessels that feed the brain can lead to the death of brain cells.
Such a phenomenon is called a stroke or a Trans-Ischemic Attack. However, if the heart stops, blood flow to the brain ceases; not because of blockage of the blood vessels that feed the brain, but because the pump that propels through the bloodstream has stopped and, therefore, blood flow stops. Such a condition is known as global cerebral ischemia or GCI.
GCI is one of the most challenging clinical issues encountered during cardiac arrest and, unfortunately, typically indicates a poor prognosis. Severe neurological damage develops in 33%–50% of GCI patients who have survived a cardiac arrest that was documented by a medical professional. In those rare cases of survival after cardiac arrest that was not documented by a medical professional, the percentage of neurological defects is 100%. I hope this convinces you that CGI is a problem.
In order to treat GCI, physicians usually induce hypothermia, which lowers and maintains the core body temperature at 32°C–34°C. Presently, this is the only treatment regime that has been demonstrated to improve neurological recovery. Unfortunately, there are many technical difficulties in the application of this therapy. Special equipment is required, and complications such as blood clots and infection are perennial problems. Is there a better way to treat GCI?
Sang Won Suh from the Hallym University College of Medicine in South Korea and his colleagues have used fat-based mesenchymal stem cells to treat laboratory animals that have suffered GCI. The results of their study are encouraging.
Suh and his coworkers used Sprague-Dawley rats for this study. They anesthetized the rats and then clamped their carotid arteries to reduce blood flow to the brain for seven minutes. This effectively simulates GCI in these laboratory animals. After the clamps were removed, some animals were given one million fat-based mesenchymal stem cells, and others were simply restored by means of unclamping the carotid arteries plus fluid reconstitution. The rats were subjected to behavioral tests three days before the procedure and seven days after it. These tests consisted of placing adhesive tape the forepaws of the animals and then measuring the day it tool for the animals to remove to adhesive tape. After the seventh day post-procedure, the rats were put down and their brains were examined for cell death, structure, blood vessel densities, and degree of inflammation.
When the brains of these animals were examined, it was clear that the animals that had received fat-based mesenchymal stem cells suffered much less cell death than the untreated animals.
In the figure above you can see a Fluoro-Jade B staining of these brains. FJB stains detect dying cells. As you can see, the brain from the rats that experienced GCI without any stem cell treatments had lots of dying cells in their brains. The “sham” operated rats – rats that were operated, but their carotid arteries were not clamped – had no cell death in their brains. The animals that had their carotid arteries clamped, but were given fat-based mesenchymal stem cells had a little cell death. The graph above shows the vast differences between the stem cell-treated and the non-stem cell-treated groups. Truly these are significant results. Other experiments that detected Now this is no a surprise, since Ohtaki and others showed a very similar result in 2008 (Ohtaki H, et al. Proc Natl Acad Sci USA 105:14638–14643). Suh, and his group, however, took these experiments further to determine why these cells prevented cell death in the brain after GCI.
When Suh and his team examined the leakage of large proteins into the brain, they saw something quite remarkable; the mesenchymal stem cell-treated rats only leaked a little protein into their brains compared to the non-stem cell-treated rats.
The presence of the brown color indicated the presence of a protein in the brain that normally does not find its way to the brain unless the integrity of the blood-brain barrier is compromised. As you can see, the non-treated animals have a truckload of this protein in their brains, which indicates that their blood-brain barriers are very leaky. On the contrary, the stem cell-treated brains are not nearly as leaky and the sham operated brains are not leaky at all.
These results suggest that the stem cells help maintain the structural integrity of the blood-brain barrier in GCI patients and this prevents nasty things from the bloodstream, such as immune cells and so on from accessing the brain and ravaging it. To test this hypothesis, Suh and others examined the brains for the presence of neutrophils, which are white blood cells that show up when inflammation occurs. These cells are not found in the brain unless the blood-brain barrier is damaged. Sure enough, brains from the sham-operated rats showed no signs of neutrophils, brains from the non-stem cell-treated rats were chock full of neutrophils, and the brains from the stem cell-treated rats only had a few neutrophils.
A conclusion from this paper states: “Administration of MSCs decreased the delayed neuronal damage in a transient global cerebral ischemia model by prevention of BBB disruption, endothelial damage, and neutrophil infiltration.”
Clearly this merits more work. Larger animal models will need to be examined, and also it would be nice to know if administration of exosomes from mesenchymal stem cells can elicit a similar biological response. However his is a very hopeful beginning to what might become a fruitful bit of clinical research.