Читать книгу The SAGE Encyclopedia of Stem Cell Research - Группа авторов - Страница 456

No other organ system is a greater embodiment of who we are than the nervous system. To call the nervous system simply the headquarters of the body would be a gross understatement. That is one of the main reasons that malignancies of the nervous system are so dire. Diseases of the nervous system vary widely in pathology, but the most severe among them leave only a life of debilitation in their wake. For decades, the only course of action against diseases of the nervous system was to manage the symptoms and any subsequent complications that would arise from the disease, while not targeting the true cause of the disease itself.

The nervous system is comprised of the brain, spinal cord, and a plethora of nerves that run throughout every inch of the body. At the very core of the nervous system rests the neuron. It is neurons that collectively mediate the countless messages of the brain to the rest of the body. Malformations within the signaling processes of neurons can produce devastating effects for any individual. Some of the most prevalent neurological diseases include Parkinson’s disease, Alzheimer’s disease, and strokes. Stem cells may provide a unique and effective means to counteract the deleterious effects of all of these diseases.

Parkinson’s disease is a degenerative disease of the central nervous system. It results from the death of dopamine-generating cells in the midbrain. Dopamine is a neurotransmitter involved in motor control. A decrease in the levels of dopamine leads to the characteristic signs of Parkinson’s: erratic shaking, rigidity of the body, diminished range of movement, and an impaired gait. The exact cause of the death of the dopamine-generating cells is still unknown. However, there are some pharmaceutical interventions for the disease.

Levodopa has been the staple drug used to treat Parkinson’s for the better part of the last 30 years. The drug acts as a dopamine substitute. Its main ingredient, L-DOPA, is converted into dopamine in the dopamine-producing neurons of the midbrain. The end result is a temporary decrease in the motor symptoms of Parkinson’s. However, there are some drawbacks to Levodopa. Only a minute portion of the L-DOPA crosses into the brain through the blood-brain barrier. The rest of the L-DOPA is sent throughout the body where it causes a variety of adverse effects, from nausea to joint stiffness. These adverse effects have actually dissuaded some physicians from prescribing the medication at all. The need for a much safer and more permanent solution is at hand.

Stem cells provide a unique insight into possible avenues of regeneration of the dopamine-generating cells of the brain. As of now, it has been seen that stem cells derived from cord blood can differentiate into the dopamine-generating cells in vitro. These cells were infused into the midbrain of mice and a greater control of motor functions was exhibited. Furthermore, human embryonic stem cells (hESCs) have also shown positive test results in mice. The hESCs were able to differentiate in neural progenitor cells in vitro. These neural progenitor cells were then grafted into the midbrains of Parkinson’s-induced rats. The grafts were only temporary, surviving for roughly 12 weeks. The level of dopamine production within the rats increased and motor function proceeded to be less erratic.

Parkinson’s disease is not the only illness of the nervous system that has been positively affected by stem cells. Alzheimer’s disease within mice has been shown to effectively respond to stem cell treatment. Alzheimer’s disease is a form of dementia with no known cure. In 2010, it was reported that 35.6 million people were living with the disease worldwide. The causes of Alzheimer’s are still being determined. However, it has been linked to an increase in the buildup of amyloid beta plaques within the gray matter of the brain. Alzheimer’s ultimately leads to long-term memory loss. The degradation of the mind goes so far that vital bodily functions are eventually lost, ultimately ending in death.

Currently, there is no known cure for Alzheimer’s disease. The medications available on the market can only alleviate some of the light symptoms of the disease, including confusion, irritability, aggression, and mood swings. However, a means to combat the cause of the disease still evades modern medicine. To date, over 1,000 clinical trials have been performed, testing a barrage of medications and chemical compounds to combat the disease. Stem cells, however, may very well hold to the key to unlocking the mystery of this disease.

In 2012, a study in South Korea brought a great deal of hope to the fight against the disease. Researchers in Korea used fat-derived adult stem cells (adMSCs: human adipose-derived mesenchymal stem cells) to counterattack the effects of Alzheimer’s within mice in which the disease had been induced. The researchers injected these cells intravenously through the tail of the mice, and something remarkable occurred. The cells traveled the length of the animal’s body and actually crossed the blood-brain barrier, a feat that had long been thought impossible for adult stem cells. The cell treatment worked wonders on the mice. In every neurological benchmark, the mice showed improvement, from the ability to learn to the ability to remember.

The treatment of Alzheimer’s with stem cells in humans is still a long way off. However, the trial’s positive test results in South Korea have greatly opened the doors toward human-based clinical studies. More evidence will need to be found to corroborate the results of this initial study. However, stem cells are quickly emerging as the premier form of intervention for Alzheimer’s disease.

Along with Parkinson’s and Alzheimer’s diseases, stem cells have shown promising results in early trials against the damage caused by strokes. A heart attack is to the heart as a stroke is to the brain. To put it quite simply, a stroke is the result of an occlusion of a vessel to any part of the brain. This occlusion blocks off the flow of oxygen to the brain, resulting in death of the surrounding tissue. This is analogous to the ischemic damage sustained by the heart post-MI. Since the brain is the control center of all bodily functions, a stroke can have catastrophic effects on an individual. Even those who are lucky enough to survive a stroke are only met with a life filled with hardships and, in some cases, in need of years of rehabilitation.

The possibility of regenerating the sections of the brain left in ruin by a stroke has long evaded the scientific community. As with a litany of other diseases, stem cells may finally provide answers to reverse what has for so long been deemed irreversible. The regenerative potential of stem cells is, arguably, unlimited. In the case of stroke victims, the most heavily damaged portions of the brain may soon be revitalized. Trials are still in their very early phases, but results look promising.

A revolutionary study at Lund University in Sweden hopes to usher in a new age of stem cell research focusing on the cells’ efficacy to treat the effects of stroke. The Swedish research team harvested adult skin cells from humans and reprogrammed them into pluripotent cells, known as induced pluripotent stem cells. They then reintroduced these stem cells into cerebral cortices of stroke-induced rats. Upon transplantation of the cells, the rats exhibited great progress in motor capabilities. The study posits new avenues of research on the subject. The viability of induced pluripotent stem cells could possibly curb a likely shortage of stem cells in the future. The ability to reprogram common, differentiated cells into a pluripotent, progenitor state will do wonders for the field of stem cell research as a whole.

The effectiveness of this new variant of stem cells on the effects of stroke will have huge implications moving forward. Full-blown clinical trials are still a while away. However, the promising results from this Swedish trial as well as the astounding results from the clinical trial in heart attack victims add credibility to the use of stem cells in a clinical setting as an intervention for stroke.

For too long, the brain has appeared far too abstract for the grasp of medicine to reach, but no longer is that the case. The stem cell has provided a unique and unforeseen opportunity into the realm of the brain. Now, even the direst of conditions may soon be cured, not simply treated, with the aid of these marvelous cells. More research is undoubtedly needed to validate these early findings. However, with each passing day, a new breakthrough is discovered. We are but on the shores of a sea of endless possibilities, and the stem cell is our ship.