Parkinson disease is a gradually progressive neurodegenerative disorder affecting the dopaminergic neurons in the nigrostriatal region of the brain. Damage to the nigro striatal region leads to a loss of dopaminergic neurons, which leads to slowing of the movements, tremors, rigidity, lack of muscle control and coordination, and freezing of gait in the advanced stages. The disease affects millions of people worldwide annually, and is very difficult to diagnose and cure because of the overlapping atypical Parkinsonian syndromes.
Keeping this in mind, the Stem cell therapy is growing in popularity globally particularly for neurological disorders and neurodegenerative diseases like Parkinson’s disease. Researchers have confirmed the possibility of development of dopaminergic neurons from human embryonic stem cells, which have the potential to become any cell of the body. Clinics offering stem cell therapy are now accessible globally and with constant advancements in stem cell technology, there is significant hope that it will be the ‘magic bullet’ in the treatment of Parkinson’s disease. However, to date there is no reliable evidence to suggest that any available stem cell therapy can cure Parkinson’s disease. This, however, does not mean that stem cell therapy cannot offer some improvement in the condition.
An Overview of Stem Cell Therapy for Parkinson’s Disease
Stem cells are immature cells which differentiate into different cells in the body. They are most abundant in fetal life but small amounts of partially differentiated stem cells are available in various tissues even in adulthood. Some tissues have large amounts of stem cells, like the bone marrow with its hematopoietic stems cells, but these cells are partially differentiated already and therefore only capable of forming the necessary blood cells.
A recent procedure has been able to ‘wipe’ clean these partially differentiated stems cells to once again form ‘blank’ stem cells that can then be stimulated to differentiate into a cell types of choice. These cells are known as induced pluripotent stem cells (iPSC’s) and made waves in the medical science community in 2010. It holds much promise for a number of conditions, not only Parkinson’s disease.
Parkinson’s disease arises due to a progressive decrease in the number of dopamine-producing neurons (dopaminergic neurons) in the substantia nigra of the brain. The lower than normal levels of dopamine, a neurotransmitter, is responsible for the features of Parkinson’s disease. In a nutshell, stem cell therapy holds the hope that by differentiating ‘blank cells’ into dopamine-producing neurons, at least partially, and injecting it into the substantia nigra, more dopamine-producing neurons will be available.
A recent study from a university in Sweden, shows the possibility of production of new dopaminergic neurons by injecting human embryonic stem cells into rat’s brain. These newly synthesized cells are hypothesized to function same, and possess similar properties as that of the native dopaminergic cells in the human brain.
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Stem Cell Clinics for Parkinson’s Disease
One of the challenges with regards to induced pluripotent stem cells is controlling the ‘reprogramming’ of the cell to form the dopaminergic neurons and integrating it into the brain tissue. In experiments on lab rats it was seen that integrating these dopaminergic neurons could be achieved on the rat. The net result could be an improvement in the clinical symptoms of Parkinson’s disease. The next and the most important step is to prepare for human clinical trials. However, the efficacy on human subjects has to be ascertained by properly structured and controlled clinical trials.
The pluripotent stem cells used to produce new dopaminergic neurons are derived from human embryonic stem cells. The problem lies in the fact that fetal cells are harder to source and there are abundant ethical concerns whilst harnessing stem cell tissues from aborted fetuses for the purpose of commercial utilization. Also, there is not enough fetal stem cell tissue available to address the therapeutic needs of large number of PD patients worldwide.
Stem cell therapy is available at a number of clinics but the long term effects and potential complications have yet to be ascertained. Although many of clinics market these techniques quite aggressively, particularly on the internet, none can truly lay claim to ‘curing’ Parkinson’s disease. There are also the concerns that undifferentiated stem cells contained in the ‘mix’ may also be delivered into the brain tissue. These cells may have the potential to differentiate abnormally and grow rapidly and become tumors. The other factor to consider is that the exact pathogenic mechanism of Parkinson’s disease is still not clearly known. Therefore the very mechanism that can affect the naturally-occurring dopaminergic neurons may also affect the iPS dopaminergic neurons. Considering the cost factor of stem cell therapy, this can be an expensive procedure that may only offer short term results, if any.
This is not to say that the therapy offered by these clinics are not beneficial to some patients to some degree but it should not offer false hope. Most dedicated Parkinson disease organizations are critical of these clinics and the therapy on offer not because of the therapy itself, but rather in the manner that it is marketed and the sometimes blatant but often subtle promise of a cure.
Side effects of the stem cell therapy for Parkinson’s disease
Pluripotent human embryo stem cells have been harvested and grown into dopamine producing nerve cells in various subject models and injected into the patients as a controlled trial to study the therapeutic potentials of the technology. However, various studies have also shed light on the possible side effects of the stem cell therapy for Parkinson’s disease, most common of them being the involuntary graft induced movements. Similar side effects are observed in many patients on long term L-levodopa treatment. Some of the patients also reportedly demonstrated the development of PD pathology in their stem cells graft even after 20 years of administration. This opens the gateway to the hypothesis that Parkinson’s disease involves a sequence of spread through the passing of abnormal forms of alpha synuclein from one nerve cell to another.
Thus, it can be effectively concluded that even though stem cell therapy aiming to be the cure for Parkinson’s disease is a ground breaking discovery, it’s potential, safety, and consistent efficacy is yet to to extensively researched and studied.