Parkinson’s disease is a common neurodegenerative disorder characterized by selective loss of nigro-striatal dopaminergic neurons, which manifests as motor deficits in the form of tremors, rigidity, lack of muscle movements and coordination, frequent falls and freezing of gait. Pathophysiology, diagnosis, and treatment of PD is currently one of the most studied and researched subject. The treatment options available can only ease the quality of life, but cannot halt or retard the inevitable progression of disease.
One of the latest medico-technological advancement in the field of parkinson’s research is the advent of pluripotent stem cell technology as means of therapeutic intervention. Although in the early stages, the potential use of induced pluripotent stem cells (iPSCs) in the treatment of Parkinson’s disease (PD) holds tremendous possibilities for the future. A significant amount of research is still necessary and the practical application of such a treatment option is probably still a long way. However, the promise of acquiring an undifferentiated stem cell from the patient’s body and then stimulating differentiation into a nerve cell may make this sort of therapy one of the more exciting developments in recent years.
What are Pluripotent Stem Cells?
Stem cells are those unspecialized or undifferentiated cells that have the potential to develop into different types of cells in our body during early life. There are also some partially differentiated stem cells in different tissues in adults which can replenish worn out cells. The most significant quantity of these cells lie within the hemopoietic tissue where new blood cells are constantly produced. In other tissues, cell replacement is via cell division although small amounts of stem cells will allow for replacement of tissue.
Types of Stem Cells
Embryonic stem cells – All cell types of the body are derived from these cells. These stem cells are also capable of dividing and replicating over a long period of time without differentiating into other cell types. Human embryonic stem cells are derived from human embryos and grown in the laboratory. Present research is aiming at stimulating these stem cells to undergo differentiation into specific cell types which can be used in the treatment of various diseases, including Parkinson’s disease, by transplanting these differentiated cells into specific diseased regions of the body.
Although human embryonic stem cells culture carries various ethical issues, as it requires the harnessing of tissues from a dead or aborted fetus. Also, the voluntary fetal tissue available for research purposes is unable to suffice the therapeutic and research associated needs of the large number of Parkinson’s patients worldwide.
Read more on Stem cells clinics for Parkinson’s disease patients
Non-embryonic stem cells (adult or somatic stem cells) – these are undifferentiated or partially differentiated cells present amongst differentiated cells in a tissue or organ. These stem cells undergo differentiation into cells similar to the neighboring ones only and are mainly involved with tissue repair.
Induced pluripotent stem cells (iPSCs) – specialized adult cells may be reprogrammed genetically (through introduction of embryonic genes) to behave like embryonic stem cells. These are known as induced pluripotent stem cells, which have the potential of differentiating into and generating specific cells and tissues. They can be generated from different origins including liver cells, stomach cells, neural stem cells, and peripheral blood cells. The most striking feature of induced pluripotent stem cells lies in the fact they are ridden of the ethical stigma carried by human embryonic stem cells.
Also, the induced pluripotent stem cells or iPSCs can be induced and differentiated into human dopamine producing neurons, and hence can be successfully used as a human disease research model. Moreover, they can be used as an in-vivo model for the purpose of drug screening and for carrying out studies for various stem cell replacement therapies. It provides an excellent opportunity to enhance the understanding of Parkinson’s disease as the studies are carried out on live Dopaminergic neurons on human models, instead of cellular or animal models.
Induced Pluripotent Stem Cell Therapy in Parkinson’s Disease
An insufficient number of of dopamine-producing neurons (nerve cells) due to cell degeneration causes the symptoms of Parkinson’s disease. Replacing these cells with other dopaminergic neurons is the basis of iPSC therapy in PD. Differentiation of the iPSCs into specific cells and generation of new cells may cause improvement in PD.
IPSCs produce a renewable source of replacement cells which may be effective in treating various disorders, including PD. By using the patient’s own adult stem cells to produce these iPSCs, chances of rejection by the immune system are greatly reduced. Cells generated from human iPSCs may be used to test the efficacy and safety of new drugs. The ideal neuron cells generated must be the functional units with no oncological risks. Development of the disease process may be studied and better understood, thus helping in finding new ways of controlling and preventing the disease.
The clinical trial approach should include careful screening of appropriate candidates under standard safety protocols. The candidates selected are usually the genetic carriers of Parkinson’s disease and are evaluated and monitored by the functional neuroimaging of both dopaminergic agonists and non dopaminergic agonists systems.
Challenges of iPSC Therapy
Scientists face the challenge of controlling the development of iPSCs into different cells in the body. Ethical issues also need to be addressed although iPSC therapy is less contentious since embryonic stem cells from discarded fertilized embryos are not used.
Before iPSCs can be used successfully in therapy for Parkinson’s disease or any other disorder, certain points have to be kept in mind, which are very essential if transplantation and grafting are to be effective during treatment. The iPSCs should :
- It should pose no risk of tumorigenesis or cancerous transformation in the host patient. The oncological risk is an important issue to be addressed by the iPSC researchers, as some of the genes involved in the generation of iPSCs are known to cause tumors.
- Survive in the recipient after transplant.
- Integrate into the surrounding tissue after transplant.
- Function properly for the duration of the patient’s life.
- Cause no harm to the recipient.
- Viruses used to introduce the reprogramming factors into adult cells in animals may have other health consequences and the safety in humans needs to be considered.