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Performed Rescue Dopaminergic Neurons in Monkeys
Despite the presence of endogenous neural stem cells, it is recognized that intrinsic “self-repair” activity for the most devastating injuries is inadequate or ineffective. This poor regenerative ability, particularly in the adult central nervous system, may be because of the limited number and restricted location of native neural stem cells, and/or limitations imposed by the surrounding microenvironment, which may not be supportive or instructive for neuronal differentiation.

Stem cells expanded ex vivo in culture, and then implanted into regions needing repair, may overcome those limitations. Whether the environment may also inhibit exogenous stem cells from surviving or differentiating toward replacement cells is a possibility. However, several transplantation experiments have suggested that neurogenic cues are transiently elaborated during degenerative processes (perhaps recapitulating developmental cues), and that exogenous stem cells are able to sense, home in on, and respond appropriately to those. In other words, stem cells appear to respond in vivo to neurogenic signals, not only when they occur during development, even at later stages by certain neurodegenerative processes.

Parkinson's Disease

Parkinson's disease is a chronic disease of the central nervous system (CNS). Parkinson’s disease is a degenerative disorder characterized by a loss of mesencephalon dopamine (DA) neurons. The loss of dopamine can cause many of motor symptoms, including tremor, slowness of movement, muscle stiffness, and impaired balance... Non-motor symptoms can cause constipation, sleep disturbances, dizziness, fatigue, depression and memory problems...

As the disease progresses, situation is getting worse, and death may result from pneumonia or pulmonary embolism due to immobility. However, patients can live many years after diagnosis, which means that the condition may not necessarily cause a reduction in lifetime.

The symptoms of Parkinson's appear when about 80 per cent of dopamine neurons are lost. That usually does not occur until age of 60, although there have been cases reported in young people. Similar to other neurodegenerative disorders, Parkinson's disease usually occurs sporadically; only 10-15% of cases are inherited and they are linked to multiple genes that can be inherited among family members.

Treatment of Parkinson's Disease

Most treatments for Parkinson's disease focus on dopamine replacement therapies. The standard for treatment of Parkinson's disease is a drug called levodopa (dopamine precursor). The effect of pharmacologic treatment tends to reduce as the disease progresses, patients also become more sensitive to treatment, and they are related side effects over time. Side effects and complications of levodopa have fuelled the search for other drugs, which are less effective, but do some benefits. These drugs are dopamine agonists, and drugs that block dopamine metabolism. Other treatments are only neuroprotective in their aim. Up to now, there are still no drugs that can slow disease progression and that is why scientists are devoting considerable efforts towards developing treatment approaches based on gene therapy, and treatment by stem cells.

Stem cell research has the potential to significantly impact the development of disease. Since the Parkinson’s disease is related to loss of dopamine (one specific chemical), stem cell therapy is theoretically possible. One of the primary goals in Parkinson's disease research is to identify a stem cell population that can be grown in appropriate conditions, maintained in the laboratory and differentiated efficiently into dopaminergic neurons. That has motivated scientists to study both embryonic and adult stem cells as an alternative source of dopamine-producing neurons.

Fetal Stem Cells

Studies in animals confirmed that the transplanted neurons could grow and make functional connections which somewhat reduced the severity of symptoms. But, the results were variable, and there are ethical also as practical problems, and this is why fetal tissue is not the best long-term source of renewable cells.

Embryonic Stem Cells

Embryonic stem cells can be readily grown and differentiated into various cell types in the body. Studies in animals using embryonic stem cell transplants are very encouraging, but there are two main challenges that impede the translation of results to clinical trials. The first is risk of developing tumours, and the second is possibility that, after many years, some of the transplanted dopamine neurons may succumb to illness.

Neural Stem Cells

Neural stem cells may be the best way to avoid the problems, which can be caused by using of embryonic stem cells. The regeneration capacity of neural cells is dependent on growth hormones and other signalling molecules that help the cells growth. Therefore, the right combination of growth factors should allow stem cells to be cultivated to a point where they are committed to becoming dopamine neurons which could then implanted in the brain.

Pluripotent Stem Cells

Pluripotent stem cells are important progress for treating neurological disease such as Parkinson's disease. Pluripotent stem cells can be used to create patient-specific cells. Scientists are now making pluripotent stem cells from people with Parkinson’s disease and using them to produce neurons in the laboratory.

New Study

In a new study, researchers obtained derived dopaminergic neurons from bone marrow stem cells in monkeys. The cells were retrieved by a regular bone marrow aspiration and then treated with growth factors. Those stem cells were directed to become dopaminergic neurons. The monkeys were treated first with a chemical to induce Parkinson's disease and then they received a transplant of the new dopaminergic neurons that had been derived from their own bone marrow stem cells. This study demonstrating that monkeys which received the transplant showed significant improvement in motor defects. This study revealed that dopaminergic neurons derived from adult bone marrow stem cells can be safely used to improve motor function in Parkinson's disease in monkeys.

There are needed further researches to understand the basic science and the various strategies for testing stem cells. It is necessary multi-disciplinary approach of scientists in order to determine safe and effective protocol for transplanting stem cells into the brain. If these therapeutic strategies are successful, it will be a great improvement in the treatment of Parkinson’s disease.
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