Parkinson’s Disease occurs as a result of the gradual loss of a specific type of nerve cell located in an area of the brain called the substantia nigra. These nerve cells produce a natural chemical called dopamine and are known as dopaminergic neurons. The reduction of dopamine in the brain, caused by the loss of dopaminergic neurons, results in difficulty in moving freely, holding a posture, talking and writing1 – classic Parkinson’s symptoms. There is much hope that stem cell treatment may provide the so far elusive therapy that either halts the progress of the disease or provides a cure. Current therapies treat the symptoms but their effects are not always long lasting and they may also bring with them unwanted side effects. Success with stem cell treatment would represent a significant advance in treatment.
The aim of stem cell research in Parkinson’s is to understand the mechanisms behind a single cell developing into an organism and how healthy cells might be used to replace damaged dopaminergic neurons. With this knowledge it may be possible to replace the damaged cells by introducing similar but healthy neurons into the brain which have been derived from laboratory-grown stem cells and induced to become dopamine-producing cells. Healthy dopamine-producing cells derived from stem cells could also be useful to researchers in testing new treatments.
Researchers are particularly interested in embryonic stem cells as they have the potential to develop into all types of cells in the body, including the brain. One of the main advantages in using a stem cell population for treatments, as compared with foetal cells, is the renewable and expandable source. This has immediate impact in better characterisation of the cell source and standardisation of the treatment, both of which are currently hurdles in getting a successful outcome in cell transplantation efforts. However, they do carry the risk of uncontrolled growth which could lead to other illnesses including tumours. More research needs to be conducted in order to understand the way these cells work to ensure that replication can be controlled and a safe treatment developed.
There is also considerable interest in foetal stem cells, in particular foetal brain cells. Immature cells from the developing brain differentiate well into dopamine neurons but do not divide as extensively and have not been possible to expand in laboratory conditions. Cell lines generated from foetal brain and sustained in the laboratory no longer retain their ability to make dopamine neurons. It is as if the precursors that have this ability are lost in the process.
It is worth pointing out that neural brain implants using foetal brain material differ from stem cell research – they are both types of neural replacement therapy but the techniques and the material used are different. Foetal brain implants use developing cells that have been extracted from aborted foetuses and which are already programmed to become dopamine cells, unlike stem cells which are as yet unspecialised. It is hoped that such implants will start producing enough dopamine in the brain to correct the symptoms of a dopamine deficiency. But, so far, results have been mixed, partly because it is difficult to control the amount of dopamine produced and partly because it is impossible to ensure that cells used for implantation are standardised. Scientists hope that stem cells will make it possible to produce large amounts of dopamine-producing cells that can, importantly, be both controlled in terms of dopamine production and also standardised to ensure reliable outcomes.
At present rather less attention is focussed on adult stem cells since these do not divide as quickly and are found in smaller numbers in limited areas of the body. However, some research is being conducted to see if adult brain stem cells can be induced to form nerve cells. If this can be achieved it may be a potential future treatment for Parkinson’s disease.
