New Treatment Research: Neurotrophic Factor (GDNF) Gene Therapy
GDNF works so well because it is a biological molecule designed to enable neuron survival. As all of the neurotrophic factors, GDNF is responsible for the growth and survival of neurons in the brain. In fact, that is what "neurotrophic" means; it is derived from the Greek "neuro" meaning nerve, and "troph", meaning nourish. GDNF is a natural substance used during development and to maintain adult neurons. Neurotrophic factors such as GDNF offer exciting possibilities to the field of nerve regrowth; they have actually been able to cause damaged neurons to regrow their processes in test tubes. The research on this kind of chemical for use in Parkinson's disease has a potential for substantially reducing the suffering of patients.
Unfortunately, GDNF can cause problems in cells when administered alone, as a pure drug. However, research has found GDNF to be most effective when it is administered directly to the substantia nigra in the brain (the dopamine producing part of the brain) inside of a virus. More specifically, a viral vector was created for GDNF (basically, GDNF-synthesizing genetic material was placed in a virus), injected directly into the brain, and the virus infects cells in the substantia nigra and continuously produces GDNF growth factor. This is why it is considered gene therapy; the actual DNA of the cells in the brain changes.
The virus used in many recent studies is an adeno-virus, which is an adenosine antagonist. In the research, rats are injected with both the GDNF-producing virus and with fluorogold (for retrograde labeling of metabolic function in the brain), and then allowed to recover. Some cells are then tested in order to make sure the infection and production of GDNF has occurred. Seven days later, the rats are given either MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, a street drug that induces Parkinsonian symptoms), or 6-OHDA (striatal 6-hydroxydopamine, which also causes progressively degenerating Parkinson's symptoms). The rats are then killed, and compared to both a group of rats infected with a mutant form of GDNF and to a control group. The human form of GDNF-infected rats turned out to have the most promising results: significantly more dopamine-producing cells were found in the human-GDNF group (many cells were prevented from dying), and the tissue where the human-GDNF adenovirus was injected were still producing the growth factor. In this way, the GDNF factor protects neurons from dying, and may allow Parkinson's patients hope if their symptoms are diagnosed early on in the onset of the disease.
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