Stem cells may aid Parkinson's treatment
There is much excitement in the medical profession about how stem-cell-based therapies could someday affect how Parkinson's disease is treated.
Parkinson's disease is a neurological disorder caused by the dying off of a certain type of brain cells. These cells are located in the midbrain of the brainstem in an area called the substantia nigra.
They are responsible for making a neurotransmitter called dopamine. Without the effect of dopamine, a patient can develop problems with initiating and coordinating movement, along with other symptoms characteristic of Parkinson's disease.
Current drug treatments of Parkinson's disease work by increasing dopamine levels or activity at dopamine receptors. But Parkinson's experts are hopeful that stem-cell therapies will soon provide new treatment options or even a cure for the disease by reproducing the lost dopamine-making cells.
The four cardinal symptoms of Parkinson's disease are tremor (shaking of the hand or other parts of the body), bradykinesia (slowing of movement), postural instability (problems with balance) and rigidity (muscle stiffness).
Other characteristic symptoms include loss of facial expression, reduction in volume of the voice (called hypophonia), small handwriting (called micrographia), drooling, trouble swallowing, difficulty initiating movement (called freezing), stooped posture and a shuffling gait.
There are also "non-motor" symptoms, which refer to problems not related to movement, including sleep disturbances, fatigue and pain.
As the disease progresses, worsening mobility occurs, and death may result from pneumonia from aspiration or pulmonary embolism due to immobility. Falls are also common as the disease progresses, which can lead to injury. However, patients can live for decades after diagnosis, meaning the condition may not necessarily lead to a reduction in life span.
The gold-standard pharmacologic treatment for Parkinson's disease is a medication called Sinemet, which has been around since the late 1960s. It contains levodopa, which is the precursor of dopamine.
Because levodopa is converted to dopamine in the central nervous system, Parkinson's symptoms improve with this medication because it is replacing exactly what is missing in the disorder.
In fact, demonstrating a clear beneficial response from Sinemet has been the traditional way to confirm the diagnosis of Parkinson's disease.
However, the effect of pharmacologic treatment tends to diminish as the disease progresses, and patients also become more sensitive to treatment-related side effects over time.
Consequently, complex, multidrug regimens are often required to maintain adequate symptom control with good tolerability in advanced stages of the disease.
The excitement surrounding stem-cell-based therapies is that the stem cells can be induced to grow into a particular type of mature cell, including the dopamine-producing cells that are lost in Parkinson's disease. Stem cells can be embryonic or they can be induced from adult cells.
The efficacy of stem-cell treatments has been variable in animal models, and there have been safety concerns, including the risk of tumor development and rejection of transplanted cells.
Future research will be required to determine the effectiveness and safety of these various treatments, but there is hope that the way Parkinson's disease and possibly other neurodegenerative disorders are treated may be on the verge of dramatic change.
Dr. Mark Saleh is a neurologist at the Sutter Pacific Medical Foundation and the director of General Neuroconsultative and Referral Services at California Pacific Medical Center.