One of the enduring questions in Parkinson's disease research has been how treatment with levodopa and other dopaminergic drugs affects progression of the disease. Researchers are continuing to try to clarify these effects.
One study has suggested that people with Parkinson's with a low-activity variant of the gene for COMT (which breaks down dopamine) perform worse than others on tests of cognition, and that dopaminergic drugs may worsen cognition in these people, perhaps because the reduced COMT activity causes dopamine to build up to harmful levels in some parts of the brain. In the future, it may become possible to test for such individual gene differences in order to improve treatment of PD.
A variety of new drug treatments are in clinical trials for Parkinson's. These include a drug called GM1 ganglioside that increases dopamine levels in the brain. Researchers are testing whether this drug can reduce symptoms, delay disease progression, or partially restore damaged brain cells in PD patients.
Other studies are testing whether a drug called istradefylline can improve motor function in PD, and whether a drug called ACP-103 that blocks receptors for the neurotransmitter serotonin will lessen the severity of parkinsonian symptoms and levodopa-associated complications in PD patients. Other topics of research include controlled-release formulas of PD drugs and implantable pumps that give a continuous supply of levodopa.
Some researchers are testing potential neuroprotective drugs to see if they can slow the progression of PD. One study, called NET-PD (Neuroexploratory Trials in Parkinson's Disease), is evaluating minocycline, creatine, coenzyme Q10, and GPI-1485 to determine if any of these agents should be considered for further testing. The NET-PD study may evaluate other possible neuroprotective agents in the future.
Drugs found to be successful in the pilot phases may move to large phase III trials involving hundreds of patients. A separate group of researchers is investigating the effects of either 1200 or 2400 milligrams of coenzyme Q10 in 600 patients. Several MAO-B inhibitors, including selegiline, lazabemide, and rasagiline, also are in clinical trials to determine if they have neuroprotective effects in people with Parkinson's.