Parkinson's disease (PD) is a neurodegenerative brain disorder that impairs the ability to perform functions such as grooming, dressing, cooking, and other activities of daily living. PD affected between 4.1 and 4.6 million people worldwide in 2005, and it is projected that up to 9.3 million people will be affected by 2030. Although current pharmacological therapies provide beneficial effects on motor symptoms of the disease (tremor, rigidity, and bradykinesia), intolerable disability eventually develops in most patients. A disease-modifying therapy that slows disease progression is a major unmet medical need in PD. Numerous agents have neuroprotective effects in pre-clinical laboratory models, but none have been shown to have indisputable disease-modifying effects in clinical trials for patients with PD.