Clinical neuroprotection in Parkinson's disease — Still waiting for the breakthrough

Recent research in the pharmacotherapy of Parkinson's disease (PD) has been able to provide numerous agents for the symptomatic control of motor impairments, but has failed to identify substances capable to slow down or even halt the progression of the disease. In the absence of disease-modifying therapies, affected patients develop marked disability within some years after the onset of motor symptoms, which can be alleviated but eventually not prevented with currently available medical and surgical therapies. Despite promising results from preclinical studies, outcomes of clinical neuroprotection trials have been repeatedly disappointing, which calls for a review of our approach to this topic. This article attempts to explain the need for neuroprotective therapies in PD, discusses results and limitations of previous clinical trials and provides some food for thought for the future research of neuroprotection in PD. Previous experiences from neuroprotection studies may have been discouraging, but also teach us some important lessons for the next generation of preclinical and clinical trials. Firstly, our currently used animal models for PD need to be refined in order to more reliably predict the efficacy of putative neuroprotective agents in subsequent clinical studies. Furthermore, changes in the methodology and design of future neuroprotection trials are required in order to exclude an impact of confounding symptomatic effects on observations. Finally, coordination and concentration of future research on the most promising agents will be necessary in order to accelerate the search for neuroprotective therapies in PD. Just as the pathogenesis of the disease is manifold, it may be this multilateral approach that eventually leads us to a breakthrough in finding neuroprotective agents for PD, if they exist.