Neuroprotection in idiopathic Parkinson's disease

Neuroprotection may be defined as measures to protect neurons from degenerative processes by use of medication, to stop or prolong cell death and to positively interfere with the underlying cell death mechanism(s) in Parkinson's disease. So far, the question whether neuroprotection exists in parkinsonian treatment was difficult to answer because we had no objective method to check for dopaminergic cell death. Imaging techniques such as beta-CIT-SPECT or F-Dopa-PET are the best methods to approach this goal. This paper critically reviews the two most recently published studies on the possible neuroprotective effect of the dopamine agonists pramipexole and ropinirole. For the first time, these two drugs have shown a significantly smaller decrease in dopamine cell function when compared to levodopa. Nonetheless, there may still be some hesitation to accept the good correlation between imaging techniques and dopamine cell function. For obvious reasons, neither study included a placebo arm, since ethical reasons forbid a period of 2 to 4 years without treatment. Thus, the question, whether these two dopamine agonists are really neuroprotective or whether levodopa increases cell death in Parkinson's disease has to stay open. A rather remarkable finding was that, in both studies, motor function was slightly better in the levodopa arm, which raises the question whether imaging techniques really reflect improvement in cell function in those patients treated with dopamine agonists. We certainly have to continue our search for even better tools to evaluate neuroprotection.