Neurotrophic Factors in Parkinson's Disease: What Have we Learned from Pre-Clinical and Clinical Studies?

Background: Parkinson´s Disease (PD) is a chronic, progressive condition, being the second most common neurodegenerative disorder worldwide. The classical features include: bradykinesia, resting tremor, rigidity and festination. These neurological alterations are probably due to the death of dopaminergic neurons in the Substantia Nigra pars compacta and consequent reduction of dopamine input into the striatum. The decrease of dopamine levels may also be involved in the emergence of non-motor symptoms, including cognitive impairment, anxiety and depression symptoms. Neurotrophic Factors (NF) are proteins that modulate neuronal function, development, and survival. It has been reported that NF might exert a protective role in PD. Objective: We aim to discuss the emerging evidence from pre-clinical and clinical studies regarding the role of NF in PD as well as their potential as promising therapeutic strategies. Methods: We carried out an extensive literature search in PubMed central. Results: Pre-clinical studies using NF to treat PD are divergent probably due to several methodological differences, thus precluding any conclusion. Clinical studies findings obtained with the administration of NF in patients with PD were even more disappointed. On the other hand, pre-clinical and clinical studies generally support that physical activity is a low-cost, non-pharmacologic strategy with good results to treat PD. Conclusion: The use of NF as a treatment for PD is still a promise not incorporated in clinical practice. Methods to deliver NFs, doses and compounds administered, side effects, population characteristics and duration of disease may probably contribute to the unsuccessful results.