Neurotrophic factors in the therapy of Parkinson's disease.

Neurotrophic factors (NTs) are secreted proteins that regulate survival and differentiation of nerve cells. Nerve growth factor (NGF), the first discovered NT, together with brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT3 ) and neurotrophin-4/5 (NT-4/5), form the classical family of NTs. However, many other growth factors, which are effective also outside the nervous system, such as glial cell line-derived neurotrophic factor (GDNF), insulin-like growth factor (IGF I), ciliary neurotrophic factor (CNTF), basic fibroblast growth factor (bFGF) and members of the tumor growth factorb e t a (TGF-beta) superfamily, fulfill the functional definition of “neurotrophic factors”. NTs were originally identified as target-derived compounds regulating neuronal survival, growth and diff e rentiation during development. In the adult brain, N Ts are necessary to maintain neuronal function and phenotype. Increased expression of NTs is a common response to brain damage (1) that may have a neuroprotective role given the ability of N Ts to protect neurons against free radical damage, excitotoxicity and apoptosis (2). Idiopathic Parkinson’s disease (PD) is a neurodegenerative disorder pathologically de-