Intracranial delivery of proteins and peptides as a therapy for neurodegenerative diseases.

Parkinson's disease is characterized by a progressive degeneration of the substantia nigra pars compacta dopamine neurons that innervate the striatum. Unlike current treatments for PD, GDNF administration could potentially slow or halt the continued degeneration of nigral dopaminergic neurons. GDNF does not cross the blood-brain barrier and needs to be administered directly into the brain. Due to the progressive nature of PD, sustained delivery of trophic factors may be necessary for optimal, long-term neuronal effects. Novel methods for sustained delivery of GDNF into the nigrostriatal pathway are currently being studied in non-human primates, including computer-controlled infusion pumps. Using this approach, we have demonstrated that chronic infusions of nominally 7.5 or 22.5 microg/day GDNF into the lateral ventricle, the putamen or the substantia nigra, using programmable pumps, promotes restoration of the nigrostriatal dopaminergic system and significantly improves motor functions in MPTP-lesioned rhesus monkeys with neural deficits modeling the terminal stages of PD and in aged rhesus monkeys modeling the early stages of PD. Based on the promising studies of the chronic effects of GDNF in non-human primate models of PD, a study was recently conducted in England on five advanced PD patients. Chronic GDNF infusion into the dorsal putamen, via programmable pumps, resulted in improved motor function in all patients and limited side effects were observed. However, while the data from this intraparenchymal clinical trial in humans look encouraging, extensive blinded efficacy trials will need to be conducted before it can be determined if chronic treatment with GDNF or other trophic molecules will prove useful in treating patients with PD.