An experimental treatment that delivers a drug directly to the brain has shown promise for slowing, stopping, or even reversing Parkinson's disease, say researchers.

The study, by a team led by University of Bristol researchers, in a clinical trial investigated whether the treatment called Glial Cell Line Derived Neurotrophic Factor (GDNF) -- a natural protein, found in the brain -- can regenerate dying dopamine brain cells in patients with Parkinson's and reverse their condition, something no existing treatment can do.

The results potentially demonstrated that the new treatment was starting to reawaken and restore damaged brain cells and that repeated brain infusion is clinically feasible and tolerable, according in the Journal of Parkinson's Disease.  The study "represents some of the most compelling evidence yet that we may have a means to possibly reawaken and restore the dopamine brain cells that are gradually destroyed in Parkinson's", said principal investigator Alan L. Whone, from the University of Bristol in the UK.

After an initial safety study of six people, 35 individuals were enrolled in the nine-month double blind trial, in which half were randomly assigned to receive monthly infusions of GDNF and the other half placebo infusions. All participants underwent robot-assisted surgery to have four tubes placed into their brains, which allowed GDNF or placebo to be infused directly to the affected areas with pinpoint accuracy, via a port in their head.

After implantation the team administered, more than 1,000 brain infusions, once every four weeks. After nine months, there was no change in the PET scans of those who received placebo. On the other hand, the group who received GDNF showed an improvement of 100 per cent in a key area of the brain affected in the condition.

"This trial has shown that we can safely and repeatedly infuse drugs directly into patients' brains over months or years," said Steven Gill, lead neurosurgeon at North Bristol NHS Trust, Bristol, UK. "This is a significant breakthrough in our ability to treat neurological conditions, such as Parkinson's, because most drugs that might work cannot cross from the blood stream into the brain due to a natural protective barrier."