A PRELIMINARY trial in which a nerve growth factor is being delivered directly to the brains of five people with Parkinson鈥檚 has produced very promising results. But doctors are being cautious, pointing out that other experimental treatments have produced dramatic results early on, only for hopes to be dashed.
Indeed, a previous trial of the same growth factor, called glial cell line-derived neurotrophic factor (GDNF), ended in failure. However, in that trial it was injected into the cerebrospinal fluid once a month. 鈥淏asically, it was washing all over the place,鈥� says Peter Heywood at Britain鈥檚 Frenchay Hospital in Bristol. The patients did not improve and suffered unpleasant side effects such as nausea and vomiting.
Heywood thinks this was because not enough of the drug was getting to the striatum, the brain region affected by Parkinson鈥檚. Instead, his team implanted pumps that continuously deliver a tiny amount of GDNF to the striatum of five patients. The pump is placed in the abdomen, with a catheter linking it to the brain. After a year of treatment, the patients have improved by 39 per cent on a standard scale of symptoms, with no significant side effects (Nature Medicine, DOI: 10.1038/nm850).
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The researchers think that GDNF may prevent the progressive death of dopamine-producing cells in the brain that causes Parkinson鈥檚, and perhaps even prompt some regrowth. PET scans of the patients鈥� brains indicated a 28 per cent increase in dopamine storage, a sign of improvement.
But the trial is tiny and there is no control group. 鈥淭here is a vast opportunity for a placebo effect,鈥� Heywood admits. And even if bigger trials are successful, the researchers don鈥檛 envisage implanting pumps into millions of Parkinson鈥檚 patients. Instead, they want to engineer cells that secrete GDNF. 鈥淭hey will act as minipumps,鈥� says team member Clive Svendson of the University of Wisconsin, Madison.