A drug which has been used for decades to treat high blood pressure may turn out to be a key treatment for multiple sclerosis, say British researchers.
Amiloride was found to reduce degeneration of nerve tissue in mice and the team at Oxford University are now planning a trial in MS patients.
It works by blocking the build up of high levels of calcium in nerve cells, which can lead to nerve damage.
There are about 85,000 people with MS in the UK.
The condition is caused by a defect in the body's immune system, which turns in on itself, and attacks the fatty myelin sheath which coats the nerves.
This damage to nerve cells is caused in part by a build up of calcium.
Professor Lars Fugger and colleagues investigated the effects of a specific channel, ASIC1, which controls the entry of calcium molecules into cells.
In mice with a condition that mimics MS, they found that when the channel remains open, calcium can flood into nerve cells in higher than normal proportions and cause damage.
Inflammation like that found in MS leads to acidic conditions, which would lead to the channel opening and too much calcium accumulating in nerve cells, Professor Fugger said.
Amiloride, a drug used for many years to treat high blood pressure and heart failure, was found to stop calcium entering through the ASIC1 channel and prevent degeneration of nerve tissue in mice, the journal Nature Medicine reported.
Professor Fugger from the Medical Research Council Human Immunology Unit said the fact the drug was already licensed would speed up the process of getting the treatment to patients should it be prove effective.
He is currently working out what the appropriate dose would be in humans and plans to start a clinical trial next year.
"To develop a drug from scratch takes 10-15 years and a billion dollars and some of them are abruptly halted by unexpected side effects," he said.
"It was known that calcium is not good for nerve cells but it's not been appreciated how simple it is to block it."
Dr Laura Bell, from the MS Society, said: "Protection of nerve fibres is a promising and vital area of research and this is why the MS Society is currently spending half a million pounds on a clinical trial investigating this type of nerve protection in people with MS.
"The early stage results from Oxford are interesting and we look forward to seeing the findings of future studies."
The research is published in Nature Medicine. ( BBC )