US researchers have discovered a group of plant extracts that may have benefits in early treatment of stroke.
Stroke can cause paralysis
Cardiac glycosides, compounds which include heart drug digoxin, were found to protect rat brain tissue against the lack of blood which occurs in stroke.
The study published in the National Academy of Sciences may help scientists develop new treatments.
Many drugs thought to have protective effects after stroke have been tested but as yet none have been effective.
The researchers from Duke University Medical Center in North Carolina screened a large number of small compounds for neuroprotective activity by testing them on slices of rat brain deprived of oxygen and glucose.
Using the test - which is designed to mimic stroke in the brain - a compound called neriifolin which comes from the yellow oleander was found to be significantly protective against neurons in the brain that otherwise would have died.
Neriifolin appeared to show neuroprotective properties even if given several hours after the brain tissue was starved of oxygen and glucose.
Although they hadn't initially been identified in the screening test, the researchers hypothesised that several other compounds related to neriifolin would also protect brain tissue against ischaemic injury.
They tested digoxin and digitoxin - which come from the foxglove and have both been used for several decades in the treatment of congestive heart failure and arrhythmia - and ouabain in a mouse model.
Although not as potent as neriifolin, all of the plant extracts had a neuroprotective effect.
The researchers said as cardiac glycosides are already in use, it could speed up the process towards clinical trials.
Dr Donald Lo, Director of the Center for Drug Discovery, at Duke University, said: "It's always a helpful stroke of luck when you find something that already has clinical usage because we know many things about dosage and side-effects."
He added that finding the activity of the compounds in the rat model was the very first step.
"The aim of this study was to survey as many different drug targets as possible because the last 50 to 100 that have been tested have not fared well in clinical trials."
He added: "It was surprising because this is a class that is generally toxic."
A spokesperson for the Stroke Association said: "The researchers are correct in identifying the failure of many compounds that have shown the potential to protect neurons between the stage of animal model testing and clinical trials, and it is welcome to have other compounds to investigate.
"The advantage of this group of compounds is that they have been in clinical use for other conditions over many years, and we therefore know a great deal about the possible doses and side effects.
"The negative side is that these drugs have effects on the heart that will certainly limit the doses that could be given, and it has been the case with other neuroprotectant drugs in the past that cardiac side effects have meant that insufficient amounts of drug to protect the brain cold be given safely.
"[This model] might be useful as a means of identifying candidate drugs in the future.
"However, the difficulty usually arises not in identification of possible neuroprotectant molecules but in their successful translation into clinical trials, and our track record speaks for itself.
"Over the past 15 years there have been dozens of molecules that have gone as far as clinical trials involving tens of thousands of patients after showing great promise in animal studies, yet we still have no drug of this class that is effective."