And while that does not prove the drug would work for humans, another study using a second statin drug on a small number of MS patients is showing early positive signs.
"The animal data is quite striking," said the senior author of the mouse study, neurologist Scott S. Zamvil of the University of California-San Francisco. "We didn't have any conflicting data."
Other researchers said the California results, if they can be repeated in humans, could help launch statins into the exceptional class of drugs like aspirin that were developed to treat one type of illness but turn out to offer a range of medical benefits.
They said the drugs' anti-inflammatory effects might also be effective in treating rheumatoid arthritis, juvenile diabetes and other autoimmune diseases in which the body mistakenly turns its biochemical guns on healthy tissue. Other trials suggest statins might protect against Alzheimer's, too.
But scientists urged physicians and their patients not to rush to use statins to treat MS until the mice study finding is safely evaluated in humans, which could take several years.
"Anyone who looks at an animal model as a suggestion for a drug's use in humans is mistaken," said Stephen Reingold, vice president for research at the National Multiple Sclerosis Society.
Currently, the small clinical trial is evaluating simvastatin - sold as Zocor - on 32 MS patients in three states. Those results could be published next spring, researchers said.
"There is accumulating data that would strongly suggest that statins should have a positive effect," said neurologist William R. Tyor of the Medical University of South Carolina in Charleston who is coordinating part of the human trial.
"There may be unforeseen problems with administering statins to patients with MS, although admittedly this is unlikely," he said.
MS is a degenerative disease of the central nervous system. High levels of one of the body's immune chemicals - gamma interferon - wrongly activate T-helper cells to mount an inflammatory attack on the myelin sheath that insulates nerve fibers.
Accumulating scar tissue slows the transmission of nerve impulses and interrupts cell communication, leading to episodes of paralysis, tremors and blurry vision.
The California study published in the current issue of the journal Nature was limited to high doses of atorvastatin, which is sold under the brand-name Lipitor.
At UCSF and Stanford University, mice were bred to develop experimental autoimmune encephalomyelitis, or EAE, which mimics MS in lab animals.
The mice were given doses of atorvastatin equal to 80 milligrams, the highest dosage approved for humans. Heart patients typically receive lower doses to reduce cholesterol.
Among mice experiencing their first MS-like attack, Zamvil said high doses prevented the animals from developing permanent symptoms.
Among animals that were suffering a relapse, the drug reversed emerging paralysis and restored mobility.
Zamvil said statin therapy also reduced paralysis among a third group of animals that had developed chronic symptoms associated with late-stage MS.
He said all of the mice treated with atorvastatin suffered less brain and spinal damage than expected.
Zamvil said the drug appeared to reprogram the immune cells that attack myelin so they instead would produce anti-inflammatory agents and protect the nerve coatings.
Current MS therapies include regular injections of synthetic beta interferon after an MS attack to counterbalance the gamma interferon overload.
Beta interferon carries strong side effects and fails to work about half the time. In contrast, statins are oral medications with few side effects - at least at lower doses.
Federal regulators are considering Zamvil's proposal for a nationwide human clinical trial in 2003.
In October, MS researchers in Germany reported that a third statin - lovastatin - reduced autoimmune activity in blood samples, especially when combined with beta interferon.
Hartmut Wekerle of the Max Planck Institute of Neurobiology said statins are an "attractive candidate" for MS therapies, but more experiments must determine which statin might work best.
MS affects about 1 out of 1,000 people. Women are affected more commonly than men. Attacks typically begin when patients are in their 30s.
By Joseph B. Verrengia