A hormone released during pregnancy could help reverse damage in the cortex of the brain caused by multiple sclerosis (MS), a recent study led by UCLA has found.

In people with MS, a potentially disabling autoimmune disease, immune cells attack and damage a protective coating called myelin, which surrounds nerves in the brain and spinal cord. 

When myelin is damaged, the nerve cells can no longer communicate with each other, which triggers symptoms of the disease.

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"Atrophy in the cortex, the largest and most complex part of the brain, is associated with permanent disability worsening, including cognition impairment and paralysis," lead author Allan MacKenzie-Graham, an associate professor of neurology at UCLA, told Fox News Digital in an emailed statement.

In the study — published last month in Laboratory Investigation, a peer-reviewed medical journal of pathology — researchers gave a pregnancy hormone called estriol to mice that had a preclinical model of MS. 

The hormone was shown to slow damage, while also generating new myelin in the brains of the mice.

Currently, there are no FDA-approved treatments to repair MS-induced damage in the brain’s cortex — only treatments to decrease inflammation and slow the disease.

Many groups have been trying for over a decade to achieve brain repair, but the results have been discouraging, said MacKenzie-Graham.

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"We were surprised (and very happy) that we were able to do it," he also said.

One possible reason for the successful outcome is that estriol is a natural estrogen produced during pregnancy, the researcher said. 

In a way, the hormone could have simulated the process of myelin creation during brain development in the womb.

"Estriol targets the cells that produce myelin, encouraging them to produce more," he said. "It also inhibits the cells that block new myelin production."

He added, "Since we are using a natural hormone, there are complementary effects on multiple cell types, as opposed to synthetic drugs that target only one cell type."

Dr. Mary Ann Picone, medical director of the MS Center at Holy Name Medical Center in Teaneck, New Jersey, was not involved in the study but said she was "very excited" to see the results.

"We have seen in earlier phase 2 studies the positive effect of estriol on decreasing inflammatory activity within the brain, but this study shows even greater ability of estriol to help in preserving brain volume, which could translate into slowing of disability progression and possibly reversing disability," she told Fox News Digital in an emailed statement. 

Estriol has long been known to have an immunoprotective benefit during pregnancy, particularly in the third trimester, Picone noted.

So she wasn’t surprised to learn that it could help protect brain health. 

The study highlights a successful example of a treatment designed specifically for women, MacKenzie-Graham said, taking into account the biological differences between men and women.

"This accomplishment aligns with the National Institutes of Health (NIH) prioritizing the study of sex as a biological variable in all research grants," he said.

In prior studies, estriol has been used to treat menopausal women who are experiencing cognitive impairment, while testosterone has been used to treat men with MS, "an approach that reduced brain atrophy in a pilot clinical trial," MacKenzie-Graham said.

"A personalized medicine approach, which uses tailored treatments optimized for biologic processes in each sex, holds promise for finding new treatments for neurodegenerative diseases," he said.

The main limitation of the study is that it was conducted in a preclinical model of MS using mice, said MacKenzie-Graham.

"The next step is to test these findings in human clinical trials to determine if estriol treatment can induce remyelination in the brains of people with MS," he told Fox News Digital. 

There is also a need to determine the safety of long-term estriol use in humans, Picone added.

Overall, the researchers believe this research brings hope for better treatments for multiple sclerosis.

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"The discovery of estriol's ability to induce repair in the cortex is an exciting breakthrough," said MacKenzie-Graham. "Patients should remain optimistic about the potential for treatments that can repair myelin damage and improve disabilities."

He also said, "This may be accomplished by considering biological variables, such as sex, in developing tailored treatments."

Additionally, he calls for researchers to further investigate the beneficial effects of estrogens in protecting and repairing the brain in neurodegenerative diseases such as MS and Alzheimer's disease.

"Instead of the standard estrogens that have used for over 30 years in birth control pills and hormone replacement therapy, neuroscientists should investigate unique estrogens that can induce brain repair, particularly those that recapitulate the effect of pregnancy on brain development," he added.

Nearly one million people are currently living with MS in the U.S., according to the National Multiple Sclerosis Society, a nonprofit headquartered in New York.