Researchers are eyeing a widely available probiotic as a possible treatment for dry eye disease, a common condition where a lack of moisture causes vision problems and leaves the eye vulnerable to injury.
In the results of a study presented at the American Society for Microbiology’s Microbe conference in Houston, researchers from Baylor College of Medicine showed that the commercialized oral probiotic Limosilactobacillus reuteri improved eye health in mouse models of dry eye disease.
“The ‘friendly’ bacteria that live in the human gastrointestinal tract have been linked to health and protection against disease in many parts of the body, including the gut, brain and lung,” presenting author Laura Schaefer, Ph.D., said in a press release. “It’s therefore not surprising that the gut microbiome also has effects on our eyes.”
Strains of L. reuteri are renowned for their anti-inflammatory properties and ability to police “bad” bacteria in the gut by producing antimicrobial molecules. They naturally colonize the GI tract, urinary tract, skin and breast milk. The strain studied by Schaefer’s team, DSM 17938, is well-documented as having a range of potential benefits for gut, liver and immune health. In fact, it's found in probiotic supplements from dozens of brands.
While L. reuteri’s efficacy against GI tract troubles is well-established, much less is known about how it or any other probiotic impacts the eye. The little evidence that existed prior to the study by Schaefer’s team did hint at benefits, though: Researchers from Seoul National University College of Medicine in South Korea showed in 2017 that a probiotic combo including L. reuteri reduced inflammatory markers in a rat model of uveitis, or middle eye inflammation.
Schaefer’s team, too, had some initial findings that linked the gut and the eye. As part of an earlier study, they used antibiotics to clear out the gut bacteria of mice, then re-colonized them with bacteria from either healthy humans or people who had developed severe dry eyes as a symptom of the autoimmune condition Sjögren's syndrome. Under conditions designed to induce dry eyes—an experimental technique known as “desiccating stress”—the mice with gut bacteria from Sjögren's patients developed worse dry eyes than the ones with bacteria from healthy people.
Given these findings, the researchers wondered whether introducing “good” bacteria could reverse the symptoms. After clearing out the microbes in the mice’s guts, the scientists exposed the animals to desiccating stress for five days. Over the same period, they gave them an oral solution containing L. reuteri DSM 17938 or a control solution with saline.
At the end of the study, the researchers found that the corneas of the mice who had received the probiotic bacteria were in better condition than those who received the control solution. Their eyes had also experienced a 26% increase in goblet cells, which secrete a component of tears called mucin. This suggested that the healthy bacteria had protected their eyes.
The demand for effective treatments for dry eye disease is growing. While the vast majority of the 16.4 million people in the U.S. with the condition use over-the-counter artificial tears to keep symptoms at bay, patients are increasingly turning to prescription drugs. Leading the pack are AbbVie’s Restasis—which now faces competition from Viatris’ generic—and Novartis’ Xiidra.