The i3.1 probiotic blend—comprised of Pedioccoccus acidilactici, Lactiplantibacillus plantarum and Lactiplantibacillus plantarum—reinforced barrier function in an in vitro trial, restoring it to levels comparable to that of the healthy controls after just three hours.
Writing in Gut Microbes, the researchers from AB-Biotics and the Gastroenterology Unit of University of Bologna, Italy, said the results suggest that the combination may aid in the recovery of permeability alterations induced by IBS mediators.
“These findings highlight the potential of [a] nutritional approach such as probiotics to favorably modulate the intestinal epithelial barrier and improve IBS symptoms and more in general consumer’s health,” they wrote.
Probiotics and leaky gut: what does the evidence say?
Increased intestinal permeability, or leaky gut, occurs when the gut lining becomes more permeable, allowing potentially harmful bacteria to enter the bloodstream.
Research suggests that this condition is more common in patients with IBS and that this may be due to alterations in the localization and expression of tight junction proteins, which are crucial for maintaining the integrity of the gut lining.
Since probiotics have been shown to promote the production of tight junction proteins, this has emerged as a potential intervention for maintaining a healthy gut barrier.
However, while previous research has shown that two strains of Lactiplantibacillus plantarum and one strain of Pediococcus acidilactici induced an improvement in IBS-related quality of life, until now, the underlying molecular mechanisms remained unclear.
Study details
To conduct their study, the researchers took mucosal biopsies from 21 non-constipated IBS patients and seven healthy controls. Each of the participants had either IBS with predominant diarrhea (IBS-D) or IBS with mixed bowel habits (IBS-M) according to the ROME IV criteria.
“A recent review of several studies found permeability seems to be more of an issue in IBS-D than IBS-C,” Jordi Espadaler, director of innovation at AB-Biotics, told NutraIngredients. “Therefore, it made more sense to start these mechanistic studies in IBS-D patients, while IBS-M were also included because they represent a mix of symptoms of IBS-D and IBS-C.”
The cells were then incubated with the i3.1 probiotic blend. Using a lab-grown layer of human intestinal cells called Caco-2 cells, which form a barrier similar to the intestinal lining, the researchers measured how easily substances could pass through this cell layer.
The researchers found that supernatants (the liquid obtained after incubating the biopsies) of patients with IBS induced a significant increase of paracellular permeability compared to the healthy controls, indicating that increased intestinal permeability is a feature of IBS.
Comparatively, when the cells were incubated with the probiotic blend, both doses reduced this leakiness, suggesting i3.1 may aid in maintaining a healthy gut barrier.
Barbaro et al. also found that the cells incubated with the probiotic blend showed increased expression of genes associated with the actin cytoskeleton (β-actin) —a crucial structure that maintains the shape and function of intestinal cells—and gut detoxification via CYP1A1, an essential enzyme that breaks down toxins and harmful compounds.
Metabolic analysis also revealed that all three strains used in the probiotic blend produced high levels of indole-3-lactic acid, a molecule also known to activate CYP1A1 expression.
Together, these findings suggest that the i3.1 probiotic blend may be able to ‘reprogram’ gene expression in the intestinal cells of IBS patients in order to restore intestinal permeability.
The gut-brain axis
The researchers reported that the study substantiates existing evidence for the efficacy of the probiotic blend and clarifies the mechanism by which i3.1 could benefit IBS patients, particularly through the gut-brain axis.
“Previous clinical trials have shown that i3.1 can improve mood, productivity and quality of life in patients with stress-related diarrhea and IBS,” said Espadaler. “Therefore, we know i3.1 has an effect on the gut-brain axis. Of course, the size of that effect will depend on the specific conditions and therefore additional targeted studies are necessary.”
The study authors said the results also suggest a role for i3.1 in indole production, opening up future research avenues to characterize this relationship in depth.
“We are expanding our research with clinical trials and exploring new accessible product formats, while we also keep unravelling the mechanisms of action through which i3.1 supports gut integrity and overall wellbeing,” Espadaler said.
Source: Gut Microbes. doi: 10.1080/19490976.2025.2452235. “Lactiplantibacillus plantarum (CECT7484 and CECT7485) and Pedioccoccus acidilactici (CECT7483) enhance actin cytoskeleton and CYP1A1 expression restoring epithelial permeability alterations induced by irritable bowel syndrome mediators.” Authors: M. Barbaroa, et al.