Synbiotics regulate gut microbiota-derived indole-3-acetic acid production to modulate the intestinal barrier and improve antibiotic-associated diarrhea

Given the global risks associated with antibiotic overuse, antibiotic-associated diarrhea (AAD) has become a widespread public health concern worldwide. Human milk oligosaccharides (HMOs) and Bifidobacteria are often used to prepare synbiotics to enhance their health effects. However, the synergistic effect of this combination in alleviating AAD remains unclear. In this study, lincomycin was used to establish a mouse model of AAD, and the effects of the 3-fucosyllactose (3-FL) +6'-sialyllactose (6'-SL), as well as the Bifidobacterium bifidum, were evaluated. Further analyses examined the impact of HMOs plus probiotics on the gut microbiota and its associated metabolites. In addition, the roles and underlying mechanisms of specific metabolites in AAD were investigated. The results indicate that HMOs plus probiotics significantly ameliorate diarrheal symptoms in mice with AAD. This effect is reflected by increased body weight, markedly reduced diarrhea scores and fecal water content, significantly elevated aquaporin-3 (AQP3) expression, and substantially decreased levels of the inflammatory mediators tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β). Moreover, the combination of HMOs and probiotics demonstrated superior efficacy compared with either intervention alone. Integrated microbiome-metabolomics analysis revealed that HMOs plus probiotics significantly enriched Lactobacillus, a change that was potentially associated with increased levels of the gut metabolite indole-3-acetic acid (IAA). IAA plays a crucial role in intestinal barrier repair by promoting Muc2 expression and thereby enhancing the intestinal chemical barrier. Concurrently, IAA contributes to the restoration of the mechanical barrier by regulating claudin-1 protein expression. Furthermore, the effects of IAA were significantly attenuated following intervention with aryl hydrocarbon receptor (AhR) inhibitors, indicating that IAA exerts its actions via activation of AhR. In summary, this study suggests that HMOs plus probiotics may alleviate AAD by promoting IAA production via the gut microbiota, thereby activating the IAA/AhR/Muc2/claudin-1 axis. This research provides novel insights into microbiota-based interventions targeting intestinal health.