Possible role of the gut microbiome in mediating the beneficial effects of the six-herbal formulation STW 5-II on digestive health

STW 5-II is a combination of six herbal extracts with clinically proven efficacy in functional dyspepsia (FD) and irritable bowel syndrome (IBS). STW 5-II contains a wide variety of secondary plant constituents that may interact with the human gut microbiome. In addition to complex carbohydrates, secondary plant metabolites, such as polyphenols, are known to exert prebiotic-like effects.This study aimed to assess the bidirectional interactions between STW 5-II and the human gut microbiome.STW 5-II was incubated with human fecal microbiota in a short-term colonic model. In the samples, the impact of STW 5-II on microbial fermentation capacity (pH, gas production), short chain fatty acid (SCFA) production, and microbial composition (Illumina 16S rRNA gene sequencing) was analyzed. In addition, the biotransformation of STW 5-II constituents by the fecal microbiota was assessed by UHPLCHRMS-based metabolite profiling. Furthermore, Caco-2/THP1 co-culture assay was used to explore the effect on gut barrier integrity and inflammatory markers.Fermentation of STW 5-II by fecal microbiota led to consistent changes in pH and gas production and increased production of SCFAs (acetate, propionate, and butyrate). STW 5-II promoted the enrichment of Bifidobacteriaceae, Lachnospiraceae, Ruminococcaceae, Erysipelotrichaceae, and Eggerthellaceae and suppressed the growth of pathogenic species from the Enterobacteriaceae family. In Caco2/THP1 culture, treatment with STW 5-II-incubated samples resulted in significantly increased transepithelial electrical resistance, indicating enhanced barrier function. Among inflammatory markers, STW 5-II-incubated samples increased LPS-induced secretion of the anti-inflammatory cytokine IL-10, as well as NF-κB activity, and significantly decreased the secretion of the pro-inflammatory chemokine MCP-1. UHPLCHRMS analysis identified 110 constituents of STW 5-II with changed levels during incubation with fecal microbiota: 63 constituents that were metabolized, 22 intermittently increased metabolites, and 25 final metabolites, including compounds with established anti-inflammatory activity, such as 18β-glycyrrhetinic acid.These findings indicate a microbiome-mediated digestive health-promoting effect of STW 5-II via three different routes, namely enhanced microbial SCFA production, microbial production of potentially bioactive metabolites from STW 5-II constituents, and prebiotic-like action by promoting the proliferation/growth of beneficial bacteria.