N-Acetylglucosamine and Immunoglobulin Strengthen Gut Barrier Integrity via Complementary Microbiome Modulation

<b>Background</b>: Gut barrier dysfunction and altered gut microbial metabolism are emerging signatures of chronic gut disorders. Considering growing interest in combining structurally and mechanistically distinct bioactives, we investigated the individual and combined effects of serum-derived bovine immunoglobulin (SBI) and <i>N</i>-acetylglucosamine (NAG) on the gut microbiome and barrier integrity. <b>Methods</b>: The validated ex vivo SIFR^® (Systemic Intestinal Fermentation Research) technology, using microbiota from healthy adults (<i>n</i> = 6), was combined with a co-culture of epithelial/immune (Caco-2/THP-1) cells. <b>Results</b>: While SBI and NAG already significantly improved gut barrier integrity (TEER, transepithelial electrical resistance, +21% and +29%, respectively), the strongest effect was observed for SBI_NAG (+36%). This potent combined effect related to the observation that SBI and NAG each induced distinct, complementary shifts in microbial composition and metabolite output. SBI most selectively increased propionate (~Bacteroidota families) and health-associated indole derivatives (e.g., indole-3-propionic acid), while NAG most specifically boosted acetate and butyrate (~<i>Bifidobacteriaceae</i>, <i>Ruminococcaceae</i>, and <i>Lachnospiraceae</i>). The combination of SBI_NAG displayed effects of the individual ingredients, thus, for instance, enhancing all three short-chain fatty acids (SCFA) and elevating microbial diversity (CMS, community modulation score). <b>Conclusions</b>: Overall, SBI and NAG exert complementary, metabolically balanced effects on the gut microbiota, supporting combined use, particularly in individuals with gut barrier impairment or dysbiosis linked to lifestyle or early-stage gastrointestinal disorders.