The pleiotropic effects of prebiotic galacto-oligosaccharides on the aging gut

Abstract

Background: Prebiotic galacto-oligosaccharides (GOS) have an extensively demonstrated beneficial impact on intestinal health. In this study, we determined the mechanistic impact of GOS diets on hallmarks of gut aging: microbiome dysbiosis, inflammation, and intestinal barrier defects (“leaky gut”). We also evaluated if short-term GOS feeding influenced how the aging gut responded to antibiotic challenges, since these interventions are common and relevant in older adults. Finally, we assessed the ability of colonic organoids to reproduce in vivo responses to GOS.Results: Old animals had a distinct microbiome characterized by lower diversity, increased ratios of non-saccharolytic versus saccharolytic bacteria and lower abundance of O-Glycosyl hydrolases . GOS treatment increased abundance of non-saccharolytic ( Akkermansia muciniphila ) and saccharolytic bacteria (species of Bacteroides and Lactobacillus ), and increased the abundance of β-galactosidases and β-glucosidases in young and old animals . Clyndamicin treatment reduced the abundance of beneficial bacteria including Bifidobacterium and Lactobacillus , while increasing Akkermansia, Clostridium, Coprococcus, Enterococcus, Bacillus, Bacteroides, and Paenibacillus . Prebiotics impacted the effects of the antibiotics decreasing the abundance of Akkermansia in the GOS-antibiotic groups compared to the control-antibiotics groups. GOS reduced the age-associated increased intestinal permeability via increased MUC2 expression and mucus biosynthesis. T ranscriptomics analysis of colon from old animals fed GOS diets showed increased expression of genes involved in small molecule metabolic processes and specifically the respirasome, which could indicate an increased oxidative metabolism and energetic efficiency. In young mice, GOS induced expression of binding-related genes and the galectin gene Lgals1 , a β-galactosyl-binding lectin that bridges molecules by their sugar moieties, forming a signaling and adhesion network. Further analysis showed higher expression levels of genes in focal adhesion, PI3K-Akt and ECM-receptor interaction pathways. GOS reduced the expression of TNF  in old animals, and altered serum levels of inflammatory biomarkers IL-6, IL-17, IP-10 and Eotaxin. Stools from young mice exhibiting variable bifidogenic response to GOS, injected into colon organoids in the presence of prebiotics, reproduced the response and non-response phenotypes.Conclusions: GOS modulation of intestinal homeostasis likely occurs through direct GOS-host interactions via modulation of host gene expression and mucus production, as well as through interactions mediated by the gut microbiota that result in increased or restored saccharolytic potential.

Safety and Modulatory Effects of Humanized Galacto-Oligosaccharides on the Gut Microbiome

“…In addition, we did not observe differences in dietary consumption or weight in prebiotic-fed animals compared to the control group. We have recently reported an initial decreased diversity in 6- and 60-week old GOS-fed C57BL/6J mice after 2 weeks ( 15 ), which is in accordance with studies of GOS-supplemented infant formula ( 61 ) but contrast with other studies on human adults ( 6 , 62 ) and young or adult BALB/c mice that showed no changes on diversity due to GOS feeding ( 63 , 64 ). Considering the biochemical structure of GOS and hGOS and their similarity to HMOs, it makes sense that these prebiotics exert a restrictive selection of microorganisms to only microbes capable of establishing a mutualistic relationship with the host as observed in breastfed infants ( 65 ).…”

“…Members of the gut microbial community including strains of Bifidobacterium and Lactobacillus encode galactosidases genes that hydrolyze complex carbohydrates including GOS, as demonstrated in our previous and current studies ( 15 – 17 , 19 , 69 ) generating products which other members of the gut microbiota can further utilize through cross-feeding ( 19 , 70 ). Due to structural similarities between the dietary carbohydrate structures contained in GOS and hGOS, it can be expected that their hydrolysis will result in similar molecules, including lactate and acetate, which could subsequently be utilized to generate other SCFAs of biological relevance, including butyrate.…”

“…Among other changes in the gut microbiota, feeding GOS and hGOS increased the abundance of Akkermansia muciniphila , a microorganism that predominantly utilizes mucin as its energy source. GOS enrichment of Akkermansia is likely a consequence of increased mucin production ( 15 ). However, hGOS (containing LacNAc) may be utilized directly by Akkermansia due to a similar LacNAc structure found in hGOS and mucin ( 71 ).…”

“…Total DNA was extracted from fecal pellets using the Qiagen ClearMag Extraction system on KingFisher Flex Magnetic Bead processing instrument as described ( 15 ). Briefly, stool samples were transferred to a screwcap tube containing 10 mg of sterile acid-washed glass beads (0.1–0.5 mm diameter) and 700 μl PM1 solution (Qiagen, Valencia, CA).…”

“…In previous studies we evaluated highly pure β(1–4) galacto-oligosaccharides (GOS) formulations produced by the optimized version of the hexosyl-transferase gene from Hamamotoa (Sporobolomyces) singularis heterologously expressed in Komagataella ( Pichia ) pastoris ( 13 , 14 ). This enzyme is one of the most promising catalysts in the field of glycobiology due to its high stability, highly desirable enzymatic properties, and the metabolism of its reaction products (GOS) by specific members of the gut microbial community, impacting its composition and function ( 15 , 16 ). Beneficial members of the gut microbiota, including Lactobacillus and Bifidobacterium , hydrolyze GOS via β-galactosidases ( 17 ).…”