Unraveling the Prebiotic Effects of Phenolic Compounds Towards Probiotic Gut Bacteria via Metabolomics

OBJECTIVES: Ellagic acid (EA) is a polyphenol abundantly present in plant-based diet and exhibits multifarious health benefits. Due to its low oral bioavailability, biotransformation of EA into urolithins (Uros) is crucial to achieving its bio-efficacy in vivo. Gordonibacter urolithinfaciens (GUro) is one of the three known gut bacteria that can convert EA to Uro C, a key intermediate metabolite leading to the generation of highly bioavailable and bioactive Uro A and Uro B. Our earlier studies showed that dietary-level EA promoted the growth of probiotic genera while inhibiting opportunistic pathogens in the microbiota. However, the effects of EA and Uros on GUro and other individual gut bacteria remain unclear. This study aims to investigate the crosstalk between EA/Uros and probiotic-like gut bacteria using a metabolomics approach. METHODS: GUro and probiotic strains including Bifidobacterium infantis (BInf), Lacticaseibacillus rhamnosus GG (LGG), and Akkermansia muciniphila (AMuc) were anaerobically fermented with 10 - 90 μM of EA, or 30 μM of Uro A or C. Bacterial growth indicated by OD600 values were monitored daily, and bacterial enumeration by plate count method was conducted at the end point. Following immediate quenching, intracellular metabolites were extracted with cold methanol and analyzed by UHPLC with hybrid quadrupole time-of-flight mass spectrometry (QTOF-MS). Metabolomics data was analyzed by Progenesis QI and MetaboAnalyst 5.0. RESULTS: Results showed that dietary-level (10 and 30 μM) EA promoted the growth of LGG and BInf but had no significant impact on GUro. Uro C promoted the growth of AMuc and BInf. Untargeted metabolomic profiling revealed that intracellular levels of certain ribonucleic acids and amino alcohols were upregulated in bacteria treated with dietary-level EA. Moreover, there was a remarkable influence of both EA and Uro C on cellular metabolic cycle and metabolic pathways associated with cell division. CONCLUSIONS: This is the first study to investigate the metabolic regulatory effects of EA and Uros on probiotic gut bacteria to account for the prebiotic benefits of EA. Ongoing study is examining the biotransformation/accumulation of EA and Uros by bacterial cells to provide more insights on the xenobiotic-bacteria interaction. FUNDING SOURCES: Research Institute for Future Food of PolyU.