Microbial aromatic amino acid metabolism is modifiable in fermented food matrices to promote bioactivity.

Ingestion of fermented foods impacts human immune function, yet the bioactive food components underlying these effects are not understood. Here, we interrogated whether fermented food bioactivity relates to microbial metabolites derived from aromatic amino acids, termed aryl-lactates. Using targeted metabolomics, we established the presence of aryl-lactates in commercially available fermented foods. After pinpointing fermented food-associated lactic acid bacteria that produce high levels of aryl-lactates, we identified fermentation conditions to increase aryl-lactate production in food matrices up to 5 × 103 fold vs. standard fermentation conditions. Using ex vivo reporter assays, we found that food matrix conditions optimized for aryl-lactate production exhibited enhanced agonist activity for the human aryl-hydrocarbon receptor (AhR) as compared to standard fermentation conditions and commercial products. Reduced microbial-induced AhR activity has emerged as a hallmark of many chronic inflammatory diseases, thus we envision strategies to enhance AhR bioactivity of fermented foods to be leveraged to improve human health.

Aging amplifies a gut microbiota immunogenic signature linked to heightened inflammation.

Aging is associated with low-grade inflammation that increases the risk of infection and disease, yet the underlying mechanisms remain unclear. Gut microbiota composition shifts with age, harboring microbes with varied immunogenic capacities. We hypothesized the gut microbiota acts as an active driver of low-grade inflammation during aging. Microbiome patterns in aged mice strongly associated with signs of bacterial-induced barrier disruption and immune infiltration, including marked increased levels of circulating lipopolysaccharide (LPS)-binding protein (LBP) and colonic calprotectin. Ex vivo immunogenicity assays revealed that both colonic contents and mucosa of aged mice harbored increased capacity to activate toll-like receptor 4 (TLR4) whereas TLR5 signaling was unchanged. We found patterns of elevated innate inflammatory signaling (colonic Il6, Tnf, and Tlr4) and endotoxemia (circulating LBP) in young germ-free mice after 4 weeks of colonization with intestinal contents from aged mice compared with young counterparts, thus providing a direct link between aging-induced shifts in microbiota immunogenicity and host inflammation. Additionally, we discovered that the gut microbiota of aged mice exhibited unique responses to a broad-spectrum antibiotic challenge (Abx), with sustained elevation in Escherichia (Proteobacteria) and altered TLR5 immunogenicity 7 days post-Abx cessation. Together, these data indicate that old age results in a gut microbiota that differentially acts on TLR signaling pathways of the innate immune system. We found that these age-associated microbiota immunogenic signatures are less resilient to challenge and strongly linked to host inflammatory status. Gut microbiota immunogenic signatures should be thus considered as critical factors in mediating chronic inflammatory diseases disproportionally impacting older populations.

Exercise training modifies xenometabolites in gut and circulation of lean and obese adults.

Regular, moderate exercise modifies the gut microbiome and contributes to human metabolic and immune health. The microbiome may exert influence on host physiology through the microbial production and modification of metabolites (xenometabolites); however, this has not been extensively explored. We hypothesized that 6 weeks of supervised, aerobic exercise 3×/week (60%-75% heart rate reserve [HRR], 30-60 min) in previously sedentary, lean (n = 14) and obese (n = 10) adults would modify both the fecal and serum xenometabolome. Serum and fecal samples were collected pre- and post-6 week intervention and analyzed by liquid chromatography/tandem mass spectrometry (LC-MS/MS). Linear mixed models (LMMs) identified multiple fecal and serum xenometabolites responsive to exercise training. Further cluster and pathway analysis revealed that the most prominent xenometabolic shifts occurred within aromatic amino acid (ArAA) metabolic pathways. Fecal and serum ArAA derivatives correlated with body composition (lean mass), markers of insulin sensitivity (insulin, HOMA-IR) and cardiorespiratory fitness ( V ̇ O 2 max $$ \dot{\mathrm{V}}{\mathrm{O}}_{2\max } $$ ), both at baseline and in response to exercise training. Two serum aromatic microbial-derived amino acid metabolites that were upregulated following the exercise intervention, indole-3-lactic acid (ILA: fold change: 1.2, FDR p < 0.05) and 4-hydroxyphenyllactic acid (4-HPLA: fold change: 1.3, FDR p < 0.05), share metabolic pathways within the microbiota and were associated with body composition and markers of insulin sensitivity at baseline and in response to training. These data provide evidence of physiologically relevant shifts in microbial metabolism that occur in response to exercise training, and reinforce the view that host metabolic health influences gut microbiota population and function. Future studies should consider the microbiome and xenometabolome when investigating the health benefits of exercise.