Unveiling the roles of dietary Tryptophan and Arginine metabolism in Lactobacillus rhamnosus GG-mediated barrier protection

Abstract

Inflammatory bowel disease (IBD) is often characterized by increased intestinal paracellular permeability and abnormalities in tight junctions (TJ). IBD patients commonly exhibit reduced serum tryptophan (TRP) levels. Furthermore, animal models on low-TRP diets are more susceptible to chemically induced intestinal inflammation, while those on high-TRP diets show reduced inflammation. The interaction between TRP and gut microbiota in reinforcing the intestinal barrier warrants further investigation. To address this, we introduced Lactobacillus rhamnosus GG (LGG), known for enhancing the gut barrier, and PBS as a control into germ-free mice fed TRP-suffcient or -deficient diets. Our analysis of the mouse ileal transcriptome revealed dramatic upregulation of key genes in arginine metabolism only in LGG-TRP mice, particularly of argininosuccinate lyase ( Asl) that catabolizes argininosuccinate (ASA). Interestingly, our in-silico analysis of human IBD data GEO 179285 transcriptome showed marked dysregulation of similar genes, including inappropriate increases in ASA synthetase ( Ass1). Moreover, this unique expression pattern in the mouse ileum was TRP-dependent and specific to LGG, and not observed in mice monocolonized with pathobiont Ruminococcus gnavus or specific pathogen-free mice. LC-MS analysis of fecal and serum metabolites in LGG-TRP mice revealed elevated levels of fecal arginine, glutamine, and aspartate, suggesting their involvement in host arginine biosynthesis, along with significant reductions in serum ASA levels. ASA was highly negatively correlated with numerous TJ genes, suggesting its potential to compromise barrier function. Indeed, treating mouse enteroids with ASA enhanced dextran permeability, exacerbated LPS disruption of the gut barrier, and decreased expression of TJ genes Ocln and Tjp1. Furthermore, elevated serum ASA and decreased colonic ASL levels were observed in colitis-afflicted mice, perturbing gut homeostasis, as indicated by increased fecal lipocalin-2 and delayed colitis recovery after intraperitoneal ASA administration. We propose that LGG-TRP stimulates gut-mediated ASA turnover as evidenced by substantial increases in Asl levels. Interestingly, LGG alone reduced ASA concentration in the culture medium under anaerobic and aerobic conditions. Collectively, our study identifies ASA as a potential biomarker of gut inflammation and enhanced permeability. Moreover, we highlight the potential of LGG-TRP therapy for IBD-associated leaky gut conditions, offering novel insights for gut health interventions. NIHR01-AT010243 (NG,RF), R01DK119198 (NG), NSF 1754783 (RF). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.