We report direct in vivo confirmation of transcellular lipopolysaccharides (LPS) uptake from the intestine into the portal vein (PV) involving CD36 and lipid rafts, with minor uptake via the canonical chylomicron pathway. The gut hormone glucagon-like peptide-2 (GLP-2) inhibited uptake into the PV. These data suggest that the bulk of LPS absorption is via the PV to the liver, helping clarify the mechanism of LPS transport into the PV as part of the “gut-liver” axis. These data do not support the paracellular transport of LPS, which has been implicated in the pathogenesis of the “leaky gut” syndrome.

Background/Aims Although studies using conventional animal models have shown that specific stressors cause irritable bowel syndrome (IBS), it is unclear whether depression itself causes IBS. Our aim was to establish a rat model to determine if depression itself promotes the onset of IBS and to elucidate the role of gut microbiota in brain-gut axis pathogenesis during coincident depression and IBS. Methods Rat models of depression were induced using our shuttle box method of learned helplessness. Visceral hypersensitivity was evaluated by colorectal distension (CRD) to diagnose IBS. Gut microbiota compositions were analyzed using high-throughput sequencing. In the subanalysis of rats without depression-like symptoms, rats with posttraumatic stress disorder (PTSD) were also examined. Results The threshold value of CRD in depressed rats was significantly lower than that in control rats. Microbial community analysis of cecal microbiota showed that the relative abundance of Clostridiales incertae sedis , the most prevalent microbe, was significantly lower in depressed rats than in control rats. The distribution pattern of the microbiota clearly differed between depressed rats and control rats. Neither visceral hypersensitivity nor the composition of gut microbiota was altered in rats with PTSD-like phenotypes. Conclusions Our rat model of depression is useful for clarifying the effect of depression on IBS and suggests that depression itself, rather than specific stressors, promotes the onset of IBS. Further, we provided evidence that various psychiatric diseases, viz., depression and PTSD, are associated with unique gut microbiota profiles, which could differentially affect the onset and progression of coincident IBS.

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Lipopolysaccharide (LPS) is a cell wall component of Gram‐negative bacteria that is associated with the metabolic syndrome at one extreme and multiple organ failure at the other, the latter associated with increased intestinal paracellular permeability. We have found that LPS is acutely transported into the portal vein (PV) during lipid absorption via CD36‐ and lipid raft‐mediated transcellular pathways and that GLP‐2 acutely reduces intestinal paracellular permeability during systemic inflammation. We thus hypothesized that a stable GLP‐2 analog teduglutide (TDG) affects LPS transport during lipid absorption and reduces intestinal permeability during systemic inflammation.FITC‐LPS was infused into small intestine from the duodenum with oleic acid (30 mM)/taurocholic acid (10 mM) in anesthetized rats. The appearance of FITC‐LPS was simultaneously monitored in the PV and mesenteric lymph with or without TDG pretreatment (0.5 – 50 μg/kg, iv) 15 min before FITC‐LPS infusion. Intestinal permeability was increased by ip injection of LPS (5 mg/kg). FD4 transport into the PV was measured in vivo at 6 hr after LPS injection with or without TDG treatment (50 μg/kg, ip) at 0, 3, or 6 hr after LPS treatment.LPS was acutely transported into PV at 15 min during lipid absorption, followed by gradual transport into lymph by incorporation to chylomicron at 60 – 90 min. Luminal co‐infusion of the selective agonist for short‐chain fatty acid receptor FFA3, AR420626 (10 μM), which increased GLP‐2 release, inhibited LPS transport into the PV. A DPP4 inhibitor NVP728 (3 μmol/kg, iv) reduced LPS transport into the PV and lymph, suggesting that enhanced endogenous GLP‐2 concentrations reduce LPS transport. TDG iv injection acutely inhibited LPS transport into PV, but enhanced LPS transport into lymph, accompanied by increased lymph output. Luminal L‐NAME (0.1 mM) reversed TDG effects on LPS transport into PV and lymph, suggesting mediation by NO production from myenteric nNOS neurons, which expresses GLP‐2 receptors. Systemic LPS treatment at 6 hr, but not at 1 or 3 hr, increased FD4 movement from the lumen to PV, accompanied by increased expression of the proinflammatory cytokines TNFα, IL‐1β and IL‐6 in the ileal mucosa, suggesting that LPS‐induced subepithelial inflammation increases intestinal epithelial permeability for macromolecules. TDG pretreatment prior to LPS injection aggravated LPS‐induced FD4 permeability into the PV, whereas TDG treatment at 3 – 6 hr after LPS injection inhibited FD4 permeability. Pretreatment with the GLP‐2 receptor antagonist GLP‐2(3‐33) (3 nmol/kg, ip) prior to LPS injection enhanced FD4 permeability.These results suggest that TDG acutely inhibits LPS transport and intestinal permeability, the latter with therapeutic windows at 3 – 6 hr after the induction of systemic inflammation, consistent with half‐life of TDG ~ 2 hr in the circulation. TDG may be a therapeutic candidate for metabolic syndrome such as fatty liver and obesity, and secondary endotoxemia such as occurs in serious illness by inhibiting LPS transport under physiological and pathological conditions.Support or Funding InformationShire Pharmaceuticals, VA Merit Review, NIDDK R01 DK54221This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

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