Xenin-25, a neurotensin (NT)-related anorexigenic gut hormone generated mostly in the duodenal mucosa, is believed to increase the rate of duodenal ion secretion, because xenin-induced diarrhea is not present after Roux-en-Y gastric bypass surgery. Because the local effects of xenin on duodenal ion secretion have remained uninvestigated, we thus examined the neural pathways underlying xenin-induced duodenal anion secretion. Intravenous infusion of xenin-8, a bioactive C-terminal fragment of xenin-25, dose dependently increased the rate of duodenal HCO₃^- secretion in perfused duodenal loops of anesthetized rats. Xenin was immunolocalized to a subset of enteroendocrine cells in the rat duodenum. The mRNA of the xenin/NT receptor 1 (NTS1) was predominantly expressed in the enteric plexus, nodose and dorsal root ganglia, and in the lamina propria rather than in the epithelium. The serosal application of xenin-8 or xenin-25 rapidly and transiently increased short-circuit current in Ussing-chambered mucosa-submucosa preparations in a concentration-dependent manner in the duodenum and jejunum, but less so in the ileum and colon. The selective antagonist for NTS1, substance P (SP) receptor (NK1), or 5-hydroxytryptamine (5-HT)₃, but not NTS2, inhibited the responses to xenin. Xenin-evoked Cl^- secretion was reduced by tetrodotoxin (TTX) or capsaicin-pretreatment, and abolished by the inhibitor of TTX-resistant sodium channel Nav1.8 in combination with TTX, suggesting that peripheral xenin augments duodenal HCO₃^- and Cl^- secretion through NTS1 activation on intrinsic and extrinsic afferent nerves, followed by release of SP and 5-HT. Afferent nerve activation by postprandial, peripherally released xenin may account for its secretory effects in the duodenum.

Background

Therapy with nonsteroidal anti-inflammatory drugs (NSAIDs) is associated with enteropathy in humans and experimental animals, a cause of considerable morbidity. Unlike foregut NSAID-associated mucosal lesions, most treatments for this condition are of little efficacy. We propose that the endogenously released intestinotrophic hormone glucagon-like peptide-2 (GLP-2) prevents the development of NSAID-induced enteropathy. Since the short-chain fatty acid receptor FFA3 is expressed on enteroendocrine L cells and on enteric nerves in the gastrointestinal tract, we further hypothesized that activation of FFA3 on L cells protects the mucosa from injury via GLP-2 release with enhanced duodenal HCO₃^- secretion. We thus investigated the effects of synthetic selective FFA3 agonists with consequent GLP-2 release on NSAID-induced enteropathy.

Methods

We measured duodenal HCO₃^- secretion in isoflurane-anesthetized rats in a duodenal loop perfused with the selective FFA3 agonists MQC or AR420626 (AR) while measuring released GLP-2 in the portal vein (PV). Intestinal injury was produced by indomethacin (IND, 10 mg/kg, sc) with or without MQC (1-10 mg/kg, ig) or AR (0.01-0.1 mg/kg, ig or ip) treatment.

Results

Luminal perfusion with MQC or AR (0.1-10 µM) dose-dependently augmented duodenal HCO₃^- secretion accompanied by increased GLP-2 concentrations in the PV. The effect of FFA3 agonists was inhibited by co-perfusion of the selective FFA3 antagonist CF3-MQC (30 µM). AR-induced augmented HCO₃^- secretion was reduced by iv injection of the GLP-2 receptor antagonist GLP-2(3-33) (3 nmol/kg), or by pretreatment with the cystic fibrosis transmembrane conductance regulator (CFTR) inhibitor CFTR_inh-172 (1 mg/kg, ip). IND-induced small intestinal ulcers were dose-dependently inhibited by intragastric administration of MQC or AR. GLP-2(3-33) (1 mg/kg, ip) or CF3-MQC (1 mg/kg, ig) reversed AR-associated reduction in IND-induced enteropathy. In contrast, ip injection of AR had no effect on enteropathy.

Conclusion

These results suggest that luminal FFA3 activation enhances mucosal defenses and prevents NSAID-induced enteropathy via the GLP-2 pathway. The selective FFA3 agonist may be a potential therapeutic candidate for NSAID-induced enteropathy.

Background

Circulating endotoxin (lipopolysaccharide, LPS) increases the gut paracellular permeability. We hypothesized that glucagon-like peptide-2 (GLP-2) acutely reduces LPS-related increased intestinal paracellular permeability by a mechanism unrelated to its intestinotrophic effect.

Methods

We assessed small intestinal paracellular permeability in vivo by measuring the appearance of intraduodenally perfused FITC-dextran 4000 (FD4) into the portal vein (PV) in rats 1-24 h after LPS treatment (5 mg/kg, ip). We also examined the effect of a stable GLP-2 analog teduglutide (TDG) on FD4 permeability.

Results

FD4 movement into the PV was increased 6 h, but not 1 or 3 h after LPS treatment, with increased PV GLP-2 levels and increased mRNA expressions of proinflammatory cytokines and proglucagon in the ileal mucosa. Co-treatment with a GLP-2 receptor antagonist enhanced PV FD4 concentrations. PV FD4 concentrations 24 h after LPS were higher than FD4 concentrations 6 h after LPS, reduced by exogenous GLP-2 treatment given 6 or 12 h after LPS treatment. FD4 uptake measured 6 h after LPS was reduced by TDG 3 or 6 h after LPS treatment. TDG-associated reduced FD4 uptake was reversed by the VPAC1 antagonist PG97-269 or L-NAME, not by EGF or IGF1 receptor inhibitors.

Conclusions

Systemic LPS releases endogenous GLP-2, reducing LPS-related increased permeability. The therapeutic window of exogenous GLP-2 administration is at minimum within 6-12 h after LPS treatment. Exogenous GLP-2 treatment is of value in the prevention of increased paracellular permeability associated with endotoxemia.