Diindoles produced from commensal microbiota metabolites function as endogenous CAR/Nr1i3 ligands.

Numerous studies have demonstrated the correlation between human gut bacteria and host physiology, mediated primarily via nuclear receptors (NRs). Despite this body of work, the systematic identification and characterization of microbe-derived ligands that regulate NRs remain a considerable challenge. In this study, we discover a series of diindole molecules produced from commensal bacteria metabolites that act as specific agonists for the orphan constitutive androstane receptor (CAR). Using various biophysical analyses we show that their nanomolar affinities are comparable to those of synthetic CAR agonists, and that they can activate both rodent and human CAR orthologues, which established synthetic agonists cannot. We also find that the diindoles, diindolylmethane (DIM) and diindolylethane (DIE) selectively up-regulate bona fide CAR target genes in primary human hepatocytes and mouse liver without causing significant side effects. These findings provide new insights into the complex interplay between the gut microbiome and host physiology, as well as new tools for disease treatment.

Durability of Linear Small-Intestinal Growth Following Treatment Discontinuation of Long-Acting Glucagon-Like Peptide 2 (GLP-2) Analogues.

BACKGROUND: Short-bowel syndrome is the leading cause of pediatric intestinal failure, resulting in dependency on long-term parenteral nutrition (PN). To promote enteral autonomy in neonates, a key outcome may be intestinal growth in length. The purpose of this study was to determine if intestinal lengthening persists following discontinuation of treatment with 1 of 2 GLP-2 analogues with different pharmacokinetic profiles. METHODS: Neonatal short-bowel piglets were assigned to saline control (S), 7-day treatment with teduglutide (T) (0.05 mg/kg twice daily), or 7-day treatment with apraglutide (A) (5 mg/kg twice weekly). Comparisons were made between day 7 and day 14 endpoints using analysis of variance. Data included small-intestine length, weight, histology, and quantitative polymerase chain reaction analysis of mucosal transcripts for peptide growth factors and their receptors, nutrient transporters, and tight-junction proteins. RESULTS: Compared with control, 7 days of GLP-2 analogue treatment induced mucosal adaptation based on villus hyperplasia (P = .003), which was not durable 7 days after treatment cessation (day 14; P = .081). Treatment increased intestinal growth in length by day 7 (P = .005), which was maintained (by T) or further increased (by A) at day 14 (P < .001). No significant differences in mucosal transcripts were detected. CONCLUSION: Unlike mucosal adaptation, intestinal growth appears to be a lasting outcome of treatment with long-acting GLP-2 analogues in a neonatal piglet short-bowel model. This has significant clinical implications for neonates, given their potential for intestinal growth. Intestinal lengthening varies between analogues with different half-lives; however, molecular mechanisms require further elucidation.

Essential Role of Syntaxin-Binding Protein-1 in the Regulation of Glucagon-Like Peptide-1 Secretion.

Circadian secretion of the incretin, glucagon-like peptide-1 (GLP-1), correlates with expression of the core clock gene, Bmal1, in the intestinal L-cell. Several SNARE proteins known to be circadian in pancreatic α- and ß-cells are also necessary for GLP-1 secretion. However, the role of the accessory SNARE, Syntaxin binding protein-1 (Stxbp1; also known as Munc18-1) in the L-cell is unknown. The aim of this study was to determine whether Stxbp1 is under circadian regulation in the L-cell and its role in the control of GLP-1 secretion. Stxbp1 was highly-enriched in L-cells, and STXBP1 was expressed in a subpopulation of L-cells in mouse and human intestinal sections. Stxbp1 transcripts and protein displayed circadian patterns in mGLUTag L-cells line, while chromatin-immunoprecipitation revealed increased interaction between BMAL1 and Stxbp1 at the peak time-point of the circadian pattern. STXBP1 recruitment to the cytosol and plasma membrane within 30 minutes of L-cell stimulation was also observed at this time-point. Loss of Stxbp1 in vitro and in vivo led to reduced stimulated GLP-1 secretion at the peak time-point of circadian release, and impaired GLP-1 secretion ex vivo. In conclusion, Stxbp1 is a circadian regulated exocytotic protein in the intestinal L-cell that is an essential regulatory component of GLP-1 secretion.