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Polyphenol-induced improvements in glucose metabolism are associated with bile acid signaling to intestinal farnesoid X receptor.

ABSTRACT: INTRODUCTION:Bile acid (BA) biotransformation by gut bacteria impacts BA profile and signaling to nuclear receptors, such as the farnesoid X receptor (FXR) regulating glucose metabolism. Altered BA-FXR signaling was therefore investigated as a potential mechanism linking polyphenol-induced gut bacterial changes and improved glucose metabolism. RESEARCH DESIGN AND METHODS:Diabetic db/db were fed low-fat diet (LFD) or LFD supplemented with a proanthocyanidin-rich extract of grape polyphenols (LFD-GP) for 4 weeks. Metabolic phenotypes, serum BAs, gut microbiota composition, and gene expression markers relevant to gut barrier and glucose metabolism were assessed. Gut organoids were used to investigate effects of individual BAs on ileal FXR activity. RESULTS:Compared with LFD-fed controls, GP supplemented db/db mice showed improved glucose metabolism, decreased relative abundance of gut bacteria associated with production of secondary BAs (SBAs), and depleted serum levels of SBAs taurohyodeoxycholic acid (THDCA), ?-muricholic acid (?MCA), and tauro-?-muricholic acid (T?MCA). Serum levels of primary BAs (PBAs) increased, consistent with higher gene expression of PBA synthesis enzyme Cyp7a1. GP-induced BA changes associated with FXR inhibition as evidenced by reduced expression of FXR-responsive genes Shp, Fgf15, and Fabp6 in ileum tissue as well as hepatic Shp, which negatively regulates PBA synthesis. GP treatment did not affect expression of hepatic Fxr or expression of Abcb11, Slc51b, and Obp2a genes controlling BA transport. Ceramide biosynthesis genes Smpd3, Sptlc2, and Cers4 were decreased in liver and intestine suggesting lower tissue ceramides levels may contribute to improved glucose metabolism. THDCA, ?MCA, and T?MCA behaved as FXR agonists in ileal organoid experiments; therefore, their depletion in serum of GP-supplemented db/db and wild type (WT) mice was consistent with FXR inhibition. CONCLUSION:These data suggest that by altering the gut microbiota, GPs modify BA-FXR signaling pathways to promote glucoregulation.

SUBMITTER: Tveter KM

PROVIDER: S-EPMC7418775 | biostudies-literature | 2020 Aug

REPOSITORIES: biostudies-literature

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Polyphenol-induced improvements in glucose metabolism are associated with bile acid signaling to intestinal farnesoid X receptor.

Tveter Kevin M KM Villa-Rodriguez Jose A JA Cabales Alrick J AJ Zhang Li L Bawagan Fiona G FG Duran Rocio M RM Roopchand Diana E DE

BMJ open diabetes research & care 20200801 1

<h4>Introduction</h4>Bile acid (BA) biotransformation by gut bacteria impacts BA profile and signaling to nuclear receptors, such as the farnesoid X receptor (FXR) regulating glucose metabolism. Altered BA-FXR signaling was therefore investigated as a potential mechanism linking polyphenol-induced gut bacterial changes and improved glucose metabolism.<h4>Research design and methods</h4>Diabetic <i>db/db</i> were fed low-fat diet (LFD) or LFD supplemented with a proanthocyanidin-rich extract of g ...[more]

PMID: 32771984

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Project description:Bile acids activate farnesoid X receptor (FXR) and G protein-coupled bile acid receptor-1 (aka Takeda G protein-coupled receptor-5 [TGR5]) to regulate bile acid metabolism and glucose and insulin sensitivity. FXR and TGR5 are coexpressed in the enteroendocrine L cells, but their roles in integrated regulation of metabolism are not completely understood. We reported recently that activation of FXR induces TGR5 to stimulate glucagon-like peptide-1 (GLP-1) secretion to improve insulin sensitivity and hepatic metabolism. In this study, we used the intestine-restricted FXR agonist fexaramine (FEX) to study the effect of activation of intestinal FXR on the gut microbiome, bile acid metabolism, and FXR and TGR5 signaling. The current study revealed that FEX markedly increased taurolithocholic acid, increased secretion of fibroblast growth factors 15 and 21 and GLP-1, improved insulin and glucose tolerance, and promoted white adipose tissue browning in mice. Analysis of 16S ribosomal RNA sequences of the gut microbiome identified the FEX-induced and lithocholic acid-producing bacteria Acetatifactor and Bacteroides. Antibiotic treatment completely reversed the FEX-induced metabolic phenotypes and inhibited taurolithocholic acid synthesis, adipose tissue browning, and liver bile acid synthesis gene expression but further increased intestinal FXR target gene expression. FEX treatment effectively improved lipid profiles, increased GLP-1 secretion, improved glucose and insulin tolerance, and promoted adipose tissue browning, while antibiotic treatment reversed the beneficial metabolic effects of FEX in obese and diabetic mice. CONCLUSION:This study uncovered a mechanism in which activation of intestinal FXR shaped the gut microbiota to activate TGR5/GLP-1 signaling to improve hepatic glucose and insulin sensitivity and increase adipose tissue browning; the gut microbiota plays a critical role in bile acid metabolism and signaling to regulate metabolic homeostasis in health and disease. (Hepatology 2018).

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Polyphenol-induced improvements in glucose metabolism are associated with bile acid signaling to intestinal farnesoid X receptor.

Publications

Polyphenol-induced improvements in glucose metabolism are associated with bile acid signaling to intestinal farnesoid X receptor.

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