Intestinal FXR agonism promotes adipose tissue browning and reduces obesity and insulin resistance

Abstract

The systemic expression of the bile acid (BA) sensor farnesoid X receptor (FXR) has led to promising new therapies targeting cholesterol metabolism, triglyceride production, hepatic steatosis and biliary cholestasis. In contrast to systemic therapy, bile acid release during a meal selectively activates intestinal FXR. By mimicking this tissue-selective effect, the gut-restricted FXR agonist fexaramine (Fex) robustly induces enteric fibroblast growth factor 15 (FGF15), leading to alterations in BA composition, but does so without activating FXR target genes in the liver. However, unlike systemic agonism, we find that Fex reduces diet-induced weight gain, body-wide inflammation and hepatic glucose production, while enhancing thermogenesis and browning of white adipose tissue (WAT). These pronounced metabolic improvements suggest tissue-restricted FXR activation as a new approach in the treatment of obesity and metabolic syndrome.

Figure 1

Orally delivered Fex is an intestine-restricted FXR agonist. (a) Scheme for determining serum concentrations of Fex. Mice were treated daily with vehicle or Fex (100 mg kg⁻¹) by p.o. gavage or i.p. injection for 5 d, with tissues and serum collected 1 h after the final treatment. (b) Serum Fex concentrations from a. (c) Relative induction of the canonical FXR target gene SHP in tissues with abundant FXR expression after p.o. or i.p. delivery of Fex, compared with vehicle. (d) Induction of FXR target genes in intestine, liver and kidney after p.o. Fex treatment (8-week-old mice treated daily for 3 d 100 mg kg⁻¹). Data are mean ± sd. Statistical analysis was done using Student’s unpaired t-test. *P < 0.05, **P < 0.01. n = 3–5 per group.

Figure 2

Fex prevents diet-induced obesity and improves metabolic homeostasis. Mice fed control or an HFD for 14 weeks were chronically treated with vehicle or Fex (100 mg kg⁻¹ d⁻¹ p.o. for 5 weeks, n = 6–8 per group). (a) Body weights. (b) Body composition by magnetic resonance imaging. (c) Wet weight of inguinal WAT (iWAT), gonadal WAT (gWAT) and mesenteric WAT (mWAT), liver, kidney, heart and spleen. (d) Serum parameters after 8-h fast. TG, triglycerides. (e) Serum cytokines. (f) Glucose tolerance test. (g) Insulin tolerance test. Data are mean ± sd. Statistical analysis was done using Student’s unpaired t-test. *P < 0.05, **P < 0.01.

Figure 3

Fex increases oxidative phosphorylation to enhance metabolic rate in BAT. Mice fed an HFD for 14 weeks were chronically treated with vehicle or Fex (100 mg kg⁻¹ d⁻¹ p.o. for 5 weeks, n = 6–8 per group). (a) Daily food intake during first week of treatment. (b) Carbon dioxide production. (c) Oxygen consumption. (d) Cumulative ambulatory counts. (e) Core body temperature. (f) Representative images (three total images per group) of H&E staining of BAT. (g) Relative mRNA expression of selected nuclear receptors and genes involved in mitochondrial biogenesis and fatty acid oxidation in BAT. (h) Quantification of phosphorylated p38 in BAT. Scale bars, 50 µm. Data are mean ± sd. Statistical analysis was done using Student’s unpaired t-test. *P < 0.05, **P < 0.01.

Figure 4

Fex increases endogenous Fgf15 signaling and alters serum BA composition. Mice fed an HFD for 14 weeks were chronically treated with vehicle or Fex (100 mg kg⁻¹ d⁻¹ p.o. for 5 weeks, n = 6–8 per group). (a) Expression of direct FXR target genes in ileum. (b) Fgf15 protein in ileum. (c) Serum Fgf15 levels. (d) Expression of hepatic genes involved in BA metabolism. (e,f) Serum BA levels (e) and composition ratio (f). BW, body weight. (g,h) Intestinal permeability (g) and mucosal defense gene expression (h) in ileum. Scale bars, 50 µm. Data are mean ± sd. N.D., not determined. Statistical analysis was done using Student’s unpaired t-test. *P < 0.05, **P < 0.01.

Figure 5

Fex reduces inflammation and increases lipolysis in adipose tissues. Mice fed an HFD for 14 weeks were chronically treated with vehicle or Fex (5 weeks of 100 mg kg⁻¹ d⁻¹ p.o. delivery, n = 6–8 per group). (a) Representative images (three total images per group) of H&E staining of mWAT. (b) Protein expression levels in gWAT. (c) Gene expression of inflammatory cytokines and β-adrenergic receptor in gWAT. (d) Protein expression levels of Hsl (pHsl) in gWAT and inguinal WAT (iWAT). (e) Serum catecholamine levels. (f) Serum FFA levels. (g) Representative images (three total images per group) of Ucp1 staining in iWAT. Scale bars, 50 µm. Data are mean ± sd. Statistical analysis was done using Student’s unpaired t-test. *P < 0.05, **P < 0.01.

Figure 6

Fex treatment improves glucose homeostasis. (a–d) Hyperinsulinemic-euglycemic clamps performed on weight-matched mice fed an HFD chronically treated with vehicle or Fex (3 weeks of 100 mg kg⁻¹ d⁻¹ p.o. delivery, n = 12–14 per group). (a) Basal HGP. (b) GDR. (c) Percentage FFA suppression by insulin. (d) HGP suppression by insulin. (e–h) Mice were fed an HFD for 14 weeks, after which they were subjected to daily p.o. injection of vehicle or Fex (100 mg kg⁻¹) for 5 weeks with HFD (n = 6–8 per group). (e) Representative images (three total images per group) of liver H&E staining. (f) Hepatic triglyceride (TG) levels. (g) Relative mRNA expression of hepatic genes involved in gluconeogenesis and lipogenesis. (h) ALT (alanine aminotransferase) serum levels. Scale bars, 50 µm. Data are mean ± sd. Statistical analysis was done using Student’s unpaired t-test. *P < 0.05, **P < 0.01.