Intestinal TGR5 agonism improves hepatic steatosis and insulin sensitivity in Western diet-fed mice

Abstract

Takeda G protein-coupled receptor 5 (TGR5) agonists induce systemic release of glucagon-like peptides (GLPs) from intestinal L cells, a potentially therapeutic action against metabolic diseases such as nonalcoholic steatohepatitis (NASH), nonalcoholic fatty liver disease (NAFLD), and Type 2 diabetes. Historically, TGR5 agonist use has been hindered by side effects, including inhibition of gallbladder emptying. Here, we characterize RDX8940, a novel, orally administered TGR5 agonist designed to have minimal systemic effects and investigate its activity in mice fed a Western diet, a model of NAFLD and mild insulin resistance. Agonist activity, binding selectivity, toxicity, solubility, and permeability of RDX8940 were characterized in standard in vitro models. RDX8940 pharmacokinetics and effects on GLP secretion, insulin sensitivity, and liver steatosis were assessed in C57BL/6 mice fed normal or Western diet chow and given single or repeated doses of RDX8940 or vehicle, with or without dipeptidyl peptidase-4 (DPP4) inhibitors. Gallbladder effects were assessed in CD-1 mice fed normal chow and given RDX8940 or a systemic TGR5 agonist or vehicle. Our results showed that RDX8940 is minimally systemic, potent, and selective, and induces incretin (GLP-1, GLP-2, and peptide YY) secretion. RDX8940-induced increases in plasma active GLP-1 (aGLP-1) levels were enhanced by repeated dosing and by coadministration of DPP4 inhibitors. RDX8940 increased hepatic exposure to aGLP-1 without requiring coadministration of a DPP4 inhibitor. In mice fed a Western diet, RDX8940 improved liver steatosis and insulin sensitivity. Unlike systemic TGR5 agonists, RDX8940 did not inhibit gallbladder emptying. These results indicate that RDX8940 may have therapeutic potential in patients with NAFLD/NASH. NEW & NOTEWORTHY Takeda G protein-coupled receptor 5 (TGR5) agonists have potential as a treatment for nonalcoholic steatohepatitis and nonalcoholic fatty liver disease (NAFLD) but have until now been associated with undesirable side effects associated with systemic TGR5 agonism, including blockade of gallbladder emptying. We demonstrate that RDX8940, a potent, selective, minimally systemic oral TGR5 agonist, improves liver steatosis and insulin sensitivity in a mouse model of NAFLD and does not inhibit gallbladder emptying in mice.

The Role of the Gut Microbiota in Lipid and Lipoprotein Metabolism

“…Similar to FXR, TGR5 activity can regulate glucose and lipid homeostasis. Several in vivo studies in mice have suggested that TGR5 activation by synthetic agonists could improve insulin and glucose tolerance as well as liver and pancreatic function [82], decrease plasma triglycerides and LDL-cholesterol [83], and ameliorate hepatic steatosis [84]. However, controversial results have been reported with a TGR5 KO mice model, as TGR5 KO female mice gained much more body weight and accumulated more fat mass under HFD feeding, while TGR5 knockout male mice did not show significant difference in body weight gain or fat mass accumulation when compared to the wild-type control [85].…”

TGR5 Signaling in Hepatic Metabolic Health

“…Treatment of HFD-fed mice with INT-777 decreased plasma free fatty acids and liver steatosis, liver fibrosis and plasma AST and ALT levels [9]. Similarly, the TGR5 agonist, RDX8940, was shown to decrease liver weight and hepatic triglyceride and cholesterol levels in mice fed a Western diet [27]. Moreover, dual agonists of TGR5 and FXR protect against NAFLD.…”

“…Previous work has also shown that whole body Tgr5 −/− mice fed a HFD are more insulin-resistant than Tgr5 +/+ mice, as assessed by an insulin tolerance test [25]. Furthermore, TGR5 agonists have been shown to ameliorate glucose intolerance and improve insulin resistance in obese and diabetic mice [9,13,[27][28][29]48]. Treatment of diet-induced obese (DIO) mice with INT-777, a semi-synthetic TGR5 agonist, has been shown to promote GLP-1 secretion from L-cells, improve insulin sensitivity in liver and muscle and decrease hepatic glucose production [9].…”

“…(B) TGR5 signaling decreases hepatic CYP8B1 expression, leading to a decrease in the production of 12-α-hydroxylated bile acids [26,33], and upregulates the alternative pathway of bile acid synthesis, thereby decreasing bile acid profile hydrophobicity [7,26]. (C) TGR5 signaling may protect against non-alcoholic fatty liver disease (NAFLD) by reducing hepatic cytokine expression in Kupffer cells [15,20] and decreasing hepatic lipid deposition [9,27], which together, attenuate hepatic insulin resistance. TGR5 signaling also decreases serum AST and ALT concentrations [9], as well as hepatic fibrosis [9], ultimately improving hepatic function.…”

“…Genetic ablation of TGR5 has been shown to make mice more susceptible to impaired glucose tolerance, hepatic insulin resistance, hepatic steatosis and fibrosis, as well as altered bile acid metabolism [9,25,26]. Additionally, treatment of mice with TGR5-specific agonists has been shown to ameliorate many of these metabolic impairments, underscoring the potential therapeutic nature of TGR5 in treating metabolic disease [7,9,13,24,[27][28][29][30]. However, the clinical development of TGR5 agonists is complicated by the breadth of effects associated with systemic TGR5 activation, particularly in regard to TGR5-specific effects on gallbladder filling and gallstone formation [22,24,30,31].…”