Date Published: March 1, 2019
Publisher: American Physiological Society
Author(s): Patricia D. Finn, David Rodriguez, Jill Kohler, Zhengfeng Jiang, Sindy Wan, Erick Blanco, Andrew J. King, Tao Chen, Noah Bell, Dean Dragoli, Jeffrey W. Jacobs, Rakesh Jain, Michael Leadbetter, Matthew Siegel, Christopher W. Carreras, Samantha Koo-McCoy, Karen Shaw, Cathy Le, Sandra Vanegas, I-Hsin Hsu, Kenji Kozuka, Keiko Okamoto, Jeremy S. Caldwell, Jason G. Lewis.
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.
Bile acid signaling in the gastrointestinal tract is important for the integrated regulation of lipid, glucose, and energy metabolism (21). Dysregulated bile acid signaling is associated with a wide range of diseases, including cholestatic liver diseases, dyslipidemia, fatty liver diseases, cardiovascular diseases, and Type 2 diabetes (21). The G protein-coupled bile acid receptor 1, also known as TGR5 (Takeda G protein-coupled receptor 5), is a cell-surface receptor widely expressed in human tissue, including the intestine (15). In intestinal L cells, a type of enteroendocrine cell abundant in the ileum and colon, TGR5 agonists induce systemic release of glucagon-like peptides (GLPs) 1 and 2 and peptide YY (PYY) (34). GLP-1 is an incretin that has insulinotropic effects in the pancreas to regulate glucose homeostasis, as well as extra pancreatic indirect metabolic effects (6). GLP-1 analogs have been found to be useful for the treatment of patients with Type 2 diabetes (11, 13), and they are currently under investigation as a treatment for nonalcoholic steatohepatitis (NASH), a severe form of nonalcoholic fatty liver disease (NAFLD) (1, 2). NASH is histologically characterized by excessive accumulation of hepatic fat (steatosis) that is associated with hepatocyte injury and inflammation, steatohepatitis, and fibrosis (18). Both insulin resistance in the liver and adipose tissue and excessive hepatic lipogenesis contribute to NAFLD/NASH progression (4, 20, 27). Studies in animal models of NASH have shown that GLP-1 therapy improves insulin sensitivity and reduces hepatic glucose production, and can reduce hepatic steatosis, inflammation, steatohepatitis, and fibrosis (12, 25, 33). In patients with NASH, the GLP-1 analog liraglutide promotes histological resolution of the condition and reduces metabolic dysfunction, insulin resistance, and lipotoxicity (1, 2). Subcutaneous injection of GLP-2 has been found to improve intestinal epithelial barrier function (3) and accelerate liver regeneration in mice that had undergone partial hepatectomy (16).
TGR5 agonists have the potential to be an effective treatment for metabolic diseases, such as NAFLD/NASH, owing to their ability to lower glucose-stimulated insulin release, slow gastric emptying, and decrease food intake via stimulation of GLP-1 release, and improve intestinal barrier function, thereby lowering whole body inflammation, via GLP-2 production (3, 5, 8, 22, 31, 35). However, their use has until now been associated with undesirable side effects, such as excessive gallbladder filling and blockade of gallbladder emptying, caused by systemic TGR5 agonism in off-target tissues (5, 8, 14, 20, 23, 25). Here, we have shown that RDX8940 is a potent, selective, and minimally systemic oral TGR5 agonist that induces GLP-1, GLP-2, and PYY secretion from mouse intestinal L cells and improves liver steatosis and insulin sensitivity in a model of NAFLD and mild insulin resistance. Furthermore, we have shown that RDX8940 does not inhibit gallbladder emptying in mice.
Medical writing support was provided by Dr. Tim Ellison of Oxford PharmaGenesis, funded by Ardelyx.
This study was funded by Ardelyx. All authors are current or former employees of Ardelyx.
PDF, AJK, JSC, JGL, and JWJ conceived and designed the research. PDF, DR, JK, ZJ, SW, EB, TC, NB, DD, RJ, ML, MS, CWC, SK, KS, CL, SV, IH, KK performed experiments. PDF, AJK, KK, KO, CWC analyzed data. PDF, AJK, KK, KO, JGL interpreted results of experiments. PDF drafted the manuscript and prepared figures. AJK, JSC, JGL, KK and PDF edited and revised the manuscript. All authors approved the final version of the manuscript.