Pharmacological potential of novel agonists for FFAR4 on islet and enteroendocrine cell function and glucose homeostasis

Background: To investigate the metabolic effects of FFAR4-selective agonists on islet and enteroendocrine cell hormone release and the combined therapeutic effectiveness with DPP-IV inhibitors. Methods: Insulinotropic activity and specificity of FFAR4 agonists were determined in clonal pancreatic BRIN-BD11 cells. Expression of FFAR4 was assessed by qPCR and western blotting following agonist treatment in BRIN-BD11 cells and by immunohistochemistry in mouse islets. Acute in-vivo effects of agonists was investigated after intraperitoneal (i.p.) or oral administration in lean and HFF-obese diabetic mice. Results: GSK137647 (10^{– 11}–10^{– 4} M) and Compound-A (10^{– 10}–10^{– 4} M) stimulated insulin secretion at 5.6 mM (p < 0.05-p < 0.001) and 16.7 mM (p < 0.05-p < 0.001) glucose in BRIN-BD11 cells, with no cytotoxicity effects as assessed by MTT. FFAR4 antagonist (AH-7614) abolished the insulintropic effect of GSK137647 (p < 0.05-p < 0.001), whilst FFAR1 antagonist (GW1100) had no effect. Incubation of BRIN-BD11 cells with GSK137647 and Compound-A increased FFAR4 (p < 0.01) gene expression at 16.7 mM glucose, with a corresponding increase in FFAR4 (p < 0.01) protein concentrations. FFAR4 upregulation was attenuated under normoglycaemic conditions. Immunohistochemistry demonstrated co-localisation of FFAR4 and insulin in mouse islets. Orally administered GSK137647 or Compound-A (0.1 µmol/kgBW) improved glucose tolerance (p < 0.001), increased plasma insulin (p < 0.001), GLP-1 (p < 0.05), GIP (p < 0.05) and induced satiety (p < 0.001) in HFF mice, with glucose-lowering effects enhanced in combination with DPP-IV inhibitor (Sitagliptin) (p < 0.05). Conclusions: Specific FFAR4 agonism improves glucose tolerance through insulin and incretin secretion, with enhanced DPP-IV inhibition in combination with Sitagliptin. General significance: These findings have for the first time demonstrated that selective FFAR4 activation regulates both islet and enteroendocrine hormone function with agonist combinational therapy, presenting a promising strategy for the treatment of type-2-diabetes.