The alpha-7 nicotinic acetylcholine receptor agonist GTS-21 engages the glucagon-like peptide-1 incretin hormone axis to lower levels of blood glucose in db/db mice

Aim To establish if alpha-7 nicotinic acetylcholine receptor (alpha 7nAChR) agonist GTS-21 exerts a blood glucose-lowering action in db/db mice, and to test if this action requires coordinate alpha 7nAChR and GLP-1 receptor (GLP-1R) stimulation by GTS-21 and endogenous GLP-1, respectively. Materials and Methods Blood glucose levels were measured during an oral glucose tolerance test (OGTT) using db/db mice administered intraperitoneal GTS-21. Plasma GLP-1, peptide tyrosine tyrosine 1-36 (PYY1-36), glucose-dependent insulinotropic peptide (GIP), glucagon, and insulin levels were measured by ELISA. A GLP-1R-mediated action of GTS-21 that is secondary to alpha 7nAChR stimulation was evaluated using alpha 7nAChR and GLP-1R knockout (KO) mice, or by co-administration of GTS-21 with the dipeptidyl peptidase-4 inhibitor, sitagliptin, or the GLP-1R antagonist, exendin (9-39). Insulin sensitivity was assessed in an insulin tolerance test. Results Single or multiple dose GTS-21 (0.5-8.0 mg/kg) acted in a dose-dependent manner to lower levels of blood glucose in the OGTT using 10-14 week-old male and female db/db mice. This action of GTS-21 was reproduced by the alpha 7nAChR agonist, PNU-282987, was enhanced by sitagliptin, was counteracted by exendin (9-39), and was absent in alpha 7nAChR and GLP-1R KO mice. Plasma GLP-1, PYY1-36, GIP, glucagon, and insulin levels increased in response to GTS-21, but insulin sensitivity, body weight, and food intake were unchanged. Conclusions alpha 7nAChR agonists improve oral glucose tolerance in db/db mice. This action is contingent to coordinate alpha 7nAChR and GLP-1R stimulation. Thus alpha 7nAChR agonists administered in combination with sitagliptin might serve as a new treatment for type 2 diabetes.