A DPP-IV-resistant triple-acting agonist of GIP, GLP-1 and glucagon receptors with potent glucose-lowering and insulinotropic actions in high-fat-fed mice.

AIMS/HYPOTHESIS: We designed a chemically modified, enzyme-resistant peptide with triple-acting properties based on human glucagon with amino acid substitutions aligned to strategic positions in the sequence of glucose-dependent insulinotropic polypeptide (GIP). METHODS: Y(1)-dA(2)-I(12)-N(17)-V(18)-I(27)-G(28,29)-glucagon (termed YAG-glucagon) was incubated with dipeptidylpeptidase IV (DPP-IV) to assess stability, BRIN-BD11 cells to evaluate insulin secretion, and receptor-transfected cells to examine cAMP production. Acute glucose-lowering and insulinotropic properties of YAG-glucagon were assessed in National Institutes of Health (NIH) Swiss mice, while longer-term actions on glucose homeostasis, insulin secretion, food intake and body weight were examined in high-fat-fed mice. RESULTS: YAG-glucagon was resistant to DPP-IV, increased in vitro insulin secretion (1.5-3-fold; p < 0.001) and stimulated cAMP production in GIP receptor-, glucagon-like peptide-1 (GLP-1) receptor- and glucagon receptor-transfected cells. Plasma glucose levels were significantly reduced (by 51%; p < 0.01) and insulin concentrations increased (1.2-fold; p < 0.01) after acute injection of YAG-glucagon in NIH Swiss mice. Acute actions were countered by established GIP, GLP-1 and glucagon antagonists. In high-fat-fed mice, twice-daily administration of YAG-glucagon for 14 days reduced plasma glucose (40% reduction; p < 0.01) and increased plasma insulin concentrations (1.8-fold; p < 0.05). Glycaemic responses were markedly improved (19-48% reduction; p < 0.05) and insulin secretion enhanced (1.5-fold; p < 0.05) after a glucose load, which were independent of changes in insulin sensitivity, food intake and body weight. CONCLUSIONS/INTERPRETATION: YAG-glucagon is a DPP-IV-resistant triple agonist of GIP, GLP-1 and glucagon receptors and exhibits beneficial biological properties suggesting that it may hold promise for treatment of type 2 diabetes.

Four weeks administration of Liraglutide improves memory and learning as well as glycaemic control in mice with high fat dietary-induced obesity and insulin resistance.

AIM: Liraglutide is a long-acting glucagon-like peptide-1 (GLP-1) mimetic which is a treatment option for type 2 diabetes. GLP-1 peptides, including Liraglutide, cross the blood-brain barrier and may additionally act to improve brain function. The present study tested the hypothesis that, in addition to its antihyperglycaemic actions, peripheral administration of Liraglutide exerts positive actions on cognitive function in mice with high fat dietary-induced obesity and insulin resistance. METHODS: Young Swiss TO mice maintained on high fat diet for 20 weeks received twice-daily injections of Liraglutide (200 µg/kg bw; sc) or saline vehicle over 28 days. An additional group of mice on standard diet received twice-daily saline injections. Energy intake, bodyweight, non-fasting plasma glucose and insulin concentrations were monitored at regular intervals. Glucose tolerance, open field assessment, object recognition testing and electrophysiological long-term potentiation (LTP) were performed at termination of the study. RESULTS: Liraglutide treatment resulted in significant time-dependent reduction in bodyweight and energy intake, whilst improving non-fasting glucose and normalizing glucose tolerance. Although Liraglutide did not alter general behaviour, treated mice exhibited marked increase in recognition index (RI) during object recognition testing, indicative of enhanced learning and memory ability. Furthermore, Liraglutide rescued the deleterious effects of high fat diet on hippocampal LTP of neurotransmission following both chronic and direct intracerebroventricular (icv) administration. CONCLUSION: Liraglutide administered peripherally not only improves metabolic parameters but exerts additional beneficial effects on cognitive function and hippocampal synaptic plasticity. Whether therapy with GLP-1 mimetics has similar effects in humans with type 2 diabetes needs to be established.