Liraglutide is a glucagon-like peptide-1 (GLP-1) analog developed for type 2 diabetes. Long-term liraglutide exposure in rodents was associated with thyroid C-cell hyperplasia and tumors. Here, we report data supporting a GLP-1 receptor-mediated mechanism for these changes in rodents. The GLP-1 receptor was localized to rodent C-cells. GLP-1 receptor agonists stimulated calcitonin release, up-regulation of calcitonin gene expression, and subsequently C-cell hyperplasia in rats and, to a lesser extent, in mice. In contrast, humans and/or cynomolgus monkeys had low GLP-1 receptor expression in thyroid C-cells, and GLP-1 receptor agonists did not activate adenylate cyclase or generate calcitonin release in primates. Moreover, 20 months of liraglutide treatment (at >60 times human exposure levels) did not lead to C-cell hyperplasia in monkeys. Mean calcitonin levels in patients exposed to liraglutide for 2 yr remained at the lower end of the normal range, and there was no difference in the proportion of patients with calcitonin levels increasing above the clinically relevant cutoff level of 20 pg/ml. Our findings delineate important species-specific differences in GLP-1 receptor expression and action in the thyroid. Nevertheless, the long-term consequences of sustained GLP-1 receptor activation in the human thyroid remain unknown and merit further investigation.

The long-acting GLP-1 derivative NN2211 ameliorates glycemia and increases ␤-cell mass in diabetic mice.

Lifestyle interventions including exercise programs are cornerstones in the prevention of obesity-related diabetes. The AMP-activated protein kinase (AMPK) has been proposed to be responsible for many of the beneficial effects of exercise on glucose and lipid metabolism. The effects of long-term exercise training or 5-aminoimidazole-4-carboxamide-1-␤-D-riboruranoside (AICAR) treatment, both known AMPK activators, on the development of diabetes in male Zucker diabetic fatty (ZDF) rats were examined. Five-week-old, prediabetic ZDF rats underwent daily treadmill running or AICAR treatment over an 8-week period and were compared with an untreated group. In contrast to the untreated, both the exercised and AICAR-treated rats did not develop hyperglycemia during the intervention period. Whole-body insulin sensitivity, as assessed by a hyperinsulinemic-euglycemic clamp at the end of the intervention period, was markedly increased in the exercised and AICAR-treated animals compared with the untreated ZDF rats (P < 0.01). In addition, pancreatic ␤-cell morphology was almost normal in the exercised and AICAR-treated animals, indicating that chronic AMPK activation in vivo might preserve ␤-cell function. Our results suggest that activation of AMPK may represent a therapeutic approach to improve insulin action and prevent a decrease in ␤-cell function associated with type 2 diabetes. Diabetes 54:928 -934, 2005

Metabolic effects of the glucagon-like peptide-1 analog liraglutide and the dipeptidyl peptidase-IV inhibitor vildagliptin were compared in rats made obese by supplementary candy feeding. Female Sprague-Dawley rats were randomized to 12-week diets of chow or chow plus candy. The latter were randomized for 12 further weeks to continue their diet while receiving 0.2 mg/kg liraglutide twice daily subcutaneously, 10 mg/kg vildagliptin twice daily orally, or vehicle or to revert to chow-only diet. Energy expenditure was measured, and oral glucose tolerance tests (OGTTs) were performed. Body composition was determined by dual-energy X-ray absorptiometry scanning, and pancreatic ␤-cell mass was determined by histology. Candy feeding increased weight, fat mass, and feedingassociated energy expenditure. Liraglutide or reversal to chow diet fully reversed weight and fat gains. Liraglutide was associated with decreased calorie intake and shifted food preference (increased chow/decreased candy consumption). Despite weight loss, liraglutide-treated rats did not decrease energy expenditure compared with candy-fed controls. Vildagliptin affected neither weight, food intake, nor energy expenditure. OGTTs, histology, and blood analyses indirectly suggested that both drugs increased insulin sensitivity. Liraglutide and vildagliptin inhibited obesityassociated increases in ␤-cell mass. This was associated with weight and fat mass normalization with liraglutide, but not vildagliptin, where the ratio of ␤-cell to body mass was low. Diabetes 56:8 -15, 2007

1 Liraglutide is a long-acting GLP-1 derivative, designed for once daily administration in type II diabetic patients. To investigate the effects of liraglutide on glycemic control and b-cell mass in rat models of b-cell deficiencies, studies were performed in male Zucker diabetic fatty (ZDF) rats and in 60% pancreatectomized rats. 2 When liraglutide was dosed s.c. at 150 mg kg À1 b.i.d. for 6 weeks in ZDF rats 6 -8 weeks of age at study start, diabetes development was markedly attenuated. Blood glucose was approximately 12 mm lower compared to vehicle (Po0.0002), and plasma insulin was 2 -3-fold higher during a normal 24-h feeding period (Po0.001). Judged by pair feeding, approximately 53% of the antihyperglycemic effect observed on 24-h glucose profiles was mediated by a reduction in food intake, which persisted throughout the study and averaged 16% (Po0.02). 3 Histological analyses revealed that b-cell mass and proliferation were significantly lower in prediabetic animals still normoglycemic after 2 weeks treatment compared to vehicle-treated animals that had begun to develop diabetes. When the treatment period was 6 weeks, the liraglutide-treated animals were no longer completely normoglycemic and the b-cell mass was significantly increased compared to overtly diabetic vehicle-treated animals, while b-cell proliferation was unaffected. 4 In the experiments with 60% pancreatectomized rats, 8 days treatment with liraglutide resulted in a significantly lower glucose excursion in response to oral glucose compared to vehicle treatment. Again, part of the antihyperglycemic effect was due to reduced food intake. No effect of liraglutide on b-cell mass was observed in these virtually normoglycemic animals. 5 In conclusion, treatment with liraglutide has marked antihyperglycemic effects in rodent models of b-cell deficiencies, and the in vivo effect of liraglutide on b-cell mass may in part depend on the metabolic state of the animals.

Intermediate NIA doses induced moderate changes of glucose tolerance [glucose area under the curve increased from 940 Ϯ 175 to 1,598 Ϯ 462 mM ⅐ min, P Ͻ 0.001 (100 mg/kg) and from 890 Ϯ 109 to 1,669 Ϯ 691 mM ⅐ min, P ϭ 0.003 (67 mg/kg)] with reduced insulin secretion [1,248 Ϯ 602 pM ⅐ min after 16 days and 1,566 Ϯ 190 pM ⅐ min after 60 days vs. 3,251 Ϯ 804 pM ⅐ min in normal animals (P Ͻ 0.001)] and ␤-cell mass [5.5 Ϯ 1.4 mg/kg after 27 days and 7.9 Ϯ 4.1 mg/kg after 60 days vs. 17.7 Ϯ 4.7 mg/kg in normal animals (P ϭ 0.009)]. The combination of NIA and STZ provided a model characterized by fasting and especially postprandial hyperglycemia and reduced, but maintained, insulin secretion and ␤-cell mass. This model holds promise as an important tool for studying the pathophysiology of diabetes and development of new pharmacological agents for treatment of the disease.in vivo pharmacology; large-animal model; glucose tolerance; ␤-cell reduction; glucose-stimulated insulin secretion.THE STUDY OF THE PATHOPHYSIOLOGY and treatment of diabetes requires well characterized animal models that resemble aspects of the disease in humans. Various forms of diabetes occur spontaneously or can be induced in several species of animals. Most of the available models are based on rodents; however, nonrodent models of diabetes are urgently needed as a valuable supplement to rodents for both practical and physiological reasons.The pig is useful as a model for human physiology and pathophysiology, because many organ systems resemble those of the human. Of special interest for the study of diabetes is the similarities to humans found in the clinical chemistry (7,10,12,14,24,26,55), nutrition and gastrointestinal tract (4,8,11,20,35,40,51), pancreas development and morphology (21,36,37,44,49,54), and metabolism (3, 35). These characteristics make swine an interesting species for studies of metabolic abnormalities in diabetes. The Göttingen minipig is especially suitable for long-term studies because of its small size and ease of handling, even at full maturity (6).Pancreatectomy has been investigated as a method of inducing diabetes in pigs (33,34,50,55). However, high rates of mortality have been observed postoperatively (50, 55), meaning that this technique should be used with great caution, and alternatives should be considered because of welfare considerations. Chemical induction of diabetes offers the advantage of preservation of both exocrine and endocrine cell populations other than ␤-cells, thus resembling the situation in human diabetes (55). Several stable models have been established for overt type 1 diabetes in the pig by the use of pharmacological induction of ␤-cell damage with streptozotocin (STZ), either as single or repeated injections (2, 15, 16, 27-29, 46, 55). Substantially increased fasting plasma glucose (FPG) levels and decreased insulin secretion in response to glucose stimuli have been obtained as well as increases in plasma triglycerides and total cholesterol (27,29). Late complications typical of diabetes, such...

Aims/hypothesis The hormone glucagon-like peptide 1 (GLP-1) is released in response to a meal from the intestinal L-cells, where it is processed from proglucagon by the proconvertase (PC)1/3. In contrast, in the adult islets proglucagon is processed to glucagon by the PC2 enzyme.

We have monitored whole-cell and single channel ATP-sensitive K+ (KATP) currents in isolated rat glucagon-secreting pancreatic A-cells. Tolbutamide produced a concentration-dependent decrease in the whole-cell KATP conductance (Ki = 6 microM) and initiated action potential firing. The K+ channel opener diazoxide, but not cromakalim or pinacidil, inhibited electrical activity and increased the whole-cell K+ conductance fourfold. ATP applied to the intracellular face of the membrane inhibited KATP channel activity with a Ki of 17 microM, an effect that could be counteracted by Mg-ADP and Mg-GDP. GTP and UTP did not affect KATP channel activity. Phosphatidylinositol 4,5-bisphosphate activated KATP channels inhibited by ATP after a delay of 90 s. In situ hybridisation demonstrated the expression of the mRNA encoding KATP channel subunits Kir6.2 and SUR1 but not Kir6.1 and SUR2. We conclude that rat pancreatic A-cells express KATP channels with the nucleotide-, sulphonylurea- and K+ channel-opener sensitivities expected for a channel formed by Kir6.2 and SUR1 subunits.