No abstract

This study explored the role of irisin as a new pancreatic β-cell secretagogue and survival factor and its potential role in the communication between skeletal muscle and pancreatic β-cells under lipotoxic conditions. Recombinant irisin stimulated insulin biosynthesis and glucose-stimulated insulin secretion (GSIS) in a PKA-dependent manner and prevented saturated fatty acid-induced apoptosis in human and rat pancreatic β-cells, as well as in human and murine pancreatic islets, via AKT/BCL2 signaling. Treatment of myotubes with 0.5 mmol/L palmitate for 4 h, but not with oleate, promoted an increase in irisin release in the culture medium. Moreover, increased serum levels of irisin were observed in mice fed with a high-fat diet. Mouse serum rich in irisin and the conditioned medium from myotubes exposed to palmitate for 4 h significantly reduced apoptosis of murine pancreatic islets and insulin-secreting INS-1E cells, respectively, and this was abrogated in the presence of an irisin-neutralizing antibody. Finally, in vivo administration of irisin improved GSIS and increased β-cell proliferation. In conclusion, irisin can promote β-cell survival and enhance GSIS and may thus participate in the communication between skeletal muscle and β-cells under conditions of excess saturated fatty acids.

Aims/hypothesis The mechanisms of the protective effects of exendin-4 on NEFA-induced beta cell apoptosis were investigated. Methods The effects of exendin-4 and palmitate were evaluated in human and murine islets, rat insulin-secreting INS-1E cells and murine glucagon-secreting alpha-TC1-6 cells. mRNA and protein expression/phosphorylation were measured by real-time RT-PCR and immunoblotting or immunofluorescence, respectively. Small interfering (si)RNAs for Ib1 and Gpr40 were used. Cell apoptosis was quantified by two independent assays. Insulin release was assessed with an insulin ELISA. Results Exposure of human and murine primary islets and INS-1E cells, but not alpha-TC1-6 cells, to exendin-4 inhibited phosphorylation of the stress kinases, c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (MAPK), and prevented apoptosis in response to palmitate. Exendin-4 increased the protein content of islet-brain 1 (IB1), an endogenous JNK blocker; however, siRNA-mediated reduction of IB1 did not impair the ability of exendin-4 to inhibit JNK and prevent apoptosis. Exendin-4 reduced G-protein-coupled receptor 40 (GPR40) expression and inhibited palmitateinduced phosphorylation of mitogen-activated kinase kinase (MKK)4 and MKK7. The effects of exendin-4 were abrogated in the presence of the protein kinase A (PKA) inhibitors, H89 and KT5720. Knockdown of GPR40, as well as use of a specific GPR40 antagonist, resulted in diminished palmitateinduced JNK and p38 MAPK phosphorylation and apoptosis. Furthermore, inhibition of JNK and p38 MAPK activity prevented palmitate-induced apoptosis. Conclusions/interpretation Exendin-4 counteracts the proapoptotic effects of palmitate in beta cells by reducing GPR40 expression and inhibiting MKK7-and MKK4-dependent phosphorylation of the stress kinases, JNK and p38 MAPK, in a PKA-dependent manner.

Laparoscopic distal pancreatectomy has become an increasingly used procedure in the surgical treatment of benign or borderline cystic and endocrine tumours. The feasibility and safety of this technique is well known but its results when compared with open distal pancreatectomy were rarely reported in literature. Data from 22 consecutive patients who underwent laparoscopic distal pancreatectomy were recorded in a prospective database from January 2006 to January 2010. These patients were matched with 22 patients who underwent open distal pancreatectomy from January 2000 to December 2005, regarding age, gender, American Society of Anesthesiologists score, pancreatic pathology. Intraoperative parameters and postoperative outcome were compared between the two groups. Blood loss, amount of analgesic drugs administered, postoperative mortality and morbidity and pancreatic fistula rate were similar in laparoscopic and open groups. Tumour size was significantly smaller in laparoscopic group (2.0 ± 3.3 vs. 5.0 ± 4.2 cm; P = 0.038). Operative time was significantly shorter in open group (145 ± 49 vs. 225 ± 83 min, P = 0.045). Time to adequate oral intake and length of postoperative hospital stay were significantly better in laparoscopic group than in open group (3.0 ± 0.8 vs. 4.0 ± 0.7 days; P = 0.030 and 8.0 ± 1.3 vs. 11.0 ± 3.0 days; P = 0.011, respectively). Laparoscopic distal pancreatectomy is a feasible and safe surgical approach as well as open distal pancreatectomy.

No abstract

Incretins are gut hormones that potentiate glucose-stimulated insulin secretion (GSIS) after meals. Glucagon-like peptide-1 (GLP-1) is the most investigated incretin hormone, synthesized mainly by L cells in the lower gut tract. GLP-1 promotes β-cell function and survival and exerts beneficial effects in different organs and tissues. Irisin, a myokine released in response to a high-fat diet and exercise, enhances GSIS. Similar to GLP-1, irisin augments insulin biosynthesis and promotes accrual of β-cell functional mass. In addition, irisin and GLP-1 share comparable pleiotropic effects and activate similar intracellular pathways. The insulinotropic and extra-pancreatic effects of GLP-1 are reduced in type 2 diabetes (T2D) patients but preserved at pharmacological doses. GLP-1 receptor agonists (GLP-1RAs) are therefore among the most widely used antidiabetes drugs, also considered for their cardiovascular benefits and ability to promote weight loss. Irisin levels are lower in T2D patients, and in diabetic and/or obese animal models irisin administration improves glycemic control and promotes weight loss. Interestingly, recent evidence suggests that both GLP-1 and irisin are also synthesized within the pancreatic islets, in α- and β-cells, respectively. This review aims to describe the similarities between GLP-1 and irisin and to propose a new potential axis–involving the gut, muscle, and endocrine pancreas that controls energy homeostasis.

Aims/hypothesis The role of the redox adaptor protein p66 Shc as a potential mediator of saturated fatty acid (FA)-induced beta cell death was investigated. Methods The effects of the FA palmitate on p66 Shc expression were evaluated in human and murine islets and in rat insulinsecreting INS-1E cells. p66 Shc expression was also measured in islets from mice fed a high-fat diet (HFD) and from human donors with different BMIs. Cell apoptosis was quantified by two independent assays. The role of p66 Shc was investigated using pancreatic islets from p66 Shc−/− mice and in INS-1E cells with knockdown of p66 Shc or overexpression of wildtype and phosphorylation-defective p66 Shc . Production of reactive oxygen species (ROS) was evaluated by the dihydroethidium oxidation method. Results Palmitate induced a selective increase in p66 Shc protein expression and phosphorylation on Ser 36 and augmented apoptosis in human and mouse islets and in INS-1E cells. Inhibiting the tumour suppressor protein p53 prevented both the palmitate-induced increase in p66 Shc expression and beta cell apoptosis. Palmitate-induced apoptosis was abrogated in islets from p66 Shc−/− mice and following p66 Shc knockdown in INS-1E cells; by contrast, overexpression of p66 Shc , but not that of the phosphorylation-defective p66 Shc mutant, enhanced palmitate-induced apoptosis. The pro-apoptotic effects of p66 Shc were dependent upon its c-Jun N-terminal kinasemediated phosphorylation on Ser 36 and associated with generation of ROS. p66 Shc protein expression and function were also elevated in islets from HFD-fed mice and from obese/ overweight cadaveric human donors. Conclusions/interpretation p53-dependent augmentation of p66 Shc expression and function represents a key signalling response contributing to beta cell apoptosis under conditions of lipotoxicity.

The effects of prolonged exposure of pancreatic β-cells to high saturated fatty acids on glucagon-like peptide-1 (GLP-1) action were investigated. Murine islets, human pancreatic 1.1B4 cells, and rat INS-1E cells were exposed to palmitate for 24 hours. mRNA and protein expression/phosphorylation were measured by real-time RT-PCR and immunoblotting, respectively. Specific short interfering RNAs were used to knockdown expression of the GLP-1 receptor (Glp1r) and Srebf1. Insulin release was assessed with a specific ELISA. Exposure of murine islets, as well as of human and INS-1E β-cells, to palmitate reduced the ability of exendin-4 to augment insulin mRNA levels, protein content, and release. In addition, palmitate blocked exendin-4-stimulated cAMP-response element-binding protein and v-akt murine thymoma viral oncogene homolog phosphorylation, whereas phosphorylation of MAPK-ERK kinase-1/2 and ERK-1/2 was not altered. Similarly, RNA interference-mediated suppression of Glp1r expression prevented exendin-4-induced cAMP-response element-binding protein and v-akt murine thymoma viral oncogene homolog phosphorylation, but did not impair exendin-4 stimulation of MAPK-ERK kinase-1/2 and ERK-1/2. Both islets from mice fed a high fat diet and human and INS-1E β-cells exposed to palmitate showed reduced GLP-1 receptor and pancreatic duodenal homeobox-1 (PDX-1) and increased sterol regulatory element-binding protein (SREBP-1C) mRNA and protein levels. Furthermore, suppression of SREBP-1C protein expression prevented the reduction of PDX-1 and GLP-1 receptor levels and restored exendin-4 signaling and action. Finally, treatment of INS-1E cells with metformin for 24 h resulted in inhibition of SREBP-1C expression, increased PDX-1 and GLP-1 receptor levels, consequently, enhancement of exendin-4-induced insulin release. Palmitate impairs exendin-4 effects on β-cells by reducing PDX-1 and GLP-1 receptor expression and signaling in a SREBP-1C-dependent manner. Metformin counteracts the impairment of GLP-1 receptor signaling induced by palmitate.