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Free access

Ashley I Taylor, Nigel Irwin, Aine M McKillop, Steven Patterson, Peter R Flatt and Victor A Gault

Recently, glucagon-like peptide 1 (GLP1) and glucose-dependent insulinotropic polypeptide (GIP) have received much attention regarding possible roles in aetiology and treatment of type 2 diabetes. However, peptides co-secreted from the same enteroendocrine cells are less well studied. The present investigation was designed to characterise the in vitro and in vivo effects of xenin, a peptide co-secreted with GIP from intestinal K-cells. We examined the enzymatic stability, insulin-releasing activity and associated cAMP production capability of xenin in vitro. In addition, the effects of xenin on satiety, glucose homoeostasis and insulin secretion were examined in vivo. Xenin was time dependently degraded (t 1/2=162±6 min) in plasma in vitro. In clonal BRIN-BD11 cells, xenin stimulated insulin secretion at 5.6 mM (P<0.05) and 16.7 mM (P<0.05 to P<0.001) glucose levels compared to respective controls. Xenin also exerted an additive effect on GIP, GLP1 and neurotensin-mediated insulin secretion. In clonal β-cells, xenin did not stimulate cellular cAMP production, alter membrane potential or elevate intra-cellular Ca2 +. In normal mice, xenin exhibited a short-acting (P<0.01) satiety effect at high dosage (500 nmol/kg). In overnight fasted mice, acute injection of xenin enhanced glucose-lowering and elevated insulin secretion when injected concomitantly or 30 min before glucose. These effects were not observed when xenin was administered 60 min before the glucose challenge, reflecting the short half-life of the native peptide in vivo. Overall, these data demonstrate that xenin may have significant metabolic effects on glucose control, which merit further study.

Free access

RN Kulkarni, ZL Wang, RM Wang, DM Smith, MA Ghatei and SR Bloom

We have studied the effects of first and second generation sulphonylureas on the release of insulin and neuropeptide tyrosine (NPY) from hamster insulinoma tumour (HIT T15) cells and isolated rat islets. In the presence of 5.5 mmol/l glucose all sulphonylureas stimulated insulin release from the HIT cells (P<0.01 ANOVA, n> or =4) but only glibenclamide (GLIB, 10 micromol/l) stimulated the release of NPY (mean+/-s.e.m. control 11.1+/-1.3 vs GLIB 28.4+/-4.1 fmol/h per 10(6) cells, P<0001, n=16). In isolated perifused rat islets both glibenclamide (10 micromol/l) (control 3.5+/-0.3 vs GLIB 6. 3+/-0.2 fmol/min per islet, P<0.01, n=6) and tolbutamide (50 micromol/l) (control 4.7+/-0.1 vs TOLB 6.7+/-0.3 fmol/min per islet, P<0.01, n=6) enhanced glucose (8 mmol/l)-stimulated insulin release. However, only glibenclamide stimulated the release of NPY from the islets (control 3.4+/-0.8 vs GLIB 24.5+/-5 attomol/min per islet, P<0.01, n=6). Similar results were obtained in islets isolated from dexamethasonetreated rats. Glibenclamide treatment of HIT cells showed a prompt insulin release (10 min) while NPY secretion was slower (60 min), suggesting that internalization of the sulphonylurea is required to stimulate NPY release. Glibenclamide, the most common oral therapeutic agent in type 2 diabetes mellitus, is associated with release of the autocrine insulin secretion inhibitor, NPY.

Free access

Andréa M Caricilli, Paula H Nascimento, José R Pauli, Daniela M L Tsukumo, Lício A Velloso, José B Carvalheira and Mário J A Saad

The aims of the present study were to investigate the expression of toll-like receptor 2 (TLR2) in muscle and white adipose tissue (WAT) of diet-induced obesity (DIO) mice, and also the effects of its inhibition, with the use of TLR2 antisense oligonucleotide (ASON), on insulin sensitivity and signaling. The expression of TLR2 was increased in muscle and WAT of DIO mice, compared with those that received standard chow. Inhibition of TLR2 in DIO mice, by TLR2 ASON, improved insulin sensitivity and signaling in muscle and WAT. In addition, data show that the inhibition of TLR2 expression prevents the activation of IKBKB, MAPK8, and serine phosphorylation of IRS1 in DIO mice, suggesting that TLR2 is a key modulator of the crosstalk between inflammatory and metabolic pathways. We, therefore, suggest that a selective interference with TLR2 presents an attractive opportunity for the treatment of insulin resistance in obesity and type 2 diabetes.

Open access

A Edlund, M Barghouth, M Hühn, M Abels, J S E Esguerra, I G Mollet, E Svedin, A Wendt, E Renström, E Zhang, N Wierup, B J Scholte, M Flodström-Tullberg and L Eliasson

Cystic fibrosis-related diabetes (CFRD) is a common complication for patients with cystic fibrosis (CF), a disease caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR). The cause of CFRD is unclear, but a commonly observed reduction in first-phase insulin secretion suggests defects at the beta cell level. Here we aimed to examine alpha and beta cell function in the Cftr tm1 EUR/F508del mouse model (C57BL/6J), which carries the most common human mutation in CFTR, the F508del mutation. CFTR expression, beta cell mass, insulin granule distribution, hormone secretion and single cell capacitance changes were evaluated using islets (or beta cells) from F508del mice and age-matched wild type (WT) mice aged 7–10 weeks. Granular pH was measured with DND-189 fluorescence. Serum glucose, insulin and glucagon levels were measured in vivo, and glucose tolerance was assessed using IPGTT. We show increased secretion of proinsulin and concomitant reduced secretion of C-peptide in islets from F508del mice compared to WT mice. Exocytosis and number of docked granules was reduced. We confirmed reduced granular pH by CFTR stimulation. We detected decreased pancreatic beta cell area, but unchanged beta cell number. Moreover, the F508del mutation caused failure to suppress glucagon secretion leading to hyperglucagonemia. In conclusion, F508del mice have beta cell defects resulting in (1) reduced number of docked insulin granules and reduced exocytosis and (2) potential defective proinsulin cleavage and secretion of immature insulin. These observations provide insight into the functional role of CFTR in pancreatic islets and contribute to increased understanding of the pathogenesis of CFRD.

Restricted access

Monisha Rajasekaran, Ok-Joo Sul, Eun-Kyung Choi, Ji-Eun Kim, Jae-Hee Suh and Hye-Seon Choi

Obesity is strongly associated with chronic inflammation for which adipose tissue macrophages play a critical role. The objective of this study is to identify monocyte chemoattractant protein-1 (MCP-1, CCL2) as a key player governing M1–M2 macrophage polarization and energy balance. We evaluated body weight, fat mass, adipocyte size and energy expenditure as well as core body temperature of Ccl2 knockout mice compared with wild-type mice. Adipose tissues, differentiated adipocyte and bone marrow-derived macrophages were assessed by qPCR, Western blot analysis and histochemistry. MCP-1 deficiency augmented energy expenditure by promoting browning in white adipose tissue and brown adipose tissue activity via increasing the expressions of Ucp1, Prdm16, Tnfrsf9, Ppargc1a, Nrf1 and Th and mitochondrial DNA copy number. MCP-1 abrogation promoted M2 polarization which is characterized by increased expression of Arg1, Chil3, Il10 and Klf4 whereas it decreased M1 polarization by decreased p65 nuclear translocation and attenuated expression of Itgax, Tnf and Nos2, leading to increased browning of adipocytes. Enhanced M2 polarization and attenuated M1 polarization in the absence of MCP-1 are independent. Collectively, our results suggest that the action of MCP-1 in macrophages modulates energy expenditure by impairing browning in adipose tissue.

Free access

Jae Woo Jung, Chihoon Ahn, Sun Young Shim, Peter C Gray, Witek Kwiatkowski and Senyon Choe

Activins and bone morphogenetic proteins (BMPs) share activin type 2 signaling receptors but utilize different type 1 receptors and Smads. We designed AB215, a potent BMP2-like Activin A/BMP2 chimera incorporating the high-affinity type 2 receptor-binding epitope of Activin A. In this study, we compare the signaling properties of AB215 and BMP2 in HEK293T cells and gonadotroph LβT2 cells in which Activin A and BMP2 synergistically induce FSHβ. In HEK293T cells, AB215 is more potent than BMP2 and competitively blocks Activin A signaling, while BMP2 has a partial blocking activity. Activin A signaling is insensitive to BMP pathway antagonism in HEK293T cells but is strongly inhibited by constitutively active (CA) BMP type 1 receptors. By contrast, the potencies of AB215 and BMP2 are indistinguishable in LβT2 cells and although AB215 blocks Activin A signaling, BMP2 has no inhibitory effect. Unlike HEK293T, Activin A signaling is strongly inhibited by BMP pathway antagonism in LβT2 cells but is largely unaffected by CA BMP type 1 receptors. BMP2 increases phospho-Smad3 levels in LβT2 cells, in both the absence and the presence of Activin A treatment, and augments Activin A-induced FSHβ. AB215 has the opposite effect and sharply decreases basal phospho-Smad3 levels and blocks Smad2 phosphorylation and FSHβ induction resulting from Activin A treatment. These findings together demonstrate that while AB215 activates the BMP pathway, it has opposing effects to those of BMP2 on FSHβ induction in LβT2 cells apparently due to its ability to block Activin A signaling.

Free access

Junhong Chen, Jing Sun, Michelle E Doscas, Jin Ye, Ashley J Williamson, Yanchun Li, Yi Li, Richard A Prinz and Xiulong Xu

p70 S6 kinase (S6K1) is a serine/threonine kinase that phosphorylates the insulin receptor substrate-1 (IRS-1) at serine 1101 and desensitizes insulin receptor signaling. S6K1 hyperactivation due to overnutrition leads to hyperglycemia and type 2 diabetes. Our recent study showed that A77 1726, the active metabolite of the anti-rheumatoid arthritis (RA) drug leflunomide, is an inhibitor of S6K1. Whether leflunomide can control hyperglycemia and sensitize the insulin receptor has not been tested. Here we report that A77 1726 increased AKTS473/T308 and S6K1T389 phosphorylation but decreased S6S235/236 and IRS-1S1101 phosphorylation in 3T3-L1 adipocytes, C2C12 and L6 myotubes. A77 1726 increased insulin receptor tyrosine phosphorylation and binding of the p85 subunit of the PI-3 kinase to IRS-1. A77 1726 enhanced insulin-stimulated glucose uptake in L6 myotubes and 3T3-L1 adipocytes, and enhanced insulin-stimulated glucose transporter type 4 (GLUT4) translocation to the plasma membrane of L6 cells. Finally, we investigated the anti-hyperglycemic effect of leflunomide on ob/ob and high-fat diet (HFD)-induced diabetes mouse models. Leflunomide treatment normalized blood glucose levels and overcame insulin resistance in glucose and insulin tolerance tests in ob/ob and HFD-fed mice but had no effect on mice fed a normal chow diet (NCD). Leflunomide treatment increased AKTS473/T308 phosphorylation in the fat and muscle of ob/ob mice but not in normal mice. Our results suggest that leflunomide sensitizes the insulin receptor by inhibiting S6K1 activity in vitro, and that leflunomide could be potentially useful for treating patients with both RA and diabetes.

Restricted access

Wang-Yang Xu, Yan Shen, Houbao Zhu, Junhui Gao, Chen Zhang, Lingyun Tang, Shun-Yuan Lu, Chun-Ling Shen, Hong-Xin Zhang, Ziwei Li, Peng Meng, Ying-Han Wan, Jian Fei and Zhu-Gang Wang

Obesity and type 2 diabetes (T2D) are both complicated endocrine disorders resulting from an interaction between multiple predisposing genes and environmental triggers, while diet and exercise have key influence on metabolic disorders. Previous reports demonstrated that 2-aminoadipic acid (2-AAA), an intermediate metabolite of lysine metabolism, could modulate insulin secretion and predict T2D, suggesting the role of 2-AAA in glycolipid metabolism. Here, we showed that treatment of diet-induced obesity (DIO) mice with 2-AAA significantly reduced body weight, decreased fat accumulation and lowered fasting glucose. Furthermore, Dhtkd1−/− mice, in which the substrate of DHTKD1 2-AAA increased to a significant high level, were resistant to DIO and obesity-related insulin resistance. Further study showed that 2-AAA induced higher energy expenditure due to increased adipocyte thermogenesis via upregulating PGC1α and UCP1 mediated by β3AR activation, and stimulated lipolysis depending on enhanced expression of hormone-sensitive lipase (HSL) through activating β3AR signaling. Moreover, 2-AAA could alleviate the diabetic symptoms of db/db mice. Our data showed that 2-AAA played an important role in regulating glycolipid metabolism independent of diet and exercise, implying that improving the level of 2-AAA in vivo could be developed as a strategy in the treatment of obesity or diabetes.

Free access

Ruben Rodriguez, Jacqueline N Minas, Jose Pablo Vazquez-Medina, Daisuke Nakano, David G Parkes, Akira Nishiyama and Rudy M Ortiz

Obesity is associated with the inappropriate activation of the renin-angiotensin system (RAS), which increases arterial pressure, impairs insulin secretion and decreases peripheral tissue insulin sensitivity. RAS blockade reverses these detriments; however, it is not clear whether the disease state of the organism and treatment duration determine the beneficial effects of RAS inhibition on insulin secretion and insulin sensitivity. Therefore, the objective of this study was to compare the benefits of acute vs chronic angiotensin receptor type 1 (AT1) blockade started after the onset of obesity, hyperglycemia and hypertension on pancreatic function and peripheral insulin resistance. We assessed adipocyte morphology, glucose intolerance, pancreatic redox balance and insulin secretion after 2 and 11 weeks of AT1 blockade in the following groups of rats: (1) untreated Long-Evans Tokushima Otsuka (lean control; n = 10), (2) untreated Otsuka Long-Evans Tokushima Fatty (OLETF; n = 12) and (3) OLETF + ARB (ARB; 10 mg olmesartan/kg/day by oral gavage; n = 12). Regardless of treatment duration, AT1 blockade decreased systolic blood pressure and fasting plasma triglycerides, whereas chronic AT1 blockade decreased fasting plasma glucose, glucose intolerance and the relative abundance of large adipocytes by 22, 36 and 70%, respectively. AT1 blockade, however, did not improve pancreatic oxidative stress or reverse impaired insulin secretion. Collectively, these data show that AT1 blockade after the onset of obesity, hyperglycemia and hypertension improves peripheral tissue insulin sensitivity, but cannot completely reverse the metabolic derangement characterized by impaired insulin secretion once it has been compromised.

Free access

Christian Hölscher

The incretin hormone glucagon-like peptide 1 (GLP-1) has many effects in the body. It is best known for the ‘incretin effect’, facilitating insulin release from the pancreas under hyperglycaemic conditions. Building on this, GLP-1 mimetics have been developed as a treatment for type 2 diabetes. In the course of monitoring of patients, it has become apparent that GLP-1 mimetics have a range of other physiological effects in the body. In preclinical trials, a substantial body of evidence has been built that these mimetics have neuroprotective and anti-inflammatory effects. GLP-1 also has very similar growth-factor-like properties to insulin, which is presumably the underlying basis of the neuroprotective effects. In preclinical studies of Alzheimer's disease (AD), Parkinson's disease (PD), stroke and other neurodegenerative disorders, it has been shown that most GLP-1 mimetics cross the blood–brain barrier and show impressive neuroprotective effects in numerous studies. In animal models of AD, GLP-1 mimetics such as exendin-4, liraglutide and lixisenatide have shown protective effects in the CNS by reducing β-amyloid plaques, preventing loss of synapses and memory impairments, and reducing oxidative stress and the chronic inflammatory response in the brain. In animal models of PD, exendin-4 showed protection of dopaminergic neurons in the substantia nigra and prevention of dopamine loss in the basal ganglia while preserving motor control. These encouraging findings have spawned several clinical trials, some of which have shown encouraging initial results. Therefore, GLP-1 mimetics show great promise as a novel treatment for neurodegenerative conditions.