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Chun Zeng, Xin Yi, Danny Zipris, Hongli Liu, Lin Zhang, Qiaoyun Zheng, Krishnamurthy Malathi, Ge Jin, and Aimin Zhou

The cause of type 1 diabetes continues to be a focus of investigation. Studies have revealed that interferon α (IFNα) in pancreatic islets after viral infection or treatment with double-stranded RNA (dsRNA), a mimic of viral infection, is associated with the onset of type 1 diabetes. However, how IFNα contributes to the onset of type 1 diabetes is obscure. In this study, we found that 2-5A-dependent RNase L (RNase L), an IFNα-inducible enzyme that functions in the antiviral and antiproliferative activities of IFN, played an important role in dsRNA-induced onset of type 1 diabetes. Using RNase L-deficient, rat insulin promoter-B7.1 transgenic mice, which are more vulnerable to harmful environmental factors such as viral infection, we demonstrated that deficiency of RNase L in mice resulted in a significant delay of diabetes onset induced by polyinosinic:polycytidylic acid (poly I:C), a type of synthetic dsRNA, and streptozotocin, a drug which can artificially induce type 1-like diabetes in experimental animals. Immunohistochemical staining results indicated that the population of infiltrated CD8+T cells was remarkably reduced in the islets of RNase L-deficient mice, indicating that RNase L may contribute to type 1 diabetes onset through regulating immune responses. Furthermore, RNase L was responsible for the expression of certain proinflammatory genes in the pancreas under induced conditions. Our findings provide new insights into the molecular mechanism underlying β-cell destruction and may indicate novel therapeutic strategies for treatment and prevention of the disease based on the selective regulation and inhibition of RNase L.

Free access

JA Shaw, MI Delday, AW Hart, HM Docherty, CA Maltin, and K Docherty

The objective of these studies was to evaluate human insulin gene expression following intramuscular plasmid injection in non-diabetic rats as a potential approach to gene therapy for diabetes mellitus avoiding the need for immunosuppression. A wild-type human preproinsulin construct and a mutant construct in which PC2/PC3 sites were engineered to form furin consensus sites were evaluated in in vitro transfections of hepatocyte (HepG2) and myoblast (C2C12/L6) cell lines, primary rat myoblasts, and dermal fibroblasts. In vivo gene transfer by percutaneous plasmid injection of soleus muscle +/- prior notexin-induced myolysis was assessed in rats. In vitro transfection of non-neuroendocrine cell lines and primary cultures with wild-type human preproinsulin resulted in secretion of predominantly unprocessed proinsulin. Employing the mutant construct, there was significant processing to mature insulin (HepG2, 95%; C2C12, 75%; L6, 65%; primary myoblasts, 48%; neonatal fibroblasts, 56%; adult fibroblasts, 87%). In rats aged 5 weeks, circulating human (pro)insulin was detected from 1 to 37 days following plasmid injection and the potential of augmenting transfection efficiency by prior notexin injection was demonstrated (wild-type processing, 87%; mutant, 90%). Relative hypoglycaemia was confirmed by HbA1C (saline, 5.5%; wild type, 5.1%; mutant, 5.1% (P<0.05)). Human (pro)insulin levels and processing (wild-type, 8%; mutant, 53%) were lower in rats aged 9 months but relative hypoglycaemia was confirmed by serum glucose at 10 days (saline, 6.4 mmol/l; wild-type, 6.0 mmol/l; mutant, 5.4 mmol/l). In conclusion, prolonged constitutive systemic secretion of bioactive human (pro)insulin has been attained in non-neuroendocrine cells in vitro and in growing and mature rats following intramuscular plasmid injection.

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C Y Shan, J H Yang, Y Kong, X Y Wang, M Y Zheng, Y G Xu, Y Wang, H Z Ren, B C Chang, and L M Chen

For centuries, Berberine has been used in the treatment of enteritis in China, and it is also known to have anti-hyperglycemic effects in type 2 diabetic patients. However, as Berberine is insoluble and rarely absorbed in gastrointestinal tract, the mechanism by which it works is unclear. We hypothesized that it may act locally by ameliorating intestinal barrier abnormalities and endotoxemia. A high-fat diet combined with low-dose streptozotocin was used to induce type 2 diabetes in male Sprague Dawley rats. Berberine (100 mg/kg) was administered by lavage to diabetic rats for 2 weeks and saline was given to controls. Hyperinsulinemia and insulin resistance improved in the Berberine group, although there was no significant decrease in blood glucose. Berberine treatment also led to a notable restoration of intestinal villi/mucosa structure and less infiltration of inflammatory cells, along with a decrease in plasma lipopolysaccharide (LPS) level. Tight junction protein zonula occludens 1 (ZO1) was also decreased in diabetic rats but was restored by Berberine treatment. Glutamine-induced glucagon-like peptide 2 (GLP2) secretion from ileal tissue decreased dramatically in the diabetic group but was restored by Berberine treatment. Fasting insulin, insulin resistance index, plasma LPS level, and ZO1 expression were significantly correlated with GLP2 level. In type 2 diabetic rats, Berberine treatment not only augments GLP2 secretion and improves diabetes but is also effective in repairing the damaged intestinal mucosa, restoring intestinal permeability, and improving endotoxemia. Whether these effects are mechanistically related will require further studies, but they certainly support the hypothesis that Berberine acts via modulation of intestinal function.

Free access

L van Bloemendaal, J S ten Kulve, S E la Fleur, R G Ijzerman, and M Diamant

The delivery of nutrients to the gastrointestinal tract after food ingestion activates the secretion of several gut-derived mediators, including the incretin hormone glucagon-like peptide 1 (GLP-1). GLP-1 receptor agonists (GLP-1RA), such as exenatide and liraglutide, are currently employed successfully in the treatment of patients with type 2 diabetes mellitus. GLP-1RA improve glycaemic control and stimulate satiety, leading to reductions in food intake and body weight. Besides gastric distension and peripheral vagal nerve activation, GLP-1RA induce satiety by influencing brain regions involved in the regulation of feeding, and several routes of action have been proposed. This review summarises the evidence for a physiological role of GLP-1 in the central regulation of feeding behaviour and the different routes of action involved. Also, we provide an overview of presently available data on pharmacological stimulation of GLP-1 pathways leading to alterations in CNS activity, reductions in food intake and weight loss.

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Bernard Khoo and Tricia Mei-Mei Tan

Obesity represents an important public health challenge for the twenty-first century: globalised, highly prevalent and increasingly common with time, this condition is likely to reverse some of the hard-won gains in mortality accomplished in previous centuries. In the search for safe and effective therapies for obesity and its companion, type 2 diabetes mellitus (T2D), the gut hormone glucagon-like peptide-1 (GLP-1) has emerged as a forerunner and analogues thereof are now widely used in treatment of obesity and T2D, bringing proven benefits in improving glycaemia and weight loss and, notably, cardiovascular outcomes. However, GLP-1 alone is subject to limitations in terms of efficacy, and as a result, investigators are evaluating other gut hormones such as glucose-dependent insulinotropic peptide (GIP), glucagon and peptide YY (PYY) as possible partner hormones that may complement and enhance GLP-1’s therapeutic effects. Such combination gut hormone therapies are in pharmaceutical development at present and are likely to make it to market within the next few years. This review examines the physiological basis for combination gut hormone therapy and presents the latest clinical results that underpin the excitement around these treatments. We also pose, however, some hard questions for the field which need to be answered before the full benefit of such treatments can be realised.

Free access

ME Guibbolini, PM Pierson, and B Lahlou

Neurohypophysial hormone receptors and second messengers were studied in trout (Oncorhynchus mykiss) hepatocytes. Arginine vasotocin (AVT) and isotocin (IT) elicited a concentration-dependent inhibition of cAMP accumulation in the presence of 5x10(-8) M glucagon (maximal effect for 4.5x10(-7) M and 1.4x10(-7) M, half-maximal effect for 2.1x10(-8) M and 0.7x10(-8) M, AVT and IT respectively). The effect of glucagon was inhibited up to 90% by AVT and 80% by IT. While AVT inhibited (up to 50%) the basal cAMP production, IT had no such action. Specific V(1) or V(2) analogues (with reference to vasopressin in mammals) were used for pharmacological characterization of the type of neurohypophysial hormone receptor involved in this inhibition. The V(1) agonist [Phe(2), Orn(8)]-oxytocin inhibited the glucagon-stimulated cAMP production with a maximal effect for 6x10(-7) M and a half-maximal effect for 0.9x10(-8) M concentrations of the analogue. While the V(1) agonist reduced the glucagon-stimulated cAMP level by 70%, it showed only a tendency to reduce the basal level. The V(2) agonist [deamino(1), Val(4),d -Arg(8)]-vasopressin had no effect either on basal or on glucagon-stimulated cAMP production. The V(1) antagonist [d(CH(2))(5)(1), O-Me-Tyr(2), Arg(8)]-vasopressin totally reversed the 10(-8) M AVT-induced inhibition of 5x10(-8) M glucagon-stimulated cAMP production, whereas the V(2) antagonist [d(CH(2))(5)(1),d -Ile(2), Ile(4), Arg(8), Ala(9)]-vasopressin had no such effect. In this particular case, maximal and half-maximal effects of the V(1) antagonist were obtained for 2.3x10(-6) M and 1. 2x10(-6 )M respectively. Changes in intracellular calcium content were measured using the fluorescent probe FURA-2/AM. AVT and IT elicited a concentration-dependent increase in Ca(2+) accumulation. The comparison of the effect of 10(-8) M agonists versus AVT showed the following order of potency: AVT=IT>V(1) agonist>V(2) agonist. The V(1) antagonist reversed the AVT-induced Ca(2+) accumulation whereas the V(2) antagonist had no such effect. These results are taken as evidence for the presence in trout hepatocytes of neurohypophysial hormone receptors functionally close to the V(1a)-type linked to cAMP production and Ca(2+) mobilization.

Free access

SJ Fisher, ZQ Shi, HL Lickley, S Efendic, M Vranic, and A Giacca

At supraphysiological levels, IGF-I bypasses some forms of insulin resistance and has been proposed as a therapeutic agent in the treatment of diabetes. Unfortunately, side effects of high-dose IGF-I (100-250 microg/kg) have precluded its clinical use. Low-dose IGF-I (40-80 microg/kg), however, shows minimal side effects but has not been systematically evaluated. In our previous study under conditions of declining glucose, low-dose IGF-I infusion was more effective in stimulating glucose utilization, but less effective in suppressing glucose production and lipolysis than low-dose insulin. However, under conditions of hyperglycemia, we could not observe any differential effects between high-dose infusions of IGF-I and insulin. To determine whether the differential effects of IGF-I and insulin are dose-related or related to the prevailing glucose level, 3 h glucose clamps were performed in the same animal model as in the previous studies, i.e. the moderately hyperglycemic (175 mg/dl) insulin-infused depancreatized dog, with additional infusions of low-dose IGF-I (67.8 microg/kg, i.e. 29.1 microg/kg bolus plus 0.215 microg/kg( )per min infusion; n=5) or insulin 49.5 mU/kg (9 mU/kg bolus plus 0.45 mU/kg per min; n=7). As in the previous study under conditions of declining glucose, low-dose IGF-I had significant metabolic effects in vivo, in our model of complete absence of endogenous insulin secretion. Glucose production was similarly suppressed with both IGF-I and insulin, by 54+/-3 and 56+/-2% s.e. (P=NS) respectively. Glucose utilization was stimulated to the same extent (IGF-I 5.2+/-0.2, insulin 5.5+/-0.3 mg/kg per min, P=NS). Glucagon, free fatty acid, glycerol, alanine and beta-hydroxybutyrate, were suppressed, while lactate and pyruvate levels were raised, similarly with IGF-I and insulin. We conclude that: (i) differential effects of IGF-I and insulin may be masked under hyperglycemic conditions, independent of the hormone dose; (ii) low-dose IGF-I has no selective advantage over additional insulin in suppressing glucose production and lipolysis, nor in stimulating glucose utilization during hyperglycemia and subbasal insulin infusion when insulin secretion is absent, as in type 1 diabetes mellitus.

Free access

Zhengu Liu, Violeta Stanojevic, Luke J Brindamour, and Joel F Habener

Type 2 diabetes, often associated with obesity, results from a deficiency of insulin production and action manifested in increased blood levels of glucose and lipids that further promote insulin resistance and impair insulin secretion. Glucolipotoxicity caused by elevated plasma glucose and lipid levels is a major cause of impaired glucose-stimulated insulin secretion from pancreatic β-cells, due to increased oxidative stress, and insulin resistance. Glucagon-like peptide-1 (GLP1), an insulinotropic glucoincretin hormone, is known to promote β-cell survival via its actions on its G-protein-coupled receptor on β-cells. Here, we report that a nonapeptide, GLP1(28–36)amide, derived from the C-terminal domain of the insulinotropic GLP1, exerts cytoprotective actions on INS-1 β-cells and on dispersed human islet cells in vitro in conditions of glucolipotoxicity and increased oxidative stress independently of the GLP1 receptor. The nonapeptide appears to enter preferably stressed, glucolipotoxic cells compared with normal unstressed cells. It targets mitochondria and improves impaired mitochondrial membrane potential, increases cellular ATP levels, inhibits cytochrome c release, caspase activation, and apoptosis, and enhances the viability and survival of INS-1 β-cells. We propose that GLP1(28–36)amide might be useful in alleviating β-cell stress and might improve β-cell functions and survival.

Free access

B D Green, N Irwin, V A Gault, C J Bailey, F P M O’Harte, and P R Flatt

Glucagon-like peptide-1 (GLP-1) is a potent insulinotropic hormone proposed to play a role in both the pathophysiology and treatment of type 2 diabetes. This study has employed the GLP-1 receptor antagonist, exendin-4(9–39)amide (Ex(9–39)) to evaluate the role of endogenous GLP-1 in genetic obesity-related diabetes and related metabolic abnormalities using ob/ob and normal mice. Acute in vivo antagonistic potency of Ex(9–39) was confirmed in ob/ob mice by blockade of the insulin-releasing and anti-hyperglycaemic actions of intraperitoneal GLP-1. In longer term studies, ob/ob mice were given once daily injections of Ex(9–39) or vehicle for 11 days. Feeding activity, body weight, and both basal and glucose-stimulated insulin secretion were not significantly affected by chronic Ex(9–39) treatment. However, significantly elevated basal glucose concentrations and impaired glucose tolerance were evident at 11 days. These disturbances in glucose homeostasis were independent of changes of insulin sensitivity and reversed by discontinuation of the Ex(9–39) for 9 days. Similar treatment of normal mice did not affect any of the parameters measured. These findings illustrate the physiological extrapancreatic glucose-lowering actions of GLP-1 in ob/ob mice and suggest that the endogenous hormone plays a minor role in the metabolic abnormalities associated with obesity-related diabetes.

Free access

L Monetini, F Barone, L Stefanini, A Petrone, T Walk, G Jung, R Thorpe, P Pozzilli, and MG Cavallo

Enhanced cellular immune response to bovine beta-casein has been reported in patients with type 1 diabetes. In this study we aimed to establish beta-casein-specific T cell lines from newly diagnosed type 1 diabetic patients and to characterise these cell lines in terms of phenotype and epitope specificity. Furthermore, since sequence homologies exist between beta-casein and putative beta-cell autoantigens, reactivity to the latter was also investigated. T cell lines were generated from the peripheral blood of nine recent onset type 1 diabetic patients with different HLA-DQ and -DR genotypes, after stimulation with antigen pulsed autologous irradiated antigen presenting cells (APCs) and recombinant human interleukin-2 (rhIL-2). T cell line reactivity was evaluated in response to bovine beta-casein, to 18 overlapping peptides encompassing the whole sequence of beta-casein and to beta-cell antigens, including the human insulinoma cell line, CM, and a peptide from the beta-cell glucose transporter, GLUT-2. T cell lines specific to beta-casein could not be isolated from HLA-matched and -unmatched control subjects. beta-Casein T cell lines reacted to different sequences of the protein, however a higher frequency of T cell reactivity was observed towards the C-terminal portion (peptides B05-14, and B05-17 in 5/9 and 4/9 T cell lines respectively). Furthermore, we found that 1 out of 9 beta-casein-specific T cell lines reacted also to the homologous peptide from GLUT-2, and that 3 out of 4 of tested cell lines reacted also to extracts of the human insulinoma cell line, CM. We conclude that T cell lines specific to bovine beta-casein can be isolated from the peripheral blood of patients with type 1 diabetes; these cell lines react with multiple and different sequences of the protein particularly towards the C-terminal portion. In addition, reactivity of beta-casein T cell lines to human insulinoma extracts and GLUT-2 peptide was detected, suggesting that the potential cross-reactivity with beta-cell antigens deserves further investigation.