In vivo expression of GLP-1/IgG-Fc fusion protein enhances beta-cell mass and protects against streptozotocin-induced diabetes

Glucagon-like peptide 1 (GLP-1) and its analogue exendin-4 (Ex4) have displayed potent glucose homeostasis-modulating characteristics in type 2 diabetes (T2D). However, there are few reports of effectiveness in type 1 diabetes (T1D) therapy, where there is massive loss of beta cells. We previously described a novel GLP-1 analogue consisting of the fusion of active GLP-1 and IgG heavy chain constant regions (GLP-1/IgG-Fc), and showed that in vivo expression of the protein, via electroporation-enhanced intramuscular plasmid-based gene transfer, normalized blood glucose levels in T2D-prone db/db mice. In the present study, GLP-1/IgG-Fc and Ex4/IgG-Fc were independently tested in multiple low-dose streptozotocin-induced T1D. Both GLP-1/IgG-Fc and Ex4/IgG-Fc effectively reduced fed blood glucose levels in treated mice and ameliorated diabetes symptoms, where as control IgG-Fc had no effect. Treatment with GLP-1/IgG-Fc or Ex4/IgG-Fc improved glucose tolerance and increased circulating insulin and GLP-1 levels. It also significantly enhanced islet beta-cell mass, which is likely a major factor in the amelioration of diabetes. This suggests that GLP-1/IgG-Fc gene therapy may be applicable to diseases where there is either acute or chronic beta-cell injury.     

GLP-1 gene delivery for the treatment of type 2 diabetes

Glucagon-like peptide-1 (GLP-1) is a potent insulinotrophic hormone, which makes GLP-1 an attractive candidate for the treatment of type 2 diabetes. However, the short plasma half-life of the active forms of GLP-1 poses an obstacle to the sustained delivery of this peptide. In this study, we evaluated the effect of GLP-1 gene delivery both in vitro and in vivo using a new plasmid constructed with a modified GLP-1 (7-37) cDNA. This cDNA contains a furin cleavage site between the start codon and the GLP-1 coding region. The expression of the GLP-1 gene was driven by a chicken β-actin promoter (pβGLP1). The level of the GLP-1 mRNA was evaluated by RT-PCR 24 h after transfection. The in vitro results showed a dose-dependent expression of GLP-1. Coculture assay of the GLP-1 plasmid-transfected cells with isolated rat islet cells demonstrated that GLP-1 increased insulin secretion by twofold, compared to controls during a hyperglycemic challenge. A single injection of polyethyleneimine/pβGLP1 complex into ZDF rats resulted in increasing insulin secretion and decreasing blood glucose level that was maintained for 2 weeks. This GLP-1 gene delivery system may provide an effective and safe treatment modality for type 2 diabetes.     

Effective and safe gene-based delivery of GLP-1 using chitosan/plasmid-DNA therapeutic nanocomplexes in an animal model of type 2 diabetes

Glucagon-like peptide-1 (GLP-1) is an incretin hormone that regulates blood glucose level post-prandially. It has been proposed that GLP-1 can be used in type 2 diabetes (T2D) mellitus treatment because of its insulinotropic action. Despite its remarkable advantages, GLP-1 suffers the disadvantage of an extremely short half-life owing to its degradation by the dipeptidyl peptidase IV protease. One way of overcoming this drawback is GLP-1 gene delivery. Here we show effective and safe gene-based delivery of GLP-1 using chitosan/plasmid-DNA therapeutic nanocomplexes (TNCs) in Zucker diabetic fatty (ZDF) animal model of T2D. The expression plasmid fused the GLP-1 gene to a Furin cleavage site was driven by a cytomegalovirus promoter/enhancer. TNCs were prepared by mixing this plasmid with chitosans of specific molecular weight (MW), degree of deacetylation (DDA) and ratio of chitosan amine to DNA phosphate (N:P ratio). Animals injected with the TNC chitosan 92-10-5 (DDA-MW-N:P) showed GLP-1 plasma levels of about fivefold higher than that in non-treated animals and the insulinotropic effect of recombinant GLP-1 was shown by a threefold increase in plasma insulin concentration when compared with untreated animals. Intraperitoneal glucose tolerance tests revealed an efficacious decrease of blood glucose compared with controls for up to 24 days after treatment, where injections of this formulation allowed near-normalization of blood glucose level. TNCs composed of specific chitosans and GLP-1-expressing plasmid constructs showed an impressive ability to harness the profound therapeutic potential of GLP-1 for the treatment of T2D mellitus.     

Ectopic expression of glucagon-like peptide 1 for gene therapy of type II diabetes

Glucagon-like peptide 1 (GLP-1) is a promising candidate for the treatment of type II diabetes. However, the short in vivo half-life of GLP-1 has made peptide-based treatments challenging. Gene therapy aimed at achieving continuous GLP-1 expression presents one way to circumvent the rapid turnover of GLP-1. We have created a GLP-1 minigene that can direct the secretion of active GLP-1 (amino acids 7-37). Plasmid and adenoviral expression vectors encoding the 31-amino-acid peptide linked to leader sequences required for secretion of GLP-1 yielded sustained levels of active GLP-1 that were significantly greater than endogenous levels. Systemic administration of expression vectors to animals using two diabetic rodent models, db/db mice and Zucker Diabetic Fatty (ZDF) rats, yielded elevated GLP-1 levels that lowered both the fasting and random-fed hyperglycemia present in these animals. Because the insulinotropic actions of GLP-1 are glucose dependent, no evidence of hypoglycemia was observed. Improved glucose homeostasis was demonstrated by improvements in %HbA1c (glycated hemoglobin) and in glucose tolerance tests. GLP-1-treated animals had higher circulating insulin levels and increased insulin immunostaining of pancreatic sections. GLP-1-treated ZDF rats showed diminished food intake and, in the first few weeks following vector administration, a diminished weight gain. These results demonstrate the feasibility of gene therapy for type II diabetes using GLP-1 expression vectors.     

Cell type specific and glucose responsive expression of interleukin-4 by using insulin promoter and water soluble lipopolymer.

For gene therapy, tissue targeting of gene delivery systems is required for the maximum efficiency. In this study, we constructed pRIP-IL4 in which the expression of interleukin-4 (IL-4) was driven by the rat insulin promoter. WSLP-pRIP-IL4 complex was characterized by pancreas beta-cell specific and glucose responsive expression of IL-4. pRIP-IL4 was completely retarded at a 6:1 or higher N/P (nitrogen atom of WSLP/phosphate of plasmid) ratio in 1% agarose gel. In addition, WSLP protected plasmid DNA from DNase I for more than 1 h. In cytotoxicity assay, WSLP showed less cytotoxicity than PEI (25000 Da) to mouse insulinoma (MIN6) cells. ELISA showed that pRIP-IL4 expressed much higher levels of IL-4 in MIN6 cells than in NIH3T3 cells. The expression level of IL-4 by pRIP-IL4 increased with increasing concentration of glucose. Also, IL-4 was expressed in a dose-dependent manner. This WSLP-pRIP-IL4 system will be useful in the development of a pancreas specific expression system for the prevention of diabetes without systemic side effects.     

Gene therapy of diabetes using a novel GLP-1/IgG1-Fc fusion construct normalizes glucose levels in db/db mice

Glucagon-like peptide (GLP-1), a major physiological incretin, plays numerous important roles in modulating blood glucose homeostasis and has been proposed for the treatment of type 2 diabetes. The major obstacles for using native GLP-1 as a therapeutic agent are that it must be delivered by a parenteral route and has a short half-life. In an attempt to develop a strategy to prolong the physiological t(1/2) and enhance the potency of GLP-1, a fusion protein consisting of active human GLP-1 and mouse IgG(1) heavy chain constant regions (GLP-1/Fc) was generated. A plasmid encoding an IgK leader peptide-driven secretable fusion protein of the active GLP-1 and IgG(1)-Fc was constructed for mammalian expression. This plasmid allows for expression of bivalent GLP-1 peptide ligands as a result of IgG-Fc homodimerization. In vitro studies employing purified GLP-1/Fc indicate that the fusion protein is functional and elevates cAMP levels in insulin-secreting INS-1 cells. In addition, it stimulates insulin secretion in a glucose concentration-dependent manner. Intramuscular gene transfer of the plasmid in db/db mice demonstrated that expression of the GLP-1/Fc peptide normalizes glucose tolerance by enhancing insulin secretion and suppressing glucagon release. This strategy of using a bivalent GLP-1/Fc fusion protein as a therapeutic agent is a novel approach for the treatment of diabetes.     

Glucagon-like peptide-1 plasmid construction and delivery for the treatment of type 2 diabetes.

Glucagon-like peptide-1 (GLP-1) is a 30-amino-acid hormone produced by intestinal L cells. It has been proposed that GLP-1 can be used as a new treatment for type 2 diabetes mellitus because it acts to augment insulin secretion and its effectiveness is maintained in type 2 diabetic patients. Despite its many remarkable advantages as a therapeutic agent for diabetes, GLP-1 is not immediately clinically applicable because of its extremely short half-life. One way to overcome this drawback is GLP1 gene delivery, which enables GLP-1 production in the body. In this study, the effect of GLP1 gene delivery was evaluated both in vitro and in vivo using a new plasmid constructed with a GLP1 (7-37) cDNA. The expression of the GLP1 gene was driven by a SV40 promoter/enhancer. To increase the expression level of GLP-1, nuclear factor kappaB binding sites were introduced. The in vitro results showed expression of GLP-1 and in vitro activity of GLP-1, which is a glucose-dependent insulinotropic action. A single systemic administration of polyethyleneimine/pSIGLP1NFkappaB complex into DIO mice resulted in increasing insulin secretion and decreasing blood glucose levels for a duration longer than 2 weeks.     

Protection and reversal of excitotoxic neuronal damage by glucagon-like peptide-1 and exendin-4

Glucagon-like peptide-1 (7-36)-amide (GLP-1) is an endogenous insulinotropic peptide that is secreted from the L cells of the gastrointestinal tract in response to food. It has potent effects on glucose-dependent insulin secretion, insulin gene expression, and pancreatic islet cell formation. In type 2 diabetes, GLP-1, by continuous infusion, can normalize blood glucose and is presently being tested in clinical trials as a therapy for this disease. More recently, GLP-1 has been found to have central nervous system (CNS) effects and to stimulate neurite outgrowth in cultured cells. We now report that GLP-1, and its longer-acting analog exendin-4, can completely protect cultured rat hippocampal neurons against glutamate-induced apoptosis. Extrapolating these effects to a well defined rodent model of neurodegeneration, GLP-1 and exendin-4 greatly reduced ibotenic acid-induced depletion of choline acetyltransferase immunoreactivity in basal forebrain cholinergic neurons. These findings identify a novel neuroprotective/neurotrophic function of GLP-1 and suggest that such peptides may have potential for halting or reversing neurodegenerative processes in CNS disorders, such as Alzheimer's disease, and in neuropathies associated with type 2 diabetes mellitus.     

Exenatide Treatment for 6 Months Improves Insulin Sensitivity in Adults With Type 1 Diabetes

OBJECTIVE

Exenatide treatment improves glycemia in adults with type 2 diabetes and has been shown to reduce postprandial hyperglycemia in adolescents with type 1 diabetes. We studied the effects of exenatide on glucose homeostasis in adults with long-standing type 1 diabetes.

RESEARCH DESIGN AND METHODS

Fourteen patients with type 1 diabetes participated in a crossover study of 6 months'' duration on exenatide (10 μg four times a day) and 6 months off exenatide. We assessed changes in fasting and postprandial blood glucose and changes in insulin sensitivity before and after each study period.

RESULTS

High-dose exenatide therapy reduced postprandial blood glucose but was associated with higher fasting glucose concentrations without net changes in hemoglobin A_1c. Exenatide increased insulin sensitivity beyond the effects expected as a result of weight reduction.

CONCLUSIONS

Exenatide is a promising adjunctive agent to insulin therapy because of its beneficial effects on postprandial blood glucose and insulin sensitivity in patients with type 1 diabetes.Glucagon-like peptide 1 (GLP-1) agonists, including exenatide, are promising agents for the treatment of type 2 diabetes. Exenatide, the first GLP-1 agonist to be Food and Drug Administration approved, and other members of this class of drugs have been shown to improve fasting and postprandial blood glucose and hemoglobin A_1c (A1C) and to promote weight loss, resulting in increased insulin sensitivity (1–3). Few reports have focused on GLP-1 agonist treatment in patients with type 1 diabetes. Herein, we report the effects of 6 months of therapy with exenatide in patients with long-standing type 1 diabetes focusing on outcomes related to glucose homeostasis, including fasting and postprandial blood glucose and insulin sensitivity, as determined by the reference glucose clamp method (4).     

Unresolved bereavement

Abstract

Type 2 diabetes mellitus and comorbidities related to overweight/obesity are risk factors for the development of cardiovascular disease (CVD). In addition to insulin resistance and progressive β-cell failure as key factors in the pathogenesis of type 2 diabetes mellitus, defects in the incretin system are now known to contribute as well. Lifestyle modifications including diet and exercise are often insufficient for reducing glucose and weight, and most patients with type 2 diabetes will require pharmacotherapy to treat their hyperglycemia. Goals of therapy should be to reduce blood glucose to as low as possible, for as long as possible, without weight gain and hypoglycemia, and correcting cardiovascular risk factors. Numerous antidiabetes medications lower blood glucose; however, many are associated with weight gain and do not address risk factors present for CVD. Newer pharmacotherapies include the glucagon-like peptide-1 (GLP-1) receptor agonists, dipeptidyl peptidase-4 (DPP-4) inhibitors, and amylinomimetics. The GLP-1 receptor agonists and amylinomimetics reduce glucose while promoting weight loss and improving other cardiovascular risk factors with a low incidence of hypoglycemia. The DPP-4 inhibitors effectively lower glucose and are weight neutral.     

糖尿病患者胰高血糖素样肽-1在糖耐量试验前后的变化及意义

目的探讨2型糖尿病患者胰高血糖素样肽-1（glucagon-like peptical-1,GLP-1）水平与血糖、胰岛素及胰岛素抵抗的关系。方法 2型糖尿病患者50例（糖尿病组）及体检健康者30例（对照组）,2组均禁食10h后行糖耐量试验,采集空腹及餐后2h血标本,分别检测血浆葡萄糖、胰岛素、GLP-1水平。结果糖尿病组空腹及餐后2h血糖明显高于对照组（P〈0.05）,餐后2hGLP-1水平明显低于对照组（P〈0.05）,空腹和餐后2h胰岛素水平及空腹GLP-1水平与对照组比较差异无统计学意义（P〉0.05）。结论 2型糖尿病患者餐后2hGLP-1水平较正常人明显降低;餐后GLP-1分泌水平可反映2型糖尿病患者胰岛功能受损程度。     

糖尿病患者胰高血糖素样肽-1在糖耐量试验前后的变化及意义

目的探讨2型糖尿病患者胰高血糖素样肽-1(glucagon-like peptical-1,GLP-1)水平与血糖、胰岛素及胰岛素抵抗的关系。方法 2型糖尿病患者50例(糖尿病组)及体检健康者30例(对照组),2组均禁食10h后行糖耐量试验,采集空腹及餐后2h血标本,分别检测血浆葡萄糖、胰岛素、GLP-1水平。结果糖尿病组空腹及餐后2h血糖明显高于对照组(P<0.05),餐后2hGLP-1水平明显低于对照组(P<0.05),空腹和餐后2h胰岛素水平及空腹GLP-1水平与对照组比较差异无统计学意义(P>0.05)。结论 2型糖尿病患者餐后2hGLP-1水平较正常人明显降低;餐后GLP-1分泌水平可反映2型糖尿病患者胰岛功能受损程度。     

Metformin causes reduction of food intake and body weight gain and improvement of glucose intolerance in combination with dipeptidyl peptidase IV inhibitor in Zucker fa/fa rats

An incretin hormone, glucagon-like peptide-1 (GLP-1), has been shown to lower plasma glucose via glucose-dependent insulin secretion and to reduce appetite. We previously found that the biguanide metformin, an antidiabetic agent, causes a significant increase of plasma active GLP-1 level in the presence of dipeptidyl peptidase IV (DPPIV) inhibitor in normal rats. This finding suggested that the combination treatment might produce a greater antidiabetic and anorectic effect, based on enhanced GLP-1 action. In this study, we assessed the effects of subchronic treatment with metformin and a DPPIV inhibitor, valine-pyrrolidide (val-pyr), on glycemic control, food intake, and weight gain using Zucker fa/fa rats, a model of obesity and impaired glucose tolerance. The combination treatment caused a significant increase of GLP-1 level in Zucker fa/fa rats. In a subchronic study, val-pyr, metformin, or both compounds were administered orally b.i.d. for 14 days. The combination treatment significantly decreased food intake and body weight gain, although neither metformin nor val-pyr treatment alone had any effect. In an oral glucose tolerance test on day 1, the coadministration caused a greater improvement of glucose tolerance and a prominent increase of plasma active GLP-1 without marked insulin secretion. The 14-day combination treatment produced a potent reduction of fasting blood glucose and plasma insulin levels. These results demonstrate that the combination therapy of metformin with DPPIV inhibitor leads to reduced food intake and body weight gain, most likely through the significant increase of plasma GLP-1 level. The combination therapy seems to be a good candidate for treatment of type 2 diabetes with obesity.     

Incretin related drugs

Incretin, GIP and GLP-1, are blood glucose lowering hormones secreted from K cells and L cells, and are rapidly degenerated by DPP-4 within a few minutes. Recently incretin related drugs, GLP-1 analogs and DPP-4 inhibitors are developed. GLP-1 analogs have amino acid substitutions, which make the GLP-1 peptide resistant to degeneration by DPP-4, while DPP-4 inhibitors prevent endogenous GLP-1 to be degenerated by DPP-4. Since they exert blood glucose lowering effect only when blood glucose levels are high, hypoglycemia rarely occurs when administrated without other anti-diabetic drugs. Incretin related drugs are expected to be a new strategy for treating type 2 diabetes.     

Incretin-based therapy in patients with type 1 diabetes mellitus

GLP-1 has multiple physiological functions including glucose-dependent insulin secretion and glucagon suppression, delay of gastic emptying, suppression of hepatic glucose production, stimulation of beta cell replication and neogenesis, inhibition of beta cell apoptosis. All of these actions are beneficial for the treatment of diabetes. Therefore, incretin-based therapy may be still worthwhile as evidenced by studies demonstrating that beta cell mass may be preserved or expand in animals and that residual insulin secretion may be elevated to reduce the risk of hypoglycemia in patients treated with intensive insulin therapy, although the effect of GLP-1R agonists and DPP-4 inhibitors(DPP-4is) on beta cells may be small because destruction of beta cells leads to absolute insulin deficiency by cell-mediated autoimmune attack. Recent report also showed that DPP-4i might ameliorate an autoimmune attack against beta cells by restoring or increasing the number of regulatory T lymphocytes. Furthermore, GLP-1R-mediated signals might suppress the expression of chemokine ligand CXCL10 which binds to newly identified receptor TLR4 (Toll-like receptor 4), and impairs beta cell function and viability in diabetes. Taken together, incretin-based therapy may be worth testing in patients with type 1 diabetes.     

不同糖耐量水平人群血浆胰高血糖素样肽-1和葡萄糖依赖的促胰岛素样多肽水平比较

目的 了解不同糖代谢状态的人群空腹及口服葡萄糖耐量实验(oral glucose tolerance test,OGTT)餐后胰高血糖素样态-1(GLP-1)和葡萄糖依赖的促胰岛素多态(GIP)水平.方法 将受试者根据OGTT结果分为3组:正常糖耐量组(NGT,n=61例),糖耐量受损组(IGT,n=53)和2型糖尿病...     

肥胖型和非肥胖型PCOS患者血清中GLP-1变化水平及其与BMI、激素水平相关性研究

目的 研究肥胖型和非肥胖型多囊卵巢综合征(PCOS)患者空腹血浆胰高血糖素样肽1(GLP-1)的分泌水平并评估其与体重指数(BMI)、激素间的相关性.方法 选取34例PCOS患者为PCOS组,16例正常健康妇女为对照组,根据BMI将PCOS组分为肥胖型PCOS患者和非肥胖型PCOS患者,采用酶联免疫法检测空腹血清GLP...     

Additive effects of glucagon-like peptide 1 and pioglitazone in patients with type 2 diabetes

OBJECTIVE: To evaluate the effect of combination therapy with pioglitazone and glucagon-like peptide (GLP)-1 in patients with type 2 diabetes. RESEARCH DESIGN AND METHODS: Eight patients with type 2 diabetes (BMI 32.7 +/- 1.3 kg/m(2) and fasting plasma glucose 13.5 +/- 1.2 mmol/l) underwent four different treatment regimens in random order: saline therapy, monotherapy with continuous subcutaneous infusion of GLP-1 (4.8 pmol x kg(-1) x min(-1)), monotherapy with pioglitazone (30-mg tablet of Actos), and combination therapy with GLP-1 and pioglitazone. The observation period was 48 h. End points were plasma levels of glucose, insulin, glucagon, free fatty acids (FFAs), and sensation of appetite. RESULTS: Fasting plasma glucose decreased from 13.5 +/- 1.2 mmol/l (saline) to 11.7 +/- 1.2 (GLP-1) and 11.5 +/- 1.2 (pioglitazone) and further decreased to 9.9 +/- 1.0 (combination) (P < 0.001). Eight-hour mean plasma glucose levels were reduced from 13.7 +/- 1.1 mmol/l (saline) to 10.6 +/- 1.0 (GLP-1) and 12.0 +/- 1.2 (pioglitazone) and were further reduced to 9.5 +/- 0.8 (combination) (P < 0.0001). Insulin levels increased during monotherapy with GLP-1 compared with monotherapy with pioglitazone (P < 0.01). Glucagon levels were reduced in GLP-1 and combination therapy compared with saline and monotherapy with pioglitazone (P < 0.01). FFAs during breakfast (area under the curve, 0-3 h) were reduced in combination therapy compared with saline (P = 0.03). Sensation of appetite was reduced during monotherapy with GLP-1 and combination therapy (P < 0.05). CONCLUSIONS: GLP-1 and pioglitazone show an additive glucose-lowering effect. A combination of the two agents may, therefore, be a valuable therapeutic approach for the treatment of type 2 diabetes.