Glucagon-Like Peptide-1 Gene Therapy in Obese Diabetic Mice Results in Long-Term Cure of Diabetes by Improving Insulin Sensitivity and Reducing Hepatic Gluconeogenesis

Abstract

Long-term treatment with glucagon-like peptide (GLP)-1 or its analog can improve insulin sensitivity. However, continuous administration is required due to its short half-life. We hypothesized that continuous production of therapeutic levels of GLP-1 in vivo by a gene therapy strategy may remit hyperglycemia and maintain prolonged normoglycemia. We produced a recombinant adenovirus expressing GLP-1 (rAd-GLP-1) under the cytomegalovirus promoter, intravenously injected it into diabetic ob/ob mice, and investigated the effect of this treatment on remission of diabetes, as well as the mechanisms involved. rAd-GLP-1-treated diabetic ob/ob mice became normoglycemic 4 days after treatment, remained normoglycemic over 60 days, and had reduced body weight gain. Glucose tolerance tests found that exogenous glucose was cleared normally. rAd-GLP-1-treated diabetic ob/ob mice showed improved ␤-cell function, evidenced by glucose-responsive insulin release, and increased insulin sensitivity, evidenced by improved insulin tolerance and increased insulin-stimulated glucose uptake in adipocytes. rAd-GLP-1 treatment increased basal levels of insulin receptor substrate (IRS)-1 in the liver and activation of IRS-1 and protein kinase C by insulin in liver and muscle; increased Akt activation was only observed in muscle. rAd-GLP-1 treatment reduced hepatic glucose production and hepatic expression of phosphoenolpyruvate carboxykinase, glucose-6-phosphatase, and fatty acid synthase in ob/ob mice. Taken enhances ␤-cell function; stimulates ␤-cell growth, survival, differentiation, and proliferation; and promotes satiety and delaying gastric emptying (1,2). Furthermore, impaired GLP-1 secretion was observed in patients with type 2 diabetes (3). Therefore, GLP-1 has been proposed as a treatment for type 2 diabetes. Treatment with GLP-1 or its analog, exendin-4, improved insulin sensitivity and glucose tolerance and reduced hyperinsulinemia in animal models of type 2 diabetes (4,5). In type 2 diabetic patients, subcutaneous infusion of GLP-1 for 6 weeks resulted in improved insulin sensitivity and ␤-cell function (6). However, the precise mechanisms by which insulin sensitivity and glucose tolerance are improved are not known.Although subcutaneous injections or intravenous or subcutaneous infusions of GLP-1 showed therapeutic effects on lowering blood glucose levels, the short half-life (ϳ2 min) and rapid clearance of GLP-1 limits the maintenance of therapeutic levels by exogenous administration. GLP-1 is degraded by the enzyme dipeptidyl peptidase IV (7,8); therefore, GLP-1 agonists that are resistant to dipeptidyl peptidase IV degradation and inhibitors of dipeptidyl peptidase IV have been investigated for the treatment of type 2 diabetes (9). We hypothesized that continuous expression of GLP-1 in vivo by a gene therapy strategy may remit hyperglycemia and maintain normoglycemia. In this study, we produced a recombinant adenovirus that expresses and secretes GLP-1 under the control of the cytomegalovirus promoter (recombinant adenovir...

DsAAV8-mediated expression of glucagon-like peptide-1 in pancreatic beta-cells ameliorates streptozotocin-induced diabetes

“…The majority of these studies have employed constitutive promoters such as CMV or ubiquitin to drive unregulated expression and secretion of DPP-IV-resistant GLP-1-receptor agonists from tissues such as muscle and liver. [53][54][55] Others have fused GLP-1 to various proteins such as IgG or albumin to improve circulating half-lives. 18,56 In each of these studies, the therapeutic effects of GLP-1 were achieved following systemic increase in GLP-1 levels.…”

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

“…GLP-1 plays an important role in insulin secretion and synthesis, as well as b-cell proliferation and prevention of apoptosis. 46 Insulin concentration in ZDF-treated rats increased more than twofold when compared with untreated rats ( Figure 5). Insulin expression remained high 14 days following the last injection of chitosan/pVax1-GLP-1 nanocomplex.…”

“…However, there have been several reports showing that serum insulin levels in GLP-1-treated animals decreased because of an improvement in insulin sensitivity. 46,48 These contrasting observations might result from the different properties of diabetic animal models such as the severity of diabetes and the preserved function of b-cells. Furthermore, increased insulin plasma levels in our study may be also due to the proliferative/antiapoptotic effect of GLP-1 on pancreatic b-cells.…”

Transgene and islet cell delivery systems using nano-sized carriers for the treatment of diabetes mellitus

“…Increased insulin-stimulated glucose uptake in adipocytes. Decreased blood glucose levelLee et al (2007)[15] Double-stranded AAVGLP-1(7–37)-DNAIntestinesPortal vein injectionIncreased plasma GLP-1 level. Increased insulin secretion and β cell mass.…”

“…Improved glucose toleranceLiu et al (2007)[17] Recombinant adenovirusGLP-1(7–37)-DNAIntestinesIntra-intestinal injectionIncreased plasma insulin and GLP-1 levels. Decreased blood glucose levelLee et al (2007)[15] Double-stranded AAVGLP-1 and HGF/NK1-DNAIntestinesIntraperitoneal injectionDelayed onset of diabetes mellitus. Increased pancreatic β cell mass and insulin secretionGaddy et al (2010)[18] Double-stranded AAV-8GLP-1-DNAIntestinesIntraperitoneal injectionIncreased serum GLP-1 expression.…”