Gene Therapy for Diabetes: Metabolic Effects of Helper-dependent Adenoviral Exendin 4 Expression in a Diet-induced Obesity Mouse Model

Abstract

Exendin 4 (Ex4) is a glucagon-like peptide-1 receptor (GLP- 1R) agonist which is available as a short-acting injectable treatment for type 2 diabetes. Our aim was to characterize the long-term effects of elevated steady-state levels of Ex4 provided by in vivo gene therapy. We constructed a helper-dependent adenoviral (HDAd) vector for long-term expression of Ex4 in vivo. A high-fat diet (HFD)-induced obesity (DIO) mouse model was chosen to approximate the metabolic derangements seen in obese patients. Mice were treated with a single injection of HDAd-Ex4 and were monitored for 15 weeks. Both hepatic Ex4 RNA and plasma Ex4 were detectable at the end of the study. HDAd-Ex4 treatment improved glucose homeostasis without increasing insulin levels. However, there was evidence of enhanced insulin action and decreased gluconeogenic enzyme expression. HDAd-Ex4 caused decreased weight gain without detectable changes in food intake, in part, due to increases in energy expenditure (EE). HDAd-Ex4 DIO mice also had reduced hepatic fat and an improved adipokine profile. In the liver, there was decreased expression of genes that were involved in de novo fatty acid synthesis. These observations are important in considering the development of longer acting GLP-1R agonists for the treatment of type 2 diabetes.

Glucagon-like peptide-1 receptor agonism improves metabolic, biochemical, and histopathological indices of nonalcoholic steatohepatitis in mice

“…Here we demonstrate the unequivocal development of hepatic fibrosis in the absence of circulating leptin and expand on the previously reported beneficial effect of GLP-1R agonism on body weight, liver size, and liver lipid (10,31) by demonstrating a potential benefit of GLP-1R agonism on fibrosis (assessed both histologically and biochemically). We also demonstrate that benefits of GLP-1R agonism on NAFLD/ NASH are largely, but not entirely, accounted for by weight loss.…”

“…Functional GLP-1R has been localized on primary rat hepatocytes, immortalized mouse liver cell lines, and human hepatocytes (10,13). GLP-1R agonism has been associated with reduced hepatic lipogenesis and enhanced fat oxidation in rodents (5,10,31,37). More recently, a role for GLP-1R agonism in the regulation of endoplasmic reticulum (ER) stress and the unfolded protein response has emerged.…”

“…These agents enhance glucose-dependent insulin secretion, regulate gastric emptying, decrease postprandial glucagon secretion, and reduce food intake/body weight. Recent studies in mice and rats have shown that GLP-1R agonism exerts beneficial effects on body weight, liver mass, and liver lipid, plasma ALT, and plasma triglycerides (5,10,31,35,39). In clinical studies, exenatide therapy lowered plasma ALT levels in patients with type 2 diabetes (17).…”

New Insights from Rodent Models of Fatty Liver Disease

“…In one study, mice fed a high-energy diet for 23 weeks and then treated with pioglitazone for an additional 8 weeks exhibited normal insulin sensitivity at the end of the study but showed no improvement in hepatic steatosis or serum ALT (17). By contrast, mice fed a high-energy diet for 8 weeks and then treated with an adenovirus expressing exendin-4 (a long-acting agonist of glucagon-like peptide receptor-1) while continuing the diet for 15 more weeks showed improvements in both glucose utilization and hepatic steatosis (106). Anti-inflammatory drugs have also been used to reduce insulin resistance in the setting of high-energy feeding, based on evidence that insulin resistance is the consequence of a diet-induced pro-inflammatory state (11).…”

Development of a Protocol for Selection of GenesFit for the <i>In Vivo</i> Knockdown Method and its Application to Insulin Receptor Substrate Genesin Mice

“…Delivery methods are divided into viral [19,21] and non-viral [17] methods. the latter includes those using liposomes [3,16,21], nanoparticles [23], and a hydrodynamic method [2].…”