Enhancing the Therapeutic Efficacy of GLP-1 for Hyperglycemia Treatment: Overcoming Barriers of Oral Gene Therapy with Taurocholic Acid-Conjugated Protamine Sulfate and Calcium Phosphate

Abstract

Activating the glucagon-like peptide-1 (GLP-1) receptor by oral nucleic acid delivery would be a promising treatment strategy against hyperglycemia due to its various therapeutic actions. However, GLP-1 receptor agonists are effective only in subcutaneous injections because they face multiple barriers due to harsh gastrointestinal tract (GIT) conditions before reaching the site of action. The apical sodium bile acid transporter (ASBT) pathway at the intestinal site could be an attractive target to overcome the problem. Herein, we used our previously established multimodal carrier system utilizing bile salt, protamine sulfate, and calcium phosphate as excipients (PTCA) and the GLP-1 gene as an active ingredient (GENE) to test the effects of different formulation doses against diabetes and obesity. The carrier system demonstrated the ability to protect the GLP-1 model gene encoded within the plasmid at the GIT and transport it via ASBT at the target site. A single oral dose, regardless of quantity, showed the generation of GLP-1 and insulin from the body and maintained the normoglycemic condition by improving insulin sensitivity and blood sugar tolerance for a prolonged period. This oral gene therapy approach shows significantly higher therapeutic efficacy in preclinical studies than currently available US Food and Drug Administration-approved GLP-1 receptor agonists such as semaglutide and liraglutide. Also, a single oral dose of GENE/PTCA is more effective than 20 insulin injections. Our study suggests that oral GENE/PTCA formulation could be a promising alternative to injection-based therapeutics for diabetics, which is effective in long-term treatment and has been found to be highly safe in all aspects of toxicology.