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.