Naked plasmid-mediated gene transfer to skeletal muscle ameliorates diabetes mellitus

Background The ability of tissues to take up naked plasmid DNA in vivo sugg ests an approach for reconstituting systemic metabolic deficiencies without the disadvantages of viral vectors and lipid-DNA complexes. Plasmid-mediat ed gene transfer into skeletal muscle was investigated as a means of provid ing a therapeutic source of insulin. Methods Four plasmid constructs, each bearing a mouse furin cDNA transgene and rat proinsulin cDNA (modified for processing by furin) driven by four d ifferent promoters were injected into the calf muscles of male Balb/c mice. insulin and C-peptide concentrations were measured by radioimmunoassays ha ving minimal crossreactivity for proinsulin and partially processed proinsu lin. Results Intramuscular insulin concentrations increased by up to 3.6-fold ov er controls seven days after single injections of CMV, rho-actin, hsp70 and myoglobin promoter constructs. The optimal dose for most constructs was 10 0 mu g plasmid DNA. Intramuscular plasmid injection into streptozotocin-ind uced diabetic Balb/c mice raised plasma insulin and C-peptide concentration s, and reduced hyperglycaemia. Two injections (100 mu g plasmid DNA each) c aused higher plasma insulin concentrations and significantly reduced hyperg lycemia in diabetic mice than a single injection. Best results were obtaine d when plasmid injections preceded induction of diabetes by 14 days. Conclusions Skeletal muscle is a potentially useful platform for ectopic se cretion of insulin using naked plasmid as a gene transfer vector. Injection at two sites 14 days before the onset of severe hyperglycemia is optimal. This approach could protect Type I diabetics from fatal ketoacidosis and en hance the action of agents that sensitize tissues to insulin in type II dia betes. Copyright (C) 1999 John Wiley & Sons, Ltd.