title: Naked plasmid-mediated gene transfer to skeletal muscle ameliorates diabetes mellitus.
abstract: BACKGROUND
  The ability of tissues to take up naked plasmid DNA in vivo suggests an approach for reconstituting systemic metabolic deficiencies without the disadvantages of viral vectors and lipid-DNA complexes. Plasmid-mediated gene transfer into skeletal muscle was investigated as a means of providing 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 different promoters were injected into the calf muscles of male Balb/c mice. Insulin and C-peptide concentrations were measured by radio-immunoassays having minimal crossreactivity for proinsulin and partially processed proinsulin.
  
  
  RESULTS
  Intramuscular insulin concentrations increased by up to 3.6-fold over controls seven days after single injections of CMV, beta-actin, hsp70 and myoglobin promoter constructs. The optimal dose for most constructs was 100 micrograms plasmid DNA. Intramuscular plasmid injection into streptozotocin-induced diabetic Balb/c mice raised plasma insulin and C-peptide concentrations, and reduced hyperglycaemia. Two injections (100 micrograms plasmid DNA each) caused higher plasma insulin concentrations and significantly reduced hyperglycemia in diabetic mice than a single injection. Best results were obtained when plasmid injections preceded induction of diabetes by 14 days.
  
  
  CONCLUSIONS
  Skeletal muscle is a potentially useful platform for ectopic secretion 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 enhance the action of agents that sensitize tissues to insulin in type II diabetes.
authors.affiliation: Department of Biochemistry, National University of Singapore, Republic of Singapore. dmskal@nccs.com.sg
authors.forename: O L
authors.initials: OL
authors.lastname: Kon
authors.forename: S
authors.initials: S
authors.lastname: Sivakumar
authors.forename: K L
authors.initials: KL
authors.lastname: Teoh
authors.forename: S H
authors.initials: SH
authors.lastname: Lok
authors.forename: Y C
authors.initials: YC
authors.lastname: Long
mesh_terms: D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D003921:Diabetes Mellitus, Experimental / Q000235:genetics / Q000378:metabolism / Q000628:therapy*; D018014:Gene Transfer Techniques; D015316:Genetic Therapy; D007328:Insulin / Q000097:blood / Q000378:metabolism; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D018482:Muscle, Skeletal / Q000378:metabolism*; D010957:Plasmids / Q000235:genetics*; D011384:Proinsulin / Q000235:genetics*; D051381:Rats
chemical_list: D001786:Blood Glucose; D007328:Insulin; D011384:Proinsulin