EXPRESSION OF BIOLOGICALLY-ACTIVE HUMAN INSULIN-LIKE GROWTH-FACTOR-I FOLLOWING INTRAMUSCULAR INJECTION OF A FORMULATED PLASMID IN RATS

Recent evidence has shown that insulin-like growth factor-I (IGF-I) pl ays an important role in the development, maintenance, and regeneratio n of peripheral nerves and skeletal muscle, IGF-I offers the potential to treat neuromuscular diseases in humans, We have developed a nonvir al gene therapy method to express and produce localized and sustained therapeutic levels of IGF-I within target muscles by intramuscular inj ection of formulated plasmids, The purpose of the present study was to demonstrate that intramuscular injection of a plasmid encoding human IGF-I (hIGF-I) and engineered to restrict expression to skeletal muscl e produces sustained local concentrations of biologically active hIGF- I. Normal rats received a single intramuscular injection of plasmids f ormulated as a complex with polyvinypyrrolidone (PVP), Results show th at hIGF-I mRNA and hIGF-I protein were detectable in the injected musc les for the duration of the study (28 days), whereas the hIGF-I protei n was not detected in blood, Biological activity of hIGF-I was determi ned by immunodetection of a nerve-specific growth-associated protein, GAP-43, an indicator of motor neuron sprouting, Placement of human gro wth hormone (hGH) 3' untranslated region enhanced GAP-43 staining, pro bably due to improved secretion of hIGF-I, Enhanced immunoreactivity o f GAP-43 was observed in muscles injected with the formulated hIGF-I p lasmid when compared to controls, These results demonstrate that intra muscular injection of hIGF-I plasmid formulated as a complex with PVP produces a localized and sustained level of biologically active hIGF-I .