Biodistribution and feasibility of non-viral IGF-I gene transfers in thermally injured skin

Gene therapy using cationic liposomes containing cDNA is a relatively new a pproach with great potential; however, little is known about the mechanisms of dermal gene transfer, its biodistribution, systemic transfection, and c ellular uptake. This study identifies mechanisms, transfection rates, and b iodistribution of liposomal gene transfers in the skin of thermally injured rats using cDNA gene constructs coding for insulin-like growth factor-I (I GF-I) and Lac Z. Male Sprague-Dawley rats (350 to 375 g) were given a 60% t otal body surface area full-thickness scald burn that was followed by weekl y subcutaneous injections of normal saline (control, n = 10), liposomes plu s 0.2 mu g Lac Z cDNA construct driven by a cytomegalovirus (CMV) promoter (vehicle, n = 10), or liposomes containing 2.2 mu g cDNA coding for IGF-I p lus 0.2 mu g Lac Z cDNA construct driven by a CMV promoter (IGF-I cDNA, n = 10). Gene transfection was determined by histochemical and luminescent p-g alactosidase assays of blood, skin, liver, spleen, and kidney. Transcriptio n of IGF-I cDNA to IGF-I mRNA was determined in skin cells by Northern blot analyses. Levels of IGF-I protein in blood, skin, liver, spleen, and kidne y were measured by radioimmunoassay. The biological activity of the transla ted IGF-I was evaluated by the mitogenic activity in dermal cells and the r ate of re-epithelization. Gene transfection was observed only in skin cells . The expression of IGF-I mRNA increased in skin cells of burned rats recei ving liposomes containing the IGF-I cDNA construct compared with liposomes without the construct or normal saline. IGF-I protein levels in the skin of rats receiving the IGF-I cDNA was 176 +/- 4 ng/ml compared with 105 +/- 6 ng/ml for liposomes alone or 90 +/- 3 ng/ml for saline (p < 0.05). The tran slated IGF-I protein was found biologically active in the skin by increasin g skin cell proliferation and accelerating re-epithelization 33 days after thermal injury (p < 0.05). No systemic transfection could be detected. Skin cells transfected with liposomes encapsulating the IGF-I cDNA constructs i ncreased the expression of IGF-I mRNA transcript and the expression of a bi ologically active IGF-I protein. Liposomes containing the cDNA coding for I GF-I present an effective approach to gene therapy in the skin.