Studies of effective factors of plasmid DNA-loaded chitosan microspheres I. Plasmid size, chitosan concentration and plasmid addition techniques

Gene therapy strategies depend on efficient devices for the delivery of nuc leic acid into target cells. In this study, DNA-chitosan microspheres were investigated from a pharmaceutical standpoint and the effects of different factors such as plasmid size, chitosan concentration and plasmid addition t echniques, on the characterization and in vivo transfection of microspheres were studied Different doses of DNA-chitosan microspheres were also tested for their gene expression properties. Large and small plasmids (pMK3 and p UC18, respectively) were used to study the importance of plasmid size to in vitro DNA release and transfection properties. Naked and encapsulated plas mids were injected into the muscle of the rats and their beta-galactosidase production was measured. According to our data, the effect of plasmid size and chitosan concentration on transfection efficacy was not clear. However , the DNA dose injected in rats was of importance to beta-galactosidase pro duction. The highest levels of beta-galactosidase expression were obtained with low-dose DNA-chitosan microspheres. The injection of naked plasmid DNA to rats resulted in negligible expression. On the other hand the structura l and functional integrity of encapsulated plasmid DNA remained unchanged d uring the study.