Comparison of lacZ reporter gene expression in gilthead sea bream (Sparus aurata) following oral or intramuscular administration of plasmid DNA in chitosan nanoparticles

The development of non-parenteral delivery systems allowing efficient intestinal absorption in fish is a current research topic drawing much interest. Different aspects would benefit from such oral delivery, especially those related to immunization, owing to the convenience of this route in terms of time saving, safety, and lack of stressful effects among others. In the last years, DNA vaccines are evidencing their suitability for fish immunization, although commercial preparations currently available require parenteral administration. In this regard, this work was aimed at assessing a chitosan-based oral delivery system for plasmid DNA (pDNA) in fish. Plasmid pCMVβ was encapsulated in chitosan nanoparticles with the aim of evaluating the ability of inert capsules to retain and protect pDNA from in vitro conditions mimicking the fish gut environment. Furthermore, the feasibility of in vivo oral gene delivery was also assessed in fish by administrating pDNA nanoparticles comparing oral and intramuscular routes. The results indicated that lacZ gene expression (β-galactosidase activity) could be detected in fish tissues following both oral and i.m. administration of pDNA-chitosan nanoparticles up to 60 days. However, organ distribution of the reporter gene expression was more evident after oral (β-gal activity measured in gut, liver and muscle) than after parenteral administration (mostly restricted to adjacent tissues). The results suggest that chitosan nanoparticles enabled efficient oral delivery of pDNA, followed by organ migration and further sustained expression of the reporter gene encoding for β-galactosidase. The intensity of such expression was similar to that obtained by intramuscular injection, a fact that might suppose valuable practical applications in terms of on-farm administration of DNA-based vaccines to fish.