Zebrafish as a visual and dynamic model to study the transport of nanosized drug delivery systems across the biological barriers.

With the wide application of nanotechnology to drug delivery systems, a simple, dynamic and visual in vivo model for high-throughput screening of novel formulations with fluorescence markers across biological barriers is desperately needed. In vitro cell culture models have been widely used, although they are far from a complimentary in vivo system. Mammalian animal models are common predictive models to study transport, but they are costly and time consuming. Zebrafish (Danio rerio), a small vertebrate model, have the potential to be developed as an "intermediate" model for quick evaluations. Based on our previously established coumarin 6 nanocrystals (C6-NCs), which have two different sizes, the present study investigates the transportation of C6-NCs across four biological barriers, including the chorion, blood brain barrier (BBB), blood retinal barrier (BRB) and gastrointestinal (GI) barrier, using zebrafish embryos and larvae as in vivo models. The biodistribution and elimination of C6 from different organs were quantified in adult zebrafish. The results showed that compared to 200nm C6-NCs, 70nm C6-NCs showed better permeability across these biological barriers. A FRET study suggested that intact C6-NCs together with the free dissolved form of C6 were absorbed into the larval zebrafish. More C6 was accumulated in different organs after incubation with small sized NCs via lipid raft-mediated endocytosis in adult zebrafish, which is consistent with the findings from in vitro cell monolayers and the zebrafish larvae model. C6-NCs could be gradually eliminated in each organ over time. This study demonstrated the successful application of zebrafish as a simple and dynamic model to simultaneously assess the transport of nanosized drug delivery systems across several biological barriers and biodistribution in different organs, especially in the brain, which could be used for central nervous system (CNS) drug and delivery system screening.