The characteristics and mechanisms of uptake of PLGA nanoparticles in rabbit conjunctival epithelial cell layers

Purpose. To delineate the characteristics and mechanisms of uptake of biodegradable poly(D,L-lactide-co-glycolide) (PLGA) nanoparticles in primary cultured rabbit conjunctival epithelial cells (RCECs). Methods. Poly(D, L-lactide-co-glycolide) nanoparticles (PLGA 50: 50, 100 nm in diameter) containing 6-coumarin (as a fluorescent marker) were used. The effect of size was studied using various particle sizes ( 100 nm, 800 nm, and 10 mum). The effect of cytochalasin D, nocodazole, and metabolic inhibitors on nanoparticle uptake was investigated. The capability of nanoparticles to enhance the uptake of an encapsulated protein, BSA bound to Texas red (TR-BSA), was evaluated. Results. Maximal uptake of nanoparticles at 37 degreesC occurred at 2 h, and 100-nm particles had the highest uptake in RCECs in comparison with 800-nm and 10-mum particles. Nanoparticle uptake was saturable over the 0.1 - 4 mg/ml concentration range. Nanoparticle uptake was confirmed by confocal microscopy and was inhibited significantly by coumarin-free nanoparticles ( of similar size), by lower incubation temperature, and by the presence of metabolic inhibitors and cytochalasin D. The uptake of encapsulated TR-BSA in RCECs at 4 h was 28% higher than free BSA application. Conclusion. Our findings suggest that PLGA nanoparticle uptake in primary cultured rabbit conjunctival epithelial cells occurs most likely by adsorptive-type endocytosis.