Feasibility of drug delivery to the eye's posterior segment by topical instillation of PLGA nanoparticles.

We investigated the delivery of drugs to the posterior segment of the eye by non-invasive topical instillation using submicron-sized poly(D,L-lactide-co-glycolide) (PLGA) nanoparticles (NPs). Surface-modified PLGA NPs were developed to improve the drug delivery efficiency to the retina and were administered as topical eye drops to mice. Chitosan (CS) and glycol chitosan (GCS), which are mucoadhesive polymers, and polysorbate 80 (P80) were used as surface modifiers, and have been reported to increase the association of NPs with cells. Coumarin-6 was used as a model drug and fluorescent marker, and after ocular administration of PLGA NP eye drops, the fluorescence intensity of coumarin-6 was observed in the retina. The fluorescence image analysis indicated that there are several possible routes to the retina and fates of PLGA NPs in ocular tissue, and that these pathways involved the corneal, non-corneal, or uveal routes. Delivery to the mouse retina segments after topical administration was increased by surface modification with CS, GCS, or P80. Surface-modified PLGA NPs are a promising method for retinal drug delivery via topical instillation.

Retinal drug delivery using eyedrop preparations of poly-L-lysine-modified liposomes.

The purpose of this study was to develop surface-modified liposomes that enhance the efficiency of eye drop drug delivery to the retina. Various molecular weights and concentrations of the water-soluble cationic polymer poly-L-lysine (PLL) were used to modify the surface of submicronized (100 nm) liposomes. Physicochemical properties of surface-modified liposomes were determined in vitro, and the efficiency of drug delivery to the retina was investigated in vivo. Using coumarin-6 as a model drug and fluorescent marker, we show that liposome surface modification by PLL dramatically increased delivery to mouse retina segments after eye drop administration. However, when PLL of high molecular weight (>30,000) was used at higher concentrations (>0.05%), aggregation of surface-modified liposomes increased particle size and hampered distribution to inner ocular tissues. As a result, the efficiency of drug delivery of these aggregated surface-modified liposomes was the same as unmodified liposomes. The optimal molecular weight and concentration of PLL in drug-delivering liposomes were 15,000-30,000 and 0.005%, respectively. Under these conditions, PLL-modified liposomes were not cytotoxic in corneal or conjunctival cells. In conclusion, surface-modified liposomes have great potential as effective retinal drug delivery carriers in eye drop formulations.