Investigating the Impact of the Surface Properties of Intravitreally Injected Carriers on Their Retinal Bio-Distribution in a Single Nanoplatform

Efficient retinal targeted delivery is essential for the treatment of ocular diseases including glaucoma, age-related macular degeneration and diabetic retinopathy. Regarding the complexity of the anatomical structure of the retina, drug and gene delivery via nanocarriers to target specific retinal cell layer remains challenging. It has been proved that distribution and targeting site in the retina for intravitreally injected nanocarriers can be tuned by their physicochemical properties such as size, surface properties, ligand modification, etc. However, current studies for the impacts of these physical properties on the retinal bio-distribution of nanoparticles within retina were based on bundled parameters and separate systems, which are not sufficient and comprehensive to interpret the effect of a single property in the real delivery system. Therefore, a single platform, which can be tuned to achieve diversified surface charge with consistent size range, is highly demanded to evaluate the effect of the surface charge on the bio-distribution of intravitreally injected carriers within retina. Herein, we developed a lipid nanoplatform for the systematically study of this effect.

Ethanol-injection-dilution method was applied for lipid nanoparticles preparation. Charged nanoparticles were shaped through changing the molar ratio of cationic/anionic lipids. Fluorescent-labeled nanoparticles with various surface charges were applied for both in vitro and in vivo experiments. Cellular uptake was observed by confocal microscope and quantified by flow cytometry. Tissue slices of the eyes were obtained by cryosectioning. Retinal biodistribution was confirmed by confocal microscope and co-localization of nanoparticles and antibody-stained retinal ganglion cells.

Lipid nanoparticles were successfully prepared with the size around 100 nm and the zeta potential ranged from -13.9 mV to +18.0 mV. Nanoparticles with positive, neutral and negative surface charge could all be internalized into cells after incubation for 4 hours. It was observed that cationic lipid nanoparticles had significantly higher cellular uptake than neutral and anionic nanoparticles. Based on preliminary results of in vivo experiments, only weakly charged cationic lipid nanoparticles could efficiently cross the barrier of vitreous with targeting retinal ganglion cells. Lipid nanoparticles with neutral and negative surface charges were rapidly cleared and showed no penetrating effects within the retina.

This study establishes that nanoparticles with weak cationic charge are superior to the ones with neutral or negative charges to target retinal ganglion cell layer. Therefore, these parameters may be adaptive to other delivery systems to develop drug delivery carriers for the treatment of ocular diseases (e.g. glaucoma).