Microparticles but not nanoparticles are retained in the subconjunctival space at 2–months post–administration.

Abstract

Abstract: : Purpose: To compare the disposition of non–degradable, fluorescent nano– and micro– particles following subconjunctival administration. Methods: Bodipy dye–loaded, polystyrene micro– (2 µm) or nano–particles (20 nm) (Fluospheres^TM) were administered subconjunctivally to rats at a dose of 400µg in 25 µl PBS, under anesthesia. Animals were sacrificed at 0, 1, 7 or 60 days after treatment. After sacrifice, the eyes were enucleated, frozen and the cornea, lens, vitreous, retina and sclera–choroid were isolated, extracted for intact particles, and quantified. The residual tissue overlying the sclera including the conjunctiva and the connective and adipose tissue was isolated after enucleation and removal of eyelids, and quantified. To study the effect of dilution on particle aggregation, micro– and nanoparticles were administered at a dose of 40 µg in 25 µl of PBS. The animals were sacrificed at 0 or 60 days post–administration and the tissues were analyzed for the particles as above. Results: The micro– or nano– particles could not be detected in any of the ocular tissues at 0, 7 or 60 days post subconjunctival administration. One day following subconjunctival administration (400 ng), trace quantities of the nano–particles could be detected in the sclera–choroid but not in any other ocular tissue. About 82% and 77% of the dose of nano–particles and micro–particles, respectively, could be quantified in the subconjunctival space immediately following administration (day 0). The micro–particle quantities in the subconjunctival space remained fairly constant with 71 ± 4%, 73 ± 17% and 60 ± 11% of the particles remaining at the end of 1, 7 and 60 days, respectively. The nano–particle quantities declined rapidly with 15 ± 3% and 8 ± 3.5% particles remaining at the end of 1 and 7 days, respectively. The nano–particles could not be detected in the subconjunctival space at 60 days post–administration. With the lower dose (40 µg in 25 µl), 64 ± 9% of the micro–particles remained in the subconjunctival space at the end of 60 days whereas the nano–particles could not be detected at the end of that time period. Conclusions: Nano– and micro– particles cannot enter the ocular tissues following subconjunctival administration to a significant extent. The retention of the particles is not dependent on the dose of the administered particles, under the conditions of this study. The micro–particles are retained for longer periods in the subconjunctival space and would be a better delivery device for sustained release of encapsulated drugs to the ocular tissues following subconjunctival administration.

Keywords: sclera • retina • conjunctiva