Improving the penetration of Dexamethasone to the posterior segment of eye using topically applied penetration enhancing agents

Abstract

Purpose : Disease and damage in the posterior segment of the eye are a major global cause of blindness. Topical eye-drop treatments are less effective because therapeutic molecules penetrate ocular tissue barriers poorly. We investigated penetration enhancement of the most commonly used anti-inflammatory drug, dexamethasone sodium phosphate (DSP), after topical delivery with three penetration enhancing agents (PEAs) — an in-house synthesized novel helical polymer and two commonly used cell penetrating peptides (CPPs), TAT and Penetratin.

Methods : Trans-corneal penetration of the three PEAs and DSP formulations with PEAs were assayed ex-vivo in a rapid and cost-effective screening model of excised porcine cornea and quantified using UV & fluorescence spectroscopy for PEAs and by high performance liquid chromatography (HPLC) for DSP. Immunostaining of corneal sections with tight junction markers, ZO-1 and Claudin-5, assessed the integrity of tight junctions and also provided a reference for visualizing the internalized PEA in corneal epithelium by confocal microscopy. Trans-epithelial electrical resistance (TEER) measurements for the corneal epithelium before and 60 minutes after application were used to determine the integrity of corneal barriers and barrier function. Furthermore, in-vitro cytotoxicity of PEAs was performed by the MTT assay in ARPE-19 and HCE-2 cells, whilst immunocytochemistry (ICC) was used in assays involving adult rat primary retinal cultures.

Results : All three PEAs effectively crossed the cornea individually. There was almost 15-fold enhancement of DSP trans-corneal permeation after topical application with PEAs. Confocal microscopy after immunostaining showed retention and epithelial internalization of PEAs on corneal epithelial surfaces while also revealing intact tight junctions. TEER measurements confirmed that there was no damage to the integrity of barrier function after PEA/DSP application. Finally, MTT assays and ICC showed no toxicity in ARPE-19, HCE-2 cells, or primary rat retinal cells, respectively.

Conclusions : Topically applied novel polymers, TAT and Penetratin all increased trans-corneal penetration efficiency of DSP without causing any damage to the corneal barrier integrity or in-vitro toxicity. This can potentially increase the bioavailability of DSP in the posterior segment tissues.

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.