Thermo-Responsive PLGA-PEG-PLGA Hydrogels as Novel Injectable Platforms for Neuroprotective Combined Therapies in the Treatment of Retinal Degenerative Diseases.

José Javier López-Cano,Hongyun Tai,Rocío Herrero-Vanrell,Irene Teresa Molina-Martínez,Irene Bravo-Osuna,Wenxin Wang,Vanessa Andrés-Guerrero,Sigen A Sigen A

doi:10.3390/pharmaceutics13020234

Abstract

The present study aims to develop a thermo-responsive-injectable hydrogel (HyG) based on PLGA-PEG-PLGA (PLGA = poly-(DL-lactic acid co-glycolic acid); PEG = polyethylene glycol) to deliver neuroprotective agents to the retina over time. Two PLGA-PEG PLGA copolymers with different PEG:LA:GA ratios (1:1.54:23.1 and 1:2.25:22.5) for HyG-1 and HyG-2 development respectively were synthetized and characterized by different techniques (gel permeation chromatography (GPC), nuclear magnetic resonance (NMR), dynamic light scattering (DLS), critical micelle concentration (CMC), gelation and rheological behaviour). According to the physicochemical characterization, HyG-1 was selected for further studies and loaded with anti-inflammatory drugs: dexamethasone (0.2%), and ketorolac (0.5%), alone or in combination with the antioxidants idebenone (1 µM) and D-α-Tocopherol polyethylene glycol 1000 succinate (TPGS) (0.002%). In vitro drug release and cytotoxicity studies were performed for the active substances and hydrogels (loaded and drug-free). A cellular model based on oxidative stress was optimized for anti-inflammatory and antioxidant screening of the formulations by using retinal-pigmented epithelial cell line hTERT (RPE-1). The copolymer 1, used to prepare thermo-responsive HyG-1, showed low polydispersity (PDI = 1.22) and a strong gel behaviour at 25% (w/v) in an isotonic buffer solution close to the vitreous temperature (31–34 °C). Sustained release of dexamethasone and ketorolac was achieved between 47 and 62 days, depending on the composition. HyG-1 was well tolerated (84.5 ± 3.2%) in retinal cells, with values near 100% when the anti-inflammatory and antioxidant agents were included. The combination of idebenone and dexamethasone promoted high oxidative protection in the cells exposed to H2O2, with viability values of 86.2 ± 14.7%. Ketorolac and dexamethasone-based formulations ameliorated the production of TNF-α, showing significant results (p ≤ 0.0001). The hydrogels developed in the present study entail a novel biodegradable tool to treat neurodegenerative processes of the retina overtime.

Highlights

Retinal diseases comprise one of the leading global causes of visual loss in the world.The proportion of the total visual impairment and blindness caused by age related macular degeneration (AMD), glaucoma and diabetic retinopathy (DR) involve neurodegenerative events and are currently greater than from infective causes [1]
The molecular weight of the poly-(DL-lactic acid coglycolic acid) (PLGA)-polyethylene glycol (PEG)-PLGA copolymer was selected based on the needs of the ophthalmic application, in order to achieve a proper and quick gelation of the polymer solution at intravitreal temperature (31–34 ◦ C) [26]
Yuan Gao et al studied the development of a dexamethasone acetate (0.1%) loaded PLGA-PEG-PLGA hydrogel at 20% w/v as an alternative to effective dexamethasone eye drops and suggested the possibility of using PLGA-PEGPLGA to develop therapies for the posterior segment of the eye [36]

Summary

Introduction

Retinal diseases comprise one of the leading global causes of visual loss in the world.The proportion of the total visual impairment and blindness caused by age related macular degeneration (AMD), glaucoma and diabetic retinopathy (DR) involve neurodegenerative events and are currently greater than from infective causes [1]. Retinal diseases comprise one of the leading global causes of visual loss in the world. AMD is the leading cause of irreversible vision loss in the world [2]. The main differences between these are the damage and progression in the fundus structures including neovascularization, atrophy and retinal degeneration [5]. If the disease progresses to late AMD, neovascularization can be present or absent, i.e., wet or exudative AMD, and dry or atrophic AMD. While wet AMD rapidly results in untreatable blindness, dry AMD is considered more as a chronic disease, that slowly evolves into irreversible vision loss [6,7]. Oxidative stress has been related to AMD and its progression, being hypothesized that undesired metabolic debris that have not been properly eliminated become oxidized, promoting inflammation and cellular damage [8]

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