Abstract
Abstract: :
Purpose: Sustained release of ophthalmic drugs is a rapidly developing field, suitable for treatment of conditions where systemic therapy may be accompanied by serious side effects, and where the repeated intravitreal drug administration carries significant risks. We are currently developing a novel technology aiming at the treatment with anti-angiogenic and antioxidant compounds with relevance for ocular disorders, e. g. diabetic retinopathy (DR), age-related macular degeneration (AMD), etc. This technology is based on the encapsulation of drugs in implantable devices, limited by membranes with pores of sizes in the tens of nanometer range. Methods: We studied by ELISA the diffusion rate of endostatin from solution, at the initial concentration of 10 µg/ml, across an aluminum oxide filter with pores of 20 nm. We also cultivated human retinal endothelial cells (HREC) in filter-limited tissue culture inserts, immersed in endostatin solutions of various concentrations (0-50 µg/ml). Hydrogen peroxide (1mM), catalase (500 U/ml), pyrogalol (a source of superoxide, 100 µM) and a superoxide dismutase mimetic (SODm, MnTMPyP at 25 µM) were induced to diffuse across the filter, in order to produce or to protect HREC from oxidative injury. Results: We found that endostatin diffusion is linear up to 18 h, after which it tends to decrease. In the absence of endostatin, HREC adhered and proliferated very well on untreated aluminum oxide inorganic membranes. However, when endostatin at 10 µg/ml diffused from the opposite compartment to the cells, it blocked the adhesion and induced apoptosis. Hydrogen peroxide and superoxide also induced cell death. We were able to counteract this effect by catalase and SODm that diffused from the opposite side across the membrane, respectively. Conclusions: 1) HREC are sensitive to the presence of endostatin, an anti-angiogenic molecule deficient in some conditions of retinal neo-vascularization. 2) Oxidative stress induces cell death in cultured HREC, and available anti-oxidants protect against this injury; these findings may be relevant for the initial insults which trigger DR and AMD. 3) The aluminum oxide membranes are biocompatible for HREC. 4) A drug delivery system based on the diffusion of angiostatic and antioxidant agents across inorganic nanoporous membranes, can be developed with the available technologies. Support: Patti Blow Research Fund in Ophthalmology.
Keywords: drug toxicity/drug effects • retinal neovascularization • diabetic retinopathy