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T.G. Deering, A. Demetriades, E. Duh, F. MacGabhann, A. Popel, P. Campochiaro; Trans–scleral Penetration of Recombinant Human Pigment Epithelial–Derived Growth Factor (PEDF) . Invest. Ophthalmol. Vis. Sci. 2004;45(13):5054.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: : Previous studies have shown that periocular injection of adenoviral vectors containing a PEDF expression cassette results in high levels of PEDF in the choroid and strongly inhibits choroidal neovascularization. The purpose of this study was to try to gain insight into the mechanism by which trans–scleral penetration of proteins occurs (eg. passive diffusion or some other mode of transport) by investigating PEDF levels within intraocular compartments as a function of amount injected into the periocular space and the time after injection. Methods: Adult C57BL/6 mice were given a periocular injection of 5 µl containing 0.3 or 3.65 µg/ml of human recombinant PEDF. At 2, 6, and 24 hours after injection, 4 mice from each group and 4 uninjected controls were euthanized. The eye and orbital tissue were rapidly removed, and sclera, RPE/choroid, and retina were dissected. Each of these tissues was homogenized and after total protein was measured, PEDF levels were measured by ELISA. Results: PEDF levels were significantly elevated above control for both injection amounts in orbit (600 pg/ml for 0.3 µg/ml and 383 for 3.65 µg/ml vs 106 pg/ml for control), sclera (600 and 383 vs 72 pg/ml), RPE/choroid (746 and 199 vs 98 pg/ml), and retina (168 and 250 vs 62 pg/ml) at 2 hours after injection (p<0.001). At 6 hours after injection of either dose of PEDF, all tissues had PEDF levels significantly elevated above control in both dose groups with the exception of the retina samples. At 24 hours, there were no differences in PEDF levels in any tissues between injected and control eyes. The data are used in a mathematical model of protein diffusion through the ocular compartments to obtain quantitative characterization of the transport resistances of the compartments. Conclusions: These data suggest that PEDF, a 50 kDa protein, is able to rapidly penetrate the sclera and achieve equivalent levels in the choroid, however entry into the sclera is easily saturated so that there is no advantage to administration of large bolus doses. There is a barrier at the level of the RPE, which limits levels in the retina, and between 2 and 6 hours after injection, egress from the retina exceeds entry so that retinal levels fall more rapidly than choroidal levels. These data suggest that trans–scleral delivery of proteins in the 50 kDa range is feasible provided a mechanism of sustained release is utilized.
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