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T. Yong, L. Xiaoxin, J. Yanrong; Diffusion of Macromolecule Across Retina After Experimental Branch Retinal Vein Occlusion and Estimate of Intraretinal Barriers. Invest. Ophthalmol. Vis. Sci. 2007;48(13):5789.
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© ARVO (1962-2015); The Authors (2016-present)
Intravitreal injection of macromolecule drugs has been tried to treat choroidal diseases, whereas rare study focused on how large molecule can diffuse through retina, especially in pathological condition. This study aimed to determine maximum size of molecule (MSM) capable of freely diffusing across the neuroretina of retinal vein occlusion (RVO) and the location of sites of high resistance to diffusion in neuroretina.
Experimental branch RVO in pigs was established by photodynamic method. Both the normal pig retinas from local abattoir and the retinas of RVO model were mounted in a specially designed apparatus for diffusion test. Various molecular weights (MR) FITC-dextrans dissolved in RPMI-1640 solutions were used and the rate of transretinal diffusion was determined with a spectrophotometer. Theoretical MSM was calculated by extrapolating the trend-linear relationship with the diffusion rate. In separate experiments to determine the sites of barrier to diffusion, FITC-dextrans were applied to either the inner or outer retinal surface, processed as frozen sections, and viewed with a fluorescence microscope. Paired-Samples T test was used to compared the diffusion rate of dextran of the both eyes of one pig.
The theoretical data extrapolated from the straight-line portion of the graph plotting rate of diffusion against the x-axis (Ln of MR and Stokes-Einstein radius of dextran) were: RVO eyes 83.4+2.2kDa (6.5+0.39nm), contralateral eyes 70.1+2.4 kDa (6.18+0.54nm) (t=4.143, P=0.0001). FITC-dextrans applying to inner retinal surface, 4.4 kDa dextran were largely arrested at inner nuclear layer (INL). The INL of 19.6~71.2 kDa dextrans diffusion retina section became dark and the nerve fiber layer (NFL) and inner plexiform layer got brighter. As for 150 kDa dextran, the NFL showed brightest and the other layers were dark. FITC-dextrans applying to outer retinal surface, most dextrans were blocked before outer nuclear layer (ONL).
ONL and INL may act as important barriers to diffusion (Fig.1). Compared with normal neuroretina, the MSM of fresh edema retina after RVO increased limitedly.
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