The disposition and diffusion knowledge of intravitreally injected macromolecule drugs through retina in pathological condition is crucial but the related studies are absent. Retinal edema is a common pathological change of fundus diseases and retinal vein occlusion (RVO) pig model were established to emulate it. FITC-dextrans of various molecular weights were dissolved in RPMI-1640 solutions and the rate of transretinal diffusion was determined with a spectrophotometer. Theoretical maximum size of molecule (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 dextrans of the both eyes of one pig. The MSM in RVO tissues and normal tissue was 6.5+0.39nm and 6.18+0.54nm respectively (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 the 19.6∼71.2 kDa dextran diffusion retina section became dark and the nerve fiber layer (NFL) and inner plexiform layer got brighter. As for 150 kDa dextran, the NFL was bright and the other layers were dark. FITC-dextrans applying to outer retinal surface, most dextrans were blocked before outer nuclear layer (ONL). In summary, ONL and INL may act as bottle-neck barriers to diffusion of macromolecules. Compared with normal neuroretina, the MSM of fresh edema retina after RVO increased limitedly.
Keywords: Retinal vein occlusion, drug diffusion, macromolecule, intraretinal diffusion barrier, intravitreous drug delivery
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