Evidence For Transport Of Bevacizumab (Avastin) Through The Retina By Muller Cells In Rabbits

Abstract

Purpose: : Bevacizumab is a recombinant humanized monoclonal IgG1 antibody that binds to and inhibits the biologic activity of human vascular endothelial growth factor (VEGF). Bevacizumab has been approved for anti–angiogenic treatment of metastatic colorectal cancer. Here, we tested whether Bevacizumab can permeate the retina after intra vitreal injection.

Methods: : Bevacizumab was biotinylated using EZ–LinkTM Sulfo–NHS–SS_Biotin (Pierce) according to the manufacturer's instructions. Three rabbits were injected intravitreally with 0.375 mg biotin labelled Bevacizumab. Then the eyes were enucleated, fixed with 4 % paraformaldehyd and embedded for immune (LR–White) or routine (Epon) electron microscopy after 24 h and 3 days following routine procedures. Biotin–labelled antibodies were localized in retinal ultrathin sections using streptavidin – gold (10 nm).

Results: : Gold granules were localized within the vitreous close to or within the inner limiting membrane. Elongated cells that cross the retina from the vitreous to the photoreceptors also were specifically labelled with gold granules. Clusters of gold granules were observed within the subretinal space. Bevacizumab did not alter the fenestration of choriocapillaris in routine EM.

Conclusions: : The elongated retinal cells that were labelled with streptavidin gold probably represent Mueller glial cells. Bevacizumab seems to be actively transported by these cells from vitreous to the subretinal space. Therefore, Bevacizumab can be used as a treatment strategy for choroidal neovascularization and macula oedema.

Keywords: age-related macular degeneration • neovascularization • Muller cells