Retinal Electrophysiologic, Morphologic and Penetration Studies Following Intravitreal Injection of Bevacizumab (Avastin ®)

Abstract

Purpose: : Intravitreal bevacizumab (Avastin; Genentech Inc., San Francisco, CA) is a new promising treatment for age–related macular degeneration, used widely off–label. Our aim was to evaluate retinal penetration and toxicity of bevacizumab.

Methods: : 10 albino rabbits were injected intravitreally with 0.1 ml (2.5 mg) of bevacizumab to one eye and 0.1 ml saline into the fellow eye. To assess toxicity, electroretinogram (ERG) was recorded 3–hours, 3–days, 1–, 2–, 4–weeks after injection. At the termination of the ERG follow–up (4–weeks), the visual evoked potential (VEP) was recorded. Then, the rabbits were sacrificed and the retinas prepared for histological examination at the light microscopy level. To assess retinal penetration of the humanized bevacizumab antibody, donkey anti–human IgG conjugated to the fluorochrome Cy3 was added to 100 um thick vibratome sections. Muller cell and microglia reactivity was assessed by labeling retinal sections with anti–vimentin and the isolectin B4, respectively. Images were collected using a laser scanning confocal microscope (Olympus FluoView 500).

Results: : The ERG responses of the control and experimental eyes were similar in amplitude and pattern throughout the follow–up period. The flash VEP responses of the experimental eyes were of normal pattern and amplitude and did not differ from those recorded by stimulation of the control eye alone. No morphological changes were observed in any of the examined eyes. Full thickness retinal penetration to the RPE (but not within the RPE) was present at 24 hours and 7 days and was essentially absent at 4 weeks. No reactivity was observed in either Muller cells or microglia; the intermediate filament expression in Muller cells and the distribution of microglia were similar to uninjected control, as well as saline injected eyes.

Conclusions: : Bevacizumab was found to be non–toxic to the rabbit retina . Full thickness retinal penetration may explain observed clinical effects of intravitreal bevacizumab. Although extrapolation to humans should be done with caution, our study supports the safe use of intravitreal bevacizumab injection

Keywords: age-related macular degeneration • choroid: neovascularization • electroretinography: non-clinical