Toxicity assessment of intravitreal triamcinolone and bevacizumab in a retinal explant mouse model using two-photon microscopy

Intravitreal drug administration leads to high intraocular concentrations with potentially toxic effects on ocular tissues. This study was an assessment of the toxicity of triamcinolone and bevacizumab in living retinal explants using two-photon (2P) microscopy. METHODS: Wild-type mice received intravitreal injections of triamcinolone, bevacizumab, or vehicle. Ten and 45 days after injection, wholemounted retinal explants were incubated with the fluorescent dye sulforhodamine 101 (SR101) to analyze morphology and tissue damage with 2P microscopy ex vivo. Retinas that received the same treatment were stained for apoptosis (TUNEL) and glial activation (GFAP). An intravitreal injection of NMDA (N-methyl-d-aspartate) was used as a positive control to ensure the fidelity of detection of retinal damage with ex vivo 2P microscopy. RESULTS: Overall retinal morphology was undisturbed after all procedures and time points. NMDA injection resulted in a strong increase in the number of SR101-labeled cells and increased apoptosis and glial activation when compared with sham-injected eyes. This result was in contrast to exposure to bevacizumab, which caused no appreciable damage. After triamcinolone treatment, marked damage in the inner retina was observed. However, damaged cells were restricted to sharply demarcated areas, and only mild changes in TUNEL-positive cells and GFAP activation was observed when compared to sham-injected eyes. CONCLUSIONS: 2P microscopy in combination with SR101 staining allows fast morphologic assessment of living retinal explants and can be used to evaluate adverse effects on retinal viability of test substances. Bevacizumab treatment did not cause any detectable retinal damage, whereas triamcinolone was associated with substantial, although spatially restricted, damage