Tempol Protects Against Indocyanine Green Induced Retinal Changes in vivo

Abstract

Purpose: : Indocyanine green (ICG) selectively stains the internal limiting membrane (ILM) of the retina and has been widely used to assist peeling of the ILM in vitreoretinal surgery. However, there is accumulating evidence that ICG can be toxic to retinal cells. Aim of this study was to evaluate whether Tempol (4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl), a free radical scavenger, can protect against intravitreal ICG induced structural and functional changes in rat retinas.

Methods: : Adult brown Norway rats received intravitreal injections of 2 µl of a 0.5% ICG solution dissolved in sterile BSS with BSS serving as a control. Tempol at a dose of 20 mg/kg BW was administered intraperitoneally 24 hours and 30 minutes before intravitreal ICG injections and then once daily for 7 consecutive days. Control rats were treated with vehicle (PBS, pH 7.2) only. The effects of tempol treatment on retinal toxicity was assessed by retinal ganglion cell (RGC) backlabeling and counting as well as by light microscopy 7 days after intravitreal ICG injections. Additionally electroretinography (ERG) was performed 1 and 2 weeks after ICG administration.

Results: : ICG administration reduced RGC numbers by 17% (1943±45 RGCs/mm2 vs. 2342±31). Tempol treatment rescued RGCs in a significant manner (2258±36, p<0.001) and led to morphological changes detected by light microscopy. ERG showed a significant reduction of Vmax in ICG injected eyes only in PBS treated animals (530.1 ±145µV vs. 778.9 ±179µV, p=0.0052), but not in the tempol treated group.

Conclusions: : Tempol significantly attenuates ICG induced toxicity in rat retinas and may, therefore, be considered for further evaluation as accompanying treatment in ICG assisted chromovitrectomy.

Keywords: ganglion cells • neuroprotection • vitreoretinal surgery