Abstract
Purpose :
DARC (Detection of Apoptosis Retinal Cells) consists of a fluorescently-labelled annexin A5 molecule (ANX776) which binds to externalised phosphatidylserine (PS) on retinal cells undergoing apoptosis and stress. However, recently, endothelial cell PS externalisation has been demonstrated as one of the earliest stages in neovascularization. Here we assess if DARC can be used as a biomarker of vascular leakage and angiogenesis in vivo.
Methods :
Pilot experiments were performed on 3 New Zealand White (NZW) rabbits to evaluate the natural history of vessel leakage and neovascularisation using FFA. Following this, 6 NZW rabbits had intravitreal injections humanVEGF165 (1 ug, Sigma, UK) into the left eye only of each animal, with 3 being given ranibizumab treatment. Animals were assessed 2 and 4 days later, using intravenous ANX776 (0.2mg) and 1% sodium fluorescein after baseline autofluorescence.
Results :
Although not present at 2 days, all control rabbit eyes treated with hVEGF had fluorescein leakage at 4 days compared to ranibizumab eyes. All left hVEGF eyes were found to have significantly (p<0.05) more DARC positive-staining compared to the untreated contralateral right eye 2 days after treatment; however, ranibizumab eyes had significantly less (p<0.05) than untreated hVEGF eyes.. Staining appeared as single spots localised to the vascular branches of the main stems of the retinal vessels.
Conclusions :
This is the first time in vivo that DARC has been shown to identify phosphatidylserine in angiogenic processes, and illustrates its use as a biomarker for anti-angiogenic treatments. DARC can be therefore used in vivo to identify the earliest stages of leakage and angiogenesis in choroidal neovascularisation, diabetic eye disease and potentially any retinal disease in which pathological angiogenesis occurs.
This is a 2021 ARVO Annual Meeting abstract.