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Richard Foxton, Andrew Osborne, Keith R Martin, Yin Shan Eric Ng, David T Shima; VEGF antagonism accelerates RGC apoptosis in diabetic mice; a potential role for VEGF in axonal transport. Invest. Ophthalmol. Vis. Sci. 2014;55(13):2181. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
There is increasing evidence that ocular anti-VEGF-A agents are detrimental to the health of neurons in the retina. Here we investigate the effect of VEGF-A antagonism on retinal ganglion cell (RGC) apoptosis in the Ins2Akita mouse, a genetic model of type I diabetes. We also explored the hypothesis that VEGF-A plays a normal role in RGC health and function, which could explain the neuronal liability accompanying anti-VEGF-A treatment.
6-week-old diabetic Ins2Akita mice were treated with 2 weekly intravitreal (IVT) injections of 4 pmoles anti-VEGF-A. At 8 weeks, the number of apoptotic nuclei was assessed using TUNEL staining. Axonal transport in normal animals was investigated in female Brown Norway rats injected IVT with 20 pmoles anti-VEGF-A. 0.2% Alexfluor 488-labelled cholera toxin beta subunit (CTB) was administered IVT 5 days later, and retinas, optic nerves and brains were harvested after an additional 2 days. Axonal transport to the superior colliculus was quantified using epifluorescence microscopy.
In retinas from diabetic Ins2Akita mice, a 2.4-fold increase in the number of TUNEL positive cells were found in the RGC layer in comparison to wild-type mice. Following anti-VEGF-A treatment, apoptotic labelling was further increased; 2.2-fold above vehicle-treated Ins2Akita levels, and 6.3-fold above wild-type mice. In axonal transport studies, a decrease in CTB transport (fluorescence intensity) was observed throughout the superior colliculus following VEGF-A antagonism, in particular around the midline of the brain. Cumulative fluorescent intensity significantly decreased 32%, mean gray level fluorescence fell 25% and peak intensity around the inner (midline) region of the superior colliculus was reduced by as much as 44%
These data provide further evidence of the potential risks of VEGF-A antagonists to the neuronal retina. We have now demonstrated this in a mouse model where VEGF-A levels are pathologically elevated, as well as extending our data to suggest that VEGF-A plays a role in the normal physiological processes of RGCs. These findings emphasize that further studies are necessary to determine if neurons will be adversely affected following long-term treatment with VEGF-A antagonists, and highlight the need to explore non-anti-VEGF-A therapies for ocular neovascular disease.
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