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    Researchers image single cell deaths in glaucoma patients


    Enter annexin 5

    Professor Cordeiro and colleagues hit upon the idea of using annexin 5, an endogenous protein common in humans. In the presence of calcium, annexin 5 has a high affinity for phosphatidylserine, which is exposed on apoptotic cell membranes.

    Annexin 5 has already proved useful in in vitro assays to measure apoptosis. When radiolabelled, it has helped identify apoptosis, but not down to the level of individual cells.

    In experimental models, Professor Cordeiro and colleagues have shown that it can identify apoptosis in Alzheimer's disease, Parkinson's disease, optic neuropathy, retinal neurodegeneration, and glaucoma.

    To test it out in humans, the researchers labelled annexin 5 with fluorescent dye DY-776 to create ANX776. They randomly assigned eight patients with progressive glaucoma and eight healthy subjects to intravenous doses of 0.1, 0.2, 0.4, and 0.5 mg of ANX776.

    They used a confocal scanning laser ophthalmoscope set to ICGA infrared fluorescence after pupillary dilation to acquire images of the subjects' retinas. They only dosed one subject per day, with a minimum of 72 hours between doses of the first and second participant. They required the subjects to stay in the hospital to monitor them for adverse events.

    The glaucoma patients all had significantly increased cupping, with a mean cup-to-disc ratio of 0.53, and elevated IOP, with a mean of 13.9 mm Hg. Over a mean period of 7.3 months, they showed structural and visual field progression.

    Apoptotic cells appeared as hyperfluorescent spots on the retina measuring between 12 and 16 µm diameter in a retinal area in each image of 78.73 mm2.

    Spots had different fluorescent signal profiles over time and appeared at the level of the retinal ganglion cell layer, as judged by focusing in the reflective mode of the confocal scanning laser ophthalmoscope.

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