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Richard Thompson, Lajos Csincsik, Kavita Hegde, Trevor J McGill, Martha Neuringer, Hillary Baruch, Jacob Tatum, Adam Puche, Imre Lengyel; Comparison of Hydroxyapatite Deposits in Primate and Human sub-Retinal Pigment Epithelial Deposits. Invest. Ophthalmol. Vis. Sci. 2016;57(12):5799.
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While sub-RPE deposits such as drusen are widely accepted as precursors to age-related macular degeneration (AMD), the molecular events that initiate deposit formation have not yet been fully elucidated. We recently discovered that sub-RPE deposits in human cadaver eyes have microscopic spherules of hydroxyapatite (HAP, also called hydroxylapatite), the hard, insoluble form of calcium phosphate found predominantly in bones and teeth. These spherules are distinct from the well-known calcification of the Bruch's membrane itself. In this study we compared the morphology and incidence of HAP deposition in human and macaque retinas.
: HAP deposition was visualized by the use of LiCor BoneTag 680RD or Alizarin Red S, two bone stains that fluoresce when bound to HAP. We labelled unfixed and fixed macaque and human flatmounts of Bruch’s membrane/choroid complexes after the removal of the neurosensory retina and the RPE or sections from whole eyes. We examined eyes from ages ranging 16 to 38 years (comparable to 48 to 114 years in humans) for primates and 34 to 95 years for humans. In some cases fundus photographs of the macaques were available. HAP deposition was imaged by scanning the flatmount using the Odyssey system from LiCor and bright field and fluorescence confocal microscopy.
: By comparison with human tissues the macaque tissues generally had smaller and less numerous HAP depositions with fewer hollow spherules in sub-RPE deposits, however the pattern of distribution did not differ from those in human tissues. Deposits were present both centrally as well as peripherally. Fixation and post mortem time showed increased background autofluorescence as well as increased non-specific LiCor BoneTag 680RD or Alizarin Red S fluorescence.
Our results show that HAP deposition is present in both primate and human eyes with similar distribution. The reduced numbers of spherules and particularly hollow spherules in primates compared to fresh human tissue suggest that the molecular events involved in deposit formation in primate and human eyes are similar but not identical. Our results clearly indicate that fresh tissues with short post-mortem time are preferable when analyzing HAP deposition in the eye.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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