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I. Lengyel, C.J. Frederickson, T. Peto, A.C. Bird, F.J. G. M. van Kuijk; The Distribution of Free Zinc Within Drusen in AMD Donor Eyes . Invest. Ophthalmol. Vis. Sci. 2006;47(13):857.
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One of the hallmarks of AMD is the appearance of drusen, the lipid and protein rich deposits between the retinal pigment epithelium and the choroidal vasculature. We have shown previously that drusen also contain weakly–bound zinc. In this study we investigated the distribution of this zinc pool in drusen in characterised AMD donor eyes.
Frozen donor eyes from the Montana Eye Bank were used and were photographed before dissection. Following defrosting, the choroid, neuronal retina and the retinal pigment epithelial cells were removed to expose the underlying Bruch’s membrane with or without drusen. Samples from individual eyes were treated with 10 µM ZP1 (a zinc specific fluorescence probe) in PBS for 5 min. Excess ZP1 was removed by rinsing the samples in fresh PBS and the changes in fluorescence was viewed by a NIKON fluorescence microscope (excitation: 460–500 nm; emission: 530–560 nm). Structural details of these preparations were further elucidated by viewing the tissues with a Zeiss LSM 50 confocal microscope (excitation of 488 nm; emitted light was filtered by 530–560 nm cut–off filter).
Apart from the overall increase in fluorescence, incubation with ZP1 resulted in zinc–dependent punctate staining within drusen suggesting that internal structures like, for example, the spherules formed by amyloid beta peptides might also be loaded with weakly–bound zinc. There were other structures that showed high levels of fluorescence, while many were completely devoid of ZP1 labeling. The lack of labeling at the core of some drusen was always associated with an apparent brake of ∼1 µm in ZP1 labeling of the Bruch’s membrane.
We showed here that distribution of weakly–bound zinc is not homogenously distributed in drusen. The enrichment or the lack of enrichment in drusen substructures indicated that zinc might be involved in several aspects of drusen formation which might play a specific role in the pathogenesis of AMD. Therefore, altered retinal or plasma zinc levels in the early stages of AMD might be involved in the development of the disease. However, the exact role for zinc in AMD is yet to be determined.
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