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Antje K. Biesemeier, Ulrich Schraermeyer, Oliver Eibl; AMD Affected Donors Accumulate High Amounts Of Heavy Metal Ions In Melanosomes Of The Retinal Pigment Epithelium (RPE) And Calcified Areas Of Bruch’s Membrane. Invest. Ophthalmol. Vis. Sci. 2012;53(14):4761.
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To identify differences in the ultrastructure, heavy metal storage ability and elemental composition of melanosomes of human RPE of five AMD affected donors compared to five age-matched healthy individuals. RPE melanosomes, lying above or below different pathological tissues (drusen, basal deposits, thickening and calcification of Bruch’s membrane or neovascularisation membranes and retinal damage) were measured.
Analytical Electron Microscopy (AEM) including Energy-Filtered Transmission Electron Microscopy (EFTEM), Energy-Dispersive X-ray microanalysis (EDX) and Electron Energy-Loss Spectroscopy (EELS).
Eyes of AMD affected donors were investigated ultrastructurally and using AEM. Melanosomes of the RPE of AMD affected donors contained increased amounts of iron (0.04 - 0.09 at%) compared to controls where Fe was at or below the detection limit of 0.02 at%. In addition, AMD melanosomes showed a significant lead mole fraction (0.03 - 0.1 at%), which was undetectable in control samples. First experiments showed no clear differences in the elemental composition of melanosomes overlying drusen and basal deposits. Some areas of Bruch’s membrane were calcified containing CaPO4 crystals in the elastic layer. These areas could be recognized by AEM, and P elemental maps identified their ultrastructural location in the tissue. These calcified layers contained heavy metal depositions with additional Fe and Pb mole fractions. P, Ca and Pb were not identified in the other areas of Bruch’s membrane.
Iron and lead were significantly increased in the melanosomes of all AMD donor eyes investigated. They were also found in calcified areas of the elastic layer of Bruch’s membrane. Heavy metals promote oxidative stress in the retina and are thought to be potential initiators of AMD. Whether the specific accumulation in melanosomal stores and Bruch’s membrane has beneficial or toxic effects on the surrounding tissues must be further elucidated.
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