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W. W. Dawson, T. J. Garrett; Primate Fundus-Lipid Geography by Imaging Mass Spectrometry. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3430.
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The presence of lipids in human donor pigmented epithelium (PE) cells and its role in the conduit function of the PE was explored by Fine and Kwapein (1978) many years ago. They coined the name "lipoidal degeneration" without pathology data because of the "balloon" appearance of the cells. Later Ishibashi etal (IOVS, 1986) reported evidence of lipid filled monkey PE cells and adjacent debris. Other reports have been few, probably because most histology techniques use quantities of lipid solvents in the drying and in the embedment processes. Further, donor tissue is often marginal to the extent that receptor layers and PEs are usually separated. The microscopic effects of necrosis on the PE is not clearly established. Recently Anderson (Veterinary Ophthal., 2006) from Curcio’s laboratory used lipid-friendly methods to rapidly process and stain PE from aging Florida-inbred rhesus monkeys, bearing hard, soft and confluent clinical drusen. Large numbers of lipid filled PE cell clumps and single lipid filled PE cells were found in the perimacula. As usual it was not practical to reconstruct the clinical geography from the histology.
Garrett (Int. J. Mass Spectrum. 2007) has expanded the technology of tandem mass spectrometry to image-geography elucidation by scanning. Previous work has been done in flat brain slices (10um) where the geographic distribution of several lipids such as phosphatidylcholines, sphingomyelins, phosphatidylethanolames, and phosphatidylserines was clarified. We have fixed several drusen-monkey and donor eyes with four percent paraformaldehyde, sclera removed. Approximately 50° of the central fundus was vacuum desiccated on nitrocellulose slides, coated with 2,5-dihydroxybenzoic acid (necessary for matrix-assisted laser desorption ionization) and scanned using a Finnigan LTQ with vMALDI source. The laser spot diameter was 100 um and the sample plate was rastered in 100 um steps. Fundus images were constructed using custom software.
Five AMD-drusen Florida colony monkey eyes and six human donor eyes consistently showed: (1) Phosphatidylcholine species (PC) (m/z 700-900) dominated the images. (2) PC clumps (>100 um) were mainly macular. (3) Clinical drusen were found only in geographic areas showing PC clumps. (4) All eyes, all ages had some central PC markers. (5) Young eyes showed significantly fewer PC clumps.
PE and nearby lipid deposits are an important feature of the aging primate eyes macular region.
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