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C. A. Curcio, L. Wang, M. E. Clark; Lipid Composition of Isolated Extra-Macular Drusen. Invest. Ophthalmol. Vis. Sci. 2009;50(13):4935.
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To characterize the lipid composition of drusen, for comparison to histochemical studies demonstrating the ubiquity of esterified and unesterified cholesterol (EC, UC) in these lesions (1), and for comparison to the lipid profile of lipoprotein particles isolated from Bruch’s membrane (BrM) (2). (2).
Drusen capped with retinal pigment epithelium (RPE) were isolated manually from 7 eyes of 7 donors (66-90 yr) with grossly normal maculas preserved in 4% paraformaldehyde within 6 hr of death. The prevalence of druse types in extra-macular retina was previously determined to be 74% hard and 26% compound (3). RPE sheets from each eye were assayed for comparison. Lipids were extracted with chloroform: methanol, dried under nitrogen, solubilized in chloroform, and separated by thin layer chromatography, with standards, using a solvent system preferred for neutral lipids (petroleum ether: diethyl ether: acetic acid, 84:15:1). Bands for EC, UC, triglyceride (TG) and fatty acids (FA) on chromatography plates were subjected to digital densitometry. The percentage of dry weight taken up by each lipid class was calculated for RPE-capped drusen and RPE sheets.
Neutral lipids were a consistent proportion of dry weight of RPE-capped drusen, at 7.1% (SD, 1.1%). The largest component was EC, which is 4.8% (SD, 1.0%) of dry weight and 68% of neutral lipid. TG and FA acid content were both low, and the TG/EC ratio was only 0.038. In contrast, 1.7% (SD, 0.9%) and 1.2% (SD, 0.5%) of RPE sheets were neutral lipid and EC, respectively, indicating that RPE contributes relatively little to the neutral lipid measured in RPE-capped drusen.
Oil red O stainable neutral lipids in drusen were described 45 yr ago. We find that the largest component of this material is EC. The composition of druse-associated neutral lipid resembles that of lipoproteins isolated from BrM (2), with regard to low TG levels, suggesting that these lipoproteins are the major source for EC in drusen. EC is the first druse constituent for which abundance has been expressed as a proportion of weight rather than as number of affected eyes or prevalence within an eye. With nearly 150 known druse constituents, EC at 4.8% is disproportionately large. Studies in progress will address polar lipid components of drusen.1. Li (2007) Exp Eye Res 85, 1922. Wang (2008) IOVS in press3. Rudolf (2008) IOVS 49, 1200
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