Lipoprotein particles of intraocular origin in human Bruch membrane: an unusual lipid profile.
OBJECTIVE
Throughout adulthood, Bruch membrane (BrM) accumulates esterified cholesterol (EC) associated with abundant 60- to 80-nm-diameter lipoprotein-like particles (LLP), putative apolipoprotein B (apoB) lipoproteins secreted by the retinal pigment epithelium (RPE). In the present study, neutral lipid, phospholipids, and retinoid components of human BrM-LLP were assayed.


METHODS
Particles isolated from paired choroids of human donors were subjected to comprehensive lipid profiling (preparative liquid chromatography [LC] gas chromatography [GC]), thin-layer chromatography (TLC), high-performance liquid chromatography (HPLC), Western blot analysis, and negative stain electron microscopy. Results were compared to plasma lipoproteins isolated from normolipemic volunteers and to conditioned medium from RPE-J cells supplemented with palmitate to induce particle synthesis and secretion.


RESULTS
EC was the largest component (32.4+/-7.9 mol%) of BrM-LLP lipids. EC was 11.3-fold more abundant than triglyceride (TG), unlike large apoB lipoproteins in plasma. Of the fatty acids (FA) esterified to cholesterol, linoleate (18:2n6) was the most abundant (41.7+/-4.7 mol%). Retinyl ester (RE) was detectable at picomolar levels in BrM-LLP. Notably scarce in any BrM-LLP lipid class was the photoreceptor-abundant FA docosahexaenoate (DHA, 22:6n3). RPE-J cells synthesized apoB and numerous EC-rich spherical particles.


CONCLUSIONS
BrM-LLP composition resembles plasma LDL more than it does photoreceptors. An EC-rich core is possible for newly synthesized lipoproteins as well as those processed in plasma. Abundant EC could contribute to a transport barrier in aging and lesion formation in age-related maculopathy (ARM). Analysis of BrM-LLP composition has revealed new aspects of retinal cholesterol and retinoid homeostasis.
Wang
Lan
L
Department of Ophthalmology, University of Alabama at Birmingham, Birmingham, Alabama 35294-0009, USA.
Li
Chuan-Ming
CM
Rudolf
Martin
M
Belyaeva
Olga V
OV
Chung
Byung Hong
BH
Messinger
Jeffrey D
JD
Kedishvili
Natalia Y
NY
Curcio
Christine A
CA
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001055:Apolipoproteins B / Q000378:metabolism; D015153:Blotting, Western; D016570:Bruch Membrane / Q000378:metabolism*; D018929:Cell Culture Techniques; D002788:Cholesterol Esters / Q000378:metabolism; D002829:Choroid / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D002853:Chromatography, Liquid; D002855:Chromatography, Thin Layer; D005260:Female; D006801:Humans; D008074:Lipoproteins / Q000378:metabolism*; D008268:Macular Degeneration / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D055213:Retinal Pigment Epithelium / Q000378:metabolism
D001055:Apolipoproteins B; D002788:Cholesterol Esters; D008074:Lipoproteins