Advanced glycation end products impair the scavenger function of rat hepatic sinusoidal endothelial cells.
OBJECTIVE
We have previously reported that advanced glycation end products are eliminated from the circulation mainly by scavenger receptor-mediated uptake in hepatic sinusoidal endothelial cells. Our experiments showed that the degradation of AGE-modified protein after endocytosis in hepatic sinusoidal endothelial cells occurs slowly compared with that of other scavenger receptor ligands. The aim of this study was to investigate further the mechanism whereby AGE-modified protein affects the important scavenger function of hepatic sinusoidal endothelial cells.


METHODS
Primary cultures of hepatic sinusoidal endothelial cells were pre-incubated with unlabelled ligand, unbound ligand was washed off, and the endocytic capacity was measured by addition of radiolabelled ligand, and immune electron microscopy.


RESULTS
Pre-incubation with unlabelled AGE-modified bovine serum albumin reduced subsequent endocytosis of radiolabelled scavenger receptor ligands AGE-modified bovine serum albumin, formaldehyde-treated serum albumin, oxidized low density lipoprotein and acetylated low density lipoprotein by 50, 56, 32 and 20%, respectively. Non-scavenger receptor-mediated endocytosis was not affected by pre-exposure to AGE-modified protein. Pre-incubation with a number of non-AGE-ligands did not affect subsequent endocytosis via any of the major endocytosis receptors in hepatic sinusoidal endothelial cells. Incubation in fresh medium for 6 h after pre-exposure to AGE-modified protein almost completely restored normal scavenger receptor-mediated endocytic activity. Quantitative immune electron microscopy showed that the amount of a newly described scavenger receptor for AGE-modified protein is reduced after pre-incubation with AGE-modified protein. Subcellular fractionation showed that pre-incubation with AGE-modified protein delays intracellular transport of scavenger receptor ligands.


CONCLUSIONS
Endocytosis of AGE-modified protein leads to loss of scavenger receptors and delayed intracellular transport in hepatic sinusoidal endothelial cells.
Hansen
B
B
Department of Experimental Pathology, Institute of Medical Biology, University of Tromsø, 9037 Tromsø, Norway. berit.hansen@haut.ma.uni-heidelberg.de
Svistounov
D
D
Olsen
R
R
Nagai
R
R
Horiuchi
S
S
Smedsrød
B
B
D000818:Animals; D004072:Digitonin / Q000494:pharmacology; D004705:Endocytosis; D004727:Endothelium / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D016166:Free Radical Scavengers / Q000037:antagonists & inhibitors*; D017127:Glycation End Products, Advanced / Q000378:metabolism*; D008099:Liver / Q000502:physiology*; D008297:Male; D016253:Microscopy, Immunoelectron; D051381:Rats; D017207:Rats, Sprague-Dawley; D012710:Serum Albumin, Bovine / Q000378:metabolism*
D016166:Free Radical Scavengers; D017127:Glycation End Products, Advanced; C081628:advanced glycation end products-bovine serum albumin; D012710:Serum Albumin, Bovine; D004072:Digitonin