Alzheimer's soluble amyloid beta protein is secreted by HepG2 cells as an apolipoprotein.

Recently we reported that the soluble form of amyloid beta protein (sA beta) in normal human plasma and cerebrospinal fluid is associated with lipoprotein (LP) particles. In this paper we tested the sA beta secretion by cells in association with LP in the model of the human hepatoma HepG2 cell line. These cells secreted sA beta to the culture media and expressed intracellular sA beta immunoreactivity. Soluble A beta in the cell supernatant was detected in 200-300 kDa LP complexes in association with apoA-I, apoJ, transthyrethin and phospholipids, triglycerides and free and esterified cholesterol. This was assessed by size exclusion HPLC, immunoprecipitation with corresponding antibodies and by analysis of sA beta associated metabolically-labeled lipids, respectively. Our results suggest that sA beta to LP association represents a unique mechanism, governing the normal biology of sA beta.