The low-density-lipoprotein pathway of native and chemically modified low-density lipoproteins isolated from plasma incubated in vitro

Abstract

Normal fasting human plasma was incubated for 24 h at 37 degrees C in the presence or absence of lecithin:cholesterol acyltransferase (LCAT) inhibitors. The low-density lipoprotein (LDL) fractions of incubated plasma (control LDL and LCAT-modified LDL) were studied with respect to their chemical and functional properties. LCAT-modified LDL differed from control LDL by a decreased phospholipid and free-cholesterol content, but increased cholesteryl esters. Furthermore, an increase of the relative protein content in LDL by 16-20% was found. Apolipoproteins of LCAT-modified LDL exhibited a 10-fold increase of apo AI, a 4-5-fold increase of apo E, and a 2-fold increase of apo C. All these apolipoproteins resided together with apo B on the same particles. LCAT-modified LDL displayed a higher electrophoretic mobility, a higher hydrated density, a decreased flotation constant and a smaller diameter. Cultured human fibroblasts bound and internalized LCAT-modified LDL to a lower extent than control LDL. The degradation, however, was faster. Modified LDL suppressed 3-hydroxy-3-methylglutaryl-CoA reductase activity to a lower extent than did control LDL. Our results demonstrate that LCAT action, together with lipid transfer and exchange processes, markedly alters the chemical and physiochemical properties of LDL. This in turn significantly influences LDL catabolism in vitro.

High-Level Expression of Various Apolipoprotein (a) Isoforms by "Transferrinfection": The Role of Kringle IV Sequences in the Extracellular Association with Low-Density Lipoprotein

“…LDL was prepared by ultracentrifugation in a density range from 1.020 to 1.63 g/mL from plasma obtained from healthy subjects as previously described (Zechner et al, 1984). All subjects were Lp(a)-negative in our immunoassay, and LDL fractions were additionally subjected to immunoabsorption chromatography on an anti-apo(a)-Sepharose column to remove any contaminating Lp(a).…”

Intralipid infusion abolishes ability of human serum to cholesterol-load cultured macrophages.

“…Support for this concept comes from the recent observation that chylomicron remnants increased 3 H-oleate incorporation into macrophage triglycerides, while decreasing its incorporation into macrophage cholesteryl ester. 7 Finally, it has been shown that binding and uptake of LDL is reduced by alterations in the phospholipid composition of cultured cells 35 and by alterations in the surface lipids of LDL 36 Intralipid and its components also affected macrophage cholesterol balance by promoting cellular cholesterol efflux. Previous studies have shown that cholesterol efflux from cells in the presence of lipoproteins 37 ' 38 -39 or liposomes 39 -40 is mediated by desorptjon of unesterified cholesterol from the plasma membrane, followed by hydrolysis of intracellular stores of cholesteryl ester.…”

Lipoprotein lipase modulates net secretory output of apolipoprotein B in vitro. A possible pathophysiologic explanation for familial combined hyperlipidemia.

“…The other two-thirds may have abnormalities in other factors known to affect lipoprotein binding to receptors (5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) or in factors known to affect LpL (24,73). Ofparticular interest are cholesteryl ester transfer protein, which can change the neutral lipid composition of nascent lipoproteins (38) and might therefore alter receptor affinity (1 1, 14), and apoproteins CIII and AIV, which inhibit apo E-mediated binding (20,21) and modulate LpL activity (73,74).…”

“…Several factors have been reported to affect the binding of mature plasma lipoproteins to the cell surface, and might therefore affect the binding and reuptake ofapo B-rich nascent particles. These factors include lipoprotein lipase (LpL) (5-10), hepatic lipase (5, 10, 1 1), phospholipase A2 (12,13), cholesteryl ester transfer protein (11,14), lecithin: cholesterol acyl transferase (15), lysophosphatidylcholine (16), apo E (17)(18)(19), apo AIV (20), and the C-apoproteins (21,22).…”