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Abstract

We have recently demonstrated that lipids, particularly cholesterol, covalently bound to apolipoprotein B (apoB) are a stable marker of low density lipoprotein (LDL) oxidation (Tertov et al. 1995). The present study is an attempt to assess the relationship between the degree of LDL oxidation, evaluated by the content of apoB-bound cholesterol and the ability of LDL to induce cholesterol accumulation in cultured human aortic intimal smooth muscle cells, i.e. LDL atherogenicity. Native LDL was oxidized in vitro by copper ions, 2,2-azobis-(2-aminopropane hydrochloride), or sodium hypochlorite. Minimum degree of LDL in vitro oxidation necessary to convert LDL into atherogenic one was accompanied by an increase of apoB-bound cholesterol to the level much higher than that usually observed in freshly isolated atherogenic LDL from human blood. Moreover, elimination of LDL aggregates from in vitro oxidized LDL preparations by gel filtration led to loss of its atherogenic properties. Thus, the ability to induce cholesterol accumulation in cells, i.e. the atherogenicity of in vitro oxidized LDL is a result of LDL aggregation but not oxidation. We also studied the relationship between LDL atherogenicity and apoB-bound cholesterol content in LDL freshly isolated from healthy subjects and normo- and hypercholesterolemic patients with coronary atherosclerosis. The ability of human LDL to induce cholesterol accumulation in aortic smooth muscle cells did not correlate with the degree of in vivo LDL oxidation (r = 0.12, n = 90). It is concluded that LDL atherogenicity does not depend on the degree of lipid peroxidation in LDL particle.

Resistance of native and circulating modified low-density lipoproteins in human blood to association

“…It should be emphasized that association is an irreversible process. These results are consistent with published data [11,12] that human blood cmLDL can be easily engulfed by cultured smooth muscle cells in human aortic intima and macrophages. Moreover, accumulation of LDL in cells increases with increasing in the size of particles.…”

“…Total LDL fraction was isolated by two-step ultracentrifugation in a NaBr density gradient [11]. nLDL and cmLDL were separated by lectin chromatography on a column packed with Ricinus communis agglutinin agarose (Boehringer Mannheim GmbH) [14].…”

Low ionic strength promotes association of circulating modified LDL human blood

“…This association was irreversible, at least under our experimental conditions. Probably, such irreversibility results from peculiarities of physicochemical properties of the surface of cmLDL [3,10,13]. Bearing in mind that the efficiency of LDL uptake by cells increases with increasing the size of these particles [3,[12][13][14], we can hypothesize that the ability of cmLDL to accumulate cholesterol in cultured smooth muscle cells isolated from human aortic intima and in macrophages [3,11,15] results from predisposition of these particles to association.…”

“…The total fraction of LDL was isolated by two-step ultracentrifugation in a NaBr density gradient [10].…”

“…The total fraction of LDL was isolated by two-step ultracentrifugation in a NaBr density gradient [10]. nLDL and cmLDL subfractions were separated by affinity lectin-chromatography on Ricinus communis agglutinin-agarose column (Boehringer Mannheim, GmbH) [13].…”