Effects of oxidatively modified LDL on cholesterol esterification in cultured macrophages

Oxidative modification of low density lipoproteins (LDL) has been shown to cause accelerated degradation of LDL via the scavenger receptor pathway in cultured macrophages, and it has been proposed that this process might lead to cholesterol accumulation in macrophages in the arterial wall in vivo. However, oxidation of LDL is accompanied by a substantial reduction in LDL total cholesterol content and hence the amount of cholesterol delivered by oxidatively modified LDL may be less than that delivered by scavenger receptor ligands such as acetyl LDL which results in massive cholesterol accumulation in cultured macrophages. The present studies were done to determine whether the decrease in total cholesterol content during LDL oxidation was due to oxidation of cholesterol and cholesteryl ester, and to determine whether the resulting oxidized sterols could affect cholesterol esterification in cultured macrophages. It was found that when LDL prelabeled with [3H]cholesteryl linoleate was oxidized, there was a decrease in cholesterol mass but no change in radioactivity. The radioactive substances derived from cholesteryl linoleate appeared more polar than the parent compound when analyzed by reverse-phase liquid chromatography, but were not identical with free cholesterol. Thin-layer chromatography of oxidized LDL lipids confirmed the loss of esterified cholesterol, and revealed multiple new bands, some of which matched reference oxysterols including 7-ketocholesterol, 5,6-epoxycholesterol, and 7-hydroxycholesterol. In addition to oxysterols, oxidized cholesteryl esters were also present. Quantitation by gas chromatography indicated that 7-ketocholesterol was the major oxysterol present.(ABSTRACT TRUNCATED AT 250 WORDS)