Effects of oxidatively modified LDL on cholesterol esterification in cultured macrophages

H. Zhang, H. J K Basra, U. P. Steinbrecher

Research output: Contribution to journalArticle

108 Citations (Scopus)

Abstract

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. The retention times of 25-hydroxycholesterol and 7-hydroxycholesterol were very similar under the conditions used for gas chromatography, but mass spectrometry showed that only 7-hydroxycholesterol was detectable in oxidized LDL. Incubation of mouse peritoneal macrophages with 5 μg/ml 7-ketocholesterol resulted in stimulation of cholesterol esterification, while 7-hydroxycholesterol had a much smaller effect. When oxysterols were added to macrophages together with 5 μg/ml acetyl LDL, 7-ketocholesterol resulted in further enhancement of cholesterol esterification while 7-hydroxycholesterol produced 55% inhibition of the cholesterol esterification caused by acetyl LDL. Oxysterols extracted from oxidized LDL resulted inup to 72% inhibition of acetyl LDL-induced cholesterol esterification. Oxidized LDL resulted in much less cholesterol esterification than the same concentration of acetyl LDL. Even after correction for the amount of intact cholesterol delivered to the cells, acetyl LDL was twofold more efficient at stimulating cholesterol esterification than oxidized LDL. It was noted that almost 50% of the internalized oxidized LDL was not degraded and hence might not be accessible to acyl-CoA: cholesterol acyltransferase (ACAT), whereas the proportion of acetyl LDL that was degraded exceeded 90%. When the stimulation of cholesterol esterification was corrected for the amount of cholesterol delivered via degraded LDL, the effects of oxidized LDL and acetyl LDL were very similar. These results indicate that apparently inefficient stimulation of cholesterol esterification by oxidized LDL can be explained in large part by a lower content of cholesterol per LDL particle and altered intracellular processing, resulting in reduced delivery of cholesterol to the ACAT substrate pool. The different oxysterols present in oxidized LDL appear to have opposing effects on cholesterol esterification and, depending on the extent of oxidation of LDL and the relative proportions of oxysterols as well as the availability of cholesterol for esterification, the net result of the oxysterols could be either a modest inhibition or stimulation.

Original languageEnglish (US)
Pages (from-to)1361-1369
Number of pages9
JournalJournal of Lipid Research
Volume31
Issue number8
StatePublished - Jan 1 1990

Fingerprint

Macrophages
Esterification
LDL Lipoproteins
LDL Cholesterol
Cholesterol
Hydroxycholesterols
Cholesterol Esters
Sterol O-Acyltransferase
Scavenger Receptors
Oxidation
Gas chromatography
oxidized low density lipoprotein
acetyl-LDL
Oxysterols

Keywords

  • Acyl CoA: cholesterol acyltransferase
  • Foam cells
  • Oxidized LDL
  • Oxysterols

ASJC Scopus subject areas

  • Endocrinology

Cite this

Zhang, H., Basra, H. J. K., & Steinbrecher, U. P. (1990). Effects of oxidatively modified LDL on cholesterol esterification in cultured macrophages. Journal of Lipid Research, 31(8), 1361-1369.

Effects of oxidatively modified LDL on cholesterol esterification in cultured macrophages. / Zhang, H.; Basra, H. J K; Steinbrecher, U. P.

In: Journal of Lipid Research, Vol. 31, No. 8, 01.01.1990, p. 1361-1369.

Research output: Contribution to journalArticle

Zhang, H, Basra, HJK & Steinbrecher, UP 1990, 'Effects of oxidatively modified LDL on cholesterol esterification in cultured macrophages', Journal of Lipid Research, vol. 31, no. 8, pp. 1361-1369.
Zhang, H. ; Basra, H. J K ; Steinbrecher, U. P. / Effects of oxidatively modified LDL on cholesterol esterification in cultured macrophages. In: Journal of Lipid Research. 1990 ; Vol. 31, No. 8. pp. 1361-1369.
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N2 - 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. The retention times of 25-hydroxycholesterol and 7-hydroxycholesterol were very similar under the conditions used for gas chromatography, but mass spectrometry showed that only 7-hydroxycholesterol was detectable in oxidized LDL. Incubation of mouse peritoneal macrophages with 5 μg/ml 7-ketocholesterol resulted in stimulation of cholesterol esterification, while 7-hydroxycholesterol had a much smaller effect. When oxysterols were added to macrophages together with 5 μg/ml acetyl LDL, 7-ketocholesterol resulted in further enhancement of cholesterol esterification while 7-hydroxycholesterol produced 55% inhibition of the cholesterol esterification caused by acetyl LDL. Oxysterols extracted from oxidized LDL resulted inup to 72% inhibition of acetyl LDL-induced cholesterol esterification. Oxidized LDL resulted in much less cholesterol esterification than the same concentration of acetyl LDL. Even after correction for the amount of intact cholesterol delivered to the cells, acetyl LDL was twofold more efficient at stimulating cholesterol esterification than oxidized LDL. It was noted that almost 50% of the internalized oxidized LDL was not degraded and hence might not be accessible to acyl-CoA: cholesterol acyltransferase (ACAT), whereas the proportion of acetyl LDL that was degraded exceeded 90%. When the stimulation of cholesterol esterification was corrected for the amount of cholesterol delivered via degraded LDL, the effects of oxidized LDL and acetyl LDL were very similar. These results indicate that apparently inefficient stimulation of cholesterol esterification by oxidized LDL can be explained in large part by a lower content of cholesterol per LDL particle and altered intracellular processing, resulting in reduced delivery of cholesterol to the ACAT substrate pool. The different oxysterols present in oxidized LDL appear to have opposing effects on cholesterol esterification and, depending on the extent of oxidation of LDL and the relative proportions of oxysterols as well as the availability of cholesterol for esterification, the net result of the oxysterols could be either a modest inhibition or stimulation.

AB - 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. The retention times of 25-hydroxycholesterol and 7-hydroxycholesterol were very similar under the conditions used for gas chromatography, but mass spectrometry showed that only 7-hydroxycholesterol was detectable in oxidized LDL. Incubation of mouse peritoneal macrophages with 5 μg/ml 7-ketocholesterol resulted in stimulation of cholesterol esterification, while 7-hydroxycholesterol had a much smaller effect. When oxysterols were added to macrophages together with 5 μg/ml acetyl LDL, 7-ketocholesterol resulted in further enhancement of cholesterol esterification while 7-hydroxycholesterol produced 55% inhibition of the cholesterol esterification caused by acetyl LDL. Oxysterols extracted from oxidized LDL resulted inup to 72% inhibition of acetyl LDL-induced cholesterol esterification. Oxidized LDL resulted in much less cholesterol esterification than the same concentration of acetyl LDL. Even after correction for the amount of intact cholesterol delivered to the cells, acetyl LDL was twofold more efficient at stimulating cholesterol esterification than oxidized LDL. It was noted that almost 50% of the internalized oxidized LDL was not degraded and hence might not be accessible to acyl-CoA: cholesterol acyltransferase (ACAT), whereas the proportion of acetyl LDL that was degraded exceeded 90%. When the stimulation of cholesterol esterification was corrected for the amount of cholesterol delivered via degraded LDL, the effects of oxidized LDL and acetyl LDL were very similar. These results indicate that apparently inefficient stimulation of cholesterol esterification by oxidized LDL can be explained in large part by a lower content of cholesterol per LDL particle and altered intracellular processing, resulting in reduced delivery of cholesterol to the ACAT substrate pool. The different oxysterols present in oxidized LDL appear to have opposing effects on cholesterol esterification and, depending on the extent of oxidation of LDL and the relative proportions of oxysterols as well as the availability of cholesterol for esterification, the net result of the oxysterols could be either a modest inhibition or stimulation.

KW - Acyl CoA: cholesterol acyltransferase

KW - Foam cells

KW - Oxidized LDL

KW - Oxysterols

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