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7-Ketocholesterol is Not Cytotoxic to U937 Cells When Incorporated into Acetylated Low Density Lipoprotein

  • Original Article
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Lipids

Abstract

The growth of the necrotic core region within advanced atherosclerotic plaque is thought to be driven by oxidised low density lipoprotein (oxLDL)-induced death of macrophage cells. OxLDL and atherosclerotic plaque are rich in oxysterols, especially 7-ketocholesterol (7KC). As 7KC triggers cell death at physiological concentrations when added directly to the cell culture media, 7KC and other oxysterols have been suggested to be the main cytotoxic agent of oxLDL. We investigated this hypothesis by examining the toxicity of 7KC to monocyte-like U937 cells when incorporated into high-uptake non-toxic acetylated LDL (acLDL). Incorporation of 7KC into acLDL greatly reduced the oxysterol toxicity when compared with an equivalent amount of 7KC added directly to U937 cells. Enrichment of oxLDL with 7KC did not significantly enhance lipoprotein toxicity. OxLDL was highly cytotoxic yet generated only low levels of intracellular 7KC. In comparison, 7KC-acLDL generated high intracellular 7KC concentrations with little loss in cell viability. The data show that when incorporated into lipoprotein, 7KC cytotoxicity is greatly reduced, even though intracellular levels exceed those measured when cells are incubated with oxLDL, which suggests 7KC is not the significant toxic agent within oxLDL.

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Abbreviations

acLDL:

Acetylated LDL

oxLDL:

Oxidised low density lipoprotein

7KC:

7-Ketocholesterol

HNE:

4-Hydroxynonenal

HPLC:

High performance liquid chromatography

MDA:

Malondialdehyde

MTT:

3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide

PBS:

Phosphate buffered saline

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Acknowledgments

This work was partly funded through a project grant from the National Heart Foundation of New Zealand and Student Research Support from the School of Biological Sciences, University of Canterbury. We would like to thank our blood donors for our source of blood and the Nurses from The Health Centre for carrying out the blood collection.

Conflict of interest

The authors have no conflict of interest.

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Authors and Affiliations

  1. Free Radical Biochemistry Laboratory, School of Biological Sciences, University of Canterbury, Private Bag 4800, Christchurch, 8140, New Zealand

    Lucy D. Rutherford & Steven P. Gieseg

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  1. Lucy D. Rutherford
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  2. Steven P. Gieseg
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Correspondence to Steven P. Gieseg.

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Rutherford, L.D., Gieseg, S.P. 7-Ketocholesterol is Not Cytotoxic to U937 Cells When Incorporated into Acetylated Low Density Lipoprotein. Lipids 47, 239–247 (2012). https://doi.org/10.1007/s11745-011-3634-1

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  • DOI: https://doi.org/10.1007/s11745-011-3634-1

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