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Human (THP-1) macrophages oxidize LDL by a thiol-dependent mechanism
A Graham1, J L Wood, V J O'Leary
1Department of Biochemical Sciences, Wellcome Research Laboratories, Beckenham, Kent, UK.
Abstract:
The oxidative modification of low-density lipoprotein by macrophages may be an important mechanism in the pathogenesis of atherosclerosis. The human monocytic leukaemic cell line THP-1, when stimulated with phorbol ester, shares many properties with human monocyte-derived macrophages. Oxidation of LDL by these cells was characterised by depletion of alpha-tocopherol, increases in thiobarbituric acid reactive substances and increases in electrophoretic mobility. The LDL particles were also converted to a form which increased accumulation of cholesteryl esters within macrophages. The oxidative mechanism appeared to be dependent upon the presence of thiols in the cellular medium. Oxidation of LDL by THP-1 macrophages, and production of thiols by these cells, were dependent upon the presence of L-cystine in the medium. Furthermore, cellular oxidation of LDL could be partially mimicked by the addition of cysteine to Hams F10 medium. Macrophage-independent oxidation of LDL, mediated by the addition of copper ions, was inhibited by cystine and cysteine in phosphate buffered saline, but not in Hams F10 medium. The glutathione content of THP-1 macrophages was also dependent upon the presence of cysteine or cystine in the medium, but inhibition of glutathione synthesis by buthionine sulfoximine did not prevent the production of thiols or the oxidation of LDL by THP-1 macrophages.
Insights
Oxidative modification of low-density lipoprotein (LDL) by macrophages, crucial in atherosclerosis, is dependent on thiols. L-cystine in the medium drives LDL oxidation and thiol production by THP-1 cells.
Area of Science:
- Biochemistry
- Cell Biology
- Pathology
Context:
- Atherosclerosis pathogenesis involves oxidative modification of low-density lipoprotein (LDL).
- THP-1 cells, a human monocytic cell line, mimic human monocyte-derived macrophages upon phorbol ester stimulation.
- Understanding macrophage-mediated LDL oxidation is key to studying atherosclerosis.
Purpose:
- To investigate the role of thiols in macrophage-mediated LDL oxidation.
- To characterize the oxidative modification of LDL by THP-1 cells.
- To explore the influence of L-cystine and related compounds on this process.
Summary:
- THP-1 cells induced LDL oxidation, characterized by alpha-tocopherol depletion, increased thiobarbituric acid reactive substances, and altered electrophoretic mobility.
- LDL modification led to enhanced cholesteryl ester accumulation in macrophages.
- The oxidative mechanism and thiol production by THP-1 cells were dependent on L-cystine, with cysteine partially mimicking the effect.
- Macrophage-independent LDL oxidation by copper ions was differentially affected by cystine/cysteine depending on the buffer.
- Glutathione synthesis inhibition did not abolish thiol production or LDL oxidation, suggesting alternative thiol sources.
Impact:
- Provides insights into the biochemical mechanisms underlying LDL oxidation in atherosclerosis.
- Highlights the critical role of extracellular thiols, particularly from L-cystine, in macrophage-mediated LDL modification.
- Suggests potential therapeutic targets related to thiol metabolism in preventing or treating atherosclerosis.