HUMAN (THP-1) MACROPHAGES OXIDIZE LDL BY A THIOL-DEPENDENT MECHANISM

The oxidative modification of low-density lipoprotein by macrophages m ay be an important mechanism in the pathogenesis of atherosclerosis. T he human monocytic leukaemia cell line THP-1, when stimulated with pho rbol ester, shares many properties with human monocyte-derived macroph ages. Oxidation of LDL by these cells was characterised by depletion o f alpha-tocopherol, increases in thiobarbituric acid reactive substanc es and increases in electrophoretic mobility. The LDL particles were a lso converted to a form which increased accumulation of cholesteryl es ters within macrophages. The oxidative mechanism appeared to be depend ent upon the presence of thiols in the cellular medium. Oxidation of L DL 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 LD L, mediated by the addition of copper ions, was inhibited by cystine a nd cysteine in phosphate buffered saline, but not in Hams F10 medium. The glutathione content of THP-1 macrophages was also dependent upon t he presence of cysteine or cystine in the medium, but inhibition of gl utathione synthesis by buthionine sulfoximine did not prevent the prod uction of thiols or the oxidation of LDL by THP-1 macrophages.