LYSOSOMAL SEQUESTRATION OF FREE AND ESTERIFIED CHOLESTEROL FROM OXIDIZED LOW-DENSITY-LIPOPROTEIN IN MACROPHAGES OF DIFFERENT SPECIES

Macrophage foam cells of atherosclerotic lesions store lipid in lysoso mes and cytoplasmic inclusions. Oxidized low density lipoprotein (oxLD L) has been proposed to be the atherogenic particle responsible for th e free and esterified cholesterol stores in macrophages, Currently, ho wever, there is a paucity of data showing that oxLDL can induce much c holesterol accumulation in cells, The present studies compare the abil ity of mildly oxLDL (TBARS = 5 to 10 nmols/mg LDL protein) with acetyl ated LDL to induce free cholesterol (FC) and esterified cholesterol (E C) accumulation in pigeon, THP-1, and mouse macrophages, Mildly oxLDL stimulated high levels of loading comparable to acLDL where the cellul ar cholesterol concentrations ranged from 160 to 420 mu g/mg cell prot ein with EC accounting for 52-80% of the cholesterol, Pigeon and THP-1 macrophages stored most (60-90%) of oxLDL cholesterol (both FC and EC ) in lysosomes, and the bulk (64-88%) of acLDL cholesterol in cytoplas mic inclusions. Consistent with lysosomal accumulation, cholesterol es terification was 75% less in THP-1 macrophages enriched with oxLDL cho lesterol compared with acLDL, Furthermore, addition of an acyl-CoA:cho lesterol acyltransferase inhibitor did not significantly affect either cholesterol loading or the percent distribution of FC and EC in THP-1 and pigeon cells incubated with oxLDL. Surprisingly, mouse macrophage s stored most of oxLDL (71%) and acLDL (83%) cholesterol within cytopl asmic inclusions. Also, in mouse macrophages, esterification parallele d cholesterol loading, and was 3-fold more in oxLDL treated cells comp ared with acLDL treated cells. Inhibition of ACAT led to a 62% and 90% reduction in the %EC in oxLDL and acLDL treated mouse macrophages, re spectively. The results demonstrate that mildly oxidized low density l ipoprotein (oxLDL) stimulates macrophage foam cell formation and lipid engorgement of lysosomes, However, the fate of oxLDL cholesterol mark edly differs in macrophages of different species.