EDTA DIFFERENTIALLY AND INCOMPLETELY INHIBITS COMPONENTS OF PROLONGEDCELL-MEDIATED OXIDATION OF LOW-DENSITY-LIPOPROTEIN

The extent to which cells can oxidize LDL may be underestimated becaus e of the use of standard and arbitrary 24 hour in vitro incubations of cells with LDL. Such incubations have resulted in inconsistent result s regarding the ability of cell-mediated LDL oxidation to generate rel atively advanced oxidation products such as 7-ketocholesterol (7-KC). We studied prolonged oxidation of low density lipoprotein (LDL) by mou se peritoneal macrophages using HPLC measurement of cholesterol, chole steryl esters and their oxidation products 7-KC and cholesteryl linole ate hydroperoxide (CL-OOH). Cell-mediated oxidation in Ham's F10 consi stently followed the successive stages previously described during 24 hour-10 mu M copper-mediated LDL oxidation, always generating 7-KC if allowed to proceed for sufficient time. The degree of inhibition of LD L oxidation achieved by metal chelators EDTA and DTPA at more advanced stages of cell-mediated LDL oxidation was not predictable from the pu blished effects of such chelators upon early stages of metal-mediated and cell-mediated LDL oxidation. EDTA and DTPA only incompletely preve nted the consumption of cholesteryl esters and the loss of preformed C L-OOH when added after cell-mediated LDL oxidation was established, wh ile effectively concurrently inhibiting the generation of 7-KC. These data indicate that progressive cell-mediated peroxidation of LDL chole steryl eaters and decomposition of CL-OOH may be less dependent upon a continuing supply of redox active metals than is the generation of 7- KC. In addition, they confirm the plausibility of prolonged cell media ted oxidation of LDL as a source of oxysterols found in human atherosc lerotic plaque, and imply that active redox cycling of metals is parti cularly important for their generation in vivo.