MODIFIED LOW-DENSITY-LIPOPROTEIN DELIVERS SUBSTRATE FOR CERAMIDE FORMATION AND STIMULATES THE SPHINGOMYELIN-CERAMIDE PATHWAY IN HUMAN MACROPHAGES

Exposure of human blood monocytes derived macrophages to modified (oxi dized or acetylated) LDL induced a similar to 40% elevation (60 pmol/1 0(6) cells) of the endogenous level of the sphingolipid ceramide. A ri se of both neutral and acidic SMase activity was found after treatment with oxidized LDL (250 and 80%), while addition of acLDL stimulated o nly the neutral enzyme (280%). Sphingo(phospho)lipids from LDL were tr ansferred to the cell membrane and distributed into intracellular comp artments as observed with acLDL containing BODIPY-FL-C-5-SM. Quantitat ion of ceramide after the addition of [H-3-N-acetyl]- or BODIPY-FL-C-5 -SM-labeled modified LDL (27 mu g/ml) to the cell culture medium indic ated that approximately 210 pmol CA/10(6) cells was generated from exo genous (ox/acLDL) SM. These results demonstrate a stimulation of the s phingomyelin-ceramide pathway by modified LDL utilizing primarily exog enous (LDL-derived) substrate and suggest that the effects of modified LDL are at least partially due to an increased level of the messenger ceramide. (C) 1997 Federation of European Biochemical Societies.