Mildly oxidised LDL induces more macrophage death than moderately oxidised LDL: roles of peroxidation, lipoprotein-associated phospholipase A2 and PPARgamma

Death of macrophages and smooth muscle cells (SMC) can lead to progression of atherosclerosis. Mildly oxidised low-density lipoprotein (mildly-oxLDL) induced more overall death and apoptosis than moderately oxidised LDL, in human monocyte-macrophages (HMM). Mildly-oxLDL also induced more overall death in human SMC than did moderately-oxLDL. Mildly-oxLDL contained more hydroperoxides, but less oxysterol, malondialdehyde and negative charge than moderately-oxLDL. Specific inhibition of lipoprotein-associated phospholipase A(2) (by SB222657) diminished death induction in HMM by both oxLDL types. Peroxisome proliferator-activated receptor gamma (PPARgamma) antagonist (GW9662) and agonist (ciglitazone) experiments suggested that non-hydrolysed, oxidised phospholipids in oxLDL activate PPARgamma as a cellular defence mechanism. These results may be relevant to LDL oxidation within atherosclerotic plaques and may suggest strategies for combating atherosclerosis progression.