Oxidized low-density lipoproteins induce apoptosis in macrophages

AIM: To examine whether oxidized low density lipoproteins (ox-LDL) might induce apoptosis in mouse peritoneal macrophages (MPM). METHODS: Low density lipoproteins (LDL) were isolated from healthy human plasma by ultracentrifugation and oxidized by CuSO4 10 mu mol . L(-1). MPM were incubated in a medium containing ox-LDL, LDL, or phosphate-buffer solution (PBS) as control. DNA fragmentation was visualized by agarose gel electrophoresis and determined quantitatively using Hoechst 33258 fluorochrome. RESULTS: Ox-LDL, not LDL, elicited typical apoptotic morphological changes (shrinkage of cytoplasm and condensation of chromatin) and DNA fragmentation in a time- and dose-dependent manner. Incubation for 24 h was necessary for ox-LDL 200 mg protein . L(-1) to induce DNA fragmentation, and the maximal effect reached at 72 h. The DNA fragmentation after 24-h incubation with ox-LDL at concentrations of 100, 200, and 400 mg protein . L(-1) amounted to 0.0 % (P > 0.05), 9.3 % (P < 0.05), and 30.9 % (P < 0.01), respectively vs PBS control. Dextran sulfate, a scavenger receptor blocker and cycloheximide, a protein synthesis inhibitor, exhibited no effect on DNA fragmentation. However, antioxidant butylated hydroxytoluene (BHT) 20 mu mol . L(-1) completely inhibited Cu2+-mediated oxidation of LDL as well as the apoptosis-inducing effect of Cu2+-exposed LDL. Lysophosphatidylcholine ( LPC), an active component in ox-LDL, at concentration up to 60 mu mol . L(-1), did not elicit DNA fragmentation in MPM. CONCLUSION: Ox-LDL induces apoptosis in MPM without involving LPC.