Inhibition of oxidized low-density lipoprotein-induced apoptosis in endothelial cells by nitric oxide - Peroxyl radical scavenging as an antiapoptotic mechanism

Proatherogenic oxidized low-density lipoprotein (oxLDL) induces endothelial apoptosis, We investigated the anti-apoptotic effects of intracellular and extracellular nitric oxide ((NO)-N-.) donors, iron chelators, cell-permeab le superoxide dismutase (SOD), glutathione peroxidase mimetics, and nitrone spin traps. Peroxynitrite (ONOO-)-modified oxLDL induced endothelial apopt osis was measured by DNA fragmentation, TUNEL assay, and caspase-3 activati on. Results indicated the following: (i) the lipid fraction of oxLDL was pr imarily responsible for endothelial apoptosis, (ii) Endothelial apoptosis w as potently inhibited by (NO)-N-. donors and lipophilic phenolic antioxidan ts, OxLDL severely depleted Bcl-2 levels in endothelial cells and (NO)-N-. donors restored Bcl-2 protein in oxLDL-treated cells. (iii) The pretreatmen t of a lipid fraction derived from oxLDL with sodium borohydride or potassi um iodide completely abrogated apoptosis in endothelial cells, suggesting t hat lipid hydroperoxides induce apoptosis, (iv) Metalloporphyrins dramatica lly inhibited oxLDL-induced apoptosis in endothelial cells. Neither S-nitro sation of caspase-3 nor induction of Hsp70 appeared to play a significant r ole in the antiapoptotic mechanism of (NO)-N-. in oxLDL-induced endothelial apoptosis, We propose that cellular lipid peroxyl radicals or lipid hydrop eroxides induce an apoptotic signaling cascade in endothelial cells exposed to oxLDL, and that (NO)-N-. inhibits apoptosis by scavenging cellular lipi d peroxyl radicals.