CYTOTOXICITY OF OXIDIZED LDL TO PORCINE AORTIC SMOOTH-MUSCLE CELLS ISASSOCIATED WITH THE OXYSTEROLS 7-KETOCHOLESTEROL AND 7-HYDROXYCHOLESTEROL

The cytotoxicity of oxidized low-density lipoprotein (Ox-LDL) to arter ial smooth muscle cells (SMCs) may contribute to atherogenesis by caus ing cell death in core regions of plaques. The aim of the present stud y was to identify the components of copper-oxidized LDL responsible fo r its toxicity to porcine aortic SMCs. Toxicity to SMCs was assessed a s the decrease in viable cell counts after 3-day cell incubation. Extr acts of LDL were tested for toxicity at concentrations equivalent to t hat derived from 100 mu g LDL protein per milliliter. Lipid extracts o f Ox-LDL but not native-LDL were toxic to SMCs. When separated into ne utral and polar lipid classes, only the neutral lipids were toxic (89. 7+/-0.7% cell loss). The neutral lipids were fractionated further by u se of solid-phase extraction and high-performance liquid chromatograph y (HPLC). Two toxic fractions, causing 93.3% and 60.3% cell loss, were isolated from HPLC and analyzed by gas chromatography/mass spectromet ry. The most toxic of these fractions contained 7-ketocholesterol, and the other contained 7 alpha- and 7 beta-hydroxycholesterol. Quantific ation of these unesterified oxysterols in LDL extracts and comparison with the toxicity of authentic standards indicate that 7-ketocholester ol and 7-hydroxycholesterol are present in Ox-LDL at levels sufficient to account for its toxicity to SMCs.