MITOCHONDRIAL-FUNCTION IS INVOLVED IN LDL OXIDATION MEDIATED BY HUMANCULTURED ENDOTHELIAL-CELLS

Human endothelial cells (ECs) grown under standard conditions are able to generate a basal level of oxygen free radicals and induce progress ive oxidation of LDLs. Inhibition of cell-mediated LDL oxidation by su peroxide dismutase, EDTA, or desferrioxamine implicates a role for sup eroxide anion and/or transition metals in this process. The potential role of the mitochondrion was investigated by inducing mitochondrial d eenergization by selective photosensitization or the addition of inhib itors of the mitochondrial respiratory chain. Mitochondria of human cu ltured ECs were selectively damaged by photosensitization of cells lab eled with the mitochondrion-selective fluorescent dye 2-(4-dimethylami nostyryl)-1-methylpyridinium iodide under conditions that induced only low levels of toxicity during the time of the experiment. Photosensit ized ECs exhibited severe mitochondrial dysfunction, as suggested by t he defect in mitochondrial uptake of the mitochondrion-selective fluor escent dyes [rhodamine 123 and 2-(4-dimethylaminostyryl)-1-methylpyrid inium iodide] and morphological alterations as shown by transmission e lectron microscopy. In mitochondria-photosensitized cells, superoxide anion generation was strongly decreased, as was LDL oxidation and the subsequent cytotoxicity. When ECs were incubated with the mitochondria l respiratory-chain inhibitors antimycin A or rotenone or with the car bonylcyanide-m-chlorophenylhydrazone uncoupler rhodamine 123, uptake a nd subcellular distribution were altered, and concomitantly superoxide anion production and LDL oxidation were strongly decreased. In conclu sion, these data suggest that mitochondrial function is required, dire ctly or indirectly, for the production of superoxide anion and the sub sequent LDL oxidation by human vascular ECs.