Alpha-tocopherol preserves endothelial cell migration in the presence of cell-oxidized low-density lipoprotein by inhibiting changes in cell membrane fluidity.

Abstract

Endothelial cell (EC) migration is essential for healing areas of arterial injury and angioplasty sites. Iron or copper-oxidized low-density lipoprotein (oxLDL(Cu)) inhibits EC migration in vitro, but the effect of physiologically relevant monocyte/macrophage-oxidized LDL (oxLDL(cell)) is unknown. We postulated that oxLDL(cell) would inhibit EC migration and that this inhibition would be reversed by antioxidants. The effect of oxLDL(Cu) and oxLDL(cell) on EC migration was studied by using a razor scrape assay, and migration was assessed after 24 hours. In addition, ECs were incubated with various antioxidants, including butylated hydroxytoluene (BHT), probucol, or alpha-tocopherol, for 1 hour prior to initiation of the scrape assay and application of oxLDL. Both oxLDL(Cu) and oxLDL(cell) inhibited migration. The antioxidants did not alter the antimigratory activity of oxLDL(Cu), but alpha-tocopherol preserved EC migration in the presence of oxLDL(cell). The lack of effect of BHT or probucol suggested that the effect of alpha-tocopherol resided not in its antioxidant activity but in its membrane-stabilizing properties. To test this theory, the effect of oxLDL and alpha-tocopherol on relative cell membrane fluidity was assessed by fluorescence recovery after photobleaching. Both oxLDL(Cu) and oxLDL(cell) increased relative membrane fluidity. Preincubation with alpha-tocopherol inhibited the increase in membrane fluidity of ECs incubated in oxLDL(cell) but not in oxLDL(Cu). These studies show that alpha-tocopherol preserves EC migration in oxLDL(cell) and hastens restoration of the endothelial monolayer after injury by inhibiting changes in membrane integrity caused by oxLDL. Recent studies find that vitamin E is not efficacious in the secondary prevention of cardiovascular events, perhaps because vitamin E does not efficiently block oxidation pathways known to be operative in atherosclerotic arteries. "Non-antioxidant" properties of vitamin E, however, could be important in the primary prevention of atherosclerosis and its complications. Our in vitro studies show that alpha-tocopherol can preserve endothelial migration in the presence of cell-oxidized LDL. This effect might improve the healing of endothelial injuries at sites of arterial repair or angioplasties, especially in lipid-laden arterial walls.