Effects of eicosapentaenoic acid and docosahexaenoic acid on plasma membrane fluidity of aortic endothelial cells

We investigated the relative effects of n-3 eicosapentaenoic acid (EPA, 20: 5n-3) and docosahexaenoic acid (DHA, 22:6n-3) on the plasma membrane fluidi ty of endothelial cells (EC) cultured from the thoracic aorta by determinin g fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene (DPH) and its cationic derivative trimethylamino-DPH (TMA-DPH). Fluidity assessed by TMA- DPH demonstrated no significant differences in plasma membranes of vehicle (dimethyl sulfoxide; DMSO)-, EPA-, and DHA-treated EC. Plasma membrane flui dity assessed by DPH polarization, however, was significantly higher in the order of DHA > EPA > DMSO. Total cholesterol content decreased significant ly by 28.4 and 15.9% in the plasma membranes of DHA- and EPA-treated cells, respectively. Total phospholipid content remained unaltered in the plasma membranes of the three groups of cells; however, the molar ratio of total c holesterol to phospholipid decreased significantly only in the membranes of DHA-treated EC. The unsaturation index in the plasma membranes of EPA- and DHA-treated cells increased by 35.7 and 64.3%, respectively, compared with that in the plasma membranes of control cells. The activities of catalase and glutathione peroxidase in the whole-cell homogenates, and levels of lip id peroxides in either the whole-cell homogenates or in plasma membrane fra ctions were not altered in EPA- or DHA-treated EC. These results indicate t hat the influence of DHA is greater than that of EPA in increasing plasma m embrane fluidity of vascular EC. We speculate that the greater effect of DH A compared to EPA is due to its greater ability to decrease membrane choles terol content or the cholesterol/phospholipid molar ratio, or both, and als o to its greater ability in elevating the unsaturation index in the plasma membranes of EC.