Abstract 16909: Eicosapentaenoic Acid and Docosahexaenoic Acid Have Competing Effects on Membrane Lipid Dynamics Due to Differences in Structure

Abstract

Background: Omega-3 fatty acids (n3-FAs) incorporate into vascular cell membranes where they modulate protein function and signal transduction. The n3-FA eicosapentaenoic acid (EPA) delivered in ethyl ester form (icosapent ethyl) reduced a broad range of cardiovascular events in high-risk patients (REDUCE-IT). This was not observed with mixed n3-FA formulations containing docosahexaenoic acid (DHA) in STRENGTH and other trials. These discordant outcomes indicate DHA may counter certain EPA effects due to its additional carbons and double bond. We compared these n3-FA effects on membrane lipid dynamics and width, key determinants of protein function. Methods: Membrane lipid fluidity was measured by fluorescence anisotropy approaches in large unilamellar vesicles (LUVs) of 100 nm diameter containing 1-palmitoyl-2-oleoyl-3-sn-phosphatidylcholine (POPC) and 50 mol% cholesterol with EPA and/or DHA (0-10 mol%). LUVs were treated with the fluorescent probe, 1,6-diphenyl-1,3,5-hexatriene (DPH), at 1 mol% and evaluated using a spectrofluorometer with a polarization accessory. Membrane width ( i.e ., unit cell periodicity) of the samples was determined by small angle x-ray scattering (SAXS). Results: DHA alone increased bulk lipid fluidity as indicated by a dose-dependent reduction in apparent rotational correlation time (ARCT); at 10 mol%, there was a ~20% (p<0.05) reduction from ~19 to ~16 nsec compared to control (untreated membranes). By contrast, EPA had no significant disordering effect except when combined at equimolar levels; the EPA/DHA combination showed a reduction in ARCT to ~18 nsec at 10 mol% that was different from EPA alone (p<0.05). Consistent with these findings, SAXS analysis showed DHA containing membranes had a reduced width compared to EPA by 5% or 3 Å (p<0.05) due to increased trans-gauche isomerizations in the phospholipid acyl chains. Conclusion: EPA maintained membrane fluidity while DHA increased fluidity and thereby reduced membrane width due to its additional carbons and double bond. The EPA/DHA combination increased membrane fluidity compared to control and EPA alone. The disordering effects of DHA may counter EPA stabilizing effects and explain discordant clinical outcomes with different n3-FA formulations.