Interfacial properties of phosphatidylcholine bilayers containing vitamin E derivatives

Abstract

α-Tocopherol and α-tocopheryl succinate are biologically active lipids. The activity of these lipids may be related to how they affect membrane physical–chemical properties. Utilizing fluorescence methods, we have investigated the effect of α-tocopherol, α-tocopheryl succinate, and α-tocopheryl acetate on the properties of model membranes consisting of 1-palmitoyl-2-oleoyl- sn-glycero-3-phosphocholine and 1,2-dipalmitoyl- sn-glycero-3-phosphocholine. In liquid–crystalline phase phospholipid bilayers, α-tocopherol decreased acyl chain mobility and decreased the interfacial polarity, but had no effect on the interfacial surface charge. In contrast, α-tocopheryl succinate had little effect on acyl chain motion or interfacial hydration, but increased the interfacial surface charge. α-Tocopheryl acetate had very little effect on any of the measurements of these bilayer properties. In a gel phase bilayer, α-tocopherol decreased acyl chain order, whereas α-tocopheryl succinate and α-tocopheryl acetate did not. Each α-tocopheryl derivative had a different effect on interfacial polarity, however, only α-tocopheryl succinate increased the interfacial surface charge. The acylation of α-tocopherol abolishes its antioxidant activity and generates molecules with different membrane physical properties. The non-polar acetate group of α-tocopheryl acetate locates this compound in a region of the bilayer where it has little effect on bilayer interfacial properties. The free carboxyl group of α-tocopheryl succinate is located in the interfacial region of the bilayer where it increases the membrane surface charge.