Abstract
Polyunsaturated fatty acids (PUFA) are nutritionally essential since they cannot be synthesized de novo from two-carbon fragments. As a result of their unsaturated double bonds, PUFA are susceptible to chemical reactions with reactive oxygen and nitrogen species (ROS and RNS, respectively). PUFA incorporated into phospholipids and present in biological membranes not only influence membrane fluidity, curvature, and the properties of membrane microdomains, but increase also the risk for chain reactions of lipid peroxidation leading to membrane destabilization and cellular dysfunction. Vitamin E, the main lipid-soluble antioxidant, stabilizes membranes by itself and protects PUFA by scavenging lipid peroxyl radicals. Thus, vitamin E and PUFA form an interdependent chemical pair in which vitamin E protects PUFA, whereas excess PUFA “consume” vitamin E, a high PUFA/vitamin E ratio being generally assumed as disadvantageous. In cells, both PUFA and vitamin E have their own redox-independent regulatory functions, mostly after being metabolized to active lipid mediators able to bind to specific enzymes and receptors involved in modulating specific signal transduction and gene expression pathways. Thus, the efficiency of uptake, transport, and metabolism of vitamin E and PUFA, their interaction, and their consequent relative levels in cells and tissues are important determinants for both physiological and pathophysiological cellular functions and therefore influence the risk for a number of diseases.