ABSTRACT
Long-chain n-3 polyunsaturated fatty acids (linolenic acid, 18:3n-3; LNA; eico-sapentaenoic acid, 20:5n-3, EPA; and docosahexaenoic acid 22:6n-3, DHA) are essential for vertebrates, because, in contrast to saturated and monounsaturated fatty acids, they cannot be formed de novo, and at least their precursor, the 18:3n-3, has to be taken up from the diet. These fatty acids, and the complex lipids formed from them, are important constituents of cellular membranes and contribute to maintain the structural and functional integrity of these structures. Though these polyunsaturated fatty acids occur in various proportions in all organs, the nervous tissue is characterized by the absence of LNA and EPA and presence of high levels DHA. Level of DHA is strictly controlled in brain and retina: any deviation from the physiological level results in impairments in cognitive or visual functions.[1] It has been proposed that the nervous system requires specific molecular species for its functions.[2] The exact mode of action of DHA-containing phospholipids (first of all ethanolamine and serine phosphoglycerides) 132is not known but it might be possible that they exert their beneficial effect by regulating blood-brain barrier,[3] membrane fluidity,[4] activity of certain enzymes,[5] ionic channels,[6] and nerve growth factor.[7] However, the question arises whether DHA-containing phospholipid molecules control neural functions on some other levels than their effect on membrane molecular architecture. It has already been shown that polyunsaturated fatty acids of both structures control gene expression in a variety of tissues.[8 – 10] One of the major functions of neural tissue is to receive, store, process, and retrieve information. Extensive studies have been done at morphological, electrophysiological, and biochemical levels to understand the underlying mechanisms. Effect of DHA on learning and memory in animal and human models has been demonstrated,[11] but the question remains unanswered whether these highly complex and sophisticated processes can be explained by the sole effect of DHA in particular, or of long-chain poly-unsaturated fatty acids in general, on biophysical properties and molecular architecture of neural membranes. To find a relation between the effects of DHA on molecular composition of membranes, on cognitive functions, and on genetic machinery of neurons is an exciting research task.
