Omega-3 polyunsaturated fatty acids in the brain and visual system: Focus on invertebrates

A critical role of omega-3 polyunsaturated fatty acids (PUFA), mainly docosahexaenoic acid 22:6ω3 (DHA), in the development and function of the brain and visual system is well established. DHA, the most abundant omega-3 PUFA in the vertebrate brain, contributes to neuro- and synaptogenesis, neuronal differentiation, synaptic transmission and plasticity, neuronal network formation, memory and behaviour formation. Based on these data, the unique importance of DHA and its irreplaceability in neural and retinal tissues has been postulated. In this review, we consider omega-3 PUFA composition in the brain and retina of various invertebrates, and show that DHA has only been found in marine mollusks and crustaceans. A gradual decrease in the DHA content until its disappearance can be observed in the brain lipids of the series marine-freshwater-terrestrial crustaceans and marine-terrestrial mollusks, suggesting that the transition to the land lifestyle in the evolution of invertebrates, but not vertebrates, was accompanied by a loss of DHA. As with terrestrial crustaceans and mollusks, DHA was not found in insects, either terrestrial or aquatic, or in nematodes. We show that the nervous and visual systems of various DHA-free invertebrates can be highly enriched in alpha-linolenic acid 18:3ω3 or eicosapentaenoic acid 20:5ω3, which affect neurological and visual function, stimulating synaptogenesis, synaptic transmission, visual processing, learning and even cognition. The review data show that, in animals at different levels of organization, omega-3 PUFA are required for the functioning of the nervous and visual systems and that their specific needs can be met by various omega-3 PUFA.

Omega-3 PUFA profoundly affect neural, physiological, and behavioural competences - implications for systemic changes in trophic interactions

In recent decades, much conceptual thinking in trophic ecology has been guided by theories of nutrient limitation and the flow of elements, such as carbon and nitrogen, within and among ecosystems. More recently, ecologists have also turned their attention to examining the value of specific dietary nutrients, in particular polyunsaturated fatty acids (PUFA), among which the omega-3 PUFA, especially eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) play a central role as essential components of neuronal cell membranes in many organisms. This review focuses on a new neuro-ecological approach stemming from the biochemical (mechanistic) and physiological (functional) role of DHA in neuronal cell membranes, in particular in conjunction with G-protein coupled receptors (GPCRs). We link the co-evolution of these neurological functions to metabolic dependency on dietary omega-3 PUFA. We outline ways in which deficiencies in dietary DHA supply may affect, cognition, vision, and behaviour, and ultimately, the biological fitness of consumers. We then review emerging evidence that changes in access to dietary omega-3 PUFA may ultimately have profound impacts on trophic interactions leading to potential changes in community structure and ecosystem functioning that, in turn, may affect the supply of DHA within and across ecosystems, including the supply for human consumption.

Long-chain Omega-3 Polyunsaturated Fatty Acids in Natural Ecosystems and the Human Diet: Assumptions and Challenges

Over the past three decades, studies of essential biomolecules, long-chain polyunsaturated fatty acids of the omega-3 family (LC-PUFAs), namely eicosapentaenoic acid (20:5n-3, EPA) and docosahexaenoic acid (22:6n-3, DHA), have made considerable progress, resulting in several important assumptions. However, new data, which continue to appear, challenge these assumptions. Based on the current literature, an attempt is made to reconsider the following assumptions: 1. There are algal classes of high and low nutritive quality. 2. EPA and DHA decrease with increasing eutrophication in aquatic ecosystems. 3. Animals need EPA and DHA. 4. Fish are the main food source of EPA and DHA for humans. 5. Culinary treatment decreases EPA and DHA in products. As demonstrated, some of the above assumptions need to be substantially specified and changed.