Submitted to: Journal of Lipid Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 7, 1999
Publication Date: N/A
Interpretive Summary: Omega-3 fatty acids are essential components brain cells and in the blood vessels needed to supply the brain with nutrition. DHA is only poorly and slowly synthesized in mammals, but an essential component in brain growth/function. The abundance of omega-3 fatty acids in snail and shellfish in lacustrine habitats is proposed as the specific source of these nutrients without which the brain could not develop into its present large capacity. An explanation is proposed as to why exactly DHA is so essential a nutrient component in brain and lipid chemistry and slightly different DPA (with one less double bond) is not. Computational chemistry shows that the free fatty acid for both chemicals is in a "U" shape. As a phopholipid containing two DHA versus two DPA molecules however, the calculated structures are markedly different. In the former case, the phosphate group remains aligned with the two DHA. Thus a series of compounds can align uniformly within a membrane. In the second case, the phosphate group is twisted away from the fatty acids. Calculations predict packing within a membrane would be much more complicated and non-uniform. The nutritional and evolutionary value of DPA is thus primarily as a precursor of the DHA needed for fuller expression of brain development.
Lacustrine habitats provide an abundant nutritional source of arachidonic acid (AA) and docosahexaenoic acid (DHA). Both are nutritional pre-requisites for developing both the brain and the vascular support system for the brain. The omega-3 docosapentanenoic acid precursor (omega-3-DPA) was the major omega-3 metabolite in savanna mammals. Despite ethis abundance, neither it nor the corresponding omega-6-DPA was used biochemically neither in photoreceptors nor in nerve synapses. A substantial difference between DHA and other fatty acids is required to explain this high specificity. Studies on fluidity and other mechanical features of cell membranes have not revealed a difference of such a magnitude between even alpha-linolenic acid (LNA) and DHA sufficient to explain the exclusive use of DHA. We suggest that the evolution of the large human brain depended upon a rich source of DHA from the land/water interface. We review a number of proposals for the possible influence of DHA on physical properties of the brain that are essential for its function.