fjrigjwwe9r0Board:Content
THE IMPACT OF ESSENTIAL FATTY ACIDS
ON THE AGING PROCESS (7)
Rashid Buttar, D. O. and Andrew Halpner, Ph. D.
Most long-chain EFAs in the diet come from fish and fish oils. Atlantic cod contains 17% EPA and 38% DHA, while pink salmon contains 14% EPA and 19% DHA.
Given the different effects that n-6 and n-3 fatty acids have on important physiological functions, maintaining a balance of both types of EFAs is important. A diet high in EFAs results in a greater incorporation of these fatty acids in to cellular membranes, while simultaneously displacing AA. Consequently, less AA is available for conversion to harmful metabolites. This is of note, as diets high in EPA, DHA, and other EFAs have been correlated with beneficial health outcomes. These include reductions in the risk for developing atherosclerosis, osteoporosis, and depression.
Neurological importance of essential fatty acids
For years, EFAs have been known to affect the central nervous system. However, only recently have we begun to learn more about their functions with respect to the brain. The phospholipid fraction of the brain contains very little LA. Although AA is a dominant fatty acid in brain tissue, DHA is the major polyunsaturated fatty acid present.
The brain appears to require fatty acids with a high degree of unsaturation, and prefers DHA. In both adult and young animals, supplementation of various dietary oils can modulate brain levels of polyunsaturated fatty acids (PUFAs). Interestingly, it appears that of all the fatty acids, DHA can exert the most profound influence on brain PUFA levels. However, when animals are fed a diet deficient in DHA, a compensatory increase in docosapentaenoic acid (DPA, 22: 5n-6), another highly unsaturated fatty acid, has been observed. This alteration can be reversed when the animals are again fed diets containing sufficient amounts of DHA.
These declines in brain DHA (but not in other tissues) are harder to achieve when an aged animal is fed a DHA-deficient diet. This further emphasizes the importance the body places on maintaining brain levels of DHA, even at the expense of other tissues. The exact mechanisms for why PUFAs are so important in the brain are not fully understood, but many relationships between DHA and EPA and brain function have been observed.
Shikano et al demonstrated that in vitro supplementation of cultured human eosinophilic leukemia cells with DHA resulted in a decrease in the platelet activating factor. It also reduced the activity of phospholipase A2 (PLA2). PLA2 is the key enzyme involved in the release of AA from membrane phospholipids, which allows AA to then be further metabolized to biologically active eicosanoids. If PLA2 activity is decreased, then less AA is available for the production of harmful metabolites.
DHA may also be involved in synaptic signal transduction. Jones et al reported that when radio-labeled DHA was given intravenously to rats, DHA was selectively incorporated into synaptic membrane phospholipids in response to cholinergic activation. This may indicate a role for DHA in phospholipid-mediated signal transduction at the synapse.
In addition to these cellular effects, behavioral effects related to brain function of PUFA supplementation have also been observed. |