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United States Department of Agriculture

Agricultural Research Service

Research Project: THE EFFECTS OF WALNUTS ON AGE RELATED CHANGES IN NEUROPROTECTION, INFLAMMATORY SIGNALING AND BEHAVIOR
2012 Annual Report


1a.Objectives (from AD-416):
We hypothesize that walnuts will reverse age-related disturbances in behavior, neuronal functioning, and microglial activation and will test this hypothesis with the following aims:.
1)Determine the effects of dietary supplementation with walnuts or walnut components on motor and cognitive function..
2)Determine the efficacy of walnuts or walnut components on reversing the age-associated increase in neuronal vulnerability..
3)Investigate the anti-inflammatory actions of walnuts and walnut components on microglial activation. These studies will serve to characterize the effects of dietary walnut supplementation in aging, focusing on cognitive, behavioral, neuronal, and microglial effects of walnuts. In addition, these studies will examine the neuroprotective effects of individual walnut components in order to determine the efficacy of the whole food versus individual components of walnuts.


1b.Approach (from AD-416):
1) Determine the effects of dietary supplementation with walnuts or walnut components on motor and cognitive function. Walnuts will be supplemented in the diet at 6%, walnut components will be given as a portion of the 6% concentration that they comprise in the whole food. The effects of these diets on age-sensitive motor (probes sensitive to balance, strength, and coordination) and cognitive behaviors (short- and long-term memory) will then be examined in Fischer 344 (F344) rats after 8 weeks of supplementation.

2) Determine the efficacy of walnuts or walnut components on reversing the age-associated increase in neuronal vulnerability. The effects of dietary supplementation with walnuts and walnut components on hippocampal neurogenesis (proliferation and survival of newly born neurons) will be assessed in subjects utilized for Aim 1. Additionally, the effects of walnuts on neuronal stress and protective signaling will be accomplished through the use of a hippocampal cell line. Hippocampal cells will be used to determine if walnuts and walnut components alter neuronal stress and protective signaling pathways which have been reported to be altered in the aging brain.

3) Investigate the anti-inflammatory actions of walnuts and walnut components on microglial activation. Prolonged microglial activation is a hallmark of neurodegenerative disorders as well as normal brain aging. The effects of dietary walnut supplementation on age-associated microglial activation will be quantified in tissues harvested from subjects in Aim 1. Further studies on the molecular mechanisms of the anti-inflammatory properties of walnut oil and walnut components will be undertaken in the BV2 microglial cell line.


3.Progress Report:

We had shown previously under this agreement that exposure of BV-2 microglia to walnut extract suppresses inflammation and oxidative stress, thereby protecting neurons. We also previously determined that walnut extract and two of the major components of walnuts, the omega-6 fatty acid linoleic acid (LA) and the omega-3 fatty acid, alpha-linolenic acid (ALA), may mediate some of these beneficial effects in both hippocampal neurons and microglia. This year we investigated the effects of walnut fatty acid metabolites (the components that walnuts are broken down into when in the body) on microglia-induced release of inflammatory mediators. Microglia mediate the brain’s immune response; when “activated” by a pathogen they can release a variety of toxic substances in an attempt to eliminate invading organisms or infected neurons, or act as “house-keepers” and engulf and remove cellular debris. However, in an aging brain, or one with a disease, microglia can remain activated for an extended period of time, causing chronic inflammation and detrimental collateral damage to neurons. We examined how the fatty acids that are likely to be found in the brain after eating walnuts may reduce some of the toxic products released by microglia when they are in this “high-alert” state. In the brain, ALA is metabolized into the omega-3 fatty acids docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), while LA is metabolized into the omega-6 fatty acid arachidonic acid (AA). Walnuts also contain oleic acid (OA), an omega-9 fatty acid. We assessed the ability of DHA, EPA, AA, and OA to reduce the release of inflammatory mediators from BV-2 microglia cells. It was found that DHA and EPA reduced the release of toxic inflammatory mediators in activated microglia. To some extent AA was also beneficial; however OA did not reduce the release of inflammatory mediators. As the omega-3 fatty acids were more effective at reducing the overabundant release of inflammatory mediators from microglia than omega-6 or omega-9 fatty acids, this suggests that all fatty acids may not provide the same level of protection or may have differential effects on brain cells. The effects of walnut extract and walnut fatty acids on BV-2 microglial cells are novel and demonstrate that components of nuts can induce dramatic alterations in the stress responses of cells involved in age-related cognitive decline. We plan to submit a manuscript detailing these results this year.


Last Modified: 10/24/2014
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