Cognitive deficits in docosahexaenoic acid-deficient rats

The role of docosahexaenoic and the marine food web as determinants of evolution and hominid brain development: the challenge for human sustainability

Life originated on this planet about 3 billion years ago. For the first 2.5 billion years of life there was ample opportunity for DNA modification. Yet there is no evidence of significant change in life forms during that time. It was not until about 600 million years ago, when the oxygen tension rose to a point where air-breathing life forms became thermodynamically possible, that a major change can be abruptly seen in the fossil record. The sudden appearance of the 32 phyla in the Cambrian fossil record was also associated with the appearance of intracellular detail not seen in previous life forms. That detail was provided by cell membranes made with lipids (membrane fats) as structural essentials. Lipids thus played a major, as yet unrecognised, role as determinants in evolution. The compartmentalisation of intracellular, specialist functions as in the nucleus, mitochondria, reticulo-endothelial system and plasma membrane led to cellular specialisation and then speciation. Thus, not only oxygen but also the marine lipids were drivers in the Cambrian explosion. Docosahexaenoic acid (DHA) (all-cis-docosa-4,7,10,13,16,19-hexaenoic acid, C22:6ω3 or C22:6, n-3, DHA) is a major feature of marine lipids. It requires six oxygen atoms to insert its six double bonds, so it would not have been abundant before oxidative metabolism became plentiful. DHA provided the membrane backbone for the emergence of new photoreceptors that converted photons into electricity, laying the foundation for the evolution of other signalling systems, the nervous system and the brain. Hence, the ω3 DHA from the marine food web must have played a critical role in human evolution. There is also clear evidence from molecular biology that DHA is a determinant of neuronal migration, neurogenesis and the expression of several genes involved in brain growth and function. That same process was essential to the ultimate cerebral expansion in human evolution. There is now incontrovertible support of this hypothesis from fossil evidence of human evolution taking advantage of the marine food web. Lipids are still modifying the present evolutionary phase of our species; their signature is evident in the changing panorama of non-communicable diseases. The most worrying change in disease pattern is the sharp rise in brain disorders, which, in the European Union, has overtaken the cost of all other burdens of ill health at €386 billion for the 25 member states at 2004 prices. In 2007, the UK cost was estimated at £77 billion and confirmed in 2010 at £105 billion - greater than heart disease and cancer combined. The rise in mental ill health is now being globalised. The solution to the rising vascular disorders in the last century and now brain disorders in this century lies in a radical reappraisal of the food system, which last century was focussed on protein and calories, with little attention paid to the requirements of the brain - the very organ that was the determinant of human evolution. With the marine fish catch having plateaued 20 years ago and its sustainability now under threat, a critical aspect of this revision is the development of marine agriculture from estuarine, coastal and oceanic resources. Such action is likely to play a key role in future health and intelligence.

Effects of docosahexaenoic acid on mouse brain synaptic plasma membrane proteome analyzed by mass spectrometry and (16)O/(18)O labeling

Docosahexenoic acid (DHA, 22:6n-3) plays an important role in development of proper brain function in mammals. We have previously reported that DHA promotes synaptogenesis and synaptic function in hippocampal neurons while DHA-depletion in the brain due to n-3 fatty acid deficiency produces opposite effects. To gain insight into underlying molecular mechanisms, we investigated whether the brain DHA status affects the synaptic plasma membrane (SPM) proteome by using nanoLC-ESI-MS/MS and (16)O/(18)O labeling. The DHA level in mouse brains was lowered by dietary depletion of n-3 fatty acids, and SPM was prepared by differential centrifugation followed by osmotic shock. SPM proteins from DHA-adequate and depleted brains were analyzed by nanoLC-ESI-MS/MS after SDS-PAGE, in-gel digestion, and differential O(18)/O(16) labeling. This strategy allowed comparative quantitation of more than 200 distinct membrane or membrane-associated proteins from DHA-adequate or depleted brains. We found that 18 pre- and postsynaptic proteins that are relevant to synaptic physiology were significantly down-regulated in DHA-depleted mouse brains. The protein network analysis suggests involvement of CREB and caspase-3 pathways in the DHA-dependent modulation of synaptic proteome. Reduction of specific synaptic proteins due to brain DHA-depletion may be an important mechanism for the suboptimal brain function associated with n-3 fatty acid deficiency.

Identification of novel mammalian phospholipids containing threonine, aspartate, and glutamate as the base moiety

In this study, we showed the occurrence of phosphatidyl-L-threonine (PThr), phosphatidyl-L-aspartate (PAsp), and phosphatidyl-L-glutamate (PGlu) in rat brain. Analyses using an HPLC-ESI-MS and an amino acid analyzer showed the presence of L-threonine, L-aspartate, and L-glutamate in the acid-hydrolysates of phospholipids from porcine cerebrum, rat cerebrum, and rat liver. Results of ESI-MS/MS analyses with neutral loss scanning and product ion scanning suggest the presence of PThr-(18:0, 18:1), PThr-(18:0, 22:6), PAsp-(18:0, 18:1), PAsp-(18:0, 22:6), PGlu-(18:0, 18:1), and PGlu-(18:0, 22:6) in rat brain. This is the first study to identify 2 novel phospholipids, PAsp and PGlu, with a carboxylate-phosphate anhydride bond, in living organisms.

Dietary n-3 polyunsaturated fatty acid deprivation together with early maternal separation increases anxiety and vulnerability to stress in adult rats

Low concentrations of n-3 polyunsaturated fatty acid (PUFA) and chronic stress are implicated in susceptibility to mood disorders. We have investigated the combined effects of chronic n-3 PUFA dietary deficiency and early maternal separation (MS) stress on the reactivity to stressful situations of rats as adults. Pups fed a control or an n-3 PUFA deficient diet were daily separated for two weeks before weaning They were all tested at 3 month-old to determine their anxiety, and their ability to learn two aversive tasks differing in the control they could exert on the situation: auditory fear conditioning and brightness avoidance discrimination. Neither the n-3 PUFA-deficient diet nor MS alone significantly affected behavior. But n-3 PUFA-deficient rats that had been separated were more anxious and fearful in inescapable situations, while their ability to cope with an aversive avoidance task remained unaffected. These results support the notion that PUFA-unbalanced diet, together with stress, may be a determinant risk factor in emotional disorders.

Chronic dietary intake of α-linolenic acid does not replicate the effects of DHA on passive properties of entorhinal cortex neurons

n-3 PUFA are receiving growing attention for their therapeutic potential in central nervous system (CNS) disorders. We have recently shown that long-term treatment with DHA alters the physiology of entorhinal cortex (EC) neurons. In the present study, we investigated by patch-clamp the effect of another major dietary n-3 PUFA, α-linolenic acid (LNA), on the intrinsic properties of EC neurons. Mice were chronically exposed to isoenergetic diets deficient in n-3 PUFA or enriched in either DHA or LNA on an equimolar basis. GC analyses revealed an increase in DHA (34%) and a decrease in arachidonic acid (AA, - 23%) in brain fatty acid concentrations after consumption of the DHA-enriched diet. Dietary intake of LNA similarly affected brain fatty acid profiles, but at a lower magnitude (DHA: 23%, AA: - 13%). Compared to the n-3 PUFA-deficient diet, consumption of DHA, but not LNA, induced membrane hyperpolarisation ( -60 to -70 mV), increased cellular capacitance (32%) and spontaneous excitatory postsynaptic current frequency (50%). We propose that the inefficiency of LNA to modulate cellular capacitance was related to its inability to increase the brain DHA:AA ratio over the threshold necessary to up-regulate syntaxin-3 (46%) and translocate drebrin (40% membrane:cytosol ratio). In summary, our present study shows that the increase in brain DHA content following chronic administration of LNA was not sufficient to alter the passive and synaptic properties of EC neurons, compared to direct dietary intake of DHA. These diverging results have important implications for the therapeutic use of n-3 PUFA in CNS disease, favouring the use of preformed DHA.

Animal studies of the functional consequences of suboptimal polyunsaturated fatty acid status during pregnancy, lactation and early post-natal life

Scores of animal studies demonstrate that seed oils replete with linoleic acid and very low in linolenic acid fed as the exclusive source of fat through pregnancy and lactation result in visual, cognitive, and behavioural deficits in the offspring. Commodity peanut, sunflower, and safflower oils fed to mother rats, guinea pigs, rhesus monkeys, and baboons induce predictable changes in tissue polyunsaturated fatty acid composition that are abnormal in free-living land mammals as well as changes in neurotransmitter levels, catecholamines, and signalling compounds compared with animals with a supply of ω3 polyunsaturated fatty acid. These diets consistently induce functional deficits in electroretinograms, reflex responses, reward or avoidance induced learning, maze learning, behaviour, and motor development compared with ω3 replete groups. Boosting neural tissue docosahexaenoic acid (DHA) by feeding preformed DHA enhances visual and cognitive function. Though no human randomized controlled trials on minimal ω3 requirements in pregnancy and lactation have been conducted, the weight of animal evidence compellingly shows that randomizing pregnant or lactating humans to diets that include high linoleate oils as the sole source of fat would be frankly unethical because they would result in suboptimal child development. Increasing use of commodity ω3-deficient oils in developing countries, many in the name of heart health, will limit brain development of the next generation and can be easily corrected at minimal expense by substituting high oleic acid versions of these same oils, in many cases blended with small amounts of α-linolenic acid oils like flax or perilla oil. Inclusion of DHA in these diets is likely to further enhance visual and neural development.

Benefits versus risks associated with consumption of fish and other seafood

Fish provide nutrition for much of the world's population, and when not contaminated with chemicals, fish is a very good food. A major benefit of fish is that they are high in polyunsaturated fatty acids (PUFAs), low in saturated fat, and they contain other critical nutrients. Much of the benefit of fish consumption derives from their high levels of long chain omega-3 PUFAs, which are produced by aquatic microorganisms and bioconcentrate in the aquatic food supply. The PUFAs are essential, in that humans and other vertebrates are not able to synthesize them and therefore must obtain them from the diet. The PUFAs particularly concentrate in the nervous system, alter immune system function reduce serum triglyceride levels and have been reported to reduce the risk of sudden death after a myocardial infarction. But the problem is that most fish have at least some degree of chemical contamination with methylmercury, (which binds to muscle) and/or with persistent organic pollutants such as dioxins, polychlorinated biphenyls, polybrominated diphenyl ethers, chlorinated pesticides (which concentrate in fish fat). These chemicals have adverse effects on nervous system function, modulate the immune system, and are associated with elevations in risk of cardiovascular disease. Thus the question of benefits and risk from fish consumption is complex but very important.

Retailoring docosahexaenoic acid-containing phospholipid species during impaired neurogenesis following omega-3 alpha-linolenic acid deprivation

Diminished levels of docosahexaenoic acid (22:6n-3), the major fatty acid (FA) synthesized from alpha-linolenic acid (18:3n-3), have been implicated in functional impairment in the developing and adult brain. We have now examined the changes in phospholipid (PL) molecular species in the developing postnatal cortex, a region recently shown to be affected by a robust aberration in neuronal cell migration, after maternal diet alpha-linolenic acid deprivation (Yavin et al. (2009)Neuroscience162(4),1011). The frontal cortex PL composition of 1- to 4-week-old rats was analyzed by gas chromatography and electrospray ionization/tandem mass spectrometry. Changes in the cortical PL molecular species profile by dietary means appear very specific as 22:6n-3 was exclusively substituted by docosapentaenoic acid (22:5n-6). However, molecular species were conserved with respect to the combination of specific polar head groups (i.e. ethanolamine and serine) in sn-3 and defined saturated/mono-unsaturated FA in sn-1 position even when the sn-2 FA moiety underwent diet-induced changes. Our results suggest that substitution of docosahexaenoic acid by docosapentaenoic acid is tightly regulated presumably to maintain a proper biophysical characteristic of membrane PL molecular species. The importance of this conservation may underscore the possible biochemical consequences of this substitution in regulating certain functions in the developing brain.

Phosphatidylserine-dependent neuroprotective signaling promoted by docosahexaenoic acid

Enrichment of polyunsaturated fatty acids, particularly docosahexaenoic acid (DHA, 22:6n-3), in the brain is known to be critical for optimal brain development and function. Mechanisms for DHA's beneficial effects in the nervous system are not clearly understood at present. DHA is incorporated into the phospholipids in neuronal membranes, which in turn can influence not only the membrane chemical and physical properties but also the cell signaling involved in neuronal survival, proliferation and differentiation. Our studies have indicated that DHA supplementation promotes phosphatidylserine (PS) accumulation and inhibits neuronal cell death under challenged conditions, supporting a notion that DHA is an important neuroprotective agent. This article summarizes our findings on the DHA-mediated membrane-related signaling mechanisms that might explain some of the beneficial effects of DHA, particularly on neuronal survival.

Therapeutic potential of n-3 polyunsaturated fatty acids in disease

PURPOSE

The potential therapeutic benefits of supplementation with n-3 polyunsaturated fatty acids (PUFAs) in various diseases are reviewed, and the antiinflammatory actions, activity, and potential drug interactions and adverse effects of n-3 PUFAs are discussed.

SUMMARY

Fish oils are an excellent source of long-chain n-3 PUFAs, such as eicosapentaenoic acid and docosahexaenoic acid. After consumption, n-3 PUFAs can be incorporated into cell membranes and reduce the amount of arachidonic acid available for the synthesis of proinflammatory eicosanoids (e.g., prostaglandins, leukotrienes). Likewise, n-3 PUFAs can also reduce the production of inflammatory cytokines, such as tumor necrosis factor alpha, interleukin-1, and interleukin-6. Considerable research has been conducted to evaluate the potential therapeutic effects of fish oils in numerous conditions, including arthritis, coronary artery disease, inflammatory bowel disease, asthma, and sepsis, all of which have inflammation as a key component of their pathology. Additional investigations into the use of supplementation with fish oils in patients with neural injury, cancer, ocular diseases, and critical illness have recently been conducted. The most commonly reported adverse effects of fish oil supplements are a fishy aftertaste and gastrointestinal upset. When recommending an n-3 PUFA, clinicians should be aware of any possible adverse effect or drug interaction that, although not necessarily clinically significant, may occur, especially for patients who may be susceptible to increased bleeding (e.g., patients taking warfarin).

CONCLUSION

The n-3 PUFAs have been shown to be efficacious in treating and preventing various diseases. The wide variation in dosages and formulations used in studies makes it difficult to recommend dosages for specific treatment goals.

Docosahexaenoic acid promotes hippocampal neuronal development and synaptic function

Docosahexaenoic acid (DHA, 22:6n-3), the major polyunsaturated fatty acid accumulated in the brain during development, has been implicated in learning and memory, but underlying cellular mechanisms are not clearly understood. Here, we demonstrate that DHA significantly affects hippocampal neuronal development and synaptic function in developing hippocampi. In embryonic neuronal cultures, DHA supplementation uniquely promoted neurite growth, synapsin puncta formation and synaptic protein expression, particularly synapsins and glutamate receptors. In DHA-supplemented neurons, spontaneous synaptic activity was significantly increased, mostly because of enhanced glutamatergic synaptic activity. Conversely, hippocampal neurons from DHA-depleted fetuses showed inhibited neurite growth and synaptogenesis. Furthermore, n-3 fatty acid deprivation during development resulted in marked decreases of synapsins and glutamate receptor subunits in the hippocampi of 18-day-old pups with concomitant impairment of long-term potentiation, a cellular mechanism underlying learning and memory. While levels of synapsins and NMDA receptor subunit NR2A were decreased in most hippocampal regions, NR2A expression was particularly reduced in CA3, suggesting possible role of DHA in CA3-NMDA receptor-dependent learning and memory processes. The DHA-induced neurite growth, synaptogenesis, synapsin, and glutamate receptor expression, and glutamatergic synaptic function may represent important cellular aspects supporting the hippocampus-related cognitive function improved by DHA.

Cellular and molecular events mediated by docosahexaenoic acid-derived neuroprotectin D1 signaling in photoreceptor cell survival and brain protection

Deficiency in docosahexaenoic acid (DHA) is associated with impaired visual and neurological postnatal development, cognitive decline, macular degeneration, and other neurodegenerative diseases. DHA is an omega-3 polyunsaturated fatty acyl chain concentrated in phospholipids of brain and retina, with photoreceptor cells displaying the highest content of DHA of all cell membranes. The identification and characterization of neuroprotectin D1 (NPD1, 10R, 17S-dihydroxy-docosa-4Z,7Z,11E,13E,15Z,19Z-hexaenoic acid) contributes in understanding the biological significance of DHA. In oxidative stress-challenged human retinal pigment epithelial (RPE) cells, human brain cells, or rat brains undergoing ischemia-reperfusion, NPD1 synthesis is enhanced as a response for sustaining homeostasis. Thus, neurotrophins, Abeta peptide 42 (Abeta42), calcium ionophore A23187, interleukin (IL)-1beta, or DHA supply enhances NPD1 synthesis. NPD1, in turn, up-regulates the antiapoptotic proteins of the Bcl-2 family and decreases the expression of proapoptotic Bcl-2 family members. Moreover, NPD1 inhibits IL-1beta-stimulated expression of cyclooxygenase-2 (COX-2). Because both RPE and photoreceptors are damaged and then die in retinal degenerations, elucidating how NPD1 signaling contributes to retinal cell survival may lead to a new understanding of disease mechanisms. In human neural cells, DHA attenuates amyloid-beta (Abeta) secretion, resulting in concomitant formation of NPD1. NPD1 was found to be reduced in the Alzheimer's disease (AD) cornu ammonis region 1 (CA1) hippocampal region, but not in other areas of the brain. The expression of key enzymes for NPD1 biosynthesis, cytosolic phospholipase A(2) (cPLA(2)), and 15-lipoxygenase (15-LOX) was found altered in the AD hippocampal CA1 region. NPD1 repressed Abeta42-triggered activation of pro-inflammatory genes and upregulated the antiapoptotic genes encoding Bcl-2, Bcl-xl, and Bfl-1(A1) in human brain cells in culture. Overall, these results support the concept that NPD1 promotes brain and retina cell survival via the induction of antiapoptotic and neuroprotective gene-expression programs that suppress Abeta42-induced neurotoxicity and other forms of cell injury, which in turn fosters homeostasis during development in aging, as well as during the initiation and progression of neurodegenerative diseases.

AMPA receptor-mediated cell death is reduced by docosahexaenoic acid but not by eicosapentaenoic acid in area CA1 of hippocampal slice cultures

Over the last decade, several studies have shown that high levels of polyunsaturated fatty acids (PUFAs) in the brain might limit neuronal damage in various pathological conditions. For example, in animal models of Alzheimer's disease, omega-3 type PUFAs such as docosahexaenoic (DHA) and eicosapentaenoic (EPA) acids have been proposed to decrease both the cognitive and the cellular manifestations of premature ageing. The mechanisms by which they promote brain integrity remain to be established, and the experiments on cultured hippocampal slices described here examine the possibility that omega-3 fatty acids can modulate brain cell viability by interacting with glutamate receptors. We observed, by lactate dehydrogenase release and propidium iodide (PI) uptake, that excitotoxicity triggered by an alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptor agonist was markedly reduced in hippocampal slices treated with DHA. PI uptake experiments also revealed that neuroprotection by DHA was restricted to the hippocampal CA1 region and could not be reproduced by EPA or arachidonic acid, an omega-6 PUFA. Moreover, the beneficial effect of DHA was specific to AMPA receptor stimulation, insofar as the toxicity induced by N-methyl-D-aspartate or kainate receptor agonists was not diminished by DHA preincubation. Biotinylation experiments finally indicated that the neuroprotective actions of DHA could result from down-regulation of AMPA receptors in hippocampal membranes. This investigation thus provides the first indication that a beneficial outcome of DHA on the brain could derive from specific modulation of AMPA-mediated toxicity, reinforcing the notion that dietary DHA uptake might be useful in preventing neurodegenerative diseases.

Effect of dietary docosahexaenoic acid on biosynthesis of docosahexaenoic acid from alpha-linolenic acid in young rats

Docosahexaenoic acid (DHA), a crucial nervous system n-3 PUFA, may be obtained in the diet or synthesized in vivo from dietary alpha-linolenic acid (LNA). We addressed whether DHA synthesis is regulated by the availability of dietary DHA in artificially reared rat pups, during p8 to p28 development. Over 20 days, one group of rat pups was continuously fed deuterium-labeled LNA (d5-LNA) and no other n-3 PUFA (d5-LNA diet), and a second group of rat pups was fed a d5-LNA diet with unlabeled DHA (d5-LNA + DHA diet). The rat pups were then euthanized, and the total amount of deuterium-labeled docosahexaenoic acid (d5-DHA) (synthesized DHA) as well as other n-3 fatty acids present in various body tissues, was quantified. In the d5-LNA + DHA group, the presence of dietary DHA led to a marked decrease (3- to 5-fold) in the total amount of d5-DHA that accumulated in all tissues that we examined, except in adipose. Overall, DHA accretion from d5-DHA was generally diminished by availability of dietary preformed DHA, inasmuch as this was found to be the predominant source of tissue DHA. When preformed DHA was unavailable, d5-DHA and unlabeled DHA were preferentially accreted in some tissues along with a net loss of unlabeled DHA from other organs.

Moderation of breastfeeding effects on the IQ by genetic variation in fatty acid metabolism

Children's intellectual development is influenced by both genetic inheritance and environmental experiences. Breastfeeding is one of the earliest such postnatal experiences. Breastfed children attain higher IQ scores than children not fed breast milk, presumably because of the fatty acids uniquely available in breast milk. Here we show that the association between breastfeeding and IQ is moderated by a genetic variant in FADS2, a gene involved in the genetic control of fatty acid pathways. We confirmed this gene-environment interaction in two birth cohorts, and we ruled out alternative explanations of the finding involving gene-exposure correlation, intrauterine growth, social class, and maternal cognitive ability, as well as maternal genotype effects on breastfeeding and breast milk. The finding shows that environmental exposures can be used to uncover novel candidate genes in complex phenotypes. It also shows that genes may work via the environment to shape the IQ, helping to close the nature versus nurture debate.

Peripheral ethanolamine plasmalogen deficiency: a logical causative factor in Alzheimer's disease and dementia

Although dementia of the Alzheimer's type (DAT) is the most common form of dementia, the severity of dementia is only weakly correlated with DAT pathology. In contrast, postmortem measurements of cholinergic function and membrane ethanolamine plasmalogen (PlsEtn) content in the cortex and hippocampus correlate with the severity of dementia in DAT. Currently, the largest risk factor for DAT is age. Because the synthesis of PlsEtn occurs via a single nonredundant peroxisomal pathway that has been shown to decrease with age and PlsEtn is decreased in the DAT brain, we investigated potential relationships between serum PlsEtn levels, dementia severity, and DAT pathology. In total, serum PlsEtn levels were measured in five independent population collections comprising >400 clinically demented and >350 nondemented subjects. Circulating PlsEtn levels were observed to be significantly decreased in serum from clinically and pathologically diagnosed DAT subjects at all stages of dementia, and the severity of this decrease correlated with the severity of dementia. Furthermore, a linear regression model predicted that serum PlsEtn levels decrease years before clinical symptoms. The putative roles that PlsEtn biochemistry play in the etiology of cholinergic degeneration, amyloid accumulation, and dementia are discussed.

An n-3 fatty acid deficient diet affects mouse spatial learning in the Barnes circular maze

Deficiency in n-3 fatty acids has been accomplished through the use of an artificial rearing method in which ICR mouse pups were hand fed a deficient diet starting from the 2nd day of life. There was a 51% loss of total brain DHA in mice with an n-3 fatty acid-deficient diet relative to those with a diet sufficient in n-3 fatty acids. n-3 fatty acid adequate and deficient mice did not differ in terms of locomotor activity in the open field test or in anxiety-related behavior in the elevated plus maze. The n-3 fatty acid-deficient mice demonstrated impaired learning in the reference-memory version of the Barnes circular maze as they spent more time and made more errors in search of an escape tunnel. No difference in performance between all dietary groups in the cued and working memory version of the Barnes maze was observed. This indicated that motivational, motor and sensory factors did not contribute to the reference memory impairment.

Phospholipid and fatty acid specificity of endothelial lipase: potential role of the enzyme in the delivery of docosahexaenoic acid (DHA) to tissues

Docosahexaenoic acid (DHA; 22:6 n-3) is an essential fatty acid required for the normal function of several tissues, especially the brain. Previous studies suggested that lysophosphatidylcholine (lysoPC) is a preferred carrier of DHA to the brain, although the pathways of the formation of DHA-containing lysophospholipids in plasma have not been delineated. We propose that endothelial lipase (EL), a phospholipase A1 that plays an important role in the metabolism of high density lipoproteins, may be responsible for the generation of DHA lysophospholipids in plasma. Here we studied the substrate specificity of EL using deuterium-labeled phospholipids with different polar head groups, as well as DHA-enriched natural phospholipids to test this hypothesis. Glycerol-stabilized phospholipids were treated with recombinant EL, and the products were analyzed by liquid chromatography/electrospray ionization mass spectrometry. EL showed the polar head group specificity in the order of phosphatidylethanolamine>phosphatidylcholine>phosphatidylserine>phosphatidic acid. Within the same phospholipid class, the enzyme showed preference for the species containing DHA at the sn-2 position, and was inactive in the hydrolysis of phospholipids containing an ether linkage. Since EL is known to be secreted by the cells of blood-brain barrier, we suggest that it plays an important role in the delivery of DHA lysophospholipid carriers to the brain.

Hyperactivity in the rat is associated with spontaneous low level of n-3 polyunsaturated fatty acids in the frontal cortex

Inattention, hyperactivity and impulsiveness are the main symptoms of the heterogeneous attention-deficit/hyperactivity disorder (ADHD). It has been suggested that ADHD is associated with an imbalance in polyunsaturated fatty acid (PUFA) composition, with abnormal low levels of the main n-3 PUFA, DHA (22: 6n-3). DHA is highly accumulated in nervous tissue membranes and is implicated in neural function. Animal studies have shown that diet-induced lack of DHA in the brain leads to alterations in cognitive processes, but the relationship between DHA and hyperactivity is unclear. We examined the membrane phospholipid fatty acid profile in frontal cortex of rats characterized for attention, impulsiveness and motricity in various environmental contexts to determine the relationship between brain PUFA composition and the symptoms of ADHD. The amounts of n-3 PUFA in the PE were significantly correlated with nocturnal locomotor activity and the locomotor response to novelty: hyperactive individuals had less n-3 PUFA than hypoactive ones. We conclude that spontaneous hyperactivity in rats is the symptom of ADHD that best predicts the n-3 PUFA content of the frontal cortex. This differential model in rats should help to better understand the role of PUFA in several psychopathologies in which PUFA composition is modified.

Survival signaling in retinal pigment epithelial cells in response to oxidative stress: significance in retinal degenerations

Photoreceptor survival depends on the integrity of retinal pigment epithelial (RPE) cells. The pathophysiology of several retinal degenerations involves oxidative stress-mediated injury and RPE cell death; in some instances it has been shown that this event is mediated by A2E and its epoxides. Photoreceptor outer segments display the highest DHA content of any cell type. RPE cells are active in DHA uptake, conservation, and delivery. Delivery of DHA to photoreceptor inner segments is mediated by the interphotoreceptor matrix. DHA is necessary for photoreceptor function and at the same time is a target of oxidative stress-mediated lipid peroxidation. It has not been clear whether specific mediators generated from DHA contribute to its biological properties. Using ARPE-19 cells, we demonstrated the synthesis of 10,17S-docosatriene [neuroprotectin Dl (NPDI)]. This synthesis was enhanced by the calcium ionophore A-23187, by IL-1 3P, or by supplying DHA. Added NPD1 (50nM) potently counteracted H2O2/tumor necrosis factor-alpha oxidative stress-triggered apoptotic DNA damage in RPE. NPD1 also up-regulated the anti-apoptotic proteins Bcl-2 and Bcl-xL and decreased pro-apoptotic Bax and Bad expression. Moreover, NPD1 (50nM) inhibited oxidative stress-induced caspase-3 activation. NPD1 also inhibited IL-1beta-stimulated expression of COX-2. Furthermore, A2E-triggered oxidative stress induction of RPE cell apoptosis was also attenuated by NPD1. Overall, NPD1 protected RPE cells from oxidative stress-induced apoptosis. In conclusion, we have demonstrated an additional function of the RPE: its capacity to synthesize NPD1. This new survival signaling is potentially of interest in the understanding of the pathophysiology of retinal degenerations and in exploration of new therapeutic modalities.

Nutrition challenges for the twenty-first century

Although progress has been made towards international goals for the eradication of hunger and malnutrition, considerable work is still required to achieve them and to respond to emerging public health nutrition challenges. The present paper outlines sixteen major inter-linked nutrition challenges recently identified by the UN Standing Committee on Nutrition. While many of the challenges relate to the nutritional needs of children and mothers, an increased emphasis on nutrition-related chronic diseases that affect later life is also evident. Promoting healthy ageing and the maintenance of physical and mental function in older age are undoubtedly major challenges for the future, and the present paper also informs on the role of nutrition, specifically n-3 essential fatty acids, in the prevention of cognitive decline. The importance of determining the cost-effectiveness of nutrition interventions is advocated, in order that the nutrition community can respond appropriately to global nutrition challenges.

Omega-3 fatty acids, pro-inflammatory signaling and neuroprotection

PURPOSE OF REVIEW

To summarize recent findings that docosahexaenoate (DHA) is the precursor of stereospecific derivatives with anti-inflammatory and cytoprotective properties.

RECENT FINDINGS

The docosahexaenoate-derived mediator neuroprotectin D1 is formed in retinal pigment epithelial cells when confronted with oxidative stress, in the brain during experimental stroke, and in the human brain from Alzheimer's disease patients as well as in human brain cells in culture. Neuroprotectin D1 displays potent anti-inflammatory and neuroprotective bioactivity.

SUMMARY

Here, we summarize recent studies demonstrating that in brain ischemia-reperfusion and in retinal pigment epithelial cells exposed to oxidative stress stereospecific docosahexaenoate-oxygenation pathways are activated and lead to the formation of docosanoid messengers. Two docosahexaenoate-oxygenation pathways were identified: the first is responsible for the formation of the messenger neuroprotectin D1 and the second pathway, which is active in the presence of aspirin, leads to the formation of the resolvin-type mediators (17R-DHA). Neuroprotectin D1 induces antiapoptotic, anti-inflammatory signaling and is neuroprotective.

Docosahexaenoic acid, the aquatic diet, and hominin encephalization: difficulties in establishing evolutionary links

Distinctive characteristics of modern humans, including language, tool manufacture and use, culture, and behavioral plasticity, are linked to changes in the organization and size of the brain during hominin evolution. As brain tissue is metabolically and nutritionally costly to develop and maintain, early hominin encephalization has been linked to a release of energetic and nutritional constraints. One such nutrient-based approach has focused on the n-3 long-chained polyunsaturated fatty acid docosahexaenoic acid (DHA), which is a primary constituent of membrane phospholipids within the synaptic networks of the brain essential for optimal cognitive functioning. As biosynthesis of DHA from n-3 dietary precursors (alpha-linolenic acid, LNA) is relatively inefficient, it has been suggested that preformed DHA must have been an integral dietary constituent during evolution of the genus Homo to facilitate the growth and development of an encephalizing brain. Furthermore, preformed DHA has only been identified to an appreciable extent within aquatic resources (marine and freshwater), leading to speculation that hominin encephalization is linked specifically to access and consumption of aquatic resources. The key premise of this perspective is that biosynthesis of DHA from LNA is not only inefficient but also insufficient for the growth and maturation demands of an encephalized brain. However, this assumption is not well-supported, and much evidence instead suggests that consumption of LNA, available in a wider variety of sources within a number of terrestrial ecosystems, is sufficient for normal brain development and maintenance in modern humans and presumably our ancestors.

Omega-3 fatty acids and antioxidants in neurological and psychiatric diseases: an overview

RATIONALE

Omega-3 fatty acids are known to play a role in nervous system activity, cognitive development, memory-related learning, neuroplasticity of nerve membranes, synaptogenesis and synaptic transmission. The brain is considered abnormally sensitive to oxidative damage, and aging is considered one of the most significant risk factors for degenerative neurological disorders. Recently, clinical trials of several neurodegenerative diseases have increasingly targeted the evaluation of the effectiveness of various antioxidants.

OBJECTIVES

The effects of omega-3 fatty acids and antioxidants on the anatomic and functional central nervous system development and their possible therapeutical use in some neurological and psychiatric pathologies are evaluated.

RESULTS

A number of critical trials have confirmed the benefits of dietary supplementation with omega-3 fatty acids not only in several psychiatric conditions, but also in inflammatory and autoimmune and neurodegenerative diseases. Many evidences indicate that antioxidants are also essential in maintaining a correct neurophysiology.

CONCLUSIONS

Omega-3 fatty acids could be useful in the prevention of different pathologies, such as cardiovascular, psychiatric, neurological, dermatological and rheumatological disorders. A number of studies suggest that antioxidants can prevent the oxidation of various macromolecules such as DNA, proteins, and lipids. The ideal use of antioxidants should be a prophylactic and continue treatment before aging.

Beneficial effects of docosahexaenoic acid on active avoidance performance in 1K-1C hypertensive rats

The present study evaluated the role of chronic docosahexaenoic acid (DHA) supplementation on active avoidance learning task performance in experimental hypertension. Male Wistar rats were randomly divided into five experimental groups as follows: control, sham, DHA treated, 1K-1C hypertensive, and 1K-1C hypertensive+DHA treated. Hypertension was induced in 1K-1C rats via placing a silver clip (0.20-mm ID) around the left renal artery following a right uninephrectomy. DHA (36 mg/kg/day) was given to the treatment groups for 60 days by gastric gavage. Arterial blood pressure was measured by using the tail-cuff method. Active avoidance responses were determined by an automated shuttle-box. In brain (cerebrum) and hippocampus tissues, thiobarbituric acid reactive substances (TBARS) and nitrite levels were measured by fluorometric methods. DHA supplementation decreased blood pressure in hypertensive rats. Data from active avoidance training indicated that performance of active avoidance learning tasks were significantly impaired in 1K-1C hypertensive rats, but was completely restored by DHA supplementation. Increased cerebrum TBARS levels in 1K-1C rats were abolished by DHA administration. Cerebrum nitrite levels were lower in the DHA, 1K-1C and 1K-1C+DHA treated groups compared to controls. Hippocampus nitrite levels were lower in DHA treated and 1K-1C hypertensive rats compared to controls and higher in 1K-1C+DHA treated rats compared to the 1K-1C group. Our data indicates that DHA supplementation improves the performance of active avoidance learning tasks which is impaired in experimental hypertension. These affirmative changes might be due to a DHA-induced decrease in lipid peroxidation which may in turn limit the consumption of nitric oxide (NO) which promotes active avoidance learning.

Mice raised on milk transgenically enriched with n-3 PUFA have increased brain docosahexaenoic acid

The brain contains high levels of the long-chain n-3 FA DHA (22:6n-3), mainly in the gray matter and synaptosomes. Adequate intake of DHA is crucial for optimal nervous system function, particularly in infants. Supplementation of infant formulas with DHA at levels similar to human breast milk is recommended for biochemical and functional benefits to neonates. We generated transgenic mice that produce elevated levels of n-3 PUFA in their milk by expressing the Caenorhabditis elegans n-3 FA desaturase under the control of a lactation-induced goat beta-casein promoter. To examine the postnatal effects of consuming the n-3-enriched milk, we compared the growth and brain and plasma FA composition of mouse pups raised on milk from transgenic dams with those observed for pups raised on milk from nontransgenic dams. A significant decrease in arachidonic acid (ARA, 20:4n-6) and concomitant increases in n-3 PUFA were observed in the phospholipid fraction of transgenic mouse milk. The n-6:n-3 FA ratios were 4.7 and 34.5 for the transgenic and control milk phospholipid fractions, respectively. DHA and DPA (22:5n-6) comprised 15.1% and 2.8% of brain FA from weanling mice nursed on transgenic dams, as compared with 6.9% and 9.2% for weanling mice nursed on control dams, respectively. This transgenic mouse model offers a unique approach to disassociate the effects and fetal programming resulting from a high n-6:n-3 FA ratio gestational environment from the postnatal nutritional effects of providing milk with differing n-6:n-3 FA ratios.

Fish oil and mental health: the role of n-3 long-chain polyunsaturated fatty acids in cognitive development and neurological disorders

Epidemiological and experimental studies have indicated that consumption of more n-3 long-chain polyunsaturated fatty acids may reduce the risk for a variety of diseases, including cardiovascular, neurological and immunological disorders, diabetes and cancer. This article focuses on the role of marine n-3 long-chain polyunsaturated fatty acids in brain functions, including the development of the central nervous system and neurological disorders. An overview of the major animal studies and clinical trials is provided here, focusing on fatty acid supplementation during pregnancy and infancy, and prevention and management of Alzheimer's disease, schizophrenia, depression and attention deficit hyperactive disorder. Although an optimal balance in n-3/n-6 long-chain polyunsaturated fatty acid ratio is important for proper neurodevelopment and cognitive functions, results from randomized controlled trials are controversial and do not confirm any useful effect of supplementation on development of preterm and term infants. The relationship between fatty acid status and mental disorders is confirmed by reduced levels of n-3 long-chain polyunsaturated fatty acids in erythrocyte membranes of patients with central nervous system disorders. Nevertheless, there are very little data supporting the use of fish oil in those patients. The only way to verify whether n-3 long-chain polyunsaturated fatty acids are a potential therapeutic option in the management and prevention of mental disorders is to conduct a large definitive randomized controlled trials similar to those required for the licensing of any new pharmacological treatment.

Cultural symbolism of fish and the psychotropic properties of omega-3 fatty acids

Fish is a food with unique psychotropic properties. Consumption of long-chain omega-3 fatty acids, rich in seafood, reduces depression, aggression and anger while improving mental well-being. We posit that symbols of fish have become linked to the emotional states induced by long-chain fatty acid by associative pairings, both conscious and unconscious. The limbic and hippocampal activity necessary for memory formation containing emotional content and the labeling of social context by cortical processes appears to be optimized by diets rich in long-chain omega-3 fatty acid. In this critical literature survey, we find that fish have been culturally labeled as symbols of emotional well-being and social healing in religious and medical practices among independent cultures, for at least six millennia. This understanding of the perception of fish as a symbolically healing or purifying food can assist current messages improving public health.

Omega-3 fatty acids and rodent behavior

This paper reviews the role of the n-3 fatty acids in the regulation of cognitive functions, locomotor and exploratory activity and emotional status in rodents. There are disparate data on the performance of n-3 fatty acid deficient animals in the open field test and elevated plus maze. Results obtained in our laboratory indicated slower habituation to the open field in deficient mice, which affects total locomotor and exploratory parameters. We also observed no change in plus maze performance of deficient mice under low-stress but elevated anxiety under high-stress conditions. There is some evidence of elevated aggression and increased immobility time in the forced swimming test caused by n-3 fatty acid deficiency in rodents. Effects of n-3 fatty acid deficiency and supplementation on learning in several tests such as the Morris water maze, two odor olfactory discriminations, radial arm maze performance and avoidance tasks are reviewed in detail. There is some evidence of an enhanced vulnerability to stress of n-3 fatty acid deficient animals and this factor can influence performance in a variety of tests. Thus, behavioral tasks that involve a higher level of stress may better differentiate behavioral effects related to brain docosahexaenoic acid (DHA) status. It is suggested that a fruitful area for future investigations of functional alterations related to brain DHA status will be the delineation of the factors underlying changes in performance in behavioral tasks. The possible role of non-cognitive factors like emotionality and attention in the impaired performance of n-3 fatty acid deficient animals also requires further investigation.

Versatile roles of docosahexaenoic acid in the prenatal brain: from pro- and anti-oxidant features to regulation of gene expression

Docosahexaenoic acid (DHA) is the most ubiquitous polyunsaturated fatty acid (FA) in brain tissue. It is selectively esterified to amino phospholipids (PL) and therefore it is highly prevalent at the cytofacial site of the plasma membrane where it may specifically participate in intracellular events. A highly selective DHA accumulation prior to birth is the result of maternal supply via the placenta through a bio-magnification process. Supplements of DHA via the intra-amniotic route to the fetal rat increase brain DHA levels and also confer neuroprotection to fetuses subjected to global ischemic stress. The protective effect has been attributed to an enhanced free radical scavenging capacity of DHA. Dietary deprivation of linolenic acid (LNA) during the perinatal life on the other hand, resulted in losses of DHA from cerebral PLs [M. Schiefermeier, E. Yavin, n-3 deficient and DHA-enriched diets during critical periods of the developing prenatal rat brain, J. Lipid Res. 43 (2002) 124-131]. LNA deprivation also caused changes in a number of gene markers the identification of which was attained by a labor-intensive suppression subtractive hybridization protocol using mRNA from 2-week-old postnatal brains [E. Yakubov, P. Dinerman, F. Kuperstein, S. Saban, E. Yavin, Improved representation of gene markers on microarray by PCR-select subtracted cDNA targets, Mol. Brain Res. 137 (2005) 110-118]. Most notable was a remarkable elevation of dopamine (DA) receptor (D1 and D2) genes as evaluated by quantitative RT-PCR, SDS-PAGE gel electrophoresis and immunochemical staining [F. Kuperstein, E. Yakubov, P. Dinerman, S. Gil, R. Eylam, N. Salem Jr., E. Yavin, Overexpression of dopamine receptor genes and their products in the postnatal rat brain following maternal n-3 FA dietary deficiency, J. Neurochem. 95 (2005) 1550-1562]. Over-expression of DA receptors has been attributed to a compensatory mechanism resulting from impairment in DA neurotransmitter production, storage and processing. In conclusion, DHA is a versatile molecule with a wide range of actions spanning from participation in cellular oxidative processes and intracellular signaling to modulatory roles in gene expression and growth regulation.

Evidence for growth-promoting effects of omega n - 3 fatty acids alone and in combination with a specific vitamin and mineral complex in rat neuroblastoma cells

The beneficial effects of Omega n - 3 polyunsaturated fatty acids (n - 3 PUFA) in situations of cognitive impairment may be associated with enhanced neuronal growth. Since neuronal growth is impaired in n - 3 PUFA deficiency, and enhanced by certain vitamins and trace elements, the effects of n - 3 PUFA, vitamin and mineral cell complex (VMC) and their association on neuronal growth were investigated in cultured rat neuroblastoma cells. Treatment of cells for 3 days with n - 3 PUFA significantly enhanced neurite length without affecting the number of neurites or cells. VMC significantly increased cell number without affecting neurite length or their number. Combined n - 3 PUFA and VMC significantly enhanced all three growth parameters. The data confirm the growth promoting effects of n - 3 PUFA and VMC in cultured neurons over a relatively short time frame.

N-3 fatty acids and cognitive and visual acuity development: methodologic and conceptual considerations

Several randomized clinical studies in infants born preterm and at term have explored the effects on visual acuity development of postnatal supplementation with various sources of docosahexaenoic acid (DHA). Higher visual acuity after DHA supplementation is a consistent finding in infants born preterm. For infants born at term, the results are less consistent and are better explained by differences in sensitivity of the visual acuity test (electrophysiologic tests being more sensitive than subjective tests) or by differences in the amount of DHA included in the experimental formula. Differences in the sensitivity of the test may also be relevant in discussions of whether the effects of DHA on visual acuity are transient or persistent. A smaller number of studies have attempted to study the effects of DHA on cognitive development. The major focus of this article is to review the types of methods that have been used to evaluate the effects of DHA on cognition and to provide the rationale for measures that are a better conceptual fit. Research is needed (1) to probe the effects of variable DHA exposure on infant and child development, (2) to measure outcomes that better relate to preschool and school-age cognitive function, and (3) to reinforce, and in some cases demonstrate, links between specific infant and preschool measures of cognitive development. We strongly encourage collaborations with developmental cognitive neuroscientists to facilitate these research goals.

Nutrigenomic approaches to study the effects of n-3 PUFA diet in the central nervous system

Deficiencies in essential, mainly omega-3 and omega-6 (n-3, n-6) long chain polyunsaturated fatty acids (LC-PUFA) result in visual and cognitive impairment and disturbances in mental functions in animals and could be the main reason for the increasing incidence of different mental disorders in humans. Traditional approaches cannot give us a detailed picture on how dietary lipids exert their effects, because they focus on only a few genes or biomarkers. Dietary lipids not only influence the biophysical state of the cell membranes but, via direct and indirect routes, they also act on multiple pathways including signalling and gene and protein activities. Therefore, to understand the molecular basis of the effects and roles of n-3 PUFA in the central nervous system global screening techniques such as DNA- or protein microarrays were used to assess the changes, in a global way, at the transcriptome and at the proteome level. With DNA microarrays we found that cholesterol and fish oil (high in PUFA) diets altered the expression of several genes involved in raft formation and membrane protrusions. By using protein microarrays we detected a decreased concentration of protein kinase C beta, gamma, phospholipase C gamma and other changes in the expression level of proteins involved in the signal transduction pathway in the brain in response to high cholesterol diet. Besides the known cellular effects of lipid nutritions (changing eicosanoid make up, effects on membrane fluidity and raft stability) it is now evident that dietary lipids influence gene and protein activity levels, protein modifications and probably play important role in modulating protein aggregation.

Docosahexaenoic acid protects from amyloid and dendritic pathology in an Alzheimer's disease mouse model

Genetic data argues that Alzheimer's disease (AD) can be initiated by aggregates of a 42 amino acid beta amyloid peptide (Abeta42). The Abeta aggregates, notably small oligomer species, cause a cascade of events including oxidative damage, inflammation, synaptic toxicity and accumulation of intraneuronal inclusions; notably neurofibrillary tangles. Cognitive deficits are likely to begin with a failure of synaptogenesis and synaptic plasticity with dendritic spine loss and dying back of dendritic arbor. This is followed by neuron loss in key areas involved in learning and memory. Significant prevention or delay of clinical onset may be achievable by modifying environmental risk factors that impact the underlying pathogenic pathways. Because low fish intake and low blood levels of the marine lipid, docosahexaenoic acid (DHA) have been associated with increased AD risk we have tested the impact of depleting or supplementing with dietary DHA on AD pathogenesis in transgenic mice bearing a mutant human gene known to cause AD in people. We reported that even with intervention late in life dietary DHA depletion dramatically enhanced oxidative damage and the loss of dendritic markers, while DHA supplementation markedly reduced Abeta42 accumulation and oxidative damage, corrected many synaptic deficits and improved cognitive function. Loss of brain DHA was exacerbated in mice expressing the mutant human AD transgene, this is consistent with evidence for increased oxidative attack on DHA oxidation in AD. Treatment with the curry spice extract curcumin, a polyphenolic antioxidant that inhibits AP aggregation, has been strongly protective in the same mouse model. Many Western diets are typically deficient in DHA and low in polyphenolic antioxidant intake. These and other data argue that increasing dietary intake of both DHA and polyphenolic antioxidants may be useful for AD prevention.

A role for docosahexaenoic acid-derived neuroprotectin D1 in neural cell survival and Alzheimer disease

Deficiency in docosahexaenoic acid (DHA), a brain-essential omega-3 fatty acid, is associated with cognitive decline. Here we report that, in cytokine-stressed human neural cells, DHA attenuates amyloid-beta (Abeta) secretion, an effect accompanied by the formation of NPD1, a novel, DHA-derived 10,17S-docosatriene. DHA and NPD1 were reduced in Alzheimer disease (AD) hippocampal cornu ammonis region 1, but not in the thalamus or occipital lobes from the same brains. The expression of key enzymes in NPD1 biosynthesis, cytosolic phospholipase A2 and 15-lipoxygenase, was altered in AD hippocampus. NPD1 repressed Abeta42-triggered activation of proinflammatory genes while upregulating the antiapoptotic genes encoding Bcl-2, Bcl-xl, and Bfl-1(A1). Soluble amyloid precursor protein-alpha stimulated NPD1 biosynthesis from DHA. These results indicate that NPD1 promotes brain cell survival via the induction of antiapoptotic and neuroprotective gene-expression programs that suppress Abeta42-induced neurotoxicity.

An extraordinary degree of structural specificity is required in neural phospholipids for optimal brain function: n-6 docosapentaenoic acid substitution for docosahexaenoic acid leads to a loss in spatial task performance

This study was conducted to determine whether provision of preformed dietary docosapentaenoic acid (DPAn-6) can replace docosahexaenoic acid (DHA) for brain function as assessed by spatial task performance. A newly modified artificial rearing method was employed to generate n-3 fatty acid-deficient rats. Newborn pups were separated from their mothers at 2 days of age and given artificial rat milk containing linoleic acid (LA), or LA supplemented with 1% DHA (DHA), 1% DPAn-6 (DPA) or 1% DHA plus 0.4% DPAn-6 (DHA/DPA). The animals were then weaned onto similar pelleted diets. At adulthood, behavioural tasks were administered and then the brains were collected for fatty acid analysis. The LA and DPA groups showed a lower (63-65%) brain DHA than the dam-reared, DHA and DHA/DPA groups and this loss was largely compensated for by an increase in brain DPAn-6. The brain fatty acid composition in the DPA group was the same as that in the LA group at adulthood. In the Morris water maze, the LA and DPA groups exhibited a longer escape latency than the dam-reared and DHA groups and had a defect in spatial retention. In conclusion, DPAn-6 could not replace DHA for brain function, indicating a highly specific structural requirement for DHA.

N-3 fatty acid deficiency induced by a modified artificial rearing method leads to poorer performance in spatial learning tasks

Docosahexaenoic acid (DHA) is a major structural component of the nervous system, and depletion may lead to losses in neural function. Our objective was to demonstrate a deficit in spatial task performance in rats with low brain DHA due to a low n-3 fatty acid intake using a first-generational artificial rearing technique. Newborn rat pups were separated on d 2 and assigned to two artificial rearing groups or a dam-reared control group. Pups were hand fed artificial milk via custom-designed nursing bottles containing either 0.02% (n-3 Def) or 3.1% (n-3 Adq) of total fatty acids as LNA. At d 21, rats were weaned to either n-3 Def or n-3 Adq pelleted diets and several behavioral tasks were evaluated at 9 wk of age. Brain DHA was lower (58% and 61%, p < 0.001) in n-3 Def in comparison to n-3 Adq and dam-reared rats, respectively. At adulthood, the n-3 fatty acid-deficient rats had a significantly greater moving time than the dam-reared group (p < 0.05), but there were no differences among the three groups in the elevated plus maze test. The n-3 fatty acid deficient rats exhibited a longer escape latency (p < 0.05) and poorer memory retention in the Morris water maze compared with n-3 fatty acid adequate and dam-reared rats. We concluded that artificial rearing can be used to produce n-3 fatty acid deficiency in the first generation. This deficiency was associated with significantly reduced spatial learning. Adequate brain DHA levels are required for optimal spatial learning.

Dietary n-3 polyunsaturated fatty acid depletion activates caspases and decreases NMDA receptors in the brain of a transgenic mouse model of Alzheimer's disease

Epidemiological data indicate that low n-3 polyunsaturated fatty acids (PFA) intake is a readily manipulated dietary risk factor for Alzheimer's disease (AD). Studies in animals confirm the deleterious effect of n-3 PFA depletion on cognition and on dendritic scaffold proteins. Here, we show that in transgenic mice overexpressing the human AD gene APPswe (Tg2576), safflower oil-induced n-3 PFA deficiency caused a decrease in N-methyl-D-aspartate (NMDA) receptor subunits, NR2A and NR2B, in the cortex and hippocampus with no loss of the presynaptic markers, synaptophysin and synaptosomal-associated protein 25 (SNAP-25). n-3 PFA depletion also decreased the NR1 subunit in the hippocampus and Ca2+/calmodulin-dependent protein kinase (CaMKII) in the cortex of Tg2576 mice. These effects of dietary n-3 PFA deficiency were greatly amplified in Tg2576 mice compared to nontransgenic mice. Loss of the NR2B receptor subunit was not explained by changes in mRNA expression, but correlated with p85alpha phosphatidylinositol 3-kinase levels. Most interestingly, n-3 PFA deficiency dramatically increased levels of protein fragments, corresponding to caspase/calpain-cleaved fodrin and gelsolin in Tg2576 mice. This effect was minimal in nontransgenic mice suggesting that n-3 PFA depletion potentiated caspase activation in the Tg2576 mouse model of AD. Dietary supplementation with docosahexaenoic acid (DHA; 22 : 6n-3) partly protected from NMDA receptor subunit loss and accumulation of fodrin and gelsolin fragments but fully prevented CaMKII decrease. The marked effect of dietary n-3 PFA on NMDA receptors and caspase/calpain activation in the cortex of an animal model of AD provide new insights into how dietary essential fatty acids may influence cognition and AD risk.

Is docosahexaenoic acid, an n-3 long-chain polyunsaturated fatty acid, required for development of normal brain function? An overview of evidence from cognitive and behavioral tests in humans and animals

This review is part of a series intended for nonspecialists that will summarize evidence relevant to the question of whether causal relations exist between micronutrient deficiencies and brain function. Here, we focus on experiments that used cognitive or behavioral tests as outcome measures in experimental designs that were known to or were likely to result in altered brain concentrations of the n-3 fatty acid docosahexaenoic acid (DHA) during the perinatal period of "brain growth spurt." Experimental designs reviewed include observational breastfeeding studies and randomized controlled trials in humans and studies in rodents and nonhuman primates. This review is based on a large number of expert reviews and commentaries and on some 50 recent studies in humans and animals that have not yet been included in published reviews. Expert opinion regarding the strengths and weaknesses of the major experimental systems and uncertainties associated with interpreting results is summarized. On the basis of our reading of this literature, we conclude that evidence from several types of studies, particularly studies in animals, suggests that, within the context of specific experimental designs, changes in brain concentrations of DHA are positively associated with changes in cognitive or behavioral performance. Additional experimental information required to conclude that a causal association exists is discussed, as are uncertainties associated with applying results from specific experimental designs to the question of whether infant formula should be supplemented with DHA.