Docosahexaenoic acid provides protection from impairment of learning ability in Alzheimer's disease model rats

The Δ4-desaturation pathway for DHA biosynthesis is operative in the human species: differences between normal controls and children with the Zellweger syndrome

Background

Docosahexaenoic acid (DHA, 22:6ω3) is a fundamental component of cell membranes, especially in the brain and retina. In the experimental animal, DHA deficiency leads to suboptimal neurological performance and visual deficiencies. Children with the Zellweger syndrome (ZS) have a profound DHA deficiency and symptoms that can be attributed to their extremely low DHA levels. These children seem to have a metabolic defect in DHA biosynthesis, which has never been totally elucidated. Treatment with DHA ethyl ester greatly improves these patients, but if we could normalize their endogenous DHA production we could get additional benefits. We examined whether DHA biosynthesis by Δ4-desaturation could be enhanced in the human species by transfecting the enzyme, and if this could normalize the DHA levels in cells from ZS patients.

Results

We showed that the Δ4-desaturase gene (Fad4) from Thraustochytrium sp, which can be expressed by heterologous transfection in other plant and yeast cells, can also be transfected into human lymphocytes, and that it expresses the enzyme (FAD4, Δ4-desaturase) by producing DHA from direct Δ4-desaturation of 22:5ω3. We also found that the other substrate for Δ4-desaturase, 22:4ω6, was parallely desaturated to 22:5ω6.

Conclusions

The present "in vitro" study demonstrates that Δ4-desaturase can be transfected into human cells and synthesize DHA (as well as 22:5ω6, DPA) from 22:5ω3 and 22:4ω6, respectively, by putative Δ4-desaturation. Even if this pathway may not be the physiological route for DHA biosynthesis "in vivo", the present study opens new perspectives for the treatment of patients within the ZS spectrum.

Fatty acids from fish: the anti-inflammatory potential of long-chain omega-3 fatty acids

Omega-6 (n-6) and omega-3 (n-3) polyunsaturated fatty acids (PUFA) are precursors of potent lipid mediators, termed eicosanoids, which play an important role in the regulation of inflammation. Eicosanoids derived from n-6 PUFAs (e.g., arachidonic acid) have proinflammatory and immunoactive functions, whereas eicosanoids derived from n-3 PUFAs [e.g., eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)] have anti-inflammatory properties, traditionally attributed to their ability to inhibit the formation of n-6 PUFA-derived eicosanoids. While the typical Western diet has a much greater ratio of n-6 PUFAs compared with n-3 PUFAs, research has shown that by increasing the ratio of n-3 to n-6 fatty acids in the diet, and consequently favoring the production of EPA in the body, or by increasing the dietary intake of EPA and DHA through consumption of fatty fish or fish-oil supplements, reductions may be achieved in the incidence of many chronic diseases that involve inflammatory processes; most notably, these include cardiovascular diseases, inflammatory bowel disease (IBD), cancer, and rheumatoid arthritis, but psychiatric and neurodegenerative illnesses are other examples.

Rapid Determination of Docosahexaenoic Acid in Powdered Oil by Near-Infrared Spectroscopy

Near-infrared spectroscopy (NIRS) was used as a rapid and nondestructive method to determine the content of docosahexaenoic acid (DHA) in powdered oil samples. A total of 82 samples were scanned in the diffuse reflectance mode by Nicolet 5700 FTIR spectrometer and the reference values for DHA was measured by gas chromatography. Calibration equations were developed using partial least-squares regression (PLS) with internal cross-validation. Samples were split in two sets, one set used as calibration (n = 66) whereas the remaining samples (n=16) were used as validation set. Two mathematical treatments (first and second derivative), none (log(1/R)) and standard normal variate as scatter corrections and Savitzky—Golay smoothing were explored. To decide upon the number of PLS factors included in the PLS model, the model with the lowest root mean square error of cross-validation (RMSECV=0.44) for the validation set is chosen. The correlation coefficient (r) between the predicted and the reference results which used as an evaluation parameter for the models is 0.968. The root mean square error of prediction of the final model is 0.59. The results reported in this article demonstrate that FT-NIR measurements can serve as a rapid method to determine DHA in powdered oil.

Impact of administered bifidobacterium on murine host fatty acid composition

Recently, we reported that administration of Bifidobacteria resulted in increased concentrations of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in murine adipose tissue [1]. The objective of this study was to assess the impact of co-administration of Bifidobacterium breve NCIMB 702258 and the substrate for EPA, alpha-linolenic acid, on host fatty acid composition. alpha-Linolenic acid-supplemented diets (1%, wt/wt) were fed to mice (n = 8), with or without B. breve NCIMB 702258 (daily dose of 10(9) microorganisms) for 8 weeks. Two further groups received either supplement of B. breve alone or unsupplemented diet. Tissue fatty acid composition was assessed by gas liquid chromatography. Dietary supplementation of alpha-linolenic acid resulted in higher (P < 0.05) alpha-linolenic acid and EPA concentrations in liver and adipose tissue and lower (P < 0.05) arachidonic acid in liver, adipose tissue and brain compared with mice that did not receive alpha-linolenic acid. Supplementation with B. breve NCIMB 702258 in combination with alpha-linolenic acid resulted in elevated (P < 0.05) liver EPA concentrations compared with alpha-linolenic acid supplementation alone. Furthermore, the former group had higher (P < 0.05) DHA in brain compared with the latter group. These results suggest a role for interactions between fatty acids and commensals in the gastrointestinal tract. This interaction between administered microbes and fatty acids could result in a highly effective nutritional approach to the therapy of a variety of inflammatory and neurodegenerative conditions.

Omega-3 fatty acids: potential role in the management of early Alzheimer's disease

Omega-3 fatty acids are essential for brain growth and development. They play an important role throughout life, as critical modulators of neuronal function and regulation of oxidative stress mechanisms, in brain health and disease. Docosahexanoic acid (DHA), the major omega-3 fatty acid found in neurons, has taken on a central role as a target for therapeutic intervention in Alzheimer’s disease (AD). A plethora of in vitro, animal model, and human data, gathered over the past decade, highlight the important role DHA may play in the development of a variety of neurological and psychiatric disorders, including AD. Cross sectional and prospective cohort data have demonstrated that reduced dietary intake or low brain levels of DHA are associated with accelerated cognitive decline or the development of incipient dementia, including AD. Several clinical trials investigating the effects of omega-3 fatty acid supplementation in AD have been completed and all failed to demonstrate its efficacy in the treatment of AD. However, these trials produced intriguing data suggesting that the beneficial effects of omega-3 fatty acid supplementation may depend on the stage of disease, other dietary mediators, and apolipoprotein E status.

Dietary fatty acids in dementia and predementia syndromes: epidemiological evidence and possible underlying mechanisms

Drugs currently used in the treatment of cognitive impairment and dementia have a very limited therapeutic value, suggesting the necessity to potentially individualize new strategies able to prevent and to slow down the progression of predementia and dementia syndromes. An increasing body of epidemiological evidence suggested that elevated saturated fatty acids (SFA) could have negative effects on age-related cognitive decline (ARCD) and mild cognitive impairment (MCI). Furthermore, a clear reduction of risk for cognitive decline has been found in population samples with elevated fish consumption, high intake of monounsaturated fatty acids (MUFA) and polyunsaturated fatty acids (PUFA), particularly n-3 PUFA. Epidemiological findings demonstrated that high PUFA intake appeared to have borderline non-significant trend for a protective effect against the development of MCI. Several hypotheses could explain the association between dietary unsaturated fatty acids and cognitive functioning, including mechanisms through the co-presence of antioxidant compounds in food groups rich in fatty acids, via atherosclerosis and thrombosis, inflammation, accumulation of b-amyloid, or via an effect in maintaining the structural integrity of neuronal membranes, determining the fluidity of synaptosomal membranes that thereby regulate neuronal transmission. However, recent findings from clinical trials with n-3 PUFA supplementation showed efficacy on depressive symptoms only in non-apolipoprotein E (APOE) epsilon4 carriers, and on cognitive symptoms only in very mild Alzheimer's disease (AD) subgroups, MCI patients, and cognitively unimpaired subjects non-APOE epsilon4 carriers. These data together with epidemiological evidence support a possible role of fatty acid intake in maintaining adequate cognitive functioning and possibly for the prevention and management of cognitive decline and dementia, but not when the AD process has already taken over.

Mechanisms of n-3 fatty acid-mediated development and maintenance of learning memory performance

Docosahexaenoic acid (DHA, 22:6n-3) is specifically enriched in the brain and mainly anchored in the neuronal membrane, where it is involved in the maintenance of normal neurological function. Most DHA accumulation in the brain takes place during brain development in the perinatal period. However, hippocampal DHA levels decrease with age and in the brain disorder Alzheimer's disease (AD), and this decrease is associated with reduced hippocampal-dependent spatial learning memory ability. A potential mechanism is proposed by which the n-3 fatty acids DHA and eicosapentaenoic acid (20:5n-3) aid the development and maintenance of spatial learning memory performance. The developing brain or hippocampal neurons can synthesize and take up DHA and incorporate it into membrane phospholipids, especially phosphatidylethanolamine, resulting in enhanced neurite outgrowth, synaptogenesis and neurogenesis. Exposure to n-3 fatty acids enhances synaptic plasticity by increasing long-term potentiation and synaptic protein expression to increase the dendritic spine density, number of c-Fos-positive neurons and neurogenesis in the hippocampus for learning memory processing. In aged rats, n-3 fatty acid supplementation reverses age-related changes and maintains learning memory performance. n-3 fatty acids have anti-oxidative stress, anti-inflammation, and anti-apoptosis effects, leading to neuron protection in the aged, damaged, and AD brain. Retinoid signaling may be involved in the effects of DHA on learning memory performance. Estrogen has similar effects to n-3 fatty acids on hippocampal function. It would be interesting to know if there is any interaction between DHA and estrogen so as to provide a better strategy for the development and maintenance of learning memory.

Docosahexaenoic acid withstands the Aβ(25-35)-induced neurotoxicity in SH-SY5Y cells

BACKGROUND

Docosahexaenoic acid (DHA, C22:6, n-3) ameliorates the memory-related learning deficits of Alzheimer's disease (AD), which is characterized by fibrillar amyloid deposits in the affected brains. Here, we have investigated whether DHA-induced inhibition of Amyloid β-peptide(25-35) (Aβ(25-35)) fibrillation limits or deteriorates the toxicity of the human neuroblastoma cells (SH-SY5Y).

EXPERIMENTAL METHODS

In vitro fibrillation of Aβ(25-35) was performed in the absence or presence of DHA. Afterwards, SH-SY5Y cells were incubated with Aβ(25-35) in absence or presence 20 μM DHA to evaluate its effect on the Aβ(25-35)-induced neurotoxicity by MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide)]-redox and TUNEL (TdT-mediated dUTP-biotin nick end-labeling) assay and immunohistochemistry. The level of Aβ(25-35)-induced lipid peroxide (LPO) was determined in the absence or presence of oligomer-specific antibody. Fatty acid profile was estimated by gas chromatography.

RESULTS

DHA significantly reduced the Aβ(25-35) in vitro fibrillation, as indicated by fluorospectroscopy and transmission electron microscopy. Aβ(25-35) decreased the MTT-redox activity and increased the apoptotic damage and levels of LPO when compared with those of the controls. However, when the SH-SY5Y cells were treated with Aβ(25-35) in the presence of DHA, MTT redox potential significantly increased and the levels LPO decreased, suggesting an inhibition of the Aβ(25-35)-induced neurotoxicity. DHA improved the Aβ(25-35) induced DNA damage and axodendritic loss, with a concomitant increase in the cellular level of DHA, suggesting DHA protects the cell from neurotoxic degeneration.

CONCLUSION

DHA not only inhibits the in vitro fibrillation but also resists the Aβ(25-35)-induced toxicity in the neuronal cells. This might be the basis of the DHA-induced amelioration of Aβ-induced neurodegeneration and related cognitive deficits.

Amyloid-Beta Peptide, Oxidative Stress and Inflammation in Alzheimer's Disease: Potential Neuroprotective Effects of Omega-3 Polyunsaturated Fatty Acids

Alzheimer's disease is the most common form of dementia in the elderly and is a progressive neurodegenerative disorder characterised by a decline in cognitive function and also profound alterations in mood and behaviour. The pathology of the disease is characterised by the presence of extracellular amyloid peptide deposits and intracellular neurofibrillary tangles in the brain. Although many hypotheses have been put forward for the aetiology of the disease, increased inflammation and oxidative stress appear key to be features contributing to the pathology. The omega-3 polyunsaturated fats, eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) have well-characterised effects on inflammation and may have neuroprotective effects in a number of neurodegenerative conditions including Alzheimer's disease. The aims of this paper are to review the neuroprotective effects of EPA and DHA in Alzheimer's disease, with special emphasis on their role in modulating oxidative stress and inflammation and also examine their potential as therapeutic agents.

Omega-3 fatty acids and cognitive function in women

Omega-3 fatty acids (FAs) could play an important role in maintaining cognitive function in aging individuals. The omega-3 FA docosahexaenoic acid is a major constituent of neuronal membranes and, along with the other long-chain omega-3 FAs from fish such as eicosapentaentoic acid, has been shown to have a wide variety of beneficial effects on neuronal functioning, inflammation, oxidation and cell death, as well as on the development of the characteristic pathology of Alzheimer's disease. Omega-3 FAs may prevent vascular dementia via salutary effects on lipids, inflammation, thrombosis and vascular function. Epidemiologic studies have generally supported a protective association between fish and omega-3 FA levels and cognitive decline. Some of the small, short-term, randomized trials of docosahexaenoic acid and/or eicosapentaentoic acid supplementation have found positive effects on some aspects of cognition in older adults who were cognitively intact or had mild cognitive impairment, although little effect was found in participants with Alzheimer's disease. Large, long-term trials in this area are needed.

Nutrition and Alzheimer's disease: pre-clinical concepts

Alzheimer's disease (AD) is a progressive condition characterized by neurodegeneration and the dense deposition of proteins in the brain. There is no cure for AD and current treatments usually only provide a temporary reduction of symptoms. There is thus a strong unmet need for effective preventative and therapeutic strategies and the potential role for nutrition in such strategies is rapidly gaining interest. An Alzheimer's brain contains fewer synapses and reduced levels of synaptic proteins and membrane phosphatides. Brain membrane phosphatide synthesis requires at least three dietary precursors: polyunsaturated fatty acids, uridine monophosphate (UMP) and choline. Animal studies have shown that administration of these nutrients increases the level of phosphatides, specific pre- or post-synaptic proteins and the number of dendritic spines - a requirement for new synapse formation. These effects are markedly enhanced when animals receive all three compounds together. This multi-nutrient approach in animals has also been shown to decrease amyloid beta protein (Abeta) plaque burden, improve learning and memory through increased cholinergic neurotransmission and have a neuroprotective effect in several mouse models of AD. Whether these potential therapeutic effects of a multi-nutrient approach observed in animal models can also be replicated in a clinical setting warrants further investigation.

Modulation of brain-derived neurotrophic factor as a potential neuroprotective mechanism of action of omega-3 fatty acids in a parkinsonian animal model

While we recently reported the beneficial effects of omega-3 polyunsaturated fatty acids (n-3 PUFAs) in a mouse model of Parkinson's disease (PD), the mechanisms of action remain largely unknown. Here, we specifically investigated the contribution of the brain-derived neurotrophic factor (BDNF) to the neuroprotective effect of n-3 PUFA observed in a mouse model of PD generated by a subacute exposure to MPTP using a total of 7 doses of 20mg/kg over 5 days. The ten-month high n-3 PUFA treatment which preceded the MPTP exposure induced an increase of BDNF mRNA expression in the striatum, but not in the motor cortex of animals fed the high n-3 PUFA diet. In contrast, n-3 PUFA treatment increased BDNF protein levels in the motor cortex of MPTP-treated mice, an effect not observed in vehicle-treated mice. The mRNA expression of the high-affinity BDNF receptor tropomyosin-related kinase B (TrkB) was increased in the striatum of MPTP-treated mice fed the high n-3 PUFA diet compared to vehicle and MPTP-treated mice on the control diet and to vehicle mice on the high n-3 PUFA diet. These data suggest that the modulation of BDNF expression contributes, in part, to n-3 PUFA-induced neuroprotection in an animal model of PD.

Dietary fats, cerebrovasculature integrity and Alzheimer's disease risk

An emerging body of evidence is consistent with the hypothesis that dietary fats influence Alzheimer's disease (AD) risk, but less clear is the mechanisms by which this occurs. Alzheimer's is an inflammatory disorder, many consider in response to fibrillar formation and extracellular deposition of amyloid-beta (Abeta). Alternatively, amyloidosis could notionally be a secondary phenomenon to inflammation, because some studies suggest that cerebrovascular disturbances precede amyloid plaque formation. Hence, dietary fats may influence AD risk by either modulating Abeta metabolism, or via Abeta independent pathways. This review explores these two possibilities taking into consideration; (i) the substantial affinity of Abeta for lipids and its ordinary metabolism as an apolipoprotein; (ii) evidence that Abeta has potent vasoactive properties and (iii) studies which show that dietary fats modulate Abeta biogenesis and secretion. We discuss accumulating evidence that dietary fats significantly influence cerebrovascular integrity and as a consequence altered Abeta kinetics across the blood-brain barrier (BBB). Specifically, chronic ingestion of saturated fats or cholesterol appears to results in BBB dysfunction and exaggerated delivery from blood-to-brain of peripheral Abeta associated with lipoproteins of intestinal and hepatic origin. Interestingly, the pattern of saturated fat/cholesterol induced cerebrovascular disturbances in otherwise normal wild-type animal strains is analogous to established models of AD genetically modified to overproduce Abeta, consistent with a causal association. Saturated fats and cholesterol may exacerbate Abeta induced cerebrovascular disturbances by enhancing exposure of vessels of circulating Abeta. However, presently there is no evidence to support this contention. Rather, SFA and cholesterol appear to more broadly compromise BBB integrity with the consequence of plasma protein leakage into brain, including lipoprotein associated Abeta. The latter findings are consistent with the concept that AD is a dietary-fat induced phenotype of vascular dementia, reflecting the extraordinary entrapment of peripherally derived lipoproteins endogenously enriched in Abeta. Rather than being the initiating trigger for inflammation in AD, accumulation of extracellular lipoprotein-Abeta may be a secondary amplifier of dietary induced inflammation, or possibly, simply be consequential. Clearly, delineating the mechanisms by which dietary fats increase AD risk may be informative in developing new strategies for prevention and treatment of AD.

Dietary fat intake and risk of Parkinson's disease: a case-control study in Japan

The present case-control study examined the relationship between dietary intake of individual fatty acids and the risk of Parkinson's disease (PD) in Japan. Included were 249 cases within 6 years of onset of PD. Controls were 368 inpatients and outpatients without a neurodegenerative disease. Information on dietary factors was collected using a validated self-administered diet history questionnaire. Compared with arachidonic acid intake in the first quartile, consumption of that in the fourth quartile was significantly related to an increased risk of PD: the adjusted odds ratio between extreme quartiles was 2.09 (95% confidence interval: 1.21-3.64, P for trend=0.008). Cholesterol intake was also significantly positively associated with the risk of PD: the adjusted odds ratio between extreme quartiles was 1.78 (95% confidence interval: 1.04-3.05, P for trend=0.01). Consumption of total fat, saturated fatty acids, monounsaturated fatty acids, n-3 polyunsaturated fatty acids, alpha-linolenic acid, eicosapentaenoic acid, docosahexaenoic acid, n-6 polyunsaturated fatty acids, and linoleic acid and the ratio of n-3 to n-6 polyunsaturated fatty acid intake were not associated with PD. Higher consumption of arachidonic acid and cholesterol may be related to an increased risk of PD.

Use of phosphatide precursors to promote synaptogenesis

New brain synapses form when a postsynaptic structure, the dendritic spine, interacts with a presynaptic terminal. Brain synapses and dendritic spines, membrane-rich structures, are depleted in Alzheimer's disease, as are some circulating compounds needed for synthesizing phosphatides, the major constituents of synaptic membranes. Animals given three of these compounds, all nutrients-uridine, the omega-3 polyunsaturated fatty acid docosahexaenoic acid, and choline-develop increased levels of brain phosphatides and of proteins that are concentrated within synaptic membranes (e.g., PSD-95, synapsin-1), improved cognition, and enhanced neurotransmitter release. The nutrients work by increasing the substrate-saturation of low-affinity enzymes that synthesize the phosphatides. Moreover, uridine and its nucleotide metabolites activate brain P2Y receptors, which control neuronal differentiation and synaptic protein synthesis. A preparation containing these compounds is being tested for treating Alzheimer's disease.

Polyunsaturated fatty acids protect against prion-mediated synapse damage in vitro

A loss of synapses is characteristic of the early stages of the prion diseases. Here we modelled the synapse damage that occurs in prion diseases by measuring the amount of synaptophysin, a pre-synaptic membrane protein essential for neurotransmission, in cortical or hippocampal neurones incubated with the disease associated isoform of the prion protein (PrP(Sc)), or with the prion-derived peptide PrP82-146. The addition of PrP(Sc) or PrP82-146 caused a dose-dependent reduction in the synaptophysin content of PrP wildtype neurones indicative of synapse damage. They did not affect the synaptophysin content of PrP null neurones. The loss of synaptophysin in PrP wildtype neurones was preceded by the accumulation of PrP82-146 within synapses. Since supplements containing polyunsaturated fatty acids (PUFA) are frequently taken for their perceived health benefits including reported amelioration of neurodegenerative conditions, the effects of some common PUFA on prion-mediated synapse damage were examined. Pre-treatment of cortical or hippocampal neurones with docosahexaenoic (DHA) or eicosapentaenoic acids (EPA) protected neurones against the loss of synaptophysin induced by PrP82-146 or PrP(Sc). This effect of DHA and EPA was selective as they did not alter the loss of synaptophysin induced by a snakevenom neurotoxin. The effects of DHA and EPA were associated with a significant reduction in the amount of FITC-PrP82-146 that accumulated within synapses. Such observations raise the possibility that supplements containing PUFA may protect against the synapse damage and cognitive loss seen during the early stages of prion diseases.

EFFECTS OF DIETARY LONG CHAIN PUFAs ON HIPPOCAMPAL LIPID PEROXIDATION AND NMDA RECEPTOR SUBUNITS A AND B CONCENTRATION IN STREPTOZOTOCIN-DIABETIC RATS

This study examined the effects of streptozotocin (STZ)-diabetes and dietary long chain polyunsaturated fatty acids (LC-PUFAs) on hippocampal N-methyl-D-aspartate (NMDA) receptor subunit expression and lipid peroxidation. MDA level was significantly increased after 8 weeks of STZ-diabetes. LC-PUFAs administration significantly reduced MDA levels in diabetic rats. NR2A and NR2B protein concentrations were significantly decreased by about 30% in diabetic rats. Dietary LC-PUFAs partially restored NR2A and NR2B in diabetic rats whereas the most significant increase was seen in nondiabetic rats. Consequently, dietary LC-PUFAs can partially restore hippocampal NMDA receptors and decrease lipid peroxidation in diabetes. LC-PUFAs are thus a possible prophylactic means for preventing the cognitive deficiencies of diabetes.

Dietary intake of fish and omega-3 fatty acids in relation to long-term dementia risk

BACKGROUND

Greater fish and omega-3 (n-3) polyunsaturated fatty acid (PUFA) intake may reduce dementia risk; however, previous studies have reported conflicting results, which were largely based on short-term follow-up.

OBJECTIVE

The objective was to study the dietary consumption of fish and omega-3 PUFAs in relation to long-term dementia risk.

DESIGN

We studied 5395 participants aged > or =55 y in the Rotterdam Study who were free of dementia and reported dietary information at baseline. We used age- and sex-adjusted Cox proportional hazard and multivariate-adjusted models to evaluate the relative risk of dementia and Alzheimer disease (AD) across categories of typical fish intake (none, low, and high) and fish type consumed (none, lean, and fatty). We also evaluated dementia and AD risk across tertiles of omega-3 PUFA intake, specifically, total long-chain omega-3 fatty acids: eicosapentaenoic acid (EPA) + docosahexaenoic acid (DHA), alpha-linolenic acid, and EPA and DHA individually.

RESULTS

During an average follow-up of 9.6 y, dementia developed in 465 participants (365 with a diagnosis of AD). In multivariate-adjusted models, total fish intake was unrelated to dementia risk (P for trend = 0.7). Compared with participants who typically ate no fish, those with a high fish intake had a similar dementia risk (hazard ratio: 0.95; 95% CI: 0.76, 1.19), as did those who typically ate fatty fish (hazard ratio: 0.98; 95% CI: 0.77, 1.24). Dietary intakes of omega-3 PUFAs were also not associated with dementia risk, and the results were similar when we considered AD specifically.

CONCLUSION

In this Dutch cohort, who had a moderate consumption of fish and omega-3 PUFAs, these dietary factors do not appear to be associated with long-term dementia risk.

The rat as an animal model of Alzheimer's disease

As a disease model, the laboratory rat has contributed enormously to neuroscience research over the years. It has also been a popular animal model for Alzheimer's disease but its popularity has diminished during the last decade, as techniques for genetic manipulation in rats have lagged behind that of mice. In recent years, the rat has been making a comeback as an Alzheimer's disease model and the appearance of increasing numbers of transgenic rats will be a welcome and valuable complement to the existing mouse models. This review summarizes the contributions and current status of the rat as an animal model of Alzheimer's disease.

Effects of eicosapentaenoic acid on synaptic plasticity, fatty acid profile and phosphoinositide 3-kinase signaling in rat hippocampus and differentiated PC12 cells

Placebo-controlled clinical studies suggest that intake of n-3 polyunsaturated fatty acids improves neurological disorders such as Alzheimer's disease, Huntington's disease and schizophrenia. To evaluate the impact of eicosapentaenoic acid (EPA), we orally administered highly purified ethyl EPA (EPA-E) to rats at a dose of 1.0 mg/g per day and measured long-term potentiation of the CA1 hippocampal region, a physiological correlate of synaptic plasticity that is thought to underlie learning and memory. The mean field excitatory postsynaptic potential slope of the EPA-E group was significantly greater than that of the control group in the CA1 region. Gene expression of hippocampal p85alpha, one of the regulatory subunits of phosphatidylinositol 3-kinase (PI3-kinase), was increased with EPA-E administration. Investigation of fatty acid profiles of neuronal and glia-enriched fractions demonstrated that a single administration of EPA-E significantly increased neuronal and glial EPA content and glial docosahexaenoic acid content, clearly suggesting that EPA was indeed taken up by both neurons and glial cells. In addition, we investigated the direct effects of EPA on the PI3-kinase/Akt pathway in differentiated PC12 cells. Phosphorylated-Akt expression was significantly increased in EPA-treated cells, and nerve growth factor withdrawal-induced increases in cell death and caspase-3 activity were suppressed by EPA treatment. These findings suggest that EPA protects against neurodegeneration by modulating synaptic plasticity and activating the PI3-kinase/Akt pathway, possibly by its own functional effects in neurons and glial cells and by its capacity to increase brain docosahexaenoic acid.

Fish, docosahexaenoic acid and Alzheimer's disease

Cognitive decline in the elderly, particularly Alzheimer's disease (AD), is a major socio-economic and healthcare concern. We review here the literature on one specific aspect of diet affecting AD, that of the omega3 fatty acids, particularly the brain's principle omega3 fatty acid - docosahexaenoic acid (DHA). DHA has deservedly received wide attention as a nutrient supporting both optimal brain development and for cardiovascular health. Our aim here is to critically assess the quality of the present literature as well as the potential of omega3 fatty acids to treat or delay the onset of AD. We start with a brief description of cognitive decline in the elderly, followed by an overview of well recognized biological functions of DHA. We then turn to epidemiological studies, which are largely supportive of protective effects of fish and DHA against risk of AD. However, biological studies, including blood and brain DHA analyses need careful interpretation and further investigation, without which the success of clinical trials with DHA may continue to struggle. We draw attention to some of the methodological issues that need resolution as well as an emerging mechanism that may explain how DHA could be linked to protecting brain function in the elderly.

The essential role of lipids in Alzheimer's disease

In the absence of efficient diagnostic and therapeutic tools, Alzheimer's disease (AD) is a major public health concern due to longer life expectancy in the Western countries. Although the precise cause of AD is still unknown, soluble beta-amyloid (Abeta) oligomers are considered the proximate effectors of the synaptic injury and neuronal death occurring in the early stages of AD. Abeta oligomers may directly interact with the synaptic membrane, leading to impairment of synaptic functions and subsequent signalling pathways triggering neurodegeneration. Therefore, membrane structure and lipid status should be considered determinant factors in Abeta-oligomer-induced synaptic and cell injuries, and therefore AD progression. Numerous epidemiological studies have highlighted close relationships between AD incidence and dietary patterns. Among the nutritional factors involved, lipids significantly influence AD pathogenesis. It is likely that maintenance of adequate membrane lipid content could prevent the production of Abeta peptide as well as its deleterious effects upon its interaction with synaptic membrane, thereby protecting neurons from Abeta-induced neurodegeneration. As major constituents of neuronal lipids, n-3 polyunsaturated fatty acids are of particular interest in the prevention of AD valuable diet ingredients whose neuroprotective properties could be essential for designing preventive nutrition-based strategies. In this review, we discuss the functional relevance of neuronal membrane features with respect to susceptibility to Abeta oligomers and AD pathogenesis, as well as the prospective capacities of lipids to prevent or to delay the disease.

Docosahexaenoic acid promotes neuronal differentiation by regulating basic helix-loop-helix transcription factors and cell cycle in neural stem cells

Recent studies have suggested that docosahexaenoic acid (DHA) enhances neuronal differentiation of neural stem cells (NSCs) isolated from rat embryonic day 14.5. However the underlying mechanism remains largely unknown. One hypothesis supported by DHA controls the expression level of basic helix-loop-helix (bHLH) transcription factors, such as hairy and enhancer of split 1 (Hes1), Mash1, neurogenin1, and NeuroD; another is that previous studies in retinal progenitor cells DHA affects the cell cycle. In this study, we show that treatment with DHA under differentiation conditions without basic fibroblast growth factor, (1) increases Tuj-1 and MAP2 positive cells in NSCs, (2) that the expression level of Hes1 mRNA and protein decreased significantly from day 1 to day 4, on the other hand, the NeuroD mRNA expression level increased from day 1 to day 4 after treatment with DHA and (3) decreased the percentage of S-phase cells, which correlated with prolonged expression of cyclin-dependent kinase inhibitor p27(kip1), suggesting that DHA enhances neuronal differentiation of NSCs, in part, by controlling the bHLH transcription factors and promoting cell cycle exit. We therefore speculate that DHA is one of the essential key molecules for neuronal differentiation of NSCs.

Effect of dietary n-3 polyunsaturated fatty acids on brain lipid fatty acid composition, learning ability, and memory of senescence-accelerated mouse

Animal studies have shown that a deficiency in brain of the n-3 polyunsaturated fatty acid (PUFA) docosahexaenoic acid (DHA) is associated with memory loss and diminished cognitive function. The senescence-accelerated prone 8 (SAMP8) mouse develops impairments in learning and memory at 8-12 months of age. The effect of diet supplemented with n-3 PUFA on brain phospholipid DHA status, learning, and memory ability in aged SAMP8 mice was investigated. At the age of 10 months, SAMP8 mice were fed either a low-DHA or a high-DHA diet for 8 weeks. In comparison to SAMP8 mice fed the low-DHA diet, those fed a high-DHA diet had improved acquisition and retention in a T-maze foot shock avoidance test and a higher proportion of DHA in hippocampal and amygdala phospholipids. This study demonstrates that, in mature animals, DHA is incorporated into brain phospholipids and that dietary n-3 PUFA is associated with delay in cognitive decline.

The protective effect of dietary eicosapentaenoic acid against impairment of spatial cognition learning ability in rats infused with amyloid beta(1-40)

BACKGROUND

Amyloid beta (Abeta) peptide (1-40) can cause cognitive impairment.

EXPERIMENTAL DESIGN

We investigated whether dietary preadministration of eicosapentaenoic acid (EPA) is conducive to cognition learning ability and whether it protects against the impairment of learning ability in rats infused with Abeta peptide (1-40) into the cerebral ventricle.

RESULTS

Dietary EPA administered to rats for 12 weeks before the infusion of Abeta into the rat brain significantly decreased the number of reference memory errors (RMEs) and working memory errors (WMEs), suggesting that chronic administration of EPA improves cognition learning ability in rats. EPA preadministered to the Abeta-infused rats significantly reduced the increase in the number of RMEs and WMEs, with concurrent proportional increases in the levels of corticohippocampal EPA and docosahexaenoic acid (DHA) and in the DHA/arachidonic acid molar ratio. Decrease in oxidative stress in these tissues was evaluated by determining the reactive oxygen species and lipid peroxide levels. cDNA microarray analysis revealed that altered genes included those that control synaptic signal transduction, cell communication, membrane-related vesicular transport functions, and enzymes and several other proteins.

CONCLUSION

The present study suggests that EPA, by acting as a precursor for DHA, ameliorates learning deficits associated with Alzheimer's disease and that these effects are modulated by the expression of proteins involved in neuronal plasticity.

Docosahexaenoic acid disrupts in vitro amyloid beta(1-40) fibrillation and concomitantly inhibits amyloid levels in cerebral cortex of Alzheimer's disease model rats

We have previously reported that dietary docosahexaenoic acid (DHA) improves and/or protects against impairment of cognition ability in amyloid beta(1-40) (Abeta(1-40))-infused Alzheimer's disease (AD)-model rats. Here, after the administration of DHA to AD model rats for 12 weeks, the levels of Abeta(1-40), cholesterol and the composition of fatty acids were investigated in the Triton X100-insoluble membrane fractions of their cerebral cortex. The effects of DHA on the in vitro formation and kinetics of fibrillation of Abeta(1-40) were also investigated by thioflavin T fluorescence spectroscopy, transmission electron microscopy and fluorescence microscopy. Dietary DHA significantly decreased the levels of Abeta(1-40), cholesterol and saturated fatty acids in the detergent insoluble membrane fractions of AD rats. The formation of Abeta fibrils was also attenuated by their incubation with DHA, as demonstrated by the decreased intensity of thioflavin T-derived fluorescence and by electron micrography. DHA treatment also decreased the intensity of thioflavin fluorescence in preformed-fibril Abeta peptides, demonstrating the anti-amyloidogenic effects of DHA. We then investigated the effects of DHA on the levels of oligomeric amyloid that is generated during its in vitro transformation from monomers to fibrils, by an anti-oligomer-specific antibody and non-reducing Tris-Glycine gradient (4-20%) gel electrophoresis. DHA concentration-dependently reduced the levels of oligomeric amyloid species, suggesting that dietary DHA-induced suppression of in vivo Abeta(1-40) aggregation occurs through the inhibitory effect of DHA on oligomeric amyloid species.

Space radiation-induced inhibition of neurogenesis in the hippocampal dentate gyrus and memory impairment in mice: ameliorative potential of the melatonin metabolite, AFMK

Evaluation of potential health effects from high energy charged particle radiation exposure during long duration space travel is important for the future of manned missions. Cognitive health of an organism is considered to be maintained by the capacity of hippocampal precursors to proliferate and differentiate. Environmental stressors including irradiation have been shown to inhibit neurogenesis and are associated with the onset of cognitive impairments. The present study reports on the protective effects of N(1)-acetyl-N(2)-formyl-5-methoxykynuramine (AFMK), a melatonin metabolite, against high energy charged particle radiation-induced oxidative damage to the brain. We observed that radiation exposure (2.0 Gy of 500 MeV/nucleon (56)Fe beams, a ground-based model of space radiation) impaired the spatial memory of mice at later intervals without affecting the motor activities. AFMK pretreatment significantly ameliorated these neurobehavioral ailments. Radiation-induced changes in the population of immature and proliferating neurons in the dentate gyrus were localized using anti-doublecortin (Dcx) and anti-Ki-67 expression. AFMK pretreatment significantly inhibited the loss of Dcx and Ki-67 positive cells. Moreover, AFMK pretreatment ameliorated the radiation-induced augmentation of protein carbonyls and 4-hydroxyalkenal + malondialdehyde (MDA + HAE) in the brain and maintained the total antioxidant capacity of plasma and nonprotein sulfhydryl contents in brain.

Docosahexaenoic acid dietary supplementation enhances the effects of exercise on synaptic plasticity and cognition

Omega-3 fatty acids (i.e. docosahexaenoic acid; DHA), similar to exercise, improve cognitive function, promote neuroplasticity, and protect against neurological lesion. In this study, we investigated a possible synergistic action between DHA dietary supplementation and voluntary exercise on modulating synaptic plasticity and cognition. Rats received DHA dietary supplementation (1.25% DHA) with or without voluntary exercise for 12 days. We found that the DHA-enriched diet significantly increased spatial learning ability, and these effects were enhanced by exercise. The DHA-enriched diet increased levels of pro-brain-derived neurotrophic factor (BDNF) and mature BDNF, whereas the additional application of exercise boosted the levels of both. Furthermore, the levels of the activated forms of CREB and synapsin I were incremented by the DHA-enriched diet with greater elevation by the concurrent application of exercise. While the DHA diet reduced hippocampal oxidized protein levels, a combination of a DHA diet and exercise resulted in a greater reduction rate. The levels of activated forms of hippocampal Akt and CaMKII were increased by the DHA-enriched diet, and with even greater elevation by a combination of diet and exercise. Akt and CaMKII signaling are crucial step by which BDNF exerts its action on synaptic plasticity and learning and memory. These results indicate that the DHA diet enhanced the effects of exercise on cognition and BDNF-related synaptic plasticity, a capacity that may be used to promote mental health and reduce risk of neurological disorders.

Neurological benefits of omega-3 fatty acids

The central nervous system is highly enriched in long-chain polyunsaturated fatty acid (PUFA) of the omega-6 and omega-3 series. The presence of these fatty acids as structural components of neuronal membranes influences cellular function both directly, through effects on membrane properties, and also by acting as a precursor pool for lipid-derived messengers. An adequate intake of omega-3 PUFA is essential for optimal visual function and neural development. Furthermore, there is increasing evidence that increased intake of the long-chain omega-3 PUFA, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), may confer benefits in a variety of psychiatric and neurological disorders, and in particular neurodegenerative conditions. However, the mechanisms underlying these beneficial effects are still poorly understood. Recent evidence also indicates that in addition to the positive effects seen in chronic neurodegenerative conditions, omega-3 PUFA may also have significant neuroprotective potential in acute neurological injury. Thus, these compounds offer an intriguing prospect as potentially new therapeutic approaches in both chronic and acute conditions. The purpose of this article is to review the current evidence of the neurological benefits of omega-3 PUFA, looking specifically at neurodegenerative conditions and acute neurological injury.

Oligomers of the amyloid-beta protein disrupt working memory: confirmation with two behavioral procedures

Converging lines of evidence suggest that oligomers of amyloid-beta play a role in the cognitive impairment characteristic of Alzheimer's disease, but only three studies have provided experimental evidence of such impairment. To provide additional information about the effects of these oligomers on memory, the present study examined the memory of groups of rats exposed to ICV injections of the culture media (CM) of Chinese Hamster Ovary cells that were (7PA2) and were not (CHO-) transfected with a human mutation of amyloid precursor protein that appears to cause early-onset Alzheimer's disease. The 7PA2 CM, which contained concentrations of soluble amyloid-beta oligomers physiologically relevant to those found in human brain, significantly disrupted working memory in rats tested in a radial-arm maze. In contrast, CHO- CM, which did not contain such oligomers, had no effect on memory. The disruptive effects of 7PA2-derived amyloid-beta oligomers, evident 2h after exposure, disappeared within a day. These findings are compared to results from 7PA2 CM tested under a complex procedure thought to measure aspects of executive function. The results confirm the disruptive effects of low-n amyloid-beta oligomers and extend them to a well-established rat model of memory.

Fish oil supplementation of control and (n-3) fatty acid-deficient male rats enhances reference and working memory performance and increases brain regional docosahexaenoic acid levels

Most previous studies have focused on improved reference memory and recovery of whole brain docosahexaenoic acid [DHA, 22:6(n-3)] levels in DHA-deficient animals supplemented with fish oil (FO) or switched to an adequate DHA-enriched diet. The aims of this study were to determine whether reference and working memory performance can be enhanced in control male rats and improved in (n-3) fatty acid-deficient male rats given an FO supplement and whether brain DHA accumulation, deficiency, and recovery are region specific. From the embryo to postnatal d 140, 4 groups of rats were fed a nonpurified or sunflower oil-based (n-3) fatty acid-deficient diet alone or supplemented with (n-3) fatty acids from FO representing approximately 0.3% of the energy source. The male rats were tested at postnatal d 102-130 for spatial learning memory performance in the Morris water maze. The fatty acid composition of different brain regions was analyzed by GC. Rats fed the (n-3) fatty acid-deficient diet showed significantly poorer reference and working memory, and FO supplementation partially rescued both memory performances. Furthermore, FO supplementation during brain development and adulthood in normal rats resulted in significant enhancement of both memories. Following dietary DHA repletion, the hippocampus and olfactory bulbs accumulated more DHA, were more resistant to dietary DHA deprivation, and showed better DHA recovery than the visual cortex, frontal cortex, and cerebellum. These results suggest that DHA is critical for the development and maintenance of learning memory performance.

The potential role of nutritional components in the management of Alzheimer's Disease

Epidemiological evidence linking nutrition to the incidence and risk of Alzheimer Disease is rapidly increasing. The specific nutritional deficiencies in Alzheimer patients may suggest a relative shortage of specific macro- and micronutrients. These include omega-3 fatty acids, several B-vitamins and antioxidants such as vitamins E and C. Recent mechanistic studies in cell systems and animal models also support the idea that nutritional components are able to counteract specific aspects of the neurodegenerative and pathological processes in the brain. In addition, it has been shown that several nutritional components can also effectively stimulate membrane formation and synapse formation as well as improve behavior and cerebrovascular health. The suggested synergy between nutritional components to improve neuronal plasticity and function is supported by epidemiological studies as well as experimental studies in animal models. The ability of nutritional compositions to stimulate synapse formation and effectively reduce Alzheimer Disease neuropathology in these preclinical models provides a solid basis to predict potential to modify the disease process, especially during the early phases of Alzheimer Disease.

Melatonin mitigates oxidative damage and apoptosis in mouse cerebellum induced by high-LET 56Fe particle irradiation

Cerebellum is a vital organ responsible for the motor coordination and recently it has been reported to be involved in cognitive function. Reactive oxygen species are implicated in neurodegeneration and cognitive disorders because of higher vulnerability of neuronal tissues. Therefore, the present study aimed at investigating the role of melatonin against high-LET (linear energy transfer) (56)Fe particle irradiation-induced oxidative damage and apoptosis in the mouse cerebellum. Radiation-induced oxidative damage was examined using a neuronal-specific terminal deoxynucleotidyl transferase-mediated nick end-labeling (TUNEL), quantitative histopathology, DNA damage (comet assay), carbonyl content and 4-HAE + MDA (4-hydroxyalkenal + malondialdehyde) status of the cerebellum. Radiation exposure augmented the number of TUNEL positive cell, DNA migration in the comet tail and carbonyl and 4-HAE + MDA level in the cerebellum. Melatonin pretreatment significantly inhibited the oxidative damage to biomolecules as well as cerebellar apoptosis. Melatonin-treated irradiated mice showed higher counts of intact Purkinje cells as compared to vehicle-treated irradiated mice. In addition, radiation induced augmentation of 8-hydroxy-2'-deoxyguanosine (8-OHdG) and a decline in the total antioxidant capacity in serum; these changes were also ameliorated by melatonin pretreatment. The present results provide evidence supporting the antioxidant and neuroprotective function of melatonin.