Docosahexaenoic acid synthesis from n-3 polyunsaturated fatty acids in differentiated rat brain astrocytes

Nervonic Acid Synthesis Substrates as Essential Components in Profiled Lipid Supplementation for More Effective Central Nervous System Regeneration

Central nervous system (CNS) damage leads to severe neurological dysfunction as a result of neuronal cell death and axonal degeneration. As, in the mature CNS, neurons have little ability to regenerate their axons and reconstruct neural loss, demyelination is one of the hallmarks of neurological disorders such as multiple sclerosis (MS). Unfortunately, remyelination, as a regenerative process, is often insufficient to prevent axonal loss and improve neurological deficits after demyelination. Currently, there are still no effective therapeutic tools to restore neurological function, but interestingly, emerging studies prove the beneficial effects of lipid supplementation in a wide variety of pathological processes in the human body. In the future, available lipids with a proven beneficial effect on CNS regeneration could be included in supportive therapy, but this topic still requires further studies. Based on our and others' research, we review the role of exogenous lipids, pointing to substrates that are crucial in the remyelination process but are omitted in available studies, justifying the properly profiled supply of lipids in the human diet as a supportive therapy during CNS regeneration.

The Conventional and Breakthrough Tool for the Study of L-Glutamate Transporters

In our recent report, we clarified the direct interaction between the excitatory amino acid transporter (EAAT) 1/2 and polyunsaturated fatty acids (PUFAs) by applying electrophysiological and molecular biological techniques to Xenopus oocytes. Xenopus oocytes have a long history of use in the scientific field, but they are still attractive experimental systems for neuropharmacological studies. We will therefore summarize the pharmacological significance, advantages (especially in the study of EAAT2), and experimental techniques that can be applied to Xenopus oocytes; our new findings concerning L-glutamate (L-Glu) transporters and PUFAs; and the significant outcomes of our data. The data obtained from electrophysiological and molecular biological studies of Xenopus oocytes have provided us with further important questions, such as whether or not some PUFAs can modulate EAATs as allosteric modulators and to what extent docosahexaenoic acid (DHA) affects neurotransmission and thereby affects brain functions. Xenopus oocytes have great advantages in the studies about the interactions between molecules and functional proteins, especially in the case when the expression levels of the proteins are small in cell culture systems without transfections. These are also proper to study the mechanisms underlying the interactions. Based on the data collected in Xenopus oocyte experiments, we can proceed to the next step, i.e., the physiological roles of the compounds and their significances. In the case of EAAT2, the effects on the neurotransmission should be examined by electrophysiological approach using acute brain slices. For new drug development, pharmacokinetics pharmacodynamics (PKPD) data and blood brain barrier (BBB) penetration data are also necessary. In order not to miss the promising candidate compounds at the primary stages of drug development, we should reconsider using Xenopus oocytes in the early phase of drug development.

A Review of Oxylipins in Alzheimer's Disease and Related Dementias (ADRD): Potential Therapeutic Targets for the Modulation of Vascular Tone and Inflammation

There is now a convincing body of evidence from observational studies that the majority of modifiable Alzheimer's disease and related dementia (ADRD) risk factors are vascular in nature. In addition, the co-existence of cerebrovascular disease with AD is more common than AD alone, and conditions resulting in brain ischemia likely promote detrimental effects of AD pathology. Oxylipins are a class of bioactive lipid mediators derived from the oxidation of long-chain polyunsaturated fatty acids (PUFAs) which act as modulators of both vascular tone and inflammation. In vascular cognitive impairment (VCI), there is emerging evidence that oxylipins may have both protective and detrimental effects on brain structure, cognitive performance, and disease progression. In this review, we focus on oxylipin relationships with vascular and inflammatory risk factors in human studies and animal models pertinent to ADRD. In addition, we discuss future research directions with the potential to impact the trajectory of ADRD risk and disease progression.

Lipidome changes in alcohol-related brain damage

Alcohol-related brain injury is characterized by cognitive deficits and brain atrophy with the prefrontal cortex particularly susceptible. White matter in the human brain is lipid rich and a major target of damage from chronic alcohol abuse; yet, there is sparse information on how these lipids are affected. Here, we used untargeted lipidomics as a discovery tool to describe these changes in the prefrontal, middle temporal, and visual cortices of human subjects with alcohol use disorder and controls. Significant changes to the lipidome, predominantly in the prefrontal and visual cortices, and differences between the white and grey matter of each brain region were identified. These effects include broad decreases to phospholipids and ceramide, decreased polyunsaturated fatty acids, decreased sphingadiene backbones, and selective decreases in cholesteryl ester fatty acid chains. Our findings show that chronic alcohol abuse results in selective changes to the neurolipidome, which likely reflects both the directs effects on the brain and concurrent effects on the liver.

Omega-3 nutraceuticals, climate change and threats to the environment: The cases of Antarctic krill and Calanus finmarchicus

The nutraceutical market for EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) is promoting fishing for Euphasia superba (Antarctic krill) in the Southern Ocean and Calanus finmarchicus in Norwegian waters. This industry argues that these species are underexploited, but they are essential in their ecosystems, and climate change is altering their geographical distribution. In this perspective, we advocate the cessation of fishing for these species to produce nutraceuticals with EPA and DHA. We argue that this is possible because, contrary to what this industry promotes, the benefits of these fatty acids only seem significant to specific population groups, and not for the general population. Next, we explain that this is desirable because there is evidence that these fisheries may interact with the impact of climate change. Greener sources of EPA and DHA are already available on the market, and their reasonable use would ease pressure on the Arctic and Antarctic ecosystems.

Brain foods - the role of diet in brain performance and health

The performance of the human brain is based on an interplay between the inherited genotype and external environmental factors, including diet. Food and nutrition, essential in maintenance of brain performance, also aid in prevention and treatment of mental disorders. Both the overall composition of the human diet and specific dietary components have been shown to have an impact on brain function in various experimental models and epidemiological studies. This narrative review provides an overview of the role of diet in 5 key areas of brain function related to mental health and performance, including: (1) brain development, (2) signaling networks and neurotransmitters in the brain, (3) cognition and memory, (4) the balance between protein formation and degradation, and (5) deteriorative effects due to chronic inflammatory processes. Finally, the role of diet in epigenetic regulation of brain physiology is discussed.

Ovarian Hormone-Dependent Effects of Dietary Lipids on APP/PS1 Mouse Brain

The formation of senile plaques through amyloid-β peptide (Aβ) aggregation is a hallmark of Alzheimer’s disease (AD). Irrespective of its actual role in the synaptic alterations and cognitive impairment associated with AD, different therapeutic approaches have been proposed to reduce plaque formation. In rodents, daily intake of omega-3 (n-3) long-chain polyunsaturated fatty acids (LC-PUFAs) is required for neural development, and there is experimental and epidemiological evidence that their inclusion in the diet has positive effects on several neurodegenerative diseases. Similarly, estradiol appears to reduce senile plaque formation in primary mouse cell cultures, human cortical neurons and mouse AD models, and it prevents Aβ toxicity in neural cell lines. We previously showed that differences in dietary n-6/n-3 LC-PUFAs ratios modify the lipid composition in the cerebral cortex of female mice and the levels of amyloid precursor protein (APP) in the brain. These effects depended in part on the presence of circulating estradiol. Here we explored whether this potentially synergistic action between diet and ovarian hormones may influence the progression of amyloidosis in an AD mouse model. Our results show that a diet with high n-3 LC-PUFA content, especially DHA (22:6n-3), reduces the hippocampal accumulation of Aβ_1–40, but not amyloid Aβ_1–42 in female APPswe/PS1 E9A mice, an effect that was counteracted by the loss of the ovaries and that depended on circulating estradiol. In addition, this interaction between dietary lipids and ovarian function also affects the composition of the brain lipidome as well as the expression of certain neuronal signaling and synaptic proteins. These findings provide new insights into how ovarian hormones and dietary composition affect the brain lipidome and amyloid burden. Furthermore, they strongly suggest that when designing dietary or pharmacological strategies to combat human neurodegenerative diseases, hormonal and metabolic status should be specifically taken into consideration as it may affect the therapeutic response.

Differentiated HASTR/ci35 cells: A promising in vitro human astrocyte model for facilitating CNS drug development studies

Astrocytes have shown longstanding promise as therapeutic targets for various central nervous system diseases. To facilitate drug development targeting astrocytes, we have recently developed a new conditionally immortalized human astrocyte cell line, termed HASTR/ci35 cells. In this study, in order to further increase their chances to contribute to various astrocyte studies, we report on the development of a culture method that improves HASTR/ci35 cell differentiation status and provide several proofs related to their astrocyte characteristics. The culture method is based on the simultaneous elimination of serum effects and immortalization signals. The results of qPCR showed that the culture method significantly enhanced several astrocyte marker gene expression levels. Using the differentiated HASTR/ci35, we examined their response profiles to nucleotide treatment and inflammatory stimuli, along with their membrane fatty acid composition. Consequently, we found that they responded to ADP or UTP treatment with a transient increase of intracellular Ca²⁺ concentration, and that they could show reactive response to interleukin-1β treatments. Furthermore, the membrane phospholipids of the cells were enriched with polyunsaturated fatty acids. To summarize, as a unique human astrocyte model carrying the capability of a differentiation induction properties, HASTR/ci35 cells are expected to contribute substantially to astrocyte-oriented drug development studies.

Ovarian Function Modulates the Effects of Long-Chain Polyunsaturated Fatty Acids on the Mouse Cerebral Cortex

Different dietary ratios of n−6/n−3 long-chain polyunsaturated fatty acids (LC-PUFAs) may alter brain lipid profile, neural activity, and brain cognitive function. To determine whether ovarian hormones influence the effect of diet on the brain, ovariectomized and sham-operated mice continuously treated with placebo or estradiol were fed for 3 months with diets containing low or high n−6/n−3 LC-PUFA ratios. The fatty acid (FA) profile and expression of key neuronal proteins were analyzed in the cerebral cortex, with intact female mice on standard diet serving as internal controls of brain lipidome composition. Diets containing different concentrations of LC-PUFAs greatly modified total FAs, sphingolipids, and gangliosides in the cerebral cortex. Some of these changes were dependent on ovarian hormones, as they were not detected in ovariectomized animals, and in the case of complex lipids, the effect of ovariectomy was partially or totally reversed by continuous administration of estradiol. However, even though differential dietary LC-PUFA content modified the expression of neuronal proteins such as synapsin and its phosphorylation level, PSD-95, amyloid precursor protein (APP), or glial proteins such as glial fibrillary acidic protein (GFAP), an effect also dependent on the presence of the ovary, chronic estradiol treatment was unable to revert the dietary effects on brain cortex synaptic proteins. These results suggest that, in addition to stable estradiol levels, other ovarian hormones such as progesterone and/or cyclic ovarian secretory activity could play a physiological role in the modulation of dietary LC-PUFAs on the cerebral cortex, which may have clinical implications for post-menopausal women on diets enriched with different proportions of n−3 and n−6 LC-PUFAs.

Omega-3 polyunsaturated fatty acids improve the antioxidative defense in rat astrocytes via an Nrf2-dependent mechanism

BACKGROUND

Neuronal tolerance to hypoxia and nutrient defficiency highly depends on GSH levels and antioxidant enzyme activity in astrocytes. Omega-3 polyunsaturated fatty acids (ω-3PUFA) enhance antioxidant defence in different cells. The aim of present study was to investigate if ω-3PUFA improve antioxidant status in astrocytes.

METHODS

Rat primary astrocytes were incubated for 24h with DHA and EPA (30μM), then lysed, fractioned and fatty acids were determined by gas chromatography. GSH and protein thiols were assayed by enzymatic methods. Glutamate cysteine ligase (GCL), glutathione synthetase (GS), glutathione peroxidase 4 (GPx4) and Nrf2 protein expression was validated by Western blot. Intracellular ROS level using H₂DCF-DA, and Nrf2 activation by ELISA were measured.

RESULTS

Incubation of cells with DHA doubled DHA, not EPA content in the membranes, and incubation with EPA increased both fatty acids content compared to control. However, both ω-3PUFAs reduced ROS generation in dose-dependent manner in basal condition and in H₂O₂-treated cells, and significantly increased GSH, GCL and GPx4 levels. The thiols level was higher only in DHA-treated cells. DHA and EPA activated Nrf2 in a dose-dependent manner but p38MAPK-Nrf2 activation was found only in DHA-enriched astrocytes.

CONCLUSION

Both ω-3PUFA improved the antioxidant defense in astrocytes via an Nrf2-dependent mechanism, however, upstream pathways of Nrf2 activation may depend on proportion of DHA to EPA incorporated into membrane phospholipids. These results suggest that enrichment of astrocytes with ω-3PUFA may better protect neurons during harmful conditions.

Increased ω6-Containing Phospholipids and Primary ω6 Oxidation Products in the Brain Tissue of Rats on an ω3-Deficient Diet

Polyunsaturated fatty acyl (PUFA) chains in both the ω3 and ω6 series are essential for normal animal brain development, and cannot be interconverted to compensate for a dietary deficiency of one or the other. Paradoxically, a dietary ω3-PUFA deficiency leads to the accumulation of docosapentaenoate (DPA, 22:5ω6), an ω6-PUFA chain that is normally scarce in the brain. We applied a high-precision LC/MS method to characterize the distribution of DPA chains across phospholipid headgroup classes, the fatty acyl chains with which they were paired, and the extent to which they were oxidatively damaged in the cortical brain of rats on an ω3-deficient diet. Results indicate that dietary ω3-PUFA deficiency markedly increased the concentrations of phospholipids with DPA chains across all headgroup subclasses, including plasmalogen species. The concentrations of phospholipids containing docosahexaenoate chains (22:6ω3) decreased 20-25%, while the concentrations of phospholipids containing arachidonate chains (20:4ω6) did not change significantly. Although DPA chains are more saturated than DHA chains, a larger fraction of DPA chains were monohydroxylated, particularly among diacyl-phosphatidylethanolamines and plasmalogen phosphatidylethanolamines, suggesting that they were disproportionately subjected to oxidative stress. Differences in the pathological significance of ω3 and ω6 oxidation products suggest that greater oxidative damage among the ω6 PUFAs that increase in response to dietary ω3 deficiency may have pathological significance in Alzheimer's disease.

Fatty Acid Binding Protein 5 Modulates Docosahexaenoic Acid-Induced Recovery in Rats Undergoing Spinal Cord Injury

Omega-3 polyunsaturated fatty acids (n-3 PUFAs) promote functional recovery in rats undergoing spinal cord injury (SCI). However, the precise molecular mechanism coupling n-3 PUFAs to neurorestorative responses is not well understood. The aim of the present study was to determine the spatiotemporal expression of fatty acid binding protein 5 (FABP5) after contusive SCI and to investigate whether this protein plays a role in n-3 PUFA-mediated functional recovery post-SCI. We found that SCI resulted in a robust spinal cord up-regulation in FABP5 mRNA levels (556 ± 187%) and protein expression (518 ± 195%), when compared to sham-operated rats, at 7 days post-injury (dpi). This upregulation coincided with significant alterations in the metabolism of fatty acids in the injured spinal cord, as revealed by metabolomics-based lipid analyses. In particular, we found increased levels of the n-3 series PUFAs, particularly docosahexaenoic acid (DHA; 22:6 n-3) and eicosapentaenoic acid (EPA; 20:5 n-3) at 7 dpi. Animals consuming a diet rich in DHA and EPA exhibited a significant upregulation in FABP5 mRNA levels at 7 dpi. Immunofluorescence showed low basal FABP5 immunoreactivity in spinal cord ventral gray matter NeuN(+) neurons of sham-operated rats. SCI resulted in a robust induction of FABP5 in glial (GFAP(+), APC(+), and NG2(+)) and precursor cells (DCX(+), nestin(+)). We found that continuous intrathecal administration of FABP5 silencing with small interfering RNA (2 μg) impaired spontaneous open-field locomotion post-SCI. Further, FABP5 siRNA administration hindered the beneficial effects of DHA to ameliorate functional recovery at 7 dpi. Altogether, our findings suggest that FABP5 may be an important player in the promotion of cellular uptake, transport, and/or metabolism of DHA post-SCI. Given the beneficial roles of n-3 PUFAs in ameliorating functional recovery, we propose that FABP5 is an important contributor to basic repair mechanisms in the injured spinal cord.

Role of docosahexaenoic acid in the modulation of glial cells in Alzheimer's disease

Docosahexaenoic acid (DHA) is an omega-3 (ω-3) long-chain polyunsaturated fatty acid (LCPUFA) relevant for brain function. It has largely been explored as a potential candidate to treat Alzheimer’s disease (AD). Clinical evidence favors a role for DHA in the improvement of cognition in very early stages of the AD. In response to stress or damage, DHA generates oxygenated derivatives called docosanoids that can activate the peroxisome proliferator-activated receptor γ (PPARγ). In conjunction with activated retinoid X receptors (RXR), PPARγ modulates inflammation, cell survival, and lipid metabolism. As an early event in AD, inflammation is associated with an excess of amyloid β peptide (Aβ) that contributes to neural insult. Glial cells are recognized to be actively involved during AD, and their dysfunction is associated with the early appearance of this pathology. These cells give support to neurons, remove amyloid β peptides from the brain, and modulate inflammation. Since DHA can modulate glial cell activity, the present work reviews the evidence about this modulation as well as the effect of docosanoids on neuroinflammation and in some AD models. The evidence supports PPARγ as a preferred target for gene modulation. The effective use of DHA and/or its derivatives in a subgroup of people at risk of developing AD is discussed.

Polyunsaturated fatty acid biosynthesis is involved in phenylephrine-mediated calcium release in vascular smooth muscle cells

Stimulation of vascular smooth muscle (VSM) α1-adrenoceptors induces myosin phosphorylation and vasoconstriction via mobilisation of intracellular calcium and production of specific eicosanoids. Polyunsaturated fatty acid (PUFA) biosynthesis in VSM cells is involved, although the precise mechanism is not known. To address this, we characterised PUFA biosynthesis in VSM cells and determined its role in intracellular calcium release and eicosanoid production. Murine VSM cells converted 18:2n-6 to longer chain PUFA including 22:5n-6. Δ6 (D6d) and Δ5 (D5d) desaturase, and elongase (Elovl) 5 were expressed. Elovl2 was not detected in human, mouse or rat VSM cells, or in rat or mouse aortae, but tit was not associated with hypermethylation of its promoter. D6d or D5d inhibition reduced 18:3n-6 and 20:4n-6 synthesis, respectively, and induced concentration-related decrease in phenylephrine-mediated calcium release, and in PGE2 and PGF2α secretion. Together these findings suggest that PUFA biosynthesis in VSM cells is involved in calcium release associated with vasoconstriction.

Metabolic conversion of intra-amniotically-injected deuterium-labeled essential fatty acids by fetal rats following maternal n-3 fatty acid deficiency

Accumulation of polyunsaturated fatty acids (PUFA) in the fetal brain is accomplished predominantly via a highly selective flow of docosahexaenoic acid (22:6n-3, DHA) and arachidonic acid (20:4n-6, AA) through the placenta. Little is known regarding the endogenous capability of the fetus to generate its own DHA and AA from lower homologues such as linolenic (18:3n-3, ALA) and linoleic (18:2n-6, LA) acids, respectively. Deuterium-labeled d5-ALA and d5-LA at millimolar concentrations were injected directly into the amniotic fluid in order to investigate maternal-independent metabolic conversion of the stable isotopes in brain and liver of the fetus near delivery. After 48h under adequate maternal diet, the levels of d5-ALA metabolites in the fetal brain and fetal liver were 45±2.2 pmol/mg and 86±4 pmol/mg of which 79% and 63.6% were comprised of d5-DHA. At this time point, incorporation of d5-LA metabolites was 103±5 pmol/mg and 772±46 pmol/mg for brain and liver, of which 50% and 30% were comprised of d5-AA. Following sustained maternal dietary ALA deficiency, the levels of total d5-ALA derived metabolites in the fetal brain and fetal liver were increased to 231 pmol/mg and 696 pmol/mg of which 71% and 26% were comprised of d5-DHA. From the time course and relative rates of d5-ALA precursor displacement by d5-DHA in cellular phosphoglycerides, it is concluded that the fetal rat brain can generate its own DHA from its d5-ALA precursors particularly under dietary stress.

Docosahexaenoic acid and human brain development: evidence that a dietary supply is needed for optimal development

Humans evolved a uniquely large brain among terrestrial mammals. Brain and nervous tissue is rich in the omega-3 polyunsaturated fatty acid (PUFA) docosahexaenoic acid (DHA). Docosahexaenoic acid is required for lower and high order functions in humans because of understood and emerging molecular mechanisms. Among brain components that depend on dietary components, DHA is limiting because its synthesis from terrestrial plant food precursors is low but its utilization when consumed in diet is very efficient. Negligible DHA is found in terrestrial plants, but in contrast, DHA is plentiful at the shoreline where it is made by single-celled organisms and plants, and in the seas supports development of very large marine mammal brains. Modern human brains accumulate DHA up to age 18, most aggressively from about half-way through gestation to about two years of age. Studies in modern humans and non-human primates show that modern infants consuming infant formulas that include only DHA precursors have lower DHA levels than for those with a source of preformed DHA. Functional measures show that infants consuming preformed DHA have improved visual and cognitive function. Dietary preformed DHA in the breast milk of modern mothers supports many-fold greater breast milk DHA than is found in the breast milk of vegans, a phenomenon linked to consumption of shore-based foods. Most current evidence suggests that the DHA-rich human brain required an ample and sustained source of dietary DHA to reach its full potential.

Dietary Omega-3 Fatty Acids and Depression in a Community Sample

To evaluate the association between omega-3 polyunsaturated essential fatty acids and depression, data regarding prevalence rates of self-reported depression and median daily dietary intakes of these fatty acids were obtained from an age-stratified, population-based sample of women (n = 755; 23-97 year) in the Barwon Statistical Division of south-eastern Australia. A self-report questionnaire based on Diagnostic and Statistical Manual-IV criteria was utilised to determine 12-month prevalence rates of depression in this sample, and data from biennial food frequency questionnaires examining seafood and fish oil consumption over a 6-year period were examined. Differences in median dietary intakes of omega-3 fatty acids between the depressed and nondepressed cohorts were analysed and results were adjusted for age, weight and smoking status. No significant differences in median intakes were identified between the two groups of women (median, interquartile range; depressed = 0.09g/day, 0.04-0.18 versus nondepressed = 0.11 g/day, 0.05-0.22, p = 0.3), although overall average intakes of omega-3 fatty acids were lower than recommended and rates of depression within this sample higher than expected, based on previous data. Further research that takes into account ratios of omega-6 to omega-3 polyunsaturated essential fatty acids, as well as other dietary sources of omega-3 fatty acids, is warranted.

Omega-3 fatty acids and brain resistance to ageing and stress: body of evidence and possible mechanisms

The increasing life expectancy in the populations of rich countries raises the pressing question of how the elderly can maintain their cognitive function. Cognitive decline is characterised by the loss of short-term memory due to a progressive impairment of the underlying brain cell processes. Age-related brain damage has many causes, some of which may be influenced by diet. An optimal diet may therefore be a practical way of delaying the onset of age-related cognitive decline. Nutritional investigations indicate that the ω-3 poyunsaturated fatty acid (PUFA) content of western diets is too low to provide the brain with an optimal supply of docosahexaenoic acid (DHA), the main ω-3 PUFA in cell membranes. Insufficient brain DHA has been associated with memory impairment, emotional disturbances and altered brain processes in rodents. Human studies suggest that an adequate dietary intake of ω-3 PUFA can slow the age-related cognitive decline and may also protect against the risk of senile dementia. However, despite the many studies in this domain, the beneficial impact of ω-3 PUFA on brain function has only recently been linked to specific mechanisms. This review examines the hypothesis that an optimal brain DHA status, conferred by an adequate ω-3 PUFA intake, limits age-related brain damage by optimizing endogenous brain repair mechanisms. Our analysis of the abundant literature indicates that an adequate amount of DHA in the brain may limit the impact of stress, an important age-aggravating factor, and influences the neuronal and astroglial functions that govern and protect synaptic transmission. This transmission, particularly glutamatergic neurotransmission in the hippocampus, underlies memory formation. The brain DHA status also influences neurogenesis, nested in the hippocampus, which helps maintain cognitive function throughout life. Although there are still gaps in our knowledge of the way ω-3 PUFA act, the mechanistic studies reviewed here indicate that ω-3 PUFA may be a promising tool for preventing age-related brain deterioration.

Docosahexaenoic acid (DHA): an ancient nutrient for the modern human brain

Modern humans have evolved with a staple source of preformed docosahexaenoic acid (DHA) in the diet. An important turning point in human evolution was the discovery of high-quality, easily digested nutrients from coastal seafood and inland freshwater sources. Multi-generational exploitation of seafood by shore-based dwellers coincided with the rapid expansion of grey matter in the cerebral cortex, which characterizes the modern human brain. The DHA molecule has unique structural properties that appear to provide optimal conditions for a wide range of cell membrane functions. This has particular implications for grey matter, which is membrane-rich tissue. An important metabolic role for DHA has recently been identified as the precursor for resolvins and protectins. The rudimentary source of DHA is marine algae; therefore it is found concentrated in fish and marine oils. Unlike the photosynthetic cells in algae and higher plants, mammalian cells lack the specific enzymes required for the de novo synthesis of alpha-linolenic acid (ALA), the precursor for all omega-3 fatty acid syntheses. Endogenous synthesis of DHA from ALA in humans is much lower and more limited than previously assumed. The excessive consumption of omega-6 fatty acids in the modern Western diet further displaces DHA from membrane phospholipids. An emerging body of research is exploring a unique role for DHA in neurodevelopment and the prevention of neuropsychiatric and neurodegenerative disorders. DHA is increasingly being added back into the food supply as fish oil or algal oil supplementation.

Dietary fish oil replacement with lard and soybean oil affects triacylglycerol and phospholipid muscle and liver docosahexaenoic acid content but not in the brain and eyes of surubim juveniles Pseudoplatystoma sp

Triplicate groups of juvenile suribim were fed for 183 days one of four different isonitrogenous (47.6% crude protein) and isolipidic (18.7% lipid) diets formulated using three different lipid sources: 100% fish oil (FO, diet 1); 100% pig lard (L, diet 2); 100% soybean oil (SO, diet 3), and FO/L/SO (1:1:1, w/w/w; diet 4). The tissue levels of fatty acids 18:2n-6 and 18:3n-3 decreased relative to corresponding dietary fatty acid values. The 20:5n-3 and 22:6n-3 composition of muscle and liver neutral lipids were linearly correlated with corresponding dietary fatty acid composition. In contrast, the 22:6n-3 composition of the brain and eye were similar among treatments. The 22:6n-3 level was enriched in all tissues, particularly in the neural tissues. Similar results were observed for tissue polar lipids: fatty acids content reflected dietary composition, with the exception of the 22:6n-3 level, which showed enrichment and no differences between groups. Given these results, the importance of the biochemical functions (transport and/or metabolism) of 22:6n-3 in the development of the neural system of surubim warrants further investigation.

Alpha-linolenic acid and its conversion to longer chain n-3 fatty acids: benefits for human health and a role in maintaining tissue n-3 fatty acid levels

There is little doubt regarding the essential nature of alpha-linolenic acid (ALA), yet the capacity of dietary ALA to maintain adequate tissue levels of long chain n-3 fatty acids remains quite controversial. This simple point remains highly debated despite evidence that removal of dietary ALA promotes n-3 fatty acid inadequacy, including that of docosahexaenoic acid (DHA), and that many experiments demonstrate that dietary inclusion of ALA raises n-3 tissue fatty acid content, including DHA. Herein we propose, based upon our previous work and that of others, that ALA is elongated and desaturated in a tissue-dependent manner. One important concept is to recognize that ALA, like many other fatty acids, rapidly undergoes beta-oxidation and that the carbons are conserved and reused for synthesis of other products including cholesterol and fatty acids. This process and the differences between utilization of dietary DHA or liver-derived DHA as compared to ALA have led to the dogma that ALA is not a useful fatty acid for maintaining tissue long chain n-3 fatty acids, including DHA. Herein, we propose that indeed dietary ALA is a crucial dietary source of n-3 fatty acids and its dietary inclusion is critical for maintaining tissue long chain n-3 levels.

Differential effects of steroids on the synthesis of polyunsaturated fatty acids by human neuroblastoma cells

Polyunsaturated fatty acids (PUFA) are crucial for proper functioning of cell membranes, particularly in brain. Biologically important PUFA include docosahexaenoic acid (n-3 series) and arachidonic acid (n-6 series) which can be formed from their respective dietary essential precursors, alpha-linolenic acid (ALA) and linoleic acid (LA). Steroid hormones are thought to modulate PUFA synthesis in humans but whether they regulate PUFA status in brain and/or in neural membranes is unknown. In human neuroblastoma SH-SY5Y cells, we compared the effect of estradiol, testosterone, and progesterone on PUFA synthesis. Cells were incubated with ALA and/or LA 7 microM in combination with estradiol, testosterone, or progesterone at 10 nM without serum. The fatty acid composition was determined by gas chromatography and the mRNA expression of genes involved in PUFA metabolism by real-time RT-PCR. Estradiol affected both the n-3 and the n-6 PUFA conversion, the n-3 PUFA pathway being more sensitive to the estradiol treatment. In ALA-supplemented cells, estradiol increased while testosterone decreased the long-chain n-3 PUFA content (+17% and -15%, respectively) and the mRNA expression of the Delta5-desaturase (+11% and -9%), these two events being strongly correlated. Progesterone did not affect the PUFA composition. The positive effect of estradiol was blocked by the estrogen receptor antagonist ICI-182,780. We conclude that steroids have differential effects on PUFA synthesis and that their mode of action could involve the modulation of the Delta5-desaturase mRNA expression in neuroblastoma cells. These results help our understanding of the regulation of brain PUFA metabolism by steroid hormones.

The low density lipoprotein receptor is not necessary for maintaining mouse brain polyunsaturated fatty acid concentrations

The brain cannot synthesize n-6 or n-3 PUFAs de novo and requires their transport from the blood. Two models of brain fatty acid uptake have been proposed. One requires the passive diffusion of unesterified fatty acids through endothelial cells of the blood-brain barrier, and the other requires the uptake of lipoproteins via a lipoprotein receptor on the luminal membrane of endothelial cells. This study tested whether the low density lipoprotein receptor (LDLr) is necessary for maintaining brain PUFA concentrations. Because the cortex has a low basal expression of LDLr and the anterior brain stem has a relatively high expression, we analyzed these regions separately. LDLr knockout (LDLr(-/-)) and wild-type mice consumed an AIN-93G diet ad libitum until 7 weeks of age. After microwaving, the cortex and anterior brain stem (pons and medulla) were isolated for phospholipid fatty acid analyses. There were no differences in phosphatidylserine, phosphatidylinositol, ethanolamine, or choline glycerophospholipid esterified PUFA or saturated or monounsaturated fatty acid concentrations in the cortex or brain stem between LDLr(-/-) and wild-type mice. These findings demonstrate that the LDLr is not necessary for maintaining brain PUFA concentrations and suggest that other mechanisms to transport PUFAs into the brain must exist.

Estradiol Favors the Formation of Eicosapentaenoic Acid (20:5n-3) and n-3 Docosapentaenoic Acid (22:5n-3) from Alpha-Linolenic Acid (18:3n-3) in SH-SY5Y Neuroblastoma Cells

Whether neurosteroids regulate the synthesis of long chain polyunsaturated fatty acids in brain cells is unknown. We examined the influence of 17-beta-estradiol (E2) on the capacity of SH-SY5Y cells supplemented with alpha-linolenic acid (ALA), to produce eicosapentaenoic acid (EPA), docosapentaenoic acid (DPA) and docosahexaenoic acid (DHA). Cells were incubated for 24 or 72 h with ALA added alone or in combination with E2 (ALA + E2). Fatty acids were analyzed by gas chromatography of ethanolamine glycerophospholipids (EtnGpl) and phosphatidylcholine (PtdCho). Incubation for 24 h with ALA alone increased EPA and DPA in EtnGpl, by 330 and 430% compared to controls (P < 0.001) and DHA by only 10% (P < 0.05). Although DHA increased by 30% (P < 0.001) in ALA + E2-treated cells, the difference between the ALA and ALA + E2 treatments were not significant after 24 h (Anova-1, Fisher's test). After 72 h, EPA, DPA and DHA further increased in EtnGpl and PtdCho of cells supplemented with ALA or ALA + E2. Incubation for 72 h with ALA + E2 specifically increased EPA (+34% in EtnGpl, P < 0.001) and DPA (+15%, P < 0.001) compared to ALA alone. Thus, SH-SY5Y cells produced membrane EPA, DPA and DHA from supplemental ALA. The formation of DHA was limited, even in the presence of E2. E2 significantly favored EPA and DPA production in cells grown for 72 h. Enhanced synthesis of ALA-elongation products in neuroblastoma cells treated with E2 supports the hypothesis that neurosteroids could modulate the metabolism of PUFA.

Dietary n-3 PUFA deprivation for 15 weeks upregulates elongase and desaturase expression in rat liver but not brain

Fifteen weeks of dietary n-3 PUFA deprivation increases coefficients of conversion of circulating alpha-linolenic acid (alpha-LNA; 18:3n-3) to docosahexaenoic acid (DHA; 22:6n-3) in rat liver but not brain. To determine whether these increases reflect organ differences in enzymatic activities, we examined brain and liver expression of converting enzymes and of two of their transcription factors, peroxisome proliferator-activated receptor alpha (PPARalpha) and sterol-regulatory element binding protein-1 (SREBP-1), in rats fed an n-3 PUFA "adequate" (4.6% alpha-LNA of total fatty acid, no DHA) or "deficient" (0.2% alpha-LNA, no DHA) diet for 15 weeks after weaning. In rats fed the deficient compared with the adequate diet, mRNA and activity levels of Delta5 and Delta6 desaturases and elongases 2 and 5 were upregulated in liver but not brain, but liver PPARalpha and SREBP-1 mRNA levels were unchanged. In rats fed the adequate diet, enzyme activities generally were higher in liver than brain. Thus, differences in conversion enzyme expression explain why the liver has a greater capacity to synthesize DHA from circulating alpha-LNA than does the brain in animals on an adequate n-3 PUFA diet and why liver synthesis capacity is increased by dietary deprivation. These data suggest that liver n-3 PUFA metabolism determines DHA availability to the brain when DHA is absent from the diet.

Expression of free fatty acid receptor GPR40 in the central nervous system of adult monkeys

The G-protein coupled receptor 40 (GRP40) is a transmembrane receptor for free fatty acids, and is known for its relation to insulin secretion in the pancreas. Recent studies demonstrated that spatial memory and hippocampal long-term potentiation of rodents and cognitive function of humans are improved by a dietary supplementation with arachidonic and/or docosahexaenoic acids, which are possible ligands for GPR40. While free fatty acid effects on the brain might be related to GPR40 activation, the role of GPR40 in the central nervous system (CNS) is at present not known. Here, we studied expression and distribution of GPR40 in CNS of adult monkeys by immunoblotting and immunohistochemistry. Immunoblotting analysis showed a band of approximately 31 kDa consistent with the size of GPR40 protein. GPR40 immunoreactivity of was observed in the nuclei and/or perikarya of a wide variety of neurons including neurons in the cerebral cortex, hippocampus, amygdala, hypothalamus, cerebellum, spinal cord. In addition, astrocytes of the cerebral white matter, the molecular layer and multiform layer of the cerebral cortex, the subventricular zone along the anterior horn of the lateral ventricle, and the subgranular zone of the hippocampal dentate gyrus showed GPR40 immunoreactivity. The present data first provide a morphological basis for clarifying the role of GPR40 in the primate CNS.

Docosahexaenoic acid synthesis from α-linolenic acid by rat brain is unaffected by dietary n-3 PUFA deprivation

Rates of conversion of alpha-linolenic acid (alpha-LNA, 18:3n-3) to docosahexaenoic acid (DHA, 22:6n-3) by the mammalian brain and the brain's ability to upregulate these rates during dietary deprivation of n-3 polyunsaturated fatty acids (PUFAs) are unknown. To answer these questions, we measured conversion coefficients and rates in post-weaning rats fed an n-3 PUFA deficient (0.2% alpha-LNA of total fatty acids, no DHA) or adequate (4.6% alpha-LNA, no DHA) diet for 15 weeks. Unanesthetized rats in each group were infused intravenously with [1-(14)C]alpha-LNA, and their arterial plasma and microwaved brains collected at 5 minutes were analyzed. The deficient compared with adequate diet reduced brain DHA by 37% and increased brain arachidonic (20:4n-6) and docosapentaenoic (22:5n-6) acids. Only 1% of plasma [1-(14)C]alpha-LNA entering brain was converted to DHA with the adequate diet, and conversion coefficients of alpha-LNA to DHA were unchanged by the deficient diet. In summary, the brain's ability to synthesize DHA from alpha-LNA is very low and is not altered by n-3 PUFA deprivation. Because the liver's reported ability is much higher, and can be upregulated by the deficient diet, DHA converted by the liver from circulating alphaLNA is the source of the brain's DHA when DHA is not in the diet.

Inflammation and skin cholesterol in LDLr-/-, apoA-I-/- mice: link between cholesterol homeostasis and self-tolerance?

Diet-fed low density lipoprotein receptor-deficient/apolipoprotein A-I-deficient (LDLr-/-, apoA-I-/-) mice accumulate a 10-fold greater mass of cholesterol in their skin despite a 1.5- to 2-fold lower plasma cholesterol concentration compared with diet-fed LDLr-/- mice. The accumulation of cholesterol predominantly in the skin has been shown to occur in a growing number of other hypercholesterolemic double knockout mouse models sharing deficits in genes regulating cellular cholesterol homeostasis. Exploring the relationship between cholesterol balance and inflammation, we have examined the time course of cholesterol accumulation in a number of extrahepatic tissues and correlated with the onset of inflammation in diet-fed LDLr-/-, apoA-I-/- mice. After 4 weeks of diet, LDLr-/-, apoA-I-/- mice showed a significant increase in skin cholesterol mass compared with LDLr-/- mice. In addition, after 4 weeks on the diet, cholesterol accumulation in the skin was also found to be associated with macrophage infiltration and accompanied by increases in tumor necrosis factor-alpha, cyclooxygenase-2, and langerin mRNA, which were not seen in the liver. Overall, these data suggest that as early as 4 weeks after starting the diet, the accumulation of skin cholesterol and the onset of inflammation occur concurrently. In summary, the use of hypercholesterolemic LDLr-/-, apoA-I-/- mice may provide a useful tool to investigate the role that apoA-I plays in maintaining cholesterol homeostasis and its relationship to inflammation.

Upregulated liver conversion of alpha-linolenic acid to docosahexaenoic acid in rats on a 15 week n-3 PUFA-deficient diet

We quantified incorporation rates of plasma-derived alpha-linolenic acid (alpha-LNA, 18:3n-3) into "stable" liver lipids and the conversion rate of alpha-LNA to docosahexaenoic acid (DHA, 22:6n-3) in male rats fed, after weaning, an n-3 PUFA-adequate diet (4.6% alpha-LNA, no DHA) or an n-3 PUFA-deficient diet (0.2% alpha-LNA, no DHA) for 15 weeks. Unanesthetized rats were infused intravenously with [1-14C]alpha-LNA, and arterial plasma was sampled until the liver was microwaved at 5 min. Unlabeled alpha-LNA and DHA concentrations in arterial plasma and liver were reduced >90% by deprivation, whereas unlabeled arachidonic acid (20:4n-6) and docosapentaenoic acid (22:5n-6) concentrations were increased. Deprivation did not change alpha-LNA incorporation coefficients into stable liver lipids but increased synthesis-incorporation coefficients of DHA from alpha-LNA by 6.6-, 8.4-, and 2.3-fold in triacylglycerol, phospholipid, and cholesteryl ester, respectively. Assuming that synthesized-incorporated DHA eventually would be secreted within lipoproteins, calculated liver DHA secretion rates equaled 2.19 and 0.82 micromol/day in the n-3 PUFA-adequate and -deprived rats, respectively. These rates exceed the published rates of brain DHA consumption by 6- and 10-fold, respectively, and should be sufficient to maintain normal and reduced brain DHA concentrations, respectively, in the two dietary conditions.

Action of epoxyeicosatrienoic acids on cellular function

Epoxyeicosatrienoic acids (EETs), which function primarily as autocrine and paracrine mediators in the cardiovascular and renal systems, are synthesized from arachidonic acid by cytochrome P-450 epoxygenases. They activate smooth muscle large-conductance Ca(2+)-activated K(+) channels, producing hyperpolarization and vasorelaxation. EETs also have anti-inflammatory effects in the vasculature and kidney, stimulate angiogenesis, and have mitogenic effects in the kidney. Many of the functional effects of EETs occur through activation of signal transduction pathways and modulation of gene expression, events probably initiated by binding to a putative cell surface EET receptor. However, EETs are rapidly taken up by cells and are incorporated into and released from phospholipids, suggesting that some functional effects may occur through a direct interaction between the EET and an intracellular effector system. In this regard, EETs and several of their metabolites activate peroxisome proliferator-activated receptor alpha (PPARalpha) and PPARgamma, suggesting that some functional effects may result from PPAR activation. EETs are metabolized primarily by conversion to dihydroxyeicosatrienoic acids (DHETs), a reaction catalyzed by soluble epoxide hydrolase (sEH). Many potentially beneficial actions of EETs are attenuated upon conversion to DHETs, which do not appear to be essential under routine conditions. Therefore, sEH is considered a potential therapeutic target for enhancing the beneficial functions of EETs.

Brain elongation of linoleic acid is a negligible source of the arachidonate in brain phospholipids of adult rats

The extent to which the adult brain can derive some of its arachidonic acid (AA) through internalized synthesis from linoleic acid (LA) is uncertain. Thus, we determined for plasma-derived LA in vivo rates for brain incorporation, beta-oxidation, and conversion to AA. Adult male unanesthetized rats, reared on a diet enriched in LA but low in AA, were infused intravenously for 5 min with [1-(14)C]LA. Timed arterial samples were collected until the animals were killed at 5 min and the brain was removed after microwaving. Within plasma lipids, >96% of radioactivity was in the form of unchanged [1-(14)C]LA, but [(14)C]AA was insignificant (<0.2%). Eighty-six percent of brain radioactivity at 5 min was present as beta-oxidation products, whereas the remainder was mainly in 'stable' phospholipid or triglyceride as LA or AA (11 and <1%, respectively). Unesterified unlabeled LA rapidly enters brain from plasma, but its incorporation into brain total phospholipid and triglyceride, in the form of synthesized AA, is <1% of the amount that enters the brain. Thus, in rats fed even a diet containing low amounts of AA, the LA that enters brain is largely beta-oxidized, and is not a major source of AA in brain.

Impact of different saturated fatty acid, polyunsaturated fatty acid and cholesterol containing diets on beta-amyloid accumulation in APP/PS1 transgenic mice

The present study assessed the influence of dietary lipids on accumulation of amyloid beta-peptide (Abeta) in the brain. Seven experimental diets with varying n-6/n-3-ratio, saturated and polyunsaturated fatty acid and cholesterol contents were fed to transgenic APPswe/PS1dE9 mice for 3-4 months beginning at a young adult age (6 months). Hippocampal Abeta levels were determined with ELISA and plaque load by using immunocytochemistry. A typical Western diet with 40% saturated fatty acids and 1% of cholesterol increased, while diets supplemented with docosahexaenoic acid (DHA) decreased Abeta levels compared to regular (soy oil based) diet. DHA diet also decreased the number of activated microglia in hippocampus and increased exploratory activity of transgenic mice, but did not improve their spatial learning in the water maze. The favorable effect of DHA on Abeta production was verified in two different cell lines. Regulation of dietary lipid intake may offer a new tool to reduce the risk of Alzheimer's disease at the population level.

Peroxisomal multifunctional protein-2 deficiency causes motor deficits and glial lesions in the adult central nervous system

In humans, mutations inactivating multifunctional protein-2 (MFP-2), and thus peroxisomal beta-oxidation, cause neuronal heterotopia and demyelination, which is clinically reflected by hypotonia, seizures, and death within the first year of life. In contrast, our recently generated MFP-2-deficient mice did not show neurodevelopmental abnormalities but exhibited aberrations in bile acid metabolism and one of three of them died early postnatally. In the postweaning period, all survivors developed progressive motor deficits, including abnormal cramping reflexes of the limbs and loss of mobility, with death at 6 months. Motor impairment was not accompanied by lesions of peripheral nerves or muscles. However, in the central nervous system MFP-2-deficient mice overexpressed catalase in glial cells, accumulated lipids in ependymal cells and in the molecular layer of the cerebellum, exhibited severe astrogliosis and reactive microglia predominantly within the gray matter of the brain and the spinal cord, whereas synaptic and myelin markers were not affected. This culminated in degenerative changes of astroglia cells but not in overt neuronal lesions. Neither the motor deficits nor the brain lesions were aggravated by increasing the branched-chain fatty acid concentration through dietary supplementation. These data indicate that MFP-2 deficiency in mice causes a neurological phenotype in adulthood that is manifested primarily by astroglial damage.

Low liver conversion rate of alpha-linolenic to docosahexaenoic acid in awake rats on a high-docosahexaenoate-containing diet

We quantified the rates of incorporation of alpha-linolenic acid (alpha-LNA; 18:3n-3) into "stable" lipids (triacylglycerol, phospholipid, cholesteryl ester) and the rate of conversion of alpha-LNA to docosahexaenoic acid (DHA; 22: 6n-3) in the liver of awake male rats on a high-DHA-containing diet after a 5-min intravenous infusion of [1-(14)C]alpha-LNA. At 5 min, 72.7% of liver radioactivity (excluding unesterified fatty acid radioactivity) was in stable lipids, with the remainder in the aqueous compartment. Using our measured specific activity of liver alpha-LNA-CoA, in the form of the dilution coefficient lambda(alpha-LNA-CoA), we calculated incorporation rates of unesterified alpha-LNA into liver triacylglycerol, phospholipid, and cholesteryl ester as 2,401, 749, and 9.6 nmol/s/g x 10(-4), respectively, corresponding to turnover rates of 3.2, 8.7, and 2.9%/min and half-lives of 8-24 min. A lower limit for the DHA synthesis rate from alpha-LNA equaled 15.8 nmol/s/g x 10(-4) (0.5% of the net in corporation rate). Thus, in rats on a high-DHA-containing diet, rates of beta-oxidation and esterification of alpha-LNA into stable liver lipids are high, whereas its conversion to DHA is comparatively low and insufficient to supply significant DHA to the brain. High incorporation and turnover rates likely reflect a high secretion rate by liver of stable lipids within very low density lipoproteins.

Changes of the transcriptional and fatty acid profiles in response to n-3 fatty acids in SH-SY5Y neuroblastoma cells

Synthesis of docosahexaenoic acid (DHA) from its metabolic precursors contributes to membrane incorporation of this FA within the central nervous system. Although cultured neural cells are able to produce DHA, the membrane DHA contents resulting from metabolic conversion do not match the high values of those resulting from supplementation with preformed DHA. We have examined whether the DHA precursors down-regulate the incorporation of newly formed DHA within human neuroblastoma cells. SH-SY5Y cells were incubated with gradual doses of alpha-linolenic acid (alpha-LNA), EPA, or docosapentaenoic acid (DPA), and the incorporation of DHA into ethanolamine glycerophospholipids was analyzed as a reflection of synthesizing activity. The incorporation of EPA, DPA, and preformed DHA followed a dose-response saturating curve, whereas that of DHA synthesized either from alpha-LNA, EPA, or DPA peaked at concentrations of precursors below 15-30 microM and sharply decreased with higher doses. The mRNA encoding for six FA metabolism genes were quantified using real-time PCR. Two enzymes of the peroxisomal beta-oxidation, L-bifunctional protein and peroxisomal acyl-CoA oxidase, were expressed at lower levels than fatty acyl-CoA ligase 3 (FACL3) and delta6-desaturase (delta6-D). The delta6-D mRNA slightly increased between 16 and 48 h of culture, and this effect was abolished in the presence of 70 microM EPA. In contrast, the EPA treatment resulted in a time-dependent increase of FACL3 mRNA. The terminal step of DHA synthesis seems to form a "metabolic bottleneck," resulting in accretion of EPA and DPA when the precursor concentration exceeds a specific threshold value. We conclude that the critical precursor- concentration window of responsiveness may originate from the low basal expression level of peroxisomal enzymes.