Quantitative and carbon isotope ratio analysis of fatty acids isolated from human brain hemispheres.

Our knowledge surrounding the overall fatty acid profile of the adult human brain has been largely limited to extrapolations from brain regions in which the distribution of fatty acids varies. This is especially problematic when modeling brain fatty acid metabolism, therefore, an updated estimate of whole-brain fatty acid concentration is necessitated. Here, we sought to conduct a comprehensive quantitative analysis of fatty acids from entire well-characterized human brain hemispheres (n = 6) provided by the Douglas-Bell Canada Brain Bank. Additionally, exploratory natural abundance carbon isotope ratio (CIR; δ13 C, 13 C/12 C) analysis was performed to assess the origin of brain fatty acids. Brain fatty acid methyl esters (FAMEs) were quantified by gas chromatography (GC)-flame ionization detection and minor n-6 and n-3 polyunsaturated fatty acid pentafluorobenzyl esters by GC-mass spectrometry. Carbon isotope ratio values of identifiable FAMEs were measured by GC-combustion-isotope ratio mass spectrometry. Overall, the most abundant fatty acid in the human brain was oleic acid, followed by stearic acid (STA), palmitic acid (PAM), docosahexaenoic acid (DHA), and arachidonic acid (ARA). Interestingly, cholesterol as well as saturates including PAM and STA were most enriched in 13 C, while PUFAs including DHA and ARA were most depleted in 13 C. These findings suggest a contribution of endogenous synthesis utilizing dietary sugar substrates rich in 13 C, and a combination of marine, animal, and terrestrial PUFA sources more depleted in 13 C, respectively. These results provide novel insights on cerebral fatty acid origin and concentration, the latter serving as a valuable resource for future modeling of fatty acid metabolism in the human brain.

Quantitative High-Field NMR- and Mass Spectrometry-Based Fatty Acid Sequencing Reveals Internal Structure in Ru-Catalyzed Deuteration of Docosahexaenoic Acid.

Ru-based catalysis results in highly unsaturated fatty acid (HUFA) ethyl esters (EE) deuterated to various extents. The products carry 2H (D) mainly at their bis-allylic positions, where they are resistant to autoxidation compared to natural HUFA and are promising as neurological and retinal drugs. We characterized the extent of deuteration at each allylic position of docosa-4,7,10,13,16,19-hexaenoic acid deuterated to completion at bis-allylic and allylic positions (D-DHA) by two-dimensional (2D) and high-field (600 and 950 MHz) NMR. In separate experiments, the kinetics of docosahexaenoic acid (DHA) EE deuteration was evaluated using Paternò-Büchi (PB) reaction tandem mass spectrometry (MS/MS) analysis, enabling deuteration to be quantitatively characterized for isotopologues (D0-D14 DHA) at each internal allylic position. NMR analysis shows that the net deuteration of the isotopologue mixture is about 94% at the bis-allylic positions, and less than 1% remained as the protiated -CH2-. MS analysis shows that deuteration kinetics follow an increasing curve at bis-allylic positions with higher rate for internal bis-allylic positions. Percent D of bis-allylic positions increases linearly from D1 to D9 in which all internal bis-allylic positions (C9, C12, C15) deuterate uniformly and more rapidly than external bis-allylic positions (C6, C18). The mono-allylic positions near the methyl end (C21) show a steep increase of D only after the D10 isotopologue has been deuterated to >90%, while the mono-allylic position near the carboxyl position, C3, deuterates last and least. These data establish detailed methods for the characterization of Ru-catalyzed deuteration of HUFA as well as the phenomenological reaction kinetics as net product is formed.

Biochemical Alterations in White Matter Tracts of the Aging Mouse Brain Revealed by FTIR Spectroscopy Imaging.

White matter degeneration in the central nervous system (CNS) has been correlated with a decline in cognitive function during aging. Ultrastructural examination of the aging human brain shows a loss of myelin, yet little is known about molecular and biochemical changes that lead to myelin degeneration. In this study, we investigate myelination across the lifespan in C57BL/6 mice using electron microscopy and Fourier transform infrared (FTIR) spectroscopic imaging to better understand the relationship between structural and biochemical changes in CNS white matter tracts. A decrease in the number of myelinated axons was associated with altered lipid profiles in the corpus callosum of aged mice. FTIR spectroscopic imaging revealed alterations in functional groups associated with phospholipids, including the lipid acyl, lipid ester and phosphate vibrations. Biochemical changes in white matter were observed prior to structural changes and most predominant in the anterior regions of the corpus callosum. This was supported by biochemical analysis of fatty acid composition that demonstrated an overall trend towards increased monounsaturated fatty acids and decreased polyunsaturated fatty acids with age. To further explore the molecular mechanisms underlying these biochemical alterations, gene expression profiles of lipid metabolism and oxidative stress pathways were investigated. A decrease in the expression of several genes involved in glutathione metabolism suggests that oxidative damage to lipids may contribute to age-related white matter degeneration.

Low linoleic acid foods with added DHA given to Malawian children with severe acute malnutrition improve cognition: a randomized, triple-blinded, controlled clinical trial.

BACKGROUND: There is concern that the PUFA composition of ready-to-use therapeutic food (RUTF) for the treatment of severe acute malnutrition (SAM) is suboptimal for neurocognitive recovery. OBJECTIVES: We tested the hypothesis that RUTF made with reduced amounts of linoleic acid, achieved using high-oleic (HO) peanuts without added DHA (HO-RUTF) or with added DHA (DHA-HO-RUTF), improves cognition when compared with standard RUTF (S-RUTF). METHODS: A triple-blind, randomized, controlled clinical feeding trial was conducted among children with uncomplicated SAM in Malawi with 3 types of RUTF: DHA-HO-RUTF, HO-RUTF, and S-RUTF. The primary outcomes, measured in a subset of subjects, were the Malawi Developmental Assessment Tool (MDAT) global z-score and a modified Willatts problem-solving assessment (PSA) intention score for 3 standardized problems, measured 6 mo and immediately after completing RUTF therapy, respectively. MDAT domain z-scores, plasma fatty acid content, anthropometry, and eye tracking were secondary outcomes. Comparisons were made between the novel PUFA RUTFs and S-RUTF. RESULTS: Among the 2565 SAM children enrolled, mean global MDAT z-scores were -0.69 ± 1.19 and -0.88 ± 1.27 for children receiving DHA-HO-RUTF and S-RUTF, respectively (difference 0.19, 95% CI: 0.01, 0.38). Children receiving DHA-HO-RUTF had higher gross motor and social domain z-scores than those receiving S-RUTF. The PSA problem 3 scores did not differ by dietary group (OR: 0.92, 95% CI: 0.67, 1.26 for DHA-HO-RUTF). After 4 wk of treatment, plasma phospholipid EPA and α-linolenic acid were greater in children consuming DHA-HO-RUTF or HO-RUTF when compared with S-RUTF (for all 4 comparisons P values < 0.001), but only plasma DHA was greater in DHA-HO-RUTF than S-RUTF (P < 0.001). CONCLUSIONS: Treatment of uncomplicated SAM with DHA-HO-RUTF resulted in an improved MDAT score, conferring a cognitive benefit 6 mo after completing diet therapy. This treatment should be explored in operational settings. This trial was registered at clinicaltrials.gov as NCT03094247.

A Scoping Review of Clinical Studies in Infants Fed Formulas Containing Palm Oil or Palm Olein and Sn-2 Palmitate.

BACKGROUND: Palmitic acid (PA; 16:0) is added to infant formula in the form of palm oil/palm olein (PO/POL) and stereospecific numbered-2 palmitate (SN2). Several studies have examined the effects of PO/POL and or SN2 in formulas on health outcomes, mainly growth, digestion, and absorption of nutrients. However, the roles of PA, PO/POL, and SN2 on neurodevelopment remains unknown. OBJECTIVES: The objective of this scoping review was to map out studies in infants fed formula with PO/POL or SN2 to identify current knowledge on the role of PA in infant nutrition, specifically neurodevelopment. METHODS: Data sources, including Medline, Embase, CAB Abstracts, and the Cochrane Database, were searched. Eligible articles were randomized controlled trials (RCTs) and observational studies examining outcomes in term singleton infants fed formula containing PO/POL or SN2. Studies examining preterm infants or infants with infections, mixed-feeding interventions, or outcomes not concerned with PO/POL or SN2 were excluded. Screening and data extraction were performed by 2 independent reviewers, and results were charted into 10 outcome categories. RESULTS: We identified 28 RCTs and 2 observational studies. Only 1 RCT examined a neurodevelopmental outcome, reporting infants fed SN2 formula had higher fine motor skill scores compared to those fed a vegetable oil formula with a lower amount of SN2; however, only after adjustment for maternal education and at an earlier, but not a later time point. Anthropometric measures do not appear to be influenced by PO/POL or SN2 within formulas. Alternatively, it was reported that infants fed PO/POL within formulas had a decreased absorption of calcium, total fat, and PA compared to those fed vegetable oil formulas. However, studies were heterogenous, making it difficult to isolate the effects of PO/POL or SN2 in formulas. CONCLUSIONS: Our review reiterates the need for future studies to address the effects of PO/POL and SN2 on neurodevelopment in infants. This study is registered at Open Science Framework as osf.io/697he.

Toward Quantitative Sequencing of Deuteration of Unsaturated Hydrocarbon Chains in Fatty Acids.

No general method currently is available for the quantitative determination of deuterium (D) at C positions along a hydrocarbon chain. Bis-allylic deuterated highly unsaturated fatty acids (D-HUFA) are a novel class of drugs stabilized against H-abstraction-mediated oxidation by deuteration at the most labile positions. Ru-based catalytic deuteration overcomes the limited scale of bis-allylic D-HUFA production by total organic synthesis; however, it produces a complex mixture of bis-allylic D isotopologues and isotopomers, requiring detailed sequencing for characterization. We report here adaptation and application of the Paternó-Büchi (PB) reaction of 2-acetylpyridine to a series of D-HUFA with analysis by shotgun lipidomics to determine position-specific quantitative D abundances. Sodiated PBD-HUFA result in diagnostic ions of high abundance upon collision-induced dissociation (CID) activation, enabling sensitive differentiation and quantification of D fraction at each bis- and mono-allylic position for each isotopologue. Catalytically deuterated isotopologues D5-7 linolenic acid (D5-7 LnA), D6-8 arachidonic acid (D6-8 ARA), D7-9 eicosapentaenoic acid (D7-9 EPA), and D9-11 docosahexaenoic acid (D9-11 DHA) incorporate 80-98, 95-100, 81-100, and 83-100% D at their bis-allylic positions, respectively. D-HUFA isotopologues having D number greater than or equal to bis-allylic sites (e.g., D10-DHA or D11-DHA) deuterated >95% at bis-allylic positions, except for D-LnA. The mono-allylic position near the methyl end deuterates to a much greater extent than the mono-allylic position near the carboxyl end, and both positions deuterate only when bis-allylic D is near-saturated. This method enables rapid, accurate characterization of position and isotopomer-specific D composition and enables sequencing along the chain.

Plasma unesterified eicosapentaenoic acid is converted to docosahexaenoic acid (DHA) in the liver and supplies the brain with DHA in the presence or absence of dietary DHA.

Recent meta-analyses suggest that high eicosapentaenoic acid (EPA, 20:5n-3) supplements may be beneficial in managing the symptoms of major depression. However, brain EPA levels are hundreds-fold lower than docosahexaenoic acid (DHA, 22:6n-3), making the potential mechanisms of action of EPA in the brain less clear. Using a kinetic model the goal of this study was to determine how EPA impacts brain DHA levels. Following 8 weeks feeding of a 2% alpha-linolenic acid (ALA, 18:3n-3) or DHA diet (2% ALA + 2% DHA), 11-week-old Long Evans rats were infused with unesterified 13C-EPA at steady-state for 3 h with plasma collected at 30 min intervals and livers and brains collected after 3 h for determining DHA synthesis-accretion kinetics in multiple lipid fractions. Most of the newly synthesized liver 13C-DHA was in phosphatidylethanolamine (PE, 37%-56%), however, 75-80% of plasma 13C-DHA was found in triacylglycerols (TAG) at 14 ± 5 and 46 ± 12 nmol/g/day (p < 0.05) in the ALA and DHA group, respectively. In the brain, PE and phosphatidylserine (PS) accreted the most 13C-DHA, and DHA compared to ALA feeding shortened DHA half-lives in most lipid fractions, resulting in total brain DHA half-lives of 32 ± 6 and 96 ± 24 (days/g ± SEM), respectively (p < 0.05). EPA was predominantly converted and stored as PE-DHA in the liver, secreted to plasma as TAG-DHA and accumulated in brain as PE and PS-DHA. In conclusion, EPA is a substantial source for brain DHA turnover and suggests an important role for EPA in maintaining brain DHA levels.

Natural abundance carbon isotope ratio analysis and its application in the study of diet and metabolism.

Due to differences in carbon assimilation pathways between plants, there are subtle but distinct variations in the carbon isotope ratios of foods and animal products throughout the food supply. Although it is well understood that the carbon isotope ratio composition of the diet influences that of the consumers' tissues, the application of natural abundance carbon isotope ratio analysis in nutrition has long been underappreciated. Over the past decade, however, several studies have investigated the utility of carbon isotope ratio analysis for evaluation of nutritional biomarker status, primarily focusing on its application as an objective indicator of sugar and animal protein intake. More recently, research investigating the application of natural abundance measurements has been extended to study fatty acid metabolism and has yielded encouraging results. Collectively, data from large-scale observational studies and experimental animal studies highlight the potential for carbon isotope ratio analysis as an additional and effective tool to study diet and metabolism. The purpose of this review is to provide an overview of natural abundance carbon isotope ratio analysis, its application to studying nutrition, and an update of the research in the field.

Turnover of brain DHA in mice is accurately determined by tracer-free natural abundance carbon isotope ratio analysis.

The brain is highly enriched in the long-chain omega-3 (n-3) PUFA DHA. Due to the limited capacity for local DHA synthesis in the brain, it relies on a continual supply from the circulation to replenish metabolized DHA. Previous studies investigating brain DHA turnover and metabolism have relied on isotope tracers to determine brain fatty acid kinetics; however, this approach is cumbersome and costly. We applied natural abundance carbon isotope ratio analysis via high-precision gas chromatography combustion isotope ratio mass spectrometry, without the use of labeled tracers, to determine the half-life of brain DHA in mice following a dietary switch experiment. Mice fed diets containing either α-linolenic acid (ALA) or DHA as the sole dietary n-3 PUFA were switched onto diets containing ALA, DHA, or ALA + DHA at 6 weeks of age, while control mice were maintained on their respective background diet. We measured brain DHA carbon isotope ratios (reported as δ13CDHA signatures) over a 168-day time course. Brain δ13CDHA signatures of control mice maintained on background diets over the time course were stable (P > 0.05). Brain δ13CDHA signatures of mice switched to the DHA or ALA + DHA diet from the ALA diet changed over time, yielding brain incorporation half-lives of 40 and 34 days, respectively. These half-lives determined by natural abundance carbon isotope ratio analysis were consistent with estimates from kinetic isotope tracer studies. Our results demonstrate the feasibility of natural abundance carbon isotope ratio analysis in the study of fatty acid metabolism without the use of isotopically labeled fatty acid tracers.

DHA Esterified to Phosphatidylserine or Phosphatidylcholine is More Efficient at Targeting the Brain than DHA Esterified to Triacylglycerol.

SCOPE: Docosahexaenoic acid (DHA, 22:6n-3) is crucial for optimal neuronal development and function, but the brain has a poor capacity to synthesize this fatty acid. When consumed acutely esterified to phosphatidylcholine, DHA is more efficient at targeting the brain than when consumed esterified to triacylglycerol. However, the brain DHA bioavailability of other forms of DHA-containing phospholipids, after oral ingestion, is unknown. The objective of this study is to compare brain uptake of DHA after acute gavage with different DHA carriers. METHODS AND RESULTS: Ten-week-old rats were gavaged with 3 H-labeled DHA esterified to phosphatidylcholine (DHA-PtdCho), phosphatidylethanolamine (DHA-PtdEtn), phosphatidylserine (DHA-PtdSer) or triacylglycerol (DHA-TG). Six hours post-gavage, the animals were euthanized and radioactivity was quantified in the cortex and serum lipid classes. Radioactivity recovered in cortex total phospholipids was similar between the DHA-PtdCho and DHA-PtdSer groups and were 5.8 and 6.7 times higher than in the DHA-TG group, respectively. Serum total lipid radioactivity was higher in the DHA-PtdSer group than in the DHA-PtdCho and DHA-PtdEtn groups, but not compared to the DHA-TG group. CONCLUSION: These results suggest that different mechanisms must be present to explain the serum and brain bioavailability differences between DHA-PtdCho and DHA-PtdSer, but these require further investigation.

Maternal dietary n-6 polyunsaturated fatty acid deprivation does not exacerbate post-weaning reductions in arachidonic acid and its mediators in the mouse hippocampus.

OBJECTIVES: The present study examines how lowering maternal dietary n-6 polyunsaturated fatty acids (PUFA) (starting from pregnancy) compared to offspring (starting from post-weaning) affect the levels of n-6 and n-3 fatty acids in phospholipids (PL) and lipid mediators in the hippocampus of mice. METHODS: Pregnant mice were randomly assigned to consume either a deprived or an adequate n-6 PUFA diet during pregnancy and lactation (maternal exposure). On postnatal day (PND) 21, half of the male pups were weaned onto the same diet as their dams, and the other half were switched to the other diet for 9 weeks (offspring exposure). At PND 84, upon head-focused high-energy microwave irradiation, hippocampi were collected for PL fatty acid and lipid mediator analyses. RESULTS: Arachidonic acid (ARA) concentrations were significantly decreased in both total PL and PL fractions, while eicosapentaenoic acid (EPA) concentrations were increased only in PL fractions upon n-6 PUFA deprivation of offspring, regardless of maternal exposure. Several ARA-derived eicosanoids were reduced, while some of the EPA-derived eicosanoids were elevated by n-6 PUFA deprivation in offspring. There was no effect of diet on docosahexaenoic acid (DHA) or DHA-derived docosanoids concentrations under either maternal or offspring exposure. DISCUSSION: These results indicate that the maternal exposure to dietary n-6 PUFA may not be as important as the offspring exposure in regulating hippocampal ARA and some lipid mediators. Results from this study will be helpful in the design of experiments aimed at testing the significance of altering brain ARA levels over different stages of life.

Docosahexaenoic acid is both a product of and a precursor to tetracosahexaenoic acid in the rat.

Tetracosahexaeoic acid (THA; 24:6n-3) is thought to be the immediate precursor of DHA in rodents; however, the relationship between THA and DHA metabolism has not been assessed in vivo. Here, we infused unesterified 2H5-THA and 13C22-DHA, at a steady state, into two groups of male Long-Evans rats and determined the synthesis-secretion kinetics, including daily synthesis-secretion rates of all 20-24 carbon n-3 PUFAs. We determined that the synthesis-secretion coefficient (a measure of the capacity to synthesize a given fatty acid) for the synthesis of DHA from plasma unesterified THA to be 134-fold higher than for THA from DHA. However, when considering the significantly higher endogenous plasma unesterified DHA pool, the daily synthesis-secretion rates were only 7-fold higher for DHA synthesis from THA (96.3 ± 31.3 nmol/d) compared with that for THA synthesis from DHA (11.4 ± 4.1 nmol/d). Furthermore, plasma unesterified THA was converted to DHA and secreted into the plasma at a 2.5-fold faster rate than remaining as THA itself (26.2 ± 6.3 nmol/d), supporting THA's primary role as a precursor to DHA. In conclusion, using a 3 h infusion model in rats, we demonstrate for the first time in vivo that DHA is both a product and a precursor to THA.

Applying stable carbon isotopic analysis at the natural abundance level to determine the origin of docosahexaenoic acid in the brain of the fat-1 mouse.

A key factor limiting the study of the origin and metabolism of brain fatty acids is the lack of cost-efficient methods available to trace fatty acids. Here, through the application of compound-specific isotope analysis (CSIA), a novel, cost-efficient method, we successfully differentiated between brain DHA originating directly from dietary omega (n)-3 polyunsaturated fatty acids (PUFA), and brain DHA biochemically synthesized to determine the origin of brain DHA in fat-1 mice. Fat-1 mice and their wild-type littermates were either weaned onto n-6 PUFA rich, n-3 PUFA deficient diets or diets rich in both n-3 and n-6 PUFA. Isotopic analysis of fatty acid methyl esters from brain and liver tissue was conducted via gas chromatography- isotope ratio mass spectrometry. Our data demonstrates that in the presence of n-3 and n-6 PUFA, fat-1 mice obtain their brain DHA solely from n-3 PUFA sources. This study reflects the first application of CSIA to a complex multivariate model to determine the origin of brain fatty acids.

Two weeks of docosahexaenoic acid (DHA) supplementation increases synthesis-secretion kinetics of n-3 polyunsaturated fatty acids compared to 8 weeks of DHA supplementation.

Docosahexaenoic acid (DHA, 22:6n-3) must be consumed in the diet or synthesized from n-3 polyunsaturated fatty acid (PUFA) precursors. However, the effect of dietary DHA on the metabolic pathway is not fully understood. Presently, 21-day-old Long Evans rats were weaned onto one of four dietary protocols: 1) 8 weeks of 2% ALA (ALA), 2) 6 weeks ALA followed by 2 weeks of 2% ALA + 2% DHA (DHA), 3) 4 weeks ALA followed by 4 weeks DHA and 4) 8 weeks of DHA. After the feeding period, 2H5-ALA and 13C20-eicosapentaenoic acid (EPA, 20:5n-3) were co-infused and blood was collected over 3 h for determination of whole-body synthesis-secretion kinetics. The synthesis-secretion coefficient (ml/min, means ± SEM) for EPA (0.238±0.104 vs. 0.021±0.001) and DPAn-3 (0.194±0.060 vs. 0.020±0.008) synthesis from plasma unesterified ALA, and DPAn-3 from plasma unesterified EPA (2.04±0.89 vs. 0.163±0.025) were higher (P<.05) after 2 weeks compared to 8 weeks of DHA feeding. The daily synthesis-secretion rate (nmol/d) of DHA from EPA was highest after 4 weeks of DHA feeding (843±409) compared to no DHA (70±22). Liver gene expression of ELOVL2 and FADS2 were lower (P<.05) after 4 vs. 8 weeks of DHA. Higher synthesis-secretion kinetics after 2 and 4 weeks of DHA feeding suggests an increased throughput of the PUFA metabolic pathway. Furthermore, these findings may lead to novel dietary strategies to maximize DHA levels while minimizing dietary requirements.

Natural Abundance Carbon Isotopic Analysis Indicates the Equal Contribution of Local Synthesis and Plasma Uptake to Palmitate Levels in the Mouse Brain.

Saturated fatty acids are the most abundant fatty acids in the brain, however, there has been some debate regarding the ability of intact dietary saturated fatty acids to be incorporated into the brain. In the present study, we use compound specific isotope analysis to measure the natural abundance carbon isotopic signature of brain, liver, and blood palmitic acid (PAM) and compare it to the dietary PAM and sugar isotopic signatures to calculate the relative contribution of both the incorporation of intact and endogenously synthesized PAM to these pools. Mice were equilibrated to the study diet, and extracted fatty acids were analyzed with gas chromatography isotope ratio mass spectrometry to determine the carbon isotopic signature of PAM (δ13 CPAM ). Liver, serum total, and serum unesterified fatty acid δ13 CPAM ranged between -20.6 and -21.1 mUr and were approximately 8.5 mUr more enriched in 13 C when compared to the dietary PAM signature. Brain δ13 CPAM was found to be more enriched than liver or blood pools (-16.7 ± 0.2 mUr, mean ± SD). Two end-member-mixed modeling using the carbon isotopic signature of dietary PAM and dietary sugars determined the contribution of synthesis to the total tissue PAM pool to range between 44% and 48%. This suggests that endogenous synthesis and dietary PAM are near equal contributors to brain, liver, and blood PAM pools. In conclusion, our data provide evidence that brain PAM levels are maintained by both local endogenous synthesis and through the uptake of intact PAM from the blood.

Directly quantified dietary n-3 fatty acid intakes of Canadian toddlers are lower than current dietary recommendations.

To date, few studies have evaluated the intake of dietary n-3 polyunsaturated fatty acids (PUFA) in young North American children and current estimates are based on indirect approaches which have concerning limitations. Furthermore, there is a lack of available knowledge regarding the proportion of children meeting current dietary recommendations for the consumption of long-chain n-3 PUFA as α-linolenic acid (ALA) and eicosapentaenoic acid (EPA)/docosahexaenoic acid (DHA). The objective of the present study was to directly quantify the intake of n-3 PUFA in toddlers aged 2 to 3 years and determine if intakes met international recommendations. Given the low intakes of fish in North America, we predicted that n-3 PUFA intakes in toddlers would fall short of recommended intakes. Duplicated diets were collected from 20 Canadian children over a 3-day period. Diets were then directly analyzed by gas chromatography. Daily intakes (means ± SEM) of ALA, EPA, and DHA were as follows: 710.1 ± 69.7, 9.6 ± 2.9, and 19.2 ± 6.8 mg/d, respectively. Compared with North American dietary reference intakes, 45% of our children met the minimal recommended intake of ALA, whereas only 5% consumed the target intake of EPA plus DHA. These results indicate that Canadian children aged 2 to 3 years struggle to consume adequate intakes of the n-3 PUFA ALA and particularly EPA/DHA; efforts to narrow this gap should focus on increasing EPA and DHA intakes by appropriate fish/seafood consumption along with enriched foods or supplements if necessary.

Brain docosahexaenoic acid uptake and metabolism.

Docosahexaenoic acid (DHA) is the most abundant n-3 polyunsaturated fatty acid in the brain where it serves to regulate several important processes and, in addition, serves as a precursor to bioactive mediators. Given that the capacity of the brain to synthesize DHA locally is appreciably low, the uptake of DHA from circulating lipid pools is essential to maintaining homeostatic levels. Although, several plasma pools have been proposed to supply the brain with DHA, recent evidence suggests non-esterified-DHA and lysophosphatidylcholine-DHA are the primary sources. The uptake of DHA into the brain appears to be regulated by a number of complementary pathways associated with the activation and metabolism of DHA, and may provide mechanisms for enrichment of DHA within the brain. Following entry into the brain, DHA is esterified into and recycled amongst membrane phospholipids contributing the distribution of DHA in brain phospholipids. During neurotransmission and following brain injury, DHA is released from membrane phospholipids and converted to bioactive mediators which regulate signaling pathways important to synaptogenesis, cell survival, and neuroinflammation, and may be relevant to treating neurological diseases. In the present review, we provide a comprehensive overview of brain DHA metabolism, encompassing many of the pathways and key enzymatic regulators governing brain DHA uptake and metabolism. In addition, we focus on the release of non-esterified DHA and subsequent production of bioactive mediators and the evidence of their proposed activity within the brain. We also provide a brief review of the evidence from post-mortem brain analyses investigating DHA levels in the context of neurological disease and mood disorder, highlighting the current disparities within the field.

Complete assessment of whole-body n-3 and n-6 PUFA synthesis-secretion kinetics and DHA turnover in a rodent model.

Previous assessments of the PUFA biosynthesis pathway have focused on DHA and arachidonic acid synthesis. Here, we determined whole-body synthesis-secretion kinetics for all downstream products of PUFA metabolism, including direct measurements of DHA and n-6 docosapentaenoic acid (DPAn-6, 22:5n-6) turnover, and compared n-6 and n-3 homolog kinetics. We infused labeled α-linolenic acid (ALA, 18:3n-3), linoleic acid (LNA, 18:2n-6), DHA, and DPAn-6 as 2H5-ALA, 13C18-LNA, 13C22-DHA, and 13C22-DPAn-6. Eight 11-week-old Long Evans rats fed a 10% fat diet were infused with the labeled PUFAs over 3 h, and plasma enrichment of labeled products was measured every 30 min. The DHA synthesis-secretion rate (94 ± 34 nmol/day) did not differ from other PUFA products (range, 21.8 ± 4.3 nmol/day to 408 ± 116 nmol/day). Synthesis-secretion rates of n-6 and n-3 PUFA homologs were similar, except 22:4n-6 and DPAn-6 had lower synthesis rates. However, daily turnover from newly synthesized DHA (0.067 ± 0.023%) was 56-fold to 556-fold slower than all other PUFA turnover and was 130-fold slower than that determined directly from the total plasma unesterified DHA pool. In conclusion, n-6 and n-3 PUFA synthesis-secretion kinetics suggest that differences in turnover, not in synthesis-secretion rates, primarily determine PUFA plasma levels.

Mechanisms regulating brain docosahexaenoic acid uptake: what is the recent evidence?

PURPOSE OF REVIEW: To summarize recent advances pertaining to the mechanisms regulating brain docosahexaenoic acid (DHA) uptake. DHA is an omega-3 polyunsaturated fatty acid highly enriched in neuronal membranes and it is implicated in several important neurological processes. However, DHA synthesis is extremely limited within the brain. RECENT FINDINGS: There are two main plasma pools that supply the brain with DHA: the nonesterified pool and the lysophosphatidylcholine (lysoPtdCho) pool. Quantitatively, plasma nonesterified-DHA (NE-DHA) is the main contributor to brain DHA. Fatty acid transport protein 1 (FATP1) in addition to fatty acid-binding protein 5 (FABP5) are key players that regulate brain uptake of NE-DHA. However, the plasma half-life of lysoPtdCho-DHA and its brain partition coefficient are higher than those of NE-DHA after intravenous administration. SUMMARY: The mechanisms regulating brain DHA uptake are more complicated than once believed, but recent advances provide some clarity notably by suggesting that FATP1 and FABP5 are key contributors to cellular uptake of DHA at the blood-brain barrier. Elucidating how DHA enters the brain is important as we might be able to identify methods to better deliver DHA to the brain as a potential therapeutic.