Quantitative contributions of diet and liver synthesis to docosahexaenoic acid homeostasis

Modulation of Δ5- and Δ6-desaturases in the brain-liver axis

OBJECTIVE

Obesity is associated with liver depletion of ω-3 polyunsaturated fatty acids (ω-3 PUFAS) promoting steatosis and inflammation, whose levels are maintained by diet or biosynthesis involving Δ-5D, Δ-6D desaturases and elongases.

METHOD

We aimed to assess Δ-5D and Δ-6D activities in liver and brain from mice fed a control diet (CD) or high-fat diet (HFD) for four to sixteen weeks.

RESULTS

HFD led to (1) an early (4 weeks) enhancement in liver Δ-5D, Δ-6D, and PPAR-α activities, without changes in oxidative stress, liver damage or fat accumulation; (2) a latter progressive loss in hepatic desaturation with insufficient compensatory increases in mRNA and protein expression, leading to ω-3 PUFA depletion, PPAR-α down-regulation reducing FA oxidation, and liver steatosis with enhancement in lipogenesis; and (3) brain ω-3 PUFA depletion after 12 to 16 weeks of HFD feeding.

CONCLUSION

In conclusion, the brain-liver axis is drastically affected by obesity in a time dependent fashion.

Serum measures of docosahexaenoic acid (DHA) synthesis underestimates whole body DHA synthesis in male and female mice

Females have higher docosahexaenoic acid (DHA) levels than males, proposed to be a result of higher DHA synthesis rates from α-linolenic acid (ALA). However, DHA synthesis rates are reported to be low, and have not been directly compared between sexes. Here, we apply a new compound specific isotope analysis model to determine n-3 PUFA synthesis rates in male and female mice and assess its potential translation to human populations. Male and female C57BL/6N mice were allocated to one of three 12-week dietary interventions with added ALA, eicosapentaenoic acid (EPA) or DHA. The diets included low carbon-13 (δ13C)-n-3 PUFA for four weeks, followed by high δ13C-n-3 PUFA for eight weeks (n=4 per diet, time point, sex). Following the diet switch, blood and tissues were collected at multiple time points, and fatty acid levels and δ13C were determined and fit to one-phase exponential decay modeling. Hepatic DHA synthesis rates were not different (P>.05) between sexes. However, n-3 docosapentaenoic acid (DPAn-3) synthesis from dietary EPA was 66% higher (P<.05) in males compared to females, suggesting higher synthesis downstream of DPAn-3 in females. Estimates of percent conversion of dietary ALA to serum DHA was 0.2%, in line with previous rodent and human estimates, but severely underestimates percent dietary ALA conversion to whole body DHA of 9.5%. Taken together, our data indicates that reports of low human DHA synthesis rates may be inaccurate, with synthesis being much higher than previously believed. Future animal studies and translation of this model to humans are needed for greater understanding of n-3 PUFA synthesis and metabolism, and whether the higher-than-expected ALA-derived DHA can offset dietary DHA recommendations set by health agencies.

Protein concentrations and activities of fatty acid desaturase and elongase enzymes in liver, brain, testicle, and kidney from mice: Substrate dependency

The synthesis rates of n-3 and n-6 polyunsaturated fatty acids (PUFAs) in rodents and humans are not agreed upon and depend on substrate availability independently of the capacity for synthesis. Therefore, we aimed to assess the activities of the enzymes for n-3 and n-6 PUFA synthesis pathways in liver, brain, testicle, kidney, heart, and lung, in relation to their protein concentration levels. Eight-week-old Balb/c mice (n = 8) were fed a standard chow diet (6.2% fat, 18.6% protein, and 44.2% carbohydrates) until 14 weeks of age, anesthetized with isoflurane and tissue samples were collected (previously perfused) and stored at -80°C. The protein concentration of the enzymes (Δ-6D, Δ-5D, Elovl2, and Elovl5) were assessed by ELISA kits; their activities were assayed using specific PUFA precursors and measuring the respective PUFA products as fatty acid methyl esters by gas chromatographic analysis. The liver had the highest capacity for PUFA biosynthesis, with limited activity in the brain, testicles, and kidney, while we failed to detect activity in the heart and lung. The protein concentration and activity of the enzymes were significantly correlated. Furthermore, Δ-6D, Δ-5D, and Elovl2 have a higher affinity for n-3 PUFA precursors compared to n-6 PUFA. The capacity for PUFA synthesis in mice mainly resides in the liver, with enzymes having preference for n-3 PUFAs.

GWAS-identified bipolar disorder risk allele in the FADS1/2 gene region links mood episodes and unsaturated fatty acid metabolism in mutant mice

Large-scale genome-wide association studies (GWASs) on bipolar disorder (BD) have implicated the involvement of the fatty acid desaturase (FADS) locus. These enzymes (FADS1 and FADS2) are involved in the metabolism of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which are thought to potentially benefit patients with mood disorders. To model reductions in the activity of FADS1/2 affected by the susceptibility alleles, we generated mutant mice heterozygously lacking both Fads1/2 genes. We measured wheel-running activity over six months and observed bipolar swings in activity, including hyperactivity and hypoactivity. The hyperactivity episodes, in which activity was far above the norm, usually lasted half a day; mice manifested significantly shorter immobility times on the behavioral despair test performed during these episodes. The hypoactivity episodes, which lasted for several weeks, were accompanied by abnormal circadian rhythms and a marked decrease in wheel running, a spontaneous behavior associated with motivation and reward systems. We comprehensively examined lipid composition in the brain and found that levels of certain lipids were significantly altered between wild-type and the heterozygous mutant mice, but no changes were consistent with both sexes and either DHA or EPA was not altered. However, supplementation with DHA or a mixture of DHA and EPA prevented these episodic behavioral changes. Here we propose that heterozygous Fads1/2 knockout mice are a model of BD with robust constitutive, face, and predictive validity, as administration of the mood stabilizer lithium was also effective. This GWAS-based model helps to clarify how lipids and their metabolisms are involved in the pathogenesis and treatment of BD.

Elevated plasma phospholipid n-3 docosapentaenoic acid concentrations during hibernation

Factors for initiating hibernation are unknown, but the condition shares some metabolic similarities with consciousness/sleep, which has been associated with n-3 fatty acids in humans. We investigated plasma phospholipid fatty acid profiles during hibernation and summer in free-ranging brown bears (Ursus arctos) and in captive garden dormice (Eliomys quercinus) contrasting in their hibernation patterns. The dormice received three different dietary fatty acid concentrations of linoleic acid (LA) (19%, 36% and 53%), with correspondingly decreased alpha-linolenic acid (ALA) (32%, 17% and 1.4%). Saturated and monounsaturated fatty acids showed small differences between summer and hibernation in both species. The dormice diet influenced n-6 fatty acids and eicosapentaenoic acid (EPA) concentrations in plasma phospholipids. Consistent differences between summer and hibernation in bears and dormice were decreased ALA and EPA and marked increase of n-3 docosapentaenoic acid and a minor increase of docosahexaenoic acid in parallel with several hundred percent increase of the activity index of elongase ELOVL2 transforming C20-22 fatty acids. The highest LA supply was unexpectantly associated with the highest transformation of the n-3 fatty acids. Similar fatty acid patterns in two contrasting hibernating species indicates a link to the hibernation phenotype and requires further studies in relation to consciousness and metabolism.

Enrichment of Brain n-3 Docosapentaenoic Acid (DPA) and Retinal n-3 Eicosapentaenoic Acid (EPA) in Lambs Fed Nannochloropsis oceanica Microalga

Omega-3 polyunsaturated fatty acids (n-3 PUFAs) have special physiological functions in both brain and retinal tissues that are related to the modulation of inflammatory processes and direct effects on neuronal membrane fluidity, impacting mental and visual health. Among them, the long-chain (LC) n-3 PUFAs, as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), are of special importance. Scarce data are available about the fatty acid (FA) composition of the ruminant brain in response to dietary intervention. However, we decided to examine the brain and retina FA composition of lambs supplemented with an EPA-rich microalga feed for 21 days, as it is known that despite the extensive biohydrogenation of dietary PUFAs in the rumen, ruminants can selectively accumulate some n-3 LC-PUFAs in their brain and retinal tissues. Twenty-eight male lambs were fed a control diet, or the same diet further supplemented with Nannochloropsis sp. microalga. Their brains and retina were collected for FA characterization. Overall, the brain FA profile remained unchanged, with little alteration in omega-3 docosapentaenoic acid (DPA) enhancement in both the hippocampus and prefrontal cortex. Retinal tissues were particularly responsive to the dietary intervention, with a 4.5-fold enhancement of EPA in the freeze-dried-fed lambs compared with the control lambs. We conclude that retinal tissues are sensitive to short-term n-3 PUFA supplementation in lambs.

α-linolenic acid interconversion is sufficient as a source of longer chain ω-3 polyunsaturated fatty acids in humans: An opinion

α-linolenic acid (αLNA) conversion into the functionally important ω-3 polyunsaturated fatty acids (PUFA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA), has been regarded as inadequate for meeting nutritional requirements for these PUFA. This view is based on findings of small αLNA supplementation trials and stable isotope tracer studies that have been interpreted as indicating human capacity for EPA and, in particular, DHA synthesis is limited. The purpose of this review is to re-evaluate this interpretation. Markedly differing study designs, inconsistent findings and lack of trial replication preclude robust consensus regarding the nutritional adequacy of αLNA as a source of EPC and DHA. The conclusion that αLNA conversion in humans is constrained is inaccurate because it presupposes the existence of an unspecified, higher level of metabolic activity. Since capacity for EPA and DHA synthesis is the product of evolution it may be argued that the levels of EPA and DHA it maintains are nutritionally appropriate. Dietary and supra-dietary EPA plus DHA intakes confer health benefits. Paradoxically, such health benefits are also found amongst vegetarians who do not consume EPA and DHA, and for whom αLNA conversion is the primary source of ω-3 PUFA. Since there are no reported adverse effects on health or cognitive development of diets that exclude EPA and DHA, their synthesis from αLNA appears to be nutritionally adequate. This is consistent with the dietary essentiality of αLNA and has implications for developing sustainable nutritional recommendations for ω-3 PUFA.

Perspective: Moving Toward Desirable Linoleic Acid Content in Infant Formula

Infant formula should provide the appropriate nutrients and adequate energy to facilitate healthy infant growth and development. If conclusive data on quantitative nutrient requirements are not available, the composition of human milk (HM) can provide some initial guidance on the infant formula composition. This paper provides a narrative review of the current knowledge, unresolved questions, and future research needs in the area of HM fatty acid (FA) composition, with a particular focus on exploring appropriate intake levels of the essential FA linoleic acid (LA) in infant formula. The paper highlights a clear gap in clinical evidence as to the impact of LA levels in HM or formula on infant outcomes, such as growth, development, and long-term health. The available preclinical information suggests potential disadvantages of high LA intake in the early postnatal period. We recommend performing well-designed clinical intervention trials to create clarity on optimal levels of LA to achieve positive impacts on both short-term growth and development and long-term functional health outcomes.

FADS1 gene polymorphism(s) and fatty acid composition of serum lipids in adolescents

Polyunsaturated fatty acids (PUFA) influence many physiological functions. Associations have been found between single nucleotide polymorphisms (SNP) in the FADS1 (Fatty acid desaturase 1) gene and the relative abundance of PUFA in serum lipids. This study examines the relationship between two SNPs in the FADS1 gene (rs174546, rs174537) and the fatty acid (FA) composition of serum lipids in adolescents (13-18 years). We used DNA samples (670 children; 336 girls and 334 boys) from the Childhood Obesity Prevalence and Treatment (COPAT) project. Genomic DNA was extracted from peripheral blood leukocytes in whole blood samples. For genotype analysis, TaqMan SNP Genotyping assays (Applied Biosystems) were used. Fatty acid composition of serum lipids was assessed using gas chromatography. The T-statistic and regression were used for statistical evaluations. Minor allele T carriers in both SNPs had significant lower level of palmitic acid (16:0, phospholipids) and arachidonic acid (20:4[n-6], phospholipids) in both sexes. In girls, we found a significant positive association between minor allele T carriers and eicosadienoic acid (20:2[n-6], cholesteryl esters) in both SNPs. Being a minor allele T carrier was significantly positively associated with dihomo-γ-linolenic acid (20:3[n-6], phospholipids) in boys in both SNPs. SNPs (including rs174546, rs174537) in the FADS gene cluster should have impacted desaturase activity, which may contribute to different efficiency of PUFA synthesis.

Beneficial effects of natural compounds on experimental liver ischemia-reperfusion injury

Liver ischemia-reperfusion injury (IRI) is a phenomenon inherent to hepatic surgery that severely compromises the organ functionality, whose underlying mechanisms involve cellular and molecular interrelated processes leading to the development of an excessive inflammatory response. Liver resident cells and those recruited in response to injury generate pro-inflammatory signals such as reactive oxygen species, cytokines, chemokines, proteases and lipid mediators that contribute to hepatocellular necrosis and apoptosis. Besides, dying hepatocytes release damage-associated molecular patterns that actívate inflammasomes to further stimulate inflammatory responses leading to massive cell death. Since liver IRI is a complication of hepatic surgery in man, extensive preclinical studies have assessed potential protective strategies, including the supplementation with natural compounds, with the objective to downregulate nuclear factor-κB functioning, the main effector of inflammatory responses. This can be accomplished by either the activation of peroxisome proliferator-activated receptor-α, G protein-coupled receptor 120 or antioxidant signaling pathways, the synthesis of specific pro-resolving mediators, downregulation of Toll-like receptor 4 activity or additional contributory mechanisms that are beginning to be understood. The latter aspect is a crucial issue to be accomplished in preclinical studies, in order to establish adequate conditions for the supplementation with natural products before major liver surgeries in man involving warm IR, such as hepatic trauma or resection of large intrahepatic tumors.

Targeting neuroinflammation: The therapeutic potential of ω-3 PUFAs in substance abuse

Substance abuse is a chronic relapsing disorder that results in serious health and socioeconomic issues worldwide. Addictive drugs induce long-lasting morphologic and functional changes in brain circuits and account for the formation of compulsive drug-seeking and drug-taking behaviors. Yet, there remains a lack of reliable therapy. In recent years, accumulating evidence indicated that neuroinflammation was implicated in the development of drug addiction. Findings from both our and other laboratories suggest that ω-3 polyunsaturated fatty acids (PUFAs) are effective in treating neuroinflammation-related mental diseases, and indicate that they could exert positive effects in treating drug addiction. Thus, in the present review, we summarized and evaluated recently published articles reporting the neuroinflammation mechanism in drug addiction and the immune regulatory ability of ω-3 PUFAs. We also sought to identify some of the challenges ahead in the translation of ω-3 PUFAs into addiction treatment.

Targeting n-3 Polyunsaturated Fatty Acids in Non-Alcoholic Fatty Liver Disease

BACKGROUND

Non-Alcoholic Fatty Liver Disease (NAFLD) is characterized by abnormal hepatic accumulation of triacylglycerides in the absence of alcohol consumption, in association with Oxidative Stress (OS), a pro-inflammatory state and Insulin Resistance (IR), which are attenuated by n-3 long-chain polyunsaturated Fatty Acids (FAs) C20-C22 (LCPUFAs) supplementation. Main causes of NAFLD comprise high caloric intake and a sedentary lifestyle, with high intakes of saturated FAs.

METHODS

The review includes several searches considering the effects of n-3 LCPUFAs in NAFLD in vivo and in vitro models, using the PubMed database from the National Library of Medicine- National Institutes of Health.

RESULT

The LCPUFAs eicosapentaenoic acid (C20:5 n-3, EPA) and docosahexaenoic acid (C22:6 n- 3, DHA) have a positive effect in diminishing liver steatosis, OS, and the levels of aspartate aminotransferase, alanine aminotransferase and pro-inflammatory cytokines, with improvement of insulin sensitivity and adiponectin levels. The molecular pathways described for n-3 LCPUFAs in cellular and animal models and humans include peroxisome proliferator-activated receptor-α activation favouring FA oxidation, diminution of lipogenesis due to sterol responsive element binding protein-1c downregulation and inflammation resolution. Besides, nuclear factor erythroid-2-related factor-2 activation is elicited by n-3 LCPUFA-derived oxidation products producing direct and indirect antioxidant responses, with concomitant anti-fibrogenic action.

CONCLUSION

The discussed effects of n-3 LCPUFA supplementation support its use in NAFLD, although having a limited value in NASH, a contention that may involve n-3 LCPUFA oxygenated derivatives. Clinical trials establishing optimal dosages, intervention times, type of patients and possible synergies with other natural products are needed in future studies.

Iron-induced derangement in hepatic Δ-5 and Δ-6 desaturation capacity and fatty acid profile leading to steatosis: Impact on extrahepatic tissues and prevention by antioxidant-rich extra virgin olive oil

The administration of iron induces liver oxidative stress and depletion of long-chain polyunsaturated fatty acids (LCPUFAs), n-6/n-3 LCPUFA ratio enhancement and fat accumulation, which may be prevented by antioxidant-rich extra virgin olive oil (AR-EVOO) supplementation. Male Wistar rats were subjected to a control diet (50 mg iron/kg diet) or iron-rich diet (IRD; 200 mg/kg diet) with alternate AR-EVOO for 21 days. Liver fatty acid (FA) analysis was performed by gas-liquid chromatography (GLC) after lipid extraction and fractionation, besides Δ-5 desaturase (Δ-5 D) and Δ6-D mRNA expression (qPCR) and activity (GLC) measurements. The IRD significantly (p < 0.05) increased hepatic total fat, triacylglycerols, free FA contents and serum transaminases levels, with diminution in those of n-6 and n-3 LCPUFAs, higher n-6/n-3 ratios, lower unsaturation index and Δ5-D and Δ6-D activities, whereas the mRNA expression of both desaturases was enhanced over control values, changes that were prevented by concomitant AR-EVOO supplementation. N-6 and n-3 LCPUFAs were also decreased by IRD in extrahepatic tissues and normalized by AR-EVOO. In conclusion, AR-EVOO supplementation prevents IRD-induced changes in parameters related to liver FA metabolism and steatosis, an effect that may have a significant impact in the treatment of iron-related pathologies or metabolic disorders such as non-alcoholic fatty liver disease.

The highly unnatural fatty acid profile of cells in culture

The fatty acid profile of cells in culture are unlike those of natural cells with twice the monounsaturated (MUFA) and half the polyunsaturated fatty acids (PUFA) level (Mol%). This is not due to cell lines primarily being derived from cancers but is due to limited access to lipid and an inability to make PUFA de novo as vertebrate cells. Classic culture methods use media with 10% serum (the only exogenous source of lipid). Fetal bovine serum (FBS), the serum of choice has a low level of lipid and cholesterol compared to other sera and at 10% of media provides 2-3% of the fatty acid and cholesterol, 1% of the PUFA and 0.3% of the essential fatty acid linoleic acid (18:2n-6) available to cells in the body. Since vertebrate cell lines cannot make PUFA they synthesise MUFA, offsetting their PUFA deficit and reducing their fatty acid diversity. Stem and primary cells in culture appear to be similarly affected, with a rapid loss of their natural fatty acid compositions. The unnatural lipid composition of cells in culture has substantial implications for examining natural stems cell in culture, and for investigations of cellular mechanisms using cell lines based on the pervasive influence of fats.

The effects of omega-3 fatty acid deficiency during development on oxidative fatty acid degradation during maturity in a mouse model of Alzheimer's disease

Metabolic conditions during brain development may have long-term consequences on brain metabolism, thereby influencing the risk of neurodegenerative disease in later life. To ascertain the long-term consequences of omega-3 (ω3) fatty acid deficiency during brain development on oxidative fatty acid degradation in the brain and the development of Alzheimer-like pathology, wild-type (WT) female mice were fed diets that were either replete or deficient in ω3 fatty acids for 5 weeks. These females were then mated with hemizygous 5xFAD male transgenic (TG) mouse models of Alzheimer's disease, and the progeny were continued on diets that were either ω3-replete or ω3-deficient. When the progeny were 6 months of age, they received radiolabeled arachidonic acid (ARA) by intracerebroventricular injection. Five days after these injections, the brains were harvested and oxidative degradation of the radiolabeled ARA was characterized. Among the progeny of female mice on an ω3-replete diet, TG progeny had lower PSD-95 expression and higher oxidative ARA degradation than WT progeny. Progeny on an ω3-deficient diet, however, had no significant differences in PSD-95 expression between TG and WT mice, or in the extent of ARA degradation. In TG mice, an ω3-deficient diet reduced oxidative ARA degradation to a greater extent than in WT mice. The reductions in oxidative ARA degradation occurred even if the progeny of female mice on an ω3-deficient diet resumed an ω3-replete diet immediately on weaning. These results demonstrate that dietary ω3 fatty acid deficiency during development can cause long-term changes in the expression of a synaptic marker and long-term reductions in the rate of ARA degradation in the WT brain, which are not completely alleviated by an ω3-replete diet after weaning. The elimination of differences between TG and WT mice by an ω3-deficient diet suggests that mechanisms regulating PSD-95 expression and the oxidative degradation of ARA are related and that the timing of dietary ω3 intake during development may influence Alzheimer's disease-related pathological changes later in 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.

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.

Metabolome-wide association study identified the association between a circulating polyunsaturated fatty acids variant rs174548 and lung cancer

Quantitative trait loci (QTLs) are widely used as instruments to infer causal risk factors of diseases based on the idea of mendelian randomization. Plasma metabolites can serve as risk factors of cancer, and the heritability of many circulating metabolites was high. We conducted a metabolome-wide association study (MWAS) to systematically investigate the effects of genetic variants on metabolites and lung cancer based on published genome-wide association study (GWASs) and metabolic-QTL (mQTL) study. Then we confirmed the results by subsequent genetic and metabolic validations and inferred the causal relationship between identified metabolites and lung cancer through genetic variant(s). We firstly identified six polyunsaturated fatty acids (PUFAs) represented by rs174548-linked haplotype were significantly associated with lung cancer risk in a Chinese GWAS (2311 cases and 3077 controls). Rs174548 was further confirmed to be associated with lung cancer in 13 821 Europeans and 18 471 Asians (ORmeta = 0.87, Pmeta = 1.76 × 10-15) and the effect was much stronger in females (Pinteraction = 6.00 × 10-4). We next validated rs174548-plasma PUFA association in 253 Chinese subjects (β = -0.57, P = 1.68 × 10-3). Rs174548 was also found associated with FADS1 (the major fatty acid desaturase of identified PUFAs) expression in liver tissues. Taken together, we found that rs174548 was associated with both PUFAs and lung cancer. Because rs174548 was the only mQTL variant of PUFAs reported by previous GWASs and explained a large proportion of heritability, we proposed that plasma PUFAs could be causally associated with lung cancer based on the idea of mendelian randomization. These findings provide a diet-related risk factor and may have important implications for prevention on lung cancer.

Maternal liver docosahexaenoic acid (DHA) stores are increased via higher serum unesterified DHA uptake in pregnant long Evans rats

Maternal docosahexaenoic acid (DHA, 22:6n-3) supplies the developing fetus during pregnancy; however, the mechanisms are unclear. We utilized pregnant rats to determine rates of DHA accretion, tissue unesterified DHA uptake and whole-body DHA synthesis-secretion. Female rats maintained on a DHA-free, 2% α-linolenic acid diet were either:1) sacrificed at 56 days for baseline measures, 2) mated and sacrificed at 14-18 days of pregnancy or 3) or sacrificed at 14-18 days as age-matched virgin controls. Maternal brain, adipose, liver and whole body fatty acid concentrations was determined for balance analysis, and kinetic modeling was used to determine brain and liver plasma unesterified DHA uptake and whole-body DHA synthesis-secretion rates. Total liver DHA was significantly higher in pregnant (95±5 μmol) versus non-pregnant (49±5) rats with no differences in whole-body DHA synthesis-secretion rates. However, liver uptake of plasma unesterified DHA was 3.8-fold higher in pregnant animals compared to non-pregnant controls, and periuterine adipose DHA was lower in pregnant (0.89±0.09 μmol/g) versus non-pregnant (1.26±0.06) rats. In conclusion, higher liver DHA accretion during pregnancy appears to be driven by higher unesterified DHA uptake, potentially via DHA mobilization from periuterine adipose for delivery to the fetus during the brain growth spurt.

Whole-Body Docosahexaenoic Acid Synthesis-Secretion Rates in Rats Are Constant across a Large Range of Dietary α-Linolenic Acid Intakes

BACKGROUND

Docosahexaenoic acid (DHA) is an ω-3 (n-3) polyunsaturated fatty acid (PUFA) thought to be important for brain function. Although the main dietary source of DHA is fish, DHA can also be synthesized from α-linolenic acid (ALA), which is derived from plants. Enzymes involved in DHA synthesis are also active toward ω-6 (n-6) PUFAs to synthesize docosapentaenoic acid n-6 (DPAn-6). It is unclear whether DHA synthesis from ALA is sufficient to maintain brain DHA.

OBJECTIVE

The objective of this study was to determine how different amounts of dietary ALA would affect whole-body DHA and DPAn-6 synthesis rates.

METHODS

Male Long-Evans rats were fed an ALA-deficient diet (ALA-D), an ALA-adequate (ALA-A) diet, or a high-ALA (ALA-H) diet for 8 wk from weaning. Dietary ALA concentrations were 0.07%, 3%, and 10% of the fatty acids, and ALA was the only dietary PUFA that differed between the diets. After 8 wk, steady-state stable isotope infusion of labeled ALA and linoleic acid (LA) was performed to determine the in vivo synthesis-secretion rates of DHA and DPAn-6.

RESULTS

Rats fed the ALA-A diet had an ∼2-fold greater capacity to synthesize DHA than did rats fed the ALA-H and ALA-D diets, and a DHA synthesis rate that was similar to that of rats fed the ALA-H diet. However, rats fed the ALA-D diet had a 750% lower DHA synthesis rate than rats fed the ALA-A and ALA-H diets. Despite enrichment into arachidonic acid, we did not detect any labeled LA appearing as DPAn-6.

CONCLUSIONS

Increasing dietary ALA from 3% to 10% of fatty acids did not increase DHA synthesis rates, because of a decreased capacity to synthesize DHA in rats fed the ALA-H diet. Tissue concentrations of DPAn-6 may be explained at least in part by longer plasma half-lives.

Reduction in the desaturation capacity of the liver in mice subjected to high fat diet: Relation to LCPUFA depletion in liver and extrahepatic tissues

α-Linolenic (ALA) and linoleic (LA) acids are precursors of long chain polyunsaturated fatty acids (LCPUFAs), FAs with important biochemical and physiological functions. In this process, desaturation reactions catalyzed by Δ5- and Δ6-desaturase play a major role, enzymes that are subjected to hormonal and dietary regulation. The aim of this study was to assess the influence of a high fat diet (HFD) on activity of liver Δ5 and Δ6 desaturases, in relation to LCPUFA composition in liver and extrahepatic tissues. Male C57BL/6J mice received control diet (CD) (10% fat, 20% protein and 70% carbohydrate) or high fat diet (HFD) (60% fat, 20% protein, and 20% carbohydrate) for 12 weeks. After this time, blood and liver samples were taken for metabolic, morphologic, inflammatory, oxidative stress and desaturase activity assessment, besides FA phospholipid analysis in erythrocytes, heart, adipose tissue and brain. HFD significantly increased hepatic total fat, triacylglycerides and free FA content with macrovesicular steatosis and oxidative stress enhancement, concomitantly with higher fasting serum glucose and insulin levels, HOMA, and serum cholesterol, triacylglycerols, TNF-α, and IL-6. Diminution in liver Δ5- and Δ6-desaturase activities and LCPUFA depletion were induced by HFD, the later finding being also observed in extrahepatic tissues. In conclusion, HFD-induced reduction in the bioavailability of liver LCPUFA is associated with defective desaturation of ALA and LA, with Δ5- and Δ6-desaturase activities being correlated with insulin resistance development. Data analyzed point to the liver as a major organ responsible for extrahepatic LCPUFA homeostasis, which is markedly deranged by HFD.

Novel function of vitamin E in regulation of zebrafish (Danio rerio) brain lysophospholipids discovered using lipidomics

We hypothesized that brains from vitamin E-deficient (E-) zebrafish (Danio rerio) would undergo increased lipid peroxidation because they contain highly polyunsaturated fatty acids, thus susceptible lipids could be identified. Brains from zebrafish fed for 9 months defined diets without (E-) or with (E+) added vitamin E (500 mg RRR-α-tocopheryl acetate per kilogram diet) were studied. Using an untargeted approach, 1-hexadecanoyl-2-docosahexaenoyl-sn-glycero-3-phosphocholine [DHA-PC 38:6, PC 16:0/22:6]was the lipid that showed the most significant and greatest fold-differences between groups. DHA-PC concentrations were approximately 1/3 lower in E- (4.3 ± 0.6 mg/g) compared with E+ brains (6.5 ± 0.9 mg/g, mean ± SEM, n = 10 per group, P = 0.04). Using lipidomics, 155 lipids in brain extracts were identified. Only four phospholipids (PLs) were different (P < 0.05) between groups; they were lower in E- brains and contained DHA with DHA-PC 38:6 at the highest abundances. Moreover, hydroxy-DHA-PC 38:6 was increased in E- brains (P = 0.0341) supporting the hypothesis of DHA peroxidation. More striking was the depletion in E- brains of nearly 60% of 19 different lysophospholipids (lysoPLs) (combined P = 0.0003), which are critical for membrane PL remodeling. Thus, E- brains contained fewer DHA-PLs, more hydroxy-DHA-PCs, and fewer lysoPLs, suggesting that lipid peroxidation depletes membrane DHA-PC and homeostatic mechanisms to repair the damage resulting in lysoPL depletion.

Pathways of polyunsaturated fatty acid utilization: implications for brain function in neuropsychiatric health and disease

Essential polyunsaturated fatty acids (PUFAs) have profound effects on brain development and function. Abnormalities of PUFA status have been implicated in neuropsychiatric diseases such as major depression, bipolar disorder, schizophrenia, Alzheimer's disease, and attention deficit hyperactivity disorder. Pathophysiologic mechanisms could involve not only suboptimal PUFA intake, but also metabolic and genetic abnormalities, defective hepatic metabolism, and problems with diffusion and transport. This article provides an overview of physiologic factors regulating PUFA utilization, highlighting their relevance to neuropsychiatric disease.

Fatty acid desaturase 1 gene polymorphisms control human hepatic lipid composition

Fatty acid desaturase (FADS) genes and their variants have been associated with multiple metabolic phenotypes, including liver enzymes and hepatic fat accumulation, but the detailed mechanism remains unclear. We aimed to delineate the role of FADSs in modulating lipid composition in human liver. We performed a targeted lipidomic analysis of a variety of phospholipids, sphingolipids, and ceramides among 154 human liver tissue samples. The associations between previously genome-wide association studies (GWASs)-identified six FADS single-nucleotide polymorphisms (SNPs), and these lipid levels as well as total hepatic fat content (HFC) were tested. The potential function of these SNPs in regulating transcription of three FADS genes (FADS1, FADS2, and FADS3) in the locus was also investigated. We found that though these SNPs were in high linkage disequilibrium (r(2) > 0.8), the rare alleles of these SNPs were consistently and significantly associated with the accumulation of multiple long-chain fatty acids (LCFAs), with C47H85O13P (C36:4), a phosphatidylinositol (PI), and C43H80O8PN (C38:3), a phosphatidylethanolamine (PE), reached the Bonferroni corrected significance (P < 3 × 10(-4)). Meanwhile, these SNPs were significantly associated with increased ratios between the more saturated and relatively less saturated forms of LCFAs, especially between PEs, PIs, and phosphatidylcholines (PCs; P ≤ 3.5 × 10(-6)). These alleles were also associated with increased total HFC (P < 0.05). Further analyses revealed that these alleles were associated with decreased hepatic expression of FADS1 (P = 0.0018 for rs174556), but not FADS2 or FADS3 (P > 0.05).

CONCLUSION

Our findings revealed critical insight into the mechanism underlying FADS1 and its polymorphisms in modulating hepatic lipid deposition by altering gene transcription and controlling lipid composition in human livers.

Whole body synthesis rates of DHA from α-linolenic acid are greater than brain DHA accretion and uptake rates in adult rats

Docosahexaenoic acid (DHA) is important for brain function, however, the exact amount required for the brain is not agreed upon. While it is believed that the synthesis rate of DHA from α-linolenic acid (ALA) is low, how this synthesis rate compares with the amount of DHA required to maintain brain DHA levels is unknown. The objective of this work was to assess whether DHA synthesis from ALA is sufficient for the brain. To test this, rats consumed a diet low in n-3 PUFAs, or a diet containing ALA or DHA for 15 weeks. Over the 15 weeks, whole body and brain DHA accretion was measured, while at the end of the study, whole body DHA synthesis rates, brain gene expression, and DHA uptake rates were measured. Despite large differences in body DHA accretion, there was no difference in brain DHA accretion between rats fed ALA and DHA. In rats fed ALA, DHA synthesis and accretion was 100-fold higher than brain DHA accretion of rats fed DHA. Also, ALA-fed rats synthesized approximately 3-fold more DHA than the DHA uptake rate into the brain. This work indicates that DHA synthesis from ALA may be sufficient to supply the brain.

Potential treatment of human nonalcoholic fatty liver disease with long-chain omega-3 polyunsaturated fatty acids

Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disorder in the Western world. Its prevalence has increased with the growing obesity epidemic, yet no definitive treatment has been developed, and optimal management remains a clinical challenge. Long-chain omega-3 polyunsaturated fatty acids (PUFAs) have recently been proposed as a potential treatment for liver inflammation associated with fat accumulation. PubMed literature and the ClinicalTrials.gov database were reviewed for the effects of omega-3 PUFA treatment on NAFLD, from mechanisms to the results of preclinical studies, human studies, and unreported ongoing clinical trials, using terms such as NAFLD, nonalcoholic steatohepatitis, omega-3 fatty acids, and fish oil. Articles published over the last 3-4 years were emphasized, and relevancy was ensured by scanning their abstracts. Preliminary studies have confirmed an ameliorative effect, yet the translation of promising early data into therapeutic interventions will have to await the results of larger, properly conducted, ongoing clinical trials.

Treatment of ovariectomized rats with 17β-estradiol increases hepatic delta-6 desaturase enzyme expression and docosahexaenoic acid levels in hepatic and plasma phospholipids

Higher docosahexaenoic acid (DHA) in females compared with males suggests ovarian hormones increase DHA production. Eight-week old rats were ovariectomized or sham operated (SHAM), and ovariectomized rats were treated with implanted pellets providing 17β-estradiol (OVX+E), progesterone (OVX+P), both (OVX+PE) or neither (OVX) for 14 days. Immunoblot and fatty acid analysis were performed on all samples, and microarray analysis was performed on OVX and SHAM groups. Increased Δ6-desaturase in OVX relative to SHAM was observed by microarray (12% higher) and immunoblot (31% higher). OVX+E and OVX+PE rats had 39% and 42% higher Δ6-desaturase content, respectively, compared with OVX. OVX+E and OVX+PE also increased phospholipid DHA concentrations in liver (increase of 34% and 40%, respectively) and plasma (increase of 70% and 74%, respectively) relative to OVX. Progesterone exerted no effect on Δ6-desaturase or DHA. These results indicate that 17β-estradiol increases DHA through increased Δ6-desaturase, possibly explaining sex differences in DHA.

Aging decreases rate of docosahexaenoic acid synthesis-secretion from circulating unesterified α-linolenic acid by rat liver

Docosahexaenoic acid (DHA, 22:6n-3), an n-3 polyunsaturated fatty acid (PUFA) found at high concentrations in brain and retina and critical to their function, can be obtained from fish products or be synthesized from circulating α-linolenic acid (α-LNA, 18:3n-3) mainly in the liver. With aging, liver synthetic enzymes are reported reduced or unchanged in the rat. To test whether liver synthesis-secretion of DHA from α-LNA changes with age, we measured whole-body DHA conversion coefficients and rates in unanesthetized adult male Fischer-344 rats aged 10, 20, or 30 months, fed an eicosapentaenoic acid (EPA, 20:5n-3)- and DHA-containing diet. Unesterified [U- (13) C]α-LNA bound to albumin was infused intravenously for 2 h, while [(13) C]-esterified n-3 PUFAs were measured in arterial plasma, as were unlabeled unesterified and esterified PUFA concentrations. Plasma unesterified n-3 PUFA concentrations declined with age, but esterified n-3 PUFA concentrations did not change significantly. Calculated conversion coefficients were not changed significantly with age, whereas synthesis-secretion rates (product of conversion coefficient and unesterified plasma α-LNA concentration) of esterified DHA and n-3 DPA were reduced. Turnovers of esterified n-3 PUFAs in plasma decreased with age, whereas half-lives increased. The results suggest that hepatic capacity to synthesize DHA and other n-3 PUFAs from circulating α-LNA is maintained with age in the rat, but that reduced plasma α-LNA availability reduces net synthesis-secretion. As unesterified plasma DHA is the form that is incorporated preferentially into brain phospholipid, its reduced synthesis may be deleterious to brain function in aged rats.

Altered fatty acid concentrations in prefrontal cortex of schizophrenic patients

BACKGROUND

Disturbances in prefrontal cortex phospholipid and fatty acid composition have been reported in patients with schizophrenia (SCZ), often as an incomplete lipid profile or a percent of total lipid concentration. In this study, we quantified absolute concentrations (nmol/g wet weight) and fractional concentrations (i.e. percent of total fatty acids) of several lipid classes and their constituent fatty acids in postmortem prefrontal cortex of SCZ patients (n = 10) and age-matched controls (n = 10).

METHODS

Lipids were extracted, fractionated with thin layer chromatography and assayed.

RESULTS

Mean total lipid, phospholipid, individual phospholipids, plasmalogen, triglyceride and cholesteryl ester concentrations did not differ significantly between the groups. Compared to controls, SCZ brains showed significant increases in several monounsaturated and polyunsaturated fatty acid absolute concentrations in cholesteryl ester. Significant increases or decreases occurred in palmitoleic, linoleic, γ-linolenic and n-3 docosapentaenoic acid absolute concentrations in total lipids, triglycerides or phospholipids. Changes in fractional concentrations did not consistently reflect absolute concentration changes.

CONCLUSION

These findings suggest disturbed prefrontal cortex fatty acid absolute concentrations, particularly within cholesteryl esters, as a pathological aspect of schizophrenia.

Plasticity of mouse brain docosahexaenoic acid: modulation by diet and age

Decreases in brain docosahexaenoic acid (DHA) have been associated with losses in brain function leading to an interest in the conditions which lead to such brain decreases, and such variables as age. Also of relevance would be the rate of repletion of DHA when the n-3 dietary deficiency is reversed. This experiment describes dietary deficiency in n-3 fatty acids induced in weanling (3 week) and young adult (7 week) mice. There was an immediate and continuous loss of brain DHA with similar rates in the two age groups. Serum DHA declined more rapidly in younger animals with respect to similarly treated adults. Brain and serum docosapentaenoic acid (DPAn-6) increased more rapidly and to higher levels in the younger animals. A second experiment determined the rates of normalization of brain fatty acid profiles when alpha-linolenic acid was added to the diets of n-3 deficient mice. Brain DHA recovery occurred at a faster rate (half-time, T 1/2 = 1.4 weeks) when begun at weaning relative to young adult mice (T 1/2 = 3.5 weeks). Correspondingly, brain DPAn-6 recovered faster in the younger animals; the adult group had a half-time of more than twice that of the 3-week old group. This study therefore demonstrates that the young adult mouse brain DHA is somewhat plastic and can be partially depleted via a low n-3 fatty acid diet and subsequently restored when dietary n-3 fatty acids are repleted. Relevance of these findings for human nutrition is discussed.

Translational studies on regulation of brain docosahexaenoic acid (DHA) metabolism in vivo

One goal in the field of brain polyunsaturated fatty acid (PUFA) metabolism is to translate the many studies that have been conducted in vitro and in animal models to the clinical setting. Doing so should elucidate the role of PUFAs in the human brain, and effects of diet, drugs, disease and genetics on this role. This review discusses new in vivo radiotracer kinetic and neuroimaging techniques that allow us to do this, with a focus on docosahexaenoic acid (DHA). We illustrate how brain PUFA metabolism is influenced by graded reductions in dietary n-3 PUFA content in unanesthetized rats. We also show how kinetic tracer techniques in rodents have helped to identify mechanisms of action of mood stabilizers used in bipolar disorder, how DHA participates in neurotransmission, and how brain DHA metabolism is regulated by calcium-independent iPLA₂β. In humans, regional rates of brain DHA metabolism can be quantitatively imaged with positron emission tomography following intravenous injection of [1-¹¹C]DHA.

Tissue-specific sex differences in docosahexaenoic acid and Δ6-desaturase in rats fed a standard chow diet

Docosahexaenoic acid (DHA, 22:6n-3) is higher in the blood and tissues of females relative to males, but the underlying mechanism is not clear. The present study examined the expression of enzymes involved in the biosynthesis of DHA from short-chain n-3 polyunsaturated fatty acids in male and female rats (n = 6 for each sex). Rats were maintained on an AIN-93G diet and sacrificed at 14 weeks of age after an overnight fast. Plasma, erythrocytes, liver, heart, and brain were collected for fatty acid composition analysis and the determination of enzyme and transcription factor expression by RT-PCR and immunoblotting. Females had higher DHA concentrations in the total lipids of liver, plasma, erythrocyte, and heart (53%, 75%, 36%, and 25% higher, respectively, compared with males) with no sex differences in brain DHA concentrations. The mRNA content of Δ5-desaturase, Δ6-desaturase, and elongase 2 was 1.0-, 1.4-, and 1.1-fold higher, respectively, in the livers of female rats compared with males, with no differences in the hearts or brains. The protein content of Δ6-desaturase was also higher in females. Higher hepatic mRNA of sterol-regulatory element-binding protein 1-c and estrogen receptor α in the females suggests that lipogenic and estrogen signaling mechanisms are involved. The sex difference in DHA concentration is tissue specific and is associated with higher Δ6-desaturase expression in females relative to males, which appears to be limited to the liver.

Altered lipid concentrations of liver, heart and plasma but not brain in HIV-1 transgenic rats

Disturbed lipid metabolism has been reported in antiretroviral-naive HIV-1-infected patients suggesting a direct effect of the virus on lipid metabolism. To test that the HIV-1 virus alone could alter lipid concentrations, we measured these concentrations in an HIV-1 transgenic (Tg) rat model of human HIV-1 infection, which demonstrates peripheral and central pathology by 7-9 months of age. Concentrations were measured in high-energy microwaved heart, brain and liver from 7-9 month-old HIV-1 Tg and wildtype rats, and in plasma from non-microwaved rats. Plasma triglycerides and liver cholesteryl ester and total cholesterol concentrations were significantly higher in HIV-1 Tg rats than controls. Heart and plasma fatty acid concentrations reflected concentration differences in liver, which showed higher n-3 and n-6 polyunsaturated fatty acid (PUFA) concentrations in multiple lipid compartments. Fatty acid concentrations were increased or decreased in heart and liver phospholipid subfractions. Brain fatty acid concentrations differed significantly between the groups for minor fatty acids such as linoleic acid and n-3 docosapentaenoic acid. The profound changes in heart, plasma and liver lipid concentrations suggest a direct effect of chronic exposure to the HIV-1 virus on peripheral lipid (including PUFA) metabolism.

Omega-3 fatty acid supplementation and cardiovascular disease

Epidemiological studies on Greenland Inuits in the 1970s and subsequent human studies have established an inverse relationship between the ingestion of omega-3 fatty acids [C(20-22) ω 3 polyunsaturated fatty acids (PUFA)], blood levels of C(20-22) ω 3 PUFA, and mortality associated with cardiovascular disease (CVD). C(20-22) ω 3 PUFA have pleiotropic effects on cell function and regulate multiple pathways controlling blood lipids, inflammatory factors, and cellular events in cardiomyocytes and vascular endothelial cells. The hypolipemic, anti-inflammatory, anti-arrhythmic properties of these fatty acids confer cardioprotection. Accordingly, national heart associations and government agencies have recommended increased consumption of fatty fish or ω 3 PUFA supplements to prevent CVD. In addition to fatty fish, sources of ω 3 PUFA are available from plants, algae, and yeast. A key question examined in this review is whether nonfish sources of ω 3 PUFA are as effective as fatty fish-derived C(20-22) ω 3 PUFA at managing risk factors linked to CVD. We focused on ω 3 PUFA metabolism and the capacity of ω 3 PUFA supplements to regulate key cellular events linked to CVD. The outcome of our analysis reveals that nonfish sources of ω 3 PUFA vary in their capacity to regulate blood levels of C(20-22) ω 3 PUFA and CVD risk factors.

Gabapentin's minimal action on markers of rat brain arachidonic acid metabolism agrees with its inefficacy against bipolar disorder

In rats, FDA-approved mood stabilizers used for treating bipolar disorder (BD) selectively downregulate brain markers of the arachidonic acid (AA) cascade, which are upregulated in postmortem BD brain. Phase III clinical trials show that the anticonvulsant gabapentin (GBP) is ineffective in treating BD. We hypothesized that GBP would not alter the rat brain AA cascade. Chronic GBP (10 mg/kg body weight, injected i.p. for 30 days) compared to saline vehicle did not significantly alter brain expression or activity of AA-selective cytosolic phospholipase A(2) (cPLA(2)) IVA or secretory (s)PLA(2) IIA, activity of cyclooxygenase-2, or prostaglandin E(2) or thromboxane B(2) concentrations. Plasma esterified and unesterified AA concentration was unaffected. These results, taken with evidence of an upregulated AA cascade in the BD brain and that approved mood stabilizers downregulate the rat brain AA cascade, support the hypothesis that effective anti-BD drugs act by targeting the brain AA cascade whereas ineffective drugs (such as GBP) do not target this pathway, and suggest that the rat model might be used for screening new anti-BD drugs.

Effects of oestradiol on brain lipid class and Fatty Acid composition: comparison between pregnant and ovariectomised oestradiol-treated rats

To determine the involvement of physiological doses of oestradiol on brain lipid composition, we have analysed the lipid class and fatty acid composition of phospholipids in the brain from pregnant and 17β-oestradiol-treated rats. Rats were randomly divided into three groups: ovariectomised control (OVX + VEH), ovariectomised oestradiol-treated (OVX + E(2) ) and pregnant (PREG) rats. Rats from the OVX + E(2) group were injected daily with different doses of 17β-oestradiol mimicking the plasma levels observed during pregnancy. Analyses of brain lipid class composition showed that physiological doses of oestradiol increased cholesterol levels of the OVX + E(2) group compared to the OVX + VEH group. It was also found that cholesterol levels in the PREG group were significantly lower than in the OVX + VEH and OVX + E(2) groups, indicating the involvement of gestational hormones other than oestradiol in the regulation of brain cholesterol during pregnancy. Brains from pregnant rats also exhibited reduced levels of plasmalogens and saturated fatty acids compared to the ovariectomised groups, especially in the second half of pregnancy. Interestingly, analyses of fatty acid composition of phospholipids revealed that physiological doses of oestradiol increased brain docosahexaenoic acid (DHA; 22:6 n-3) levels. Moreover, DHA levels in pregnant rats were similar to those observed in the OVX + E(2) group at all stages, suggesting that oestradiol is the main hormone in the regulation of brain DHA levels during pregnancy. Liver appears to be the major source for n-3 and n-6 long chain polyunsaturated fatty acids (LCPUFAs) DHA and arachidonic acid, which are released and transported to the maternal brain and the developing foetus under the influence of oestrogens. We also observed that the largest depots of n-3 and n-6 LCPUFA precursors (linolenic acid and linoleic acid, respectively) occur in adipose tissue triglycerides, which, in turn are significantly increased during pregnancy. Our observations are in accordance with an oestradiol-induced increased bioavailability of brain DHA in pregnant rats. We hypothesise that the reduction of maternal brain DHA observed at the end of pregnancy is a result of the very high demand DHA of foetal brain, which overcomes the maximal maternal (and likely foetal) capacity for de novo DHA synthesis in the liver and brain.

The fraction of α-linolenic acid present in the sn-2 position of structured triacylglycerols decreases in lymph chylomicrons and plasma triacylglycerols during the course of lipid absorption in rats

Little is known about the ability of α-linolenic acid (Ln) to remain in the sn-2 position of TG during the absorption process. The goal of this study was to determine the Ln distribution in the lymph (Study 1) and plasma (Study 2) TG of rats fed a single i.g. load of structured TG [300 mg/rat of either oleic acid (O)/Ln/O TG (OLnO) or Ln/O/O TG (LnOO), n = 7 rats]. In an early fraction (3-4 h) of lymph (OLnO group; 100% Ln in the sn-2 position), 46 ± 2% Ln was maintained in this position in lymph TG. There was even less (29 ± 6%) in the last fraction (7-24 h) (P < 0.05). Ln was also found (9 ± 3%) in the sn-2 position of lymph TG in the LnOO group. The Ln content in lymph phospholipids was twice as high in rats when they were fed LnOO (4.2 ± 0.1%) than OLnO (2.3 ± 0.2%) (P < 0.005). Six hours postprandially (Study 2), 21 ± 3% of the Ln incorporated into plasma TG was located in the sn-2 position in the OLnO group compared to 13 ± 2% in the LnOO group (P < 0.001). Overall, these results indicate that the amount of Ln that moved from the sn-2 position of structured TG to the sn-1(3) position of lymph TG increased during absorption. This may account for a substantial hydrolysis of the 2-monolinolenylglycerols in enterocytes, leading to the intramolecular redistribution of Ln in lymph TG and, consequently, in plasma TG.

Docosahexaenoic acid signalolipidomics in nutrition: significance in aging, neuroinflammation, macular degeneration, Alzheimer's, and other neurodegenerative diseases

Essential polyunsaturated fatty acids (PUFAs) are critical nutritional lipids that must be obtained from the diet to sustain homeostasis. Omega-3 and -6 PUFAs are key components of biomembranes and play important roles in cell integrity, development, maintenance, and function. The essential omega-3 fatty acid family member docosahexaenoic acid (DHA) is avidly retained and uniquely concentrated in the nervous system, particularly in photoreceptors and synaptic membranes. DHA plays a key role in vision, neuroprotection, successful aging, memory, and other functions. In addition, DHA displays anti-inflammatory and inflammatory resolving properties in contrast to the proinflammatory actions of several members of the omega-6 PUFAs family. This review discusses DHA signalolipidomics, comprising the cellular/tissue organization of DHA uptake, its distribution among cellular compartments, the organization and function of membrane domains rich in DHA-containing phospholipids, and the cellular and molecular events revealed by the uncovering of signaling pathways regulated by DHA and docosanoids, the DHA-derived bioactive lipids, which include neuroprotectin D1 (NPD1), a novel DHA-derived stereoselective mediator. NPD1 synthesis agonists include neurotrophins and oxidative stress; NPD1 elicits potent anti-inflammatory actions and prohomeostatic bioactivity, is anti-angiogenic, promotes corneal nerve regeneration, and induces cell survival. In the context of DHA signalolipidomics, this review highlights aging and the evolving studies on the significance of DHA in Alzheimer's disease, macular degeneration, Parkinson's disease, and other brain disorders. DHA signalolipidomics in the nervous system offers emerging targets for pharmaceutical intervention and clinical translation.

Hypothalamic gene expression in ω-3 PUFA-deficient male rats before, and following, development of hypertension

Dietary deficiency of ω-3 fatty acids (ω-3 DEF) produces hypertension in later life. This study examined the effect of ω-3 DEF on blood pressure and hypothalamic gene expression in young rats, before the development of hypertension, and in older rats following the onset of hypertension. Animals were fed experimental diets that were deficient in ω-3 fatty acids, sufficient in short-chain ω-3 fatty acids or sufficient in short- and long-chain ω-3 fatty acids, from the prenatal period until 10 or 36 weeks-of-age. There was no difference in blood pressure between groups at 10 weeks-of-age; however, at 36 weeks-of-age ω-3 DEF animals were hypertensive in relation to sufficient groups. At 10 weeks, expression of angiotensin-II(1A) receptors and dopamine D(3) receptors were significantly increased in the hypothalamic tissue of ω-3 DEF animals. In contrast, at 36 weeks, α(2a) and β(1) adrenergic receptor expression was significantly reduced in the ω-3 DEF group. Brain docosahexaenoic acid was significantly lower in ω-3 DEF group compared with sufficient groups. This study demonstrates that dietary ω-3 DEF causes changes both in the expression of key genes involved in central blood pressure regulation and in blood pressure. The data may indicate that hypertension resulting from ω-3 DEF is mediated by the central adrenergic system.

Docosahexaenoic acid (DHA) incorporation into the brain from plasma, as an in vivo biomarker of brain DHA metabolism and neurotransmission

Docosahexaenoic acid (DHA) is critical for maintaining normal brain structure and function, and is considered neuroprotective. Its brain concentration depends on dietary DHA content and hepatic conversion from its dietary derived n-3 precursor, α-linolenic acid (α-LNA). We have developed an in vivo method in rats using quantitative autoradiography and intravenously injected radiolabeled DHA to image net incorporation into the brain of unesterified plasma DHA, and showed with this method that the incorporation rate of DHA equals the rate of brain metabolic DHA consumption. The method has been extended for use in humans with positron emission tomography (PET). Furthermore, imaging in unanesthetized rats using DHA incorporation as a biomarker in response to acute N-methyl-D-aspartate administration confirms that regional DHA signaling is independent of extracellular calcium, and likely mediated by a calcium-independent phospholipase A(2) (iPLA(2)). Studies in mice in which iPLA(2)-VIA (β) was knocked out confirmed that this enzyme is critical for baseline and muscarinic cholinergic signaling involving DHA. Thus, quantitative imaging of DHA incorporation from plasma into brain can be used as an in vivo biomarker of brain DHA metabolism and neurotransmission.