Sex-dependent differences in tissue and blood n-3 PUFA levels following ALA or ALA + DHA feeding of liver-specific Elovl2-KO and control mice

Docosahexaenoic acid (DHA, 22:6n-3) must be consumed from the diet or synthesized from polyunsaturated fatty acid (PUFA) precursors, such as α-linolenic acid (ALA, 18:3n-3). Elongase 2 (encoded by Elovl2 gene) catalyzes two elongation reactions in the PUFA biosynthesis pathway and may be important in regulating the observed sex differences in n-3 PUFA levels. Our aim was to determine how targeted knockout of liver Elovl2 affects tissue and blood n-3 PUFA levels in male and female C57BL/6J mice. Twenty-eight-day old male and female liver Elovl2-KO and control mice were placed onto one of two dietary protocols for a total of 8 weeks (4-8 mice per genotype, per diet, per sex): 1) an 8-week 2 % ALA in total fat diet or 2) a 4-week 2 % ALA diet followed by a 4-week 2 % ALA + 2 % DHA diet. Following this 8-week feeding period, 12-week-old mice were sacrificed and serum, red blood cells (RBC), liver, heart and brain were collected and fatty acid levels measured. Significant interaction effects (p < 0.05, sex x genotype) for serum, RBC, liver and heart DHA levels were identified. In serum and liver, DHA levels were significantly different (p < 0.01) between all groups with male controls > female controls > female KO > male KO in serum and female controls > male controls > female KO > male KO in liver. In RBCs and the heart, female controls = male controls > female KO > male KO (p < 0.001). The addition of DHA to diet removed the interaction effects on DHA levels in the serum, liver and heart, yielding a significant sex effect in serum, liver (female > male, p < 0.01) and brain (male > female, p < 0.05) and genotype effect in serum and heart (control > KO, p < 0.05). Ablation of liver Elovl2 results in significantly lower blood and tissue DHA in a sex-dependent manner, suggesting a role for Elovl2 on sex differences in n-3 PUFA levels.

Dietary docosahexaenoic acid (DHA) downregulates liver DHA synthesis by inhibiting eicosapentaenoic acid elongation

DHA is abundant in the brain where it regulates cell survival, neurogenesis, and neuroinflammation. DHA can be obtained from the diet or synthesized from alpha-linolenic acid (ALA; 18:3n-3) via a series of desaturation and elongation reactions occurring in the liver. Tracer studies suggest that dietary DHA can downregulate its own synthesis, but the mechanism remains undetermined and is the primary objective of this manuscript. First, we show by tracing 13C content (δ13C) of DHA via compound-specific isotope analysis, that following low dietary DHA, the brain receives DHA synthesized from ALA. We then show that dietary DHA increases mouse liver and serum EPA, which is dependant on ALA. Furthermore, by compound-specific isotope analysis we demonstrate that the source of increased EPA is slowed EPA metabolism, not increased DHA retroconversion as previously assumed. DHA feeding alone or with ALA lowered liver elongation of very long chain (ELOVL2, EPA elongation) enzyme activity despite no change in protein content. To further evaluate the role of ELOVL2, a liver-specific Elovl2 KO was generated showing that DHA feeding in the presence or absence of a functional liver ELOVL2 yields similar results. An enzyme competition assay for EPA elongation suggests both uncompetitive and noncompetitive inhibition by DHA depending on DHA levels. To translate our findings, we show that DHA supplementation in men and women increases EPA levels in a manner dependent on a SNP (rs953413) in the ELOVL2 gene. In conclusion, we identify a novel feedback inhibition pathway where dietary DHA downregulates its liver synthesis by inhibiting EPA elongation.

Blood and tissue docosahexaenoic acid (DHA, 22:6n-3) turnover rates from Ahiflower® oil are not different than from DHA ethyl ester oil in a diet switch mouse model

Ahiflower® oil is high in α-linolenic and stearidonic acids, however, tissue/blood docosahexaenoic acid (DHA, 22:6n-3) turnover from dietary Ahiflower oil has not been investigated. In this study, we use compound-specific isotope analysis to determine tissue DHA synthesis/turnover from Ahiflower, flaxseed and DHA oils. Pregnant BALB/c mice (13-17 days) were placed on a 2 % algal DHA oil diet of high carbon-13 content (δ13C) and pups (n = 132) were maintained on the diet until 9 weeks old. Mice were then randomly allocated to a low δ13C-n-3 PUFA diet of either: 1) 4 % Ahiflower oil, 2) 4.35 % flaxseed oil or 3) 1 % fish DHA ethyl ester oil for 1, 3, 7, 14, 30, 60 or 120 days (n = 6). Serum, liver, adipose and brains were collected and DHA levels and δ13C were determined. DHA concentrations were highest (p < 0.05) in the liver and adipose of DHA-fed animals with no diet differences in serum or brain (p > 0.05). Based on the presence or absence of overlapping 95 % C.I.'s, DHA half-lives and synthesis/turnover rates were not different between Ahiflower and DHA diets in the liver, adipose or brain. DHA half-lives and synthesis/turnover rates from flaxseed oil were significantly slower than from the DHA diet in all serum/tissues. These findings suggest that the distinct Ahiflower oil n-3 PUFA composition could support tissue DHA needs at a similar rate to dietary DHA, making it a unique plant-based dietary option for maintaining DHA turnover comparably to dietary DHA.

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.

Dietary triacetin, but not medium chain triacylglycerides, blunts weight gain in diet-induced rat model of obesity

Consumption of a Western diet (WD) is known to increase the risk of obesity. Short or medium chain fatty acids influence energy metabolism, and triacetin, a synthetic short chain triacylglyceride, has been shown to lower body fat under normal conditions. This study aimed to investigate if triacetin as part of a WD modifies rat weight and body fat. Male rats were fed a control diet or WD for 8 weeks. At week 8, rats in the WD group were maintained on a WD diet or switched to a WD diet containing 30% energy from medium-chain triacylglyceride (WD-MCT) or triacetin (WD-T) for another 8 weeks. At week 16, rats were euthanized and liver, adipose and blood were collected. Tissue fatty acids (FAs) were quantified by gas chromatography (GC) and hepatic FAs were measured by GC-combustion-isotope ratio mass spectrometry for δ13 C-palmitic acid (PAM)-a novel marker of de novo lipogenesis (DNL). Rats fed WD-T had a body weight not statistically different to the control group, and gained less body weight than rats fed WD alone. Furthermore, WD-T fed rats had a lower fat mass, and lower total liver and plasma FAs compared to the WD group. Rats fed WD-T did not differ from WD in blood ketone or glucose levels, however, had a significantly lower hepatic δ13 C-PAM value than WD fed rats; suggestive of lower DNL. In summary, we show that triacetin has the potential to blunt weight gain and adipose tissue accumulation in a rodent model of obesity, possibly due to a decrease in DNL.

Analysis of omega-3 and omega-6 polyunsaturated fatty acid metabolism by compound-specific isotope analysis in humans

Natural variations in the 13C:12C ratio (carbon-13 isotopic abundance [δ13C]) of the food supply have been used to determine the dietary origin and metabolism of fatty acids, especially in the n-3 PUFA biosynthesis pathway. However, n-6 PUFA metabolism following linoleic acid (LNA) intake remains under investigation. Here, we sought to use natural variations in the δ13C signature of dietary oils and fatty fish to analyze n-3 and n-6 PUFA metabolism following dietary changes in LNA and eicosapentaenoic acid (EPA) + DHA in adult humans. Participants with migraine (aged 38.6 ± 2.3 years, 93% female, body mass index of 27.0 ± 1.1 kg/m2) were randomly assigned to one of three dietary groups for 16 weeks: 1) low omega-3, high omega-6 (H6), 2) high omega-3, high omega-6 (H3H6), or 3) high omega-3, low omega-6 (H3). Blood was collected at baseline, 4, 10, and 16 weeks. Plasma PUFA concentrations and δ13C were determined. The H6 intervention exhibited increases in plasma LNA δ13C signature over time; meanwhile, plasma LNA concentrations were unchanged. No changes in plasma arachidonic acid δ13C or concentration were observed. Participants on the H3H6 and H3 interventions demonstrated increases in plasma EPA and DHA concentration over time. Plasma δ13C-EPA increased in total lipids of the H3 group and phospholipids of the H3H6 group compared with baseline. Compound-specific isotope analysis supports a tracer-free technique that can track metabolism of dietary fatty acids in humans, provided that the isotopic signature of the dietary source is sufficiently different from plasma δ13C.

Novel 13C enrichment technique reveals early turnover of DHA in peripheral tissues

The brain is rich in DHA, which plays important roles in regulating neuronal function. Recently, using compound-specific isotope analysis (CSIA) that takes advantage of natural differences in carbon-13 content (¹³C/¹²C ratio or δ¹³C) of the food supply, we determined the brain DHA half-life. However, due to methodological limitations, we were unable to capture DHA turnover rates in peripheral tissues. In the current study, we applied CSIA via high-precision gas chromatography combustion isotope ratio mass spectrometry (GC/C/IRMS) to determine half-lives of brain, liver, and plasma DHA in mice following a dietary switch experiment. To model DHA tissue turnover rates in peripheral tissues, we added earlier timepoints within the diet switch study and took advantage of natural variations in the δ¹³C-DHA of algal and fish DHA sources to maintain DHA pool sizes and used an enriched (uniformly labeled ¹³C) DHA treatment. Mice were fed a fish-DHA diet (control) for 3 months, then switched to an algal-DHA treatment diet, the ¹³C enriched-DHA treatment diet, or they stayed on the control diet for the remainder of the study time course. In mice fed the algal and ¹³C enriched-DHA diets, the brain DHA half-life was 47 and 46 days, the liver half-life was 5.6 and 7.2 days, and the plasma half-life was 4.7 and 6.4 days respectively. By using improved methodologies, we calculated DHA turnover rates in the liver and plasma, and our study for the first time, by using an artificially enriched DHA source (very high δ¹³C), validated its utility in diet switch studies.

Increases in plasma n-3 tetracosapentaenoic acid and tetracosahexaenoic acid following 12 weeks of EPA, but not DHA, supplementation in women and men

Dietary feeding and stable isotope studies in rodents support that the 24-carbon omega-3 polyunsaturated fatty acids, tetracosapentaenoic acid (24:5n-3, TPAn-3) and tetracosahexaenoic acid (24:6n-3, THA), are immediate precursors to docosahexaenoic acid (DHA, 22:6n-3). In this study, we assessed for the first time, changes in TPAn-3 or THA levels following omega-3 PUFA supplementation in humans, providing insight into human omega-3 PUFA metabolism. In this secondary analysis of a double-blind randomized control trial, women and men (19 - 30 years, n = 10 - 14 per sex, per diet) were supplemented with 3 g/day EPA, DHA, or olive oil control for 12 weeks. Plasma TPAn-3 and THA concentrations were determined by gas chromatography-mass spectrometry to determine changes following supplementation in a sex-specific manner (sex x time). EPA supplementation significantly increased (p < 0.0001) plasma TPAn-3 by 215% (1.3 ± 0.1 - 4.1 ± 0.7, nmol/mL ± SEM) and THA by 112% (1.7 ± 0.2 - 3.6 ± 0.5, nmol/mL ± SEM). Furthermore, women had 111% and 99% higher plasma TPAn-3 and THA in the EPA supplemented group compared to men (p < 0.0001). There were no significant effects of time on plasma TPAn-3 or THA concentrations in the DHA supplemented or olive oil supplemented groups. In conclusion, EPA, but not DHA, supplementation in humans increased plasma TPAn-3 and THA levels, suggesting that THA accumulates prior to conversion to DHA in the n-3 PUFA synthesis pathway. Furthermore, women generally exhibit higher plasma TPAn-3 and THA concentrations compared with men, suggesting that women have a greater ability to accumulate 24-carbon n-3 PUFA in plasma via EPA and DPAn-3 elongation, which may explain the known higher DHA levels in women. Summary: In this secondary analysis of a double-blind randomized control trial, we assessed changes in omega-3 (n-3) tetracosapentaenoic acid (24:5n-3, TPAn-3) and tetracosahexaenoic acid (24:6n-3, THA) plasma levels in women and men (19 - 30 years, n = 10 - 14 per sex, per diet) following 12-weeks of n-3 PUFA supplementation (3 g/day EPA, DHA or olive oil). Women had higher plasma TPAn-3 in all supplementation groups and higher THA levels in the EPA and olive oil groups (p < 0.0001) compared to men. EPA supplementation increased (p < 0.0001) plasma TPAn-3 by 215% (1.3 ± 0.1 - 4.1 ± 0.7, nmol/mL ± SEM) and THA by 112% (1.7 ± 0.2 - 3.6 ± 0.5, nmol/mL ± SEM), but DHA supplementation had no effect. For the first time in humans, we show that plasma TPAn-3 and THA levels are higher in women and increased with EPA, but not DHA supplementation, suggesting an accumulation of THA prior to conversion to DHA in the n-3 PUFA synthesis pathway.

The omega-3 hydroxy fatty acid 7(S)-HDHA is a high-affinity PPARα ligand that regulates brain neuronal morphology

The nuclear receptor peroxisome proliferator-activated receptor alpha (PPARα) is emerging as an important target in the brain for the treatment or prevention of cognitive disorders. The identification of high-affinity ligands for brain PPARα may reveal the mechanisms underlying the synaptic effects of this receptor and facilitate drug development. Here, using an affinity purification-untargeted mass spectrometry (AP-UMS) approach, we identified an endogenous, selective PPARα ligand, 7(S)-hydroxy-docosahexaenoic acid [7(S)-HDHA]. Results from mass spectrometric detection of 7(S)-HDHA in mouse and rat brain tissues, time-resolved FRET analyses, and thermal shift assays collectively revealed that 7(S)-HDHA potently activated PPARα with an affinity greater than that of other ligands identified to date. We also found that 7(S)-HDHA activation of PPARα in cultured mouse cortical neurons stimulated neuronal growth and arborization, as well as the expression of genes associated with synaptic plasticity. The findings suggest that this DHA derivative supports and enhances neuronal synaptic capacity in the brain.

Influence of the nutritional status and oxidative stress in the desaturation and elongation of n-3 and n-6 polyunsaturated fatty acids: Impact on non-alcoholic fatty liver disease

Polyunsaturated fatty acids (PUFA) play essential roles in cell membrane structure and physiological processes including signal transduction, cellular metabolism and tissue homeostasis to combat diseases. PUFA are either consumed from food or synthesized by enzymatic desaturation, elongation and peroxisomal β-oxidation. The nutritionally essential precursors α-linolenic acid (C18:3n-3; ALA) and linoleic acid (C18:2n-6; LA) are subjected to desaturation by Δ6D/Δ5D desaturases and elongation by elongases 2/5, enzymes that are induced by insulin and repressed by PUFA. Maintaining an optimally low n-6/n-3 PUFA ratio is linked to prevention of the development of several diseases, including nonalcoholic fatty liver disease (NAFLD) that is characterized by depletion of PUFA promoting hepatic steatosis and inflammation. In this context, supplementation with n-3 PUFA revealed significant lowering of hepatic steatosis in obese patients, whereas prevention of fatty liver by high-fat diet in mice is observed in n-3 PUFA and hydroxytyrosol co-administration. The aim of this work is to review the role of nutritional status and nutrient availability on markers of PUFA biosynthesis. In addition, the impact of oxidative stress developed as a result of NAFLD, a redox imbalance that may alter the expression and activity of the enzymes involved, and diminished n-3 PUFA levels by free-radical dependent peroxidation processes will be discussed.

Serum lipid analysis and isotopic enrichment is suggestive of greater lipogenesis in young long-term cannabis users: A secondary analysis of a case-control study

Cannabis is now legal in many countries and while numerous studies have reported on its impact on cognition and appetite regulation, none have examined fatty acid metabolism in young cannabis users. We conducted an exploratory analysis to evaluate cannabis impact on fatty acid metabolism in cannabis users (n = 21) and non-cannabis users (n = 16). Serum levels of some saturated and monounsaturated fatty acids, including palmitic, palmitoleic, and oleic acids were higher in cannabis users compared to nonusers. As palmitic acid can be derived from diet or lipogenesis from sugars, we evaluated lipogenesis using a de novo lipogenesis index (palmitate/linoleic acid) and carbon-specific isotope analysis, which allows for the determination of fatty acid ¹³ C signature. The significantly higher de novo lipogenesis index in the cannabis users group along with a more enriched ¹³ C signature of palmitic acid suggested an increase in lipogenesis. In addition, while serum glucose concentration did not differ between groups, pyruvate and lactate were lower in the cannabis user group, with pyruvate negatively correlating with palmitic acid. Furthermore, the endocannabinoid 2-arachidonoylglycerol was elevated in cannabis users and could contribute to lipogenesis by activating the cannabinoid receptor 1. Because palmitic acid has been suggested to increase inflammation, we measured peripheral cytokines and observed no changes in inflammatory cytokines. Finally, an anti-inflammatory metabolite of palmitic acid, palmitoylethanolamide was elevated in cannabis users. Our results suggest that lipogenic activity is increased in cannabis users; however, future studies, including prospective studies that control dietary intake are required.

The Majority of Brain Palmitic Acid is Maintained by Lipogenesis from Dietary Sugars and is Augmented in Mice fed Low Palmitic Acid Levels from Birth

Previously, results from studies investigating if brain palmitic acid (16:0; PAM) was maintained by either dietary uptake or lipogenesis de novo (DNL) varied. Here, we utilize naturally occurring carbon isotope ratios (¹³ C/¹² C; δ¹³ C) to uncover the origin of brain PAM. Additionally, we explored brain and liver fatty acid concentration, total brain metabolomic profile, and behaviour. BALB/c dams were equilibrated onto either a low PAM diet (LP; <2%) or high PAM diet (HP; >95%) prior to producing one generation of offspring. Offspring stayed on the respective diet of the dam until 15-weeks of age, at which time the Open Field test was conducted in the offspring, prior to euthanasia and tissue lipid extraction. Although liver PAM was lower in offspring fed the LP diet, as well as female offspring, brain PAM was not affected by diet or sex. Across offspring of either sex on both diets, brain ¹³ C-PAM revealed compared to dietary uptake, DNL from dietary sugars contributed 68.8%-79.5% and 46.6%-58.0% to the total brain PAM pool by both peripheral and local brain DNL, and local brain DNL alone, respectively. DNL was augmented in offspring fed the LP diet, and the ability to upregulate DNL in the liver or the brain depended on sex. Anxiety-like behaviours were decreased in offspring fed the LP diet and were correlated with markers of LP diet consumption including increased liver ¹³ C-PAM, warranting further investigation. Altogether, our results indicate that DNL from dietary sugars is a compensatory mechanism to maintain brain PAM in response to a LP diet.

Effect of Storage Conditions on the Quality of Arbequina Extra Virgin Olive Oil and the Impact on the Composition of Flavor-Related Compounds (Phenols and Volatiles)

Commercialization of extra virgin olive oil (EVOO) requires a best before date recommended at up to 24 months after bottling, stored under specific conditions. Thus, it is expected that the product retains its chemical properties and preserves its 'extra virgin' category. However, inadequate storage conditions could alter the properties of EVOO. In this study, Arbequina EVOO was exposed to five storage conditions for up to one year to study the effects on the quality of the oil and the compounds responsible for flavor. Every 15 or 30 days, samples from each storage condition were analyzed, determining physicochemical parameters, the profiles of phenols, volatile compounds, α-tocopherol, and antioxidant capacity. Principal component analysis was utilized to better elucidate the relationships between the composition of EVOOs and the storage conditions. EVOOs stored at -23 and 23 °C in darkness and 23 °C with light, differed from the oils stored at 30 and 40 °C in darkness. The former was associated with a higher quantity of non-oxidized phenolic compounds and the latter with higher elenolic acid, oxidized oleuropein, and ligstroside derivatives, which also increased with storage time. (E)-2-nonenal (detected at trace levels in fresh oil) was selected as a marker of the degradation of Arbequina EVOO quality over time, with significant linear regressions identified for the storage conditions at 30 and 40 °C. Therefore, early oxidation in EVOO could be monitored by measuring (E)-2-nonenal levels.

Hepatic Igf1-Deficiency Protects Against Atherosclerosis in Female Mice

Atherosclerosis is the leading cause of cardiovascular disease (CVD), with distinct sex-specific pathogenic mechanisms that are poorly understood. Aging, a major independent risk factor for atherosclerosis, correlates with a decline in circulating insulin-like growth factor-1 (IGF-1). However, the precise effects of Igf1 on atherosclerosis remain unclear. In the present study, we assessed the essential role of hepatic Igf1, the major source of circulating IGF-1, in atherogenesis. We generated hepatic Igf1-deficient atherosclerosis-prone apolipoprotein E (ApoE)-null mice (L-Igf1-/-ApoE-/-) using the Cre-loxP system driven by the Albumin promoter. Starting at 6 weeks of age, these mice and their littermate controls, separated into male and female groups, were placed on an atherogenic diet for 18 to 19 weeks. We show that hepatic Igf1-deficiency led to atheroprotection with reduced plaque macrophages in females, without significant effects in males. This protection from atherosclerosis in females was associated with increased subcutaneous adiposity and with impaired lipolysis. Moreover, this impaired lipid homeostasis was associated with disrupted adipokine secretion with reduced circulating interleukin-6 (IL-6) levels. Together, our data show that endogenous hepatic Igf1 plays a sex-specific regulatory role in atherogenesis, potentially through athero-promoting effects of adipose tissue-derived IL-6 secretion. These data provide potential novel sex-specific mechanisms in the pathogenesis of atherosclerosis.

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.

Effects of menopausal hormone therapy on erythrocyte n-3 and n-6 PUFA concentrations in the Women's Health Initiative randomized trial

BACKGROUND

The factors other than dietary intake that determine tissue concentrations of EPA and DHA remain obscure. Prior studies suggested that, in women, endogenous estrogen may accelerate synthesis of DHA from ɑ-linolenic acid (ALA), but the effects of exogenous estrogen on RBC n-3 (ɷ-3) PUFA concentrations are unknown.

OBJECTIVE

We tested the hypothesis that menopausal hormone therapy (HT) would increase RBC n-3 PUFA concentrations.

METHODS

Postmenopausal women (ages 50-79 y) were assigned to HT or placebo in the Women's Health Initiative (WHI) randomized trial. The present analyses included a subset of 1170 women (ages 65-79 y) who had RBC PUFA concentrations measured at baseline and at 1 y as participants in the WHI Memory Study. HT included conjugated equine estrogens (E) alone for women without a uterus (n = 560) and E plus medroxyprogesterone acetate (P) for those with an intact uterus (n = 610). RBC n-3 and n-6 (ɷ-6) PUFAs were quantified.

RESULTS

Effects of E alone and E+P on PUFA profiles were similar and were thus combined in the analyses. Relative to the changes in the placebo group after 1 y of HT, docosapentaenoic acid (DPA; n-3) concentrations decreased by 10% (95% CI: 7.3%, 12.5%), whereas DHA increased by 11% (95% CI: 7.4%, 13.9%) in the HT group. Like DHA, DPA n-6 increased by 13% from baseline (95% CI: 10.0%, 20.3%), whereas linoleic acid decreased by 2.0% (95% CI: 1.0%, 4.1%; P values at least <0.01 for all). EPA and arachidonic acid concentrations were unchanged.

CONCLUSIONS

HT increased RBC concentrations of the terminal n-3 and n-6 PUFAs (DHA and DPA n-6). These findings are consistent with an estrogen-induced increase in DHA and DPA n-6 synthesis, which is consistent with an upregulation of fatty acid elongases and/or desaturases in the PUFA synthetic pathway. The clinical implications of these changes require further study. The Women's Health Initiative Memory Study is registered at clinicaltrials.gov as NCT00685009. Note that the data presented here were not planned as part of the original trial, and therefore are to be considered exploratory.

Do Eicosapentaenoic Acid and Docosahexaenoic Acid Have the Potential to Compete against Each Other?

Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are n-3 polyunsaturated fatty acids (PUFAs) consumed in low abundance in the Western diet. Increased consumption of n-3 PUFAs may have beneficial effects for a wide range of physiological outcomes including chronic inflammation. However, considerable mechanistic gaps in knowledge exist about EPA versus DHA, which are often studied as a mixture. We suggest the novel hypothesis that EPA and DHA may compete against each other through overlapping mechanisms. First, EPA and DHA may compete for residency in membrane phospholipids and thereby differentially displace n-6 PUFAs, which are highly prevalent in the Western diet. This would influence biosynthesis of downstream metabolites of inflammation initiation and resolution. Second, EPA and DHA exert different effects on plasma membrane biophysical structure, creating an additional layer of competition between the fatty acids in controlling signaling. Third, DHA regulates membrane EPA levels by lowering its rate of conversion to EPA's elongation product n-3 docosapentaenoic acid. Collectively, we propose the critical need to investigate molecular competition between EPA and DHA in health and disease, which would ultimately impact dietary recommendations and precision nutrition trials.

Higher Increase in Plasma DHA in Females Compared to Males Following EPA Supplementation May Be Influenced by a Polymorphism in ELOVL2: An Exploratory Study

Young adult females have higher blood docosahexaenoic acid (DHA), 22:6n-3 levels than males, and this is believed to be due to higher DHA synthesis rates, although DHA may also accumulate due to a longer half-life or a combination of both. However, sex differences in blood fatty acid responses to eicosapentaenoic acid (EPA), 20:5n-3 or DHA supplementation have not been fully investigated. In this exploratory analysis, females and males (n = 14-15 per group) were supplemented with 3 g/day EPA, 3 g/day DHA, or olive oil control for 12 weeks. Plasma was analyzed for sex effects at baseline and changes following 12 weeks' supplementation for fatty acid levels and carbon-13 signature (δ¹³ C). Following EPA supplementation, the increase in plasma DHA in females (+23.8 ± 11.8, nmol/mL ± SEM) was higher than males (-13.8 ± 9.2, p < 0.01). The increase in plasma δ¹³ C-DHA of females (+2.79 ± 0.31, milliUrey (mUr ± SEM) compared with males (+1.88 ± 0.44) did not reach statistical significance (p = 0.10). The sex effect appears driven largely by increased plasma DHA in the AA genotype of females (+58.8 ± 11.5, nmol/mL ± SEM, n = 5) compared to GA + GG in females (+4.34 ± 13.5, n = 9) and AA in males (-29.1 ± 17.2, n = 6) for rs953413 in the ELOVL2 gene (p < 0.001). In conclusion, EPA supplementation increases plasma DHA levels in females compared to males, which may be dependent on the AA genotype for rs953413 in ELOVL2.

Nonesterified Fatty Acids and Depression in Cancer Patients and Caregivers

BACKGROUND

Nonesterified fatty acids (NEFAs) are known to have inflammatory effects. The inflammatory hypothesis of depression suggests that omega-3 (ω-3) and omega-6 (ω-6) fatty acids might be negatively and positively correlated with depression, respectively.

OBJECTIVE

An exploratory study was conducted to determine the association between dietary free fatty acids and depressive symptoms in cancer patients and caregivers.

METHODS

Associations between depression and the NEFA pool were investigated in 56 cancer patients and 23 caregivers using a combination of nonparametric tests and regularized regression. Plasma NEFAs were measured using thin layer and gas chromatography with flame ionization detection. Depression was characterized both as a continuous severity score using the GRID-Hamilton Depression Rating Scale (GRID Ham-D), and as a categorical diagnosis of major depression by structured clinical interview.

RESULTS

Initial hypotheses regarding the relation between depression and omega-3 or omega-6 fatty acids were not well supported. However, elaidic acid, a trans-unsaturated fatty acid found in hydrogenated vegetable oils, was found to be negatively correlated with continuous depression scores in cancer patients. No significant associations were found in caregivers.

CONCLUSIONS

An unexpected negative association between elaidic acid and depression was identified, supporting recent literature on the role of G protein-coupled receptors in depression. Further research is needed to confirm this result and to evaluate the potential role of G protein agonists as therapeutic agents for depression in cancer patients.

Tetracosahexaenoylethanolamide, a novel N-acylethanolamide, is elevated in ischemia and increases neuronal output

N-acylethanolamines (NAEs) are endogenous lipid-signaling molecules derived from fatty acids that regulate numerous biological functions, including in the brain. Interestingly, NAEs are elevated in the absence of fatty acid amide hydrolase (FAAH) and following CO₂-induced ischemia/hypercapnia, suggesting a neuroprotective response. Tetracosahexaenoic acid (THA) is a product and precursor to DHA; however, the NAE product, tetracosahexaenoylethanolamide (THEA), has never been reported. Presently, THEA was chemically synthesized as an authentic standard to confirm THEA presence in biological tissues. Whole brains were collected and analyzed for unesterified THA, total THA, and THEA in wild-type and FAAH-KO mice that were euthanized by either head-focused microwave fixation, CO₂ + microwave, or CO₂ only. PPAR activity by transient transfection assay and ex vivo neuronal output in medium spiny neurons (MSNs) of the nucleus accumbens by patch clamp electrophysiology were determined following THEA exposure. THEA in the wild-type mice was nearly doubled (P < 0.05) following ischemia/hypercapnia (CO₂ euthanization) and up to 12 times higher (P < 0.001) in the FAAH-KO compared with wild-type. THEA did not increase (P > 0.05) transcriptional activity of PPARs relative to control, but 100 nM of THEA increased (P < 0.001) neuronal output in MSNs of the nucleus accumbens. Here were identify a novel NAE, THEA, in the brain that is elevated upon ischemia/hypercapnia and by KO of the FAAH enzyme. While THEA did not activate PPAR, it augmented the excitability of MSNs in the nucleus accumbens. Overall, our results suggest that THEA is a novel NAE that is produced in the brain upon ischemia/hypercapnia and regulates neuronal excitation.

Brain eicosapentaenoic acid metabolism as a lead for novel therapeutics in major depression

The results of several meta-analyses suggest that eicosapentaenoic acid (EPA) supplementation is therapeutic in managing the symptoms of major depression. It was previously assumed that because EPA is extremely low in the brain it did not cross the blood-brain barrier and any therapeutic effects it exerted would be via the periphery. However, more recent studies have established that EPA does enter the brain, but is rapidly metabolised following entry. While EPA does not accumulate within the brain, it is present in microglia and homeostatic mechanisms may regulate its esterification to phospholipids that serve important roles in cell signaling. Furthermore, a variety of signaling molecules from EPA have been described in the periphery and they have the potential to exert effects within the brain. If EPA is confirmed to be therapeutic in major depression as a result of adequately powered randomized clinical trials, future research on brain EPA metabolism could lead to the discovery of novel targets for treating or preventing major depression.

Acute Hypercapnia/Ischemia Alters the Esterification of Arachidonic Acid and Docosahexaenoic Acid Epoxide Metabolites in Rat Brain Neutral Lipids

In the brain, approximately 90% of oxylipins are esterified to lipids. However, the significance of this esterification process is not known. In the present study, we (1) validated an aminopropyl solid phase extraction (SPE) method for separating esterified lipids using 100 and 500 mg columns and (2) applied the method to quantify the distribution of esterified oxylipins within phospholipids (PL) and neutral lipids (NL) (i.e. triacylglycerol and cholesteryl ester) in rats subjected to head-focused microwave fixation (controls) or CO2 -induced hypercapnia/ischemia. We hypothesized that oxylipin esterification into these lipid pools will be altered following CO2 -induced hypercapnia/ischemia. Lipids were extracted from control (n = 8) and CO2 -asphyxiated (n = 8) rat brains and separated on aminopropyl cartridges to yield PL and NL. The separated lipid fractions were hydrolyzed, purified with hydrophobic-lipophilic-balanced SPE columns, and analyzed with ultra-high-pressure liquid chromatography coupled to tandem mass spectrometry. Method validation showed that the 500 mg (vs 100 mg) aminopropyl columns yielded acceptable separation and recovery of esterified fatty acid epoxides but not other oxylipins. Two epoxides of arachidonic acid (ARA) were significantly increased, and three epoxides of docosahexaenoic acid (DHA) were significantly decreased in brain NL of CO2 -asphyxiated rats compared to controls subjected to head-focused microwave fixation. PL-bound fatty acid epoxides were highly variable and did not differ significantly between the groups. This study demonstrates that hypercapnia/ischemia alters the concentration of ARA and DHA epoxides within NL, reflecting an active turnover process regulating brain fatty acid epoxide concentrations.

EPA and DHA have divergent effects on serum triglycerides and lipogenesis, but similar effects on lipoprotein lipase activity: a randomized controlled trial

BACKGROUND

Comparative studies suggest that DHA may have stronger serum triglyceride-lowering effects than EPA; however, the molecular basis for this differential effect remains unexplored in humans. Differential regulation of lipogenesis and triglyceride clearance are 2 possible mechanisms of action.

OBJECTIVES

We compared the effects of EPA and DHA supplementation on serum triglycerides, markers of lipogenesis, and lipoprotein lipase (LPL) activity in adults participating in a double-blind, multiarm, placebo-controlled parallel-group randomized trial. Lipogenesis was assessed with the lipogenic index and compound specific isotope analysis (CSIA).

METHODS

Young, healthy normolipidemic men and women (n = 89; 21.6 ± 0.23 y; mean ± SEM) were randomly allocated into 1 of 3 supplement groups for 12 wk: 1) olive oil, 2) ∼3 g EPA/d, and 3) ∼3 g DHA/d. Omega-3 supplements were provided in triglyceride form. Blood was collected before and after supplementation for the analysis of fatty acids and preheparin LPL activity. Variations in the 13C:12C ratio (δ13C) of palmitate (16:0) and linoleate (18:2n-6) were measured by CSIA.

RESULTS

DHA supplementation reduced blood triglycerides (0.85 ± 0.04 mmol/L to 0.65 ± 0.03 mmol/L; P < 0.01), with no change seen with EPA supplementation. DHA supplementation did not change the lipogenic index or δ13C-16:0, whereas EPA supplementation increased the lipogenic index by 11% (P < 0.01) and δ13C-16:0 (P = 0.03) from -23.2 ± 0.2 to -22.8 ± 0.2 milliUrey ± SEM.

CONCLUSIONS

Reduced triglyceride concentrations after DHA supplementation are associated with increased LPL activity, whereas the null effect of EPA supplementation on blood triglycerides may stem from the concomitant increases in lipogenesis and LPL activity. Further investigation of the differential triglyceride-lowering effects of EPA and DHA is warranted in both normolipidemic and hyperlipidemic individuals. This trial was registered at clinicaltrials.gov as NCT03378232.

Updates to the n-3 polyunsaturated fatty acid biosynthesis pathway: DHA synthesis rates, tetracosahexaenoic acid and (minimal) retroconversion

N-3 polyunsaturated fatty acids (PUFA) and the numerous families of lipid mediators derived from them collectively regulate numerous biological processes. The mechanisms by which n-3 PUFA regulate biological processes begins with an understanding of the n-3 biosynthetic pathway that starts with alpha-linolenic acid (18:3n-3) and is commonly thought to end with the production of docosahexaenoic acid (DHA, 22:6n-3). However, our understanding of this pathway is not as complete as previously believed. In the current review we provide a background of the evidence supporting the pathway as currently understood and provide updates from recent studies challenging three central dogma of n-3 PUFA metabolism. By building on nearly three decades of research primarily in cell culture and oral dosing studies, recent evidence presented focuses on in vivo kinetic modelling and compound-specific isotope abundance studies in rodents and humans that have been instrumental in expanding our knowledge of the pathway. Specifically, we highlight three main updates to the n-3 PUFA biosynthesis pathway: (1) DHA synthesis rates cannot be as low as previously believed, (2) DHA is both a product and a precursor to tetracosahexaenoic acid (24:6n-3) and (3) increases in EPA in response to DHA supplementation are not the result of increased retroconversion.

Compound-specific isotope analysis reveals no retroconversion of DHA to EPA but substantial conversion of EPA to DHA following supplementation: a randomized control trial

BACKGROUND

It has long been believed that DHA supplementation increases plasma EPA via the retroconversion pathway in mammals. However, in rodents this increase in EPA is likely due to a slower metabolism of EPA, but this has never been tested directly in humans.

OBJECTIVE

The aim of this study was to use the natural variations in 13C:12C ratio (carbon-13 isotopic abundance [δ13C]) of n-3 PUFA supplements to assess n-3 PUFA metabolism following DHA or EPA supplementation in humans.

METHODS

Participants (aged 21.6 ± 2.2 y) were randomly assigned into 1 of 3 supplement groups for 12 wk: 1) olive oil control, 2) ∼3 g/d DHA, or 3) ∼3 g/d EPA. Blood was collected before and after the supplementation period, and concentrations and δ13C of plasma n-3 PUFA were determined.

RESULTS

DHA supplementation increased (P < 0.05) plasma EPA concentrations by 130% but did not affect plasma δ13C-EPA (-31.0 ± 0.30 to -30.8 ± 0.19, milliUrey ± SEM, P > 0.05). In addition, EPA supplementation did not change plasma DHA concentrations (P > 0.05) but did increase plasma δ13C-DHA (-27.9 ± 0.2 to -25.6 ± 0.1, P < 0.05) toward δ13C-EPA of the supplement (-23.5 ± 0.22). EPA supplementation increased plasma concentrations of EPA and docosapentaenoic acid (DPAn-3) by 880% and 200%, respectively, and increased plasma δ13C-EPA (-31.5 ± 0.2 to -25.7 ± 0.2) and δ13C-DPAn-3 (-28.9 ± 0.3 to -25.0 ± 0.1) toward δ13C-EPA of the supplement.

CONCLUSIONS

In this study, we show that the increase in plasma EPA following DHA supplementation in humans does not occur via retroconversion, but instead from a slowed metabolism and/or accumulation of plasma EPA. Furthermore, substantial amounts of supplemental EPA can be converted into DHA. δ13C of n-3 PUFA in humans is a powerful and underutilized tool that can track dietary n-3 PUFA and elucidate complex metabolic questions. This trial was registered at clinicaltrials.gov as NCT03378232.

DHA Cycling Halves the DHA Supplementation Needed to Maintain Blood and Tissue Concentrations via Higher Synthesis from ALA in Long-Evans Rats

BACKGROUND

Eicosapentaenoic acid (EPA) plus docosahexaenoic acid (DHA) recommendations are frequently stated at 500 mg/d; however, adherence to these recommendations would result in a large global commercial EPA/DHA production deficit. Previously, our laboratory demonstrated that acute DHA intake in rats can increase the capacity for synthesis-secretion of n-3 (ω-3) polyunsaturated fatty acids (PUFAs).

OBJECTIVE

We aimed to investigate the utility of a dietary DHA cycling strategy that employs 2 wk of repeated DHA feeding for a total of 3 cycles over 12 wk.

METHODS

Male Long-Evans rats were fed a 10% fat diet by weight comprised of either 1) a 2-wk, 2% α-linolenic acid (ALA, DHA-ALA group 18:3n-3) diet followed by a 2-wk, 2% DHA + 2% ALA diet over 3 consecutive 4-wk periods ("DHA cycling," DHA-ALA group); 2) a 2% DHA + 2% ALA diet (DHA group) for 12 wk; or 3) a 2% ALA-only diet (ALA group) for 12 wk. At 15 wk old, blood and tissue fatty acid concentrations and liver mRNA expression and 13C-DHA natural abundances were determined.

RESULTS

DHA concentrations in plasma, erythrocytes, and whole blood between the DHA-ALA group and the DHA groups were not different (P ≥ 0.05), but were 72-110% higher (P < 0.05) than in the ALA group. Similarly, DHA concentrations in liver, heart, adipose, and brain were not different (P ≥ 0.05) between the DHA-fed groups, but were at least 62%, 72%, 320%, and 68% higher (P < 0.05) than in the ALA group in liver, heart, adipose, and skeletal muscle, respectively. Compound-specific isotope analysis indicated that 310% more liver DHA in the DHA-ALA group compared with the DHA group is derived from dietary ALA, and this was accompanied by a 123% and 93% higher expression of elongation of very long-chain (Elovl)2 and Elovl5, respectively, in the DHA-ALA group compared with the ALA group.

CONCLUSIONS

DHA cycling requires half the dietary DHA while achieving equal blood and tissue DHA concentrations in rats. Implementation of such dietary strategies in humans could reduce the gap between global dietary n-3 PUFA recommendations and commercial production.

Brain oxylipin concentrations following hypercapnia/ischemia: effects of brain dissection and dissection time

PUFAs are precursors to bioactive oxylipin metabolites that increase in the brain following CO2-induced hypercapnia/ischemia. It is not known whether the brain-dissection process and its duration also alter these metabolites. We applied CO2 with or without head-focused microwave fixation for 2 min to evaluate the effects of CO2-induced asphyxiation, dissection, and dissection time on brain oxylipin concentrations. Compared with head-focused microwave fixation (control), CO2 followed by microwave fixation prior to dissection increased oxylipins derived from lipoxygenase (LOX), 15-hydroxyprostaglandin dehydrogenase (PGDH), cytochrome P450 (CYP), and soluble epoxide hydrolase (sEH) enzymatic pathways. This effect was enhanced when the duration of postmortem ischemia was prolonged by 6.4 min prior to microwave fixation. Brains dissected from rats subjected to CO2 without microwave fixation showed greater increases in LOX, PGDH, CYP and sEH metabolites compared with all other groups, as well as increased cyclooxygenase metabolites. In nonmicrowave-irradiated brains, sEH metabolites and one CYP metabolite correlated positively and negatively with dissection time, respectively. This study presents new evidence that the dissection process and its duration increase brain oxylipin concentrations, and that this is preventable by microwave fixation. When microwave fixation is not available, lipidomic studies should account for dissection time to reduce these artifacts.

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.

Dietary fatty acids augment tissue levels of n-acylethanolamines in n-acylphosphatidylethanolamine phospholipase D (NAPE-PLD) knockout mice

N-acylethanolamines (NAEs) are lipid signaling mediators, which can be synthesized from dietary fatty acids via n-acylphosphatidylethanolamine-phospholipase D (NAPE-PLD) and in turn influence physiological outcomes; however, the roles of NAPE-PLD upon dietary fatty acid modulation are not fully understood. Presently, we examine if NAPE-PLD is necessary to increase NAEs in response to dietary fatty acid manipulation. Post-weaning male wild-type (C57Bl/6), NAPE-PLD (-/+) and NAPE-PLD (-/-) mice received isocaloric fat diets containing either beef tallow, corn oil, canola oil or fish oil (10% wt/wt from fat) for 9 weeks. Brain docosahexaenoic acid (DHA) levels were higher (P<.01) in NAPE-PLD (-/+) (10.01±0.31 μmol/g) and NAPE-PLD (-/-) (10.89±0.61 μmol/g) than wild-type (7.72±0.61 μmol/g) consuming fish oil. In NAPE-PLD (-/-) mice, brain docosahexaenoylethanolamide (DHEA) levels were higher (P<.01) after fish oil feeding suggesting that NAPE-PLD was not necessary for DHEA synthesis. Liver and jejunum arachidonoylethanolamide, 1,2-arachidonoylglycerol and DHEA levels reflected their corresponding fatty acid precursors suggesting that alternate pathways are involved in NAE synthesis. NAPE-PLD (-/-) mice had lower oleoylethanolamide levels in the jejunum and a leaner phenotype compared to wild-type mice. Overall, these results demonstrate that dietary fatty acid can augment tissue NAEs in the absence of NAPE-PLD.

Alterations in peripheral fatty acid composition in bipolar and unipolar depression

BACKGROUND

Lipid metabolism has been shown to play an important role in unipolar and bipolar depression. In this study, we aimed to evaluate levels of fatty acids in patients with unipolar (MDD) and bipolar depression (BDD) in comparison to patients with bipolar disorder in euthymia (BDE) and non-psychiatric controls.

METHODS

Levels of saturated fatty acids (SFAs), monounsaturated fatty acids (MUFAs) and polyunsaturated fatty acids (PUFAs) were assessed in serum of (87) patients with BD (31 euthymic, 22 depressive) or MDD (34) and (31) non-psychiatric controls through GC-FID.

RESULTS

No significant difference in total levels of PUFAs (polyunsaturated fatty acids), SFAs (saturated fatty acids), MUFAs (monounsaturated fatty acids) and total fatty acids were found between groups. Our results demonstrated higher levels AA: EPA and AA: EPA+DHA in patients with BDD. Additionally, we observed that overall omega-6 present a positive correlation with illness duration in patients with BDD and AA: EPA ratio positively associated with illness duration in MDD group. Depression severity was positively associated with AA: EPA+DHA ratio in all participants.

CONCLUSION

Together, our results support the relevance for the balance of omega-3 and omega-6 in BDD. Also, our results suggest a potential subset of stage-related lipid biomarkers that further studies are needed to help clarify the dynamics of lipid alteration in BD and MDD.

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.

Retroconversion is a minor contributor to increases in eicosapentaenoic acid following docosahexaenoic acid feeding as determined by compound specific isotope analysis in rat liver

Dietary docosahexaenoic acid (DHA, 22:6n-3) not only increases blood and tissue levels of DHA, but also eicosapentaenoic acid (EPA, 20:5n-3). It is generally believed that this increase is due to DHA retroconversion to EPA, however, a slower conversion of α-linolenic acid (ALA, 18:3n-3) derived EPA to downstream metabolic products (i.e. slower turnover of EPA) is equally plausible. In this study, 21-day old Long Evans rats were weaned onto an ALA only or DHA + ALA diet for 12 weeks. Afterwards, livers were collected and the natural abundance ¹³C-enrichment was determined by compound specific isotope analysis (CSIA) of liver EPA by isotope ratio mass-spectrometry and compared to dietary ALA and DHA ¹³C-enrichment. Isotopic signatures (per mil, ‰) for liver EPA were not different (p > 0.05) between the ALA only diet (−25.89 ± 0.39 ‰, mean ± SEM) and the DHA + ALA diet (−26.26 ± 0.40 ‰), suggesting the relative contribution from dietary ALA and DHA to liver EPA did not change. However, with DHA feeding estimates of absolute EPA contribution from ALA increased 4.4-fold (147 ± 22 to 788 ± 153 nmol/g) compared to 3.2-fold from DHA (91 ± 14 to 382 ± 13 nmol/g), respectively. In conclusion, CSIA of liver EPA in rats following 12-weeks of dietary DHA suggests that retroconversion of DHA to EPA is a relatively small contributor to increases in EPA, and that this increase in EPA is largely coming from elongation/desaturation of ALA.

Docosahexaenoic acid (DHA) accretion in the placenta but not the fetus is matched by plasma unesterified DHA uptake rates in pregnant Long Evans rats

Maternal delivery of docosahexaenoic acid (DHA, 22:6n-3) to the developing fetus via the placenta is required for fetal neurodevelopment, and is the only mechanism by which DHA can be accreted in the fetus. The aim of the current study was to utilize a balance model of DHA accretion combined with kinetic measures of serum unesterified DHA uptake to better understand the mechanism by which maternal DHA is delivered to the fetus via the placenta. Female rats maintained on a 2% α-linolenic acid diet free of DHA for 56 days were mated, and for balance analysis, sacrificed at 18 days of pregnancy, and fetus, placenta and maternal carcass fatty acid concentration were determined. For tissue DHA uptake, pregnant dams (14-18 days) were infused for 5 min with radiolabeled ¹⁴C-DHA and kinetic modeling was used to determine fetal and placental serum unesterified DHA uptake rates. DHA accretion rates in the fetus were determined to be 38 ± 2 nmol/d/g, 859 ± 100 nmol/d/litter and 74 ± 3 nmol/d/pup, which are all higher (P < 0.05) than the fetal serum unesterified DHA uptake rates of 16 ± 6 nmol/d/g, 239 ± 145 nmol/d/litter and 14 ± 8 nmol/d/pup. No differences (p > 0.05) in placental DHA accretion rates versus serum unesterified DHA uptake rates were observed as values varied only 6-35% between studies. No differences in placental accretion and uptake rates suggests that serum unesterified DHA is a significant pool for the maternal-placental transfer of DHA, and lower fetal DHA uptake compared to accretion supports remodeling of placental DHA for delivery to the fetus.

Hepatic JAK2 protects against atherosclerosis through circulating IGF-1

Atherosclerosis is considered both a metabolic and inflammatory disease; however, the specific tissue and signaling molecules that instigate and propagate this disease remain unclear. The liver is a central site of inflammation and lipid metabolism that is critical for atherosclerosis, and JAK2 is a key mediator of inflammation and, more recently, of hepatic lipid metabolism. However, precise effects of hepatic Jak2 on atherosclerosis remain unknown. We show here that hepatic Jak2 deficiency in atherosclerosis-prone mouse models exhibited accelerated atherosclerosis with increased plaque macrophages and decreased plaque smooth muscle cell content. JAK2's essential role in growth hormone signalling in liver that resulted in reduced IGF-1 with hepatic Jak2 deficiency played a causal role in exacerbating atherosclerosis. As such, restoring IGF-1 either pharmacologically or genetically attenuated atherosclerotic burden. Together, our data show hepatic Jak2 to play a protective role in atherogenesis through actions mediated by circulating IGF-1 and, to our knowledge, provide a novel liver-centric mechanism in atheroprotection.

Linoleic acid participates in the response to ischemic brain injury through oxidized metabolites that regulate neurotransmission

Linoleic acid (LA; 18:2 n-6), the most abundant polyunsaturated fatty acid in the US diet, is a precursor to oxidized metabolites that have unknown roles in the brain. Here, we show that oxidized LA-derived metabolites accumulate in several rat brain regions during CO2-induced ischemia and that LA-derived 13-hydroxyoctadecadienoic acid, but not LA, increase somatic paired-pulse facilitation in rat hippocampus by 80%, suggesting bioactivity. This study provides new evidence that LA participates in the response to ischemia-induced brain injury through oxidized metabolites that regulate neurotransmission. Targeting this pathway may be therapeutically relevant for ischemia-related conditions such as stroke.

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.

Tailored Extraction Procedure Is Required To Ensure Recovery of the Main Lipid Classes in Whole Blood When Profiling the Lipidome of Dried Blood Spots

The use of dried blood spots has increased in research and clinical settings recently, particularly in field studies and screening, but comprehensive acyl-specific lipidomic profiling of dried blood spots has yet to be examined. An untargeted ultrahigh-performance liquid chromatography-tandem mass spectrometry method was adapted for the analysis of lipid extracts from human whole blood samples and dried blood spots collected on chromatography paper. Lipid recoveries were examined after different durations of exposure to extraction solvents (chloroform/methanol), physical disruption (homogenization or sonication) of the paper containing the dried blood spots, and acidification of extraction solvents. We demonstrated that comprehensive untargeted profiles can be obtained from dried blood spot samples that are comparable with whole blood for several species of lipids including phosphatidylcholine, lyso-phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, triacylglycerol, and cholesteryl ester. However, homogenization of the dried blood spots, followed by a 24 h exposure to solvents, and extraction with an acidic buffer (0.2 M NaHPO₄ + 0.1 M hydrochloric acid) was required. Dried blood spots can be used for comprehensive, untargeted lipidomics of the most abundant lipid species in whole blood, but additional sample processing steps are required.

Effect of dietary docosahexaenoic acid (DHA) in phospholipids or triglycerides on brain DHA uptake and accretion

Tracer studies suggest that phospholipid DHA (PL-DHA) more effectively targets the brain than triglyceride DHA (TAG-DHA), although the mechanism and whether this translates into higher brain DHA concentrations are not clear. Rats were gavaged with [U-(3)H]PL-DHA and [U-(3)H]TAG-DHA and blood sampled over 6h prior to collection of brain regions and other tissues. In another experiment, rats were supplemented for 4weeks with TAG-DHA (fish oil), PL-DHA (roe PL) or a mixture of both for comparison to a low-omega-3 diet. Brain regions and other tissues were collected, and blood was sampled weekly. DHA accretion rates were estimated using the balance method. [U-(3)H]PL-DHA rats had higher radioactivity in cerebellum, hippocampus and remainder of brain, with no differences in other tissues despite higher serum lipid radioactivity in [U-(3)H]TAG-DHA rats. TAG-DHA, PL-DHA or a mixture were equally effective at increasing brain DHA. There were no differences between DHA-supplemented groups in brain region, whole-body, or tissue DHA accretion rates except heart and serum TAG where the PL-DHA/TAG-DHA blend was higher than TAG-DHA. Apparent DHA β-oxidation was not different between DHA-supplemented groups. This indicates that more labeled DHA enters the brain when consumed as PL; however, this may not translate into higher brain DHA concentrations.

Essential fatty acid composition and correlates in children with severe acute malnutrition

BACKGROUND

Severe acute malnutrition (SAM) is a common condition in children living in low-income countries and may be associated with reduced polyunsaturated fatty acids (PUFA) blood levels. The purpose of this study was to describe whole blood fatty acid composition and correlates of PUFA in children admitted with SAM.

METHODS

We conducted a cross-sectional study among children admitted with SAM at Mulago National Referral Hospital and healthy controls. Whole blood fatty acid composition was measured and correlated with clinical data such as oedema, levels of haemoglobin, C-reactive protein and HIV-infection status. Multiple linear regression analyses were used to identify correlates of PUFA.

RESULTS

The relative contribution of saturated fatty acid to the fatty acids in whole blood (FA%) were lower in 108 children with SAM compared to 24 well-nourished controls whereas most monounsaturated fatty acids were higher in children with SAM. Total and all n-6 PUFA including linoleic (18:2n-6, LA) and arachidonic acid (20:4n-6, AA), as well as total n-3 PUFA and docosahexaenoic acid (22:6n-3, DHA) were lower in children with SAM. The n-6:n-3 PUFA ratio was also lower in the children with SAM. Haemoglobin was a positive correlate of AA, n-3 docosapentaenoic acid (22:5n-3, n-3 DPA), DHA, total n-6 long chain (LC) PUFA and total n-3 LCPUFA. HIV infected children had 0.87 (0.47; 1.58) %-points less n-6 LCPUFA and 0.61 (0.03; 1.19) %-points less AA than the un-infected children.

CONCLUSION

Children with SAM presented with lower FA% of LCPUFA. HIV infection and low haemoglobin were also associated with lower FA% of LCPUFA, which may be related to lower numbers of blood cells. Nutrition rehabilitation interventions need to pay more attention to the intake of PUFA.

Translating plasma and whole blood fatty acid compositional data into the sum of eicosapentaenoic and docosahexaenoic acid in erythrocytes

Specific blood levels of eicosapentaenoic plus docosahexaenoic acid (EPA+DHA, wt% of total) in erythrocytes or "the omega-3 index" have been recommended for cardio-protection, but fatty acids are often measured in different blood fractions. The ability to estimate the % of EPA+DHA in erythrocytes from the fatty acid composition of other blood fractions would enable clinical assessments of omega-3 status when erythrocyte fractions are not available and increase the ability to compare blood levels of omega-3 fatty acids across clinical studies. The fatty acid composition of baseline plasma, erythrocytes and whole blood samples from participants (n=1104) in a prospective, multicenter study examining acute coronary syndrome were determined. The ability to predict the % of EPA+DHA in erythrocytes from other blood fractions were examined using bivariate and multiple linear regression modelling. Concordance analysis was also used to compare the actual erythrocytes EPA+DHA values to values estimated from other blood fractions. EPA+DHA in erythrocytes was significantly (p<0.001) correlated EPA+DHA in plasma (r(2)=0.54) and whole blood (r(2)=0.79). Using multiple linear regression to predict EPA+DHA in erythrocytes resulted in stronger coefficients of determination in both plasma (R(2)=0.70) and whole blood (R(2)=0.84). Concordance analyses indicated agreement between actual and estimated EPA+DHA in erythrocytes, although estimating from plasma fatty acids appears to require translation by categorization rather than by translation as continuous data. This study shows that the fatty acid composition of different blood fractions can be used to estimate erythrocyte EPA+DHA in a population with acute coronary syndrome.

The stability of blood fatty acids during storage and potential mechanisms of degradation: A review

Fatty acids in blood samples, particularly polyunsaturated fatty acids (PUFAs), are susceptible to degradation through peroxidation reactions during long-term storage. Storage of blood samples is necessary in almost all studies and is crucial for larger clinical studies and in field research settings where it is not plausible for analytical infrastructure. Despite this, PUFA stability during blood storage is often overlooked. This review introduces and discusses lipid peroxidation and popular strategies employed to prevent or minimize peroxidation reactions during fatty acid analysis. Further, an in-depth examination of fatty acid stability during storage of blood is discussed in detail for all blood fractions including plasma/serum, erythrocytes and whole blood stored both in cryovials and on chromatography paper before discussing the associated mechanisms of degradation during storage. To our knowledge this is the first review of its kind and will provide researchers with the necessary information to confidently store blood samples for fatty acid analysis.