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

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.

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.

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.

The Dose-Response Effect of Docosahexaenoic Acid on the Omega-3 Index in American Football Athletes

PURPOSE

American-style football (ASF) players are at increased risk for head injuries and cardiovascular disease. n-3 polyunsaturated fatty acids are cardioprotective, and emerging evidence suggests benefits for protection against head injuries. However, fundamental knowledge of n-3 polyunsaturated fatty acid dosing in athletes such as ASF players remains poorly understood. Therefore, this study investigated the dose-response effect of docosahexaenoic acid (DHA) supplementation in red blood cells (RBC) and as the Omega-3 Index (O3I), in collegiate ASF players throughout a competitive season.

METHODS

Sixty-nine ASF players were randomly assigned placebo (corn oil), or 2, 4, or 6 g·d -1 of DHA supplement. Blood samples were collected at eight time points (T1-T8) over 27 wk. RBC were extracted and analyzed by gas-liquid chromatography. Compliant players who had samples collected at all time points were analyzed. A repeated-measures ANOVA was conducted to assess the dose-response effect of DHA over time, and between-group differences at individual time points were assessed by one-way ANOVA followed by Tukey post hoc test.

RESULTS

A significant dose and time interaction was found, and all supplement groups had significantly greater DHA in RBC compared with placebo from T2-T8 ( P < 0.05). Athletes receiving 6 g·d -1 of DHA had the greatest O3I, relative to other groups, and the O3I reached steady state by 15 wk. The 6 g·d -1 group surpassed >8% on the O3I at approximately twice the rate of the 4 g·d -1 group (8 vs 15 wk).

CONCLUSIONS

Our findings provide important fundamental knowledge demonstrating a dose-response incorporation of DHA into RBC membranes up to 6 g·d -1 . Furthermore, 6 g·d -1 of DHA can be used to rapidly achieve a desired O3I (>8%) in athletes in only 8 wk.

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.

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.

Overview of how N32 and N34 elovanoids sustain sight by protecting retinal pigment epithelial cells and photoreceptors

The essential fatty acid DHA (22:6, omega-3 or n-3) is enriched in and required for the membrane biogenesis and function of photoreceptor cells (PRCs), synapses, mitochondria, etc. of the CNS. PRC DHA becomes an acyl chain at the sn-2 of phosphatidylcholine, amounting to more than 50% of the PRC outer segment phospholipids, where phototransduction takes place. Very long chain PUFAs (n-3, ≥ 28 carbons) are at the sn-1 of this phosphatidylcholine molecular species and interact with rhodopsin. PRC shed their tips (DHA-rich membrane disks) daily, which in turn are phagocytized by the retinal pigment epithelium (RPE), where DHA is recycled back to PRC inner segments to be used for the biogenesis of new photoreceptor membranes. Here, we review the structures and stereochemistry of novel elovanoid (ELV)-N32 and ELV-N34 to be ELV-N32: (14Z,17Z,20R,21E,23E,25Z,27S,29Z)-20,27-dihydroxydo-triaconta-14,17,21,23,25,29-hexaenoic acid; ELV-N34: (16Z,19Z,22R,23E,25E,27Z,29S,31Z)-22,29-dihydroxytetra-triaconta-16,19,23,25,27,31-hexaenoic acid. ELVs are low-abundance, high-potency, protective mediators. Their bioactivity includes enhancing of antiapoptotic and prosurvival protein expression with concomitant downregulation of proapoptotic proteins when RPE is confronted with uncompensated oxidative stress. ELVs also target PRC/RPE senescence gene programming, the senescence secretory phenotype in the interphotoreceptor matrix, as well as inflammaging (chronic, sterile, low-grade inflammation). An important lesson on neuroprotection is highlighted by the ELV mediators that target the terminally differentiated PRC and RPE, sustaining a beautifully synchronized renewal process. The role of ELVs in PRC and RPE viability and function uncovers insights on disease mechanisms and the development of therapeutics for age-related macular degeneration, Alzheimer's disease, and other pathologies.

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.

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

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

Membrane-type frizzled-related protein regulates lipidome and transcription for photoreceptor function

Molecular decision‐makers of photoreceptor (PRC) membrane organization and gene regulation are critical to understanding sight and retinal degenerations that lead to blindness. Using Mfrp^rd6mice, which develop PRC degeneration, we uncovered that membrane‐type frizzled‐related protein (MFRP) participates in docosahexaenoic acid (DHA, 22:6) enrichment in a manner similar to adiponectin receptor 1 (AdipoR1). Untargeted imaging mass spectrometry demonstrates cell‐specific reduction of phospholipids containing 22:6 and very long‐chain polyunsaturated fatty acids (VLC‐PUFAs) in Adipor1^−/−and Mfrp^rd6 retinas. Gene expression of pro‐inflammatory signaling pathways is increased and gene‐encoding proteins for PRC function decrease in both mutants. Thus, we propose that both proteins are necessary for retinal lipidome membrane organization, visual function, and to the understanding of the early pathology of retinal degenerative diseases.

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.