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

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.

Lipid Peroxidation of the Docosahexaenoic Acid/Arachidonic Acid Ratio Relating to the Social Behaviors of Individuals with Autism Spectrum Disorder: The Relationship with Ferroptosis

Polyunsaturated fatty acids (PUFAs) undergo lipid peroxidation and conversion into malondialdehyde (MDA). MDA reacts with acetaldehyde to form malondialdehyde-modified low-density lipoprotein (MDA-LDL). We studied unsettled issues in the association between MDA-LDL and the pathophysiology of ASD in 18 individuals with autism spectrum disorders (ASD) and eight age-matched controls. Social behaviors were assessed using the social responsiveness scale (SRS). To overcome the problem of using small samples, adaptive Lasso was used to enhance the interpretability accuracy, and a coefficient of variation was used for variable selections. Plasma levels of the MDA-LDL levels (91.00 ± 16.70 vs. 74.50 ± 18.88) and the DHA/arachidonic acid (ARA) ratio (0.57 ± 0.16 vs. 0.37 ± 0.07) were significantly higher and the superoxide dismutase levels were significantly lower in the ASD group than those in the control group. Total SRS scores in the ASD group were significantly higher than those in the control group. The unbeneficial DHA/ARA ratio induced ferroptosis via lipid peroxidation. Multiple linear regression analysis and adaptive Lasso revealed an association of the DHA/ARA ratio with total SRS scores and increased MDA-LDL levels in plasma, resulting in neuronal deficiencies. This unbeneficial DHA/ARA-ratio-induced ferroptosis contributes to autistic social behaviors and is available for therapy.

Heterogeneity in the response to n-3 polyunsaturated fatty acids

PURPOSE OF REVIEW

A central goal in the study of long chain n-3 polyunsaturated fatty acids (PUFA) is to translate findings from the basic sciences to the population level to improve human health and prevent chronic diseases. A tenet of this vision is to think in terms of precision medicine and nutrition, that is, stratification of individuals into differing groups that will have different needs across the lifespan for n-3 PUFAs. Therefore, there is a critical need to identify the sources of heterogeneity in the human population in the dietary response to n-3 PUFA intervention.

RECENT FINDINGS

We briefly review key sources of heterogeneity in the response to intake of long chain n-3 PUFAs. These include background diet, host genome, composition of the gut microbiome, and sex. We also discuss the need to integrate data from newer rodent models (e.g. population-based approaches), multi -omics, and analyses of big data using machine learning and data-driven cluster analyses.

SUMMARY

Accounting for vast heterogeneity in the human population, particularly with the use of big data integrated with preclinical evidence, will drive the next generation of precision nutrition studies and randomized clinical trials with long-chain n-3 PUFAs.

Unsaturated Fatty Acids and Their Immunomodulatory Properties

Oils are an essential part of the human diet and are primarily derived from plant (or sometimes fish) sources. Several of them exhibit anti-inflammatory properties. Specific diets, such as Mediterranean diet, that are high in ω-3 polyunsaturated fatty acids (PUFAs) and ω-9 monounsaturated fatty acids (MUFAs) have even been shown to exert an overall positive impact on human health. One of the most widely used supplements in the developed world is fish oil, which contains high amounts of PUFAs docosahexaenoic and eicosapentaenoic acid. This review is focused on the natural sources of various polyunsaturated and monounsaturated fatty acids in the human diet, and their role as precursor molecules in immune signaling pathways. Consideration is also given to their role in CNS immunity. Recent findings from clinical trials utilizing various fatty acids or diets high in specific fatty acids are reviewed, along with the mechanisms through which fatty acids exert their anti-inflammatory properties. An overall understanding of diversity of polyunsaturated fatty acids and their role in several molecular signaling pathways is useful in formulating diets that reduce inflammation and increase longevity.

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

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

The synaptic lipidome in health and disease

Adequate homeostasis of lipid, protein and carbohydrate metabolism is essential for cells to perform highly specific tasks in our organism, and the brain, with its uniquely high energetic requirements, posesses singular characteristics. Some of these are related to its extraordinary dotation of synapses, the specialized subcelluar structures where signal transmission between neurons occurs in the central nervous system. The post-synaptic compartment of excitatory synapses, the dendritic spine, harbors key molecules involved in neurotransmission tightly packed within a minute volume of a few femtoliters. The spine is further compartmentalized into nanodomains that facilitate the execution of temporo-spatially separate functions in the synapse. Lipids play important roles in this structural and functional compartmentalization and in mechanisms that impact on synaptic transmission. This review analyzes the structural and dynamic processes involving lipids at the synapse, highlighting the importance of their homeostatic balance for the physiology of this complex and highly specialized structure, and underscoring the pathologies associated with disbalances of lipid metabolism, particularly in the perinatal and late adulthood periods of life. Although small variations of the lipid profile in the brain take place throughout the adult lifespan, the pathophysiological consequences are clinically manifested mostly during late adulthood. Disturbances in lipid homeostasis in the perinatal period leads to alterations during nervous system development, while in late adulthood they favor the occurrence of neurodegenerative diseases.

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.

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.

Accumulation of Arachidonic Acid, Precursor of Pro-Inflammatory Eicosanoids, in Adipose Tissue of Obese Women: Association with Breast Cancer Aggressiveness Indicators

While obesity is linked to cancer risk, no studies have explored the consequences of body mass index (BMI) on fatty acid profiles in breast adipose tissue and on breast tumor aggressiveness indicators. Because of this, 261 breast adipose tissue samples of women with invasive breast carcinoma were analyzed. Fatty acid profile was established by gas chromatography. For normal-weight women, major changes in fatty acid profile occurs after menopause, with the enrichment of long-chain polyunsaturated fatty acids (LC-PUFAs) of both n-6 and n-3 series enrichment, but a stable LC-PUFAs n-6/n-3 ratio across age. BMI impact was analyzed by age subgroups to overcome the age effect. BMI increase is associated with LC-PUFAs n-6 accumulation, including arachidonic acid. Positive correlations between BMI and several LC-PUFAs n-6 were observed, as well as a strong imbalance in the LC-PUFAs n-6/n-3 ratio. Regarding cancer, axillary lymph nodes (p = 0.02) and inflammatory breast cancer (p = 0.08) are more frequently involved in obese women. Increased BMI induces an LC-PUFAs n-6 accumulation, including arachidonic acid, in adipose tissue. This may participate in the development of low-grade inflammation in obese women and breast tumor progression. These results suggest the value of lifestyle and LC-PUFAs n-3 potential, in the context of obesity and breast cancer secondary/tertiary prevention.

The effects of a high eicosapentaenoic acid multinutrient supplement on measures of stress, anxiety and depression in young adults: Study protocol for NutriMOOD, a randomised double-blind placebo-controlled trial

Anxiety disorders affect nearly 20% of young adults aged 18-29 years. First-line treatment for anxiety disorders comprises pharmacotherapy and Cognitive Behavioural Therapy, options often criticised for their low efficacy and safety. In contrast, fish-oil-based supplements comprising omega-3 polyunsaturated fatty acids and supporting nutrients are gaining recognition as safe and effective alternatives. Here we present the protocol for a randomised, double-blind, placebo-controlled trial investigating the effects of a high eicosapentaenoic acid multinutrient supplement on validated measures of anxiety and depression in healthy university students experiencing non-clinical levels of anxiety and depression. The primary outcome is improvement in anxiety compared to the placebo group assessed via the Generalised Anxiety Disorder Assessment-7 scale. The participants will be randomised to active treatment comprising a daily dose of 1125 mg eicosapentaenoic acid, 441 mg docosahexaenoic acid, 330 mg magnesium and 7.5 mg vitamin E, or placebo, for 24 weeks, and will complete validated questionnaires and tablet-based tasks sensitive to mood at baseline and end of intervention. Circulating fatty acids and key biomarkers will also be assessed. The students will be genotyped for polymorphisms thought to influence the relationship between long-chain omega-3 polyunsaturated fatty acids and affect. Trial registration; ClinicalTrials.gov, NCT04844034.

Sex Differences in Pulmonary Eicosanoids and Specialized Pro-Resolving Mediators in Response to Ozone Exposure

Ozone (O3) is a criteria air pollutant known to increase the morbidity and mortality of cardiopulmonary diseases. This occurs through a pulmonary inflammatory response characterized by increased recruitment of immune cells into the airspace, pro-inflammatory cytokines, and pro-inflammatory lipid mediators. Recent evidence has demonstrated sex-dependent differences in the O3-induced pulmonary inflammatory response. However, it is unknown if this dimorphic response is evident in pulmonary lipid mediator metabolism. We hypothesized that there are sex-dependent differences in lipid mediator production following acute O3 exposure. Male and female C57BL/6J mice were exposed to 1 part per million O3 for 3 hours and were necropsied at 6 or 24 hours following exposure. Lung lavage was collected for cell differential and total protein analysis, and lung tissue was collected for mRNA analysis, metabololipidomics, and immunohistochemistry. Compared to males, O3-exposed female mice had increases in airspace neutrophilia, neutrophil chemokine mRNA, pro-inflammatory eicosanoids such as prostaglandin E2, and specialized pro-resolving mediators (SPMs) such as resolvin D5 in lung tissue. Likewise, precursor fatty acids (arachidonic and docosahexaenoic acid; DHA) were increased in female lung tissue following O3 exposure compared to males. Experiments with ovariectomized females revealed that loss of ovarian hormones exacerbates pulmonary inflammation and injury. However, eicosanoid and SPM production were not altered by ovariectomy despite depleted pulmonary DHA concentrations. Taken together, these data indicate that O3 drives an increased pulmonary inflammatory and bioactive lipid mediator response in females. Furthermore, ovariectomy increases susceptibility to O3-induced pulmonary inflammation and injury, as well as decreases pulmonary DHA concentrations.