Genome-Wide Association Studies of Estimated Fatty Acid Desaturase Activity in Serum and Adipose Tissue in Elderly Individuals: Associations with Insulin Sensitivity

Patterns of perinatal polyunsaturated fatty acid status and associated dietary or candidate-genetic factors

Perinatal exposure to omega-3 and omega-6 polyunsaturated fatty acids (PUFAs) can be characterized through biomarkers in maternal or cord blood or breast milk. Objectives were to describe perinatal PUFA status combining multiple biofluids and to investigate how it was influenced by dietary intake during pregnancy and maternal FADS and ELOVL gene polymorphisms. This study involved 1,901 mother-child pairs from the EDEN cohort, with PUFA levels measured in maternal and cord erythrocytes, and colostrum. Maternal dietary PUFA intake during the last trimester was derived from a food frequency questionnaire. Twelve single-nucleotide polymorphisms in FADS and ELOVL genes were genotyped from maternal DNA. Principal component analysis incorporating PUFA levels from the three biofluids identified patterns of perinatal PUFA status. Spearman's correlations explored associations between patterns and PUFA dietary intake, and linear regression models examined pattern associations with FADS or ELOVL haplotypes. Five patterns were retained: "High omega-3 LC-PUFAs, low omega-6 LC-PUFAs"; "Omega-6 LC-PUFAs"; "Colostrum LC-PUFAs"; "Omega-6 precursor (LA) and DGLA"; "Omega-6 precursor and colostrum ALA". Maternal omega-3 LC-PUFA intakes were correlated with "High omega-3 LC-PUFAs, low omega-6 LC-PUFAs" (r(DHA) = 0.33) and "Omega-6 LC-PUFAs" (r(DHA) = -0.19) patterns. Strong associations were found between FADS haplotypes and PUFA patterns except for "High omega-3 LC-PUFAs, low omega-6 LC-PUFAs". Lack of genetic association with the "High omega-3 LC-PUFAs, low omega-6 LC-PUFAs" pattern, highly correlated with maternal omega-3 LC-PUFA intake, emphasizes the importance of adequate omega-3 LC-PUFA intake during pregnancy and lactation. This study offers a more comprehensive assessment of perinatal PUFA status and its determinants.

Fatty Acids and Their Lipogenic Enzymes in Anorexia Nervosa Clinical Subtypes

Disordered eating behavior differs between the restricting subtype (AN-R) and the binging and purging subtype (AN-BP) of anorexia nervosa (AN). Yet, little is known about how these differences impact fatty acid (FA) dysregulation in AN. To address this question, we analyzed 26 FAs and 7 FA lipogenic enzymes (4 desaturases and 3 elongases) in 96 women: 25 AN-R, 25 AN-BP, and 46 healthy control women. Our goal was to assess subtype-specific patterns. Lauric acid was significantly higher in AN-BP than in AN-R at the fasting timepoint (p = 0.038) and displayed significantly different postprandial changes 2 h after eating. AN-R displayed significantly higher levels of n-3 alpha-linolenic acid, stearidonic acid, eicosapentaenoic acid (EPA), docosapentaenoic acid, and n-6 linoleic acid and gamma-linolenic acid compared to controls. AN-BP showed elevated EPA and saturated lauric acid compared to controls. Higher EPA was associated with elevated anxiety in AN-R (p = 0.035) but was linked to lower anxiety in AN-BP (p = 0.043). These findings suggest distinct disordered eating behaviors in AN subtypes contribute to lipid dysregulation and eating disorder comorbidities. A personalized dietary intervention may improve lipid dysregulation and enhance treatment effectiveness for AN.

Genetic analysis of blood molecular phenotypes reveals common properties in the regulatory networks affecting complex traits

We evaluate the shared genetic regulation of mRNA molecules, proteins and metabolites derived from whole blood from 3029 human donors. We find abundant allelic heterogeneity, where multiple variants regulate a particular molecular phenotype, and pleiotropy, where a single variant associates with multiple molecular phenotypes over multiple genomic regions. The highest proportion of share genetic regulation is detected between gene expression and proteins (66.6%), with a further median shared genetic associations across 49 different tissues of 78.3% and 62.4% between plasma proteins and gene expression. We represent the genetic and molecular associations in networks including 2828 known GWAS variants, showing that GWAS variants are more often connected to gene expression in trans than other molecular phenotypes in the network. Our work provides a roadmap to understanding molecular networks and deriving the underlying mechanism of action of GWAS variants using different molecular phenotypes in an accessible tissue.

The impact of fatty acids biosynthesis on the risk of cardiovascular diseases in Europeans and East Asians: a Mendelian randomization study

Despite early interest, the evidence linking fatty acids to cardiovascular diseases (CVDs) remains controversial. We used Mendelian randomization to explore the involvement of polyunsaturated (PUFA) and monounsaturated (MUFA) fatty acids biosynthesis in the etiology of several CVD endpoints in up to 1 153 768 European (maximum 123 668 cases) and 212 453 East Asian (maximum 29 319 cases) ancestry individuals. As instruments, we selected single nucleotide polymorphisms mapping to genes with well-known roles in PUFA (i.e. FADS1/2 and ELOVL2) and MUFA (i.e. SCD) biosynthesis. Our findings suggest that higher PUFA biosynthesis rate (proxied by rs174576 near FADS1/2) is related to higher odds of multiple CVDs, particularly ischemic stroke, peripheral artery disease and venous thromboembolism, whereas higher MUFA biosynthesis rate (proxied by rs603424 near SCD) is related to lower odds of coronary artery disease among Europeans. Results were unclear for East Asians as most effect estimates were imprecise. By triangulating multiple approaches (i.e. uni-/multi-variable Mendelian randomization, a phenome-wide scan, genetic colocalization and within-sibling analyses), our results are compatible with higher low-density lipoprotein (LDL) cholesterol (and possibly glucose) being a downstream effect of higher PUFA biosynthesis rate. Our findings indicate that PUFA and MUFA biosynthesis are involved in the etiology of CVDs and suggest LDL cholesterol as a potential mediating trait between PUFA biosynthesis and CVDs risk.

Interplay between fatty acid desaturase2 (FADS2) rs174583 genetic variant and dietary antioxidant capacity: cardio-metabolic risk factors in obese individuals

OBJECTIVE

Polymorphisms of the fatty acid desaturase (FADS) gene cluster have been associated with obesity and its-related consequences. This cross-sectional study aimed to investigate whether the adherence to dietary non-enzymatic antioxidant capacity (NEAC), reflecting the antioxidant potential of the whole diet, modifies the association of FADS2 rs174583 polymorphism with cardio-metabolic risk factors in obese adults.

METHODS

The present study included 347 healthy obese adults (aged 20-50 years). Dietary NEAC was assessed by a validated food frequency questionnaire with 147 items and estimated through total radical-trapping antioxidant parameters (TRAP), oxygen radical absorbance capacity (ORAC), and ferric reducing ability of plasma (FRAP) with the use of published databases. FADS2 rs174583 polymorphism was characterized using PCR-RFLP. ANCOVA multivariate interaction model was used to analyze gene-diet interactions.

RESULTS

after adjustment for the confounding variables (age, physical activity, SES and WC), this study showed significant interactions between rs174583 polymorphism and adherence to dietary ORAC on the serum cholesterol (P _Interaction = 0.029), LDL-C (P _Interaction = 0.025) and HDL-C levels (P _Interaction = 0.049) among the male group; minor allele carriers who had the highest adherence to the NEAC (ORAC) showed a better metabolic profile (lower TG and LDL-C and higher HDL-C) (P < 0.05). Among women, the dietary ORAC-rs174583 interactions were statistically significant for the serum insulin concentration (P _Interaction = 0.020), QUICKI (P _Interaction = 0.023) and HOMA-IR (P _Interaction = 0.017); the highest QUICKI and the lowest HOMA-IR and serum insulin levels were observed in the CC homozygote carriers with the moderate compliance with the dietary ORAC (P < 0.05). In addition, the dietary TRAP modified the association between FADS2 variant and change in LDL-C levels (P _Interaction = 0.037); the homozygous wild-type (CC) women who placed in the top tertile of TRAP had significantly the lowest LDL-C levels than those in the second tertile (P < 0.05).

CONCLUSION

These data indicate that the FADS2 rs174583 polymorphism interacts with the dietary NEAC to influence cardio-metabolic risk factors in obese subjects. Replication in prospective cohort studies among other populations is required to confirm the results of our study.

FADS Polymorphisms Affect the Clinical and Biochemical Phenotypes of Metabolic Syndrome

Long-chain polyunsaturated fatty acids (LC-PUFAs) play important roles in human health, from controlling inflammation to lipid and glucose homeostasis. In our previous study, which employed a cluster analysis of a plasma fatty acid (FA) pattern, we identified two clusters of metabolic syndrome (MetS) independent of clinical and biochemical parameters within the whole study group (controls together with metabolic syndrome (MetS) patients). FA desaturase (FADS) genes are the key regulators of LC-PUFA metabolism. The aim of this study was to analyze associations between FADS polymorphisms and clusters of MetS. The study group consisted of 188 controls and 166 patients with MetS. The first cluster contained 71 controls (CON1) and 109 MetS patients (MetS1). The second cluster consisted of 117 controls (CON2) and 57 MetS patients (MetS2). In comparison with MetS2, cluster MetS1 displayed a more adverse risk profile. Cluster CON1 had, in comparison with CON2, higher body weight and increased triacylglycerol levels (p < 0.05). We found that the FADS rs174537 (p < 0.001), rs174570 (p < 0.01), and rs174602 (p < 0.05) polymorphisms along with two inferred haplotypes had statistically significant genotype associations with the splitting of MetS into MetS1 and MetS2. Conversely, we observed no significant differences in the distribution of FADS polymorphisms between MetS and CON subjects, or between CON1 and CON2. These associations between FADS polymorphisms and two clusters of MetS (differing in waist circumference, HOMA-IR, lipolysis, and oxidative stress) implicate the important influence of genetic factors on the phenotypic manifestation of MetS.

The Different Insulin-Sensitising and Anti-Inflammatory Effects of Palmitoleic Acid and Oleic Acid in a Prediabetes Model

INTRODUCTION

Monounsaturated fatty acids (MUFA) are understood to have therapeutic and preventive effects on chronic complications associated with type 2 diabetes mellitus (T2DM); however, there are differences between individual MUFAs. Although the effects of palmitoleic acid (POA) are still debated, POA can regulate glucose homeostasis, lipid metabolism, and cytokine production, thus improving metabolic disorders. In this study, we investigated and compared the metabolic effects of POA and oleic acid (OA) supplementation on glucose and lipid metabolism, insulin sensitivity, and inflammation in a prediabetic model, the hereditary hypertriglyceridemic rat (HHTg). HHTg rats exhibiting genetically determined hypertriglyceridemia, insulin resistance, and impaired glucose tolerance were fed a standard diet. POA and OA were each administered intragastrically at a dose of 100 mg/kg b.wt. for four weeks.

RESULTS

Supplementation with both MUFAs significantly elevated insulin and glucagon levels, but only POA decreased nonfasting glucose. POA-treated rats showed elevated circulating NEFA associated with increased lipolysis, lipoprotein lipase gene expression, and fatty acid reesterification in visceral adipose tissue (VAT). The mechanism of improved insulin sensitivity of peripheral tissues (measured as insulin-stimulated lipogenesis and glycogenesis) in POA-treated HHTg rats could contribute increased circulating adiponectin and omentin levels together with elevated FADS1 gene expression in VAT. POA-supplemented rats exhibited markedly decreased proinflammatory cytokine production by VAT, which can alleviate chronic inflammation. OA-supplemented rats exhibited decreased arachidonic acid (AA) profiles and decreased proinflammatory AA-derived metabolites (20-HETE) in membrane phospholipids of peripheral tissues. Slightly increased FADS1 gene expression after OA along with increased adiponectin production by VAT was reflected in slightly ameliorated adipose tissue insulin sensitivity (increased insulin-stimulated lipogenesis).

CONCLUSIONS

Our results show that POA served as a lipokine, ameliorating insulin sensitivity in peripheral tissue and markedly modulating the metabolic activity of VAT including cytokine secretion. OA had a beneficial effect on lipid metabolism and improved inflammation by modulating AA metabolism.

Fatty Acid Metabolism and Associations with Insulin Sensitivity Differs Between Black and White South African Women

PURPOSE

Genetic differences in desaturase genes and consequently fatty acid metabolism have been reported. The aims were to examine ethnic differences in serum fatty acid composition and desaturase indices, and assess the ethnic-specific associations with insulin sensitivity (IS) and liver fat in black and white South African (SA) women.

METHODS

In this cross-sectional study including 92 premenopausal black (n = 46) and white (n = 46) SA women, serum fatty acid composition was measured in cholesteryl ester (CE) and nonesterified fatty acid (NEFA) fractions. Desaturase activities were estimated as product-to-precursor ratios: stearoyl-CoA desaturase-1 (SCD1-16, 16:1n-7/16:0); δ-5 desaturase (D5D, 20:4n-6/20:3n-6), and δ-6 desaturase (D6D, 18:3n-6/18:2n-6). Whole-body IS was estimated from an oral glucose tolerance test using the Matsuda index. In a subsample (n = 30), liver fat and hepatic IS were measured by 1H-magnetic resonance spectroscopy and hyperinsulinemic euglycemic clamp, respectively.

RESULTS

Despite lower whole-body IS (P = .006), black women had higher CE D5D and lower D6D and SCD1-16 indices than white women (P < .01). CE D6D index was associated with lower IS in white women only (r = -0.31, P = .045), whereas D5D index was associated with higher IS in black women only (r = 0.31, P = .041). In the subsample, D6D and SCD1-16 indices were positively and D5D was negatively associated with liver fat (P < .05). Conversely, CE SCD1-16 was negatively associated with hepatic IS (P < .05), but not independently of liver fat.

CONCLUSIONS

Ethnic differences in fatty acid-derived desaturation indices were observed, with insulin-resistant black SA women paradoxically showing a fatty acid pattern typical for higher insulin sensitivity in European populations.

Intake and metabolism of omega-3 and omega-6 polyunsaturated fatty acids: nutritional implications for cardiometabolic diseases

Prospective observational studies support the use of long-chain omega-3 polyunsaturated fatty acids (PUFAs) in the primary prevention of atherosclerotic cardiovascular disease; however, randomised controlled trials, have often reported neutral findings. There is a long history of debate about the potential harmful effects of a high intake of omega-6 PUFAs, although this idea is not supported by prospective observational studies or randomised controlled trials. Health effects of PUFAs might be influenced by Δ-5 and Δ-6 desaturases, the key enzymes in the metabolism of PUFAs. The activity of these enzymes and modulation by variants in encoding genes (FADS1-2-3 gene cluster) are linked to several cardiometabolic traits. This Review will further consider non-genetic determinants of desaturase activity, which have the potential to modify the availability of PUFAs to tissues. Finally, we discuss the consequences of altered desaturase activity in the context of PUFA intake, that is, gene-diet interactions and their clinical and public health implications.

Desaturase Activity and the Risk of Type 2 Diabetes and Coronary Artery Disease: A Mendelian Randomization Study

Estimated Δ5-desaturase (D5D) and Δ6-desaturase (D6D) are key enzymes in metabolism of polyunsaturated fatty acids (PUFA) and have been associated with cardiometabolic risk; however, causality needs to be clarified. We applied two-sample Mendelian randomization (MR) approach using a representative sub-cohort of the European Prospective Investigation into Cancer and Nutrition (EPIC)-Potsdam Study and public data from DIAbetes Genetics Replication And Meta-analysis (DIAGRAM) and Coronary ARtery DIsease Genome wide Replication and Meta-analysis (CARDIoGRAM) genome-wide association studies (GWAS). Furthermore, we addressed confounding by linkage disequilibrium (LD) as all instruments from FADS1 (encoding D5D) are in LD with FADS2 (encoding D6D) variants. Our univariable MRs revealed risk-increasing total effects of both, D6D and D5D on type 2 diabetes (T2DM) risk; and risk-increasing total effect of D6D on risk of coronary artery disease (CAD). The multivariable MR approach could not unambiguously allocate a direct causal effect to either of the individual desaturases. Our results suggest that D6D is causally linked to cardiometabolic risk, which is likely due to downstream production of fatty acids and products resulting from high D6D activity. For D5D, we found indication for causal effects on T2DM and CAD, which could, however, still be confounded by LD.

Biological Role of Unsaturated Fatty Acid Desaturases in Health and Disease

Polyunsaturated fatty acids (PUFAs) are considered one of the most important components of cells that influence normal development and function of many organisms, both eukaryotes and prokaryotes. Unsaturated fatty acid desaturases play a crucial role in the synthesis of PUFAs, inserting additional unsaturated bonds into the acyl chain. The level of expression and activity of different types of desaturases determines profiles of PUFAs. It is well recognized that qualitative and quantitative changes in the PUFA profile, resulting from alterations in the expression and activity of fatty acid desaturases, are associated with many pathological conditions. Understanding of underlying mechanisms of fatty acid desaturase activity and their functional modification will facilitate the development of novel therapeutic strategies in diseases associated with qualitative and quantitative disorders of PUFA.

Persistent Abnormalities of Fatty Acids Profile in Children With Idiopathic Nephrotic Syndrome in Stable Remission

Steroid-sensitive nephrotic syndrome is an immunological disorder mediated by still poorly defined circulating factor(s) that target the podocyte and damage the filtration barrier. Fatty acids (FA) have several biological roles and, in particular, are strictly involved in cell to cell communication, inflammatory processes and regulation of lymphocyte pools. Studies of FAs during INS have been mainly focused on biochemical changes during the phase of proteinuria; while no information is available about FA profile in patients with idiopathic nephrotic syndrome (INS) on stable remission. Aim of this study is to assess differences in blood FA profile between pediatric patients with INS during the phase of stable remission. Blood fatty acid profile of 47 pediatric patients on stable remission and 47 matched healthy controls were evaluated with gas chromatography. Patients with INS on stable remission had significantly higher levels of PUFA and omega-6 than controls (40.17 vs. 37.91% and 36.95 vs. 34.79%), lower levels of SFA and MUFA. Considering the single fatty acids, levels of omega-6 18:2n6 linoleic acid and omega-6 20:4n6 arachidonic acid were significantly higher in patients with INS than in controls (23.01 vs. 21.55%, p-value 0.003 and 10.37 vs. 9.65%, p-value 0.01). Moreover, patients with INS showed lower levels of SFA 14:0 (0.74 vs. 0.92%) and 18:0 (10.74 vs. 11.74%) and MUFA 18:1n9 oleic acid (18.50 vs. 19.83%). To the best of our knowledge this is the first study assessing FAs profile in children with INS in stable remission. In a population of 47 patients, we were able to demonstrate a higher blood level of linoleic and arachidonic acid, and consequently of omega-6 and PUFA, compared to controls. Persistently higher than normal levels of either linoleic or arachidonic acid, could be viewed as candidate biomarker for a state of risk of relapse in children with idiopathic nephrotic syndrome.

Food-Intake Normalization of Dysregulated Fatty Acids in Women with Anorexia Nervosa

Anorexia nervosa (AN) is a psychiatric disorder affected by psychological, environmental, and biological factors. Individuals with AN avoid high-fat, high-calorie diets and have shown abnormal metabolism of fatty acids (FAs), which are essential for brain and cognitive/neuropsychiatric health. To clarify the relationship between FAs and AN, fasting and postprandial plasma FAs in AN patients and age-matched control women were analyzed via mass-spectrometry. Clinical phenotypes were assessed using Becker Anxiety Inventory and Becker Depression Inventory. AN patients and controls exhibited different FA signatures at both fasting and postprandial timepoints. Lauric acid, eicosapentaenoic acid (EPA), docosapentaenoic acid (DPA), and alpha-linoleic acid (ALA) were higher in AN than in controls (lauric acid: 15,081.6 ± 14,970.2 vs. 8257.4 ± 4740.2 pmol/mL; ALA at fasting: 2217.7 ± 1587.6 vs. 1087.9 ± 821.2 pmol/mL; ALA at postprandial: 1830.9 ± 1115.6 vs. 1159.4 ± 664.7 pmol/mL. EPA: 33,788.3 ± 17,487.5 vs. 22,860.6 ± 12,642.4 pmol/mL; DPA: 32,664.8 ± 16,215.0 vs. 20,969.0 ± 12,350.0 pmol/mL. FDR-adjusted p-values < 0.05). Food intake and AN status modified the correlations of FAs with body mass index (BMI), depression, and anxiety. Desaturases SCD-18 and D6D showed lower activities in AN compared to controls. Altered FA signature, specifically correlations between elevated n-3 FAs and worsened symptoms, illustrate metabolic underpinnings in AN. Future studies should investigate the mechanisms by which FA dysregulation, specifically elevated n-3 FAs, affects AN risk and outcome.

Omega-3 fatty acid decreases oleic acid by decreasing SCD-1 expression in the liver and kidney of a cyclosporine-induced nephropathy rat model

Aim: Stearoyl-CoA desaturase (SCD)-1 and elongase-6 (Elovl-6) are associated with fatty acid (FA) synthesis. We evaluated the effect of omega-3 FA on erythrocyte membrane FA contents through SCD-1 and Elovl-6 expression in the liver and kidney of a cyclosporine (CsA)-induced rat model.

Methods: Male Sprague Dawley rats were divided into control, CsA, and CsA treated with omega-3 FA groups. We measured SCD-1 and Elovl-6 expression levels via western blot and immunohistochemistry analysis.

Results: Erythrocyte membrane oleic acid content was lower in the CsA with omega-3 FA group compared to the CsA group. Compared to the control group, CsA-induced rats showed elevated SCD-1 expression in the kidney and liver, which omega-3 FA treatment reversed. Elovl-6 expression was increased in the liver, but decreased in the kidney in CsA group compared to control, which omega-3 FA treatment also reversed.

Conclusions: Omega-3 FA supplementation decreased erythrocyte membrane oleic acid content by modulating SCD-1 and Elovl-6 expression in the kidney and liver of CsA-induced rats.

Effect of linoleic acid on ischemic heart disease and its risk factors: a Mendelian randomization study

BACKGROUND

The role of n-6 polyunsaturated fatty acids (PUFAs) in ischemic heart disease (IHD) is controversial, and dietary guidelines vary. Observationally, lower saturated fat intake and higher intake of vegetable oils rich in linoleic acid (LA), the main n-6 PUFA, is associated with lower IHD and diabetes; however, randomized controlled trials have not fully corroborated these benefits. We assessed how genetically predicted LA affected IHD and its risk factors, including diabetes, lipids, and blood pressure. We also assessed the role of LA in reticulocyte count, the red blood cell precursor, which has recently been identified as a possible causal factor in IHD.

METHODS

Two-sample instrumental variable analysis with genetic instruments, i.e., Mendelian randomization, was used to obtain unconfounded estimates using genetic variants strongly (p value < 5 × 10^-8) and solely associated with LA, applied to an IHD case (n ≤ 76,014)-control (n ≤ 264,785) study (mainly based on the meta-analysis of CARDIoGRAMplusC4D 1000 Genomes and UK Biobank CAD SOFT GWAS), the DIAbetes Genetics Replication And Meta-analysis diabetes case (n = 26,676)-control (n = 132,532) study, lipids from the Global Lipids Genetics Consortium Results (n = 196,475), and reticulocyte count and blood pressure from the UK Biobank (n ≤ 361,194). A weighted median and Mendelian randomization Egger were used for sensitivity analysis.

RESULTS

Genetically predicted LA was not associated with IHD or systolic blood pressure. Genetically predicted higher serum LA was associated with lower diabetes (odds ratio (OR) 0.97 per percentage in total fatty acid increase in LA, 95% confidence interval (CI) 0.96 to 0.99) and lower lipids (low-density lipoprotein, high-density lipoprotein, and total cholesterol), but may be associated with higher diastolic blood pressure. The findings were robust to different single nucleotide polymorphism (SNP) selections, analytic methods, and correction for multiple testing.

CONCLUSIONS

Our novel study suggests a benefit of LA for diabetes and lipids but no benefit for IHD, blood pressure, or reticulocyte count. Explicating these paradoxical findings would facilitate identification of effective new interventions for diabetes and IHD.