Molecular interplay between Δ5/Δ6 desaturases and long-chain fatty acids in the pathogenesis of non-alcoholic steatohepatitis

Targeted and untargeted lipidomics with integration of liver dynamics and microbiome after dietary reversal of obesogenic diet targeting inflammation-resolution signaling in aging mice

Obesity, a global epidemic linked to around 4 million deaths yearly, arises from lifestyle imbalances impacting inflammation-related conditions like non-alcoholic fatty liver disease and gut dysbiosis. But the long-term effects of inflammation caused by lifestyle-related dietary changes remain unexplained. In this study, we used young male C57Bl/6 mice which were fed either an obesogenic diet (OBD) or a control diet (CON) for six months. Later, a group of mice from the OBD group were intervened to the CON diet (OBD-R) for four months, while another OBD group remained on the OBD diet. The OBD induced distinct changes in gut microbial, notably elevating Firmicutes and Actinobacteria, while reducing Bacteroidetes and Tenericutes. OBD-R restored microbial abundance like CON. Analyzing liver, plasma, and fecal samples revealed OBD-induced alterations in various structural and bioactive lipids, which were normalized to CON in the OBD-R, showcasing lipid metabolism flexibility and adaptability to dietary shifts. OBD increased omega 6 fatty acid, Arachidonic Acid (AA) and decreased omega 3-derived lipid mediators in the OBD mimicking non-alcoholic fatty liver disease thus impacting inflammation-resolution pathways. OBD also induced hepatic inflammation via increasing alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels and proinflammatory markers CCR2, TNF-α, and IL-1β in liver. Transitioning from OBD to CON mitigated inflammatory gene expression and restored lipid and cholesterol networks. This study underscores the intricate interplay between lifestyle-driven dietary changes, gut microbiota, lipid metabolism, and liver health. Notably, it suggests that shift from an OBD (omega-6 enriched) to CON partially alleviates signs of chronic inflammation during aging. Understanding these microbial, lipidomic, and hepatic inflammatory dynamics reveals potential therapeutic avenues for metabolic disorders induced by diet, emphasizing the pivotal role of diet in sustaining metabolic health.

Paraoxonase-2 agonist vutiglabridin promotes autophagy activation and mitochondrial function to alleviate non-alcoholic steatohepatitis

BACKGROUND AND PURPOSE

Only limited therapeutic agents have been developed for non-alcoholic steatohepatitis (NASH). Glabridin, a promising anti-obesity candidate, has only limited druggability due to its low in vivo chemical stability and bioavailability. Therefore, we developed vutiglabridin (VUTI), which is based on a glabridin backbone, and investigated its mechanism of action in treating NASH in animal models.

EXPERIMENTAL APPROACH

Anti-NASH effects of VUTI were determined in in vitro fatty liver models, spheroids of primary human hepatocytes and L02 normal liver cell lines. To identify VUTI possible cellular target/s, biotin-labelled VUTI was synthesized and underwent chemical proteomic analysis. Further, the evaluation of VUTI therapeutic efficacy was carried out using an amylin-NASH and high-fat (HF) diet-induced obese (DIO) mouse models. This was carried out using transcriptomic, lipidomic and proteomic analyses of the livers from the amylin-NASH mouse model.

KEY RESULTS

VUTI treatment markedly reduces hepatic steatosis, fibrosis and inflammation by promoting lipid catabolism, activating autophagy and improving mitochondrial dysfunction, all of which are hallmarks of effective NASH treatment. The cellular target of VUTI was identified as paraoxonase 2 (PON2), a newly proposed protein target for the treatment of NASH, VUTI enhanced PON2 activity. The results using PON2 knockdown cells demonstrated that PON2 is important for VUTI- activation of autophagy, promoting mitochondrial function, decreasing oxidative stress and alleviating lipid accumulation under lipotoxic condition.

CONCLUSION AND IMPLICATIONS

Our data demonstrated that VUTI is a promising therapeutic for NASH. Targeting PON2 may be important for improving liver function in various immune-metabolic diseases including NASH.

Effect of FADS1 SNPs rs174546, rs174547 and rs174550 on blood fatty acid profiles and plasma free oxylipins

Introduction

Previous studies have indicated that activity of fatty acid desaturase 1 (FADS1), is involved in cardiometabolic risk. Recent experimental data have shown that FADS1 knockdown can promote lipid accumulation and lipid droplet formation in liver cells. In this study, we aimed to characterize whether different FADS1 genotypes affect liver fat content, essential fatty acid content and free oxylipin mediators in the blood.

Methods

We analyzed the impact of FADS1 single-nucleotide polymorphisms (SNPs) rs174546, rs174547, and rs174550 on blood fatty acids and free oxylipins in a cohort of 85 patients from an academic metabolic medicine outpatient center. Patients were grouped based on their genotype into the homozygous major (derived) allele group, the heterozygous allele group, and the homozygous minor (ancestral) allele group. Omega-3 polyunsaturated fatty acids (n-3 PUFA) and omega-6 polyunsaturated fatty acids (n-6 PUFA) in the blood cell and plasma samples were analyzed by gas chromatography. Free Oxylipins in plasma samples were analyzed using HPLC-MS/MS. Liver fat content and fibrosis were evaluated using Fibroscan technology.

Results

Patients with the homozygous ancestral (minor) FADS1 genotype exhibited significantly lower blood levels of the n-6 PUFA arachidonic acid (AA), but no significant differences in the n-3 PUFAs eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). There were no significant differences in liver fat content or arachidonic acid-derived lipid mediators, such as thromboxane B2 (TXB2), although there was a trend toward lower levels in the homozygous ancestral genotype group.

Discussion

Our findings suggest that FADS1 genotypes influence the blood levels of n-6 PUFAs, while not significantly affecting the n-3 PUFAs EPA and DHA. The lack of significant differences in liver fat content and arachidonic acid-derived lipid mediators suggests that the genotype-related variations in fatty acid levels may not directly translate to differences in liver fat or inflammatory lipid mediators in this cohort. However, the trend towards lower levels of certain lipid mediators in the homozygous ancestral genotype group warrants further investigation to elucidate the underlying mechanisms of different FADS1 genotypes and potential implications for cardiometabolic risk.

Effects of Combined Low-Dose Spironolactone Plus Vitamin E versus Vitamin E Monotherapy on Lipidomic Profile in Non-Alcoholic Fatty Liver Disease: A Post Hoc Analysis of a Randomized Controlled Trial

Background/Objectives: Lipid dysmetabolism seems to contribute to the development and progression of nonalcoholic fatty liver disease (NAFLD). Our aim was to compare serum lipidomic profile between patients with NAFLD having received monotherapy with vitamin E (400 IU/d) and those having received combination therapy with vitamin E (400 IU/d) and low-dose spironolactone (25 mg/d) for 52 weeks. Methods: This was a post hoc study of a randomized controlled trial (NCT01147523). Serum lipidomic analysis was performed in vitamin E monotherapy group (n = 15) and spironolactone plus vitamin E combination therapy group (n = 12). We employed an untargeted liquid chromatography-mass spectrometry lipid profiling approach in positive and negative ionization mode. Results: Univariate analysis revealed 36 lipid molecules statistically different between groups in positive mode and seven molecules in negative mode. Multivariate analysis in negative mode identified six lipid molecules that remained robustly different between groups. After adjustment for potential confounders, including gender, omega-3 supplementation, leptin concentration and homeostasis model assessment-insulin resistance (HOMA-IR), four lipid molecules remained significant between groups: FA 20:5, SM 34:2;O2, SM 42:3;O2 and CE 22:6, all being higher in the combination treatment group. Conclusions: The combination of spironolactone with vitamin E led to higher circulating levels of four lipid molecules than vitamin E monotherapy, after adjustment for potential confounders. Owing to very limited relevant data, we could not support that these changes in lipid molecules may be beneficial or not for the progression of NAFLD. Thus, mechanistic studies are warranted to clarify the potential clinical significance of these findings.

Hepatocyte-Specific Fads1 Overexpression Attenuates Western Diet-Induced Metabolic Phenotypes in a Rat Model

Fatty acid desaturase 1 (FADS1) is a rate-limiting enzyme in long-chain polyunsaturated fatty acid (LCPUFA) synthesis. Reduced activity of FADS1 was observed in metabolic dysfunction-associated steatotic liver disease (MASLD). The aim of this study was to determine whether adeno-associated virus serotype 8 (AAV8) mediated hepatocyte-specific overexpression of Fads1 (AAV8-Fads1) attenuates western diet-induced metabolic phenotypes in a rat model. Male weanling Sprague-Dawley rats were fed with a chow diet, or low-fat high-fructose (LFHFr) or high-fat high-fructose diet (HFHFr) ad libitum for 8 weeks. Metabolic phenotypes were evaluated at the endpoint. AAV8-Fads1 injection restored hepatic FADS1 protein levels in both LFHFr and HFHFr-fed rats. While AAV8-Fads1 injection led to improved glucose tolerance and insulin signaling in LFHFr-fed rats, it significantly reduced plasma triglyceride (by ~50%) and hepatic cholesterol levels (by ~25%) in HFHFr-fed rats. Hepatic lipidomics analysis showed that FADS1 activity was rescued by AAV8-FADS1 in HFHFr-fed rats, as shown by the restored arachidonic acid (AA)/dihomo-γ-linolenic acid (DGLA) ratio, and that was associated with reduced monounsaturated fatty acid (MUFA). Our data suggest that the beneficial role of AAV8-Fads1 is likely mediated by the inhibition of fatty acid re-esterification. FADS1 is a promising therapeutic target for MASLD in a diet-dependent manner.

Emerging role of ferroptosis in metabolic dysfunction-associated steatotic liver disease: revisiting hepatic lipid peroxidation

Metabolic dysfunction-associated steatohepatitis (MASH) is characterised by cell death of parenchymal liver cells which interact with their microenvironment to drive disease activity and liver fibrosis. The identification of the major death type could pave the way towards pharmacotherapy for MASH. To date, increasing evidence suggest a type of regulated cell death, named ferroptosis, which occurs through iron-catalysed peroxidation of polyunsaturated fatty acids (PUFA) in membrane phospholipids. Lipid peroxidation enjoys renewed interest in the light of ferroptosis, as druggable target in MASH. This review recapitulates the molecular mechanisms of ferroptosis in liver physiology, evidence for ferroptosis in human MASH and critically appraises the results of ferroptosis targeting in preclinical MASH models. Rewiring of redox, iron and PUFA metabolism in MASH creates a proferroptotic environment involved in MASH-related hepatocellular carcinoma (HCC) development. Ferroptosis induction might be a promising novel approach to eradicate HCC, while its inhibition might ameliorate MASH disease progression.

The fecal microbiota of patients with primary biliary cholangitis (PBC) causes PBC-like liver lesions in mice and exacerbates liver damage in a mouse model of PBC

The role of the gut microbiota in the occurrence and progression of primary biliary cholangitis (PBC) is not fully understood. First, the fecal microbiota of patients with PBC (n = 4) (PBC-FMT) or healthy individuals (n = 3) (HC-FMT) was transplanted into pseudo germ-free mice or 2OA-BSA-induced PBC models. The functions, histology and transcriptome of the liver, and microbiota and metabolome of the feces were analyzed. Second, the liver transcriptomes of PBC patients (n = 7) and normal individuals (n = 7) were analyzed. Third, the liver transcriptomes of patients with other liver diseases were collected from online databases and compared with our human and mouse data. Our results showed that PBC-FMT increased the serum ALP concentration, total bile acid content, liver injury and number of disease-related pathways enriched with upregulated liver genes in pseudo germ-free mice and increased the serum glycylproline dipeptidyl aminopeptidase level and liver damage in a 2OA-BSA-induced PBC model. The gut microbiota and metabolome differed between PBC-FMT and HC-FMT mice and reflected those of their donors. PBC-FMT tended to upregulate hepatic immune and signal transduction pathways but downregulate metabolic pathways, as in some PBC patients. The hematopoietic cell lineage, Toll-like receptor, and PPAR signaling pathway were not affected in patients with alcoholic hepatitis, HBV, HCV, HCV cirrhosis, or NASH, indicating their potential roles in the gut microbiota affecting PBC. In conclusion, the altered gut microbiota of PBC patients plays an important role in the occurrence and progression of PBC. The improvement of the gut microbiota is worthy of in-depth research and promotion as a critical aspect of PBC prevention and treatment.

Engineered human hepatocyte organoids enable CRISPR-based target discovery and drug screening for steatosis

The lack of registered drugs for nonalcoholic fatty liver disease (NAFLD) is partly due to the paucity of human-relevant models for target discovery and compound screening. Here we use human fetal hepatocyte organoids to model the first stage of NAFLD, steatosis, representing three different triggers: free fatty acid loading, interindividual genetic variability (PNPLA3 I148M) and monogenic lipid disorders (APOB and MTTP mutations). Screening of drug candidates revealed compounds effective at resolving steatosis. Mechanistic evaluation of effective drugs uncovered repression of de novo lipogenesis as the convergent molecular pathway. We present FatTracer, a CRISPR screening platform to identify steatosis modulators and putative targets using APOB-/- and MTTP-/- organoids. From a screen targeting 35 genes implicated in lipid metabolism and/or NAFLD risk, FADS2 (fatty acid desaturase 2) emerged as an important determinant of hepatic steatosis. Enhancement of FADS2 expression increases polyunsaturated fatty acid abundancy which, in turn, reduces de novo lipogenesis. These organoid models facilitate study of steatosis etiology and drug targets.

Fructose induced KHK-C can increase ER stress independent of its effect on lipogenesis to drive liver disease in diet-induced and genetic models of NAFLD

Non-alcoholic fatty liver disease (NAFLD) is a liver manifestation of metabolic syndrome, and is estimated to affect one billion individuals worldwide. An increased intake of a high-fat diet (HFD) and sugar-sweetened beverages are risk-factors for NAFLD development, but how their combined intake promotes progression to a more severe form of liver injury is unknown. Here we show that fructose metabolism via ketohexokinase (KHK) C isoform leads to unresolved endoplasmic reticulum (ER) stress when coupled with a HFD intake. Conversely, a liver-specific knockdown of KHK in mice consuming fructose on a HFD is adequate to improve the NAFLD activity score and exert a profound effect on the hepatic transcriptome. Overexpression of KHK-C in cultured hepatocytes is sufficient to induce ER stress in fructose free media. Upregulation of KHK-C is also observed in mice with genetically induced obesity or metabolic dysfunction, whereas KHK knockdown in these mice improves metabolic function. Additionally, in over 100 inbred strains of male or female mice hepatic KHK expression correlates positively with adiposity, insulin resistance, and liver triglycerides. Similarly, in 241 human subjects and their controls, hepatic Khk expression is upregulated in early, but not late stages of NAFLD. In summary, we describe a novel role of KHK-C in triggering ER stress, which offers a mechanistic understanding of how the combined intake of fructose and a HFD propagates the development of metabolic complications.

Associations of fatty acids composition and estimated desaturase activities in erythrocyte phospholipids with biochemical and clinical indicators of cardiometabolic risk in non-diabetic Serbian women: the role of level of adiposity

Introduction

Fatty acids (FAs) composition and desaturase activities can be altered in different metabolic conditions, but the adiposity-independent associations with clinical and biochemical indicators of cardiometabolic risk are still unclear. This study aimed to analyze the associations of FAs composition and estimated desaturase activities with anthropometric, clinical, and biochemical cardiometabolic risk indicators in non-diabetic Serbian women, and to investigate if these associations were independent of the level of adiposity and other confounders.

Methods

In 76 non-diabetic, otherwise healthy Serbian women, aged 24-68 years, with or without metabolic syndrome or obesity (BMI=23.6±5.6 kg/m2), FA composition in erythrocyte phospholipids was measured by gas-liquid chromatography. Desaturase activities were estimated from product/precursor FAs ratios (D9D:16:1n-7/16:0; D6D:20:3n-6/18:2n-6; D5D:20:4n-6/20:3n-6). Correlations were made with anthropometric, biochemical (serum glucose, triacylglycerols, LDL-C, HDL-C, ALT, AST, and their ratios) and clinical (blood pressure) indicators of cardiometabolic risk. Linear regression models were performed to test the independence of these associations.

Results

Estimated desaturase activities and certain FAs were associated with anthropometric, clinical and biochemical indicators of cardiometabolic risk: D9D, D6D, 16:1n-7 and 20:3n-6 were directly associated, while D5D and 18:0 were inversely associated. However, the associations with clinical and biochemical indicators were not independent of the associations with the level of adiposity, since they were lost after controlling for anthropometric indices. After controlling for multiple confounders (age, postmenopausal status, education, smoking, physical activity, dietary macronutrient intakes, use of supplements, alcohol consumption), the level of adiposity was the most significant predictor of desaturase activities and aforementioned FAs levels, and mediated their association with biochemical/clinical indicators. Vice versa, desaturase activities predicted the level of adiposity, but not other components of cardiometabolic risk (if the level of adiposity was accounted). While the associations of anthropometric indices with 16:1n-7, 20:3n-6, 18:0 and D9D and D6D activities were linear, the associations with D5D activity were the inverse U-shaped. The only adiposity-independent association of FAs profiles with the indicators of cardiometabolic risk was a positive association of 20:5n-3 with ALT/AST ratio, which requires further exploration.

Discussion

Additional studies are needed to explore the mechanisms of the observed associations.

Caiman's fat enriched with n-3 fatty acids: potential food supplement

Broad-snouted caiman (Caiman latirostris) products (meat, fat and oil) are currently beginning to be valued as a food of special interest due to its high content of n-3 fatty acids. Thus, the objective of this study was to characterize the fats of caiman fed with diets enriched with flaxseeds (Linus usitatissimun) rich in n-3 fatty acids, lignans and antioxidants. Caimans were fed six days a week with: a control diet (C), and a diet enriched with ground flaxseed = 90% C + 10% flaxseed ground (FS), during 30 (FS30) and 60 (FS60) days. Animals fed the flaxseed-enriched diets increased linolenic acid content and reduced the n-6/n-3 ratio of fats relative to controls, and this improvement increased over time. The proportion of eicosapentaenoic acid also increased, but there was no difference at the time the enriched diets were offered. Caiman fat of the FS30 and FS60, showed a decrease in lipoperoxidation (24% and 40%) and reactive oxygen species (44% and 76%) accompanied by an increase in antioxidant systems. Consumption of a flax-enriched diet by caimans increases the content of essential fatty acids and improves the lipoperoxidative status of fat. This provides an enriched fat with potential for the development products for human consumption.

Essential lipid autacoids rewire mitochondrial energy efficiency in metabolic dysfunction-associated fatty liver disease

BACKGROUND AND AIM

Injury to hepatocyte mitochondria is common in metabolic dysfunction-associated fatty liver disease. Here, we investigated whether changes in the content of essential fatty acid-derived lipid autacoids affect hepatocyte mitochondrial bioenergetics and metabolic efficiency.

APPROACH AND RESULTS

The study was performed in transgenic mice for the fat-1 gene, which allows the endogenous replacement of the membrane omega-6-polyunsaturated fatty acid (PUFA) composition by omega-3-PUFA. Transmission electron microscopy revealed that hepatocyte mitochondria of fat-1 mice had more abundant intact cristae and higher mitochondrial aspect ratio. Fat-1 mice had increased expression of oxidative phosphorylation complexes I and II and translocases of both inner (translocase of inner mitochondrial membrane 44) and outer (translocase of the outer membrane 20) mitochondrial membranes. Fat-1 mice also showed increased mitofusin-2 and reduced dynamin-like protein 1 phosphorylation, which mediate mitochondrial fusion and fission, respectively. Mitochondria of fat-1 mice exhibited enhanced oxygen consumption rate, fatty acid β-oxidation, and energy substrate utilization as determined by high-resolution respirometry, [1- 14 C]-oleate oxidation and nicotinamide adenine dinucleotide hydride/dihydroflavine-adenine dinucleotide production, respectively. Untargeted lipidomics identified a rich hepatic omega-3-PUFA composition and a specific docosahexaenoic acid (DHA)-enriched lipid fingerprint in fat-1 mice. Targeted lipidomics uncovered a higher content of DHA-derived lipid autacoids, namely resolvin D1 and maresin 1, which rescued hepatocytes from TNFα-induced mitochondrial dysfunction, and unblocked the tricarboxylic acid cycle flux and metabolic utilization of long-chain acyl-carnitines, amino acids, and carbohydrates. Importantly, fat-1 mice were protected against mitochondrial injury induced by obesogenic and fibrogenic insults.

CONCLUSION

Our data uncover the importance of a lipid membrane composition rich in DHA and its lipid autacoid derivatives to have optimal hepatic mitochondrial and metabolic efficiency.

Enzymatically-epoxidized docosahexaenoic acid, 19,20-EpDPE, suppresses hepatic crown-like structure formation and nonalcoholic steatohepatitis fibrosis through GPR120

A hepatic crown-like structure (hCLS) formed by macrophages accumulating around lipid droplets and dead cells in the liver is a unique feature of nonalcoholic steatohepatitis (NASH) that triggers progression of liver fibrosis. As hCLS plays a key role in the progression of NASH fibrosis, hCLS formation has emerged as a potential therapeutic target. n-3 polyunsaturated fatty acids (n-3 PUFAs) have potential suppressive effects on NASH fibrosis; however, the mechanisms underlying this effect are poorly understood. Here, we report that n-3 PUFA-enriched Fat-1 transgenic mice are resistant to hCLS formation and liver fibrosis in a NASH model induced by a combination of high-fat diet, CCl4 and a Liver X receptor (LXR) agonist. Liquid chromatography-tandem mass spectrometry-based mediator lipidomics revealed that the amount of endogenous n-3 PUFA-derived metabolites, such as 17,18-dihydroxyeicosatetraenoic acid (17,18-diHETE), and 19,20-epoxy docosapentaenoic acid (19,20-EpDPE), was significantly elevated in Fat-1 mice, along with hCLS formation. In particular, DHA-derived 19,20-EpDPE produced by Cyp4f18 attenuated the hCLS formation and liver fibrosis in a G protein-coupled receptor 120 (GPR120)-dependent manner. These results indicated that 19,20-EpDPE is an endogenous active metabolite that mediates the preventive effect of n-3 PUFAs against NASH fibrosis.

Fructose Induced KHK-C Increases ER Stress and Modulates Hepatic Transcriptome to Drive Liver Disease in Diet-Induced and Genetic Models of NAFLD

Non-alcoholic fatty liver disease (NAFLD) is a liver manifestation of metabolic syndrome, and is estimated to affect one billion individuals worldwide. An increased intake of a high-fat diet (HFD) and sugar-sweetened beverages are risk-factors for NAFLD development, but how their combined intake promotes progression to a more severe form of liver injury is unknown. Here we show that fructose metabolism via ketohexokinase (KHK) C isoform increases endoplasmic reticulum (ER) stress in a dose dependent fashion, so when fructose is coupled with a HFD intake it leads to unresolved ER stress. Conversely, a liver-specific knockdown of KHK in C57BL/6J male mice consuming fructose on a HFD is adequate to improve the NAFLD activity score and exert a profound effect on the hepatic transcriptome. Overexpression of KHK-C in cultured hepatocytes is sufficient to induce ER stress in fructose free media. Upregulation of KHK-C is also observed in genetically obesity ob/ob, db/db and lipodystrophic FIRKO male mice, whereas KHK knockdown in these mice improves metabolic function. Additionally, in over 100 inbred strains of male or female mice hepatic KHK expression correlates positively with adiposity, insulin resistance, and liver triglycerides. Similarly, in 241 human subjects and their controls, hepatic Khk expression is upregulated in early, but not late stages of NAFLD. In summary, we describe a novel role of KHK-C in triggering ER stress, which offers a mechanistic understanding of how the combined intake of fructose and a HFD propagates the development of metabolic complications.

Perilla seed oil improves bone health by inhibiting bone resorption in healthy Japanese adults: A 12-month, randomized, double-blind, placebo-controlled trial

Accumulating evidence suggests the beneficial effect of omega-3 polyunsaturated fatty acids (PUFAs) on bone mineral density (BMD). However, the effects of perilla (Perilla frutescens) seed oil (PO), a rich source of α-linoleic acid (LNA), on human bone have not yet been elucidated. This randomized, double-blind, placebo-controlled trial investigated the effects of long-term PO intake on bone health in Japanese adults. After screening for eligibility, 52 participants (mean age 54.2 ± 6.4 years) were randomly assigned to placebo (n = 25) and PO (n = 27) groups, which received 7.0 ml of olive oil and PO daily, respectively. At baseline and 12-month, quantitative ultrasound of the right calcaneus was measured with an ultrasound bone densitometer and percentage of the Young Adult Mean (%YAM) was calculated. Serum levels of tartrate-resistant acid phosphatase 5b (TRACP-5b), and bone alkaline phosphatase (BALP) were evaluated. In addition, PUFA levels in the erythrocyte plasma membrane (RBC-PM), serum biological antioxidant potential (BAP), and diacron reactive oxygen metabolites (d-ROM) were evaluated. Compared with the placebo group, %YAM levels increased and serum TRACP-5b levels decreased significantly in the PO group at 12-month, while serum BALP levels remained unchanged. Moreover, RBC-PM LNA levels and BAP/d-ROM ratios increased significantly in the PO compared with the placebo group. These results suggest that long-term PO intake may improve age-related BMD decline by suppressing bone resorption and increasing LNA levels.

Alterations in circulating lipidomic profile in patients with type 2 diabetes with or without non-alcoholic fatty liver disease

Objective: Non-alcoholic fatty liver disease (NAFLD) and Type 2 diabetes mellitus (T2DM) often coexist and drive detrimental effects in a synergistic manner. This study was designed to understand the changes in circulating lipid and lipoprotein metabolism in patients with T2DM with or without NAFLD. Methods: Four hundred thirty-four T2DM patients aged 18-60 years were included in this study. Fatty liver was assessed by FibroScan. The comprehensive metabolic lipid profiling of serum samples was assessed by using high-throughput proton NMR metabolomics. Results: Our data revealed a significant association between steatosis and serum total lipids in VLDL and LDL lipoprotein subclasses, while total lipids in HDL subclasses were negatively associated. A significant positive association was found between steatosis and concentration of lipids, phospholipids, cholesterol, and triglycerides in VLDL and LDL subclasses, while HDL subclasses were negatively associated. Furthermore, a significant, association was observed between fibrosis and concentrations of lipids, phospholipids, cholesterol, and triglycerides in very small VLDL, large, and very large HDL subclasses. Subgroup analysis revealed a decrease in the concentrations of lipids, phospholipids, cholesterol, and other lipid biomolecules in patients using antilipemic medications. Conclusion: The metabolomics results provide evidence that patients with T2DM with higher steatosis grades have altered lipid metabolomics compared to patients without steatosis. Increased lipid, phospholipids, cholesterol, and triglycerides concentration of VLDL and LDL subclasses are associated with steatosis in patients with T2DM.

Lipidomic profiling of the hepatic esterified fatty acid composition in diet-induced nonalcoholic fatty liver disease in genetically diverse Collaborative Cross mice

Non-alcoholic fatty liver disease (NAFLD), one of the most common forms of chronic liver disease, is characterized by the excessive accumulation of lipid species in hepatocytes. Recent studies have indicated that in addition to the total lipid quantities, changes in lipid composition are a determining factor in hepatic lipotoxicity. Using ultra-high performance liquid chromatography coupled with electrospray tandem mass spectrometry, we analyzed the esterified fatty acid composition in 24 strains of male and female Collaborative Cross (CC) mice fed a high fat/high sucrose (HF/HS) diet for 12 weeks. Changes in lipid composition were found in all strains after the HF/HS diet, most notably characterized by increases in monounsaturated fatty acids (MUFA) and decreases in polyunsaturated fatty acids (PUFA). Similar changes in MUFA and PUFA were observed in a choline- and folate-deficient (CFD) mouse model of NAFLD, as well as in hepatocytes treated in vitro with free fatty acids. Analysis of fatty acid composition revealed that alterations were accompanied by an increase in the estimated activity of MUFA generating SCD1 enzyme and an estimated decrease in the activity of PUFA generating FADS1 and FADS2 enzymes. PUFA/MUFA ratios were inversely correlated with lipid accumulation in male and female CC mice fed the HF/HS diet and with morphological markers of hepatic injury in CFD diet-fed mouse model of NAFLD. These results demonstrate that different models of NAFLD are characterized by similar changes in the esterified fatty acid composition and that alterations in PUFA/MUFA ratios may serve as a diagnostic marker for NAFLD severity.

Omega-3 Polyunsaturated Fatty Acids Protect against High-Fat Diet-Induced Morphological and Functional Impairments of Brown Fat in Transgenic Fat-1 Mice

The role of omega-3 polyunsaturated fatty acids (n-3 PUFAs) in the regulation of energy homeostasis remains poorly understood. In this study, we used a transgenic fat-1 mouse model, which can produce n-3 PUFAs endogenously, to investigate how n-3 PUFAs regulate the morphology and function of brown adipose tissue (BAT). We found that high-fat diet (HFD) induced a remarkable morphological change in BAT, characterized by “whitening” due to large lipid droplet accumulation within BAT cells, associated with obesity in wild-type (WT) mice, whereas the changes in body fat mass and BAT morphology were significantly alleviated in fat-1 mice. The expression of thermogenic markers and lypolytic enzymes was significantly higher in fat-1 mice than that in WT mice fed with HFD. In addition, fat-1 mice had significantly lower levels of inflammatory markers in BAT and lipopolysaccharide (LPS) in plasma compared with WT mice. Furthermore, fat-1 mice were resistant to LPS-induced suppression of UCP1 and PGC-1 expression and lipid deposits in BAT. Our data has demonstrated that high-fat diet-induced obesity is associated with impairments of BAT morphology (whitening) and function, which can be ameliorated by elevated tissue status of n-3 PUFAs, possibly through suppressing the effects of LPS on inflammation and thermogenesis.

Screening of co-pathogenic genes of non-alcoholic fatty liver disease and hepatocellular carcinoma

Background

Non-alcoholic fatty liver disease (NAFLD) is a risk factor for hepatocellular carcinoma (HCC). However, its carcinogenic mechanism is still unclear, looking for both diseases’ transcriptome levels, the same changes as we are looking for NAFLD may provide a potential mechanism of action of HCC. Thus, our study aimed to discover the coexisting pathogenic genes of NAFLD and HCC.

Methods

We performed a variance analysis with public data for both diseases. At the same time, weighted gene correlation network analysis (WGCNA) was used to find highly correlated gene modules in both diseases. The darkturquoise gene module was found to be highly correlated with both diseases. Based on the diagnosis related module genes and the differential genes of the two diseases, we constructed diagnostic and prognostic models by logistic regression, univariate Cox regression, and LASSO regression. Public datasets verified the results. Meanwhile, we built a competing endogenous RNA (ceRNA) network based on the model genes and explored the related pathways and immune correlation involved in the two diseases by using Gene Ontology, Kyoto Encyclopedia of Genes and Genomes, and gene set enrichment analyses. Immunohistochemistry was used to verify the different expression of ABCC5 and TUBG1 among the normal liver, NAFLD, and HCC tissues. Sodium palmitate/sodium oleate was used to establish high-fat cell models, and Real Time Quantitative Polymerase Chain Reaction (RT-qPCR) was used to verify the messenger RNA (mRNA) expression of ABCC5 in lipidization cells.

Results

A total of 26 upregulated genes and 87 downregulated genes were found using limma package identification analysis. According to WGCNA, the darkturquoise gene module was highly correlated with the prognosis of both diseases. The coexisting genes acquired by the two groups were only three central genes, that is, ABCC5, DHODH and TUBG1. The results indicated that the diagnostic and prognostic models constructed by ABCC5 and TUBG1 genes had high accuracy in both diseases. The results of immunohistochemistry showed that ABCC5 and TUBG1 were significantly overexpressed in NAFLD and HCC tissues compared with normal liver tissues. The Oil Red O staining and triglyceride identified the successful construction of HepG2 and LO2 high-fat models using PA/OA. The results of RT-qPCR showed that the lipidization of LO2 and HepG2 increased the mRNA expression of ABCC5.

Conclusions

The gene model constructed by ABCC5 and TUBG1 has high sensibility and veracity in the diagnosis of NAFLD as well as the diagnosis and prognosis of HCC. ABCC5 and TUBG1 may play an important role in the development of NAFLD to HCC. In addition, lipidization could upregulate the mRNA expression of ABCC5 in HCC.

FADS1 overexpression promotes fatty acid synthesis and triacylglycerol accumulation via inhibiting the AMPK/SREBP1 pathway in goat mammary epithelial cells

Delta-5 desaturase (D5D), encoded by the fatty acid desaturase 1 (FADS1) gene, is a rate-limiting enzyme in polyunsaturated fatty acid (PUFA) synthesis that influences the PUFA levels in milk fat. However, the function and molecular mechanism of FADS1 in milk fat metabolism remain largely unknown. The FADS1 overexpression increased the triglyceride content, lipid droplet size, and expression of genes related to fatty acid de novo synthesis (SREBP1 and ACC), intracellular fatty acid transporters (FABP3 and FABP4) and triacylglycerol synthesis gene (DGAT2). It also significantly promoted the SREBP1 nuclear translocation by inhibiting the AMPK activation. In addition, FADS1 overexpression inhibited cell proliferation and arrested cell cycle at the G1 phase. These findings reveal a novel FADS1-AMPK-SREBP1 pathway regulating milk fat production in the goat mammary gland.

Key hepatic signatures of human and mouse nonalcoholic steatohepatitis: A transcriptome-proteome data meta-analysis

BACKGROUND

Despite the global prevalence of nonalcoholic fatty liver disease (NAFLD), its pathophysiology remains unclear. In this study, we established highly confident nonalcoholic steatohepatitis (NASH) gene signatures and evaluated the pathological mechanisms underlying NASH through a systematic meta-analysis of transcriptome and proteome datasets obtained from NASH patients and mouse models.

METHODS

We analyzed NASH transcriptome datasets from 539 patients and 99 mice. A whole-liver tissue proteome dataset was used to confirm the protein level dysregulation of NASH signatures significant in both humans and mice.

RESULTS

In total, 254 human and 1,917 mouse NASH gene signatures were established. Up-regulated genes of 254 human signatures were associated with inflammation, steatosis, apoptosis, and extracellular matrix organization, whereas down-regulated genes were associated with response to metal ions and lipid and amino acid metabolism. When different mouse models were compared against humans, models with high fat and high fructose diet most closely resembled the genetic features of human NAFLD. Cross-species analysis revealed 66 genes that were concordantly dysregulated between human and mouse NASH. Among these, 14 genes were further validated to be dysregulated at the protein level. The resulting 14 genes included some of the well-established NASH associated genes and a promising NASH drug target. Functional enrichment analysis revealed that dysregulation of amino acid metabolism was the most significant hepatic perturbation in both human and mouse NASH.

CONCLUSIONS

We established the most comprehensive hepatic gene signatures for NASH in humans and mice to date. To the best of our knowledge, this is the first study to collectively analyze the common signatures between human and mouse NASH on a transcriptome-proteome scale.

PUFA, genotypes and risk for cardiovascular disease

Polyunsaturated fatty acids (PUFAs) are long chain fatty acids that are characterized by the presence of more than one double bond. These include fatty acids such as ꞷ-3-α-linolenic acid (ALA) and ꞷ-6 -linoleic acid (LA) which can only be obtained from dietary sources and are therefore termed essential fatty acids. They contain the building blocks for dihomo-γ-linolenic acid and arachidonic acid in the ꞷ-6 family as well as eicosapentaenoic acid and docosahexaenoic acid in the ꞷ-3 family. Both ALA and LA are important constituents of animal and plant cell membranes and are important components of anti-inflammatory and pro-inflammatory hormones and therefore, often modulate cellular immunity under chronic inflammatory states. The variation in physiological PUFA levels is under significant genetic influence, the fatty acid desaturase (FADS) genes being key regulators of PUFA metabolism. These genetic variants have been shown to alter fatty acid metabolism and influence the onset and progression of various metabolic conditions. This detailed review discusses the role of PUFAs, diet and genotypes in risk for cardiovascular diseases.

Omega-6 and omega-3 oxylipins as potential markers of cardiometabolic risk in young adults

OBJECTIVE

Omega-6 and omega-3 oxylipins are known to play a role in inflammation and cardiometabolic diseases in preclinical models. The associations between plasma levels of omega-6 and omega-3 polyunsaturated fatty acid-derived oxylipins and body composition and cardiometabolic risk factors in young adults were assessed.

METHODS

Body composition, brown adipose tissue, traditional serum cardiometabolic risk factors, inflammatory markers, and a panel of 83 oxylipins were analyzed in 133 young adults (age 22.1[SD 2.2] years, 67% women).

RESULTS

Plasma levels of four omega-6 oxylipins (15-HeTrE, 5-HETE, 14,15-EpETrE, and the oxidative stress-derived 8,12-iso-iPF_2α -VI) correlated positively with adiposity, prevalence of metabolic syndrome, fatty liver index, and homeostatic model assessment of insulin resistance index and lipid parameters. By contrast, the plasma levels of three omega-3 oxylipins (14,15-DiHETE, 17,18-DiHETE, and 19,20-DiHDPA) were negatively correlated with adiposity, prevalence of metabolic syndrome, fatty liver index, homeostatic model assessment of insulin resistance index, and lipid parameters. The panel of seven oxylipins predicted adiposity better than traditional inflammatory markers such as interferon gamma or tumor necrosis factor-alpha. Pathway analyses revealed that individuals with obesity had higher plasma levels of omega-6 and lower plasma levels of omega-3 oxylipins than normal-weight individuals.

CONCLUSION

Plasma levels of seven omega-6 and omega-3 oxylipins may have utility as early markers of cardiometabolic risk in young adults.

The role of hepatic lipid composition in obesity-related metabolic disease

Obesity is a primary antecedent to non-alcoholic fatty liver disease whose cardinal feature is excessive hepatic lipid accumulation. Although total hepatic lipid content closely associates with hepatic and systemic metabolic dysfunction, accumulating evidence suggests that the composition of hepatic lipids may be more discriminatory. This review summarises cross-sectional human studies using liver biopsy/lipidomics and proton magnetic resonance spectroscopy to characterise hepatic lipid composition in people with obesity and related metabolic disease. A comprehensive literature search identified 26 relevant studies published up to 31st March 2021 which were included in the review. The available evidence provides a consistent picture showing that people with hepatic steatosis possess elevated saturated and/or monounsaturated hepatic lipids and a reduced proportion of polyunsaturated hepatic lipids. This altered hepatic lipid profile associates more directly with metabolic derangements, such as insulin resistance, and may be exacerbated in non-alcoholic steatohepatitis. Further evidence from lipidomic studies suggests that these deleterious changes may be related to defects in lipid desaturation and elongation, and an augmentation of the de novo lipogenic pathway. These observations are consistent with mechanistic studies implicating saturated fatty acids and associated bioactive lipid intermediates (ceramides, lysophosphatidylcholines and diacylglycerol) in the development of hepatic lipotoxicity and wider metabolic dysfunction, whilst monounsaturated fatty acids and polyunsaturated fatty acids may exhibit a protective role. Future studies are needed to prospectively determine the relevance of hepatic lipid composition for hepatic and non-hepatic morbidity and mortality; and to further evaluate the impact of therapeutic interventions such as pharmacotherapy and lifestyle interventions.

GADD45β stabilized by direct interaction with HSP72 ameliorates insulin resistance and lipid accumulation

Growth arrest and DNA damage-inducible 45β (GADD45β) belongs to the GADD45 family which is small acidic proteins in response to cellular stress. GADD45β has already been reported to have excellent capabilities against cancer, innate immunity and neurological diseases. However, there is little information regard GADD45β and non-alcoholic fatty liver disease (NAFLD). In the current work, we found that the expression of GADD45β was markedly decreased in the livers of NAFLD patients via analyzing Gene Expression Omnibus (GEO) dataset and in mouse model through detecting its mRNA in high-fat-high-fructose diet (HFHFr)-fed mice. Moreover, the results from in vivo experiment demonstrated that overexpression of GADD45β by AAV8-mediated gene transfer in HFHFr-fed mouse model could reduce the level of serum and hepatic triglyceride (TG), and alleviate insulin resistance. Subsequently, by combining immunoprecipitation (IP) and mass spectrometry, we identified that HSP72 directly interacted with GADD45β to prevent GADD45β from being degraded by the proteasome pathway. Finally, the benefits of GADD45β in regulating key factors of TG synthesis and insulin signaling pathway were abolished after HSP72 knockdown. In conclusion, GADD45β stabilized by the interaction with HSP72 could alleviate the NAFLD-related pathologies, suggested it might be a potential target for the treatment of NAFLD.

DRAK2 aggravates nonalcoholic fatty liver disease progression through SRSF6-associated RNA alternative splicing

Nonalcoholic steatohepatitis (NASH) is an advanced stage of nonalcoholic fatty liver disease (NAFLD) with serious consequences that currently lacks approved pharmacological therapies. Recent studies suggest the close relationship between the pathogenesis of NAFLD and the dysregulation of RNA splicing machinery. Here, we reveal death-associated protein kinase-related apoptosis-inducing kinase-2 (DRAK2) is markedly upregulated in the livers of both NAFLD/NASH patients and NAFLD/NASH diet-fed mice. Hepatic deletion of DRAK2 suppresses the progression of hepatic steatosis to NASH. Comprehensive analyses of the phosphoproteome and transcriptome indicated a crucial role of DRAK2 in RNA splicing and identified the splicing factor SRSF6 as a direct binding protein of DRAK2. Further studies demonstrated that binding to DRAK2 inhibits SRSF6 phosphorylation by the SRSF kinase SRPK1 and regulates alternative splicing of mitochondrial function-related genes. In conclusion, our findings reveal an indispensable role of DRAK2 in NAFLD/NASH and offer a potential therapeutic target for this disease.

Proresolving lipid mediators and liver disease

Inflammation is a characteristic feature of virtually all acute and chronic liver diseases. It intersects different liver pathologies from the early stages of liver injury, when the inflammatory burden is mild-to-moderate, to very advanced stages of liver disease, when the inflammatory response is very intense and drives multiple organ dysfunction and failure(s). The current review describes the most relevant features of the inflammatory process in two different clinical entities across the liver disease spectrum, namely non-alcoholic steatohepatitis (NASH) and acute-on-chronic liver failure (ACLF). Special emphasis is given within these two disease conditions to gather the most relevant data on the specialized pro-resolving mediators that orchestrate the resolution of inflammation, a tightly controlled process which dysregulation commonly associates with chronic inflammatory conditions.

Effects of Dietary n-3 and n-6 Polyunsaturated Fatty Acids in Inflammation and Cancerogenesis

The dietary recommendation encourages reducing saturated fatty acids (SFA) in diet and replacing them with polyunsaturated fatty acids (PUFAs) n-3 (omega-3) and n-6 (omega-6) to decrease the risk of metabolic disturbances. Consequently, excessive n-6 PUFAs content and high n-6/n-3 ratio are found in Western-type diet. The importance of a dietary n-6/n-3 ratio to prevent chronic diseases is linked with anti-inflammatory functions of linolenic acid (ALA, 18:3n-3) and longer-chain n-3 PUFAs. Thus, this review provides an overview of the role of oxylipins derived from n-3 PUFAs and oxylipins formed from n-6 PUFAs on inflammation. Evidence of PUFAs' role in carcinogenesis was also discussed. In vitro studies, animal cancer models and epidemiological studies demonstrate that these two PUFA groups have different effects on the cell growth, proliferation and progression of neoplastic lesions.

PNPLA3 Genotype, Arachidonic Acid Intake, and Unsaturated Fat Intake Influences Liver Fibrosis in Hispanic Youth with Obesity

Non-alcoholic fatty liver disease impacts 15.2% of Hispanic adolescents and can progress to a build-up of scared tissue called liver fibrosis. If diagnosed early, liver fibrosis may be reversible, so it is necessary to understand risk factors. The aims of this study in 59 Hispanic adolescents with obesity were to: (1) identify potential biological predictors of liver fibrosis and dietary components that influence liver fibrosis, and (2) determine if the association between dietary components and liver fibrosis differs by PNPLA3 genotype, which is highly prevalent in Hispanic adolescents and associated with elevated liver fat. We examined liver fat and fibrosis, genotyped for PNPLA3 gene, and assessed diet via 24-h diet recalls. The prevalence of increased fibrosis was 20.9% greater in males, whereas participants with the GG genotype showed 23.7% greater prevalence. Arachidonic acid was associated with liver fibrosis after accounting for sex, genotype, and liver fat (β = 0.072, p = 0.033). Intakes of several dietary types of unsaturated fat have different associations with liver fibrosis by PNPLA3 genotype after accounting for sex, caloric intake, and liver fat. These included monounsaturated fat (βCC/CG = -0.0007, βGG = 0.03, p-value = 0.004), polyunsaturated fat (βCC/CG = -0.01, βGG = 0.02, p-value = 0.01), and omega-6 (βCC/CG = -0.0102, βGG = 0.028, p-value = 0.01). Results from this study suggest that reduction of arachidonic acid and polyunsaturated fatty acid intake might be important for the prevention of non-alcoholic fatty liver disease progression, especially among those with PNPLA3 risk alleles.

Impact of curcumin on fatty acid metabolism

Free fatty acids (FFAs) and fatty acid synthesis (FAS) activity have significantly contributed to disease states such as insulin resistance, obesity, type 2 diabetes, myocardial infarction, blood pressure, and several types of cancer. Currently, several treatment options are available for patients with these conditions. Due to safety concerns, adverse effects, limited efficacy, and low tolerability associated with many medications, the identification of novel agents with less toxicity and a more favorable outcome is warranted. Curcumin is a phenolic compound derived from the turmeric plant with various biological activities, including anticarcinogenic, antioxidant, antiinflammatory, and hypolipidemic properties. PubMed, Scopus, and Web of Science were searched up to February 2020 for studies that demonstrated the efficacy and mechanisms of curcumin action on FFAs, FAS, and β-oxidation activity, as well as the desaturation system. Most of the evidence is in-vivo and in-vitro studies that demonstrate that curcumin possesses regulatory properties on FFAs levels through its effects on FAS and β-oxidation activity as well as desaturation system, which could improve insulin resistance, obesity, and other FFAs-related disorders. The present study provides a review of the existing in-vitro, in-vivo, and clinical evidence on the effect of curcumin on FFAs and FAS activity, β-oxidation, and desaturation system.

Alternative RNA Splicing in Fatty Liver Disease

Alternative RNA splicing is a process by which introns are removed and exons are assembled to construct different RNA transcript isoforms from a single pre-mRNA. Previous studies have demonstrated an association between dysregulation of RNA splicing and a number of clinical syndromes, but the generality to common disease has not been established. Non-alcoholic fatty liver disease (NAFLD) is the most common liver disease affecting one-third of adults worldwide, increasing the risk of cirrhosis and hepatocellular carcinoma (HCC). In this review we focus on the change in alternative RNA splicing in fatty liver disease and the role for splicing regulation in disease progression.

Plasma and Red Blood Cell PUFAs in Home Parenteral Nutrition Paediatric Patients-Effects of Lipid Emulsions

Background: Mixed lipid emulsions (LE) containing fish oil present several advantages compared to the sole soybean oil LE, but little is known about the safety of essential fatty acids (EFA) profile in paediatric patients on long-term Parenteral Nutrition (PN). Aim of the study: to assess glycerophosfolipid polyunsaturated fatty acids (PUFA) levels on plasma and red blood cell (RBC) membrane of children on long term PN with composite LE containing fish oil (SMOF), and to compare it with a group receiving olive oil LE (Clinoleic^®) and to the reference range for age, previously determined on a group of healthy children. Results: A total of 38 patients were enrolled, median age 5.56 (0.9-21.86) years, 15 receiving Clinoleic^®, 23 receiving SMOF. Patients on SMOF showed significantly higher levels of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), lower levels of arachidonic acid (ARA) and Mead acid (MEAD)/ARA ratio in plasma and RBC compared with patients on Clinoleic^® and with healthy children. Triene:tetraene (T:T) ratio of both groups of patients did not differ from that of healthy children-median plasma (MEAD/ARA: 0.01, interquartile rage (IQR) 0.01, p = 0.61 and 0.02, IQR 0.02, p = 0.6 in SMOF and Clinoleic^® patients, respectively), and was considerably lower than Holman index (>0.21). SMOF patients showed no statistically significant differences in growth parameters compared with Clinoleic^® patients. Patients of both groups showed stiffness class F0-F1 of liver stiffness measure (LSM) 5.6 (IQR 0.85) in SMOF patients and 5.3 (IQR 0.90) in Clinoleic^® patients, p = 0.58), indicating absence of liver fibrosis. Conclusions: Fatty acids, measured as concentrations (mg/L), revealed specific PUFA profile of PN patients and could be an accurate method to evaluate nutritional status and eventually to detect essential fatty acid deficiency (EFAD). SMOF patients showed significantly higher EPA, DHA and lower ARA concentrations compared to Clinoleic^® patients. Both LEs showed similar hepatic evolution and growth.

The Role of Omega-3 Polyunsaturated Fatty Acids from Different Sources in Bone Development

N-3 polyunsaturated fatty acids (PUFAs) are essential nutrients that must be obtained from the diet. We have previously showed that endogenous n-3 PUFAs contribute to skeletal development and bone quality in fat-1 mice. Unlike other mammals, these transgenic mice, carry the n-3 desaturase gene and thus can convert n-6 to n-3 PUFAs endogenously. Since this model does not mimic dietary exposure to n-3 PUFAs, diets rich in fish and flaxseed oils were used to further elucidate the role of n-3 PUFAs in bone development. Our investigation reveals that dietary n-3 PUFAs decrease fat accumulation in the liver, lower serum fat levels, and alter fatty acid (FA) content in liver and serum. Bone analyses show that n-3 PUFAs improve mechanical properties, which were measured using a three-point bending test, but exert complex effects on bone structure that vary according to its source. In a micro-CT analysis, we found that the flaxseed oil diet improves trabecular bone micro-architecture, whereas the fish oil diet promotes higher bone mineral density (BMD) with no effect on trabecular bone. The transcriptome characterization of bone by RNA-seq identified regulatory mechanisms of n-3 PUFAs via modulation of the cell cycle and peripheral circadian rhythm genes. These results extend our knowledge and provide insights into the molecular mechanisms of bone remodeling regulation induced by different sources of dietary n-3 PUFAs.

Consequences of Lipid Remodeling of Adipocyte Membranes Being Functionally Distinct from Lipid Storage in Obesity

Obesity is a complex disorder where the genome interacts with diet and environmental factors to ultimately influence body mass, composition, and shape. Numerous studies have investigated how bulk lipid metabolism of adipose tissue changes with obesity and, in particular, how the composition of triglycerides (TGs) changes with increased adipocyte expansion. However, reflecting the analytical challenge posed by examining non-TG lipids in extracts dominated by TGs, the glycerophospholipid composition of cell membranes has been seldom investigated. Phospholipids (PLs) contribute to a variety of cellular processes including maintaining organelle functionality, providing an optimized environment for membrane-associated proteins, and acting as pools for metabolites (e.g. choline for one-carbon metabolism and for methylation of DNA). We have conducted a comprehensive lipidomic study of white adipose tissue in mice which become obese either through genetic modification (ob/ob), diet (high fat diet), or a combination of the two, using both solid phase extraction and ion mobility to increase coverage of the lipidome. Composition changes in seven classes of lipids (free fatty acids, diglycerides, TGs, phosphatidylcholines, lyso-phosphatidylcholines, phosphatidylethanolamines, and phosphatidylserines) correlated with perturbations in one-carbon metabolism and transcriptional changes in adipose tissue. We demonstrate that changes in TGs that dominate the overall lipid composition of white adipose tissue are distinct from diet-induced alterations of PLs, the predominant components of the cell membranes. PLs correlate better with transcriptional and one-carbon metabolism changes within the cell, suggesting that the compositional changes that occur in cell membranes during adipocyte expansion have far-reaching functional consequences. Data are available at MetaboLights under the submission number: MTBLS1775.

The role of omics in the pathophysiology, diagnosis and treatment of non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is a multifaceted metabolic disorder, whose spectrum covers clinical, histological and pathophysiological developments ranging from simple steatosis to non-alcoholic steatohepatitis (NASH) and liver fibrosis, potentially evolving into cirrhosis, hepatocellular carcinoma and liver failure. Liver biopsy remains the gold standard for diagnosing NAFLD, while there are no specific treatments. An ever-increasing number of high-throughput Omics investigations on the molecular pathobiology of NAFLD at the cellular, tissue and system levels produce comprehensive biochemical patient snapshots. In the clinical setting, these applications are considerably enhancing our efforts towards obtaining a holistic insight on NAFLD pathophysiology. Omics are also generating non-invasive diagnostic modalities for the distinct stages of NAFLD, that remain though to be validated in multiple, large, heterogenous and independent cohorts, both cross-sectionally as well as prospectively. Finally, they aid in developing novel therapies. By tracing the flow of information from genomics to epigenomics, transcriptomics, proteomics, metabolomics, lipidomics and glycomics, the chief contributions of these techniques in understanding, diagnosing and treating NAFLD are summarized herein.

Lipidomics in non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD), the most common chronic liver disorder in Western countries, comprises steatosis to nonalcoholic steatohepatitis (NASH), with the latter having the potential to progress to cirrhosis. The transition from isolated steatosis to NASH is still poorly understood, but lipidomics approach revealed that the hepatic lipidome is extensively altered in the setting of steatosis and steatohepatitis and these alterations correlate with disease progression. Recent data suggest that both quantity and quality of the accumulated lipids are involved in pathogenesis of NAFLD. Changes in glycerophospholipid, sphingolipid, and fatty acid composition have been described in both liver biopsies and plasma of patients with NAFLD, implicating that specific lipid species are involved in oxidative stress, inflammation, and cell death. In this article, we summarize the findings of main human lipidomics studies in NAFLD and delineate the currently available information on the pathogenetic role of each lipid class in lipotoxicity and disease progression.

fat-1 transgenic zebrafish are protected from abnormal lipid deposition induced by high-vegetable oil feeding

High dietary concentration of vegetable oil, particularly those rich in n-6 polyunsaturated fatty acids (PUFAs), can induce negative physiological effects including excessive lipid deposition in teleost fish. Omega-3 desaturase (Fat-1) of Caenorhabditis elegans is able to convert n-6 PUFAs to n-3 PUFAs and thus induces a low n-6/n-3 PUFAs ratio alleviating lipid deposition. In this study, we investigated the effects of dietary n-6 PUFAs on lipid metabolism of fat-1 transgenic zebrafish (Tg:fat-1), to explore the role of fat-1 in fish lipid metabolism. We first generated Tg:fat-1 zebrafish and assayed the effects of a low-fat diet (LFD) and a high-fat diet (HFD) prepared from soybean oil. Wild type zebrafish (WT) fed with HFD (HFD-WT) exhibited increased obesity and lipid deposition, especially in the abdominal cavity and liver. These defects were absent from HFD-Tg:fat-1. For each diet group, Tg:fat-1 exhibited significantly decreased levels of almost all hepatic lipid classes compared with WT. Expression levels of lipid synthesis-related genes and lipid deposition-related genes were markedly lower in the liver of HFD-Tg:fat-1 compared with HFD-WT. In contrast, the steatolysis-related genes significantly upregulated in HFD-Tg:fat-1. Then expression profiles of mitochondrial energy metabolism-related genes and ATP contents in the livers from LFD-WT, LFD-Tg:fat-1, HFD-WT, and HFD-Tg:fat-1 were determined. Our findings suggest that fat-1 protects fish from abnormal lipid deposition induced by high-vegetable oil feeding, through endogenously converting n-6 PUFAs to n-3 PUFAs. KEY POINTS: • fat-1 transgenic zebrafish (Tg:fat-1) can endogenously convert n-6 PUFAs to n-3 PUFAs. • Tg:fat-1 avoid serious abnormal lipid deposition induced by high-vegetable oil feeding. • fat-1 transgenosis effectively improved lipid metabolism and mitochondrial energy metabolism in zebrafish.

Relationship between changes in the exon-recognition machinery and SLC22A1 alternative splicing in hepatocellular carcinoma

Changes in the phenotype that characterizes cancer cells are partly due to altered processing of pre-mRNA by the spliceosome. We have previously reported that aberrant splicing plays an essential role in the impaired response of hepatocellular carcinoma (HCC) to sorafenib by reducing the expression of functional organic cation transporter type 1 (OCT1, gene SLC22A1) that constitutes the primary way for HCC cells to take up this and other drugs. The present study includes an in silico analysis of publicly available databases to investigate the relationship between alternative splicing of SLC22A1 pre-mRNA and the expression of genes involved in the exon-recognition machinery in HCC and adjacent non-tumor tissue. Using Taqman Low-Density Arrays, the findings were validated in 25 tumors that were resected without neoadjuvant chemotherapy. The results supported previous reports showing that there was a considerable degree of alternative splicing of SLC22A1 in adjacent non-tumor tissue, which was further increased in the tumor in a stage-unrelated manner. Splicing perturbation was associated with changes in the profile of proteins determining exon recognition. The results revealed the importance of using paired samples for splicing analysis in HCC and confirmed that aberrant splicing plays an essential role in the expression of functional OCT1. Changes in the exon recognition machinery may also affect the expression of other proteins in HCC. Moreover, these results pave the way to further investigations on the mechanistic bases of the relationship between the expression of spliceosome-associated genes and its repercussion on the appearance of alternative and aberrant splicing in HCC.

rs953413 Regulates Polyunsaturated Fatty Acid Metabolism by Modulating ELOVL2 Expression

Long-chain polyunsaturated fatty acids (LC-PUFAs) influence human health in several areas, including cardiovascular disease, diabetes, fatty liver disease, and cancer. ELOVL2 encodes one of the key enzymes in the in vivo synthesis of LC-PUFAs from their precursors. Variants near ELOVL2 have repeatedly been associated with levels of LC-PUFA-derived metabolites in genome-wide association studies (GWAS), but the mechanisms behind these observations remain poorly defined. In this study, we found that rs953413, located in the first intron of ELOVL2, lies within a functional FOXA and HNF4α cooperative binding site. The G allele of rs953413 increases binding of FOXA1/FOXA2 and HNF4α to an evolutionarily conserved enhancer element, conferring allele-specific upregulation of the rs953413-associated gene ELOVL2. The expression of ELOVL2 was significantly downregulated by both FOXA1 and HNF4α knockdown and CRISPR/Cas9-mediated direct mutation to the enhancer element. Our results suggest that rs953413 regulates LC-PUFAs metabolism by altering ELOVL2 expression through FOXA1/FOXA2 and HNF4α cooperation.

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rs953413 resides in an evolutionarily conserved enhancer region

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rs953413 mediates the cooperative binding of FOXA and HNF4α to the enhancer region

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The rs953413 locus plays a key role in regulating ELOVL2 expression

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rs953413 is implicated in PUFA metabolism by regulating ELOVL2 expression

Role of cytochrome P450-derived, polyunsaturated fatty acid mediators in diabetes and the metabolic syndrome

Over the last decade, cases of metabolic syndrome and type II diabetes have increased exponentially. Exercise and ω-3 polyunsaturated fatty acid (PUFA)-enriched diets are usually prescribed but no therapy is effectively able to restore the impaired glucose metabolism, hypertension, and atherogenic dyslipidemia encountered by diabetic patients. PUFAs are metabolized by different enzymes into bioactive metabolites with anti- or pro-inflammatory activity. One important class of PUFA metabolizing enzymes are the cytochrome P450 (CYP) enzymes that can generate a series of bioactive products, many of which have been attributed protective/anti-inflammatory and insulin-sensitizing effects in animal models. PUFA epoxides are, however, further metabolized by the soluble epoxide hydrolase (sEH) to fatty acid diols. The biological actions of the latter are less well understood but while low concentrations may be biologically important, higher concentrations of diols derived from linoleic acid and docosahexaenoic acid have been linked with inflammation. One potential application for sEH inhibitors is in the treatment of diabetic retinopathy where sEH expression and activity is elevated as are levels of a diol of docosahexaenoic acid that can induce the destabilization of the retina vasculature.

Lipidomic biomarkers and mechanisms of lipotoxicity in non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) represents the most common form of chronic liver disease worldwide (about 25% of the general population) and 3-5% of patients develop non-alcoholic steatohepatitis (NASH), characterized by hepatocytes damage, inflammation and fibrosis, which increase the risk of developing liver failure, cirrhosis and hepatocellular carcinoma. The pathogenesis of NAFLD, particularly the mechanisms whereby a minority of patients develop a more severe phenotype, is still incompletely understood. In this review we examine the available literature on initial mechanisms of hepatocellular damage and inflammation, deriving from toxic effects of excess lipids. Accumulating data indicate that the total amount of triglycerides stored in the liver cells is not the main determinant of lipotoxicity and that specific lipid classes act as damaging agents. These lipotoxic species affect the cell behavior via multiple mechanisms, including activation of death receptors, endoplasmic reticulum stress, modification of mitochondrial function and oxidative stress. The gut microbiota, which provides signals through the intestine to the liver, is also reported to play a key role in lipotoxicity. Finally, we summarize the most recent lipidomic strategies utilized to explore the liver lipidome and its modifications in the course of NALFD. These include measures of lipid profiles in blood plasma and erythrocyte membranes that can surrogate to some extent lipid investigation in the liver.

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.

Docosahexaenoic acid inhibits hepatic stellate cell activation to attenuate liver fibrosis in a PPARγ-dependent manner

Docosahexaenoic acid (DHA) has been found to have a hepatoprotective effect. In this study, we investigated the role of peroxisome proliferator-activated receptor γ (PPARγ) in DHA regulation of liver fibrosis. DHA was found to inhibit hepatic stellate cell (HSC)-LX2 cell viability and downregulate marker proteins of HSC activation. Furthermore, DHA induced cell cycle arrest at G1 phase in HSCs. Antagonism of PPARγ by GW9662 abrogated the effects of DHA on HSCs. Computer-aided molecular docking predicted that DHA bound to PPARγ via hydrogen bonding with residues Ser289, His323, Tyr473, and His499. We overexpressed Ser289 mutant PPARγ in HSC-LX2 cells and investigated fibrotic marker modulation, and found that DHA effects on HSCs were diminished. Thus, bonding with the Ser289 residue might be indispensable for DHA to activate PPARγ to exert its inhibiting effect on activated HSCs. Last, data from a CCl₄-treated mouse model confirmed that PPARγ activation was required for DHA to attenuate liver fibrosis.

Dysregulation of the Splicing Machinery Is Associated to the Development of Nonalcoholic Fatty Liver Disease

CONTEXT

Nonalcoholic fatty liver disease (NAFLD) is a common obesity-associated pathology characterized by hepatic fat accumulation, which can progress to fibrosis, cirrhosis, and hepatocellular carcinoma. Obesity is associated with profound changes in gene-expression patterns of the liver, which could contribute to the onset of comorbidities.

OBJECTIVE

As these alterations might be linked to a dysregulation of the splicing process, we aimed to determine whether the dysregulation in the expression of splicing machinery components could be associated with NAFLD.

PARTICIPANTS

We collected 41 liver biopsies from nonalcoholic individuals with obesity, with or without hepatic steatosis, who underwent bariatric surgery.

INTERVENTIONS

The expression pattern of splicing machinery components was determined using a microfluidic quantitative PCR-based array. An in vitro approximation to determine lipid accumulation using HepG2 cells was also implemented.

RESULTS

The liver of patients with obesity and steatosis exhibited a severe dysregulation of certain splicing machinery components compared with patients with obesity without steatosis. Nonsupervised clustering analysis allowed the identification of three molecular phenotypes of NAFLD with a unique fingerprint of alterations in splicing machinery components, which also presented distinctive hepatic and clinical-metabolic alterations and a differential response to bariatric surgery after 1 year. In addition, in vitro silencing of certain splicing machinery components (i.e., PTBP1, RBM45, SND1) reduced fat accumulation and modulated the expression of key de novo lipogenesis enzymes, whereas conversely, fat accumulation did not alter spliceosome components expression.

CONCLUSION

There is a close relationship between splicing machinery dysregulation and NAFLD development, which should be further investigated to identify alternative therapeutic targets.

Multi-omic analysis in transgenic mice implicates omega-6/omega-3 fatty acid imbalance as a risk factor for chronic disease

An unbalanced increase in dietary omega-6 (n-6) polyunsaturated fatty acids (PUFA) and decrease in omega-3 (n-3) PUFA in the Western diet coincides with the global rise in chronic diseases. Whether n-6 and n-3 PUFA oppositely contribute to the development of chronic disease remains controversial. By using transgenic mice capable of synthesizing PUFA to eliminate confounding factors of diet, we show here that alteration of the tissue n-6/n-3 PUFA ratio leads to correlated changes in the gut microbiome and fecal and serum metabolites. Transgenic mice able to overproduce n-6 PUFA and achieve a high tissue n-6/n-3 PUFA ratio exhibit an increased risk for metabolic diseases and cancer, whereas mice able to convert n-6 to n-3 PUFA, and that have a lower n-6/n-3 ratio, show healthy phenotypes. Our study demonstrates that n-6 PUFA may be harmful in excess and suggests the importance of a low tissue n-6/n-3 ratio in reducing the risk for chronic diseases.

Arid1a Loss Drives Nonalcoholic Steatohepatitis in Mice Through Epigenetic Dysregulation of Hepatic Lipogenesis and Fatty Acid Oxidation

Nonalcoholic steatohepatitis (NASH) is a rapidly growing cause of chronic liver damage, cirrhosis, and hepatocellular carcinoma. How fatty liver pathogenesis is subject to epigenetic regulation is unknown. We hypothesized that chromatin remodeling is important for the pathogenesis of fatty liver disease. AT-rich interactive domain-containing protein 1A (ARID1A), a DNA-binding component of the SWItch/sucrose nonfermentable adenosine triphosphate-dependent chromatin-remodeling complex, contributes to nucleosome repositioning and access by transcriptional regulators. Liver-specific deletion of Arid1a (Arid1a liver knockout [LKO]) caused the development of age-dependent fatty liver disease in mice. Transcriptome analysis revealed up-regulation of lipogenesis and down-regulation of fatty acid oxidation genes. As evidence of direct regulation, ARID1A demonstrated direct binding to the promoters of many of these differentially regulated genes. Additionally, Arid1a LKO mice were more susceptible to high-fat diet-induced liver steatosis and fibrosis. We deleted Pten in combination with Arid1a to synergistically drive fatty liver progression. Inhibition of lipogenesis using CAT-2003, a potent sterol regulatory element-binding protein inhibitor, mediated improvements in markers of fatty liver disease progression in this Arid1a/Pten double knockout model. Conclusion: ARID1A plays a role in the epigenetic regulation of hepatic lipid homeostasis, and its suppression contributes to fatty liver pathogenesis. Combined Arid1a and Pten deletion shows accelerated fatty liver disease progression and is a useful mouse model for studying therapeutic strategies for NASH.

Nutritional and lipidomics biomarkers of docosahexaenoic acid-based multivitamin therapy in pediatric NASH

Two recent randomized controlled trials demonstrated improved radiographic, histological and hepatometabolic cues of non-alcoholic steatohepatitis (NASH) in pediatric patients treated with the ω-3 fatty acid docosahexaenoic acid (DHA) in combination with vitamin D (VD) or with choline (CHO) and vitamin E (VE), the DHA-VD and DHA-CHO-VE trials, respectively). In the present study we verified the nutritional compliance to these DHA-based multivitamin treatments; lipidomics biomarkers of the reported outcome on NASH indicators were also investigated. Samples were obtained from 30 biopsy-proven pediatric NASH patients of the DHA-CHO-VE trial randomized in multivitamin treatment group and placebo group (n = 15 each), and from 12 patients of the treatment group of the DHA-VD trial. All patients underwent 6-month therapy plus 6 months of follow-up. Plasma samples and clinical data were obtained at baseline and at the end of the study (12 months). Selected biomarkers included the free form of DHA and other ω-3 fatty acid arachidonic acid (AA), indices of the vitamin E status, and some hepatic metabolites of these lipids. Radiographic and histological improvements of treated patients were associated with increased concentrations of DHA, α-linolenic acid and α-tocopherol (i.e. VE), and with decreased AA that was also investigated in complex lipids by untargetd lipidomics. As a result a significantly lowered AA/DHA ratio was observed to represent the main indicator of the response to the DHA-based therapy. Furthermore, baseline levels of AA/DHA showed strong association with NAS and US improvement. A stable correction of DHA AA metabolism interaction is associated with the curative effect of this therapy and may represent a key nutritional endpoint in the clinical management of pediatric NASH.

The cirrhotic liver is depleted of docosahexaenoic acid (DHA), a key modulator of NF-κB and TGFβ pathways in hepatic stellate cells

Liver cirrhosis results from chronic hepatic damage and is characterized by derangement of the organ architecture with increased liver fibrogenesis and defective hepatocellular function. It frequently evolves into progressive hepatic insufficiency associated with high mortality unless liver transplantation is performed. We have hypothesized that the deficiency of critical nutrients such as essential omega-3 fatty acids might play a role in the progression of liver cirrhosis. Here we evaluated by LC-MS/MS the liver content of omega-3 docosahexaenoic fatty acid (DHA) in cirrhotic patients and investigated the effect of DHA in a murine model of liver injury and in the response of hepatic stellate cells (HSCs) (the main producers of collagen in the liver) to pro-fibrogenic stimuli. We found that cirrhotic livers exhibit a marked depletion of DHA and that this alteration correlates with the progression of the disease. Administration of DHA exerts potent anti-fibrogenic effects in an acute model of liver damage. Studies with HSCs show that DHA inhibits fibrogenesis more intensely than other omega-3 fatty acids. Data from expression arrays revealed that DHA blocks TGFβ and NF-κB pathways. Mechanistically, DHA decreases late, but not early, SMAD3 nuclear accumulation and inhibits p65/RelA-S536 phosphorylation, which is required for HSC survival. Notably, DHA increases ADRP expression, leading to the formation of typical quiescence-associated perinuclear lipid droplets. In conclusion, a marked depletion of DHA is present in the liver of patients with advanced cirrhosis. DHA displays anti-fibrogenic activities on HSCs targeting NF-κB and TGFβ pathways and inducing ADPR expression and quiescence in these cells.

Possible Role of CYP450 Generated Omega-3/Omega-6 PUFA Metabolites in the Modulation of Blood Pressure and Vascular Function in Obese Children

Obesity is often accompanied by metabolic and haemodynamic disorders such as hypertension, even during childhood. Arachidonic acid (AA) is metabolized by cytochrome P450 (CYP450) enzymes to epoxyeicosatrienoic acids (EETs) and 20-hydroxyeicosatetraenoic acid (20-HETE), vasoactive and natriuretic metabolites that contribute to blood pressure (BP) regulation. Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) omega-3 polyunsaturated fatty acids may compete with AA for CYP450-dependent bioactive lipid mediator formation. We aimed at investigating the role of AA, EPA and DHA and their CYP450-dependent metabolites in BP control and vascular function in 66 overweight/obese children. Fatty acid profile moderately correlated with the corresponding CYP450-derived metabolites but their levels did not differ between children with normal BP (NBP) and high BP (HBP), except for higher EPA-derived epoxyeicosatetraenoic acids (EEQs) and their diols in HBP group, in which also the estimated CYP450-epoxygenase activity was higher. In the HBP group, EPA inversely correlated with BP, EEQs inversely correlated both with systolic BP and carotid Intima-Media Thickness (cIMT). The DHA-derived epoxydocosapentaenoic acids (EDPs) were inversely correlated with diastolic BP. Omega-3 derived epoxymetabolites appeared beneficially associated with BP and vascular structure/function only in obese children with HBP. Further investigations are needed to clarify the role of omega-3/omega-6 epoxymetabolites in children's hemodynamics.