Endogenously synthesized n-3 polyunsaturated fatty acids in fat-1 mice ameliorate high-fat diet-induced non-alcoholic fatty liver disease

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.

Dysregulation of lipid metabolism in the pseudolobule promotes region-specific autophagy in hepatitis B liver cirrhosis

BACKGROUND

Chronic hepatitis B (CHB) infection leads to liver cirrhosis (LC), the end stage of liver fibrosis. The precise diagnosis and effective therapy for hepatitis B cirrhosis are still lacking. It is highly necessary to elucidate the metabolic alteration, especially the spatial distribution of metabolites, in LC progression.

METHODS

In this study, LC-MS/MS together with an airflow-assisted ionization mass spectrometry imaging system was applied to analyze and compare the metabolites' spatial distribution in healthy control (HC) and hepatitis B LC tissue samples. The liver samples were further divided into several subregions in HC and LC groups based on the anatomical characteristics and clinical features.

RESULTS

Both the LC-MS/MS and mass spectrometry imaging results indicated separated metabolite clusters between the HC and LC groups. The differential metabolites were mainly concentrated in lipid-like molecules and amino acids. The phosphatidylcholines (PCs), lysoPCs, several fatty acids, and amino acids reduced expression in the LC group with region specific. Acyl-CoA thioesterase 2 and choline/ethanolamine phosphotransferase 1, which regulate PC and fatty acid metabolism, were significantly decreased in the pseudolobule. Meanwhile, the increased expression of LC3B and p62 in the pseudolobule indicated the upregulation of autophagy.

CONCLUSIONS

Hepatitis B LC induced region-specific autophagy by increasing the expression of LC3B and p62 in the pseudolobule and by dysregulation of unsaturated fatty acids, amino acids, and PC metabolism. The mass spectrometry imaging system provided additional metabolites' spatial information, which can promote biomarker screening technology and support the exploration of novel mechanisms in LC.

Prevention of colitis-induced liver oxidative stress and inflammation in a transgenic mouse model with increased omega-3 polyunsaturated fatty acids

Inflammatory bowel disease (IBD) is an immune-mediated gut dysfunction, which might also be associated with an inflammatory phenotype in the liver. It is known that the nutritional intake of omega-3 polyunsaturated fatty acids (n-3 PUFA) is inversely correlated to the severity and occurrence of IBD. In order to investigate whether n-3 PUFA can also reduce liver inflammation and oxidative liver damage due to colon inflammation, we explored the dextran sulfate sodium (DSS)-induced colitis model in wild-type and fat-1 mice with endogenously increased n-3 PUFA tissue content. Besides confirming previous data of alleviated DSS-induced colitis in the fat-1 mouse model, the increase of n-3 PUFA also resulted in a significant reduction of liver inflammation and oxidative damage in colitis-affected fat-1 mice as compared to wild-type littermates. This was accompanied by a remarkable increase of established inflammation-dampening n-3 PUFA oxylipins, namely docosahexaenoic acid-derived 19,20-epoxydocosapentaenoic acid and eicosapentaenoic acid-derived 15-hydroxyeicosapentaenoic acid and 17,18-epoxyeicosatetraenoic acid. Taken together, these observations demonstrate a strong inverse correlation between the anti-inflammatory lipidome derived from n-3 PUFA and the colitis-triggered inflammatory changes in the liver by reducing oxidative liver stress.

Comparing Transgenic Production to Supplementation of ω-3 PUFA Reveals Distinct But Overlapping Mechanisms Underlying Protection Against Metabolic and Hepatic Disorders

We compared endogenous ω-3 PUFA production to supplementation for improving obesity-related metabolic dysfunction. Fat-1 transgenic mice, who endogenously convert exogenous ω-6 to ω-3 PUFA, and wild-type littermates were fed a high-fat diet and a daily dose of either ω-3 or ω-6 PUFA-rich oil for 12 wk. The endogenous ω-3 PUFA production improved glucose intolerance and insulin resistance but not hepatic steatosis. Conversely, ω-3 PUFA supplementation fully prevented hepatic steatosis but failed to improve insulin resistance. Both models increased hepatic levels of ω-3 PUFA-containing 2-monoacylglycerol and N-acylethanolamine congeners, and reduced levels of ω-6 PUFA-derived endocannabinoids with ω-3 PUFA supplementation being more efficacious. Reduced hepatic lipid accumulation associated with the endocannabinoidome metabolites EPEA and DHEA, which was causally demonstrated by lower lipid accumulation in oleic acid-treated hepatic cells treated with these metabolites. While both models induced a significant fecal enrichment of the beneficial Allobaculum genus, mice supplemented with ω-3 PUFA displayed additional changes in the gut microbiota functions with a significant reduction of fecal levels of the proinflammatory molecules lipopolysaccharide and flagellin. Multiple-factor analysis identify that the metabolic improvements induced by ω-3 PUFAs were accompanied by a reduced production of the proinflammatory cytokine TNFα, and that ω-3 PUFA supplementation had a stronger effect on improving the hepatic fatty acid profile than endogenous ω-3 PUFA. While endogenous ω-3 PUFA production preferably improves glucose tolerance and insulin resistance, ω-3 PUFA intake appears to be required to elicit selective changes in hepatic endocannabinoidome signaling that are essential to alleviate high-fat diet-induced hepatic steatosis.

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.

Protective Effect of Diet-Supplemented and Endogenously Produced Omega-3 Fatty Acids against HFD-Induced Colon Inflammation in Mice

Perilla (Perilla frutescens) oil reduces high-fat-diet-induced colon inflammation by suppressing the NF-κB pathway. In the current study, we compared the effect of endogenously produced and externally supplemented omega-3 fatty acids on high-fat-diet-induced colon inflammation. The fat-1 transgenic mice that endogenously synthesize omega-3 fatty acids were backcrossed with C57BL/6J wild-type mice to obtain transgenic (TR) and wild-type (WT) littermates. Five-week-old male littermates were divided into five groups: two groups fed 10% normal diet (WTLD, TRLD) and three groups fed with a 60% fat high-fat diet (WTHD, TRHD, and WTPO). In the WTPO group, 8% (w/w) of perilla oil was added. Perilla oil supplemented WT mice and fat-1 transgenic mice suppressed high-fat-diet-induced body weight and improved serum lipid levels. Furthermore, the WTPO and TRHD groups exhibited increased colon length, lower macroscopic scores, and reduced levels of pro-inflammatory markers and improved epithelial integrity barrier markers. The expression of GPR120 was increased in the WTPO group. Altogether, our results indicated that perilla oil could improve the symptoms of colon inflammation as an alternate omega-3 fatty acid supplement.

N-3 Polyunsaturated Fatty Acid Dehydrogenase Fat-1 Regulates Mitochondrial Energy Metabolism by Altering DNA Methylation in Isolated Cells of Transgenic Cattle

The fatty acid dehydrogenase fat-1 gene, derived from Caenorhabditis elegans, encodes n-3 polyunsaturated fatty acid dehydrogenase (Δ15 desaturase) and catalyzes the 18–20-carbon n-6 polyunsaturated fatty acids (n-6 PUFA) to generate corresponding n-3 polyunsaturated fatty acids (n-3 PUFA). Subsequently, fat-1 can influence the n-6: n-3 PUFA ratio in fat-1 transgenic cells. This study aimed to explore which processes of energy metabolism are affected exogenous fat-1 transgene and the relationship between these effects and DNA methylation. Compared with the wild-type group, the n-3 PUFA content in fat-1 transgenic bovine fetal fibroblasts was significantly increased, and the n-6 PUFA content and the n-6: n-3 PUFA ratio decreased. In the context of energy metabolism, the increase of exogenous fat-1 transgene decreased ATP synthesis by 39% and reduced the activity and expression of key rate-limiting enzymes in glycolysis, the tricarboxylic acid cycle, and oxidative phosphorylation, thus weakening the cells’ capacity for ATP production. DNA methylation sequencing indicated that this inhibition of gene expression may be due to altered DNA methylation that regulates cell energy metabolism. Exogenous fat-1 transgenic cells showed changes in the degree of methylation in the promoter region of genes related to energy metabolism rate-limiting enzymes. We suggest that alters the balance of n-6/n-3 PUFA could regulate altered DNA methylation that affect mitochondrial energy metabolism.

Synthesis of encapsulated fish oil using whey protein isolate to prevent the oxidative damage and cytotoxicity of titanium dioxide nanoparticles in rats

Fish oil exhibited several beneficial effects on human health; however, its applications face several challenges such as its effects on the organoleptic properties of food and its susceptibility to oxidation. Titanium dioxide NPs (TiO₂-NPs) are utilized widely in pharmaceutical and food applications although there are some reports about their oxidative damage to living organisms. The current work was undertaken to identify fatty acids content in mullet fish oil, encapsulation, and characterization of the oil, and to assess the protective efficiency of the encapsulated mullet fish oil (EMFO) against the oxidative damage and genotoxicity of TiO₂-NPs in rats. Sixty female Sprague-Dawley rats were distributed to 6 groups and treated for 21 days included the control group; TiO₂-NPs-treated group (50 mg/kg b.w); the groups treated with EMFO (50 or 100 mg/kg b.w) and the groups received TiO₂-NPs plus EMFO at the low or high dose. Samples of blood, liver, and kidney were taken for different assays and histological studies. The GC-FID analysis showed that a total of 14 different fatty acids were found in Mullet fish oil included 41.4% polyunsaturated fatty acids (PUFAs), 31.1% monounsaturated fatty acids (MUFAs), and 25.1% saturated fatty acids (SFAs). The structure of EMFO was spherical with an average diameter of 234.5 nm and a zeta potential of -6.24 mV and was stable up to 10 days at 25 °C with EE of 81.08%. The PV of EMFO was decreased at 5 days then increased at 15 days; however, TBARS was increased throughout the storage time over 15 days. The biological evaluation showed that TiO₂-NPs disturb the hepato-nephro functions, lipid profile, inflammatory cytokines, oxidative stress markers, antioxidant enzymes activity, and their corresponding gene expression along with severe pathological alterations in both hepatic and renal tissue. Co-administration of EMFO induced a strong antioxidant role, and the high level could normalize the majority of the parameters tested and the histological picture of the hepatic and renal tissues. These results pointed out that the encapsulation technology enhances the protective role of EMFO against oxidative stress and genotoxicity of TiO₂-NPs through the prevention of ω-3 PUFAs oxidation and controlling their release.

Concise syntheses and anti-inflammatory effects of isocorniculatolide B and corniculatolide B and C

The first total syntheses of isocorniculatolide B, corniculatolide B, and corniculatolide C, consisting of isomeric corniculatolide skeletons, have been accomplished in a divergent manner. The key features of the synthesis involve the construction of diaryl ether linkages by nucleophilic aromatic substitution, installation of a C14-substituted alkyl side chain via a sequence of Baeyer-Villiger reaction and Claisen rearrangement, and efficient construction of corniculatolide and isocorniculatolide frameworks, including 17-membered (exterior) macrolactone skeletons from a versatile diaryl ether intermediate by Mitsunobu macrolactonization. Moreover, we prepared the structural congeners of isomeric corniculatolides via diverted total synthesis approach including desmethyl analogues and related dimeric macrolides. The anti-inflammatory activities of the synthesized natural products, analogues and synthetic intermediates were also investigated. In particular, corniculatolide B significantly inhibited the protein expression of COX-2 and the mRNA expressions of TNF-α, IL-1β and IL-6 by inhibiting of NF-κB signaling in intestinal epithelial cells induced by lipopolysaccharide treatment. It also significantly inhibited the promoter activity and the phosphorylation of subunits p50 and p65 of NF-κB to the same extent as Bay 11-7082, a potent IκB kinase inhibitor. These results suggest that corniculatolide B might have therapeutic potential in inflammatory bowel disease via NF-κB signaling pathway.

Effects of a Fish Oil Rich in Docosahexaenoic Acid on Cardiometabolic Risk Factors and Oxidative Stress in Healthy Rats

Omega-3 polyunsaturated fatty acids are associated with a lower risk of cardiometabolic diseases. However, docosahexaenoic acid (DHA) is easily oxidized, leading to cellular damage. The present study examined the effects of an increased concentration of DHA in fish oil (80% of total fatty acids) on cardiometabolic risk factors and oxidative stress compared to coconut oil, soybean oil, and fish oil containing eicosapentaenoic acid (EPA) and DHA in a balanced ratio. Forty healthy male Sprague-Dawley rats were supplemented with corresponding oil for 10 weeks. Supplementation with the fish oil containing 80% DHA decreased plasma fat, plasma total cholesterol and muscle fat compared to the coconut oil and the soybean oil. Increasing concentrations of DHA induced incorporation of DHA and EPA in cell membranes and tissues along with a decrease in ω-6 arachidonic acid. The increase in DHA promoted lipid peroxidation, protein carbonylation and antioxidant response. Taken together, the increased concentration of DHA in fish oil reduced fat accumulation compared to the coconut oil and the soybean oil. This benefit was accompanied by high lipid peroxidation and subsequent protein carbonylation in plasma and in liver. In our healthy framework, the slightly higher carbonylation found after receiving fish oil containing 80% DHA might be a protecting mechanism, which fit with the general improvement of antioxidant defense observed in those rats.

Hepatic cholesterol transport and its role in non-alcoholic fatty liver disease and atherosclerosis

Non-alcoholic fatty liver disease (NAFLD) is a quickly emerging global health problem representing the most common chronic liver disease in the world. Atherosclerotic cardiovascular disease represents the leading cause of mortality in NAFLD patients. Cholesterol metabolism has a crucial role in the pathogenesis of both NAFLD and atherosclerosis. The liver is the major organ for cholesterol metabolism. Abnormal hepatic cholesterol metabolism not only leads to NAFLD but also drives the development of atherosclerotic dyslipidemia. The cholesterol level in hepatocytes reflects the dynamic balance between endogenous synthesis, uptake, esterification, and export, a process in which cholesterol is converted to neutral cholesteryl esters either for storage in cytosolic lipid droplets or for secretion as a major constituent of plasma lipoproteins, including very-low-density lipoproteins, chylomicrons, high-density lipoproteins, and low-density lipoproteins. In this review, we describe decades of research aimed at identifying key molecules and cellular players involved in each main aspect of hepatic cholesterol metabolism. Furthermore, we summarize the recent advances regarding the biological processes of hepatic cholesterol transport and its role in NAFLD and atherosclerosis.

Renin angiotensin system blockage by losartan neutralize hypercholesterolemia-induced inflammatory and oxidative injuries

Objectives: This study explores the protective role of losartan (LT) against oxidative and inflammatory damages in different physiological systems including heart, liver, and kidney tissue in hypercholesterolemic rats.

Methods: After induction of hypercholesterolemia by high cholesterol diet for 6 weeks, LT was administered for 4 weeks. In serum, the levels of lipoproteins, aminotransferases, creatine kinases, urea, apoptosis, and inflammatory markers were measured. In cardiac, hepatic, and renal tissues, lipid peroxidation product and GSH as well as antioxidant enzymatic activities were assayed. Finally, histopathological assessment evaluated the structural damage in cardiac, hepatic, and renal tissues.

Results: Serum markers of cardiac, hepatic, and renal toxicities including creatine kinases, aminotransferases, and urea were attenuated by LT in hypercholesterolemic animals. Moreover, LT markedly corrected the elevated levels of lipoproteins, apoptosis, and inflammatory biomarkers. Hypercholesterolemia-induced lipid peroxidation, low GSH levels, and diminished activities of antioxidant enzymes were prominently improved in LT treated animals. Histopathological alterations by hypercholesterolemia in heart, liver, and kidney tissues were ameliorated by LT.

Conclusion: This study confirmed the pathological enrollment of renin–angiotensin system in hypercholesterolemia-associated metabolic alterations. LT had a significant cardiac, hepatic, and renal protective role against these impairments through down-regulation of oxidative damage, inflammation and necrosis.

Sitosterolemia: Twenty Years of Discovery of the Function of ABCG5ABCG8

Sitosterolemia is a lipid disorder characterized by the accumulation of dietary xenosterols in plasma and tissues caused by mutations in either ABCG5 or ABCG8. ABCG5 ABCG8 encodes a pair of ABC half transporters that form a heterodimer (G5G8), which then traffics to the surface of hepatocytes and enterocytes and promotes the secretion of cholesterol and xenosterols into the bile and the intestinal lumen. We review the literature from the initial description of the disease, the discovery of its genetic basis, current therapy, and what has been learned from animal, cellular, and molecular investigations of the transporter in the twenty years since its discovery. The genomic era has revealed that there are far more carriers of loss of function mutations and likely pathogenic variants of ABCG5 ABCG8 than previously thought. The impact of these variants on G5G8 structure and activity are largely unknown. We propose a classification system for ABCG5 ABCG8 mutants based on previously published systems for diseases caused by defects in ABC transporters. This system establishes a framework for the comprehensive analysis of disease-associated variants and their impact on G5G8 structure-function.

The Effects of the Combination of Buckwheat D-Fagomine and Fish Omega-3 Fatty Acids on Oxidative Stress and Related Risk Factors in Pre-Obese Rats

The combined supplementation of buckwheat D-fagomine (FG) and fish omega-3 polyunsaturated fatty acids (ω-3 PUFA) attenuates the development of insulin resistance in rats fed a high-fat (HF) diet. This study aimed to examine the effects of combined supplementation with FG and ω-3 PUFA on dyslipidemia, transaminases, interleukin-6, and oxidative stress. Forty-five male Sprague-Dawley rats were fed a standard diet, an HF diet, an HF diet supplemented with FG, an HF diet supplemented with ω-3 PUFA, or an HF diet supplemented with FG and ω-3 PUFA for 21 weeks. Triacylglycerol, cholesterol, aspartate aminotransferase, alanine aminotransferase, and interleukin-6 were measured. The assessment of oxidative stress included plasma antioxidant capacity, antioxidant enzyme activities, glutathione content, lipid peroxidation, and protein carbonylation. The combined supplementation with FG and ω-3 PUFA did not attenuate the slight accumulation of liver cholesterol induced by the HF diet but normalized the plasma alanine aminotransferase activity. Rats fed the HF diet supplemented with the combination showed a lower amount of plasma interleukin-6 than those fed a standard diet. The combination attenuated oxidative damage induced by the HF diet, decreased antioxidant enzyme activities, and enhanced glutathione status. The beneficial effects of the combination of FG and ω-3 PUFA on oxidative stress and related risk factors in pre-obese rats were mainly modulated by ω-3 PUFA.

Deletion of KLF10 Leads to Stress-Induced Liver Fibrosis upon High Sucrose Feeding

Liver fibrosis is a consequence of chronic liver injury associated with chronic viral infection, alcohol abuse, and nonalcoholic fatty liver. The evidence from clinical and animal studies indicates that transforming growth factor-β (TGF-β) signaling is associated with the development of liver fibrosis. Krüppel-like factor 10 (KLF10) is a transcription factor that plays a significant role in TGF-β-mediated cell growth, apoptosis, and differentiation. In recent studies, it has been reported to be associated with glucose homeostasis and insulin resistance. In the present study, we investigated the role of KLF10 in the progression of liver disease upon a high-sucrose diet (HSD) in mice. Wild type (WT) and Klf10 knockout (KO) mice were fed either a control chow diet or HSD (50% sucrose) for eight weeks. Klf10 KO mice exhibited significant hepatic steatosis, inflammation, and liver injury upon HSD feeding, whereas the WT mice exhibited mild hepatic steatosis with no apparent liver injury. The livers of HSD-fed Klf10 KO mice demonstrated significantly increased endoplasmic reticulum stress, oxidative stress, and proinflammatory cytokines. Klf10 deletion led to the development of sucrose-induced hepatocyte cell death both in vivo and in vitro. Moreover, it significantly increased fibrogenic gene expression and collagen accumulation in the liver. Increased liver fibrosis was accompanied by increased phosphorylation and nuclear localization of Smad3. Here, we demonstrate that HSD-fed mice develop a severe liver injury in the absence of KLF10 due to the hyperactivation of the endoplasmic reticulum stress response and CCAAT/enhance-binding protein homologous protein (CHOP)-mediated apoptosis of hepatocytes. The current study suggests that KLF10 plays a protective role against the progression of hepatic steatosis into liver fibrosis in a lipogenic state.

Limited potential of resolvin D1 in treatment of cholestatic liver fibrosis

Background

Several studies suggest a role for EPA- and DHA-derived pro-resolving mediators like resolvins in reversing metabolic and inflammatory disturbances seen in various chronic diseases. Here, we investigated the effects of resolvin D1 (RvD1) on bile duct ligation (BDL)-induced cholestatic liver injury.

Methods

Mice were treated daily with RvD1 or 0.1% ethanol (control) from the day of BDL until the final observation time points. Blood and liver tissue were collected 2, 5 and 14 days after BDL for different analyses.

Results

RvD1 treatment of mice had no impact on the extent of cholestatic liver injury upon BDL, neither in the acute phase nor in the progressive state of liver fibrosis. Although RvD1 treatment resulted in a significantly reduced activity of hepatic stellate cells as well as reduced deposition of extracellular matrix 2 days after BDL, mice were not protected from inflammation and further fibrosis progression.

Conclusions

These data indicate that RvD1 has a limited therapeutic potential to treat cholestatic liver diseases, as it has no significant impact on regression of hepatic necroinflammation and fibrotic changes in bile duct-ligated mice.

Role of n-3 Fatty Acids on Bile Acid Metabolism and Transport in Dyslipidemia: A Review

Dietary n-3 fatty acids, especially of marine origin, eicosapentaenoic acid (20:5n-3) and docosahexaenoic acid (22:6n-3), have always been lauded for their profound effects on regulating the risk factors for major metabolic disorders. Yet, their consumption rate is poor compared to n-6 fatty acids [linoleic acid (18:2n-6)], which are predominantly consumed. Hence, the skewed n-6 to n-3 fatty acid ratio may have a bearing on the risk factors of various diseases, including dyslipidemia. Dyslipidemia and other lifestyle diseases associated with it, such as diabetes, obesity, hypertension, are a growing concern in both developed and developing countries. A common strategy for addressing dyslipidemia involves bile acid (BA) sequestration, to interrupt the enterohepatic circulation of BA, resulting in the modulation of lipid absorption in the intestine, thereby normalizing the levels of circulating lipids. The BA homeostasis is under the tight control of hepatic and enteric BA transporters. Many investigations have reported the effects of dietary constituents, including certain fatty acids on the reabsorption and transport of BA. However, a critical review of the effects of n-3 fatty acids on BA metabolism and transport is not available. The present review attempts to explore certain unmapped facets of the n-3 fatty acids on BA metabolism and transport in dyslipidemia, and their interplay with biological processes involving lipid rafts and gut microbiome.

Targeting n-3 Polyunsaturated Fatty Acids in Non-Alcoholic Fatty Liver Disease

BACKGROUND

Non-Alcoholic Fatty Liver Disease (NAFLD) is characterized by abnormal hepatic accumulation of triacylglycerides in the absence of alcohol consumption, in association with Oxidative Stress (OS), a pro-inflammatory state and Insulin Resistance (IR), which are attenuated by n-3 long-chain polyunsaturated Fatty Acids (FAs) C20-C22 (LCPUFAs) supplementation. Main causes of NAFLD comprise high caloric intake and a sedentary lifestyle, with high intakes of saturated FAs.

METHODS

The review includes several searches considering the effects of n-3 LCPUFAs in NAFLD in vivo and in vitro models, using the PubMed database from the National Library of Medicine- National Institutes of Health.

RESULT

The LCPUFAs eicosapentaenoic acid (C20:5 n-3, EPA) and docosahexaenoic acid (C22:6 n- 3, DHA) have a positive effect in diminishing liver steatosis, OS, and the levels of aspartate aminotransferase, alanine aminotransferase and pro-inflammatory cytokines, with improvement of insulin sensitivity and adiponectin levels. The molecular pathways described for n-3 LCPUFAs in cellular and animal models and humans include peroxisome proliferator-activated receptor-α activation favouring FA oxidation, diminution of lipogenesis due to sterol responsive element binding protein-1c downregulation and inflammation resolution. Besides, nuclear factor erythroid-2-related factor-2 activation is elicited by n-3 LCPUFA-derived oxidation products producing direct and indirect antioxidant responses, with concomitant anti-fibrogenic action.

CONCLUSION

The discussed effects of n-3 LCPUFA supplementation support its use in NAFLD, although having a limited value in NASH, a contention that may involve n-3 LCPUFA oxygenated derivatives. Clinical trials establishing optimal dosages, intervention times, type of patients and possible synergies with other natural products are needed in future studies.

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.

Improved Diabetic Wound Healing by EGF Encapsulation in Gelatin-Alginate Coacervates

Topical imageplication of epidermal growth fctor (EGF) has been used to accelerate diabetic foot ulcers but with limited efficacy. In this study, we selected a complex coacervate (EGF-Coa) composed of the low molecular weight gelatin type A and sodium alginate as a novel delivery system for EGF, based on encapsulation efficiency and protection of EGF from protease. EGF-Coa enhanced in vitro migration of keratinocytes and accelerated wound healing in streptozotocin-induced diabetic mice with increased granulation and re-epithelialization. While diabetic wound sites without treatment showed downward growth of hyperproliferative epidermis along the wound edges with poor matrix formation, EGF-Coa treatment recovered horizontal migration of epidermis over the newly deposited dermal matrix. EGF-Coa treatment also resulted in reduced levels of proinflammatory cytokines IL-1, IL-6, and THF-α. Freeze-dried coacervates packaged in aluminum pouches were stable for up to 4 months at 4 and 25 °C in terms of appearance, purity by RP-HPLC, and in vitro release profiles. There were significant physical and chemical changes in relative humidity above 33% or at 37 °C, suggesting the requirement for moisture-proof packaging and cold chain storage for long term stability. We propose low molecular weight gelatin type A and sodium alginate (LWGA-SA) coacervates as a novel EGF delivery system with enhanced efficacy for chronic wounds.

Cyanidin Chloride Induces Apoptosis by Inhibiting NF-κB Signaling through Activation of Nrf2 in Colorectal Cancer Cells

Colorectal cancer (CRC) is the third most common cancer worldwide and a leading cause of cancer-related deaths in developed countries. Anthocyanins are a class of flavonoids, widely distributed in food, exhibiting important biological effects. Cyanidin chloride (CyCl) is the common type of anthocyanin with antioxidative and anti-inflammatory potential. The present study aimed to investigate the molecular mechanisms underlying the chemotherapeutic effects of CyCl in colorectal cancer cells. We found that CyCl treatment induced apoptosis as well as a significant inhibition of cellular proliferation and colony formation in three colon cancer HCT116, HT29, and SW620 cells. In addition, CyCl suppressed nuclear factor-kappa B (NF-κB) signaling and induced the activation of the nuclear factor erythroid 2-related factor 2 (Nrf2) pathway in tumor necrosis factor-alpha (TNF-α)-stimulated colon cancer cells. Nrf2 and NF-κB are two key transcription factors regulating antioxidative responses and cellular proliferation, respectively. In this study, knockdown of Nrf2 by small interfering RNA (siRNA) transfection inhibited the effect of CyCl on NF-κB signaling and apoptosis, suggesting that there is functional crosstalk between Nrf2 and NF-κB. Our findings demonstrate the important role of Nrf2 in inducing apoptosis through the involvement of NF-κB signaling in colorectal cancer cells, suggesting that CyCl may be used as a potential therapeutic agent for CRC.

Hepatoprotective Effects of Steamed and Freeze-Dried Mature Silkworm Larval Powder against Ethanol-Induced Fatty Liver Disease in Rats

Silkworm, Bombyx mori, contains high amounts of beneficial nutrients, including amino acids, proteins, essential minerals, and omega-3 fatty acids. We have previously reported a technique for producing steamed and freeze-dried mature silkworm larval powder (SMSP), which makes it easier to digest mature silkworm. In this study, we investigated the preventive effects of SMSP on alcoholic fatty liver disease and elucidated its mechanism of action. Male Sprague-Dawley rats treated with SMSP (50 mg/kg) or normal diet (AIN-76A) were administered 25% ethanol (3 g/kg body weight) by oral gavage for 4 weeks. SMSP administration for 4 weeks significantly decreased hepatic fat accumulation in ethanol-treated rats by modulating lipogenesis and fatty acid oxidation-related molecules such as sirtuin 1, AMP-activated protein kinase, and acetyl-CoA carboxylase 1. Moreover, SMSP administration significantly diminished the levels of triglyceride in liver tissues by as much as 35%, as well as lowering the serum levels of triglyceride, gamma glutamyl transpeptidase, alanine transaminase, and aspartate aminotransferase in ethanol-treated rats. SMSP supplementation also decreased the pro-inflammatory tumor necrosis factor-alpha and interleukin 1 beta levels and cytochrome P450 2E1 generating oxidative stress. These results suggest that SMSP administration may be possible for the prevention of alcoholic liver disease.

Administration of Steamed and Freeze-Dried Mature Silkworm Larval Powder Prevents Hepatic Fibrosis and Hepatocellular Carcinogenesis by Blocking TGF-β/STAT3 Signaling Cascades in Rats

Hepatocellular carcinoma (HCC) is the leading cause of cancer-related deaths worldwide and the majority of HCC patients occur with a background of hepatic fibrosis and cirrhosis. We have previously reported the hepatoprotective effects of steamed and freeze-dried mature silkworm larval powder (SMSP) in a chronic ethanol-treated rat model. Here, we assessed the anti-fibrotic and anti-carcinogenic effects of SMSP on diethylnitrosamine (DEN)-treated rats. Wistar rats were intraperitoneally injected with DEN once a week for 12 or 16 weeks with or without SMSP administration (0.1 and 1 g/kg). SMSP administration significantly attenuated tumor foci formation and proliferation in the livers of the rats treated with DEN for 16 weeks. SMSP administration also inhibited hepatic fibrosis by decreasing the levels of collagen fiber and the expression of pro-collagen I and alpha-smooth muscle actin (α-SMA). Moreover, SMSP supplementation improved the major parameters of fibrosis such as transforming growth factor-β (TGF-β), connective tissue growth factor (CTGF), tumor necrosis factor-alpha (TNF-α), plasminogen activator inhibitor-1 (PAI-1), and collagen type I (Col1A1) in the livers from the rats treated with DEN for 16 weeks. As s possible mechanisms, we investigated the effects of SMSP on the TGF-β and signal transducer and activator of transcription 3 (STAT3)-mediated signaling cascades, which are known to promote hepatic fibrosis. We found that SMSP treatment inhibited the activation of TGF-β and the phosphorylation of STAT3 pathway in DEN-treated rats. Moreover, SMSP administration suppressed the expressions of the target genes of TGF-β and STAT3 induced by DEN treatment. Our findings provide experimental evidences that SMSP administration has inhibitory effects of hepatic fibrosis and HCC induced by DEN in vivo and could be a promising strategy for the prevention or treatment of hepatic fibrosis and hepatocellular carcinogenesis.

Endogenously increased n-3 PUFA levels in fat-1 transgenic mice do not protect from non-alcoholic steatohepatitis

Background

Non-alcoholic fatty liver disease (NAFLD) is the most common chronic liver disease worldwide, ranging from simple steatosis to non-alcoholic steatohepatitis (NASH) and fibrosis. Possible reasons for the NAFLD epidemic in industrialized countries are the high intake of pro-inflammatory n-6 polyunsaturated fatty acids (n-6 PUFAs) and low consumption of healthy n-3 PUFAs. Due to their anti-inflammatory properties, n-3 PUFAs may have the potential to alleviate chronic liver disease. Herein, we examined the therapeutic effect of increased n-3 PUFA tissue levels in fat-1 transgenic mice on progressive NASH.

Methods

Disease was induced in mice by streptozotocin and high fat diet (STZ/HFD) resulting in NASH. NAFLD in 6 and 8 weeks old wild type and fat-1 transgenic STZ/HFD treated mice was analyzed. Unlike all other mammals, fat-1 transgenic mice ubiquitously express an n-3 fatty acid desaturase, which converts n-6 to n-3 PUFAs, leading to increased n-3 and decreased n-6 PUFA tissue contents.

Results

Liver damage, NAFLD activity score (NAS), hepatic lipid accumulation and inflammation were significantly reduced in fat-1 transgenic STZ/HFD treated mice in the early (6 weeks) but not late (8 weeks) phase of NASH. Simultaneously, mRNA expression of genes involved in fatty acid uptake and storage (Cd36 and Plin3, respectively) was significantly down-regulated in 6 week old but not 8 week old fat-1 transgenic STZ/HFD treated mice.

Conclusions

Endogenously elevated n-3 PUFA levels in fat-1 transgenic mice transiently delay the onset of STZ/HFD induced NASH but failed to efficiently protect from NASH development.

Anti-Obesity Effect of Standardized Extract of Microalga Phaeodactylum tricornutum Containing Fucoxanthin

Fucoxanthin (FX), a marine carotenoid found in macroalgae and microalgae, exhibits several beneficial effects to health. The anti-obesity activity of FX is well documented, but FX has not been mass-produced or applied extensively or commercially because of limited availability of raw materials and complex extraction techniques. In this study, we investigated the anti-obesity effect of standardized FX powder (Phaeodactylum extract (PE)) developed from microalga Phaeodactylum tricornutum as a commercial functional food. The effects of PE on adipogenesis inhibition in 3T3-L1 adipocytes and anti-obesity in high-fat diet (HFD)-fed C57BL/6J mice were evaluated. PE and FX dose-dependently decreased intracellular lipid contents in adipocytes without cytotoxicity. In HFD-fed obese mice, PE supplementation for six weeks decreased body weight, organ weight, and adipocyte size. In the serum parameter analysis, the PE-treated groups showed attenuation of lipid metabolism dysfunction and liver damage induced by HFD. In the liver, uncoupling protein-1 (UCP1) upregulation and peroxisome proliferator activated receptor γ (PPARγ) downregulation were detected in the PE-treated groups. Additionally, micro computed tomography revealed lower fat accumulation in PE-treated groups compared to that in the HFD group. These results indicate that PE exerts anti-obesity effects by inhibiting adipocytic lipogenesis, inducing fat mass reduction and decreasing intracellular lipid content, adipocyte size, and adipose weight.

Beneficial role of bioactive lipids in the pathobiology, prevention, and management of HBV, HCV and alcoholic hepatitis, NAFLD, and liver cirrhosis: A review

It has been suggested that hepatitis B virus (HBV)- and hepatitis C virus (HCV)-induced hepatic damage and cirrhosis and associated hypoalbuminemia, non-alcoholic fatty liver disease (NAFLD), and alcoholic fatty liver disease (AFLD) are due to an imbalance between pro-inflammatory and anti-inflammatory bioactive lipids. Increased tumour necrosis factor (TNF)-α production induced by HBV and HCV leads to a polyunsaturated fatty acid (PUFA) deficiency and hypoalbuminemia. Albumin mobilizes PUFAs from the liver and other tissues and thus may aid in enhancing the formation of anti-inflammatory lipoxins, resolvins, protectins, maresins and prostaglandin E1 (PGE1) and suppressing the production of pro-inflammatory PGE2. As PUFAs exert anti-viral and anti-bacterial effects, the presence of adequate levels of PUFAs could inactivate HCV and HBV and prevent spontaneous bacterial peritonitis observed in cirrhosis. PUFAs, PGE1, lipoxins, resolvins, protectins, and maresins suppress TNF-α and other pro-inflammatory cytokines, exert cytoprotective effects, and modulate stem cell proliferation and differentiation to promote recovery following hepatitis, NAFLD and AFLD. Based on this evidence, it is proposed that the administration of albumin in conjunction with PUFAs and their anti-inflammatory products could be beneficial for the prevention of and recovery from NAFLD, hepatitis and cirrhosis of the liver. NAFLD is common in obesity, type 2 diabetes mellitus, and metabolic syndrome, suggesting that even these diseases could be due to alterations in the metabolism of PUFAs and other bioactive lipids. Hence, PUFAs and co-factors needed for their metabolism and albumin may be of benefit in the prevention and management of HBV, HCV, alcoholic hepatitis and NAFLD, and liver cirrhosis.

A maresin 1/RORα/12-lipoxygenase autoregulatory circuit prevents inflammation and progression of nonalcoholic steatohepatitis

Retinoic acid-related orphan receptor α (RORα) is considered a key regulator of polarization in liver macrophages that is closely related to nonalcoholic steatohepatitis (NASH) pathogenesis. However, hepatic microenvironments that support the function of RORα as a polarity regulator were largely unknown. Here, we identified maresin 1 (MaR1), a docosahexaenoic acid (DHA) metabolite with a function of specialized proresolving mediator, as an endogenous ligand of RORα. MaR1 enhanced the expression and transcriptional activity of RORα and thereby increased the M2 polarity of liver macrophages. Administration of MaR1 protected mice from high-fat diet-induced NASH in a RORα-dependent manner. Surprisingly, RORα increased the level of MaR1 through transcriptional induction of 12-lipoxygenase (12-LOX), a key enzyme in MaR1 biosynthesis. Furthermore, we demonstrated that modulation of 12-LOX activity enhanced the protective function of DHA against NASH. Together, these results suggest that the MaR1/RORα/12-LOX autoregulatory circuit could offer potential therapeutic strategies for curing NASH.

N-3 polyunsaturated fatty acids: An innovative strategy against obesity and related metabolic disorders, intestinal alteration and gut microbiota dysbiosis

Obesity is now widely recognized to be associated with low-grade systemic inflammation. It has been shown that high-fat feeding modulates gut microbiota which strongly increased intestinal permeability leading to lipopolysaccharide absorption causing metabolic endotoxemia that triggers inflammation and metabolic disorders. N-3 polyunsaturated fatty acids (PUFAs) have been shown associated with anti-obesity properties, but results still remain heterogeneous and very few studies underlined the metabolic pathways involved. Thus, the use of Fat-1 transgenic mice allows to better understanding whether endogenous n-3 PUFAs enrichment contributes to obesity and associated metabolic disorders prevention. It specially evidence that such effects occur through modulations of gut microbiota and intestinal permeability. Then, by remodeling gut microbiota, endogenous n-3 PUFAs improve HF/HS-diet induced features of the metabolic syndrome which in turn affects host metabolism. Thus, increasing anti-obesogenic microbial species in the gut microbiota population (i.e Akkermansia) by appropriate n-3 PUFAs may represent a promising strategy to control or prevent metabolic diseases.

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.

The Transplantation of ω3 PUFA-Altered Gut Microbiota of fat-1 Mice to Wild-Type Littermates Prevents Obesity and Associated Metabolic Disorders

Altering the gut microbiome may be beneficial to the host and recently arose as a promising strategy to manage obesity. Here, we investigated the relative contribution of ω3 polyunsaturated fatty acid (PUFA)-mediated alterations in the microbiota to metabolic parameter changes in mice. Four groups were compared: male fat-1 transgenic mice (with constitutive production of ω3 PUFAs) and male wild-type (WT) littermates fed an obesogenic (high fat/high sucrose [HFHS]) or a control diet. Unlike WT mice, HFHS-fed fat-1 mice were protected against obesity, glucose intolerance, and hepatic steatosis. Unlike WT mice, fat-1 mice maintained a normal barrier function, resulting in a significantly lower metabolic endotoxemia. The fat-1 mice displayed greater phylogenic diversity in the cecum, and fecal microbiota transplantation from fat-1 to WT mice was able to reverse weight gain and to normalize glucose tolerance and intestinal permeability. We concluded that the ω3 PUFA-mediated alteration of gut microbiota contributed to the prevention of metabolic syndrome in fat-1 mice. It occurred independently of changes in the PUFA content of host tissues and may represent a promising strategy to prevent metabolic disease and preserve a lean phenotype.

Substitution of linoleic acid with α-linolenic acid or long chain n-3 polyunsaturated fatty acid prevents Western diet induced nonalcoholic steatohepatitis

Imbalance in the n-6 polyunsaturated fatty acids (PUFA) and n-3 PUFA in the Western diet may increase the risk of nonalcoholic fatty liver disease (NAFLD). This study investigates the impact of substitution of linoleic acid with α-linolenic acid (ALA) or long chain (LC) n-3 PUFA and hence decreasing n-6:n-3 fatty acid ratio on high fat, high fructose (HFHF) diet induced nonalcoholic steatohepatitis (NASH). Male Sprague-Dawley rats were divided into four groups and fed control diet, HFHF diet (n-6:n-3 ratio of 200), HFHF diet with ALA (n-6:n-3 ratio of 2) or HFHF diet with LC n-3 PUFA (n-6:n-3 ratio of 5) for 24 weeks. Rats fed HFHF diet with n-6:n-3 ratio of 200 resulted in hepatic steatosis, induced glucose intolerance, insulin resistance and oxidative stress accompanied by increase in markers of inflammation, plasma lipids and aminotransferase levels. Histopathological examination of liver further confirmed the establishment of NASH. ALA and LC n-3 PUFA supplementation prevented hepatic steatosis and dyslipidemia by inhibiting lipogenesis and increasing insulin sensitivity. Furthermore, n-3 PUFA supplementation attenuated hepatic oxidative stress by restoring antioxidant status, decreased inflammation and preserved hepatic architecture. These finding suggest that decreasing n-6:n-3 ratio prevented HFHF induced NASH by attenuating oxidative stress and inflammation.

fat-1 mice prevent high-fat plus high-sugar diet-induced non-alcoholic fatty liver disease

High-fat and high-sugar (HFS) diets have been suggested to play a causal role in the pathogenesis of non-alcoholic fatty liver disease (NAFLD). This study aimed to investigate whether fat-1 transgenic mice with a higher tissue content of n-3 polyunsaturated fatty acids (PUFAs) could prevent HFS diet-induced NAFLD, compared with wild-type mice. The fat-1 and wild-type littermates had free access to a 15% fructose solution plus high-fat diet, a 15% glucose solution plus high-fat diet, or a 15% sucrose solution plus high-fat diet, respectively. Caloric intake, weight gain, biochemical parameters, histology, and gene and protein expression levels were measured after 8 weeks of intervention. Liquid intake in glucose- or sucrose-fed mice was about 2-fold compared with that in fructose-fed mice. The wild-type mice given glucose showed the highest total caloric intake and weight gain compared to the other groups. The serum concentrations of total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), and alanine transaminase (ALT) were significantly lowered in fat-1 groups compared with their paired wild-type groups. Histological analysis showed that the wild-type groups fed the HFS diets developed hepatic lipid accumulation and steatosis, compared with the fat-1 groups. The gene and protein expression levels involved in fatty acid synthesis and the toll-like receptor (TLR)-4 signaling pathway were significantly inhibited in the fat-1 groups compared with the wild-type groups. The endogenously synthesized n-3 PUFAs of the three fat-1 groups, which inhibit fatty acid synthesis and the TLR-4 signaling pathway, prevent HFS diet-induced NAFLD.

A new perspective on lipid research in age-related macular degeneration

There is an urgency to find new treatment strategies that could prevent or delay the onset or progression of AMD. Different classes of lipids and lipoproteins metabolism genes have been associated with AMD in a multiple ways, but despite the ever-increasing knowledge base, we still do not understand fully how circulating lipids or local lipid metabolism contribute to AMD. It is essential to clarify whether dietary lipids, systemic or local lipoprotein metabolismtrafficking of lipids in the retina should be targeted in the disease. In this article, we critically evaluate what has been reported in the literature and identify new directions needed to bring about a significant advance in our understanding of the role for lipids in AMD. This may help to develop potential new treatment strategies through targeting the lipid homeostasis.

FFA4 (GPR120) as a fatty acid sensor involved in appetite control, insulin sensitivity and inflammation regulation

Unsaturated long-chain fatty acids have been suggested to be beneficial in the context of cardiovascular disorders based in epidemiologic studies conducted in Greenland and Mediterranean. DHA and EPA are omega-3 polyunsaturated fatty acids that are plentiful in fish oil, and oleic acid is an omega-9 monounsaturated fatty acid, rich in olive oil. Dietary intake of these unsaturated long-chain fatty acids have been associated with insulin sensitivity and weight loss, which contrasts with the impairment of insulin sensitivity and weight gain associated with high intakes of saturated long-chain fatty acids. The recent discovery that free fatty acid receptor 4 (FFA4, also known as GPR120) acts as a sensor for unsaturated long-chain fatty acids started to unveil the molecular mechanisms underlying the beneficial functions played by these unsaturated long-chain fatty acids in various physiological processes, which include the secretions of gastrointestinal peptide hormones and glucose homeostasis. In this review, the physiological roles and therapeutic significance of FFA4 in appetite control, insulin sensitization, and inflammation reduction are discussed in relation to obesity and type 2 diabetes from pharmacological viewpoints.

Lipid oxidation products in the pathogenesis of non-alcoholic steatohepatitis

Non-alcoholic fatty liver disease (NAFLD) is the major public health challenge for hepatologists in the twenty-first century. NAFLD comprises a histological spectrum ranging from simple steatosis or fatty liver, to steatohepatitis, fibrosis, and cirrhosis. It can be categorized into two principal phenotypes: (1) non-alcoholic fatty liver (NAFL), and (2) non-alcoholic steatohepatitis (NASH). The mechanisms of NAFLD progression consist of lipid homeostasis alterations, redox unbalance, insulin resistance, and inflammation in the liver. Even though several studies show an association between the levels of lipid oxidation products and disease state, experimental evidence suggests that compounds such as reactive aldehydes and cholesterol oxidation products, in addition to representing hallmarks of hepatic oxidative damage, may behave as active players in liver dysfunction and the development of NAFLD. This review summarizes the processes that contribute to the metabolic alterations occurring in fatty liver that produce fatty acid and cholesterol oxidation products in NAFLD, with a focus on inflammation, the control of insulin signalling, and the transcription factors involved in lipid metabolism.

Insights into the function of n-3 PUFAs in fat-1 transgenic cattle

The n-3 PUFAs have many beneficial effects on human health, including roles in immunity, neurodevelopment, and preventing cardiovascular disease. In this study, we established reliable model fat-1 transgenic cattle using transgenic technology and performed a systematic investigation to examine the function of n-3 PUFAs. Our results showed that expression of the fat-1 gene improved several biochemical parameters related to liver function and to plasma glucose and plasma lipid metabolism. Results of global gene and plasma protein expression analysis showed that 310 genes and 13 plasma proteins differed significantly in the blood of fat-1 transgenic cattle compared with WT cattle, reflecting their regulatory roles in the immune and cardiovascular systems. Finally, changes in the gut microflora were also noted in the fat-1 transgenic cattle, suggesting novel roles for n-3 PUFAs in the metabolism of glucose and lipids, as well as anti-stress properties. To the best of our knowledge, this is the first report using multiple parallel analyses to investigate the role of n-3 PUFAs using models such as fat-1 transgenic cattle. This study provides novel insights into the regulatory mechanism of fat-1 in the immune and cardiovascular systems, as well as its anti-stress role.

Hydroxyeicosapentaenoic acids and epoxyeicosatetraenoic acids attenuate early occurrence of nonalcoholic fatty liver disease

BACKGROUND AND PURPOSE

The ω-3 polyunsaturated fatty acids (PUFAs) mediate protective effects on several metabolic disorders. However, the functions of their metabolites in the early stage of nonalcoholic fatty liver disease (NAFLD) are largely unknown.

EXPERIMENTAL APPROACH

Mice were fed a control diet, high-fat diet (HFD) or ω-3 PUFA-enriched HFD (ω3HFD) for 4 days and phenotypes were analysed. LC-MS/MS was used to determine the eicosanoid profiles. Primary hepatocytes and peritoneal macrophages were used for the mechanism study.

KEY RESULTS

In short-term HFD-fed mice, the significantly increased lipid accumulation in the liver was reversed by ω-3 PUFA supplementation. Metabolomics showed that the plasma concentrations of hydroxyeicosapentaenoic acids (HEPEs) and epoxyeicosatetraenoic acids (EEQs) were reduced by a short-term HFD and markedly increased by the ω3HFD. However, HEPE/EEQ treatment had no direct protective effect on hepatocytes. ω3HFD also significantly attenuated HFD-induced adipose tissue inflammation. Furthermore, the expression of pro-inflammatory cytokines and activation of the JNK pathway induced by palmitate were suppressed by HEPEs and EEQs in macrophages. 17,18-EEQ, 5-HEPE and 9-HEPE were identified as the effective components among these metabolites, as indicated by their greater suppression of the palmitate-induced expression of inflammatory factors, chemotaxis and JNK activation compared to other metabolites in macrophages. A mixture of 17,18-EEQ, 5-HEPE and 9-HEPE significantly ameliorated the short-term HFD-induced accumulation of macrophages in adipose tissue and hepatic steatosis.

CONCLUSION AND IMPLICATIONS

17,18-EEQ, 5-HEPE and 9-HEPE may be potential approaches to prevent NAFLD in the early stage by inhibiting the inflammatory response in adipose tissue macrophages via JNK signalling.

Fatty acid and non-alcoholic fatty liver disease: Meta-analyses of case-control and randomized controlled trials

BACKGROUND AND AIMS

Blood and/or liver fatty acid contents of healthy subjects and non-alcoholic fatty liver disease (NAFLD) patients have shown inconsistent associations. In addition, the results of randomized controlled trials (RCTs) in relation to the effects of n-3 polyunsaturated fatty acid (PUFA) supplementation on alanine aminotransferase (ALT), aspartate aminotransferase (AST), liver fat, triglyceride (TAG) and fasting glucose levels are inconsistent. The present study aimed to investigate the differences of fatty acid content in the blood and/or liver tissue between healthy subjects and NAFLD patients, and to quantify the benefits of n-3 PUFA therapy in NAFLD patients.

METHODS

A systematic literature search was performed up to November 2016 using PubMed and Scopus databases. The differences of fatty acid content between cases and controls were calculated as weighted mean differences (WMD) by using a random-effects model. The intervention effects of RCTs were calculated as WMD for net changes in ALT, AST, liver fat, TAG and fasting glucose levels, respectively. Meta-regression with restricted maximum likelihood estimation was used to evaluate a potential linear relationship between confounding factors and effect sizes. Generalized least square was performed for dose-response analysis.

RESULTS

Ten eligible case-control studies and 11 RCTs were included. The pooled estimates of case-control studies showed that blood and/or liver docosahexaenoic acid (DHA) content was significantly higher in the controls compared with cases. The pooled estimates of RCTs showed that n-3 PUFA supplementation significantly reduced the ALT (-7.53 U/L; 95% CI: -9.98, -5.08 U/L), ASL (-7.10 U/L, 95% CI: -11.67, -2.52 U/L) and TAG (-36.16 mg/dL, 95% CI: -49.15, -23.18 mg/dL) concentrations, and marginally reduced the liver fat content (-5.11%, 95% CI: -10.24, 0.02%, P = 0.051), but not fasting glucose. Dose-response analysis of RCTs showed that 1 g per day increment of eicosapentaenoic acid (EPA)+DHA was associated with a 3.14 U/L, 2.43 U/L, 2.74% and 9.97 mg/dL reduction in ALT (95% CI: -5.25, -1.02 U/L), AST (95% CI: -3.90, -0.90 U/L), liver fat (95% CI: -4.32, -1.16%) and TAG (95% CI: -14.47, -5.48 mg/dL) levels, respectively.

CONCLUSIONS

The present meta-analysis provides substantial evidence that n-3 PUFA supplementation, especially DHA, has a favorable effect in treatment of NAFLD.

Amelioration of non-alcoholic fatty liver disease with NPC1L1-targeted IgY or n-3 polyunsaturated fatty acids in mice

Patients with non-alcoholic fatty liver disease (NAFLD) have an increased risk for progression to hepatocellular carcinoma in addition to comorbidities such as cardiovascular and serious metabolic diseases; however, the current therapeutic options are limited. Based on our previous report that omega-3 polyunsaturated fatty acids (n-3 PUFAs) can significantly ameliorate high fat diet (HFD)-induced NAFLD, we explored the therapeutic efficacy of n-3 PUFAs and N-IgY, which is a chicken egg yolk-derived IgY specific for the Niemann-Pick C1-Like 1 (NPC1L1) cholesterol transporter, on NAFLD in mice. We generated N-IgY and confirmed its efficient cholesterol transport-blocking activity in HepG2 and Caco-2 cells, which was comparable to the effect of ezetimibe (EZM). C57BL/6 wild type and fat-1 transgenic mice, capable of producing n-3 PUFAs, were fed a high fat diet (HFD) alone or supplemented with N-IgY. Endogenously synthesized n-3 PUFAs combined with N-IgY led to significant decreases in hepatic steatosis, fibrosis, and inflammation (p<0.01). The combination of N-IgY and n-3 PUFAs resulted in significant upregulation of genes involved in cholesterol uptake (LDLR), reverse cholesterol transport (ABCG5/ABCG8), and bile acid metabolism (CYP7A1). Moreover, fat-1 transgenic mice treated with N-IgY showed significant downregulation of genes involved in cholesterol-induced hepatic stellate cell activation (Tgfb1, Tlr4, Col1a1, Col1a2, and Timp2). Collectively, these data suggest that n-3 PUFAs and N-IgY, alone or in combination, represent a promising treatment strategy to prevent HFD-induced fatty liver through the activation cholesterol catabolism to bile acids and by decreasing cholesterol-induced fibrosis.

Genomics of human fatty liver disease reveal mechanistically linked lipid droplet-associated gene regulations in bland steatosis and nonalcoholic steatohepatitis

Nonalcoholic fatty liver disease (NAFLD) is a common disorder hallmarked by excessive lipid deposits. Based on our recent research on lipid droplet (LD) formation in hepatocytes, we investigated LD-associated gene regulations in NAFLD of different grades, that is, steatosis vs steatohepatitis by comparing liver biopsies from healthy controls (N = 13) and NAFLD patients (N = 102). On average, more than 700 differentially expressed genes (DEGs) were identified of which 146 are mechanistically linked to LD formation. We identified 51 LD-associated DEGs frequently regulated in patient samples (range ≥5 to ≤102) with the liver-receptor homolog-1(NR5A2), that is, a key regulator of cholesterol metabolism being commonly repressed among 100 patients examined. With bland steatosis, notable regulations involved hypoxia-inducible lipid droplet-associated-protein and diacylglycerol-O-acyltransferase-2 renowned for their role in LD-growth. Conversely, nonalcoholic steatohepatitis-associated DEGs coded for epidermal growth factor receptor and TLR4 signaling with decreased expression of the GTPase Rab5 and the lipid phosphohydrolase PPAP2B thus highlighting adaptive responses to inflammation, LDL-mediated endocytosis and lipogenesis, respectively. Studies with steatotic primary human hepatocyte cultures demonstrated induction of LD-associated PLIN2, CIDEC, DNAAF1, whereas repressed expression of CPT1A, ANGPTL4, and PKLR informed on burdened mitochondrial metabolism. Equally, repressed expression of the B-lymphocyte chemoattractant CXCL13 and STAT4 as well as induced FGF21 evidenced amelioration of steatosis-related inflammation. In-vitro/in-vivo patient sample comparisons confirmed C-reactive protein, SOCS3, NR5A2, and SOD2 as commonly regulated. Lastly, STRING network analysis highlighted potential "druggable" targets with PLIN2, CIDEC, and hypoxia-inducible lipid droplet-associated-protein being confirmed by immunofluorescence microscopy. In conclusion, steatosis and steatohepatitis specific gene regulations informed on the pathogenesis of NAFLD to broaden the perspective of targeted therapies.

Endogenous n-3 Polyunsaturated Fatty Acids Attenuate T Cell-Mediated Hepatitis via Autophagy Activation

Omega-3 polyunsaturated fatty acids (n-3 PUFAs) exert anti-inflammatory effects in several liver disorders, including cirrhosis, acute liver failure, and fatty liver disease. To date, little is known about their role in immune-mediated liver diseases. In this study, we used fat-1 transgenic mice rich in endogenous n-3 PUFAs to examine the role of n-3 PUFAs in immune-mediated liver injury. Concanavalin A (Con A) was administered intravenously to wild-type (WT) and fat-1 transgenic mice to induce T cell-mediated hepatitis. Reduced liver damage was shown in Con A-administrated fat-1 transgenic mice, as evidenced by decreased mortality, attenuated hepatic necrosis, lessened serum alanine aminotransferase activity, and inhibited production of pro-inflammatory cytokines (e.g., TNF-α, IL-6, IL-17A, and IFN-γ). In vivo and in vitro studies demonstrated that n-3 PUFAs significantly inhibited the activation of hepatic T cells and the differentiation of Th1 cells after Con A challenge. Further studies showed that n-3 PUFAs markedly increased autophagy level in Con A-treated fat-1 T cells compared with the WT counterparts. Blocking hepatic autophagy activity with chloroquine diminished the differences in T cell activation and liver injury between Con A-injected WT and fat-1 transgenic mice. We conclude that n-3 PUFAs limit Con A-induced hepatitis via an autophagy-dependent mechanism and could be exploited as a new therapeutic approach for autoimmune hepatitis.

Molecular mechanism of hepatic steatosis: pathophysiological role of autophagy

Steatosis is an early characteristic in the pathogenesis of fatty liver disease (FLD). Mechanisms of hepatic steatosis are aetiology-dependent. Activation of autophagy in liver ameliorates hepatic steatosis. A modulation of hepatic autophagy affects the degree of hepatocyte steatosis and the progression of FLD as demonstrated by pre-clinical models and clinical trials. This review summarises recent advances on pathophysiological roles of autophagy in hepatic lipid metabolism. A comprehensive regulation of autophagic networks holds promise for the improvement of hepatic steatosis. Autophagic signalling pathway may be a novel therapeutic target against FLD.

HIGHLIGHTS

• Hepatic steatosis is a pathological condition wherein vacuoles of triglyceride (TG) fat are overaccumulated in liver because of abnormal metabolism of lipids. • Hepatic autophagy regulates lipid metabolism as demonstrated by macrolipophagy in response to starvation and hepatic overabundance of TG in obesity. • Autophagic signals are closely associated with apoptotic pathways. There is distinctive relationship between hepatic autophagy and apoptosis, which affects the progression of fatty liver. • Regulation of autophagic process can be a novel therapeutic strategy for fatty liver disease.

Microarray Analysis of the Gene Expression Profile and Lipid Metabolism in Fat-1 Transgenic Cattle

Long-chain n-3 polyunsaturated fatty acids (n-3 PUFAs) are beneficial for human health. However, humans and mammals are unable to synthesize n-3 PUFAs because they lack the n-3 desaturase gene fat-1 and must therefore obtain this type of fatty acid through their diet. Through the production of fat-1 transgenic animals, it is possible to obtain animal products that are rich in n-3 PUFAs, such as meat and milk. The aim of this study was to analyze the gene expression profile and the mechanism of lipid metabolism in fat-1 transgenic cattle and to accumulate important basic data that are required to obtain more efficient fat-1 transgenic cattle. Transcriptome profiling of fat-1 transgenic and wild-type cattle identified differentially expressed genes that are involved in 90 biological pathways, eight pathways of which were related to lipid metabolism processes 36 genes of which were related to lipid metabolism. This analysis also identified 11 significantly enriched genes that were involved in the peroxisome proliferator-activated receptor signaling pathway. These findings were verified by quantitative polymerase chain reaction. The information obtained in this study indicated that the introduction of an exogenous fat-1 gene into cattle affects the gene expression profile and the process of lipid metabolism in these animals. These results may provide important insights into how an exogenous fat-1 gene synthesizes n-3 PUFAs in transgenic cattle and other mammals.

Omega-3 polyunsaturated fatty acids as an angelus custos to rescue patients from NSAID-induced gastroduodenal damage

Nonsteroidal anti-inflammat ory drugs (NSAIDs) are one of the drug types frequently prescribed for their analgesic, anti-inflammatory, and antithrombotic actions, but carry a risk of major gastroduodenal damage from mild erosive changes to serious ulceration leading to fatal outcomes. From the long history of willow tree bark and its extracts being applied for the relief of pain and fever, the synthesis of acetylsalicylic acid, the development of selective cyclooxygenase 2 inhibitors (coxibs), and the identification of a G-protein-coupled receptor for prostaglandin, the popular combination regimen of an NSAID and a proton pump inhibitor was invented, but development was continued for further improvement. With regard to major NSAID adverse effects, gastrointestinal (GI) and cardiovascular (CV) risks still remained as problems to be solved. In this review, it is shown that n-3 polyunsaturated fatty acid (PUFA) based NSAIDs can be an angelus custos, supported with facts that an intake of essential n-3 PUFAs orchestrates concerted protective actions against two notorious side effects of NSAIDs, the aforementioned GI risk and CV risk of NSAIDs. Since pills containing n-3 PUFAs, omega-3-acid ethyl ester capsules (Lovaza, Omarcor), have already been safely prescribed to prevent atherosclerosis through lessening lipid burdening, the introduction of a drug delivery system such as a gastroretentive form of n-3 PUFA based NSAIDs will highlight newer hope for GI safety under the guarantee of reduced CV risk. Because n-3 PUFAs have been proven to attenuate cytotoxicity, inhibit lipid-raft-associated harmful signaling, and relieve oxidative stress relevant to NSAIDs, n-3 PUFA based NSAIDs will be next-generation GI-safe NSAIDs.

The beneficial effects of n-3 polyunsaturated fatty acids on diet induced obesity and impaired glucose control do not require Gpr120

GPR120 (Ffar4) has been postulated to represent an important receptor mediating the improved metabolic profile seen upon ingestion of a diet enriched in polyunsaturated fatty acids (PUFAs). GPR120 is highly expressed in the digestive system, adipose tissue, lung and macrophages and also present in the endocrine pancreas. A new Gpr120 deficient mouse model on pure C57bl/6N background was developed to investigate the importance of the receptor for long-term feeding with a diet enriched with fish oil. Male Gpr120 deficient mice were fed two different high fat diets (HFDs) for 18 weeks. The diets contained lipids that were mainly saturated (SAT) or mainly n-3 polyunsaturated fatty acids (PUFA). Body composition, as well as glucose, lipid and energy metabolism, was studied. As expected, wild type mice fed the PUFA HFD gained less body weight and had lower body fat mass, hepatic lipid levels, plasma cholesterol and insulin levels and better glucose tolerance as compared to those fed the SAT HFD. Gpr120 deficient mice showed a similar improvement on the PUFA HFD as was observed for wild type mice. If anything, the Gpr120 deficient mice responded better to the PUFA HFD as compared to wild type mice with respect to liver fat content, plasma glucose levels and islet morphology. Gpr120 deficient animals were found to have similar energy, glucose and lipid metabolism when fed HFD PUFA compared to wild type mice. Therefore, GPR120 appears to be dispensable for the improved metabolic profile associated with intake of a diet enriched in n-3 PUFA fatty acids.

The use of genetic engineering techniques to improve the lipid composition in meat, milk and fish products: a review

The health-promoting properties of dietary long-chain n-3 polyunsaturated fatty acids (n-3 LCPUFAs) for humans are well-known. Products of animal-origin enriched with n-3 LCPUFAs can be a good example of functional food, that is food that besides traditionally understood nutritional value may have a beneficial influence on the metabolism and health of consumers, thus reducing the risk of various lifestyle diseases such as atherosclerosis and coronary artery disease. The traditional method of enriching meat, milk or eggs with n-3 LCPUFA is the manipulation of the composition of animal diets. Huge progress in the development of genetic engineering techniques, for example transgenesis, has enabled the generation of many kinds of genetically modified animals. In recent years, one of the aims of animal transgenesis has been the modification of the lipid composition of meat and milk in order to improve the dietetic value of animal-origin products. This article reviews and discusses the data in the literature concerning studies where techniques of genetic engineering were used to create animal-origin products modified to contain health-promoting lipids. These studies are still at the laboratory stage, but their results have demonstrated that the transgenesis of pigs, cows, goats and fishes can be used in the future as efficient methods of production of healthy animal-origin food of high dietetic value. However, due to high costs and a low level of public acceptance, the introduction of this technology to commercial animal production and markets seems to be a distant prospect.