Suppression of acute ethanol-induced hepatic steatosis by docosahexaenoic acid is associated with downregulation of stearoyl-CoA desaturase 1 and inflammatory cytokines

Excessive alcohol consumption can lead to hepatic steatosis. Omega-3 (n-3) polyunsaturated fatty acids (PUFA) have been shown to be effective in reducing hepatic accumulation of triglycerides (TG) by downregulation of TG biosynthesis in the liver. The aim of this study was to examine whether supplementation with the n-3 PUFA, docosahexaenoic acid (DHA), can effectively reduce acute alcohol-induced hepatic steatosis. Acute alcohol-induced hepatic steatosis was generated in 9-week-old male mice (C57BL/6J) by oral gavage of ethanol (4.7 g/kg BW) diluted in water (60%, v/v), with or without DHA (250 mg/kg BW), every 12 h for 3 administrations. Compared to the control (ethanol-alone) group, animals supplemented with DHA were protected against ethanol-induced TG accumulation in the liver. Accordingly, hepatic stearoyl-CoA desaturase-1 (SCD-1) expression, serum alanine aminotransferase (ALT) activity, and the levels of inflammatory cytokines (such as IL-6 and TNF-α) in the liver were significantly reduced, whereas the expression of heme oxygenase-1 (HO-1), an enzyme that can improve cell survival in liver tissue, was markedly increased in DHA-supplemented mice compared to the control animals. There were no differences in serum TG level and hepatic production of reactive oxygen species (ROS) between the two groups. Our findings demonstrate that DHA supplementation protects against acute ethanol-induced hepatic steatosis, which may be associated with reduced expression of SCD-1 and inflammatory cytokines.     

Involvement of SIRT1–AMPK signaling in the protective action of indole-3-carbinol against hepatic steatosis in mice fed a high-fat diet

This study addressed the effect of indole-3-carbinol (I3C) supplementation on hepatic steatosis in mice fed a high-fat diet (HFD) and clarified the underlying mechanism. Male C57BL/6N mice were divided into three groups: those who received a normal diet, those fed with HFD and those fed with 0.1% I3C-supplemented diet (I3CD). In the present study, an HFD supplemented with 0.1% I3C significantly decreased body and liver weight as well as plasma and hepatic lipid levels. The activation of the silent mating type information regulation 2 homolog 1 (SIRT1)–AMP-activated protein kinase (AMPK) signaling system by I3C correlated with decreased mRNA levels of sterol regulatory element-binding protein-1c-regulated lipogenic enzymes. In addition, I3C significantly reversed HFD-induced up-regulation of ER stress-mediated signaling molecules in the liver, which may have contributed to the protective effects of I3C against hepatic steatosis. Furthermore, HFD-induced up-regulations of inflammatory genes such as tumor necrosis factor α and interleukin 6 were significantly reversed by dietary I3C supplementation. Our study suggests that the protective action of I3C against hepatic steatosis is mediated, at least in part, through the up-regulation of a SIRT1–AMPK signaling system in the livers of HFD-fed mice. Further investigations revealed that alleviation of the ER stress response represented a critical mechanism underlying the beneficial effects of I3C on hepatic steatosis.     

Hydroxytyrosol ameliorates insulin resistance by modulating endoplasmic reticulum stress and prevents hepatic steatosis in diet-induced obesity mice

Endoplasmic reticulum (ER) is a principal organelle responsible for energy and nutrient management. Its dysfunction has been viewed in the context of obesity and related glucolipid metabolic disorders. However, therapeutic approaches to improve ER adaptation and systemic energy balance in obesity are limited. Thus, we examined whether hydroxytyrosol (HT), an important polyphenolic compound found in virgin olive oil, could correct the metabolic impairments in diet-induced obesity (DIO) mice. Here, we found that HT gavage for 10 weeks significantly ameliorated glucose homeostasis and chronic inflammation and decreased hepatic steatosis in DIO mice. At the molecular level, ER stress indicators, inflammatory and insulin signaling markers demonstrated that high-fat diet (HFD)-induced ER stress and insulin resistance (IR) in insulin sensitive tissue were corrected by HT. In vitro studies confirmed that HT supplementation (100 μM) attenuated palmitate-evoked ER stress, thus rescuing the downstream JNK/IRS pathway. As a result from suppression of ER stress in the liver, HT further decreased hepatic sterol regulatory element-binding protein-1 expression (SREBP1). Additionally, aberrant expression of genes involved in hepatic lipogenesis (SREBP1, ACC, FAS, SCD1) caused by HFD was restored by HT. These findings suggested that HT ameliorated chronic inflammation and IR and decreased hepatic steatosis in obesity by beneficial modulation of ER stress.     

Reversal of high-fat diet-induced hepatic steatosis by n-3 LCPUFA: role of PPAR-α and SREBP-1c

Nonalcoholic fatty liver disease is characterized by an abnormal accumulation of triacylglycerides in the liver in absence of significant alcohol consumption. Under these conditions, it has been observed an impaired bioavailability of hepatic n-3 long-chain polyunsaturated fatty acids (LCPUFAs). The aim of this study was to test the reversion of the prosteatotic and proinflammatory effects of high-fat diet (HFD) in the mouse liver by changing to normocaloric diet and n-3 LCPUFA supplementation. Male C57BL/6J mice were given either control diet (CD) or HFD for 12 weeks. Control and HFD groups were divided into subgroups that continue with CD or subjected to CD plus n-3 LCPUFA for 8 additional weeks. After this time, blood and liver samples were taken and metabolic, morphologic, oxidative stress, inflammatory and signaling parameters were analyzed. The dietary change from HFD to a normocaloric diet with n-3 LCPUFA supplementation significantly reduced insulin resistance and liver steatosis when compared to switching HFD to normocaloric diet alone. In addition, HFD-induced increases in adiposity, adipocyte enlargement and liver oxidative stress and inflammatory cytokine expression were suppressed by n-3 LCPUFA to control values. Importantly, n-3 LCPUFA supplementation abolish HFD-induced enhancement in hepatic SREBP-1c/PPAR-α ratios, suggesting a change in the metabolic status of the liver from a lipogenic condition to one favoring fatty acid oxidation and steatosis attenuation. These findings may provide the rational basis for the use of normocaloric diets supplemented with n-3 LCPUFA in patients with liver steatosis.     

Resolvin d1 and aspirin-triggered resolvin d1 promote resolution of allergic airways responses

Asthma is a disease of airway inflammation that in most cases fails to resolve. The resolution of inflammation is an active process governed by specific chemical mediators, including D-series resolvins. In this study, we determined the impact of resolvin D1 (RvD1) and aspirin-triggered RvD1 (AT-RvD1) on the development of allergic airway responses and their resolution. Mice were allergen sensitized, and RvD1, AT-RvD1 (1, 10, or 100 ng), or vehicle was administered at select intervals before or after aerosol allergen challenge. RvD1 markedly decreased airway eosinophilia and mucus metaplasia, in part by decreasing IL-5 and IκBα degradation. For the resolution of established allergic airway responses, AT-RvD1 was even more efficacious than RvD1, leading to a marked decrease in the resolution interval for lung eosinophilia, decrements in select inflammatory peptide and lipid mediators, and more rapid resolution of airway hyperreactivity to methacholine. Relative to RvD1, AT-RvD1 resisted metabolic inactivation by macrophages, and AT-RvD1 significantly enhanced macrophage phagocytosis of IgG-OVA-coated beads in vitro and in vivo, a new proresolving mechanism for the clearance of allergen from the airways. In conclusion, RvD1 and AT-RvD1 can serve as important modulators of allergic airway responses by decreasing eosinophils and proinflammatory mediators and promoting macrophage clearance of allergen. Together, these findings identify D-series resolvins as potential proresolving therapeutic agents for allergic responses.     

Effects of Dietary Eicosapentaenoic Acid (EPA) Supplementation in High-Fat Fed Mice on Lipid Metabolism and Apelin/APJ System in Skeletal Muscle

Various studies have shown that eicosapentaenoic acid (EPA) has beneficial effects on obesity and associated disorders. Apelin, the ligand of APJ receptor also exerts insulin-sensitizing effects especially by improving muscle metabolism. EPA has been shown to increase apelin production in adipose tissue but its effects in muscle have not been addressed. Thus, the effects of EPA supplementation (36 g/kg EPA) in high-fat diet (HFD) (45% fat, 20% protein, 35% carbohydrate) were studied in mice with focus on muscle lipid metabolism and apelin/APJ expression. Compared with HFD mice, HFD+EPA mice had significantly less weight gain, fat mass, lower blood glucose, insulinemia and hepatic steatosis after 10 weeks of diet. In addition, EPA prevented muscle metabolism alterations since intramuscular triglycerides were decreased and β-oxidation increased. In soleus muscles of HFD+EPA mice, apelin and APJ expression were significantly increased compared to HFD mice. However, plasma apelin concentrations in HFD and HFD+EPA mice were similar. EPA-induced apelin expression was confirmed in differentiated C2C12 myocytes but in this model, apelin secretion was also increased in response to EPA treatment. In conclusion, EPA supplementation in HFD prevents obesity and metabolic alterations in mice, especially in skeletal muscle. Since EPA increases apelin/APJ expression in muscle, apelin may act in a paracrine/autocrine manner to contribute to these benefical effects.     

Omega-3 PUFA derived anti-inflammatory lipid mediator resolvin E1

Inflammation is a defensive response to injury and infection, but excessive or inappropriate inflammation contributes to a range of acute and chronic human diseases. Clinical assessment of dietary supplementation of omega-3 polyunsaturated fatty acids (PUFA) including eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) indicate their beneficial impact on human diseases in which inflammation is suspected as a key component of the pathogenesis. Although the mechanism of EPA and DHA action is still not fully defined in molecular terms, recent studies have revealed that, during the course of acute inflammation, omega-3 PUFA-derived mediators including resolvins and protectins with potent anti-inflammatory and pro-resolving properties are produced. In this review, we provide an overview of the formation and actions of EPA-derived anti-inflammatory lipid mediator resolvin E1.     

A dual role of 12/15-lipoxygenase in LPS-induced acute renal inflammation and injury

Recent studies suggest a potential role of bioactive lipids in acute kidney injury induced by lipopolysaccharide (LPS). The current study was designed to determine the profiling activities of various polyunsaturated fatty acid (PUFA) metabolizing enzymes, including lipoxygenases (LO), cyclooxygenase, and cytochrome P450 in the plasma of LPS-injected mice using LC-MS. Heat map analysis revealed that out of 126 bioactive lipids screened, only the 12/15-LO metabolite, 12-HETE, had a significant (2.24 ± 0.4) fold increase relative to control (P = 0.0001) after Bonferroni Correction (BCF α = 0.003). We then determined the role of the 12/15-LO in LPS-induced acute kidney injury using genetic and pharmacological approaches. Treatment of LPS injected mice with the 12/15-LO inhibitor, baicalein, significantly reduced levels of renal injury and inflammation markers including urinary thiobarbituric acid reactive substance (TBARs), urinary monocyte chemoattractant protein-1 (MCP-1), renal interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α). Similarly, knocking-out of 12/15-LO reduced levels of renal inflammation and injury markers elicited by LPS injection. Next, we tested whether exogenous supplementation with docosahexaenoic acid (DHA) as a substrate would divert the role of 12/15-LO from being pro-inflammatory to anti-inflammatory via increased production of the anti-inflammatory metabolite. DHA treatment restored the decreased in plasma level of resolvin D2 (RvD2) and reduced renal injury in LPS-injected mice whereas DHA treatment failed to provide any synergistic effects in reducing renal injury in LPS injected 12/15-LO knock-out mice. The ability of RvD2 to protect kidney against LPS-induced renal injury was further confirmed by exogenous RvD2 which significantly reduced the elevation in renal injury in LPS injected mice. These data suggest a double-edged sword role of 12/15-LO in LPS-induced acute renal inflammation and injury, depending on the type of substrate available for its activity.     

High Fat Diet Feeding Exaggerates Perfluorooctanoic Acid-Induced Liver Injury in Mice via Modulating Multiple Metabolic Pathways

High fat diet (HFD) is closely linked to a variety of health issues including fatty liver. Exposure to perfluorooctanoic acid (PFOA), a synthetic perfluorinated carboxylic acid, also causes liver injury. The present study investigated the possible interactions between high fat diet and PFOA in induction of liver injury. Mice were pair-fed a high-fat diet (HFD) or low fat control with or without PFOA administration at 5 mg/kg/day for 3 weeks. Exposure to PFOA alone caused elevated plasma alanine aminotransferase (ALT) and alkaline phosphatase (ALP) levels and increased liver weight along with reduced body weight and adipose tissue mass. HFD alone did not cause liver damage, but exaggerated PFOA-induced hepatotoxicity as indicated by higher plasma ALT and AST levels, and more severe pathological changes including hepatocyte hypertrophy, lipid droplet accumulation and necrosis as well as inflammatory cell infiltration. These additive effects of HFD on PFOA-induced hepatotoxicity correlated with metabolic disturbance in liver and blood as well as up-regulation of hepatic proinflammatory cytokine genes. Metabolomic analysis demonstrated that both serum and hepatic metabolite profiles of PFOA, HFD, or HFD-PFOA group were clearly differentiated from that of controls. PFOA affected more hepatic metabolites than HFD, but HFD showed positive interaction with PFOA on fatty acid metabolites including long chain fatty acids and acylcarnitines. Taken together, dietary high fat potentiates PFOA-induced hepatic lipid accumulation, inflammation and necrotic cell death by disturbing hepatic metabolism and inducing inflammation. This study demonstrated, for the first time, that HFD increases the risk of PFOA in induction of hepatotoxicity.     

Conjunctival goblet cell secretion stimulated by leukotrienes is reduced by resolvins D1 and E1 to promote resolution of inflammation

The conjunctiva is a mucous membrane that covers the sclera and lines the inside of the eyelids. Throughout the conjunctiva are goblet cells that secrete mucins to protect the eye. Chronic inflammatory diseases such as allergic conjunctivitis and early dry eye lead to increased goblet cell mucin secretion into tears and ocular surface disease. The purpose of this study was to determine the actions of the inflammatory mediators, the leukotrienes and the proresolution resolvins, on secretion from cultured rat and human conjunctival goblet cells. We found that both cysteinyl leukotriene (CysLT) receptors, CysLT(1) and CysLT(2,) were present in rat conjunctiva and in rat and human cultured conjunctival goblet cells. All leukotrienes LTB(4), LTC(4), LTD(4), and LTE(4), as well as PGD(2), stimulated goblet cell secretion in rat goblet cells. LTD(4) and LTE(4) increased the intracellular Ca(2+) concentration ([Ca(2+)](i)), and LTD(4) activated ERK1/2. The CysLT(1) receptor antagonist MK571 significantly decreased LTD(4)-stimulated rat goblet cell secretion and the increase in [Ca(2+)](i). Resolvins D1 (RvD1) and E1 (RvE1) completely reduced LTD(4)-stimulated goblet cell secretion in cultured rat goblet cells. LTD(4)-induced secretion from human goblet cells was blocked by RvD1. RvD1 and RvE1 prevented LTD(4)- and LTE(4)-stimulated increases in [Ca(2+)](i), as well as LTD(4) activation of ERK1/2. We conclude that cysteinyl leukotrienes stimulate conjunctival goblet cell mucous secretion with LTD(4) using the CysLT(1) receptor. Stimulated secretion is terminated by preventing the increase in [Ca(2+)](i) and activation of ERK1/2 by RvD1 and RvE1.     

Metabolipidomic profiling reveals an age‐related deficiency of skeletal muscle pro‐resolving mediators that contributes to maladaptive tissue remodeling

Specialized pro‐resolving mediators actively limit inflammation and support tissue regeneration, but their role in age‐related muscle dysfunction has not been explored. We profiled the mediator lipidome of aging muscle via liquid chromatography‐tandem mass spectrometry and tested whether treatment with the pro‐resolving mediator resolvin D1 (RvD1) could rejuvenate the regenerative ability of aged muscle. Aged mice displayed chronic muscle inflammation and this was associated with a basal deficiency of pro‐resolving mediators 8‐oxo‐RvD1, resolvin E3, and maresin 1, as well as many anti‐inflammatory cytochrome P450‐derived lipid epoxides. Following muscle injury, young and aged mice produced similar amounts of most pro‐inflammatory eicosanoid metabolites of cyclooxygenase (e.g., prostaglandin E₂) and 12‐lipoxygenase (e.g., 12‐hydroxy‐eicosatetraenoic acid), but aged mice produced fewer markers of pro‐resolving mediators including the lipoxins (15‐hydroxy‐eicosatetraenoic acid), D‐resolvins/protectins (17‐hydroxy‐docosahexaenoic acid), E‐resolvins (18‐hydroxy‐eicosapentaenoic acid), and maresins (14‐hydroxy‐docosahexaenoic acid). Similar absences of downstream pro‐resolving mediators including lipoxin A₄, resolvin D6, protectin D1/DX, and maresin 1 in aged muscle were associated with greater inflammation, impaired myofiber regeneration, and delayed recovery of strength. Daily intraperitoneal injection of RvD1 had minimal impact on intramuscular leukocyte infiltration and myofiber regeneration but suppressed inflammatory cytokine expression, limited fibrosis, and improved recovery of muscle function. We conclude that aging results in deficient local biosynthesis of specialized pro‐resolving mediators in muscle and that immunoresolvents may be attractive novel therapeutics for the treatment of muscular injuries and associated pain in the elderly, due to positive effects on recovery of muscle function without the negative side effects on tissue regeneration of non‐steroidal anti‐inflammatory drugs.     

Retinoic acid ameliorates high-fat diet-induced liver steatosis through Sirt1

In this study, treatment of C57 BL/6 J(wild type, WT) mice fed a high-fat diet(HFD) with retinoic acid(RA) decreased body weight and subcutaneous and visceral fat content, reversed the apparent hepatosteatosis, and reduced hepatic intracellular triglyceride and serum alanine transaminase(ALT) and aspartate aminotransferase(AST) concentrations. Moreover, RA treatment improved glucose tolerance and insulin sensitivity in WT mice fed a HFD. However, these RA-induced effects in WT mice fed a HFD were alleviated in liver specific Sirtuin 1(Sirt1) deficient(LKO) mice fed a HFD. Furthermore,RA also could not improve glucose tolerance and insulin sensitivity in LKO mice fed a HFD. The mechanism studies indicated that RA indeed increased the expression of hepatic Sirt1 and superoxide dismutase 2(Sod2), and inhibited the expression of sterol regulatory element binding protein 1 c(Srebp-1 c) in WT mice in vivo and in vitro. RA decreased mitochondrial reactive oxygen species(ROS) production in WT primary hepatocytes and increased mitochondrial DNA(mtDNA) copy number in WT mice liver. However, these RA-mediated molecular effects were also abolished in the liver and primary hepatocytes from LKO mice. In summary, RA protected against HFD-induced hepato steatosis by decreasing Srebp-1 c expression and improving antioxidant capacity through a Sirtl-mediated mechanism.     

DHA and its derived lipid mediators MaR1, RvD1 and RvD2 block TNF-α inhibition of intestinal sugar and glutamine uptake in Caco-2 cells

Tumor necrosis factor-alfa (TNF-α) is a pro-inflammatory cytokine highly-involved in intestinal inflammation. Omega-3 polyunsaturated fatty acids (n3-PUFAs) show anti-inflammatory actions. We previously demonstrated that the n3-PUFA EPA prevents TNF-α inhibition of sugar uptake in Caco-2 cells. Here, we investigated whether the n3-PUFA DHA and its derived specialized pro-resolving lipid mediators (SPMs) MaR1, RvD1 and RvD2, could block TNF-α inhibition of intestinal sugar and glutamine uptake. DHA blocked TNF-α-induced inhibition of α-methyl-D-glucose (αMG) uptake and SGLT1 expression in the apical membrane of Caco-2 cells, through a pathway independent of GPR120. SPMs showed the same preventive effect but acting at concentrations 1000 times lower. In diet-induced obese (DIO) mice, oral gavage of MaR1 reversed the up-regulation of pro-inflammatory cytokines found in intestinal mucosa of these mice. However, MaR1 treatment was not able to counteract the reduced intestinal transport of αMG and SGLT1 expression in the DIO mice. In Caco-2 cells, TNF-α also inhibited glutamine uptake being this inhibition prevented by EPA, DHA and the DHA-derived SPMs. Interestingly, TNF-α increased the expression in the apical membrane of the glutamine transporter B⁰AT1. This increase was partially blocked by the n-3 PUFAs. These data reveal DHA and its SPMs as promising biomolecules to restore intestinal nutrients transport during intestinal inflammation.     

Immune responsive resolvin D1 programs peritoneal macrophages and cardiac fibroblast phenotypes in diversified metabolic microenvironment

Bioactive lipid mediators derived from n-3 and n-6 fatty acids are known to modulate leukocytes. Metabolic transformation of essential fatty acids to endogenous bioactive molecules plays a major role in human health. Here we tested the potential of substrates; linoleic acid (LA) and docosahexaenoic acid (DHA) and their bioactive products; resolvin D1 (RvD1) and 12- S-hydroxyeicosatetraenoic acids (HETE) to modulate macrophage plasticity and cardiac fibroblast phenotype in presence or absence of lipid metabolizing enzyme 12/15-lipoxygenase (LOX). Peritoneal macrophages and cardiac fibroblasts were isolated from wild-type (C57BL/6J) and 12/15LOX ^−/− mice and treated with DHA, LA, 12(S)-HETE, and RvD1 for 4, 8, 12, and 24 hr. LA, DHA, 12(S)-HETE, and RvD1 elicited mRNA expression of proinflammatory markers; tumor necrosis factor-α ( Tnf-α), interleukin 6 ( IL-6), chemokine (C–C motif) ligand 2  (Ccl2), and IL-1β in wild type (WT) and in 12/15LOX ^−/− macrophages at early time point (4 hr). Bioactive immunoresolvent RvD1 lowered the levels of Tnf-α, IL-6, and IL-1β at 24 hr time point. Both DHA and RvD1 stimulated the proresolving markers such as arginase 1 ( Arg-1), chitinase-like protein 3 ( Ym-1), and mannose receptor C-type 1 in WT macrophage. RvD1 induced proresolving phenotype Arg-1 expression in both WT 12/15LOX ^−/− macrophages even in presence of 12(S)-HETE. RvD1 peaked 5LOX expression in both WT and 12/15LOX ^−/− at 24 hr time point compared with DHA. RvD1 diminished cyclooxygenase-2 but upregulated 5LOX expression in fibroblast compared with DHA. In summary, the feed-forward enzymatic interaction with fatty acids substrates and direct mediators (RvD1 and 12(S)-HETE) are responsive in determining macrophages phenotype and cardiac fibroblast plasticity. Particularly, macrophages and fibroblast phenotypes are responsive to milieu and RvD1 governs the milieu-dependent chemokine signaling in presence or absence of 12/15LOX enzyme to resolve inflammation.     

Dietary omega-3 fatty acids modulate the eicosanoid profile in man primarily via the CYP-epoxygenase pathway

Cytochrome P450 (CYP)-dependent metabolites of arachidonic acid (AA) contribute to the regulation of cardiovascular function. CYP enzymes also accept EPA and DHA to yield more potent vasodilatory and potentially anti-arrhythmic metabolites, suggesting that the endogenous CYP-eicosanoid profile can be favorably shifted by dietary omega-3 fatty acids. To test this hypothesis, 20 healthy volunteers were treated with an EPA/DHA supplement and analyzed for concomitant changes in the circulatory and urinary levels of AA-, EPA-, and DHA-derived metabolites produced by the cyclooxygenase-, lipoxygenase (LOX)-, and CYP-dependent pathways. Raising the Omega-3 Index from about four to eight primarily resulted in a large increase of EPA-derived CYP-dependent epoxy-metabolites followed by increases of EPA- and DHA-derived LOX-dependent monohydroxy-metabolites including the precursors of the resolvin E and D families; resolvins themselves were not detected. The metabolite/precursor fatty acid ratios indicated that CYP epoxygenases metabolized EPA with an 8.6-fold higher efficiency and DHA with a 2.2-fold higher efficiency than AA. Effects on leukotriene, prostaglandin E, prostacyclin, and thromboxane formation remained rather weak. We propose that CYP-dependent epoxy-metabolites of EPA and DHA may function as mediators of the vasodilatory and cardioprotective effects of omega-3 fatty acids and could serve as biomarkers in clinical studies investigating the cardiovascular effects of EPA/DHA supplementation.     

Identification and structure determination of novel anti-inflammatory mediator resolvin E3, 17,18-dihydroxyeicosapentaenoic acid

Bioactive mediators derived from omega-3 eicosapentaenoic acid (EPA) elicit potent anti-inflammatory actions. Here, we identified novel EPA metabolites, including 8,18-dihydroxyeicosapentaenoic acid (8,18-diHEPE), 11,18-diHEPE, 12,18-diHEPE, and 17,18-diHEPE from 18-HEPE. Unlike resolvins E1 and E2, both of which are biosynthesized by neutrophils via the 5-lipoxygenase pathway, these metabolites are biosynthesized by eosinophils via the 12/15-lipoxygenase pathway. Among them, two stereoisomers of 17,18-diHEPE, collectively termed resolvin E3 (RvE3), displayed a potent anti-inflammatory action by limiting neutrophil infiltration in zymosan-induced peritonitis. The planar structure of RvE3 was unambiguously determined to be 17,18-dihydroxy-5Z,8Z,11Z,13E,15E-EPE by high resolution NMR, and the two stereoisomers were assigned to have 17,18R- and 17,18S-dihydroxy groups, respectively, using chemically synthesized 18R- and 18S-HEPE as precursors. Both 18R- and 18S-RvE3 inhibited neutrophil chemotaxis in vitro at low nanomolar concentrations. These findings suggest that RvE3 contributes to the beneficial actions of EPA in controlling inflammation and related diseases.     

Group VIA phospholipase A2 deficiency in mice chronically fed with high-fat-diet attenuates hepatic steatosis by correcting a defect of phospholipid remodeling

A defect of hepatic remodeling of phospholipids (PL) is seen in non-alcoholic fatty liver disease and steatohepatitis (NASH) indicating pivotal role of PL metabolism in this disease. The deletion of group VIA calcium-independent phospholipase A2 (iPla2β) protects ob/ob mice from hepatic steatosis (BBAlip 1861, 2016, 440–461), however its role in high-fat diet (HFD)-induced NASH is still elusive. Here, wild-type and iPla2β-null mice were subjected to chronic feeding with HFD for 6 months. We showed that protection was observed in iPla2β-null mice with an attenuation of diet-induced body and liver-weight gains, liver enzymes, serum free fatty acids as well as hepatic TG and steatosis scores. iPla2β deficiency under HFD attenuated the levels of 1-stearoyl lysophosphatidylcholine (LPC), lysophosphatidylethanolamine (LPE), and lysophosphatidylinositol (LPI) as well as elevation of hepatic arachidonate, arachidonate-containing cholesterol esters and prostaglandin E₂. More importantly, this deficiency rescued a defect in PL remodeling and attenuated the ratio of saturated and unsaturated PL. The protection by iPla2β deficiency was not observed during short-term HFD feeding of 3 or 5 weeks which showed no PL remodeling defect. In addition to PC/PE, this deficiency reversed the suppression of PC/PI and PE/PI among monounsaturated PL. However, this deficiency did not modulate hepatic PL contents and PL ratios in ER fractions, ER stress, fibrosis, and inflammation markers. Hence, iPla2β inactivation protected mice against hepatic steatosis and obesity during chronic dietary NASH by correcting PL remodeling defect and PI composition relative to PC and PE.     

Hydroxytyrosol prevents metabolic impairment reducing hepatic inflammation and restoring duodenal integrity in a rat model of NAFLD

The potential mechanisms of action of polyphenols in nonalcoholic fatty liver disease (NAFLD) are overlooked. Here, we evaluate the beneficial therapeutic effects of hydroxytyrosol (HT), the major metabolite of the oleuropein, in a nutritional model of insulin resistance (IR) and NAFLD by high-fat diet. Young male rats were divided into three groups receiving (1) standard diet (STD; 10.5% fat), (2) high-fat diet (HFD; 58.0% fat) and (3) HFD + HT (10 mg/kg/day by gavage). After 5 weeks, the oral glucose tolerance test was performed, and at 6th week, blood sample and tissues (liver and duodenum) were collected for following determinations. The HT-treated rats showed a marked reduction in serum AST, ALT and cholesterol and improved glucose tolerance and insulin sensitivity, reducing homeostasis model assessment index. HT significantly corrected the metabolic impairment induced by HFD, increasing hepatic peroxisome proliferator-activated receptor PPAR-α and its downstream-regulated gene fibroblast growth factor 21, the phosphorylation of acetyl-CoA carboxylase and the mRNA carnitine palmitoyltransferase 1a. HT also reduced liver inflammation and nitrosative/oxidative stress decreasing the nitrosylation of proteins, reactive oxygen species production and lipid peroxidation. Moreover, HT restored intestinal barrier integrity and functions (fluorescein isothiocyanate-dextran permeability and mRNA zona occludens ZO-1). Our data demonstrate the beneficial effect of HT in the prevention of early inflammatory events responsible for the onset of IR and steatosis, reducing hepatic inflammation and nitrosative/oxidative stress and restoring glucose homeostasis and intestinal barrier integrity.     

Calcium supplementation relieves high-fat diet-induced liver steatosis by reducing energy metabolism and promoting lipolysis

Nonalcoholic fatty liver disease (NAFLD) is a chronic disease affecting the health of many people worldwide. Previous studies have shown that dietary calcium supplementation may alleviate NAFLD, but the underlying mechanism is not clear. In this study investigating the effect of calcium on hepatic lipid metabolism, 8-week-old male C57BL/6J mice were divided into four groups (n = 6): (1) mice given a normal chow containing 0.5% calcium (CN0.5), (2) mice given a normal chow containing 1.2% calcium (CN1.2), (3) mice given a high-fat diet (HFD) containing 0.5% calcium (HFD0.5), and (4) mice fed a HFD containing 1.2% calcium (HFD1.2). To understand the underlying mechanism, cells were treated with oleic acid and palmitic acid to mimic the HFD conditions in vitro. The results showed that calcium alleviated the increase in triglyceride accumulation induced by oleic acid and/or palmitic acid in HepG2, AML12, and primary hepatocyte cells. Our data demonstrated that calcium supplementation alleviated HFD-induced hepatic steatosis through increased liver lipase activity, proving calcium is involved in the regulation of hepatic lipid metabolism. Moreover, calcium also increased the level of glycogen in the liver, and at the same time had the effect of reducing glycolysis and promoting glucose absorption. Calcium addition increased calcium levels in the mitochondria and cytoplasm. Taken together, we concluded that calcium supplementation could relieve HFD-induced hepatic steatosis by changing energy metabolism and lipase activity.