Stimulation of fat accumulation in hepatocytes by PGE₂-dependent repression of hepatic lipolysis, β-oxidation and VLDL-synthesis

Liposomal quercetin: A promising strategy to combat hepatic insulin resistance and inflammation in type 2 diabetes mellitus

In type 2 diabetes mellitus, hepatic insulin resistance is intricately associated with oxidative stress and inflammation. Nonetheless, the lack of therapeutic interventions directly targeting hepatic dysfunction represents a notable gap in current treatment options. Flavonoids have been explored due to their potential anti-diabetic effects. However, these compounds are associated with low bioavailability and high metabolization. In the present study, four flavonoids, kaempferol, quercetin, kaempferol-7-O-glucoside and quercetin-7-O-glucoside, were studied in a cellular model of hepatic insulin resistance using HepG2 cells. Quercetin was selected as the most promising flavonoid and incorporated into liposomes to enhance its therapeutic effect. Quercetin liposomes had a mean size of 0.12 µm, with an incorporation efficiency of 93 %. Quercetin liposomes exhibited increased efficacy in modulating insulin resistance. This was achieved through the modulation of Akt expression and the attenuation of inflammation, particularly via the NF-κB pathway, as well as the regulation of PGE2 and COX-2 expression. Furthermore, quercetin liposomes displayed a significant advantage over free quercetin in attenuating the production of reactive pro-oxidant species. These findings open new avenues for developing innovative therapeutic strategies to manage diabetes, emphasizing the potential of quercetin liposomes as a promising approach for targeting both hepatic insulin resistance and associated inflammation.

Discovery and validation of COX2 as a target of flavonoids in Apocyni Veneti Folium: Implications for the treatment of liver injury

ETHNOPHARMACOLOGICAL RELEVANCE

Apocyni Veneti Folium (AVF), a popular traditional Chinese medicine (TCM), is known for its effects in soothing the liver and nerves and eliminating heat and water. It is relevant from an ethnopharmacological perspective. Pharmacological research has confirmed its benefits on antihypertension, antihyperlipidemia, antidepression, liver protection, immune system boosting, antiaging, and diabetic vascular lesions. Previous studies have shown that flavonoids, the active ingredients, have a hepatoprotective effect. However, the exact mechanism has not been clarified.

AIM OF THE STUDY

This study aimed to identify the active flavonoids in AVF and their corresponding targets for liver injury. Multiple methods were introduced to confirm the targets.

MATERIAL AND METHODS

AVF compounds were analyzed using liquid chromatography-mass spectrometry (LC-MS). Then, network pharmacology was utilized to screen potential hepatoprotection targets of the compounds. An enzyme activity assay was performed to determine the effect of the compounds on the targets. Biolayer interferometry (BLI) was applied to confirm the direct interaction between the compounds and the targets.

RESULTS

A total of 71 compounds were identified by LC-MS and 19 compounds and 112 shared targets were screened using network pharmacology. These common targets were primarily involved in the TNF signaling pathway, cancer pathways, hepatitis B, drug responses, and negative regulation of the apoptotic process. Flavonoids were the primary pharmacological substance basis of AVF. The cyclooxygenase 2 (COX2) protein was one of the direct targets of flavonoids in AVF. The enzyme activity assay and BLI-based intermolecular interactions demonstrated that the compounds astragalin, isoquercitrin, and hyperoside exhibited stronger inhibition of enzyme activity and a higher affinity with COX2 compared to epigallocatechin, quercetin, and catechin.

CONCLUSIONS

COX2 was preliminarily identified as a target of flavonoids, and the mechanism of the hepatoprotective effect of AVF might be linked to flavonoids inhibiting the activity of COX2. The findings can establish the foundation for future research on the traditional hepatoprotective effect of AVF on the liver and for clinical studies on liver disorders.

Size matters: the biochemical logic of ligand type in endocrine crosstalk

The endocrine system is a fundamental type of long-range cell-cell communication that is important for maintaining metabolism, physiology, and other aspects of organismal homeostasis. Endocrine signaling is mediated by diverse blood-borne ligands, also called hormones, including metabolites, lipids, steroids, peptides, and proteins. The size and structure of these hormones are fine-tuned to make them bioactive, responsive, and adaptable to meet the demands of changing environments. Why has nature selected such diverse ligand types to mediate communication in the endocrine system? What is the chemical, signaling, or physiologic logic of these ligands? What fundamental principles from our knowledge of endocrine communication can be applied as we continue as a field to uncover additional new circulating molecules that are claimed to mediate long-range cell and tissue crosstalk? This review provides a framework based on the biochemical logic behind this crosstalk with respect to their chemistry, temporal regulation in physiology, specificity, signaling actions, and evolutionary development.

Increased Perfluorooctanesulfonate (PFOS) Toxicity and Accumulation Is Associated with Perturbed Prostaglandin Metabolism and Increased Organic Anion Transport Protein (OATP) Expression

Perfluorooctanesulfonate (PFOS) is a widespread environmental pollutant with a long half-life and clearly negative outcomes on metabolic diseases such as fatty liver disease and diabetes. Male and female Cyp2b-null and humanized CYP2B6-transgenic (hCYP2B6-Tg) mice were treated with 0, 1, or 10 mg/kg/day PFOS for 21 days, and surprisingly it was found that PFOS was retained at greater concentrations in the serum and liver of hCYP2B6-Tg mice than those of Cyp2b-null mice, with greater differences in the females. Thus, Cyp2b-null and hCYP2B6-Tg mice provide new models for investigating individual mechanisms for PFOS bioaccumulation and toxicity. Overt toxicity was greater in hCYP2B6-Tg mice (especially females) as measured by mortality; however, steatosis occurred more readily in Cyp2b-null mice despite the lower PFOS liver concentrations. Targeted lipidomics and transcriptomics from PFOS-treated Cyp2b-null and hCYP2B6-Tg mouse livers were performed and compared to PFOS retention and serum markers of toxicity using PCA. Several oxylipins, including prostaglandins, thromboxanes, and docosahexaenoic acid metabolites, are associated or inversely associated with PFOS toxicity. Both lipidomics and transcriptomics indicate PFOS toxicity is associated with PPAR activity in all models. GO terms associated with reduced steatosis were sexually dimorphic with lipid metabolism and transport increased in females and circadian rhythm associated genes increased in males. However, we cannot rule out that steatosis was initially protective from PFOS toxicity. Moreover, several transporters are associated with increased retention, probably due to increased uptake. The strongest associations are the organic anion transport proteins (Oatp1a4-6) genes and a long-chain fatty acid transport protein (fatp1), enriched in female hCYP2B6-Tg mice. PFOS uptake was also reduced in cultured murine hepatocytes by OATP inhibitors. The role of OATP1A6 and FATP1 in PFOS transport has not been tested. In summary, Cyp2b-null and hCYP2B6-Tg mice provided unique models for estimating the importance of novel mechanisms in PFOS retention and toxicity.

Ginsenoside Rb1 Promotes Hepatic Glycogen Synthesis to Ameliorate T2DM Through 15-PGDH/PGE2/EP4 Signaling Pathway

Purpose

Ginsenoside Rb1 (Rb1), one of the crucial bioactive constituents in Panax ginseng C. A. Mey., possesses anti-type 2 diabetes mellitus (T2DM) property. Nevertheless, the precise mechanism, particularly the impact of Rb1 on hepatic glycogen production, a crucial process in the advancement of T2DM, remains poorly understood. 15-hydroxyprostaglandin dehydrogenase (15-PGDH) is responsible for prostaglandin E2 (PGE2) inactivation. A recent study has reported that inhibition of 15-PGDH promoted hepatic glycogen synthesis and improved T2DM. Therefore, herein, we aimed to investigate whether Rb1 ameliorated T2DM through 15-PGDH/PGE2-regulated hepatic glycogen synthesis.

Methods

By combining streptozotocin with a high-fat diet, we successfully established a mouse model for T2DM. Afterward, these mice were administered Rb1 or metformin for 8 weeks. An insulin-resistant cell model was established by incubating LO2 cells with palmitic acid. Liver glycogen and PGE2 levels, the expression levels of 15-PGDH, serine/threonine kinase AKT (AKT), and glycogen synthase kinase 3 beta (GSK3β) were measured. Molecular docking was used to predict the binding affinity between 15-PGDH and Rb1.

Results

Rb1 administration increased the phosphorylation levels of AKT and GSK3β to enhance glycogen synthesis in the liver of T2DM mice. Molecular docking indicated that Rb1 had a high affinity for 15-PGDH. Moreover, Rb1 treatment resulted in the suppression of elevated 15-PGDH levels and the elevation of decreased PGE2 levels in the liver of T2DM mice. Furthermore, in vitro experiments showed that Rb1 administration might enhance glycogen production by modulating the 15-PGDH/PGE2/PGE2 receptor EP4 pathway.

Conclusion

Our findings indicate that Rb1 may enhance liver glycogen production through a 15-PGDH-dependent pathway to ameliorate T2DM, thereby offering a new explanation for the positive impact of Rb1 on T2DM and supporting its potential as an effective therapeutic approach for T2DM.

The Crosstalk between Mesenchymal Stromal/Stem Cells and Hepatocytes in Homeostasis and under Stress

Liver diseases, characterized by high morbidity and mortality, represent a substantial medical problem globally. The current therapeutic approaches are mainly aimed at reducing symptoms and slowing down the progression of the diseases. Organ transplantation remains the only effective treatment method in cases of severe liver pathology. In this regard, the development of new effective approaches aimed at stimulating liver regeneration, both by activation of the organ's own resources or by different therapeutic agents that trigger regeneration, does not cease to be relevant. To date, many systematic reviews and meta-analyses have been published confirming the effectiveness of mesenchymal stromal cell (MSC) transplantation in the treatment of liver diseases of various severities and etiologies. However, despite the successful use of MSCs in clinical practice and the promising therapeutic results in animal models of liver diseases, the mechanisms of their protective and regenerative action remain poorly understood. Specifically, data about the molecular agents produced by these cells and mediating their therapeutic action are fragmentary and often contradictory. Since MSCs or MSC-like cells are found in all tissues and organs, it is likely that many key intercellular interactions within the tissue niches are dependent on MSCs. In this context, it is essential to understand the mechanisms underlying communication between MSCs and differentiated parenchymal cells of each particular tissue. This is important both from the perspective of basic science and for the development of therapeutic approaches involving the modulation of the activity of resident MSCs. With regard to the liver, the research is concentrated on the intercommunication between MSCs and hepatocytes under normal conditions and during the development of the pathological process. The goals of this review were to identify the key factors mediating the crosstalk between MSCs and hepatocytes and determine the possible mechanisms of interaction of the two cell types under normal and stressful conditions. The analysis of the hepatocyte-MSC interaction showed that MSCs carry out chaperone-like functions, including the synthesis of the supportive extracellular matrix proteins; prevention of apoptosis, pyroptosis, and ferroptosis; support of regeneration; elimination of lipotoxicity and ER stress; promotion of antioxidant effects; and donation of mitochondria. The underlying mechanisms suggest very close interdependence, including even direct cytoplasm and organelle exchange.

Eight Zhes Decoction ameliorates the lipid dysfunction of nonalcoholic fatty liver disease using integrated lipidomics, network pharmacology and pharmacokinetics

Nonalcoholic fatty liver disease (NAFLD) has developed into the most common chronic liver disease and can lead to liver cancer. Our laboratory previously developed a novel prescription for NAFLD, "Eight Zhes Decoction" (EZD), which has shown good curative effects in clinical practice. However, the pharmacodynamic material basis and mechanism have not yet been revealed. A strategy integrating lipidomics, network pharmacology and pharmacokinetics was used to reveal the active components and mechanisms of EZD against NAFLD. The histopathological results showed that EZD attenuated the degrees of collagen deposition and steatosis in the livers of nonalcoholic steatofibrosis model mice. Furthermore, glycerophospholipid metabolism, arachidonic acid metabolism, glycerolipid metabolism and linoleic acid metabolism with phospholipase A2 group IVA (PLA2G4A) and cytochrome P450 as the core targets and 12,13-cis-epoxyoctadecenoic acid, 12(S)-hydroxyeicosatetraenoic acid, leukotriene B4, prostaglandin E2, phosphatidylcholines (PCs) and triacylglycerols (TGs) as the main lipids were found to be involved in the treatment of NAFLD by EZD. Importantly, naringenin, artemetin, canadine, and bicuculline were identified as the active ingredients of EZD against NAFLD; in particular, naringenin reduces PC consumption by inhibiting the expression of PLA2G4A and thus promotes sufficient synthesis of very-low-density lipoprotein to transport excess TGs in the liver. This research provides valuable data and theoretical support for the application of EZD against NAFLD.

Identified and potential internalization signals involved in trafficking and regulation of Na+/K+ ATPase activity

The sodium-potassium pump (NKA) or Na+/K+ ATPase consumes around 30-40% of the total energy expenditure of the animal cell on the generation of the sodium and potassium electrochemical gradients that regulate various electrolyte and nutrient transport processes. The vital role of this protein entails proper spatial and temporal regulation of its activity through modulatory mechanisms involving its expression, localization, enzymatic activity, and protein-protein interactions. The residence of the NKA at the plasma membrane is compulsory for its action as an antiporter. Despite the huge body of literature reporting on its trafficking between the cell membrane and intracellular compartments, the mechanisms controlling the trafficking process are by far the least understood. Among the molecular determinants of the plasma membrane proteins trafficking are intrinsic sequence-based endocytic motifs. In this review, we (i) summarize previous reports linking the regulation of Na+/K+ ATPase trafficking and/or plasma membrane residence to its activity, with particular emphasis on the endocytic signals in the Na+/K+ ATPase alpha-subunit, (ii) map additional potential internalization signals within Na+/K+ ATPase catalytic alpha-subunit, based on canonical and noncanonical endocytic motifs reported in the literature, (iii) pinpoint known and potential phosphorylation sites associated with NKA trafficking, (iv) highlight our recent studies on Na+/K+ ATPase trafficking and PGE2-mediated Na+/K+ ATPase modulation in intestine, liver, and kidney cells.

Serotonin transporter-deficient mice display enhanced adipose tissue inflammation after chronic high-fat diet feeding

Introduction

Serotonin is involved in leukocyte recruitment during inflammation. Deficiency of the serotonin transporter (SERT) is associated with metabolic changes in humans and mice. A possible link and interaction between the inflammatory effects of serotonin and metabolic derangements in SERT-deficient mice has not been investigated so far.

Methods

SERT-deficient (Sert -/-) and wild type (WT) mice were fed a high-fat diet, starting at 8 weeks of age. Metabolic phenotyping (metabolic caging, glucose and insulin tolerance testing, body and organ weight measurements, qPCR, histology) and assessment of adipose tissue inflammation (flow cytometry, histology, qPCR) were carried out at the end of the 19-week high-fat diet feeding period. In parallel, Sert -/- and WT mice received a control diet and were analyzed either at the time point equivalent to high-fat diet feeding or as early as 8-11 weeks of age for baseline characterization.

Results

After 19 weeks of high-fat diet, Sert -/- and WT mice displayed similar whole-body and fat pad weights despite increased relative weight gain due to lower starting body weight in Sert -/-. In obese Sert -/- animals insulin resistance and liver steatosis were enhanced as compared to WT animals. Leukocyte accumulation and mRNA expression of cytokine signaling mediators were increased in epididymal adipose tissue of obese Sert -/- mice. These effects were associated with higher adipose tissue mRNA expression of the chemokine monocyte chemoattractant protein 1 and presence of monocytosis in blood with an increased proportion of pro-inflammatory Ly6C+ monocytes. By contrast, Sert -/- mice fed a control diet did not display adipose tissue inflammation.

Discussion

Our observations suggest that SERT deficiency in mice is associated with inflammatory processes that manifest as increased adipose tissue inflammation upon chronic high-fat diet feeding due to enhanced leukocyte recruitment.

Lipidomics in pathogenesis, progression and treatment of nonalcoholic steatohepatitis (NASH): Recent advances

Nonalcoholic fatty liver disease (NAFLD) is a chronic liver disease affecting up to 30% of the general adult population. NAFLD encompasses a histological spectrum ranging from pure steatosis to non-alcoholic steatohepatitis (NASH). NASH can progress to cirrhosis and is becoming the most common indication for liver transplantation, as a result of increasing disease prevalence and of the absence of approved treatments. Lipidomic readouts of liver blood and urine samples from experimental models and from NASH patients disclosed an abnormal lipid composition and metabolism. Collectively, these changes impair organelle function and promote cell damage, necro-inflammation and fibrosis, a condition termed lipotoxicity. We will discuss the lipid species and metabolic pathways leading to NASH development and progression to cirrhosis, as well as and those species that can contribute to inflammation resolution and fibrosis regression. We will also focus on emerging lipid-based therapeutic opportunities, including specialized proresolving lipid molecules and macrovesicles contributing to cell-to-cell communication and NASH pathophysiology.

15-Hydroxyprostaglandin dehydrogenase inhibitor SW033291 ameliorates hepatic abnormal lipid metabolism, ER stress, and inflammation through PGE2/EP4 in T2DM mice

Type 2 diabetes mellitus (T2DM) is a rapidly growing epidemic that results in increased morbidity, mortality, and soaring medical costs. Prostaglandin E₂ (PGE₂), a vital lipid mediator, has been reported to protect against hepatic steatosis, inflammation, endoplasmic reticulum (ER) stress, and insulin resistance, indicating its potential therapeutic role in T2DM. PGE₂ can be degraded by 15-hydroxyprostaglandin dehydrogenase (15-PGDH). SW033291, an inhibitor of 15-PGDH, has been reported to increase PGE₂ levels, however, the effect of SW033291 in T2DM remains to be explored. This study aims to evaluate whether SW033291 protects against T2DM and explore its potential mechanisms. A T2DM mouse model was established through high-fat diet/streptozotocin injection, while palmitic acid-treated mouse primary hepatocytes were used as insulin-resistant cell models. SW033291 treatment reduced body weight, fat weight, fasting blood glucose, and improved impaired glucose tolerance and insulin resistance in T2DM mice. More importantly, SW033291 alleviated steatosis, inflammation, and ER stress in the liver of T2DM mice. Mechanistically, SW033291 decreased the expressions of SREBP-1c and ACC1, and increased the expression of PPARα in T2DM mice. Additionally, SW033291 inhibited NF-κB and eIF2α/CHOP signaling in T2DM mice. Further, we showed that the protective effects of SW033291 on the above-mentioned pathophysiological processes could be hindered by inhibition of the PGE₂ receptor EP4. Overall, our study reveals a novel role of SW033291 in alleviating T2DM and suggests its potential as a new therapeutic strategy for T2DM.

Gut mycobiome and metabolic diseases: The known, the unknown, and the future

Metabolic diseases, such as type 2 diabetes mellitus (T2DM), non-alcoholic fatty liver disease (NAFLD) and obesity, have become a major public health problem worldwide. In recent years, most research on the role of gut microbes in metabolic diseases has focused on bacteria, whereas fungal microbes have been neglected. This review aims to provide a comprehensive overview of gut fungal alterations in T2DM, obesity, and NAFLD, and to discuss the mechanisms associated with disease development. In addition, several novel strategies targeting gut mycobiome and/or their metabolites to improve T2DM, obesity and NAFLD, including fungal probiotics, antifungal drugs, dietary intervention, and fecal microbiota transplantation, are critically discussed. The accumulated evidence suggests that gut mycobiome plays an important role in the occurrence and development of metabolic diseases. The possible mechanisms by which the gut mycobiome affects metabolic diseases include fungal-induced immune responses, fungal-bacterial interactions, and fungal-derived metabolites. Candida albicans, Aspergillus and Meyerozyma may be potential pathogens of metabolic diseases because they can activate the immune system and/or produce harmful metabolites. Moreover, Saccharomyces boulardii, S. cerevisiae, Alternaria, and Cochliobolus fungi may have the potential to improve metabolic diseases. The information may provide an important reference for the development of new therapeutics for metabolic diseases based on gut mycobiome.

The 15-hydroxyprostaglandin dehydrogenase inhibitor SW033291 ameliorates abnormal hepatic glucose metabolism through PGE2-EP4 receptor-AKT signaling in a type 2 diabetes mellitus mouse model

Type 2 diabetes mellitus (T2DM) is associated with high rates of morbidity and mortality worldwide. Prostaglandin E₂ (PGE₂) is a lipid signaling molecule that can ameliorate the symptoms of some metabolic diseases, including T2DM, and improve tissue repair and regeneration. Although SW033291 can increase PGE₂ levels through its action as a small molecule inhibitor of the PGE₂-degrading enzyme 15-hydroxyprostaglandin dehydrogenase, its effects on T2DM remain unclear. In the present study, we evaluated whether SW033291 treatment exerts a protective effect against T2DM and explored the underlying mechanisms. A T2DM mouse model was established using a high-fat diet combined with streptozotocin treatment. Palmitic acid-treated LO2 cells were used as an insulin-resistant cell model. SW033291 treatment reduced body weight and fasting blood glucose levels as well as serum triglyceride, total cholesterol, and low-density lipoprotein cholesterol levels in vivo. In addition to ameliorating glucose and insulin tolerance, SW033291 treatment reversed the T2DM-induced decrease in glycogen synthesis and increase in gluconeogenesis in the liver. Furthermore, SW033291 administration increased hepatic glycogen synthase kinase 3 beta (GSK3β) phosphorylation levels to promote glycogen synthesis. SW033291 treatment also inhibited gluconeogenesis by upregulating AKT serine/threonine kinase (AKT) and forkhead box O1 (FOXO1) phosphorylation and reducing glucose-6-phosphatase and phosphoenolpyruvate carboxykinase 1 expression in the livers of T2DM model mice. Additionally, SW033291 treatment improved abnormal hepatic glucose metabolism through the PGE₂-EP4 receptor-AKT-GSK3β/FOXO1 signaling pathway in vitro. These results suggest a novel role of SW033291 in improving T2DM and support its potential as a novel therapeutic agent.

Microsomal Prostaglandin E Synthase-1 and -2: Emerging Targets in Non-Alcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) affects a substantial proportion of the general population and is even more prevalent in obese and diabetic patients. NAFLD, and particularly the more advanced manifestation of the disease, nonalcoholic steatohepatitis (NASH), increases the risk for both liver-related and cardiovascular morbidity. The pathogenesis of NAFLD is complex and multifactorial, with many molecular pathways implicated. Emerging data suggest that microsomal prostaglandin E synthase-1 and -2 might participate in the development and progression of NAFLD. It also appears that targeting these enzymes might represent a novel therapeutic approach for NAFLD. In the present review, we discuss the association between microsomal prostaglandin E synthase-1 and -2 and NAFLD.

Polychlorinated biphenyls alter hepatic m6A mRNA methylation in a mouse model of environmental liver disease

Exposure to polychlorinated biphenyls (PCBs) has been associated with liver injury in human cohorts and with nonalcoholic steatohepatitis (NASH) in mice fed a high fat diet (HFD). N (6)-methyladenosine (m6A) modification of mRNA regulates transcript fate, but the contribution of m6A modification on the regulation of transcripts in PCB-induced steatosis and fibrosis is unknown. This study tested the hypothesis that PCB and HFD exposure alters the levels of m6A modification in transcripts that play a role in NASH in vivo. Male C57Bl6/J mice were fed a HFD (12 wks) and administered a single oral dose of Aroclor1260, PCB126, or Aroclor1260 + PCB126. Genome-wide identification of m6A peaks was accomplished by m6A mRNA immunoprecipitation sequencing (m6A-RIP) and the mRNA transcriptome identified by RNA-seq. Exposure of HFD-fed mice to Aroclor1260 decreased the number of m6A peaks and m6A-containing genes relative to PCB vehicle control whereas PCB126 or the combination of Aroclor1260 + PCB126 increased m6A modification frequency. ∼41% of genes had one m6A peak and ∼49% had 2-4 m6A peaks. 117 m6A peaks were common in the four experimental groups. The Aroclor1260 + PCB126 exposure group showed the highest number (52) of m6A-peaks. qRT-PCR confirmed enrichment of m6A-containing fragments of the Apob transcript with PCB exposure. A1cf transcript abundance, m6A peak count, and protein abundance was increased with Aroclor1260 + PCB126 co-exposure. Irrespective of the PCB type, all PCB groups exhibited enriched pathways related to lipid/lipoprotein metabolism and inflammation through the m6A modification. Integrated analysis of m6A-RIP-seq and mRNA-seq identified 242 differentially expressed genes (DEGs) with increased or reduced number of m6A peaks. These data show that PCB exposure in HFD-fed mice alters the m6A landscape offering an additional layer of regulation of gene expression affecting a subset of gene responses in NASH.

Integrated analysis of effect of daisaikoto, a traditional Japanese medicine, on the metabolome and gut microbiome in a mouse model of nonalcoholic fatty liver disease

Dysregulation of lipid metabolism and diabetes are risk factors for nonalcoholic fatty liver disease (NAFLD), and the gut-liver axis and intestinal microbiome are known to be highly associated with the pathogenesis of this disease. In Japan, the traditional medicine daisaikoto (DST) is prescribed for individuals affected by hepatic dysfunction. Herein, we evaluated the therapeutic potential of DST for treating NAFLD through modification of the liver and stool metabolome and microbiome by using STAM mice as a model of NAFLD. STAM mice were fed a high-fat diet with or without 3 % DST for 3 weeks. Plasma and liver of STAM, STAM with DST, and C57BL/6J ("Normal") mice were collected at 9 weeks, and stools at 4, 6, and 9 weeks of age. The liver pathology, metabolome and stool microbiome were analyzed. DST ameliorated the NAFLD activity score of STAM mice and decreased the levels of several liver lipid mediators such as arachidonic acid and its derivatives. In normal mice, nine kinds of family accounted for 94.1 % of microbiome composition; the total percentage of these family was significantly decreased in STAM mice (45.6 %), and DST administration improved this imbalance in microbiome composition (65.2 %). In stool samples, DST increased ursodeoxycholic acid content and altered several amino acids, which were correlated with changes in the gut microbiome and liver metabolites. In summary, DST ameliorates NAFLD by decreasing arachidonic acid metabolism in the liver; this amelioration seems to be associated with crosstalk among components of the liver, intestinal environment, and microbiome.

The biological actions of prostanoids in adipose tissue in physiological and pathophysiological conditions

Adipose tissue has been established as an endocrine organ that plays an important role in maintaining metabolic homeostasis. Adipose tissue releases several bioactive molecules called adipokines. Inflammation, dysregulation of adipokine synthesis, and secretion are observed in obesity and related diseases and cause adipose tissue dysfunction. Prostanoids, belonging to the eicosanoid family of lipid mediators, can be synthesized in adipose tissue and play a critical role in adipose tissue biology. In this review, we summarized the current knowledge regarding the interaction of prostanoids with adipokines, the expression of prostanoid receptors, and prostanoid synthase enzymes in adipose tissues in health and disease. Furthermore, the involvement of prostanoids in the physiological function or dysfunction of adipose tissue including inflammation, lipolysis, adipogenesis, thermogenesis, browning of adipocytes, and vascular tone regulation was also discussed by examining studies using pharmacological approaches or genetically modified animals for prostanoid receptors/synthase enzymes. Overall, the present review provides a perspective on the evidence from literature regarding the biological effects of prostanoids in adipose tissue. Among prostanoids, prostaglandin E2 (PGE₂) is prominent in regards to its substantial role in both adipose tissue physiology and pathophysiology. Targeting prostanoids may serve as a potential therapeutic strategy for preventing or treating obesity and related diseases.

Fatty Acids and Eicosanoids Change during High-Fiber Diet in NAFLD Patients-Randomized Control Trials (RCT)

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD) is a wide spectrum condition characterized by excessive liver fat accumulation in people who do not abuse alcohol. There is no effective medical treatment for NAFLD; therefore, most important recommendations to reduce liver steatosis are diet and lifestyle, including proper physical activity. The aim of our study was to analyze the fatty acids and eicosanoids changes in the serum of patients who consumed high-fiber rolls for 8 weeks.

MATERIALS AND METHODS

The group of 28 Caucasian participants was randomly divided into two groups, those who received 24 g of fiber/day-from 2 buns of 12 g each (n = 14), and those who received 12 g of fiber/day-from 2 buns of 6 g (n = 14). At the beginning and on the last visit of the 8-week intervention, all patients underwent NAFLD evaluation, biochemical parameter measurements, and fatty acids and eicosanoids evaluation.

RESULTS

Patients who received 12 g of fiber had significantly reduced liver steatosis and body mass index. In the group who received 24 g of fiber/day, we observed a trend to liver steatosis reduction (p = 0.07) and significant decrease in aspartate aminotransferase (p = 0.03) and total cholesterol (p = 0.03). All changes in fatty acid and eicosanoids profile were similar. Fatty acids analysis revealed that extra fiber intake was associated with a significant increase in monounsaturated fatty acids and decrease in saturated fatty acids. Moreover, both groups showed increased concentration of gamma linoleic acid and docosahexaenoic acid. We also observed reduction in prostaglandin E₂.

CONCLUSIONS

Our study revealed that a high amount of fiber in the diet is associated with a reduction in fatty liver, although this effect was more pronounced in patients in the lower fiber group. However, regardless of the amount of fiber consumed, we observed significant changes in the profile of FAs, which may reflect the positive changes in the lipids liver metabolism. Regardless of the amount of fiber consumed, patients decreased the amount of PGE₂, which may indicate the lack of disease progression associated with the development of inflammation.

Hepatic circadian and differentiation factors control liver susceptibility for fatty liver disease and tumorigenesis

Hepatocellular carcinoma (HCC) is a leading cause of cancer deaths, and the most common primary liver malignancy to present in the clinic. With the exception of liver transplant, treatment options for advanced HCC are limited, but improved tumor stratification could open the door to new treatment options. Previously, we demonstrated that the circadian regulator Aryl Hydrocarbon-Like Receptor Like 1 (ARNTL, or Bmal1) and the liver-enriched nuclear factor 4 alpha (HNF4α) are robustly co-expressed in healthy liver but incompatible in the context of HCC. Faulty circadian expression of HNF4α- either by isoform switching, or loss of expression- results in an increased risk for HCC, while BMAL1 gain-of-function in HNF4α-positive HCC results in apoptosis and tumor regression. We hypothesize that the transcriptional programs of HNF4α and BMAL1 are antagonistic in liver disease and HCC. Here, we study this antagonism by generating a mouse model with inducible loss of hepatic HNF4α and BMAL1 expression. The results reveal that simultaneous loss of HNF4α and BMAL1 is protective against fatty liver and HCC in carcinogen-induced liver injury and in the "STAM" model of liver disease. Furthermore, our results suggest that targeting Bmal1 expression in the absence of HNF4α inhibits HCC growth and progression. Specifically, pharmacological suppression of Bmal1 in HNF4α-deficient, BMAL1-positive HCC with REV-ERB agonist SR9009 impairs tumor cell proliferation and migration in a REV-ERB-dependent manner, while having no effect on healthy hepatocytes. Collectively, our results suggest that stratification of HCC based on HNF4α and BMAL1 expression may provide a new perspective on HCC properties and potential targeted therapeutics.

Prostaglandin 2α Promotes Autophagy and Mitochondrial Energy Production in Fish Hepatocytes

Fatty liver, characterized by excessive lipid droplet (LD) accumulation in hepatocytes, is a common physiological condition in humans and aquaculture species. Lipid mobilization is an important strategy for modulating the number and size of cellular LDs. Cyclooxygenase (COX)-mediated arachidonic acid derivatives are known to improve lipid catabolism in fish; however, the specific derivatives remain unknown. In the present study, we showed that serum starvation induced LD degradation via autophagy, lipolysis, and mitochondrial energy production in zebrafish hepatocytes, accompanied by activation of the COX pathway. The cellular concentration of PGF2α, but not other prostaglandins, was significantly increased. Administration of a COX inhibitor or interference with PGF2α synthase abolished serum deprivation-induced LD suppression, LD–lysosome colocalization, and expression of autophagic genes. Additionally, exogenous PGF2α suppressed the accumulation of LDs, promoted the accumulation of lysosomes with LD and the autophagy marker protein LC3A/B, and augmented the expression of autophagic genes. Moreover, PGF2α enhanced mitochondrial accumulation and ATP production, and increased the transcript levels of β-oxidation- and mitochondrial respiratory chain-related genes. Collectively, these findings demonstrate that the COX pathway is implicated in lipid degradation induced by energy deprivation, and that PGF2α is a key molecule triggering autophagy, lipolysis, and mitochondrial development in zebrafish hepatocytes.

Platelet-Activating Factor Promotes the Development of Non-Alcoholic Fatty Liver Disease

Non-alcoholic fatty liver disease (NAFLD) is a multifaceted clinicopathological syndrome characterised by excessive hepatic lipid accumulation that causes steatosis, excluding alcoholic factors. Platelet-activating factor (PAF), a biologically active lipid transmitter, induces platelet activation upon binding to the PAF receptor. Recent studies have found that PAF is associated with gamma-glutamyl transferase, which is an indicator of liver disease. Moreover, PAF can stimulate hepatic lipid synthesis and cause hypertriglyceridaemia. Furthermore, the knockdown of the PAF receptor gene in the animal models of NAFLD helped reduce the inflammatory response, improve glucose homeostasis and delay the development of NAFLD. These findings suggest that PAF is associated with NAFLD development. According to reports, patients with NAFLD or animal models have marked platelet activation abnormalities, mainly manifested as enhanced platelet adhesion and aggregation and altered blood rheology. Pharmacological interventions were accompanied by remission of abnormal platelet activation and significant improvement in liver function and lipids in the animal model of NAFLD. These confirm that platelet activation may accompany a critical importance in NAFLD development and progression. However, how PAFs are involved in the NAFLD signalling pathway needs further investigation. In this paper, we review the relevant literature in recent years and discuss the role played by PAF in NAFLD development. It is important to elucidate the pathogenesis of NAFLD and to find effective interventions for treatment.

Fluoxetine-induced hepatic lipid accumulation is mediated by prostaglandin endoperoxide synthase 1 and is linked to elevated 15-deoxy-Δ12,14 PGJ2

Major depressive disorder and other neuropsychiatric disorders are often managed with long-term use of antidepressant medication. Fluoxetine, an SSRI antidepressant, is widely used as a first-line treatment for neuropsychiatric disorders. However, fluoxetine has also been shown to increase the risk of metabolic diseases such as non-alcoholic fatty liver disease. Fluoxetine has been shown to increase hepatic lipid accumulation in vivo and in vitro. In addition, fluoxetine has been shown to alter the production of prostaglandins which have also been implicated in the development of non-alcoholic fatty liver disease. The goal of this study was to assess the effect of fluoxetine exposure on the prostaglandin biosynthetic pathway and lipid accumulation in a hepatic cell line (H4-II-E-C3 cells). Fluoxetine treatment increased mRNA expression of prostaglandin biosynthetic enzymes (Ptgs1, Ptgs2, and Ptgds), PPAR gamma (Pparg), and PPAR gamma downstream targets involved in fatty acid uptake (Cd36, Fatp2, and Fatp5) as well as production of 15-deoxy-Δ^12,14 PGJ₂ a PPAR gamma ligand. The effects of fluoxetine to induce lipid accumulation were attenuated with a PTGS1 specific inhibitor (SC-560), whereas inhibition of PTGS2 had no effect. Moreover, SC-560 attenuated 15-deoxy-Δ^12,14 PGJ₂ production and expression of PPAR gamma downstream target genes. Taken together these results suggest that fluoxetine-induced lipid abnormalities appear to be mediated via PTGS1 and its downstream product 15d-PGJ₂ and suggest a novel therapeutic target to prevent some of the adverse effects of fluoxetine treatment.

Omega-3 carboxylic acids and fenofibrate differentially alter plasma lipid mediators in patients with non-alcoholic fatty liver disease

Fibrates and omega-3 polyunsaturated acids are used for the treatment of hypertriglyceridemia but have not demonstrated consistent effects on cardiovascular (CV) risk. In this study, we investigate how these two pharmacological agents influence plasma levels of bioactive lipid mediators, aiming to explore their efficacy beyond that of lipid-lowering agents. Plasma from overweight patients with non-alcoholic fatty liver disease (NAFLD) and hypertriglyceridemia, participating in a randomized placebo-controlled study investigating the effects of 12 weeks treatment with fenofibrate or omega-3 free carboxylic acids (OM-3CA) (200 mg or 4 g per day, respectively), were analyzed for eicosanoids and related PUFA species, N-acylethanolamines (NAE) and ceramides. OM-3CA reduced plasma concentrations of proinflammatory PGE₂ , as well as PGE₁ , PGD₁ and thromboxane B2 but increased prostacyclin, and eicosapentaenoic acid- and docosahexaenoic acid-derived lipids of lipoxygenase and cytochrome P450 monooxygenase (CYP) (e.g., 17-HDHA, 18-HEPE, 19,20-DiHDPA). Fenofibrate reduced plasma concentrations of vasoactive CYP-derived eicosanoids (DHETs). Although OM-3CA increased plasma levels of the NAE docosahexaenoyl ethanolamine and docosapentaenoyl ethanolamine, and fenofibrate increased palmitoleoyl ethanolamine, the effect of both treatments may have been masked by the placebo (olive oil). Fenofibrate was more efficacious than OM-3CA in significantly reducing plasma ceramides, pro-inflammatory lipids associated with CV disease risk. Neither treatment affected putative lipid species associated with NAFLD. Our results show that OM-3CA and fenofibrate differentially modulate the plasma mediator lipidome, with OM-3CA promoting the formation of lipid mediators with potential effects on chronic inflammation, while fenofibrate mainly reducing ceramides. These findings suggest that both treatments could ameliorate chronic inflammation with possible impact on disease outcomes, independent of triglyceride reduction.

Role of 2‑series prostaglandins in the pathogenesis of type 2 diabetes mellitus and non‑alcoholic fatty liver disease (Review)

Nowadays, metabolic syndromes are emerging as global epidemics, whose incidence are increasing annually. However, the efficacy of therapy does not increase proportionately with the increased morbidity. Type 2 diabetes mellitus (T2DM) and non-alcoholic fatty liver disease (NAFLD) are two common metabolic syndromes that are closely associated. The pathogenic mechanisms of T2DM and NAFLD have been studied, and it was revealed that insulin resistance, hyperglycemia, hepatic lipid accumulation and inflammation markedly contribute to the development of these two diseases. The 2-series prostaglandins (PGs), a subgroup of eicosanoids, including PGD₂, PGE₂, PGF_2α and PGI₂, are converted from arachidonic acid catalyzed by the rate-limiting enzymes cyclooxygenases (COXs). Considering their wide distribution in almost every tissue, 2-series PG pathways exert complex and interlinked effects in mediating pancreatic β-cell function and proliferation, insulin sensitivity, fat accumulation and lipolysis, as well as inflammatory processes. Previous studies have revealed that metabolic disturbances, such as hyperglycemia and hyperlipidemia, can be improved by treatment with COX inhibitors. At present, an accumulating number of studies have focused on the roles of 2-series PGs and their metabolites in the pathogenesis of metabolic syndromes, particularly T2DM and NAFLD. In the present review, the role of 2-series PGs in the highly intertwined pathogenic mechanisms of T2DM and NAFLD was discussed, and important therapeutic strategies based on targeting 2-series PG pathways in T2DM and NAFLD treatment were provided.

Pathophysiological role of prostaglandin E synthases in liver diseases

Prostaglandin E synthases (PGESs) convert cyclooxygenase (COX)-derived prostaglandin H₂ (PGH₂) into prostaglandin E₂ (PGE₂) and comprise at least three types of structurally and biologically distinct enzymes. Two of these, namely microsomal prostaglandin E synthase-1 (mPGES-1) and mPGES-2, are membrane-bound enzymes. mPGES-1 is an inflammation-inducible enzyme that converts PGH₂ into PGE₂. mPGES-2 is a bifunctional enzyme that generally forms a complex with haem in the presence of glutathione. This enzyme can metabolise PGH₂ into malondialdehyde and can produce PGE₂ after its separation from haem. In this review, we discuss the role of PGESs, particularly mPGES-1 and mPGES-2, in the pathogenesis of liver diseases. A better understanding of the roles of PGESs in liver disease may aid in the development of treatments for patients with liver diseases.

PPARγ as an E3 Ubiquitin-Ligase Impedes Phosphate-Stat6 Stability and Promotes Prostaglandins E2-Mediated Inhibition of IgE Production in Asthma

Increased serum IgE level is one of the features of allergic asthma. It is reported that IgE production can be enhanced by E-prostanoid 2 (EP2) receptor of prostaglandin E₂ (PGE₂); however, whether E-prostanoid 4 (EP4) receptor (encoded by Ptger4) has a unique or redundant role is still unclear. Here, we demonstrated the mice with B cell-specific deletion of the EP4 receptor (Ptger4^fl/flMb1^cre+/−) showed their serum levels of IgE were markedly increased. A much more severe airway allergic inflammation was observed in the absence of EP4 signal using the OVA-induced asthma model. Mechanistic studies demonstrated that the transcription levels of AID, GLTε, and PSTε in EP4-deficient B cells were found to be significantly increased, implying an enhanced IgE class switch. In addition, we saw higher levels of phosphorylated STAT6, a vital factor for IgE class switch. Biochemical analyses indicated that inhibitory effect of EP4 signal on IgE depended on the activation of the PI3K-AKT pathway. Further downstream, PPARγ expression was up-regulated. Independent of its activity as a transcription factor, PPARγ here primarily functioned as an E3 ubiquitin-ligase, which bound the phosphorylated STAT6 to initiate its degradation. In support of PPARγ as a key mediator downstream of the EP4 signal, PPARγ agonist induced the down-regulation of phospho-STAT6, whereas its antagonist was able to rescue the EP4-mediated inhibition of STAT6 activation and IgE production. Thus, our findings highlight a role for the PGE₂-EP4-AKT-PPARγ-STAT6 signaling in IgE response, highlighting the therapeutic potential of combined application of EP4 and PPARγ agonists in asthma.

Augmented liver inflammation in a microsomal prostaglandin E synthase 1 (mPGES-1)-deficient diet-induced mouse NASH model

In a subset of patients, non-alcoholic fatty liver disease (NAFLD) is complicated by cell death and inflammation resulting in non-alcoholic steatohepatitis (NASH), which may progress to fibrosis and subsequent organ failure. Apart from cytokines, prostaglandins, in particular prostaglandin E₂ (PGE₂), play a pivotal role during inflammatory processes. Expression of the key enzymes of PGE₂ synthesis, cyclooxygenase 2 and microsomal PGE synthase 1 (mPGES-1), was increased in human NASH livers in comparison to controls and correlated with the NASH activity score. Both enzymes were also induced in NASH-diet-fed wild-type mice, resulting in an increase in hepatic PGE₂ concentration that was completely abrogated in mPGES-1-deficient mice. PGE₂ is known to inhibit TNF-α synthesis in macrophages. A strong infiltration of monocyte-derived macrophages was observed in NASH-diet-fed mice, which was accompanied with an increase in hepatic TNF-α expression. Due to the impaired PGE₂ production, TNF-α expression increased much more in livers of mPGES-1-deficient mice or in the peritoneal macrophages of these mice. The increased levels of TNF-α resulted in an enhanced IL-1β production, primarily in hepatocytes, and augmented hepatocyte apoptosis. In conclusion, attenuation of PGE₂ production by mPGES-1 ablation enhanced the TNF-α-triggered inflammatory response and hepatocyte apoptosis in diet-induced NASH.

Invalidation of Microsomal Prostaglandin E Synthase-1 (mPGES-1) Reduces Diet-Induced Low-Grade Inflammation and Adiposity

Chronic low-grade inflammation is known to be linked to obesity, and to occur in the early stages of the disease. This mechanism is complex and involves numerous organs, cells, and cytokines. In this context, inflammation of white adipose tissue seems to play a key role in the development of obesity. Because of its properties, prostaglandin E2 (PGE2), an emblematic inflammatory mediator, has been proposed as an actor linking inflammation and obesity. Indeed, PGE2 is involved in mechanisms that are dysregulated in obesity such as lipolysis and adipogenesis. Microsomal prostaglandin E synthase-1 (mPGES-1) is an enzyme, which specifically catalyzes the final step of PGE2 biosynthesis. Interestingly, mPGES-1 invalidation dramatically alters the production of PGE2 during inflammation. In the present work, we sought to determine whether mPGES-1 could contribute to inflammation associated with obesity. To this end, we analyzed the energy metabolism of mPGES-1 deficient mice (mPGES-1^-/-) and littermate controls, fed with a high-fat diet. Our data showed that mPGES-1^-/- mice exhibited resistance to diet-induced obesity when compared to wild-type littermates. mPGES-1^-/- mice fed with a high-fat diet, showed a lower body weight gain and a reduced adiposity, which were accompanied by a decrease in adipose tissues inflammation. We also observed an increase in energy expenditures in mPGES-1^-/- mice fed with a high-fat diet without any changes in activity and browning process. Altogether, these data suggest that mPGES-1 inhibition may prevent diet-induced obesity.

Application of a dye-based mitochondrion-thermometry to determine the receptor downstream of prostaglandin E2 involved in the regulation of hepatocyte metabolism

Temperature distributions inside a living cell reflect the thermodynamics and functions of cellular components. We used a newly-developed method of mitochondrial thermometry based on Rhodamine B methyl ester, which equilibrates as a thermosensitive mixture of nonfluorescent and fluorescent resonance forms. Prostaglandin E₂ (PGE₂) is released from hepatic non-parenchymal Kupffer cells and acts as an inflammatory factor to impact various functions of hepatocytes. The activity of PGE₂ on energy mechanism of hepatocytes has not been fully elucidated and in particular, which PGE₂ receptor mediates the functions has been elusive. We identified EP4 as the major receptor of PGE₂ via our mitochondrion-thermometry approach and then substantiated this receptor's role in hepatic metabolism. We discovered that PGE₂ is able to decrease intracellular temperature of hepatocytes, via increasing some lipogenic genes' expressions, hampering lipolysis and mitochondrial β-oxidation, reducing intracellular ATP level and elevating cAMP level through EP4 receptor. The redox status of hepatocytes represented by FAD vs FAD + NADH ratio is influenced by PGE₂ in an EP4 receptor-dependent manner. Collectively, these data demonstrate that PGE₂ regulates metabolism of hepatocytes mainly through EP4 receptor.

Bioactive Lipid Species and Metabolic Pathways in Progression and Resolution of Nonalcoholic Steatohepatitis

The prevalence of nonalcoholic steatohepatitis (NASH) is increasing worldwide, yet there are no effective treatments. A decade has passed since the initial lipidomics analyses of liver tissues from patients with nonalcoholic fatty liver disease. We have learned that liver cells from patients with NASH have an abnormal lipid composition and that the accumulation of lipids leads to organelle dysfunction, cell injury and death, and chronic inflammation, called lipotoxicity. We review the lipid species and metabolic pathways that contribute to the pathogenesis of NASH and potential therapeutic targets, including enzymes involved in fatty acid and triglyceride synthesis, bioactive sphingolipids and polyunsaturated-derived eicosanoids, and specialized pro-resolving lipid mediators. We discuss the concept that NASH is a disease that can resolve and the roles of lipid molecules in the resolution of inflammation and regression of fibrosis.

The Eicosanoids, Redox-Regulated Lipid Mediators in Immunometabolic Disorders

SIGNIFICANCE

The oxidation of arachidonic acid via cyclooxygenase (COX) and lipoxygenase (LOX) activity to produce eicosanoids during inflammation is a well-known biosynthetic pathway. These lipid mediators are involved in fever, pain, and thrombosis and are produced from multiple cells as well as cell/cell interactions, for example, immune cells and epithelial/endothelial cells. Metabolic disorders, including hyperlipidemia, hypertension, and diabetes, are linked with chronic low-grade inflammation, impacting the immune system and promoting a variety of chronic diseases. Recent Advances: Multiple studies have corroborated the important function of eicosanoids and their receptors in (non)-inflammatory cells in immunometabolic disorders (e.g., insulin resistance, obesity, and cardiovascular and nonalcoholic fatty liver diseases). In this context, LOX and COX products are involved in both pro- and anti-inflammatory responses. In addition, recent work has elucidated the potent function of specialized proresolving mediators (i.e., lipoxins and resolvins) in resolving inflammation, protecting organs, and stimulating tissue repair and remodeling.

CRITICAL ISSUES

Inhibiting/stimulating selected eicosanoid pathways may result in anti-inflammatory and proresolution responses leading to multiple beneficial effects, including the abrogation of reactive oxygen species production, increased speed of resolution, and overall improvement of diseases related to immunometabolic perturbations.

FUTURE DIRECTIONS

Despite many achievements, it is crucial to understand the molecular and cellular mechanisms underlying immunological/metabolic cross talk to offer substantial therapeutic promise. Antioxid. Redox Signal. 29, 275-296.

Non-alcoholic fatty liver disease: A sign of systemic disease

Non-alcoholic fatty liver disease (NAFLD) is the most common form of liver disease and leading cause of cirrhosis in the United States and developed countries. NAFLD is closely associated with obesity, insulin resistance and metabolic syndrome, significantly contributing to the exacerbation of the latter. Although NAFLD represents the hepatic component of metabolic syndrome, it can also be found in patients prior to their presentation with other manifestations of the syndrome. The pathogenesis of NAFLD is complex and closely intertwined with insulin resistance and obesity. Several mechanisms are undoubtedly involved in its pathogenesis and progression. In this review, we bring together the current understanding of the pathogenesis that makes NAFLD a systemic disease.

Role of cyclooxygenase-mediated metabolites in lipid metabolism and expression of some immune-related genes in juvenile grass carp (Ctenopharyngodon idellus) fed arachidonic acid

Cyclooxygenase (COX) catalyzes the conversion of arachidonic acid (ARA) to prostaglandins, and COX-mediated metabolites play important roles in the regulation of lipid metabolism and immunity in mammals. However, such roles of COX in fish remain largely unknown. In this study, we designed three semi-purified diets, namely ARA-free (control), ARA, and ARA + acetylsalicylic acid (ASA; a COX inhibitor), and used them to feed grass carp (27.65 ± 3.05 g) for 8 weeks. The results showed that dietary ARA significantly increased the amount of ARA in the hepatopancreas, muscle, and kidney (P < 0.05), whereas this increase was reduced by dietary ASA. The hepatopancreatic prostaglandin E₂ content increased in the ARA group, and this increase was inhibited by ASA (P < 0.05). ARA decreased the lipid content in the hepatopancreas, whereas ASA recovered lipid content to a significant level (P < 0.05). ARA significantly decreased the messenger RNA (mRNA) expression levels of fatty acid synthase and stearoyl-CoA desaturase in the hepatopancreas (P < 0.05). However, ASA did not rescue the mRNA expression of these genes (P > 0.05). Interestingly, ARA significantly enhanced the level of peroxisome proliferator-activated receptor α gene expression, and this increase was attenuated by ASA (P < 0.05). Finally, ARA significantly enhanced the mRNA expression of myeloid differentiation factor 88 (MyD88) in the kidney, and ASA attenuated the expression of toll-like receptor 22 and MyD88 (P < 0.05). In conclusion, our findings suggest that COX metabolites play important roles in the inhibition of lipid accumulation in the hepatopancreas of grass carp fed with ARA and that regulation of gene expression promotes lipid catabolism rather than lipogenic activities. Additionally, these eicosanoids might participate in the upregulation of immunity-related genes in the kidney.

Cyclooxygenase 2 in liver dysfunction and carcinogenesis: Facts and perspectives

The biosynthesis of prostaglandins and thromboxanes has been a focus of interest in the management of many liver diseases. Cyclooxygenases are the enzymes involved in the first step of the biosynthesis of these lipid mediators and selective inhibitors for these isoenzymes as well as pharmacological analogues of prostaglandins have been developed and are currently applied therapeutically. Here we discuss the implications of these enzymes in the onset of metabolic and lipid disorders in the liver and their potential role in the progression of the diseases towards fibrosis and hepatocellular carcinogenesis.

Induction of steatohepatitis (NASH) with insulin resistance in wildtype B6 mice by a western-type diet containing soybean oil and cholesterol

Non-alcoholic fatty liver disease (NAFLD) and non-alcoholic steatohepatitis (NASH) are hepatic manifestations of the metabolic syndrome. Many currently used animal models of NAFLD/NASH lack clinical features of either NASH or metabolic syndrome such as hepatic inflammation and fibrosis (e.g. high-fat diets) or overweight and insulin resistance (e.g. methionine-choline-deficient diets) or they are based on monogenetic defects (e.g. ob/ob mice). In the current study, a western-type diet containing soybean oil with high n 6-PUFA and 0.75% cholesterol (SOD+Cho) induced steatosis, inflammation and fibrosis accompanied by hepatic lipid peroxidation and oxidative stress in livers of C57BL/6-mice which in addition showed increased weight gain and insulin resistance, thus displaying a phenotype closely resembling all clinical features of NASH in patients with metabolic syndrome. In striking contrast a soybean oil-containing western-type diet without cholesterol (SOD) induced only mild steatosis but neither hepatic inflammation nor fibrosis, weight gain or insulin resistance. Another high-fat diet mainly consisting of lard and supplemented with fructose in drinking water (LAD+Fru) resulted in more prominent weight gain, insulin resistance and hepatic steatosis than SOD+Cho but livers were devoid of inflammation and fibrosis. Although both LAD+Fru- and SOD+Cho-fed animals had high plasma cholesterol, liver cholesterol was elevated only in SOD+Cho animals. Cholesterol induced expression of chemotactic and inflammatory cytokines in cultured Kupffer cells and rendered hepatocytes more susceptible to apoptosis. Summarizing, dietary cholesterol in SOD+Cho diet may trigger hepatic inflammation and fibrosis. SOD+Cho-fed animals may be a useful disease model displaying many clinical features of patients with the metabolic syndrome and NASH.

Prenatal hyperandrogenism induces alterations that affect liver lipid metabolism

Prenatal hyperandrogenism is hypothesized as one of the main factors contributing to the development of polycystic ovary syndrome (PCOS). PCOS patients have high risk of developing fatty liver and steatosis. This study aimed to evaluate the role of prenatal hyperandrogenism in liver lipid metabolism and fatty liver development. Pregnant rats were hyperandrogenized with testosterone. At pubertal age, the prenatally hyperandrogenized (PH) female offspring displayed both ovulatory (PHov) and anovulatory (PHanov) phenotypes that mimic human PCOS features. We evaluated hepatic transferases, liver lipid content, the balance between lipogenesis and fatty acid oxidation pathway, oxidant/antioxidant balance and proinflammatory status. We also evaluated the general metabolic status through growth rate curve, basal glucose and insulin levels, glucose tolerance test, HOMA-IR index and serum lipid profile. Although neither PH group showed signs of liver lipid content, the lipogenesis and fatty oxidation pathways were altered. The PH groups also showed impaired oxidant/antioxidant balance, a decrease in the proinflammatory pathway (measured by prostaglandin E2 and cyclooxygenase-2 levels), decreased glucose tolerance, imbalance of circulating lipids and increased risk of metabolic syndrome. We conclude that prenatal hyperandrogenism generates both PHov and PHanov phenotypes with signs of liver alterations, imbalance in lipid metabolism and increased risk of developing metabolic syndrome. The anovulatory phenotype showed more alterations in liver lipogenesis and a more impaired balance of insulin and glucose metabolism, being more susceptible to the development of steatosis.

Insulin-induced cytokine production in macrophages causes insulin resistance in hepatocytes

Overweight and obesity are associated with hyperinsulinemia, insulin resistance, and a low-grade inflammation. Although hyperinsulinemia is generally thought to result from an attempt of the β-cell to compensate for insulin resistance, there is evidence that hyperinsulinaemia itself may contribute to the development of insulin resistance and possibly the low-grade inflammation. To test this hypothesis, U937 macrophages were exposed to insulin. In these cells, insulin induced expression of the proinflammatory cytokines IL-1β, IL-8, CCL2, and OSM. The insulin-elicited induction of IL-1β was independent of the presence of endotoxin and most likely mediated by an insulin-dependent activation of NF-κB. Supernatants of the insulin-treated U937 macrophages rendered primary cultures of rat hepatocytes insulin resistant; they attenuated the insulin-dependent induction of glucokinase by 50%. The cytokines contained in the supernatants of insulin-treated U937 macrophages activated ERK1/2 and IKKβ, resulting in an inhibitory serine phosphorylation of the insulin receptor substrate. In addition, STAT3 was activated and SOCS3 induced, further contributing to the interruption of the insulin receptor signal chain in hepatocytes. These results indicate that hyperinsulinemia per se might contribute to the low-grade inflammation prevailing in overweight and obese patients and thereby promote the development of insulin resistance particularly in the liver, because the insulin concentration in the portal circulation is much higher than in all other tissues.

Omega-3 fatty acids: Mechanisms of benefit and therapeutic effects in pediatric and adult NAFLD

Non-alcoholic fatty liver disease (NAFLD) is currently considered the most common liver disease in industrialized countries, and it is estimated that it will become the most frequent indication for liver transplantation in the next decade. NAFLD may be associated with moderate (i.e. steatosis) to severe (i.e. steatohepatitis and fibrosis) liver damage and affects all age groups. Furthermore, subjects with NAFLD may be at a greater risk of other obesity-related complications later in life, and people with obesity and obesity-related complications (e.g. metabolic syndrome, type 2 diabetes and cardiovascular disease) are at increased risk of developing NAFLD. To date, there is no licensed treatment for NAFLD and therapy has been mainly centered on weight loss and increased physical activity. Unfortunately, it is often difficult for patients to adhere to the advised lifestyle changes. Therefore, based on the known pathogenesis of NAFLD, several clinical trials with different nutritional supplementation and prescribed drugs have been undertaken or are currently underway. Experimental evidence has emerged about the health benefits of omega-3 fatty acids, a group of polyunsaturated fatty acids that are important for a number of health-related functions. Omega-3 fatty acids are present in some foods (oils, nuts and seeds) that also contain omega-6 fatty acids, and the best sources of exclusively omega-3 fatty acids are oily fish, krill oil and algae. In this review, we provide a brief overview of the pathogenesis of NAFLD, and we also discuss the molecular and clinical evidence for the benefits of different omega-3 fatty acid preparations in NAFLD.

PGE2, Kidney Disease, and Cardiovascular Risk: Beyond Hypertension and Diabetes

An important measure of cardiovascular health is obtained by evaluating the global cardiovascular risk, which comprises a number of factors, including hypertension and type 2 diabetes, the leading causes of illness and death in the world, as well as the metabolic syndrome. Altered immunity, inflammation, and oxidative stress underlie many of the changes associated with cardiovascular disease, diabetes, and the metabolic syndrome, and recent efforts have begun to elucidate the contribution of PGE2 in these events. This review summarizes the role of PGE2 in kidney disease outcomes that accelerate cardiovascular disease, highlights the role of cyclooxygenase-2/microsomal PGE synthase 1/PGE2 signaling in hypertension and diabetes, and outlines the contribution of PGE2 to other aspects of the metabolic syndrome, particularly abdominal adiposity, dyslipidemia, and atherogenesis. A clearer understanding of the role of PGE2 could lead to new avenues to improve therapeutic options and disease management strategies.

Roles of lipid-modulating enzymes diacylglycerol kinase and cyclooxygenase under pathophysiological conditions

Lipid not only represents a constituent of the plasma membrane, but also plays a pivotal role in intracellular signaling. Lipid-mediated signaling system is strictly regulated by several enzymes, which act at various steps of the lipid metabolism. Under pathological conditions, prolonged or insufficient activation of this system results in dysregulated signaling, leading to diseases such as cancer or metabolic syndrome. Of the lipid-modulating enzymes, diacylglycerol kinase (DGK) and cyclooxygenase (COX) are intimately involved in the signaling system. DGK consists of a family of enzymes that phosphorylate a second messenger diacylglycerol (DG) to produce phosphatidic acid (PA). Both DG and PA are known to activate signaling molecules such as protein kinase C. COX catalyzes the committed step in prostanoid biosynthesis, which involves the metabolism of arachidonic acid to produce prostaglandins. Previous studies have shown that the DGK and COX are engaged in a number of pathological conditions. This review summarizes the functional implications of these two enzymes in ischemia, liver regeneration, vascular events, diabetes, cancer and inflammation.

NOD1 expression is increased in the adipose tissue of women with gestational diabetes

Maternal peripheral insulin resistance and increased inflammation are two features of pregnancies, complicated by gestational diabetes mellitus (GDM). The nucleotide-binding oligomerisation domain (NOD) intracellular molecules recognise a wide range of microbial products, as well as other intracellular danger signals, thereby initiating inflammation through activation of nuclear factor κB (NFκB). The aim of this study was to determine whether levels of NOD1 and NOD2 are increased in adipose tissue of women with GDM. The effect of NOD1 and NOD2 activation on inflammation and the insulin signalling pathway was also assessed. NOD1, but not NOD2, expression was higher in omental and subcutaneous adipose tissues obtained from women with GDM when compared with those from women with normal glucose tolerance (NGT). In both omental and subcutaneous adipose tissues from NGT and GDM women, the NOD1 ligand g-d-glutamyl-meso-diaminopimelic acid (iE-DAP) significantly induced the expression and secretion of the pro-inflammatory cytokine interleukin 6 (IL6) and chemokine IL8; COX2 (PTGS2) gene expression and subsequent prostaglandin production; the expression and secretion of the extracellular matrix remodelling enzyme matrix metalloproteinase 9 (MMP9) and the gene expression and secretion of the adhesion molecules ICAM1 and VCAM1. There was no effect of the NOD2 ligand muramyl dipeptide on any of the endpoints tested. The effects of the NOD1 ligand iE-DAP were mediated via NFκB, as the NFκB inhibitor BAY 11-7082 significantly attenuated iE-DAP-induced expression and secretion of pro-inflammatory cytokines, COX2 gene expression and subsequent prostaglandin production, MMP9 expression and secretion and ICAM1 and VCAM1 gene expression and secretion. In conclusion, the present findings describe an important role for NOD1 in the development of insulin resistance and inflammation in pregnancies complicated by GDM.

Pediatric non-alcoholic steatohepatitis: The first report on the ultrastructure of hepatocyte mitochondria

AIM: To investigate the ultrastructure of abnormal hepatocyte mitochondria, including their cellular and hepatic zonal distribution, in bioptates in pediatric non-alcoholic steatohepatitis (NASH).

METHODS: Ultrastructural investigations were conducted on biopsy liver specimens obtained from 10 children (6 boys and 4 girls) aged 2-14 years with previously clinicopathologically diagnosed NASH. The disease was diagnosed if liver biopsy revealed steatosis, inflammation, ballooned hepatocytes, Mallory hyaline, or focal necrosis, varying degrees of fibrosis in the absence of clinical, serological, or histological findings of infectious liver diseases, autoimmune hepatitis, metabolic liver diseases, or celiac disease. For ultrastructural analysis, fresh small liver blocks (1 mm³ volume) were fixed in a solution containing 2% paraformaldehyde and 2.5% glutaraldehyde in 0.1 mol/L cacodylate buffer. The specimens were postfixed in osmium tetroxide, subsequently dehydrated through a graded series of ethanols and propylene oxide, and embedded in Epon 812. The material was sectioned on a Reichert ultramicrotome to obtain semithin sections, which were stained with methylene blue in sodium borate. Ultrathin sections were contrasted with uranyl acetate and lead citrate, and examined using an Opton EM 900 transmission electron microscope.

RESULTS: Ultrastructural analysis of bioptates obtained from children with non-alcoholic steatohepatitis revealed characteristic repetitive mitochondrial abnormalities within hepatocytes; mainly mitochondrial polymorphisms such as megamitochondria, loss of mitochondrial cristae, and the presence of linear crystalline inclusions within the mitochondrial matrix of an increased electron density. The crystalline inclusions were particularly evident within megamitochondria (MMC), which seemed to be distributed randomly both within the hepatic parenchymal cell and the zones of hepatic lobule, without special variations in abundance. The inclusions appeared as bundles viewed longitudinally, or as an evenly spaced matrix in cross section, and frequently caused mitochondrial deformation. The average diameter of these linear structures was 10 nm and the average space between them 20 nm. Sometimes enlarged intramitochondrial granules were seen in their vicinity. Foamy cytoplasm of hepatocytes was found, resulting from the proliferation of smooth endoplasmic reticulum and glycogen accumulation. The perivascular space of Disse was frequently dilated, and contained transitional hepatic stellate cells, as well as mature and/or newly forming collagen fiber bundles.

CONCLUSION: Marked ultrastructural abnormalities observed in hepatocyte mitochondria, especially their polymorphism in the form of MMC and loss of mitochondrial cristae, accompanied by foamy cytoplasm, clearly indicate a major role of these organelles in the morphogenesis of pediatric NASH. Our findings seem to prove the high effectiveness of electron microscopy in the diagnosis of the disease.

Hepatic trans-Golgi action coordinated by the GTPase ARFRP1 is crucial for lipoprotein lipidation and assembly

The liver is a major organ in whole body lipid metabolism and malfunctioning can lead to various diseases including dyslipidemia, fatty liver disease, and type 2 diabetes. Triglycerides and cholesteryl esters are packed in the liver as very low density lipoproteins (VLDLs). Generation of these lipoproteins is initiated in the endoplasmic reticulum and further maturation likely occurs in the Golgi. ADP-ribosylation factor-related protein 1 (ARFRP1) is a small trans-Golgi-associated guanosine triphosphatase (GTPase) that regulates protein sorting and is required for chylomicron lipidation and assembly in the intestine. Here we show that the hepatocyte-specific deletion of Arfrp1 (Arfrp1(liv-/-)) results in impaired VLDL lipidation leading to reduced plasma triglyceride levels in the fasted state as well as after inhibition of lipoprotein lipase activity by Triton WR-1339. In addition, the concentration of ApoC3 that comprises 40% of protein mass of secreted VLDLs is markedly reduced in the plasma of Arfrp1(liv-/-) mice but accumulates in the liver accompanied by elevated triglycerides. Fractionation of Arfrp1(liv-/-) liver homogenates reveals more ApoB48 and a lower concentration of triglycerides in the Golgi compartments than in the corresponding fractions from control livers. In conclusion, ARFRP1 and the Golgi apparatus play an important role in lipoprotein maturation in the liver by influencing lipidation and assembly of proteins to the lipid particles.