Alcoholic and non-alcoholic fatty liver disease: Focus on ceramide

Gut microbial diversity and functional characterization in people with alcohol use disorder: A case-control study

Individuals with Alcohol Use Disorder (AUD) typically have comorbid chronic health conditions, including anxiety and depression disorders, increased sleep disruption, and poor nutrition status, along with gut microbial dysbiosis. To better understand the effects of gut dysbiosis previously shown in individuals with AUD, gut microbiome and metabolome were investigated between three cohorts. Two groups of individuals with AUD included treatment-seeking newly abstinent for at least six weeks (AB: N = 10) and non-treatment-seeking currently drinking (CD: N = 9) individuals. The third group was age, gender, and BMI-matched healthy controls (HC: N = 12). Deep phenotyping during two weeks of outpatient National Institutes of Health Clinical Center visits was performed, including clinical, psychological, medical, metabolic, dietary, and experimental assessments. Alpha and beta diversity and differential microbial taxa and metabolite abundance of the gut microbiome were examined across the three groups. Metabolites derived from the lipid super-pathway were identified to be more abundant in the AB group compared to CD and HC groups. The AB individuals appeared to be most clinically different from CD and HC individuals with respect to their gut microbiome and metabolome. These findings highlight the potential long-term effects of chronic alcohol use in individuals with AUD, even during short-term abstinence.

Harnessing Metabolites as Serum Biomarkers for Liver Graft Pathology Prediction Using Machine Learning

Graft injury affects over 50% of liver transplant (LT) recipients, but non-invasive biomarkers to diagnose and guide treatment are currently limited. We aimed to develop a biomarker of graft injury by integrating serum metabolomic profiles with clinical variables. Serum from 55 LT recipients with biopsy confirmed metabolic dysfunction-associated steatohepatitis (MASH), T-cell mediated rejection (TCMR) and biliary complications was collected and processed using a combination of LC-MS/MS assay. The metabolomic profiles were integrated with clinical information using a multi-class Machine Learning (ML) classifier. The model's efficacy was assessed through the Out-of-Bag (OOB) error estimate evaluation. Our ML model yielded an overall accuracy of 79.66% with an OOB estimate of the error rate at 19.75%. The model exhibited a maximum ability to distinguish MASH, with an OOB error estimate of 7.4% compared to 22.2% for biliary and 29.6% for TCMR. The metabolites serine and serotonin emerged as the topmost predictors. When predicting binary outcomes using three models: Biliary (biliary vs. rest), MASH (MASH vs. rest) and TCMR (TCMR vs. rest); the AUCs were 0.882, 0.972 and 0.896, respectively. Our ML tool integrating serum metabolites with clinical variables shows promise as a non-invasive, multi-class serum biomarker of graft pathology.

Chronic sucralose consumption inhibits farnesoid X receptor signaling and perturbs lipid and cholesterol homeostasis in the mouse livers, potentially by altering gut microbiota functions

Sucralose has raised concerns regarding its safety and recent studies have demonstrated that sucralose consumption can disrupt the normal gut microbiome and alter metabolic profiles in mice. However, the extent to which this perturbation affects the functional interaction between the microbiota and the host, as well as its potential impact on host health, remains largely unexplored. Here, we aimed to investigate whether chronic sucralose consumption, at levels within the Acceptable Daily Intake (ADI), could disturb key gut microbial functions and lead to adverse health effects in mice. Following six-month sucralose consumption, several bacterial genera associated with bile acid metabolism were decreased, including Lactobacillus and Ruminococcus. Consequently, the richness of secondary bile acid biosynthetic pathway and bacterial bile salt hydrolase gene were decreased in the sucralose-treated gut microbiome. Compared to controls, sucralose-consuming mice exhibited significantly lower ratios of free bile acids and taurine-conjugated bile acids in their livers. Additionally, several farnesoid X receptor (FXR) agonists were decreased in sucralose-treated mice. This reduction in hepatic FXR activation was associated with altered expression of down-stream genes, in the liver. Moreover, the expression of key lipogenic genes was up-regulated in the livers of sucralose-treated mice. Changes in hepatic lipid profiles were also observed, characterized by lower ceramide levels, a decreased PC/PE ratio, and a mildly increase in lipid accumulation. Additionally, sucralose-consumed mice exhibited higher hepatic cholesterol level compared to control mice, with up-regulation of cholesterol efflux genes and down-regulation of genes associated with reverse cholesterol transport. In conclusion, chronic sucralose consumption disrupts FXR signaling activation and perturbs hepatic lipid and cholesterol homeostasis, potentially by diminishing the bile acid metabolic capacity of the gut microbiome. These findings shed light on the complex interplay between sucralose, the gut microbiota, and host metabolism, raising important questions about the safety of its long-term consumption.

Novel insight into the lipid network of plasma extracellular vesicles reveal sex-based differences in the lipidomic profile of alcohol use disorder patients

BACKGROUND

Alcohol use disorder (AUD) is one of the most common psychiatric disorders, with the consumption of alcohol considered a leading cause of preventable deaths worldwide. Lipids play a crucial functional role in cell membranes; however, we know little about the role of lipids in extracellular vesicles (EVs) as regulatory molecules and disease biomarkers.

METHODS

We employed a sensitive lipidomic strategy to characterize lipid species from the plasma EVs of AUD patients to evaluate functional roles and enzymatic activity networks to improve the knowledge of lipid metabolism after alcohol consumption. We analyzed plasma EV lipids from AUD females and males and healthy individuals to highlight lipids with differential abundance and biologically interpreted lipidomics data using LINEX2, which evaluates enzymatic dysregulation using an enrichment algorithm.

RESULTS

Our results show, for the first time, that AUD females exhibited more significant substrate-product changes in lysophosphatidylcholine/phosphatidylcholine lipids and phospholipase/acyltransferase activity, which are potentially linked to cancer progression and neuroinflammation. Conversely, AUD males suffer from dysregulated ceramide and sphingomyelin lipids involving sphingomyelinase, sphingomyelin phosphodiesterase, and sphingomyelin synthase activity, which relates to hepatotoxicity. Notably, the analysis of plasma EVs from AUD females and males demonstrates enrichment of lipid ontology terms associated with "negative intrinsic curvature" and "positive intrinsic curvature", respectively.

CONCLUSIONS

Our methodological developments support an improved understanding of lipid metabolism and regulatory mechanisms, which contribute to the identification of novel lipid targets and the discovery of sex-specific clinical biomarkers in AUD.

Sphingolipids in mitochondria-from function to disease

Sphingolipids are not only structural components of cellular membranes but also play vital roles in cell signaling and modulation of cellular processes. Within mitochondria, sphingolipids exert diverse effects on mitochondrial dynamics, energy metabolism, oxidative stress, and cell death pathways. In this review, we summarize literature addressing the crucial role of sphingolipids in mitochondria, highlighting their impact on mitochondrial dynamics, cellular bioenergetics, and important cell processes including apoptosis and mitophagy.

A lipidomic approach to bisphenol F-induced non-alcoholic fatty liver disease-like changes: altered lipid components in a murine model

Bisphenol A (BPA), a typical environmental endocrine disruptor, is an "obesogen" that can induce lipid accumulation in the liver. Highly similar in structure to BPA, bisphenol F (BPF) is becoming the dominant BPA substitute on the market, which attracts more and more attention due to its potential adverse effects. Recently, BPF exposure is found to cause non-alcoholic fatty liver disease (NAFLD)-like changes; however, the underlying toxic effects remain poorly understood. Therefore, in the current study, we focused on BPF-mediated lipid homeostasis, especially the alterations of lipid components and metabolism. In human serum, the BPF levels in healthy controls and NAFLD patients were assessed by ELISA, and BPF-induced disturbance of lipid metabolism was evaluated in mouse model via non-targeted lipomic methods with ultra-high performance liquid chromatography-quadrupole time-of-flight mass spectrometry. It suggested that BPF exposure was positively correlated with NAFLD severity and triglyceride level in patients. Based on the relationships, lipid metabolites were assessed in mouse livers between control and BPF-treated group, and it revealed that twenty-six lipid metabolites (including phospholipids, sphingolipids, and glycerides) were significantly changed in mouse livers. Phosphatidylcholine, phosphatidylethanolamine, and diglyceryl ester levels were lower than those in the control mice; hexose ceramide content in sphingolipids markedly increased in BPF-treated mouse livers. Noteworthily, the glycerophospholipid metabolic pathway was found to be the most pronounced in BPF-induced disturbance of lipid metabolism. Therefore, the current study, for the first time, is deciphering the BPF-induced lipid metabolic disturbance, which may provide novel intervention strategies for BPF-induced NAFLD-like changes.

High fat diet and PCSK9 knockout modulates lipid profile of the liver and changes the expression of lipid homeostasis related genes

BACKGROUND

High fat diet (HFD) increases the likelihood of dyslipidemia, which can be a serious risk factor for atherosclerosis, diabetes or hepatosteatosis. Although changes in different blood lipid levels were broadly investigated, such alterations in the liver tissue have not been studied before. The aim of the current study was to investigate the effect of HFD on hepatic triglyceride (TG), diglyceride (DG) and ceramide (CER) levels and on the expression of four key genes involved in lipid homeostasis (Pcsk9, Ldlr, Cd36 and Anxa2) in the liver. In addition, the potential role of PCSK9 in the observed changes was further investigated by using PCSK9 deficient mice.

METHODS

We used two in vivo models: mice kept on HFD for 20 weeks and PCSK9^-/- mice. The amount of the major TGs, DGs and CERs was measured by using HPLC-MS/MS analysis. The expression profiles of four lipid related genes, namely Pcsk9, Ldlr, Cd36 and Anxa2 were assessed. Co-localization studies were performed by confocal microscopy.

RESULTS

In HFD mice, hepatic PCSK9 expression was decreased and ANXA2 expression was increased both on mRNA and protein levels, and the amount of LDLR and CD36 receptor proteins was increased. While LDLR protein level was also elevated in the livers of PCSK9^-/- mice, there was no significant change in the expression of ANXA2 and CD36 in these animals. HFD induced a significant elevation in the hepatic levels of all measured TG and DG but not of CER types, and increased the proportion of monounsaturated vs. saturated TGs and DGs. Similar changes were detected in the hepatic lipid profiles of HFD and PCSK9^-/- mice. Co-localization of PCSK9 with LDLR, CD36 and ANXA2 was verified in HepG2 cells.

CONCLUSIONS

Our results show that obesogenic HFD downregulates PCSK9 expression in the liver and causes alterations in the hepatic lipid accumulation, which resemble those observed in PCSK9 deficiency. These findings suggest that PCSK9-mediated modulation of LDLR and CD36 expression might contribute to the HFD-induced changes in lipid homeostasis.

Liver Lipidomics Analysis Revealed the Novel Ameliorative Mechanisms of L-Carnitine on High-Fat Diet-Induced NAFLD Mice

The beneficial effects of L-carnitine on non-alcoholic fatty liver disease (NAFLD) were revealed in previous reports. However, the underlying mechanisms remain unclear. In this study, we established a high fat diet (HFD)-induced NAFLD mice model and systematically explored the effects and mechanisms of dietary L-carnitine supplementation (0.2% to 4%) on NAFLD. A lipidomics approach was conducted to identify specific lipid species involved in the ameliorative roles of L-carnitine in NAFLD. Compared with a normal control group, the body weight, liver weight, concentrations of TG in the liver and serum AST and ALT levels were dramatically increased by HFD feeding (p < 0.05), accompanied with obvious liver damage and the activation of the hepatic TLR4/NF-κB/NLRP3 inflammatory pathway. L-carnitine treatment significantly improved these phenomena and exhibited a clear dose–response relationship. The results of a liver lipidomics analysis showed that a total of 12 classes and 145 lipid species were identified in the livers. Serious disorders in lipid profiles were noticed in the livers of the HFD-fed mice, such as an increased relative abundance of TG and a decreased relative abundance of PC, PE, PI, LPC, LPE, Cer and SM (p < 0.05). The relative contents of PC and PI were significantly increased and that of DG were decreased after the 4% L-carnitine intervention (p < 0.05). Moreover, we identified 47 important differential lipid species that notably separated the experimental groups based on VIP ≥ 1 and p < 0.05. The results of a pathway analysis showed that L-carnitine inhibited the glycerolipid metabolism pathway and activated the pathways of alpha-linolenic acid metabolism, glycerophospholipid metabolism, sphingolipid metabolism and Glycosylphosphatidylinositol (GPI)-anchor biosynthesis. This study provides novel insights into the mechanisms of L-carnitine in attenuating NAFLD.

Association of plasma metabolites and diagnostic imaging findings with hepatic lipidosis in bearded dragons (Pogona vitticeps) and effects of gemfibrozil therapy

OBJECTIVES

To evaluate the association between plasma metabolites, biochemical analytes, diagnostic imaging findings, and the histologic diagnosis of hepatic lipidosis in bearded dragons. To assess the effects of gemfibrozil therapy on hepatic lipid accumulation and associated diagnostic tests.

ANIMALS

Fourteen bearded dragons (Pogona vitticeps) with varying severity of hepatic lipid accumulation (with and without hepatic lipidosis) were included.

PROCEDURES

Animals underwent coelomic ultrasound, computed tomography (CT) scans, and coelioscopic hepatic biopsies. Clinical pathology tests included lipidologic tests, hepatic biomarkers, and mass spectrometry-based metabolomics. Animals were medicated with gemfibrozil 6mg/kg orally once a day for 2 months in a randomized blinded clinical trial prior to repeating previous diagnostic testing.

RESULTS

Hounsfield units on CT were negatively associated with increased hepatic vacuolation, while ultrasound and gross evaluation of the liver were not reliable. Beta-hydroxybutyric-acid (BHBA) concentrations were significantly associated with hepatic lipidosis. Metabolomics and lipidomics data found BHBA and succinic acid to be potential biomarkers for diagnosing hepatic lipidosis in bearded dragons. Succinic acid concentrations were significantly lower in the gemfibrozil treatment group. There was a tendency for improvement in the biomarkers and reduced hepatic fat in bearded dragons with hepatic lipidosis when treated with gemfibrozil, though the improvement was not statistically significant.

CONCLUSIONS

These findings provide information on the antemortem assessment of hepatic lipidosis in bearded dragons and paves the way for further research in diagnosis and treatment of this disease.

Preclinical models of non-alcoholic steatohepatitis leading to hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the third leading cause of cancer related deaths worldwide and its incidence is increasing due to endemic obesity and the growing burden of non-alcoholic steatohepatitis (NASH) associated liver cancer. Although much is known about the clinical and histological pathology of NASH-driven HCC in humans, its etiology remains unclear and there is a lack of reliable biomarkers and limited effective therapies. Progress has been hampered by the scarcity of standardized animal models that recapitulate the gradual progression of NASH towards HCC observed in humans. Here we review existing mouse models and their suitability for studying NASH-driven HCC with special emphasis on a preclinical model that we recently developed that faithfully mimics all the clinical endpoints of progression of the human disease. Moreover, it is highly translatable, allows the use of gene-targeted mice, and is suitable for gaining knowledge of how NASH progresses to HCC and development of new targets for treatment.

Lipidomics Revealed Alteration of the Sphingolipid Metabolism in the Liver of Nonalcoholic Steatohepatitis Mice Treated with Scoparone

Perturbation in sphingolipid metabolism has been regarded as a risk factor for nonalcoholic steatohepatitis (NASH) development, predisposing to inflammation, insulin resistance, and weight gain. Scoparone can regulate the level of ceramide in primary hepatocytes and effectively ameliorate hepatic inflammation, apoptosis, steatosis, and fibrogenesis in a mice model of NASH. Nevertheless, the potential effects of scoparone in sphingolipid metabolism, which is dysregulated in NASH, have not been explored so far. To uncover the impact of scoparone on sphingolipid metabolism in NASH and potential therapeutic targets for treating NASH, the liver tissue samples were collected and lipidomics analysis based on UPLC-QTRAP-MRM/MS was carried out. The collected raw data was handled with multivariate data treatment to discover the potential biomarkers in sphingolipid metabolism. Compared to the control group, 22 potential sphingolipid biomarkers were discovered in the NASH group, of which 10 were downregulated and 12 were upregulated. Orally administrated scoparone contributed to the reversal of the levels of these potential biomarkers. Ten differential metabolites showed a tendency of recovery compared to the control group and may be potential targets for scoparone to treat NASH. This study indicated that lipidomics can detect the perturbed sphingolipids to unravel the therapeutic effects of scoparone on NASH.

Emerging Evidence of Pathological Roles of Very-Low-Density Lipoprotein (VLDL)

Embraced with apolipoproteins (Apo) B and Apo E, triglyceride-enriched very-low-density lipoprotein (VLDL) is secreted by the liver into circulation, mainly during post-meal hours. Here, we present a brief review of the physiological role of VLDL and a systemic review of the emerging evidence supporting its pathological roles. VLDL promotes atherosclerosis in metabolic syndrome (MetS). VLDL isolated from subjects with MetS exhibits cytotoxicity to atrial myocytes, induces atrial myopathy, and promotes vulnerability to atrial fibrillation. VLDL levels are affected by a number of endocrinological disorders and can be increased by therapeutic supplementation with cortisol, growth hormone, progesterone, and estrogen. VLDL promotes aldosterone secretion, which contributes to hypertension. VLDL induces neuroinflammation, leading to cognitive dysfunction. VLDL levels are also correlated with chronic kidney disease, autoimmune disorders, and some dermatological diseases. The extra-hepatic secretion of VLDL derived from intestinal dysbiosis is suggested to be harmful. Emerging evidence suggests disturbed VLDL metabolism in sleep disorders and in cancer development and progression. In addition to VLDL, the VLDL receptor (VLDLR) may affect both VLDL metabolism and carcinogenesis. Overall, emerging evidence supports the pathological roles of VLDL in multi-organ diseases. To better understand the fundamental mechanisms of how VLDL promotes disease development, elucidation of the quality control of VLDL and of the regulation and signaling of VLDLR should be indispensable. With this, successful VLDL-targeted therapies can be discovered in the future.

Non-Alcoholic Fatty Liver Disease, Liver Fibrosis, and Regional Amyloid-β and Tau Pathology in Middle-Aged Adults: The Framingham Study

BACKGROUND

Liver steatosis and fibrosis are emerging as risk factors for multiple extrahepatic health conditions; however, their relationship with Alzheimer's disease pathology is unclear.

OBJECTIVE

To examine whether non-alcoholic fatty liver disease (NAFLD) and FIB-4, a non-invasive index of advanced fibrosis, are associated with brain amyloid-β (Aβ) and tau pathology.

METHODS

The study sample included Framingham Study participants from the Offspring and Third generation cohorts who attended exams 9 (2011-2014) and 2 (2008-2011), respectively. Participants underwent 11C-Pittsburgh Compound-B amyloid and 18F-Flortaucipir tau positron emission tomography (PET) imaging and abdomen computed tomography, or had information on all components of the FIB-4 index. Linear regression models were used to assess the relationship of NAFLD and FIB-4 with regional tau and Aβ, adjusting for potential confounders and multiple comparisons.

RESULTS

Of the subsample with NAFLD information (N = 169; mean age 52±9 y; 57% males), 57 (34%) had NAFLD. Of the subsample with information on liver fibrosis (N = 177; mean age 50±10 y; 51% males), 34 (19%) had advanced fibrosis (FIB-4 > 1.3). Prevalent NAFLD was not associated with Aβ or tau PET. However, FIB-4 index was significantly associated with increased rhinal tau (β= 1.03±0.33, p = 0.002). Among individuals with prevalent NAFLD, FIB-4 was related to inferior temporal, parahippocampal gyrus, entorhinal and rhinal tau (β= 2.01±0.47, p < 0.001; β= 1.60±0.53, p = 0.007, and β= 1.59±0.47, p = 0.003 and β= 1.60±0.42, p = 0.001, respectively) and to Aβ deposition overall and in the inferior temporal and parahippocampal regions (β= 1.93±0.47, p < 0.001; β= 1.59±0.38, p < 0.001, and β= 1.52±0.54, p = 0.008, respectively).

CONCLUSION

This study suggests a possible association between liver fibrosis and early Alzheimer's disease pathology, independently of cardio-metabolic risk factors.

Dietary Folic Acid Alters Metabolism of Multiple Vitamins in a CerS6- and Sex-Dependent Manner

Folic acid, an oxidized synthetic pro-vitamin B₉, is widely used in vitamin supplement formulations and food fortification to maintain optimal folate status in humans. Studies on folic acid (FA) efficiency in improving folate status and correcting folate deficiency pathologies are abundant, but precise knowledge of FA effects on human and animal tissues is not available. In our recent study, 10-week-old wild-type and CerS6 knockout (KO) mice were placed on FA-deficient, control, or FA over-supplemented diet for 4 weeks. Untargeted metabolomics characterization of mouse liver, brain, and testes tissues after the dietary treatment revealed profound effects of FA on the liver metabolome. Here, we present the analysis of dietary FA effects on tissue concentrations of other vitamins in mice. Despite the expectation that identical dietary supply of the vitamins (excluding FA) to each group should support similar tissue vitamins concentrations, metabolomics data demonstrate significant alterations of tissue concentrations of multiple vitamins by different levels of FA supplementation that were sex- and genotype-dependent. Moreover, we found significant differences in the liver concentration of retinol, thiamin diphosphate, pantetheine, pyridoxal, and pyridoxamine between males and females. While the liver had more changes in vitamins and vitamin derivative levels, the brain tissue and testes also showed changes linked to FA supplementation. Over-supplementation with FA had negative effects on concentrations of vitamins A, B₁, B₂, and B₆, or their metabolites in the liver, but increased intermediates in coenzyme A (CoA) biosynthesis, as well as gamma/beta-tocopherol and phosphorylated forms of B₆ in the CerS6 KO brain. Overall, our data demonstrate that dietary FA supplementation significantly affects the metabolism of other vitamins, and that these effects depend on the CerS6 status and sex of the animal. Further research is required to determine whether the observed effects are specific to FA, and the mechanisms that are involved.

Caveolin-1 attenuates acetaminophen aggravated lipid accumulation in alcoholic fatty liver by activating mitophagy via the Pink-1/Parkin pathway

Alcoholic fatty liver (AFL) is a disease characterized by the abnormal structure and dysfunction of hepatocytes caused by long-term, excessive drinking. Acetaminophen (APAP) is a commonly used painkiller, but it can aggravate lipid deposition in the liver and cause liver injury when used in fatty liver disease. Here, we investigated the effect of caveolin-1 (CAV-1), an intracellular stent protein, on the pathogenesis of APAP aggravated lipid deposition in AFL mice. This study shows that lipid accumulation was more severe in APAP groups than in alcohol-treated mice. The CAV-1 stent-like domain (CSD, 82-101 amino acids of caveolin-1), used to upregulate CAV-1 expression, could reduce lipid accumulation and activate autophagy in AFL mice treated with APAP. The levels of CAV-1 and autophagy-related proteins (LC3-II/I and Beclin-1) had decreased, whereas SREBP-1c had increased in A/O (alcohol and oleic acid) and APAP-co-treated L02 cells. CAV-1 small interfering RNA and CAV1-overexpressing plasmid were separately transfected into A/O and APAP co-treated L02 cells. When CAV-1 was downregulated, the levels of Pink-1, Parkin, and autophagy-related proteins (LC3-II/I and Beclin-1) were decreased, whereas SREBP-1c was increased. The opposite trend was observed when CAV-1 was overexpressed. The results show that CAV-1 reduced lipid accumulation in L02 cells and activated Pink-1/Parkin-related mitophagy. This study highlights the positive role of CAV-1 in APAP-increased lipid accumulation under the AFL status and provides a new understanding of the function of CAV-1 in the liver through mitophagy associated with the Pink-1/Parkin pathway.

Hepatic Lipidomics Analysis Reveals the Ameliorative Effects of Highland Barley β-Glucan on Western Diet-Induced Nonalcoholic Fatty Liver Disease Mice

Nonalcoholic fatty liver disease (NAFLD) is characterized by marked imbalances in lipid storage and metabolism. Because the beneficial health effects of cereal β-glucan (BG) include lowering cholesterol and regulating lipid metabolism, BG may alleviate the imbalances in lipid metabolism observed during NAFLD. The aim of our study was to investigate whether BG from highland barley has an effect on western diet-induced NAFLD in mice. Using lipidomics, we investigated the underlying mechanisms of BG intervention, and identified potential lipid biomarkers. The results reveal that BG (300 mg/kg body weight) significantly alleviated liver steatosis. Lipidomics analysis demonstrated that BG also altered lipid metabolic patterns. We were able to identify 13 differentially regulated lipid species that may be useful as lipid biomarkers. Several genes in the hepatic lipid and cholesterol metabolism pathways were also modulated. These findings provide evidence that BG ameliorates NAFLD by altering liver lipid metabolites and regulating lipid metabolism-related genes.

Ceramide synthase 6 mediates sex-specific metabolic response to dietary folic acid in mice

Folic acid-fortified foods and multi-vitamin supplements containing folic acid (FA) are widely used around the world, but the exact mechanisms/metabolic effects of FA are not precisely identified. We have demonstrated that Ceramide Synthase 6 (CerS6) and C_16:0-ceramide mediate response to folate stress in cultured cells. Here we investigated the dietary FA effects on mouse liver metabolome, with a specific focus on sphingolipids, CerS6 and C_16:0-ceramide. Wild-type and CerS6^-/- mice were fed FA-deficient, control, or FA over-supplemented diets for 4 weeks. After dietary treatment, liver concentrations of ceramides, sphingomyelins and hexosylceramides were measured by LC-MS/MS and complemented by untargeted metabolomic characterization of mouse livers. Our study shows that alterations in dietary FA elicit multiple sphingolipid responses mediated by CerS6 in mouse livers. Folic acid-deficient diet elevated C_14:0-, C_18:0- and C_20:0- but not C_16:0-ceramide in WT male and female mice. Additionally, FA over-supplementation increased multiple sphingomyelin species, including total sphingomyelins, in both sexes. Of note, concentrations of C_14:0- and C_16:0-ceramides and hexosylceramides were significantly higher in female livers than in male. The latter were increased by FD diet, with no difference between sexes in total pools of these sphingolipid classes. Untargeted liver metabolomic analysis concurred with the targeted measurements and showed broad effects of dietary FA and CerS6 status on multiple lipid classes including sex-specific effects on phosphatidylethanolamines and diacylglycerols. Our study demonstrates that both dietary FA and CerS6 status exhibit pleiotropic and sex-dependent effects on liver metabolism, including hepatic sphingolipids, diacylglycerols, long chain fatty acids, and phospholipids.

Advances in paediatric nonalcoholic fatty liver disease: Role of lipidomics

Due its close relationship with obesity, nonalcoholic fatty liver disease (NAFLD) has become a major worldwide health issue even in childhood. The most accepted pathophysiological hypothesis is represented by the “multiple hits” theory, in which both hepatic intracellular lipid accumulation and insulin resistance mainly contribute to liver injury through several factors. Among these, lipotoxicity has gained particular attention. In this view, the pathogenic role of different lipid classes in NAFLD (e.g., sphingolipids, fatty acids, ceramides, etc.) has been highlighted in recent lipidomics studies. Although there is some contrast between plasma and liver findings, lipidomic profile in the NAFLD context provides novel insights by expanding knowledge in the intricate field of NAFLD pathophysiology as well as by suggesting innovative therapeutic approaches in order to improve both NAFLD prevention and treatment strategies. Selective changes of distinct lipid species might be an attractive therapeutic target for treating NAFLD. Herein the most recent evidence in this attractive field has been summarized to provide a comprehensive overview of the lipidomic scenario in paediatric NAFLD.

Blood-Based Targeted Metabolomics Discriminate Patients with Alcoholic Liver Cirrhosis from Those with Non-Cirrhotic Liver Damage: An Explorative Study

BACKGROUND

Early detection of liver cirrhosis is crucial for secondary prevention of complications. However, noninvasive blood-based patient monitoring tools are lacking. In this explorative study, we conducted a targeted metabolomic analysis in order to identify possible serum markers indicating alcoholic liver cirrhosis (aLiC) with or without hepatocellular carcinoma (HCC).

METHODS

Venous blood of 30 individuals was collected: healthy controls ("Con", n = 12), patients with aLiC without and with HCC ("aLiC": n = 6 and "aLiC + HCC": n = 6), and patients with other liver diseases ("oLiD": n = 6). A targeted metabolomic analysis was conducted using the AbsoluteIDQ® p180 Kit (Biocrates Life Sciences®, Innsbruck, Austria). Statistical analysis was performed by applying a one-way ANOVA on all subgroups followed by a t test for pairwise comparison of subgroups and logistic regression analysis.

RESULTS

ANOVA revealed 29 metabolites that significantly discriminate between the different cohorts. Among these analytes, 25 were significantly altered in Con versus aLiC, as indicated by t test, most importantly SM C18:1 (p < 0.001), SM C20:2 (p = 0.001), SM (OH) C22:2 (p < 0.001), lysoPC a C20:4 (p < 0.001), and PC aa C36:5 (p < 0.001). To a similar extent, the metabolites discriminated also between the oLiD and aLiC but less between the Con or oLiD and aLiC + HCC cohorts. Most of these analytes were either lyso- and phosphatidylcholines or sphingomyelins. Results were not significant for comparison of Con versus oLiD and aLiC versus aLiC + HCC.

CONCLUSION

Decreased lyso- and phosphatidylcholine as well as sphingomyelin species in venous blood could help to detect liver cirrhosis in patients with non-cirrhotic liver disease.

Cognitive Dysfunction in Non-Alcoholic Fatty Liver Disease-Current Knowledge, Mechanisms and Perspectives

Non-alcoholic fatty liver disease (NAFLD) has emerged as the hepatic component of the metabolic syndrome and now seemingly affects one-fourth of the world population. Features associated with NAFLD and the metabolic syndrome have frequently been linked to cognitive dysfunction, i.e. systemic inflammation, vascular dysfunction, and sleep apnoea. However, emerging evidence suggests that NAFLD may be a cause of cognitive dysfunction independent of these factors. NAFLD in addition exhibits dysbiosis of the gut microbiota and impaired urea cycle function, favouring systemic ammonia accumulation and further promotes systemic inflammation. Such disruption of the gut–liver–brain axis is essential in the pathogenesis of hepatic encephalopathy, the neuropsychiatric syndrome associated with progressive liver disease. Considering the growing burden of NAFLD, the morbidity from cognitive impairment is expected to have huge societal and economic impact. The present paper provides a review of the available evidence for cognitive dysfunction in NAFLD and outlines its possible mechanisms. Moreover, the clinical challenges of characterizing and diagnosing cognitive dysfunction in NAFLD are discussed.

Organ function, sphingolipid levels and inflammation in tunicamycin induced endoplasmic reticulum stress in male rats

Disorders of the endoplasmic reticulum (ER) lead to cellular damage but can cause cell death if ER dysfunction is prolonged. We aimed to examine liver/kidney functions, neutral sphingomyelinase (N-SMase) activity, sphingolipid levels, cytosolic phospholipase A2 (cPLA2) and cyclooxygenase-2 (COX-2) protein expression in rats under ER stress. ER stress was induced by tunicamycin (TM) and the ER stress inhibitor taurodeoxycholic acid (TUDCA) was injected before induction of ER stress. ER stress was confirmed by increased tissue levels of GRP78. Hematological and biochemical profiles were measured by autoanalyzers while hepatic and renal injury was evaluated via microscopy and histopathological scoring. Tissue levels of C16-C24 sphingomyelins (SM), C16-C24 ceramides (CERs) and sphingosine-1-phosphate (S1P) were determined by LC-MS/MS. Tissue cPLA2 and COX-2 were measured by western blot and activity assays. Tunicamycin treatment caused kidney and liver function test abnormalities, increased hematocrit and hemoglobin levels but decreased white blood cell counts. Histopathological findings showed hepatic necroinflammation and renal tubular damage in rats treated with TM. TUDCA administration attenuated WBC abnormalities and TM- induced hepatic/renal functional impairment in ER stress, as evident by significantly restored serum ALT, AST, creatinine, and total bilirubin levels. A significant increase was observed in N-SMase activity, tissue levels of C16-C24 CERs, cPLA2 and COX-2 expression in liver and kidney tissue under ER stress. TUDCA administration decreased tissue CER levels, cPLA2 and COX-2 expression as well as prostaglandin E2 (PGE2) formation. These results signify that ER stress causes hepatic and renal toxicity as well as CER-induced PGE2 formation in liver and kidney.

Dihydroceramides in Triglyceride-Enriched VLDL Are Associated with Nonalcoholic Fatty Liver Disease Severity in Type 2 Diabetes

Plasma dihydroceramides are predictors of type 2 diabetes and related to metabolic dysfunctions, but the underlying mechanisms are not characterized. We compare the relationships between plasma dihydroceramides and biochemical and hepatic parameters in two cohorts of diabetic patients. Hepatic steatosis, steatohepatitis, and fibrosis are assessed by their plasma biomarkers. Plasma lipoprotein sphingolipids are studied in a sub-group of diabetic patients. Liver biopsies from subjects with suspected non-alcoholic fatty liver disease are analyzed for sphingolipid synthesis enzyme expression. Dihydroceramides, contained in triglyceride-rich very-low-density lipoprotein (VLDL), are associated with steatosis and steatohepatitis. Expression of sphingolipid synthesis enzymes is correlated with histological steatosis and inflammation grades. In conclusion, association of plasma dihydroceramides with nonalcoholic fatty liver might explain their predictive character for type 2 diabetes. Our results suggest a relationship between hepatic sphingolipid metabolism and steatohepatitis and an involvement of dihydroceramides in the synthesis/secretion of triglyceride-rich VLDL, a hallmark of NAFLD and type 2 diabetes dyslipidemia.

Plasma dihydroceramides are associated with NAFLD severity in type 2 diabetic patients

Plasma dihydroceramides are found in triglyceride-enriched VLDL

A role for dihydroceramide in triglyceride-rich VLDL synthesis/secretion is suggested

Expression of enzymes of hepatic sphingolipid synthesis increases with NAFLD severity

Sphingomyelinases and Liver Diseases

Sphingolipids (SLs) are critical components of membrane bilayers that play a crucial role in their physico-chemical properties. Ceramide is the prototype and most studied SL due to its role as a second messenger in the regulation of multiple signaling pathways and cellular processes. Ceramide is a heterogeneous lipid entity determined by the length of the fatty acyl chain linked to its carbon backbone sphingosine, which can be generated either by de novo synthesis from serine and palmitoyl-CoA in the endoplasmic reticulum or via sphingomyelin (SM) hydrolysis by sphingomyelinases (SMases). Unlike de novo synthesis, SMase-induced SM hydrolysis represents a rapid and transient mechanism of ceramide generation in specific intracellular sites that accounts for the diverse biological effects of ceramide. Several SMases have been described at the molecular level, which exhibit different pH requirements for activity: neutral, acid or alkaline. Among the SMases, the neutral (NSMase) and acid (ASMase) are the best characterized for their contribution to signaling pathways and role in diverse pathologies, including liver diseases. As part of a Special Issue (Phospholipases: From Structure to Biological Function), the present invited review summarizes the physiological functions of NSMase and ASMase and their role in chronic and metabolic liver diseases, of which the most relevant is nonalcoholic steatohepatitis and its progression to hepatocellular carcinoma, due to the association with the obesity and type 2 diabetes epidemic. A better understanding of the regulation and role of SMases in liver pathology may offer the opportunity for novel treatments of liver diseases.

A Novel Combination of Fruits and Vegetables Prevents Diet-Induced Hepatic Steatosis and Metabolic Dysfunction in Mice

BACKGROUND

Epidemiological studies suggest that higher fruits and vegetables (F&V) consumption correlates with reduced risk of hepatic steatosis, yet evidence for causality and the underlying mechanisms is lacking.

OBJECTIVES

We aimed to determine the causal relation between F&V consumption and improved metabolic disorders in mice fed high-fat (HF) (Experiment-1) or normal-fat (Experiment-2) diets and its underlying mechanisms.

METHODS

Six-week-old male C57BL/6J mice were randomly grouped and fed diets supplemented at 0%-15% (wt:wt) with a freeze-dried powder composed of 24 commonly consumed F&V (human equivalent of 0-9 servings/d) for 20 wk. In Experiment-1, mice were fed an HF (45% kcal fat) diet with 0% (HF0), 5%, 10%, or 15% (HF15) F&V or a matched low-fat control diet (10% kcal fat). In Experiment-2, mice were fed an AIN-93 diet (basal) (B, 16% kcal fat) with 0% (B0), 5%, 10%, or 15% (B15) F&V supplementation. Body weight and composition, food intake, hepatic steatosis, inflammation, ceramide levels, sphingomyelinase activity, and gut microbiota were assessed.

RESULTS

In Experiment-1, mice fed the HF15 diet had lower weight gain (17.9%), hepatic steatosis (48.4%), adipose tissue inflammation, blood (24.6%) and liver (33.9%) ceramide concentrations, and sphingomyelinase activity (38.8%) than HF0 mice (P < 0.05 for all). In Experiment-2, mice fed the B15 diet had no significant changes in weight gain but showed less hepatic steatosis (28.5%), blood and adipose tissue inflammation, and lower blood (30.0%) ceramide concentrations than B0 mice (P < 0.05 for all). These F&V effects were associated with favorable microbiota changes.

CONCLUSIONS

These findings represent the first evidence for a causal role of high F&V intake in mitigating hepatic steatosis in mice. These beneficial effects may be mediated through changes in ceramide and/or gut microbiota, and suggest that higher than currently recommended servings of F&V may be needed to achieve maximum health benefits.

DNA methylation of JAK3/STAT5/PPARγ regulated the changes of lipid levels induced by di (2-ethylhexyl) phthalate and high-fat diet in adolescent rats

Di (2-ethylhexyl) phthalate (DEHP) and high-fat diet (HFD) could induce lipid metabolic disorder. This study was undertaken to identify the effect of DNA methylation of JAK3/STAT5/PPARγ on lipid metabolic disorder induced by DEHP and HFD. Wistar rats were divided into a normal diet (ND) group and HFD group. Each diet group treated with DEHP (0, 5, 50, 500 mg/kg/d) for 8 weeks' gavage. The DNA-methylated levels of PPARγ, JAK3, STAT5a, and STAT5b in rats' livers and adipose were analyzed with MethylTarget. The lipid levels of rats' livers and adipose were detected with ELISA. Results showed in ND group that the DNA methylation levels of PPARγ, JAK3 in livers, and STAT5b in adipose were lower in 500 mg/kg/d group than the control. And the level of total cholesterol (TC) in adipose was higher in 500 mg/kg/d group than the control. In HFD group, the DNA methylation level of JAK3 was the lowest in livers and the highest in adipose in 50 mg/kg/d group. And the level of TC in livers was the lowest in 50 mg/kg/d group. In the 500 mg/kg/d group, the DNA methylation level of STAT5b was lower in livers and higher in adipose in HFD group than that in ND group. And the levels of TC in livers were lower in HFD group than those in ND group. Therefore, DNA methylation of JAK3/STAT5/PPARγ regulated the changes in lipid levels induced by DEHP and HFD in adolescent rats.

An Overview of Lipid Metabolism and Nonalcoholic Fatty Liver Disease

The occurrence of nonalcoholic fatty liver disease (NAFLD) is associated with major abnormalities of hepatic lipid metabolism. We propose that lipid abnormalities directly or indirectly contribute to NAFLD, especially fatty acid accumulation, arachidonic acid metabolic disturbance, and ceramide overload. The effects of lipid intake and accumulation on NAFLD and NAFLD treatment are explained with theoretical and experimental details. Overall, these findings provide further understanding of lipid metabolism in NAFLD and may lead to novel therapies.

Macrophages in the pathophysiology of NAFLD: The role of sex differences

Nonalcoholic fatty liver disease (NAFLD) is a multifactorial pathological condition, which recognizes a certain sexual dimorphism. Experimental and clinical studies provided evidence for a critical role of macrophages in NAFLD development and progression. Especially, liver-resident macrophages (also known as Kupffer cells) are likely the common final pathway of several pro-steatosic signals. A huge amount of danger-associated molecular patterns recognized by Kupffer cells is provided within the liver by lipid and glucose toxicity. Other pro-inflammatory signals come from surrounding tissues into the portal vein, directly to the liver: they come from dysfunctional adipocytes, adipose tissue macrophages and gut dysbiosis. These complex crosstalks are differently represented across sexes, as sexual hormones control many of these processes. Sexual dimorphism then modulates metabolic and inflammatory cascades driving the liver from a simple steatosis to NAFLD and beyond. Here, metabolic and inflammatory mechanisms underlying NALFD pathophysiology will be updated. A special attention will be paid to describe sex-related differences that could provide insights for patient stratification and more tailored therapeutic approaches.

Exogenous Liposomal Ceramide-C6 Ameliorates Lipidomic Profile, Energy Homeostasis, and Anti-Oxidant Systems in NASH

In non-alcoholic steatohepatitis (NASH), many lines of investigation have reported a dysregulation in lipid homeostasis, leading to intrahepatic lipid accumulation. Recently, the role of dysfunctional sphingolipid metabolism has also been proposed. Human and animal models of NASH have been associated with elevated levels of long chain ceramides and pro-apoptotic sphingolipid metabolites, implicated in regulating fatty acid oxidation and inflammation. Importantly, inhibition of de novo ceramide biosynthesis or knock-down of ceramide synthases reverse some of the pathology of NASH. In contrast, cell permeable, short chain ceramides have shown anti-inflammatory actions in multiple models of inflammatory disease. Here, we investigated non-apoptotic doses of a liposome containing short chain C6-Ceramide (Lip-C6) administered to human hepatic stellate cells (hHSC), a key effector of hepatic fibrogenesis, and an animal model characterized by inflammation and elevated liver fat content. On the basis of the results from unbiased liver transcriptomic studies from non-alcoholic fatty liver disease patients, we chose to focus on adenosine monophosphate activated kinase (AMPK) and nuclear factor-erythroid 2-related factor (Nrf2) signaling pathways, which showed an abnormal profile. Lip-C6 administration inhibited hHSC proliferation while improving anti-oxidant protection and energy homeostasis, as indicated by upregulation of Nrf2, activation of AMPK and an increase in ATP. To confirm these in vitro data, we investigated the effect of a single tail-vein injection of Lip-C6 in the methionine-choline deficient (MCD) diet mouse model. Lip-C6, but not control liposomes, upregulated phospho-AMPK, without inducing liver toxicity, apoptosis, or exacerbating inflammatory signaling pathways. Alluding to mechanism, mass spectrometry lipidomics showed that Lip-C6-treatment reversed the imbalance in hepatic phosphatidylcholines and diacylglycerides species induced by the MCD-fed diet. These results reveal that short-term Lip-C6 administration reverses energy/metabolic depletion and increases protective anti-oxidant signaling pathways, possibly by restoring homeostatic lipid function in a model of liver inflammation with fat accumulation.

Emerging targets and potential therapeutic agents in non-alcoholic fatty liver disease treatment

Nonalcoholic Fatty Liver Disease (NAFLD) is the most common chronic liver disease in the world, which is characterized by liver fat accumulation unrelated to excessive drinking. Indeed, it attracts growing attention and becomes a global health problem. Due to the complexity of the NAFLD pathogenic mechanism, no related drugs were approved by Food and Drug Administration (FDA) till now. However, it is encouraging that a series of candidate drugs have entered the clinical trial stage with expectation to treat NAFLD. In this review, we summarized the main pathways and pathogenic mechanisms of NAFLD, as well as introduced the main potential therapeutic targets and the corresponding compounds involved in metabolism, inflammation and fibrosis. Furthermore, we also discuss the progress of these compounds, such as drug design and optimization, the choice of pharmacological properties and druglikeness, and the analysis of structure-activity relationship. This review offers a medium on future drug design and development, to be beneficial to relevant studies.

Sphingolipids and the link between alcohol and cancer

Epidemiological evidence underscores alcohol consumption as a strong risk factor for multiple cancer types, with liver cancer being most commonly associated with alcohol intake. While mechanisms linking alcohol consumption to malignant tumor development are not fully understood, the likely players in ethanol-induced carcinogenesis are genotoxic stress caused by formation of acetaldehyde, increased oxidative stress, and altered nutrient metabolism, including the impairment of methyl transfer reactions. Alterations of sphingolipid metabolism and associated signaling pathways are another potential link between ethanol and cancer development. In particular, ceramides are involved in the regulation of cellular proliferation, differentiation, senescence, and apoptosis and are known to function as important regulators of malignant transformation as well as tumor progression. However, to date, the cross-talk between ceramides and alcohol in cancer disease is largely an open question and only limited data are available on this subject. Most studies linking ceramide to cancer considered liver steatosis as the underlying mechanism, which is not surprising taking into consideration that ceramide pathways are an integral part of the overall lipid metabolism. This review summarizes the latest studies pointing to ceramide as an important mediator of cancer-promoting effects of chronic alcohol consumption and underscores the necessity of understanding the role of sphingolipids and lipid signaling in response to alcohol in order to prevent and/or successfully manage diseases caused by alcohol.

The hepatic lipidome: From basic science to clinical translation

The liver is the key organ involved in lipid metabolism and transport. Excessive lipid accumulation due to dysregulated lipid metabolism predisposes the liver to steatosis, cirrhosis, and hepatocellular carcinoma. Lipids are generally compartmentalized in specialized organelles called lipid droplets that enable cells to store and release lipids in a regulated manner. However, during flux-in and flux-out of droplets, lipids are converted into toxic species leading to lipid-mediated liver damage. Lipids are categorized into 'toxic' or 'healthy' lipids that are involved in liver disease pathogenesis or resolution, respectively. Lipidomic analysis have revealed unique lipid signature that correlates with the disease progression therefore being used for disease diagnosis. In this comprehensive review, we provide an overview on hepatic lipid homeostasis, lipid compartmentalization mechanisms and lipidomic profiles in different liver diseases. We further discuss promising therapeutics targeting the hepatic lipidome including pro-resolving lipids, liposomes, and small-molecule inhibitors for the treatment of liver diseases.

Peripheral Acid Sphingomyelinase Activity Is Associated with Biomarkers and Phenotypes of Alcohol Use and Dependence in Patients and Healthy Controls

By catalyzing the hydrolysis of sphingomyelin into ceramide, acid sphingomyelinase (ASM) changes the local composition of the plasma membrane with effects on receptor-mediated signaling. Altered enzyme activities have been noted in common human diseases, including alcohol dependence. However, the underlying mechanisms remain largely unresolved. Blood samples were collected from early-abstinent alcohol-dependent in-patients (n[♂] = 113, n[♀] = 87) and matched healthy controls (n[♂] = 133, n[♀] = 107), and analyzed for routine blood parameters and serum ASM activity. We confirmed increased secretory ASM activities in alcohol-dependent patients compared to healthy control subjects, which decreased slightly during detoxification. ASM activity correlated positively with blood alcohol concentration, withdrawal severity, biomarkers of alcohol dependence (liver enzyme activities of gamma-glutamyl transferase, alanine aminotransferase, aspartate aminotransferase; homocysteine, carbohydrate-deficient transferrin; mean corpuscular volume, and creatine kinase). ASM activity correlated negatively with leukocyte and thrombocyte counts. ASM and gamma-glutamyl transferase were also associated in healthy subjects. Most effects were similar for males and females with different strengths. We describe previously unreported associations between ASM activity and markers of liver damage and myelosuppression. Further research should investigate whether this relationship is causal, or whether these parameters are part of a common pathway in order to gain insights into underlying mechanisms and develop clinical applications.