Ceramide as a mediator of non-alcoholic Fatty liver disease and associated atherosclerosis

Ablation of Hepatic Asah1 Gene Disrupts Hepatic Lipid Homeostasis and Promotes Fibrotic Nonalcoholic Steatohepatitis in Mice

Nonalcoholic fatty liver disease (NAFLD) encompasses a spectrum of chronic liver conditions, ranging from simple steatosis to nonalcoholic steatohepatitis, which may progress to fibrosis/cirrhosis. Here, the GSE163211 data set was analyzed, and Asah1 (encoding acid ceramidase) was identified as a crucial lysosomal gene that positively correlated with NAFLD stages in obese patients. To evaluate the role of Asah1 in the progression of NAFLD, Asah1fl/fl/Albcre mice (hepatocyte-specific deletion of Asah1) and Asah1 floxed (Asah1fl/fl/wild-type) mice were fed with either a normal diet or a high-fat, high-cholesterol paigen diet (PD) for 20 weeks. Hepatocyte-specific Asah1 ablation markedly aggravated PD-induced hepatic steatosis, hepatitis, and apoptosis, and resulted in marked fibrotic changes. In addition, Asah1 gene ablation exacerbated PD-induced portal venous hemodynamic abnormality. In cultured hepatocytes, Asah1 gene knockdown resulted in increased ceramide and cholesterol levels but did not affect triglyceride level. Knocking down Asah1 gene also exhibited broad impacts on lipid homeostasis pathways, including lipogenesis, fatty acid uptake, fatty acid oxidation, and lipid transport. Furthermore, Asah1 knockdown resulted in increased endoplasmic reticulum stress and lipid droplet biogenesis. Finally, Asah1 gene knockdown impaired chaperone-mediated autophagy. These results suggest that Asah1 functions as an important regulator of hepatic lipid homeostasis, and its deficiency exacerbates hepatocyte lipotoxicity and injury, and promotes the development of fibrotic nonalcoholic steatohepatitis.

A Comprehensive Review of Beneficial Effects of Phytosterols on Glycolipid Metabolism and Related Mechanisms

Phytosterols are widely distributed in various plant foods, such as nuts, grains, vegetables, and so on. Phytosterols have been broadly applied in functional foods, supplements, and pharmaceutical products due to their excellent cholesterol-lowering effect. Besides the cholesterol-lowering effect, recently, phytosterols have been found to exert a beneficial effect on glycolipid metabolism, which contributes to multiple metabolic diseases, such as diabetes, cardiovascular disease, and fatty liver. Constant development of new drugs with a single target fails to effectively curb the occurrence of metabolic diseases and complications, such as multiple organ damage, and phytosterols attract special attention due to varieties of biological activities, especially the regulation of glycolipid metabolism through multiple targets. Present review gives a comprehensive review of the effects of phytosterols on glycolipid metabolism and related mechanism. We also review the promising update of phytosterol in the treatment of two major metabolic diseases, including diabetes and nonalcohol fatty liver disease. This review can help to extend the understanding of the potential of phytosterols for mixed dyslipidemia and related metabolic diseases.

Altered sphingolipid biosynthetic flux and lipoprotein trafficking contribute to trans-fat-induced atherosclerosis

Dietary fat drives the pathogenesis of atherosclerotic cardiovascular disease (ASCVD), particularly through circulating cholesterol and triglyceride-rich lipoprotein remnants. Industrially produced trans-unsaturated fatty acids (TFAs) incorporated into food supplies significantly promote ASCVD. However, the molecular trafficking of TFAs responsible for this association is not well understood. Here, we demonstrate that TFAs are preferentially incorporated into sphingolipids by serine palmitoyltransferase (SPT) and secreted from cells in vitro. Administering high-fat diets (HFDs) enriched in TFAs to Ldlr-/- mice accelerated hepatic very-low-density lipoprotein (VLDL) and sphingolipid secretion into circulation to promote atherogenesis compared with a cis-unsaturated fatty acid (CFA)-enriched HFD. SPT inhibition mitigated these phenotypes and reduced circulating atherogenic VLDL enriched in TFA-derived polyunsaturated sphingomyelin. Transcriptional analysis of human liver revealed distinct regulation of SPTLC2 versus SPTLC3 subunit expression, consistent with human genetic correlations in ASCVD, further establishing sphingolipid metabolism as a critical node mediating the progression of ASCVD in response to specific dietary fats.

Lipidome profiling in advanced metabolic liver disease identifies phosphatidylserine synthase 1 as a regulator of hepatic lipoprotein metabolism

Metabolic dysfunction-associated steatohepatitis (MASH) is characterized by defective lipid metabolism, which causes disease progression. MASH is also linked to various cardiometabolic risk factors, including obesity and type 2 diabetes. The contribution of defective lipid metabolism in MASH to cardiometabolic comorbidities is incompletely understood. Using hepatic lipidome profiling in eight mouse strains that differ in MASH susceptibility and patients with MASH, we show that phosphatidylserine (PS) accumulation and preservation of PS synthase 1 (PSS1) expression is associated with resistance to MASH and hypertriglyceridemia. Mechanistically, hepatocyte-specific PSS1 overexpression remodels the hepatic and very-low-density lipoprotein (VLDL) lipidome in mice with MASH. Specifically, we show an increase in VLDL ceramide that suppresses the expression and activity of lipoprotein lipase in skeletal muscle, thereby reducing VLDL-triglyceride clearance, fatty acid uptake, and lipid accumulation in muscle, overall exacerbating hypertriglyceridemia. Together, the results of this study identify hepatic PSS1 as a regulator of systemic lipoprotein metabolism.

Atypical sphingosine-1-phosphate metabolites-biological implications of alkyl chain length

Sphingosine-1-phosphate (S1P) is a bioactive lipid signaling molecule with pleiotropic implications by both auto- and paracrine signaling. Signaling occurs by engaging five G protein-coupled receptors (S1P1-5) or intracellular pathways. While the extensively studied S1P with a chain length of 18 carbon atoms (d18:1 S1P) affects lymphocyte trafficking, immune cell survival and inflammatory responses, the biological implication of atypical S1Ps such as d16:1 or d20:1 remains elusive. As S1P lipids have far-reaching implications in health and disease states in mammalian organisms, the previous contrasting results may be attributed to differences in S1P's alkyl chain length. Current research is beginning to appreciate these less abundant atypical S1P moieties. This review provides an up-to-date foundation of recent findings on the biological implications of atypical S1P chain lengths and offers a perspective on future research endeavors on S1P alkyl chain length-influenced signaling and its implications for drug discovery.

Insulin increases type I collagen synthesis in hepatic stellate cells via α5β1 integrin

Aim: A direct effect of insulin on the synthesis of extracellular matrix proteins has been described in extrahepatic organs. The current study investigates the role of insulin in type 1 collagen production in hepatic stellate cells (HSCs).

Methods: Primary HSC cultures from wild-type mice and from L-SACC1 transgenic mice that exhibit hyperinsulinemia and resultant insulin resistance due to a defect in hepatic insulin clearance were used.

Results: Insulin significantly increased type I collagen synthesis in HSC primary cultures in the presence of high but not low glucose concentrations. Although HSCs contain a functional, insulin-activated PI3 kinase signaling pathway, insulin increases type I collagen synthesis by mechanisms independent of PI3 kinase. Insulin stimulated α5β1 integrin levels and phosphorylation of focal adhesion kinase, a major signaling mediator in the integrin pathway. In addition, α5β1 integrin siRNA interference abolished insulin-mediated type I collagen synthesis by HSCs. L-SACC1 mice showed increased hepatic collagen deposition as compared to wild-type mice. HSCs isolated from L-SACC1 mice synthesize more type I collagen and α5β1 integrin than HSCs isolated from wild-type controls.

Conclusion: Insulin exerts a direct profibrotic impact on HSCs by an α5β1 integrin-mediated mechanism, independently of the PI3 kinase signaling pathway. Thus, chronic hyperinsulinemia may potentiate liver collagen deposition in insulin resistance states. This likely increases the risk of significant fibrosis burden in chronic liver disease associated with insulin resistance.

Mechanisms coupling lipid droplets to MASLD pathophysiology

Hepatic steatosis, the buildup of neutral lipids in lipid droplets (LDs), is commonly referred to as metabolic dysfunction-associated steatotic liver disease when alcohol or viral infections are not involved. Metabolic dysfunction-associated steatotic liver disease encompasses simple steatosis and the more severe metabolic dysfunction-associated steatohepatitis, characterized by inflammation, hepatocyte injury, and fibrosis. Previously viewed as inert markers of disease, LDs are now understood to play active roles in disease etiology and have significant nonpathological and pathological functions in cell signaling and function. These dynamic properties of LDs are tightly regulated by hundreds of proteins that coat the LD surface, controlling lipid metabolism, trafficking, and signaling. The following review highlights various facets of LD biology with the primary goal of discussing key mechanisms through which LDs promote the development of advanced liver diseases, including metabolic dysfunction-associated steatohepatitis.

Emerging Roles for Sphingolipids in Cardiometabolic Disease: A Rational Therapeutic Target?

Cardiovascular disease is a leading cause of morbidity and mortality. New research elucidates increasingly complex relationships between cardiac and metabolic health, giving rise to new possible therapeutic targets. Sphingolipids are a heterogeneous class of bioactive lipids with critical roles in normal human physiology. They have also been shown to play both protective and deleterious roles in the pathogenesis of cardiovascular disease. Ceramides are implicated in dysregulating insulin signalling, vascular endothelial function, inflammation, oxidative stress, and lipoprotein aggregation, thereby promoting atherosclerosis and vascular disease. Ceramides also advance myocardial disease by enhancing pathological cardiac remodelling and cardiomyocyte death. Glucosylceramides similarly contribute to insulin resistance and vascular inflammation, thus playing a role in atherogenesis and cardiometabolic dysfunction. Sphingosing-1-phosphate, on the other hand, may ameliorate some of the pathological functions of ceramide by protecting endothelial barrier integrity and promoting cell survival. Sphingosine-1-phosphate is, however, implicated in the development of cardiac fibrosis. This review will explore the roles of sphingolipids in vascular, cardiac, and metabolic pathologies and will evaluate the therapeutic potential in targeting sphingolipids with the aim of prevention and reversal of cardiovascular disease in order to improve long-term cardiovascular outcomes.

Sphingolipids and Chronic Kidney Disease

Sphingolipids (SLs) are bioactive signaling molecules essential for various cellular processes, including cell survival, proliferation, migration, and apoptosis. Key SLs such as ceramides, sphingosine, and their phosphorylated forms play critical roles in cellular integrity. Dysregulation of SL levels is implicated in numerous diseases, notably chronic kidney disease (CKD). This review focuses on the role of SLs in CKD, highlighting their potential as biomarkers for early detection and prognosis. SLs maintain renal function by modulating the glomerular filtration barrier, primarily through the activity of podocytes. An imbalance in SLs can lead to podocyte damage, contributing to CKD progression. SL metabolism involves complex enzyme-catalyzed pathways, with ceramide serving as a central molecule in de novo and salvage pathways. Ceramides induce apoptosis and are implicated in oxidative stress and inflammation, while sphingosine-1-phosphate (S1P) promotes cell survival and vascular health. Studies have shown that SL metabolism disorders are linked to CKD progression, diabetic kidney disease, and glomerular diseases. Targeting SL pathways could offer novel therapeutic approaches for CKD. This review synthesizes recent research on SL signaling regulation in kidney diseases, emphasizing the importance of maintaining SL balance for renal health and the potential therapeutic benefits of modulating SL pathways.

[Relationship between lipid metabolism molecules in plasma and carotid atheroscle-rotic plaques, traditional cardiovascular risk factors, and dietary factors]

OBJECTIVE

To explore the relationship between lipid metabolism molecules in plasma and carotid atherosclerotic plaques, traditional cardiovascular risk factors and possible dietary related factors.

METHODS

Firstly, among 1 312 community people from those who participated in a 10-year follow-up study of subclinical atherosclerosis cohort in Shijingshan District, Beijing, 85 individuals with 2 or more carotid soft plaques or mixed plaques and 89 healthy individuals without plaques were selected according to the inclusive and the exclusive criteria (< 70 years, not having clinical cardiovascular disease and other diseases, etc.). Secondly, 10 cases and 10 controls were randomly selected in the above 85 and 89 individuals respectively. Carotid plaques were detected using GE Vivid i Ultrasound Machine with 8L detector. Lipid metabolism molecules were detected by high performance liquid chromatography-mass spectrometry. The detection indexes included 113 lipid metabolism molecules. Traditional cardiovascular risk factors were collected by unified standard questionnaires, and dietary related factors were collected by main dietary frequency and weight scale. The difference of lipid metabolism molecules between the case group and the control group was analyzed by Wilcoxin rank test. In the control group, the Spearman correlation method was used to analyze the correlation between statistically significant lipid metabolism molecules and traditional cardiovascular risk factors and dietary factors.

RESULTS

Among the 113 lipid metabolism molecules, 53 lipid metabolism molecules were detected. C24:0 sphingomyelin (SM), C22:0/ C24:0 ceramide molecules, C18:0 phosphoethanolamine (PE) molecules, and C18:0/C18:2 (Cis) phosphatidylcholine (PC) were significantly higher in the carotid atherosclerotic plaque group than in the control group. The correlation analysis showed that C24:0 SM was significantly positively correlated with low density lipoprotein cholesterol (LDL-C, r=0.636, P < 0.05), C18:2 (Cis) PC (DLPC) was significantly positively correlated with systolic pressure (r=0.733, P < 0.05), C18:0 PE was significantly positively correlated with high sensitivity C-response protein (r=0.782, P < 0.01), C22:0, C24:0 ceramide and C18:0 PE were negatively correlated with vegetable intake (r=-0.679, P < 0.05;r=-0.711, P < 0.05;r=-0.808, P < 0.01), C24:0 ceramide was also negatively correlated with beans food intake (r=-0.736, P < 0.05) in the control group.

CONCLUSIONS

The increase of plasma C24:0 SM, C22:0, C24:0 ceramide, C18:0 PE, C18:2 (Cis) PC (DLPC), C18:0 PC (DSPC) may be new risk factors for human atherosclerotic plaques. These molecules may be related to blood lipid, blood pressure or inflammatory level and the intake of vegetables and soy products, but the nature of the association needs to be verified in a larger sample population.

Sphingolipid and Trimethylamine-N-Oxide (TMAO) Levels in Women with Obesity after Combined Physical Training

Obesity causes metabolic changes, such as the development of cardiovascular diseases. Moreover, physical exercise promotes protection against these diseases. Thus, the objective of the present study was to evaluate whether combined physical training can improve the metabolic system of women with obesity, reducing plasma concentrations of trimethylamine N-oxide (TMAO) and sphingolipids, regardless of weight loss. Fourteen obese women (BMI 30-40 kg/m2), aged 20-40 years, sedentary, were submitted to 8 weeks of combined physical training (strength and aerobic exercises). The training was performed three times/week, 55 min/session, at 75-90% maximum heart rate. All participants were evaluated pre- and post-exercise intervention, and their body composition, plasma TMAO, creatinine, lipid profile, and sphingolipid concentrations were recorded. Maximum oxygen consumption (VO2max), Speed lactate threshold 1 (SpeedLT1), and Speed lactate threshold 2 (SpeedLT2) evaluated physical performance. Results: After combined exercise, it did not change body composition, but TMAO, total cholesterol, and sphingolipid concentrations significantly decreased (p < 0.05). There was an increase in physical performance by improving VO2max, SpeedLT1, and SpeedLT2 (p < 0.05). The combined physical exercise could induce cardiovascular risk protection by decreasing TMAO in obese women, parallel to physical performance improvement, independent of weight loss.

Ceramides are fuel gauges on the drive to cardiometabolic disease

Ceramides are signals of fatty acid excess that accumulate when a cell's energetic needs have been met and its nutrient storage has reached capacity. As these sphingolipids accrue, they alter the metabolism and survival of cells throughout the body including in the heart, liver, blood vessels, skeletal muscle, brain, and kidney. These ceramide actions elicit the tissue dysfunction that underlies cardiometabolic diseases such as diabetes, coronary artery disease, metabolic-associated steatohepatitis, and heart failure. Here, we review the biosynthesis and degradation pathways that maintain ceramide levels in normal physiology and discuss how the loss of ceramide homeostasis drives cardiometabolic pathologies. We highlight signaling nodes that sense small changes in ceramides and in turn reprogram cellular metabolism and stimulate apoptosis. Finally, we evaluate the emerging therapeutic utility of these unique lipids as biomarkers that forecast disease risk and as targets of ceramide-lowering interventions that ameliorate disease.

Lipidomics Analysis Unravels Aberrant Lipid Species and Pathways Induced by Zinc Oxide Nanoparticles in Kidney Cells

Zinc oxide nanoparticles (ZnO NPs) are widely used in versatile applications, from high technology to household products. While numerous studies have examined the toxic gene profile of ZnO NPs across various tissues, the specific lipid species associated with adverse effects and potential biomarkers remain elusive. In this study, we conducted a liquid chromatography-mass spectrometry based lipidomics analysis to uncover potential lipid biomarkers in human kidney cells following treatment with ZnO NPs. Furthermore, we employed lipid pathway enrichment analysis (LIPEA) to elucidate altered lipid-related signaling pathways. Our results demonstrate that ZnO NPs induce cytotoxicity in renal epithelial cells and modulate lipid species; we identified 64 lipids with a fold change (FC) > 2 and p < 0.01 with corrected p < 0.05 in HK2 cells post-treatment with ZnO NPs. Notably, the altered lipids between control HK2 cells and those treated with ZnO NPs were associated with the sphingolipid, autophagy, and glycerophospholipid pathways. This study unveils novel potential lipid biomarkers of ZnO NP nanotoxicity, representing the first lipidomic profiling of ZnO NPs in human renal epithelial cells.

Ceramide on the road to insulin resistance and immunometabolic disorders in transition dairy cows: driver or passenger?

Dairy cows must undergo profound metabolic and endocrine adaptations during their transition period to meet the nutrient requirements of the developing fetus, parturition, and the onset of lactation. Insulin resistance in extrahepatic tissues is a critical component of homeorhetic adaptations in periparturient dairy cows. However, due to increased energy demands at calving that are not followed by a concomitant increase in dry matter intake, body stores are mobilized, and the risk of metabolic disorders dramatically increases. Sphingolipid ceramides involved in multiple vital biological processes, such as proliferation, differentiation, apoptosis, and inflammation. Three typical pathways generate ceramide, and many factors contribute to its production as part of the cell's stress response. Based on lipidomic profiling, there has generally been an association between increased ceramide content and various disease outcomes in rodents. Emerging evidence shows that ceramides might play crucial roles in the adaptive metabolic alterations accompanying the initiation of lactation in dairy cows. A series of studies also revealed a negative association between circulating ceramides and systemic insulin sensitivity in dairy cows experiencing severe negative energy balance. Whether ceramide acts as a driver or passenger in the metabolic stress of periparturient dairy cows is an unknown but exciting topic. In the present review, we discuss the potential roles of ceramides in various metabolic dysfunctions and the impacts of their perturbations. We also discuss how this novel class of bioactive sphingolipids has drawn interest in extrahepatic tissue insulin resistance and immunometabolic disorders in transition dairy cows. We also discuss the possible use of ceramide as a new biomarker for predicting metabolic diseases in cows and highlight the remaining problems.

Hypoxia-induced signaling in the cardiovascular system: pathogenesis and therapeutic targets

Hypoxia, characterized by reduced oxygen concentration, is a significant stressor that affects the survival of aerobic species and plays a prominent role in cardiovascular diseases. From the research history and milestone events related to hypoxia in cardiovascular development and diseases, The "hypoxia-inducible factors (HIFs) switch" can be observed from both temporal and spatial perspectives, encompassing the occurrence and progression of hypoxia (gradual decline in oxygen concentration), the acute and chronic manifestations of hypoxia, and the geographical characteristics of hypoxia (natural selection at high altitudes). Furthermore, hypoxia signaling pathways are associated with natural rhythms, such as diurnal and hibernation processes. In addition to innate factors and natural selection, it has been found that epigenetics, as a postnatal factor, profoundly influences the hypoxic response and progression within the cardiovascular system. Within this intricate process, interactions between different tissues and organs within the cardiovascular system and other systems in the context of hypoxia signaling pathways have been established. Thus, it is the time to summarize and to construct a multi-level regulatory framework of hypoxia signaling and mechanisms in cardiovascular diseases for developing more therapeutic targets and make reasonable advancements in clinical research, including FDA-approved drugs and ongoing clinical trials, to guide future clinical practice in the field of hypoxia signaling in cardiovascular diseases.

Preconception and developmental DEHP exposure alter liver metabolism in a sex-dependent manner in adult mouse offspring

Environmental exposure to endocrine disrupting chemicals (EDCs) during critical periods of development is associated with an increased risk of metabolic diseases, including hepatic steatosis and obesity. Di-2-ethylhexyl-phthalate (DEHP) is an EDC strongly associated with these metabolic abnormalities. DEHP developmental windows of susceptibility are unknown yet have important public health implications. The purpose of this study was to identify these windows of susceptibility and determine whether developmental DEHP exposure alters hepatic metabolism later in life. Dams were exposed to control or feed containing human exposure relevant doses of DEHP (50 μg/kg BW/d) and high dose DEHP (10 mg/kg BW/d) from preconception until weaning or only exposed to DEHP during preconception. Post-weaning, all offspring were fed a control diet throughout adulthood. Using the Metabolon Untargeted Metabolomics platform, we identified 148 significant metabolites in female adult livers that were altered by preconception-gestation-lactation DEHP exposure. We found a significant increase in the levels of acylcarnitines, diacylglycerols, sphingolipids, glutathione, purines, and pyrimidines in DEHP-exposed female livers compared to controls. These changes in fatty acid oxidation and oxidative stress-related metabolites were correlated with hepatic changes including microvesicular steatosis, hepatocyte swelling, inflammation. In contrast to females, we observed fewer metabolic alterations in male offspring, which were uniquely found in preconception-only low dose DEHP exposure group. Although we found that preconception-gestational-lactation exposure causes the most liver pathology, we surprisingly found preconception exposure linked to an abnormal liver metabolome. We also found that two doses exhibited non-monotonic DEHP-induced changes in the liver. Collectively, these findings suggest that metabolic changes in the adult liver of offspring exposed periconceptionally to DHEP depends on the timing of exposure, dose, and sex.

Circulating Sphingolipids in Insulin Resistance, Diabetes and Associated Complications

Sphingolipids play an important role in the development of diabetes, both type 1 and type 2 diabetes, as well as in the development of both micro- and macro-vascular complications. Several reviews have been published concerning the role of sphingolipids in diabetes but most of the emphasis has been on the possible mechanisms by which sphingolipids, mainly ceramides, contribute to the development of diabetes. Research on circulating levels of the different classes of sphingolipids in serum and in lipoproteins and their importance as biomarkers to predict not only the development of diabetes but also of its complications has only recently emerged and it is still in its infancy. This review summarizes the previously published literature concerning sphingolipid-mediated mechanisms involved in the development of diabetes and its complications, focusing on how circulating plasma sphingolipid levels and the relative content carried by the different lipoproteins may impact their role as possible biomarkers both in the development of diabetes and mainly in the development of diabetic complications. Further studies in this field may open new therapeutic avenues to prevent or arrest/reduce both the development of diabetes and progression of its complications.

Integrated omics approach for the identification of HDL structure-function relationships in PCSK9-related familial hypercholesterolemia

BACKGROUND

The role of proprotein convertase subtilisin/kexin type 9 (PCSK9) in dyslipidemia may go beyond its immediate effects on low-density lipoprotein receptor (LDL-R) activity.

OBJECTIVE

This study aimed to assess PCSK9-derived alterations of high-density lipoprotein (HDL) physiology, which bear a potential to contribute to cardiovascular risk profile.

METHODS

HDL was isolated from 33 patients with familial autosomal dominant hypercholesterolemia (FH), including those carrying PCSK9 gain-of-function (GOF) genetic variants (FH-PCSK9, n = 11), together with two groups of dyslipidemic patients employed as controls and carrying genetic variants in the LDL-R not treated (ntFH-LDLR, n = 11) and treated (tFH-LDLR, n = 11) with statins, and 11 normolipidemic controls. Biological evaluations paralleled by proteomic, lipidomic and glycomic analyses were applied to characterize functional and compositional properties of HDL.

RESULTS

Multiple deficiencies in the HDL function were identified in the FH-PCSK9 group relative to dyslipidemic FH-LDLR patients and normolipidemic controls, which involved reduced antioxidative, antiapoptotic, anti-thrombotic and anti-inflammatory activities. By contrast, cellular cholesterol efflux capacity of HDL was unchanged. In addition, multiple alterations of the proteomic, lipidomic and glycomic composition of HDL were found in the FH-PCSK9 group. Remarkably, HDLs from FH-PCSK9 patients were systematically enriched in several lysophospholipids as well as in A2G2S2 (GP13) glycan and apolipoprotein A-IV. Based on network analysis of functional and compositional data, a novel mosaic structure-function model of HDL biology involving FH was developed.

CONCLUSION

Several metrics of anti-atherogenic HDL functionality are altered in FH-PCSK9 patients paralleled by distinct compositional alterations. These data provide a first-ever overview of the impact of GOF PCSK9 genetic variants on structure-function relationships in HDL.

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.

A high-fat diet increases hepatic mitochondrial turnover through restricted acetylation in a NAFLD mouse model

Lysine acetylation of proteins has emerged as a key posttranslational modification (PTM) that regulates mitochondrial metabolism. Acetylation may regulate energy metabolism by inhibiting and affecting the stability of metabolic enzymes and oxidative phosphorylation (OxPhos) subunits. Although protein turnover can be easily measured, due to the low abundance of modified proteins, it has been difficult to evaluate the effect of acetylation on the stability of proteins in vivo. We applied 2H2O-metabolic labeling coupled with immunoaffinity and high-resolution mass spectrometry method to measure the stability of acetylated proteins in mouse liver based on their turnover rates. As a proof-of-concept, we assessed the consequence of high-fat diet (HFD)-induced altered acetylation in protein turnover in LDL receptor-deficient (LDLR-/-) mice susceptible to diet-induced nonalcoholic fatty liver disease (NAFLD). HFD feeding for 12 wk led to steatosis, the early stage of NAFLD. A significant reduction in acetylation of hepatic proteins was observed in NAFLD mice, based on immunoblot analysis and label-free quantification with mass spectrometry. Compared with control mice on a normal diet, NAFLD mice had overall increased turnover rates of hepatic proteins, including mitochondrial metabolic enzymes (0.159 ± 0.079 vs. 0.132 ± 0.068 day-1), suggesting their reduced stability. Also, acetylated proteins had slower turnover rates (increased stability) than native proteins in both groups (0.096 ± 0.056 vs. 0.170 ± 0.059 day-1 in control, and 0.111 ± 0.050 vs. 0.208 ± 0.074 day-1 in NAFLD). Furthermore, association analysis revealed a relationship between the HFD-induced decrease in acetylation and increased turnover rates for hepatic proteins in NAFLD mice. These changes were associated with increased expressions of the hepatic mitochondrial transcriptional factor (TFAM) and complex II subunit without any changes to other OxPhos proteins, suggesting that enhanced mitochondrial biogenesis prevented restricted acetylation-mediated depletion of mitochondrial proteins. We conclude that decreased acetylation of mitochondrial proteins may contribute to adaptive improved hepatic mitochondrial function in the early stages of NAFLD.NEW & NOTEWORTHY This is the first method to quantify acetylome dynamics in vivo. This method revealed acetylation-mediated altered hepatic mitochondrial protein turnover in response to a high-fat diet in a mouse model of NAFLD.

Lipidomics Profiling and Risk of Coronary Artery Disease in the BioHEART-CT Discovery Cohort

The current coronary artery disease (CAD) risk scores for predicting future cardiovascular events rely on well-recognized traditional cardiovascular risk factors derived from a population level but often fail individuals, with up to 25% of first-time heart attack patients having no risk factors. Non-invasive imaging technology can directly measure coronary artery plaque burden. With an advanced lipidomic measurement methodology, for the first time, we aim to identify lipidomic biomarkers to enable intervention before cardiovascular events. With 994 participants from BioHEART-CT Discovery Cohort, we collected clinical data and performed high-performance liquid chromatography with mass spectrometry to determine concentrations of 683 plasma lipid species. Statin-naive participants were selected based on subclinical CAD (sCAD) categories as the analytical cohort (n = 580), with sCAD+ (n = 243) compared to sCAD- (n = 337). Through a machine learning approach, we built a lipid risk score (LRS) and compared the performance of the existing Framingham Risk Score (FRS) in predicting sCAD+. We obtained individual classifiability scores and determined Body Mass Index (BMI) as the modifying variable. FRS and LRS models achieved similar areas under the receiver operating characteristic curve (AUC) in predicting the validation cohort. LRS enhanced the prediction of sCAD+ in the healthy-weight group (BMI < 25 kg/m²), where FRS performed poorly and identified individuals at risk that FRS missed. Lipid features have strong potential as biomarkers to predict CAD plaque burden and can identify residual risk not captured by traditional risk factors/scores. LRS compliments FRS in prediction and has the most significant benefit in healthy-weight individuals.

Physiological and pathological roles of lipogenesis

Lipids are essential metabolites, which function as energy sources, structural components and signalling mediators. Most cells are able to convert carbohydrates into fatty acids, which are often converted into neutral lipids for storage in the form of lipid droplets. Accumulating evidence suggests that lipogenesis plays a crucial role not only in metabolic tissues for systemic energy homoeostasis but also in immune and nervous systems for their proliferation, differentiation and even pathophysiological roles. Thus, excessive or insufficient lipogenesis is closely associated with aberrations in lipid homoeostasis, potentially leading to pathological consequences, such as dyslipidaemia, diabetes, fatty liver, autoimmune diseases, neurodegenerative diseases and cancers. For systemic energy homoeostasis, multiple enzymes involved in lipogenesis are tightly controlled by transcriptional and post-translational modifications. In this Review, we discuss recent findings regarding the regulatory mechanisms, physiological roles and pathological importance of lipogenesis in multiple tissues such as adipose tissue and the liver, as well as the immune and nervous systems. Furthermore, we briefly introduce the therapeutic implications of lipogenesis modulation.

Relationship between hepatic and mitochondrial ceramides: a novel in vivo method to track ceramide synthesis

Ceramides (CERs) are key intermediate sphingolipids implicated in contributing to mitochondrial dysfunction and the development of multiple metabolic conditions. Despite the growing evidence of CER role in disease risk, kinetic methods to measure CER turnover are lacking, particularly using in vivo models. The utility of orally administered 13C3, 15N l-serine, dissolved in drinking water, was tested to quantify CER 18:1/16:0 synthesis in 10-week-old male and female C57Bl/6 mice. To generate isotopic labeling curves, animals consumed either a control diet or high-fat diet (HFD; n = 24/diet) for 2 weeks and varied in the duration of the consumption of serine-labeled water (0, 1, 2, 4, 7, or 12 days; n = 4 animals/day/diet). Unlabeled and labeled hepatic and mitochondrial CERs were quantified using liquid chromatography tandem MS. Total hepatic CER content did not differ between the two diet groups, whereas total mitochondrial CERs increased with HFD feeding (60%, P < 0.001). Within hepatic and mitochondrial pools, HFD induced greater saturated CER concentrations (P < 0.05) and significantly elevated absolute turnover of 16:0 mitochondrial CER (mitochondria: 59%, P < 0.001 vs. liver: 15%, P = 0.256). The data suggest cellular redistribution of CERs because of the HFD. These data demonstrate that a 2-week HFD alters the turnover and content of mitochondrial CERs. Given the growing data on CERs contributing to hepatic mitochondrial dysfunction and the progression of multiple metabolic diseases, this method may now be used to investigate how CER turnover is altered in these conditions.

Dihydrosphingolipids are associated with steatosis and increased fibrosis damage in non-alcoholic fatty liver disease

Dihydrosphingolipids are lipids biosynthetically related to ceramides. An increase in ceramides is associated with enhanced fat storage in the liver and inhibition of their synthesis is reported to prevent the appearance of steatosis in animal models. However, the precise association of dihydrosphingolipids with non-alcoholic fatty liver disease (NAFLD) is yet to be established. We employed a diet induced NAFLD mouse model to study the association between this class of compounds and disease progression. Mice fed a high-fat diet were sacrificed at 22, 30 and 40 weeks to reproduce the full spectrum of histological damage found in human disease, steatosis (NAFL) and steatohepatitis (NASH) with and without significant fibrosis. Blood and liver tissue samples were obtained from patients whose NAFLD severity was assessed histologically. To demonstrate the effect of dihydroceramides over NAFLD progression we treated mice with fenretinide an inhibitor of dihydroceramide desaturse-1 (DEGS1). Lipidomic analyses were performed using liquid chromatography-tandem mass spectrometry. Triglycerides, cholesteryl esters and dihydrosphingolipids were increased in the liver of model mice in association with the degree of steatosis and fibrosis. Dihydroceramides increased with the histological severity observed in liver samples of mice (0.024 ± 0.003 nmol/mg vs 0.049 ± 0.005 nmol/mg, non-NAFLD vs NASH-fibrosis, p < 0.0001) and patients (0.105 ± 0.011 nmol/mg vs 0.165 ± 0.021 nmol/mg, p = 0.0221). Inhibition of DEGS1 induce a four-fold increase in dihydroceramides improving steatosis but increasing the inflammatory activity and fibrosis. In conclusion, the degree of histological damage in NAFLD correlate with dihydroceramide and dihydrosphingolipid accumulation. LAY SUMMARY: Accumulation of triglyceride and cholesteryl ester lipids is the hallmark of non-alcoholic fatty liver disease. Using lipidomics, we examined the role of dihydrosphingolipids in NAFLD progression. Our results demonstrate that de novo dihydrosphingolipid synthesis is an early event in NAFLD and the concentrations of these lipids are correlated with histological severity in both mouse and human disease.

Phospholipid analysis of two influenza A virus-infected cell lines differing in their viral replication kinetics

Fluctuations in phospholipid composition in infected cells during influenza A virus replication were analyzed using two different susceptible host cell lines: H292 cells, exhibiting a rapid cytopathic effect, and A549 cells, exhibiting a retarded cytopathic effect. Microarray analysis demonstrated that A549 cells recognized influenza A virus invasion, expression of pathogen recognition genes was affected, and antiviral genes were activated. On the other hand, H292 cells did not display such an antiviral state, and in these cells, rapid virus amplification and a rapid cytopathic effect were observed. Levels of ceramide, diacylglycerol, and lysolipids were higher in virus-infected cells than in the corresponding mock-infected cells at the later stages of infection. The accumulation of these lipids in IAV-infected cells occurred together with viral replication. The relationship between the characteristic features of ceramide, diacylglycerol, and lysolipid in the plasma membrane, where enveloped viruses are released, and their role in viral envelope formation are discussed. Our results indicate that viral replication disturbs cellular lipid metabolism, with consequences for viral replication kinetics.

Contribution of Hepatic Steatosis-Intensified Extracellular Vesicle Release to Aggravated Inflammatory Endothelial Injury in Liver-Specific Asah1 Gene Knockout Mice

To study the mechanism by which nonalcoholic fatty liver disease (NAFLD) contributes to vascular endothelial Nod-like receptor pyrin domain 3 (NLRP3) inflammasome activation and neointima hyperplasia, NAFLD was established in high-fat diet (HFD)-treated Asah1fl/fl/Albcre (liver-specific deletion of the acid ceramidase gene Asah1) mice. Compared with Asah1 flox [Asah1fl/fl/wild type (WT)] and wild-type (WT/WT) mice, Asah1fl/fl/Albcre mice exhibited significantly enhanced ceramide levels and lipid deposition on HFD in the liver. Moreover, Asah1fl/fl/Albcre mice showed enhanced expression of extracellular vesicle (EV) markers, CD63 and annexin II, but attenuated lysosome-multivesicular body fusion. All these changes were accompanied by significantly increased EV counts in the plasma. In a mouse model of neointima hyperplasia, liver-specific deletion of the Asah1 gene enhanced HFD-induced neointima proliferation, which was associated with increased endothelial NLRP3 inflammasome formation and activation and more severe endothelial damage. The EVs isolated from plasma of Asah1fl/fl/Albcre mice on HFD were found to markedly enhance NLRP3 inflammasome formation and activation in primary cultures of WT/WT endothelial cells compared with those isolated from WT/WT mice or normal diet-treated Asah1fl/fl/Albcre mice. These results suggest that the acid ceramidase/ceramide signaling pathway controls EV release from the liver, and its deficiency aggravates NAFLD and intensifies hepatic EV release into circulation, which promotes endothelial NLRP3 inflammasome activation and consequent neointima hyperplasia in the mouse carotid arteries.

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.

Ceramide concentrations in liver, plasma, and very low-density lipoproteins of humans with severe obesity

We investigated the relationships between ceramide species concentrations in liver, plasma and very low-density lipoproteins (VLDL) particles of humans with obesity as well as the relationships between hepatic fat content and hepatic ceramide concentrations and proportional distribution. Twenty-five obese (body mass index >35 kg/m² ) adults participated in this study. Plasma, VLDL and hepatocellular ceramide concentrations were measured by liquid chromatography/tandem mass spectrometry. The proportionate distribution of measured ceramide species differed between liver, whole plasma and the VLDL fraction. We found significant, positive correlations between the proportion of C14:0, C18:0, C20:0 and C24:1 ceramide in the liver and whole plasma (γ = 0.491, p = 0.013; γ = 0.573, p = 0.003; γ = 0.479, p = 0.015; γ = 0.716, p = 0.00006; respectively). In contrast, only the proportional contribution of C24:1 ceramide correlated positively between VLDL and liver (γ = 0.425, p = 0.013). The percent hepatic fat correlated positively with the proportion of C18:1, C18:0 and C20:0 hepatic ceramides (γ = 0.415, p = 0.039; γ = 0.426, p = 0.034; γ = 0.612, p = 0.001; respectively), but not with total hepatic ceramide concentration. The proportions of whole plasma ceramide subspecies, especially C14:0, C18:0, C20:0 and C24:1chain length, are reflective of those of hepatic ceramide subspecies in obese humans; these appear to be markers of hepatic ceramide species composition.

The interplay between nonalcoholic fatty liver disease and atherosclerotic cardiovascular disease

Therapeutic approaches that lower circulating low-density lipoprotein (LDL)-cholesterol significantly reduced the burden of cardiovascular disease over the last decades. However, the persistent rise in the obesity epidemic is beginning to reverse this decline. Alongside obesity, the incidence of nonalcoholic fatty liver disease (NAFLD) has substantially increased in the last three decades. Currently, approximately one third of world population is affected by NAFLD. Notably, the presence of NAFLD and particularly its more severe form, nonalcoholic steatohepatitis (NASH), serves as an independent risk factor for atherosclerotic cardiovascular disease (ASCVD), thus, raising interest in the relationship between these two diseases. Importantly, ASCVD is the major cause of death in patients with NASH independent of traditional risk factors. Nevertheless, the pathophysiology linking NAFLD/NASH with ASCVD remains poorly understood. While dyslipidemia is a common risk factor underlying both diseases, therapies that lower circulating LDL-cholesterol are largely ineffective against NASH. While there are no approved pharmacological therapies for NASH, some of the most advanced drug candidates exacerbate atherogenic dyslipidemia, raising concerns regarding their adverse cardiovascular consequences. In this review, we address current gaps in our understanding of the mechanisms linking NAFLD/NASH and ASCVD, explore strategies to simultaneously model these diseases, evaluate emerging biomarkers that may be useful to diagnose the presence of both diseases, and discuss investigational approaches and ongoing clinical trials that potentially target both diseases.

Crosstalk Between Cholesterol, ABC Transporters, and PIP2 in Inflammation and Atherosclerosis

The lowering of plasma low-density lipoprotein cholesterol (LDL-C) is an easily achievable and highly reliable modifiable risk factor for preventing cardiovascular disease (CVD), as validated by the unparalleled success of statins in the last three decades. However, the 2021 American Heart Association (AHA) statistics show a worrying upward trend in CVD deaths, calling into question the widely held belief that statins and available adjuvant therapies can fully resolve the CVD problem. Human biomarker studies have shown that indicators of inflammation, such as human C-reactive protein (hCRP), can serve as a reliable risk predictor for CVD, independent of all traditional risk factors. Oxidized cholesterol mediates chronic inflammation and promotes atherosclerosis, while anti-inflammatory therapies, such as an anti-interleukin-1 beta (anti-IL-1β) antibody, can reduce CVD in humans. Cholesterol removal from artery plaques, via an athero-protective reverse cholesterol transport (RCT) pathway, can dampen inflammation. Phosphatidylinositol 4,5-bisphosphate (PIP2) plays a role in RCT by promoting adenosine triphosphate (ATP)-binding cassette transporter A1 (ABCA1)-mediated cholesterol efflux from arterial macrophages. Cholesterol crystals activate the nod-like receptor family pyrin domain containing 3 (Nlrp3) inflammasome in advanced atherosclerotic plaques, leading to IL-1β release in a PIP2-dependent fashion. PIP2 thus is a central player in CVD pathogenesis, serving as a critical link between cellular cholesterol levels, ATP-binding cassette (ABC) transporters, and inflammasome-induced IL-1β release.

Liver-derived metabolites as signaling molecules in fatty liver disease

Excessive fat accumulation in the liver has become a major health threat worldwide. Unresolved fat deposition in the liver can go undetected until it develops into fatty liver disease, followed by steatohepatitis, fibrosis, cirrhosis, and eventually hepatocellular carcinoma. Lipid deposition in the liver is governed by complex communication, primarily between metabolic organs. This can be mediated by hormones, organokines, and also, as has been more recently discovered, metabolites. Although how metabolites from peripheral organs affect the liver is well documented, the effect of metabolic players released from the liver during the development of fatty liver disease or associated comorbidities needs further attention. Here we focus on interorgan crosstalk based on metabolites released from the liver and how these molecules act as signaling molecules in peripheral tissues. Due to the liver's specific role, we are covering lipid and bile mechanism-derived metabolites. We also discuss the high sucrose intake associated with uric acid release from the liver. Excessive fat deposition in the liver during fatty liver disease development reflects disrupted metabolic processes. As a response, the liver secretes a variety of signaling molecules as well as metabolites which act as a footprint of the metabolic disruption. In the coming years, the reciprocal exchange of metabolites between the liver and other metabolic organs will gain further importance and will help to better understand the development of fatty liver disease and associated diseases.

Inhibitory Effects of Myriocin on Non-Enzymatic Glycation of Bovine Serum Albumin

Advanced glycation end products (AGEs) are the compounds produced by non-enzymatic glycation of proteins, which are involved in diabetic-related complications. To investigate the potential anti-glycation activity of Myriocin (Myr), a fungal metabolite of Cordyceps, the effect of Myr on the formation of AGEs resulted from the glycation of bovine serum albumin (BSA) and the interaction between Myr and BSA were studied by multiple spectroscopic techniques and computational simulations. We found that Myr inhibited the formation of AGEs at the end stage of glycation reaction and exhibited strong anti-fibrillation activity. Spectroscopic analysis revealed that Myr quenched the fluorescence of BSA in a static process, with the possible formation of a complex (approximate molar ratio of 1:1). The binding between BSA and Myr mainly depended on van der Waals interaction, hydrophobic interactions and hydrogen bond. The synchronous fluorescence and UV-visible (UV-vis) spectra results indicated that the conformation of BSA altered in the presence of Myr. The fluorescent probe displacement experiments and molecular docking suggested that Myr primarily bound to binding site 1 (subdomain IIA) of BSA. These findings demonstrate that Myr is a potential anti-glycation agent and provide a theoretical basis for the further functional research of Myr in the prevention and treatment of AGEs-related diseases.

Targeting acid ceramidase ameliorates fibrosis in mouse models of non-alcoholic steatohepatitis

Non-alcoholic fatty liver disease (NAFLD) is a common cause of liver disease worldwide, and is characterized by the accumulation of fat in the liver. Non-alcoholic steatohepatitis (NASH), an advanced form of NAFLD, is a leading cause of liver transplantation. Fibrosis is the histologic feature most associated with liver-related morbidity and mortality in patients with NASH, and treatment options remain limited. In previous studies, we discovered that acid ceramidase (aCDase) is a potent antifibrotic target using human hepatic stellate cells (HSCs) and models of hepatic fibrogenesis. Using two dietary mouse models, we demonstrate that depletion of aCDase in HSC reduces fibrosis without worsening metabolic features of NASH, including steatosis, inflammation, and insulin resistance. Consistently, pharmacologic inhibition of aCDase ameliorates fibrosis but does not alter metabolic parameters. The findings suggest that targeting aCDase is a viable therapeutic option to reduce fibrosis in patients with NASH.

Molecular Advances in MAFLD—A Link between Sphingolipids and Extracellular Matrix in Development and Progression to Fibrosis

Metabolic-Associated Fatty Liver Disease (MAFLD) is a major cause of liver diseases globally and its prevalence is expected to grow in the coming decades. The main cause of MAFLD development is changed in the composition of the extracellular matrix (ECM). Increased production of matrix molecules and inflammatory processes lead to progressive fibrosis, cirrhosis, and ultimately liver failure. In addition, increased accumulation of sphingolipids accompanied by increased expression of pro-inflammatory cytokines in the ECM is closely related to lipogenesis, MAFLD development, and its progression to fibrosis. In our work, we will summarize all information regarding the role of sphingolipids e.g., ceramide and S1P in MAFLD development. These sphingolipids seem to have the most significant effect on macrophages and, consequently, HSCs which trigger the entire cascade of overproduction matrix molecules, especially type I and III collagen, proteoglycans, elastin, and also tissue inhibitors of metalloproteinases, which as a result cause the development of liver fibrosis.

Endothelial Cell Dysfunction and Nonalcoholic Fatty Liver Disease (NAFLD): A Concise Review

Nonalcoholic fatty liver disease (NAFLD) is one of the most common liver diseases worldwide. It is strongly associated with obesity, type 2 diabetes (T2DM), and other metabolic syndrome features. Reflecting the underlying pathogenesis and the cardiometabolic disorders associated with NAFLD, the term metabolic (dysfunction)-associated fatty liver disease (MAFLD) has recently been proposed. Indeed, over the past few years, growing evidence supports a strong correlation between NAFLD and increased cardiovascular disease (CVD) risk, independent of the presence of diabetes, hypertension, and obesity. This implies that NAFLD may also be directly involved in the pathogenesis of CVD. Notably, liver sinusoidal endothelial cell (LSEC) dysfunction appears to be implicated in the progression of NAFLD via numerous mechanisms, including the regulation of the inflammatory process, hepatic stellate activation, augmented vascular resistance, and the distortion of microcirculation, resulting in the progression of NAFLD. Vice versa, the liver secretes inflammatory molecules that are considered pro-atherogenic and may contribute to vascular endothelial dysfunction, resulting in atherosclerosis and CVD. In this review, we provide current evidence supporting the role of endothelial cell dysfunction in the pathogenesis of NAFLD and NAFLD-associated atherosclerosis. Endothelial cells could thus represent a "golden target" for the development of new treatment strategies for NAFLD and its comorbid CVD.

Ceramide de novo synthesis in non-alcoholic fatty liver disease: Pathogenic mechanisms and therapeutic perspectives

Non-alcoholic fatty liver disease (NAFLD) is the most common chronic liver disease, and its advanced form non-alcoholic steatohepatitis (NASH) may progress to cirrhosis and hepatocellular carcinoma. Ceramides have been shown to exacerbate NAFLD development through enhancing insulin resistance, reactive oxygen species production, liver steatosis, lipotoxicity and hepatocyte apoptosis, and eventually causing hepatic inflammation and fibrosis. Emerging evidence indicates that ceramide production in NAFLD is predominantly attributed to activation of the de novo synthesis pathway of ceramides in hepatocytes. More importantly, pharmacological modulation of ceramide de novo synthesis in preclinical studies seems efficacious for the treatment of NAFLD. In this review, we provide an overview of the pathogenic mechanisms of ceramides in NAFLD, discuss recent advances and challenges in pharmacological interventions targeting ceramide de novo synthesis, and propose some research directions in the field.

Contribution of specific ceramides to obesity-associated metabolic diseases

Ceramides are a heterogeneous group of bioactive membrane sphingolipids that play specialized regulatory roles in cellular metabolism depending on their characteristic fatty acyl chain lengths and subcellular distribution. As obesity progresses, certain ceramide molecular species accumulate in metabolic tissues and cause cell-type-specific lipotoxic reactions that disrupt metabolic homeostasis and lead to the development of cardiometabolic diseases. Several mechanisms for ceramide action have been inferred from studies in vitro, but only recently have we begun to better understand the acyl chain length specificity of ceramide-mediated signaling in the context of physiology and disease in vivo. New discoveries show that specific ceramides affect various metabolic pathways and that global or tissue-specific reduction in selected ceramide pools in obese rodents is sufficient to improve metabolic health. Here, we review the tissue-specific regulation and functions of ceramides in obesity, thus highlighting the emerging concept of selectively inhibiting production or action of ceramides with specific acyl chain lengths as novel therapeutic strategies to ameliorate obesity-associated diseases.

The Role of Obesity, Inflammation and Sphingolipids in the Development of an Abdominal Aortic Aneurysm

Abdominal aortic aneurysm (AAA) is a local dilatation of the vessel equal to or exceeding 3 cm. It is a disease with a long preclinical period commonly without any symptoms in its initial stage. Undiagnosed for years, aneurysm often leads to death due to vessel rupture. The basis of AAA pathogenesis is inflammation, which is often associated with the excess of adipose tissue, especially perivascular adipose tissue, which synthesizes adipocytokines that exert a significant influence on the formation of aneurysms. Pro-inflammatory cytokines such as resistin, leptin, and TNFα have been shown to induce changes leading to the formation of aneurysms, while adiponectin is the only known compound that is secreted by adipose tissue and limits the development of aneurysms. However, in obesity, adiponectin levels decline. Moreover, inflammation is associated with an increase in the amount of macrophages infiltrating adipose tissue, which are the source of matrix metalloproteinases (MMP) involved in the degradation of the extracellular matrix, which are an important factor in the formation of aneurysms. In addition, an excess of body fat is associated with altered sphingolipid metabolism. It has been shown that among sphingolipids, there are compounds that play an opposite role in the cell: ceramide is a pro-apoptotic compound that mediates the development of inflammation, while sphingosine-1-phosphate exerts pro-proliferative and anti-inflammatory effects. It has been shown that the increase in the level of ceramide is associated with a decrease in the concentration of adiponectin, an increase in the concentration of TNFα, MMP-9 and reactive oxygen species (which contribute to the apoptosis of vascular smooth muscle cell). The available data indicate a potential relationship between obesity, inflammation and disturbed sphingolipid metabolism with the formation of aneurysms; therefore, the aim of this study was to systematize the current knowledge on the role of these factors in the pathogenesis of abdominal aortic aneurysm.

Influence of the Human Lipidome on Epicardial Fat Volume in Mexican American Individuals

Introduction

Cardiovascular disease (CVD) is the leading cause of mortality worldwide and is the leading cause of death in the US. Lipid dysregulation is a well-known precursor to metabolic diseases, including CVD. There is a growing body of literature that suggests MRI-derived epicardial fat volume, or epicardial adipose tissue (EAT) volume, is linked to the development of coronary artery disease. Interestingly, epicardial fat is also actively involved in lipid and energy homeostasis, with epicardial adipose tissue having a greater capacity for release and uptake of free fatty acids. However, there is a scarcity of knowledge on the influence of plasma lipids on EAT volume.

Aim

The focus of this study is on the identification of novel lipidomic species associated with CMRI-derived measures of epicardial fat in Mexican American individuals.

Methods

We performed lipidomic profiling on 200 Mexican American individuals. High-throughput mass spectrometry enabled rapid capture of precise lipidomic profiles, providing measures of 799 unique species from circulating plasma samples. Because of our extended pedigree design, we utilized a standard quantitative genetic linear mixed model analysis to determine whether lipids were correlated with EAT by formally testing for association between each lipid species and the CMRI epicardial fat phenotype.

Results

After correction for multiple testing using the FDR approach, we identified 135 lipid species showing significant association with epicardial fat. Of those, 131 lipid species were positively correlated with EAT, where increased circulating lipid levels were correlated with increased epicardial fat. Interestingly, the top 10 lipid species associated with an increased epicardial fat volume were from the deoxyceramide (Cer(m)) and triacylglycerol (TG) families. Deoxyceramides are atypical and neurotoxic sphingolipids. Triacylglycerols are an abundant lipid class and comprise the bulk of storage fat in tissues. Pathologically elevated TG and Cer(m) levels are related to CVD risk and, in our study, to EAT volume.

Conclusion

Our results indicate that specific lipid abnormalities such as enriched saturated triacylglycerols and the presence of toxic ceramides Cer(m) in plasma of our individuals could precede CVD with increased EAT volume.

You aren't IMMUNE to the ceramides that accumulate in cardiometabolic disease

Obesity leads to persistent increases in immune responses that contribute to cardiometabolic pathologies such as diabetes and cardiovascular disease. Pro-inflammatory macrophages infiltrate the expanding fat mass, which leads to increased production of cytokines such as tumor necrosis factor-alpha. Moreover, saturated fatty acids enhance signaling through the toll-like receptors involved in innate immunity. Herein we discuss the evidence that ceramides-which are intermediates in the biosynthetic pathway that produces sphingolipids-are essential intermediates that link these inflammatory signals to impaired tissue function. We discuss the mechanisms linking these immune insults to ceramide production and review the numerous ceramide actions that alter cellular metabolism, induce oxidative stress, and stimulate apoptosis. Lastly, we evaluate the correlation of ceramides in humans with inflammation-linked cardiometabolic disease and discuss preclinical studies which suggest that ceramide-lowering interventions may be an effective strategy to treat or prevent such maladies.

Mitochondria and the NLRP3 Inflammasome in Alcoholic and Nonalcoholic Steatohepatitis

Alcoholic (ASH) and nonalcoholic steatohepatitis (NASH) are advanced stages of fatty liver disease and two of the most prevalent forms of chronic liver disease. ASH and NASH are associated with significant risk of further progression to cirrhosis and hepatocellular carcinoma (HCC), the most common type of liver cancer, and a major cause of cancer-related mortality. Despite extensive research and progress in the last decades to elucidate the mechanisms of the development of ASH and NASH, the pathogenesis of both diseases is still poorly understood. Mitochondrial damage and activation of inflammasome complexes have a role in inducing and sustaining liver damage. Mitochondrial dysfunction produces inflammatory factors that activate the inflammasome complexes. NLRP3 inflammasome (nucleotide-binding oligomerization domain-like receptor protein 3) is a multiprotein complex that activates caspase 1 and the release of pro-inflammatory cytokines, including interleukin-1β (IL-1β) and interleukin-18 (IL-18), and contributes to inflammatory pyroptotic cell death. The present review, which is part of the issue "Mitochondria in Liver Pathobiology", provides an overview of the role of mitochondrial dysfunction and NLRP3 activation in ASH and NASH.

Long-chain ceramides are cell non-autonomous signals linking lipotoxicity to endoplasmic reticulum stress in skeletal muscle

The endoplasmic reticulum (ER) regulates cellular protein and lipid biosynthesis. ER dysfunction leads to protein misfolding and the unfolded protein response (UPR), which limits protein synthesis to prevent cytotoxicity. Chronic ER stress in skeletal muscle is a unifying mechanism linking lipotoxicity to metabolic disease. Unidentified signals from cells undergoing ER stress propagate paracrine and systemic UPR activation. Here, we induce ER stress and lipotoxicity in myotubes. We observe ER stress-inducing lipid cell non-autonomous signal(s). Lipidomics identifies that palmitate-induced cell stress induces long-chain ceramide 40:1 and 42:1 secretion. Ceramide synthesis through the ceramide synthase 2 de novo pathway is regulated by UPR kinase Perk. Inactivation of CerS2 in mice reduces systemic and muscle ceramide signals and muscle UPR activation. The ceramides are packaged into extracellular vesicles, secreted and induce UPR activation in naïve myotubes through dihydroceramide accumulation. This study furthers our understanding of ER stress by identifying UPR-inducing cell non-autonomous signals.

Lipidomics Indicates the Hepatotoxicity Effects of EtOAc Extract of Rhizoma Paridis

Rhizoma Paridis is a traditional Chinese medicine commonly used in the clinical treatment of gynecological diseases. Previous studies have shown that aqueous extracts of Rhizoma Paridis exhibit some hepatotoxicity to hepatocytes. Here, using lipidomics analysis, we investigated the potential hepatotoxicity of Rhizoma Paridis and its possible mechanism. The hepatic damaging of different solvent extracts of Rhizoma Paridis on zebrafish larvae were determined by a combination of mortality dose, biochemical, morphological, and functional tests. We found that ethyl acetate extracts (AcOEtE) were the most toxic fraction. Notably, lipidomic responsible for the pharmacological effects of AcOEtE were investigated by Q-Exactive HF-X mass spectrometer (Thermo Scientific high-resolution) coupled in tandem with a UHPLC system. Approximately 1958 unique spectral features were detected, of which 325 were identified as unique lipid species. Among these lipid species, phosphatidylethanolamine cardiolipin Ceramide (Cer), lysophosphatidylinositol sphingosine (Sph), etc., were significantly upregulated in the treated group. Pathway analysis indicates that Rhizoma Paridis may cause liver damage via interfering with the glycerophospholipid metabolism. Collectively, this study has revealed previously uncharacterized lipid metabolic disorder involving lipid synthesis, metabolism, and transport that functionally determines hepatic fibrosis procession.

The Neglected Role of Bile Duct Epithelial Cells in NASH

Nonalcoholic fatty liver disease (NAFLD) is the most prevalent liver disease worldwide, and affects 25% of the population in Western countries. NAFLD is the hepatic manifestation of the metabolic syndrome, linked to insulin resistance, which is the common pathogenetic mechanism. In approximately 40% of NAFLD patients, steatosis is associated with necro-inflammation and fibrosis, resulting in nonalcoholic steatohepatitis (NASH), a severe condition that may progress to cirrhosis and liver cancer. Although the hepatocyte represents the main target of the disease, involvement of the bile ducts occurs in a subset of patients with NASH, and is characterized by ductular reaction and activation of the progenitor cell compartment, which incites portal fibrosis and disease progression. We aim to dissect the multiple biological effects that adipokines and metabolic alterations exert on cholangiocytes to derive novel information on the mechanisms driven by insulin resistance, which promote fibro-inflammation and carcinogenesis in NASH.

Role of Ceramides in the Molecular Pathogenesis and Potential Therapeutic Strategies of Cardiometabolic Diseases: What we Know so Far

Ceramides represent a class of biologically active lipids that are involved in orchestrating vital signal transduction pathways responsible for regulating cellular differentiation and proliferation. However, accumulating clinical evidence have shown that ceramides are playing a detrimental role in the pathogenesis of several diseases including cardiovascular disease, type II diabetes and obesity, collectively referred to as cardiometabolic disease. Therefore, it has become necessary to study in depth the role of ceramides in the pathophysiology of such diseases, aiming to tailor more efficient treatment regimens. Furthermore, understanding the contribution of ceramides to the pathological molecular mechanisms of those interrelated conditions may improve not only the therapeutic but also the diagnostic and preventive approaches of the preceding hazardous events. Hence, the purpose of this article is to review currently available evidence on the role of ceramides as a common factor in the pathological mechanisms of cardiometabolic diseases as well as the mechanism of action of the latest ceramides-targeted therapies.

Sphingolipid Profiling: A Promising Tool for Stratifying the Metabolic Syndrome-Associated Risk

Metabolic syndrome (MetS) is a multicomponent risk condition that reflects the clustering of individual cardiometabolic risk factors related to abdominal obesity and insulin resistance. MetS increases the risk for cardiovascular diseases (CVD) and type 2 diabetes mellitus (T2DM). However, there still is not total clinical consensus about the definition of MetS, and its pathophysiology seems to be heterogeneous. Moreover, it remains unclear whether MetS is a single syndrome or a set of diverse clinical conditions conferring different metabolic and cardiovascular risks. Indeed, traditional biomarkers alone do not explain well such heterogeneity or the risk of associated diseases. There is thus a need to identify additional biomarkers that may contribute to a better understanding of MetS, along with more accurate prognosis of its various chronic disease risks. To fulfill this need, omics technologies may offer new insights into associations between sphingolipids and cardiometabolic diseases. Particularly, ceramides –the most widely studied sphingolipid class– have been shown to play a causative role in both T2DM and CVD. However, the involvement of simple glycosphingolipids remains controversial. This review focuses on the current understanding of MetS heterogeneity and discuss recent findings to address how sphingolipid profiling can be applied to better characterize MetS-associated risks.

Extent and features of liver steatosis in vitro pave the way to endothelial dysfunction without physical cell-to-cell contact

BACKGROUND AND AIMS

Several chronic multifactorial diseases originate from energy unbalance between food intake and body energy expenditure, including non-alcoholic fatty liver disease (NAFLD), diabetes, and cardiovascular disorders. Vascular endothelium plays a central role in body homeostasis, and NAFLD is often associated with endothelial dysfunction (ED), the first step in atherosclerosis. Both sugars and fatty acids (FAs) are fuel sources for energy production, but their excess leads to liver steatosis which may trigger ED through a network of mechanisms which need to be clarified. Here, we investigated the crosstalk pathways between in vitro cultured steatotic hepatocytes (FaO) and endothelial cells (HECV) being mediated by soluble factors.

METHODS AND RESULTS

We employed the conditioned medium approach to test how different extent and features of hepatic steatosis distinctively affect endothelium leading to ED. The steatogenic media collected from steatotic hepatocytes were characterized by high triglyceride content and led to lipid accumulation and fat-dependent dysfunction in HECV cells. We found a parallelism between (i) extent of hepatocyte steatosis and level of lipid accumulation in HECV cells; (ii) type of hepatocyte steatosis (with macro- or microvesicular LDs) and extent of oxidative stress, lipid peroxidation, nitric oxide release and expression of ED markers in HECV cells.

CONCLUSIONS

The present findings seem to suggest that, in addition to triglycerides, other soluble mediators should be released by steatotic hepatocytes and may influence lipid accumulation and function of HECV cells. Further studies need to depict the exact profile of soluble factors involved in steatotic hepatocyte-endothelium crosstalk.