sphingosine-1-phosphate and Non-alcoholic-Fatty-Liver-Disease

Patients with unresectable hepatocellular carcinoma (HCC) cannot generally be cured by systemic chemotherapy or radiotherapy due to their poor response to conventional therapeutic agents. The development of novel and efficient targeted therapies to increase their treatment options depends on the elucidation of the molecular mechanisms that underlie the pathogenesis of HCC. The DNA damage response (DDR) is a network of cell-signaling events that are triggered by DNA damage. Its dysregulation is thought to be one of the key mechanisms underlying the generation of HCC. Sphingosine-1-phosphate (S1P), a lipid mediator, has emerged as an important signaling molecule that has been found to be involved in many cellular functions. In the liver, the alteration of S1P signaling potentially affects the DDR pathways. In this review, we explore the role of the DDR in hepatocarcinogenesis of various etiologies, including hepatitis B and C infection and non-alcoholic steatohepatitis. Furthermore, we discuss the metabolism and functions of S1P that may affect the hepatic DDR. The elucidation of the pathogenic role of S1P may create new avenues of research into therapeutic strategies for patients with HCC.

Topics: Adaptor Proteins, Signal Transducing; Carcinoma, Hepatocellular; DNA Damage; Hepatitis B; Hepatitis C; Humans; Liver Neoplasms; Lyases; Lysophospholipids; Molecular Targeted Therapy; Non-alcoholic Fatty Liver Disease; Phosphoric Monoester Hydrolases; Phosphotransferases (Alcohol Group Acceptor); Signal Transduction; Sphingosine

To investigate the therapeutic role of calorie-restricted diet (CR) and raspberry ketone (RK) in non-alcoholic fatty liver disease (NAFLD) and the implication of sphingosine kinase-1 (SphK1)/sphingosine-1-phosphate (S1P) and toll-like receptor 4 (TLR4) signalling.. NAFLD was induced by feeding rats high-fat-fructose-diet (HFFD) for 6 weeks. Rats were then randomly assigned to three groups (n = 6 each); NAFLD group continued on HFFD for another 8 weeks. CR group was switched to CR diet (25% calorie restriction) for 8 weeks and RK group was switched to normal diet and received RK (55 mg/kg/day; orally) for 8 weeks. Another six rats were used as normal control.. HFFD induced a state of NAFLD indicated by increased fat deposition in liver tissue along with dyslipidemia, elevated liver enzymes, oxidative stress and inflammation. Either CR diet or RK reversed these changes and decreased HFFD-induced elevation of hepatic SphK1, S1P, S1PR1 and TLR4. Of notice, RK along with a normal calorie diet was even better than CR alone in most studied parameters.. SphK1/S1P and TLR4 are interconnected and related to the establishment of HFFD-induced NAFLD and can be modulated by RK. Supplementation of RK without calorie restriction to patients with NAFLD unable to follow CR diet to achieve their treatment goals would be a promising therapeutic modality.

Topics: Animals; Diet, High-Fat; Liver; Non-alcoholic Fatty Liver Disease; Phosphates; Rats; Sphingosine; Toll-Like Receptor 4

Nonalcoholic fatty liver disease (NAFLD) is characterized by an increase in hepatic lipid accumulation due to impaired lipid metabolism. Although a correlation was found between NAFLD and sphingosine-1-phosphate (S1P), the role of the sphingolipid remains controversial. The aim of this study was to investigate any involvement of S1P in steatosis using its analog FTY720P and HepG2 cells. Lipid accumulation was induced by incubating the cells in a mixture of oleic and palmitic acid, and was quantified using Oil Red O. The involvement of signaling mediators was studied using pharmacological inhibitors and western blot analysis. FTY720P increased lipid accumulation, but this increase wasn't maintained in the presence of inhibitors of S1PR3, Gq, SREBP, mTOR, PI3K, and PPARγ indicating their involvement in the process. The results revealed that FTY720P binds to S1PR3 which activates sequentially Gq, PI3K, and mTOR leading to an increase in SREBP expression and PPARγ activation. It was concluded that in presence of a high level of fatty acids, lipid accumulation is increased in hepatocytes by the exogenously added FTY720P.

Topics: Hep G2 Cells; Humans; Lipid Metabolism; Liver; Lysophospholipids; Non-alcoholic Fatty Liver Disease; Phosphatidylinositol 3-Kinases; PPAR gamma; Sterol Regulatory Element Binding Protein 1; TOR Serine-Threonine Kinases

Aberrant concentration, structure and functionality of High Density Lipoprotein (HDL) are associated with many prevalent diseases, including cardiovascular disease and non-alcoholic fatty liver disease (NAFLD). Mice with liver-specific ablation of Hnf4α (H4LivKO) present steatosis and dyslipidemia by mechanisms that are not completely understood. The aim of this study was to explore the role of liver HNF4A in HDL metabolism and the development of steatosis.. Serum and tissue samples were obtained from 6-weeks old H4LivKO mice and their littermate controls. Liver and serum lipids were measured and HDL structure and functionality were assessed. Global gene expression changes in the liver were analyzed by expression arrays, validations were performed by RT-qPCR and DNA-protein interactions were studied by chromatin immunoprecipitation (ChIP). H4LivKO mice presented liver steatosis, increased liver triglyceride content and decreased concentration of serum total cholesterol, HDL cholesterol, triglycerides, phospholipids and cholesteryl esters. Most classes of phospholipids showed significant changes in species ratio and sphingosine-1-phosphate (S1P) levels were reduced. H4LivKO serum was enriched in the smaller, denser HDL particles, devoid of APOA2 and APOM apolipoproteins, exhibiting decreased activity of paraoxonase-1 but retaining macrophage cholesterol efflux capacity and phospho-AKT activation in endothelial cells. Global gene expression analysis revealed the association of liver HNF4A with known and novel regulators of HDL metabolism as well as NAFLD-susceptibility genes.. HNF4A ablation in mouse liver causes hepatic steatosis, perturbations in HDL structure and function and significant global changes in gene expression. This study reveals new targets of HNF4A involved in HDL metabolism and the development of steatosis and enriches our knowledge on HDL functionality in NAFLD.

Topics: Animals; Aryldialkylphosphatase; ATP Binding Cassette Transporter 1; Gene Expression Profiling; Hepatocyte Nuclear Factor 4; Lipid Metabolism; Lipoproteins, HDL; Lysophospholipids; Mice; Mice, Knockout; Non-alcoholic Fatty Liver Disease; Sphingosine

Nonalcoholic fatty liver (NAFL) is emerging as a leading risk factor of hepatic ischemia/reperfusion (I/R) injury lacking of effective therapy. Lipid dyshomeostasis has been implicated in the hepatopathy of NAFL. Herein, we investigate the bioactive lipids that critically regulate I/R injury in NAFL.. Lipidomics were performed to identify dysregulated lipids in mouse and human NAFL with I/R injury. The alteration of corresponding lipid-metabolizing genes was examined. The effects of the dysregulated lipid metabolism on I/R injury in NAFL were evaluated in mice and primary hepatocytes.. Sphingolipid metabolic pathways responsible for the generation of sphingosine-1-phosphate (S1P) were uncovered to be substantially activated by I/R in mouse NAFL. Sphingosine kinase 1 (Sphk1) was found to be essential for hepatic S1P generation in response to I/R in hepatocytes of NAFL mice. Sphk1 knockdown inhibited the hepatic S1P rise while accumulating ceramides in hepatocytes of NAFL mice, leading to aggressive hepatic I/R injury with upregulation of oxidative stress and increase of reactive oxygen species (ROS). In contrast, administration of exogenous S1P protected hepatocytes of NAFL mice from hepatic I/R injury. Clinical study revealed a significant activation of S1P generation by I/R in liver specimens of NAFL patients. In vitro studies on the L02 human hepatocytes consolidated that inhibiting the generation of S1P by knocking down SPHK1 exaggerated I/R-induced damage and oxidative stress in human hepatocytes of NAFL.. Generation of S1P by SPHK1 is important for protecting NAFL from I/R injury, which may serve as therapeutic targets for hepatic I/R injury in NAFL.

Topics: Animals; Hepatocytes; Humans; Ischemia; Lysophospholipids; Mice; Non-alcoholic Fatty Liver Disease; Phosphotransferases (Alcohol Group Acceptor); Reactive Oxygen Species; Reperfusion Injury; Signal Transduction; Sphingosine

Nonalcoholic fatty liver disease is a progressive disease involving the accumulation of lipid droplets in the liver. In this study, we investigated the anti-hepatosteatosis effects of fermented

Topics: Animals; Cell Line; Cordyceps; Fatty Acids; Fermentation; Hepatocytes; Humans; Lysophospholipids; Mice; Non-alcoholic Fatty Liver Disease; Oxidation-Reduction; Pediococcus pentosaceus; Phosphotransferases (Alcohol Group Acceptor); Plant Extracts; Sphingosine; Stearoyl-CoA Desaturase

Renin-angiotensin-aldosterone system (RAS) has been implicated in non-alcoholic fatty liver disease (NAFLD); the most common cause of chronic liver diseases. There is accumulating evidence that altered TLR4 and Sphingosine kinase 1(SphK1)/sphingosine1phosphate (S1P) signaling pathways are key players in the pathogenesis of NAFLD. Cross talk of the sphingosine signaling pathway, toll-4 (TLR4) receptors, and angiotensin II was reported in various tissues. Therefore, the aim of this study was to define the contribution of these two pathways to the hepatoprotective effects of telmisartan and/or chlorogenic acid (CGA) in NAFLD. CGA is a strong antioxidant that was previously reported to inhibit angiotensin converting enzyme. Male Wistar rats were treated with either high-fructose, with or without telmisartan, CGA, telmisartan + CGA for 8 weeks. Untreated NAFL rats showed characteristics of NAFLD, as evidenced by significant increase in the body weight, insulin resistance, and serum hepatotoxicity markers (Alanine and Aspartate transaminases) and lipids as compared to the negative control group, in addition to characteristic histopathological alterations. Treatment with either telmisartan and/or CGA improved aforementioned parameters, in addition to upregulation of antioxidant enzymes (Superoxide dismutase and Glutathione peroxidase). Effect of inhibiting RAS on both sphingosine pathway and TLR4 was evident by the suppressing effect of telmisartan and/or CGA on high fructose-induced upregulation of hepatic SPK1 and S1P, in addition to concomitant up-regulation of Sphingosine-1-Phosphate receptor (S1PR)3 protein level and increased expression of S1PR1 and TLR4. As TLR4 and SPK/S1P signaling pathways play important roles in the progression of liver inflammation, the effect on sphingosine pathway and TLR4 was associated with decreased concentrations of inflammatory markers, enzyme kB kinase (IKK), nuclear factor-kB and tumor necrosis factor-α as compared to untreated NAFL group. In conclusion, the present data strongly suggests the cross-talk between angiotensin, the Sphingosine SPK/S1P Axis and TLR4 Receptors, and their role in the pathogenesis of fructose-induced NAFLD, and the protection afforded by drugs inhibiting RAS.

Topics: Angiotensin II Type 1 Receptor Blockers; Angiotensins; Animals; Chlorogenic Acid; Drug Therapy, Combination; Fructose; Lysophospholipids; Male; Non-alcoholic Fatty Liver Disease; Phosphotransferases (Alcohol Group Acceptor); Rats; Rats, Wistar; Signal Transduction; Sphingosine; Telmisartan; Toll-Like Receptor 4

Nonalcoholic fatty liver disease (NAFLD), a leading cause of liver dysfunction, is a metabolic disease that begins with steatosis. Sphingolipid metabolites, particularly ceramide and sphingosine-1-phosphate (S1P), have recently received attention for their potential roles in insulin resistance and hepatic steatosis. FTY720/fingolimod, a prodrug for the treatment of multiple sclerosis, is phosphorylated in vivo to its active phosphorylated form by sphingosine kinase 2 and has been shown to interfere with the actions of S1P and to inhibit ceramide biosynthesis. Therefore, in this study we investigated the effects of FTY720 in a diet-induced animal model of NAFLD (DIAMOND) that recapitulates the hallmarks of the human disease. The oral administration of FTY720 to these mice fed a high-fat diet and sugar water improved glucose tolerance and reduced steatosis. In addition to decreasing liver triglycerides, FTY720 also reduced hepatic sphingolipid levels, including ceramides, monohexosylceramides, and sphingomyelins, particularly the C16:0 and C24:1 species, as well as S1P and dihydro-S1P. FTY720 administration decreased diet-induced fatty acid synthase (FASN) expression in DIAMOND mice without affecting other key enzymes in lipogenesis. FTY720 had no effect on the expression of SREBP-1c, which transcriptionally activates FASN. However, in agreement with the notion that the active phosphorylated form of FTY720 is an inhibitor of histone deacetylases, FTY720-P accumulated in the liver, and histone H3K9 acetylation was markedly increased in these mice. Hence, FTY720 might be useful for attenuating FASN expression and triglyceride accumulation associated with steatosis.

Topics: Acetylation; Animals; Diet, High-Fat; Fatty Acid Synthases; Female; Fingolimod Hydrochloride; Immunoblotting; Insulin Resistance; Liver; Lysophospholipids; Male; Mice; Mice, Inbred C57BL; Non-alcoholic Fatty Liver Disease; Organophosphates; Sphingolipids; Sphingosine; Triglycerides

Topics: Animals; Cell Line; Chemotaxis; Diet, Atherogenic; Diet, Carbohydrate Loading; Diet, High-Fat; Disease Models, Animal; Extracellular Vesicles; Gene Knockout Techniques; Hepatocytes; Humans; Liver; Lysophospholipids; Macrophages; Male; Mice; Mice, Inbred C57BL; Non-alcoholic Fatty Liver Disease; Palmitic Acid; Receptors, Lysosphingolipid; Sphingosine; Sphingosine-1-Phosphate Receptors

Nonalcoholic steatohepatitis (NASH) is a lipotoxic disease wherein activation of endoplasmic reticulum (ER) stress response and macrophage-mediated hepatic inflammation are key pathogenic features. However, the lipid mediators linking these two observations remain elusive. We postulated that ER stress-regulated release of pro-inflammatory extracellular vesicles (EVs) from lipotoxic hepatocytes may be this link. EVs were isolated from cell culture supernatants of hepatocytes treated with palmitate (PA) to induce lipotoxic ER stress, characterized by immunofluorescence, Western blotting, electron microscopy, and nanoparticle tracking analysis. Sphingolipids were measured by tandem mass spectrometry. EVs were employed in macrophage chemotaxis assays. PA induced significant EV release. Because PA activates ER stress, we used KO hepatocytes to demonstrate that PA-induced EV release was mediated by inositol requiring enzyme 1α (IRE1α)/X-box binding protein-1. PA-induced EVs were enriched in C16:0 ceramide in an IRE1α-dependent manner, and activated macrophage chemotaxis via formation of sphingosine-1-phosphate (S1P) from C16:0 ceramide. This chemotaxis was blocked by sphingosine kinase inhibitors and S1P receptor inhibitors. Lastly, elevated circulating EVs in experimental and human NASH demonstrated increased C16:0 ceramide. PA induces C16:0 ceramide-enriched EV release in an IRE1α-dependent manner. The ceramide metabolite, S1P, activates macrophage chemotaxis, a potential mechanism for the recruitment of macrophages to the liver under lipotoxic conditions.

Topics: Cells, Cultured; Ceramides; Endoplasmic Reticulum Stress; Endoribonucleases; Extracellular Vesicles; Hepatocytes; Humans; Inflammation; Inositol; Lysophospholipids; Macrophages; Non-alcoholic Fatty Liver Disease; Palmitates; Protein Serine-Threonine Kinases; Sphingosine

Ectopic lipid accumulation in hepatocytes has been identified as a risk factor for the progression of liver fibrosis and is strongly associated with obesity. In particular, the saturated fatty acid palmitate is involved in initiation of liver fibrosis via formation of secondary metabolites by hepatocytes that in turn activate hepatic stellate cells (HSCs) in a paracrine manner.. α-smooth muscle actin-expression (α-SMA) as a marker of liver fibrosis was investigated via western blot analysis and immunofluorescence microscopy in HSCs (LX-2). Sphingolipid metabolism and the generation of the bioactive secondary metabolite sphingosine 1-phosphate (S1P) in response to palmitate were analyzed by LC-MS/MS in hepatocytes (HepG2). To identify the molecular mechanism involved in the progression of liver fibrosis real-time PCR analysis and pharmacological modulation of S1P receptors were performed.. Palmitate oversupply increased intra- and extracellular S1P-concentrations in hepatocytes. Conditioned medium from HepG2 cells initiated fibrosis by enhancing α-SMA-expression in LX-2 in a S1P-dependent manner. In accordance, fibrotic response in the presence of S1P was also observed in HSCs. Pharmacological inhibition of S1P receptors demonstrated that S1P3 is the crucial receptor subtype involved in this process.. S1P is synthesized in hepatocytes in response to palmitate and released into the extracellular environment leading to an activation of HSCs via the S1P3 receptor.

Topics: Actins; Culture Media, Conditioned; Hep G2 Cells; Hepatic Stellate Cells; Hepatocytes; Humans; Liver Cirrhosis; Lysophospholipids; Non-alcoholic Fatty Liver Disease; Palmitates; Receptors, Lysosphingolipid; Sphingosine