Elevated plasma sphingomyelin (d18:1/22:0) is closely related to hepatic steatosis in patients with chronic hepatitis C virus infection

Virus infection and sphingolipid metabolism

Cellular sphingolipids have vital roles in human virus replication and spread as they are exploited by viruses for cell entry, membrane fusion, genome replication, assembly, budding, and propagation. Intracellular sphingolipid biosynthesis triggers conformational changes in viral receptors and facilitates endosomal escape. However, our current understanding of how sphingolipids precisely regulate viral replication is limited, and further research is required to comprehensively understand the relationships between viral replication and endogenous sphingolipid species. Emerging evidence now suggests that targeting and manipulating sphingolipid metabolism enzymes in host cells is a promising strategy to effectively combat viral infections. Additionally, serum sphingolipid species and concentrations could function as potential serum biomarkers to help monitor viral infection status in different patients. In this work, we comprehensively review the literature to clarify how viruses exploit host sphingolipid metabolism to accommodate viral replication and disrupt host innate immune responses. We also provide valuable insights on the development and use of antiviral drugs in this area.

The potential serum sphingolipid biomarkers for distinguishing Wilson disease

BACKGROUND

The diagnosis of Wilson's disease (WD) remains a challenging endeavor in clinical practice. Serum sphingolipids play a significant role in the development of liver disease. In this study, we examined the serum sphingolipid profile in patients with WD and explored the potential diagnostic utility of serum sphingolipid metabolites. These metabolites may aid in distinguishing WD patients from healthy controls and identifying those with a risk of cirrhosis.

METHODS

This study consecutively enrolled 26 WD patients and 88 healthy controls. We utilized high-performance liquid chromatography-tandem mass spectrometry to analyze a panel of 88 serum sphingolipid metabolites. The data were analyzed by multivariate statistical methods.

RESULTS

Among the 88 sphingolipids metabolites analyzed, 17 sphingolipids were observed significant differences between WD and HC groups (all P < 0.05). Notably, five sphingolipids, namely S1P (d18:1), Cer (d18:2/21:0), SM41:2, sph(d18:1), and Cer (d18:2/22:0), each with an AUC exceeding 0.9, emerged as potential biomarkers for WD. Additionally, in the comparison between WD patients with and without cirrhosis, 24 sphingolipid metabolites exhibited significant differences (all P < 0.05). We identified Cer(d18:1/20:0), Cer(d18:2/22:0), Cer(d18:2/24:0), Cer(d18:2/20:0), and Cer(d18:2/18:0), each with an AUC exceeding 0.9, as potential serological markers for WD patients with cirrhosis.

CONCLUSION

For enhanced clinical applicability, we propose considering Cer (d18:2/22:0) as a predictive marker applicable to both WD patients and their susceptibility to cirrhosis. This particular ceramide has exhibited strong diagnostic and predictive performance. These findings have the potential to facilitate non-invasive WD diagnosis.

NAFLD, MAFLD, and beyond: one or several acronyms for better comprehension and patient care

The term non-alcoholic fatty liver disease (NAFLD) has rapidly become the most common type of chronic liver disease. NAFLD points to excessive hepatic fat storage and no evidence of secondary hepatic fat accumulation in patients with "no or little alcohol consumption". Both the etiology and pathogenesis of NAFLD are largely unknown, and a definitive therapy is lacking. Since NAFLD is very often and closely associated with metabolic dysfunctions, a consensus process is ongoing to shift the acronym NAFLD to MAFLD, i.e., metabolic-associated fatty liver disease. The change in terminology is likely to improve the classification of affected individuals, the disease awareness, the comprehension of the terminology and pathophysiological aspects involved, and the choice of more personalized therapeutic approaches while avoiding the intrinsic stigmatization due to the term "non-alcoholic". Even more recently, other sub-classifications have been proposed to concentrate the heterogeneous causes of fatty liver disease under one umbrella. While awaiting additional validation studies in this field, we discuss the main reasons underlying this important shift of paradigm.

Gender-Specific Differences in Serum Sphingomyelin Species in Patients with Hepatitis C Virus Infection-Sphingomyelin Species Are Related to the Model of End-Stage Liver Disease (MELD) Score in Male Patients

Hepatitis C virus (HCV) replication depends on cellular sphingomyelin (SM), but serum SM composition in chronic HCV infection has been hardly analyzed. In this work, 18 SM species could be quantified in the serum of 178 patients with chronic HCV infection before therapy with direct-acting antivirals (DAAs) and 12 weeks later, when therapy was completed. Six SM species were higher in the serum of females than males before therapy and nine at the end of therapy; thus, sex-specific analysis was performed. Type 2 diabetes was associated with lower serum levels of SM 36:2;O2 and 38:2;O2 in men. Serum SM species did not correlate with the viral load in both sexes. Of note, three SM species were lower in males infected with HCV genotype 3 in comparison to genotype 1 infection. These SM species normalized after viral cure. SM 38:1;O2, 40:1;O2, 41:1;O2, and 42:1;O2 (and, thus, total SM levels) were higher in the serum of both sexes at the end of therapy. In males, SM 39:1;O2 was induced in addition, and higher levels of all of these SM species were already detected at 4 weeks after therapy has been started. Serum lipids are related to liver disease severity, and in females 15 serum SM species were low in patients with liver cirrhosis before initiation of and after treatment with DAAs. The serum SM species did not correlate with the model of end-stage liver disease (MELD) score in the cirrhosis and the non-cirrhosis subgroups in females. In HCV-infected male patients, nine SM species were lower in the serum of patients with cirrhosis before DAA treatment and eleven at the end of the study. Most of the SM species showed strong negative correlations with the MELD score in the male cirrhosis patients before DAA treatment and at the end of therapy. Associations of SM species with the MELD score were not detected in the non-cirrhosis male subgroup. In summary, the current analysis identified sex-specific differences in the serum levels of SM species in HCV infection, in liver cirrhosis, and during DAA therapy. Correlations of SM species with the MELD score in male but not in female patients indicate a much closer association between SM metabolism and liver function in male patients.

Synergistic and Detrimental Effects of Alcohol Intake on Progression of Liver Steatosis

Nonalcoholic fatty liver disease (NAFLD) and alcoholic liver disease (ALD) are the most common liver disorders worldwide and the major causes of non-viral liver cirrhosis in the general population. In NAFLD, metabolic abnormalities, obesity, and metabolic syndrome are the driving factors for liver damage with no or minimal alcohol consumption. ALD refers to liver damage caused by excess alcohol intake in individuals drinking more than 5 to 10 daily units for years. Although NAFLD and ALD are nosologically considered two distinct entities, they show a continuum and exert synergistic effects on the progression toward liver cirrhosis. The current view is that low alcohol use might also increase the risk of advanced clinical liver disease in NAFLD, whereas metabolic factors increase the risk of cirrhosis among alcohol risk drinkers. Therefore, special interest is now addressed to individuals with metabolic abnormalities who consume small amounts of alcohol or who binge drink, for the role of light-to-moderate alcohol use in fibrosis progression and clinical severity of the liver disease. Evidence shows that in the presence of NAFLD, there is no liver-safe limit of alcohol intake. We discuss the epidemiological and clinical features of NAFLD/ALD, aspects of alcohol metabolism, and mechanisms of damage concerning steatosis, fibrosis, cumulative effects, and deleterious consequences which include hepatocellular carcinoma.

Intestinal Barrier and Permeability in Health, Obesity and NAFLD

The largest surface of the human body exposed to the external environment is the gut. At this level, the intestinal barrier includes luminal microbes, the mucin layer, gastrointestinal motility and secretion, enterocytes, immune cells, gut vascular barrier, and liver barrier. A healthy intestinal barrier is characterized by the selective permeability of nutrients, metabolites, water, and bacterial products, and processes are governed by cellular, neural, immune, and hormonal factors. Disrupted gut permeability (leaky gut syndrome) can represent a predisposing or aggravating condition in obesity and the metabolically associated liver steatosis (nonalcoholic fatty liver disease, NAFLD). In what follows, we describe the morphological-functional features of the intestinal barrier, the role of major modifiers of the intestinal barrier, and discuss the recent evidence pointing to the key role of intestinal permeability in obesity/NAFLD.

Transcriptomic Analysis Reveals the Protective Effects of Empagliflozin on Lipid Metabolism in Nonalcoholic Fatty Liver Disease

Empagliflozin is a novel type of sodium-glucose cotransporter two inhibitor with diverse beneficial effects in the treatment of nonalcoholic fatty liver disease (NAFLD). Although empagliflozin impacts NAFLD by regulating lipid metabolism, the underlying mechanism has not been fully elucidated. In this study, we investigated transcriptional regulation pathways affected by empagliflozin in a mouse model of NAFLD. In this study, NAFLD was established in male C57BL/6J mice by administration of a high-fat diet; it was then treated with empagliflozin and whole transcriptome analysis was conducted. Gene expression levels detected by transcriptome analysis were then verified by quantitative real-time polymerase chain reaction, protein levels detected by Western Blot. Differential expression genes screened from RNA-Seq data were enriched in lipid metabolism and synthesis. The Gene Set Enrichment Analysis (GSEA) results showed decreased lipid synthesis and improved lipid metabolism. Empagliflozin improved NAFLD through enhanced triglyceride transfer, triglyceride lipolysis and microsomal mitochondrial β-oxidation. This study provides new insights concerning the mechanisms by which sodium-glucose cotransporter two inhibitors impact NAFLD, particularly in terms of liver lipid metabolism. The lipid metabolism-related genes identified in this experiment provide robust evidence for further analyses of the mechanism by which empagliflozin impacts NAFLD.

Glucosylceramide synthase regulates hepatocyte repair after concanavalin A-induced immune-mediated liver injury

BACKGROUND

Sphingolipids produce pleiotropic signaling pathways, and participate in the pathological mechanism of hepatocyte apoptosis and necrosis during liver injury. However, the role of glucosylceramide synthase (GCS)-key enzyme that catalyzes the first glycosylation step, in liver injury is still vague.

METHODS

All experiments were conducted using 7-9-week-old pathogen-free male C57BL/6 mice. Serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels were detected in murine models of liver disease, in addition to histological characterization of liver injuries. Quantitative real-time polymerase chain reaction (qRT-PCR) was used to detect the relative expression of the GCS, matrix metallopeptidase-1 (MMP-1), and tissue inhibitor of metalloproteinase-1 (TIMP-1) genes. The GCS was observed through a fluorescence microscope, and the flow cytometry was used to detect hepatocyte apoptosis. The concentrations of serum IL-4, IL-6, and IL-10 were measured using enzyme-linked immune-sorbent assay (ELISA) kit. MMP-1 and TIMP-1 protein expression was measured via western blot (WB) analysis.

RESULTS

Con A is often used as a mitogen to activate T lymphocytes and promote mitosis. A single dose of Con A injected intravenously will cause a rapid increase of ALT and AST, which is accompanied by the release of cytokines that cause injury and necrosis of hepatocytes. In this study, we successfully induced acute immune hepatitis in mice by Con A. Con A administration resulted in GCS upregulation in liver tissues. Moreover, the mice in the Con A group had significantly higher levels of ALT, AST, IL-4, IL-6, IL-10 and increased hepatocyte apoptosis than the control group. In contrast, all of the aforementioned genes were significantly downregulated after the administration of a GCS siRNA or Genz-123346 (i.e., a glucosylceramide synthase inhibitor) to inhibit the GCS gene. Additionally, the histopathological changes observed herein were consistent with our ALT, AST, IL-4, IL-6, and IL-10 expression results. However, unlike this, hepatocyte apoptosis has been further increased on the basis of the Con A group. Moreover, our qRT-PCR and WB results indicated that the expression of MMP-1 in the Con A group was significantly lower than that in the control group, whereas TIMP-1 exhibited the opposite trend. Conversely, MMP-1 expression in the GCS siRNA and Genz-123346 groups was higher than that in the Con A group, whereas TIMP-1 expression was lower.

CONCLUSIONS

GCS inhibition reduces Con A-induced immune-mediated liver injury in mice, which may be due to the involvement of GCS in the hepatocyte repair process after injury.

Invariant natural killer T cells: Not to be ignored in liver disease

The liver is an important immune organ. Hepatocellular injury can be caused by many factors, which further leads to chronic liver diseases by activating the immune system. Multiple immune cells, such as T lymphocytes, B lymphocytes, natural killer cells (NKs), natural killer T cells (NKTs), and γδT cells, accumulate and participate in the immune regulation of the liver. NKTs are an indispensable component of immune cells in the liver, and invariant natural killer T cells (iNKTs) are the main subpopulation of NKTs. iNKTs activated by glycolipid antigen presented on CD1d secrete a series of cytokines and also act on other immune cells through cell-to-cell contact. Studies on the relationship between iNKTs and liver immunity have provided clues to uncover the pathogenesis of liver diseases and develop a promising strategy for the diagnosis and treatment of liver diseases.

Sphingomyelinases and Liver Diseases

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

Cholesterol and Phospholipid Distribution Pattern in the Erythrocyte Membrane of Patients with Hepatitis C and Severe Fibrosis, before and after Treatment with Direct Antiviral Agents: A pilot Study

Objectives: Hepatitis C virus requires and induces changes in liver lipidome for its life cycle. In addition, alterations in plasma and erythrocyte lipidome are observed during a range of chronic liver diseases. Methods: A total of six subjects (three males and three females) were included in our study. All subjects were HCV positive according to virus RNA detection. Erythrocyte ghosts were prepared from blood and collected upon diagnosis and also at the end of the treatment with Direct Antiviral Agents (DAA). Lipids were extracted from the erythrocyte ghosts, and cholesterol and phospholipids were analyzed by thin layer chromatography. A semi-quantitative estimation of cholesterol (CHOL), phosphatidylethanolamine (PE), phosphatidylinositol (PI), phosphatidylserine (PS), phosphatidylcholine (PC) and sphingomyelin (SM) was performed by densitometric analysis of the chromatographs. Results: After the antiviral treatment, PE percentage decreased, whereas the PC/PE and CHOL/PE ratio increased significantly. There were also other weaker differences for CHOL, PI, PS, PC and SM. Before DAA there was a very weak correlation between ALT and PC/PE ratio. In contrast, there was a steep negative correlation between these two parameters after DAA. Conclusion: Red blood cell lipid composition and especially the PC/PE ratio could be a candidate real time biological marker for inflammation resolution during hepatitis C treatment.

Upregulation of Serum Sphingosine (d18:1)-1-P Potentially Contributes to Distinguish HCC Including AFP-Negative HCC From Cirrhosis

BACKGROUND

Serum sphingolipids are widely involved in the development of hepatocellular carcinoma (HCC). We investigated the serum sphingolipid profile in patients with HCC or cirrhosis and explored the potential diagnostic efficiency of serum sphingolipid metabolites which may be helpful in differentiating HCC including α-fetoprotein (AFP)-negative HCC from cirrhosis.

METHODS

Seventy-two HCC patients (including 24 AFP-negative HCC) and 104 cirrhotic patients were consecutively enrolled in this study. High-performance liquid chromatography-tandem mass spectrometry was used to detect a panel of 57 serum sphingolipid metabolites.

RESULTS

Twenty-four sphingolipid metabolites showed significant differences between HCC and cirrhotic patients (all P < 0.05). Sphingosine (d18:1)-1-P was found to have the potential to differentiate HCC from cirrhosis by orthogonal partial least squares discriminant analysis (OPLS-DA). There was no significant difference in the efficacy of Sphingosine (d18:1)-1-P and AFP to distinguish HCC from cirrhosis, and the area under the receiver operating curve (AUC) were 0.85 and 0.83 (P > 0.05), respectively. When the cut-off value of Sphingosine (d18:1)-1-P was set at 56.29 pmol/0.1 ml, the sensitivity and specificity were 79.20% and 78.70%, respectively. Notably, the upregulation of Sphingosine (d18:1)-1-P could also distinguish AFP-negative HCC from cirrhosis with an AUC of 0.79. The sensitivity and specificity were 62.50% and 77.90% at a cut-off value of 56.29 pmol/0.1 ml. Spearman rank correlation analysis revealed that serum Sphingosine (d18:1)-1-P was not correlated with AFP in patients with cirrhosis, AFP-positive HCC, and AFP-negative HCC. Moreover, the difference in the diagnostic efficiency of serum Sphingosine (d18:1)-1-P was not statistically significant between tumor size (≤2 cm vs. >2 cm, P = 0.476). Also, there was no difference among patients with different TNM stages and BCLC stages.

CONCLUSION

The upregulation of serum Sphingosine (d18:1)-1-P exhibits good diagnostic performance for HCC. Particularly, Sphingosine (d18:1)-1-P could also serve as a biomarker for the diagnosis of AFP-negative HCC. These findings may contribute to the non-invasive diagnosis of HCC including AFP-negative HCC.

The protection of indolealkylamines from LPS-induced inflammation in zebrafish

ETHNOPHARMACOLOGICAL RELEVANCE

Toad skin came from Bufo bufo gargarizans Cantor and Bufo melanostictus Schneider. As the traditional Chinese medicine, it had the effect of clearing away heat and detoxification. In traditional applications, toad skin was often used for the treatment of cancer and inflammation. Total indolealkylamines (IAAs) from this medicine were proved the main compounds exert anti-inflammatory activity in our previous research.

AIM OF THE STUDY

In the present study, we aimed to investigate the potential mechanism of anti-inflammatory activity of IAAs on LPS induced zebrafish.

MATERIALS AND METHODS

LPS induced zebrafish was applicated as an in vivo inflammation model to clarify the structure-activity relationship of 4 major IAAs (N-methyl serotonin, bufotenine, dehydrobufotenine and bufothionine) from toad skin. Quantitative RT-PCR was applied to detect key cytokines and members of the MyD88-dependent signaling pathway. In addition, the targeted lipidomics was conducted to find out the potential biomarkers in the inflammatory zebrafish. Network pharmacology was used to unveil the main enzymes closely related to the target lipids.

RESULTS

Our results showed that the anti-inflammatory activity of free IAAs (N-methyl serotonin, bufotenine and dehydrobufotenine) was more potent than that of combined IAAs (bufothionine). RT-PCR demonstrated that 4 IAAs exerted antiendotoxin inflammatory effect via suppressing the TLR4/MyD88/NF-κB and TLR4/MyD88/MAPKs signaling pathway. A total of 33 possible inflammatory biomarkers, including 14 SM, 6 Cer, 11 PC and 2 GlcCer, triggered by LPS were screened out. The levels of most of candidates could be regulated toward a normal level by IAAs, especially in N-methyl serotonin and dehydrobufotenine groups. Enzymes especially LBP, PLA₂, CERK, SMPD and SGMS were found closely associated with the regulation of most lipid markers.

CONCLUSIONS

Overall, the mechanism underlying the anti-inflammatory activity of IAAs probably attributed to their capability to suppress NF-κB and MAPKs inflammatory pathway. Meanwhile, IAAs could also interfere the metabolism of SM, Cer and PC probably by regulating LBP, PLA₂, CERK, SMPD and SGMS.

Modulation of Lipid Metabolism by Celastrol

Hyperlipidemia, characterized by high serum lipids, is a risk factor for cardiovascular disease. Recent studies have identified an important role for celastrol, a proteasome inhibitor isolated from Tripterygium wilfordii Hook. F., in obesity-related metabolic disorders. However, the exact influences of celastrol on lipid metabolism remain largely unknown. Celastrol inhibited the terminal differentiation of 3T3-L1 adipocytes and decreased the levels of triglycerides in wild-type mice. Lipidomics analysis revealed that celastrol increased the metabolism of lysophosphatidylcholines (LPCs), phosphatidylcholines (PCs), sphingomyelins (SMs), and phosphatidylethanolamines (PEs). Further, celastrol reversed the tyloxapol-induced hyperlipidemia induced associated with increased plasma LPCs, PCs, SMs, and ceramides (CMs). Among these lipids, LPC(16:0), LPC(18:1), PC(22:2/15:0), and SM(d18:1/22:0) were also decreased by celastrol in cultured 3T3-L1 adipocytes, mice, and tyloxapol-treated mice. The mRNAs encoded by hepatic genes associated with lipid synthesis and catabolism, including Lpcat1, Pld1, Smpd3, and Sptc2, were altered in tyloxapol-induced hyperlipidemia, and significantly recovered by celastrol treatment. The effect of celastrol on lipid metabolism was significantly reduced in Fxr-null mice, resulting in decreased Cers6 and Acer2 mRNAs compared to wild-type mice. These results establish that FXR was responsible in part for the effects of celastrol in controlling lipid metabolism and contributing to the recovery of aberrant lipid metabolism in obesity-related metabolic disorders.

Alkaline sphingomyelinase (NPP7) in hepatobiliary diseases: A field that needs to be closely studied

Alkaline sphingomyelinase cleaves phosphocholine from sphingomyelin, platelet-activating factor, lysophosphatidylcholine, and less effectively phosphatidylcholine. The enzyme shares no structure similarities with acid or neutral sphingomyelinase but belongs to ecto-nucleotide pyrophosphatase/phosphodiesterase (NPP) family and therefore is also called NPP7 nowadays. The enzyme is expressed in the intestinal mucosa in many species and additionally in human liver. The enzyme in the intestinal tract has been extensively studied but not that in human liver. Studies on intestinal alkaline sphingomyelinase show that it inhibits colonic tumorigenesis and inflammation, hydrolyses dietary sphingomyelin, and stimulates cholesterol absorption. The review aims to summarize the current knowledge on liver alkaline sphingomyelinase in human and strengthen the necessity for close study on this unique human enzyme in hepatobiliary diseases.

Glucosylceramide synthase regulates the proliferation and apoptosis of liver cells in vitro by Bcl‑2/Bax pathway

Our previous study found that glucosylceramide, a type of sphingolipids, was associated with liver inflammation and fibrosis. Glucosylceramide is generated by glucosylceramide synthase (GCS), which is encoded by the UDP‑glucose ceramide glucosyltransferase (UGCG) gene. GCS is a key enzyme to regulate the physiological activity of cells. However, the role of GCS in hepatic cells remains unclear. The aim of the present study was to explore the mechanism of GCS in the proliferation and apoptosis of liver cells. Following the interference of expression of GCS in vitro by UGCG small interfering (si)RNA, the MTT method was performed to detect the proliferation of HL‑7702 hepatocytes, and ELISA was used to determine the concentration of tumor necrosis factor (TNF) α and cytochrome c in the supernatant of culture system. Fluorescence microscopy was used to observe the apoptosis of liver cells stained by Annexin V‑fluorescein isothiocyanate/propidium iodide. Reverse transcription‑quantitative polymerase chain reaction was used to detect the gene expression apoptosis regulator Bcl‑2 (Bcl‑2), apoptosis regulator Bax (Bax) and caspase-3. Western blot analysis was used to detect the expression of caspase-3 protein in the liver cells. Following treatment with UGCG siRNA for 24 h, the proliferation of HL‑7702 hepatocytes was significantly inhibited when compared with the transfection reagent group. Furthermore, the early and advanced apoptosis of liver cells showed an increasing trend. Additionally, concentrations of TNF α and cytochrome c showed no significant difference between the UGCG siRNA and transfection reagent groups. Compared with the transfection reagent group, Bcl‑2 mRNA expression decreased, and Bax and caspase-3 mRNA expression increased in the UGCG siRNA transfection group. The protein expression level of caspase-3 showed increased in hepatocytes following the treatment with UGCG siRNA. In conclusion, the metabolic changes of sphingolipids caused by the lack of GCS may be involved in the proliferation and apoptosis of liver cells through the Bcl‑2/Bax signaling pathway.

The lipid-sensor TREM2 aggravates disease in a model of LCMV-induced hepatitis

Lipid metabolism is increasingly being appreciated to affect immunoregulation, inflammation and pathology. In this study we found that mice infected with lymphocytic choriomeningitis virus (LCMV) exhibit global perturbations of circulating serum lipids. Mice lacking the lipid-sensing surface receptor triggering receptor expressed on myeloid cells 2 (Trem2 ^-/-) were protected from LCMV-induced hepatitis and showed improved virus control despite comparable virus-specific T cell responses. Non-hematopoietic expression of TREM2 was found to be responsible for aggravated hepatitis, indicating a novel role for TREM2 in the non-myeloid compartment. These results suggest a link between virus-perturbed lipids and TREM2 that modulates liver pathogenesis upon viral infection. Targeted interventions of this immunoregulatory axis may ameliorate tissue pathology in hepatitis.

Imbalance of plasma amino acids, metabolites and lipids in patients with lysinuric protein intolerance (LPI)

BACKGROUND

Lysinuric protein intolerance (LPI [MIM 222700]) is an aminoaciduria with defective transport of cationic amino acids in epithelial cells in the small intestine and proximal kidney tubules due to mutations in the SLC7A7 gene. LPI is characterized by protein malnutrition, failure to thrive and hyperammonemia. Many patients also suffer from combined hyperlipidemia and chronic kidney disease (CKD) with an unknown etiology.

METHODS

Here, we studied the plasma metabolomes of the Finnish LPI patients (n=26) and healthy control individuals (n=19) using a targeted platform for analysis of amino acids as well as two analytical platforms with comprehensive coverage of molecular lipids and polar metabolites.

RESULTS

Our results demonstrated that LPI patients have a dichotomy of amino acid profiles, with both decreased essential and increased non-essential amino acids. Altered levels of metabolites participating in pathways such as sugar, energy, amino acid and lipid metabolism were observed. Furthermore, of these metabolites, myo-inositol, threonic acid, 2,5-furandicarboxylic acid, galactaric acid, 4-hydroxyphenylacetic acid, indole-3-acetic acid and beta-aminoisobutyric acid associated significantly (P<0.001) with the CKD status. Lipid analysis showed reduced levels of phosphatidylcholines and elevated levels of triacylglycerols, of which long-chain triacylglycerols associated (P<0.01) with CKD.

CONCLUSIONS

This study revealed an amino acid imbalance affecting the basic cellular metabolism, disturbances in plasma lipid composition suggesting hepatic steatosis and fibrosis and novel metabolites correlating with CKD in LPI. In addition, the CKD-associated metabolite profile along with increased nitrite plasma levels suggests that LPI may be characterized by increased oxidative stress and apoptosis, altered microbial metabolism in the intestine and uremic toxicity.

Up-regulation of Plasma Hexosylceramide (d18: 1/18: 1) Contributes to Genotype 2 Virus Replication in Chronic Hepatitis C: A 20-Year Cohort Study

The aim of the present study was to explore the relationship between plasma sphingolipids and hepatitis C virus (HCV) replication in chronic hepatitis C (CHC) patients.A cohort of 120 treatment-naïve CHC patients was included. Liver biopsies and the Scheuer scoring system were used to assess hepatic inflammatory activity. Blood biochemical indicators, HCV-RNA load, and immunological markers were also measured. Forty-four plasma sphingolipids were identified and quantified using high-performance liquid chromatography-tandem mass spectrometry.The hexosylceramide (HexCer) (d18:1/18:1) level was significantly different between patients with a low HCV load (<10 IU/mL) and a high HCV load (≥10 IU/mL), and it was positively correlated with the HCV-RNA load (r = 0.337, P = 0.001) in CHC patients. Additionally, the plasma HexCer (d18:1/18:1) level (odds ratio 1.302, 95% confidence interval 1.129-1.502) was an independent factor for a high HCV-RNA load. For patients with hepatic inflammation grade ≤2 or HCV genotype 2, HexCer (d18:1/18:1) was independently related to a high HCV-RNA load.Plasma HexCer (d18:1/18:1) might be involved in the high viral replication level in chronic HCV infection, especially for CHC patients with genotype 2.

Nonalcoholic fatty liver disease and hepatic cirrhosis: Comparison with viral hepatitis-associated steatosis

Nonalcoholic fatty liver disease (NAFLD) including nonalcoholic steatohepatitis (NASH) is globally increasing and has become a world-wide health problem. Chronic infection with hepatitis B virus or hepatitis C virus (HCV) is associated with hepatic steatosis. Viral hepatitis-associated hepatic steatosis is often caused by metabolic syndrome including obesity, type 2 diabetes mellitus and/or dyslipidemia. It has been reported that HCV genotype 3 exerts direct metabolic effects that lead to hepatic steatosis. In this review, the differences between NAFLD/NASH and viral hepatitis-associated steatosis are discussed.

Rapid quantitative analysis of human serum sphingomyelin species using MALDI-TOF mass spectrometry with lipid hydrolase treatment

BACKGROUND

Sphingomyelin (SM) is a key component of extracellular membranes and lipoproteins, and plays roles in cell signaling and as a component of lipoproteins. SM species differ in terms of fatty acid (FA) composition. However, no simple, rapid, quantitative assay for identifying different SM species has yet been reported. In this study, lipid hydrolase treatment and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) were used to identify serum SM species.

METHODS

Sera were collected from healthy young individuals. To identify SM species, sera were treated with phospholipase A2 and lipoprotein lipase, and lipids were extracted using the standard chloroform/methanol (2/1 v/v) method.

RESULTS

We detected 15 peaks from serum using MALDI-TOF MS, which were assigned to SM species bound with FA components ranging from C15:0 to C24:2. The most prominent serum SM species was SM [C16:0], which accounted for approximately 26% of serum SM. Some SM species contained an odd-carbon FA (C15, C21, and C23), and these accounted for approximately 4% of serum SM. The reproducibility of major SM species within and between application positions on MS-sample plate was CV=3.0%-7.9% and CV=3.1%-6.8%, respectively. The concentration and dilution ratio were linearly related. The SM species composition of 10 healthy young subjects showed a similar profile.

CONCLUSIONS

We developed a rapid, and quantitative method for identifying serum SM species using lipid hydrolase treatment and MALDI-TOF MS. This method will be suitable for clinical laboratory studies to examine the associations between SM species and disease states.

Serum vitamin D₃ does not correlate with liver fibrosis in chronic hepatitis C

AIM

To investigate the relationship between serum vitamin D3 levels and liver fibrosis or inflammation in treatment-naive Chinese patients with chronic hepatitis C (CHC).

METHODS

From July 2010 to June 2011, we enrolled 122 CHC patients and 11 healthy controls from Dingxi city, Gansu Province, China. The patients were infected with Hepatitis C virus (HCV) during blood cell re-transfusion following plasma donation in 1992-1995, and had never received antiviral treatment. At present, all the patients except two underwent liver biopsy with ultrasound guidance. The Scheuer Scoring System was used to evaluate hepatic inflammation and the Metavir Scoring System was used to evaluate hepatic fibrosis. Twelve-hour overnight fasting blood samples were collected in the morning of the day of biopsy. Serum levels of alanine aminotransferase, aspartate aminotransferase, total bilirubin, direct bilirubin, cholinesterase, prothrombin activity, albumin, γ-glutamyl transpeptidase, hemoglobin, calcium and phosphorus were determined. Serum HCV RNA levels were measured by real-time PCR. Serum levels of 25-hydroxyvitamin D3 [25(OH)D3] and 24,25-dihydroxyvitamin D3 [24,25(OH)2D3] were measured by high-performance liquid chromatography tandem mass spectrometry.

RESULTS

Serum levels of 25(OH)D3 but not 24,25(OH)2D3 were significantly lower in CHC patients than in control subjects. Serum 25(OH)D3 levels did not correlate with liver fibrosis, inflammation, patient age, or levels of alanine aminotransferase, aspartate aminotransferase, total bilirubin, direct bilirubin, prothrombin activity, cholinesterase or HCV RNA. However, serum 25(OH)D3 levels did correlate with serum 24,25(OH)2D3 levels. Serum 25(OH)D3 and 24,25(OH)2D3 levels, and the 25(OH)D3/24,25(OH)2D3 ratio, have no difference among the fibrosis stages or inflammation grades.

CONCLUSION

We found that serum levels of 25(OH)D3 and its degradation metabolite 24,25(OH)2D3 did not correlate with liver fibrosis in treatment-naive Chinese patient with CHC.

Serum sphingomyelin has potential to reflect hepatic injury in chronic hepatitis B virus infection

OBJECTIVE

To explore the relation between serum sphingolipids and hepatic injury in chronic HBV infection.

METHODS

A cohort of participants including 48 healthy persons, 103 chronic HBV-infected patients containing chronic hepatitis B (CHB) and HBV-related cirrhosis were included. High performance liquid chromatography coupled to tandem mass spectrometry (HPLC-MS/MS) was performed to detect serum sphingolipids. The serological indicators were detected and quantified. The valid liver biopsy specimens were acquired from twenty five CHB.

RESULTS

Twenty four serum sphingolipids were detected. There were eighteen sphingolipids showing significant differences between the healthy control and chronic HBV infection groups. In patients with chronic HBV infection, fourteen sphingolipids differed significantly between CHB and HBV-related cirrhosis. Among sphingolipids with a significant difference in both HBV infection vs healthy control and CHB vs cirrhosis, seven sphingolipids were independently related to the presence of cirrhosis. SM(d18:1/24:0), a sphingomyelin (SM) compound, was found to have a negative correlation with model for end-stage liver disease (MELD) score. Additionally, SM(d18:1/24:0) was demonstrated to have a correlation with inflammation grades by liver biopsy in CHB patients.

CONCLUSIONS

Serum sphingolipids have close relation with hepatic injury in chronic HBV infection, especially that SM(d18:1/24:0) might be a potential serum biomarker.