Bile acids and sphingolipids in non-alcoholic fatty liver disease

Unveiling the Antiobesity Mechanism of Sweet Potato Extract by Microbiome, Transcriptome, and Metabolome Analyses in Mice

This study aimed to elucidate the antiobesity mechanisms of sweet potato extract (SPE) through biochemical, gut microbiome, liver transcriptome, and metabolome analyses. Administration of SPE to high-fat-diet-fed mice significantly reduced body weight gain, serum low-density lipoprotein cholesterol, hepatic lipid accumulation, and adipocyte hypertrophy, which were closely linked to gut microbiome composition. SPE notably increased the abundance of Eubacterium_coprostanoligenes_group_unclassified and decreased that of Kineothrix, both of which were strongly associated with short-chain fatty acid (SCFA) production. LC-QTOF-MS analysis identified resin glycoside compounds from SPE with reduced levels in mouse feces, suggesting their utilization in vivo. SPE also promoted dietary fat excretion. Liver transcriptomic and metabolomic profiling revealed that SPE may exert antiobesity effects by modulating the bile-sphingolipid metabolism, which was closely correlated with the reshaped gut microbiomes and SCFAs. These findings provide new insights into the antiobesity effects and mechanisms of SPE.

Transcriptomics, lipidomics, and single-nucleus RNA sequencing integration: exploring sphingolipids in MASH-HCC progression

BACKGROUND & AIMS

Metabolic dysfunction-associated steatotic liver disease (MASLD) encompasses various conditions, ranging from simple steatosis to metabolic dysfunction-associated steatohepatitis (MASH) and cirrhosis. MASLD is a significant risk factor for hepatocellular carcinoma (HCC) and is rapidly becoming the primary cause of liver transplantation. Dysregulated sphingolipid metabolism has been linked to the development of MASH-HCC. However, detailed insight into the sphingolipid profiles and cell type-specific changes in key genes involved in sphingolipid metabolism remains limited and forms the primary focus of this study.

APPROACHES & RESULTS

This study used the well-characterized diet-induced MASH-HCC mouse model (DIAMOND). Total RNA sequencing data, NanoString nCounter® Gene profiling, and single-nucleus RNA sequencing (snRNA-seq) GEO data (GSE225381) were used in characterizing gene regulation in MASH-HCC progression. Sphingolipids in the serum and liver were profiled using targeted lipidomics. RNA data analysis showed dysregulation of key genes involved in sphingolipid metabolism, including ceramide synthase 6 (Cers6), serine palmitoyltransferase long chain base subunit 2 (Sptlc2), sphingosine kinase 2 (SphK2), and sphingosine-1-phosphate receptor 1-3 (S1pr1-3) which paralleled significant changes in sphingolipid composition and levels in both serum and liver. Furthermore, TCGA-LIHC patient data were analyzed and potential prognostic genes for MASH-HCC were identified using univariate and multivariate Cox analysis. The multivariate Cox analysis underscored the prognostic significance of several genes related to sphingolipid metabolism, including CERS6, SPTLC2, and S1PR1.

CONCLUSION

Our findings provided valuable insights into the role of sphingolipids in the progression of MASH to HCC. Specific serum and liver sphingolipid profiles may serve as valuable biomarkers for diagnosis and prognosis in MASH-HCC.

Interplay among IL1R1, gut microbiota, and bile acids in metabolic dysfunction-associated steatotic liver disease: a comprehensive review

Metabolic dysfunction-associated steatotic liver disease (MASLD) is a prevalent metabolic disorder characterized by hepatic steatosis associated with metabolic abnormalities. Recent research has shed light on the intricate interplay among interleukin-1 receptor 1 (IL1R1), gut microbiota, and bile acids in the pathogenesis of MASLD. This review aims to provide a comprehensive overview of the current understanding of the role of IL1R1, gut microbiota, and bile acids in MASLD, exploring their interrelationships and potential mechanisms. We summarize the evidence supporting the involvement of IL1R1 in inflammation, discuss the influence of gut microbiota on bile acid metabolism and its influence on liver health, and elucidate the bidirectional interactions among IL1R1 signaling, gut microbiota composition, and bile acid homeostasis in MASLD. Furthermore, we highlight emerging therapeutic strategies targeting these interrelated pathways for the management of MASLD.

Sphingosine kinase 2 (SphK2) depletion alters redox metabolism and enhances inflammation in a diet-induced MASH mouse model

BACKGROUND

Sphingosine-1 phosphate (S1P) is a bioactive lipid molecule that modulates inflammation and hepatic lipid metabolism in MASLD, which affects 1 in 3 people and increases the risk of liver fibrosis and hepatic cancer. S1P can be generated by 2 isoforms of sphingosine kinase (SphK). SphK1 is well-studied in metabolic diseases. In contrast, SphK2 function is not well characterized. Both sphingolipid and redox metabolism dysregulation contribute to MASLD pathologic progression. While SphK2 localizes to both the nucleus and mitochondria, its specific role in early MASH is not well defined.

METHODS

This study examined SphK2 depletion effects on hepatic redox metabolism, mitochondrial function, and inflammation in a 16-week western diet plus sugar water (WDSW)-induced mouse model of early MASH.

RESULTS

WDSW-SphK2-/- mice exhibit increased hepatic lipid accumulation and hepatic redox dysregulation. In addition, mitochondria-localized cholesterol and S1P precursors were increased. We traced SphK2-/--mediated mitochondrial electron transport chain impairment to respiratory complex-IV and found that decreased mitochondrial redox metabolism coincided with increased oxidase gene expression and oxylipin production. Consistent with this relationship, we observed pronounced increases in hepatic inflammatory gene expression, prostaglandin accumulation, and innate immune homing in WDSW-SphK2-/- mice compared to WDSW-wild-type mice.

CONCLUSIONS

These studies suggest SphK2-derived S1P maintains hepatic redox metabolism and describe the potential consequences of SphK2 depletion on proinflammatory gene expression, lipid mediator production, and immune infiltration in MASH progression.

Gut microbiota and bile acids: Metabolic interactions and impacts on diabetic kidney disease

The intestinal microbiota comprises approximately 1013-1014 species of bacteria and plays a crucial role in host metabolism by facilitating various chemical reactions. Secondary bile acids (BAs) are key metabolites produced by gut microbiota.Initially synthesized by the liver, BA undergoes structural modifications through the activity of various intestinal microbiota enzymes, including eukaryotic, bacterial, and archaeal enzymes. These modified BA then activate specific receptors that regulate multiple metabolic pathways in the host, such as lipid and glucose metabolism, energy balance, inflammatory response, and cell proliferation and death. Recent attention has been given to intestinal flora disorders in diabetic kidney disease (DKD), where activation of BA receptors has shown promise in alleviating diabetic kidney damage by modulating renal lipid metabolism and mitochondrial production. Imbalances in the intestinal flora can influence the progression of DKD through the regulation of bile acid and its receptor pathways. This review aims to propose a mechanism involving the gut-BA-diabetes and nephropathy axes with the goal of optimizing new strategies for treating DKD.

Metabolomic profiling of human feces and plasma from extrauterine growth restriction infants

BACKGROUND

Extrauterine growth restriction (EUGR) affects a substantial proportion of preterm infants and may influence both short-term complications and long-term sequelae. While many preterm infants with EUGR are secondary to small for gestational age (SGA) or very low birth weight (VLBW), a subset of EUGR infants do not exhibit these conditions. The purpose of this study is to investigate the metabolic profiles and biomarkers of EUGR infants in the absence of SGA and VLBW.

METHODS

A total of 100 feces (n = 50) and plasma samples (n = 50) were collected from participants categorized as either EUGR (EUGR group) or non-EUGR (NonEUGR group) in the absence of SGA and VLBW. Metabolites were characterized via UPLC-MS/MS using the Discovery HD4® platform. Data normalization, partial least squares discriminant analysis (PLSDA), and KEGG enrichment analysis of metabolite profiles were performed using the MetaboAnalyst 6.0.

RESULTS

The clinical characteristics of preterm infants differed significantly between the EUGR and NonEUGR groups at discharge, including length of stay, weight Z-score, weight, height Z-score, height, head circumference, and fat-free mass. The PLSDA model exhibited clustering within groups and separation between groups. A total of 58 and 71 differential metabolites were identified in feces and plasma samples, respectively. They were involved in pathways such as caffeine, galactose, glutathione, cysteine, and methionine metabolisms. In the feces sample, 1-palmitoyl-galactosylglycerol exhibited a significant negative correlation with the growth characteristics of preterm infants, while 1-palmitoyl-2-palmitoleoyl-GPC displayed the opposite pattern. In plasma samples, androsterone glucuronide displayed a significant positive correlation with the growth characteristics of preterm infants, whereas 2-methoxyhydroquinone sulfate generated an opposite pattern. Moreover, 2-oleoylglycerol and sphinganine-1-phosphate exhibited the highest area under the curve in feces and plasma samples, respectively, according to diagnostic ROC curves.

CONCLUSION

Preterm infants with EUGR, in the absence of SGA and VLBW, exhibit specific clinical characteristics and metabolomic profiles. Sphinganine-1-phosphate and 2-oleoylglycerol may hold promise as diagnostic markers for EUGR in the absence of SGA and VLBW.

IMPACT

The objective of this study is to identify the differential metabolites in preterm infants with extrauterine growth restriction (EUGR) in the absence of small for gestational age (SGA) or very low birth weight (VLBW). Preterm infants with EUGR without SGA and VLBW exhibit specific clinical characteristics and metabolomic profiles. Sphinganine-1-phosphate and 2-oleoylglycerol emerged as potential diagnostic biomarkers for EUGR. This study enhances our understanding of the metabolomic profile in preterm infants with EUGR without SGA or VLBW. Our findings will offer valuable evidence for improving nutritional management and shedding light on the associated pathophysiological mechanisms of EUGR.

The mitochondrial translocator protein (TSPO, 18 kDa): A key multifunctional molecule in liver diseases

Translocator protein (TSPO, 18 kDa), previously known as peripheral-type benzodiazepine receptor, is an evolutionarily conserved and tryptophan-rich 169-amino-acid protein located on the outer mitochondrial membrane. TSPO plays a crucial role in various fundamental physiological functions and cellular processes. Its expression is altered in pathological conditions, thus rendering TSPO a potential tool for diagnostic imaging and an appealing therapeutic target. The investigation of synthetic TSPO ligands as both agonists and antagonists has provided valuable insights into the regulatory mechanisms and functional properties of TSPO. Recently, accumulating evidence has highlighted the significance of TSPO in liver diseases. However, a comprehensive summary of TSPO function in the normal liver and diverse liver diseases is lacking. This review aims to provide an overview of recent advances in understanding TSPO function in both normal liver cells and various liver diseases, with a particular emphasis on its involvement in liver fibrosis and inflammation and addresses the existing knowledge gaps in the field that require further investigation.

Increase in bile acids after sleeve gastrectomy improves metabolism by activating GPBAR1 to increase cAMP in mice with nonalcoholic fatty liver disease

BACKGROUND

Bile acids (BAs) concentration can affect metabolic improvement caused by bariatric surgery and BA concentrations increase in patients after sleeve gastrectomy (SG). Here, how BAs after SG affect metabolism in nonalcoholic fatty liver disease (NAFLD) was studied.

METHODS

Mice were given high-fat diet (HFD) to induce NAFLD and received SG surgery. Hepatic and fecal BA concentrations in mice were detected by liquid chromatography-tandem mass spectrometry method. BA-related genes were detected by quantitative real-time polymerase chain reaction. G protein BA receptor 1 (GPBAR1) expression was identified using western blot analysis. NAFLD mice after SG received GPBAR1 inhibitor Triamterene. The weight of mice and mice liver was detected. Mouse liver tissue was observed by hematoxylin-eosin and Oil Red O staining. Triglyceride (TG), nonesterified fatty acid (NEFA), and cyclic adenosine monophosphate (cAMP) levels in mouse liver tissue were analyzed by metabolic assay and enzyme-linked immune sorbent assay.

RESULTS

SG boosted increase in hepatic total/conjugated BAs and related genes and GPBAR1 expression, and attenuated increase in fecal total BAs/muricholic acid in HFD-induced mice and increased fecal taurine-BAs in HFD-induced mice. Triamterene (72 mg/kg) reversed the inhibitory role of SG in HFD-induced increase of body weight, lipid accumulation, inflammatory cell infiltration, and increase of hepatic weight and TG/NEFA content, and counteracted the positive role of SG in HFD-induced increase of hepatic cAMP concentration in mice.

CONCLUSIONS

BAs improve metabolism via activating GPBAR1 to increase cAMP in NAFLD mice after SG.

Therapeutic implications for sphingolipid metabolism in metabolic dysfunction-associated steatohepatitis

The prevalence of metabolic dysfunction-associated steatotic liver disease (MASLD), a leading cause of chronic liver disease, has increased worldwide along with the epidemics of obesity and related dysmetabolic conditions characterized by impaired glucose metabolism and insulin signaling, such as type 2 diabetes mellitus (T2D). MASLD can be defined as an excessive accumulation of lipid droplets in hepatocytes that occurs when the hepatic lipid metabolism is totally surpassed. This metabolic lipid inflexibility constitutes a central node in the pathogenesis of MASLD and is frequently linked to the overproduction of lipotoxic species, increased cellular stress, and mitochondrial dysfunction. A compelling body of evidence suggests that the accumulation of lipid species derived from sphingolipid metabolism, such as ceramides, contributes significantly to the structural and functional tissue damage observed in more severe grades of MASLD by triggering inflammatory and fibrogenic mechanisms. In this context, MASLD can further progress to metabolic dysfunction-associated steatohepatitis (MASH), which represents the advanced form of MASLD, and hepatic fibrosis. In this review, we discuss the role of sphingolipid species as drivers of MASH and the mechanisms involved in the disease. In addition, given the absence of approved therapies and the limited options for treating MASH, we discuss the feasibility of therapeutic strategies to protect against MASH and other severe manifestations by modulating sphingolipid metabolism.

Neutral Sphingomyelinase 2 Inhibition Limits Hepatic Steatosis and Inflammation

Non-alcoholic fatty liver disease (NAFLD) is manifested by hepatic steatosis, insulin resistance, hepatocyte death, and systemic inflammation. Obesity induces steatosis and chronic inflammation in the liver. However, the precise mechanism underlying hepatic steatosis in the setting of obesity remains unclear. Here, we report studies that address this question. After 14 weeks on a high-fat diet (HFD) with high sucrose, C57BL/6 mice revealed a phenotype of liver steatosis. Transcriptional profiling analysis of the liver tissues was performed using RNA sequencing (RNA-seq). Our RNA-seq data revealed 692 differentially expressed genes involved in processes of lipid metabolism, oxidative stress, immune responses, and cell proliferation. Notably, the gene encoding neutral sphingomyelinase, SMPD3, was predominantly upregulated in the liver tissues of the mice displaying a phenotype of steatosis. Moreover, nSMase2 activity was elevated in these tissues of the liver. Pharmacological and genetic inhibition of nSMase2 prevented intracellular lipid accumulation and TNFα-induced inflammation in in-vitro HepG2-steatosis cellular model. Furthermore, nSMase2 inhibition ameliorates oxidative damage by rescuing PPARα and preventing cell death associated with high glucose/oleic acid-induced fat accumulation in HepG2 cells. Collectively, our findings highlight the prominent role of nSMase2 in hepatic steatosis, which could serve as a potential therapeutic target for NAFLD and other hepatic steatosis-linked disorders.

Diagnostic value of sphingolipid metabolism-related genes CD37 and CXCL9 in nonalcoholic fatty liver disease

The development of nonalcoholic fatty liver disease (NAFLD) has been reported to be caused by sphingolipid family inducing insulin resistance, mitochondrial dysfunction, and inflammation, which can be regulated by multiple sphingolipid metabolic pathways. This study aimed to explore the molecular mechanism of crucial sphingolipid metabolism related genes (SMRGs) in NAFLD. Firstly, the datasets (GSE48452, GSE126848, and GSE63067) from the Gene Expression Omnibus database and sphingolipid metabolism genes (SMGs) from previous research were collected for this study. The differentially expressed genes (DEGs) between different NAFLD and controls were acquired through "limma," and the SMRGs were authenticated via weighted gene co-expression network analysis (WGCNA). After overlapping the DEGs and SMRGs, the causality between the intersection genes (DE-SMRGs) and NAFLD was explored to sort out the candidate biomarkers by Mendelian randomization (MR) study. The receiver operating characteristic (ROC) curves of candidate biomarkers in GSE48452 and GSE126848 were yielded to determine the biomarkers, followed by the nomogram construction and enrichment analysis. Finally, the immune infiltration analysis, the prediction of transcription factors (TFs) and drugs targeting biomarkers were put into effect. A total of 23 DE-SMRGs were acquired based on the differential analysis and weighted gene co-expression network analysis (WGCNA), of which 3 DE-SMRGs (CD37, CXCL9 and IL7R) were picked out for follow-up analysis through univariate and multivariate MR analysis. The values of area under ROC curve of CD37 and CXCL9 were >0.7 in GSE48452 and GSE126848, thereby being regarded as biomarkers, which were mainly enriched in amino acid metabolism. With respect to the Spearman analysis between immune cells and biomarkers, CD37 and CXCL9 were significantly positively associated with M1 macrophages (P < .001), whose proportion was observably higher in NAFLD patients compared with controls. At last, TFs (ZNF460 and ZNF384) of CD37 and CXCL9 and a total of 79 chemical drugs targeting CD37 and CXCL9 were predicted. This study mined the pivotal SMRGs, CD37 and CXCL9, and systematically explored the mechanism of action of both biomarkers based on the public databases, which could tender a fresh reference for the clinical diagnosis and therapy of NAFLD.

Role of fecal microbiota transplant in management of hepatic encephalopathy: Current trends and future directions

Fecal microbiota transplantation (FMT) offers a potential treatment avenue for hepatic encephalopathy (HE) by leveraging beneficial bacterial displacement to restore a balanced gut microbiome. The prevalence of HE varies with liver disease severity and comorbidities. HE pathogenesis involves ammonia toxicity, gut-brain communication disruption, and inflammation. FMT aims to restore gut microbiota balance, addressing these factors. FMT's efficacy has been explored in various conditions, including HE. Studies suggest that FMT can modulate gut microbiota, reduce ammonia levels, and alleviate inflammation. FMT has shown promise in alcohol-associated, hepatitis B and C-associated, and non-alcoholic fatty liver disease. Benefits include improved liver function, cognitive function, and the slowing of disease progression. However, larger, controlled studies are needed to validate its effectiveness in these contexts. Studies have shown cognitive improvements through FMT, with potential benefits in cirrhotic patients. Notably, trials have demonstrated reduced serious adverse events and cognitive enhancements in FMT arms compared to the standard of care. Although evidence is promising, challenges remain: Limited patient numbers, varied dosages, administration routes, and donor profiles. Further large-scale, controlled trials are essential to establish standardized guidelines and ensure FMT's clinical applications and efficacy. While FMT holds potential for HE management, ongoing research is needed to address these challenges, optimize protocols, and expand its availability as a therapeutic option for diverse hepatic conditions.

The Dynamic Role of Endoplasmic Reticulum Stress in Chronic Liver Disease

Chronic liver disease (CLD) is a major worldwide public health threat, with an estimated prevalence of 1.5 billion individuals with CLD in 2020. Chronic activation of endoplasmic reticulum (ER) stress-related pathways is recognized as substantially contributing to the pathologic progression of CLD. The ER is an intracellular organelle that folds proteins into their correct three-dimensional shapes. ER-associated enzymes and chaperone proteins highly regulate this process. Perturbations in protein folding lead to misfolded or unfolded protein accumulation in the ER lumen, resulting in ER stress and concomitant activation of the unfolded protein response (UPR). The adaptive UPR is a set of signal transduction pathways evolved in mammalian cells that attempts to reestablish ER protein homeostasis by reducing protein load and increasing ER-associated degradation. However, maladaptive UPR responses in CLD occur due to prolonged UPR activation, leading to concomitant inflammation and cell death. This review assesses the current understanding of the cellular and molecular mechanisms that regulate ER stress and the UPR in the progression of various liver diseases and the potential pharmacologic and biological interventions that target the UPR.

Gut microbiota derived bile acid metabolites maintain the homeostasis of gut and systemic immunity

Bile acids (BAs) as cholesterol-derived molecules play an essential role in some physiological processes such as nutrient absorption, glucose homeostasis and regulation of energy expenditure. They are synthesized in the liver as primary BAs such as cholic acid (CA), chenodeoxycholic acid (CDCA) and conjugated forms. A variety of secondary BAs such as deoxycholic acid (DCA) and lithocholic acid (LCA) and their derivatives is synthesized in the intestine through the involvement of various microorganisms. In addition to essential physiological functions, BAs and their metabolites are also involved in the differentiation and functions of innate and adaptive immune cells such as macrophages (Macs), dendritic cells (DCs), myeloid derived suppressive cells (MDSCs), regulatory T cells (Treg), Breg cells, T helper (Th)17 cells, CD4 Th1 and Th2 cells, CD8 cells, B cells and NKT cells. Dysregulation of the BAs and their metabolites also affects development of some diseases such as inflammatory bowel diseases. We here summarize recent advances in how BAs and their metabolites maintain gut and systemic homeostasis, including the metabolism of the BAs and their derivatives, the role of BAs and their metabolites in the differentiation and function of immune cells, and the effects of BAs and their metabolites on immune-associated disorders.

Gut-Liver Axis and Non-Alcoholic Fatty Liver Disease: A Vicious Circle of Dysfunctions Orchestrated by the Gut Microbiome

Non-alcoholic fatty liver disease (NAFLD) is a prevalent, multifactorial, and poorly understood liver disease with an increasing incidence worldwide. NAFLD is typically asymptomatic and coupled with other symptoms of metabolic syndrome. The prevalence of NAFLD is rising in tandem with the prevalence of obesity. In the Western hemisphere, NAFLD is one of the most prevalent causes of liver disease and liver transplantation. Recent research suggests that gut microbiome dysbiosis may play a significant role in the pathogenesis of NAFLD by dysregulating the gut-liver axis. The so-called "gut-liver axis" refers to the communication and feedback loop between the digestive system and the liver. Several pathological mechanisms characterized the alteration of the gut-liver axis, such as the impairment of the gut barrier and the increase of the intestinal permeability which result in endotoxemia and inflammation, and changes in bile acid profiles and metabolite levels produced by the gut microbiome. This review will explore the role of gut-liver axis disruption, mediated by gut microbiome dysbiosis, on NAFLD development.