Metabolomics Analysis Revealed Distinct Cyclic Changes of Metabolites Altered by Chronic Ethanol-Plus-Binge and Shp Deficiency

The pyruvate dehydrogenase kinase inhibitor dichloroacetate mitigates alcohol-induced hepatic inflammation and metabolic disturbances in mice

BACKGROUND

Dichloroacetate (DCA), a pan-pyruvate dehydrogenase kinase inhibitor, ameliorates multiple pathological conditions and tissue injury and shows strong potential for clinical applications. Here, we investigated the preventive effects of DCA in a murine model of alcohol-associated liver disease.

METHODS

C57BL/6J mice were subjected to the acute-on-chronic model of alcohol-associated liver disease and treated with DCA. Livers were assessed in liver histology, biochemistry, and gene expression. Mass spectrometry was used to compare protein expression and metabolite levels.

RESULTS

DCA inhibited hepatic expression of inflammatory genes but did not prevent steatosis and hepatocellular injury in ethanol-fed mice. Consistently, DCA repressed the expression of mRNAs for inflammatory genes in LPS-stimulated murine bone-marrow-derived macrophages and human monocytic THP-1 cells and inhibited both gene expression and protein release of interleukin-1 beta. DCA prevented hepatic accumulation of isovaleric acid in ethanol-fed mice, a short-chain fatty acid primarily produced by gut microbiota. In vitro, isovaleric acid potentiated LPS's effects, while DCA prevented this proinflammatory action. Ethanol feeding increased the expression of proteins involved in diverse metabolic pathways, including branched-chain amino acid (BCAA) degradation. In ethanol-fed mice, hepatic Fischer's ratio (the molar ratio of BCAAs to aromatic amino acids Phe and Tyr) and BTR (the molar ratio of BCAAs to Tyr) showed a decrease compared to pair-fed mice; however, this decrease was not observed in DCA-treated ethanol-fed mice. DCA blunted the ethanol-induced increase of BCKDHA, the rate-limiting enzyme in BCAA catabolism, and cytochrome P450 2E1.

CONCLUSIONS

Ethanol-induced hepatic inflammatory responses and metabolic disturbances were prevented by DCA in mice, indicating the potential to develop pyruvate dehydrogenase kinase inhibitors as an effective therapy to treat alcohol-associated liver disease.

Unique urine and serum metabolomic signature in patients with excessive alcohol use: An exploratory study

BACKGROUND

Excessive alcohol consumption has a multifaceted impact on the body's metabolic pathways and organ systems. The objectives of this study were to characterize global metabolomic changes and identify specific pathways that are altered in individuals with excessive alcohol use.

METHODS

This exploratory study included 22 healthy controls with no known history of excessive alcohol use and 38 patients identified as using alcohol excessively. A Fibrosis-4 score was used to determine the risk of underlying alcohol-associated liver disease among the excessive drinkers.

RESULTS

We found significantly altered urinary and serum metabolites among excessive drinkers, affecting various metabolic pathways including the metabolism of lipids, amino acids and peptides, cofactors and vitamins, carbohydrates, and nucleotides. Levels of two steroid hormones-5alpha-androstan-3beta,17beta-diol disulfate and androstenediol (3beta,17beta) disulfate-were significantly higher in both the serum and urine samples of excessive drinkers. These elevated levels may be associated with a higher risk of liver fibrosis in individuals with excessive alcohol use.

CONCLUSION

Alcohol consumption leads to marked alterations in multiple metabolic pathways, highlighting the systemic impact of alcohol on various tissues and organ systems. These findings provide a foundation for future mechanistic studies aimed at elucidating alcohol-induced changes in these metabolic pathways and their implications.

Untargeted Metabolome Analysis Reveals Reductions in Maternal Hepatic Glucose and Amino Acid Content That Correlate with Fetal Organ Weights in a Mouse Model of Fetal Alcohol Spectrum Disorders

Prenatal alcohol exposure (PAE) causes fetal growth restrictions. A major driver of fetal growth deficits is maternal metabolic disruption; this is under-investigated following PAE. Untargeted metabolomics on the dam and fetus exposed to alcohol (ALC) revealed that the hepatic metabolome of ALC and control (CON) dams were distinct, whereas that of ALC and CON fetuses were similar. Alcohol reduced maternal hepatic glucose content and enriched essential amino acid (AA) catabolites, N-acetylated AA products, urea content, and free fatty acids. These alterations suggest an attempt to minimize the glucose gap by increasing gluconeogenesis using AA and glycerol. In contrast, ALC fetuses had unchanged glucose and AA levels, suggesting an adequate draw of maternal nutrients, despite intensified stress on ALC dams. Maternal metabolites including glycolytic intermediates, AA catabolites, urea, and one-carbon-related metabolites correlated with fetal liver and brain weights, whereas lipid metabolites correlated with fetal body weight, indicating they may be drivers of fetal weight outcomes. Together, these data suggest that ALC alters maternal hepatic metabolic activity to limit glucose availability, thereby switching to alternate energy sources to meet the high-energy demands of pregnancy. Their correlation with fetal phenotypic outcomes indicates the influence of maternal metabolism on fetal growth and development.

Beyond Isocitrate Dehydrogenase Mutations: Emerging Mechanisms for the Accumulation of the Oncometabolite 2-Hydroxyglutarate

2-Hydroxyglutarate (2-HG) is an unconventional oncometabolite of α-ketoglutarate. Isocitrate dehydrogenase mutation is generally acknowledged to be the main cause of 2-HG accumulation. In isocitrate dehydrogenase mutant tumors, 2-HG accumulation inhibits α-ketoglutarate/Fe(II)-dependent dioxygenases, resulting in epigenetic alterations. Recently, the increase of 2-HG has also been observed in the cases of mitochondrial dysfunction and hypoxia. In these cases, 2-HG not only inhibits α-ketoglutarate/Fe(II)-dependent dioxygenases to regulate epigenetics but also affects other cellular pathways, such as regulating hypoxia-inducible transcription factors and glycolysis. These provide a new perspective for the study of 2-HG.

Lack of Multidrug Resistance-associated Protein 4 Prolongs Partial Hepatectomy-induced Hepatic Steatosis

Multidrug resistance-associated protein 4 (Mrp4) is an efflux transporter involved in the active transport of several endogenous and exogenous chemicals. Previously, we have shown that hepatic Mrp4 expression increases following acetaminophen overdose. In mice, these increases in Mrp4 expression are observed specifically in hepatocytes undergoing active proliferation. From this, we hypothesized that Mrp4 plays a key role in hepatocyte proliferation and that lack of Mrp4 impedes liver regeneration following liver injury and/or tissue loss. To evaluate the role of Mrp4 in these processes, we employed two-third partial hepatectomy (PH) as an experimental liver regeneration model. In this study, we performed PH-surgery on male wildtype (C57BL/6J) and Mrp4 knockout mice. Plasma and liver tissues were collected at 24, 48, and 72 h postsurgery and evaluated for liver injury and liver regeneration endpoints, and for PH-induced hepatic lipid accumulation. Our results show that lack of Mrp4 did not alter hepatocyte proliferation and liver injury following PH as evaluated by Ki-67 antigen staining and plasma alanine aminotransferase levels. To our surprise, Mrp4 knockout mice exhibited increased hepatic lipid content, in particular, di- and triglyceride levels. Gene expression analysis showed that lack of Mrp4 upregulated hepatic lipin1 and diacylglycerol O-acyltransferase 1 and 2 gene expression, which are involved in the synthesis of di- and triglycerides. Our observations indicate that lack of Mrp4 prolonged PH-induced hepatic steatosis in mice and suggest that Mrp4 may be a novel genetic factor in the development of hepatic steatosis.

Animal models for liver disease - A practical approach for translational research

Animal models are crucial for improving our understanding of human pathogenesis, enabling researchers to identify therapeutic targets and test novel drugs. In the current review, we provide a comprehensive summary of the most widely used experimental models of chronic liver disease, starting from early stages of fatty liver disease (non-alcoholic and alcoholic) to steatohepatitis, advanced cirrhosis and end-stage primary liver cancer. We focus on aspects such as reproducibility and practicality, discussing the advantages and weaknesses of available models for researchers who are planning to perform animal studies in the near future. Additionally, we summarise current and prospective models based on human tissue bioengineering.

Circadian and Sleep Metabolomics Across Species

Under normal circadian function, metabolic control is temporally coordinated across tissues and behaviors with a 24-h period. However, circadian disruption results in negative consequences for metabolic homeostasis including energy or redox imbalances. Yet, circadian disruption has become increasingly prevalent within today's society due to many factors including sleep loss. Metabolic consequences of both have been revealed by metabolomics analyses of circadian biology and sleep. Specifically, two primary analytical platforms, mass spectrometry and nuclear magnetic resonance spectroscopy, have been used to study molecular clock and sleep influences on overall metabolic rhythmicity. For example, human studies have demonstrated the prevalence of metabolic rhythms in human biology, as well as pan-metabolome consequences of sleep disruption. However, human studies are limited to peripheral metabolic readouts primarily through minimally invasive procedures. For further tissue- and organism-specific investigations, a number of model systems have been studied, based upon the conserved nature of both the molecular clock and sleep across species. Here we summarize human studies as well as key findings from metabolomics studies using mice, Drosophila, and zebrafish. While informative, a limitation in existing literature is a lack of interpretation regarding dynamic synthesis or catabolism within metabolite pools. To this extent, future work incorporating isotope tracers, specific metabolite reporters, and single-cell metabolomics may provide a means of exploring dynamic activity in pathways of interest.

Rosmarinic acid alleviates ethanol-induced lipid accumulation by repressing fatty acid biosynthesis

Recent studies have demonstrated that rosmarinic acid is a valuable natural product for treatment of alcoholic liver disease. However, the mechanisms whereby rosmarinic acid improves alcoholic liver disease remain unclear. Here we performed experiments using a non-transformed mouse hepatocyte cell line (AML12). Oil-red O staining demonstrated that rosmarinic acid reduced ethanol-induced lipid accumulation. It was shown that rosmarinic acid prevented ethanol-induced elevation of the malondialdehyde level. We also found that rosmarinic acid inhibited ethanol-induced mRNA expression of tumor necrosis factor-α and interleukin 6. Metabolomics analysis revealed that rosmarinic acid ameliorated ethanol-induced fatty acid biosynthesis in the cytoplasm. In addition, palmitic acid was a candidate biomarker in cells exposed to ethanol or ethanol plus rosmarinic acid. Rosmarinic acid prevented the ethanol-induced increase in sorbitol that is a component of the polyol pathway. Moreover, we confirmed that rosmarinic acid attenuated ethanol-induced mRNA expression of fatty acid synthase, probably by modulating the AMPK/SREBP-1c pathway. Furthermore, rosmarinic acid prevented the ethanol-induced decrease in eight metabolites that are involved in mitochondrial metabolism, including glycine and succinic acid which are the components of carnitine synthesis. These results provide a crucial insight into the molecular mechanism of rosmarinic acid in alleviating ethanol-induced injury.

Serum Metabolomic Profiling Identifies Key Metabolic Signatures Associated With Pathogenesis of Alcoholic Liver Disease in Humans

Alcoholic liver disease (ALD) develops in a subset of heavy drinkers (HDs). The goals of our study were to (1) characterize the global serum metabolomic changes in well‐characterized cohorts of controls (Cs), HDs, and those with alcoholic cirrhosis (AC); (2) identify metabolomic signatures as potential diagnostic markers, and (3) determine the trajectory of serum metabolites in response to alcohol abstinence. Serum metabolic profiling was performed in 22 Cs, 147 HDs, and 33 patients with AC using ultraperformance liquid chromatography–tandem mass spectrometry. Hepatic gene expression was conducted in Cs (n = 16) and those with AC (n = 32). We found progressive changes in the quantities of metabolites from heavy drinking to AC. Taurine‐conjugated bile acids (taurocholic acid [TCA], 127‐fold; taurochenodeoxycholic acid [TCDCA], 131‐fold; and tauroursodeoxycholic acid, 56‐fold) showed more striking elevations than glycine‐conjugated forms (glycocholic acid [GCA], 22‐fold; glycochenodeoxycholic acid [GCDCA], 22‐fold; and glycoursodeoxycholic acid [GUDCA], 11‐fold). This was associated with increased liver cytochrome P450, family 7, subfamily B, member 1 and taurine content (more substrates); the latter was due to dysregulation of homocysteine metabolism. Increased levels of GCDCA, TCDCA, GCA, and TCA positively correlated with disease progression from Child‐Pugh A to C and Model for End‐Stage Liver Disease scores, whereas GCDCA, GCA, and GUDCA were better predictors of alcohol abstinence. The levels of glucagon‐like peptide 1 (GLP‐1) and fibroblast growth factor (FGF) 21 but not FGF19 were increased in HDs, and all three were further increased in those with AC. Conclusion: Serum taurine/glycine‐conjugated bile acids could serve as noninvasive markers to predict the severity of AC, whereas GLP‐1 and FGF21 may indicate a progression from heavy drinking to AC.

Effect of ethanol on lipid metabolism

Hepatic lipid metabolism is a series of complex processes that control influx and efflux of not only hepatic lipid pools, but also organismal pools. Lipid homeostasis is usually tightly controlled by expression, substrate supply, oxidation and secretion that keep hepatic lipid pools relatively constant. However, perturbations of any of these processes can lead to lipid accumulation in the liver. Although it is thought that these responses are hepatic arms of the 'thrifty genome', they are maladaptive in the context of chronic fatty liver diseases. Ethanol is likely unique among toxins, in that it perturbs almost all aspects of hepatic lipid metabolism. This complex response is due in part to the large metabolic demand placed on the organ by alcohol metabolism, but also appears to involve more nuanced changes in expression and substrate supply. The net effect is that steatosis is a rapid response to alcohol abuse. Although transient steatosis is largely an inert pathology, the chronicity of alcohol-related liver disease seems to require steatosis. Better and more specific understanding of the mechanisms by which alcohol causes steatosis may therefore translate into targeted therapies to treat alcohol-related liver disease and/or prevent its progression.

Label‑free quantitative proteomics and bioinformatics analyses of alcoholic liver disease in a chronic and binge mouse model

As a significant cause of mortality and morbidity, alcoholic liver disease (ALD) has been widely investigated. However, little is known about the underlying metabolic mechanisms involved in the complicated pathological processes of ALD. The present study used label‑free quantitative proteomics and bioinformatics analyses to investigate the differentially expressed proteins (DEPs) and their functions in the livers of alcohol‑feed (AF) and control pair‑feed (PF) mice. As a result, 87 upregulated DEPs and 133 downregulated DEPs were identified in AF liver tissues compared with PF livers. Gene ontology and Kyoto encyclopedia of genes and genomes bioinformatics analyses demonstrated that the DEPs were significantly enriched in 'protein binding', 'metabolism', 'signal conduction' and 'immune response'. The expression of several core proteins including thyroid hormone receptor interactor 12 (TRIP12), NADH dehydrogenase (ubiquinone)1 α subcomplex, assembly factor 3 (NDUFAF3) and guanine monophosphate synthetase (GMPS) was validated by reverse transcription‑quantitative polymerase chain reaction (RT‑qPCR) in a larger series of samples. The RT‑qPCR results confirmed that TRIP12, NDUFAF3 and GMPS genes were significantly differentially expressed in between the AF and PF samples. These results extend our understanding of the molecular mechanisms underlying the occurrence and development of ALD. The present study indicated that the majority of DEPs serve vital roles in multiple metabolic pathways and this extends our knowledge of the molecular mechanisms involved in the occurrence and progression of ALD.

Nuclear receptors and liver disease: Summary of the 2017 basic research symposium

The nuclear receptor superfamily contains important transcriptional regulators that play pleiotropic roles in cell differentiation, development, proliferation, and metabolic processes to govern liver physiology and pathology. Many nuclear receptors are ligand-activated transcription factors that regulate the expression of their target genes by modulating transcriptional activities and epigenetic changes. Additionally, the protein complex associated with nuclear receptors consists of a multitude of coregulators, corepressors, and noncoding RNAs. Therefore, acquiring new information on nuclear receptors may provide invaluable insight into novel therapies and shed light on new interventions to reduce the burden and incidence of liver diseases. (Hepatology Communications 2018;2:765-777).

Intestinal dysbiosis and permeability: the yin and yang in alcohol dependence and alcoholic liver disease

Alcohol dependence and alcoholic liver disease represent a major public health problem with substantial morbidity and mortality. By yet incompletely understood mechanisms, chronic alcohol abuse is associated with increased intestinal permeability and alterations of the gut microbiota composition, allowing bacterial components, bacteria, and metabolites to reach the portal and the systemic circulation. These gut-derived bacterial products are recognized by immune cells circulating in the blood or residing in remote organs such as the liver leading to the release of pro-inflammatory cytokines which are considered important mediators of the liver-gut-brain communication. Although circulating cytokines are likely not the sole factors involved, they can induce liver inflammation/damage and reach the central nervous system where they favor neuroinflammation which is associated with change in mood, cognition, and drinking behavior. In this review, the authors focus on the current evidence describing the changes that occur in the intestinal microbiota with chronic alcohol consumption in conjunction with intestinal barrier breakdown and inflammatory changes sustaining the concept of a gut-liver-brain axis in the pathophysiology of alcohol dependence and alcoholic liver disease.

Rodent Models of Alcoholic Liver Disease: Role of Binge Ethanol Administration

Both chronic and acute (binge) alcohol drinking are important health and economic concerns worldwide and prominent risk factors for the development of alcoholic liver disease (ALD). There are no FDA-approved medications to prevent or to treat any stage of ALD. Therefore, discovery of novel therapeutic strategies remains a critical need for patients with ALD. Relevant experimental animal models that simulate human drinking patterns and mimic the spectrum and severity of alcohol-induced liver pathology in humans are critical to our ability to identify new mechanisms and therapeutic targets. There are several animal models currently in use, including the most widely utilized chronic ad libitum ethanol (EtOH) feeding (Lieber–DeCarli liquid diet model), chronic intragastric EtOH administration (Tsukamoto–French model), and chronic-plus-binge EtOH challenge (Bin Gao—National Institute on Alcohol Abuse and Alcoholism (NIAAA) model). This review provides an overview of recent advances in rodent models of binge EtOH administration which help to recapitulate different features and etiologies of progressive ALD. These models include EtOH binge alone, and EtOH binge coupled with chronic EtOH intake, a high fat diet, or endotoxin challenge. We analyze the strengths, limitations, and translational relevance of these models, as well as summarize the liver injury outcomes and mechanistic insights. We further discuss the application(s) of binge EtOH models in examining alcohol-induced multi-organ pathology, sex- and age-related differences, as well as circadian rhythm disruption.

Loss of miR-141/200c ameliorates hepatic steatosis and inflammation by reprogramming multiple signaling pathways in NASH

Accumulation of lipid droplets and inflammatory cell infiltration is the hallmark of nonalcoholic steatohepatitis (NASH). The roles of noncoding RNAs in NASH are less known. We aim to elucidate the function of miR-141/200c in diet-induced NASH. WT and miR-141/200c-/- mice were fed a methionine and choline deficient (MCD) diet for 2 weeks to assess markers of steatosis, liver injury, and inflammation. Hepatic miR-141 and miR-200c RNA levels were highly induced in human patients with NASH fatty liver and in WT MCD mice. miR-141/200c-/- MCD mice had reduced liver weights and triglyceride (TG) levels, which was associated with increased microsomal TG transfer protein (MTTP) and PPARα but reduced SREBP1c and FAS expression. Inflammation was attenuated and F4/80 macrophage activation was suppressed in miR-141/200c-/- mice, as evidenced by decreased serum aminotransferases and IL-6 and reduced hepatic proinflammatory, neutrophil, and profibrotic genes. Treatment with LPS in BM-derived macrophages isolated from miR-200c/141-/- mice polarized macrophages toward the M2 antiinflammatory state by increasing Arg1 and IL-10 levels while decreasing the M1 marker iNOS. In addition, elevated phosphorylated AMPK (p-AMPK), p-AKT, and p-GSK3β and diminished TLR4 and p-mTOR/p-4EBP1 proteins were observed. Lipidomics and metabolomics revealed alterations of TG and phosphatidylcholine (PC) lipid species by miR-141/200c deficiency. In summary, miR-141/200c deficiency diminished NASH-associated hepatic steatosis and inflammation by reprogramming lipid and inflammation signaling pathways.

LncRNA AK054921 and AK128652 are potential serum biomarkers and predictors of patient survival with alcoholic cirrhosis

Alcoholic liver disease (ALD) is one of the leading causes of chronic liver disease. Recent studies have demonstrated the roles of long noncoding RNAs (lncRNAs) in the pathogenesis of several disease processes. However, the roles of lncRNAs in patients with ALD remain unexplored. Global profiling for human lncRNAs from peripheral blood RNA was performed in a well‐characterized cohort of healthy controls (HC; n = 4), excessive drinkers (ED) without liver disease (n = 4), and those with alcoholic cirrhosis (AC) with different severities (n = 12). The expression of unique lncRNA signatures were validated in a separate cohort of HC (n = 17), ED (n = 19), AC (n = 48), and human liver tissues with ALD (n = 19). A detailed analysis of plasma lncRNAs in AC subjects with different severities compared with HC identified 244 commonly up‐regulated lncRNAs and 181 commonly down‐regulated lncRNAs. We further validated top 20 most differentially up‐ and down‐regulated lncRNAs in ED and AC compared with HC and also determined the expression of selected lncRNAs in human liver tissues with or without AC. Among those lncRNAs, AK128652 and AK054921 were two of the most abundantly expressed lncRNAs in normal human plasma and liver, and their levels were significantly elevated in AC. The prognostic significance of AK128652 and AK054921 was determined in 48 subjects with AC who were followed prospectively for 520 days. The expression of AK128652 and AK054921 was inversely associated with survival in patients with AC. Conclusion: lncRNAs AK054921 and AK128652 are potential biomarkers to predict the progression to ALD in individuals with excessive alcohol consumption and are predictors of survival in patients with AC. (Hepatology Communications 2017;1:513–523)

Animal Models of Alcoholic Liver Disease: Pathogenesis and Clinical Relevance

Alcoholic liver disease (ALD), a leading cause of chronic liver injury worldwide, comprises a range of disorders including simple steatosis, steatohepatitis, cirrhosis, and hepatocellular carcinoma. Over the last five decades, many animal models for the study of ALD pathogenesis have been developed. Recently, a chronic-plus-binge ethanol feeding model was reported. This model induces significant steatosis, hepatic neutrophil infiltration, and liver injury. A clinically relevant model of high-fat diet feeding plus binge ethanol was also developed, which highlights the risk of excessive binge drinking in obese/overweight individuals. All of these models recapitulate some features of the different stages of ALD and have been widely used by many investigators to study the pathogenesis of ALD and to test for therapeutic drugs/components. However, these models are somewhat variable, depending on mouse genetic background, ethanol dose, and animal facility environment. This review focuses on these models and discusses these variations and some methods to improve the feeding protocol. The pathogenesis, clinical relevance, and translational studies of these models are also discussed.

Clock Regulation of Metabolites Reveals Coupling between Transcription and Metabolism

The intricate connection between the circadian clock and metabolism remains poorly understood. We used high temporal resolution metabolite profiling to explore clock regulation of mouse liver and cell-autonomous metabolism. In liver, ∼50% of metabolites were circadian, with enrichment of nucleotide, amino acid, and methylation pathways. In U2 OS cells, 28% were circadian, including amino acids and NAD biosynthesis metabolites. Eighteen metabolites oscillated in both systems and a subset of these in primary hepatocytes. These 18 metabolites were enriched in methylation and amino acid pathways. To assess clock dependence of these rhythms, we used genetic perturbation. BMAL1 knockdown diminished metabolite rhythms, while CRY1 or CRY2 perturbation generally shortened or lengthened rhythms, respectively. Surprisingly, CRY1 knockdown induced 8 hr rhythms in amino acid, methylation, and vitamin metabolites, decoupling metabolite from transcriptional rhythms, with potential impact on nutrient sensing in vivo. These results provide the first comprehensive views of circadian liver and cell-autonomous metabolism.