Altered hepatic lipid metabolism in C57BL/6 mice fed alcohol: a targeted lipidomic and gene expression study

Gowda SG, K. Shukla P, Gowda D, Nath LR, Chiba H, Rao R, Hui SP. Sex-Specific Effect of Ethanol on Colon Content Lipidome in a Mice Model Using Nontargeted LC/MS

Consumption of alcohol has widespread effects on the human body. The organs that are most significantly impacted are the liver and digestive system. When alcohol is consumed, it is absorbed in the intestines and processed by the liver. However, excessive alcohol use may affect gut epithelial integrity, microbiome composition, and lipid metabolism. Despite past studies investigating the effect of ethanol on hepatic lipid metabolism, the focus on colonic lipid metabolism has not been well explored. In this study, we investigated the sex-specific effect of ethanol on the colonic content lipidome in a mouse model using nontargeted liquid chromatography-mass spectrometry. Comprehensive lipidome analysis of colonic flush samples was performed using ethanol-fed (EF) and pair-fed (PF) mice of each sex. Partial least-squares discriminant analysis revealed that ethanol altered colonic lipid composition largely in male mice compared with female mice. A significant increase in free fatty acids, ceramides, and hexosylceramides and decreased phosphatidylglycerols (PG) was observed in the EF group compared to the PF group in male mice. Phosphatidylethanolamine (PE) levels were increased significantly in the EF group of both sexes compared to the PF group. The volcanic plot shows that PG (O-15:1/15:0) and PE (O-18:2/15:0) are common markers that are increased in both sexes of the EF group. In addition, decreased fatty acid esters of hydroxy fatty acids (FAHFA) were observed specifically in the EF group of female mice. Overall, a significant variation in the mice colonic content lipidome between the EF and PF groups was observed. Target pathways, such as sphingolipid metabolism in males, FAHFA in females, and PE metabolism in both sexes, were suggested. This study provides new insight into the sex-dependent lipid change associated with alcohol-induced gut-microbiota dysfunction and its potential health impacts.

Metabolic Reprogramming of HCC: A New Microenvironment for Immune Responses

Hepatocellular carcinoma is the most common primary liver cancer, ranking third among the leading causes of cancer-related mortality worldwide and whose incidence varies according to geographical area and ethnicity. Metabolic rewiring was recently introduced as an emerging hallmark able to affect tumor progression by modulating cancer cell behavior and immune responses. This review focuses on the recent studies examining HCC's metabolic traits, with particular reference to the alterations of glucose, fatty acid and amino acid metabolism, the three major metabolic changes that have gained attention in the field of HCC. After delivering a panoramic picture of the peculiar immune landscape of HCC, this review will also discuss how the metabolic reprogramming of liver cancer cells can affect, directly or indirectly, the microenvironment and the function of the different immune cell populations, eventually favoring the tumor escape from immunosurveillance.

Lipidomic Analysis of Liver Lipid Droplets after Chronic Alcohol Consumption with and without Betaine Supplementation

The earliest manifestation of alcohol-associated liver disease is hepatic steatosis, which is characterized by fat accumulation in specialized organelles called lipid droplets (LDs). Our previous studies reported that alcohol consumption elevates the numbers and sizes of LDs in hepatocytes, which is attenuated by simultaneous treatment with the methyl group donor, betaine. Here, we examined changes in the hepatic lipidome with respect to LD size and dynamics in male Wistar rats fed for 6 weeks with control or ethanol-containing liquid diets that were supplemented with or without 10 mg betaine/mL. At the time of sacrifice, three hepatic LD fractions, LD1 (large droplets), LD2 (medium-sized droplets), and LD3 (small droplets) were isolated from each rat. Untargeted lipidomic analyses revealed that each LD fraction of ethanol-fed rats had higher phospholipids, cholesteryl esters, diacylglycerols, ceramides, and hexosylceramides compared with the corresponding fractions of pair-fed controls. Interestingly, the ratio of phosphatidylcholine to phosphatidylethanolamine (the two most abundant phospholipids on the LD surface) was lower in LD1 fraction compared with LD3 fraction, irrespective of treatment; however, this ratio was significantly lower in ethanol LD fractions compared with their respective control fractions. Betaine supplementation significantly attenuated the ethanol-induced lipidomic changes. These were mainly associated with the regulation of LD surface phospholipids, ceramides, and glycerolipid metabolism in different-sized LD fractions. In conclusion, our results show that ethanol-induced changes in the hepatic LD lipidome likely stabilizes larger-sized LDs during steatosis development. Furthermore, betaine supplementation could effectively reduce the size and dynamics of LDs to attenuate alcohol-associated hepatic steatosis.

Circadian clock disruption aggravates alcohol liver disease in an acute mouse model

Circadian rhythms are important for organisms to adapt to the environment and maintain homeostasis. Disruptions of circadian rhythms contribute to the occurrence, progression, and exacerbation of diseases, such as cancer, psychiatric disorders, and metabolic disorders. Alcohol-induced liver disease (ALD) is one of the most prevalent liver diseases. Disruptions of the circadian clock enhance the ALD symptoms using chronic mice models or genetic manipulated mice. However, chronic models are time consuming and clock gene deletions interfere with metabolisms. Here, we report that constant light (LL) condition significantly disrupted the circadian clock in an acute ALD model, resulting in aggravated ALD phenotypes in wild type mice. Comparative transcriptome analysis revealed that the alcohol feeding affected the circadian pathway, as well as metabolic pathways. The acute alcohol feeding plus the LL condition further interfered with metabolic pathways and dysregulated canonical circadian gene expressions. These findings support the idea that disrupting the circadian clock could provide an improved ALD mouse model for further applications, such as facilitating identification of potential therapeutic targets for the prevention and treatment of ALD.Abbreviations: ALD, alcohol-induced liver disease; LD, 12 h light _ 12 h dark; LL, constant light; HF, high-fat liquid control diet; ETH, ethanol-containing diet; NIAAA, National Institute on Alcohol Abuse and Alcoholism; TTFLs, transcription-translation feedback loops; FDA, US Foods and Drug Administration; NAFLD, non-alcoholic fatty liver disease; RER, respiratory exchange rate; DEGs, differentially expressed genes; H&E, haematoxylin and eosin; ALT, alanine transaminase; AST, aspartate transaminase; TG, triglycerides.

Pathogenesis of Alcohol-Associated Fatty Liver: Lessons From Transgenic Mice

Alcohol-associated liver disease (ALD) is a major public health issue that significantly contributes to human morbidity and mortality, with no FDA-approved therapeutic intervention available. The health burden of ALD has worsened during the COVID-19 pandemic, which has been associated with a spike in alcohol abuse, and a subsequent increase in hospitalization rates for ALD. A key knowledge gap that underlies the lack of novel therapies for ALD is a need to better understand the pathogenic mechanisms that contribute to ALD initiation, particularly with respect to hepatic lipid accumulation and the development of fatty liver, which is the first step in the ALD spectrum. The goal of this review is to evaluate the existing literature to gain insight into the pathogenesis of alcohol-associated fatty liver, and to synthesize alcohol’s known effects on hepatic lipid metabolism. To achieve this goal, we specifically focus on studies from transgenic mouse models of ALD, allowing for a genetic dissection of alcohol’s effects, and integrate these findings with our current understanding of ALD pathogenesis. Existing studies using transgenic mouse models of ALD have revealed roles for specific genes involved in hepatic lipid metabolic pathways including fatty acid uptake, mitochondrial β-oxidation, de novo lipogenesis, triglyceride metabolism, and lipid droplet formation. In addition to reviewing this literature, we conclude by identifying current gaps in our understanding of how alcohol abuse impairs hepatic lipid metabolism and identify future directions to address these gaps. In summary, transgenic mice provide a powerful tool to understand alcohol’s effect on hepatic lipid metabolism and highlight that alcohol abuse has diverse effects that contribute to the development of alcohol-associated fatty liver disease.

Metabolomic Analysis Uncovers Lipid and Amino Acid Metabolism Disturbance During the Development of Ascites in Alcoholic Liver Disease

Ascites is one of the most common complications of cirrhosis, and there is a dearth of knowledge about ascites-related pathologic metabolism. In this study, 122 alcoholic liver disease (ALD) patients, including 49 cases without ascites, 18 cases with mild-ascites, and 55 cases with large-ascites (1) were established according to the International Ascites Club (2), and untargeted metabolomics coupled with pattern recognition approaches were performed to profile and extract metabolite signatures. A total of 553 metabolites were uniquely discovered in patients with ascites, of which 136 metabolites had been annotated in the human metabolome database. Principal component analysis (PCA) analysis was used to further identify 21 ascites-related fingerprints. The eigenmetabolite calculated by reducing the dimensions of the 21 metabolites could be used to effectively identify those ALD patients with or without ascites. The eigenmetabolite showed a decreasing trend during ascites production and accumulation and was negatively related to the disease progress. These metabolic fingerprints mainly belong to the metabolites in lipid metabolism and the amino acid pathway. The results imply that lipid and amino acid metabolism disturbance may play a critical role in the development of ascites in ALD patients and could be a potent prognosis marker.

Lipidomics for the Prediction of Progressive Liver Disease in Patients with Alcohol Use Disorder

Alcohol-related liver disease is a public health care burden globally. Only 10-20% of patients with alcohol use disorder have progressive liver disease. This study aimed to identify lipid biomarkers for the early identification of progressive alcohol-related liver disease, which is a key step for early intervention. We performed untargeted lipidomics analysis in serum and fecal samples for a cohort of 49 subjects, including 17 non-alcoholic controls, 16 patients with non-progressive alcohol-related liver disease, and 16 patients with progressive alcohol-related liver disease. The serum and fecal lipidome profiles in the two patient groups were different from that in the controls. Nine lipid biomarkers were identified that were significantly different between patients with progressive liver disease and patients with non-progressive liver disease in both serum and fecal samples. We further built a random forest model to predict progressive alcohol-related liver disease using nine lipid biomarkers. Fecal lipids performed better (Area Under the Curve, AUC = 0.90) than serum lipids (AUC = 0.79). The lipid biomarkers identified are promising candidates for the early identification of progressive alcohol-related liver disease.

Oxidative Stress and Redox Signaling in the Pathophysiology of Liver Diseases

The increased production of derivatives of molecular oxygen and nitrogen in the form of reactive oxygen species (ROS) and reactive nitrogen species (RNS) lead to molecular damage called oxidative stress. Under normal physiological conditions, the ROS generation is tightly regulated in different cells and cellular compartments. Any disturbance in the balance between the cellular generation of ROS and antioxidant balance leads to oxidative stress. In this article, we discuss the sources of ROS (endogenous and exogenous) and antioxidant mechanisms. We also focus on the pathophysiological significance of oxidative stress in various cell types of the liver. Oxidative stress is implicated in the development and progression of various liver diseases. We narrate the master regulators of ROS-mediated signaling and their contribution to liver diseases. Nonalcoholic fatty liver diseases (NAFLD) are influenced by a "multiple parallel-hit model" in which oxidative stress plays a central role. We highlight the recent findings on the role of oxidative stress in the spectrum of NAFLD, including fibrosis and liver cancer. Finally, we provide a brief overview of oxidative stress biomarkers and their therapeutic applications in various liver-related disorders. Overall, the article sheds light on the significance of oxidative stress in the pathophysiology of the liver. © 2022 American Physiological Society. Compr Physiol 12:3167-3192, 2022.

Hepatoprotective effects of sea cucumber ether-phospholipids against alcohol-induced lipid metabolic dysregulation and oxidative stress in mice

Sea cucumber is widely consumed as food and folk medicine in Asia, and its phospholipids are rich sources of dietary eicosapentaenoic acid enriched ether-phospholipids (ether-PLs). Emerging evidence suggests that ether-PLs are associated with neurodegenerative disease and steatohepatitis. However, the function and mechanism of ether-PLs in alcoholic liver disease (ALD) are not well understood. To this end, the present study sought to investigate the hepatoprotective effects of sea cucumber ether-PLs, including plasmenyl phosphatidylethanolamine (PlsEtn) and plasmanyl phosphatidylcholine (PlsCho), and their underlying mechanisms. Our results showed that compared with EtOH-induced mice, ether-PL treated mice showed improved liver histology, decreased serum ALT and AST levels, and reduced alcohol metabolic enzyme (ALDH2 and ADH1) expressions. Mechanistic studies showed that ether-PLs attenuated "first-hit" hepatic steatosis and lipid accumulation evoked by alcohol administration. Moreover, PlsEtn more effectively restored endogenous plasmalogen levels than PlsCho, thereby enhancing hepatic antioxidation against "second-hit" reactive oxygen species (ROS) due to the damaged mitochondria and abnormal ethanol metabolism. Taken together, sea cucumber ether-PLs show great potential to become a natural functional food against chronic alcohol-induced hepatic steatosis and lipid metabolic dysregulation.

Lipidomics and Redox Lipidomics Indicate Early Stage Alcohol-Induced Liver Damage

Alcoholic fatty liver disease (AFLD) is characterized by lipid accumulation and inflammation and can progress to cirrhosis and cancer in the liver. AFLD diagnosis currently relies on histological analysis of liver biopsies. Early detection permits interventions that would prevent progression to cirrhosis or later stages of the disease. Herein, we have conducted the first comprehensive time-course study of lipids using novel state-of-the art lipidomics methods in plasma and liver in the early stages of a mouse model of AFLD, i.e., Lieber-DeCarli diet model. In ethanol-treated mice, changes in liver tissue included up-regulation of triglycerides (TGs) and oxidized TGs and down-regulation of phosphatidylcholine, lysophosphatidylcholine, and 20-22-carbon-containing lipid-mediator precursors. An increase in oxidized TGs preceded histological signs of early AFLD, i.e., steatosis, with these changes observed in both the liver and plasma. The major lipid classes dysregulated by ethanol play important roles in hepatic inflammation, steatosis, and oxidative damage. Conclusion: Alcohol consumption alters the liver lipidome before overt histological markers of early AFLD. This introduces the exciting possibility that specific lipids may serve as earlier biomarkers of AFLD than those currently being used.

ZFP36L1 Regulates Fgf21 mRNA Turnover and Modulates Alcoholic Hepatic Steatosis and Inflammation in Mice

Zinc finger protein 36 like 1 (ZFP36L1) enhances the turnover of mRNAs containing AU-rich elements (AREs) in their 3'-untranslated regions (3'UTR). The physiological and pathological functions of ZFP36L1 in liver, however, remain largely unknown. Liver-specific ZFP36L1-deficient (Zfp36l1^flox/flox/Cre⁺; L1^LKO) mice were generated to investigate the role of ZFP36L1 in liver physiology and pathology. Under normal conditions, the L1^LKO mice and their littermate controls (Zfp36l1^flox/flox/Cre^-; L1^FLX) appeared normal. When fed a Lieber-DeCarli liquid diet containing alcohol, L1^LKO mice were significantly protected from developing alcohol-induced hepatic steatosis, injury, and inflammation compared with L1^FLX mice. Most importantly, fibroblast growth factor 21 (Fgf21) mRNA was significantly increased in the livers of alcohol diet-fed L1^LKO mice compared with the alcohol diet-fed L1^FLX group. The Fgf21 mRNA contains three AREs in its 3'UTR, and Fgf21 3'UTR was directly regulated by ZFP36L1 in luciferase reporter assays. Steady-state levels of Fgf21 mRNA were significantly decreased by wild-type ZFP36L1, but not by a non-binding zinc finger ZFP36L1 mutant. Finally, wild-type ZFP36L1, but not the ZFP36L1 mutant, bound to the Fgf21 3'UTR ARE RNA probe. These results demonstrate that ZFP36L1 inactivation protects against alcohol-induced hepatic steatosis and liver injury and inflammation, possibly by stabilizing Fgf21 mRNA. These findings suggest that the modulation of ZFP36L1 may be beneficial in the prevention or treatment of human alcoholic liver disease.

Alcohol induced hepatic retinoid depletion is associated with the induction of multiple retinoid catabolizing cytochrome P450 enzymes

Chronic alcohol consumption leads to a spectrum of liver disease that is associated with significant global mortality and morbidity. Alcohol is known to deplete hepatic vitamin A content, which has been linked to the pathogenesis of alcoholic liver disease. It has been suggested that induction of Cytochrome P450 2E1 (CYP2E1) contributes to alcohol-induced hepatic vitamin A depletion, but the possible contributions of other retinoid-catabolizing CYPs have not been well studied. The main objective of this study was to better understand alcohol-induced hepatic vitamin A depletion and test the hypothesis that alcohol-induced depletion of hepatic vitamin A is due to CYP-mediated oxidative catabolism. This hypothesis was tested in a mouse model of chronic alcohol consumption, including wild type and Cyp2e1 -/- mice. Our results show that chronic alcohol consumption is associated with decreased levels of hepatic retinol, retinyl esters, and retinoic acid. Moreover, the depletion of hepatic retinoid is associated with the induction of multiple retinoid catabolizing CYPs, including CYP26A1, and CYP26B1 in alcohol fed wild type mice. In Cyp2e1 -/- mice, alcohol-induced retinol decline is blunted but retinyl esters undergo a change in their acyl composition and decline upon alcohol exposure like WT mice. In conclusion, the alcohol induced decline in hepatic vitamin A content is associated with increased expression of multiple retinoid-catabolizing CYPs, including the retinoic acid specific hydroxylases CYP26A1 and CYP26B1.

Effect of intravenous ghrelin administration, combined with alcohol, on circulating metabolome in heavy drinking individuals with alcohol use disorder

BACKGROUND

Ghrelin may influence several alcohol-related behaviors in animals and humans by modulating central and/or peripheral biological pathways. The aim of this exploratory analysis was to investigate associations between ghrelin administration and the human circulating metabolome during alcohol exposure in nontreatment seeking, heavy drinking individuals with alcohol use disorder (AUD).

METHODS

We used serum samples from a randomized, crossover, double-blind, placebo-controlled human laboratory study with intravenous (IV) ghrelin or placebo infusion in two experiments. During each session, participants received a loading dose (3 µg/kg) followed by continuous infusion (16.9 ng/kg/min) of acyl ghrelin or placebo. The first experiment included an IV alcohol self-administration (IV-ASA) session and the second experiment included an IV alcohol clamp (IV-AC) session, both with the counterbalanced infusion of ghrelin or placebo. Serum metabolite profiles were analyzed from repeated blood samples collected during each session.

RESULTS

In both experiments, ghrelin infusion was associated with an altered serum metabolite profile, including significantly increased levels of cortisol (IV-ASA q-value = 0.0003 and IV-AC q < 0.0001), corticosterone (IV-ASA q = 0.0202 and IV-AC q < 0.0001), and glycochenodeoxycholic acid (IV-ASA q = 0.0375 and IV-AC q = 0.0013). In the IV-ASA experiment, ghrelin infusion increased levels of cortisone (q = 0.0352) and fatty acids 18:1 (q = 0.0406) and 18:3 (q = 0.0320). Moreover, in the IV-AC experiment, ghrelin infusion significantly increased levels of glycocholic acid (q < 0.0001) and phenylalanine (q = 0.0458).

CONCLUSION

IV ghrelin infusion, combined with IV alcohol administration, was associated with increases in the circulating metabolite levels of corticosteroids and glycine-conjugated bile acids, among other changes. Further research is needed to understand the role that metabolomic changes play in the complex interaction between ghrelin and alcohol.

Convergent somatic mutations in metabolism genes in chronic liver disease

The progression of chronic liver disease to hepatocellular carcinoma is caused by the acquisition of somatic mutations that affect 20-30 cancer genes1-8. Burdens of somatic mutations are higher and clonal expansions larger in chronic liver disease9-13 than in normal liver13-16, which enables positive selection to shape the genomic landscape9-13. Here we analysed somatic mutations from 1,590 genomes across 34 liver samples, including healthy controls, alcohol-related liver disease and non-alcoholic fatty liver disease. Seven of the 29 patients with liver disease had mutations in FOXO1, the major transcription factor in insulin signalling. These mutations affected a single hotspot within the gene, impairing the insulin-mediated nuclear export of FOXO1. Notably, six of the seven patients with FOXO1S22W hotspot mutations showed convergent evolution, with variants acquired independently by up to nine distinct hepatocyte clones per patient. CIDEB, which regulates lipid droplet metabolism in hepatocytes17-19, and GPAM, which produces storage triacylglycerol from free fatty acids20,21, also had a significant excess of mutations. We again observed frequent convergent evolution: up to fourteen independent clones per patient with CIDEB mutations and up to seven clones per patient with GPAM mutations. Mutations in metabolism genes were distributed across multiple anatomical segments of the liver, increased clone size and were seen in both alcohol-related liver disease and non-alcoholic fatty liver disease, but rarely in hepatocellular carcinoma. Master regulators of metabolic pathways are a frequent target of convergent somatic mutation in alcohol-related and non-alcoholic fatty liver disease.

Stress-Responsive Gene FK506-Binding Protein 51 Mediates Alcohol-Induced Liver Injury Through the Hippo Pathway and Chemokine (C-X-C Motif) Ligand 1 Signaling

BACKGROUND AND AIMS

Chronic alcohol drinking is a major risk factor for alcohol-associated liver disease (ALD). FK506-binding protein 51 (FKBP5), a cochaperone protein, is involved in many key regulatory pathways. It is known to be involved in stress-related disorders, but there are no reports regarding its role in ALD. This present study aimed to examine the molecular mechanism of FKBP5 in ALD.

APPROACH AND RESULTS

We found a significant increase in hepatic FKBP5 transcripts and protein expression in patients with ALD and mice fed with chronic-plus-single binge ethanol. Loss of Fkbp5 in mice protected against alcohol-induced hepatic steatosis and inflammation. Transcriptomic analysis revealed a significant reduction of Transcriptional enhancer factor TEF-1 (TEA) domain transcription factor 1 (Tead1) and chemokine (C-X-C motif) ligand 1 (Cxcl1) mRNA in ethanol-fed Fkbp5-/- mice. Ethanol-induced Fkbp5 expression was secondary to down-regulation of methylation level at its 5' untranslated promoter region. The increase in Fkbp5 expression led to induction in transcription factor TEAD1 through Hippo signaling pathway. Fkbp5 can interact with yes-associated protein (YAP) upstream kinase, mammalian Ste20-like kinase 1 (MST1), affecting its ability to phosphorylate YAP and the inhibitory effect of hepatic YAP phosphorylation by ethanol leading to YAP nuclear translocation and TEAD1 activation. Activation of TEAD1 led to increased expression of its target, CXCL1, a chemokine-mediated neutrophil recruitment, causing hepatic inflammation and neutrophil infiltration in our mouse model.

CONCLUSIONS

We identified an FKBP5-YAP-TEAD1-CXCL1 axis in the pathogenesis of ALD. Loss of FKBP5 ameliorates alcohol-induced liver injury through the Hippo pathway and CXCL1 signaling, suggesting its potential role as a target for the treatment of ALD.

Comprehensive lipidomics reveals phenotypic differences in hepatic lipid turnover in ALD and NAFLD during alcohol intoxication

Background & Aims

In experimental models, alcohol induces acute changes in lipid metabolism that cause hepatocyte lipoapoptosis and inflammation. Here we study human hepatic lipid turnover during controlled alcohol intoxication.

Methods

We studied 39 participants with 3 distinct hepatic phenotypes: alcohol-related liver disease (ALD), non-alcoholic fatty liver disease (NAFLD), and healthy controls. Alcohol was administrated via nasogastric tube over 30 min. Hepatic and systemic venous blood was sampled simultaneously at 3 time points: baseline, 60, and 180 min after alcohol intervention. Liver biopsies were sampled 240 min after alcohol intervention. We used ultra-high performance liquid chromatography mass spectrometry to measure levels of more than 250 lipid species from the blood and liver samples.

Results

After alcohol intervention, the levels of blood free fatty acid (FFA) and lysophosphatidylcholine (LPC) decreased, while triglyceride (TG) increased. FFA was the only lipid class to decrease in NAFLD after alcohol intervention, whereas LPC and FFA decreased and TG increased after intervention in ALD and healthy controls. Fatty acid chain uptake preference in FFAs and LPCs were oleic acid, linoleic acid, arachidonic acid, and docosahexaenoic acid. Hepatic venous blood FFA and LPC levels were lower when compared with systemic venous blood levels throughout the intervention. After alcohol intoxication, liver lipidome in ALD was similar to that in NAFLD.

Conclusions

Alcohol intoxication induces rapid changes in circulating lipids including hepatic turnaround from FFA and LPC, potentially leading to lipoapoptosis and steatohepatitis. TG clearance was suppressed in NAFLD, possibly explaining why alcohol and NAFLD are synergistic risk factors for disease progression. These effects may be central to the pathogenesis of ALD.

Clinical Trials Registration

The study is registered at Clinicaltrials.gov (NCT03018990).

Lay summary

We report that alcohol induces hepatic extraction of free unsaturated fatty acids and lysophosphatidylcholines, hepatotoxic lipids which have not been previously associated with alcohol-induced liver injury. We also found that individuals with non-alcoholic fatty liver disease have reduced lipid turnover during alcohol intoxication when compared with people with alcohol-related fatty liver disease. This may explain why alcohol is particularly more harmful in people with non-alcoholic fatty liver and why elevated BMI and alcohol have a synergistic effect on the risk of liver-related death.

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Alcohol intoxication induces rapid changes in the profile of circulating lipids.

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Alcohol has a profound effect on monosaturated fatty acids.

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Triglyceride clearance is suppressed in NAFLD during alcohol intoxication.

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Hepatic lipid turnover differentiates ALD and NAFLD during alcohol intoxication.

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A suppressed metabolic response may explain why alcohol is particularly harmful in NAFLD.

FOXO4 ameliorates alcohol-induced chronic liver injury via inhibiting NF-κB and modulating gut microbiota in C57BL/6J mice

BACKGROUND

Intestinal mucosa barrier function and gut-liver axis are impaired by ethanol in chronic alcoholic liver disease (ALD). However, the possible mechanism is not clear. This study aimed to investigate the effects of Forkhead Box O4 (FOXO4) on alcohol-induced chronic liver injury and its molecular mechanism(s).

METHODS

Male C57BL/6J mice were injected with or without FOXO4-WT, FOXO4-TB or NF-κB vectors, and fed with Lieber-DeCarli liquid diets containing 36% ethanol for eight weeks to induce chronic ALD. Thereafter, blood, liver, colon and fecal samples were collected. Biochemical parameters, endotoxin and inflammatory cytokines in the blood and antioxidant enzymes in the liver were tested by commercial kits. Histopathological changes in the liver were evaluated by HE staining. In addition, the mRNA and protein expression of FOXO4, NF-κB, ZO-1 and Occluding in the colon were measured by quantitative real-time PCR and Western blot, respectively. Furthermore, gut microbiota composition in the fecal samples was investigated with 16S rDNA sequencing.

RESULTS

FOXO4 significantly ameliorated liver histopathological damage. Moreover, FOXO4 reduced the serum endotoxin, biochemical parameters (ALT, AST, ALP and TG), antioxidant enzymes (ROS and MDA), inflammatory cytokines (IL-6, IL-1β, and TNF-α), but restored the levels of GSH, SOD and IL-10. Furthermore, FOXO4 significantly inhibited the expression of NF-κB, p-NF-κB p65, p-IKKα and p-IKKβ, and up-regulated the expression of ZO-1 and Occludin. Additionally, FOXO4 modulated the gut microbiota composition and certain bacteria including Odoribacter, Parasutterella and Psychrobacter.

CONCLUSION

These findings suggest that FOXO4 protects against alcohol-induced chronic liver injury via inhibiting NF-κB and modulating gut microbiota in C57BL/6J mice.

Metabolic alterations and vulnerabilities in hepatocellular carcinoma

Liver cancer is a serious disease. It is ranked as the cancer with the second highest number of cancer-related deaths worldwide. Hepatocellular carcinoma (HCC), which arises from transformed hepatocytes, is the major subtype of liver cancer. It accounts for 85% of total liver-cancer cases. An important aspect of HCC that has been actively studied is its metabolism. With the liver as the primary site of numerous metabolic processes in the body, it has been shown that the metabolism of HCC cells is highly dysregulated compared to that of normal hepatocytes. It is therefore crucial to understand the metabolic alterations caused by HCC and the underlying mechanisms for these alterations. This deeper understanding will allow diagnostic and therapeutic advancements in the treatment of HCC. In this review, we will summarize the current literature in HCC metabolic alterations, induced vulnerabilities, and potential therapeutic interventions.

Alcohol and Liver Clock Disruption Increase Small Droplet Macrosteatosis, Alter Lipid Metabolism and Clock Gene mRNA Rhythms, and Remodel the Triglyceride Lipidome in Mouse Liver

Heavy alcohol drinking dysregulates lipid metabolism, promoting hepatic steatosis – the first stage of alcohol-related liver disease (ALD). The molecular circadian clock plays a major role in synchronizing daily rhythms in behavior and metabolism and clock disruption can cause pathology, including liver disease. Previous studies indicate that alcohol consumption alters liver clock function, but the impact alcohol or clock disruption, or both have on the temporal control of hepatic lipid metabolism and injury remains unclear. Here, we undertook studies to determine whether genetic disruption of the liver clock exacerbates alterations in lipid metabolism and worsens steatosis in alcohol-fed mice. To address this question, male liver-specific Bmal1 knockout (LKO) and flox/flox (Fl/Fl) control mice were fed a control or alcohol-containing diet for 5 weeks. Alcohol significantly dampened diurnal rhythms of mRNA levels in clock genes Bmal1 and Dbp, phase advanced Nr1d1/REV-ERBα, and induced arrhythmicity in Clock, Noct, and Nfil3/E4BP4, with further disruption in livers of LKO mice. Alcohol-fed LKO mice exhibited higher plasma triglyceride (TG) and different time-of-day patterns of hepatic TG and macrosteatosis, with elevated levels of small droplet macrosteatosis compared to alcohol-fed Fl/Fl mice. Diurnal rhythms in mRNA levels of lipid metabolism transcription factors (Srebf1, Nr1h2, and Ppara) were significantly altered by alcohol and clock disruption. Alcohol and/or clock disruption significantly altered diurnal rhythms in mRNA levels of fatty acid (FA) synthesis and oxidation (Acaca/b, Mlycd, Cpt1a, Fasn, Elovl5/6, and Fads1/2), TG turnover (Gpat1, Agpat1/2, Lpin1/2, Dgat2, and Pnpla2/3), and lipid droplet (Plin2/5, Lipe, Mgll, and Abdh5) genes, along with protein abundances of p-ACC, MCD, and FASN. Lipidomics analyses showed that alcohol, clock disruption, or both significantly altered FA saturation and remodeled the FA composition of the hepatic TG pool, with higher percentages of several long and very long chain FA in livers of alcohol-fed LKO mice. In conclusion, these results show that the liver clock is important for maintaining temporal control of hepatic lipid metabolism and that disrupting the liver clock exacerbates alcohol-related hepatic steatosis.

Effect of probiotics Lactobacillus paracasei GKS6, L. plantarum GKM3, and L. rhamnosus GKLC1 on alleviating alcohol-induced alcoholic liver disease in a mouse model

BACKGROUND/OBJECTIVES

Heavy alcohol consumption causes the development of alcoholic liver disease (ALD), a neglected but important public health problem. Many studies have pointed out that probiotics could improve gut health, which is also considered to be a cause of ALD. Therefore, this study screened the probiotics, Lactobacillus casei GKC1 (GKC1), L. fermentum GKF3 (GKF3), Bifidobacterium lactis GKK2 (GKK2), L. rhamnosus GKLC1 (GKLC1), L. paracasei GKS6 (GKS6), and L. plantarum GKM3 (GKM3), for their potential benefits in alleviating ALD for applications to disease prevention.

SUBJECTS/METHODS

C57BL/6N mice were divided into 8 groups (n = 6 in each): normal control, positive control (alcohol-diet fed), and treatments of feeding probiotics GKC1, GKF3, GKK2, GKLC1, GKS6, and GKM3 under an oral dose 0.82 g/kg B.W. per day by oral gavage. The experiment was conducted for 8 weeks, and the concentrations of alanine aminotransferase (ALT), aspartate aminotransferase, triglyceride (TG), and total cholesterol (TC) in mice were measured. The glutathione (GSH), catalase (CAT), and histology were analyzed after sacrifice.

RESULTS

The results showed a decrease in the serum ALT, liver TG, and liver TC levels in the GKS6, GKM3, and GKLC1 groups compared to the positive control. In addition, the decreasing GSH and CAT levels were inhibited in the GKS6 and GKM3 groups. The histopathological results showed that all probiotics could reduce the accumulation of liver fat. Furthermore, there was a significant difference in GKLC1 with lower stomach damage compared to the alcohol-fed mice without any addition of probiotics.

CONCLUSIONS

GKLC1, GKS6, and GKM3 can be used as supplements for alleviating the development of ALD.

Retinol-binding protein 2 (RBP2) binds monoacylglycerols and modulates gut endocrine signaling and body weight

Expressed in the small intestine, retinol-binding protein 2 (RBP2) facilitates dietary retinoid absorption. Rbp2-deficient (Rbp2-/- ) mice fed a chow diet exhibit by 6-7 months-of-age higher body weights, impaired glucose metabolism, and greater hepatic triglyceride levels compared to controls. These phenotypes are also observed when young Rbp2-/- mice are fed a high fat diet. Retinoids do not account for the phenotypes. Rather, RBP2 is a previously unidentified monoacylglycerol (MAG)-binding protein, interacting with the endocannabinoid 2-arachidonoylglycerol (2-AG) and other MAGs with affinities comparable to retinol. X-ray crystallographic studies show that MAGs bind in the retinol binding pocket. When challenged with an oil gavage, Rbp2-/- mice show elevated mucosal levels of 2-MAGs. This is accompanied by significantly elevated blood levels of the gut hormone GIP (glucose-dependent insulinotropic polypeptide). Thus, RBP2, in addition to facilitating dietary retinoid absorption, modulates MAG metabolism and likely signaling, playing a heretofore unknown role in systemic energy balance.

Alcohol effects on hepatic lipid metabolism

Alcoholic liver disease (ALD) is the most prevalent type of chronic liver disease with significant morbidity and mortality worldwide. ALD begins with simple hepatic steatosis and progresses to alcoholic steatohepatitis, fibrosis, and cirrhosis. The severity of hepatic steatosis is highly associated with the development of later stages of ALD. This review explores the disturbances of alcohol-induced hepatic lipid metabolism through altered hepatic lipid uptake, de novo lipid synthesis, fatty acid oxidation, hepatic lipid export, and lipid droplet formation and catabolism. In addition, we review emerging data on the contributions of genetics and bioactive lipid metabolism in alcohol-induced hepatic lipid accumulation.

Dietary citrus peel essential oil ameliorates hypercholesterolemia and hepatic steatosis by modulating lipid and cholesterol homeostasis

Integration of lipidomics and gene expression analysis provided new insights into in-depth mechanistic understanding of the effects of dietary CPEO.

Constitutive androstane receptor mediates PCB-induced disruption of retinoid homeostasis

Environmental exposure to polychlorinated biphenyls (PCBs) is associated with an increased risk of incidence of metabolic disease, however the molecular mechanisms underlying this phenomenon are not fully understood. Our study provides new insights into molecular interactions between PCBs and retinoids (vitamin A and its metabolites) by defining a role for constitutive androstane receptor (CAR) in the disruption of retinoid homeostasis by non-coplanar 2,2',4,4',5,5'-hexachlorobiphenyl (PCB153). Administration of four weekly 50 mg/kg doses of PCB153 to C57BL/6 male mice resulted in a significant decline in the tissue concentrations of retinyl esters, retinol and all-trans-retinoic acid (atRA), while no decline in hepatic and adipose tissue retinoid levels were detected in Car-null littermates. Our data imply that disrupted retinoid homeostasis occurs as a consequence of PCB153-induced activation of CAR, and raise the possibility that CAR signaling can affect atRA homeostasis in vivo. A strong correlation between the changes in retinoid metabolism and extensive upregulation of hepatic CAR-driven Cyp2b10 expression implicates this CYP isoform as contributing to retinoid homeostasis disruption via atRA oxidation during PCB153 exposure. In response to PCB153-induced CAR activation and disruption of retinoid homeostasis, expression of hepatic Pepck, Cd36 and adipose tissue Pparγ, Cd36, Adipoq, and Rbp4 were altered; however, this was reversed by administration of exogenous dietary retinoids (300 IU daily for 4 weeks). Our study establishes that PCB153 exposure enables a significant disruption of retinoid homeostasis in a CAR-dependent manner. We propose that this contributes to the obesogenic properties of PCB153 and may contribute to the predisposition to the metabolic disease.

Lipidomic Profiling Reveals Disruption of Lipid Metabolism in Valproic Acid-Induced Hepatotoxicity

Valproic acid (VPA) is one of the most widely prescribed antiepileptic drugs, as VPA-induced hepatotoxicity is one of the most severe adverse reaction that can lead to death. The objective of this study was to gain an understanding of dysregulated lipid metabolism in mechanism of hepatotoxicity. Nontargeted lipidomics analysis with liquid chromatography-quadrupole-time-of-flight mass spectrometry (LC-Q-TOF/MS) was performed to explore differential lipids from the patient serum and L02 cells. Lipidomics data interpretation was augmented by gene expression analyses for the key enzymes in lipid metabolism pathways. From patient serum lipidomics, pronouncedly changed lipid species between abnormal liver function (ALF) patients and normal liver function (NLF) patients were identified. Among these lipid species, LPCs, Cers, and SMs were markedly reduced in the ALF group and showed negative relationships with liver injury severity [alanine aminotransferase (ALT) levels], while significantly increased triacylglycerols (TAG) with higher summed carbon numbers demonstrated a positive relationship with ALT levels. Regarding lipidomics in hepatic L02 cells, TAG was markedly elevated after VPA exposure, especially in TAGs with more than 53 summed carbons. Besides, gene expression analysis revealed dysregulated lipid metabolism in VPA-treated L02 cells. Peroxime proliferators-activated receptor (PPARγ) pathway played an important role in VPA-induced lipid disruption through inducing long-chain fatty acid uptake and TAG synthesis, which was also regulated by Akt pathway. Our findings present that VPA-induced lipid metabolism disruption might lead to lipotoxicity in the liver. This approach is expected to be applicable for other drug-induced toxicity assessments.

Enhanced Alcohol Preference and Anxiolytic Alcohol Effects in Niemann-Pick Disease Model in Mice

Major depression and alcohol use disorder are severe psychiatric diseases affecting the world's population with high comorbidity level. However, the pathogenesis of this comorbidity remains unclear, and no selective treatment for this condition is available. A pathogenic pathway and a possible therapeutic target for the treatment of depression-alcoholism comorbidity based on the hyperfunction of acid sphingomyelinase (Asm) were recently suggested. Here we analyzed the effects of alcohol on the depression/anxiety state of homozygous Asm-knockout mice (Asm − /−), which can be considered as a model of an early stage of Niemann-Pick disease, as well as their drinking pattern under normal and stress conditions. It was observed that forced treatment with alcohol (2 g/kg, i.p.) reduces the anxiety level of Asm−/− mice as measured in the elevated plus maze (EPM) test, but enhances the depression level in the forced swim test (FST). The analysis of drinking pattern of these animals in a free-choice alcohol drinking paradigm revealed higher alcohol intake and preference in Asm−/− mice compared to wild type (wt) littermates. However, this difference was overwritten by the stress exposure. Stronger sedating effects of alcohol were observed in Asm−/− mice compared to wt animals in the loss of righting reflex test after single and repeated alcohol injections (3 g/kg, i.p.). Altogether, the present findings might indicate an Asm involvement in the mechanisms of comorbidity between alcoholism and anxiety/depression.

The Hepatic Lipidome: A Gateway to Understanding the Pathogenes is of Alcohol-Induced Fatty Liver

Chronic alcohol consumption can lead to the development of alcoholic fatty liver disease. The underlying pathogenic mechanisms however, have not been fully elucidated. Here, we review the current state of the art regarding the application of lipidomics to study alcohol's effect on hepatic lipids. It is clear that alcohol has a profound effect on the hepatic lipidome, with documented changes in the major lipid categories (i.e. fatty acyls, glycerolipids, glycerophospholipids, sphingolipids, sterol lipids and prenol lipids). Alcohol's most striking effect is the marked change in the hepatic fatty acyl pool. This effect includes increased levels of 18-carbon fatty acyl chains incorporated into multiple lipid species, as well as a general shift toward increased unsaturation of fatty acyl moieties. In addition to our literature review, we also make several recommendations to consider when designing lipidomic studies into alcohol's effects. These recommendations include integration of lipidomic data with other measures of lipid metabolism, inclusion of multiple experimental time points, and presentation of quantitative data. We believe rigorous analysis of the hepatic lipidome can yield new insight into the pathogenesis of alcohol-induced fatty liver. While the existing literature has been largely descriptive, the field is poised to apply lipidomics to yield a new level of understanding on alcohol's effects on hepatic lipid metabolism.

Hepatic stellate cell activation: A source for bioactive lipids

Hepatic stellate cells (HSCs) are non-parenchymal liver cells that characteristically contain multiple retinoid (vitamin A)-containing lipid droplets. In this study, we addressed the metabolic fate of non-retinoid lipids originating from lipid droplet loss during HSCs activation. UPLC/MS/MS and qRT-PCR were used to monitor the lipid composition and mRNA expression of selected genes regulating lipid metabolism in freshly isolated, overnight-, 3- and 7-day cultures or primary mouse HSCs. A preferential accumulation of specific C20-C24 fatty acid species, especially arachidonic (C20:4) and docosahexaenoic acids (C22:6), was revealed in culture-activated HSCs along with an upregulation of transcription of fatty acid desaturases (Scd1, Scd2) and elongases (Elovl5, Elovl6). This was accompanied with an enrichment of activated HSCs with 36:4 and 38:4 phosphatidylcholine species containing polyunsaturated fatty acids and associated accumulation of selective lipid mediators, including endocannabinoids and related N-acylethanolamides, as well as ceramides. An increase in 2-arachidonoylglycerol and N-arachydonoylethanolamide concentrations was observed along with an upregulation of Daglα mRNA expression in HSCs during culture activation. N-palmitoylethanolamide was identified as the most abundant endocannabinoid-like species in activated HSCs. An increase in total ceramide levels and enrichment with N-palmitoyl (C16:0), N-tetracosenoyl (C24:1), N-tetracosanoyl (C24:0) and N-docosanoyl (C22:0) ceramides was detected in activated HSC cultures and was preceded by increased mRNA expression of ceramide synthesizing enzymes (CerS2, CerS5 and Smpd1). Our data suggest an active redistribution of non-retinoid lipids in HSCs underlying the formation of low abundance, highly bioactive lipid species that may affect signaling during HSC activation, as well as extracellularly within the liver.

Dietary Macronutrient Composition Determines the Contribution of DGAT1 to Alcoholic Steatosis

Background

The first stage of alcoholic liver disease is hepatic steatosis. While alcohol is known to profoundly impact hepatic lipid metabolism, gaps in our knowledge remain regarding the mechanisms leading to alcohol‐induced hepatic triglyceride (TG) accumulation. As the sole enzymes catalyzing the final step in TG synthesis, diacylglycerol O‐acyltransferase (DGAT) 1 and 2 are potentially important contributors to alcoholic steatosis. Our goal was to study the effects of dietary fat content on alcohol‐induced hepatic TG accumulation, and the relative contribution of DGAT1 and DGAT2 to alcoholic steatosis.

Methods

These studies were carried out in wild‐type (WT) mice fed alcohol‐containing high‐fat or low‐fat formulations of Lieber‐DeCarli liquid diets, as well as follow‐up studies in Dgat1^−/− mice.

Results

A direct comparison of the low‐fat and high‐fat liquid diet in WT mice revealed surprisingly similar levels of alcoholic steatosis, although there were underlying differences in the pattern of hepatic lipid accumulation and expression of genes involved in hepatic lipid metabolism. Follow‐up studies in Dgat1^−/− mice revealed that these animals are protected from alcoholic steatosis when consumed as part of a high‐fat diet, but not a low‐fat diet.

Conclusions

Dietary macronutrient composition influences the relative contribution of DGAT1 and DGAT2 to alcoholic steatosis, such that in the context of alcohol and a high‐fat diet, DGAT1 predominates.

β-Hydroxybutyrate protects from alcohol-induced liver injury via a Hcar2-cAMP dependent pathway

BACKGROUND & AIMS

Sterile inflammation resulting in alcoholic hepatitis (AH) occurs unpredictably after many years of excess alcohol intake. The factors responsible for the development of AH are not known but mitochondrial damage with loss of mitochondrial function are common features. Hcar2 is a G-protein coupled receptor which is activated by β-hydroxybutyrate (BHB). We aimed to determine the relevance of the BHB-Hcar2 pathway in alcoholic liver disease.

METHODS

We tested if loss of BHB production can result in increased liver inflammation. We further tested if BHB supplementation is protective in AH through interaction with Hcar2, and analyzed the immune and cellular basis for protection.

RESULTS

Humans with AH have reduced hepatic BHB, and inhibition of BHB production in mice aggravated ethanol-induced AH, with higher plasma alanine aminotransferase levels, increased steatosis and greater neutrophil influx. Conversely supplementation of BHB had the opposite effects with reduced alanine aminotransferase levels, reduced steatosis and neutrophil influx. This therapeutic effect of BHB is dependent on the receptor Hcar2. BHB treatment increased liver Il10 transcripts, and promoted the M2 phenotype of intrahepatic macrophages. BHB also increased the transcriptional level of M2 related genes in vitro bone marrow derived macrophages. This skewing towards M2 related genes is dependent on lower mitochondrial membrane potential (Δψ) induced by BHB.

CONCLUSIONS

Collectively, our data shows that BHB production during excess alcohol consumption has an anti-inflammatory and hepatoprotective role through an Hcar2 dependent pathway. This introduces the concept of metabolite-based therapy for AH.

LAY SUMMARY

Alcoholic hepatitis is a life-threatening condition with no approved therapy that occurs unexpectedly in people who consume excess alcohol. The liver makes many metabolites, and we demonstrate that loss of one such metabolite β-hydroxybutyrate occurs in patients with alcoholic hepatitis. This loss can increase alcohol-induced liver injury, and β-hydroxybutyrate can protect from alcohol-induced liver injury via a receptor on liver macrophages. This opens the possibility of metabolite-based therapy for alcoholic hepatitis.

Inhibition of Hepatotoxicity by a LXR Inverse Agonist in a Model of Alcoholic Liver Disease

Alcohol abuse is a major cause of liver disease and mortality worldwide and is a significant public health issue. Patients with alcoholic liver disease (ALD) have severe hepatic lipid accumulation, inflammation, and fibrosis. Therapies for ALD are very limited and even abstinence from alcohol consumption does not necessarily protect patients from progression of the disease. We sought to evaluate the efficacy of a liver X receptor (LXR) inverse agonist, SR9238, in an animal model of ALD. SR9238 suppresses hepatic lipogenesis, a pathological hallmark of ALD, and we hypothesized that targeting suppression of hepatic metabolic pathways that are activated in ALD may be an effective treatment for the disease. A chronic ethanol diet with or without a final ethanol binge treatment was used to induce ALD in mice. Mice were administered the liver specific LXR inverse agonist SR9238 for 4 weeks after the mice had been maintained on the ethanol diet for 14 days. Mice developed all the hallmarks of advanced ALD demonstrating significant pathophysiology and hepatotoxicity. SR9238 significantly attenuated liver injury and hepatic steatosis and fibrosis was nearly eliminated in SR9238 treated mice. SR9238 treatment reversed the damage associated with chronic ethanol use returning the liver to near normal morphology. These results indicate that inhibiting LXR activity using the inverse agonist has a hepatoprotective effect in rodent models of ALD; thus, this pharmacological approach may be efficacious for treatment of ALD in humans.

Mitochondria-targeted ubiquinone (MitoQ) enhances acetaldehyde clearance by reversing alcohol-induced posttranslational modification of aldehyde dehydrogenase 2: A molecular mechanism of protection against alcoholic liver disease

Alcohol metabolism in the liver generates highly toxic acetaldehyde. Breakdown of acetaldehyde by aldehyde dehydrogenase 2 (ALDH2) in the mitochondria consumes NAD⁺ and generates reactive oxygen/nitrogen species, which represents a fundamental mechanism in the pathogenesis of alcoholic liver disease (ALD). A mitochondria-targeted lipophilic ubiquinone (MitoQ) has been shown to confer greater protection against oxidative damage in the mitochondria compared to untargeted antioxidants. The present study aimed to investigate if MitoQ could preserve mitochondrial ALDH2 activity and speed up acetaldehyde clearance, thereby protects against ALD. Male C57BL/6 J mice were exposed to alcohol for 8 weeks with MitoQ supplementation (5 mg/kg/d) for the last 4 weeks. MitoQ ameliorated alcohol-induced oxidative/nitrosative stress and glutathione deficiency. It also reversed alcohol-reduced hepatic ALDH activity and accelerated acetaldehyde clearance through modulating ALDH2 cysteine S-nitrosylation, tyrosine nitration and 4-hydroxynonenol adducts formation. MitoQ ameliorated nitric oxide (NO) donor-mediated ADLH2 S-nitrosylation and nitration in Hepa-1c1c7 cells under glutathion depletion condition. In addition, alcohol-increased circulating acetaldehyde levels were accompanied by reduced intestinal ALDH activity and impaired intestinal barrier. In accordance, MitoQ reversed alcohol-increased plasma endotoxin levels and hepatic toll-like receptor 4 (TLR4)-NF-κB signaling along with subsequent inhibition of inflammatory cell infiltration. MitoQ also reversed alcohol-induced hepatic lipid accumulation through enhancing fatty acid β-oxidation. Alcohol-induced ER stress and apoptotic cell death signaling were reversed by MitoQ. This study demonstrated that speeding up acetaldehyde clearance by preserving ALDH2 activity critically mediates the beneficial effect of MitoQ on alcohol-induced pathogenesis at the gut-liver axis.

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PTMs of ALDH2 participated in the pathogenesis of alcoholic liver disease.

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MitoQ treatment accelerated acetaldehyde detoxification.

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MitoQ ameliorated acetaldehyde-related tight junction disruption.

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MitoQ reversed TLR4-mediated inflammatory response in alcoholic liver disease.

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MitoQ counteracts alcohol-induced ER stress and cell apoptosis.

Cyp8b1 ablation prevents Western diet-induced weight gain and hepatic steatosis because of impaired fat absorption

Bile acids (BAs) are cholesterol derivatives that regulate lipid metabolism, through their dual abilities to promote lipid absorption and activate BA receptors. However, different BA species have varying abilities to perform these functions. Eliminating 12α-hydroxy BAs in mice via Cyp8b1 knockout causes low body weight and improved glucose tolerance. The goal of this study was to determine mechanisms of low body weight in Cyp8b1^-/- mice. We challenged Cyp8b1^-/- mice with a Western-type diet and assessed body weight and composition. We measured energy expenditure, fecal calories, and lipid absorption and performed lipidomic studies on feces and intestine. We investigated the requirement for dietary fat in the phenotype using a fat-free diet. Cyp8b1^-/- mice were resistant to Western diet-induced body weight gain, hepatic steatosis, and insulin resistance. These changes were associated with increased fecal calories, due to malabsorption of hydrolyzed dietary triglycerides. This was reversed by treating the mice with taurocholic acid, the major 12α-hydroxylated BA species. The improvements in body weight and steatosis were normalized by feeding mice a fat-free diet. The effects of BA composition on intestinal lipid handling are important for whole body energy homeostasis. Thus modulating BA composition is a potential tool for obesity or diabetes therapy.

The effect of alcohol on the differential expression of cluster of differentiation 14 gene, associated pathways, and genetic network

Alcohol consumption affects human health in part by compromising the immune system. In this study, we examined the expression of the Cd14 (cluster of differentiation 14) gene, which is involved in the immune system through a proinflammatory cascade. Expression was evaluated in BXD mice treated with saline or acute 1.8 g/kg i.p. ethanol (12.5% v/v). Hippocampal gene expression data were generated to examine differential expression and to perform systems genetics analyses. The Cd14 gene expression showed significant changes among the BXD strains after ethanol treatment, and eQTL mapping revealed that Cd14 is a cis-regulated gene. We also identified eighteen ethanol-related phenotypes correlated with Cd14 expression related to either ethanol responses or ethanol consumption. Pathway analysis was performed to identify possible biological pathways involved in the response to ethanol and Cd14. We also constructed a genetic network for Cd14 using the top 20 correlated genes and present several genes possibly involved in Cd14 and ethanol responses based on differential gene expression. In conclusion, we found Cd14, along with several other genes and pathways, to be involved in ethanol responses in the hippocampus, such as increased susceptibility to lipopolysaccharides and neuroinflammation.

Increased de novo ceramide synthesis and accumulation in failing myocardium

Abnormal lipid metabolism may contribute to myocardial injury and remodeling. To determine whether accumulation of very long-chain ceramides occurs in human failing myocardium, we analyzed myocardial tissue and serum from patients with severe heart failure (HF) undergoing placement of left ventricular assist devices and controls. Lipidomic analysis revealed increased total and very long-chain ceramides in myocardium and serum of patients with advanced HF. After unloading, these changes showed partial reversibility. Following myocardial infarction (MI), serine palmitoyl transferase (SPT), the rate-limiting enzyme of the de novo pathway of ceramide synthesis, and ceramides were found increased. Blockade of SPT by the specific inhibitor myriocin reduced ceramide accumulation in ischemic cardiomyopathy and decreased C16, C24:1, and C24 ceramides. SPT inhibition also reduced ventricular remodeling, fibrosis, and macrophage content following MI. Further, genetic deletion of the SPTLC2 gene preserved cardiac function following MI. Finally, in vitro studies revealed that changes in ceramide synthesis are linked to hypoxia and inflammation. In conclusion, cardiac ceramides accumulate in the failing myocardium, and increased levels are detectable in circulation. Inhibition of de novo ceramide synthesis reduces cardiac remodeling. Thus, increased de novo ceramide synthesis contributes to progressive pathologic cardiac remodeling and dysfunction.

Chronic alcohol consumption decreases brown adipose tissue mass and disrupts thermoregulation: a possible role for altered retinoid signaling

Retinoic acid, an active metabolite of dietary vitamin A, acts as a ligand for nuclear receptor transcription factors with more than 500 known target genes. It is becoming increasingly clear that alcohol has a significant impact on cellular retinoic acid metabolism, with resultant effects on its function. Here, we test the hypothesis that chronic alcohol consumption impairs retinoic acid signaling in brown adipose tissue (BAT), leading to impaired BAT function and thermoregulation. All studies were conducted in age-matched, male mice consuming alcohol-containing liquid diets. Alcohol’s effect on BAT was assessed by histology, qPCR, HPLC, LC/MS and measures of core body temperature. Our data show that chronic alcohol consumption decreases BAT mass, with a resultant effect on thermoregulation. Follow-up mechanistic studies reveal a decreased triglyceride content in BAT, as well as impaired retinoic acid homeostasis, associated with decreased BAT levels of retinoic acid in alcohol-consuming mice. Our work highlights a hitherto uncharacterized effect of alcohol on BAT function, with possible implications for thermoregulation and energy metabolism in drinkers. Our data indicate that alcohol’s effects on brown adipose tissue may be mediated through altered retinoic acid signaling.

Alcohol, Adipose Tissue and Lipid Dysregulation

Chronic alcohol consumption perturbs lipid metabolism as it increases adipose tissue lipolysis and leads to ectopic fat deposition within the liver and the development of alcoholic fatty liver disease. In addition to the recognition of the role of adipose tissue derived fatty acids in liver steatosis, alcohol also impacts other functions of adipose tissue and lipid metabolism. Lipid balance in response to long-term alcohol intake favors adipose tissue loss and fatty acid efflux as lipolysis is upregulated and lipogenesis is either slightly decreased or unchanged. Study of the lipolytic and lipogenic pathways has identified several regulatory proteins modulated by alcohol that contribute to these effects. Glucose tolerance of adipose tissue is also impaired by chronic alcohol due to decreased glucose transporter-4 availability at the membrane. As an endocrine organ, white adipose tissue (WAT) releases several adipokines that are negatively modulated following chronic alcohol consumption including adiponectin, leptin, and resistin. When these effects are combined with the enhanced expression of inflammatory mediators that are induced by chronic alcohol, a proinflammatory state develops within WAT, contributing to the observed lipodystrophy. Lastly, while chronic alcohol intake may enhance thermogenesis of brown adipose tissue (BAT), definitive mechanistic evidence is currently lacking. Overall, both WAT and BAT depots are impacted by chronic alcohol intake and the resulting lipodystrophy contributes to fat accumulation in peripheral organs, thereby enhancing the pathological state accompanying chronic alcohol use disorder.

Structure, Function and Metabolism of Hepatic and Adipose Tissue Lipid Droplets: Implications in Alcoholic Liver Disease

For more than 30 years, lipid droplets (LDs) were considered as an inert bag of lipid for storage of energy-rich fat molecules. Following a paradigm shift almost a decade ago, LDs are presently considered an active subcellular organelle especially designed for assembling, storing and subsequently supplying lipids for generating energy and membrane synthesis (and in the case of hepatocytes for VLDL secretion). LDs also play a central role in many other cellular functions such as viral assembly and protein degradation. Here, we have explored the structural and functional changes that occur in hepatic and adipose tissue LDs following chronic ethanol consumption in relation to their role in the pathogenesis of alcoholic liver injury.

Acute alcohol exposure during mouse gastrulation alters lipid metabolism in placental and heart development: Folate prevention

Background

Embryonic acute exposure to ethanol (EtOH), lithium, and homocysteine (HCy) induces cardiac defects at the time of exposure; folic acid (FA) supplementation protects normal cardiogenesis (Han et al., 2009, 2012; Serrano et al., 2010). Our hypothesis is that EtOH exposure and FA protection relate to lipid and FA metabolism during mouse cardiogenesis and placentation.

Methods

On the morning of conception, pregnant C57BL/6J mice were placed on either of two FA‐containing diets: a 3.3 mg health maintenance diet or a high FA diet of 10.5 mg/kg. Mice were injected a binge level of EtOH, HCy, or saline on embryonic day (E) 6.75, targeting gastrulation. On E15.5, cardiac and umbilical blood flow were examined by ultrasound. Embryonic cardiac tissues were processed for gene expression of lipid and FA metabolism; the placenta and heart tissues for neutral lipid droplets, or for medium chain acyl‐dehydrogenase (MCAD) protein.

Results

EtOH exposure altered lipid‐related gene expression on E7.5 in comparison to control or FA‐supplemented groups and remained altered on E15.5 similarly to changes with HCy, signifying FA deficiency. In comparison to control tissues, the lipid‐related acyl CoA dehydrogenase medium length chain gene and its protein MCAD were altered with EtOH exposure, as were neutral lipid droplet localization in the heart and placenta.

Conclusion

EtOH altered gene expression associated with lipid and folate metabolism, as well as neutral lipids, in the E15.5 abnormally functioning heart and placenta. In comparison to controls, the high FA diet protected the embryo and placenta from these effects allowing normal development. Birth Defects Research (Part A) 106:749–760, 2016. © 2016 The Authors Birth Defects Research Part A: Clinical and Molecular Teratology Published by Wiley Periodicals, Inc.

Compounds of the sphingomyelin-ceramide-glycosphingolipid pathways as secondary messenger molecules: new targets for novel therapies for fatty liver disease and insulin resistance

The compounds of sphingomyelin-ceramide-glycosphingolipid pathways have been studied as potential secondary messenger molecules in various systems, along with liver function and insulin resistance. Secondary messenger molecules act directly or indirectly to affect cell organelles and intercellular interactions. Their potential role in the pathogenesis of steatohepatitis and diabetes has been suggested. Data samples collected from patients with Gaucher's disease, who had high levels of glucocerebroside, support a role for compounds from these pathways as a messenger molecules in the pathogenesis of fatty liver disease and diabetes. The present review summarizes some of the recent data on the role of glycosphingolipid molecules as messenger molecules in various physiological and pathological conditions, more specifically including insulin resistance and fatty liver disease.

Susceptibility of Different Mouse Wild Type Strains to Develop Diet-Induced NAFLD/AFLD-Associated Liver Disease

Although non-alcoholic and alcoholic fatty liver disease have been intensively studied, concerning pathophysiological mechanisms are still incompletely understood. This may be due to the use of different animal models and resulting model-associated variation. Therefore, this study aimed to compare three frequently used wild type mouse strains in their susceptibility to develop diet-induced features of non-alcoholic/alcoholic fatty liver disease. Fatty liver disease associated clinical, biochemical, and histological features in C57BL/6, CD-1, and 129Sv WT mice were induced by (i) high-fat diet feeding, (ii) ethanol feeding only, and (iii) the combination of high-fat diet and ethanol feeding. Hepatic and subcutaneous adipose lipid profiles were compared in CD-1 and 129Sv mice. Additionally hepatic fatty acid composition was determined in 129Sv mice. In C57BL/6 mice dietary regimens resulted in heterogeneous hepatic responses, ranging from pronounced steatosis and inflammation to a lack of any features of fatty liver disease. Liver-related serum biochemistry showed high deviations within the regimen groups. CD-1 mice did not exhibit significant changes in metabolic and liver markers and developed no significant steatosis or inflammation as a response to dietary regimens. Although 129Sv mice showed no weight gain, this strain achieved most consistent features of fatty liver disease, apparent from concentration alterations of liver-related serum biochemistry as well as moderate steatosis and inflammation as a result of all dietary regimens. Furthermore, the hepatic lipid profile as well as the fatty acid composition of 129Sv mice were considerably altered, upon feeding the different dietary regimens. Accordingly, diet-induced non-alcoholic/alcoholic fatty liver disease is most consistently promoted in 129Sv mice compared to C57BL/6 and CD-1 mice. As a conclusion, this study demonstrates the importance of genetic background of used mouse strains for modeling diet-induced non-alcoholic/alcoholic fatty liver disease.

Palmitic Acid Reduces Circulating Bone Formation Markers in Obese Animals and Impairs Osteoblast Activity via C16-Ceramide Accumulation

Obesity and impaired lipid metabolism increase circulating and local fatty acid (FA) levels. Our previous studies showed that a high high-saturated -fat diet induced greater bone loss in mice than a high high-unsaturated-fat diet due to increased osteoclast numbers and activity. The impact of elevated FA levels on osteoblasts is not yet clear. We induced obesity in 4 week old male mice using a palmitic acid (PA)- or oleic acid (OA)-enriched high fat high-fat diet (HFD) (20 % of calories from FA), and compared them to mice on a normal (R) caloric diet (10 % of calories from FA). We collected serum to determine FA and bone metabolism marker levels. Primary osteoblasts were isolated; cultured in PA, OA, or control (C) medium; and assessed for mineralization activity, gene expression, and ceramide levels. Obese animals in the PA and OA groups had significantly lower serum levels of bone formation markers P1NP and OC compared to normal weight animals (*p < 0.001), with the lowest marker levels in animals on an PA-enriched HFD (*p < 0.001). Accordingly, elevated levels of PA significantly reduced osteoblast mineralization activity in vitro (*p < 0.05). Elevated PA intake significantly increased C16 ceramide accumulation. This accumulation was preventable through inhibition of SPT2 (serine palmitoyl transferase 2) using myriocin. Elevated levels of PA reduce osteoblast function in vitro and bone formation markers in vivo. Our findings suggest that saturated PA can compromise bone health by affecting osteoblasts, and identify a potential mechanism through which obesity promotes bone loss.

Carboxylesterase 1 Is Regulated by Hepatocyte Nuclear Factor 4α and Protects Against Alcohol- and MCD diet-induced Liver Injury

The liver is a major organ that controls hepatic and systemic homeostasis. Dysregulation of liver metabolism may cause liver injury. Previous studies have demonstrated that carboxylesterase 1 (CES1) regulates hepatic triglyceride metabolism and protects against liver steatosis. In the present study, we investigated whether CES1 played a role in the development of alcoholic liver disease (ALD) and methionine and choline-deficient (MCD) diet-induced liver injury. Both hepatocyte nuclear factor 4α (HNF4α) and CES1 were markedly reduced in patients with alcoholic steatohepatitis. Alcohol repressed both HNF4α and CES1 expression in primary hepatocytes. HNF4α regulated CES1 expression by directly binding to the proximal promoter of CES1. Global inactivation of CES1 aggravated alcohol- or MCD diet-induced liver inflammation and liver injury, likely as a result of increased production of acetaldehyde and reactive oxygen species and mitochondrial dysfunctions. Knockdown of hepatic CES1 exacerbated ethanol-induced steatohepatitis. These data indicate that CES1 plays a crucial role in protection against alcohol- or MCD diet-induced liver injury.

High resolution metabolomics technology reveals widespread pathway changes of alcoholic liver disease

The current study provides insights into the molecular mechanisms of ALD from widespread pathway changes.

Increased hepatocellular protein carbonylation in human end-stage alcoholic cirrhosis

OBJECTIVE

Oxidative stress is a significant contributing factor in the pathogenesis of alcoholic liver disease (ALD). In the murine models of chronic alcohol consumption, induction of oxidative stress results in increased peroxidation of polyunsaturated fatty acids to form highly reactive electrophilic α/β unsaturated aldehydes that post-translationally modify proteins altering activity. Data are presented here suggesting that oxidative stress and the resulting carbonylation of hepatic proteins is an ongoing process involved in alcohol-induced cirrhosis.

METHODS

Using age-matched pooled hepatic tissue obtained from healthy humans and patients with end stage cirrhotic ALD, overall carbonylation was assessed by immunohistochemistry and LC-MS/MS of streptavidin purified hepatic whole cell extracts treated with biotin hydrazide. Identified carbonylated proteins were further evaluated using bioinformatics analyses.

RESULTS

Using immunohistochemistry and Western blotting, protein carbonylation was increased in end stage ALD occurring primarily in hepatocytes. Mass spectrometric analysis revealed a total of 1224 carbonylated proteins in normal hepatic and end-stage alcoholic cirrhosis tissue. Of these, 411 were unique to cirrhotic ALD, 261 unique to normal hepatic tissue and 552 common to both groups. Bioinformatic pathway analysis of hepatic carbonylated proteins revealed a propensity of long term EtOH consumption to increase post-translational carbonylation of proteins involved in glutathione homeostatic, glycolytic and cytoskeletal pathways. Western analysis revealed increased expression of GSTA4 and GSTπ in human ALD. Using LC-MS/MS analysis, a nonenaldehyde post-translational modification was identified on Lysine 235 of the cytoskeletal protein vimentin in whole cell extracts prepared from human end stage ALD hepatic tissue.

CONCLUSIONS

These studies are the first to use LC-MS/MS analysis of carbonylated proteins in human ALD and begin exploring possible mechanistic links with end-stage alcoholic cirrhosis and oxidative stress.

The Role of Ceramide in the Pathogenesis of Alcoholic Liver Disease

AIMS

Ceramide is an important second messenger in the sphingomyelin signaling pathway. In this review, we will focus on the potential role of ceramide in the pathogenesis of alcoholic liver disease (ALD).

METHODS

We have summarized the relevant studies and reviews about the role of ceramide in ALD. In addition, we have discussed the role of acid sphingomyelinase and protein phosphatase 2A in ALD, which are associated with ceramide and hepatic steatosis.

RESULTS

Recent studies have proved that the immunoreactivity and content of ceramide were increased, both in experimental models of chronic alcohol-induced steatohepatitis and human livers with severe chronic alcohol-related liver disease. Consistent with that, the levels of protein phosphatase 2A and acid sphingomyelinase were increased. Of relevance, the phosphorylation of adenosine monophosphate-activated protein kinase (AMPK) was inhibited, which could block the fatty acid oxidation and promote its synthesis.

CONCLUSIONS

It was hypothesized that ethanol promoted ceramide accumulation and increased PP2A activity by activating ASMase, which may be an important mechanism in the inhibitory effect on AMPK phosphorylation and then contributed to the progression of steatosis. ASMase, a specific mechanism of ceramide generation, was proved to be a regulator of steatosis, fibrosis, lipotoxicity and endoplasmic reticulum stress.