The transcriptional and DNA binding activity of peroxisome proliferator-activated receptor alpha is inhibited by ethanol metabolism. A novel mechanism for the development of ethanol-induced fatty liver

Endogenous ethanol production in health and disease

The gut microbiome exerts metabolic actions on distal tissues and organs outside the intestine, partly through microbial metabolites that diffuse into the circulation. The disruption of gut homeostasis results in changes to microbial metabolites, and more than half of the variance in the plasma metabolome can be explained by the gut microbiome. Ethanol is a major microbial metabolite that is produced in the intestine of nearly all individuals; however, elevated ethanol production is associated with pathological conditions such as metabolic dysfunction-associated steatotic liver disease and auto-brewery syndrome, in which the liver's capacity to metabolize ethanol is surpassed. In this Review, we describe the mechanisms underlying excessive ethanol production in the gut and the role of ethanol catabolism in mediating pathogenic effects of ethanol on the liver and host metabolism. We conclude by discussing approaches to target excessive ethanol production by gut bacteria.

New advances in drug development for metabolic dysfunction-associated diseases and alcohol-associated liver disease

Metabolic disorders are currently threatening public health worldwide. Discovering new targets and developing promising drugs will reduce the global metabolic-related disease burden. Metabolic disorders primarily consist of lipid and glucose metabolic disorders. Specifically, metabolic dysfunction-associated steatosis liver disease (MASLD) and alcohol-associated liver disease (ALD) are two representative lipid metabolism disorders, while diabetes mellitus is a typical glucose metabolism disorder. In this review, we aimed to summarize the new drug candidates with promising efficacy identified in clinical trials for these diseases. These drug candidates may provide alternatives for patients with metabolic disorders and advance the progress of drug discovery for the large disease burden.

Molecular insights on intracellular Wnt/β-catenin signaling in alcoholic liver disease

Alcoholic liver disease (ALD) is one of the most common health problems worldwide, especially in developing countries caused by chronic consumption of alcohol on a daily basis. The ALD spectrum is initiated with the early stages of alcoholic fatty liver (steatosis), progressing to alcoholic steatohepatitis, followed by the later stages of fibrosis and in some cases, cirrhosis and hepatocellular carcinoma (HCC). The Wnt/β-catenin signaling required for healthy liver development, function, and regeneration is found to be aberrated in ALD, attributed to its progression. This review is to elucidate the association of Wnt/β-catenin signaling with various stages of ALD progression. Alcohol causes downregulation of Wnt/β-catenin signaling components and thereby suppressing the pathway. Reports have been published that aberrated Wnt/β-catenin signaling, especially the absence of β-catenin, results in decreased alcohol metabolism, causing steatosis followed by steatohepatitis via lipid accumulation, lipid peroxidation, liver injury, increased oxidative stress and apoptosis of hepatocytes, contributing to the advancement of ALD. Contrastingly, the progression of later stages of ALD like fibrosis and HCC depends on the increased activation of Wnt/β-catenin signaling and its components. Existing studies reveal the varied expression of Wnt/β-catenin signaling in ALD. However, the dual role of the Wnt/β-catenin pathway in earlier and later stages of ALD is not clear. Therefore, studies on the Wnt/β-catenin pathway and its components in various manifestations of ALD might provide insight in targeting the Wnt/β-catenin pathway in ALD treatment.

Nuclear miR-150 enhances hepatic lipid accumulation by targeting RNA transcripts overlapping the PLIN2 promoter

Alcohol-associated liver disease is a prevalent chronic liver disease caused by excessive ethanol consumption. This study aims to investigate the role of miR-150 in regulating hepatic lipid homeostasis in alcoholic fatty liver (AFL). miR-150 was mainly distributed in the nucleus of hepatocytes and correlated with the degree of liver injury. The decreased expression of miR-150 observed in AFL was a compensatory response to ethanol-induced hepatic steatosis. Overexpression of miR-150 facilitated hepatic lipid accumulation in cellulo and exacerbated ethanol-induced liver steatosis in vivo. In silico analysis identified perilipin-2 (PLIN2) as a potential target gene of miR-150. miR-150 activated PLIN2 transcription by directly binding the RNA transcripts overlapping PLIN2 promoter and facilitating the recruitment of DNA helicase DHX9 and RNA polymeraseⅡ. Overall, our study provides fresh insights into the homeostasis regulation of hepatic steatosis induced by ethanol and identifies miR-150 as a pro-steatosis effector driving transcriptional PLIN2 gene activation.

Synergistic Protective Effect of Fermented Schizandrae Fructus Pomace and Hoveniae Semen cum Fructus Extracts Mixture in the Ethanol-Induced Hepatotoxicity

Schizandrae Fructus (SF), fruits of Schisandra chinensis (Turcz.) Baill. and Hoveniae Semen cum Fructus (HSCF), the dried peduncle of Hovenia dulcis Thunb., have long been used for alcohol detoxification in the traditional medicine of Korea and China. In the current study, we aimed to evaluate the potential synergistic hepatoprotective effect of a combination mixture (MSH) comprising fermented SF pomace (fSFP) and HSCF hot water extracts at a 1:1 (w:w) ratio against ethanol-induced liver toxicity. Subacute ethanol-mediated hepatotoxicity was induced by the oral administration of ethanol (5 g/kg) in C57BL/6J mice once daily for 14 consecutive days. One hour after each ethanol administration, MSH (50, 100, and 200 mg/kg) was also orally administered daily. MSH administration significantly reduced the serum activities of alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, and γ-glutamyl transpeptidase. Histological observation indicated that MSH administration synergistically and significantly decreased the fatty changed region of hepatic parenchyma and the formation of lipid droplet in hepatocytes. Moreover, MSH significantly attenuated the hepatic triglyceride accumulation through reducing lipogenesis genes expression and increasing fatty acid oxidation genes expression. In addition, MSH significantly inhibited protein nitrosylation and lipid peroxidation by lowering cytochrome P450 2E1 enzyme activity and restoring the glutathione level, superoxide dismutase and catalase activity in liver. Furthermore, MSH synergistically decreased the mRNA level of tumor necrosis factor-α in the hepatic tissue. These findings indicate that MSH has potential for preventing alcoholic liver disease through inhibiting hepatic steatosis, oxidative stress, and inflammation.

Pathogenesis of Alcoholic Fatty Liver a Narrative Review

Alcohol effect hepatic lipid metabolism through various mechanisms, leading synergistically to an accumulation of fatty acids (FA) and triglycerides. Obesity, as well as dietary fat (saturated fatty acids (FA) versus poly-unsaturated fatty acids (PUFA)) may modulate the hepatic fat. Alcohol inhibits adenosine monophosphate activated kinase (AMPK). AMPK activates peroxisome proliferator activated receptor a (PPARα) and leads to a decreased activation of sterol regulatory element binding protein 1c (SRABP1c). The inhibition of AMPK, and thus of PPARα, results in an inhibition of FA oxidation. This ß-oxidation is further reduced due to mitochondrial damage induced through cytochrome P4502E1 (CYP2E1)-driven oxidative stress. Furthermore, the synthesis of FAs is stimulated through an activation of SHREP1. In addition, alcohol consumption leads to a reduced production of adiponectin in adipocytes due to oxidative stress and to an increased mobilization of FAs from adipose tissue and from the gut as chylomicrons. On the other side, the secretion of FAs via very-low-density lipoproteins (VLDL) from the liver is inhibited by alcohol. Alcohol also affects signal pathways such as early growth response 1 (Egr-1) associated with the expression of tumour necrosis factor α (TNF α), and the mammalian target of rapamycin (mTOR) a key regulator of autophagy. Both have influence the pathogenesis of alcoholic fatty liver. Alcohol-induced gut dysbiosis contributes to the severity of ALD by increasing the metabolism of ethanol in the gut and promoting intestinal dysfunction. Moreover, pathogen-associated molecular patterns (PAMPS) via specific Toll-like receptor (TLR) bacterial overgrowth leads to the translocation of bacteria. Endotoxins and toxic ethanol metabolites enter the enterohepatic circulation, reaching the liver and inducing the activation of the nuclear factor kappa-B (NFκB) pathway. Pro-inflammatory cytokines released in the process contribute to inflammation and fibrosis. In addition, cellular apoptosis is inhibited in favour of necrosis.

Autophagy, Oxidative Stress, and Alcoholic Liver Disease: A Systematic Review and Potential Clinical Applications

Ethanol consumption triggers oxidative stress by generating reactive oxygen species (ROS) through its metabolites. This process leads to steatosis and liver inflammation, which are critical for the development of alcoholic liver disease (ALD). Autophagy is a regulated dynamic process that sequesters damaged and excess cytoplasmic organelles for lysosomal degradation and may counteract the harmful effects of ROS-induced oxidative stress. These effects include hepatotoxicity, mitochondrial damage, steatosis, endoplasmic reticulum stress, inflammation, and iron overload. In liver diseases, particularly ALD, macroautophagy has been implicated as a protective mechanism in hepatocytes, although it does not appear to play the same role in stellate cells. Beyond the liver, autophagy may also mitigate the harmful effects of alcohol on other organs, thereby providing an additional layer of protection against ALD. This protective potential is further supported by studies showing that drugs that interact with autophagy, such as rapamycin, can prevent ALD development in animal models. This systematic review presents a comprehensive analysis of the literature, focusing on the role of autophagy in oxidative stress regulation, its involvement in organ-organ crosstalk relevant to ALD, and the potential of autophagy-targeting therapeutic strategies.

Caulerpa lentillifera improves ethanol-induced liver injury and modulates the gut microbiota in rats

Caulerpa lentillifera (CL), also called sea grape, is a type of edible green alga which was reported to have antioxidative and immunomodulatory potential. This study aimed to investigate the hepatoprotective effects of CL in a rat model of chronic ethanol exposure. Wistar rats were assigned to four groups and supplied with an isocaloric control liquid diet (group C), an ethanol liquid diet (group E), a control liquid diet supplemented with 5% CL (group CC), or an ethanol liquid diet supplemented with 5% CL (group EC) for a 12-week experimental period. Ethanol feeding induced steatosis, inflammation, and changes in the gut microbiota by the end of the study, whereas CL supplementation significantly improved liver injuries and decreased circulatory endotoxin levels. Moreover, we also found that CL reversed ethanol-induced elevation of hepatic toll-like receptor 4 (TLR4), MyD88 protein expression, the phosphorylated-nuclear factor (NF)-κB-to-NF-κB ratio, and proinflammatory cytokine concentrations. Additionally, CL also increased the abundance of Akkermansia and tight junction proteins and diminished the Firmicutes-to-Bacteroidetes ratio. Dietary CL inhibited the progression of alcoholic liver disease, and some of the possible mechanisms may be strengthening the intestinal barrier function, alleviating dysbiosis, and modulating the TLR4 pathway.

A clinical experience-based Chinese herbal formula improves ethanol-induced drunken behavior and hepatic steatohepatitis in mice models

BACKGROUND

Bao-Gan-Xing-Jiu-Wan (BGXJW) is a clinical experience-based Chinese herbal formula. Its efficacy, pharmacological safety, targeted function, process quality, and other aspects have met the evaluation standards and the latest requirements of preparations. It could prevent and alleviate the symptoms of drunkenness and alcoholic liver injury clinically. The present work aims to elucidate whether BGXJW could protect against drunkenness and alcoholic liver disease in mice and explore the associated mechanism.

MATERIAL AND METHODS

We used acute-on-chronic (NIAAA) mice model to induce alcoholic steatosis, and alcohol binge-drinking model to reappear the drunk condition. BGXJW at indicated doses were administered by oral gavage respectively to analyze its effects on alcoholic liver injury and the associated molecular mechanisms.

RESULTS

BGXJW had no cardiac, hepatic, renal, or intestinal toxicity in mice. Alcoholic liver injury and steatosis in the NIAAA mode were effectively prevented by BGXJW treatment. BGXJW increased the expression of alcohol metabolizing enzymes ADH, CYP2E1, and ALDH2 to enhance alcohol metabolism, inhibited steatosis through regulating lipid metabolism, counteracted alcohol-induced upregulation of lipid synthesis related proteins SREBP1, FASN, and SCD1, meanwhile it enhanced fatty acids β-oxidation related proteins PPAR-α and CPT1A. Alcohol taken enhanced pro-inflammatory TNF-α, IL-6 and down-regulated the anti-inflammatory IL-10 expression in the liver, which were also reversed by BGXJW administration. Moreover, BGXJW significantly decreased the blood ethanol concentration and alleviated drunkenness in the alcohol binge-drinking mice model.

CONCLUSIONS

BGXJW could effectively relieve drunkenness and prevent alcoholic liver disease by regulating lipid metabolism, inflammatory response, and alcohol metabolism.

Fatty Liver Disease, Metabolism and Alcohol Interplay: A Comprehensive Review

Non-alcoholic fatty liver disease (NAFLD) is the most common cause of chronic liver disease worldwide, and its incidence has been increasing in recent years because of the high prevalence of obesity and metabolic syndrome in the Western population. Alcohol-related liver disease (ArLD) is the most common cause of cirrhosis and constitutes the leading cause of cirrhosis-related deaths worldwide. Both NAFLD and ArLD constitute well-known causes of liver damage, with some similarities in their pathophysiology. For this reason, they can lead to the progression of liver disease, being responsible for a high proportion of liver-related events and liver-related deaths. Whether ArLD impacts the prognosis and progression of liver damage in patients with NAFLD is still a matter of debate. Nowadays, the synergistic deleterious effect of obesity and diabetes is clearly established in patients with ArLD and heavy alcohol consumption. However, it is still unknown whether low to moderate amounts of alcohol are good or bad for liver health. The measurement and identification of the possible synergistic deleterious effect of alcohol consumption in the assessment of patients with NAFLD is crucial for clinicians, since early intervention, advising abstinence and controlling cardiovascular risk factors would improve the prognosis of patients with both comorbidities. This article seeks to perform a comprehensive review of the pathophysiology of both disorders and measure the impact of alcohol consumption in patients with NAFLD.

Deficiency of NLR family member NLRC5 alleviates alcohol induced hepatic injury and steatosis by enhancing autophagy of hepatocytes

Steatosis is regarded as an early response of the liver to excessive alcohol consumption, which ultimately results in alcoholic liver disease (ALD). Hepatocytes are the primary drivers of the pathological process known as hepatic damage and steatosis, which is characterized by significant fat accumulation and an abundance of fat vacuoles. NLRs, a family member of pattern recognition receptors, have recently been found to be crucial in liver disorders. In this study, we examined the possible impact of NLRC5, the largest NLR family member, on alcohol-induced fatty liver development using a gene knock-out mouse model. The mouse liver was severely damaged and developed steatosis as a result of chronic and excessive ethanol use, and this damage was prevented by the lack of NLRC5. Additionally, NLRC5 deletion reversed ethanol's ability to increase the serum concentrations of TG, T-CHO, ALT, and AST. Absence of NLRC5 reduced ethanol-stimulated aberrant expression of the vital regulators of lipid synthesis and metabolism, SREBP-1c, FAS and PPAR-α. Furthermore, loss- and gain-of-function research indicated that NLRC5 might affect the autophagy pathway in alcohol-induced hepatic steatosis progression. The functional role of NLRC5 in ALD is obviously impacted by the autophagy inducer rapamycin as well as the autophagy inhibitor 3-MA. Our research showed that NLRC5 was involved in ethanol-induced injury and steatosis of the liver, and may be considered a suitable therapeutic target for treating ALD.

Study on mechanism of action of total flavonoids from Cortex Juglandis Mandshuricae against alcoholic liver disease based on "gut-liver axis"

The objective of this study was to investigate the effects and molecular mechanisms of total flavonoids from Cortex Juglandis Mandshuricae (TFC) on preventing alcohol-induced chronic liver injury and regulating gut microbiota in mice. The results showed that oral administration of TFC significantly attenuated alcoholic liver injury in mice. TFC improved lipid accumulation in mice with chronic alcoholic liver injury through activation of the AMPK/PPARα pathway. In addition, TFC maintained the integrity of the intestinal barrier in alcoholic mice, reducing endotoxin leakage from the intestine and further inhibiting the TLR4/NF-κB inflammatory pathway. More importantly, TFC regulated the intestinal microbiota composition and certain bacteria, including Akkermansia muciniphila, Lactobacillus and others. At the same time, reduced levels of short-chain fatty acids due to alcohol consumption were restored. In summary, TFC upregulated AMPK/PPARα signaling pathway to improve hepatic fat accumulation and oxidative stress; TFC positively regulated intestinal flora composition to reduce intestinal disorders caused by alcohol consumption, and further inhibited alcohol-induced inflammatory responses through the intestinal-liver axis. The above findings may be the mechanism of TFC's pharmacological effects against alcoholic liver injury.

Natural Compounds with Aldose Reductase (AR) Inhibition: A Class of Medicative Agents for Fatty Liver Disease

Fatty liver disease (FLD), which includes both non-alcoholic fatty liver disease (NAFLD) and alcoholic fatty liver disease (ALD), is a worldwide health concern. The etiology of ALD is long-term alcohol consumption, while NAFLD is defined as an abnormal amount of lipid present in liver cells, which is not caused by alcohol intake and has recently been identified as a hepatic manifestation of metabolic syndrome (such as type 2 diabetes, obesity, hypertension, and obesity). Inflammation, oxidative stress, and lipid metabolic dysregulation are all known to play a role in FLD progression. Alternative and natural therapies are desperately needed to treat this disease since existing pharmaceuticals are mostly ineffective. The aldose reductase (AR)/polyol pathway has recently been shown to play a role in developing FLD by contributing to inflammation, oxidative stress, apoptosis, and fat accumulation. Herein, we review the effects of plantderived compounds capable of inhibiting AR in FLD models. Natural AR inhibitors have been found to improve FLD in part by suppressing inflammation, oxidative stress, and steatosis via the regulation of several critical pathways, including the peroxisome proliferator-activated receptor (PPAR) pathway, cytochrome P450 2E1 (CYP2E1) pathway, AMP-activated protein kinase (AMPK) pathway, etc. This review revealed that natural compounds with AR inhibitory effects are a promising class of therapeutic agents for FLD.

Hif-2α regulates lipid metabolism in alcoholic fatty liver disease through mitophagy

BACKGROUND

Disordered lipid metabolism plays an essential role in both the initiation and progression of alcoholic fatty liver disease (AFLD), and fatty acid β-oxidation is increasingly considered as a crucial factor for controlling lipid metabolism. Hif-2α is a member of the Hif family of nuclear receptors, which take part in regulating hepatic fatty acid β-oxidation. However, its functional role in AFLD and the underlying mechanisms remain unclear.

RESULTS

Hif-2α was upregulated in EtOH-fed mice and EtOH-treated AML-12 cells. Inhibition or silencing of Hif-2α led to increased fatty acid β-oxidation and BNIP3-dependent mitophagy. Downregulation of Hif-2α activates the PPAR-α/PGC-1α signaling pathway, which is involved in hepatic fatty acid β-oxidation, by mediating BNIP3-dependent mitophagy, ultimately delaying the progression of AFLD.

CONCLUSIONS

Hif-2α induces liver steatosis, which promotes the progression of AFLD. Here, we have described a novel Hif-2α-BNIP3-dependent mitophagy regulatory pathway interconnected with EtOH-induced lipid accumulation, which could be a potential therapeutic target for the prevention and treatment of AFLD.

Pathogenesis of Alcohol-Associated Liver Disease

Excessive alcohol consumption is a global healthcare problem with enormous social, economic, and clinical consequences. While chronic, heavy alcohol consumption causes structural damage and/or disrupts normal organ function in virtually every tissue of the body, the liver sustains the greatest damage. This is primarily because the liver is the first to see alcohol absorbed from the gastrointestinal tract via the portal circulation and second, because the liver is the principal site of ethanol metabolism. Alcohol-induced damage remains one of the most prevalent disorders of the liver and a leading cause of death or transplantation from liver disease. Despite extensive research on the pathophysiology of this disease, there are still no targeted therapies available. Given the multifactorial mechanisms for alcohol-associated liver disease pathogenesis, it is conceivable that a multitherapeutic regimen is needed to treat different stages in the spectrum of this disease.

Alcohol-Related Liver Disease: An Overview on Pathophysiology, Diagnosis and Therapeutic Perspectives

Alcohol-related liver disease (ALD) refers to a spectrum of liver manifestations ranging from fatty liver diseases, steatohepatitis, and fibrosis/cirrhosis with chronic inflammation primarily due to excessive alcohol use. Currently, ALD is considered as one of the most prevalent causes of liver disease-associated mortality worldwide. Although the pathogenesis of ALD has been intensively investigated, the present understanding of its biomarkers in the context of early clinical diagnosis is not complete, and novel therapeutic targets that can significantly alleviate advanced forms of ALD are limited. While alcohol abstinence remains the primary therapeutic intervention for managing ALD, there are currently no approved medications for treating ALD. Furthermore, given the similarities and the differences between ALD and non-alcoholic fatty liver disease in terms of disease progression and underlying molecular mechanisms, numerous studies have demonstrated that many therapeutic interventions targeting several signaling pathways, including oxidative stress, inflammatory response, hormonal regulation, and hepatocyte death play a significant role in ALD treatment. Therefore, in this review, we summarized several key molecular targets and their modes of action in ALD progression. We also described the updated therapeutic options for ALD management with a particular emphasis on potentially novel signaling pathways.

Molecular Changes in Relation to Alcohol Consumption and Hepatocellular Carcinoma

Alcohol is the one of the major causes of liver diseases and promotes liver cirrhosis and hepatocellular carcinoma (HCC). In hepatocytes, alcohol is converted to acetaldehyde, which causes hepatic steatosis, cellular apoptosis, endoplasmic reticulum stress, peroxidation, production of cytokines and reduces immune surveillance. Endotoxin and lipopolysaccharide produced from intestinal bacteria also enhance the production of cytokines. The development of hepatic fibrosis and the occurrence of HCC are induced by these alcohol metabolites. Several host genetic factors have recently been identified in this process. Here, we reviewed the molecular mechanism associated with HCC in alcoholic liver disease.

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.

Roxadustat, a Hypoxia-Inducible Factor 1α Activator, Attenuates Both Long- and Short-Term Alcohol-Induced Alcoholic Liver Disease

Alcoholic liver disease (ALD) is a worldwide healthcare problem featured by inflammation, reactive oxygen species (ROS), and lipid dysregulation. Roxadustat is used for chronic kidney disease anemia treatment. As a specific inhibitor of prolyl hydroxylase, it can maintain high levels of hypoxia-inducible factor 1α (HIF-1α), through which it can further influence many important pathways, including the three featured in ALD. However, its effects on ALD remain to be elucidated. In this study, we used chronic and acute ALD mouse models to investigate the protective effects of roxadustat in vivo. Our results showed that long- and short-term alcohol exposure caused rising activities of serum transaminases, liver lipid accumulation, and morphology changes, which were reversed by roxadustat. Roxadustat-reduced fatty liver was mainly contributed by the reducing sterol-responsive element-binding protein 1c (SREBP1c) pathway, and enhancing β-oxidation through inducing peroxisome proliferator-activated receptor α (PPARα) and carnitine palmitoyltransferase 1A (CPT1A) expression. Long-term alcohol treatment induced the infiltration of monocytes/macrophages to hepatocytes, as well as inflammatory cytokine expression, which were also blocked by roxadustat. Moreover, roxadustat attenuated alcohol caused ROS generation in the liver of those two mouse models mainly by reducing cytochrome P450 2E1 (CYP2E1) and enhancing superoxidase dismutase 1 (SOD1) expression. In vitro, we found roxadustat reduced inflammation and lipid accumulation mainly via HIF-1α regulation. Taken together, our study demonstrates that activation of HIF-1α can ameliorate ALD, which is contributed by reduced hepatic lipid synthesis, inflammation, and oxidative stress. This study suggested that roxadustat could be a potential drug for ALD treatment.

Improving Lipophagy by Restoring Rab7 Cycle: Protective Effects of Quercetin on Ethanol-Induced Liver Steatosis

Chronic alcohol consumption retards lipophagy, which contributes to the pathogenesis of liver steatosis. Lipophagy-related Rab7 has been presumed as a crucial regulator in the progression of alcohol liver disease despite elusive mechanisms. More importantly, whether or not hepatoprotective quercetin targets Rab7-associated lipophagy disorder is unknown. Herein, alcoholic fatty liver induced by chronic-plus-single-binge ethanol feeding to male C57BL/6J mice was manifested by hampering autophagosomes formation with lipid droplets and fusion with lysosomes compared with the normal control, which was normalized partially by quercetin. The GST-RILP pulldown assay of Rab7 indicated an improved GTP-Rab7 as the quercetin treatment for ethanol-feeding mice. HepG2 cells transfected with CYP2E1 showed similar lipophagy dysfunction when exposed to ethanol, which was blocked when cells were transfected with siRNA-Rab7 in advance. Ethanol-induced steatosis and autophagic flux disruption were aggravated by the Rab7-specific inhibitor CID1067700 while alleviated by transfecting with the Rab7Wt plasmid, which was visualized by immunofluorescence co-localization analysis and mCherry-GFP-LC3 transfection. Furthermore, TBC1D5, a Rab GTPase-activating protein for the subsequent normal circulation of Rab7, was downregulated after alcohol administration but regained by quercetin. Rab7 circulation retarded by ethanol and corrected by quercetin was further revealed by fluorescence recovery after photobleaching (FRAP). Altogether, quercetin attenuates hepatic steatosis by normalizing ethanol-imposed Rab7 turnover disorders and subsequent lipophagy disturbances, highlighting a novel mechanism and the promising prospect of quercetin-like phytochemicals against the crucial first hit from alcohol.

Crosstalk between Oxidative Stress and Inflammatory Liver Injury in the Pathogenesis of Alcoholic Liver Disease

Alcoholic liver disease (ALD) is characterized by the injury, inflammation, and scarring in the liver owing to excessive alcohol consumption. Currently, ALD is a leading cause for liver transplantation. Therefore, extensive studies (in vitro, in experimental ALD models and in humans) are needed to elucidate pathological features and pathogenic mechanisms underlying ALD. Notably, oxidative changes in the liver have been recognized as a signature trait of ALD. Progression of ALD is linked to the generation of highly reactive free radicals by reactions involving ethanol and its metabolites. Furthermore, hepatic oxidative stress promotes tissue injury and, in turn, stimulates inflammatory responses in the liver, forming a pathological loop that promotes the progression of ALD. Accordingly, accumulating further knowledge on the relationship between oxidative stress and inflammation may help establish a viable therapeutic approach for treating ALD.

Crosstalk between gut microbiota and host lipid metabolism in a mouse model of alcoholic liver injury by chronic baijiu or ethanol feeding

A growing body of evidence highlights the important role of gut microbiota and host metabolism, particularly for lipid metabolism, in the development and progression of alcoholic liver disease (ALD). However, the effects of fermented alcoholic beverages on gut microbiota and host lipid metabolism remain under-investigated. Moreover, the crosstalk between gut microbiota and host lipid metabolism is still unclear in experimental ALD. Baijiu is a traditional Chinese alcoholic beverage. It contains large amounts of small molecule bioactive compounds in addition to a significant amount of ethanol (EtOH). In this study, we showed that baijiu caused lower degrees of liver injury than pure EtOH as revealed by phenotypic, biochemical and histologic analyses. Furthermore, baijiu and EtOH gavage resulted in different gut microbiota structures. Specifically, the baijiu group had a significantly higher abundance of Ruminococcus, Oscillospira, Mucispirillum, Bilophila, Parabacteroides and Odoribacter and a lower abundance of Helicobacter and Prevotella than that of the EtOH group. Using a targeted metabolomics approach, we also observed a greater than 19% increase of total hepatic free fatty acids (FFAs) after baijiu feeding and a 33% increase of hepatic FFAs after EtOH feeding. Baijiu feeding significantly increased total hepatic mono-unsaturated FAs (MUFAs). In contrast, polyunsaturated fatty acids (PUFAs), MUFAs and saturated FAs were significantly increased by EtOH feeding. Finally, Spearman's rank correlation showed that the increased levels of FFAs (mainly C20 and C22 unsaturated FAs) significantly correlated with key different gut microbiota, including a positive correlation with Desulfovibrio, Maihella, Helicobacter, Acholeplasma, Parasutterella, Prevotella, AF12 and Alistipes, and a negative correlation with Dorea, Olsenella, Adlercreutzia and Akkermansia. Our results suggest that compounds in baijiu attenuated the development of ALD and thus provided supporting evidence that the host-gut microbiota metabolic interactions play an important role in the development of ALD.

Betulin Targets Lipin1/2-Meidated P2X7 Receptor as a Therapeutic Approach to Attenuate Lipid Accumulation and Metaflammation

The present study focused on the potential mechanism of betulin (BT), a pentacyclic triterpenoid isolated from the bark of white birch (Betula pubescens), against chronic alcohol-induced lipid accumulation and metaflammation. AML-12 and RAW 264.7 cells were administered ethanol (EtOH), lipopolysaccharide (LPS) or BT. Male C57BL/6 mice were fed Lieber-DeCarli liquid diets containing 5% EtOH for 4 weeks, followed by single EtOH gavage on the last day and simultaneous treatment with BT (20 or 50 mg/kg) by oral gavage once per day. In vitro, MTT showed that 0-25 mM EtOH and 0-25 μM BT had no toxic effect on AML-12 cells. BT could regulate sterolregulatory-element-binding protein 1 (SREBP1), lipin1/2, P2X7 receptor (P2X7r) and NOD-like receptor family, pyrin domains-containing protein 3 (NLRP3) expressions again EtOH-stimulation. Oil Red O staining also indicated that BT significantly reduced lipid accumulation in EtOH-stimulated AML-12 cells. Lipin1/2 deficiency indicated that BT might mediate lipin1/2 to regulate SREBP1 and P2X7r expression and further alleviate lipid accumulation and inflammation. In vivo, BT significantly alleviated histopathological changes, reduced serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) and triglyceride (TG) levels, and regulated lipin1/2, SREBP1, peroxisome proliferator activated receptor α/γ (PPARα/γ) and PGC-1α expression compared with the EtOH group. BT reduced the secretion of inflammatory factors and blocked the P2X7r-NLRP3 signaling pathway. Collectively, BT attenuated lipid accumulation and metaflammation by regulating the lipin1/2-mediated P2X7r signaling pathway.

Targeting Peroxisome Proliferator-Activated Receptor-β/δ (PPARβ/δ) for the Treatment or Prevention of Alcoholic Liver Disease

Excessive, chronic alcohol consumption can lead to alcoholic liver disease. The etiology of alcoholic liver disease is multifactorial and is influenced by alterations in gene expression and changes in fatty acid metabolism, oxidative stress, and insulin resistance. These events can lead to steatosis, fibrosis, and eventually to cirrhosis and liver cancer. Many of these functions are regulated by peroxisome proliferator-activated receptors (PPARs). Thus, it is not surprising that PPARs can modulate the mechanisms that cause alcoholic liver disease. While the roles of PPARα and PPARγ are clearer, the role of PPARβ/δ in alcoholic liver disease requires further clarification. This review summarizes the current understanding based on recent studies that indicate that PPARβ/δ can likely be targeted for the treatment and/or the prevention of alcoholic liver disease.

Alcohol Abstinence Rescues Hepatic Steatosis and Liver Injury via Improving Metabolic Reprogramming in Chronic Alcohol-Fed Mice

Background: Alcoholic liver disease (ALD) caused by chronic ethanol overconsumption is a common type of liver disease with a severe mortality burden throughout the world. The pathogenesis of ALD is complex, and no effective clinical treatment for the disease has advanced so far. Prolonged alcohol abstinence is the most effective therapy to attenuate the clinical course of ALD and even reverse liver damage. However, the molecular mechanisms involved in alcohol abstinence-improved recovery from alcoholic fatty liver remain unclear. This study aims to systematically evaluate the beneficial effect of alcohol abstinence on pathological changes in ALD.

Methods: Using the Lieber-DeCarli mouse model of ALD, we analysed whether 1-week alcohol withdrawal reversed alcohol-induced detrimental alterations, including oxidative stress, liver injury, lipids metabolism, and hepatic inflammation, by detecting biomarkers and potential targets.

Results: Alcohol withdrawal ameliorated alcohol-induced hepatic steatosis by improving liver lipid metabolism reprogramming via upregulating phosphorylated 5′-AMP -activated protein kinase (p-AMPK), peroxisome proliferator-activated receptor-α (PPAR-α), and carnitine palmitoyltransferase-1 (CPT-1), and downregulating fatty acid synthase (FAS) and diacylglycerol acyltransferase-2 (DGAT-2). The activities of antioxidant enzymes, including superoxide dismutase (SOD) and glutathione peroxidase (GSH-px), were significantly enhanced by alcohol withdrawal. Importantly, the abstinence recovered alcohol-fed induced liver injury, as evidenced by the improvements in haematoxylin and eosin (H&E) staining, plasma alanine aminotransferase (ALT) levels, and liver weight/body weight ratio. Alcohol-stimulated toll-like receptor 4/mitogen-activated protein kinases (TLR4/MAPKs) were significantly reversed by alcohol withdrawal, which might mechanistically contribute to the amelioration of liver injury. Accordingly, the hepatic inflammatory factor represented by tumour necrosis factor-alpha (TNF-α) was improved by alcohol abstinence.

Conclusion: In summary, we reported that alcohol withdrawal effectively restored hepatic lipid metabolism and reversed liver injury and inflammation by improving metabolism reprogramming. These findings enhanced our understanding of the biological mechanisms involved in the beneficial role of alcohol abstinence as an effective treatment for ALD.

Gut Microbiota-Induced Changes in β-Hydroxybutyrate Metabolism Are Linked to Altered Sociability and Depression in Alcohol Use Disorder

Patients with alcohol use disorder (AUD) present with important emotional, cognitive, and social impairments. The gut microbiota has been recently shown to regulate brain functions and behavior but convincing evidence of its role in AUD is lacking. Here, we show that gut dysbiosis is associated with metabolic alterations that affect behavioral (depression, sociability) and neurobiological (myelination, neurotransmission, inflammation) processes involved in alcohol addiction. By transplanting the gut microbiota from AUD patients to mice, we point out that the production of ethanol by specific bacterial genera and the reduction of lipolysis are associated with a lower hepatic synthesis of β-hydroxybutyrate (BHB), which thereby prevents the neuroprotective effect of BHB. We confirm these results in detoxified AUD patients, in which we observe a persisting ethanol production in the feces as well as correlations among low plasma BHB levels and social impairments, depression, or brain white matter alterations.

Alcohol's Impact on the Gut and Liver

Alcohol is inextricably linked with the digestive system. It is absorbed through the gut and metabolised by hepatocytes within the liver. Excessive alcohol use results in alterations to the gut microbiome and gut epithelial integrity. It contributes to important micronutrient deficiencies including short-chain fatty acids and trace elements that can influence immune function and lead to liver damage. In some people, long-term alcohol misuse results in liver disease progressing from fatty liver to cirrhosis and hepatocellular carcinoma, and results in over half of all deaths from chronic liver disease, over half a million globally per year. In this review, we will describe the effect of alcohol on the gut, the gut microbiome and liver function and structure, with a specific focus on micronutrients and areas for future research.

PPARs as Metabolic Sensors and Therapeutic Targets in Liver Diseases

Carbohydrates and lipids are two components of the diet that provide the necessary energy to carry out various physiological processes to help maintain homeostasis in the body. However, when the metabolism of both biomolecules is altered, development of various liver diseases takes place; such as metabolic-associated fatty liver diseases (MAFLD), hepatitis B and C virus infections, alcoholic liver disease (ALD), and in more severe cases, hepatocelular carcinoma (HCC). On the other hand, PPARs are a family of ligand-dependent transcription factors with an important role in the regulation of metabolic processes to hepatic level as well as in other organs. After interaction with specific ligands, PPARs are translocated to the nucleus, undergoing structural changes to regulate gene transcription involved in lipid metabolism, adipogenesis, inflammation and metabolic homeostasis. This review aims to provide updated data about PPARs’ critical role in liver metabolic regulation, and their involvement triggering the genesis of several liver diseases. Information is provided about their molecular characteristics, cell signal pathways, and the main pharmacological therapies that modulate their function, currently engaged in the clinic scenario, or in pharmacological development.

Protective Mechanism of Edible Food Plants against Alcoholic Liver Disease with Special Mention to Polyphenolic Compounds

Alcoholic liver disease (ALD) is one type of liver disease, causing a global healthcare problem and mortality. The liver undergoes tissue damage by chronic alcohol consumption because it is the main site for metabolism of ethanol. Chronic alcohol exposure progresses from alcoholic fatty liver (AFL) to alcoholic steatohepatitis (ASH), which further lead to fibrosis, cirrhosis, and even hepatocellular cancer. Therapeutic interventions to combat ALD are very limited such as use of corticosteroids. However, these therapeutic drugs are not effective for long-term usage. Therefore, additional effective and safe therapies to cope with ALD are urgently needed. Previous studies confirmed that edible food plants and their bioactive compounds exert a protective effect against ALD. In this review article, we summarized the hepatoprotective potential of edible food plants and their bioactive compounds. The underlying mechanism for the prevention of ALD by edible food plants was as follows: anti-oxidation, anti-inflammation, lipid regulation, inhibition of apoptosis, gut microbiota composition modulation, and anti-fibrosis.

PCSK9 and the Gut-Liver-Brain Axis: A Novel Therapeutic Target for Immune Regulation in Alcohol Use Disorder

Alcohol use disorder (AUD) is a chronic relapsing disorder characterized by an impaired ability to control or stop alcohol intake and is associated with organ damage including alcohol-associated liver disease (ALD) and progressive neurodegeneration. The etiology of AUD is complex, but organ injury due to chronic alcohol use can be partially attributed to systemic and local inflammation along the gut-liver-brain axis. Excessive alcohol use can result in translocation of bacterial products into circulation, increased expression of pro-inflammatory cytokines, and activation of immune cells, including macrophages and/or microglia in the liver and brain. One potential mediator of this alcohol-induced inflammation is proprotein convertase subtilisin/kexin type 9 (PCSK9). PCSK9 is primarily known for its regulation of plasma low-density lipoprotein cholesterol but has more recently been shown to influence inflammatory responses in the liver and brain. In rodent and post-mortem brain studies, chronic alcohol use altered methylation of the PCSK9 gene and increased expression of PCSK9 in the liver and cerebral spinal fluid. Additionally, PCSK9 inhibition in a rat model of ALD attenuated liver inflammation and steatosis. PCSK9 may play an important role in alcohol-induced pathologies along the gut-liver-brain axis and may be a novel therapeutic target for AUD-related liver and brain inflammation.

Mesencephalic astrocyte-derived neurotrophic factor alleviates alcohol induced hepatic steatosis via activating Stat3-mediated autophagy

Alcoholic fatty liver disease (AFLD) is induced by alcohol consumption and may progress to more severe liver diseases such as alcoholic steatohepatitis, fibrosis and cirrhosis, and even hepatocellular carcinoma. Mesencephalic astrocyte-derived neurotrophic factor (MANF) participates in maintaining lipid homeostasis. However, the role of MANF in the pathogenesis of AFLD remains unclear. We established an AFLD mouse model following the US National Institute on Alcohol Abuse and Alcoholism procedure. Both mRNA and protein levels of MANF were significantly increased in the chronic binge alcohol feeding model. Liver-specific knockout of MANF aggravated hepatic lipid accumulation. Similarly, liver-specific overexpression of MANF alleviated AFLD in mouse livers. MANF affected hepatic lipid metabolism by modulating autophagy. The levels of LC3-II and Atg5-Atg12 were decreased in mouse livers with MANF liver-specific knockout and increased with MANF liver-specific overexpression. Furthermore, MANF changed the phosphorylation of Stat3 and its nuclear localization. MANF may have a protective role in the development of AFLD.

The History of Alcoholic Liver Disease: From an Unrecognized Disease to One of the Most Frequent Diseases in Hepatology

This review describes the history of alcoholic liver disease from the beginning of the 1950s until now. It details how the hepatotoxicity of alcohol was discovered by epidemiology and basic research primarily by using new feeding techniques in rodents and primates. The article also recognizes the pioneering work of scientists who contributed to the understanding of the pathophysiology of alcoholic liver disease. In addition, clinical aspects, such as the development of diagnostics and treatment options for alcoholic liver disease, are discussed. Up-to-date knowledge of the mechanism of the disease in 2020 is presented.

Echinacoside ameliorates alcohol-induced oxidative stress and hepatic steatosis by affecting SREBP1c/FASN pathway via PPARα

Alcoholic liver disease (ALD) is one of the most common health problems for drinkers, especially in men. Echinacoside (ECH), a natural phenylethanoid glycoside welcomed by the market, has been shown to have a variety of biological activities, such as neuroprotective, anti-fatigue, anti-diabetes and so on. Here, the protective effect and the underlying mechanism of ECH on ethanol-induced liver injuries were studied. In vitro, the HepG2 cells were treated with ECH prior to ethanol. In vivo, C57BL/6 J mice were fed a Lieber-DeCarli ethanol liquid diet and gave with or without 100 mg/kg ECH for 10 days. Our experiments showed that ECH significantly enhanced the levels of antioxidants and reduced the level of ROS, thus attenuating ethanol-induced oxidative stress. Besides, ECH attenuated lipid accumulation caused by ethanol, as evidenced by oil-red O staining, histological examination and the quantification of TG and TC. Finally, ECH increased the level of PPAR-α, and reduced the levels of SREBP-1c and FASN. When PPAR-α inhibitor was introduced in the system, the effects of ECH on SREBP-1c and FASN were reversed. Taken together, our study suggest that ECH can protect against ethanol-induced liver injuries via alleviating oxidative stress and hepatic steatosis by affecting SREBP-1c/FASN pathway via PPAR-α.

Hylocereus polyrhizus Peel Extract Retards Alcoholic Liver Disease Progression by Modulating Oxidative Stress and Inflammatory Responses in C57BL/6 Mice

Alcoholic liver disease (ALD) has become a health problem as alcohol consumption has increased annually. Hepatic lipid accumulation, oxidative stress, and inflammation are important factors in the progression of ALD. Red pitaya (Hylocereus polyrhizus (Weber) Britt. & Rose) peel is rich in polyphenols and betanins, which possess antioxidative and anti-inflammatory properties. Therefore, the aim of this study was to investigate the effects of red pitaya peel extract (PPE) on ALD and explore the associated mechanisms. C57BL/6 J mice were administered an ethanol liquid diet for 11 weeks with or without two different doses of PPE (500 and 1000 mg/kg BW). PPE treatment significantly ameliorated liver injury and hepatic fat accumulation, and it improved hepatic lipid metabolism via increases in AMPK and PPAR-α protein expression and a decrease in SREBP-1 expression. In addition, PPE inhibited CYP2E1 and Nrf2 protein expression, reduced endotoxin levels in the serum, and decreased TLR4 and MyD88 expression and inflammatory cytokine TNF-α and IL-1β levels in the liver. In conclusion, these findings suggest that PPE may prevent the progression of ALD by modulating lipid metabolism and reducing oxidative stress and inflammatory responses.

cAMP Signaling in Pathobiology of Alcohol Associated Liver Disease

The importance of cyclic adenosine monophosphate (cAMP) in cellular responses to extracellular signals is well established. Many years after discovery, our understanding of the intricacy of cAMP signaling has improved dramatically. Multiple layers of regulation exist to ensure the specificity of cellular cAMP signaling. Hence, disturbances in cAMP homeostasis could arise at multiple levels, from changes in G protein coupled receptors and production of cAMP to the rate of degradation by phosphodiesterases. cAMP signaling plays critical roles in metabolism, inflammation and development of fibrosis in several tissues. Alcohol-associated liver disease (ALD) is a multifactorial condition ranging from a simple steatosis to steatohepatitis and fibrosis and ultimately cirrhosis, which might lead to hepatocellular cancer. To date, there is no FDA-approved therapy for ALD. Hence, identifying the targets for the treatment of ALD is an important undertaking. Several human studies have reported the changes in cAMP homeostasis in relation to alcohol use disorders. cAMP signaling has also been extensively studied in in vitro and in vivo models of ALD. This review focuses on the role of cAMP in the pathobiology of ALD with emphasis on the therapeutic potential of targeting cAMP signaling for the treatment of various stages of ALD.

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.

Roles of peroxisome proliferator-activated receptor α in the pathogenesis of ethanol-induced liver disease

Alcoholic liver disease (ALD) is a progressively aggravated liver disease with high incidence in alcoholics. Ethanol-induced fat accumulation and the subsequent lipopolysaccharide (LPS)-driven inflammation bring liver from reversible steatosis, to irreversible hepatitis, fibrosis, cirrhosis, and even hepatocellular carcinoma. Peroxisome proliferator-activated receptor α (PPARα) is a member of the nuclear receptor superfamily of ligand-activated transcription factors and plays pivotal roles in the regulation of fatty acid homeostasis as well as the inflammation control in the liver. It has been well documented that PPARα activity and/or expression are downregulated in liver of mice exposed to ethanol, which is thought to be one of the prime contributors to ethanol-induced steatosis, hepatitis and fibrosis. This article summarizes the current evidences from in vitro and animal models for the critical roles of PPARα in the onset and progression of ALD. Importantly, it should be noted that the expression of PPARα in human liver is reported to be similar to that in mice, and PPARα expression is downregulated in the liver of patients with nonalcoholic fatty liver disease (NAFLD), a disease sharing many similarities with ALD. Therefore, clinical trials investigating the expression of PPARα in the liver of ALD patients and the efficacy of strong PPARα agonists for the prevention and treatment of ALD are warranted.

NIK links inflammation to hepatic steatosis by suppressing PPARα in alcoholic liver disease

Background: Inflammation and steatosis are the main pathological features of alcoholic liver disease (ALD), in which, inflammation is one of the critical drivers for the initiation and development of alcoholic steatosis. NIK, an inflammatory pathway component activated by inflammatory cytokines, was suspected to link inflammation to hepatic steatosis during ALD. However, the underlying pathogenesis is not well-elucidated. Methods: Alcoholic steatosis was induced in mice by chronic-plus-binge ethanol feeding. Both the loss- and gain-of-function experiments by the hepatocyte-specific deletion, pharmacological inhibition and adenoviral transfection of NIK were utilized to elucidate the role of NIK in alcoholic steatosis. Rate of fatty acid oxidation was assessed in vivo and in vitro. PPARα agonists or antagonists of MEK1/2 and ERK1/2 were used to identify the NIK-induced regulation of PPARα, MEK1/2, and ERK1/2. The potential interactions between NIK, MEK1/2, ERK1/2 and PPARα and the phosphorylation of PPARα were clarified by immunoprecipitation, immunoblotting and far-western blotting analysis. Results: Hepatocyte-specific deletion of NIK protected mice from alcoholic steatosis by sustaining hepatic fatty acid oxidation. Moreover, overexpression of NIK contributed to hepatic lipid accumulation with disrupted fatty acid oxidation. The pathological effect of NIK in ALD may be attributed to the suppression of PPARα, the main controller of fatty acid oxidation in the liver, because PPARα agonists reversed NIK-mediated hepatic steatosis and malfunction of fatty acid oxidation. Mechanistically, NIK recruited MEK1/2 and ERK1/2 to form a complex that catalyzed the inhibitory phosphorylation of PPARα. Importantly, pharmacological intervention against NIK significantly attenuated alcoholic steatosis in ethanol-fed mice. Conclusions: NIK targeting PPARα via MEK1/2 and ERK1/2 disrupts hepatic fatty acid oxidation and exhibits high value in ALD therapy.

Distinct metabolic adaptation of liver circadian pathways to acute and chronic patterns of alcohol intake

Binge drinking and chronic exposure to ethanol contribute to alcoholic liver diseases (ALDs). A potential link between ALDs and circadian disruption has been observed, though how different patterns of alcohol consumption differentially impact hepatic circadian metabolism remains virtually unexplored. Using acute versus chronic ethanol feeding, we reveal differential reprogramming of the circadian transcriptome in the liver. Specifically, rewiring of diurnal SREBP transcriptional pathway leads to distinct hepatic signatures in acetyl-CoA metabolism that are translated into the subcellular patterns of protein acetylation. Thus, distinct drinking patterns of alcohol dictate differential adaptation of hepatic circadian metabolism.

Natural compounds in the chemoprevention of alcoholic liver disease

Alcoholic liver disease (ALD), caused by excessive consumption of alcohol, is a major cause of chronic liver disease worldwide. Much effort has been expended to explore the pathogenesis of ALD. Hepatic cell injury, oxidative stress, inflammation, regeneration, and bacterial translocation are all involved in the pathogenesis of ALD. Immediate abstinence is the most important therapeutic treatment for affected individuals. However, the medical treatment for ALD had not advanced in a long period. Intriguingly, an increasing body of research indicates the potential of natural compounds in the targeted therapy of ALD. A plethora of dietary natural products such as flavonoids, resveratrol, saponins, and β-carotene are found to exert protective effects on ALD. This occurs through various mechanisms composed of antioxidative, anti-inflammatory, iron chelation, pro-apoptosis, and/or antiproliferation of hepatic stellate cells and hepatocellular carcinoma cells. In this review, we will summarize current knowledge about the pathogenesis and treatments of ALD and focus on the potential of natural compounds in ALD therapies and underlying mechanisms.

Hepatic Inactivation of the Type 2 Deiodinase Confers Resistance to Alcoholic Liver Steatosis

BACKGROUND

A mouse with hepatocyte-specific deiodinase type II inactivation (Alb-D2KO) is resistant to diet-induced obesity, hepatic steatosis, and hypertriglyceridemia due to perinatal epigenetic modifications in the liver. This phenotype is linked to low levels of Zfp125, a hepatic transcriptional repressor that promotes liver steatosis by inhibiting genes involved in packaging and secretion of very-low-density lipoprotein.

METHODS

Here, we used chronic and binge ethanol (EtOH) in mice to cause liver steatosis.

RESULTS

The EtOH treatment causes a 2.3-fold increase in hepatic triglyceride content; Zfp125 levels were approximately 50% higher in these animals. In contrast, Alb-D2KO mice did not develop EtOH-induced liver steatosis. They also failed to elevate Zfp125 to the same levels, despite being on the EtOH-containing diet for the same period of time. Their phenotype was associated with 1.3- to 2.9-fold up-regulation of hepatic genes involved in lipid transport and export that are normally repressed by Zfp125, that is, Mttp, Abca1, Ldlr, Apoc1, Apoc3, Apoe, Apoh, and Azgp1. Furthermore, genes involved in the EtOH metabolic pathway, that is, Aldh2 and Acss2, were also 1.6- to 3.1-fold up-regulated in Alb-D2KO EtOH mice compared with control animals kept on EtOH.

CONCLUSIONS

EtOH consumption elevates expression of Zfp125. Alb-D2KO animals, which have lower levels of Zfp125, are much less susceptible to EtOH-induced liver steatosis.

Pathogenesis, Early Diagnosis, and Therapeutic Management of Alcoholic Liver Disease

Alcoholic liver disease (ALD) refers to the damages to the liver and its functions due to alcohol overconsumption. It consists of fatty liver/steatosis, alcoholic hepatitis, steatohepatitis, chronic hepatitis with liver fibrosis or cirrhosis, and hepatocellular carcinoma. However, the mechanisms behind the pathogenesis of alcoholic liver disease are extremely complicated due to the involvement of immune cells, adipose tissues, and genetic diversity. Clinically, the diagnosis of ALD is not yet well developed. Therefore, the number of patients in advanced stages has increased due to the failure of proper early detection and treatment. At present, abstinence and nutritional therapy remain the conventional therapeutic interventions for ALD. Moreover, the therapies which target the TNF receptor superfamily, hormones, antioxidant signals, and MicroRNAs are used as treatments for ALD. In particular, mesenchymal stem cells (MSCs) are gaining attention as a potential therapeutic target of ALD. Therefore, in this review, we have summarized the current understandings of the pathogenesis and diagnosis of ALD. Moreover, we also discuss the various existing treatment strategies while focusing on promising therapeutic approaches for ALD.

Lipophagy and Alcohol-Induced Fatty Liver

This review describes the influence of ethanol consumption on hepatic lipophagy, a selective form of autophagy during which fat-storing organelles known as lipid droplets (LDs) are degraded in lysosomes. During classical autophagy, also known as macroautophagy, all forms of macromolecules and organelles are sequestered in autophagosomes, which, with their cargo, fuse with lysosomes, forming autolysosomes in which the cargo is degraded. It is well established that excessive drinking accelerates intrahepatic lipid biosynthesis, enhances uptake of fatty acids by the liver from the plasma and impairs hepatic secretion of lipoproteins. All the latter contribute to alcohol-induced fatty liver (steatosis). Here, our principal focus is on lipid catabolism, specifically the impact of excessive ethanol consumption on lipophagy, which significantly influences the pathogenesis alcohol-induced steatosis. We review findings, which demonstrate that chronic ethanol consumption retards lipophagy, thereby exacerbating steatosis. This is important for two reasons: (1) Unlike adipose tissue, the liver is considered a fat-burning, not a fat-storing organ. Thus, under normal conditions, lipophagy in hepatocytes actively prevents lipid droplet accumulation, thereby maintaining lipostasis; (2) Chronic alcohol consumption subverts this fat-burning function by slowing lipophagy while accelerating lipogenesis, both contributing to fatty liver. Steatosis was formerly regarded as a benign consequence of heavy drinking. It is now recognized as the "first hit" in the spectrum of alcohol-induced pathologies that, with continued drinking, progresses to more advanced liver disease, liver failure, and/or liver cancer. Complete lipid droplet breakdown requires that LDs be digested to release their high-energy cargo, consisting principally of cholesteryl esters and triacylglycerols (triglycerides). These subsequently undergo lipolysis, yielding free fatty acids that are oxidized in mitochondria to generate energy. Our review will describe recent findings on the role of lipophagy in LD catabolism, how continuous heavy alcohol consumption affects this process, and the putative mechanism(s) by which this occurs.

Regulatory T cells suppress excessive lipid accumulation in alcoholic liver disease

Sensitization of hepatic immune cells from chronic alcohol consumption gives rise to inflammatory accumulation, which is considered a leading cause of liver damage. Regulatory T cells (Tregs) are an immunosuppressive cell subset that plays an important role in a variety of liver diseases; however, data about pathological involvement of Tregs in liver steatosis of alcoholic liver disease (ALD) is insufficient. In mouse models of ALD, we found that increased lipid accumulation by chronic alcohol intake was accompanied by oxidative stress, inflammatory accumulation, and Treg decline in the liver. Adoptive transfer of Tregs relieved lipid metabolic disorder, oxidative stress, inflammation, and, consequently, ameliorated the alcoholic fatty liver. Macrophages are a dominant source of inflammation in ALD. Aberrant macrophage activation and cytokine production were activated during chronic alcohol consumption, but were significantly inhibited after Treg transfer. In vitro, macrophages were co-activated by alcohol and lipopolysaccharide to mimic a condition for alcoholic liver microenvironment. Tregs suppressed monocyte chemoattractant protein-1 and TNF-α production from these macrophages. However, such effects of Tregs were remarkably neutralized when interleukin (IL)-10 was blocked. Altogether, our data uncover a novel role of Tregs in restoring liver lipid metabolism in ALD, which partially relies on IL-10-mediated suppression of hepatic pro-inflammatory macrophages.

The hepatic BMAL1/AKT/lipogenesis axis protects against alcoholic liver disease in mice via promoting PPARα pathway

Alcohol liver disease (ALD) is one of the major chronic liver diseases worldwide, ranging from fatty liver, alcoholic hepatitis, cirrhosis, and potentially, hepatocellular carcinoma. Epidemiological studies suggest a potential link between ALD and impaired circadian rhythms, but the role of hepatic circadian proteins in the pathogenesis of ALD remains unknown. Here we show that the circadian clock protein BMAL1 in hepatocytes is both necessary and sufficient to protect mice from ALD. Ethanol diet-fed mice with liver-specific knockout (Bmal1-LKO) or depletion of Bmal1 develop more severe liver steatosis and injury as well as a simultaneous suppression of both de novo lipogenesis and fatty acid oxidation, which can be rescued by the supplementation of synthetic PPARα ligands. Restoring de novo lipogenesis in the liver of Bmal1-LKO mice by constitutively active AKT not only elevates hepatic fatty acid oxidation but also alleviates ethanol-induced fatty liver and liver injury. Furthermore, hepatic over-expression of lipogenic transcription factor ChREBP, but not SREBP-1c, in the liver of Bmal1-LKO mice also increases fatty acid oxidation and partially reduces ethanol-induced fatty liver and liver injury. Conclusion: we identified a protective role of BMAL1 in hepatocytes against ALD. The protective action of BMAL1 during alcohol consumption depends on its ability to couple ChREBP-induced de novo lipogenesis with PPARα-mediated fatty oxidation. (Hepatology 2018).

Nrf2 in alcoholic liver disease

Alcoholic liver disease (ALD) is a leading cause of morbidity and mortality of liver disorders and a major health issue globally. ALD refers to a spectrum of liver pathologies ranging from steatosis, steatohepatitis, fibrosis, cirrhosis and even hepatocellular carcinoma. Various mechanisms, including oxidative stress, protein and DNA modification, inflammation and impaired lipid metabolism, have been implicated in the pathogenesis of ALD. Further, reactive oxygen species (ROS) in particular, have been identified as a key component in the initiation and progression of ALD. Nuclear factor erythroid 2 like 2 (Nrf2) is a master regulator of the intracellular adaptive antioxidant response to oxidative stress, and aids in the detoxification of a variety of toxicants. Given its cytoprotective role, Nrf2 has been extensively studied as a therapeutic target for ALD. Paradoxically, however, emerging evidence have revealed that Nrf2 may be implicated in the progression of ALD. In this review, we summarize the role of Nrf2 in the development of ALD and discuss the underlying mechanisms. Clearly, more comprehensive studies with proper animal and cell models and in human are needed to verify the potential therapeutic role of Nrf2 in ALD.