ALDH2 deficiency increases susceptibility to binge alcohol-induced gut leakiness, endotoxemia, and acute liver injury in mice through the gut-liver axis

New developments on the effects of alcohol use on immunity, inflammation and organ function: A summary of the 2024 Alcohol and Immunology Research Interest Group (AIRIG) meeting

The 29th annual Alcohol and Immunology Research Interest Group (AIRIG) meeting was held on November 22nd, 2024, at Loyola University Chicago, Health Science Campus, Maywood, Illinois. The meeting was divided into three plenary sessions and a poster session. The overall focus of this year's meeting was on alcohol and host immunity, alcohol and organ dysfunction, and alcohol, inflammation, and tissue injury. The presentations in each session shared the latest developments on the impact of alcohol in a wide variety of fields including trauma, emergency care and hospitalization, cardiovascular health, neurodegenerative disease, gut microbiome, and hepatology.

The Link Between Alcohol Consumption and Kidney Injury

Alcohol consumption contributes to systemic organ dysfunction, but its direct effect on kidney health is unclear. Epidemiological studies show inconsistent findings due to reliance on conventional markers like serum creatinine (sCr) and blood urea nitrogen (BUN), which are insensitive to early chronic kidney disease (CKD) and influenced by factors such as muscle mass, diet, and hydration status. Experimental studies indicate that alcohol may directly exacerbate renal damage through mitochondrial dysfunction, oxidative stress, and inflammation. Furthermore, indirect effects from alcohol-induced altered intestinal permeability and microbiome, liver injury, microcirculatory/cardiac dysfunction and muscle damage may also facilitate kidney damage. Notably, alcohol-related liver disease can lead to hepatorenal syndrome, a severe form of kidney dysfunction driven by circulatory disturbances and systemic inflammation. This overview explores the adverse effects of alcohol misuse on kidney health and disease, emphasizing the need for comprehensive epidemiological studies with more sensitive kidney injury biomarkers. It also highlights the importance of using clinically relevant preclinical models to clarify the underlying mechanisms of alcohol-related kidney injury and to enhance our understanding of its long-term clinical consequences.

Intestinal Microbes, Metabolites, and Hormones in Alcohol-Associated Liver Disease

Alcohol-associated liver disease (ALD)-encompassing conditions including steatosis, fibrosis, cirrhosis, and hepatocellular carcinoma-refers to hepatic damage arising from excessive or hazardous alcohol consumption, and is now recognized as a significant global health burden. Although the mechanisms underlying ALD remain incompletely understood, several pathways have been substantiated over the last five decades, notably the involvement of intestinal microorganisms and the involvement of the gut-liver axis in alcohol metabolism and ALD pathogenesis. Ethanol intake disrupts the intestinal microbial balance and compromises the gut barrier, resulting in increased permeability to microbial products. The subsequent translocation of microbial metabolites and other antigenic substances to the liver activates hepatic immune responses, thereby contributing to liver injury. In addition, gastrointestinal hormones are also implicated in ALD progression through various mechanisms. Although no therapies for ALD have been approved by the Food and Drug Administration, various therapeutic strategies targeting the intestinal microbiota and gut barrier have been identified. In conclusion, this review discusses the role of the gut-liver axis in alcohol metabolism and ALD pathogenesis and explores the emerging therapeutic strategies.

Evaluation of Anti-Hyperlipidemic and Anti-Atherogenic Activity of Asiatic Acid and Its Effect on Lipid Peroxidation in Hyperlipidemic Rats

Atherosclerosis is associated with several illnesses, such as coronary heart disease (CHD), peripheral vascular disease, and ischemic cerebrovascular disease. Atherosclerosis development and accompanying complications are predominantly influenced by Hyperlipidemia, which plays a crucial role. These illnesses are the primary cause of most sickness and death among those who are in their middle age or older. The incidence of dyslipidemia among Chinese adults aged 18 and older is 18.6%, indicating that there are around 160 million individuals affected by this condition. This represents the smallest number of patients globally. This analysis was derived from research undertaken in the field of epidemiology. Hence, developing a comprehensive approach for early prevention and treatment of Hyperlipidemia is imperative. The reason for this is that Hyperlipidemia has the potential to deteriorate progressively. Despite the notable progress made in treating Hyperlipidemia with synthetic drugs, there has been a renewed interest in medicinal plants and phytoconstituents known for their therapeutic capabilities. Asiatic acid, primarily present in Centella asiatica (L.), is classified as one of the phytocompounds that can decrease plasma lipids and lipid peroxidation. This plant may include asiaticoside, asiatic acid, and other components. Asiatic acid has the potential to prevent Hyperlipidemia. The aim of our research is to explore the anti-Hyperlipidemic and anti-atherosclerosis potential of Asiatic acid, which will help to explore its potential mechanism of action and a possibility of its usefulness in this regard.

Kaempferol ameliorated central nervous injury induced by alcohol uptake through improving intestinal barrier function

Excessive neuroinflammation resulting from chronic alcohol intake is an important risk factor for central nervous system injury. The aim of this study was to investigate the effect of kaempferol (KAE) on alcohol-induced neural injury and its underlying mechanism. C57BL/6 N mice were employed to develop a binge-on-chronic alcohol exposure model, with different doses of KAE as an interventional drug for 6 weeks. Neuronal damage and microglial activation in the brain, as well as colonic tissue damage and serum lipopolysaccharide (LPS) concentrations, were systematically assessed. Additionally, Caco-2 cells were exposed to alcohol to induce intestinal epithelial injury in vitro. Chronic alcohol exposure let to significant neuronal damage in the cortex and hippocampus of mice. KAE treatment effectively attenuated microglial activation and reduced neuronal damage in the brains of alcohol-exposed mice. Analysis of colonic tissues revealed that KAE administration inhibited miRNA-122a expression, alleviated pathological damage, and enhanced occludin expression, thereby significantly lowing serum LPS concentrations in alcohol-fed mice. In vitro, KAE markedly decreased miRNA-122a expression and enhanced occludin levels in Caco-2 cells treated with alcohol. Furthermore, overexpression of miRNA-122a was found to diminish occludin protein production in Caco-2 cells, which was significantly counteracted by KAE treatment. KAE treatment enhanced intestinal barrier function to alleviate neuronal damage caused by microglial activation mediated by gut-derived LPS under alcohol expose. This effect of KAE was involved in the enhance of intestinal occludin expression by inhibiting the expression of miRNA-122a. This suggested that KAE had the potential to prevent alcohol-induced neurological damage.

Acidic polysaccharide CP-2 from Dioscoreae Rhizoma ameliorated acute alcoholic liver injury through the gut-liver axis and AMPK/PPAR pathway

Dioscoreae Rhizoma polysaccharides exhibit gastrointestinal protective properties, yet their efficacy against acute alcoholic liver injury (AALI) remains unexplored. This study identifies a novel acidic heteropolysaccharide (CP-2, Mw = 8.4 × 103 kDa) with galactose/galacturonic acid dominance and delineates its multimodal hepatoprotective mechanisms. In AALI mice, CP-2 attenuated liver injury by enhancing ADH and ALDH activities while restoring redox balance via SOD/CAT activation and MDA reduction, and suppressed inflammation by inhibiting IL-1β, IL-6, and TNF-α levels. Gut-liver axis modulation was achieved through intestinal barrier reinforcement (ZO-1, Occludin, Claudin-1) and microbiota rebalancing. CP-2 could reduce gram-negative bacteria ([Ruminococcus]_ torques_ group and Escherichia- Shigella) and Proteobacteria abundance while enriching Bacteroides and Akkermansia abundance, which collectively suppressed serum LPS level. In addition, CP-2 could activate the AMPK/PPAR signaling pathway to reduce the production of fatty acids and promote their degradation in AALI. CP-2 can improve AALI by adjusting the composition of gut microbiota, repairing intestinal barrier function, decreasing systemic inflammation and oxidative reactions, and regulating the AMPK/PPAR pathway. Our findings unveil CP-2 as a prebiotic candidate for AALI intervention and may advance functional food development for alcohol-related hepatopathies.

Neutrophil extracellular traps (NETs) and NETosis in alcohol-associated diseases: A systematic review

Heavy alcohol consumption is implicated in the alteration of the antimicrobial function of neutrophils, such as phagocytosis, chemotaxis, the formation of neutrophil extracellular traps (NETs), and the occurrence of NETosis. NETosis is an endogenous process of elimination of invading microbes, autoantibodies, and inflammatory elements such as danger-associated molecular patterns (DAMPs) and pathogen-associated patterns (PAMPs). However, both exaggeration and suppression of NETosis modulate normal physiological and metabolic processes by influencing events at the molecular and cellular levels. Recent research shows that binge alcohol consumption induces NETosis, leading to tissue damage and inflammation. Binge alcohol consumption, chronic alcohol intake, and alcohol use disorder (AUD) can affect immunity and often lead to alcohol-associated liver disease (ALD) and/or other organ damage. Alcohol can lead to detrimental consequences in multiple organs, including the brain, liver, pancreas, and gut. Gut-derived microbial substances, such as endotoxins in the circulation, induce systemic inflammation. Sterile danger signals from damaged cells, cytokines, and prostaglandins act as proinflammatory stimuli and are involved in multiple signaling pathways. The alcohol-induced proinflammatory cytokines chemoattract neutrophils, which interact and coordinate with other immune cells to exaggerate or suppress inflammation within the inflammatory milieu, depending on the alcohol effects. Several proteins, including different receptors, play important roles in the activation and formation of NETs as well as the initiation and execution of NETosis. This review article specifically gathers the current information on NETosis, its biological components, and signaling pathways relating to the formation of NETs and the occurrence of NETosis associated with ALD and AUD in multiorgans, specifically in the brain, liver, and gut. We also briefly describe various therapeutic strategies against AUD-associated NETosis in experimental models and human disease states.

Network pharmacology and experimental validation reveal dexmedetomidine's protective mechanisms against acute liver injury in mice

This study explored the role and molecular mechanisms of dexmedetomidine (DEX), an α2-adrenergic receptor agonist, in the treatment of a mouse model of acute liver injury (ALI). DEX significantly mitigated hepatic tissue damage and reduced serum levels of liver function biomarkers and proinflammatory cytokines. Network pharmacology analysis revealed 81 common targets between DEX and ALI, identifying 10 crucial hub genes. Kyoto Encyclopedia of Genes and Genomes pathway analysis indicated that DEX's therapeutic effect on ALI is likely linked to the activation of the PI3K/AKT pathway. Immunohistochemical experiments verified DEX's activation of the PI3K/AKT pathway. Molecular docking and dynamic simulations confirmed the stable interaction between DEX and the epidermal growth factor receptor (EGFR). Immunohistochemistry and western blotting further validated that DEX pretreatment upregulated EGFR expression. Our findings indicate that DEX may mitigate ALI by interacting with EGFR and triggering the PI3K/AKT pathway. These findings provide a solid theoretical and experimental basis for using DEX as a potential therapeutic regimen for treating inflammatory liver diseases.

Alcohol Plus Additional Risk Factors: Rodent Model of Liver Injury

Alcohol-associated liver disease (ALD), primarily caused by chronic excessive alcohol consumption, is a leading cause of chronic liver disease worldwide. ALD includes alcohol-associated steatotic liver, alcohol-associated hepatitis (AH), fibrosis, cirrhosis, and can even progress to hepatocellular carcinoma (HCC). Existing research indicates that the risk factors of ALD are quite numerous. In addition to drinking patterns, factors such as aldehyde dehydrogenase 2 (ALDH2) deficiency, smoking, medication administration, high-fat diet (HFD), hepatitis virus infection, and disruption of circadian rhythms can also increase susceptibility to ALD. However, there is limited understanding regarding the exacerbation of liver injury by alcohol plus additional risk factors. This review presents rodent models of EtOH + "X," which simulate the synergistic effects of alcohol and additional risk factors in causing liver injury. These models offer a further exploration of the interactions between alcohol and additional risk factors, advancing the simulation of human ALD and providing a more reliable platform for studying disease mechanisms and exploring therapeutic interventions. We summarize the modeling methods, relevant indicators of liver injury, and focus on the targets of the synergistic effects as well as the associated mechanisms.

Establishment and application of murine models of alcoholic liver disease: A narrative review

In recent years, there have been significant advances in pathological research on alcoholic liver disease (ALD), with suitable animal models making a significant contribution. However, the currently established animal ALD models still have some significant drawbacks, especially the inability to induce the entire human ALD lineage, which may be related to physiological differences between animals and humans. This review comprehensively summarized the most widely used experimental models of ALD, including voluntary drinking, Lieber-DeCarli, Meadows-Cook, Tsukamoto-French, NIAAA, and the "second hit" model. "Second hit" refers to an additional factor that damages the liver. There are various "second hit" models that fall into two main categories: particular diets and drugs. These models can either simulate human drinking patterns more accurately or produce varying degrees of ALD without significantly increasing animal mortality. We introduced the established method of the original models, discussed the advantages and disadvantages of the existing models from the aspects of operability and practicality, and provided existing improvement methods, hoping to provide a reference for future researchers.

The role of ALDHs in lipid peroxidation-related diseases

Lipid peroxidation presents the oxidative degradation of polyunsaturated fatty acids lincited by reactive species. Excessive accumulation of lipid peroxidation byproducts, including 4-hydroxy-2-nonenal (4-HNE) and malondialdehyde (MDA), causes protein dysfunction and various illnesses. Aldehyde dehydrogenases (ALDHs) catalyze the metabolism of both endogenous and exogenous aldehydes. These enzymes participate in detoxification and intermediary metabolism. Contemporary research has affirmed the involvement of both enzymatic and non-enzymatic pathways of ALDHs in modulating the evolution of diseases associated with lipid peroxidation. This review provides an overview of the biological functions and clinical implications concerning the enzymatic and non-enzymatic pathways of ALDHs in diseases related to lipid peroxidation, such as, non-alcoholic fatty liver disease (NAFLD), atherosclerosis, and type 2 diabetes (T2DM). Furthermore, the activators or inhibitors of ALDHs represent a promising therapeutic strategy for lipid peroxidation-related diseases.

Gut-liver axis: Recent concepts in pathophysiology in alcohol-associated liver disease

The growing recognition of the role of the gut microbiome's impact on alcohol-associated diseases, especially in alcohol-associated liver disease, emphasizes the need to understand molecular mechanisms involved in governing organ-organ communication to identify novel avenues to combat alcohol-associated diseases. The gut-liver axis refers to the bidirectional communication and interaction between the gut and the liver. Intestinal microbiota plays a pivotal role in maintaining homeostasis within the gut-liver axis, and this axis plays a significant role in alcohol-associated liver disease. The intricate communication between intestine and liver involves communication between multiple cellular components in each organ that enable them to carry out their physiological functions. In this review, we focus on novel approaches to understanding how chronic alcohol exposure impacts the microbiome and individual cells within the liver and intestine, as well as the impact of ethanol on the molecular machinery required for intraorgan and interorgan communication.

Alcohol-related liver disease (ALD): current perspectives on pathogenesis, therapeutic strategies, and animal models

Alcohol-related liver disease (ALD) is a major cause of morbidity and mortality worldwide. It encompasses conditions such as fatty liver, alcoholic hepatitis, chronic hepatitis with liver fibrosis or cirrhosis, and hepatocellular carcinoma. Numerous recent studies have demonstrated the critical role of oxidative stress, abnormal lipid metabolism, endoplasmic reticulum stress, various forms of cell death (including apoptosis, necroptosis, and ferroptosis), intestinal microbiota dysbiosis, liver immune response, cell autophagy, and epigenetic abnormalities in the pathogenesis of ALD. Currently, abstinence, corticosteroids, and nutritional therapy are the traditional therapeutic interventions for ALD. Emerging therapies for ALD mainly include the blockade of inflammatory pathways, the promotion of liver regeneration, and the restoration of normal microbiota. Summarizing the advances in animal models of ALD will facilitate a more systematic investigation of the pathogenesis of ALD and the exploration of therapeutic targets. This review summarizes the latest insight into the pathogenesis and molecular mechanisms of ALD, as well as the pros and cons of ALD rodent models, providing a basis for further research on therapeutic strategies for ALD.

Mitochondrial quality control in alcohol-associated liver disease

Excessive alcohol consumption is a leading cause of alcohol-associated liver disease (ALD), a significant global health concern with limited therapeutic options. Understanding the key factors contributing to ALD pathogenesis is crucial for identifying potential therapeutic targets. Central to ALD pathogenesis is the intricate interplay between alcohol metabolism and cellular processes, particularly involving mitochondria. Mitochondria are essential organelles in the liver, critical for energy production and metabolic functions. However, they are particularly vulnerable to alcohol-induced damage due to their involvement in alcohol metabolism. Alcohol disrupts mitochondrial function, impairing ATP production and triggering oxidative stress, which leads to cellular damage and inflammation. Mitochondrial quality control mechanisms, including biogenesis, dynamics, and mitophagy, are crucial for maintaining optimal mitochondrial function. Chronic alcohol consumption disrupts mitochondrial quality control checkpoints, leading to mitochondrial dysfunction that impairs fatty acid oxidation and contributes to hepatic steatosis in ALD. Moreover, alcohol promotes the accumulation of damaged mitochondria and the release of proinflammatory components, exacerbating liver damage and inflammation. Preserving mitochondrial health presents a promising therapeutic approach to mitigate ALD progression. In this review, we provide a comprehensive overview of the effects of alcohol on mitochondrial function and quality control mechanisms, highlighting their role in ALD pathogenesis. Understanding these mechanisms may pave the way for the development of novel therapeutic interventions for ALD.

The interplay between microbiome and host factors in pathogenesis and therapy of head and neck cancer

Heterogeneous cancers that lack strong driver mutations with high penetrance, such as head and neck squamous cell carcinoma (HNSCC), present unique challenges to understanding their aetiology due to the complex interactions between genetics and environmental factors. The interplay between lifestyle factors (such as poor oral hygiene, smoking, or alcohol consumption), the oral and gut microbiome, and host genetics appears particularly important in the context of HNSCC. The complex interplay between the gut microbiota and cancer treatment outcomes has also received increasing attention in recent years. This review article describes the bidirectional communication between the host and the oral/gut microbiome, focusing on microbiome-derived metabolites and their impact on systemic immune responses and the modulation of the tumour microenvironment. In addition, we review the role of host lifestyle factors in shaping the composition of the oral/gut microbiota and its impact on cancer progression and therapy. Overall, this review highlights the rationality of considering the oral/gut microbiota as a critical determinant of cancer therapy outcomes and points to therapeutic opportunities offered by targeting the oral/gut microbiota in the management of HNSCC.

Trilobatin, a Novel Naturally Occurring Food Additive, Ameliorates Alcoholic Liver Disease in Mice: Involvement of Microbiota-Gut-Liver Axis and Yap/Nrf2 Signaling Pathway

Trilobatin, a novel natural food additive, exerts a protective effect on acute liver injury. However, whether Trilobatin can protect against alcoholic liver disease (ALD) has not been elucidated. This research is intended to ascertain the impact of Trilobatin on ALD in mice and decipher the potential underlying mechanisms. Lieber-DeCarli liquid alcohol diet was used to induce ALD in mice, followed by administration of Trilobatin (10, 20, 40 mg·kg-1·d-1) for 15 days. The results suggested that Trilobatin significantly alleviated ethanol-induced hepatic injury in mice. Furthermore, RNA-Seq analysis revealed that yes-associated protein (YAP) downregulation occurred in the liver after Trilobatin treatment. Mechanistically, Trilobatin directly bound to YAP and hindered its nuclear translocation, which activated the Nrf2 pathway to reduce pro-inflammatory cytokines and oxidative stress. Intriguingly, 16S rDNA analysis results revealed that Trilobatin reshaped the gut microbiota, reducing harmful bacteria and increasing beneficial bacteria. It also enhanced tight junction proteins, defending against damage to the intestinal barrier. These findings not only highlight the microbiota-gut-liver axis and YAP/Nrf2 pathway as crucial potential targets to treat ALD but also reveal that Trilobatin effectively protects against ALD, at least partly, through modulating the microbiota-gut-liver axis and YAP/Nrf2 pathway.

New insights into the intestinal barrier through "gut-organ" axes and a glimpse of the microgravity's effects on intestinal barrier

Gut serves as the largest interface between humans and the environment, playing a crucial role in nutrient absorption and protection against harmful substances. The intestinal barrier acts as the initial defense mechanism against non-specific infections, with its integrity directly impacting the homeostasis and health of the human body. The primary factor attributed to the impairment of the intestinal barrier in previous studies has always centered on the gastrointestinal tract itself. In recent years, the concept of the "gut-organ" axis has gained significant popularity, revealing a profound interconnection between the gut and other organs. It speculates that disruption of these axes plays a crucial role in the pathogenesis and progression of intestinal barrier damage. The evaluation of intestinal barrier function and detection of enterogenic endotoxins can serve as "detecting agents" for identifying early functional alterations in the heart, kidney, and liver, thereby facilitating timely intervention in the disorders. Simultaneously, consolidating intestinal barrier integrity may also present a potential therapeutic approach to attenuate damage in other organs. Studies have demonstrated that diverse signaling pathways and their corresponding key molecules are extensively involved in the pathophysiological regulation of the intestinal barrier. Aberrant activation of these signaling pathways and dysregulated expression of key molecules play a pivotal role in the process of intestinal barrier impairment. Microgravity, being the predominant characteristic of space, can potentially exert a significant influence on diverse intestinal barriers. We will discuss the interaction between the "gut-organ" axes and intestinal barrier damage, further elucidate the signaling pathways underlying intestinal barrier damage, and summarize alterations in various components of the intestinal barrier under microgravity. This review aims to offer a novel perspective for comprehending the etiology and molecular mechanisms of intestinal barrier injury as well as the prevention and management of intestinal barrier injury under microgravity environment.

Sirtuin 5-Mediated Desuccinylation of ALDH2 Alleviates Mitochondrial Oxidative Stress Following Acetaminophen-Induced Acute Liver Injury

Acetaminophen (APAP) overdose is a major cause of drug-induced liver injury. Sirtuins 5 (SIRT5) has been implicated in the development of various liver diseases. However, its involvement in APAP-induced acute liver injury (AILI) remains unclear. The present study aimed to explore the role of SIRT5 in AILI. SIRT5 expression is dramatically downregulated by APAP administration in mouse livers and AML12 hepatocytes. SIRT5 deficiency not only exacerbates liver injury and the inflammatory response, but also worsens mitochondrial oxidative stress. Conversely, the opposite pathological and biochemical changes are observed in mice with SIRT5 overexpression. Mechanistically, quantitative succinylome analysis and site mutation experiments revealed that SIRT5 desuccinylated aldehyde dehydrogenase 2 (ALDH2) at lysine 385 and maintained the enzymatic activity of ALDH2, resulting in the suppression of inflammation and mitochondrial oxidative stress. Furthermore, succinylation of ALDH2 at lysine 385 abolished its protective effect against AILI, and the protective effect of SIRT5 against AILI is dependent on the desuccinylation of ALDH2 at K385. Finally, virtual screening of natural compounds revealed that Puerarin promoted SIRT5 desuccinylase activity and further attenuated AILI. Collectively, the present study showed that the SIRT5-ALDH2 axis plays a critical role in AILI progression and might be a strategy for therapeutic intervention.

Alcohol Consumption and Cardiovascular Disease: A Narrative Review of Evolving Perspectives and Long-Term Implications

Cardiovascular illnesses remain the primary cause of death, accounting for at least 17.9 million fatalities per year and posing a significant public health problem because of its extensive predominance and effect on healthcare systems. The etiology of cardiovascular disease is complex and involves several environmental and lifestyle factors. Alcohol use is a highly important determinant because of its dual-edged effect on cardiovascular health. Multiple studies indicate that moderate alcohol consumption may have certain advantages, such as slight enhancements in lipid profiles. Conversely, excessive alcohol intake is associated with serious negative consequences, including cardiomyopathy, hypertension, arrhythmias, and even mortality. The aim of this study is to provide a comprehensive analysis of the several effects of alcohol on cardiovascular health and their understanding within the medical field over time. It uses an interpretative narrative review methodology and analyzes studies that focus on genetic risk factors, gender differences, and shifts in paradigms in recent years. This article highlights the need for obtaining a thorough understanding of the effects of alcohol on cardiovascular health to support public health guidelines and clinical practice, and it underscores the significance of including alcohol consumption into the broader context of cardiovascular risk management and identifies important subjects for further study.

Melatonin Prevents Thioacetamide-Induced Gut Leakiness and Liver Fibrosis Through the Gut-Liver Axis via Modulating Sirt1-Related Deacetylation of Gut Junctional Complex and Hepatic Proteins

Intestinal barrier dysfunction with high serum endotoxin is common in patients with liver fibrosis, but the mechanisms underlying liver fibrosis remain unclear. Melatonin is a well-recognized antioxidant and an anti-inflammatory agent that benefits multiple organs. However, the beneficial effects of melatonin on gut leakiness-associated liver fibrosis have not been systemically studied. Here, we investigated the protective mechanisms of melatonin against thioacetamide (TAA)-induced gut barrier dysfunction and hepatic fibrosis by focusing on posttranslational protein modifications through the gut-liver axis. Our results showed that gut leakiness markers, including decreased gut tight/adherens junction proteins (TJ/AJs) with increased intestinal deformation, apoptosis, and serum endotoxin, were observed early at 1 week after TAA exposure. Liver injury, apoptosis, and fibrosis were prominent at 2 and 4 weeks. Mechanistically, we found that gut TJ/AJs were hyper-acetylated, followed by ubiquitin-dependent proteolysis, leading to their degradation and gut leakiness. Gut dysbiosis, hepatic protein hyper-acetylation, and SIRT1 downregulation were also observed. Consistently, intestinal Sirt1 deficiency greatly enhanced protein hyper-acetylation, gut leakiness, endotoxemia, and liver fibrosis. Pretreatment with melatonin prevented or improved all these changes in both the gut and liver. Furthermore, melatonin blunted protein acetylation and injury in TAA-exposed T84 human intestinal and AML12 mouse liver cells. Overall, this study demonstrated novel mechanisms by which melatonin prevents gut leakiness and liver fibrosis through the gut-liver axis by attenuating the acetylation of intestinal and hepatic proteins. Thus, melatonin consumption can become a potentially safe supplement for liver fibrosis patients by preventing protein hyper-acetylation and gut leakiness.

Direct effects of alcohol on gut-epithelial barrier: Unraveling the disruption of physical and chemical barrier of the gut-epithelial barrier that compromises the host-microbiota interface upon alcohol exposure

The development of alcohol-associated diseases is multifactorial, mechanism of which involves metabolic alteration, dysregulated immune response, and a perturbed intestinal host-environment interface. Emerging evidence has pinpointed the critical role of the intestinal host-microbiota interaction in alcohol-induced injuries, suggesting its contribution to disease initiation and development. To maintain homeostasis in the gut, the intestinal mucosa serves as the first-line defense against exogenous factors in the gastrointestinal tract, including dietary contents and the commensal microbiota. The gut-epithelial barrier comprises a physical barrier lined with a single layer of intestinal epithelial cells and a chemical barrier with mucus trapping host regulatory factors and gut commensal bacteria. In this article, we review recent studies pertaining to the disrupted gut-epithelial barrier upon alcohol exposure and examine how alcohol and its metabolism can affect the regulatory ability of intestinal epithelium.

Risk of de novo esophageal cancer in liver transplant recipients: systematic review and meta-analysis

BACKGROUND

De novo malignancy is the leading cause of death in liver transplant recipients. Numerous studies consistently show a significantly increased risk of esophageal cancer after liver transplantation. Therefore, this study aims to investigate the incidence and risk factors associated with de novo esophageal cancer post-liver transplantation.

METHODS

PubMed, Embase, Medline and Cochrane Library were systematically searched. Screening, quality assessment, and data extraction were completed. The search was completed in November 2023. Standardized incidence rates (SIRs) were used to measure the risk of esophageal cancer among liver transplant recipients, along with corresponding 95% confidence intervals (CI). A random effects model was employed for comprehensive analysis, and results were presented using a forest plot. Sensitivity analysis was undertaken by systematically excluding individual studies one by one, while potential publication bias was assessed using funnel plots and Egger's test. Additionally, subgroup analyses were also performed to explore sources of heterogeneity.

RESULTS

Out of 1,037 articles collected, only twelve met the inclusion criteria after rigorous screening. Statistical analysis showed a significantly increased risk of esophageal cancer following liver transplantation compared to the general population (SIR =6.75, 95% CI: 4.35-10.46).

CONCLUSIONS

The risk of esophageal cancer significantly increases after liver transplantation, so regular gastrointestinal endoscopy is necessary after the procedure.

Mitochondrial Aldehyde Dehydrogenase 2 (ALDH2) Protects against Binge Alcohol-Mediated Gut and Brain Injury

Mitochondrial aldehyde dehydrogenase-2 (ALDH2) metabolizes acetaldehyde to acetate. People with ALDH2 deficiency and Aldh2-knockout (KO) mice are more susceptible to alcohol-induced tissue damage. However, the underlying mechanisms behind ALDH2-related gut-associated brain damage remain unclear. Age-matched young female Aldh2-KO and C57BL/6J wild-type (WT) mice were gavaged with binge alcohol (4 g/kg/dose, three doses) or dextrose (control) at 12 h intervals. Tissues and sera were collected 1 h after the last ethanol dose and evaluated by histological and biochemical analyses of the gut and hippocampus and their extracts. For the mechanistic study, mouse neuroblast Neuro2A cells were exposed to ethanol with or without an Aldh2 inhibitor (Daidzin). Binge alcohol decreased intestinal tight/adherens junction proteins but increased oxidative stress-mediated post-translational modifications (PTMs) and enterocyte apoptosis, leading to elevated gut leakiness and endotoxemia in Aldh2-KO mice compared to corresponding WT mice. Alcohol-exposed Aldh2-KO mice also showed higher levels of hippocampal brain injury, oxidative stress-related PTMs, and neuronal apoptosis than the WT mice. Additionally, alcohol exposure reduced Neuro2A cell viability with elevated oxidative stress-related PTMs and apoptosis, all of which were exacerbated by Aldh2 inhibition. Our results show for the first time that ALDH2 plays a protective role in binge alcohol-induced brain injury partly through the gut-brain axis, suggesting that ALDH2 is a potential target for attenuating alcohol-induced tissue injury.

Pellino1 orchestrates gut-kidney axis to perpetuate septic acute kidney injury through activation of STING pathway and NLRP3 inflammasome

AIMS

Intestinal barrier dysfunction is the initial and propagable factor of sepsis in which acute kidney injury (AKI) has been considered as a common life-threatening complication. Our recent study identifies the regulatory role of Pellino1 in tubular death under inflammatory conditions in vitro. The objective of our current study is to explore the impact of Pellino1 on gut-kidney axis during septic AKI and uncover the molecular mechanism (s) underlying this process.

MATERIALS AND METHODS

Immunohistochemistry (IHC) was conducted to evaluate Pellino1 and NOD-like receptor thermal protein domain associated protein 3 (NLRP3) levels in renal biopsies from critically ill patients with a clinical diagnosis of sepsis. Functional and mechanistic studies were characterized in septic models of the Peli-knockout (Peli1-/-) mice by histopathological staining, enzyme-linked immunosorbent assay (ELISA), flow cytometry, immunofluorescence, biochemical detection, CRISPR/Cas9-mediated gene editing and intestinal organoid.

KEY FINDINGS

Pellino1, together with NLRP3, are highly expressed in renal biopsies from critically ill patients diagnosed with sepsis and kidney tissues of septic mice. The Peli1-/- mice with sepsis become less prone to develop AKI and have markedly compromised NLRP3 activation in kidney. Loss of Peli1 endows septic mice refractory to intestinal inflammation, barrier permeability and enterocyte apoptosis that requires stimulator of interferons genes (STING) pathway. Administration of STING agonist DMXAA deteriorates AKI and mortality of septic Peli1-/- mice in the presence of kidney-specific NLRP3 reconstitution.

SIGNIFICANCE

Our studies suggest that Pellino1 has a principal role in orchestrating gut homeostasis towards renal pathophysiology, thus providing a potential therapeutic target for septic AKI.

Interaction between fatty acid oxidation and ethanol metabolism in liver

Fatty acid oxidation (FAO) releases the energy stored in fat to maintain basic biological processes. Dehydrogenation is a major way to oxidize fatty acids, which needs NAD+ to accept the released H+ from fatty acids and form NADH, which increases the ratio of NADH/NAD+ and consequently inhibits FAO leading to the deposition of fat in the liver, which is termed fatty liver or steatosis. Consumption of alcohol (ethanol) initiates simple steatosis that progresses to alcoholic steatohepatitis, which constitutes a spectrum of liver disorders called alcohol-associated liver disease (ALD). ALD is linked to ethanol metabolism. Ethanol is metabolized by alcohol dehydrogenase (ADH), microsomal ethanol oxidation system (MEOS), mainly cytochrome P450 2E1 (CYP2E1), and catalase. ADH also requires NAD+ to accept the released H+ from ethanol. Thus, ethanol metabolism by ADH leads to increased ratio of NADH/NAD+, which inhibits FAO and induces steatosis. CYP2E1 directly consumes reducing equivalent NADPH to oxidize ethanol, which generates reactive oxygen species (ROS) that lead to cellular injury. Catalase is mainly present in peroxisomes, where very long-chain fatty acids and branched-chain fatty acids are oxidized, and the resultant short-chain fatty acids will be further oxidized in mitochondria. Peroxisomal FAO generates hydrogen peroxide (H2O2), which is locally decomposed by catalase. When ethanol is present, catalase uses H2O2 to oxidize ethanol. In this review, we introduce FAO (including α-, β-, and ω-oxidation) and ethanol metabolism (by ADH, CYP2E1, and catalase) followed by the interaction between FAO and ethanol metabolism in the liver and its pathophysiological significance.

Contributing roles of mitochondrial dysfunction and hepatocyte apoptosis in liver diseases through oxidative stress, post-translational modifications, inflammation, and intestinal barrier dysfunction

This review provides an update on recent findings from basic, translational, and clinical studies on the molecular mechanisms of mitochondrial dysfunction and apoptosis of hepatocytes in multiple liver diseases, including but not limited to alcohol-associated liver disease (ALD), metabolic dysfunction-associated steatotic liver disease (MASLD), and drug-induced liver injury (DILI). While the ethanol-inducible cytochrome P450-2E1 (CYP2E1) is mainly responsible for oxidizing binge alcohol via the microsomal ethanol oxidizing system, it is also responsible for metabolizing many xenobiotics, including pollutants, chemicals, drugs, and specific diets abundant in n-6 fatty acids, into toxic metabolites in many organs, including the liver, causing pathological insults through organelles such as mitochondria and endoplasmic reticula. Oxidative imbalances (oxidative stress) in mitochondria promote the covalent modifications of lipids, proteins, and nucleic acids through enzymatic and non-enzymatic mechanisms. Excessive changes stimulate various post-translational modifications (PTMs) of mitochondrial proteins, transcription factors, and histones. Increased PTMs of mitochondrial proteins inactivate many enzymes involved in the reduction of oxidative species, fatty acid metabolism, and mitophagy pathways, leading to mitochondrial dysfunction, energy depletion, and apoptosis. Unique from other organelles, mitochondria control many signaling cascades involved in bioenergetics (fat metabolism), inflammation, and apoptosis/necrosis of hepatocytes. When mitochondrial homeostasis is shifted, these pathways become altered or shut down, likely contributing to the death of hepatocytes with activation of inflammation and hepatic stellate cells, causing liver fibrosis and cirrhosis. This review will encapsulate how mitochondrial dysfunction contributes to hepatocyte apoptosis in several types of liver diseases in order to provide recommendations for targeted therapeutics.

Unveiling the covert interaction between gut microbiota and neutrophils to drive colorectal cancer metastasis

The formation of the microenvironment preceding liver metastasis is intricately linked to the intestinal tract. In recent years, mounting evidence has revealed the significant involvement of neutrophil extracellular traps (NETs) in tumor metastasis, particularly in liver metastasis. Disruption of the intestinal barrier can lead to the translocation of bacteria and their metabolites, such as lipopolysaccharide, into the liver. As the primary defense against pathogens, NETs help eliminate gut-derived toxins and shape the liver's inflammatory and immunosuppressive environment. However, this double-edged sword effect can potentially stimulate tumor metastasis by creating a fertile ground for the growth of intestinal tumor cells due to impaired liver tissue and reduced activity of killer immune cells. This comprehensive review systematically describes the influence factors and mechanisms of NETs in colon cancer metastasis and explores their potential as biomarkers and therapeutic targets for liver metastasis.

Melatonin Prevents Alcohol- and Metabolic Dysfunction- Associated Steatotic Liver Disease by Mitigating Gut Dysbiosis, Intestinal Barrier Dysfunction, and Endotoxemia

Melatonin (MT) has often been used to support good sleep quality, especially during the COVID-19 pandemic, as many have suffered from stress-related disrupted sleep patterns. It is less known that MT is an antioxidant, anti-inflammatory compound, and modulator of gut barrier dysfunction, which plays a significant role in many disease states. Furthermore, MT is produced at 400-500 times greater concentrations in intestinal enterochromaffin cells, supporting the role of MT in maintaining the functions of the intestines and gut-organ axes. Given this information, the focus of this article is to review the functions of MT and the molecular mechanisms by which it prevents alcohol-associated liver disease (ALD) and metabolic dysfunction-associated steatotic liver disease (MASLD), including its metabolism and interactions with mitochondria to exert its antioxidant and anti-inflammatory activities in the gut-liver axis. We detail various mechanisms by which MT acts as an antioxidant, anti-inflammatory compound, and modulator of intestinal barrier function to prevent the progression of ALD and MASLD via the gut-liver axis, with a focus on how these conditions are modeled in animal studies. Using the mechanisms of MT prevention and animal studies described, we suggest behavioral modifications and several exogenous sources of MT, including food and supplements. Further clinical research should be performed to develop the field of MT in preventing the progression of liver diseases via the gut-liver axis, so we mention a few considerations regarding MT supplementation in the context of clinical trials in order to advance this field of research.

Post-translational modifications of histone and non-histone proteins in epigenetic regulation and translational applications in alcohol-associated liver disease: Challenges and research opportunities

Epigenetic regulation is a process that takes place through adaptive cellular pathways influenced by environmental factors and metabolic changes to modulate gene activity with heritable phenotypic variations without altering the DNA sequences of many target genes. Epigenetic regulation can be facilitated by diverse mechanisms: many different types of post-translational modifications (PTMs) of histone and non-histone nuclear proteins, DNA methylation, altered levels of noncoding RNAs, incorporation of histone variants, nucleosomal positioning, chromatin remodeling, etc. These factors modulate chromatin structure and stability with or without the involvement of metabolic products, depending on the cellular context of target cells or environmental stimuli, such as intake of alcohol (ethanol) or Western-style high-fat diets. Alterations of epigenetics have been actively studied, since they are frequently associated with multiple disease states. Consequently, explorations of epigenetic regulation have recently shed light on the pathogenesis and progression of alcohol-associated disorders. In this review, we highlight the roles of various types of PTMs, including less-characterized modifications of nuclear histone and non-histone proteins, in the epigenetic regulation of alcohol-associated liver disease (ALD) and other disorders. We also describe challenges in characterizing specific PTMs and suggest future opportunities for basic and translational research to prevent or treat ALD and many other disease states.

Alcohol and the Brain-Gut Axis: The Involvement of Microglia and Enteric Glia in the Process of Neuro-Enteric Inflammation

Binge or chronic alcohol consumption causes neuroinflammation and leads to alcohol use disorder (AUD). AUD not only affects the central nervous system (CNS) but also leads to pathologies in the peripheral and enteric nervous systems (ENS). Thus, understanding the mechanism of the immune signaling to target the effector molecules in the signaling pathway is necessary to alleviate AUD. Growing evidence shows that excessive alcohol consumption can activate neuroimmune cells, including microglia, and change the status of neurotransmitters, affecting the neuroimmune system. Microglia, like peripheral macrophages, are an integral part of the immune defense and represent the reticuloendothelial system in the CNS. Microglia constantly survey the CNS to scavenge the neuronal debris. These cells also protect parenchymal cells in the brain and spinal cord by repairing nerve circuits to keep the nervous system healthy against infectious and stress-derived agents. In an activated state, they become highly dynamic and mobile and can modulate the levels of neurotransmitters in the CNS. In several ways, microglia, enteric glial cells, and macrophages are similar in terms of causing inflammation. Microglia also express most of the receptors that are constitutively present in macrophages. Several receptors on microglia respond to the inflammatory signals that arise from danger-associated molecular patterns (DAMPs), pathogen-associated molecular patterns (PAMPs), endotoxins (e.g., lipopolysaccharides), and stress-causing molecules (e.g., alcohol). Therefore, this review article presents the latest findings, describing the roles of microglia and enteric glial cells in the brain and gut, respectively, and their association with neurotransmitters, neurotrophic factors, and receptors under the influence of binge and chronic alcohol use, and AUD.

Host ALDH2 deficiency aggravates nonalcoholic steatohepatitis through gut-liver axis

Nonalcoholic steatohepatitis (NASH) is the major cause of liver dysfunction. Animal and population studies have shown that mitochondrial aldehyde dehydrogenase (ALDH2) is implicated in fatty liver disease. However, the role of ALDH2 in NASH and the underlying mechanisms remains unclear. To address this issue, ALDH2 knockout (ALDH2-/-) mice and wild-type littermate mice were fed a methionine-and choline-deficient (MCD) diet to induce a NASH model. Fecal, serum, and liver samples were collected and analyzed to investigate the impact of the gut microbiota and bile acids on this process. We found that MCD-fed ALDH2-/- mice exhibited increased serum pro-inflammation cytokines, hepatic inflammation and fat accumulation than their wild-type littermates. MCD-fed ALDH2-/- mice exhibited worsened MCD-induced intestinal inflammation and barrier damage, and gut microbiota disorder. Furthermore, mice receiving microbiota from MCD-fed ALDH2-/- mice had increased severity of NASH compared to those receiving microbiota from MCD-fed wild-type mice. Notably, the intestinal Lactobacillus was significantly reduced in MCD-fed ALDH2-/- mice, and gavage with Lactobacillus cocktail significantly improved MCD-induced NASH. Finally, we found that ALDH2-/- mice had reduced levels of bile salt hydrolase and specific bile acids, especially lithocholic acid (LCA), accompanied by downregulated expression of the intestinal FXR-FGF15 pathway. Supplementation of LCA in ALDH2-/- mice upregulated intestinal FXR-FGF15 pathway and alleviated NASH. In summary, ALDH2 plays a critical role in the development of NASH through modulation of gut microbiota and bile acid. The findings suggest that supplementing with Lactobacillus or LCA could be a promising therapeutic approach for treating NASH exacerbated by ALDH2 deficiency.

Recent insights into the pathogenesis and therapeutic targets of chronic liver diseases

Viral hepatitis, alcohol-associated liver disease (ALD) and non-alcoholic fatty liver disease (NAFLD) are the three major causes of chronic liver diseases, which account for approximately 2 million deaths per year worldwide. The current direct-acting antiviral drugs and vaccinations have effectively reduced and ameliorated viral hepatitis infection, but there are still no effective drug treatments for ALD, NAFLD and liver cancer due to the poor understanding of their pathogenesis. To better understand the pathogenesis, the fifth Chinese American Liver Society/Society of Chinese Bioscientists in America Hepatology Division Annual Symposium, which was held virtually on 21-22 October 2022, focused on the topics related to ALD, NAFLD and liver cancer. Here, we briefly highlight the presentations that focus on the current progress in basic and translational research in ALD, NAFLD and liver cancer. The roles of non-coding RNA, autophagy, extrahepatic signalling, macrophages, etc in liver diseases are deliberated, and the application of single-cell RNA sequencing in the study of liver disease is also discussed.

Molecular Toxicology and Pathophysiology of Comorbid Alcohol Use Disorder and Post-Traumatic Stress Disorder Associated with Traumatic Brain Injury

The increasing comorbidity of alcohol use disorder (AUD) and post-traumatic stress disorder (PTSD) associated with traumatic brain injury (TBI) is a serious medical, economic, and social issue. However, the molecular toxicology and pathophysiological mechanisms of comorbid AUD and PTSD are not well understood and the identification of the comorbidity state markers is significantly challenging. This review summarizes the main characteristics of comorbidity between AUD and PTSD (AUD/PTSD) and highlights the significance of a comprehensive understanding of the molecular toxicology and pathophysiological mechanisms of AUD/PTSD, particularly following TBI, with a focus on the role of metabolomics, inflammation, neuroendocrine, signal transduction pathways, and genetic regulation. Instead of a separate disease state, a comprehensive examination of comorbid AUD and PTSD is emphasized by considering additive and synergistic interactions between the two diseases. Finally, we propose several hypotheses of molecular mechanisms for AUD/PTSD and discuss potential future research directions that may provide new insights and translational application opportunities.