Gut microbiota mediated molecular events and therapy in liver diseases

From Dysbiosis to Hepatic Inflammation: A Narrative Review on the Diet-Microbiota-Liver Axis in Steatotic Liver Disease

The gut microbiota has emerged as a critical player in metabolic and liver health, with its influence extending to the pathogenesis and progression of steatotic liver diseases. This review delves into the gut-liver axis, a dynamic communication network linking the gut microbiome and liver through metabolic, immunological, and inflammatory pathways. Dysbiosis, characterized by altered microbial composition, contributes significantly to the development of hepatic steatosis, inflammation, and fibrosis via mechanisms such as gut barrier dysfunction, microbial metabolite production, and systemic inflammation. Dietary patterns, including the Mediterranean diet, are highlighted for their role in modulating the gut microbiota, improving gut-liver axis integrity, and attenuating liver injury. Additionally, emerging microbiota-based interventions, such as fecal microbiota transplantation and bacteriophage therapy, show promise as therapeutic strategies for steatotic liver disease. However, challenges such as population heterogeneity, methodological variability, and knowledge gaps hinder the translational application of current findings. Addressing these barriers through standardized approaches and integrative research will pave the way for microbiota-targeted therapies to mitigate the global burden of steatotic liver disease.

Guardians of the Gut: Harnessing the Power of Probiotic Microbiota and Their Exopolysaccharides to Mitigate Heavy Metal Toxicity in Human for Better Health

Heavy metal pollution is a significant global health concern, posing risks to both the environment and human health. Exposure to heavy metals happens through various channels like contaminated water, food, air, and workplaces, resulting in severe health implications. Heavy metals also disrupt the gut's microbial balance, leading to dysbiosis characterized by a decrease in beneficial microorganisms and proliferation in harmful ones, ultimately exacerbating health problems. Probiotic microorganisms have demonstrated their ability to adsorb and sequester heavy metals, while their exopolysaccharides (EPS) exhibit chelating properties, aiding in mitigating heavy metal toxicity. These beneficial microorganisms aid in restoring gut integrity through processes like biosorption, bioaccumulation, and biotransformation of heavy metals. Incorporating probiotic strains with high affinity for heavy metals into functional foods and supplements presents a practical approach to mitigating heavy metal toxicity while enhancing gut health. Utilizing probiotic microbiota and their exopolysaccharides to address heavy metal toxicity offers a novel method for improving human health through modulation of the gut microbiome. By combining probiotics and exopolysaccharides, a distinctive strategy emerges for mitigating heavy metal toxicity, highlighting promising avenues for therapeutic interventions and health improvements. Further exploration in this domain could lead to groundbreaking therapies and preventive measures, underscoring probiotic microbiota and exopolysaccharides as natural and environmentally friendly solutions to heavy metal toxicity. This, in turn, could enhance public health by safeguarding the gut from environmental contaminants.

Flavonoids and Their Role in Preventing the Development and Progression of MAFLD by Modifying the Microbiota

With the increasing prevalence and serious health consequences of metabolic-associated fatty liver disease (MAFLD), early diagnosis and intervention are key to effective treatment. Recent studies highlight the important role of dietary factors, including the use of flavonoids, in improving liver health. These compounds possess anti-inflammatory, antioxidant, and liver-protective properties. Flavonoids have been shown to affect the gut microbiota, which plays a key role in liver function and disease progression. Therefore, their role in preventing the development and progression of MAFLD through modulation of the microbiome seems to be of interest. This narrative review aims to consolidate the current evidence on the effects of selected flavonoids on MAFLD progression, their potential mechanisms of action, and the implications for the development of personalized dietary interventions for the management of liver disease.

The gut microbiota-bile acid axis in cholestatic liver disease

Cholestatic liver diseases (CLD) are characterized by impaired normal bile flow, culminating in excessive accumulation of toxic bile acids. The majority of patients with CLD ultimately progress to liver cirrhosis and hepatic failure, necessitating liver transplantation due to the lack of effective treatment. Recent investigations have underscored the pivotal role of the gut microbiota-bile acid axis in the progression of hepatic fibrosis via various pathways. The obstruction of bile drainage can induce gut microbiota dysbiosis and disrupt the intestinal mucosal barrier, leading to bacteria translocation. The microbial translocation activates the immune response and promotes liver fibrosis progression. The identification of therapeutic targets for modulating the gut microbiota-bile acid axis represents a promising strategy to ameliorate or perhaps reverse liver fibrosis in CLD. This review focuses on the mechanisms in the gut microbiota-bile acids axis in CLD and highlights potential therapeutic targets, aiming to lay a foundation for innovative treatment approaches.

Bacteroides and NAFLD: pathophysiology and therapy

Non-alcoholic fatty liver disease (NAFLD) is a prevalent chronic liver condition observed globally, with the potential to progress to non-alcoholic steatohepatitis (NASH), cirrhosis, and even hepatocellular carcinoma. Currently, the US Food and Drug Administration (FDA) has not approved any drugs for the treatment of NAFLD. NAFLD is characterized by histopathological abnormalities in the liver, such as lipid accumulation, steatosis, hepatic balloon degeneration, and inflammation. Dysbiosis of the gut microbiota and its metabolites significantly contribute to the initiation and advancement of NAFLD. Bacteroides, a potential probiotic, has shown strong potential in preventing the onset and progression of NAFLD. However, the precise mechanism by which Bacteroides treats NAFLD remains uncertain. In this review, we explore the current understanding of the role of Bacteroides and its metabolites in the treatment of NAFLD, focusing on their ability to reduce liver inflammation, mitigate hepatic steatosis, and enhance intestinal barrier function. Additionally, we summarize how Bacteroides alleviates pathological changes by restoring the metabolism, improving insulin resistance, regulating cytokines, and promoting tight-junctions. A deeper comprehension of the mechanisms through which Bacteroides is involved in the pathogenesis of NAFLD should aid the development of innovative drugs targeting NAFLD.

Components from Curcuma longa (Turmeric) Against Hepatobiliary Diseases Based on Gut-Liver Axis: Pharmacotherapeutic Properties and Potential Clinical Applications

Turmeric is widely used worldwide, and there are many examples of its use in treating hepatobiliary diseases. The gut-liver axis is a bidirectional relationship between gut microorganisms and the liver that is closely related to the pathogenesis of hepatobiliary diseases. This review systematically summarizes the components of turmeric. It links the studies on turmeric affecting gut microorganisms to its effects on liver and biliary diseases to explain the potential mechanism of turmeric's regulation of the gut-liver axis. Besides, ethnopharmacology, phytochemicals, and clinical adverse events associated with turmeric have been researched. Furthermore, turmeric is a safe agent with good clinical efficacy and without apparent toxicity at a certain amount. By summarizing the influence of turmeric on the liver by regulating the gut-liver axis, especially the gut microbiota, it provides a preclinical basis for using turmeric as a safe and effective therapeutic agent for the prevention and treatment of hepatobiliary diseases based on the gut-liver axis. However, more efforts should be made to exploit its clinical application further.

Immunology of gut microbiome and liver in non-alcoholic fatty liver disease (NAFLD): mechanisms, bacteria, and novel therapeutic targets

Non-alcoholic fatty liver disease (NAFLD) is the most common chronic liver disease in the world. Most important contributors to its development are diet and obesity. Gut microbiome's importance for immune system and inflammatory pathways more widely accepted as an important component in NAFLD and other liver diseases' pathogenesis. In this article we review potential mechanisms of microbiome alteration of local and systemic immune responses leading to NAFLD's development, and how can modulate them for the treatment. Our review mentions different immune system pathways and microorganisms regulating metabolism, liver inflammation and fibrosis. We specifically point out TLR-4 as a potential key immune pathway activated by bacterial lipopolysaccharides producing pro-inflammatory cytokines in NAFLD. Also, we discuss three endotoxin-producing strains (Enterobacter cloacae B29, Escherichia coli PY102, Klebsiella pneumoniae A7) that can promote NAFLD development via TLR4-dependent immune response activation in animal models and how they potentially contribute to disease progression in humans. Additionally, we discuss their other immune and non-immune mechanisms contributing to NAFLD pathogenesis. In the end we point out gut microbiome researches' future perspective in NAFLD as a potential new target for both diagnostic and treatment.

Gut microbiota and metabolite interface-mediated hepatic inflammation

Immunologic and metabolic signals regulated by gut microbiota and relevant metabolites mediate bidirectional interaction between the gut and liver. Gut microbiota dysbiosis, due to diet, lifestyle, bile acids, and genetic and environmental factors, can advance the progression of chronic liver disease. Commensal gut bacteria have both pro- and anti-inflammatory effects depending on their species and relative abundance in the intestine. Components and metabolites derived from gut microbiota-diet interaction can regulate hepatic innate and adaptive immune cells, as well as liver parenchymal cells, significantly impacting liver inflammation. In this mini review, recent findings of specific bacterial species and metabolites with functions in regulating liver inflammation are first reviewed. In addition, socioeconomic and environmental factors, hormones, and genetics that shape the profile of gut microbiota and microbial metabolites and components with the function of priming or dampening liver inflammation are discussed. Finally, current clinical trials evaluating the factors that manipulate gut microbiota to treat liver inflammation and chronic liver disease are reviewed. Overall, the discussion of microbial and metabolic mediators contributing to liver inflammation will help direct our future studies on liver disease.

Hepatic Stellate Cell- and Liver Microbiome-Specific Delivery System for Dihydrotanshinone I to Ameliorate Liver Fibrosis

Liver fibrosis is a major contributor to the morbidity and mortality associated with liver diseases, yet effective treatment options remain limited. Hepatic stellate cells (HSCs) are a promising target for hepatic fibrogenesis due to their pivotal role in disease progression. Our previous research has demonstrated the potential of Dihydrotanshinone I (DHI), a lipophilic component derived from the natural herb Salvia miltiorrhiza Bunge, in treating liver fibrosis by inhibiting the YAP/TEAD2 interaction in HSCs. However, the clinical application of DHI faces challenges due to its poor aqueous solubility and lack of specificity for HSCs. Additionally, recent studies have implicated the impact of liver microbiota, distinct from gut microbiota, on the pathogenesis of liver diseases. In this study, we have developed an HSC- and microbiome-specific delivery system for DHI by conjugating prebiotic-like cyclodextrin (CD) with vitamin A, utilizing PEG2000 as a linker (VAP2000@CD). Our results demonstrate that VAP2000@CD markedly enhances the cellular uptake in human HSC line LX-2 and enhances the deposition of DHI in the fibrotic liver in vivo. Subsequently, intervention with DHI-VAP2000@CD has shown a notable reduction in bile duct-like structure proliferation, collagen accumulation, and the expression of fibrogenesis-associated genes in rats subjected to bile duct ligation. These effects may be attributed to the regulation of the YAP/TEAD2 interaction. Importantly, the DHI-VAP2000@CD intervention has also restored microbial homeostasis in the liver, promoting the amelioration of liver inflammation. Overall, our findings indicate that DHI-VAP2000@CD represents a promising therapeutic approach for liver fibrosis by specifically targeting HSCs and restoring the liver microbial balance.

The Gut Microbiome and Autoimmune Hepatitis: Implications for Early Diagnostic Biomarkers and Novel Therapies

Autoimmune hepatitis (AIH) is a serious chronic liver disease that may last for decades and eventually develop into cirrhosis and liver failure. In recent years, people have paid more attention to the microbiome-gut-liver axis, which provides guidance for all to explore the role of microbiome in the occurrence and development of liver diseases. In this review, the possible mechanism of intestinal microbes promoting the occurrence of AIH, mainly expounding the key ways such as bacterial ecological imbalance, intestinal leakage, and molecular simulation between microbes and autoantigens is summarized. In addition, this paper also discusses that intestinal microbiome has great potential as a biomarker for early diagnosis of AIH, and intestinal microbiome is also a candidate target for prevention and treatment of AIH. Finally, the study summarizes and prospects the targeted therapy of intestinal microorganisms to prevent the occurrence and development of AIH.

Discussion on treatment of liver fibrosis with traditional Chinese medicine from the perspective of gut microbiota

Liver fibrosis is the key stage of various chronic liver diseases, and its occurrence and development are closely related to the imbalance of the gut microbiota. In terms of treatment, there is still a lack of ideal chemical drugs, but traditional Chinese medicine has shown unique clinical efficacy in the treatment of hepatic fibrosis. In recent years, research on the regulation of the gut microbiota by traditional Chinese medicine has attracted widespread attention in the academic community. The primary target of the active ingredients of traditional Chinese medicine compound in hepatic fibrosis may be the gut microbiota, or they exert biological effects through the intestinal flora medium and the characteristic reconstruction of the gut microbiota. From the perspective of the "gut-liver axis", the therapetuic effect of traditional Chinese medicine on liver fibrosis is closely connected with regulating the intestinal flora and "treating the liver and spleen together". Based on the viewpoint of the gut-liver axis, this paper discusses the anti-hepatic fibrosis effects of traditional Chinese medicine and its active ingredients by regulating the gut microbiota, with an aim to provide a new research perspective for the therapetuic effect of traditional Chinese medicine on hepatic fibrosis.

The Species of Gut Bacteria Associated with Antitumor Immunity in Cancer Therapy

Both preclinical and clinical studies have demonstrated that the modulation of gut microbiota could be a promising strategy for enhancing antitumor immune responses and reducing resistance to immunotherapy in cancer. Various mechanisms, including activation of pattern recognition receptors, gut commensals-produced metabolites and antigen mimicry, have been revealed. Different gut microbiota modulation strategies have been raised, such as fecal microbiota transplantation, probiotics, and dietary selection. However, the identification of gut bacteria species that are either favorable or unfavorable for cancer therapy remains a major challenge. Herein, we summarized the findings related to gut microbiota species observed in the modulation of antitumor immunity. We also discussed the different mechanisms underlying different gut bacteria's functions and the potential applications of these bacteria to cancer immunotherapy in the future.

[The gut-liver axis: how the gut promotes liver disease]

Research over the last two decades has highlighted the major role played by the gut microbiota in health and disease, including chronic liver diseases. The liver and intestine communicate via the portal vein, biliary system, and mediators in the circulation (gut-liver axis). Microbes in the intestine are involved in the maintenance of liver homeostasis. Conversely, alterations in the normal composition or diversity of the gut microbiome-a condition called dysbiosis-can also serve as a source of pathogens and molecules that contribute to the onset or progression of chronic liver diseases, like non-alcoholic fatty liver disease. Through the increased production of bacteria-derived ethanol, altered bile acid metabolism, altered production of short-chain fatty acids, greater abundance of lipopolysaccharide (LPS) containing Gram-negative bacteria and an increased intestinal permeability, dysbiosis impacts metabolic pathways and inflammatory processes. However, the clinical relevance of specific gut microbial alterations associated with chronic liver diseases remains unclear. This review discusses how microbes and their products contribute to liver disease pathogenesis and how targeting the microbiota might be used for therapeutic approaches.

The gut microbiota–bile acid axis: A potential therapeutic target for liver fibrosis

Liver fibrosis involves the proliferation and deposition of extracellular matrix on liver tissues owing to various etiologies (including viral, alcohol, immune, and metabolic factors), ultimately leading to structural and functional abnormalities in the liver. If not effectively treated, liver fibrosis, a pivotal stage in the path to chronic liver disease, can progress to cirrhosis and eventually liver cancer; unfortunately, no specific clinical treatment for liver fibrosis has been established to date. In liver fibrosis cases, both the gut microbiota and bile acid metabolism are disrupted. As metabolites of the gut microbiota, bile acids have been linked to the progression of liver fibrosis via various pathways, thus implying that the gut microbiota–bile acid axis might play a critical role in the progression of liver fibrosis and could be a target for its reversal. Therefore, in this review, we examined the involvement of the gut microbiota–bile acid axis in liver fibrosis progression to the end of discovering new targets for the prevention, diagnosis, and therapy of chronic liver diseases, including liver fibrosis.

Elevation of enterococcus-specific antibodies associated with bacterial translocation is predictive of survival rate in chronic liver disease

INTRODUCTION/PURPOSE

The gut-liver axis contributes to disease progression, a rise in infection rate, organ failure and a poor overall outcome in chronic liver diseases (CLD). Monitoring of the gut-liver axis is critical in understanding disease status, but biomarkers have not been elucidated. The aim of this study is to determine the level of serum antibodies against Enterococcus (E.) faecalis in evaluating patients with CLD, including those treated with rifaximin (a minimally absorbed antibiotic), and in patients with alcohol-associated liver disease (ALD).

MATERIALS AND METHODS

We enrolled 109 CLD patients (cohort 1), 30 hepatic encephalopathy patients treated with rifaximin (cohort 2), 53 inpatients with ALD undergoing alcohol cessation (cohort 3) and 33 healthy subjects. To assess the consequences of E. faecalis translocation, we developed an assay for the detection of a serum antibody against E. faecalis capsular polysaccharide (E.CPS).

RESULTS

Serum E.CPS antibody titer was elevated only in those patients with advanced CLD and ALD. The E.CPS antibody titer was an independent prognostic factor (p < 0.05), while Mac-2 binding protein and albumin-bilirubin score were not independent predictors of survival. The improvement of predictive model in integrated factors was significant [continuous net reclassification index (value 0.699, p < 0.05) and integrated discrimination improvement (value 0.164, p = 0.051)]. Furthermore, rifaximin treatment led to a decrease of serum E.CPS antibody titer resulting in a significantly longer overall rate of survival.

CONCLUSION

The E.CPS antibody titer appears to be a strong predictor of survival in CLD patients. Serum E.CPS levels decrease in CLD patients receiving rifaximin, and may be associated with an overall improvement in rate of survival.

Regulatory T cells and their associated factors in hepatocellular carcinoma development and therapy

Liver cancer is the third leading cause of cancer-related death worldwide with primary type hepatocellular carcinoma (HCC). Factors, including carcinogens, infection of hepatitis viruses, alcohol abuse, and non-alcoholic fatty liver disease (NAFLD), can induce HCC initiation and promote HCC progression. The prevalence of NAFLD accompanying the increased incidence of obesity and type 2 diabetes becomes the most increasing factor causing HCC worldwide. However, the benefit of current therapeutic options is still limited. Intrahepatic immunity plays critically important roles in HCC initiation, development, and progression. Regulatory T cells (Tregs) and their associated factors such as metabolites and secreting cytokines mediate the immune tolerance of the tumor microenvironment in HCC. Therefore, targeting Tregs and blocking their mediated factors may prevent HCC progression. This review summarizes the functions of Tregs in HCC-inducing factors including alcoholic and NAFLD, liver fibrosis, cirrhosis, and viral infections. Overall, a better understanding of the role of Tregs in the development and progression of HCC provides treatment strategies for liver cancer treatment.

Hepatocellular Carcinoma: How the Gut Microbiota Contributes to Pathogenesis, Diagnosis, and Therapy

The gut microbiota is gaining increasing attention, and the concept of the "gut-liver axis" is gradually being recognized. Leaky gut resulting from injury and/or inflammation can cause the translocation of flora to the liver. Microbiota-associated metabolites and components mediate the activation of a series of signalling pathways, thereby playing an important role in the development of hepatocellular carcinoma (HCC). For this reason, targeting the gut microbiota in the diagnosis, prevention, and treatment of HCC holds great promise. In this review, we summarize the gut microbiota and the mechanisms by which it mediates HCC development, and the characteristic alterations in the gut microbiota during HCC pathogenesis. Furthermore, we propose several strategies to target the gut microbiota for the prevention and treatment of HCC, including antibiotics, probiotics, faecal microbiota transplantation, and immunotherapy.

Oral and Gut Microbial Dysbiosis and Non-alcoholic Fatty Liver Disease: The Central Role of Porphyromonas gingivalis

Gut microbiota play many important roles, such as the regulation of immunity and barrier function in the intestine, and are crucial for maintaining homeostasis in living organisms. The disruption in microbiota is called dysbiosis, which has been associated with various chronic inflammatory conditions, food allergies, colorectal cancer, etc. The gut microbiota is also affected by several other factors such as diet, antibiotics and other medications, or bacterial and viral infections. Moreover, there are some reports on the oral-gut-liver axis indicating that the disruption of oral microbiota affects the intestinal biota. Non-alcoholic fatty liver disease (NAFLD) is one of the systemic diseases caused due to the dysregulation of the oral-gut-liver axis. NAFLD is the most common liver disease reported in the developed countries. It includes liver damage ranging from simple steatosis to nonalcoholic steatohepatitis (NASH), cirrhosis, and cancer. Recently, accumulating evidence supports an association between NAFLD and dysbiosis of oral and gut microbiota. Periodontopathic bacteria, especially Porphyromonas gingivalis, have been correlated with the pathogenesis and development of NAFLD based on the clinical and basic research, and immunology. P. gingivalis was detected in the liver, and lipopolysaccharide from this bacteria has been shown to be involved in the progression of NAFLD, thereby indicating a direct role of P. gingivalis in NAFLD. Moreover, P. gingivalis induces dysbiosis of gut microbiota, which promotes the progression of NAFLD, through disrupting both metabolic and immunologic pathways. Here, we review the roles of microbial dysbiosis in NAFLD. Focusing on P. gingivalis, we evaluate and summarize the most recent advances in our understanding of the relationship between oral-gut microbiome symbiosis and the pathogenesis and progression of non-alcoholic fatty liver disease, as well as discuss novel strategies targeting both P. gingivalis and microbial dysbiosis.

Diet and Gut Microbiota Interaction-Derived Metabolites and Intrahepatic Immune Response in NAFLD Development and Treatment

Nonalcoholic fatty liver disease (NAFLD) with pathogenesis ranging from nonalcoholic fatty liver (NAFL) to the advanced form of nonalcoholic steatohepatitis (NASH) affects about 25% of the global population. NAFLD is a chronic liver disease associated with obesity, type 2 diabetes, and metabolic syndrome, which is the most increasing factor that causes hepatocellular carcinoma (HCC). Although advanced progress has been made in exploring the pathogenesis of NAFLD and penitential therapeutic targets, no therapeutic agent has been approved by Food and Drug Administration (FDA) in the United States. Gut microbiota-derived components and metabolites play pivotal roles in shaping intrahepatic immunity during the progression of NAFLD or NASH. With the advance of techniques, such as single-cell RNA sequencing (scRNA-seq), each subtype of immune cells in the liver has been studied to explore their roles in the pathogenesis of NAFLD. In addition, new molecules involved in gut microbiota-mediated effects on NAFLD are found. Based on these findings, we first summarized the interaction of diet-gut microbiota-derived metabolites and activation of intrahepatic immunity during NAFLD development and progression. Treatment options by targeting gut microbiota and important molecular signaling pathways are then discussed. Finally, undergoing clinical trials are selected to present the potential application of treatments against NAFLD or NASH.

Impact of COVID-19 in Liver Disease Progression

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is a novel coronavirus that causes coronavirus disease 19 (COVID-19), which has infected millions of people worldwide in only a few months. A minority, but significant number, of infected individuals require hospitalization and intensive care. From the start of this new virus pandemic, it was apparent that obese and/or diabetic individuals had a bad prognosis for COVID-19 progression, strongly suggesting an association between liver disease and severe COVID-19. Because chronic liver disease (CLD) is associated with immune dysregulation and inflammation, it is unsurprising that patients with CLD may carry a greater risk of adverse outcomes following SARS-CoV-2 infection. Initial COVID-19 data have also indicated that healthy infected individuals display abnormal liver function tests, suggesting a possible direct implication of SARS-CoV-2 in liver damage. Here we show that COVID-19 affects the liver metabolism and increases the morbidity and mortality of individuals with underlying CLD.