Compositional alterations of gut microbiota in nonalcoholic fatty liver disease patients: a systematic review and Meta-analysis

Metabolic dysfunction-associated steatotic liver disease and the gut microbiome: pathogenic insights and therapeutic innovations

Metabolic dysfunction-associated steatotic liver disease (MASLD) is a major cause of liver disease worldwide, and our understanding of its pathogenesis continues to evolve. MASLD progresses from steatosis to steatohepatitis, fibrosis, and cirrhosis, and this Review explores how the gut microbiome and their metabolites contribute to MASLD pathogenesis. We explore the complexity and importance of the intestinal barrier function and how disruptions of the intestinal barrier and dysbiosis work in concert to promote the onset and progression of MASLD. The Review focuses on specific bacterial, viral, and fungal communities that impact the trajectory of MASLD and how specific metabolites (including ethanol, bile acids, short chain fatty acids, and other metabolites) contribute to disease pathogenesis. Finally, we underscore how knowledge of the interaction between gut microbes and the intestinal barrier may be leveraged for MASLD microbial-based therapeutics. Here, we include a discussion of the therapeutic potential of prebiotics, probiotics, postbiotics, and microbial-derived metabolites.

Multi-omics analyses of the gut microbiota and metabolites in children with metabolic dysfunction-associated steatotic liver disease

The development and severity of metabolic dysfunction-associated steatotic liver disease (MASLD) in children are closely related to alterations of gut microbiota. This study aims to investigate changes in the gut microbiota signature and microbial metabolites in children with MASLD. We collected fecal samples from children and adolescents aged 6-16 years, and the presence of MASLD was diagnosed by ultrasound. We performed 16S ribosomal DNA sequencing and targeted metabolomics in 36 and 25 subjects, consisting of healthy controls, children with obesity, and children with MASLD. The α-diversity was significantly lower in children with obesity and MASLD compared with healthy controls. Linear discriminant analysis of effect size analysis identified Anaerostipes and A. hadrus as the top biomarkers differentiating the obesity group from the MASLD group. In MASLD patients with high alanine aminotransferase values (≥50 U/L for boys and 44 U/L for girls), we observed a decrease in the gut microbiota health index. MASLD patients with high shear wave elastography (E) values (≥6.2 kPa) showed an increased abundance of Ruminococcus torques, which was positively correlated with the levels of deoxycholic acid (DCA) and E values. Importantly, the mediation analysis identified positive associations between R. torques and clinical indicators of MASLD that were mediated by DCA. Overall, our study suggests that gut microbiota and metabolites are significantly altered in children with MASLD, and targeting R. torques may offer potential benefits for disease management.IMPORTANCEThis study investigated alterations in the gut microbiota signature and microbial metabolites in children with metabolic dysfunction-associated steatotic liver disease (MASLD). We found that an increased abundance of Ruminococcus torques was associated with increased levels of deoxycholic acid and the progression of MASLD, suggesting that R. torques may serve as a novel clinical target in pediatric MASLD.

Effects of dietary live microbes intake on a newly proposed classification system for steatotic liver disease

Steatotic liver disease (SLD) is a common chronic liver disease without effective therapeutic options. Some studies suggest potential health benefits of dietary live microbes. This study aims to investigate the association between dietary live microbes intake and metabolic dysfunction-associated steatotic liver disease (MASLD) / metabolic alcohol-related liver disease (MetALD) / alcoholic liver disease (ALD) in adults. Data from the National Health and Nutrition Examination Survey 1999-2018 were analyzed. MASLD was defined according to the latest Delphi Consensus standard. Participants were grouped based on estimated dietary live microbe intake: low (< 104 CFU/g), moderate (104-107 CFU/g), and high (> 107 CFU/g). Multivariable logistic regression analysis was employed to assess the impact of dietary live microbes on MASLD/MetALD/ALD, along with further investigations into non-dietary probiotic/prebiotic relationships. Participants had a weighted mean age of 47.05 years (SE, 0.24) and 50.59% were female. MASLD proportions differ among low (21.76%), moderate (22.24%), and high (18.96%) microbe groups. Similarly, for MetALD, proportions are 7.75%, 6.95%, and 6.44%, and for ALD, 5.42%, 3.59%, and 2.97% in respective groups. The high dietary live microbe intake group was associated with a 16% lower risk of MASLD compared to those in the low intake group (trend test, P = 0.02), while the risk of ALD was reduced by 25% in the moderate intake group. A lack of association was identified between non-dietary prebiotic/probiotic and MASLD/MetALD/ALD. Our study suggests that a relatively high intake of live microbes diets in adults is associated with a lower risk of SLD.

The relationship between probiotics and prebiotics, kidney dysfunction and mortality - Results from a longitudinal cohort study and Mendelian randomization

INTRODUCTION

The benefits of probiotics/prebiotics consumption on chronic kidney disease (CKD) and mortality remains controversial.

OBJECTIVES

This study investigates the association of probiotics/prebiotics consumption with chronic kidney disease (CKD) and mortality.

METHODS

Clinical data were retrieved from the National Health and Nutrition Examination Survey (NHANES) 2005-2016 database. Weighted multivariable logistic and liner regression models, cox proportional hazards models and stratified analysis were used to analyse the relationships between consumption of probiotics/prebiotics, renal parameters, CKD and mortality. We also conducted a two-sample Mendelian randomization (MR) analysis of single nucleotide polymorphisms (SNPs) related to different genera of gut microbiota to assess their causal relationships with CKD and mortality.

RESULTS

15,291 subjects were analysed (897 with consumption of probiotics/prebiotics and 14,394 without). The use of probiotics/prebiotics showed an inverse correlation with urinary albumin-to-creatinine ratio (UACR) (P < 0.05). Probiotics/prebiotics use was associated with lower risk of CKD in subjects with hypertension, hyperlipidaemia and diabetes mellitus. The consumption of probiotics/prebiotics was associated with a significantly lower risk of all-cause mortality in different regression models (P < 0.001, for all), but the lower risk of cardiovascular mortality did not reach statistical significance (P > 0.05, for all)]. MR analysis showed negative associations between the genetically predicted genus Flavonifractor and risk of CKD and diabetic kidney disease (DKD).

CONCLUSION

After multivariable regression, and cox proportional hazards analysis, we found that the use of probiotics/prebiotics was associated with improved kidney and mortality outcomes in the general population from NHANES database. The two-sample MR analysis provided further genetic evidence that a distinct genus of gut microbiota was associated with reduced risk of CKD, DKD and mortality.

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.

Dietary Influences on Gut Microbiota and Their Role in Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD)

Metabolic dysfunction-associated steatotic liver disease (MASLD) is a major contributor to liver-related morbidity, cardiovascular disease, and metabolic complications. Lifestyle interventions, including diet and exercise, are first line in treating MASLD. Dietary approaches such as the low-glycemic-index Mediterranean diet, the ketogenic diet, intermittent fasting, and high fiber diets have demonstrated potential in addressing the metabolic dysfunction underlying this condition. The development and progression of MASLD are closely associated with taxonomic shifts in gut microbial communities, a relationship well-documented in the literature. Given the importance of diet as a primary treatment for MASLD, it is important to understand how gut microbiota and their metabolic byproducts mediate favorable outcomes induced by healthy dietary patterns. Conversely, microbiota changes conferred by unhealthy dietary patterns such as the Western diet may induce dysbiosis and influence steatotic liver disease through promoting hepatic inflammation, up-regulating lipogenesis, dysregulating bile acid metabolism, increasing insulin resistance, and causing oxidative damage in hepatocytes. Although emerging evidence has identified links between diet, microbiota, and development of MASLD, significant gaps remain in understanding specific microbial roles, metabolite pathways, host interactions, and causal relationships. Therefore, this review aims to provide mechanistic insights into the role of microbiota-mediated processes through the analysis of both healthy and unhealthy dietary patterns and their contribution to MASLD pathophysiology. By better elucidating the interplay between dietary nutrients, microbiota-mediated processes, and the onset and progression of steatotic liver disease, this work aims to identify new opportunities for targeted dietary interventions to treat MASLD efficiently.

Gut Microbiota and Metabolic Dysfunction-Associated Steatotic Liver Disease

Background: The gut microbiota constitutes a complex microorganism community that harbors bacteria, viruses, fungi, protozoa, and archaea. The human gut bacterial microbiota has been extensively proven to participate in human metabolism, immunity, and nutrient absorption. Its imbalance, namely "dysbiosis", has been linked to disordered metabolism. Metabolic dysfunction-associated steatotic liver disease (MASLD) is one of the features of deranged human metabolism and is the leading cause of liver cirrhosis and hepatocellular carcinoma. Thus, there is a pathophysiological link between gut dysbiosis and MASLD. Aims and Methods: We aimed to review the literature data on the composition of the human bacterial gut microbiota and its dysbiosis in MASLD and describe the concept of the "gut-liver axis". Moreover, we reviewed the approaches for gut microbiota modulation in MASLD treatment. Results: There is consolidated evidence of particular gut dysbiosis associated with MASLD and its stages. The model explaining the relationship between gut microbiota and the liver has a bidirectional organization, explaining the physiopathology of MASLD. Oxidative stress is one of the keystones in the pathophysiology of MASLD and fibrosis generation. There is promising and consolidated evidence for the efficacy of pre- and probiotics in reversing gut dysbiosis in MASLD patients, with therapeutic effects. Few yet encouraging data on fecal microbiota transplantation (FMT) in MASLD are available in the literature. Conclusions: The gut dysbiosis characteristic of MASLD is a key target in its reversal and treatment via diet, pre/probiotics, and FMT treatment. Oxidative stress modulation remains a promising target for MASLD treatment, prevention, and reversal.

Gut Microbiota Disorders and Metabolic Syndrome: Tales of a Crosstalk Process

The microbiota in humans consists of trillions of microorganisms that are involved in the regulation of the gastrointestinal tract and immune and metabolic homeostasis. The gut microbiota (GM) has a prominent impact on the pathogenesis of metabolic syndrome (MetS). This process is reciprocal, constituting a crosstalk process between the GM and MetS. In this review, GM directly or indirectly inducing MetS via the host-microbial metabolic axis has been systematically reviewed. Additionally, the specifically altered GM in MetS are detailed in this review. Moreover, short-chain fatty acids (SCFAs), as unique gut microbial metabolites, have a remarkable effect on MetS, and the role of SCFAs in MetS-related diseases is highlighted to supplement the gaps in this area. Finally, the existing therapeutics are outlined, and the superiority and shortcomings of different therapeutic approaches are discussed, in hopes that this review can contribute to the development of potential treatment strategies.

Insights of gut-liver axis in hepatic diseases: Mechanisms, clinical implications, and therapeutic potentials

With the rising prevalence of chronic liver diseases worldwide, there exists a need to diversify our artillery to incorporate a plethora of diagnostic and therapeutic methods to combat this disease. Currently, the most common causes of liver disease are non-alcoholic fatty liver disease, hepatitis, and alcoholic liver disease. Some of these chronic diseases have the potential to transform into hepatocellular carcinoma with advancing fibrosis. In this review, we analyse the relationship between the gut and liver and their significance in liver disease. This two-way relationship has interesting effects on each other in liver diseases. The gut microbiota, through its metabolites, influences the metabolism in numerous ways. Careful manipulation of its composition can lead to the discovery of numerous therapeutic potentials that can be applied in the treatment of various liver diseases. Numerous cohort studies with a pan-omics approach are required to understand the association between the gut microbiome and hepatic disease progression through which we can identify effective ways to deal with this issue.

Altered gut microbial profile accompanied by abnormal short chain fatty acid metabolism exacerbates nonalcoholic fatty liver disease progression

Dysregulation of the gut microbiome has associated with the occurrence and progression of non-alcoholic fatty liver disease (NAFLD). To determine the diagnostic capacity of this association, we compared fecal microbiomes across 104 participants including non-NAFLD controls and NAFLD subtypes patients that were distinguished by magnetic resonance imaging. We measured their blood biochemical parameters, 16 S rRNA-based gut microbiota and fecal short-chain fatty acids (SCFAs). Multi-omic analyses revealed that NAFLD patients exhibited specific changes in gut microbiota and fecal SCFAs as compared to non-NAFLD subjects. Four bacterial genera (Faecalibacterium, Subdoligranulum, Haemophilus, and Roseburia) and two fecal SCFAs profiles (acetic acid, and butyric acid) were closely related to NAFLD phenotypes and could accurately distinguish NAFLD patients from healthy non-NAFLD subjects. Twelve genera belonging to Faecalibacterium, Subdoligranulum, Haemophilus, Intestinibacter, Agathobacter, Lachnospiraceae_UCG-004, Roseburia, Butyricicoccus, Actinomycetales_unclassified, [Eubacterium]_ventriosum_group, Rothia, and Rhodococcus were effective to distinguish NAFLD subtypes. Of them, combination of five genera can distinguish effectively mild NAFLD from non-NAFLD with an area under curve (AUC) of 0.84. Seven genera distinguish moderate NAFLD with an AUC of 0.83. Eight genera distinguish severe NAFLD with an AUC of 0.90. In our study, butyric acid distinguished mild-NAFLD from non-NAFLD with AUC value of 0.83. And acetic acid distinguished moderate-NAFLD and severe-NAFLD from non-NAFLD with AUC value of 0.84 and 0.70. In summary, our study and further analysis showed that gut microbiota and fecal SCFAs maybe a method with convenient detection advantages and invasive manner that are not only a good prediction model for early warning of NAFLD occurrence, but also have a strong ability to distinguish NAFLD subtypes.

Nonalcoholic Fatty Liver Disease and Cardiovascular Disease: Causation or Association

Nonalcoholic fatty liver disease (NAFLD) is a disease process that is gaining increasing recognition. The global prevalence of NAFLD is increasing in parallel with growing rates of risk factors for NAFLD such as hypertension, obesity, diabetes, and metabolic syndrome. NAFLD has been referred to as a risk factor for cardiovascular disease (CVD). As CVD is the leading cause of morbidity and mortality worldwide, there are constant efforts to describe and alleviate its risk factors. Although there is conflicting data supporting NAFLD as a causative or associative factor for CVD, NAFLD has been shown to be associated with structural, electrical, and atherosclerotic disease processes of the heart. Shared risk factors and pathophysiologic mechanisms between NAFLD and CVD warrant further explication. Pathologic mechanisms such as endothelial dysfunction, oxidative stress, insulin resistance, genetic underpinnings, and gut microbiota dysregulation have been described in both CVD and NAFLD. The mainstay of treatment for NAFLD is lifestyle intervention including physical exercise and hypocaloric intake in addition to bariatric surgery. Investigations into various therapeutic targets to alleviate hepatic steatosis and fibrosis by way of maintaining the balance between lipid synthesis and breakdown. A major obstacle preventing the success of many pharmacologic approaches has been the effects of these medications on CVD risk. The future of pharmacologic treatment of NAFLD is promising as effective medications with limited CVD harm are being investigated.

Multi-omics analysis of the biological mechanism of the pathogenesis of non-alcoholic fatty liver disease

Background

Non-alcoholic fatty liver disease (NAFLD) is a type of liver metabolic syndrome. Employing multi-omics analyses encompassing the microbiome, metabolome and transcriptome is crucial for comprehensively elucidating the biological processes underlying NAFLD.

Methods

Hepatic tissue, blood and fecal samples were obtained from 9 NAFLD model mice and 8 normal control mice. Total fecal microbiota DNA was extracted, and 16S rRNA was amplified, to analyze alterations in the gut microbiota (GM) induced by NAFLD. Subsequently, diagnostic strains for NAFLD were screened, and their functional aspects were examined. Differential metabolites and differentially expressed genes were also screened, followed by enrichment analysis. Correlations between the differential microbiota and metabolites, as well as between the DEGs and differential metabolites were studied. A collinear network involving key genes-, microbiota-and metabolites was constructed.

Results

Ileibacterium and Ruminococcaceae, both belonging to Firmicutes; Olsenella, Duncaniella and Paramuribaculum from Bacteroidota; and Bifidobacterium, Coriobacteriaceae_UCG_002 and Olsenella from Actinobacteriota were identified as characteristic strains associated with NAFLD. Additionally, differentially expressed metabolites were predominantly enriched in tryptophan, linoleic acid and methylhistidine metabolism pathways. The functions of 2,510 differentially expressed genes were found to be associated with disease occurrence. Furthermore, a network comprising 8 key strains, 14 key genes and 83 key metabolites was constructed.

Conclusion

Through this study, we conducted a comprehensive analysis of NAFLD alterations, exploring the gut microbiota, genes and metabolites of the results offer insights into the speculated biological mechanisms underlying NAFLD.

The Therapeutic Potential of the Specific Intestinal Microbiome (SIM) Diet on Metabolic Diseases

Exploring the intricate crosstalk between dietary prebiotics and the specific intestinal microbiome (SIM) is intriguing in explaining the mechanisms of current successful dietary interventions, including the Mediterranean diet and high-fiber diet. This knowledge forms a robust basis for developing a new natural food therapy. The SIM diet can be measured and evaluated to establish a reliable basis for the management of metabolic diseases, such as diabetes, metabolic (dysfunction)-associated fatty liver disease (MAFLD), obesity, and metabolic cardiovascular disease. This review aims to delve into the existing body of research to shed light on the promising developments of possible dietary prebiotics in this field and explore the implications for clinical practice. The exciting part is the crosstalk of diet, microbiota, and gut-organ interactions facilitated by producing short-chain fatty acids, bile acids, and subsequent metabolite production. These metabolic-related microorganisms include Butyricicoccus, Akkermansia, and Phascolarctobacterium. The SIM diet, rather than supplementation, holds the promise of significant health consequences via the prolonged reaction with the gut microbiome. Most importantly, the literature consistently reports no adverse effects, providing a strong foundation for the safety of this dietary therapy.

The role of gut microbiota, exosomes, and their interaction in the pathogenesis of ALD

BACKGROUND

The liver disorders caused by alcohol abuse are termed alcoholic-related liver disease (ALD), including alcoholic steatosis, alcoholic steatohepatitis, alcoholic hepatitis, and alcoholic cirrhosis, posing a significant threat to human health. Currently, ALD pathogenesis has not been completely clarified, which is likely to be related to the direct damage caused by alcohol and its metabolic products, oxidative stress, gut dysbiosis, and exosomes.

AIMS

The existing studies suggest that both the gut microbiota and exosomes contribute to the development of ALD. Moreover, there exists an interaction between the gut microbiota and exosomes. We discuss whether this interaction plays a role in the pathogenesis of ALD and whether it can be a potential therapeutic target for ALD treatment.

KEY SCIENTIFIC CONCEPTS OF REVIEW

Chronic alcohol intake alters the diversity and composition of gut microbiota, which greatly contributes to ALD's progression. Some approaches targeting the gut microbiota, including probiotics, fecal microbiota transplantation, and phage therapy, have been confirmed to effectively ameliorate ALD in many animal experiments and/or several clinical trials. In ALD, the levels of exosomes and the expression profile of microRNA have also changed, which affects the pathogenesis of ALD. Moreover, there is an interplay between exosomes and the gut microbiota, which also putatively acts as a pathogenic factor of ALD.

A Comprehensive Pilot Study to Elucidate the Distinct Gut Microbial Composition and Its Functional Significance in Cardio-Metabolic Disease

Cardio-metabolic disease is a significant global health challenge with increasing prevalence. Recent research underscores the disruption of gut microbial balance as a key factor in disease susceptibility. We aimed to characterize the gut microbiota composition and function in cardio-metabolic disease and healthy controls. For this purpose, we collected stool samples of 18 subjects (12 diseased, 6 healthy) and we performed metagenomics analysis and functional prediction using QIIME2 and PICRUSt. Furthermore, we carried out assessments of microbe-gene interactions, gene ontology, and microbe-disease associations. Our findings revealed distinct microbial patterns in the diseased group, particularly evident in lower taxonomic levels with significant variations in 14 microbial features. The diseased cohort exhibited an enrichment of Lachnospiraceae family, correlating with obesity, insulin resistance, and metabolic disturbances. Conversely, reduced levels of Clostridium, Gemmiger, and Ruminococcus genera indicated a potential inflammatory state, linked to compromised butyrate production and gut permeability. Functional analyses highlighted dysregulated pathways in amino acid metabolism and energy equilibrium, with perturbations correlating with elevated branch-chain amino acid levels-a known contributor to insulin resistance and type 2 diabetes. These findings were consistent across biomarker assessments, microbe-gene associations, and gene ontology analyses, emphasizing the intricate interplay between gut microbial dysbiosis and cardio-metabolic disease progression. In conclusion, our study unveils significant shifts in gut microbial composition and function in cardio-metabolic disease, emphasizing the broader implications of microbial dysregulation. Addressing gut microbial balance emerges as a crucial therapeutic target in managing cardio-metabolic disease burden.

Coprococcus protects against high-fat diet-induced nonalcoholic fatty liver disease in mice

AIMS

The incidence of nonalcoholic fatty liver disease (NAFLD) is increasing annually, leading to substantial medical and health burdens. Numerous studies have demonstrated the potential effectiveness of intestinal probiotics as a treatment strategy for NAFLD. Therefore, the objective of this study is to identify a probiotic for the treatment of NAFLD.

METHODS AND RESULTS

In this study, blood and fecal samples were collected from 41 healthy volunteers and 44 patients diagnosed with NAFLD. Analysis of the 16S rDNA sequencing data and quantitative real-time PCR (RT-qPCR) revealed a significant reduction in the abundance of Coprococcus in NAFLD patients. Subsequent animal experiments demonstrated that Coprococcus was able to effectively reverse liver lipid accumulation, inflammation, and fibrosis induced by a high-fat diet (HFD) in mice.

CONCLUSIONS

This study provides the first in vivo evidence that Coprococcus is a beneficial bacterium capable of preventing NAFLD and has the same probiotic effect in mice as Lactobacillus GG (LGG), a positive control. Therefore, Coprococcus has the potential to serve as a probiotic for the prevention and treatment of NAFLD in humans.

Changes in the Gastrointestinal Microbiota Induced by Proton Pump Inhibitors-A Review of Findings from Experimental Trials

The use of proton pump inhibitors (PPIs) has increased considerably in many Western countries, and there is concern that numerous conditions and diseases associated with PPI use may be adverse events. The main function of gastric acid is to defend the organism against orally ingested microorganisms, and there is also concern that alterations not only in the gastric microbiome but also the downstream intestinal microbiome may increase the risk of disease or alter the course of preexisting disease. The current study is a systematic review of the available evidence from experimental trials investigating the effects of PPIs on the gastrointestinal microbiota by next-generation sequencing. Thirteen studies were identified. The effects of PPIs were seen on alterations in diversity and richness in some of the studies, while a larger proportion of the studies detected alterations at various taxonomic levels. The general finding was that PPI use caused an increase in bacteria normally found in the oral microbiota in both the upper and lower GI tract. The most consistent taxonomic alterations seemed to be increases in oral flora along the axis Streptococcaceae and Streptococcus at genus level and various Streptococcus spp., as well as Veillonellaceae, Veillonella and Haemophilus.

Implications of Microbiota and Immune System in Development and Progression of Metabolic Dysfunction-Associated Steatotic Liver Disease

Metabolic dysfunction-associated steatotic liver disease (MASLD) is the most prevalent type of liver disease worldwide. The exact pathophysiology behind MASLD remains unclear; however, it is thought that a combination of factors or "hits" act as precipitants for disease onset and progression. Abundant evidence supports the roles of diet, genes, metabolic dysregulation, and the intestinal microbiome in influencing the accumulation of lipids in hepatocytes and subsequent progression to inflammation and fibrosis. Currently, there is no cure for MASLD, but lifestyle changes have been the prevailing cornerstones of management. Research is now focusing on the intestinal microbiome as a potential therapeutic target for MASLD, with the spotlight shifting to probiotics, antibiotics, and fecal microbiota transplantation. In this review, we provide an overview of how intestinal microbiota interact with the immune system to contribute to the pathogenesis of MASLD and metabolic dysfunction-associated steatohepatitis (MASH). We also summarize key microbial taxa implicated in the disease and discuss evidence supporting microbial-targeted therapies in its management.

Chaihu Guizhi Ganjiang Decoction attenuates nonalcoholic steatohepatitis by enhancing intestinal barrier integrity and ameliorating PPARα mediated lipotoxicity

BACKGROUND

Nonalcoholic steatohepatitis (NASH) is a prominent cause of liver-related death that poses a threat to global health and is characterized by severe hepatic steatosis, lobular inflammation, and ballooning degeneration. To date, no Food and Drug Administration-approved medicine is commercially available. The Chaihu Guizhi Ganjiang Decoction (CGGD) shows potential curative effects on regulation of blood lipids and blood glucose, mitigation of organism inflammation, and amelioration of hepatic function. However, the overall regulatory mechanisms underlying its effects on NASH remain unclear.

PURPOSE

This study aimed to investigate the efficiency of CGGD on methionine- and choline-deficient (MCD)-induced NASH and unravel its underlying mechanisms.

METHODS

A NASH model of SD rats was established using an MCD diet for 8 weeks, and the efficacy of CGGD was evaluated based on hepatic lipid accumulation, inflammatory response, and fibrosis. The effects of CGGD on the intestinal barrier, metabolic profile, and differentially expressed genes (DEGs) profile were analyzed by integrating gut microbiota, metabolomics, and transcriptome sequencing to elucidate its mechanisms of action.

RESULTS

In MCD-induced NASH rats, pathological staining demonstrated that CGGD alleviated lipid accumulation, inflammatory cell infiltration, and fibrosis in the hepatic tissue. After CGGD administration, liver index, liver weight, serum alanine aminotransferase (ALT), and aspartate aminotransferase (AST) contents, liver triglycerides (TG), and free fatty acids (FFAs) were decreased, meanwhile, it down-regulated the level of proinflammatory mediators (TNF-α, IL-6, IL-1β, MCP-1), and up-regulated the level of anti-inflammatory factors (IL-4, IL-10), and the expression of liver fibrosis markers TGFβ, Acta2, Col1a1 and Col1a2 were weakened. Mechanistically, CGGD treatment altered the diversity of intestinal flora, as evidenced by the depletion of Allobaculum, Blautia, norank_f_Erysipelotrichaceae, and enrichment of the probiotic genera Roseburia, Lactobacillus, Lachnoclostridium, etc. The colonic histopathological results indicated that the gut barrier damage recovered in the CGGD treatment group, and the expression levels of colonic short-chain fatty acids (SCFAs)-specific receptors FFAR2, FFAR3, and tight junction (TJs) proteins ZO-1, Occludin, Claudin-1 were increased compared with those in the model group. Further metabolomic and transcriptomic analyses suggested that CGGD mitigated the lipotoxicity caused by glycerophospholipid and eicosanoid metabolism disorders by decreasing the levels of PLA2G4A, LPCAT1, COX2, and LOX5. In addition, CGGD could activate the inhibitory lipotoxic transcription factor PPARα, regulate the proteins of FABP1, APOC2, APOA2, and LPL to promote fatty acid catabolism, and suppress the TLR4/MyD88/NFκB pathway to attenuate NASH.

CONCLUSION

Our study demonstrated that CGGD improved steatosis, inflammation, and fibrosis on NASH through enhancing intestinal barrier integrity and alleviating PPARα mediated lipotoxicity, which makes it an attractive candidate for potential new strategies for NASH prevention and treatment.

Effect of circadian rhythm change on gut microbiota and the development of nonalcoholic fatty liver disease in mice

BACKGROUND

This study was to investigate the effect and possible mechanism of circadian rhythm change on the development of nonalcoholic fatty liver disease (NAFLD) in mice.

METHODS

A total of 80 male SPF-grade 4-week C57BL/6J mice were randomly divided into normal diet normal light/dark cycle (ND-LD) and high-fat diet all dark (HFD-DD) groups. Weight measurements were taken weekly, and after 24 weeks of intervention, 24 mice from both groups were randomly selected and analyzed. Additionally, the remaining mice in the HFD-DD group were divided into two groups: one group continued the high-fat all-dark treatment (HFD-DD-DD), and the other group was restored to normal light/dark cycle treatment (HFD-DD-LD). Mice were euthanized after a total of 48 weeks of intervention. Measurements were taken for each mouse including liver function serum indicators, liver tissue pathological sections, rhythm-related proteins, and determination of the gut microbiota community.

RESULTS

The HFD induced NAFLD in mice, exhibiting symptoms such as obesity, lipid and glucose metabolism disorders, elevated liver enzymes, and decreased gut microbiota diversity. The composition of the gut microbiota was significantly different from that of the normal diet group, with a significant increase in the ratio of Firmicutes to Bacteroides. Restoration of normal light/dark cycles exacerbated the disorder of lipid metabolism, liver steatosis, and the expression of BMAL1 in mice and significantly reduced the diversity of gut microbiota.

CONCLUSIONS

Circadian rhythm changes aggravate the development of NAFLD induced by a high-fat diet by affecting glucose metabolism, liver steatosis, and gut microbiota diversity. Restoration of normal circadian rhythm did not improve NAFLD. Our findings open up new avenues for the prevention, diagnosis, and treatment of NAFLD.

Approach to the diagnosis and management of dysbiosis

All microorganisms like bacteria, viruses and fungi that reside within a host environment are considered a microbiome. The number of bacteria almost equal that of human cells, however, the genome of these bacteria may be almost 100 times larger than the human genome. Every aspect of the physiology and health can be influenced by the microbiome living in various parts of our body. Any imbalance in the microbiome composition or function is seen as dysbiosis. Different types of dysbiosis are seen and the corresponding symptoms depend on the site of microbial imbalance. The contribution of the intestinal and extra-intestinal microbiota to influence systemic activities is through interplay between different axes. Whole body dysbiosis is a complex process involving gut microbiome and non-gut related microbiome. It is still at the stage of infancy and has not yet been fully understood. Dysbiosis can be influenced by genetic factors, lifestyle habits, diet including ultra-processed foods and food additives, as well as medications. Dysbiosis has been associated with many systemic diseases and cannot be diagnosed through standard blood tests or investigations. Microbiota derived metabolites can be analyzed and can be useful in the management of dysbiosis. Whole body dysbiosis can be addressed by altering lifestyle factors, proper diet and microbial modulation. The effect of these interventions in humans depends on the beneficial microbiome alteration mostly based on animal studies with evolving evidence from human studies. There is tremendous potential for the human microbiome in the diagnosis, treatment, and prognosis of diseases, as well as, for the monitoring of health and disease in humans. Whole body system-based approach to the diagnosis of dysbiosis is better than a pure taxonomic approach. Whole body dysbiosis could be a new therapeutic target in the management of various health conditions.

Alteration of Gut Microbiota Composition in the Progression of Liver Damage in Patients with Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD)

Metabolic dysfunction-associated steatotic liver disease (MASLD) is a complex disorder whose prevalence is rapidly growing in South America. The disturbances in the microbiota-gut-liver axis impact the liver damaging processes toward fibrosis. Gut microbiota status is shaped by dietary and lifestyle factors, depending on geographic location. We aimed to identify microbial signatures in a group of Chilean MASLD patients. Forty subjects were recruited, including healthy controls (HCs), overweight/obese subjects (Ow/Ob), patients with MASLD without fibrosis (MASLD/F-), and MASLD with fibrosis (MASLD/F+). Both MASLD and fibrosis were detected through elastography and/or biopsy, and fecal microbiota were analyzed through deep sequencing. Despite no differences in α- and β-diversity among all groups, a higher abundance of Bilophila and a lower presence of Defluviitaleaceae, Lachnospiraceae ND3007, and Coprobacter was found in MASLD/F- and MASLD/F+, compared to HC. Ruminococcaceae UCG-013 and Sellimonas were more abundant in MASLD/F+ than in Ow/Ob; both significantly differed between MASLD/F- and MASLD/F+, compared to HC. Significant positive correlations were observed between liver stiffness and Bifidobacterium, Prevotella, Sarcina, and Acidaminococcus abundance. Our results show that MASLD is associated with changes in bacterial taxa that are known to be involved in bile acid metabolism and SCFA production, with some of them being more specifically linked to fibrosis.

Non-alcoholic fatty liver disease in patients with morbid obesity: the gut microbiota axis as a potential pathophysiology mechanism

BACKGROUND/AIM

Alterations in gut microbiota are associated with the pathogenesis of metabolic diseases, including metabolic-associated fatty liver disease (MAFLD). The aim of this study was to evaluate gut microbiota composition and functionality in patients with morbid obesity with different degrees of MAFLD, as assessed by biopsy.

SUBJECTS/METHODS

110 patients with morbid obesity were evaluated by biopsy obtained during bariatric surgery for MAFLD. Stool samples were collected prior to surgery for microbiota analysis.

RESULTS

Gut microbiota from patients with steatosis and non-alcoholic steatohepatitis (NASH) were characterized by an enrichment in Enterobacteriaceae (an ethanol-producing bacteria), Acidaminococcus and Megasphaera and the depletion of Eggerthellaceae and Ruminococcaceae (SCFA-producing bacteria). MAFLD was also associated with enrichment of pathways related to proteinogenic amino acid degradation, succinate production, menaquinol-7 (K2-vitamin) biosynthesis, and saccharolytic and proteolytic fermentation. Basic histological hepatic alterations (steatosis, necroinflammatory activity, or fibrosis) were associated with specific changes in microbiota patterns. Overall, the core microbiome related to basic histological alterations in MAFLD showed an increase in Enterobacteriaceae and a decrease in Ruminococcaceae. Specifically, Escherichia coli was associated with steatosis and necroinflammatory activity, whilst Escherichia-shigella was associated with fibrosis and necroinflammatory activity.

CONCLUSIONS

We established a link between gut microbiota alterations and histological injury in liver diagnosis using biopsy. Harmful products such as ethanol or succinate may be involved in the pathogenesis and progression of MAFLD. Thus, these alterations in gut microbiota patterns and their possible metabolic pathways could add information to the classical predictors of MAFLD severity and suggest novel metabolic targets.

Changes in the intestinal microbiota of individuals with non-alcoholic fatty liver disease based on sequencing: An updated systematic review and meta-analysis

BACKGROUND

Alterations in the composition and abundance of the intestinal microbiota occur in non-alcoholic fatty liver disease (NAFLD). However, the results are inconsistent because of differences in the study design, subject area, and sequencing methodology. In this study, we compared the diversity and abundance of the intestinal microbiota of patients with NAFLD and healthy individuals through a systematic review and meta-analysis.

METHODS

Three databases (PubMed, EMBASE, and Cochrane Library) were searched from their inception to March 20, 2023. A meta-analysis was performed using Stata software to analyze variations in the richness and abundance of the intestinal microbiota in patients with NAFLD. The Newcastle-Ottawa Quality Assessment Scale (NOS) was used for quality assessment.

RESULTS

A total of 28 articles were included. Shannon diversity was reduced in patients with NAFLD (SMD = -0.24 (95% CI -0.43-0.05, I2 = 71.7%). The relative abundance of Ruminococcus, Faecalibacterium, and Coprococcus all decreased, with total SMDs of -0.96 (95% CI -1.29 to -0.63, I2 = 4.8%), -1.13 (95% CI -2.07 to -0.19, I2 = 80.5%), and -1.66 (95% CI -3.04 to -0.28, I2 = 91.5%). Escherichia was increased in individuals with NAFLD (SMD = 1.78, 95% CI 0.12 to 3.45, I2 = 94.4%).

CONCLUSION

Increasing the species diversity and altering the abundance of specific gut microbiota, including Coprococcus, Faecalibacterium, Ruminococcus, and Escherichia, may be beneficial for improving NAFLD.

Gut microbiota and metabolic biomarkers in metabolic dysfunction-associated steatotic liver disease

Metabolic dysfunction-associated steatotic liver disease (MASLD), a replacement of the nomenclature employed for NAFLD, is the most prevalent chronic liver disease worldwide. Despite its high global prevalence, NAFLD is often under-recognized due to the absence of reliable noninvasive biomarkers for diagnosis and staging. Growing evidence suggests that the gut microbiome plays a significant role in the occurrence and progression of NAFLD by causing immune dysregulation and metabolic alterations due to gut dysbiosis. The rapid advancement of sequencing tools and metabolomics has enabled the identification of alterations in microbiome signatures and gut microbiota-derived metabolite profiles in numerous clinical studies related to NAFLD. Overall, these studies have shown a decrease in α-diversity and changes in gut microbiota abundance, characterized by increased levels of Escherichia and Prevotella, and decreased levels of Akkermansia muciniphila and Faecalibacterium in patients with NAFLD. Furthermore, bile acids, short-chain fatty acids, trimethylamine N-oxide, and tryptophan metabolites are believed to be closely associated with the onset and progression of NAFLD. In this review, we provide novel insights into the vital role of gut microbiome in the pathogenesis of NAFLD. Specifically, we summarize the major classes of gut microbiota and metabolic biomarkers in NAFLD, thereby highlighting the links between specific bacterial species and certain gut microbiota-derived metabolites in patients with NAFLD.

Microbial Dysbiosis Linked to Metabolic Dysfunction-Associated Fatty Liver Disease in Asians: Prevotella copri Promotes Lipopolysaccharide Biosynthesis and Network Instability in the Prevotella Enterotype

Metabolic dysfunction-associated fatty liver disease (MAFLD), formerly known as non-alcoholic fatty liver disease (NAFLD), is characterized by hepatic fat accumulation by metabolic dysfunction. The rising prevalence of MAFLD, especially among Asians, may be associated with changes in gut microbiota. We investigated gut microbiota characteristics and potential mechanisms leading to MAFLD development according to enterotypes. Case-control studies examining the gut microbiota composition between MAFLD and non-MAFLD participants were searched in public databases until July 2023. Gut microbiota was categorized into two enterotypes by principal component analysis. According to the enterotypes, LEfSe, ALDEx2, XGBoost, and DCiPatho were utilized to identify differential abundances and pathogenic microbes in the gut between the MAFLD and non-MAFLD groups. We analyzed microbial community networks with the SprCC module and predicted microbial functions. In the Prevotella enterotype (ET-P), 98.6% of Asians and 65.1% of Caucasians were associated with MAFLD (p = 0.049). MAFLD incidence was correlated with enterotype, age, obesity, and ethnicity (p < 0.05). Asian MAFLD patients exhibited decreased Firmicutes and Akkermansia muciniphila and increased Bacteroidetes and P. copri. The pathogenicity scores were 0.006 for A. muciniphila and 0.868 for P. copri. The Asian MAFLD group showed decreased stability and complexity in the gut microbiota network. Metagenome function analysis revealed higher fructose metabolism and lipopolysaccharide (LPS) biosynthesis and lower animal proteins and α-linolenic acid metabolism in Asians with MAFLD compared with the non-MAFLD group. LPS biosynthesis was positively correlated with P. copri (p < 0.05). In conclusion, P. copri emerged as a potential microbial biomarker for MAFLD. These findings enhance our understanding of the pathological mechanisms of MAFLD mediated through the gut microbiota, providing insights for future interventions.

Gut Microbiota in Patients with Non-Alcoholic Fatty Liver Disease without Type 2 Diabetes: Stratified by Body Mass Index

The relationship between gut dysbiosis and body mass index (BMI) in non-diabetic patients with non-alcoholic fatty liver disease (NAFLD) is not adequately characterized. This study aimed to assess gut microbiota's signature in non-diabetic individuals with NAFLD stratified by BMI. The 16S ribosomal RNA sequencing was performed for gut microbiota composition in 100 patients with NAFLD and 16 healthy individuals. The differential abundance of bacterial composition between groups was analyzed using the DESeq2 method. The alpha diversity (Chao1, Shannon, and observed feature) and beta diversity of gut microbiota significantly differed between patients with NAFLD and healthy controls. However, significant differences in their diversities were not observed among subgroups of NAFLD. At the phylum level, there was no trend of an elevated Firmicutes/Bacteroidetes ratio according to BMI. At the genus level, patients with lean NAFLD displayed a significant enrichment of Escherichia-Shigella and the depletion of Lachnospira and Subdoligranulum compared to the non-lean subgroups. Combining these bacterial genera could discriminate lean from non-lean NAFLD with high diagnostic accuracy (AUC of 0.82). Non-diabetic patients with lean NAFLD had a significant difference in bacterial composition compared to non-lean individuals. Our results might provide evidence of gut microbiota signatures associated with the pathophysiology and potential targeting therapy in patients with lean NAFLD.

A systematic review and meta-analysis of randomized controlled trials to evaluate plant-based omega-3 polyunsaturated fatty acids in nonalcoholic fatty liver disease patient biomarkers and parameters

CONTEXT

Nonalcoholic fatty liver disease (NAFLD) is prevalent in 25-30% of British and European populations, representing a potential global public health crisis. Marine omega-3 (n-3) polyunsaturated fatty acids offer well-evidenced benefits to NAFLD biomarkers; however, the effect of plant-based n-3 has not been evaluated with a systematic review and meta-analysis.

OBJECTIVE

The review aimed to systematically evaluate the effect of plant-based n-3 supplementation on NAFLD surrogate biomarkers and parameters.

DATA SOURCES

Medline (EBSCO), PubMed, CINAHL (EBSCO), Cochrane Central Register of Controlled Trials, the International Clinical Trials Registry Platform, and Google Scholar databases were searched to identify randomized controlled trials published between January 1970 and March 2022 evaluating the impact of plant-based n-3 interventions on diagnosed NAFLD. The review followed the PRISMA checklist and is PROSPERO registered (CRD42021251980).

DATA EXTRACTION

A random-effects model and generic inverse variance methods synthesized quantitative data, followed by a leave-one-out method for sensitivity analysis. We identified 986 articles; after the application of selection criteria, six studies remained with 362 patients with NAFLD.

RESULTS

The meta-analysis showed that plant-based n-3 fatty acid supplementation significantly reduced alanine aminotransferase (ALT) (mean difference: 8.04 IU/L; 95% confidence interval: 14.70, 1.38; I2 = 48.61%) and plasma/serum triglycerides (44.51 mg/dL; 95% confidence interval: -76.93, -12.08; I2 = 69.93%), alongside body-composition markers in patients with NAFLD (P < 0.05).

CONCLUSION

Plant-based n-3 fatty acid supplementation improves ALT enzyme biomarkers, triglycerides, body mass index, waist circumference, and weight loss when combined with lifestyle interventions to increase physical activity and a calorie-controlled diet. Further research is needed to identify the most effective plant-based n-3 sources in larger numbers of patients with NAFLD over longer study durations.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO registration no. CRD42021251980.

Antibiotics attenuate diet-induced nonalcoholic fatty liver disease without altering intestinal barrier dysfunction

To date the role of the alterations of intestinal microbiota in the development of intestinal barrier dysfunction in settings of nonalcoholic fatty liver disease (NAFLD) has not been fully understood. Here, we assessed the effect of antibiotics on development of NAFLD and their impact on intestinal barrier dysfunction. Male C57BL/6J mice were either pair-fed a liquid control diet (C) or fat- and fructose-rich diet (FFr) +/- antibiotics (AB, ampicillin/vancomycin/metronidazole/gentamycin) for 7 weeks. Fasting blood glucose was determined and markers of liver damage, inflammation, intestinal barrier function, and microbiota composition were assessed. The development of hepatic steatosis with early signs of inflammation found in FFr-fed mice was significantly abolished in FFr+AB-fed mice. Also, while prevalence of bacteria in feces was not detectable and TLR4 ligand levels in portal plasma were at the level of controls in FFr+AB-fed mice, impairments of intestinal barrier function like an increased permeation of xylose and iNOS protein levels persisted to a similar extent in both FFr-fed groups irrespective of AB use. Exposure of everted small intestinal tissue sacs of naïve mice to fructose resulted in a significant increase in tissue permeability and loss of tight junction proteins, being not affected by the presence of AB, whereas the concomitant treatment of tissue sacs with the NOS inhibitor aminoguanidine attenuated these alterations. Taken together, our data suggest that intestinal barrier dysfunction in diet-induced NAFLD in mice may not be predominantly dependent on changes in intestinal microbiota but rather that fructose-induced alterations of intestinal NO-homeostasis might be critically involved.

Gut microbes in metabolic disturbances. Promising role for therapeutic manipulations?

The prevalence of overweight, obesity, type 2 diabetes, metabolic syndrome and steatotic liver disease is rapidly increasing worldwide with a huge economic burden in terms of morbidity and mortality. Several genetic and environmental factors are involved in the onset and development of metabolic disorders and related complications. A critical role also exists for the gut microbiota, a complex polymicrobial ecology at the interface of the internal and external environment. The gut microbiota contributes to food digestion and transformation, caloric intake, and immune response of the host, keeping the homeostatic control in health. Mechanisms of disease include enhanced energy extraction from the non-digestible dietary carbohydrates, increased gut permeability and translocation of bacterial metabolites which activate a chronic low-grade systemic inflammation and insulin resistance, as precursors of tangible metabolic disorders involving glucose and lipid homeostasis. The ultimate causative role of gut microbiota in this respect remains to be elucidated, as well as the therapeutic value of manipulating the gut microbiota by diet, pre- and pro- synbiotics, or fecal microbial transplantation.

The Role of Bifidobacterium in Liver Diseases: A Systematic Review of Next-Generation Sequencing Studies

The physiopathology of liver diseases is complex and can be caused by various factors. Bifidobacterium is a bacterial genus commonly found in the human gut microbiome and has been shown to influence the development of different stages of liver diseases significantly. This study investigated the relationship between the Bifidobacterium genus and liver injury. In this work, we performed a systematic review in major databases using the key terms "Bifidobacterium", "ALD", "NAFLD", "NASH", "cirrhosis", and "HCC" to achieve our purpose. In total, 31 articles were selected for analysis. In particular, we focused on studies that used next-generation sequencing (NGS) technologies. The studies focused on assessing Bifidobacterium levels in the diseases and interventional aimed at examining the therapeutic potential of Bifidobacterium in the mentioned conditions. Overall, the abundance of Bifidobacterium was reduced in hepatic pathologies. Low levels of Bifidobacterium were associated with harmful biochemical and physiological parameters, as well as an adverse clinical outcome. However, interventional studies using different drugs and treatments were able to increase the abundance of the genus and improve clinical outcomes. These results strongly support the hypothesis that changes in the abundance of Bifidobacterium significantly influence both the pathophysiology of hepatic diseases and the related clinical outcomes. In addition, our critical assessment of the NGS methods and related statistical analyses employed in each study highlights concerns with the methods used to define the differential abundance of Bifidobacterium, including potential biases and the omission of relevant information.

Association between gut microbiota and NAFLD/NASH: a bidirectional two-sample Mendelian randomization study

Background

Recent studies have suggested a relationship between gut microbiota and non-alcoholic fatty liver disease (NAFLD)/nonalcoholic steatohepatitis (NASH). However, the nature and direction of this potential causal relationship are still unclear. This study used two-sample Mendelian randomization (MR) to clarify the potential causal links.

Methods

Summary-level Genome-Wide Association Studies (GWAS) statistical data for gut microbiota and NAFLD/NASH were obtained from MiBioGen and FinnGen respectively. The MR analyses were performed mainly using the inverse-variance weighted (IVW) method, with sensitivity analyses conducted to verify the robustness. Additionally, reverse MR analyses were performed to examine any potential reverse causal associations.

Results

Our analysis, primarily based on the IVW method, strongly supports the existence of causal relationships between four microbial taxa and NAFLD, and four taxa with NASH. Specifically, associations were observed between Enterobacteriales (P =0.04), Enterobacteriaceae (P =0.04), Lachnospiraceae UCG-004 (P =0.02), and Prevotella9 (P =0.04) and increased risk of NAFLD. Dorea (P =0.03) and Veillonella (P =0.04) could increase the risks of NASH while Oscillospira (P =0.04) and Ruminococcaceae UCG-013 (P=0.005) could decrease them. We also identified that NAFLD was found to potentially cause an increased abundance in Holdemania (P =0.007) and Ruminococcus2 (P =0.002). However, we found no evidence of reverse causation in the microbial taxa associations with NASH.

Conclusion

This study identified several specific gut microbiota that are causally related to NAFLD and NASH. Observations herein may provide promising theoretical groundwork for potential prevention and treatment strategies for NAFLD and its progression to NASH in future.

Non-alcoholic fatty liver disease and gut microbial dysbiosis- underlying mechanisms and gut microbiota mediated treatment strategies

Non-alcoholic fatty liver disease (NAFLD) is by far the most prevalent form of liver disease worldwide. It's also the leading cause of liver-related hospitalizations and deaths. Furthermore, there is a link between obesity and NAFLD risk. A projected 25% of the world's population grieves from NAFLD, making it the most common chronic liver disorder. Several factors, such as obesity, oxidative stress, and insulin resistance, typically accompany NAFLD. Weight loss, lipid-lowering agents, thiazolidinediones, and metformin help prominently control NAFLD. Interestingly, pre-clinical studies demonstrate gut microbiota's potential causal role in NAFLD. Increased intestinal permeability and unhindered transport of microbial metabolites into the liver are the major disruptions due to gut microbiome dysbiosis, contributing to the development of NAFLD by dysregulating the gut-liver axis. Hence, altering the pathogenic bacterial population using probiotics, prebiotics, synbiotics, and fecal microbiota transplantation (FMT) could benefit patients with NAFLD. Therefore, it is crucial to acknowledge the importance of microbiota-mediated therapeutic approaches for NAFLD and comprehend the underlying mechanisms that establish a connection between NAFLD and gut microbiota. This review provides a comprehensive overview of the affiliation between dysbiosis of gut microbiota and the progress of NAFLD, as well as the potential benefits of prebiotic, probiotic, synbiotic supplementation, and FMT in obese individuals with NAFLD.

Microbiome and Genetic Factors in the Pathogenesis of Liver Diseases

Our genetic background has not changed over the past century, but chronic diseases are on the rise globally. In addition to the genetic component, among the critical factors for many diseases are inhabitants of our intestines (gut microbiota) as a crucial environmental factor. Dysbiosis has been described in liver diseases with different etiologies like non-alcoholic fatty liver disease (NAFLD), alcohol-related liver disease (ALD), viral hepatitis, autoimmune hepatitis (AIH), primary sclerosing cholangitis (PSC), primary biliary cholangitis (PBC), cirrhosis, hepatocellular carcinoma (HCC). On the other hand, new technologies have increased our understanding of liver disease genetics and treatment options. Genome-wide association studies (GWAS) identify unknown genetic risk factors, positional cloning of unknown genes associated with different diseases, gene tests for single nucleotide variations (SNVs), and next-generation sequencing (NGS) of selected genes or the complete genome. NGS also allowed studying the microbiome and its role in various liver diseases has begun. These genes have proven their effect on microbiome composition in host genome–microbiome association studies. We focus on altering the intestinal microbiota, and supplementing some bacterial metabolites could be considered a potential therapeutic strategy. The literature data promote probiotics/synbiotics role in reducing proinflammatory cytokines such as TNF-α and the interleukins (IL-1, IL-6, IL-8), therefore improving transaminase levels, hepatic steatosis, and NAFLD activity score. However, even though microbial therapy appears to be risk-free, evaluating side effects related to probiotics or synbiotics is imperative. In addition, safety profiles for long-term usage should be researched. Thus, this review focuses on the human microbiome and liver diseases, recent GWASs on liver disease, the gut-liver axis, and the associations with the microbiome and microbiome during/after liver disease therapy.

Association between the gut microbiota and nonalcoholic fatty liver disease: A two-sample Mendelian randomization study

BACKGROUND

Increasing studies have shown that there is a significant association between gut microbiota and non-alcoholic fatty liver disease.

AIMS

To show the potential association between gut microbiota and non-alcoholic fatty liver disease, we performed a two-sample Mendelian randomization analysis.

METHODS

We analyzed summary statistics from genome-wide association studies of gut microbiota and non-alcoholic fatty liver disease and conducted Mendelian randomization studies to evaluate relationships between these factors.

RESULTS

Of the 211 gut microbiota taxa examined, the inverse variance weighted method identified Lactobacillaceae (OR = 0.83, 95% CI = 0.72 - 0.95, P = 0.007), Christensenellaceae (OR = 0.74, 95% CI = 0.59 - 0.92, P = 0.007), and Intestinibacter (OR = 0.85, 95% CI = 0.73 - 0.99, P = 0.035) were negatively correlated with non-alcoholic fatty liver disease. And Coriobacteriia (OR = 1.22, 95% CI = 1.01 - 1.42, P = 0.038), Actinomycetales (OR = 1.25, 95% CI = 1.02 - 1.53, P = 0.031), Oxalobacteraceae (OR = 1.10, 95% CI = 1.01 - 1.21, P = 0.036), Ruminococcaceae_UCG005 (OR = 1.18, 95% CI = 1.01 - 1.38, P = 0.033) are positively associated with non-alcoholic fatty liver disease.

CONCLUSIONS

Our study found that the abundance of certain strains was associated with the progression of nonalcoholic fatty liver disease.

Gut ecological networks reveal associations between bacteria, exercise, and clinical profile in non-alcoholic fatty liver disease patients

IMPORTANCE

Our study is applying a community-based approach to examine the influence of exercise on gut microbiota (GM) and discover GM structures linked with NAFLD improvements during exercise. The majority of microbiome research has focused on finding specific species that may contribute to the development of human diseases. However, we believe that complex diseases, such as NAFLD, would be more efficiently treated using consortia of species, given that bacterial functionality is based not only on its own genetic information but also on the interaction with other microorganisms. Our results revealed that exercise significantly changes the GM interaction and that structural alterations can be linked with improvements in intrahepatic lipid content and metabolic functions. We believe that the identification of these characteristics in the GM enhances the development of exercise treatment for NAFLD and will attract general interest in this field.

Which Comes First, Nonalcoholic Fatty Liver Disease or Arterial Hypertension?

Non-alcoholic fatty liver disease (NAFLD) and arterial hypertension (AH) are widespread noncommunicable diseases in the global population. Since hypertension and NAFLD are diseases associated with metabolic syndrome, they are often comorbid. In fact, many contemporary published studies confirm the association of these diseases with each other, regardless of whether other metabolic factors, such as obesity, dyslipidemia, and type 2 diabetes mellites, are present. This narrative review considers the features of the association between NAFLD and AH, as well as possible pathophysiological mechanisms.

An international multidisciplinary consensus statement on MAFLD and the risk of CVD

BACKGROUND

Fatty liver disease in the absence of excessive alcohol consumption is an increasingly common condition with a global prevalence of ~ 25-30% and is also associated with cardiovascular disease (CVD). Since systemic metabolic dysfunction underlies its pathogenesis, the term metabolic (dysfunction)-associated fatty liver disease (MAFLD) has been proposed for this condition. MAFLD is closely intertwined with obesity, type 2 diabetes mellitus and atherogenic dyslipidemia, which are established cardiovascular risk factors. Unlike CVD, which has received attention in the literature on fatty liver disease, the CVD risk associated with MAFLD is often underestimated, especially among Cardiologists.

METHODS AND RESULTS

A multidisciplinary panel of fifty-two international experts comprising Hepatologists, Endocrinologists, Diabetologists, Cardiologists and Family Physicians from six continents (Asia, Europe, North America, South America, Africa and Oceania) participated in a formal Delphi survey and developed consensus statements on the association between MAFLD and the risk of CVD. Statements were developed on different aspects of CVD risk, ranging from epidemiology to mechanisms, screening, and management.

CONCULSIONS

The expert panel identified important clinical associations between MAFLD and the risk of CVD that could serve to increase awareness of the adverse metabolic and cardiovascular outcomes of MAFLD. Finally, the expert panel also suggests potential areas for future research.

Characteristics of gut microbiota in patients with metabolic associated fatty liver disease

Metabolic associated fatty liver disease (MAFLD) is rising in incidence and is an increasingly common cause of cirrhosis and hepatocellular carcinoma (HCC). Alterations in the gut microbiota have been shown to correlate with the development and progression of MAFLD. However, little is known regarding differences in the gut microbiomes of MAFLD patients and healthy cohorts, and subgroups at the abnormal activity of hepatic enzymes in China. In this study, we enrolled 81 MAFLD patients and 25 healthy volunteers. The fecal microbiota was assessed using 16S rRNA gene sequencing and metagenomic sequencing. The results suggested that Ruminococcus obeum and Alistipes were most enriched in healthy individuals when compared with MAFLD patients. Microbe-set Enrichment Analysis (MSEA) results showed Dorea, Lactobacillus and Megasphaera are enriched in MAFLD group. We also found that Alistipes has negatively related to serum glucose (GLU), gamma-glutamyl transferase (GGT), and alanine aminotransferase (ALT). Moreover, the abundance of Dorea was found to be significantly overrepresented in the MAFLD patients and the degree of enrichment increased with the increasing abnormal liver enzyme. An increase in Dorea, combined with decreases in Alistipes appears to be characteristic of MAFLD patients. Further study of microbiota may provide a novel insight into the pathogenesis of MAFLD as well as a novel treatment strategy.

Faecal Microbiota Transplantation, Paving the Way to Treat Non-Alcoholic Fatty Liver Disease

Non-alcoholic fatty liver disease (NAFLD) is currently the most prevalent cause of chronic liver disease (CLD). Currently, the only therapeutic recommendation available is a lifestyle change. However, adherence to this approach is often difficult to guarantee. Alteration of the microbiota and an increase in intestinal permeability seem to be key in the development and progression of NAFLD. Therefore, the manipulation of microbiota seems to provide a promising therapeutic strategy. One way to do so is through faecal microbiota transplantation (FMT). Here, we summarize the key aspects of FMT, detail its current indications and highlight the most recent advances in NAFLD.

Crosstalk between Gut Microbiota and Epigenetic Markers in Obesity Development: Relationship between Ruminococcus, BMI, and MACROD2/SEL1L2 Methylation

Changes in gut microbiota composition and in epigenetic mechanisms have been proposed to play important roles in energy homeostasis, and the onset and development of obesity. However, the crosstalk between epigenetic markers and the gut microbiome in obesity remains unclear. The main objective of this study was to establish a link between the gut microbiota and DNA methylation patterns in subjects with obesity by identifying differentially methylated DNA regions (DMRs) that could be potentially regulated by the gut microbiota. DNA methylation and bacterial DNA sequencing analysis were performed on 342 subjects with a BMI between 18 and 40 kg/m². DNA methylation analyses identified a total of 2648 DMRs associated with BMI, while ten bacterial genera were associated with BMI. Interestingly, only the abundance of Ruminococcus was associated with one BMI-related DMR, which is located between the MACROD2/SEL1L2 genes. The Ruminococcus abundance negatively correlated with BMI, while the hypermethylated DMR was associated with reduced MACROD2 protein levels in serum. Additionally, the mediation test showed that 19% of the effect of Ruminococcus abundance on BMI is mediated by the methylation of the MACROD2/SEL1L2 DMR. These findings support the hypothesis that a crosstalk between gut microbiota and epigenetic markers may be contributing to obesity development.

Targeting nonalcoholic fatty liver disease via gut microbiome-centered therapies

Humans possess abundant amounts of microorganisms, including bacteria, fungi, viruses, and archaea, in their gut. Patients with nonalcoholic fatty liver disease (NAFLD) exhibit alterations in their gut microbiome and an impaired gut barrier function. Preclinical studies emphasize the significance of the gut microbiome in the pathogenesis of NAFLD. In this overview, we explore how adjusting the gut microbiome could serve as an innovative therapeutic strategy for NAFLD. We provide a summary of current information on untargeted techniques such as probiotics and fecal microbiota transplantation, as well as targeted microbiome-focused therapies including engineered bacteria, prebiotics, postbiotics, and phages for the treatment of NAFLD.

Utility of Human Relevant Preclinical Animal Models in Navigating NAFLD to MAFLD Paradigm

Fatty liver disease is an emerging contributor to disease burden worldwide. The past decades of work established the heterogeneous nature of non-alcoholic fatty liver disease (NAFLD) etiology and systemic contributions to the pathogenesis of the disease. This called for the proposal of a redefinition in 2020 to that of metabolic dysfunction-associated fatty liver disease (MAFLD) to better reflect the current understanding of the disease. To date, several clinical cohort studies comparing NAFLD and MAFLD hint at the relevancy of the new nomenclature in enriching for patients with more severe hepatic injury and extrahepatic comorbidities. However, the underlying systemic pathogenesis is still not fully understood. Preclinical animal models have been imperative in elucidating key biological mechanisms in various contexts, including intrahepatic disease progression, interorgan crosstalk and systemic dysregulation. Furthermore, they are integral in developing novel therapeutics against MAFLD. However, substantial contextual variabilities exist across different models due to the lack of standardization in several aspects. As such, it is crucial to understand the strengths and weaknesses of existing models to better align them to the human condition. In this review, we consolidate the implications arising from the change in nomenclature and summarize MAFLD pathogenesis. Subsequently, we provide an updated evaluation of existing MAFLD preclinical models in alignment with the new definitions and perspectives to improve their translational relevance.

Gut-Liver Axis and Non-Alcoholic Fatty Liver Disease: A Vicious Circle of Dysfunctions Orchestrated by the Gut Microbiome

Non-alcoholic fatty liver disease (NAFLD) is a prevalent, multifactorial, and poorly understood liver disease with an increasing incidence worldwide. NAFLD is typically asymptomatic and coupled with other symptoms of metabolic syndrome. The prevalence of NAFLD is rising in tandem with the prevalence of obesity. In the Western hemisphere, NAFLD is one of the most prevalent causes of liver disease and liver transplantation. Recent research suggests that gut microbiome dysbiosis may play a significant role in the pathogenesis of NAFLD by dysregulating the gut-liver axis. The so-called "gut-liver axis" refers to the communication and feedback loop between the digestive system and the liver. Several pathological mechanisms characterized the alteration of the gut-liver axis, such as the impairment of the gut barrier and the increase of the intestinal permeability which result in endotoxemia and inflammation, and changes in bile acid profiles and metabolite levels produced by the gut microbiome. This review will explore the role of gut-liver axis disruption, mediated by gut microbiome dysbiosis, on NAFLD development.

Fecal Microbiota Transplantation in NAFLD Treatment

Introduction: Gut microbiota is not only a taxonomic biologic ecosystem but is also involved in human intestinal and extra-intestinal functions such as immune system modulation, nutrient absorption and digestion, as well as metabolism regulation. The latter is strictly linked to non-alcoholic fatty liver disease (NAFLD) pathophysiology. Materials and methods: We reviewed the literature on the definition of gut microbiota, the concepts of “dysbiosis” and “eubiosis”, their role in NAFLD pathogenesis, and the data on fecal microbiota transplantation (FMT) in these patients. We consulted the main medical databases using the following keywords, acronyms, and their associations: gut microbiota, eubiosis, dysbiosis, bile acids, NAFLD, and FMT. Results: Gut microbiota qualitative and quantitative composition is different in healthy subjects vs. NALFD patients. This dysbiosis is associated with and involved in NAFLD pathogenesis and evolution to non-acoholic steatohepatitis (NASH), liver cirrhosis, and hepatocellular carcinoma (HCC). In detail, microbial-driven metabolism of bile acids (BAs) and interaction with hepatic and intestinal farnesoid nuclear X receptor (FXR) have shown a determinant role in liver fat deposition and the development of fibrosis. Over the use of pre- or probiotics, FMT has shown preclinical and initial clinical promising results in NAFLD treatment through re-modulation of microbial dysbiosis. Conclusions: Promising clinical data support a larger investigation of gut microbiota dysbiosis reversion through FMT in NAFLD using randomized clinical trials to design precision-medicine treatments for these patients at different disease stages.

Integrative analysis of gut microbiota and fecal metabolites in metabolic associated fatty liver disease patients

Objective

Metabolic associated fatty liver disease (MAFLD) affects nearly a quarter of the world’s population. Our study aimed to characterize the gut microbiome and overall changes in the fecal and serum metabolomes in MAFLD patients.

Methods

Thirty-two patients diagnosed with MAFLD and 30 healthy individuals (control group, CG) were included in this study, the basic clinical characteristics and laboratory test results including routine biochemistry, etc. were recorded for all, and their serum and fecal samples were collected. A portion of the fecal samples was subjected to 16S rDNA sequencing, and the other portion of the fecal samples and serum samples were subjected to non-targeted metabolomic detection based on liquid chromatography-mass spectrometry (LC–MS). Statistical analysis of clinical data was performed using SPSS software package version 25.0 (SPSS Inc., Chicago, IL, United States). The analysis of 16S rDNA sequencing results was mainly performed by R software (V. 2.15.3), and the metabolomics data analysis was mainly performed by CD 3.1 software. Two-tailed p value &lt; 0.05 was considered statistically significant.

Results

The 16S sequencing data suggested that the species richness and diversity of MAFLD patients were reduced compared with controls. At the phylum level, the relative abundance of Bacteroidota, Pseudomonadota, and Fusobacteriota increased and Bacillota decreased in MAFLD patients. At the genus level, the relative abundances of Prevotella, Bacteroides, Escherichia-Shigella, etc. increased. 2,770 metabolites were detected in stool samples and 1,245 metabolites were detected in serum samples. The proportion of differential lipid metabolites in serum (49%) was higher than that in feces (21%). There were 22 differential metabolites shared in feces and serum. And the association analysis indicated that LPC 18:0 was positively correlated with Christensenellaceae_R-7_group, Oscillospiraceae_UCG-002; neohesperidin was also positively correlated with Peptoniphilus, Phycicoccus, and Stomatobaculum.

Conclusion

Microbial sequencing data suggested decreased species richness and diversity and altered β-diversity in feces. Metabolomic analysis identified overall changes in fecal and serum metabolites dominated by lipid molecules. And the association analysis with gut microbes provided potentially pivotal gut microbiota-metabolite combinations in MAFLD patients, which might provide new clues for further research on the disease mechanism and the development of new diagnostic markers and treatments.

Changes in intestinal microbiota of HBV-associated liver cirrhosis with/without hepatic encephalopathy

The compositional balance of intestinal microbiota plays an important role in maintaining homeostasis. This study aimed to investigate the intestinal flora of hepatitis B virus-associated liver cirrhosis (HBV-LC) with or without hepatic encephalopathy (HE) and how it relates to the disease. A total of 20 patients with HBV-LC were enrolled in this study, along with 10 healthy adults. The participants were divided into HE group, non-HE group, and control group. Fecal samples were collected under the condition of patients' daily diet, and the 16S rRNA test was performed for each fecal sample. The relative abundance of Bacteroidia, Streptococcaceae, Streptococcus, Veillonella, Bacteroidales, Lactobacillales, Pasteurellales, and Veillonella parvula increased in the HBV-LC group. Meanwhile, the relative weights of Pasteurellales, Pasteurellaceae, Haemophilus, and Selenomonas significantly increased in the HE group. Furthermore, in the non-HE group, the relative abundance of Veillonella increased. Intestinal microbiota was significantly different from controls with respect to a lack of potentially beneficial autochthonous bacteria and overgrowth of potentially pathogenic genera in patients with HBV-LC. Moreover, there was a greater change in the relative abundance of intestinal flora when complicated with HE.

Metagenomic identification of gut microbiota distribution on the colonic mucosal biopsy samples in patients with non-alcoholic fatty liver disease

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD) is known to be the most common liver disease in the world, and there are currently no approved pharmacological treatments to prevent or treat this condition. In addition to being associated with an increased risk of hepatocellular carcinoma and cirrhosis, NAFLD has now become the leading cause of liver failure-associated transplantation. The 16S rRNA gene which conserved regions can serve as universal primer binding sites for PCR amplification of gene fragments, while hypervariable regions contain significant sequence diversity useful for prokaryotic identification purposes. 16S rRNA gene sequences can be use by researchers to identify prokaryotic taxonomy found in clinical samples. As a result of increasing microbiota studies with developing technological developments, the role of intestinal microbiota in the pathogenesis of NAFLD is revealed in an important way. In this study, it was aimed to determine the clinical prognostic importance of gut microbiota in the pathogenesis of NAFLD and to determine the microbial composition with intestinal mucosal biopsy samples in NAFLD patients.

MATERIAL AND METHOD

We included 20 patients diagnosed with NAFLD as a result of liver function tests, histological, ultrasonographic, biopsy evidence and 20 normal control groups created under exclusion criteria in this study. The healthy control group of the same age and gender as the patients were determined to be equal, and the age, gender, BMI, insulin resistance, AST, ALT levels of the individuals were recorded for analysis. İntestinal mucosal biopsy samples were taken from the individuals included in the study under sterile conditions. Microbial results were obtained as a result of 16S rRNA amplicon metagenomic processes. The region of approximately 1500 bp covering the V1-V9 region of the 16S rRNA gene was targeted to detect microbial diversity. The amplified regions were sequenced using next-generation sequencing. Operational Taxonomic Unit (OTU) value was obtained with bioinformatics software with the obtained sequence data. The analysis of the recorded parameters was done with the SPSS.19 statistical program.

RESULTS

In the designed study, 16 phyla, 28 class, 56 order, 128 family, 415 genera, 1041 species microorganisms were analyzed taxonomically in a total of 40 individuals. In our study, Intestinal microbial diversity is lower in NAFLD patients compared to control group individuals. In addition, gram-negative bacteria were found to be more dominant in NAFLD patients. As a phylum, Proteobacteria increased in NAFLD group, Bacteroidetes and Actinobacteria in control group, while Firmicutes had equal distribution in both groups. BMI OR = 6.37, 95 %CI (0.39-0.40) p value was 0.001 in laboratory data, whereas Proteobacteria OR = 1.754, 95% CI (0.901-3.416), p value 0.05 in microbial profile.

CONCLUSION

The 16S rRNA metagenomic study of intestinal microbiota using colonic mucosal biopsy samples in NAFLD disease was the first study in the Turkish population, and important data were obtained for other studies. In the data obtained, we think Proteobacteria, Ruminococcaceae, Escherichia coli and Bacilli are very important in both diagnostic and treatment options as a microbial profile in NAFLD.

Litchi-Derived Polyphenol Alleviates Liver Steatosis and Gut Dysbiosis in Patients with Non-Alcoholic Fatty Liver Disease: A Randomized Double-Blinded, Placebo-Controlled Study

Preclinical data suggest the role of litchi extract in alleviating non-alcoholic fatty liver disease (NAFLD) by modulating gut microbiota. We aimed at investigating whether oligonol, a litchi-derived polyphenol, could improve liver steatosis and gut dysbiosis in patients with NAFLD. Adults with grade ≥2 steatosis, defined by an MRI proton density fat fraction (MRI-PDFF) of ≥11%, were randomly assigned to receive either oligonol or placebo for 24 weeks. The alteration in the MRI-PDFF and gut microbiota composition assessed by 16S ribosomal RNA sequencing were examined. There were 38 patients enrolled (n = 19 in each group). A significant reduction in the MRI-PDFF between week 0 and week 24 was observed in the oligonol group, while there was a non-significant decrease in the placebo group. A significant improvement in alpha-diversity was demonstrated in both of the groups. The oligonol-induced microbiota changes were characterized by reduced abundance of pathogenic bacteria, including Dorea, Romboutsia, Erysipelotrichaceae UCG-003 and Agathobacter, as well as increased abundance of short-chain fatty acids (SCFAs)-producing bacteria, such as Akkermansia, Lachnospira, Dialister and Faecalibacterium. In summary, this study is the first to provide evidence that supports that oligonol improves steatosis through the modulation of gut bacterial composition. Our results also support the beneficial and complementary role of oligonol in treating NAFLD.