Sage Journals: Discover world-class research

Abstract

Metabolic dysfunction-associated fatty liver disease (MAFLD), formerly known as nonalcoholic fatty liver disease, is becoming a significant contributor to chronic liver disease globally, surpassing other etiologies, such as viral hepatitis. Prevention and early treatment strategies to curb its growing prevalence are urgently required. Recent evidence suggests that targeting the gut microbiota may help treat and alleviate disease progression in patients with MAFLD. This review aims to explore the complex relationship between MAFLD and the gut microbiota in relation to disease pathogenesis. Additionally, it delves into the therapeutic strategies targeting the gut microbiota, such as diet, exercise, antibiotics, probiotics, synbiotics, glucagon-like peptide-1 receptor agonists, and fecal microbiota transplantation, and discusses novel biomarkers, such as microbiota-derived testing and liquid biopsy, for their diagnostic and staging potential. Overall, the review emphasizes the urgent need for preventive and therapeutic strategies to address the devastating consequences of MAFLD at both individual and societal levels and recognizes that further exploration of the gut microbiota may open avenues for managing MAFLD effectively in the future.

Keywords

diagnostic implications fatty liver fatty liver disease liver transplantation microbiota therapeutic interventions

Introduction

Metabolic dysfunction-associated fatty liver disease (MAFLD), formerly known as nonalcoholic fatty liver disease (NAFLD), represents a complex disease entity characterized by a broad range of manifestations from mild to severe hepatic steatosis, which can progress to fibrosis, cirrhosis, decompensated liver disease, hepatocellular carcinoma (HCC), and cardiometabolic-related events.¹ It is emerging as a significant factor in the global burden of chronic liver disease.^2,3 It is poised to surpass other etiologies, including viral hepatitis, in becoming the leading cause for liver transplantation worldwide.^4,5 The impact of MAFLD is exacerbated further by the growing prevalence of obesity, a leading etiology for metabolic dysfunction-associated steatohepatitis [MASH, formerly known as nonalcoholic steatohepatitis (NASH)].^6,7

A multitude of factors contribute to the presentation and progression of MAFLD, such as age, gender, metabolic changes, activity, dietary habits, genetic predispositions, and the intricate balance of the gut microbiota.^8–10 The latter plays a complex role in the gut–liver axis, where the gut microbiota, intestinal barrier, immune system, and liver interact intricately to influence the development and progression of MAFLD.¹¹

This review extensively explores the literature and new evidence to explain the factors influencing gut dysbiosis and its involvement in MAFLD pathogenesis. It summarizes techniques that aim to quantify gut microbiota parameters and use them as diagnostic tools for MAFLD. Lastly, the review discusses the emerging therapeutic interventions that target specific processes of gut dysbiosis to help alleviate symptom manifestations and disease progression of MAFLD. The gut microbiota may hold key mechanistic, diagnostic, and therapeutic opportunities for relieving the health and economic burden of MAFLD, and future studies and clinical trials should focus on these exciting possibilities.

Methods

A comprehensive literature search was conducted in May 2023 in PubMed and Embase databases using the keywords ‘metabolic dysfunction-associated fatty liver disease’, ‘nonalcoholic steatohepatitis’, ‘MAFLD’, ‘NASH’, ‘microbiota’, AND ‘microbiome’. The search encompassed articles published from January 2000 to May 2023. Preference was given to English language meta-analyses and randomized controlled trials (RCTs) in humans to ensure high-quality evidence. In cases where such studies were lacking, nonrandomized studies, controlled cohorts, or animal studies were also included, although with limitations. The search strategy aimed to identify relevant studies for an in-depth review, providing valuable insights into the relationship between MAFLD, the gut microbiota, and advancements in diagnosis and treatment approaches.

Results

From gut dysbiosis to MAFLD

The pathogenesis of MAFLD is complex and involves dynamic mechanisms. Accordingly, the proposed theory mandates a parallel and ‘multiple-hit’ dynamic interplay between multiple factors. One such factor that may strongly influence MAFLD symptoms and progression is gut dysbiosis, which includes dysregulation of gut permeability, diet, microbiome alteration, changes in gut receptors and biomarkers, endotoxemia, endogenous alcohol production, intestinal metabolites, short-chain fatty acids (SCFAs), and bile acids (BAs).^12–14 The multilevel interactions and mechanisms of these factors that may collectively contribute to the development of MAFLD are illustrated in Figure 1.¹⁵ The pathogenesis cascade can start with increased gut permeability, leading to enhanced bacterial translocation, and the release of toxic products, which in turn triggers inflammation mediated by multiple proinflammatory mechanisms, including Toll-like receptor (TLR) 4. The altered gut microbiota in patients with MAFLD includes an increased abundance of certain species (e.g., Proteus, Enterobacter, Escherichia, etc.) with a reduced population of others (e.g., Ruminococcus, Lactobacillus, etc.). In addition, disruption in the gut microbial balance is linked to changes in BA metabolism, modulation of farnesoid X receptor (FXR) stimulation, and alterations in fat and glucose homeostasis. The dysbiosis-induced release of metabolites, such as 2-butanone and 4-methyl-2-pentanone, along with ethanol production by gut bacteria, contributes to oxidative damage.^16–24 Notably, variations in the gut microbiota composition and the Firmicutes/Bacteroidetes (F/B) ratio have been observed in different studies. In addition, they have not only been associated with MAFLD but also linked to its severity.^21,25–29 Further comprehensive investigations are required to establish microbial signatures associated with MAFLD, enabling the development of targeted preventive and therapeutic strategies.

Figure 1.

Interactions between gut microbiome, bile salts, lipid metabolism, inflammation markers, and hepatocytes in the pathophysiology of MAFLD¹⁵

Gut permeability and endotoxemia

Multiple studies have established a connection between impaired gut barrier function and bacterial translocation.^30–33 De Munck et al.³⁴ conducted a systematic review and meta-analysis of 14 studies addressing intestinal permeability and MAFLD. Increased permeability was noted on dual sugar tests and zonulin levels [0.79; 95% confidence interval (CI): 0.49–1.08 and 1.04 ng/mL; 95% CI: 0.40–1.68]. An association with hepatic steatosis was noted in four studies but not with hepatic inflammation or fibrosis. In individuals with MASH, compromised intestinal permeability is proposed as a potential mechanism, resulting in elevated serum endotoxin levels and subsequent liver injury. A total of 34 studies were included in the meta-analysis conducted by Soppert et al.³⁵ Serum endotoxin levels were notably elevated in simple steatosis versus healthy controls (0.86; 95% CI: 0.62–1.11) and in MASH versus MAFLD/MASH (0.81: 95% CI:0.27–1.35; p = 0.0078). Moreover, they observed an association between advanced disease histology and endotoxin levels, adding more evidence to the value of blood endotoxin levels as a potential future diagnostic and staging maker of MAFLD.

Diet and gut microbiota

Recent evidence has emphasized the significant impact of diet on the gut microbiota and its role in metabolic health. Diverse dietary regimens have the potential to induce varying alterations in the composition of the intestinal microbiome. Low-carbohydrate diets (LCD) and ketogenic diets (KD) have been shown to cause distinct alterations in the gut microbiota, including changes in Actinobacteria, Bacteroidetes, Firmicutes, and Bifidobacterium populations. For example, β-hydroxybutyrate synthesized during KD is linked to reduced Bifidobacterium abundance. Furthermore, the microbiota associated with KD has been found to reduce proinflammatory Th17 cells, suggesting potential anti-inflammatory effects. Another example is the ability of a high fructose diet to disrupt metabolism, increase energy intake, and induce microbiota dysbiosis through increasing intestinal permeability.^36–40

The Mediterranean diet can positively alter gut microbiota composition, promoting intestinal barrier integrity and reducing inflammation and harmful bacteria like Escherichia/Shigella. Furthermore, high-fat diets (HFD) have been found to increase specific Lactobacillus species resistant to BAs, which may influence lipid metabolism and contribute to MAFLD development.³⁷ These findings highlight the dynamic interplay between diet, gut microbiota composition, and metabolic health, offering potential avenues for targeted interventions in patients with MAFLD.^41–46

Toll-like receptors

The TLR signaling pathway plays a pivotal role in establishing a connection between gut dysbiosis and the initiation of MAFLD by detecting molecules from the gut microbiota.^47–50 Activation of this pathway leads to the production of cytokines, and sustained elevation of these cytokines poses potential harm to the host. Recent literature highlights that TLR signaling contributes to the exacerbation of hepatic injury in various chronic liver diseases, encompassing conditions such as alcoholic liver disease (ALD), chronic viral hepatitis, and MAFLD/MASH.^49,51–53 TLRs, including TLR2, TLR3, TLR4, TLR5, TLR7, TLR8, and TLR9, exhibit heightened sensitivity to microbial component alterations, such as peptidoglycans and lipopolysaccharides, distinguishing between physiological colonization and pathogenic presence and actively contributing to initiating inflammatory responses.^49,54–56 Dysregulation of the lipopolysaccharide/TLR4 signaling pathway, affected by compromised gut barriers and dietary and microbial composition, emerges as a major mechanism in the pathogenesis and trajectory of MAFLD.^49,57–59 Robust evidence supports the significant role of TLR4 in hepatic steatosis development, particularly through lipopolysaccharide-mediated activation, inducing NF-κB-dependent inflammatory cytokine production.^49,60–62 Conversely, TLR9 signaling under chronic overnutrition stress serves as a driving force for hepatic steatosis progression, with decreased TLR9 expression mitigating steatohepatitis and liver fibrosis.^49,63 However, TLR9 signaling can be associated with liver injury and may promote the progression of MAFLD.^49,64–67 While the involvement of TLR2 in MAFLD remains controversial with variable outcomes, TLR3 signaling induces inflammatory processes, impacting cholesterol efflux genes and influencing proinflammatory cytokine expression.^49,68–72

The progression from hepatic steatosis to liver fibrosis involves complex interactions between damaged hepatocytes, inflammatory signals, and hepatic stellate cells (HSCs).^49,73 Contributing factors include genetic predisposition, advanced age, ethnicity, and comorbidities like obesity, dyslipidemia, and diabetes.⁷⁴ TLR4, activated by Lipopolysaccharides (LPS), plays a significant role in MAFLD-related fibrosis, regulating inflammatory responses.^75–80 TLR2 and TLR3 exhibit conflicting roles in the literature, with studies demonstrating both profibrotic and antifibrotic effects in different models.^69,81–84 TLR5’s role in liver fibrosis also conflicts, while TLR7 signaling demonstrates a protective role.^49,85–87 TLR9, recognizing CpG-containing DNA, influences fibrogenic responses in HSCs, but its role is complex and conflicting, with both profibrotic and antifibrotic outcomes reported.^{49,51,88–90}

Furthermore, TLRs are key players in the interplay between chronic hepatic inflammation and HCC pathogenesis. TLR4, implicated in HCC development, exhibits multifaceted roles by promoting proinflammatory and malignancy-related molecules (e.g., Treg cell counts) and contributing to HCC cell proliferation and resistance to apoptosis.^91–93 TLR9 is associated with aggressiveness and poor prognosis in patients with HCC.⁹⁴ A similar link was noticed with TLR5.^94,95 Literature on TLR3 signaling appears to show antitumor activity, suggesting therapeutic potential for HCC.^{49,93,96–98} Collectively, TLR4, TLR9, TLR5, and TLR3 emerge as potential targets for therapeutic interventions, highlighting the intricate involvement of TLRs in hepatic steatosis, progression to fibrosis, and HCC pathogenesis.⁴⁹

Macrophages

Macrophages emerge as pivotal contributors to the MAFLD and progression to steatohepatitis. Targeting their pathways emerges as a promising avenue for therapeutic strategies aimed at mitigating MAFLD progression. Clinical evidence highlights portal macrophage infiltration in the early stages of MAFLD, preceding overt inflammation and exhibiting association with hepatocyte damage and a positive correlation with disease severity.^99–101 Depletion of macrophages through diverse methods showed potential protective benefits against steatosis development, highlighting the indispensable role of macrophages in the MAFLD dynamics.^101,102 Additionally, proinflammatory macrophages contribute to hepatic insulin resistance, influencing the responsiveness of hepatocytes to insulin.^101,103

In the broader context of chronic liver diseases, macrophages intricately interact with HSCs, establishing bidirectional signaling that profoundly influences inflammation and fibrosis.^101,104 Notably, M2 macrophages, associated with hepatic injury in MAFLD, orchestrate a fibrotic response conducive to liver remodeling and tissue repair.^101,105,106 The identification of ‘restorative’ hepatic macrophages in mice, Ly-6Clocells, introduces complexity with their human counterpart remaining to be clarified.^101,107 Furthermore, macrophage autophagy has been implicated in attenuating liver fibrosis in mouse models.^101,108 Overall, macrophages play important regulatory roles in inflammation, fibrosis, and fibrolysis at different stages of hepatic injury within the MAFLD spectrum.

Endogenous alcohol production

Several studies have proposed a connection between endogenous alcohol production and MAFLD. Studies have detected elevated blood alcohol levels in patients with MAFLD, indicating that gut bacteria, particularly Enterobacteriaceae, might contribute to endogenous alcohol production within the body.^29,109,110 This internal alcohol production can lead to hepatotoxicity through both direct mechanisms and indirect pathways, including increased oxidative stress in the liver. Therefore, the alcohol produced by gut bacteria represents a potential factor in the development and progression of MAFLD and highlights the role of endogenous alcohol in the liver pathology associated with this metabolic disorder.^29,111,112

BAs and SCFAs

The interplay between the gut microbiota, BAs, and their receptors plays a pivotal role in the development and progression of MAFLD. Patients with MAFLD show elevated levels of total fecal BAs, including cholic acid and chenodeoxycholic acid, along with an altered balance of primary and secondary BAs. Notably, BAs interact with FXR in the intestines, affecting BA absorption, transport, hepatic lipogenesis, lipid metabolism, and inflammation regulation.^113,114 Manipulating the gut microbiota and antagonizing FXR in animal models have shown promising results in reducing hepatic lipogenesis and improving lipid metabolism. Moreover, stimulating the G-protein-coupled receptor 5 by gut-bacteria-derived secondary BAs influences glucose homeostasis through glucagon-like peptide-1 (GLP-1) action. Clinical trials using FXR agonists have demonstrated encouraging outcomes in ameliorating hepatic steatosis and reducing inflammation in patients with MAFLD. Collectively, these findings underscore the significant role of gut-microbiota-mediated alterations in BAs and their receptors in lipid metabolism, glucose homeostasis, and the pathogenesis of MAFLD.^22,115–120

Microbiota-derived metabolites

Gut microbiota produces SCFAs like acetate, propionate, and butyrate through fermentation. SCFAs are important to maintain intestinal integrity and function.^121,122 They serve as important precursors for gluconeogenesis and lipogenesis, providing energy in normal conditions. The activation of G-protein-coupled receptors by SCFAs triggers the release of peptide YY and GLP-1, contributing to feelings of satiety and reduced food intake.^123–125 Moreover, SCFAs activate adenosine monophosphate-activated protein kinase, promoting hepatic autophagy and lipid oxidation. They also inhibit histone deacetylases, influence gene transcription, and exhibit potential anti-inflammatory properties.^126,127 Studies have revealed variations in SCFA levels among individuals at different stages of MAFLD, and experiments involving SCFA supplementation in animal models have demonstrated beneficial effects on inflammation in the liver and adipose tissue.^128–130

Genetics, microbiota, and MAFLD

Heritability of MAFLD, estimated to be around 20–70%,¹³¹ is underlined by gene–environment interactions, supported by epidemiological, familial aggregation, and twin studies extending even to disease-related metabolic traits. Genes involved with steatosis pathogenesis may also be involved with fibrosis pathogenesis. Hepatic steatosis and fibrosis had a highly significant shared gene effect of 0.756 (95% CI: 0.716–1, p < 0.0001).¹³² We are in an era of genome-wide association studies and gut microbiome signatures where many key genetic variants shaping MAFLD manifestations and severity have been identified, notably variants in PNPLA3, transmembrane 6 superfamily member 2 (TM6SF2), glucokinase regulator (GCKR), membrane-bound O-acyltransferase domain-containing 7 (MBOAT7), and hydroxysteroid 17β- dehydrogenase (HSD17B13). This is a major milestone in advancing the wheel of MAFLD treatment targets and personalized medicine approaches.

The PNPLA3p.I148M polymorphism is a cornerstone variant associated with the entire spectrum of MAFLD. It is also associated with an increased risk for disease progression and the occurrence of liver-related events and HCC throughout the literature.^133,134 Elevated body mass index (BMI), the presence of the PNPLA3 risk variant, diminished relative abundances of Faecalibacterium sp. or Prevotella sp., augmented relative abundances of Gemmiger sp., and dietary patterns characterized by low fiber and specific vitamin content, coupled with enrichment in amino acids, uric acid, and purine, emerge as pivotal determinants influencing the severity of MAFLD.¹³⁵

The contribution of impaired TM6SF2, a major regulator of plasma lipids levels, function to MAFLD was described first in 2014.^136,137 This has been further validated in the literature and a meta-analysis.^138–142 Elevated levels of lipopolysaccharide-binding protein (LBP) were observed in individuals diagnosed with NASH. Intriguingly, individuals carrying the TM6SF2 rs58542926 T-allele, associated with susceptibility to NAFLD/NASH, exhibited higher LBP levels. TM6SF2 exhibits pronounced expression in the gastrointestinal tract, potentially surpassing its expression levels in the liver. This prompted the hypothesis that intestinal TM6SF2 plays an additional role in the progression of MAFLD by augmenting endotoxemia.¹⁴³ The link between TM6SF2 polymorphism and endotoxemia requires further investigations and studies.

Loss-of-function mutation (rs1260326) coding for the P446L protein in the GCKR gene variant, governing de novo lipogenesis, has been linked to MAFLD.^144–146 MBOAT7 has a critical role in processes pivotal for systemic immune homeostasis, including for a broad range of TLR responses. These effects are further regulated by the genotype at MBOAT7 rs8736. Modulation of MBOAT7 may provide therapeutic benefits for suppressing inflammation in human diseases associated with dysregulation of the TLR signaling cascade, including in MAFLD.¹⁴⁷ HSD17B13 gene (rs72613567:TA) is strongly linked to decreased serum transaminase levels and a reduced risk of NASH through its lipid droplet-associated retinol dehydrogenase activity. Yet, further functional studies are required to clarify its role in MAFLD.^148–150

The dynamic interplay between gut microbiome communities and their interactions with the host holds significant implications for the initiation and advancement of MAFLD, presenting a promising avenue for the identification of novel diagnostic and prognostic biomarkers. In the early stages of MAFLD, Desulfobacteraceae bacterium, and Mushu phage emerged as pivotal hub species. On the other hand, Fonticula alba, Faecalibacterium prausnitzii, and Mushu phage activity were identified as critical regulators influencing the progression toward steatohepatitis.¹⁵¹

Lean MAFLD and microbiota

Lean MAFLD constitutes a globally acknowledged distinct pathophysiologic entity, with approximately 47–65% of cases exhibiting steatohepatitis.¹⁵² While there is a recognized need for additional evidence to comprehensively characterize its spectrum, including disease pathogenesis, natural history, and prognosis, the prevailing definition centers on hepatic steatosis with a BMI below 25 kg/m² (or below 23 kg/m² in Asians).^153–156 Chen et al. noted distinct disparities in gut microbiome constitution and bile acid profiles when comparing lean MAFLD to its nonlean counterpart. Notably, patients with lean NAFLD displayed elevated levels of total, primary, and secondary BAs compared to their nonlean counterparts, with statistical significance observed specifically for secondary BAs (p = 0.01). The composition of individual BAs also differed, as lean patients exhibited lower levels of deoxycholate, glycochenodeoxycholic acid, and chenodeoxycholic acid but higher levels of glycocholic acid compared to nonlean patients. Intriguingly, no significant difference between lean and nonlean patients was observed concerning more severe fibrosis. Patients with lean MAFLD exhibited enrichment in Erysipelotrichaceae UCG-003, Ruminococcus, Clostridium sensu stricto 1, Romboutsia, and Ruminococcaceae UCG-008. Conversely, Ruminiclostridium and Streptococcus were enriched in patients with obesity and MAFLD (Mann–Whitney test, p < 0.05). Notably, these changes remained significant for Ruminococcaceae UCG-008 even after correction for multiple comparisons (FDR p = 0.010). Consistent trends were observed in mice subjects with lean NAFLD, mirroring what was observed in humans, particularly the abundance of Ruminococcaceae bacterial family. These trends were further evident in several phylotypes within the Erysipelotrichaceae.¹⁵⁷ Duarte et al. observed that patients with NASH exhibited notable distinctions in the abundance of Faecalibacterium, Ruminococcus, Lactobacillus, and Bifidobacterium compared to the control group. Specifically, patients with lean NASH had a threefold reduction in the abundance of Faecalibacterium and Ruminococcus (p = 0.004). In contrast, patients with obesity and NASH demonstrated an abundance of Lactobacilli (p = 0.002), while patients with NASH who were overweight displayed a diminished abundance of Bifidobacterium (p = 0.018). Furthermore, patients with lean NASH displayed a deficiency in Lactobacillus in comparison to their overweight and obese NASH counterparts. Interestingly, this lean NASH subgroup exhibited a gut microbiome alpha diversity akin to that of the control group. Despite qualitative distinctions between lean NASH and overweight/obese NASH, these disparities did not achieve statistical significance (p = 0.618).¹⁵⁸

Macrophages derived from individuals with lean MAFLD exhibit heightened production of inflammatory cytokines, mirroring levels similar to their nonlean counterparts, suggesting a potential loss of metabolic adaptation over time. Comprehensive analyses of the transcriptome and chromatin landscape unveil that metabolic endotoxemia in lean MAFLD prompts a proinflammatory gene program and increases TLR4 production, consequently hindering BA signaling.¹⁵⁵ Long-term outcomes for patients with lean MAFLD prove comparable to or worse than those observed in nonlean MAFLD counterparts, signifying a gradual waning of early metabolic adaptation.^156,157,159 The instigation of microbial dysbiosis induced by a Western-style diet contributes to endotoxemia, hepatic inflammation, and the infiltration of proinflammatory immune cells within the milieu of lean MAFLD.^101,160

Both lean and nonlean patients manifest analogous macrophage responses, implying that macrophages may constitute early sites of adaptive mechanism exhaustion in the context of lean MAFLD. A metabolic–epigenetic axis governs macrophage inflammatory and metabolic responses, with lean MAFLD exhibiting modified chromatin accessibility and transcription factor networks.^155,161 Overall, the complex interplay of microbial dysbiosis, compromised bile acid signaling, and altered epigenetic regulation contribute to the subtle progression of lean MAFLD, shedding light on potential avenues for therapeutic intervention.

Gut Microbiota and MAFLD diagnosis

Until now, no existing microbiota-derived testing has been validated for diagnosing or staging MAFLD. Currently, the most used diagnostic method is invasive (liver biopsy), and the available noninvasive biomarkers lack validity and an inability to evaluate a wide spectrum of MAFLD. Transient elastography offers the most reliable and consistent diagnosis. Therefore, there is a vast need for novel biomarkers that are accurate and reliable, and microbiota-associated biomarkers may hold some potential for diagnosing MAFLD.^20,162 Table 1 lists the microbiota-associated biomarkers for MAFLD.

Table 1.

Microbiota-associated biomarkers for MAFLD.

Biomarker	Description	Findings	References
Fecal Calprotectin	A marker of intestinal inflammation	Increased FC levels observed in patients with MAFLD.	70 –72
Gut Microbiome	Characterized using shotgun sequencing of DNA extracted from stool samples	Distinct gut microbiome composition associated with advanced fibrosis in MAFLD. Incorporating other variables such as age, serum albumin, and ALT levels can increase diagnostic accuracy.	16,73
13 C-Octanoate Breath Test	A noninvasive test that measures the metabolism of a 13 C-labeled substrate	Shown to be effective in differentiating MASH from MAFLD. Potential to be a useful noninvasive biomarker in the future.	74
Liquid Biopsy Test	Involves peripheral blood monocyte PLIN2 and RAB14	Shown to be accurate, sensitive, and specific in diagnosing and staging MAFLD. Deemed reliable over existing biomarkers in a large multicenter cohort.	77

ALT, alanine aminotransferase; FC, Fecal calprotectin; MASH: Metabolic dysfunction-associated steatohepatitis; MAFLD, Metabolic dysfunction-associated fatty liver disease.

Fecal calprotectin

Recent studies show a correlation between MAFLD and inflammatory bowel disease, which supports the proposed theory of intestinal inflammation and permeability in the pathogenesis of MAFLD.^163–165 Markers of systemic inflammation, like calprotectin, were studied in patients with MAFLD. Ponziani et al.¹⁶⁶ studied 41 patients and 20 healthy controls. They concluded that in patients with MAFLD cirrhosis, gut microbiota, and systemic inflammation were significantly correlated in the process of hepatocarcinogenesis. Moreover, Bourgonje et al.¹⁶⁷ found that higher plasma calprotectin levels are associated with suspected MAFLD and the risk of all-cause mortality. Demirbas et al.¹⁶⁸ also observed elevated fecal calprotectin (FC) levels in a pediatric cohort, including patients with obesity and MAFLD. Unfortunately, serum FC and myeloperoxidase levels did not show the same correlation as demonstrated by Bıçakçı et al.¹⁶⁹ Interestingly, Stehura et al.¹⁷⁰ added more complexity to the FC/MAFLD correlation question by investigating FC in 46 patients with MAFLD and coronavirus disease 2019 and observed higher FC levels. Further investigation is warranted to determine precise serum or fecal calprotectin levels before it can be used as a marker of MAFLD. However, it can still be used as a good indicator of gut inflammation.

Gut microbiome

Loomba et al.²² developed a novel model that demonstrated robust diagnostic accuracy (area under the receiver operating characteristic curve: 0.94) by exploring a panel of gut microbiome-derived biomarkers to envision the presence of advanced fibrosis in 86 patients with biopsy-proven MAFLD. It was further validated in an independent cohort. Dong et al.¹⁷¹ in 2020 recruited 50 patients with chronic liver diseases, including MAFLD, and 25 healthy controls. Microbiome composition was unique in patients with advanced fibrosis (p = 0.003), who had enriched levels of Prevotella copri, the most predictive microbiome in the classifier. Taking other biomarkers and variables, like age, serum albumin, and alanine aminotransferase levels, into account can increase the accuracy of detecting advanced disease stage and cirrhosis, as demonstrated by Oh et al.²¹ All these findings stress the fact that a distinct microbiome signature is present and may play a diagnostic role in staging patients with MAFLD.

Other noninvasive tests

Several studies were conducted to identify novel surrogate biomarkers that could have diagnostic utility in MAFLD. Fierbinteanu-Braticevici et al.¹⁷² demonstrated the efficacy of 13C-Octanoate breath test in differentiating MASH from MAFLD and its potential to become a useful noninvasive biomarker in the future. Octanoate is quickly absorbed in the small intestine and metabolized in the liver via beta-oxidation to acetyl-CoA and carbon dioxide (CO₂). The exhaled CO₂, collected at varied time points, allows for time-sensitive hepatic function evaluation. Other studies examined the potential effect of microbiota metabolites, such as amino acids, on steatosis in MAFLD.^173,174 Women exhibiting steatosis demonstrated reduced microbial gene diversity alongside heightened endotoxin production, particularly from Proteobacteria. Additionally, these patients showed imbalances in the metabolism of aromatic and branched-chain amino acids. Another study showed the consistency of microbial metabolite, 3-(4-hydroxyphenyl) lactate and its significant association with MAFLD and liver fibrosis. Noteworthy, Angelini et al.¹⁷⁵ demonstrated in their large multicenter cohort that the novel PLIN2/RAB14- based liquid biopsy test was accurate, sensitive, reliable, and specific in diagnosing and staging MAFLD compared with existing biomarkers; however, the study was limited to Caucasians, and further investigations are required.

Gut dysbiosis and MAFLD: therapeutic interventions

There are several potential microbiota-related therapeutic targets for MAFLD. Some of those are listed in Table 2, while Figure 2 depicts the overview of current microbiota-related avenues for MAFLD regarding diagnosis, pathophysiology, and therapeutics.

Table 2.

Therapeutic MAFLD targets related to microbiota.

Therapeutic targets	Description	Outcomes/Findings	References
Diet and weight loss	Hypocaloric, high fiber, low-fat and/or low-carb diet	High-fiber diet linked to increased presence of Akkermansia muciniphila.	80 –86
Caffiene	Caffeine consumption	Caffeine consumption may protect against MASH.	87 –91
Exercise	Endurance or weight training	Exercise led to increased presence of Verrucomicrobia and reduced Proteobacteria. It also decreased the F/B ratio.	4, 92 –95
Antibiotics	May improve liver function by altering microbiota.	Metronidazole, in combination with inulin supplementation, showed a positive effect on ALT.	97 –102
Probiotics	Beneficial microbes	A systematic review showed that probiotics may reduce BMI, total fat percentage, total cholesterol, as well as triglycerides.	106, 107
Prebiotics	Nourishing substrates for beneficial gut bacteria	May reduce intra-hepatocellular lipids, NASH score, and it can increase Bifidobacterium levels	111, 112

ALT, alanine transaminase; F/B, Firmicutes/Bacteroidetes; MASH, Metabolic dysfunction-associated steatohepatitis; NASH, nonalcoholic steatohepatitis.

Figure 2.

Overview of the current microbiota-related avenues for MAFLD.

Diet

Multiple scientific studies have emphasized the importance of weight loss, aiming for a 7−10% reduction in body weight through a hypocaloric diet (aiming for an energy deficit of 500–1000 kcal/day) in addition to exercise to create a caloric deficit.^78,79 However, there are divergent opinions on specific dietary recommendations (e.g., processed food and alcohol consumption). Limited evidence exists for some diets, like LCD or low-fat diets. Certain associations specifically highlight the potential benefits of the Mediterranean diet for patients with MAFLD. It is worth mentioning that similar diet recommendations apply to patients with MAFLD and type-2 diabetes, emphasizing that an individualized approach that focuses on calorie restriction and adherence to the Mediterranean diet could be hugely beneficial.^{162,176–180}

Dietary interventions can target gut dysbiosis and restore gut homeostasis. In rodents, chronic administration of an HFD was associated with an increased abundance of Firmicutes and a decreased presence of Bacteroidetes species, resulting in a higher F/B ratio.¹⁸¹ On the other hand, a high-fiber diet has shown protective effects against hepatic inflammation and has been linked to an increased presence of Akkermansia muciniphila.¹⁸²

Caffeine consumption is suggested to protect against MASH and its progression. Various mechanisms have been proposed, including glutathione production, scavenging reactive oxygen species, and gut microbiota modulation, driven by the active alkaloids and phenolic compounds in coffee and its ability to restore the F/B ratio and promote the growth of Bifidobacterium species.^183–187

Exercise

Exercise training has been found to induce changes in the gut microbiota composition. Clarke et al.¹⁸⁸ showed evidence that athletes and healthy persons with a low BMI have different microbiota compositions with higher proportions of Akkermansia than healthy controls with a high BMI. Animal models have demonstrated that exercise is associated with a decreased abundance of certain species (e.g., Lactobacillaceae, Proteobacteria, Bacteroidetes, Flavobacterium, Alkaliphilus, F/B ratio, etc.) and increased numbers of others (e.g., Verrucomicrobia, Turicibacteraceae, etc.). The effects of exercise can go beyond those of diet alone, as shown when comparing exercise to calorie restriction in high-fat diet-fed animals. Exercise not only improved insulin sensitivity but also resulted in a greater reduction of low-density lipoprotein (LDL) cholesterol, primarily due to exercise-induced changes in the gut microbiome. These microbiota modifications have been associated with improved serum LDL cholesterol levels, liver fat mass, and triglycerides.^189–191 In humans, we already know that exercise is associated with reduced rates of MAFLD,⁹ but future studies are needed to confirm the link between exercise and the effects on the microbiome in patients with MAFLD.

Antibiotics

Antibiotics and their effect on gut microbiota have been explored as therapeutic targets in MAFLD. Norfloxacin and neomycin improved liver function by altering microbiota and causing bacterial translocation. On the contrary, another study showed no hepatic benefit for norfloxacin in patients with MAFLD.¹⁹² Metronidazole has shown a positive effect on alanine transaminase (ALT) levels in combination with inulin supplementation compared to placebo (mean ALT change −19.6 versus −0.2 U/L, respectively; p = 0.026).¹⁹³

Several studies examined the use of rifaximin, a nonabsorbable antibiotic, in MAFLD. Kakiyama et al.¹⁹⁴ documented the effect of rifaximin in patients with cirrhosis, including the reduction in the ratio of secondary BAs to primary BAs. However, no substantial alteration was seen in the gut microbiota’s bacterial composition, apart from the decrease in Veillonellaceae. It is pertinent to highlight that most of the study participants were patients with hepatitis C and ALD. Gangarapu et al.¹⁹⁵ showed the beneficial effect of 4 weeks of rifaximin (1200 mg/day) on liver functions, such as ALT. Interestingly, Cobbold et al.’s¹⁹⁶ study showed no alteration in ALT following 6 weeks of rifaximin (800 mg/day). Notably, Abdel-Razik et al.¹⁹⁷ showed that rifaximin (1100 mg/day) significantly decreased serum ALT (from 64.6 ± 34.2 to 38.2 ± 29.2; p = 0.01) and serum aspartate transaminase (AST) (from 66.5 ± 42.5 to 41.8 ± 30.4; p = 0.02) after 6 months in patients with MAFLD. In addition, rifaximin reduced serum endotoxin and improved insulin resistance, proinflammatory cytokines, CK-18, and NAFLD liver fat score. Evidence suggests the benefits of rifaximin for MAFLD, but more studies are needed to establish the length and dose of administration.

Probiotics, prebiotics, and synbiotics

Researchers have increasingly investigated the therapeutic potential of microbiota modulators, such as probiotics, prebiotics, and synbiotics, to shape gut microbiota for hepatic health. Probiotics, beneficial microorganisms, can potentially improve hepatic inflammation, oxidative stress, and steatosis. Prebiotics serve as nourishing substrates for beneficial gut bacteria, while synbiotics, which combine probiotics and prebiotics, provide an innovative strategy to restore gut dysbiosis and bolster the survival and function of beneficial gut microbes. Keeping in mind that microbiota modulators do not possess curative effects, they hold potential as adjunct therapies to reach therapeutic goals in MAFLD. Escouto et al.¹⁹⁸ observed a significant improvement in AST to platelet ratio index after 6 months of probiotics supplementation. Manzhalii et al.¹⁹⁹ conducted an open-label trial using a probiotic cocktail over 12 weeks, which showed improved liver inflammation. Unfortunately, only a few research works have explored the role of probiotics on histologic markers of MAFLD and MASH. Focusing more on cardiovascular risk factors, Barcelos et al. showed that 24 weeks of supplementation with probiotics was not superior to placebo in reducing cardiovascular risk markers in MASH.²⁰⁰

Preclinical studies of prebiotics have demonstrated their potential to improve biochemical and histologic markers of MAFLD.²⁰¹ A randomized trial with a placebo crossover design involving patients with biopsy-proven MASH (n = 7) received prebiotic administration, specifically oligofructose (16 g/day). The results showed a significant reduction in hepatic levels of AST compared to placebo (p < 0.05) and a nonsignificant decrease in triglyceride concentrations after 8 weeks of treatment.²⁰² However, a systematic review encompassing four clinical studies involving patients with obesity-related MAFLD did not provide substantial support for using prebiotics, primarily due to limitations in study quality.²⁰³ A recent systematic review that included 13 trials showed that probiotics could reduce BMI, total fat percentage, total cholesterol, triglycerides, fasting insulin, lipopolysaccharide, homeostatic model assessment-insulin resistance, AST, ALT, gamma-glutamyl transferase (GGT), tumor necrosis factor-alpha (TNF-α), interleukin-6, liver stiffness, fat fraction, fat liver index, vaspin, and Clostridia and Erysipelotrichia classes. Prebiotics can reduce intra-hepatocellular lipids, NASH score, Roseburia, and Dialister and increase Bifidobacterium levels. Synbiotics can reduce BMI, AST, ALT, GGT, TNF-α, NAFLD fibrosis score, and liver stiffness, as well as improve Bifidobacterium levels.²⁰⁴ A larger systematic review of 26 RCTs showed that synbiotics and probiotics are potentially the most effective therapies that can reduce AST and ALT in adult patients with MAFLD, respectively.²⁰⁵

In a study by Malaguarnera et al.,²⁰⁶ 66 patients with histologically diagnosed MASH were randomly divided into two groups. One group received a synbiotic treatment consisting of Bifidobacterium longum and a prebiotic (fructooligosaccharides), while the other group received placebo. Both groups went through lifestyle modifications and received a vitamin B regimen. The results showed that the active treatment group had significantly lower levels of TNF-α and C-reactive protein (CRP), as well as histologic improvement with decreased hepatocellular injury, inflammation, and steatosis after 24 weeks of treatment. In the largest double-blind, placebo-controlled trial, patients with ultrasound-diagnosed MAFLD (n = 80) were randomized to obtain an 8-week synbiotic treatment (probiotics including Lactobacillus casei and others) or placebo. At the end of the intervention period, the synbiotic group showed a significant reduction in steatosis as determined using an ultrasound scan, while those who received placebo showed no significant improvement.²⁰⁷ Although there were no significant differences in CRP, ALT, or AST levels between the synbiotic and placebo groups (adjusted for energy intake), another study of 28-week supplementation in 50 lean patients with MAFLD showed a significant decrease in fibrosis, hepatic steatosis, fasting blood sugar, triglyceride levels, and inflammation markers.²⁰⁸

GLP-1 receptor agonists

Numerous studies have highlighted the impact of the gut microbiota on glucose regulation and satiety.^209–212 GLP-1 agonists have demonstrated their effectiveness in curbing calorie intake, promoting weight loss, improving glucose tolerance, and reducing cholesterol levels and cellular apoptosis in both MASH and obesity.^213,214 Hupa-Breier et al.²¹⁵ examined the effects of GLP-1 in nondiabetic mice with MASH, finding that dulaglutide, alone and in combination with empagliflozin, led to significant weight loss, improved glucose regulation, and reduced anti-inflammatory and antifibrotic responses.

In addition, liraglutide has shown promising results in enhancing glucose and lipid metabolism in obese rat groups, regardless of their hyperglycemia status. Notably, liraglutide induced significant alterations in the gut microbiota composition, decreasing its diversity and abundance while promoting lean-related microbial characteristics and reducing obesity-related phenotypes.²¹⁶ These findings suggest that GLP-1 agonists may play a role in preventing weight gain by modulating the gut microbiota, but further in-depth investigations are required to fully comprehend the underlying mechanisms responsible for these weight-controlling effects.

Fecal microbiota transplantation

Fecal microbiota transplantation (FMT) has been investigated as an intervention for MAFLD, with multiple trials registered. However, the results have been contradictory. In a study by Craven et al., a single FMT infusion did not lead to a reduction in liver steatosis.²¹⁷ In contrast, another study involving a 3-day FMT infusion demonstrated a modest yet significant decrease in the severity of steatosis.²¹⁸ In a >12-month follow-up study by Bajaj et al., patients in the FMT arm showed sustained improvement in clinical and cognitive function parameters, with no recurrent hepatic encephalopathy occurrence and hospitalizations due to liver complications.²¹⁹ These findings highlight the variability in outcomes observed with FMT as a therapeutic approach for MAFLD up to this point.

Conclusion and future perspectives

In the field of MAFLD, there remains a significant need for improved diagnostic and therapeutic approaches. Currently, available methods are limited, emphasizing the importance of early detection for effective interventions. Well-designed, randomized studies exploring microbiota, microbiome signatures, and metabolites are essential to uncover underlying disease mechanisms and identify individuals at risk of MAFLD at an early stage. While the gut–liver axis has shown promise in managing MAFLD through interventions like rifaximin, prebiotics, probiotics, GLP-1 agonists, and fecal transplantation, the effects are often indirect, and individual responses can vary. More comprehensive studies are needed to precisely characterize microbial changes at different disease stages, including bacteria, viruses, and fungi, and to assess the benefits, dosages, duration of supplementation, long-term effects, and safety of probiotics, prebiotics, and synbiotics for preventing and treating MAFLD. Large-scale intervention studies with well-defined patient groups and reproducible endpoints are necessary to assess the effectiveness of microbiota-based interventions in managing MAFLD and its potential as a therapeutic avenue. Despite challenges, innovative diagnostic and therapeutic approaches focusing on the gut microbiota hold the potential to tackle the complex and challenging spectrum of MAFLD, emphasizing the need for continuous research and exploration in this field.

Footnotes

Acknowledgements

None.

Declarations

ORCID iD

Saleh A. Alqahtani

References

Younossi

ZM.

Non-alcoholic fatty liver disease – a global public health perspective. J Hepatol 2019; 70: 531–544.

Younossi

Tacke

Arrese

, et al. Global Perspectives on nonalcoholic fatty liver disease and nonalcoholic steatohepatitis. Hepatology 2019; 69: 2672–2682.

Younossi

Harring

Younossi

, et al. The impact of NASH to liver transplantations with hepatocellular carcinoma in the United States. Clin Gastroenterol Hepatol 2022; 20: 2915–2917.e1.

Byrne

Targher

NAFLD: a multisystem disease. J Hepatol 2015; 62: S47–S64.

Younossi

Stepanova

Ong

, et al. Nonalcoholic steatohepatitis is the most rapidly increasing indication for liver transplantation in the United States. Clin Gastroenterol Hepatol 2021; 19: 580–589.e5.

Polyzos

Kountouras

Mantzoros

CS.

Obesity and nonalcoholic fatty liver disease: from pathophysiology to therapeutics. Metabolism 2019; 92: 82–97.

Ilagan-Ying

Banini

, et al. Screening, diagnosis, and staging of Non-Alcoholic fatty liver disease (NAFLD): application of society guidelines to Clinical Practice. Curr Gastroenterol Rep 2023; 25: 213–224.

Schneider

Fromme

Schneider

, et al. Mortality in patients with genetic and environmental risk of liver disease. Am J Gastroenterol 2021; 116: 1741–1745.

Schneider

Zandvakili

Thaiss

, et al. Physical activity is associated with reduced risk of liver disease in the prospective UK Biobank cohort. JHEP Rep 2021; 3: 100263.

10.

Scorletti

Creasy

Vujkovic

, et al. Dietary vitamin E intake is associated with a reduced risk of developing digestive diseases and nonalcoholic fatty liver disease. Am J Gastroenterol 2022; 117: 927–930.

11.

Martín-Mateos

Albillos

The role of the gut-liver axis in metabolic dysfunction-associated fatty liver disease. Front Immunol 2021; 12: 660179.

12.

Buzzetti

Pinzani

Tsochatzis

EA.

The multiple-hit pathogenesis of non-alcoholic fatty liver disease (NAFLD). Metabolism 2016; 65: 1038–1048.

13.

Fang

Chen

Wang

, et al. Pathogenesis of non-alcoholic fatty liver disease in children and adolescence: from ‘two hit theory’ to ‘multiple hit model’. World J Gastroenterol 2018; 24: 2974–2983.

14.

Tilg

Moschen

AR.

Evolution of inflammation in nonalcoholic fatty liver disease: the multiple parallel hits hypothesis. Hepatology 2010; 52: 1836–1846.

15.

Jiang

Zheng

Zhang

, et al. Advances in the involvement of gut microbiota in pathophysiology of NAFLD. Front Med 2020; 7: 361.

16.

Schneider

Mohs

Gui

, et al. Imbalanced gut microbiota fuels hepatocellular carcinoma development by shaping the hepatic inflammatory microenvironment. Nat Commun 2022; 13: 3964.

17.

Mencin

Kluwe

Schwabe

RF.

Toll-like receptors as targets in chronic liver diseases. Gut 2009; 58: 704–720.

18.

Than

Newsome

PN.

A concise review of non-alcoholic fatty liver disease. Atherosclerosis 2015; 239: 192–202.

19.

Baldwin

The NF-kappa B and I kappa B proteins: new discoveries and insights. Annu Rev Immunol 1996; 14: 649–683.

20.

Kim

Caussy

, et al. A universal Gut-microbiome-derived signature predicts cirrhosis. Cell Metab 2020; 32: 878–888.e6. e6.

21.

Loomba

Seguritan

, et al. Gut microbiome-based metagenomic signature for non-invasive detection of advanced fibrosis in human nonalcoholic fatty liver disease. Cell Metab 2017; 25: 1054–1062.e5. e5.

22.

Jiang

Xie

, et al. Intestinal farnesoid X receptor signaling promotes nonalcoholic fatty liver disease. J Clin Investig 2015; 125: 386–402.

23.

Albillos

de Gottardi

Rescigno

The gut-liver axis in liver disease: pathophysiological basis for therapy. J Hepatol 2020; 72: 558–577.

24.

Chen

Vitetta

Gut Microbiota metabolites in NAFLD pathogenesis and therapeutic implications. Int J Mol Sci 2020; 21: 5214.

25.

Boursier

Mueller

Barret

, et al. The severity of nonalcoholic fatty liver disease is associated with gut dysbiosis and shift in the metabolic function of the gut microbiota. Hepatology 2016; 63: 764–775.

26.

Del Chierico

Nobili

Vernocchi

, et al. Gut microbiota profiling of pediatric nonalcoholic fatty liver disease and obese patients unveiled by an integrated meta-omics-based approach. Hepatology 2017; 65: 451–464.

27.

Mouzaki

Comelli

Arendt

, et al. Intestinal microbiota in patients with nonalcoholic fatty liver disease. Hepatology 2013; 58: 120–127.

28.

Raman

Ahmed

Gillevet

, et al. Fecal microbiome and volatile organic compound metabolome in obese humans with nonalcoholic fatty liver disease. Clin Gastroenterol Hepatol 2013; 11: 868–75.e1. e1-3.

29.

Zhu

Baker

Gill

, et al. Characterization of gut microbiomes in nonalcoholic steatohepatitis (NASH) patients: a connection between endogenous alcohol and NASH. Hepatology 2013; 57: 601–609.

30.

Bischoff

Barbara

Buurman

, et al. Intestinal permeability – a new target for disease prevention and therapy. BMC Gastroenterol 2014; 14: 189.

31.

Kasai

Kessoku

Tanaka

, et al. Association of Serum and fecal bile acid patterns with liver fibrosis in biopsy-proven nonalcoholic fatty liver disease: an observational study. Clin Transl Gastroenterol 2022; 13: e00503.

32.

Miele

Valenza

La Torre

, et al. Increased intestinal permeability and tight junction alterations in nonalcoholic fatty liver disease. Hepatology 2009; 49: 1877–1887.

33.

Wigg

Roberts-Thomson

Dymock

, et al. The role of small intestinal bacterial overgrowth, intestinal permeability, endotoxaemia, and tumour necrosis factor alpha in the pathogenesis of non-alcoholic steatohepatitis. Gut 2001; 48: 206–211.

34.

De Munck

TJI

Verwijs

HJA

, et al. Intestinal permeability in human nonalcoholic fatty liver disease: a systematic review and meta-analysis. Liver Int 2020; 40: 2906–2916.

35.

Soppert

Brandt

Heussen

, et al. Blood endotoxin levels as biomarker of nonalcoholic fatty liver disease: a systematic review and meta-analysis. Clin Gastroenterol Hepatol 2023; 21: 2746–2758.

36.

Ang

Alexander

Newman

, et al. Ketogenic diets alter the gut microbiome resulting in decreased intestinal Th17 cells. Cell 2020; 181: 1263–1275.e16. e16.

37.

Jung

Bae

Song

, et al. Dietary fructose and fructose-induced pathologies. Annu Rev Nutr 2022; 42: 45–66.

38.

Mardinoglu

Bjornson

, et al. An integrated understanding of the rapid metabolic benefits of a carbohydrate-restricted diet on hepatic steatosis in humans. Cell Metab 2018; 27: 559–571.e5.

39.

Mokkala

Houttu

Cansev

, et al. Interactions of dietary fat with the gut microbiota: evaluation of mechanisms and metabolic consequences. Clin Nutr 2020; 39: 994–1018.

40.

Shortt

Hasselwander

Meynier

, et al. Systematic review of the effects of the intestinal microbiota on selected nutrients and non-nutrients. Eur J Nutr 2018; 57: 25–49.

41.

Zeng

Liu

Jackson

, et al. Fatty liver accompanies an increase in lactobacillus species in the hind gut of C57BL/6 mice fed a high-fat diet. J Nutr 2013; 143: 627–631.

42.

Abenavoli

Di Renzo

Boccuto

, et al. Health benefits of Mediterranean diet in nonalcoholic fatty liver disease. Expert Rev Gastroenterol Hepatol 2018; 12: 873–881.

43.

Scheppach

Bartram

Richter

, et al. Effect of short-chain fatty acids on the human colonic mucosa in vitro. JPEN J Parenter Enteral Nutr 1992; 16: 43–48.

44.

Yin

Peng

Zhao

, et al. Structural changes of gut microbiota in a rat non-alcoholic fatty liver disease model treated with a Chinese herbal formula. Syst Appl Microbiol 2013; 36: 188–196.

45.

Yang

Sun

Wang

, et al. Regulatory effect of a Chinese herbal medicine formula on non-alcoholic fatty liver disease. World J Gastroenterol 2019; 25: 5105–5119.

46.

Lian

Zhai

, et al. High fat diet-triggered non-alcoholic fatty liver disease: a review of proposed mechanisms. Chem Biol Interact 2020; 330: 109199.

47.

de Kivit

Tobin

Forsyth

, et al. Regulation of intestinal immune responses through TLR activation: implications for pro- and prebiotics. Front Immunol 2014; 5: 60.

48.

Kawai

Akira

The role of pattern-recognition receptors in innate immunity: update on toll-like receptors. Nat Immunol 2010; 11: 373–384.

49.

Khanmohammadi

Kuchay

MS.

Toll-like receptors and metabolic (dysfunction)-associated fatty liver disease. Pharmacol Res 2022; 185: 106507.

50.

Miura

Ohnishi

Role of gut microbiota and toll-like receptors in nonalcoholic fatty liver disease. World J Gastroenterol 2014; 20: 7381–7391.

51.

Miura

Kodama

Inokuchi

, et al. Toll-like receptor 9 promotes steatohepatitis by induction of interleukin-1beta in mice. Gastroenterology 2010; 139: 323–34.e7. e7.

52.

Inokuchi

Tsukamoto

Park

, et al. Toll-like receptor 4 mediates alcohol-induced steatohepatitis through bone marrow-derived and endogenous liver cells in mice. Alcohol Clin Exp Res 2011; 35: 1509–1518.

53.

Dhillon

Walsh

Krüger

, et al. A single nucleotide polymorphism of toll-like receptor 4 identifies the risk of developing graft failure after liver transplantation. J Hepatol 2010; 53: 67–72.

54.

Le Noci

Bernardo

Bianchi

, et al. Toll like receptors as sensors of the tumor microbial dysbiosis: implications in cancer progression. Front Cell Dev Biol 2021; 9: 732192.

55.

Nijland

Hofland

van Strijp

JA.

Recognition of LPS by TLR4: potential for anti-inflammatory therapies. Mar Drugs 2014; 12: 4260–4273.

56.

Ley

Turnbaugh

Klein

, et al. Microbial ecology: human gut microbes associated with obesity. Nature 2006; 444: 1022–1023.

57.

Ishioka

Miura

Minami

, et al. Altered Gut microbiota composition and immune response in experimental steatohepatitis mouse models. Dig Dis Sci 2017; 62: 396–406.

58.

Cani

Amar

Iglesias

, et al. Metabolic endotoxemia initiates obesity and insulin resistance. Diabetes 2007; 56: 1761–1772.

59.

Carpino

Del Ben

Pastori

, et al. Increased liver localization of lipopolysaccharides in human and experimental NAFLD. Hepatology 2020; 72: 470–485.

60.

Wagnerberger

Spruss

Kanuri

, et al. Toll-like receptors 1-9 are elevated in livers with fructose-induced hepatic steatosis. Br J Nutr 2012; 107: 1727–1738.

61.

Kudo

Takahara

Yata

, et al. Lipopolysaccharide triggered TNF-α-induced hepatocyte apoptosis in a murine non-alcoholic steatohepatitis model. J Hepatol 2009; 51: 168–175.

62.

Imajo

Fujita

Yoneda

, et al. Hyperresponsivity to low-dose endotoxin during progression to nonalcoholic steatohepatitis is regulated by leptin-mediated signaling. Cell Metab 2012; 16: 44–54.

63.

Alegre

Garcia

Billordo

, et al. Limited expression of TLR9 on T cells and its functional consequences in patients with nonalcoholic fatty liver disease. Clin Mol Hepatol 2020; 26: 216–226.

64.

Imaeda

Watanabe

Sohail

, et al. Acetaminophen-induced hepatotoxicity in mice is dependent on Tlr9 and the Nalp3 inflammasome. J Clin Investig 2009; 119: 305–314.

65.

Jiang

Sun

Zhou

, et al. TLR-9 activation aggravates concanavalin A-induced hepatitis via promoting accumulation and activation of liver CD4+ NKT cells. J Immunol 2009; 182: 3768–3774.

66.

Csak

Ganz

Pespisa

, et al. Fatty acid and endotoxin activate inflammasomes in mouse hepatocytes that release danger signals to stimulate immune cells. Hepatology 2011; 54: 133–144.

67.

Huang

Chen

Evankovich

, et al. Histones activate the NLRP3 inflammasome in Kupffer cells during sterile inflammatory liver injury. J Immunol 2013; 191: 2665–2679.

68.

Rivera

Gaskin

Allman

, et al. Toll-like receptor-2 deficiency enhances non-alcoholic steatohepatitis. BMC Gastroenterol 2010; 10: 52.

69.

Cengiz

Ozenirler

Elbeg

Role of serum toll-like receptors 2 and 4 in non-alcoholic steatohepatitis and liver fibrosis. J Gastroenterol Hepatol 2015; 30: 1190–1196.

70.

Szabo

Velayudham

Romics

Jr , et al. Modulation of non-alcoholic steatohepatitis by pattern recognition receptors in mice: the role of toll-like receptors 2 and 4. Alcohol Clin Exp Res 2005; 29: 140S–145S.

71.

Miura

Yang

van Rooijen

, et al. Toll-like receptor 2 and palmitic acid cooperatively contribute to the development of nonalcoholic steatohepatitis through inflammasome activation in mice. Hepatology 2013; 57: 577–589.

72.

Huang

Adhikarakunnathu

, et al. Loss of toll-like receptor 3 function improves glucose tolerance and reduces liver steatosis in obese mice. Metabolism 2012; 61: 1633–1645.

73.

Kuchay

Choudhary

Mishra

SK.

Pathophysiological mechanisms underlying MAFLD. Diabetes Metab Syndr 2020; 14: 1875–1887.

74.

Dufour

J-F

Scherer

Balp

, et al. The global epidemiology of nonalcoholic steatohepatitis (NASH) and associated risk factors–a targeted literature review. Endocr Metab Sci 2021; 3: 100089.

75.

Shi

Dong

Jiang

, et al. Chlorogenic acid reduces liver inflammation and fibrosis through inhibition of toll-like receptor 4 signaling pathway. Toxicology 2013; 303: 107–114.

76.

Yao

, et al. Protective effects of curcumin against hepatic fibrosis induced by carbon tetrachloride: modulation of high-mobility group box 1, toll-like receptor 4 and 2 expression. Food Chem Toxicol 2012; 50: 3343–3351.

77.

Jagavelu

Routray

Shergill

, et al. Endothelial cell toll-like receptor 4 regulates fibrosis-associated angiogenesis in the liver. Hepatology 2010; 52: 590–601.

78.

Shirai

Yoshiji

Noguchi

, et al. Cross talk between toll-like receptor-4 signaling and angiotensin-II in liver fibrosis development in the rat model of non-alcoholic steatohepatitis. J Gastroenterol Hepatol 2013; 28: 723–730.

79.

Deng

Bai

, et al. Resolvin D1 mitigates non-alcoholic steatohepatitis by suppressing the TLR4-MyD88-mediated NF-κB and MAPK pathways and activating the Nrf2 pathway in mice. Int Immunopharmacol 2020; 88: 106961.

80.

Csak

Velayudham

Hritz

, et al. Deficiency in myeloid differentiation factor-2 and toll-like receptor 4 expression attenuates nonalcoholic steatohepatitis and fibrosis in mice. Am J Physiol Gastrointest Liver Physiol 2011; 300: G433–G441.

81.

Hartmann

Haimerl

Mazagova

, et al. Toll-like receptor 2-mediated intestinal injury and enteric tumor necrosis factor receptor I contribute to liver fibrosis in mice. Gastroenterology 2012; 143: 1330–1340.e1. e1.

82.

Xue

Tang

, et al. Toll like receptor 2 knock-out attenuates carbon tetrachloride (ccl4)-induced liver fibrosis by downregulating MAPK and NF-κB signaling pathways. FEBS Lett 2014; 588: 2095–2100.

83.

Radaeva

Sun

Jaruga

, et al. Natural killer cells ameliorate liver fibrosis by killing activated stellate cells in NKG2D-dependent and tumor necrosis factor-related apoptosis-inducing ligand-dependent manners. Gastroenterology 2006; 130: 435–452.

84.

Seo

Eun

Kim

, et al. Exosome-mediated activation of toll-like receptor 3 in stellate cells stimulates interleukin-17 production by γδ T cells in liver fibrosis. Hepatology 2016; 64: 616–631.

85.

Shu

Huang

Hung

, et al. Inhibition of MAPK and NF-κB signaling pathways alleviate carbon tetrachloride (ccl4)-induced liver fibrosis in toll-like receptor 5 (TLR5) deficiency mice. Biochem Biophys Res Commun 2016; 471: 233–239.

86.

Zhou

Kim

, et al. Toll-like receptor 5 signaling ameliorates liver fibrosis by inducing interferon β-Modulated IL-1 receptor antagonist in mice. Am J Pathol 2020; 190: 614–629.

87.

Roh

Park

Kim

, et al. Toll-like receptor 7-mediated type I interferon signaling prevents cholestasis- and hepatotoxin-induced liver fibrosis. Hepatology 2014; 60: 237–249.

88.

Gäbele

Mühlbauer

Dorn

, et al. Role of TLR9 in hepatic stellate cells and experimental liver fibrosis. Biochem Biophys Res Commun 2008; 376: 271–276.

89.

Gäbele

Dostert

Hofmann

, et al. DSS induced colitis increases portal LPS levels and enhances hepatic inflammation and fibrogenesis in experimental NASH. J Hepatol 2011; 55: 1391–1399.

90.

Abu-Tair

Axelrod

Doron

, et al. Natural killer cell-dependent anti-fibrotic pathway in liver injury via Toll-like receptor-9. PLoS One 2013; 8: e82571.

91.

Sepehri

Kiani

Kohan

, et al. Toll like receptor 4 and hepatocellular carcinoma: a systematic review. Life Sci 2017; 179: 80–87.

92.

Dapito

Mencin

Gwak

, et al. Promotion of hepatocellular carcinoma by the intestinal microbiota and TLR4. Cancer Cell 2012; 21: 504–516.

93.

Eiró

Altadill

Juárez

, et al. Toll-like receptors 3, 4 and 9 in hepatocellular carcinoma: relationship with clinicopathological characteristics and prognosis. Hepatol Res 2014; 44: 769–778.

94.

Kairaluoma

Kemi

Huhta

, et al. Toll-like receptor 5 and 8 in hepatocellular carcinoma. APMIS 2021; 129: 470–479.

95.

Nischalke

Fischer

Klüners

, et al. A genetic variant in toll-like receptor 5 is linked to chemokine levels and hepatocellular carcinoma in steatohepatitis. Liver Int 2021; 41: 2139–2148.

96.

Guo

Chen

Zhu

, et al. Double-stranded RNA-induced TLR3 activation inhibits angiogenesis and triggers apoptosis of human hepatocellular carcinoma cells. Oncol Rep 2012; 27: 396–402.

97.

Shen

Jiang

, et al. Combination of Poly I:C and arsenic trioxide triggers apoptosis synergistically via activation of TLR3 and mitochondrial pathways in hepatocellular carcinoma cells. Cell Biol Int 2011; 35: 803–810.

98.

Yuan

Chen

, et al. TLR3 expression correlates with apoptosis, proliferation and angiogenesis in hepatocellular carcinoma and predicts prognosis. BMC Cancer 2015; 15: 245.

99.

Gadd

Skoien

Powell

, et al. The portal inflammatory infiltrate and ductular reaction in human nonalcoholic fatty liver disease. Hepatology 2014; 59: 1393–1405.

100.

Lotowska

Sobaniec-Lotowska

Lebensztejn

DM.

The role of Kupffer cells in the morphogenesis of nonalcoholic steatohepatitis – ultrastructural findings. The first report in pediatric patients. Scand J Gastroenterol 2013; 48: 352–357.

101.

Alharthi

Latchoumanin

George

, et al. Macrophages in metabolic associated fatty liver disease. World J Gastroenterol 2020; 26: 1861–1878.

102.

Neyrinck

Cani

Dewulf

, et al. Critical role of Kupffer cells in the management of diet-induced diabetes and obesity. Biochem Biophys Res Commun 2009; 385: 351–356.

103.

Huang

Metlakunta

Dedousis

, et al. Depletion of liver Kupffer cells prevents the development of diet-induced hepatic steatosis and insulin resistance. Diabetes 2010; 59: 347–357.

104.

Wynn

Barron

Macrophages: master regulators of inflammation and fibrosis. Semin Liver Dis 2010; 30: 245–257.

105.

Wan

Benkdane

Teixeira-Clerc

, et al. M2 Kupffer cells promote M1 Kupffer cell apoptosis: a protective mechanism against alcoholic and nonalcoholic fatty liver disease. Hepatology 2014; 59: 130–142.

106.

Rensen

Slaats

Nijhuis

, et al. Increased hepatic myeloperoxidase activity in obese subjects with nonalcoholic steatohepatitis. Am J Pathol 2009; 175: 1473–1482.

107.

Ramachandran

Pellicoro

Vernon

, et al. Differential Ly-6C expression identifies the recruited macrophage phenotype, which orchestrates the regression of murine liver fibrosis. Proc Natl Acad Sci USA 2012; 109: E3186–E3195.

108.

Lodder

Denaës

Chobert

, et al. Macrophage autophagy protects against liver fibrosis in mice. Autophagy 2015; 11: 1280–1292.

109.

Engstler

Aumiller

Degen

, et al. Insulin resistance alters hepatic ethanol metabolism: studies in mice and children with non-alcoholic fatty liver disease. Gut 2016; 65: 1564–1571.

110.

Volynets

Küper

Strahl

, et al. Nutrition, intestinal permeability, and blood ethanol levels are altered in patients with nonalcoholic fatty liver disease (NAFLD). Dig Dis Sci 2012; 57: 1932–1941.

111.

Mbaye

Borentain

Magdy Wasfy

, et al. Endogenous ethanol and triglyceride production by Gut Pichia kudriavzevii, Candida albicans and Candida glabrata yeasts in Non-Alcoholic steatohepatitis. Cells 2022; 11: 3390.

112.

Yuan

Chen

Cui

, et al. Fatty liver disease caused by high-alcohol-producing Klebsiella pneumoniae. Cell Metab 2019; 30: 1172–1688. e7.

113.

Modica

Gofflot

Murzilli

, et al. The intestinal nuclear receptor signature with epithelial localization patterns and expression modulation in tumors. Gastroenterology 2010; 138: 636–NaN48, 648.e1. 648 e1-12.

114.

Mouzaki

Wang

Bandsma

, et al. Bile acids and dysbiosis in Non-Alcoholic fatty liver disease. PLoS One 2016; 11: e0151829.

115.

Aron-Wisnewsky

Gaborit

Dutour

, et al. Gut microbiota and non-alcoholic fatty liver disease: new insights. Clin Microbiol Infect 2013; 19: 338–348.

116.

Cipriani

Mencarelli

Palladino

, et al. FXR activation reverses insulin resistance and lipid abnormalities and protects against liver steatosis in Zucker (fa/fa) obese rats. J Lipid Res 2010; 51: 771–784.

117.

Neuschwander-Tetri

Loomba

Sanyal

, et al. Farnesoid X nuclear receptor ligand obeticholic acid for non-cirrhotic, non-alcoholic steatohepatitis (FLINT): a multicentre, randomised, placebo-controlled trial. Lancet 2015; 385: 956–965.

118.

Sinal

Tohkin

Miyata

, et al. Targeted disruption of the nuclear receptor FXR/BAR impairs bile acid and lipid homeostasis. Cell 2000; 102: 731–744.

119.

Thomas

Gioiello

Noriega

, et al. TGR5-mediated bile acid sensing controls glucose homeostasis. Cell Metab 2009; 10: 167–177.

120.

Wang

Chen

Wang

, et al. Farnesoid X receptor antagonizes nuclear factor kappaB in hepatic inflammatory response. Hepatology 2008; 48: 1632–1643.

121.

den Besten

Bleeker

Gerding

, et al. Short-chain fatty acids protect against High-Fat diet–induced obesity via a PPARγ-Dependent switch from lipogenesis to fat oxidation. Diabetes 2015; 64: 2398–2408.

122.

Gao

Yin

Zhang

, et al. Butyrate improves insulin sensitivity and increases energy expenditure in mice. Diabetes 2009; 58: 1509–1517.

123.

Samuel

Shaito

Motoike

, et al. Effects of the gut microbiota on host adiposity are modulated by the short-chain fatty-acid binding G protein-coupled receptor, Gpr41. Proc Natl Acad Sci USA 2008; 105: 16767–16772.

124.

Sinha

You

Zhou

, et al. Thyroid hormone stimulates hepatic lipid catabolism via activation of autophagy. J Clin Investig 2012; 122: 2428–2438.

125.

Arslan

Obesity, fatty liver disease and intestinal microbiota. World J Gastroenterol 2014; 20. 63: 16452–16463.

126.

Weiszmann

, et al. Activation of G protein-coupled receptor 43 in adipocytes leads to inhibition of lipolysis and suppression of plasma free fatty acids. Endocrinology 2008; 149: 4519–4526.

127.

Waldecker

Kautenburger

Daumann

, et al. Inhibition of histone-deacetylase activity by short-chain fatty acids and some polyphenol metabolites formed in the colon. J Nutr Biochem 2008; 19: 587–593.

128.

den Besten

Lange

Havinga

, et al. Gut-derived short-chain fatty acids are vividly assimilated into host carbohydrates and lipids. Am J Physiol Gastrointest Liver Physiol 2013; 305: G900–G910.

129.

Loomba

Hwang

O’Donnell

, et al. Parental obesity and offspring serum alanine and aspartate aminotransferase levels: the Framingham heart study. Gastroenterology 2008; 134: 953–959.

130.

Zhai

Qin

, et al. Dietary butyrate suppresses inflammation through modulating gut microbiota in high-fat diet-fed mice. FEMS Microbiol Lett 2019; 366: fnz153.

131.

Eslam

George

Genetic and epigenetic mechanisms of NASH. Hepatol Int 2016; 10: 394–406.

132.

Cui

Chen

, et al. Shared genetic effects between hepatic steatosis and fibrosis: a prospective twin study. Hepatology 2016; 64: 1547–1558.

133.

Grimaudo

Pipitone

Pennisi

, et al. Association between PNPLA3 rs738409 C>G variant and liver-related outcomes in patients with nonalcoholic fatty liver disease. Clin Gastroenterol Hepatol 2020; 18: 935–944.e3. e3.

134.

Liu

Patman

Leathart

JBS

, et al. Carriage of the PNPLA3 rs738409 C >G polymorphism confers an increased risk of non-alcoholic fatty liver disease associated hepatocellular carcinoma. J Hepatol 2014; 61: 75–81.

135.

Lang

Martin

Zhang

, et al. Combined analysis of gut microbiota, diet and PNPLA3 polymorphism in biopsy-proven non-alcoholic fatty liver disease. Liver Int 2021; 41: 1576–1591.

136.

Kozlitina

Smagris

Stender

, et al. Exome-wide association study identifies a TM6SF2 variant that confers susceptibility to nonalcoholic fatty liver disease. Nat Genet 2014; 46: 352–356.

137.

Peng

, et al. TM6SF2: a novel target for plasma lipid regulation. Atherosclerosis 2018; 268: 170–176.

138.

Wong

VWS

Wong

GLH

Tse

, et al. Prevalence of the TM6SF2 variant and non-alcoholic fatty liver disease in Chinese. J Hepatol 2014; 61: 708–709.

139.

Dongiovanni

Petta

Maglio

, et al. Transmembrane 6 superfamily member 2 gene variant disentangles nonalcoholic steatohepatitis from cardiovascular disease. Hepatology 2015; 61: 506–514.

140.

Sookoian

Castaño

Scian

, et al. Genetic variation in transmembrane 6 superfamily member 2 and the risk of nonalcoholic fatty liver disease and histological disease severity. Hepatology 2015; 61: 515–525.

141.

Eslam

Mangia

Berg

, et al.; International Liver Disease Genetics Consortium. Diverse impacts of the rs58542926 E167K variant in TM6SF2 on viral and metabolic liver disease phenotypes. Hepatology 2016; 64: 34–46.

142.

Pirola

Sookoian

The dual and opposite role of the TM6SF2-rs58542926 variant in protecting against cardiovascular disease and conferring risk for nonalcoholic fatty liver: a meta-analysis. Hepatology 2015; 62: 1742–1756.

143.

Pang

Zhang

, et al. Significant positive association of endotoxemia with histological severity in 237 patients with non-alcoholic fatty liver disease. Aliment Pharmacol Ther 2017; 46: 175–182.

144.

Palmer

Musani

Yerges-Armstrong

, et al. Characterization of European ancestry nonalcoholic fatty liver disease-associated variants in individuals of African and Hispanic descent. Hepatology 2013; 58: 966–975.

145.

Speliotes

Yerges-Armstrong

, et al.; NASH CRN, GIANT Consortium, MAGIC Investigators and GOLD Consortium. Genome-wide association analysis identifies variants associated with nonalcoholic fatty liver disease that have distinct effects on metabolic traits. PLoS Genet 2011; 7: e1001324.

146.

Valenti

Alisi

Nobili

Unraveling the genetics of fatty liver in obese children: additive effect of P446L GCKR and I148M PNPLA3 polymorphisms. Hepatology 2012; 55: 661–663.

147.

Alharthi

Bayoumi

Thabet

, et al. A metabolic associated fatty liver disease risk variant in MBOAT7 regulates toll like receptor induced outcomes. Nat Commun 2022; 13: 7430.

148.

Eslam

George

Genetic contributions to NAFLD: leveraging shared genetics to uncover systems biology. Nat Rev Gastroenterol Hepatol 2020; 17: 40–52.

149.

Abul-Husn

Cheng

, et al. A Protein-TruncatingHSD17B13Variant and protection from chronic liver disease. New Engl J Med 2018; 378: 1096–1106.

150.

Belyaeva

Brown

, et al.; for the Nonalcoholic Steatohepatitis Clinical Research Network. 17-Beta hydroxysteroid dehydrogenase 13 is a hepatic retinol dehydrogenase associated with histological features of nonalcoholic fatty liver disease. Hepatology 2019; 69: 1504–1519.

151.

Mascardi

Mazzini

Suárez

, et al. Integrated analysis of the transcriptome and its interaction with the metabolome in metabolic associated fatty liver disease: gut microbiome signatures, correlation networks, and effect of PNPLA3 genotype. Proteomics 2023; 23: e2200414.

152.

Younossi

Koenig

Abdelatif

, et al. Global epidemiology of nonalcoholic fatty liver disease-Meta-analytic assessment of prevalence, incidence, and outcomes. Hepatology 2016; 64: 73–84.

153.

Das

Chowdhury

Lean NASH: distinctiveness and clinical implication. Hepatol Int 2013; 7 Suppl 2: 806–813.

154.

Hagström

Nasr

Ekstedt

, et al. Risk for development of severe liver disease in lean patients with nonalcoholic fatty liver disease: a long-term follow-up study. Hepatol Commun 2018; 2: 48–57.

155.

Alharthi

Pan

Gloss

, et al. Loss of metabolic adaptation in lean MAFLD is driven by endotoxemia leading to epigenetic reprogramming. Metabolism 2023; 144: 155583.

156.

Eslam

El-Serag

Francque

, et al. Metabolic (dysfunction)-associated fatty liver disease in individuals of normal weight. Nat Rev Gastroenterol Hepatol 2022; 19: 638–651.

157.

Chen

Esmaili

Rogers

, et al. Lean NAFLD: a distinct entity shaped by differential metabolic adaptation. Hepatology 2020; 71: 1213–1227.

158.

Duarte

SMB

Stefano

Miele

, et al. Gut microbiome composition in lean patients with NASH is associated with liver damage independent of caloric intake: a prospective pilot study. Nutr Metab Cardiovasc Dis 2018; 28: 369–384.

159.

Younes

Govaere

Petta

, et al. Caucasian lean subjects with non-alcoholic fatty liver disease share long-term prognosis of non-lean: time for reappraisal of BMI-driven approach? Gut 2022; 71: 382–390.

160.

Eslam

Chen

George

NAFLD in Lean Asians. Clin Liver Dis 2020; 16: 240–243.

161.

Zheng

Karki

Williams

, et al. TLR2 senses the SARS-CoV-2 envelope protein to produce inflammatory cytokines. Nat Immunol 2021; 22: 829–838.

162.

European Association for the Study of, the L and D. EASL–EASD–EASO Clinical Practice Guidelines for the management of non-alcoholic fatty liver disease. J Hepatol 2016; 64: 1388–1402.

163.

van Lingen

Tushuizen

Steenhuis

MEJ

, et al. Disease activity in inflammatory bowel disease patients is associated with increased liver fat content and liver fibrosis during follow-up. Int J Colorectal Dis 2022; 37: 349–356.

164.

Yen

Huang

, et al. Evaluation of non-alcoholic fatty liver disease in patients with inflammatory bowel disease using controlled attenuation parameter technology: a Taiwanese retrospective cohort study. PLoS One 2021; 16: e0252286.

165.

Magrì

Paduano

Chicco

, et al. Nonalcoholic fatty liver disease in patients with inflammatory bowel disease: beyond the natural history. World J Gastroenterol 2019; 25: 5676–5686.

166.

Ponziani

Bhoori

Castelli

, et al. Hepatocellular carcinoma is associated with gut Microbiota profile and inflammation in nonalcoholic fatty liver disease. Hepatology 2019; 69: 107–120.

167.

Bourgonje

van den Berg

Kieneker

, et al. Plasma calprotectin levels associate with suspected metabolic-associated fatty liver disease and All-Cause mortality in the general population. Int J Mol Sci 2022; 23: 15708.

168.

Demirbaş

Çaltepe

Comba

, et al. Association of obesity and non-alcoholic fatty liver disease with the fecal calprotectin level in children. Arab J Gastroenterol 2020; 21: 211–215.

169.

Bicakci

Demirtas

Celikel

, et al.; Department of Gastroenterology, Marmara University School of Medicine, Istanbul, Turkey, Department of Gastroenterology, Marmara University School of Medicine, Istanbul, Turkey, Department of Pathology, Marmara University School of Medicine, Istanbul, Turkey, Department of Biochemistry, Marmara University School of Medicine, Istanbul, Turkey and Department of Gastroenterology, Marmara University School of Medicine, Istanbul, Turkey. Myeloperoxidase and calprotectin; any role as non-invasive markers for the prediction of ınflammation and fibrosis in non-alcoholic steatohepatitis? Turk J Gastroenterol 2020; 31: 681–687.

170.

Stehura

Sirchak

YS.

Intestinal lesions occurring in patients with Non-Alcoholic fatty liver disease after suffering the covid-19 infection. Wiad Lek 2021; 74: 2560–2565.

171.

Dong

Katzka

Lagishetty

, et al. A microbial signature identifies advanced fibrosis in patients with chronic liver disease mainly due to NAFLD. Sci Rep 2020; 10: 2771.

172.

Fierbinteanu-Braticevici

Calin-Necula

Enciu

, et al. The role of noninvasive (13)C-octanoate breath test in assessing the diagnosis of nonalcoholic steatohepatitis. Diagnostics 2022; 12: 2935.

173.

Hoyles

Fernández-Real

Federici

, et al. Molecular phenomics and metagenomics of hepatic steatosis in non-diabetic obese women. Nat Med 2018; 24: 1070–1080.

174.

Caussy

Hsu

, et al.; Genetics of NAFLD in Twins Consortium. Link between gut-microbiome derived metabolite and shared gene-effects with hepatic steatosis and fibrosis in NAFLD. Hepatology 2018; 68: 918–932.

175.

Angelini

Panunzi

Castagneto-Gissey

, et al. Accurate liquid biopsy for the diagnosis of non-alcoholic steatohepatitis and liver fibrosis. Gut 2023; 72: 392–403.

176.

Chalasani

Younossi

Lavine

, et al. The diagnosis and management of nonalcoholic fatty liver disease: practice guidance from the American Association for the study of Liver Diseases. Hepatology 2018; 67: 328–357.

177.

American Diabetes A; American Diabetes Association. 5. Lifestyle management: Standards of Medical Care in diabetes-2019. Diabetes Care 2019; 42: S46–S60.

178.

Eslam

Sarin

Wong

VWS

, et al. The Asian Pacific Association for the study of the liver clinical practice guidelines for the diagnosis and management of metabolic associated fatty liver disease. Hepatol Int 2020; 14: 889–919.

179.

Plauth

Bernal

Dasarathy

, et al. ESPEN guideline on clinical nutrition in liver disease. Clin Nutr 2019; 38: 485–521.

180.

Semmler

Datz

Reiberger

, et al. Diet and exercise in NAFLD/NASH: beyond the obvious. Liver Int 2021; 41: 2249–2268.

181.

Murphy

Cotter

Healy

, et al. Composition and energy harvesting capacity of the gut microbiota: relationship to diet, obesity and time in mouse models. Gut 2010; 59: 1635–1642.

182.

Turnbaugh

Bäckhed

Fulton

, et al. Diet-induced obesity is linked to marked but reversible alterations in the mouse distal gut microbiome. Cell Host Microbe 2008; 3: 213–223.

183.

Nakayama

Oishi

Influence of coffee (Coffea arabica) and galacto-oligosaccharide consumption on intestinal microbiota and the host responses. FEMS Microbiol Lett 2013; 343: 161–168.

184.

Cowan

Palmnäs

Yang

, et al. Chronic coffee consumption in the diet-induced obese rat: impact on gut microbiota and serum metabolomics. J Nutr Biochem 2014; 25: 489–495.

185.

Vitaglione

Morisco

Mazzone

, et al. Coffee reduces liver damage in a rat model of steatohepatitis: the underlying mechanisms and the role of polyphenols and melanoidins. Hepatology 2010; 52: 1652–1661.

186.

Molloy

Calcagno

Williams

, et al. Association of coffee and caffeine consumption with fatty liver disease, nonalcoholic steatohepatitis, and degree of hepatic fibrosis. Hepatology 2012; 55: 429–436.

187.

Shen

Letter: gut microbiota modulation contributes to coffee’s benefits for non-alcoholic fatty liver disease. Aliment Pharmacol Ther 2014; 39: 1441–1442.

188.

Clarke

Murphy

O’Sullivan

, et al. Exercise and associated dietary extremes impact on gut microbial diversity. Gut 2014; 63: 1913–1920.

189.

Monda

Villano

Messina

, et al. Exercise modifies the gut Microbiota with positive health effects. Oxid Med Cell Longev 2017; 2017: 3831972.

190.

Ortiz-Alvarez

Martinez-Tellez

Influence of exercise on the Human Gut Microbiota of Healthy Adults: A systematic review. Clin Transl Gastroenterol 2020; 11: e00126.

191.

Evans

LePard

Kwak

, et al. Exercise prevents weight gain and alters the gut microbiota in a mouse model of high fat diet-induced obesity. PLoS One 2014; 9: e92193.

192.

Reijnders

Goossens

Hermes

, et al. Effects of gut Microbiota manipulation by antibiotics on host metabolism in obese humans: A randomized double-blind placebo-controlled trial. Cell Metab 2016; 24: 341–374.

193.

Chong

CYL

Orr

Plank

, et al. Randomised double-blind placebo-controlled trial of inulin with metronidazole in Non-Alcoholic fatty liver disease (NAFLD). Nutrients 2020; 12: 937.

194.

Kakiyama

Pandak

Gillevet

, et al. Modulation of the fecal bile acid profile by gut microbiota in cirrhosis. J Hepatol 2013; 58: 949–955.

195.

Gangarapu

Ince

Baysal

, et al. Efficacy of rifaximin on circulating endotoxins and cytokines in patients with nonalcoholic fatty liver disease. Eur J Gastroenterol Hepatol 2015; 27: 840–845.

196.

Cobbold

JFL

Atkinson

Marchesi

, et al. Rifaximin in non-alcoholic steatohepatitis: an open-label pilot study. Hepatol Res 2018; 48: 69–77.

197.

Abdel-Razik

Mousa

Shabana

, et al. Rifaximin in nonalcoholic fatty liver disease: hit multiple targets with a single shot. Eur J Gastroenterol Hepatol 2018; 30: 1237–1246.

198.

Escouto

Port

Tovo

, et al. Probiotic supplementation, hepatic fibrosis, and the Microbiota profile in patients with nonalcoholic steatohepatitis: a randomized controlled trial. J Nutr 2023; 153: 1984–1993.

199.

Manzhalii

Virchenko

Falalyeyeva

, et al. Treatment efficacy of a probiotic preparation for non-alcoholic steatohepatitis: a pilot trial. J Dig Dis 2017; 18: 698–703.

200.

Barcelos

STA

Silva-Sperb

Moraes

, et al. Oral 24-week probiotics supplementation did not decrease cardiovascular risk markers in patients with biopsy proven NASH: a double-blind placebo-controlled randomized study. Ann Hepatol 2023; 28: 100769.

201.

Parnell

Raman

Rioux

, et al. The potential role of prebiotic fibre for treatment and management of non-alcoholic fatty liver disease and associated obesity and insulin resistance. Liver Int 2012; 32: 701–711.

202.

Daubioul

Horsmans

Lambert

, et al. Effects of oligofructose on glucose and lipid metabolism in patients with nonalcoholic steatohepatitis: results of a pilot study. Eur J Clin Nutr 2005; 59: 723–726.

203.

Tarantino

Finelli

Systematic review on intervention with prebiotics/probiotics in patients with obesity-related nonalcoholic fatty liver disease. Future Microbiol 2015; 10: 889–902.

204.

Carpi

Barbalho

Sloan

, et al. The effects of probiotics, prebiotics and synbiotics in non-alcoholic fat liver disease (NAFLD) and non-alcoholic steatohepatitis (NASH): a systematic review. Int J Mol Sci 2022; 23: 8805.

205.

Kanchanasurakit

Kositamongkol

Lanoi

, et al. Effects of synbiotics, probiotics, and prebiotics on liver enzymes of patients with non-alcoholic fatty liver disease: a systematic review and network meta-analysis. Front Nutr 2022; 9: 880014.

206.

Malaguarnera

Vacante

Antic

, et al. Bifidobacterium longum with fructo-oligosaccharides in patients with non alcoholic steatohepatitis. Dig Dis Sci 2012; 57: 545–553.

207.

Asgharian

Askari

Esmailzade

, et al. The effect of symbiotic supplementation on liver enzymes, C-reactive protein and ultrasound findings in patients with non-alcoholic fatty liver disease: a clinical trial. Int J Prev Med 2016; 7: 59.

208.

Mofidi

Poustchi

Yari

, et al. Synbiotic supplementation in lean patients with non-alcoholic fatty liver disease: a pilot, randomised, double-blind, placebo-controlled, clinical trial. Br J Nutr 2017; 117: 662–668.

209.

Tolhurst

Heffron

Lam

, et al. Short-chain fatty acids stimulate glucagon-like peptide-1 secretion via the G-protein-coupled receptor FFAR2. Diabetes 2012; 61: 364–371.

210.

Aoki

Kamikado

Suda

, et al. A proliferative probiotic Bifidobacterium strain in the gut ameliorates progression of metabolic disorders via microbiota modulation and acetate elevation. Sci Rep 2017; 7: 43522.

211.

Kimura

Ozawa

Inoue

, et al. The gut microbiota suppresses insulin-mediated fat accumulation via the short-chain fatty acid receptor GPR43. Nat Commun 2013; 4: 1829.

212.

Psichas

Sleeth

Murphy

, et al. The short chain fatty acid propionate stimulates GLP-1 and PYY secretion via free fatty acid receptor 2 in rodents. Int J Obes 2015; 39: 424–429.

213.

Kim

Park

Kim

, et al. A GLP-1/GLP-2 receptor dual agonist to treat NASH: targeting the gut-liver axis and microbiome. Hepatology 2022; 75: 1523–1538.

214.

Madsen

MSA

Holm

Pallejà

, et al. Metabolic and gut microbiome changes following GLP-1 or dual GLP-1/glp-2 receptor agonist treatment in diet-induced obese mice. Sci Rep 2019; 9: 15582.

215.

Hupa-Breier

Dywicki

Hartleben

, et al. Dulaglutide alone and in combination with empagliflozin attenuate inflammatory pathways and microbiome dysbiosis in a non-diabetic mouse model of NASH. Biomedicines 2021; 9: 353.

216.

Zhao

Chen

Xia

, et al. A glucagon-like peptide-1 receptor agonist lowers weight by modulating the structure of gut Microbiota. Front Endocrinol 2018; 9: 233.

217.

Craven

Rahman

Nair Parvathy

, et al. Allogenic fecal microbiota transplantation in patients with nonalcoholic fatty liver disease improves abnormal small intestinal permeability: a randomized control trial. Am J Gastroenterol 2020; 115: 1055–1065.

218.

Xue

Luo

, et al. Fecal microbiota transplantation for the treatment of nonalcoholic fatty liver disease. Exploratory Res Hypothesis Med 2019; 4: 12–18.

219.

Bajaj

Fagan

Gavis

, et al. Long-term outcomes of fecal Microbiota transplantation in patients with cirrhosis. Gastroenterology 2019; 156: 1921–1923.e3.

Gut microbiota in MAFLD: therapeutic and diagnostic implications

Abstract

Keywords

Introduction

Methods

Results

From gut dysbiosis to MAFLD

Gut permeability and endotoxemia

Diet and gut microbiota

Toll-like receptors

Macrophages

Endogenous alcohol production

BAs and SCFAs

Microbiota-derived metabolites

Genetics, microbiota, and MAFLD

Lean MAFLD and microbiota

Gut Microbiota and MAFLD diagnosis

Fecal calprotectin

Gut microbiome

Other noninvasive tests

Gut dysbiosis and MAFLD: therapeutic interventions

Diet

Exercise

Antibiotics

Probiotics, prebiotics, and synbiotics

GLP-1 receptor agonists

Fecal microbiota transplantation

Conclusion and future perspectives

Footnotes

Acknowledgements

Declarations

ORCID iD

References