Ileal Bile Acid Transporter Inhibitor Improves Hepatic Steatosis by Ameliorating Gut Microbiota Dysbiosis in NAFLD Model Mice

Castration alters the ileum microbiota of Holstein bulls and promotes beef flavor compounds

BACKGROUND

In the beef industry, bull calves are usually castrated to improve flavor and meat quality; however, this can reduce their growth and slaughter performance. The gut microbiota is known to exert a significant influence on growth and slaughter performance. However, there is a paucity of research investigating the impact of castration on gut microbiota composition and its subsequent effects on slaughter performance and meat flavor.

RESULT

The objective of this study was to examine the processes via which castration hinders slaughter productivity and enhances meat quality. Bull and castrated calves were maintained under the same management conditions, and at slaughter, meat quality was assessed, and ileum and epithelial tissue samples were obtained. The research employed metagenomic sequencing and non-targeted metabolomics techniques to investigate the makeup of the microbiota and identify differential metabolites. The findings of this study revealed the Carcass weight and eye muscle area /carcass weight in the bull group were significantly higher than those in the steer group. There were no significant differences in the length, width, and crypt depth of the ileum villi between the two groups. A total of 53 flavor compounds were identified in the two groups of beef, of which 16 were significantly higher in the steer group than in the bull group, and 5 were significantly higher in the bull group than in the steer group. In addition, bacteria, Eukaryota, and virus species were significantly separated between the two groups. The lipid metabolism pathways of α-linolenic acid, linoleic acid, and unsaturated fatty acids were significantly enriched in the Steers group. Compared with the steer group, the organic system pathway is significantly enriched in the bull group. The study also found that five metabolites (LPC (0:0/20:3), LPC (20:3/0:0), LPE (0:0/22:5), LPE (22:5/0:0), D-Mannosamine), and three species (s_Cloning_vector_Hsp70_LexA-HP1, s_Bacteroides_Coprophilus_CAG: 333, and s_Clostridium_nexile-CAG: 348) interfere with each other and collectively have a positive impact on the flavor compounds of beef.

CONCLUSIONS

These findings provide a basic understanding that under the same management conditions, castration does indeed reduce the slaughter performance of bulls and improve the flavor of beef. Microorganisms and metabolites contribute to these changes through interactions.

Bacteroides fragilis aggravates high-fat diet-induced non-alcoholic fatty liver disease by regulating lipid metabolism and remodeling gut microbiota

Gut microbiota dysbiosis is a prominent determinant that significantly contributes to the disruption of lipid metabolism. Consequently, it is essential to the occurrence and development of non-alcoholic fatty liver disease (NAFLD). Nevertheless, the connection between diet and symbiotic gut microbiota in the progression of NAFLD remains uncertain. The purpose of this study was to explore the role of supplementing commensal Bacteroides fragilis (B. fragilis) on lipid metabolism, gut microbiota, and metabolites in high-fat diet (HFD)-fed mice, elucidating the impact of gut microbiota and metabolites on the development of NAFLD. Our study revealed that supplementation with B. fragilis exacerbated both weight gain and obesity in mice. B. fragilis exacerbated blood glucose levels and liver dysfunction in mice. Furthermore, an increase in liver lipid accumulation and the upregulation of genes correlated with lipid metabolism were observed in mice. Under an HFD, supplementation of commensal B. fragilis resulted in alterations in the gut microbiota, notably a significant increase in Desulfovibrionaceae, which led to elevated endotoxin levels and thereby influenced the progression of NAFLD. It was interesting that the simultaneous examination of gut microbiota metabolites revealed a more pronounced impact of diet on short-chain fatty acids. This study represented the pioneering investigation into the impact of B. fragilis on NAFLD. Our findings demonstrated that B. fragilis induced dysregulation in the intestinal microbiota, leading to elevated levels of lipopolysaccharide and dysfunction in glucose and lipid metabolism, thereby exacerbating NAFLD.IMPORTANCESome intestinal symbiotic microbes are involved in the occurrence of the metabolic disorders. Our study investigated the impact of supplementing commensal Bacteroides fragilis on host metabolism in high-fat diet-fed mice. Research results indicated that adding a specific bacterial strain to the complex intestinal microecology can worsen metabolic conditions. This effect mainly affects the structural diversity of intestinal microorganisms, the increase in harmful bacteria in the gut, and the elevation of endotoxin levels, blood glucose, and lipid metabolism, thereby impacting the progression of non-alcoholic fatty liver disease (NAFLD). Understanding the principles that govern the establishment of microbial communities comprising multiple species is crucial for preventing or repairing dysfunctions in these communities, thereby enhancing host health and facilitating disease treatment. This study demonstrated that gut microbiota dysbiosis could contribute to metabolic dysfunction and provides new insights into how to promote gut microbiota in the prevention and therapy of NAFLD.

Paediatric research sets new standards for therapy in paediatric and adult cholestasis

Children with Alagille syndrome and progressive familial intrahepatic cholestasis (PFIC) experience debilitating pruritus, for which there have been few effective treatment options. In the past 2 years, the ileal bile acid transporter (IBAT) inhibitors maralixibat and odevixibat have been approved for the management of cholestatic pruritus in these individuals, representing an important step forward in improving their quality of life. Emerging data suggest these drugs might also improve event-free survival, therefore potentially altering the typical disease course currently seen in these disorders. This Review will discuss how genetic advances have clarified the molecular basis of cholestatic disorders, facilitating the development of new therapeutic options that have only been evaluated in children. We focus specifically on the newly licensed IBAT inhibitors for patients with Alagille syndrome and PFIC and explore the next steps for these drugs in relation to other paediatric and adult cholestatic disorders, recognising that they have the potential to benefit a wider group of patients with gastrointestinal and liver disease.

NASH/NAFLD-Related Hepatocellular Carcinoma: An Added Burden

Hepatocellular carcinoma (HCC) is the most frequently found primary malignancy of the liver, showing an accelerated upward trend over the past few years and exhibiting an increasing relationship with metabolic syndrome, obesity, dyslipidemia and type 2 diabetes mellitus. The connection between these risk factors and the occurrence of HCC is represented by the occurrence of non-alcoholic fatty liver disease (NAFLD) which later, based on genetic predisposition and various triggers (including the presence of chronic inflammation and changes in the intestinal microbiome), may evolve into HCC. HCC in many cases is diagnosed at an advanced stage and can be an incidental finding. We present such a scenario in the case of a 41-year-old male patient who had mild obesity and mixed dyslipidemia, no family or personal records of digestive pathologies and who recently developed a history of progressive fatigue, dyspepsia and mild upper abdominal discomfort initially thought to be linked to post-COVID syndrome, as the patient had COVID-19 pneumonia a month prior. The abdominal ultrasound revealed a mild hepatomegaly with bright liver aspect of the right lobe (diffuse steatosis), a large zone of focal steatosis (segments IV, III and II) and a left lobe tumoral mass, highly suggestive of malignancy. Point shear wave elastography at the right lobe ruled out an end-stage chronic liver disease. Additional laboratory investigations, imaging studies (magnetic resonance imaging) and histopathological examination of liver fragments confirmed a highly aggressive HCC, with poorly differentiation-G3, (T4, N 1M 0) and stage IVA, associated with nonalcoholic steatohepatitis (NASH). A sorafenib course of treatment was attempted, but the patient discontinued it due to severe side effects. The subsequent evolution was extremely unfavorable, with rapid degradation, a few episodes of upper digestive bleeding, hepatic insufficiency and mortality in a couple of months. Conclusions: Diagnosis of NASH-related HCC is either an accidental finding or is diagnosed at an advanced stage. In order to earn time for a proper treatment, it becomes important to diagnose it at an early stage, for which regular check-ups should be performed in groups having the risk factors related to it. Patients suffering from obesity and mixed dyslipidemia should undergo periodic abdominal ultrasound examinations. This should be emphasized even more in the cases showing NASH. Complaints of any kind post-COVID-19 should be dealt with keenly as little is yet known about its virulence and its long-term side effects.

Combined, elobixibat, and colestyramine reduced cholesterol toxicity in a mouse model of metabolic dysfunction-associated steatotic liver disease

BACKGROUND

Cholesterol levels and bile acid metabolism are important drivers of metabolic dysfunction-associated steatohepatitis (MASH) progression. Using a mouse model, we investigated the mechanism by which cholesterol exacerbates MASH and the effect of colestyramine (a bile acid adsorption resin) and elobixibat (an apical sodium-dependent bile acid transporter inhibitor) concomitant administration on bile acid adsorption and MASH status.

METHODS

Mice were fed a high-fat high-fructose diet with varying concentrations of cholesterol to determine changes in fatty liver according to liver status, water intake, defecation status, insulin resistance, bile acid levels, intestinal permeability, atherosclerosis (in apolipoprotein E knockout mice), and carcinogenesis (in diethylnitrosamine mice). Using small interfering ribonucleic acid (siRNA), we evaluated the effect of sterol regulatory element binding protein 1c (SREBP1c) knockdown on triglyceride synthesis and fatty liver status following the administration of elobixibat (group E), colestyramine (group C), or both (group EC).

RESULTS

We found greater reductions in serum alanine aminotransferase levels, serum lipid parameters, serum primary bile acid concentrations, hepatic lipid levels, and fibrosis area in EC group than in the monotherapy groups. Increased intestinal permeability and watery diarrhea caused by elobixibat were completely ameliorated in group EC. Group EC showed reduced plaque formation rates in the entire aorta and aortic valve of the atherosclerosis model, and reduced tumor counts and tumor burden in the carcinogenesis model.

CONCLUSIONS

Excessive free cholesterol in the liver can promote fatty liver disease. Herein, combination therapy with EC effectively reduced free cholesterol levels in MASH model mice. Our study provides strong evidence for combination therapy as an effective treatment for MASH.

Theabrownin inhibits obesity and non-alcoholic fatty liver disease in mice via serotonin-related signaling pathways and gut-liver axis

INTRODUCTION

Non-alcoholic fatty liver disease (NAFLD) with obesity seriously threats public health. Our previous studies showed that dark tea had more potential on regulating lipid metabolism than other teas, and theabrownin (TB) was considered to be a main contributor to the bioactivity of dark tea.

OBJECTIVES

This in vivo study aims to reveal the effects and molecular mechanisms of TB on NAFLD and obesity, and the role of the gut-liver axis is explored.

METHODS

The histopathological examinations, biochemical tests, and nuclear magnetic resonance were applied to evaluate the effects of TB on NAFLD and obesity. The untargeted metabolomics was used to find the key molecule for further exploration of molecular mechanisms. The 16S rRNA gene sequencing was used to assess the changes in gut microbiota. The antibiotic cocktail and fecal microbiota transplant were used to clarify the role of gut microbiota.

RESULTS

TB markedly reduced body weight gain (67.01%), body fat rate (62.81%), and hepatic TG level (51.35%) in the preventive experiment. Especially, TB decreased body weight (32.16%), body fat rate (42.56%), and hepatic TG level (42.86%) in the therapeutic experiment. The mechanisms of action could be the improvement of fatty acid oxidation, lipolysis, and oxidative stress via the regulation of serotonin-related signaling pathways. Also, TB increased the abundance of serotonin-related gut microbiota, such as Akkermansia, Bacteroides and Parabacteroides. Antibiotics-induced gut bacterial dysbiosis disrupted the regulation of TB on serotonin-related signaling pathways in liver, whereas the beneficial regulation of TB on target proteins was regained with the restoration of gut microbiota.

CONCLUSION

We find that TB has markedly preventive and therapeutic effects on NAFLD and obesity by regulating serotonin level and related signaling pathways through gut microbiota. Furthermore, gut microbiota and TB co-contribute to alleviating NAFLD and obesity. TB could be a promising medicine for NAFLD and obesity.

Gentiopicroside improves high-fat diet-induced NAFLD in association with modulation of host serum metabolome and gut microbiome in mice

Objective

The incidence of non-alcoholic fatty liver disease is increasing every year, and there is growing evidence that metabolites and intestinal bacteria play a causal role in NAFLD. Gentiopicroside, a major iridoids compound in gentian, has been reported to reduce hepatic lipid accumulation. However to date, no studies have confirmed whether the predominance of Gentiopicroside is related to metabolites and intestinal bacteria. Therefore, we sought to study whether the hypolipidemic effect of Gentiopicroside is related to metabolic function and intestinal flora regulation.

Methods

In the present study, C57BL/6J mice were fed a high-fat diet for 12 weeks, followed by a high-fat diet with or without Gentiopicroside for 8 weeks, respectively. The Gentiopicroside intervention reduced body weight gain, liver index, and decreased serum biochemical parameters such as alanine aminotransferase, aspartate aminotransferase, and triglycerides in high-fat fed mice. The effect of Gentiopicroside on non-alcoholic fatty liver disease was studied using serum untargeted metabolomics and 16S rDNA assay.

Results

Metabolomic analysis showed that the addition of Gentiopicroside significantly altered the levels of amino acids, unmetabolized Gentiopicroside after administration, and metabolites such as Cinnoline, Galabiosylceramide, and Tryptophyl-Tyrosine, which are involved in the pathways regulating bile secretion, tryptophan metabolism, and lipid metabolism. Analysis of intestinal bacteria showed that Gentiopicrosides altered the community composition structure of intestinal bacteria, characterized by an increase and a decrease in beneficial and harmful bacteria, respectively. In addition, correlation analysis showed that the effect of Gentiopicroside on metabolites was positively correlated with intestinal flora Bacteroides, Lactobacillus, Muribaculum, and Prevotellaceae_UCG_001. Finally, the combined analysis revealed that metabolites were associated with the regulation of Firmicutes and Actinobacteria and positively correlated with lipid levels.

Conclusion

These results suggest that Gentiopicroside may be a potential agent for the prevention of intestinal disorders and the alleviation of non-alcoholic fatty liver disease.

Taxonomic identification of bile salt hydrolase-encoding lactobacilli: Modulation of the enterohepatic bile acid profile

Bile salt hydrolases (BSHs) are enzymes that are essential for the enterohepatic metabolism of bile acids (BAs). BSHs catalyze the production of unconjugated BAs and regulate the homeostasis of BA pool. This study identified Lactobacillus as a crucial BSH-encoding genus, and 16 main species were obtained using metagenomic data from publicly available human gut microbiome databases. Then, the 16 species of lactobacilli were classified into four typical categories by BSH phylotypes, including five species encoding BSH-T0, six species encoding BSH-T2, four species encoding BSH-T3, and Ligilactobacillus salivarius encoding both BSH-T0 and BSH-T3. The lactobacilli with the highest in vitro deconjugation activities against seven conjugated BAs were the BSH-T3-encoding strains. Furthermore, in vivo studies in mice administered four representative lactobacilli strains encoding different BSH phylotypes showed that treatment with BSH-T3-encoding Limosilactobacillus reuteri altered the structure of the gut microbiome and metabolome and significantly increased the levels of unconjugated BAs and total BA excretion. Our findings facilitated the taxonomic identification of crucial BSH-encoding lactobacilli in human gut microbiota and shed light on their contributions toward modulation of the enterohepatic circulation of BAs, which will contribute to future therapeutic applications of BSH-encoding probiotics to improve human health.

Lactobacillus fermentum MCC2760 abrogate high-fat induced perturbations in the enterohepatic circulation of bile acids in rats

AIM

This study in hyperlipidemic rats elucidated the effect of Lactobacillus fermentum MCC2760 on intestinal bile acid (BA) uptake, hepatic BA synthesis, and enterohepatic BA transporters.

MAIN METHODS

Diets rich in saturated fatty acids [coconut oil (CO)] and omega-6 fatty acids [sunflower oil (SFO)] at 25 g fat/100 g diet were fed to rats with or without MCC2760 (10⁹ cells/kg body weight). After 60 days of feeding, intestinal BA uptake and expression of Asbt, Osta/b mRNA and protein, and hepatic expression of Ntcp, Bsep, Cyp7a1, Fxr, Shp, Lrh-1, and Hnf4a mRNA were measured. Hepatic expression of HMG-CoA reductase protein and its activity and total BAs in serum, liver, and feces were assessed.

KEY FINDINGS

Hyperlipidaemic groups (HF-CO and HF-SFO) had: 1) increased intestinal BA uptake, Asbt and Osta/b mRNA expression, and ASBT staining 2) increased BA in serum, 3) decreased hepatic expression of Ntcp, Bsep, and Cyp7a1 mRNA, and NTCP staining 4) increased activity of HMG-CoA reductase, 5) increased hepatic expression of Fxr and Shp mRNA, 6) decreased hepatic expression of Lrh-1 and Hnf4a mRNA, and 7) decreased BA in Feces when compared to their respective controls (N-CO and N-SFO) and experimental groups (HF-CO + LF and HF-SFO + LF). Immunostaining revealed increased intestinal Asbt and hepatic Ntcp protein expression in the HF-CO and HF-SFO groups compared to control and experimental groups.

SIGNIFICANCE

Incorporating probiotics like MCC2760 abrogated hyperlipidemia-induced changes in the intestinal uptake, hepatic synthesis, and enterohepatic transporters of BA in rats. Probiotic MCC2760 can be used to modulate lipid metabolism in high-fat-induced hyperlipidemic conditions.

Gut microbiota and bile acids partially mediate the improvement of fibroblast growth factor 21 on methionine-choline-deficient diet-induced non-alcoholic fatty liver disease mice

Non-alcoholic fatty liver disease (NAFLD) is characterized by hepatic steatosis, inflammation, and fibrosis, as well as gut dysbiosis. Fibroblast growth factor 21 (FGF21), which regulates glucose and lipid metabolism, has been proven to have a good effect on NAFLD. However, the modulating process between FGF21 and gut microbiota remains unclear in treating NAFLD. Here, the fecal microbiota composition of 30 patients with NAFLD who had undergone liver biopsy and 29 matched healthy participants were studied, together with the fecal bile acid (BA) profile. Treatment with FGF21 was given in methionine-choline-deficient (MCD) diet-induced NAFLD model C57BL/6 mice. An antibiotic cocktail and fecal microbiota transplantation were used to further confirm the benefits of FGF21 that were partially attributable to the change in gut microbiota. Patients with NAFLD had higher serum FGF21 levels and dysregulated fecal microbiota compositions and fecal BA profiles. In NAFLD mice, FGF21 significantly reduced steatohepatitis and collagen deposition in vivo and restored intestinal structure. FGF21 treatment also changed gut microbiota composition and regulated dysbiosis in BA metabolism. After treatment with an antibiotic cocktail, FGF21 partially alleviated hepatic and intestinal damage in NAFLD mice. Furthermore, fecal microbiota transplantation from FGF21-treated mice showed benefits similar to FGF21 therapy. The improvement using FGF21 in MCD diet-induced NAFLD mice is partially mediated via gut microbiota and BA. Gut microbiota-regulated BA metabolism may be a potential target of FGF21 in improving NAFLD.

Diosgenin alleviates nonalcoholic steatohepatitis through affecting liver-gut circulation

Nonalcoholic steatohepatitis (NASH), as the aggressive form of nonalcoholic fatty liver disease (NAFLD), rapidly becomes the leading cause of end-stage liver disease or liver transplantation. Nowadays, there has no approved drug for NASH treatment. Diosgenin possesses multiple beneficial effects towards inhibition of lipid accumulation, cholesterol metabolism, fibrotic progression and inflammatory response. However, there has been no report concerning its effects on NASH so far. Using methionine and choline-deficient (MCD) feeding mice, we evaluated the anti-NASH effects of diosgenin. 16 S rDNA was used to investigate gut microbiota composition. Transcriptome sequencing, LC/MS and GC/MS analysis were used to evaluate bile acids (BAs) metabolism and their related pathway. Compared with the MCD group, diosgenin treatment improved the hepatic dysfunction, especially decreased the serum and hepatic TC, TG, ALT, AST and TBA to nearly 50%. Content of BAs, especially CA and TCA, were decreased from 59.30 and 26.00-39.71 and 11.48 ng/mg in liver and from 0.96 and 2.1-0.47 and 1.13 μg/mL in serum, and increased from 7.01 and 11.08-3.278 and 5.11 ng/mg in feces, respectively. Antibiotic and fecal microbiota transplantation (FMT) treatment further confirmed the therapeutic effect of diosgenin on gut microbiota, especially Clostridia (LDA score of 4.94), which regulated BAs metabolism through the hepatic FXR-SHP and intestinal FXR-FGF15 pathways. These data indicate that diosgenin prevents NASH by altering Clostridia and BAs metabolism. Our results shed light on the mechanisms of diosgenin in treating NASH, which pave way for the design of novel clinical therapeutic strategies.

The role of bile acid metabolism in the occurrence and development of NAFLD

Non-alcoholic fatty liver disease (NAFLD) has become one of the important causes of cirrhosis and liver cancer, resulting in a huge medical burden worldwide. Currently, effective non-invasive diagnostic indicators and drugs for NAFLD are still lacking. With the development of metabolomics technology, the changes in metabolites during the development of NAFLD have been gradually revealed. Bile acid (BA) is the main endpoint of cholesterol metabolism in the body. In addition, it also acts as a signaling factor to regulate metabolism and inflammation in the body through the farnesyl X receptor and G protein-coupled BA receptor. Studies have shown that BA metabolism is associated with the development of NAFLD, but a large number of animal and clinical studies are still needed. BA homeostasis is maintained through multiple negative feedback loops and the enterohepatic circulation of BA. Recently, treatment of NAFLD by interfering with BA synthesis and metabolism has become a new research direction. Here, we review the changes in BA metabolism and its regulatory mechanisms during the development of NAFLD and describe the potential of studies exploring novel non-invasive diagnostic indicators and therapeutic targets for NAFLD based on BA metabolism.

Interventions for non-alcoholic liver disease: a gut microbial metabolites perspective

Over the past two decades, non-alcoholic fatty liver disease (NAFLD) has become a leading burden of hepatocellular carcinoma and liver transplantation. Although the exact pathogenesis of NAFLD has not been fully elucidated, recent hypotheses placed more emphasis on the crucial role of the gut microbiome and its derivatives. Reportedly, microbial metabolites such as short-chain fatty acids, amino acid metabolites (indole and its derivatives), bile acids (BAs), trimethylamine N-oxide (TMAO), and endogenous ethanol exhibit sophisticated bioactive properties. These molecules regulate host lipid, glucose, and BAs metabolic homeostasis via modulating nutrient absorption, energy expenditure, inflammation, and the neuroendocrine axis. Consequently, a broad range of research has studied the therapeutic effects of microbiota-derived metabolites. In this review, we explore the interaction of microbial products and NAFLD. We also discuss the regulatory role of existing NAFLD therapies on metabolite levels and investigate the potential of targeting those metabolites to relieve 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.

Recent advances in modulation of cardiovascular diseases by the gut microbiota

The gut microbiota has recently gained attention due to its association with cardiovascular health, cancers, gastrointestinal disorders, and non-communicable diseases. One critical question is how the composition of the microbiota contributes to cardiovascular diseases (CVDs). Insightful reviews on the gut microbiota, its metabolites and the mechanisms that underlie its contribution to CVD are limited. Hence, the aim of this review was to describe linkages between the composition of the microbiota and CVD, CVD risk factors such as hypertension, diet, ageing, and sex differences. We have also highlighted potential therapies for improving the composition of the gut microbiota, which may result in better cardiovascular health.

Potential role of gut microbiota-LCA-INSR axis in high fat-diet-induced non-alcoholic fatty liver dysfunction: From perspective of radiation variation

Non-alcoholic fatty liver disease (NAFLD) is a progressive disease of the liver covering a range of conditions from hepatic steatosis to liver fibrosis. NAFLD could be induced by High-fat-diet(HFD). Ionizing radiation is widely used in medical diagnosis and therapy as well as is a common risk factor in occupational environment. Whether the exposure of various dose of radiation has effects on HFD-induced NAFLD remains unclear. Here, we reported that radiation exposure promoted HFD-induced NAFLD in a dose-response manner. Furthermore, the gut microbiota composition had significant difference among mice with or without radiation treatment. Specifically, the Bacteroidetes/Firmicutes ratio, the abundance of A. muciniphila, Butyricococcus, and Clostridiaceae decreased significantly in the mice with co-exposure of high dose of radiation and HFD treatment. A fecal transplantation trial (FMT) further verified the role of gut microbiota in the regulation of the liver response to co-exposure of high dose of radiation and HFD treatment. Notably, the gut microbiome analysis showed plasma lithocholic acid (LCA) level increased in the mice with co-exposure of high dose of radiation and HFD treatment. Following antibiotic and probiotic treatments there was a significantly decreased LCA bile acid concentration and subsequent promotion of INSR/PI3K/Akt insulin signaling in the liver tissues. Our results demonstrate that the co-exposure of radiation and HFD aggravates the HFD-induced NAFLD through gut microbiota-LCA-INSR axis. Probiotics supplementation is a potential way to protect against co-exposure of radiation and HFD-induced liver damage. Meanwhile, our study provide a new insight that population with potential HFD-induced damage should pay more attention on preventing from liver damage while exposing radiation.

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Gut microbiota-lithocholic acid-insulin receptor (LCA-INSR) axis involves the promotion effects of radiation on HFD-induced NAFLD.

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Probiotics improve the liver damage induced by co-exposure of radiation and HFD.