Microbiota and Fatty Liver Disease-the Known, the Unknown, and the Future

The liver communicates with the intestine via the portal vein, biliary system, and mediators in the circulation. Microbes in the intestine maintain liver homeostasis but can also serve as a source of pathogens and molecules that contribute to fatty liver diseases. We review changes in the gut microbiota that can promote development or progression of alcohol-associated and non-alcoholic fatty liver disease-the most common chronic liver diseases in Western countries. We discuss how microbes and their products contribute to liver disease pathogenesis, putative microbial biomarkers of disease, and potential treatment approaches based on manipulation of the gut microbiota. Increasing our understanding of interactions between the intestinal microbiome and liver might help us identify patients with specific disease subtypes and select specific microbiota-based therapies.

Allicin Modifies the Composition and Function of the Gut Microbiota in Alcoholic Hepatic Steatosis Mice

The intestinal microbiome plays an important role in the pathogenesis of liver diseases. Alcohol intake induces gut microbiota dysbiosis and alters its function. This study investigated the antibiotic effect of allicin in mice with hepatic steatosis. Male C57BL/6 mice were administered an ethanol diet supplemented with allicin (5 and 20 mg/(kg bw day)) for 4 weeks. Allicin modified the gut microbiota composition. Cecal microbiota exhibited a positive correlation with alcohol and hepatic triacylglycerol, but were suppressed with allicin. Ethanol diet with 5 mg of allicin induced a lower intestinal permeability compared to the ethanol diet alone. Allicin mediated the lipopolysaccharide (LPS)-CD14-toll-like receptor 4 (TLR4)-induced hepatic inflammation pathway by reducing LPS, CD14, TLR4, and pro-inflammatory cytokines-tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and IL-6. However, hepatic inflammation primarily resulted from alcohol toxicity rather than LPS production in the gut. The prediction of functional profiles from metagenomic 16S ribosomal RNA (rRNA) data revealed different functional profiles in each group. The predicted aldehyde dehydrogenase tended to increase in alcoholic mice administered allicin. The predicted LPS-related pathway and LPS biosynthesis protein results exhibited a similar trend as plasma LPS levels. Thus, alcohol and allicin intake shapes the gut microbiota and its functional profile and improves the CD14-TLR4 pathway to alleviate inflammation in the liver.

Combination of Chronic Alcohol Consumption and High-Salt Intake Elicits Gut Microbial Alterations and Liver Steatosis in Mice

Alcohol is a globally well-established cause of fatty liver disease (FLD). Increased salt consumption is associated with an increased prevalence of adipocyte hypertrophy and liver injury. In this study, high dietary salt potentiated chronic alcohol-induced hepatic damage. We explored the physiological mechanism of alcoholic FLD in the gastrointestinal tract. Male C57BL/6J mice (8-week-old) were fed a high-salt diet (HSD; 4% NaCl) with or without chronic ethanol (CE) for 1 month. The fecal microbiota, serum biochemical indices, intestinal permeability, level of liver damage, and liver mitochondria were evaluated. The HSD, CE, and their combination (HSDE) significantly changed the gut microbiota's structure, and the HSDE mice contained more probiotic species (e.g., Bifidobacterium and Lactobacillus). The serum aspartate aminotransferase, alanine aminotransferase, and alkaline phosphatase levels were increased, and the lipid was accumulated in the liver tissues in the CE, HSD, and HSDE groups, which indicated liver damage, especially in the HSDE group. The increased intestinal permeability and mitochondrial dysfunction in the liver cells caused greater injury in the HSDE group than in the other groups. Thus, consuming HSD with alcohol contributes to FLD development and progression.

Gut Microbiota's Relationship with Liver Disease and Role in Hepatoprotection by Dietary Natural Products and Probiotics

A variety of dietary natural products have shown hepatoprotective effects. Increasing evidence has also demonstrated that gut microorganisms play an important role in the hepatoprotection contributed by natural products. Gut dysbiosis could increase permeability of the gut barrier, resulting in translocated bacteria and leaked gut-derived products, which can reach the liver through the portal vein and might lead to increased oxidative stress and inflammation, thereby threatening liver health. Targeting gut microbiota modulation represents a promising strategy for hepatoprotection. Many natural products could protect the liver from various injuries or mitigate hepatic disorders by reverting gut dysbiosis, improving intestinal permeability, altering the primary bile acid, and inhibiting hepatic fatty acid accumulation. The mechanisms underlying their beneficial effects also include reducing oxidative stress, suppressing inflammation, attenuating fibrosis, and decreasing apoptosis. This review discusses the hepatoprotective effects of dietary natural products via modulating the gut microbiota, mainly focusing on the mechanisms of action.

Astaxanthin Prevents Alcoholic Fatty Liver Disease by Modulating Mouse Gut Microbiota

The development and progression of alcoholic fatty liver disease (AFLD) is influenced by the intestinal microbiota. Astaxanthin, a type of oxygenated carotenoid with strong antioxidant and anti-inflammatory properties, has been proven to relieve liver injury. However, the relationship between the gut microbiota regulation effect of astaxanthin and AFLD improvement remains unclear. The effects of astaxanthin on the AFLD phenotype, overall structure, and composition of gut microbiota were assessed in ethanol-fed C57BL/6J mice. The results showed that astaxanthin treatment significantly relieves inflammation and decreases excessive lipid accumulation and serum markers of liver injury. Furthermore, astaxanthin was shown to significantly decrease species from the phyla Bacteroidetes and Proteobacteria and the genera Butyricimonas, Bilophila, and Parabacteroides, as well as increase species from Verrucomicrobia and Akkermansia compared with the Et (ethanol)group. Thirteen phylotypes related to inflammation as well as correlated with metabolic parameters were significantly altered by ethanol, and then notably reversed by astaxanthin. Additionally, astaxanthin altered 18 and 128 KEGG (Kyoto Encyclopedia of Genes and Genomes) pathways involved in lipid metabolism and xenobiotic biodegradation and metabolism at levels 2 and 3, respectively. These findings suggest that Aakkermansia may be a potential target for the astaxanthin-induced alleviation of AFLD and may be a potential treatment for bacterial disorders induced by AFLD.

Precision medicine in alcoholic and nonalcoholic fatty liver disease via modulating the gut microbiota

Alcoholic liver disease (ALD) and nonalcoholic fatty liver disease (NAFLD) represent a major health burden in industrialized countries. Although alcohol abuse and nutrition play a central role in disease pathogenesis, preclinical models support a contribution of the gut microbiota to ALD and NAFLD. This review describes changes in the intestinal microbiota compositions related to ALD and NAFLD. Findings from in vitro, animal, and human studies are used to explain how intestinal pathology contributes to disease progression. This review summarizes the effects of untargeted microbiome modifications using antibiotics and probiotics on liver disease in animals and humans. While both affect humoral inflammation, regression of advanced liver disease or mortality has not been demonstrated. This review further describes products secreted by Lactobacillus- and microbiota-derived metabolites, such as fatty acids and antioxidants, that could be used for precision medicine in the treatment of liver disease. A better understanding of host-microbial interactions is allowing discovery of novel therapeutic targets in the gut microbiota, enabling new treatment options that restore the intestinal ecosystem precisely and influence liver disease. The modulation options of the gut microbiota and precision medicine employing the gut microbiota presented in this review have excellent prospects to improve treatment of liver disease.

Intestinal REG3 Lectins Protect against Alcoholic Steatohepatitis by Reducing Mucosa-Associated Microbiota and Preventing Bacterial Translocation

Approximately half of all deaths from liver cirrhosis, the tenth leading cause of mortality in the United States, are related to alcohol use. Chronic alcohol consumption is accompanied by intestinal dysbiosis and bacterial overgrowth, yet little is known about the factors that alter the microbial composition or their contribution to liver disease. We previously associated chronic alcohol consumption with lower intestinal levels of the antimicrobial-regenerating islet-derived (REG)-3 lectins. Here, we demonstrate that intestinal deficiency in REG3B or REG3G increases numbers of mucosa-associated bacteria and enhances bacterial translocation to the mesenteric lymph nodes and liver, promoting the progression of ethanol-induced fatty liver disease toward steatohepatitis. Overexpression of Reg3g in intestinal epithelial cells restricts bacterial colonization of mucosal surfaces, reduces bacterial translocation, and protects mice from alcohol-induced steatohepatitis. Thus, alcohol appears to impair control of the mucosa-associated microbiota, and subsequent breach of the mucosal barrier facilitates progression of alcoholic liver disease.

Changes in the Intestinal Microbiome and Alcoholic and Nonalcoholic Liver Diseases: Causes or Effects?

The prevalence of fatty liver diseases is increasing rapidly worldwide; after treatment of hepatitis C virus infection becomes more widespread, fatty liver diseases are likely to become the most prevalent liver disorders. Although fatty liver diseases are associated with alcohol, obesity, and the metabolic syndrome, their mechanisms of pathogenesis are not clear. The development and progression of fatty liver, alcoholic, and nonalcoholic liver disease (NAFLD) all appear to be influenced by the composition of the microbiota. The intestinal microbiota have been shown to affect precirrhotic and cirrhotic stages of liver diseases, which could lead to new strategies for their diagnosis, treatment, and study. We review differences and similarities in the cirrhotic and precirrhotic stages of NAFLD and alcoholic liver disease. Differences have been observed in these stages of alcohol-associated disease in patients who continue to drink compared with those who stop, with respect to the composition and function of the intestinal microbiota and intestinal integrity. NAFLD and the intestinal microbiota also differ between patients with and without diabetes. We also discuss the potential of microbial therapy for patients with NAFLD and ALD.

[Effect of jianpi huoxue recipe on gut flora in rats with alcoholic fatty liver induced by Lieber-DeCarli liquid diet]

OBJECTIVE

To study the effect of Jianpi Huoxue Recipe(JPHXR) on the gut flora in rats with alcoholic fatty liver (AFL) induced by Lieber-DeCarli liquid diet.

METHODS

Forty Sprague-Dawley rats were divided into 4 groups: A: normal rats, B: rats fed with non-alcoholic liquid diet, C: rats fed with ethanol liquid diet to make AFL model, and D: AFL model rats intervened by gastrogavage of JPHXR 1.0 mL/100 g per day for 8 successive weeks, 10 rats in each group. Except those in Group D (to them an equal volume normal saline was given for Successive instead), JPXHR was administered to rats in other three groups. At the end of experiment, rats were sacrificed, their blood and liver tissue samples were collected for determining serum activities of alanine transaminase (ALT) and aspartate aminotransferase (AST), endotoxin level in portal vein (expressed by lipopolysacchrides content, abbr. as LPS), and pathological examination of liver with HE staining and oil O red staining. Moreover, total DNA of gut flora were extracted from fresh rat fecal samples by Bead-beating method for determining the ERIC-PCR fingerprint, and a cluster analysis on the fingerprint was performed.

RESULTS

Compared with the levels of ALT and AST in Group A (31.15 +/- 7.04 U/L, and 53.23 +/- 10.28 U/L respectively) and Group B (26.96 +/- 8.12 and 52.09 +/- 8.62), the corresponding levels in Group C (92.72 +/- 25.83 and 72.60 +/- 23.31) significantly increased (P < 0.01), while the increments in Group D (65.28 +/- 20.36 and 59.11 +/- 10.32) were decreased (P < 0.01, P < 0.05). Pathological examination showed marked fat deposition in Group C, but which was significantly reduced in Group D. Endotoxin level in the portal vein was (0.033 +/- 0.010, EU/mL) in Group A and 0.043 +/- 0.018 in Group B, which was increased significantly in Group C (0.541 +/- 0.085, P < 0.01) and Group D (0.349 +/- 0.098 EU/mL, P < 0.01), but the increase in Group C was more significant (P < 0.01). The cluster analysis of ERIC-PCR fingerprint showed significant changes in gut flora of Group C and D, which was in Group D partially recovered.

CONCLUSIONS

JPHXR had good preventive effect against alcoholic fatty liver in rats, and could modify the structure of gut flora to some extent.

Non-alcoholic steatohepatitis associated with small intestinal diverticulosis and bacterial overgrowth

A patient with hepatic histological features of steatohepatitis in association with small bowel diverticulosis and bacterial overgrowth is described. A similar histological picture in the liver is well recognised in association with bacterial overgrowth in excluded loops of small intestine. Jejunal diverticulosis should be considered as a correlate of para-alcoholic hepatitis.