Gut Microbiota and the Liver: A Tale of 2 Cities: A Narrative View in 2 Acts

Inulin Supplementation Modulates the Hepatic Transcriptome, Metabolome, and Ferritin Content in Ovariectomized Rats

SCOPE

Liver is an important metabolic organ regulating whole-body homeostasis. This study aims to investigate how prebiotic-induced changes in the metabolic activity of the gut microbiome (GM) and dietary calcium depletion modulates the hepatic metabolome and transcriptome.

METHODS AND RESULTS

The serum metabolome, liver metabolome, and transcriptome are determined on samples from ovariectomized (OVX) rats fed a control diet (Control, n = 7), a control diet supplemented with 5% w/w inulin (Inulin, n = 7), or a calcium-deficient diet (CaDef, n = 7). Inulin fortification is associated with higher serum concentrations of acetate, 3-hydroxybutyrate, and reduced concentration of dimethyl sulfone, revealing that changes in the metabolic activity of the GM are reflected in circulating metabolites. Metabolomics also reveal that the inulin-fortified diet results in lower concentrations of hepatic glutamate, serine, and hypoxanthine while transcriptomics reveal accompanying effects on the hepatic expression of ferric iron binding-related genes. Inulin fortification also induces effects on the hepatic expression of genes involved in olfactory transduction, suggesting that prebiotics regulate liver function through yet unidentified mechanisms involving olfactory receptors.

CONCLUSION

Inulin ingestion impacts hepatic gene expression and is associated with an upregulation of ferritin synthesis-related genes and liver ferritin content.

Clinical features and management issues of NAFLD-related HCC: what we know so far

INTRODUCTION

Nonalcoholic fatty liver disease (NAFLD) is replacing viral hepatitis as the leading cause of chronic liver disease and hepatocellular carcinoma (HCC) in many Western countries. NAFLD-associated HCC usually affects older patients with multiple comorbidities, frequently develops in the absence of cirrhosis, and is often diagnosed later with worse chance of survival. The worse prognosis is also due to limited surveillance strategies and a lower efficacy of standard treatments.

AREAS COVERED

We evaluate the available literature to understand the current surveillance strategies and treatment limitations in the workup of NAFLD-associated HCC, focusing on the differences with HCC associated with other liver diseases.

EXPERT OPINION

In this review we discuss epidemiology and risk factors for HCC in NAFLD patients and address key HCC surveillance and management issues. Although most data are still preliminary, the detection of non-cirrhotic NAFLD patients at increased risk for HCC and the potential adoption of novel screening tools could lead to accurate and suitable HCC surveillance and management strategies for NAFLD patients.

The Role of Gut Microbiota in Some Liver Diseases: From an Immunological Perspective

Gut microbiota is a microecosystem composed of various microorganisms. It plays an important role in human metabolism, and its metabolites affect different tissues and organs. Intestinal flora maintains the intestinal mucosal barrier and interacts with the immune system. The liver is closely linked to the intestine by the gut-liver axis. As the first organ that comes into contact with blood from the intestine, the liver will be deeply influenced by the gut microbiota and its metabolites, and the intestinal leakage and the imbalance of the flora are the trigger of the pathological reaction of the liver. In this paper, we discuss the role of gut microbiota and its metabolites in the pathogenesis and development of autoimmune liver diseases((including autoimmune hepatitis, primary biliary cirrhosis, primary sclerosing cholangitis), metabolic liver disease such as non-alcoholic fatty liver disease, cirrhosisits and its complications, and liver cancer from the perspective of immune mechanism. And the recent progress in the treatment of these diseases was reviewed from the perspective of gut microbiota.

Liver disease in obesity and underweight: the two sides of the coin. A narrative review

PURPOSE

Malnutrition, whether characterized by not enough or too much nutrient intake, is detrimental to the liver. We herein provide a narrative literature revision relative to hepatic disease occurrence in over or undernourished subjects, to shed light on the paradox where both sides of malnutrition lead to similar liver dysfunction and fat accumulation.

METHODS

Medline, EMBASE, and Cochrane Library were searched for publications up to July 2020. Articles discussing the association between both chronic and acute liver pathology and malnutrition were evaluated together with studies reporting the dietary intake in subjects affected by malnutrition.

RESULTS

The association between overnutrition and non-alcoholic fatty liver disease (NAFLD) is well recognized, as the beneficial effects of calorie restriction and very low carbohydrate diets. Conversely, the link between undernutrition and liver injury is more complex and less understood. In developing countries, early exposure to nutrient deficiency leads to marasmus and kwashiorkor, accompanied by fatty liver, whereas in developed countries anorexia nervosa is a more common form of undernutrition, associated with liver injury. Weight gain in undernutrition is associated with liver function improvement, whereas no study on the impact of macronutrient distribution is available. We hypothesized a role for very low carbohydrate diets in the management of undernutrition derived liver pathology, in addition to the established one in overnutrition-related NAFLD.

CONCLUSIONS

Further studies are warranted to update the knowledge regarding undernutrition-related liver disease, and a specific interest should be paid to macronutrient distribution both in the context of refeeding and relative to its role in the development of hepatic complications of anorexia nervosa.

LEVEL OF EVIDENCE

Narrative review, Level V.

Gut-liver axis, cirrhosis and portal hypertension: the chicken and the egg

The term gut-liver axis is used to highlight the close anatomical and functional relationship between the intestine and the liver. The intestine has a highly specialized epithelial membrane which regulates transport across the mucosa. Due to dysbiosis, impairment of the intestinal barrier and altered immunity status, bacterial products can reach the liver through the portal vein, where they are recognized by specific receptors, activate the immune system and lead to a proinflammatory response. Gut microbiota and bacterial translocation play an important role in the pathogenesis of chronic liver diseases, including alcoholic and non-alcoholic fatty liver disease, cirrhosis, and its complications, such as portal hypertension, spontaneous bacterial peritonitis and hepatic encephalopaty. The gut microbiota also plays a critical role as a modulator of bile acid metabolism which can also influence intestinal permeability and portal hypertension through the farnesoid-X receptor. On the other hand, cirrhosis and portal hypertension affect the microbiota and increase translocation, leading to a "chicken and egg" situation, where translocation increases portal pressure, and vice versa. A myriad of therapies targeting gut microbiota have been evaluated specifically in patients with chronic liver disease. Further studies targeting intestinal microbiota and its possible hemodynamic and metabolic effects are needed. This review summarizes the current knowledge about the role of gut microbiota in the pathogenesis of chronic liver diseases and portal hypertension.