Gut-liver axis in the progression of nonalcoholic fatty liver disease: From the microbial derivatives-centered perspective

Bile acid and short chain fatty acid metabolism of gut microbiota mediate high-fat diet induced intestinal barrier damage in Macrobrachium rosenbergii

The limited tolerance of crustacean tissue physiology to a high-fat diet has captured the attention of researchers. Yet, investigations into the physiological response mechanisms of the crustacean intestinal barrier system to a high-fat diet are progressing slowly. Elucidating potential physiological mechanisms and determining the precise regulatory targets would be of great physiological and nutritional significance. This study established a high-fat diet-induced intestinal barrier damage model in Macrobrachium rosenbergii, and systematically investigated the functions of gut microbiota and its functional metabolites. The study achieved this by monitoring phenotypic indicators, conducting 16S rDNA sequencing, targeted metabolomics, and in vitro anaerobic fermentation of intestinal contents. Feeding prawns with control and high-fat diets for 8 weeks, the lipid level of 7 % in the CON diet and 12 % in the HF diet. Results showed that high-fat intake impaired the intestinal epithelial cells, intestinal barrier structure, and permeability of M. rosenbergii, activated the tight junction signaling pathway inhibiting factor NF-κB transcription factor Relish/myosin light chain kinase (MLCK), and suppressed the expression of downstream tight junction proteins zona occludens protein 1 (ZO-1) and Claudin. High-fat intake resulted in a significant increase in abundance of Aeromonas, Enterobacter, and Clostridium sensu stricto 3 genera, while Lactobacillus, Lactococcus, Bacteroides, and Ruminococcaceae UCG-010 genera were significantly decreased. Targeted metabolomics results of bile acids and short-chain fatty acids in intestinal contents and in vitro anaerobic fermentation products showed a marked rise in the abundance of DCA, 12-KetoLCA, 7,12-diketoLCA, and Isovaleric acid, and a significant reduction in the abundance of HDCA, CDCA, and Acetate in the HF group. Pearson correlation analysis revealed a substantial correlation between various genera (Clostridium sensu stricto 3, Lactobacillus, Bacteroides) and secondary metabolites (DCA, HDCA, 12-KetoLCA, Acetate), and the latter was significantly correlated with intestinal barrier function related genes (Relish, ZO-1, MLCK, vitamin D receptor, and ecdysone receptor). These findings indicate that gut microorganisms and their specific bile acids and short-chain fatty acid secondary metabolites play a crucial role in the process of high-fat-induced intestinal barrier damage of M. rosenbergii. Moreover, identifying and targeting these factors could facilitate precise regulation of high-fat nutrition for crustaceans.

Complementary role of peripheral and central autonomic nervous system on insulin-like growth factor-1 activation to prevent fatty liver disease

BACKGROUND

Insulin-like growth factor-1 (IGF-1) is involved in the pathology of non-alcoholic fatty liver disease (NAFLD) and ameliorates fatty infiltration in the liver. It is activated by growth hormone (GH); however, the role of GH-IGF-1 axis in NAFLD developmental phase has not been well identified. Therefore, in this study, we focused on the effect of IGF-1 in NAFLD pathology and GH excretion activation from the pituitary gland by peripheral autonomic neural pathways relaying liver-brain-gut pathway and by central neuropeptides.

METHODS

GH and IGF-1 levels were assessed in wild-type and melanocortin-4 receptor knockout mice upon the development of diet-induced NAFLD. The contribution of the peripheral autonomic nervous system connecting the liver-brain-gut axis was assessed by its blockade using capsaicin and that of the central nervous system was assessed by the expression of hypothalamic brain-derived neurotrophic factor (BDNF) and corticotropin-releasing factor (CRH), which activates GH release from the pituitary gland.

RESULTS

In the NAFLD mouse models, the levels of GH and IGF-1 increased (p < .05). Further, hepatic fatty infiltration was suppressed even under peripheral autonomic nervous system blockade (p < .001), which inhibited gastric ghrelin expression. In mice with peripheral autonomic nervous blockade, hypothalamic BDNF and CRH were inhibited (p < .05), resulting in GH and IGF-1 excretion, whereas other neuropeptides of somatostatin and cortistatin showed no changes. These complementary effects were canceled in melanocortin-4 receptor knockout mice, which diminished BDNF and CRH release control.

CONCLUSIONS

Our study demonstrates that the release of IGF-1 by the nervous system is a key factor in maintaining the pathological homeostasis of NAFLD, suggesting its therapeutic potential.

Immunology of gut microbiome and liver in non-alcoholic fatty liver disease (NAFLD): mechanisms, bacteria, and novel therapeutic targets

Non-alcoholic fatty liver disease (NAFLD) is the most common chronic liver disease in the world. Most important contributors to its development are diet and obesity. Gut microbiome's importance for immune system and inflammatory pathways more widely accepted as an important component in NAFLD and other liver diseases' pathogenesis. In this article we review potential mechanisms of microbiome alteration of local and systemic immune responses leading to NAFLD's development, and how can modulate them for the treatment. Our review mentions different immune system pathways and microorganisms regulating metabolism, liver inflammation and fibrosis. We specifically point out TLR-4 as a potential key immune pathway activated by bacterial lipopolysaccharides producing pro-inflammatory cytokines in NAFLD. Also, we discuss three endotoxin-producing strains (Enterobacter cloacae B29, Escherichia coli PY102, Klebsiella pneumoniae A7) that can promote NAFLD development via TLR4-dependent immune response activation in animal models and how they potentially contribute to disease progression in humans. Additionally, we discuss their other immune and non-immune mechanisms contributing to NAFLD pathogenesis. In the end we point out gut microbiome researches' future perspective in NAFLD as a potential new target for both diagnostic and treatment.

Current insights into the interplay between gut microbiota-derived metabolites and metabolic-associated fatty liver disease

Metabolic dysfunction-associated fatty liver disease (MAFLD) is a prevalent and challenging disease associated with a significant health and economic burden. MAFLD has been subjected to and widely investigated in many studies; however, the underlying pathogenesis and its progression have yet to understand fully. Furthermore, precise biomarkers for diagnosing and specific drugs for treatment are yet to be discovered. Increasing evidence has proven gut microbiota as the neglected endocrine organ that regulates homeostasis and immune response. Targeting gut microbiota is an essential strategy for metabolic diseases, including MAFLD. Gut microbiota in the gut-liver axis is connected through tight bidirectional links through the biliary tract, portal vein, and systemic circulation, producing gut microbiota metabolites. This review focuses on the specific correlation between gut microbiota metabolites and MAFLD. Gut microbiota metabolites are biologically active in the host and, through subsequent changes and biological activities, provide implications for MAFLD. Based on the review studies, gut-liver axis related-metabolites including short-chain fatty acids, bile acids (BAs), lipopolysaccharide, choline and its metabolites, indole and its derivates, branched-chain amino acids, and methionine cycle derivates was associated with MAFLD and could be promising MAFLD diagnosis biomarkers, as well as the targets for MAFLD new drug discovery.