Liver and gut widely communicate through the bile ducts, the portal vein and the systemic mediators: this relationship is called the gut-liver axis (GLA), in which bile acids (BA) and their receptors play a critical role. GLA strongly influences inflammatory processes and immune responses. GLA dysfunctions underlie several hepatic metabolic diseases such as non-alcoholic fatty liver disease (NAFLD) and non-alcoholic steatohepatitis (NASH).
NAFLD includes a wide spectrum of chronic liver disorders ranging from liver steatosis to NASH, the latter characterized by different degrees of inflammation, hepatocellular damage and fibrosis. The mechanisms whereby hepatic inflammation occurs in NASH remain incompletely understood, but recent evidences a role of gut microbiota and GLA dysfunction.
The present project aims to assess the role of intestinal inflammation in contributing to NAFLD occurrence and its progression into NASH. Particular emphasis will be placed on the relationship between gut inflammation, the associated microbial dysbiosis, bile receptor expression and NASH severity.
For this purpose, two murine models of NASH (High fat diet (HFD) treatment) and NASH+gut inflammation (HFD+ dextran sodium sulfate (DSS) treatments) as well as liver specimens from children with NASH and co-cultures of intestinal (Cavco2) and liver (HepG2) cells will be used.
The expression of BA receptors (FXR, PXR, TGR) and inflammatory cytokines (IL-6, IL-1beta, TNFalpha) will be analyzed by RT-PCR and will be related to gut inflammation and liver disease severity. The composition of gut microbiota will be assessed in mice fecal specimens, through NGS metagenomics. The potential use of glycyrrethic acid (DPG) to improve liver damage by reducing gut inflammation will be also analyzed.
This study will improve the knowledge of NASH pathogenesis by focusing on the GLA role aiming at exploring how the occurrence of gut inflammation influences the severity and progression of the disease.
Many efforts have been made to characterize the cellular and molecular events underlying the pathogenetic mechanisms of NAFLD and NASH and translate this knowledge into therapeutic tools aimed at improving and enhancing the possibilities of treating the disease. Hepatic steatosis is the most common chronic liver disease in adults (25%) and, very worryingly, in the pediatric population of industrialized countries; in a significant percentage of the subjects it assumes the characteristics of steatohepatitis (NASH). The clinical relevance of NAFLD is motivated by epidemiological data and by the impact on liver morbidity as well as on cardiovascular and metabolic diseases. The therapeutic approach very often represents a great challenge for the clinician, in particular for pediatric hepatologists who must also take into consideration the peculiarities of the pediatric age, such as growth, pubertal development, the nutritional status.
GLA disfunctions, often due to the occurrence of gut microbiota dysbiosis and alteration of BA receptor levels, have been recently demonstrated to contribute to the pathogenesis NAFLD.
The innovation of the study is based on a deep analysis of the role of intestinal inflammation in the onset and progression of liver disease, highlighting the effect of the intestinal microbiota composition and the modulation of BA receptors. Novel evidence will be presented by investigations performed in NASH animal models, including a traditional NASH (HFD) model and a novel model of NASH+intestinal inflammation (HFD+ DSS), that will be used to follow the progression of the steatosis to steatohepatitis, also exploring, during the course of the disease, the influence of gut inflammation on liver disease. Particular emphasis will be given to the relationship between bacterial composition (assessed by shotgun metagenomics) and BA receptors levels in mice, either with or without gut inflammation. Obtained results will be related to the liver disease severity. Results obtained from these analyses could also allow the identification of new molecular markers predictive of the course and progression of NAFLD in NASH.
Furthermore, the BA receptors levels will be investigated in liver samples of children with NASH alone and with NASH and intestinal inflammation: the availability of these specimens will allow, for the first time, to find out likely peculiarities characterizing the two groups of patients. In general, the pediatric NASH remains under-studied, under-recognized and, possibly, undermanaged. Therefore, there is quite wide agreement across the scientific community on the need to deeply explore the peculiarities of the pediatric/adolescent disease that deserves specific consideration and management. This if of critical interest if we consider that NASH occurring in children and young adults has often a more active and severe degree at presentation than the full adult-onset.
Due to the complexity of NASH, a deeper understanding of the key events that regulate disease progression can lead to a more rational and targeted therapeutic approach, such as the use of therapies focused on pro-inflammatory events both at intrahepatic and extrahepatic levels. In this context, the use of DPG, already known for its anti-inflammatory properties and absence of toxic effects, in intestinal and liver established cell lines could prove to be useful as a treatment to complement the traditional therapies.
In conclusion, this project will allow to deeply understand the mechanisms of interaction between the liver and the gut in physiological and pathological conditions, through a multidisciplinary and innovative approach that will add new items in the knowledge of NAFLD/NASH pathogenesis.