Introduction
Liver cirrhosis (LC) is the end stage of liver fibrosis that leads to various critical conditions, including hepatic encephalopathy (HE). Although recent evidence indicates that liver fibrosis is reversible, there is no intervention to promote this recovery process to date. The gut microbiota is thought to be involved in the pathogenesis of LC and HE. Rifaximin (RFX), a nonabsorbable broad-spectrum antibiotic, is widely used for HE treatment. Although the efficacy of RFX for HE has been established, the underlying mechanism of the efficacy of RFX remains unclear, while this antibiotic is considered to affect the gut microbiome. Since the microbial compositions are different between anatomical sites in the gastrointestinal (GI) tract, we hypothesized that the effects of RFX on the gut microbiome can vary among GI sites. Hence, we conceived the present study investigating the impacts of RFX on the gut microbiome along the GI tract to clarify the mechanism of RFX as well as to explore the role of the gut microbiota in the pathophysiology of LC and HE.
Aims & Methods
To investigate the impact of RFX on the gut microbiota and clinical manifestations of LC, RFX was orally administered to a carbon tetrachloride (CCl4)-induced LC murine model. Blood ammonia (NH3) concentration, liver pathological findings, and endotoxin concentration in the portal vein were examined. In each GI site, bacterial loads using qPCR of the Tuf gene and the bacterial compositions with 16S rRNA gene amplicon sequencing were assessed. Shotgun metagenomic sequencing was performed for jejunal and ileal contents to analyze the functional pathways in the small intestinal microbiota. On the host side, the gene expressions of the intestinal mucosa were examined using qPCR. To explore the clinical efficacy of A. muciniphila as a microbial intervention, we orally administered A. muciniphila ATCC BAA-835 (AKK) to the CCl4-induced LC murine model. The analyses described above for investigating the impacts of RFX were also performed for animals.
Results
RFX administration improved blood NH3 concentration, liver fibrosis, and endotoxin concentration in the portal vein. The 16S rRNA gene amplicon sequencing analyses showed that the changes in the bacterial compositions were larger in the small intestine (jejunum and ileum) compared to the cecum, colon, and stool. The genus-level analysis of the small intestinal microbiota demonstrated that increases in Faecalibaculum, Akkermansia, and Muribaculaceae were associated with the improvement of liver fibrosis. Shotgun metagenomic sequencing showed that RFX administration altered the metabolic functions of the small intestinal microbiota. On the host side, the mRNA expression levels of tight junction proteins, antimicrobial peptides, and toll-like receptors in the small intestinal mucosa were altered by RFX administration. In the analyses of a microbial intervention, AKK administration improved liver fibrosis and blood NH3 concentration. In addition, AKK administration significantly changed the small intestinal bacterial compositions in the murine LC model. The mRNA expression levels of tight junction proteins, antimicrobial peptides, and toll-like receptors in the small intestinal mucosa were altered by AKK administration.
Conclusion
This study demonstrated that the small intestinal microbiota was involved in the pathophysiology of LC and HE and proposed a new concept of “small intestine-liver axis” in LC and HE. The present study also suggests that oral administration of A. muciniphila is promising as a microbial intervention for these pathological conditions.
Disclosure
Mitsubishi Tanabe Pharma Corp., Takeda Pharmaceutical Co., Ltd., Janssen Pharmaceutical K.K., AbbVie GK, EA Pharma Co., Ltd., Pfizer Japan Inc., Alfresa Pharma Corp., Kyorin Pharmaceutical Co., Ltd., Mochida Pharmaceutical Co., Ltd., Daiichi Sankyo CO., Ltd., JIMRO Co., Ltd.
