Bile acid dysmetabolism in the gut-microbiota-liver axis under hepatitis C virus infection

VSV infection and LPS treatment alter serum bile acid profiles, bile acid biosynthesis, and bile acid receptors in mice

Pathogen infections remain a significant public health problem worldwide. Accumulating evidence regarding the crosstalk between bile acid (BA) metabolism and immune response reveals that BA metabolism regulates host immunity and microbial pathogenesis, making it an attractive target for disease prevention and infection control. However, the effect of infection on circulating BA profiles, the biosynthesis-related enzymes, and their receptors remains to be depicted. Here, we investigated the effect of viral (vesicular stomatitis virus, VSV) and bacterial (lipopolysaccharide, LPS) infections on BA metabolism and signaling. Infection models were successfully established by intraperitoneally injecting VSV and LPS, respectively. VSV and LPS injection significantly changed the circulating BA profiles, with highly increased levels of taurine-conjugated BAs and significant decreases in unconjugated BAs. Consistent with the decreased levels of circulating cholic acid (CA) and chenodeoxycholic acid (CDCA), the expression of BA biosynthesis-related rate-limiting enzymes (Cyp7a1, Cyp27a1, Cyp8b1, and Hsd3b7) were significantly reduced. Furthermore, hepatic and pulmonary BA receptors (BARs) expression varied in different infection models. LPS treatment had an extensive impact on tested hepatic and pulmonary BARs, resulting in the upregulation of TGR5, S1PR2, and VDR, while VSV infection only promoted VDR expression. Our study provides insights into the involvement of BA metabolism in the pathophysiology of infection, which may provide potential clues for targeting BA metabolism and BAR signaling to boost innate immunity and control infection.

IMPORTANCE

This study focuses on the crosstalk between bile acid (BA) metabolism and immune response in VSV infection and LPS treatment models and depicts the effect of infection on circulating BA profiles, the biosynthesis-related enzymes, and their receptors. These findings provide insights into the effect of infection on BA metabolism and signaling, adding a more comprehensive understanding to the relationship between infection, BA metabolism and immune responses.

Gut microbiota-mediated ursodeoxycholic acids regulate the inflammation of microglia through TGR5 signaling after MCAO

Ischemic stroke has been demonstrated to cause an imbalance of gut microbiota. However, the change in gut microbiota-mediated bile acids (BAs) metabolites remains unclear. Here, we observed a decrease in gut microbiota-mediated BAs, especially ursodeoxycholic acid (UDCA), in the serum of stroke patients as well as in the intestine, serum and brain of stroke mice. Restoration of UDCA could decrease the area of infarction and improve the neurological function and cognitive function in mice in association with inhibition of NLRP3-related pro-inflammatory cytokines through TGR5/PKA pathway. Furthermore, knocking out TGR5 and inhibiting PKA activity reduce the protective effect of UDCA. Taken together, our results suggest that microbiota-mediated UDCA plays an important role in alleviating inflammatory responses and might be a promising therapeutic target in ischemic stroke.

Impact of elobixibat on liver tumors, microbiome, and bile acid levels in a mouse model of nonalcoholic steatohepatitis

BACKGROUND

Elevated bile acid levels have been associated with liver tumors in fatty liver. Ileal bile acid transporter inhibitors may inhibit bile acid absorption in the distal ileum and increase bile acid levels in the colon, potentially decreasing the serum and hepatic bile acid levels. This study aimed to investigate the impact of these factors on liver tumor.

METHODS

C57BL/6J mice received a one-time intraperitoneal injection of 25-mg/kg diethylnitrosamine. They were fed a choline-deficient high-fat diet for 20 weeks starting from 8 weeks of age, with or without elobixibat (EA Pharma, Tokyo, Japan).

RESULTS

Both groups showed liver fat accumulation and fibrosis, with no significant differences between the two groups. However, mice with elobixibat showed fewer liver tumors. The total serum bile acid levels, including free, tauro-conjugated, glyco-conjugated, and tauro-α/β-muricholic acids in the liver, were noticeably reduced following elobixibat treatment. The proportion of gram-positive bacteria in feces was significantly lower in the group treated with elobixibat (5.4%) than in the group without elobixibat (33.7%).

CONCLUSION

Elobixibat suppressed tumor growth by inhibiting bile acid reabsorption, and decreasing total bile acid and primary bile acid levels in the serum and liver. Additionally, the presence of bile acids in the colon may have led to a significant reduction in the proportion of gram-positive bacteria, potentially resulting in decreased secondary bile acid synthesis.

Effect of Liver Fibrosis on Oral and Gut Microbiota in the Japanese General Population Determined by Evaluating the FibroScan-Aspartate Aminotransferase Score

The association between liver fibrosis and oral or gut microbiota has been studied before. However, epidemiological studies in the general population are limited owing to the difficulty of noninvasive liver-fibrosis assessment. FibroScan-asparate aminotransferase (FAST) scores can be used to accurately and non-invasively evaluate liver fibrosis. This study aimed to determine the association between liver fibrosis and oral or gut microbiota using the FAST score in the general population. After propensity score matching of 1059 participants based on sex, age, body mass index, homeostasis model assessment of insulin resistance, and triglyceride levels, 125 (non-liver-fibrosis group, 100; liver fibrosis group, 25) were included. The diversity of gut microbiota differed significantly between the two groups; however, no significant differences were noted in their oral microbiota. The liver fibrosis group showed an increase in the relative abundance of Fusobacteria strains and a decrease in the relative abundance of Faecalibacterium, with the presence of Fusicatenibacter in the gut microbiota. Feacalibacterium was not identified as an independent factor of liver fibrosis in adjusting the fatty liver index. In the general population, gut microbiota may be more involved in liver fibrosis than oral microbiota.

The gut microbiota: A new perspective for tertiary prevention of hepatobiliary and gallbladder diseases

The gut microbiota is a complex ecosystem that has coevolved with the human body for hundreds of millions of years. In the past 30 years, with the progress of gene sequencing and omics technology, the research related to gut microbiota has developed rapidly especially in the field of digestive system diseases and systemic metabolic diseases. Mechanical, biological, immune, and other factors make the intestinal flora form a close bidirectional connection with the liver and gallbladder, which can be called the "gut-liver-biliary axis." Liver and gallbladder, as internal organs of the peritoneum, suffer from insidious onset, which are not easy to detect. The diagnosis is often made through laboratory chemical tests and imaging methods, and intervention measures are usually taken only when organic lesions have occurred. At this time, some people may have entered the irreversible stage of disease development. We reviewed the literature describing the role of intestinal flora in the pathogenesis and biotherapy of hepatobiliary diseases in the past 3-5 years, including the dynamic changes of intestinal flora at different stages of the disease, as well as the signaling pathways involved in intestinal flora and its metabolites, etc. After summarizing the above contents, we hope to highlight the potential of intestinal flora as a new clinical target for early prevention, early diagnosis, timely treatment and prognosis of hepatobiliary diseases. GRAPHICAL ABSTRACT.

Microbiota and hepatitis C virus in the era of direct-acting antiviral agents

The gut microbiota plays a fundamental role in Hepatitis C Virus (HCV)-related liver disease. Indeed, HCV infection alters the gut microbiota, whereas intestinal dysbiosis induces an underlying inflammatory state. This status may lead to liver disease progression. The advent of direct acting antivirals (DAAs) was a turning point in the history of HCV infection, which enhances the chances of recovery. Beyond the elimination of the virus, DAA therapy can affect the gut microbiota of the HCV patient. The study of the gut microbiota in the patient with HCV-related liver disease could be the first step in understanding the etiopathogenesis of hepatopathy thereby opening the way to new therapeutic opportunities. Herein we evaluate current knowledge regarding the gut microbiota in patients with HCV infection and the impact of DAA therapy.

New Insights into the Relationship between Gut Microbiota and Radiotherapy for Cancer

Cancer is the second most common cause of death among humans in the world, and the threat that it presents to human health is becoming more and more serious. The mechanisms of cancer development have not yet been fully elucidated, and new therapies are changing with each passing day. Evidence from the literature has validated the finding that the composition and modification of gut microbiota play an important role in the development of many different types of cancer. The results also demonstrate that there is a bidirectional interaction between the gut microbiota and radiotherapy treatments for cancer. In a nutshell, the modifications of the gut microbiota caused by radiotherapy have an effect on tumor radiosensitivity and, as a result, affect the efficacy of radiotherapy and show a certain radiation toxicity, which leads to numerous side effects. What is of new research significance is that the "gut-organ axis" formed by the gut microbiota may be one of the most interesting potential mechanisms, although the relevant research is still very limited. In this review, we combine new insights into the relationship between the gut microbiota, cancer, and radiotherapy. Based on our current comprehensive understanding of this relationship, we give an overview of the new cancer treatments based on the gut microbiota.

The contribution of the gut-liver axis to the immune signaling pathway of NAFLD

Nonalcoholic fatty liver disease (NAFLD) is the liver manifestation of metabolic syndrome and is the most common chronic liver disease in the world. The pathogenesis of NAFLD has not been fully clarified; it involves metabolic disturbances, inflammation, oxidative stress, and various forms of cell death. The “intestinal-liver axis” theory, developed in recent years, holds that there is a certain relationship between liver disease and the intestinal tract, and changes in intestinal flora are closely involved in the development of NAFLD. Many studies have found that the intestinal flora regulates the pathogenesis of NAFLD by affecting energy metabolism, inducing endotoxemia, producing endogenous ethanol, and regulating bile acid and choline metabolism. In this review, we highlighted the updated discoveries in intestinal flora dysregulation and their link to the pathogenesis mechanism of NAFLD and summarized potential treatments of NAFLD related to the gut microbiome.