Upregulation of Taurine Biosynthesis and Bile Acid Conjugation with Taurine through FXR in a Mouse Model with Human-like Bile Acid Composition

Imbalance of Bile Acids Metabolism Mediated by Gut Microbiota Contributed to Metabolic Disorders in Diabetic Model Mice

Type 2 diabetes (T2D) is a chronic disease prevalent in the world, accompanied by a variety of diseases, endangering human health and safety. Bile acids (BAs) play an important role in the regulation of host glucose and lipid metabolism homeostasis, and are strictly regulated by gut microbiota. However, the relationship between key BAs, BAs transporters and signaling, as well as gut microbiota, and host metabolism in T2D remains elusive. In this study, 9-week-old db/db mice were used as diabetes model (db/db group, n = 10), and their wild-type (wt) littermates of same age were used as the healthy control (CON group, n = 10). After 8 weeks of feeding, the BA profiles and microbial composition in the colon, and gene expression level of BA regulatory factors were analyzed in the db/db and CON groups to explore the underlying mechanisms of T2D. Compared with healthy mice, the body weight, blood glucose and lipid levels of db/db mice were significantly increased. The concentrations of total BAs, primary BAs, conjugated BAs and non-12α-hydroxylated BAs (non-12-OH BAs) were significantly decreased, while Deoxycholic acid (DCA) in secondary BAs was increased in db/db group. Compared with wt mice, the synthesis of BAs in the liver was transformed from the alternative pathway to the classical pathway, and hepatic BAs transporters (NTCP, BSEP, MRP2, OATP-1 and OSTβ) and receptors (FXR and TGR5) were significantly down-regulated in the db/db mice. In the colon, the mRNA level of FXR was up-regulated, while TGR5 was down-regulated. The diabetic (db/db) mice presented a changed gut microbiota composition, including an increased abundance of secondary BAs-producing bacteria, Escherichia-Shigella, and a decreased the abundance of Akkermansia, which are involved in the synthesis of non-12-OH BAs. We further found that the reduced BA types in db/db mice were negatively correlated with metabolic-disorder-related indicators, while an increased DCA level had the opposite correlation. Our results shed light into how the imbalance of BAs' metabolism mediated by intestinal flora may be potential mechanisms of T2D.

Immunobiology of bile and cholangiocytes

The biliary tract is now recognized as an immune organ, and within the biliary tract, both bile and cholangiocytes play a key role in maintaining immune defense and homeostasis. First, immunoreactive proteins such as secretory IgA provide local antimicrobial effects. Second, bile acids (BAs) protect the biliary tree from immune-related injury through receptor signaling, mainly via the membrane-bound receptor TGR5 on cholangiocytes. Third, the biliary microbiota, similar to the intestinal microbiota, contributes to sustaining a stable physiobiological microenvironment. Fourth, cholangiocytes actively modulate the expression/release of adhesion molecules and cytokines/chemokines and are involved in antigen presentation; additionally, cholangiocyte senescence and apoptosis also influence immune responses. Conversely, aberrant bile composition, altered BA profiles, imbalances in the biliary microbiota, and cholangiocyte dysfunction are associated with immune-mediated cholangiopathies, including primary biliary cholangitis, primary sclerosing cholangitis, and biliary atresia. While current therapeutic agents that modulate BA homeostasis and receptor signaling have shown promise in preclinical and clinical studies, future research on biliary/intestinal microbiota and cholangiocyte function should focus on developing novel therapeutic strategies for treating cholangiopathies.

Bile acids as a key target: traditional Chinese medicine for precision management of insulin resistance in type 2 diabetes mellitus through the gut microbiota-bile acids axis

Type 2 diabetes mellitus (T2DM) is a chronic metabolic disease caused by insulin resistance (IR) and insufficient insulin secretion. Its characteristic pathophysiological processes involve the interaction of multiple mechanisms. In recent years, globally, the prevalence of T2DM has shown a sharp rise due to profound changes in socio-economic structure, the persistent influence of environmental factors, and the complex role of genetic background. It is worth noting that most T2DM patients show significant IR, which further exacerbates the difficulty of disease progression and prevention. In the process of extensively exploring the pathogenesis of T2DM, the dynamic equilibrium of gut microbes and its diverse metabolic activities have increasingly emphasized its central role in the pathophysiological process of T2DM. Bile acids (BAs) metabolism, as a crucial link between gut microbes and the development of T2DM, not only precisely regulates lipid absorption and metabolism but also profoundly influences glucose homeostasis and energy balance through intricate signaling pathways, thus playing a pivotal role in IR progression in T2DM. This review aims to delve into the specific mechanism through which BAs contribute to the development of IR in T2DM, especially emphasizing how gut microbes mediate the metabolic transformation of BAs based on current traditional Chinese medicine research. Ultimately, it seeks to offer new insights into the prevention and treatment of T2DM. Diet, genetics, and the environment intricately sculpt the gut microbiota and BAs metabolism, influencing T2DM-IR. The research has illuminated the significant impact of single herbal medicine, TCM formulae, and external therapeutic methods such as electroacupuncture on the BAs pool through perturbations in gut microbiota structure. This interaction affects glucose and lipid metabolism as well as insulin sensitivity. Additionally, multiple pathways including BA-FXR-SHP, BA-FXR-FGFR15/19, BA-FXR-NLRP3, BA-TGR5-GLP-1, BAs-TGR5/FXR signaling pathways have been identified through which the BAs pool significantly alter blood glucose levels and improve IR. These findings offer novel approaches for enhancing IR and managing metabolic disorders among patients with T2DM.

Insights into the molecular mechanisms of malnutrition-associated steatohepatitis: A review

Malnutrition is a public health epidemic mainly targeting poverty-stricken people, young ones, older people, pregnant women, and individuals with metabolic disorders. Severe malnutrition is linked with several metabolic defects, such as hepatic dysfunction, hypertension, cardiovascular disease, and osteoarthritis. The proper functioning of the liver plays a crucial role in ensuring the supply of nutrients to the body. Consequently, inadequate nutrition can lead to severe periportal hepatic steatosis due to compromised mitochondrial and peroxisome functions. Reduced protein intake disrupts essential metabolic processes like the TCA cycle, oxidative phosphorylation, and β-oxidation, ultimately affecting ATP production. Furthermore, this can trigger a cascade of events, including disturbances in amino acid metabolism, iron metabolism, and gut microbiota, which activate genes involved in de novo lipogenesis, leading to the accumulation of lipids in the liver. The condition, in prolonged cases, progresses to steatohepatitis and liver fibrosis. Limited therapeutic solutions are available; however, few dietary supplements and drugs have demonstrated positive effects on the growth and health of malnourished individuals. These supplements improve parameters such as inflammatory and oxidative status, reduce triglyceride accumulation, enhance insulin sensitivity, and downregulate gene expression in hepatic lipid metabolism. This review elucidates the various mechanisms involved in malnutrition-associated steatohepatitis and provides an overview of the available approaches for treating this condition.

Investigation of the effects of in ovo taurine injection on hatching characteristics and stress reduction potential

BACKGROUND

In ovo application is the process of administering some nutrients or components into the egg. The main purpose of this application is to ensure that some nutrients are provided to chicks with a short incubation period. Few studies were conducted with taurine in fertile eggs; especially, no observation of hatchability and chick quality has been found. In addition, taurine has an anti-stress impact that fights oxidative factors.

OBJECTIVE

To assess the hatchability and chick quality after in ovo taurine administration. To determine the stress that may occur as a result of in ovo application and whether taurine has a stress-reducing effect.

METHODS

A total of 1200 fertile eggs from a 34-week-old broiler breeder (Ross 308) flock were categorized into 4 groups with 75 eggs per replicate: control (uninjected), taurine group (0.30 mL dissolved taurine in distilled water), sham control (sterile distilled water) and perforation (eggs perforated and then waxed). On day 14 of incubation, an in ovo injection was administered to the albumen. Data on hatching parameters and hepatic HSP70 levels were obtained using relevant formulas and western blotting, respectively.

RESULTS

Control chicks exhibited higher hatchability than other groups, with the taurine group showing the lowest hatchability. The HSP70 levels were the highest in the perforation group compared to the control group. An increase of 21.37% in the taurine group and 83.45% in the sham control group was observed compared to the control group.

CONCLUSIONS

The findings suggest that in ovo application may induce increased stress, whereas taurine may have positive effects in mitigating the stress caused by in ovo application.

Identification of a novel enzyme and the regulation of key enzymes in mammalian taurine synthesis

Taurine has many pharmacological roles on various tissues. The maintenance of abundant taurine content in the mammalian body through endogenous synthesis, in addition to exogenous intake, is the essential factor for morphological and functional maintenances in most tissues. The synthesis of taurine from sulfur-containing amino acids is influenced by various factors. Previous literature findings indicate the influence of the intake of proteins and sulfur-containing amino acids on the activity of the rate-limiting enzymes cysteine dioxygenase and cysteine sulfinate decarboxylase. In addition, the regulation of the activity and expression of taurine-synthesis enzymes by hormones, bile acids, and inflammatory cytokines through nuclear receptors have been reported in liver and reproductive tissues. Furthermore, flavin-containing monooxygenase subtype 1 was recently identified as the taurine-synthesis enzyme that converts hypotaurine to taurine. This review introduces the novel taurine synthesis enzyme and the nuclear receptor-associated regulation of key enzymes in taurine synthesis.

Bile acids impact the microbiota, host, and C. difficile dynamics providing insight into mechanisms of efficacy of FMTs and microbiota-focused therapeutics

Clostridioides difficile is a major nosocomial pathogen, causing significant morbidity and mortality worldwide. Antibiotic usage, a major risk factor for Clostridioides difficile infection (CDI), disrupts the gut microbiota, allowing C. difficile to proliferate and cause infection, and can often lead to recurrent CDI (rCDI). Fecal microbiota transplantation (FMT) and live biotherapeutic products (LBPs) have emerged as effective treatments for rCDI and aim to restore colonization resistance provided by a healthy gut microbiota. However, much is still unknown about the mechanisms mediating their success. Bile acids, extensively modified by gut microbes, affect C. difficile's germination, growth, and toxin production while also shaping the gut microbiota and influencing host immune responses. Additionally, microbial interactions, such as nutrient competition and cross-feeding, contribute to colonization resistance against C. difficile and may contribute to the success of microbiota-focused therapeutics. Bile acids as well as other microbial mediated interactions could have implications for other diseases being treated with microbiota-focused therapeutics. This review focuses on the intricate interplay between bile acid modifications, microbial ecology, and host responses with a focus on C. difficile, hoping to shed light on how to move forward with the development of new microbiota mediated therapeutic strategies to combat rCDI and other intestinal diseases.