TGR5, Not Only a Metabolic Regulator

Activation of FXR receptor reduces damage of ET-1 on H9C2 cardiomyocytes by activating AMPK signaling pathway

BACKGROUND

The aim of this study was to investigate the effect of Farnesoid X receptor (FXR) on oxidative stress injury of H9C2 cardiomyocytes induced by endothelin-1 (ET-1), and to explore the possible mechanism.

METHODS

H9C2 cardiomyocytes were treated with ET-1 at concentrations of 10-8, 10-7 and 10-6 mmol/L for 12, 24, 36, and 48 h, respectively. At the same time, oxidative stress injury models were established. After the oxidative stress injury model was established, GW4064 (FXR agonist), siRNA-FXR (the virus interfered with FXR expression) and FXR empty virus were treated for 48 h. CCK-8 method was used to observe the survival rate of cardiomyocytes. Biochemical kit method was used to detect Creatine Kinase (CK) contents, CAT, and mitochondrial activity. Western blot was used to detect the protein expression of SOD1, AMPK and p-AMPK. And real-time PCR was used to detect GPX1 mRNA, GPX3 mRNA, Sirt1 mRNA, PGC-1α mRNA expression levels.

RESULTS

At the concentrations of 10-8, 10-7 and 10-6 mmol/L, ET-1 could induce the decrease of mitochondrial complex I and III activity and increase of CK content in H9C2 cardiomyocytes. Moreover, with the increase of ET-1 concentration and the extension of culture time, the oxidative stress damage of cardiomyocytes became more serious. After ET-1 intervention, the expressions of p-AMPK protein, Sirt1 mRNA and PGC-1α mRNA were decreased. The 2 μmol/L GW4064 could effectively improve the oxidative stress induced by ET-1, and compared with the ET-1 group, the survival rate of H9C2 cardiomyocytes increased obviously. In addition, the CK content was decreased. On the contrary, the mitochondrial complex I and III, and CAT activity increased significantly, and the expressions of SOD1 and p-AMPK protein, Sirt1 mRNA and PGC-1α mRNA increased obviously. However, siRNA-FXR can partially block the improvement effect of FXR agonist on cardiomyocytes injury.

CONCLUSIONS

Activation of FXR receptor may reduce the damage of ET-1 on H9C2 cardiomyocytes by activating AMPK signaling pathway.

Bile Acids and Bilirubin Role in Oxidative Stress and Inflammation in Cardiovascular Diseases

Bile acids (BAs) and bilirubin, primarily known for their role in lipid metabolism and as heme catabolite, respectively, have been found to have diverse effects on various physiological processes, including oxidative stress and inflammation. Indeed, accumulating evidence showed that the interplay between BAs and bilirubin in these processes involves intricate regulatory mechanisms mediated by specific receptors and signaling pathways under certain conditions and in specific contexts. Oxidative stress plays a significant role in the development and progression of cardiovascular diseases (CVDs) due to its role in inflammation, endothelial dysfunction, hypertension, and other risk factors. In the cardiovascular (CV) system, recent studies have suggested that BAs and bilirubin have some opposite effects related to oxidative and inflammatory mechanisms, but this area of research is still under investigation. This review aims to introduce BAs and bilirubin from a biochemical and physiological point of view, emphasizing their potential protective or detrimental effects on CVDs. Moreover, clinical studies that have assessed the association between BAs/bilirubin and CVD were examined in depth to better interpret the possible link between them.

Update on the development of TGR5 agonists for human diseases

The G protein-coupled bile acid receptor 1 (GPBAR1) or TGR5 is widely distributed across organs, including the small intestine, stomach, liver, spleen, and gallbladder. Many studies have established strong correlations between TGR5 and glucose homeostasis, energy metabolism, immune-inflammatory responses, and gastrointestinal functions. These results indicate that TGR5 has a significant impact on the progression of tumor development and metabolic disorders such as diabetes mellitus and obesity. Targeting TGR5 represents an encouraging therapeutic approach for treating associated human ailments. Notably, the GLP-1 receptor has shown exceptional efficacy in clinical settings for diabetes management and weight loss promotion. Currently, numerous TGR5 agonists have been identified through natural product-based approaches and virtual screening methods, with some successfully progressing to clinical trials. This review summarizes the intricate relationships between TGR5 and various diseases emphasizing recent advancements in research on TGR5 agonists, including their structural characteristics, design tactics, and biological activities. We anticipate that this meticulous review could facilitate the expedited discovery and optimization of novel TGR5 agonists.

Proanthocyanidin B2 derived metabolites may be ligands for bile acid receptors S1PR2, PXR and CAR: an in silico approach

Bile acids (BAs) act as signaling molecules via their interactions with various nuclear (FXR, VDR, PXR and CAR) and G-protein coupled (TGR5, M3R, S1PR2) BA receptors. Stimulation of these BA receptors influences several processes, including inflammatory responses and glucose and xenobiotic metabolism. BA profiles and BA receptor activity are deregulated in cardiometabolic diseases; however, dietary polyphenols were shown to alter BA profile and signaling in association with improved metabolic phenotypes. We previously reported that supplementing mice with a proanthocyanidin (PAC)-rich grape polyphenol (GP) extract attenuated symptoms of glucose intolerance in association with changes to BA profiles, BA receptor gene expression, and/or downstream markers of BA receptor activity. Exact mechanisms by which polyphenols modulate BA signaling are not known, but some hypotheses include modulation of the BA profile via changes to gut bacteria, or alteration of ligand-availability via BA sequestration. Herein, we used an in silico approach to investigate putative binding affinities of proanthocyanidin B2 (PACB2) and PACB2 metabolites to nuclear and G-protein coupled BA receptors. Molecular docking and dynamics simulations revealed that certain PACB2 metabolites had stable binding affinities to S1PR2, PXR and CAR, comparable to that of known natural and synthetic BA ligands. These findings suggest PACB2 metabolites may be novel ligands of S1PR2, CAR, and PXR receptors.Communicated by Ramaswamy H. Sarma.

Bile acid metabolism and signaling in health and disease: molecular mechanisms and therapeutic targets

Bile acids, once considered mere dietary surfactants, now emerge as critical modulators of macronutrient (lipid, carbohydrate, protein) metabolism and the systemic pro-inflammatory/anti-inflammatory balance. Bile acid metabolism and signaling pathways play a crucial role in protecting against, or if aberrant, inducing cardiometabolic, inflammatory, and neoplastic conditions, strongly influencing health and disease. No curative treatment exists for any bile acid influenced disease, while the most promising and well-developed bile acid therapeutic was recently rejected by the FDA. Here, we provide a bottom-up approach on bile acids, mechanistically explaining their biochemistry, physiology, and pharmacology at canonical and non-canonical receptors. Using this mechanistic model of bile acids, we explain how abnormal bile acid physiology drives disease pathogenesis, emphasizing how ceramide synthesis may serve as a unifying pathogenic feature for cardiometabolic diseases. We provide an in-depth summary on pre-existing bile acid receptor modulators, explain their shortcomings, and propose solutions for how they may be remedied. Lastly, we rationalize novel targets for further translational drug discovery and provide future perspectives. Rather than dismissing bile acid therapeutics due to recent setbacks, we believe that there is immense clinical potential and a high likelihood for the future success of bile acid therapeutics.

The role of bile acid receptor TGR5 in regulating inflammatory signalling

Takeda G protein-coupled receptor 5 (TGR5) is a bile acid receptor, and its role in regulating metabolism after binding with bile acids has been established. Since the immune response depends on metabolism to provide biomolecules and energy to cope with challenging conditions, emerging evidence reveals the regulatory effects of TGR5 on the immune response. An in-depth understanding of the effect of TGR5 on immune regulation can help us disentangle the interaction of metabolism and immune response, accelerating the development of TGR5 as a therapeutic target. Herein, we reviewed more than 200 articles published in the last 20 years in PubMed, to discuss the roles of TGR5 in regulating inflammatory response, the molecular mechanism, as well as existing problems. Particularly, its anti-inflammation effect is emphasized.

TGR5 signalling in heart and brain injuries: focus on metabolic and ischaemic mechanisms

The heart and brain are the core organs of the circulation and central nervous system, respectively, and play an important role in maintaining normal physiological functions. Early neuronal and cardiac damage affects organ function. The relationship between the heart and brain is being continuously investigated. Evidence-based medicine has revealed the concept of the "heart- brain axis," which may provide new therapeutic strategies for certain diseases. Takeda protein-coupled receptor 5 (TGR5) is a metabolic regulator involved in energy homeostasis, bile acid homeostasis, and glucose and lipid metabolism. Inflammation is critical for the development and regeneration of the heart and brain during metabolic diseases. Herein, we discuss the role of TGR5 as a metabolic regulator of heart and brain development and injury to facilitate new therapeutic strategies for metabolic and ischemic diseases of the heart and brain.

Proanthocyanidins-Based Synbiotics as a Novel Strategy for Nonalcoholic Fatty Liver Disease (NAFLD) Risk Reduction

Nonalcoholic fatty liver disease (NAFLD), the most common liver disease worldwide, is a spectrum of liver abnormalities ranging from steatosis to nonalcoholic steatohepatitis (NASH) characterized by excessive lipid accumulation. The prevalence of NAFLD is predicted to increase rapidly, demanding novel approaches to reduce the global NAFLD burden. Flavonoids, the most abundant dietary polyphenols, can reduce the risk of NAFLD. The majority of dietary flavonoids are proanthocyanidins (PACs), which are oligomers and polymers of the flavonoid sub-group flavan-3-ols. The efficacy of PAC in reducing the NAFLD risk can be significantly hindered by low bioavailability. The development of synbiotics by combining PAC with probiotics may increase effectiveness against NAFLD by biotransforming PAC into bioavailable metabolites. PAC and probiotic bacteria are capable of mitigating steatosis primarily through suppressing de novo lipogenesis and promoting fatty acid β-oxidation. PAC and probiotic bacteria can reduce the progression of steatosis to NASH mainly through ameliorating hepatic damage and inflammation induced by hepatic oxidative stress, endoplasmic reticulum stress, and gut microbiota dysbiosis. Synbiotics of PAC are superior in reducing the risk of NAFLD compared to independent administration of PAC and probiotics. The development of PAC-based synbiotics can be a novel strategy to mitigate the increasing incidence of NAFLD.

Mechanism of action of the bile acid receptor TGR5 in obesity

G protein-coupled receptors (GPCRs) are a large family of membrane protein receptors, and Takeda G protein-coupled receptor 5 (TGR5) is a member of this family. As a membrane receptor, TGR5 is widely distributed in different parts of the human body and plays a vital role in regulating metabolism, including the processes of energy consumption, weight loss and blood glucose homeostasis. Recent studies have shown that TGR5 plays an important role in glucose and lipid metabolism disorders such as fatty liver, obesity and diabetes. With the global obesity situation becoming more and more serious, a comprehensive explanation of the mechanism of TGR5 and filling the gaps in knowledge concerning clinical ligand drugs are urgently needed. In this review, we mainly explain the anti-obesity mechanism of TGR5 to promote the further study of this target, and show the electron microscope structure of TGR5 and review recent studies on TGR5 ligands to illustrate the specific binding between TGR5 receptor binding sites and ligands, which can effectively provide new ideas for ligand research and promote drug research.

TGR5 deficiency-induced anxiety and depression-like behaviors: The role of gut microbiota dysbiosis

BACKGROUND AND PURPOSE

Anxiety and depression have been associated with imbalances in the gut microbiota and bile acid metabolism. Takeda G protein-coupled receptor 5 (TGR5), a bile acid receptor involved in metabolism, is influenced by the gut microbiota. This study aimed to investigate the relationship between anxiety, depression, and microbiota using TGR5 knockout mice.

METHODS

We employed the following methods: (1) Assessment of behavioral changes, (2) Measurement of 5-HT levels and protein expression, (3) Analysis of stool samples, (4) Utilization of gene sequencing and statistical analysis to identify microbial signatures, (5) Examination of correlations between microbial signatures and 5-HT levels, and (6) Fecal microbiota transplantation experiments of TGR5-/- mice.

RESULTS

The deletion of TGR5 was found to result in increased anxiety- and depression-like behaviors in mice. TGR5 knockout mice exhibited significant reductions in 5-hydroxytryptamine (5-HT) levels in both serum and hippocampus, accompanied by a decrease in the expression of 5-HT1A receptor in the hippocampus. Moreover, TGR5 deficiency was associated with a decrease in the species richness of the gut microbiota. Specifically, the gut microbiota compositions of TGR5 knockout mice displayed distinct differences compared to their littermates, characterized by higher abundances of Anaeroplasma, Prevotella, Staphylococcus, Jeotgalicoccus, and Helicobacter, and a lower abundance of Bifidobacterium. Notably, a strong association between Jeotgalicoccus as well as Staphylococcus and serum 5-HT levels was observed in co-occurrence network. Furthermore, mice that received fecal microbiota transplants from TGR5-/- mice displayed anxiety and depression -like behaviors, accompanied by alterations in 5-HT levels in the hippocampus and serum.

LIMITATIONS

Study limitations for gut bacteria were analyzed at the genus level only.

CONCLUSION

TGR5 deletion in mice induces anxiety and depression-like behaviors, linked to reduced 5-HT levels in serum and the hippocampus. Gut microbiota changes play a direct role in these behaviors and serotonin alterations. This implicates TGR5 and gut bacteria in mood regulation, with potential therapeutic implications.

Review on chronic metabolic diseases surrounding bile acids and gut microbiota: What we have explored so far

Bile acid, the final product of cholesterol breakdown, functions as a complex regulator and signaling factor in human metabolism. Chronic metabolic diseases pose significant medical challenges. Growing research underscores bile acids' capacity to enhance metabolism via diverse pathways, regulating disorders and offering treatment potential. Numerous bile-acid-triggered pathways have become treatment targets. This review outlines bile acid synthesis, its role as a signal in chronic metabolic diseases, and highlights its interaction with gut microbiota in different metabolic conditions. Exploring host-bacteria-bile acid links emerges as a valuable future research direction with clinical implications.

Bile Acids as Signaling Molecules: Role of Ursodeoxycholic Acid in Cholestatic Liver Disease

Ursodeoxycholic acid (UDCA) is a natural substance physiologically produced in the liver. Initially used to dissolve gallstones, it is now successfully used in treating primary biliary cirrhosis and as adjuvant therapy for various hepatobiliary cholestatic diseases. However, the mechanisms underlying its beneficial effects still need to be clarified. Evidence suggests three mechanisms of action for UDCA that could benefit humans with cholestatic liver disease (CLD): protection of cholangiocytes against hydrophobic bile acid (BA) cytotoxicity, stimulation of hepatobiliary excretion, and protection of hepatocytes against BA-induced apoptosis. These mechanisms may act individually or together to potentiate them. At the molecular level, it has been observed that UDCA can generate modifications in the transcription and translation of proteins essential in the transport of BA, correcting the deficit in BA secretion in CLD, in addition to activating signaling pathways to translocate these transporters to the sites where they should fulfill their function. Inhibition of BA-induced hepatocyte apoptosis may play a role in CLD, characterized by BA retention in the hepatocyte. Thus, different mechanisms of action contribute to the improvement after UDCA administration in CLD. On the other hand, the effects of UDCA on tissues that possess receptors that may interact with BAs in pathological contexts, such as skeletal muscle, are still unclear. This work aims to describe the main molecular mechanisms by which UDCA acts in the human body, emphasizing the interaction in tissues other than the liver.

Bile acids, gut microbiota, and therapeutic insights in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a prevalent and aggressive liver malignancy. The interplay between bile acids (BAs) and the gut microbiota has emerged as a critical factor in HCC development and progression. Under normal conditions, BA metabolism is tightly regulated through a bidirectional interplay between gut microorganisms and BAs. The gut microbiota plays a critical role in BA metabolism, and BAs are endogenous signaling molecules that help maintain liver and intestinal homeostasis. Of note, dysbiotic changes in the gut microbiota during pathogenesis and cancer development can disrupt BA homeostasis, thereby leading to liver inflammation and fibrosis, and ultimately contributing to HCC development. Therefore, understanding the intricate interplay between BAs and the gut microbiota is crucial for elucidating the mechanisms underlying hepatocarcinogenesis. In this review, we comprehensively explore the roles and functions of BA metabolism, with a focus on the interactions between BAs and gut microorganisms in HCC. Additionally, therapeutic strategies targeting BA metabolism and the gut microbiota are discussed, including the use of BA agonists/antagonists, probiotic/prebiotic and dietary interventions, fecal microbiota transplantation, and engineered bacteria. In summary, understanding the complex BA-microbiota crosstalk can provide valuable insights into HCC development and facilitate the development of innovative therapeutic approaches for liver malignancy.

The Interplay between Helicobacter pylori and Gut Microbiota in Non-Gastrointestinal Disorders: A Special Focus on Atherosclerosis

The discovery of Helicobacter pylori (H. pylori) in the early 1980s by Nobel Prize winners in medicine Robin Warren and Barry Marshall led to a revolution in physiopathology and consequently in the treatment of peptic ulcer disease. Subsequently, H. pylori has also been linked to non-gastrointestinal diseases, such as autoimmune thrombocytopenia, acne rosacea, and Raynaud's syndrome. In addition, several studies have shown an association with cardiovascular disease and atherosclerosis. Our narrative review aims to investigate the connection between H. pylori infection, gut microbiota, and extra-gastric diseases, with a particular emphasis on atherosclerosis. We conducted an extensive search on PubMed, Google Scholar, and Scopus, using the keywords "H. pylori", "dysbiosis", "microbiota", "atherosclerosis", "cardiovascular disease" in the last ten years. Atherosclerosis is a complex condition in which the arteries thicken or harden due to plaque deposits in the inner lining of an artery and is associated with several cardiovascular diseases. Recent research has highlighted the role of the microbiota in the pathogenesis of this group of diseases. H. pylori is able to both directly influence the onset of atherosclerosis and negatively modulate the microbiota. H. pylori is an important factor in promoting atherosclerosis. Progress is being made in understanding the underlying mechanisms, which could open the way to interesting new therapeutic perspectives.

Oleanolic acid rescues critical features of umbilical vein endothelial cells permanently affected by hyperglycemia

Skin wound healing is a physiological process that involves several cell types. Among them, endothelial cells are required for inflammation resolution and neo-angiogenesis, both necessary for tissue restoration after injury. Primary human umbilical vein endothelial cells (C-HUVECs) are derived from the umbilical cord. When women develop gestational diabetes, chronic exposure to hyperglycemia induces epigenetic modifications in these cells (GD-HUVECs), leading to a permanent pro-inflammatory phenotype and impaired angiogenesis in contrast to control cells. Oleanolic acid (OA) is a bioactive triterpenoid known for its epithelial cell migration promotion stimulation and higher tensile strength of wounds. However, the potentially anti-inflammatory and pro-angiogenic properties of OA are still under investigation. We tested OA on C- and GD-HUVECs under inflammatory conditions induced by low levels of the inflammatory cytokine TNF-α. Reduced expression of adhesion molecules VCAM1, ICAM1, and SELE was obtained in OA-pre-treated C- and GD-HUVECs. Additionally, protein VCAM1 levels were also decreased by OA. Coherently, monocyte adhesion assays showed that a lower number of monocytes adhered to GD-HUVEC endothelium under OA pre-treatment when compared to untreated ones. It is noteworthy that OA improved angiogenesis parameters in both phenotypes, being especially remarkable in the case of GD-HUVECs, since OA strongly rescued their poor tube formation behavior. Moreover, endothelial cell migration was improved in C- and GD-HUVECs in scratch assays, an effect that was further confirmed by focal adhesion (FA) remodeling, revealed by paxillin staining on immunocytochemistry assays. Altogether, these results suggest that OA could be an emergent wound healing agent due to its capacity to rescue endothelial malfunction caused by hyperglycemia.

Hepatic β-arrestins: potential roles in liver health and disease

Β-arrestins are intracellular scaffolding proteins that have multifaceted roles in different types of disorders. In this review article, we gave a summary about the discovery, characterization and classification of these proteins and their intracellular functions. Moreover, this review article focused on the hepatic expression of β-arrestins and their hepatocellular distribution and function in each liver cell type. Also, we showed that β-arrestins are key regulators of distinct types of hepatic disorders. On the other hand, we addressed some important points that have never been studied before regarding the role of β-arrestins in certain types of hepatic disorders which needs more research efforts to cover.

The role of the gut microbiota and bile acids in heart failure: A review

Heart failure (HF) is the terminal manifestation of various cardiovascular diseases. Recently, accumulating evidence has demonstrated that gut microbiota are involved in the development of various cardiovascular diseases. Gut microbiota and their metabolites might play a pivotal role in the development of HF. However, previous studies have rarely described the complex role of gut microbiota and their metabolites in HF. In this review, we mainly discussed bile acids (BAs), the metabolites of gut microbiota. We explained the mechanisms by which BAs are involved in the pathogenesis of HF. We also discussed the use of gut microbiota and BAs for treating HF in Chinese medicine, highlighting the advantages of Chinese medicine in treating HF.

Deciphering the role of gut metabolites in non-alcoholic fatty liver disease

Perturbations in microbial abundance or diversity in the intestinal lumen leads to intestinal inflammation and disruption of intestinal membrane which eventually facilitates the translocation of microbial metabolites or whole microbes to the liver and other organs through portal vein. This process of translocation finally leads to multitude of health disorders. In this review, we are going to focus on the mechanisms by which gut metabolites like SCFAs, tryptophan (Trp) metabolites, bile acids (BAs), ethanol, and choline can either cause the development/progression of non-alcoholic fatty liver disease (NAFLD) or serves as a therapeutic treatment for the disease. Alterations in some metabolites like SCFAs, Trp metabolites, etc., can serve as biomarker molecules whereas presence of specific metabolites like ethanol definitely leads to disease progression. Thus, proper understanding of these mechanisms will subsequently help in designing of microbiome-based therapeutic approaches. Furthermore, we have also focussed on the role of dysbiosis on the mucosal immune system. In addition, we would also compile up the microbiome-based clinical trials which are currently undergoing for the treatment of NAFLD and non-alcoholic steatohepatitis (NASH). It has been observed that the use of microbiome-based approaches like prebiotics, probiotics, symbiotics, etc., can act as a beneficial treatment option but more research needs to be done to know how to manipulate the composition of gut microbes.

Estrogen deficiency induces bone loss through the gut microbiota

Postmenopausal osteoporosis is a common bone metabolic disease, and gut microbiota (GM) imbalance plays an important role in the development of metabolic bone disease. Here, we show that ovariectomized mice had high levels of lipopolysaccharide in serum and gut microbiota dysbiosis through increases in luminal Firmicutes:Bacteroidetes ratio. We depleted the GM through antibiotic treatment and observed improvements in bone mass, bone microstructure, and bone strength in ovariectomized mice. Conversely, transplantation of GM adapted to ovariectomy induced bone loss. However, GM depletion reversed ovariectomy-induced gene expression in the tibia and increased periosteal bone formation. Furthermore, bioinformatics analysis revealed that the G-protein-coupled bile acid receptor (TGR5) and systemic inflammatory factors play key roles in bone metabolism. Silencing TGR5 expression through small interfering RNA (siRNA) in the local tibia and knockout of TGR5 attenuated the effects of GM depletion in ovariectomized mice, confirming these findings. Thus, this study highlights the critical role of the GM in inducing bone loss in ovariectomized mice and suggests that targeting TGR5 within the GM may have therapeutic potential for postmenopausal osteoporosis.

Bear bile powder alleviates Parkinson's disease-like behavior in mice by inhibiting astrocyte-mediated neuroinflammation

Parkinson's disease (PD) is a common neurodegenerative disease in middle-aged and elderly people. In particular, increasing evidence has showed that astrocyte-mediated neuroinflammation is involved in the pathogenesis of PD. As a precious traditional Chinese medicine, bear bile powder (BBP) has a long history of use in clinical practice. It has numerous activities, such as clearing heat, calming the liver wind and anti-inflammation, and also exhibits good therapeutic effect on convulsive epilepsy. However, whether BBP can prevent the development of PD has not been elucidated. Hence, this study was designed to explore the effect and mechanism of BBP on suppressing astrocyte-mediated neuroinflammation in a mouse model of PD. PD-like behavior was induced in the mice by intraperitoneal injection of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) (30 mg·kg-1) for five days, followed by BBP (50, 100, and 200 mg·kg-1) treatment daily for ten days. LPS stimulated rat C6 astrocytic cells were used as a cell model of neuroinflammation. THe results indicated that BBP treatment significantly ameliorated dyskinesia, increased the levels of tyrosine hydroxylase (TH) and inhibited astrocyte hyperactivation in the substantia nigra (SN) of PD mice. Furthermore, BBP decreased the protein levels of glial fibrillary acidic protein (GFAP), cyclooxygenase 2 (COX2) and inducible nitric oxide synthase (iNOS), and up-regulated the protein levels of takeda G protein-coupled receptor 5 (TGR5) in the SN. Moreover, BBP significantly activated TGR5 in a dose-dependent manner, and decreased the protein levels of GFAP, iNOS and COX2, as well as the mRNA levels of GFAP, iNOS, COX2, interleukin (IL) -1β, IL-6 and tumor necrosis factor-α (TNF-α) in LPS-stimulated C6 cells. Notably, BBP suppressed the phosphorylation of protein kinase B (AKT), inhibitor of NF-κB (IκBα) and nuclear factor-κB (NF-κB) proteins in vivo and in vitro. We also observed that TGR5 inhibitor triamterene attenuated the anti-neuroinflammatory effect of BBP on LPS-stimulated C6 cells. Taken together, BBP alleviates the progression of PD mice by suppressing astrocyte-mediated inflammation via TGR5.

Altered bile acid metabolism in skin tissues in response to ionizing radiation: deoxycholic acid (DCA) as a novel treatment for radiogenic skin injury

OBJECTIVE

Radiogenic skin injury (RSI) is a common complication during cancer radiotherapy or accidental exposure to radiation. The aim of this study is to investigate the metabolism of bile acids (BAs) and their derivatives during RSI.

METHODS

Rat skin tissues were irradiated by an X-ray linear accelerator. The quantification of BAs and their derivatives were performed by liquid chromatography-mass spectrometry (LC-MS)-based quantitative analysis. Key enzymes in BA biosynthesis were analyzed from single-cell RNA sequencing (scRNA-Seq) data of RSI in the human patient and animal models. The in vivo radioprotective effect of deoxycholic acid (DCA) was detected in irradiated SD rats.

RESULTS

Twelve BA metabolites showed significant differences during the progression of RSI. Among them, the levels of cholic acid (CA), DCA, muricholic acid (MCA), chenodeoxycholic acid (CDCA), glycocholic acid (GCA), glycohyodeoxycholic acid (GHCA), 12-ketolithocholic acid (12-ketoLCA) and ursodeoxycholic acid (UDCA) were significantly elevated in irradiated skin, whereas lithocholic acid (LCA), tauro-β-muricholic acid (Tβ-MCA) and taurocholic acid (TCA) were significantly decreased. Additionally, the results of scRNA-Seq indicated that genes involved in 7a-hydroxylation process, the first step in BA synthesis, showed pronounced alterations in skin fibroblasts or keratinocytes. The alternative pathway of BA synthesis is more actively altered than the classical pathway after ionizing radiation. In the model of rat radiogenic skin damage, DCA promoted wound healing and attenuated epidermal hyperplasia.

CONCLUSIONS

Ionizing radiation modulates the metabolism of BAs. DCA is a prospective therapeutic agent for the treatment of RSI.

Integration of plasma and CSF metabolomics with CSF proteomic reveals novel associations between lipid mediators and central nervous system vascular and energy metabolism

Integration of the omics data, including metabolomics and proteomics, provides a unique opportunity to search for new associations within metabolic disorders, including Alzheimer's disease. Using metabolomics, we have previously profiled oxylipins, endocannabinoids, bile acids, and steroids in 293 CSF and 202 matched plasma samples from AD cases and healthy controls and identified both central and peripheral markers of AD pathology within inflammation-regulating cytochrome p450/soluble epoxide hydrolase pathway. Additionally, using proteomics, we have identified five cerebrospinal fluid protein panels, involved in the regulation of energy metabolism, vasculature, myelin/oligodendrocyte, glia/inflammation, and synapses/neurons, affected in AD, and reflective of AD-related changes in the brain. In the current manuscript, using metabolomics-proteomics data integration, we describe new associations between peripheral and central lipid mediators, with the above-described CSF protein panels. Particularly strong associations were observed between cytochrome p450/soluble epoxide hydrolase metabolites, bile acids, and proteins involved in glycolysis, blood coagulation, and vascular inflammation and the regulators of extracellular matrix. Those metabolic associations were not observed at the gene-co-expression level in the central nervous system. In summary, this manuscript provides new information regarding Alzheimer's disease, linking both central and peripheral metabolism, and illustrates the necessity for the "omics" data integration to uncover associations beyond gene co-expression.

Bile acid-activated receptors in innate and adaptive immunity: targeted drugs and biological agents

Bile acid-activated receptors (BARs) such as a G-protein bile acid receptor 1 and the farnesol X receptor are activated by bile acids (BAs) and have been implicated in the regulation of microbiota-host immunity in the intestine. The mechanistic roles of these receptors in immune signaling suggest that they may also influence the development of metabolic disorders. In this perspective, we provide a summary of recent literature describing the main regulatory pathways and mechanisms of BARs and how they affect both innate and adaptive immune system, cell proliferation, and signaling in the context of inflammatory diseases. We also discuss new approaches for therapy and summarize clinical projects on BAs for the treatment of diseases. In parallel, some drugs that are classically used for other therapeutic purposes and BAR activity have recently been proposed as regulators of immune cells phenotype. Another strategy consists of using specific strains of gut bacteria to regulate BA production in the intestine.

Revisited role of the placenta in bile acid homeostasis

To date, the discussion concerning bile acids (BAs) during gestation is almost exclusively linked to pregnancy complications such as intrahepatic cholestasis of pregnancy (ICP) when maternal serum BA levels reach very high concentrations (>100 μM). Generally, the placenta is believed to serve as a protective barrier avoiding exposure of the growing fetus to excessive amounts of maternal BAs that might cause detrimental effects (e.g., intrauterine growth restriction and/or increased vulnerability to metabolic diseases). However, little is known about the precise role of the placenta in BA biosynthesis, transport, and metabolism in healthy pregnancies when serum BAs are at physiological levels (i.e., low maternal and high fetal BA concentrations). It is well known that primary BAs are synthesized from cholesterol in the liver and are later modified to secondary BA species by colonic bacteria. Besides the liver, BA synthesis in extrahepatic sites such as the brain elicits neuroprotective actions through inhibition of apoptosis as well as oxidative and endoplasmic reticulum stress. Even though historically BAs were thought to be only "detergent molecules" required for intestinal absorption of dietary fats, they are nowadays acknowledged as full signaling molecules. They modulate a myriad of signaling pathways with functional consequences on essential processes such as gluconeogenesis -one of the principal energy sources of the fetus- and cellular proliferation. The current manuscript discusses the potential multipotent roles of physiologically circulating BAs on developmental processes during gestation and provides a novel perspective in terms of the importance of the placenta as a previously unknown source of BAs. Since the principle "not too much, not too little" applicable to other signaling molecules may be also true for BAs, the risks associated with fetal exposure to excessive levels of BAs are discussed.

Gut microbiota Turicibacter strains differentially modify bile acids and host lipids

Bacteria from the Turicibacter genus are prominent members of the mammalian gut microbiota and correlate with alterations in dietary fat and body weight, but the specific connections between these symbionts and host physiology are poorly understood. To address this knowledge gap, we characterize a diverse set of mouse- and human-derived Turicibacter isolates, and find they group into clades that differ in their transformations of specific bile acids. We identify Turicibacter bile salt hydrolases that confer strain-specific differences in bile deconjugation. Using male and female gnotobiotic mice, we find colonization with individual Turicibacter strains leads to changes in host bile acid profiles, generally aligning with those produced in vitro. Further, colonizing mice with another bacterium exogenously expressing bile-modifying genes from Turicibacter strains decreases serum cholesterol, triglycerides, and adipose tissue mass. This identifies genes that enable Turicibacter strains to modify host bile acids and lipid metabolism, and positions Turicibacter bacteria as modulators of host fat biology.

Bile acid-mediated signaling in cholestatic liver diseases

Chronic cholestatic liver diseases, such as primary biliary cholangitis (PBC) and primary sclerosing cholangitis (PSC), are associated with bile stasis and gradually progress to fibrosis, cirrhosis, and liver failure, which requires liver transplantation. Although ursodeoxycholic acid is effective in slowing the disease progression of PBC, it has limited efficacy in PSC patients. It is challenging to develop effective therapeutic agents due to the limited understanding of disease pathogenesis. During the last decade, numerous studies have demonstrated that disruption of bile acid (BA) metabolism and intrahepatic circulation promotes the progression of cholestatic liver diseases. BAs not only play an essential role in nutrition absorption as detergents but also play an important role in regulating hepatic metabolism and modulating immune responses as key signaling molecules. Several excellent papers have recently reviewed the role of BAs in metabolic liver diseases. This review focuses on BA-mediated signaling in cholestatic liver disease.

Unraveling the Crosstalk between Lipids and NADPH Oxidases in Diabetic Kidney Disease

Diabetic kidney disease (DKD) is a serious complication of diabetes mellitus and a leading cause of end-stage renal disease. Abnormal lipid metabolism and intrarenal accumulation of lipids have been shown to be strongly correlated with the development and progression of diabetic kidney disease (DKD). Cholesterol, phospholipids, triglycerides, fatty acids, and sphingolipids are among the lipids that are altered in DKD, and their renal accumulation has been linked to the pathogenesis of the disease. In addition, NADPH oxidase-induced production of reactive oxygen species (ROS) plays a critical role in the development of DKD. Several types of lipids have been found to be tightly linked to NADPH oxidase-induced ROS production. This review aims to explore the interplay between lipids and NADPH oxidases in order to provide new insights into the pathogenesis of DKD and identify more effective targeted therapies for the disease.

Characterization of Two Parabacteroides distasonis Candidate Strains as New Live Biotherapeutics against Obesity

The gut microbiota is now considered as a key player in the development of metabolic dysfunction. Therefore, targeting gut microbiota dysbiosis has emerged as a new therapeutic strategy, notably through the use of live gut microbiota-derived biotherapeutics. We previously highlighted the anti-inflammatory abilities of two Parabacteroides distasonis strains. We herein evaluate their potential anti-obesity abilities and show that the two strains induced the secretion of the incretin glucagon-like peptide 1 in vitro and limited weight gain and adiposity in obese mice. These beneficial effects are associated with reduced inflammation in adipose tissue and the improvement of lipid and bile acid metabolism markers. P. distasonis supplementation also modified the Actinomycetota, Bacillota and Bacteroidota taxa of the mice gut microbiota. These results provide better insight into the capacity of P. distasonis to positively influence host metabolism and to be used as novel source of live biotherapeutics in the treatment and prevention of metabolic-related diseases.

Taurochenodeoxycholic acid reduces astrocytic neuroinflammation and alleviates experimental autoimmune encephalomyelitis in mice

OBJECTIVE

Multiple sclerosis (MS) is an immune regulatory disease that affects the central nervous system (CNS). The main pathological features include demyelination and neurodegeneration, and the pathogenesis is associated with astrocytic neuroinflammation. Taurochenodeoxycholic acid (TCDCA) is one of the conjugated bile acids in animal bile, and it is not clear whether TCDCA could improve MS by inhibiting the activation of astrocytes. This study was aimed to evaluate the effects of TCDCA on experimental autoimmune encephalomyelitis (EAE)-a classical animal model of MS, and to probe its mechanism from the aspect of suppressing astrocytic neuroinflammation. It is expected to prompt the potential application of TCDCA for the treatment of MS.

RESULTS

TCDCA effectively alleviated the progression of EAE and improved the impaired neurobehavior in mice. It mitigated the hyperactivation of astrocytes and down-regulated the mRNA expression levels of inducible nitric oxide synthase (iNOS), cyclooxygenase 2 (COX2), tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β) and IL-6 in the brain cortex. In the C6 astrocytic cell line induced by lipopolysaccharide (LPS), TCDCA treatment dose-dependently decreased the production of NO and the protein expression of iNOS and glial fibrillary acidic protein (GFAP). TCDCA consistently inhibited the mRNA expressions of COX2, iNOS and other inflammatory mediators. Furthermore, TCDCA decreased the protein expression of phosphorylated serine/threonine kinase (AKT), inhibitor of NFκB α (IκBα) and nuclear factor κB (NFκB). And TCDCA also inhibited the nuclear translocation of NFκB. Conversely, as an inhibitor of the G-protein coupled bile acid receptor Gpbar1 (TGR5), triamterene eliminated the effects of TCDCA in LPS-stimulated C6 cells.

CONCLUSION

TCDCA improves the progress of EAE by inhibiting the astrocytic neuroinflammation, which might be exerted by the regulation of TGR5 mediated AKT/NFκB signaling pathway. These findings may prompt the potential application of TCDCA for MS therapy by suppressing astrocyte inflammation.

The TGR5 Agonist INT-777 Promotes Peripheral Nerve Regeneration by Activating cAMP-dependent Protein Kinase A in Schwann Cells

Schwann cell (SC) myelination is a pivotal event in the normal physiological functioning of the peripheral nervous system (PNS), where myelination is finely controlled by a series of factors within SCs to ensure timely onset and correct myelin thickness for saltatory conduction. Among these, cyclic AMP (cAMP) is a promising factor for driving myelin gene expression in SCs. It has been shown that TGR5 activation is often associated with increased production of cAMP. Therefore, we speculated that the G-protein-coupled receptor (TGR5) might be involved in the PNS myelination. To test this hypothesis, sciatic nerve crush-injured mice were treated with INT-777, a specific agonist of TGR5, which significantly improved remyelination and functional recovery. Furthermore, rats that underwent sciatic nerve transection were treated with INT-777, which also promoted nerve regeneration and functional recovery. In primary SCs, the stimulatory effect of INT-777 on myelin gene expression was largely counteracted by H89, a potent inhibitor of cAMP-dependent protein kinase A (PKA). Additionally, INT-777 stimulated cell migration was blunted in the presence of H89. Overall, these data indicate that INT-777 is capable of promoting peripheral nerve regeneration and functional recovery after injury, and these benefits are likely due to the activation of the TGR5/cAMP/PKA axis. As such, INT-777, together with other TGR5 agonists, may hold great therapeutic potential for treating peripheral nerve injury.

The discovery of 12β-methyl-17-epi-18-nor-bile acids as potent and selective TGR5 agonists

Recent discoveries have demonstrated that the physiological function of bile acids extends to the regulation of diverse signaling processes through interactions with nuclear and G protein-coupled receptors, most notably the Farnesoid-X nuclear receptor (FXR) and the G protein-coupled bile acid receptor 1 (GPBAR1, also known as TGR5). Targeting such signaling pathways pharmacologically, i.e. with bile acid-derived therapeutics, presents great potential for the treatment of various metabolic, inflammatory immune, liver, and neurodegenerative diseases. Here we report the discovery of two potent and selective TGR5 agonists (NZP196 and 917). These compounds are the taurine conjugates of 6α-ethyl-substituted 12β-methyl-18-nor-bile acids with the side chain being located on the α-face of the steroid scaffold. The compounds emerged from a screening effort of a diverse library of 12β-methyl-18-nor-bile acids that were synthesized from 12β-methyl-18-nor-chenodeoxycholic acid and its C17-epimer. Upon testing for FXR activity, both compounds were found to be inactive, thus revealing selectivity for TGR5.

Tauroursodeoxycholic Acid Alleviates Endoplasmic Reticulum Stress-Mediated Visual Deficits in Diabetic tie2-TNF Transgenic Mice via TGR5 Signaling

Purpose: This study evaluated if tauroursodeoxycholic acid (TUDCA) alleviates pro-inflammatory and endoplasmic reticulum (ER) stress-mediated visual deficits in diabetic tie2-TNF transgenic mice via Takeda G protein-coupled receptor 5 (TGR5) receptor signaling. Methods: Adult tie2-TNF transgenic or age-matched C57BL/6J (wildtype, WT) mice were made diabetic and treated subcutaneously with TUDCA. After 4 weeks, visual function, vascular permeability, immunohistology, and molecular analyses were assessed. Human retinal endothelial cells (HRECs) silenced for TGR5, followed by TNF and high glucose (HG) stress-mediated endothelial permeability, and transendothelial migration of activated leukocytes were assessed with TUDCA in vitro. Results: Compared with WT mice, tie2-TNF mice showed a decreased visual function correlated with a decrease in protein kinase C α (PKCα) in rod bipolar cells, and increased vascular permeability was further exacerbated in diabetic-tie2-TNF mice. Conversely, TUDCA alleviated these changes in diabetic mice. An increase in inflammation and ER stress in retina coincided with an increase in TGR5 expression in diabetic tie2-TNF mice that decreased with TUDCA. In vitro, HRECs exposed to TNF+HG demonstrated >2-fold increase in TGR5 expression, a 3-fold increase in leukocyte transmigration with a concomitant increase in permeability. Although TUDCA reversed these effects, HRECs silenced for TGR5 and challenged with TUDCA or TGR5 agonist failed to reverse the TNF+HG induced effects. Conclusions: Our data suggest that TUDCA will serve as an excellent therapeutic agent for diabetic complications addressing both vascular and neurodegenerative changes in the retina. Perturbation of the TGR5 receptor in the retina might play a role in linking retinal ER stress to neurovascular dysfunction in diabetic retinopathy.

Hepatocytic AP-1 and STAT3 contribute to chemotaxis in alphanaphthylisothiocyanate-induced cholestatic liver injury

The development of cholestatic liver injury (CLI) involves inflammation, but the dominant pathway mediating the chemotaxis is not yet established. This work explored key signaling pathway mediating chemotaxis in CLI and the role of Kupffer cells in the inflammatory liver injury. Probe inhibitors T-5224 (100 mg/kg) for AP-1 and C188-9 (100 mg/kg) for STAT3 were used to validate key inflammatory pathways in alpha-naphthylisothiocyanate (ANIT, 100 mg/kg)-induced CLI. Two doses of GdCl₃ (10 mg/kg and 40 mg/kg) were used to delete Kupffer cells and explore their role in CLI. Serum and liver samples were collected for biochemical and mechanism analysis. The liver injury in ANIT-treated mice were significantly increased supported by biochemical and histopathological changes, and neutrophils gathering around the necrotic loci. Inhibitor treatments down-regulated liver injury biomarkers except the level of total bile acid. The chemokine Ccl2 increased by 170-fold and to a less degree Cxcl2 by 45-fold after the ANIT treatment. p-c-Jun and p-STAT3 were activated in the group A but inhibited by the inhibitors in western blot analysis. The immunofluorescence results showed AP-1 not STAT3 responded to inhibitors in ANIT-induced CLI. With or without GdCl₃, there was no significant difference in liver injury among the CLI groups. In necrotic loci in CLI, CXCL2 colocalized with hepatocyte biomarker Albumin, not with the F4/80 in Kupffer cells. Conclusively, AP-1 played a more critical role in the inflammation cascade than STAT3 in ANIT-induced CLI. Hepatocytes, not the Kupffer cells released chemotactic factors mediating the chemotaxis in CLI.

G protein-coupled bile acid receptor 1 reduced hepatic immune response and inhibited NFκB, PI3K/AKT, and PKC/P38 MAPK signaling pathway in hybrid grouper

The mammalian G protein-coupled bile acid receptor 1 (TGR5) is involved in the inflammatory response. However, the functions of TGR5 in the immune response of fish remain unclear. In this study, the full-length sequence of tgr5 from hybrid grouper (Epinephelus fuscoguttatus ♀ × E. lanceolatus ♂) was cloned, and the function of TGR5 in the immune response was explored. The results showed that the ORF of tgr5 gene in hybrid grouper was 1029 bp and encoded 342 amino acids. Activation of TGR5 by INT-777 significantly decreased the activities and mRNA expression of TNFα and IL1β, whereas inhibition of TGR5 by SBI-115 showed the opposite effect. SBI-115 treatment significantly increased the expression of phosphorylated inhibitor κB α (p-IKBα) protein. After the INT-777 treatment, the concentration of protein kinase C (PKC) and expression of the p38 mitogen-activated protein kinases (p38a), p38b and p38c, were significantly decreased in vivo. INT-777 agonist significantly decreased the expression of phosphorylated phosphoinositide 3-kinase (p-PI3K) protein and the ratio of phosphorylated and nonphosphorylated serine/threonine-protein kinase (p-AKT/AKT). In conclusion, activation of hepatic TGR5 inhibited the PKC/P38 MAPK, PI3K/AKT, NFκB signaling pathway and improved hepatic immune responses of hybrid grouper in vivo and in vitro.

Intrauterine growth retardation affects liver bile acid metabolism in growing pigs: effects associated with the changes of colonic bile acid derivatives

BACKGROUND

Intrauterine growth retardation (IUGR) is associated with severely impaired nutrient metabolism and intestinal development of pigs. Our previous study found that IUGR altered intestinal microbiota and metabolites in the colon. However, the consequences of IUGR on bile acid metabolism in pigs remained unclear. The present study aimed to investigate the bile acid metabolism in the liver and the profile of bile acid derivatives in the colon of growing pigs with IUGR using bile acid targeted metabolomics. Furthermore, we determined correlations between colonic microbiota composition and metabolites of IUGR and normal birth weight (NBW) pigs at different growth stages that were 7, 21, and 28-day-old, and the average body weight (BW) of 25, 50, and 100 kg of the NBW pigs.

RESULTS

The results showed that the plasma total bile acid concentration was higher (P < 0.05) at the 25 kg BW stage and tended to increase (P = 0.08) at 28-day-old in IUGR pigs. The hepatic gene expressions related to bile acid synthesis (CYP7A1, CYP27A1, and NTCP) were up-regulated (P < 0.05), and the genes related to glucose and lipid metabolism (ATGL, HSL, and PC) were down-regulated (P < 0.05) at the 25 kg BW stage in IUGR pigs when compared with the NBW group. Targeted metabolomics analysis showed that 29 bile acids and related compounds were detected in the colon of pigs. The colonic concentrations of dehydrolithocholic acid and apocholic acid were increased (P < 0.05), while isodeoxycholic acid and 6,7-diketolithocholic acid were decreased (P < 0.05) in IUGR pigs, when compared with the NBW pigs at the 25 kg BW stage. Moreover, Spearman's correlation analysis revealed that colonic Unclassified_[Mogibacteriaceae], Lachnospira, and Slackia abundances were negatively correlated (P < 0.05) with dehydrolithocholic acid, as well as the Unclassified_Clostridiaceae abundance with 6,7-diketolithocholic acid at the 25 kg BW stage.

CONCLUSIONS

These findings suggest that IUGR could affect bile acid and glucolipid metabolism in growing pigs, especially at the 25 kg BW stage, these effects being paralleled by a modification of bile acid derivatives concentrations in the colonic content. The plausible links between these modified parameters are discussed.

The altered lipidome of hepatocellular carcinoma

Alterations in metabolic pathways are a hallmark of cancer. A deeper understanding of the contribution of different metabolites to carcinogenesis is thus vitally important to elucidate mechanisms of tumor initiation and progression to inform therapeutic strategies. Hepatocellular carcinoma (HCC) is a leading cause of cancer-related death worldwide and its altered metabolic landscape is beginning to unfold with the advancement of technologies. In particular, characterization of the lipidome of human HCCs has accelerated, and together with biochemical analyses, are revealing recurrent patterns of alterations in glycerophospholipid, sphingolipid, cholesterol and bile acid metabolism. These widespread alterations encompass a myriad of lipid species with numerous roles affecting multiple hallmarks of cancer, including aberrant growth signaling, metastasis, evasion of cell death and immunosuppression. In this review, we summarize the current trends and findings of the altered lipidomic landscape of HCC and discuss their potential biological significance for hepatocarcinogenesis.

Bile Acid and Gut Microbiota in Irritable Bowel Syndrome

Gut microbiota and their metabolites like bile acid (BA) have been investigated as causes of irritable bowel syndrome (IBS) symptoms. Primary BAs are synthesized and conjugated in the liver and released into the duodenum. BA biotransformation by gut microbiota begins in the intestine and results in production of a broad range of secondary BAs. Deconjugation is considered the gateway reaction for further modification and is mediated by bile salt hydrolase, which is widely expressed by the gut microbiota. However, gut bacteria that convert primary BAs to secondary BAs belong to a limited number of species, mainly Clostridiales. Like gut microbiota modify BA profile, BAs can shape gut microbiota via direct and indirect actions. BAs have prosecretory effects and regulates gut motility. BAs can also affect gut sensitivity. Because of the vital role of the gut microbiota and BAs in gut function, their bidirectional relationship may contribute to the pathophysiology of IBS. Individuals with IBS have been reported to have altered microbial profiles and modified BA profiles. A significant increase in fecal primary BA and a corresponding decrease in secondary BA have been observed in IBS with predominant diarrhea. In addition, primary BA was positively correlated with IBS symptoms. In IBS with predominant diarrhea, bacteria with reduced abundance mainly belonged to the genera in Ruminococcaceae and exhibited a negative correlation with primary BAs. Integrating the analysis of the gut microbiota and BAs could better understanding of IBS pathophysiology. The gap in this field needs to be further filled in the future.

The role of TGR5 as an onco-immunological biomarker in tumor staging and prognosis by encompassing the tumor microenvironment

The relationship between G protein–coupled bile acid receptor 1 (TGR5, GPBAR1) and, specifically, cancer has been studied in in vivo and in vitro experiments, but there is still a lack of pan-cancer analysis to understand the prognostic significance and functioning mechanism of TGR5 in different cancer-driving oncogenic processes. Here, we used Gene Expression Integration, Human Protein Atlas, and The Cancer Genome Atlas (TCGA) to perform a pan-cancer analysis of the role of TGR5 in all 33 tumors. In all TCGA tumors, the TGR5 gene expression has been assessed, and we found that the high TGR5 gene expression in most cancers is associated with poor prognosis of overall survival for cancers such as glioblastoma multiforme (p = 0.0048), kidney renal papillary cell carcinoma (p = 0.033), lower grade glioma (p = 0.0028), thymoma (p = 0.048), and uveal melanoma (p = 0.004), and then the lower expression of TGR5 was linked with poor prognosis in cervical squamous cell carcinoma and endocervical adenocarcinoma (p = 0.014), malignant mesothelioma (MESO) (p = 0.048), sarcoma (p = 0.018), and skin cutaneous melanoma (p = 0.0085). The TGR5 expression was linked with the immune infiltration level of the macrophage M2_TIDE and was also associated with DNA methylation in ovarian and breast cancers. The regulation of hormone secretion, Rap1 pathway, osteoclast differentiation, and bile acid pathway was involved in the functional mechanism of TGR5. Besides, gene expressions were different in different tumors detected by RT-PCR, and cell activity experiments have also found that TGR5 can increase the activity of renal cell carcinoma and reduce the activity of skin cancer and osteosarcoma cells. In this investigation, the aim was to assess the comprehensive overview of the oncogenic roles of TGR5 in all TCGA tumors using pan-analysis.

Deoxycholic acid induces gastric intestinal metaplasia by activating STAT3 signaling and disturbing gastric bile acids metabolism and microbiota

Intestinal metaplasia (IM) is the inevitable precancerous stage to develop intestinal-type gastric cancer (GC). Deoxycholic acid (DCA) is the main bile acid (BA) component of duodenogastric reflux and has shown an increased concentration during the transition from chronic gastritis to IM associated with continued STAT3 activation. However, the mechanisms underlying how DCA facilitates IM in the gastric epithelium need exploration. We evaluated IM and bile reflux in corpus tissues from 161 subjects undergoing GC screening. Cell survival and proliferation, proinflammatory cytokine expression and TGR5/STAT3/KLF5 axis activity were measured in normal human gastric cells, cancer cells, and organoid lines derived from C57BL/6, FVB/N and insulin-gastrin (INS-GAS) mice treated with DCA. The effects of DCA on IM development were determined in INS-GAS mice with long-term DCA supplementation, after which the gastric bacterial and BA metabolic profiles were measured by 16S rRNA gene sequencing and LC-MS. We revealed a BA-triggered TGR5/STAT3/KLF5 pathway in human gastric IM tissues. In gastric epithelial cells, DCA promoted proliferation and apoptotic resistance, upregulated proinflammatory cytokines and IM markers, and facilitated STAT3 phosphorylation, nuclear accumulation and DNA binding to the KLF5 promoter. DCA triggered STAT3 signaling and the downstream IM marker KLF5 in mouse gastric organoids in vitro and in vivo. In INS-GAS mice, DCA promoted the accumulation of serum total BAs and accelerated the stepwise development of gastric IM and dysplasia. DCA induced gastric environmental alterations involving abnormal BA metabolism and microbial dysbiosis, in which the Gemmobacter and Lactobacillus genera were specifically enriched. Lactobacillus genus enrichment was positively correlated with increased levels of GCA, CA, T-α-MCA, TCA and β-MCA in DCA-administrated INS-GAS mice. DCA promotes nuclear STAT3 phosphorylation, which mediates KLF5 upregulation associated with gastric inflammation and IM development. DCA disturbs the gastric microbiome and BA metabolism homeostasis during IM induction.

Bacillus Subtilis Promotes the Release of 5-HT to Regulate Intestinal Peristalsis in STC Mice via Bile Acid and Its Receptor TGR5 Pathway

BACKGROUND

Slow transit constipation (STC) is caused by intestinal peristalsis dysfunction and is closely associated with disturbance of the intestinal microecological balance. Bacillus subtilis plays a positive role in the treatment of STC, but its mechanism needs to be further explored.

AIMS

The purpose of the present study was to explore the effects and mechanism of B. subtilis on the pathophysiology of STC.

METHODS

A STC mouse model was established with compound diphenoxylate, following which B. subtilis was used to treat STC. The effects and possible mechanism of B. subtilis on STC were investigated by assessing intestinal motility, histology of the colon, release of 5-HT in enterochromaffin cells (ECs) and the TGR5/TRPA1 pathway. Moreover, LC-MS targeted metabolomics was used to analyze the regulation of Bacillus subtilis on bile acid metabolisms in STC mice.

RESULTS

Bacillus subtilis significantly increased 24 h defecations, fecal moisture and intestinal transport rate of STC mice, improved pathological damage of the colon and showed protective effects on the intestinal tract. The release of 5-HT from ECs and the bile acid receptor TGR5/TRPA1 pathway were significantly increased in STC mice treated with B. subtilis. In addition, the metabolomics results showed that the bile acid contents of STC mice were significantly decreased, and B. subtilis could increase the bile acid composition and content of STC mice.

CONCLUSION

Bacillus subtilis regulates intestinal peristalsis of STC by promoting the release of 5-HT from ECs through bile acid metabolism and its receptor TGR5 pathway and plays a positive role in the treatment of STC.

The Bile Acid Membrane Receptor TGR5 in Cancer: Friend or Foe?

The G-protein-coupled bile acid receptor, Gpbar1 or TGR5, is characterized as a membrane receptor specifically activated by bile acids. A series of evidence shows that TGR5 induces protein kinase B (AKT), nuclear factor kappa-B (NF-κB), extracellular regulated protein kinases (ERK1/2), signal transducer and activator of transcription 3 (STAT3), cyclic adenosine monophosphate (cAMP), Ras homolog family member A (RhoA), exchange protein activated by cAMP (Epac), and transient receptor potential ankyrin subtype 1 protein (TRPA1) signaling pathways, thereby regulating proliferation, inflammation, adhesion, migration, insulin release, muscle relaxation, and cancer development. TGR5 is widely distributed in the brain, lung, heart, liver, spleen, pancreas, kidney, stomach, jejunum, ileum, colon, brown adipose tissue (BAT), white adipose tissue (WAT), and skeletal muscle. Several recent studies have demonstrated that TGR5 exerts inconsistent effects in different cancer cells upon activating via TGR5 agonists, such as INT-777, ursodeoxycholic acid (UDCA), and taurolithocholic acid (TLCA). In this review, we discuss both the ‘friend’ and ‘foe’ features of TGR5 by summarizing its tumor-suppressing and oncogenic functions and mechanisms.

Versatile Triad Alliance: Bile Acid, Taurine and Microbiota

Taurine is the most abundant free amino acid in the body, and is mainly derived from the diet, but can also be produced endogenously from cysteine. It plays multiple essential roles in the body, including development, energy production, osmoregulation, prevention of oxidative stress, and inflammation. Taurine is also crucial as a molecule used to conjugate bile acids (BAs). In the gastrointestinal tract, BAs deconjugation by enteric bacteria results in high levels of unconjugated BAs and free taurine. Depending on conjugation status and other bacterial modifications, BAs constitute a pool of related but highly diverse molecules, each with different properties concerning solubility and toxicity, capacity to activate or inhibit receptors of BAs, and direct and indirect impact on microbiota and the host, whereas free taurine has a largely protective impact on the host, serves as a source of energy for microbiota, regulates bacterial colonization and defends from pathogens. Several remarkable examples of the interaction between taurine and gut microbiota have recently been described. This review will introduce the necessary background information and lay out the latest discoveries in the interaction of the co-reliant triad of BAs, taurine, and microbiota.

New Insights into Bile Acids Related Signaling Pathways in the Onset of Colorectal Cancer

Colorectal cancer (CRC) ranks as the second among the causes of tumor death worldwide, with an estimation of 1.9 million new cases in 2020 and more than 900,000 deaths. This rate might increase by 60% over the next 10 years. These data are unacceptable considering that CRC could be successfully treated if diagnosed in the early stages. A high-fat diet promotes the hepatic synthesis of bile acids (BAs) increasing their delivery to the colonic lumen and numerous scientific reports correlate BAs, especially secondary BAs, with CRC incidence. We reviewed the physicochemical and biological characteristics of BAs, focusing on the major pathways involved in CRC risk and progression. We specifically pointed out the role of BAs as signaling molecules and the tangled relationships among their nuclear and membrane receptors with the big bang of molecular and cellular events that trigger CRC occurrence.

Bile acids and their receptors: modulators and therapeutic targets in liver inflammation

Bile acids participate in the intestinal emulsion, digestion, and absorption of lipids and fat-soluble vitamins. When present in high concentrations, as in cholestatic liver diseases, bile acids can damage cells and cause inflammation. After the discovery of bile acids receptors about two decades ago, bile acids are considered signaling molecules. Besides regulating bile acid, xenobiotic, and nutrient metabolism, bile acids and their receptors have shown immunomodulatory properties and have been proposed as therapeutic targets for inflammatory diseases of the liver. This review focuses on bile acid-related signaling pathways that affect inflammation in the liver and provides an overview of the preclinical and clinical applications of modulators of these pathways for the treatment of cholestatic and autoimmune liver diseases.

Tauroursodeoxycholic Acid Reduces Neuroinflammation but Does Not Support Long Term Functional Recovery of Rats with Spinal Cord Injury

The bile acid tauroursodeoxycholic acid (TUDCA) reduces cell death under oxidative stress and inflammation. Implants of bone marrow-derived stromal cells (bmSC) are currently under investigation in clinical trials of spinal cord injury (SCI). Since cell death of injected bmSC limits the efficacy of this treatment, the cytoprotective effect of TUDCA may enhance its benefit. We therefore studied the therapeutic effect of TUDCA and its use as a combinatorial treatment with human bmSC in a rat model of SCI. A spinal cord contusion injury was induced at thoracic level T9. Treatment consisted of i.p. injections of TUDCA alone or in combination with one injection of human bmSC into the cisterna magna. The recovery of motor functions was assessed during a surveillance period of six weeks. Biochemical and histological analysis of spinal cord tissue confirmed the anti-inflammatory activity of TUDCA. Treatment improved the recovery of autonomic bladder control and had a positive effect on motor functions in the subacute phase, however, benefits were only transient, such that no significant differences between vehicle and TUDCA-treated animals were observed 1–6 weeks after the lesion. Combinatorial treatment with TUDCA and bmSC failed to have an additional effect compared to treatment with bmSC only. Our data do not support the use of TUDCA as a treatment of SCI.

Human Cholangiocytes Form a Polarized and Functional Bile Duct on Hollow Fiber Membranes

Liver diseases affect hundreds of millions of people worldwide; most often the hepatocytes or cholangiocytes are damaged. Diseases of the biliary tract cause severe patient burden, and cholangiocytes, the cells lining the biliary tract, are sensitive to numerous drugs. Therefore, investigations into proper cholangiocyte functions are of utmost importance, which is restricted, in vitro, by the lack of primary human cholangiocytes allowing such screening. To investigate biliary function, including transepithelial transport, cholangiocytes must be cultured as three-dimensional (3D) ductular structures. We previously established murine intrahepatic cholangiocyte organoid-derived cholangiocyte-like cells (CLCs) and cultured them onto polyethersulfone hollow fiber membranes (HFMs) to generate 3D duct structures that resemble native bile ducts at the structural and functional level. Here, we established an efficient, stepwise method for directed differentiation of human intrahepatic cholangiocyte organoids (ICOs) into CLCs. Human ICO-derived CLCs showed key characteristics of cholangiocytes, such as the expression of structural and functional markers, formation of primary cilia, and P-glycoprotein-mediated transport in a polarized fashion. The organoid cultures exhibit farnesoid X receptor (FXR)-dependent functions that are vital to liver bile acid homeostasis in vivo. Furthermore, human ICO-derived CLCs cultured on HFMs in a differentiation medium form tubular architecture with some tight, confluent, and polarized monolayers that better mimic native bile duct characteristics than differentiated cultures in standard 2D or Matrigel-based 3D culture plates. Together, our optimized differentiation protocol to obtain CLC organoids, when applied on HFMs to form bioengineered bile ducts, will facilitate studying cholangiopathies and allow developing therapeutic strategies.

Inflammatory-Dependent Bidirectional Effect of Bile Acids on NLRP3 Inflammasome and Its Role in Ameliorating CPT-11-Induced Colitis

Irinotecan (CPT-11) in combination with 5-fluorouracil and leucovorin is a first-line chemotherapy regimen for the treatment of colorectal cancer; however, its clinical application is limited by the dose-limiting gastrointestinal toxicity of colitis. In our previous studies, several bile acids (BAs) were found significantly elevated in the colon of the CPT-11-induced rat colitis model. On the other hand, NLRP3 inflammasome has been reported to play important roles in mediating colitis. Interestingly, BA was stated to activate the NLRP3 inflammasome in some studies, while in some other reports, it showed an inhibitory effect. We assumed that the inflammatory status in different circumstances might have contributed to the controversial findings. In this study, we first discovered, under non-inflammatory conditions, that supplementing BA could activate the NLRP3 inflammasome in THP-1-differentiated macrophages and promote inflammation. In lipopolysaccharide (LPS)-induced inflammatory macrophages, however, BA inhibited the NLRP3 inflammasome and reduced inflammation. Further experiments demonstrated that Takeda G protein-coupled receptor 5 (TGR5) is essential in mediating the inhibitory effect of BA, while phospho-SP1 (p-SP1) is key to the activation. Furthermore, we applied the above findings to ameliorate CPT-11-caused colitis in rats by inhibiting SP1 with mithramycin A (MitA) or activating TGR5 using oleanolic acid (OA). Our findings may shed light on the discovery of effective interventions for reducing dose-limiting chemotherapy-induced colitis.

Investigation of the potential role of TGR5 in pancreatic cancer by a comprehensive molecular experiments and the liquid chromatography mass spectrometry (LC-MS) based metabolomics

BACKGROUND

Takeda G protein receptor 5 (TGR5) is widely recognized as a potential drug target for the treatment of metabolic diseases. TGR5 is not only a metabolic regulator, but also has a potential role that participating in developing and progressing of gastrointestinal cancer. We aimed to investigate the potential role of TGR5 in pancreatic cancer by utilizing molecular experiments and the liquid chromatography mass spectrometry (LC-MS) based metabolomics.

METHODS

Herein, we assessed pancreatic cancer proliferation, migration and invasion in response to TGR5 antagonist SBI-115 in vitro experiments. Cell death was examined by using TUNEL assay on agarose-embedded sections. Then we investigated the effects of TGR5 on PANC-1 and BXPC3 cells via transmission electron microscopy (TEM). Moreover, LC-MS-based metabolomics was performed to explore the potential underlying mechanisms of TGR5 in pancreatic cancer. The correlations between TGR5 and the metabolism-related genes were further analysed by GEPIA 2 database.

RESULTS

We found the proliferation capacities were decreased significantly in PANC-1 and BXPC3 cells after the treatment of SBI-115 for 48 h. The results of TUNEL assay showed that antagonism of TGR5 by SBI-115 had a remarkable effect on inducing cell death. Analysis of TEM demonstrated that SBI-115 treatment could impair the morphology of mitochondria in most PANC-1 and BXPC3 cells. The LC-MS-based analyses revealed that antagonism of TGR5 could alter the metabolic profiles of PANC-1 cells in vitro. Moreover, TGR5 was associated with some metabolism-related genes in pancreatic cancer.

CONCLUSION

Our data suggests that antagonism of TGR5 may suppress cell proliferation and induce apoptosis in pancreatic cancer cells. TGR5 may affect the metabolism of pancreatic cancer, and TGR5 would be an attractive target for pancreatic cancer treatment.