TGR5 activation inhibits atherosclerosis by reducing macrophage inflammation and lipid loading

Bile Acid Dysregulation Is Intrinsically Related to Cachexia in Tumor-Bearing Mice

Simple Summary

Cancer cachexia is considered a multi-organ syndrome. An improved understanding of how circulating molecules can affect tissues and mediate their crosstalk in the pathogenesis of cancer cachexia is emerging. Considering the various actions of bile acids on host metabolism and immunity, they could represent innovative targets in cancer cachexia. In this study, we investigated how bile acids could contribute to this syndrome by assessing the bile flow, by comparing the impact on bile acid pathways of cachexia-inducing and non-cachexia-inducing cell sublines, and by investigating the effects of ursodeoxycholic acid, a choleretic compound, in cachectic mice. Altogether, our analyses strengthen the importance of bile acids and their receptors as key players in the metabolic disorders associated with cancer, thereby laying the foundation for new therapeutic opportunities.

Abstract

Bile acids exert diverse actions on host metabolism and immunity through bile acid-activated receptors, including Takeda G protein-coupled receptor 5 (TGR5). We have recently evidenced an alteration in bile acids in cancer cachexia, an inflammatory and metabolic syndrome contributing to cancer death. This current study aims to further explore the links emerging between bile acids and cancer cachexia. First, we showed that bile flow is reduced in cachectic mice. Next, comparing mice inoculated with cachexia-inducing and with non-cachexia-inducing C26 colon carcinoma cells, we demonstrated that alterations in the bile acid pathways and profile are directly associated with cachexia. Finally, we performed an interventional study using ursodeoxycholic acid (UDCA), a compound commonly used in hepatobiliary disorders, to induce bile acid secretion and decrease inflammation. We found that UDCA does not improve hepatic inflammation and worsens muscle atrophy in cachectic mice. This exacerbation of the cachectic phenotype upon UDCA was accompanied by a decreased TGR5 activity, suggesting that TGR5 agonists, known to reduce inflammation in several pathological conditions, could potentially counteract cachectic features. This work brings to light major evidence sustaining the emerging links between bile acids and cancer cachexia and reinforces the interest in studying bile acid-activated receptors in this context.

Atorvastatin protects against liver and vascular damage in a model of diet induced steatohepatitis by resetting FXR and GPBAR1 signaling

Farnesoid-x-receptor (FXR) agonists, currently trialed in patients with non-alcoholic steatosis (NAFLD), worsen the pro-atherogenic lipid profile and might require a comedication with statin. Here we report that mice feed a high fat/high cholesterol diet (HFD) are protected from developing a pro-atherogenic lipid profile because their ability to dispose cholesterol through bile acids. This protective mechanism is mediated by suppression of FXR signaling in the liver by muricholic acids (MCAs) generated in mice from chenodeoxycholic acid (CDCA). In contrast to CDCA, MCAs are FXR antagonists and promote a CYP7A1-dependent increase of bile acids synthesis. In mice feed a HFD, the treatment with obeticholic acid, a clinical stage FXR agonist, failed to improve the liver histopathology while reduced Cyp7a1 and Cyp8b1 genes expression and bile acids synthesis and excretion. In contrast, treating mice with atorvastatin mitigated liver and vascular injury caused by the HFD while increased the bile acids synthesis and excretion. Atorvastatin increased the percentage of 7α-dehydroxylase expressing bacteria in the intestine promoting the formation of deoxycholic acid and litocholic acid, two GPBAR1 agonists, along with the expression of GPBAR1-regulated genes in the white adipose tissue and colon. In conclusion, present results highlight the central role of bile acids in regulating lipid and cholesterol metabolism in response to atorvastatin and provide explanations for limited efficacy of FXR agonists in the treatment of NAFLD.

Metabolite G-Protein Coupled Receptors in Cardio-Metabolic Diseases

G protein-coupled receptors (GPCRs) have originally been described as a family of receptors activated by hormones, neurotransmitters, and other mediators. However, in recent years GPCRs have shown to bind endogenous metabolites, which serve functions other than as signaling mediators. These receptors respond to fatty acids, mono- and disaccharides, amino acids, or various intermediates and products of metabolism, including ketone bodies, lactate, succinate, or bile acids. Given that many of these metabolic processes are dysregulated under pathological conditions, including diabetes, dyslipidemia, and obesity, receptors of endogenous metabolites have also been recognized as potential drug targets to prevent and/or treat metabolic and cardiovascular diseases. This review describes G protein-coupled receptors activated by endogenous metabolites and summarizes their physiological, pathophysiological, and potential pharmacological roles.

Bile acids contribute to the development of non-alcoholic steatohepatitis in mice

Background & Aims

Through FXR and TGR5 signaling, bile acids (BAs) modulate lipid and glucose metabolism, inflammation and fibrosis. Hence, BAs returning to the liver after enteric secretion, modification and reabsorption may contribute to the pathogenesis of non-alcoholic steatohepatitis (NASH). Herein, we characterized the enterohepatic profile and signaling of BAs in preclinical models of NASH, and explored the consequences of experimental manipulation of BA composition.

Methods

We used high-fat diet (HFD)-fed foz/foz and high-fructose western diet-fed C57BL/6J mice, and compared them to their respective controls. Mice received a diet supplemented with deoxycholic acid (DCA) to modulate BA composition.

Results

Compared to controls, mice with NASH had lower concentrations of BAs in their portal blood and bile, while systemic BA concentrations were not significantly altered. Notably, the concentrations of secondary BAs, and especially of DCA, and the ratio of secondary to primary BAs were strikingly lower in bile and portal blood of mice with NASH. Hence, portal blood was poor in FXR and TGR5 ligands, and conferred poor anti-inflammatory protection in mice with NASH. Enhanced primary BAs synthesis and conversion of secondary to primary BAs in NASH livers contributed to the depletion in secondary BAs. Dietary DCA supplementation in HFD-fed foz/foz mice restored the BA concentrations in portal blood, increased TGR5 and FXR signaling, improved the dysmetabolic status, protected from steatosis and hepatocellular ballooning, and reduced macrophage infiltration.

Conclusions

BA composition in the enterohepatic cycle, but not in systemic circulation, is profoundly altered in preclinical models of NASH, with specific depletion in secondary BAs. Dietary correction of the BA profile protected from NASH, supporting a role for enterohepatic BAs in the pathogenesis of NASH.

Lay summary

This study clearly demonstrates that the alterations of enterohepatic bile acids significantly contribute to the development of non-alcoholic steatohepatitis in relevant preclinical models. Indeed, experimental modulation of bile acid composition restored perturbed FXR and TGR5 signaling and prevented non-alcoholic steatohepatitis and associated metabolic disorders.

Taurochenodeoxycholic Acid Increases cAMP Content via Specially Interacting with Bile Acid Receptor TGR5

Taurochenodeoxycholic acid (TCDCA) is one of the main components of bile acids (BAs). TCDCA has been reported as a signaling molecule, exerting anti-inflammatory and immunomodulatory functions. However, it is not well known whether those effects are mediated by TGR5. This study aimed to elucidate the interaction between TCDCA and TGR5. To achieve this aim, first, the TGR5 eukaryotic vector was constructed. The expression level of TGR5 in 293T cells was determined by immunofluorescence, real-time quantitative PCR (RT-PCR, qPCR), and Western blot. The luciferase assay, fluorescence microscopy, and enzyme-linked immunosorbent assay (ELISA) were recruited to check the interaction of TCDCA with TGR5. TCDCA treatment in 293T cells resulted in TGR5 internalization coupled with a significant increase in cAMP luciferase expression. Our results demonstrated that TCDCA was able to bind to the TGR5 receptor and activate it. These results provide an excellent potential therapeutic target for TCDCA research. Moreover, these findings also provide theoretical evidence for further TCDCA research.

Circulating bile acids concentration is predictive of coronary artery disease in human

Synthetized by the liver and metabolized by the gut microbiota, BA are involved in metabolic liver diseases that are associated with cardiovascular disorders. Animal models of atheroma documented a powerful anti-atherosclerotic effect of bile acids (BA). This prospective study examined whether variations in circulating BA are predictive of coronary artery disease (CAD) in human. Consecutive patients undergoing coronary angiography were enrolled. Circulating and fecal BA were measured by high pressure liquid chromatography and tandem mass spectrometry. Of 406 screened patients, 80 were prospectively included and divided in two groups with (n = 45) and without (n = 35) CAD. The mean serum concentration of total BA was twice lower in patients with, versus without CAD (P = 0.005). Adjusted for gender and age, this decrease was an independent predictor of CAD. In a subgroup of 17 patients, statin therapy doubled the serum BA concentration. Decreased serum concentrations of BA were predictors of CAD in humans. A subgroup analysis showed a possible correction by statins. With respect to the anti-atherosclerotic effect of BA in animal models, and their role in human lipid metabolism, this study describe a new metabolic disturbance associated to CAD in human.

Taurolithocholic acid but not tauroursodeoxycholic acid rescues phagocytosis activity of bone marrow-derived macrophages under inflammatory stress

Spinal cord injury (SCI) causes cell death and consequently the breakdown of axons and myelin. The accumulation of myelin debris at the lesion site induces inflammation and blocks axonal regeneration. Hematogenous macrophages contribute to the removal of myelin debris. In this study, we asked how the inflammatory state of macrophages affects their ability to phagocytose myelin. Bone marrow‐derived macrophages (BMDM) and Raw264.7 cells were stimulated with lipopolysaccharides (LPS) or interferon gamma (IFNγ), which induce inflammatory stress, and the endocytosis of myelin was examined. We found that activation of the TLR4‐NFκB pathway reduced myelin uptake by BMDM, while IFNγ‐Jak/STAT1 signaling did not. Since bile acids regulate lipid metabolism and in some cases reduce inflammation, our second objective was to investigate whether myelin clearance could be improved with taurolithocholic acid (TLCA), tauroursodeoxycholic acid or hyodeoxycholic acid. In BMDM only TLCA rescued myelin phagocytosis, when this activity was suppressed by LPS. Inhibition of protein kinase A blocked the effect of TLCA, while an agonist of the farnesoid X receptor did not rescue phagocytosis, implicating TGR5‐PKA signaling in the effect of TLCA. To shed light on the mechanism, we measured whether TLCA affected the expression of CD36, triggering receptor on myeloid cells‐2 (TREM2), and Gas6, which are known to be involved in phagocytosis and affected by inflammatory stimuli. Concomitant with an increase in expression of tumour necrosis factor alpha, LPS reduced expression of TREM2 and Gas6 in BMDM, and TLCA significantly diminished this downregulation. These findings suggest that activation of bile acid receptors may be used to improve myelin clearance in neuropathologies.

An Integrated Bile Acids Profile Determination by UHPLC-MS/MS to Identify the Effect of Bile Acids Supplement in High Plant Protein Diet on Common Carp (Cyprinus carpio)

Bile acids (BAs) have considerable importance in the metabolism of glycolipid and cholesterol. The purpose of the present study is to clarify the effects of bile acids supplementary in a high plant protein diet for the common carp BA profiles and hepatopancreas and intestine health. An 11-week feeding trial was conducted with high plant protein diet (18% soybean meal and 18% cottonseed protein concentrated) (HP) and HP added 600 mg/kg BAs (HP+BAs) for common carp, and then, the UHPLC-MS/MS technology was used to analyze the BAs in the bile and plasma of two groups. HP could induce vacuolation of hepatocytes and accumulation of glycogen in the common carp, while these phenotypes were significantly improved in the HP+BAs group. In addition, the BA profile of the HP group and HP+BAs group are described in detail, for the common carp bile with treatment by exogenous BAs, TCA, CA, TβMCA, and TωMCA were the main components. Furthermore, in the HP+BAs group plasma, CDCA, CA, LCA, and GCDCA increased significantly; they could activate TGR5, and the activation of hepatopancreas TGR5 might regulate glucose metabolism to relieve hepatopancreas glycogen accumulation. This study proved that BAs supplemented to plant protein diet could relieve the common carp hepatopancreas glycogen accumulation by changing the BAs’ profile, thereby promoting its healthy growth, which has important guiding significance for the promotion of aquaculture development and makes an important contribution to expanding the strategic space of food security.

The Aged Intestine: Performance and Rejuvenation

Owing to the growing elderly population, age-related problems are gaining increasing attention from the scientific community. With senescence, the intestine undergoes a spectrum of changes and infirmities that are likely the causes of overall aging. Therefore, identification of the aged intestine and the search for novel strategies to rescue it, are required. Although progress has been made in research on some components of the aged intestine, such as intestinal stem cells, the comprehensive understanding of intestinal aging is still limited, and this restricts the in-depth search for efficient strategies. In this concise review, we discuss several aspects of intestinal aging. More emphasis is placed on the appraisal of current and potential strategies to alleviate intestinal aging, as well as future targets to rejuvenate the aged intestine.

Inflammatory and Non-Inflammatory Mechanisms Controlling Cirrhosis Development

Simple Summary

The liver is continuously exposed to several harmful factors, subsequently activating sophisticated mechanisms set-up in order to repair and regenerate the damaged liver and hence to prevent its failure. When the injury becomes chronic, the regenerative response becomes perpetual and goes awry, leading to cirrhosis with a fatal liver dysfunction. Cirrhosis is a well-known risk factor for hepatocellular carcinoma (HCC), the most common, usually lethal, human primary liver neoplasm with very limited therapeutic options. Considering the pivotal role of immune factors in the development of cirrhosis, here we review and discuss the inflammatory pathways and components implicated in the development of cirrhosis. A better understanding of these circuits would help the design of novel strategies to prevent and treat cirrhosis and HCC, two lethal diseases.

Abstract

Because the liver is considered to be one of the most important metabolic organs in the body, it is continuously exposed to damaging environmental agents. Upon damage, several complex cellular and molecular mechanisms in charge of liver recovery and regeneration are activated to prevent the failure of the organ. When liver injury becomes chronic, the regenerative response goes awry and impairs the liver function, consequently leading to cirrhosis, a liver disorder that can cause patient death. Cirrhosis has a disrupted liver architecture and zonation, along with the presence of fibrosis and parenchymal nodules, known as regenerative nodules (RNs). Inflammatory cues contribute to the cirrhotic process in response to chronic damaging agents. Cirrhosis can progress to HCC, the most common and one of the most lethal liver cancers with unmet medical needs. Considering the essential role of inflammatory pathways in the development of cirrhosis, further understanding of the relationship between immune cells and the activation of RNs and fibrosis would guide the design of innovative therapeutic strategies to ameliorate the survival of cirrhotic and HCC patients. In this review, we will summarize the inflammatory mechanisms implicated in the development of cirrhosis.

Synthesis of 12β-Methyl-18-nor-bile Acids

Decoupling the roles of the farnesoid X nuclear receptor and Takeda G-protein-coupled bile acid receptor 5 is essential for the development of novel bile acid therapeutics targeting metabolic and neurodegenerative diseases. Herein, we describe the synthesis of 12β-methyl-18-nor-bile acids which may serve as probes in the search for new bile acid analogues with clinical applicability. A Nametkin-type rearrangement was applied to protected cholic acid derivatives, giving rise to tetra-substituted Δ13,14- and Δ13,17-unsaturated 12β-methyl-18-nor-bile acid intermediates (24a and 25a). Subsequent catalytic hydrogenation and deprotection yielded 12β-methyl-18-nor-chenodeoxycholic acid (27a) and its 17-epi-epimer (28a) as the two major reaction products. Optimization of the synthetic sequence enabled a chromatography-free route to prepare these bile acids at a multi-gram scale. In addition, the first cis-C-D ring-junctured bile acid and a new 14(13 → 12)-abeo-bile acid are described. Furthermore, deuteration experiments were performed to provide mechanistic insights into the formation of the formal anti-hydrogenation product 12β-methyl-18-nor-chenodeoxycholic acid (27a).

Gut microbiota-mediated secondary bile acids regulate dendritic cells to attenuate autoimmune uveitis through TGR5 signaling

Gut microbiota-mediated secondary bile acids (BAs) play an important role in energy balance and host metabolism via G protein-coupled receptors and/or nuclear receptors. Emerging evidence suggests that BAs are important for maintaining innate immune responses via these receptors. However, the effect of BAs on autoimmune uveitis is still unknown. Here, we demonstrate decreased microbiota-related secondary BA concentration in feces and serum of animals with experimental autoimmune uveitis (EAU). Restoration of the gut BAs pool attenuates severity of EAU in association with inhibition of nuclear factor κB (NF-κB)-related pro-inflammatory cytokines in dendritic cells (DCs). TGR5 deficiency partially reverses the inhibitory effect of deoxycholic acid (DCA) on DCs. TGR5 signaling also inhibits NF-κB activation via the cyclic AMP (cAMP)-protein kinase A (PKA) pathway in DCs. Additionally, both DCA and TGR5 agonists inhibit human monocyte-derived DC activation. Taken together, our results suggest that BA metabolism plays an important role in adaptive immune responses and might be a therapeutic target in autoimmune uveitis.

Crosstalk Between Intestinal Microbiota Derived Metabolites and Tissues in Allogeneic Hematopoietic Cell Transplantation

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is an evidence based- cellular immunotherapy for hematological malignancies. Immune reactions not only promote graft-versus-tumor effects that kill hematological malignant cells but also graft-versus-host disease (GVHD) that is the primary complication characterized by systemic organ damages consisting of T-cells and antigen presenting cells (APCs) activation. GVHD has long been recognized as an immunological reaction that requires an immunosuppressive treatment targeting immune cells. However immune suppression cannot always prevent GVHD or effectively treat it once it has developed. Recent studies using high-throughput sequencing technology investigated the impact of microbial flora on GVHD and provided profound insights of the mechanism of GVHD other than immune cells. Allo-HSCT affects the intestinal microbiota and microbiome-metabolome axis that can alter intestinal homeostasis and the severity of experimental GVHD. This axis can potentially be manipulated via dietary intervention or metabolites produced by intestinal bacteria affected post-allo-HSCT. In this review, we discuss the mechanism of experimental GVHD regulation by the complex microbial community-metabolites-host tissue axis. Furthermore, we summarize the major findings of microbiome-based immunotherapeutic approaches that protect tissues from experimental GVHD. Understanding the complex relationships between gut microbiota-metabolites-host tissues axis provides crucial insight into the pathogenesis of GVHD and advances the development of new therapeutic approaches.

(E)-7-Ethylidene-lithocholic Acid (7-ELCA) Is a Potent Dual Farnesoid X Receptor (FXR) Antagonist and GPBAR1 Agonist Inhibiting FXR-Induced Gene Expression in Hepatocytes and Stimulating Glucagon-like Peptide-1 Secretion From Enteroendocrine Cells

Bile acids (BAs) are key signaling steroidal molecules that regulate glucose, lipid, and energy homeostasis via interactions with the farnesoid X receptor (FXR) and G-protein bile acid receptor 1 (GPBAR1). Extensive medicinal chemistry modifications of the BA scaffold led to the discovery of potent selective or dual FXR and GPBAR1 agonists. Herein, we discovered 7-ethylidene-lithocholic acid (7-ELCA) as a novel combined FXR antagonist/GPBAR1 agonist (IC₅₀ = 15 μM/EC₅₀ = 26 nM) with no off-target activation in a library of 7-alkyl substituted derivatives of BAs. 7-ELCA significantly suppressed the effect of the FXR agonist obeticholic acid in BSEP and SHP regulation in human hepatocytes. Importantly, 7-ELCA significantly stimulated the production of glucagon-like peptide-1 (GLP-1), an incretin with insulinotropic effect in postprandial glucose utilization, in intestinal enteroendocrine cells. We can suggest that 7-ELCA may be a prospective approach to the treatment of type II diabetes as the dual modulation of GPBAR1 and FXR has been supposed to be effective in the synergistic regulation of glucose homeostasis in the intestine.

Bile acid activated receptors: Integrating immune and metabolic regulation in non-alcoholic fatty liver disease

Bile acids are a family of atypical steroids generated at the interface of liver-intestinal microbiota acting on a ubiquitously expressed family of membrane and nuclear receptors known as bile acid activated receptors. The two best characterized receptors of this family are the nuclear receptor, farnesoid X receptor (FXR) and the G protein-coupled receptor, G protein-coupled bile acid receptor 1 (GPBAR1). FXR and GPBAR1 regulate major aspects of lipid and glucose metabolism, energy balance, autophagy and immunity and have emerged as potential pharmaceutical targets for the treatment of metabolic and inflammatory disorders. Clinical trials in non-alcoholic fatty liver disease (NAFLD), however, have shown that selective FXR agonists cause side effects while their efficacy is partial. Because FXR and GPBAR1 exert additive effects, dual FXR/GPBAR1 ligands have been developed for the treatment of metabolic disorders and are currently advanced to clinical trials. Here, we will review the role of FXR and GPBAR1 agonism in NAFLD and how the two receptors could be exploited to target multiple components of the disease.

Bile acid receptors and signaling crosstalk in the liver, gut and brain

Bile acids are physiological detergents derived from cholesterol that aid in digestion and nutrient absorption, and they play roles in glucose, lipid, and energy metabolism and in gut microbiome and metabolic homeostasis. Bile acids mediate crosstalk between the liver and gut through bactericidal modulation of the gut microbiome, while gut microbes influence the composition of the circulating bile acid pool. Recent research indicates bile acids may also be important mediators of neurological disease by acting as peripheral signaling molecules that activate bile acid receptors in the blood-brain barrier and in the brain itself. This review highlights the role of bile acids in maintaining liver and gut microbe homeostasis, as well as their function as mediators of cellular signaling in the liver-gut-brain axis.

TGR5 protects against cholestatic liver disease via suppressing the NF-κB pathway and activating the Nrf2/HO-1 pathway

Background

Characterized by the presence of inflammation, fibrosis, and bile duct proliferation, cholestatic liver disease (CLD) affects people of all age groups. Takeda G-protein-coupled receptor (TGR5) has been implicated in the suppression of inflammation via toll-like receptor 4 (TLR4) and nuclear factor kappa B (NF-κB). Kupffer cells and their M1 polarization play important roles in inflammation and cholestatic liver injury via production of pro-inflammatory cytokines. Nevertheless, the function of TGR5 signaling in CLD is largely unknown.

Methods

We conducted liver tissue experiments, animal experiments, serum marker testing, liver histology analysis, Kupffer cell experiments, RNA extraction and Real-time PCR, western blotting, evaluation of ROS production by flow cytometry and statistical differences were analyzed by student t-test using GraphPad Prism.

Results

We found that serum bile acid (BA) and TGR5 levels were elevated in patients with cholestasis cirrhosis. Knockout of TGR5 in animals significantly increased bile duct ligation (BDL)-caused liver injury through increasing oxidative stress, promoting M1-predominant polarization of Kupffer cells, and elevating the serum levels of inflammatory cytokines. In contrast, TGR5 activation inhibited ROS production, secretion of pro-inflammatory cytokines, and M1-predominant polarization of Kupffer cells. Moreover, results showed that TGR5 exerted its effects via suppressing NF-κB signaling and activating nuclear factor 2 (Nrf2)/HO-1 signaling. Finally, the effect of TGR5 on cholestatic liver damage was also confirmed in vivo.

Conclusions

TGR5 activation protected against BDL-induced CLD by both suppressing inflammation via inhibiting the NF-κB pathway and reducing ROS production via activation of Nrf2/HO-1 signaling. These findings show the importance of TGR5 in CLD and provide new insight into therapeutic strategies for CLD.

Roles and Mechanisms of TGR5 in the Modulation of CD4+ T Cell Functions in Myocardial Infarction

Bile acid receptor TGR5 has been proved to play protective roles in the process of myocardial infarction (MI). Recently, we found spleen weight of Tgr5^+/+ mice was increased at 7-day post-MI but not in Tgr5^-/- mice. Since the spleen is one of the main resources of immune and inflammatory cells post-MI, we conducted flow cytometry analysis of multiple immune cells in the heart post-MI. It showed the recruitment of CD4⁺ T cells and CD8⁺ T cells was continuously more in the heart of Tgr5^-/- mice post-MI until 7 days after MI. Furthermore, CD4-specific TGR5 depletion mice exhibited aggravated ischemic injury. The mRNA expressions of the markers of Th1 and Treg were upregulated in the heart of Tgr5^-/- mice at 7-day post-MI. These results suggested TGR5 modulates CD4⁺ T cell functions and subsets distribution in the heart, and plays protective roles in myocardial infarction.

Interaction Between the Microbiota, Epithelia, and Immune Cells in the Intestine

The gastrointestinal tract harbors numerous commensal bacteria, referred to as the microbiota, that benefit host health by digesting dietary components and eliminating pathogens. The intestinal microbiota maintains epithelial barrier integrity and shapes the mucosal immune system, balancing host defense and oral tolerance with microbial metabolites, components, and attachment to host cells. To avoid aberrant immune responses, epithelial cells segregate the intestinal microbiota from immune cells by constructing chemical and physical barriers, leading to the establishment of host-commensal mutualism. Furthermore, intestinal immune cells participate in the maintenance of a healthy microbiota community and reinforce epithelial barrier functions. Perturbations of the microbiota composition are commonly observed in patients with autoimmune diseases and chronic inflammatory disorders. An understanding of the intimate interactions between the intestinal microbiota, epithelial cells, and immune cells that are crucial for the maintenance of intestinal homeostasis might promote advances in diagnostic and therapeutic approaches for various diseases.

Medical and Surgical Obesity Treatments and Atherosclerosis: Mechanisms beyond Typical Risk Factors

PURPOSE OF REVIEW

This study aims to discuss the mechanisms by which GLP-1 agonists and bariatric surgery improve cardiovascular outcomes in severely obese patients.

RECENT FINDINGS

Recent studies have demonstrated that both GLP-1 agonist use and bariatric surgery reduce adverse cardiovascular outcomes. Improvements in traditional atherosclerosis risk factors in association with weight loss likely contribute, but weight loss-independent mechanisms are also suggested to have roles. We review the clinical and preclinical evidence base for cardiovascular benefit of LP-1 agonists and bariatric surgery beyond traditional risk factors, including improvements in endothelial function, direct impacts on atherosclerotic plaques, and anti-inflammatory effects.

GPBAR1 Promotes Proliferation of Serous Ovarian Cancer by Inducing Smad4 Ubiquitination

BACKGROUND

Ovarian cancer (OC) is the most lethal malignancy of all female cancers and lacks an effective prognostic biomarker. Serous ovarian cancer (SOC) is the most common OC histologic type. The expression and function of bile acid receptor, G-protein-coupled bile acid receptor-1 (GPBAR1), in tumor progression remains controversial, and its clinical significance in SOC is unclear.

MATERIALS AND METHODS

In our study, we detected the expression of GPBAR1 in SOCs and normal ovarian tissues with quantitative real-time polymerase chain reaction and immunohistochemistry to detect its expression pattern. Moreover, the prognostic significance of GPBAR1 was investigated with univariate and multivariate analyses. The function of GPBAR1 in regulating SOC proliferation was studied and the underlying mechanism was investigated with experiments in vitro.

RESULTS

GPBAR1 was overexpressed in SOCs compared with the normal ovarian tissues. In the 166 SOCs, subsets with low and high GPBAR1 accounted for 57.23% and 42.77%, respectively. Moreover, our results suggested that GPBAR1 expression was significantly associated with poor prognosis and can be considered as an independent prognostic biomarker. With experiments in vitro, we suggested that GPBAR1 promoted SOC proliferation by increasing Smad4 ubiquitination, which required the involvement of GPBAR1-induced ERK phosphorylation.

CONCLUSIONS

GPBAR1 was overexpressed in SOC and predicted the poor prognosis of SOC. We showed that GPBAR1 promoted SOC proliferation by activating ERK and ubiquitining Smad4. Our results suggested that GPBAR1 was a supplement to better classify SOC on the basis of the molecular profile and that GPBAR1 may be a potential drug target of SOC.

Role of bile acids in liver diseases mediated by the gut microbiome

The intensive crosstalk between the liver and the intestine performs many essential functions. This crosstalk is important for natural immune surveillance, adaptive immune response regulation and nutrient metabolism and elimination of toxic bacterial metabolites. The interaction between the gut microbiome and bile acids is bidirectional. The gut microbiome regulates the synthesis of bile acids and their biological signaling activity and circulation via enzymes. Similarly, bile acids also shape the composition of the gut microbiome by modulating the host’s natural antibacterial defense and the intestinal immune system. The interaction between bile acids and the gut microbiome has been implicated in the pathophysiology of many intestinal and extra intestinal diseases, especially liver diseases. As essential mediators of the gut-liver crosstalk, bile acids regulate specific host metabolic pathways and modulate the inflammatory responses through farnesoid X-activated receptor and G protein-coupled bile acid receptor 1. Several clinical trials have demonstrated the signaling effects of bile acids in the context of liver diseases. We hypothesize the existence of a gut microbiome-bile acids-liver triangle and explore the potential therapeutic strategies for liver diseases targeting the triangle.

Takeda G Protein-Coupled Receptor 5 Modulates Depression-like Behaviors via Hippocampal CA3 Pyramidal Neurons Afferent to Dorsolateral Septum

BACKGROUND

Takeda G protein-coupled receptor 5 (TGR5) is recognized as a promising target for type 2 diabetes and metabolic syndrome; its expression has been demonstrated in the brain and is thought to be neuroprotective. Here, we hypothesize that dysfunction of central TGR5 may contribute to the pathogenesis of depression.

METHODS

In well-established chronic social defeat stress (CSDS) and chronic restraint stress (CRS) models of depression, we investigated the functional roles of TGR5 in CA3 pyramidal neurons (PyNs) and underlying mechanisms of the neuronal circuit in depression (for in vivo studies, n = 10; for in vitro studies, n = 5-10) using fiber photometry; optogenetic, chemogenetic, pharmacological, and molecular profiling techniques; and behavioral tests.

RESULTS

Both CSDS and CRS most significantly reduced TGR5 expression of hippocampal CA3 PyNs. Genetic overexpression of TGR5 in CA3 PyNs or intra-CA3 infusion of INT-777, a specific agonist, protected against CSDS and CRS, exerting significant antidepressant-like effects that were mediated via CA3 PyN activation. Conversely, genetic knockout or TGR5 knockdown in CA3 facilitated stress-induced depression-like behaviors. Re-expression of TGR5 in CA3 PyNs rather than infusion of INT-777 significantly improved depression-like behaviors in Tgr5 knockout mice exposed to CSDS or CRS. Silencing and stimulation of CA3 PyNs→somatostatin-GABAergic (gamma-aminobutyric acidergic) neurons of the dorsolateral septum circuit bidirectionally regulated depression-like behaviors, and blockade of this circuit abrogated the antidepressant-like effects from TGR5 activation of CA3 PyNs.

CONCLUSIONS

These findings indicate that TGR5 can regulate depression via CA3 PyNs→somatostatin-GABAergic neurons of dorsolateral septum transmission, suggesting that TGR5 could be a novel target for developing antidepressants.

TGR5 Attenuated Liver Ischemia-Reperfusion Injury by Activating the Keap1-Nrf2 Signaling Pathway in Mice

Hepatic ischemia/reperfusion injury (IRI) still remains an unavoidable problem in hepatectomy. The inflammatory response plays an important role in its pathogenesis. The plasma membrane-bound G protein-coupled bile acid receptor (TGR5), as one of G protein-coupled receptor (GPCR) families, has been proved to serve a protective role in several liver diseases. However, the exact function of TGR5 in modulating IRI remains obscure. We injected wild mice with a small interfering RNA of TGR5 (si-TGR5) or TGR5 agonist (INT-777) and established liver partial warm ischemia/reperfusion model. The results showed that knockdown of TGR5 significantly aggravated hepatic tissue injury, but treatment with INT-777 could reverse it, as evidenced by serum ALT and AST tests, liver histological injury, cytokines expressions, liver immunohistochemical analysis, and TUNEL staining. The apoptosis-associated proteins were evaluated after reperfusion. Moreover, we used primary bone marrow-derived macrophages (BMDMs) to establish hypoxia/reoxygenation (H/R) model to verify the anti-inflammation effect of TGR5. In in vivo experiments, we used TGR5-siRNA and TGR5 agonist (INT-777) to determine that TGR5 significantly attenuated liver damage after IRI through activating the Keap1-Nrf2 pathway. In addition, we found that overexpression of INT-777-activated TGR5 could reduce oxidative stress and inflammatory response in H/R-induced BMDMs through regulation of Keap1-Nef2 pathway during in vitro experiment. Importantly, these results were completely reversed in si-TGR5 BMDMs. In conclusion, the results indicated that TGR5 could effectively alleviated inflammation response via accelerating the activation of Keap1-Nrf2 signaling pathway during hepatic IRI, which may be meaningful in reducing related inflammatory molecules and adjusting inherent immunity.

Aspiration of conjugated bile acids predicts adverse lung transplant outcomes and correlates with airway lipid and cytokine dysregulation

INTRODUCTION

Duodeno-gastroesophageal reflux aspiration is associated with chronic lung allograft dysfunction (CLAD). Reflux aspirate can contain bile acids (BA), functional molecules in the gastro-intestinal tract with emulsifying properties. We sought to determine and quantify the various BA species in airways of the lung transplant recipients to better understand the various effects of aspirated BA that contribute to post-transplantation outcomes.

METHODS

Bronchial washings (BW) were prospectively collected from lung transplant recipients and subsequently assayed by liquid chromatography-mass spectrometry for 13 BA and 25 lipid families. Patients were monitored for CLAD, rejection, inflammation and airway infections.

RESULTS

Detectable BA were present in 45/50 patients (90%) at 3 months after transplant. Elevated BA and predominance of conjugated species were independent predictors of CLAD (hazard ratio 7.9; 95% confidence interval 2.7-23.6; p < 0.001 and 7.3; 2.4-22; p < 0.001, respectively) and mortality (hazard ratio 4.4; 1.5-12.7; p = 0.007 and 4.8; 1.4-15.8; p = 0.01, respectively). High BA associated with increased positive bacterial cultures (60% vs 25%, p = 0.02). Primary conjugated species independently correlated with the rate of bacterial cultures during the first-year post-transplant (Beta coefficient: 0.77; 0.28-1.26; p = 0.003) and changes in airway lipidome and cytokines.

CONCLUSIONS

Higher BA levels and predominance of conjugated BA are independent predictors of chronic lung allograft dysfunction, mortality and bacterial infections. Primary conjugated BA are related to distinct changes in airway lipidome and inflammatory cytokines. This elucidates novel evidence into the mechanism following BA aspiration and proposes novel markers for prediction of adverse post-transplant outcomes.

Marine Bile Natural Products as Agonists of the TGR5 Receptor

Agonism of the G protein-coupled bile acid receptor "Takeda G-protein receptor 5" (TGR5) aids in attenuating cholesterol accumulation due to atherosclerotic progression. Although mammalian bile compounds can activate TGR5, they are generally weak agonists, and more effective compounds need to be identified. In this study, two marine bile compounds (5β-scymnol and its sulfate) were compared with mammalian bile compounds deoxycholic acid (DCA) and ursodeoxycholic acid (UDCA) using an in vitro model of TGR5 agonism. The response profiles of human embryonic kidney 293 cells (HEK293) transfected to overexpress TGR5 (HEK293-TGR5) and incubated with subcytotoxic concentrations of test compounds were compared to nontransfected HEK293 control cells using the specific calcium-binding fluorophore Fura-2AM to measure intracellular calcium [Ca²⁺]_i release. Scymnol and scymnol sulfate caused a sustained increase in [Ca²⁺]_i within TGR5 cells only, which was abolished by a specific inhibitor for G_αq protein (UBO-QIC). Sustained increases in [Ca²⁺]_i were seen in both cell types with DCA exposure; this was unaffected by UBO-QIC, indicating that TGR5 activation was not involved. Exposure to UDCA did not alter [Ca²⁺]_i, suggesting a lack of TGR5 bioactivity. These findings demonstrated that both scymnol and scymnol sulfate are novel agonists of TGR5 receptors, showing therapeutic potential for treating atherosclerosis.

Critical roles of bile acids in regulating intestinal mucosal immune responses

Bile acids are a class of cholesterol derivatives that have been known for a long time for their critical roles in facilitating the digestion and absorption of lipid from the daily diet. The transformation of primary bile acids produced by the liver to secondary bile acids appears under the action of microbiota in the intestine, greatly expanding the molecular diversity of the intestinal environment. With the discovery of several new receptors of bile acids and signaling pathways, bile acids are considered as a family of important metabolites that play pleiotropic roles in regulating many aspects of human overall health, especially in the maintenance of the microbiota homeostasis and the balance of the mucosal immune system in the intestine. Accordingly, disruption of the process involved in the metabolism or circulation of bile acids is implicated in many disorders that mainly affect the intestine, such as inflammatory bowel disease and colon cancer. In this review, we discuss the different metabolism profiles in diseases associated with the intestinal mucosa and the diverse roles of bile acids in regulating the intestinal immune system. Furthermore, we also summarize recent advances in the field of new drugs that target bile acid signaling and highlight the importance of bile acids as a new target for disease intervention.

Supplemental Leuconostoc mesenteroides strain NTM048 attenuates imiquimod-induced psoriasis in mice

AIMS

Psoriasis, a chronic inflammatory skin disease, is associated with altered intestinal microbiota. Here, we investigated the ameliorative effect of Leuconostoc mesenteroides NTM048 strain in imiquimod (IMQ)-induced psoriasis in mice.

METHODS AND RESULTS

Mice were administered NTM048 for 21 days alongside the topical application of IMQ on the dorsal skin for 6 consecutive days. IMQ induced psoriatic symptoms such as erythema and scaling and also upregulated interleukin (IL)-17, a key effector cytokine of psoriasis, in the skin. Supplemental NTM048 suppressed these abnormalities, increased the levels of plasma deoxycholic acid (DCA), a secondary bile acid and altered the faecal microbiota composition, as indicated by the increased abundance of Akkermansia and decreased abundance of Staphylococcus and Streptococcus. Notably, DCA treatment of murine splenocytes reduced IL-17 production.

CONCLUSIONS

The NTM048-mediated reduction of psoriasis was shown to involve the downregulation of IL-17 in mouse skin, which was possibly associated with the plasma DCA derived from intestinal microbiota.

SIGNIFICANCE AND IMPACT OF THE STUDY

Our findings propose not only a novel approach for psoriasis reduction but also a crosstalk between the skin and intestine in psoriasis.

Gut microbiome and bile acids in obesity-related diseases

Dysbiosis has been implemented in the etiologies of obesity-related chronic diseases such as type 2 diabetes, NAFLD and cardiovascular diseases. Bile acids, a class of amphipathic steroids produced in the liver and extensively modified by the microbiome, are increasingly recognized as actors in onset and progression of these diseases. Indeed, human obesity is associated with altered bile acid metabolism. Bile acids facilitate intestinal fat absorption but also exert hormone-like functions through activation of nuclear and membrane-bound receptors and thereby modulate glucose, lipid and energy metabolism, intestinal integrity and immunity. Bile acid-signaling pathways have thus been identified as potential pharmacological targets for obesity-related diseases. Interfering with microbiome composition may also be considered, as liver- and microbiome-derived bile acid species have different signaling functions. This review summarizes recent developments in this rapidly expanding field of research and addresses potential clinical prospects of interference with bile acid signaling pathways in human diseases.

Central anorexigenic actions of bile acids are mediated by TGR5

Bile acids (BAs) are signalling molecules that mediate various cellular responses in both physiological and pathological processes. Several studies report that BAs can be detected in the brain1, yet their physiological role in the central nervous system is still largely unknown. Here we show that postprandial BAs can reach the brain and activate a negative-feedback loop controlling satiety in response to physiological feeding via TGR5, a G-protein-coupled receptor activated by multiple conjugated and unconjugated BAs2 and an established regulator of peripheral metabolism3-8. Notably, peripheral or central administration of a BA mix or a TGR5-specific BA mimetic (INT-777) exerted an anorexigenic effect in wild-type mice, while whole-body, neuron-specific or agouti-related peptide neuronal TGR5 deletion caused a significant increase in food intake. Accordingly, orexigenic peptide expression and secretion were reduced after short-term TGR5 activation. In vitro studies demonstrated that activation of the Rho-ROCK-actin-remodelling pathway decreases orexigenic agouti-related peptide/neuropeptide Y (AgRP/NPY) release in a TGR5-dependent manner. Taken together, these data identify a signalling cascade by which BAs exert acute effects at the transition between fasting and feeding and prime the switch towards satiety, unveiling a previously unrecognized role of physiological feedback mediated by BAs in the central nervous system.

Amelioration of Endothelial Dysfunction in Diabetes: Role of Takeda G Protein-Coupled Receptor 5

Diabetes mellitus (DM) eventually leads to chronic vascular complications, resulting in cardiovascular diseases. DM-associated endothelial dysfunction (ED) plays an important role in the development of chronic vascular complications. Low endothelial nitric oxide synthase (eNOS) activity, inflammation, and oxidative stress all contribute to ED. The G protein-coupled receptor Takeda G protein-coupled receptor 5 (TGR5) is a membrane receptor for bile acids that plays an important role in the regulation of glucose metabolism. Recent studies have shown that TGR5 is involved in the regulation of various mediators of ED, which suggests that TGR5 may represent a target for the treatment of DM-associated ED. In this review, we summarize the principal mechanisms of DM-associated ED, then propose TGR5 as a novel therapeutic target on the basis of its mechanistic involvement, and suggest potential directions for future research.

Berberine attenuates choline-induced atherosclerosis by inhibiting trimethylamine and trimethylamine-N-oxide production via manipulating the gut microbiome

Trimethylamine-N-oxide (TMAO), a derivative from the gut microbiota metabolite trimethylamine (TMA), has been identified to be an independent risk factor for promoting atherosclerosis. Evidences suggest that berberine (BBR) could be used to treat obesity, diabetes and atherosclerosis, however, its mechanism is not clear mainly because of its poor oral bioavailability. Here, we show that BBR attenuated TMA/TMAO production in the C57BL/6J and ApoE KO mice fed with choline-supplemented chow diet, and mitigated atherosclerotic lesion areas in ApoE KO mice. Inhibition of TMA/TMAO production by BBR-modulated gut microbiota was proved by a single-dose administration of d9-choline in vivo. Metagenomic analysis of cecal contents demonstrated that BBR altered gut microbiota composition, microbiome functionality, and cutC/cntA gene abundance. Furthermore, BBR was shown to inhibit choline-to-TMA conversion in TMA-producing bacteria in vitro and in gut microbial consortium from fecal samples of choline-fed mice and human volunteers, and the result was confirmed by transplantation of TMA-producing bacteria in mice. These results offer new insights into the mechanisms responsible for the anti-atherosclerosis effects of BBR, which inhibits commensal microbial TMA production via gut microbiota remodeling.

Gut microbiota-derived metabolites in the regulation of host immune responses and immune-related inflammatory diseases

The gut microbiota has a critical role in the maintenance of immune homeostasis. Alterations in the intestinal microbiota and gut microbiota-derived metabolites have been recognized in many immune-related inflammatory disorders. These metabolites can be produced by gut microbiota from dietary components or by the host and can be modified by gut bacteria or synthesized de novo by gut bacteria. Gut microbiota-derived metabolites influence a plethora of immune cell responses, including T cells, B cells, dendritic cells, and macrophages. Some of these metabolites are involved in the pathogenesis of immune-related inflammatory diseases, such as inflammatory bowel diseases, diabetes, rheumatoid arthritis, and systemic lupus erythematosus. Here, we review the role of microbiota-derived metabolites in regulating the functions of different immune cells and the pathogenesis of chronic immune-related inflammatory diseases.

TGR5/Cathepsin E signaling regulates macrophage innate immune activation in liver ischemia and reperfusion injury

The role and underlying mechanism of plasma membrane-bound G protein-coupled bile acid receptor (TGR5) in regulating macrophage innate immune activation during liver ischemia and reperfusion (IR) injury remains largely unclear. Here, we demonstrated that TGR5 depletion in myeloid cells aggravated liver injury with increased macrophage infiltration and enhanced inflammation in livers post-IR. While TGR5 deficiency enhanced mobility and proinflammatory M1 polarization of macrophages, TGR5 agonist enhanced the anti-inflammatory effect of TGR5 both in vivo and in vitro. Microarray profiling revealed that TGR5-deficient macrophages exhibited enhanced proinflammatory characteristics and cathepsin E (Cat E) was the most upregulated gene. Knockdown of Cat E abolished the enhanced mobility and shift of macrophage phenotypes induced by TGR5 depletion. Moreover, Cat E knockdown attenuated liver IR injury and liver inflammation in myeloid TGR5-deficient mice. In patients undergoing partial hepatectomy, IR stress promoted TGR5 activation of CD11b+ cells in peripheral blood mononuclear cells, correlating with the shift in macrophage M2 polarization. Ursodeoxycholic acid administration enhanced TGR5 activation and the trend in macrophage M2 polarization. Our results suggest that TGR5 attenuates proinflammatory immune activation by restraining macrophage migration and facilitating macrophage M2 polarization via suppression of Cat E and thereby protects against liver IR injury.

Vitamin D receptor is overexpressed in the duodenum of patients with irritable bowel syndrome

BACKGROUND AND AIM

Irritable bowel syndrome (IBS) is one of the most common functional gastrointestinal disorders, and bile acids are thought to be associated with the pathogenesis of IBS. Bile acid receptors are expressed on intestinal epithelial cells. However, no study has assessed bile acid receptor proteins in IBS. Therefore, we examined the intestinal mucosal expression of bile acid receptors in patients with IBS.

METHODS

Intestinal biopsies were performed in patients with IBS and controls. Mast cells, vitamin D receptor (VDR), and somatostatin were stained with specific antibodies. Levels of VDR, farnesoid X receptor (FXR), takeda-G-protein-receptor-5 (TGR5), claudins, and transient-receptor-potential-cation-channel-subfamily-V-member 6 (TRPV6) were assessed by western blotting.

RESULTS

3Mast cell counts in the second part of the duodenum were significantly higher in patients with IBS than in controls. VDR protein levels were significantly elevated in the duodenum and terminal ileum of patients with IBS compared with controls, although this difference was not seen in the cecum or rectum. FXR and TGR5 protein levels did not differ in any part of the intestine. VDR-positive cryptal epithelia in IBS were distributed not only at basal crypt but also along the upper part of the basal crypt epithelial cells. In contrast, the pattern of gut somatostatin-positive cells, claudins, and TRPV6 levels did not differ.

CONCLUSIONS

The number of mast cells in the duodenum was significantly increased, and the protein expression levels of VDR, but not those of FXR or TGR5, were elevated in the duodenal epithelial crypt in patients with IBS.

Gut microbiota in coronary artery disease: a friend or foe?

There is a growing interest in the role of gut microbiota in the pathophysiology of several diseases, including coronary artery diseases (CAD). Gut microorganisms may produce beneficial effects in myocardial ischemia either directly in the form of exogenous administration or indirectly by acting on fiber-rich food to produce important cardioprotective components. The harmful effects of gut microbiota in CAD are due to alteration in their composition with a significant decrease in Bacteroidetes and an increase in Firmicutes, Escherichia, Shigella, and Enterococcus. The altered microbiota may produce potentially toxic metabolites, including trimethylamine-N-oxide (TMAO). Indeed, the fasting plasma levels of TMAO are directly correlated to increased risk of major cardiovascular events in CAD patients, and it is proposed as a potential biomarker to predict the onset of major cardiovascular events. It is concluded that the change in the composition of gut microbiota in CAD patients may predispose to more harmful effects. However, exogenous delivery of probiotics may overcome the detrimental effects of myocardial ischemia.

Overexpression of TGR5 alleviates myocardial ischemia/reperfusion injury via AKT/GSK-3β mediated inflammation and mitochondrial pathway

Ischemia/reperfusion (I/R) injury reduces cell proliferation, triggers inflammation, promotes cell apoptosis and necrosis, which are the leading reasons of morbidity and mortality in patients with cardiac disease. TGR5 is shown to express in hearts, but its functional role in I/R-induced myocardial injury is unclear. In the present study, we aimed to explore the underlying molecular mechanism of TGR5 in hypoxia/reoxygenation (H/R)-induced cardiomyocyte injury in vitro. The results showed that TGR5 was significantly up-regulated in H9C2 (rat cardiomyocyte cells) and human cardiomyocytes (HCMs) after H/R. Overexpression of TGR5 significantly improved cell proliferation, alleviated apoptosis rate, the activities of caspase-3, cleaved caspases-3 and Bax protein expression levels, and increased Bcl-2 level. Overexpression of TGR5 significantly up-regulated ROS generation, stabilized the mitochondrial membrane potential (MMP), and reduced the concentration of intracellular Ca²⁺ as well as cytosolic translocation of mitochondrial cytochrome c (cyto-c). Meanwhile, overexpressed TGR5 also enhanced the mRNA and protein levels of interleukin (IL)-10, and decreased the mRNA and protein levels of IL-6 and tumor necrosis factor α (TNF-α). The shTGR5+H/R group followed opposite trends. In addition, overexpressed TGR5 induced an increase in the levels of p-AKT and p-GSK-3β. The protective effects of TGR5 were partially reversed by AKT inhibitor MK-2206. Taken together, these results suggest that TGR5 attenuates I/R-induced mitochondrial dysfunction and cell apoptosis as well as inflammation, and these protections may through AKT/GSK-3β pathway.

Selective release of gastrointestinal hormones induced by an orally active GPR39 agonist

OBJECTIVES

Obesity is a complex disease associated with a high risk of comorbidities. Gastric bypass surgery, an invasive procedure with low patient eligibility, is currently the most effective intervention that achieves sustained weight loss. This beneficial effect is attributed to alterations in gut hormone signaling. An attractive alternative is to pharmacologically mimic the effects of bariatric surgery by targeting several gut hormonal axes. The G protein-coupled receptor 39 (GPR39) expressed in the gastrointestinal tract has been shown to mediate ghrelin signaling and control appetite, food intake, and energy homeostasis, but the broader effect on gut hormones is largely unknown. A potent and efficacious GPR39 agonist (Cpd1324) was recently discovered, but the in vivo function was not addressed. Herein we studied the efficacy of the GPR39 agonist, Cpd1324, on metabolism and gut hormone secretion.

METHODS

Body weight, food intake, and energy expenditure in GPR39 agonist-treated mice and GPR39 KO mice were studied in calorimetric cages. Plasma ghrelin, glucose-dependent insulinotropic polypeptide (GIP), glucagon-like peptide-1 (GLP-1), and peptide YY (PYY) levels were measured. Organoids generated from murine and human small intestine and mouse colon were used to study GLP-1 and PYY release. Upon GPR39 agonist administration, dynamic changes in intracellular GLP-1 content were studied via immunostaining and changes in ion transport across colonic mucosa were monitored in Ussing chambers. The G protein activation underlying GPR39-mediated selective release of gut hormones was studied using bioluminescence resonance energy transfer biosensors.

RESULTS

The GPR39 KO mice displayed a significantly increased food intake without corresponding increases in respiratory exchange ratios or energy expenditure. Oral administration of a GPR39 agonist induced an acute decrease in food intake and subsequent weight loss in high-fat diet (HFD)-fed mice without affecting their energy expenditure. The tool compound, Cpd1324, increased GLP-1 secretion in the mice as well as in mouse and human intestinal organoids, but not in GPR39 KO mouse organoids. In contrast, the GPR39 agonist had no effect on PYY or GIP secretion. Transepithelial ion transport was acutely affected by GPR39 agonism in a GLP-1- and calcitonin gene-related peptide (CGRP)-dependent manner. Analysis of Cpd1324 signaling properties showed activation of Gα_q and Gα_i/o signaling pathways in L cells, but not Gα_s signaling.

CONCLUSIONS

The GPR39 agonist described in this study can potentially be used by oral administration as a weight-lowering agent due to its stimulatory effect on GLP-1 secretion, which is most likely mediated through a unique activation of Gα subunits. Thus, GPR39 agonism may represent a novel approach to effectively treat obesity through selective modulation of gastrointestinal hormonal axes.

Activation of TGR5 restores AQP2 expression via the HIF pathway in renal ischemia-reperfusion injury

Renal ischemia-reperfusion (I/R) injury is associated with markedly reduced protein expression of aquaporins (AQPs). Membrane G protein-coupled bile acid receptor-1 (TGR5) has shown protective roles in some kidney diseases. The purpose of the current study was to investigate whether activation of TGR5 prevented the decreased protein expression of AQPs in rodents with renal I/R injury and potential mechanisms. TGR5 agonist lithocholic acid (LCA) treatment reduced polyuria after renal I/R injury in rats. LCA prevented the decreased abundance of AQP2 protein and upregulated hypoxia-inducible factor (HIF)-1α protein expression, which were associated with decreased protein abundance of NF-κB p65 and IL-1β. After renal I/R, mice with tgr5 gene deficiency exhibited further decreases in AQP2 and HIF-1α protein abundance and increases of IL-1β and NF-κB p65 protein expression compared with wild-type mice. In primary cultured inner medullary collecting duct cells with hypoxia/reoxygenation, LCA induced markedly increased protein expression of AQP2 and HIF-1α, which were partially prevented by the PKA inhibitor H89. FG4592, a prolyl-4-hydroxylase domain-containing protein inhibitor, increased HIF-1α and AQP2 protein abundance in association with decreased NF-κB p65 protein expression in inner medullary collecting duct cells with hypoxia/reoxygenation. In conclusion, TGR5 stimulation by LCA prevented downregulation of renal AQPs in kidney with I/R injury, likely through activating HIF-1α signaling and suppressing inflammatory responses.NEW & NOTEWORTHY Stimulation of the membrane G protein-coupled bile acid receptor TGR5 by lithocholic acid (LCA) reduced polyuria in rats with renal ischemia-reperfusion (I/R) injury. LCA increased abundance of aquaporin-2 (AQP2) protein and upregulated hypoxia-inducible factor (HIF)-1α protein expression in association with decreased NF-κB p65 and IL-1β. After I/R, mice with tgr5 gene deficiency exhibited more severe decreases in AQP2 and HIF-1α protein abundance and inflammatory responses. TGR5 activation exhibits a protective role in acute renal injury induced by I/R.

Bile acids profile, histopathological indices and genetic variants for non-alcoholic fatty liver disease progression

OBJECTIVE

Metabolomic studies suggest plasma levels of bile acids (BAs) are elevated amongst subjects with non-alcoholic fatty liver disease (NAFLD) compared to healthy controls. However, it remains unclear whether or not specific BAs are associated with the clinically relevant transition from nonalcoholic fatty liver (i.e. simple steatosis) to non-alcoholic steatohepatitis (NASH), or enhanced progression of hepatic fibrosis, or genetic determinants of NAFLD/NASH.

METHODS

Among sequential subjects (n=102) undergoing diagnostic liver biopsy, we examined the associations of a broad panel of BAs with distinct histopathological features of NAFLD, the presence of NASH, and their associations with genetic variants linked to NAFLD and NASH.

RESULTS

Plasma BA alterations were observed through the entire spectrum of NAFLD, with several glycine conjugated forms of the BAs demonstrating significant associations with higher grades of inflammation and fibrosis. Plasma 7-Keto-DCA levels showed the strongest associations with advanced stages of hepatic fibrosis [odds ratio(95% confidence interval)], 4.2(1.2-16.4), NASH 24.5(4.1-473), and ballooning 18.7(4.8-91.9). Plasma 7-Keto-LCA levels were associated with NASH 9.4(1.5-185) and ballooning 5.9(1.4-28.8). Genetic variants at several NAFLD/NASH loci were nominally associated with increased levels of 7-Keto- and glycine-conjugated forms of BAs, and the NAFLD risk allele at the TRIB1 locus showed strong tendency toward increased plasma levels of GCA (p=0.02) and GUDCA (p=0.009).

CONCLUSIONS

Circulating bile acid levels are associated with histopathological and genetic determinants of the transition from simple hepatic steatosis into NASH. Further studies exploring the potential involvement of bile acid metabolism in the development and/or progression of distinct histopathological features of NASH are warranted.

Bile acids and their receptors in metabolic disorders

Bile acids are a large family of atypical steroids which exert their functions by binding to a family of ubiquitous cell membrane and nuclear receptors. There are two main bile acid activated receptors, FXR and GPBAR1, that are exclusively activated by bile acids, while other receptors CAR, LXRs, PXR, RORγT, S1PR2and VDR are activated by bile acids in addition to other more selective endogenous ligands. In the intestine, activation of FXR and GPBAR1 promotes the release of FGF15/19 and GLP1 which integrate their signaling with direct effects exerted by theother receptors in target tissues. This network is tuned in a time ordered manner by circadian rhythm and is critical for the regulation of metabolic process including autophagy, fast-to-feed transition, lipid and glucose metabolism, energy balance and immune responses. In the last decade FXR ligands have entered clinical trials but development of systemic FXR agonists has been proven challenging because their side effects including increased levels of cholesterol and Low Density Lipoproteins cholesterol (LDL-c) and reduced High-Density Lipoprotein cholesterol (HDL-c). In addition, pruritus has emerged as a common, dose related, side effect of FXR ligands. Intestinal-restricted FXR and GPBAR1 agonists and dual FXR/GPBAR1 agonists have been developed. Here we review the last decade in bile acids physiology and pharmacology.

TGR5 Regulates Macrophage Inflammation in Nonalcoholic Steatohepatitis by Modulating NLRP3 Inflammasome Activation

Nonalcoholic steatohepatitis (NASH) is a chronic liver disease associated with dysregulation of liver metabolism and inflammation. G-protein coupled bile acid receptor 1 (TGR5) is a cell surface receptor that is involved in multiple metabolic pathways. However, the functions of TGR5 in regulating macrophage innate immune activation in NASH remain unclear. Here, we found that TGR5 expression was decreased in liver tissues from humans and mice with NASH. Compared to wild type (WT) mice, TGR5-knockout (TGR5-/-) mice exhibited exacerbated liver damage, increased levels of proinflammatory factors, and enhanced M1 macrophage polarization. Moreover, TGR5 deficiency facilitated M1 macrophage polarization by promoting NLRP3 inflammasome activation and caspase-1 cleavage. Taken together, our findings revealed that TGR5 signaling attenuated liver steatosis and inflammation and inhibited NLRP3-mediated M1 macrophage polarization in NASH.

The Liver under the Spotlight: Bile Acids and Oxysterols as Pivotal Actors Controlling Metabolism

Among the myriad of molecules produced by the liver, both bile acids and their precursors, the oxysterols are becoming pivotal bioactive lipids which have been underestimated for a long time. Their actions are ranging from regulation of energy homeostasis (i.e., glucose and lipid metabolism) to inflammation and immunity, thereby opening the avenue to new treatments to tackle metabolic disorders associated with obesity (e.g., type 2 diabetes and hepatic steatosis) and inflammatory diseases. Here, we review the biosynthesis of these endocrine factors including their interconnection with the gut microbiota and their impact on host homeostasis as well as their attractive potential for the development of therapeutic strategies for metabolic disorders.

DCA-TGR5 signaling activation alleviates inflammatory response and improves cardiac function in myocardial infarction

AIMS

The progression of myocardial infarction (MI) involves multiple metabolic disorders. Bile acid metabolites have been increasingly recognized as pleiotropic signaling molecules that regulate multiple cardiovascular functions. G protein-coupled bile acid receptor (TGR5) is one of the receptors sensing bile acids to mediate their biological functions. In this study, we aimed to elucidate the effects of bile acids-TGR5 signaling pathways in myocardial infarction (MI).

METHODS AND RESULTS

Blood samples of AMI patients or control subjects were collected and plasma was used for bile acid metabolism analysis. We discovered that bile acid levels were altered and deoxycholic acid (DCA) was substantially reduced in the plasma of AMI patients. Mice underwent either the LAD ligation model of MI or sham operation. Both MI and sham mice were gavaged with 10 mg/kg/d DCA or vehicle control since 3-day before the operation. Cardiac function was assessed by ultrasound echocardiography, infarct area was evaluated by TTC staining and Masson trichrome staining. Administration of DCA improved cardiac function and reduced ischemic injury at the 7th-day post-MI. The effects of DCA were dependent on binding to its receptor TGR5. Tgr5-/- mice underwent the same MI model. Cardiac function deteriorated and infarct size was increased at the 7th-day post-MI, which were not savaged by DCA administration. Moreover, DCA inhibited interleukin (IL)-1β expression in the infarcted hearts, and ameliorated IL-1β activation at 1-day post-MI. DCA inhibited NF-κB signaling and further IL-1β expression in cultured neonatal mouse cardiomyocytes under hypoxia as well as cardio-fibroblasts with the treatment of LPS.

CONCLUSIONS

DCA-TGR5 signaling pathway activation decreases inflammation and ameliorates heart function post-infarction. Strategies that control bile acid metabolism and TGR5 signaling to ameliorate the inflammatory responses may provide beneficial effects in patients with myocardial infarction.

Changes in fasting bile acid profiles after Roux-en-Y gastric bypass and sleeve gastrectomy

BACKGROUND

Bile acid is an essential factor that plays a role in metabolic regulation, but how bile acid is regulated after Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy (SG) remains unclear. This meta-analysis aimed to investigate changes in the levels of fasting bile acids following RYGB and SG.

METHODS

A systematic literature search of the PubMed, EMBASE, Cochrane Library and Web of Science databases through July 2020 was performed in accordance with the Meta-analysis Of Observational Studies in Epidemiology (MOOSE) guidelines and Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. The concentrations of bile acids were evaluated.

RESULTS

Thirteen studies with 289 patients were included. Our results showed that patients who underwent RYGB had increased levels of fasting total bile acids, primary bile acids, secondary bile acids, conjugated bile acids, and unconjugated bile acids, but no significant differences in all these bile acid levels were observed in patients who underwent SG. Furthermore, 12a-hydroxylated bile acid levels and the 12a-hydroxylated/non-12a-hydroxylated bile acid ratio also increased following RYGB.

CONCLUSION

In this study, we found that fasting bile acid levels, especially 12a-hydroxylated bile acids levels, were increased after RYGB. However, no differences in fasting bile acid levels were observed following SG.

Bile acid-receptor TGR5 deficiency worsens liver injury in alcohol-fed mice by inducing intestinal microbiota dysbiosis

Background & Aims

Bile-acid metabolism and the intestinal microbiota are impaired in alcohol-related liver disease. Activation of the bile-acid receptor TGR5 (or GPBAR1) controls both biliary homeostasis and inflammatory processes. We examined the role of TGR5 in alcohol-induced liver injury in mice.

Methods

We used TGR5-deficient (TGR5-KO) and wild-type (WT) female mice, fed alcohol or not, to study the involvement of liver macrophages, the intestinal microbiota (16S sequencing), and bile-acid profiles (high-performance liquid chromatography coupled to tandem mass spectrometry). Hepatic triglyceride accumulation and inflammatory processes were assessed in parallel.

Results

TGR5 deficiency worsened liver injury, as shown by greater steatosis and inflammation than in WT mice. Isolation of liver macrophages from WT and TGR5-KO alcohol-fed mice showed that TGR5 deficiency did not increase the pro-inflammatory phenotype of liver macrophages but increased their recruitment to the liver. TGR5 deficiency induced dysbiosis, independently of alcohol intake, and transplantation of the TGR5-KO intestinal microbiota to WT mice was sufficient to worsen alcohol-induced liver inflammation. Secondary bile-acid levels were markedly lower in alcohol-fed TGR5-KO than normally fed WT and TGR5-KO mice. Consistent with these results, predictive analysis showed the abundance of bacterial genes involved in bile-acid transformation to be lower in alcohol-fed TGR5-KO than WT mice. This altered bile-acid profile may explain, in particular, why bile-acid synthesis was not repressed and inflammatory processes were exacerbated.

Conclusions

A lack of TGR5 was associated with worsening of alcohol-induced liver injury, a phenotype mainly related to intestinal microbiota dysbiosis and an altered bile-acid profile, following the consumption of alcohol.

Lay summary

Excessive chronic alcohol intake can induce liver disease. Bile acids are molecules produced by the liver and can modulate disease severity. We addressed the specific role of TGR5, a bile-acid receptor. We found that TGR5 deficiency worsened alcohol-induced liver injury and induced both intestinal microbiota dysbiosis and bile-acid pool remodelling. Our data suggest that both the intestinal microbiota and TGR5 may be targeted in the context of human alcohol-induced liver injury.

Role of Gut Microbiota and Their Metabolites on Atherosclerosis, Hypertension and Human Blood Platelet Function: A Review

Emerging data have demonstrated a strong association between the gut microbiota and the development of cardiovascular disease (CVD) risk factors such as atherosclerosis, inflammation, obesity, insulin resistance, platelet hyperactivity, and plasma lipid abnormalities. Several studies in humans and animal models have demonstrated an association between gut microbial metabolites such as trimethylamine-N-oxide (TMAO), short-chain fatty acids, and bile acid metabolites (amino acid breakdown products) with CVD. Human blood platelets are a critical contributor to the hemostatic process. Besides, these blood cells play a crucial role in developing atherosclerosis and, finally, contribute to cardiac events. Since the TMAO, and other metabolites of the gut microbiota, are asociated with platelet hyperactivity, lipid disorders, and oxidative stress, the diet-gut microbiota interactions have become an important research area in the cardiovascular field. The gut microbiota and their metabolites may be targeted for the therapeutic benefit of CVD from a clinical perspective. This review's main aim is to highlight the complex interactions between microbiota, their metabolites, and several CVD risk factors.

INT-777 prevents cognitive impairment by activating Takeda G protein-coupled receptor 5 (TGR5) and attenuating neuroinflammation via cAMP/ PKA/ CREB signaling axis in a rat model of sepsis

BACKGROUND

Survivors of sepsis must often endure significant cognitive and behavioral impairments after discharge, but research on the relevant mechanisms and interventions remains lacking. TGR5, a member of the class A GPCR family, plays an important role in many physiological processes, and recent studies have shown that agonists of TGR5 show neuroprotective effects in a variety of neurological disorders. To date, no studies have assessed the effects of TGR5 on neuroinflammatory, cognitive, or behavioral changes in sepsis models.

METHODS

A total of 267 eight-week-old male Sprague-Dawley rats were used in this study. Sepsis was induced via cecal ligation and puncture (CLP). All animals received volume resuscitation. The rats were given TGR5 CRISPR oligonucleotide intracerebroventricularly 48 h before CLP surgery. INT-777 was administered intranasally 1 h after CLP, and the cAMP inhibitor, SQ22536, was administered intracerebroventricularly 1 h after CLP. Survival rate, bodyweight change, and clinical scores were assessed, and neurobehavioral tests, western blot, and immunofluorescence staining were performed. The cognitive function of rats was measured using the Morris water maze during 15-20 days after CLP.

RESULTS

The expression of TGR5 in the rat hippocampus was upregulated, and peaked at 3 days after CLP. The survival rate of rats after CLP was less than 50%, and the growth rate, in terms of weight, was significantly decreased. While INT-777 treatment did not improve these changes, the treatment did reduce the clinical scores of rats at 24 h after CLP. On day 15 and later, the surviving mice completed a series of behavioral tests. CLP rats showed spatial and memory deficits and anxiety-like behaviors, but INT-777 treatment significantly improved these effects. Mechanistically, immunofluorescence analysis showed that INT-777 treatment reduced the number of microglia in the hippocampus, neutrophilic infiltration, and the expression of inflammatory factors after CLP in rats. Moreover, INT-777 treatment significantly increased the expression of TGR5, cAMP, p-PKA, and p-CREB, but downregulated the expression of IL-1β, IL-6, and TNF-α. CRISPR-mediated TGR5 knockdown and SQ22536 treatment abolished the neuroprotective effects of TGR5 activation after CLP.

CONCLUSION

This study demonstrates that INT-777 treatment reduced neuroinflammation and microglial cell activation, but improved cognitive impairment in the experimental sepsis rats. TGR5 has translational potential as a therapeutic target to improve neurological outcomes in sepsis survivors.