The bile acid TUDCA increases glucose-induced insulin secretion via the cAMP/PKA pathway in pancreatic beta cells

Bile acid metabolism in health and ageing-related diseases

Bile acids (BAs) have surpassed their traditional roles as lipid solubilizers and regulators of BA homeostasis to emerge as important signalling molecules. Recent research has revealed a connection between microbial dysbiosis and metabolism disruption of BAs, which in turn impacts ageing-related diseases. The human BAs pool is primarily composed of primary BAs and their conjugates, with a smaller proportion consisting of secondary BAs. These different BAs exert complex effects on health and ageing-related diseases through several key nuclear receptors, such as farnesoid X receptor and Takeda G protein-coupled receptor 5. However, the underlying molecular mechanisms of these effects are still debated. Therefore, the modulation of signalling pathways by regulating synthesis and composition of BAs represents an interesting and novel direction for potential therapies of ageing-related diseases. This review provides an overview of synthesis and transportion of BAs in the healthy body, emphasizing its dependence on microbial community metabolic capacity. Additionally, the review also explores how ageing and ageing-related diseases affect metabolism and composition of BAs. Understanding BA metabolism network and the impact of their nuclear receptors, such as farnesoid X receptor and G protein-coupled receptor 5 agonists, paves the way for developing therapeutic agents for targeting BA metabolism in various ageing-related diseases, such as metabolic disorder, hepatic injury, cardiovascular disease, renal damage and neurodegenerative disease.

Study on the mechanism of modified Gegen Qinlian decoction in regulating the intestinal flora-bile acid-TGR5 axis for the treatment of type 2 diabetes mellitus based on macro genome sequencing and targeted metabonomics integration

BACKGROUND

Currently, there are many drugs available for the treatment of type 2 diabetes mellitus (T2DM), but most of them cause various side effects due to the need for long-term use. As a traditional Chinese medicine, Gegen Qinlian Decoction (GQD) has shown good efficacy and low side effects in the treatment of T2DM in both clinical and basic research. Based on relevant traditional Chinese medicine theories, dried ginger is innovatively added the formula of traditional GQD to create a modified GQD. This modification reduces the side effects of traditional GQD while exerting its therapeutic effect on T2DM. Previous studies have found that the modified GQD can regulate endoplasmic reticulum stress in the liver, inhibit hepatic gluconeogenesis, protect pancreatic islet β cells, and control blood sugar levels by inhibiting the FXR/neuronal ceramide signaling pathway. GQD can also regulate the intestinal microbiota to achieve therapeutic and protective effects in various gastrointestinal diseases. However, there is no research exploring whether the modified GQD achieves its therapeutic mechanism for T2DM by regulating the intestinal microbiota.

PURPOSE

To explore the mechanism of modified GQD in the treatment of T2DM based on multi-omics, focusing on its effect on the "intestinal flora bile acid TGR5'' axis.

METHODS

The T2DM model was established using db/db mice, which were randomly divided into a model group, metformin group, high-dose GQD group, medium-dose GQD group, low-dose GQD group, while m/m mice were used as blank control. The drug intervention lasted for 12 weeks, during which the general conditions, oral glucose tolerance (OGT), blood glucose, and lipid-related indexes were recorded. Additionally, the fasting insulin (FINS), c-peptide, GLP-1 in serum, and cAMP in the ileum were measured by ELISA assay. Furthermore, the composition, abundance, and function of the intestinal microbiota were determined by macro genome sequencing, while bile acid was detected by targeted metabonomics. For histological evaluation, HE staining was used to observe the pathological changes of the ileum and pancreas, and the ultrastructure of the ileum and pancreas was observed by transmission electron microscopy. Apoptosis in the ileum tissue was detected by Tunel staining. Moreover, the mRNA and protein expressions of TGR5, PKA, CREB, PC1/3, GLP-1, and their phosphorylation levels in the ileum were detected by qPCR, immunohistochemistry, and Western blot; The expression of INS in the pancreas was also evaluated using immunohistochemistry. Finally, double immunofluorescence staining was used to detect the co-localization expression of TGR5 and GLP-1, NeuroD1, and GLP-1 in the ileum.

RESULTS

The modified GQD was found to significantly reduce blood glucose, improve oral glucose tolerance, and blood lipid levels, as well as alleviate the injury of the ileum and pancreas in T2DM mice. Furthermore, modified GQD was found to effectively regulate intestinal flora, improve bile acid metabolism, activate the TRG5/cAMP/PKA/CREB signal pathway, and stimulate GLP-1 secretion.

CONCLUSION

GQD can regulate the "intestinal flora-bile acid-TGR5" axis and has a therapeutic effect on T2DM in mice.

Oleanolic acid improved intestinal immune function by activating and potentiating bile acids receptor signaling in E. coli-challenged piglets

BACKGROUND

Infection with pathogenic bacteria during nonantibiotic breeding is one of the main causes of animal intestinal diseases. Oleanolic acid (OA) is a pentacyclic triterpene that is ubiquitous in plants. Our previous work demonstrated the protective effect of OA on intestinal health, but the underlying molecular mechanisms remain unclear. This study investigated whether dietary supplementation with OA can prevent diarrhea and intestinal immune dysregulation caused by enterotoxigenic Escherichia coli (ETEC) in piglets. The key molecular role of bile acid receptor signaling in this process has also been explored.

RESULTS

Our results demonstrated that OA supplementation alleviated the disturbance of bile acid metabolism in ETEC-infected piglets (P < 0.05). OA supplementation stabilized the composition of the bile acid pool in piglets by regulating the enterohepatic circulation of bile acids and significantly increased the contents of UDCA and CDCA in the ileum and cecum (P < 0.05). This may also explain why OA can maintain the stability of the intestinal microbiota structure in ETEC-challenged piglets. In addition, as a natural ligand of bile acid receptors, OA can reduce the severity of intestinal inflammation and enhance the strength of intestinal epithelial cell antimicrobial programs through the bile acid receptors TGR5 and FXR (P < 0.05). Specifically, OA inhibited NF-κB-mediated intestinal inflammation by directly activating TGR5 and its downstream cAMP-PKA-CREB signaling pathway (P < 0.05). Furthermore, OA enhanced CDCA-mediated MEK-ERK signaling in intestinal epithelial cells by upregulating the expression of FXR (P < 0.05), thereby upregulating the expression of endogenous defense molecules in intestinal epithelial cells.

CONCLUSIONS

In conclusion, our findings suggest that OA-mediated regulation of bile acid metabolism plays an important role in the innate immune response, which provides a new diet-based intervention for intestinal diseases caused by pathogenic bacterial infections in piglets.

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.

Impacts of dietary fat on multi tissue gene expression in the desert-adapted cactus mouse

Understanding the relationship between dietary fat and physiological responses is crucial in species adapted to arid environments where water scarcity is common. In this study, we present a comprehensive exploration of gene expression across five tissues (kidney, liver, lung, gastrointestinal tract, and hypothalamus) and 19 phenotypic measurements, investigating the effects of dietary fat in the desert-adapted cactus mouse ( Peromyscus eremicus ). We show impacts on immune function, circadian gene regulation, and mitochondrial function for mice fed a lower-fat diet compared to mice fed a higher-fat diet. In arid environments with severe water scarcity, even subtle changes in organismal health and water balance can affect physical performance, potentially impacting survival and reproductive success. The study sheds light on the complex interplay between diet, physiological processes, and environmental adaptation, providing valuable insights into the multifaceted impacts of dietary choices on organismal well-being and adaptation strategies in arid habitats.

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.

Mogrol stimulates G-protein-coupled bile acid receptor 1 (GPBAR1/TGR5) and insulin secretion from pancreatic β-cells and alleviates hyperglycemia in mice

Target identification is a crucial step in elucidating the mechanisms by which functional food components exert their functions. Here, we identified the G-protein-coupled bile acid receptor 1 (GPBAR1, also known as TGR5) as a target of the triterpenoid mogrol, a class of aglycone mogroside derivative from Siraitia grosvenorii. Mogrol, but not mogrosides, activated cAMP-response element-mediated transcription in a TGR5-dependent manner. Additionally, mogrol selectively activated TGR5 but not the other bile acid-responsive receptors (i.e., farnesoid X receptor, vitamin D receptor, or muscarinic acetylcholine receptor M3). Several amino acids in TGR5 (L71A2.60, W75AECL1, Q77AECL1, R80AECL1, Y89A3.29, F161AECL2, L166A5.39, Y240A6.51, S247A6.58, Y251A6.62, L262A7.35, and L266A7.39) were found to be important for mogrol-induced activation. Mogrol activated insulin secretion under low-glucose conditions in INS-1 pancreatic β-cells, which can be inhibited by a TGR5 inhibitor. Similar effects of mogrol on insulin secretion were observed in the isolated mouse islets. Mogrol administration partially but significantly alleviated hyperglycemia in KKAy diabetic mice by increasing the insulin levels without affecting the β-cell mass or pancreatic insulin content. These results suggest that mogrol stimulates insulin secretion and alleviates hyperglycemia by acting as a TGR5 agonist.

Tauroursodeoxycholic acid protects Schwann cells from high glucose-induced cytotoxicity by targeting NLRP3 to regulate cell migration and pyroptosis

Diabetic peripheral neuropathy (DPN) is the most prevalent complication of type 2 diabetes mellitus (T2DM), and it seriously affects the quality of life of patients. Tauroursodeoxycholic acid (TUDCA) is a bile acid that plays a protective role against various diseases. However, the function of TUDCA in DPN progression needs to be elucidated. Hence, this study clarified the action of TUDCA on DPN development and explored its mechanism of action. Fecal samples were collected from 50 patients with T2DM or DPN. Schwann cells induced by high levels were constructed to simulate an uncontrolled diabetic state. Cell viability and migration were measured using the CCK-8 and wound-healing assays, respectively. Reactive oxygen species and pyroptosis were detected using flow cytometry. Parabacteroides goldsteinii and Parabacteroides distasonis levels were decreased in the feces of patients with DPN. TUDCA enhanced the viability and migration ability of high glucose-stimulated Schwann cells. In addition, Schwann cell pyroptosis stimulated by high glucose levels was inhibited by TUDCA. Furthermore, the protective roles of TUDCA in cell viability, migration ability, and pyroptosis of Schwann cells stimulated by high glucose were suppressed by the overexpression of NLRP3. TUDCA enhanced cell viability and migration and suppressed pyroptosis in Schwann cells stimulated by high glucose levels by modulating NLRP3 expression. Thus, TUDCA may be a promising drug for DPN therapy.

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.

Physical exercise plays a role in rebalancing the bile acids of enterohepatic axis in non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is considered as one of the most common diseases of lipid metabolism disorders, which is closely related to bile acids disorders and gut microbiota disorders. Bile acids are synthesized from cholesterol in the liver, and processed by gut microbiota in intestinal tract, and participate in metabolic regulation through the enterohepatic circulation. Bile acids not only promote the consumption and absorption of intestinal fat but also play an important role in biological metabolic signaling network, affecting fat metabolism and glucose metabolism. Studies have demonstrated that exercise plays an important role in regulating the composition and function of bile acid pool in enterohepatic axis, which maintains the homeostasis of the enterohepatic circulation and the health of the host gut microbiota. Exercise has been recommended by several health guidelines as the first-line intervention for patients with NAFLD. Can exercise alter bile acids through the microbiota in the enterohepatic axis? If so, regulating bile acids through exercise may be a promising treatment strategy for NAFLD. However, the specific mechanisms underlying this potential connection are largely unknown. Therefore, in this review, we tried to review the relationship among NAFLD, physical exercise, bile acids, and gut microbiota through the existing data and literature, highlighting the role of physical exercise in rebalancing bile acid and microbial dysbiosis.

Research progress on the relationship between bile acid metabolism and type 2 diabetes mellitus

Bile acids, which are steroid molecules originating from cholesterol and synthesized in the liver, play a pivotal role in regulating glucose metabolism and maintaining energy balance. Upon release into the intestine alongside bile, they activate various nuclear and membrane receptors, influencing crucial processes. These bile acids have emerged as significant contributors to managing type 2 diabetes mellitus, a complex clinical syndrome primarily driven by insulin resistance. Bile acids substantially lower blood glucose levels through multiple pathways: BA-FXR-SHP, BA-FXR-FGFR15/19, BA-TGR5-GLP-1, and BA-TGR5-cAMP. They also impact blood glucose regulation by influencing intestinal flora, endoplasmic reticulum stress, and bitter taste receptors. Collectively, these regulatory mechanisms enhance insulin sensitivity, stimulate insulin secretion, and boost energy expenditure. This review aims to comprehensively explore the interplay between bile acid metabolism and T2DM, focusing on primary regulatory pathways. By examining the latest advancements in our understanding of these interactions, we aim to illuminate potential therapeutic strategies and identify areas for future research. Additionally, this review critically assesses current research limitations to contribute to the effective management of T2DM.

Drug-microbiota interactions: an emerging priority for precision medicine

Individual variability in drug response (IVDR) can be a major cause of adverse drug reactions (ADRs) and prolonged therapy, resulting in a substantial health and economic burden. Despite extensive research in pharmacogenomics regarding the impact of individual genetic background on pharmacokinetics (PK) and pharmacodynamics (PD), genetic diversity explains only a limited proportion of IVDR. The role of gut microbiota, also known as the second genome, and its metabolites in modulating therapeutic outcomes in human diseases have been highlighted by recent studies. Consequently, the burgeoning field of pharmacomicrobiomics aims to explore the correlation between microbiota variation and IVDR or ADRs. This review presents an up-to-date overview of the intricate interactions between gut microbiota and classical therapeutic agents for human systemic diseases, including cancer, cardiovascular diseases (CVDs), endocrine diseases, and others. We summarise how microbiota, directly and indirectly, modify the absorption, distribution, metabolism, and excretion (ADME) of drugs. Conversely, drugs can also modulate the composition and function of gut microbiota, leading to changes in microbial metabolism and immune response. We also discuss the practical challenges, strategies, and opportunities in this field, emphasizing the critical need to develop an innovative approach to multi-omics, integrate various data types, including human and microbiota genomic data, as well as translate lab data into clinical practice. To sum up, pharmacomicrobiomics represents a promising avenue to address IVDR and improve patient outcomes, and further research in this field is imperative to unlock its full potential for precision medicine.

Bile Acids and Microbiota Interplay in Pancreatic Cancer

Evidence suggests the involvement of the microbiota, including oral, intra-tumoral and gut, in pancreatic cancer progression and response to therapy. The gut microbiota modulates the bile acid pool and is associated with maintaining host physiology. Studies have shown that the bile acid/gut microbiota axis is dysregulated in pancreatic cancer. Bile acid receptor expression and bile acid levels are dysregulated in pancreatic cancer as well. Studies have also shown that bile acids can cause pancreatic cell injury and facilitate cancer cell proliferation. The microbiota and its metabolites, including bile acids, are also altered in other conditions considered risk factors for pancreatic cancer development and can alter responses to chemotherapeutic treatments, thus affecting patient outcomes. Altogether, these findings suggest that the gut microbial and/or bile acid profiles could also serve as biomarkers for pancreatic cancer detection. This review will discuss the current knowledge on the interaction between gut microbiota interaction and bile acid metabolism in pancreatic cancer.

GPCR-mediated effects of fatty acids and bile acids on glucose homeostasis

Fatty acids and glucose are key biomolecules that share several commonalities including serving as energy substrates and as signaling molecules. Fatty acids can be synthesized endogenously from intermediates of glucose catabolism via de-novo lipogenesis. Bile acids are synthesized endogenously in the liver from the biologically important lipid molecule, cholesterol. Evidence abounds that fatty acids and bile acids play direct and indirect roles in systemic glucose homeostasis. The tight control of plasma glucose levels during postprandial and fasted states is principally mediated by two pancreatic hormones, insulin and glucagon. Here, we summarize experimental studies on the endocrine effects of fatty acids and bile acids, with emphasis on their ability to regulate the release of key hormones that regulate glucose metabolism. We categorize the heterogenous family of fatty acids into short chain fatty acids (SCFAs), unsaturated, and saturated fatty acids, and highlight that along with bile acids, these biomolecules regulate glucose homeostasis by serving as endogenous ligands for specific G-protein coupled receptors (GPCRs). Activation of these GPCRs affects the release of incretin hormones by enteroendocrine cells and/or the secretion of insulin, glucagon, and somatostatin by pancreatic islets, all of which regulate systemic glucose homeostasis. We deduce that signaling induced by fatty acids and bile acids is necessary to maintain euglycemia to prevent metabolic diseases such as type-2 diabetes and related metabolic disorders.

Emerging Anti-Diabetic Drugs for Beta-Cell Protection in Type 1 Diabetes

Type 1 diabetes (T1D) is a chronic autoimmune disorder that damages beta cells in the pancreatic islets of Langerhans and results in hyperglycemia due to the loss of insulin. Exogenous insulin therapy can save lives but does not halt disease progression. Thus, an effective therapy may require beta-cell restoration and suppression of the autoimmune response. However, currently, there are no treatment options available that can halt T1D. Within the National Clinical Trial (NCT) database, a vast majority of over 3000 trials to treat T1D are devoted to insulin therapy. This review focuses on non-insulin pharmacological therapies. Many investigational new drugs fall under the category of immunomodulators, such as the recently FDA-approved CD-3 monoclonal antibody teplizumab. Four intriguing candidate drugs fall outside the category of immunomodulators, which are the focus of this review. Specifically, we discuss several non-immunomodulators that may have more direct action on beta cells, such as verapamil (a voltage-dependent calcium channel blocker), gamma aminobutyric acid (GABA, a major neurotransmitter with effects on beta cells), tauroursodeoxycholic acid (TUDCA, an endoplasmic reticulum chaperone), and volagidemab (a glucagon receptor antagonist). These emerging anti-diabetic drugs are expected to provide promising results in both beta-cell restoration and in suppressing cytokine-derived inflammation.

Understanding cell fate acquisition in stem-cell-derived pancreatic islets using single-cell multiome-inferred regulomes

Pancreatic islet cells derived from human pluripotent stem cells hold great promise for modeling and treating diabetes. Differences between stem-cell-derived and primary islets remain, but molecular insights to inform improvements are limited. Here, we acquire single-cell transcriptomes and accessible chromatin profiles during in vitro islet differentiation and pancreas from childhood and adult donors for comparison. We delineate major cell types, define their regulomes, and describe spatiotemporal gene regulatory relationships between transcription factors. CDX2 emerged as a regulator of enterochromaffin-like cells, which we show resemble a transient, previously unrecognized, serotonin-producing pre-β cell population in fetal pancreas, arguing against a proposed non-pancreatic origin. Furthermore, we observe insufficient activation of signal-dependent transcriptional programs during in vitro β cell maturation and identify sex hormones as drivers of β cell proliferation in childhood. Altogether, our analysis provides a comprehensive understanding of cell fate acquisition in stem-cell-derived islets and a framework for manipulating cell identities and maturity.

Insights by which TUDCA is a potential therapy against adiposity

Adipose tissue is an organ with metabolic and endocrine activity. White, brown and ectopic adipose tissues have different structure, location, and function. Adipose tissue regulates energy homeostasis, providing energy in nutrient-deficient conditions and storing it in high-supply conditions. To attend to the high demand for energy storage during obesity, the adipose tissue undergoes morphological, functional and molecular changes. Endoplasmic reticulum (ER) stress has been evidenced as a molecular hallmark of metabolic disorders. In this sense, the ER stress inhibitor tauroursodeoxycholic acid (TUDCA), a bile acid conjugated to taurine with chemical chaperone activity, has emerged as a therapeutic strategy to minimize adipose tissue dysfunction and metabolic alterations associated with obesity. In this review, we highlight the effects of TUDCA and receptors TGR5 and FXR on adipose tissue in the setting of obesity. TUDCA has been demonstrated to limit metabolic disturbs associated to obesity by inhibiting ER stress, inflammation, and apoptosis in adipocytes. The beneficial effect of TUDCA on perivascular adipose tissue (PVAT) function and adiponectin release may be related to cardiovascular protection in obesity, although more studies are needed to clarify the mechanisms. Therefore, TUDCA has emerged as a potential therapeutic strategy for obesity and comorbidities.

The bile acid TUDCA reduces age-related hyperinsulinemia in mice

Aging is associated with glucose metabolism disturbances, such as insulin resistance and hyperinsulinemia, which contribute to the increased prevalence of type 2 diabetes (T2D) and its complications in the elderly population. In this sense, some bile acids have emerged as new therapeutic targets to treat TD2, as well as associated metabolic disorders. The taurine conjugated bile acid, tauroursodeoxycholic acid (TUDCA) improves glucose homeostasis in T2D, obesity, and Alzheimer's disease mice model. However, its effects in aged mice have not been explored yet. Here, we evaluated the actions of TUDCA upon glucose-insulin homeostasis in aged C57BL/6 male mice (18-month-old) treated with 300 mg/kg of TUDCA or its vehicle. TUDCA attenuated hyperinsulinemia and improved glucose homeostasis in aged mice, by enhancing liver insulin-degrading enzyme (IDE) expression and insulin clearance. Furthermore, the improvement in glucose-insulin homeostasis in these mice was accompanied by a reduction in adiposity, associated with adipocyte hypertrophy, and lipids accumulation in the liver. TUDCA-treated aged mice also displayed increased energy expenditure and metabolic flexibility, as well as a better cognitive ability. Taken together, our data highlight TUDCA as an interesting target for the attenuation of age-related hyperinsulinemia and its deleterious effects on metabolism.

Gut and obesity/metabolic disease: Focus on microbiota metabolites

Obesity is often associated with the risk of chronic inflammation and other metabolic diseases, such as diabetes, cardiovascular disease, and cancer. The composition and activity of the gut microbiota play an important role in this process, affecting a range of physiological processes, such as nutrient absorption and energy metabolism. The active gut microbiota can produce a large number of physiologically active substances during the process of intestinal metabolism and reproduction, including short‐chain/long‐chain fatty acids, secondary bile acids, and tryptophan metabolites with beneficial effects on metabolism, as well as negative metabolites, including trimethylamine N‐oxide, delta‐valerobetaine, and imidazole propionate. How gut microbiota specifically affect and participate in metabolic and immune activities, especially the metabolites directly produced by gut microbiota, has attracted extensive attention. So far, some animal and human studies have shown that gut microbiota metabolites are correlated with host obesity, energy metabolism, and inflammation. Some pathways and mechanisms are slowly being discovered. Here, we will focus on the important metabolites of gut microbiota (beneficial and negative), and review their roles and mechanisms in obesity and related metabolic diseases, hoping to provide a new perspective for the treatment and remission of obesity and other metabolic diseases from the perspective of metabolites.

Inhibition of Endoplasmic Reticulum Stress Improves Acetylcholine-Mediated Relaxation in the Aorta of Type-2 Diabetic Rats

Endoplasmic reticulum (ER) stress contributes to insulin resistance and macro- and microvascular complications associated with diabetes. This study aimed to evaluate the effect of ER stress inhibition on endothelial function in the aorta of type-2 diabetic rats. Type-2 diabetes was developed in male Sprague–Dawley rats using a high-fat diet and low-dose streptozotocin. Rat aortic tissues were harvested to study endothelial-dependent relaxation. The mechanisms for acetylcholine-mediated relaxation were investigated using pharmacological blockers, Western blotting, oxidative stress, and inflammatory markers. Acetylcholine-mediated relaxation was diminished in the aorta of diabetic rats compared to control rats; supplementation with TUDCA improved relaxation. In the aortas of control and diabetic rats receiving TUDCA, the relaxation was mediated via eNOS/PI3K/Akt, NAD(P)H, and the K_ATP channel. In diabetic rats, acetylcholine-mediated relaxation involved eNOS/PI3K/Akt and NAD(P)H, but not the K_ATP channel. The expression of ER stress markers was upregulated in the aorta of diabetic rats and reduced with TUDCA supplementation. The expression of eNOS and Akt were lower in diabetic rats but were upregulated after supplementation with TUDCA. The levels of MDA, IL-6, and SOD activity were higher in the aorta of the diabetic rats compared to control rats. This study demonstrated that endothelial function was impaired in diabetes, however, supplementation with TUDCA improved the function via eNOS/Akt/PI3K, NAD(P)H, and the K_ATP channel. The improvement of endothelial function was associated with increased expressions of eNOS and Akt. Thus, ER stress plays a crucial role in the impairment of endothelial-dependent relaxation. Mitigating ER stress could be a potential strategy for improving endothelial dysfunction in type-2 diabetes.

Tauroursodeoxycholic acid (TUDCA) improves intestinal barrier function associated with TGR5-MLCK pathway and the alteration of serum metabolites and gut bacteria in weaned piglets

Background

Tauroursodeoxycholic acid (TUDCA), a hydrophilic bile acid, is the main medicinal component of bear bile and is commonly used to treat a variety of hepatobiliary diseases. Meanwhile, TUDCA has been shown to modulate the intestinal barrier function and alleviate DSS-induced colitis in mice. However, the effect of TUDCA on the intestinal barrier of weaned piglets remains largely unclear.

Methods

The weaned piglets and porcine IPEC-J2 intestinal epithelial cells were used to investigate the effects of TUDCA on intestinal barrier function in weaned piglets and explore the possible underlying mechanisms. In vivo, 72 healthy weaned piglets were randomly allocated into 2 groups according to their gender and body weight, and piglets were fed the basal diet with 0 (control, CON) and 200 mg/kg TUDCA for 30 d, respectively. Three female and three male piglets reflecting the average bodyweight were slaughtered in each group and samples were collected. In vitro, IPEC-J2 cells were subjected to 100 μmol/L TUDCA to explore the possible underlying mechanisms.

Results

Our results demonstrated that dietary TUDCA supplementation significantly reduced the diarrhea incidence of weaned piglets, possibly attributing to the TUDCA-enhanced intestinal barrier function and immunity. In addition, TUDCA supplementation altered serum metabolites and the relative abundance of certain gut bacteria, which might contribute to the improved intestinal barrier function. Furthermore, the in-vitro results showed that TUDCA improved the E. coli-induced epithelial barrier impairment of IPEC-J2 cells and increased Takeda G-coupled protein receptor 5 (TGR5) protein expression. However, knockdown of TGR5 and inhibition of myosin light chain kinase (MLCK) pathway abolished the TUDCA-improved epithelial barrier impairment in E. coli-treated IPEC-J2 cells, indicating the involvement of TGR5-MLCK in this process.

Conclusions

These findings showed that TUDCA improved intestinal barrier function associated with TGR5-MLCK pathway and the alteration of serum metabolites and gut bacteria in weaned piglets, suggesting the potential application of TUDCA in improving gut health in piglet production.

Gut Microbiota and Antidiabetic Drugs: Perspectives of Personalized Treatment in Type 2 Diabetes Mellitus

Alterations in the composition and function of the gut microbiota have been reported in patients with type 2 diabetes mellitus (T2DM). Emerging studies show that prescribed antidiabetic drugs distort the gut microbiota signature associated with T2DM. Even more importantly, accumulated evidence provides support for the notion that gut microbiota, in turn, mediates the efficacy and safety of antidiabetic drugs. In this review, we highlight the current state-of-the-art knowledge on the crosstalk and interactions between gut microbiota and antidiabetic drugs, including metformin, α-glucosidase inhibitors, glucagon-like peptide-1 receptor agonists, dipeptidyl peptidase-4 inhibitors, sodium-glucose cotransporter 2 inhibitors, traditional Chinese medicines and other antidiabetic drugs, as well as address corresponding microbial-based therapeutics, aiming to provide novel preventative strategies and personalized therapeutic targets in T2DM.

Taurine Supplementation as a Neuroprotective Strategy upon Brain Dysfunction in Metabolic Syndrome and Diabetes

Obesity, type 2 diabetes, and their associated comorbidities impact brain metabolism and function and constitute risk factors for cognitive impairment. Alterations to taurine homeostasis can impact a number of biological processes, such as osmolarity control, calcium homeostasis, and inhibitory neurotransmission, and have been reported in both metabolic and neurodegenerative disorders. Models of neurodegenerative disorders show reduced brain taurine concentrations. On the other hand, models of insulin-dependent diabetes, insulin resistance, and diet-induced obesity display taurine accumulation in the hippocampus. Given the possible cytoprotective actions of taurine, such cerebral accumulation of taurine might constitute a compensatory mechanism that attempts to prevent neurodegeneration. The present article provides an overview of brain taurine homeostasis and reviews the mechanisms by which taurine can afford neuroprotection in individuals with obesity and diabetes. We conclude that further research is needed for understanding taurine homeostasis in metabolic disorders with an impact on brain function.

Association of Promoter Methylation and Expression of Inflammatory Genes IL-6 and TNF-α with the Risk of Coronary Artery Disease in Diabetic and Obese Subjects among Asian Indians

The inflammatory cytokines such as interleukin-6 (IL-6) and tumour necrosis factor-alpha (TNF-α) are considered as the most important contributors to the endothelial dysfunction in subjects with type 2 diabetes mellitus (T2DM) and obesity. The hypomethylation of CpG sites in the promoter region of the IL-6 and TNF-α have shown to be associated with the increased expression of IL-6 and TNF-α. However, there are no studies on the methylation and expression of IL-6 and TNF-α with the risk of coronary artery disease (CAD) in subjects with T2DM and obesity in Asian Indians. Hence, the present study was aimed to investigate whether the IL-6, TNF-α promoter methylation and expression in blood leukocyte DNA is associated with the risk of CAD in diabetic and obese subjects in Asian Indians. For this study, we recruited 574 subjects which includes, 207 angiographically confirmed CAD patients, 100 T2DM patients, 82 obese subjects and 185 healthy controls. The methylation status of IL-6 and TNF-α gene loci was determined by methylation specific PCR (MPCR) and gene expression was determined by qPCR. We found significant hypomethylation of IL-6 in CAD and T2DM subjects (OR 1.98 95% CI: 1.32-2.97, p = 0.001, OR: 2.23 95% CI:1.34-3.76, p = 0.001, respectively). Further, a significant increase in the expression of IL-6 in CAD and T2DM subjects (fold change: 26.39 & 14.7, p = 0.0001) compared to the control subjects was observed. A significant increase in the hypomethylation of TNF-α in CAD, T2DM and obese subjects was observed as compared to the control (OR: 2.04 95% CI: 1.36-3.05, p = 0.0005, OR: 1.81 95% CI 1.10-2.96, p = 0.01, and OR: 2.1 95% CI 1.24-3.57, p = 0.007, respectively).We also found an increased expression of TNF-α in CAD, T2DM and obese subjects as compared to controls. In addition, presence of low folate, and hyperhomocysteinemia was observed in the present study, may be the contributing factors for the hypomethylation of IL-6 and TNF-α and oxidative stress. In conclusion, increased expression of IL-6 and TNF-α due to hypomethylation in T2DM and obese individuals may contribute to CAD risk in these subjects. The presence of hyperhomocysteinemia and increased oxidative risk may enhance the CAD risk further.

Effects of tauroursodeoxycholic acid on glucose homeostasis: Potential binding of this bile acid with the insulin receptor

AIMS

The bile acid (BA), tauroursodeoxycholic acid (TUDCA) regulates glucose homeostasis; however, it is not clear whether its effects on insulin signaling are due to its direct interaction with the insulin receptor (IR) or through activation of the G-coupled BA receptor, TGR5. We, herein, investigated whether the actions of TUDCA on glucose homeostasis occur via IR or TGR5 activation.

MAIN METHODS

Glucose homeostasis was evaluated in high-fat diet (HFD)-obese or control (CTL) mice, after 30 days or one intraperitoneal (ip) injection of 300 mg/kg TUDCA, respectively. Molecular docking was performed to investigate the potential binding of TUDCA on the IR and TGR5.

KEY FINDINGS

After 30 days of TUDCA treatment, HFD mice exhibited improvements in glucose tolerance and insulin sensitivity, which were abolished when these rodents received the IR antagonist, S961. Molecular docking experiments showed that TUDCA demonstrates high binding affinity for TGR5 and IR and strongly interacts with the insulin binding sites 1 and 2 of the IR. Consistent with this potential agonist activity of TUDCA on IR, CTL mice displayed increased hepatic phosphorylation of AKT after an ip injection of TUDCA. This effect was not associated with altered glycemia in CTL mice and was dependent on IR activation, as S961 prevented hepatic AKT activation by TUDCA. Furthermore, TUDCA activated the hepatic protein kinase A (PKA) and cAMP response element-binding protein (CREB) pathway in CTL mice, even after the administration of S961.

SIGNIFICANCE

We provide novel evidence that TUDCA may be an agonist of the IR, in turn activating AKT and contributing, at least in part, to its beneficial effects upon glucose homeostasis.

Targeted metabolomic analysis identifies increased serum levels of GABA and branched chain amino acids in canine diabetes

INTRODUCTION

Dogs with naturally occurring diabetes mellitus represent a potential model for human type 1 diabetes, yet significant knowledge voids exist in terms of the pathogenic mechanisms underlying the canine disorder. Untargeted metabolomic studies from a limited number of diabetic dogs identified similarities to humans with the disease.

OBJECTIVE

To expand and validate earlier metabolomic studies, identify metabolites that differ consistently between diabetic and healthy dogs, and address whether certain metabolites might serve as disease biomarkers.

METHODS

Untargeted metabolomic analysis via liquid chromatography-mass spectrometry was performed on serum from diabetic (n = 15) and control (n = 15) dogs. Results were combined with those of our previously published studies using identical methods (12 diabetic and 12 control dogs) to identify metabolites consistently different between the groups in all 54 dogs. Thirty-two candidate biomarkers were quantified using targeted metabolomics. Biomarker concentrations were compared between the groups using multiple linear regression (corrected P < 0.0051 considered significant).

RESULTS

Untargeted metabolomics identified multiple persistent differences in serum metabolites in diabetic dogs compared with previous studies. Targeted metabolomics showed increases in gamma amino butyric acid, valine, leucine, isoleucine, citramalate, and 2-hydroxyisobutyric acid in diabetic versus control dogs while indoxyl sulfate, N-acetyl-L-aspartic acid, kynurenine, anthranilic acid, tyrosine, glutamine, and tauroursodeoxycholic acid were decreased.

CONCLUSION

Several of these findings parallel metabolomic studies in both human diabetes and other animal models of this disease. Given recent studies on the role of GABA and branched chain amino acids in human diabetes, the increase in serum concentrations in canine diabetes warrants further study of these metabolites as potential biomarkers, and to identify similarity in mechanisms underlying this disease in humans and dogs.

TGR5 agonists for diabetes treatment: a patent review and clinical advancements (2012-present)

INTRODUCTION

A cell surface bile acid receptor TGR5 can be considered a promising target for the treatment of various metabolic diseases. The TGR5 receptor is expressed in various tissues, including the liver, kidney, intestine, and adrenal glands, causing its effect in each tissue to differ. A major role for TGR5 is to maintain blood sugar levels. Also, TGR5 is postulated to contribute to an increase in energy expenditure. These benefits make it a potential candidate for the treatment of type 2 diabetes, obesity, and other metabolic diseases.

AREA COVERED

This paper highlights recent advances in the development of potent steroidal and non-steroidal TGR5 agonists and the peer-reviewed scientific articles that have led to understanding the structure-activity relationship for TGR5 agonists (2012-2020). The review also discusses the clinical progress made by some TGR5 agonists over the past eight years.

EXPERT OPINION

Preclinical studies have suggested a key role for the TGR5 receptor in GLP-1 secretion and have shown promising outcomes such as weight loss, anti-inflammatory, anti-diabetic effects. Along with the evaluation of semisynthetic derivatives, synthetic compounds can also be considered as a possible avenue for the discovery of novel TGR5 agonists. Currently, few TGR5 agonists have reached the clinical trial stage, and, likely, we will soon discover a novel TGR5 modulator with fewer adverse effects. In silico studies can be performed with these scaffolds ranging from steroidal to heterocyclic rings to discover selective and safe TGR5 agonists.

TUDCA receptors and their role on pancreatic beta cells

Bile acids have received increasing attention over the past years as their multiple alternative roles became clearer. Tauroursodeoxycholic Acid (TUDCA) in specific has generated special interest due to its ability to promote pancreatic survival and function, as well as reduce endoplasmic reticulum stress. However, there are few studies explaining the molecular mechanisms behind TUDCA's beneficial actions on pancreatic beta cells. In this review, we decided to review the literature in order to craft a primer for researchers on what is known about TUDCA's receptors and the molecular pathways involved in this bile acid's function in the endocrine pancreas. We review the studies that focused on G protein-coupled bile acid receptor (TGR5), Sphingosine-1-phosphate receptor 2 (S1PR2) and α5β1 Integrin function in pancreatic cells. Our hope is to provide a basis for future studies to expand upon, especially considering the current lack of studies focusing on the importance of these receptors, either through TUDCA signaling or other signaling molecules.

Local administration with tauroursodeoxycholic acid could improve osseointegration of hydroxyapatite-coated titanium implants in ovariectomized rats

Despite advances in the pathogenesis of Tauroursodeoxycholic acid (TUDCA) on bone, the understanding of the effects and mechanisms of bone osseointegration in TUDCA-associated Hydroxyapatite (HA)-coated titanium implants remains poor. Therefore, the present work was aimed to evaluate the effect of local administration with TUDCA on HA-coated titanium implants osseointegration in ovariectomized(OVX) rats and further investigation of the possible mechanism. Twelve weeks after bilateral ovariectomy, all animals were randomly divided into three groups: sham operation(Sham) group, OVX group and TUDCA group, and all the rats from Sham group and OVX group received HA implants and animals belonging to group TUDCA received TUDCA-HA implants until death at 12 weeks. The bilateral femurs of rats were harvested for evaluation. TUDCA increased new bone formation around the surface of titanium rods and push-out force other than group OVX. Histology, Micro-CT and biochemical analysis results showed systemic TUDCA showed positive effects than OVX group on bone formation in osteopenic rats, with beneficial effect on via activation OPG/RANKL pathway and BMP-2/Smad1 pathway and microarchitecture as well as by reducing protein expression of TNF-α and IFN-γ. The present study suggests that local use of TUDCA may bring benefits to the osseointegration of HA-coated titanium implants in patients with osteoporosis, and this effect may be related to the inhibition of inflammatory reaction and promotion of osteogenesis.

Obesity-induced changes in human islet G protein-coupled receptor expression: Implications for metabolic regulation

G protein-coupled receptors (GPCRs) are a large family of cell surface receptors that are the targets for many different classes of pharmacotherapy. The islets of Langerhans are central to appropriate glucose homeostasis through their secretion of insulin, and islet function can be modified by ligands acting at the large number of GPCRs that islets express. The human islet GPCRome is not a static entity, but one that is altered under pathophysiological conditions and, in this review, we have compared expression of GPCR mRNAs in human islets obtained from normal weight range donors, and those with a weight range classified as obese. We have also considered the likely outcomes on islet function that the altered GPCR expression status confers and the possible impact that adipokines, secreted from expanded fat depots, could have at those GPCRs showing altered expression in obesity.

The bile acid TUDCA and neurodegenerative disorders: An overview

Bear bile has been used in Traditional Chinese Medicine for thousands of years due to its therapeutic potential and clinical applications. The tauroursodeoxycholic acid (TUDCA), one of the acids found in bear bile, is a hydrophilic bile acid and naturally produced in the liver by conjugation of taurine to ursodeoxycholic acid (UDCA). Several studies have shown that TUDCA has neuroprotective action in several models of neurodegenerative disorders (ND), including Alzheimer's disease, Parkinson's disease, and Huntington's disease, based on its potent ability to inhibit apoptosis, attenuate oxidative stress, and reduce endoplasmic reticulum stress in different experimental models of these illnesses. Our research extends the knowledge of the bile acid TUDCA actions in ND and the mechanisms and pathways involved in its cytoprotective effects on the brain, providing a novel perspective and opportunities for treatment of these diseases.

The bile acid TUDCA improves glucose metabolism in streptozotocin-induced Alzheimer's disease mice model

Alzheimer's disease (AD) is a neurodegenerative disorder and the major cause of dementia. According to predictions of the World Health Organization, more than 150 million people worldwide will suffer from dementia by 2050. An increasing number of studies have associated AD with type 2 diabetes mellitus (T2DM), since most of the features found in T2DM are also observed in AD, such as insulin resistance and glucose intolerance. In this sense, some bile acids have emerged as new therapeutic targets to treat AD and metabolic disorders. The taurine conjugated bile acid, tauroursodeoxycholic (TUDCA), reduces amyloid oligomer accumulation and improves cognition in APP/PS1 mice model of AD, and also improves glucose-insulin homeostasis in obese and type 2 diabetic mice. Herein, we investigated the effect of TUDCA upon glucose metabolism in streptozotocin-induced AD mice model (Stz). The Stz mice that received 300 mg/kg TUDCA during 10 days (Stz + TUDCA), showed improvement in glucose tolerance and insulin sensitivity, reduced fasted and fed glycemia, increased islet mass and β-cell area, as well as increased glucose-stimulated insulin secretion, compared with Stz mice that received only PBS. Stz + TUDCA mice also displayed lower neuroinflammation, reduced protein content of amyloid oligomer in the hippocampus, improved memory test and increased protein content of insulin receptor β-subunit in the hippocampus. In conclusion, TUDCA treatment enhanced glucose homeostasis in the streptozotocin-induced Alzheimer's disease mice model, pointing this bile acid as a good strategy to counteract glucose homeostasis disturbance in AD pathology.

Bisphenol-S and Bisphenol-F alter mouse pancreatic β-cell ion channel expression and activity and insulin release through an estrogen receptor ERβ mediated pathway

Bisphenol-S (BPS) and Bisphenol-F (BPF) are current Bisphenol-A (BPA) substitutes. Here we used pancreatic β-cells from wild type (WT) and estrogen receptor β (ERβ) knockout (BERKO) mice to investigate the effects of BPS and BPF on insulin secretion, and the expression and activity of ion channels involved in β-cell function. BPS or BPF rapidly increased insulin release and diminished ATP-sensitive K⁺ (K_ATP) channel activity. Similarly, 48 h treatment with BPS or BPF enhanced insulin release and decreased the expression of several ion channel subunits in β-cells from WT mice, yet no effects were observed in cells from BERKO mice. PaPE-1, a ligand designed to preferentially trigger extranuclear-initiated ER pathways, mimicked the effects of bisphenols, suggesting the involvement of extranuclear-initiated ERβ pathways. Molecular dynamics simulations indicated differences in ERβ ligand-binding domain dimer stabilization and solvation free energy among different bisphenols and PaPE-1. Our data suggest a mode of action involving ERβ whose activation alters three key cellular events in β-cell, namely ion channel expression and activity, and insulin release. These results may help to improve the hazard identification of bisphenols.

INT-777 attenuates NLRP3-ASC inflammasome-mediated neuroinflammation via TGR5/cAMP/PKA signaling pathway after subarachnoid hemorrhage in rats

BACKGROUND

Inflammasome-mediated neuroinflammation plays an important role in the pathogenesis of early brain injury (EBI) following subarachnoid hemorrhage (SAH). The activation of the TGR5 receptor has been shown to be neuroprotective in a variety of neurological diseases. This study aimed to investigate the effects of the specific synthetic TGR5 agonist, INT-777, in attenuating NLRP3-ASC inflammasome activation and reducing neuroinflammation after SAH.

METHODS

One hundred and eighty-four male Sprague Dawley rats were used. SAH was induced by the endovascular perforation. INT-777 was administered intranasally at 1 h after SAH induction. To elucidate the signaling pathway involved in the effect of INT-777 on inflammasome activation during EBI, TGR5 knockout CRISPR and PKA inhibitor H89 were administered intracerebroventricularly and intraperitoneally at 48 h and 1 h before SAH. The SAH grade, short- and long-term neurobehavioral assessments, brain water content, western blot, immunofluorescence staining, and Nissl staining were performed.

RESULTS

The expressions of endogenous TGR5, p-PKA, and NLRP3-ASC inflammasome were increased after SAH. INT-777 administration significantly decreased NLRP3-ASC inflammasome activation in microglia, reduced brain edema and neuroinflammation, leading to improved short-term neurobehavioral functions at 24 h after SAH. The administration of TGR5 CRISPR or PKA inhibitor (H89) abolished the anti-inflammation effects of INT-777, on NLRP3-ASC inflammasome, pro-inflammatory cytokines (IL-6, IL-1β, and TNF-a), and neutrophil infiltration at 24 h after SAH. Moreover, early administration of INT-777 attenuated neuronal degeneration in hippocampus on 28 d after SAH.

CONCLUSIONS

INT-777 attenuated NLRP3-ASC inflammasome-dependent neuroinflammation in the EBI after SAH, partially via TGR5/cAMP/PKA signaling pathway. Early administration of INT-777 may serve as a potential therapeutic strategy for EBI management in the setting of SAH.

Tauroursodeoxycholic acid attenuates neuronal apoptosis via the TGR5/ SIRT3 pathway after subarachnoid hemorrhage in rats

Background

Neuronal apoptosis plays a critical event in the pathogenesis of early brain injury after subarachnoid hemorrhage (SAH). This study investigated the roles of Tauroursodeoxycholic acid (TUDCA) in attenuate neuronal apoptosis and underlying mechanisms after SAH.

Methods

Sprague–Dawley rats were subjected to model of SAH and TUDCA was administered via the internal carotid injection. Small interfering RNA (siRNA) for TGR5 were administered through intracerebroventricular injection 48 h before SAH. Neurological scores, brain water content, Western blot, TUNEL staining and immunofluorescence staining were evaluated.

Results

TUDCA alleviated brain water content and improved neurological scores at 24 h and 72 h after SAH. TUDCA administration prevented the reduction of SIRT3 and BCL-2 expressions, as well as the increase of BAX and cleaved caspase-3.Endogenous TGR5 expression were upregulated after SAH and treatment with TGR5 siRNA exacerbated neurological outcomes after SAH and the protective effects of TUDCA at 24 h after SAH were also abolished by TGR5 siRNA.

Conclusions

Our findings demonstrate that TUDCA could attenuated neuronal apoptosis and improve neurological functions through TGR5/ SIRT3 signaling pathway after SAH. TUDCA may be an attractive candidate for anti-apoptosis treatment in SAH.

ASBT(SLC10A2): A promising target for treatment of diseases and drug discovery

Bile acids has gradually become a new focus in various diseases, and ASBT as a transporter responsible for the reabsorption of ileal bile acids, is a key hinge associated to the bile acids-cholesterol balance and bile acids of enterohepatic circulation. The cumulative studies have also shown that ASBT is a promising target for treatment of liver, gallbladder, intestinal and metabolic diseases. This article briefly reviewed the process of bile acids enterohepatic circulation, as well as the regulations of ASBT expression, covering transcription factors, nuclear receptors and gut microbiota. In addition, the relationship between ASBT and various diseases were discussed in this paper. According to the structural classification of ASBT inhibitors, the research status of ASBT inhibitors and potential ASBT inhibitors of traditional Chinese medicine (such resveratrol, jatrorrhizine in Coptis chinensis) were summarized. This review provides a basis for the development of ASBT inhibitors and the treatment strategy of related diseases.

Maternal glucose homeostasis is impaired in mouse models of gestational cholestasis

Women with intrahepatic cholestasis of pregnancy (ICP), a disorder characterised by raised serum bile acids, are at increased risk of developing gestational diabetes mellitus and have impaired glucose tolerance whilst cholestatic. FXR and TGR5 are modulators of glucose metabolism, and FXR activity is reduced in normal pregnancy, and further in ICP. We aimed to investigate the role of raised serum bile acids, FXR and TGR5 in gestational glucose metabolism using mouse models. Cholic acid feeding resulted in reduced pancreatic β-cell proliferation and increased apoptosis in pregnancy, without altering insulin sensitivity, suggesting that raised bile acids affect β-cell mass but are insufficient to impair glucose tolerance. Conversely, pregnant Fxr-/- and Tgr5-/- mice are glucose intolerant and have reduced insulin secretion in response to glucose challenge, and Fxr-/- mice are also insulin resistant. Furthermore, fecal bile acids are reduced in pregnant Fxr-/- mice. Lithocholic acid and deoxycholic acid, the principal ligands for TGR5, are decreased in particular. Therefore, we propose that raised serum bile acids and reduced FXR and TGR5 activity contribute to the altered glucose metabolism observed in ICP.

Therapeutic Potential of Tauroursodeoxycholic Acid for the Treatment of Osteoporosis

Tauroursodeoxycholic acid (TUDCA) is a US FDA-approved hydrophilic bile acid for the treatment of chronic cholestatic liver disease. In the present study, we investigate the effects of TUDCA on the proliferation and differentiation of osteoblasts and its therapeutic effect on a mice model of osteoporosis. Following treatment with different concentrations of TUDCA, cell viability, differentiation, and mineralization were measured. Three-month-old female C57BL/6 mice were randomly divided into three groups (n = 8 mice per group): (i) normal mice as the control group, (ii) ovariectomy (OVX) group (receiving phosphate-buffered saline (PBS) treatment every other day for 4 weeks), and (iii) OVX group with TUDCA (receiving TUDCA treatment every other day for 4 weeks starting 6 weeks after OVX). At 11 weeks post-surgery, serum levels of procollagen type I N-terminal propeptides (PINP) and type I collagen crosslinked C-telopeptides (CTX) were measured, and all mice were sacrificed to examine the distal femur by micro-computed tomography (CT) scans and histology. TUDCA (100 nM, 1 µM) significantly increased the proliferation and viability of osteoblasts and osteoblast differentiation and mineralization when used in vitro. Furthermore, TUDCA neutralized the detrimental effects of methylprednisolone (methylprednisolone-induced osteoblast apoptosis). In the TUDCA treatment group the PINP level was higher and the CTX level was lower, but these levels were not significantly different compared to the PBS treatment group. Micro-CT and histology showed that the TUDCA treatment group preserved more trabecular structures in the distal femur compared to the PBS treatment group. In addition, the TUDCA treatment group increased the percentage bone volume with respect to the total bone volume, bone mineral density, and mice distal femur trabeculae compared with the PBS treatment group. Taken together, our findings suggest that TUDCA may provide a favorable effect on bones and could be used for the prevention and treatment of osteoporosis.

From role of gut microbiota to microbial-based therapies in type 2-diabetes

The incidence of type 2 diabetes mellitus (T2DM) has increased dramatically at an alarming level around the world.T2DM is associated with changeable risk factors in lifestyle as well as genetic and family associated risk factors. More importantly, imbalanced or impaired gut microbial distribution (dysbiosis) has been reported as a contributing risk factor in insulin resistance progression in T2DM. Dysbiosis may restructure the metabolic and functional pathways in the intestine which are involved in the development of T2DM. However, several studies have indicated the constructive and helpful effect of prebiotics, probiotics, and fecal microbiota transplantation (FMT) on the improvement of gut microbiota (GM) and accordingly host metabolism. In this review, the association between GM and T2DM have been evaluated and the role of prebiotics, probiotics and FMT, as potential therapeutic approaches have been discussed. Relevant studies were obtained randomly from online databases such as PubMed/Medline and ISI Web of Science.

Regulation of Adipsin Expression by Endoplasmic Reticulum Stress in Adipocytes

Adpsin is an adipokine that stimulates insulin secretion from β-cells and improves glucose tolerance. Its expression has been found to be markedly reduced in obese animals. However, it remains unclear what factors lead to downregulation of adipsin in the context of obesity. Endoplasmic reticulum (ER) stress response is activated in various tissues under obesity-related conditions and can induce transcriptional reprogramming. Therefore, we aimed to investigate the relationship between adipsin expression and ER stress in adipose tissues during obesity. We observed that obese mice exhibited decreased levels of adipsin in adipose tissues and serum and increased ER stress markers in adipose tissues compared to lean mice. We also found that ER stress suppressed adipsin expression via adipocytes-intrinsic mechanisms. Moreover, the ER stress-mediated downregulation of adipsin was at least partially attributed to decreased expression of peroxisome proliferator-activated receptor γ (PPARγ), a key transcription factor in the regulation of adipocyte function. Finally, treatment with chemical chaperones recovered the ER stress-mediated downregulation of adipsin and PPARγ in vivo and in vitro. Our findings suggest that activated ER stress in adipose tissues is an important cause of the suppression of adipsin expression in the context of obesity.

Oral gavage of nano-encapsulated conjugated acrylic acid-bile acid formulation in type 1 diabetes altered pharmacological profile of bile acids, and improved glycaemia and suppressed inflammation

BACKGROUND

Ursodeoxycholic acid (UDCA) is a secondary hydrophilic bile acid, metabolised in the gut, by microbiota. UDCA is currently prescribed for primary biliary cirrhosis, and of recently has shown β-cell protective effects, which suggests potential antidiabetic effects. Thus, this study aimed to design targeted-delivery microcapsules for oral uptake of UDCA and test its effects in type 1 diabetes (T1D).

METHODS

UDCA microcapsules were produced using alginate-NM30 matrix. Three equal groups of mice (6-7 mice per group) were gavaged daily UDCA powder, empty microcapsules and UDCA microcapsules for 7 days, then T1D was induced by alloxan injection and treatments continued until mice had to be euthanised due to weight loss > 10% or severe symptoms develop. Plasma, tissues, and faeces were collected and analysed for bile acids' concentrations.

RESULTS

UDCA microcapsules brought about reduction in elevated blood glucose, reduced inflammation and altered concentrations of the primary bile acid chenodeoxycholic acid and the secondary bile acid lithocholic acid, without affecting survival rate of mice.

CONCLUSION

The findings suggest that UDCA exerted direct protective effects on pancreatic β-cells and this is likely to be associated with alterations of concentrations of primary and secondary bile acids in plasma and tissues. Three equal groups of mice were gavaged daily UDCA (ursodeoxycholic acid) powder, empty microcapsules and UDCA microcapsules for 7 days, then T1D was induced and treatments continued until mice had to be euthanised. UDCA microcapsules brought about reduction in elevated blood glucose, reduced inflammation and altered concentrations of the primary bile acid chenodeoxycholic acid and the secondary bile acid lithocholic acid, without affecting survival rate of mice. The findings suggest that UDCA exerted direct protective effects on pancreatic β-cells and this is likely to be associated with alterations of concentrations of primary and secondary bile acids in plasma and tissues.

D2-Like Receptors Mediate Dopamine-Inhibited Insulin Secretion via Ion Channels in Rat Pancreatic β-Cells

Dopamine (DA) has a vital role in the central nervous system and also modulates lipid and glucose metabolism. The present study aimed to investigate the effect of dopamine on insulin secretion and the underlying mechanisms in rat pancreatic β-cells. Data from the radioimmunoassay indicated that dopamine inhibited insulin secretion in a glucose- and dose-dependent manner. This inhibitory effect of dopamine was mediated mainly by D2-like receptors, but not D1-like receptors. Whole-cell patch-clamp recordings showed that dopamine decreased voltage-dependent Ca²⁺ channel currents, which could be reversed by inhibition of the D2-like receptor. Dopamine increased voltage-dependent potassium (K_V) channel currents and shortened action potential duration, which was antagonized by inhibition of D2-like receptors. Further experiments showed that D2-like receptor activation by quinpirole increased K_V channel currents. In addition, using calcium imaging techniques, we found that dopamine reduced intracellular Ca²⁺ concentration, which was also reversed by D2-like receptor antagonists. Similarly, quinpirole was found to decrease intracellular Ca²⁺ levels. Taken together, these findings demonstrate that dopamine inhibits insulin secretion mainly by acting on D2-like receptors, inhibiting Ca²⁺ channels, and activating Kv channels. This process results in shortened action potential duration and decreased intracellular Ca²⁺ levels in β-cells. This work offers new insights into a glucose-dependent mechanism whereby dopamine regulates insulin secretion.

Bile acids in glucose metabolism and insulin signalling - mechanisms and research needs

Of all the novel glucoregulatory molecules discovered in the past 20 years, bile acids (BAs) are notable for the fact that they were hiding in plain sight. BAs were well known for their requirement in dietary lipid absorption and biliary cholesterol secretion, due to their micelle-forming properties. However, it was not until 1999 that BAs were discovered to be endogenous ligands for the nuclear receptor FXR. Since that time, BAs have been shown to act through multiple receptors (PXR, VDR, TGR5 and S1PR2), as well as to have receptor-independent mechanisms (membrane dynamics, allosteric modulation of N-acyl phosphatidylethanolamine phospholipase D). We now also have an appreciation of the range of physiological, pathophysiological and therapeutic conditions in which endogenous BAs are altered, raising the possibility that BAs contribute to the effects of these conditions on glycaemia. In this Review, we highlight the mechanisms by which BAs regulate glucose homeostasis and the settings in which endogenous BAs are altered, and provide suggestions for future research.

Tauroursodeoxycholate-Bile Acid with Chaperoning Activity: Molecular and Cellular Effects and Therapeutic Perspectives

Tauroursodeoxycholic acid (TUDCA) is a naturally occurring hydrophilic bile acid that has been used for centuries in Chinese medicine. Chemically, TUDCA is a taurine conjugate of ursodeoxycholic acid (UDCA), which in contemporary pharmacology is approved by Food and Drug Administration (FDA) for treatment of primary biliary cholangitis. Interestingly, numerous recent studies demonstrate that mechanisms of TUDCA functioning extend beyond hepatobiliary disorders. Thus, TUDCA has been demonstrated to display potential therapeutic benefits in various models of many diseases such as diabetes, obesity, and neurodegenerative diseases, mostly due to its cytoprotective effect. The mechanisms underlying this cytoprotective activity have been mainly attributed to alleviation of endoplasmic reticulum (ER) stress and stabilization of the unfolded protein response (UPR), which contributed to naming TUDCA as a chemical chaperone. Apart from that, TUDCA has also been found to reduce oxidative stress, suppress apoptosis, and decrease inflammation in many in-vitro and in-vivo models of various diseases. The latest research suggests that TUDCA can also play a role as an epigenetic modulator and act as therapeutic agent in certain types of cancer. Nevertheless, despite the massive amount of evidence demonstrating positive effects of TUDCA in pre-clinical studies, there are certain limitations restraining its wide use in patients. Here, molecular and cellular modes of action of TUDCA are described and therapeutic opportunities and limitations of this bile acid are discussed.

Activation of TGR5 with INT-777 attenuates oxidative stress and neuronal apoptosis via cAMP/PKCε/ALDH2 pathway after subarachnoid hemorrhage in rats

BACKGROUND

Oxidative stress and neuronal apoptosis play important roles in the pathogenesis of early brain injury (EBI) after subarachnoid hemorrhage (SAH). The activation of TGR5, a novel membrane-bound bile acid receptor, possesses anti-oxidative stress and anti-apoptotic effects in hepatobiliary disease and kidney disease. The present study aimed to explore the neuroprotective effect of TGR5 activation against EBI after SAH and the potential underlying mechanisms.

METHODS

The endovascular perforation model of SAH was performed on 199 Sprague Dawley rats to investigate the beneficial effects of TGR5 activation after SAH. INT-777, a specific synthetic TGR5 agonist, was administered intranasally at 1 h after SAH induction. TGR5 CRISPR and ALDH2 CRISPR were administered intracerebroventricularly at 48 h before SAH to illuminate potential mechanisms. The SAH grade, short-term and long-term neurobehavioral tests, TUNEL staining, Fluoro-Jade C staining, Nissl staining, immunofluorescence staining, and western blots were performed at 24 h after SAH.

RESULTS

The expressions of endogenous TGR5 and ALDH2 gradually increased and peaked at 24 h after SAH. TGR5 was expressed primarily in neurons, as well as in astrocytes and microglia. The activation of TGR5 with INT-777 significantly improved the short-term and long-term neurological deficits, accompanied by reduced the oxidative stress and neuronal apoptosis at 24 h after SAH. Moreover, INT-777 treatment significantly increased the expressions of TGR5, cAMP, phosphorylated PKCε, ALDH2, HO-1, and Bcl-2, while downregulated the expressions of 4-HNE, Bax, and Cleaved Caspase-3. TGR5 CRISPR and ALDH2 CRISPR abolished the neuroprotective effects of TGR5 activation after SAH.

CONCLUSIONS

In summary, the activation of TGR5 with INT-777 attenuated oxidative stress and neuronal apoptosis via the cAMP/PKCε/ALDH2 signaling pathway after SAH in rats. Furthermore, TGR5 may serve as a novel therapeutic target to ameliorate EBI after SAH.

The Bile Acid TUDCA Improves Beta-Cell Mass and Reduces Insulin Degradation in Mice With Early-Stage of Type-1 Diabetes

Type 1 diabetes (T1D) is characterized by impairment in beta-cell mass and insulin levels, resulting in hyperglycemia and diabetic complications. Since diagnosis, appropriate control of glycaemia in T1D requires insulin administration, which can result in side effects, such as hypoglycemia. In this sense, some bile acids have emerged as new therapeutic targets to treat T1D and T2D, as well as metabolic diseases. The taurine conjugated bile acid, tauroursodeoxycholic (TUDCA) reduces the incidence of T1D development and improves glucose homeostasis in obese and T2D mice. However, its effects in early-stage of T1D have not been well explored. Therefore, we have assessed the effects of TUDCA on the glycemic control of mice with early-stage T1D. To achieve this, C57BL/6 mice received intraperitoneal administration of streptozotocin (STZ, 40 mg/kg) for 5 days. Once diabetes was confirmed in the STZ mice, they received TUDCA treatment (300 mg/kg) or phosphate buffered saline (PBS) for 24 days. After 15 days of treatment, the STZ+TUDCA mice showed a 43% reduction in blood glucose, compared with the STZ group. This reduction was likely due to an increase in insulinemia. This increase in insulinemia may be explained, at least in part, by a reduction in hepatic IDE activity and, consequently, reduction on insulin clearance, as well as an increase in beta-cell mass and a higher beta-cell number per islet. Also, the groups did not present any alterations in insulin sensitivity. All together, these effects contributed to the improvement of glucose metabolism in T1D mice, pointing TUDCA as a potential therapeutic agent for the glycemic control in early-stage of T1D.