Pharmacological activation of TGR5 promotes intestinal growth via a GLP-2-dependent pathway in mice

Cholecystitis following the initiation of glucagon-like peptide-2 analogue for short bowel syndrome: A case report

Patients with short bowel syndrome (SBS) have a risk for cholelithiasis and cholecystitis, particularly those who have received long-term parenteral nutrition (PN). Teduglutide (Revestive), a glucagon-like peptide-2 (GLP-2) analogue, is the first effective therapy approved for treating patients with SBS via self-subcutaneous injection. It also pharmacologically inhibits gallbladder contraction, which may increase the risks for cholelithiasis and cholecystitis. Here, we report a case of cholecystitis occurring after the introduction of a GLP-2 analogue in a patient with SBS and cholelithiasis. A 16-year-old girl, with a residual intestinal anatomy of 5 cm jejunum and left colon, was referred to our hospital for further treatment of SBS. She underwent jejunocolic anastomosis 2 months later. After that, she received PN for 2.5 years. Teduglutide treatment was initiated to reduce PN dependence. Several asymptomatic gallbladder stones were found during a routine ultrasound examination before drug initiation. On day 31 of teduglutide treatment, right subcostal pain with fever occurred, and the patient was diagnosed with acute cholecystitis. GLP-2 analogue treatment was temporarily discontinued. The patient underwent gallbladder drainage followed by cholecystectomy 3 weeks later. Histopathological findings illustrated mucosal hyperplasia of the gallbladder. Her postoperative course was uneventful, and teduglutide was restarted 2 weeks postoperatively. GLP-2 analogues promote gallbladder refilling and epithelial hyperplasia, which may be a risk factor for cholecystitis in patients with cholelithiasis, as observed in our patient. Based on our experience, patients with SBS and established asymptomatic cholelithiasis may be considered for prophylactic cholecystectomy before the administration of GLP-2 analogues.

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.

Biased GLP-2 agonist with strong G protein-coupling but impaired arrestin recruitment and receptor desensitization enhances intestinal growth in mice

BACKGROUND AND PURPOSE

Glucagon-like peptide-2 (GLP-2) is secreted postprandially by enteroendocrine L-cells and stimulates growth of the gut and bone. One GLP-2 analogue is approved for short bowel syndrome (SBS). To improve therapeutic efficacy, we developed biased GLP-2 receptor (GLP-2R) agonists through N-terminal modifications.

EXPERIMENTAL APPROACH

Variants with Ala and Trp substitutions of the first seven positions of GLP-2(1-33) were studied in vitro for affinity, G protein activation (cAMP accumulation), recruitment of β-arrestin 1 and 2, and internalization of the human and mouse GLP-2R. The intestinotrophic actions of the most efficacious (cAMP) biased variant were examined in mice.

KEY RESULTS

Ala substitutions had more profound effects than Trp substitutions. For both, alterations at positions 1, 3 and 6 most severely impaired activity. β-arrestin recruitment was more affected than cAMP accumulation. Among Ala substitutions, [H1A], [D3A] and [F6A] impaired potency (EC₅₀ ) for cAMP-accumulation >20-fold and efficacy (E_max ) to 48%-87%, and were unable to recruit arrestins. The Trp substitutions, [A2W], [D3W] and [G4W] were partial agonists (E_max of 46%-59%) with 1.7-12-fold decreased potencies in cAMP and diminished β-arrestin recruitment. The biased variants, [F6A], [F6W] and [S7W] induced less GLP-2R internalization compared with GLP-2, which induced internalization in a partly arrestin-independent manner. In mice, [S7W] enhanced gut trophic actions with increased weight of the small intestine, increased villus height and crypt depth compared with GLP-2.

CONCLUSION AND IMPLICATIONS

G protein-biased GLP-2R agonists with diminished receptor desensitization have superior intestinotrophic effects and may represent improved treatment of intestinal insufficiency including SBS.

Design and exploration of gut-restricted bifunctional molecule with TGR5 agonistic and DPP4 inhibitory effects for treating ulcerative colitis

Ulcerative colitis (UC) is a gastrointestinal disease with complex etiology, and the shortage of the treatment further intensifies the need to discover new therapies based on novel mechanisms and strategies. TGR5 and DPP4 are beneficial to treat UC through multiple mechanisms, notably increasing GLP-2 levels by promoting secretion and inhibiting degradation respectively. However, some unwanted systemic effects caused by systemic exposure hinder development, especially the gallbladder-filling effects. Herein, we firstly reported a series of high-potency gut-restricted TGR5-DPP4 bifunctional molecules by gut-restriction and multitarget strategies to utilize the positive impacts of TGR5 and DPP4 on UC and avoid unwanted systemic effects. In particularly, racemic compound 15, a high-potency TGR5-DPP4 bifunctional molecule, showed favorable intestinal distribution, preferable efficacy in mice colitis model and good gallbladder safety. Therefore, the feasibility of gut-restricted TGR5-DPP4 bifunctional molecule was confirmed for the treatment UC, providing a new insight into the development of anti-UC drugs.

Saponins from Camellia sinensis Seeds Stimulate GIP Secretion in Mice and STC-1 Cells via SGLT1 and TGR5

Glucose-dependent insulinotropic polypeptide (GIP) is one of the important incretins and possesses lots of physiological activities such as stimulating insulin secretion and maintaining glucose homeostasis. The pentacyclic triterpenoid saponins are the major active ingredients in tea (Camellia sinensis) seeds. This study aimed to investigate the effect of tea seed saponins on the GIP secretion and related mechanisms. Our data showed that the total tea seed saponins (TSS, 65 mg/kg BW) and theasaponin E₁ (TSE1, 2–4 µM) could increase the GIP mRNA and protein levels in mice and STC-1 cells. Phlorizin, the inhibitor of Sodium/glucose cotransporter 1 (SGLT1), reversed the TSE1-induced increase in Ca²⁺ and GIP mRNA level. In addition, TSE1 upregulated the protein expression of Takeda G protein-coupled receptor 5 (TGR5), and TGR5 siRNA significantly decreased GIP expression in TSE1-treated STC-1 cells. Network pharmacology analysis revealed that six proteins and five signaling pathways were associated with SGLT1, TGR5 and GIP regulated by TSE1. Taken together, tea seed saponins could stimulate GIP expression via SGLT1 and TGR5, and were promising natural active ingredients for improving metabolism and related diseases.

Enterohepatic Takeda G-Protein Coupled Receptor 5 Agonism in Metabolic Dysfunction-Associated Fatty Liver Disease and Related Glucose Dysmetabolism

Metabolic dysfunction-associated fatty liver disease (MAFLD) is a major health concern with no approved pharmacological therapies. Molecules developed to activate the bile acid-receptor TGR5 regulate pathways involved in MALFD pathogenesis, but the therapeutic value of TGR5 activation on the active form of MAFLD, non-alcoholic steatohepatitis (NASH), still needs to be evaluated. As TGR5 agonism is low in MAFLD, we used strategies to promote the production of endogenous TGR5 ligands or administered pharmacological TGR5 agonists, INT-777 and RO5527239, to study the effect of TGR5 activation on liver and metabolic diseases in high-fat diet-fed foz/foz mice. Although described in the literature, treatment with fexaramine, an intestine-restricted FXR agonist, did not raise the concentrations of TGR5 ligands nor modulate TGR5 signaling and, accordingly, did not improve dysmetabolic status. INT-777 and RO5527239 directly activated TGR5. INT-777 only increased the TGR5 activation capacity of the portal blood; RO5527239 also amplified the TGR5 activation capacity of systemic blood. Both molecules improved glucose tolerance. In spite of the TGR5 activation capacity, INT-777, but not RO5527239, reduced liver disease severity. In conclusion, TGR5 activation in enterohepatic, rather than in peripheral, tissues has beneficial effects on glucose tolerance and MAFLD.

A GLP-1/GLP-2 receptor dual agonist to treat NASH: Targeting the gut-liver axis and microbiome

BACKGROUND AND AIMS

Currently there is no Food and Drug Administration-approved drug to treat NAFLD and NASH, the rates of which are increasing worldwide. Although NAFLD/NASH are highly complex and heterogeneous conditions, most pharmacotherapy pipelines focus on a single mechanistic target. Considering the importance of the gut-liver axis in their pathogenesis, we investigated the therapeutic effect of a long-acting dual agonist of glucagon-like peptide (GLP)-1 and GLP-2 receptors in mice with NAFLD/NASH.

APPROACH AND RESULTS

C57BL/6J mice were fed a choline-deficient high-fat diet/high fructose and sucrose solution. After 16 weeks, mice were randomly allocated to receive vehicle, GLP1-Fc, GLP2-Fc, or GLP1/2-Fc fusion (GLP1/2-Fc) subcutaneously every 2 days for 4 weeks. Body weight was monitored, insulin/glucose tolerance tests were performed, feces were collected, and microbiome profiles were analyzed. Immobilized cell systems were used to evaluate direct peptide effect. Immunohistochemistry, quantitative PCR, immunoblot analysis, tunnel assay, and biochemical assays were performed to assess drug effects on inflammation, hepatic fibrosis, cell death, and intestinal structures. The mice had well-developed NASH phenotypes. GLP1/2-Fc reduced body weight, glucose levels, hepatic triglyceride levels, and cellular apoptosis. It improved liver fibrosis, insulin sensitivity, and intestinal tight junctions, and increased microvillus height, crypt depth, and goblet cells of intestine compared with a vehicle group. Similar effects of GLP1/2-Fc were found in in vitro cell systems. GLP1/2-Fc also changed microbiome profiles. We applied fecal microbiota transplantation (FMT) gain further insight into the mechanism of GLP1/2-Fc-mediated protection. We confirmed that FMT exerted an additive effect on GLP1-Fc group, including the body weight change, liver weight, hepatic fat accumulation, inflammation, and hepatic fibrosis.

CONCLUSIONS

A long-acting dual agonist of GLP-1 and GLP-2 receptors is a promising therapeutic strategy to treat NAFLD/NASH.

A systems-level analysis of bile acids effects on rat colon epithelial cells

Bile acid diarrhea is a chronic condition caused by increased delivery of bile acids to the colon. The underlying mechanisms remain to be elucidated. To investigate genes involved in bile acid diarrhea, systems-level analyses were used on a rat bile acid diarrhea model. Twelve male Wistar Munich rats, housed in metabolic cages, were fed either control or bile acid-mixed (1% wt/wt) diets for 10 days. Food intake, water intake, urine volume, body weight, and fecal output were monitored daily. After euthanasia, colonic epithelial cells were isolated using calcium chelation and processed for systems-level analyses, that is, RNA-sequencing transcriptomics and mass spectrometry proteomics. Bile acid-fed rats suffered diarrhea, indicated by increased drinking, feces weight, and fecal water content compared with control rats. Urine output was unchanged. With bile acid feeding, RNA-sequencing revealed 204 increased and 401 decreased mRNAs; mass spectrometry revealed 183 increased and 111 decreased proteins. Among the altered genes were genes associated with electrolyte and water transport (including Slc12a7, Clca4, and Aqp3) and genes associated with bile acid transport (Slc2b1, Abcg2, Slc51a, Slc51b, and Fabps). Correlation analysis showed a significant positive correlation (Pearson's r = 0.28) between changes in mRNA expression and changes in protein expression. However, caution must be exercised in making a direct correlation between experimentally determined transcriptomes and proteomes. Genes associated with bile acid transport responded to bile acid feeding, suggesting that colonic bile acid transport also occur by regulated protein facilitated mechanisms in addition to passive diffusion. In summary, the study provides annotated rat colonic epithelial cell transcriptome and proteome with response to bile acid feeding.NEW & NOTEWORTHY Feeding rats with a bile acid caused changes in fecal output, underlining this bile acid diarrhea model's usefulness. Colonic epithelial expression of genes associated with facilitated transport of bile acids was altered during bile acid feeding. The study raises the possibility of regulated colonic transepithelial transport of bile acids in response to luminal bile acids. In addition, this study provides annotated rat colonic epithelial cell transcriptome and proteome with response to bile acid feeding.

Review article: insights into the bile acid-gut microbiota axis in intestinal failure-associated liver disease-redefining the treatment approach

BACKGROUND

Intestinal failure-associated liver disease (IFALD) increases mortality of patients with intestinal failure (IF), but lacks effective prevention or treatment approaches. Bile acids, gut microbiota and the host have close and complex interactions, which play a central role in modulating host immune and metabolic homeostasis. Increasing evidence suggests that derangement of the bile acid-gut microbiota (BA-GM) axis contributes to the development of IFALD.

AIMS

To review the BA-GM axis in the pathogenesis and clinical applications of IFALD, and to explore future directions for effective disease management.

METHODS

We conducted a literature search on bile acid and gut microbiota in IF and liver diseases.

RESULTS

The BA-GM axis demonstrates a unique IF signature manifesting as an increase in primary-to-secondary bile acids ratio, disturbed enterohepatic circulation, blunted bile acid signalling pathways, gut microbial dysbiosis, and altered microbial metabolic outputs. Bile acids and gut microbiota shape the compositional and functional alterations of each other in IF; collaboratively, they promote immune dysfunction and metabolic aberration in the liver. Diagnostic markers and treatments targeting the BA-GM axis showed promising potential in the management of IFALD.

CONCLUSIONS

Bile acids and gut microbiota play a central role in the development of IFALD and make attractive biomarkers as well as therapeutic targets. A multitarget, individualised therapy aiming at different parts of the BA-GM axis may provide optimal clinical benefits and requires future investigation.

Dietary Fiber Is Essential to Maintain Intestinal Size, L-Cell Secretion, and Intestinal Integrity in Mice

Dietary fiber has been linked to improved gut health, yet the mechanisms behind this association remain poorly understood. One proposed mechanism is through its influence on the secretion of gut hormones, including glucagon-like peptide-1 (GLP-1) and glucagon-like peptide-2 (GLP-2). We aimed to: 1) investigate the impact of a fiber deficient diet on the intestinal morphological homeostasis; 2) evaluate L-cell secretion; and 3) to ascertain the role of GLP-1, GLP-2 and Takeda G protein-receptor-5 (TGR5) signaling in the response using GLP-1 receptor, GLP-2 receptor and TGR5 knockout mice. Female C57BL/6JRj mice (n = 8) either received a standard chow diet or were switched to a crude fiber-deficient diet for a short (21 days) and long (112 days) study period. Subsequent identical experiments were performed in GLP-1 receptor, GLP-2 receptor and TGR5 knockout mice. The removal of fiber from the diet for 21 days resulted in a decrease in small intestinal weight (p < 0.01) and a corresponding decrease in intestinal crypt depth in the duodenum, jejunum and ileum (p < 0.001, p < 0.05, and p < 0.01, respectively). Additionally, colon weight was decreased (p < 0.01). These changes were associated with a decrease in extractable GLP-1, GLP-2 and PYY in the colon (p < 0.05, p < 0.01, and p < 0.01). However, we could not show that the fiber-dependent size decrease was dependent on GLP-1 receptor, GLP-2 receptor or TGR5 signaling. Intestinal permeability was increased following the removal of fiber for 112 days. In conclusion, our study highlights the importance of dietary fiber to maintain intestinal weight, colonic L-cell secretion and intestinal integrity.

Intestinal Adaptation upon Chemotherapy-Induced Intestinal Injury in Mice Depends on GLP-2 Receptor Activation

Intestinal adaptation is an important response and a natural repair mechanism in acute intestinal injury and is critical for recovery. Glucagon-like peptide 2 (GLP-2) has been demonstrated to enhance mucosal repair following intestinal damage. In this study, we aimed to investigate the role of GLP-2 receptor activation on intestinal protection and adaptation upon chemotherapy-induced intestinal injury. The injury was induced with a single injection of 5-fluorouracil in female GLP-2 receptor knockout (GLP-2R(-/-)) mice and their wild type (WT) littermates. The mice were euthanized in the acute or the recovery phase of the injury; the small intestines were analysed for weight changes, morphology, histology, inflammation, apoptosis and proliferation. In the acute phase, only inflammation was slightly increased in the GLP-2R(-/-) mice compared to WT. In the recovery phase, we observed the natural compensatory response with an increase in small intestinal weight, crypt depth and villus height in WT mice, and this was absent in the GLP-2R(-/-) mice. Both genotypes responded with hyperproliferation. From this, we concluded that GLP-2R signalling does not have a major impact on acute intestinal injury but is pivotal for the adaptive response in the small intestine.

Berberine compounds improves hyperglycemia via microbiome mediated colonic TGR5-GLP pathway in db/db mice

Berberine compounds (BC), consisting of berberine (BBR), oryzanol and vitamin B₆, have been used to treat diabetes and hyperlipidemia in recent years, but the potential mechanisms under the effects have not been well determined. In this study, we evaluated the effect of BC in db/db mice, and found that BC treatment reversed the increased levels of fasting glucose and hemoglobin A1c in db/db mice, which was superior to BBR treatment. Fecal 16S rRNA gene sequencing indicated that BC increased relative abundance of microbiomes Bacteroidaceae and Clostridiaceae, which may promote conversion of primary bile acid cholic acid (CA) into secondary bile acid deoxycholic acid (DCA). Gas chromatography/mass spectrometry (GC/MS)-based metabolomics revealed that BC treatment increased fecal DCA level. Since DCA processes the potential to activate bile acid receptor-takeda G protein-coupled receptor 5 (TGR5) and induce glucagon-like peptide (GLP) secretion, we detected TGR5 expression, and found that BC-treatment significantly increased the colonic TGR5 and serum GLP-1/-2 levels in db/db mice. Modulation of TGR5-GLP pathway may also affect metabolomic profiles of serum and liver, and BC treatment showed effects on restoring the altered carbohydrate, lipid, amino acid and nucleotide metabolism. Our study suggested that BC improved hyperglycemia, the effect might attribute to the increased microbiome mediated DCA production, which up-regulated colonic TGR5 expression and GLP secretion, and improved glucose, lipid and energy metabolism in db/db mice.