Gentiana scabra extracts stimulate glucagon-like peptide-1 secretion via G protein-coupled receptor pathway

Effects of a bitter substance, denatonium benzoate, on pancreatic hormone secretion

There is increasing evidence linking bitter taste receptor (BTR) signaling to gut hormone secretion and glucose homeostasis. However, its effect on islet hormone secretion has been poorly characterized. This study investigated the effect of the bitter substance, denatonium benzoate (DB), on hormone secretion from mouse pancreatic islets and INS-1 832/13 cells. DB (0.5-1 mM) augmented insulin secretion at both 2.8 mM and 16.7 mM glucose. This effect was no longer present at 5 mM DB likely due to the greater levels of cellular apoptosis. DB-stimulated insulin secretion involved closure of the KATP channel, activation of T2R signaling in beta-cells, and intraislet glucagon-like peptide-1 (GLP-1) release. DB also enhanced glucagon and somatostatin secretion, but the underlying mechanism was less clear. Together, this study demonstrates that the bitter substance, DB, is a strong potentiator of islet hormone secretion independent of glucose. This observation highlights the potential for widespread off-target effects associated with the clinical use of bitter-tasting substances.NEW & NOTEWORTHY We show that the bitter substance, denatonium benzoate (DB), stimulates insulin, glucagon, somatostatin, and GLP-1 secretion from pancreatic islets, independent of glucose, and that DB augments insulin release via the KATP channel, bitter taste receptor signaling, and intraislet GLP-1 secretion. Exposure to a high dose of DB (5 mM) induces cellular apoptosis in pancreatic islets. Therefore, clinical use of bitter substances to improve glucose homeostasis may have unintended negative impacts beyond the gut.

miRNA-Gene Regulatory Network in Gnotobiotic Mice Stimulated by Dysbiotic Gut Microbiota Transplanted From a Genetically Obese Child

Gut microbiota (GM) dysbiosis has been considered a pathogenic origin of many chronic diseases. In our previous trial, a shift in GM structure caused by a complex fiber-rich diet was associated with the health improvement of obese Prader-Willi syndrome (PWS) children. The pre- and post-intervention GMs (pre- and post-group, respectively) from one child were then transplanted into gnotobiotic mice, which resulted in significantly different physiological phenotypes, each of which was similar to the phenotype of the corresponding GM donor. This study was designed to investigate the miRNA-gene regulatory networks involved in causing these phenotypic differences. Using the post-group as a reference, we systematically identified and annotated the differentially expressed (DE) miRNAs and genes in the colon and liver of the pre-group in the second and fourth weeks after GM inoculation. Most of the significantly enriched GO terms and KEGG pathways were observed in the liver and were in the second week after GM transplantation. We screened 23 key genes along with their 73 miRNA regulators relevant to the host phenotype changes and constructed a network. The network contained 92 miRNA-gene regulation relationships, 51 of which were positive, and 41 of which were negative. Both the colon and liver had upregulated pro-inflammatory genes, and genes involved in fatty acid oxidation, lipolysis, and plasma cholesterol clearance were downregulated in only the liver. These changes were consistent with lipid and cholesterol accumulation in the host and with a high inflammation level. In addition, the colon showed an impacted glucagon-like peptide 1 (GLP-1) signaling pathway, while the liver displayed decreased insulin receptor signaling pathway activity. These molecular changes were mainly found in the second week, 2 weeks before changes in body fat occurred. This time lag indicated that GM dysbiosis might initially induce cholesterol and lipid metabolism-related miRNA and gene expression disorder and then lead to lipid accumulation and obesity development, which implicates a causative role of GM dysbiosis in obesity development rather than a result of obesity. This study provides fundamental molecular information that elucidates how dysbiotic GM increases host inflammation and disturbs host lipid and glucose metabolism.

Effects of the inhaled treatment of liriope radix on an asthmatic mouse model

As a treatment for allergic asthma, inhaled treatments such as bronchodilators that contain β2-agonists have an immediate effect, which attenuates airway obstructions and decreases airway hypersensitivity. However, bronchodilators only perform on a one off basis, but not consistently. Asthma is defined as a chronic inflammatory disease of the airways accompanying the overproduction of mucus, airway wall remodeling, bronchial hyperreactivity and airway obstruction. Liriope platyphylla radix extract (LPP), a traditional Korean medicine, has been thoroughly studied and found to be an effective anti-inflammatory medicine. Here, we demonstrate that an inhaled treatment of LPP can attenuate airway hyperresponsiveness (AHR) in an ovalbumin-induced asthmatic mouse model, compared to the saline-treated group (p < 0.01). Moreover, LPP decreases inflammatory cytokine levels, such as eotaxin (p < 0.05), IL-5 (p < 0.05), IL-13 (p < 0.001), RANTES (p < 0.01), and TNF-α (p < 0.05) in the bronchoalveolar lavage (BAL) fluid of asthmatic mice. A histopathological study was carried out to determine the effects of LPP inhalation on mice lung tissue. We performed UPLC/ESI-QTOF-MS, LC/MS, and GC/MS analyses to analyze the chemical constituents of LPP, finding that these are ophiopogonin D, spicatoside A, spicatoside B, benzyl alcohol, and 5-hydroxymethylfurfural. This study demonstrates the effect of an inhaled LPP treatment both on airway AHR and on the inflammatory response in an asthmatic mouse model. Hence, LPP holds significant promise as a nasal inhalant for the treatment of asthmatic airway disease.

Medicinal Plants Qua Glucagon-Like Peptide-1 Secretagogue via Intestinal Nutrient Sensors

Glucagon-like peptide-1 (GLP-1) participates in glucose homeostasis and feeding behavior. Because GLP-1 is rapidly inactivated by the enzymatic cleavage of dipeptidyl peptidase-4 (DPP4) long-acting GLP-1 analogues, for example, exenatide and DPP4 inhibitors, for example, liraglutide, have been developed as therapeutics for type 2 diabetes mellitus (T2DM). However, the inefficient clinical performance and the incidence of side effects reported on the existing therapeutics for T2DM have led to the development of a novel therapeutic strategy to stimulate endogenous GLP-1 secretion from enteroendocrine L cells. Since the GLP-1 secretion of enteroendocrine L cells depends on the luminal nutrient constituents, the intestinal nutrient sensors involved in GLP-1 secretion have been investigated. In particular, nutrient sensors for tastants, cannabinoids, and bile acids are able to recognize the nonnutritional chemical compounds, which are abundant in medicinal plants. These GLP-1 secretagogues derived from medicinal plants are easy to find in our surroundings, and their effectiveness has been demonstrated through traditional remedies. The finding of GLP-1 secretagogues is directly linked to understanding of the role of intestinal nutrient sensors and their recognizable nutrients. Concurrently, this study demonstrates the possibility of developing novel therapeutics for metabolic disorders such as T2DM and obesity using nutrients that are readily accessible in our surroundings.

A bitter herbal medicine Gentiana scabra root extract stimulates glucagon-like peptide-1 secretion and regulates blood glucose in db/db mouse

ETHNOPHARMACOLOGICAL RELEVANCE

Gentiana scabra root extract (GS) is frequently prescribed as an internal remedy in traditional Korean medicine for treatment of diabetes mellitus. GS contains bitter iridoid glycosides including loganic acid, gentiopicrin, trifloroside, and rindoside. We previously reported that the intestinal bitter taste sensation stimulates GLP-1 secretion, and thereupon hypothesized that the blood glucose regulatory effect of GS is due to its GLP-1 secreting effect in enteroendocrine L cells.

MATERIALS AND METHOD

We studied GLP-1 secreting effect of GS treatment and its cellular downstream mechanism in human enteroendocrine NCI-H716 cells using the G protein-coupled receptor (GPCR) pathway inhibitors. Intracellular calcium assay also demonstrated the signal transduction pathway stimulated by the GS treatment. Using db/db mice, we performed oral glucose tolerance test (OGTT) to examine the blood glucose lowering effect of GS administration. We also collected the mouse plasma during the OGTT to measure the GLP-1 and insulin levels.

RESULT

We demonstrated dose-dependent GLP-1 secreting effect of GS on the NCI-H716 cells. The GLP-1 secreting effect of GS is mediated by the G protein βγ-subunit and inositol triphosphate. Using db/db mice, we found that the effect of GS on lowering blood glucose is due to its GLP-1 secretion, and consequential insulinotropic effect. The chemical fingerprint of GS was obtained through a direct analysis in realtime mass spectrometry (DART-MS) and high-performance liquid chromatography (HPLC)/MS. Through the GLP-1 secretion study, we found that loganic acid, an iridoid glycoside, contributes to the GLP-1 secreting effect of GS.

CONCLUSION

The findings of this study highlight the potential of exploiting the antidiabetic effect of GS on type 2 diabetes mellitus patients.

Denatonium induces secretion of glucagon-like peptide-1 through activation of bitter taste receptor pathways

AIMS/HYPOTHESIS

This study was designed to ascertain whether human enteroendocrine cells express bitter taste receptors, and whether activation of these receptors with bitter-tasting ligands induces secretion of glucagon-like peptide-1 (GLP-1) and peptide YY (PYY).

METHODS

We used human enteroendocrine NCI-H716 cells, isolated duodenal segments from mice, and whole mice as our experimental systems for investigating stimuli and mechanisms underlying GLP-1- and PYY-stimulated release. We measured hormone levels by ELISA and determined bitter taste receptor expression by real-time quantitative PCR. We adopted a pharmacological approach using inhibitors and enhancers of downstream signalling pathways known to be involved in bitter taste transduction in taste bud cells to investigate these pathways in NCI-H716 cells.

RESULTS

Using a pharmacological approach, we identified signalling pathways triggered by the denatonium benzoate (DB)-activated bitter receptors. This involved activation of α-gustducin (Gαgust)-the specific G-protein subunit that is also present in taste bud cells-reduction of intracellular cAMP levels and enhancement of phospholipase C (PLC) activity, which ultimately led to increased intracellular calcium concentrations and hormone release. Gavage of DB, followed by gavage of glucose, to db/db mice stimulated GLP-1 and subsequent insulin secretion, leading to lower blood glucose levels.

CONCLUSIONS/INTERPRETATION

Our study demonstrates that activation of gut-expressed bitter taste receptors stimulates GLP-1 secretion in a PLC-dependent manner. In diabetic mice, DB (a ligand of bitter taste receptor cells), when given via gavage, lowers blood glucose levels in diabetic mice after oral glucose administration, through increased secretion of GLP-1.

Effects of β-sitosterol derived from Artemisia capillaris on the activated human hepatic stellate cells and dimethylnitrosamine-induced mouse liver fibrosis

Background

β-sitosterol is a cholesterol-like phytosterol, which widely distributed in the plant kingdom. Here, anti-fibrotic effect of the β-sitosterol was studied using the activated human hepatic stellate cell (HSC) model and dimethylnitrosamine (DMN)-induced mouse hepatic fibrosis model.

Method

HSCs were activated by transforming growth factor-β (TGF-β) and the collagen-1 and α-smooth muscle actin (α-SMA) expressions were measured at the mRNA and protein level. We also studied the effect β-sitosterol using DMN-induced mouse hepatic fibrosis model. We then measured the collagen-1 and α-SMA expression levels in vivo to investigate anti-hepatofibrotic effect of β-sitosterol, at both of the mRNA and protein level.

Results

β-sitosterol down regulated the mRNA and protein expression levels of collagen-1 and α-SMA in activated HSC. Oral administration of the β-sitosterol successfully alleviated the DMN-induced mouse liver damage and prevented collagen accumulation. The mRNA and protein expression levels of collagen-1 and α-SMA were also down regulated in β-sitosterol treated mouse group.

Conclusions

This study shows the effect of β-sitosterol on the TGF-β -or DMN-induced hepatofibrosis. Hence, we demonstrate the β-sitosterol as a potential therapeutic agent for the hepatofibrosis.

A rapid and sensitive UFLC-MS/MS method for the simultaneous determination of gentiopicroside and swertiamarin in rat plasma and its application in pharmacokinetics

Objectives

R adix G entianae is a traditional Chinese medicine derived from medicinal plants of the family Gentianaceae. Its pharmacological effects have been primarily attributed to the presence of a number of secoiridoid glycosides, in particular gentiopicroside and swertiamarin. In this study, a rapid and sensitive method based on ultrafast liquid chromatography-tandem mass spectrometry has been developed for the simultaneous determination of gentiopicroside and swertiamarin in rat plasma using paeoniflorin as internal standard (IS).

Methods

After liquid-liquid extraction with ethyl acetate-isopropanol (95 : 5, v/v), separation was achieved on a Shim-pack XR-ODS C18 column (75 mm × 3.0 mm, 2.2 μm) with a mobile phase consisting of methanol : 0.1% formic acid (30 : 70, v/v) at a flow rate of 0.4 ml/min. Detection on an API 3200 QTRAP mass spectrometer equipped with an electrospray ionization source operated in the negative ionization mode was performed by multiple reaction monitoring of the precursor-to-product ion transitions of gentiopicroside, swertiamarin and IS at m/z 401.0 → 179.0, 419.0 → 179.1 and 525.1 → 121.0 respectively. The calibration curves were linear over the concentration range of 20–10 000 and 2–1000 ng/ml for gentiopicroside and swertiamarin with corresponding lower limits of quantification of 20 and 2 ng/ml. The limits of detection were 4 and 0.5 ng/ml for gentiopicroside and swertiamarin, respectively. The intraday and interday precisions were below 11.9% for gentiopicroside and below 9.5% for swertiamarin in terms of relative standard deviation, and the accuracy was within ±8.3% for gentiopicroside and within ±10.2% for swertiamarin in terms of relative error. Extraction recovery, matrix effect and stability were satisfactory in rat plasma. The method was fully validated and applied to a pharmacokinetic study involving oral administration of a RadixGentianae extract to groups of male and female rats.

Key findings

Results showed that in female rats, both compounds were absorbed to a greater extent and eliminated more slowly than in male rats, although the rate of absorption was similar in the two groups.

Conclusions

There were remarkable differences in pharmacokinetic properties of gentiopicroside and swertiamarin between male and female rats. The results will provide helpful information for the development of suitable dosage forms and clinical references on rational administration.

Hexane Fractions of Bupleurum falcatum L. Stimulates Glucagon-Like Peptide-1 Secretion through G β γ -Mediated Pathway

Bupleurum falcatum L. has been used traditionally as a medicinal herb in Korean medicine. The hexane fraction of BF (HFBF), which was profiled with Direct Analysis in Real Time-Mass Spectrometry (DART-MS), activates the secretion of glucagon-like peptide-1 (GLP-1) in NCI-H716 cells significantly. We performed a microarray analysis and GLP-1 ELISA assay, as well as calcium imaging experiments with inhibitors, to investigate the mechanism of action of the HFBF. Through the microarray analysis, it was found that the ITPR2 gene that encodes the inositol 1,4,5-trisphosphate (IP₃) receptor is up-regulated and the HFBF induces cell depolarization by inhibiting the voltage-gated channel expression in NCI-H716 cells. In addition, we found that the intracellular calcium in NCI-H716 cells, with Gallein, U73122, and 2APB as inhibitors, was decreased. These results suggest that the HFBF activates the GLP-1 secretion through the G_βγ pathways in the enteroendocrine L cells after treatment with the HFBF.