Effects of bitter receptor antagonists on behavioral lick responses of mice

Activation of bitter taste receptor TAS2R4 alleviates diabetic nephropathy in mice

Activation of bitter taste receptor member 4 (TAS2R4) signaling alleviates podocyte injury caused by chronic high glucose; however, whether TAS2R4 activation in podocytes can improve diabetic nephropathy (DN) is to be verified. This study aims to confirm the beneficial effects of quinine, a dual human and rodent TAS2R4 agonist, and matrine with a potent anti-inflammatory activity and binding with TAS2R4 via online prediction and receptor docking on DN in vivo and in vitro. In this study, we found that quinine and matrine markedly ameliorated renal dysfunction, as evidenced by decreases in creatinine and urea nitrogen levels in plasma as well as protein excretion in urine, increased podocyte slit diaphragm and adaptor proteins including Nephrin, Podocin, and Zonula occluden 1, and suppressed activations of NF-κB and the NLRP3 inflammasome in the kidney of DN mice. Meanwhile, quinine and matrine activated TAS2R4 signaling, as revealed by increased protein expressions of TAS2R4 and its key downstream molecule phospholipase C β2. Furthermore, quinine and matrine attenuated podocyte injury, activated TAS2R4 signaling, and suppressed the above inflammatory pathways in the high glucose-cultured MPC cells, a mouse podocyte cell line, while the effects of both quinine and matrine were eliminated when TAS2R4 signaling was inhibited by using either a TAS2R4 blocker abscisic acid or a Gβγ inhibitor Gallein. In summary, quinine and matrine alleviated DN in mice through activation of TAS2R4 signaling in podocytes, which was achieved by inhibiting the activation of NF-κB mediated NLRP3 inflammasome in the kidney. Moreover, TAS2R4 could be a drug target.

The bitter flavor of Banxia Xiexin decoction activates TAS2R38 to ameliorate low-grade inflammation in the duodenum of mice with functional dyspepsia

ETHNOPHARMACOLOGICAL RELEVANCE

Banxia Xiexin Decoction (BXD) is a traditional herbal formulation with a bitter flavor that has a long-standing history of use in Asia for treating functional dyspepsia (FD). In traditional Chinese medicine, the bitter flavor is believed to play a critical role in the therapeutic activity of BXD. The ethnopharmacological properties of bitter plant extracts are closely associated with their anti-inflammatory effects, which may contribute to their efficacy in FD. However, the specific mechanisms remain unknown.

AIM OF THE STUDY

The objective of this study is to uncover the bitter active compounds of BXD and their effects in the treatment of FD.

MATERIALS AND METHODS

The chemical compounds of BXD were identified using HPLC-Q-Exactive-MS. Active compounds in BXD were obtained from the Traditional Chinese Medicine Systems Pharmacology Database and Analysis Platform (TCMSP) database, and bitter active compounds were further identified using BitterDB and PlantMolecularTasteDB. Molecular docking was employed to identify potential targets of these bitter active compounds, and their activation was validated through flow cytometry analysis of Ca2+. Subsequently, a mouse model of FD was established, and our hypothesis was further validated using enzyme linked immunosorbent assay, immunohistochemistry, immunofluorescence, and western blotting.

RESULTS

Through HPLC-Q-Exactive-MS analysis, TCMSP, BitterDB, and PlantMolecularTasteDB database, a total of 11 bitter active compounds in BXD were identified: Baicalein, Baicalin, Berberine, Coptisine, Formononetin, Isorhamnetin, Kaempferol, Naringenin, Palmatine, Quercetin, and Wogonin. Molecular docking results indicated that these active compounds exhibited strong affinity for TAS2R38, with Berberine showing the highest scoring. Flow cytometry analysis of Ca2+ revealed that both Berberine and BXD elevated intracellular calcium concentrations, although this effect was partially antagonized by the TAS2R38 inhibitor probenecid. In vivo experiments demonstrated that BXD effectively improved eosinophil infiltration in the duodenum of FD mice, downregulated the expression of inflammatory factors IL-1β, IL-5, and TNF-α, inhibition of NF-κB signaling pathway activation, alleviated damage to the duodenal mucosal barrier, and reversed gastrointestinal motility disorders, with the therapeutic effect enhancing with increasing doses of BXD. However, this therapeutic effect was partially inhibited following probenecid intervention.

CONCLUSION

BXD contains numerous bitter active compounds that play a significant role in regulating inflammatory activity in the duodenum of FD through the activation of TAS2R38. This finding unveils, for the first time, the ethnopharmacological activity of bitter plant taste agents in anti-inflammatory effects, providing new insights for the treatment and drug development of FD.

A review on natural sweeteners, sweet taste modulators and bitter masking compounds: structure-activity strategies for the discovery of novel taste molecules

Growing demand for the tasty and healthy food has driven the development of low-calorie sweeteners, sweet taste modulators, and bitter masking compounds originated from natural sources. With the discovery of human taste receptors, increasing numbers of sweet taste modulators have been identified through human taste response and molecular docking techniques. However, the discovery of novel taste-active molecules in nature can be accelerated by using advanced spectrometry technologies based on structure-activity relationships (SARs). SARs explain why structurally similar compounds can elicit similar taste qualities. Given the characterization of structural information from reported data, strategies employing SAR techniques to find structurally similar compounds become an innovative approach to expand knowledge of sweeteners. This review aims to summarize the structural patterns of known natural non-nutritive sweeteners, sweet taste enhancers, and bitter masking compounds. Innovative SAR-based approaches to explore sweetener derivatives are also discussed. Most sweet-tasting flavonoids belong to either the flavanonols or the dihydrochalcones and known bitter masking molecules are flavanones. Based on SAR findings that structural similarities are related to the sensory properties, innovative methodologies described in this paper can be applied to screen and discover the derivatives of taste-active compounds or potential taste modulators.

Refinement of IntelliCage protocols for complex cognitive tasks through replacement of drinking restrictions by incentive-disincentive paradigms

The IntelliCage allows automated testing of cognitive abilities of mice in a social home cage environment without handling by human experimenters. Restricted water access in combination with protocols in which only correct responses give access to water is a reliable learning motivator for hippocampus-dependent tasks assessing spatial memory and executive function. However, water restriction may negatively impact on animal welfare, especially in poor learners. To better comply with the 3R principles, we previously tested protocols in which water was freely available but additional access to sweetened water could be obtained by learning a task rule. While this purely appetitive motivation worked for simple tasks, too many mice lost interest in the sweet reward during more difficult hippocampus-dependent tasks. In the present study, we tested a battery of increasingly difficult spatial tasks in which water was still available without learning the task rule, but rendered less attractive either by adding bitter tasting quinine or by increasing the amount of work to obtain it. As in previous protocols, learning of the task rule provided access to water sweetened with saccharin. The two approaches of dual motivation were tested in two cohorts of female C57BL/6 N mice. Compared to purely appetitive motivation, both novel protocols strongly improved task engagement and increased task performance. Importantly, neither of the added disincentives had an adverse impact on liquid consumption, health status or body weight of the animals. Our results show that it is possible to refine test protocols in the IntelliCage so that they challenge cognitive functions without restricting access to water.

New strategies for identifying and masking the bitter taste in traditional herbal medicines: The example of Huanglian Jiedu Decoction

Suppressing the bitter taste of traditional Chinese medicine (TCM) largely has been a major clinical challenge due to complex and diverse metabolites and high dispersion of bitter metabolites in liquid preparations. In this work, we developed a novel strategy for recognizing bitter substances, hiding their bitter taste, and elucidated the mechanism of flavor masking in TCM. Huanglian Jie-Du Decoction (HLJDD) with an intense bitter taste was studied as a typical case. UHPLC-MS/MS was used to analyze the chemical components in HLJDD, whereas the bitter substances were identified by pharmacophores. Additionally, the screening results of the pharmacophores were further validated by using experimental assays. The mask formula of HLJDD was effectively screened under the condition of clear bitter substances. Subsequently, computational chemistry, molecular docking, and infrared characterization (IR) techniques were then used to explicate the mechanism of flavor masking. Consequently, neotame, γ-CD, and mPEG₂₀₀₀-PLLA₂₀₀₀ significantly reduced the bitterness of HLJDD. Specifically, mPEG₂₀₀₀-PLLA₂₀₀₀ increased the colloid proportion in the decoction system and minimized the distribution of bitter components in the real solution. Sweetener neotame suppressed the perception of bitter taste and inhibited bitter taste receptor activation to eventually reduce the bitter taste. The γ-CD included in the decoction bound the hydrophobic groups of the bitter metabolites in real solution and “packed” all or part of the bitter metabolites into the “cavity”. We established a novel approach for screening bitter substances in TCM by integrating virtual screening and experimental assays. Based on this strategy, the bitter taste masking of TCM was performed from three different aspects, namely, changing the drug phase state, component distribution, and interfering with bitter taste signal transduction. Collectively, the methods achieved a significant effect on bitter taste suppression and taste masking. Our findings will provide a novel strategy for masking the taste of TCM liquid preparation/decoction, which will in return help in improving the clinical efficacy of TCM.

The Hidden One: What We Know About Bitter Taste Receptor 39

Over thousands of years of evolution, animals have developed many ways to protect themselves. One of the most protective ways to avoid disease is to prevent the absorption of harmful components. This protective function is a basic role of bitter taste receptors (TAS2Rs), a G protein-coupled receptor family, whose presence in extraoral tissues has intrigued many researchers. In humans, there are 25 TAS2Rs, and although we know a great deal about some of them, others are still shrouded in mystery. One in this latter category is bitter taste receptor 39 (TAS2R39). Besides the oral cavity, it has also been found in the gastrointestinal tract and the respiratory, nervous and reproductive systems. TAS2R39 is a relatively non-selective receptor, which means that it can be activated by a range of mostly plant-derived compounds such as theaflavins, catechins and isoflavones. On the other hand, few antagonists for this receptor are available, since only some flavones have antagonistic properties (all of them detailed in the document). The primary role of TAS2R39 is to sense the bitter components of food and protect the organism from harmful compounds. There is also some indication that this bitter taste receptor regulates enterohormones and in turn, regulates food intake. In the respiratory system, it may be involved in the congestion process of allergic rhinitis and may stimulate inflammatory cytokines. However, more thorough research is needed to determine the precise role of TAS2R39 in these and other tissues.