Probing the Binding Pocket of the Broadly Tuned Human Bitter Taste Receptor TAS2R14 by Chemical Modification of Cognate Agonists

Sensing potentially harmful bitter substances in the oral cavity is achieved by a group of ^?25 receptors, named TAS2Rs, which are expressed in specialized sensory cells and recognize individual but overlapping sets of bitter compounds. The receptors differ in their tuning breadths ranging from narrowly to broadly tuned receptors. One of the most broadly tuned human bitter taste receptors is the TAS2R14 recognizing an enormous variety of chemically diverse synthetic and natural bitter compounds, including numerous medicinal drugs. This suggests that this receptor possesses a large readily accessible ligand binding pocket. To allow probing the accessibility and size of the ligand binding pocket, we chemically modified cognate agonists and tested receptor responses in functional assays. The addition of large functional groups to agonists was usually possible without abolishing agonistic activity. The newly synthesized agonist derivatives were modeled in the binding site of the receptor, providing comparison to the mother substances and rationalization of the in vitro activities of this series of compounds.     

Bitter taste receptors as a target for bronchodilation

Despite the present treatments for asthma (β(2)-adrenoceptor agonists, glucocorticoids, leukotriene receptor antagonists), many subjects with asthma have difficulty controlling it. Bitter taste receptors have recently been identified on human lung. The paper evaluated considers these receptors as a target for bronchodilation, by characterizing the effects of agonists in cultured human airway smooth muscle cells, isolated human bronchial smooth muscle and a mouse model of allergic asthma. The study confirmed that a bitter taste receptor (TAS2R) is a viable target for bronchodilation. Many diverse chemicals are known to stimulate the bitter taste receptors to produce the bitter taste, and many of these have more than one mechanism of action. Thus, it is not known whether any of these have clinical potential in asthma. It may be necessary to design and develop selective agonists for TAS2R, before the clinical potential of this target can be thoroughly investigated.     

苦味中药激活肠道苦味受体分泌胰高血糖素样肽-1的研究现状

胰高血糖素样肽-1(GLP-1)可以刺激胰岛素释放以及抑制胰高血糖素释放,与2型糖尿病有关.苦味中药可以激活肠道上的苦味受体(TAS2Rs),通过磷脂酶C通路和磷酸二酯酶通路刺激肠道内分泌L细胞未分泌GLP-1,广泛用于2型糖尿病的防治.本文综述了苦味中药对肠道TAS2 Rs介导的GLP-1分泌的调控作用,为苦味中药防...     

Bitter taste receptors on airway smooth muscle as targets for novel bronchodilators

Introduction: There is an unmet need for a new class of direct bronchodilators for the treatment of asthma and chronic obstructive lung disease. Unexpectedly, bitter taste receptors (TAS2Rs) have been localized on airway smooth muscle and when activated cause marked smooth muscle relaxation through a mechanism that is distinct from β₂-adrenegic receptors. Thus TAS2R agonists have emerged as a novel class of bronchodilator.

Areas covered: A synopsis of the TAS2R family and its biology for bitter taste perception on the tongue is provided, followed by a review of the identification and molecular and physiological characterization of TAS2R subtypes on human and mouse airway smooth muscle. The proposed molecular mechanisms leading to the relaxation response are provided, along with gaps in our understanding at certain points in the signaling cascade. Unresolved issues that may need to be considered for drug development are discussed.

Expert opinion: TAS2R agonists show promise as a new class of highly efficacious bronchodilators for treatment of obstructive lung disease. With tens of thousands of known natural and synthetic bitter compounds, there is substantial diversity within the known agonists, and, a ready source of agents for screening and further development of an inhaled TAS2R agonist for therapeutic purposes.     

Bitterless guaifenesin prodrugs—design,synthesis, characterization,in vitro kinetics,and bitterness studies

A respected number of drugs suffer from bitter taste which results in patient incompliance. With the aim of solving the bitterness of guaifenesin, dimethyl maleate, maleate, glutarate, succinate, and dimethyl succinate prodrugs were designed and synthesized. Molecular orbital methods were utilized for the design of the ester prodrugs. The density functional theory (DFT) calculations revealed that the hydrolysis efficiency of the synthesized prodrugs is significantly sensitive to the pattern of substitution on C=C bond and distance between the nucleophile and the electrophile. The hydrolysis of the prodrugs was largely affected by the pH of the medium. The experimental t_1/2 for the hydrolysis of guaifenesin dimaleate ester prodrugs in 1N HCl was the least and for guaifenesin dimethyl succinate was the highest. Functional heterologous expression of TAS2R14, a broadly tuned bitter taste receptor responding to guaifenesin, and experiments using these prodrugs revealed that, while some of the prodrugs still activated the receptor similarly or even stronger than the parent substance, succinate derivatization resulted in the complete loss of receptor responses. The predicted binding modes of guaifenesin and its prodrugs to the TAS2R14 homology model suggest that the decreased activity of the succinate derivatives may be caused by a clash with Phe247.     

Identification of human dopamine receptors agonists from Chinese herbs

AIM: To find human dopamine receptors, especially D1-like receptor specific agonists from Chinese herbs as potential antihypertension drug leads. METHODS: Two D1-like receptor cell lines carrying a beta-lactamase reporter gene, and a D2 receptor cell line coexpressing a promiscuous G protein G15 were constructed using HEK293 cells. A natural compound library made from fractionated samples of herbal extracts was used for high-throughput screening (HTS) against one of the cell lines, HEK/D5R/CRE-blax. The interested hits were evaluated for their activities against various dopamine receptors. RESULTS: Fourteen hits were identified from primary screening, of which 2 of the better hit samples, HD0522 and HD0059, were selected for further material and activity analysis, and to obtain 2 compounds that appeared as 2 single peaks in HPLC, HD0522H01 and HD0059H01. HD0059H01 could activate D1, D2, and D5 receptors, with EC(50 ) values of 2.28 microg/mL, 0.85 microg/mL, and 1.41 microg/mL, respectively. HD0522H01 could only activate D1R and D5R with EC(50 ) values of 2.95 microg/mL and 8.38 microg/mL. CONCLUSION: We established cellbased assays for 3 different human dopamine receptors and identified specific agonists HD0522H01 and HD0059H01 through HTS. The specific agonist to D1-like receptors, HD0522H01, may become a new natural product-based drug lead for antihypertension treatment.     

Multiple receptor systems for glutamate detection in the taste organ

L-Glutamate and 5'-ribonucleotides such as guanosine-5'-monophosphate (GMP) and inosine-5'-monophosphate (IMP) elicit a unique taste called 'umami' that is distinct from the tastes of sweet, salty, sour, and bitter. For umami, like sweet and bitter compounds, taste signaling is initiated by binding of tastants to G-protein-coupled receptors (GPCR) in taste bud cells. To date, several GPCRs for umami compounds have been identified in taste cells, including the heterodimer T1R1/T1R3, and truncated type 1 and 4 metabotropic glutamate receptors missing most of the N-terminal extracellular domain (taste-mGluR4 and truncated-mGluR1). Apparently contradictory data in T1R3 knock-out (KO) mouse models have been reported. One study showed that behavioral preference and taste nerve responses to umami stimuli in T1R3-KO mice were totally abolished, suggesting that T1R1/T1R3 is a sole receptor for umami taste. The other reported reduced but not abolished responses to umami in T1R3-KO mice, suggesting existence of multiple receptors for umami taste. In this paper, we summarized the data from recent studies that further addressed this issue by using different experimental techniques. Some of the studies provided additional evidence for the existence of umami receptor systems mediated by mGluR1 and mGluR4 in addition to T1R1/T1R3. It is proposed that the signal mediated by the pathway involving T1R1/T1R3 may play a different role from that derived from the mGluRs. The former occurs mainly in the anterior tongue, and plays a major role in preference behavior, whereas the latter occurs mainly in the posterior tongue and contributes to behavioral discrimination between umami and other taste compounds.     

Traditional chinese medicine in treatment of metabolic syndrome

In management of metabolic syndrome, the traditional Chinese medicine (TCM) is an excellent representative in alternative and complementary medicines with a complete theory system and substantial herb remedies. In this article, basic principle of TCM is introduced and 25 traditional Chinese herbs are reviewed for their potential activities in the treatment of metabolic syndrome. Three herbs, ginseng, rhizoma coptidis (berberine, the major active compound) and bitter melon, were discussed in detail on their therapeutic potentials. Ginseng extracts made from root, rootlet, berry and leaf of Panax quinquefolium (American ginseng) and Panax ginseng (Asian ginseng), are proved for anti-hyperglycemia, insulin sensitization, islet protection, anti-obesity and anti-oxidation in many model systems. Energy expenditure is enhanced by ginseng through thermogenesis. Ginseng-specific saponins (ginsenosides) are considered as the major bioactive compounds for the metabolic activities of ginseng. Berberine from rhizoma coptidis is an oral hypoglycemic agent. It also has anti-obesity and anti-dyslipidemia activities. The action mechanism is related to inhibition of mitochondrial function, stimulation of glycolysis, activation of AMPK pathway, suppression of adipogenesis and induction of low-density lipoprotein (LDL) receptor expression. Bitter melon or bitter gourd (Momordica charantia) is able to reduce blood glucose and lipids in both normal and diabetic animals. It may also protect beta cells, enhance insulin sensitivity and reduce oxidative stress. Although evidence from animals and humans supports the therapeutic activities of ginseng, berberine and bitter melon, multi-center large-scale clinical trials have not been conducted to evaluate the efficacy and safety of these herbal medicines.     

Active phytochemicals from Chinese herbs as therapeutic agents for the heart

Naturally occurring plant alkaloids, in particular those identified from herbal medicines, are finding therapeutic use. Heart diseases can be well managed with specific formulations of herbal medicines. The combined action of multiple constituents of herbal medicines works with therapeutic benefits in humans. The established formulations of Traditional Chinese medicines show efficacy in treatment of diseases. However, individual herbal principles seldom show pharmacological activity. Nevertheless, some of the active alkaloids and terpenoids from medicinal herbs have been identified. The pharmacological activities of these herbal compounds have been studied. These active constituents of herbal medicine are also used in nutrient supplements, but the modes of action of the active component remain sketchy. The present review describes the recent development of those active principles from herbal medicines as cardiovascular agents. The study will provide insights into herbal medicines for drug development for the treatment of cardiovascular disease.     

Receptors for bitter, sweet and umami taste couple to inhibitory G protein signaling pathways

Taste receptors are thought to couple to the G protein Galpha-gustducin to initiate signal transduction cascades leading to taste perception. To further characterize the G protein-coupling selectivity of these receptors, we expressed them in HEK293 cells and monitored the modulation of different signaling pathways upon stimulation. We found that the bitter compound cycloheximide induces phosphorylation of extracellular signal-regulated kinases1 and 2 (ERK 1/2) and inhibits cAMP accumulation in HEK293 cells expressing the mouse bitter T2R(5) receptor. These effects are totally abolished upon treatment with pertussis toxin. On the other hand, sweeteners and monosodium glutamate induce phosphorylation of ERK1/2 and inhibit cAMP accumulation in HEK293 cells expressing the human sweet T1R(2)/T1R(3) receptor and the human umami T1R(1)/T1R(3) receptor, respectively. The effects of these taste modalities are also prevented by treatment with pertussis toxin. Collectively, our results show that taste receptors can functionally couple to Galpha(i/o) proteins to transmit intracellular signals.     

中药在皮肤疾病中的应用的研究进展

目的综述中药在皮肤疾病中的应用的研究进展。方法查阅国内外相关文献,以其中的25篇为依据,结合中医及现代医学理论概述中药在皮肤疾病中的应用的研究进展。结果研究表明中药在皮肤疾病中应用广泛,利用中医及现代医学理论指导临床用药获得良好的疗效,但一些中药组方在作用机制上仍缺乏一定的药理依据。结论为治疗皮肤疾病药物的开发与研究提供依据。     

中药治疗海洛因依赖急性戒断症状的Meta分析

目的:系统评价中药治疗海洛因依赖急性戒断症状的有效性与安全性。方法:计算机检索多种中英文数据库,收集中、西药(α2-肾上腺素受体激动剂或阿片受体激动剂)对比研究海洛因脱毒的随机对照实验(RCT)。采用Jadad量表对纳入研究进行质量评价,并采用RevM an软件以固定效应和随机效应模型进行M eta分析。评价指标包括:戒断症状评分、焦虑评分及不良反应发生率。结果:共纳入21个实验(共2949位受试者)。结果显示:对于戒断症状的缓解,在疗程的d4-10(d8除外),中药组优于α2-受体激动剂组,在疗程的前3 d,两者无显著性差异。与阿片受体激动剂相比,在疗程前3 d,中药略显逊色,但在疗程d4-9,两者疗效相当。对于焦虑的缓解,中药组与阿片受体激动剂组相比无显著性差异,但与α2-受体激动剂组相比,中药在疗程后期显示出优越性。另外,在某些不良反应(疲乏、眩晕)发生率上,中药组也显著低于α2-受体激动剂组(阿片受体激动剂组数据不足,未分析)。结论:现有数据表明,中药是海洛因依赖脱毒有效而安全的治疗方法。但对于中药特定方剂的特定疗效还需要有进一步的研究。     

Herbal medicine revisited: science looks anew at ancient Chinese pharmacology

There is now increasing evidence that significant advances have been made in herbal medicine during the past 20-25 years since the official policy of China was established that encouraged a blend of Western and Chinese traditional medicine. Scientific studies in China and the United States, as well as other countries, are directed at collecting and cataloguing a great variety of the herbs listed in the folk pharmacopias. 1 of the most significant single agents identified recently is isodamine, an alkaloid isolated from the solancea plant. Its formula, pharmacological action, and clinical effects are very similar to those of atropine. On the basis of experimental and clinical studies, Chinese scientists report that anisodamine is a better spasmolytic agent than atropine by virtue of its milder activity on the salivary glands, the pupils, and the central nervous system. Several herbal drugs have recently been developed and subjected to successful clinical trials. These drugs tend to be combinations of herbs. The Chinese have made progress recently in the treatment of burns with herbal medicine. 1 of the reasons given for past failures of Western investigators to identify the medicinal properties of Chinese medications is that the research usually began with the isolation of individual chemical compounds. New studies in the U.S. are focusing on single ingredients, entire herbal concoctions, and the use of herbal medicines in conjunction with Western drug products. Virtually every city in the U.S. with a sizable Chinese ethnic community has 1 or more herbal "pharmacies."     

G-protein coupled receptors: conformations and states.

Activation of G-protein coupled receptors by agonists is thought to involve the stabilisation of a ternary complex of agonist/receptor/G-protein, leading to effector activation, but this mechanism may be an oversimplification, as follows: (a) Agonist binding to the free receptor (uncoupled from G-proteins) is not a neutral event, but includes a component of the activation process and may be described in terms of the stabilisation of a partly activated form of the receptor (R*) that is able to couple to the G-protein. Stabilisation of R*, therefore, may contribute to agonist efficacy. Also, determinations of agonist affinity even in the absence of G-protein coupling do not necessarily describe the affinities of agonists for the ground state of the receptor. (b) R* is a partly activated intermediate between the ground state of the receptor (R) and the activated form coupled to G-protein (R*G). There is some indication that different agonists may stabilise different conformational states of the receptor, i.e. different R* species. (c) Agonists also stabilise the activated, coupled form of the receptor (AR*G), and for some agonists acting at a single receptor, the activated states may be similar, although there is evidence for other agonists that different activated states with different activities may be stabilised. (d) Two or more efficacy-generating steps are involved in the activation of G-protein coupled receptors by agonists: the stabilisation of R*, the stabilisation of R*G, and possibly the modulation of the activity of the activated state (AR*G). (e) The experimentally observed excess of G-proteins over receptors in membranes is inconsistent with data obtained from ligand-binding assays on these receptors. Receptors and G-proteins, therefore, may exist in some form of higher order array with cooperative interactions.     

Recent advances in gut nutrient chemosensing

The field of gut nutrient chemosensing is evolving rapidly. Recent advances have uncovered the mechanism by which specific nutrient components evoke multiple metabolic responses. Deorphanization of G protein-coupled receptors (GPCRs) in the gut has helped identify previously unliganded receptors and their cognate ligands. In this review, we discuss nutrient receptors, their ligand preferences, and the evoked neurohormonal responses. Family A GPCRs includes receptor GPR93, which senses protein and proteolytic degradation products, and free fatty acid-sensing receptors. Short-chain free fatty acids are ligands for FFA2, previously GPR43, and FFA3, previously GPR41. FFA1, previously GPR40, is activated by long-chain fatty acids with GPR120 activated by medium- and long-chain fatty acids. The GPR119 agonist ethanolamide oleoylethanolamide (OEA) and bile acid GPR131 agonists have also been identified. Family C receptors ligand preferences include L-amino acids, carbohydrate, and tastants. The metabotropic glutamate receptor (mGluR), calcium-sensing receptor (CaR), and GPCR family C, group 6, subtype A receptor (GPRC6A) mediate L-amino acid-sensing. Taste receptors have a proposed role in intestinal chemosensing; sweet, bitter, and umami evoke responses in the gut via GPCRs. The mechanism of carbohydrate-sensing remains controversial: the heterodimeric taste receptor T1R2/T1R3 and sodium glucose cotransporter 1 (SGLT-1) expressed in L cells are the two leading candidates. Identification of specific nutrient receptors and their respective ligands can provide novel therapeutic targets for the treatment of diabetes, acid reflux, foregut mucosal injury, and obesity.     

G蛋白偶联受体组成性活性及反向激动剂研究进展

G蛋白偶联受体（GPCR）是受体中家族成员最多的一大类，其活性涉及体内绝大部分的生理功能，在药物研发过程中是主要的药物作用靶标。研究表明，GPCR及其突变体在缺乏配体结合的情况下，能自发地产生一定程度的内在活性，即GPCR的组成性活性（constitutive activity）；其相应的反向激动剂与GPCR结合能降低受体的组成性活性，在药物治疗学上具有重要意义。愈来愈多的实验表明，GPCR组成性活性及反向激动剂的研究具有广阔和实际的应用前景，对其进行深入研究在受体学说领域和药物研发过程中具有重要理论意义。     

有效专利中防治呼吸系统疾病的中药复方用药规律探索

目的 探索防治呼吸系统疾病的中药复方有效专利的用药规律,为新药研制提供参考,为其专利保护提供战略依据。方法 以维持时间为5年的防治呼吸系统疾病的中药复方专利为研究对象,通过频数分析法对其核心药物的组成、分类、功效、归经及药对配伍进行统计分析。结果 防治呼吸系统疾病的中药复方有效专利中高频中药包括金银花、甘草、黄芩等22味,按照功效分类多属于清热药、化痰止咳平喘药和补虚药等,主要归肺、心经,高频药对配伍多来自于古(经)方。结论 上述用药规律探索体现了防治呼吸系统疾病中药复方的组方特点,为新的中药复方研发及专利保护策略提供了新思路。     

再次介绍五种泉州新发现名优中草药

本文继2018年6期后,再次介绍五种泉州新发现名优中草药,具有广泛应用的价值。收载入《新编泉州本草》内。这五种草药再次反映近60年来泉州地区中医药发展历程和实践应用情况。     

Motivational properties of kappa and mu opioid receptor agonists studied with place and taste preference conditioning

The reinforcing properties of various opioid agonists acting preferentially on the kappa and mu opioid receptors were assessed using taste and place preference conditioning procedures.Kappa receptor agonists produced conditioned aversions. Taste aversions were produced by all of the drugs used, including racemic mixtures of ethylketazocine, tifluadom, and U50-488, and active isomers (+)-tifluadom, (-)-bremazocine, and Mr 2034; corresponding inactive isomers either produced no effect of were less potent. Place aversions were produced by U50-488 and (-)-bremazocine, but not (+)-bremazocine or any of the other kappa receptor agonists tested with the taste procedure. The mu agonists produced predominantly conditioned preferences. Place preferences were produced by morphine, fentanyl and sufentanil. Taste preferences were produced by low doses of these substances; at higher doses the taste preferences were absent or replaced by aversions. Finally, with naloxone and lithium chloride it was shown that the taste procedure was more sensitive to punishing effects than the place procedure.It is concluded that kappa and mu opioid receptor agonists are effective unconditioned stimuli. From the lower portions of the dose response curves it is further concluded that activation of kappa opioid receptors has aversive properties and activation of mu receptors appetitive reinforcing properties. The findings are also discussed with regard to the prevailing notions of taste conditioning with opiates, and the reinforcing properties of activity of the endogenous opioid peptide systems.