Mosapride citrate increases postprandial glucagon-like peptide-1, insulin, and gene expression of sweet taste receptors

BACKGROUND AND AIM

Mosapride citrate-a prokinetic agent-improves hemoglobin A1c levels in diabetic patients; however, the underlying mechanism is unclear. We aimed to clarify this mechanism.

METHODS

Preprandial and postprandial (90 min after a meal) blood was obtained from 12 healthy men, and serum insulin and plasma active glucagon-like peptide-1 concentrations were measured. Measurements were also taken after the administration of 5 mg of mosapride citrate three times per day after every meal for 14 days. In addition, C57BL/6 mice were permitted free access to water containing 0.04 % domperidone (D group) or 0.02 % mosapride citrate (M group) for 2 weeks (four mice per group). T1r2 (taste receptor, type 1, member 2), T1r3, and Gnat3 (guanine nucleotide-binding protein, alpha transducing 3) mRNA expression levels of the stomach, duodenum, and proximal and mid-jejunum were evaluated.

RESULTS

In human subjects, postprandial plasma active glucagon-like peptide-1 and serum insulin concentrations after administration of mosapride citrate were significantly higher than those pre-administration (4.8 ± 2.2 pmol/L, 45.6 ± 41.6 μIU/mL, and 3.7 ± 1.2 pmol/L, 34.1 ± 28.4 μIU/mL, respectively). The mouse expression levels of T1r2 and Gnat3 in the proximal jejunum and mid-jejunum in the M group (4.1 ± 1.8-fold, 3.1 ± 1.6-fold, and 4.6 ± 0.8-fold, 3.1 ± 0.9-fold increases, respectively), were significantly higher than those of the control group.

CONCLUSIONS

The administration of mosapride citrate for 2 weeks enhanced postprandial plasma active glucagon-like peptide-1 and serum insulin concentration and increased the expression of sweet taste receptors in the upper intestine.

The advancement of the onset of vaginal opening in female rats subjected to chronic testosterone treatment occurs independently of hypothalamic Kiss1 and RFRP expression

OBJECTIVE

The neonatal and/or prepubertal androgen milieu affects sexual maturation. In rodents, neonatal chronic testosterone treatment, which is used as a model of polycystic ovary syndrome (PCOS), results in the onset of vaginal opening occurring earlier in the pubertal period.

DESIGN

In the present study, the changes in hypothalamic Kiss1 (a gonadotropin-releasing hormone (GnRH)-stimulating factor) and RF-amide related peptide (RFRP; a GnRH inhibitory factor) mRNA expression induced by testosterone treatment were examined in order to clarify whether these factors are involved in the testosterone-induced acceleration of sexual maturation.

RESULTS

The onset of vaginal opening occurred earlier and uterine weight was increased in female rats subjected to chronic (from postnatal day 23 to day 31) testosterone treatment. Contrary to our expectations, the rats' hypothalamic Kiss1 and Kiss1 receptor mRNA levels were not changed, and their serum luteinizing hormone (LH) levels were decreased. Although hypothalamic RFRP mRNA expression was decreased in the testosterone-treated rats, this change was not reflected in their serum LH levels.

CONCLUSIONS

These results indicate that the advancement of sexual maturation observed in chronic testosterone-treated rats might be caused by a peripheral, rather than a central, mechanism.

Diethylstilbestrol affects the expression of GPER in the gubernaculum testis

Recent evidence suggested a positive correlation between environmental estrogens (EEs) and high incidence of abnormalities in male urogenital system. EEs are known to cause the abnormalities of testes development and testicular descent. Diethylstilbestrol (DES) is a nonsteroidal synthetic estrogen that disrupts the morphology and proliferation of gubernacular cells, and its nongenomic effects on gubernaculum testis cells may be mediated by G protein-coupled estrogen receptor (GPER). In this study, we detected the expression of GPER in mouse gubernacular testis and investigated the effects of DES on the expression of GPER in gubernaculum testis cells. RT-PCR analysis revealed that GPER mRNA was expressed in the gubernaculum. GPER protein was detected in the parenchymal cells of the gubernaculum early in development. Furthermore, we demonstrate that GPER inhibitor G15 relieved DES-induced inhibition of GPER expression in gubernaculum testis cell, but ER inhibitor ICI 182780 had the converse effects on DES-induced inhibition of GPER expression in these cells. These data suggest that the effects of DES on mouse gubernaculum testis cells are mediated at least partially by the regulation of GPER expression.

Activation of G-protein-coupled receptor 30 increases T-type calcium currents in trigeminal ganglion neurons via the cholera toxin-sensitive protein kinase A pathway

G protein-coupled receptor 30 (GPR30) is a seven transmembrane domain G protein coupled receptor. In our study, GPR30 expression was found in trigeminal ganglia (TG) in mice, detected by RT-PCR and western blotting. We examined the effects of GPR30 activation on T-type calcium channels using GPR30-specific compound 1 (G-1), a GPR30-selective agonist, in TG neurons and demonstrated that G-1 induced an increase in T-type calcium channel currents (T-currents) in TGs. Intracellular infusion of GDP-β-S and pre-treatment of the neurons with cholera toxin (CTX) blocked the effects of G-1, suggesting that the G(s)-protein was involved. Intracellular application of the protein kinase A (PKA) inhibitor PKI 6-22 or pretreatment of the neurons with H89 abolished G-1 -induced enhancement of T-currents in TG neurons. However, incubation with PKC inhibitor elicited no such effects. In conclusion, our study shows that activation of GPR30 by G-1 increases T-currents via the CTX-sensitive and PKA-dependent pathway.

In vitro evaluation of potential bitterness-masking terpenoids from the Canada goldenrod (Solidago canadensis)

In a screening of extracts of selected plants native to Ohio against the human bitterness receptor hTAS2R31, a chloroform-soluble extract of the aerial parts of Solidago canadensis (Canada goldenrod) was determined to have hTAS2R31 antagonistic activity and, thus, was fractionated for isolation of potential bitterness-masking agents. One new labdane diterpenoid, solidagol (1), and six known terpenoids, including two labdane diterpenoids (2 and 3), three clerodane diterpenoids (6β-angeloyloxykolavenic acid, 6β-tigloyloxykolavenic acid, and crotonic acid), and a triterpenoid (longispinogenin), were isolated. Among these compounds, 3β-acetoxycopalic acid (2) was found to be the first member of the labdane diterpene class shown to have inhibitory activity against hTAS2R31 activation (IC50 8 μM). A homology model of hTAS2R31 was constructed, and the molecular docking of 2 to this model indicated that this diterpenoid binds well to the active site of hTAS2R31, whereas this was not the case for the closely structurally related compound 3 (sempervirenic acid). The content of 2 in the chloroform-soluble portion of the methanolic extract of S. canadensis was up to 2.24 g/100 g dry weight, as determined by HPLC.

Role of GPR30 in mediating estradiol effects on acetylcholine release in the hippocampus

We have hypothesized that estradiol enhances basal forebrain cholinergic function and cognitive performance, at least in part, via activation of the novel estrogen receptor GPR30. Here we evaluated the effects of estradiol, G-1 (a selective GPR30 agonist), and tamoxifen (TAM; an ERα/ERβ antagonist that also acts as a GPR30 agonist), on acetylcholine (ACh) release in the hippocampus, as well as the ability to block the effects of 17β-estradiol (E) or TAM with the GPR30 antagonist G-15. Note that G-1 was included to evaluate the effects of selectively activating GPR30, whereas TAM was included to differentiate effects of E associated with activation of GPR30 vs. ERα or ERβ. The study was designed to test effects on potassium-stimulated release, as well as on ACh release stimulated by feeding. Effects of feeding were included because the tasks we used previously to demonstrate beneficial effects of E on cognitive performance were motivated by food reward, and we hypothesized that E may enhance performance by increasing ACh release in association with that reward. Ovariectomized rats were treated for 1week, and ACh release was evaluated using in vivo microdialysis. In addition, rats were fed at the same time daily for several days and were fasted overnight prior to microdialysis. For each rat, ACh release was evaluated under basal conditions, in response to feeding, and in response to elevated potassium. Both feeding and elevated potassium increased ACh release in the hippocampus. In response to feeding, E, G-1, and TAM all significantly increased the percent change in release. The effects of E and TAM were blocked by G-15, and the effects of combining E+TAM did not differ significantly from the effects of E or TAM alone. In response to elevated potassium, E, and TAM significantly increased the percent change in ACh release. G-1 produced a slightly lesser effect. The effect of TAM was reduced by G-15, but the effect of E was not. These findings suggest that activation of GPR30 is both necessary and sufficient to account for the effects of E on ACh release associated with feeding. In contrast, activation of GPR30 appears to be sufficient, but may not be necessary for increased release associated with elevated potassium. The changes associated with feeding are consistent with the effects of E, G-1 and G-15 on acquisition of a spatial learning task previously described. These data confirm and extend previous reports, and support a hypothesis wherein E treatment can improve learning on specific tasks by activating GPR30 and enhancing ACh release in association with food reward.

Expression of hedgehog signalling pathway in anaplastic thyroid cancer

The purpose of this work is to study the activation of the hedgehog signalling pathway is associated with tumour progression in various types of cancer, hence the development of specific antagonists raises hope for new therapeutic strategies. Therefore, the expression of hedgehog pathway components in anaplastic thyroid cancer (ATC) and effects of the hedgehog inhibitor Cyclopamine on ATC cells were investigated in this study. Expression of the ligand Sonic Hedgehog (SHh), the transmembrane protein Smoothened (Smo), the receptor Patched (Ptc) and the target gene Gli-1 was evaluated in two ATC cell lines (Hth 74, C643) by RT-PCR and in tumour specimens by immunohistochemistry. The corresponding gene products were examined by western blotting analysis. After treatment with different concentrations of Cyclopamine the time-dependent course of cell viability in ATC cell lines was evaluated by MTT assay. SHh, Smo, Ptc and Gli were clearly expressed on mRNA and protein levels in both cell lines and in tumour samples (41 %SHh, 65 %Smo, 65 %Ptc and 65 %Gli). Treatment with Cyclopamine showed a time- and dose-dependent inhibition of cell numbers with IC50 values between 1 and 4 μM in both cell lines, comparable to other types of cancer. In conclusion, we believe that the hedgehog pathway is expressed in anaplastic thyroid carcinoma specimens and proliferation of ATC cell lines can be influenced by the Hh inhibitor Cyclopamine. Aberrant activation of this pathway might be involved in the aggressive biology of anaplastic cancer and further evaluation regarding a possible clinical impact of pathway inhibition is warranted.

G protein-coupled receptors: abnormalities in signal transmission, disease states and pharmacotherapy

The aim of this review is to present the research results and draw new conclusions about the impact of alterations in the signal transmission through the G protein-coupled receptors (GPCRs) on the formation of diseases and drug therapy. GPCR family is the largest and the most diverse group of membrane receptors. They transmit signals into the cell by interaction with different ligands, which include, inter alia, hormones, neurotransmitters, and photons. GPCRs are responsible for the proper conduction of many physiological processes such as vision, intercellular communication, the neuronal transmission, hormonal signaling and are involved in many pathological processes. They are also point on the binding pathway of multiple drugs. They are targets of nearly one third of the drugs at the current pharmaceutical market. The genes encoding GPCRs represent about 4% of the human genome. Mutations that occur in them are associated with a broad spectrum of diseases of diverse etiology. As a mutations result, there is a change in receptor activity (GPCR become inactive, overactive, or constitutively active), in the process of ligand binding and signal transduction. Changes in the GPCRs functioning can cause diseases such as retinitis pigmentosa (rhodopsin mutations), nephrogenic diabetes insipidus (vasopressin receptor mutations), obesity (melanocortin receptor mutations). Many mutational changes in genes encoding GPCR can change drug therapy of already existed diseases: heart failure (adrenergic receptors), asthma (cysteinyl leukotriene receptors). Studies concerning the structure and function of genetically modified GPCRs allow to get know a variety of mechanisms of its action, which in turn can contribute to broaden the knowledge on the etiology and pharmacotherapy of many currently incurable diseases.

GPCRs and arrestins in airways: implications for asthma

The obstructive lung disease asthma is treated by drugs that target, either directly or indirectly, G protein-coupled receptors (GPCRs). GPCRs coupled to Gq are the primary mediators of airway smooth muscle (ASM) contraction and increased airway resistance, whereas the Gs-coupled beta-2-adrenoceptor (β2AR) promotes pro-relaxant signaling in and relaxation of ASM resulting in greater airway patency and reversal of life-threatening bronchoconstriction. In addition, GPCR-mediated functions in other cell types, including airway epithelium and hematopoietic cells, are involved in the control of lung inflammation that causes most asthma. The capacity of arrestins to regulate GPCR signaling, via either control of GPCR desensitization/resensitization or G protein-independent signaling, renders arrestins an intriguing therapeutic target for asthma and other obstructive lung diseases. This review will focus on the potential role of arrestins in those GPCR-mediated airway cell functions that are dysregulated in asthma.

β-arrestins: regulatory role and therapeutic potential in opioid and cannabinoid receptor-mediated analgesia

Pain is a complex disorder with neurochemical and psychological components contributing to the severity, the persistence, and the difficulty in adequately treating the condition. Opioid and cannabinoids are two classes of analgesics that have been used to treat pain for centuries and are arguably the oldest of "pharmacological" interventions used by man. Unfortunately, they also produce several adverse side effects that can complicate pain management. Opioids and cannabinoids act at G protein-coupled receptors (GPCRs), and much of their effects are mediated by the mu-opioid receptor (MOR) and cannabinoid CB1 receptor (CB1R), respectively. These receptors couple to intracellular second messengers and regulatory proteins to impart their biological effects. In this chapter, we review the role of the intracellular regulatory proteins, β-arrestins, in modulating MOR and CB1R and how they influence the analgesic and side-effect profiles of opioid and cannabinoid drugs in vivo. This review of the literature suggests that the development of opioid and cannabinoid agonists that bias MOR and CB1R toward G protein signaling cascades and away from β-arrestin interactions may provide a novel mechanism by which to produce analgesia with less severe adverse effects.

Glucose promotes its own metabolism by acting on the cell-surface glucose-sensing receptor T1R3

A homodimer of taste type 1 receptor 3 (T1R3) functions as a sweet taste-sensing receptor in pancreatic β-cells. This receptor is activated by various sweet molecules including sugars such as glucose. To determine the role of this receptor in glucose-induced insulin secretion, we addressed whether or not this receptor modulates glucose metabolism in MIN6 cells. We measured changes in intracellular ATP ([ATP]i) in MIN6 cells expressing luciferase. Sucralose, an agonist of T1R3, induced immediate and sustained elevation of [ATP]i in the presence of 5.5 mM glucose. The effect of sucralose was dose-dependent and, at 5 mM, was greater than that induced by 25 mM glucose. In contrast, carbachol, GLP-1 or high concentration of potassium did not reproduce the sucralose action. Sucralose facilitated the increase in [ATP]i induced by a mitochondrial fuel methylsuccinate, and potentiated glucose-induced elevation of [ATP]i. Administration of a non-metabolizable glucose analogue, 3-O-methylglucose, which acts as an agonist of T1R3, induced a small and transient increase in [ATP]i. 3-O-Methylglucose augmented elevation of [ATP]i induced by methylsuccinate, and also enhanced glucose-induced increase in [ATP]i. Knock down of T1R3 by using shRNA attenuated [ATP]i-response to high concentration of glucose and also reduced the glucose-induced insulin secretion. These results indicate that activation of the homodimer of T1R3 facilitates the metabolic pathway in mitochondria and augments ATP production. The results obtained by using 3-O-methylglucose suggest that glucose, by acting on the homodimer of T1R3, promotes its own metabolism.

QRFP induces aldosterone production via PKC and T-type calcium channel-mediated pathways in human adrenocortical cells: evidence for a novel role of GPR103

Hormonal regulation of adrenal function occurs primarily through activation of GPCRs. GPCRs are central to many of the body's endocrine and neurotransmitter pathways. Recently, it was shown that activation of GPR103 by its ligand QRFP induced feeding, locomotor activity, and metabolic rate, and QRFP is bioactive in adipose tissue of obese individuals. Given that the adrenal gland is a pivotal organ for energy balance and homeostasis, we hypothesized that GPR103 and QRFP are involved in steroidogenic responses. Using qRT-PCR and immunohistochemistry, we mapped both GPR103 and QRFP in human fetal and adult adrenal gland as well as rat adrenals. Both were primarily localized in the adrenal cortex but not in the medulla. Activation of GPR103 in human adrenocortical H295R cells led to a decrease in forskolin-increased cAMP and an increase of intracellular Ca(2+) levels. In addition, treatment of H295R cells with QRFP induced aldosterone and cortisol secretion as measured by ELISA. These increases were accompanied by increased expression and activity of StAR, CYB11B1, and CYP11B2 as assessed by qRT-PCR and luciferase reporter assay, respectively. Using specific inhibitors, we also demonstrated that aldosterone induction involves MAPK, PKC, and/or T-type Ca(2+) channel-dependent pathways. These novel data demonstrate that QRFP induces adrenal steroidogenesis in vitro by regulating key steroidogenic enzymes involving MAPK/PKC and Ca(2+) signaling pathways.

Activation of the MAS receptor by angiotensin-(1-7) in the renin-angiotensin system mediates mesenteric vasodilatation in cirrhosis

BACKGROUND & AIMS

Splanchnic vascular hypocontractility with subsequent increased portal venous inflow leads to portal hypertension. Although the renin-angiotensin system contributes to fibrogenesis and increased hepatic resistance in patients with cirrhosis, little is known about its effects in the splanchnic vasculature, particularly those of the alternate system in which angiotensin (Ang) II is cleaved by the Ang-converting enzyme-2 (ACE2) to Ang-(1-7), which activates the G-protein-coupled Mas receptor (MasR). We investigated whether this system contributes to splanchnic vasodilatation and portal hypertension in cirrhosis.

METHODS

We measured levels of renin-angiotensin system messenger RNA and proteins in splanchnic vessels from patients and rats with cirrhosis. Production of Ang-(1-7) and splanchnic vascular reactivity to Ang-(1-7) was measured in perfused mesenteric vascular beds from rats after bile-duct ligation. Ang-(1-7) and MasR were blocked in rats with cirrhosis to examine splanchnic vascular hemodynamics and portal pressure response.

RESULTS

Levels of ACE2 and MasR were increased in splanchnic vessels from cirrhotic patients and rats compared with healthy controls. We also observed an ACE2-dependent increase in Ang-(1-7) production. Ang-(1-7) mediated splanchnic vascular hypocontractility in ex vivo splanchnic vessels from rats with cirrhosis (but not control rats) via MasR stimulation. Identical effects were observed in the splanchnic circulation in vivo. MasR blockade reduced portal pressure, indicating that activation of this receptor in splanchnic vasculature promotes portal inflow to contribute to development of portal hypertension. In addition, the splanchnic effects of MasR required nitric oxide. Interestingly, Ang-(1-7) also decreased hepatic resistance.

CONCLUSIONS

In the splanchnic vessels of patients and rats with cirrhosis, increased levels of ACE2 appear to increase production of Ang-(1-7), which leads to activation of MasR and splanchnic vasodilatation in rats. This mechanism could cause vascular hypocontractility in patients with cirrhosis, and might be a therapeutic target for portal hypertension.

Propofol up-regulates Mas receptor expression in dorsal root ganglion neurons

Mas is a functional binding site for angiotensin (Ang)-(1-7), a critical component of the renin-angiotensin system that is involved in processing nociceptive information. A recent study reported the localization of Mas in rat dorsal root ganglia (DRG) and demonstrated that Ang-(1-7) produced a dose-dependent peripheral antinociceptive effect in rats through the Mas receptor by an opioid-independent mechanism. In the present study, we for the first time examined the effect of propofol on Mas expression in cultured DRG neurons. We treated rat DRG neurons with propofol at different concentrations (0.1, 0.5, 1, 5 or 10 microM) for different length of time (0.5, 1, 2, 4 or 6 h) with or without transcription inhibitor actinomycin D or different kinase inhibitors. Propofol increased the Mas receptormRNA level in a statistically significant dose- and time-dependent manner within 4 h, which led to dose-dependent up-regulation of the Mas receptor protein level as well as Ang-(1-7) binding on the cell membrane. Actinomycin D (1 mg/ml) and p38 mitogen-activated protein kinase inhibitor PD169316 (25 microM) completely abolished the effect of propofol on Mas receptor expression in DRG neurons. In conclusion, we demonstrate that propofol markedly up-regulates Mas receptor expression at the transcription level in DRG neurons by a p38 MAPK-dependent mechanism. This study provides new insights into the mechanisms of action of propofol in peripheral antinociception, and suggests a new regulatory mechanism on the Ang-(1-7)/Mas axis in the peripheral nervous system.

Piperazine modification in 2,4,6-triaminopyrimidine derivatives as histamine H4 receptor ligands

The human histamine H4 receptor (hH4R) is a promising new target in the therapy of inflammatory and immunomodulatory diseases. The 2,4,6-triaminopyrimidine structure has been established as a potent hH4R affinity scaffold. By using the inverse agonist ST-1012 as reference ligand, piperazine modifications were performed to get larger structural variations. Therefore, different spacers were introduced into the lead structure and the influence on affinity of this basic element was evaluated. While a short distance between aminopyrimidine and basic moiety is beneficial, a lipophilic group in the eastern part is necessary to maintain hH4R affinity.

Opportunities for targeting the angiotensin-converting enzyme 2/angiotensin-(1-7)/mas receptor pathway in hypertension

It is well known that the renin-angiotensin system (RAS) plays a pivotal role in the pathophysiology of cardiovascular diseases. This is well illustrated by the great success of ACE inhibitors and angiotensin (Ang) II AT(1) blockers in the treatment of hypertension and its complications. In the past decade, the classical concept of RAS orchestrated by a series of enzymatic reactions culminating in the linear generation and action of Ang II has expanded and become more complex. From the discoveries of new components such as the angiotensin converting enzyme 2 and the receptor Mas emerged a novel concept of dual opposite branches of the RAS: one vasoconstrictor and pro-hypertensive composed of ACE/Ang II/AT1; and other vasodilator and anti-hypertensive composed of ACE2/Ang-(1-7)/Mas. In this review we will discuss recent findings concerning the biological role of the ACE2/Ang-(1-7)/Mas arm in the cardiovascular system and highlight the initiatives to develop potential therapeutic strategies based on this axis for treating hypertension.

Structure-based approaches to ligands for G-protein-coupled adenosine and P2Y receptors, from small molecules to nanoconjugates

Adenosine receptor (ARs) and P2Y receptors (P2YRs) that respond to extracellular nucleosides/nucleotides are associated with new directions for therapeutics. The X-ray structures of the A2AAR complexes with agonists and antagonists are examined in relationship to the G-protein-coupled receptor (GPCR) superfamily and applied to drug discovery. Much of the data on AR ligand structure from early SAR studies now are explainable from the A2AAR X-ray crystallography. The ligand-receptor interactions in related GPCR complexes can be identified by means of modeling approaches, e.g., molecular docking. Thus, molecular recognition in binding and activation processes has been studied effectively using homology modeling and applied to ligand design. Virtual screening has yielded new nonnucleoside AR antagonists, and existing ligands have been improved with knowledge of the receptor interactions. New agonists are being explored for central nervous system and peripheral therapeutics based on in vivo activity, such as chronic neuropathic pain. Ligands for receptors more distantly related to the X-ray template, i.e., P2YRs, have been introduced and are mainly used as pharmacological tools for elucidating the physiological role of extracellular nucleotides. Other ligand tools for drug discovery include fluorescent probes, radioactive probes, multivalent probes, and functionalized nanoparticles.

Human trace amine-associated receptor TAAR5 can be activated by trimethylamine

In addition to the canonical olfactory receptors, TAARs were currently suggested to be a second class of chemosensory receptors in the olfactory epithelium of vertebrates. In contrast to several deorphanized murine TAARs, agonists for the intact human TAAR genes 2, 5, 6, 8 and 9 that are potentially expressed in the human olfactory epithelium have not been determined so far. Moreover, the physiological relevance of TAARs still remains elusive. We present the first successful functional expression of a human TAAR and agonists of human TAAR5. We performed a ligand screening using recombinantly expressed human TAAR5 in HANA3A cells and Xenopus laevis oocytes. In order to measure receptor activity, we used a cAMP-dependent reporter gene assay and two-electrode voltage clamp technique. As a result, human TAAR5 can be activated in a concentration-dependent manner by trimethylamine and with less efficacy by dimethylethylamine. It could neither be activated by any other of the tested single amines with a related chemical structure (42 in total), nor by any of the tested odorant mixtures. The hypothesis that Single Nucleotide Polymorphisms (SNP) within the reading frame of an olfactory receptor gene can cause a specific anosmia, formed the basis for clarifying the question, if anosmia for trimethylamine is caused by a SNP in a TAAR coding sequence. All functional human TAAR gene reading frames of subjects with specific anosmia for trimethylamine were amplified and products analyzed regarding SNP distribution. We demonstrated that the observed specific anosmia for trimethylamine is not correlated with a SNP in the coding sequence of one of the putatively functional human TAAR genes.

Amino acids and peptides activate at least five members of the human bitter taste receptor family

Amino acids and peptides represent important flavor molecules eliciting various taste sensations. Here, we present a comprehensive assessment of the interaction of various peptides and all proteinogenic amino acids with the 25 human TAS2Rs expressed in cell lines. L-Phenylalanine and L-tryptophan activate TAS2R1 and TAS2R4, respectively, whereas TAS2R4 and TAS2R39 responded to D-tryptophan. Structure-function analysis uncovered the basis for the lack of stereoselectivity of TAS2R4. The same three TAS2Rs or subsets thereof were also sensitive to various dipeptides containing L-tryptophan, L-phenylalanine, or L-leucine and to Trp-Trp-Trp, whereas Leu-Leu-Leu specifically activated TAS2R4. Trp-Trp-Trp also activated TAS2R46 and TAS2R14. Two key bitter peptides from Gouda cheese, namely, Tyr-Pro-Phe-Pro-Gly-Pro-Ile-His-Asn-Ser and Leu-Val-Tyr-Pro-Phe-Pro-Gly-Pro-Ile-His-Asn, both activated TAS2R1 and TAS2R39. Thus, the data demonstrate that the bitterness of amino acids and peptides is not mediated by specifically tuned TAS2Rs but rather is brought about by an unexpectedly complex pattern of sensitive TAS2Rs.

IUPHAR-DB: updated database content and new features

The International Union of Basic and Clinical Pharmacology (IUPHAR) database, IUPHAR-DB (http://www.iuphar-db.org) is an open access, online database providing detailed, expert-driven annotation of the primary literature on human and rodent receptors and other drug targets, together with the substances that act on them. The present release includes information on the products of 646 genes from four major protein classes (G protein-coupled receptors, nuclear hormone receptors, voltage- and ligand-gated ion channels) and ∼3180 bioactive molecules (endogenous ligands, licensed drugs and key pharmacological tools) that interact with them. We have described previously the classification and curation of data for small molecule ligands in the database; in this update we have annotated 366 endogenous peptide ligands with their amino acid sequences, post-translational modifications, links to precursor genes, species differences and relationships with other molecules in the database (e.g. those derived from the same precursor). We have also matched targets with their endogenous ligands (peptides and small molecules), with particular attention paid to identifying bioactive peptide ligands generated by post-translational modification of precursor proteins. Other improvements to the database include enhanced information on the clinical relevance of targets and ligands in the database, more extensive links to other databases and a pilot project for the curation of enzymes as drug targets.

Overexpression of melatonin membrane receptors increases calcium-binding proteins and protects VSC4.1 motoneurons from glutamate toxicity through multiple mechanisms

Melatonin has shown particular promise as a neuroprotective agent to prevent motoneuron death in animal models of both amyotrophic lateral sclerosis (ALS) and spinal cord injuries (SCI). However, an understanding of the roles of endogenous melatonin receptors including MT1, MT2, and orphan G-protein receptor 50 (GPR50) in neuroprotection is lacking. To address this deficiency, we utilized plasmids for transfection and overexpression of individual melatonin receptors in the ventral spinal cord 4.1 (VSC4.1) motoneuron cell line. Receptor-mediated cytoprotection following exposure to glutamate at a toxic level (25 μm) was determined by assessing cell viability, apoptosis, and intracellular free Ca(2+) levels. Our findings indicate a novel role for MT1 and MT2 for increasing expression of the calcium-binding proteins calbindin D28K and parvalbumin. Increased levels of calbindin D28K and parvalbumin in VSC4.1 cells overexpressing MT1 and MT2 were associated with cytoprotective effects including inhibition of proapoptotic signaling, downregulation of inflammatory factors, and expression of prosurvival markers. Interestingly, the neuroprotective effects conferred by overexpression of MT1 and/or MT2 were also associated with increases in the estrogen receptor β (ERβ): estrogen receptor α (ERα) ratio and upregulation of angiogenic factors. GPR50 did not exhibit cytoprotective effects. To further confirm the involvement of the melatonin receptors, we silenced both MT1 and MT2 in VSC4.1 cells using RNA interference technology. Knockdown of MT1 and MT2 led to an increase in glutamate toxicity, which was only partially reversed by melatonin treatment. Taken together, our findings suggest that the neuroprotection against glutamate toxicity exhibited by melatonin may depend on MT1 and MT2 but not GPR50.

The molecular basis for neuroimmune receptor signaling

Many of the receptors which are responsible for the responses to the common drugs of abuse belong to the G protein-coupled receptor (GPCR) family. In this special issue of the Journal of Neuroimmune Pharmacology a collection of papers is presented which deals with signaling events that are important for the function of these receptors. Because these receptors are expressed by both neuronal and immune cells, and because these receptors play a complex role in regulating function in both the nervous and immune systems, a more complete understanding of the regulation of expression of these receptors is essential. Moreover, once these receptors are expressed and activated, a complex series of signaling events are initiated that can have substantial significance. We have only a limited understanding of these signaling events, but with more complete information, we may be able to control the undesirable and/or desirable consequences of receptor activation by drugs of abuse.

The recent progress in research on effects of anesthetics and analgesics on G protein-coupled receptors

The exact mechanisms of action behind anesthetics and analgesics are still unclear. Much attention was focused on ion channels in the central nervous system as targets for anesthetics and analgesics in the 1980s. During the 1990s, major advances were made in our understanding of the physiology and pharmacology of G protein coupled receptor (GPCR) signaling. Thus, several lines of studies have shown that G protein coupled receptors (GPCRs) are one of the targets for anesthetics and analgesics and especially, that some of them inhibit the functions of GPCRs, i.e,, muscarinic receptors and substance P receptors. However, these studies had been focused on only G(q) coupled receptors. There has been little work on G(s)- and G(i)-coupled receptors. In the last decade, a new assay system, using chimera G(i/o)-coupled receptor fused to Gq(i5), has been established and the effects of anesthetics and analgesics on the function of G(i)-coupled receptors is now more easily studied. This review highlights the recent progress of the studies regarding the effects of anesthetics and analgesics on GPCRs.

G protein-coupled adenosine (P1) and P2Y receptors: ligand design and receptor interactions

The medicinal chemistry and pharmacology of the four subtypes of adenosine receptors (ARs) and the eight subtypes of P2Y receptors (P2YRs, activated by a range of purine and pyrimidine mono- and dinucleotides) has recently advanced significantly leading to selective ligands. X-ray crystallographic structures of both agonist- and antagonist-bound forms of the A(2A)AR have provided unprecedented three-dimensional detail concerning molecular recognition in the binding site and the conformational changes in receptor activation. It is apparent that this ubiquitous cell signaling system has implications for understanding and treating many diseases. ATP and other nucleotides are readily released from intracellular sources under conditions of injury and organ stress, such as hypoxia, ischemia, or mechanical stress, and through channels and vesicular release. Adenosine may be generated extracellularly or by cellular release. Therefore, depending on pathophysiological factors, in a given tissue, there is often a tonic activation of one or more of the ARs or P2YRs that can be modulated by exogenous agents for a beneficial effect. Thus, this field has provided fertile ground for pharmaceutical development, leading to clinical trials of selective receptor ligands as imaging agents or for conditions including cardiac arrhythmias, ischemia/reperfusion injury, diabetes, pain, thrombosis, Parkinson's disease, rheumatoid arthritis, psoriasis, dry eye disease, pulmonary diseases such as cystic fibrosis, glaucoma, cancer, chronic hepatitis C, and other diseases.