Angiotensin-(1-7) suppresses oxidative stress and improves glucose uptake via Mas receptor in adipocytes

Although reactive oxygen species (ROS) contribute to glucose intolerance induced by the renin-angiotensin system (RAS) is well documented, the role of the newly discovered pathway of RAS, angiotensin (Ang)-(1-7)/Mas axis, in this process remains unknown. Here, we examined the effect of Ang-(1-7) on oxidative stress and glucose uptake in adipocytes. We used primary cultured epididymal adipocytes from C57 mice to study Ang-(1-7) effects on glucose uptake. We also treated fully differentiated 3T3-L1 adipocytes with exogenous Ang-(1-7) or overexpression of angiotensin-converting enzyme 2 (ACE2) to induce endogenous generation of Ang-(1-7) to clarify its effects on ROS production. Intracellular ROS was measured by flow cytometry, dihydroethidium (DHE), and nitroblue tetrazolium assay. Levels of NADPH oxidase and adiponectin mRNA were measured by real-time PCR. Ang-(1-7) improved glucose uptake both in basal and insulin-stimulated states. ROS production was slightly but significantly decreased in adipocytes treated with Ang-(1-7). Additionally, Mas receptor antagonist D-Ala7-Ang-(1-7) (A779) reversed the effect of Ang-(1-7) on glucose uptake and oxidative stress. Furthermore, treatment of adipocytes with Ang-(1-7) decreased NADPH oxidase mRNA levels. We also found that oxidative stress induced by glucose oxidase-suppressed expression of adiponectin, an insulin-sensitive protein. However, the suppression of oxidative stress by Ang-(1-7) restored adiponectin expression, while A779 agonists these changes induced by Ang-(1-7). In conclusion, Ang-(1-7) can protect against oxidative stress and improve glucose metabolism in adipocytes. These results show that Ang-(1-7) is a novel target for the improvement of glucose metabolism by preventing oxidative stress.

GPR55 and GPR35 and their relationship to cannabinoid and lysophospholipid receptors

This review presents a summary of what is known about the G-protein coupled receptors GPR35 and GPR55 and their potential characterization as lysophospholipid or cannabinoid receptors, respectively. Both GPR35 and GPR55 have been implicated as important targets in pain and cancer, and additional diseases as well. While kynurenic acid was suggested to be an endogenous ligand for GPR35, so was 2-arachidonoyl lysophosphatidic acid (LPA). Similarly, GPR55 has been suggested to be a cannabinoid receptor, but is quite clearly also a receptor for lysophosphatidylinositol. Interestingly, 2-arachidonyl glycerol (2-AG), an endogenous ligand for cannabinoid receptors, can be metabolized to 2-arachidonoyl LPA through the action of a monoacylglycerol kinase; the reverse reaction has also been demonstrated. Thus, it appears that mutual interconversion is possible between 2-arachidonoyl LPA and 2-AG within a cell, though the direction of the reaction may be site-dependent. The GPR55 natural ligand, 2-arachidonoyl LPI, can be degraded either to 2-AG by phospholipase C or to 2-arachidonoyl LPA by phospholipase D. Thus, GPR35, GPR55 and CB receptors are linked together through their natural ligand conversions. Additional agonists and antagonists have been identified for both GPR35 and GPR55, which will facilitate the future study of these receptors with respect to their physiological function. Potential therapeutic targets include pain, cancer, metabolic diseases and drug addiction.

Predicting drug-target interactions from chemical and genomic kernels using Bayesian matrix factorization

MOTIVATION

Identifying interactions between drug compounds and target proteins has a great practical importance in the drug discovery process for known diseases. Existing databases contain very few experimentally validated drug-target interactions and formulating successful computational methods for predicting interactions remains challenging.

RESULTS

In this study, we consider four different drug-target interaction networks from humans involving enzymes, ion channels, G-protein-coupled receptors and nuclear receptors. We then propose a novel Bayesian formulation that combines dimensionality reduction, matrix factorization and binary classification for predicting drug-target interaction networks using only chemical similarity between drug compounds and genomic similarity between target proteins. The novelty of our approach comes from the joint Bayesian formulation of projecting drug compounds and target proteins into a unified subspace using the similarities and estimating the interaction network in that subspace. We propose using a variational approximation in order to obtain an efficient inference scheme and give its detailed derivations. Finally, we demonstrate the performance of our proposed method in three different scenarios: (i) exploratory data analysis using low-dimensional projections, (ii) predicting interactions for the out-of-sample drug compounds and (iii) predicting unknown interactions of the given network.

AVAILABILITY

Software and Supplementary Material are available at http://users.ics.aalto.fi/gonen/kbmf2k.

CONTACT

mehmet.gonen@aalto.fi

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

Rediocide A, an Insecticide, induces G-protein-coupled receptor desensitization via activation of conventional protein kinase C

In order to identify small-molecule antagonists of Methuselah (Mth), a Drosophila G-protein-coupled receptor (GPCR) involved in life-span control, a library of natural compounds was screened, and it was found that rediocide A (1), a daphnane ester from the roots of Trigonostemon reidioides and used currently for flea control, potently inhibited calcium mobilization mediated by this receptor. Compound 1 inhibited calcium mobilization in GPCRs other than Mth, indicating that the inhibitory effect was not due to receptor antagonism but rather to a more general mechanism. It was found that 1 can induce GPCR desensitization and internalization, and such effects were mediated by the activation of conventional protein kinase C.

17β-Estradiol induces vasorelaxation in a G-protein-coupled receptor 30-independent manner

17β-Estradiol (E2) exerts rapid non-genomic vascular effects through activation of its plasma membrane receptors. We tested the hypothesis that E2 induces vasorelaxation through activation of the G-protein-coupled receptor 30 (GPR30) in rat aorta. Rat aortic rings were mounted in organ baths and subjected to contraction followed by relaxation. Whether endothelium was intact or denuded, both E2 and G1, a GPR30 agonist, induced vasorelaxation in concentration-dependent manners. Although G15, a specific GPR30 antagonist, blocked G1-induced vasorelaxation, it did not block E2-induced vasorelaxation. In conclusion, 17β-estradiol induces vasorelaxation in a GPR30-independent manner in rat aorta.

VENNTURE--a novel Venn diagram investigational tool for multiple pharmacological dataset analysis

As pharmacological data sets become increasingly large and complex, new visual analysis and filtering programs are needed to aid their appreciation. One of the most commonly used methods for visualizing biological data is the Venn diagram. Currently used Venn analysis software often presents multiple problems to biological scientists, in that only a limited number of simultaneous data sets can be analyzed. An improved appreciation of the connectivity between multiple, highly-complex datasets is crucial for the next generation of data analysis of genomic and proteomic data streams. We describe the development of VENNTURE, a program that facilitates visualization of up to six datasets in a user-friendly manner. This program includes versatile output features, where grouped data points can be easily exported into a spreadsheet. To demonstrate its unique experimental utility we applied VENNTURE to a highly complex parallel paradigm, i.e. comparison of multiple G protein-coupled receptor drug dose phosphoproteomic data, in multiple cellular physiological contexts. VENNTURE was able to reliably and simply dissect six complex data sets into easily identifiable groups for straightforward analysis and data output. Applied to complex pharmacological datasets, VENNTURE's improved features and ease of analysis are much improved over currently available Venn diagram programs. VENNTURE enabled the delineation of highly complex patterns of dose-dependent G protein-coupled receptor activity and its dependence on physiological cellular contexts. This study highlights the potential for such a program in fields such as pharmacology, genomics, and bioinformatics.

Bis-spirolabdane diterpenoids from Leonotis nepetaefolia

Ten new bis-spirolabdane diterpenoids, leonepetaefolins A-E (1, 3, 5, 7, 9) and 15-epi-leonepetaefolins A-E (2, 4, 6, 8, 10), together with eight known labdane diterpenoids (11-18) as well as two known flavonoids, apigenin and cirsiliol, were isolated from the leaves of Leonotis nepetaefolia. The structures of the new compounds were determined on the basis of 1D- and 2D-NMR experiments including (1)H, (13)C, DEPT, (1)H-(1)H COSY, HSQC, HMBC, and NOESY. The absolute configuration of an epimeric mixture of 1 and 2 was determined by X-ray crystallographic analysis. The compounds isolated were evaluated for their binding propensity in several CNS G-protein-coupled receptor assays in vitro.

Glucocorticoid acts on a putative G protein-coupled receptor to rapidly regulate the activity of NMDA receptors in hippocampal neurons

Glucocorticoids (GCs) have been demonstrated to act through both genomic and nongenomic mechanisms. The present study demonstrated that corticosterone rapidly suppressed the activity of N-methyl-D-aspartate (NMDA) receptors in cultured hippocampal neurons. The effect was maintained with corticosterone conjugated to bovine serum albumin and blocked by inhibition of G protein activity with intracellular GDP-β-S application. Corticosterone increased GTP-bound G(s) protein and cyclic AMP (cAMP) production, activated phospholipase Cβ(3) (PLC-β(3)), and induced inositol-1,4,5-triphosphate (IP(3)) production. Blocking PLC and the downstream cascades with PLC inhibitor, IP(3) receptor antagonist, Ca(2+) chelator, and protein kinase C (PKC) inhibitors prevented the actions of corticosterone. Blocking adenylate cyclase (AC) and protein kinase A (PKA) caused a decrease in NMDA-evoked currents. Application of corticosterone partly reversed the inhibition of NMDA currents caused by blockage of AC and PKA. Intracerebroventricular administration of corticosterone significantly suppressed long-term potentiation (LTP) in the CA1 region of the hippocampus within 30 min in vivo, implicating the possibly physiological significance of rapid effects of GC on NMDA receptors. Taken together, our results indicate that GCs act on a putative G protein-coupled receptor to activate multiple signaling pathways in hippocampal neurons, and the rapid suppression of NMDA activity by GCs is dependent on PLC and downstream signaling.

Anti-inflammatory effects of nicotinic acid in human monocytes are mediated by GPR109A dependent mechanisms

OBJECTIVE

Nicotinic acid (NA) treatment has been associated with benefits in atherosclerosis that are usually attributed to effects on plasma lipoproteins. The NA receptor GPR109A is expressed in monocytes and macrophages, suggesting a possible additional role for NA in modulating function of these immune cells. We hypothesize that NA has the potential to act directly on monocytes to alter mediators of inflammation that may contribute to its antiatherogenic effects in vivo.

METHODS AND RESULTS

In human monocytes activated by Toll-like receptor (TLR)-4 agonist lipopolysaccharide, NA reduced secretion of proinflammatory mediators: TNF-α (by 49.2±4.5%); interleukin-6 (by 56.2±2.8%), and monocyte chemoattractant protein-1 (by 43.2±3.1%) (P<0.01). In TLR2 agonist, heat-killed Listeria monocytogenes-activated human monocytes, NA reduced secretion of TNF-α (by 48.6±7.1%), interleukin-6 (by 60.9±1.6%), and monocyte chemoattractant protein-1 (by 59.3±5.3%) (P<0.01; n=7). Knockdown of GPR109A by siRNA resulted in a loss of this anti-inflammatory effect in THP-1 monocytes. However, inhibition of prostaglandin D2 receptor by MK0524 or COX2 by NS398 did not alter the anti-inflammatory effects of NA observed in activated human monocytes. Preincubation of THP-1 monocytes with NA 0.1 mmol/L reduced phosphorylated IKKβ by 42±2% (P<0.001) IKB-α by 54±14% (P<0.01). Accumulation of nuclear p65 NF-κB in response to lipopolysaccharide treatment was also profoundly inhibited, by 89±1.3% (n=4; P<0.01). NA potently inhibited monocyte adhesion to activated HUVEC, and VCAM, mediated by the integrin, very late antigen 4. Monocyte chemotaxis was also significantly reduced (by 45.7±1.2%; P<0.001).

CONCLUSION

NA displays a range of effects that are lipoprotein-independent and potentially antiatherogenic. These effects are mediated by GPR109A and are independent of prostaglandin pathways. They suggest a rationale for treatment with NA that is not dependent on levels of plasma cholesterol and possible applications beyond the treatment of dyslipidemia.

RAMPs as drug targets

The receptor activity-modifying protein (RAMP) family of membrane proteins regulates G protein-coupled receptor (GPCR) function in several ways. RAMPs can alter their pharmacology and signalling as well as the trafficking of these receptors to and from the cell surface. Accordingly, RAMPs may be exploited as drug targets, offering new opportunities for regulating the function of therapeutically relevant RAMP-interacting GPCRs. For example, several small molecule antagonists of RAMP1/ calcitonin receptor-like receptor complexes, which block the actions of the neuropeptide calcitonin gene-related peptide are in development for the treatment of migraine headache.

Upregulation of KCC2 activity by zinc-mediated neurotransmission via the mZnR/GPR39 receptor

Vesicular Zn(2+) regulates postsynaptic neuronal excitability upon its corelease with glutamate. We previously demonstrated that synaptic Zn(2+) acts via a distinct metabotropic zinc-sensing receptor (mZnR) in neurons to trigger Ca(2+) responses in the hippocampus. Here, we show that physiological activation of mZnR signaling induces enhanced K(+)/Cl(-) cotransporter 2 (KCC2) activity and surface expression. As KCC2 is the major Cl(-) outward transporter in neurons, Zn(2+) also triggers a pronounced hyperpolarizing shift in the GABA(A) reversal potential. Mossy fiber stimulation-dependent upregulation of KCC2 activity is eliminated in slices from Zn(2+) transporter 3-deficient animals, which lack synaptic Zn(2+). Importantly, activity-dependent ZnR signaling and subsequent enhancement of KCC2 activity are also absent in slices from mice lacking the G-protein-coupled receptor GPR39, identifying this protein as the functional neuronal mZnR. Our work elucidates a fundamentally important role for synaptically released Zn(2+) acting as a neurotransmitter signal via activation of a mZnR to increase Cl(-) transport, thereby enhancing inhibitory tone in postsynaptic cells.

Actions of Artemisia vulgaris extracts and isolated sesquiterpene lactones against receptors mediating contraction of guinea pig ileum and trachea

AIM OF THE STUDY

The present study evaluates the Philippine medicinal plant Artemisia vulgaris for antagonistic activity at selected biogenic amine receptors on smooth muscle of the airways and gastrointestinal tract in order to explain its traditional use in asthma and hyperactive gut.

MATERIALS AND METHODS

The antagonistic activity of chloroform crude extract (AV-CHCl(3)) and methanol crude extract (AV-MeOH) of Artemisia vulgaris was studied against concentration-response curves for contractions of the guinea pig ileum and trachea to 5-hydroxytrptamine (5-HT(2) receptors), methacholine (M(3) muscarinic receptors), histamine (H(1) receptors) and β-phenylethylamine (trace amine-associated receptors, TAAR1).

RESULTS AND DISCUSSION

The Artemisia vulgaris chloroform (AV-CHCl(3)) and methanol (AV-MeOH) extract showed histamine H1 antagonism in the ileum and trachea. Further analysis of AV-CHCl(3) isolated two major components, yomogin and 1,2,3,4-diepoxy-11(13)-eudesmen-12,8-olide. Yomogin, a sesquiterpene lactone, exhibited a novel histamine H1 receptor antagonism in the ileum.

CONCLUSION

The presence of a specific, competitive histamine receptor antagonist and smooth muscle relaxant activity in Artemisia vulgaris extracts on the smooth muscle in ileum and trachea explains its traditional use in the treatment of asthma and hyperactive gut.

Stereoselective synthesis of amides sharing the guanosine 5'-monophosphate scaffold and Umami enhancement studies using human sensory and hT1R1/rT1R3 receptor assays

Recent studies led to the identification of umami-enhancing (S)-N(2)-(1-carboxyethyl)- and (S)-N(2)-(1-alkylamino)carbonylalkyl)guanosine 5'-monophosphates that, together with their sensorially inactive (R)-stereoisomers, were found to be formed upon Maillard-type glycation of guanosine 5'-monophosphate (5'-GMP) with 1,3-dihydroxyacetone or glyceraldehyde, respectively. As the efficiency of this Maillard-type procedure to generate the amidated derivatives is limited by the low solubility and reactivity of long-chain alkyl amines as well as by the tedious separation of the diastereomers formed, a versatile synthesis for the (R)- and (S)-configured amides of N(2)-carboxyalkylated guanosine 5'-monophosphate was developed. Sensory evaluation of a series of N(2)-(1-alkylamino)carbonylalkyl)guanosine 5'-monophosphates revealed β-values for umami enhancement between 0.1 and 7.7 and identified a strong influence of the stereochemistry as well as the chain length of the N(2)-substituent on the umami-enhancing activity. The observed sensory impact of the (S)-configured isomers was confirmed by recording the enhancing effect of these nucleotides on the l-glutamate-induced response of the functionally expressed T1R1/T1R3 umami receptor in a cell-based assay, thus underscoring the stereospecifity of the umami taste receptor binding site.

Effects of ginger constituents on the gastrointestinal tract: role of cholinergic M3 and serotonergic 5-HT3 and 5-HT4 receptors

The herbal drug ginger (Zingiber officinale Roscoe) may be effective for treating nausea, vomiting, and gastric hypomotility. In these conditions, cholinergic M (3) receptors and serotonergic 5-HT (3) and 5-HT (4) receptors are involved. The major chemical constituents of ginger are [6]-gingerol, [8]-gingerol, [10]-gingerol, and [6]-shogaol. We studied the interaction of [6]-gingerol, [8]-gingerol, [10]-gingerol (racemates), and [6]-shogaol with guinea pig M (3) receptors, guinea pig 5-HT (3) receptors, and rat 5-HT (4) receptors. In whole segments of guinea pig ileum (bioassay for contractile M (3) receptors), [6]-gingerol, [8]-gingerol, [10]-gingerol, and [6]-shogaol slightly but significantly depressed the maximal carbachol response at an antagonist concentration of 10 µM. In the guinea pig myenteric plexus preparation (bioassay for contractile 5-HT (3) receptors), 5-HT maximal responses were depressed by [10]-gingerol from 93 ± 3 % to 65 ± 6 % at an antagonist concentration of 3 µM and to 48 ± 3 % at an antagonist concentration of 5 µM following desensitization of 5-HT (4) receptors and blockade of 5-HT (1) and 5-HT (2) receptors. [6]-Shogaol (3 µM) induced depression to 61 ± 3 %. In rat esophageal tunica muscularis mucosae (bioassay for relaxant 5-HT (4) receptors), [6]-gingerol, [8]-gingerol, [10]-gingerol, and [6]-shogaol (2-6.3 µM) showed no agonist effects. The maximal 5-HT response remained unaffected in the presence of the compounds. It is concluded that the efficiency of ginger in reducing nausea and vomiting may be based on a weak inhibitory effect of gingerols and shogaols at M (3) and 5-HT (3) receptors. 5-HT (4) receptors, which play a role in gastroduodenal motility, appear not to be involved in the action of these compounds.

Depletion of calcium stores contributes to progesterone-induced attenuation of calcium signaling of G protein-coupled receptors

Progesterone non-genomically attenuates the calcium signaling of the human oxytocin receptor and several other Galpha(q) protein-coupled receptors. High progesterone concentrations are found in the endometrium during pregnancy opposing the responsiveness of the underlying myometrium to labor-inducing hormones. Here, we demonstrate that within minutes, progesterone inhibits oxytocin- and bradykinin-induced contractions of rat uteri, calcium responses induced by platelet-activating factor in the human endometrial cell line MFE-280, and oxytocin-induced calcium signals in PHM1-31 immortalized pregnant human myometrial cells. Using human embryonic kidney (HEK293) cells as model system, we analyzed the molecular mechanisms underlying these effects. Our data indicate that progesterone rapidly depletes intracellular calcium stores. The resulting desensitization of the cells might contribute to the quiescence of the uterus during pregnancy.

Molecular pharmacology of G protein-coupled receptors. Editorial

G protein-coupled receptors are the largest group of membrane proteins and are the targets for approximately 30% of drugs currently used therapeutically. These 7-transmembrane-spanning proteins continue to provide new opportunities to develop therapeutics based on emerging knowledge of their structure, signalling properties and interactions with other proteins. This themed issue of the British Journal of Pharmacology contains a series of papers that cover these issues and identify approaches that may determine future directions. Many of these papers contain material that was presented at the 5th International Molecular Pharmacology of G Protein-Coupled Receptors meeting held in Sydney Australia in late 2008.

Role of antibodies in developing drugs that target G-protein-coupled receptor dimers

G-protein-coupled receptors are important molecular targets in drug discovery. These receptors play a pivotal role in physiological signaling pathways and are targeted by nearly 50% of currently available drugs. Mounting evidence suggests that G-protein-coupled receptors form dimers, and various studies have shown that dimerization is necessary for receptor maturation, signaling, and trafficking. However, the physiological implications of dimerization in vivo have not been well explored because detection of GPCR dimers in endogenous systems has been a challenging task. One exciting new approach to this challenge is the generation of antibodies against specific G-protein-coupled receptor dimers. Such antibodies could be used as tools for characterization of heteromer-specific function; as reagents for their purification, tissue localization, and regulation in vivo; and as probes for mapping their functional domains. In addition, such antibodies could serve as alternative ligands for G-protein-coupled receptor heteromers. Thus, heteromer-specific antibodies represent novel tools for the exploration and manipulation of G-protein-coupled receptor-dimer pharmacology.

A snake venom peptide with the contrary effects on rat stomach fundus and guinea pig ileum

A bradykinin potentiating peptide (BPP), Thr-Pro-Pro-Ala-Gly-Pro-Asp-Val-Gly-Pro-Arg-OH, was isolated from the venoms of Crotalus viridis viridis (here named Cvv peptide). Compared with other BPP, Cvv peptide has special Thr at N-terminal and Arg at C-terminal. In order to clarify whether these two special amino acids lead to special bioactivities relative to other BPPs, we made bioassays on isolated guinea pig ileum (GPI) and rat stomach fundus. Cvv peptide can observably inhibit bradykinin's contractivity on GPI, but potentiate the bradykinin-induced contractivity on rat stomach fundus. The discrepant bioactivity of Cvv peptide may occur via binding different receptors, B2 receptor on GPI and anaphylatoxin C3a receptor on rat stomach fundus, respectively.

A kisspeptin-10 analog with greater in vivo bioactivity than kisspeptin-10

The kisspeptins are neuropeptides that stimulate the hypothalamo-pituitary-gonadal (HPG) axis. The smallest endogenous kisspeptin, kisspeptin-10 (KP-10), binds to the receptor KISS1R with a similar affinity to the full-length peptide, kisspeptin-54 (KP-54), but is less effective in vivo, possibly because of increased enzymatic breakdown or clearance. The kisspeptin system may have therapeutic potential in the treatment of reproductive disorders and endocrine cancers. We have rationally modified the structure of KP-10 and tested the binding affinity of these analogs for the KISS1R. Those analogs that bound with relatively high affinity to KISS1R were tested for ability to stimulate ERK1/2 phosphorylation in vitro and for their ability to stimulate the HPG axis in vivo. One analog, [dY](1)KP-10, bound to KISS1R with lower affinity to KP-10 and exhibited similar bioactivity in vitro. However, in vivo peripheral administration of [dY](1)KP-10 increased plasma LH and testosterone more potently than KP-10 itself at 20 min postinjection in mice. In addition, 60 min postinjection, 0.15 nmol [dY](1)KP-10 significantly increased total testosterone levels in mice whereas the same dose of KP-10 had no significant effect. Should manipulation of the kisspeptin/KISS1R signaling system prove therapeutically useful, long-lasting analogs such as [dY](1)KP-10 may have greater therapeutic potential than endogenous forms of kisspeptin.

Receptor-based discovery strategies for insecticides and parasiticides: a review

Drug discovery is an iterative process with high risks and low chance of success. New genomics technologies allow veterinary medicine and agrochemical companies to validate and functionally screen new receptor-based targets, including neuropeptide G-protein coupled receptors, which were previously not amenable to high throughput screening. However this is just the first step in a long process to translate a mechanistic assay hit into a drug on the market. In addition to effectively eradicating pests on crops and parasites on their host, the molecules must also be safe, cheap to synthesise, formulatable and patentable. This is a costly process in which early attrition of unsuitable molecules is key to any successful program. Although first principle discovery is risky the ultimate benefits are considerable and future genomics resources will help to generate higher quality hits to strengthen the discovery pipeline.

Interactions of the sweet-tasting proteins thaumatin and lysozyme with the human sweet-taste receptor

This study investigated the sweetness of the sweet-tasting protein thaumatin and lysozyme by both an in vitro cell-based assay and an in vivo sensory analysis to elucidate the differences between in vitro and in vivo response profiles. Hek293 cells were constructed that stably expressed the human T1R2+T1R3 sweet-taste receptor, and their responses to thaumatin and lysozyme were analyzed by monitoring the levels of intracellular cAMP. The results indicated that thaumatin and lysozyme as well as aspartame induced a decrease in the intracellular cAMP accumulation of the T1R2+T1R3-transfected cells and that EC(50) values of thaumatin and lysozyme determined by cell-based assay are well-consistent with the results of the sweetness threshold value determined by sensory analysis in the presence of 140 mM NaCl. The results of both in vitro and in vivo experiments confirmed that the sweetness inhibitor lactisole significantly suppressed the sweetness of thaumatin and lysozyme.

Involvement of NMDA receptor in nociceptive effects elicited by intrathecal [Tyr6] gamma2-MSH(6-12), and the interaction with nociceptin/orphanin FQ in pain modulation in mice

The mas-related genes (Mrgs, also known as sensory neuron-specific receptors, SNSRs) are specifically expressed in small diameter sensory neurons in the trigeminal and dorsal root ganglia, suggesting an important role of the receptors in pain transmission. The present study aimed to investigate the underlying mechanism of the nociceptive effects after activation of MrgC, and the interaction between MrgC and N/OFQ-NOP receptor system in modulation of nociception in mice. Intrathecal (i.t.) administration of [Tyr(6)] gamma2-MSH(6-12), the most potent agonist for MrgC receptor, produced a significant hyperalgesic response as assayed by tail withdrawal test and a series of characteristic nociceptive responses, including biting, licking and scratching, in a dose-dependent manner (0.01-10 pmol and 0.01-10 nmol, respectively) in mice. These pronociceptive effects induced by [Tyr(6)] gamma2-MSH(6-12) were inhibited dose-dependently by co-injection of competitive NMDA receptor antagonist D-APV, non-competitive NMDA receptor antagonist MK-801, and nitric oxide (NO) synthase inhibitor L-NAME. However, the tachykinin NK(1) receptor antagonist L-703,606, and tachykinin NK(2) receptor antagonist MEN-10,376, had no influence on pronociceptive effects elicited by [Tyr(6)] gamma2-MSH(6-12). In other groups, [Tyr(6)] gamma2-MSH(6-12)-induced nociceptive responses were bidirectionally regulated by the co-injection of N/OFQ. N/OFQ inhibited nociceptive responses at high doses (0.01-1 nmol), but potentiated the behaviors at low doses (1 fmol-3 pmol). Furthermore, both hyperalgesia and nociceptive responses were enhanced after the co-administration with NOP receptor antagonist [Nphe(1)]N/OFQ(1-13)-NH(2). These results suggest that intrathecal [Tyr(6)] gamma2-MSH(6-12)-induced pronociceptive effects may be mediated through NMDA receptor-NO system in the spinal cord, and demonstrate the interaction between MrgC and N/OFQ-NOP receptor system in pain transmission.

pH-Dependent inhibition of the human bitter taste receptor hTAS2R16 by a variety of acidic substances

Some acidic peptides are known to reduce bitterness, but the detailed mechanism underlying this effect remains to be elucidated. In this study, we analyzed the effects of acidic dipeptides on the inhibition of the human bitter taste receptor hTAS2R16. Calcium imaging analysis of HEK293T cells expressing hTAS2R16 revealed that their response to the bitter tastant salicin was reduced in the presence of acidic dipeptides. A similar inhibitory effect was observed in a variety of other acids. The inhibition depended on the pH values resulting from the addition of acids but not on their concentrations. Our results suggest that the inhibition of the bitter taste receptors can be attributed to the bitterness-masking effect of the acidic dipeptides and that acidic pH may be one of the critical factors responsible for this sensory event.