[Gamma-35S]GTP autoradiography allows region-specific detection of muscarinic receptor-dependent G-protein activation in the chick optic tectum

The Plant Derived 3-3'-Diindolylmethane (DIM) Behaves as CB2 Receptor Agonist in Prostate Cancer Cellular Models

3-3'-Diindolylmethane (DIM) is a biologically active dimer derived from the endogenous conversion of indole-3-carbinol (I3C), a naturally occurring glucosinolate found in many cruciferous vegetables (i.e., Brassicaceae). DIM was the first pure androgen receptor antagonist isolated from the Brassicaceae family and has been recently investigated for its potential pharmacological use in prostate cancer prevention and treatment. Interestingly, there is evidence that DIM can also interact with cannabinoid receptors. In this context, by considering the well-known involvement of the endocannabinoid system in prostate cancer, we have pharmacologically characterized the properties of DIM on both CB₁ and CB₂ cannabinoid receptors in two human prostate cancer cell lines: PC3 (androgen-independent/androgen receptor negative) and LNCaP (androgen-dependent). In the PC3 cell line, DIM was able to activate CB₂ receptors and potentially associated apoptotic pathways. On the other hand, although DIM was also able to activate CB₂ receptors in the LNCaP cell line, no apoptotic effects were observed. Our evidence confirms that DIM is a CB₂ receptor ligand and, moreover, it has a potential anti-proliferative effect on androgen-independent/androgen receptor-negative prostate cancer cells.

Ultrasensitive Detection of COVID-19 Causative Virus (SARS-CoV-2) Spike Protein Using Laser Induced Graphene Field-Effect Transistor

COVID-19 is a highly contagious human infectious disease caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), and the war with the virus is still underway. Since no specific drugs have been made available yet and there is an imbalance between supply and demand for vaccines, early diagnosis and isolation are essential to control the outbreak. Current nucleic acid testing methods require high sample quality and laboratory conditions, which cannot meet flexible applications. Here, we report a laser-induced graphene field-effect transistor (LIG-FET) for detecting SARS-CoV-2. The FET was manufactured by different reduction degree LIG, with an oyster reef-like porous graphene channel to enrich the binding point between the virus protein and sensing area. After immobilizing specific antibodies in the channel, the FET can detect the SARS-CoV-2 spike protein in 15 min at a concentration of 1 pg/mL in phosphate-buffered saline (PBS) and 1 ng/mL in human serum. In addition, the sensor shows great specificity to the spike protein of SARS-CoV-2. Our sensors can realize fast production for COVID-19 rapid testing, as each LIG-FET can be fabricated by a laser platform in seconds. It is the first time that LIG has realized a virus sensing FET without any sample pretreatment or labeling, which paves the way for low-cost and rapid detection of COVID-19.

High-Resolution Confocal Fluorescence Imaging of Serine Hydrolase Activity in Cryosections - Application to Glioma Brain Unveils Activity Hotspots Originating from Tumor-Associated Neutrophils

Background

Serine hydrolases (SHs) are a functionally diverse family of enzymes playing pivotal roles in health and disease and have emerged as important therapeutic targets in many clinical conditions. Activity-based protein profiling (ABPP) using fluorophosphonate (FP) probes has been a powerful chemoproteomic approach in studies unveiling roles of SHs in various biological systems. ABPP utilizes cell/tissue proteomes and features the FP-warhead, linked to a fluorescent reporter for in-gel fluorescence imaging or a biotin tag for streptavidin enrichment and LC-MS/MS-based target identification. Existing ABPP approaches characterize global SH activity based on mobility in gel or MS-based target identification and cannot reveal the identity of the cell-type responsible for an individual SH activity originating from complex proteomes.

Results

Here, by using an activity probe with broad reactivity towards the SH family, we advance the ABPP methodology to glioma brain cryosections, enabling for the first time high-resolution confocal fluorescence imaging of global SH activity in the tumor microenvironment. Tumor-associated cell types were identified by extensive immunohistochemistry on activity probe-labeled sections. Tissue-ABPP indicated heightened SH activity in glioma vs. normal brain and unveiled activity hotspots originating from tumor-associated neutrophils (TANs), rather than tumor-associated macrophages (TAMs). Thorough optimization and validation was provided by parallel gel-based ABPP combined with LC-MS/MS-based target verification.

Conclusions

Our study advances the ABPP methodology to tissue sections, enabling high-resolution confocal fluorescence imaging of global SH activity in anatomically preserved complex native cellular environment. To achieve global portrait of SH activity throughout the section, a probe with broad reactivity towards the SH family members was employed. As ABPP requires no a priori knowledge of the identity of the target, we envisage no imaginable reason why the presently described approach would not work for sections regardless of species and tissue source.

Cannabinoid receptor-dependent and -independent anti-proliferative effects of omega-3 ethanolamides in androgen receptor-positive and -negative prostate cancer cell lines

The omega-3 fatty acid ethanolamides, docosahexaenoyl ethanolamide (DHEA) and eicosapentaenoyl ethanolamide (EPEA), displayed greater anti-proliferative potency than their parent omega-3 fatty acids, docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), in LNCaP and PC3 prostate cancer cells. DHEA and EPEA activated cannabinoid CB(1) and CB(2) receptors in vitro with significant potency, suggesting that they are endocannabinoids. Both LNCaP and PC3 cells expressed CB(1) and CB(2) receptors, and the CB(1)- and CB(2)-selective antagonists, AM281 and AM630, administered separately or together, reduced the anti-proliferative potencies of EPEA and EPA but not of DHEA or DHA in PC3 cells and of EPA but not of EPEA, DHEA or DHA in LNCaP cells. Even so, EPEA and EPA may not have inhibited PC3 or LNCaP cell proliferation via cannabinoid receptors since the anti-proliferative potency of EPEA was well below the potency it displayed as a CB(1) or CB(2) receptor agonist. Indeed, these receptors may mediate a protective effect because the anti-proliferative potency of DHEA in LNCaP and PC3 cells was increased by separate or combined administration of AM281 and AM630. The anandamide-metabolizing enzyme, fatty acid amide hydrolase (FAAH), was highly expressed in LNCaP but not PC3 cells. Evidence was obtained that FAAH metabolizes EPEA and DHEA and that the anti-proliferative potencies of these ethanolamides in LNCaP cells can be enhanced by inhibiting this enzyme. Our findings suggest that the expression of cannabinoid receptors and of FAAH in some tumour cells could well influence the effectiveness of DHA and EPA or their ethanolamide derivatives as anticancer agents.

3-Heterocycle-phenyl N-alkylcarbamates as FAAH inhibitors: design, synthesis and 3D-QSAR studies

Carbamates are a well-established class of fatty acid amide hydrolase (FAAH) inhibitors. Here we describe the synthesis of meta-substituted phenolic N-alkyl/aryl carbamates and their in vitro FAAH inhibitory activities. The most potent compound, 3-(oxazol-2yl)phenyl cyclohexylcarbamate (2 a), inhibited FAAH with a sub-nanomolar IC(50) value (IC(50)=0.74 nM). Additionally, we developed and validated three-dimensional quantitative structure-activity relationships (QSAR) models of FAAH inhibition combining the newly disclosed carbamates with our previously published inhibitors to give a total set of 99 compounds. Prior to 3D-QSAR modeling, the degree of correlation between FAAH inhibition and in silico reactivity was also established. Both 3D-QSAR methods used, CoMSIA and GRID/GOLPE, produced statistically significant models with coefficient of correlation for external prediction (R(2) (PRED)) values of 0.732 and 0.760, respectively. These models could be of high value in further FAAH inhibitor design.

Evidence that the plant cannabinoid cannabigerol is a highly potent alpha2-adrenoceptor agonist and moderately potent 5HT1A receptor antagonist

BACKGROUND AND PURPOSE

Cannabis is the source of at least seventy phytocannabinoids. The pharmacology of most of these has been little investigated, three notable exceptions being Delta(9)-tetrahydrocannabinol, cannabidiol and Delta(9)-tetrahydrocannabivarin. This investigation addressed the question of whether the little-studied phytocannabinoid, cannabigerol, can activate or block any G protein-coupled receptor.

EXPERIMENTAL APPROACH

The [(35)S]GTPgammaS binding assay, performed with mouse brain membranes, was used to test the ability of cannabigerol to produce G protein-coupled receptor activation or blockade. Its ability to displace [(3)H]CP55940 from mouse CB(1) and human CB(2) cannabinoid receptors and to inhibit electrically evoked contractions of the mouse isolated vas deferens was also investigated.

KEY RESULTS

In the brain membrane experiments, cannabigerol behaved as a potent alpha(2)-adrenoceptor agonist (EC(50)= 0.2 nM) and antagonized the 5-HT(1A) receptor agonist, R-(+)-8-hydroxy-2-(di-n-propylamino)tetralin (apparent K(B)= 51.9 nM). At 10 microM, it also behaved as a CB(1) receptor competitive antagonist. Additionally, cannabigerol inhibited evoked contractions of the vas deferens in a manner that appeared to be alpha(2)-adrenoceptor-mediated (EC(50)= 72.8 nM) and displayed significant affinity for mouse CB(1) and human CB(2) receptors.

CONCLUSIONS AND IMPLICATIONS

This investigation has provided the first evidence that cannabigerol can activate alpha(2)-adrenoceptors, bind to cannabinoid CB(1) and CB(2) receptors and block CB(1) and 5-HT(1A) receptors. It will now be important to investigate why cannabigerol produced signs of agonism more potently in the [(35)S]GTPgammaS binding assay than in the vas deferens and also whether it can inhibit noradrenaline uptake in this isolated tissue and in the brain.

Inverse agonist exposure enhances ligand binding and G protein activation of the human MT1 melatonin receptor, but leads to receptor down-regulation

Melatonin binds and activates G protein-coupled melatonin receptors. The density and affinity of the endogenous melatonin receptors change throughout the 24-hr day, and the exposure of recombinant melatonin receptors to melatonin often results in desensitization of the receptors. Receptor density, G protein activation and expression level were analyzed in CHO cell lines stably expressing the human MT1 receptors after 1 or 72 hr of exposure to melatonin (agonist, 10 nm) and luzindole (antagonist/inverse agonist, 10 microm). The 72-hr exposure to luzindole significantly increased the apparent receptor density in cell lines with both high and low MT1 receptor expression levels (MT1(high) and MT1(low) cells, respectively). In the constitutively active MT1(high) cells, luzindole pretreatment also stimulated the functional response to melatonin in [(35)S]GTPgammaS binding assays, whereas melatonin pretreatment attenuated the functional response at both time points. Receptor ELISA was used to analyze the cell membrane and total expression level of the MT1 receptor in intact and permeabilized cells, respectively. Luzindole pretreatment decreased the total cellular level of MT1 receptor in the MT1(high) cells at both time points but increased the cell surface expression of MT1 receptor at 72 hr. Melatonin significantly decreased MT1 receptor cell surface expression only in MT1(high) cells after a 1-hr treatment. These results indicate that melatonin treatment desensitizes MT1 receptors, whereas luzindole increases ligand binding and G-protein activation. Luzindole also stimulates downregulation of the MT1 receptor protein, interfering with the synthesis and/or degradation of the receptor.

Design, synthesis, and in vitro evaluation of carbamate derivatives of 2-benzoxazolyl- and 2-benzothiazolyl-(3-hydroxyphenyl)-methanones as novel fatty acid amide hydrolase inhibitors

Fatty acid amide hydrolase (FAAH) is an intracellular serine hydrolase, which catalyzes the hydrolysis of the endocannabinoid N-arachidonoylethanolamide to arachidonic acid and ethanolamine. FAAH also hydrolyzes another endocannabinoid, 2-arachidonoylglycerol (2-AG). However, 2-AG has been assumed to be hydrolyzed mainly by monoacylglycerol lipase (MAGL) or a MAGL-like enzyme. Inhibition of FAAH or MAGL activity might lead to beneficial effects in many physiological disorders such as pain, inflammation, and anxiety due to increased endocannabinoid-induced activation of cannabinoid receptors CB1 and CB2. In the present study, a total of 34 novel compounds were designed, synthesized, characterized, and tested against FAAH and MAGL-like enzyme activity. Altogether, 16 compounds were found to inhibit FAAH with half-maximal inhibition concentrations (IC50) between 28 and 380 nM. All the active compounds belong to the structural family of carbamates. Compounds 14 and 18 were found to be the most potent FAAH inhibitors, which may serve as lead structures for novel FAAH inhibitors.

The psychoactive plant cannabinoid, Delta9-tetrahydrocannabinol, is antagonized by Delta8- and Delta9-tetrahydrocannabivarin in mice in vivo

BACKGROUND AND PURPOSE

To follow up in vitro evidence that Delta(9)-tetrahydrocannabivarin extracted from cannabis (eDelta(9)-THCV) is a CB(1) receptor antagonist by establishing whether synthetic Delta(9)-tetrahydrocannabivarin (O-4394) and Delta(8)-tetrahydrocannabivarin (O-4395) behave as CB(1) antagonists in vivo.

EXPERIMENTAL APPROACH

O-4394 and O-4395 were compared with eDelta(9)-THCV as displacers of [(3)H]-CP55940 from specific CB(1) binding sites on mouse brain membranes and as antagonists of CP55940 in [(35)S]GTPgammaS binding assays performed with mouse brain membranes and of R-(+)-WIN55212 in mouse isolated vasa deferentia. Their ability to antagonize in vivo effects of 3 or 10 mg kg(-1) (i.v.) Delta(9)-tetrahydrocannabinol in mice was then investigated.

KEY RESULTS

O-4394 and O-4395 exhibited similar potencies to eDelta(9)-THCV as displacers of [(3)H]-CP55940 (K (i)=46.6 and 64.4 nM, respectively) and as antagonists of CP55940 in the [(35)S]GTPgammaS binding assay (apparent K (B)=82.1 and 125.9 nM, respectively) and R-(+)-WIN55212 in the vas deferens (apparent K (B)=4.8 and 3.9 nM respectively). At i.v. doses of 0.1, 0.3, 1.0 and/or 3 mg kg(-1) O-4394 and O-4395 attenuated Delta(9)-tetrahydrocannabinol-induced anti-nociception (tail-flick test) and hypothermia (rectal temperature). O-4395 but not O-4394 also antagonized Delta(9)-tetrahydrocannabinol-induced ring immobility. By themselves, O-4395 and O-4394 induced ring immobility at 3 or 10 mg kg(-1) (i.v.) and antinociception at doses above 10 mg kg(-1) (i.v.). O-4395 also induced hypothermia at 3 mg kg(-1) (i.v.) and above.

CONCLUSIONS AND IMPLICATIONS

O-4394 and O-4395 exhibit similar in vitro potencies to eDelta(9)-THCV as CB(1) receptor ligands and as antagonists of cannabinoid receptor agonists and can antagonize Delta(9)-tetrahydrocannabinol in vivo.

Fatty Acid Amide Hydrolase Inhibitors from Virtual Screening of the Endocannabinoid System

The endocannabinoid system consists of two cannabinoid receptors (CB1 and CB2), endogenous ligands (endocannabinoids), and the enzymes involved in the metabolism of the endocannabinoids, including fatty acid amide hydrolase (FAAH) and monoglyceride lipase (MGL). In the present study, virtual screening of MGL inhibitors was performed by utilizing a comparative model of the human MGL enzyme. All hit molecules were tested for their potential MGL inhibitory activity, but no compounds were found capable of inhibiting MGL-like enzymatic activity in rat cerebellar membranes. However, these compounds were also tested for their potential FAAH inhibitory activity and five compounds (2-6) inhibiting FAAH were found with IC50 values between 4 and 44 microM. In addition, the hit molecules from the virtual screening of CB2 receptor ligands (reported previously in Salo et al. J. Med. Chem. 2005, 48, 7166) were also tested in our FAAH assay, and four active compounds (7-10) were found with IC50 values between 0.52 and 22 microM. Additionally, compound 7 inhibited MGL-like enzymatic activity with an IC50 value of 31 microM.

The 'allosteric modulator' SCH-202676 disrupts G protein-coupled receptor function via sulphydryl-sensitive mechanisms

1. Previous studies suggest that the thiadiazole compound SCH-202676 (N-(2,3-diphenyl-1,2,4-thiadiazol-5-(2H)-ylidene)methanamine) acts as an allosteric modulator of a variety of structurally distinct G protein-coupled receptors (GPCRs). It was postulated that SCH-202676 would directly bind a structural motif in the receptor molecule common to divergent members of the GPCR family. The molecular mechanisms of such a promiscuous action, however, remain obscure. 2. To clarify the mechanism of SCH-202676 action, we used the functional approach of [35S]GTPgammaS autoradiography with rat brain cryostat sections together with classical membrane [35S]GTPgammaS binding assays to evaluate how the thiadiazole affects G protein activity mediated by various receptors linked to the Gi-family of G proteins. 3. We found that in the absence of dithiotreitol (DTT), SCH-202676 (10(-7)-10(-5) M) elicits nonspecific effects in the [35S]GTPgammaS-based G protein activation assays, thereby severely compromising interpretations on the compounds ability to allosterically inhibit receptor-mediated G protein activity. Such a nonspecific behaviour was fully reversed upon addition of DTT (1 mM), revealing thiol-based mechanism of action. 4. In routine incubations containing DTT, SCH-202676 had no effect on receptor-driven G protein activity, as assessed for adenosine A1, alpha2-adrenergic, cannabinoid CB1, lysophosphatidic acid LPA1, muscarinic M2/M4, purinergic P2Y12 or sphingosine 1-phosphate receptors, suggesting that the thiadiazole does not act as an allosteric modulator of GPCR function. 5. 1H NMR analysis indicated that SCH-202676 underwent structural changes after incubation with the reducing agent DTT or with brain tissue. 6. We conclude that SCH-202676 modulates GPCRs via thiol modification rather than via true allosteric mechanisms.

Evidence that the plant cannabinoid Delta9-tetrahydrocannabivarin is a cannabinoid CB1 and CB2 receptor antagonist

Delta9-tetrahydrocannabivarin (THCV) displaced [(3)H]CP55940 from specific binding sites on mouse brain and CHO-hCB(2) cell membranes (K(i)=75.4 and 62.8 nM, respectively).THCV (1 microM) also antagonized CP55940-induced stimulation of [(35)S]GTPgammaS binding to these membranes (apparent K(B)=93.1 and 10.1 nM, respectively). In the mouse vas deferens, the ability of Delta9-tetrahydrocannabinol (THC) to inhibit electrically evoked contractions was antagonized by THCV, its apparent K(B)-value (96.7 nM) approximating the apparent K(B)-values for its antagonism of CP55940- and R-(+)-WIN55212-induced stimulation of [(35)S]GTPgammaS binding to mouse brain membranes. THCV also antagonized R-(+)-WIN55212, anandamide, methanandamide and CP55940 in the vas deferens, but with lower apparent K(B)-values (1.5, 1.2, 4.6 and 10.3 nM, respectively).THCV (100 nM) did not oppose clonidine, capsaicin or (-)-7-hydroxy-cannabidiol-dimethylheptyl-induced inhibition of electrically evoked contractions of the vas deferens. Contractile responses of the vas deferens to phenylephrine hydrochloride or beta,gamma-methylene-ATP were not reduced by 1microM THCV or R-(+)-WIN55212, suggesting that THCV interacts with R-(+)-WIN55212 at prejunctional sites. At 32 microM, THCV did reduce contractile responses to phenylephrine hydrochloride and beta,gamma-methylene-ATP, and above 3 microM it inhibited electrically evoked contractions of the vas deferens in an SR141716A-independent manner. In conclusion, THCV behaves as a competitive CB(1) and CB(2) receptor antagonist. In the vas deferens, it antagonized several cannabinoids more potently than THC and was also more potent against CP55940 and R-(+)-WIN55212 in this tissue than in brain membranes. The bases of these agonist- and tissue-dependent effects remain to be established.

Characterization of the sulfhydryl-sensitive site in the enzyme responsible for hydrolysis of 2-arachidonoyl-glycerol in rat cerebellar membranes

We have previously reported that the endocannabinoid, 2-arachidonoyl-glycerol (2-AG), is hydrolyzed in rat cerebellar membranes by monoglyceride lipase (MGL)-like enzymatic activity. The present study shows that, like MGL, 2-AG-degrading enzymatic activity is sensitive to inhibition by sulfhydryl-specific reagents. Inhibition studies of this enzymatic activity by N-ethylmaleimide analogs revealed that analogs with bulky hydrophobic N-substitution were more potent inhibitors than hydrophilic or less bulky agents. Interestingly, the substrate analog N-arachidonylmaleimide was found to be the most potent inhibitor. A comparison model of MGL was constructed to get a view on the cysteine residues located near the binding site. These findings support our previous conclusion that the 2-AG-degrading enzymatic activity in rat cerebellar membranes corresponds to MGL or MGL-like enzyme and should facilitate further efforts to develop potent and more selective MGL inhibitors.

The functional role of cysteines adjacent to the NRY motif of the human MT1 melatonin receptor

All G protein-coupled melatonin receptors have two conserved cysteines in the interphase between transmembrane helix III and the second intracellular loop, in the region assumed important in receptor/G protein coupling. The cysteines are also potential targets of receptor S-nitrosylation. The effects of site-directed mutagenesis of these cysteines in the human MT1 melatonin receptor were investigated. The cysteines were mutated into serines either individually or as a pair and stable Chinese hamster ovary cell lines expressing the wild-type and mutant MT1 receptors were created. Receptor expression level, subcellular localization, ligand binding and G protein activation of the cell lines were analyzed. Serine substitution of C127 (Cys(3.52)) did not affect the ligand binding affinity and agonist potency but had an influence on receptor trafficking and G protein activation capacity. Serine substitution of C130 (Cys(3.55)) resulted in a decrease in the potency of melatonin to activate G proteins. When both cysteines were mutated into serines, normal MT1 receptor binding and activation were abolished. Computer modeling revealed that the mutations did not change the structure of the ligand binding pocket. Cysteine S-nitrosylation had no influence on G protein activation through MT1 receptors. Taken together, these data show that the two conserved cysteines in the end of transmembrane domain III of the MT1 melatonin receptor, especially C130 (Cys(3.55)), are needed for normal G protein activation and receptor trafficking.

S-nitrosothiols modulate G protein-coupled receptor signaling in a reversible and highly receptor-specific manner

Background

Recent studies indicate that the G protein-coupled receptor (GPCR) signaling machinery can serve as a direct target of reactive oxygen species, including nitric oxide (NO) and S-nitrosothiols (RSNOs). To gain a broader view into the way that receptor-dependent G protein activation – an early step in signal transduction – might be affected by RSNOs, we have studied several receptors coupling to the G_i family of G proteins in their native cellular environment using the powerful functional approach of [³⁵S]GTPγS autoradiography with brain cryostat sections in combination with classical G protein activation assays.

Results

We demonstrate that RSNOs, like S-nitrosoglutathione (GSNO) and S-nitrosocysteine (CysNO), can modulate GPCR signaling via reversible, thiol-sensitive mechanisms probably involving S-nitrosylation. RSNOs are capable of very targeted regulation, as they potentiate the signaling of some receptors (exemplified by the M2/M4 muscarinic cholinergic receptors), inhibit others (P2Y₁₂ purinergic, LPA₁lysophosphatidic acid, and cannabinoid CB₁ receptors), but may only marginally affect signaling of others, such as adenosine A₁, μ-opioid, and opiate related receptors. Amplification of M2/M4 muscarinic responses is explained by an accelerated rate of guanine nucleotide exchange, as well as an increased number of high-affinity [³⁵S]GTPγS binding sites available for the agonist-activated receptor. GSNO amplified human M4 receptor signaling also under heterologous expression in CHO cells, but the effect diminished with increasing constitutive receptor activity. RSNOs markedly inhibited P2Y₁₂ receptor signaling in native tissues (rat brain and human platelets), but failed to affect human P2Y₁₂ receptor signaling under heterologous expression in CHO cells, indicating that the native cellular signaling partners, rather than the P2Y₁₂ receptor protein, act as a molecular target for this action.

Conclusion

These in vitro studies show for the first time in a broader general context that RSNOs are capable of modulating GPCR signaling in a reversible and highly receptor-specific manner. Given that the enzymatic machinery responsible for endogenous NO production is located in close proximity with the GPCR signaling complex, especially with that for several receptors whose signaling is shown here to be modulated by exogenous RSNOs, our data suggest that GPCR signaling in vivo is likely to be subject to substantial, and highly receptor-specific modulation by NO-derived RSNOs.

Pontine and basal forebrain cholinergic interaction: implications for sleep and breathing

Pontine and forebrain cholinergic nuclei contribute to the regulation of breathing and arousal. This report summarizes experiments in rat (n = 20) concerning the cholinergic interaction between pons and basal forebrain. In vitro [(35)S]guanylyl-5'-O-(gamma-thio)-triphosphate ([(35)S]GTPgammaS) autoradiography quantified carbachol-stimulated guanine nucleotide binding (G) protein activation in seven basal forebrain nuclei. Carbachol significantly increased [(35)S]GTPgammaS binding in the vertical and horizontal limbs of the diagonal band of Broca, medial and lateral septum, and nucleus basalis (B)/substantia innominata (SI). In vitro receptor autoradiography demonstrated muscarinic receptors in the same nuclei where carbachol caused G protein activation. In vivo experiments showed that carbachol administered to the pontine reticular formation (PnO) significantly decreased the number of 7-14Hz spindles in the electroencephalogram (EEG), decreased acetylcholine release in SI, and decreased respiratory rate. Carbachol microinjection into SI did not alter the number of EEG spindles or respiratory rate. The results help clarify that EEG and rate of breathing are more effectively modulated by cholinergic neurotransmission in PnO than in SI.

Monoglyceride lipase-like enzymatic activity is responsible for hydrolysis of 2-arachidonoylglycerol in rat cerebellar membranes

2-Arachidonoylglycerol (2-AG) is an endogenous cannabinoid that binds to CB1 and CB2 cannabinoid receptors, inducing cannabimimetic effects. However, the cannabimimetic effects of 2-AG are weak in vivo due to its rapid enzymatic hydrolysis. The enzymatic hydrolysis of 2-AG has been proposed to mainly occur by monoglyceride lipase (monoacylglycerol lipase). Fatty acid amide hydrolase (FAAH), the enzyme responsible for the hydrolysis of N-arachidonoylethanolamide (AEA), is also able to hydrolyse 2-AG. In the present study, we investigated the hydrolysis of endocannabinoids in rat cerebellar membranes and observed that enzymatic activity towards 2-AG was 50-fold higher than that towards AEA. Furthermore, various inhibitors for 2-AG hydrolase activity were studied in rat cerebellar membranes. 2-AG hydrolysis was inhibited by methyl arachidonylfluorophosphonate, hexadecylsulphonyl fluoride and phenylmethylsulphonyl fluoride with ic(50) values of 2.2 nM, 241 nM and 155 microM, respectively. Potent FAAH inhibitors, such as OL-53 and URB597, did not inhibit the hydrolysis of 2-AG, suggesting that 2-AG is inactivated in rat cerebellar membranes by an enzyme distinct of FAAH. The observation that the hydrolysis of 1(3)-AG and 2-AG occurred at equal rates supports the role of MGL in 2-AG inactivation. This enzyme assay provides a useful method for future inhibition studies of 2-AG degrading enzyme(s) in brain membrane preparation having considerably higher MGL-like activity when compared to FAAH activity.

Hypocretin-1 causes G protein activation and increases ACh release in rat pons

The effects of the arousal-promoting peptide hypocretin on brain stem G protein activation and ACh release were examined using 16 adult Sprague-Dawley rats. In vitro[35S]GTPgammaS autoradiography was used to test the hypothesis that hypocretin-1-stimulated G protein activation is concentration-dependent and blocked by the hypocretin receptor antagonist SB-334867. Activated G proteins were quantified in dorsal raphe nucleus (DR), locus coeruleus (LC) and pontine reticular nucleus oral part (PnO) and caudal part (PnC). Concentration-response data revealed a significant (P < 0.001) effect of hypocretin-1 (2-2000 nm) in all brain regions examined. Maximal increases over control levels of [35S]GTPgammaS binding were 37% (DR), 58% (LC), 52% (PnO) and 44% (PnC). SB-334867 (2 micro m) significantly (P < 0.002) blocked hypocretin-1 (200 nm)-stimulated [35S]GTPgammaS binding in all four nuclei. This is the first autoradiographic demonstration that hypocretin-1 activates G proteins in arousal-related brain stem nuclei as a result of specific receptor interactions. This finding suggests that some hypocretin receptors in brain stem couple to inhibitory G proteins. In vivo microdialysis was used to test the hypothesis that PnO administration of hypocretin-1 increases ACh release in PnO. Dialysis delivery of hypocretin-1 (100 micro m) significantly (P < 0.002) increased (87%) ACh release. This finding is consistent with the interpretation that one mechanism by which hypocretin promotes arousal is by enhancing cholinergic neurotransmission in the pontine reticular formation.

Important amino acids for the function of the human MT1 melatonin receptor

Models of G protein-coupled melatonin receptor structure suggest that ligand recognition occurs in a binding pocket formed by transmembrane helices III, V and VII. Constitutively active mutations in G protein-coupled receptors have revealed that transmembrane helix III/intracellular loop 2 interface and transmembrane domain VI are critical regions in receptor activation. In this study, nine site-directed mutants of the human MT1 melatonin receptor were created to test the importance of specific amino acids in these regions in ligand recognition and receptor activation events. We analyzed ligand binding, G protein activation and subcellular localization of MT1 receptors transiently expressed in COS-7 cells. Receptor ELISA was employed to study expression levels of N-terminally HA epitope tagged wild-type and mutant MT1 receptors. Mutations in histidine H195 (His(5.46)) in transmembrane domain V reduced receptor affinity for 2-[125I]iodomelatonin. Several other mutants had diminished expression on the plasma membrane. Amino acids M107 (Met(3.32)) in transmembrane domain III and S280 (Ser(7.46)) in transmembrane domain VII were found not to participate in ligand recognition in human MT1 receptor. Constitutive activity was not obtained with mutations in N124 (Asn(3.49)) or P253 (Pro(6.50)). These mutants failed to bind 2-[125I]iodomelatonin and had reduced expression levels. The need to upgrade current melatonin receptor models has become evident. Several important amino acids for the human MT1 melatonin receptor function were revealed in the current study, with effects of mutations ranging from slightly reduced affinity or efficacy to complete loss of function.

Differential cholinergic activation of G proteins in rat and mouse brainstem: relevance for sleep and nociception

Murine models are increasingly used for investigations of sleep, yet no previous studies have characterized cholinergic activation of guanine nucleotide binding proteins (G proteins) in mouse brainstem nuclei known to regulate sleep. This study used in vitro [(35)S]guanylyl-5'-O-(gamma-thio)-triphosphate ([(35)S]GTPgammaS) autoradiography to test the hypothesis that muscarinic cholinergic receptors activate G proteins in C57BL/6J (B6) mouse brainstem. The nuclei studied are homologous to those known in rat and cat to modulate sleep and nociception. In B6 mouse, carbachol significantly increased specific binding of [(35)S]GTPgammaS in the pontine reticular nucleus, caudal part (79%); pontine reticular nucleus, oral part (131%); laterodorsal tegmental nucleus (56%); pedunculopontine tegmental nucleus (86%); dorsal raphe nucleus (53%); dorsal medial periaqueductal gray (54%); and ventrolateral periaqueductal gray (52%) when compared with basal binding. Carbachol-induced G protein activation was concentration-dependent and blocked by atropine, demonstrating mediation by muscarinic receptors. G protein activation by carbachol was heterogeneous across B6 mouse brainstem nuclei. Comparison of [(35)S]GTPgammaS binding between mouse and rat revealed different magnitudes of G protein activation in the pontine reticular formation. In the same pontine reticular formation area of B6 mouse where in vitro treatment with carbachol activates G proteins, in vivo microinjection of cholinomimetics causes a rapid eye movement sleep-like state. These data provide the first direct measurement of muscarinic receptor-activated G proteins in B6 mouse brainstem nuclei known in other species to regulate sleep.

Hypocretin-1 activates G proteins in arousal-related brainstem nuclei of rat

The hypocretin (hcrt) ligand-receptor system contributes to the maintenance of wakefulness. Hypocretin receptors are coupled to guanine nucleotide binding (G) proteins and the present study tested the hypothesis that hcrt-1 would activate G proteins in rat brainstem nuclei known to regulate arousal states. In vitro [35S]GTPgammaS autoradiography was performed using coronal brain stem sections from six rats. Hcrt-1 (200 nM) significantly increased [35S]GTPgammaS binding over basal levels in locus coeruleus (24%), dorsal raphe nucleus (12%), pontine reticular nucleus, oral part (28%), and pontine reticular nucleus, caudal part (40%). This is the first study to quantify and localize hcrt-1-induced G protein activation in specific brain stem nuclei. The finding that hcrt-1 stimulated [35S]GTPgammaS binding suggests that some hcrt receptors in pontine brain stem couple to inhibitory G proteins.

Despite substantial degradation, 2-arachidonoylglycerol is a potent full efficacy agonist mediating CB(1) receptor-dependent G-protein activation in rat cerebellar membranes

1. Two endocannabinoids, arachidonoyl ethanolamide (AEA) and 2-arachidonoylglycerol (2-AG) bind and activate G-protein-coupled cannabinoid receptors, but limited data exist on their relative ability to activate G-proteins. 2. Here we assess agonist potency and efficacy of various cannabinoids, including 2-AG, HU-310 (2-arachidonoyl glyceryl ether, a third putative endocannabinoid), HU-313 (another ether analogue of 2-AG), AEA, R-methanandamide (an enzymatically stable analogue of AEA), and CP-55,940 at rat brain CB(1) receptors using agonist-stimulated [(35)S]-GTPgammaS binding to cerebellar membranes and whole brain sections. Degradation of endocannabinoids under experimental conditions was monitored by HPLC. 3. To enhance efficacy differences, agonist dose-response curves were generated using increasing GDP concentrations. At 10(-6) M GDP, all compounds, except HU-313, produced full agonists responses approximately 2.5 fold over basal. The superior efficacy of 2-AG over all other compounds became evident by increasing GDP (10(-5) and 10(-4) M). 4. In membrane incubations, 2-AG was degraded by 85% whereas AEA and HU-310 were stable. Pretreatment of membranes with phenylmethylsulphonyl fluoride inhibited 2-AG degradation, resulting in 2 fold increase in agonist potency. Such pretreatment had no effect on AEA potency. 5. Responses in brain sections were otherwise consistent with membrane binding data, but 2-AG evoked only a weak signal in brain sections, apparently due to more extensive degradation. 6. These data establish that even under conditions of substantial degradation, 2-AG is a full efficacy agonist, clearly more potent than AEA, in mediating CB(1) receptor-dependent G-protein activity in native membranes.

[(35)S]GTPgammaS autoradiography reveals a wide distribution of G(i/o)-linked ADP receptors in the nervous system: close similarities with the platelet P2Y(ADP) receptor

No G(i)-linked P2Y receptors have been cloned to date but the presence of such receptors is thought to be restricted to platelets and certain clonal cell lines. Using the functional approach of [(35)S]guanosine 5'-[gamma-thio]-triphosphate autoradiography, we uncovered the widespread presence of such receptors in the CNS. Under conditions in which the prominent signal due to tonic adenosine receptor activity is masked, ADP and ATP stimulated G-protein activity in multiple grey and white matter regions. Localization in the grey matter suggests inhibitory auto-/heteroreceptor function. In the white matter, activated G proteins appeared as 'hot spots' (presumed oligodendrocyte progenitors) with scattered distribution along the main fibre tracts. Responses to ATP were diminished under conditions that inhibited degradation, suggesting that prior conversion to ADP explained agonist action. Uracil nucleotides were ineffective but 2-methylthio-ADP activated G proteins approximately 500-fold more potently than ADP, although both were similarly degraded. Throughout the brain, ADP-dependent G-protein activity was reversed by 2-hexylthio-AdoOC(O)Asp(2), a non-phosphate ATP analogue, whereas selective P2Y(1) receptor antagonists proved ineffective. A similar receptor was also disclosed from the adrenal medulla. These data witness a hitherto unrecognized abundance of G(i/o)-linked ADP receptors in the nervous system. Biochemical and pharmacological behaviour suggests striking similarities to the elusive platelet P2Y(ADP) receptor.

Autoradiographic characterisation of beta-adrenoceptors in chick brain using [3H]CGP 12177

An autoradiographic method for labelling beta(1)- and beta(2)-adrenoceptors using [3H]CGP 12177 as a radioligand is described as well as the procedure for an autoradiographic saturation kinetic study. The method afforded higher quality autoradiographs as well as an improvement in the tissue preservation when assayed in birds and chick embryos. The results confirmed the K(d) values previously reported for membrane homogenate binding. The use of different radioligands to characterise beta-adrenoceptors, the higher B(max) values found with autoradiography than those obtained by the membrane homogenate binding method and the typical errors in quantifying autoradiography are discussed. It is concluded that the method described here considerably improves autoradiographic beta-adrenergic characterisation.

Selective detection of adenosine A1 receptor-dependent G-protein activity in basal and stimulated conditions of rat brain [35S]guanosine 5'-(gamma-thio)triphosphate autoradiography

[35S]Guanosine 5'-(gamma-thio)triphosphate autoradiography is a novel technique to detect receptor-dependent activation of G-proteins in brain tissue sections. While an increasing number of reports using this approach are beginning to appear, little effort has been directed to the identification of factors responsible for the heterogeneously distributed [35S]guanosine 5'-(gamma-thio)triphosphate signal in basal conditions. The present study demonstrates that endogenously formed adenosine generates a widespread and prominent adenosine A1 receptor-dependent signal in basal conditions using this technique. Treatment of rat brain tissue sections with the A1-selective antagonist 8-cyclopentyl-1,3-dipropylxanthine dose-dependently (EC50 < 10 nM) suppressed basal [35S]guanosine 5'-(gamma-thio)triphosphate binding in a region-specific manner, an effect fully mimicked by the adenosine-depleting enzyme adenosine deaminase, and less so by the A1 antagonist cirsimarin and by caffeine. That adenosine was continuously formed during the incubation is supported by the constant requirements of adenosine deaminase in order to suppress basal radioligand binding and further by the fact that low micromolar concentrations of adenine nucleotides evoked only adenosine-mimicking and fully 8-cyclopentyl-1,3-dipropylxanthine-sensitive binding responses. In the presence of adenosine deaminase, all responses to adenine nucleotides were abolished, indicating that prior conversion to adenosine was required. Upon stimulation, this technique selectively detected A1 receptor-activated G-proteins, as the non-selective agonists adenosine and 2-chloroadenosine and the A1-selective agonist N6-p-sulfophenyladenosine all evoked only 8-cyclopentyl-1,3-dipropylxanthine-sensitive responses in identical gray matter areas, and also in several white matter areas such as the corpus callosum, anterior commissure, optic tract and cerebellar white matter. Dose-response studies revealed region-specific differences in the magnitude of A1 receptor-stimulated G-protein activation, with the highest response (nine-fold over basal) detectable in the hippocampus. No response to the A2A-selective agonist 2-[(2-aminoethylamino)carbonylethylphenylethylamino]-5'-N-et hylcarboxamidoadenosine or the A3-selective agonist 2-chloro-N6-(3-iodobenzyl)-adenosine-5'-N-methyluronamide was detected in any region. These data reveal that a significant amount of noise inherent to [35S]guanosine 5'-(gamma-thio)triphosphate autoradiography can be eliminated by removal of the adenosine signal, a step likely facilitating detection of responses to other receptors. Furthermore, the data establish [35S]guanosine 5-(gamma-thio)triphosphate autoradiography as a novel and selective approach to directly assess A1 receptor-G-protein coupling in anatomically defined regions of the central nervous system.

Dopamine receptor coupling to adenylyl cyclase in rat olfactory pathway: a combined pharmacological-radioautographic approach

Dopamine binding sites of D1 and D2/D3 subtypes had been detected in the rat peripheral olfactory system and postulated to account for dopamine-dependent enhancement of olfactory memory and retro-inhibition of olfactory input within the olfactory bulb, respectively. We further assessed, in the present study, the mechanisms of these dopamine actions by using adenylyl cyclase activity assay and [35S]GTP radioautography in rat olfactory bulb and mucosa. The D1 agonist SKF 38393 increased adenylyl cyclase activity on membranes of the olfactory bulb, but not on those of the olfactory mucosa. Stimulation of adenylyl cyclase by SKF 38393 in the olfactory bulb was dose dependent, with a half-maximal effect (EC50) at 0.16 microM SKF 38393, reaching 40% over basal adenylyl cyclase activity, and was blocked by the D1 antagonist SCH 23390. The D2 agonists bromocriptine and quinpirole inhibited both basal and forskolin-stimulated adenylyl cyclase activities in the olfactory bulb and mucosa. These adenylyl cyclase inhibitions were dose dependent, with EC50 values of 0.1-0.3 microM for bromocriptine and 1-3 microM for quinpirole, equal to 25% of basal enzyme activity at concentrations of 1-10 microM, and were blocked by the D2 antagonist eticlopride. The D2 antagonist was devoid of any effect on basal and forskolin-stimulated adenylyl cyclase activities in the olfactory bulb and mucosa. Odorant-induced stimulation of adenylyl cyclase was blocked by D2 agonist in olfactory mucosa membranes, which suggests dopaminergic regulation of odor detection in the olfactory mucosa. By using microdissected fractions of the olfactory mucosa, D2 agonist-induced inhibition of adenylyl cyclase was shown to occur only in lamina propria, thus co-localizing with D2 binding sites. [35S]GTP radioautography on tissue sections revealed D2 agonist-induced G-protein activation in olfactory nerve and glomerular layers of the olfactory bulb, and in the chorion of the olfactory mucosa. Taken together, these data demonstrate functional coupling of the dopamine receptors with adenylyl cyclase in both the olfactory bulb and mucosa, and document novel aspects of dopamine's physiological involvement in olfaction and of D2-mediated signal transduction.