Pharmacological targeting of G protein-coupled receptor heteromers.

A main rationale for the role of G protein-coupled receptor (GPCR) heteromers as targets for drug development is the putative ability of selective ligands for specific GPCRs to change their pharmacological properties upon GPCR heteromerization. The present study provides a proof of concept for this rationale by demonstrating that heteromerization of dopamine D1 and D3 receptors (D1R and D3R) influences the pharmacological properties of three structurally similar selective dopamine D3R ligands, the phenylpiperazine derivatives PG01042, PG01037 and VK4-116. By using D1R-D3R heteromer-disrupting peptides, it could be demonstrated that the three D3R ligands display different D1R-D3R heteromer-dependent pharmacological properties: PG01042, acting as G protein-biased agonist, counteracted D1R-mediated signaling in the D1R-D3R heteromer; PG01037, acting as a D3R antagonist cross-antagonized D1R-mediated signaling in the D1R-D3R heteromer; and VK4-116 specifically acted as a ß-arrestin-biased agonist in the D1R-D3R heteromer. Molecular dynamics simulations predicted potential molecular mechanisms mediating these qualitatively different pharmacological properties of the selective D3R ligands that are dependent on D1R-D3R heteromerization. The results of in vitro experiments were paralleled by qualitatively different pharmacological properties of the D3R ligands in vivo. The results supported the involvement of D1R-D3R heteromers in the locomotor activation by D1R agonists in reserpinized mice and L-DOPA-induced dyskinesia in rats, highlighting the D1R-D3R heteromer as a main pharmacological target for L-DOPA-induced dyskinesia in Parkinson's disease. More generally, the present study implies that when suspecting its pathogenetic role, a GPCR heteromer, and not its individual GPCR units, should be considered as main target for drug development.

Cardiovascular outcomes, heart failure and mortality in type 2 diabetic patients treated with glucagon-like peptide 1 receptor agonists (GLP-1 RAs): A systematic review and meta-analysis of observational cohort studies.

BACKGROUND: Cardiovascular outcomes trials (CVOTs) have assessed the effects of glucagon-like peptide-1 receptor agonists (GLP-1 RAs) on major adverse cardiovascular events (MACE) and mortality in high cardiovascular (CV) risk populations. Observational research can provide complementary evidence about these effects in unselected populations. AIM: To systematically review retrospective observational cohort studies conducted in electronic healthcare databases (EHDs) assessing GLP-1 RAs´ effects on MACE and/or hospitalisation for heart failure (HHF) and/or all-cause mortality in Type 2 diabetes mellitus (T2DM) patients. METHODS: We systematically searched studies meeting inclusion criteria, compared design, methods and population characteristics, assessed risk for bias and did a meta-analysis (MA) using a random-effects model to calculate overall hazard ratios (HRs) and 95% CI (confidence intervals). RESULTS: Sixteen studies included 285,436 T2DM patients exposed to GLP-1 RAs (exenatide bid, liraglutide, lixisenatide, long-acting exenatide), n ranged from 219 to 160,803 patients. Comparators included: no exposure, other antidiabetic medications (OADs), combined OADs, canagliflozin or multiple comparators. Ten studies estimated all-cause mortality, hazard ratios (HRs) ranged from 0.17 (95% CI 0.02-1.22) to 1.29 (95% CI 0.54-3.13). Thirteen studies assessed cardiovascular events and/or MACE; HRs ranged from 0.27 (95% CI 0.14-0.53) to 1.11 (95% CI 0.99-1.24). Eight studies assessed HHF, HRs ranged from 0.12 (95% CI 0.02-0.66) to 1.64 (95% CI 1.28-2.13). Excluding two studies because of temporal bias, we obtained pooled estimates for all-cause mortality: HR 0.63 (0.44-0.89), CV outcomes HR 0.84 (0.75-0.94) and HHF; HR 0.94 (0.78-1.14), (high between-study variability: I2  = 83.35%; I2  = 70.3%; and I2  = 90.1%, respectively). CONCLUSION: Pooled results of EHDs' studies assessing GLP-1 RAs effects favoured GLP-1 RAs for all-cause mortality and MACE while were neutral for HHF. Results should be interpreted cautiously because of studies' substantial heterogeneity and limitations of observational research.

Targeting hypersensitive corticostriatal terminals in restless legs syndrome.

OBJECTIVE: The first aim was to demonstrate a previously hypothesized increased sensitivity of corticostriatal glutamatergic terminals in the rodent with brain iron deficiency (BID), a pathogenetic model of restless legs syndrome (RLS). The second aim was to determine whether these putative hypersensitive terminals could constitute a significant target for drugs effective in RLS, including dopamine agonists (pramipexole and ropinirole) and α2 δ ligands (gabapentin). METHODS: A recently introduced in vivo optogenetic-microdialysis approach was used, which allows the measurement of the extracellular concentration of glutamate upon local light-induced stimulation of corticostriatal glutamatergic terminals. The method also allows analysis of the effect of local perfusion of compounds within the same area being sampled for glutamate. RESULTS: BID rats showed hypersensitivity of corticostriatal glutamatergic terminals (lower frequency of optogenetic stimulation to induce glutamate release). Both hypersensitive and control glutamatergic terminals were significant targets for locally perfused pramipexole, ropinirole, and gabapentin, which significantly counteracted optogenetically induced glutamate release. The use of selective antagonists demonstrated the involvement of dopamine D4 and D2 receptor subtypes in the effects of pramipexole. INTERPRETATION: Hypersensitivity of corticostriatal glutamatergic terminals can constitute a main pathogenetic mechanism of RLS symptoms. Selective D4 receptor agonists, by specifically targeting these terminals, should provide a new efficient treatment with fewer secondary effects. Ann Neurol 2017;82:951-960.

G protein-coupled receptor oligomerization revisited: functional and pharmacological perspectives.

Most evidence indicates that, as for family C G protein-coupled receptors (GPCRs), family A GPCRs form homo- and heteromers. Homodimers seem to be a predominant species, with potential dynamic formation of higher-order oligomers, particularly tetramers. Although monomeric GPCRs can activate G proteins, the pentameric structure constituted by one GPCR homodimer and one heterotrimeric G protein may provide a main functional unit, and oligomeric entities can be viewed as multiples of dimers. It still needs to be resolved if GPCR heteromers are preferentially heterodimers or if they are mostly constituted by heteromers of homodimers. Allosteric mechanisms determine a multiplicity of possible unique pharmacological properties of GPCR homomers and heteromers. Some general mechanisms seem to apply, particularly at the level of ligand-binding properties. In the frame of the dimer-cooperativity model, the two-state dimer model provides the most practical method to analyze ligand-GPCR interactions when considering receptor homomers. In addition to ligand-binding properties, unique properties for each GPCR oligomer emerge in relation to different intrinsic efficacy of ligands for different signaling pathways (functional selectivity). This gives a rationale for the use of GPCR oligomers, and particularly heteromers, as novel targets for drug development. Herein, we review the functional and pharmacological properties of GPCR oligomers and provide some guidelines for the application of discrete direct screening and high-throughput screening approaches to the discovery of receptor-heteromer selective compounds.

Equilibrative nucleoside transporter ENT1 as a biomarker of Huntington disease.

The initial goal of this study was to investigate alterations in adenosine A2A receptor (A2AR) density or function in a rat model of Huntington disease (HD) with reported insensitivity to an A2AR antagonist. Unsuspected negative results led to the hypothesis of a low striatal adenosine tone and to the search for the mechanisms involved. Extracellular striatal concentrations of adenosine were measured with in vivo microdialysis in two rodent models of early neuropathological stages of HD disease, the Tg51 rat and the zQ175 knock-in mouse. In view of the crucial role of the equilibrative nucleoside transporter (ENT1) in determining extracellular content of adenosine, the binding properties of the ENT1 inhibitor [3H]-S-(4-Nitrobenzyl)-6-thioinosine were evaluated in zQ175 mice and the differential expression and differential coexpression patterns of the ENT1 gene (SLC29A1) were analyzed in a large human cohort of HD disease and controls. Extracellular striatal levels of adenosine were significantly lower in both animal models as compared with control littermates and striatal ENT1 binding sites were significantly upregulated in zQ175 mice. ENT1 transcript was significantly upregulated in HD disease patients at an early neuropathological severity stage, but not those with a higher severity stage, relative to non-demented controls. ENT1 transcript was differentially coexpressed (gained correlations) with several other genes in HD disease subjects compared to the control group. The present study demonstrates that ENT1 and adenosine constitute biomarkers of the initial stages of neurodegeneration in HD disease and also predicts that ENT1 could constitute a new therapeutic target to delay the progression of the disease.

Functional selectivity of allosteric interactions within G protein-coupled receptor oligomers: the dopamine D1-D3 receptor heterotetramer.

The dopamine D1 receptor-D3 receptor (D1R-D3R) heteromer is being considered as a potential therapeutic target for neuropsychiatric disorders. Previous studies suggested that this heteromer could be involved in the ability of D3R agonists to potentiate locomotor activation induced by D1R agonists. It has also been postulated that its overexpression plays a role in L-dopa-induced dyskinesia and in drug addiction. However, little is known about its biochemical properties. By combining bioluminescence resonance energy transfer, bimolecular complementation techniques, and cell-signaling experiments in transfected cells, evidence was obtained for a tetrameric stoichiometry of the D1R-D3R heteromer, constituted by two interacting D1R and D3R homodimers coupled to Gs and Gi proteins, respectively. Coactivation of both receptors led to the canonical negative interaction at the level of adenylyl cyclase signaling, to a strong recruitment of ß-arrestin-1, and to a positive cross talk of D1R and D3R agonists at the level of mitogen-activated protein kinase (MAPK) signaling. Furthermore, D1R or D3R antagonists counteracted ß-arrestin-1 recruitment and MAPK activation induced by D3R and D1R agonists, respectively (cross-antagonism). Positive cross talk and cross-antagonism at the MAPK level were counteracted by specific synthetic peptides with amino acid sequences corresponding to D1R transmembrane (TM) domains TM5 and TM6, which also selectively modified the quaternary structure of the D1R-D3R heteromer, as demonstrated by complementation of hemiproteins of yellow fluorescence protein fused to D1R and D3R. These results demonstrate functional selectivity of allosteric modulations within the D1R-D3R heteromer, which can be involved with the reported behavioral synergism of D1R and D3R agonists.

Falls in hospitalized older adults and the use of fall risk-increasing drugs and anticholinergic medications in Colombia: a case‒control study.

Introduction: In-hospital falls are multicausal in older hospitalized patients. Drugs with anticholinergic load and psychotropic effects can increase the risk of falling. Objective: This study aimed to determine the associations between fall risk-increasing drugs (FRIDs) and the anticholinergic risk score (ARS) with falls in hospitalized older hospitalized patients. Methods: This was a case‒control study of patients ≥65 years of age of either sex treated in four clinics in Colombia between 2018 and 2020. Each patient who suffered a fall during hospitalization was matched with four hospitalized patients who did not. Sociodemographic, clinical, and pharmacologic variables and the use of the ARS and FRIDs were evaluated. The risk associated with FRIDs was estimated using conditional logistic regression. Results: There were 250 patients and 1,000 controls (ratio of 1:4), with a mean age of 77.4 ± 7.4 years and a predominance of men (n = 800, 64.0%). The majority of falls occurred during hospitalization (n = 192 patients, 76.8%). Polypharmacy, calcium channel blockers, antiepileptics, antipsychotics, sodium-glucose cotransporter type 2 inhibitors, and nonsteroidal anti-inflammatory drugs were associated with falls during hospitalization. With an ARS score of 3, the probability of falling during the hospital stay increased (aOR: 2.34; 95% CI: 1.64-3.32). Conclusion: There is an association between suffering a fall and the use of drugs with anticholinergic load or FRIDs in hospitalized adults more than 65 years of age in Colombia.

Challenging dogmas: Intravenous versus oral beta-lactam antibiotic provocation tests.

Background: Drug provocation tests (DPT) are considered the gold standard procedure to ascertain the diagnosis of beta-lactam (BL) allergy. Regarding route of administration, current recommendations prioritize oral challenges, considering them safer, and reserving the intravenous route for drugs for which this is the only formulation. Objective: To compare in terms of tolerance and safety two protocols of BL DPT, using an oral protocol (OR-DPT) and an intravenous protocol (IV-DPT). Methods: A descriptive, retrospective study was performed, including adult patients who underwent IV-DPT or OR-DPT for suspected immediate or delayed hypersensitivity to BL antibiotics, over a period of 4 years (between January 2018 and December 2021). Demographical data, index hypersensivity reactions' characteristics and tolerance to DPT were reviewed. Results: A total of 1036 patients underwent DPT, mean age of 56.8 (standard deviation, SD, 17.8) years, 655 were women (63.2%). Immediate drug hypersensitivity reactions (DHR) had occurred in 564 of patients (54.4%). OR-DPT were performed in 439 (42.4%) and IV-DPT in 597 (57.6%). The frequency of reactions during DPT, regardless of the route used, was low (3.6%): only 16 (3.6%) in OR-DPT and 21 (3.5%) in IV-DPT. From IV-DPT, 16 out 21 DHR during DPT were immediate compared with 4 out of 16 in OR-DPT. Adjusted relative risk of developing a hypersensitivity reaction during IV-DPT versus OR-DPT was 1.13 (95% confidence interval (CI)0.57-2.22). Conclusion: The results suggest that OR-DPT and IV-DPT are both safe procedures when adequately performed. However, IV-DPT protocols showed a higher rate of immediate DHR during DPT probably due to the selection of basal high-risk patients to undergo IV-DPT. In conclusion, IV-DPT may be considered as an option for challenges in drug-allergy studies, entailing a precise administration.

Predictive validity of the functional capacity of the CUPAX questionnaire in older adults with hip fracture. / Validez predictiva de la capacidad funcional del cuestionario CUPAX en pacientes ancianos afectos de fractura de cadera.

BACKGROUND AND OBJECTIVES: Osteoporotic hip fracture is a relevant pathology due to its prevalence and social and health impact. The aim of this study is to explore the predictive validity of the CUPAX questionnaire on mortality, place of residence and post-fracture functionality. MATERIALS AND METHODS: Prospective observational study. Two hundred and six patients older than 65 years were included, admitted after a hip fracture. The CUPAX questionnaire score was collected before fracture and one year later, and the place of residence and survival at hospital discharge, and after 6 and 12 months. The statistical analysis was carried out with the SAS® 9.4 and Stata® 13.1 programmes. RESULTS: The median age of the sample was 87.0 years (80.1% women). The in-hospital and one-year mortality rate were 5.8% and 19.1%, respectively. Most of the patients were admitted from home (71.4%), and the most frequent discharge destination was a social health centre (48.2%). The percentage of retention of previous functional level in the total sample was 50%, being higher in the younger patients. The area under the curve ROC for mortality one year later was .697 (95% CI .626-.760) and .659 (95% CI .576-.741) for the discharge destination of patients admitted from home. Evaluation of functional retention one year after the fracture, identified three groups of patients based on the pre-fracture CUPAX value. CONCLUSIONS: These findings support the clinical utility of the CUPAX questionnaire as a predictive functional tool in elderly patients with hip fracture.

Incidence and characteristics of adverse drug reactions in a cohort of patients treated with PD-1/PD-L1 inhibitors in real-world practice.

Background: Data related to adverse drug reactions (ADRs), specifically immune-related adverse events (irAEs), in long-term treatment with immunotherapy in real-world practice is scarce, as is general information regarding the management of ADRs. Objectives: To characterize and describe the incidence of ADRs in patients who began immunotherapy treatment in clinical practice. Methods: In a prospective observational study cancer patients ≥18 years of age who were treated with a monotherapy regime of PD-1/PD-L1 inhibitors were evaluated. The study period was from November 2017 to June 2019 and patients were followed up until June 2021. Patients were contacted monthly by telephone and their electronic health records were reviewed. Each ADR was graded according to the Common Terminology Criteria for Adverse Events (CTCAE 5.0). Results: Out of 99 patients, 86 met the inclusion criteria. Most were male (67.4%), with a median age of 66 (interquartile range, IQR: 59-76). The most frequent cancer was non-small cellular lung cancer (46 cases, 53.5%), followed by melanoma (22, 25.6%). A total of 74 patients (86%) were treated with anti-PD-1 drugs and 12 (14%) were treated with anti-PD-L1 drugs. The median treatment durations were 4.9 (IQR: 1.9-17.0) and 5.9 months (IQR: 1.2-12.3), respectively. Sixty-three patients (73%) developed from a total of 156 (44% of the total number of ADR) irADRs, wherein the most frequent were skin disorders (50 cases, 32%, incidence = 30.5 irADRs/100 patients per year [p-y]), gastrointestinal disorders (29, 19%, 17.7 irADRs/100 p-y), musculoskeletal disorders (17, 11%, 10.4 irADRs/100 p-y), and endocrine disorders (14, 9%, 8.6 irADRs/100 p-y). A total of 22 irADRs (14%) had a latency period of ≥12 months. Twelve irADRs (7.7%) were categorized as grade 3-4, and while 2 (1.3%) were categorized as grade 5 (death). Sixty-one irADRs (39.1%) in 36 patients required pharmacological treatment and 47 irADRs (30.1%) in 22 patients required treatment with corticosteriods. Conclusion: The majority of patients treated with anti-PD1/PDL1-based immunotherapy experienced adverse reactions. Although most of these reactions were mild, 11.5% were categorized as grade 3 or above. A high percentage of the reactions were immune-related and occurred throughout the treatment, thereby indicating that early identification and close monitoring is essential.

Cardiovascular events and mortality among type 2 diabetes mellitus patients newly prescribed first-line blood glucose-lowering drugs monotherapies: A population-based cohort study in the Catalan electronic medical record database, SIDIAP, 2010-2015.

AIM: To assess cardiovascular (CV) events and all-cause mortality in type 2 diabetes mellitus (T2DM) patients treated with first-line monotherapies of non-insulin antidiabetic drugs (NIADs). METHODS: Longitudinal retrospective cohort study in the Catalan database SIDIAP (Information System for the Development of Research in Primary Care). T2DM patients ≥18 years newly prescribed first-line monotherapies during 2010-2015 were followed since their first prescription until the composite of major adverse CV events, MACE (myocardium infarction [MI], stroke and all-cause death), its components, heart failure (HF) and peripheral artery disease (PAD) or censoring. Cox proportional hazard models were used to estimate hazard ratios 95% confidence interval (HR [95%CI]). RESULTS: Compared with metformin, the use of sulfonylureas, dipeptidyl peptidase-4 inhibitors (DPP-4 i) and meglitinides were significantly associated with higher risk for MACE (1.55 [1.42-1.68]); 1.49 [1.22-1.84] and 2.01 [1.29-3.12]) and all-cause mortality (1.67 [1.52-1.84], 1.65 [1.30-2.] and 2.08 [1.26-3.42]). Sulfonylureas users had increased risk of MI (1.38 [1.03-1.85]) stroke (1.31 [1.11-1.54]), HF (1.49 [1.28-1.72]) and PAD (1.24 [1.02-1.51]). Meglitinides users were at increased risks of MI, HR 2.03 (1.10-3.74). CONCLUSION: In first-line monotherapies, compared with metformin, sulfonylureas were associated with increased risks in all the outcomes; DPP-4 i and repaglinide showed increased risks of MACE and mortality. Residual confounding cannot be ruled out.

Akathisia and Restless Legs Syndrome: Solving the Dopaminergic Paradox.

Akathisia is an urgent need to move that is associated with treatment with dopamine receptor blocking agents (DRBAs) and with restless legs syndrome (RLS). The pathogenetic mechanism of akathisia has not been resolved. This article proposes that it involves an increased presynaptic dopaminergic transmission in the ventral striatum and concomitant strong activation of postsynaptic dopamine D1 receptors, which form complexes (heteromers) with dopamine D3 and adenosine A1 receptors. It also proposes that in DRBA-induced akathisia, increased dopamine release depends on inactivation of autoreceptors, whereas in RLS it depends on a brain iron deficiency-induced down-regulation of striatal presynaptic A1 receptors.

The CUPAX questionnaire: Development and validation of a new scale for assessment of the functional level of elderly patients with a hip fracture. / Cuestionario CUPAX: desarrollo y validación de una nueva escala para la valoración del nivel funcional de pacientes mayores de 65 años con fractura de cadera.

BACKGROUND AND AIM: Hip fractures in elderly patients are very frequent and are associated with high morbidity and mortality. We do not have validated instruments in Spanish that can faithfully assess functional capacity prior to fracture. The aim of this study was to develop and validate the CUPAX questionnaire in elderly patients with a hip fracture. MATERIALS AND METHODS: Prospective and observational validation study. We included 215 patients older than 65 years, who were admitted to our centre after suffering a hip fracture. They were evaluated using the CUPAX questionnaire, Barthel Index and Parker Score. The statistical study was performed to corroborate the validity and reliability of the questionnaire. RESULTS: The median age of the patient population was 84.0 years (75.3% women). The majority were patients who had suffered an extracapsular fracture; they had walking capacity and suffered a fall in their place of residence. The statistical analysis on the validity and reliability of the questionnaire obtained the following results: Cronbach's alpha coefficient showed excellent internal consistency (value of .94). Factor analysis showed 3 underlying factors. The interobserver intraclass correlation coefficient (ICC) was .82 (95% CI:.75-.87), and the intraobserver ICC was .96 (95% CI:.95-.97). Correlation with other functional scales was assessed using the Spearman correlation coefficient, which was .83 with the Barthel Index and .81 with the Parker score. CONCLUSIONS: These findings support the validity of the CUPAX questionnaire as a tool to measure the previous functional level in elderly patients affected by a hip fracture.

Genome-wide gene expression profiling in GluR1 knockout mice: key role of the calcium signaling pathway in glutamatergically mediated hippocampal transmission.

Alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptors (AMPARs) convey fast synaptic transmission in the CNS and mediate various forms of hippocampal plasticity. Disruption of glutamate receptor type 1 (GluR1), a member of the AMPAR family, causes synaptic alterations and learning/memory deficits in mice. To gain mechanistic insight into the synaptic and behavioral changes associated with GluR1 deletion, hippocampal genome-wide expression profiling was conducted using groups of GluR1 knockout (KO) mice and their wild-type littermates. Regulation of 38 genes was found to be altered more than 30% (P < 0.01, n = 8), and seven of these genes were studied with additional quantitative experiments. A large portion of the altered genes encoded molecules involved in calcium signaling, including calcium channel components, calcium-binding proteins and calcium-calmodulin-dependent protein kinase II subunits. At the protein level, we further evaluated some genes in the calcium pathway that were altered in GluR1 KO mice. Protein levels of two key molecules in the calcium pathway - GluR, ionotropic, N-methyl-d-aspartate-1 and calcium/calmodulin-dependent protein kinase II alpha - showed similar changes to those observed in mRNA levels. These findings raise the possibility that calcium signaling and other plasticity molecules may contribute to the hippocampal plasticity and behavioral deficits observed in GluR1 KO mice.

Adenosine mechanisms and hypersensitive corticostriatal terminals in restless legs syndrome. Rationale for the use of inhibitors of adenosine transport.

Our working hypothesis is that a hypoadenosinergic state is a main pathogenetic factor that determines the sensory-motor symptoms and hyperarousal of restless legs syndrome (RLS). We have recently demonstrated that brain iron deficiency (BID) in rodents, a well-accepted animal model of RLS, is associated with a generalized downregulation of adenosine A1 receptors (A1R) in the brain and with hypersensitivity of corticostriatal glutamatergic terminals. Here, we first review the experimental evidence for a pivotal role of adenosine and A1R in the control of striatal glutamatergic transmission and the rationale for targeting putative downregulated striatal A1R in RLS patients, which is supported by recent clinical results obtained with dipyridamole, an inhibitor of the nucleoside transporters ENT1 and ENT2. Second, we perform optogenetic-microdialysis experiments in rats to demonstrate that A1R determine the sensitivity of corticostriatal glutamatergic terminals and the ability of dipyridamole to counteract optogenetically-induced corticostriatal glutamate release in both animals with BID and controls. Thus, a frequency of optogenetic stimulation that was ineffective at inducing cortico-striatal glutamate release in control rats became effective with the local perfusion of a selective A1R antagonist. Furthermore, in animals with and without BID, the striatal application of dipyridamole blocked the optogenetic-induced glutamate release and decreased basal levels of glutamate, which was counteracted by the A1R antagonist. The results support the clinical application of ENT1 inhibitors in RLS.

Biased G Protein-Independent Signaling of Dopamine D1-D3 Receptor Heteromers in the Nucleus Accumbens.

Several studies found in vitro evidence for heteromerization of dopamine D1 receptors (D1R) and D3 receptors (D3R), and it has been postulated that functional D1R-D3R heteromers that are normally present in the ventral striatum mediate synergistic locomotor-activating effects of D1R and D3R agonists in rodents. Based also on results obtained in vitro, with mammalian transfected cells, it has been hypothesized that those behavioral effects depend on a D1R-D3R heteromer-mediated G protein-independent signaling. Here, we demonstrate the presence on D1R-D3R heteromers in the mouse ventral striatum by using a synthetic peptide that selectively destabilizes D1R-D3R heteromers. Parallel locomotor activity and ex vivo experiments in reserpinized mice and in vitro experiments in D1R-D3R mammalian transfected cells were performed to dissect the signaling mechanisms of D1R-D3R heteromers. Co-administration of D1R and D3R agonists in reserpinized mice produced synergistic locomotor activation and a selective synergistic AKT phosphorylation in the most ventromedial region of the striatum in the shell of the nucleus accumbens. Application of the destabilizing peptide in transfected cells and in the shell of the nucleus accumbens allowed demonstrating that both in vitro and in vivo co-activation of D3R induces a switch from G protein-dependent to G protein-independent D1R-mediated signaling determined by D1R-D3R heteromerization. The results therefore demonstrate that a biased G protein-independent signaling of D1R-D3R heteromers localized in the shell of the nucleus accumbens mediate the locomotor synergistic effects of D1R and D3R agonists in reserpinized mice.

Opioid-galanin receptor heteromers mediate the dopaminergic effects of opioids.

Identifying non-addictive opioid medications is a high priority in medical sciences, but µ-opioid receptors mediate both the analgesic and addictive effects of opioids. We found a significant pharmacodynamic difference between morphine and methadone that is determined entirely by heteromerization of µ-opioid receptors with galanin Gal1 receptors, rendering a profound decrease in the potency of methadone. This was explained by methadone's weaker proficiency to activate the dopaminergic system as compared to morphine and predicted a dissociation of therapeutic versus euphoric effects of methadone, which was corroborated by a significantly lower incidence of self-report of "high" in methadone-maintained patients. These results suggest that µ-opioid-Gal1 receptor heteromers mediate the dopaminergic effects of opioids that may lead to a lower addictive liability of opioids with selective low potency for the µ-opioid-Gal1 receptor heteromer, exemplified by methadone.

Treatment of restless legs syndrome/Willis-Ekbom disease with the non-selective ENT1/ENT2 inhibitor dipyridamole: testing the adenosine hypothesis.

OBJECTIVES: Recent animal models of restless legs syndrome (RLS) suggest that brain iron deficiency is associated with a hypoadenosinergic state, with downregulation of adenosine A1 receptors (A1R) in the striatum and cortex. We hypothesized that an increase in extracellular adenosine induced by inhibitors of adenosine transporters, such as the non-selective ENT1/ENT2 inhibitor dipyridamole, would result in an improvement in RLS symptoms. METHODS: In a prospective two-month open-label, non-placebo controlled clinical trial, 15 untreated idiopathic RLS patients began treatment with 100 mg dipyridamole (with uptitration to 400 mg if necessary). Multiple Suggested Immobilization Tests and polysomnography were performed at baseline and at eight weeks. Severity was assessed at four and eight weeks using the IRLS, and the CGI scales. The primary endpoint was therapeutic response (50% improvement in IRLS total score). RESULTS: Thirteen patients completed the study. IRLS score improved from a mean (±S.D.) of 23.4 ± 4.6 at baseline to 10.7 ± 4.5 at eight weeks. Six out of 13 patients were full responders and four were partial responders. The mean (±S.D.) effective dose of dipyridamole at eight weeks was 281.8 ± 57.5 mg/day. Sleep variables also improved, and the mean (±S.D.) periodic leg movement index decreased from 26.7 ± 7.2 to 4.3 ± 1.9. Dipyridamole was generally well tolerated. Main side effects were abdominal cramps, diarrhea, dizziness, and flushing. CONCLUSIONS: These preliminary results suggest that dipyridamole has significant therapeutic effects on both sensory and motor symptoms, as well as sleep. In addition, it provides evidence that hypoadenosinergic mechanisms play a central role in RLS. CLASSIFICATION OF EVIDENCE: The study provides class III evidence supporting the therapeutic effects of dipyridamole in RLS.

Pivotal Role of Adenosine Neurotransmission in Restless Legs Syndrome.

The symptomatology of Restless Legs Syndrome (RLS) includes periodic leg movements during sleep (PLMS), dysesthesias, and hyperarousal. Alterations in the dopaminergic system, a presynaptic hyperdopaminergic state, seem to be involved in PLMS, while alterations in glutamatergic neurotransmission, a presynaptic hyperglutamatergic state, seem to be involved in hyperarousal and also PLMS. Brain iron deficiency (BID) is well-recognized as a main initial pathophysiological mechanism of RLS. BID in rodents have provided a pathogenetic model of RLS that recapitulates the biochemical alterations of the dopaminergic system of RLS, although without PLMS-like motor abnormalities. On the other hand, BID in rodents reproduces the circadian sleep architecture of RLS, indicating the model could provide clues for the hyperglutamatergic state in RLS. We recently showed that BID in rodents is associated with changes in adenosinergic transmission, with downregulation of adenosine A1 receptors (A1R) as the most sensitive biochemical finding. It was hypothesized that A1R downregulation leads to hypersensitive striatal glutamatergic terminals and facilitation of striatal dopamine release. Hypersensitivity of striatal glutamatergic terminals was demonstrated by an optogenetic-microdialysis approach in the rodent with BID, indicating that it could represent a main pathogenetic factor that leads to PLMS in RLS. In fact, the dopaminergic agonists pramipexole and ropinirole and the α2δ ligand gabapentin, used in the initial symptomatic treatment of RLS, completely counteracted optogenetically-induced glutamate release from both normal and BID-induced hypersensitive corticostriatal glutamatergic terminals. It is a main tenet of this essay that, in RLS, a single alteration in the adenosinergic system, downregulation of A1R, disrupts the adenosine-dopamine-glutamate balance uniquely controlled by adenosine and dopamine receptor heteromers in the striatum and also the A1R-mediated inhibitory control of glutamatergic neurotransmission in the cortex and other non-striatal brain areas, which altogether determine both PLMS and hyperarousal. Since A1R agonists would be associated with severe cardiovascular effects, it was hypothesized that inhibitors of nucleoside equilibrative transporters, such as dipyridamole, by increasing the tonic A1R activation mediated by endogenous adenosine, could represent a new alternative therapeutic strategy for RLS. In fact, preliminary clinical data indicate that dipyridamole can significantly improve the symptomatology of RLS.

Synthesis of new benzoxazinone derivatives as neuropeptide Y5 antagonists for the treatment of obesity.

Screening of our internal chemical collection against the neuropeptide Y5 (NPY Y5) receptor allowed the identification of a benzoxazine derivative 5f as a hit that showed moderate affinity (IC(50) = 300 nM). With the aim of improving the in vitro potency, a series of 2-benzoxazinone derivatives have been synthesized and tested for NPY Y5 activity. Most of the compounds were found to be potent and selective NPY Y5 antagonists having nanomolar binding affinities for the NPY Y5 receptor and showing functional antagonism in the forskolin-induced cyclic AMP test. Prelimminary studies in order to understand the structure-activity relationship were undertaken. Selected compounds were further evaluated for in vivo efficacy, affording the lead compound 2-[4-(8-methyl-2-oxo-4H-benzo[d][1,3]oxazin-1-yl)piperidin-1-yl]-N-(9-oxo-9H-fluoren-3-yl)acetamide 5p, which displayed in vivo activity reducing food intake in rodents.