3,4-Methylenedioxy-methamphetamine induces in vivo regional up-regulation of central nicotinic receptors in rats and potentiates the regulatory effects of nicotine on these receptors

Nicotine (NIC), the main psychostimulant compound of smoked tobacco, exerts its effects through activation of central nicotinic acetylcholine receptors (nAChR), which become up-regulated after chronic administration. Recent work has demonstrated that the recreational drug 3,4-methylenedioxymethamphetamine (MDMA) has affinity for nAChR and also induces up-regulation of nAChR in PC 12 cells. Tobacco and MDMA are often consumed together. In the present work we studied the in vivo effect of a classic chronic dosing schedule of MDMA in rats, alone or combined with a chronic schedule of NIC, on the density of nAChR and on serotonin reuptake transporters. MDMA induced significant decreases in [3H]paroxetine binding in the cortex and hippocampus measured 24 h after the last dose and these decreases were not modified by the association with NIC. In the prefrontal cortex, NIC and MDMA each induced significant increases in [3H]epibatidine binding (29.5 and 34.6%, respectively) with respect to saline-treated rats, and these increases were significantly potentiated (up to 72.1%) when the two drugs were associated. Also in this area, [3H]methyllycaconitine binding was increased a 42.1% with NIC + MDMA but not when they were given alone. In the hippocampus, MDMA potentiated the a7 regulatory effects of NIC (raising a 25.5% increase to 52.5%) but alone was devoid of effect. MDMA had no effect on heteromeric nAChR in striatum and a coronal section of the midbrain containing superior colliculi, geniculate nuclei, substantia nigra and ventral tegmental area. Specific immunoprecipitation of solubilised receptors suggests that the up-regulated heteromeric nAChRs contain a4 and b2 subunits. Western blots with specific a4 and a7 antibodies showed no significant differences between the groups, indicating that, as reported for nicotine, up-regulation caused by MDMA is due to post-translational events rather than increased receptor synthesis

The Interplay between Homogeneous and Heterogeneous Phases of PdAu Catalysts for the Oxidation of Alcohols

The relationship between the homogeneous and heterogeneous phases of a catalyst is widely neglected in part due to the inherent differences between the experimental and theoretical techniques employed to study them. It is well-known that, under reaction conditions, many homogeneous catalysts deactivate and generate black metals (i.e., nanoparticles). Simultaneously, heterogeneous catalysts tend to suffer of leaching processes under harsh conditions, which produce the formation of species in the homogeneous phase (i.e., volatile or organometallic species). To unravel the links between these two types of catalytic species, we have taken PdAu catalysts in the oxidation of crotyl alcohol to crotonaldehyde and investigated the reaction process for both homogeneous and heterogeneous phases. We show that the process is possible in both phases and, essentially, contains the same elementary steps. The results indicate that the homogeneous catalyst is slightly more active; however, the enhanced stability of the heterogeneous phase provides a better performance under relevant reaction conditions. Both catalytic systems are connected through two simple steps that can be computed: oxidative leaching and deposition. The oxidative leaching of the PdAu nanoparticles in the presence of dioxygen can produce Pd(II) monomeric species able to catalyze the alcohol oxidation in homogeneous conditions. After the reaction the reduced Pd(0) homogeneous catalyst is reabsorbed onto the PdAu nanoparticles, preventing the aggregation process. The present work shows that the full homogeneous/heterogeneous catalytic cycle can be analyzed in a holistic manner with computational techniques

Evidence for a novel neuronal mechanism driving Alzheimer's disease, upstream of amyloid

This perspective offers an alternative to the amyloid hypothesis in the etiology of Alzheimer's disease (AD). We review evidence for a novel signaling mechanism based on a little‐known peptide, T14. T14 could drive neurodegeneration as an aberrantly activated process of plasticity selective to interconnecting subcortical nuclei, the isodendritic core, where cell loss starts at the pre‐symptomatic stages of the disease. Each of these cell groups has the capacity to form T14, which can stimulate production of p‐Tau and β‐amyloid, suggestive of an upstream driver of neurodegeneration. Moreover, results in an animal AD model show that antagonism of T14 with a cyclated variant, NBP14, prevents formation of β‐amyloid, and restores cognitive function to that of wild‐type counterparts. Any diagnostic and/or therapeutic strategy based on T14‐NBP14 awaits validation in clinical trials. However, an understanding of this novel signaling system could bring much‐needed fresh insights into the progression of cell loss underlying AD. Highlights: The possible primary mechanism of neurodegeneration upstream of amyloid. Primary involvement of selectively vulnerable subcortical nuclei, isodendritic core. Bioactive peptide T14 trophic in development but toxic in context of mature brain. Potential for early‐stage biomarker to detect Alzheimer's disease. Effective therapeutic halting neurodegeneration, validated already in 5XFAD mice

Molecular basis of the selective binding of MDMA enantiomers to the Alpha4Beta2 nicotinic receptor subtype: synthesis, pharmacological evaluation and mechanistic studies

The α4β2 nicotinic acetylcholine receptor (nAChR) is a molecular target of 3,4-methylenedioxymethamphetamine (MDMA), a synthetic drug also known as ecstasy, and it modulates the MDMA-mediated reinforcing properties. However, the enantioselective preference of the α4β2 nAChR subtype still remains unknown. Since the two enantiomers exhibit different pharmacological profiles and stereoselective metabolism, the aim of this study is to assess a possible difference in the interaction of the MDMA enantiomers with this nAChR subtype. To this end, we report a novel simple, yet highly efficient enantioselective synthesis of the MDMA enantiomers, in which the key step is the diastereoselective reduction of imides derived from optically pure tert-butylsulfinamide. The enantioselective binding to the receptor is examined using [3H]epibatidine in a radioligand assay. Even though the two enantiomers induced a concentration-dependent binding displacement, (S)-MDMA has an inhibition constant 13-fold higher than (R)-MDMA, which shows a Hill's coefficient not significantly different from unity, implying a competitive interaction. Furthermore, when NGF-differentiated PC12 cells were pretreated with the compounds, a significant increase in binding of [3H]epibatidine was found for (R)-MDMA, indicating up-regulation of heteromeric nAChR in the cell surface. Finally, docking and molecular dynamics studies have been used to identify the binding mode of the two enantiomers, which provides a structural basis to justify the differences in affinity from the differential interactions played by the substituents at the stereogenic center of MDMA. The results provide a basis to explore the distinct psychostimulant profiles of the MDMA enantiomers mediated by the α4β2 nAChR subtype

Involvement of nicotinic receptors in methamphetamine and MDMA induced neurotoxicity: Pharmacological studies

Podeu consultar el llibre complet a: http://hdl.handle.net/2445/32392During the last years, our emphasis has focused in the study of the neurotoxic effects of 3,4-methylenedioxymethamphetamine (MDMA) and methamphetamine (METH) on central nervous system and their pharmacological prevention. In the process of this research, we have used a semipurified synaptosomal preparation from striatum of mice or rats as a reliable in vitro model to study reactive oxygen species (ROS) production by these amphetamine derivatives, which is well correlated with their dopaminergic injury in in vivo models. Using this preparation we have demonstrated that blockade of alpha7 nicotinic receptors with methyllycaconitine (MLA) and memantine (MEM) prevents ROS production induced by MDMA and METH. Studies at molecular level showed that both, MDMA and METH, displaced competitively the binding of radioligands for homomeric alpha7 and heteromeric nAChRs, indicating that they can directly interact with them. In all the cases MDMA displayed higher affinity than METH and it was higher for heteromeric than for alpha7 subtype. Preincubation of differentiated PC12 cells with MDMA or METH induces nicotinic acetylcholine receptors (nAChR) up-regulation in a concentration- and time-dependent manner, as many nicotinic ligands do, supporting their functional interaction with nAChRs. Such interaction expands the pharmacological profile of amphetamines and can account for some of their effects

The Interplay between Homogeneous and Heterogeneous Phases of PdAu Catalysts for the Oxidation of Alcohols

The relationship between the homogeneous and heterogeneous phases of a catalyst is widely neglected in part due to the inherent differences between the experimental and theoretical techniques employed to study them. It is well-known that, under reaction conditions, many homogeneous catalysts deactivate and generate black metals (i.e., nanoparticles). Simultaneously, heterogeneous catalysts tend to suffer of leaching processes under harsh conditions, which produce the formation of species in the homogeneous phase (i.e., volatile or organometallic species). To unravel the links between these two types of catalytic species, we have taken PdAu catalysts in the oxidation of crotyl alcohol to crotonaldehyde and investigated the reaction process for both homogeneous and heterogeneous phases. We show that the process is possible in both phases and, essentially, contains the same elementary steps. The results indicate that the homogeneous catalyst is slightly more active; however, the enhanced stability of the heterogeneous phase provides a better performance under relevant reaction conditions. Both catalytic systems are connected through two simple steps that can be computed: oxidative leaching and deposition. The oxidative leaching of the PdAu nanoparticles in the presence of dioxygen can produce Pd(II) monomeric species able to catalyze the alcohol oxidation in homogeneous conditions. After the reaction the reduced Pd(0) homogeneous catalyst is reabsorbed onto the PdAu nanoparticles, preventing the aggregation process. The present work shows that the full homogeneous/heterogeneous catalytic cycle can be analyzed in a holistic manner with computational techniques

Involvement of nicotinic receptors in methamphetamine and MDMA induced neurotoxicity: Pharmacological studies

Podeu consultar el llibre complet a: http://hdl.handle.net/2445/32392During the last years, our emphasis has focused in the study of the neurotoxic effects of 3,4-methylenedioxymethamphetamine (MDMA) and methamphetamine (METH) on central nervous system and their pharmacological prevention. In the process of this research, we have used a semipurified synaptosomal preparation from striatum of mice or rats as a reliable in vitro model to study reactive oxygen species (ROS) production by these amphetamine derivatives, which is well correlated with their dopaminergic injury in in vivo models. Using this preparation we have demonstrated that blockade of alpha7 nicotinic receptors with methyllycaconitine (MLA) and memantine (MEM) prevents ROS production induced by MDMA and METH. Studies at molecular level showed that both, MDMA and METH, displaced competitively the binding of radioligands for homomeric alpha7 and heteromeric nAChRs, indicating that they can directly interact with them. In all the cases MDMA displayed higher affinity than METH and it was higher for heteromeric than for alpha7 subtype. Preincubation of differentiated PC12 cells with MDMA or METH induces nicotinic acetylcholine receptors (nAChR) up-regulation in a concentration- and time-dependent manner, as many nicotinic ligands do, supporting their functional interaction with nAChRs. Such interaction expands the pharmacological profile of amphetamines and can account for some of their effects

Neuronal nicotinic receptors as new targets foramphetamine-induced oxidative damage and neurotoxicity

Amphetamine derivatives such as methamphetamine (METH) and 3,4-methylenedioxymethamphetamine (MDMA, ecstasy) are drugs widely abused in a recreational context. This has led to concern because of the evidence that they are neurotoxic in animal models and cognitive impairments have been described in heavy abusers. The main targets of these drugs are plasmalemmal and vesicular monoamine transporters, leading to reverse transport and increased monoamine efflux to the synapse. As far as neurotoxicity is concerned, increased reactive oxygen species (ROS) production seems to be one of the main causes. Recent research has demonstrated that blockade of 7 nicotinic acetylcholine receptors (nAChR) inhibits METH- and MDMA-induced ROS production in striatal synaptosomes which is dependent on calcium and on NO-synthase activation. Moreover, 7 nAChR antagonists (methyllycaconitine and memantine) attenuated in vivo the neurotoxicity induced by METH and MDMA, and memantine prevented the cognitive impairment induced by these drugs. Radioligand binding experiments demonstrated that both drugs have affinity to 7 and heteromeric nAChR, with MDMA showing lower Ki values, while fluorescence calcium experiments indicated that MDMA behaves as a partial agonist on 7 and as an antagonist on heteromeric nAChR. Sustained Ca increase led to calpain and caspase-3 activation. In addition, modulatory effects of MDMA on 7 and heteromeric nAChR populations have been found

3,4-Methylenedioxy-methamphetamine induces in vivo regional up-regulation of central nicotinic receptors in rats and potentiates the regulatory effects of nicotine on these receptors

Nicotine (NIC), the main psychostimulant compound of smoked tobacco, exerts its effects through activation of central nicotinic acetylcholine receptors (nAChR), which become up-regulated after chronic administration. Recent work has demonstrated that the recreational drug 3,4-methylenedioxymethamphetamine (MDMA) has affinity for nAChR and also induces up-regulation of nAChR in PC 12 cells. Tobacco and MDMA are often consumed together. In the present work we studied the in vivo effect of a classic chronic dosing schedule of MDMA in rats, alone or combined with a chronic schedule of NIC, on the density of nAChR and on serotonin reuptake transporters. MDMA induced significant decreases in [3H]paroxetine binding in the cortex and hippocampus measured 24 h after the last dose and these decreases were not modified by the association with NIC. In the prefrontal cortex, NIC and MDMA each induced significant increases in [3H]epibatidine binding (29.5 and 34.6%, respectively) with respect to saline-treated rats, and these increases were significantly potentiated (up to 72.1%) when the two drugs were associated. Also in this area, [3H]methyllycaconitine binding was increased a 42.1% with NIC + MDMA but not when they were given alone. In the hippocampus, MDMA potentiated the a7 regulatory effects of NIC (raising a 25.5% increase to 52.5%) but alone was devoid of effect. MDMA had no effect on heteromeric nAChR in striatum and a coronal section of the midbrain containing superior colliculi, geniculate nuclei, substantia nigra and ventral tegmental area. Specific immunoprecipitation of solubilised receptors suggests that the up-regulated heteromeric nAChRs contain a4 and b2 subunits. Western blots with specific a4 and a7 antibodies showed no significant differences between the groups, indicating that, as reported for nicotine, up-regulation caused by MDMA is due to post-translational events rather than increased receptor synthesis

Molecular basis of the selective binding of MDMA enantiomers to the Alpha4Beta2 nicotinic receptor subtype: synthesis, pharmacological evaluation and mechanistic studies

The α4β2 nicotinic acetylcholine receptor (nAChR) is a molecular target of 3,4-methylenedioxymethamphetamine (MDMA), a synthetic drug also known as ecstasy, and it modulates the MDMA-mediated reinforcing properties. However, the enantioselective preference of the α4β2 nAChR subtype still remains unknown. Since the two enantiomers exhibit different pharmacological profiles and stereoselective metabolism, the aim of this study is to assess a possible difference in the interaction of the MDMA enantiomers with this nAChR subtype. To this end, we report a novel simple, yet highly efficient enantioselective synthesis of the MDMA enantiomers, in which the key step is the diastereoselective reduction of imides derived from optically pure tert-butylsulfinamide. The enantioselective binding to the receptor is examined using [3H]epibatidine in a radioligand assay. Even though the two enantiomers induced a concentration-dependent binding displacement, (S)-MDMA has an inhibition constant 13-fold higher than (R)-MDMA, which shows a Hill's coefficient not significantly different from unity, implying a competitive interaction. Furthermore, when NGF-differentiated PC12 cells were pretreated with the compounds, a significant increase in binding of [3H]epibatidine was found for (R)-MDMA, indicating up-regulation of heteromeric nAChR in the cell surface. Finally, docking and molecular dynamics studies have been used to identify the binding mode of the two enantiomers, which provides a structural basis to justify the differences in affinity from the differential interactions played by the substituents at the stereogenic center of MDMA. The results provide a basis to explore the distinct psychostimulant profiles of the MDMA enantiomers mediated by the α4β2 nAChR subtype