2,3-Benzodiazepine-type AMPA receptor antagonists and their neuroprotective effects

AMPA receptor neurotransmission and therapeutic applications: A comprehensive review of their multifaceted modulation

The neuropharmacological community has shown a strong interest in AMPA receptors as critical components of excitatory synaptic transmission during the last fifteen years. AMPA receptors, members of the ionotropic glutamate receptor family, allow rapid excitatory neurotransmission in the brain. AMPA receptors, which are permeable to sodium and potassium ions, manage the bulk of the brain's rapid synaptic communications. This study thoroughly examines the recent developments in AMPA receptor regulation, focusing on a shift from single chemical illustrations to a more extensive investigation of underlying processes. The complex interplay of these modulators in modifying the function and structure of AMPA receptors is the main focus, providing insight into their influence on the speed of excitatory neurotransmission. This research emphasizes the potential of AMPA receptor modulation as a therapy for various neurological disorders such as epilepsy and Alzheimer's disease. Analyzing these regulators' sophisticated molecular details enhances our comprehension of neuropharmacology, representing a significant advancement in using AMPA receptors for treating intricate neurological conditions.

Electrophysiological Assessment of Newly Synthesized 2,3-Benzodiazepine Derivatives for Inhibiting the AMPA Receptor Channel

Three major subtypes of ionotropic receptors regulate glutamatergic synaptic transmission, one of which is α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors (AMPARs). They are tetrameric, cation-permeable ionotropic glutamate receptors found across the brain. Abnormalities in AMPA receptor trafficking and synaptic assembly are linked to cognitive decline and neurological diseases such as Alzheimer's, Parkinson's, and Huntington's. The present study will investigate the effects of four novel 2,3-benzodiazepine derivatives on AMPA receptor subunits by comparing their effects on synaptic responses, desensitization, and deactivation rate in human embryonic kidney cells (HEK293T) recombinant AMPAR subunits using whole-cell patch-clamp electrophysiology. All four 2,3-BDZ compounds showed inhibitory activity against all the homomeric and heteromeric subunits tested. While the desensitization and deactivation rates in 2,3-BDZ-1 and 2,3-BDZ-2 decreased and increased, respectively, in the other two compounds (i.e., 2,3-BDZ-3 and 2,3-BDZ-4), there was no change in the desensitization or deactivation rates. These results contribute to a better understanding of AMPARs by identifying potential 2,3-BDZ drugs that demonstrate inhibitory effects on the AMPAR subunits.

Photoredox synthesis of 6- and 7-membered ring scaffolds via N-centered radicals

N-Containing heterocycles are important scaffolds due to their ubiquitous presence in bioactive compounds. Their synthesis has been considered as an important research field. In this work we report the access to 6- and 7-membered rings via a photoinduced strategy. To our knowledge, this work represents the first exemple of photo-induced 7-endo-trig cyclization with N-centered radicals.

Experimental and Computational Structural Studies of 2,3,5-Trisubstituted and 1,2,3,5-Tetrasubstituted Indoles as Non-Competitive Antagonists of GluK1/GluK2 Receptors

The blockade of kainate receptors, in particular with non-competitive antagonists, has—due to their anticonvulsant and neuroprotective properties—therapeutic potential in many central nervous system (CNS) diseases. Deciphering the structural properties of kainate receptor ligands is crucial to designing medicinal compounds that better fit the receptor binding pockets. In light of that fact, here, we report experimental and computational structural studies of four indole derivatives that are non-competitive antagonists of GluK1/GluK2 receptors. We used X-ray studies and Hirshfeld surface analysis to determine the structure of the compounds in the solid state and quantum chemical calculations to compute HOMO and LUMO orbitals and the electrostatic potential. Moreover, non-covalent interaction maps were also calculated. It is worth emphasizing that compounds 3 and 4 are achiral molecules crystallising in non-centrosymmetric space groups, which is a relatively rare phenomenon.

New 2,3-Benzodiazepine Derivative: Synthesis, Activity on Central Nervous System, and Toxicity Study in Mice

We report the design and synthesis of a new diazepine derivative, 4-(4-methoxyphenyl)-2,3,4,5-tetrahydro-2,3-benzodiazepin-1-one (VBZ102), and the evaluation of its anxiolytic-like profile, memory impairment effect, and toxicity in Swiss mice. VBZ102 was evaluated for central nervous system effects in an open field, light–dark box, and novel object recognition tests under oral administration for acute and sub-acute treatment. We tested the VBZ102 toxicity in mice through a determination of LD₅₀ values and examination of the biochemical and histopathological parameters. The VBZ102 induced an anxiolytic effect at different doses both in the light–dark box and open field tests. Unlike other benzodiazepines (e.g., bromazepam), a sedative effect was noted only after administration of the VBZ102 at 10.0 mg/kg.

Ortho versus Meta Chlorophenyl-2,3-Benzodiazepine Analogues: Synthesis, Molecular Modeling, and Biological Activity as AMPAR Antagonists

2,3-Benzodiazepine compounds are an important family of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) antagonists that act in a noncompetitive manner. Due to the critical role of AMPARs in the synapse and various neurological diseases, significant scientific interest in elucidating the molecular basis of the function of the receptors has spiked. The analogues were synthesized to assess the functional consequence of removing the amine group of the phenyl ring, the potency and efficacy of inhibition by substituting a halogen group at the meta vs ortho position of the phenyl ring, and layout the prediction of potential drug candidates for AMPAR hyperactivation. Using the whole-cell patch-clamp technique, we assessed the effect of the derivative on the amplitude of various AMPA-type glutamate receptors and calculated the desensitization and deactivation rates before and after treatment of HEK293 cells. We noticed that the amino group is not necessary for inhibition as long as an electron-withdrawing group is placed on the meta position of the phenyl ring of BDZ. Furthermore, compound 4a significantly inhibited and affected the desensitization rate of the tested AMPARs but showed no effect on the deactivation rate. The current study paves the way to a better understanding of AMPARs and provides possible drug candidates of 2,3-BDZ different from the conventional derivatives.

Prevention of an increase in cortical ligand binding to AMPA receptors may represent a novel mechanism of endogenous brain protection by G-CSF after ischemic stroke

PURPOSE

Using G-CSF deficient mice we recently demonstrated neuroprotective properties of endogenous G-CSF after ischemic stroke. The present follow-up study was designed to check, whether specific alterations in ligand binding densities of excitatory glutamate or inhibitory GABAA receptors may participate in this effect.

METHODS

Three groups of female mice were subjected to 45 minutes of MCAO: wildtype, G-CSF deficient and G-CSF deficient mice substituted with G-CSF. Infarct volumes were determined after 24 hours and quantitative in vitro receptor autoradiography was performed using [3H]MK-801, [3H]AMPA and [3H]muscimol for labeling of NMDA, AMPA and GABAA receptors, respectively. Ligand binding densities were analyzed in regions in the ischemic core, peri-infarct areas and corresponding contralateral regions.

RESULTS

Infarct volumes did not significantly differ between the experimental groups. Ligand binding densities of NMDA and GABAA receptors were widely in the same range. However, AMPA receptor binding densities in G-CSF deficient mice were substantially enhanced compared to wildtype mice. G-CSF substitution in mice lacking G-CSF largely reversed this effect.

CONCLUSIONS

Although infarct volumes did not differ 24 hours after ischemia the increase of AMPA receptor binding densities in G-CSF deficient mice may explain the bigger infarcts previously observed at later time-points with the same stroke model.

EGAR, A Food Protein-Derived Tetrapeptide, Reduces Seizure Activity in Pentylenetetrazole-Induced Epilepsy Models Through α-Amino-3-Hydroxy-5-Methyl-4-Isoxazole Propionate Receptors

A primary pathogeny of epilepsy is excessive activation of α-amino-3-hydroxy-5-methyl-4-isoxazole propionate receptors (AMPARs). To find potential molecules to inhibit AMPARs, high-throughput screening was performed in a library of tetrapeptides in silico. Computational results suggest that some tetrapeptides bind stably to the AMPAR. We aligned these sequences of tetrapeptide candidates with those from in vitro digestion of the trout skin protein. Among salmon-derived products, Glu-Gly-Ala-Arg (EGAR) showed a high biological affinity toward AMPAR when tested in silico. Accordingly, natural EGAR was hypothesized to have anticonvulsant activity, and in vitro experiments showed that EGAR selectively inhibited AMPAR-mediated synaptic transmission without affecting the electrophysiological properties of hippocampal pyramidal neurons. In addition, EGAR reduced neuronal spiking in an in vitro seizure model. Moreover, the ability of EGAR to reduce seizures was evaluated in a rodent epilepsy model. Briefer and less severe seizures versus controls were shown after mice were treated with EGAR. In conclusion, the promising experimental results suggest that EGAR inhibitor against AMPARs may be a target for antiepilepsy pharmaceuticals. Epilepsy is a common brain disorder characterized by the occurrence of recurring, unprovoked seizures. Twenty to 30 % of persons with epilepsy do not achieve adequate seizure control with any drug. Here we provide a possibility in which a natural and edible tetrapeptide, EGAR, can act as an antiepileptic agent. We have combined computation with in vitro experiments to show how EGAR modulates epilepsy. We also used an animal model of epilepsy to prove that EGAR can inhibit seizures in vivo. This study suggests EGAR as a potential pharmaceutical for the treatment of epilepsy.

Structural Bases of Noncompetitive Inhibition of AMPA-Subtype Ionotropic Glutamate Receptors by Antiepileptic Drugs

Excitatory neurotransmission plays a key role in epileptogenesis. Correspondingly, AMPA-subtype ionotropic glutamate receptors, which mediate the majority of excitatory neurotransmission and contribute to seizure generation and spread, have emerged as promising targets for epilepsy therapy. The most potent and well-tolerated AMPA receptor inhibitors act via a noncompetitive mechanism, but many of them produce adverse side effects. The design of better drugs is hampered by the lack of a structural understanding of noncompetitive inhibition. Here, we report crystal structures of the rat AMPA-subtype GluA2 receptor in complex with three noncompetitive inhibitors. The inhibitors bind to a novel binding site, completely conserved between rat and human, at the interface between the ion channel and linkers connecting it to the ligand-binding domains. We propose that the inhibitors stabilize the AMPA receptor closed state by acting as wedges between the transmembrane segments, thereby preventing gating rearrangements that are necessary for ion channel opening.

Seizure control by decanoic acid through direct AMPA receptor inhibition

See Rogawski (doi:10.1093/awv369) for a scientific commentary on this article. 

The medium chain triglyceride ketogenic diet is an established treatment for drug-resistant epilepsy that increases plasma levels of decanoic acid and ketones. Recently, decanoic acid has been shown to provide seizure control in vivo, yet its mechanism of action remains unclear. Here we show that decanoic acid, but not the ketones β-hydroxybutryate or acetone, shows antiseizure activity in two acute ex vivo rat hippocampal slice models of epileptiform activity. To search for a mechanism of decanoic acid, we show it has a strong inhibitory effect on excitatory, but not inhibitory, neurotransmission in hippocampal slices. Using heterologous expression of excitatory ionotropic glutamate receptor AMPA subunits in Xenopus oocytes, we show that this effect is through direct AMPA receptor inhibition, a target shared by a recently introduced epilepsy treatment perampanel. Decanoic acid acts as a non-competitive antagonist at therapeutically relevant concentrations, in a voltage- and subunit-dependent manner, and this is sufficient to explain its antiseizure effects. This inhibitory effect is likely to be caused by binding to sites on the M3 helix of the AMPA-GluA2 transmembrane domain; independent from the binding site of perampanel. Together our results indicate that the direct inhibition of excitatory neurotransmission by decanoic acid in the brain contributes to the anti-convulsant effect of the medium chain triglyceride ketogenic diet.

Developing drug strategies for the neuroprotective treatment of acute ischemic stroke

Developing new treatment strategies for acute ischemic stroke in the last twenty years has offered some important successes, but also several failures. Most trials of neuroprotective therapies have been uniformly negative to date. Recent research has reported how excitatory amino acids act as the major excitatory neurotransmitters in the cerebral cortex and hippocampus. Furthermore, other therapeutic targets such as free radical scavenger strategies and the anti-inflammatory neuroprotective strategy have been evaluated with conflicting data in animal models and human subjects with acute ischemic stroke. Whereas promising combinations of neuroprotection and neurorecovery, such as citicoline, albumin and cerebrolysin have been tested with findings worthy of further evaluation in larger randomized clinical trials. Understanding the complexities of the ischemic cascade is essential to developing pharmacological targets for acute ischemic stroke in neuroprotective or flow restoration therapeutic strategies.

Perspectives on treatment options for mesial temporal lobe epilepsy with hippocampal sclerosis

INTRODUCTION

Mesial temporal lobe epilepsy associated with hippocampal sclerosis (MTLE-HS) is a syndrome that is often refractory to drug treatment. The effects on specific syndromes are not currently available from the pre-marketing clinical development of new AEDs; this does not allow the prediction of whether new drugs will be more effective in the treatment of some patients.

AREAS COVERED

We have reviewed all the existing literature relevant to the understanding of a potential effectiveness in MTLE-HS patients for the latest AEDs, namely brivaracetam, eslicarbazepine, lacosamide, perampanel and retigabine also including the most relevant clinical data and a brief description of their pharmacological profile. Records were identified using predefined search criteria using electronic databases (e.g., PubMed, Cochrane Library Database of Systematic Reviews). Primary peer-reviewed articles published up to the 15 June 2015 were included.

EXPERT OPINION

All the drugs considered have the potential to be effective in the treatment of MTLE-HS; in fact, they possess proven efficacy in animal models; currently considered valuable tools for predicting drug efficacy in TLE. Furthermore, for some of these (e.g., lacosamide and eslicarbazepine) data are already available from post-marketing studies while brivaracetam acting on SV2A like levetiracetam might have the same potential effectiveness with the possibility to be more efficacious considering its ability to inhibit voltage gated sodium channels; finally, perampanel and retigabine are very effective drugs in animal models of TLE.

Mechanism and site of inhibition of AMPA receptors: substitution of one and two methyl groups at the 4-aminophenyl ring of 2,3-benzodiazepine and implications in the "E" site

2,3-Benzodiazepines are a well-known group of compounds for their potential antagonism against AMPA receptors. It has been previously reported that the inhibitory effect of 2,3-benzodiazepine derivatives with a 7,8-ethylenedioxy moiety can be enhanced by simply adding a chlorine atom at position 3 of the 4-aminophenyl ring. Here we report that adding a methyl group at position 3 on the 4-aminophenyl ring, termed as BDZ-11-7, can similarly enhance the inhibitory activity, as compared with the unsubstituted one or BDZ-11-2. Our kinetic studies have shown that BDZ-11-7 is a noncompetitive antagonist of GluA2Q homomeric receptors and prefers to inhibit the closed-channel state. However, adding another methyl group at position 5 on the 4-aminophenyl ring, termed as BDZ-11-6, fails to yield extra inhibition on GluA2Q receptors. Instead, BDZ-11-6 exhibits a diminished inhibition of GluA2Q. Site interaction test indicates the two compounds, BDZ-11-6 and BDZ-11-7, bind to the same site on GluA2Q, which is also the binding site for their prototype, BDZ-11-2. Based on the results from this and our earlier studies, we propose that the binding site that accommodates the 4-aminophenyl ring must contain two interactive points, with one preferring polar groups like chlorine and the other preferring nonpolar groups such as a methyl group. Either adding a chlorine or a methyl group may enhance the inhibitory activity of 2,3-benzodiazepine derivatives with a 7,8-ethylenedioxy moiety. Adding any two of the same group on positions 3 and 5 of the 4-aminophenyl ring, however, significantly reduces the interaction between these 2,3-benzodiazepines and their binding site, because one group is always repelled by one interactive point. We predict therefore that adding a chlorine atom at position 3 and a methyl group at position 5 of the 4-aminophenyl ring of 2,3-benzodiazepine derivatives with a 7,8-ethylenedioxy moiety may produce a new compound that is more potent.

Synthesis and molecular docking of novel non-competitive antagonists of GluK2 receptor

Here we present the synthesis, pharmacological activity, and molecular docking of novel non-competitive antagonists of GluK2 receptor. The compounds concerned are derivatives of indole and carbazole and are the second reported series of non-competitive antagonists of the GluK2 receptor (the first one was also published by our group). The activity of the indole derivatives is in the micromolar range, as in the case of the first series of non-competitive GluK2 receptor antagonists. We have found that designed carbazole derivatives are devoid of activity. Active indole derivatives interact with the transduction domain of the GluK2 receptor, i.e., the domain which links the transmembrane region of the receptor with the agonist-binding domain. The binding pocket is situated within one receptor subunit.

Mechanism and site of inhibition of AMPA receptors: pairing a thiadiazole with a 2,3-benzodiazepine scaffold

2,3-Benzodiazepine compounds are synthesized as drug candidates for treatment of various neurological disorders involving excessive activity of AMPA receptors. Here we report that pairing a thiadiazole moiety with a 2,3-benzodiazepine scaffold via the N-3 position yields an inhibitor type with >28-fold better potency and selectivity on AMPA receptors than the 2,3-benzodiazepine scaffold alone. Using whole-cell recording, we characterized two thiadiazolyl compounds, that is, one contains a 1,3,4-thiadiazole moiety and the other contains a 1,2,4-thiadiazole-3-one moiety. These compounds exhibit potent, equal inhibition of both the closed-channel and the open-channel conformations of all four homomeric AMPA receptor channels and two GluA2R-containing complex AMPA receptor channels. Furthermore, these compounds bind to the same receptor site as GYKI 52466 does, a site we previously termed as the "M" site. A thiadiazole moiety is thought to occupy more fully the side pocket of the receptor site or the "M" site, thereby generating a stronger, multivalent interaction between the inhibitor and the receptor binding site. We suggest that, as a heterocycle, a thiadiazole can be further modified chemically to produce a new class of even more potent, noncompetitive inhibitors of AMPA receptors.

Structural studies, homology modeling and molecular docking of novel non-competitive antagonists of GluK1/GluK2 receptors

Non-competitive ligands of kainate receptors have focused significant attention as medicinal compounds because they seem to be better tolerated than competitive antagonists and uncompetitive blocker of these receptors. Here we present structural studies (X-ray structure determination, NMR and MS spectra) of novel indole-derived non-competitive antagonists of GluK1/GluK2 receptors, homology models of GluK1 and GluK2 receptors based on novel AMPA receptor template as well as molecular docking of ligands to their molecular targets. We find that the allosteric site is in the receptor transduction domain, in one receptor subunit, not between the two subunits as it was indicated by our earlier studies.

Mechanism of inhibition of the GluA2 AMPA receptor channel opening by talampanel and its enantiomer: the stereochemistry of the 4-methyl group on the diazepine ring of 2,3-benzodiazepine derivatives

Stereoselectivity of 2,3-benzodiazepine compounds provides a unique way for the design of stereoisomers as more selective and more potent inhibitors as drug candidates for treatment of the neurological diseases involving excessive activity of AMPA receptors. Here we investigate a pair of enantiomers known as Talampanel and its (+) counterpart about their mechanism of inhibition and selectivity toward four AMPA receptor subunits or GluA1-4. We show that Talampanel is the eutomer with the endismic ratio being 14 for the closed-channel and 10 for the open-channel state of GluA2. Kinetic evidence supports that Talampanel is a noncompetitive inhibitor and it binds to the same site for those 2,3-benzodiazepine compounds with the C-4 methyl group on the diazepine ring. This site, which we term as the "M" site, recognizes preferentially those 2,3-benzodiazepine compounds with the C-4 methyl group being in the R configuration, as in the chemical structure of Talampanel. Given that Talampanel inhibits GluA1 and GluA2, but is virtually ineffective on the GluA3 and GluA4 AMPA receptor subunits, we hypothesize that the "M" site(s) on GluA1 and GluA2 to which Talampanel binds is different from that on GluA3 and GluA4. If the molecular properties of the AMPA receptors and Talampanel are used for selecting an inhibitor as a single drug candidate for controlling the activity of all AMPA receptors in vivo, Talampanel is not ideal. Our results further suggest that addition of longer acyl groups to the N-3 position should produce more potent 2,3-benzodiazepine inhibitors for the "M" site.

Levodopa/benserazide microspheres reduced levodopa-induced dyskinesia by downregulating phosphorylated GluR1 expression in 6-OHDA-lesioned rats

Background

Levodopa is the gold standard in the treatment of Parkinson’s disease (PD). However, long-term levodopa replacement therapy is accompanied by abnormal involuntary movements (AIMs), known as levodopa-induced dyskinesia (LID). Until now, the precise mechanisms of LID were only partially understood. Previous studies have shown that continuous dopamine stimulation was helpful in reducing the expression of LID. In addition to dopamine D1 receptor, glutamatergic receptors such as α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor also contribute to the expression of LID. The current authors have previously reported that levodopa/benserazide-loaded microspheres could ameliorate the expression of LID by reducing the protein kinase A signaling pathway in dyskinetic rats. However, whether AMPA receptor is involved in the mechanism by which levodopa/benserazide-loaded microspheres ameliorate the expression of LID in dyskinetic rats was unknown.

Methods

In the present study, as reported previously, levodopa and benserazide were loaded by poly(lactic-co-glycolic acid) microspheres, which can release levodopa and benserazide in a sustained manner. 6-Hydroxydopamine was injected into the right medial forebrain bundle to produce a rat model of PD. Then valid PD rats were treated with levodopa plus benserazide for 3 weeks to induce a rat model of LID. Dyskinetic rats were treated with levodopa/beserazide-loaded microspheres containing levodopa (6 mg/kg) plus benserazide (15 mg/kg) or same dose of levodopa plus benserazide. Abnormal involuntary movements were measured in rats on days 1, 5, 10, 15, and 20 during the treatment. The levels of GluR1 at serine-831 (pGluR1S831) and serine-845 (pGluR1S845) were determined by Western blot. Arc and proenkephalin (Penk) levels were measured by real-time polymerase chain reaction.

Results

Three-week levodopa plus benserazide treatment induced dyskinesia in PD rats. Levodopa/benserazide-loaded microsphere-treated dyskinetic rats showed lower AIM scores than levodopa plus benserazide-treated dyskinetic rats. Microsphere treatment downregulated the phosphrylated levels of pGluR1S831 and pGluR1S845 in the striatum of dyskinetic rats. In addition, microsphere treatment reduced the levels of Arc and Penk.

Conclusion

These data indicated that levodopa/benserazide-loaded microspheres could be used to ameliorate the expression of LID by reducing the expression of pGluR1S831 and pGluR1S845 as well as Arc and Penk.

Cocaine-taking and cocaine-seeking behaviors in rats remain stable after systemic administration of GYKI 52466: a non-competitive AMPA receptor antagonist

Given the posited role of enhanced AMPA-mediated synaptic transmission in relapse to drug seeking, we investigated whether systemic administration of the AMPA receptor antagonist GYKI 52466 inhibits cocaine-taking and cocaine-seeking behavior in rats. Rats were trained to self-administer cocaine until stable self-administration was achieved. Effects of GYKI 52466 (1, 3, or 10mg/kg, i.v.) on cocaine self-administration were assessed. Animals were allowed to re-establish stable cocaine self-administration and were then behaviorally extinguished from drug taking. The effects of GYKI 52466 (3, 10mg/kg, i.v.) on cocaine-induced reinstatement of drug-seeking behavior were assessed. We found that GYKI 52466 failed to inhibit cocaine-taking and cocaine-seeking in both the self-administration and reinstatement paradigms. We suggest that although AMPA receptors may be involved in cocaine reward and addiction, the AMPA receptor antagonist GYKI 52466 has low therapeutic potential for cocaine addiction treatment.

Revisiting AMPA receptors as an antiepileptic drug target

In the 1990s there was intense interest in ionotropic glutamate receptors as therapeutic targets for diverse neurological disorders, including epilepsy. NMDA receptors were thought to play a key role in the generation of seizures, leading to clinical studies of NMDA receptor blocking drugs in epilepsy. Disappointing results dampened enthusiasm for ionotropic glutamate receptors as a therapeutic target. Eventually it became appreciated that another type of ionotropic glutamate receptor, the AMPA receptor, is actually the predominant mediator of excitatory neurotransmission in the central nervous system and moreover that AMPA receptors are critical to the generation and spread of epileptic activity. As drugs became available that selectively target AMPA receptors, it was possible to demonstrate that AMPA receptor antagonists have powerful antiseizure activity in in vitro and in vivo models. A decade later, promising clinical studies with AMPA receptor antagonists, including the potent noncompetitive antagonist perampanel, are once again focusing attention on AMPA receptors as a drug target for epilepsy therapy.

T-cell production of matrix metalloproteinases and inhibition of parasite clearance by TIMP-1 during chronic Toxoplasma infection in the brain

Chronic infection with the intracellular protozoan parasite Toxoplasma gondii leads to tissue remodelling in the brain and a continuous requirement for peripheral leucocyte migration within the CNS (central nervous system). In the present study, we investigate the role of MMPs (matrix metalloproteinases) and their inhibitors in T-cell migration into the infected brain. Increased expression of two key molecules, MMP-8 and MMP-10, along with their inhibitor, TIMP-1 (tissue inhibitor of metalloproteinases-1), was observed in the CNS following infection. Analysis of infiltrating lymphocytes demonstrated MMP-8 and -10 production by CD4+ and CD8+ T-cells. In addition, infiltrating T-cells and CNS resident astrocytes increased their expression of TIMP-1 following infection. TIMP-1-deficient mice had a decrease in perivascular accumulation of lymphocyte populations, yet an increase in the proportion of CD4+ T-cells that had trafficked into the CNS. This was accompanied by a reduction in parasite burden in the brain. Taken together, these findings demonstrate a role for MMPs and TIMP-1 in the trafficking of lymphocytes into the CNS during chronic infection in the brain.

Tumor necrosis factor alpha enhances glutamatergic transmission onto spinal motoneurons

The early stages of spinal cord injury (SCI) start with excitotoxic damage caused by a massive release of glutamate. However, glutamate release is not the only factor to consider. Inflammatory molecules like tumor necrosis factor alpha (TNFalpha), belonging to a group of cytokines initially identified and named for their ability to kill tumor cells, is also a key factor in neuronal death and inflammation. TNFalpha is released from macrophages and activated microglia following a SCI, reaching a peak 1 h after the primary injury. Motoneurons whose survival is necessary for successful rehabilitation are especially vulnerable to the effects of TNFalpha release. While TNFalpha has been postulated to increase glutamatergic synaptic transmission, evidence for this has been indirect. Here, we show using whole-cell recording from lumbar motoneurons that AMPA and NMDA receptor-mediated excitatory postsynaptic currents are rapidly increased following bath application of TNFalpha. Concurrently, the single-channel open probability of AMPA and NMDA channels were also augmented by TNFalpha. Overall, our data lead us to propose the idea that motoneuronal vulnerability to excitotoxicity is not only due to the excessive release of glutamate, but may also be attributable to the increased sensitivity of AMPARs and NMDARs to the proinflammatory factor, TNFalpha, released after SCI.

The AMPA receptor as a therapeutic target: current perspectives and emerging possibilities

The α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) is a subtype of the ionotropic glutamate receptors that plays a prominent role in neurotransmission and is widespread throughout the CNS. Because of this, its malfunction can result in a multitude of nervous system diseases. This review looks at compounds that are able to modulate AMPAR function by binding to one of several sites on the receptor that either downregulate its function (competitive, noncompetitive and uncompetitive antagonists) or upregulate its function (positive modulators). It will also give an account of the various diseases that have implicated AMPAR dysfunction and how specific types of AMPAR modulator may be beneficial in their treatment. The AMPAR remains an unexploited but important therapeutic target.

Glutamate responsiveness of medial vestibular nucleus neurons in aged rats

Disequilibrium, dizziness, vertigo and falls are vestibular system-related problems which are very common especially in older people. In order to clarify these age-related disorders one must understand first the age-related changes in the properties of vestibular neurons that are responsible for equilibrium. The responsiveness of medial vestibular nucleus (MVN) neurons to the NMDA and AMPA/kainate receptor agonists was investigated in slices prepared from young and aged rats using extracellular single cell recording techniques. In both young and aged rats bath application of NMDA and AMPA caused a reversible, dose-dependant increase in the spontaneous discharge of the MVN neurons. The excitatory effects of both NMDA and AMPA on the spontaneous activity of aged MVN neurons were similar to those of young MVN neurons. The spontaneous firing rates of the MVN cells were also similar in young and aged rats. These results suggest that the responsiveness of the NMDA and AMPA/kainate receptors and the excitability of the MVN neurons do not change with age.

Rosuvastatin induces delayed preconditioning against L-glutamate excitotoxicity in cultured cortical neurons

We tested whether rosuvastatin (RST) protected against excitotoxic neuronal cell death in rat primary cortical neuronal cultures. L-glutamate (200 microM, 1h) reduced neuronal viability (% of naive controls, mean+/-SEM, n=8-32, *p<0.05) from 100+/-2% to 60+/-1%*, but pretreatment with RST (0.5 microM, 3 days) increased survival to 88+/-2%*. RST-induced neuroprotection was not affected by co-application with mevalonate (10 microM), although the same dose of mevalonate fully prevented the neurotoxic effects of a high dose (20 microM) of RST. RST (0.5 microM) pretreatment did not affect mitochondrial membrane potential or superoxide anion levels in quiescent neurons. However, RST pretreatment blunted elevations in free intracellular Ca(2+) and reduced increases in superoxide anion levels following glutamate exposure. Manganese superoxide dismutase (SOD), copper-zinc SOD, catalase, and reduced glutathione levels were unaffected by RST pretreatment. In contrast, acute, one time RST application did not affect either baseline or L-glutamate-induced increases in superoxide levels. In summary, three-day RST pretreatment induces resistance to the excitotoxic effect of L-glutamate in cultured neurons apparently by a mechanism that is independent of 3-hydroxy-3-methyl-glutaryl-coenzyme A reductase inhibition. The delayed neuroprotection by RST against excitotoxicity does not involve sustained mitochondrial depolarization or superoxide anion production as initiating events, although it is associated with reduced Ca(2+) influx and superoxide anion production upon L-glutamate challenge.

Anticonvulsant and antioxidant effects of 3-alkynyl selenophene in 21-day-old rats on pilocarpine model of seizures

This study investigated the anticonvulsant effect of 3-alkynyl selenophene (3-ASP) on pilocarpine (PC)-, pentylenetetrazole (PTZ)- and kainic acid (KA)-induced seizures and mortality in 21-day-old rats. Rats were pretreated by oral route (p.o.) with 3-ASP (10, 25 and 50mg/kg) before intraperitoneal (i.p.) administration of PC (400mg/kg), PTZ (80 mg/kg) or KA (45 mg/kg). 3-ASP increased the latency to the seizure onset on PTZ and KA models. At the dose of 50mg/kg, 3-ASP avoided the death caused by PTZ and KA. 3-ASP (50mg/kg) abolished seizures and death induced by PC in rats. To investigate the antioxidant effect of 3-ASP on rats exposed to PC, the activity of glutathione peroxidase (GPx), glutathione-S-transferase (GST), acetylcholinesterase (AChE), Na(+)K(+)ATPase, superoxide dismutase (SOD) and catalase (CAT) as well as the levels of reactive species (RS) and ascorbic acid (AA) were determined in brains of rats. 3-ASP protected against the increase in RS levels and CAT activity induced by PC in brains of rats. The decrease in the levels of AA and inhibition of Na(+)K(+)ATPase, SOD and AChE activities caused by PC were protected by 3-ASP. Subeffective doses of 3-ASP plus diazepam, 5S,10R-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate (MK-801) or 6,7-dinitroquinoxaline-2,3-dione (DNQX) increased the latency to the seizure onset induced by PC, suggesting the involvement of ionotropic glutamatergic and GABAergic receptors in anticonvulsant action of 3-ASP. The anticonvulsant and antioxidant effects of 3-ASP in 21-day-old rats on PC model were demonstrated.