Neuroprotective effect of the 3α5β-pregnanolone glutamate treatment in the model of focal cerebral ischemia in immature rats

Phenoxytacrine derivatives: Low-toxicity neuroprotectants exerting affinity to ifenprodil-binding site and cholinesterase inhibition

Tacrine (THA), a long withdrawn drug, is still a popular scaffold used in medicinal chemistry, mainly for its good reactivity and multi-targeted effect. However, THA-associated hepatotoxicity is still an issue and must be considered in drug discovery based on the THA scaffold. Following our previously identified hit compound 7-phenoxytacrine (7-PhO-THA), we systematically explored the chemical space with 30 novel derivatives, with a focus on low hepatotoxicity, anticholinesterase action, and antagonism at the GluN1/GluN2B subtype of the NMDA receptor. Applying the down-selection process based on in vitro and in vivo pharmacokinetic data, two candidates, I-52 and II-52, selective GluN1/GluN2B inhibitors thanks to the interaction with the ifenprodil-binding site, have entered in vivo pharmacodynamic studies. Finally, compound I-52, showing only minor affinity to AChE, was identified as a lead candidate with favorable behavioral and neuroprotective effects using open-field and prepulse inhibition tests, along with scopolamine-based behavioral and NMDA-induced hippocampal lesion models. Our data show that compound I-52 exhibits low toxicity often associated with NMDA receptor ligands, and low hepatotoxicity, often related to THA-based compounds.

Novel neurosteroid pregnanolone pyroglutamate suppresses neurotoxicity syndrome induced by tetramethylenedisulfotetramine but is ineffective in a rodent model of infantile spasms

BACKGROUND

Neurosteroids are investigated as effective antidotes for the poisoning induced by tetramethylenedisulfotetramine (TMDT) as well as treatments for epileptic spasms during infancy. Both these conditions are quite resistant to pharmacotherapy; thus, a search for new treatments is warranted.

METHODS

In this study, we determined the efficacy of two novel neurosteroids, pregnanolone glutamate (PAG) and pregnanolone pyroglutamate (PPG), and tested these drugs in doses of 1-10 mg/kg (ip) against the TMDT syndrome and in our rodent model of infantile spasms.

RESULTS

Only PPG in doses 5 and 10 mg/kg suppressed the severity of the TMDT syndrome and TMDT-induced lethality, while the 1 mg/kg dose was without an effect. Interestingly, the 1 mg/kg dose of PPG in combination with 1 mg/kg of diazepam was also effective against TMDT poisoning. Neither PAG nor PPG were effective against experimental spasms in the N-methyl-D-aspartate (NMDA)-triggered model of infantile spasms.

CONCLUSIONS

While evidence suggests that PAG can act through multiple actions which include allosteric inhibition of NMDA-induced and glycine receptor-evoked currents as well as augmentation of ɣ-aminobutyric acid subtype A (GABAA) receptor-induced currents, the agent appears to neither have the appropriate mechanistic signature for activity in the infantile spasm model, nor the adequate potency, relative to PPG, for ameliorating the TMDT syndrome. The full mechanisms of action of PPG, which may become a potent TMDT antidote either alone or in combination with diazepam are yet unknown and thus require further investigation.

Neonatal Arterial Ischaemic Stroke: Advances in Pathologic Neural Death, Diagnosis, Treatment, and Prognosis

Neonatal arterial ischaemic stroke (NAIS) is caused by focal arterial occlusion and often leads to severe neurological sequelae. Neural deaths after NAIS mainly include necrosis, apoptosis, necroptosis, autophagy, ferroptosis, and pyroptosis. These neural deaths are mainly caused by upstream stimulations, including excitotoxicity, oxidative stress, inflammation, and death receptor pathways. The current clinical approaches to managing NAIS mainly focus on supportive treatments, including seizure control and anticoagulation. In recent years, research on the pathology, early diagnosis, and potential therapeutic targets of NAIS has progressed. In this review, we summarise the latest progress of research on the pathology, diagnosis, treatment, and prognosis of NAIS and highlight newly potential diagnostic and treatment approaches.

Identification of N-methyl-D-aspartate receptor antagonists using the rat postnatal mixed cortical and hippocampal neurons

The goal of this study was to evaluate mixed cortical and hippocampal primary rat postnatal neuronal culture as in vitro tool for identification of N-methyl-D-aspartate receptor (NMDAR) antagonists and to find out, whether this model is comparable with other commonly used primary rat neuronal models differing in their origin (pure cortical vs. mixed cortical and hippocampal) and differentiation state (embryonal vs. postnatal). Induced pluripotent stem cell (iPSC) - derived human glutamatergic neurons have been included in this study as well. First, the cultures were characterized by their neuron/astrocyte composition, the mRNA expression of NR2B/NR2A NMDAR subunit ratios, and the expression of glutamate transporters (GLT1, GLAST). Then, selected endogenous steroids and synthetic neuroactive steroids that have been previously identified as negative allosteric modulators of recombinant GluN1/GluN2B NMDA receptors, were evaluated for their ability to prevent an NMDA or glutamate-induced Ca²⁺ influx (acute effect) and excitotoxicity over 24 h. Though the neuroprotective potential against excitotoxic stimuli varied among the models studied, postnatal mixed cortical and hippocampal culture proved to be a convenient and robust tool for NMDAR antagonist screening. The most widely used embryonal (E18) cultures offered higher cell yields but at the expense of a higher sensitivity to compounds' cytotoxicity. iPSC-derived neurons were not found to be superior to rat cultures for screening purposes.

The Neuroactive Steroid Pregnanolone Glutamate: Anticonvulsant Effect, Metabolites and Its Effect on Neurosteroid Levels in Developing Rat Brains

Pregnanolone glutamate (PA-G) is a neuroactive steroid that has been previously demonstrated to be a potent neuroprotective compound in several biological models in vivo. Our in vitro experiments identified PA-G as an inhibitor of N-methyl-D-aspartate receptors and a potentiator of γ-aminobutyric acid receptors (GABA_ARs). In this study, we addressed the hypothesis that combined GABA_AR potentiation and NMDAR antagonism could afford a potent anticonvulsant effect. Our results demonstrated the strong age-related anticonvulsive effect of PA-G in a model of pentylenetetrazol-induced seizures. PA-G significantly decreased seizure severity in 12-day-old animals, but only after the highest dose in 25-day-old animals. Interestingly, the anticonvulsant effect of PA-G differed both qualitatively and quantitatively from that of zuranolone, an investigational neurosteroid acting as a potent positive allosteric modulator of GABA_ARs. Next, we identified 17-hydroxy-pregnanolone (17-OH-PA) as a major metabolite of PA-G in 12-day-old animals. Finally, the administration of PA-G demonstrated direct modulation of unexpected neurosteroid levels, namely pregnenolone and dehydroepiandrosterone sulfate. These results suggest that compound PA-G might be a pro-drug of 17-OH-PA, a neurosteroid with a promising neuroprotective effect with an unknown mechanism of action that may represent an attractive target for studying perinatal neural diseases.

Rapid effects of neurosteroids on neuronal plasticity and their physiological and pathological implications

Current neuroscience research on neurosteroids and their synthetic analogues - neuroactive steroids - clearly demonstrate their drug likeness in a variety of neurological and psychiatric conditions. Moreover, research on neurosteroids continues to provide novel mechanistic insights into receptor activation or inhibition of various receptors. This mini-review will provide a high-level overview of the research area and discuss the various classes of potential physiological and pathological implications discovered so far.

7-phenoxytacrine is a dually acting drug with neuroprotective efficacy in vivo

N-methyl-D-aspartaterecepro receptor (NMDARs) are a subclass of glutamate receptors, which play an essential role in excitatory neurotransmission, but their excessive overactivation by glutamate leads to excitotoxicity. NMDARs are hence a valid pharmacological target for the treatment of neurodegenerative disorders; however, novel drugs targeting NMDARs are often associated with specific psychotic side effects and abuse potential. Motivated by currently available treatment against neurodegenerative diseases involving the inhibitors of acetylcholinesterase (AChE) and NMDARs, administered also in combination, we developed a dually-acting compound 7-phenoxytacrine (7-PhO-THA) and evaluated its neuropsychopharmacological and drug-like properties for potential therapeutic use. Indeed, we have confirmed the dual potency of 7-PhO-THA, i.e. potent and balanced inhibition of both AChE and NMDARs. We discovered that it selectively inhibits the GluN1/GluN2B subtype of NMDARs via an ifenprodil-binding site, in addition to its voltage-dependent inhibitory effect at both GluN1/GluN2A and GluN1/GluN2B subtypes of NMDARs. Furthermore, whereas NMDA-induced lesion of the dorsal hippocampus confirmed potent anti-excitotoxic and neuroprotective efficacy, behavioral observations showed also a cholinergic component manifesting mainly in decreased hyperlocomotion. From the point of view of behavioral side effects, 7-PhO-THA managed to avoid these, notably those analogous to symptoms of schizophrenia. Thus, CNS availability and the overall behavioral profile are promising for subsequent investigation of therapeutic use.

Combination of Memantine and 6-Chlorotacrine as Novel Multi-Target Compound against Alzheimer's Disease

BACKGROUND

Alzheimer's disease (AD) is the most common form of dementia in the elderly. It is characterized as a multi-factorial disorder with a prevalent genetic component. Due to the unknown etiology, current treatment based on acetylcholinesterase (AChE) inhibitors and N-methyl-D-aspartate receptors (NMDAR) antagonist is effective only temporary. It seems that curative treatment will necessarily be complex due to the multifactorial nature of the disease. In this context, the so-called "multi-targeting" approach has been established.

OBJECTIVES

The aim of this study was to develop a multi-target-directed ligand (MTDL) combining the support for the cholinergic system by inhibition of AChE and at the same time ameliorating the burden caused by glutamate excitotoxicity mediated by the NMDAR receptors.

METHODS

We have applied common approaches of organic chemistry to prepare a hybrid of 6-chlorotacrine and memantine. Then, we investigated its blocking ability towards AChE and NMDRS in vitro, as well as its neuroprotective efficacy in vivo in the model of NMDA-induced lessions. We also studied cytotoxic potential of the compound and predicted the ability to cross the blood-brain barrier.

RESULTS

A novel molecule formed by combination of 6-chlorotacrine and memantine proved to be a promising multipotent hybrid capable of blocking the action of AChE as well as NMDARs. The presented hybrid surpassed the AChE inhibitory activity of the parent compound 6-Cl-THA twofold. According to results it has been revealed that our novel hybrid blocks NMDARs in the same manner as memantine, potently inhibits AChE and is predicted to cross the blood-brain barrier via passive diffusion. Finally, the MTDL design strategy was indicated by in vivo results which showed that the novel 6-Cl-THA-memantine hybrid displayed a quantitatively better neuroprotective effect than the parent compound memantine.

CONCLUSION

We conclude that the combination of two pharmacophores with a synergistic mechanism of action into a single molecule offers great potential for the treatment of CNS disorders associated with cognitive decline and/or excitotoxicity mediated by NMDARs.

Synthetic structural modifications of neurosteroid pregnanolone sulfate: Assessment of neuroprotective effects in vivo

Neuroactive steroid 20-oxo-5β-pregnan-3α-yl L-glutamyl 1-ester (PA-Glu), a synthetic analogue of naturally occurring 20-oxo-5β-pregnan-3α-yl sulfate (pregnanolone sulfate, PA-S), inhibits N-methyl-D-aspartate (NMDA) receptors and possesses neuroprotective properties and minimal adverse effects. Herein, we report in vivo effects of new structural modifications of the PA-S molecule: a nonpolar modification of the steroid D-ring (5β-androstan-3α-yl L-glutamyl 1-ester, AND-Glu), attachment of a positively charged group to C3 (20-oxo-5β-pregnan-3α-yl L-argininate dihydrochloride salt, PA-Arg) and their combination (5β-androstan-3α-yl L-argininate dihydrochloride salt, AND-Arg). The first aim of this study was to determine the structure-activity relationship for neuroprotective effects in a model of excitotoxic hippocampal damage in rats, based on its behavioral correlate in Carousel maze. The second aim was to explore side effects of neuroprotective steroids on motor functions, anxiety (elevated plus maze) and locomotor activity (open field) and the effect of their high doses in mice. The neuroprotective properties of PA-Glu and AND-Glu were proven, with the effect of the latter appearing to be more pronounced. In contrast, neuroprotective efficacy failed when positively charged molecules (PA-Arg, AND-Arg) were used. AND-Glu and PA-Glu at the neuroprotective dose (1 mg/kg) did not unfavorably influence motor functions of intact mice. Moreover, anxiolytic effects of AND-Glu and PA-Glu were ascertained. These findings corroborate the value of research of steroidal inhibitors of NMDA receptors as potential neuroprotectants with slight anxiolytic effect and devoid of behavioral adverse effects. Taken together, the results suggest the benefit of the nonpolar D-ring modification, but not of the attachment of a positively charged group to C3.

Screening of novel 3α5β-neurosteroids for neuroprotective activity against glutamate- or NMDA-induced excitotoxicity

A broad variety of central nervous system diseases have been associated with glutamate induced excitotoxicity under pathological conditions. The neuroprotective effects of neurosteroids can combat this excitotoxicity. Herein, we have demonstrated the neuroprotective effect of novel steroidal N-methyl-D-aspartate receptor inhibitors against glutamate- or NMDA- induced excitotoxicity. Pretreatment with neurosteroids significantly reduced acute L-glutamic acid or NMDA excitotoxicity mediated by Ca²⁺ entry and consequent ROS (reactive oxygen species) release and caspase-3 activation. Compounds 6 (IC₅₀ = 5.8 μM), 7 (IC₅₀ = 12.2 μM), 9 (IC₅₀ = 7.8 μM), 13 (IC₅₀ = 1.1 μM) and 16 (IC₅₀ = 8.2 μM) attenuated glutamate-induced Ca²⁺ entry more effectively than memantine (IC₅₀ = 18.9 μM). Moreover, compound 13 shows comparable effect with MK-801 (IC₅₀ = 1.2 μM) and also afforded significant protection without any adverse effect upon prolonged exposure. This drop in Ca²⁺ level resulted in corresponding ROS suppression and prevented glutamate-induced caspase-3 activation. Therefore, compound 13 has great potential for development into a therapeutic agent for improving glutamate-related nervous system diseases.

Repurposing of the β-Lactam Antibiotic, Ceftriaxone for Neurological Disorders: A Review

To date, there is no cure or disease-modifying agents available for most well-known neurological disorders. Current therapy is typically focused on relieving symptoms and supportive care in improving the quality of life of affected patients. Furthermore, the traditional de novo drug discovery technique is more challenging, particularly for neurological disorders. Therefore, the repurposing of existing drugs for these conditions is believed to be an efficient and dynamic approach that can substantially reduce the investments spent on drug development. Currently, there is emerging evidence that suggests the potential effect of a beta-lactam antibiotic, ceftriaxone (CEF), to alleviate the symptoms of different experimentally-induced neurological disorders: Parkinson's disease, Alzheimer's disease, amyotrophic lateral sclerosis, epileptic-seizure, brain ischemia, traumatic brain injuries, and neuropathic pain. CEF also affects the markers of oxidative status and neuroinflammation, glutamatergic systems as well as various aggregated toxic proteins involved in the pathogenesis of different neurological disorders. Moreover, it was found that CEF administration to drug dependent animal models improved the withdrawal symptoms upon drug discontinuation. Thus, this review aimed to describe the effects of CEF against multiple models of neurological illnesses, drug dependency, and withdrawal. It also emphasizes the possible mechanisms of neuroprotective actions of CEF with respective neurological maladies.

Strong Inhibitory Effect, Low Cytotoxicity and High Plasma Stability of Steroidal Inhibitors of N-Methyl-D-Aspartate Receptors With C-3 Amide Structural Motif

Herein, we report the synthesis, structure-activity relationship study, and biological evaluation of neurosteroid inhibitors of N-methyl-D-aspartate receptors (NMDARs) receptors that employ an amide structural motif, relative to pregnanolone glutamate (PAG) – a compound with neuroprotective properties. All compounds were found to be more potent NMDAR inhibitors (IC₅₀ values varying from 1.4 to 21.7 μM) than PAG (IC₅₀ = 51.7 μM). Selected compound 6 was evaluated for its NMDAR subtype selectivity and its ability to inhibit AMPAR/GABAR responses. Compound 6 inhibits the NMDARs (8.3 receptors (8.3 ± 2.1 μM) more strongly than it does at the GABAR and AMPARs (17.0 receptors (17.0 ± 0.2 μM and 276.4 ± 178.7 μM, respectively). In addition, compound 6 (10 μM) decreases the frequency of action potentials recorded in cultured hippocampal neurons. Next, compounds 3, 5–7, 9, and 10 were not associated with mitotoxicity, hepatotoxicity nor ROS induction. Lastly, we were able to show that all compounds have improved rat and human plasma stability over PAG.

Modulation of GABA and glycine receptors in rat pyramidal hippocampal neurones by 3α5β-pregnanolone derivatives

The ability of pregnanolone glutamate (PA-Glu), pregnanolone hemisuccinate (PA-hSuc) and pregnanolone hemipimelate (PA-hPim), neuroactive steroids with a negative modulatory effect on excitatory N-methyl-d-aspartate receptors, to influence the functional activity of inhibitory γ-aminobutyric acid and glycine receptors was estimated. The GABA- and glycine-induced chloride currents (I_GABA and I_Gly) were measured in isolated pyramidal neurons of the rat hippocampus using the patch-clamp technique. Compound PA-Glu was found to potentiate I_GABA and to inhibit I_Gly, while PA-hSuc and PA-hPim inhibited both I_GABA and I_Gly. Moreover, PA-Glu, PA-hSuc, and PA-hPim had a greater effect on desensitization than on the peak amplitude of I_Gly. At a high concentration of glycine (500 μM), the effect of neurosteroids on the peak amplitude of I_Gly disappeared, and the acceleration of desensitization remained. The conversion of PA-Glu into androstane glutamate (AND-Glu), an analogue that lacks the C-17 acetyl moiety, completely eliminated the effects on these receptors. Our results indicate that the C-17 acetyl moiety is crucial for the action on I_GABA and I_Gly. Our results indicate that the pregnanolone derivatives, in contrast to the androstane analogues, modulate I_GABA and I_Gly at low micromolar concentrations and this family of neurosteroids can be useful for future structure-activity relationship studies of the steroid modulation of other receptor types.

Calcium-engaged Mechanisms of Nongenomic Action of Neurosteroids

BACKGROUND

Neurosteroids form the unique group because of their dual mechanism of action. Classically, they bind to specific intracellular and/or nuclear receptors, and next modify genes transcription. Another mode of action is linked with the rapid effects induced at the plasma membrane level within seconds or milliseconds. The key molecules in neurotransmission are calcium ions, thereby we focus on the recent advances in understanding of complex signaling crosstalk between action of neurosteroids and calcium-engaged events.

METHODS

Short-time effects of neurosteroids action have been reviewed for GABAA receptor complex, glycine receptor, NMDA receptor, AMPA receptor, G protein-coupled receptors and sigma-1 receptor, as well as for several membrane ion channels and plasma membrane enzymes, based on available published research.

RESULTS

The physiological relevance of neurosteroids results from the fact that they can be synthesized and accumulated in the central nervous system, independently from peripheral sources. Fast action of neurosteroids is a prerequisite for genomic effects and these early events can significantly modify intracellular downstream signaling pathways. Since they may exert either positive or negative effects on calcium homeostasis, their role in monitoring of spatio-temporal Ca2+ dynamics, and subsequently, Ca2+-dependent physiological processes or initiation of pathological events, is evident.

CONCLUSION

Neurosteroids and calcium appear to be the integrated elements of signaling systems in neuronal cells under physiological and pathological conditions. A better understanding of cellular and molecular mechanisms of nongenomic, calcium-engaged neurosteroids action could open new ways for therapeutic interventions aimed to restore neuronal function in many neurological and psychiatric diseases.

Physicochemical and biological properties of novel amide-based steroidal inhibitors of NMDA receptors

Herein, we report a new class of amide-based inhibitors (1-4) of N-methyl-d-aspartate receptors (NMDARs) that were prepared as analogues of pregnanolone sulfate (PAS) and pregnanolone glutamate (PAG) - the steroidal neuroprotective NMDAR inhibitors. A series of experiments were conducted to evaluate their physicochemical and biological properties: (i) the inhibitory effect of compounds 3 and 4 on NMDARs was significantly improved (IC₅₀=1.0 and 1.4μM, respectively) as compared with endogenous inhibitor - pregnanolone sulfate (IC₅₀=24.6μM) and pregnanolone glutamate (IC₅₀=51.7μM); (ii) physicochemical properties (logP and logD) were calculated; (iii) Caco-2 assay revealed that the permeability properties of compounds 2 and 4 are comparable with pregnanolone glutamate; (iv) compounds 1-4 have minimal or no adverse hepatic effect; (v) compounds 1-4 cross blood-brain-barrier.

Ischemic postconditioning protects against ischemic brain injury by up-regulation of acid-sensing ion channel 2a

Ischemic postconditioning renders brain tissue tolerant to brain ischemia, thereby alleviating ischemic brain injury. However, the exact mechanism of action is still unclear. In this study, a rat model of global brain ischemia was subjected to ischemic postconditioning treatment using the vessel occlusion method. After 2 hours of ischemia, the bilateral common carotid arteries were blocked immediately for 10 seconds and then perfused for 10 seconds. This procedure was repeated six times. Ischemic postconditioning was found to mitigate hippocampal CA1 neuronal damage in rats with brain ischemia, and up-regulate acid-sensing ion channel 2a expression at the mRNA and protein level. These findings suggest that ischemic postconditioning up-regulates acid-sensing ion channel 2a expression in the rat hippocampus after global brain ischemia, which promotes neuronal tolerance to ischemic brain injury.

Attention-Deficit/Hyperactivity Disorder: Focus upon Aberrant N-Methyl-D-Aspartate Receptors Systems

Attention-deficit/hyperactivity disorder (ADHD) pathophysiology persists in an obscure manner with complex interactions between symptoms, staging, interventions, genes, and environments. Only on the basis of increasing incidence of the disorder, the need for understanding is greater than ever. The notion of an imbalance between central inhibitory/excitatory neurotransmitters is considered to exert an essential role. In this chapter, we first review how the default mode network functions and dysfunction in individuals diagnosed with ADHD. We also present and briefly review some of the animal models used to examine the neurobiological aspects of ADHD. There is much evidence indicating that compounds/interventions that antagonize/block glutamic acid receptors and/or block the glutamate signal during the "brain growth spurt" or in the adult animal may induce functional and biomarker deficits. Additionally, we present evidence suggesting that animals treated with glutamate blockers at the period of the "brain growth spurt" fail to perform the exploratory activity, observed invariably with control mice, that is associated with introduction to a novel environment (the test cages). Later, when the control animals show less locomotor and rearing activity, i.e., interest in the test cages, the MK-801, ketamine and ethanol treated mice showed successively greater levels of locomotion and rearing (interest), i.e., they fail to "habituate" effectively, implying a cognitive dysfunction. These disturbances of glutamate signaling during a critical period of brain development may contribute to the ADHD pathophysiology. As a final addition, we have briefly identified new research venues in the interaction between ADHD, molecular studies, and personality research.

GLT-1 transporter: an effective pharmacological target for various neurological disorders

L-Glutamate is the predominant excitatory neurotransmitter in the central nervous system (CNS) and is directly and indirectly involved in a variety of brain functions. Glutamate is released in the synaptic cleft at a particular concentration that further activates the various glutaminergic receptors. This concentration of glutamate in the synapse is maintained by either glutamine synthetase or excitatory amino acid proteins which reuptake the excessive glutamate from the synapse and named as excitatory amino acid transporters (EAATs). Out of all the subtypes GLT-1 (glutamate transporter 1) is abundantly distributed in the CNS. Down-regulation of GLT-1 is reported in various neurological diseases such as, epilepsy, stroke, Alzheimer's disease and movement disorders. Therefore, positive modulators of GLT-1 which up-regulate the GLT-1 expression can serve as a potential target for the treatment of neurological disorders. GLT-1 translational activators such as ceftriaxone are found to have significant protective effects in ALS and epilepsy animal models, suggesting that this translational activation approach works well in rodents and that these compounds are worth further pursuit for various neurological disorders. This drug is currently in human clinical trials for ALS. In addition, a thorough understanding of the mechanisms underlying translational regulation of GLT-1, such as identifying the molecular targets of the compounds, signaling pathways involved in the regulation, and translational activation processes, is very important for this novel drug-development effort. This review mainly emphasizes the role of glutamate and its transporter, GLT-1 subtype in excitotoxicity. Further, recent reports on GLT-1 transporters for the treatment of various neurological diseases, including a summary of the presumed physiologic mechanisms behind the pharmacology of these disorders are also explained.