Preferential Inhibition of Tonically over Phasically Activated NMDA Receptors by Pregnane Derivatives.

Postsynaptic N-methyl-d-aspartate receptors (NMDARs) phasically activated by presynaptically released glutamate are critical for synaptic transmission and plasticity. However, under pathological conditions, excessive activation of NMDARs by tonically increased ambient glutamate contributes to excitotoxicity associated with various acute and chronic neurological disorders. Here, using heterologously expressed GluN1/GluN2A and GluN1/GluN2B receptors and rat autaptic hippocampal microisland cultures, we show that pregnanolone sulfate inhibits NMDAR currents induced by a prolonged glutamate application with a higher potency than the NMDAR component of EPSCs. For synthetic pregnanolone derivatives substituted with a carboxylic acid moiety at the end of an aliphatic chain of varying length and attached to the steroid skeleton at C3, the difference in potency between tonic and phasic inhibition increased with the length of the residue. The steroid with the longest substituent, pregnanolone hemipimelate, had no effect on phasically activated receptors while inhibiting tonically activated receptors. In behavioral tests, pregnanolone hemipimelate showed neuroprotective activity without psychomimetic symptoms. These results provide insight into the influence of steroids on neuronal function and stress their potential use in the development of novel therapeutics with neuroprotective action. SIGNIFICANCE STATEMENT: Synaptic activation of N-methyl-d-aspartate receptors (NMDARs) plays a key role in synaptic plasticity, but excessive tonic NMDAR activation mediates excitotoxicity associated with many neurological disorders. Therefore, there is much interest in pharmacological agents capable of selectively blocking tonically activated NMDARs while leaving synaptically activated NMDARs intact. Here, we show that an endogenous neurosteroid pregnanolone sulfate is more potent at inhibiting tonically than synaptically activated NMDARs. Further, we report that a novel synthetic analog of pregnanolone sulfate, pregnanolone hemipimelate, inhibits tonic NMDAR currents without inhibiting the NMDAR component of the EPSC and shows neuroprotective activity in vivo without inducing psychomimetic side effects. These results suggest steroids may have a clinical advantage over other known classes of NMDAR inhibitors.

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.

Review: Genes Involved in Mitochondrial Physiology Within 22q11.2 Deleted Region and Their Relevance to Schizophrenia.

BACKGROUND AND HYPOTHESIS: Schizophrenia is associated with altered energy metabolism, but the cause and potential impact of these metabolic changes remain unknown. 22q11.2 deletion syndrome (22q11.2DS) represents a genetic risk factor for schizophrenia, which is associated with the loss of several genes involved in mitochondrial physiology. Here we examine how the haploinsufficiency of these genes could contribute to the emergence of schizophrenia in 22q11.2DS. STUDY DESIGN: We characterize changes in neuronal mitochondrial function caused by haploinsufficiency of mitochondria-associated genes within the 22q11.2 region (PRODH, MRPL40, TANGO2, ZDHHC8, SLC25A1, TXNRD2, UFD1, and DGCR8). For that purpose, we combine data from 22q11.2DS carriers and schizophrenia patients, in vivo (animal models) and in vitro (induced pluripotent stem cells, IPSCs) studies. We also review the current knowledge about seven non-coding microRNA molecules located in the 22q11.2 region that may be indirectly involved in energy metabolism by acting as regulatory factors. STUDY RESULTS: We found that the haploinsufficiency of genes of interest is mainly associated with increased oxidative stress, altered energy metabolism, and calcium homeostasis in animal models. Studies on IPSCs from 22q11.2DS carriers corroborate findings of deficits in the brain energy metabolism, implying a causal role between impaired mitochondrial function and the development of schizophrenia in 22q11.2DS. CONCLUSIONS: The haploinsufficiency of genes within the 22q11.2 region leads to multifaceted mitochondrial dysfunction with consequences to neuronal function, viability, and wiring. Overlap between in vitro and in vivo studies implies a causal role between impaired mitochondrial function and the development of schizophrenia in 22q11.2DS.

Glycolytic and Krebs cycle enzymes activity in rat prefrontal cortex, hippocampus, and striatum after single and repeated NMDA inhibition by MK-801.

Psychosis is a state of altered thoughts which often accompanies schizophrenia. It was suggested that changes in energetic metabolism accompany psychosis and post-psychosis states. Here, we use the N-methyl-D-aspartate (NMDA) receptor antagonist MK-801 to experimentally induce psychosis-like behavior in rats. We addressed an effect of single and repeated (5×) MK-801 application (0.3 mg/kg; i.p.) on the energy metabolism in homogenates and crude mitochondrial fraction (CMF) of the striatum (STR), prefrontal cortex (PFC), and the hippocampus (HIP) of the adult male Wistar rat (n = 39). In each brain region, we assessed activity of glycolytic (hexokinase (HK) and lactate dehydrogenase (LDH)) and Krebs cycle enzymes (citrate synthase (CS) and malate dehydrogenase (MDH)) 2 h and 3 days (3d) after the last MK-801 application together with relative respiratory rates assessment in tissue homogenate. In STR, a single MK-801 application led to a decrease in the LDH (p = 0.0035) and the increase of the MDH (p = 0.0043) activities following 3d. Therein, repeated MK-801 doses evoked increased LDH (p = 0.0204) and CS (p = 0.0019) activities in the homogenate 2 h and increased HK (p = 0.0007) 3d after the last application. Elevated HK activity within CMF was observed after 3d (p = 0.0054). In PFC, repeated MK-801 application decreased HK activity in the homogenate 3d after the final application (p = 0.0234). Correspondingly, PFC HK activity in CMF of repeated administration samples dropped (p = 0.003). In HIP, repeated MK-801 administration led to increased respiration of SDH (p = 0.0475) only 2 h after the last application and decreased CS activity (p = 0.0160) was observed 3d after the last application. Our results indicate a progressive metabolic dysregulation of glycolytic and Krebs cycle enzymes following repeated inhibition of NMDA receptors activity in a region-specific manner. Energetic alterations may form a basis for persisting cognitive problems during and following a psychosis in schizophrenia patients.

Mini-review: Brain energy metabolism and its role in animal models of depression, bipolar disorder, schizophrenia and autism.

Mitochondria are cellular organelles essential for energy metabolism and antioxidant defense. Mitochondrial impairment is implicated in many psychiatric disorders, including depression, bipolar disorder, schizophrenia, and autism. To characterize and eventually find effective treatments of bioenergetic impairment in psychiatric disease, researchers find animal models indispensable. The present review focuses on brain energetics in several environmental, genetic, drug-induced, and surgery-induced animal models of depression, bipolar disorder, schizophrenia, and autism. Most reported deficits included decreased activity in the electron transport chain, increased oxidative damage, decreased antioxidant defense, decreased ATP levels, and decreased mitochondrial potential. Models of depression, bipolar disorder, schizophrenia, and autism shared many bioenergetic deficits. This is in concordance with the absence of a disease-specific brain energy phenotype in human patients. Unfortunately, due to the absence of null results in examined literature, indicative of reporting bias, we refrain from making generalized conclusions. Present review can be a valuable tool for comparing current findings, generating more targeted hypotheses, and selecting fitting models for further preclinical research.

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.

Effects of adipokinetic hormone/red pigment-concentrating hormone family of peptides in olfactory bulbectomy model and posttraumatic stress disorder model of rats.

One of the major neuropeptide groups in insects is adipokinetic hormone/red pigment-concentrating hormone (AKH/RPCH) family of peptides. AKH had improving effects on depression and anxiety in animal models and it may be a new treatment choice in these disorders. Aim of this study was to investigate effects of Anax imperator AKH (Ani-AKH), Libellula auripennis AKH (Lia-AKH) and Phormia-Terra hypertrehalosemic hormone (Pht-HrTH) on animal behavior in olfactory bulbectomy (OBX) model and in posttraumatic stress disorder (PTSD) model of Wistar-albino rats. Lia-AKH and Pht-HrTH significantly increased time spent in escape platform's quadrant compared to sham control while Lia-AKH significantly increased time spent in escape platform's quadrant compared to OBX controls in probe trial of Morris water maze (MWM). Ani-AKH, Lia-AKH and Pht-HrTH significantly decreased immobility time compared to OBX controls in forced swimming test (FST). Pht-HrTH significantly increased %open arm time compared to OBX controls in elevated plus maze (EPM) test. Ani-AKH significantly increased %open arm entry compared to sham control while Ani-AKH and Pht-HrTH significantly increased %open arm entry compared to OBX controls in EPM. In PTSD study Ani-AKH and Lia-AKH significantly decreased immobility time compared to traumatized controls in FST. In acoustic startle reflex test, Ani-AKH, Lia-AKH and Pht-HrTH significantly decreased average startle amplitude compared to non-traumatized controls in PTSD study. Metabolomic studies showed that AKH may affect glutamatergic and dopaminergic system and neurochemistry. In conclusion, AKH peptides had wide ranging effects on behavior and improved performance in OBX and PTSD models in rats.

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.

Novel tacrine-tryptophan hybrids: Multi-target directed ligands as potential treatment for Alzheimer's disease.

A combination of tacrine and tryptophan led to the development of a new family of heterodimers as multi-target agents with potential to treat Alzheimer's disease. Based on the in vitro biological profile, compound S-K1035 was found to be the most potent inhibitor of human acetylcholinesterase (hAChE) and human butyrylcholinesterase (hBChE), demonstrating balanced IC50 values of 6.3 and 9.1 nM, respectively. For all the tacrine-tryptophan heterodimers, favorable inhibitory effect on hAChE as well as on hBChE was coined to the optimal spacer length ranging from five to eight carbon atoms between these two pharmacophores. S-K1035 also showed good ability to inhibit Aß42 self-aggregation (58.6 ±â€¯5.1% at 50 µM) as well as hAChE-induced Aß40 aggregation (48.3 ±â€¯6.3% at 100 µM). The X-ray crystallographic analysis of TcAChE in complex with S-K1035 pinpointed the utility of the hybridization strategy applied and the structures determined with the two K1035 enantiomers in complex with hBChE could explain the higher inhibition potency of S-K1035. Other in vitro evaluations predicted the ability of S-K1035 to cross blood-brain barrier and to exert a moderate inhibition potency against neuronal nitric oxide synthase. Based on the initial promising biochemical data and a safer in vivo toxicity compared to tacrine, S-K1035 was administered to scopolamine-treated rats being able to dose-dependently revert amnesia.

7-Methoxyderivative of tacrine is a 'foot-in-the-door' open-channel blocker of GluN1/GluN2 and GluN1/GluN3 NMDA receptors with neuroprotective activity in vivo.

N-methyl-d-aspartate receptors (NMDARs) are ionotropic glutamate receptors that mediate excitatory neurotransmission in the mammalian central nervous system (CNS), and their dysregulation results in the aetiology of many CNS syndromes. Several NMDAR modulators have been used successfully in clinical trials (including memantine) and NMDARs remain a promising pharmacological target for the treatment of CNS syndromes. 1,2,3,4-Tetrahydro-9-aminoacridine (tacrine; THA) was the first approved drug for Alzheimer's disease (AD) treatment. 7-methoxyderivative of THA (7-MEOTA) is less toxic and showed promising results in patients with tardive dyskinesia. We employed electrophysiological recordings in HEK293 cells and rat neurones to examine the mechanism of action of THA and 7-MEOTA at the NMDAR. We showed that both THA and 7-MEOTA are "foot-in-the-door" open-channel blockers of GluN1/GluN2 receptors and that 7-MEOTA is a more potent but slower blocker than THA. We found that the IC50 values for THA and 7-MEOTA exhibited the GluN1/GluN2A < GluN1/GluN2B < GluN1/GluN2C = GluN1/GluN2D relationship and that 7-MEOTA effectively inhibits human GluN1/GluN2A-M817V receptors that carry a pathogenic mutation. We also showed that 7-MEOTA is a "foot-in-the-door" open-channel blocker of GluN1/GluN3 receptors, although these receptors were not inhibited by memantine. In addition, the inhibitory potency of 7-MEOTA at synaptic and extrasynaptic hippocampal NMDARs was similar, and 7-MEOTA exhibited better neuroprotective activity when compared with THA and memantine in rats with NMDA-induced lesions of the hippocampus. Finally, intraperitoneal administration of 7-MEOTA attenuated MK-801-induced hyperlocomotion and pre-pulse inhibition deficit in rats. We conclude that 7-MEOTA may be considered for the treatment of diseases associated with the dysfunction of NMDARs.

Rapamycin blocks the antidepressant effect of ketamine in task-dependent manner.

OBJECTIVE: The aim of our study was to test whether ketamine produces an antidepressant effect in animal model of olfactory bulbectomy and assess the role of mammalian target of rapamycin (mTOR) pathway in ketamine's antidepressant effect. METHODS: Bulbectomized (OBX) rats and sham controls were assigned to four subgroups according to the treatment they received (ketamine, saline, ketamine + rapamycin, and saline + rapamycin). The animals were subjected to open field (OF), elevated plus maze (EPM), passive avoidance (PA), Morris water maze (MWM), and Carousel maze (CM) tests. Blood samples were collected before and after drug administration for analysis of phosphorylated mTOR level. After behavioral testing, brains were removed for evaluation of brain-derived neurotrophic factor (BDNF) in prefrontal cortex (PFC) and hippocampus. RESULTS: Ketamine normalized hyperactivity of OBX animals in EPM and increased the time spent in open arms. Rapamycin pretreatment resulted in elimination of ketamine effect in EPM test. In CM test, ketamine + rapamycin administration led to cognitive impairment not observed in saline-, ketamine-, or saline + rapamycin-treated OBX rats. Prefrontal BDNF content was significantly decreased, and level of mTOR was significantly elevated in OBX groups. CONCLUSIONS: OBX animals significantly differed from sham controls in most of the tests used. Treatment had more profound effect on OBX phenotype than controls. Pretreatment with rapamycin eliminated the anxiolytic and antidepressant effects of ketamine in task-dependent manner. The results indicate that ketamine + rapamycin application resulted in impaired stress responses manifested by cognitive deficits in active place avoidance (CM) test. Intensity of stressor (mild vs. severe) used in the behavioral tests had opposite effect on controls and on OBX animals.

Rat intra-hippocampal NMDA infusion induces cell-specific damage and changes in expression of NMDA and GABAA receptor subunits.

Excessive stimulation of NMDA receptors with glutamate or other potent agonists such as NMDA leads to excitotoxicity and neural injury. In this study, we aimed to provide insight into an animal model of brain excitotoxic damage; single unilateral infusion of NMDA at mild dose into the hippocampal formation. NMDA infusion induced chronic, focal neurodegeneration in the proximity of the injection site. The lesion was accompanied by severe and progressive neuroinflammation and affected preferentially principal neurons while sparing GABAergic interneurons. Furthermore, the unilateral lesion did not cause significant impairment of spatial learning abilities. Finally, GluN1 and GluN2B subunits of NMDA receptor were significantly upregulated up to 3 days after the NMDA infusion, while GABAA α5 subunit was downregulated at 30 days after the lesion. Taken together, a single infusion of NMDA into the hippocampal formation represents an animal model of excitotoxicity-induced chronic neurodegeneration of principal neurons accompanied by severe neuroinflammation and subunit specific changes in NMDA and GABAA receptors.

Neuroprotective effect of the 3α5ß-pregnanolone glutamate treatment in the model of focal cerebral ischemia in immature rats.

The perinatal hypoxic-ischemic insult frequently leads to mortality, morbidity and plays a key role in the later pathological consequences. The ischemic insult causes a massive release of glutamate and subsequent excitotoxic damage. The neuroactive steroid 3α5ß-pregnanolone glutamate (PG) is a NMDA receptor antagonist acting via use-dependent mechanism and can be used as a neuroprotective agent that may alleviate glutamatergic excitotoxicity in the brain. First, a possible neurotoxic effect of the PG, a novel use-dependent NMDA antagonist, was studied in immature rats. In addition, to compare this effect with a well-described non-competitive NMDA antagonist, the MK-801 (positive control) was used. Animals at postnatal day 12 (P12) were injected intraperitoneally with PG in a doses 1 or 10mg/kg or with MK-801 in a dose 1mg/kg. Effect of PG treatment on the immature brain was evaluated on Fluoro Jade B (FJB) stained sections. Second, a neuroprotective effect of the PG was studied in the model of focal cerebral ischemia in P12. Focal cerebral ischemia was induced by the infusion of the endothelin-1 (ET-1) into the right dorsal hippocampus. PG at the doses 1 or 10mg/kg was administrated intraperitoneally 5min after the end of ET-1 infusion. To evaluate the neuroprotective effect after the PG treatment FJB staining was used. Our results demonstrate a lack of the neurotoxicity of the PG in intact P12. In the second part of the study in the model of the focal ischemia we detected significantly lower occurrence of FJB-positive cells in the afflicted hippocampus in PG treated groups, while animals without PG treatment exhibited massive neurodegeneration. The neuroprotective potential of the PG can serve in the development of therapeutic strategies for brain damage induced by the glutamate excitotoxicity.