The role of memantine in the treatment of major depressive disorder: Clinical efficacy and mechanisms of action

Memantine and the Kynurenine Pathway in the Brain: Selective Targeting of Kynurenic Acid in the Rat Cerebral Cortex

Cytoprotective and neurotoxic kynurenines formed along the kynurenine pathway (KP) were identified as possible therapeutic targets in various neuropsychiatric conditions. Memantine, an adamantane derivative modulating dopamine-, noradrenaline-, serotonin-, and glutamate-mediated neurotransmission is currently considered for therapy in dementia, psychiatric disorders, migraines, or ischemia. Previous studies have revealed that memantine potently stimulates the synthesis of neuroprotective kynurenic acid (KYNA) in vitro via a protein kinase A-dependent mechanism. Here, the effects of acute and prolonged administration of memantine on brain kynurenines and the functional changes in the cerebral KP were assessed in rats using chromatographic and enzymatic methods. Five-day but not single treatment with memantine selectively activated the cortical KP towards neuroprotective KYNA. KYNA increases were accompanied by a moderate decrease in cortical tryptophan (TRP) and L-kynurenine (L-KYN) concentrations without changes in 3-hydroxykynurenine (3-HK) levels. Enzymatic studies revealed that the activity of cortical KYNA biosynthetic enzymes ex vivo was stimulated after prolonged administration of memantine. As memantine does not directly stimulate the activity of KATs' proteins, the higher activity of KATs most probably results from the increased expression of the respective genes. Noteworthy, the concentrations of KYNA, 3-HK, TRP, and L-KYN in the striatum, hippocampus, and cerebellum were not affected. Selective cortical increase in KYNA seems to represent one of the mechanisms underlying the clinical efficacy of memantine. It is tempting to hypothesize that a combination of memantine and drugs could strongly boost cortical KYNA and provide a more effective option for treating cortical pathologies at early stages. Further studies should evaluate this issue in experimental animal models and under clinical scenarios.

A scientometric analysis of research on the role of NMDA receptor in the treatment of depression

Background

There have been numerous studies on NMDA receptors as therapeutic targets for depression. However, so far, there has been no comprehensive scientometric analysis of this field. Thus, we conducted a scientometric analysis with the aim of better elucidating the research hotspots and future trends in this field.

Methods

Publications on NMDAR in Depression between 2004 and 2023 were retrieved from the Web of Science Core Collection (WoSCC) database. Then, VOSviewer, CiteSpace, Scimago Graphica, and R-bibliometrix-were used for the scientometric analysis and visualization.

Results

5,092 qualified documents were identified to scientometric analysis. In the past 20 years, there has been an upward trend in the number of annual publications. The United States led the world in terms of international collaborations, publications, and citations. 15 main clusters were identified from the co-cited references analysis with notable modularity (Q-value = 0.7628) and silhouette scores (S-value = 0.9171). According to the keyword and co-cited references analysis, treatment-resistant depression ketamine (an NMDAR antagonist), oxidative stress, synaptic plasticity, neuroplasticity related downstream factors like brain-derived neurotrophic factor were the research hotspots in recent years.

Conclusion

As the first scientometric analysis of NMDAR in Depression, this study shed light on the development, trends, and hotspots of research about NMDAR in Depression worldwide. The application and potential mechanisms of ketamine in the treatment of major depressive disorder (MDD) are still a hot research topic at present. However, the side effects of NMDAR antagonist like ketamine have prompted research on new rapid acting antidepressants.

Ketamine in neuropsychiatric disorders: an update

The discovery of ketamine as a rapid-acting antidepressant led to a new era in the development of neuropsychiatric therapeutics, one characterized by an antidepressant response that occurred within hours or days rather than weeks or months. Considerable clinical research supports the use of-or further research with-subanesthetic-dose ketamine and its (S)-enantiomer esketamine in multiple neuropsychiatric disorders including depression, bipolar disorder, anxiety spectrum disorders, substance use disorders, and eating disorders, as well as for the management of chronic pain. In addition, ketamine often effectively targets symptom domains associated with multiple disorders, such as anxiety, anhedonia, and suicidal ideation. This manuscript: 1) reviews the literature on the pharmacology and hypothesized mechanisms of subanesthetic-dose ketamine in clinical research; 2) describes similarities and differences in the mechanism of action and antidepressant efficacy between racemic ketamine, its (S) and (R) enantiomers, and its hydroxynorketamine (HNK) metabolite; 3) discusses the day-to-day use of ketamine in the clinical setting; 4) provides an overview of ketamine use in other psychiatric disorders and depression-related comorbidities (e.g., suicidal ideation); and 5) provides insights into the mechanisms of ketamine and therapeutic response gleaned from the study of other novel therapeutics and neuroimaging modalities.

GluN2A and GluN2B N-Methyl-D-Aspartate Receptor (NMDARs) Subunits: Their Roles and Therapeutic Antagonists in Neurological Diseases

N-methyl-D-aspartate receptors (NMDARs) are ion channels that respond to the neurotransmitter glutamate, playing a crucial role in the permeability of calcium ions and excitatory neurotransmission in the central nervous system (CNS). Composed of various subunits, NMDARs are predominantly formed by two obligatory GluN1 subunits (with eight splice variants) along with regulatory subunits GluN2 (GluN2A-2D) and GluN3 (GluN3A-B). They are widely distributed throughout the CNS and are involved in essential functions such as synaptic transmission, learning, memory, plasticity, and excitotoxicity. The presence of GluN2A and GluN2B subunits is particularly important for cognitive processes and has been strongly implicated in neurodegenerative diseases like Parkinson's disease and Alzheimer's disease. Understanding the roles of GluN2A and GluN2B NMDARs in neuropathologies provides valuable insights into the underlying causes and complexities of major nervous system disorders. This knowledge is vital for the development of selective antagonists targeting GluN2A and GluN2B subunits using pharmacological and molecular methods. Such antagonists represent a promising class of NMDA receptor inhibitors that have the potential to be developed into neuroprotective drugs with optimal therapeutic profiles.

Current Insights into the Use of Probiotics and Fatty Acids in Alleviating Depression

(1) Background: Depression is the most prevalent psychiatric symptom present among individuals of all ages and backgrounds, impacting an estimated 300 million people globally. Therefore, it demands a significant amount of attention when it comes to managing depression. A growing amount of data reveal that probiotics and fatty acids could be beneficial to depression. However, the opposing position maintains that they have no influence on depression. A network meta-analyses of existing datasets aid in the estimation of comparative efficacy as well as in achieving an understanding of the relative merits of different therapies. The purpose of this study was to investigate the current evidence for probiotic or fatty acid depression therapy and to establish a practical alternative for depression patients using a meta-analysis and metagenomic data from a Wistar-Kyoto (WKY) depressed rat model. (2) Methods: Probiotic data were obtained from seven randomized controlled trial studies (n = 394), and fatty acid data were obtained from 24 randomized controlled trial studies (n = 1876). Meanwhile, a metagenomics analysis of data on animal gut flora was also applied to validate the preceding evidence. (3) Results: The fatty acid studies were separated into three sections based on the duration of probiotic delivery: ≤8 weeks, 9-12 weeks, and >12 weeks. The results were as follows: for ≤8 weeks, MD = -1.65 (95% CI: -2.96--0.15), p = 0.01; for 9-12 weeks, MD = -2.22 (95% CI: -3.03--1.22), p < 0.001; for >12 weeks, MD = -1.23 (95% CI: -2.85-0.39), p = 0.14. Regarding the probiotics, the meta-analysis revealed MD = -2.19 (95% CI: -3.38--2.43), p < 0.001. The research presented herein illustrates that probiotics and fatty acids may successfully lower depression scores. Additionally, the probiotics were drastically reduced in the WKY rats. (4) Conclusions: According to the data, a depression intervention utilizing probiotics outperformed the control, implying that the use of probiotics and fatty acids may be a successful strategy for depression treatment.

The modified outer membrane protein Amuc_1100 of Akkermansia muciniphila improves chronic stress-induced anxiety and depression-like behavior in mice

Akkermansia muciniphila is a next-generation probiotic. The interaction between outer membrane protein Amuc_1100 of A. muciniphila and toll-like receptor 2 (TLR2) in intestinal epithelial cells influences the level of intestinal 5-hydroxytryptamine (5-HT). Amuc_1100^Δ80 is a truncated form of Amuc_1100 lacking the first 80 N-terminal amino acids and has a higher affinity for TLR2 than the wild-type protein. Here, we report that Amuc_1100^Δ80 could significantly reduce anxiety and depression-like behavior of mice when they were exposed to chronic unpredictable mild stress (CUMS). The experimental results of the rat insulinoma cell line RIN-14B showed that Amuc_1100^Δ80 also induced a significantly higher upregulation of tryptophan hydroxylase 1 (Tph1), a rate-limiting enzyme of intestinal 5-HT synthesis. The imbalance of the gut microflora could be diminished when CUMS mice were fed with Amuc_1100^Δ80. These results reveal that Amuc_1100^Δ80 could affect the 5-HT level and the downstream 5-HTR1A-CREB-BDNF signal pathway via interacting with TLR2 and by altering the gut microbial composition. In parallel, the downregulation exerted by Amuc_1100^Δ80 on the inflammation and hyperactivated HPA axis was closely related to the improvement of depression-like symptoms in CUMS mice. This study not only provides new insights into the antidepressant effect of A. muciniphila and its outer membrane protein Amuc_1100 but also identifies new potential targets and pathways in the gut for future research and the development of antidepressant drugs.

Adverse Effects of Esketamine for the Treatment of Major Depression Disorder: Findings from Randomized Controlled Trials

Esketamine is a promising drug which can induce antidepressant effects in Major Depression Disorder (MDD). Several randomized controlled trials (RCTs) have been implemented to assess the efficacy and safety of esketamine for the treatment of MDD. Therefore, we carried out a meta-analysis to assess adverse effect profiles of esketamine for the treatment of MDD. We searched RCTs which were implemented from January 2010 to June 2020 by searching PubMed, Embase and Cochrane Library databases. Finally, four RCTs with 551 patients were included in our study. We pooled 551 patients from 4 RCTs. Compared with placebo, an increased risk of adverse effects was observed in our analysis. After using esketamine, the risk of nausea (RR = 2.34, 95% CI, 1.04 to 5.25, P = 0.04), dissociation (RR = 4.54, 95% CI, 2.36 to 8.73, P < 0.00001), dizziness (RR = 3.00, 95% CI, 1.80 to 5.00, P < 0.0001), vertigo (RR = 7.47, 95% CI, 2.55 to 21.86, P = 0.0002), hypoesthesia (RR = 5.68, 95% CI, 2.06 to 15.63, P = 0.0008), sedation (RR = 3.96, 95% CI, 1.29 to 12.15, P = 0.02) and paresthesia(RR = 3.05, 95% CI, 1.07 to 8.65, P = 0.04)were significantly increased compared with placebo. Our synthesized data analysis revealed drug specific risk profiles. The most frequent adverse effects under treatment with esketamine were nausea, dissociation, dizziness, vertigo, hypoesthesia,sedation and paresthesia.

Memantine and its benefits for cancer, cardiovascular and neurological disorders

Memantine is a non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist that was initially indicated for the treatment of moderate to severe Alzheimer's disease. It is now also considered for a variety of other pathologies in which activation of NMDA receptors apparently contributes to the pathogenesis and progression of disease. In addition to the central nervous system (CNS), NMDA receptors can be found in non-neuronal cells and tissues that recently have become an interesting research focus. Some studies have shown that glutamate signaling plays a role in cell transformation and cancer progression. In addition, these receptors may play a role in cardiovascular disorders. In this review, we focus on the most recent findings for memantine with respect to its pharmacological effects in a range of diseases, including inflammatory disorders, cardiovascular diseases, cancer, neuropathy, as well as retinopathy.

The effects of JNJ-39393406 a positive allosteric nicotine modulator on mood and cognition in patients with unipolar depression: A double-blind, add-on, placebo-controlled trial

Nicotinic agonists have been shown to improve cognition and mood, but this improvement is inconsistent and short-lived, possibly due to receptor desensitization. Positive Allosteric Modulators (PAMs) of the nicotinic alpha-7 nicotinic-acetyl-choline receptor (a7nAChR) are hypothesized to change the configuration of the nicotinic receptor and delay desensitization, potentially increasing the duration of the activation of the receptor, and improving clinical efficacy. This was a randomized controlled trial (RCT) adding JNJ-39393406 9 (a PAM of the a7nAChR) (n=35) or placebo (n=36) to treatment as usual for two weeks in 71 patients with unipolar depression. Mixed models for repeated measures analyses were performed Primary outcome measures were the Brief Assessment of Cognition in Schizophrenia (BACS) composite and the Montgomery-Asperg Depression Rating Scale (MADRS) scores. The drug was well tolerated, however mixed models for repeated measures comparing JNJ-39393406 to placebo showed no significant difference for MADRS total score (p=0.78), BACS composite score (p=0.34), or any of the secondary outcome measures. There was no significant difference in adverse events between the study groups (p=0.44). In conclusion, this study's findings do not support the hypothesis that a positive nicotinic receptor modulator can improve cognitive or depressive symptomatology in patients with unipolar depression.

Anxiogenic and anxiolytic effects of memantine injected into the ventral hippocampus in male stressed mice

OBJECTIVES

The effects of intra-ventral hippocampal memantine administration in male NMRI stressed mice were studied.

METHODS

Two stainless steel gauge 23 guide cannulas were placed in the middle part of the mice ventral hippocampus using stereotaxic coordination. Seven days later, the animals were undergone to the stress protocol as follows: They experience four consecutive electro-foot shock stress sessions lasting for 10 min. Five or 30 min before each stress session, the animals received intra-ventral hippocampal (0.1, 1 and, 5 µg/mouse) or intraperitoneal (1, 5, and 10 mg/kg) memantine respectively. Eight days after stress termination, the animals were tested either for the maintenance of either anxiety (elevated plus maze) or depression (forced swimming test).

RESULTS

Animals show anxiety eight days after stress termination. Intra-ventral hippocampal infusion of memantine (5 µg/mouse) 5 min before stress inhibited the anxiety-like behaviors. However, other doses of the drug exacerbate the stress effect. The drug, when injected peripherally exacerbated the stress effect in all doses. The drug by itself had no effect. In addition, animals also show depression nine days after stress termination and memantine (0.1, 1, and 5 µg/mouse) reduced the stress effect. The drug (0.1 µg/mouse) by itself induced depression in the animals. However, the drug when injected peripherally reduced the stress effect in all doses.

CONCLUSIONS

It could be concluded that NMDA glutamate receptors in the ventral hippocampus may play a pivotal role in the mediation of maintenance of anxiety and depression induced by stress in the mice.

Pharmacokinetic and tissue distribution study of ZCY-15, a novel compound against Alzheimer's disease, in rats by liquid chromatography-tandem mass spectrometry

ZCY-15, N-(3,5-dimethyladamatan-1-yl)-N-(3-methylphenyl) urea, is a candidate compound synthesized from the memantine structure and has been shown to be remarkably effective in treating Alzheimer's disease. To elucidate the pharmacokinetics and tissue distribution of ZCY-15 in rats after oral and intravenous administration, a rapid and selective LC-MS/MS method was established for the determination of ZCY-15 in rat plasma and tissues. According to the dissolution characteristics, the plasma samples were prepared by acetonitrile protein precipitation and carbamazepine was selected as the internal standard (IS). After separation by gradient elution using Aqela Venusil ASB C₈ (2.1 × 50 mm, 3 µm), the pretreated samples were analyzed in MRM mode in positive ESI mode. The effective detection limit of this method was 1.95-1000 ng·mL^-1. Tissue samples were collected from the heart, liver, spleen, lung, kidney, fat, muscle, brain, hippocampus, testicles or ovaries, large intestine, small intestine and stomach. The proposed method demonstrated fine precision and accuracy for analyzing ZCY-15 in selected tissues within the concentration range of standard liquid chromatography-tandem mass spectrometry. The whole analysis time was 3.6 min per sample. After oral administration, the blood and tissue concentrations of ZCY-15 in female rats were significantly higher than those in male rats. The clearance rate of ZCY-15 in female rats was lower than that in male rats. The results confirmed that there were gender differences. It has been shown that ZCY-15 could pass through the blood-brain barrier and was highly concentrated in the hippocampus. We established the first bioanalytical method to quantify ZCY-15 in rodent bio-samples for ongoing pharmacokinetic and tissue distribution studies, and the results were expected to lay foundation for the subsequent studies.

Does the application of acetylcholinesterase inhibitors in the treatment of Alzheimer's disease lead to depression?

Introduction: Alzheimer's disease and depression are health conditions affecting millions of people around the world. Both are strongly related to the level of the neurotransmitter acetylcholine. Since cholinergic deficit is characteristic of Alzheimer's disease, acetylcholinesterase inhibitors are applied as relevant drugs for the treatment of this disease, elevating the level of acetylcholine. On the other hand, a high level of acetylcholine is found to be associated with the symptoms of clinical depression.Areas covered: This article aims to discuss if acetylcholinesterase inhibitors used as anti-Alzheimer's drugs could be the cause of the symptoms of clinical depression often linked to this neurological disorder. Emphasis will be put on drugs currently in use and on newly investigated natural products, which can inhibit AChE activity.Expert opinion: Currently, it is not proven that the patient treated for Alzheimer's disease is prone to increased risk for depression due to the acetylcholinesterase inhibition, but there are strong indications. The level of acetylcholine is not the only factor in highly complicated diseases like AD and depression. Still, it needs to be considered isolated, keeping in mind the nature of presently available therapy, especially during a rational drug design process.

miR‑146a reduces depressive behavior by inhibiting microglial activation

Depression is one of the major psychiatric diseases affecting the quality of life for individuals worldwide. Numerous reports have investigated depression, although its etiology remains to be elucidated. microRNA (miR)-146a is suggested to regulate innate immune and inflammatory responses. However, it is unclear whether miR-146a is involved in depression. Depression model mice were established using lipopolysaccharide-induced depression and chronic unpredictable mild stress, separately. miR-146a mimic and short interfering RNA were used to treat depressed mice. Depression-like behaviors and levels of pro-inflammatory cytokines were measured, while ionized calcium binding adapter molecule 1 (Iba-1) expression in hippocampus was quantified by immunohistochemistry. Neuroinflammatory factor levels in hippocampus were measured by western blotting. BV-2 cells were used to confirm that miR-146a suppressed microglia activation. Compared with control mice, the two depressed mouse models showed clearly decreased sucrose preference and significantly increased immobility time in the forced swimming test and tail suspension test (P<0.05). miR-146a overexpression significantly increased sucrose preference and reduced immobility time in depressed mice (P<0.05). However, total distance traveled in the locomotor activity test did not differ among groups. Compared with controls, expression levels of Iba-1, inducible nitric oxide, IL-1β, TNF-α, interleukin 1 receptor associated kinase 1 (IRAK1), TNF receptor-associated factor 6 (TRAF6) and phosphorylated NF-κB p65 were significantly increased in depressed mice (P<0.05). miR-146a overexpression effectively inhibited expression of these neuroinflammatory proteins, while miR-146a silencing significantly upregulated their expression (P<0.05). Consistent with these in vivo results, miR-146a mimic treatment inhibited TNF-α, IL-1β, IRAK1 and TRAF6 expression in BV-2 cells. miR-146a improved depressive behaviors in depressed model mice by inhibiting microglial activation and neuroinflammatory factor expression.

Does mismatch negativity have utility for NMDA receptor drug development in depression?

CLINICAL TRIAL REGISTRATION

Rapid antidepressant effects associated with ketamine have shifted the landscape for the development of therapeutics to treat major depressive disorder (MDD) from a monoaminergic to glutamatergic model. Treatment with ketamine, an N-methyl-D-aspartate (NMDA) receptor antagonist, may be effective, but has many non-glutamatergic targets, and clinical and logistical problems are potential challenges. These factors underscore the importance of manipulations of binding mechanics to produce antidepressant effects without concomitant clinical side effects. This will require identification of efficient biomarkers to monitor target engagement. The mismatch negativity (MMN) is a widely used electrophysiological signature linked to the activity of NMDA receptors (NMDAR) in humans and animals and validated in pre-clinical and clinical studies of ketamine. In this review, we explore the flexibility of the MMN and its capabilities for reliable use in drug development for NMDAR antagonists in MDD. We supplement this with findings from our own research with three distinct NMDAR antagonists. The research described illustrates that there are important distinctions between the mechanisms of NMDAR antagonism, which are further crystallized when considering the paradigm used to study the MMN. We conclude that the lack of standardized methodology currently prevents MMN from being ready for common use in drug discovery. This manuscript describes data collected from the following National Institutes of Health (NIH) and Veterans Affairs (VA) studies: AV-101, NCT03583554; lanicemine, NCT03166501; ketamine, NCT02556606.

Memantine in neurological disorders - schizophrenia and depression

Memantine is used in Alzheimer's disease treatment as a non-competitive modern-affinity strong voltage-dependent N-methyl-D-aspartate receptor antagonist. The fundamental role of these receptors is to bind glutamate: the main excitatory neurotransmitter in the brain, believed to play a crucial role in neuronal plasticity and learning mechanisms. Glutamate transmission plays an important role in all internal CNS structures and maintains the physiological state of the brain. Excessive glutamate transmission can lead to enlarged calcium ion current which may cause neurotoxicity; however, insufficient transmission can drastically alter the information flow in neurons and the brain, potentially causing schizophrenia-like symptoms by replacing lost information with completely new stimuli. Hence, it is possible that the modulation of NMDA activity may give rise to pathophysiological states. Available literature and clinical trials indicate that memantine is well tolerated by patients, with very few and light side effects. There is a belief that memantine may also benefit other conditions such as schizophrenia and depression.

Memantine treatment exerts an antidepressant-like effect by preventing hippocampal mitochondrial dysfunction and memory impairment via upregulation of CREB/BDNF signaling in the rat model of chronic unpredictable stress-induced depression

Mitochondrial and cognitive dysfunctions have long been associated with major depressive disorders (MDDs). Studies have shown that Memantine, an N-methyl-D-aspartate (NMDA) receptor antagonist, possesses an antidepressant-like effect. Hence, the NMDA receptor can be a better therapeutic target for MDD. Therefore, the present study was designed to study the impact of Memantine on mitochondrial functional status and depression-like symptoms in the chronic unpredictable stress (CUS) model of depression. CUS for 28 days resulted in depression-like symptoms (as indicated by increased immobility time in the forced swim test) and a decline in the spatial learning and retention memory in the Morris water maze (MWM) test, which was prevented by Memantine (10 mg/kg/day) treatment. We observed elevated plasma corticosterone (CORT) levels, microdialysates glutamate concentration, and synaptosomal calcium (Ca2+) ion levels after 28 days of CUS. Memantine treatment prevented only increased plasma CORT and synaptosomal Ca2+ ion levels. Memantine treatment also restored CUS induced increase in oxidative stress parameters [increased neuronal nitric oxide synthase (nNOS) expression, nitric oxide (NO) levels, lipid peroxidation (LPO) and superoxide dismutase (SOD) activity], decrease in mitochondrial electron transport chain (ETC) enzymes activity and mitochondrial membrane potential (MMP). CUS also reduced the expression of cell survival genes, cyclic-AMP response element-binding protein (CREB), and brain-derived nerve growth factor (BDNF), which was reversed by treatment with Memantine. CUS, however, caused a non-significant decrease in the hippocampal adenosine triphosphate (ATP) levels and a non-significant increase in the expression of pro-apoptotic genes, Caspase 3, and the number of TUNEL positive cells, indicating that hippocampal mitochondrial dysfunction caused due to CUS was not severe enough to affect overall energy production, mitochondrial integrity, and cellular apoptosis status. Thus, Memantine treatment exerts an antidepressant-like effect by preventing CUS induced excitotoxicity, oxidative stress, and enhancing CUS induced decrease in mitochondrial functioning and expression of cell survival genes via upregulation of stress-responsive CREB/BDNF signaling.

Interplay between Gating and Block of Ligand-Gated Ion Channels

Drugs that inhibit ion channel function by binding in the channel and preventing current flow, known as channel blockers, can be used as powerful tools for analysis of channel properties. Channel blockers are used to probe both the sophisticated structure and basic biophysical properties of ion channels. Gating, the mechanism that controls the opening and closing of ion channels, can be profoundly influenced by channel blocking drugs. Channel block and gating are reciprocally connected; gating controls access of channel blockers to their binding sites, and channel-blocking drugs can have profound and diverse effects on the rates of gating transitions and on the stability of channel open and closed states. This review synthesizes knowledge of the inherent intertwining of block and gating of excitatory ligand-gated ion channels, with a focus on the utility of channel blockers as analytic probes of ionotropic glutamate receptor channel function.

Regional White Matter Integrity Predicts Treatment Response to Escitalopram and Memantine in Geriatric Depression: A Pilot Study

Background: Geriatric depression with subjective memory complaints increases the risk for Alzheimer's Disease. Memantine, a neuroprotective drug, can improve depression and help prevent cognitive decline. In our 6-months clinical trial, escitalopram/memantine (ESC/MEM) improved mood and cognition compared to escitalopram/placebo treatment (ESC/PBO; NCT01902004). In this report, we investigated whether baseline brain white matter integrity in fronto-limbic-striatal tracts can predict clinical outcomes using fractional anisotropy (FA). Methods: Thirty-eight older depressed adults (mean age = 70.6, SD = 7.2) were randomized to ESC/MEM or ESC/PBO and underwent diffusion-weighted imaging (DWI) at 3 Tesla at baseline. Mood was assessed using the Hamilton Depression Rating Scale (HAMD), apathy using the Apathy Evaluation Scale (AES) and anxiety using the Hamilton Anxiety Scale (HAMA) at baseline and 6-months follow-up. FA was extracted from seven tracts of interest (six in each hemisphere and one commissural tract) associated with geriatric depression. Non-parametric General Linear Models were used to examine group differences in the association between FA and symptom improvement, controlling for age, sex, baseline symptom scores and scanner model, correcting for false discovery rate (FDR). Post-hoc tests further investigated group differences in axial, mean and radial diffusivity (AD, MD, and RD, respectively). Lastly, we performed an exploratory whole-brain model to test whether FA might be related to treatment response with memantine. Results: There were no differences in remission rates or HAMD change between groups. In bilateral anterior and posterior internal capsule tracts and bilateral inferior and right superior fronto-occipital (IFO and SFO) fasciculus, higher FA was associated with larger improvements in depressive symptoms for ESC/MEM, but not ESC/PBO, correcting for FDR. Lower MD in the left IFO and RD in the right anterior internal capsule were associated with improved treatment responses. We found no significant associations in the whole-brain analysis. Limitations: Included small sample size and high dropout. Conclusions: Higher baseline FA and lower RD and MD in hypothesized fronto-limbic-striatal tracts predicted greater improvement in mood and anxiety with ESC/MEM compared to ESC/PBO in geriatric depression. FA as a biomarker for white matter integrity may serve as a predictor of treatment response but requires confirmation in larger future studies.

Stress-Induced Spatial Memory Deficit Reversed by Basolateral Amygdala NMDA Receptor Inhibition in Male Wistar Rats

INTRODUCTION

The present study investigated the role of the Basolateral Amygdala (BLA) N-methyl-D-aspartate (NMDA) receptors in stress-induced spatial memory disturbance among the male Wistar rats.

METHODS

The male Wistar rats (Average weight =200 g) were cannulated bilaterally in the BLA, and entered the study (n=6-8) after one week. They received seven electro-foot-shock stress sessions on seven consecutive days. Memantine (0.1, 1, and 5 μg/rat) or saline (0.5 μL/ rat) was injected into the BLA, five minutes before each stress session. The control groups received the same doses of memantine and no stress. After the end of the stress sessions, blood samples were taken from all animals to evaluate their plasma corticosterone. Also, the spatial learning and memory of the study animals were evaluated using the Barnes maze method. The animals experienced five consecutive days of training on the maze for spatial learning. On the sixth day, their spatial memory was evaluated on the maze. Time, distance, the number of errors, and the taking strategy for reaching the target hole were considered as the parameters for the spatial learning and memory evaluation.

RESULTS

Stress increases the plasma corticosterone level, while memantine preadministration reduces the stress effects. Besides, stress increases the time and distance to the target hole and the number of errors. Stress changed the animals' strategy from serial to random type. However, the intra-BLA memantine reversed all the disturbances induced by the stress.

CONCLUSION

This study indicated that the BLA glutamate NMDA receptors modulate the effect of stress on spatial learning and memory deficit.

The role of CREB and BDNF in neurobiology and treatment of Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia worldwide. β-amyloid peptide (Aβ) is currently assumed to be the main cause of synaptic dysfunction and cognitive impairments in AD, but the molecular signaling pathways underlying its neurotoxic consequences have not yet been completely explored. Additional investigations regarding these pathways will contribute to development of new therapeutic targets. In context, developing evidence suggest that Aβ decreases brain-derived neurotrophic factor (BDNF) mostly by lowering phosphorylated cyclic adenosine monophosphate (cAMP) response element binding protein (CREB) protein. In fact, it has been observed that brain or serum levels of BDNF appear to be beneficial markers for cognitive condition. In addition, the participation of transcription mediated by CREB has been widely analyzed in the memory process and AD development. Designing pharmacologic or genetic therapeutic approaches based on the targeting of CREB-BDNF signaling could be a promising treatment potential for AD. In this review, we summarize data demonstrating the role of CREB-BDNF signaling pathway in cognitive status and mediation of Aβ toxicity in AD. Finally, we also focus on the developing intervention methods for improvement of cognitive decline in AD based on targeting of CREB-BDNF pathway.

Natural and synthetic drugs used for the treatment of the dementia

This review is devoted to comparative pharmacological analysis of synthetic drugs such as memantine and its isomers, as well as tacrine, velnacrine, rivastigmine, and donepezil, with natural alkaloids, terpenoids, and triterpenoid peroxides, which are used to treat dementia, Alzheimer's and Parkinson's diseases, myasthenia gravis and other neurodegenerative diseases. Recently discovered by French scientists from Marseille triterpenoid hydroperoxides demonstrate high activity as potential therapeutic agents for the treatment of dementia. The information presented in this review is of great interest to pharmacologists, medical chemists, physiologists, neurologists and doctors, as well as for the pharmaceutical industry.

Gut microbiota-brain axis in depression: The role of neuroinflammation

Major depressive disorder (MDD) is a psychiatric condition that affects a large number of people in the world, and the treatment existents do not work for all individuals affected. Thus, it is believed that other systems or pathways which regulate brain networks involved in mood regulation and cognition are associated with MDD pathogenesis. Studies in humans and animal models have been shown that in MDD there are increased levels of inflammatory mediators, including cytokines and chemokines in both periphery and central nervous system (CNS). In addition, microglial activation appears to be a key event that triggers changes in signaling cascades and gene expression that would be determinant for the onset of depressive symptoms. Recent researches also point out that changes in the gut microbiota would lead to a systemic inflammation that in different ways would reach the CNS modulating inflammatory pathways and especially the microglia, which could influence responses to treatments. Moreover, pre- and probiotics have shown antidepressant responses and anti-inflammatory effects. This review will focus on studies that show the relationship of inflammation with the gut microbiota-brain axis and its relation with MDD.

The role of NMDA receptor in neurobiology and treatment of major depressive disorder: Evidence from translational research

There is accumulating evidence demonstrating that dysfunction of glutamatergic neurotransmission, particularly via N-methyl-d-aspartate (NMDA) receptors, is involved in the pathophysiology of major depressive disorder (MDD). Several studies have revealed an altered expression of NMDA receptor subtypes and impaired NMDA receptor-mediated intracellular signaling pathways in brain circuits of patients with MDD. Clinical studies have demonstrated that NMDA receptor antagonists, particularly ketamine, have rapid antidepressant effects in treatment-resistant depression, however, neurobiological mechanisms are not completely understood. Growing body of evidence suggest that signal transduction pathways involved in synaptic plasticity play critical role in molecular mechanisms underlying rapidly acting antidepressant properties of ketamine and other NMDAR antagonists in MDD. Discovering the molecular mechanisms underlying the unique antidepressant actions of ketamine will facilitate the development of novel fast acting antidepressants which lack undesirable effects of ketamine. This review provides a critical examination of the NMDA receptor involvement in the neurobiology of MDD including analyses of alterations in NMDA receptor subtypes and their interactive signaling cascades revealed by postmortem studies. Furthermore, to elucidate mechanisms underlying rapid-acting antidepressant properties of NMDA receptor antagonists we discussed their effects on the neuroplasticity, mostly based on signaling systems involved in synaptic plasticity of mood-related neurocircuitries.

Pharmacokinetics, bioavailability and tissue distribution study of JCC-02, a novel N-methyl-d-aspartate (NMDA) receptor inhibitor, in rats by LC-MS/MS

JCC-02, N-(3,5-dimethyladamantan-1-yl)-N'-(3-chlorophenyl) urea, has been developed as a novel N-methyl-d-aspartate (NMDA) receptor inhibitor for the treatment of Alzheimer's disease (AD). In this study, a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed to determine the concentration of JCC-02 in rat plasma and different tissues to investigate its pharmacokinetic behavior in vivo and distribution character in organs. The matrix samples were prepared by protein precipitation method with acetonitrile using gliclazide as the internal standard (IS). This validated method was successfully applied to JCC-02 pharmacokinetic study in rats after oral administration of low (0.7 mg·kg^-1), medium (2 mg·kg^-1) and high (6 mg·kg^-1) concentration, intravenous administration (2 mg·kg^-1) as well as tissue distribution in rats after administration of JCC-02 (2 mg·kg^-1) orally. The results indicated that the area under the time curve (AUC_0-∞) and peak plasma concentration (C_max) were directly proportional to dosage and the pharmacokinetic behavior of JCC-02 in rats was a linear process with respect to dosage. JCC-02 could be absorbed into blood circulation rapidly because of its short time to reach peak plasma concentration (t_max). Meanwhile, JCC-02 has a low clearance and a high volume of distribution, which might result in its long half-time. Oral absolute bioavailability (F) of JCC-02 was (14.61 ± 5.81)%, which was turned out to be low relatively. In tissues, the differences of JCC-02 concentration were quite large. After administration, small intestine (22.29 ± 15.86 μg·mL^-1), stomach (7.21 ± 2.87 μg·mL^-1), large intestine (1.27 ± 0.57 μg·mL^-1), liver (0.96 ± 0.52 μg·mL^-1) and fat (0.48 ± 0.24 μg·mL^-1) were the first five organs with the largest drug concentration. Small intestine could be the main part of drug absorption where most of the drug was distributed after oral administration. More importantly, JCC-02 could cross the blood-brain barrier (BBB), which may probably have a pretty good therapeutic effect on AD.