Glycine Transporter Research Articles

Stable isotope synthesis of glycine transporter 1 inhibitor Iclepertin (BI 425809) and its major metabolites.

Stable isotope labeled Iclepertin (BI 425809, 1) and its major metabolites are needed as internal standards in bioanalytical studies. BI 425809 consists of two main building blocks, 5-methylsulfonyl-2-[(1R)-2,2,2-trifluoro-1-methyl-ethoxy]benzoic acid (2) and 3-[(1R,5R)-3-azabicyclo[3.1.0]hexan-5-yl]-5-(trifluoromethyl)isoxazole (3) linked to each other via an amide bond. We used fluoro[13 C6 ]benzene as the starting material in the preparation of [13 C6 ]-2. This intermediate was then employed to access carbon 13 labeled Iclepertin ([13 C6 ]-1) and other metabolites. The major metabolite BI 761036 (6), which resulted from cytochrome P450 oxidation and amide hydrolysis of BI 425809, was prepared labeled with carbon 13 and nitrogen 15 via two synthetic routes. In the first route, diethyl [13 C3 ]malonate, [13 C]methyl iodide, and hydroxyl[15 N]amine were used to provide [13 C4 ,15 N]-BI 761036 ([13 C4 ,15 N]-6a) in 13 steps in 6% overall yield, whereas in the second route, [13 C3 ]propargyl alcohol, potassium [13 C]cyanide, and [15 N]ammonia were used to furnish [13 C4 ,15 N]-BI 761036 ([13 C4 ,15 N]-6b) in 11 steps in 1% overall yield. The detailed stable isotope synthesis of 1 and its major metabolites is described.

Update on Oxytocin, Phosphodiesterase, Neurokinin, Glycine as a Therapeutic Approach in the Treatment of Schizophrenia.

Schizophrenia is a chronic psychiatric disorder characterized by disrupted thoughts, perception, mood, and behavior. It has a heterogeneous genetic and neurobiological background and affects about 0.5-1% of the adult population worldwide. Herein, we review the current approaches and advances in schizophrenia. The potential therapeutic compounds for the treatment of schizophrenia act on the oxytocin receptor, phosphodiesterase system, neurokinin receptor, and glycine transport 1 receptor. Therefore, this article provides an update on the pharmacology of different receptors in addition to the dopaminergic system. These findings would guide the readers on novel targets for schizophrenia with the potential to be therapeutic agents in the future. To provide the researchers an update on the emerging role of oxytocin, phosphodiesterase, neurokinin, and glycine which can be explored as potential pharmacotherapeutic targets in the treatment of schizophrenia. An extensive literature search was conducted using PubMed, Science Direct, and NCBI with the following keywords: schizophrenia, novel receptors, oxytocin, phosphodiesterase, neurokinin, and glycine. Furthermore, to provide insights into newer drug treatments for Schizophrenia, Furthermore, Clinicaltrials.gov website was searched for newer receptor-based drugs. Current literature supported by preclinical and clinical provides substantial evidence that oxytocin, phosphodiesterase, neurokinin, and glycine play a crucial role in Schizophrenia. Our findings indicate that though multiple antipsychotic drugs are prescribed to treat schizophrenia, novel approaches and/or mechanisms are plausible. Moreover, sensitive and specific diagnostic tools and safe and effective interventions, including novel therapeutic agents, are required to yield substantially improved future outcomes.

Novel Phenylene Lipids That Are Positive Allosteric Modulators of Glycine Receptors and Inhibitors of Glycine Transporter 2.

Chronic pain is a complex condition that remains resistant to current therapeutics. We previously synthesized a series of N-acyl amino acids (NAAAs) that inhibit the glycine transporter, GlyT2, some of which are also positive allosteric modulators of glycine receptors (GlyRs). In this study, we have synthesized a library of NAAAs that contain a phenylene ring within the acyl tail with the objective of improving efficacy at both GlyT2 and GlyRs and also identifying compounds that are efficacious as dual-acting modulators to enhance glycine neurotransmission. The most efficacious positive allosteric modulator of GlyRs was 2-[8-(2-octylphenyl)octanoylamino]acetic acid (8-8 OPGly) which potentiates the EC5 for glycine activation of GlyRα1 by 1500% with an EC50 of 664 nM. Phenylene-containing NAAAs with a lysine headgroup were the most potent inhibitors of GlyT2 with (2S)-6-amino-2-[8-(3-octylphenyl)octanoylamino]hexanoic acid (8-8 MPLys) inhibiting GlyT2 with an IC50 of 32 nM. The optimal modulator across both proteins was (2S)-6-amino-2-[8-(2-octylphenyl)octanoylamino]hexanoic acid (8-8 OPLys), which inhibits GlyT2 with an IC50 of 192 nM and potentiates GlyRs by up to 335% at 1 μM. When tested in a dual GlyT2/GlyRα1 expression system, 8-8 OPLys caused the greatest reductions in the EC50 for glycine. This suggests that the synergistic effects of a dual-acting modulator cause greater enhancements in glycinergic activity compared to single-target modulators and may provide an alternate approach to the development of new non-opioid analgesics for the treatment of chronic pain.

Carbon 14 synthesis of glycine transporter 1 inhibitor Iclepertin (BI 425809) and its major metabolites.

Carbon 14 labeled Iclepertin (BI 425809, 1) and its major metabolites were needed for ADME and several other studies necessary for the advancement of this drug candidate in clinical trials. Iclepertin is composed of two main chemical blocks, (R)-5-(methylsulfonyl)-2-([1,1,1-trifluoropropan-2-yl]oxy)benzoic acid (2), and 3-[(1R,5R)-3-azabicyclo[3.1.0]hexan-5-yl]-5-(trifluoromethyl)isoxazole (3) linked to each other via an amide bond. In the first synthesis of carbon 14 labeled 1, 2-fluorobenzoic acid, carboxyl-14 C was converted to [14 C]-2 in three steps and then coupled to 3 to provide [14 C]-1a in 45% overall yield. In the second synthesis, [14 C]-3 was prepared in six radioactive steps and coupled to the acid 2 to furnish [14 C]-1b in 20% overall yield. Both synthetic routes provided [14 C]-1a and [14 C]-1b with specific activities higher than 53 mCi/mmol and radiochemical, chemical, and enantiomeric purities above 98%. Two major metabolites of 1, BI 761036 and BI 758790, were also prepared labeled with carbon 14 using intermediates already available from the synthesis of [14 C]-1.

Investigation of SLC6A9 and SLC5A1 as a promising therapeutic target for obesity and diabetes using in silico characterization, 3D structure prediction and molecular docking analysis

AbstractBackgroundObesity is a multi‐factorial clinical condition resulting from energy dyshomeostasis. Obesity is known to be linked with the development of Type‐1 and Type‐2 diabetes due to abnormal glucose regulation. Additionally, it is associated with the onset of insulin resistance as well as atypical nutrient and hormonal sensing in the CNS. The role of GLYT1 has been implicated in the Dorsal Vagal Complex (DVC) which forms the brain‐liver axis for glucose release into the bloodstream. On the other hand, SGLT1 is majorly responsible for glucose absorption in the intestinal lumen.MethodThe current work focuses on in silico approaches to characterize the transporter proteins: Glycine Transporter‐1 (GLYT1) and Sodium‐Glucose Linked Transporter‐1 (SGLT1) as a potential target for the treatment of obesity and diabetes in an insulin independent manner. The sequence of the two proteins were obtained from the UniProt database which was used to calculate various physicochemical parameters giving detailed insight into its molecular weight, amino acid composition, theoretical PI, extinction coefficients and GRAVY index.ResultPrimary sequence analysis using ProtParam revealed the stability of SLC6A9 and SLC5A1 in test‐tube classifying it as stable and unstable respectively while secondary structure analysis using SOPMA shed light on its alpha helix and beta sheet composition as well as random coils. Three‐dimensional (3D) protein structures were generated using SWISS‐MODEL, an integrated web‐based homology modeling server, which were then verified using the SAVES server. Docking studies were performed using AutoDock4 which yielded potential drug candidates. The validated models of SLC6A9 and SLC5A1 were successfully submitted to PMDB ‐Protein Model Database with PMDB ID: PM0082326 and PM0082333 respectively which could be utilized for further Docking analysis and spectroscopy experiments.ConclusionA thorough explication of these results can aid the future research in development of a novel therapeutic strategy to battle this enigmatic rising epidemic of obesity and diabetes.

Bidirectional Modulation of Nociception by GlyT2+ Neurons in the Ventrolateral Periaqueductal Gray.

The midbrain periaqueductal gray (PAG), particularly its ventrolateral column (vlPAG), is part of a key descending pathway that modulates nociception, fear and anxiety behaviors in both humans and rodents. It has been previously demonstrated that inhibitory GABAergic neurons within the vlPAG have a major role in this nociceptive modulation. However, the PAG contains a diverse range of neuronal subtypes and the contribution of different subtypes of inhibitory neurons to nociceptive control has not been investigated. Here, we employed a chemogenetic strategy in mice that express Cre recombinase under the promotor for the glycine transporter 2 (GlyT2::cre) to modulate a novel group of glycinergic neurons within the vlPAG and then investigate their role in nociceptive control. We show that activation of GlyT2-PAG neurons enhances cold and noxious heat responses and increases locomotor activity (LMA) in both male and female mice. In contrast, inhibition of GlyT2-PAG neurons reduced nociceptive responses, while locomotor behaviors were unaffected. Our findings demonstrate that GlyT2+ neurons in the vlPAG modulate nociception and suggest that strategies targeting GlyT2-PAG neurons could be used to design novel analgesic therapies.

Rapid, activity-dependent co-release of GABA and glycine in the mouse brainstem

Presympathetic neurons in the ventrolateral and ventromedial medulla (VLM/VMM) control the sympathetic tone, and GABA was identified as a primary mechanism for sympathoinhibition. Intriguingly, there is evidence that both GABA and glycine efficiently inhibit sympathetic tone; however, the mechanism of glycine release is unknown. In this study, we tested the hypothesis that GABA and glycine are co-released in the VLM/VMM. Glycine is recycled by glycine transporter 2 (GlyT2), which is a reliable marker of glycinergic neurons. Therefore, we crossed heterozygous GlyT2Cre mice with floxed channelrhodopsin 2 (ChR2-EYFP) mice to generate GlyT2 reporter mice (GlyT2ChR2/EYFP), which were used to determine the mechanism of glycine release and reveal the location of glycinergic neurons. Whole-cell patch-clamp recordings from presympathetic VLM/VMM neurons revealed that GABA mediates most spontaneous inhibitory postsynaptic currents (sIPSCs); whereas increased activity of inhibitory inputs promotes the release of glycine. Light stimulation of glycinergic fibers expressing ChR2 in GlyT2ChR2/EYFP mice evoked IPSCs (eIPSCs) with glycinergic and GABAergic components. Bath application of GABAA receptors antagonist (bicuculline, 10 μM) decreased the amplitude of eIPSCs, suggesting that approximately 70% of the eIPSCs are generated by glycine. Moreover, blockade of GlyT2 partially diminished the glycinergic component of the light-evoked IPSCs. Using GlyT2ChR2/EYFP mice, we found that glycinergic fibers are abundant throughout the rostral brainstem, and GlyT2-expressing neurons were distributed within the ventral gigantocellular nucleus and medial reticular formation. Immunofluorescence labeling of glycine receptor subunits in the VLM/VMM revealed the expression of two prevalent forms of glycine receptors formed by α1 and α3. In summary, we found that GABA and glycine are co-released in the VLM/VMM, and blockage of GlyT2 decreased the amplitude of light-evoked IPSCs, suggesting that GABA and glycine are likely located in separate vesicles. Our data provide evidence for the co-inhibition of presympathetic neurons in the VLM/VMM by GABA and glycine and suggest that GABA controls the threshold excitability, while glycine is released on demand to increase the strength of inhibition. Supported by: NIDDK122842 and Tulane Brain Institute Marko Spark Innovation Research Fund This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Bile acid interactions with neurotransmitter transporters.

Synthesized in the liver from cholesterol, the bile acids (BAs) primary role is emulsifying fats to facilitate their absorption. BAs can cross the blood-brain barrier (BBB) and be synthesized in the brain. Recent evidence suggests a role for BAs in the gut-brain signaling by modulating the activity of various neuronal receptors and transporters, including the dopamine transporter (DAT). In this study, we investigated the effects of BAs and their relationship with substrates in three transporters of the solute carrier 6 family. The exposure to obeticholic acid (OCA), a semi-synthetic BA, elicits an inward current (IBA) in the DAT, the GABA transporter 1 (GAT1), and the glycine transporter 1 (GlyT1b); this current is proportional to the current generated by the substrate, respective to the transporter. Interestingly, a second consecutive OCA application to the transporter fails to elicit a response. The full displacement of BAs from the transporter occurs only after exposure to a saturating concentration of a substrate. In DAT, perfusion of secondary substrates norepinephrine (NE) and serotonin (5-HT) results in a second OCA current, decreased in amplitude and proportional to their affinity. Moreover, co-application of 5-HT or NE with OCA in DAT, and GABA with OCA in GAT1, did not alter the apparent affinity or the Imax, similar to what was previously reported in DAT in the presence of DA and OCA. The findings support the previous molecular model that suggested the ability of BAs to lock the transporter in an occluded conformation. The physiological significance is that it could possibly avoid the accumulation of small depolarizations in the cells expressing the neurotransmitter transporter. This achieves better transport efficiency in the presence of a saturating concentration of the neurotransmitter and enhances the action of the neurotransmitter on their receptors when they are present at reduced concentrations due to decreased availability of transporters.

Synaptic Targets of Glycinergic Neurons in Laminae I-III of the Spinal Dorsal Horn.

A great deal of evidence supports the inevitable importance of spinal glycinergic inhibition in the development of chronic pain conditions. However, it remains unclear how glycinergic neurons contribute to the formation of spinal neural circuits underlying pain-related information processing. Thus, we intended to explore the synaptic targets of spinal glycinergic neurons in the pain processing region (laminae I-III) of the spinal dorsal horn by combining transgenic technology with immunocytochemistry and in situ hybridization accompanied by light and electron microscopy. First, our results suggest that, in addition to neurons in laminae I-III, glycinergic neurons with cell bodies in lamina IV may contribute substantially to spinal pain processing. On the one hand, we show that glycine transporter 2 immunostained glycinergic axon terminals target almost all types of excitatory and inhibitory interneurons identified by their neuronal markers in laminae I-III. Thus, glycinergic postsynaptic inhibition, including glycinergic inhibition of inhibitory interneurons, must be a common functional mechanism of spinal pain processing. On the other hand, our results demonstrate that glycine transporter 2 containing axon terminals target only specific subsets of axon terminals in laminae I-III, including nonpeptidergic nociceptive C fibers binding IB4 and nonnociceptive myelinated A fibers immunoreactive for type 1 vesicular glutamate transporter, indicating that glycinergic presynaptic inhibition may be important for targeting functionally specific subpopulations of primary afferent inputs.

The Effects of N-Linked Glycosylation on SLC6 Transporters.

Membrane transporters of the solute carrier 6 (SLC6) family mediate various physiological processes by facilitating the translocation of amino acids, neurotransmitters, and other metabolites. In the body, the activity of these transporters is tightly controlled through various post-translational modifications with implications on protein expression, stability, membrane trafficking, and dynamics. While N-linked glycosylation is a universal regulatory mechanism among eukaryotes, a consistent mechanism of how glycosylation affects the SLC6 transporter family remains elusive. It is generally believed that glycans influence transporter stability and membrane trafficking; however, the role of glycosylation on transporter dynamics remains disputable, with differing conclusions among individual transporters across the SLC6 family. In this study, we collected over 1 ms of aggregated all-atom molecular dynamics (MD) simulation data to systematically identify the impact of N-glycans on SLC6 transporter dynamics. We modeled four human SLC6 transporters, the serotonin, dopamine, glycine, and B0AT1 transporters, by first simulating all possible combinations of a glycan attached to each glycosylation site followed by investigating the effect of larger, oligo-N-linked glycans to each transporter. The simulations reveal that glycosylation does not significantly affect the transporter structure but alters the dynamics of the glycosylated extracellular loop and surrounding regions. The structural consequences of glycosylation on the loop dynamics are further emphasized with larger glycan molecules attached. However, no apparent differences in ligand stability or movement of the gating helices were observed, and as such, the simulations suggest that glycosylation does not have a profound effect on conformational dynamics associated with substrate transport.

Efficacy and Safety of Iclepertin (BI 425809) in Patients With Schizophrenia: CONNEX, A Phase III Randomized Controlled Trial Program

AbstractIntroductionCognitive impairment is a major determinant of poor functional outcome in schizophrenia and there are currently no available pharmacotherapies. Deficits in glutamatergic signaling play a key role in the neuropathology of cognitive symptoms. Iclepertin (BI 425809), an inhibitor of glycine transporter-1, enhances glutamatergic signaling by increasing synaptic levels of the N-methyl-D-aspartate receptor co-agonist, glycine. A 12-week, Phase II trial (NCT02832037) in 509 patients with schizophrenia demonstrated that iclepertin was well tolerated and significantly improved cognition. The Phase III CONNEX program aims to confirm the efficacy, safety, and tolerability of iclepertin in improving cognition and functioning in a larger cohort of patients.MethodsCONNEX consists of three replicate randomized, double-blind, placebo-controlled parallel-group trials in patients with schizophrenia (NCT04846868, NCT04846881, NCT04860830) currently stable on antipsychotic treatment. Each trial aims to recruit ~586 patients, 18–50 years old, treated with 1–2 antipsychotic medications (≥12 weeks on current drug; ≥35 days on current dose prior to treatment), who have functional impairment in day-to-day activities, and interact ≥1 hour per week with a designated study partner. Patients with cognitive impairment due to developmental, neurological, or other disorders, or receiving cognitive remediation therapy within 12 weeks prior to screening, will be excluded. Patients will be recruited from multiple centers across 32 countries in Asia, North and South America, and Europe, and randomized 1:1 to receive either oral iclepertin 10 mg (n=293), or placebo (n=293) once daily over 26 weeks. The primary efficacy endpoint is change from baseline (CfB) in the MATRICS Consensus Cognitive Battery overall composite T-score. Key secondary efficacy endpoints are CfB in Schizophrenia Cognition Rating Scale total score and CfB in the adjusted total time in the Virtual Reality Functional Capacity Assessment Tool. Long-term safety and tolerability data will be collected in an open-label safety extension study (CONNEX-X).ResultsThe studies are currently recruiting (first patients enrolled Aug–Sept 2021), with completion expected in Q2 2024. Here we present an overview of the current study status, including any information relating to screening failures, and the experience of collecting these data as part of a large multi-country, multi-center study.ConclusionTo date, most large, industry-sponsored studies testing various compounds to address cognitive function have failed to show proof-of-clinical concept. Demonstration of efficacy of iclepertin in improving cognition in this Phase III program would provide important insight into the role of glutamate in cognitive symptoms that may also have relevance for other cognitive disorders. Iclepertin may represent the first efficacious medication for cognitive impairment associated with schizophrenia.FundingBoehringer Ingelheim International GmbH (1346-0011, NCT04846868; 1346-0012, NCT04846881; 1346-0013, NCT04860830)

Combining Iclepertin (BI 425809) With Computerized Cognitive Training in Patients With Schizophrenia: Baseline Data From an Ongoing Phase II Trial

AbstractIntroductionThere are currently no approved pharmacotherapies to treat cognitive impairment associated with schizophrenia (CIAS). Iclepertin (BI 425809) is a novel glycine transporter-1 inhibitor under development for treatment of CIAS. A previous study demonstrated pro-cognitive effects of iclepertin in patients with schizophrenia; however, concurrent cognitive stimulation could in theory enhance any pro-cognitive pharmacological effects on neuroplasticity. We present preliminary demographics and baseline data from a trial exploring the efficacy of iclepertin together with at-home computerized cognitive training (CCT).MethodsThis is an ongoing Phase II, double-blind, placebo-controlled, parallel-group trial in patients with schizophrenia on stable antipsychotic therapy across ~58 centers in 6 countries. Patients aged 18–50 years, compliant with CCT during the run-in period (completing ≥2 hours/week for 2 weeks), were randomized (1:1) to receive once-daily iclepertin 10 mg or placebo together with CCT for 12 weeks. Thereafter, minimum compliance for at-home CCT is 1 hour/week, with a target of ~30 hours across 3–5 sessions totaling 2.5 hours/week. Patients have been stratified to balance potential effects of age (18–40; 41–50 years). Primary endpoint is change from baseline (CfB) in neurocognitive composite T-score of the MATRICS Consensus Cognitive Battery (MCCB) at Week 12. Secondary endpoints include CfB in the Schizophrenia Cognition Rating Scale (SCoRS) total score, MCCB overall composite T-score, and Positive and Negative Syndrome Scale (PANSS) total scores. Novel exploratory endpoints include the Virtual Reality Functional Capacity Assessment Tool to assess daily functioning and the Balloon Effort Task to assess motivation in cognitive performance.ResultsOf the planned sample of 200 randomized patients, the overall treated population currently includes 183: 67% (n=122) are male; mean (standard deviation [SD]) age and time since first diagnosis are 38.2 (7.9) years and 13.5 (8.5) years. Overall, 49% (n=89) are White and 43% (n=79) are Black or African American; 80% (n=147) are from North America, 15% (n=28) from Europe, and 4% (n=8) from Australia/New Zealand. Mean (SD) baseline MCCB neurocognitive composite and overall T-scores (n=178) are 33.7 (11.9) and 32.5 (12.6). Mean (SD) baseline SCoRS total score (n=167) is 35.2 (8.7). Mean (SD) baseline PANSS total and negative symptom scale scores (n=183) are 64.7 (14.6) and 17.3 (5.4). Median (Q1, Q3) CCT compliance over the on-treatment period for patients who have completed or discontinued early is 2.00 (1.21, 2.51) hours/week.ConclusionThis trial is, to our knowledge, the largest of its kind combining daily pharmacotherapy for CIAS with at-home CCT. It will indicate whether iclepertin together with concurrent cognitive stimulation provides enhanced cognitive benefit, and whether any improvements in neurocognition can translate into improved measures of daily functioning in patients.FundingBoehringer Ingelheim International GmbH (NCT03859973/1346-0038)

PDZ interaction of the GABA transporter GAT1 with the syntenin-1 in Neuro-2a cells

The GABA transporter GAT1 regulates brain inhibitory neurotransmission and it is considered a potential therapeutic target for the treatment of wide spectrum of neurological diseases including epilepsy, stroke and autism. Syntenin-1 binds to syntaxin 1A, which is known to regulate the plasma membrane insertion of several neurotransmitter transporters. Previously, a direct interaction of syntenin-1 with the glycine transporter GlyT2 was reported. Here, we show that the GABA transporter GAT1 also directly interacts with syntenin-1, involving both unidentified protein interaction interface and the GAT1 C-terminal PDZ binding motif interacting mainly with syntenin-1 PDZ domain 1. The PDZ interaction was eliminated by the mutation of GAT1 isoleucine 599 and tyrosine 598 located in PDZ positions 0 and -1, respectively. This indicates an unconventional PDZ interaction and possible regulation of the transporter PDZ motif via tyrosine phosphorylation. Whole syntenin-1 protein fused to GST protein and immobilised on glutathione resin coprecipitated intact GAT1 transporter from an extract of GAT1 transfected neuroblastoma N2a cells. This coprecipitation was inhibited by tyrosine phosphatases inhibitor pervanadate. The fluorescence tagged GAT1 and syntenin-1 colocalized upon coexpression in N2a cells. The above results show that syntenin-1 might be, in addition to GlyT2, directly involved in the trafficking of GAT1 transporter.

Rescue of synaptic and cognitive functions in polysialic acid-deficient mice and dementia models by short polysialic acid fragments

Dysregulated cortical expression of the neural cell adhesion molecule (NCAM) and deficits of its associated polysialic acid (polySia) have been found in Alzheimer's disease and schizophrenia. However, the functional role of polySia in cortical synaptic plasticity remains poorly understood. Here, we show that acute enzymatic removal of polySia in medial prefrontal cortex (mPFC) slices leads to increased transmission mediated by the GluN1/GluN2B subtype of N-methyl-d-aspartate receptors (NMDARs), increased NMDAR-mediated extrasynaptic tonic currents, and impaired long-term potentiation (LTP). The latter could be fully rescued by pharmacological suppression of GluN1/GluN2B receptors, or by application of short soluble polySia fragments that inhibited opening of GluN1/GluN2B channels. These treatments and augmentation of synaptic NMDARs with the glycine transporter type 1 (GlyT1) inhibitor sarcosine also restored LTP in mice deficient in polysialyltransferase ST8SIA4. Furthermore, the impaired performance of polySia-deficient mice and two models of Alzheimer's disease in the mPFC-dependent cognitive tasks could be rescued by intranasal administration of polySia fragments. Our data demonstrate the essential role of polySia-NCAM in the balancing of signaling through synaptic/extrasynaptic NMDARs in mPFC and highlight the therapeutic potential of short polySia fragments to restrain GluN1/GluN2B-mediated signaling.

QSAR, ADME-Tox, molecular docking and molecular dynamics simulations of novel selective glycine transporter type 1 inhibitors with memory enhancing properties

A structural class of forty glycine transporter type 1 (GlyT1) inhibitors, was examined using molecular modeling techniques. The quantitative structure-activity relationships (QSAR) technology confirmed that human GlyT1 activity is strongly and significantly affected by constitutional, geometrical, physicochemical and topological descriptors. ADME-Tox in-silico pharmacokinetics revealed that L28 and L30 ligands were predicted as non-toxic inhibitors with a good ADME profile and the highest probability to penetrate the central nervous system (CNS). Molecular docking results indicated that the predicted inhibitors block GlyT1, reacting specifically with Phe319, Phe325, Tyr123, Tyr 124, Arg52, Asp475, Ala117, Ala479, Ile116 and Ile483 amino acids of the dopamine transporter (DAT) membrane protein. These results were qualified and strengthened using molecular dynamics (MD) study, which affirmed that the established intermolecular interactions for (L28, L30–DAT protein) complexes remain perfectly stable along 50 ns of MD simulation time. Therefore, they could be strongly recommended as therapeutics in medicine to improve memory performance.

Efficacy and safety of the novel GlyT1 inhibitor BI 425809 in Alzheimer’s dementia: a randomized controlled trial

BackgroundThis phase II proof-of-concept study assessed the efficacy and safety of BI 425809, a novel selective glycine transporter-1 inhibitor, for the treatment of cognitive impairment associated with probable Alzheimer’s disease dementia.MethodsThis 12-week, multicenter, double-blind, placebo-controlled, parallel-group study randomized (1:1:1:1:1) patients with mild-to-moderate probable Alzheimer’s disease dementia to BI 425809 2, 5, 10, and 25 mg or placebo once daily. The primary efficacy endpoint was the change from baseline in Alzheimer’s Disease Assessment Scale-Cognitive Subscale 11-item total score after 12 weeks of treatment. Safety was also assessed.ResultsSix hundred and ten male and female patients were randomized to BI 425809 2 mg (n = 123), 5 mg (n = 122), 10 mg (n = 122), and 25 mg (n = 123) or placebo (n = 120). Approximately 47% (n = 286) were male; the mean (standard deviation) age was 72.9 (7.7) years. Treatment compliance was above 97% for all dose groups. The Mini-Mental State Examination category on the median score was < 22 in 47% (n = 287) of patients and ≥ 22 in 53% (n = 322) of patients. No significant, non-flat dose–response relationship was detected for the primary endpoint (adjusted p-value > 0.76 for all models). BI 425809 was generally well-tolerated. Overall, 47.9% (n = 292) of patients reported at least one adverse event during the trial; the frequency of patients with investigator-defined drug-related adverse events was similar in all treatment groups, ranging from 15.4 to 19.5% across the BI 425809 treatment groups and 15.8% for placebo.ConclusionsNo clinically meaningful changes from baseline were observed following treatment with BI 425809 in patients with mild-to-moderate probable Alzheimer’s disease dementia.Trial registrationClinicalTrials.gov NCT02788513 (1346-0023). Registered on June 2, 2016. EU Clinical Trials Register 2015-005438-24. Registered on May 6, 2016

Membrane cholesterol regulates inhibition and substrate transport by the glycine transporter, GlyT2.

Membrane cholesterol binds to and modulates the function of various SLC6 neurotransmitter transporters, including stabilizing the outward-facing conformation of the dopamine and serotonin transporters. Here, we investigate how cholesterol binds to GlyT2 (SLC6A5), modulates glycine transport rate, and influences bioactive lipid inhibition of GlyT2. Bioactive lipid inhibitors are analgesics that bind to an allosteric site accessible from the extracellular solution when GlyT2 adopts an outward-facing conformation. Using molecular dynamics simulations, mutagenesis, and cholesterol depletion experiments, we show that bioactive lipid inhibition of glycine transport is modulated by the recruitment of membrane cholesterol to a binding site formed by transmembrane helices 1, 5, and 7. Recruitment involves cholesterol flipping from its membrane orientation, and insertion of the 3' hydroxyl group into the cholesterol binding cavity, close to the allosteric site. The synergy between cholesterol and allosteric inhibitors provides a novel mechanism of inhibition and a potential avenue for the development of potent GlyT2 inhibitors as alternative therapeutics for the treatment of neuropathic pain and therapeutics that target other SLC6 transporters.

Pharmacokinetic profile of bitopertin, a selective GlyT1 inhibitor, in the rat.

Bitopertin, a selective glycine transporter 1 (GlyT1) inhibitor, has been extensively studied for the treatment of schizophrenia, with known safety and tolerability profiles in the clinic. Whereas several rodent experiments have been reported, the pharmacokinetic (PK) profile of bitopertin in rodents has not been extensively reported, as only two studies disclosed limited PK parameters in male rats after oral administration. Here, we determined the PK profile of bitopertin in female Sprague-Dawley rats. Blood samples were taken serially, before and after sub-cutaneous (0.03, 0.1, 0.3, 1, and 3mg/kg) or intra-venous (0.1mg/kg) administration. Plasma levels were determined by high-performance liquid chromatography coupled with heat-assisted electrospray ionisation tandem mass spectrometry (HPLC-HESI MS/MS). Subsequently, PK parameters were calculated using non-compartmental analysis, including area under the curve (AUC), time (Tmax) to maximal plasma concentration (Cmax), clearance (CL), volume of distribution (Vz), as well as half-life (T1/2). Following sub-cutaneous injection, bitopertin exhibited dose-dependent AUC0-∞ (439.6-34,018.9ng/mL) and Tmax (3.7-24.0h), a very long terminal T1/2 (35.06-110.32h) and low CL (0.07-0.13 L/h/kg), suggesting that bitopertin is slowly absorbed and eliminated in the rat. The observed relationship between dose and the extent of drug exposure (AUC) was linear. Following administration of all sub-cutaneous doses, measured bitopertin plasma levels were comparable to levels achieved with doses already administered in the clinic. We hope that our results will be useful in the design of pre-clinical experiments in which this drug will eventually be administered sub-cutaneously.

Sarcosine (glycine transporter inhibitor) attenuates behavioural and biochemical changes induced by ketamine, in the rat model of schizophrenia

Schizophrenia is a neurological disorder that alters the behavior and affects the quality of life of a patient. It is characterized by hallucinations, disorganized behavior, cognitive dysfunction, hyperlocomotion, and loss of the reward system. Schizophrenia constitutes three symptoms' domains, viz. positive, negative and cognitive. Typical and atypical antipsychotics do not fully resolve all the symptoms' domains thus paving the way to the genesis of the glutamatergic hypothesis, i.e. N-methyl-D-aspartate (NMDA) receptor hypofunction in the pathophysiology of schizophrenia. Positive modulation of NMDA receptors by enhancing co-agonist, glycine effect is proposed to produce a therapeutic effect in schizophrenia. Hence, sarcosine (N-methyl glycine), natural amino acid, and a glycine transporter inhibitor (GlyT-1) which also acts on NMDA receptors were used in the present study. The present study unravels the role of sarcosine in the attenuation of ketamine-induced three symptom domains in a rat model through modulation of oxidative stress, mitochondrial dysfunction, and neuroinflammatory pathways. The animal model of schizophrenia was established by injecting ketamine intraperitoneal (ip) at a 30mg/kg dose for 10 consecutive days, after which sarcosine (300, 600mg/kg, ip) as a treatment was given for 7days followed by behavioral, biochemical, molecular, and histopathological analysis. It was revealed that sarcosine reversed ketamine-induced behavioral impairments. Moreover, sarcosine ameliorated oxidative and nitrosative stress, mitochondrial dysfunction, and neuroinflammation and showed protective effects in histopathological examination by hematoxylin and eosin staining. Hence, conclusively, sarcosine was regarded to attenuate the behavioural symptoms of schizophrenia by alleviating oxidative stress, neuroinflammation, and mitochondrial dysfunction established by the ketamine.

Cross-Linking and Functional Analyses for Dimerization of a Cysteine Mutant of Glycine Transporter 1.

Glycine transporter 1 (GlyT1) is responsible for the reuptake of glycine, which regulates glutamate signaling as a co-agonist with N-methyl-D-aspartic acid (NMDA) receptors in the excitatory synapse and has been proposed to be a potential target in the development of therapies for a broad range of disorders of the central nervous system. Despite significant progress in characterizing structure and transport mechanism of the transporter, the regulation of transport function through oligomerization remains to be understood. In the present work, association of two forms of GlyT1 into dimers and higher order oligomers was detected by coimmunoprecipitation. To investigate functional properties of dimers of a GlyT1 cysteine mutant L288C, we performed oxidative cross-linking of the positioned cysteine residues in extracellular loop 3 (EL3) near the extracellular end of TM6. By analyzing the effect of copper phenanthroline (CuP)-induced dimerization on transport function, cross-linking of L288C was found to inhibit transport activity. In addition, an intramolecular ion pair Lys286-Glu289 was revealed to be critical for stabilizing EL3 in a conformation that modulates CuP-induced dimerization and transport function of the GlyT1 L288C mutant. Furthermore, the influence of transporter conformation on GlyT1 L288C dimerization was investigated. The substrate glycine, in the presence of both Na+ and Cl-, significantly reduced oxidative cross-linking, suggesting a large-scale rotation of the bundle domain during substrate transport impairs interfacial interactions between L288C protomers. The present study provides new insights into structural and functional elements regulating GlyT1 transport activity through its dimerization or oligomerization.