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N-methyl-d-aspartate (NMDA) receptor hypofunctionality is a well-studied hypothesis for schizophrenia pathophysiology, and daily dosing of the NMDA receptor co-agonist, d-serine, in clinical trials has shown positive effects in patients. Therefore, inhibition of d-amino acid oxidase (DAAO) has the potential to be a new therapeutic approach for the treatment of schizophrenia. TAK-831 (luvadaxistat), a novel, highly potent inhibitor of DAAO, significantly increases d-serine levels in the rodent brain, plasma, and cerebrospinal fluid. This study shows luvadaxistat to be efficacious in animal tests of cognition and in a translational animal model for cognitive impairment in schizophrenia. This is demonstrated when luvadaxistat is dosed alone and in conjunction with a typical antipsychotic. When dosed chronically, there is a suggestion of change in synaptic plasticity as seen by a leftward shift in the maximum efficacious dose in several studies. This is suggestive of enhanced activation of NMDA receptors in the brain and confirmed by modulation of long-term potentiation after chronic dosing. DAAO is highly expressed in the cerebellum, an area of increasing interest for schizophrenia, and luvadaxistat was shown to be efficacious in a cerebellar-dependent associative learning task. While luvadaxistat ameliorated the deficit seen in sociability in two different negative symptom tests of social interaction, it failed to show an effect in endpoints of negative symptoms in clinical trials. These results suggest that luvadaxistat potentially could be used to improve cognitive impairment in patients with schizophrenia, which is not well addressed with current antipsychotic medications. [ABSTRACT FROM AUTHOR]

Correction to: Neurochemical Research https://doi.org/10.1007/s11064-023-03956-2 The article "Luvadaxistat: A Novel Potent and Selective d-Amino Acid Oxidase Inhibitor Improves Cognitive and Social Defcits in Rodent Models for Schizophrenia", written by Rosa Fradley, Pascal Goetghebeur, David Miller, Russell Burley, Sarah Almond, Agnès Gruart i Massó, José M. Delgado García, Bin Zhu, Eimear Howley, Jo C. Neill, Ben Grayson, Philip Gaskin, Mark Carlton, Ian Gray, Jordi Serrats, and Ceri H. Davies, was originally published electronically on the publisher's internet portal (https://link.springer.com/article/10.1007/s11064-023-03956-2) on 8 June 2023 without open access. The original article can be found online at https://doi.org/10.1007/s11064-023-03956-2. [Extracted from the article]

Non-selective benzodiazepines, such as diazepam, interact with equivalent affinity and agonist efficacy at GABAA receptors containing either an α1, α2, α3 or α5 subunit. However, which of these particular subtypes are responsible for the anticonvulsant effects of diazepam remains uncertain. In the present study, we examined the ability of diazepam to reduce pentylenetetrazole (PTZ)-induced and maximal electroshock (MES)-induced seizures in mice containing point mutations in single (α1H101R, α2H101R or α5H105R) or multiple (α125H→R) α subunits that render the resulting GABAA receptors diazepam-insensitive. Furthermore, the anticonvulsant properties of diazepam, the α1- and α3-selective compounds zolpidem and TP003, respectively, and the α2/α3 preferring compound TP13 were studied against PTZ-induced seizures. In the transgenic mice, no single subtype was responsible for the anticonvulsant effects of diazepam in either the PTZ or MES assay and neither the α3 nor α5 subtypes appeared to confer anticonvulsant activity. Moreover, whereas the α1 and α2 subtypes played a modest role with respect to the PTZ assay, they had a negligible role in the MES assay. With respect to subtype-selective compounds, zolpidem and TP003 had much reduced anticonvulsant efficacy relative to diazepam in both the PTZ and MES assays whereas TP13 had high anticonvulsant efficacy in the PTZ but not the MES assay. Taken together, these data not only indicate a role for α2-containing GABAA receptors in mediating PTZ and MES anticonvulsant activity but also suggest that efficacy at more than one subtype is required and that these subtypes act synergistically. [ABSTRACT FROM AUTHOR]

In the mammalian central nervous system, transporter-mediated reuptake may be critical for terminating the neurotransmitter action ofd-serine at the strychnine insensitive glycine site of the NMDA receptor. The Na+ independent amino acid transporter alanine–serine–cysteine transporter 1 (Asc-1) has been proposed to account for synaptosomald-serine uptake by virtue of its high affinity ford-serine and widespread neuronal expression throughout the brain. Here, we sought to validate the contribution of Asc-1 tod-serine uptake in mouse brain synaptosomes using Asc-1 gene knockout (KO) mice. Total [3H]d-serine uptake in forebrain and cerebellar synaptosomes from Asc-1 knockout mice was reduced to 34 ± 5% and 22 ± 3% of that observed in wildtype (WT) mice, respectively. When the Na+ dependent transport components were removed by omission of Na+ ions in the assay buffer,d-serine uptake in knockout mice was reduced to 8 ± 1% and 3 ± 1% of that measured in wildtype mice in forebrain and cerebellum, respectively, suggesting Asc-1 plays a major role in the Na+ independent transport ofd-serine. Potency determination ofd-serine uptake showed that Asc-1 mediated rapid high affinity Na+ independent uptake with an IC50 of 19 ± 1 µm. The remaining uptake was mediated predominantly via a low affinity Na+ dependent transporter with an IC50 of 670 ± 300 µm that we propose is the glial alanine–serine–cysteine transporter 2 (ASCT2) transporter. The results presented reveal that Asc-1 is the only high affinityd-serine transporter in the mouse CNS and is the predominant mechanism ford-serine reuptake. [ABSTRACT FROM AUTHOR]

Abstract: Schizophrenia is a chronic and debilitating disease which is thought to arise from a neuro-developmental disorder. Both the stable tubule-only polypeptide (STOP) protein and the N-methyl-d-aspartate (NMDA) NR1 subunit are involved in neuronal development and physiology. It has therefore been postulated that transgenic mice lacking either the STOP or the NMDAR1 gene would show a ‘schizophrenic-like’ phenotype. Here, STOP knockout and NMDA NR1 hypomorphic mice were assessed in a behavioural measure that can be used to detect schizophrenic-like phenotypes: a change in sensorimotor gating, measured through prepulse inhibition (PPI). STOP knockout mice were further assessed in another measure of ‘schizophrenic-like behaviour’: hyperlocomotion. The PPI deficit exhibited by both the STOP knockout and NMDA knockdown mice could not be reversed by acute treatment with the atyptical antipsychotic, clozapine (1mg/kg, i.p.) but the hyperlocomotion shown by the STOP knockout mice was reversed with the same acute dose of clozapine. [Copyright &y& Elsevier]

Irregular N-methyl- d-aspartate receptor (NMDAR) function is one of the main hypotheses employed to facilitate understanding of the underlying disease state of schizophrenia. Although direct agonism of the NMDAR has not yielded promising therapeutics, advances have been made by modulating the NMDAR co-agonist site which is activated by glycine and d-serine. One approach to activate the co-agonist site is to increase synaptic d-serine levels through inhibition of d-amino acid oxidase (DAO), the major catabolic clearance pathway for this and other d-amino acids. A number of DAO inhibitors have been developed but most have not entered clinical trials. One exception to this is sodium benzoate which has demonstrated efficacy in small trials of schizophrenia and Alzheimer's disease. Herein we provide data on the effect of sodium benzoate and an optimised Takeda compound, PGM030756 on ex vivo DAO enzyme occupancy and cerebellar d-serine levels in mice. Both compounds achieve high levels of enzyme occupancy; although lower doses of PGM030756 (1, 3 and 10 mg/kg) were required to achieve this compared to sodium benzoate (300, 1000 mg/kg). Cerebellar d-serine levels were increased by both agents with a delay of approximately 6 h after dosing before the peak effect was achieved. Our data and methods may be useful in understanding the effects of sodium benzoate that have been seen in clinical trials of schizophrenia and Alzheimer's disease and to support the potential clinical assessment of other DAO inhibitors, such as PGM030756, which demonstrate good enzyme occupancy and d-serine increases following administration of low oral doses. [ABSTRACT FROM AUTHOR]

The GABAA receptor subtypes responsible for the anxiolytic effects of nonselective benzodiazepines (BZs) such as chlordiazepoxide (CDP) and diazepam remain controversial. Hence, molecular genetic data suggest that α2- rather than α3-containing GABAA receptors are responsible for the anxiolytic effects of diazepam, whereas the anxiogenic effects of an α3-selective inverse agonist suggest that an agonist selective for this subtype should be anxiolytic. We have extended this latter pharmacological approach to identify a compound, 4,2′-difluoro-5′-[8-fluoro-7-(1-hydroxy-1-methylethyl)imidazo[1,2-á]pyridin-3-yl]biphenyl-2-carbonitrile (TP003), that is an α3 subtype selective agonist that produced a robust anxiolytic-like effect in both rodent and non-human primate behavioral models of anxiety. Moreover, in mice containing a point mutation that renders α2-containing receptors BZ insensitive (α2H101R mice), TP003 as well as the nonselective agonist CDP retained efficacy in a stress-induced hyperthermia model. Together, these data show that potentiation of α3-containing GABAA receptors is sufficient to produce the anxiolytic effects of BZs and that α2 potentiation may not be necessary. [ABSTRACT FROM AUTHOR]

Purpose: TAK-831 is a highly selective and potent inhibitor of D-amino acid oxidase (DAAO) currently under clinical development for schizophrenia. In this study, a mechanistic multilayer quantitative model that parsimoniously connects pharmacokinetics (PK), target occupancy (TO) and D-serine concentrations as a pharmacodynamic (PD) readout was established in mice. Methods: PK, TO and PD time-profiles were obtained in mice and analyzed by mechanistic binding kinetics model connected with an indirect response model in a step wise fashion. Brain distribution was investigated to elucidate a possible mechanism driving the hysteresis between PK and TO. Results: The observed nonlinear PK/TO/PD relationship was well captured by mechanistic modeling framework within a wide dose range of TAK-831 in mice. Remarkably different brain distribution was observed between target and reference regions, suggesting that the target-mediated slow binding kinetics rather than slow penetration through the blood brain barrier caused the observed distinct kinetics between PK and TO. Conclusion: A quantitative mechanistic model for concentration- and time-dependent nonlinear PK/TO/PD relationship was established for TAK-831 in mice with accounting for possible rate-determining process. The established mechanistic modeling framework will provide a quantitative means for multilayer biomarker-assisted clinical development in multiple central nervous system indications. [ABSTRACT FROM AUTHOR]

Abstract: Behavioural studies using transgenic techniques in mice usually require extensive backcrossing to a defined background strain, e.g. to C57BL/6. In this study we investigated whether backcrossing can be replaced by using the 129SvEv strain from which the embryonic stem cells are generally obtained for gene targeting strategies to analyze e.g. depression-like behaviour. For that purpose we subjected male and female 129SvEv mice to two frequently used depression tests and compared them with commonly used C57BL/6 mice. 129SvEv and C57BL/6 mice exhibited differing profiles with regard to locomotion and pain sensitivity. However, in the learned helplessness paradigm, a procedure, which represents a valid method to detect depressive-like behaviour, 129SvEv animals develop a similar level of helplessness as C57BL/6 mice. One great advantage of the 129SvEv animals though, is the fact that in this strain even females develop helplessness, which could not be produced in C57BL/6 mice. In the tail suspension test, both genders of 129SvEv exhibited more despair behaviour than C57BL/6 animals. We therefore suggest that this strain may be utilized in the establishment of new test procedures for affective diseases, since costly and time-consuming backcrossing can be prevented, depressive-like behaviour may be analyzed effectively, and gender-specific topics could be addressed in an adequate way. [Copyright &y& Elsevier]

Abstract: Selective antagonism of N-methyl-d-aspartate (NMDA) 2B subunit containing receptors has been suggested to have potential therapeutic application for multiple CNS disorders. The amino terminal NR2B residues 1 to 282 were found to be both necessary and sufficient for the binding and function of highly NR2B subunit specific antagonists like ifenprodil and CP-101,606. Using a genetic approach in mice, we successfully replaced the murine NR2B gene function by “knocking-in” (KI) a chimeric human NR2A/B cDNA containing the minimal domain abolishing ifenprodil binding into the endogenous NR2B locus. Patch-clamp recording from hippocampal cultures of the NR2B KI mice demonstrated that their NMDA receptors have reduced sensitivity to both ifenprodil and CP-101,606, as predicted, but also have a lower affinity for glycine. The NR2B KI mice exhibited normal locomotor activity making this ifenprodil-insensitive mouse model a valuable tool to test the specificity of NR2B selective antagonists in vivo. [Copyright &y& Elsevier]