Pharmacological characterization of SAGE-718, a novel positive allosteric modulator of N-methyl-d-aspartate receptors

Hydrogen Sulfide (H2S) Generated in the Colon Induces Neuropathic Pain by Activating Spinal NMDA Receptors in a Rodent Model of Chronic Constriction Injury

Neuropathic pain (NP) imposes a significant burden on individuals, manifesting as nociceptive anaphylaxis, hypersensitivity, and spontaneous pain. Previous studies have shown that traumatic stress in the nervous system can lead to excessive production of hydrogen sulfide (H2S) in the gut. As a toxic gas, it can damage the nervous system through the gut-brain axis. However, whether traumatic stress in the nervous system leading to excessive production of H2S in the gut can ultimately cause neuropathic pain through the gut-brain axis remains to be investigated. This study established a model of chronic constriction injury (CCI) in mice to determine its effects on gut H2S production, the associated damage via the gut-brain axis, the potential neuropathic pain, as well as the probable mechanism. A CCI mouse model was developed using a spinal nerve ligation approach. Subsequently, the mechanical withdrawal threshold (MWT) and thermal withdrawal latency (TWL) were used to determine the mice's pain thresholds. A variety of assays were performed, including immunofluorescence, western blotting, real-time quantitative Polymerase Chain Reaction (PCR), and membrane clamp whole-cell recordings. Mice subjected to CCI showed decreased MWT and TWL, decreased ZO-1 staining, decreased HuD staining, increased Glial fibrillary acidic protein (GFAP) staining, increased expression of tumor necrosis factor-alpha (TNF-α) protein and interleukin-6 (IL-6) protein, increased expression of NMDAR2B (NR2B) protein and NR2B mRNA, increased colocalization of vGlut2- and c-fos-positive cells, and a higher amplitude of evoked excitatory postsynaptic potential (EPSP) compared to Sham group. These changes were significantly reversed by H2S inhibitor treatment, and the specific NMDA receptor inhibitor MK-801 effectively restored the neurotoxicity of H2S. H2S is involved in CCI-induced neuropathic pain in mice, which might be mediated by the activation of the NMDA signaling pathway.

Changes in 24(S)-Hydroxycholesterol Are Associated with Cognitive Performance in Early Huntington's Disease: Data from the TRACK and ENROLL HD Cohorts

BACKGROUND

There is evidence for dysregulated cholesterol homeostasis in Huntington's disease (HD). The brain-specific cholesterol metabolite 24(S)-hydroxycholesterol (24(S)-OHC) is decreased in manifest HD. 24(S)-OHC is an endogenous positive allosteric modulator (PAM) of the N-methyl-D-aspartate (NMDA) receptor, suggesting lower 24(S)-OHC may contribute to NMDA receptor hypofunction in HD. We hypothesized changes in 24(S)-OHC would be associated with cognitive impairment in early HD.

OBJECTIVE

To determine the interactions between oxysterols (24(S)-OHC, 25-OHC, and 27-OHC) at the NMDA receptor, the plasma levels of these oxysterols, and how these levels relate to cognitive performance.

METHODS

An in vitro competition assay was used to evaluate interactions at the NMDA receptor, liquid chromatography coupled tandem mass spectrometry (LC-MS/MS) was used to measure plasma 24(S)-OHC, 25-OHC, and 27-OHC levels, and correlation analyses investigated their relationship to performance on cognitive endpoints in TRACK and ENROLL-HD (NCT01574053).

RESULTS

In vitro, 25-OHC and 27-OHC attenuated the PAM activity of 24(S)-OHC on the NMDA receptor. Lower plasma 24(S)-OHC levels and 24(S)/25-OHC ratios were detected in participants with early HD. Moderate and consistent associations were detected between plasma 24(S)/25-OHC ratio and performance on Stroop color naming, symbol digit modality, Trails A/B, and emotion recognition. Little association was observed between the ratio and psychiatric or motor endpoints, suggesting specificity for the relationship to cognitive performance.

CONCLUSIONS

Our findings support growing evidence for dysregulated CNS cholesterol homeostasis in HD, demonstrate a relationship between changes in oxysterols and cognitive performance in HD, and propose that NMDA receptor hypofunction may contribute to cognitive impairment in HD.

Structural and functional remodeling of neural networks in β-amyloid driven hippocampal hyperactivity

Early detection of Alzheimer's disease (AD) is essential for improving the patients outcomes and advancing our understanding of disease, allowing for timely intervention and treatment. However, accurate biomarkers are still lacking. Recent evidence indicates that hippocampal hyperexcitability precedes the diagnosis of AD decades ago, can predict cognitive decline. Thus, could hippocampal hyperactivity be a robust biomarker for early-AD, and what drives hippocampal hyperactivity in early-AD? these critical questions remain to be answered. Increasing clinical and experimental studies suggest that early hippocampal activation is closely associated with longitudinal β-amyloid (Aβ) accumulation, Aβ aggregates, in turn, enhances hippocampal activity. Therefore, in this narrative review, we discuss the role of Aβ-induced altered intrinsic neuronal properties as well as structural and functional remodeling of glutamatergic, GABAergic, cholinergic, noradrenergic, serotonergic circuits in hippocampal hyperactivity. In addition, we analyze the available therapies and trials that can potentially be used clinically to attenuate hippocampal hyperexcitability in AD. Overall, the present review sheds lights on the mechanism behind Aβ-induced hippocampal hyperactivity, and highlights that hippocampal hyperactivity could be a robust biomarker and therapeutic target in prodromal AD.

Dalzanemdor (SAGE-718), a novel, investigational N-methyl-D-aspartate receptor positive allosteric modulator: Safety, tolerability, and clinical pharmacology in randomized dose-finding studies in healthy participants and an open-label study in participants with Huntington's disease

N-methyl-D-aspartate receptor (NMDAR)-positive allosteric modulators (PAMs) represent a potential therapeutic strategy for cognitive impairment in disorders associated with NMDAR hypofunction, including Huntington's disease (HD) and Alzheimer's disease. Dalzanemdor (SAGE-718) is a novel, investigational NMDAR PAM being evaluated for the potential treatment of cognitive impairment in these disorders. We report first-in-human, phase I, double-blind, dose-finding studies to assess the safety, tolerability, and clinical pharmacology of dalzanemdor. A single-ascending dose study (dalzanemdor 0.35, 0.75, 1.5, or 3.0 mg vs. placebo) was conducted in healthy participants and included food effects. A multiple-ascending dose study (14 days) was conducted in healthy participants (dalzanemdor 0.5 or 1.0 mg vs. placebo) and HD participants (open-label dalzanemdor 1.0 mg) and included exploratory pharmacodynamics on cognitive performance. Dalzanemdor was generally well tolerated with no adverse events leading to discontinuation. Dalzanemdor exhibited pharmacokinetic parameters appropriate for once-daily dosing. Following single and multiple doses in healthy participants, median terminal half-life was 8-118 h, and the median time to reach maximum plasma concentration was 4-7 h. Exposures were dose-proportional after single dose (6-46 ng/mL) and more than dose-proportional after multiple doses (6-41 ng/mL). With multiple dosing, a steady state was achieved after 11 days in healthy participants and 13 days in HD participants. Dalzanemdor exposure decreased slightly with food. In HD participants, results suggest that dalzanemdor may improve cognitive performance on tests of executive function. These results support continued clinical development of dalzanemdor for the potential treatment of cognitive impairment in disorders of NMDAR hypofunction.

New Therapeutic Targets and Drugs for Schizophrenia Beyond Dopamine D2 Receptor Antagonists

Schizophrenia is a disease with a complex pathological mechanism that is influenced by multiple genes. The study of its pathogenesis is dominated by the dopamine hypothesis, as well as other hypotheses such as the 5-hydroxytryptamine hypothesis, glutamate hypothesis, immune-inflammatory hypothesis, gene expression abnormality hypothesis, and neurodevelopmental abnormality hypothesis. The first generation of antipsychotics was developed based on dopaminergic receptor antagonism, which blocks dopamine D2 receptors in the brain to exert antipsychotic effects. The second generation of antipsychotics acts by dual blockade of 5-hydroxytryptamine and dopamine receptors. From the third generation of antipsychotics onwards, the therapeutic targets for antipsychotic schizophrenia expanded beyond D2 receptor blockade to explore D2 receptor partial agonism and the antipsychotic effects of new targets such as D3, 5-HT1A, 5-HT7, and mGlu2/3 receptors. The main advantages of the second and third generation antipsychotics over first-generation antipsychotics are the reduction of side effects and the improvement of negative symptoms, and even though third-generation antipsychotics do not directly block D2 receptors, the modulation of the dopamine transmitter system is still an important part of their antipsychotic process. According to recent research, several receptors, including 5-hydroxytryptamine, glutamate, γ-aminobutyric acid, acetylcholine receptors and norepinephrine, play a role in the development of schizophrenia. Therefore, the focus of developing new antipsychotic drugs has shifted towards agonism or inhibition of these receptors. Specifically, the development of NMDARs stimulants, GABA receptor agonists, mGlu receptor modulators, cholinergic receptor modulators, 5-HT2C receptor agonists and alpha-2 receptor modulators has become the main direction. Animal experiments have confirmed the antipsychotic effects of these drugs, but their pharmacokinetics and clinical applicability still require further exploration. Research on alternative targets for antipsychotic drugs, beyond the dopamine D2 receptor, has expanded the potential treatment options for schizophrenia and gives an important way to address the challenge of refractory schizophrenia. This article aims to provide a comprehensive overview of the research on therapeutic targets and medications for schizophrenia, offering valuable insights for both treatment and further research in this field.