Emerging role of glutamate in the pathophysiology and therapeutics of Gulf War illness

Impact of a pyridazine derivative on tripartite synapse ultrastructure in hippocampus: a three-dimensional analysis

Introduction

We previously discovered a pyridazine derivative compound series that can improve cognitive functions in mouse models of Alzheimer's disease. One of the advanced compounds from this series, LDN/OSU-0215111-M3, was selected as the preclinical development candidate. This compound activates local protein translation at the perisynaptic astrocytic process (PAP) and enhances synaptic plasticity sequentially. While biochemical evidence supports the hypothesis that the compound enhances the structural plasticity of the tripartite synapse, its direct structural impact has not been investigated.

Methods

Volume electron microscopy was used to study the hippocampal tripartite synapse three-dimensional structure in 3-month-old wild-type FVB/NJ mice after LDN/OSU-0215111-M3 treatment.

Results

LDN/OSU-0215111-M3 increased the size of tertiary apical dendrites, the volume of mushroom spines, the proportion of mushroom spines containing spine apparatus, and alterations in the spine distribution across the surface area of tertiary dendrites. Compound also increased the number of the PAP interacting with the mushroom spines as well as the size of the PAP in contact with the spines. Furthermore, proteomic analysis of the isolated synaptic terminals indicated an increase in dendritic and synaptic proteins as well as suggested a possible involvement of the phospholipase D signaling pathway. To further validate that LDN/OSU-0215111-M3 altered synaptic function, electrophysiological studies showed increased long-term potentiation following compound treatment.

Discussion

This study provides direct evidence that pyridazine derivatives enhance the structural and functional plasticity of the tripartite synapse.

Investigation of the low glutamate diet as an adjunct treatment for pediatric epilepsy: A pilot randomized controlled trial

INTRODUCTION

Current dietary therapies for epilepsy have side effects and are low in nutrients, which would make an alternative dietary treatment, which addresses these issues, advantageous. One potential option is the low glutamate diet (LGD). Glutamate is implicated in seizure activity. Blood brain barrier permeability in epilepsy could enable dietary glutamate to reach the brain and contribute to ictogenesis.

OBJECTIVE

to assess the LGD as an adjunct treatment for pediatric epilepsy.

METHODS

This study was a nonblinded, parallel, randomized clinical trial. The study was conducted virtually due to COVID-19 and registered on clinicaltrials.gov (NCT04545346). Participants were eligible if they were between the ages of 2 and 21 with ≥4 seizures per month. Baseline seizures were assessed for 1-month, then participants were allocated via block randomization to the intervention month (N=18), or a wait-listed control month followed by the intervention month (N=15). Outcome measures included seizure frequency, caregiver global impression of change (CGIC), non-seizure improvements, nutrient intake, and adverse events.

RESULTS

Nutrient intake significantly increased during the intervention. No significant differences in seizure frequency were observed between intervention and control groups. However, efficacy was assessed at 1-month compared to the standard 3-months in diet research. Additionally, 21% of participants were observed to be clinical responders to the diet. Overall health (CGIC) significantly improved in 31%, 63% experienced ≥1 non-seizure improvements, and 53% experienced adverse events. Clinical response likelihood decreased with increasing age (0.71 [0.50-0.99], p=0.04), as did the likelihood of overall health improvement (0.71 [0.54-0.92], p=0.01).

DISCUSSION

This study provides preliminary support for the LGD as an adjunct treatment before epilepsy becomes drug resistant, which is in contrast to the role of current dietary therapies in drug resistant epilepsy.

Low glutamate diet improves working memory and contributes to altering BOLD response and functional connectivity within working memory networks in Gulf War Illness

Gulf War Illness is a chronic multi-symptom disorder with severe cognitive impairments which may be related to glutamate excitotoxicity and central nervous system dysfunction. The low glutamate diet has been proposed as a comprehensive intervention for Gulf War Illness. We examined the effects of the low glutamate diet on verbal working memory using a fMRI N-back task. Accuracy, whole-brain blood oxygen level dependency (BOLD) response, and task-based functional connectivity were assessed at baseline and after 1 month on the diet (N = 24). Multi-voxel pattern analysis identified regions of whole-brain BOLD pattern differences after the diet to be used as seeds for subsequent seed-to-voxel functional connectivity analyses. Verbal working memory accuracy improved after the diet (+ 13%; p = 0.006). Whole-brain BOLD signal changes were observed, revealing lower activation within regions of the frontoparietal network and default mode network after the low glutamate diet. Multi-voxel pattern analysis resulted in 3 clusters comprising parts of the frontoparietal network (clusters 1 and 2) and ventral attention network (cluster 3). The seed-to-voxel analyses identified significant functional connectivity changes post-diet for clusters 1 and 2 (peak p < 0.001, cluster FDR p < 0.05). Relative to baseline, clusters 1 and 2 had decreased functional connectivity with regions in the ventral attention and somatomotor networks. Cluster 2 also had increased functional connectivity with regions of the default mode and frontoparietal networks. These findings suggest that among veterans with Gulf War Illness, the low glutamate diet improves verbal working memory accuracy, alters BOLD response, and alters functional connectivity within two networks central to working memory.

Pharmacological induction of AMFR increases functional EAAT2 oligomer levels and reduces epileptic seizures in mice

Dysregulation of excitatory amino acid transporter 2 (EAAT2) contributes to the development of temporal lobe epilepsy (TLE). Several strategies for increasing total EAAT2 levels have been proposed. However, the mechanism underlying the oligomeric assembly of EAAT2, impairment of which inhibits the formation of functional oligomers by EAAT2 monomers, is still poorly understood. In the present study, we identified E3 ubiquitin ligase AMFR as an EAAT2-interacting protein. AMFR specifically increased the level of EAAT2 oligomers rather than inducing protein degradation through K542-specific ubiquitination. By using tissues from humans with TLE and epilepsy model mice, we observed that AMFR and EAAT2 oligomer levels were simultaneously decreased in the hippocampus. Screening of 2386 FDA-approved drugs revealed that the most common analgesic/antipyretic medicine, acetaminophen (APAP), can induce AMFR transcriptional activation via transcription factor SP1. Administration of APAP protected against pentylenetetrazol-induced epileptogenesis. In mice with chronic epilepsy, APAP treatment partially reduced the occurrence of spontaneous seizures and greatly enhanced the antiepileptic effects of 17AAG, an Hsp90 inhibitor that upregulates total EAAT2 levels, when the 2 compounds were administered together. In summary, our studies reveal an essential role for AMFR in regulating the oligomeric state of EAAT2 and suggest that APAP can improve the efficacy of EAAT2-targeted antiepileptic treatments.