Neuronal PAS domain protein 4 (Npas4) controls neuronal homeostasis in pentylenetetrazole-induced epilepsy through the induction of Homer1a

Acute rapamycin treatment reveals novel mechanisms of behavioral, physiological, and functional dysfunction in a maternal inflammation mouse model of autism and sensory over-responsivity

Maternal inflammatory response (MIR) during early gestation in mice induces a cascade of physiological and behavioral changes that have been associated with autism spectrum disorder (ASD). In a prior study and the current one, we find that mild MIR results in chronic systemic and neuro-inflammation, mTOR pathway activation, mild brain overgrowth followed by regionally specific volumetric changes, sensory processing dysregulation, and social and repetitive behavior abnormalities. Prior studies of rapamycin treatment in autism models have focused on chronic treatments that might be expected to alter or prevent physical brain changes. Here, we have focused on the acute effects of rapamycin to uncover novel mechanisms of dysfunction and related to mTOR pathway signaling. We find that within 2 hours, rapamycin treatment could rapidly rescue neuronal hyper-excitability, seizure susceptibility, functional network connectivity and brain community structure, and repetitive behaviors and sensory over-responsivity in adult offspring with persistent brain overgrowth. These CNS-mediated effects are also associated with alteration of the expression of several ASD-,ion channel-, and epilepsy-associated genes, in the same time frame. Our findings suggest that mTOR dysregulation in MIR offspring is a key contributor to various levels of brain dysfunction, including neuronal excitability, altered gene expression in multiple cell types, sensory functional network connectivity, and modulation of information flow. However, we demonstrate that the adult MIR brain is also amenable to rapid normalization of these functional changes which results in the rescue of both core and comorbid ASD behaviors in adult animals without requiring long-term physical alterations to the brain. Thus, restoring excitatory/inhibitory imbalance and sensory functional network modularity may be important targets for therapeutically addressing both primary sensory and social behavior phenotypes, and compensatory repetitive behavior phenotypes.

The neuron-specific IIS/FOXO transcriptome in aged animals reveals regulatory mechanisms of cognitive aging

Cognitive decline is a significant health concern in our aging society. Here, we used the model organism C. elegans to investigate the impact of the IIS/FOXO pathway on age-related cognitive decline. The daf-2 Insulin/IGF-1 receptor mutant exhibits a significant extension of learning and memory span with age compared to wild-type worms, an effect that is dependent on the DAF-16 transcription factor. To identify possible mechanisms by which aging daf-2 mutants maintain learning and memory with age while wild-type worms lose neuronal function, we carried out neuron-specific transcriptomic analysis in aged animals. We observed downregulation of neuronal genes and upregulation of transcriptional regulation genes in aging wild-type neurons. By contrast, IIS/FOXO pathway mutants exhibit distinct neuronal transcriptomic alterations in response to cognitive aging, including upregulation of stress response genes and downregulation of specific insulin signaling genes. We tested the roles of significantly transcriptionally-changed genes in regulating cognitive functions, identifying novel regulators of learning and memory. In addition to other mechanistic insights, a comparison of the aged vs young daf-2 neuronal transcriptome revealed that a new set of potentially neuroprotective genes is upregulated; instead of simply mimicking a young state, daf-2 may enhance neuronal resilience to accumulation of harm and take a more active approach to combat aging. These findings suggest a potential mechanism for regulating cognitive function with age and offer insights into novel therapeutic targets for age-related cognitive decline.

RNA Sequencing Demonstrates Ex Vivo Neocortical Transcriptomic Changes Induced by Epileptiform Activity in Male and Female Mice

Seizures are generally associated with epilepsy but may also be a symptom of many other neurological conditions. A hallmark of a seizure is the intensity of the local neuronal activation, which can drive large-scale gene transcription changes. Such changes in the transcriptional profile likely alter neuronal function, thereby contributing to the pathological process. Therefore, there is a strong clinical imperative to characterize how gene expression is changed by seizure activity. To this end, we developed a simplified ex vivo technique for studying seizure-induced transcriptional changes. We compared the RNA sequencing profile in mouse neocortical tissue with up to 3 h of epileptiform activity induced by 4-aminopyridine (4AP) relative to control brain slices not exposed to the drug. We identified over 100 genes with significantly altered expression after 4AP treatment, including multiple genes involved in MAPK, TNF, and neuroinflammatory signaling pathways, all of which have been linked to epilepsy previously. Notably, the patterns in male and female brain slices were almost identical. Various immediate early genes were among those showing the largest upregulation. The set of down-regulated genes included ones that might be expected either to increase or to decrease neuronal excitability. In summary, we found the seizure-induced transcriptional profile complex, but the changes aligned well with an analysis of published epilepsy-associated genes. We discuss how simple models may provide new angles for investigating seizure-induced transcriptional changes.

Age-related dysregulation of homeostatic control in neuronal microcircuits

Neuronal homeostasis prevents hyperactivity and hypoactivity. Age-related hyperactivity suggests homeostasis may be dysregulated in later life. However, plasticity mechanisms preventing age-related hyperactivity and their efficacy in later life are unclear. We identify the adult cortical plasticity response to elevated activity driven by sensory overstimulation, then test how plasticity changes with age. We use in vivo two-photon imaging of calcium-mediated cellular/synaptic activity, electrophysiology and c-Fos-activity tagging to show control of neuronal activity is dysregulated in the visual cortex in late adulthood. Specifically, in young adult cortex, mGluR5-dependent population-wide excitatory synaptic weakening and inhibitory synaptogenesis reduce cortical activity following overstimulation. In later life, these mechanisms are downregulated, so that overstimulation results in synaptic strengthening and elevated activity. We also find overstimulation disrupts cognition in older but not younger animals. We propose that specific plasticity mechanisms fail in later life dysregulating neuronal microcircuit homeostasis and that the age-related response to overstimulation can impact cognitive performance.

Blocking salt-inducible kinases with YKL-06-061 prevents PTZ-induced seizures in mice

INTRODUCTION

Epilepsy is one of the most common neurological diseases, while over one third of adults with epilepsy still have inadequate seizure control. Although mutations in salt-inducible kinases (SIKs) have been identified in epileptic encephalopathy, it is not known whether blocking SIKs can prevent pentylenetetrazole (PTZ)-induced seizures.

METHODS

We first determined the time course of SIKs (including SIK 1, 2, and 3) in the hippocampus of PTZ treated mice. And then, we evaluated the effects of anti-epilepsy drug valproate acid (VPA) on the expression of SIK 1, 2, and 3 in the hippocampus of PTZ treated mice. Next, we investigated the effect of different dose of SIKs inhibitor YKL-06-061 on the epileptic seizures and neuronal activation by determining the expression of immediate early genes (IEGs) in the PTZ treated mice.

RESULTS

We found that PTZ selectively induced enhanced expression of SIK1 in the hippocampus, which was blocked by VPA treatment. Notably, YKL-06-061 decreased seizure activity and prevented neuronal overactivity, as indicated by the reduced expression of IEGs in the hippocampus and prefrontal cortex.

CONCLUSION

Our findings provide the first evidence that SIK1 affects gene regulation in neuronal hyperactivity, which is involved in seizure behavior. Targeting SIK1 through the development of selective inhibitors may lead to disease-modifying therapies that reduce epilepsy progression.

Zebrafish as a robust preclinical platform for screening plant-derived drugs with anticonvulsant properties-a review

Traditionally, selected plant sources have been explored for medicines to treat convulsions. This continues today, especially in countries with low-income rates and poor medical systems. However, in the low-income countries, plant extracts and isolated drugs are in high demand due to their good safety profiles. Preclinical studies on animal models of seizures/epilepsy have revealed the anticonvulsant and/or antiepileptogenic properties of, at least some, herb preparations or plant metabolites. Still, there is a significant number of plants known in traditional medicine that exert anticonvulsant activity but have not been evaluated on animal models. Zebrafish is recognized as a suitable in vivo model of epilepsy research and is increasingly used as a screening platform. In this review, the results of selected preclinical studies are summarized to provide credible information for the future development of effective screening methods for plant-derived antiseizure/antiepileptic therapeutics using zebrafish models. We compared zebrafish vs. rodent data to show the translational value of the former in epilepsy research. We also surveyed caveats in methodology. Finally, we proposed a pipeline for screening new anticonvulsant plant-derived drugs in zebrafish ("from tank to bedside and back again").

Transcriptome Sequencing of CeRNA Network Constructing in Status Epilepticus Mice Treated by Low-Frequency Repetitive Transcranial Magnetic Stimulation

It is shown that great progress was recently made in the treatment of repetitive transcranial magnetic stimulation (rTMS) for neurological and psychiatric diseases. This study aimed to address how rTMS exerted it therapeutic effects by regulating competitive endogenous RNAs (ceRNAs) of lncRNA-miRNA-mRNA. The distinction of lncRNA, miRNA and mRNA expression in male status epilepticus (SE) mice treated by two different ways, low-frequency rTMS (LF-rTMS) vs. sham rTMS, was analyzed by high-throughput sequencing. The Gene Ontology (GO) functional enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses were carried out. Gene-Gene Cross Linkage Network was established; pivotal genes were screened out. qRT-PCR was used to verify gene-gene interactions. Our results showed that there were 1615 lncRNAs, 510 mRNAs, and 17 miRNAs differentially which were expressed between the LF-rTMS group and the sham rTMS group. The expression difference of these lncRNAs, mRNAs, and miRNAs by microarray detection were consistent with the results by qPCR. GO functional enrichment showed that immune-associated molecular mechanisms, biological processes, and GABA-A receptor activity played a role in SE mice treated with LF-rTMS. KEGG pathway enrichment analysis revealed that differentially expressed genes were correlated to T cell receptor signaling pathway, primary immune deficiency and Th17 cell differentiation signaling pathway. Gene-gene cross linkage network was established on the basis of Pearson's correlation coefficient and miRNA. In conclusion, LF-rTMS alleviates SE through regulating the GABA-A receptor activity transmission, improving immune functions, and biological processes, suggesting the underlying ceRNA molecular mechanisms of LF-rTMS treatment for epilepsy.

CircHOMER1 inhibits porcine adipogenesis via the miR-23b/SIRT1 axis

Fat deposition is critical to pork quality. However, the mechanism of fat deposition remains to be elucidated. Circular RNAs (circRNAs) are ideal biomarkers and are involved in adipogenesis. Here, we investigated the effect and mechanism of circHOMER1 on porcine adipogenesis in vitro and in vivo. Western blotting, Oil red O staining, and HE staining were used to assess the function of circHOMER1 in adipogenesis. The results showed that circHOMER1 inhibited adipogenic differentiation of porcine preadipocytes and suppressed adipogenesis in mice. Dual-luciferase reporter gene, RIP, and pull-down assays demonstrated that miR-23b directly bound to circHOMER1 and the 3'-UTR of SIRT1. Rescue experiments further illustrated the regulatory relationship among circHOMER1, miR-23b, and SIRT1. Conclusively, we demonstrate that circHOMER1 plays an inhibitory role in porcine adipogenesis through miR-23b and SIRT1. The present study revealed the mechanism of porcine adipogenesis, which may be helpful to improve pork quality.

Molecular mechanisms underlying activity-dependent ischemic tolerance in the brain

Ischemic stroke is one of the leading causes of death and disability worldwide. The inhibition of cerebral blood flow triggers intertwined pathological events, resulting in cell death and loss of brain function. Interestingly, animals pre-exposed to short-term ischemia can tolerate subsequent severe ischemia. This phenomenon is called ischemic tolerance and is also triggered by other noxious stimuli. However, whether short-term exposure to non-noxious stimuli can induce ischemic tolerance remains unknown. Recently, we found that pre-exposing mice to an enriched environment for 40 min is sufficient to facilitate cell survival after a subsequent stroke. The neuroprotective process depends on the neuronal activity soon before stroke, of which the activity-dependent transcription factor Npas4 is essential. Excessive Ca²⁺ influx triggers Npas4 expression in ischemic neurons, leading to the activation of neuroprotective programs. Pre-induction of Npas4 in the normal brain effectively supports cell survival after stroke. Furthermore, our study revealed that Npas4 regulates L-type voltage-gated Ca²⁺ channels through expression of the small Ras-like GTPase Gem in ischemic neurons. Ischemic tolerance is a good model for understanding how to promote neuroprotective mechanisms in the normal and injured brain. Here, we highlight activity-dependent ischemic tolerance and discuss its role in promoting neuroprotection against stroke.

Remembering and forgetting in sleep: Selective synaptic plasticity during sleep driven by scaling factors Homer1a and Arc

Sleep is a conserved and essential process that supports learning and memory. Synapses are a major target of sleep function and a locus of sleep need. Evidence in the literature suggests that the need for sleep has a cellular or microcircuit level basis, and that sleep need can accumulate within localized brain regions as a function of waking activity. Activation of sleep promoting kinases and accumulation of synaptic phosphorylation was recently shown to be part of the molecular basis for the localized sleep need. A prominent hypothesis in the field suggests that some benefits of sleep are mediated by a broad but selective weakening, or scaling-down, of synaptic strength during sleep in order to offset increased excitability from synaptic potentiation during wake. The literature also shows that synapses can be strengthened during sleep, raising the question of what molecular mechanisms may allow for selection of synaptic plasticity types during sleep. Here I describe mechanisms of action of the scaling factors Arc and Homer1a in selective plasticity and links with sleep need. Arc and Homer1a are induced in neurons in response to waking neuronal activity and accumulate with time spent awake. I suggest that during sleep, Arc and Homer1a drive broad weakening of synapses through homeostatic scaling-down, but in a manner that is sensitive to the plasticity history of individual synapses, based on patterned phosphorylation of synaptic proteins. Therefore, Arc and Homer1a may offer insights into the intricate links between a cellular basis of sleep need and memory consolidation during sleep.

Induction of A Disintegrin and Metalloproteinase with Thrombospondin motifs 1 by a rare variant or cognitive activities reduces hippocampal amyloid-β and consequent Alzheimer’s disease risk

Amyloid-β (Aβ) derived from amyloid precursor protein (APP) hydrolysis is acknowledged as the predominant hallmark of Alzheimer’s disease (AD) that especially correlates to genetics and daily activities. In 2019, meta-analysis of AD has discovered five new risk loci among which A Disintegrin and Metalloproteinase with Thrombospondin motifs 1 (ADAMTS1) has been further suggested in 2021 and 2022. To verify the association, we re-sequenced ADAMTS1 of clinical AD samples and subsequently identified a novel rare variant c.–2067A > C with watchable relevance (whereas the P-value was not significant after adjustment). Dual-luciferase assay showed that the variant sharply stimulated ADAMTS1 expression. In addition, ADAMTS1 was also clearly induced by pentylenetetrazol-ignited neuronal activity and enriched environment (EE). Inspired by the above findings, we investigated ADAMTS1’s role in APP metabolism in vitro and in vivo. Results showed that ADAMTS1 participated in APP hydrolysis and consequently decreased Aβ generation through inhibiting β-secretase-mediated cleavage. In addition, we also verified that the hippocampal amyloid load of AD mouse model was alleviated by the introduction of ADAMTS1, and thus spatial cognition was restored as well. This study revealed the contribution of ADAMTS1 to the connection of genetic and acquired factors with APP metabolism, and its potential in reducing hippocampal amyloid and consequent risk of AD.

The epilepsy-associated protein PCDH19 undergoes NMDA receptor-dependent proteolytic cleavage and regulates the expression of immediate-early genes

Protocadherin-19 (PCDH19) is a synaptic cell-adhesion molecule encoded by X-linked PCDH19, a gene linked with epilepsy. Here, we report a synapse-to-nucleus signaling pathway through which PCDH19 bridges neuronal activity with gene expression. In particular, we describe the NMDA receptor (NMDAR)-dependent proteolytic cleavage of PCDH19, which leads to the generation of a PCDH19 C-terminal fragment (CTF) able to enter the nucleus. We demonstrate that PCDH19 CTF associates with chromatin and with the chromatin remodeler lysine-specific demethylase 1 (LSD1) and regulates expression of immediate-early genes (IEGs). Our results are consistent with a model whereby PCDH19 favors maintenance of neuronal homeostasis via negative feedback regulation of IEG expression and provide a key to interpreting PCDH19-related hyperexcitability.

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PCDH19 undergoes NMDAR-dependent cleavage by ADAM10 and possibly gamma secretase

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In the nucleus, PCDH19 C-terminal fragment (CTF) associates with the chromatin remodeler LSD1

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PCDH19 CTF favors immediate-early gene (IEG) repression

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PCDH19 downregulation affects LSD1 splicing by NOVA1 and increases IEG expression

Homer signaling pathways as effective therapeutic targets for ischemic and traumatic brain injuries and retinal lesions

Ischemic and traumatic insults to the central nervous system account for most serious acute and fatal brain injuries and are usually characterized by primary and secondary damage. Secondary damage presents the greatest challenge for medical staff; however, there are currently few effective therapeutic targets for secondary damage. Homer proteins are postsynaptic scaffolding proteins that have been implicated in ischemic and traumatic insults to the central nervous system. Homer signaling can exert either positive or negative effects during such insults, depending on the specific subtype of Homer protein. Homer 1b/c couples with other proteins to form postsynaptic densities, which form the basis of synaptic transmission, while Homer1a expression can be induced by harmful external factors. Homer 1c is used as a unique biomarker to reveal alterations in synaptic connectivity before and during the early stages of apoptosis in retinal ganglion cells, mediated or affected by extracellular or intracellular signaling or cytoskeletal processes. This review summarizes the structural features, related signaling pathways, and diverse roles of Homer proteins in physiological and pathological processes. Upregulating Homer1a or downregulating Homer1b/c may play a neuroprotective role in secondary brain injuries. Homer also plays an important role in the formation of photoreceptor synapses. These findings confirm the neuroprotective effects of Homer, and support the future design of therapeutic drug targets or gene therapies for ischemic and traumatic brain injuries and retinal disorders based on Homer proteins.

Npas4 regulates IQSEC3 expression in hippocampal somatostatin interneurons to mediate anxiety-like behavior

Activity-dependent GABAergic synapse plasticity is important for normal brain functions, but the underlying molecular mechanisms remain incompletely understood. Here, we show that Npas4 (neuronal PAS-domain protein 4) transcriptionally regulates the expression of IQSEC3, a GABAergic synapse-specific guanine nucleotide-exchange factor for ADP-ribosylation factor (ARF-GEF) that directly interacts with gephyrin. Neuronal activation by an enriched environment induces Npas4-mediated upregulation of IQSEC3 protein specifically in CA1 stratum oriens layer somatostatin (SST)-expressing GABAergic interneurons. SST+ interneuron-specific knockout (KO) of Npas4 compromises synaptic transmission in these GABAergic interneurons, increases neuronal activity in CA1 pyramidal neurons, and reduces anxiety behavior, all of which are normalized by the expression of wild-type IQSEC3, but not a dominant-negative ARF-GEF-inactive mutant, in SST+ interneurons of Npas4-KO mice. Our results suggest that IQSEC3 is a key GABAergic synapse component that is directed by Npas4 and ARF activity, specifically in SST+ interneurons, to orchestrate excitation-to-inhibition balance and control anxiety-like behavior.

The aging mouse brain: cognition, connectivity and calcium

Aging is a complex process that differentially impacts multiple cognitive, sensory, neuronal and molecular processes. Technological innovations now allow for parallel investigation of neuronal circuit function, structure and molecular composition in the brain of awake behaving adult mice. Thus, mice have become a critical tool to better understand how aging impacts the brain. However, a more granular systems-based approach, which considers the impact of age on key features relating to neural processing, is required. Here, we review evidence probing the impact of age on the mouse brain. We focus on a range of processes relating to neuronal function, including cognitive abilities, sensory systems, synaptic plasticity and calcium regulation. Across many systems, we find evidence for prominent age-related dysregulation even before 12 months of age, suggesting that emerging age-related alterations can manifest by late adulthood. However, we also find reports suggesting that some processes are remarkably resilient to aging. The evidence suggests that aging does not drive a parallel, linear dysregulation of all systems, but instead impacts some processes earlier, and more severely, than others. We propose that capturing the more fine-scale emerging features of age-related vulnerability and resilience may provide better opportunities for the rejuvenation of the aged brain.

Essential Functions of the Transcription Factor Npas4 in Neural Circuit Development, Plasticity, and Diseases

Signaling from the synapse to nucleus is mediated by the integration and propagation of both membrane potential changes (postsynaptic potentials) and intracellular second messenger cascades. The electrical propagation of postsynaptic potentials allows for rapid neural information processing, while propagating second messenger pathways link synaptic activity to the transcription of genes required for neuronal survival and adaptive changes (plasticity) underlying circuit formation and learning. The propagation of activity-induced calcium signals to the cell nucleus is a major synapse-to-nucleus communication pathway. Neuronal PAS domain protein 4 (Npas4) is a recently discovered calcium-dependent transcription factor that regulates the activation of genes involved in the homeostatic regulation of excitatory–inhibitory balance, which is critical for neural circuit formation, function, and ongoing plasticity, as well as for defense against diseases such as epilepsy. Here, we summarize recent findings on the neuroprotective functions of Npas4 and the potential of Npas4 as a therapeutic target for the treatment of acute and chronic diseases of the central nervous system.

Activity-Regulated Transcription: Bridging the Gap between Neural Activity and Behavior

Gene transcription is the process by which the genetic codes of organisms are read and interpreted as a set of instructions for cells to divide, differentiate, migrate, and mature. As cells function in their respective niches, transcription further allows mature cells to interact dynamically with their external environment while reliably retaining fundamental information about past experiences. In this Review, we provide an overview of the field of activity-dependent transcription in the vertebrate brain and highlight contemporary work that ranges from studies of activity-dependent chromatin modifications to plasticity mechanisms underlying adaptive behaviors. We identify key gaps in knowledge and propose integrated approaches toward a deeper understanding of how activity-dependent transcription promotes the refinement and plasticity of neural circuits for cognitive function.

[Exploring Molecular Targets for Epilepsy Treatment from the Perspective of Neuronal Homeostasis]

Brain function is controlled by the balance between the excitatory and inhibitory systems. If this balance is disrupted and the excitatory system dominates, convulsions or epileptic seizures are induced. Neuronal hyperexcitability in the brain leads to marked changes in the function of the neurons, which adversely affect the stability of the neural network. Many of the currently used antiepileptic drugs are symptomatic treatments that suppress the electrical hyperexcitability of the cerebrum. Although patients with epilepsy should continuously take antiepileptic drugs to control their seizures, approximately 20% of patients are drug resistant. The brain has the ability to control neuronal functions within acceptable limits while it maintains the amount of synaptic inputs that form the basis of information accumulation. Neuronal self-regulation is known as homeostatic scaling by which the intensity of all excitatory synapses is suppressed when neuronal excitability is increased. However, the molecular mechanisms of homeostatic scaling and their pathophysiological significance in vivo remain unclear. Repeated treatment with a subconvulsive dosage of pentylenetetrazol (PTZ), a γ-aminobutyric acid (GABA)_A receptor antagonist, is known to induce kindling in mice, which is a common animal model used to study epilepsy. We found that PTZ-induced kindling was potentiated in mice deficient in the transcription factor neuronal PAS domain protein 4 (Npas4), the expression of which is immediately induced in response to neuronal activity. At this symposium, we will discuss the possibility of Npas4 as a novel target molecule for epilepsy treatment.

REST: An epigenetic regulator of neuronal stress responses in the young and ageing brain

The transcriptional repressor REST (Repressor Element-1 Silencing Transcription factor) is a key modulator of the neuronal epigenome and targets genes involved in neuronal differentiation, axonal growth, vesicular transport, ion channel conductance and synaptic plasticity. Whilst its gene expression-modifying properties have been examined extensively in neuronal development, REST's response towards stress-induced neuronal insults has only recently been explored. Overall, REST appears to be an ideal candidate to fine-tune neuronal gene expression following different forms of cellular, neuropathological, psychological and physical stressors. Upregulation of REST is reportedly protective against premature neural stem cell depletion, neuronal hyperexcitability, oxidative stress, neuroendocrine system dysfunction and neuropathology. In contrast, neuronal REST activation has also been linked to neuronal dysfunction and neurodegeneration. Here, we highlight key findings and discrepancies surrounding our current understanding of REST's function in neuronal adaptation to stress and explore its potential role in neuronal stress resilience in the young and ageing brain.

A predictive index of biomarkers for ictogenesis from tier I safety pharmacology testing that may warrant tier II EEG studies

Three significant contributions to the field of safety pharmacology were recently published detailing the use of electroencephalography (EEG) by telemetry in a critical role in the successful evaluation of a compound during drug development (1] Authier, Delatte, Kallman, Stevens & Markgraf; JPTM 2016; 81:274-285; 2] Accardi, Pugsley, Forster, Troncy, Huang & Authier; JPTM; 81: 47-59; 3] Bassett, Troncy, Pouliot, Paquette, Ascaha, & Authier; JPTM 2016; 70: 230-240). These authors present a convincing case for monitoring neocortical biopotential waveforms (EEG, ECoG, etc) during preclinical toxicology studies as an opportunity for early identification of a central nervous system (CNS) risk during Investigational New Drug (IND) Enabling Studies. This review is about "ictogenesis" not "epileptogenesis". It is intended to characterize overt behavioral and physiological changes suggestive of drug-induced neurotoxicity/ictogenesis in experimental animals during Tier 1 safety pharmacology testing, prior to first dose administration in man. It is the presence of these predictive or comorbid biomarkers expressed during the requisite conduct of daily clinical or cage side observations, and in early ICH S7A Tier I CNS, pulmonary and cardiovascular safety study designs that should initiate an early conversation regarding Tier II inclusion of EEG monitoring. We conclude that there is no single definitive clinical marker for seizure liability but plasma exposures might add to set proper safety margins when clinical convulsions are observed. Even the observation of a study-related full tonic-clonic convulsion does not establish solid ground to require the financial and temporal investment of a full EEG study under the current regulatory standards.

PREFATORY NOTE

For purposes of this review, we have adopted the FDA term "sponsor" as it refers to any person who takes the responsibility for and initiates a nonclinical investigations of new molecular entities; FDA uses the term "sponsor" primarily in relation to investigational new drug application submissions.