Brain Stimulation as a Therapeutic Tool in Amyotrophic Lateral Sclerosis: Current Status and Interaction With Mechanisms of Altered Cortical Excitability

ALSUntangled #75: Portable neuromodulation stimulator therapy

Spurred by patient interest, ALSUntangled herein examines the potential of the Portable Neuromodulation Stimulator (PoNS™) in treating amyotrophic lateral sclerosis (ALS). The PoNS™ device, FDA-approved for the treatment of gait deficits in adult patients with multiple sclerosis, utilizes translingual neurostimulation to stimulate trigeminal and facial nerves via the tongue, aiming to induce neuroplastic changes. While there are early, promising data for PoNS treatment to improve gait and balance in multiple sclerosis, stroke, and traumatic brain injury, no pre-clinical or clinical studies have been performed in ALS. Although reasonably safe, high costs and prescription requirements will limit PoNS accessibility. At this time, due to the lack of ALS-relevant data, we cannot endorse the use of PoNS as an ALS treatment.

Advances in Brain Stimulation, Nanomedicine and the Use of Magnetoelectric Nanoparticles: Dopaminergic Alterations and Their Role in Neurodegeneration and Drug Addiction

Recent advancements in brain stimulation and nanomedicine have ushered in a new era of therapeutic interventions for psychiatric and neurodegenerative disorders. This review explores the cutting-edge innovations in brain stimulation techniques, including their applications in alleviating symptoms of main neurodegenerative disorders and addiction. Deep Brain Stimulation (DBS) is an FDA-approved treatment for specific neurodegenerative disorders, including Parkinson's Disease (PD), and is currently under evaluation for other conditions, such as Alzheimer's Disease. This technique has facilitated significant advancements in understanding brain electrical circuitry by enabling targeted brain stimulation and providing insights into neural network function and dysfunction. In reviewing DBS studies, this review places particular emphasis on the underlying main neurotransmitter modifications and their specific brain area location, particularly focusing on the dopaminergic system, which plays a critical role in these conditions. Furthermore, this review delves into the groundbreaking developments in nanomedicine, highlighting how nanotechnology can be utilized to target aberrant signaling in neurodegenerative diseases, with a specific focus on the dopaminergic system. The discussion extends to emerging technologies such as magnetoelectric nanoparticles (MENPs), which represent a novel intersection between nanoformulation and brain stimulation approaches. These innovative technologies offer promising avenues for enhancing the precision and effectiveness of treatments by enabling the non-invasive, targeted delivery of therapeutic agents as well as on-site, on-demand stimulation. By integrating insights from recent research and technological advances, this review aims to provide a comprehensive understanding of how brain stimulation and nanomedicine can be synergistically applied to address complex neuropsychiatric and neurodegenerative disorders, paving the way for future therapeutic strategies.

Pathological mechanisms of amyotrophic lateral Sclerosis

Amyotrophic lateral sclerosis refers to a neurodegenerative disease involving the motor system, the cause of which remains unexplained despite several years of research. Thus, the journey to understanding or treating amyotrophic lateral sclerosis is still a long one. According to current research, amyotrophic lateral sclerosis is likely not due to a single factor but rather to a combination of mechanisms mediated by complex interactions between molecular and genetic pathways. The progression of the disease involves multiple cellular processes and the interaction between different complex mechanisms makes it difficult to identify the causative factors of amyotrophic lateral sclerosis. Here, we review the most common amyotrophic lateral sclerosis-associated pathogenic genes and the pathways involved in amyotrophic lateral sclerosis, as well as summarize currently proposed potential mechanisms responsible for amyotrophic lateral sclerosis disease and their evidence for involvement in amyotrophic lateral sclerosis. In addition, we discuss current emerging strategies for the treatment of amyotrophic lateral sclerosis. Studying the emergence of these new therapies may help to further our understanding of the pathogenic mechanisms of the disease.

Development of novel treatments for amyotrophic lateral sclerosis

Amyotrophic Lateral Sclerosis (ALS) is a neurodegenerative disease that causes paralysis whose etiology and pathogenesis have not been fully elucidated. Presently it is incurable and rapidly progressive with a survival of 2-5 years from onset, and no treatments could cure it. Therefore, it is urgent to identify which therapeutic target(s) are more promising to develop treatments that could effectively treat ALS. So far, more than 90 novel treatments for ALS patients have been registered on ClinicalTrials.gov, of which 23 are in clinical trials, 12 have been terminated and the rest suspended. This review will systematically summarize the possible targets of these novel treatments under development or failing based on published literature and information released by sponsors, so as to provide basis and support for subsequent drug research and development.

Understanding depression with amyotrophic lateral sclerosis: a short assessment of facts and perceptions

Depression with an average prevalence of 25-40% is a serious condition in amyotrophic lateral sclerosis (ALS) that can impact quality of life and survival of patients and caregiver burden, yet the underlying neurobiology is poorly understood. Preexisting depression has been associated with a higher risk of developing ALS, while people with ALS have a significantly higher risk of developing depression that can cause multiple complications. Depression may be a prodromal or subclinical symptom prior to motor involvement, although its relations with disease progression and impairment of quality of life are under discussion. Unfortunately, there are no studies existing that explore the pathogenic mechanisms of depression associated with the basic neurodegenerative process, and no specific neuroimaging data or postmortem findings for the combination of ALS and depression are currently available. Experience from other neurodegenerative processes suggests that depressive symptoms in ALS may be the consequence of cortical thinning in prefrontal regions and other cortex areas, disruption of mood-related brain networks, dysfunction of neurotransmitter systems, changing cortisol levels and other, hitherto unknown mechanisms. Treatment of both ALS and depression is a multidisciplinary task, depression generally being treated with a combination of antidepressant medication, physiotherapy, psychological and other interventions, while electroconvulsive therapy and deep brain stimulation might not be indicated in the majority of patients in view of their poor prognosis. Since compared to depression in other neurodegenerative diseases, our knowledge of its molecular basis in ALS is missing, multidisciplinary clinicopathological studies to elucidate the pathomechanism of depression in motor system disorders including ALS are urgently warranted.

Novel approaches to motoneuron disease/ALS treatment using non-invasive brain and spinal stimulation: IFCN handbook chapter

Non-invasive brain stimulation techniques have been exploited in motor neuron disease (MND) with multifold objectives: to support the diagnosis, to get insights in the pathophysiology of these disorders and, more recently, to slow down disease progression. In this review, we consider how neuromodulation can now be employed to treat MND, with specific attention to amyotrophic lateral sclerosis (ALS), the most common form with upper motoneuron (UMN) involvement, taking into account electrophysiological abnormalities revealed by human and animal studies that can be targeted by neuromodulation techniques. This review article encompasses repetitive transcranial magnetic stimulation methods (including low-frequency, high-frequency, and pattern stimulation paradigms), transcranial direct current stimulation as well as experimental findings with the newer approach of trans-spinal direct current stimulation. We also survey and discuss the trials that have been performed, and future perspectives.

[Promising approaches to the pathogenetic therapy of amyotrophic lateral sclerosis]

Amyotrophic lateral sclerosis is a severe incurable disease of the nervous system. Currently only methods of palliative care for the patients with this disease are available. Few medications for the pathogenetic therapy are registered in some countries, i.e. riluzole, edaravon, sodium phenylbutyrate/taurursodiol as well as tofersen (conditionally). Their efficacy is relatively low. The main directions in the development of pathogenetic therapy of ALS include gene therapy, use of stem cells, immunomodulators, agents affecting gut microbiota. A search is also underway for low-molecular compounds with neuroprotective and antioxidant properties. Perspective direction is prevention of ALS. This will be possible when biomarkers for identification of patients in pre-manifest/prodromal stage are detected.

Intranasal neuropeptide Y1 receptor antagonism improves motor deficits in symptomatic SOD1 ALS mice

OBJECTIVE

Neuropeptide Y (NPY) is a 36 amino acid peptide widely considered to provide neuroprotection in a range of neurodegenerative diseases. In the fatal motor neuron disease amyotrophic lateral sclerosis (ALS), recent evidence supports a link between NPY and ALS disease processes. The goal of this study was to determine the therapeutic potential and role of NPY in ALS, harnessing the brain-targeted intranasal delivery of the peptide, previously utilised to correct motor and cognitive phenotypes in other neurological conditions.

METHODS

To confirm the association with clinical disease characteristics, NPY expression was quantified in post-mortem motor cortex tissue of ALS patients and age-matched controls. The effect of NPY on ALS cortical pathophysiology was investigated using slice electrophysiology and multi-electrode array recordings of SOD1G93A cortical cultures in vitro. The impact of NPY on ALS disease trajectory was investigated by treating SOD1G93A mice intranasally with NPY and selective NPY receptor agonists and antagonists from pre-symptomatic and symptomatic phases of disease.

RESULTS

In the human post-mortem ALS motor cortex, we observe a significant increase in NPY expression, which is not present in the somatosensory cortex. In vitro, we demonstrate that NPY can ameliorate ALS hyperexcitability, while brain-targeted nasal delivery of NPY and a selective NPY Y1 receptor antagonist modified survival and motor deficits specifically within the symptomatic phase of the disease in the ALS SOD1G93A mouse.

INTERPRETATION

Taken together, these findings highlight the capacity for non-invasive brain-targeted interventions in ALS and support antagonism of NPY Y1Rs as a novel strategy to improve ALS motor function.

Effect of whole-hand water flow stimulation on the neural balance between excitation and inhibition in the primary somatosensory cortex

Sustained peripheral somatosensory stimulations, such as high-frequency repetitive somatosensory stimulation (HF-RSS) and vibrated stimulation, are effective in altering the balance between excitation and inhibition in the somatosensory cortex (S1) and motor cortex (M1). A recent study reported that whole-hand water flow (WF) stimulation induced neural disinhibition in the M1. Based on previous results, we hypothesized that whole-hand WF stimulation would lead to neural disinhibition in the S1 because there is a strong neural connection between M1 and S1 and aimed to examine whether whole-hand WF stimulation would change the neural balance between excitation and inhibition in the S1. Nineteen healthy volunteers were studied by measuring excitation and inhibition in the S1 before and after each of the four 15-min interventions. The excitation and inhibition in the S1 were assessed using somatosensory evoked potentials (SEPs) and paired-pulse inhibition (PPI) induced by single- and paired-pulse stimulations, respectively. The four interventions were as follows: control, whole-hand water immersion, whole-hand WF, and HF-RSS. The results showed no significant changes in SEPs and PPI following any intervention. However, changes in PPI with an interstimulus interval (ISI) of 30 ms were significantly correlated with the baseline value before whole-hand WF. Thus, the present findings indicated that the whole-hand WF stimulation had a greater decreased neural inhibition in participants with higher neural inhibition in the S1 at baseline. Considering previous results on M1, the present results possibly show that S1 has lower plasticity than M1 and that the duration (15 min) of each intervention may not have been enough to alter the balance of excitation and inhibition in the S1.

A comprehensive review of transcranial magnetic stimulation in secondary dementia

Although primary degenerative diseases are the main cause of dementia, a non-negligible proportion of patients is affected by a secondary and potentially treatable cognitive disorder. Therefore, diagnostic tools able to early identify and monitor them and to predict the response to treatment are needed. Transcranial magnetic stimulation (TMS) is a non-invasive neurophysiological technique capable of evaluating in vivo and in “real time” the motor areas, the cortico-spinal tract, and the neurotransmission pathways in several neurological and neuropsychiatric disorders, including cognitive impairment and dementia. While consistent evidence has been accumulated for Alzheimer’s disease, other degenerative cognitive disorders, and vascular dementia, to date a comprehensive review of TMS studies available in other secondary dementias is lacking. These conditions include, among others, normal-pressure hydrocephalus, multiple sclerosis, celiac disease and other immunologically mediated diseases, as well as a number of inflammatory, infective, metabolic, toxic, nutritional, endocrine, sleep-related, and rare genetic disorders. Overall, we observed that, while in degenerative dementia neurophysiological alterations might mirror specific, and possibly primary, neuropathological changes (and hence be used as early biomarkers), this pathogenic link appears to be weaker for most secondary forms of dementia, in which neurotransmitter dysfunction is more likely related to a systemic or diffuse neural damage. In these cases, therefore, an effort toward the understanding of pathological mechanisms of cognitive impairment should be made, also by investigating the relationship between functional alterations of brain circuits and the specific mechanisms of neuronal damage triggered by the causative disease. Neurophysiologically, although no distinctive TMS pattern can be identified that might be used to predict the occurrence or progression of cognitive decline in a specific condition, some TMS-associated measures of cortical function and plasticity (such as the short-latency afferent inhibition, the short-interval intracortical inhibition, and the cortical silent period) might add useful information in most of secondary dementia, especially in combination with suggestive clinical features and other diagnostic tests. The possibility to detect dysfunctional cortical circuits, to monitor the disease course, to probe the response to treatment, and to design novel neuromodulatory interventions in secondary dementia still represents a gap in the literature that needs to be explored.

Neuronal Hyperexcitability and Free Radical Toxicity in Amyotrophic Lateral Sclerosis: Established and Future Targets

Amyotrophic lateral sclerosis (ALS) is a devastating disease with evidence of degeneration involving upper and lower motor neuron compartments of the nervous system. Presently, two drugs, riluzole and edaravone, have been established as being useful in slowing disease progression in ALS. Riluzole possesses anti-glutamatergic properties, while edaravone eliminates free radicals (FRs). Glutamate is the excitatory neurotransmitter in the brain and spinal cord and binds to several inotropic receptors. Excessive activation of these receptors generates FRs, inducing neurodegeneration via damage to intracellular organelles and upregulation of proinflammatory mediators. FRs bind to intracellular structures, leading to cellular impairment that contributes to neurodegeneration. As such, excitotoxicity and FR toxicities have been considered as key pathophysiological mechanisms that contribute to the cascade of degeneration that envelopes neurons in ALS. Recent advanced technologies, including neurophysiological, imaging, pathological and biochemical techniques, have concurrently identified evidence of increased excitability in ALS. This review focuses on the relationship between FRs and excitotoxicity in motor neuronal degeneration in ALS and introduces concepts linked to increased excitability across both compartments of the human nervous system. Within this cellular framework, future strategies to promote therapeutic development in ALS, from the perspective of neuronal excitability and function, will be critically appraised.

OUP accepted manuscript

Familial adult myoclonic epilepsy type 2 is a hereditary condition characterized by cortical tremor, myoclonus and epilepsy. It belongs to the spectrum of cortical myoclonus and the sensorimotor cortex hyperexcitability represents an important pathogenic mechanism underlying this condition. Besides pericentral cortical structures, the impairment of subcortical networks seems also to play a pathogenetic role, mainly via the thalamo-cortical pathway. However, the mechanisms underlying cortical–subcortical circuits dysfunction, as well as their impact on clinical manifestations, are still unknown. Therefore, the main aims of our study were to systematically study with an extensive electrophysiological battery, the cortical sensorimotor, as well as thalamo-cortical networks in genetically confirmed familial adult myoclonic epilepsy patients and to establish reliable neurophysiological biomarkers for the diagnosis.

In 26 familial myoclonic epilepsy subjects, harbouring the intronic ATTTC repeat expansion in the StAR-related lipid transfer domain-containing 7 gene, 17 juvenile myoclonic epilepsy patients and 22 healthy controls, we evaluated the facilitatory and inhibitory circuits within the primary motor cortex using single and paired-pulse transcranial magnetic stimulation paradigms. We also probed the excitability of the somatosensory, as well as the thalamo-somatosensory cortex connection by using ad hoc somatosensory evoked potential protocols. The sensitivity and specificity of transcranial magnetic stimulation and somatosensory evoked potential metrics were derived from receiver operating curve analysis. Familial adult myoclonic epilepsy patients displayed increased facilitation and decreased inhibition within the sensorimotor cortex compared with juvenile myoclonic epilepsy patients (all P < 0.05) and healthy controls (all P < 0.05). Somatosensory evoked potential protocols also displayed a significant reduction of early high-frequency oscillations and less inhibition at paired-pulse protocol, suggesting a concomitant failure of thalamo-somatosensory cortex circuits. Disease onset and duration and myoclonus severity did not correlate either with sensorimotor hyperexcitability or thalamo-cortical measures (all P > 0.05). Patients with a longer disease duration had more severe myoclonus (r = 0.467, P = 0.02) associated with a lower frequency (r = −0.607, P = 0.001) and higher power of tremor (r = 0.479, P = 0.02). Finally, familial adult myoclonic epilepsy was reliably diagnosed using transcranial magnetic stimulation, demonstrating its superiority as a diagnostic factor compared to somatosensory evoked potential measures. In conclusion, deficits of sensorimotor cortical and thalamo-cortical circuits are involved in the pathophysiology of familial adult myoclonic epilepsy even if these alterations are not associated with clinical severity. Transcranial magnetic stimulation-based measurements display an overall higher accuracy than somatosensory evoked potential parameters to reliably distinguish familial adult myoclonic epilepsy from juvenile myoclonic epilepsy and healthy controls.

Diagnostic contribution and therapeutic perspectives of transcranial magnetic stimulation in dementia

Transcranial magnetic stimulation (TMS) is a powerful tool to probe in vivo brain circuits, as it allows to assess several cortical properties such asexcitability, plasticity and connectivity in humans. In the last 20 years, TMS has been applied to patients with dementia, enabling the identification of potential markers of thepathophysiology and predictors of cognitive decline; moreover, applied repetitively, TMS holds promise as a potential therapeutic intervention. The objective of this paper is to present a comprehensive review of studies that have employed TMS in dementia and to discuss potential clinical applications, from the diagnosis to the treatment. To provide a technical and theoretical framework, we first present an overview of the basic physiological mechanisms of the application of TMS to assess cortical excitability, excitation and inhibition balance, mechanisms of plasticity and cortico-cortical connectivity in the human brain. We then review the insights gained by TMS techniques into the pathophysiology and predictors of progression and response to treatment in dementias, including Alzheimer's disease (AD)-related dementias and secondary dementias. We show that while a single TMS measure offers low specificity, the use of a panel of measures and/or neurophysiological index can support the clinical diagnosis and predict progression. In the last part of the article, we discuss the therapeutic uses of TMS. So far, only repetitive TMS (rTMS) over the left dorsolateral prefrontal cortex and multisite rTMS associated with cognitive training have been shown to be, respectively, possibly (Level C of evidence) and probably (Level B of evidence) effective to improve cognition, apathy, memory, and language in AD patients, especially at a mild/early stage of the disease. The clinical use of this type of treatment warrants the combination of brain imaging techniques and/or electrophysiological tools to elucidate neurobiological effects of neurostimulation and to optimally tailor rTMS treatment protocols in individual patients or specific patient subgroups with dementia or mild cognitive impairment.