Neuroprotective effect of anodal transcranial direct current stimulation on 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced neurotoxicity in mice through modulating mitochondrial dynamics

High frequency electrical stimulation reduces α-synuclein levels and α-synuclein-mediated autophagy dysfunction

Accumulation of α-synuclein (α-Syn) has been implicated in proteasome and autophagy dysfunction in Parkinson's disease (PD). High frequency electrical stimulation (HFS) mimicking clinical parameters used for deep brain stimulation (DBS) in vitro or DBS in vivo in preclinical models of PD have been found to reduce levels of α-Syn and, in certain cases, provide possible neuroprotection. However, the mechanisms by which this reduction in α-Syn improves cellular dysfunction associated with α-Syn accumulation remains elusive. Using HFS parameters that recapitulate DBS in vitro, we found that HFS led to a reduction of mutant α-Syn and thereby limited proteasome and autophagy impairments due to α-Syn. Additionally, we observed that HFS modulates via the ATP6V0C subunit of V-ATPase and mitigates α-Syn mediated autophagic dysfunction. This study highlights a role for autophagy in reduction of α-Syn due to HFS which may prove to be a viable approach to decrease pathological protein accumulation in neurodegeneration.

Transcranial direct current stimulation improves motor function in rats with 6-hydroxydopamine-induced Parkinsonism

Transcranial direct current stimulation (tDCS) is increasingly being used for Parkinson's disease (PD); however, the evaluation of its clinical impact remains complex owing to the heterogeneity of patients and treatments. Therefore, we used a unilateral 6-hydroxydopamine-induced PD rat model to investigate whether anodal tDCS of the primary motor cortex (M1) alleviates PD motor deficits. Before tDCS treatment, unilateral PD rats preferentially used the forelimb ipsilateral to the lesion in the exploratory cylinder test and showed reduced locomotor activity in the open field test. In addition, PD-related clumsy forelimb movements during treadmill walking were detected using deep learning-based video analysis (DeepLabCut). When the 5-day tDCS treatment began, the forelimb-use asymmetry was ameliorated gradually, and locomotor activity increased to pre-lesion levels. tDCS treatment also normalized unnatural forelimb movement during walking and restored a balanced gait. However, these therapeutic effects were rapidly lost or gradually disappeared when the tDCS treatment was terminated. Histological analysis at the end of the experiment revealed that the animals had moderately advanced PD, with 40-50% of dopamine neurons and fibers preserved on the injured side compared with those on the intact side. Although it remains a challenge to elucidate the neural mechanisms of the transient improvement in motor function induced by tDCS, the results of this study provide evidence that tDCS of the M1 produces positive behavioral outcomes in PD animals and provides the basis for further clinical research examining the application of tDCS in patients with PD.

Molecular Insights into Transcranial Direct Current Stimulation Effects: Metabolomics and Transcriptomics Analyses

INTRODUCTION

Transcranial direct current stimulation (tDCS) is an evolving non-invasive neurostimulation technique. Despite multiple studies, its underlying molecular mechanisms are still unclear. Several previous human studies of the effect of tDCS suggest that it generates metabolic effects. The induction of metabolic effects by tDCS could provide an explanation for how it generates its long-term beneficial clinical outcome.

AIM

Given these hints of tDCS metabolic effects, we aimed to delineate the metabolic pathways involved in its mode of action.

METHODS

To accomplish this, we utilized a broad analytical approach of co-analyzing metabolomics and transcriptomic data generated from anodal tDCS in rat models. Since no metabolomic dataset was available, we performed a tDCS experiment of bilateral anodal stimulation of 200 µA for 20 min and for 5 consecutive days, followed by harvesting the brain tissue below the stimulating electrode and generating a metabolomics dataset using LC-MS/MS. The analysis of the transcriptomic dataset was based on a publicly available dataset.

RESULTS

Our analyses revealed that tDCS alters the metabolic profile of brain tissue, affecting bioenergetic-related pathways, such as glycolysis and mitochondrial functioning. In addition, we found changes in calcium-related signaling.

CONCLUSIONS

We conclude that tDCS affects metabolism by modulating energy production-related processes. Given our findings concerning calcium-related signaling, we suggest that the immediate effects of tDCS on calcium dynamics drive modifications in distinct metabolic pathways. A thorough understanding of the underlying molecular mechanisms of tDCS has the potential to revolutionize its applicability, enabling the generation of personalized medicine in the field of neurostimulation and thus contributing to its optimization.

A clinical approach to diagnosis and management of mitochondrial myopathies

This paper provides an overview of the different types of mitochondrial myopathies (MM), associated phenotypes, genotypes as well as a practical clinical approach towards disease diagnosis, surveillance, and management. nDNA-related MM are more common in pediatric-onset disease whilst mtDNA-related MMs are more frequent in adults. Genotype-phenotype correlation in MM is challenging due to clinical and genetic heterogeneity. The multisystemic nature of many MMs adds to the diagnostic challenge. Diagnostic approaches utilizing genetic sequencing with next generation sequencing approaches such as gene panel, exome and genome sequencing are available. This aids molecular diagnosis, heteroplasmy detection in MM patients and furthers knowledge of known mitochondrial genes. Precise disease diagnosis can end the diagnostic odyssey for patients, avoid unnecessary testing, provide prognosis, facilitate anticipatory management, and enable access to available therapies or clinical trials. Adjunctive tests such as functional and exercise testing could aid surveillance of MM patients. Management requires a multi-disciplinary approach, systemic screening for comorbidities, cofactor supplementation, avoidance of substances that inhibit the respiratory chain and exercise training. This update of the current understanding on MMs provides practical perspectives on current diagnostic and management approaches for this complex group of disorders.

Cognitive Effect of Transcranial Direct Current Stimulation on Left Dorsolateral Prefrontal Cortex in Mild Alzheimer's Disease: A Randomized, Double-Blind, Cross-Over Small-Scale Exploratory Study

Background

Transcranial direct current stimulation (tDCS) is considered a potential therapeutic instrument for Alzheimer's disease (AD) because it affects long-term synaptic plasticity through the processes of long-term potentiation and long-term depression, thereby improving cognitive ability. Nevertheless, the efficacy of tDCS in treating AD is still debated. Dorsal lateral prefrontal cortex is the main role in executive functions.

Objective

We investigate the cognitive effects of tDCS on AD patients.

Methods

Thirty mild AD patients aged 66-86 years (mean = 75.6) were included in a double-blind, randomized, sham-controlled crossover study. They were randomly assigned to receive 10 consecutive daily sessions of active tDCS (2 mA for 30 min) or a sham intervention and switched conditions 3 months later. The anodal and cathodal electrodes were placed on the left dorsal lateral prefrontal cortex and the right supraorbital area, respectively. Subjects underwent various neuropsychological assessments before and after the interventions.

Results

The results showed that tDCS significantly improved Cognitive Abilities Screening Instrument scores, especially on the items of "concentration and calculation", "orientation", "language ability", and "categorical verbal fluency". Mini-Mental State Examination and Wisconsin Card Sorting Test scores in all domains of "concept formation", "abstract thinking", "cognitive flexibility", and "accuracy" also improved significantly after tDCS. For the sham condition, no difference was found between the baseline scores and the after-intervention scores on any of the neuropsychological tests.

Conclusion

>: Using tDCS improves the cognition of AD patients. Further large size clinical trials are necessary to validate the data.

10 Minutes Frontal 40 Hz tACS-Effects on Working Memory Tested by Luck-Vogel Task

Working memory is a cognitive process that involves short-term active maintenance, flexible updating, and processing of goal- or task-relevant information. All frequency bands are involved in working memory. The activities of the theta and gamma frequency bands in the frontoparietal network are highly involved in working memory processes; theta oscillations play a role in the temporal organization of working memory items, and gamma oscillations influence the maintenance of information in working memory. Transcranial alternating current stimulation (tACS) results in frequency-specific modulation of endogenous oscillations and has shown promising results in cognitive neuroscience. The electrophysiological and behavioral changes induced by the modulation of endogenous gamma frequency in the prefrontal cortex using tACS have not been extensively studied in the context of working memory. Therefore, we aimed to investigate the effects of frontal gamma-tACS on working memory outcomes. We hypothesized that a 10-min gamma tACS administered over the frontal cortex would significantly improve working memory outcomes. Young healthy participants performed Luck-Vogel cognitive behavioral tasks with simultaneous pre- and post-intervention EEG recording (Sham versus 40 Hz tACS). Data from forty-one participants: sham (15 participants) and tACS (26 participants), were used for the statistical and behavioral analysis. The relative changes in behavioral outcomes and EEG due to the intervention were analyzed. The results show that tACS caused an increase in the power spectral density in the high beta and low gamma EEG bands and a decrease in left-right coherence. On the other hand, tACS had no significant effect on success rates and response times. Conclusion: 10 min of frontal 40 Hz tACS was not sufficient to produce detectable behavioral effects on working memory, whereas electrophysiological changes were evident. The limitations of the current stimulation protocol and future directions are discussed in detail in the following sections.

Neuroprotection and Non-Invasive Brain Stimulation: Facts or Fiction?

Non-Invasive Brain Stimulation (NIBS) techniques, such as transcranial Direct Current Stimulation (tDCS) and repetitive Magnetic Transcranial Stimulation (rTMS), are well-known non-pharmacological approaches to improve both motor and non-motor symptoms in patients with neurodegenerative disorders. Their use is of particular interest especially for the treatment of cognitive impairment in Alzheimer's Disease (AD), as well as axial disturbances in Parkinson's (PD), where conventional pharmacological therapies show very mild and short-lasting effects. However, their ability to interfere with disease progression over time is not well understood; recent evidence suggests that NIBS may have a neuroprotective effect, thus slowing disease progression and modulating the aggregation state of pathological proteins. In this narrative review, we gather current knowledge about neuroprotection and NIBS in neurodegenerative diseases (i.e., PD and AD), just mentioning the few results related to stroke. As further matter of debate, we discuss similarities and differences with Deep Brain Stimulation (DBS)-induced neuroprotective effects, and highlight possible future directions for ongoing clinical studies.

Therapeutic non-invasive brain treatments in Alzheimer's disease: recent advances and challenges

Alzheimer's disease (AD) is one of the major neurodegenerative diseases and the most common form of dementia. Characterized by the loss of learning, memory, problem-solving, language, and other thinking abilities, AD exerts a detrimental effect on both patients' and families' quality of life. Although there have been significant advances in understanding the mechanism underlying the pathogenesis and progression of AD, there is no cure for AD. The failure of numerous molecular targeted pharmacologic clinical trials leads to an emerging research shift toward non-invasive therapies, especially multiple targeted non-invasive treatments. In this paper, we reviewed the advances of the most widely studied non-invasive therapies, including photobiomodulation (PBM), transcranial magnetic stimulation (TMS), transcranial direct current stimulation (tDCS), and exercise therapy. Firstly, we reviewed the pathological changes of AD and the challenges for AD studies. We then introduced these non-invasive therapies and discussed the factors that may affect the effects of these therapies. Additionally, we review the effects of these therapies and the possible mechanisms underlying these effects. Finally, we summarized the challenges of the non-invasive treatments in future AD studies and clinical applications. We concluded that it would be critical to understand the exact underlying mechanisms and find the optimal treatment parameters to improve the translational value of these non-invasive therapies. Moreover, the combined use of non-invasive treatments is also a promising research direction for future studies and sheds light on the future treatment or prevention of AD.

Brain-Targeted Biomimetic Nanodecoys with Neuroprotective Effects for Precise Therapy of Parkinson's Disease

Parkinson's disease (PD) is a neurodegenerative disorder characterized by the gradual loss of dopaminergic neurons in the substantia nigra and the accumulation of α-synuclein aggregates called Lewy bodies. Here, nanodecoys were designed from a rabies virus polypeptide with a 29 amino acid (RVG29)-modified red blood cell membrane (RBCm) to encapsulate curcumin nanocrystals (Cur-NCs), which could effectively protect dopaminergic neurons. The RVG29-RBCm/Cur-NCs nanodecoys effectively escaped from reticuloendothelial system (RES) uptake, enabled prolonged blood circulation, and enhanced blood-brain barrier (BBB) crossing after systemic administration. Cur-NCs loaded inside the nanodecoys exhibited the recovery of dopamine levels, inhibition of α-synuclein aggregation, and reversal of mitochondrial dysfunction in PD mice. These findings indicate the promising potential of biomimetic nanodecoys in treating PD and other neurodegenerative diseases.

Using dual polarities of transcranial direct current stimulation in global cerebral ischemia and its following reperfusion period attenuates neuronal injury

Multiple neuronal injury pathways are activated during cerebral ischemia and reperfusion (I/R). This study was designed to decrease potential neuronal injuries by using both transcranial direct current stimulation (tDCS) polarities in cerebral ischemia and its following reperfusion period. Ninety rats were randomly divided into six groups. In the sham group, rats were intact. In the I/R group, global cerebral I/R was only induced. In the I/R + c-tDCS and I/R + a-tDCS groups, cathodal and anodal currents were applied, respectively. In the I/R + c/a-tDCS, cathodal current was used in the cerebral ischemia and anodal in the reperfusion. In the I/R + a/c-tDCS group, cathodal and anodal currents were applied in the I/R, respectively. Hippocampal tissue was used to determine the levels of IL-1β, TNF-α, NOS, SOD, MDA, and NMDAR. Hot plate and open field tests evaluated sensory and locomotor performances. The cerebral edema was also measured. Histological assessment was assessed by H/E and Nissl staining of the hippocampal CA1 region. All tDCS modes significantly decreased IL-1β and TNF-α levels, especially in the c/a-tDCS. All tDCS caused a significant decrease in MDA and NOS levels while increasing SOD activity compared to the I/R group, especially in the c/a-tDCS mode. In the c-tDCS and a/c-tDCS groups, the NMDAR level was significantly decreased. The c/a-tDCS group improved sensory and locomotor performances more than other groups receiving tDCS. Furthermore, the least neuronal death was observed in the c/a-tDCS mode. Using two different polarities of tDCS could induce more neuroprotective versus pathophysiological pathways in cerebral I/R, especially in c/a-tDCS mode. HIGHLIGHTS: Multiple pathways of neuronal injury are activated in cerebral ischemia and reperfusion (I/R). Using tDCS could modulate neuroinflammation and oxidative stress pathways in global cerebral I/R. Using c/a-tDCS mode during cerebral I/R causes more neuroprotective effects against neuronal injuries of cerebral I/R.

Sinapic Acid Ameliorates REV-ERB α Modulated Mitochondrial Fission against MPTP-Induced Parkinson's Disease Model

Parkinson’s disease (PD) is the second most common neurodegenerative disease worldwide, and accumulating evidence indicates that mitochondrial dysfunction is associated with progressive deterioration in PD patients. Previous studies have shown that sinapic acid has a neuroprotective effect, but its mechanisms of action remain unclear. The neuroprotective effect of sinapic acid was assayed in a PD mouse model generated by the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) as well as in SH-SY5Y cells. Target protein expression was detected by western blotting. Sinapic acid treatment attenuated the behavioral defects and loss of dopaminergic neurons in the PD models. Sinapic acid also improved mitochondrial function in the PD models. MPTP treatment increased the abundance of mitochondrial fission proteins such as dynamin-related protein 1 (Drp1) and phospho-Drp1 Ser616. In addition, MPTP decreased the expression of the REV-ERB α protein. These changes were attenuated by sinapic acid treatment. We used the pharmacological REV-ERB α inhibitor SR8278 to confirmation of protective effect of sinapic acid. Treatment of SR8278 with sinapic acid reversed the protein expression of phospho-Drp1 Ser616 and REV-ERB α on MPTP-treated mice. Our findings demonstrated that sinapic acid protects against MPTP-induced PD and these effects might be related to the inhibiting abnormal mitochondrial fission through REV-ERB α.

Anodal Transcranial Direct Current Stimulation Could Modulate Cortical Excitability and the Central Cholinergic System in Akinetic Rigid-Type Parkinson's Disease: Pilot Study

Background

Transcranial direct current stimulation (tDCS) is a non-invasive technique that has been widely studied as an alternative treatment for Parkinson's disease (PD). However, its clinical benefit remains unclear. In this study, we aimed to investigate the effect of tDCS on the central cholinergic system and cortical excitability in mainly akinetic rigid-type patients with PD.

Methods

In total, 18 patients with PD were prospectively enrolled and underwent 5 sessions of anodal tDCS on the M1 area, which is on the contralateral side of the dominant hand. We excluded patients with PD who had evident resting tremor of the hand to reduce the artifact of electrophysiologic findings. We compared clinical scales reflecting motor, cognitive, and mood symptoms between pre- and post-tDCS. Additionally, we investigated the changes in electrophysiologic parameters, such as short latency afferent inhibition (SAI) (%), which reflects the central cholinergic system.

Results

The United Parkinson's Disease Rating Scale Part 3 (UPDRS-III), the Korean-Montreal Cognitive Assessment (MoCA-K), and Beck Depression Inventory (BDI) scores were significantly improved after anodal tDCS (p < 0.01, p < 0.01, and p < 0.01). Moreover, motor evoked potential amplitude ratio (MEPAR) (%) and integrated SAI showed significant improvement after tDCS (p < 0.01 and p < 0.01). The mean values of the change in integrated SAI (%) were significantly correlated with the changes in UPDRS-III scores; however, the MoCA-K and BDI scores did not show differences.

Conclusions

Anodal tDCS could influence the central cholinergic system, such as frontal cortical excitability and depression in PD. This mechanism could underlie the clinical benefit of tDCS in patients with PD.

Mitochondrial quality control: Epigenetic signatures and therapeutic strategies

Mitochondria are semi-autonomous organelle staging a crucial role in cellular stress response, energy metabolism and cell survival. Maintaining mitochondrial quality control is very important for its homeostasis. Pathological conditions such as oxidative stress and neurodegeneration, disrupt this quality control, and involvement of genetic and epigenetic materials in this disruption have been reported. These regulatory factors trigger mitochondrial imbalance, as seen in many neurodegenerative diseases like Alzheimer's disease, Parkinson's disease, Amyotrophic lateral sclerosis, and Huntington's disease. The dynamic regulatory pathways i.e. mitophagy, biogenesis, permeability pore transitioning, fusion-fission are affected as a consequence and have been reviewed in this article. Moreover, several epigenetic mechanisms such as DNA methylation and histone modulation participating in such neurological disorders have also been discussed. Apart from it, therapeutic approaches targeting mitochondrial quality control have been tremendously explored showing ameliorative effects for these diseases, and have been discussed here with a novel perspective.

Direct current stimulation enhances neuronal alpha-synuclein degradation in vitro

Despite transcranial Direct Current Stimulation (DCS) is currently proposed as a symptomatic treatment in Parkinson's disease, the intracellular and molecular mechanisms elicited by this technique are still unknown, and its disease-modifying potential unexplored. Aim of this study was to elucidate the on-line and off-line effects of DCS on the expression, aggregation and degradation of alpha-synuclein (asyn) in a human neuroblastoma cell line under basal conditions and in presence of pharmachologically-induced increased asyn levels. Following DCS, gene and protein expression of asyn and its main autophagic catabolic pathways were assessed by real-time PCR and Western blot, extracellular asyn levels by Dot blot. We found that, under standard conditions, DCS increased monomeric and reduced oligomeric asyn forms, with a concomitant down-regulation of both macroautophagy and chaperone-mediated autophagy. Differently, in presence of rotenone-induced increased asyn, DCS efficiently counteracted asyn accumulation, not acting on its gene transcription, but potentiating its degradation. DCS also reduced intracellular and extracellular asyn levels, increased following lysosomal inhibition, independently from autophagic degradation, suggesting that other mechanisms are also involved. Collectively, these findings suggest that DCS exerts on-line and off-line effects on the expression, aggregation and autophagic degradation of asyn, indicating a till unknown neuroprotective role of tDCS.

Non-invasive brain stimulation for Parkinson's disease: Clinical evidence, latest concepts and future goals: A systematic review

Parkinson's disease (PD) is becoming a major public-health issue in an aging population. Available approaches to treat advanced PD still have limitations; new therapies are needed. The non-invasive brain stimulation (NIBS) may offer a complementary approach to treat advanced PD by personalized stimulation. Although NIBS is not as effective as the gold-standard levodopa, recent randomized controlled trials show promising outcomes in the treatment of PD symptoms. Nevertheless, only a few NIBS-stimulation paradigms have shown to improve PD's symptoms. Current clinical recommendations based on the level of evidence are reported in Table 1 through Table 3. Furthermore, novel technological advances hold promise and may soon enable the non-invasive stimulation of deeper brain structures for longer periods.

Memory and Cognition-Related Neuroplasticity Enhancement by Transcranial Direct Current Stimulation in Rodents: A Systematic Review

Brain stimulation techniques, including transcranial direct current stimulation (tDCS), were identified as promising therapeutic tools to modulate synaptic plasticity abnormalities and minimize memory and learning deficits in many neuropsychiatric diseases. Here, we revised the effect of tDCS on the modulation of neuroplasticity and cognition in several animal disease models of brain diseases affecting plasticity and cognition. Studies included in this review were searched following the terms (“transcranial direct current stimulation”) AND (mice OR mouse OR animal) and according to the PRISMA statement requirements. Overall, the studies collected suggest that tDCS was able to modulate brain plasticity due to synaptic modifications within the stimulated area. Changes in plasticity-related mechanisms were achieved through induction of long-term potentiation (LTP) and upregulation of neuroplasticity-related proteins, such as c-fos, brain-derived neurotrophic factor (BDNF), or N-methyl-D-aspartate receptors (NMDARs). Taken into account all revised studies, tDCS is a safe, easy, and noninvasive brain stimulation technique, therapeutically reliable, and with promising potential to promote cognitive enhancement and neuroplasticity. Since the use of tDCS has increased as a novel therapeutic approach in humans, animal studies are important to better understand its mechanisms as well as to help improve the stimulation protocols and their potential role in different neuropathologies.

Early transcranial direct current stimulation treatment exerts neuroprotective effects on 6-OHDA-induced Parkinsonism in rats

BACKGROUND

Transcranial direct current stimulation (tDCS) has been proven to be able to modulate motor cortical plasticity might have potential as an alternative, adjunctive therapy for Parkinson's disease (PD). However, the efficacy of tDCS in PD is still uncertain. A disease animal model may be useful to clarify the existence of a treatment effect and to explore an effective therapeutic strategy using tDCS protocols.

OBJECTIVE

The current study was designed to identify the comprehensive therapeutic effects of tDCS in 6-hydroxydopamine (6-OHDA)-lesioned PD rats.

METHODS

Following early and long-term tDCS application (starting 24 h after PD lesion, 300 μA anodal tDCS, 20 min/day, 5 days/week) in awake PD animals for a total of 4 weeks, the effects of tDCS on motor and non-motor behaviors as well as dopaminergic neuron degeneration levels, were identified.

RESULTS

We found that the 4-week tDCS intervention significantly alleviated 6-OHDA-induced motor deficits in locomotor activity, akinesia, gait pattern and anxiety-like behavior, but not in apomorphine-induced rotations, recognition memory and depression-like behavior. Immunohistochemically, tyrosine hydroxylase (TH)-positive neurons in the substantia nigra were significantly preserved in the tDCS intervention group.

CONCLUSIONS

These results suggest that early and long-term tDCS could exert neuroprotective effects and reduce the aggravation of motor dysfunctions in a 6-OHDA-induced PD rat model. Furthermore, this preclinical model may enhance the promising possibility of the potential use of tDCS and serve as a translational platform to further identify the therapeutic mechanism of tDCS for PD or other neurological disorders.