New insight into Parkinson's disease pathogenesis from reactive oxygen species-mediated extracellular Zn2+ influx

Editors' Choice-Review-The Future of Carbon-Based Neurochemical Sensing: A Critical Perspective

Carbon-based sensors have remained critical materials for electrochemical detection of neurochemicals, rooted in their inherent biocompatibility and broad potential window. Real-time monitoring using fast-scan cyclic voltammetry has resulted in the rise of minimally invasive carbon fiber microelectrodes as the material of choice for making measurements in tissue, but challenges with carbon fiber's innate properties have limited its applicability to understudied neurochemicals. Here, we provide a critical review of the state of carbon-based real-time neurochemical detection and offer insight into ways we envision addressing these limitations in the future. This piece focuses on three main hinderances of traditional carbon fiber based materials: diminished temporal resolution due to geometric properties and adsorption/desorption properties of the material, poor selectivity/specificity to most neurochemicals, and the inability to tune amorphous carbon surfaces for specific interfacial interactions. Routes to addressing these challenges could lie in methods like computational modeling of single-molecule interfacial interactions, expansion to tunable carbon-based materials, and novel approaches to synthesizing these materials. We hope this critical piece does justice to describing the novel carbon-based materials that have preceded this work, and we hope this review provides useful solutions to innovate carbon-based material development in the future for individualized neurochemical structures.

Tempol and silymarin rescue from zinc-induced degeneration of dopaminergic neurons through modulation of oxidative stress and inflammation

Oxidative stress and inflammation are the key players in the toxic manifestation of sporadic Parkinson's disease and zinc (Zn)-induced dopaminergic neurodegeneration. A synthetic superoxide dismutase (SOD) mimetic, tempol, and a naturally occurring antioxidant, silymarin protect against oxidative stress-mediated damage. The study intended to explore the effects of tempol and silymarin against Zn-induced dopaminergic neurodegeneration. Exposure to Zn produced neurobehavioral deficits and striatal dopamine depletion. Zn reduced glutathione content and glutathione-S-transferase activity and increased lipid peroxidation, superoxide dismutase activity, and level of pro-inflammatory mediators [nuclear factor-kappa B (NF-κB), tumor necrosis factor-alpha (TNF-α), interleukin-1 beta (IL-1β), and interleukin-6 (IL-6)]. Zn also attenuated the expression of tyrosine hydoxylase (TH), vesicular monoamine transporter 2 (VMAT-2), mitochondrial B-cell lymphoma-2 (Bcl-2), and procaspase-3 and 9 proteins and number of TH-positive neurons. Conversely, Zn elevated the expression of dopamine transporter (DAT) and mitochondrial Bcl-2-associated X (Bax) protein along with mitochondrial cytochrome c release. Administration of tempol significantly alleviated Zn-induced motor impairments, dopamine depletion, reduction in TH expression, and loss of TH-positive neurons similar to silymarin. Silymarin mitigated Zn-induced oxidative stress and inflammation and restored the expression of dopamine transporters and levels of pro-apoptotic proteins akin to tempol. The results demonstrate that both tempol and silymarin protect against Zn-induced dopaminergic neuronal loss through the suppression of oxidative stress and inflammation.

The α7 nAChR allosteric modulator PNU-120596 amends neuroinflammatory and motor consequences of parkinsonism in rats: Role of JAK2/NF-κB/GSk3β/ TNF-α pathway

Parkinson's disease (PD) is the second most common neurodegenerative disorder and a leading cause of disability. The current gold standard for PD treatment, L-Dopa, has limited clinical efficacy and multiple side effects. Evidence suggests that activation of α7 nicotinic acetylcholine receptors (α7nAChRs) abrogates neuronal and inflammatory insults. Here we tested whether PNU-120596 (PNU), a type II positive allosteric modulator of α7 nAChR, has a critical role in regulating motor dysfunction and neuroinflammation correlated with the associated PD dysfunction. Neuroprotective mechanisms were investigated through neurobehavioral, molecular, histopathological, and immunohistochemical studies. PNU reversed motor incoordination and hypokinesia induced via the intrastriatal injection of 6-hydroxydopamine and manifested by lower falling latency in the rotarod test, short ambulation time and low rearing incidence in open field test. Tyrosine hydroxylase immunostaining showed a significant restoration of dopaminergic neurons following PNU treatment, in addition to histopathological restoration in nigrostriatal tissues. PNU halted striatal neuroinflammation manifested as a suppressed expression of JAK2/NF-κB/GSk3β accompanied by a parallel decline in the protein expression of TNF-α in nigrostriatal tissue denoting the modulator anti-inflammatory capacity. Moreover, the protective effects of PNU were partially reversed by the α7 nAChR antagonist, methyllycaconitine, indicating the role of α7 nAChR modulation in the mechanism of action of PNU. This is the first study to reveal the positive effects of PNU-120596 on motor derangements of PD via JAK2/NF-κB/GSk3β/ TNF-α neuroinflammatory pathways, which could offer a potential therapeutic strategy for PD.

Extended sawhorse waveform for stable zinc detection with fast-scan cyclic voltammetry

Zinc (Zn(II)) is a divalent cation involved in regulating intracellular signal transduction and gene expression through transcription factor activity, and can act as a metal neurotransmitter by modulating synaptic activity and neuronal plasticity. Previous research has demonstrated spatial heterogeneity of Zn(II) in the brain, has estimated extracellular concentrations of Zn(II) across various brain regions, and has measured rapid intracellular changes in Zn(II) concentration during glutamate flux. Despite this work, quantification of rapid extracellular Zn(II) release from neurons, on a millisecond time scale, in real time has remained difficult with existing technologies. Here, we have developed an electrochemical waveform, called the "extended sawhorse waveform (ESW)," for fast-scan cyclic voltammetry detection at carbon-fiber microelectrodes which enabled rapid and stable Zn(II) monitoring over time. This waveform was developed to overcome existing challenges in monitoring metallotransmitters stably over time electrochemically by introducing a brief cleaning step to facilitate rapid cleaning of the electrode surface in between scans. The ESW scans from 0.5 V down to -1.0 V, up to 1.45 V for 3 ms (cleaning step), and back to 0.5 V at a scan rate of 400 V/s. Repeated introductions of Zn(II) at the electrode using a traditional waveform cause plating which ultimately deteriorates the sensitivity over time; however, using the ESW, significant improvements in stability were observed. Overall, we provide a unique approach to monitor and quantitate rapid Zn(II) signaling in the brain at carbon electrodes which will impact our ability to advance fundamental knowledge of Zn(II) involvement in extracellular signaling pathways in the brain.

The Impact of Environmental Factors on Monogenic Mendelian Diseases

Environmental factors and gene-environment interactions modify the variable expressivity, progression, severity, and onset of some classic (monogenic) Mendelian-inherited genetic diseases. Cystic fibrosis, Huntington disease, Parkinson's disease, and sickle cell disease are examples of well-known Mendelian disorders that are influenced by exogenous exposures. Environmental factors may act by direct or indirect mechanisms to modify disease severity, timing, and presentation, including through epigenomic influences, protein misfolding, miRNA alterations, transporter activity, and mitochondrial effects. Because pathological features of early-onset Mendelian diseases can mimic later onset complex diseases, we propose that studies of environmental exposure vulnerabilities using monogenic model systems of rare Mendelian diseases have high potential to provide insight into complex disease phenotypes arising from multi-genetic/multi-toxicant interactions. Mendelian disorders can be modeled by homologous mutations in animal model systems with strong recapitulation of human disease etiology and natural history, providing an important advantage for study of these diseases. Monogenic high penetrant mutations are ideal for toxicant challenge studies with a wide variety of environmental stressors, because background genetic variability may be less able to alter the relatively strong phenotype driving disease-causing mutations. These models promote mechanistic understandings of gene-environment interactions and biological pathways relevant to both Mendelian and related sporadic complex disease outcomes by creating a sensitized background for relevant environmental risk factors. Additionally, rare disease communities are motivated research participants, creating the potential of strong research allies among rare Mendelian disease advocacy groups and disease registries and providing a variety of translational opportunities that are under-utilized in genetic or environmental health science.

Dehydroeffusol Pprevents Amyloid β1-42-mediated Hippocampal Neurodegeneration via Reducing Intracellular Zn2+ Toxicity

Dehydroeffusol, a phenanthrene isolated from Juncus effusus, is a Chinese medicine. To explore an efficacy of dehydroeffusol administration for prevention and cure of Alzheimer's disease, here we examined the effect of dehydroeffusol on amyloid β_1-42 (Aβ_1-42)-mediated hippocampal neurodegeneration. Dehydroeffusol (15 mg/kg body weight) was orally administered to mice once a day for 6 days and then human Aβ_1-42 was injected intracerebroventricularly followed by oral administration for 12 days. Neurodegeneration in the dentate granule cell layer, which was determined 2 weeks after Aβ_1-42 injection, was rescued by dehydroeffusol administration. Aβ staining (uptake) was not reduced in the dentate granule cell layer by pre-administration of dehydroeffusol for 6 days, while increase in intracellular Zn²⁺ induced with Aβ_1-42 was reduced, suggesting that pre-administration of dehydroeffusol prior to Aβ_1-42 injection is effective for Aβ_1-42-mediated neurodegeneration that was linked with intracellular Zn²⁺ toxicity. As a matter of fact, pre-administration of dehydroeffusol rescued Aβ_1-42-mediated neurodegeneration. Interestingly, pre-administration of dehydroeffusol increased synthesis of metallothioneins, intracellular Zn²⁺-binding proteins, in the dentate granule cell layer, which can capture Zn²⁺ from Zn-Aβ_1-42 complexes. The present study indicates that pre-administration of dehydroeffusol protects Aβ_1-42-mediated neurodegeneration in the hippocampus by reducing intracellular Zn²⁺ toxicity, which is linked with induced synthesis of metallothioneins. Dehydroeffusol, a novel inducer of metallothioneins, may protect Aβ_1-42-induced pathogenesis in Alzheimer's disease.