Dopamine Autoxidation Is Controlled by Acidic pH

Molecular Investigation of the Self-Assembly Mechanism Underlying Polydopamine Coatings: The Synergistic Effect of Typical Building Blocks Acting on Interfacial Adhesion

Polydopamine (PDA) is well known as a mussel-inspired adhesive material composed of oligomeric heteropolymers. However, the conventional eumelanin-like structural assumption of PDA seems deficient in explaining its interfacial adhesion. To determine the decisive mechanism of PDA coating formation, experiments and simulations were performed in this study. 5,6-Dihydroxyindole (DHI), the signature building block of eumelanin, was introduced as the control group. Various typical building blocks in PDA were quantified by physicochemical characterizations, and the polar-group-dominated interfacial interaction was evaluated by classic molecular dynamics and metadynamics methods. Aminoethyl has been proven to be the key functional group inducing the adsorption of PDA on the hydroxylated silica substrates, while DHI shows limited adhesion to the substrate due to the absence of aminoethyl as the catechol-indole structure of DHI exhibits poor affinity to the silica surface. Pyrrole carboxylic acid, as an oxidative product detected from PDA/DHI, is unfavorable for its adhesion to silica substrates. Overall, the coating formation and self-aggregating precipitation of PDA are two competitive aminoethyl-consuming paths; thus, the in situ oxidative coupling of dopamine is indispensable for the PDA coating preparation. The collected PDA precipitates can no longer present satisfactory coating forming behavior, resulting from a shortage of aminoethyl moieties.

Heterogenous Copper(0)-Assisted Dopamine Oxidation: A New Pathway to Controllable and Scalable Polydopamine Synthesis

In this study, we introduce an approach for synthesizing polydopamine (PDA) through the controlled oxidation of dopamine using metallic copper. Traditional methods of PDA synthesis often encounter challenges such as scalability, reproducibility, and control over polymerization. Our approach utilizes the catalytic properties of metallic copper in the presence of dissolved oxygen to generate reactive oxygen species (ROS) without additional chemicals. This process allows for precise control over dopamine oxidation, leading to reliable, materials and cost-effective upscalable PDA production. We investigated the reaction kinetics and the role of copper and ROS in dopamine oxidation, using several different experimental techniques. Our results demonstrate that, even at low pH, the copper-assisted method produces PDA with properties comparable to those synthesized through conventional means. We propose a mechanism for PDA synthesis that is initiated by oxygen adsorption onto copper surface, leading to the generation of various ROS which act as oxidizing agents in PDA synthesis. This method presents an advancement in the scalable and controlled production of PDA, with potential applications in various scientific and industrial fields.

L-DOPA Autoxidation: An Empirical Valence Bond Simulation of the Reactive Step

L-DOPA, or levodopa, plays an important role in the treatment of Parkinson's disease, a debilitating neurological disorder. It acts as a precursor to dopamine, a neurotransmitter crucial for the regulation of motor functions. Administered orally, L-DOPA easily crosses the blood-brain barrier and converts into dopamine in the brain, relieving symptoms such as tremors and rigidity. However, its prolonged use can lead to complications. A significant concern with L-DOPA is its conversion to dopaquinone, a quinone metabolite that enters the redox cycle and continuously produces hydrogen peroxide. In addition, L-DOPA, which resembles tyrosine with an additional hydroxyl group, can randomly incorporate into the proteins of dopaminergic neurons and thus become an additional source of oxidative stress in Parkinson's patients. In this study, we scrutinized the rate-limiting step of L-DOPA autoxidation in aqueous solution. The reaction we studied is an intramolecular Michael addition concerted with a proton transfer from the amino group. Using the Empirical Valence Bond (EVB) method, we computed the free energy profiles of the reaction in water. The calculated barrier of 30.93 ± 1.12 kcal/mol is in reasonable agreement with the experimental barrier of 27.55 kcal/mol. This agreement confirms the validity of the studied mechanism and demonstrates the applicability of our simulation methodology for studying the autoxidation kinetics of L-DOPA within proteins.

Dopamine and Citicoline-Co-Loaded Solid Lipid Nanoparticles as Multifunctional Nanomedicines for Parkinson's Disease Treatment by Intranasal Administration

This work aimed to evaluate the potential of the nanosystems constituted by dopamine (DA) and the antioxidant Citicoline (CIT) co-loaded in solid lipid nanoparticles (SLNs) for intranasal administration in the treatment of Parkinson disease (PD). Such nanosystems, denoted as DA-CIT-SLNs, were designed according to the concept of multifunctional nanomedicine where multiple biological roles are combined into a single nanocarrier and prepared by the melt emulsification method employing the self-emulsifying Gelucire® 50/13 as lipid matrix. The resulting DA-CIT-SLNs were characterized regarding particle size, surface charge, encapsulation efficiency, morphology, and physical stability. Differential scanning calorimetry, FT-IR, and X ray diffraction studies were carried out to gain information on solid-state features, and in vitro release tests in simulated nasal fluid (SNF) were performed. Monitoring the particle size at two temperatures (4 °C and 37 °C), the size enlargement observed over the time at 37 °C was lower than that observed at 4 °C, even though at higher temperature, color changes occurred, indicative of possible neurotransmitter decomposition. Solid-state studies indicated a reduction in the crystallinity when DA and CIT are co-encapsulated in DA-CIT-SLNs. Interestingly, in vitro release studies in SNF indicated a sustained release of DA. Furthermore, DA-CIT SLNs displayed high cytocompatibility with both human nasal RPMI 2650 and neuronal SH-SY5Y cells. Furthermore, OxyBlot assay demonstrated considerable potential to assess the protective effect of antioxidant agents against oxidative cellular damage. Thus, such protective effect was shown by DA-CIT-SLNs, which constitute a promising formulation for PD application.

Paper-in-Tip Bipolar Electrospray Mass Spectrometry for Real-Time Chemical Reaction Monitoring

Capturing short-lived intermediates at the molecular level is key to understanding the mechanism and dynamics of chemical reactions. Here, we have developed a paper-in-tip bipolar electrolytic electrospray mass spectrometry platform, in which a piece of triangular conductive paper incorporated into a plastic pipette tip serves not only as an electrospray emitter but also as a bipolar electrode (BPE), thus triggering both electrospray and electrolysis simultaneously upon application of a high voltage. The bipolar electrolysis induces a pair of redox reactions on both sides of BPE, enabling both electro-oxidation and electro-reduction processes regardless of the positive or negative ion mode, thus facilitating access to complementary structural information for mechanism elucidation. Our method enables real-time monitoring of transient intermediates (such as N,N-dimethylaniline radical cation, dopamine o-quinone (DAQ) and sulfenic acid with half-lives ranging from microseconds to minutes) and transient processes (such as DAQ cyclization with a rate constant of 0.15 s-1). This platform also provides key insights into electrocatalytic reactions such as Fe (III)-catalyzed dopamine oxidation to quinone species at physiological pH for neuromelanin formation.

Highly Sensitive and Selective Fluorescence and Smartphone-Based Sensor for Detection of Rutin Using Boron Nitrogen Co-doped Graphene Quantum Dots

This research explores the fluorescence properties and photostability of boron nitrogen co-doped graphene quantum dots (BN-GQDs), evaluating their effectiveness as sensors for rutin (RU). BN-GQDs are biocompatible and exhibit notable absorbance and fluorescence characteristics, making them suitable for sensing applications. The study utilized various analytical techniques to investigate the chemical composition, structure, morphology, optical attributes, elemental composition, and particle size of BN-GQDs. Techniques included X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The average particle size of the BN-GQDs was determined to be approximately 3.5 ± 0.3 nm. A clear correlation between the emission intensity ratio and RU concentration was identified across the range of 0.42 to 4.1 μM, featuring an impressively low detection limit (LOD) of 1.23 nM. The application of BN-GQDs as fluorescent probes has facilitated the development of a highly sensitive and selective RU detection method based on Förster resonance energy transfer (FRET) principles. This technique leverages emission at 465 nm. Density Functional Theory (DFT) analyses confirm that FRET is the primary mechanism behind fluorescence quenching, as indicated by the energy levels of the lowest unoccupied molecular orbitals (LUMOs) of BN-GQDs and RU. The method's effectiveness has been validated by measuring RU concentrations in human serum samples, showing a recovery range between 97.8% and 103.31%. Additionally, a smartphone-based detection method utilizing BN-GQDs has been successfully implemented, achieving a detection limit (LOD) of 49 nM.

The Skin-Brain Axis: From UV and Pigmentation to Behaviour Modulation

The skin-brain axis has been suggested to play a role in several pathophysiological conditions, including opioid addiction, Parkinson's disease and many others. Recent evidence suggests that pathways regulating skin pigmentation may directly and indirectly regulate behaviour. Conversely, CNS-driven neural and hormonal responses have been demonstrated to regulate pigmentation, e.g., under stress. Additionally, due to the shared neuroectodermal origins of the melanocytes and neurons in the CNS, certain CNS diseases may be linked to pigmentation-related changes due to common regulators, e.g., MC1R variations. Furthermore, the HPA analogue of the skin connects skin pigmentation to the endocrine system, thereby allowing the skin to index possible hormonal abnormalities visibly. In this review, insight is provided into skin pigment production and neuromelanin synthesis in the brain and recent findings are summarised on how signalling pathways in the skin, with a particular focus on pigmentation, are interconnected with the central nervous system. Thus, this review may supply a better understanding of the mechanism of several skin-brain associations in health and disease.

Sodium Bicarbonate Decreases Alcohol Consumption in Mice

We previously reported that mice with low neuronal pH drink more alcohol, demonstrating the importance of pH for alcohol reward and motivation. In this study, we tested whether systemic pH affects alcohol consumption and if so, whether it occurs by changing the alcohol reward. C57BL/6J mice were given NaHCO3 to raise their blood pH, and the animals' alcohol consumption was measured in the drinking-in-the-dark and two-bottle free choice paradigms. Alcohol consumption was also assessed after suppressing the bitterness of NaHCO3 with sucrose. Alcohol reward was evaluated using a conditioned place preference. In addition, taste sensitivity was assessed by determining quinine and sucrose preference. The results revealed that a pH increase by NaHCO3 caused mice to decrease their alcohol consumption. The decrease in high alcohol contents (20%) was significant and observed at different ages, as well as in both males and females. Alcohol consumption was also decreased after suppressing NaHCO3 bitterness. Oral gavage of NaHCO3 did not alter quinine and sucrose preference. In the conditioned place preference, NaHCO3-treated mice spent less time in the alcohol-injected chamber. Conclusively, the results show that raising systemic pH with NaHCO3 decreases alcohol consumption, as it decreases the alcohol reward value.

Metabolic energy decline coupled dysregulation of catecholamine metabolism in physiologically highly active neurons: implications for selective neuronal death in Parkinson's disease

Parkinson's disease (PD) is an age-related irreversible neurodegenerative disease which is characterized as a progressively worsening involuntary movement disorder caused by the loss of dopaminergic (DA) neurons in substantia nigra pars compacta (SNpc). Two main pathophysiological features of PD are the accumulation of inclusion bodies in the affected neurons and the predominant loss of neuromelanin-containing DA neurons in substantia nigra pars compacta (SNpc) and noradrenergic (NE) neurons in locus coeruleus (LC). The inclusion bodies contain misfolded and aggregated α-synuclein (α-Syn) fibrils known as Lewy bodies. The etiology and pathogenic mechanisms of PD are complex, multi-dimensional and associated with a combination of environmental, genetic, and other age-related factors. Although individual factors associated with the pathogenic mechanisms of PD have been widely investigated, an integration of the findings to a unified causative mechanism has not been envisioned. Here we propose an integrated mechanism for the degeneration of DA neurons in SNpc and NE neurons in LC in PD, based on their unique high metabolic activity coupled elevated energy demand, using currently available experimental data. The proposed hypothetical mechanism is primarily based on the unique high metabolic activity coupled elevated energy demand of these neurons. We reason that the high vulnerability of a selective group of DA neurons in SNpc and NE neurons in LC in PD could be due to the cellular energy modulations. Such cellular energy modulations could induce dysregulation of DA and NE metabolism and perturbation of the redox active metal homeostasis (especially copper and iron) in these neurons.

[Recent research on the role of oxidative stress in the pathogenesis of attention deficit hyperactivity disorder]

Attention deficit hyperactivity disorder (ADHD) is a common neurodevelopmental disorder in children and adolescents, and its etiology and pathogenesis are still unclear. Brain is the organ with the largest oxygen consumption in human body and is easily affected by oxidative imbalance. Oxidative stress has become the key research direction for the pathogenesis of ADHD, but there is still a lack of relevant studies in China. Based on the latest research findings in China and overseas, this article reviews the clinical and experimental studies on oxidative stress in ADHD and explores the association of oxidative stress with neurotransmitter imbalance, neuroinflammation, and cell apoptosis in the pathogenesis of ADHD, so as to provide new research ideas for exploring the pathogenesis of ADHD.

The High-Precision Liquid Chromatography with Electrochemical Detection (HPLC-ECD) for Monoamines Neurotransmitters and Their Metabolites: A Review

This review highlights the advantages of high-precision liquid chromatography with an electrochemical detector (HPLC-ECD) in detecting and quantifying biological samples obtained through intracerebral microdialysis, specifically the serotonergic and dopaminergic systems: Serotonin (5-HT), 5-hydroxyindolacetic acid (5-HIAA), 3,4-dihydroxyphenylacetic acid (DOPAC), dopamine (DA), 3-metoxytryptamin (3-MT) and homovanillic acid (HVA). Recognized for its speed and selectivity, HPLC enables direct analysis of intracerebral microdialysis samples without complex derivatization. Various chromatographic methods, including reverse phase (RP), are explored for neurotransmitters (NTs) and metabolites separation. Electrochemical detector (ECD), particularly with glassy carbon (GC) electrodes, is emphasized for its simplicity and sensitivity, aimed at enhancing reproducibility through optimization strategies such as modified electrode materials. This paper underscores the determination of limits of detection (LOD) and quantification (LOQ) and the linear range (L.R.) showcasing the potential for real-time monitoring of compounds concentrations. A non-exhaustive compilation of literature values for LOD, LOQ, and L.R. from recent publications is included.

Insight into the degradation of amino substituted benzimidazo[1,2-a]quinolines via a combined experimental and density functional theory study

Heterocyclic compounds have been shown to be potential chemotherapeutic agents, especially the benzimidazole derivatives studied in this work. The ultimate goal in the search for biologically active and effective molecules is to commercialize a product whose stability must be reliable. Therefore, in the development of drugs, forced degradation experiments are performed under the environmental conditions to which they are subjected during transportation and storage to ensure quality and safety before marketing. Hydrolytic, thermal, photolytic, and degradation in the presence of hydrogen peroxide are experimental stress tests to which the newly synthesized compounds were subjected to gain insight into the degradation pathways of the analytes. Degradation of two benzimidazole derivatives was observed under all applied conditions while the major impact showed photolysis with ten and four degradation products, respectively. In total, eighteen major degradation products were detected and identified using high-resolution mass spectrometry. Computer models in the TEST program were applied to the proposed structures to evaluate the bioaccumulation factor, toxicity, and mutagenicity of the analyzed compounds, while density functional theory analysis (DFT) revealed factors affecting the vulnerability of systems towards exceeding acidic/basic conditions and H2O2.

Development of novel nanocomposite-modified photoelectrochemical sensor based on the association of bismuth vanadate and MWCNT-grafted-molecularly imprinted poly(acrylic acid) for dopamine determination at nanomolar level

This study proposes the development of a new photoelectrochemical (PEC) sensor for the determination of dopamine (DA) at nanomolar levels. The PEC sensor was based on a physical mixture of bismuth vanadate (BiVO4) with nanocomposite molecularly imprinted poly(acrylic acid) (MIP-AA) grafted onto MWCNTox by using the surface-controlled radical polymerization strategy with an INIFERTER reagent. XRD, diffuse reflectance spectroscopy (DRE), SEM, TEM, and TGA were employed to characterize the materials. Photoelectrochemical analyses were carried out with GCE/BiVO4/MIP-AA sensor under visible light using a potential of 0.6 V, phosphate buffer (0.1 mol L-1) at pH 7.0, and modifying the GCE with a film composed of monoclinic BiVO4 at 3.5 mg mL-1 and nanocomposite MIP prepared with acrylic acid (MIP-AA) at 0.1 mg mL-1. The proposed method using the GCE/BiVO4/MIP-AA sensor presented a limit of detection (LOD) of 2.9 nmol L-1, a linear range from 9.7 to 150 nmol L-1 and it was successfully applied for analysis of DA in urine samples using external calibration curve yielding recovery values of 90-105%. Additionally, the proposed PEC sensor allowed DA determination without interference from uric acid, ascorbic acid, epinephrine, norepinephrine, and other unwanted interferences.

Carboxymethyl chitosan dopamine conjugates: Synthesis and evaluation for intranasal anti Parkinson therapy

With respect to the Parkinson's disease (PD), herein, we aimed at synthetizing and characterizing two novel macromolecular conjugates where dopamine (DA) was linked to N,O-carboxymethyl chitosan or O-carboxymethyl chitosan, being both conjugates obtained from an organic solvent free synthetic procedure. They were characterized by FT-IR, 1H NMR spectroscopies, whereas thermal analysis (including Differential Scanning Calorimetry and Thermal Gravimetric Analysis) revealed good stability of the two conjugates after exposure at temperatures close to 300 °C. Release studies in simulated nasal fluid elucidated that a faster release occurred since O-carboxymethyl chitosan-DA conjugate maybe due to the less steric hindrance exerted by the polymeric moiety. The CMCS-DA conjugates prepared in aqueous medium may self-assembly to form polymeric micelles and/or may form polymeric nanoparticles. TEM and Photon correlation spectroscopy lent support for polymeric nanoparticle formation. Moreover, such CMCS-DA conjugates showed antioxidant activity, as demonstrated by DPPH radical scavenging assay. Finally, cytocompatibility studies with neuroblastoma SH-SY5Y cells showed no cytotoxicity of both conjugates, whereas their uptake increased from 2.5 to 24 h and demonstrated in 40-66 % of cells.

Peroxiredoxin 5 overexpression decreases oxidative stress and dopaminergic cell death mediated by paraquat

Peroxiredoxins (Prdxs) are thiol-dependent enzymes that scavenge peroxides. Previously, we found that Prdxs were hyperoxidized in a Parkinson's disease model induced by paraquat (PQ), which led to their inactivation, perpetuating reactive oxygen species (ROS) formation. Herein, we evaluated the redox state of the typical 2-Cys-Prx subgroup. We found that PQ induces ROS compartmentalization in different organelles, reflected by the 2-Cys-Prdx hyperoxidation pattern detected by redox eastern blotting. 2-Cys Prdxs are most vulnerable to hyperoxidation, while atypical 2-Cys Peroxiredoxin 5 (Prdx5) is resistant and is expressed in multiple organelles, such as mitochondria, peroxisomes, and cytoplasm. Therefore, we overexpressed human Prdx5 in the dopaminergic SHSY-5Y cell line using the adenoviral vector Ad-hPrdx5. Prdx5 overexpression was confirmed by western blotting and immunofluorescence (IF) and effectively decreased PQ-mediated mitochondrial and cytoplasmic ROS assessed with a mitochondrial superoxide indicator and DHE through IF or flow cytometry. Decreased ROS mediated by Prdx5 in the main subcellular compartments led to overall cell protection against PQ-induced cell death, which was demonstrated by flow cytometry using Annexin V labeling and 7-AAD. Therefore, Prdx5 is an attractive therapeutic target for PD, as its overexpression protects dopaminergic cells from ROS and death, which warrants further experimental animal studies for its subsequent application in clinical trials.

Selective dopaminergic vulnerability in Parkinson's disease: new insights into the role of DAT

One of the hallmarks of Parkinson's disease (PD) is the progressive loss of dopaminergic neurons and associated dopamine depletion. Several mechanisms, previously considered in isolation, have been proposed to contribute to the pathophysiology of dopaminergic degeneration: dopamine oxidation-mediated neurotoxicity, high dopamine transporter (DAT) expression density per neuron, and autophagy-lysosome pathway (ALP) dysfunction. However, the interrelationships among these mechanisms remained unclear. Our recent research bridges this gap, recognizing autophagy as a novel dopamine homeostasis regulator, unifying these concepts. I propose that autophagy modulates dopamine reuptake by selectively degrading DAT. In PD, ALP dysfunction could increase DAT density per neuron, and enhance dopamine reuptake, oxidation, and neurotoxicity, potentially contributing to the progressive loss of dopaminergic neurons. This integrated understanding may provide a more comprehensive view of aspects of PD pathophysiology and opens new avenues for therapeutic interventions.

A chemical probe unravels the reactive proteome of health-associated catechols

Catechol-containing natural products are common constituents of foods, drinks, and drugs. Natural products carrying this motif are often associated with beneficial biological effects such as anticancer activity and neuroprotection. However, the molecular mode of action behind these properties is poorly understood. Here, we apply a mass spectrometry-based competitive chemical proteomics approach to elucidate the target scope of catechol-containing bioactive molecules from diverse foods and drugs. Inspired by the protein reactivity of catecholamine neurotransmitters, we designed and synthesised a broadly reactive minimalist catechol chemical probe based on dopamine. Initial labelling experiments in live human cells demonstrated broad protein binding by the probe, which was largely outcompeted by its parent compound dopamine. Next, we investigated the competition profile of a selection of biologically relevant catechol-containing substances. With this approach, we characterised the protein reactivity and the target scope of dopamine and ten biologically relevant catechols. Strikingly, proteins associated with the endoplasmic reticulum (ER) were among the main targets. ER stress assays in the presence of reactive catechols revealed an activation of the unfolded protein response (UPR). The UPR is highly relevant in oncology and cellular resilience, which may provide an explanation of the health-promoting effects attributed to many catechol-containing natural products.

Laser-induced graphene electrodes on polyimide membranes modified with gold nanoparticles for the simultaneous detection of dopamine and uric acid in human serum

The level control of biological active molecules in human body fluids is important for the surveillance of several human diseases. Dopamine (DA) and uric acid (UA) are two important biomarkers of neurological and bone diseases, respectively. Design of sensitive and cost-effective sensors for their detection is an effervescent research field. We report on the straightforward design of laser-induced graphene electrodes (LIGEs) from the laser ablation of a polyimide substrate and their modification by electrochemical deposition of gold nanoparticles (AuNPs/LIGE) and their uses as chemosensors. Electrochemical investigations showed that the presence of gold nanoclusters onto the electrode surface improved the electrochemical surface area (ECSA) and the heterogenous electron transfer (HET) rate. Furthermore, the AuNPs/LIGEs can be used to detect simultaneously low concentrations of DA and UA in presence of ascorbic acid (AA) as an potentially interfering substance at redox potentials of 300 mV, 230 mV and 450 mV and 91 mV, respectively, compared with the Ag/AgCl (3 M KCl) reference electrode in cyclic voltametric. The method displayed linear ranges varying from 2 to 20 μM and 5 to 50 μM, led to limits of detection of 0.37 μM and 0.71 μM for DA and UA, respectively. The AuNPs/LIGE was applied to simultaneously detect both analytes in scarcely diluted human serum with good recoveries. The data show that the recovery percentages ranged from 94% ± 2.1 to 102 % ± 0.5 and from 94% ±0.3 to 112% ± 1.4 for dopamine and uric acid, respectively. Thus, the AuNPs/LIGEs are promising candidates for the detection of other biologically active molecules such as drugs, pesticides, and metabolites.

A Reliable Method Based on Liquid Chromatography-Tandem Mass Spectrometry for the Simultaneous Quantification of Neurotransmitters in Caenorhabditis elegans

Neurotransmitters like dopamine (DA), serotonin (SRT), γ-aminobutyric acid (GABA) and acetylcholine (ACh) are messenger molecules that play a pivotal role in transmitting excitation between neurons across chemical synapses, thus enabling complex processes in the central nervous system (CNS). Balance in neurotransmitter homeostasis is essential, and altered neurotransmitter levels are associated with various neurological disorders, e.g., loss of dopaminergic neurons (Parkinson's disease) or altered ACh synthesis (Alzheimer's disease). Therefore, it is crucial to possess adequate tools to assess precise neurotransmitter levels, and to apply targeted therapies. An established in vivo model to study neurotoxicity is the model organism Caenorhabditis elegans (C. elegans), as its neurons have been well characterized and functionally are analogous to mammals. We have developed a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method including a sample preparation assuring neurotransmitter stability, which allows a simultaneous neurotransmitter quantification of DA, SRT, GABA and ACh in C. elegans, but can easily be applied to other matrices. LC-MS/MS combined with isotope-labeled standards is the tool of choice, due to its otherwise unattainable sensitivity and specificity. Using C. elegans together with our analytically validated and verified method provides a powerful tool to evaluate mechanisms of neurotoxicity, and furthermore to identify possible therapeutic approaches.

Rotenone-Induced Model of Parkinson's Disease: Beyond Mitochondrial Complex I Inhibition

Parkinson's disease (PD) is usually diagnosed through motor symptoms that make the patient incapable of carrying out daily activities; however, numerous non-motor symptoms include olfactory disturbances, constipation, depression, excessive daytime sleepiness, and rapid eye movement at sleep; they begin years before motor symptoms. Therefore, several experimental models have been studied to reproduce several PD functional and neurochemical characteristics; however, no model mimics all the PD motor and non-motor symptoms to date, which becomes a limitation for PD study. It has become increasingly relevant to find ways to study the disease from its slowly progressive nature. The experimental models most frequently used to reproduce PD are based on administering toxic chemical compounds, which aim to imitate dopamine deficiency. The most used toxic compounds to model PD have been 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and 6-hydroxydopamine (6-OHDA), which inhibit the complex I of the electron transport chain but have some limitations. Another toxic compound that has drawn attention recently is rotenone, the classical inhibitor of mitochondrial complex I. Rotenone triggers the progressive death of dopaminergic neurons and α-synuclein inclusions formation in rats; also, rotenone induces microtubule destabilization. This review presents information about the experimental model of PD induced by rotenone, emphasizing its molecular characteristics beyond the inhibition of mitochondrial complex I.

DOPAL initiates αSynuclein-dependent impaired proteostasis and degeneration of neuronal projections in Parkinson's disease

Dopamine dyshomeostasis has been acknowledged among the determinants of nigrostriatal neuron degeneration in Parkinson's disease (PD). Several studies in experimental models and postmortem PD patients underlined increasing levels of the dopamine metabolite 3,4-dihydroxyphenylacetaldehyde (DOPAL), which is highly reactive towards proteins. DOPAL has been shown to covalently modify the presynaptic protein αSynuclein (αSyn), whose misfolding and aggregation represent a major trait of PD pathology, triggering αSyn oligomerization in dopaminergic neurons. Here, we demonstrated that DOPAL elicits αSyn accumulation and hampers αSyn clearance in primary neurons. DOPAL-induced αSyn buildup lessens neuronal resilience, compromises synaptic integrity, and overwhelms protein quality control pathways in neurites. The progressive decline of neuronal homeostasis further leads to dopaminergic neuron loss and motor impairment, as showed in in vivo models. Finally, we developed a specific antibody which detected increased DOPAL-modified αSyn in human striatal tissues from idiopathic PD patients, corroborating the translational relevance of αSyn-DOPAL interplay in PD neurodegeneration.

Emerging Materials, Wearables, and Diagnostic Advancements in Therapeutic Treatment of Brain Diseases

Among the most critical health issues, brain illnesses, such as neurodegenerative conditions and tumors, lower quality of life and have a significant economic impact. Implantable technology and nano-drug carriers have enormous promise for cerebral brain activity sensing and regulated therapeutic application in the treatment and detection of brain illnesses. Flexible materials are chosen for implantable devices because they help reduce biomechanical mismatch between the implanted device and brain tissue. Additionally, implanted biodegradable devices might lessen any autoimmune negative effects. The onerous subsequent operation for removing the implanted device is further lessened with biodegradability. This review expands on current developments in diagnostic technologies such as magnetic resonance imaging, computed tomography, mass spectroscopy, infrared spectroscopy, angiography, and electroencephalogram while providing an overview of prevalent brain diseases. As far as we are aware, there hasn't been a single review article that addresses all the prevalent brain illnesses. The reviewer also looks into the prospects for the future and offers suggestions for the direction of future developments in the treatment of brain diseases.

Core-shell Au-Ag nanoparticles as colorimetric sensing probes for highly selective detection of a dopamine neurotransmitter under different pH conditions

Dopamine (DA) is a vital biomarker for the early diagnosis of dopaminergic dysfunction; therefore, it is important to establish a direct and selective detection tool for DA neurotransmitters. This work reports facilely synthesized Au-Ag core-shell nanoparticles (Au@Ag NPs) as colorimetric sensing probes for highly selective detection of the DA neurotransmitter. Our sensing strategy is based on DA-mediated aggregation of the Au@Ag NPs, which can show a distinct color transition from yellow to greenish grey. With the increase of pH from 6 to 10, the response time of colorimetric transition was significantly reduced by a factor of 10 and the limit of detection (LOD) for DA by a spectroscopic device was estimated to be 0.08 μM. Notably, optimized sensing probes of Au@Ag NPs at pH 10 demonstrated an excellent selectivity to DA against various interfering components (including catecholamines (norepinephrine and epinephrine), lysine, glutamic acid, glucose, or metal ions). Our sensing system also exhibited the reliable detection of DA in spiked human serum with the relative standard deviation lower than 4.0%, suggesting its possible application to the direct detection of DA in biological fluids.

Transformation of L-DOPA and Dopamine on the Surface of Gold Nanoparticles: An NMR and Computational Study

Gold nanoparticles (AuNPs) have found applications in biomedicine as diagnostic tools, but extensive research efforts have been also directed toward their development as more efficient drug delivery agents. The high specific surface area of AuNPs may provide dense loading of molecules like catechols (L-DOPA and dopamine) on nanosurfaces, enabling functionalization strategies for advancing conventional therapy and diagnostic approaches of neurodegenerative diseases. Despite numerous well-described procedures in the literature for preparation of different AuNPs, possible transformation and structural changes of surface functionalization agents have not been considered thoroughly. As a case in point, the catechols L-DOPA and dopamine were selected because of their susceptibility to oxidation, cyclization, and polymerization. To assess the fate of coating and functionalization agents during the preparation of AuNPs or interaction at the nano-bio interface, a combination of spectroscopy, light scattering, and microscopy techniques was used while structural information and reaction mechanism were obtained by NMR in combination with computational tools. The results revealed that the final form of catechol on the AuNP nanosurface depends on the molar ratio of Au used for AuNP preparation. A large molar excess of L-DOPA or dopamine is needed to prepare AuNPs funtionalized with fully reduced catechols. In the case of molar excess of Au, the oxidation of catechols to dopamine quinone and dopaquinone was promoted, and dopaquinone underwent intramolecular cyclization in which additional oxidation products, leukodopachrome, dopachrome, or its tautomer, were formed because of the larger intrinsic acidity of the more nucleophilic amino group in dopaquinone. MD simulations showed that, of the oxidation products, dopachrome had the highest affinity for binding to the AuNPs surface. The results highlight how a more versatile methodological approach, combining experimental and in silico techniques, allows more reliable characterization of binding events at the surface of AuNPs for possible applications in biomedicine.

Amyloid-mimicking toxic nanofibers generated via self-assembly of dopamine

Molecular self-assembly of biologically relevant aromatic metabolites is known to generate cytotoxic nanostructures and this unique property has opened up new concepts in the molecular mechanisms of metabolite-linked disorders. Because aromaticity is intrinsic to the chemical structure of some important neuromodulators, the question of whether this property can promote their self-assembly into toxic higher order structures is highly relevant to the advancement of both fundamental and applied research. We show here that dopamine, an aromatic neuromodulator of high significance, undergoes self-assembly, under physiological buffer conditions, yielding cytotoxic supramolecular nanostructures. The oxidation of dopamine seems crucial in driving the self-assembly, and substantial inhibition effect was observed in the presence of antioxidants and acidic buffers. Strong H-bonds and π-π interactions between optimally-oriented dopamine molecules were found to stabilize the dopamine nanostructure which displayed characteristic β-structure-patterns with hydrophobic exterior and hydrophilic interior moieties. Furthermore, dopamine nanostructures were found to be highly toxic to human neuroblastoma cells, revealing apoptosis and necrosis-mediated cytotoxicity. Abnormal fluctuation in the dopamine concentration is known to predispose a multitude of neuronal complications, hence, the new findings of this study on oxidation-driven buildup of amyloid-mimicking neurotoxic dopamine assemblies may have direct relevance to the molecular origin of several dopamine related disorders.

Highly sensitive and selective detection of dopamine with boron and sulfur co-doped graphene quantum dots

In this work, we report, the synthesis of Boron and Sulfur co-doped graphene quantum dots (BS-GQDs) and its applicability as a label-free fluorescence sensing probe for the highly sensitive and selective detection of dopamine (DA). Upon addition of DA, the fluorescence intensity of BS-GQDs were effectively quenched over a wide concentration range of DA (0–340 μM) with an ultra-low detection limit of 3.6 μM. The quenching mechanism involved photoinduced electron transfer process from BS-GQDs to dopamine-quinone, produced by the oxidization of DA under alkaline conditions. The proposed sensing mechanism was probed using a detailed study of UV–Vis absorbance, steady state and time resolved fluorescence spectroscopy. The high selectivity of the fluorescent sensor towards DA is established. Our study opens up the possibility of designing a low-cost biosensor which will be suitable for detecting DA in real samples.

The catalytic mechanism of the mitochondrial methylenetetrahydrofolate dehydrogenase/cyclohydrolase (MTHFD2)

Methylenetetrahydrofolate dehydrogenase/cyclohydrolase (MTHFD2) is a new drug target that is expressed in cancer cells but not in normal adult cells, which provides an Achilles heel to selectively kill cancer cells. Despite the availability of crystal structures of MTHFD2 in the inhibitor- and cofactor-bound forms, key information is missing due to technical limitations, including (a) the location of absolutely required Mg2+ ion, and (b) the substrate-bound form of MTHFD2. Using computational modeling and simulations, we propose that two magnesium ions are present at the active site whereby (i) Arg233, Asp225, and two water molecules coordinate MgA2+, while MgA2+ together with Arg233 stabilize the inorganic phosphate (Pi); (ii) Asp168 and three water molecules coordinate MgB2+, and MgB2+ further stabilizes Pi by forming a hydrogen bond with two oxygens of Pi; (iii) Arg201 directly coordinates the Pi; and (iv) through three water-mediated interactions, Asp168 contributes to the positioning and stabilization of MgA2+, MgB2+ and Pi. Our computational study at the empirical valence bond level allowed us also to elucidate the detailed reaction mechanisms. We found that the dehydrogenase activity features a proton-coupled electron transfer with charge redistribution connected to the reorganization of the surrounding water molecules which further facilitates the subsequent cyclohydrolase activity. The cyclohydrolase activity then drives the hydration of the imidazoline ring and the ring opening in a concerted way. Furthermore, we have uncovered that two key residues, Ser197/Arg233, are important factors in determining the cofactor (NADP+/NAD+) preference of the dehydrogenase activity. Our work sheds new light on the structural and kinetic framework of MTHFD2, which will be helpful to design small molecule inhibitors that can be used for cancer treatment.

Dopamine Photochemical Behaviour under UV Irradiation

To understand the photochemical behaviour of the polydopamine polymer in detail, one would also need to know the behaviour of its building blocks. The electronic absorption, as well as the fluorescence emission and excitation spectra of the dopamine were experimentally and theoretically investigated considering time-resolved fluorescence spectroscopy and first-principles quantum theory methods. The shape of the experimental absorption spectra obtained for different dopamine species with standard, zwitterionic, protonated, and deprotonated geometries was interpreted by considering the advanced equation-of-motion coupled-cluster theory of DLPNO-STEOM. Dynamical properties such as fluorescence lifetimes or quantum yield were also experimentally investigated and compared with theoretically predicted transition rates based on Fermi's Golden Rule-like equation. The results show that the photochemical behaviour of dopamine is strongly dependent on the concentration of dopamine, whereas in the case of a high concentration, the zwitterionic form significantly affects the shape of the spectrum. On the other hand, the solvent pH is also a determining factor for the absorption, but especially for the fluorescence spectrum, where at lower pH (5.5), the protonated and, at higher pH (8.0), the deprotonated forms influence the shape of the spectra. Quantum yield measurements showed that, besides the radiative deactivation mechanism characterized by a relatively small QY value, non-radiative deactivation channels are very important in the relaxation process of the electronic excited states of different dopamine species.

Human Pluripotent Stem Cell-Derived Medium Spiny Neuron-like Cells Exhibit Gene Desensitization

Gene desensitization in response to a repeated stimulus is a complex phenotype important across homeostatic and disease processes, including addiction, learning, and memory. These complex phenotypes are being characterized and connected to important physiologically relevant functions in rodent systems but are difficult to capture in human models where even acute responses to important neurotransmitters are understudied. Here through transcriptomic analysis, we map the dynamic responses of human stem cell-derived medium spiny neuron-like cells (hMSN-like cells) to dopamine. Furthermore, we show that these human neurons can reflect and capture cellular desensitization to chronic versus acute administration of dopamine. These human cells are further able to capture complex receptor crosstalk in response to the pharmacological perturbations of distinct dopamine receptor subtypes. This study demonstrates the potential utility and remaining challenges of using human stem cell-derived neurons to capture and study the complex dynamic mechanisms of the brain.

In Situ Grown Nanohydroxyapatite Hybridized Graphene Oxide: Enhancing the Strength and Bioactivity of Polymer Scaffolds

Graphene oxide (GO) and nanohydroxyapatite (nHA) are usually used for improving the strength and bioactivity of polymer scaffolds. However, due to the nano-aggregation effect, these applications often face the problems of uneven dispersion and poor interface bonding. In this work, their hybrids (GO@nHA) were constructed by combining chemical modification and in situ growth methods, realizing the perfect combination of nHA and GO. First, the functionalization of GO was realized through oxidative self-polymerization of dopamine (DA), and the product was denoted GO@DA. Furthermore, the in situ growth of nHA on GO@DA was induced by hydrothermal reactions to prepare GO@nHA hybrids. Then, the obtained hybrid was added to the polymer matrix, and a composite scaffold was prepared through a selective laser sintering process. The results demonstrated that with the addition of GO@DA and GO@nHA, the ultimate strength was increased to 16.8 and 18.6 MPa, respectively, which is 66 and 84% higher than the 10.1 MPa of the polylactic acid (PLA) scaffold. In addition, composite scaffolds exhibited good biomineralization ability in vitro and also promoted the adhesion and proliferation of MG63 cells.

Pairing structural reconstruction with catalytic competence to evaluate the mechanisms of key enzymes in the folate-mediated one-carbon pathway

Mammalian metabolism comprises a series of interlinking pathways that include two major cycles: the folate and methionine cycles. The folate-mediated metabolic cycle uses several oxidation states of tetrahydrofolate to carry activated one-carbon units to be readily used and interconverted within the cell. They are required for nucleotide synthesis, methylation and metabolism, and particularly for proliferation of cancer cells. Based on the latest progress in genome-wide CRISPR loss-of-function viability screening of 789 cell lines, we focus on the most cancer-dependent enzymes in this pathway, especially those that are hyperactivated in cancer, to provide new insight into the chemical basis for cancer drug development. Since the complete 3D structure of several of these enzymes of the one-carbon pathway in their active form are not available, we used homology modelling integrated with the interpretation of the reaction mechanism. In addition, have reconstructed the most likely scenario for the reactions taking place paired with their catalytic competence that provides a testable framework for this pathway.

Multivalent non-covalent interactions lead to strongest polymer adhesion

Multivalent interactions play a leading role in biological processes such as the inhibition of inflammation or virus internalization. The multivalent interactions show enhanced strength and better selectivity compared to monovalent interactions, but they are much less understood due to their complexity. Here, we detect molecular interactions in the range of a few piconewtons to several nanonewtons and correlate them with the formation and subsequent breaking of one or several bonds and assign these bonds. This becomes possible by performing atomic force microcopy (AFM)-based single molecule force spectroscopy of a multifunctional polymer covalently attached to an AFM cantilever tip on a substrate bound polymer layer of the multifunctional polymer. Varying the pH value and the crosslinking state of the polymer layer, we find that bonds of intermediate strength (non-covalent), like coordination bonds, give the highest multivalent bond strength, even outperforming strong (covalent) bonds. At the same time, covalent bonds enhance the polymer layer density, increasing in particular the number of non-covalent bonds. In summary, we can show that the key for the design of stable and durable polymer coatings is to provide a variety of multivalent interactions and to keep the number of non-covalent interactions at a high level.

Carving the senescent phenotype by the chemical reactivity of catecholamines: An integrative review

Macromolecules damaged by covalent modifications produced by chemically reactive metabolites accumulate in the slowly renewable components of living bodies and compromise their functions. Among such metabolites, catecholamines (CA) are unique, compared with the ubiquitous oxygen, ROS, glucose and methylglyoxal, in that their high chemical reactivity is confined to a limited set of cell types, including the dopaminergic and noradrenergic neurons and their direct targets, which suffer from CA propensities for autoxidation yielding toxic quinones, and for Pictet-Spengler reactions with carbonyl-containing compounds, which yield mitochondrial toxins. The functions progressively compromised because of that include motor performance, cognition, reward-driven behaviors, emotional tuning, and the neuroendocrine control of reproduction. The phenotypic manifestations of the resulting disorders culminate in such conditions as Parkinson's and Alzheimer's diseases, hypertension, sarcopenia, and menopause. The reasons to suspect that CA play some special role in aging accumulated since early 1970-ies. Published reviews address the role of CA hazardousness in the development of specific aging-associated diseases. The present integrative review explores how the bizarre discrepancy between CA hazardousness and biological importance could have emerged in evolution, how much does the chemical reactivity of CA contribute to the senescent phenotype in mammals, and what can be done with it.

COVID-19 infection and neurodegeneration: Computational evidence for interactions between the SARS-CoV-2 spike protein and monoamine oxidase enzymes

Although COVID-19 has been primarily associated with pneumonia, recent data show that its causative agent, the SARS-CoV-2 coronavirus, can infect many vital organs beyond the lungs, including the heart, kidneys and the brain. The literature agrees that COVID-19 is likely to have long-term mental health effects on infected individuals, which signifies a need to understand the role of the virus in the pathophysiology of brain disorders that is currently unknown and widely debated. Our docking and molecular dynamics simulations show that the affinity of the spike protein from the wild type (WT) and the South African B.1.351 (SA) variant towards MAO enzymes is comparable to that for its ACE2 receptor. This allows for the WT/SA⋅⋅⋅MAO complex formation, which changes MAO affinities for their neurotransmitter substrates, thereby impacting their metabolic conversion and misbalancing their levels. Knowing that this fine regulation is strongly linked with the etiology of various brain pathologies, these results are the first to highlight the possibility that the interference with the brain MAO catalytic activity is responsible for the increased neurodegenerative illnesses following a COVID-19 infection, thus placing a neurobiological link between these two conditions in the spotlight. Since the obtained insight suggests that a more contagious SA variant causes even larger disturbances, and with new and more problematic strains likely emerging in the near future, we firmly advise that the presented prospect of the SARS-CoV-2 induced neurological complications should not be ignored, but rather requires further clinical investigations to achieve an early diagnosis and timely therapeutic interventions.

Neuroprotective Properties of Quinone Reductase 2 Inhibitor M-11, a 2-Mercaptobenzimidazole Derivative

The ability of NQO2 to increase the production of free radicals under enhanced generation of quinone derivatives of catecholamines is considered to be a component of neurodegenerative disease pathogenesis. The present study aimed to investigate the neuroprotective mechanisms of original NQO2 inhibitor M-11 (2-[2-(3-oxomorpholin-4-il)-ethylthio]-5-ethoxybenzimidazole hydrochloride) in a cellular damage model using NQO2 endogenous substrate adrenochrome (125 µM) and co-substrate BNAH (100 µM). The effects of M-11 (10-100 µM) on the reactive oxygen species (ROS) generation, apoptosis and lesion of nuclear DNA were evaluated using flow cytometry and single-cell gel electrophoresis assay (comet assay). Results were compared with S29434, the reference inhibitor of NQO2. It was found that treatment of HT-22 cells with M-11 results in a decline of ROS production triggered by incubation of cells with NQO2 substrate and co-substrate. Pre-incubation of HT-22 cells with compounds M-11 or S29434 results in a decrease of DNA damage and late apoptotic cell percentage reduction. The obtained results provide a rationale for further development of the M-11 compound as a potential neuroprotective agent.

DOPA Homeostasis by Dopamine: A Control-Theoretic View

Dopamine (DA) is an important signal mediator in the brain as well as in the periphery. The term "dopamine homeostasis" occasionally found in the literature refers to the fact that abnormal DA levels can be associated with a variety of neuropsychiatric disorders. An analysis of the negative feedback inhibition of tyrosine hydroxylase (TH) by DA indicates, with support from the experimental data, that the TH-DA negative feedback loop has developed to exhibit 3,4-dihydroxyphenylalanine (DOPA) homeostasis by using DA as a derepression regulator. DA levels generally decline when DOPA is removed, for example, by increased oxidative stress. Robust DOPA regulation by DA further implies that maximum vesicular DA levels are established, which appear necessary for a reliable translation of neural activity into a corresponding chemical transmitter signal. An uncontrolled continuous rise (windup) in DA occurs when Levodopa treatment exceeds a critical dose. Increased oxidative stress leads to the successive breakdown of DOPA homeostasis and to a corresponding reduction in DA levels. To keep DOPA regulation robust, the vesicular DA loading requires close to zero-order kinetics combined with a sufficiently high compensatory flux provided by TH. The protection of DOPA and DA due to a channeling complex is discussed.

Insights into the Pathogenesis of Neurodegenerative Diseases: Focus on Mitochondrial Dysfunction and Oxidative Stress

As the population ages, the incidence of neurodegenerative diseases is increasing. Due to intensive research, important steps in the elucidation of pathogenetic cascades have been made and significantly implicated mitochondrial dysfunction and oxidative stress. However, the available treatment in Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis is mainly symptomatic, providing minor benefits and, at most, slowing down the progression of the disease. Although in preclinical setting, drugs targeting mitochondrial dysfunction and oxidative stress yielded encouraging results, clinical trials failed or had inconclusive results. It is likely that by the time of clinical diagnosis, the pathogenetic cascades are full-blown and significant numbers of neurons have already degenerated, making it impossible for mitochondria-targeted or antioxidant molecules to stop or reverse the process. Until further research will provide more efficient molecules, a healthy lifestyle, with plenty of dietary antioxidants and avoidance of exogenous oxidants may postpone the onset of neurodegeneration, while familial cases may benefit from genetic testing and aggressive therapy started in the preclinical stage.

Polydopamine Shell as a Ga3+ Reservoir for Triggering Gallium-Indium Phase Separation in Eutectic Gallium-Indium Nanoalloys

Low melting point eutectic systems, such as the eutectic gallium-indium (EGaIn) alloy, offer great potential in the domain of nanometallurgy; however, many of their interfacial behaviors remain to be explored. Here, a compositional change of EGaIn nanoalloys triggered by polydopamine (PDA) coating is demonstrated. Incorporating PDA on the surface of EGaIn nanoalloys renders core-shell nanostructures that accompany Ga-In phase separation within the nanoalloys. The PDA shell keeps depleting the Ga³⁺ from the EGaIn nanoalloys when the synthesis proceeds, leading to a Ga³⁺-coordinated PDA coating and a smaller nanoalloy. During this process, the eutectic nanoalloys turn into non-eutectic systems that ultimately result in the solidification of In when Ga is fully depleted. The reaction of Ga³⁺-coordinated PDA-coated nanoalloys with nitrogen dioxide gas is presented as an example for demonstrating the functionality of such hybrid composites. The concept of phase-separating systems, with polymeric reservoirs, may lead to tailored materials and can be explored on a variety of post-transition metals.

Examining the Toxicity of α-Synuclein in Neurodegenerative Disorders

Simple Summary

Neurodegenerative disorders are complex disorders that display a variety of clinical manifestations. The second-most common neurodegenerative disorder is Parkinson’s disease, and the leading pathological protein of the disorder is considered to be α-synuclein. Nonetheless, α-synuclein accumulation also seems to result in multiple system atrophy and dementia with Lewy bodies. In order to obtain a more proficient understanding in the pathological progression of these synucleinopathies, it is crucial to observe the post-translational modifications of α-synuclein and the conformations of α-synuclein, as well as its role in the dysfunction of cellular pathways.

Abstract

α-synuclein is considered the main pathological protein in a variety of neurodegenerative disorders, such as Parkinson’s disease, multiple system atrophy, and dementia with Lewy bodies. As of now, numerous studies have been aimed at examining the post-translational modifications of α-synuclein to determine their effects on α-synuclein aggregation, propagation, and oligomerization, as well as the potential cellular pathway dysfunctions caused by α-synuclein, to determine the role of the protein in disease progression. Furthermore, α-synuclein also appears to contribute to the fibrilization of tau and amyloid beta, which are crucial proteins in Alzheimer’s disease, advocating for α-synuclein’s preeminent role in neurodegeneration. Due to this, investigating the mechanisms of toxicity of α-synuclein in neurodegeneration may lead to a more proficient understanding of the timeline progression in neurodegenerative synucleinopathies and could thereby lead to the development of potent targeted therapies.

An Unrecognized Fundamental Relationship between Neurotransmitters: Glutamate Protects against Catecholamine Oxidation

Neurotransmitter catecholamines (dopamine, epinephrine, and norepinephrine) are liable to undergo oxidation, which copper is deeply involved in. Catecholamine oxidation-derived neurotoxicity is recognized as a pivotal pathological mechanism in neurodegenerative diseases. Glutamate, as an excitatory neurotransmitter, is enriched in the brain at extremely high concentrations. However, the chemical biology relationship of these two classes of neurotransmitters remains largely unknown. In the present study, we assessed the influences of glutamate on the autoxidation of catecholamines, the copper- and copper-containing ceruloplasmin-mediated oxidation of catecholamines, the catecholamine-induced formation of quinoprotein, catecholamine/copper-induced hydroxyl radicals, and DNA damage in vitro. The results demonstrate that glutamate, at a physiologically achievable molar ratio of glutamate/catecholamines, has a pronounced inhibitory effect on catecholamine oxidation, catecholamine oxidation-evoked hydroxyl radicals, quinoprotein, and DNA damage. The protective mechanism of glutamate against catecholamine oxidation could be attributed to its restriction of the redox activity of copper via chelation. This previously unrecognized link between glutamate, catecholamines, and copper suggests that neurodegenerative disorders may occur and develop once the built-in equilibrium is disrupted and brings new insight into developing more effective prevention and treatment strategies for neurodegenerative diseases.

Dopamine in Parkinson's disease

Parkinson's disease is a neurodegenerative disease caused by the death of neurons, ie, cells critical to the production of dopamine, an important neurotransmitter in the brain. Here, we present a brief review of the dopamine synthetic pathway, binding to the dopamine receptors, and subsequent action. The production of dopamine (a monoamine neurotransmitter) occurs in the ventral tegmental area (VTA) of the substantia nigra, specifically in the hypothalamic nucleus and midbrain. Compared to other monoamines, dopamine is widely distributed in the olfactory bulb, midbrain substantia nigra, hypothalamus, VTA, retina, and the periaqueductal gray area. Dopamine receptors are large G-protein coupled receptor family members, of which there are five subtypes including D1, D2, D3, D4, and D5. These subtypes are further divided into two subclasses: D1-like family receptors (types 1 and 5) and D2-like family receptors (types 2, 3, and 4). Four different pathways and functions of the dopaminergic system are presented in this review. In the oxidation of dopamine, 5,6-indolequinone, dopamine-o-quinone, and aminochrome are formed. It is difficult to separate the roles of 5,6-indolequinone and dopamine-o-quinone in the degenerative process of Parkinson's diseases due to their instability. The role of aminochrome in Parkinson's disease is to form and stabilize the neurotoxic protofibrils of alpha-synuclein, mitochondrial dysfunction, oxidative stress, and the degradation of protein by lysosomal systems and proteasomes. The neurotoxic effects of aminochrome can be inhibited by preventing the polymerization of 5,6-indolequinone, dopamine-o-quinone, and aminochrome into neuromelanin, by reducing aminochrome catalysis by DT-diaphorase, and by preventing dopamine oxidative deamination catalyzed by monoamine oxidase. In addition to these, the conversion of dopamine in the neuromelanin (NM) shows both protective and toxic roles. Therefore, the aims of this review were to discuss and explain the role of dopamine and explore its physiology and specificity in Parkinson's disease, as well as its role in other physiological functions.

Histidine protonation states are key in the LigI catalytic reaction mechanism

Lignin is one of the world's most abundant organic polymers, and 2-pyrone-4,6-dicarboxylate lactonase (LigI) catalyzes the hydrolysis of 2-pyrone-4,6-dicarboxylate (PDC) in the degradation of lignin. The pH has profound effects on enzyme catalysis and therefore we studied this in the context of LigI. We found that changes of the pH mostly affects surface residues, while the residues at the active site are more subject to changes of the surrounding microenvironment. In accordance with this, a high pH facilitates the deprotonation of the substrate. Detailed free energy calculations by the empirical valence bond (EVB) approach revealed that the overall hydrolysis reaction is more likely when the three active site histidines (His31, His33 and His180) are protonated at the ɛ site, however, protonation at the δ site may be favored during specific steps of the reaction. Our studies have uncovered the determinant role of the protonation state of the active site residues His31, His33 and His180 in the hydrolysis of PDC.

A pH-eQTL Interaction at the RIT2-SYT4 Parkinson's Disease Risk Locus in the Substantia Nigra

Parkinson's disease causes severe motor and cognitive disabilities that result from the progressive loss of dopamine neurons in the substantia nigra. The rs12456492 variant in the RIT2 gene has been repeatedly associated with increased risk for Parkinson's disease. From a transcriptomic perspective, a meta-analysis found that RIT2 gene expression is correlated with pH in the human brain. To assess these pH associations in relation to Parkinson's disease risk, we examined the two datasets that assayed rs12456492, gene expression, and pH in the postmortem human brain. Using the BrainEAC dataset, we replicate the positive correlation between RIT2 gene expression and pH in the human brain (n = 100). Furthermore, we found that the relationship between expression and pH is influenced by rs12456492. When tested across ten brain regions, this interaction is specifically found in the substantia nigra. A similar association was found for the co-localized SYT4 gene. In addition, SYT4 associations are stronger in a combined model with both genes, and the SYT4 interaction appears to be specific to males. In the Genotype-Tissue Expression (GTEx) dataset, the pH associations involving rs12456492 and expression of either SYT4 and RIT2 were not seen. This null finding may be due to the short postmortem intervals of the GTEx tissue samples. In the BrainEAC data, we tested the effect of postmortem interval and only observed the interactions in samples with the longer intervals. These previously unknown associations suggest novel roles for rs12456492, RIT2, and SYT4 in the regulation and response to pH in the substantia nigra.

Oxidized Alginate Dopamine Conjugate: In Vitro Characterization for Nose-to-Brain Delivery Application

BACKGROUND

The blood-brain barrier (BBB) bypass of dopamine (DA) is still a challenge for supplying it to the neurons of Substantia Nigra mainly affected by Parkinson disease. DA prodrugs have been studied to cross the BBB, overcoming the limitations of DA hydrophilicity. Therefore, the aim of this work is the synthesis and preliminary characterization of an oxidized alginate-dopamine (AlgOX-DA) conjugate conceived for DA nose-to-brain delivery.

METHODS

A Schiff base was designed to connect oxidized polymeric backbone to DA and both AlgOX and AlgOX-DA were characterized in terms of Raman, XPS, FT-IR, and 1H- NMR spectroscopies, as well as in vitro mucoadhesive and release tests.

RESULTS

Data demonstrated that AlgOX-DA was the most mucoadhesive material among the tested ones and it released the neurotransmitter in simulated nasal fluid and in low amounts in phosphate buffer saline. Results also demonstrated the capability of scanning near-field optical microscopy to study the structural and fluorescence properties of AlgOX, fluorescently labeled with fluorescein isothiocyanate microstructures. Interestingly, in SH-SY5Y neuroblastoma cell line up to 100 μg/mL, no toxic effect was derived from AlgOX and AlgOX-DA in 24 h.

CONCLUSIONS

Overall, the in vitro performances of AlgOX and AlgOX-DA conjugates seem to encourage further ex vivo and in vivo studies in view of nose-to-brain administration.

Expression, Purification, and Characterization of a Well-Adapted Tyrosinase from Peatlands Identified by Partial Community Analysis

In peatlands, bacterial tyrosinases (TYRs) are proposed to act as key regulators of carbon storage by removing phenolic compounds, which inhibit the degradation of organic carbon. Historically, TYR activity has been blocked by anoxia resulting from persistent waterlogging; however, recent events of prolonged summer drought have boosted TYR activity and, consequently, the release of carbon stored in the form of organic compounds from peatlands. Since 30% of the global soil carbon stock is stored in peatlands, a profound understanding of the production and activity of TYRs is essential to assess the impact of carbon dioxide emitted from peatlands on climate change. TYR partial sequences identified by degenerated primers suggest a versatile TYR enzyme community naturally present in peatlands, which is produced by a phylogenetically diverse spectrum of bacteria, including Proteobacteria and Actinobacteria. One full-length sequence of an extracellular TYR (SzTYR) identified from a soda-rich inland salt marsh has been heterologously expressed and purified. SzTYR exhibits a molecular mass of 30 891.8 Da and shows a pH optimum of 9.0. Spectroscopic studies and kinetic investigations characterized SzTYR as a tyrosinase and proved its activity toward monophenols (coumaric acid), diphenols (caffeic acid, protocatechuic acid), and triphenols (gallic acid) naturally present in peatlands.

Hypoxia, Acidification and Inflammation: Partners in Crime in Parkinson’s Disease Pathogenesis?

Like in other neurodegenerative diseases, protein aggregation, mitochondrial dysfunction, oxidative stress and neuroinflammation are hallmarks of Parkinson’s disease (PD). Differentiating characteristics of PD include the central role of α-synuclein in the aggregation pathology, a distinct vulnerability of the striato-nigral system with the related motor symptoms, as well as specific mitochondrial deficits. Which molecular alterations cause neurodegeneration and drive PD pathogenesis is poorly understood. Here, we summarize evidence of the involvement of three interdependent factors in PD and suggest that their interplay is likely a trigger and/or aggravator of PD-related neurodegeneration: hypoxia, acidification and inflammation. We aim to integrate the existing knowledge on the well-established role of inflammation and immunity, the emerging interest in the contribution of hypoxic insults and the rather neglected effects of brain acidification in PD pathogenesis. Their tight association as an important aspect of the disease merits detailed investigation. Consequences of related injuries are discussed in the context of aging and the interaction of different brain cell types, in particular with regard to potential consequences on the vulnerability of dopaminergic neurons in the substantia nigra. A special focus is put on the identification of current knowledge gaps and we emphasize the importance of related insights from other research fields, such as cancer research and immunometabolism, for neurodegeneration research. The highlighted interplay of hypoxia, acidification and inflammation is likely also of relevance for other neurodegenerative diseases, despite disease-specific biochemical and metabolic alterations.