Dopamine Oxidation Products Research Articles

Exploring the Complex Impact of Proteins on Dopamine Polymerization: Mechanisms and Strategies for Modulation.

Polydopamine (pDA) is a valuable material with wide-ranging potential applications. However, the complex and debated nature of dopamine polymerization complicates our understanding. Specifically, the impact of foreign substances, especially proteins, on pDA formation adds an additional layer of subtlety and complexity. This study delves into specific surface features of proteins that predominantly shape their impact on dopamine polymerization. Notably, the biotin-binding site emerges as a critical region responsible for the pronounced inhibitory effect of avidin and neutravidin on the dopamine polymerization process. The binding of biotin successfully mitigates these inhibitory effects. Moreover, several nucleases demonstrated a significant hindrance to pDA formation, with their impact substantially alleviated through the introduction of DNA. It is speculated that hydrogen bonding, electrostatic, cation-π, and/or hydrophobic interactions may underlie the binding between protein surfaces and diverse oligomeric intermediates formed by the oxidation products of dopamine. Additionally, we observed a noteworthy blocking effect on the dopamine polymerization reaction induced by erythropoietin (EPO), a glycoprotein hormone known for its role in stimulating red blood cell production and demonstrating neuroprotective effects. The inhibitory influence of EPO persisted even after deglycosylation. These findings not only advance our comprehension of the mechanisms underlying dopamine polymerization but also provide strategic insights for manipulating the reaction to tailor desired biomaterials.

Oxidative Stress and Neuroinflammation in Parkinson's Disease: The Role of Dopamine Oxidation Products.

Parkinson's disease (PD) is a chronic neurodegenerative condition affecting more than 1% of people over 65 years old. It is characterized by the preferential degeneration of nigrostriatal dopaminergic neurons, which is responsible for the motor symptoms of PD patients. The pathogenesis of this multifactorial disorder is still elusive, hampering the discovery of therapeutic strategies able to suppress the disease's progression. While redox alterations, mitochondrial dysfunctions, and neuroinflammation are clearly involved in PD pathology, how these processes lead to the preferential degeneration of dopaminergic neurons is still an unanswered question. In this context, the presence of dopamine itself within this neuronal population could represent a crucial determinant. In the present review, an attempt is made to link the aforementioned pathways to the oxidation chemistry of dopamine, leading to the formation of free radical species, reactive quinones and toxic metabolites, and sustaining a pathological vicious cycle.

Confined electrochemiluminescence imaging microarray for high-throughput biosensing of single cell-released dopamine

The quantitative detection of single cell secretions is always limited by their accurate collection and the heterogeneity of different cells. In this work, a confined electrochemiluminescence (ECL) imaging microarray (CEIM) chip was designed to capture single or a few cells in each cylindrical microwell for high-throughput quantitation of cell-secreted dopamine (DA). The ITO surface at the bottom of microwells was functionalized with the film of DA aptamer modified coreactant-embedded polymer dots (Pdots), which endowed the chip with the abilities to both in situ recognize the target DA secreted from the cells and emit the ECL signal for responding the secreted target without need of any additional coreactant. At the applied potential of +1.4 V, the Pdots in the film emitted strong ECL signal, which could be quenched by the electrochemical oxidation product of DA in individual microwell for sensitive detection of single cell-released DA. The practicability of the proposed CEIM chip along with the ECL imaging and biosensing strategy was demonstrated by evaluating the amounts of single cell-released DA in different microwells under hypoxia stimulation. This protocol revealed the heterogeneity of cell secretion, and could be extended for quantitation of other secretions from different kinds of single cells.

Electrosynthesized Poly(o-aminophenol) Films as Biomimetic Coatings for Dopamine Detection on Pt Substrates

Dopamine (DA) is a neurotransmitter, and its levels in the human body are associated with serious diseases. The need for a suitable detection method in medical practice has encouraged the development of electrochemical sensors that take advantage of DA electroactivity. Molecularly imprinted polymers (MIPs) are biomimetic materials able to selectively recognize target analytes. A novel MIP sensor for DA is proposed here based on a thin film of poly(o-aminophenol) electrosynthesized on bare Pt. A fast and easy method for executing the procedure for MIP deposition has been developed based on mild experimental conditions that are able to prevent electrode fouling from DA oxidation products. The MIP exhibited a limit of detection of 0.65 μM, and appreciable reproducibility and stability. The high recognition capability of poly(o-aminophenol) towards DA allowed for the achievement of notable selectivity: ascorbic acid, uric acid, serotonin, and tyramine did not interfere with DA detection, even at higher concentrations. The proposed sensor was successfully applied for DA detection in urine samples, showing good recovery.

Post-treatments of polydopamine coatings influence cellular response

Polydopamine (PDA) is the final oxidation product of dopamine or other catecholamines. Since the first reports of PDA coatings starting around 2007, these coatings have been widely studied as a versatile and inexpensive one-step coating option for biomaterial functionalization. The coating attach to a wide range of materials and can subsequently be modified with biomolecules or nanoparticles. However, as a strong candidate for biomaterial research and even clinical use, it is important to unravel the changes in physico-chemical properties and the cell-PDA interaction as a function of heat sterilization procedures and shelf storage periods. Four groups were examined in this study: titanium (Ti), PDA-coated Ti samples and PDA-coated Ti samples either stored for up to two weeks at room temperature or heated at 121 °C for 24 h, respectively. We used X-ray Photoelectron Spectroscopy (XPS), Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) and Water contact angle (WCA) to characterize chemical composition and surface properties of the groups. Cell adhesion and proliferation was examined by three different cell types: human primary dermal fibroblasts (hDF), human epidermal keratinocytes (HaCaTs) and a murine preosteoblastic cell line (MC3T3-E1), respectively. Cells were cultured on PDA coated samples for 4 h, 3 days and 5 days. Both thermal treatment of PDA at 121℃ for 24 h and storage of the samples for 2 weeks increased the amount of quinone groups at the surface and decreased the amount of primary amine groups as detected by XPS and ToF-SIMS. Even though these surface reactions increased the WCA of the PDA coating, we found that the post-treatments increased cell proliferation for both hDFs, HaCaTs and MC3T3-E1 s as compared to pristine PDA. This emphasizes the importance of post-treatment and shelf-time for PDA coatings.

Upconversion-luminescent hydrogel optical probe for in situ dopamine monitoring

Dopamine (DA), as a neurotransmitter in human brain, plays a crucial role in reward motivation and motor control. An improper level of DA can be associated with neurological disorders such as schizophrenia and Parkinson’s disease. To quantify DA, optical DA sensors have emerged as an attractive platform due to their capability of high-precision and label-free measurement, and immunity to electromagnetic interference. However, the lack of selectivity, limited biocompatibility, and complex fabrication processes are challenges that hinder their clinical applications. Here, we report a soft and biocompatible luminescent hydrogel optical sensor capable of recognizing and quantifying DA with a simple and compact interrogation setup. The sensor is made of a hydrogel optical fiber (HOF) incorporated with upconversion nanoparticles (UCNPs). DA molecules are detected through the luminescence energy transfer (LET) between the UCNPs and the oxidation products of DA, while the light-guiding HOF enables both excitation and emission collection of the UCNPs. The hydrogel sensor provides an optical readout that shows a linear response up to 200 μmol/L with a detection limit as low as 83.6 nmol/L. Our results show that the UCNP-based hydrogel sensor holds great promise of serving as a soft and biocompatible probe for monitoring DA in situ.

Effectiveness of the Iron Chelator CN128 in Mitigating the Formation of Dopamine Oxidation Products Associated with the Progression of Parkinson's Disease.

The occurrence and progression of Parkinson's disease (PD) has been associated with the observation of elevated iron concentrations in the substantia nigra pars compacta (SNpc). While the reasons for the impact of elevated iron concentrations remain unclear, one hypothesis is that the presence of labile iron induces the oxidation of dopamine (DA) to toxic quinones such as aminochrome (DAC) and reactive oxygen species (ROS). As such, one of the proposed therapeutic strategies has been the use of iron chelators such as deferiprone (DFP) (which is recognized to have limitations related to its rapid degradation in the liver) to reduce the concentration of labile iron. In this study, a detailed investigation regarding the novel iron chelator, CN128, was conducted and a kinetic model developed to elucidate the fundamental behavior of this chelator. The results in this work reveal that CN128 is effective in alleviating the toxicity induced by iron and DA to neurons when DA is present at moderate concentrations. When all the iron is chelated by CN128, the formation of DAC and the oxidation of DA can be reduced to levels identical to that in the absence of iron. The production of H2O2 is lower than that generated via the autoxidation of the same amount of DA. However, when severe leakage of DA occurs, the application of CN128 is insufficient to alleviate the associated toxicity. This is attibuted to the less important role of iron in the production of toxic intermediates at high concentrations of DA. CN128 is superior to DFP with regard to the reduction in formation of DAC and elevation in DA concentration. In summary, the results of this study suggest that prodromal application of the chelator CN128 could be effective in preventing the onset and slowing the early stage development of PD symptoms associated with oxidants and toxic intermediates resulting from the iron-mediated oxidation of the neurotransmitter dopamine with CN128 likely to be superior to DFP in view of its greater in vivo availability and less problematic side effects.

Hydrogenating carbon electrodes by n-butylsilane reduction to achieve an antifouling surface for selective dopamine detection

In this work, we have developed an antifouling carbon surface by hydrogenating it using n-butylsilane reduction. After incubating physically small electrodes with such an antifouling carbon surface for 30 min in a synthetic fouling solution containing 1.0 % (v/v) caproic acid (a lipid), 4 % (w/v) bovine serum albumin and 0.01 % (w/v) cytochrome c (both are proteins), and 0.002 % (w/v) human fibrinopeptide B (a peptide), a ∼35 % lower dopamine detection signal was measured. However, no further significant change in dopamine detection signal was observed at electrodes that were incubated in the same synthetic fouling solution for one week, compared to a total loss of detection signal at non-hydrogenated carbon electrodes. We have also demonstrated the unique characteristic of these hydrogenated carbon electrodes in detecting dopamine with minimal interference from as high as 500 μM ascorbic acid that is generally expected in extracellular fluid. Meanwhile, there was also no observable fouling effect at hydrogenated carbon electrodes by the dopamine oxidation product, dopamine-o-quinone (itself a well-known fouling reagent), in the presence of ≤1.0 μM dopamine, which is a 100-fold higher concentration than that in the central nervous system. These results support minimal fouling at n-butylsilane hydrogenated carbon electrodes during dopamine detection in vitro.

Nitrogen-doped carbon quantum dots as a “turn off-on” fluorescence sensor based on the redox reaction mechanism for the sensitive detection of dopamine and alpha lipoic acid

A simple and reliable fluorescence sensing strategy, which depends on the strong fluorescence emission of nitrogen-doped carbon quantum dots (N-CQDs) and efficient catalytic oxidation of tyrosinase (Tyr), was demonstrated for the sensitive detection of dopamine (DA) and alpha lipoic acid (ALA). Under optimized conditions, the fluorescence intensity of N-CQDs was easily quenched by dopamine oxidation product dopaquinone with the addition of Tyr. When ALA was introduced into the sensing system, ALA could inhibit and reduce the oxidation process of DA, resulting in the fluorescence recovery of N-CQDs. This sensing platform showed a sensitive relationship to the DA and ALA concentrations within certain ranges of 0.05–15 and 0.5−55 μM, and low detection limits of 0.035 and 0.39 μM, respectively. Given the above mechanisms, the proposed biosensor was utilized for the detection of DA and ALA in real samples with satisfactory results. Moreover, we successfully measured ALA through spectrometry, which is expected to provide valuable information in medical and disease diagnosis.

3,4-Dihydroxyphenylacetaldehyde Is More Efficient than Dopamine in Oligomerizing and Quinonizing α-Synuclein.

Lewy body diseases such as Parkinson's disease involve intraneuronal deposition of the protein α-synuclein (AS) and depletion of nigrostriatal dopamine (DA). Interactions of AS with DA oxidation products may link these neurohistopathologic and neurochemical abnormalities via two potential pathways: spontaneous oxidation of DA to dopamine-quinone and enzymatic oxidation of DA catalyzed by monoamine oxidase to form 3,4-dihydroxyphenylacetaldehyde (DOPAL), which is then oxidized to DOPAL-Q. We compared these two pathways in terms of the ability of DA and DOPAL to modify AS. DOPAL was far more potent than DA both in oligomerizing and forming quinone-protein adducts with (quinonizing) AS. The DOPAL-induced protein modifications were enhanced similarly by pro-oxidation with Cu(II) or tyrosinase and inhibited similarly by antioxidation with N-acetylcysteine. Dopamine oxidation evoked by Cu(II) or tyrosinase did not quinonize AS. In cultured MO3.13 human oligodendrocytes DOPAL resulted in the formation of numerous intracellular quinoproteins that were visualized by near-infrared spectroscopy. We conclude that of the two routes by which oxidation of DA modifies AS and other proteins the route via DOPAL is more prominent. The results support developing experimental therapeutic strategies that might mitigate deleterious modifications of proteins such as AS in Lewy body diseases by targeting DOPAL formation and oxidation. SIGNIFICANCE STATEMENT: Interactions of the protein α-synuclein with products of dopamine oxidation in the neuronal cytoplasm may link two hallmark abnormalities of Parkinson disease: Lewy bodies (which contain abundant AS) and nigrostriatal DA depletion (which produces the characteristic movement disorder). Of the two potential routes by which DA oxidation may alter AS and other proteins, the route via the autotoxic catecholaldehyde 3,4-dihydroxyphenylacetaldehyde is more prominent; the results support experimental therapeutic strategies targeting DOPAL formation and DOPAL-induced protein modifications.

Nanoporous gold-based dopamine sensor with sensitivity boosted by interferant ascorbic acid

Tuning electrochemical reactivity of nanoporous gold (NPG) by controlling its fabrication parameters is a convenient strategy to realize a selective electroanalytical platform for dopamine (DA), whose detection in real biological samples is hampered by the presence of structurally similar ascorbic acid (AA) typically in 1000-fold excess. Accordingly, a simple strategy was devised to overcome such a problem by exploiting the electrocatalytic properties associated with higher surface energy (220), (200) and (311) Au planes, which are formed in larger amounts as a function of the thickness of the NPG films prepared by an electrodeposition method. Such selectivity in DA electrooxidation could only be retained at thicker NPG films and this was attributed to the higher density of reactive electrocatalytic sites, which enhance the rate of the electron transfer reaction associated to the AA anodic process. Such proposition was confirmed by a comprehensive electron transfer kinetics study by Scanning Electrochemical Microscopy. The current response due to DA oxidation was enhanced by the follow-up chemical reaction between dopamine-o-quinone (the oxidation product of DA) and AA present in large excess, converting a potential interferant into a partner. In this way, detection limit as low as 60 nmol L−1 allied to sensitivity as high as 6.7 μA/μmol L−1 were achieved under up to 10000 times excess of that interferant, demonstrating the high potentiality of such NPG3 modified electrode as a sensor for analyses of DA in real biological samples.

Are Proteinopathy and Oxidative Stress Two Sides of the Same Coin?

Parkinson’s disease, like other neurodegenerative diseases, exhibits two common features: Proteinopathy and oxidative stress, leading to protein aggregation and mitochondrial damage respectively. Because both protein aggregates and dysfunctional mitochondria are eliminated by autophagy, we suggest that inadequate clearance may couple the two phenomena. If a neuron’s autophagy machinery is overwhelmed, whether by excessive oxidative stress or by excessive protein aggregation, protein aggregates and dysfunctional mitochondria will both accumulate. Parkinson’s disease may provide a unique window into this because there is evidence that both sides contribute. Mutations amplifying the aggregation of α-synuclein are associated with Parkinson’s disease. Likewise, mutations in Parkin and PINK1, proteins involved in mitophagy, suggest that impaired mitochondrial clearance is also a contributing factor. Many have suggested that dopamine oxidation products lead to oxidative stress accounting for the dopaminergic selectivity of the disease. We have presented evidence for the specific involvement of hypochlorite-oxidized cysteinyl-dopamine (HOCD), a redox-cycling benzothiazine derivative. While toxins like 6-hydroxydopamine and 1-methyl-4-phenyl pyridinium (MPP+) have been used to study mitochondrial involvement in Parkinson’s disease, HOCD may provide a more physiologically relevant approach. Understanding the role of mitochondrial dysfunction and oxidative stress in Parkinson’s disease and their relation to α-synuclein proteinopathy is important to gain a full picture of the cause, especially for the great majority of cases which are idiopathic.

Polydopamine Nanomaterials: Recent Advances in Synthesis Methods and Applications.

Polydopamine (PDA), the final oxidation product of dopamine or other catecholamines, attracted much attention as versatile coatings that can be used to cover the surface of almost all materials with a conformal layer of adjustable thickness ranging from a few to about 100 nm. These PDA layers can be subsequently modified with molecules carrying nucleophilic groups or with metallic nanoparticles from solutions containing metallic cations. However, during the deposition of PDA film on the surfaces, the reaction products that are simultaneously obtained from the oxidation of catecholamines in solution precipitate. Hence, some recent effort has been devoted to produce PDA in the form of nanoparticles. The aim of this short review is to give a comprehensive description of the synthesis methods yielding of PDA nanoparticles in the absence or in the presence of templating agents (polymers, polyelectrolytes, surfactants, proteins, and even some small organic molecules). We will also describe the use of thin PDA layers to coat already synthesized nanoparticles or nanotubes. Finally, several first applications of the obtained PDA nanoparticles will be described.

Dopamine Oxidation Products as Mitochondrial Endotoxins, a Potential Molecular Mechanism for Preferential Neurodegeneration in Parkinson's Disease.

The preferential degeneration of dopaminergic neurons in the substantia nigra pars compacta is responsible for the motor impairment associated with Parkinson's disease. Dopamine is a highly reactive molecule, which is usually stored inside synaptic vesicles where it is stabilized by the ambient low pH. However, free cytosolic dopamine can auto-oxidize, generating reactive oxygen species, and lead to the formation of toxic quinones. In the present work, we have analyzed the mechanisms through which the dysfunction of dopamine homeostasis could induce cell toxicity, by focusing in particular on the damage induced by dopamine oxidation products at the mitochondrial level. Our results indicate that dopamine derivatives affect mitochondrial morphology and induce mitochondrial membrane depolarization, leading to a reduction of ATP synthesis. Moreover, our results suggest that opening of the mitochondrial transition pore induced by dopamine-derived quinones may contribute to the specific Parkinson's disease-associated vulnerability of dopamine containing neurons.

Diabetes Mellitus as a Risk Factor for Parkinson's Disease: a Molecular Point of View.

Type 2 diabetes mellitus (T2DM) is a metabolic disorder characterized by elevated concentrations of glucose in the blood. The chronic hyperglycemic state accounts for most of the vascular complications associated to the disease and the prevalent mechanism proposed is related to the glycating chemistry mediated by methylglyoxal (MG), which accumulates in T2DM. In recent years, a higher risk of Parkinson's disease (PD) onset in people affected by T2DM has become evident, but the molecular mechanisms underlying the interplay between T2DM and PD are still unknown. The oxidative chemistry of dopamine and its reactivity towards the protein α-Synuclein (aS) has been associated to the pathogenesis of PD. Recently, aS has also been described to interact with MG. Interestingly, MG and the dopamine oxidation products share both structural similarity and chemical reactivity. The ability of MG to spread over the site of its production and react with aS could represent the rationale to explain the higher incidence of PD in T2DM-affected people and may open opportunities for the development of novel strategies to antagonize the raise of PD.

Detection of transient dopamine antioxidant radicals using electrochemistry in electrospray ionization mass spectrometry

We describe formation and detection of transient radical intermediates and 2e−, 2H+ oxidation products (OPs) of dopamine (DA) by electrospray ionization (ESI) mass spectrometry (MS) which has not been reported previously. The results confirm formation of DA radicals by proton coupled electron transfer pathway. DA radicals and 2e−, 2H+ oxidation products that were identified are of interest because of their reported neurotoxicity. Using different solution compositions and MS detection conditions three different DA radicals were identified that have different stability. DA reactions with reactive oxygen species (ROS) relevant to DA reactivity in vivo are discussed. Detection of DA OPs by electrochemistry/mass spectrometry with a floated on-line electrochemical cell is also illustrated.

Increased gait variability during 5-minute walking in children with cerebral palsy detected with on the feet placed accelerometers

We describe formation and detection of transient radical intermediates and 2e−, 2H+ oxidation products (OPs) of dopamine (DA) by electrospray ionization (ESI) mass spectrometry (MS) which has not been reported previously. The results confirm formation of DA radicals by proton coupled electron transfer pathway. DA radicals and 2e−, 2H+ oxidation products that were identified are of interest because of their reported neurotoxicity. Using different solution compositions and MS detection conditions three different DA radicals were identified that have different stability. DA reactions with reactive oxygen species (ROS) relevant to DA reactivity in vivo are discussed. Detection of DA OPs by electrochemistry/mass spectrometry with a floated on-line electrochemical cell is also illustrated.

Hypochlorite converts cysteinyl-dopamine into a cytotoxic product: A possible factor in Parkinson's Disease

The dopamine oxidation product cysteinyl-dopamine has attracted attention as a contributor to the death of dopaminergic neurons in Parkinson's disease. Treatment of cysteinyl-dopamine with hypochlorite yields an even more cytotoxic product. This product has potent redox-cycling activity and initiates production of superoxide in PC12 cells. Taurine, which scavenges hypochlorite, protects PC12 cells from cysteinyl-dopamine but not from the hypochlorite product, suggesting that the product, not cysteinyl-dopamine itself, is toxic. Furthermore, rotenone, which enhances expression of the hypochlorite-producing enzyme myeloperoxidase, increases the cytotoxicity of cysteinyl-dopamine but not of the hypochlorite product. This suggests that dopamine oxidation to cysteinyl-dopamine followed by hypochlorite-dependent conversion to a cytotoxic redox-cycling product leads to the generation of reactive oxygen species and oxidative stress and may contribute to the death of dopaminergic neurons.

Enhanced dopamine detection sensitivity by PEDOT/graphene oxide coating on in vivo carbon fiber electrodes

Dopamine (DA) is a monoamine neurotransmitter responsible for regulating a variety of vital life functions. In vivo detection of DA poses a challenge due to the low concentration and high speed of physiological signaling. Fast scan cyclic voltammetry at carbon fiber microelectrodes (CFEs) is an effective method to monitor real-time in vivo DA signaling, however the sensitivity is somewhat limited. Electrodeposition of poly(3,4-ethylene dioxythiophene) (PEDOT)/graphene oxide (GO) onto the CFE surface is shown to increase the sensitivity and lower the limit of detection for DA compared to bare CFEs. Thicker PEDOT/GO coatings demonstrate higher sensitivities for DA, but display the negative drawback of slow adsorption and electron transfer kinetics. The moderate thickness resulting from 25 s electrodeposition of PEDOT/GO produces the optimal electrode, exhibiting an 880% increase in sensitivity, a 50% decrease in limit of detection and minimally altered electrode kinetics. PEDOT/GO coated electrodes rapidly and robustly detect DA, both in solution and in the rat dorsal striatum. This increase in DA sensitivity is likely due to increasing the electrode surface area with a PEDOT/GO coating and improved adsorption of DA's oxidation product (DA-o-quinone). Increasing DA sensitivity without compromising electrode kinetics is expected to significantly improve our understanding of the DA function in vivo.

Polyelectrolytes to produce nanosized polydopamine

“Polydopamine” (PDA) is the oxidation product of dopamine and can be obtained as thin films covering the surface of all kinds of known materials and simultaneously as insoluble and useless precipitates from dopamine solutions in the presence of appropriate oxidants. The valorization of such precipitates to obtain stable suspensions of functional nanomaterials is highly desirable owing to the chemical and optical properties of PDA. We show that a vast repertoire of polyelectrolytes polycations as well as polyanions, allow to control the size of PDA particles in the 10–100nm size range. Simultaneously to the production of smaller nanoparticles, a progressive inhibition of PDA deposition on the surface of quartz plates (as well as on the surface of the reaction vessel) is found as the concentration of the polyelectrolytes is increased in the dopamine solution. The mechanism of size control-inhibition of film deposition is investigated in the particular case of poly(allylamine) but remains not understood in the case of polyanions.