Role of dopamine in the pathophysiology of Parkinson's disease.

A pathological feature of Parkinson's disease (PD) is the progressive loss of dopaminergic neurons and decreased dopamine (DA) content in the substantia nigra pars compacta in PD brains. DA is the neurotransmitter of dopaminergic neurons. Accumulating evidence suggests that DA interacts with environmental and genetic factors to contribute to PD pathophysiology. Disturbances of DA synthesis, storage, transportation and metabolism have been shown to promote neurodegeneration of dopaminergic neurons in various PD models. DA is unstable and can undergo oxidation and metabolism to produce multiple reactive and toxic by-products, including reactive oxygen species, DA quinones, and 3,4-dihydroxyphenylacetaldehyde. Here we summarize and highlight recent discoveries on DA-linked pathophysiologic pathways, and discuss the potential protective and therapeutic strategies to mitigate the complications associated with DA.

The Singapore National Precision Medicine Strategy.

Precision medicine promises to transform healthcare for groups and individuals through early disease detection, refining diagnoses and tailoring treatments. Analysis of large-scale genomic-phenotypic databases is a critical enabler of precision medicine. Although Asia is home to 60% of the world's population, many Asian ancestries are under-represented in existing databases, leading to missed opportunities for new discoveries, particularly for diseases most relevant for these populations. The Singapore National Precision Medicine initiative is a whole-of-government 10-year initiative aiming to generate precision medicine data of up to one million individuals, integrating genomic, lifestyle, health, social and environmental data. Beyond technologies, routine adoption of precision medicine in clinical practice requires social, ethical, legal and regulatory barriers to be addressed. Identifying driver use cases in which precision medicine results in standardized changes to clinical workflows or improvements in population health, coupled with health economic analysis to demonstrate value-based healthcare, is a vital prerequisite for responsible health system adoption.

Defining Essential Enhancers for Pluripotent Stem Cells Using a Features-Oriented CRISPR-Cas9 Screen.

cis-regulatory elements (CREs) regulate the expression of genes in their genomic neighborhoods and influence cellular processes such as cell-fate maintenance and differentiation. To date, there remain major gaps in the functional characterization of CREs and the identification of their target genes in the cellular native environment. In this study, we perform a features-oriented CRISPR-utilized systematic (FOCUS) screen of OCT4-bound CREs using CRISPR-Cas9 to identify functional enhancers important for pluripotency maintenance in mESCs. From the initial 235 candidates tested, 16 CREs are identified to be essential stem cell enhancers. Using RNA-seq and genomic 4C-seq, we further uncover a complex network of candidate CREs and their downstream target genes, which supports the growth and self-renewal of mESCs. Notably, an essential enhancer, CRE111, and its target, Lrrc31, form the important switch to modulate the LIF-JAK1-STAT3 signaling pathway.

Transcriptomics analysis of salt stress tolerance in the roots of the mangrove Avicennia officinalis.

Salinity affects growth and development of plants, but mangroves exhibit exceptional salt tolerance. With direct exposure to salinity, mangrove roots possess specific adaptations to tolerate salt stress. Therefore, studying the early effects of salt on mangrove roots can help us better understand the tolerance mechanisms. Using two-month-old greenhouse-grown seedlings of the mangrove tree Avicennia officinalis subjected to NaCl treatment, we profiled gene expression changes in the roots by RNA-sequencing. Of the 6547 genes that were differentially regulated in response to salt treatment, 1404 and 5213 genes were significantly up- and down-regulated, respectively. By comparative genomics, 93 key salt tolerance-related genes were identified of which 47 were up-regulated. Upon placing all the differentially expressed genes (DEG) in known signaling pathways, it was evident that most of the DEGs involved in ethylene and auxin signaling were up-regulated while those involved in ABA signaling were down-regulated. These results imply that ABA-independent signaling pathways also play a major role in salt tolerance of A. officinalis. Further, ethylene response factors (ERFs) were abundantly expressed upon salt treatment and the Arabidopsis mutant aterf115, a homolog of AoERF114 is characterized. Overall, our results would help in understanding the possible molecular mechanism underlying salt tolerance in plants.

Data in support of the proteomic analysis of plasma membrane and tonoplast from the leaves of mangrove plant Avicennia officinalis.

The data provides information in support of the research article, Proteomics 2014, 14, 2545-2557 [1]. Raw data is available from the ProteomeXchange Consortium via the PRIDE partnerRepository [2] with the dataset identifier PXD000837. Plasma membrane and tonoplast proteins from the leaves of Avicennia officinalis were identified using gel electrophoresis (one and two dimensional) combined with LC-MS analysis. Based on GO annotation, identified proteins were predicted to be involved in various biological processes.

Systematic identification of factors for provirus silencing in embryonic stem cells.

Embryonic stem cells (ESCs) repress the expression of exogenous proviruses and endogenous retroviruses (ERVs). Here, we systematically dissected the cellular factors involved in provirus repression in embryonic carcinomas (ECs) and ESCs by a genome-wide siRNA screen. Histone chaperones (Chaf1a/b), sumoylation factors (Sumo2/Ube2i/Sae1/Uba2/Senp6), and chromatin modifiers (Trim28/Eset/Atf7ip) are key determinants that establish provirus silencing. RNA-seq analysis uncovered the roles of Chaf1a/b and sumoylation modifiers in the repression of ERVs. ChIP-seq analysis demonstrates direct recruitment of Chaf1a and Sumo2 to ERVs. Chaf1a reinforces transcriptional repression via its interaction with members of the NuRD complex (Kdm1a, Hdac1/2) and Eset, while Sumo2 orchestrates the provirus repressive function of the canonical Zfp809/Trim28/Eset machinery by sumoylation of Trim28. Our study reports a genome-wide atlas of functional nodes that mediate proviral silencing in ESCs and illuminates the comprehensive, interconnected, and multi-layered genetic and epigenetic mechanisms by which ESCs repress retroviruses within the genome.

F-box protein 7 mutations promote protein aggregation in mitochondria and inhibit mitophagy.

The mutations of F-box protein 7 (FBXO7) gene (T22M, R378G and R498X) are associated with a severe form of autosomal recessive juvenile-onset Parkinson's disease (PD) (PARK 15). Here we demonstrated that wild-type (WT) FBXO7 is a stress response protein and it can play both cytoprotective and neurotoxic roles. The WT FBXO7 protein is vital to cell mitophagy and can facilitate mitophagy to protect cells, whereas mutant FBXO7 inhibits mitophagy. Upon stress, the endogenous WT FBXO7 gets up-regulated, concentrates into mitochondria and forms FBXO7 aggregates in mitochondria. However, FBXO7 mutations aggravate deleterious FBXO7 aggregation in mitochondria. The FBXO7 aggregation and toxicity can be alleviated by Proline, glutathione (GSH) and coenzyme Q10, whereas deleterious FBXO7 aggregation in mitochondria can be aggravated by prohibitin 1 (PHB1), a mitochondrial protease inhibitor. The overexpression of WT FBXO7 could lead to FBXO7 protein aggregation and dopamine neuron degeneration in transgenic Drosophila heads. The elevated FBXO7 expression and aggregation were identified in human fibroblast cells from PD patients. FBXO7 can also form aggregates in brains of PD and Alzheimer's disease. Our study provides novel pathophysiologic insights and suggests that FBXO7 may be a potential therapeutic target in FBXO7-linked neuron degeneration in PD.

Cytoplasmic nucleophosmin has elevated T199 phosphorylation upon which G2/M phase progression is dependent.

The cytoplasmic mutant of nucleophosmin (NPMc) is found approximately in one-third of acute myeloid leukemia (AML) cases and is highly associated with normal karyotype. Whereas previous studies have focused on wtNPM in centrosome duplication, we further elucidate the role of NPM in the cell cycle by utilizing the increased cytoplasmic load of NPMc. Overexpression of NPMc causes increased phosphorylation of NPM on T199 and, to a lesser degree, S4. T199 phosphorylation is dependent on cdk2 but activators of cdk2 were not elevated. Upon inhibition of cdk2, NPMc-overexpressing cells demonstrate a greater G2/M phase arrest than wtNPM or GFP counterparts. However, the number of cells with 2 centrosomes did not increase concordantly. This suggests that the arrest was caused by a delay in centrosome duplication, most likely due to the inhibition of centrosome duplication caused by unphosphorylated NPMc. Overall, these results suggest that the phosphorylation of T199 is important in the mitotic progression of NPMc-expressing cells. This further supports the hypothesis that NPMc is associated with normal karyotypes in AML because the higher cytoplasmic load of NPM can better suppress centrosome overduplication which would otherwise result in unequal segregation of chromosomes during mitosis, leading to aneuploidy and other genomic instabilities.

Proteome profile of salt gland-rich epidermis extracted from a salt-tolerant tree species.

Preparation of proteins from salt-gland-rich tissues of mangrove plant is necessary for a systematic study of proteins involved in the plant's unique desalination mechanism. Extraction of high-quality proteins from the leaves of mangrove tree species, however, is difficult due to the presence of high levels of endogenous phenolic compounds. In our study, preparation of proteins from only a part of the leaf tissues (i.e. salt gland-rich epidermal layers) was required, rendering extraction even more challenging. By comparing several extraction methods, we developed a reliable procedure for obtaining proteins from salt gland-rich tissues of the mangrove species Avicennia officinalis. Protein extraction was markedly improved using a phenol-based extraction method. Greater resolution 1D protein gel profiles could be obtained. More promising proteome profiles could be obtained through 1D-LC-MS/MS. The number of proteins detected was twice as much as compared to TUTS extraction method. Focusing on proteins that were solely present in each extraction method, phenol-based extracts contained nearly ten times more proteins than those in the extracts without using phenol. The approach could thus be applied for downstream high-throughput proteomic analyses involving LC-MS/MS or equivalent. The proteomics data presented herein are available via ProteomeXchange with identifier PXD001691.

Identification of salt gland-associated genes and characterization of a dehydrin from the salt secretor mangrove Avicennia officinalis.

BACKGROUND: Salt stress is a major challenge for growth and development of plants. The mangrove tree Avicennia officinalis has evolved salt tolerance mechanisms such as salt secretion through specialized glands on its leaves. Although a number of structural studies on salt glands have been done, the molecular mechanism of salt secretion is not clearly understood. Also, studies to identify salt gland-specific genes in mangroves have been scarce. RESULTS: By subtractive hybridization (SH) of cDNA from salt gland-rich cell layers (tester) with mesophyll tissues as the driver, several Expressed Sequence Tags (ESTs) were identified. The major classes of ESTs identified include those known to be involved in regulating metabolic processes (37%), stress response (17%), transcription (17%), signal transduction (17%) and transport functions (12%). A visual interactive map generated based on predicted functional gene interactions of the identified ESTs suggested altered activities of hydrolase, transmembrane transport and kinases. Quantitative Real-Time PCR (qRT-PCR) was carried out to validate the expression specificity of the ESTs identified by SH. A Dehydrin gene was chosen for further experimental analysis, because it is significantly highly expressed in salt gland cells, and dehydrins are known to be involved in stress remediation in other plants. Full-length Avicennia officinalis Dehydrin1 (AoDHN1) cDNA was obtained by Rapid Amplification of cDNA Ends. Phylogenetic analysis and further characterization of this gene suggested that AoDHN1 belongs to group II Late Embryogenesis Abundant proteins. qRT-PCR analysis of Avicennia showed up-regulation of AoDHN1 in response to salt and drought treatments. Furthermore, some functional insights were obtained by growing E. coli cells expressing AoDHN1. Growth of E. coli cells expressing AoDHN1 was significantly higher than that of the control cells without AoDHN1 under salinity and drought stresses, suggesting that the mangrove dehydrin protein helps to mitigate the abiotic stresses. CONCLUSIONS: Thirty-four ESTs were identified to be enriched in salt gland-rich tissues of A. officinalis leaves. qRT-PCR analysis showed that 10 of these were specifically enriched in the salt gland-rich tissues. Our data suggest that one of the selected genes, namely, AoDHN1 plays an important role to mitigate salt and drought stress responses.

Proteomic analysis of plasma membrane and tonoplast from the leaves of mangrove plant Avicennia officinalis.

In order to understand the salt tolerance and secretion in mangrove plant species, gel electrophoresis coupled with LC-MS-based proteomics was used to identify key transport proteins in the plasma membrane (PM) and tonoplast fractions of Avicennia officinalis leaves. PM and tonoplast proteins were purified using two-aqueous-phase partitioning and density gradient centrifugation, respectively. Forty of the 254 PM proteins and 31 of the 165 tonoplast proteins identified were predicted to have transmembrane domains. About 95% of the identified proteins could be classified based on their functions. The major classes of proteins were predicted to be involved in transport, metabolic processes, defense/stress response, and signal transduction, while a few of the proteins were predicted to be involved in other functions such as membrane trafficking. The main classes of transporter proteins identified included H(+) -ATPases, ATP-binding cassette transporters, and aquaporins, all of which could play a role in salt secretion. These data will serve as the baseline membrane proteomic dataset for Avicennia species. Further, this information can contribute to future studies on understanding the mechanism of salt tolerance in halophytes in addition to salt secretion in mangroves. All MS data have been deposited in the ProteomeXchange with identifier PXD000837 (http://proteomecentral.proteomexchange.org/dataset/PXD000837).

Electrochemical detection of leukemia oncogenes using enzyme-loaded carbon nanotube labels.

We describe an ultrasensitive electrochemical nucleic acid assay amplified by carbon nanotubes (CNTs)-based labels for the detection of human acute lymphocytic leukemia (ALL)-related p185 BCR-ABL fusion transcript. The carboxylated CNTs were functionalized with horseradish peroxidase (HRP) molecules and target-specific detection probes (DP) via diimide-activated amidation and used to label and amplify the target hybridization signal. The activity of captured HRP was monitored by square-wave voltammetry measuring the electroactive enzymatic product in the presence of 2-aminophenol and hydrogen peroxide substrate solution. The signal-amplified assay achieved a detection limit of 83 fM (5 × 10(-18) mol in 60 µL) targets oligonucleotides and has a 4-order-wide dynamic range of target concentration. The resulting assay allowed robust discrimination between the perfect match and a three-base mismatch sequence. When exposed to the full-length (491 bp) DNA oncogene, the approach demonstrated a detection limit of 1 × 10(-16) mol in 60 µL, corresponding to approximately 33 pg of the target gene. The high sensitivity and specificity of the assay enabled a PCR-free detection of target transcripts in as little as 65 ng of mRNA extracted from positive ALL cell lines SUP-B15 in comparison to those obtained from negative cell line HL-60. The approach enables a simple, low-cost and ultrasensitive electrochemical nucleic acid detection in portable devices, point-of-care and early disease diagnostic applications.

High Mdm4 levels suppress p53 activity and enhance its half-life in acute myeloid leukaemia.

UNLABELLED: Although p53 is found mutated in almost 50% of all cancers, p53 mutations in leukaemia are relatively rare. Acute myeloid leukaemia (AML) cells employ other strategies to inactivate their wild type p53 (WTp53), like the overexpression of the p53 negative regulators Mdm2 and Mdm4. As such, AMLs are excellent candidates for therapeutics involving the reactivation of their WTp53 to restrict and destroy cancer cells, and the Mdm2 antagonist nutlin-3 is one such promising agent. Using AML cell lines with WTp53, we identified stable and high levels of p53 in the OCI/AML-2 cell lines. We demonstrate that this nutlin-3 sensitive cell line overexpressed Mdm4 to sequester, stabilise and inhibit p53 in the cytoplasm. We also show that elevated Mdm4 competed with Mdm2-p53 interaction and therefore extended p53 half-life while preventing p53 transcriptional activity. Our results provide biochemical evidence on the dynamics of the p53-Mdm2-Mdm4 interactions in affecting p53 levels and activity, and unlike previously reported findings derived from genetically manipulated systems, AML cells with naturally high levels of Mdm4 remain sensitive to nutlin treatment. KEY POINTS: Endogenously high levels of Mdm4 inhibit and sequester p53 in AML. High levels of Mdm4 do not block function of Mdm2 inhibitors in AML.

Mutant PINK1 upregulates tyrosine hydroxylase and dopamine levels, leading to vulnerability of dopaminergic neurons.

PINK1 mutations cause autosomal recessive forms of Parkinson disease (PD). Previous studies suggest that the neuroprotective function of wild-type (WT) PINK1 is related to mitochondrial homeostasis. PINK1 can also localize to the cytosol; however, the cytosolic function of PINK1 has not been fully elucidated. In this study we demonstrate that the extramitochondrial PINK1 can regulate tyrosine hydroxylase (TH) expression and dopamine (DA) content in dopaminergic neurons in a PINK1 kinase activity-dependent manner. We demonstrate that overexpression of full-length (FL) WT PINK1 can downregulate TH expression and DA content in dopaminergic neurons. In contrast, overexpression of PD-linked G309D, A339T, and E231G PINK1 mutations upregulates TH and DA levels in dopaminergic neurons and increases their vulnerability to oxidative stress. Furthermore transfection of FL WT PINK1 or PINK1 fragments with the PINK1 kinase domain can inhibit TH expression, whereas kinase-dead (KD) FL PINK1 or KD PINK1 fragments upregulate TH level. Our findings highlight a potential novel function of extramitochondrial PINK1 in dopaminergic neurons. Deregulation of these functions of PINK1 may contribute to PINK1 mutation-induced dopaminergic neuron degeneration. However, deleterious effects caused by PINK1 mutations may be alleviated by iron-chelating agents and antioxidant agents with DA quinone-conjugating capacity.

Dynamic secretion changes in the salt glands of the mangrove tree species Avicennia officinalis in response to a changing saline environment.

The specialized salt glands on the epidermis of halophytic plants secrete excess salts from tissues by a mechanism that is poorly understood. We examined the salt glands as putative salt and water bi-regulatory units that can respond swiftly to altering environmental cues. The tropical mangrove tree species (Avicennia officinalis) is able to grow under fluctuating salinities (0.7-50.0 dS m(-1)) at intertidal zones, and its salt glands offer an excellent platform to investigate their dynamic responses under rapidly changing salinities. Utilizing a novel epidermal peel system, secretion profiles of hundreds of individual salt glands examined revealed that these glands could secrete when exposed to varying salinities. Notably, rhythmic fluctuations observed in secretion rates were reversibly inhibited by water channel (aquaporin) blocker, and two aquaporin genes (PIP and TIP) preferentially expressed in the salt gland cells were rapidly induced in response to increasing salt concentration. We propose that aquaporins are involved and contribute to the re-absorption of water during salt removal in Avicennia officinalis salt glands. This constitutes an adaptive feature that contributes to salt balance of trees growing in saline environments where freshwater availability is limited.

Wild-type and mutant p53 mediate cisplatin resistance through interaction and inhibition of active caspase-9.

The p53 gene has been implicated in many cancers due to its frequent mutations as well as mutations in other genes whose proteins directly affect p53's functions. In addition, high expression of p53 [wild-type (WT) or mutant] has been found in the cytoplasm of many tumor cells, and studies have associated these observations with more aggressive tumors and poor prognosis. Cytoplasmic mis-localization of p53 subsequently reduced its transcriptional activity and this loss-of-function (LOF) was used to explain the lack of response to chemotherapeutic agents. However, this hypothesis seemed inadequate in explaining the apparent selection for tumor cells with high levels of p53 protein, a phenomenon that suggests a gain-of-function (GOF) of these mis-localized p53 proteins. In this study, we explored whether the direct involvement of p53 in the apoptotic response is via regulation of the caspase pathway in the cytoplasm. We demonstrate that p53, when present at high levels in the cytoplasm, has an inhibitory effect on caspase-9. Concurrently, knockdown of endogenous p53 caused an increase in the activity of caspase-9. p53 was found to interact with the p35 fragment of caspase-9, and this interaction inhibits the caspase-9 activity. In a p53-null background, the high-level expression of both exogenous WT and mutant p53 increased the resistance of these cells to cisplatin, and the data showed a correlation between high p53 expression and caspase-9 inhibition. These results suggest the inhibition of caspase-9 as a potential mechanism in evading apoptosis in tumors with high-level p53 expression that is cytoplasmically localized.

Antiglioma effects of combined use of a baculovirual vector expressing wild-type p53 and sodium butyrate.

BACKGROUND: Combination therapy is usually desirable for successful cancer treatment, especially in cancers that are resistant to single forms of therapy. METHODS: To achieve an optimal therapeutic effect against glioblastoma, we tested a strategy that combines baculovirus-mediated transfer of the p53 tumor suppressor gene with the use of sodium butyrate, a histone deacetylase inhibitor. This strategy was designed based on the findings that the transduction efficiency of baculovirus in mammalian cells can be markedly enhanced by the addition of histone deacetylase inhibitors and that these inhibitors are effective in inducing cell cycle arrest, differentiation, or apoptosis in tumor cells. RESULTS: We observed a synergistic effect of the combination of the two treatments in provoking apoptosis in glioblastoma cells with mutant p53. In a mouse glioma xenograft model, the tumor inhibitory effect of baculovirus-expressed p53 was significantly enhanced by co-administration of sodium butyrate. CONCLUSIONS: These findings suggest a new approach to treat glioblastoma using baculovirus-mediated gene transfer in combination with administration of histone deacetylase inhibitor.

A simple, rapid method to isolate salt glands for three-dimensional visualization, fluorescence imaging and cytological studies.

BACKGROUND: Some plants inhabiting saline environment remove salts via the salt glands embedded in the epidermal tissues. Cytological studies of salt glands will provide valuable information to our understanding of the secretory process. Previous studies on salt gland histology relied mainly on two-dimensional microscopic observations of microtome sections. Optical sectioning properties of confocal laser scanning microscope offer alternative approach for obtaining three-dimensional structural information of salt glands. Difficulty in light penetration through intact leaves and interference from neighbouring leaf cells, however, impede the acquiring of good optical salt gland sections and limit its applications in salt gland imaging. Freeing the glands from adjacent leaf tissues will allow better manipulations for three-dimensional imaging through confocal laser scanning microscopy. RESULTS: Here, we present a simple and fast method for the isolation of individual salt glands released from the interference of neighbouring cells. About 100-200 salt glands could be isolated from just one cm2 of Avicennia officinalis leaf within hours and microscopic visualization of isolated salt glands was made possible within a day. Using these isolated glands, confocal laser scanning microscopic techniques could be applied and better resolution salt gland images could be achieved. By making use of their intrinsic fluorescent properties, optical sections of the gland cells could be acquired without the use of fluorescent probes and the corresponding three-dimensional images constructed. Useful cytological information of the salt gland cells could also be obtained through the applications of fluorescent dyes (e.g., LysoTracker® Red, FM®4-64, Texas Red®). CONCLUSIONS: The study of salt glands directly at the glandular level are made possible with the successful isolation of these specialized structures. Preparation of materials for subsequent microscopic observations of salt glands could be achieved within a day. Potential applications of confocal fluorescence microscopic techniques could also be performed using these isolated glands. Experiments designed and targeted directly at the salt glands were explored and cytological information obtained herein could be further incorporated towards the understanding of the mechanism underlying secretion in plant salt glands.

Iron species-mediated dopamine oxidation, proteasome inhibition, and dopaminergic cell demise: implications for iron-related dopaminergic neuron degeneration.

Iron species have been suggested to be highly involved in the pathogenesis of Parkinson disease. However, the detailed mechanism of iron-induced dopaminergic degeneration is still unclear. In this study, we demonstrate that free iron ions (trivalent or bivalent) and iron ions in stable complex with cyanide ions (K(4)Fe(CN)(6) and K(3)Fe(CN)(6)) can induce dopamine (DA) oxidation with different profiles and subsequently lead to proteasome inhibition and even dopaminergic MN9D cell demise via different mechanisms. The free iron ions could mediate extensive DA oxidation in an iron-DA complex-dependent manner. However, iron ions in stable complex with cyanide ions could not induce, or could induce only brief, DA oxidation. Deferoxamine, a specific iron ion chelator, could disrupt iron-DA complex formation and thus abrogate free iron ion-catalyzed DA oxidation and subsequent cell toxicity. Glutathione could neither disrupt iron-DA complex formation nor influence free iron ion-catalyzed DA oxidation but could protect against iron-mediated toxicity via detoxification of toxic by-products of iron-mediated DA oxidation. The resulting DA oxidation could inhibit chymotrypsin-like, trypsin-like, and caspase-like proteasome activities. However, we demonstrated that oxidative damage was not the major toxic mechanism of MN9D cell degeneration, but it was the DA quinones derived from iron-induced DA oxidation that contributed significantly to proteasome inhibition and even dopaminergic cell demise.

Glutathione conjugates with dopamine-derived quinones to form reactive or non-reactive glutathione-conjugates.

In this study we demonstrate for the first time that short-lived intermediate glutathione (GSH) conjugates (5-S-GSH-DA-o-quinone and 2-S-GSH-DA-o-quinone) must have first formed when GSH reacted with dopamine (DA)-derived DA-o-quinones without enzymatic catalysis in solutions. These intermediate GSH-conjugates are unstable and would finally transform into reactive or non-reactive GSH-conjugates dependent on ambient reductive forces. We demonstrated that, under sufficient reductive force, the intermediate GSH-conjugates could be reduced and transform into non-reactive 5-S-GSH-DA and 2-S-GSH-DA. However, under insufficient reductive forces, the intermediate GSH-conjugates could cyclize spontaneously to form reactive 7-S-GSH-aminochrome (7-S-GSH-AM). The 7-S-GSH-AM is so reactive and toxic that it could further conjugate with another GSH to form non-reactive 4,7-bi-GSH-5,6-dihydroindole in solutions. Furthermore 7-S-GSH-AM could abrogate tyrosinase activity rapidly and even inhibit proteasome activity in solutions. However, 7-S-GSH-AM could undergo automatically internal rearrangement and transform into non-reactive 7-S-GSH-5,6-dihydroindole if it had not conjugated with GSH. Therefore, insufficient ambient reductive force, such as decreased GSH concentration, could lead to decreased GSH detoxification efficiency for toxic DA quinones. Based on findings in this study, we propose two potential detrimental positive feedback loops involving accelerated DA oxidation, increased GSH consumption and impaired GSH detoxification efficiency, as the potential underlying chemical explanation for dopaminergic neuron degeneration in Parkinson's disease.