Evaluation of the pro-oxidant and antioxidant actions of L-DOPA and dopamine in vitro: implications for Parkinson's disease

How to Design Catechol-Containing Hydrogels for Cell Encapsulation Despite Catechol Toxicity

Catechol (cat) is a highly adhesive diphenol that can be chemically grafted to polymers such as chitosan (CH) to make them adhesive as well. However, catechol-containing materials experimentally show a large variability of toxicity, especially in vitro. While it is unclear how this toxicity emerges, most concerns are directed toward the oxidation of catechol into quinone that releases reactive oxygen species (ROS) which can, in turn, cause cell apoptosis through oxidative stress. To better understand the mechanisms at play, we examined the leaching profiles, hydrogen peroxide (H₂O₂) production, and in vitro cytotoxicity of several cat-chitosan (cat-CH) hydrogels that were prepared with different oxidation levels and cross-linking methods. To create cat-CH with different propensities toward oxidation, we grafted either hydrocaffeic acid (HCA, more prone to oxidation) or dihydrobenzoic acid (DHBA, less prone to oxidation) to the backbone of CH. Hydrogels were cross-linked either covalently, using sodium periodate (NaIO₄) to trigger oxidative cross-linking, or physically, using sodium bicarbonate (SHC). While using NaIO₄ as a cross-linker increased the oxidation levels of the hydrogels, it also significantly reduced in vitro cytotoxicity, H₂O₂ production, and catechol and quinone leaching in the media. For all gels tested, cytotoxicity could be directly related to the release of quinones rather than H₂O₂ production or catechol release, showing that oxidative stress may not be the main reason for catechol cytotoxicity, as other pathways of quinone toxicity come into play. Results also suggest that the indirect cytotoxicity of cat-CH hydrogels fabricated through carbodiimide chemistry can be reduced if (i) catechol groups are chemically bound to the polymer backbone to prevent leaching or (ii) the chosen cat-bearing molecule has a high resistance to oxidation. Coupled with the use of other cross-linking chemistries or more efficient purification methods, these strategies can be adopted to synthesize various types of cytocompatible cat-containing scaffolds.

Dopamine Inhibits Arabidopsis Growth through Increased Oxidative Stress and Auxin Activity

Like some bacterial species and all animals, plants synthesize dopamine and react to its exogenous applications. Despite dopamine’s widespread presence and activity in plants, its role in plant physiology is still poorly understood. Using targeted experimentation informed by the transcriptomic response to dopamine exposure, we identify three major effects of dopamine. First, we show that dopamine causes hypersensitivity to auxin indole-3-acetic acid by enhancing auxin activity. Second, we show that dopamine increases oxidative stress, which can be mitigated with glutathione. Third, we find that dopamine downregulates iron uptake mechanisms, leading to a decreased iron content—a response possibly aimed at reducing DA-induced oxidative stress. Finally, we show that dopamine-induced auxin sensitivity is downstream of glutathione biosynthesis, indicating that the auxin response is likely a consequence of DA-induced oxidative stress. Collectively, our results show that exogenous dopamine increases oxidative stress, which inhibits growth both directly and indirectly by promoting glutathione-biosynthesis-dependent auxin hypersensitivity.

Therapeutic Potential of Dopamine and Related Drugs as Anti-Inflammatories and Antioxidants in Neuronal and Non-Neuronal Pathologies

Dopamine (DA), its derivatives, and dopaminergic drugs are compounds widely used in the management of diseases related to the nervous system. However, DA receptors have been identified in nonneuronal tissues, which has been related to their therapeutic potential in pathologies such as sepsis or septic shock, blood pressure, renal failure, diabetes, and obesity, among others. In addition, DA and dopaminergic drugs have shown anti-inflammatory and antioxidant properties in different kinds of cells.

AIM

To compile the mechanism of action of DA and the main dopaminergic drugs and show the findings that support the therapeutic potential of these molecules for the treatment of neurological and non-neurological diseases considering their antioxidant and anti-inflammatory actions.

METHOD

We performed a review article. An exhaustive search for information was carried out in specialized databases such as PubMed, PubChem, ProQuest, EBSCO, Scopus, Science Direct, Web of Science, Bookshelf, DrugBank, Livertox, and Clinical Trials.

RESULTS

We showed that DA and dopaminergic drugs have emerged for the management of neuronal and nonneuronal diseases with important therapeutic potential as anti-inflammatories and antioxidants.

CONCLUSIONS

DA and DA derivatives can be an attractive treatment strategy and a promising approach to slowing the progression of disorders through repositioning.

Variability in the Beneficial Effects of Phenolic Compounds: A Review

When analysing the beneficial effects of phenolic compounds, several factors that exert a clear influence should be taken into account. The content of phenolic compounds in foods is highly variable, directly affecting individual dietary intake. Once ingested, these compounds have a greater or lesser bioaccessibility, defined as the amount available for absorption in the intestine after digestion, and a certain bioavailability, defined as the proportion of the molecule that is available after digestion, absorption and metabolism. Among the external factors that modify the content of phenolic compounds in food are the variety, the cultivation technique and the climate. Regarding functional foods, it is important to take into account the role of the selected food matrix, such as dairy matrices, liquid or solid matrices. It is also essential to consider the interactions between phenolic compounds as well as the interplay that occurs between these and several other components of the diet (macro- and micronutrients) at absorption, metabolism and mechanism of action levels. Furthermore, there is a great inter-individual variability in terms of phase II metabolism of these compounds, composition of the microbiota, and metabolic state or metabotype to which the subject belongs. All these factors introduce variability in the responses observed after ingestion of foods or nutraceuticals containing phenolic compounds.

Impairment of neuronal mitochondrial function by L-DOPA in the absence of oxygen-dependent auto-oxidation and oxidative cell damage

L-3,4-Dihydroxyphenylalanin (L-DOPA or levodopa) is currently the most used drug to treat symptoms of Parkinson's disease (PD). After crossing the blood-brain barrier, it is enzymatically converted to dopamine by neuronal cells and restores depleted endogenous neurotransmitter levels. L-DOPA is prone to auto-oxidation and reactive intermediates of its degradation including reactive oxygen species (ROS) have been implicated in cellular damage. In this study, we investigated how oxygen tension effects L-DOPA stability. We applied oxygen tensions comparable to those in the mammalian brain and demonstrated that 2% oxygen almost completely stopped its auto-oxidation. L-DOPA even exerted a ROS scavenging function. Further mechanistic analysis indicated that L-DOPA reprogrammed mitochondrial metabolism and reduced oxidative phosphorylation, depolarized the mitochondrial membrane, induced reductive glutamine metabolism, and depleted the NADH pool. These results shed new light on the cellular effects of L-DOPA and its neuro-toxicity under physiological oxygen levels that are very distinct to normoxic in vitro conditions.

New insights on neurotransmitters signaling mechanisms in plants

Neurotransmitters (NTs) such as acetylcholine, biogenic amines (dopamine, noradrenaline, adrenaline, histamine), indoleamines [(melatonin (MEL) & serotonin (SER)] have been found not only in mammalians, but also in diverse living organisms-microorganisms to plants. These NTs have emerged as potential signaling molecules in the last decade of investigations in various plant systems. NTs have been found to play important roles in plant life including-organogenesis, flowering, ion permeability, photosynthesis, circadian rhythm, reproduction, fruit ripening, photomorphogenesis, adaptation to environmental changes. This review will provide an overview of recent advancements on the physiological and molecular mechanism of NTs in plants. Moreover, molecular crosstalk of SER and MEL with various biomolecules is also discussed. The study of these NTs may serve as new understanding of the mechanisms of signal transmission and cell sensing in plants subjected to various environmental stimulus.

Combining the lack of chromogranins with chronic L-DOPA treatment affects motor activity in mice

We have tested whether the lack of chromogranins (Cgs) A and B could provoke CNS disorders when combined with an excess of dopamine. We chronically treated (over 6 months) mice lacking both chromogranins A and B (Cgs-KO) with a low oral dosage of L-DOPA/benserazide (10/2.5 mg/kg). Motor performance in the rota-rod test, open field activity, and metabolic cages indicated a progressive impairment in motor coordination in these mice, and an increase in rearing behavior, which was accompanied by an increase in DA within the substantia nigra. We conclude that mild chronic L-DOPA treatment does not produce nigro-striatal toxicity that could be associated with parkinsonism, neither in control nor Cgs-KO mice. Rather, Cgs-KO mice exhibit behaviors compatible with an amphetamine-like effect, probably caused by the excess of catecholamines in the CNS.

Modulation of Apoptotic Cell Death and Neuroprotective Effects of Glutathione-L-Dopa Codrug Against H2O2-Induced Cellular Toxicity

The L-3,4-dihydroxyphenylalanine (LD) is the gold standard drug currently used to manage Parkinson’s disease (PD) and to control its symptoms. However, LD could cause disease neurotoxicity due to the generation of pro-oxidant intermediates deriving from its autoxidation. In order to overcome this limitation, we have conjugated LD to the natural antioxidant glutathione (GSH) to form a codrug (GSH-LD). Here we investigated the effect of GSH-LD on H₂O₂-induced cellular toxicity in undifferentiated and differentiated lymphoma U-937 and dopaminergic neuroblastoma SH-SY5Y cell lines, used respectively as models to study the involvement of macrophages/microglia and dopaminergic neurons in PD. We analyzed the effect of GSH-LD on apoptosis and cellular oxidative stress, both considered strategic targets for the prevention and treatment of neurodegenerative diseases. Compared to LD and GSH, GSH-LD had a stronger effect in preventing hydrogen peroxide (H₂O₂) induced apoptosis in both cell lines. Moreover, GSH-LD was able to preserve cell viability, cellular redox status, gluthation metabolism and prevent reactive oxygen species (ROS) formation, in a phosphinositide 3-kinase (PI3K)/kinase B (Akt)-dependent manner, in a neurotoxicity cellular model. Our findings indicate that the GSH-LD codrug offers advantages deriving from the additive effect of LD and GSH and it could represent a promising candidate for PD treatment.

In vitro models of synucleinopathies: informing on molecular mechanisms and protective strategies

Alpha-synuclein (α-Syn) is a central player in Parkinson's disease (PD) and in a spectrum of neurodegenerative diseases collectively known as synucleinopathies. The protein was first associated with PD just over 20 years ago, when it was found to (i) be a major component of Lewy bodies and (ii) to be also associated with familial forms of PD. The characterization of α-Syn pathology has been achieved through postmortem studies of human brains. However, the identification of toxic mechanisms associated with α-Syn was only achieved through the use of experimental models. In vitro models are highly accessible, enable relatively rapid studies, and have been extensively employed to address α-Syn-associated neurodegeneration. Given the diversity of models used and the outcomes of the studies, a cumulative and comprehensive perspective emerges as indispensable to pave the way for further investigations. Here, we subdivided in vitro models of α-Syn pathology into three major types: (i) models simulating α-Syn fibrillization and the formation of different aggregated structures in vitro, (ii) models based on the intracellular expression of α-Syn, reporting on pathogenic conditions and cellular dysfunctions induced, and (iii) models using extracellular treatment with α-Syn aggregated species, reporting on sites of interaction and their downstream consequences. In summary, we review the underlying molecular mechanisms discovered and categorize protective strategies, in order to pave the way for future studies and the identification of effective therapeutic strategies. This article is part of the Special Issue "Synuclein".

Aroclor 1254 and BDE-47 inhibit dopaminergic function manifesting as changes in locomotion behaviors in zebrafish embryos

Contamination with polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) in the environment is a major concern due to their persistent bioaccumulative toxicity that can disturb neurobehavioral functions including movements. Recently, it was reported that some PBDE including BDE-47 stimulates locomotor activities of zebrafish embryos by unknown mechanism. In this study, motor movements of the zebrafish embryo were used as a model system to evaluate the neuronal toxicity of a non-coplanar PCB-dominant mixture (Aroclor 1254) and BDE-47. Both organohalogens increased tail shaking and rotation of embryos in a concentration-dependent manner. Chemical inhibition and gene knock-down of tyrosine hydroxylase and vesicular monoamine transporter 2 (VMAT2) also induced hyperactivities. Hyperactivities induced by these treatments were all inhibited by supplementation of l-tyrosine and l-dopa, precursors of dopamine synthesis. Both organohalogens reduced dopamine contents and increased the 3,4-dihydroxyphenylacetic acid (DOPAC)/dopamine ratio in whole embryos. The results suggest that functional inhibition of dopaminergic neurons is involved in hyperactivities of zebrafish embryos caused by Aroclor 1254 and BDE-47.

Molecular Mechanisms behind Free Radical Scavengers Function against Oxidative Stress

Accumulating evidence shows that oxidative stress is involved in a wide variety of human diseases: rheumatoid arthritis, Alzheimer's disease, Parkinson's disease, cancers, etc. Here, we discuss the significance of oxidative conditions in different disease, with the focus on neurodegenerative disease including Parkinson's disease, which is mainly caused by oxidative stress. Reactive oxygen and nitrogen species (ROS and RNS, respectively), collectively known as RONS, are produced by cellular enzymes such as myeloperoxidase, NADPH-oxidase (nicotinamide adenine dinucleotide phosphate-oxidase) and nitric oxide synthase (NOS). Natural antioxidant systems are categorized into enzymatic and non-enzymatic antioxidant groups. The former includes a number of enzymes such as catalase and glutathione peroxidase, while the latter contains a number of antioxidants acquired from dietary sources including vitamin C, carotenoids, flavonoids and polyphenols. There are also scavengers used for therapeutic purposes, such as 3,4-dihydroxyphenylalanine (L-DOPA) used routinely in the treatment of Parkinson's disease (not as a free radical scavenger), and 3-methyl-1-phenyl-2-pyrazolin-5-one (Edaravone) that acts as a free radical detoxifier frequently used in acute ischemic stroke. The cell surviving properties of L-DOPA and Edaravone against oxidative stress conditions rely on the alteration of a number of stress proteins such as Annexin A1, Peroxiredoxin-6 and PARK7/DJ-1 (Parkinson disease protein 7, also known as Protein deglycase DJ-1). Although they share the targets in reversing the cytotoxic effects of H₂O₂, they seem to have distinct mechanism of function. Exposure to L-DOPA may result in hypoxia condition and further induction of ORP150 (150-kDa oxygen-regulated protein) with its concomitant cytoprotective effects but Edaravone seems to protect cells via direct induction of Peroxiredoxin-2 and inhibition of apoptosis.

Elucidation of the interplay between Fe(II), Fe(III), and dopamine with relevance to iron solubilization and reactive oxygen species generation by catecholamines

The non-enzymatically catalyzed oxidation of dopamine (DA) and the resultant formation of powerful oxidants such as the hydroxyl radical ((•) OH) through 'Fenton chemistry' in the presence of iron within dopaminergic neurons are thought to contribute to the damage of cells or even lead to neuronal degenerative diseases such as Parkinson's disease. An understanding of DA oxidation as well as the transformation of the intermediates that are formed in the presence of iron under physiological conditions is critical to understanding the mechanism of DA and iron induced oxidative stress. In this study, the generation of H2 O2 through the autoxidation and iron-catalyzed oxidation of DA, the formation of the dominant complex via the direct reaction with Fe(II) and Fe(III) in both oxygen saturated and deoxygenated conditions and the oxidation of Fe(II) in the presence of DA at physiological pH 7.4 were investigated. The oxidation of DA resulted in the generation of significant amounts of H2 O2 with this process accelerated significantly in the presence of Fe(II) and Fe(III). At high DA:Fe(II) ratios, the results from this study suggest that DA plays a protective role by complexing Fe(II) and preventing it from reacting with the generated H2 O2 . However, the accumulation of H2 O2 may result in cellular damage as high intracellular H2 O2 concentrations will result in the oxidation of remaining Fe(II) mainly through the peroxidation pathway. At low DA:Fe(II) ratios however, it is likely that DA will act as a pro-oxidant by generating H2 O2 which, in the presence of Fe(II), will result in the production of strongly oxidizing (•) OH radicals. Powerful oxidants such as the hydroxyl radical ((•) OH) have previously been thought to be generated through the interplay between dopamine (DA) and iron, contributing to damage to cells and, potentially, leading to neuronal degenerative diseases such as Parkinson's disease. Our results suggest that DA plays a dual role as high DA/Fe(II) ratios prevent Fe(II) from reacting with the generated H2 O2 thereby reducing (•) OH generation, whereas low DA/Fe(II) ratios enhance (•) OH generation as a result of reaction of unbound Fe(II) and H2 O2 produced via both autoxidation and iron-catalyzed oxidation of DA.

Enhanced Neuroprotective Effects of Coadministration of Tetrandrine with Glutathione in Preclinical Model of Parkinson's Disease

Aim. In this study we examined the influence of tetrandrine (Tet) on the neuroprotective effects of glutathione (GSH) in the 6-hydroxydopamine- (6-OHDA-) lesioned rat model of Parkinson's disease (PD). Methods. Levels in the redox system, dopamine (DA) metabolism, dopaminergic neuronal survival, and apoptosis of the substantia nigra (SN) and striatum, as well as the rotational behavior of animals were examined after a 50-day administration of GSH + Tet (or GSH) and/or L-3,4-dihydroxyphenylalanine (L-dopa) to PD rats. Ethics Committee of Huashan Hospital, Fudan University approved the protocol (number SYXK2009-0082). Results. Administration of GSH or Tet alone did not show any significant effects on the factors evaluated in the PD rats. However, in the GSH + Tet group, we observed markedly decreased oxidative damage, inhibition of DA metabolism and enhanced DA synthesis, increased tyrosine hydroxylase- (TH-) immunopositive neuronal survival, and delayed apoptosis of dopaminergic neurons in the SN. Animal rotational behavior was improved in the GSH + Tet group. Additionally, coadministration of GSH + Tet appeared to offset the possible oxidative neurotoxicity induced by L-dopa. Conclusion. In this study, we demonstrated that tetrandrine allowed occurrence of the neuroprotective effect of glutathione probably due to inhibition of P-glycoprotein on 6-hydroxydopamine-lesioned rat models of Parkinson's disease, including rats undergoing long-term L-dopa treatment.

A comprehensive review of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a late-onset fatal neurodegenerative disease affecting motor neurons with an incidence of about 1/100,000. Most ALS cases are sporadic, but 5–10% of the cases are familial ALS. Both sporadic and familial ALS (FALS) are associated with degeneration of cortical and spinal motor neurons. The etiology of ALS remains unknown. However, mutations of superoxide dismutase 1 have been known as the most common cause of FALS. In this study, we provide a comprehensive review of ALS. We cover all aspects of the disease including epidemiology, comorbidities, environmental risk factor, molecular mechanism, genetic factors, symptoms, diagnostic, treatment, and even the available supplement and management of ALS. This will provide the reader with an advantage of receiving a broad range of information about the disease.

Betalain induction by l-DOPA application confers photoprotection to saline-exposed leaves of Disphyma australe

The capacity to synthesize betalains has arisen in diverse phylogenetic lineages across the Caryophyllales, and because betalainic plants often grow in deserts, sand dunes, or salt marshes, it is likely that these pigments confer adaptive advantages. However, possible functional roles of foliar betalains remain largely unexplored and are difficult to test experimentally. We adopted a novel approach to examine putative photoprotective roles of betalains in leaves for which chloroplast function has been compromised by salinity. Responses of l-DOPA-treated red shoots of Disphyma australe to high light and salinity were compared with those of naturally red- and green-leafed morphs. Betalain content and tyrosinase activity were measured, and Chl fluorescence profiles and H2 O2 production were compared under white, red or green light. Green leaves lacked tyrosinase activity, but when supplied with exogenous l-DOPA they produced five betacyanins. Both the naturally red and l-DOPA-induced red leaves generated less H2 O2 and showed smaller declines in photosystem II quantum efficiency than did green leaves when exposed to white or green light, although not when exposed to red light. Light screening by epidermal betalains effectively reduces the propensity for photoinhibition and photo-oxidative stress in subjacent chlorenchyma. This may assist plant survival in exposed and saline environments.

Evaluation of levodopa and carbidopa antioxidant activity in normal human lymphocytes in vitro: implication for oxidative stress in Parkinson's disease

The main pathochemical hallmark of Parkinson's disease (PD) is the loss of dopamine in the striatum of the brain, and the oral administration of levodopa (L-dopa) is a treatment that partially restores the dopaminergic transmission. In vitro assays have demonstrated both toxic and protective effects of L-dopa on dopaminergic cells, while in vivo studies have not provided any convincing data. The peripheral metabolic pathways significantly decrease the amount of L-dopa reaching the brain; therefore, all of the current commercial formulations require an association with an inhibitor of dopa-decarboxylase, such as carbidopa. However, the dosage and the actual effectiveness of carbidopa have not yet been well defined. PD patients exhibit a reduced efficiency of the endogenous antioxidant system, and peripheral blood lymphocytes (PBLs) represent a dopaminergic system for use as a cellular model to study the pharmacological treatments of neurodegenerative disorders in addition to analysing the systemic oxidative stress. According to our previous studies demonstrating a protective effect of both L-dopa and carbidopa on neuroblastoma cells in vitro, we used the PBLs of healthy donors to evaluate the modulation of DNA damage by different concentrations of L-dopa and carbidopa in the presence of oxidative stress that was exogenously induced by H2O2. We utilised a TAS assay to evaluate the in vitro direct scavenging activity of L-dopa and carbidopa and analysed the expression of genes that were involved in cellular oxidative metabolism. Our data demonstrate the antioxidant capacity of L-dopa and carbidopa and their ability to protect DNA against oxidative-induced damage that derives from different mechanisms of action.

1-Benzyl-1,2,3,4-tetrahydroisoquinoline, an endogenous neurotoxic compound, disturbs the behavioral and biochemical effects of L-DOPA: in vivo and ex vivo studies in the rat

Environmental factors and endogenously produced toxins, such as 1-benzyl-1,2,3,4-tetrahydroisoquinoline (1BnTIQ), are considered to be involved in the pathogenesis of Parkinson's disease (PD). In this study, we investigated the impact of single and multiple 1BnTIQ (25 and 50 mg/kg i.p.) administration on L-DOPA-induced changes in the rate of dopamine and serotonin metabolism in the rat brain. Additionally, using in vivo microdialysis, we measured the impact of acute and multiple 1BnTIQ administrations on L-DOPA-induced dopamine release in the striatum. These data were compared with results from behavioral tests in which we measured the effect of 1BnTIQ and L-DOPA on locomotor activity. Finally, we determined the effect of the repeated administration of 1BnTIQ on the L-DOPA-induced elevation of caspase-3 activity in the hippocampus. An ex vivo neurochemical study indicated that both acute and chronic 1BnTIQ injections strongly inhibited L-DOPA-induced increases in the concentration of dopamine and all of its metabolites in dopaminergic structures. In contrast, in vivo microdialysis studies suggested that the differences in 1BnTIQ's effects are dependent on the type of treatment. A single dose of 1BnTIQ intensified the elevation of dopamine release induced by L-DOPA administration (~1,300 %; P < 0.01), while multiple administrations of 1BnTIQ significantly enhanced the basal dopamine levels while partially diminishing the effects of L-DOPA injection (~200 %; P < 0.01). Additionally, we found that chronic administration of 1BnTIQ completely blocked the L-DOPA-induced increase in caspase-3 activity in the hippocampus. These findings indicate that both acute and chronic administrations of 1BnTIQ disturbs the behavioral and biochemical effects of L-DOPA in the rat. The data presented from ex vivo and in vivo studies clearly suggest that 1BnTIQ's effects may be connected with the inhibition of DAT and/or COMT activity in the brain. Furthermore, elevated endogenous levels of 1BnTIQ may pose a serious risk in PD patients undergoing L-DOPA therapy.

Proteome analysis reveals roles of L-DOPA in response to oxidative stress in neurons

Background

Parkinson’s disease (PD) is the second most common neurodegenerative movement disorder, caused by preferential dopaminergic neuronal cell death in the substantia nigra, a process also influenced by oxidative stress. L-3,4-dihydroxyphenylalanine (L-DOPA) represents the main treatment route for motor symptoms associated with PD however, its exact mode of action remains unclear. A spectrum of conflicting data suggests that L-DOPA may damage dopaminergic neurons due to oxidative stress whilst other data suggest that L-DOPA itself may induce low levels of oxidative stress, which in turn stimulates endogenous antioxidant mechanisms and neuroprotection.

Results

In this study we performed a two-dimensional gel electrophoresis (2DE)-based proteomic study to gain further insight into the mechanism by which L-DOPA can influence the toxic effects of H₂O₂ in neuronal cells. We observed that oxidative stress affects metabolic pathways as well as cytoskeletal integrity and that neuronal cells respond to oxidative conditions by enhancing numerous survival pathways. Our study underlines the complex nature of L-DOPA in PD and sheds light on the interplay between oxidative stress and L-DOPA.

Conclusions

Oxidative stress changes neuronal metabolic routes and affects cytoskeletal integrity. Further, L-DOPA appears to reverse some H₂O₂-mediated effects evident at both the proteome and cellular level.

The Magic Velvet Bean of Mucuna pruriens

Mucuna pruriens (Fabaceae) is an established herbal drug used for the management of male infertility, nervous disorders, and also as an aphrodisiac. It has been shown that its seeds are potentially of substantial medicinal importance. The ancient Indian medical system, Ayurveda, traditionally used M. pruriens, even to treat such things as Parkinson's disease. M. pruriens has been shown to have anti-parkinson and neuroprotective effects, which may be related to its anti-oxidant activity. In addition, anti-oxidant activity of M. pruriens has been also demonstrated in vitro by its ability to scavenge DPPH radicals and reactive oxygen species. In this review the medicinal properties of M. pruriens are summarized, taking in consideration the studies that have used the seeds extracts and the leaves extracts.

Cu(II) and dopamine bind to α-synuclein and cause large conformational changes

α-Synuclein (AS) is an intrinsically disordered protein that can misfold and aggregate to form Lewy bodies in dopaminergic neurons, a classic hallmark of Parkinson's disease. The binding of Cu(II) and dopamine to AS was evaluated by nanopore analysis with α-hemolysin. In the absence of Cu(II), wild-type AS (1 μM) readily translocated through the pore with a blockade current of--85 pA, but mostly bumping events were observed in the presence of 25 μM Cu(II). A binding site in the N-terminus was confirmed, because Cu(II) had no effect on the event profile of a peptide consisting of the C-terminal 96-140 residues. In the presence of dopamine (25 μM), the translocation events at--85 pA shifted to--80 pA, which also represents translocation events, because the event time decreases with increasing voltage. Events at--80 pA were also observed for the mutant A30P AS in the presence of dopamine. Event profiles for an N-terminal 1-60-residue peptide and a C-terminal 96-140-residue peptide were both altered in the presence of 25 μM dopamine. In contrast, dopamine had little effect on the CD spectrum of AS, and a single binding site with a Ka of 3.5 × 10(3) m(-1) was estimated by isothermal titration calorimetry. Thus, dopamine can interact with both the N-terminus and the C-terminus. Two-dimensional NMR spectroscopy of AS in the presence of dopamine showed that there were significant changes in the spectra in all regions of the protein. According to these findings, a model is presented in which dopamine induces folding between the N-terminus and C-terminus of AS. Partially folding conformations such as this may represent important intermediates in the misfolding of AS that leads to fibrillization.

Maladaptive plasticity in levodopa-induced dyskinesias and tardive dyskinesias: old and new insights on the effects of dopamine receptor pharmacology

Maladaptive plasticity can be defined as behavioral loss or even development of disease symptoms resulting from aberrant plasticity changes in the human brain. Hyperkinetic movement disorders, in the neurological or psychiatric realms, have been associated with maladaptive neural plasticity that can be expressed by functional changes such as an increase in transmitter release, receptor regulation, and synaptic plasticity or anatomical modifications such as axonal regeneration, sprouting, synaptogenesis, and neurogenesis. Recent evidence from human and animal models provided support to the hypothesis that these phenomena likely depend on altered dopamine turnover induced by long-term drug treatment. However, it is still unclear how and where these altered mechanisms of cortical plasticity may be localized. This study provides an up-to-date overview of these issues together with some reflections on future studies in the field, particularly focusing on two specific disorders (levodopa-induced dyskinesias in Parkinson’s disease patients and tardive dyskinesias in schizophrenic patients) where the modern neuroimaging approaches have recently provided new fundamental insights.

The role of L-DOPA in plants

Since higher plants regularly release organic compounds into the environment, their decay products are often added to the soil matrix and a few have been reported as agents of plant-plant interactions. These compounds, active against higher plants, typically suppress seed germination, cause injury to root growth and other meristems, and inhibit seedling growth. Mucuna pruriens is an example of a successful cover crop with several highly active secondary chemical agents that are produced by its seeds, leaves and roots. The main phytotoxic compound encountered is the non-protein amino acid L-DOPA, which is used in treating the symptoms of Parkinson disease. In plants, L-DOPA is a precursor of many alkaloids, catecholamines, and melanin and is released from Mucuna into soils, inhibiting the growth of nearby plant species. This mini-review summarizes knowledge regarding L-DOPA in plants, providing a brief overview about its metabolic actions.

The effects of dopamine on antioxidant enzymes activities and reactive oxygen species levels in soybean roots

In the current work, we investigated the effects of dopamine, an neurotransmitter found in several plant species on antioxidant enzyme activities and ROS in soybean (Glycine max L. Merrill) roots. The effects of dopamine on SOD, CAT and POD activities, as well as H2O2, O2(•-), melanin contents and lipid peroxidation were evaluated. Three-day-old seedlings were cultivated in half-strength Hoagland nutrient solution (pH 6.0), without or with 0.1 to 1.0 mM dopamine, in a growth chamber (25°C, 12 h photoperiod, irradiance of 280 μmol m(-2) s(-1)) for 24 h. Significant increases in melanin content were observed. The levels of ROS and lipid peroxidation decreased at all concentrations of dopamine tested. The SOD activity increased significantly under the action of dopamine, while CT activity was inhibited and POD activity was unaffected. The results suggest a close relationship between a possible antioxidant activity of dopamine and melanin and activation of SOD, reducing the levels of ROS and damage on membranes of soybean roots.

Effects of antiparkinsonian agents on β-amyloid and α-synuclein oligomer formation in vitro

The aggregation of β-amyloid protein (Aβ) and α-synuclein (αS) are hypothesized to be the key pathogenic event in Alzheimer's disease (AD) and Lewy body diseases (LBD), with oligomeric assemblies thought to be the most neurotoxic. Inhibitors of oligomer formation, therefore, could be valuable therapeutics for patients with AD and LBD. Here, we examined the effects of antiparkinsonian agents (dopamine, levodopa, trihexyphenidyl, selegiline, zonisamide, bromocriptine, peroxide, ropinirole, pramipexole, and entacapone) on the in vitro oligomer formation of Aβ40, Aβ42, and αS using a method of photo-induced cross-linking of unmodified proteins (PICUP), electron microscopy, and atomic force microscopy. The antiparkinsonian agents except for trihexyphenidyl inhibited both Aβ and αS oligomer formations, and, among them, dopamine, levodopa, pramipexole, and entacapone had the stronger in vitro activity. Circular dichroism and thioflavin T(S) assays showed that secondary structures of Aβ and αS assemblies inhibited by antiparkinsonian agents were statistical coil state and that their seeding activities had disappeared. The antiparkinsonian agents could be potential therapeutic agents to prevent or delay AD and LBD progression.

Evidence of oxidative stress in young and aged DJ-1-deficient mice

Loss of DJ-1 function contributes to pathogenesis in Parkinson's disease. Here, we investigate the impact of aging and DJ-1 deficiency in transgenic mice. Ventral midbrain from young DJ-1-deficient mice revealed no change in 4-hydroxy-2-nonenal (4-HNE), but HSP60, HSP40 and striatal dopamine turnover were significantly elevated compared to wildtype. In aged mice, the chaperone response observed in wildtype animals was absent from DJ-1-deficient transgenics, and nigral 4-HNE immunoreactivity was enhanced. These changes were concomitant with increased striatal dopamine levels and uptake. Thus, increased oxidants and diminished protein quality control may contribute to nigral oxidative damage with aging in the model.

Intervention of mitochondrial dysfunction-oxidative stress-dependent apoptosis as a possible neuroprotective mechanism of α-lipoic acid against rotenone-induced parkinsonism and L-dopa toxicity

The current study evidenced hypothesis that mitochondrial dysfunction-oxidative stress-dependent apoptotic pathways play a critical role in degeneration of dopaminergic neurons in Parkinson's disease. Model of rotenone-induced parkinsonism in rats produced decrease in striatal complex I activity and reduced glutathione with increase in nitrites concentration and caspase-3 activity. This was confirmed by significant correlation of catalepsy score with neurochemical parameters. Moreover, electron microscopic examination of striatal neurons displayed ultrastructure affection as hyperchromatic nuclei and disrupted mitochondria that are typical features of undergoing apoptosis. Administration of L-dopa as replacement therapy, although caused symptomatic improvement in catalepsy score, but further worsening in neurochemical parameters. Therefore, efforts are not only to improve effect of L-dopa, but also to introduce drugs provide antiparkinsonian and neuroprotective effects. In this study, α-lipoic acid exhibited noticeable neuroprotective effects by a mechanism via intervention of mitochondrial dysfunction-oxidative stress-dependent apoptotic pathways. Combination of α-lipoic acid efficiently halting deleterious toxic effects of L-dopa, revealed normalization of catalepsy score in addition to amelioration of neurochemical parameters and apparent preservation of striatal ultrastructure integrity, indicating benefit of both symptomatic and neuroprotective therapy. In conclusion, α-lipoic acid could be recommended as a disease-modifying therapy when given with L-dopa early in course of Parkinson's disease.

Effect of some naturally occurring iron ion chelators on the formation of radicals in the reaction mixtures of rat liver microsomes with ADP, Fe and NADPH

In order to clarify the mechanism by polyphenols of protective effects against oxidative damage or by quinolinic acid of its neurotoxic and inflammatory actions, effects of polyphenols or quinolinic acid on the radical formation were examined. The ESR measurements showed that some polyphenols such as caffeic acid, catechol, gallic acid, D-(+)-catechin, L-dopa, chlorogenic acid and L-noradrenaline inhibited the formation of radicals in the reaction mixture of rat liver microsomes with ADP, Fe³⁺ and NADPH. The ESR measurements showed that α-picolinic acid, 2,6-pyridinedicarboxylic acid and quinolinic acid (2,3-pyridinedicarboxylic acid) enhanced the formation of radicals in the reaction mixture of rat liver microsomes with Fe³⁺ and NADPH. Caffeic acid and α-picolinic acid had no effects on the formation of radicals in the presence of EDTA, suggesting that the chelation of iron ion seems to be related to the inhibitory and enhanced effects. The polyphenols may exert protective effects against oxidative damage of erythrocyte membrane, ethanol-induced fatty livers, cardiovascular diseases, inflammatory and cancer through the mechanism. On the other hand, quinolinic acid may exert its neurotoxic and inflammatory effects because of the enhanced effect on the radical formation.

The allelochemical L-DOPA increases melanin production and reduces reactive oxygen species in soybean roots

The non-protein amino acid, L-3,4-dihydroxyphenylalanine (L-DOPA), is the main allelochemical released from the roots of velvetbean and affects seed germination and root growth of several plant species. In the work presented here, we evaluated, in soybean roots, the effects of L-DOPA on the following: polyphenol oxidase (PPO), superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activities; superoxide anion (O·-2), hydrogen peroxide (H(2)O(2)), and melanin contents; and lipid peroxidation. To this end, 3-day-old seedlings were cultivated in half-strength Hoagland's solution (pH 6.0), with or without 0.1 to 1.0 mM L-DOPA in a growth chamber (at 25°C, with a light/dark photoperiod of 12/12 hr and a photon flux density of 280 μmol m(-2) s(-1)) for 24 hr. The results showed that L-DOPA increased the PPO activity and, further, the melanin content. The activities of SOD and POD increased, but CAT activity decreased after the chemical exposure. The contents of reactive oxygen species (ROS), such as O·-2 and H(2)O(2), and the levels of lipid peroxidation significantly decreased under all concentrations of L-DOPA tested. These results suggest that L-DOPA was absorbed by the soybean roots and metabolized to melanin. It was concluded that the reduction in the O·-2 and H(2)O(2) contents and lipid peroxidation in soybean roots was due to the enhanced SOD and POD activities and thus a possible antioxidant role of L-DOPA.

S-glutathionylation: from molecular mechanisms to health outcomes

Redox homeostasis governs a number of critical cellular processes. In turn, imbalances in pathways that control oxidative and reductive conditions have been linked to a number of human disease pathologies, particularly those associated with aging. Reduced glutathione is the most prevalent biological thiol and plays a crucial role in maintaining a reduced intracellular environment. Exposure to reactive oxygen or nitrogen species is causatively linked to the disease pathologies associated with redox imbalance. In particular, reactive oxygen species can differentially oxidize certain cysteine residues in target proteins and the reversible process of S-glutathionylation may mitigate or mediate the damage. This post-translational modification adds a tripeptide and a net negative charge that can lead to distinct structural and functional changes in the target protein. Because it is reversible, S-glutathionylation has the potential to act as a biological switch and to be integral in a number of critical oxidative signaling events. The present review provides a comprehensive account of how the S-glutathionylation cycle influences protein structure/function and cellular regulatory events, and how these may impact on human diseases. By understanding the components of this cycle, there should be opportunities to intervene in stress- and aging-related pathologies, perhaps through prevention and diagnostic and therapeutic platforms.

L-DOPA: a scapegoat for accelerated neurodegeneration in Parkinson's disease?

There is consensus that amelioration of the motor symptoms of Parkinson's disease is most effective with L-DOPA (levodopa). However, this necessary therapeutic step is biased by an enduring belief that L-DOPA is toxic to the remaining substantia nigra dopaminergic neurons by itself, or by specific metabolites such as dopamine. The concept of L-DOPA toxicity originated from pre-clinical studies conducted mainly in cell culture, demonstrating that L-DOPA or its derivatives damage dopaminergic neurons due to oxidative stress and other mechanisms. However, the in vitro data remain controversial as some studies showed neuroprotective, rather than toxic action of the drug. The relevance of this debate needs to be considered in the context of the studies conducted on animals and in clinical trials that do not provide convincing evidence for L-DOPA toxicity in vivo. This review presents the current views on the pathophysiology of Parkinson's disease, focusing on mitochondrial dysfunction and oxidative/proteolytic stress, the factors that can be affected by L-DOPA or its metabolites. We then critically discuss the evidence supporting the two opposing views on the effects of L-DOPA in vitro, as well as the animal and human data. We also address the problem of inadequate experimental models used in these studies. L-DOPA remains the symptomatic 'hero' of Parkinson's disease. Whether it contributes to degeneration of nigral dopaminergic neurons, or is a 'scapegoat' for explaining undesirable or unexpected effects of the treatment, remains a hotly debated topic.

Caffeic acid inhibits the formation of 1-hydroxyethyl radical in the reaction mixture of rat liver microsomes with ethanol partly through its metal chelating activity

Effect of caffeic acid on the formation of 1-hydroxyethyl radicals via the microsomal ethanol-oxidizing system pathway was examined. The electron spin resonance spin trapping showed that 1-hydroxyethyl radicals form in the control reaction mixture which contained 0.17 M ethanol, 1 mg protein/ml rat river microsomes, 0.1 M α-(4-pyridyl-1-oxide)-N-tert-butylnitrone, 5 mM nicotinamide adenine dinucleotide phosphate and 30 mM phosphate buffer (pH 7.4). When the electron spin resonance spectra of the control reaction mixtures with caffeic acid were measured, caffeic acid inhibited the formation of 1-hydroxyethyl radicals in a concentration dependent manner. Gallic acid, dopamine, l-dopa, chlorogenic acid and catechin also inhibited the formation of 1-hydroxyethyl radicals. Above results indicated that the catechol moiety is essential to the inhibitory effect. Caffeic acid seems to chelate of iron ion at the catechol moiety. Indeed, the inhibitory effect by caffeic acid was greatly diminished in the presence of desferrioxamine, a potent iron chelator which removes iron ion in the Fe (III)-caffeic acid complex. Since Fe (III)-desferrioxamine complex is active for the 1-hydroxyethyl radicals formation, caffeic acid inhibits the formation of 1-hydroxyethyl radicals in the reaction mixture partly through its metal chelating activity.

Levodopa deactivates enzymes that regulate thiol-disulfide homeostasis and promotes neuronal cell death: implications for therapy of Parkinson's disease

Parkinson's disease (PD), characterized by dopaminergic neuronal loss, is attributed to oxidative stress, diminished glutathione (GSH) levels, mitochondrial dysfunction, and protein aggregation. Treatment of PD involves chronic administration of Levodopa (l-DOPA) which is a pro-oxidant and may disrupt sulfhydryl homeostasis. The goal of these studies is to elucidate the effects of l-DOPA on thiol homeostasis in a model akin to PD, i.e., immortalized dopaminergic neurons (SHSY5Y cells) with diminished GSH content. These neurons exhibit hypersensitivity to l-DOPA-induced cell death, which is attributable to concomitant inhibition of the intracellular thiol disulfide oxidoreductase enzymes. Glutaredoxin (Grx) was deactivated in a dose-dependent fashion, but its content was unaffected. Glutathione disulfide (GSSG) reductase (GR) activity was not altered. Selective knockdown of Grx resulted in an increased level of apoptosis, documenting the role of the Grx system in neuronal survival. l-DOPA treatments also led to decreased activities of thioredoxin (Trx) and thioredoxin reductase (TR), concomitant with diminution of their cellular contents. Selective chemical inhibition of TR activity led to an increased level of apoptosis, documenting the Trx system's contribution to neuronal viability. To investigate the mechanism of inhibition at the molecular level, we treated the each isolated enzyme with oxidized l-DOPA. GR, Trx, and TR activities were little affected. However, Grx was inactivated in a time- and concentration-dependent fashion indicative of irreversible adduction of dopaquinone to its nucleophilic active-site Cys-22, consistent with the intracellular loss of Grx activity but not Grx protein content after l-DOPA treatment. Overall l-DOPA is shown to impair the collaborative contributions of the Grx and Trx systems to neuron survival.

Melatonin inhibits 6-hydroxydopamine production in the brain to protect against experimental parkinsonism in rodents

We tested the hypothesis that melatonin regulates formation of 6-hydroxydopamine (6-OHDA) in the brain and thereby protects animals from dopaminergic neurotoxicity and the development of parkinsonism in animals. Employing a ferrous-ascorbate-dopamine (FAD) hydroxyl radical ((*)OH) generating system, in the present study we demonstrate a dose-dependent attenuation of 6-OHDA generation by melatonin in vitro. Intra-median forebrain bundle infusion of FAD caused significant depletion of striatal dopamine (DA), which was blocked by melatonin. Per-oral administration of l-3,4-dihydroxyphenylalanine (L-DOPA) for 7 days caused a dose-dependent increase in the formation of 6-OHDA in the mouse striatum, which was increased synergistically by the systemic administration of the parkinsonian neurotoxin, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) on the 7th day of L-DOPA treatment. Melatonin treatment significantly attenuated both the L-DOPA and MPTP-induced increases in the levels of striatal 6-OHDA, and protected against striatal DA depletion caused by the neurotoxin. These observations suggest a novel mode of melatonin-induced dopaminergic neuroprotection in two models of Parkinson's disease, and suggest the possible therapeutic use of this well-known antioxidant indoleamine neurohormone in parkinsonism.

Free and Peptide-bound DOPA Can Inhibit Initiation of Low Density Lipoprotein Oxidation

Hydroxyl radicals have been shown to convert free tyrosine to 3,4-dihydroxyphenyl-alanine (DOPA) which has reducing properties. During protein or peptide oxidation such reducing species are also formed from tyrosine residues. Free DOPA or peptide-bound DOPA (PB-DOPA) is able to promote radical-generating events, facilitating the damage of biomolecules such as nucleic acids. Radical induced lipid oxidation in low density lipoprotein (LDL) transforms the lipoprotein into an atherogenic particle. As PB-DOPA has been found in atherosclerotic plaques, we tested the ability of free and PB-DOPA to influence LDL oxidation. Free DOPA, in contrast to tyrosine had strong inhibitory action on both, the copper-ion initiated and metal ion independent (AAPH-induced) lipid oxidation. Free DOPA also inhibited LDL oxidation induced by the copper transport protein ceruloplasmin. To test if PB-DOPA was also able to inhibit LDL oxidation, DOPA residues were generated enzymatically in the model peptides insulin and tyr-tyr-tyr, respectively. PB-DOPA formation substantially increased the ability of both molecules to inhibit LDL oxidation by copper or AAPH. We hypothesize that DOPA-peptides and -proteins may have the potential to act as efficacious antioxidants in the atherosclerotic plaque.

Protection against Parkinson's disease progression: clinical experience

Treatments with potential neuroprotective capability for Parkinson's disease (PD) have been investigated in randomized, controlled, clinical trials and other studies since the mid-1980s. Although promising leads have arisen, no therapy has been proven to halt or slow disease progression. Several large-scale studies have highlighted progress in methodology, as well as the frustrations of translating laboratory science to practical applications. This review summarizes findings from clinical trials with several classes of compounds, including monoamine oxidase-B inhibitors (selegiline, lazabemide, rasagiline), dopaminergic drugs (ropinirole, pramipexole, levodopa), antioxidant strategies (alpha-tocopherol), mitochondrial energy enhancers (coenzyme Q(10), creatine), antiapoptotic agents (TCH346, minocycline, CEP-1347), and antiglutamatergic compounds (riluzole). Beyond small-molecule pharmacology, gene therapy approaches, such as delivering neurotrophic substances (e.g., neurturin) by viral vector, are the next generation of treatment options.

Vitamin A potently destabilizes preformed α-synuclein fibrils in vitro: Implications for Lewy body diseases

Alpha-synuclein (alphaS) is the major component of the filamentous inclusions that constitute defining characteristics of Lewy body diseases (LBD) and multiple system atrophy (MSA). Clinically, antioxidant vitamins, such as vitamin E and the vitamin-like substance coenzyme Q10, have been used in the treatment of LBD with some efficacy. Using fluorescence spectroscopy with thioflavin S, electron microscopy and atomic force microscopy, here we examined the effects of ten antioxidant vitamins and vitamin-like substances, vitamin A (retinol, retinal and retinoic acid), beta-carotene, vitamins B2, B6, C, E, coenzyme Q10 and alpha-lipoic acid, on the formation of alphaS fibrils (falphaS) and on preformed falphaS. Among them, vitamin A, beta-carotene and coenzyme Q10 dose-dependently inhibited the formation of falphaS. Moreover, they also dose-dependently destabilized preformed falphaS. With such potent anti-fibrillogenic as well as fibril-destabilizing activities, these compounds could be useful in the treatment and prevention of LBD and MSA.

Anti-fibrillogenic and fibril-destabilizing activities of anti-Parkinsonian agents for α-synuclein fibrils in vitro

The aggregation of alpha-synuclein (alphaS) in the brain has been implicated as a critical step in the development of Lewy body diseases (LBD) and multiple system atrophy (MSA). Among the antioxidant strategies proposed, increasing evidence points to the possibility of achieving neuroprotection by dopamine agonists, as well as monoamine oxidase B inhibitors. We showed previously that the anti-Parkinsonian agents dose-dependently inhibited beta-amyloid fibrils (fAbeta)(1-40) and fAbeta(1-42) formation as well as destabilized preformed fAbetas. Using fluorescence spectroscopy with thioflavin S, electron microscopy, and atomic force microscopy, we examined the effects of anti-Parkinsonian agents, selegiline, dopamine, pergolide, bromocriptine, and trihexyphenidyl on the formation of alphaS fibrils (falphaS) and on preformed falphaS. All molecules except for trihexyphenidyl, dose-dependently inhibited the formation of falphaS. Moreover, these molecules dose-dependently destabilized preformed falphaS. The overall activity of the molecules examined was in the order of: selegiline = dopamine > pergolide > bromocriptine. These agents and other compounds related structurally could be key molecules for the development of therapeutics for LBD and MSA.

Effect of dopamine on rat diaphragm apoptosis and muscle performance

The purpose of this study was to determine whether dopamine (DA) decreases diaphragm apoptosis and attenuates the decline in diaphragmatic contractile performance associated with repetitive isometric contraction using an in vitro diaphragm preparation. Strenuous diaphragm contractions produce free radicals and muscle apoptosis. Dopamine is a free radical scavenger and, at higher concentrations, increases muscle contractility by simulating beta2-adrenoreceptors. A total of 47 male Sprague-Dawley rats weighing 330-450 g were used in a prospective, randomized, controlled in vitro study. Following animal anaesthetization, diaphragms were excised, and muscle strips prepared and placed in a temperature-controlled isolated tissue bath containing Krebs-Ringer solution (KR) or KR plus 100 microm DA. The solutions were equilibrated with oxygen (O2) at 10, 21 or 95% and 5% carbon dioxide, with the balance being nitrogen. Diaphragm isometric twitch and subtetanic contractions were measured intermittently over 65 min. The diaphragms were then removed and, using a nuclear differential dye uptake method, the percentages of normal, apoptotic and necrotic nuclei were determined using fluorescent microscopy. There were significantly fewer apoptotic nuclei in the DA group diaphragms than in the KR-only group diaphragms in 10 and 21% O2 following either twitch or subtetanic contractions. Dopamine at 100 microm produced only modest increases in muscle performance in both 10 and 21% O2. The attenuation of apoptosis by DA was markedly greater than the effect of DA on muscle performance. Dopamine decreased diaphragmatic apoptosis, perhaps by preventing the activation of intricate apoptotic pathways, stimulating antiapoptotic mechanisms and/or scavenging free radicals.

Apomorphine-induced myocardial protection is due to antioxidant and not adrenergic/dopaminergic effects

Apomorphine (Apo), a dopaminergic agonist used for treatment of Parkinson disease, is a potent antioxidant. In addition to its antioxidative effects, the dopaminergic and adrenergic effects of Apo were studied. Isolated perfused rat hearts were exposed to 25 min of no-flow global ischemia (37 degrees C) and 60 min of reperfusion (I/R, control). Drugs were introduced for the first 20 min of reperfusion. The LVDP of the control group recovered to 54.6 +/- 3.3%. Apo-treated hearts had significantly improved recovery (61.6 +/- 5%, p < 0.05). The recovery of the work index LVDP x HR was even bigger: 67.8 +/- 3.7% (Apo treatment) vs 41.7 +/- 4.6% (control, p < 0.001). Haloperidol, a dopaminergic antagonist, did not affect the recovery with Apo. Propranolol, a beta-adrenergic blocker, initially inhibited the effect of Apo. However, the recovery of the combined group (Apo + propranolol) increased and reached significance (LVDP, p < 0.05 vs control group) after cessation of propranolol perfusion. At 60 min of reperfusion this group was superior to Apo-treated hearts (LVDP, p < 0.05). Propranolol (without Apo) did not improve the hemodynamic recovery. The same pattern of recovery applies also to the recovery of the +dP/dt during the reperfusion. L-DOPA was less effective than Apo. I/R caused significant increase in carbonylation of proteins. Apomorphine inhibited the increase in carbonylation. Haloperidol did not affect this beneficial effect of Apo. L-DOPA significantly decreased the carbonylation of proteins. We conclude that the antioxidative effect of Apo is its main mechanism of cardioprotection.

Antioxidant compounds have potent anti-fibrillogenic and fibril-destabilizing effects for alpha-synuclein fibrils in vitro

The aggregation of alpha-synuclein (alphaS) in the brain has been implicated as a critical step in the development of Lewy body diseases (LBD) and multiple system atrophy (MSA). Various antioxidants not only inhibit the formation of beta-amyloid fibrils (fAbeta), but also destabilize preformed fAb in vitro. Using fluorescence spectroscopy with thioflavin S and electron microscopy, here we examined the effects of the antioxidants nordihydroguaiaretic acid, curcumin, rosmarinic acid, ferulic acid, wine-related polyphenols [tannic acid, myricetin, kaempferol (+)-catechin and (-)-epicatechin], docosahexaenoic acid, eicosapentaenoic acid, rifampicin and tetracycline on the formation of alphaS fibrils (falphaS) and on preformed falphaS. All molecules, except for docosahexaenoic acid and eicosapentaenoic acid, dose-dependently inhibited the formation of falphaS. Moreover, these molecules dose-dependently destabilized preformed falphaS. The overall activity of the molecules examined was in the order of: tannic acid=nordihydroguaiaretic acid=curcumin=rosmarinic acid=myricetin>kaempferol=ferulic acid>(+)-catechin=(-)-epicatechin>rifampicin=tetracycline. These compounds with anti-fibrillogenic as well as antioxidant activities could be key molecules for the development of preventives and therapeutics for LBD and MSA as well as Alzheimer's disease.

Anti-Parkinsonian agents have anti-amyloidogenic activity for Alzheimer's β-amyloid fibrils in vitro

Inhibition of the accumulation of amyloid beta-peptide (Abeta) and the formation of beta-amyloid fibrils (fAbeta) from Abeta, as well as the destabilization of preformed fAbeta in the central nervous system would be attractive therapeutic targets for the treatment of Alzheimer's disease (AD). Many studies have demonstrated that oxidative damage plays a central role in AD pathogenesis, as well as Parkinson disease (PD). Among the antioxidant strategies proposed, increasing evidence points to the possibility of achieving neuroprotection by dopamine agonists, as well as monoamine oxidase B (MAO-B) inhibitors. Actually, the beneficial effect of selegiline, a MAO-B inhibitor, in AD has been noted in several clinical studies. On the reverse, antimuscarinic agents have been reported to accelerate beta-amyloidosis and senile plaque formation in PD. Using fluorescence spectroscopic analysis with thioflavin T and electron microscopic studies, we examined the effects of anti-Parkinsonian agents, dopamine, levodopa, pergolide, bromocriptine, selegiline, and trihexyphenidyl on the formation, extension, and destabilization of fAbeta(1-40) and fAbeta(1-42) at pH 7.5 at 37 degrees C in vitro. The anti-Parkinsonian agents other than trihexyphenidyl dose-dependently inhibited fAbeta formation from Abeta(1-40) and Abeta(1-42), as well as their extension. Moreover, these agents dose-dependently destabilized preformed fAbetas. The overall activity of the molecules examined was in the order of: dopamine>selegiline>levodopa=pergolide>bromocriptine. Although the exact mechanism of the anti-amyloidogenic activity of these agents is unclear, these and other structurally related compounds could be key molecules for the development of therapeutics for AD and other conformational diseases.

Production of reactive oxygen species following acute ethanol or acetaldehyde and its reduction by acamprosate in chronically alcoholized rats

The salicylate trap method, combined with microdialysis, has been used to validate whether reactive oxygen species, particularly hydroxyl radicals, ((*)OH), are generated in the hippocampus of male Wistar rats after acute intraperitoneal administration of either ethanol, 2 and 3 g/kg, or acetaldehyde, 200 mg, or during the initial stages of ethanol withdrawal after chronic ethanol intoxication. Salicylate (5 mM) was infused into the hippocampus via the microdialysis probe and the products of its metabolism by hydroxyl radical, particularly 2,3-dihydroxybenzoic acid (2,3-DHBA) as well as 2,5-dihydroxybenzoic acid (2,5-DHBA) assayed by HPLC (High Pressure Liquid Chromatography). Acetaldehyde, 200 mg/kg, and the higher acute dose of ethanol, 3 g/kg, induced transitory increases in 2,3-DHBA and 2,5-DHBA microdialysate content. At the cessation of four weeks of chronic ethanol intoxication, (by the vapour inhalation method), the mean blood alcohol level was 1.90 g/l. Significant increases of microdialysate 2,3-DHBA and 2,5-DHBA levels were assayed 3 h after alcohol withdrawal which were sustained for a further 5 and 1 h 40 min respectively. Oral administration of Acamprosate, 400 mg/kg/day, during the chronic ethanol intoxication procedure prevented the increased formation of 2,3- and 2,5-DHBA by comparison to rats chronically ethanol intoxicated alone.

Dopamine inhibits cell growth and cell cycle by blocking ribonucleotide reductase

Dopamine (DA) is a classical neurotransmitter modulating various brain functions by acting on its specific receptors. In addition, DA is a reactive molecule that has been implicated in neurodegeneration, especially in Parkinson's disease. Here we show that DA inhibited cell growth of dopamine transporter transfected cells by intracellularly blocking cell cycle progression. To pinpoint the site of this effect, we measured DNA distribution and 5-bromo-2'-deoxyuridine (BrdU) incorporation, as well as the levels of the key cell cycle proteins. DA increased number of cells with a G1 DNA content, decreased BrdU incorporation and simultaneously increased cyclin A but had no effect on cyclin D2, D3, E, nor on cdk4 and p21. These results narrowed down the DA effect to the beginning of S phase, suggesting inhibition of the ribonucleotide reductase, an enzyme essential for DNA synthesis. Indeed, measurement of enzyme activity in situ revealed that DA, within 1h of addition to cells labelled with [3H]cytidine, strongly reduced the cell content of [3H]2'-deoxycytidine 5'-triphophate. The time course of this DA effect preceded the cell cycle progression. This novel molecular mechanism of intracellular DA action independent of plasmamembrane receptors may be involved in processes controlling the development and survival of brain dopaminergic neurons.