Molecular mechanism in activation of glutathione system by ropinirole, a selective dopamine D2 agonist

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.

Glutathione and Related Molecules in Parkinsonism

Glutathione (GSH) is the most abundant intrinsic antioxidant in the central nervous system, and its substrate cysteine readily becomes the oxidized dimeric cystine. Since neurons lack a cystine transport system, neuronal GSH synthesis depends on cystine uptake via the cystine/glutamate exchange transporter (xCT), GSH synthesis, and release in/from surrounding astrocytes. Transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2), a detoxifying master transcription factor, is expressed mainly in astrocytes and activates the gene expression of various phase II drug-metabolizing enzymes or antioxidants including GSH-related molecules and metallothionein by binding to the antioxidant response element (ARE) of these genes. Accumulating evidence has shown the involvement of dysfunction of antioxidative molecules including GSH and its related molecules in the pathogenesis of Parkinson’s disease (PD) or parkinsonian models. Furthermore, we found several agents targeting GSH synthesis in the astrocytes that protect nigrostriatal dopaminergic neuronal loss in PD models. In this article, the neuroprotective effects of supplementation and enhancement of GSH and its related molecules in PD pathology are reviewed, along with introducing new experimental findings, especially targeting of the xCT-GSH synthetic system and Nrf2–ARE pathway in astrocytes.

A selective D2 dopamine receptor agonist alleviates depression through up-regulation of tyrosine hydroxylase and increased neurogenesis in hippocampus of the prenatally stressed rats

Prenatal stress (PNS) has its negative impact on both the infant hippocampal neurogenesis and pregnancy outcomes in the neonates that serves as a risk factor for postnatal depression in adult offsprings. Therefore, main objectives of the present study were to evaluate the effect of maternal chronic unpredictable mild stress (CUMS) on behavioural changes, levels of oxidative stress, changes in selective developmental signaling genes and neurogenesis in the adult brain of Wistar rats and its reversal through a selective non-ergoline D2 type dopamine receptor (D2R) agonist Ropinirole (ROPI). Effects of ROPI treatment on CUMS induced adult rats offspring were measured by assessment of behavioural tests (sucrose preference test and forced swim test), biomarkers of oxidative stress, protein expression of tyrosine hydroxylase (TH), mRNA expression of SHH, GSK-3β, β-catenin, Notch, brain-derived neurotrophic factor (BDNF), Dopamine receptor 2 (Drd2) and bromodeoxyuridine (BrdU) cell proliferation assay. The oxidative stress, protein and mRNA expression were determined in the hippocampus and prefrontal cortex while the BrdU cell proliferation was observed in the hippocampus of rat brain. PNS induced changes resulted in depression validated by the depression-like behaviours, increased oxidative stress, decreased TH expression, altered expression of selective developmental genes, along with the reduced hippocampal neurogenesis and BDNF expression in the brain of adult offsprings. Chronic ROPI treatment reversed those effects and was equally effective like Imipramine (IMI) treatment. So, the present study suggested that ROPI can be used as an antidepressant drug for the treatment of depressive disorders.

Pyridoxine induces glutathione synthesis via PKM2-mediated Nrf2 transactivation and confers neuroprotection

Oxidative stress is a major pathogenic mechanism in Parkinson's disease (PD). As an important cellular antioxidant, glutathione (GSH) balances the production and incorporation of free radicals to protect neurons from oxidative damage. GSH level is decreased in the brains of PD patients. Hence, clarifying the molecular mechanism of GSH deficiency may help deepen our knowledge of PD pathogenesis. Here we report that the astrocytic dopamine D2 receptor (DRD2) regulates GSH synthesis via PKM2-mediated Nrf2 transactivation. In addition we find that pyridoxine can dimerize PKM2 to promote GSH biosynthesis. Further experiments show that pyridoxine supplementation increases the resistance of nigral dopaminergic neurons to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced neurotoxicity in wild-type mice as well as in astrocytic Drd2 conditional knockout mice. We conclude that dimerizing PKM2 may be a potential target for PD treatment.

Ropinirole hydrochloride remedy for amyotrophic lateral sclerosis - Protocol for a randomized, double-blind, placebo-controlled, single-center, and open-label continuation phase I/IIa clinical trial (ROPALS trial)

Introduction

Amyotrophic lateral sclerosis (ALS) is an intractable and incurable neurological disease. It is a progressive disease characterized by muscle atrophy and weakness caused by selective vulnerability of upper and lower motor neurons. In disease research, it has been common to use mouse models carrying mutations in responsible genes for familial ALS as pathological models of ALS. However, there is no model that has reproduced the actual conditions of human spinal cord pathology. Thus, we developed a method of producing human spinal motor neurons using human induced pluripotent stem cells (iPSCs) and an innovative experimental technique for drug screening. As a result, ropinirole hydrochloride was eventually discovered after considering such results as its preferable transitivity in the brain and tolerability, including possible adverse reactions. Therefore, we explore the safety, tolerability and efficacy of ropinirole hydrochloride as an ALS treatment in this clinical trial.

Methods

The ROPALS trial is a single-center double-blind randomized parallel group-controlled trial of the safety, tolerability, and efficacy of the ropinirole hydrochloride extended-release tablet (Requip CR) at 2- to 16-mg doses in patients with ALS. Twenty patients will be recruited for the active drug group (fifteen patients) and placebo group (five patients). All patients will be able to receive the standard ALS treatment of riluzole if not changed the dosage during this trial. The primary outcome will be safety and tolerability at 24 weeks, defined from the date of randomization. Secondary outcome will be the efficacy, including any change in the ALS Functional Rating Scale-Revised (ALSFRS-R), change in the Combined Assessment of Function and Survival (CAFS), and the composite endpoint as a sum of Z-transformed scores on various clinical items. Notably, we will perform an explorative search for a drug effect evaluation using the patient-derived iPSCs to prove this trial concept. Eligible patients will have El Escorial Possible, clinically possible and laboratory-supported, clinically probable, or clinically definite amyotrophic lateral sclerosis with disease duration less than 60 months (inclusive), an ALSFRS-R score ≥2 points on all items and age from 20 to 80 years.

Conclusion

Patient recruitment began in December 2018 and the last patient is expected to complete the trial protocol in November 2020.

Trial registration

Current controlled trials UMIN000034954 and JMA-IIA00397.

Protocol version

version 1.6 (Date; 5/Apr/2019).

Distinct Effects of Chronic Dopaminergic Stimulation on Hippocampal Neurogenesis and Striatal Doublecortin Expression in Adult Mice

While adult neurogenesis is considered to be restricted to the hippocampal dentate gyrus (DG) and the subventricular zone (SVZ), recent studies in humans and rodents provide evidence for newly generated neurons in regions generally considered as non-neurogenic, e.g., the striatum. Stimulating dopaminergic neurotransmission has the potential to enhance adult neurogenesis in the SVZ and the DG most likely via D2/D3 dopamine (DA) receptors. Here, we investigated the effect of two distinct preferential D2/D3 DA agonists, Pramipexole (PPX), and Ropinirole (ROP), on adult neurogenesis in the hippocampus and striatum of adult naïve mice. To determine newly generated cells in the DG incorporating 5-bromo-2'-deoxyuridine (BrdU) a proliferation paradigm was performed in which two BrdU injections (100 mg/kg) were applied intraperitoneally within 12 h after a 14-days-DA agonist treatment. Interestingly, PPX, but not ROP significantly enhanced the proliferation in the DG by 42% compared to phosphate buffered saline (PBS)-injected control mice. To analyze the proportion of newly generated cells differentiating into mature neurons, we quantified cells co-expressing BrdU and Neuronal Nuclei (NeuN) 32 days after the last of five BrdU injections (50 mg/kg) applied at the beginning of 14-days DA agonist or PBS administration. Again, PPX only enhanced neurogenesis in the DG significantly compared to ROP- and PBS-injected mice. Moreover, we explored the pro-neurogenic effect of both DA agonists in the striatum by quantifying neuroblasts expressing doublecortin (DCX) in the entire striatum, as well as in the dorsal and ventral sub-regions separately. We observed a significantly higher number of DCX(+) neuroblasts in the dorsal compared to the ventral sub-region of the striatum in PPX-injected mice. These results suggest that the stimulation of hippocampal and dorsal striatal neurogenesis may be up-regulated by PPX. The increased generation of neural cells, both in constitutively active and quiescent neurogenic niches, might be related to the proportional higher D3 receptor affinity of PPX, non-dopaminergic effects of PPX, or altered motor behavior.

Cabergoline, dopamine D2 receptor agonist, prevents neuronal cell death under oxidative stress via reducing excitotoxicity

Several lines of evidence demonstrate that oxidative stress is involved in the pathogenesis of neurodegenerative diseases, including Parkinson's disease. Potent antioxidants may therefore be effective in the treatment of such diseases. Cabergoline, a dopamine D2 receptor agonist and antiparkinson drug, has been studied using several cell types including mesencephalic neurons, and is recognized as a potent radical scavenger. Here, we examined whether cabergoline exerts neuroprotective effects against oxidative stress through a receptor-mediated mechanism in cultured cortical neurons. We found that neuronal death induced by H₂O₂ exposure was inhibited by pretreatment with cabergoline, while this protective effect was eliminated in the presence of a dopamine D₂ receptor inhibitor, spiperone. Activation of ERK1/2 by H₂O₂ was suppressed by cabergoline, and an ERK signaling pathway inhibitor, U0126, similarly protected cortical neurons from cell death. This suggested the ERK signaling pathway has a critical role in cabergoline-mediated neuroprotection. Furthermore, increased extracellular levels of glutamate induced by H₂O₂, which might contribute to ERK activation, were reduced by cabergoline, while inhibitors for NMDA receptor or L-type Ca²⁺ channel demonstrated a survival effect against H₂O₂. Interestingly, we found that cabergoline increased expression levels of glutamate transporters such as EAAC1. Taken together, these results suggest that cabergoline has a protective effect on cortical neurons via a receptor-mediated mechanism including repression of ERK1/2 activation and extracellular glutamate accumulation induced by H₂O₂.

The role of oxidative stress in Parkinson's disease

Oxidative stress plays an important role in the degeneration of dopaminergic neurons in Parkinson's disease (PD). Disruptions in the physiologic maintenance of the redox potential in neurons interfere with several biological processes, ultimately leading to cell death. Evidence has been developed for oxidative and nitrative damage to key cellular components in the PD substantia nigra. A number of sources and mechanisms for the generation of reactive oxygen species (ROS) are recognized including the metabolism of dopamine itself, mitochondrial dysfunction, iron, neuroinflammatory cells, calcium, and aging. PD causing gene products including DJ-1, PINK1, parkin, alpha-synuclein and LRRK2 also impact in complex ways mitochondrial function leading to exacerbation of ROS generation and susceptibility to oxidative stress. Additionally, cellular homeostatic processes including the ubiquitin-proteasome system and mitophagy are impacted by oxidative stress. It is apparent that the interplay between these various mechanisms contributes to neurodegeneration in PD as a feed forward scenario where primary insults lead to oxidative stress, which damages key cellular pathogenetic proteins that in turn cause more ROS production. Animal models of PD have yielded some insights into the molecular pathways of neuronal degeneration and highlighted previously unknown mechanisms by which oxidative stress contributes to PD. However, therapeutic attempts to target the general state of oxidative stress in clinical trials have failed to demonstrate an impact on disease progression. Recent knowledge gained about the specific mechanisms related to PD gene products that modulate ROS production and the response of neurons to stress may provide targeted new approaches towards neuroprotection.

Neuroprotective and anti-stress effect of A68930 in acute and chronic unpredictable stress model in rats

The neurorescuing effect of A68930 (a potent selective D(1) agonist) and its role on the regulation of hypothalamus-pituitary-adrenal (HPA)-axis have been investigated. Acute (AS) and chronic unpredictable (CUS) stress models were used to evaluate the effect of A68930 on HPA-axis regulation in relation to the change in the fiber density and number of immunoreactive (ir) neurons of tyrosine hydroxylase (TH) and glucocorticoid receptor (GR) in the dopamine (DA) and GR rich brain regions in rats. CUS caused a significant decrease in the number of TH ir neurons in the striatum, medial forebrain bundle, ventral tegmental area and substansia nigra and GR in the cortex, striatum and hippocampus as compared to the non-stress controls (NS). Administration of A68930 (0.25mg/kg i.p.) significantly normalized these CUS-induced alterations. We also examined the role of A68930 on stress-induced brain oxidative status. AS enhanced the activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) in the cortex and striatum, while CUS reduced the activities of SOD and catalase (CAT) in the cortex, striatum and hippocampus, when compared with NS. Increased GSH-Px activity, with reduced glutathione and increased lipid peroxidation was observed in both AS and CUS in selected brain regions as compared to NS. Administration of A68930 normalized the antioxidant enzyme activities, replenished GSH and decreased the extent of lipid peroxidation. In conclusion, present findings suggest that the stress-induced immunoreactivity of TH and GR in distinct brain regions are modulated by A68930 leading to the normalization of HPA-axis response. Ours results show the therapeutic importance of DA D(1) agonist in stress-induced dopaminergic-related neurological disorders. A68930 also influenced the brain antioxidant machinery probably through the restoration of stress-induced changes in the dopaminergic system and its crosstalk with GR.

Mitochondria-targeted antioxidant effects of S(-) and R(+) pramipexole

Background

Pramipexole exists as two isomers. The S(-) enantiomer is a potent D₃/D₂ receptor agonist and is extensively used in the management of PD. In contrast, the R(+) enantiomer is virtually devoid of any of the DA agonist effects. Very limited studies are available to characterize the pharmacological spectrum of the R(+) enantiomer of pramipexole.

Results

Using differentiated SH-SY5Y neuroblastoma cells as an experimental model, here we show that S(-) and R(+) pramipexole are endowed with equipotent efficacy in preventing cell death induced by H₂O₂ and inhibiting mitochondrial reactive oxygen species generation. Both pramipexole enantiomers prevented mitochondrial ROS generation with a potency about ten times higher then that elicited for neuroprotection.

Conclusions

These results support the concept of both S(-) and R(+) pramipexole enantiomers as mitochondria-targeted antioxidants and suggest that the antioxidant, neuroprotective activity of these drugs is independent of both the chiral 6-propylamino group in the pramipexole molecule and the DA receptor stimulation.

Potential neuroprotection mechanisms in PD: focus on dopamine agonist pramipexole

BACKGROUND

The death of dopaminergic neurons in Parkinson's disease (PD) appears to have various causes, including oxidative stress, excitotoxicity, mitochondrial dysfunction (and associated apoptosis), ubiquitin/proteasomal dysfunction, and inflammation, any of which could in principle be the therapeutic target of a neuroprotective drug. The biology of dopaminergic neurons offers further potential targets, involving neurotrophic factors, dopamine-neuron genes, and even neurogenesis.

OBJECTIVE

To outline each hypothetical neuroprotective mechanism, the evidence suggesting its relevance to PD, and the research on pharmacologic intervention.

METHODS

A PubMed search was conducted to identify relevant preclinical and clinical literature published between 1989 and 2009. Additional articles were identified by reviewing the reference lists of papers selected in the original search. To circumscribe the survey and facilitate consideration of the conditions required for a neuroprotective effect, emphasis was placed on a single drug class, dopamine agonists, and in particular pramipexole. REVIEW OF THE FIELD: In a variety of in vitro and in vivo PD models, pramipexole exhibited preclinical evidence of neuroprotective actions of all hypothesized types, and in human neuroimaging studies it slowed the rate of loss of markers of dopaminergic function, consistent with drug-conferred neuroprotection in PD itself. Interpretation of the preclinical data was hampered by differences among models and by uncertainties concerning each model's mimicry of PD. Overall, the identified neuroprotection almost always required pretreatment (i.e., before insult) and high drug concentration. Interpretation of the clinical data was hampered by absence of placebo control and of a direct measure of neuroprotection.

CONCLUSIONS

Although the evidence is promising, neuroprotection in PD remains an elusive goal. In whatever form it emerges, neuroprotective therapy would be a strong argument against deferring PD treatment until symptoms are a significant life impediment, and thus would add urgency to early PD identification.

Red beet (Beta vulgaris L.) leaf supplementation improves antioxidant status in C57BL/6J mice fed high fat high cholesterol diet

The effect of diet supplemented with red beet (Beta vulgaris L.) leaf on antioxidant status of plasma and tissue was investigated in C57BL/6J mice. The mice were randomly divided into two groups after one-week acclimation, and fed a high fat (20%) and high cholesterol (1%) diet without (control group) or with 8% freeze-dried red beet leaf (RBL group) for 4 weeks. In RBL mice, lipid peroxidation determined as 2-thiobarbituric acid-reactive substances (TBARS value) was significantly reduced in the plasma and selected organs (liver, heart, and kidney). Levels of antioxidants (glutathione and β-carotene) and the activities of antioxidant enzyme (glutathione peroxidase) in plasma and liver were considerably increased, suggesting that antioxidant defenses were improved by RBL diet. Comet parameters such as tail DNA (%), tail extent moment, olive tail moment and tail length were significantly reduced by 25.1%, 49.4%, 35.4%, and 23.7%, respectively, in plasma lymphocyte DNA of RBL mice compared with control mice, and indicated the increased resistance of lymphocyte DNA to oxidative damage. In addition, the RBL diet controlled body weight together with a significant reduction of fat pad (retroperitoneal, epididymal, inguinal fat, and total fat). Therefore, the present study suggested that the supplementation of 8% red beet leaf in high fat high cholesterol diet could prevent lipid peroxidation and improve antioxidant defense system in the plasma and tissue of C57BL/6J mice.

Effects of dietary supplementation with red-pigmented leafy lettuce (Lactuca sativa) on lipid profiles and antioxidant status in C57BL/6J mice fed a high-fat high-cholesterol diet

The present study was undertaken to assess the beneficial effects of a daily consumption of 8 % freeze-dried red-pigmented leafy lettuce (Lactuca sativa) on CVD. C57BL/6J mice were fed a high-fat high-cholesterol diet supplemented with or without red-pigmented leafy lettuce for 4 weeks. The present results showed that the red-pigmented leafy lettuce-supplemented diet significantly decreased the level of total and LDL-cholesterol and TAG in the plasma of the mice. The atherosclerotic index was calculated to be 46 % lower in the mice fed with the lettuce diet compared with the control diet. Lipid peroxidation measured by 2-thiobarbituric acid-reactive substances was markedly reduced in the plasma, liver, heart and kidney of the mice fed the lettuce diet. The content of antioxidants (total glutathione and beta-carotene) was significantly increased by lettuce supplementation. The antioxidant defence system by antioxidant enzymes including glutathione S-transferase, glutathione peroxidase, glutathione reductase, superoxide dismutase and paraoxanase in blood or liver tissues was also increased, and showed the improved oxidative stress in the mice fed the lettuce diet. The measurement of tail DNA (%), tail extent moment and olive tail moment indicated that the lettuce diet increased the resistance of hepatocyte and lymphocyte DNA to oxidative damage. The present study showed that the supplementation of a high-cholesterol high-fat diet with 8 % red-pigmented leafy lettuce resulted in an improvement of plasma cholesterol and lipid levels, prevention of lipid peroxidation and an increase of the antioxidant defence system and, therefore, could contribute to reduce the risk factors of CVD.

Protection against paraquat and A53T alpha-synuclein toxicity by cabergoline is partially mediated by dopamine receptors

Both genetic and environmental factors are thought to be involved in the aetiology of Parkinson's disease (PD). Oxidative damage, mitochondrial and proteasomal dysfunction, and inflammatory change are considered to participate in PD pathogenesis. Dopamine agonists are used in the symptomatic treatment of PD but attention has recently also been focussed on their potential for use in slowing disease progression. We have studied the protective actions of the D2 dopamine agonist cabergoline in toxin (paraquat) and genetic (wild-type and mutant [A53T] alpha-synuclein) models of PD using SHSY-5Y cells. Cabergoline increased glutathione content, reduced free radical production and caspase-3 activation, increased mitochondrial membrane potential and ameliorated cell death in SHSY-5Y cells exposed to paraquat and this action was inhibited in part by D2 receptor blockade. Cabergoline also reduced the toxicity of wild-type and mutant alpha-synuclein expression following paraquat exposure by similar mechanisms. These results confirm the protective action of cabergoline in reducing cell death in two separate genetic and environmental model systems of PD.

Approaches to prevent dopamine quinone-induced neurotoxicity

Dopamine (DA) and its metabolites containing two hydroxyl residues exert cytotoxicity in dopaminergic neuronal cells, primarily due to the generation of highly reactive DA and DOPA quinones. Quinone formation is closely linked to other representative hypotheses such as mitochondrial dysfunction, inflammation, oxidative stress, and dysfunction of the ubiquitin-proteasome system, in the pathogenesis of neurodegenerative diseases such as Parkinson's disease and methamphetamine-induced neurotoxicity. Therefore, pathogenic effects of the DA quinone have focused on dopaminergic neuron-specific oxidative stress. Recently, various studies have demonstrated that some intrinsic molecules and several drugs exert protective effects against DA quinone-induced damage of dopaminergic neurons. In this article, we review recent studies on some neuroprotective approaches against DA quinone-induced dysfunction and/or degeneration of dopaminergic neurons.

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.

Candidate genes and their regulatory elements: alcohol preference and tolerance

QTL analysis of behavioral traits and mouse brain gene expression studies were combined to identify candidate genes involved in the traits of alcohol preference and acute functional alcohol tolerance. The systematic application of normalization and statistical analysis of differential gene expression, behavioral and expression QTL location, and informatics methodologies resulted in identification of 8 candidate genes for the trait of alcohol preference and 22 candidate genes for acute functional tolerance. Pathway analysis, combined with clustering by ontology, indicated the importance of transcriptional regulation and DNA and protein binding elements in the acute functional tolerance trait, and protein kinases and intracellular signal transduction elements in the alcohol preference trait. A rudimentary search for transcription control elements that could indicate coregulation of the panels of candidate genes produced modest results, implicating SMAD-3 in the regulation of four of the eight candidate genes for alcohol preference. However, the realization of the many caveats related to transcription factor binding site analysis, and attempts to correlate between transcription factor binding and function, forestalled any definitive global analysis of transcriptional control of differentially expressed candidate genes.

Effect of ropinirole on visuo-motor test in newly diagnosed Parkinson's disease patients

OBJECTIVES

The aim of this study was to assess the sensitivity of the visuo-motor test (VMT) compared with the Unified Parkinson's Disease Rating Scale (UPDRS) in newly diagnosed Parkinson's disease (PD) patients.

METHODS

VMT and UPDRS were carried out in 20 patients before treatment onset, 2 weeks after treatment with ropinirole 1.5 mg/day and 2 weeks following increasing the dose of ropinirole to 3.0 mg/day.

RESULTS

Improvement in clinical status was seen in all patients, with a mean UPDRS reduction of 16.6% following treatment with ropinirole 1.5 mg/day, and 38.9% reduction in UPDRS observed with ropinirole 3.0 mg/day. Initial improvement was not correlated with severity of PD, although further improvement with ropinirole 3.0 mg/day correlated linearly with patient's baseline UPDRS. Improvement in the ability to control the direction of the moving hand during tracing is expressed by the reduction of VMT variables following treatment. Mean VMT variables were 36.2% at baseline, 34.0% with ropinirole 1.5 mg/day and 31.7% with ropinirole 3.0 mg/day. Although changes in VMT variables were less uniform across patients, on average, it did correlate with patients UPDRS.

CONCLUSIONS

We suggest that VMT can be useful in the assessment of treatment effect on high-level motor planning and cognitive capabilities in newly diagnosed PD patients, added to the UPDRS which does not appropriately comply with those skills.

L-DOPA treatment from the viewpoint of neuroprotection. Possible mechanism of specific and progressive dopaminergic neuronal death in Parkinson's disease

With regard to the mechanism of selective dopaminergic neuronal death, experimental results of studies on the neurotoxicity of MPTP and rotenone indicate that degeneration of dopamine neurons is closely related to mitochondrial dysfunction, inflammatory process and oxidative stress, particularly with regard to the generation of quinones as dopamine neuron-specific oxidative stress. Thus, it is now clear that the presence of high levels of discompartmentalized free dopamine in dopaminergic neurons may explain the specific vulnerability of dopaminergic neurons through the generation of highly toxic quinones.

Bromocriptine reduces lipid peroxidation and enhances spatial learning and hippocampal neuron survival in a rodent model of focal brain trauma

Oxidative stress is a significant contributor to the secondary sequelae of traumatic brain injury (TBI), and may mediate subsequent neurobehavioral deficits and histopathology. The present study examined the neuroprotective effects of bromocriptine (BRO), a dopamine D2 receptor agonist with significant antioxidant properties, on cognition, histopathology, and lipid peroxidation in a rodent model of focal brain trauma. BRO (5 mg/kg) or a comparable volume of vehicle (VEH) was administered intraperitoneally 15 min prior to cortical impact or sham injury. In experiment 1, spatial learning was assessed in an established water maze task on post-surgery days 14-18, followed by quantification of hippocampal cell survival and cortical lesion volume at 4 weeks. In experiment 2, rats were sacrificed 1 hr post-surgery, and malondialdehyde (MDA), the end product of lipid peroxidation, was measured in the frontal cortex, striatum, and substantia nigra using a thiobarbituric acid reactive substances assay. The TBI+BRO group was significantly more adept at locating a hidden platform in the water maze compared to the TBI+VEH group and also exhibited a greater percentage of surviving CA3 hippocampal neurons. TBI increased MDA in all examined regions of the VEH-treated, but not BRO-treated group versus SHAMs. MDA was significantly decreased in both the striatum (4.22 +/- 0.52 versus 5.60 +/- 0.44 nmol per mg/tissue +/- SEM) and substantia nigra (4.18 +/- 0.35 versus 7.76 +/- 2.05) of the TBI+BRO versus TBI+VEH groups, respectively, while only a trend toward decreased MDA was observed in the frontal cortex (5.44 +/- 0.44 versus 6.96 +/- 0.77). These findings suggest that TBI-induced oxidative stress is attenuated by acute BRO treatment, which may, in part, explain the benefit in cognitive and histological outcome.

Decreased glutathione transferase levels in rd1/rd1 mouse retina: Replenishment protects photoreceptors in retinal explants

Currently much attention is focused on glutathione S transferase (GST)-induced suppression of apoptosis. The objective of our studies was therefore to see if GST isoenzymes rescue photoreceptors in retinal explants from rd1/rd1 mice, in which photoreceptors degenerate rapidly. Eyes from C3H rd1/rd1 and +/+ mice were collected at various time points between postnatal day (PN) 2 and PN28. Localization and content of alpha-GST and mu-GST was investigated by immunofluorescence and semi-quantitative Western blot analysis, respectively. In addition, PN2 and PN7 retinal explants were cultured till PN28, during which they were treated with 10 ng/ml alpha-GST or mu-GST. The spatiotemporal expression of both GST isoforms was closely similar: early presence in ganglion cell layer after which staining became restricted to Muller cells (particularly in the endfeet) and horizontal cell fibers in both rd1/rd1 and +/+. Doublets of alpha-GST and mu-GST were detected by Western blot analysis. Densitometry of these bands indicated steady reduction of alpha-GST content in rd1/rd1 retina starting from the second postnatal week. When alpha-GST and mu-GST were added exogenously to rd1/rd1 explants, photoreceptor rescue was produced that was more prominent in PN2 than in PN7 explants and more effective by alpha-GST than mu-GST. We propose that alpha-GST neuroprotection is mediated by reduction of tissue oxidative stress.

Cabergoline stimulates synthesis and secretion of nerve growth factor, brain-derived neurotrophic factor and glial cell line-derived neurotrophic factor by mouse astrocytes in primary culture

Neuroprotection is the primary concern in patients with newly diagnosed Parkinson's disease. The D2/weak D1 dopamine agonist cabergoline elicits neuroprotection by antioxidation and scavenging free radicals, and may protect neurons by up-regulating endogenous neurotrophic factors synthesis in the brain. In primary cultured mouse astrocytes, cabergoline 37 micromol/l immediately elevated concentrations of nerve growth factor, brain-derived neurotrophic factor, and glial cell line-derived neurotrophic factor (GDNF) in culture medium, reaching 9.9-, 2.6- and 30-fold, respectively, of control levels at 16 h. Relative mRNA levels were 3.0-, 1.5- and 1.9-fold, respectively, of controls at 3 h. These effects may be mediated partly by the dopamine D2 receptor. Cabergoline may be a good candidate for an inducer of GDNF, which may have neuroprotective and neurorestorative properties in dopaminergic nigral neurons.

Plasma and CSF markers of oxidative stress are increased in Parkinson's disease and influenced by antiparkinsonian medication

We determined systemic oxidative stress in Parkinson's disease (PD) patients, patients with other neurological diseases (OND) and healthy controls by measurement of in vitro lipoprotein oxidation and levels of hydro- and lipophilic antioxidants in plasma and cerebrospinal fluid (CSF). Additionally, we investigated the influence of levodopa (LD) and dopamine agonist therapy (DA) on the oxidative status in PD patients. We found increased oxidative stress, seen as higher levels of lipoprotein oxidation in plasma and CSF, decrease of plasma levels of protein sulfhydryl (SH) groups and lower CSF levels of alpha-tocopherol in PD patients compared to OND patients and controls. Levodopa treatment did not significantly change the plasma lipoprotein oxidation but LD monotherapy tended to result in an increase of autooxidation and in a decrease of plasma antioxidants with significance for ubiquinol-10. DA monotherapy was significantly associated with higher alpha-tocopherol levels. Patients with DA monotherapy or co-medication with DA showed a trend to lower lipoprotein oxidation. These data support the concept of oxidative stress as a factor in the pathogenesis of PD and might be an indicator of a potential prooxidative role of LD and a possible antioxidative effect of DA in PD treatment.

Neuroprotective mechanisms of antiparkinsonian dopamine D2-receptor subfamily agonists

Numerous studies have shown that endogenous and/or environmental neurotoxins and oxidative stress may participate in the pathogenesis of Parkinson's disease (PD), but the detailed mechanisms are still unclear. While dopamine (DA) replacement therapy with L-DOPA (levodopa) improves PD symptoms, it does not inhibit the degeneration of DA neurons in the substantia nigra. Recently, bromocriptine, pramipexole and several other agonists of the dopamine D2-receptor subfamily (including D2, D3 and D4-subtypes) have been shown to have neuroprotective effects in parkinsonian models in vitro and in vivo. Their neuroprotective effects may be mediated directly and/or indirectly by antioxidant effects, mitochondrial stabilization or induction of the antiapoptotic Bcl-2 family.

Apoptosis-inducing neurotoxicity of dopamine and its metabolites via reactive quinone generation in neuroblastoma cells

Neurotoxic properties of L-dopa and dopamine (DA)-related compounds were assessed in human neuroblastoma SH-SY5Y cells with reference to their structural relationship. L-Dopa and its metabolites containing two free hydroxyl residues on their benzene ring showed toxicity in the cell, which was prevented by superoxide dismutase (SOD) and reduced glutathione (GSH), but not by catalase. Furthermore, a synthetic derivative of DA, 3-hydroxy-4-methoxyphenethylamine (HMPE) containing methoxy residue at position 4 in the benzene ring, exerted partial cytotoxicity, which was not prevented by SOD, GSH or catalase. However, the metabolites containing methoxy residue at position 3 failed to show a toxic effect in the SH-SY5Y cells. Moreover, DA induced apoptotic cell death, which was observed by nuclear and terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) staining and measurement of caspase-3 activity; this compound up-regulated apoptotic factor p53 while down-regulating anti-apoptotic factor Bcl-2. In the cell-free in vitro electron spin resonance (ESR) spectrometry, DA possessing two hydroxyl groups showed generation of DA-semiquinone radicals, which were markedly prevented by addition of SOD or GSH but not by catalase. On the other hand, methylation of one of the hydroxyl residues on the benzene ring of DA converted DA to an unoxidizable compound (3-MT or HMPE), and caused it to lose the property to produce semiquinone radicals. It has been previously reported that SOD acting as a superoxide:semiquinone oxidoreductase prevents quinone formation, and that reduced GSH through forming a complex with DA-quinone prevents quinone binding to the thiol group of the intact protein. Therefore, the present results suggest that DA and its metabolites containing two hydroxyl residues exert cytotoxicity mainly due to generation of highly reactive quinones.

The dopamine agonist cabergoline provides neuroprotection by activation of the glutathione system and scavenging free radicals

Free radicals are involved in the pathogenesis and/or progression of Parkinson's disease (PD). Several ergot derivative dopamine (DA) agonists have been reported to scavenge free radicals in vitro and to show a neuroprotective effect in vivo. We investigated the in vitro free radical scavenging and antioxidant activities of cabergoline, a long-acting ergot DA agonist, as well as its ability to activate glutathione (GSH), catalase (Cat) and superoxide dismutase (SOD) activating effects and its in vivo neuroprotective properties against 6-hydroxydopamine (6-OHDA) intracerebroventricularly (i.c.v.) in mice. The striatal DA turnover induced by i.c.v. injection of 6-OHDA was completely normalized by pretreatment with cabergoline. Moreover, cabergoline scavenged free radicals in vitro and significantly reduced lipid peroxidation in vitro and in vivo. Furthermore, daily administration of cabergoline to mice significantly increased striatal GSH levels by activation of RNA expressions of GSH-related enzymes, although striatal Cat and SOD activities did not change. In addition, our present results suggest that repeated administration of cabergoline attenuates both 6-OHDA-induced nigrostriatal DAergic dysfunction and DA neuronal cell death, since cabergoline also had a neuroprotective effect in the immunohistochemical experiment. In conclusion, our findings indicate that the multiple antioxidant mechanisms of cabergoline, such as activation of the GSH system and the direct free radical scavenging activity, may explain the neuroprotective effect of this ergot DA agonist.

Attenuation of working memory and spatial acquisition deficits after a delayed and chronic bromocriptine treatment regimen in rats subjected to traumatic brain injury by controlled cortical impact

Cognitive impairments are pervasive and persistent sequelae of human traumatic brain injury (TBI). In vivo models of TBI, such as the controlled cortical impact (CCI) and fluid percussion (FP), are utilized extensively to produce deficits reminiscent of those seen clinically with the hope that empirical study will lead to viable therapeutic interventions. Both CCI and FP produce spatial learning acquisition deficits, but only the latter has been reported to impair working memory in rats tested in the Morris water maze (MWM). We hypothesized that a CCI injury would impair working memory similarly to that produced by FP, and that delayed and chronic treatment with the D2 receptor agonist bromocriptine would attenuate both working memory and spatial learning acquisition deficits. To test these hypotheses, isoflurane-anesthetized adult male rats received either a CCI (2.7 mm deformation, 4 m/sec) or sham injury, and 24 h later were administered bromocriptine (5 mg/kg, i.p.) or vehicle, with continued daily injections until all behavioral assessments were completed. Motor function was assessed on beam balance and beam walking tasks on postoperative days 1-5 and cognitive function was evaluated in the MWM on days 11-15 for working memory (experiment 1) and on days 14-18 for spatial learning acquisition (experiment 2). Histological examination (hippocampal CA1 and CA3 cell loss/survival and cortical lesion volume) was conducted 4 weeks after surgery. All injured groups exhibited initial impairments in motor function, working memory, and spatial learning acquisition. Bromocriptine did not affect motor function, but did ameliorate working memory and significantly attenuated spatial acquisition deficits relative to the injured vehicle-treated controls. Additionally, the injured bromocriptine-treated group exhibited significantly more morphologically intact CA3 neurons than the injured vehicle-treated group (55.60 +/- 3.10% vs. 38.34 +/- 7.78% [p = 0.03]). No significant differences were observed among TBI groups in CA1 cell survival (bromocriptine, 40.26 +/- 4.74% vs. vehicle, 29.13 +/- 6.63% [p = 0.14]) or cortical lesion volume (bromocriptine, 17.78 +/- 0.62 mm3 vs. vehicle, 19.01 +/- 1.49 mm3 [p > 0.05]). These data reveal that CCI produces working memory deficits in rats that are similar to those observed following FP, and that the delayed and chronic bromocriptine treatment regimen conferred cognitive and neural protection after TBI.

GPI1046 prevents dopaminergic dysfunction by activating glutathione system in the mouse striatum

We investigated both the antioxidant activities of GPI1046, a non-immunosuppressive derivative of FK506, and the in vivo neuroprotective properties against toxicity of intracerebroventricular 6-hydroxydopamine (6-OHDA) in mice. The 6-OHDA-induced reduction in dopamine and its metabolites in the striatum was significantly normalized by daily administration of GPI1046. Moreover, GPI1046 significantly reduced lipid peroxidation in vivo. Further, GPI1046 significantly increased striatal glutathione (GSH) levels by activating GSH synthesis, although the striatal catalase and superoxide dismutase activities did not change. We conclude that GPI1046 may have neuroprotective effects both in cell cultures and in vivo.

Antiparkinsonian drugs and their neuroprotective effects

In Parkinson's disease, while dopamine (DA) replacement therapy, such as with L-DOPA (levodopa), improves the symptoms, it does not inhibit the degeneration of DA neurons in the substantia nigra. Numerous studies have suggested that both endogenous and environmental neurotoxins and oxidative stress may participate in this disease, but the detailed mechanisms are still unclear. Recent genetic studies in familial Parkinson's disease and parkinsonism have shown several gene mutations. This new information regarding its pathogenesis offers novel prospects for effective strategies involving the neuroprotection of vulnerable DA neurons. This review summarizes current findings regarding the pathogenesis and antiparkinsonian drugs, and discusses their possibilities of targets to develop novel neuroprotective drugs.