Fucoxanthin Prevents Long-Term Administration l-DOPA-Induced Neurotoxicity through the ERK/JNK-c-Jun System in 6-OHDA-Lesioned Mice and PC12 Cells.

As the most abundant marine carotenoid extracted from seaweeds, fucoxanthin is considered to have neuroprotective activity via its excellent antioxidant properties. Oxidative stress is regarded as an important starting factor for neuronal cell loss and necrosis, is one of the causes of Parkinson's disease (PD), and is considered to be the cause of adverse reactions caused by the current PD commonly used treatment drug levodopa (l-DA). Supplementation with antioxidants early in PD can effectively prevent neurodegeneration and inhibit apoptosis in dopaminergic neurons. At present, the effect of fucoxanthin in improving the adverse effects triggered by long-term l-DA administration in PD patients is unclear. In the present study, we found that fucoxanthin can reduce cytotoxicity and suppress the high concentration of l-DA (200 µM)-mediated cell apoptosis in the 6-OHDA-induced PC12 cells through improving the reduction in mitochondrial membrane potential, suppressing ROS over-expression, and inhibiting active of ERK/JNK-c-Jun system and expression of caspase-3 protein. These results were demonstrated by PD mice with long-term administration of l-DA showing enhanced motor ability after intervention with fucoxanthin. Our data indicate that fucoxanthin may prove useful in the treatment of PD patients with long-term l-DA administration.

Effects of histone acetyltransferase inhibitors on L-DOPA-induced dyskinesia in a murine model of Parkinson's disease.

Histone acetylation is a key regulatory factor for gene expression in cells. Modulation of histone acetylation by targeting of histone acetyltransferases (HATs) effectively alters many gene expression profiles and synaptic plasticity in the brain. However, the role of HATs on L-DOPA-induced dyskinesia of Parkinson's disease (PD) has not been reported. Our aim was to determine whether HAT inhibitors such as anacardic acid, garcinol, and curcumin from natural plants reduce severity of L-DOPA-induced dyskinesia using a unilaterally 6-hydroxydopamine (6-OHDA)-lesioned PD mouse model. Anacardic acid 2 mg/kg, garcinol 5 mg/kg, or curcumin 100 mg/kg co-treatment with L-DOPA significantly reduced the axial, limb, and orofacial (ALO) score indicating less dyskinesia with administration of HAT inhibitors in 6-OHDA-lesioned mice. Additionally, L-DOPA's efficacy was not altered by the compounds in the early stage of treatment. The expression levels of c-Fos, Fra-2, and Arc were effectively decreased by administration of HAT inhibitors in the ipsilateral striatum. Our findings indicate that HAT inhibitor co-treatment with L-DOPA may have therapeutic potential for management of L-DOPA-induced dyskinesia in patients with PD.

Ombuoside from Gynostemma pentaphyllum Protects PC12 Cells from L-DOPA-Induced Neurotoxicity.

This study investigated the effects of ombuoside on L-3,4-dihydroxyphenylalanine (L-DOPA)-induced neurotoxicity in PC12 cells. Ombuoside did not affect cell viability at concentrations of up to 50 µM for 24 h, and ombuoside (1, 5, and 10 µM) significantly inhibited L-DOPA-induced (100 and 200 µM) decreases in cell viability. L-DOPA (100 and 200 µM) induced sustained phosphorylation of extracellular signal-regulated kinases (ERK1/2) for 6 h, which were significantly decreased by cotreatments with ombuoside (1, 5, and 10 µM). L-DOPA (100 and 200 µM) alone significantly increased c-Jun N-terminal kinase (JNK1/2) phosphorylation for 6 h and cleaved-caspase-3 expression for 24 h, both of which were partially, but significantly, blocked by ombuoside (1, 5, and 10 µM). In addition, ombuoside (1, 5, and 10 µM) significantly restored the L-DOPA-induced (100 and 200 µM) decrease in superoxide dismutase (SOD) activity for 24 h. Taken together, these findings indicate that ombuoside protects against L-DOPA-induced neurotoxicity by inhibiting L-DOPA-induced increases in sustained ERK1/2 and JNK1/2 phosphorylation and caspase-3 expression and L-DOPA-induced decrease in SOD activity in PC12 cells. Thus, ombuoside might represent a novel neuroprotective agent that warrants further study.

Ninety-day Local Tolerability and Toxicity Study of ND0612, a Novel Formulation of Levodopa/Carbidopa, Administered by Subcutaneous Continuous Infusion in Minipigs.

A 90-day study in Göttingen minipigs was conducted to test the local tolerability and systemic toxicity of ND0612, a novel aqueous solution of carbidopa (CD)/levodopa (LD) intended for the treatment of Parkinson's disease by continuous subcutaneous administration using a discrete infusion pump. To evaluate tissue site reactions, we used a unique study design involving multiple infusion sites to evaluate the effect of dose per site (270/63, 360/45, and 360/84 mg LD/CD), volume of infusion per site (4.5 and 6 ml per site), formulation concentration (60/14 and 60/7.5 mg/ml LD/CD), daily rate of infusion per site (240 µl/hr for16 hr and 80 µl/hr for 8 hr, 320 µl/hr for 16 hr and 100 µl/hr for 8 hr, or 750 µl/hr for 8 hr), frequency (once every 5, 10, 15, or 20 days), and number of infusions (4, 6, or 9) to the same infusion site. No systemic adverse effects were observed. Histopathological changes at infusion sites started with localized minimal necrosis and acute inflammation that progressed to subacute and chronic inflammatory and reparative changes with evidence of progressive recovery following the final infusion. None of the infusion site effects were judged to be adverse, and clinical exposures to ND0612 are not expected to result in adverse responses.

Protective effect of two essential oils isolated from Rosa damascena Mill. and Lavandula angustifolia Mill, and two classic antioxidants against L-dopa oxidative toxicity induced in healthy mice.

Levodopa (L-dopa) is a "gold standard" and most effective symptomatic agent in the Parkinson's disease (PD) treatment. The several treatments have been developed in an attempt to improve PD treatment, but most patients were still levodopa dependent. The issue of toxicity was raised in vitro studies, and suggests that L-dopa can be toxic to dopaminergic neurons, but it is not yet entirely proven. L-dopa prolonged treatment is associated with motor complications and some limitations. Combining the L-dopa therapy with antioxidants can reduce related sideeffects and provide symptomatic relief. The natural antioxidants can be isolated from any plant parts such as seeds, leaves, roots, bark, etc., and their extracts riched in phenols can retard the oxidative degradation of the lipids, proteins and DNA. Thus, study suggests that combination of essential oils (Rose oil and Lavender oil), Vitamin C and Trolox with Ldopa can reduce oxidative toxicity, and may play a key role in ROS/RNS disarm.

An evaluation of istradefylline treatment on Parkinsonian motor and cognitive deficits in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated macaque models.

Istradefylline (KW-6002), an adenosine A2A receptor antagonist, is used adjunct with optimal doses of L-3,4-dihydroxyphenylalanine (l-DOPA) to extend on-time in Parkinson's disease (PD) patients experiencing motor fluctuations. Clinical application of istradefylline for the management of other l-DOPA-induced complications, both motor and non-motor related (i.e. dyskinesia and cognitive impairments), remains to be determined. In this study, acute effects of istradefylline (60-100 mg/kg) alone, or with optimal and sub-optimal doses of l-DOPA, were evaluated in two monkey models of PD (i) the gold-standard 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated macaque model of parkinsonian and dyskinetic motor symptoms and (ii) the chronic low dose (CLD) MPTP-treated macaque model of cognitive (working memory and attentional) deficits. Behavioural analyses in l-DOPA-primed MPTP-treated macaques showed that istradefylline alone specifically alleviated postural deficits. When combined with an optimal l-DOPA treatment dose, istradefylline increased on-time, enhanced therapeutic effects on bradykinesia and locomotion, but exacerbated dyskinesia. Istradefylline treatment at specific doses with sub-optimal l-DOPA specifically alleviated bradykinesia. Cognitive assessments in CLD MPTP-treated macaques showed that the attentional and working memory deficits caused by l-DOPA were lowered after istradefylline administration. Taken together, these data support a broader clinical use of istradefylline as an adjunct treatment in PD, where specific treatment combinations can be utilised to manage various l-DOPA-induced complications, which importantly, maintain a desired anti-parkinsonian response.

The novel 5-HT1A receptor agonist, NLX-112 reduces l-DOPA-induced abnormal involuntary movements in rat: A chronic administration study with microdialysis measurements.

Although l-DOPA alleviates the motor symptoms of Parkinson's disease (PD), it elicits troublesome l-DOPA-induced dyskinesia (LID) in a majority of PD patients after prolonged treatment. This is likely due to conversion of l-DOPA to dopamine as a 'false neurotransmitter' from serotoninergic neurons. The highly selective and efficacious 5-HT1A receptor agonist, NLX-112 (befiradol or F13640) shows potent activity in a rat model of LID (suppression of Abnormal Involuntary Movements, AIMs) but its anti-AIMs effects have not previously been investigated following repeated administration. Acute administration of NLX-112 (0.04 and 0.16 mg/kg i.p.) reversed l-DOPA (6 mg/kg)-induced AIMs in hemiparkinsonian rats with established dyskinesia. The activity of NLX-112 was maintained following repeated daily i.p. administration over 14 days and was accompanied by pronounced decrease of striatal 5-HT extracellular levels, as measured by in vivo microdialysis, indicative of the inhibition of serotonergic activity. A concurrent blunting of l-DOPA-induced surge in dopamine levels on the lesioned side of the brain was observed upon NLX-112 administration and these neurochemical responses were also seen after 14 days of treatment. NLX-112 also suppressed the expression of AIMs in rats that were being primed for dyskinesia by repeated l-DOPA administration. However, when treatment of these rats with NLX-112 was stopped, l-DOPA then induced AIMs with scores that resembled those of control rats. The present study shows that the potent anti-AIMs activity of NLX-112 is maintained upon repeated administration and supports the ongoing clinical development of NLX-112 as a novel antidyskinetic agent for PD patients receiving l-DOPA treatment.

Gypenosides attenuate the development of L-DOPA-induced dyskinesia in 6-hydroxydopamine-lesioned rat model of Parkinson's disease.

BACKGROUND: Gypenosides (GPS) and ethanol extract of Gynostemma pentaphyllum (GP-EX) show anxiolytic effects on affective disorders in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-lesioned mouse model of Parkinson's disease (PD). Long-term administration of L-3,4-dihydroxyphenylalanine (L-DOPA) leads to the development of severe motor side effects such as L-DOPA-induced-dyskinesia (LID) in PD. The present study investigated the effects of GPS and GP-EX on LID in a 6-hydroxydopamine (6-OHDA)-lesioned rat model of PD. RESULTS: Daily administration of L-DOPA (25 mg/kg) in the 6-OHDA-lesioned rat model of PD for 22 days induced expression of LID, which was determined by the body and locomotive AIMs scores and contralateral rotational behaviors. However, co-treatments of GPS (25 and 50 mg/kg) or GP-EX (50 mg/kg) with L-DOPA significantly attenuated the development of LID without compromising the anti-parkinsonian effects of L-DOPA. In addition, the increases in ∆FosB expression and ERK1/2 phosphorylation in 6-OHDA-lesioned rats induced by L-DOPA administration were significantly reduced by co-treatment with GPS (25 and 50 mg/kg) or GP-EX (50 mg/kg). CONCLUSION: These results suggest that GPS (25 and 50 mg/kg) and GP-EX (50 mg/kg) effectively attenuate the development of LID by modulating the biomarker activities of ∆FosB expression and ERK1/2 phosphorylation in the 6-OHDA-lesioned rat model of PD. GPS and GP-EX will be useful adjuvant therapeutics for LID in PD.

AFQ056/mavoglurant, a novel clinically effective mGluR5 antagonist: identification, SAR and pharmacological characterization.

Here we describe the identification, structure-activity relationship and the initial pharmacological characterization of AFQ056/mavoglurant, a structurally novel, non-competitive mGlu5 receptor antagonist. AFQ056/mavoglurant was identified by chemical derivatization of a lead compound discovered in a HTS campaign. In vitro, AFQ056/mavoglurant had an IC50 of 30 nM in a functional assay with human mGluR5 and was selective over the other mGluR subtypes, iGluRs and a panel of 238 CNS relevant receptors, transporter or enzymes. In vivo, AFQ056/mavoglurant showed an improved pharmacokinetic profile in rat and efficacy in the stress-induced hyperthermia test in mice as compared to the prototypic mGluR5 antagonist MPEP. The efficacy of AFQ056/mavoglurant in humans has been assessed in L-dopa induced dyskinesia in Parkinson's disease and Fragile X syndrome in proof of principle clinical studies.

Striatal cholinergic cell ablation attenuates L-DOPA induced dyskinesia in Parkinsonian mice.

3,4-Dihydroxyphenyl-L-alanine (L-DOPA)-induced dyskinesia (LID) is a debilitating side effect of long-term dopamine replacement therapy in Parkinson's Disease. At present, there are few therapeutic options for treatment of LID and mechanisms contributing to the development and maintenance of these drug-induced motor complications are not well understood. We have previously shown that pharmacological reduction of cholinergic tone attenuates the expression of LID in parkinsonian mice with established dyskinesia after chronic L-DOPA treatment. The present study was undertaken to provide anatomically specific evidence for the role of striatal cholinergic interneurons by ablating them before initiation of L-DOPA treatment and determining whether it decreases LID. We used a novel approach to ablate striatal cholinergic interneurons (ChIs) via Cre-dependent viral expression of the diphtheria toxin A subunit (DT-A) in hemiparkinsonian transgenic mice expressing Cre recombinase under control of the choline acetyltransferase promoter. We show that Cre recombinase-mediated DT-A ablation selectively eliminated ChIs when injected into striatum. The depletion of ChIs markedly attenuated LID without compromising the therapeutic efficacy of L-DOPA. These results provide evidence that ChIs play a key and selective role in LID and that strategies to reduce striatal cholinergic tone may represent a promising approach to decreasing L-DOPA-induced motor complications in Parkinson's disease.

Effect of Tianqi antitremor granules on behavioral manifestations and expression of G protein-coupled receptor kinase 6 and ß-arrestin1 in levodopa-induced dyskinesia in a rat model of Parkinson's disease.

BACKGROUND: Recent studies have shown that expression of G protein-coupled receptor kinase 6 (GRK6) and ß-arrestin1 in the striatum is closely associated with hyperactive dopamine receptors in rats with levodopa-induced dyskinesia (LID). Our research group has shown that Tianqi antitremor granules have a significant effect on the motor complications of Parkinson's disease (PD). However, whether Tianqi antitremor granules have an effect on the behavioral manifestations and expression of GRK6 and ß-arrestin1 in rats with LID is unknown. METHODS: Rats with PD received twice daily intraperitoneal injections of levodopa for 4 weeks to induce dyskinesia. Rats with LID were randomly divided into five groups: an LID-control group, an LID group, a levodopa plus Tianqi antitremor granules as traditional Chinese medicine (TCM)-low group, a levodopa plus TCM-medium group, and levodopa plus TCM-high group. Peak intensity of rotations was measured. GRK6 and ß-arrestin1 expression in the striatum of the dyskinetic rats was observed by immunohistochemistry and Western blotting. RESULTS: Pulsatile treatment with levodopa induced abnormal involuntary movements in rats with PD similar to LID in patients with PD. We found that repeated levodopa administration increased peak rotations in dyskinetic rats. However, peak rotations were decreased in rats given levodopa plus the different doses of Tianqi antitremor granules. In accordance with changed behavior, GRK6 and ß-arrestin1 expression was decreased in rats with PD and was persistently low in rats with LID, but this decrease was prevented by coadministration of levodopa and Tianqi antitremor granules. CONCLUSION: Tianqi antitremor granules ameliorated levodopa-induced dyskinetic behavior, reversed the decrease in GRK6 and ß-arrestin1 expression, and acted as a useful adjunctive medicine for the treatment of LID.

Aberrant restoration of spines and their synapses in L-DOPA-induced dyskinesia: involvement of corticostriatal but not thalamostriatal synapses.

We examined the structural plasticity of excitatory synapses from corticostriatal and thalamostriatal pathways and their postsynaptic targets in adult Sprague-Dawley rats to understand how these striatal circuits change in l-DOPA-induced dyskinesias (LIDs). We present here detailed electron and light microscopic analyses that provide new insight into the nature of the structural and synaptic remodeling of medium spiny neurons in response to LIDs. Numerous studies have implicated enhanced glutamate signaling and persistent long-term potentiation as central to the behavioral sensitization phenomenon of LIDs. Moreover, experience-dependent alterations in behavior are thought to involve structural modifications, specifically alterations in patterns of synaptic connectivity. Thus, we hypothesized that in the striatum of rats with LIDs, one of two major glutamatergic pathways would form new or altered contacts, especially onto the spines of medium spiny neuron (MSNs). Our data provide compelling evidence for a dramatic rewiring of the striatum of dyskinetic rats and that this rewiring involves corticostriatal but not thalamostriatal contacts onto MSNs. There is a dramatic increase in corticostriatal contacts onto spines and dendrites that appear to be directly linked to dyskinetic behaviors, since they were not seen in the striatum of animals that did not develop dyskinesia. There is also an aberrant increase in spines receiving more than one excitatory contact(i.e., multisynaptic spines) in the dyskinetic animals compared with the 6-hydroxydopamine-treated and control rats. Such alterations could substantially impair the ability of striatal neurons to gate cortically driven signals and contribute to the loss of bidirectional synaptic plasticity.

Resveratrol attenuates L-DOPA-induced hydrogen peroxide toxicity in neuronal cells.

A variety of polyphenol antioxidant compounds derived from natural products have demonstrated neuroprotective activity against neuronal cell death. The objective of this study was to investigate the effect of resveratrol (RESV) and bioflavonoids in attenuating hydrogen peroxide (H(2)O(2))-induced oxidative stress in neuronal cells. H2O2 levels were increased by the addition of L-3,4-dihydroxyphenylalanine (L-DOPA) to cultured dopaminergic SKNSH cells. H(2)O(2) was monitored by peroxyfluor-1, a selective H(2)O(2) optical probe. To examine the neuroprotective effects of RESV and bioflavonoids against L-DOPA, we cotreated RESV, quercetin, or (-) epigallocatechin gallate with L-DOPA and monitored for H(2)O(2) levels. The combination of RESV and L-DOPA was 50% more effective at reducing H(2)O(2) levels than the combination of quercetin or epigallocatechin gallate with L-DOPA. However, the combination of each antioxidant with L-DOPA was effective at preserving cell viability.

Pallidothalamic-projecting neurons in Macaca fascicularis co-express GABAergic and glutamatergic markers as seen in control, MPTP-treated and dyskinetic monkeys.

GABAergic neurons within the internal division of the globus pallidus (GPi) are the main source of basal ganglia output reaching the thalamic ventral nuclei in monkeys. Following dopaminergic denervation, pallidothalamic-projecting neurons are known to be hyperactive, whereas a reduction in GPi activity is typically observed in lesioned animals showing levodopa-induced dyskinesia. Besides the mRNAs coding for GABAergic markers (GAD65 and GAD67), we show that all GPi neurons innervating thalamic targets also express transcripts for the isoforms 1 and 2 of the vesicular glutamate transporter (vGlut1 and vGlut2 mRNA). Indeed, dual immunofluorescent detection of GAD67 and vGlut1/2 confirmed the data gathered from in situ hybridization experiments, therefore demonstrating that the detected mRNAs are translated into the related proteins. Furthermore, the dopaminergic lesion resulted in an up-regulation of expression levels for both GAD65 and GAD67 mRNA within identified pallidothalamic-projecting neurons. This was coupled with a down-regulation of GAD65/67 mRNA expression levels in GPi neurons innervating thalamic targets in monkeys showing levodopa-induced dyskinesia. By contrast, the patterns of gene expression for both vGlut1 and vGlut2 mRNAs remained unchanged across GPi projection neurons in control, MPTP-treated and dyskinetic monkeys. In summary, both GABAergic and glutamatergic markers were co-expressed by GPi efferent neurons in primates. Although the status of the dopaminergic system directly modulates the expression levels of GAD65/67 mRNA, the observed expression of vGlut1/2 mRNA is not regulated by either dopaminergic removal or by continuous stimulation with dopaminergic agonists.

An improved model to investigate the efficacy of antidyskinetic agents in hemiparkinsonian rats.

A number of experimental models of L-DOPA-induced dyskinesia have been proposed, but these models result in a low to medium rate of dyskinetic animals with mild to severe symptoms. The objective of this study was to combine a model of 6-OHDA-induced parkinsonism and of L-DOPA-induced dyskinesia in rats to establish a reliable preclinical model. Two stereotaxic injections of 6-OHDA were administered in the left striatum. This model led to 90-100% of rats with a marked contralateral circling behaviour, significant limb use asymmetry (20%), a decrease in ipsilateral striatal dopamine content (70%) and degeneration of dopamine neurons in the substantia nigra (70%). Chronic treatment with L-DOPA was administered for 35 days and consisted of three phases with incremental daily doses. The third phase resulted in 83-90% of rats developing severe abnormal involuntary movements (AIMs) which included limb and locomotive dyskinesia, axial dystonia and orolingual dyskinesia. Reproducibility of the model, criteria of strict blinding, placebo-controlled design, randomization of study subjects and pretrial determination of sample size were used to measure efficacy of amantadine and istradefylline and to validate the protocol design. Acute or subchronic post-treatment with amantadine reduced the severity of dyskinesia while istradefylline punctually attenuated AIMs. Our experimental conditions using gradual development of dyskinesia induced by increasing doses of L-DOPA resulted in a reliable model of L-DOPA-induced dyskinesia with a high rate of dyskinetic rats.

How reliable is the behavioural evaluation of dyskinesia in animal models of Parkinson's disease?

In spite of the current availability of several pharmacological therapies for the treatment of Parkinson's disease, side effects are invariably manifested during long-term treatment. Dyskinesia, wearing-off and on-off are among the most disabling side effects produced by the dopamine precursor L-dihydroxyphenylalanine and, to a lesser degree, by other pharmacological treatments based on dopamine receptor agonism. Evaluation of the side effects, in particular dyskinesia, produced by antiparkinsonian drug treatments, therefore represents a critical issue in drug validation prior to a clinical trial. Moreover, a reliable model of dyskinesia is a fundamental requirement for the study of the as yet unknown mechanisms at the basis of this severely disabling side effect. The present review aims to provide a critical evaluation of the validity, reliability and utility of animal models of dyskinesia. In the first part of this review, we present a brief overview of the different models of Parkinson's disease focusing on those utilized for the evaluation of dyskinetic movements, then proceed to critically examine the turning behaviour model in an attempt to assess the way in which it has influenced the evaluation of drugs utilized in the treatment of Parkinson's disease. Subsequently, the various models of dyskinesia are reviewed and conclusions are drawn as to how the environment in which experiments are performed can influence the behaviour observed.

Experimental study on inhibition of neuronal toxical effect of levodopa by ginkgo biloba extract on Parkinson disease in rats.

In order to observe neuronal toxical effect of Levodopa and investigate if using Levodopa together with Ginkgo Bilobar Extract (EGb) would be an workable method to treat Parkinson disease, rat models of Parkinson disease (PD) were made by injecting 6-OHDA stereotaxically to right side of the mesencephic ventral tegmental area (VTA) and substantia nigra pars compacta (SNc). Rotational behavioral observation, TUNEL, immunocytochemistry, Nissl's body staining were performed to measure the difference between group treated by Levodopa (50 mg/kg every day for 3 days, 5 days, 7 days, L-dopa group) and group treated by Levodopa combined with EGb (100 mg/kg every day, E-D group). The results showed that in the L-dopa group, the numbers of apoptosis of substantial nigra, rings of rotational behavior were more than those in the E-D group (P < 0.05). The numbers of Nissl's cells in L-dopa group were fewer than in E-D group (P < 0.05). The results suggested that Levodopa had neur toxic effect and EGb may decrease the toxicity of levodopa. The combined use of EGb with Levodopa may be a workable method to treat PD and may be better than using Levodopa alone.

COMT-dependent protection of dopaminergic neurons by methionine, dimethionine and S-adenosylmethionine (SAM) against L-dopa toxicity in vitro.

L-dopa may be toxic to dopamine neurons, possibly due to catechol-autoxidation. Catechols are O-methylated by catechol-O-methyltransferase (COMT) in a SAM consuming reaction, preventing the initiation of catechol autoxidation. We hypothesized that SAM or SAM-precursors ameliorate L-dopa neurotoxicity, in a COMT-dependent fashion. We tested this hypothesis in primary mesencephalic cultures by adding 200 microM L-dopa with 2 mM methionine or 1 mM dimethionine or 0.5 mM SAM with or without 0.2 microM of the COMT-inhibitor 2', 5'-dinitrocatechol (OR 486). L-dopa was found to be neurotoxic as the surviving neurons had fewer and shorter processes. Methionine, dimethionine and SAM all protected DA neurons against damaged induced by L-dopa. The COMT inhibitor dinitrocatechol (DNC) completely abolished the protective effect against L-dopa toxicity. We conclude that supplementation with methionine, dimethionine or SAM ameliorates L-dopa neurotoxicity to dopamine neurons, while inhibition of COMT may aggravate or unmask L-dopa neurotoxicity.

Neurotoxic effects of amphetamine plus L-DOPA.

1. Male Swiss Webster mice were administered a series of amphetamine injections preceded by either saline or L-DOPA. 2. This injection regimen was performed for either one, two or three consecutive weeks and neurotoxic effects of the drugs were determined one week later. 3. Amphetamine treatment for two weeks produced a greater striata-dopaminergic lesion that treatment for only one week. Three weeks of treatment did not exacerbate the lesion, indicating that the damage had reached maximal levels. 4. L-DOPA pretreatment did not significantly alter any of the toxic effects of the amphetamine. Therefore, some dopaminergic neurons may be resistant to the toxic effects of amphetamine.

Effect of chronic L-dopa administration on serum luteinizing hormone levels in male rats.

We examined whether the repeated oral administration with a high dose of L-3-(3,4-dihydroxyphenyl)-alanine (L-DOPA) in 0.5% carboxymethyl cellulose increases serum luteinizing hormone (LH) levels in male rats. Serum LH levels were increased 4 h after a single administration of 1000 mg/kg L-DOPA to male rats, and returned to control levels within 8 h after administration. Four hours after a single administration, serum LH levels were significantly increased by L-DOPA at 1000 mg/kg, but not at 20, 100 or 200 mg/kg. Decreases in body weight and relative weight of the prostate were observed after 7 and 14 days of administration of 1000 mg/kg per day L-DOPA, but no changes were observed in weight of the testis, epididymis or seminal vesicle. The administration of L-DOPA at 500 or 1000 mg/kg per day for 7 or 14 days resulted in increased basal serum LH levels and decreased basal serum prolactin levels 24 h after the last administration. Serum testosterone levels tended to be higher in treated than in control rats. The levels of two metabolites of dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), in rats treated with 500 mg/kg per day tended to be slightly higher than those in control rats after 7 days of administration. Levels of DA, DOPAC and HVA were significantly increased after 7 and 14 days of administration of 1000 mg/kg per day and after 14 days of administration of 5000 mg/kg per day. The level of norepinephrine, but not its metabolite 3-methoxy-4-hydroxyphenylglycol, was significantly increased after only 7 days of administration of 1000 mg/kg per day. No significant changes were observed in levels of 5-hydroxytryptamine or its metabolite 5-hydroxyindole-3-acetic acid with administration of 500 or 1000 mg/kg per day. These findings suggest that a prolonged treatment with a high dose of L-DOPA in male rats induces release of LH from the pituitary, resulting in sustained elevation of LH levels in peripheral circulation.