Laurent Grégoire

Antiparkinsonian effect of a new selective adenosine A2A receptor antagonist in MPTP-treated monkeys

Background: Chronic treatment with l-3,4-dihydroxyphenylalanine (l-dopa) is often associated with motor side effects in PD patients. The search for new therapeutic approaches has led to study the role of other neuromodulators including adenosine. Among the four adenosine receptors characterized so far, the A2A subtype is distinctively present on striatopallidal output neurons containing enkephalin and mainly bearing dopamine (DA) D2 receptors (indirect pathway). Studies in DA-denervated rats suggest that blockade of adenosine A2A receptors might be used in PD. Objective: To evaluate the antiparkinsonian effect of a new selective adenosine A2A receptor antagonist, KW-6002, in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated monkeys. Methods: In the present study, we used six MPTP-exposed cynomolgus monkeys already primed and exhibiting l-dopa–induced dyskinesias to evaluate both the antiparkinsonian and dyskinetic effect upon challenge with two oral doses (60 and 90 mg/kg) of KW-6002 administered alone or in combination with l-dopa/benserazide (50/12.5 mg). Results: KW-6002 administered alone produced a dose-dependent antiparkinsonian response that reached the level of efficacy of l-dopa/benserazide but was less likely to reproduce dyskinesias in these animals. When co-administered, KW-6002 potentiated the effects of l-dopa/benserazide on motor activity (up to 30%) without affecting the dyskinetic response. Conclusion: Adenosine A2A receptor antagonists have antiparkinsonian effects of their own with a reduced propensity to elicit dyskinesias. They might therefore be useful agents in the treatment of PD.

Effect of a selective glutamate antagonist on L-dopa-induced dyskinesias in drug-naive parkinsonian monkeys.

Alterations of striatal glutamate receptors are believed to be responsible, at least in part, for the pathogenesis of L-dopa-induced dyskinesias (LID). To evaluate whether co-administration of CI-1041, a novel NMDA receptor antagonist selective for the NR1A/NR2B subtype, with L-dopa might prevent the appearance of this side effect, eight de novo parkinsonian monkeys were treated chronically orally with either L-dopa alone or L-dopa plus CI-1041 (n= 4 for each group). After 4 weeks of treatment with L-dopa alone, all four animals developed moderate dyskinesias either choreic or dystonic in nature. CI-1041 co-treatment completely prevented the induction of dyskinesias in three animals and only one monkey developed mild dyskinesias at the end of the fourth week of treatment in the L-dopa + CI-1041 group. The magnitude and duration of the antiparkinsonian action of L-dopa was similar in both groups. These results suggest that selective NMDA receptor antagonism may be interesting for managing LID in Parkinsons disease patients.

mGluR5 metabotropic glutamate receptors and dyskinesias in MPTP monkeys

Modulation of excessive glutamatergic transmission within the basal ganglia is considered as an alternative approach to reduce l-Dopa-induced dyskinesias (LIDs) in Parkinsons disease (PD). In this study receptor binding autoradiography of [3H]MPEP, a metabotropic glutamate receptor 5 (mGluR5) selective radioligand, was used to investigate possible changes in mGluR5 in the basal ganglia of l-Dopa-treated 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) monkeys having developed LIDs compared to animals in which LIDs was prevented by adjunct treatments. LIDs were associated with an increase of mGluR5 specific binding in the posterior putamen and pallidum (+41% and +56%) compared to controls. By contrast, prevention of dyskinesias was associated with an important decrease of mGluR5 specific binding in these areas (-37% and -48%) compared with dyskinetic animals. Moreover, an upregulation (+34%) of mGluR5 receptor binding was seen in the anterior caudate nucleus of saline treated MPTP monkeys. This study is the first to provide evidence that enhanced mGluR5 specific binding in the posterior putamen and pallidum may contribute to the pathogenesis of LIDs in PD.

Effect of the metabotropic glutamate receptor type 5 antagonists MPEP and MTEP in parkinsonian monkeys

Brain glutamate overactivity is well documented in Parkinsons disease (PD) and antiglutamatergic drugs have been proposed to relieve PD symptoms and decrease dyskinesias. Metabotropic glutamate receptors are topics of recent interest in PD. This study investigated the effects of the metabotropic glutamate receptors type 5 (mGluR5) antagonists MPEP and MTEP on motor behavior in monkeys with a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) lesion to model PD and treated with L-Dopa the gold standard therapy. Six Macaca fascicularis MPTP monkeys were initially treated repeatedly with L-Dopa; this treatment increased their locomotion and reduced their parkinsonian scores but also induced dyskinesias. Then, a dose-response of MPEP and MTEP (1.5-30 mg/kg) administered 15 and 30 min respectively prior to L-Dopa, showed that the antiparkinsonian activity of L-Dopa was generally maintained as measured with locomotion and antiparkinsonian scores as well as the onset and duration of the L-Dopa response. Interestingly the mean dyskinesia score during all the duration of the L-Dopa motor effect, the 1 h peak period dyskinesias scores as well as the maximal dyskinesias scores were dose-dependently reduced with both drugs reaching statistical significance at 10 and 30 mg/kg. Our results showed a beneficial antidyskinetic effect of blocking mGluR5 in L-Dopa-treated MPTP monkeys. This supports the therapeutic use of an mGluR5 antagonist to restore normal brain glutamate neurotransmission in PD and decrease dyskinesias.

Docosahexaenoic acid reduces levodopa-induced dyskinesias in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine monkeys

The objective of the present study was to investigate the effect of docosahexaenoic acid (DHA), a polyunsaturated fatty acid (omega‐3), on levodopa‐induced dyskinesias (LIDs) in parkinsonian 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (MPTP)–treated monkeys.

The acute antiparkinsonian and antidyskinetic effect of AFQ056, a novel metabotropic glutamate receptor type 5 antagonist, in L-Dopa-treated parkinsonian monkeys.

Overactivity of glutamatergic transmission has been implicated in Parkinsons disease (PD) and levodopa (L-Dopa)-induced dyskinesias. Striatal metabotropic glutamate receptors type 5 (mGluR5) are abundant and provide specific targets to modulate glutamatergic activity. This study investigated the acute effects of the novel mGluR5 antagonist AFQ056 on motor behavior in L-Dopa-treated monkeys with a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) lesion to model PD. Six Macaca fascicularis MPTP monkeys were treated repeatedly with L-Dopa; this treatment increased their locomotion and reduced their parkinsonian scores, but also induced dyskinesias. When AFQ056 (doses of 5, 25, 125 or 250mg/kg) was administered one hour prior to a high dose of L-Dopa, the antiparkinsonian activity of L-Dopa was maintained as measured with locomotion and antiparkinsonian scores, whereas dyskinesias were significantly reduced at 25, 125 and 250mg/kg AFQ056 for peak dyskinesia score and at 125 and 250mg/kg for the 1h peak period of dyskinesia score. Administration of AFQ056 one hour before L-Dopa led to peak or elevated plasma AFQ056 concentrations occurring close to L-Dopa peak-dose dyskinesias. We next investigated AFQ056 25mg/kg combined with a low dose of L-Dopa. The antiparkinsonian activity of L-Dopa was increased as measured with locomotion, while dyskinesias remained low at these doses. Our results show a beneficial motor effect of AFQ056 with L-Dopa in MPTP monkeys. This supports the therapeutic use of an mGluR5 antagonist to restore normal glutamatergic neurotransmission in PD and decrease dyskinesias.

Low doses of sarizotan reduce dyskinesias and maintain antiparkinsonian efficacy of L-Dopa in parkinsonian monkeys

Dyskinesia is an important complication of treatment in Parkinsons disease (PD). Sarizotan, a 5-HT(1A) agonist with high affinity for D3 and D4 receptors was investigated on L-Dopa-induced dyskinesia (LID) in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) animal model of PD. Five MPTP female cynomolgus monkeys (Macaca fascicularis) with a moderate to severe parkinsonian syndrome and LID were used. Sarizotan 0.2, 1, and 2 mg/kg administered alone did not worsen parkinsonian symptoms; there were no effect on locomotor counts or on normal behavior of the monkeys. Sarizotan 0.2, 1, and 2 mg/kg administered 30 min before a fixed dose of L-Dopa (25-30 mg/kg s.c.) + benserazide (50 mg) did not affect the antiparkinsonian response to L-Dopa. However, mean dyskinetic scores were significantly reduced with sarizotan 1 and 2 mg/kg but not at 0.2 mg/kg. Higher doses of sarizotan (4 and 8 mg/kg, administered immediately before L-Dopa) reduced L-Dopa-induced locomotor response in all monkeys. A pharmacokinetic investigation in these monkeys showed a dose-dependent increase in mean plasma sarizotan concentrations with similar mean plasma concentrations for sarizotan 1 mg/kg alone or with L-Dopa, indicating a lack of sarizotan/L-Dopa interaction. The time course of plasma sarizotan concentrations was associated with time of maximal reduction of dyskinesias. When administered daily for two weeks in combination with L-Dopa in the same MPTP monkeys, sarizotan 1 mg/kg had a sustained antidyskinetic effect while maintaining the antiparkinsonian and locomotor effect of L-Dopa. This detailed sarizotan investigation in MPTP monkeys supports the antidyskinetic activity of this drug and for 5-HT(1A) agonists.

Metabotropic glutamate receptor type 5 in levodopa-induced motor complications

Metabotropic glutamate receptors type 5 (mGluR5) are implicated in regulation of synaptic plasticity and learning, and were the focus of our investigation in human Parkinsons disease (PD) patients with dyskinesias and wearing-off, and in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) monkeys with dyskinesias. Using the selective mGluR5 ligand [(3)H]ABP688 autoradiography, we measured mGluR5 in brain slices from 11 normal and 14 PD patients and from MPTP monkeys, in relation to motor complications (dyskinesias and wearing-off) associated with treatment with l-dopa. In 16 monkeys with a bilateral MPTP lesion and four controls, [(3)H]ABP688 specific binding was elevated in the striatum of dyskinetic l-dopa-treated MPTP monkeys but not in MPTP monkeys without dyskinesias compared to controls. PD patients with motor complications (either dyskinesias or wearing-off) had higher [(3)H]ABP688 specific binding compared to those without motor complications and controls in putamen, external and internal globus pallidus. Elevated glutamatergic transmission as measured with increased mGluR5 specific binding was associated with motor complications and its antagonism could be targeted for their treatment.

Sustained cabergoline treatment reverses levodopa-induced dyskinesias in parkinsonian monkeys.

The pathophysiology of L-Dopa-induced dyskinesias (LID), a common problem after long-term use of L-dopa in the treatment of Parkinsons disease (PD), is not completely understood. Oscillations in L-Dopa concentrations in the brain are believed to be responsible, at least in part, for their pathogenesis. This study was aimed at verifying whether chronic administration of cabergoline, a long-acting dopamine D2-like receptor agonist, can reverse established LID. Four MPTP-treated cynomolgus monkeys with long-standing and stable parkinsonian syndrome and reproducible dyskinesias to L-Dopa, were used in this study. We compared the antiparkinsonian and dyskinetic responses of L-Dopa methyl ester (62.5 mg and 125 mg), given with benserazide (50 mg) (L-Dopa/benserazide), administered before and after a 6-week period during which the animals were treated only by daily administration of cabergoline (doses ranging from 0.125 to 0.185 mg/kg, subcutaneous). During cabergoline treatment, the monkeys initially showed marked dyskinesias, which were reduced significantly after 4 weeks of treatment. However, there was no tolerance to its antiparkinsonian effect. L-Dopa/benserazide given 4 days after cabergoline withdrawal produced a significant antiparkinsonian effect, but dyskinesias were dramatically reduced compared to what had been seen before chronic cabergoline treatment. The duration of the L-Dopa response was not increased after chronic administration of cabergoline. Our data suggest that sustained dopamine D2 receptor stimulation could be of value when trying to reduce or to reverse LID in patients with fluctuating advanced PD.

Correlation of functional recovery after a 6-hydroxydopamine lesion with survival of grafted fetal neurons and release of dopamine in the striatum of the rat

Female rats were lesioned with 6-hydroxydopamine in the left substantia nigra. At least two weeks later they were tested with amphetamine (5 mg/kg, s.c.) and apomorphine (0.25 mg/kg, s.c.). A cell suspension from the ventral mesencephalon of rat embryos was distributed in three sites in a triangular fashion in the center of the denervated striatum. The amphetamine test was then repeated every month for six months. The pattern of circling to amphetamine before the graft was strictly ipsiversive in all animals. From the first month we observed a progressive change and three patterns of rotation could be observed. In 21% of animals, the total number of ipsiversive turns in 90 min actually increased but during the first 20 min the animals turned contralaterally to the lesion (and to the graft). In 38% of animals, the total number of turns switched from ipsiversive to contraversive with the animals turning initially toward the intact side and during the second half of the test toward the lesion. Finally 41% of rats progressively switched to turning only toward the intact side. In all cases, maximal contraversive turning occurred during the initial 20 min. In these rats, tyrosine hydroxylase-positive cells were detected mainly in the dorsal striatum with a few in the central portion. Moreover there was a strong correlation between the number of surviving grafted neurons and the growth of their fiber into the host striatum and the extent of recovery.(ABSTRACT TRUNCATED AT 250 WORDS)