How can caffeine alleviate the motor symptoms of Parkinson’s disease? – the implications of adenosine 2A receptor antagonism

Introduction and purpose: Parkinson’s disease (PD) is the second most common neurodegenerative disease, mainly characterized by motor impairment with symptoms including rigidity, bradykinesia, rest tremor and imbalance. It develops upon degeneration of dopaminergic neurons in the substantia nigra associated with neuroinflammatory process initiated by alpha-synuclein deposits. Although, levodopa replacement therapy is the gold-standard treatment, majority of the treated patients develop dyskinesia as the side effect, resulting from altered function of dopamine receptors. It is thought that the abnormal pulsate release of dopamine can be prevented by antagonism of adenosine 2A receptors (A2ARs). Aim of the study: This review aims to outline the action mechanism of A2AR antagonism on motor performance, and thus evaluate the suggested implications of coffee consumption in PD. Material and method: The involvement of A2ARs in the pathology and treatment of PD has been analyzed based on the findings of many published studies examining the effects of A2AR modulation. Results: Blockage of A2ARs enhances the action of dopamine via D2 receptors on striatopallidal neurons, decreasing their hyperactivity, and exerts neuroprotective effect, suppressing the neuroinflammation. Conclusions: Istradefylline, being the only approved A2AR antagonist, was able to reduce total cumulative dose of levodopa, improve motor control, alleviate postural abnormalities, and provide a reduction in daily ‘off’ time experienced by patients. Recent findings suggest the effects of drinking one cup of coffee are comparable with ones obtained by the newly introduced medication, presumably via shared action mechanism by A2AR inhibition

How can caffeine alleviate the motor symptoms of Parkinson’s disease? – the implications of adenosine 2A receptor antagonism

Introduction and purpose: Parkinson’s disease (PD) is the second most common neurodegenerative disease, mainly characterized by motor impairment with symptoms including rigidity, bradykinesia, rest tremor and imbalance. It develops upon degeneration of dopaminergic neurons in the substantia nigra associated with neuroinflammatory process initiated by alpha-synuclein deposits. Although, levodopa replacement therapy is the gold-standard treatment, majority of the treated patients develop dyskinesia as the side effect, resulting from altered function of dopamine receptors. It is thought that the abnormal pulsate release of dopamine can be prevented by antagonism of adenosine 2A receptors (A2ARs). Aim of the study: This review aims to outline the action mechanism of A2AR antagonism on motor performance, and thus evaluate the suggested implications of coffee consumption in PD. Material and method: The involvement of A2ARs in the pathology and treatment of PD has been analyzed based on the findings of many published studies examining the effects of A2AR modulation. Results: Blockage of A2ARs enhances the action of dopamine via D2 receptors on striatopallidal neurons, decreasing their hyperactivity, and exerts neuroprotective effect, suppressing the neuroinflammation. Conclusions: Istradefylline, being the only approved A2AR antagonist, was able to reduce total cumulative dose of levodopa, improve motor control, alleviate postural abnormalities, and provide a reduction in daily ‘off’ time experienced by patients. Recent findings suggest the effects of drinking one cup of coffee are comparable with ones obtained by the newly introduced medication, presumably via shared action mechanism by A2AR inhibition

Pathophysiology of L-dopa-induced motor and non-motor complications in Parkinson's disease

Involuntary movements, or dyskinesia, represent a debilitating complication of levodopa (L-dopa) therapy for Parkinson's disease (PD). L-dopa-induced dyskinesia (LID) are ultimately experienced by the vast majority of patients. In addition, psychiatric conditions often manifested as compulsive behaviours, are emerging as a serious problem in the management of L-dopa therapy. The present review attempts to provide an overview of our current understanding of dyskinesia and other L-dopa-induced dysfunctions, a field that dramatically evolved in the past twenty years. In view of the extensive literature on LID, there appeared a critical need to re-frame the concepts, to highlight the most suitable models, to review the central nervous system (CNS) circuitry that may be involved, and to propose a pathophysiological framework was timely and necessary. An updated review to clarify our understanding of LID and other L-dopa-related side effects was therefore timely and necessary. This review should help in the development of novel therapeutic strategies aimed at preventing the generation of dyskinetic symptoms

An update on adenosine A2A receptors as drug target in Parkinson's disease

Adenosine receptors are G protein-coupled receptors (GPCRs) that mediate the physiological functions of adenosine. In the central nervous system adenosine A2A receptors (A2ARs) are highly enriched in striatopallidal neurons where they form functional oligomeric complexes with other GPCRs such us the dopamine D2 receptor (D2R). Furthermore, it is assumed that the formation of balanced A2AR/D2R receptor oligomers are essential for correct striatal function as the allosteric receptor-receptor interactions established within the oligomer are needed for properly sensing adenosine and dopamine. Interestingly, A2AR activation reduces the affinity of striatal D2R for dopamine and the blockade of A2AR with specific antagonists facilitates function of the D2R. Thus, it may be postulated that A2AR antagonists are pro-dopaminergic agents. Therefore, A2AR antagonists will potentially reduce the effects associated with dopamine depletion in Parkinson's disease (PD). Accordingly, this class of compounds have recently attracted considerable attention as potential therapeutic agents for PD pharmacotherapy as they have shown potential effectiveness in counteracting motor dysfunctions and also displayed neuroprotective and anti-inflammatory effects in animal models of PD. Overall, we provide here an update of the current state of the art of these A2AR-based approaches that are under clinical study as agents devoted to alleviate PD symptom

Deuterium-L-DOPA : a novel means to improve treatment of Parkinson´s disease

L-DOPA, the precursor of dopamine, is administered to restore dopamine deficiency in Parkinson´s disease (PD) patients. L-DOPA initially provides a sustained symptomatic relief with superior efficacy as compared to other treatments, while long term treatment is complicated by the gradual emergence of troublesome motor complications i.e. fluctuations in therapeutic effect and L-DOPA-induced dyskinesia. The risk for motor complications is associated with disease duration and total L-DOPA load. While the underlying mechanisms remain to be fully elucidated, the inability of the remaining dopaminergic neurons to buffer exogenously applied L-DOPA and pulsatile stimulation of dopamine receptors resulting from the short half-life of the drug seem critical. An improved treatment strategy with similar efficacy as L-DOPA and reduced side effects is therefore highly warranted. Deuterium-L-DOPA was expected to yield dopamine more resistant to enzymatic degradation, as deuterium, heavy hydrogen, forms a stronger bond with carbon. Four isoforms of deuterium-L-DOPA, carrying different combinations of α and β carbon substitutions, were screened for isotope effects on striatal dopamine metabolism by means of in vivo microdialysis in intact rats. The triple substituted isoform, α,β,β-D3-L-DOPA (D3-L-DOPA), dramatically increased the duration of dopamine output and reduced noradrenaline output as compared to L-DOPA. These effects most likely reflect reduced activity of the dopamine metabolizing enzymes MAO and DβH towards the deuterium substituted α- and β- carbons, respectively. Deuterium substitutions thus increase the half-life of dopamine formed from L-DOPA, which may reduce pulsatile stimulation of dopamine receptors as well as the total L-DOPA load in PD patients. The improved central kinetics of D3-L-DOPA may thereby significantly reduce the risk for L-DOPA induced motor complications. Reduced output of noradrenaline from D3-L-DOPA may additionally contribute to reduce the side effect profile, as noradrenaline released from L-DOPA may be involved in the expression of dyskinesias. The neurochemical and behavioral effects of D3-L-DOPA were subsequently evaluated in two, well-established animal models of PD, the reserpine and the 6-OHDA-lesion model. D3-L-DOPA produced an increased dopamine output as compared to L-DOPA in the 6-OHDA-lesioned striatum; an effect which closely resembled that of L-DOPA in combination the MAO-B inhibitor selegiline; used in clinical practice to potentiate the symptomatic effect of L-DOPA and reduce motor fluctuations. Moreover, selegiline pre-treatment did not potentiate the effect of D3-L-DOPA. The enhanced output of dopamine from D3-L-DOPA and selegiline/L-DOPA may thus be attributed to decreased metabolism of dopamine at MAO-B containing sites. An acute challenge with D3-L-DOPA was shown to produce an increased motor activation as compared to L-DOPA in both models of PD, indicating an increased behavioral potency. In addition, the behavioral effect produced by D3-L-DOPA was found to be of similar magnitude as the combination of selegiline/L-DOPA. Our data hence provide experimental support for the potential clinical advantage of D3-L-DOPA and suggest that monotherapy with D3-L-DOPA may provide equal benefit as the combination of selegiline/L-DOPA.The effects of D3-L-DOPA and L-DOPA were also compared in a chronic treatment design. Significantly, a lower dose of D3-L-DOPA, 60% of the equivalent L-DOPA dose, produced similar anti-parkinsonian benefit while the expression of dyskinesias was markedly reduced. The equivalent dose of D3-L-DOPA, as compared to L-DOPA, produced a more pronounced anti-parkinsonian effect and similar expression of dyskinesia. Taken together, these findings indicate that deuterium substitutions offer the advantage of a wider therapeutic window. In conclusion, the increased half-life of dopamine formed from D3-L-DOPA may serve to protect dopamine receptors from pulsatile stimulation and the increased behavioral potency of D3-L-DOPA may allow for adequate control of parkinsonian symptoms at an overall lower dosage. Altogether, a reduced L-DOPA load and more sustained stimulation of dopamine receptors may substantially improve PD treatment by reducing the risk for motor fluctuations and dyskinesias. Our preclinical data thus provide support for the utility of deuterium-substitutions in the L-DOPA molecule as a means to improve the therapeutic effect and reduce the side effects of L-DOPA therapy

Implication of the serotoninergic systems in Parkinson's disease and L-Dopa-induced dyskinesia

Le rôle de la sérotonine (5-hydroxytryptamine, 5-HT) dans la maladie de Parkinson (MP), et dans des complications motrices induites par son traitement pharmacologique appelées dyskinésies induites par la lévodopa (DIL)s n'est pas bien compris. Cette thèse traite principalement de l'implication des récepteurs 5-HT dans la MP et les DILs chez l'homme et chez le singe MPTP, le meilleur modèle animal de la MP, afin de développer de meilleurs traitements pharmacologiques. Ces recherches peuvent être divisées en quatre parties: 1) Evaluation du récepteur 5-HT₂A par autoradiographie avec la [³H] kétansérine chez des singes contrôles, chez des singes lésés avec le MPTP, chez des singes dyskinétiques traités avec la lévodopa et chez des singes nondyskinétiques traités avec la Lévodopa + cabergoline, un agoniste de récepteur D₂ de longue durée d'action, ou avec CI- 1041, un antagoniste glutamatergique des sous-unité NR₁A/₂B de l'acide N-méthyle-Daspartate (NMDA). 2) Évaluation du récepteur 5-HT₁A par autoradiographie avec le radioligand [³H] 8-OH-DPAT chez des singes lésés avec le MPTP, chez des singes dyskinétiques traités avec la lévodopa et chez des singes faiblement dyskinétiques traités avec la Lévodopa + Ro 61-8048, un inhibiteur de la kynurénine hydroxylase. 3) Évaluation des récepteurs 5-HT₁B par autoradiographie avec le radioligand [³H] GR 125743 chez les mêmes groupes d'animaux que ceux utilisés dans la partie 2. 4) Évaluation des axones 5- HT et de leurs varicosités visualisées par immunohistochimie avec un anticorps dirigé contre le transporteur de 5-HT (SERT) dans le noyau sous-thalamique (NST) chez des patients parkinsoniens et leurs contrôles afin de caractériser l'altération de la distribution régionale de l'innervation 5-HT de cette composante clé des ganglions de la base chez les patients parkinsoniens. Nos résultats ont démontré que le traitement à la Lévodopa augmente la liaison spécifique du récepteur 5-HT₂A dans le noyau caudé et le gyrus antérieur du cortex cingulaire (AcgG), la liaison spécifique du récepteur 5-HT₁A dans le cortex et l'hippocampe et la liaison spécifique du récepteurs 5-HT₁B dans la substance noire pars reticulata, le noyau caudé, le putamen antérieur et le globus pallidus tandis que cette augmentation n'est pas présente chez des singes nondyskinétiques traités à la lévodopa et à la cabergoline ou avec CI-1041 ou avec Ro 61-8048. Une diminution de la liaison spécifique du récepteur 5-HT₁A dans le cortex frontal et une augmentation la liaison spécifique du récepteur 5-HT₁B dans la substance noire pars reticulata chez des singes 11 MPTP ont été observées par rapport aux contrôles. Par ailleurs, une diminution du nombre de varicosités SERT + a été observée dans le NST chez les patients parkinsoniens par rapport aux contrôles et dans le NST chez le patient dyskinétique par rapport à un patient nondyskinétique. Dans l'ensemble, ces résultats fournissent la première description détaillée de l'altération du système sérotoninergique associée à la MP et à la prévention des DILs chez les primates humains et non-humains, en soutenant fortement son implication dans la MP et les DILs

Allosteric Interactions between Adenosine A2A and Dopamine D2 Receptors in Heteromeric Complexes:Biochemical and Pharmacological Characteristics, and Opportunities for PET Imaging

Adenosine and dopamine interact antagonistically in living mammals. These interactions are mediated via adenosine A2A and dopamine D2 receptors (R). Stimulation of A2AR inhibits and blockade of A2AR enhances D2R-mediated locomotor activation and goal-directed behavior in rodents. In striatal membrane preparations, adenosine decreases both the affinity and the signal transduction of D2R via its interaction with A2AR. Reciprocal A2AR/D2R interactions occur mainly in striatopallidal GABAergic medium spiny neurons (MSNs) of the indirect pathway that are involved in motor control, and in striatal astrocytes. In the nucleus accumbens, they also take place in MSNs involved in reward-related behavior. A2AR and D2R co-aggregate, co-internalize, and co-desensitize. They are at very close distance in biomembranes and form heteromers. Antagonistic interactions between adenosine and dopamine are (at least partially) caused by allosteric receptor–receptor interactions within A2AR/D2R heteromeric complexes. Such interactions may be exploited in novel strategies for the treatment of Parkinson’s disease, schizophrenia, substance abuse, and perhaps also attention deficit-hyperactivity disorder. Little is known about shifting A2AR/D2R heteromer/homodimer equilibria in the brain. Positron emission tomography with suitable ligands may provide in vivo information about receptor crosstalk in the living organism. Some experimental approaches, and strategies for the design of novel imaging agents (e.g., heterobivalent ligands) are proposed in this review

Approche expérimentale de la physiopathologie des dyskinésies L-Dopa induites dans la maladie de Parkinson : comparaison de la cible classique, le striatum avec l’ensemble du cerveau

The gold standard treatment for Parkinson’s disease (PD) remains the dopamine precursor L- 3,4-dihydroxyphenylalanine (L-Dopa). Long-term L-Dopa treatment systematically leads to abnormal involuntary movements (AIMs) called L-Dopa-induced dyskinesia (LID). These manifestations first led to investigate the neuronal dysfunctions in the motor regions of thebasal ganglia and unravelled an overexpression of ΔFosB, ARC, Zif268 and FRA2 immediate-early genes (IEG) in the dopamine-depleted striatum of dyskinetic rats. However, other several dopaminoceptive structures, likely affected by the exogenously produced dopamine, have been neglected although they might play a key role in mediating LID. Hence, we assessed the expression of ΔFosB, ARC, FRA2 and Zif268 IEGs in the whole brain of dyskinetic rats compared to non-dyskinetic ones. Such approach shed light notably upon 9 structures located outside of the basal ganglia displaying an IEG overexpression. Among them, the dorsolateral bed nucleus of the stria terminalis (dlBST) and the lateralhabenula (LHb) displayed a significant correlation between ΔFosB expression and LID severity. We therefore postulated that these structures might play a role in LID manifestation. Therefore, to assess dlBST and LHb causal roles upon LID severity, we inhibited the electrical activity of FosB/ΔFosB-expressing neurons using the selective Daun02/β- galactosidase inactivation method that we previously validated in a well known structure involve in LID: the striatum. Interestingly, the inactivation of dlBST and LHb ΔfosBexpressing neurons alleviated LID severity and increased the beneficial effect of L-Dopa in dyskinetic rats. Remarkably, BST involvement in LID was confirmed in the gold standard model of LID, the dyskinetic MPTP-lesioned macaque. Altogether, our results highlight for the first time the functional involvement of 2 structures.Le traitement de référence de la maladie de Parkinson (MP) reste l’utilisation du précurseurdirect de la dopamine: la L-3,4-dihydroxyphenylalanine (L-Dopa). Le traitement chroniquedes patients parkinsoniens à la L-Dopa induit, en revanche, systématiquement desmouvements involontaires anormaux que l’on qualifie de dyskinésies induites par la L-Dopa(DIL). L’étude de l’expression des dyskinésies s’est essentiellement focalisée sur lesdysfonctions neuronales engendrées dans les régions motrices des ganglions de la base et apermis de révéler une surexpression significative de gènes de réponse précoce (GRP) tels que: ΔFosB, ARC, Zif268 et FRA2 dans le striatum de rats dyskinétiques traités chroniquement à la L–Dopa. En revanche, plusieurs autres régions dopaminoceptives, probablement affectées par la dopamine exogène nouvellement synthétisée, ont été négligées alors qu’elles pourraient jouer un rôle clé dans l’expression des dyskinésies. Par conséquent, nous avons quantifié l’expression de ΔFosB, ARC, FRA2 et Zif268 dans l’ensemble du cerveau de rats dyskinétiques que nous avons comparée à des rats non-dyskinétiques. Cette approche nous a permis d’identifier 9 structures, localisées en dehors des ganglions de la base, présentant une surexpression d’au moins 3 des GRPs cités ci-dessus. Parmi ces structures, le domaine dorsolatéral du « bed nucleus of the stria terminalis » (dlBST) et l’habenula latérale (LHb) montrent une corrélation significative entre l’expression de ΔFosB et la sévérité des dyskinésies. Nous avons donc fait l’hypothèse que ces 2 structures pouvaient être impliquées dans l’expression des dyskinésies. Par conséquent, pour évaluer le rôle potentiel du dlBST et de la LHb dans les dyskinésies, nous avons inhibé l’activité électrique des neurones exprimant FosB/ΔFosB en utilisant la méthode d’inactivation sélective du Daun02/ß-galactosidase que nous avons précédemment validée dans une structure bien connue pour être impliquée dans les dyskinésies: le striatum. Nous avons démontré que l’inhibition de ces neurones, à la fois dans le dlBST et la LHb, diminuait la sévérité des dyskinésies sans affecter l’effet bénéfique de la L-Dopa chez les rats dyskinétiques. Nous avons ensuite pu confirmer l’implication du dlBST grâce au model de référence des dyskinésies: le macaque dyskinétique lésé au MPTP. L’ensemble de ces résultats nous a ainsi permis de montrer, pour la première fois, l’implication fonctionnelle de 2 structures externes aux ganglions de la base dans l’expression des dyskinésies, offrant de nouvelles perspectives thérapeutiques