Effect of dopaminergic medication on adenosine 2A receptor availability in patients with Parkinson's disease

ObjectiveTo assess the necessity of withdrawing dopaminergic medication in Parkinson's disease (PD) patients for accurate estimation of adenosine 2A receptor (A_2AR) availability using [¹¹C]TMSX PET imaging. This was accomplished by studying the short-term effect of the cessation of dopaminergic medication on A_2AR availability in non-dyskinetic patients with PD treated with dopaminergic medication.MethodsEight PD patients (age 67.9 ± 5.6 years; 6 men, 2 women) without dyskinesia were enrolled in this study. A_2AR availability was measured using PET imaging with a [7-methyl-¹¹C]-(E)-8-(3,4,5-trimethoxystyryl)-1,3,7-trimethylxanthine ([¹¹C]TMSX) radioligand after a short term cessation of dopaminergic medication (12hrs for levodopa, 24hrs for dopamine agonists and MAO-B inhibitors). Repeated PET imaging was performed while the patients were back ‘on’ their regular dopaminergic medication (median 13 days after first imaging). Conventional MRI was acquired for anatomical reference. Specific binding of [¹¹C]TMSX was quantified as distribution volume ratios (DVR) for caudate, pallidum and putamen using Logan graphical method with clustered gray matter reference region.ResultsNo significant differences were observed for the DVRs in all three striatal regions between ‘on’ and ‘off’ medication states. Strong correlations were also observed between the two states. Statistical equivalence was found in pallidum (TOST equivalence test, p = 0.045) and putamen (TOST equivalence test, p = 0.022), but not in caudate DVR (TOST equivalence test, p = 0.201) between the two medication states.ConclusionsOur results show that dopaminergic medication has no significant short-term effect on the availability of A_2A receptors in putamen and pallidum of patients with PD. However, relatively poor repeatability was demonstrated in the caudate.     

SCH 58261, an A(2A) adenosine receptor antagonist, counteracts parkinsonian-like muscle rigidity in rats

The aim of the present study was to find out whether blockade of adenosine A(2A) receptors by a selective antagonist, SCH 58261, influenced parkinsonian-like muscle rigidity. Muscle tone was examined using a combined mechano- and electromyographic method which simultaneously measured muscle resistance (MMG) of a rat hindfoot to passive extension and flexion in the ankle joint and electromyographic activity (EMG) of the antagonistic muscles of that joint: gastrocnemius and tibialis anterior. Muscle rigidity produced by reserpine (5 mg/kg + alpha-methyl-p-tyrosine, 250 mg/kg) was antagonized by SCH 58261 (0.1-5 mg/kg). SCH 58261 (5 mg/kg) also reduced reserpine-enhanced tonic and reflex EMG activities in both the gastrocnemius and the tibialis muscles. Moreover, SCH 58261 in doses of 1 and 5 mg/kg abolished muscle resistance induced by haloperidol (0.5 mg/kg). However, only the highest dose of SCH 58261 (5 mg/kg) decreased tonic EMG activity enhanced by haloperidol. Administration of L-DOPA (75 and 100 mg/kg) dose-dependently decreased the muscle resistance as well as tonic EMG activity evoked by haloperidol. Combined administration of SCH 58261 (0.1 mg/kg) and L-DOPA (50 mg/kg) in doses which did not affect the haloperidol-induced muscle rigidity produced a pronounced synergistic effect. The ability of SCH 58261 to diminish the parkinsonian-like muscle rigidity and to potentiate the effect of L-DOPA in this model seems to indicate a therapeutic value of this compound in the treatment of Parkinson's disease.     

A double-blind crossover, placebo-controlled study of the adenosine A2A antagonist theophylline in Parkinson's disease

Blockade of the adenosine A2A receptor potentiates the effects of levodopa in experimental animals and may offer a novel nondopaminergic target for drug therapy in Parkinson's disease (PD). Open-label trials suggest that the nonspecific adenosine antagonist theophylline improves parkinsonian symptoms and increases ON time in advanced patients with PD. In a double-blind, crossover, placebo-controlled trial, the authors investigated the ability of stable plasma levels of theophylline (between 10-20 microg/mL after 15 days of treatment) to modulate the long-duration response and the short-duration response of levodopa in 10 patients with PD. Although theophylline induced a longer duration of the effect of levodopa in all Unified Parkinson's Disease Rating Scale variables considered, including dyskinesias, maximal levodopa-induced improvement and the duration of the effect of levodopa did not differ significantly from placebo. Only the secondary variable "akinesia" showed a statistical tendency to a more prolonged beneficial response with theophylline during an acute levodopa test (short-duration response), and tremor worsened with theophylline during levodopa withdrawal (long-duration response). No differences were observed during the subacute course of study medication added to levodopa. During this exploratory study, the effects of theophylline were not strong enough to potentiate clearly the antiparkinsonian action of levodopa or to increase ON time in patients with advanced PD.     

Idazoxan, an alpha-2 antagonist, and L-DOPA-induced dyskinesias in patients with Parkinson's disease.

Dyskinesia is a frequent and disabling side effect in patients with Parkinson's disease treated with chronic dopa-therapy. Preclinical data in the 1-methyl-4-phenyl-1,2,3,6,-tetrahydropyridine (MPTP) monkey suggest that alpha-2 antagonists may reduce dihydroxyphenylalanine (L-DOPA)-induced dyskinesia. We assessed, in a pilot randomised placebo-controlled study, the effects of single oral doses (10 mg, 20 mg, and 40 mg) of idazoxan, an alpha-2 antagonist, on motor parkinsonian disability and L-DOPA-induced dyskinesia following an acute oral challenge of L-DOPA in 18 patients with Parkinson's disease. The severity of L-DOPA-induced dyskinesia improved after 20 mg idazoxan pretreatment, while there was no concommittant deterioration in the antiparkinsonian response to L-DOPA. These results suggest that blocking alpha-2 receptors in patients with Parkinson's disease might improve L-DOPA-induced dyskinesia without the cost of a return of parkinsonian symptomatology. Further studies are required to assess whether this property could have potential therapeutic applications in the long-term management of dyskinetic patients with Parkinson's disease.     

Prevention of dyskinesia by an NMDA receptor antagonist in MPTP monkeys: effect on adenosine A2A receptors

Adenosine A(2A) receptors (A(2A)R) have received increasing attention for the treatment of L-DOPA-induced dyskinesias in Parkinson disease. In the present study, A(2A)R messenger RNA (mRNA) and receptor-specific binding in the brain of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) monkeys were studied after treatment with L-DOPA and a selective NR1A/2B NMDA receptor antagonist, CI-1041. Four MPTP monkeys received L-DOPA/benserazide and all developed dyskinesias, whereas among the four MPTP monkeys who additionally received CI-1041, only one developed mild dyskinesias. Four normal monkeys and four MPTP-treated monkeys were also studied. All MPTP monkeys had similar striatal dopamine (DA) denervation. A(2A)R mRNA levels, measured by in situ hybridization, were increased in the rostral lateral caudate and putamen of saline-treated MPTP monkeys as well as in the caudal lateral and medial putamen when compared with those of controls. A(2A)R mRNA levels remained elevated in the rostral caudate and putamen of L-DOPA-treated MPTP monkeys when compared with those of controls. A(2A)R mRNA levels of L-DOPA + CI-1041-treated monkeys were at control levels and decreased in the lateral rostral caudate and caudal putamen when compared with those of L-DOPA-treated and saline-treated MPTP monkeys respectively. No change was measured in the caudal medial putamen and caudate nucleus. A(2A)Rs labeled by autoradiography with [(3)H]SCH-58261 had lower level in the L-DOPA + CI-1041-treated MPTP monkeys compared with saline- or L-DOPA-treated MPTP and control monkeys in the rostral lateral and medial caudate and the putamen. No effect of lesion or L-DOPA treatment was measured on [(3)H]SCH-58261-specific binding. These findings suggest that blockade of NMDA receptors could prevent the development of dyskinesias by altering A(2A)Rs.     

Rescue of locomotor impairment in dopamine D2 receptor-deficient mice by an adenosine A2A receptor antagonist.

In Parkinson's disease a degeneration of dopaminergic neurons of the nigrostriatal pathway is observed. Loss of dopaminergic regulation of striatal neuron activity results in altered motor functions. Adenosine A2A (A2AR) and dopamine D2 (D2R) receptors are colocalized in striatal medium spiny neurons. It has been proposed that adenosine binding to A2AR lowers the affinity of dopamine for D2R, thus modulating the function of this receptor. Absence of D2R in knockout mice (D2R-/-) results in impaired locomotion and coordinated movements. This indicates that absence of dopamine in Parkinson's disease might principally affect D2R-mediated effects with regard to locomotor functions. A2AR-selective antagonists have been demonstrated to have anti- parkinsonian activities in various models of Parkinson's disease in rodents and nonhuman primates. In this article, D2R-/- mice were used to explore the possibility that an A2AR antagonist might reestablish their motor impairment. Interestingly, blockade of A2AR rescues the behavioral parameters altered in D2R-/- mice. In addition, the level of expression of enkephalin and substance P, which were altered in D2R-/-, were also reestablished to normal levels after A2AR antagonist treatment. These results show that A2AR and D2R have antagonistic and independent activities in controlling neuronal and motor functions in the basal ganglia. They also provide evidence that selective A2AR antagonists can exhibit their anti-parkinsonian activities through a nondopaminergic mechanism.     

Adenosine,adenosine A2A antagonists,and Parkinson's disease

Adenosine derived from the degradation of ATP/AMP functions as a signalling molecule in the nervous system through the occupation of A1, A2, and A3 adenosine receptors. Adenosine A_2A receptors have a selective localization to the basal ganglia and specifically to the indirect output pathway, and as a consequence offer a unique opportunity to modulate the output from the striatum that is believed critical to the occurrence of motor components of PD. Indeed, the ability of A_2A antagonists to modulate basal ganglia neurotransmission has been shown to be associated with improved motor function in experimental models of PD. This suggests that A_2A antagonists would be effective as a symptomatic treatment in humans without provoking marked dyskinesia. Indeed, the A_2A antagonist istradefylline reduces OFF time in moderate- to late-stage patients with PD already receiving dopaminergic therapy, with an increase in non-troublesome dyskinesia. Adenosine and adenosine receptors also exert actions relevant to pathogenesis in PD, raising the possibility of their use as neuroprotective agents. Both epidemiologic evidence and the current preclinical data strongly support a role for A_2A antagonists in protecting dopaminergic neurons and influencing the onset and progression of PD.     

Istradefylline for Parkinson's disease patients experiencing motor fluctuations: results of the KW-6002-US-018 study

BackgroundIstradefylline (KW-6002) is a selective adenosine A_2A receptor antagonist investigated as adjunctive therapy to levodopa in PD patients with motor response complications. In Phase 2b/3 studies, Istradefylline reduced OFF time without worsening troublesome dyskinesia and was well tolerated.MethodsA randomized, 12-week, double-blind, placebo-controlled parallel-group study evaluated the efficacy of 10, 20, and 40 mg/day of Istradefylline in patients on levodopa therapy with motor response complications. The primary outcome measure was change from baseline to endpoint in the percentage of awake time/day spent in the OFF state as determined by patient diary.ResultsSix hundred and ten patients were randomized. Five hundred and eighty four patients were included in the Intent-to-treat (ITT) group—146 placebo patients and 149 in the 10 mg, 144 in the 20, and 145 patients in the 40 mg Istradefylline groups. Baseline demographics were similar between groups. Treatment cohorts had been diagnosed an average of 9 years diagnosis and 3.6 years from the onset of motor fluctuations; at baseline they had an average of 6.7 h of OFF time and an average UPDRS motor score of 22 when ON. At endpoint, the amount and percentage of OFF time did not differ between Istradefylline and placebo, however a dose-ordering response was observed. Changes from baseline in the UPDRS motor score in the on state for the 40 mg were modest but significant compared to placebo (2.9 vs. 0.8; p < 0.05).ConclusionsAlthough Istradefylline did not impact OFF time duration, it significantly improved motor score at 40 mg/day.     

Neuroprotective effect of L-DOPA co-administered with the adenosine A2A receptor agonist CGS 21680 in an animal model of Parkinson's disease

Adenosine A_2A receptors are a new target for drug development in Parkinson’s disease. Some experimental and clinical data suggest that A_2A receptor antagonists can provide symptomatic improvement by potentiating the effects of -DOPA as well as a decrease in secondary effects such as -DOPA-induced dyskinesia. -DOPA-induced behavioral sensitization in unilateral 6-hydroxydopamine-lesioned rats is frequently used as an experimental model of -DOPA-induced dyskinesia. In the present work this model was used to evaluate the effect of the A_2A receptor agonist CGS 21680 and the A_2A receptor antagonist MSX-3 on -DOPA-induced behavioral sensitization and 6-hydroxydopamine-induced striatal dopamine denervation. -DOPA-induced behavioral sensitization was determined as an increase in -DOPA-induced abnormal involuntary movements and enhancement of apomorphine-induced turning behavior. Striatal dopamine innervation was determined by measuring tyrosine-hydroxylase immunoreactivity. Chronic administration of MSX-3 was not found to be effective at counteracting -DOPA-induced behavioral sensitization. On the other hand, CGS 21680 completely avoided the development of -DOPA-induced behavioral sensitization. The analysis of the striatal dopamine innervation showed that -DOPA-CGS 21680 co-treatment conferred neuroprotection to the toxic effects of 6-hydroxydopamine. This neuroprotective effect was dependent on A_2A and D₂ receptor stimulation, since it was counteracted by MSX-3 and by the D₂ receptor antagonist haloperidol. These results open new therapeutic avenues in early events in Parkinson’s disease.     

Efficacy of memantine, an NMDA receptor antagonist, in the treatment of Parkinson's disease

Summary Memantine is a 1-amino-adamantane derivative which has been proposed to be useful in the treatment of Parkinson's disease. Its beneficial effect has been related to its novel properties as an NMDA receptor blocker which can neutralize the effect of glutamate at striatal and subthalamic levels. In the present study, conducted in an open-fashion, 14 parkinsonian patients with motor fluctuations taking L-dopa, were given a supplement of memantine 30 mg/day. After one month, 10 patients completed the treatment (4 discontinued it due to abdominal pain, psychomotor agitation, confusion and dizziness). In 5 patients, the main parkinsonian features improved significantly (1 point or more on the Webster scale). In 6 patients, off episodes improved (from daily mean of 273 minutes, to 172 minutes). In summary, memantine addition to parkinsonian features, could form a basis for novel therapeutic strategies directed to neutralize the effects of glutamate at striatal and subthalamic levels.     

腺苷A2A受体拮抗剂对大鼠氯化锂-毛果芸香碱所致癫痫模型的影响

目的研究腺苷A2A受体阻断剂对大鼠氯化锂-毛果芸香碱癫痫持续状态(SE)模型的影响。方法选取50只WD大鼠随机分为对照组、模型组及A2A受体阻断剂组。模型组采用氯化锂-毛果芸香碱腹腔注射复制癫痫模型,A2 A受体阻断剂组在氯化锂-毛果芸香碱注射前15 min予腹腔给药(SCH58261 0.05 mg/kg),对照组给予同等剂量生理盐水。在成功诱导癫痫发作40 min后予地西泮及水合氯醛终止发作,并于发作终止后24 h留取标本。尼氏染色法检测三组中海马神经元损伤情况,Westernblot法检测MAPKs(JNK/p-JNK、P38/p-P38和ERK/p-ERK)表达变化。结果对照组、模型组及A2A受体阻断剂组双侧海马CA3区正常形态神经元计数分别为158.6±8.4、59.8±7.4和123.4±5.0,模型组神经元计数显著低于对照组,差异具有统计学意义(P0.05),A2A受体阻断剂组神经元计数显著高于模型组,差异具有统计学意义(P0.05)。Westernblot法检测显示p-JNK、p-P38和p-ERK在模型组中表达明显增多,在A2A受体阻断剂组中p-JNK和p-P38表达减少。结论氯化锂-毛果芸香碱模型中,腺苷A2A受体阻断剂可能通过抑制p-JNK他p-P38的表达对神经元损伤起到保护作用。     

Neuroprotective and anti‐inflammatory effects of the adenosine A2A receptor antagonist ST1535 in a MPTP mouse model of Parkinson's disease

Adenosine A_2A receptor antagonists are one of the most attractive classes of drug for the treatment of Parkinson's disease (PD) as they are effective in counteracting motor dysfunctions and display neuroprotective and anti‐inflammatory effects in animal models of PD. In this study, we evaluated the neuroprotective and anti‐inflammatory properties of the adenosine A_2A receptor antagonist ST1535 in a subchronic 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (MPTP) mouse model of PD. C57BL/6J mice were repeatedly administered with vehicle, MPTP (20 mg/kg), or MPTP + ST1535 (2 mg/kg). Mice were sacrificed three days after the last administration of MPTP. Immunohistochemistry for tyrosine hydroxylase (TH) and cresyl violet staining were employed to evaluate dopaminergic neuron degeneration in the substantia nigra pars compacta (SNc) and caudate‐putamen (CPu). CD11b and glial fibrillary acidic protein (GFAP) immunoreactivity were, respectively, evaluated as markers of microglial and astroglial response in the SNc and CPu. Stereological analysis for TH revealed a 32% loss of dopaminergic neurons in the SNc after repeated MPTP administration, which was completely prevented by ST1535 coadministration. Similarly, CPu decrease in TH (25%) was prevented by ST1535. MPTP treatment induced an intense gliosis in both the SNc and CPu. ST1535 totally prevented CD11b immunoreactivity in both analyzed areas, but only partially blocked GFAP increase in the SNc and CPu. A_2A receptor antagonism is a new opportunity for improving symptomatic PD treatment. With its neuroprotective effect on dopaminergic neuron toxicity induced by MPTP and its antagonism on glial activation, ST1535 represents a new prospect for a disease‐modifying drug. Synapse, 2010. © 2010 Wiley‐Liss, Inc.     

腺苷A2A受体拮抗剂对左旋多巴诱发异动症大鼠行为、纹状体A2A受体和代谢型谷氨酸受体5亚型蛋白表达的影响

目的 评价腺苷A2A受体拮抗剂(CSC)对左旋多巴(L-DOPA)诱发异动症大鼠行为、纹状体A2A受体和代谢型谷氨酸受体5亚型(mGluR5)蛋白表达的影响.方法 6-羟多巴胺(6-OHDA)立体定向损毁大鼠右内侧前脑束,建立单侧损毁帕金森病(PD)大鼠模型.采用随机数字表法将40只成功PD大鼠随机分为4组(每组10只):生理盐水组;L-DOPA 25 mg/kg+苄丝肼6.25 mg/kg组;CSC 2.5 mg/kg组;L-DOPA 25 mg/kg+苄丝肼6.25 mg/kg联合CSC 2.5 mg/kg组.给予大鼠每日2次腹腔注射,持续21 d.在治疗第2、9、11、18、21天观察大鼠行为学变化,Western blot检测纹状体区腺苷A2A受体和mGluR5的蛋白表达水平.结果 L-DOPA联合CSC组PD大鼠损毁对侧前肢跨步数显著增加,与治疗前比较差异有统计学意义,与L-DOPA组相比,前肢功能改善程度不随时间延长而减弱.单独CSC组治疗后对侧前肢跨步数明显增加,与治疗前比较差异有统计学意义,有疗效逐渐增加至稳定趋势.L-DOPA联合CSC组[(11±5)分]部分口颌及肢体异常不自主运动评分较L-DOPA组[(17±4)分]显著减少,差异有统计学意义(t=2.44,P＜0.05).L-DOPA联合CSC治疗逆转了L-DOPA诱导的对侧旋转反应时间缩短和腺苷A2A受体、mGluR5蛋白表达的上调,差异均有统计学意义.结论 腺苷A2A受体与mGluR5均参与了L-DOPA诱发的异动症的发生发展,A2A受体拮抗剂能够改善PD运动症状,增强L-DOPA的抗PD效应且部分减轻异常不自主运动,对L-DOPA诱发的异动症的治疗有着较好的应用前景.

Abstract：

Objective To study the behavioural changes and biological effects of selective adenosine A2A receptor antagonist (CSC) in a rat model of levodopa(L-DOPA) -induced dyskinesia (LID).Methods The hemi-parkinsonian rat model was produced by stereotaxically injecting 6-OHDA to the right medial forebrain bundle. Rats were randomly divided into 4 treatment groups with a random number generating program to receive intraperitoneal injections twice daily for 21 days (n = 10): saline, L-DOPA at 25 mg/kg with benserazide at 6. 25 mg/kg, CSC at 2. 5 mg/kg alone and CSC at 2.5 mg/kg with L-DOPA at 25 mg/kg plus benserazide at 6. 25 mg/kg. Forepaw adjusting steps, abnormal involuntary movements (AIM) and rotational response duration were observed on 2, 9, 11,18 and 21 d. After sacrifice, the expression of adenosine A2A R and mGluR5 was observed by Western blot. Results Co-administration of LDOPA with CSC significantly increased the forelimb adjusting steps of parkinsonian rats during 21 days of treatment when compared to L-DOPA alone. CSC treatment alone increased the forelimb adjusting steps significantly. Co-administration of L-DOPA with CSC ( ( 11 ± 5 ) score) significantly decreased the AIM scores of limb and orolingual muscles when compared to L-DOPA alone (( 17 ± 4) score; t = 2. 44, P ＜0. 05). The subchronic L-DOPA treatment upregulated the striatal expression of adenosine A2A R and mGluR5. However, co-administration of L-DOPA with CSC reversed the shortening of the rotational motor response duration induced by L-DOPA administration during the period of the treatment and attenuated the LDOPA-induced upregulation of adenosine A2A R and mGluR5 expressions. Conclusions CSC improves motor function in a hemi-parkinson rat model, potentiates the antiparkinsonian effects with L-DOPA and partly attenuates LID. Co-administration of L-DOPA with CSC reverses the L-DOPA-induced upregulated expression of A2A R and mGluR5, indicating the involvement of both A2A R and mGluR5 in the onset and progression of LID. Adenosine A2AR antagonists may be promising drugs for treatment of LID.     

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.     

Targeting adenosine A2A receptors in Parkinson's disease

The adenosine A2A receptor has emerged as an attractive non-dopaminergic target in the pursuit of improved therapy for Parkinson's disease (PD), based in part on its unique CNS distribution. It is highly enriched in striatopallidal neurons and can form functional heteromeric complexes with other G-protein-coupled receptors, including dopamine D2, metabotropic glutamate mGlu5 and adenosine A1 receptors. Blockade of the adenosine A2A receptor in striatopallidal neurons reduces postsynaptic effects of dopamine depletion, and in turn lessens the motor deficits of PD. A2A antagonists might partially improve not only the symptoms of PD but also its course, by slowing the underlying neurodegeneration and reducing the maladaptive neuroplasticity that complicates standard 'dopamine replacement' treatments. Thus, we review here a prime example of translational neuroscience, through which antagonism of A2A receptors has now entered the arena of clinical trials with realistic prospects for advancing PD therapeutics.