Cabergoline, pramipexole and ropinirole used as monotherapy in early Parkinson's disease: an evidence-based comparison

Targeting calciumopathy for neuroprotection: focus on calcium channels Cav1, Orai1 and P2X7

As the uncontrolled entry of calcium ions (Ca2+) through plasmalemmal calcium channels is a cell death trigger, the conjecture is here raised that mitigating such an excess of Ca2+ entry should rescue from death the vulnerable neurons in neurodegenerative diseases (NDDs). However, this supposition has failed in some clinical trials (CTs). Thus, a recent CT tested whether isradipine, a blocker of the Cav1 subtype of voltage-operated calcium channels (VOCCs), exerted a benefit in patients with Parkinson's disease (PD); however, outcomes were negative. This is one more of the hundreds of CTs done under the principle of one-drug-one-target, that have failed in Alzheimer's disease (AD) and other NDDs during the last three decades. As there are myriad calcium channels to let Ca2+ ions gain the cell cytosol, it seems reasonable to predict that blockade of Ca2+ entry through a single channel may not be capable of preventing the Ca2+ flood of cells by the uncontrolled Ca2+ entry. Furthermore, as Ca2+ signaling is involved in the regulation of myriad functions in different cell types, it seems also reasonable to guess that a therapy should be more efficient by targeting different cells with various drugs. Here, we propose to mitigate Ca2+ entry by the simultaneous partial blockade of three quite different subtypes of plasmalemmal calcium channels that is, the Cav1 subtype of VOCCs, the Orai1 store-operated calcium channel (SOCC), and the purinergic P2X7 calcium channel. All three channels are expressed in both microglia and neurons. Thus, by targeting the three channels with a combination of three drug blockers we expect favorable changes in some of the pathogenic features of NDDs, namely (i) to mitigate Ca2+ entry into microglia; (ii) to decrease the Ca2+-dependent microglia activation; (iii) to decrease the sustained neuroinflammation; (iv) to decrease the uncontrolled Ca2+ entry into neurons; (v) to rescue vulnerable neurons from death; and (vi) to delay disease progression. In this review we discuss the arguments underlying our triad hypothesis in the sense that the combination of three repositioned medicines targeting Cav1, Orai1, and P2X7 calcium channels could boost neuroprotection and delay the progression of AD and other NDDs.

Impulse control disorders in Parkinson's disease patients treated with pramipexole and ropinirole: a systematic review and meta-analysis

BACKGROUND

This analysis is the first systematic review and meta-analysis assessing occurrences of ICD in PD patients treated with oral DAs: ropinirole (ROP) and pramipexole (PRX). This study compares the two oral DAs to a transdermal patch, rotigotine (RTG).

METHODS

We performed an extensive systematic search for eligible studies from PubMed, Embase, Cochrane Library, and Google Scholar. The data was analyzed by various software, including EndNote, Rayyan, PRISM, and RevMan. Two studies incorporating 658 patients collectively were assessed.

RESULTS

This meta-analysis shows a significant correlation between the usage of PRX (25.3%) or ROP (21.8%) and the development of ICD in PD patients. Compared to the transdermal patch, RTG, PRX was found to have a significant relative risk (P < 0.0001) of 3.46 (95% CI 2.07-5.76), and ROP was found to have a significant relative risk (P < 0.0001) of 2.98 (95% CI 1.77-5.02). The data collected shows RTG is approximately three times less likely to cause ICDs than oral PRX and ROP.

CONCLUSION

The present investigation provides insight into ICD occurrences with PRX, ROP, and RTG to allow physicians to make more informed decisions on risk versus reward when deciding how to treat a PD patient with these drugs. However, related to various disclosed limitations, our conclusion cannot provide definitive practice protocols.

The effect and safety of ropinirole in the treatment of Parkinson disease: A systematic review and meta-analysis

BACKGROUND

It is necessary to conduct a meta-analysis of the clinical randomized controlled trials (RCTs) on ropinirole in the treatment of Parkinson disease (PD), to explore the effects and safety of ropinirole, and to provide a theoretical basis for clinically safe and rational drug use.

METHODS

RCTs on the effectiveness and safety of ropinirole in the treatment of PD were searched. We searched Dutch medical literature database, Pubmed, Cochrane Library, China National Knowledge Infrastructure, Wanfang Knowledge Service Platform up to December 15, 2020. The Cochrane risk bias assessment tool was used to evaluate the quality of the included literature, and the RevMan5.3 software was used for meta-analysis.

RESULTS

A total of 12 RCTs with 3341 patients were included. The changes of Parkinson Disease Rating Scale Part II score (mean difference = -2.23, 95% confidence interval [CI] -2.82 to -1.64) and Parkinson Disease Rating Scale Part III scores (mean difference = -4.93, 95%CI -5.25 to -4.61) in the ropinirole group was significantly lower than that in the control group. The incidence of dizziness (odd risk [OR] = 1.85, 95%CI 1.50-2.28), nausea (OR = 2.17, 95%CI 1.81-2.59), vomiting (OR = 2.73, 95%CI 1.47-5.09), and lethargy (OR = 2.19, 95%CI 1.39-3.44) in the ropinirole group was significantly higher than that in the control group (all P < .05), and there were no significant differences in the incidence of headache (OR = 1.14, 95%CI 0.79-1.65) and insomnia (OR = 1.06, 95%CI 0.72-1.55) were found between 2 groups (all P > .05).

CONCLUSIONS

Ropinirole can help improve the ability of daily living and exercise function of PD patients, but it will increase the incidence of related adverse reactions, which needs to be further confirmed by subsequent large-scale, high-quality RCTs.

Effect of Cabergoline on Cognitive Impairments in Transgenic Drosophila Model of Parkinson’s Disease

Background:

Parkinson’s disease is a common neurodegenerative disorder characterized by selective loss of dopaminergic neurons in the substantia nigra pars compacta.

Introduction:

The effects of alpha synuclein, parkin mutation and pharmacological agents have been studied in the Drosophila model.

Methods:

The effect of cabergoline was studied on the cognitive impairments exhibited by the transgenic Drosophila expressing human alpha-synuclein in the neurons. The PD flies were allowed to feed on the diet having 0.5, 1 and 1.5 μM of cabergoline.

Results and Discussion:

The exposure of cabergoline not only showed a dose-dependent significant delay in the cognitive impairments but also prevented the loss of dopaminergic neurons. Molecular docking studies showed the positive interaction between cabergoline and alpha-synuclein.

Conclusion:

The results suggest a protective effect of cabergoline against the cognitive impairments.

Factors to Consider in the Selection of Dopamine Agonists for Older Persons with Parkinson's Disease

Dopamine agonists (DAs) are frequently used in the management of Parkinson's disease (PD), a complex multisystem disorder influenced substantially by age-related factors. Over 80% of PD patients present after age 60 years and may have clinical features exacerbated by age-related comorbidities or decline in physiological compensatory mechanisms. Pharmacotherapy for motor symptoms in older persons is more likely to involve exclusive use of levodopa combined with a peripheral decarboxylase inhibitor throughout the course of the illness. Non-ergot DAs, such as pramipexole, rotigotine and ropinirole, may be used as de novo monotherapy for the control of motor symptoms in older persons, although they are less efficacious than levodopa therapy. DAs may also be considered as adjunct therapy in older persons when motor symptoms are no longer adequately controlled by levodopa or when motor fluctuations and dyskinesia appear. DAs may be used cautiously in older persons with cognitive impairment and orthostatic hypotension but should be avoided when there is a history or risk of psychosis or impulse control disorders.

Clinical features, pathophysiology, and treatment of levodopa-induced dyskinesias in Parkinson's disease

Dyskinetic disorders are characterized by excess of motor activity that may interfere with normal movement control. In patients with Parkinson's disease, the chronic levodopa treatment induces dyskinetic movements known as levodopa-induced dyskinesias (LID). This paper analyzed the pathophysiology, clinical manifestations, pharmacological treatments, and surgical procedures to treat hyperkinetic disorders. Surgery is currently the only treatment available for Parkinson's disease that may improve both parkinsonian motor syndrome and LID. However, this paper shows the different mechanisms involved are not well understood.

Induction and expression of abnormal involuntary movements is related to the duration of dopaminergic stimulation in 6-OHDA-lesioned rats

Dyskinesia induction in Parkinson's disease (PD) appears less marked with long-acting dopamine agonists than with short-acting L-Dopa, but the relationship to duration of drug action is unknown. It is also unclear whether the duration of drug action affects the expression of established dyskinesia. This study compared the ability of L-Dopa and four dopamine agonists of different duration of action to induce abnormal involuntary movements (AIMs) in 6-hydroxydopamine (6-OHDA)-lesioned rats, and their ability to express established AIMs following prior exposure to L-Dopa. 6-OHDA-lesioned rats were treated with saline, L-Dopa/benserazide, apomorphine, ropinirole, pramipexole or pergolide once daily for 15 days. Repeated administration of the short-acting dopamine agonists, apomorphine (duration 80 min) and ropinirole (duration 90 min) induced marked axial, limb and orolingual AIMs at peak effect. L-Dopa (duration 100 min) produced moderate AIMs at peak effect, while administration of the long-acting dopamine agonists, pramipexole (duration 150 min) and pergolide (duration 240 min) resulted in mild AIMs. In rats primed to exhibit severe AIMs following repeated L-Dopa administration, acute administration of apomorphine, ropinirole and L-Dopa induced severe AIMs. By contrast, pramipexole and pergolide evoked only mild-moderate AIMs. Again, there was a negative correlation between duration of effect and the severity of AIMs expressed. These studies show that both the induction and expression of AIMs in 6-OHDA-lesioned rats are related to the duration of action of dopaminergic drugs. These findings suggest that continuous dopaminergic stimulation could be used both to avoid dyskinesia induction and to improve motor function in late-stage PD when troublesome dyskinesia is evident.

From the cell to the clinic: a comparative review of the partial D₂/D₃receptor agonist and α2-adrenoceptor antagonist, piribedil, in the treatment of Parkinson's disease

Though L-3,4-dihydroxyphenylalanine (L-DOPA) is universally employed for alleviation of motor dysfunction in Parkinson's disease (PD), it is poorly-effective against co-morbid symptoms like cognitive impairment and depression. Further, it elicits dyskinesia, its pharmacokinetics are highly variable, and efficacy wanes upon long-term administration. Accordingly, "dopaminergic agonists" are increasingly employed both as adjuncts to L-DOPA and as monotherapy. While all recognize dopamine D(2) receptors, they display contrasting patterns of interaction with other classes of monoaminergic receptor. For example, pramipexole and ropinirole are high efficacy agonists at D(2) and D(3) receptors, while pergolide recognizes D(1), D(2) and D(3) receptors and a broad suite of serotonergic receptors. Interestingly, several antiparkinson drugs display modest efficacy at D(2) receptors. Of these, piribedil displays the unique cellular signature of: 1), signal-specific partial agonist actions at dopamine D(2)and D(3) receptors; 2), antagonist properties at α(2)-adrenoceptors and 3), minimal interaction with serotonergic receptors. Dopamine-deprived striatal D(2) receptors are supersensitive in PD, so partial agonism is sufficient for relief of motor dysfunction while limiting undesirable effects due to "over-dosage" of "normosensitive" D(2) receptors elsewhere. Further, α(2)-adrenoceptor antagonism reinforces adrenergic, dopaminergic and cholinergic transmission to favourably influence motor function, cognition, mood and the integrity of dopaminergic neurones. In reviewing the above issues, the present paper focuses on the distinctive cellular, preclinical and therapeutic profile of piribedil, comparisons to pramipexole, ropinirole and pergolide, and the core triad of symptoms that characterises PD-motor dysfunction, depressed mood and cognitive impairment. The article concludes by highlighting perspectives for clarifying the mechanisms of action of piribedil and other antiparkinson agents, and for optimizing their clinical exploitation.

Parkinson's disease: emerging pharmacotherapy

Parkinson's disease (PD) is the second most common neurodegenerative disease. The prevalence is increasing with age and averages approximately 0.3% in the entire population. The clinical picture is dominated by the cardinal motor symptoms such as tremor at rest, bradykinesia, muscular rigidity, stooped posture and postural instability. Psychiatric comorbidity is common, comprising dementia, depression, anxiety and psychosis. Although many drugs have been developed and introduced into the market to provide symptomatic treatment, there is still no cure for PD and not even solid evidence for disease-modifying strategies. In addition, motor complications in advanced stages of the disease, side effects of the dopaminergic therapy, and non-motor symptoms remain huge challenges during long-term therapy. Thus, new therapeutic agents are desperately needed. Here, we describe current therapies and possible future developments that we hope will contribute to sustaining quality of life in patients suffering from Parkinson's disease for many years.

Update on the use of pramipexole in the treatment of Parkinson's disease

Pramipexole is a non-ergot dopamine agonist shown to be efficacious in the treatment of Parkinson's disease (PD). This review addresses the literature concerning pramipexole's efficacy in treating motor and non-motor symptoms in PD, its impact on the development of dyskinesias and response fluctuations, the issue of neuroprotection, and the risk for developing adverse events such as increased somnolence, attacks of sudden onset of sleep, cardiac valvulopathy and impulse control disturbances.

Optimizing long-term therapy for Parkinson disease: levodopa, dopamine agonists, and treatment-associated dyskinesia

The treatment of Parkinson disease (PD) involves pharmacological treatment, often with levodopa or dopamine agonists, to restore the dopaminergic deficit associated with parkinsonian symptoms. Either agent provides symptom relief that becomes less effective in the course of PD, and switching or combining these agents or adding other therapies becomes necessary for symptom control. In an effort to delay the development of motor complications, dopamine agonists are often used in the initial treatment of PD. However, control of PD symptoms is superior with levodopa. Moreover, dopamine agonists are less well tolerated overall and are associated with a number of rare but serious adverse effects. In the long-term management of PD, treatment-associated dyskinesia often becomes sufficiently troublesome as to compromise the effective dosing of antiparkinsonian medication. More effective strategies for managing dyskinesia are needed.

Clinical studies with ropinirole in Parkinson's disease and RLS

Ropinirole is a modern dopamine agonist with a half-life of medium extent that is highly selective for D(2)-receptors. Ropinirole is an indole derivative and thus does not belong to the group of ergoline dopamine receptor agonists. Its effect has been proved in a number of controlled studies in both monotherapy and combination treatments of Parkinson's disease. We can meanwhile refer to the long-term data of studies that have been run for more than 10 years. The substance has also been approved for the management of restless legs syndrome. A long-acting formula of the substance will be available soon.

Decreased expression of l-dopa-induced dyskinesia by switching to ropinirole in MPTP-treated common marmosets

Current concepts suggest that pulsatile stimulation of dopamine receptors following L-dopa administration leads to priming for dyskinesia in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine hydrochloride (MPTP)-treated primates, while continuous dopaminergic stimulation with long-acting dopamine agonists does not. We investigated whether L-dopa-induced dyskinesia is reduced by switching to a dopamine agonist. MPTP-treated marmosets received chronic treatment with L-dopa or ropinirole in doses producing equivalent motor activity and reversal of motor deficits. Administration of L-dopa led to the rapid onset of moderate to severe dyskinesia, whereas ropinirole produced only mild dyskinesia. Animals initially treated with L-dopa were switched to an equivalent dose of ropinirole and those treated with ropinirole were switched to an equivalent dose of L-dopa for 56 days. L-dopa-primed animals that were switched to ropinirole showed a trend towards a reduction of dyskinesia intensity, whereas animals initially treated with ropinirole and switched to L-dopa showed a trend toward increased dyskinesia intensity. A subsequent, acute L-dopa challenge reversed motor deficits and induced intense dyskinesia in both groups. This suggests that L-dopa leads to the priming and expression of dyskinesia, but that expression is not maintained when switching to a long-acting dopamine agonist. In contrast, dopamine agonists may prime for dyskinesia, but do not lead to its full expression.

A comparison of sumanirole versus placebo or ropinirole for the treatment of patients with early Parkinson's disease

To assess the safety and efficacy of sumanirole, a highly selective dopamine agonist, versus placebo and demonstrate its noninferiority to ropinirole, 614 patients with early Parkinson's disease (PD) were treated with sumanirole, 1 to 16 mg/day; ropinirole, 0.75 to 24 mg/day; or placebo. Primary end point in this flexible-dose, double-blind, double-dummy, parallel-group study of 40 weeks was the change in total sum of the United Parkinson's Disease Rating Scale (UPDRS) Parts II + III scores from baseline to end of maintenance. Approximately half the subjects in the sumanirole and placebo groups withdrew early from the study, most (51.8% and 68.5%, respectively) due to lack of efficacy. Of the ropinirole subjects who withdrew (50.5%), most discontinued because of adverse events. In sumanirole and ropinirole groups, mean changes from baseline of -2.48 and -5.20 in UPDRS II + III mean scores were significant versus 0.38 in the placebo group (P </= 0.006). Sumanirole and ropinirole are effective in the treatment of patients with early PD when compared with placebo. Noninferiority of sumanirole to ropinirole was not demonstrated, with a difference of 2.70 (90% CI, 0.92-4.49). Sumanirole was better tolerated than ropinirole.

Sumanirole versus placebo or ropinirole for the adjunctive treatment of patients with advanced Parkinson's disease

The aims of this study were to assess the safety, tolerability, and efficacy of sumanirole, a highly selective D(2) dopamine receptor agonist, versus placebo in subjects with advanced Parkinson's disease (PD), and to demonstrate noninferiority of sumanirole to ropinirole. In this flexible-dose, randomized, double-blind, double-dummy, parallel-group study, 948 subjects were treated with sumanirole 1 to 48 mg/day, ropinirole 0.75 to 24 mg/day, or placebo. Treatment consisted of 13 weeks of dose escalation, 26 weeks of maintenance, and 1 week of tapering. Approximately 70% of subjects treated with either sumanirole or ropinirole completed the study. Statistical significance (P < 0.0001) was achieved when both sumanirole and ropinirole groups were compared with placebo, with mean differences of -7.7 and -8.8 on combined sum of the Unified Parkinson's Disease Rating Scale (UPDRS) part II (average on and off) and part III total scores at the end of maintenance. Noninferiority of sumanirole to ropinirole was also demonstrated, with a sumanirole minus ropinirole difference of 1.17 (90% CI: -0.56 to 2.89). Both dopamine agonists, sumanirole and ropinirole, were statistically superior compared with placebo as adjunctive therapy for patients with advanced Parkinson's disease, based on UPDRS II + III total score. Noninferiority of sumanirole to ropinirole was established, with comparable tolerability profiles.

End-of-dose deterioration in non ergolinic dopamine agonist monotherapy of Parkinson's disease

The study was designed to investigate the possible occurrence of "wearing-off" (WO) during dopamine agonist (DA) monotherapy. Sixty patients with "de novo" idiopathic PD were randomised into one of two DA monotherapy branches to receive oral ropinirole at 15 mg per day, or pramipexole at 2.1 mg per day. DA doses could be increased in the following two years but levodopa could not be added until the study ended. WO was assessed by self-evaluation charts confirmed by a blinded observation of a 30% or greater deterioration in the Unified Parkinson's Disease Rating Scale (UPDRS) motor score. Proc Mixed and Kaplan-Meier curves evaluated treatment variables as a function of time. T-tests were used to compare post-hoc variables reclassified according to WO occurrence. Thirty patients received ropinirole, and 30 pramipexole monotherapy. Eighteen patients (30%) experienced "wearing-off" 15-21 months after beginning monotherapy. No differences were observed between treatments. WO phenomena was observed 3.4+/-0.3 hours after intake of the morning or afternoon dose and consisted of UPDRS score worsening by 11.1+/-2.1 points (69-111% more than "on" score). Statistical evaluation gave evidence of differences between patients who experienced WO and those who did not: UPDRS motor scores obtained at admission to the study were higher (by 3.4+/-0.2 points, p=0.01 t-test) and DA doses at 6-12 months were higher in fluctuating patients. UPDRS motor scores deteriorated, however. similarly and there were no differences, in UPDRS scores recorded in ON conditions, between fluctuating and non-fluctuating patients at the end of the study. Our findings provide evidence of WO phenomena in patients with early PD receiving non-ergolinic DA monotherapy.

A review of the receptor-binding and pharmacokinetic properties of dopamine agonists

BACKGROUND

Dopamine agonists (DAs), which can be categorized as ergot derived and non-ergot derived, are used in the treatment of Parkinson's disease.

OBJECTIVES

This review describes the pharmacologic and pharmacokinetic properties of selected DAs and relates these characteristics to clinical outcomes, with an emphasis on adverse events.

METHODS

Relevant articles were identified through a search of MEDLINE (to May 2006) using the terms dopamine agonists (or each individual drug name) and pbarmacokinetics, metabolism, drug-drug interaction, interactions, CYP450, fibrosis, valvular heart disease, tremor, clinical trials, reviews, and meta-analyses. Abstracts from recent sessions of the International Congress of Parkinson's Disease and Movement Disorders were also examined. Clinical studies with <20 patients overall or <10 patients per treatment group in the final analysis were excluded. All DAs that were graded at least possibly useful with respect to at least 3 of 4 items connected to the treatment/prevention of motor symptoms/complications in the most recent evidence-based medical review update were included. This resulted in a focus on the ergot-derived DAs bromocriptine, cabergoline, and pergolide, and the non-ergot-derived DAs pramipexole and ropinirole.

RESULTS

Bromocriptine, cabergoline, pergolide, and ropinirole, but not pramipexole, have the potential for drug-drug interactions mediated by the cytochrome P450 (CYP) enzyme system. The occurrence of dyskinesia may be linked to stimulation of the dopamine D(1) receptor, for which cabergoline and pergolide have a similar and relatively high affinity; bromocriptine, pramipexole, and ropinirole have been associated with a lower risk of dyskinesias. The valvular heart disease (VHD) and pulmonary and retroperitoneal fibrosis seen with long-term use appear to represent a class effect of the ergot-derived DAs that may be related to stimulation of serotonin 5-HT(2B) (and possibly 5-HT(2A)) receptors. The incidence of valvular regurgitation was 31% to 47% with ergot-derived DAs, 10% with non-ergot-derived DAs, and 13% with controls.

CONCLUSIONS

As reflected in the results of the clinical trials included in this review, dyskinesia associated with DA therapy may be linked to stimulation of the D(1) receptor. Fibrosis (including VHD) seemed to be a class effect of the ergot-derived DAs. Each of the DAs except pramipexole has the potential to interact with other drugs via the CYP enzyme system.

Astonishing diversity of natural surfactants: 6. Biologically active marine and terrestrial alkaloid glycosides

This review article presents 209 alkaloid glycosides isolated and identified from plants, microorganisms, and marine invertebrates that demonstrate different biological activities. They are of great interest, especially for the medicinal and/or pharmaceutical industries. These biologically active glycosides have good potential for future chemical preparation of compounds useful as antioxidants, anticancer, antimicrobial, and antibacterial agents. These glycosidic compounds have been subdivided into several groups, including: acridone; aporphine; benzoxazinoid; ergot; indole; enediyne alkaloidal antibiotics; glycosidic lupine alkaloids; piperidine, pyridine, pyrrolidine, and pyrrolizidine alkaloid glycosides; glycosidic quinoline and isoquinoline alkaloids; steroidal glycoalkaloids; and miscellaneous alkaloid glycosides.

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.

Switching from Levodopa to the Long-acting Dopamine D2/D3 Agonist Piribedil Reduces the Expression of Dyskinesia While Maintaining Effective Motor Activity in MPTP-treated Primates

BACKGROUND

The control of motor complications following dopaminergic medication in late-stage Parkinson disease remains problematic.

OBJECTIVE

We now investigate the potential of oral administration of the long-acting dopamine D2/D3 agonist piribedil to decrease the expression of dyskinesia induced by prior exposure to levodopa in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine hydrochloride (MPTP)-treated primates.

METHODS

MPTP-treated common marmosets were treated with equieffective doses of levodopa (10.0-12.5 mg/kg PO, twice daily) or piribedil (3.0-4.0 mg/kg PO, once daily) for 30 days and then switched to the alternative treatment for a further 35 days.

RESULTS

Levodopa administration markedly improved motor function, but dyskinesia rapidly appeared and intensified as treatment progressed. Administration of piribedil produced a similar reversal of MPTP-induced motor deficits but with comparatively mild dyskinesia. On switching from levodopa to piribedil, the intensity of dyskinesia decreased without altering the improvement in motor deficits. However, on switching from piribedil to levodopa, the rapid increase in dyskinesia despite the improvement in motor function being maintained suggests that piribedil also primes for but does not markedly express dyskinesia.

CONCLUSION

The study confirms the low dyskinesia expression resulting from piribedil treatment compared with an equieffective dose of levodopa. Importantly, the results show that switching from levodopa to piribedil rapidly results in a sustained decrease in dyskinesia intensity.

Cardiovascular dysautonomia as a cause of falls in Parkinson's disease

Parkinson's disease (PD) patients have a ninefold increased risk of recurring falls compared to healthy controls. The risk of falling due to cardiovascular dysautonomia (CVD) is not quantifiable. But, CVD is an integral part of the disease and at least 20% of PD patients suffer from orthostatic hypotension, an expression of CVD. One way to reduce falls due to CVD in PD patients could be to give adequate information on the relationship between falling risks and cardiovascular dysautonomia to patients and their caregivers. Moreover, drugs given for PD might contribute to OH and we propose that education and non-pharmacological strategies for its treatment might be preferable, especially because of the low efficacy of drugs available for the treatment of OH and the frailty of elderly PD patients.

Ropinirole, a non-ergoline dopamine agonist

Dopamine agonists have become indispensable in the treatment of Parkinson's disease. In every-day practice, however, the decision to select the best compound for an individual patient is rendered difficult because of the large number of substances available on the market. This review article provides a closer look at the experimental and clinical studies with ropinirole published so far. Ropinirole is a non-ergoline dopamine agonist which has been proven to be effective in both, monotherapy and combination therapy of idiopathic Parkinson's disease. In addition to ameliorating bradykinesia, rigor, and tremor, ropinirole facilitates the daily life and improves depressive moods of patients with Parkinson's disease. The long-term complications of levodopa are avoided, and problems commonly associated with levodopa treatment are reduced. Ropinirole appears to have a neuroprotective effect. In addition to Parkinson's disease, ropinirole has also been used successfully in the treatment of restless legs syndrome.

Sumanirole, a highly dopamine D2-selective receptor agonist: in vitro and in vivo pharmacological characterization and efficacy in animal models of Parkinson's disease

The purpose of this study is to demonstrate that sumanirole is a novel dopamine receptor agonist with high in vitro and in vivo selectivity for the D(2) receptor subtype. Sumanirole, (R)-5,6-dihydro-5-(methylamino)-4H-imidazo[4,5,1-ij]quinolin-2(1H)-one (Z)-2-butenedioate (1:1), is unique; it has greater than 200-fold selectivity for the D(2) receptor subtype versus the other dopamine receptor subtypes in radioligand binding assays. In cell-based assays, sumanirole is a fully efficacious agonist, with EC(50) values between 17 and 75 nM. In animals, sumanirole elicits many physiological responses attributed to D(2)-like receptor function. In rats, sumanirole is a full agonist for elevation of striatal acetylcholine levels (ED(50) = 12.1 micromol/kg i.p.). Sumanirole s.c. dose dependently decreased plasma prolactin levels and depressed dopamine neuron firing rates in the substantia nigra pars compacta with an ED(50) of 2.3 micromol/kg i.v. This high selectivity for D(2) receptors translates into excellent locomotor stimulant activity in animal models of Parkinson's disease. In reserpinized, alpha-methyl-para-tyrosine-treated rats, sumanirole caused a significant and sustained increase in horizontal activity at doses > or =12.5 micromol/kg s.c. In unilateral 6-hydroxydopamine-lesioned rats, sumanirole caused profound, sustained rotational behavior and was substantially more efficacious than any other agonist tested. Sumanirole-stimulated rotational behavior was blocked by the dopamine receptor antagonist haloperidol. Sumanirole dose dependently improved disability scores and locomotor activities of two of three 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-lesioned monkeys. In summary, sumanirole is the first published selective D(2) receptor agonist. The compound has activity in animal models of dopamine hypofunction and has a high level of efficacy in animal models of Parkinson's disease.

Pathophysiological basis of drug-induced dyskinesias in Parkinson's disease

Drug-induced dyskinesias (DID) represent a troublesome, dose-limiting, and common complication of long-term pharmacotherapy in Parkinson's disease (PD) patients. The pathophysiological basis and clinical nature of DID is of major interest for clinicians and neuroscientists. In this review article, we evaluate the theories of pathophysiology and molecular basis of DID, validity of various animal models used in DID related research, and electrophysiological characteristics of various basal ganglia nuclei during DID. We also discuss the relevance of various treatment strategies to the pathophysiological mechanisms.

Treatment of motor dysfunction in Parkinson's disease: an overview

Levodopa remains the most effective treatment for Parkinson's disease (PD). However, the use of this drug is complicated by several adverse effects, in particular motor fluctuations and dyskinesias. Drugs providing more continuous dopaminergic stimulation and surgical approaches, such as deep-brain stimulation, have an important ameliorative effect on these problems. Despite these advances, the progression of the disease remains unaffected and strategies that slow or stop the neurodegenerative process are currently not available. Nevertheless, several compounds or surgical procedures are candidates for being neuroprotective and some of them are under evaluation.

Alternatives to Levodopa in the Initial??Treatment of Early Parkinson???s Disease

Parkinson's disease (PD) is primarily a disease of elderly patients. This article reviews current knowledge and recent developments relating to drugs that can be used as alternatives to levodopa as initial treatment of PD. Synthetic orally acting dopamine agonists have found increasing favour as an option for early PD in relatively young patients. This strategy is based on evidence that this approach may delay the onset of motor fluctuations, at least during the first 5 years of treatment. Subcutaneous apomorphine infusions may attenuate motor fluctuations in late-stage disease, and transdermal rotigotine, a dopamine agonist in development, has also been shown to be efficacious. The greater proclivity for dopamine agonists to cause psychotoxicity has, however, limited their routine use in the elderly. Selective monoamine oxidase type B (MAO-B) inhibitors, used as monotherapy, delay the need for the introduction of levodopa by about 9 months. These agents appear to be less efficacious than dopamine agonists but are better tolerated. Concern has been expressed about the potential of the MAO-B inhibitor selegiline (deprenyl) to induce cardiovascular adverse effects (orthostatic hypotension), either directly or through its amphetamine catabolites. Rasagiline is a new MAO-B inhibitor that is not broken down to amphetamine derivatives and is indicated as both monotherapy in early PD and as adjunctive therapy in PD patients with motor fluctuations. Two older classes of agents have undergone a resurgence of interest in recent years. Amantadine, which enhances dopaminergic transmission and has antiglutamate activity, is occasionally used as monotherapy but has recently been widely used as an antidyskinetic agent in late-stage PD. Anticholinergic drugs, such as benztropine (benzatropine) and orphenadrine also provide control of symptoms when used as monotherapy, but their psychotoxic, cognitive and autonomic adverse events make them inappropriate for the treatment of the elderly. Effective therapy in PD should prevent disease progression and abolish motor and cognitive handicap. Currently, none of the existing drugs meets all these needs.