Dopamine agonists and neuroprotection in Parkinson's disease

Dopamine agonists are effective in reversing the motor symptoms of Parkinson's disease (PD). They have also shown that they can delay or prevent the onset of motor complications associated with levodopa use. Recent attention has focused on the possible role for dopamine agonists in neuroprotection. Numerous studies have demonstrated that a variety of dopamine agonists can protect dopaminergic neuronal function in several toxin model systems. Pramipexole in particular has shown efficacy in reducing toxicity to MPTP, MPP, rotenone and 6-hydroxydopamine. Recent studies in early PD using imaging parameters as a surrogate marker of dopaminergic neuronal integrity have shown that pramipexole and ropinirole can apparently retard the rate of cell loss. These observations are of considerable interest, but additional studies are required to confirm a neuroprotective function for these dopamine agonists.     

Milestones in Parkinson's disease therapeutics

In the mid‐1980s, the treatment of Parkinson's disease was quite exclusively centered on dopatherapy and was focusing on dopamine systems and motor symptoms. A few dopamine agonists and a monoamine oxidase B inhibitor (selegiline) were used as adjuncts in advanced Parkinson's disease. In the early 2010s, levodopa remains the gold standard. New insights into the organization of the basal ganglia paved the way for deep brain stimulation, especially of the subthalamic nucleus, providing spectacular improvement of drug‐refractory levodopa‐induced motor complications. Novel dopamine agonists (pramipexole, ropinirole, rotigotine), catecholmethyltransferase inhibitors (entacapone), and monoamine oxidase B inhibitors (rasagiline) have also been developed to provide more continuous oral delivery of dopaminergic stimulation in order to improve motor outcomes. Using dopamine agonists early, before levodopa, proved to delay the onset of dyskinesia, although this is achieved at the price of potentially disabling daytime somnolence or impulse control disorders. The demonstration of an antidyskinetic effect of the glutamate antagonist amantadine opened the door for novel nondopaminergic approaches of Parkinson's disease therapy. More recently, nonmotor symptoms (depression, dementia, and psychosis) have been the focus of the first randomized controlled trials in this field. Despite therapeutic advances, Parkinson's disease continues to be a relentlessly progressive disorder leading to severe disability. Neuroprotective interventions able to modify the progression of Parkinson's disease have stood out as a failed therapeutic goal over the last 2 decades, despite potentially encouraging results with compounds like rasagiline. Newer molecular targets, new animal models, novel clinical trial designs, and biomarkers to assess disease modification have created hope for future therapeutic interventions. © 2011 Movement Disorder Society     

How to succeed in using dopamine agonists in Parkinson's disease

Dopamine receptor agonists are assuming increased importance in the treatment of both early and advanced symptoms of Parkinson's disease (PD). However, tolerability of these drugs can be a problem. Identifying patients who are at increased risk of adverse effects is central to using dopamine agonists in PD. The newer agonists, pramipexole and ropinirole, are generally adequate without levodopa for early symptoms and carry the hope for a more acceptable profile of long-term side-effects. In the patient with advanced disease, all four dopamine agonists significantly augment the response to levodopa, which reduces the problems of motor fluctuations and drug related dyskinesia. Understanding the common pitfalls when prescribing these drugs will facilitate their safety and efficacy.     

Levodopa in the treatment of Parkinson's disease

The predominant motor features of Parkinson's disease (PD) are caused by degeneration of dopaminergic neurones and can be reversed in part or whole by dopamine replacement or augmentation strategies. Physicians have most experience with the use of levodopa, which remains the most potent oral dopaminergic treatment for PD. There are reservations about the long-term use of levodopa, most particularly in the context of its propensity to induce motor fluctuations and dyskinesias. Strategies exist to delay or diminish these complications, but the physician must lay the basis for these in the selection of drugs for early treatment and the sequence of drugs introduced subsequently. Levodopa efficacy and duration of effect may be enhanced by combination with a catechol- O -methyl transferase inhibitor. Maintaining good motor function and quality of life remain the primary goals of therapy and the principle that treatment must be tailored to the individual patient's needs is paramount.     

Platelet monoamine oxidase B activity in Parkinson's disease: A re-evaluation

Summary An increase in platelet monoamine oxidase (MAO) B activity in drug-free parkinsonians (n=6) compared with healthy controls (n=10) has been confirmed using both phenylethylamine (PEA) and dopamine as substrates, reaching statistical, significance in the case of PEA oxidising activity (p<0.05). Thus, certain reports of raised platelet MAO B activity towards PEA but decreased activity towards dopamine in parkinsonians, raising the possibility of the existence of an abnormal form of MAO B in this condition, cannot be supported.     

Dihydroergocriptine in Parkinson's disease: clinical efficacy and comparison with other dopamine agonists

The present paper reviews clinical studies on the use of dihydroergocriptine (DHEC), an ergot derivative with dopamine agonist activity, for the treatment of Parkinson's disease. This compound is a hydrogenated ergot derivative structurally quite similar to bromocriptine, from which it differs because of the hydrogenation in C9 C10 and the lack of bromine in C2. DHEC has a potent D2-like receptor agonist and a partial D1-like receptor agonist activity; because of this biochemical profile, it has been suggested that DHEC may produce fewer side-effects and have clinical efficacy equal to that of a classical dopamine agonist. Several open-label and double-blind studies indicate that DHEC is an efficacious remedy for parkinsonian signs and symptoms. Further studies are necessary to compare DHEC to new dopamine agonists (pergolide, cabergoline, ropinirole, and pramipexole) which have been more recently marketed.     

Selegiline as a primary treatment of Parkinson's disease

In order to investigate the efficacy of selegiline as a primary treatment in Parkinson's disease (PD), we carried out a placebo controlled, double-blind prospective trial. Fifty-four de novo patients with PD were randomized to receive either selegiline (10 mg/day) or matching placebo. We continued the monotherapy until the initiation of levodopa therapy became necessary. The disability of the patients was evaluated with three different rating scales at baseline, after 3 weeks, 2, 4, 8, and 12 months, and every 4 months thereafter. Fifty-two patients were eligible for the final analysis: 27 in the selegiline group and 25 in the placebo group. The median duration of time without levodopa was 545 ± 90 days in the selegiline treated patients and 372 ± 28 days in the placebo treated ones (p = 0.03). The disability of the patients was significantly milder in the selegiline than in the placebo group up to 12 months. More patients showed symptomatic improvement in the selegiline than in the placebo group. However, the symptomatic effect alone did not explain the prolongation of the time without levodopa in the selegiline treated patients. Selegiline was well tolerated and no severe side effects were encountered.     

Peripheral blood cell activities of monoamine oxidase B and superoxide dismutase in Parkinson's disease

Summary Monoamine oxidase type B (MAO-B) and superoxide dismutase (SOD) are two enzyme stystems that are potentially relevant to an oxidative stress model of Parkinson's disease (PD) causation. Activities of MAO-B in platelets (nmol/10⁸ cells/hr) and total SOD in lymphocytes (U/mg protein) were assayed among 28 cases of idiopathic PD and 22 controls. As anticipated, MAO-B was lowest in PD cases on selegiline (L-deprenyl) therapy (mean 1.10). There was a slight deficit of MAO-B among male cases not taking selegiline compared to controls (3.78 vs. 4.15), but the opposite trend was observed for females (6.18 vs. 4.16). SOD was slightly higher in cases (7.40), than controls (6.81). Excess SOD among PD cases was seen irrespective of gender, age, or selegiline treatment, although none of the differences was statistically significant Future research on SOD should take advantage of the availability of assays specific for the cytosolic and mitochondrial forms of the enzyme.     

Monoamine oxidase, dopamine and Parkinson's disease

Four aspects about monoamine oxidase (MAO; E.C. 1.4.3.4) are of obvious interest in relation to Parkinson's disease and its treatment with the irreversible and selective MAO-B inhibitor L-deprenyl and are discussed in this review: 1) To what extent the two forms of MAO are of importance for the deamination of dopamine and to what degree MAO localised inside and outside of dopaminergic nerve terminals contributes 2) The kinetics of the MAO-protein, i.e. the rate of recovery of MAO after irreversible inhibition. 3) To what extent MAO may be changed as a consequence of the pathophysiological processes. 4) To what extent MAO may be involved as a force in the pathophysiological processes.     

Platelet monoamine oxidase-B activity in Parkinson's disease

Summary Platelet MAO-B levels have been investigated in seventeen consecutively diagnosed and previously untreated patients with idiopathic Parkinson's disease using the non-hydroxylated catecholamine, -phenylethylamine, as substrate. Patients with Parkinson's disease had MAO-B activity levels that were considerably higher than sex and age matched normal controls or patients with Motor neurone disease or Myasthenia gravis.     

New approaches in the use of selegiline for the treatment of Parkinson's disease

Abstract– Selegiline hydrochloride (deprenyl) is a safe, useful adjuvant therapy in patients with Parkinson's disease treated with L-dopa. The optimum time for its introduction into the treatment regimen of a patient remains controversial. A multi-centre long-term study being conducted by the Parkinson's Disease Research Group of the United Kingdom to attempt to answer whether selegiline improves the natural history of Parkinson's disease is discussed. In a separate study we have been unable to demonstrate that higher doses of selegiline (up to 40 mg a day) produce additional therapeutic benefit above the conventional dose of 10 mg a day in levodopa-treated patients with motor fluctuations. Preliminary data from a neuropsychological study is also presented which suggests that selegiline may have beneficial effects on the speed of psychomotor responses supporting the anecdotal clinical observations of increased mental energy and alacrity.     

Depression in Parkinson's disease -- a review

Major depression is present, at any given time, in 20-40% of Parkinson's disease (PD) patients, several times the prevalence in the general population. In addition, depression may precede the diagnosis of PD. These observations and reports of depression during deep brain stimulation of regions contiguous to the substantia nigra, as well as reports of dopamine agonist improving depression, suggest depression, rather than being mainly a psychological reaction to a debilitating disease, is part of PD. It is postulated that mesolimbic and mesocortical dopaminergic pathways that mediate affect, behavior, and cognition, contribute to depression in PD.     

The effect of monoamine oxidase B (MAOB) and catechol-O-methyltransferase (COMT) polymorphisms on levodopa therapy in patients with sporadic Parkinson's disease

OBJECTIVES: The etiology of sporadic idiopathic Parkinson's disease (PD) is considered multifactorial with both genetic and environmental factors modifying the disease expression. Recent studies suggest that polymorphism in monoamine oxidase B (MAOB) and catechol-O-methyltransferase (COMT) might influence the risk and treatment of PD. The aim of the study was to evaluate the effect of MAOB and COMT genetic polymorphism on effective daily dose of levodopa applied during the first 5 years of treatment, and to find out if a relationship exists between MAOB and COMT haplotypes and motor disturbances onset in PD patients treated with levodopa preparations. MATERIALS AND METHODS: A total of 95 patients (40 females and 55 males) of Polish origin diagnosed with sporadic PD were enrolled into the study, and were divided into two groups. Group 1 - patients treated with doses of levodopa below 500 mg/day during the first 5 years of treatment. Group 2 - patients requiring levodopa doses exceeding 500 mg/24 h during the first 5 years of treatment. Low activity alleles of MAOB and COMT, i.e. MAOB allele A and COMT(L) as well as high activity ones, i.e. MAOB allele G and COMT(H), were determined using PCR-RFLP method. RESULTS: No statistically significant differences were found in MAOB and COMT allele distribution in the two groups. However, the frequency of COMT(L/L) homozygotes was higher in the group treated with low doses of levodopa when compared with the second group. MAOB and COMT AG-HH haplotype predominated in the group of females treated with high daily doses of levodopa when compared with AG-LL haplotype in the group of females treated with low daily doses of levodopa (<500 mg/24 h). CONCLUSION: The results of the study suggest that patients with COMT(L/L) genotype and possibly MAOB genotype A may benefit from more efficient and safer levodopa therapy.     

Motor fluctuations in Parkinson's disease: pathophysiology and treatment

At the initial stages of Parkinson's disease (PD), levodopa (LD) is able to reduce most motor symptoms and to significantly improve the patient's quality of life. However, in the vast majority of patients with prolonged LD usage, some decline in efficacy occurs and motor complications eventually begin to appear. These complications consist not only of daily fluctuations in the voluntary motor performance often accompanied by involuntary movements, but also of fluctuations in cognitive, autonomic, and sensory functions. Several recent studies on LD complications in PD have led to a better understanding of their pathophysiology and of the possible therapeutic interventions, and a summary of these findings is presented in this review. Different observations now suggest that postsynaptic pharmacodynamic factors play a major role in determining fluctuations in PD. Two explanations are given: chronic intermittent dopaminergic therapy may lead to postsynaptic receptor downregulation in PD; or, receptor changes in the striatum may occur independently of treatment as a result of structural adaptation of the postsynaptic dopaminergic system to the progressive decline of the nigrostriatal pathway. The hypothesis of reversible postsynaptic changes as the main mechanism underlying a fluctuating response to LD lends itself to a possible pharmacological manipulation of the dopaminergic response to reverse, or even avoid, motor fluctuations (initial monotherapy with dopamine agonists and early combination LD/dopamine agonists). The role of peripheral pharmacokinetics factors is also critical and the use of controlled release LD formulations, of monoamine oxidase (MAO)-B and of catechol-O-methyltransferase (COMT) inhibitors may all, to a different degree, improve such phenomena. In the last decade, there has been a resurgence in surgical therapies in advanced PD, due to higher levels of accuracy and safety provided by the new surgical devices, and to a more precise localization of the target areas allowed by the neurophysiological mapping techniques. The surgical procedures currently used in advanced PD are stereotactic brain lesions (internal globus pallidus and subthalamic nucleus), chronic brain stimulation (of the same nuclei) and striatal grafting of dopamine-producing cells. All these procedures have already shown their efficacy in the management of severe fluctuations in PD, but their indications, and relative advantages and disadvantages, are still the subject of considerable debate and controversy.     

依达拉奉对帕金森病大鼠模型的神经保护作用及黑质纹状体丙二醛和一氧化氮水平的影响

目的 探讨依达拉奉对帕金森病(PD)大鼠的神经保护作用及黑质纹状体丙二醛(MDA)和一氧化氮(NO)水平的影响.方法 将72只SD大鼠随机分为正常对照组(n=12)、生理盐水对照组(NS组,n=12)、依达拉奉治疗组(ED组,n=48),ED组又分为ED 0.3 mg、1 mg、3 mg及3 mg停药后亚组,每个亚组12只大鼠.在大鼠脑内注入6-羟基多巴胺(6-OHDA)制作PD模型,术后各组大鼠分别相应给予NS 1 ml及ED 0.3 mg/kg、1 mg/kg、3 mg/kg腹腔注射,每天2次,连续14 d.对各组大鼠并进行旋转试验;用免疫组化染色检测黑质酪氨酸羟化酶(TH)阳性细胞数,化学比色法检测黑质纹状体MDA和NO水平.结果 正常对照组大鼠旋转圈数与NS组及ED各亚组比较,差异有统计学意义(均P＜0.01).ED 3 mg及ED 3 mg停药后亚组的旋转圈数显著少于NS组及ED 0.3 mg、1 mg亚组(均P＜0.05).NS组及各ED亚组左侧黑质TH阳性神经元显著少于正常对照组及右侧(均P ＜0.05).ED 3 mg及ED 3 mg停药后亚组左侧黑质TH阳性神经元显著多于NS组和ED 0.3 mg、1 mg亚组(均P＜0.05).与正常对照组比较,NS组和各ED亚组黑质、纹状体NO和MDA水平显著升高(均P＜0.01).ED 3 mg及ED 3 mg停药后亚组黑质、纹状体NO和MDA水平较NS组和ED 0.3 mg、1 mg亚组显著降低(均P＜0.05).结论 依达拉奉对PD大鼠的神经保护作用呈剂量依赖性;其能抑制过氧化反应,降低PD大鼠黑质纹状体的MDA、NO水平.     

Evidence-based medical review update: pharmacological and surgical treatments of Parkinson's disease: 2001 to 2004.

The objective of this study is to update a previous evidence-based medicine (EBM) review on Parkinson's disease (PD) treatments, adding January 2001 to January 2004 information. The Movement Disorder Society (MDS) Task Force prepared an EBM review of PD treatments covering data up to January 2001. The authors reviewed Level I (randomized clinical trials) reports of pharmacological and surgical interventions for PD, published as full articles in English (January 2001-January 2004). Inclusion criteria and ranking followed the original program and adhered to EBM methodology. For Efficacy Conclusions, treatments were designated Efficacious, Likely Efficacious, Non-Efficacious, or Insufficient Data. Four clinical indications were considered for each intervention: prevention of disease progression; treatment of Parkinsonism, as monotherapy and as adjuncts to levodopa where indicated; prevention of motor complications; treatment of motor complications. Twenty-seven new studies qualified for efficacy review, and others covered new safety issues. Apomorphine, piribedil, unilateral pallidotomy, and subthalamic nucleus stimulation moved upward in efficacy ratings. Rasagiline, was newly rated as Efficacious monotherapy for control of Parkinsonism. New Level I data moved human fetal nigral transplants, as performed to date, from Insufficient Data to Non- efficacious for the treatment of Parkinsonism, motor fluctuations, and dyskinesias. Selegiline was reassigned as Non-efficacious for the prevention of dyskinesias. Other designations did not change. In a field as active in clinical trials as PD, frequent updating of therapy-based reviews is essential. We consider a 3-year period a reasonable time frame for published updates and are working to establish a Web-based mechanism to update the report in an ongoing manner.     

Pramipexole and pergolide in the treatment of depression in Parkinson''s disease: a national multicentre prospective randomized study

An 8-month multicentre prospective randomized study aimed at comparing the effects of dopamine receptor agonists pramipexole (PPX; Mirapexin) and pergolide (PRG; Permax) as add-on to L-dopa therapy on depression [Montgomery and Asberg Depression Rating Scale (MADRS)] in 41 non-demented patients (25 men, 16 women) suffering from both mild or moderate depression and advanced Parkinson's disease (PD). The assessment was performed by a blinded independent observer. Motor symptoms (UPDRS III), motor complications (UPDRS IV), activities of daily living (UPDRS II and VI) and depressive symptoms as measured by Self - Rating Depression Scale by Zung were evaluated in an open-label design. The average value of Zung scores decreased significantly in both groups with no statistical difference between both groups. A significant decrease in the average value of MADRS scores was present only in the PPX group. The average UPDRS scores decreased significantly with no statistical difference between both groups at the comparable average total daily dose of both preparations. In both cases, the total daily dose of L-dopa decreased significantly but the decrease was statistically more pronounced in the PRG group. Our results demonstrate the antidepressant effect of PPX in patients with PD while we can't make any conclusions with regard to antidepressant effect of PRG.     

Perspectives on recent advances in the understanding and treatment of Parkinson's disease

There have been numerous important recent advances in our understanding of the causes of Parkinson's disease (PD), the treatments available and how these are best applied for the long-term management of patients. Novel genes causing familial PD have been discovered and mechanisms leading to cell dysfunction and death identified. The PD prodrome is now a subject of great interest and clinical markers are being defined that may in future, together with biochemical markers, support an early, pre-motor diagnosis of PD. This will become important as new therapies are developed to modify disease progression. In the interim, the optimization of existing therapies remains an important priority. The value of existing and novel continuous drug delivery systems in PD is seen as providing simplified regimens, maintenance of motor control, reduction in motor complications and improved patient adherence to drug use.