Recent developments in the pharmacological treatment of Parkinson's disease

Safety overview of FDA-approved medications for the treatment of the motor symptoms of Parkinson's disease

INTRODUCTION

Parkinson's disease (PD) is among the most common of the neurodegenerative disorders. Treatment is primarily focused on correcting neurotransmitter imbalances. Several classes of medication are available for this purpose.

AREAS COVERED

A Medline search was performed to gather information about the safety of the medications approved for the treatment of the motor symptoms of PD. This was supplemented with additional articles obtained from online sources and information provided by the FDA and the manufacturers. The focus of this review is the side-effect and safety profiles of carbidopa/levodopa, dopamine agonists, selective monoamine oxidase inhibitors, catechol-o-methyltransferase inhibitors, anticholinergics and amantadine.

EXPERT OPINION

Though serious side-effects may occur, as a group, the medications used for the treatment of PD motor symptoms tend to produce side-effects that are mild to moderate in nature, and that primarily reflect the focus on dopaminergic therapies. Care plans for Parkinson's patients should be approached based on the needs of the individual as disease presentation, lifestyle, level of disability, concurrent disease states and the presence of non-motor symptoms make each case unique. Patients and caregivers must have realistic expectations about the use of PD medications.

Co-occurring chronic conditions and healthcare expenditures associated with Parkinson's disease: a propensity score matched analysis

BACKGROUND

The objective of this study was to ascertain co-occurring chronic conditions and expenditures associated with Parkinson's disease among elderly individuals (age ≥ 65 years).

METHODS

A retrospective, cross-sectional matched case-control design with data from Medical Expenditure Panel Survey (MEPS), a nationally representative survey of households in the United States was used. Elderly with Parkinson's disease (N = 350) were compared to a matched control group (N = 1050) based on propensity scores. Ordinary Least Squares regressions on logged dollars were performed to understand the association between Parkinson's disease and expenditures. All analyses accounted for the complex survey design of the MEPS and were conducted in SAS 9.3.

RESULTS

Among elderly, the average total expenditures were $15,404 for those with Parkinson's disease and $13,333 for those without Parkinson's disease. Results from regressions revealed that elderly with Parkinson's disease had 109% greater total expenditure compared to those without Parkinson's disease, when only demographic and socioeconomic variables were entered in the model. When co-occurring chronic conditions were additionally included in the model, those with Parkinson's disease had 84% greater expenditures compared to those without Parkinson's disease.

CONCLUSIONS

Excess expenditures associated with Parkinson's disease are partially driven by co-occurring conditions among individuals with Parkinson's disease.

Neurobehavioral assessment of hydroalcoholic extract of Trigonella foenum-graecum seeds in rodent models of Parkinson's disease

CONTEXT

Neuroprotective therapy to rescue dopaminergic neurons is an important trait in the management of Parkinson's disease (PD).

OBJECTIVE

The present study identified and evaluated SFSE-T, a standardized hydroalcoholic extract of Trigonella foenum-graecum L. seeds (Fabaceae), in animal models of PD.

MATERIALS AND METHODS

The identification of SFSE-T was carried out by high-performance liquid chromatography for the marker compound trigonelline (TGN). The effects of single dose oral treatment of SFSE-T (10, 30 or 100 mg/kg) were studied using animal models of PD, namely, 6-hydroxydopamine (6-OHDA)-induced unilateral lesions in rats, and 4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced neurodegeneration in C57BL/6 mice. The effects of SFSE-T on monoamino oxidase (MAO) enzyme in vitro as well as possible side effects of SFSE-T in vivo were also evaluated.

RESULTS

The concentration of TGN in a test sample of SFSE-T was found to be 82%. SFSE-T (30 mg/kg, oral) showed a significant increase in the number of ipsilateral rotations (45.67 rotations in 30-min period) as compared with vehicle control group (no rotations) when tested in 6-OHDA-induced unilateral lesioned rats. SFSE-T (30 mg/kg, oral) showed significant reversal of motor dysfunction (spontaneous motor activity scores, speed, distance traveled and number of square crossed) caused by MPTP induced lesions in C57BL/6 mice in pretreatment (1 h) schedule but not in post-treatment (1 h) schedule. SFSE-T neither showed anticholinergic effects nor showed selective MAO-B enzyme inhibition in vitro.

DISCUSSION AND CONCLUSION

SFSE-T showed reversal of motor symptoms in an animal model of PD probably through neuroprotective properties.

Efficacy and safety of standardized extract of Trigonella foenum-graecum L seeds as an adjuvant to L-Dopa in the management of patients with Parkinson's disease

The objective of this study is to evaluate disease modifying efficacy and safety of a standardized extract of Trigonella foenum-graecum L, Fenugreek (IBHB) (family Fabaceae) as a nutritional adjuvant to Levo-dopa (L-Dopa) in Parkinson's disease (PD) patients. We conducted double-blind placebo-controlled proof of concept clinical study of IBHB capsules (300 mg, twice daily) with matching placebo for 6 months of period in 50 patients of PD stabilized on L-Dopa therapy. The efficacy outcome measures were the scores of Unified Parkinson's Disease Rating Scale (UPDRS - total and its subsections), and Hoehn and Yahr (H&Y) staging at baseline and end of 6-months treatment duration. Safety evaluation included haematology, biochemistry, urinalysis parameters and adverse event monitoring. Total UPDRS scores in IBHB treatment (0.098%) showed slower rise as opposed to steep rise (13.36%) shown by placebo. Further, Clinically Important Difference for total UPDRS scores and scores of motor subsection of UPDRS was found to be 5.3 and 4.8, respectively, in favour of IBHB treatment. Similar improvement was shown by IBHB in terms of H&Y staging as compared with placebo. IBHB was found to have excellent safety and tolerability profile. In conclusion, IBHB can be useful adjuvant treatment with L-Dopa in management of PD patients.

Nitric Oxide Synthase Inhibitor Improves De Novo and Long-Term l-DOPA-Induced Dyskinesia in Hemiparkinsonian Rats

Inhibitors of neuronal and endothelial nitric oxide synthase decrease l-3,4-dihidroxifenilalanine (l-DOPA)-induced dyskinesias in rodents. The mechanism of nitric oxide inhibitor action is unknown. The aims of the present study were to investigate the decrease of l-DOPA-induced abnormal involuntary movements (AIMs) in 6-hydroxydopamine (6-OHDA)-lesioned rats by nitric oxide inhibitors following either acute or chronic treatment. The primary findings of this study were that NG-nitro-l-Arginine, an inhibitor of endothelial and neuronal nitric oxide synthase, attenuated AIMs induced by chronic and acute l-DOPA. In contrast, rotational behavior was attenuated only after chronic l-DOPA. The 6-OHDA lesion and the l-DOPA treatment induced a bilateral increase (1.5 times) in the neuronal nitric oxide synthase (nNOS) protein and nNOS mRNA in the striatum and in the frontal cortex. There was a parallel increase, bilaterally, of the FosB/ΔFosB, primarily in the ipsilateral striatum. The exception was in the contralateral striatum and the ipsilateral frontal cortex, where chronic l-DOPA treatment induced an increase of approximately 10 times the nNOS mRNA. Our results provided further evidence of an anti-dyskinetic effect of NOS inhibitor. The effect appeared under l-DOPA acute and chronic treatment. The l-DOPA treatment also revealed an over-expression of the neuronal NOS in the frontal cortex and striatum. Our results corroborated findings that l-DOPA-induced rotation differs between acute and chronic treatment. The effect of the NOS inhibitor conceivably relied on the l-DOPA structural modifications in the Parkinsonian brain. Taken together, these data provided a rationale for further evaluation of NOS inhibitors in the treatment of l-DOPA-induced dyskinesia.

Characterization of major degradation products of an adenosine A2A receptor antagonist under stressed conditions by LC-MS and FT tandem MS analysis

Parkinson's disease (PD) is a very serious neurological disorder, and current methods of treatment fail to achieve long-term control. SCH 420814 is a potent, selective and orally active adenosine A(2A) receptor antagonist discovered by Schering-Plough. Stability testing provides evidence of the quality of a bulk drug when exposed to the influence of environmental factors. Understanding the drug degradation profiles is critical to the safety and potency assessment of the drug candidate for clinical trials. As a result, identification of degradation products has taken an important role in drug development process. In this study, a rapid and sensitive method was developed for the structural determination of the degradation products of SCH 420814 formed under different forced conditions. The study utilizes a combination of liquid chromatography-tandem-mass spectrometry (LC-MS/MS) and Fourier Transform (FT) MS techniques to obtain complementary information for structure elucidation of the unknowns. This combination approach has significant impact on degradation product identification. A total of ten degradation products of SCH 420814 were characterized using the developed method.

Single-photon emission computed tomography and positron emission tomography evaluations of patients with central motor disorders

Neuroimaging biomarkers in movement disorders during the past decade have served as diagnostic agents (Europe), tools for evaluation of novel therapeutics, and a powerful means for describing pathophysiology by revealing in vivo changes at different stages of disease and within the course of an individual patient's illness. As imaging with agents tracking dopaminergic function become more available, the next decade promises to enhance our clinical sophistication in the optimal use of dopaminergic imaging biomarkers for differential diagnosis, characterization of at-risk populations, guiding selection and management of appropriate treatments. The clinical role of these agents as clinical tools goes hand in hand with the development and availability of disease-modifying drugs, which carry the additional requirement for early and accurate diagnosis and improved clinical monitoring once treatment is initiated. Challenges remain in the ideal application of neuroimaging in the clinical algorithms for patient assessment and management. Further, the application of imaging to other targets, both monamineric and nonmonoaminergic, could serve a function beyond the important delineation of pathologic change occurring in patients with Parkinson's disease to suggest some role in improved phenotyping and classification of patients with Parkinson's disease presenting with different symptom clusters. New areas of focus based on the elucidation of mechanisms at the cellular and molecular level, including intense interest in alpha-synuclein and other protein inclusions in neurons and glia, have piqued interest in their in vivo assessment using scinitigraphic methods. Perhaps ultimately, treatment that is targeted to a better delineated pathophysiology-based characterization of movement disorder patients will emerge. The application of neuroimaging biomarkers to multiple ends in movement disorders provides an important model for the multiple roles diagnostic imaging agents can serve in neurodegenerative disorders; for diagnosis, for elaborating pathophysiology in patient populations, for developing new drugs, ultimately for improving clinical management.

Enhanced striatal glutamate release after the administration of rimonabant to 6-hydroxydopamine-lesioned rats

While recent studies have shown that the blockade of cannabinoid CB(1) receptors might be beneficial to alleviate the motor inhibition typical of Parkinson's disease (PD), the neurochemical substrates for this effect remain elusive. Here we have carried out microdialysis experiments to determine whether the effects of rimonabant, a selective antagonist of CB(1) receptors, might be associated with changes in striatal glutamate release in a rat model of PD generated by intracerebroventricular injection of 6-hydroxydopamine. Our data demonstrate that the treatment with rimonabant slightly increased striatal glutamate release in control rats, although this effect was only evident with the highest dose of rimonabant tested (1mg/kg). However, the increase in glutamate release was much more marked in the parkinsonian rats where similar changes were observed at a dose of 1 and 0.1mg/kg, exactly the same dose that relieved motor inhibition in previous behavioral studies. In summary, the potential of rimonabant to act as a possible antihypokinetic agent in parkinsonian rats seems to be related to enhanced glutamate release from excitatory afferents to the striatum. This observation is of potential clinical interest, particularly for those parkinsonian patients that exhibit a poor response to classic levodopa treatment.

Identification of novel, water-soluble, 2-amino-N-pyrimidin-4-yl acetamides as A2A receptor antagonists with in vivo efficacy

Potent adenosine hA2A receptor antagonists are often accompanied by poor aqueous solubility, which presents issues for drug development. Herein we describe the early exploration of the structure-activity relationships of a lead pyrimidin-4-yl acetamide series to provide potent and selective 2-amino-N-pyrimidin-4-yl acetamides as hA2A receptor antagonists with excellent aqueous solubility. In addition, this series of compounds has demonstrated good bioavailability and in vivo efficacy in a rodent model of Parkinson's disease, despite having reduced potency for the rat A2A receptor versus the human A2A receptor.

The role of glutamate transporters in neurodegenerative diseases and potential opportunities for intervention

Extracellular concentrations of the predominant excitatory neurotransmitter, glutamate, and related excitatory amino acids are maintained at relatively low levels to ensure an appropriate signal-to-noise ratio and to prevent excessive activation of glutamate receptors that can result in cell death. The latter phenomenon is known as 'excitotoxicity' and has been associated with a wide range of acute and chronic neurodegenerative disorders, as well as disorders that result in the loss of non-neural cells such as oligodendroglia in multiple sclerosis. Unfortunately clinical trials with glutamate receptor antagonists that would logically seem to prevent the effects of excessive receptor activation have been associated with untoward side effects or little clinical benefit. In the mammalian CNS, the extracellular concentrations of glutamate are controlled by two types of transporters; these include a family of Na(+)-dependent transporters and a cystine-glutamate exchange process, referred to as system X(c)(-). In this review, we will focus primarily on the Na(+)-dependent transporters. A brief introduction to glutamate as a neurotransmitter will be followed by an overview of the properties of these transporters, including a summary of the presumed physiologic mechanisms that regulate these transporters. Many studies have provided compelling evidence that impairing the function of these transporters can increase the sensitivity of tissue to deleterious effects of aberrant activation of glutamate receptors. Over the last decade, it has become clear that many neurodegenerative disorders are associated with a change in localization and/or expression of some of the subtypes of these transporters. This would suggest that therapies directed toward enhancing transporter expression might be beneficial. However, there is also evidence that glutamate transporters might increase the susceptibility of tissue to the consequences of insults that result in a collapse of the electrochemical gradients required for normal function such as stroke. In spite of the potential adverse effects of upregulation of glutamate transporters, there is recent evidence that upregulation of one of the glutamate transporters, GLT-1 (also called EAAT2), with beta-lactam antibiotics attenuates the damage observed in models of both acute and chronic neurodegenerative disorders. While it seems somewhat unlikely that antibiotics specifically target GLT-1 expression, these studies identify a potential strategy to limit excitotoxicity. If successful, this type of approach could have widespread utility given the large number of neurodegenerative diseases associated with decreases in transporter expression and excitotoxicity. However, given the massive effort directed at developing glutamate receptor agents during the 1990s and the relatively modest advances to date, one wonders if we will maintain the patience needed to carefully understand the glutamatergic system so that it will be successfully targeted in the future.

An active transport system in the blood–brain barrier may reduce levodopa availability

Levodopa, the primary drug used to treat patients with Parkinson's disease, is transported into the brain by the facilitative amino acid transporter (L1). We present here an unanticipated discovery: levodopa may be pumped out of the brain by a Na(+)-dependent transport system that couples the naturally occurring Na(+) gradient existing between the brain's extracellular fluid and the cytoplasm of capillary endothelial cells. The activity of this system reduces the net availability of levodopa.

A renaissance in trace amines inspired by a novel GPCR family

Trace amines (TAs) are endogenous compounds that are related to biogenic amine neurotransmitters and are present in the mammalian nervous system in trace amounts. Although their pronounced pharmacological effects and tight link to major human disorders such as depression and schizophrenia have been studied for decades, the understanding of their molecular mode of action remained incomplete because of the apparent absence of specialized receptors. However, the recent discovery of a novel family of G-protein-coupled receptors (GPCRs) that includes individual members that are highly specific for TAs indicates a potential role for TAs as vertebrate neurotransmitters or neuromodulators, although the majority of these GPCRs so far have not been demonstrated to be activated by TAs. The unique pharmacology and expression pattern of these receptors make them prime candidates for targets in drug development in the context of several neurological diseases. Current research focuses on dissecting their molecular pharmacology and on the identification of endogenous ligands for the apparently TA-insensitive members of this receptor family.

Patch application of the dopamine agonist rotigotine to patients with moderate to advanced stages of restless legs syndrome: a double-blind, placebo-controlled pilot study

Efficacy and safety of the dopamine agonist rotigotine (RTG) was investigated in patients with moderate to severe idiopathic restless legs syndrome (RLS), including daytime symptoms. Three fixed doses of rotigotine (1.125 mg, 2.25 mg, and 4.5 mg) and placebo were applied by patches (size, 2.5 cm2 per 1.125 mg) in a double-blind, randomized, parallel-group, multicenter, 1-week, proof-of-principle trial. The primary efficacy measure was the total score on the International Restless Legs Syndrome Scale (IRLS). Additionally, the RLS-6 scale, the Clinical Global Impressions (CGI), and a sleep diary were used. Of 68 enrolled patients, 63 (mean age, 58+/-; 9 years; 64% women) were randomly assigned. RLS severity improved related to dose by 10.5 (1.125 mg RTG/die; P = 0.41), 12.3 (2.25 mg RTG/die; P = 0.18), and 15.7 points (4.5 mg RTG/die; P < 0.01) on the IRLS compared to placebo (8 points). According to the RLS-6 scales, daytime symptoms significantly improved with all rotigotine doses. The CGI items supported the favorable efficacy of the 4.5-mg dose. Skin tolerability of the patches and systemic side effects were similar between rotigotine and placebo. This pilot study suggests that continuous delivery of rotigotine by means of a patch may provide an effective and well-tolerated treatment of RLS symptoms both during night and day.