Population pharmacokinetic-pharmacodynamic analysis of istradefylline in patients with Parkinson disease

New insights into pathogenesis of l-DOPA-induced dyskinesia

Parkinson's disease (PD) is a progressive and self-propelling neurodegenerative disorder, which is characterized by motor symptoms, such as rigidity, tremor, slowness of movement and problems with gait. These symptoms become worse over time. To date, Dopamine (DA) replacement therapy with 3, 4-dihydroxy-l-phenylalanine (L-DOPA) is still the most effective pharmacotherapy for motor symptoms of PD. Unfortunately, motor fluctuations consisting of wearing-off effect actions and dyskinesia tend to occur in a few years of starting l-DOPA. Currently, l-DOPA-induced dyskinesia (LID) is troublesome and the pathogenesis of LID requires further investigation. Importantly, a new intervention for LID is imminent. Thus, this review mainly summarized the clinical features, risk factors and pathogenesis of LID to provide updatefor the development of therapeutic targets and new approaches for the treatment of LID.

Istradefylline to Treat Patients with Parkinson's Disease Experiencing "Off" Episodes: A Comprehensive Review

Parkinson’s disease (PD) is a common neurodegenerative disorder that leads to significant morbidity and disability. PD is caused by a loss of dopaminergic, cholinergic, serotonergic, and noradrenergic neurons in the central nervous system (CNS), and peripherally; the syndromic parkinsonism symptoms of movement disorder, gait disorder, rigidity and tremor are mostly driven by the loss of these neurons in the basal ganglia. Unfortunately, a significant proportion of patients taking levodopa, the standard of care treatment for PD, will begin to experience a decrease in effectiveness at varying times. These periods, referred to as “off episodes”, are characterized by increased symptoms and have a detrimental effect on quality of life and disability. Istradefylline, a novel adenosine A2A receptor antagonist, is indicated as a treatment addition to levodopa/carbidopa in patients experiencing “off episodes”. It promotes dopaminergic activity by antagonizing adenosine in the basal ganglia. This review will discuss istradefylline as a treatment for PD patients with off episodes.

Identification of metabolite biomarkers for L-DOPA-induced dyskinesia in a rat model of Parkinson's disease by metabolomic technology

L-DOPA-induced dyskinesia (LID) is a frequent complication of chronic L-DOPA therapy in the clinical treatment of Parkinson's disease (PD). The pathogenesis of LID involves complex molecular mechanisms in the striatum. Metabolomics can shed light on striatal metabolic alterations in LID. In the present study, we compared metabolomics profiles of striatum tissue from Parkinsonian rats with or without dyskinetic symptoms after chronic L-DOPA administration. A liquid chromatography-mass spectrometry based global metabolomics method combined with multivariate statistical analyses were used to detect candidate metabolites associated with LID. 36 dysregulated metabolites in the striatum of LID rats, including anandamide, 2-arachidonoylglycerol, adenosine, glutamate and sphingosine1-phosphate were identified. Furthermore, IMPaLA metabolite set analysis software was used to identify differentially regulated metabolic pathways. The results showed that the metabolic pathways of "Retrograde endocannabinoid signaling", "Phospholipase D signaling pathway", "Glycerophospholipid metabolism" and "Sphingolipid signaling", etc. were dysregulated in LID rats compared to non-LID controls. Moreover, integrated pathway analysis based on results from the present metabolomics and our previous gene expression data in LID rats further demonstrates that aberrant "Retrograde endocannabinoid signaling" pathway might be involved in the development of LID. The present results provide a new profile for the understanding of the pathological mechanism of LID.

The safety of istradefylline for the treatment of Parkinson's disease

INTRODUCTION

Antagonism of the A2A receptor improves motor behavior in patients with Parkinson's disease (PD), according to results of clinical studies which confirm findings of previous experimental research. The xanthine derivative, istradefylline , has the longest half-life out of the available A2A receptor antagonists. Istradefylline easily crosses the blood-brain barrier and shows a high affinity to the human A2A receptor.

AREAS COVERED

This narrative review aims to discuss the safety and tolerability of istradefylline against the background of the currently available drug portfolio for the treatment of PD patients.

EXPERT OPINION

Istradefylline was safe and well tolerated in clinical trials, which have focused on l-DOPA-treated PD patients. The future of istradefylline as a complementary drug for modulation of the dopaminergic neurotransmission also relies on its potential to act like an l-DOPA plus dopamine agonist sparing future treatment alternative and to reduce the risk of predominant l-DOPA-related onset of motor complications in addition to its direct ameliorating effect on motor symptoms. Dopamine-substituting drugs may dose-dependently produce systemic side effects, particularly onset of hypotension and nausea by peripheral dopamine receptor stimulation. Istradefylline does not interfere with these peripheral receptors and therefore shows a good safety and tolerability profile.

Two new adenosine receptor antagonists for the treatment of Parkinson's disease: istradefylline versus tozadenant

INTRODUCTION

Adenosine A2A receptors are localized in the brain, mainly within the caudate and putamen nuclei of the basal ganglia. Their activation leads to stimulation of the 'indirect' pathway. Conversely, administration of A2A receptor antagonists leads to inhibition of this pathway, which was translated into reduced hypomotility in several animal models of parkinsonism.

AREAS COVERED

In this review, the effects of two A2A receptor antagonists, istradefylline and tozadenant, on parkinsonian symptoms in animal and humans will be discussed.

EXPERT OPINION

Animal studies have shown potent antiparkinsonian effects for several A2A receptor antagonists, including istradefylline. In clinical trials, istradefylline reduced OFF time when administered with levodopa, but results are inconclusive. Results with tozadenant are scarce. Modification of thalamic blood flow compatible with reduced inhibition was noted in one small trial, followed by a significant reduction in OFF time in a larger one. Therefore, both drugs show promising efficacy for the reduction of OFF time in levodopa-treated Parkinson's disease patients, but further research is needed in order to obtain definitive conclusions.

Moonlighting proteins and protein-protein interactions as neurotherapeutic targets in the G protein-coupled receptor field

There is serious interest in understanding the dynamics of the receptor-receptor and receptor-protein interactions in space and time and their integration in GPCR heteroreceptor complexes of the CNS. Moonlighting proteins are special multifunctional proteins because they perform multiple autonomous, often unrelated, functions without partitioning into different protein domains. Moonlighting through receptor oligomerization can be operationally defined as an allosteric receptor-receptor interaction, which leads to novel functions of at least one receptor protomer. GPCR-mediated signaling is a more complicated process than previously described as every GPCR and GPCR heteroreceptor complex requires a set of G protein interacting proteins, which interacts with the receptor in an orchestrated spatio-temporal fashion. GPCR heteroreceptor complexes with allosteric receptor-receptor interactions operating through the receptor interface have become major integrative centers at the molecular level and their receptor protomers act as moonlighting proteins. The GPCR heteroreceptor complexes in the CNS have become exciting new targets for neurotherapeutics in Parkinson's disease, schizophrenia, drug addiction, and anxiety and depression opening a new field in neuropsychopharmacology.