The antiparkinson drug ropinirole inhibits movement in a Parkinson's disease mouse model with residual dopamine neurons

Dopaminergic inhibition of the inwardly rectifying potassium current in direct pathway medium spiny neurons in normal and parkinsonian striatum

Despite the profound behavioral effects of the striatal dopamine (DA) activity and the inwardly rectifying potassium channel ( Kir ) being a key determinant of striatal medium spiny neuron (MSN) activity that also profoundly affects behavior, previously reported DA regulations of Kir are conflicting and incompatible with MSN function in behavior. Here we show that in normal mice with an intact striatal DA system, the predominant effect of DA activation of D1Rs in D1-MSNs is to cause a modest depolarization and increase in input resistance by inhibiting Kir, thus moderately increasing the spike outputs from behavior-promoting D1-MSNs. In parkinsonian (DA-depleted) striatum, DA increases D1-MSN intrinsic excitability more strongly than in normal striatum, consequently strongly increasing D1-MSN spike firing that is behavior-promoting; this DA excitation of D1-MSNs is stronger when the DA depletion is more severe. The DA inhibition of Kir is occluded by the Kir blocker barium chloride (BaCl 2 ). In behaving parkinsonian mice, BaCl 2 microinjection into the dorsal striatum stimulates movement but occludes the motor stimulation of D1R agonism. Taken together, our results resolve the long-standing question about what D1R agonism does to D1-MSN excitability in normal and parkinsonian striatum and strongly indicate that D1R inhibition of Kir is a key ion channel mechanism that mediates D1R agonistic behavioral stimulation in normal and parkinsonian animals.

Efficacy and safety of non-ergot dopamine-receptor agonists as an adjunct to levodopa in advanced Parkinson's disease: A network meta-analysis

BACKGROUND AND PURPOSE

Non-ergot dopamine agonists (NEDAs) have been used as an adjunct therapy to levodopa in advanced Parkinson's disease (PD) for many years. However, there is no strong evidence that a given NEDA is more potent than another. To compare and rank the efficacy, tolerability, and safety of six commonly used NEDAs as an adjunct to levodopa in advanced PD, which includes long-acting and standard formulations, a network meta-analysis was performed.

METHODS

The MEDLINE, Embase, Cochrane Central Register of Controlled Trials, China National Knowledge Infrastructure, and Wanfang databases were searched from January 1996 to June 2022 for eligible randomized controlled trials (RCTs). Six NEDAs, including rotigotine transdermal patch, ropinirole immediate-release (IR)/prolonged-release (PR), pramipexole IR/extended-release (ER), and piribedil, were investigated.

RESULTS

A total of 34 RCTs (7868 patients) were included in the current study. The surface under the cumulative ranking curve indicated that ropinirole PR was associated with the best improvement in Unified Parkinson's Disease Rating Scale (UPDRS)-II, UPDRS-III, and UPDRS-II + III (0.811, 0.742, and 0.827). For OFF time reduction, pramipexole IR ranked first (0.979), and ropinirole PR ranked first in OFF time responder rate (0.927). Pramipexole ER ranked first in overall withdrawals, and rotigotine transdermal patch ranked first in the incidence of adverse events (≥1 AEs).

CONCLUSIONS

This network meta-analysis suggests six commonly used NEDAs are effective as an adjunct to levodopa in advanced PD. In comprehensive consideration of better symptomatic management, ropinirole PR may be a better choice than other NEDAs in advanced PD. Six NEDAs showed different profiles of AEs.

Promising biomarkers and therapeutic targets for the management of Parkinson's disease: recent advancements and contemporary research

Parkinson's disease (PD) is one of the progressive neurological diseases which affect around 10 million population worldwide. The clinical manifestation of motor symptoms in PD patients appears later when most dopaminergic neurons have degenerated. Thus, for better management of PD, the development of accurate biomarkers for the early prognosis of PD is imperative. The present work will discuss the potential biomarkers from various attributes covering biochemical, microRNA, and neuroimaging aspects (α-synuclein, DJ-1, UCH-L1, β-glucocerebrosidase, BDNF, etc.) for diagnosis, recent development in PD management, and major limitations with current and conventional anti-Parkinson therapy. This manuscript summarizes potential biomarkers and therapeutic targets, based on available preclinical and clinical evidence, for better management of PD.

Modulation of nigral dopamine signaling mitigates parkinsonian signs of aging: evidence from intervention with calorie restriction or inhibition of dopamine uptake

Identifying neurobiological mechanisms of aging-related parkinsonism, and lifestyle interventions that mitigate them, remain critical knowledge gaps. No aging study, from rodent to human, has reported loss of any dopamine (DA) signaling marker near the magnitude associated with onset of parkinsonian signs in Parkinson's disease (PD). However, in substantia nigra (SN), similar loss of DA signaling markers in PD or aging coincide with parkinsonian signs. Alleviation of these parkinsonian signs may be possible by interventions such as calorie restriction (CR), which augment DA signaling markers like tyrosine hydroxylase (TH) expression in the SN, but not striatum. Here, we interrogated respective contributions of nigral and striatal DA mechanisms to aging-related parkinsonian signs in aging (18 months old) rats in two studies: by the imposition of CR for 6 months, and inhibition of DA uptake within the SN or striatum by cannula-directed infusion of nomifensine. Parkinsonian signs were mitigated within 12 weeks after CR and maintained until 24 months old, commensurate with increased D₁ receptor expression in the SN alone, and increased GDNF family receptor, GFR-α1, in the striatum, suggesting increased GDNF signaling. Nomifensine infusion into the SN or striatum selectively increased extracellular DA. However, only nigral infusion increased locomotor activity. These results indicate mechanisms that increase components of DA signaling in the SN alone mitigate parkinsonian signs in aging, and are modifiable by interventions, like CR, to offset parkinsonian signs, even at advanced age. Moreover, these results give evidence that changes in nigral DA signaling may modulate some parameters of locomotor activity autonomously from striatal DA signaling.

Neuroprotection and Disease Modification by Astrocytes and Microglia in Parkinson Disease

Oxidative stress and neuroinflammation are common bases for disease onset and progression in many neurodegenerative diseases. In Parkinson disease, which is characterized by the degeneration of dopaminergic neurons resulting in dopamine depletion, the pathogenesis differs between hereditary and solitary disease forms and is often unclear. In addition to the pathogenicity of alpha-synuclein as a pathological disease marker, the involvement of dopamine itself and its interactions with glial cells (astrocyte or microglia) have attracted attention. Pacemaking activity, which is a hallmark of dopaminergic neurons, is essential for the homeostatic maintenance of adequate dopamine concentrations in the synaptic cleft, but it imposes a burden on mitochondrial oxidative glucose metabolism, leading to reactive oxygen species production. Astrocytes provide endogenous neuroprotection to the brain by producing and releasing antioxidants in response to oxidative stress. Additionally, the protective function of astrocytes can be modified by microglia. Some types of microglia themselves are thought to exacerbate Parkinson disease by releasing pro-inflammatory factors (M1 microglia). Although these inflammatory microglia may further trigger the inflammatory conversion of astrocytes, microglia may induce astrocytic neuroprotective effects (A2 astrocytes) simultaneously. Interestingly, both astrocytes and microglia express dopamine receptors, which are upregulated in the presence of neuroinflammation. The anti-inflammatory effects of dopamine receptor stimulation are also attracting attention because the functions of astrocytes and microglia are greatly affected by both dopamine depletion and therapeutic dopamine replacement in Parkinson disease. In this review article, we will focus on the antioxidative and anti-inflammatory effects of astrocytes and their synergism with microglia and dopamine.

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.

Effects of intrastriatal injection of the dopamine receptor agonist SKF38393 and quinpirole on locomotor behavior in hemiparkinsonism rats

Dopamine (DA) in the striatum is essential to influence motor behavior and may lead to movement impairment in Parkinson's disease (PD). The present study examined the different functions of the DA D1 receptor (D1R) and DA D2 receptor (D2R) by intrastriatal injection of the D1R agonist SKF38393 and the D2R agonist quinpirole in 6-hydroxydopamine (6-OHDA)-lesioned and control rats. All rats separately underwent dose-response behavior testing for SKF38393 (0, 0.5, 1.0, and 1.5 μg/site) or quinpirole (0, 1.0, 2.0, and 3.0 μg/site) to determine the effects of the optimal modulating threshold dose. Two behavior assessment indices, the time of latency to fall and the number of steps on a rotating treadmill, were used as reliable readouts of motor stimulation variables for quantifying the motor effects of the drugs. The findings indicate that at threshold doses, SKF38393 (1.0 μg/site) and quinpirole (1.0 μg/site) produce a dose-dependent increase in locomotor activity compared to vehicle injection. The ameliorated behavioral responses to either SKF38393 or quinpirole in lesioned rats were greater than those in unlesioned control rats. Moreover, the dose-dependent increase in locomotor capacity for quinpirole was greater than that for SKF38393 in lesioned rats. These results can clarify several key issues related to DA receptors directly and may provide a basis for exploring the potential of future selective dopamine therapies for PD in humans.