Modulation of CaMKIIa-GluN2B interaction in levodopa-induced dyskinesia in 6-OHDA-lesioned Parkinson's rats

Levodopa-induced dyskinesia: interplay between the N-methyl-D-aspartic acid receptor and neuroinflammation

Parkinson's disease (PD) is a common neurodegenerative disorder of middle-aged and elderly people, clinically characterized by resting tremor, myotonia, reduced movement, and impaired postural balance. Clinically, patients with PD are often administered levodopa (L-DOPA) to improve their symptoms. However, after years of L-DOPA treatment, most patients experience complications of varying severity, including the "on-off phenomenon", decreased efficacy, and levodopa-induced dyskinesia (LID). The development of LID can seriously affect the quality of life of patients, but its pathogenesis is unclear and effective treatments are lacking. Glutamic acid (Glu)-mediated changes in synaptic plasticity play a major role in LID. The N-methyl-D-aspartic acid receptor (NMDAR), an ionotropic glutamate receptor, is closely associated with synaptic plasticity, and neuroinflammation can modulate NMDAR activation or expression; in addition, neuroinflammation may be involved in the development of LID. However, it is not clear whether NMDA receptors are co-regulated with neuroinflammation during LID formation. Here we review how neuroinflammation mediates the development of LID through the regulation of NMDA receptors, and assess whether common anti-inflammatory drugs and NMDA receptor antagonists may be able to mitigate the development of LID through the regulation of central neuroinflammation, thereby providing a new theoretical basis for finding new therapeutic targets for LID.

Continuous dopaminergic stimulation counteracts L-DOPA-induced overactivity of Ca2+ in 6-OHDA-lesioned rats

In the clinical treatment of Parkinson's disease (PD), the emergence of L-DOPA-induced dyskinesia (LID) and other motor symptoms remains a restrictive factor for the use of levodopa (L-DOPA). Our objective was to test the effect of continuous dopaminergic stimulation (CDS) on LID and the mechanism of its effect on the calcium (Ca²⁺) signaling pathway. 6-OHDA (6-hydroxydopamine)-treated rats were administered 1% CMC-Na, L-DOPA, rotigotine behenate (RGTB), and L-DOPA + RGTB, respectively, for 28 days. During the treatment, the abnormal involuntary movement (AIM) scores were conducted on days 1, 5, 10, 14, 19, 23 and 28 after the first dose. Subsequently, the number of tyrosine hydroxylase (TH)-positive neurons was detected by immunohistochemistry. Additionally, the changes in Ca²⁺ were detected using a laser confocal technique, and the related proteins, such as neuronal NOS (nNOS), BAX, BCL2, CaMKII, P-CaMKII, and PSD-95, were measured by Western blot. Transmission electron microscopy (TEM) was used to investigate the changes in synaptic structure. The data showed that CDS reduced the AIM scores, increased the expression of TH in the substantia nigra (SN), decreased the expression of nNOS and BAX/BCL2ratio in the striatum, reduced the Ca²⁺ influx induced by L-DOPA and inhibited the Ca²⁺ signaling pathways of dopamine neurons in the striatum. Moreover, the overactivity of synapses induced by L-DOPA was inhibited by CDS. These data further support the hypothesis that continuous delivery of a dopamine agonist reduces the risk of LID induction. Moreover, RGTB could be a promising treatment for PD by simulating CDS.

Characterization in nonhuman primates of (R)-[18F]OF-Me-NB1 and (S)-[18F]OF-Me-NB1 for imaging the GluN2B subunits of the NMDA receptor

PURPOSE

GluN2B containing N-methyl-D-aspartate receptors (NMDARs) play an essential role in neurotransmission and are a potential treatment target for multiple neurological and neurodegenerative diseases, including stroke, Alzheimer's disease, and Parkinson's disease. (R)-[18F]OF-Me-NB1 was reported to be more specific and selective than (S)-[18F]OF-Me-NB1 for the GluN2B subunits of the NMDAR based on their binding affinity to GluN2B and sigma-1 receptors. Here we report a comprehensive evaluation of (R)-[18F]OF-Me-NB1 and (S)-[18F]OF-Me-NB1 in nonhuman primates.

METHODS

The radiosynthesis of (R)-[18F]OF-Me-NB1 and (S)-[18F]OF-Me-NB1 started from 18F-fluorination of the boronic ester precursor, followed by removal of the acetyl protecting group. PET scans in two rhesus monkeys were conducted on the Focus 220 scanner. Blocking studies were performed after treatment of the animals with the GluN2B antagonist Co101,244 or the sigma-1 receptor antagonist FTC-146. One-tissue compartment (1TC) model and multilinear analysis-1 (MA1) method with arterial input function were used to obtain the regional volume of distribution (VT, mL/cm3). Occupancy values by the two blockers were obtained by the Lassen plot. Regional non-displaceable binding potential (BPND) was calculated from the corresponding baseline VT and the VND derived from the occupancy plot of the Co101,244 blocking scans.

RESULTS

(R)- and (S)-[18F]OF-Me-NB1 were produced in > 99% radiochemical and enantiomeric purity, with molar activity of 224.22 ± 161.69 MBq/nmol at the end of synthesis (n = 10). Metabolism was moderate, with ~ 30% parent compound remaining for (R)-[18F]OF-Me-NB1 and 20% for (S)-[18F]OF-Me-NB1 at 30 min postinjection. Plasma free fraction was 1-2%. In brain regions, both (R)- and (S)-[18F]OF-Me-NB1 displayed fast uptake with slower clearance for the (R)- than (S)-enantiomer. For (R)-[18F]OF-Me-NB1, both the 1TC model and MA1 method gave reliable estimates of regional VT values, with MA1 VT (mL/cm3) values ranging from 8.9 in the cerebellum to 12.8 in the cingulate cortex. Blocking with 0.25 mg/kg of Co101,244 greatly reduced the uptake of (R)-[18F]OF-Me-NB1 across all brain regions, resulting in occupancy of 77% and VND of 6.36, while 0.027 mg/kg of FTC-146 reduced specific binding by 30%. Regional BPND, as a measure of specific binding signals, ranged from 0.40 in the cerebellum to 1.01 in the cingulate cortex.

CONCLUSIONS

In rhesus monkeys, (R)-[18F]OF-Me-NB1 exhibited fast kinetics and heterogeneous uptake across brain regions, while the (S)-enantiomer displayed a narrower dynamic range of uptake across regions. A Blocking study with a GluN2B antagonist indicated binding specificity. The value of BPND was > 0.5 in most brain regions, suggesting good in vivo specific binding signals. Taken together, results from the current study demonstrated the potential of (R)-[18F]OF-Me-NB1 as a useful radiotracer for imaging the GluN2B receptors.

Glycation modulates glutamatergic signaling and exacerbates Parkinson's disease-like phenotypes

Alpha-synuclein (aSyn) is a central player in the pathogenesis of synucleinopathies due to its accumulation in typical protein aggregates in the brain. However, it is still unclear how it contributes to neurodegeneration. Type-2 diabetes mellitus is a risk factor for Parkinson's disease (PD). Interestingly, a common molecular alteration among these disorders is the age-associated increase in protein glycation. We hypothesized that glycation-induced neuronal dysfunction is a contributing factor in synucleinopathies. Here, we dissected the impact of methylglyoxal (MGO, a glycating agent) in mice overexpressing aSyn in the brain. We found that MGO-glycation potentiates motor, cognitive, olfactory, and colonic dysfunction in aSyn transgenic (Thy1-aSyn) mice that received a single dose of MGO via intracerebroventricular injection. aSyn accumulates in the midbrain, striatum, and prefrontal cortex, and protein glycation is increased in the cerebellum and midbrain. SWATH mass spectrometry analysis, used to quantify changes in the brain proteome, revealed that MGO mainly increase glutamatergic-associated proteins in the midbrain (NMDA, AMPA, glutaminase, VGLUT and EAAT1), but not in the prefrontal cortex, where it mainly affects the electron transport chain. The glycated proteins in the midbrain of MGO-injected Thy1-aSyn mice strongly correlate with PD and dopaminergic pathways. Overall, we demonstrated that MGO-induced glycation accelerates PD-like sensorimotor and cognitive alterations and suggest that the increase of glutamatergic signaling may underly these events. Our study sheds new light into the enhanced vulnerability of the midbrain in PD-related synaptic dysfunction and suggests that glycation suppressors and anti-glutamatergic drugs may hold promise as disease-modifying therapies for synucleinopathies.

Neuroprotective effects of curcumin via autophagy induction in 6-hydroxydopamine Parkinson's models

Curcumin, a polyphenolic compound extracted from curcuma longa, acts as a nontoxic matter with anti-oxidant and anti-inflammatory effects as well as antiproliferative activities. Here, our research aimed to explore the neuroprotective effects of curcumin both in the 6-hydroxydopamine (6-OHDA)-lesioned rat model of Parkinson's disease (PD) in vivo and 6-OHDA-lesioned PC12 cells in vitro. In vitro, 6-OHDA caused a distinct decrease in cell viability of PC12 cells (150 μM). With the incubation of curcumin (1 μM), 6-OHDA-induced apoptosis was suppressed, increasing the autophagy markers (LC3-II/LC3-I, Beclin-1) and inhibiting phosphor-AKT/AKT, phosphor-mTOR/mTOR. In vivo, curcumin (50 mg/kg) reduced the accumulation of a-synuclein and led to higher parkinsonian disability scores in 6-OHDA-lesioned PD rats, contributing to induction of autophagy through inhibiting AKT/mTOR signal pathway. Moreover, treatment with autophagy inhibitors, such as 3-MA and chloroquine, abolished the neuroprotective effects of curcumin as evidence by compromised autophagy and declined motor behavior in PD rats. In conclusion, the present study demonstrated that curcumin repressed PC12 cell death in vitro and improved parkinsonian disability scores in vivo by inhibiting AKT/mTOR signaling pathway which mediated by autophagy, indicating a potential value of curcumin in the therapeutic intervention of Parkinson's 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.

Administration of quercetin improves mitochondria quality control and protects the neurons in 6-OHDA-lesioned Parkinson's disease models

Mounting evidence suggests that mitochondrial dysfunction and impaired mitophagy lead to Parkinson’s disease (PD). Quercetin, one of the most abundant polyphenolic flavonoids, displays many health-promoting biological effects in many diseases. We explored the neuroprotective effect of quercetin in vivo in the 6-hydroxydopamine (6-OHDA)-lesioned rat model of PD and in vitro in 6-OHDA-treated PC12 cells. In vitro, we found that quercetin (20 μM) treatment improved mitochondrial quality control, reduced oxidative stress, increased the levels of the mitophagy markers PINK1 and Parkin and decreased α-synuclein protein expression in 6-OHDA-treated PC12 cells. Moreover, our in vivo findings demonstrated that administration of quercetin also relieved 6-OHDA-induced progressive PD-like motor behaviors, mitigated neuronal death and reduced mitochondrial damage and α-synuclein accumulation in PD rats. Furthermore, the neuroprotective effect of quercetin was suppressed by knockdown of either Pink1 or Parkin.

Pivotal Role of Fyn Kinase in Parkinson's Disease and Levodopa-Induced Dyskinesia: a Novel Therapeutic Target?

The exact etiology of Parkinson's disease (PD) remains obscure, although many cellular mechanisms including α-synuclein aggregation, oxidative damage, excessive neuroinflammation, and dopaminergic neuronal apoptosis are implicated in its pathogenesis. There is still no disease-modifying treatment for PD and the gold standard therapy, chronic use of levodopa is usually accompanied by severe side effects, mainly levodopa-induced dyskinesia (LID). Hence, the elucidation of the precise underlying molecular mechanisms is of paramount importance. Fyn is a tyrosine phospho-transferase of the Src family nonreceptor kinases that is highly implicated in immune regulation, cell proliferation and normal brain development. Accumulating preclinical evidence highlights the emerging role of Fyn in key aspects of PD and LID pathogenesis: it may regulate α-synuclein phosphorylation, oxidative stress-induced dopaminergic neuronal death, enhanced neuroinflammation and glutamate excitotoxicity by mediating key signaling pathways, such as BDNF/TrkB, PKCδ, MAPK, AMPK, NF-κB, Nrf2, and NMDAR axes. These findings suggest that therapeutic targeting of Fyn or Fyn-related pathways may represent a novel approach in PD treatment. Saracatinib, a nonselective Fyn inhibitor, has already been tested in clinical trials for Alzheimer's disease, and novel selective Fyn inhibitors are under investigation. In this comprehensive review, we discuss recent evidence on the role of Fyn in the pathogenesis of PD and LID and provide insights on additional Fyn-related molecular mechanisms to be explored in PD and LID pathology that could aid in the development of future Fyn-targeted therapeutic approaches.

Modified Glutamatergic Postsynapse in Neurodegenerative Disorders

The postsynaptic density (PSD) is a complex subcellular domain important for postsynaptic signaling, function, and plasticity. The PSD is present at excitatory synapses and specialized to allow for precise neuron-to-neuron transmission of information. The PSD is localized immediately underneath the postsynaptic membrane forming a major protein network that regulates postsynaptic signaling and synaptic plasticity. Glutamatergic synaptic dysfunction affecting PSD morphology and signaling events have been described in many neurodegenerative disorders, either sporadic or familial forms. Thus, in this review we describe the main protein players forming the PSD and their activity, as well as relevant modifications in key components of the postsynaptic architecture occurring in Huntington's, Parkinson's and Alzheimer's diseases.

β-arrestin2 alleviates L-dopa-induced dyskinesia via lower D1R activity in Parkinson's rats

The cause of the L-dopa–induced dyskinesia (LID) has been ascribed to G-protein coupled receptor (GPCR) supersensitivity and uncontrolled downstream signaling. It is now supposed that β-arrestin2 affects GPCR signaling through its ability to scaffold various intracellular molecules. We used the rAAV (recombinant adeno-associated virus) vectors to overexpress and ablation of β-arrestin2. L-dopa-induced changes in expression of signaling molecules and other proteins in the striatum were examined by western blot and immunohistochemically. Our data demonstrated that via AAV-mediated overexpression of β-arrestin2 attenuated LID performance in 6-OHDA-lesioned rodent models. β-arrestin2 suppressed LID behavior without compromising the antiparkinsonian effects of L-dopa. Moreover, we also found that the anti-dyskinetic effect of β-arrestin2 was reversed by SKF38393, a D1R agonist. On the contrary, the rat knockdown study demonstrated that reduced availability of β-arrestin2 deteriorated LID performance, which was counteracted by SCH23390, a D1R antagonist. These data not only demonstrate a central role for β-arrestin2/GPCR signaling in LID, but also show the D1R signal pathway changes occurring in response to dopaminergic denervation and pulsatile administration of L-dopa.

Levodopa/Benserazide PLGA Microsphere Prevents L-Dopa-Induced Dyskinesia via Lower β-Arrestin2 in 6-Hydroxydopamine Parkinson's Rats

Prolonged pulsatile administration of Levodopa (L-dopa) can generate L-dopa–induced dyskinesia (LID). Numerous research has reported that continuous dopamine delivery (CDD) was useful in reducing the severity of LID. 6-OHDA lesioned rats were divided into two groups to receive intermittent L-dopa stimulation (L-dopa/benserazide) or Levodopa/benserazide PLGA microsphere (LBPM) for 3 weeks. rAAV (recombinant adeno-associated virus) vector was used to overexpress and ablation of β-arrestin2. We found that LBPM developed less AIM severity compared with standard L-dopa administration, whereas selective deletion of β-arrestin2 in striatum neurons dramatically enhanced the severity of dyskinesia by LBPM. On the contrary, the effects of LBPM in terms of ALO AIM were further relieved by β-arrestin2 overexpression. Furthermore, no significant change in motor behavior was seen either in inhibition or overexpression of β-arrestin2. In short, our experiments provided evidence that LBPM’s prevention of LID behavior was likely due to β-arrestin2, suggesting that a therapy modulating β-arrestin2 may offer a more efficient anti-dyskinetic method with a low risk of untoward effects.