Probenecid potentiates MPTP/MPP+toxicity by interference with cellular energy metabolism

From the Gut to the Brain: The Role of Enteric Glial Cells and Their Involvement in the Pathogenesis of Parkinson's Disease

The brain-gut axis has been identified as an important contributor to the physiopathology of Parkinson's disease. In this pathology, inflammation is thought to be driven by the damage caused by aggregation of α-synuclein in the brain. Interestingly, the Braak's theory proposes that α-synuclein misfolding may originate in the gut and spread in a "prion-like" manner through the vagus nerve into the central nervous system. In the enteric nervous system, enteric glial cells are the most abundant cellular component. Several studies have evaluated their role in Parkinson's disease. Using samples obtained from patients, cell cultures, or animal models, the studies with specific antibodies to label enteric glial cells (GFAP, Sox-10, and S100β) seem to indicate that activation and reactive gliosis are associated to the neurodegeneration produced by Parkinson's disease in the enteric nervous system. Of interest, Toll-like receptors, which are expressed on enteric glial cells, participate in the triggering of immune/inflammatory responses, in the maintenance of intestinal barrier integrity and in the configuration of gut microbiota; thus, these receptors might contribute to Parkinson's disease. External factors like stress also seem to be relevant in its pathogenesis. Some authors have studied ways to reverse changes in EGCs with interventions such as administration of Tryptophan-2,3-dioxygenase inhibitors, nutraceuticals, or physical exercise. Some researchers point out that beyond being activated during the disease, enteric glial cells may contribute to the development of synucleinopathies. Thus, it is still necessary to further study these cells and their role in Parkinson's disease.

Spatial and temporal mapping of neuron-microglia interaction modes in acute ischemic stroke

Ischemic stroke (IS) is a major cause of morbidity and mortality worldwide, accounting for 75-80% of all strokes. Under conditions of ischemia and hypoxia, neurons suffer damage or death, leading to a series of secondary immune reactions. Microglia, the earliest activated immune cells, can exert neurotoxic or neuroprotective effects on neurons through secretion of factors. There exists a complex interaction between neurons and microglia during this process. Moreover, the interaction between them becomes even more complex due to differences in the infarct area and reperfusion time. This review first elaborates on the differences in neuronal death modes between the ischemic core and penumbra, and then introduces the differences in microglial markers across different infarct areas with varying reperfusion time, indicating distinct functions. Finally, we focus on exploring the interaction modes between neurons and microglia in order to precisely target beneficial interactions and inhibit harmful ones, thus providing new therapeutic strategies for the treatment of IS.

Treadmill Exercise Alleviates Cognition Disorder by Activating the FNDC5: Dual Role of Integrin αV/β5 in Parkinson's Disease

Parkinson's disease with cognitive impairment (PD-CI) results in several clinical outcomes for which specific treatment is lacking. Although the pathogenesis of PD-CI has not yet been fully elucidated, it is related to neuronal plasticity decline in the hippocampus region. The dopaminergic projections from the substantia nigra to the hippocampus are critical in regulating hippocampal plasticity. Recently, aerobic exercise has been recognized as an effective therapeutic strategy for enhancing plasticity through the secretion of various muscle factors. The exact role of FNDC5-an upregulated, newly identified myokine produced after exercise-in mediating hippocampal plasticity and regional dopaminergic projections in PD-CI remains unclear. In this study, the effect of treadmill exercise on hippocampal synaptic plasticity was evaluated in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced chronic PD models. The results showed that treadmill exercise substantially alleviated the motor dysfunction, cognition disorder, and dopaminergic neuron degeneration induced by MPTP. Here, we discovered that the quadriceps, serum, and brain FNDC5 levels were lower in PD mice and that intervention with treadmill exercise restored FNDC5 levels. Moreover, treadmill exercise enhanced the synaptic plasticity of hippocampal pyramidal neurons via increased dopamine levels and BDNF in the PD mice. The direct protective effect of FNDC5 is achieved by promoting the secretion of BDNF in the hippocampal neurons via binding the integrin αVβ5 receptor, thereby improving synaptic plasticity. Regarding the indirect protection effect, FNDC5 promotes the dopaminergic connection from the substantia nigra to the hippocampus by mediating the interaction between the integrin αVβ5 of the hippocampal neurons and the CD90 molecules on the membrane of dopaminergic terminals. Our findings demonstrated that treadmill exercise could effectively alleviate cognitive disorders via the activation of the FNDC5-BDNF pathway and enhance the dopaminergic synaptic connection from SNpc to the hippocampus in the MPTP-induced chronic PD model.

Mood disturbances in Parkinson's disease: From prodromal origins to application of animal models

Parkinson's disease (PD) is a complex illness with a constellation of environmental insults and genetic vulnerabilities being implicated. Strikingly, many studies only focus on the cardinal motor symptoms of the disease and fail to appreciate the major non-motor features which typically occur early in the disease process and are debilitating. Common comorbid psychiatric features, notably clinical depression, as well as anxiety and sleep disorders are thought to emerge before the onset of prominent motor deficits. In this review, we will delve into the prodromal stage of PD and how early neuropsychiatric pathology might unfold, followed by later motor disturbances. It is also of interest to discuss how animal models of PD capture the complexity of the illness, including depressive-like characteristics along with motor impairment. It remains to be determined how the underlying PD disease processes contributes to such comorbidity. But some of the environmental toxicants and microbial pathogens implicated in PD might instigate pro-inflammatory effects favoring α-synuclein accumulation and damage to brainstem neurons fueling the evolution of mood disturbances. We posit that comprehensive animal-based research approaches are needed to capture the complexity and time-dependent nature of the primary and co-morbid symptoms. This will allow for the possibility of early intervention with more novel and targeted treatments that fit with not only individual patient variability, but also with changes that occur over time with the evolution of the disease.

Neuroprotective effect of thiamine-producing lactic acid bacteria in a murine Parkinsonian model

Parkinson's disease (PD) is a progressive neurodegenerative disorder characterized by deterioration and loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc), resulting in motor deficits. Many studies have...

Preventing Parkinson's Disease: An Environmental Agenda

Fueled by aging populations and continued environmental contamination, the global burden of Parkinson's disease (PD) is increasing. The disease, or more appropriately diseases, have multiple environmental and genetic influences but no approved disease modifying therapy. Additionally, efforts to prevent this debilitating disease have been limited. As numerous environmental contaminants (e.g., pesticides, metals, industrial chemicals) are implicated in PD, disease prevention is possible. To reduce the burden of PD, we have compiled preclinical and clinical research priorities that highlight both disease prediction and primary prevention. Though not exhaustive, the "PD prevention agenda" builds upon many years of research by our colleagues and proposes next steps through the lens of modifiable risk factors. The agenda identifies ten specific areas of further inquiry and considers the funding and policy changes that will be necessary to help prevent the world's fastest growing brain disease.

Treadmill exercise alleviates neuronal damage by suppressing NLRP3 inflammasome and microglial activation in the MPTP mouse model of Parkinson's disease

Treadmill exercise has been recognized as an effectively therapeutic strategy for Parkinson's disease (PD). However, its exact molecular mechanism of promoting PD remain unclear. Recently, the NLRP3 inflammasome is considered to play a critical role in the pathogenesis of PD. In this study, we investigated whether NLRP3 inflammasome was involved in treadmill exercise-induced neuroprotection and anti-inflammation effect in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of PD. 8-week-old male mice (C57BL/6 strain) were divided into four groups: Control, MPTP, MPTP + EX and EX. MPTP was intraperitoneally injected into mice to establish chronic PD model. The open-field test and pole test were used to assess motor function. The results showed that treadmill exercise significantly alleviated motor dysfunction and dopaminergic neuron degeneration induced by MPTP. In addition, we also found that treadmill exercise suppressed MPTP-triggered microglia activation and the co-localization of NLRP3+/Iba-1+ cells in the substantia nigra. These effects were associated with suppression NLRP3 inflammasome via down-regulation of TLR4/MyD88/NF-κB pathway. Overall, our study demonstrated that treadmill exercise could effectively alleviates neuronal damage via inhibition of NLRP3 inflammasome and microglial activation in MPTP-induced PD mouse model.

Optimization of N-Phenylpropenoyl-l-amino Acids as Potent and Selective Inducible Nitric Oxide Synthase Inhibitors for Parkinson's Disease

N-Phenylpropenoyl-l-amino acids (NPAs) are inducible nitric oxide synthase (iNOS) inhibitors possessing preventive effects for Parkinson's disease (PD). Here, structural modifications for improving the iNOS inhibitory activity and blood-brain barrier (BBB) permeability of NPAs were conducted, leading to 20 optimized NPA derivatives (1-20). Compound 18, with the most potent activity (IC₅₀ = 74 nM), high BBB permeability (P_e = 19.1 × 10^-6 cm/s), and high selectivity over other NOS isoforms, was selected as the lead compound. Further studies demonstrated that 18 directly binds to iNOS. In the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced acute PD model, the oral administration of 18 (1 and 2 mg/kg) exerted preventive effects by alleviating the loss of dopaminergic (DAergic) neurons. Notably, in the MPTP-/probenecid-induced chronic PD model, the same dose of 18 also displayed a therapeutic effect by repairing the damaged DAergic neurons. Finally, good pharmacokinetic properties and low toxicity made 18 a promising candidate for the treatment of PD.

Gami-Chunggan Formula Prevents Motor Dysfunction in MPTP/p-Induced and A53T α-Synuclein Overexpressed Parkinson's Disease Mouse Model Though DJ-1 and BDNF Expression

The Gami–Chunggan formula (GCF) is a modification of the Chunggan (CG) decoction, which has been used to treat movement disorders such as Parkinson’s disease (PD) in Traditional East Asian Medicine. To evaluate the neuroprotective effects of GCF in chronic PD animal models, we used either a 5-week treatment of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine with probenecid (MPTP/p) or the α-synuclein A53T overexpressed PD mouse model. C57BL/6 mice were treated with MPTP, in combination with probenecid, for 5 weeks. GCF was administered simultaneously with MPTP injection for 38 days. The A53T α-synuclein overexpressed mice were also fed with GCF for 60 days. Using behavioral readouts and western blot analyses, it was observed that GCF prevents motor dysfunction in the MPTP/p-induced and A53T α-synuclein overexpressed mice. Moreover, GCF inhibited the reduction of dopaminergic neurons in the substantia nigra (SN) and fibers in the striatum (ST) against MPTP/p challenge. The expression of DJ-1 was increased but that of α-synuclein was decreased in the SN of PD-like brains by GCF administration. In vitro experiments also showed that GCF inhibited 6-OHDA-induced neurotoxicity in SH-SY5Y neuroblastoma cell lines and that it did so to a greater degree than CG. Furthermore, GCF induced BDNF expression through phosphorylation of Akt, ERK, CREB, and AMPK in the SN of PD-like brains. Therefore, use of the herbal medicine GCF offers a potential remedy for neurodegenerative disorders, including Parkinson’s disease.

Pannexin1 knockout and blockade reduces ischemic stroke injury in female, but not in male mice

The membrane channel Pannexin 1 (Panx1) mediates apoptotic and inflammatory signaling cascades in injured neurons, responses previously shown to be sexually dimorphic under ischemic conditions. We tested the hypothesis that Panx1 plays an underlying role in mediating sex differences in stroke outcome responses. Middle-aged, 8-9 month old male and female wild type and Panx1 KO mice were subjected to permanent middle cerebral artery (MCA) occlusion, and infarct size and astrocyte and microglia activation were assessed 4 days later. The sexually dimorphic nature of Panx1 deletion was also explored by testing the effect of probenecid a known Panx1 blocker to alter stroke volume. Panx1 KO females displayed significantly smaller infarct volumes (~ 50 % reduction) compared to their wild-type counterparts, whereas no such KO effect occurred in males. This sex-specific effect of Panx1 KO was recapitulated by significant reductions in peri-infarct inflammation and astrocyte reactivity, as well as smaller infarct volumes in probenecid treated females, but not males. Finally, females showed overall, higher Panx1 protein levels than males under ischemic conditions. These findings unmask a deleterious role for Panx1 in response to permanent MCA occlusion, that is unique to females, and provide several new frameworks for understanding sex differences in stroke outcome.

Contrasting effects of selective MAGL and FAAH inhibition on dopamine depletion and GDNF expression in a chronic MPTP mouse model of Parkinson's disease

The modulation of the brain endocannabinoid system has been identified as an option to treat neurodegenerative diseases including Parkinson's disease (PD). Especially the elevation of endocannabinoid levels by inhibition of hydrolytic degradation represents a valuable approach. To evaluate whether monoacylglycerol lipase (MAGL) or fatty acid amide hydrolase (FAAH) inhibition could be beneficial for PD, we examined in parallel the therapeutic potential of the highly selective MAGL inhibitor KML29 elevating 2-arachidonoylglyerol (2-AG) levels and the highly selective FAAH inhibitor PF-3845 elevating anandamide (AEA) levels in a chronic methyl-4-phenyl-1,2,3,6-tetrahydropyridine/probenecid (MPTP/probenecid) mouse model of PD. Chronic administration of KML29 (10 mg/kg) but not PF-3845 (10 mg/kg) attenuated striatal MPTP/probenecid-induced dopamine depletion. Furthermore, KML29 induced an increase in Gdnf but not Bdnf expression, whereas PF-3845 decreased the MPTP/probenecid-induced Cnr2 expression without any effects on neurotrophin expression. Investigation of treatment-naïve striatal mRNA levels revealed a high presence of Gdnf and Mgll in contrast to Bdnf and Faah. Treatment of primary mouse microglia with 2-AG increased Gdnf but not Bdnf expression, suggesting that microglia might mediate the observed KML29-induced increase in Gdnf. In summary, pharmacological MAGL but not FAAH inhibition in the chronic MPTP/probenecid model attenuated the MPTP/probenecid-induced effects on striatal dopamine levels which were accompanied by an increase in 2-AG levels.

2',3'-Dideoxycytidine Protects Dopaminergic Neurons in a Mouse Model of Parkinson's Disease

DNA polymerase-β (DNA pol-β) plays a crucial role in the pathogenesis of Parkinson's disease (PD). The aim of this study was to investigate the neuroprotective effects of a DNA polymerase-β inhibitor 2',3'-dideoxycytidine (DDC) in PD models. In the in vitro studies, primary cultured neurons were challenged with 1-methyl-4-phenylpyridinium ion (MPP⁺). The expression of DNA pol-β was assessed using western blot. The neuroprotective effect of DNA pol-β knockdown and DNA pol-β inhibitor DDC was determined using cell viability assay and caspase-3 activity assay. We found that MPP⁺ induced neuronal death and the activation of caspase-3 in a dose-dependent manner. The expression of DNA pol-β increased after the neurons were exposed to MPP⁺. DNA pol-β siRNA or DNA pol-β inhibitor DDC attenuated neuronal death induced by MPP⁺. In the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced mouse model of PD, MPTP treatment triggered behavioral deficits and nigrostriatal lesions. Pretreatment with DDC attenuated MPTP-induced behavioral deficits, dopaminergic neuronal death and striatal dopamine depletion in the MPTP mouse model. These results indicate that DNA pol-β inhibitors may present a novel promising therapeutic option for the neuroprotective treatment of PD.

Curcumin exerts anti-inflammatory and antioxidative properties in 1-methyl-4-phenylpyridinium ion (MPP(+))-stimulated mesencephalic astrocytes by interference with TLR4 and downstream signaling pathway

Neuroinflammation is closely associated with the pathophysiology of neurodegenerative diseases including Parkinson's disease (PD). Recent evidence indicates that astrocytes also play pro-inflammatory roles in the central nervous system (CNS) by activation with toll-like receptor (TLR) ligands. Therefore, targeting anti-inflammation may provide a promising therapeutic strategy for PD. Curcumin, a polyphenolic compound isolated from Curcuma longa root, has been commonly used for the treatment of neurodegenerative diseases. However, the details of how curcumin exerts neuroprotection remain uncertain. Here, we investigated the protective effect of curcumin on 1-methyl-4-phenylpyridinium ion-(MPP(+)-) stimulated primary astrocytes. Our results showed that MPP(+) stimulation resulted in significant production of tumor necrosis factor (TNF)-α, interleukin (IL-6), and reactive oxygen species (ROS) in primary mesencephalic astrocytes. Curcumin pretreatment decreased the levels of these pro-inflammatory cytokines while increased IL-10 expression in MPP(+)-stimulated astrocytes. In addition, curcumin increased the levels of antioxidant glutathione (GSH) and reduced ROS production. Our results further showed that curcumin decreased the levels of TLR4 and its downstream effectors including NF-κB, IRF3, MyD88, and TIRF that are induced by MPP(+) as well as inhibited the immunoreactivity of TLR4 and morphological activation in MPP(+)-stimulated astrocytes. Together, data suggest that curcumin might exert a beneficial effect on neuroinflammation in the pathophysiology of PD.

Neuroprotective and anti-inflammatory effects of morin in a murine model of Parkinson's disease

Parkinson's disease (PD) is one of the most common neurodegenerative disorders and is characterized by loss of dopaminergic neurons in the substantia nigra (SN). Although the causes of PD are not understood, evidence suggests that oxidative stress, mitochondrial dysfunction, and inflammation are associated with its pathogenesis. Morin (3,5,7,2',4'-pentahydroxyflavone) is a flavonol found in wine and many herbs and fruits. Previous studies have suggested that morin prevents oxidative damage and inflammation and ameliorates mitochondrial dysfunction. The present study describes the neuroprotective effects of morin in a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced mouse model of PD, and we report the results of our investigation into its neuroprotective mechanism in primary neurons and astrocytes. In the mouse model, morin pretreatment ameliorated motor dysfunction, protected against dopaminergic neuronal losses in SN and striatum, and alleviated MPTP-induced astrocyte activation. In vitro studies revealed that morin protected primary cultured neurons against 1-methyl-4-phenylpyridine (MPP(+) )-mediated reactive oxygen species production and mitochondrial membrane potential (MMP) disruption. In addition, morin effectively reduced MPP(+) -induced astroglial activation and nuclear translocation of nuclear factor-κB in primary cultured astrocytes. These results indicate that morin acts via multiple neuroprotective mechanisms in our mouse model and suggest that morin be viewed as a potential treatment and preventative for PD. © 2016 Wiley Periodicals, Inc.

Probenecid protects against oxygen-glucose deprivation injury in primary astrocytes by regulating inflammasome activity

Inflammation is extremely important in the development of cerebral ischemia/reperfusion injury. Pannexin 1 (Panx1) channel has been reported to activate inflammasome in astrocytes and be involved in ischemic injury, but this damage effect is reversed by a Panx1 inhibitor-probenecid. However, the mechanism of probenecid protects against cerebral ischemia/reperfusion injury remains unclear. In present study, we hypothesized that probenecid protected astrocytes from ischemia/reperfusion injury in vitro by modulating the inflammasome. Primary cultured neocortical astrocytes were exposed to oxygen-glucose deprivation/reoxygenation (OGD/RX) and probenecid was added in this model. Viability and nuclear morphology of astrocytes, production of reactive oxygen species (ROS), protein expressions of NLRP3 (NOD-like receptor protein 3), caspase-1, and AQP4 (Aquaporins 4), as well as release of cellular HMGB1 and IL-1β were observed to evaluate the effect and mechanisms of probenecid on OGD/reoxygenated astrocytes. Probenecid did not affect cell viability at concentrations of 1, 5, 10, and 100μM but induced significant astrocytes death at 500μM. Probenecid inhibited cell death and ROS generation in astrocytes subjected to 6h of OGD and 24h of reoxygenation. The expression levels of NLRP3, caspase-1, and AQP4 increased after 6h of OGD, but probenecid treatment attenuated this increase. Moreover, the extracellular release of IL-1β and HMGB1 from OGD/reoxygenated astrocytes increased significantly. However, treatment by probenecid resulted in substantial reduction of these proteins levels in extracellular space. In conclusion, The Panx1 inhibitor, probenecid, which was administered before OGD, provided protective effects on the OGD/reoxygenation model of cultured astrocytes by modulating inflammasome activity and downregulating AQP4 expression.

Ginsenoside Rg1 attenuates motor impairment and neuroinflammation in the MPTP-probenecid-induced parkinsonism mouse model by targeting α-synuclein abnormalities in the substantia nigra

Parkinson's disease (PD) is pathologically characterized by the progressive loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc) and the accumulation of aggregated α-synuclein in specific central nervous system (CNS) regions. Disease development is attributed to α-synuclein abnormalities, particularly aggregation and phosphorylation. The ginsenoside Rg1, an active component of ginseng, possesses neuroprotective and anti-inflammatory effects. The purpose of the present study was to evaluate these activities of Rg1 in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)/probenecid (MPTP/p)-induced PD mouse model for the first time and to elucidate the underlying mechanisms. Oral treatment with Rg1 significantly attenuated the high MPTP-induced mortality, behavior defects, loss of dopamine neurons and abnormal ultrastructure changes in the SNpc. Other assays indicated that the protective effect of Rg1 may be mediated by its anti-neuroinflammatory properties. Rg1 regulated MPTP-induced reactive astrocytes and microglia and decreased the release of cytokines such as tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) in the SNpc. Rg1 also alleviated the unusual MPTP-induced increase in oligomeric, phosphorylated and disease-related α-synuclein in the SNpc. In conclusion, Rg1 protects dopaminergic neurons, most likely by reducing aberrant α-synuclein-mediated neuroinflammation, and holds promise for PD therapeutics.

Hydrogen sulfide functions as a neuromodulator to regulate striatal neurotransmission in a mouse model of Parkinson's disease

Hydrogen sulfide (H2S), a novel endogenous gasotransmitter, has been considered a neuromodulator to enhance hippocampal long-term potentiation and exerts neuroprotective effects against neurotoxin-induced neurodegeneration in rodent models of Parkinson's disease (PD). However, whether H2S can function as a neuromodulator to regulate the levels of nigrostriatal neurotransmitters and then impact the vulnerability of dopaminergic (DA) neurons in response to neurotoxins remains unknown. For this study, we prepared a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine plus probenecid (MPTP/p)-induced mouse subacute model of PD to explore the modulatory effect of H2S on monoamine and amino acid neurotransmitters in the striatum of MPTP-treated mice. This study shows that NaHS (an H2S donor, 5.6 mg/kg/day, i.p.) administration improves the survival rate and significantly ameliorates the weight loss of MPTP-treated mice. NaHS treatment attenuated MPTP-induced neuronal damage, restored the diminution of DA neurons, and suppressed the overactivation of astrocytes in the mouse striatum. Additionally, NaHS upregulated striatal serotonin levels and modulated the balance of excitatory glutamate and the inhibitory γ-aminobutyric acid system in response to MPTP challenge. The current study indicates that H2S may function as an effective neuromodulator to regulate striatal neurotransmission and provides insight into the potential of H2S for PD therapy.