CNS & Neurological Disorders - Drug Targets (Formerly Current Drug Targets - CNS & Neurological Disorders) - Volume 11, Issue 8, 2012

Parkinson's disease (PD) is a neurodegenerative disorder characterized by motor and non-motor symptoms and the selective loss of dopaminergic neurons. The etiology of idiopathic PD is likely a combination of genetic and environmental factors. Despite findings from mammalian studies that have provided significant insight into the disorder, the molecular mechanisms underlying its pathophysiology are still poorly understood. The nematode Caenorhabditis elegans (C. elegans) is a powerful system for genetic analysis. Considering C. elegans short lifespan, fully sequenced genome, high genetic and neurobiochemical conservation with humans, as well as the availability of facile genetic tools, the nematode represents a highly efficient and effective model system to explore the molecular basis of PD. In this review we describe the utility of C. elegans for PD research, and the opportunity the model system presents to identify therapeutic targets.

The neural protein α-synuclein aggregates both in vivo and in vitro to form insoluble fibrils that are involved in Parkinson's disease pathogenesis. We have generated α-synuclein/fluorescent-protein fusion constructs overexpressed in muscle cells of the nematode, Caenorhabdtis elegans. Green Fluorescent Protein (GFP) variants, Cerulean (C) or Venus (V), were fused to the C-terminus of human α-synuclein (S); the resultant fusion genes were designated SV and SC, plus a CV fusion as well as S, C and V singly. The aggregation behavior of the purified fusion proteins (expressed in E. coli) will be described elsewhere. These constructs were fused to a C. elegans unc-54 myosin promoter, and integrated transgenic lines generated by microinjection, λ-irradiation, and outcrossing of fluorescent progeny. All transgenic lines expressing α- synuclein showed significant reductions (p < 0.05) in lifespan, motility and pharyngeal pumping, as compared to wildtype worms or lines expressing CFP and/or YFP only. We showed that CFP and YFP labels colocalised in granular inclusions throughout the body wall in transgenic lines expressing both SC and SV fusions (SC+SV), whereas SV+C worms displayed YFP-labelled inclusions on a diffuse CFP background. These findings implied that the α-synuclein moieties of these fusion proteins still aggregated together in vivo, whereas CFP or YFP moieties alone did not. This in turn suggested that Foerster Resonanace Energy Transfer (FRET) between CFP and YFP labels in α-synuclein aggregates could allow the extent of aggregation to be quantified. Accordingly, we also showed that net FRET signals increased 2- fold between L4 and adult SC+SV worms.

Various human diseases are known to occur as a result of gene-environment interactions. Amongst such diseases, neurodegenerative Parkinson's disease (PD) is a complex disorder in which genetics and exposure to toxins constitute the main determinants in the onset of the disease. Many studies have reported on a link between pesticide exposure and increased risk of PD, however the role of different classes of pesticides vis-a-vis Parkinsonism has not been well elucidated. We carried out the present study to explore the role of six groups of pesticides viz botanicals, herbicides, fungicides, organophosphates, carbamates and pyrethroids on PD and and associated neurotoxic effects. These pesticides were studied using transgenic Caenorhabditis elegans model expressing human alpha synuclein protein tagged with yellow fluorescent protein [NL5901; (Punc-54::alphasynuclein::YFP+unc-119)] in the body wall muscle. Amongst all the classes of pesticides examined, botanical rotenone showed severe effects on PD pathogenesis. It significantly increased alpha synuclein aggregation and oxidative stress. Furthermore, it reduced mitochondrial and lipid content in the worms. Pesticides from other classes were observed to exert marginal effects as compared to rotenone thus suggesting that there is a class or structure specific effect of environmental chemicals vis-a-vis Parkinsonism. Hence it may be deduced that all classes of toxicants do not induce similar effects on neurodegeneration and associated events.

Aging, the major cause of several ailments has led to intense exploration of potential drugs that delay aging and its associated effects. We mined the information on traditional Indian medicines and identified an iridoid, 10-O-trans-p- Coumaroylcatalpol (OCC), a major ingredient of Premna integrifolia Linn. (syn: Premna serratifolia). OCC forms an important constituent of famous herbal formulation ‘‘Dashmula’’, a ten herb formulation, commonly used for its various medicinal properties. Employing model system C. elegans, the effect of OCC on life span, stress resistance, chemotaxis, the content of reactive oxygen species (ROS) and on the aggregation of alpha synuclein was studied. OCC extended the mean life span of nematodes, increased their tolerance against chemical induced stress, improved the chemotaxis index and reduced the ROS content. Further, the aggregation of Parkinson's disease (PD) associated protein, alpha synuclein (asyn), was decreased when transgenic a-syn expressing worms were raised on OCC mixed diet. We extended the studies further to explore the possible genetic mechanism that mediates the observed effects of OCC. Employing the genetic knockout mutants TK22 [mev-1(kn1)III]; GR1307 [daf-16(mgDf50)I]; VC199 [sir-2.1(ok434)IV] and transgenic GFP expressing strain TJ356 [zls356; DAF-16::GFP], our studies revealed that the effects were mediated by daf-16 and not by sir-2.1 or mev-1. Our results indicate that OCC has the ability to ameliorate a-syn aggregation, reduce oxidative stress and promote longevity in C. elegans via activation of longevity promoting transcription factor DAF-16. Thus, OCC may serve as a lead compound of plant origin for important nutraceutical intervention against aging and age associated PD.

Positive correlations have been suggested between usage of pesticides and the incidence of Parkinson's disease (PD) through epidemiological as well as few experimental evidences. Organophosphorus insecticides (OPI), which are extensively used in agricultural and household insect control, have been the subject of increasing concern in the past decades due to their neurotoxic potential. However, very few studies have demonstrated the potentials of OPI to induce features of PD in model organisms. In the present study, Caenorhabditis elegans was selected as the model organism to evaluate the potential of monocrotophos (MCP), an OPI, to elicit dopaminergic features of Parkinson's disease in terms of dopamine content, basic movement and integrity of dopaminergic neurons along with its effect on acetylcholinesterase (AChE) activity and life span. All the responses elicited by MCP were compared with that elicited by 1-methyl-4-phenyl- 1, 2, 3, 6-tetrahydropyridine (MPTP) in both N2 and BZ555 worms. N2 worms were exposed to varying concentrations of MCP (50, 100 and 200μM) or MPTP (200, 300 and 400μM) for 48 hours and locomotory rate, as measured by the number of body bends made in 20 seconds, was enumerated. Worms subjected to the same dose paradigms were also analyzed for the dopamine content by HPLC. The results indicated a significant reduction in the dopamine levels in the worms that were treated with MCP/MPTP and this correlated with the changes in locomotion compared to untreated worms. Worms treated with MCP also exhibited significant reduction in AChE activity. Both MPTP and MCP caused a marked reduction in life span in the worms. Transgenic worms (BZ555, which has GFP tagged to its 8 dopaminergic neurons) exposed to MCP and MPTP at the above concentrations showed a dose-dependent reduction in the number of green pixels in CEP and ADE neurons which also correlated with the neurodegeneration as visualized by decreased fluorescence in photomicrographs. Taken together, our data demonstrate that low levels of MCP elicits dopaminergic features of PD in C. elegans.

Neurodegenerative diseases are known to be associated with genetic and environmental factors. The multifactorial Parkinson's disease (PD) is triggered and/or further worsened by exposure to certain pesticides. Existing literature suggests a link between pesticide exposure and increased incidence of PD. We carried out the present study to look into the stress gene expression pattern of transgenic Caenorhabditis elegans (C. elegans) model of PD after exposure to pesticides from different classes. Expression level of sod-1, sod-2, sod-3, hsp-70, hsp-60, and hsp-16.2 stress responsive genes was determined using qPCR. Our findings demonstrate that the expression of stress related genes does not follow a generalized pattern to different toxicants; rather each pesticide class has a specific expression signature.

Alzheimer's disease (AD) is one of the major neurodegenerative diseases affecting almost 28 million people around the globe. It consistently remains one of the major health concerns of present world. Due to the clinical limitations like severe side effects of some synthesized drugs, alternative forms of treatments are gaining global acceptance in the treatment of AD. Neuroprotective compounds of natural origin and their synthetic derivatives exhibit promising results with minimal side effects and some of them are in their different phases of clinical trials. Alkaloids and their synthetic derivatives form one of the groups which have been used in treatment of neurodegenerative diseases like AD. We have further grouped these alkaloids into different sub groups like Indoles, piperdine and isoquinolines. Polyphenols form another important class of natural compounds used in AD management.

Many researches that discourse the treatment of prolactinomas with dopamine agonists (DA) provide data about pituitary tumor apoplexy of some prolactinomas. Therefore, DA are listed as risk factors for apoplexy of prolactinomas. The authors wish to explore the percentage (frequency) of pituitary tumor apoplexy during the treatment of prolactinomas with DA. From June 2011 to February 2012, we sought electronic databases and found 2169 articles and 71 book chapters relevant to DA. Only seven articles have been included into systematic review and from 4 articles we extracted numerical data that showed percentage of pituitary tumor apoplexy. One hundred and fifty-seven patients treated with DA were included in four studies. Results showed the following percentage of apoplexy during the treatment of prolactinomas with DA (apoplexy/therapy ratio): 1/84(1,19%), 13/29(44,83%), 1/15(6,67%) and 1/29(3,45%). One result stands out from the other (13/29-44,83%) because of retrospective search for pituitary hemorrhage by MRI imaging of sellar region and some of the patients were without clinical signs of apoplexy. Median and mean age of included patients was usually over 30 years. Pituitary tumor apoplexy appeared more frequently in macroprolactinomas than in microprolactinomas and also within a year and a half since the beginning of treatment with DA. Conclusively, clinically manifested pituitary tumor apoplexy appears in relatively small percentage of prolactinomas treated with DA. We were also concluded that apoplexy appears asymptomatic and because of that and because of more frequently appearing in macroprolactinomas, there are recommendations for performing MRI imaging of sellar region more often in patients with macroprolactinomas than in patients with microprolactinomas who are treated with DA.

Parkinson's disease (PD) is the second most common progressive neurodegenerative disorder with increased oxidative stress as central component. Till date, treatments related to PD are based on restoring dopamine either by targeting neurotransmitter and/or at receptor levels. These therapeutic approaches try to repair damage but do not address the underlying processes such as oxidative stress and neuroinflammation that contribute to cell death. The central nervous system maintains a robust antioxidant defense mechanism consisting of several cytoprotective genes and enzymes whose expression is controlled by antioxidant response element (ARE) which further depends on activation of nuclear factor erythroid 2-related factor 2 (Nrf2). In response to oxidative or electrophilic stress transcription factor Nrf2 binds to ARE and rescues the cells from oxidative stress and neuroinflammation. Recently, Nrf2 has been utilized as a drug target and some agents are currently under clinical trial. Owing to the potential role of Nrf2 in counteracting oxidative stress and neuroinflammation seen in PD, here we have focused on the molecular mechanism of the Nrf2/ARE antioxidant defense pathway in PD. Further, we also summarize published reports on the potential inducers of Nrf2 that demonstrate neuroprotective effects in experimental models of PD with possible future strategies to increase the transcriptional level of Nrf2 as a therapeutic strategy to provide neuroprotection of damaged dopaminergic neurons in PD.

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by selective neuronal loss, amyloid plaques and neurofibrillary tangles. Oxidative stress may play an important role in the pathogenesis of AD which is associated with the accumulation of β-amyloid (Aβ). Jatrorrhizine (JAT) is a novel tetrahydroisoquinoline alkaloid originally extracted from the Chinese herb coptidis rhizome. Our previous studies showed that JAT protected neuronallike cells against H2O2 -induced toxicity. In this study, we investigated the protective effects of JAT against Aβ25-35- induced cell death in rat cortical neurons. When the cortical neurons were exposed to 25μM Aβ25-35 for 24h, there was a significant reduction in cell viability and activities of SOD and GSH-Px. It also increased the production of malondialdehyde (MDA) and ROS but reduced MMP. Pretreatment of the cortical neurons with various concentrations of JAT (1-10μM) attenuated Aβ25-35-induced neurotoxicity markedly. JAT was also showed to suppress the activation of caspase-3 induced by Aβ25-35 and prevented the cytochrome c transporting into the cytosol. These results indicate that JAT demonstrates the neuroprotective effects against Aβ25-35-induced injury via its antioxidative potential, which may provide a therapeutical potential to AD.

The cannabinoid CB1-receptor is among the most abundant G-protein-coupled receptors in the mammalian brain. Whereas post-mortem studies in Alzheimer's disease (AD) brains compared to age-matched controls have reported decreased CB1-receptor binding but no change in their protein levels (immunoreactivity), decreased or increased CB1- receptor protein levels have been reported in APP/PS1 transgenic mice modelling AD. To complete the picture, the present study used functional autoradiography to assess CB1-receptor-dependent Gi protein activation in the hippocampus, entorhinal cortex and medial frontal cortex of 13- to14-month-old female APPswe/PS1dE9 transgenic and wild-type littermate control mice. The mouse brains were processed for [35S]GTPλS autoradiography so that brain sections were analysed in pairs of one transgenic and one control mouse brain. The autoradiography protocol was completed for each pair both in the absence and presence of dithiotreitol (DTT) to reveal possible redox-dependent alterations in CB1 receptor function. Five treatments were used: baseline, incubation with 10 μM GTPλS to assess nonspecific binding, and CB1 receptor agonist CP55,940 in three concentrations. By and large we found no statistically significant differences between the APP/PS1 transgenic and control mice in CB1 receptor signalling. The only exception was a modest redox-dependent alteration in entorhinal cortical CB1 receptors between the genotypes. Thus, in accordance with the majority of earlier human AD findings, we did not find evidence for notable changes in the number of functional CB1 receptors in the common APPswe/PS1dE9 mouse model of AD.

We reported previously that geniposide showed neurotrophic and neuroprotective activities with the activation of glucagons-like peptide 1 receptor (GLP-1R) in neurons. The current study was designed to further investigate the protective effect of geniposide on β-amyloid (Aβ)-induced cytotoxicity. Our results showed that pre-incubation with geniposide prevented Aβ1-42-induced cell injury in primary cultured cortical neurons. Geniposide also induced the expression of insulin-degrading enzyme (IDE), a major degrading protease of Aβ, in a dose-dependent manner. Moreover, bacitracin, an inhibitor of IDE, and RNAi on Glp-1r gene decreased the neuroprotection of geniposide in Aβ1-42-treated cortical neurons. Our findings indicated that geniposide activating GLP-1R to against Aβ-induced neurotoxicity involved in its regulation on the expression of IDE in cortical neurons, which provided an additional mechanistic insight into the role of GLP-1R in neuroprotection.

Prophylactic administration of reversible acetylcholinesterase (AChE) inhibitors can protect against the lethal effects of organophosphorus compounds (OPCs). The usefulness of pyridostigmine, the only compound approved by the Food and Drug Administration (FDA) for such pretreatment, has been questioned. In search for more efficacious alternatives, we have examined in vivo the efficacy of a group of ten compounds with known anti-AChE activity (pyridostigmine, metoclopramide, tiapride, ranitidine, physostigmine, tacrine, amiloride, methylene blue, 7- methoxytacrine and K-27) to reduce mortality induced by the OPC methyl-paraoxon. AChE inhibitors were given intraperitoneally in equitoxic dosage (25% of LD01) 30 min before OPC exposure. Protection was quantified in rats by determining the relative risk of death (RR) by Cox analysis, with RR=1 for animals given only methyl-paraoxon, but no pretreatment. Only physostigmine (RR=0.39), K-27 (RR=0.40) and tacrine (RR=0.48) significantly (p≤ 0.05) reduced methylparaoxon- induced mortality, when given prophylactically. Pretreatment with pyridostigmine, ranitidine, tiapride, amiloride, metoclopramide and methylene blue did not significantly protect against the lethal effects of methyl-paraoxon. 7-methoxytacrine (7-MEOTA) significantly (p≤ 0.05) increased the relative risk of methyl-paraoxon-induced death (RR=1.31). These results indicate that pretreatment with pyridostigmine cannot be considered a broad-spectrum approach against OPC exposure. K-27 may be a suitable alternative if passage into the brain is contraindicated.

There is a growing interest in sleep disorders in multiple sclerosis (MS) due to their high frequency and possible relationship to fatigue, a hallmark symptom in MS. Among them, insomnia and restless legs syndrome (RLS) are the most common ones. RLS is a sleep-related motor disorder characterized by a strong urge to move associated with uncomfortable sensations in the limbs. It is frequently under diagnosed in patients with MS although its course is often particularly severe. Several arguments support a symptomatic origin of RLS in MS patients. Independently of any causal relationship, the high prevalence of RLS in MS patients has clinical implications. The purpose of the present review is (i) to summarize the epidemiological data and clinical characteristics of RLS in MS patients in order to increase sensitivity to this disorder; (ii) to document the substantial body of evidence in support of a symptomatic origin of RLS in MS and from this (iii) to delineate the proposition that MS may represent a clinical model to study RLS-associated pathological changes.

Analysis of the diverse interactions of multiple signaling pathways is an emerging challenge in the era of networking pharmacology. To reveal imbalanced signaling pathways and pharmacological mechanisms involved in ischemic process, we designed systemic experiments from top-down to bottom-up for investigating the variations of multiple pathways in mouse hippocampal cells. A total of 711 focal cerebral ischemia-reperfused animals (504 mice and 207 rats), induced by occlusion of the middle cerebral artery, were obtained to conduct 4 experiments. The mice were used to analyze the pharmacological effects of four single compounds, baicalin (BA), jasminoidin (JA), ursodeoxycholic acid (UA) and concha margaritifera (CM) and two combination therapies (BA+JA, and JA+UA). Moreover, the mouse models were also used for microarray and western blotting test. The rat models were used for infarction volume test, magnetic resonance imaging (MRI) test and neurological score analysis to validate the pharmacological effects in another species. The results of western blotting confirmed that the expression of the key proteins involved in the ischemiaactivated Wnt and nuclear factor κB (NF-κB) pathway was markedly altered. In addition, based on the screened gene expression profiles of ischemia hippocampus, a variety of altered genes contributed to the 9 stroke-related pathways based on literature review [Wnt, extracellular signal-regulated kinase (ERK), janus kinase (JAK), mitogen-activated protein kinase (MAPK), gonadotropin-releasing hormone (GnRH), calcium/calmodulin-dependent protein kinase (CaMK), vascular endothelial growth factor (VEGF), epidermal growth factor (EGF), and platelet-derived growth factor (PDGF)] in different groups. Thus, we believed that the 9 signaling pathways were significantly imbalanced in different groups. However, analysis of overlapping genes was insufficient to reveal the expression profiles of imbalanced pathways between or within various conditions treated with different compounds or compound mixtures. Therefore, global similarity index (GSI) is introduced to quantify the genotypic outcomes of gene expression profiles. Independent experiments in mice on the effects of infarction volume, neurologic deficit score and the results of MRI in rats showed that GSI was suitable for the spectral measurement of imbalance in those 9 biochemical pathways with a predictive accuracy of 81.0% as assessed by leave-one-out cross-validation.