GM1 ganglioside modifies microglial and neuroinflammatory responses to α-synuclein in the rat AAV-A53T α-synuclein model of Parkinson's disease.

Among the pathological events associated with the dopaminergic neurodegeneration characteristic of Parkinson's disease (PD) are the accumulation of toxic forms of α-synuclein and microglial activation associated with neuroinflammation. Although numerous other processes may participate in the pathogenesis of PD, the two factors mentioned above may play critical roles in the initiation and progression of dopamine neuron degeneration in PD. In this study, we employed a slowly progressing model of PD using adeno-associated virus-mediated expression of human A53T α-synuclein into the substantia nigra on one side of the brain and examined the microglial response in the striatum on the injected side compared to the non-injected (control) side. We further examined the extent to which administration of the neuroprotective ganglioside GM1 influenced α-synuclein-induced glial responses. Changes in a number of microglial morphological measures (i.e., process length, number of endpoints, fractal dimension, lacunarity, density, and cell perimeter) were indicative of the presence of activated microglial and an inflammatory response on the injected side of the brain, compared to the control side. In GM1-treated animals, no significant differences in microglial morphology were observed between the injected and control striata. Follow-up studies showed that mRNA expression for several inflammation-related genes was increased on the A53T α-synuclein injected side vs. the non-injected side in saline-treated animals and that such changes were not observed in GM1-treated animals. These data show that inhibition of microglial activation and potentially damaging neuroinflammation by GM1 ganglioside administration may be among the many factors that contribute to the neuroprotective effects of GM1 in this model and possibly in human PD.

GM1 Ganglioside as a Disease-Modifying Therapeutic for Parkinson's Disease: A Multi-Functional Glycosphingolipid That Targets Multiple Parkinson's Disease-Relevant Pathogenic Mechanisms.

Parkinson's disease (PD) is a progressive neurodegenerative disorder affecting millions of patients worldwide. Many therapeutics are available for treating PD symptoms but there is no disease-modifying therapeutic that has been unequivocally shown to slow or stop the progression of the disease. There are several factors contributing to the failure of many putative disease-modifying agents in clinical trials and these include the choice of patients and clinical trial designs for disease modification trials. Perhaps more important, however, is the choice of therapeutic, which for the most part, has not taken into account the multiple and complex pathogenic mechanisms and processes involved in PD. This paper discusses some of the factors contributing to the lack of success in PD disease-modification trials, which have mostly investigated therapeutics with a singular mechanism of action directed at one of the many PD pathogenic processes, and suggests that an alternative strategy for success may be to employ multi-functional therapeutics that target multiple PD-relevant pathogenic mechanisms. Evidence is presented that the multi-functional glycosphingolipid GM1 ganglioside may be just such a therapeutic.

siRNA-mediated knockdown of B3GALT4 decreases GM1 ganglioside expression and enhances vulnerability for neurodegeneration.

Reduced levels of brain gangliosides GD1a, GD1b, GT1b and to a lesser extent GM1 have been found in substantia nigra (SN) from Parkinson's disease (PD) patients, along with decreased gene expression for key enzymes (B3Galt4, St3gal2) involved in synthesis of these gangliosides. Based on these observations, the present study examined the extent to which decreased expression of B3GALT4 mRNA and resulting decreased levels of GM1 ganglioside in dopaminergic cells may increase the vulnerability of these cells to degeneration in response to a neurotoxicant exposure that under normal circumstances would not result in neurodegeneration. Differentiated SK-N-SH cells were treated with B3GALT4 siRNA to significantly reduce B3GALT4 mRNA expression and decrease GM1 levels. Exposure of these cells to a low concentration (10 µM) of the neurotoxin MPP+ that previously produced no toxicity resulted in approximately 50% cell loss after B3GALT4 siRNA treatment. This was a similar a degree of cell loss observed with 100 µM MPP+ in normal, differentiated SK-N-SH cells. Addition of GM1 to the culture medium after siRNA treatment was able to significantly protect cells from enhanced MPP+ toxicity. These data suggest that decreased B3GALT4 and GM1 expression can increase cell vulnerability to potentially toxic stressors and that such mechanisms may contribute to dopaminergic neurodegeneration in PD.

PET imaging of dopamine release in the frontal cortex of manganese-exposed non-human primates.

Humans and non-human primates exposed to excess levels of manganese (Mn) exhibit deficits in working memory and attention. Frontal cortex and fronto-striatal networks are implicated in working memory and these circuits rely on dopamine for optimal performance. Here, we aimed to determine if chronic Mn exposure alters in vivo dopamine release (DAR) in the frontal cortex of non-human primates. We used [11 C]-FLB457 positron emission tomography with amphetamine challenge to measure DAR in Cynomolgus macaques. Animals received [11 C]-FLB457 positron emission tomography scans with and without amphetamine challenge prior to Mn exposure (baseline), at different time points during the Mn exposure period, and after 10 months of Mn exposure cessation. Four of six Mn-exposed animals expressed significant impairment of frontal cortex in vivo DAR relative to baseline. One Mn animal had no change in DAR and another Mn animal expressed increased DAR relative to baseline. In the reversal studies, one Mn-exposed animal exhibited complete recovery of DAR while the second animal had partial recovery. In both animals, frontal cortex Mn concentrations normalized after 10 months of exposure cessation based on T1-weighted magnetic resonance imaging. D1-dopamine receptor (D1R) autoradiography in frontal cortex tissue indicates that Mn animals that experienced cessation of Mn exposure expressed D1R levels that were approximately 50% lower than Mn animals that did not experience cessation of Mn exposure or control animals. The present study provides evidence of Mn-induced alterations in frontal cortex DAR and D1R that may be associated with working memory and attention deficits observed in Mn-exposed subjects.

Effect of creatine monohydrate on clinical progression in patients with Parkinson disease: a randomized clinical trial.

IMPORTANCE: There are no treatments available to slow or prevent the progression of Parkinson disease, despite its global prevalence and significant health care burden. The National Institute of Neurological Disorders and Stroke Exploratory Trials in Parkinson Disease program was established to promote discovery of potential therapies. OBJECTIVE: To determine whether creatine monohydrate was more effective than placebo in slowing long-term clinical decline in participants with Parkinson disease. DESIGN, SETTING, AND PATIENTS: The Long-term Study 1, a multicenter, double-blind, parallel-group, placebo-controlled, 1:1 randomized efficacy trial. Participants were recruited from 45 investigative sites in the United States and Canada and included 1741 men and women with early (within 5 years of diagnosis) and treated (receiving dopaminergic therapy) Parkinson disease. Participants were enrolled from March 2007 to May 2010 and followed up until September 2013. INTERVENTIONS: Participants were randomized to placebo or creatine (10 g/d) monohydrate for a minimum of 5 years (maximum follow-up, 8 years). MAIN OUTCOMES AND MEASURES: The primary outcome measure was a difference in clinical decline from baseline to 5-year follow-up, compared between the 2 treatment groups using a global statistical test. Clinical status was defined by 5 outcome measures: Modified Rankin Scale, Symbol Digit Modalities Test, PDQ-39 Summary Index, Schwab and England Activities of Daily Living scale, and ambulatory capacity. All outcomes were coded such that higher scores indicated worse outcomes and were analyzed by a global statistical test. Higher summed ranks (range, 5-4775) indicate worse outcomes. RESULTS: The trial was terminated early for futility based on results of a planned interim analysis of participants enrolled at least 5 years prior to the date of the analysis (n = 955). The median follow-up time was 4 years. Of the 955 participants, the mean of the summed ranks for placebo was 2360 (95% CI, 2249-2470) and for creatine was 2414 (95% CI, 2304-2524). The global statistical test yielded t1865.8 = -0.75 (2-sided P = .45). There were no detectable differences (P < .01 to partially adjust for multiple comparisons) in adverse and serious adverse events by body system. CONCLUSIONS AND RELEVANCE: Among patients with early and treated Parkinson disease, treatment with creatine monohydrate for at least 5 years, compared with placebo did not improve clinical outcomes. These findings do not support the use of creatine monohydrate in patients with Parkinson disease. TRIAL REGISTRATION: clinicaltrials.gov Identifier: NCT00449865.

Retinal pathology detected by optical coherence tomography in an animal model of Parkinson's disease.

BACKGROUND: Optical coherence tomography (OCT) is a noninvasive procedure for analysis of retinal morphology. Significant changes in the thickness of the peripapillary retinal nerve fiber layer (RNFL) in Parkinson's disease (PD) have been reported, and the current study was performed to examine whether such changes can also be detected in an animal model of PD. METHODS: Optical coherence tomography measurements of peripapillary RNFL thickness, macula volume, and foveal thickness were obtained from 10 normal and five 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated cynomolgus monkeys with stable Parkinsonian signs. RESULTS: Average RNFL thickness was significantly decreased in Parkinsonian monkeys compared with controls, with statistically significant RNFL thinning found in nasal and inferior quadrants. Macula volume and foveal thickness were also significantly reduced in Parkinsonian animals compared with controls. CONCLUSIONS: As described in PD, RNFL thinning, reduced macula volume, and reduced foveal thickness also occurs in monkeys with MPTP-induced Parkinsonism. These findings pave the way for additional studies in which OCT may be used to track changes in the retina that might be present very early in the PD pathological process, perhaps preceding the onset of motor signs.

The neurobiological basis of cognitive impairment in Parkinson's disease.

The recent formalization of clinical criteria for Parkinson's disease with dementia (PDD) codifies many studies on this topic, including those assessing biological correlates. These studies show that the emergence of PDD occurs on the background of severe dopamine deficits with, the main pathological drivers of cognitive decline being a synergistic effect between alpha-synuclein and Alzheimer's disease pathology. The presence of these pathologies correlates with a marked loss of limbic and cortically projecting dopamine, noradrenaline, serotonin, and acetylcholine neurons, although the exact timing of these relationships remains to be determined. Genetic factors, such as triplications in the α-synuclein gene, lead to a clear increased risk of PDD, whereas others, such as parkin mutations, are associated with a reduced risk of PDD. The very recent formalization of clinical criteria for PD with mild cognitive impairment (PD-MCI) allows only speculation on its biological and genetic bases. Critical assessment of animal models shows that chronic low-dose MPTP treatment in primates recapitulates PD-MCI over time, enhancing the current biological concept of PD-MCI as having enhanced dopamine deficiency in frontostriatal pathways as well as involvement of other neurotransmitter systems. Data from other animal models support multiple transmitter involvement in cognitive impairment in PD. Whereas dopamine dysfunction has been highlighted because of its obvious role in PD, the role of the other neurotransmitter systems, neurodegenerative pathologies, and genetic factors in PD-MCI remains to be fully elucidated.

Levodopa improves motor deficits but can further disrupt cognition in a macaque Parkinson model.

BACKGROUND: Levodopa effectively relieves motor symptoms in Parkinson's disease (PD), but has had inconsistent effects on cognition, even worsening some aspects of cognitive functioning. Therefore, remediation of PD cognitive deficits is a major unmet need. However, drug development efforts have been hampered by lack of an animal model in which motor and cognitive deficits can be examined simultaneously. METHODS: Cynomolgus monkeys were trained to perform cognitive tasks and then chronically exposed to MPTP to slowly produce cognitive and motor deficits of parkinsonism. RESULTS: Administration of L-dopa to these animals dose dependently improved motor functioning, but did not significantly improve cognitive performance. At doses that maximally improved motor function, additional cognitive deficits were observed. The present model of MPTP-induced parkinsonism recapitulates important motor and cognitive aspects of PD. Results with L-dopa mirror data derived from PD patients. CONCLUSION: This model should allow more efficient testing of potential PD therapeutics to evaluate motor and cognitive functions simultaneously. © 2012 Movement Disorder Society.

Neurotoxicity and Outcomes from Developmental Lead Exposure: Persistent or Permanent?

BACKGROUND: Childhood lead poisoning remains an important public health issue in the United States, as well as elsewhere in the world. Although primary prevention is a major goal and it is critically important to keep children from getting poisoned, it is also important to explore ways to reduce the neurotoxic effects of lead in those children already poisoned. Whether lead-induced neurotoxicity and its related adverse outcomes are viewed as "permanent" or "persistent" may influence the way in which potential remediation efforts are considered for improving outcomes from childhood lead poisoning. OBJECTIVES: The objective of this commentary was to discuss the ideas of permanence and persistence in relation to the direct neurotoxic effects of lead on the brain and the resulting adverse outcomes from these effects. Recent new insights regarding potential mitigation of lead-induced neurotoxic effects on brain and behavior are considered along with clinical information on neurorehabilitation to suggest potential strategies for improving cognitive/behavioral outcomes in lead-poisoned children. DISCUSSION: The distinction between permanent and persistent in regard to lead-induced neurotoxicity and its resulting outcomes may have broad implications for public health policies in response to the problem of childhood lead exposure. The term permanent implies that the damage is irreversible with little chance of improvement. However, there is evidence that at least some of the adverse cognitive/behavioral outcomes from lead exposure are persistent rather than permanent and potentially amenable, under the appropriate circumstances, to some level of mitigation. This author recommends that clinical, interventional research efforts be devoted to exploring optimal neurorehabilitative and enrichment conditions to stimulate plasticity and enhance functioning to determine the extent to which promising results from preclinical studies of lead-induced brain damage and the mitigation of these effects can be successfully translated to humans. https://doi.org/10.1289/EHP12371.

Current concepts in treating mild cognitive impairment in Parkinson's disease.

Impairment in various aspects of cognition is recognized as an important non-motor symptom of Parkinson's disease (PD). Mild cognitive impairment in PD (PD-MCI) is common in non-demented PD patients and is often associated with severity of motor symptoms, disease duration and increasing age. Further, PD-MCI can have a significant negative effect on performance of daily life activities and may be a harbinger of development of PD dementia. Thus, there is significant interest in developing therapeutic strategies to ameliorate cognitive deficits in PD and improve cognitive functioning of PD patients. However, due to significant questions that remain regarding the pathophysiology of cognitive dysfunction in PD, remediation of cognitive dysfunction in PD has proven difficult. In this paper, we will focus on PD-MCI and will review some of the current therapeutic approaches being taken to try to improve cognitive functioning in patients with PD-MCI.

Altered expression of glycobiology-related genes in Parkinson's disease brain.

The precise mechanisms initiating and perpetuating the cellular degeneration in Parkinson's disease (PD) remain unclear. There is decreased expression of the main brain gangliosides, and GM1 ganglioside in particular, in the PD brain along with decreased expression of the genes coding for the glycosyltranferase and the sialyltransferase responsible for the synthesis of these brain gangliosides. However, potentially important pathogenic mechanisms contributing to the neurodegeneration in PD may also include altered levels of expression of genes involved in glycosylation, sialylation and sphingolipid synthesis and metabolism. Although various studies have described pathological lipid and glycolipid changes in PD brain, there have been limited studies of expression of glycobiology-related genes in PD brain. The current study was performed as an initial attempt to gain new information regarding potential changes in glycoprotein and glycolipid-related genes in PD by investigating the gene expression status for select glycosyltransferases, sialyltransferases, sialidases, sphingosine kinases, and lysosomal enzymes in the substantia nigra and putamen from patients with PD and neurologically normal controls. Results showed altered expression of glycosyltransferase genes (B3GALT2 and B4GALT1) potentially involved in microglial activation and neuroinflammation, sphingosine-1-phosphate (S1P) modulators (SPHK1, SPHK2, and SGPL1) involved in sphingolipid synthesis and metabolism, polysialyltransferase genes (ST8SIA2 and ST8SIA4) that encode enzymes responsible for polysialic acid (polySia) biosynthesis, and the sialidase NEU4, expression of which has been linked to the clearance of storage materials from lysosomes. The data presented here underscore the complexity of the glycolipid/sphingolipid dysregulation in the PD brain and continued and expanded study of these processes may not only provide a greater understanding of the complex roles of aberrant glycosylation sialylation, and sphingolipid synthesis/metabolism in the pathophysiology of PD but may identify potential druggable targets for PD therapeutics.

Effects of the alpha-2 adrenoceptor agonist guanfacine on attention and working memory in aged non-human primates.

Alpha-2 adrenergic receptors are potential targets for ameliorating cognitive deficits associated with aging as well as certain pathologies such as attention deficit disorder, schizophrenia and Parkinson's disease. Although the alpha-2 agonist guanfacine has been reported to improve working memory in aged primates, it has been difficult to assess the extent to which these improvements may be related to drug effects on attention and/or memory processes involved in task performance. The present study investigated effects of guanfacine on specific attention and memory tasks in aged monkeys. Four Rhesus monkeys (18-21 years old) performed a sustained attention (continuous performance) task and spatial working memory task (self-ordered spatial search) that has minimal demands on attention. Effects of a low (0.0015 mg/kg) and high (0.5 mg/kg) dose of gunafacine were examined. Low-dose guanfacine improved performance on the attention task [i.e. decreased omission errors by 50.8 ± 4.3% (P = 0.001) without an effect on commission errors] but failed to improve performance on the spatial working memory task. The high dose of guanfacine had no effects on either task. Guanfacine may have a preferential effect on some aspects of attention in normal aged monkeys and in doing so may also improve performance on other tasks, including some working memory tasks that have relatively high attention demands.

A novel dopamine D3R agonist SK609 with norepinephrine transporter inhibition promotes improvement in cognitive task performance in rodent and non-human primate models of Parkinson's disease.

Mild cognitive impairment is present in a number of neurodegenerative disorders including Parkinson's disease (PD). Mild cognitive impairment in PD (PD-MCI) often manifests as deficits in executive functioning, attention, and spatial and working memory. Clinical studies have suggested that the development of mild cognitive impairment may be an early symptom of PD and may even precede the onset of motor impairment by several years. Dysfunction in several neurotransmitter systems, including dopamine (DA), norepinephrine (NE), may be involved in PD-MCI, making it difficult to treat pharmacologically. In addition, many agents used to treat motor impairment in PD may exacerbate cognitive impairment. Thus, there is a significant unmet need to develop therapeutics that can treat both motor and cognitive impairments in PD. We have recently developed SK609, a selective, G-protein biased signaling agonist of dopamine D3 receptors. SK609 was successfully used to treat motor impairment and reduce levodopa-induced dyskinesia in a rodent model of PD. Further characterization of SK609 suggested that it is a selective norepinephrine transporter (NET) inhibitor with the ability to increase both DA and NE levels in the prefrontal cortex. Pharmacokinetic analysis of SK609 under systemic administration demonstrated 98% oral bioavailability and high brain distribution in striatum, hippocampus and prefrontal cortex. To evaluate the effects of SK609 on cognitive deficits of potential relevance to PD-MCI, we used unilateral 6-hydroxydopamine (6-OHDA) lesioned rats and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated cynomolgus macaques, with deficits in performance in a sustained attention and an object retrieval task, respectively. SK609 dose dependently improved the performance of 6-OHDA-lesioned rats, with peak performance achieved using a 4 mg/kg dose. This improvement was predominantly due to a significant reduction in the number of misses and false alarm errors, contributing to an increase in sustained attention. In MPTP-lesioned monkeys, this same dose also improved performance in an object retrieval task, significantly reducing cognitive errors (barrier reaches) and motor errors (fine motor dexterity problems). These data demonstrate that SK609 with its unique pharmacological effects on modulating both DA and NE can ameliorate cognitive impairment in PD models and may provide a therapeutic option to treat both motor and cognitive impairment in PD patients.

The dopamine D3 receptor antagonist, S33138, counters cognitive impairment in a range of rodent and primate procedures.

Although dopamine D(3) receptor antagonists have been shown to enhance frontocortical cholinergic transmission and improve cognitive performance in rodents, data are limited and their effects have never been examined in primates. Accordingly, we characterized the actions of the D(3) receptor antagonist, S33138, in rats and rhesus monkeys using a suite of procedures in which cognitive performance was disrupted by several contrasting manipulations. S33138 dose-dependently (0.01-0.63 mg/kg s.c.) blocked a delay-induced impairment of novel object recognition in rats, a model of visual learning and memory. Further, S33138 (0.16-2.5 mg/kg s.c.) similarly reduced a delay-induced deficit in social novelty discrimination in rats, a procedure principally based on olfactory cues. Adult rhesus monkeys were trained to perform cognitive procedures, then chronically exposed to low doses of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine which produced cognitive impairment without motor disruption. In an attentional set-shifting task of cognitive flexibility involving an extra-dimensional shift, deficits were reversed by S33138 (0.04 and 0.16 mg/kg p.o.). S33138 also significantly improved accuracy (0.04 and 0.16 mg/kg p.o.) at short (but not long) delays in a variable delayed-response task of attention and working memory. Finally, in a separate set of experiments performed in monkeys displaying age-related deficits, S33138 significantly (0.16 and 0.63 mg/kg p.o.) improved task accuracies for long delay intervals in a delayed matching-to-sample task of working memory. In conclusion, S33138 improved performance in several rat and primate procedures of cognitive impairment. These data underpin interest in D(3) receptor blockade as a strategy for improving cognitive performance in CNS disorders like schizophrenia and Parkinson's disease.

Low-level Lead Exposure Impairs Fronto-executive Functions: A Call to Update the DSM-5 with Lead Poisoning as a Neurodevelopmental Disorder.

Lead (Pb2+) exposure continues to occur despite efforts to reduce its environmental sources, and affects millions of children in the US alone. Finding Pb2+ in blood samples indicates that exposure has resulted in absorption with the potential for distribution to all cells in the body. Research conducted during the last two decades and summarized here has demonstrated that the brain is a critical target organ for detrimental Pb effects, especially causing fronto-executive dysfunctions (FED). This review summarizes the evidence supporting this last statement and based on this evidence argues that Pb2+-poisoning should be considered as part of the neurodevelopmental disorder classifications within the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) developed by the American Psychiatric Association. Inclusion in the DSM-5 or future revisions would have impact for diagnosis acceptance and subsequent availability of resources for interventions and research.

Repeatable battery for assessment of neuropsychological status in early Parkinson's disease.

Adequate reliability and valid factor structure are prerequisites for appropriate use of a measure in a population. Although the Repeatable Battery for Assessment of Neuropsychological Status (RBANS) has been used to examine cognition in Parkinson's disease (PD), its reliability and factor structure have not been examined in this population. This study examined the reliability and factor structure of the RBANS in participants with de novo PD recruited for two NIH Exploratory Trials in Parkinson's Disease (NET-PD), using Cronbach's alpha and factor analysis. Confirmatory factor analysis (CFA) was implemented on the factor structure proposed in the RBANS manual, and exploratory factor analysis (EFA) was conducted to identify a valid factor structure given the proposed one was not supported. The RBANS exhibited poor reliability in participants with NET-PD. Cronbach's alpha ranged from 0.03 to 0.74 for the five domains and the full scale. CFA results indicated that the proposed factor structure in the RBANS manual was not supported in this sample. EFA identified a two-factor structure for six of the 12 RBANS items. Six items were eliminated due to low correlation with other items or severe ceiling effects. This new factor structure was validated by another CFA. The two domains have fair reliability. Cronbach's alpha ranged from 0.65 to 0.74 for the two factors in the two datasets. These results suggest that the current RBANS domain and total scores may not provide valid measurement of the neuropsychological status for patients with early PD.

The attention set-shifting test is sensitive for revealing sex-based impairments in executive functions following developmental lead exposure in rats.

The literature on lead (Pb) exposure has focused in large part on hippocampal-based learning and memory deficits, although frontoexecutive dysfunctions are known to exist in Pb-exposed humans. This study examined the effects of perinatal (PERI) and early postnatal (EPN) developmental low-level Pb-exposures in rats on frontoexecutive functions, using the Attention Set-Shift Test (ASST). Control males and females performed the ASST similarly. Male EPN rats had difficulty with simple discrimination (SD) of odors and failed to complete the compound discrimination (CD) stage of the ASST. All other Pb-exposed rats completed the training and testing. Male PERI rats performed worse on the SD, intradimensional (ID), and intradimensional-reversal (ID-Rev) ASST stages when compared to male Control rats. Female EPN rats performed similar to Controls on the ID-Rev rats, whereas PERI rats performed better the trials-to-criterion on the ID-Rev than EPN and Control rats. Pb-exposed female rats had significant difficulty performing the ED/ED-Rev stages, with the number of trials-to-criterion double that required by Pb-exposed and Control male rats and Control female rats. Together, the ASST results showed that developmental Pb-exposure induces frontoexecutive dysfunction that persists into adulthood, with different sex-based vulnerabilities dependent upon the time-period of neurotoxicant exposure.

Gangliosides: Treatment Avenues in Neurodegenerative Disease.

Gangliosides are cell membrane components, most abundantly in the central nervous system (CNS) where they exert among others neuro-protective and -restorative functions. Clinical development of ganglioside replacement therapy for several neurodegenerative diseases was impeded by the BSE crisis in Europe during the 1990s. Nowadays, gangliosides are produced bovine-free and new pre-clinical and clinical data justify a reevaluation of their therapeutic potential in neurodegenerative diseases. Clinical experience is greatest with monosialo-tetrahexosyl-ganglioside (GM1) in the treatment of stroke. Fourteen randomized controlled trials (RCTs) in overall >2,000 patients revealed no difference in survival, but consistently superior neurological outcomes vs. placebo. GM1 was shown to attenuate ischemic neuronal injuries in diabetes patients by suppression of ERK1/2 phosphorylation and reduction of stress to the endoplasmic reticulum. There is level-I evidence from 5 RCTs of a significantly faster recovery with GM1 vs. placebo in patients with acute and chronic spinal cord injury (SCI), disturbance of consciousness after subarachnoid hemorrhage, or craniocerebral injuries due to closed head trauma. In Parkinson's disease (PD), two RCTs provided evidence of GM1 to be superior to placebo in improving motor symptoms and long-term to result in a slower than expected symptom progression, suggesting disease-modifying potential. In Alzheimer's disease (AD), the role of gangliosides has been controversial, with some studies suggesting a "seeding" role for GM1 in amyloid ß polymerization into toxic forms, and others more recently suggesting a rather protective role in vivo. In Huntington's disease (HD), no clinical trials have been conducted yet. However, low GM1 levels observed in HD cells were shown to increase cell susceptibility to apoptosis. Accordingly, treatment with GM1 increased survival of HD cells in vitro and consistently ameliorated pathological phenotypes in several murine HD models, with effects seen at molecular, cellular, and behavioral level. Given that in none of the clinical trials using GM1 any clinically relevant safety issues have occurred to date, current data supports expanding GM1 clinical research, particularly to conditions with high, unmet medical need.

GM1 Ganglioside Modifies α-Synuclein Toxicity and is Neuroprotective in a Rat α-Synuclein Model of Parkinson's Disease.

While GM1 may interact with α-synuclein in vitro to inhibit aggregation, the ability of GM1 to protect against α-synuclein toxicity in vivo has not been investigated. We used targeted adeno-associated viral vector (AAV) overexpression of human mutant α-synuclein (A53T) in the rat substantia nigra (SN) to produce degeneration of SN dopamine neurons, loss of striatal dopamine levels, and behavioral impairment. Some animals received daily GM1 ganglioside administration for 6 weeks, beginning 24 hours after AAV-A53T administration or delayed start GM1 administration for 5 weeks beginning 3 weeks after AAV-A53T administration. Both types of GM1 administration protected against loss of SN dopamine neurons and striatal dopamine levels, reduced α-synuclein aggregation, and delayed start administration of GM1 reversed early appearing behavioral deficits. These results extend prior positive results in MPTP models, are consistent with the results of a small clinical study of GM1 in PD patients that showed slowing of symptom progression with chronic use, and argue for the continued refinement and development of GM1 as a potential disease modifying therapy for PD.