A neuroscience perspective of the gut theory of Parkinson's disease

Parkinson's disease is caused by complex interactions between environmental factors and a genetic predisposition. Environmental factors include exposure to pesticides and toxins, heavy metals and accumulation of iron and/or manganese in the brain. However, accumulating evidence indicates that gut–brain health and function are impaired in Parkinson's disease, often a decade before motor symptoms are diagnosed. We present the gut–brain theory of Parkinson's disease and summarise the peripheral and central nervous system pathology, gastrointestinal symptoms experienced by many Parkinson's patients, the route by which gut–brain dysfunction may occur and changes in gut microbiota that are associated with disease expression. Finally, we consider future gut‐based treatments to prevent or slow down the progression of Parkinson's disease and explore whether this knowledge may highlight biomarkers to be included in complex algorithms in the future to assess a person's risk of developing Parkinson's disease.     

Infectious Agents as Potential Drivers of α-Synucleinopathies

α-synucleinopathies, encompassing Parkinson's disease, dementia with Lewy bodies, and multiple system atrophy, are devastating neurodegenerative diseases for which available therapeutic options are scarce, mostly because of our limited understanding of their pathophysiology. Although these pathologies are attributed to an intracellular accumulation of the α-synuclein protein in the nervous system with subsequent neuronal loss, the trigger(s) of this accumulation is/are not clearly identified. Among the existing hypotheses, interest in the hypothesis advocating the involvement of infectious agents in the onset of these diseases is renewed. In this article, we aimed to review the ongoing relevant factors favoring and opposing this hypothesis, focusing on (1) the potential antimicrobial role of α-synuclein, (2) potential entry points of pathogens in regard to early symptoms of diverse α-synucleinopathies, (3) pre-existing literature reviews assessing potential associations between infectious agents and Parkinson's disease, (4) original studies assessing these associations for dementia with Lewy bodies and multiple system atrophy (identified through a systematic literature review), and finally (5) potential susceptibility factors modulating the effects of infectious agents on the nervous system. © 2022 International Parkinson and Movement Disorder Society     

Implications of the Gut Microbiome in Parkinson's Disease

Parkinson's disease is a common neurodegenerative disorder that presents with nonmotor and motor symptoms. The nonmotor manifestations of Parkinson's disease often begin years before the motor symptoms. Autopsy studies, including both Parkinson's disease patients and matched controls, demonstrated that α-synuclein aggregates in Parkinson's disease patients can be found in both the substantia nigra and the enteric nervous system. Therefore, it has been hypothesized that the pathological process that leads eventually to Parkinson's disease might initially take place in the enteric nervous system years before the appearance of motor features. The gut microbiome plays essential roles in the development and maintenance of different body systems. Dysbiosis of the normal gut microbiome is thought to be associated with pathophysiologic changes not only in the gastrointestinal system itself but also in the enteric and central nervous systems. These changes are thought to ultimately cause loss of dopaminergic neurons via various mechanisms including the release of neurotoxins into the systemic circulation, decreased production of neuroprotective factors, and triggering inflammatory and autoimmune responses. In this review, we review the gut microbiome changes in Parkinson's disease and discuss the mechanisms by which gut microbiome dysbiosis may be a contributing factor to the pathophysiology of Parkinson's disease. © 2020 International Parkinson and Movement Disorder Society     

Air Pollution and the Risk of Parkinson's Disease: A Review

Parkinson's disease, as well as other neurodegenerative disorders, are primarily characterized by pathological accumulation of proteins, inflammation, and neuron loss. Although there are some known genetic risk factors, most cases cannot be explained by genetics alone. Therefore, it is important to determine the environmental factors that confer risk and the mechanisms by which they act. Recent epidemiological studies have found that exposure to air pollution is associated with an increased risk for development of Parkinson's disease, although not all results are uniform. The variability between these studies is likely due to differences in what components of air pollution are measured, timing and methods used to determine exposures, and correction for other variables. There are several potential mechanisms by which air pollution could act to increase the risk for development of Parkinson's disease, including direct neuronal toxicity, induction of systemic inflammation leading to central nervous system inflammation, and alterations in gut physiology and the microbiome. Taken together, air pollution is an emerging risk factor in the development of Parkinson's disease. A number of potential mechanisms have been implicated by which it promotes neuropathology providing biological plausibility, and these mechanisms are likely relevant to the development of other neurodegenerative disorders such as Alzheimer's disease. This field is in its early stages, but a better understanding of how environmental exposures influence the pathogenesis of neurodegeneration is essential for reducing the incidence of disease and finding disease-modifying therapies. © 2022 International Parkinson and Movement Disorder Society     

Parkinson's syndrome and Parkinson's disease in mitochondrial disorders

In the majority of cases, mitochondrial disorders are multisystem conditions that most frequently affect the skeletal muscle, followed by the central nervous system. One of the clinical manifestations of central nervous system involvement is Parkinson's syndrome (PS). Evidence for an association of mitochondrial defects with PS comes from mitochondrial disorder patients who have developed Parkinson's syndrome and from Parkinson's syndrome patients who have developed a mitochondrial disorder. In addition, there are a number of patients with Parkinson's syndrome or Parkinson's disease (PD) who later develop subclinical immunohistological or biochemical indications of mitochondrial defects or accumulates mitochondrial DNA mutations within various cerebral regions. There are also Parkinson's syndrome patients who present with elevated cerebrospinal‐fluid lactate by magnetic resonance spectroscopy. Furthermore, it has been shown that mutations in genes causing PD, such as PINK1, parkin, DJ1, alpha‐synuclein, and LRRK2, also cause mitochondrial dysfunction, which is one of the reasons why they are called mitochondrial nigropathies. Parkinson's syndrome in patients with a mitochondrial disorder may also result from oxidative stress or exogenous toxins. Treatment of mitochondrial Parkinson's syndrome is not at variance with the treatment of Parkinson's syndrome due to other causes, but because of the multisystem nature of mitochondrial disorders, mitochondrial Parkinson's syndrome requires additional therapeutic support. © 2011 Movement Disorder Society     

Update on neuroimaging in infectious central nervous system disease

PURPOSE OF REVIEW: Neuroimaging constitutes an important component in the diagnosis of the underlying infectious agents in central nervous system infection. This review summarizes progress in the neuroimaging of infectious central nervous system disease since January 2003. It focuses on imaging of viral encephalitis, including that caused by exotic and emerging viruses, and on imaging in immunodeficient patients. RECENT FINDINGS: Diffusion-weighted imaging has been shown to be superior to conventional magnetic resonance imaging for the detection of early signal abnormalities in herpes simplex virus encephalitis but also in enterovirus 71 encephalitis and in West Nile encephalitis. Several studies defined the pattern of magnetic resonance imaging signal changes in endemic diseases such as West Nile encephalitis, Murray Valley encephalitis, enterovirus 71 encephalitis and Japanese encephalitis, but also in encephalitides due to ubiquitous viruses such as measles virus and Lyssavirus (rabies). In patients with HIV infection, apparent diffusion coefficient ratios obtained by diffusion-weighted imaging were significantly greater in lesions due to Toxoplasma encephalitis than in primary central nervous system lymphomas. SUMMARY: The diagnosis of unclear infectious central nervous system diseases remains a challenge. More recent magnetic resonance imaging techniques, such as diffusion-weighted imaging and magnetic resonance spectroscopy, provide additional helpful information. However, the mainstay of diagnosis remains the detection of viral DNA or serological markers of specific infectious agents within the cerebrospinal fluid.     

¿Presenta la enfermedad de Parkinson una haloenzimopatía?

Laboratory studies identified changes in the metabolism of halogens in the serum and cerebrospinal fluid (CSF) of patients with Parkinson's disease, which indicates the presence of «accelerated self-halogenation» of CSF and/or an increase in haloperoxidases, specifically serum thyroperoxidase and CSF lactoperoxidase. Furthermore, an excess of some halogenated derivatives, such as advanced oxygenation protein products (AOPP), has been detected in the CSF and serum. «Accelerated self-halogenation» and increased levels of haloperoxidases and AOPP proteins indicate that halogenative stress is present in Parkinson's disease. In addition, 3-iodo-L-tyrosine, a halogenated derivative, shows «parkinsonian» toxicity in experimental models, since it has been observed to induce α-synuclein aggregation and damage to dopaminergic neurons in the mouse brain and intestine. The hypothesis is that patients with Parkinson's disease display halogenative stress related to a haloenzymatic alteration of the synthesis or degradation of oxyacid of halogens and their halogenated derivatives. This halogenative stress would be related to nervous system damage.     

Genetic variants in levodopa-induced dyskinesia (LID): A systematic review and meta-analysis

IntroductionLevodopa-induced dyskinesia frequently complicates long-term Parkinson's disease. More in-depth knowledge regarding the role of genetic factors in dyskinesia development may be important to identify parkinsonian patients who are more prone to developing dyskinesia and clarify the molecular mechanisms underlying this condition. For this reason, we systematically reviewed studies investigating genetic factors involved in dyskinesia.MethodsA systematic search of genetic factors in Parkinson's disease dyskinesia was performed using the MEDLINE (through PubMed up to June 2019) and EMBASE databases according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. A meta-analysis was conducted using a random effect model.ResultsThe literature search retrieved 33 studies assessing genes and variants possibly associated with dyskinesia in Parkinson's disease. The studies were published between 1984 and 2019 and included a total of 27,092 subjects of different ethnicities. Overall, 37 genes were analyzed in the studies reviewed, of which 22 were possibly associated with dyskinesia. The studies reported a total of 158 variants, of which 94 were possibly related to dyskinesia.ConclusionThe studies reviewed demonstrated inconsistent results, possibly due to differences in screening methods and in the comparison of clinical data in a large variety of genetically- and ethnically-diverse populations. The meta-analysis failed to demonstrate any association between the rs6280 in the DRD3 gene, rs1799836 in the MAO-B, rs4680 in the COMT gene, rs34637584 in the LRRK2 gene and LID susceptibility. The role of genetic factors in LID susceptibility is still unclear and further studies are required.     

Etiology and pathogenesis of Parkinson's disease

The past 25 years have seen a major expansion of knowledge concerning the cause of Parkinson's disease provided by an understanding of environmental and genetic factors that underlie the loss of nigral dopaminergic neurons. Based on the actions of toxins, postmortem investigations, and gene defects responsible for familial Parkinson's disease, there is now a general consensus about the mechanisms of cell death that contribute to neuronal loss in Parkinson's disease. Mitochondrial dysfunction, oxidative stress, altered protein handling, and inflammatory change are considered to lead to cell dysfunction and death by apoptosis or autophagy. Ageing is the single most important risk factor for Parkinson's disease, and the biochemical changes that are a consequence of aging amplify these abnormalities in Parkinson's disease brain. What remains to be determined is the combination and sequence of events leading to cell death and whether this is identical in all brain regions where pathology occurs and in all individuals with Parkinson's disease. Focusing on those events that characterize Parkinson's disease, namely, mitochondrial dysfunction and Lewy body formation, may be the key to further advancing the understanding of pathogenesis and to taking these mechanisms forward as a means of defining targets for neuroprotection. © 2011 Movement Disorder Society     

Émotion et noyaux gris centraux (I) : que peut nous apprendre la maladie de Parkinson ?

Parkinson's disease provides a useful model for studying the neural substrates of emotional processing. The striato-thalamo-cortical circuits, like the mesolimbic dopamine system that modulates their function, are thought to be involved in emotional processing. As Parkinson's disease is histopathologically characterized by the selective, progressive and chronic degeneration of the nigrostriatal and mesocorticolimbic dopamine systems, it can therefore serve as a model for assessing the functional role of these circuits in humans. In the present review, after a definition of emotional processing from a multicomponential perspective, a synopsis of the emotional disturbances observed in Parkinson's disease is proposed. Note that the studies on the affective consequences of subthalamic nucleus deep brain stimulation in Parkinson's disease were excluded from this review because the subject of a companion paper in this issue. This review leads to the conclusion that several emotional components would be disrupted in Parkinson's disease: subjective feeling, neurophysiological activation, and motor expression. We then discuss the functional roles of the striato-thalamo-cortical and mesolimbic circuits, ending with the conclusion that both these pathways are indeed involved in emotional processing.     

Review: Sporadic Parkinson's disease: development and distribution of α‐synuclein pathology

The development of α‐synuclein immunoreactive aggregates in selectively vulnerable neuronal types of the human central, peripheral, and enteric nervous systems is crucial for the pathogenesis of sporadic Parkinson's disease. The presence of these lesions persists into the end phase of the disease, a process that is not subject to remission. The initial induction of α‐synuclein misfolding and subsequent aggregation probably occurs in the olfactory bulb and/or the enteric nervous system. Each of these sites is exposed to potentially hostile environmental factors. Once formed, the aggregates appear to be capable of propagating trans‐synaptically from nerve cell to nerve cell in a virtually self‐promoting pathological process. A regional distribution pattern of aggregated α‐synuclein emerges that entails the involvement of only a few types of susceptible and axonally interconnected projection neurons within the human nervous system. One major route of disease progression may originate in the enteric nervous system and retrogradely reach the dorsal motor nucleus of the vagal nerve in the lower brainstem. From there, the disease process proceeds chiefly in a caudo‐rostral direction through visceromotor and somatomotor brainstem centres to the midbrain, forebrain, and cerebral cortex. Spinal cord centres may become involved by means of descending projections from involved lower brainstem nuclei as well as by sympathetic projections connecting the enteric nervous system with postganglionic peripheral ganglia and preganglionic nuclei of the spinal cord. The development of experimental cellular and animal models is helping to explain the mechanisms of how abnormal α‐synuclein can undergo aggregation and how transmission along axonal connectivities can occur, thereby encouraging the initiation of potential disease‐modifying therapeutic strategies for sporadic Parkinson's disease.     

Parkinson's Disease: Distribution of Lewy Bodies in the Peripheral Autonomic Nervous System

This report concerns the presence and distribution of Lewy bodies in the peripheral nervous system of three patients with Parkinson's disease and ten age-matched nonparkinsonian individuals. We examined the paravertebral and celiac ganglia as representatives of the sympathetic system; the submandibular ganglion as representative of the parasympathetic system; the esophagus, stomach, duodenum, jejunum, ileum and colon as representatives of the enteric system, and the trigeminal and dorsal spinal ganglia as representatives of the somatic sensory system. Lewy bodies were observed in the peripheral sympathetic and enteric systems of two of the three patients with Parkinson's disease. These two patients had numerous Lewy bodies in the submandibular ganglia. The third patient did not have Lewy bodies in the peripheral autonomic nervous system, nor did the ten control individuals studied. Lewy bodies were not detected in the somatic sensory system of any of the three parkinsonian patients. Our findings indicate that the peripheral autonomic system, including the parasympathetic system is affected in Parkinson's disease.     

Neurotoxicity of MPTP

After the discovery of 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (MPTP), we acquired a good animal model of Parkinson's disease. The extraordinary recent growth in knowledge using MPTP parkinsonism has fostered increased understanding of Parkinson's disease. In the present paper, the discovery of MPTP and the biochemical, pathological, and clinical findings of MPTP parkinsonism are first reviewed briefly. Next, using MPTP parkinsonism, unresolved issuses such as the apoptosis of MPTP, levodopa toxicity, and neuroprotective effects of monoamine oxidase inhibitors or dopamine agonists are discussed. Finally, environmental factors such as the etiology of Parkinson's disease are examined. Some genetic factors that lead to familial Parkinson's disease have recently been reported, but most cases of Parkinson's disease are sporadic. Recent epidemiological evidence emphasizes an etiological relation of 18th and 19th century industrialization to Parkinson's disease. Man‐made toxins, such as industrial chemicals and herbicides/pesticides, have been suggested to increase the risk of developing Parkinson's disease. I would like to highlight the significance of re‐examination of environmental factors in the etiology of Parkinson's disease.     

Methylphenylpyridium ion (MPP+) enhances glutamate-induced cytotoxicity against dopaminergic neurons in cultured rat mesencephalon

Parkinson's disease is characterized by chronic progression of dopaminergic neuronal death, the mechanism of which is still unknown. Although methyl-4-phenylpyridium ion (MPP+) or MPP+-like substance, that can reduce mitochondrial complex I activity, is supposed to be a causative agent for Parkinson's disease, it is difficult to explain the chronic neuronal degeneration for years. It is important to identify other putative agents capable of causing chronic cell death besides MPP⁺. We hypothesized that treatment with small doses of MPP⁺, not causing severe damage to dopaminergic neurons but merely reducing the activity of mitochondrial complex I, can be a model of Parkinson's disease, and that glutamate can be a putative agent causing chronic neuronal degeneration. Using primary culture of the rat mesencephalon, we investigated glutamate-induced cytotoxicity against dopaminergic and non-dopaminergic neurons with or without the pretreatment with MPP⁺. Brief exposure to glutamate showed similar cytotoxicity against both dopaminergic and non-dopaminergic neurons. An N-methyl-D -aspartate receptor antagonist completely blocked the glutamate-induced cytotoxicity against both dopaminergic and non-dopaminergic neurons. In the dopaminergic neurons, MPP⁺ caused cytotoxicity that was not blocked by co-administration of MK-801. After pretreatment with small doses of MPP⁺, sub-lethal doses of glutamate caused severe cell damage restricted to dopaminergic neurons, suggesting that MPP⁺ potentiates the glutamate-induced cytotoxicity only against dopaminergic neurons. As glutamate is putatively capable of causing cytotoxicity against dopaminergic neurons, the present findings might be important in considering the pathogenesis of dopaminergic neuronal degeneration and a possible therapeutic application of glutamate receptor antagonists in Parkinson's disease. © 1996 Wiley-Liss, Inc.     

Vaccinations for Neuroinfectious Disease: A Global Health Priority

Vaccines for neuroinfectious diseases are becoming an ever-increasing global health priority, as neurologic manifestations and sequelae from existing and emerging central nervous system infections account for significant worldwide morbidity and mortality. The prevention of neurotropic infections can be achieved through globally coordinated vaccination campaigns, which have successfully eradicated nonzoonotic agents such as the variola viruses and, hopefully soon, poliovirus. This review discusses vaccines that are currently available or under development for zoonotic flaviviruses and alphaviruses, including Japanese and tick-borne encephalitis, yellow fever, West Nile, dengue, Zika, encephalitic equine viruses, and chikungunya. Also discussed are nonzoonotic agents, including measles and human herpesviruses, as well as select bacterial, fungal, and protozoal pathogens. While therapeutic vaccines will be required to treat a multitude of ongoing infections of the nervous system, the ideal vaccination strategy is pre-exposure vaccination, with the ultimate goals of minimizing disease associated with zoonotic viruses and the total eradication of nonzoonotic agents.     

Changes of brain gray matter structure in Parkinson’s disease patients with dementia

Voxel-based morphometry is gaining considerable interest for studies examining Parkinson’s disease dementia patients.In this study,12 patients with clinically defined Parkinson’s disease and dementia and 12 non-demented patients with Parkinson’s disease were examined using a T1WI three-dimensional fast spoiled gradient echo sequence.Gray matter data were analyzed using a voxel-based morphometry method and independent sample t-test based on Statistical Parametric Mapping 5 software.Differences in gray matter volume were represented with statistical parametric mapping.Compared with Parkinson’s disease patients without dementia,decreased gray matter volume in Parkinson’s disease dementia patients was observed in the bilateral superior temporal gyrus,bilateral posterior cingulate and left cingulate gyrus,right parahippocampal gyrus and hippocampus,right precuneus and right cuneus,left inferior frontal gyrus and left insular lobe.No increased gray matter volume was apparent.These data indicate that gray matter atrophy in the limbic system and cerebral neocortex is related to the presence of dementia.     

Serum lipid alterations in GBA-associated Parkinson's disease

IntroductionMutations in the GBA gene, encoding for the lysosomal enzyme glucocerebrosidase, are associated with Gaucher disease. Alterations in plasma sphingolipids have been reported in Gaucher, and similarly in brain extracts in Lewy body disease. As GBA mutations are prevalent risk factors for Parkinson's disease and overlap of molecular pathways are presumable, here we assessed the lipid profiles in Parkinson's patients with and without GBA mutations.MethodsWe sequenced all GBA exons in 415 Parkinson's patients, previously genotyped for LRRK2. 64 patients (29 GBA positive vs. 35 non-GBA-carriers including 18 LRRK2 positive and 17 non-mutated) were analyzed for chitotriosidase activity and for the concentration of 40 lipid classes using HPLC-MS.Results29/415 patients (6.9%) carried 8 different GBA mutations associated with Gaucher or Parkinson's, including one novel mutation. Chitotriosidase activity was similar across the genetic groups, while the levels of key lipids were altered in GBA mutation carriers: Monohexosylceramide, Ceramide and Sphingomyelin were elevated; while Phosphatidic acid (PA), Phosphatidylethanolamine (PE), Plasmalogen phosphatidylethanolamine (PEp) and Acyl Phosphatidylglycerol (AcylPG) were decreased.ConclusionThe results suggest an important role for these lipids in GBA mediated Parkinson's disease and assist in the identification of common pathways between Gaucher and Parkinson's. Ultimately, our findings may lead to the identification of novel biomarkers for individuals at increased risk of developing Parkinson's disease.     

Multifactorial sleep disturbance in Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder, ranking only behind Alzheimer's disease and affecting 2% of the population over the age of 65. Pathophysiologically, PD is characterized by selective degeneration of the dopaminergic neurons of the substantia nigra pars compacta (SNpc) and striatal dopamine depletion. Patients may also exhibit mild-to-severe degeneration of other central and peripheral nervous tissues. The most dramatic symptoms of the disease are profound dopamine-responsive motor disturbances, including bradykinesia, akinesia, rigidity, resting tremor, and postural instability. PD patients commonly present with debilitating non-motor symptoms, including cognitive impairment, autonomic nervous system dysfunction, and sleep disturbance. Of these, sleep disturbance is the most consistently reported, and likely represents a disorder integrative of PD-related motor impairment, autonomic nervous system dysfunction, iatrogenic insult, and central neurodegeneration. The pathophysiology of PD may also indirectly disrupt sleep by increasing susceptibility to sleep disorders, including sleep disordered breathing, periodic limb movements, and REM behavior disorder. In this review, we will discuss these systems representing a multifactorial etiology in PD sleep disturbance.     

Program: Twenty Fourth Annual Symposium on Etiology,Pathogenesis, and Treatment of Parkinson's Disease and Other Movement Disorders

The symposium will consist of current issues in genetic and environmental contributions to Parkinson's disease and other movement disorders with peer‐reviewed platform and poster presentations designed to communicate recent research advances, including new pharmacological and non‐pharmacological treatment options, in the field of Parkinson's disease, Huntington's disease, ataxia, dystonia, myoclonus, Tourette's syndrome, tremor and other movement disorders thereby enhancing patient care.