Association of Parkinson's disease with infections and occupational exposure to possible vectors

Hospital-treated infectious diseases, infection burden and risk of Parkinson disease: An observational and Mendelian randomization study

BACKGROUND

Experimental and cross-sectional evidence has suggested a potential role of infection in the ethology of Parkinson's disease (PD). We aim to examine the longitudinal association of infections with the incidence of PD and to explore whether the increased risk is limited to specific infection type rather than infection burden.

METHODS

Based on the UK Biobank, hospital-treated infectious diseases and incident PD were ascertained through record linkage to national hospital inpatient registers. Infection burden was defined as the sum of the number of infection episodes over time and the number of co-occurring infections. The polygenic risk score (PRS) for PD was calculated. The genome-wide association studies (GWAS) used in two-sample Mendelian Randomization (MR) were obtained from observational cohort participants of mostly European ancestry.

RESULTS

Hospital-treated infectious diseases were associated with an increased risk of PD (adjusted HR [aHR] 1.35 [95 % CI 1.20-1.52]). This relationship persisted when analyzing new PD cases occurring more than 10 years post-infection (aHR 1.22 [95 % CI 1.04-1.43]). The greatest PD risk was observed in neurological/eye infection (aHR 1.72 [95 % CI 1.32-2.34]), with lower respiratory tract infection (aHR 1.43 [95 % CI 1.02-1.99]) ranked the second. A dose-response association was observed between infection burden and PD risk within each PD-PRS tertile (p-trend < 0.001). Multivariable MR showed that bacterial and viral infections increase the PD risk.

CONCLUSIONS

Both observational and genetic analysis suggested a causal association between infections and the risk of developing PD. A dose-response relationship between infection burden and incident PD was revealed.

SARS-CoV-2 Spike Protein 1 Causes Aggregation of α-Synuclein via Microglia-Induced Inflammation and Production of Mitochondrial ROS: Potential Therapeutic Applications of Metformin

Abnormal aggregation of α-synuclein is the hallmark of neurodegenerative diseases, classified as α-synucleinopathies, primarily occurring sporadically. Their onset is associated with an interaction between genetic susceptibility and environmental factors such as neurotoxins, oxidative stress, inflammation, and viral infections. Recently, evidence has suggested an association between neurological complications in long COVID (sometimes referred to as 'post-acute sequelae of COVID-19') and α-synucleinopathies, but its underlying mechanisms are not completely understood. In this study, we first showed that SARS-CoV-2 Spike protein 1 (S1) induces α-synuclein aggregation associated with activation of microglial cells in the rodent model. In vitro, we demonstrated that S1 increases aggregation of α-synuclein in BE(2)M-17 dopaminergic neurons via BV-2 microglia-mediated inflammatory responses. We also identified that S1 directly affects aggregation of α-synuclein in dopaminergic neurons through increasing mitochondrial ROS, though only under conditions of sufficient α-Syn accumulation. In addition, we observed a synergistic effect between S1 and the neurotoxin MPP+ S1 treatment. Combined with a low dose of MPP+, it boosted α-synuclein aggregation and mitochondrial ROS production compared to S1 or the MPP+ treatment group. Furthermore, we evaluated the therapeutic effects of metformin. The treatment of metformin suppressed the S1-induced inflammatory response and α-synucleinopathy. Our findings demonstrate that S1 promotes α-synucleinopathy via both microglia-mediated inflammation and mitochondrial ROS, and they provide pathological insights, as well as a foundation for the clinical management of α-synucleinopathies and the onset of neurological symptoms after the COVID-19 outbreak.

SARS-CoV-2 N-protein induces the formation of composite α-synuclein/N-protein fibrils that transform into a strain of α-synuclein fibrils

The presence of deposits of alpha-synuclein (αS) fibrils in the cells of the brain is a hallmark of several α-synucleinopathies, including Parkinson's disease. As most disease cases are not familial, it is likely that external factors play a role in the disease onset. One of the external factors that may influence the disease onset is viral infection. It has recently been shown in in vitro assays that in the presence of SARS-Cov-2 N-protein, αS fibril formation is faster and proceeds in an unusual two-step aggregation process. Here, we show that faster fibril formation is not due to the SARS-CoV-2 N-protein-catalysed formation of an aggregation-prone nucleus. Instead, aggregation starts with the formation of a population of mixed αS/N-protein fibrils with low affinity for αS. Mixed amyloid fibrils, composed of two different proteins, have not been observed before. After the depletion of N-protein, fibril formation comes to a halt, until a slow transformation into fibrils with characteristics of a pure αS fibril strain occurs. This transformation into a strain of αS fibrils subsequently results in a second phase of fibril growth until a new equilibrium is reached. We hypothesize that this fibril strain transformation may be of relevance in the cell-to-cell spread of the αS pathology and disease onset.

Relevance of tissue-resident memory CD8 T cells in the onset of Parkinson's disease and examination of its possible etiologies: infectious or autoimmune?

Tissue-resident memory CD8 T cells are responsible for local immune surveillance in different tissues, including the brain. They constitute the first line of defense against pathogens and cancer cells and play a role in autoimmunity. A recently published study demonstrated that CD8 T cells with markers of residency containing distinct granzymes and interferon-γ infiltrate the parenchyma of the substantia nigra and contact dopaminergic neurons in an early premotor stage of Parkinson's disease. This infiltration precedes α-synuclein aggregation and neuronal loss in the substantia nigra, suggesting a relevant role for CD8 T cells in the onset of the disease. To date, the nature of the antigen that initiates the adaptive immune response remains unknown. This review will discuss the role of tissue-resident memory CD8 T cells in brain immune homeostasis and in the onset of Parkinson's disease and other neurological diseases. We also discuss how aging and genetic factors can affect the CD8 T cell immune response and how animal models can be misleading when studying human-related immune response. Finally, we speculate about a possible infectious or autoimmune origin of Parkinson's disease.

Infectious Microorganisms Seen as Etiologic Agents in Parkinson’s Disease

Infections represent a possible risk factor for parkinsonism and Parkinson’s disease (PD) based on information from epidemiology and fundamental science. The risk is unclear for the majority of agents. Moreover, the latency between infection and PD seems to be very varied and often lengthy. In this review, the evidence supporting the potential involvement of infectious microorganisms in the development of Parkinson’s disease is examined. Consequently, it is crucial to determine the cause and give additional treatment accordingly. Infection is an intriguing suggestion regarding the cause of Parkinson’s disease. These findings demonstrate that persistent infection with viral and bacterial microorganisms might be a cause of Parkinson’s disease. As an initiating factor, infection may generate a spectrum of gut microbiota dysbiosis, engagement of glial tissues, neuroinflammation, and alpha-synuclein accumulation, all of which may trigger and worsen the onset in Parkinson’s disease also contribute to its progression. Still uncertain is the primary etiology of PD with infection. The possible pathophysiology of PD infection remains a matter of debate. Furthermore, additional study is required to determine if PD patients develop the disease due to infectious microorganisms or solely since they are more sensitive to infectious causes.

Unaltered T cell responses to common antigens in individuals with Parkinson's disease

BACKGROUND AND OBJECTIVES

Parkinson's disease (PD) is associated with a heightened inflammatory state, including activated T cells. However, it is unclear whether these PD T cell responses are antigen specific or more indicative of generalized hyperresponsiveness. Our objective was to measure and compare antigen-specific T cell responses directed towards antigens derived from commonly encountered human pathogens/vaccines in patients with PD and age-matched healthy controls (HC).

METHODS

Peripheral blood mononuclear cells (PBMCs) from 20 PD patients and 19 age-matched HCs were screened. Antigen specific T cell responses were measured by flow cytometry using a combination of the activation induced marker (AIM) assay and intracellular cytokine staining.

RESULTS

Here we show that both PD patients and HCs show similar T cell activation levels to several antigens derived from commonly encountered human pathogens/vaccines in the general population. Similarly, we also observed no difference between HC and PD in the levels of CD4 and CD8 T cell derived cytokines produced in response to any of the common antigens tested. These antigens encompassed both viral (coronavirus, rhinovirus, respiratory syncytial virus, influenza, cytomegalovirus) and bacterial (pertussis, tetanus) targets.

CONCLUSIONS

These results suggest the T cell dysfunction observed in PD may not extend itself to abnormal responses to commonly encountered or vaccine-target antigens. Our study supports the notion that the targets of inflammatory T cell responses in PD may be more directed towards autoantigens like α-synuclein (α-syn) rather than common foreign antigens.

Machine learning analysis of the UK Biobank reveals IGF-1 and inflammatory biomarkers predict Parkinson's disease risk

INTRODUCTION

Parkinson's disease (PD) is the most common movement disorder, and its prevalence is increasing rapidly worldwide with an ageing population. The UK Biobank is the world's largest and most comprehensive longitudinal study of ageing community volunteers. The cause of the common form of PD is multifactorial, but the degree of causal heterogeneity among patients or the relative importance of one risk factor over another is unclear. This is a major impediment to the discovery of disease-modifying therapies.

METHODS

We used an integrated machine learning algorithm (IDEARS) to explore the relative effects of 1,753 measured non-genetic variables in 334,062 eligible UK Biobank participants, including 2,719 who had developed PD since their recruitment into the study.

RESULTS

Male gender was the highest-ranked risk factor, followed by elevated serum insulin-like growth factor 1 (IGF-1), lymphocyte count, and neutrophil/lymphocyte ratio. A group of factors aligned with the symptoms of frailty also ranked highly. IGF-1 and neutrophil/lymphocyte ratio were also elevated in both sexes before PD diagnosis and at the point of diagnosis.

DISCUSSION

The use of machine learning with the UK Biobank provides the best opportunity to explore the multidimensional nature of PD. Our results suggest that novel risk biomarkers, including elevated IGF-1 and NLR, may play a role in, or are indicative of PD pathomechanisms. In particular, our results are consistent with PD being a central manifestation of a systemic inflammatory disease. These biomarkers may be used clinically to predict future PD risk, improve early diagnosis and provide new therapeutic avenues.

Viruses, parkinsonism and Parkinson's disease: the past, present and future

Parkinsonism secondary to viral infections is not an uncommon occurrence and has been brought under the spotlight with the spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. A variety of viruses have been described with a potential of inducing or contributing to the occurrence of parkinsonism and Parkinson's disease (PD), although the relationship between the two remains a matter of debate originating with the description of encephalitis lethargica in the aftermath of the Spanish flu in 1918. While some viral infections have been linked to an increased risk for the development of PD, others seem to have a causal link with the occurrence of parkinsonism. Here, we review the currently available evidence on viral-induced parkinsonism with a focus on potential pathophysiological mechanisms and clinical features. We also review the evidence on viral infections as a risk factor for developing PD and the link between SARS-CoV-2 and parkinsonism, which might have important implications for future research and treatments.

Hydrogen Sulfide Produced by Gut Bacteria May Induce Parkinson's Disease

Several bacterial species can generate hydrogen sulfide (H2S). Study evidence favors the view that the microbiome of the colon harbors increased amounts of H2S producing bacteria in Parkinson's disease. Additionally, H2S can easily penetrate cell membranes and enter the cell interior. In the cells, excessive amounts of H2S can potentially release cytochrome c protein from the mitochondria, increase the iron content of the cytosolic iron pool, and increase the amount of reactive oxygen species. These events can lead to the formation of alpha-synuclein oligomers and fibrils in cells containing the alpha-synuclein protein. In addition, bacterially produced H2S can interfere with the body urate metabolism and affect the blood erythrocytes and lymphocytes. Gut bacteria responsible for increased H2S production, especially the mucus-associated species of the bacterial genera belonging to the Desulfovibrionaceae and Enterobacteriaceae families, are likely play a role in the pathogenesis of Parkinson's disease. Special attention should be devoted to changes not only in the colonic but also in the duodenal microbiome composition with regard to the pathogenesis of Parkinson's disease. Influenza infections may increase the risk of Parkinson's disease by causing the overgrowth of H2S-producing bacteria both in the colon and duodenum.

An Integrative Network Approach to Identify Common Genes for the Therapeutics in Tuberculosis and Its Overlapping Non-Communicable Diseases

Tuberculosis (TB) is the leading cause of death from a single infectious agent. The estimated total global TB deaths in 2019 were 1.4 million. The decline in TB incidence rate is very slow, while the burden of noncommunicable diseases (NCDs) is exponentially increasing in low- and middle-income countries, where the prevention and treatment of TB disease remains a great burden, and there is enough empirical evidence (scientific evidence) to justify a greater research emphasis on the syndemic interaction between TB and NCDs. The current study was proposed to build a disease-gene network based on overlapping TB with NCDs (overlapping means genes involved in TB and other/s NCDs), such as Parkinson’s disease, cardiovascular disease, diabetes mellitus, rheumatoid arthritis, and lung cancer. We compared the TB-associated genes with genes of its overlapping NCDs to determine the gene-disease relationship. Next, we constructed the gene interaction network of disease-genes by integrating curated and experimentally validated interactions in humans and find the 13 highly clustered modules in the network, which contains a total of 86 hub genes that are commonly associated with TB and its overlapping NCDs, which are largely involved in the Inflammatory response, cellular response to cytokine stimulus, response to cytokine, cytokine-mediated signaling pathway, defense response, response to stress and immune system process. Moreover, the identified hub genes and their respective drugs were exploited to build a bipartite network that assists in deciphering the drug-target interaction, highlighting the influential roles of these drugs on apparently unrelated targets and pathways. Targeting these hub proteins by using drugs combination or drug repurposing approaches will improve the clinical conditions in comorbidity, enhance the potency of a few drugs, and give a synergistic effect with better outcomes. Thus, understanding the Mycobacterium tuberculosis (Mtb) infection and associated NCDs is a high priority to contain its short and long-term effects on human health. Our network-based analysis opens a new horizon for more personalized treatment, drug-repurposing opportunities, investigates new targets, multidrug treatment, and can uncover several side effects of unrelated drugs for TB and its overlapping NCDs.

Interactions between SARS-CoV-2 N-Protein and α-Synuclein Accelerate Amyloid Formation

First cases that point at a correlation between SARS-CoV-2 infections and the development of Parkinson’s disease (PD) have been reported. Currently, it is unclear if there is also a direct causal link between these diseases. To obtain first insights into a possible molecular relation between viral infections and the aggregation of α-synuclein protein into amyloid fibrils characteristic for PD, we investigated the effect of the presence of SARS-CoV-2 proteins on α-synuclein aggregation. We show, in test tube experiments, that SARS-CoV-2 spike protein (S-protein) has no effect on α-synuclein aggregation, while SARS-CoV-2 nucleocapsid protein (N-protein) considerably speeds up the aggregation process. We observe the formation of multiprotein complexes and eventually amyloid fibrils. Microinjection of N-protein in SH-SY5Y cells disturbed the α-synuclein proteostasis and increased cell death. Our results point toward direct interactions between the N-protein of SARS-CoV-2 and α-synuclein as molecular basis for the observed correlation between SARS-CoV-2 infections and Parkinsonism.

Environmental factors in Parkinson's disease: New insights into the molecular mechanisms

Parkinson's disease is a chronic, progressive neurodegenerative disorder affecting 2-3% of the population ≥65 years. It has long been characterized by motor impairment, autonomic dysfunction, and psychological and cognitive changes. The pathological hallmarks are intracellular inclusions containing α-synuclein aggregates and the loss of dopaminergic neurons in the substantia nigra. Parkinson's disease is thought to be caused by a combination of various pathogenic factors, including genetic factors, environmental factors, and lifestyles. Although much research has focused on the genetic causes of PD, environmental risk factors also play a crucial role in the development of the disease. Here, we summarize the environmental risk factors that may increase the occurrence of PD, as well as the underlying molecular mechanisms.

Long-term Risk of Parkinson Disease Following Influenza and Other Infections

Importance

Influenza has been associated with the risk of developing Parkinson disease, but the association is controversial.

Objective

To examine whether prior influenza and other infections are associated with Parkinson disease more than 10 years after infection.

Design, Setting, and Participants

This case-control study used data from 1977 to 2016 from the Danish National Patient Registry. All individuals with Parkinson disease, excluding those with drug-induced parkinsonism, were included and matched to 5 population controls on sex, age, and date of Parkinson diagnosis. Data were analyzed from December 2019 to September 2021.

Exposures

Infections were ascertained between 1977 and 2016 and categorized by time from infection to Parkinson disease diagnosis. To increase specificity of influenza diagnoses, influenza exposure was restricted to months of peak influenza activity.

Main Outcomes and Measures

Parkinson disease diagnoses were identified between January 1, 2000, and December 31, 2016. Crude and adjusted odds ratios (ORs) and 95% CIs were calculated by conditional logistic regression overall and stratified by time between infection and Parkinson disease (5 years or less, more than 5 to 10 years, more than 10 years).

Results

Of 61 626 included individuals, 23 826 (38.7%) were female, and 53 202 (86.3%) were older than 60 years. A total of 10 271 individuals with Parkinson disease and 51 355 controls were identified. Influenza diagnosed at any time during a calendar year was associated with Parkinson disease more than 10 years later (OR, 1.73; 95% CI, 1.11-2.71). When influenza exposure was restricted to months of highest influenza activity, an elevated OR with a wider confidence interval was found (OR, 1.52; 95% CI, 0.80-2.89). There was no evidence of an association with any type of infection more than 10 years prior to Parkinson disease (OR, 1.04; 95% CI, 0.98-1.10). Several specific infections yielded increased odds of Parkinson disease within 5 years of infection, but results were null when exposure occurred more than 10 years prior.

Conclusions and Relevance

In this case-control study, influenza was associated with diagnoses of Parkinson disease more than 10 years after infection. These observational data suggest a link between influenza and Parkinson disease but do not demonstrate causality. While other infections were associated with Parkinson disease diagnoses soon after infection, null associations after more than 10 years suggest these shorter-term associations are not causal.

The Role of Pathogens and Anti-Infective Agents in Parkinson's Disease, from Etiology to Therapeutic Implications

Parkinson's disease is a debilitating neurodegenerative disorder whose etiology is still unclear, hampering the development of effective treatments. There is an urgent need to identify the etiology and provide further effective treatments. Recently, accumulating evidence has indicated that infection may play a role in the etiology of Parkinson's disease. The infective pathogens may act as a trigger for Parkinson's disease, the most common of which are hepatitis C virus, influenza virus, and Helicobacter pylori. In addition, gut microbiota is increasingly recognized to influence brain function through the gut-brain axis, showing an important role in the pathogenesis of Parkinson's disease. Furthermore, a series of anti-infective agents exhibit surprising neuroprotective effects via various mechanisms, such as interfering with α-synuclein aggregation, inhibiting neuroinflammation, attenuating oxidative stress, and preventing from cell death, independent of their antimicrobial effects. The pleiotropic agents affect important events in the pathogenesis of Parkinson's disease. Moreover, most of them are less toxic, clinically safe and have good blood-brain penetrability, making them hopeful candidates for the treatment of Parkinson's disease. However, the use of antibiotics and subsequent gut dysbiosis may also play a role in Parkinson's disease, making the long-term effects of anti-infective drugs worthy of further consideration and exploration. This review summarizes the current evidence for the association between infective pathogens and Parkinson's disease and subsequently explores the application prospects of anti-infective drugs in Parkinson's disease treatment, providing novel insights into the pathogenesis and treatment of Parkinson's disease.

A Possible Role for HSV-1-Specific Humoral Response and PILRA rs1859788 Polymorphism in the Pathogenesis of Parkinson's Disease

The etiology of Parkinson's disease (PD), a progressive nervous system disorder that affects movement, is still unknown; both genetic and environmental factor are believed to be involved in onset of the disease and its development. Herpes simplex virus type 1 (HSV-1), in particular, is suspected to have a role in PD. Paired Immunoglobulin-like type 2 receptor alpha (PILRA) is an inhibitory receptor that down-regulates inflammation and is expressed on innate immune cells. The PILRA rs1859788 polymorphism is protective against Alzheimer's disease, even in relation with HSV-1 antibody titers, but no data are available in PD. We analyzed HSV-1 antibody titers and PILRA rs1859788 in PD (n = 51) and age-and sex-matched healthy controls (HC; n = 73). Results showed that HSV-1, but not cytomegalovirus (CMV) or human herpes virus type 6 (HHV-6) antibody titers were significantly higher in PD compared to HC (p = 0.045). The rs1859788 polymorphism was not differentially distributed between PD and HC, but the minor allele A was more frequently carried by PD (68%) compared to HC (50%) (p = 0.06). Notably, the rs1859788 minor allele A was statically more frequent in male PD (65%) compared to male HC (37%) (p = 0.036). Finally, no relation was found between HSV-1 antibody titers and PILRA genotype. Results herein suggest an involvement of HSV-1 in PD and indicate a possible interaction between PILRA gene polymorphisms and this neuropathology.

AMPK activates Parkin independent autophagy and improves post sepsis immune defense against secondary bacterial lung infections

Metabolic and bioenergetic plasticity of immune cells is essential for optimal responses to bacterial infections. AMPK and Parkin ubiquitin ligase are known to regulate mitochondrial quality control mitophagy that prevents unwanted inflammatory responses. However, it is not known if this evolutionarily conserved mechanism has been coopted by the host immune defense to eradicate bacterial pathogens and influence post-sepsis immunosuppression. Parkin, AMPK levels, and the effects of AMPK activators were investigated in human leukocytes from sepsis survivors as well as wild type and Park2^−/− murine macrophages. In vivo, the impact of AMPK and Parkin was determined in mice subjected to polymicrobial intra-abdominal sepsis and secondary lung bacterial infections. Mice were treated with metformin during established immunosuppression. We showed that bacteria and mitochondria share mechanisms of autophagic killing/clearance triggered by sentinel events that involve depolarization of mitochondria and recruitment of Parkin in macrophages. Parkin-deficient mice/macrophages fail to form phagolysosomes and kill bacteria. This impairment of host defense is seen in the context of sepsis-induced immunosuppression with decreased levels of Parkin. AMPK activators, including metformin, stimulate Parkin-independent autophagy and bacterial killing in leukocytes from post-shock patients and in lungs of sepsis-immunosuppressed mice. Our results support a dual role of Parkin and AMPK in the clearance of dysfunctional mitochondria and killing of pathogenic bacteria, and explain the immunosuppressive phenotype associated Parkin and AMPK deficiency. AMPK activation appeared to be a crucial therapeutic target for the macrophage immunosuppressive phenotype and to reduce severity of secondary bacterial lung infections and respiratory failure.

Back to the future: lessons from past viral infections and the link with Parkinson's disease

During the current coronavirus disease 2019 (COVID-19) pandemic, there has been noticeable increase in the reporting of neurological symptoms in patients. There is still uncertainty around the significance and long-term consequence of these symptoms. There are also many outstanding questions on whether the causative virus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV2) can directly infect the central nervous system (CNS). Given the long association between viral infections with neurodegenerative conditions such as Parkinson's disease (PD), it seems timely to review this literature again in the context of the COVID-19 pandemic and to glean some useful information from studies on similar viruses. In this commentary, we will consider the current knowledge on viral infections in the brain. In addition, we review the link between viral infection and neurodegeneration in PD, and review the recent literature on SARS infections, the potential link with PD and the potential areas of study in the future.

Mechanisms and therapeutic potential of interactions between human amyloids and viruses

The aggregation of specific proteins and their amyloid deposition in affected tissue in disease has been studied for decades assuming a sole pathogenic role of amyloids. It is now clear that amyloids can also encode important cellular functions, one of which involves the interaction potential of amyloids with microbial pathogens, including viruses. Human expressed amyloids have been shown to act both as innate restriction molecules against viruses as well as promoting agents for viral infectivity. The underlying molecular driving forces of such amyloid-virus interactions are not completely understood. Starting from the well-described molecular mechanisms underlying amyloid formation, we here summarize three non-mutually exclusive hypotheses that have been proposed to drive amyloid-virus interactions. Viruses can indirectly drive amyloid depositions by affecting upstream molecular pathways or induce amyloid formation by a direct interaction with the viral surface or specific viral proteins. Finally, we highlight the potential of therapeutic interventions using the sequence specificity of amyloid interactions to drive viral interference.

Herpesvirus Infections and Risk of Parkinson's Disease

INTRODUCTION

Herpesviruses might play a role in the pathogenesis of neurodegenerative disorders. We sought to examine a possible association between alpha herpesvirus infections and Parkinson's disease.

METHODS

We conducted a population-based case-control study of incident Parkinson's disease in 2009 Medicare beneficiaries age 66-90 years (89,790 cases, 118,095 randomly selected comparable controls). We classified beneficiaries with any diagnosis code for "herpes simplex" and/or "herpes zoster" in the previous 5 years as having had the respective alpha herpesviruses. In beneficiaries with Part D prescription coverage, we also identified those prescribed anti-herpetic medications. We calculated odds ratios (OR) and 95% CI between alpha herpesvirus diagnosis/treatment and Parkinson's disease with logistic regression, with adjustment for age, sex, race/ethnicity, smoking, and use of medical care.

RESULTS

Parkinson's disease risk was inversely associated with herpes simplex (OR 0.79, 95% CI 0.74-0.84), herpes zoster (OR 0.88, 95% CI 0.85-0.91), and anti-herpetic medications (OR 0.87, 95% CI 0.80-0.96).

CONCLUSION

Herpesvirus infection or treatment might reduce risk of Parkinson's disease, but future studies will be required to explore whether this inverse association is causal.

Risk of Parkinson's disease among patients with herpes zoster: a nationwide longitudinal study

OBJECTIVE

Several studies suggested a potential role of viral infection in the pathophysiology of Parkinson's disease (PD). However, the association between herpes zoster and PD was not investigated well till now.

METHODS

Using the Taiwan National Health Insurance Research Database, 13 083 patients aged ≥45 years with herpes zoster and 52 332 (1:4) age-/sex-matched controls were enrolled between 1998 and 2008 and followed to the end of 2011. Those who developed PD during the follow-up period were identified.

RESULTS

The Cox regression analysis with adjustment of demographic characteristics, health system utilization, and comorbidities demonstrated that patients with herpes zoster had an increased risk (hazard ratio [HR]: 1.80, 95% confidence interval [CI]: 1.43-2.28) of developing PD in later life compared to the control group. Sensitivity tests after excluding the first year (HR: 1.50, 95% CI: 1.16-1.93) and first 2-year (HR: 1.44, 95% CI: 1.10-1.88) observation periods showed consistent results.

CONCLUSIONS

Patients with herpes zoster were more likely to develop PD in later life compared to the controls. Additional studies are necessary for validating our results and to clarify the underlying pathophysiology between herpes zoster and PD.

Infections or Sepsis Preceding Clinically Diagnosed α-Synucleinopathies: A Case-Control Study

BACKGROUND

Several studies have proposed a role for infections to induce an inflammatory response triggering Parkinson's disease. This remains controversial and the influence of severe infections on other α-synucleinopathies (Dementia with Lewy Bodies, Parkinson's disease dementia, and Multiple System Atrophy) has not been adequately investigated.

OBJECTIVES

To assess the association between hospitalization-required infections or sepsis and risk of clinically diagnosed α-synucleinopathies.

METHODS

Using the medical records-linkage system (Rochester Epidemiology Project), we identified all α-synucleinopathy cases of in Olmsted County (1991-2010). Cases were matched by symptom-onset age and sex to controls. We reviewed complete medical records to detect hospital-required infections or sepsis preceding clinical-motor onset of α-synucleinopathies. We used conditional logistic regression to calculate the odds ratio of all α-synucleinopathies, adjusting for medications, coffee, and smoking.

RESULTS

There was no association between infection-related hospitalization (odds ratio: 1.05; 95% confidence interval: 0.78-1.40; P = 0.76) or sepsis (odds ratio: 0.86; 95% confidence interval: 0.40-1.85; P = 0.70) and all α-synucleinopathies in multivariable analyses. We did not identify any associations after stratifying for type of α-synucleinopathy, sex, and age at clinical-motor onset. We analyzed sepsis separately with similar results.

CONCLUSION

We did not observe any associations between infections leading to hospitalization or sepsis and development of any α-synucleinopathies. © 2020 International Parkinson and Movement Disorder Society.

Disruption of cellular proteostasis by H1N1 influenza A virus causes α-synuclein aggregation

Neurodegenerative diseases feature specific misfolded or misassembled proteins associated with neurotoxicity. The precise mechanisms by which protein aggregates first arise in the majority of sporadic cases have remained unclear. Likely, a first critical mass of misfolded proteins starts a vicious cycle of a prion-like expansion. We hypothesize that viruses, having evolved to hijack the host cellular machinery for catalyzing their replication, lead to profound disturbances of cellular proteostasis, resulting in such a critical mass of protein aggregates. Here, we investigated the effect of influenza virus (H1N1) strains on proteostasis of proteins associated with neurodegenerative diseases in Lund human mesencephalic dopaminergic cells in vitro and infection of Rag knockout mice in vivo. We demonstrate that acute H1N1 infection leads to the formation of α-synuclein and Disrupted-in-Schizophrenia 1 (DISC1) aggregates, but not of tau or TDP-43 aggregates, indicating a selective effect on proteostasis. Oseltamivir phosphate, an antiinfluenza drug, prevented H1N1-induced α-synuclein aggregation. As a cell pathobiological mechanism, we identified H1N1-induced blocking of autophagosome formation and inhibition of autophagic flux. In addition, α-synuclein aggregates appeared in infected cell populations connected to the olfactory bulbs following intranasal instillation of H1N1 in Rag knockout mice. We propose that H1N1 virus replication in neuronal cells can induce seeds of aggregated α-synuclein or DISC1 that may be able to initiate further detrimental downstream events and should thus be considered a risk factor in the pathogenesis of synucleinopathies or a subset of mental disorders. More generally, aberrant proteostasis induced by viruses may be an underappreciated factor in initiating protein misfolding.

Bacterial, viral, and fungal infection-related risk of Parkinson's disease: Meta-analysis of cohort and case-control studies

AIMS

Recent studies showed that patients with various bacterial, viral, and fungal infections might be at increased risk of Parkinson's disease (PD). However, the risk of PD in patients with each specific infection varied. This meta-analysis estimated the association between various infections and PD risk.

METHODS

Literature published from January 1965 to October 2019 in PubMed and EMBASE databases was searched. Data were extracted and pooled using random/fixed effects model. Sensitivity analysis and meta-regression were also performed to analyze the source of heterogeneity. Publication bias was estimated by the trim and fill.

RESULTS

Twenty-three out of 6,609 studies were included. Helicobacter pylori (HP; pooled OR = 1.653, 1.426-1.915, p < .001), hepatitis C virus (HCV; pooled OR = 1.195, 1.012-1.410, p = .035), Malassezia (pooled OR = 1.694, 1.367-2.100, p < .001), and pneumoniae (pooled OR = 1.595, 1.020-2.493, p = .041) infection were associated with increased PD risk. Influenza virus, herpes virus, hepatitis B virus, scarlet fever, mumps virus, chicken pox, pertussis, German measles, and measles were not associated with PD risk. After antiviral treatment against HCV reduced the risk of PD in patients with HCV infection (OR = 0.672, 0.571-0.791, p < .001). Significant heterogeneity exists among the included studies.

CONCLUSION

Patients with infection of HP, HCV, Malassezia, pneumoniae might be an increased risk of PD. Antiviral treatment of HCV could reduce the risk of PD.

Viral mimetic priming enhances α-synuclein-induced degeneration: Implications for Parkinson's disease

Evidence is accumulating to suggest that viral infections and consequent viral-mediated neuroinflammation may contribute to the etiology of idiopathic Parkinson's disease. Moreover, viruses have been shown to influence α-synuclein oligomerization as well as the autophagic clearance of abnormal intra-cellular proteins aggregations, both of which are key neuropathological events in Parkinson's disease pathogenesis. To further investigate the interaction between viral-mediated neuroinflammation and α-synuclein aggregation in the context of Parkinson's disease, this study sought to determine the impact of viral neuroinflammatory priming on α-synuclein aggregate-induced neuroinflammation and neurotoxicity in the rat nigrostriatal pathway. To do so, male Sprague-Dawley rats were intra-nigrally injected with a synthetic mimetic of viral dsRNA (poly I:C) followed two weeks later by a peptidomimetic small molecule which accelerates α-synuclein fibril formation (FN075). The impact of the viral priming on α-synuclein aggregation-induced neuroinflammation, neurodegeneration and motor dysfunction was assessed. We found that prior administration of the viral mimetic poly I:C significantly exacerbated or precipitated the α-synuclein aggregate induced neuropathological and behavioral effects. Specifically, sequential exposure to the two challenges caused a significant increase in nigral microgliosis (p < 0.001) and astrocytosis (p < 0.01); precipitated a significant degeneration of the nigrostriatal cell bodies (p < 0.05); and precipitated a significant impairment in forelimb kinesis (p < 0.01) and sensorimotor integration (p < 0.01). The enhanced sensitivity of the nigrostriatal neurons to pathological α-synuclein aggregation after viral neuroinflammatory priming further suggests that viral infections may contribute to the etiology and pathogenesis of Parkinson's disease.

Infectious Etiologies of Parkinsonism: Pathomechanisms and Clinical Implications

Extensive research in recent decades has expanded our insights into the pathogenesis of Parkinson's disease (PD), though the underlying cause remains incompletely understood. Neuroinflammation have become a point of interest in the interconnecting areas of neurodegeneration and infectious diseases. The hypothesis concerning an infectious origin in PD stems from the observation of Parkinson-like symptoms in individuals infected with the influenza virus who then developed encephalitis lethargica. The implications of infectious pathogens have later been studied in neuronal pathways leading to the development of Parkinsonism and PD, through both a direct association and through synergistic effects of infectious pathogens in inducing neuroinflammation. This review explores the relationship between important infectious pathogens and Parkinsonism, including symptoms of Parkinsonism following infectious etiologies, infectious contributions to neuroinflammation and neurodegenerative processes associated with Parkinsonism, and the epidemiologic correlations between infectious pathogens and idiopathic PD.

Th17 cells: a promising therapeutic target for Parkinson's disease?

INTRODUCTION

Parkinson's disease (PD) is the most common neurodegenerative movement disorder caused by the progressive loss of neurons in the midbrain and other brain regions. Only symptomatic treatment is currently available. Mounting evidence suggests that T cells are a key contributor to PD pathogenesis and neurodegeneration by a mechanism that requires further elucidation. Areas covered: We discuss the evidence of imbalanced activation of effector T cell populations in PD and summarize the data of Th17 involvement and Th17-regulated mechanisms in PD pathology. Moreover, possible Th17-related molecular targets as possible neuroprotective immunomodulatory therapeutic targets for PD are examined. Expert Opinion: Existing data show that Th17 cells, their effector molecules, and signaling pathways are potentially effective therapeutic targets for neuroprotective immunomodulation in PD treatment. However, specificity of action within Th17-mediated signaling pathways for PD requires careful consideration.

Inflammation, Infectious Triggers, and Parkinson's Disease

Parkinson's disease is a neurodegenerative disorder characterized by progressive loss of dopaminergic neurons of the substantia nigra pars compacta with a reduction of dopamine concentration in the striatum. The complex interaction between genetic and environmental factors seems to play a role in determining susceptibility to PD and may explain the heterogeneity observed in clinical presentations. The exact etiology is not yet clear, but different possible causes have been identified. Inflammation has been increasingly studied as part of the pathophysiology of neurodegenerative diseases, corroborating the hypothesis that the immune system may be the nexus between environmental and genetic factors, and the abnormal immune function can lead to disease. In this review we report the different aspects of inflammation and immune system in Parkinson's disease, with particular interest in the possible role played by immune dysfunctions in PD, with focus on autoimmunity and processes involving infectious agents as a trigger and alpha-synuclein protein (α-syn).

Immune system responses in Parkinson's disease: Early and dynamic

The neuropathological hallmarks of Parkinson's disease (PD) are the degeneration and death of dopamine-producing neurons in the ventral midbrain, the widespread intraneuronal aggregation of alpha-synuclein (α) in Lewy bodies and neurites, neuroinflammation, and gliosis. Signs of microglia activation in the PD brain postmortem as well as during disease development revealed by neuroimaging, implicate immune responses in the pathophysiology of the disease. Intensive research during the last two decades has advanced our understanding of the role of these responses in the disease process, yet many questions remain unanswered. A transformative finding in the field has been the confirmation that in vivo microglia are able to respond directly to pathological a-syn aggregates but also to neuronal dysfunction due to intraneuronal a-syn toxicity well in advance of neuronal death. In addition, clinical research and disease models have revealed the involvement of both the innate and adaptive immune systems. Indeed, the data suggest that PD leads not only to a microglia response, but also to a cellular and humoral peripheral immune response. Together, these findings compel us to consider a more holistic view of the immunological processes associated with the disease. Central and peripheral immune responses aimed at maintaining neuronal health will ultimately have consequences on neuronal survival. We will review here the most significant findings that have contributed to the current understanding of the immune response in PD, which is proposed to occur early, involve peripheral and brain immune cells, evolve as neuronal dysfunction progresses, and is likely to influence disease progression.

Impact of infection on risk of Parkinson's disease: a quantitative assessment of case-control and cohort studies

Identifying modifiable risk factors for Parkinson's disease (PD) to help prevent this disease has attracted increasing interest in recent years for the limited effective drugs at present. Despite many studies indicated that infection acts as a risk factor for PD, there is no quantitative assessment of the impact of viral and bacterial infections on the risk of developing PD. The present study performed a meta-analysis on the basis of 38 datasets from 13 studies covering 287,773 PD cases and 7,102,901 controls to ascertain the association between PD and infection and the differences in the strength of the viral and bacterial infections. The overall meta-analytic results indicated that individuals with infection had a 20% increased risk of PD compared with controls (OR 1.20, 95%CI 1.07-1.32). The subgroup analysis according to the type of infection found that bacterial infection had a significant impact on increased risk of PD (OR 1.40, 95%CI 1.32-1.48). The present analysis indicated that infection could increase the risk of developing PD, and physician should be aware of the risk of developing PD in subjects with infection.

Immunology of West Nile Virus Infection and the Role of Alpha-Synuclein as a Viral Restriction Factor

West Nile virus (WNV) is a single-stranded RNA flavivirus and is a major cause of viral encephalitis worldwide. Experimental models of WNV infection in mice are commonly used to define acute neuroinflammatory responses in the brain. Alpha-synuclein (Asyn) is a protein of primarily neuronal origin and is a major cause of Parkinson's disease (PD), a disorder characterized by loss of dopaminergic neurons. Both WNV and PD pathologies are largely mediated by inflammation of the central nervous system (neuroinflammation) and have overlapping inflammatory pathways. In this review, we highlight the roles of the immune system in both diseases while comparing and contrasting both protective and pathogenic roles of immune cells and their effector proteins. Additionally, we review the current literature showing that Asyn is an important mediator of the immune response with diverging roles in PD (pathogenic) and WNV disease (neuroprotective).

No effects without causes: the Iron Dysregulation and Dormant Microbes hypothesis for chronic, inflammatory diseases

Since the successful conquest of many acute, communicable (infectious) diseases through the use of vaccines and antibiotics, the currently most prevalent diseases are chronic and progressive in nature, and are all accompanied by inflammation. These diseases include neurodegenerative (e.g. Alzheimer's, Parkinson's), vascular (e.g. atherosclerosis, pre-eclampsia, type 2 diabetes) and autoimmune (e.g. rheumatoid arthritis and multiple sclerosis) diseases that may appear to have little in common. In fact they all share significant features, in particular chronic inflammation and its attendant inflammatory cytokines. Such effects do not happen without underlying and initially 'external' causes, and it is of interest to seek these causes. Taking a systems approach, we argue that these causes include (i) stress-induced iron dysregulation, and (ii) its ability to awaken dormant, non-replicating microbes with which the host has become infected. Other external causes may be dietary. Such microbes are capable of shedding small, but functionally significant amounts of highly inflammagenic molecules such as lipopolysaccharide and lipoteichoic acid. Sequelae include significant coagulopathies, not least the recently discovered amyloidogenic clotting of blood, leading to cell death and the release of further inflammagens. The extensive evidence discussed here implies, as was found with ulcers, that almost all chronic, infectious diseases do in fact harbour a microbial component. What differs is simply the microbes and the anatomical location from and at which they exert damage. This analysis offers novel avenues for diagnosis and treatment.

A role for viral infections in Parkinson's etiology?

Despite over 200 years since its first description by James Parkinson, the cause(s) of most cases of Parkinson's disease (PD) are yet to be elucidated. The disparity between the current understanding of PD symptomology and pathology has led to numerous symptomatic therapies, but no strategy for prevention or disease cure. An association between certain viral infections and neurodegenerative diseases has been recognized, but largely ignored or dismissed as controversial, for decades. Recent epidemiological studies have renewed scientific interest in investigating microbial interactions with the central nervous system (CNS). This review examines past and current clinical findings and overviews the potential molecular implications of viruses in PD pathology.

How does parkinson's disease begin? Perspectives on neuroanatomical pathways, prions, and histology

Parkinson's disease (PD) is a multisystem disorder with involvement of the peripheral nervous system. Misfolding and aggregation of α-synuclein is central to the pathogenesis of PD, and it has been postulated that the disease may originate in olfactory and gastrointestinal nerve terminals. The prion-like behavior of α-synuclein has been convincingly demonstrated in vitro and in animal models of PD. Lewy-type pathology have been detected in peripheral organs many years prior to PD diagnosis, and 2 independent studies have now suggested that truncal vagotomy may be protective against the disorder. Other lines of evidence are difficult to reconcile with a peripheral onset of PD, most importantly the relative scarcity of post mortem cases with isolated gastrointestinal α-synuclein pathology without concomitant CNS pathology. This Scientific Perspectives article revisits some important topics with implications for the dual-hit hypothesis. An account of the neuroanatomical pathways necessary for stereotypical α-synuclein spreading is presented. Parallels to the existing knowledge on true prion disorders, including Creutzfeld-Jakob disease, are examined. Finally, the vagotomy studies and the somewhat inconsistent findings in the growing literature on peripheral α-synuclein pathology are discussed. It is concluded that the dual-hit hypothesis remains a potential explanation for PD pathogenesis, but several issues need to be resolved before more firm conclusions can be drawn. © 2017 International Parkinson and Movement Disorder Society.

Autophagy regulates MAVS signaling activation in a phosphorylation-dependent manner in microglia

Mitochondrial antiviral signaling (MAVS) protein has an important role in antiviral immunity and autoimmunity. However, the pathophysiological role of this signaling pathway, especially in the brain, remains elusive. Here we demonstrated that MAVS signaling existed and mediated poly(I:C)-induced inflammation in the brain. Along with the MAVS signaling activation, there was an induction of autophagic activation. Autophagy negatively regulated the activity of MAVS through direct binding of LC3 to the LIR motif Y(9)xxI(12) of MAVS. We also found that c-Abl kinase phosphorylated MAVS and regulated its interaction with LC3. Interestingly, tyrosine phosphorylation of MAVS was required for downstream signaling activation. Importantly, in vivo data showed that the deficiency of MAVS or c-Abl prevented MPTP-induced microglial activation and dopaminergic neuron loss. Together, our findings reveal the molecular mechanisms underlying the regulation of MAVS-dependent microglial activation in the nervous system, thus providing a potential target for the treatment of microglia-driven inflammatory brain diseases.

Alpha-Synuclein, a Novel Viral Restriction Factor Hiding in Plain Sight

Alpha-synuclein (α-syn) is a highly conserved protein encoded by the SNCA gene and is expressed uniquely in neurons of both the central and peripheral nervous systems (CNS and PNS). α-Syn is known to cause sporadic and familial forms of Parkinson's disease (PD). However, the role for neuronal expression of α-syn in the first place remains unknown. We review and discuss recently published work that suggests a novel role for α-syn expression in neurons as a restriction factor that inhibits virus transmission from the PNS to the CNS. The potential new role for α-syn expression as a virus inhibitor may provide new approaches to understand the pathogenesis of PD and provide novel approaches to prevent and treat this common neurodegenerative disease.

Exposure to bacterial endotoxin generates a distinct strain of α-synuclein fibril

A single amyloidogenic protein is implicated in multiple neurological diseases and capable of generating a number of aggregate "strains" with distinct structures. Among the amyloidogenic proteins, α-synuclein generates multiple patterns of proteinopathies in a group of diseases, such as Parkinson disease (PD), dementia with Lewy bodies (DLB), and multiple system atrophy (MSA). However, the link between specific conformations and distinct pathologies, the key concept of the strain hypothesis, remains elusive. Here we show that in the presence of bacterial endotoxin, lipopolysaccharide (LPS), α-synuclein generated a self-renewable, structurally distinct fibril strain that consistently induced specific patterns of synucleinopathies in mice. These results suggest that amyloid fibrils with self-renewable structures cause distinct types of proteinopathies despite the identical primary structure and that exposure to exogenous pathogens may contribute to the diversity of synucleinopathies.

Caspase-1 causes truncation and aggregation of the Parkinson's disease-associated protein α-synuclein

The aggregation of α-synuclein (aSyn) leading to the formation of Lewy bodies is the defining pathological hallmark of Parkinson's disease (PD). Rare familial PD-associated mutations in aSyn render it aggregation-prone; however, PD patients carrying wild type (WT) aSyn also have aggregated aSyn in Lewy bodies. The mechanisms by which WT aSyn aggregates are unclear. Here, we report that inflammation can play a role in causing the aggregation of WT aSyn. We show that activation of the inflammasome with known stimuli results in the aggregation of aSyn in a neuronal cell model of PD. The insoluble aggregates are enriched with truncated aSyn as found in Lewy bodies of the PD brain. Inhibition of the inflammasome enzyme caspase-1 by chemical inhibition or genetic knockdown with shRNA abated aSyn truncation. In vitro characterization confirmed that caspase-1 directly cleaves aSyn, generating a highly aggregation-prone species. The truncation-induced aggregation of aSyn is toxic to neuronal culture, and inhibition of caspase-1 by shRNA or a specific chemical inhibitor improved the survival of a neuronal PD cell model. This study provides a molecular link for the role of inflammation in aSyn aggregation, and perhaps in the pathogenesis of sporadic PD as well.

Early-Life Factors and Risk of Parkinson's Disease: A Register-Based Cohort Study

Parkinson’s disease (PD) may take decades to develop and early life exposures such as infection may be important. However, few epidemiological studies have evaluated early life risk factors in relation to PD risk. We therefore examined such associations in a prospective analysis of 3 545 612 individuals born in Sweden between 1932 and 1970 without PD on January 1, 2002. Incident PD cases were identified using the Swedish Patient Register during 2002–2010. Information on sibship size, number of older and younger siblings, multiple births, parental age, birth month and season was obtained from the Swedish Multi-Generation Register. Monthly data on national burden of influenza-like illness during 1932–1970 were obtained from the Swedish Public Health Agency. Hazard ratios with 95% confidence intervals (CI) were estimated using Cox proportional hazards regression. During the follow-up, 8779 incident PD cases were identified. As expected, older age, male sex, parental occupation as farmers, and family history of PD were associated with higher PD risk. Overall, early life factors, including flu burden in the year of birth, were not associated with PD risk, although we did find a lower PD risk among participants with older siblings than those without (HR = 0.93, 95%CI: 0.89, 0.98). Our study therefore provided little support for important etiological contributions of early life factors to the PD risk late in life. The finding of a lower PD risk among individuals with older siblings will need confirmation and further investigation.

Caspase-1 inhibition attenuates activation of BV2 microglia induced by LPS-treated RAW264.7 macrophages

Neuroinflammation has been recognized as a factor in the pathogenesis of neurodegenerative diseases. Emerging evidence suggests that peripheral inflammation, besides neuroinflammation, functions as a modulator of disease progression and neuropathology in several neurodegenerative diseases. However, detailed correlations among peripheral inflammation, neuroinflammation and neurodegeneration remain unknown. In the present study, we prepared a peripheral inflammation model with lipopolysaccharides (LPS)-stimulated RAW264.7 macrophages to explore its activation on BV2 microglia. We found that LPS induced the production of IL-1β, IL-6 and TNF-α in the culture medium of RAW264.7 macrophages. We further showed that LPS plus ATP activated inflammasome, evidenced by the upregulation of caspase-1 and IL-1β, which was suppressed by ZYVAD, a caspase-1 inhibitor. Furthermore, the conditioned medium obtained from LPS-treated RAW264.7 macrophages activated BV2 microglia, stimulating the release of IL-1β, IL-6 and TNF-α from BV2 cells. ZYVAD pretreatment markedly suppressed BV2 microglia activation induced by RAW264.7 cells conditioned medium. Taken together, our study indicates that macrophage-mediated peripheral inflammation subsequently evokes neuroinflammation and may aggravate neural damage. Inflammasome and caspase-1 may be potential targets for modulating systemic inflammatory responses in neurodegenerative diseases.

Association Between Tuberculosis and Parkinson Disease: A Nationwide, Population-Based Cohort Study

Few studies have investigated the association between tuberculosis (TB) and Parkinson disease (PD). This nationwide, population-based, retrospective cohort study investigated the risk of PD in patients with TB.We selected patients newly diagnosed with TB (International Classification of Diseases, Ninth Revision, Clinical Modification: 011) from 2000 to 2009 in the Taiwan National Health Insurance Database as the TB cohort. The comparison cohort (the non-TB cohort) was frequency matched to the TB cohort at a ratio of 4:1 by sex, age, and the index date. We analyzed the risks of PD by using Cox proportional hazard regression models.A total of 121,951 patients with TB and 487,800 non-TB controls were enrolled in this study. The TB cohort had a 1.38-fold risk of PD compared with the non-TB cohort after adjustment for age, sex, and comorbidities (aHR, 95% CI: 1.30-1.46). The adjusted risk of PD in the TB and non-TB cohorts increased in subgroups regardless of age, sex, and comorbidities. Combined effect of TB and comorbidities on the risk of PD were significant in patients with TB who had diabetes (aHR: 2.26, 95% CI: 2.02-2.52), hypertension (aHR: 2.23, 95% CI: 2.04-2.44), head injury (aHR: 2.32, 95% CI: 1.95-2.77), chronic kidney disease (aHR: 2.02, 95% CI: 1.49-2.72), chronic obstructive pulmonary disease (aHR: 1.84, 95% CI: 1.66-2.05), depression (aHR: 4.66, 95% CI: 3.59-6.05), dementia (aHR: 3.70, 95% CI: 2.99-4.59), and stroke (aHR: 2.56, 95% CI: 2.28-2.87). The risk of PD was higher in a follow-up within 1 year (aHR: 1.78, 95% CI: 1.58-2.00) and decreased with the follow-up period in the TB cohort.Patients with TB have an independently 1.38-fold risk of PD. The risk of PD decreased with the follow-up period in the TB cohort. Physicians should be aware of the risk of PD in patients with TB when treating such patients.

Differential pattern of motor impairments in neurotoxic, environmental and inflammation-driven rat models of Parkinson's disease

One of the reasons proposed for the paucity of drug discovery for Parkinson's disease is the lack of relevant animal models of the condition. Parkinson's disease has been modelled extensively using the selective neurotoxin, 6-hydroxydopamine (6-OHDA). However, as this model bears little etiological resemblance to the human condition, there has been a drive to develop models with improved etiological validity. Two such models are those induced by the pesticide, rotenone, and the inflammagen, lipopolysaccharide (LPS). However, to date, these models have been poorly characterised in terms of their motor profiles and have never been directly compared to the more established models. Thus, the aim of this study was to characterise the behavioural profile of the rotenone and LPS models, and to compare them with the 6-OHDA model. Animals underwent baseline testing on the Stepping, Whisker, Corridor and Cylinder Tests of motor function. They were then grouped for unilateral intra-striatal infusion of 6-OHDA, rotenone or LPS. Motor testing continued for ten weeks after which the rats were processed for immunohistochemical analysis of nigrostriatal integrity. We found that, although all neurotoxins induced a similar level of nigrostriatal neurodegeneration, neither the rotenone nor LPS models were associated with amphetamine-induced rotation, and they were associated with significantly less pronounced and stable impairments in the spontaneous tasks than the 6-OHDA model. In conclusion, this study demonstrates key differences in the pattern of motor dysfunction induced by Parkinsonian neurotoxins which should be taken into consideration when selecting the most appropriate model for Parkinson's disease preclinical studies.

Insights into Neuroinflammation in Parkinson's Disease: From Biomarkers to Anti-Inflammatory Based Therapies

Parkinson's disease (PD) is the second most common neurodegenerative disorder worldwide, being characterized by the progressive loss of dopaminergic neurons in the substantia nigra pars compacta. Among several putative factors that may contribute to PD pathogenesis, inflammatory mechanisms may play a pivotal role. The involvement of microglial activation as well as of brain and peripheral immune mediators in PD pathophysiology has been reported by clinical and experimental studies. These inflammatory biomarkers evaluated by imaging techniques and/or by biological sample analysis have become valuable tools for PD diagnosis and prognosis. Regardless of the significant increase in the number of people suffering from PD, there are still no established disease-modifying or neuroprotective therapies for it. There is growing evidence of protective effect of anti-inflammatory drugs on PD development. Herein, we reviewed the current literature regarding the central nervous system and peripheral immune biomarkers in PD and advances in diagnostic and prognostic tools as well as the neuroprotective effects of anti-inflammatory therapies.

Inflammatory dysregulation of blood monocytes in Parkinson's disease patients

Despite extensive effort on studying inflammatory processes in the CNS of Parkinson's disease (PD) patients, implications of peripheral monocytes are still poorly understood. Here, we set out to obtain a comprehensive picture of circulating myeloid cells in PD patients. We applied a human primary monocyte culture system and flow cytometry-based techniques to determine the state of monocytes from PD patients during disease. We found that the classical monocytes are enriched in the blood of PD patients along with an increase in the monocyte-recruiting chemoattractant protein CCL2. Moreover, we found that monocytes from PD patients display a pathological hyperactivity in response to LPS stimulation that correlates with disease severity. Inflammatory pre-conditioning was also reflected on the transcriptome in PD monocytes using next-generation sequencing. Further, we identified the CD95/CD95L as a key regulator for the PD-associated alteration of circulating monocytes. Pharmacological neutralization of CD95L reverses the dysregulation of monocytic subpopulations in favor of non-classical monocytes. Our results suggest that PD monocytes are in an inflammatory predisposition responding with hyperactivation to a "second hit". These results provide the first direct evidence that circulating human peripheral blood monocytes are altered in terms of their function and composition in PD patients. This study provides insights into monocyte biology in PD and establishes a basis for future studies on peripheral inflammation.

Parkinson's disease and occupation: differences in associations by case identification method suggest referral bias

METHODS

We used a population-based sample of 403 Parkinson's disease cases and 405 controls to examine risks by occupation. Results were compared to a previous clinic-based analysis.

RESULTS

With censoring of jobs held within 10 years of diagnosis, the following had significantly or strongly increased risks: social science, law and library jobs (OR = 1.8); farming and horticulture jobs (OR = 2.0); gas station jobs (OR = 2.6); and welders (OR = 3.0). The following had significantly decreased risks: management and administration jobs (OR = 0.70); and other health care jobs (OR = 0.44).

CONCLUSIONS

These results were consistent with other findings for social science and farming occupations. Risks for teaching, medicine and health occupations were not elevated, unlike our previous clinic-based study. This underscores the value of population-based over clinic-based samples. Occupational studies may be particularly susceptible to referral bias because social networks may spread preferentially via jobs.

Peripheral inflammation in neurodegeneration

Neuroinflammation is now a well-characterised feature of neurodegenerative diseases. Immune dysfunction outside the central nervous system is also increasingly recognised as part of the diseases. Peripheral inflammation has emerged as a modulator of disease progression and neuropathology in several neurodegenerative diseases, making it targetable in new therapeutic approaches. In addition, the easy accessibility of blood immune cells and markers makes them ideal candidates for use as possible biomarkers and a potential model of central immune cells.