Parkinson's disease and exposure to agricultural work and pesticide chemicals

Paraquat (herbicide) as a cause of Parkinson's Disease

The four features of Parkinson's disease (PD), which also manifests other non-motor symptoms, are bradykinesia, tremor, postural instability, and stiffness. The pathogenic causes of Parkinsonism include Lewy bodies, intracellular protein clumps of αsynuclein, and the degeneration of dopaminergic neurons in the substantia nigra's pars compacta region. The pathophysiology of PD is still poorly understood due to the complexity of the illness. The apoptotic cell death of neurons in PD, however, has been linked to a variety of intracellular mechanisms, according to a wide spectrum of study. The endoplasmic reticulum's stress, decreased levels of neurotrophic factors, oxidative stress, mitochondrial dysfunction, catabolic alterations in dopamine, and decreased activity of tyrosine hydroxylase are some of these causes. The herbicide paraquat has been used in laboratory studies to create a variety of PD pathological features in numerous in-vitro and in-vivo animals. Due to the unique neurotoxicity that paraquat causes, understanding of the pathophysiology of PD has changed. Parkinson's disease (PD) is more likely to develop among people exposed to paraquat over an extended period of time, according to epidemiological studies. Thanks to this paradigm, the hunt for new therapy targets for PD has expanded. In both in-vitro and in-vivo models, the purpose of this study is to summarise the relationship between paraquat exposure and the onset of Parkinson's disease (PD).

Caffeine plus haloperidol reduces fatigue in an experimental model of Parkinson's disease - a prospective to A2AR-D2R heterodimer antagonism

Fatigue is a non-motor symptom of Parkinson's disease (PD). Adenosine 2A receptor (A2AR) and compromised dopamine neurotransmission are linked to fatigue. Studies demonstrate that A2AR antagonism potentiates dopamine transmission via dopamine receptor D2 (D2R). However, the heterodimer form of A2AR-D2R in the striatum prompted questions about the therapeutic targets for PD patients. This study investigates the effects of caffeine (A2AR non-selective antagonist) plus haloperidol (D2R selective antagonist) treatment in the fatigue induced by the reserpine model of PD. Reserpinized mice showed impaired motor control in the open field test (p < 0.05) and fatigue in the grip strength meter test (p < 0.05). L-DOPA and caffeine plus haloperidol similarly increased motor control (p < 0.05) and mitigated fatigue (p < 0.05). Our results support the A2AR-D2R heterodimer participation in the central fatigue of PD, and highlight the potential of A2AR-D2R antagonism in the management of PD.

Elevated parkinsonism pathological markers in dopaminergic neurons with developmental exposure to atrazine

Atrazine (ATZ) is one of the most used herbicides in the US and a known endocrine disruptor. ATZ is frequently detected in drinking water, especially in Midwestern regions of the United States, exceeding the EPA regulation of maximum contamination level (MCL) of 3 ppb. Epidemiology studies have suggested an association between ATZ exposure and neurodegeneration. Less, however, is known about the neurotoxic mechanism of ATZ, particularly for exposures at a developmental stage. Here, we exposed floor plate progenitors (FPPs) derived from human induced pluripotent stem cells (hiPSCs) to low concentrations of ATZ at 0.3 and 3 ppb for two days followed by differentiation into dopaminergic (DA) neurons in ATZ-free medium. We then examined the morphology, activity, pathological protein aggregation, and transcriptomic changes of differentiated DA neurons. We observed significant decrease in the complexity of neurite network, increase of neuronal activity, and elevated tau- and α-synuclein (aSyn) pathologies after ATZ exposure. The ATZ-induced neuronal changes observed here align with pathological characteristics in Parkinson's disease (PD). Transcriptomic analysis further corroborates our findings; and collectively provides a strong evidence base that low-concentration ATZ exposure during development can elicit increased risk of neurodegeneration.

Degradation of Pesticide Residues in Water, Soil, and Food Products via Cold Plasma Technology

Water, soil, and food products contain pesticide residues. These residues result from excessive pesticides use, motivated by the fact that agricultural productivity can be increased by the use of these pesticides. The accumulation of these residues in the body can cause health problems, leading to food safety concerns. Cold plasma technology has been successfully employed in various applications, such as seed germination, bacterial inactivation, wound disinfection, surface sterilization, and pesticide degradation. In recent years, researchers have increasingly explored the effectiveness of cold plasma technology in the degradation of pesticide residues. Most studies have shown promising outcomes, encouraging further research and scaling-up for commercialization. This review summarizes the use of cold plasma as an emerging technology for pesticide degradation in terms of the plasma system and configuration. It also outlines the key findings in this area. The most frequently adopted plasma systems for each application are identified, and the mechanisms underlying pesticide degradation using cold plasma technology are discussed. The possible factors influencing pesticide degradation efficiency, challenges in research, and future trends are also discussed. This review demonstrates that despite the nascent nature of the technology, the use of cold plasma shows considerable potential in regards to pesticide residue degradation, particularly in food applications.

Developmental exposure to the Parkinson's disease-associated organochlorine pesticide dieldrin alters dopamine neurotransmission in α-synuclein pre-formed fibril (PFF)-injected mice

Parkinson's disease (PD) is the fastest-growing neurological disease worldwide, with increases outpacing aging and occurring most rapidly in recently industrialized areas, suggesting a role of environmental factors. Epidemiological, post-mortem, and mechanistic studies suggest that persistent organic pollutants, including the organochlorine pesticide dieldrin, increase PD risk. In mice, developmental dieldrin exposure causes male-specific exacerbation of neuronal susceptibility to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and synucleinopathy. Specifically, in the α-synuclein (α-syn) pre-formed fibril (PFF) model, exposure leads to increased deficits in striatal dopamine (DA) turnover and motor deficits on the challenging beam. Here, we hypothesized that alterations in DA handling contribute to the observed changes and assessed vesicular monoamine transporter 2 (VMAT2) function and DA release in this dieldrin/PFF 2-hit model. Female C57BL/6 mice were exposed to 0.3 mg/kg dieldrin or vehicle every 3 days by feeding, starting at 8 weeks of age and continuing throughout breeding, gestation, and lactation. Male offspring from independent litters underwent unilateral, intrastriatal injections of α-syn PFFs at 12 weeks of age, and vesicular 3H-DA uptake assays and fast-scan cyclic voltammetry were performed 4 months post-PFF injection. Dieldrin-induced an increase in DA release in striatal slices in PFF-injected animals, but no change in VMAT2 activity. These results suggest that developmental dieldrin exposure increases a compensatory response to synucleinopathy-triggered striatal DA loss. These findings are consistent with silent neurotoxicity, where developmental exposure to dieldrin primes the nigrostriatal striatal system to have an exacerbated response to synucleinopathy in the absence of observable changes in typical markers of nigrostriatal dysfunction and degeneration.

Sex and Brain: The Role of Sex Chromosomes and Hormones in Brain Development and Parkinson's Disease

Sex hormones and genes on the sex chromosomes are not only key factors in the regulation of sexual differentiation and reproduction but they are also deeply involved in brain homeostasis. Their action is crucial for the development of the brain, which presents different characteristics depending on the sex of individuals. The role of these players in the brain is fundamental in the maintenance of brain function during adulthood as well, thus being important also with respect to age-related neurodegenerative diseases. In this review, we explore the role of biological sex in the development of the brain and analyze its impact on the predisposition toward and the progression of neurodegenerative diseases. In particular, we focus on Parkinson's disease, a neurodegenerative disorder that has a higher incidence in the male population. We report how sex hormones and genes encoded by the sex chromosomes could protect from the disease or alternatively predispose toward its development. We finally underline the importance of considering sex when studying brain physiology and pathology in cellular and animal models in order to better understand disease etiology and develop novel tailored therapeutic strategies.

Xanthine Dehydrogenase Is a Modulator of Dopaminergic Neurodegeneration in Response to Bacterial Metabolite Exposure in C. elegans

Oxidative stress is a contributing factor to Parkinson's disease (PD). Considering the prevalence of sporadic PD, environmental exposures are postulated to increase reactive oxygen species and either incite or exacerbate neurodegeneration. We previously determined that exposure to the common soil bacterium, Streptomyces venezuelae (S. ven), enhanced oxidative stress and mitochondrial dysfunction in Caenorhabditis elegans, leading to dopaminergic (DA) neurodegeneration. Here, S. ven metabolite exposure in C. elegans was followed by RNA-Seq analysis. Half of the differentially identified genes (DEGs) were associated with the transcription factor DAF-16 (FOXO), which is a key node in regulating stress response. Our DEGs were enriched for Phase I (CYP) and Phase II (UGT) detoxification genes and non-CYP Phase I enzymes associated with oxidative metabolism, including the downregulated xanthine dehydrogenase gene, xdh-1. The XDH-1 enzyme exhibits reversible interconversion to xanthine oxidase (XO) in response to calcium. S. ven metabolite exposure enhanced XO activity in C. elegans. The chelation of calcium diminishes the conversion of XDH-1 to XO and results in neuroprotection from S. ven exposure, whereas CaCl₂ supplementation enhanced neurodegeneration. These results suggest a defense mechanism that delimits the pool of XDH-1 available for interconversion to XO, and associated ROS production, in response to metabolite exposure.

Metal-Organic Frameworks as Potential Agents for Extraction and Delivery of Pesticides and Agrochemicals

Pesticide contamination is a global issue, affecting nearly 44% of the global farming population, and disproportionately affecting farmers and agricultural workers in developing countries. Despite this, global pesticide usage is on the rise, with the growing demand of global food production with increasing population. Different types of porous materials, such as carbon and zeolites, have been explored for the remediation of pesticides from the environment. However, there are some limitations with these materials, especially due to lack of functional groups and relatively modest surface areas. In this regard, metal-organic frameworks (MOFs) provide us with a better alternative to conventionally used porous materials due to their versatile and highly porous structure. Recently, a number of MOFs have been studied for the extraction of pesticides from the environment as well as for targeted and controlled release of agrochemicals. Different types of pesticides and conditions have been investigated, and MOFs have proved their potential in agricultural applications. In this review, the latest studies on delivery and extraction of pesticides using MOFs are systematically reviewed, along with some recent studies on greener ways of pest control through the slow release of chemical compounds from MOF composites. Finally, we present our insights into the key issues concerning the development and translational applications of using MOFs for targeted delivery and pesticide control.

Impact of environmental toxicants exposure on gut-brain axis in Parkinson disease

Parkinson disease (PD) is a major public health challenge as many of the current drugs used in its management provide symptomatic relieve without preventing the underlying cause of the neurodegeneration. Similarly, the non-motor complications of PD, especially the gastrointestinal tract (GIT) disturbance increases the disease burden on both the PD patient and caregivers. Different theories have been postulated regarding the mechanisms or pathways involved in PD pathology but gut-brain axis involvement has gained much more momentum. This pathway was first suggested by Braak and colleagues in 2003, where they suggested that PD starts from the GIT before spreading to the brain. However, human exposure to environmental toxicants known to inhibit mitochondrial complex I activity such as rotenone, paraquat and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) are well associated with PD. Several reports have shown that oral exposure of laboratory animals to rotenone causes mitochondria dysfunction, GIT disturbance, overexpression of alpha synuclein and microbiota imbalance. This review focuses on the mechanism(s) through which rotenone induces PD pathogenesis and potential for therapeutic small molecules targeting these processes at the earliest stages of the disease. We also focused on the interaction between the GI microbiota and PD pathology.

Neurotoxicity of pesticides in the context of CNS chronic diseases

Following the introduction and application of pesticides in human life, they have always been along with health concerns both in acute poisoning and chronic toxicities. Neurotoxicity of pesticides in chronic exposures has been known as one of the most important human health problems, as most of these chemicals act through interacting with some elements of nervous system. Pesticide-induced neurotoxicity can be defined in different categories of neurological disorders including neurodegenerative (Alzheimer, Parkinson, amyotrophic lateral sclerosis, multiple sclerosis), neurodevelopmental (attention deficit hyperactivity disorder, autism spectrum disorders, developmental delay, and intellectual disability), neurobehavioral and neuropsychiatric (depression/suicide attempt, anxiety/insomnia, and cognitive impairment) disorders some of which are among the most debilitating human health problems. In this review, neurotoxicity of pesticides in the mentioned categories and sub-categories of neurological diseases have been systematically presented in relation to different route of exposures including general, occupational, environmental, prenatal, postnatal, and paternal.

Gender Differences in the Prevalence of Parkinson's Disease

Background

Parkinson's disease (PD) affects males more than females. The reasons for the gender differences in PD prevalence remain unclear.

Objective

The objective of this systematic review and meta-analysis was to update the overall male/female prevalence ratios (OPR).

Methods

We updated previous work by searching MEDLINE, SCOPUS, and OVID for articles reporting PD prevalence for both genders between 2011 and 2021. We calculated OPRs and investigated heterogeneity in effect estimates.

Results

We included 19 new articles and 13 articles from a previously published meta-analysis. The OPR was 1.18, 95% CI, [1.03, 1.36]. The OPR was lowest in Asia and appeared to be decreasing over time. Study design, national wealth, and participant age did not explain OPR heterogeneity.

Conclusion

Gender differences in PD prevalence may not be as stark as previously thought. Studies are needed to understand the role of other determinants of gender differences in PD prevalence.

Impact of occupational pesticide exposure assessment method on risk estimates for prostate cancer, non-Hodgkin's lymphoma and Parkinson's disease: results of three meta-analyses

Assessment of occupational pesticide exposure in epidemiological studies of chronic diseases is challenging. Biomonitoring of current pesticide levels might not correlate with past exposure relevant to disease aetiology, and indirect methods often rely on workers’ imperfect recall of exposures, or job titles. We investigated how the applied exposure assessment method influenced risk estimates for some chronic diseases. In three meta-analyses the influence of exposure assessment method type on the summary risk ratio (sRR) of prostate cancer (PC) (25 articles), non-Hodgkin’s lymphoma (NHL) (29 articles) and Parkinson’s disease (PD) (32 articles) was investigated. Exposure assessment method types analysed were: group-level assessments (eg, job titles), self-reported exposures, expert-level assessments (eg, job-exposure matrices) and biomonitoring (eg, blood, urine). Additionally, sRRs were estimated by study design, publication year period and geographic location where the study was conducted. Exposure assessment method types were not associated with statistically significant different sRRs across any of the health outcomes. Heterogeneity in results varied from high in cancer studies to moderate and low in PD studies. Overall, case–control designs showed significantly higher sRR estimates than prospective cohort designs. Later NHL publications showed significantly higher sRR estimates than earlier. For PC, studies from North America showed significantly higher sRR estimates than studies from Europe. We conclude that exposure assessment method applied in studies of occupational exposure to pesticides appears not to have a significant effect on risk estimates for PC, NHL and PD. In systematic reviews of chronic health effects of occupational exposure to pesticides, epidemiological study design, publication year and geographic location, should primarily be considered.

Autonomic behavioral impairment induced by simazine exposure during early life of male mouse is mediated by Lmx1a/Wnt1 pathway

Simazine is a widely used herbicide and known as an environmental estrogen. Multiple studies have proved simazine can induced the degeneration of dopaminergic neuron resulting in a degenerative disease-like syndrome. Herein, we explored the neurotoxicity of simazine on the dopaminergic nervous system of embryos and weaned offspring during the maternal gestation period or the maternal gestation and lactation periods. We found that simazine disturbed the crucial components expression involved in Lmx1a/Wnt1 pathway of dopaminergic neuron in embryonic and weaned offspring. Furthermore, morphological and behavioral tests performed on weaned male offspring treated by simazine suggested that the grip strength, autonomic exploring, and the space sense ability were weakened, as well as the pathological damage of dopaminergic neuron was clearly observed. But, the same neurotoxicity of simazine is less significantly observed in female offspring. Our findings will provide reliable reference for the determination of environmental limits and new insight into the pathogenesis of nonfamilial neurodegenerative diseases related to environmental risk factors.

Lipid-lowering drug targets and Parkinson's disease: A sex-specific Mendelian randomization study

Parkinson's disease (PD) affects millions of individuals worldwide, and it is the second most common late-onset neurodegenerative disorder. There is no cure and current treatments only alleviate symptoms. Modifiable risk factors have been explored as possible options for decreasing risk or developing drug targets to treat PD, including low-density lipoprotein cholesterol (LDL-C). There is evidence of sex differences for cholesterol levels as well as for PD risk. Genetic datasets of increasing size are permitting association analyses with increased power, including sex-stratified analyses. These association results empower Mendelian randomization (MR) studies, which, given certain assumptions, test whether there is a causal relationship between the risk factor and the outcome using genetic instruments. Sex-specific causal inference approaches could highlight sex-specific effects that may otherwise be masked by sex-agnostic approaches. We conducted a sex-specific two-sample cis-MR analysis based on genetic variants in LDL-C target encoding genes to assess the impact of lipid-lowering drug targets on PD risk. To complement the cis-MR analysis, we also conducted a sex-specific standard MR analysis (using genome-wide independent variants). We did not find evidence of a causal relationship between LDL-C levels and PD risk in females [OR (95% CI) = 1.01 (0.60, 1.69), IVW random-effects] or males [OR (95% CI) = 0.93 (0.55, 1.56)]. The sex-specific standard MR analysis also supported this conclusion. We encourage future work assessing sex-specific effects using causal inference techniques to better understand factors that may contribute to complex disease risk differently between the sexes.

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.

Review of Metabolomics-Based Biomarker Research for Parkinson's Disease

Parkinson's disease (PD), as the second most common neurodegenerative disease, is seriously affecting the life quality of the elderly. However, there is still a lack of efficient medical methods to diagnosis PD before apparent symptoms occur. In recent years, clinical biomarkers including genetic, imaging, and tissue markers have exhibited remarkable benefits in assisting PD diagnoses. Due to the advantages of high-throughput detection of metabolites and almost non-invasive sample collection, metabolomics research of PD is widely used for diagnostic biomarker discovery. However, there are also a few shortages for those identified biomarkers, such as the scarcity of verifications regarding the sensitivity and specificity. Thus, reviewing the research progress of PD biomarkers based on metabolomics techniques is of great significance for developing PD diagnosis. To comprehensively clarify the progress of current metabolic biomarker studies in PD, we reviewed 20 research articles regarding the discovery and validation of biomarkers for PD diagnosis from three mainstream academic databases (NIH PubMed, ISI Web of Science, and Elsevier ScienceDirect). By analyzing those materials, we summarized the metabolic biomarkers identified by those metabolomics studies and discussed the potential approaches used for biomarker verifications. In conclusion, this review provides a comprehensive and updated overview of PD metabolomics research in the past two decades and particularly discusses the validation of disease biomarkers. We hope those discussions might provide inspiration for PD biomarker discovery and verification in the future.

The influence of preconditioning with low dose of LPS on paraquat-induced neurotoxicity, microglia activation and expression of α-synuclein and synphilin-1 in the dopaminergic system

Background

Prolonged inflammation, oxidative stress, and protein aggregation are important factors contributing to Parkinson’s disease (PD) pathology. A known ROS generator, pesticide paraquat (PQ), was indicated as an environmental substance potentially increasing the incidence of PD and is used to model this disease. We investigated if a combination of inflammation and oxidative stress in subthreshold doses would exacerbate the modelled neuropathology.

Methods

We examined the late effects of acute or repeated peripheral inflammation induced by low dose of LPS (10 μg/kg, ip) on PQ toxicity in the rat nigrostriatal dopaminergic pathway, microglial activation markers and expression of major Lewy bodies proteins, α-synuclein and synphilin-1.

Results

We observed that LPS increased, while PQ decreased body temperature and microglia CD11b expression in the SN. Single LPS pretreatment, 3 h before repeated weekly PQ injections (4×) slightly aggravated neuronal degeneration in the SN. Moreover, degeneration of dopaminergic neurons after weekly repeated inflammation itself (4×) was observed. Interestingly, repeated LPS administration combined with each PQ dose counteracted such effect. The expression of α-synuclein decreased after repeated LPS injections, while only combined, repeated LPS and PQ treatment lowered the levels of synphilin-1. Therefore, α-synuclein and synphilin-1 expression change was influenced by different mechanisms. Concomitantly, decreased levels of the two proteins correlated with decreased degeneration of dopaminergic neurons and with a normalized microglia activation marker.

Conclusions

Our results indicate that both oxidative insult triggered by PQ and inflammation caused by peripheral LPS injection can individually induce neurotoxicity. Those factors act through different mechanisms that are not additive and not selective towards dopaminergic neurons, probably implying microglia. Repeated, but small insults from oxidative stress and inflammation when administered in significant time intervals can counteract each other and even act protective as a preconditioning effect. The timing of such repetitive insults is also of essence.

Supplementary Information

The online version contains supplementary material available at 10.1007/s43440-021-00340-1.

Prevalence of Parkinson's disease in China: a multicenter population-based survey

OBJECTIVE

Few data are available on the current prevalence of Parkinson's disease in China. The aim of this study was to determine the prevalence of Parkinson's disease in Chinese individuals aged 65 years and older and to analyze associated risk factors.

METHODS

We performed a population-based cross-sectional survey with a multistage cluster sampling design. Residents aged 65 and over were drawn from 11 urban districts and 10 rural counties across China. Data were entered into spreadsheets, and imported and analyzed using Statistical Package SPSS 24.

RESULTS

We identified 151 patients with Parkinson's disease among 8124 residents aged 65 and over, including 75 men (49.67%) and 76 women (50.33%). The overall prevalence of PD in the study population was 1.86% (95% confidence interval [CI]: 1.6%-2.2%), and the standardized prevalence of PD was 1.60%. The crude prevalence in men (2.12%) was higher than in women (1.66%), and standardized prevalence in urban areas (1.98%) was higher than in rural areas (1.48%). Logistic regression analysis showed that independent risk factors for PD were older age, heavy metal or pesticide exposure (odds ratio [OR]=3.83; 95% CI: 2.021-7.256), urban residence (OR=1.307; 95% CI: 1.041-1.642), rapid eye movement sleep behavior disorder (OR=1.450; 95% CI: 1.021-2.059), and heart disease (OR=2.431; 95% CI: 1.481-4.990). Conclusion：The prevalence of Parkinson's disease in individuals aged 65 and older in China has not increased significantly in recent years. The prevalence of Parkinson's disease is higher in men than in women and higher in urban areas than in rural areas.

Environmental neurotoxicants and inflammasome activation in Parkinson's disease - A focus on the gut-brain axis

Inflammasomes are multi-protein complexes expressed in immune cells that function as intracellular sensors of environmental, metabolic and cellular stress. Inflammasome activation in the brain, has been shown to drive neuropathology and disease progression by multiple mechanisms, making it one of the most attractive therapeutic targets for disease modification in Parkinson's Disease (PD). Extensive inflammasome activation is evident in the brains of people with PD at the sites of dopaminergic degeneration and synuclein aggregation. While substantial progress has been made on validating inflammasome activation as a therapeutic target for PD, the mechanisms by which inflammasome activation is triggered and sustained over the disease course remain poorly understood. A growing body of evidence point to environmental and occupational chemical exposures as possible triggers of inflammasome activation in PD. The involvement of the gastrointestinal system and gut microbiota in PD pathophysiology is beginning to be elucidated, especially the profound link between gut dysbiosis and immune activation. While large cohort studies confirmed specific changes in the gut microbiota in PD patients compared to age-matched healthy controls, recent research suggest that synuclein pathology could be initiated in the gastrointestinal tract. In this review, we present a summarized perspective on current understanding on inflammasome activation and the gut-brain-axis link during PD pathophysiology. We discuss multiple environmental toxicants that are implicated as the etiological agents in causing idiopathic PD and their mechanistic underpinnings during neuroinflammatory events. We additionally present future directions that needs to address the research questions related to the gut-microbiome-brain mechanisms in PD.

Increasing disease burden and use of drugs and chemicals in Bangladesh shrimp aquaculture: A potential menace to human health

Using structured surveys in 2008 and 2016, change in disease burden and use of chemical treatments in Bangladesh shrimp farm management was examined. Overall, disease burden had increased in all farms and was more polarized, with a fewer number of individual infectious diseases responsible for most disease in ponds. Farmers also reported physical deformities, nutritional deficiencies, and unknown diseases further indicating poor health of their stock. To combat the threat, more chemical treatments were used (5.2 treatments per farm in 2008 versus 28.8 in 2016), resulting in an average increase of 424% in the number of active substances entering shrimp ponds. Although there was a modest reduction in the use of antimicrobials, shrimp was being exposed to a wider range of chemicals during rearing. The subsequent concern for the environment, animal and human health demands further research to identify potential risks from residues of chemical products.

Does paraquat cause Parkinson's disease? A review of reviews

To examine the extent to which a consensus exists in the scientific community regarding the relationship between exposure to paraquat and Parkinson's disease, a critical review of reviews was undertaken focusing on reviews published between 2006 and the present that offered opinions on the issue of causation. Systematic searches were undertaken of scientific databases along with searches of published bibliographies to identify English language reviews on the topic of paraquat and Parkinson's disease including those on the broader topic of environmental and occupational risk factors for Parkinson's disease. Of the 269 publications identified in the searches, there were twelve reviews, some with meta-analyses, that met the inclusion criteria. Information on methods used by the reviewers, if any, and source of funding was collected; the quality of the reviews was considered. No author of any published review stated that it has been established that exposure to paraquat causes Parkinson's disease, regardless of methods used and independent of funding source. A consensus exists in the scientific community that the available evidence does not warrant a claim that paraquat causes Parkinson's disease. Future research on this topic should focus on improving the quality of epidemiological studies including better exposure measures and identifying specific mechanisms of action. Future reviews of emerging evidence should be structured as systematic narrative reviews with meta-analysis if appropriate.

Mortality from Parkinson's disease and other causes among a workforce manufacturing paraquat: an updated retrospective cohort study

BACKGROUND

Epidemiological studies of the association between Parkinson's disease (PD) and paraquat (PQ) exposure have given inconsistent findings. The aim of the study was to update information on the risk of PD and mortality from major causes of death among a UK workforce who manufactured PQ by extending the follow-up by seven and a half years.

METHODS

This retrospective cohort study included all employees who had ever worked on any of the four plants at Widnes, UK where PQ was manufactured between 1961 and 1995. The 926 male and 42 female workers were followed through 31 December 2017. Mortalities for males were compared with national and local rates, including rates for PD as a mentioned cause of death.

RESULTS

A total of 394 male and 21 female workers had died by end of follow-up. Four death certificates of male workers mentioned PD, including two deaths that were due to PD. At least 6 death certificates of male employees would have been expected to have mentioned PD (SMR = 0.67; 95% CI 0.18-1.72). Reduced mortalities compared with local rates were found for major causes of death.

CONCLUSIONS

The study provided no evidence of an increased risk of PD, or increased mortalities from other causes among PQ production workers whose exposure to PQ on a daily basis was at least comparable to that of a PQ sprayer or mixer/loader.

Parkinson's disease: Alterations in iron and redox biology as a key to unlock therapeutic strategies

A plethora of studies indicate that iron metabolism is dysregulated in Parkinson's disease (PD). The literature reveals well-documented alterations consistent with established dogma, but also intriguing paradoxical observations requiring mechanistic dissection. An important fact is the iron loading in dopaminergic neurons of the substantia nigra pars compacta (SNpc), which are the cells primarily affected in PD. Assessment of these changes reveal increased expression of proteins critical for iron uptake, namely transferrin receptor 1 and the divalent metal transporter 1 (DMT1), and decreased expression of the iron exporter, ferroportin-1 (FPN1). Consistent with this is the activation of iron regulator protein (IRP) RNA-binding activity, which is an important regulator of iron homeostasis, with its activation indicating cytosolic iron deficiency. In fact, IRPs bind to iron-responsive elements (IREs) in the 3ꞌ untranslated region (UTR) of certain mRNAs to stabilize their half-life, while binding to the 5ꞌ UTR prevents translation. Iron loading of dopaminergic neurons in PD may occur through these mechanisms, leading to increased neuronal iron and iron-mediated reactive oxygen species (ROS) generation. The "gold standard" histological marker of PD, Lewy bodies, are mainly composed of α-synuclein, the expression of which is markedly increased in PD. Of note, an atypical IRE exists in the α-synuclein 5ꞌ UTR that may explain its up-regulation by increased iron. This dysregulation could be impacted by the unique autonomous pacemaking of dopaminergic neurons of the SNpc that engages L-type Ca+2 channels, which imparts a bioenergetic energy deficit and mitochondrial redox stress. This dysfunction could then drive alterations in iron trafficking that attempt to rescue energy deficits such as the increased iron uptake to provide iron for key electron transport proteins. Considering the increased iron-loading in PD brains, therapies utilizing limited iron chelation have shown success. Greater therapeutic advancements should be possible once the exact molecular pathways of iron processing are dissected.

Assessing Vesicular Monoamine Transport and Toxicity Using Fluorescent False Neurotransmitters

Impairments in the vesicular packaging of dopamine result in an accumulation of dopamine in the cytosol. Cytosolic dopamine is vulnerable to two metabolic processes-enzymatic catabolism and enzymatic- or auto-oxidation-that form toxic metabolites and generate reactive oxygen species. Alterations in the expression or activity of the vesicular monoamine transporter 2 (VMAT2), which transports monoamines such as dopamine from the cytosol into the synaptic vesicle, result in dysregulated dopamine packaging. Here, we developed a series of assays using the fluorescent false neurotransmitter 206 (FFN206) to visualize VMAT2-mediated vesicular packaging at baseline and following pharmacological and toxicological manipulations. As a proof of principle, we observed a significant reduction in vesicular FFN206 packaging after treatment with the VMAT2 inhibitors reserpine (IC₅₀: 73.1 nM), tetrabenazine (IC₅₀: 30.4 nM), methamphetamine (IC₅₀: 2.4 μM), and methylphenidate (IC₅₀: 94.3 μM). We then applied the assay to investigate the consequences on vesicular packaging by environmental toxicants including the pesticides paraquat, rotenone, and chlorpyrifos, as well as the halogenated compounds unichlor, perfluorooctanesulfonic acid, Paroil, Aroclor 1260, and hexabromocyclododecane. Several of the environmental toxicants showed minor impairment of the vesicular FFN206 loading, suggesting that the toxicants are weak VMAT2 inhibitors at the concentrations tested. The assay presented here can be applied to investigate the effect of additional pharmacological compounds and environmental toxicants on vesicular function, which will provide insight into how exposures to such factors are involved in the pathogenesis of monoaminergic diseases such as Parkinson's disease, and the assay can be used to identify pharmacological agents that influence VMAT2 activity.

Chemically Induced Models of Parkinson's Disease: History and Perspectives for the Involvement of Ferroptosis

Ferroptosis is a newly discovered form of necrotic cell death characterized by its dependency on iron and lipid peroxidation. Ferroptosis has attracted much attention recently in the area of neurodegeneration since the involvement of ferroptosis in Parkinson’s disease (PD), a major neurodegenerative disease, has been indicated using animal models. Although PD is associated with both genetic and environmental factors, sporadic forms of PD account for more than 90% of total PD. Following the importance of environmental factors, various neurotoxins are used as chemical inducers of PD both in vivo and in vitro. In contrast to other neurodegenerative diseases such as Alzheimer’s and Huntington’s diseases (AD and HD), many of the characteristics of PD can be reproduced in vivo by the use of specific neurotoxins. Given the indication of ferroptosis in PD pathology, several studies have been conducted to examine whether ferroptosis plays role in the loss of dopaminergic neurons in PD. However, there are still few reports showing an authentic form of ferroptosis in neuronal cells during exposure to the neurotoxins used as PD inducers. In this review article, we summarize the history of the uses of chemicals to create PD models in vivo and in vitro. Besides, we also survey recent reports examining the possible involvement of ferroptosis in chemical models of PD.

Classic and evolving animal models in Parkinson's disease

Parkinson's disease (PD) is a progressive neurodegenerative disease with motor and non-motor symptoms. PD is characterized by the degeneration of dopaminergic neurons in the substantia nigra pars compacta (SNpc) and deficiency of dopamine in the striatal region. The primary objective in PD research is to understand the pathogenesis, targets, and development of therapeutic interventions to control the progress of the disease. The anatomical and physiological resemblances between humans and animals gathered the researcher's attention towards the use of animals in PD research. Due to varying age of onset, symptoms, and progression rate, PD becomes heterogeneous which demands the variety of animal models to study diverse features of the disease. Parkinson is a multifactorial disorder, selection of models become important as not a single model shows all the biochemical features of the disease. Currently, conventional pharmacological, neurotoxin-induced, genetically modified and cellular models are available for PD research, but none of them recapitulate all the biochemical characteristics of the disease. In this review, we included the updated knowledge on the main features of currently available in vivo and in vitro models as well as their strengths and weaknesses.

Exposure to pyrethroids induces behavioral impairments, neurofibrillary tangles and tau pathology in Alzheimer's type neurodegeneration in adult Wistar rats

This study investigated the exposure of pyrethroids in the development of Alzheimer's type neurodegeneration by analyzing β- amyloid, tau and Glial Fibrillary Acidic Protein (GFAP) in adult Wistar rats. Forty adult Wistar rats (130-150 g) of both sexes were assigned into five groups (n = 8). Groups A-C were treated with three different sub-lethal doses (75, 50 and 25%)of the pyrethroids formulation diluted with olive oil once/daily for 45 days, while groups D&E received olive oil and distilled water respectively (as control groups). During the treatments, physical clinical signs were monitored for cognitive behavioral studies involving object recognition tasks and novel object identification test. At the end of treatment, the rats were sacrificed by cervical dislocation, the brains were harvested and the hippocampus located and dissected out for immunohistochemical studies. Standard histochemical techniques were employed. The results showed a significant decrease (p ≤ 0.05) in the spontaneous alternation and discrimination index in the treatment groups when compared to the control groups. Histological observation showed nuclear fragmentation in treated rats in a dose dependent manner when compared to the controls. Amyloid plaques were further observed and markedly stained with Congo-red in the treated rats compared to the control groups. Immunohistochemical observation revealed that exposure to pyrethroids increased immunoreactivity of GFAP and tau protein in both CA3 and Dentate gyrus (DG) regions in the treated rats indicative of Alzheimer's type degenerative diseases.

Developmental exposure to the organochlorine pesticide dieldrin causes male-specific exacerbation of α-synuclein-preformed fibril-induced toxicity and motor deficits

Human and animal studies have shown that exposure to the organochlorine pesticide dieldrin is associated with increased risk of Parkinson's disease (PD). Previous work showed that developmental dieldrin exposure increased neuronal susceptibility to MPTP toxicity in male C57BL/6 mice, possibly via changes in dopamine (DA) packaging and turnover. However, the relevance of the MPTP model to PD pathophysiology has been questioned. We therefore studied dieldrin-induced neurotoxicity in the α-synuclein (α-syn)-preformed fibril (PFF) model, which better reflects the α-syn pathology and toxicity observed in PD pathogenesis. Specifically, we used a "two-hit" model to determine whether developmental dieldrin exposure increases susceptibility to α-syn PFF-induced synucleinopathy. Dams were fed either dieldrin (0.3 mg/kg, every 3-4 days) or vehicle corn oil starting 1 month prior to breeding and continuing through weaning of pups at postnatal day 22. At 12 weeks of age, male and female offspring received intrastriatal α-syn PFF or control saline injections. Consistent with the male-specific increased susceptibility to MPTP, our results demonstrate that developmental dieldrin exposure exacerbates PFF-induced toxicity in male mice only. Specifically, in male offspring, dieldrin exacerbated PFF-induced motor deficits on the challenging beam and increased DA turnover in the striatum 6 months after PFF injection. However, male offspring showed neither exacerbation of phosphorylated α-syn aggregation (pSyn) in the substantia nigra (SN) at 1 or 2 months post-PFF injection, nor exacerbation of PFF-induced TH and NeuN loss in the SN 6 months post-PFF injection. Collectively, these data indicate that developmental dieldrin exposure produces a male-specific exacerbation of synucleinopathy-induced behavioral and biochemical deficits. This sex-specific result is consistent with both previous work in the MPTP model, our previously reported sex-specific effects of this exposure paradigm on the male and female epigenome, and the higher prevalence and more severe course of PD in males. The novel two-hit environmental toxicant/PFF exposure paradigm established in this project can be used to explore the mechanisms by which other PD-related exposures alter neuronal vulnerability to synucleinopathy in sporadic PD.

Identification of miRNA-7 as a regulator of brain-derived neurotrophic factor/α-synuclein axis in atrazine-induced Parkinson's disease by peripheral blood and brain microRNA profiling

Atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine; ATR) is widely used as an herbicide, and its accumulation in the environment is a health risk to humans; for instance, it has been shown to cause dopaminergic neurotoxicity. MicroRNAs (miRNAs) are endogenous small RNAs that regulate gene expression in diverse physiological contexts; however, the extent of their involvement in the development of Parkinson's disease (PD) is not known. In this study, we carried out miRNA profiling of peripheral blood and brain tissue in a rat model of PD in order to identify factors that mediate PD pathogenesis. The miRNAmiR-7 is known to cause the downregulation of α-synuclein (α-syn), which is linked to the neuropathology of PD. Here we found that miR-7 was upregulated in brain tissue but downregulated in peripheral blood of rats with ATR-induced PD. We also found that miR-7 regulates the expression of brain-derived neurotrophic factor (BDNF) through an auto regulatory mechanism. These findings indicate that miRNA-7 regulates the BDNF/α-syn axis in the early stages of PD and can serve as a biomarker or therapeutic target for disease treatment.

Acute Maneb Exposure Significantly Alters Both Glycolysis and Mitochondrial Function in Neuroblastoma Cells

The pesticides paraquat (PQ) and maneb (MB) have been described as environmental risk factors for Parkinson's disease (PD), with mechanisms associated with mitochondrial dysfunction and reactive oxygen species generation. A combined exposure of PQ and MB in murine models and neuroblastoma cells has been utilized to further advance understanding of the PD phenotype. MB acts as a redox modulator through alkylation of protein thiols and has been previously characterized to inhibit complex III of the electron transport chain and uncouple the mitochondrial proton gradient. The purpose of this study was to analyze ATP-linked respiration and glycolysis in human neuroblastoma cells utilizing the Seahorse extracellular flux platform. Employing an acute, subtoxic exposure of MB, this investigation revealed a MB-mediated decrease in mitochondrial oxygen consumption at baseline and maximal respiration, with inhibition of ATP synthesis and coupling efficiency. Additionally, MB-treated cells showed an increase in nonmitochondrial respiration and proton leak. Further investigation into mitochondrial fuel flex revealed an elimination of fuel flexibility across all 3 major substrates, with a decrease in pyruvate capacity as well as glutamine dependency. Analyses of glycolytic function showed a substantial decrease in glycolytic acidification caused by lactic acid export. This inhibition of glycolytic parameters was also observed after titrating the MB dose as low as 6 μM, and appears to be dependent on the dithiocarbamate functional group, with manganese possibly potentiating the effect. Further studies into cellular ATP and NAD levels revealed a drastic decrease in cells treated with MB. In summary, MB significantly impacted both aerobic and anaerobic energy production; therefore, further characterization of MB's effect on cellular energetics may provide insight into the specificity of PD to dopaminergic neurons.

Paraquat and Parkinson's disease: a systematic review and meta-analysis of observational studies

This investigation aimed to conduct a systematic review of the literature and meta-analysis to determine whether exposure to the herbicide paraquat was associated with the development of Parkinson's disease (PD). Observational studies that enrolled adults exposed to paraquat with PD as the outcome of interest were searched in the PubMed, Embase, LILACS, TOXNET, and Web of Science databases up to May 2019. Two authors independently selected relevant studies, extracted data, and assessed methodological quality. The evidence certainty was assessed by the GRADE approach, which served as basis for a tentative causality assessment, supplemented by the Bradford Hill criteria when necessary. Results from nine case-control studies indicated that PD occurrence was 25% higher in participants exposed to paraquat. The only cohort investigation included demonstrated a non-significant OR of 1.08. Results from subgroup analyses also indicated higher PD frequency in participants that were exposed to paraquat for longer periods or individuals co-exposed with paraquat and any other dithiocarbamate. Data indicate apositive association between exposure to paraquat and PD occurrence, but the weight-of-evidence does not enable one to assume an indisputable cause-effect relationship between these two conditions. Better designed studies are needed to increase confidence in results. Systematic Review Registration: PROSPERO CRD42017069994.

Parkinson's Disease and Parkinsonism

Parkinson's disease is a progressive neurodegenerative disease characterized by tremor and bradykinesia and is a common neurologic ailment. Male sex and advancing age are independent risk factors and, as the population ages, is taking an increasing toll on productivity and medical resources. There are a number of other extrapyramidal conditions that can make the diagnosis challenging. Unlike other neurodegenerative diseases, idiopathic Parkinson's disease has effective treatments that mitigate symptoms. Medications can improve day-to-day function and, in cases where medication does not give a sustained benefit or has significant side effects, treatments like deep brain stimulation result in improved quality of life.

Occupational Exposures and Neurodegenerative Diseases-A Systematic Literature Review and Meta-Analyses

Objectives: To carry out an integrated and stratified meta-analysis on occupational exposure to electromagnetic fields (EMFs), metals and pesticides and its effects on amyotrophic lateral sclerosis (ALS) and Parkinson's and Alzheimer's disease, and investigate the possibility of publication bias. Methods: In the current study, we updated our recently published meta-analyses on occupational exposures in relation to ALS, Alzheimer's and Parkinson's disease. Based on 66 original publications of good scientific epidemiological standard, according to the Meta-analysis of Observational Studies in Epidemiology (MOOSE) and the Grading of Recommendations, Assessment, Development and Evaluations (GRADE) guidelines, we analysed subgroups by carrying out stratified meta-analyses on publication year, statistical precision of the relative risk (RR) estimates, inspection of the funnel plots and test of bias. Results: Based on 19 studies the weighted RR for occupational exposure to EMFs was 1.26 (95% confidence interval (CI) 1.07⁻1.50) for ALS, 1.33 (95% CI 1.07⁻1.64) for Alzheimer's disease and 1.02 (95% CI 0.83⁻1.26) for Parkinson's disease. Thirty-one studies concerned occupational exposure to pesticides and the weighted RR was 1.35 (95% CI 1.02⁻1.79) for ALS, 1.50 (95% CI 0.98⁻2.29) for Alzheimer's disease and 1.66 (95% CI 1.42⁻1.94) for Parkinson's disease. Finally, 14 studies concerned occupational exposure to metals and only exposure to lead (five studies) involved an elevated risk for ALS or Parkinson's disease and the weighted RR was 1.57 (95% CI 1.11⁻2.20). The weighted RR for all the non-lead exposures was 0.97 (95% CI 0.88⁻1.06). Conclusions: Exposure to pesticides increased the risk of getting the mentioned neurodegenerative diseases by at least 50%. Exposure to lead was only studied for ALS and Parkinson's disease and involved 50% increased risk. Occupational exposure to EMFs seemed to involve some 10% increase in risk for ALS and Alzheimer's disease only.

Paraquat exposure and Parkinson's disease: A systematic review and meta-analysis

To reconcile and unify available results regarding paraquat exposure and Parkinson's disease (PD), we conducted a systematic review and meta-analysis to provide a quantitative estimate of the risk of PD associated with paraquat exposure. Six scientific databases including PubMed, Cochrane libraries, EMBASE, Scopus, ISI Web of Knowledge, and TOXLINE were systematically searched. The overall odds ratios (ORs) with corresponding 95% CIs were calculated using a random-effects model. Of 7,309 articles identified, 13 case control studies with 3,231 patients and 4,901 controls were included into our analysis. Whereas, one prospective cohort studies was included into our systematic review. A subsequent meta-analysis showed an association between PD and paraquat exposure (odds ratio = 1.64 (95% CI: 1.27-2.13; I² = 24.8%). There is a statistically significant association between paraquat exposure and PD. Thus, future studies regarding paraquat and Parkinson's disease are warranted.

DJ-1 as a Biomarker of Parkinson's Disease

Parkinson's disease is a progressive, age-related, neurodegenerative disorder, and oxidative stress is an important mediator in its pathogenesis. DJ-1 has been identified as a causative gene of a familial form of Parkinson's disease, PARK7, and plays a significant role in antioxidative defense, protecting cells from oxidative stress. A cysteine residue of DJ-1 at position 106 (Cys-106) is preferentially oxidized under oxidative stress. This reactive Cys-106 plays a critical role in the biological function of DJ-1, which could act as a sensor of oxidative stress by regulating antioxidative defense depending on Cys-106 oxidation. Thus, the levels of Cys-106-oxidized DJ-1 (oxDJ-1) could be a possible biomarker of oxidative stress. This chapter focuses on the properties of DJ-1 and oxDJ-1 levels as a biomarker of Parkinson's disease. In particular, the usability of these biomarkers to prevent and treat this neurodegenerative disease is discussed. Further, this section deals with the importance of identifying a biomarker of early-phase Parkinson's disease. Finally, this chapter summarizes the features of oxDJ-1 levels in the brain and blood as a biomarker candidate for early-phase Parkinson's disease based on our results using oxDJ-1-specific antibodies.

Essential tremor and the cerebellum

Essential tremor (ET) is a progressive and highly prevalent neurologic disease. Along with the tremors, mild to moderate gait ataxia and other signs of cerebellar dysfunction may occur (i.e., subtle saccadic eye movement abnormalities and abnormalities of motor timing) as well as cognitive features, some of which may be due to cerebellar dysfunction. Numerous neuroimaging studies indicate the presence of functional, metabolic, and structural abnormalities in the cerebellum of a patient with ET. In tandem with these clinical and imaging studies, which were gathering increasing support for the notion that the cerebellum and/or cerebellar systems seemed to be at the root of ET, a growing postmortem literature is for the first time beginning to identify microscopic abnormalities in the ET brain, most of which are centered on the Purkinje cells and connected neuronal populations, and are likely to be degenerative. In terms of treatment, most of these pharmacotherapeutic agents serve to enhance GABAergic neurotransmission, further bolstering the notion that ET may very well be a disorder with a primary Purkinje cell dysfunction resulting in reduced cerebellar cortical inhibition. Similarly, the interruption of presumably abnormal cerebellar outflow pathways to the thalamus is the mechanism of deep-brain stimulation surgery, which is highly effective in treating ET.

Effect on the dopaminergic metabolism induced by oral exposure to simazine during the prepubertal period in rats

The herbicide simazine is widely used in agricultural and non-agricultural fields. Studies have shown that simazine inhibits the proliferation of dopaminergic cells and affects the developmental differentiation of dopamine neurons. However, little is known about the effects of simazine on dopaminergic metabolism. Therefore, the present study examined the effects of simazine on Sprague‑Dawley (SD) rats from weaning to puberty (40 days exposure). Simazine was administered orally to SD rats at doses of 0, 12.5, 50 and 200 mg/kg body weight. The contents of dopamine (DA), levodopa, dihydroxy-phenyl-acetic acid and homovanillic acid in the striatum were then examined by high-performance liquid chromatography with a fluorescence detector. Quantitative polymerase chain reaction and western blotting were used to analyze the mRNA and protein expression of aromatic amino acid decarboxylase (AADC), tyrosine hydroxylase, orphan nuclear hormone (Nurr1), dopamine transporter (DAT), vesicular monoamine transporter 2 (VMAT2), monoamine oxidase (MAO) and catechol-O-methyltransferase (COMT). The results indicated that simazine influenced the synthesis, transport and metabolism of DA and led to a reduction of DA levels in the striatum. One potential underlying mechanism is decreased levels of Nurr1, DAT and VMAT2 impacting upon the transport of DA; another is the decreased level of AADC and increased levels of MAO and COMT impacting upon the synthesis and metabolism of DA. These factors may eventually lead to neurological disorders of the dopaminergic system.

Mechanisms of Gene-Environment Interactions in Parkinson's Disease

PURPOSE OF REVIEW

The purpose of the study was to discuss the main mechanisms associated with environmental and genetic factors that contribute to the development of Parkinson's disease (PD).

RECENT FINDINGS

Novel genetic contributors to PD are being identified at a rapid pace in addition to novel environmental factors. The discovery of mutations in alpha-synuclein and leucine-rich repeat kinase 2 causing inherited forms of PD along with epidemiological, in vitro, and in vivo studies identifying herbicides, pesticides, and metals as risk factors have dramatically improved our understanding of mechanisms involved in the development of PD. However, at the same time, these discoveries have also added layers of complexity to the disease. Within the last several years, the genetics associated with PD has dominated the field in many ways; however, the majority of PD cases are likely due to different combinations of environmental exposures and genetic susceptibility. The most common toxicants used to model PD including rotenone, paraquat, and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine have been shown to interact with many of the genes linked with PD such as alpha-synuclein. Therefore, an understanding of mechanisms common between genetic and environmental factors is essential for early detection and successful translation of potential therapies, which is the ultimate goal.

Occupational pesticide use and Parkinson's disease in the Parkinson Environment Gene (PEG) study

OBJECTIVE

To study the influence of occupational pesticide use on Parkinson's disease (PD) in a population with information on various occupational, residential, and household sources of pesticide exposure.

METHODS

In a population-based case control study in Central California, we used structured interviews to collect occupational history details including pesticide use in jobs, duration of use, product names, and personal protective equipment use from 360 PD cases and 827 controls. We linked reported products to California's pesticide product label database and identified pesticide active ingredients and occupational use by chemical class including fungicides, insecticides, and herbicides. Employing unconditional logistic regression, we estimated odds ratios and 95% confidence intervals for PD and occupational pesticide use.

RESULTS

Ever occupational use of carbamates increased risk of PD by 455%, while organophosphorus (OP) and organochlorine (OC) pesticide use doubled risk. PD risk increased 110-211% with ever occupational use of fungicides, herbicides, and insecticides. Using any pesticide occupationally for >10years doubled the risk of PD compared with no occupational pesticide use. Surprisingly, we estimated higher risks among those reporting use of personal protective equipment (PPE).

CONCLUSIONS

Our findings provide additional evidence that occupational pesticide exposures increase PD risk. This was the case even after controlling for other sources of pesticide exposure. Specifically, risk increased with occupational use of carbamates, OPs, and OCs, as well as of fungicides, herbicides, or insecticides. Interestingly, some types of PPE use may not provide adequate protection during pesticide applications.

An Evaluation of the Proposed Worker Protection Standard with Respect to Pesticide Exposure and Parkinson's Disease

Citing a lack of information, the U.S. Environmental Protection Agency prudently did not account for the benefits of averting many chronic diseases in analyzing the Worker Protection Standards (WPS) revisions. We demonstrate that sufficient information can exist, using the example of the benefits to agricultural workers of reduced Parkinson's disease (PD) due to reduced pesticide exposure. We define the benefits as the monetary value gained by improving quality of lives of people who would otherwise develop PD, plus the value of medical care cost averted and income not lost due to being healthy. For estimation, we use readily available parameters and obtain odds ratios of developing PD by conducting a meta-analysis of studies linking pesticide exposure to PD. The sensitivity analysis varies the number of agricultural workers affected by the regulation, the probability of being diagnosed with PD, the measurement and the timing of the benefits. Our initial assessment is that the reduced PD benefits would be a small fraction of the total WPS revision costs. However, if we define benefits as the common environmental economics willingness to pay to avoid PD incidence, then they become a substantial fraction of the costs. Our analysis demonstrates that the benefits of averting PD from the WPS revisions can be estimated using existing information, and that the results are most sensitive to the choice of valuation of benefits to the worker. We encourage other researchers to extend our framework to other chronic ailments.

Parkinson's disease and pesticides: A meta-analysis of disease connection and genetic alterations

Parkinson's disease (PD) is a globally prevalent, multifactorial disorder that occurs due to interactions between genetic and environmental factors. Observational studies have shown a link between exposure to pesticides and the risk of PD. We performed this study to systemically review published case-control studies and estimate quantitatively the association between pesticide exposure and PD. We searched Medline (through PubMed) for eligible case-control studies. The association between pesticide exposure and PD risk or occurrence of certain genetic alterations, related to the pathogenesis of PD was presented as odds ratios (OR) and pooled under the random effects model, using the statistical add-in (MetaXL, version 5.0). The pooled result showed that exposure to pesticides is linked to PD (OR 1.46, 95% CI [1.21, 1.77]), but there was a significant heterogeneity among included studies. Exposure to pesticides increased the risk of alterations in different PD pathogenesis-related genes, such as GST (OR 1.97, 95% CI [1.41, 2.76]), PON-1 (OR 1.32, 95% CI [1.09, 1.6]), MDR1 (OR 2.06, 95% CI [1.58, 2.68]), and SNCA genes (OR 1.28, 95% CI [1.02, 1.37]). There was no statistically significant association between exposure to pesticides and alteration of CYP2D6 (OR 1.19, 95% CI [0.91, 1.54]), SLC6A3 (OR 0.74, 95% CI [0.55, 1]), MnSOD (OR 1.45, 95% CI [0.97, 2.16]), NQO1 (OR 1.35, 95% CI [0.91, 2.01]), and PON-2 genes (OR 0.88, 95% CI [0.53, 1.45]). In conclusion, this meta-analysis provides evidence that pesticide exposure is significantly associated with the risk of PD and alterations in genes involved in PD pathogenesis. However, the underlying mechanism of this association and the effect of the duration of exposure or the type of pesticides should be addressed by future research.

RNA-Seq Expression Analysis of Enteric Neuron Cells with Rotenone Treatment and Prediction of Regulated Pathways

The enteric nervous system (ENS) is involved in the initiation and development of the pathological process of Parkinson's disease (PD). The effect of rotenone on the ENS may trigger the progression of PD through the central nervous system (CNS). In this study, we used RNA-sequencing (RNA-seq) analysis to examine differential expression genes (DEGs) and pathways induced by in vitro treatment of rotenone in the enteric nervous cells isolated from rats. We identified 45 up-regulated and 30 down-regulated genes. The functional categorization revealed that the DEGs were involved in the regulation of cell differentiation and development, response to various stimuli, and regulation of neurogenesis. In addition, the pathway and network analysis showed that the Mitogen Activated Protein Kinase (MAPK), Toll-like receptor, Wnt, and Ras signaling pathways were intensively involved in the effect of rotenone on the ENS. Additionally, the quantitative real-time polymerase chain reaction result for the selected seven DEGs matched those of the RNA-seq analysis. Our results present a significant step in the identification of DEGs and provide new insight into the progression of PD in the rotenone-induced model.

A future perspective on neurodegenerative diseases: nasopharyngeal and gut microbiota

Neurodegenerative diseases are considered a serious life-threatening issue regardless of age. Resulting nerve damage progressively affects important activities, such as movement, coordination, balance, breathing, speech and the functioning of vital organs. Reports on the subject have concluded that neurodegenerative disease can be caused by mutations of susceptible genes, alcohol consumption, toxins, chemicals and other unknown environmental factors. Although several diagnostic techniques can be used to determine aetiologies, the process is difficult and often fails. Research shows that nasopharyngeal and gut microbiota play important roles in brain to spinal cord coordination. However, no conclusive epidemiologic evidence is available on the roles played by respiratory and gut microbiota in the development of neurodegenerative diseases. Thus, understanding the connection between respiratory and gut microbiota and the nervous system could provide information on causal links. The present review describes future perspectives on the role played by nasopharyngeal and gut microbiota in the development of neurodegenerative diseases.

Immunohistochemical Changes in the Mouse Striatum Induced by the Pyrethroid Insecticide Permethrin

Epidemiological studies have linked insecticide exposure and Parkinson's disease. In addition, some insecticides produce damage or physiological disruption within the dopaminergic nigrostriatal pathway of non-humans. This study employed immunohistochemical analysis in striatum of the C57BL/6 mouse to clarify tissue changes suggested by previous pharmacological studies of the pyrethroid insecticide permethrin. Dopamine transporter, tyrosine hydroxylase, and glial fibrillary acidic protein immunoreactivities were examined in caudate-putamen to distinguish changes in amount of dopamine transporter immunoreactive protein from degeneration or other damage to dopaminergic neuropil. Weight-matched pairs of pesticide-treated and vehicle-control mice were dosed and sacrificed on the same days. Permethrin at 0.8, 1.5 and 3.0 mg/kg were the low doses and at 200 mg/kg the high dose. Brains from matched pairs of mice were processed on the same slides using the avidin-biotin technique. Four fields were morphometrically located in each of the serial sections of caudateputamen, digitally photographed, and immunopositive image pixels were counted and compared between members of matched pairs of permethrin-treated and vehicle-control mice. For low doses, only 3.0 mg/kg produced a significant decrease in dopamine transporter immunostaining. The high dose of permethrin did not produce a significant change in dopamine transporter or tyrosine hydroxylase immunostaining, but resulted in a significant increase in glial fibrillary acidic protein immunostaining. These data suggest that a low dose of permethrin can reduce the amount of dopamine transporter immunoreactive protein in the caudate-putamen. They also suggest that previously reported reductions in dopamine uptake of striatal synaptosomes of high-dose mice may be due to nondegenerative tissue damage within this region as opposed to reductions of dopamine transporter protein or death of nigrostriatal terminals. These data provide further evidence that insecticides can affect the primary neurodegenerative substrate of Parkinson's disease.