Ecogenetics of Parkinson's disease: prevalence and environmental aspects in rural areas

The neurotoxicity of pesticides: Implications for Parkinson's disease

Parkinson's disease (PD) is the fastest-growing neurodegenerative disorder worldwide, and no effective cure is currently available. Neuropathologically, PD is characterized by the selective degeneration of dopaminergic neurons in the substantia nigra and by the accumulation of alpha-synuclein (aSyn)-rich proteinaceous inclusions within surviving neurons. As a multifactorial disorder, approximately 85 % of PD cases are sporadic with unknown etiology. Among the many risk factors implicated in PD, exposure to neurotoxic pesticides stands out as a significant contributor. While the effects of many are still uncharacterized, it has already been shown that rotenone, paraquat, maneb, and dieldrin affect critical cellular pathways, including mitochondrial and proteasomal dysfunction, aSyn aggregation, autophagy dysregulation, and disruption of dopamine metabolism. With the constant rise in pesticide usage to meet the demands of a growing human population, the risk of environmental contamination and subsequent PD development is also increasing. This review explores the molecular mechanisms by which pesticide exposure influences PD development, shedding light on their role in the pathogenesis of PD and highlighting the need for preventative measures and regulatory oversight to mitigate these risks.

Modifiable risk factors associated with the risk of developing Parkinson's disease: a critical review

The etiology of Parkinson's disease (PD) is complex and multifactorial, depending on interactions involving environmental/lifestyle and genetic factors. The genetic aspects of the disease are becoming well characterized, while the environmental factors still need further investigation. In the present narrative review, we have described the most concrete evidence of associations between environmental factors and the risk of developing PD. Physical activity, healthy dietary patterns, smoking, and caffeine intake are protective factors against PD. Head trauma, consumption of milk and dairy products, and pesticide exposure were associated with a higher risk of developing PD. The associations of alcohol consumption, living in rural areas, farming, and consumption of well water with PD are still controversial. Results of several studies strongly suggest that diabetes mellitus is a risk factor for the development of PD, as well as the pre-diabetic state. Lower serum levels of uric acid were associated with an increased risk of developing PD and with worse clinical features and faster progression of symptoms. The protective effects of nonsteroidal antiinflammatory drugs use are controversial. Several other factors were potentially associated with the risk of developing PD: environmental pollutants such as organic solvents, exposure to sunlight, vitamin D deficiency, bullous pemphigoid, bipolar disorder, inflammatory bowel disease, irritable bowel syndrome, certain infections and agents, and essential tremor. Environmental factors are important risk markers for the development of PD. Understanding these risks and protective factors could lead to the implementation of risk-modifying actions for PD.

Environmental Risk Factors for Parkinson's Disease: A Critical Review and Policy Implications

The age-standardized prevalence of Parkinson's disease (PD) has increased substantially over the years and is expected to increase further. This emphasizes the need to identify modifiable risk factors of PD, which could form a logical entry point for the prevention of PD. The World Health Organization (WHO) has recommended reducing exposure to specific environmental factors that have been reported to be associated with PD, in particular pesticides, trichloroethylene (TCE), and air pollution. In this review we critically evaluate the epidemiological and biological evidence on the associations of these factors with PD and review evidence on whether these putative associations are causal. We conclude that when considered in isolation, it is difficult to determine whether these associations are causal, in large part because of the decades-long lag between relevant exposures and the incidence of manifest PD. However, when considered in tandem with evidence from complementary research lines (such as animal models), it is increasingly likely that these associations reflect harmful causal effects. Fundamentally, whilst we highlight some evidence gaps that require further attention, we believe the current evidence base is sufficiently strong enough to support our call for stronger policy action. © 2024 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Update: Protective and risk factors for Parkinson disease

We review the epidemiologic literature on potential protective and risk factors in Parkinson's Disease (PD). Prior research identified numerous possible protective and risk factors. Potential protective factors include tobacco abuse, physical activity, urate levels, NSAID use, calcium channel blocker use, statin use, and use of some α1-adrenergic antagonists. Some potential protective factors could be products of reverse causation, including increased serum urate, tobacco abuse, and coffee-tea-caffeine consumption. Potential risk factors include traumatic brain injury, pesticide exposure, organic solvent exposure, lead exposure, air pollution, Type 2 Diabetes, some dairy products, cardiovascular disease, and some infections including Hepatitis C, H. pylori, and COVID-19. Potential non-environmental risk factors include bipolar disorder, essential tremor, bullous pemphigoid, and inflammatory bowel disease. There is an inverse relationship with PD and risk of most cancers. Though many potential protective and risk factors for PD were identified, research has not yet led to unique, rigorous prevention trials or successful disease-modifying interventions. While efforts to reduce exposure to some industrial toxicants are well justified, PD incidence might be most effectively reduced by mitigation of risks, such as Type 2 Diabetes, air pollution, traumatic brain injury, or physical inactivity, that are general public health intervention targets.

DNA Damage and Parkinson's Disease

The etiology underlying most sporadic Parkinson's' disease (PD) cases is unknown. Environmental exposures have been suggested as putative causes of the disease. In cell models and in animal studies, certain chemicals can destroy dopaminergic neurons. However, the mechanisms of how these chemicals cause the death of neurons is not understood. Several of these agents are mitochondrial toxins that inhibit the mitochondrial complex I of the electron transport chain. Familial PD genes also encode proteins with important functions in mitochondria. Mitochondrial dysfunction of the respiratory chain, in combination with the presence of redox active dopamine molecules in these cells, will lead to the accumulation of reactive oxygen species (ROS) in dopaminergic neurons. Here, I propose a mechanism regarding how ROS may lead to cell killing with a specificity for neurons. One rarely considered hypothesis is that ROS produced by defective mitochondria will lead to the formation of oxidative DNA damage in nuclear DNA. Many genes that encode proteins with neuron-specific functions are extraordinary long, ranging in size from several hundred kilobases to well over a megabase. It is predictable that such long genes will contain large numbers of damaged DNA bases, for example in the form of 8-oxoguanine (8-oxoG), which is a major DNA damage type produced by ROS. These DNA lesions will slow down or stall the progression of RNA polymerase II, which is a term referred to as transcription stress. Furthermore, ROS-induced DNA damage may cause mutations, even in postmitotic cells such as neurons. I propose that the impaired transcription and mutagenesis of long, neuron-specific genes will lead to a loss of neuronal integrity, eventually leading to the death of these cells during a human lifetime.

Cost-effectiveness analysis of insecticide ban aimed at preventing Parkinson's disease in Central California

BACKGROUND

Our study assessed whether banning specific insecticides to reduce the PD burden in three Central California (CA) counties is cost-effective.

METHOD

We applied a cost-effectiveness analysis using a cohort-based Markov model to estimate the impact and costs of banning seven insecticides that were previously associated with PD in these counties as well as mixture exposures to some of these pesticides. We relied for our estimations on the cohort of 65- and 66-year-olds living in these counties who were unaffected by PD at baseline in 2020 and projected their incidence, costs, and reduction in quality-adjusted-life-years (QALY) loss due to developing PD over a 20-year period. We included a shiny app for modeling different scenarios (https://sherlockli.shinyapps.io/pesticide_pd_economics_part_2/).

RESULTS

According to our scenarios, banning insecticides to reduce the occurrence of PD in three Central CA counties was cost-effective relative to not banning insecticides. In the worst-case scenario of exposure to a single pesticide, methomyl, versus none would result in an estimated 205 (95 % CI: 75, 348) additional PD cases or 12 % (95 % CI: 4 %, 20 %) increase in PD cases over a 20-year period based on residential proximity to pesticide applications. The increase in PD cases due to methomyl would increase health-related costs by $72.0 million (95 % CI: $5.5 million, $187.4 million). Each additional PD patient due to methomyl exposure would incur $109,327 (95 % CI, $5554, $347,757) in costs per QALY loss due to PD. Exposure to methomyl based on workplace proximity to pesticide applications generated similar estimates. The highest PD burden and associated costs would be incurred from exposure to multiple pesticides simultaneously.

CONCLUSION

Our study provides an assessment of the cost-effectiveness of banning specific insecticides to reduce PD burden in terms of health-related QALYs and related costs. This information may help policymakers and stakeholders to make decisions concerning the regulation of pesticides.

Agricultural paraquat dichloride use and Parkinson's disease in California's Central Valley

BACKGROUND

Paraquat dichloride is currently among the most widely used commercial herbicides in the USA. In the present study, we provide epidemiological assessment of ambient paraquat exposure and Parkinson's disease (PD) risk in a population-based study of PD in agricultural regions of Central California.

METHODS

Based on 829 PD patients and 824 community controls, we assessed associations between ambient paraquat dichloride exposure and PD. We estimated residential and workplace proximity to commercial agricultural applications in three California counties since 1974 using the CA pesticide use reporting (PUR) data and land use maps. We evaluated any, duration and average intensity [pounds (0.45 kilograms) per acre per year] of exposure for paraquat in four time windows.

RESULTS

Ambient paraquat exposure assessed at both residence and workplace was associated with PD, based on several different exposure measures. The PD patients both lived and worked near agricultural facilities applying greater amounts of the herbicide than community controls. For workplace proximity to commercial applications since 1974, working near paraquat applications every year in the window [odds ratio (OR) = 2.15, 95% confidence interval (CI) = 1.46, 3.19] and a higher average intensity of exposure [per 10 pounds (4.54 kilograms), OR = 2.08, 95% CI = 1.31, 3.38] were both associated with an increased odds of PD. Similar associations were observed for residential proximity (duration: OR = 1.91, 95% CI = 1.30, 2.83; average intensity: OR = 1.72, 95% CI = 0.99, 3.04). Risk estimates were comparable for men and women, and the strongest odds were observed for those diagnosed at ≤60 years of age.

CONCLUSION

This study provides further indication that paraquat dichloride exposure increases the risk of Parkinson's disease.

Parkinson's Disease Is Predominantly an Environmental Disease

Parkinson's disease is the world's fastest growing brain disorder, and exposure to environmental toxicants is the principal reason. In this paper, we consider alternative, but unsatisfactory, explanations for its rise, including improved diagnostic skills, aging populations, and genetic causes. We then detail three environmental toxicants that are likely among the main causes of Parkinson's disease- certain pesticides, the solvent trichloroethylene, and air pollution. All three environmental toxicants are ubiquitous, many affect mitochondrial functioning, and all can access humans via various routes, including inhalation and ingestion. We reach the hopeful conclusion that most of Parkinson's disease is thus preventable and that we can help to create a world where Parkinson's disease is increasingly rare.

The Prevalence of Parkinson's Disease in Poland: Regional and Sex-Related Differences

Background

Given the growing evidence for an environmental contribution to the etiology of Parkinson's disease (PD), searching for local and regional differences in PD prevalence in multiple areas across the world may further clarify the role of environmental toxins.

Objective

To provide local and regional prevalence estimates of PD in Poland.

Methods

We analyzed the prevalence of PD and its trend over the last decade (2010 to 2019) based on data from the National Health Fund in Poland. We specifically examined sex differences in PD prevalence, as well as differences across Polish regions.

Results

During the above period, the prevalence of PD in Poland increased from 226 per 100,000 to 269 per 100,000 inhabitants. Unexpectedly, we found that PD was 1.2-times more common in women than men. The increase in prevalence over the past decade was different between both sexes: an increase from 250 to 283 per 100,000 for women (13.3% increase), and from 200 to 254 per 100,000 for men (27.1% increase). In addition, we observed differences in prevalence across different Polish regions, with some regions having up to 51% lower prevalence rates than others.

Conclusions

The prevalence of PD in Poland is in line with previously reported prevalence rates across Europe. However, unlike the situation in most of the world, PD was more prevalent in women than men. We discuss several possible explanations as well as potential measures that might help to reduce the growth of PD.

The Body, the Brain, the Environment, and Parkinson's Disease

The brain- and body-first models of Lewy body disorders predict that aggregated alpha-synuclein pathology usually begins in either the olfactory system or the enteric nervous system. In both scenarios the pathology seems to arise in structures that are closely connected to the outside world. Environmental toxicants, including certain pesticides, industrial chemicals, and air pollution are therefore plausible trigger mechanisms for Parkinson's disease and dementia with Lewy bodies. Here, we propose that toxicants inhaled through the nose can lead to pathological changes in alpha-synuclein in the olfactory system that subsequently spread and give rise to a brain-first subtype of Lewy body disease. Similarly, ingested toxicants can pass through the gut and cause alpha-synuclein pathology that then extends via parasympathetic and sympathetic pathways to ultimately produce a body-first subtype. The resulting spread can be tracked by the development of symptoms, clinical assessments, in vivo imaging, and ultimately pathological examination. The integration of environmental exposures into the brain-first and body-first models generates testable hypotheses, including on the prevalence of the clinical conditions, their future incidence, imaging patterns, and pathological signatures. The proposed link, though, has limitations and leaves many questions unanswered, such as the role of the skin, the influence of the microbiome, and the effects of ongoing exposures. Despite these limitations, the interaction of exogenous factors with the nose and the gut may explain many of the mysteries of Parkinson's disease and open the door toward the ultimate goal -prevention.

Towards improved screening of toxins for Parkinson's risk

Parkinson's disease (PD) is a chronic, progressive and disabling neurodegenerative disorder. The prevalence of PD has risen considerably over the past decades. A growing body of evidence suggest that exposure to environmental toxins, including pesticides, solvents and heavy metals (collectively called toxins), is at least in part responsible for this rapid growth. It is worrying that the current screening procedures being applied internationally to test for possible neurotoxicity of specific compounds offer inadequate insights into the risk of developing PD in humans. Improved screening procedures are therefore urgently needed. Our review first substantiates current evidence on the relation between exposure to environmental toxins and the risk of developing PD. We subsequently propose to replace the current standard toxin screening by a well-controlled multi-tier toxin screening involving the following steps: in silico studies (tier 1) followed by in vitro tests (tier 2), aiming to prioritize agents with human relevant routes of exposure. More in depth studies can be undertaken in tier 3, with whole-organism (in)vertebrate models. Tier 4 has a dedicated focus on cell loss in the substantia nigra and on the presumed mechanisms of neurotoxicity in rodent models, which are required to confirm or refute the possible neurotoxicity of any individual compound. This improved screening procedure should not only evaluate new pesticides that seek access to the market, but also critically assess all pesticides that are being used today, acknowledging that none of these has ever been proven to be safe from a perspective of PD. Importantly, the improved screening procedures should not just assess the neurotoxic risk of isolated compounds, but should also specifically look at the cumulative risk conveyed by exposure to commonly used combinations of pesticides (cocktails). The worldwide implementation of such an improved screening procedure, would be an essential step for policy makers and governments to recognize PD-related environmental risk factors.

Environmental neurology: Concepts and short history of an interdisciplinary approach to etiology, treatment and prevention

Environmental Neurology (EN), a sub-discipline of Neurology and Neurological Sciences, favors an interdisciplinary collaboration allowing a holistic approach to understanding the impact of environmental factors on the nervous system and their relationship with neurological diseases. Several examples of diseases and conditions show the large scope of subjects addressed by EN. The EN sub-discipline focuses on both individual and population issues thus joining patient care and public health, respectively. Neuropathogenesis is addressed by several major questions: How do the environment and nervous system interact? Which exogenous factors can trigger neurological disease? When, where and how do they act? What are the therapeutic implications, and how can these disorders be controlled or prevented. To answer such questions, we address the incentive for, philosophy of and methods developed by EN, which seeks to safeguard Brain Health and, thus, the quality of life.

Rotenone-Induced Model of Parkinson's Disease: Beyond Mitochondrial Complex I Inhibition

Parkinson's disease (PD) is usually diagnosed through motor symptoms that make the patient incapable of carrying out daily activities; however, numerous non-motor symptoms include olfactory disturbances, constipation, depression, excessive daytime sleepiness, and rapid eye movement at sleep; they begin years before motor symptoms. Therefore, several experimental models have been studied to reproduce several PD functional and neurochemical characteristics; however, no model mimics all the PD motor and non-motor symptoms to date, which becomes a limitation for PD study. It has become increasingly relevant to find ways to study the disease from its slowly progressive nature. The experimental models most frequently used to reproduce PD are based on administering toxic chemical compounds, which aim to imitate dopamine deficiency. The most used toxic compounds to model PD have been 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and 6-hydroxydopamine (6-OHDA), which inhibit the complex I of the electron transport chain but have some limitations. Another toxic compound that has drawn attention recently is rotenone, the classical inhibitor of mitochondrial complex I. Rotenone triggers the progressive death of dopaminergic neurons and α-synuclein inclusions formation in rats; also, rotenone induces microtubule destabilization. This review presents information about the experimental model of PD induced by rotenone, emphasizing its molecular characteristics beyond the inhibition of mitochondrial complex I.

Pesticides expenditures by farming type and incidence of Parkinson disease in farmers: A French nationwide study

BACKGROUND

Professional pesticides exposure is associated with PD risk, but it remains unclear whether specific products, which strongly depend on farming type, are specifically involved. We performed a nationwide ecological study to examine the association of pesticides expenditures for the main farming types with PD incidence in French farmers.

METHODS

We used the French National Health Insurance database to identify incident PD cases in farmers (2010-2015). We combined data on pesticides expenditures with the agricultural census to compute pesticides expenditures for nine farming types in 2000 in 3571 French cantons. The association between pesticides expenditures and PD age/sex standardized incidence was examined using multilevel Poisson regression, adjusted for smoking, neurologists' density, and deprivation index.

RESULTS

10,282 incident PD cases were identified. Cantons with the highest pesticides expenditures for vineyards without designation of origin were characterized by 16% (95% CI = 6-28%) higher PD incidence (p-trend corrected for multiple testing = 0.006). This association was significant in men and older farmers. There was no association with pesticides expenditures for other farming types, including vineyards with designation of origin.

CONCLUSIONS

PD incidence increased significantly with pesticides expenditures in vineyards without designation of origin characterized by high fungicide use. This result suggests that agricultural practices and pesticides used in these vineyards may play a role in PD and that farmers in these farms should benefit from preventive measures aiming at reducing exposure. Our study highlights the importance of considering farming type in studies on pesticides and PD and the usefulness of pesticides expenditures for exposure assessment.

The vermiform appendix impacts the risk of developing Parkinson's disease

The pathogenesis of Parkinson's disease (PD) involves the accumulation of aggregated α-synuclein, which has been suggested to begin in the gastrointestinal tract. Here, we determined the capacity of the appendix to modify PD risk and influence pathogenesis. In two independent epidemiological datasets, involving more than 1.6 million individuals and over 91 million person-years, we observed that removal of the appendix decades before PD onset was associated with a lower risk for PD, particularly for individuals living in rural areas, and delayed the age of PD onset. We also found that the healthy human appendix contained intraneuronal α-synuclein aggregates and an abundance of PD pathology-associated α-synuclein truncation products that are known to accumulate in Lewy bodies, the pathological hallmark of PD. Lysates of human appendix tissue induced the rapid cleavage and oligomerization of full-length recombinant α-synuclein. Together, we propose that the normal human appendix contains pathogenic forms of α-synuclein that affect the risk of developing PD.

Phytoconstituents in the Management of Pesticide Induced Parkinson’s Disease- A Review

Recent studies have suggested that environmental factors have a crucial role in triggering and/ or propagating the pathological changes in Parkinson’s disease (PD). Although many studies have been and being performed by utilizing MPTP like chemicals to study the effectiveness of new extracts and compounds in PD, a little focus was made on the role of pesticides. Since agricultural fields account for 37.7% of land area worldwide and the use of pesticides is an important risk factor in neurodegeneration, there is a crucial need to focus on the association between pesticides and PD. Benomyl, a benzimidazole fungicide is being widely used in India in cultivation of tropical crops. Studies prove the chronic exposure of benomyl leads to aldehyde dehydrogenase inhibition caused DOPAL toxicity, subsequently leading to dopamine degradation and Parkinson’s disease. Till date, there is no remedy for pesticide induced Parkinson’s disease. This review provides an insight of the pathophysiological aspects of pesticide induced Parkinson’s disease and also enlightens the importance of aldehyde dehydrogenase enzyme in neuroprotection.

Novel Synthesis of Substituted 2-Trifluoromethyl and 2-Perfluoroalkyl N-Arylpyridinium Compounds-Mechanistic Insights

We report a new one-pot synthesis of 2-trifluoromethylated/2-perfluoroalkylated N-aryl-substituted pyridiniums, 5,6,7,8-tetrahydroquinoliniums and 6,7,8,9-tetrahydro-5H-cyclohepta[b]-pyridinium compounds starting from an activated β-dicarbonyl analogue (here a perfluoro-alkylated gem-iodoacetoxy derivative), an aromatic amine and a (cyclic or acyclic) ketone. The key step of this multicomponent reaction, involves the formation of a 3-perfluoroalkyl-N,N’-diaryl-1,5-diazapentadiene intermediate, various examples of which were isolated and characterized for the first time, together with investigation of their reactivity. We propose a mechanism involving a concurrent inverse electron demand Diels-Alder or Aza-Robinson cascade cyclisation, followed by a bis-de-anilino-elimination. Noteworthy, a meta-methoxy substituent on the aniline directs the reaction towards a 2-perfluoroalkyl-7-methoxyquinoline, resulting from the direct cyclization of the diazapentadiene intermediate, instead of pyridinium formation. This is the first evidence of synthesis of pyridinium derivatives from activated β-dicarbonyls, ketones, and an aromatic amine, the structures of which (both reactants and products) being analogous to species involved in biological systems, especially upon neurodegenerative diseases such as Parkinson’s. Beyond suggesting chemical/biochemical analogies, we thus hope to outline new research directions for understanding the mechanism of in vivo formation of pyridiniums, hence possible pharmaceutical strategies to better monitor, control or prevent it.

Spatial Distribution of Parkinson’s Disease Prevalence in Québec by Hydrographic Region

The association between environmental exposures and Parkinson’s disease continues to garner interest. In the late 1980s, Barbeau et al. reported in the Canadian Journal of Neurological Sciences a heterogeneous distribution of Parkinson’s disease cases across the province of Québec by hydrographic region. Here we report the findings of a validation study based on data obtained from the Québec medication insurance program–information which was unavailable to the previous group. Similar to Barbeau et al., our analysis showed a heterogeneous distribution of cases across the province with higher prevalence in the same region of interest, in addition to other areas.

Effects of decreased dopamine transporter levels on nigrostriatal neurons and paraquat/maneb toxicity in mice

How genetic variations in the dopamine transporter (DAT) combined with exposure to environmental toxins modulate the risk of Parkinson's disease remains unclear. Using unbiased stereology in DAT knock-down mice (DAT-KD) and wild-type (WT) littermates, we found that decreased DAT caused a loss of tyrosine hydroxylase-positive (dopaminergic) neurons in subregions of the substantia nigra pars compacta at 3-4 days, 5 weeks, and 18 months of age. Both genotypes lost dopaminergic neurons with age and remaining neurons at 11 months were resilient to paraquat/maneb. In 5-week-old mice, the toxins decreased substantia nigra pars compacta dopaminergic neurons in both genotypes but less in DAT-KD. Regional analysis revealed striking differences in the subsets of neurons affected by low DAT, paraquat/maneb, and aging. In particular, we show that a potentially protective effect of low DAT against toxin exposure is not sufficient to reduce death of all nigrostriatal dopaminergic neurons. Thus, different regional vulnerability of nigrostriatal dopaminergic neurons may contribute to an increased risk of developing Parkinson's disease when multiple factors are combined.

Environmental Exposures and Parkinson's Disease

Parkinson’s disease (PD) affects millions around the world. The Braak hypothesis proposes that in PD a pathologic agent may penetrate the nervous system via the olfactory bulb, gut, or both and spreads throughout the nervous system. The agent is unknown, but several environmental exposures have been associated with PD. Here, we summarize and examine the evidence for such environmental exposures. We completed a comprehensive review of human epidemiologic studies of pesticides, selected industrial compounds, and metals and their association with PD in PubMed and Google Scholar until April 2016. Most studies show that rotenone and paraquat are linked to increased PD risk and PD-like neuropathology. Organochlorines have also been linked to PD in human and laboratory studies. Organophosphates and pyrethroids have limited but suggestive human and animal data linked to PD. Iron has been found to be elevated in PD brain tissue but the pathophysiological link is unclear. PD due to manganese has not been demonstrated, though a parkinsonian syndrome associated with manganese is well-documented. Overall, the evidence linking paraquat, rotenone, and organochlorines with PD appears strong; however, organophosphates, pyrethroids, and polychlorinated biphenyls require further study. The studies related to metals do not support an association with PD.

Neurotoxic Effects Induced by Intracerebral and Systemic Injection of Paraquat in Rats

1 The neurotoxic effects elicited by paraquat after systemic and intracerebral injection were studied in rats.

2 Intrahippocampal microinfusion of paraquat (0.1 μmol) produced behavioural stimulation and electrocortical (ECoG) excitation followed, at 24 h, by multifocal brain damage. Similarly, microinfusion of paraquat (0.2-0.4 μmol) into the locus coeruleus, substantia nigra or into the raphe nuclei, where noradrenergic, dopaminergic and serotonergic neurons are present, respectively, elicited potent excitotoxic effects (n=6 rats per dose and area). A lower dose (0.01 μmol) of the herbicide or injection of the vehicle (1.0 μl) did not produce any behavioural, ECoG or neurodegenerative effect.

3 After systemic administration, paraquat (20 mg kg-1 s.c.) evoked limbic motor seizures and ECoG epileptogenic discharges; in 10 out of 15 treated rats neuronal cell death was observed in the pyriform cortex, but not in other brain regions. A dose of 5 mg kg-1 was ineffective.

4 Among the regions of the brain studied, high concentrations of paraquat were detected in the pyriform cortex 24 h after systemic administration (5.0 and 20 mg kg -1 s.c.) lower levels being observed in the caudate nucleus.

5 In conclusion, paraquat, given systemically or intracerebrally in rats produces neurodegenerative effects.

Occupational Characteristics and Patterns as Risk Factors for Parkinson's Disease: A Case Control Study

BACKGROUND

Associations have been reported between the risk of Parkinson's disease (PD) and employment in certain fields. Most studies have focused on toxic exposures as potential causal explanations. However, PD also has been associated with personality characteristics that may influence occupational choices and patterns.

OBJECTIVE

This study evaluates the role of personality as indicated by occupational choices and employment patterns in the risk for PD.

METHODS

In-person interviews were conducted to assess occupational histories and early-adult personality indicators among 89 PD patients and 99 controls.

RESULTS

PD cases had fewer lifetime jobs than controls (mean for cases = 4.38 ± 2.20; mean for controls = 5.00 ± 2.26; p = 0.03). Among women, PD was positively associated with more complex work with people (OR = 1.45, 95% CI 1.12-1.89), representing a 95% increased risk for PD comparing women with the greatest complexity of work with those requiring the least complexity of work with people. Women PD cases also performed less complex work with things compared with controls (OR = 0.69 (95% CI 0.53-0.90)), translating into a 13-fold increased risk for PD among women whose work involved the least complex work with things compared with the most. The numbers of jobs and job types were associated with taking more activity risks as a young-adult (r = 0.19, p = 0.02; r = 0.26, p = 0.001, respectively).

CONCLUSIONS

Cases with PD held fewer lifetime jobs compared with controls. Occupational complexity was associated with the risk for PD among women, but not men. Further consideration of the possible influence of personality on occupational choices is warranted.

Facteurs environnementaux dans l'étiologie de la maladie de Parkinson

We examined the role of the environment in the development of Parkinson's disease (PD). A group of 42 parkinsonians have been compared with a group of 84 matched controls. The epidemiological study (1987-1989) covered the territory of the Community Health Department of Valleyfield, in southern Quebec (Canada). Odds ratio adjusted for age and sex were calculated for seven environmental factors. A decreased risk for PD was associated with residence in rural areas (OR: 0.31; p ≤ 0.05) and residence near industry or mining (OR: 0.15; p ≤ 0.05). An increased risk for PD seems to be associated with occupational exposure to the three metals Mn, Fe and Al (OR: 2.28; p = 0.07) especially when the duration of exposure is longer than 30 years (OR: 13.64; p ≤ 0.05). Other environmental factors not found to be associated with PD were: pesticides manipulation, farm work, industrial work and well water consumption.

Younger age at onset of sporadic Parkinson's disease among subjects occupationally exposed to metals and pesticides

An earlier age at onset of Parkinson's disease (PD) has been reported to be associated with occupational exposures to manganese and hydrocarbon solvents suggesting that exposure to neurotoxic chemicals may hasten the progression of idiopathic PD. In this study the role of occupational exposure to metals and pesticides in the progression of idiopathic PD was assessed by looking at age at disease onset. The effects of heritable genetic risk factors, which may also influence age at onset, was minimized by including only sporadic cases of PD with no family history of the disease (n=58). Independent samples Student t-test revealed that subjects with occupational exposure to metals and/or pesticides (n=36) were significantly (p=0.013) younger than unexposed controls (n=22). These subjects were then divided into three groups [high (n=18), low (n=18), and unexposed (n=22)] to ascertain if duration of exposure further influenced age at onset of PD. One-way ANOVA revealed that subjects in the high exposure group were significantly (p=0.0121) younger (mean age: 50.33 years) than unexposed subjects (mean age: 60.45 years). Subjects were also stratified by exposure type (metals vs. pesticides). These results suggest that chronic exposure to metals and pesticides is associated with a younger age at onset of PD among patients with no family history of the disease and that duration of exposure is a factor in the magnitude of this effect.

Inhibition of polyisoprenylated methylated protein methyl esterase by synthetic musks induces cell degeneration

Synthetic fragrances are persistent environmental pollutants that tend to bioaccumulate in animal tissues. They are widely used in personal care products and cleaning agents. Worldwide production of Galaxolide and Tonalide are in excess of 4500 tons annually. Because of their widespread production and use, they have been detected in surface waters and fish in the US and Europe. Consumption of contaminated water and fish from such sources leads to bioaccumulation and eventual toxicity. Since fragrances and flavors bear structural similarities to polyisoprenes, it was of interest to determine whether toxicity by Galaxolide and Tonalide may be linked with polyisoprenylated methylated protein methyl esterase (PMPMEase) inhibition. A concentration-dependent study of PMPMEase inhibition by Galaxolide and Tonalide as well as their effects on the degeneration of cultured cells were conducted. Galaxolide and Tonalide inhibited purified porcine liver PMPMEase with Ki values of 11 and 14 μM, respectively. Galaxolide and Tonalide also induced human cancer cell degeneration with EC50 values of 26 and 98 μM (neuroblastoma SH-SY5Y cells) and 58 and 14 μM (lung cancer A549 cells), respectively. The effects on cell viability correlate well with the inhibition of PMPMEase activity in the cultured cells. Molecular docking analysis revealed that the binding interactions are most likely between the fragrance molecules and hydrophobic amino acids in the active site of the enzyme. These results appear to suggest that the reported neurotoxicity of these compounds may be associated with their inhibition of PMPMEase. Exposure to fragrances may pose a significant risk to individuals predisposed to developing degenerative disorders.

Pesticides and human chronic diseases: evidences, mechanisms, and perspectives

Along with the wide use of pesticides in the world, the concerns over their health impacts are rapidly growing. There is a huge body of evidence on the relation between exposure to pesticides and elevated rate of chronic diseases such as different types of cancers, diabetes, neurodegenerative disorders like Parkinson, Alzheimer, and amyotrophic lateral sclerosis (ALS), birth defects, and reproductive disorders. There is also circumstantial evidence on the association of exposure to pesticides with some other chronic diseases like respiratory problems, particularly asthma and chronic obstructive pulmonary disease (COPD), cardiovascular disease such as atherosclerosis and coronary artery disease, chronic nephropathies, autoimmune diseases like systemic lupus erythematous and rheumatoid arthritis, chronic fatigue syndrome, and aging. The common feature of chronic disorders is a disturbance in cellular homeostasis, which can be induced via pesticides' primary action like perturbation of ion channels, enzymes, receptors, etc., or can as well be mediated via pathways other than the main mechanism. In this review, we present the highlighted evidence on the association of pesticide's exposure with the incidence of chronic diseases and introduce genetic damages, epigenetic modifications, endocrine disruption, mitochondrial dysfunction, oxidative stress, endoplasmic reticulum stress and unfolded protein response (UPR), impairment of ubiquitin proteasome system, and defective autophagy as the effective mechanisms of action.

Effects of cypermethrin on the dopaminergic neurons in the progressive hemiparkinsonian rats

Cypermethrin is a potent pesticide derived from natural pyrethrin of the chrysanthemum plant. Cypermethrin has been known to modulate the blood-brain barrier and induce oxidative stress in rats. The oxidative stresses leading to increased reactive oxygen species generation have been identified within the degeneration of the dopaminergic (DA) neuron. However, in testing cypermethrin for its relationship to the degeneration of DA neurons, an experimental study has not yet been done. This study was designed to investigate the effects of cypermethrin on the DA neurons in the substantia nigra of normal and progressive hemiparkinsonian rats. The degree of degeneration of DA neurons was evaluated by tyrosine hydroxylase (TH) immunohistochemistry and forepaw adjusting step (FAS) test. The administration of cypermethrin (15 and 75 mg/kg/day) to the normal rats for 15 days did not decrease the number of TH-immunopositive (TH-IP) DA neurons in the substantia nigra. However, the low dose (15 mg/kg/day) of cypermethrin enhanced the rate of decline of DA neurons in the substantia nigra of hemiparkinsonian rats at 10 days and 3 weeks (p < 0.05). Also, the number of FAS in cypermethrin-treated hemiparkinsonian rats was reduced more rapidly than that of cypermethrin not-treated hemiparkinsonian rats at 10 days, 3 weeks, and 6 weeks (p < 0.05). These results suggest that cypermethrin per se cannot directly induce the degeneration of DA neurons but can accelerate a toxic effect on the degeneration of DA neurons in the progressive hemiparkinsonian rats.

Pesticide exposure and Parkinson's disease: epidemiological evidence of association

It has been suggested that exposure to pesticides might be involved in the etiology of Parkinson's disease (PD). We conducted an updated systematic review of the epidemiologic literature over the past decade on the relationship between pesticide exposure and PD, using the MEDLINE database. Despite methodological differences, a significantly increased PD risk was observed in 13 out of 23 case-control studies that considered overall exposure to pesticides (risk estimates of 1.1-2.4) and in 10 out of 12 studies using other research designs (risk estimates of 2 or higher). Various studies found stronger associations in genetically susceptible individuals. Among a growing number of studies on the effects of exposure to specific pesticides (n=20), an increased PD risk has been associated with insecticides, especially chlorpyrifos and organochlorines, in six studies (odds ratios of 1.8-4.4), and with the herbicide paraquat, the fungicide maneb or the combination of both. Findings considerably strengthen the evidence that exposure to pesticides in well water may contribute to PD, whereas studies of farming and rural residence found inconsistent or little association with the disease. Taken together, this comprehensive set of results suggests that the hypothesis of an association between pesticide exposure and PD cannot be ruled out. However, inadequate data on consistent responses to exposure hinder the establishment of a causal relationship with PD. Given the extensive worldwide use of many pesticides, further studies are warranted in larger populations that include detailed quantitative data on exposure and determination of genetic polymorphisms.

Epidemiology and etiology of Parkinson's disease: a review of the evidence

The etiology of Parkinson's disease (PD) is not well understood but likely to involve both genetic and environmental factors. Incidence and prevalence estimates vary to a large extent-at least partly due to methodological differences between studies-but are consistently higher in men than in women. Several genes that cause familial as well as sporadic PD have been identified and familial aggregation studies support a genetic component. Despite a vast literature on lifestyle and environmental possible risk or protection factors, consistent findings are few. There is compelling evidence for protective effects of smoking and coffee, but the biologic mechanisms for these possibly causal relations are poorly understood. Uric acid also seems to be associated with lower PD risk. Evidence that one or several pesticides increase PD risk is suggestive but further research is needed to identify specific compounds that may play a causal role. Evidence is limited on the role of metals, other chemicals and magnetic fields. Important methodological limitations include crude classification of exposure, low frequency and intensity of exposure, inadequate sample size, potential for confounding, retrospective study designs and lack of consistent diagnostic criteria for PD. Studies that assessed possible shared etiological components between PD and other diseases show that REM sleep behavior disorder and mental illness increase PD risk and that PD patients have lower cancer risk, but methodological concerns exist. Future epidemiologic studies of PD should be large, include detailed quantifications of exposure, and collect information on environmental exposures as well as genetic polymorphisms.

Long term exposure to cypermethrin induces nigrostriatal dopaminergic neurodegeneration in adult rats: postnatal exposure enhances the susceptibility during adulthood

The study aimed to investigate the effects of cypermethrin on biochemical, histopathological, and motor behavioral indices of the nigrostriatal dopaminergic system in adult rats treated with or without cypermethrin (1/10 adult dose) during postnatal days 5-19. Spontaneous locomotor activity (SLA) and rotarod tests were performed to assess motor behavior. Levels of dopamine, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in the striatum, and tyrosine hydroxylase (TH) immunoreactivity and 4',6-diamidino-2-phenylindole (DAPI)/Fluoro-Jade B staining in the substantia nigra were measured to assess dopaminergic neurodegeneration. Postnatal treated animals did not exhibit significant changes in any measured parameters. The significant reduction in the time of stay on rotarod, spontaneous locomotor activity, dopamine, 3,4-dihydroxyphenylacetic acid, and tyrosine hydroxylase immunoreactivity while an increase in homovanillic acid level and Fluoro-Jade B-positive cells were observed in cypermethrin treated adult rats. These changes were more pronounced in the animals treated with cypermethrin during postnatal days followed by adulthood compared with adulthood alone. The results obtained thus demonstrate that exposure to cypermethrin during adulthood induces dopaminergic neurodegeneration in rats and postnatal exposure enhances the susceptibility of animals to dopaminergic neurodegeneration if rechallenged during adulthood.

Alzheimer's disease and blood-brain barrier function-Why have anti-beta-amyloid therapies failed to prevent dementia progression?

Proteopathies of the brain are defined by abnormal, disease-inducing protein deposition that leads to functional abrogation and death of neurons. Immunization trials targeting the removal of amyloid-beta plaques in Alzheimer's disease have so far failed to stop the progression of dementia, despite autopsy findings of reduced plaque load. Here, we summarize current knowledge of the relationship between AD pathology and blood-brain barrier function, and propose that the activation of the excretion function of the blood-brain barrier might help to achieve better results in trials targeting the dissolution of cerebral amyloid-beta aggregates. We further discuss a possible role of oligomers in limiting the efficacy of immunotherapy.

Neurotoxicity of pesticides

Several pesticides such as organophosphates, carbamates and the organochlorine pesticides directly target nervous tissue as their mechanism of toxicity. In several others, such as the fumigants, the nervous system is affected by toxicological mechanisms that diffusely affect most or all tissues in the body. Both the central and peripheral nervous system are involved in the acute toxidromes of many pesticides resulting in acute short-term effects. There is strong human epidemiological evidence for persistent nervous system damage following acute intoxication with several important pesticide groups such as organophosphates and certain fumigants. However, whether persistent nervous system damage follows chronic low-level exposure to pesticides in adults (particularly organophosphpates), and whether in utero and/or early childhood exposure leads to persistent nervous system damage, is a subject of study at present. Parkinson's Disease, one of the most common chronic central nervous system diseases, has been linked to pesticide exposure in some studies, but other studies have failed to find an association. Several new pesticidal chemicals such as the neo-nicotinoids and fipronil have central nervous system effects, but only case reports are available to date on acute human intoxications with several of these. Little data are yet available on whether long-term effects result from these chemicals. Several ongoing or recently completed studies should add valuable insight into the effects of pesticides on the human nervous system particularly the effect of low-dose, chronic exposure both in adults and children.

Epidemiologic studies of environmental exposures in Parkinson's disease

Parkinson's disease (PD) is the most common cause of the parkinsonian syndromes and the most frequent neurodegenerative disease after Alzheimer's disease. Because of the ageing of Western populations, an increasing number of persons will be affected with PD in the future and neither curative treatments nor preventive measures have been identified. PD is considered as a multifactorial disease, resulting from the effect of environmental factors and genetic susceptibility. Increasing age and male sex appear to be associated with an increased risk of PD. In addition, recent epidemiological studies have identified environmental exposures that influence the risk of PD. This review provides an overview of the epidemiologic evidence for environmental etiologies in PD; we will focus on two environmental exposures that have been quite consistently associated with PD -- cigarette smoking and pesticide exposure -- and will summarize briefly the findings for other exposures. Understanding the mechanisms underlying these epidemiological associations is an essential step for the understanding of the etiology of this neurodegenerative condition and, ideally, to develop neuroprotective drugs.

Pesticide exposure exacerbates alpha-synucleinopathy in an A53T transgenic mouse model

The factors initiating or contributing to the pathogenesis of Parkinson's disease and related neurodegenerative synucleinopathies are still largely unclear, but environmental factors such as pesticides have been implicated. In this study, A53T mutant human alpha-synuclein transgenic mice (M83), which develop alpha-synuclein neuropathology, were treated with the pesticides paraquat and maneb (either singly or together), and their effects were analyzed. Immunohistochemical and biochemical analyses showed that chronic treatment of M83 transgenic mice with both pesticides (but not with either pesticide alone) drastically increased neuronal alpha-synuclein pathology throughout the central nervous system including the hippocampus, cerebellum, and sensory and auditory cortices. alpha-Synuclein-associated mitochondrial degeneration was observed in M83 but not in wild-type alpha-synuclein transgenic mice. Because alpha-synuclein inclusions accumulated in pesticide-exposed M83 transgenic mice without a motor phenotype, we conclude that alpha-synuclein aggregate formation precedes disease onset. These studies support the notion that environmental factors causing nitrative damage are closely linked to mechanisms underlying the formation of alpha-synuclein pathologies and the onset of Parkinson's-like neurodegeneration.

Pesticide exposure and risk for Parkinson's disease

OBJECTIVE

Chronic, low-dose exposure to pesticides is suspected to increase the risk for Parkinson's disease (PD), but data are inconclusive.

METHODS

We prospectively examined whether individuals exposed to pesticides have higher risk for PD than those not exposed. The study population comprised participants in the Cancer Prevention Study II Nutrition Cohort, a longitudinal investigation of US men and women initiated in 1992 by the American Cancer Society. Follow-up surveys were conducted in 1997, 1999, and 2001. The 143,325 individuals who returned the 2001 survey and did not have a diagnosis or symptoms of PD at baseline (1992) were included in the analyses.

RESULTS

Exposure to pesticides was reported by 7,864 participants (5.7%), including 1,956 farmers, ranchers, or fishermen. Individuals exposed to pesticides had a 70% higher incidence of PD than those not exposed (adjusted relative risk, 1.7; 95% confidence interval, 1.2-2.3; p = 0.002). The relative risk for pesticide exposure was similar in farmers and nonfarmers. No relation was found between risk for PD and exposure to asbestos, chemical/acids/solvents, coal or stone dust, or eight other occupational exposures.

INTERPRETATION

These data support the hypothesis that exposure to pesticides may increase risk for PD. Future studies should seek to identify the specific chemicals responsible for this association.

Prevalence of Parkinson’s disease in metropolitan and rural Queensland: A general practice survey

The prevalence of idiopathic Parkinson's disease (IPD) in Australia is unclear. We estimated the prevalence of IPD, and other forms of parkinsonism, through the study of typical caseloads in general practice. A random sample of general practitioners (GPs) throughout Queensland (401 responses from 528 validated practice addresses) was asked to estimate the numbers of patients with IPD and parkinsonism seen in the preceding year. The estimated prevalence of diagnosed IPD in Queensland was 146 per 100,000 (95% CI=136-155). A further 51 per 100,000 in the population were suspected by doctors to have IPD without formal diagnosis, whereas another 51 per 100,000 people may have non-idiopathic parkinsonism. Idiopathic Parkinson's disease was more common in rural than metropolitan areas. Although most GPs were confident in making diagnoses of IPD, the majority had little or no confidence in their ability to treat the disease, especially in its later stages. Support from neurologists was perceived by GPs to be very good in cities, but poor in remote areas.

Role of oxidative damage in protein aggregation associated with Parkinson's disease and related disorders

Parkinson's disease, the most common movement disorder, is characterized by the loss of brainstem neurons, specifically dopaminergic neurons in the substantia nigra, as well as the accumulation of neuronal cytoplasmic filamentous proteinaceous inclusions comprised of polymerized alpha-synuclein. It was reported recently that alpha-synuclein can induce the formation of filamentous tau inclusions, which are characteristic of disorders like Alzheimer's disease and Lewy body variant of Alzheimer's disease, suggesting that a similar mechanism may exist between alpha-synuclein fibrillogenesis and tau polymerization. Pathological brain inclusions comprised of alpha-synuclein or tau proteins are associated with a spectrum of neurodegenerative disorders, and oxidative and nitrative injury has been implicated in all of these diseases. However, the role of oxidative damage in alpha-synuclein and tau polymerization and pathological inclusion formation is complex. Differences in the level, type, and temporal sequence of the oxidative alterations appear to result in both inhibitory and stimulatory effects on the fibrillogenesis of these proteins.

Atypical parkinsonism on Guadeloupe, comparison with the parkinsonism-dementia complex of Guam, and environmental toxic hypotheses

INTRODUCTION

: On Guadeloupe, atypical parkinsonism is abnormally frequent, and represents 75% of progressive parkinsonism while Parkinson's disease (PD) accounts for only 25%, which is an inversed percentage in comparison with Europe. Herbal tea made with Annonaceae leaves (containing benzyltetrahydroisoquinolines (Be-TIQ), tetrahydroprotoberberines (THPB) and acetogenins (potent mitochondrial complex I inhibitors) are commonly used on Guadeloupe.

CLINICAL STUDY

: Of 265 patients studied on Guadeloupe, 66 (25%) had PD, and 199 (75%) had atypical parkinsonism. This latter group includes 58 patients (29%) with progressive supranuclear palsy (PSP), and 100 patients (50%) with unclassifiable parkinsonism (UP). This focus resembles the parkinsonism-dementia complex (PDC) described on Guam, where a very high prevalence of atypical parkinsonism has been reported since the second World War, including one-third of PSP. A preliminary case-control study on Guadeloupe showed a significant higher consumption of fruits and herbal tea of Annonaceae in atypical parkinsonian cases (PSP and unclassifiable parkinsonism, UP), compared to hospital controls and to idiopathic PD.

DISCUSSION

: The overrepresentation of atypical parkinsonism on Guadeloupe and Guam could be related to the consumption of plants containing (simultaneously) isoquinoline derivates which are toxic for dopaminergic neurons and inhibitors of the mitochondrial respiratory chain such as acetogenins. This hypothesis is in keeping with epidemiologic data and experimental studies showing neuronal loss after exposure to isoquinolines or acetogenins.

Blood-brain barrier dysfunction in parkinsonian midbrain in vivo

Parkinson's disease (PD) is associated with a loss of neurons from the midbrain. The cause of PD is unknown, but it is established that certain neurotoxins can cause similar syndromes. The brain is normally protected from these noxious blood-borne chemicals by the blood-brain barrier which includes specialized proteins on the inside of blood vessels in the brain. These act as molecular efflux pumps and P-glycoprotein (P-gp) is an abundant representative. Vulnerability to PD appears codetermined by the genotype for the P-gp gene. We hypothesized that PD patients have reduced P-gp function in the blood-brain barrier. We used positron emission tomography to measure brain uptake of [(11)C]-verapamil, which is normally extruded from the brain by P-gp. Here, we show significantly elevated uptake of [(11)C]-verapamil (18%) in the midbrain of PD patients relative to controls. This is the first evidence supporting a dysfunctional blood-brain barrier as a causative mechanism in PD.

Environmental factors and Parkinson's disease: a case–control study in the Tuscany region of Italy

To date the aetiology of Parkinson's disease (PD) is unknown although both genetic susceptibility and environmental factors appear to play an important role in the development of the disease. Recent data have also indicated that chronic exposure to a common pesticide can reproduce the neurochemical, behavioral and neuropathological features of PD. The epidemiological studies previously carried on the prevalence of PD in population exposed to environmental factors have produced controversial results, probably because of different trial design and different analysis methods. A case-control retrospective study was conducted in a well-defined geographic area in Tuscany-Italy with the aim to identify environmental factors possibly related to PD. No significant difference between PD patients and control subjects was observed in time spent in rural or industrial residence, in well water drinking and in the exposure to herbicides and pesticides. A significant difference between patients with PD and controls was reported for cigarette smoking, controls resulting more likely cigarette smokers in comparison with PD patients. The present findings support the view of a protective effect of cigarette smoking and do not show any significant association between environmental factors and the risk of development of PD.

Disease modification in Parkinson's disease

Several separate gene mutations have now been identified in familial Parkinson's disease and important environmental influences modulating risk for the idiopathic form of the disease have also been recognised. These insights have provided important clues in the development of disease modifying therapies. Some compounds have already been shown to potentially delay disease progression in early clinical trials. The most important challenge, particularly for those drugs that might have a symptomatic effect, is defining appropriate markers that will confirm a neuroprotective effect.