Association between ambient air pollution and multiple sclerosis: a systemic review and meta-analysis

Causal relationships between genetically predicted particulate air pollutants and neurodegenerative diseases: A two-sample Mendelian randomization study

Accumulating observational studies have linked particulate air pollutants to neurodegenerative diseases (NDDs). However, the causal links and the direction of their associations remain unclear. Therefore, we adopted a two-sample Mendelian randomization (TSMR) design using the GWAS-based genetic instruments of particulate air pollutants (PM2.5 and PM10) from the UK Biobank to explore their causal influence on four common neurodegenerative diseases. Estimates of causative relationships were generated by the Inverse variance weighted (IVW) method with multiple sensitive analyses. The heterogeneity and pleiotropy tests were additionally performed to verify whether our findings were robust. Genetically predicted PM2.5 and PM10 could elevate the occurrence of AD (odds ratio [OR] = 2.22, 95 % confidence interval [CI] 1.53-3.22, PIVW = 2.85×10-5, PFalsediscovery rate[FDR]= 2.85×10-4 and OR = 2.41, 95 % CI: 1.26-4.60, PIVW = 0.008, PFDR=0.039, respectively). The results were robust in sensitive analysis. However, no evidence of causality was found for other NDDs. Our present study suggests that PM2.5 and PM10 have a detrimental effect on AD, which indicates that improving air quality to prevent AD may have pivotal public health implications.

Environmental factors related to multiple sclerosis progression

Multiple Sclerosis (MS) is a complex neurological disease which prevalence is increasing worldwide. The impact of environmental factors on MS susceptibility has already been defined and highlighted in many previous reports, particularly vitamin D or ultraviolet B light exposure, Epstein-Barr virus (EBV) infection, obesity, and smoking. There is increasing evidence that environmental and lifestyle factors are not only important in triggering MS but are also implicated in MS progression. Low sun exposure and vitamin D deficiency exhibit a strong relationship with disease progression in both animal and human studies. The gestational period seems also to impact long-term disease progression as January's babies had a higher risk of requiring walking assistance than those born in other months. The implication of EBV in neurodegeneration and MS progression was also suggested even though its specific targets and mechanisms are still unclear. Cigarette smoking is correlated with faster clinical progression. The association of obesity and smoking seems to be associated with a faster progression and an increased rate of brain atrophy. Although the effect of air pollution on MS pathogenesis remains not fully understood, exposure to polluted air can stimulate several mechanisms that might contribute to MS severity. People with MS with active disease have an altered microbiota compared to patients in the remission phase. Cardiovascular comorbidities, epilepsy, and depression are also associated with a more severe disability accrual. Knowledge about MS modifiable risk factors of progression need to be incorporated into everyday clinical practice in order to ameliorate disease outcomes.

The lung-brain axis in multiple sclerosis: Mechanistic insights and future directions

Multiple sclerosis is a chronic inflammatory demyelinating disease of the central nervous system with progressive lifelong disability. Current treatments are particularly effective at the early inflammatory stage of the disease but associate with safety concerns such as increased risk of infection. While clinical and epidemiological evidence strongly support the role of a bidirectional communication between the lung and the brain in MS in influencing disease risk and severity, the exact processes underlying such relationship appear complex and not fully understood. This short review aims to summarize key findings and future perspectives that might provide new insights into the mechanisms underpinning the lung-brain axis in MS.

Air Pollution-Related Neurotoxicity Across the Life Span

Air pollution is a complex mixture of gases and particulate matter, with adsorbed organic and inorganic contaminants, to which exposure is lifelong. Epidemiological studies increasingly associate air pollution with multiple neurodevelopmental disorders and neurodegenerative diseases, findings supported by experimental animal models. This breadth of neurotoxicity across these central nervous system diseases and disorders likely reflects shared vulnerability of their inflammatory and oxidative stress-based mechanisms and a corresponding ability to produce brain metal dyshomeo-stasis. Future research to define the responsible contaminants of air pollution underlying this neurotoxicity is critical to understanding mechanisms of these diseases and disorders and protecting public health.

Impact of long-term air pollution exposure on incidence of neurodegenerative diseases: A protocol for a systematic review and exposure-response meta-analysis

BACKGROUND

Ambient air pollution is a pervasive and ubiquitous hazard, which has been linked to premature morbidity and a growing number of morbidity endpoints. Air pollution may be linked to neurodegeneration, and via this or other pathways, to neurodegenerative diseases. Emerging evidence suggests that air pollution may contribute to neurodegenerative diseases such as dementia, Parkinson's Disease (PD), Multiple Sclerosis (MS) and Motor Neuron Diseases (MND), although this evidence remains inconsistent and very limited for MS and MND. In addition, this evidence base is rapidly emerging and would benefit from a wide and critical synthesis, including a better understanding of heterogeneity.

OBJECTIVES

In this paper, we present a protocol for a systematic review and meta-analysis and specify our methods a priori. The main aim of the planned systematic review is to answer the question of whether long-term exposure (>1 year) to ambient (outdoor) air pollution (exposure, compared to lower exposure) increases the risk of adult (population) incidence of neurodegenerative diseases (outcomes) in epidemiological observational studies (study design). Another aim is to meta-analyze the associations between long-term exposure to ambient air pollutants and the risk of the selected outcomes and assess the shape of exposure-response functions. To set the stage for the proposed work, we also overview the existing epidemiological evidence in this protocol, but do not critically evaluate it, as these results will be fully presented in the planned systematic review.

SEARCH AND STUDY ELIGIBILITY

We will search the electronic databases Medline (via Ovid), Embase (via Ovid), Cochrane Library, Cinahl (via Ebscohost), Global Health (via Ebscohost), PsycINFO (via Ebscohost), Scopus, Web of Science (Core Collection), from inception to October 2022. Eligible studies must contain primary research investigating the link between 1-year + exposure to any outdoor air pollutant, from any source, and dementia, PD, MS, and MND, or dementia subtypes: Alzheimer's Disease, vascular dementia, and mixed dementia. The search strategy and eligibility criteria are pre-determined and described in full in this protocol.

STUDY APPRAISAL AND SYNTHESIS METHODS

Articles will be stored and screened using Rayyan QCRI. Title and abstract screening, full text review, data extraction, risk of bias assessment and data preparation for statistical analysis will be conducted independently by two reviewers using pre-defined forms and criteria, described in this protocol. All these steps will also be piloted and the forms and/or methods adapted if issues arise. Meta-analysis and assessment of the shape of the exposure-response functions will be conducted if four independent exposure-outcomes pairs are available, and the remainder of results will be synthesized in the forms of tables and via a narrative summary. Certainty in the body of evidence will be assessed using the OHAT approach. This protocol describes the planned analysis and synthesis a priori and serves to increase transparency and impact of this systematic review and meta-analysis.

Different components of air pollutants and neurological disorders

The harmful effects of air pollution can cause various diseases. Most research on the hazards of air pollution focuses on lung and cardiovascular diseases. In contrast, the impact of air pollution on neurological disorders is not widely recognized. Air pollution can cause various neurological conditions and diseases, such as neural inflammation, neurodegeneration, and cerebrovascular barrier disorder; however, the mechanisms underlying the neurological diseases induced by various components of air pollutants remain unclear. The present paper summarizes the effects of different components of air pollutants, including particulate matter, ozone, sulfur oxides, carbon oxides, nitrogen oxides, and heavy metals, on the nervous system and describes the impact of various air pollutants on neurological disorders, providing ideas for follow-up research.

Neurotoxic effects of environmental contaminants-measurements, mechanistic insight, and environmental relevance

Pollution is a significant and growing concern for any population regardless of age because these environmental contaminants exhibit different neurodegenerative effects on persons of different ages. These environmental contaminants are the products of human welfare projects like industry, automobile exhaust, clinical and research laboratory extrudes, and agricultural chemicals. These contaminants are found in various forms in environmental matrices like nanoparticles, particulate matter, lipophilic vaporized toxicants, and ultrafine particulate matter. Because of their small size, they can easily cross blood-brain barriers or use different cellular mechanisms for assistance. Other than this, these contaminants cause an innate immune response in different cells of the central nervous system and cause neurotoxicity. Considering the above critiques and current needs, this review summarizes different protective strategies based on bioactive compounds present in plants. Various bioactive compounds from medicinal plants with neuroprotective capacities are discussed with relevant examples. Many in vitro studies on clinical trials have shown promising outcomes using plant-based bioactive compounds against neurological disorders.

Toxic Air Pollutants and Their Effect on Multiple Sclerosis: A Review Study

Toxic air pollutants are one of the main factors that have the effect of synergism to increase the incidence of multiple sclerosis (MS). This review aims to investigate the effects of toxic air pollutants on the occurrence of multiple sclerosis (MS). A narrative review of the literature was done from 2000 to 2022 based on various databases such as Google Scholar, Web of Science, Springer, PubMed, and Science Direct. In this study, according to the databases, three hundred and sixty articles were retrieved. Of these, 28 studies were screened after review and 14 full-text articles entered into the analysis process. Finally, 9 articles were selected in this study. According to the finding of this study, toxic air pollutants including polycyclic aromatic hydrocarbons (PAHs), heavy metals (HM), volatile organic compounds (VOCs), particulate matter (PM), and gases are the main agents that cause the development and spread of chronic diseases such as respiratory and cardiovascular diseases, chronic obstructive pulmonary disease (COPD), and multiple sclerosis. The result of this study showed that the main sources of emission of toxic air pollutants include industries, cars, power plants, and the excessive consumption of fossil fuels. In general, the inhalation of high concentration of toxic air pollutants can increase the risk of chronic diseases and multiple sclerosis.

Multiple sclerosis epidemiological trends in Italy highlight the environmental risk factors

Italy is definitely a high-risk country for multiple sclerosis (MS). Over the last 50 years, several epidemiological studies, including longitudinal surveys, have disclosed that MS incidence and prevalence in Italy mainland and Islands (Sardinia and Sicily) have progressively increased, picturing a semi-parabolic curve. Based on the comprehensive scrutiny of 58 papers, we conclude that the latitude risk gradient does not fit to the Italian map of MS. The genetic heterogeneity of the Italian ethnicities, that likely forms the basis of MS predisposition, does not account for the dramatic increase of MS incidence and prevalence observed in Italy over the last half century that, rather, seems better explained by the effect of environmental factors.