Particulate matter exposure and neurodegenerative diseases: A comprehensive update on toxicity and mechanisms

Association between chronic PM2.5 exposure and neurodegenerative biomarkers in adults from critically polluted area

BACKGROUND

Air pollution is a significant public health concern, increasingly recognized for its association with adverse health outcomes including neurodegenerative and neuroinflammatory conditions. The present study aimed to characterize plasma levels of key biomarkers related to neurodegeneration and neuroinflammation among middle-aged to elderly adults living in areas designated as critically polluted.

METHODS

A total of 202 adults, aged 41 to 60 years, residing in CPA (CEPI > 70) for over ten years were recruited in the study. The exposures of air pollutant were measured as per the established protocols by CPCB. The plasma levels of neurodegenerative markers (Aβ(1-42), Total τ, α-Synuclein, BDNF and GFAP) were estimated using commercially available ultra-sensitive ELISA kits. The data analysis was performed through mean and standard deviation, percentile distribution and multivariate logistic regression using SPSS 26.0.

RESULTS

This study confirmed the elevated PM2.5 levels at the study location exceeding the regulatory limits. Women exhibited relatively higher Amyloid Aβ(1-42), α-Synuclein and GFAP levels, while men exhibited relatively higher Total τ, & BDNF levels. Further, older participants (aged 50 - 60 years) exhibited higher levels of all markers but α-Synuclein, as compared to the younger peers (aged 40 - 50 years). A weak positive trend (p = 0.08) was observed for α-Synuclein with prolonged exposure.

CONCLUSION

This study is among the first community-based investigations in India to assess plasma levels of neurodegenerative and neuroinflammatory biomarkers in apparently healthy adults chronically exposed to high ambient air pollution. By integrating chronic exposure data from a Critically Polluted Area (CEPI > 70) with biomarker profiling, the study offers early insights into potential neurobiological alterations associated with environmental pollutants, highlighting sex- and age-specific vulnerabilities. These findings emphasize the importance of considering environmental influences in neurodegenerative disease research and the potential need for tailored health interventions.

A systematic review with a Burden of Proof meta-analysis of health effects of long-term ambient fine particulate matter (PM2.5) exposure on dementia

Previous studies have indicated increased dementia risk associated with fine particulate matter (PM2.5) exposure; however, the findings are inconsistent. In this systematic review, we assessed the association between long-term PM2.5 exposure and dementia outcomes using the Burden of Proof meta-analytic framework, which relaxes log-linear assumptions to better characterize relative risk functions and quantify unexplained between-study heterogeneity (PROSPERO, ID CRD42023421869). Here we report a meta-analysis of 28 longitudinal cohort studies published up to June 2023 that investigated long-term PM2.5 exposure and dementia outcomes. We derived risk-outcome scores (ROSs), highly conservative measures of effect size and evidence strength, mapped onto a 1-5-star rating from 'weak and/or inconsistent evidence' to 'very strong and/or consistent evidence'. We identified a significant nonlinear relationship between PM2.5 exposure and dementia, with a minimum 14% increased risk averaged across PM2.5 levels between 4.5 and 26.9 µg m-3 (the 15th to 85th percentile exposure range across included studies), relative to a reference of 2.0 µg m-3 (n = 49, ROS = 0.13, two stars). We found a significant association of PM2.5 with Alzheimer's disease (n = 12, ROS = 0.32, three stars) but not with vascular dementia. Our findings highlight the potential impact of air pollution on brain aging.

Neighborhood environment and cognitive functioning in middle-aged and older population: A mediating role of physical activity

BACKGROUND

Evidence on the impact of complex neighborhood environment, including air pollution, greenness, and neighborhood socioeconomic deprivation (nSED) on cognitive health in older adults remains scarce. Both cognition and neighborhood environment are associated with physical activity, but little is known about the potential mediating role of physical activity in this association.

METHODS

Cross-sectional data of the Czech arm of the HAPIEE cohort study examined 4,178 participants (55.6% women) aged 45-69 years. Global cognitive score was constructed from memory, verbal fluency, and concentration domains. The exposures, assigned to participant's addresses, include 4-year (2000-2003) average concentrations of PM2.5, greenness index calculated from tree crown canopy cover estimation (2000), and census-based nSED characteristics. Physical activity and other covariates were assessed by a questionnaire. Structural equation modelling was used to estimate standardized β coefficients for the relationships between neighborhood environment, physical activity and cognitive performance.

RESULTS

After controlling for a range of covariates, global cognitive function was inversely associated with PM2.5 (β = -0.087; 95%CI: 0.122 to -0.052) and nSED (β = -0.147; 95%CI: 0.182 to -0.115), and positively associated with greenness (β = 0.036; 95%CI: 0.001 to 0.069). We identified a weak but statistically significant mediating role of physical activity in the associations of PM2.5 exposures and nSED on global cognitive score. Total mediation proportions ranged from 3.9% to 6.5% for nSED and PM2.5, respectively.

CONCLUSIONS

The neighborhood environment was associated with cognitive health in older individuals; the associations were partially mediated by physical activity.

Microbial signatures and therapeutic strategies in neurodegenerative diseases

Neurodegenerative diseases (NDs), including Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), and multiple sclerosis (MS), arise from complex interactions between genetic factors, environmental exposures, and aging. Additionally, gut dysbiosis has been linked to systemic inflammation and neurodegeneration. Advances in microbiome and metabolome profiling techniques have provided deeper insights into how alterations in gut microbiota and dietary patterns affect metabolic pathways and contribute to the progression of NDs. This review explores the profiles of gut microbiome and metabolome derived biomarkers and their roles in NDs. Across phyla, families, and genera, we identified 55 microbial alterations in PD, 24 in AD, 4 in ALS, and 17 in MS. Some notable results include an increase in Akkermansia in PD, AD, and MS and a decrease in short-chain fatty acids (SCFAs) in PD and AD. We examined the effects of probiotics, prebiotics, fecal microbiota transplants (FMT), sleep, exercise, and diet on the microbiota, all of which contributed to delayed onset and alleviation of symptoms. Further, artificial intelligence (AI) and machine learning (ML) algorithms applied to omics data have been crucial in identifying novel therapeutic targets, diagnosing and predicting prognosis, and enabling personalized medicine using microbiota-modulating therapies in NDs patients.

Objectively measured environmental features and their association with cognition and dementia: A systematic review and meta-analysis

Dementia affects millions of people worldwide. Since effective treatments are still lacking, it is important to identify factors that may help prevent dementia. Recent studies suggest environmental factors may affect dementia risk, but findings are inconsistent and often rely on subjective measures. This study evaluated the association between objectively measured environmental factors, such as air pollution and built environment features, and the risk of dementia and cognitive decline. We systematically reviewed studies that employed objective measures of environmental factors and reported their association with dementia risk and cognitive decline. Meta-analysis was performed to synthesize data on environmental exposures and the onset of dementia. Air pollution exposure was linked to higher dementia risk (PMx risk ratio 1.09; 95 % CI 1.06,1.12) (NOx risk ratio 1.10; 95 % CI 1.01,1.20) and cognitive decline, while exposure to park areas or green/blue spaces was generally associated with reduced dementia risk (risk ratio 0.94; 95 % CI 0.92,0.96) and slower cognitive decline. Living closer to major roads increased the risk of dementia (risk ratio 1.10; 95 % CI 1.06,1.13), and cognitive impairment. Street layouts with better connectivity and walkability are associated with a reduced risk of cognitive impairment. Access to local amenities, such as food stores, community centers, and healthcare amenities, supports cognitive health. These findings underscore the importance of considering environmental factors in dementia prevention and highlight the need for further research to clarify the role of urban design in supporting cognitive health.

Therapeutic Potential of Herbal Medicines in Combating Particulate Matter (PM)-Induced Health Effects: Insights from Recent Studies

Particulate matter (PM), particularly fine (PM2.5) and ultrafine (PM0.1) particles, originates from both natural and anthropogenic sources, such as biomass burning and vehicle emissions. These particles contain harmful compounds that pose significant health risks. Upon inhalation, ingestion, or dermal contact, PM can penetrate biological systems, inducing oxidative stress, inflammation, and DNA damage, which contribute to a range of health complications. This review comprehensively examines the protective potential of natural products against PM-induced health issues across various physiological systems, including the respiratory, cardiovascular, skin, neurological, gastrointestinal, and ocular systems. It provides valuable insights into the health risks associated with PM exposure and highlights the therapeutic promise of herbal medicines by focusing on the natural products that have demonstrated protective properties in both in vitro and in vivo PM2.5-induced models. Numerous herbal medicines and phytochemicals have shown efficacy in mitigating PM-induced cellular damage through their ability to counteract oxidative stress, suppress pro-inflammatory responses, and enhance cellular defense mechanisms. These combined actions collectively protect tissues from PM-related damage and dysfunction. This review establishes a foundation for future research and the development of effective interventions to combat PM-related health issues. However, further studies, including in vivo and clinical trials, are essential to evaluate the safety, optimal dosages, and long-term effectiveness of herbal treatments for patients under chronic PM exposure.

Cognitive Benefits of Reducing Indoor Particulate Matter Exposure During Sleep: New Evidence from a Randomized, Double-blind Crossover Trial

There is increasing evidence that particulate matter (PM) pollution may adversely impact cognition. Considering that sleep is critical for cognitive health and occupies about one-third of human life, understanding the cognitive effects of indoor PM exposure during sleep and the potential cognitive benefits of reducing such exposure is crucial, yet currently unknown. This randomized, double-blind crossover intervention trial was conducted among 80 college students with real and sham PM filtration in their dormitories. Real-time indoor PM levels and nocturnal sleep parameters were monitored, followed by quantification of serum neurotransmitter metabolites and cognitive assessments in the mornings. We found that PM exposure during sleep, particularly PM1 and PM2.5, affected immediate and delayed memory, executive function, and global cognition. Reducing PM exposure during sleep resulted in improvements in multiple cognitive domains, with a 0.21 (95% CI: 0.05, 0.36) increase in global cognitive z-score, in which increased sleep oxygen saturation (SpO2) and alterations in dopamine metabolism and histidine metabolism played important roles. Notably, even when indoor PM2.5 levels were below the WHO air quality guidelines, further reducing PM exposure could still improve sleep SpO2 and neurotransmitter metabolism. This study provides a promising strategy to mitigate indoor PM-induced cognitive impairment.

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.

Persistent Neurological Deficits in Mouse PASC Reveal Antiviral Drug Limitations

Post-Acute Sequelae of COVID-19 (PASC) encompasses persistent neurological symptoms, including olfactory and autonomic dysfunction. Here, we report chronic neurological dysfunction in mice infected with a virulent mouse-adapted SARS-CoV-2 that does not infect the brain. Long after recovery from nasal infection, we observed loss of tyrosine hydroxylase (TH) expression in olfactory bulb glomeruli and neurotransmitter levels in the substantia nigra (SN) persisted. Vulnerability of dopaminergic neurons in these brain areas was accompanied by increased levels of proinflammatory cytokines and neurobehavioral changes. RNAseq analysis unveiled persistent microglia activation, as found in human neurodegenerative diseases. Early treatment with antivirals (nirmatrelvir and molnupiravir) reduced virus titers and lung inflammation but failed to prevent neurological abnormalities, as observed in patients. Together these results show that chronic deficiencies in neuronal function in SARS-CoV-2-infected mice are not directly linked to ongoing olfactory epithelium dysfunction. Rather, they bear similarity with neurodegenerative disease, the vulnerability of which is exacerbated by chronic inflammation.

Particulate Matter-Induced Neurotoxicity: Unveiling the Role of NOX4-Mediated ROS Production and Mitochondrial Dysfunction in Neuronal Apoptosis

Urban air pollution, a significant environmental hazard, is linked to adverse health outcomes and increased mortality across various diseases. This study investigates the neurotoxic effects of particulate matter (PM), specifically PM2.5 and PM10, by examining their role in inducing oxidative stress and subsequent neuronal cell death. We highlight the novel finding that PM increases mitochondrial ROS production via stimulating NOX4 activity, not through its expression level in Neuro-2A cells. Additionally, PMs provoke ROS production via increasing the expression and activity of NOX2 in SH-SY5Y human neuroblastoma cells, implying differential regulation of NOX proteins. This increase in mitochondrial ROS triggers the opening of the mitochondrial permeability transition pore (mPTP), leading to apoptosis through key mediators, including caspase3, BAX, and Bcl2. Notably, the voltage-dependent anion-selective channel 1 (VDAC1) increases at 1 µg/mL of PM2.5, while PM10 triggers an increase from 10 µg/mL. At the same concentration (100 µg/mL), PM2.5 causes 1.4 times higher ROS production and 2.4 times higher NOX4 activity than PM10. The cytotoxic effects induced by PMs were alleviated by NOX inhibitors GKT137831 and Apocynin. In SH-SY5Y cells, both PM types increase ROS and NOX2 levels, leading to cell death, which Apocynin rescues. Variability in NADPH oxidase sources underscores the complexity of PM-induced neurotoxicity. Our findings highlight NOX4-driven ROS and mitochondrial dysfunction, suggesting a potential therapeutic approach for mitigating PM-induced neurotoxicity.

Causal association between particulate matter 2.5 and Alzheimer's disease: a Mendelian randomization study

Background

Although epidemiological evidence implies a link between exposure to particulate matter (PM) and Alzheimer's disease (AD), establishing causality remains a complex endeavor. In the present study, we used Mendelian randomization (MR) as a robust analytical approach to explore the potential causal relationship between PM exposure and AD risk. We also explored the potential associations between PM exposure and other neurodegenerative diseases.

Methods

Drawing on extensive genome-wide association studies related to PM exposure, we identified the instrumental variables linked to individual susceptibility to PM. Using summary statistics from five distinct neurodegenerative diseases, we conducted two-sample MR analyses to gauge the causal impact of PM on the risk of developing these diseases. Sensitivity analyses were undertaken to evaluate the robustness of our findings. Additionally, we executed multivariable MR (MVMR) to validate the significant causal associations identified in the two-sample MR analyses, by adjusting for potential confounding risk factors.

Results

Our MR analysis identified a notable association between genetically predicted PM2.5 (PM with a diameter of 2.5 μm or less) exposure and an elevated risk of AD (odds ratio, 2.160; 95% confidence interval, 1.481 to 3.149; p < 0.001). A sensitivity analysis supported the robustness of the observed association, thus alleviating concerns related to pleiotropy. No discernible causal relationship was identified between PM and any other neurodegenerative diseases. MVMR analyses-adjusting for smoking, alcohol use, education, stroke, hearing loss, depression, and hypertension-confirmed a persistent causal relationship between PM2.5 and AD. Sensitivity analyses, including MR-Egger and weighted median analyses, also supported this causal association.

Conclusion

The present MR study provides evidence to support a plausible causal connection between PM2.5 exposure and AD. The results emphasize the importance of contemplating air quality interventions as a public health strategy for reducing AD risk.

Association of prenatal and postnatal exposure to air pollution with clinically diagnosed attention deficit hyperactivity disorder: a systematic review

Attention deficit hyperactivity disorder (ADHD), a prevalent neurodevelopmental disorder in children, originates from a multifaceted interplay of genetic, neurological, and environmental factors. Recent studies have increasingly concentrated on environmental determinants, notably air pollution, and their impact on the risk of developing ADHD. Additionally, previous research has often conflated clinically diagnosed ADHD cases with instances of mere ADHD-like symptoms, a methodology that can introduce bias and obscure the true relationship between environmental factors and ADHD. To address this oversight, our systematic review meticulously investigates the relationship between both prenatal and postnatal exposures to particular air pollutants and strictly clinically diagnosed ADHD. Our comprehensive review encompassed 801 studies from PubMed, Cochrane Library, Web of Science, and Embase databases, out of which eight met our rigorous inclusion criteria. The Newcastle-Ottawa Scale (NOS) was utilized to gauge quality and bias. Our review found substantiated the connection between prenatal exposure to PM2.5 and NOx and a heightened risk of ADHD, while exposure to PM10 during the prenatal stage was not associated with ADHD. These findings hint at varied health impacts from different particulate matters and the prospect of gender-specific susceptibilities to such exposures. We also identified an association between postnatal exposure to PM2.5, PM10, and NO2 and an increased ADHD risk, underlining the potential neurodevelopmental harms from early exposure to these pollutants. These relationships, seemingly intricate and potentially dose-dependent, underscore the need for more detailed scrutiny. The unique value of our review is in its detailed exploration of the association between specific air pollution exposures and clinically diagnosed ADHD. Our findings offer much-needed clarity in this complex domain and emphasize the importance of future research to standardize exposure and outcome metrics, probe potential mechanisms, and reduce bias and heterogeneity.

Environmental pollutants and exosomes: A new paradigm in environmental health and disease

This study investigates the intricate interplay between environmental pollutants and exosomes, shedding light on a novel paradigm in environmental health and disease. Cellular stress, induced by environmental toxicants or disease, significantly impacts the production and composition of exosomes, crucial mediators of intercellular communication. The heat shock response (HSR) and unfolded protein response (UPR) pathways, activated during cellular stress, profoundly influence exosome generation, cargo sorting, and function, shaping intercellular communication and stress responses. Environmental pollutants, particularly lipophilic ones, directly interact with exosome lipid bilayers, potentially affecting membrane stability, release, and cellular uptake. The study reveals that exposure to environmental contaminants induces significant changes in exosomal proteins, miRNAs, and lipids, impacting cellular function and health. Understanding the impact of environmental pollutants on exosomal cargo holds promise for biomarkers of exposure, enabling non-invasive sample collection and real-time insights into ongoing cellular responses. This research explores the potential of exosomal biomarkers for early detection of health effects, assessing treatment efficacy, and population-wide screening. Overcoming challenges requires advanced isolation techniques, standardized protocols, and machine learning for data analysis. Integration with omics technologies enhances comprehensive molecular analysis, offering a holistic understanding of the complex regulatory network influenced by environmental pollutants. The study underscores the capability of exosomes in circulation as promising biomarkers for assessing environmental exposure and systemic health effects, contributing to advancements in environmental health research and disease prevention.

Air pollution and neurological diseases, current state highlights

This paper delves into the increasingly recognized yet complex relationship between air pollution and Neurological Diseases. Although the detrimental effects of air pollution on respiratory and cardiovascular health are well-documented, its impact on neurological and cognitive disorders is an emerging area of concern. In this mini review, we explore the intricate mechanisms by which various air pollutants, such as particulate matter, nitrogen oxides, and polycyclic aromatic hydrocarbons, contribute to neurological pathologies. The focus lies on the role of oxidative stress and inflammation in exacerbating conditions like Alzheimer's disease and Parkinson's disease. By unraveling these connections, the paper sheds light on the broader implications of environmental factors on neurological health and underscores the urgent need for policy interventions to mitigate air pollution's impact on the nervous system.

Exposure to the World Trade Center Particulate Matter Alters the Gut-Brain Axis in Early Onset Alzheimer's Disease Mice

Background

The September 11, 2001, catastrophe unleashed widespread destruction beyond the World Center (WTC), with fires and toxic gases leaving lasting impacts. First responders at Ground Zero faced prolonged exposure to hazardous particulate matter (PM), resulting in chronic health challenges. Among the multitude of health concerns, the potential association between the WTCPM and Alzheimer's disease (AD) has emerged as an area of intense inquiry, probing the intricate interplay between environmental factors and neurodegenerative diseases.

Objective

We posit that a genetic predisposition to AD in mice results in dysregulation of the gut-brain axis following chronic exposure to WTCPM. This, in turn, may heighten the risk of AD-like symptoms in these individuals.

Methods

3xTg-AD and WT mice were intranasally administered with WTCPM collected at Ground Zero within 72 hours after the attacks. Working memory and learning and recognition memory were monitored for 4 months. Moreover, brain transcriptomic analysis and gut barrier permeability along with microbiome composition were examined.

Results

Our findings underscore the deleterious effects of WTCPM on cognitive function, as well as notable alterations in brain genes associated with synaptic plasticity, pro-survival, and inflammatory signaling pathways. Complementary, chronic exposure to the WTCPM led to increased gut permeability in AD mice and altered bacteria composition and expression of functional pathways in the gut.

Conclusions

Our results hint at a complex interplay between gut and brain axis, suggesting potential mechanisms through which WTCPM exposure may exacerbate cognitive decline. Identifying these pathways offers opportunities for tailored interventions to alleviate neurological effects among first responders.