Particulate air pollutants, APOE alleles and their contributions to cognitive impairment in older women and to amyloidogenesis in experimental models

Comparison of the neurotoxic potency of different ultrafine particle fractions from diesel engine exhaust following direct and simulated inhalation exposure

Exposure to traffic-related air pollution and ultrafine particles (<100 nm; UFP) is linked with neurodegeneration. However, the impact of the aromatic content in fuels and the contribution of different fractions of UFP, i.e., solid UFP vs SVOC UFP, on neuronal function is unknown. We therefore studied effects on neuronal activity and viability in rat primary cortical cells exposed for up to 120 h to copper oxide particles (CuO) or UFP (solid and SVOC) emitted from a heavy-duty diesel engine fueled with petroleum diesel (A20; 20 % aromatics) or Hydrotreated Vegetable Oil-type fuel (A0; 0.1 % aromatics), or solid UFP emitted from a non-road Kubota engine fueled with A20. Moreover, effects of UFP and CuO upon simulated inhalation exposure were studied by exposing an lung model (Calu-3 and THP-1 cells) for 48 h and subsequently exposing the cortical cells to the medium collected from the basal compartment of the lung model. Additionally, cell viability, cytotoxicity, barrier function, inflammation, and oxidative and cell stress were studied in the lung model after 48 h exposure to UFP and CuO. Compared to control, direct exposure to CuO and SVOC UFP decreased neuronal activity, which was partly associated with cytotoxicity. Effects on neuronal activity upon direct exposure to solid UFP were limited. A20-derived UFP (solid and SVOC) were more potent in altering neuronal function and viability than A0 counterparts. Effects on neuronal activity from simulated inhalation exposure were minor compared to direct exposures. In the lung model, CuO and A20-derived UFP increased cytokine release compared to control, whereas CuO and SVOC A20 altered gene expression indicative for oxidative stress. Our data indicate that SVOC UFP exhibit higher (neuro)toxic potency for altering neuronal activity in rat primary cortical cells than the solid fraction. Moreover, our data suggest that reducing the aromatic content in fuel decreases the (neuro)toxic potency of emitted UFP.

Association of ambient air pollution with cognitive functioning and markers of structural brain damage: The Maastricht study

INTRODUCTION

Given the absence of curative interventions and the rising global incidence of dementia, research is increasingly focusing on lifestyle factors for prevention. However, identifying shared environmental risk for dementia, next to individual factors, is crucial for optimal risk reduction strategies. Therefore, in the present study we investigated the association between air pollution, cognitive functioning, and markers of structural brain damage.

METHODS

We used cross-sectional data from 4,002 participants of The Maastricht Study on volumetric markers of brain integrity (white and grey matter volume, cerebrospinal fluid volume, white matter hyperintensities volume, presence of cerebral small vessel disease) and cognitive functioning (memory, executive functioning and attention, processing speed, overall cognition). Individuals were matched by postal code of residence to nationwide data on air pollution exposure (particulate matter < 2.5 μm (PM2.5), particulate matter <10 μm (PM10), nitrogen dioxide (NO2), soot). Potentia linear and non-linear associations were investigated with linear, logistic, and restricted cubic splines regression. All analyses were adjusted for demographic characteristics and a compound score of modifiable dementia risk and protective factors.

RESULTS

Exposure to air pollutants was not related to cognitive functioning and most brain markers. We found curvilinear relationships between high PM2.5 exposures and grey matter and cerebrospinal fluid volume. Participants in the low and high range of exposure had lower grey matter volume. Higher cerebrospinal fluid volumes were only associated with high range of exposure, independent of demographic and individual modifiable dementia risk factors. After additional post hoc analyses, controlling for urbanicity, the associations for grey matter volume became non-significant. In men only, higher exposure to all air pollutants was associated with lower white matter volumes. No significant associations with white matter hyperintensities volume or cerebral small vessel disease were observed.

DISCUSSION

Our findings suggest that higher PM2.5 exposure is associated with more brain atrophy.

Use of machine learning algorithms to determine the relationship between air pollution and cognitive impairment in Taiwan

Air pollution has become a major global threat to human health. Urbanization and industrialization over the past few decades have increased the air pollution. Plausible connections have been made between air pollutants and dementia. This study used machine learning algorithms (k-nearest neighbors, random forest, gradient-boosted decision trees, eXtreme gradient boosting, and CatBoost) to investigate the association between cognitive impairment and air pollution. Data from the Taiwan Biobank and 75 air-pollution-monitoring stations in Taiwan were analyzed to determine individual levels of exposure to air pollutants. The pollutants examined were particulate matter with a diameter of ≤ 2.5 μm (PM2.5), nitrogen dioxide, nitric oxide, carbon monoxide, and ozone. The results revealed that the most strongly correlated with cognitive impairment were ozone, PM2.5, and carbon monoxide levels with adjustment of educational level, age, and household income. The model based on these factors achieved accuracy as high as 0.97 for detecting cognitive impairment, indicating a positive association between air pollutions and cognitive impairment.

Associations between toxicity-weighted concentrations and dementia risk: Results from the Cardiovascular Health Cognition Study

BACKGROUND

Air pollution is a modifiable risk factor for dementia. Yet, studies on specific sources of air pollution (i.e., toxic chemical emissions from industrial facilities) and dementia risk are scarce. We examined associations between toxicity-weighted concentrations of industrial pollution and dementia outcomes among a large, multi-site cohort of older adults.

METHODS

Participants (n = 2770) were ≥ 65 years old (Mean = 75.3, SD = 5.1 years) from the Cardiovascular Health Cognition Study (1992-1999). Toxicity-weighted concentrations were estimated using the Risk Screening Environmental Indicator (RSEI) model which incorporates total reported chemical emissions with toxicity, fate, and transport models. Estimates were aggregated to participants' baseline census tract, averaged across 1988-1992, and log2-transformed. Dementia status was clinically adjudicated in 1998-1999 and categorized by subtype (Alzheimer's, vascular, mixed). We assessed whether RSEI-estimated toxicity-weighted concentrations were associated with 1) odds of prevalent dementia and 2) incident dementia risk by subtype.

RESULTS

After adjusting for individual and census-tract level covariates, a doubling in toxicity-weighted concentrations was associated with 9 % higher odds of prevalent dementia (OR = 1.09, 95 % CI: 1.00, 1.19). In discrete-time survival models, each doubling in toxicity-weighted concentrations was associated with a 16 % greater hazard of vascular dementia (HR = 1.16, 95 % CI: 1.01, 1.34) but was not significantly associated with all-cause, Alzheimer's disease, or mixed dementia (p's > 0.05).

DISCUSSION

Living in regions with higher toxicity-weighted concentrations was associated with higher odds of prevalent dementia and a higher risk of incident vascular dementia in this large, community-based cohort of older adults. These findings support the need for additional studies to examine whether toxic chemical emissions from industrial and federal facilities may be a modifiable target for dementia prevention.

Neuroinflammation and Brain Health Risks in Veterans Exposed to Burn Pit Toxins

Military burn pits, used for waste disposal in combat zones, involve the open-air burning of waste materials, including plastics, metals, chemicals, and medical waste. The pits release a complex mixture of occupational toxic substances, including particulate matter (PM), volatile organic compounds (VOCs), heavy metals, dioxins, and polycyclic aromatic hydrocarbons (PAHs). Air pollution significantly impacts brain health through mechanisms involving neuroinflammation. Pollutants penetrate the respiratory system, enter the bloodstream, and cross the blood-brain barrier (BBB), triggering inflammatory responses in the central nervous system (CNS). Chronic environmental exposures result in sustained inflammation, oxidative stress, and neuronal damage, contributing to neurodegenerative diseases and cognitive impairment. Veterans exposed to burn pit toxins are particularly at risk, reporting higher rates of respiratory issues, neurological conditions, cognitive impairments, and mental health disorders. Studies demonstrate that Veterans exposed to these toxins have higher rates of neuroinflammatory markers, accelerated cognitive decline, and increased risks of neurodegenerative diseases. This narrative review synthesizes the research linking airborne pollutants such as PM, VOCs, and heavy metals to neuroinflammatory processes and cognitive effects. There is a need for targeted interventions to mitigate the harmful and escalating effects of environmental air pollution exposures on the CNS, improving public health outcomes for vulnerable populations, especially for Veterans exposed to military burn pit toxins.

Air pollution amyloidogenesis is attenuated by the gamma-secretase modulator GSM-15606

INTRODUCTION

Chronic air pollution (AirPoll) is associated with accelerated cognitive decline and risk of Alzheimer's disease (AD). Correspondingly, wild-type and AD-transgenic rodents exposed to AirPoll have increased amyloid peptides and behavioral impairments.

METHODS

We examined the γ-secretase modulator GSM-15606 for potential AirPoll protection by its attenuating of amyloid beta (Aβ)42 peptide production. Male and female wild-type mice were fed GSM-15606 during an 8-week inhalation exposure to AirPoll subfractions, ambient nanoparticulate matter (nPM), and diesel exhaust particles (DEP).

RESULTS

GSM-15606 decreased Aβ42 during nPM and DEP exposure without changing beta- or gamma-secretase activity or BACE1 and PS1 protein levels. DEP increased lateral ventricle volume by 25%.

DISCUSSION

These enzyme responses are relevant to AD drug treatments, as well as to the physiological functions of the Aβ42 peptide. GSM-15606 attenuation of Aβ42 may benefit human exposure to AirPoll.

HIGHLIGHTS

Gamma-secretase modulator (GSM-15606) attenuates the amyloidogenic amyloid beta (Aβ)42 peptide during exposure to air pollution, which may be a mechanism by which air pollution increases Alzheimer's disease (AD) risk. AD drug treatments may also consider Aβ homeostasis among the chronic effects of GSM-15606 and other amyloid reduction treatments on secretase enzymes.

Interplay between microglia and environmental risk factors in Alzheimer's disease

Alzheimer's disease, among the most common neurodegenerative disorders, is characterized by progressive cognitive impairment. At present, the Alzheimer's disease main risk remains genetic risks, but major environmental factors are increasingly shown to impact Alzheimer's disease development and progression. Microglia, the most important brain immune cells, play a central role in Alzheimer's disease pathogenesis and are considered environmental and lifestyle "sensors." Factors like environmental pollution and modern lifestyles (e.g., chronic stress, poor dietary habits, sleep, and circadian rhythm disorders) can cause neuroinflammatory responses that lead to cognitive impairment via microglial functioning and phenotypic regulation. However, the specific mechanisms underlying interactions among these factors and microglia in Alzheimer's disease are unclear. Herein, we: discuss the biological effects of air pollution, chronic stress, gut microbiota, sleep patterns, physical exercise, cigarette smoking, and caffeine consumption on microglia; consider how unhealthy lifestyle factors influence individual susceptibility to Alzheimer's disease; and present the neuroprotective effects of a healthy lifestyle. Toward intervening and controlling these environmental risk factors at an early Alzheimer's disease stage, understanding the role of microglia in Alzheimer's disease development, and targeting strategies to target microglia, could be essential to future Alzheimer's disease treatments.

Traffic-related air pollution and APOE4 can synergistically affect hippocampal volume in older women: new findings from UK Biobank

A growing research body supports the connection between neurodegenerative disorders, including Alzheimer's disease (AD), and traffic-related air pollution (TRAP). However, the underlying mechanisms are not well understood. A deeper investigation of TRAP effects on hippocampal volume (HV), a major biomarker of neurodegeneration, may help clarify these mechanisms. Here, we explored TRAP associations with the HV in older participants of the UK Biobank (UKB), taking into account the presence of APOE e4 allele (APOE4), the strongest genetic risk factor for AD. Exposure to TRAP was approximated by the distance of the participant's main residence to the nearest major road (DNMR). The left/right HV was measured by magnetic resonance imaging (MRI) in cubic millimeters (mm3). Analysis of variance (ANOVA), Welch test, and regression were used to examine statistical significance. We found significant interactions between DNMR and APOE4 that influenced HV. Specifically, DNMR <50m (equivalent of a chronically high exposure to TRAP), and carrying APOE4 were synergistically associated with a significant (P = 0.01) reduction in the right HV by about 2.5% in women aged 60-75 years (results for men didn't reach a statistical significance). Results of our study suggest that TRAP and APOE4 jointly promote neurodegeneration in women. Living farther from major roads may help reduce the risks of neurodegenerative disorders, including AD, in female APOE4 carriers.

The Role of the Neural Exposome as a Novel Strategy to Identify and Mitigate Health Inequities in Alzheimer's Disease and Related Dementias

With the continuous increase of the elderly population, there is an urgency to understand and develop relevant treatments for Alzheimer's disease and related dementias (ADRD). In tandem with this, the prevalence of health inequities continues to rise as disadvantaged communities fail to be included in mainstream research. The neural exposome poses as a relevant mechanistic approach and tool for investigating ADRD onset, progression, and pathology as it accounts for several different factors: exogenous, endogenous, and behavioral. Consequently, through the neural exposome, health inequities can be addressed in ADRD research. In this paper, we address how the neural exposome relates to ADRD by contributing to the discourse through defining how the neural exposome can be developed as a tool in accordance with machine learning. Through this, machine learning can allow for developing a greater insight into the application of transferring and making sense of experimental mouse models exposed to health inequities and potentially relate it to humans. The overall goal moving beyond this paper is to define a multitude of potential factors that can increase the risk of ADRD onset and integrate them to create an interdisciplinary approach to the study of ADRD and subsequently translate the findings to clinical research.

Exposure to source-specific air pollution in residential areas and its association with dementia incidence: a cohort study in Northern Sweden

The aim of this study was to investigate the relationship between source-specific ambient particulate air pollution concentrations and the incidence of dementia. The study encompassed 70,057 participants from the Västerbotten intervention program cohort in Northern Sweden with a median age of 40 years at baseline. High-resolution dispersion models were employed to estimate source-specific particulate matter (PM) concentrations, such as PM10 and PM2.5 from traffic, exhaust, and biomass (mainly wood) burning, at the residential addresses of each participant. Cox regression models, adjusted for potential confounding factors, were used for the assessment. Over 884,847 person-years of follow-up, 409 incident dementia cases, identified through national registers, were observed. The study population's average exposure to annual mean total PM10 and PM2.5 lag 1-5 years was 9.50 µg/m3 and 5.61 µg/m3, respectively. Increased risks were identified for PM10-Traffic (35% [95% CI 0-82%]) and PM2.5-Exhaust (33% [95% CI - 2 to 79%]) in the second exposure tertile for lag 1-5 years, although no such risks were observed in the third tertile. Interestingly, a negative association was observed between PM2.5-Wood burning and the risk of dementia. In summary, this register-based study did not conclusively establish a strong association between air pollution exposure and the incidence of dementia. While some evidence indicated elevated risks for PM10-Traffic and PM2.5-Exhaust, and conversely, a negative association for PM2.5-Wood burning, no clear exposure-response relationships were evident.

Inhaled Pollutants of the Gero-Exposome and Later-Life Health

Inhaled air pollutants (AirP) comprise extraordinarily diverse particles, volatiles, and gases from traffic, wildfire, cigarette smoke, dust, and various other sources. These pollutants contain numerous toxic components, which collectively differ in relative levels of components, but broadly share chemical classes. Exposure and health outcomes from AirP are complex, depending on pollutant source, duration of exposure, and socioeconomic status. We discuss examples in the current literature on organ responses to AirP, with a focus on lung, arteries, and brain. Some transcriptional responses are shared. It is well accepted that AirP contributes to Alzheimer's disease and other neurodegenerative conditions in the Gero-Exposome. However, we do not know which chemical compounds initiate these changes and how activation of these transcriptional pathways is further modified by genetics and prenatal development.

Environmental Toxins and Alzheimer's Disease: a Comprehensive Analysis of Pathogenic Mechanisms and Therapeutic Modulation

Alzheimer's disease is a leading cause of mortality worldwide. Inorganic and organic hazards, susceptibility to harmful metals, pesticides, agrochemicals, and air pollution are major environmental concerns. As merely 5% of AD cases are directly inherited indicating that these environmental factors play a major role in disease development. Long-term exposure to environmental toxins is believed to progress neuropathology, which leads to the development of AD. Numerous in-vitro and in-vivo studies have suggested the harmful impact of environmental toxins at cellular and molecular level. Common mechanisms involved in the toxicity of these environmental pollutants include oxidative stress, neuroinflammation, mitochondrial dysfunction, abnormal tau, and APP processing. Increased expression of GSK-3β, BACE-1, TNF-α, and pro-apoptotic molecules like caspases is observed upon exposure to these environmental toxins. In addition, the expression of neurotrophins like BDNF and GAP-43 have been found to be reduced as a result of toxicity. Further, modulation of signaling pathways involving PARP-1, PGC-1α, and MAPK/ERK induced by toxins have been reported to contribute in AD pathogenesis. These pathways are a promising target for developing novel AD therapeutics. Drugs like epigallocatechin-gallate, neflamapimod, salsalate, dexmedetomidine, and atabecestat are in different phases of clinical trials targeting the pathways for possible treatment of AD. This review aims to culminate the correlation between environmental toxicants and AD development. We emphasized upon the signaling pathways involved in the progression of the disease and the therapeutics under clinical trial targeting the altered pathways for possible treatment of AD.

ROS-dependent degeneration of human neurons induced by environmentally relevant levels of micro- and nanoplastics of diverse shapes and forms

Our study explores the pressing issue of micro- and nanoplastics (MNPs) inhalation and their subsequent penetration into the brain, highlighting a significant environmental health concern. We demonstrate that MNPs can indeed penetrate murine brain, warranting further investigation into their neurotoxic effects in humans. We then proceed to test the impact of MNPs at environmentally relevant concentrations, with focusing on variations in size and shape. Our findings reveal that these MNPs induce oxidative stress, cytotoxicity, and neurodegeneration in human neurons, with cortical neurons being more susceptible than nociceptors. Furthermore, we examine the role of biofilms on MNPs, demonstrating that MNPs can serve as a vehicle for pathogenic biofilms that significantly exacerbate these neurotoxic effects. This sequence of investigations reveals that minimal MNPs accumulation can cause oxidative stress and neurodegeneration in human neurons, significantly risking brain health and highlights the need to understand the neurological consequences of inhaling MNPs. Overall, our developed in vitro testing battery has significance in elucidating the effects of environmental factors and their associated pathological mechanisms in human neurons.

Epigenetic modifications of DNA and RNA in Alzheimer's disease

Alzheimer's disease (AD) is a complex neurodegenerative disorder and the most common form of dementia. There are two main types of AD: familial and sporadic. Familial AD is linked to mutations in amyloid precursor protein (APP), presenilin-1 (PSEN1), and presenilin-2 (PSEN2). On the other hand, sporadic AD is the more common form of the disease and has genetic, epigenetic, and environmental components that influence disease onset and progression. Investigating the epigenetic mechanisms associated with AD is essential for increasing understanding of pathology and identifying biomarkers for diagnosis and treatment. Chemical covalent modifications on DNA and RNA can epigenetically regulate gene expression at transcriptional and post-transcriptional levels and play protective or pathological roles in AD and other neurodegenerative diseases.

A study about the impact of indoor air pollution on cognitive function among middle-aged and older adult people in India

BACKGROUND

In the 21st century, people still use solid fuel for cooking at home, resulting in poor indoor air quality. Prolonged exposure to such conditions may negatively affect one's cognitive function. So, the present study examines the possible association between IAP and the cognitive function of individuals aged 45 years or above in India.

METHODS

The study utilizes secondary data, procured from the longitudinal ageing study in India (2017-18). Treatment effects through regression-adjusted models were applied to represent the association between IAP and cognitive health and the results are represented by beta coefficient (β). Three separate models with a 95% confidence interval adjusting with the other factors like housing environment, individual and behavioural were framed.

RESULTS

The study revealed that households without a separate kitchen (β = -0.64; 95%CI: -0.90 to -0.39) and electricity (β = -0.97; 95%CI: -1.34 to -0.61) significantly affect cognitive strength. Cognitive decline is likely more pronounced among older adults (β = -1.19; 95%CI: -1.42 to -0.96) than the middle-aged population. Moreover, the cognitive ability of rural residents (β = -1.11; 95%CI: -1.49 to -0.73) and women (β = -2.05; 95%CI: -2.29 to -1.81) is negatively associated with IAP exposure. Older adults with no reading habits (β = -6.28; 95%CI: -6.72; to -5.85) and physical inactivity (β = -0.96; 95%CI: -1.22 to -0.70) had a sign of notable decline in cognitive ability.

CONCLUSIONS

Findings revealed that cognitive function is negatively associated with IAP, demanding a deep intervention plan to minimize the detrimental effect.

Air pollution, APOE genotype and risk of dementia among individuals with cardiovascular diseases: A population-based longitudinal study

Individuals with cardiovascular disease (CVD) are particularly vulnerable to dementia, but it remains unclear whether air pollution exposure links with higher risk of dementia among those with CVD. The data were derived from the UK Biobank study (UKB). Dementia-free participants with CVD at baseline were included. Air pollution exposure was assessed through land use regression models, including particulate matter (PM2.5, PM2.5-10, and PM10), nitrogen dioxide (NO2), and nitrogen oxides (NOX). A Cox proportional hazards model was used to investigate the associations between air pollution exposure and incident dementia among individuals with CVD. Air pollution was associated with dementia among individuals with CVD, and the hazard ratios of dementia associated with each interquartile range (IQR) μg/m3 increase in air pollution were 1.07 (95% CI: 1.02, 1.12) for PM2.5, 1.10 (95% CI: 1.04, 1.15) for PM10, 1.08 (95% CI: 1.03, 1.14) for NO2 and 1.05 (95% CI: 1.00, 1.09) for NOx. Associations between air pollution and all-cause dementia were found to be significant among individuals with hypertension. Adverse effects of air pollution were also observed for Alzheimer's dementia (AD) and vascular dementia (VaD), with a higher effect for AD. Observed associations remained similar in subgroups of APOE ε4 carriers and noncarriers, although there was a higher risk difference across different air pollution concentration among these individuals carrying APOE ε4. Air pollution emerges as a critical risk factor for dementia among individuals with CVD, regardless of genetic susceptibility indicated by the APOE genotype. Notably, individuals with hypertension might be susceptible to the adverse effects of air pollution, leading to a higher incidence of dementia. Understanding these impacts on dementia among individuals with CVD may promote better targeted prevention and clinical management strategies.

Exercise-Mediated Protection against Air Pollution-Induced Immune Damage: Mechanisms, Challenges, and Future Directions

Air pollution, a serious risk factor for human health, can lead to immune damage and various diseases. Long-term exposure to air pollutants can trigger oxidative stress and inflammatory responses (the main sources of immune impairment) in the body. Exercise has been shown to modulate anti-inflammatory and antioxidant statuses, enhance immune cell activity, as well as protect against immune damage caused by air pollution. However, the underlying mechanisms involved in the protective effects of exercise on pollutant-induced damage and the safe threshold for exercise in polluted environments remain elusive. In contrast to the extensive research on the pathogenesis of air pollution and the preventive role of exercise in enhancing fitness, investigations into exercise resistance to injury caused by air pollution are still in their infancy. In this review, we analyze evidence from humans, animals, and cell experiments on the combined effects of exercise and air pollution on immune health outcomes, with an emphasis on oxidative stress, inflammatory responses, and immune cells. We also propose possible mechanisms and directions for future research on exercise resistance to pollutant-induced damage in the body. Furthermore, we suggest strengthening epidemiological studies at different population levels and investigations on immune cells to guide how to determine the safety thresholds for exercise in polluted environments.

Mixed Metal Components in PM2.5 Contribute to Chemokine Receptor CCR5-Mediated Neuroinflammation and Neuropathological Changes in the Mouse Olfactory Bulb

Particulate matter, especially PM2.5, can invade the central nervous system (CNS) via the olfactory pathway to induce neurotoxicity. The olfactory bulb (OB) is the key component integrating immunoprotection and olfaction processing and is necessarily involved in the relevant CNS health outcomes. Here we show that a microglial chemokine receptor, CCR5, is the target of environmentally relevant PM2.5 in the OB to trigger neuroinflammation and then neuropathological injuries. Mechanistically, PM2.5-induced CCR5 upregulation results in the pro-inflammatory paradigm of microglial activation, which subsequently activates TLR4-NF-κB neuroinflammation signaling and induces neuropathological changes that are closely related to neurodegenerative disorders (e.g., Aβ deposition and disruption of the blood-brain barrier). We specifically highlight that manganese and lead in PM2.5 are the main contributors to CCR5-mediated microglial activation and neuroinflammation in synergy with aluminum. Our results uncover a possible pathway of PM2.5-induced neuroinflammation and identify the principal neurotoxic components, which can provide new insight into efficiently diminishing the adverse health effects of PM2.5.

Molecular Mechanisms Linking Osteoarthritis and Alzheimer's Disease: Shared Pathways, Mechanisms and Breakthrough Prospects

Alzheimer's disease (AD) is a progressive neurodegenerative disease mostly affecting the elderly population. It is characterized by cognitive decline that occurs due to impaired neurotransmission and neuronal death. Even though deposition of amyloid beta (Aβ) peptides and aggregation of hyperphosphorylated TAU have been established as major pathological hallmarks of the disease, other factors such as the interaction of genetic and environmental factors are believed to contribute to the development and progression of AD. In general, patients initially present mild forgetfulness and difficulty in forming new memories. As it progresses, there are significant impairments in problem solving, social interaction, speech and overall cognitive function of the affected individual. Osteoarthritis (OA) is the most recurrent form of arthritis and widely acknowledged as a whole-joint disease, distinguished by progressive degeneration and erosion of joint cartilage accompanying synovitis and subchondral bone changes that can prompt peripheral inflammatory responses. Also predominantly affecting the elderly, OA frequently embroils weight-bearing joints such as the knees, spine and hips leading to pains, stiffness and diminished joint mobility, which in turn significantly impacts the patient's standard of life. Both infirmities can co-occur in older adults as a result of independent factors, as multiple health conditions are common in old age. Additionally, risk factors such as genetics, lifestyle changes, age and chronic inflammation may contribute to both conditions in some individuals. Besides localized peripheral low-grade inflammation, it is notable that low-grade systemic inflammation prompted by OA can play a role in AD pathogenesis. Studies have explored relationships between systemic inflammatory-associated diseases like obesity, hypertension, dyslipidemia, diabetes mellitus and AD. Given that AD is the most common form of dementia and shares similar risk factors with OA-both being age-related and low-grade inflammatory-associated diseases, OA may indeed serve as a risk factor for AD. This work aims to review literature on molecular mechanisms linking OA and AD pathologies, and explore potential connections between these conditions alongside future prospects and innovative treatments.

Elossaily G, Vellapandian C, Prajapati B. Investigating the Potential Impact of Air Pollution on Alzheimer's Disease and the Utility of Multidimensional Imaging for Early Detection

Pollution is ubiquitous, and much of it is anthropogenic in nature, which is a severe risk factor not only for respiratory infections or asthma sufferers but also for Alzheimer's disease, which has received a lot of attention recently. This Review aims to investigate the primary environmental risk factors and their profound impact on Alzheimer's disease. It underscores the pivotal role of multidimensional imaging in early disease identification and prevention. Conducting a comprehensive review, we delved into a plethora of literature sources available through esteemed databases, including Science Direct, Google Scholar, Scopus, Cochrane, and PubMed. Our search strategy incorporated keywords such as "Alzheimer Disease", "Alzheimer's", "Dementia", "Oxidative Stress", and "Phytotherapy" in conjunction with "Criteria Pollutants", "Imaging", "Pathology", and "Particulate Matter". Alzheimer's disease is not only a result of complex biological factors but is exacerbated by the infiltration of airborne particles and gases that surreptitiously breach the nasal defenses to traverse the brain, akin to a Trojan horse. Various imaging modalities and noninvasive techniques have been harnessed to identify disease progression in its incipient stages. However, each imaging approach possesses inherent limitations, prompting exploration of a unified technique under a single umbrella. Multidimensional imaging stands as the linchpin for detecting and forestalling the relentless march of Alzheimer's disease. Given the intricate etiology of the condition, identifying a prospective candidate for Alzheimer's disease may take decades, rendering the development of a multimodal imaging technique an imperative. This research underscores the pressing need to recognize the chronic ramifications of invisible particulate matter and to advance our understanding of the insidious environmental factors that contribute to Alzheimer's disease.

Leading determinants of incident dementia among individuals with and without the apolipoprotein E ε4 genotype: a retrospective cohort study

BACKGROUND

Little is known regarding the leading risk factors for dementia/Alzheimer's disease (AD) in individuals with and without APOE4. The identification of key risk factors for dementia/Alzheimer's disease (AD) in individuals with and without the APOE4 gene is of significant importance in global health.

METHODS

Our analysis included 110,354 APOE4 carriers and 220,708 age- and sex-matched controls aged 40-73 years at baseline (between 2006-2010) from UK Biobank. Incident dementia was ascertained using hospital inpatient, or death records until January 2021. Individuals of non-European ancestry were excluded. Furthermore, individuals without medical record linkage were excluded from the analysis. Moderation analysis was tested for 134 individual factors.

RESULTS

During a median follow-up of 11.9 years, 4,764 cases of incident all-cause dementia and 2065 incident AD cases were documented. Hazard ratios (95% CIs) for all-cause dementia and AD associated with APOE4 were 2.70(2.55-2.85) and 3.72(3.40-4.07), respectively. In APOE4 carriers, the leading risk factors for all-cause dementia included low self-rated overall health, low household income, high multimorbidity risk score, long-term illness, high neutrophil percentage, and high nitrogen dioxide air pollution. In non-APOE4 carriers, the leading risk factors included high multimorbidity risk score, low overall self-rated health, low household income, long-term illness, high microalbumin in urine, high neutrophil count, and low greenspace percentage. Population attributable risk for these individual risk factors combined was 65.1%, and 85.8% in APOE4 and non-APOE4 carriers, respectively. For 20 risk factors including multimorbidity risk score, unhealthy lifestyle habits, and particulate matter air pollutants, their associations with incident dementia were stronger in non-APOE4 carriers. For only 2 risk factors (mother's history of dementia, low C-reactive protein), their associations with incident all-cause dementia were stronger in APOE4 carriers.

CONCLUSIONS

Our findings provide evidence for personalized preventative approaches to dementia/AD in APOE4 and non-APOE4 carriers. A mother's history of dementia and low levels of C-reactive protein were more important risk factors of dementia in APOE4 carriers whereas leading risk factors including unhealthy lifestyle habits, multimorbidity risk score, inflammation and immune-related markers were more predictive of dementia in non-APOE4 carriers.

Particulate matter from car exhaust alters function of human iPSC-derived microglia

BACKGROUND

Air pollution is recognized as an emerging environmental risk factor for neurological diseases. Large-scale epidemiological studies associate traffic-related particulate matter (PM) with impaired cognitive functions and increased incidence of neurodegenerative diseases such as Alzheimer's disease. Inhaled components of PM may directly invade the brain via the olfactory route, or act through peripheral system responses resulting in inflammation and oxidative stress in the brain. Microglia are the immune cells of the brain implicated in the progression of neurodegenerative diseases. However, it remains unknown how PM affects live human microglia.

RESULTS

Here we show that two different PMs derived from exhausts of cars running on EN590 diesel or compressed natural gas (CNG) alter the function of human microglia-like cells in vitro. We exposed human induced pluripotent stem cell (iPSC)-derived microglia-like cells (iMGLs) to traffic related PMs and explored their functional responses. Lower concentrations of PMs ranging between 10 and 100 µg ml-1 increased microglial survival whereas higher concentrations became toxic over time. Both tested pollutants impaired microglial phagocytosis and increased secretion of a few proinflammatory cytokines with distinct patterns, compared to lipopolysaccharide induced responses. iMGLs showed pollutant dependent responses to production of reactive oxygen species (ROS) with CNG inducing and EN590 reducing ROS production.

CONCLUSIONS

Our study indicates that traffic-related air pollutants alter the function of human microglia and warrant further studies to determine whether these changes contribute to adverse effects in the brain and on cognition over time. This study demonstrates human iPSC-microglia as a valuable tool to study functional microglial responses to environmental agents.

Beneficial Effect of Societal Factors on APOE-ε2 and ε4 Carriers' Brain Health: A Systematic Review

BACKGROUND

Apolipoprotein-E (APOE) ε4 and ε2 are the most prevalent risk-increasing and risk-reducing genetic predictors of Alzheimer's disease, respectively. However, the extent to which societal factors can reduce the harmful impact of APOE-ε4 and enhance the beneficial impact of APOE-ε2 on brain health has not yet been examined systematically.

METHODS

To fill this gap, we conducted a systematic review searching for studies in MEDLINE, Embase, PsycINFO, and Scopus until June 2023, that included: (a) 1 of 5 social determinants of health (SDH) identified by Healthy People 2030, (b) APOE-ε2 or APOE-ε4 allele carriers, (c) cognitive or brain-biomarker outcomes, and (d) studies with an analysis of how APOE-ε2 and/ or APOE-ε4 carriers differ on outcomes when exposed to SDH.

RESULTS

From 14 076 articles retrieved, 124 met the inclusion criteria. In most of the studies, exposure to favorable SDH reduced APOE-ε4's detrimental effect and enhanced APOE-ε2's beneficial effect on cognitive and brain-biomarker outcomes (cognition: 70.5%, n: 74/105; brain-biomarkers: 71.4%, n: 20/28). A similar pattern of results emerged in each of the 5 Healthy People 2030 SDH categories, where finishing high school, having resources to satisfy basic needs, less air pollution, less negative external stimuli that can generate stress (eg, negative age stereotypes), and exposure to multiple favorable SDH were associated with better cognitive and brain health among APOE-ε4 and APOE-ε2 carriers.

CONCLUSIONS

Societal factors can reduce the harmful impact of APOE-ε4 and enhance the beneficial impact of APOE-ε2 on cognitive outcomes. This suggests that plans to reduce dementia should include community-level policies promoting favorable SDH.

In vitro neurotoxicity of particles from diesel and biodiesel fueled engines following direct and simulated inhalation exposure

Combustion-derived particulate matter (PM) is a major source of air pollution. Efforts to reduce diesel engine emission include the application of biodiesel. However, while urban PM exposure has been linked to adverse brain effects, little is known about the direct effects of PM from regular fossil diesel (PMDEP) and biodiesel (PMBIO) on neuronal function. Furthermore, it is unknown to what extent the PM-induced effects in the lung (e.g., inflammation) affect the brain. This in vitro study investigates direct and indirect toxicity of PMDEP and PMBIO on the lung and brain and compared it with effects of clean carbon particles (CP). PM were generated using a common rail diesel engine. CP was sampled from a spark generator. First, effects of 48 h exposure to PM and CP (1.2-3.9 µg/cm2) were assessed in an in vitro lung model (air-liquid interface co-culture of Calu-3 and THP1 cells) by measuring cell viability, cytotoxicity, barrier function, inflammation, and oxidative and cell stress. None of the exposures caused clear adverse effects and only minor changes in gene expression were observed. Next, the basal medium was collected for subsequent simulated inhalation exposure of rat primary cortical cells. Neuronal activity, recorded using microelectrode arrays (MEA), was increased after acute (0.5 h) simulated inhalation exposure. In contrast, direct exposure to PMDEP and PMBIO (1-100 µg/mL; 1.2-119 µg/cm2) reduced neuronal activity after 24 h with lowest observed effect levels of respectively 10 µg/mL and 30 µg/mL, indicating higher neurotoxic potency of PMDEP, whereas neuronal activity remained unaffected following CP exposure. These findings indicate that combustion-derived PM potently inhibit neuronal function following direct exposure, while the lung serves as a protective barrier. Furthermore, PMDEP exhibit a higher direct neurotoxic potency than PMBIO, and the data suggest that the neurotoxic effects is caused by adsorbed chemicals rather than the pure carbon core.

Potential Effects of Long-Term Exposure to Air Pollution on Dementia: A Longitudinal Analysis in American Indians Aged 55 Years and Older

(1) Background: American Indians are disproportionately affected by air pollution, an important risk factor for dementia. However, few studies have investigated the effects of air pollution on the risk of dementia among American Indians. (2) Methods: This retrospective cohort study included a total of 26,871 American Indians who were 55+ years old in 2007, with an average follow-up of 3.67 years. County-level average air pollution data were downloaded from land-use regression models. All-cause dementia was identified using ICD-9 diagnostic codes from the Indian Health Service's (IHS) National Data Warehouse and related administrative databases. Cox models were employed to examine the association of air pollution with dementia incidence, adjusting for co-exposures and potential confounders. (3) Results: The average PM2.5 levels in the IHS counties were lower than those in all US counties, while the mean O3 levels in the IHS counties were higher than the US counties. Multivariable Cox regressions revealed a positive association between dementia and county-level O3 with a hazard ratio of 1.24 (95% CI: 1.02-1.50) per 1 ppb standardized O3. PM2.5 and NO2 were not associated with dementia risk after adjusting for all covariates. (4) Conclusions: O3 is associated with a higher risk of dementia among American Indians.

Can Incorrect Analysis of Time-Dependent Exposure Explain Associations between PM2.5 Exposure and Risk of Dementia?

Background

Epidemiological studies have reported positive associations between long-term exposure to particulate matter of 2.5 microns or less in diameter (PM2.5) and risk of Alzheimer's disease and other clinical dementia. Many of these studies have analyzed data using Cox Proportional Hazards (PH) regression, which estimates a hazard ratio (HR) for the treatment (in this case, exposure) effect on the time-to-event outcome while adjusting for influential covariates. PM2.5 levels vary over time. As air quality standards for PM2.5 have become more stringent over time, average outdoor PM2.5 levels have decreased substantially.

Objective

Investigate whether a Cox PH analysis that does not properly account for exposure that varies over time could produce a biased HR of similar magnitude to the HRs reported in recent epidemiological studies of PM2.5 and dementia risk.

Methods

Simulation analysis.

Results

We found that the biased HR can affect statistical analyses that consider exposure levels at event times only, especially if PM2.5 levels decreased consistently over time. Furthermore, the direction of such bias is away from the null and of a magnitude that is consistent with the reported estimates of dementia risk in several epidemiological studies of PM2.5 exposure (HR≈1.2 to 2.0).

Conclusions

This bias can be avoided by correctly assigning exposure to study subjects throughout the entire follow-up period. We recommend that investigators provide a detailed description of how time-dependent exposure variables were accounted for in their Cox PH analyses when they report their results.

Black-White Racial Disparities in Disabilities Among Older Americans Between 2008 and 2017: Improvements in Cognitive Disabilities but no Progress in Activities of Daily Living or Functional Limitations

The objectives of this study were to examine the prevalence of race-based disparities in cognitive problems, functional limitations (FLs), and activity of daily living (ADL) limitations between US Black and White older adults in 2008 and 2017, to explore how age, sex, income, and education attenuate these racial disparities, and to determine if Black-White health disparities are narrowing. Secondary analysis of the nationally representative American Community Surveys including 423,066 respondents aged ≥65 (388,602 White, 34,464 Black) in 2008 and 536,984 (488,483 White, 48,501 Black) in 2017. Findings indicate that Black-White racial disparities were apparent for all three outcomes in 2008 and 2017. Approximately half of the racial disparities was attenuated when adjustments were made for education and income. Racial disparities in cognition declined between 2008 and 2017 (p < .001) but persisted unabated in FLs and ADL limitations. Further exploration on the mechanisms of racial disparities is warranted.

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.

Association Between Long-Term Exposure to Ambient Air Pollution and the Risk of Mild Cognitive Impairment in a Chinese Urban Area: A Case-Control Study

Background

As a prodromal stage of dementia, significant emphasis has been placed on the identification of modifiable risks of mild cognitive impairment (MCI). Research has indicated a correlation between exposure to air pollution and cognitive function in older adults. However, few studies have examined such an association among the MCI population inChina.

Objective

We aimed to explore the association between air pollution exposure and MCI risk from the Hubei Memory and Aging Cohort Study.

Methods

We measured four pollutants from 2015 to 2018, 3 years before the cognitive assessment of the participants. Logistic regression models were employed to calculate odds ratios (ORs) to assess the relationship between air pollutants and MCI risk.

Results

Among 4,205 older participants, the adjusted ORs of MCI risk for the highest quartile of PM2.5, PM10, O3, and SO2 were 1.90 (1.39, 2.62), 1.77 (1.28, 2.47), 0.56 (0.42, 0.75), and 1.18 (0.87, 1.61) respectively, compared with the lowest quartile. Stratified analyses indicated that such associations were found in both males and females, but were more significant in older participants.

Conclusions

Our findings are consistent with the growing evidence suggesting that air pollution increases the risk of mild cognitive decline, which has considerable guiding significance for early intervention of dementia in the older population. Further studies in other populations and broader geographical areas are warranted to validate these findings.

A systematic review for the development of Alzheimer's disease in in vitro models: a focus on different inducing agents

Alzheimer's disease (AD) is the most common progressive neurodegenerative disease and is associated with dementia. Presently, various chemical and environmental agents are used to induce in-vitro models of Alzheimer disease to investigate the efficacy of different therapeutic drugs. We screened literature from databases such as PubMed, ScienceDirect, and Google scholar, emphasizing the diverse targeting mechanisms of neuro degeneration explored in in-vitro models. The results revealed studies in which different types of chemicals and environmental agents were used for in-vitro development of Alzheimer-targeting mechanisms of neurodegeneration. Studies using chemically induced in-vitro AD models included in this systematic review will contribute to a deeper understanding of AD. However, none of these models can reproduce all the characteristics of disease progression seen in the majority of Alzheimer's disease subtypes. Additional modifications would be required to replicate the complex conditions of human AD in an exact manner. In-vitro models of Alzheimer's disease developed using chemicals and environmental agents are instrumental in providing insights into the disease's pathophysiology; therefore, chemical-induced in-vitro AD models will continue to play vital role in future AD research. This systematic screening revealed the pivotal role of chemical-induced in-vitro AD models in advancing our understanding of AD pathophysiology and is therefore important to understand the potential of these chemicals in AD pathogenesis.

Community-Based Strategies to Reduce Alzheimer's Disease and Related Dementia Incidence Among Rural, Racially/Ethnically Diverse Older Adults

Purpose of Review

The purpose of this paper was to address the research question "What recent advances in Alzheimer's Disease and Related Dementias (ADRD) risk reduction strategies can be tailored for rural, racially/ethnically diverse populations?" A rural resident's life story that grounded the work is shared. Next, a brief description is provided regarding ADRD risk factors of importance in rural, multicultural settings. Gaps in U.S.-based research are highlighted. Policy actions and interventions that may make a difference in alleviating rural, ADRD-related disparities are offered.

Recent Findings

More than a dozen factors, including lack of built environment, periodontitis, poor air quality, and sensory loss, were identified that are of particular relevance to rural groups. Evidence of importance to underserved residents has also emerged regarding the harmful effects of ultra-processed foods on brain health, benefits of even minimal physical activity, and importance of social engagement, on brain health.

Summary

Resident-led initiatives will be key to creating change at the community level. Health providers are also called to assist in identifying and adapting culturally specific upstream approaches, in partnership with community stakeholders. These mechanisms are vital for decreasing ADRD burdens in underserved communities facing the largest disparities in preventive care.

Association between late-life air pollution exposure and medial temporal lobe atrophy in older women

Background

Ambient air pollution exposures increase risk for Alzheimer's disease (AD) and related dementias, possibly due to structural changes in the medial temporal lobe (MTL). However, existing MRI studies examining exposure effects on the MTL were cross-sectional and focused on the hippocampus, yielding mixed results.

Method

To determine whether air pollution exposures were associated with MTL atrophy over time, we conducted a longitudinal study including 653 cognitively unimpaired community-dwelling older women from the Women's Health Initiative Memory Study with two MRI brain scans (MRI-1: 2005-6; MRI-2: 2009-10; Mage at MRI-1=77.3±3.5years). Using regionalized universal kriging models, exposures at residential locations were estimated as 3-year annual averages of fine particulate matter (PM2.5) and nitrogen dioxide (NO2) prior to MRI-1. Bilateral gray matter volumes of the hippocampus, amygdala, parahippocampal gyrus (PHG), and entorhinal cortex (ERC) were summed to operationalize the MTL. We used linear regressions to estimate exposure effects on 5-year volume changes in the MTL and its subregions, adjusting for intracranial volume, sociodemographic, lifestyle, and clinical characteristics.

Results

On average, MTL volume decreased by 0.53±1.00cm3 over 5 years. For each interquartile increase of PM2.5 (3.26μg/m3) and NO2 (6.77ppb), adjusted MTL volume had greater shrinkage by 0.32cm3 (95%CI=[-0.43, -0.21]) and 0.12cm3 (95%CI=[-0.22, -0.01]), respectively. The exposure effects did not differ by APOE ε4 genotype, sociodemographic, and cardiovascular risk factors, and remained among women with low-level PM2.5 exposure. Greater PHG atrophy was associated with higher PM2.5 (b=-0.24, 95%CI=[-0.29, -0.19]) and NO2 exposures (b=-0.09, 95%CI=[-0.14, -0.04]). Higher exposure to PM2.5 but not NO2 was also associated with greater ERC atrophy. Exposures were not associated with amygdala or hippocampal atrophy.

Conclusion

In summary, higher late-life PM2.5 and NO2 exposures were associated with greater MTL atrophy over time in cognitively unimpaired older women. The PHG and ERC - the MTL cortical subregions where AD neuropathologies likely begin, may be preferentially vulnerable to air pollution neurotoxicity.

Alzheimer's Related Neurodegeneration Mediates Air Pollution Effects on Medial Temporal Lobe Atrophy

Exposure to ambient air pollution, especially particulate matter with aerodynamic diameter <2.5 μm (PM2.5) and nitrogen dioxide (NO2), are environmental risk factors for Alzheimer's disease and related dementia. The medial temporal lobe (MTL) is an important brain region subserving episodic memory that atrophies with age, during the Alzheimer's disease continuum, and is vulnerable to the effects of cerebrovascular disease. Despite the importance of air pollution it is unclear whether exposure leads to atrophy of the MTL and by what pathways. Here we conducted a longitudinal study examining associations between ambient air pollution exposure and MTL atrophy and whether putative air pollution exposure effects resembled Alzheimer's disease-related neurodegeneration or cerebrovascular disease-related neurodegeneration. Participants included older women (n = 627; aged 71-87) who underwent two structural brain MRI scans (MRI-1: 2005-6; MRI-2: 2009-10) as part of the Women's Health Initiative Memory Study of Magnetic Resonance Imaging. Regionalized universal kriging was used to estimate annual concentrations of PM2.5 and NO2 at residential locations aggregated to 3-year averages prior to MRI-1. The outcome was 5-year standardized change in MTL volumes. Mediators included voxel-based MRI measures of the spatial pattern of neurodegeneration of Alzheimer's disease (Alzheimer's disease pattern similarity scores [AD-PS]) and whole-brain white matter small-vessel ischemic disease (WM-SVID) volume as a proxy of global cerebrovascular damage. Structural equation models were constructed to examine whether the associations between exposures with MTL atrophy were mediated by the initial level or concurrent change in AD-PS score or WM-SVID while adjusting for sociodemographic, lifestyle, clinical characteristics, and intracranial volume. Living in locations with higher PM2.5 (per interquartile range [IQR]=3.17μg/m3) or NO2 (per IQR=6.63ppb) was associated with greater MTL atrophy (βPM2.5 = -0.29, 95% confidence interval [CI]=[-0.41,-0.18]; βNO2 =-0.12, 95%CI=[-0.23,-0.02]). Greater PM2.5 was associated with larger increases in AD-PS (βPM2.5 = 0.23, 95%CI=[0.12,0.33]) over time, which partially mediated associations with MTL atrophy (indirect effect= -0.10; 95%CI=[-0.15, -0.05]), explaining approximately 32% of the total effect. NO2 was positively associated with AD-PS at MRI-1 (βNO2=0.13, 95%CI=[0.03,0.24]), which partially mediated the association with MTL atrophy (indirect effect= -0.01, 95% CI=[-0.03,-0.001]). Global WM-SVID at MRI-1 or concurrent change were not significant mediators between exposures and MTL atrophy. Findings support the mediating role of Alzheimer's disease-related neurodegeneration contributing to MTL atrophy associated with late-life exposures to air pollutants. Alzheimer's disease-related neurodegeneration only partially explained associations between exposure and MTL atrophy suggesting the role of multiple neuropathological processes underlying air pollution neurotoxicity on brain aging.

Air pollution, dementia, and lifespan in the socio-economic gradient of aging: perspective on human aging for planning future experimental studies

Air pollution (AirPoll) accelerates human aging, as assessed by increased adult mortality and earlier onset of cardiovascular diseases, and dementia. Socio-economic strata (SES) of wealth and education have parallel differences of mortality and these diseases. Children from impoverished homes differ in brain development at birth and in risk of early fat excess and hypertension. To further enhance the healthspan, biogerontologists may consider a wider range of environmental exposures from gestation through later life morbidity that comprise the Gero-Exposome. Experimental studies with rodents and nematodes document shared transcriptional responses to AirPoll. In rodents, AirPoll exposure activates gene systems for body-wide detoxification through Nrf2 and NFkB transcription factors that mediate multiple aging processes. Gestational environmental factors include maternal diet and exposure to AirPoll and cigarette smoke. Correspondingly, gestational exposure of mice to AirPoll increased adult body fat, impaired glucose clearance, and decreased adult neurogenesis in the hippocampus, a brain region damaged in dementia. Nematode larvae also respond to AirPoll with Alzheimer relevant responses. These experimental approaches could identify to interventions for expanded human health and longevity across SES gradients.

To promote healthy aging, focus on the environment

To build health equity for an aging world marked by dramatic disparities in healthy lifespan between countries, regions and population groups, research at the intersections of biology, toxicology and the social and behavioral sciences points the way: to promote healthy aging, focus on the environment. In this Perspective, we suggest that ideas and tools from the emerging field of geroscience offer opportunities to advance the environmental science of aging. Specifically, the capacity to measure the pace and progress of biological processes of aging within individuals from relatively young ages makes it possible to study how changing environments can change aging trajectories from early in life, in time to prevent or delay aging-related disease and disability and build aging health equity.

The association of long-term exposure to criteria air pollutants, fine particulate matter components, and airborne trace metals with late-life brain amyloid burden in the Atherosclerosis Risk in Communities (ARIC) study

BACKGROUND

Studies suggest associations between long-term ambient air pollution exposure and outcomes related to Alzheimer's disease (AD). Whether a link exists between pollutants and brain amyloid accumulation, a biomarker of AD, is unclear. We assessed whether long-term air pollutant exposures are associated with late-life brain amyloid deposition in Atherosclerosis Risk in Communities (ARIC) study participants.

METHODS

We used a chemical transport model with data fusion to estimate ambient concentrations of PM2.5 and its components, NO2, NOx, O3 (24-hour and 8-hour), CO, and airborne trace metals. We linked concentrations to geocoded participant addresses and calculated 10-year mean exposures (2002 to 2011). Brain amyloid deposition was measured using florbetapir amyloid positron emission tomography (PET) scans in 346 participants without dementia in 2012-2014, and we defined amyloid positivity as a global cortical standardized uptake value ratio ≥ the sample median of 1.2. We used logistic regression models to quantify the association between amyloid positivity and each air pollutant, adjusting for putative confounders. In sensitivity analyses, we considered whether use of alternate air pollution estimation approaches impacted findings for PM2.5, NO2, NOx, and 24-hour O3.

RESULTS

At PET imaging, eligible participants (N = 318) had a mean age of 78 years, 56% were female, 43% were Black, and 27% had mild cognitive impairment. We did not find evidence of associations between long-term exposure to any pollutant and brain amyloid positivity in adjusted models. Findings were materially unchanged in sensitivity analyses using alternate air pollution estimation approaches for PM2.5, NO2, NOx, and 24-hour O3.

CONCLUSIONS

Air pollution may impact cognition and dementia independent of amyloid accumulation, though whether air pollution influences AD pathogenesis later in the disease course or at higher exposure levels deserves further consideration.

Ambient Air Pollution Exposure and Cerebral White Matter Hyperintensities in Older Adults: A Cross-Sectional Analysis in the Three-City Montpellier Study

BACKGROUND

Growing epidemiological evidence suggests an adverse relationship between exposure to air pollutants and cognitive health, and this could be related to the effect of air pollution on vascular health.

OBJECTIVE

We aim to evaluate the association between air pollution exposure and a magnetic resonance imaging (MRI) marker of cerebral vascular burden, white matter hyperintensities (WMH).

METHODS

This cross-sectional analysis used data from the French Three-City Montpellier study. Randomly selected participants 65-80 years of age underwent an MRI examination to estimate their total and regional cerebral WMH volumes. Exposure to fine particulate matter (PM 2.5 ), nitrogen dioxide (NO 2 ), and black carbon (BC) at the participants' residential address during the 5 years before the MRI examination was estimated with land use regression models. Multinomial and binomial logistic regression assessed the associations between exposure to each of the three pollutants and categories of total and lobar WMH volumes.

RESULTS

Participants' (n = 582 ) median age at MRI was 70.7 years [interquartile range (IQR): 6.1], and 52% (n = 300 ) were women. Median exposure to air pollution over the 5 years before MRI acquisition was 24.3 (IQR: 1.7) μ g / m 3 for PM 2.5 , 48.9 (14.6) μ g / m 3 for NO 2 , and 2.66 (0.60) 10 - 5 / m for BC. We found no significant association between exposure to the three air pollutants and total WMH volume. We found that PM 2.5 exposure was significantly associated with higher risk of temporal lobe WMH burden [odds ratio (OR) for an IQR increase = 1.82 (95% confidence interval: 1.41, 2.36) for the second volume tercile, 2.04 (1.59, 2.61) for the third volume tercile, reference: first volume tercile]. Associations for other regional WMH volumes were inconsistent.

CONCLUSION

In this population-based study in older adults, PM 2.5 exposure was associated with increased risk of high WMH volume in the temporal lobe, strengthening the evidence on PM 2.5 adverse effect on the brain. Further studies looking at different markers of cerebrovascular damage are still needed to document the potential vascular effects of air pollution. https://doi.org/10.1289/EHP12231.

NEUROMETABOLOMIC IMPACTS OF MODELED WILDFIRE SMOKE AND PROTECTIVE BENEFITS OF ANTI-AGING THERAPEUTICS IN AGED FEMALE C57BL/6J MICE

Wildland fires have become progressively more extensive over the past 30 years in the US, and now routinely generate smoke that deteriorates air quality for most of the country. We explored the neurometabolomic impact that smoke derived from biomass has on older (18 months) female C57BL/6J mice, both acutely and after 10 weeks of recovery from exposures. Mice (N=6/group) were exposed to wood smoke (WS) 4 hours/day, every other day, for 2 weeks (7 exposures total) to an average concentration of 0.448mg/m 3 per exposure. One group was euthanized 24 hours after the last exposure. Other groups were then placed on 1 of 4 treatment regimens for 10 weeks after wood smoke exposures: vehicle; resveratrol in chow plus nicotinamide mononucleotide in water (RNMN); senolytics via gavage (dasatanib+quercetin; DQ); or both RNMN with DQ (RNDQ). Among the findings, the aging from 18 months to 21 months was associated with the greatest metabolic shift, including changes in nicotinamide metabolism, with WS exposure effects that were relatively modest. WS caused a reduction in NAD+ within the prefrontal cortex immediately after exposure and a long-term reduction in serotonin that persisted for 10 weeks. The serotonin reductions were corroborated by forced swim tests, which revealed an increased immobility (reduction in motivation) immediately post-exposure and persisted for 10 weeks. RNMN had the most beneficial effects after WS exposure, while RNDQ caused markers of brain aging to be upregulated within WS-exposed mice. Findings highlight the persistent neurometabolomic and behavioral effects of woodsmoke exposure in an aged mouse model.

Significance Statement

Neurological impacts of wildfire smoke are largely underexplored but include neuroinflammation and metabolic changes. The present study highlights modulation of major metabolites in the prefrontal cortex and behavioral consequences in aged (18 month) female mice that persists 10 weeks after wood smoke exposure ended. Supplements derived from the anti-aging field were able to mitigate much of the woodsmoke effect, especially a combination of resveratrol and nicotinamide mononucleotide.

Association of Long-term Exposure to Air Pollution and Dementia Risk: The Role of Homocysteine, Methionine, and Cardiovascular Burden

BACKGROUND AND OBJECTIVES

Growing evidence links air pollution with dementia risk, but the biological mechanisms are largely unknown. We investigated the role played by homocysteine (tHcy) and methionine in this association and explored whether this could be explained by cardiovascular diseases (CVDs).

METHODS

Data were extracted from the ongoing Swedish National study on Aging and Care in Kungsholmen (SNAC-K), a longitudinal population-based study. At baseline, 2,512 dementia-free participants were examined up to 2013 (mean follow-up: 5.18 ± 2.96 years). Two air pollutants (particulate matter ≤2.5 μm [PM2.5] and nitrogen oxides [NOx]) were assessed yearly from 1990 until 2013 using dispersion models at residential addresses. The hazard ratio of dementia over air pollution levels was estimated using Cox models adjusted for age, sex, education, smoking, socioeconomic status, physical activity, retirement age, creatinine, year of assessment, and the use of supplements. The total effect of air pollutants on dementia was decomposed into 4 pathways involving tHcy/methionine: (1) direct effect; (2) indirect effect (mediation); (3) effect due to interaction; and (4) effect due to both mediation and interaction. To test whether the association was independent from CVDs (ischemic heart disease, atrial fibrillation, heart failure, and stroke), we repeated the analyses excluding those individuals who developed CVDs.

RESULTS

The mean age of the study participants was 73.4 years (SD: 10.4), and 62.1% were female individuals. During an average period of 5 years (mean: 5.18; SD: 2.96 years), 376 cases with incident dementia were identified. There was a 70% increased hazard of dementia per unit increase of PM2.5 during the 5 years before baseline (hazard ratio [HR]: 1.71; 95% CI 1.33-2.09). Overall, 50% (51.6%; 95% CI 9.0-94.1) of the total effect of PM2.5 on dementia was due to mediation of tHcy (6.6%; 95% CI 1.6-11.6) and/or interaction (47.8%; 95% CI 4.9-91.7) with tHcy and 48.4% (p = 0.03) to the direct effect of PM2.5 on dementia. High levels of methionine reduced the dementia hazard linked to PM2.5 by 31% (HR: 0.69; 95% CI 0.56-0.85) with 24.8% attributable to the interaction with methionine and 25.9% (p = 0.001) to the direct effect of PM2.5. No mediation effect was found through methionine. Attenuated results were obtained for NOx. Findings for tHcy were attenuated after excluding those who developed CVDs, while remained similar for methionine.

DISCUSSION

High levels of homocysteine enhanced the dementia risk attributed to air pollution, while high methionine concentrations reduced this risk. The impact of homocysteine on cardiovascular conditions partly explains this association. Alternative pathways other than cardiovascular mechanisms may be at play between methionine and dementia.

Association of genetic polymorphisms with mercapturic acids in the urine of young healthy subjects before and after exposure to outdoor air pollution

We aimed to identify the relationship between variations in metabolic genes and human urinary changes in mercapturic acids (MAs), including CEMA, HMPMA, SPMA, HPMA and HEMA, before and after air pollution exposure. Genotype detection for 47 relevant single nucleotide polymorphisms (SNPs) collected by literature research was performed. Five MAs expression levels in the urinary samples of 50 young healthy individuals with short-term exposure to clean, polluted and purified air at five time points were detected by targeted online solid-phase extraction liquid chromatography tandem mass spectrometry (SPE-LC-MS/MS), followed with associations of SNPs with MAs changes. Difference in MAs between polluted and clean/purified air was significantly associated with 21 SNPs mapped into 9 genes. Five SNPs in GSTP1 showed the most prominent association with the changes in SPMA expression, indicating that those SNPs in GSTP1 and SPMA might serve as biomarkers for susceptibility and the prognosis of lung cancer.

Is the expansion of the subway network alone capable of improving local air quality? A study case in São Paulo, Brazil

One of the policies adopted to reduce vehicular emissions is subway network expansion. This work fitted interrupted regression models to investigate the effects of the inauguration of subway stations on the mean, trend, and seasonality of the NO, NO2, NOx, and PM10 local concentrations. The regions investigated in the city of São Paulo (Brazil) were Pinheiros, Butantã, and St. Amaro. In Pinheiros, after the inauguration of the subway station, there were downward trends for all pollutants. However, these trends were not significantly different from the trends observed before. In Butantã, only regarding NO, there was a significant reduction and seasonal change after the subway station's inauguration. In St. Amaro, no trend in the PM10 concentration was noted. The absence of other transportation and land use policies in an integrative way to the subway network expansion may be responsible for the low air quality improvement. This study highlights that the expansion of the subway network must be integrated with other policies to improve local air quality.

Associations of air pollution with all-cause dementia, Alzheimer's disease, and vascular dementia: a prospective cohort study based on 437,932 participants from the UK biobank

Objective

To prospectively assess whether air pollution, including PM2.5, PM10, and NOx, is associated with the risk of all-cause dementia, Alzheimer's disease (AD), and vascular dementia, and to investigate the potential relationship between air pollution and genetic susceptibility in the development of AD.

Methods and results

Our study included 437,932 participants from the UK Biobank with a median follow-up period of over 10 years. Using a Cox proportional hazards model, we found that participants exposed to PM2.5 levels of ≥10 μg/m3 had a higher risk of developing all-cause dementia (HR = 1.1; 95% CI: 1.05-1.28; p < 0.05) compared to the group exposed to PM2.5 levels of <10 μg/m3. However, there was no significant association between PM10 levels of ≥15 μg/m3 and the risk of all-cause dementia, AD, or vascular dementia when compared to the group exposed to PM10 levels of <15 μg/m3. On the other hand, participants exposed to NOx levels of ≥50 μg/m3 had a significantly higher risk of all-cause dementia (HR = 1.14; 95% CI: 1.02-1.26; p < 0.05) and AD (HR = 1.26; 95% CI: 1.08-1.48; p < 0.05) compared to the group exposed to NOx levels of <50 μg/m3. Furthermore, we examined the combined effect of air pollution (PM2.5, PM10, and NOx) and Alzheimer's disease genetic risk score (AD-GRS) on the development of AD using a Cox proportional hazards model. Among participants with a high AD-GRS, those exposed to NOx levels of ≥50 μg/m3 had a significantly higher risk of AD compared to those in the group exposed to NOx levels of <50 μg/m3 (HR = 1.36; 95% CI: 1.03-1.18; p < 0.05). Regardless of air pollutant levels (PM2.5, PM10, or NOx), participants with a high AD-GRS had a significantly increased risk of developing AD. Similar results were obtained when assessing multiple variables using inverse probability of treatment weighting (IPTW).

Conclusion

Our findings indicate that individuals living in areas with PM2.5 levels of ≥10 μg/m3 or NOx levels of ≥50 μg/m3 are at a higher risk of developing all-cause dementia. Moreover, individuals with a high AD-GRS demonstrated an increased risk of developing AD, particularly in the presence of NOx ≥ 50 μg/m3.

Air pollution is associated with faster cognitive decline in Alzheimer's disease

OBJECTIVE

Although chronic exposure to air pollution is associated with an increased risk of dementia in normal elderlies, the effect of chronic exposure to air pollution on the rates of cognitive decline in Alzheimer's disease (AD) has not been elucidated.

METHODS

In this longitudinal study, a total of 269 patients with mild cognitive impairment or early dementia due to AD with the evidence of brain β-amyloid deposition were followed-up for a mean period of 4 years. Five-year normalized hourly cumulative exposure value of each air pollutant, such as carbon monoxide (CO), nitrogen dioxide (NO2 ), sulfur dioxide (SO2 ), and particulate matter (PM2.5 and PM10 ), was computed based on nationwide air pollution database. The effects of chronic exposure to air pollution on longitudinal cognitive decline rate were evaluated using linear mixed models.

RESULTS

Higher chronic exposure to SO2 was associated with a faster decline in memory score, whereas chronic exposure to CO, NO2 , and PM10 were not associated with the rate of cognitive decline. Higher chronic exposure to PM2.5 was associated with a faster decline in visuospatial score in apolipoprotein E ε4 carriers. These effects remained significant even after adjusting for potential confounders.

INTERPRETATION

Our findings suggest that chronic exposure to SO2 and PM2.5 is associated with faster clinical progression in AD.

Exposure to quasi-ultrafine particulate matter accelerates memory impairment and Alzheimer's disease-like neuropathology in the AppNL-G-F knock-in mouse model

Exposure to traffic-related air pollution consisting of particulate matter (PM) is associated with cognitive decline leading to Alzheimer's disease (AD). In this study, we sought to examine the neurotoxic effects of exposure to ultrafine PM and how it exacerbates neuronal loss and AD-like neuropathology in wildtype (WT) mice and a knock-in mouse model of AD (AppNL-G-F/+-KI) when the exposure occurs at a prepathologic stage or at a later age with the presence of neuropathology. AppNL-G-F/+-KI and WT mice were exposed to concentrated ultrafine PM from local ambient air in Irvine, California, for 12 weeks, starting at 3 or 9 months of age. Particulate matter-exposed animals received concentrated ultrafine PM up to 8 times above the ambient levels, whereas control animals were exposed to purified air. Particulate matter exposure resulted in a marked impairment of memory tasks in prepathologic AppNL-G-F/+-KI mice without measurable changes in amyloid-β pathology, synaptic degeneration, and neuroinflammation. At aged, both WT and AppNL-G-F/+-KI mice exposed to PM showed a significant memory impairment along with neuronal loss. In AppNL-G-F/+-KI mice, we also detected an increased amyloid-β buildup and potentially harmful glial activation including ferritin-positive microglia and C3-positive astrocytes. Such glial activation could promote the cascade of degenerative consequences in the brain. Our results suggest that exposure to PM impairs cognitive function at both ages while exacerbation of AD-related pathology and neuronal loss may depend on the stage of pathology, aging, and/or state of glial activation. Further studies will be required to unveil the neurotoxic role of glial activation activated by PM exposure.

Air Pollution: Role of Extracellular Vesicles-Derived Non-Coding RNAs in Environmental Stress Response

Air pollution has increased over the years, causing a negative impact on society due to the many health-related problems it can contribute to. Although the type and extent of air pollutants are known, the molecular mechanisms underlying the induction of negative effects on the human body remain unclear. Emerging evidence suggests the crucial involvement of different molecular mediators in inflammation and oxidative stress in air pollution-induced disorders. Among these, non-coding RNAs (ncRNAs) carried by extracellular vesicles (EVs) may play an essential role in gene regulation of the cell stress response in pollutant-induced multiorgan disorders. This review highlights EV-transported ncRNAs' roles in physiological and pathological conditions, such as the development of cancer and respiratory, neurodegenerative, and cardiovascular diseases following exposure to various environmental stressors.

Air Pollution: A Silent Key Driver of Dementia

In 2017, the Lancet Commission on Dementia Prevention, Intervention, and Care included air pollution in its list of potential risk factors for dementia; in 2018, the Lancet Commission on Pollution concluded that the evidence for a causal relationship between fine particulate matter (PM) and dementia is encouraging. However, few interventions exist to delay or prevent the onset of dementia. Air quality data are becoming increasingly available, and the science underlying the associated health effects is also evolving rapidly. Recent interest in this area has led to the publication of population-based cohort studies, but these studies have used different approaches to identify cases of dementia. The purpose of this article is to review recent evidence describing the association between exposure to air pollution and dementia with special emphasis on fine particulate matter of 2.5 microns or less. We also summarize here the proposed detailed mechanisms by which air pollutants reach the brain and activate the innate immune response. In addition, the article also provides a short overview of existing limitations in the treatment of dementia.

Particulate matter and ultrafine particles in urban air pollution and their effect on the nervous system

According to the World Health Organization, both indoor and urban air pollution are responsible for the deaths of around 3.5 million people annually. During the last few decades, the interest in understanding the composition and health consequences of the complex mixture of polluted air has steadily increased. Today, after decades of detailed research, it is well-recognized that polluted air is a complex mixture containing not only gases (CO, NO_x, and SO₂) and volatile organic compounds but also suspended particles such as particulate matter (PM). PM comprises particles with sizes in the range of 30 to 2.5 μm (PM₃₀, PM₁₀, and PM_2.5) and ultrafine particles (UFPs) (less than 0.1 μm, including nanoparticles). All these constituents have different chemical compositions, origins and health consequences. It has been observed that the concentration of PM and UFPs is high in urban areas with moderate traffic and increases in heavy traffic areas. There is evidence that inhaling PM derived from fossil fuel combustion is associated with a wide variety of harmful effects on human health, which are not solely associated with the respiratory system. There is accumulating evidence that the brains of urban inhabitants contain high concentrations of nanoparticles derived from combustion and there is both epidemiological and experimental evidence that this is correlated with the appearance of neurodegenerative human diseases. Neurological disorders, such as Alzheimer's and Parkinson's disease, multiple sclerosis, and cerebrovascular accidents, are among the main debilitating disorders of our time and their epidemiology can be classified as a public health emergency. Therefore, it is crucial to understand the pathophysiology and molecular mechanisms related to PM exposure, specifically to UFPs, present as pollutants in air, as well as their correlation with the development of neurodegenerative diseases. Furthermore, PM can enhance the transmission of airborne diseases and trigger inflammatory and immune responses, increasing the risk of health complications and mortality. Therefore, understanding the different levels of this issue is important to create and promote preventive actions by both the government and civilians to construct a strategic plan to treat and cope with the current and future epidemic of these types of disorders on a global scale.

Assessing the causal effect of long-term exposure to air pollution on cognitive decline in middle-aged and older adults - Empirical evidence from a nationwide longitudinal cohort

Air pollution remains a risk factor for the global burden of disease. Middle-aged and older people are more susceptible to air pollution because of their declining physical function and are more likely to develop diseases from long-term air pollution exposure. Studies of the effects of air pollution on cognitive function in middle-aged and older adults have been inconsistent. More representative and definitive evidence is needed. This study analysed data from the Chinese Family Panel Study, an ongoing nationwide prospective cohort study, collected in waves 2014, 2016 and 2018. Rigorously tested instrument was selected for analysis and participants' PM_2.5 and instrument exposures were assessed using high-precision satellite data. The causal relationship between long-term exposure to air pollution and poor cognitive function in middle-aged and older adults was investigated using the Correlated Random Effects Control Function (CRE-CF) method within a quasi-experimental framework. This study included a total of 7042 participants aged 45 years or older. A comparison of CRE-CF with other models (OLS model, ordered probit model, and ordered probit-CRE model) demonstrated the necessity of using CRE-CF given the endogeneity of air pollution. The credibility and validity of the instrumental variable were verified. In the CRE-CF model, long-term exposure to PM_2.5 was found to accelerate cognitive decline in middle-aged and older adults (coefficients of -0.159, -0.336 and -0.244 for the total cognitive, verbal and mathematical scores, respectively). Taken together, these results suggest that chronic exposure to ambient air pollution is associated with cognitive decline in middle-aged and older adults, which highlights the need for appropriate protective policies.

Association of air pollution with dementia: a systematic review with meta-analysis including new cohort data from China

It remains unclear whether a total exposure to air pollution (AP) is associated with an increased risk of dementia. Little is known on the association in low- and middle-income countries. Two cohort studies in China (in Anhui cohort 1402 older adults aged ≥ 60 followed up for 10 years; in Zhejiang cohort 6115 older adults followed up for 5 years) were conducted to examine particulate matter - PM_2.5 associated with all dementia and air quality index (AQI) with Alzheimer's disease, respectively. A systematic literature review and meta-analysis was performed following worldwide literature searched until May 20, 2020 to identify 15 population-based cohort studies examining the association of AP with dementia (or any specific type of dementia) through PubMed, MEDLINE, PsycINFO, SocINDEX, CINHAL, and CNKI. The cohort studies in China showed a significantly increased relative risk (RR) of dementia in relation to AP exposure; in Anhui cohort the adjusted RR was 2.14 (95% CI 1.00-4.56) in people with PM_2.5 exposure at ≥ 64.5 μg/m³ versus <63.5 μg/m³ and in Zhejiang cohort the adjusted RR was 2.28 (1.07-4.87) in AQI>90 versus ≤ 80. The systematic review revealed that all 15 studies were undertaken in high income countries/regions, with inconsistent findings. While they had reasonably good overall quality of studies, seven studies did not adjust smoking in analysis and 13 did not account for depression. Pooling all eligible data demonstrated that dementia risk increased with the total AP exposure (1.13, 1.08-1.19). Data analysis of air pollutants showed that the RR significantly increased with PM_2.5 (1.06, 1.03-1.10 in 2nd tertile exposure; 1.13, 1.07-1.19 in 3rd tertile versus 1st tertile), PM₁₀ (1.05, 0.86-1.29; 1.62, 0.60-4.36), carbon monoxide (1.69, 0.72-3.93; 1.52, 1.35-1.71), nitrogen dioxide (1.06, 1.03-1.09; 1.18, 1.10-1.28) and nitrogen oxides (1.09, 1.04-1.15; 1.26, 1.13-1.41), but not ozone. Controlling air pollution and targeting on specific pollutants would reduce dementia globally.

Ambient air pollution and clinical dementia: systematic review and meta-analysis

OBJECTIVE

To investigate the role of air pollutants in risk of dementia, considering differences by study factors that could influence findings.

DESIGN

Systematic review and meta-analysis.

DATA SOURCES

EMBASE, PubMed, Web of Science, Psycinfo, and OVID Medline from database inception through July 2022.

ELIGIBILITY CRITERIA FOR SELECTING STUDIES

Studies that included adults (≥18 years), a longitudinal follow-up, considered US Environmental Protection Agency criteria air pollutants and proxies of traffic pollution, averaged exposure over a year or more, and reported associations between ambient pollutants and clinical dementia. Two authors independently extracted data using a predefined data extraction form and assessed risk of bias using the Risk of Bias In Non-randomised Studies of Exposures (ROBINS-E) tool. A meta-analysis with Knapp-Hartung standard errors was done when at least three studies for a given pollutant used comparable approaches.

RESULTS

2080 records identified 51 studies for inclusion. Most studies were at high risk of bias, although in many cases bias was towards the null. 14 studies could be meta-analysed for particulate matter <2.5 µm in diameter (PM2.5). The overall hazard ratio per 2 μg/m3 PM2.5 was 1.04 (95% confidence interval 0.99 to 1.09). The hazard ratio among seven studies that used active case ascertainment was 1.42 (1.00 to 2.02) and among seven studies that used passive case ascertainment was 1.03 (0.98 to 1.07). The overall hazard ratio per 10 μg/m3 nitrogen dioxide was 1.02 ((0.98 to 1.06); nine studies) and per 10 μg/m3 nitrogen oxide was 1.05 ((0.98 to 1.13); five studies). Ozone had no clear association with dementia (hazard ratio per 5 μg/m3 was 1.00 (0.98 to 1.05); four studies).

CONCLUSION

PM2.5 might be a risk factor for dementia, as well as nitrogen dioxide and nitrogen oxide, although with more limited data. The meta-analysed hazard ratios are subject to limitations that require interpretation with caution. Outcome ascertainment approaches differ across studies and each exposure assessment approach likely is only a proxy for causally relevant exposure in relation to clinical dementia outcomes. Studies that evaluate critical periods of exposure and pollutants other than PM2.5, and studies that actively assess all participants for outcomes are needed. Nonetheless, our results can provide current best estimates for use in burden of disease and regulatory setting efforts.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO CRD42021277083.