Particulate Matter Exposure Exacerbates Amyloid-β Plaque Deposition and Gliosis in APP/PS1 Mice

Neurodegenerative pathways and metabolic changes in the hippocampus and cortex of mice exposed to urban particulate matter: Insights from an integrated interactome analysis

Recently, urban particulate matter (UPM) exposure has been associated with the development of brain disorders. This study uses bioinformatic analyses to elucidate the molecular unexplored mechanisms underlying the effects of UPM exposure on the brain. Mice are exposed to UPM (from 3 days to 20 weeks), and their behavioral patterns measured. We measure pathology and gene expression in the hippocampus and cortical regions of the brain. An integrated interactome of genes is established, which enriches information on metabolic processes. Using this network, we isolate the core genes that are differentially expressed in the samples. We observe cognitive loss and pathological changes in the brains of mice at 16 or 20 weeks of exposure. Through network analysis of core-differential genes and measurement of pathway activity, we identify differences in the response to UPM exposure between the hippocampus and cortex. However, neurodegenerative disease pathways are implicated in both tissues following short-term exposure to UPM. There were also significant changes in metabolic function in both tissues depending on UPM exposure time. Additionally, the cortex of UPM-exposed mice shows more similarities with psychiatric disorders than with neurodegenerative diseases. The connectivity map database is used to isolate genes contributing to changes in expression due to UPM exposure. New approaches for inhibiting or preventing the brain damage caused by UPM exposure can be developed by targeting the functions and selected genes identified in this study.

Therapeutic potential of plant-derived natural compounds in Alzheimer's disease: Targeting microglia-mediated neuroinflammation

Microglia are resident immune cells of the central nervous system (CNS) with roles in sensing, housekeeping, and defense. Exploring the role of microglia in the occurrence and development of Alzheimer's disease (AD) and the possible therapeutic mechanism of plant-derived natural compounds (PDNCs) that regulate microglia-associated neuroinflammation may potentially help in elucidating the pathogenesis of AD and provide novel insights for its treatment. This review explores the role of abnormal microglial activation and its dominant neuroinflammatory response, as well as the activation of their target receptors and signaling pathways in AD pathogenesis. Additionally, we report an update on the potential pharmacological mechanisms of multiple PDNCs in modulating microglia-associated neuroinflammation in AD treatment. Dysregulated activation of microglial receptors and their downstream pathways impaired immune homeostasis in animal models of AD. Multiple signaling pathways, such as mitogen-activated protein kinase (MAPK), nuclear factor kappa light chain enhancer of activated B cells (NF-κB), and Toll-like receptors, play important roles in microglial activation and can exacerbate microglia-mediated neuroinflammation. PDNCs, such as magnolol, stigmasterol, matrine, naringenin, naringin, and resveratrol, can delay the progression of AD by inhibiting the proinflammatory receptors of microglia, activating its anti-inflammatory receptors, regulating the receptors related to β-amyloid (Aβ) clearance, reversing immune dysregulation, and maintaining the immune homeostasis of microglial downstream pathways. This review summarizes the mechanisms by which microglia cause chronic inflammation in AD and evaluates the beneficial effects of PDNCs on immune regulation in AD by regulating microglial receptors and their downstream pathways.

House dust mite-induced asthma exacerbates Alzheimer's disease changes in the brain of the AppNL-G-F mouse model of disease

Alzheimer's disease (AD) is an age-related neurodegenerative disorder characterized by the accumulation of amyloid-β (Aβ) plaques, neuroinflammation, and neuronal death. Besides aging, various comorbidities increase the risk of AD, including obesity, diabetes, and allergic asthma. Epidemiological studies have reported a 2.17-fold higher risk of dementia in asthmatic patients. However, the molecular mechanism(s) underlying this asthma-associated AD exacerbation is unknown. This study was designed to explore house dust mite (HDM)-induced asthma effects on AD-related brain changes using the AppNL-G-F transgenic mouse model of disease. Male and female 8-9 months old C57BL/6J wild type and AppNL-G-F mice were exposed to no treatment, saline sham, or HDM extract every alternate day for 16 weeks for comparison across genotypes and treatment. Mice were euthanized at the end of the experiment, and broncho-alveolar lavage fluid (BALF), blood, lungs, and brains were collected. BALF was used to quantify immune cell phenotype, cytokine levels, total protein content, lactate dehydrogenase (LDH) activity, and total IgE. Lungs were sectioned and stained with hematoxylin and eosin, Alcian blue, and Masson's trichrome. Serum levels of cytokines and soluble Aβ1-40/42 were quantified. Brains were sectioned and immunostained for Aβ, GFAP, CD68, and collagen IV. Finally, frozen hippocampi and temporal cortices were used to perform Aβ ELISAs and cytokine arrays, respectively. HDM exposure led to increased levels of inflammatory cells, cytokines, total protein content, LDH activity, and total IgE in the BALF, as well as increased pulmonary mucus and collagen staining in both sexes and genotypes. Levels of serum cytokines increased in all HDM-exposed groups. Serum from the AppNL-G-F HDM-induced asthma group also had significantly increased soluble Aβ1-42 levels in both sexes. In agreement with this peripheral change, hippocampi from asthma-induced male and female AppNL-G-F mice demonstrated elevated Aβ plaque load and increased soluble Aβ 1-40/42 and insoluble Aβ 1-40 levels. HDM exposure also increased astrogliosis and microgliosis in both sexes of AppNL-G-F mice, as indicated by GFAP and CD68 immunoreactivity, respectively. Additionally, HDM exposure elevated cortical levels of several cytokines in both sexes and genotypes. Finally, HDM-exposed groups also showed a disturbed blood-brain-barrier (BBB) integrity in the hippocampus of AppNL-G-F mice, as indicated by decreased collagen IV immunoreactivity. HDM exposure was responsible for an asthma-like condition in the lungs that exacerbated Aβ pathology, astrogliosis, microgliosis, and cytokine changes in the brains of male and female AppNL-G-F mice that correlated with reduced BBB integrity. Defining mechanisms of asthma effects on the brain may identify novel therapeutic targets for asthma and AD.

Intersection of Aging and Particulate Matter 2.5 Exposure in Real World: Effects on Inflammation and Endocrine Axis Activities in Rats

Exposure to particulate matter 2.5 (PM2.5) is detrimental to multiple organ systems. Given the factor that aging also alters the cellularity and response of immune system and dysfunction of hypothalamic-pituitary-adrenal, -gonad and -thyroid axes, it is imperative to investigate whether chronic exposure to PM2.5 interacts with aging in these aspects. In this study, two-months-old Sprague-Dawley rats were exposed to real world PM2.5 for 16 months. PM2.5 exposure diminished the relative numbers of CD4+ T cells and CD8+ T cells and increased the relative number of B cells in the peripheral blood of male rats. Conversely, only reduced relative number of CD4+ T cells was seen in the blood of female rats. These shifts resulted in elevated levels of proinflammatory factors interleukin-6 and tumor necrosis factor-α in the circulatory systems of both sex, with females also evidencing a rise in interleukin-1β levels. Moreover, heightened interleukin-6 was solely discernible in the hippocampus of female subjects, while increased tumor necrosis factor-α concentrations were widespread in female brain regions but confined to the male hypothalamus. Notable hormonal decreases were observed following PM2.5 exposure in both sex. These comprised declines in biomolecules such as corticotrophin-releasing hormone and cortisol, generated by the hypothalamic-pituitary-adrenal axis, and thyroid-releasing hormone and triiodothyronine, produced by the hypothalamic-pituitary-thyroid axis. Hormonal elements such as gonadotropin-releasing hormone, luteinizing hormone, and follicle-stimulating hormone, derived from the hypothalamic-pituitary-gonad axis, were also diminished. Exclusive to male rats was a reduction in adrenocorticotropic hormone levels, whereas a fall in thyroid-stimulating hormone was unique to female rats. Decreases in sex-specific hormones, including testosterone, estradiol, and progesterone, were also noted. These findings significantly enrich our comprehension of the potential long-term health repercussions associated with PM2.5 interaction particularly among the aging populace.

From Inhalation to Neurodegeneration: Air Pollution as a Modifiable Risk Factor for Alzheimer's Disease

Air pollution, a growing concern for public health, has been linked to various respiratory and cardiovascular diseases. Emerging evidence also suggests a link between exposure to air pollutants and neurodegenerative diseases, particularly Alzheimer's disease (AD). This review explores the composition and sources of air pollutants, including particulate matter, gases, persistent organic pollutants, and heavy metals. The pathophysiology of AD is briefly discussed, highlighting the role of beta-amyloid plaques, neurofibrillary tangles, and genetic factors. This article also examines how air pollutants reach the brain and exert their detrimental effects, delving into the neurotoxicity of air pollutants. The molecular mechanisms linking air pollution to neurodegeneration are explored in detail, focusing on oxidative stress, neuroinflammation, and protein aggregation. Preclinical studies, including in vitro experiments and animal models, provide evidence for the direct effects of pollutants on neuronal cells, glial cells, and the blood-brain barrier. Epidemiological studies have reported associations between exposure to air pollution and an increased risk of AD and cognitive decline. The growing body of evidence supporting air pollution as a modifiable risk factor for AD underscores the importance of considering environmental factors in the etiology and progression of neurodegenerative diseases, in the face of worsening global air quality.

Air pollution accelerates the development of obesity and Alzheimer's disease: the role of leptin and inflammation - a mini-review

Air pollution is an urgent concern linked to numerous health problems in low- and middle-income countries, where 92% of air pollution-related deaths occur. Particulate matter 2.5 (PM2.5) is the most harmful component of air pollutants, increasing inflammation and changing gut microbiota, favoring obesity, type 2 diabetes, and Alzheimer's Disease (AD). PM2.5 contains lipopolysaccharides (LPS), which can activate the Toll-like receptor 4 (TLR4) signaling pathway. This pathway can lead to the release of pro-inflammatory markers, including interleukins, and suppressor of cytokine signaling-3 (SOCS3), which inhibits leptin action, a hormone that keeps the energy homeostasis. Leptin plays a role in preventing amyloid plaque deposition and hyperphosphorylation of tau-protein (p-tau), mechanisms involved in the neurodegeneration in AD. Approximately 50 million people worldwide are affected by dementia, with a significant proportion living in low-and middle-income countries. This number is expected to triple by 2050. This mini-review focuses on the potential impact of PM2.5 exposure on the TLR4 signaling pathway, its contribution to leptin resistance, and dysbiosis that exacerbates the link between obesity and AD.

Long-term exposure to major constituents of fine particulate matter and neurodegenerative diseases: A population-based survey in the Pearl River Delta Region, China

BACKGROUND

Exposure to PM2.5 has been linked to neurodegenerative diseases, with limited understanding of constituent-specific contributions.

OBJECTIVES

To explore the associations between long-term exposure to PM2.5 constituents and neurodegenerative diseases.

METHODS

We recruited 148,274 individuals aged ≥ 60 from four cities in the Pearl River Delta region, China (2020 to 2021). We calculated twenty-year average air pollutant concentrations (PM2.5 mass, black carbon (BC), organic matter (OM), ammonium (NH4+), nitrate (NO3-) and sulfate (SO42-)) at the individuals' home addresses. Neurodegenerative diseases were determined by self-reported doctor-diagnosed Alzheimer's disease (AD) and Parkinson's disease (PD). Generalized linear mixed models were employed to explore associations between pollutants and neurodegenerative disease prevalence.

RESULTS

PM2.5 and all five constituents were significantly associated with a higher prevalence of AD and PD. The observed associations generally exhibited a non-linear pattern. For example, compared with the lowest quartile, higher quartiles of BC were associated with greater odds for AD prevalence (i.e., the adjusted odds ratios were 1.81; 95% CI, 1.45-2.27; 1.78; 95% CI, 1.37-2.32; and 1.99; 95% CI, 1.54-2.57 for the second, third, and fourth quartiles, respectively).

CONCLUSIONS

Long-term exposure to PM2.5 and its constituents, particularly combustion-related BC, OM, and SO42-, was significantly associated with higher prevalence of AD and PD in Chinese individuals.

ENVIRONMENTAL IMPLICATION

PM2.5 is a routinely regulated mixture of multiple hazardous constituents that can lead to diverse adverse health outcomes. However, current evidence on the specific contributions of PM2.5 constituents to health effects is scarce. This study firstly investigated the association between PM2.5 constituents and neurodegenerative diseases in the moderately to highly polluted Pearl River Delta region in China, and identified hazardous constituents within PM2.5 that have significant impacts. This study provides important implications for the development of targeted PM2.5 prevention and control policies to reduce specific hazardous PM2.5 constituents.

Fibrinaloid Microclots and Atrial Fibrillation

Atrial fibrillation (AF) is a comorbidity of a variety of other chronic, inflammatory diseases for which fibrinaloid microclots are a known accompaniment (and in some cases, a cause, with a mechanistic basis). Clots are, of course, a well-known consequence of atrial fibrillation. We here ask the question whether the fibrinaloid microclots seen in plasma or serum may in fact also be a cause of (or contributor to) the development of AF. We consider known 'risk factors' for AF, and in particular, exogenous stimuli such as infection and air pollution by particulates, both of which are known to cause AF. The external accompaniments of both bacterial (lipopolysaccharide and lipoteichoic acids) and viral (SARS-CoV-2 spike protein) infections are known to stimulate fibrinaloid microclots when added in vitro, and fibrinaloid microclots, as with other amyloid proteins, can be cytotoxic, both by inducing hypoxia/reperfusion and by other means. Strokes and thromboembolisms are also common consequences of AF. Consequently, taking a systems approach, we review the considerable evidence in detail, which leads us to suggest that it is likely that microclots may well have an aetiological role in the development of AF. This has significant mechanistic and therapeutic implications.

Update on modifiable risk factors for Alzheimer's disease and related dementias

PURPOSE OF REVIEW

All human beings undergo a lifelong cumulative exposure to potentially preventable adverse factors such as toxins, infections, traumatisms, and cardiovascular risk factors, collectively termed exposome. The interplay between the individual's genetics and exposome is thought to have a large impact in health outcomes such as cancer and cardiovascular disease. Likewise, a growing body of evidence is supporting the idea that preventable factors explain a sizable proportion of Alzheimer's disease and related dementia (ADRD) cases.

RECENT FINDINGS

Here, we will review the most recent epidemiological, experimental preclinical, and interventional clinical studies examining some of these potentially modifiable risk factors for ADRD. We will focus on new evidence regarding cardiovascular risk factors, air pollution, viral and other infectious agents, traumatic brain injury, and hearing loss.

SUMMARY

While greater and higher quality epidemiological and experimental evidence is needed to unequivocally confirm their causal link with ADRD and/or unravel the underlying mechanisms, these modifiable risk factors may represent a window of opportunity to reduce ADRD incidence and prevalence at the population level via health screenings, and education and health policies.

PM2.5 induce neurotoxicity via iron overload and redox imbalance mediated-ferroptosis in HT22 cells

PM2.5 is an important risk factor for the development and progression of cognitive impairment-related diseases. Ferroptosis, a new form of cell death driven by iron overload and lipid peroxidation, is proposed to have significant implications. To verify the possible role of ferroptosis in PM2.5-induced neurotoxicity, we investigated the cytotoxicity, intracellular iron content, iron metabolism-related genes, oxidative stress indices and indicators involving in Nrf2 and ferroptosis signaling pathways. Neurotoxicity biomarkers as well as the ferroptotic cell morphological changes were determined by Western Blot and TEM analysis. Our results revealed that PM2.5 induced cytotoxicity, lipid peroxidation, as indicated by MDA content, and neurotoxicity via Aβ deposition in a dose-related manner. Decreased cell viability and excessive iron accumulation in HT-22 cells can be partially blocked by ferroptosis inhibitors. Interestingly, GPX activity, Nrf2, and its regulated ferroptotic-related proteins (i.e. GPX4 and HO-1) were significantly up-regulated by PM2.5. Moreover, gene expression of DMT1, TfR1, IRP2 and FPN1 involved in iron homeostasis and NCOA4-dependent ferritinophagy were activated after PM2.5 exposure. The results demonstrated that PM2.5 triggered ferritinophagy-dependent ferroptotic cell death due to iron overload and redox imbalance. Activation of Nrf2 signaling pathways may confer a protective mechanism for PM2.5-induced oxidative stress and ferroptosis.

Functional identification of long non-coding RNAs induced by PM2.5 in microglia through microarray analysis

As a dominating air pollutant, atmospheric fine particulate matter within 2.5 μm in diameter (PM2.5) has attracted increasing attention from the researchers all over the world, which will lead to various adverse effects on the central nervous system (CNS), yet the potential mechanism is unclear. In this study, the microglia (BV2 cell line) were exposed to different concentrations of PM2.5 (5, 10 and 20 μg/cm2) for 24 h. It was found that PM2.5 could result in adverse effects on microglia such as decreased cell viability, structural damage and even cell death. And it was reported that long non-coding RNAs (lncRNAs) could participate in multitudinous neurological diseases. Therefore, the microarray analysis was conducted in order to disclose the underlying neurotoxicity mechanism of PM2.5 by ascertaining the differentially expressed lncRNAs (DElncRNAs). The consequences indicated that the DElncRNAs were enriched in various biological pathways, including ferroptosis, IL-17 signaling pathway and NOD-like receptor signaling pathway. Moreover, the cis- and trans-regulated mRNAs by DElncRNAs as well as the corresponding transcriptional factors (TFs) were observed, such as CEBPA, MYC, MEIS1 and KLF4. In summary, our study supplies some candidate libraries and potential preventive target against PM2.5-induced toxicity through targeting lncRNAs. Furthermore, the post-transcriptional regulation will contribute to the future research on PM2.5-induced neurotoxicity.

Neurodegenerative effects of air pollutant Particles: Biological mechanisms implicated for Early-Onset Alzheimer's disease

BACKGROUND

Sporadic Alzheimer's disease (AD) occurs in 99% of all cases and can be influenced by air pollution such as diesel emissions and more recently, an iron oxide particle, magnetite, detected in the brains of AD patients. However, a mechanistic link between air pollutants and AD development remains elusive.

AIM

To study the development of AD-relevant pathological effects induced by air pollutant particle exposures and their mechanistic links, in wild-type and AD-predisposed models.

METHODS

C57BL/6 (n = 37) and APP/PS1 transgenic (n = 38) mice (age 13 weeks) were exposed to model pollutant iron-based particle (Fe0-Fe3O4, dTEM = 493 ± 133 nm), hydrocarbon-based diesel combustion particle (43 ± 9 nm) and magnetite (Fe3O4, 153 ± 43 nm) particles (66 µg/20 µL/third day) for 4 months, and were assessed for behavioural changes, neuronal cell loss, amyloid-beta (Aβ) plaque, immune response and oxidative stress-biomarkers. Neuroblastoma SHSY5Y (differentiated) cells were exposed to the particles (100 μg/ml) for 24 h, with assessments on immune response biomarkers and reactive oxygen species generation.

RESULTS

Pollutant particle-exposure led to increased anxiety and stress levels in wild-type mice and short-term memory impairment in AD-prone mice. Neuronal cell loss was shown in the hippocampal and somatosensory cortex, with increased detection of Aβ plaque, the latter only in the AD-predisposed mice, with the wild-type not genetically disposed to form the plaque. The particle exposures however, increased AD-relevant immune system responses, including inflammation, in both strains of mice. Exposures also stimulated oxidative stress, although only observed in wild-type mice. The in vitro studies complemented the immune response and oxidative stress observations.

CONCLUSIONS

This study provides insights into the mechanistic links between inflammation and oxidative stress to pollutant particle-induced AD pathologies, with magnetite apparently inducing the most pathological effects. No exacerbation of the effects was observed in the AD-predisposed model when compared to the wild-type, indicating a particle-induced neurodegeneration that is independent of disease state.

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.

Traffic-related air pollution and dementia incidence in the Adult Changes in Thought Study

BACKGROUND

While epidemiologic evidence links higher levels of exposure to fine particulate matter (PM2.5) to decreased cognitive function, fewer studies have investigated links with traffic-related air pollution (TRAP), and none have examined ultrafine particles (UFP, ≤100 nm) and late-life dementia incidence.

OBJECTIVE

To evaluate associations between TRAP exposures (UFP, black carbon [BC], and nitrogen dioxide [NO2]) and late-life dementia incidence.

METHODS

We ascertained dementia incidence in the Seattle-based Adult Changes in Thought (ACT) prospective cohort study (beginning in 1994) and assessed ten-year average TRAP exposures for each participant based on prediction models derived from an extensive mobile monitoring campaign. We applied Cox proportional hazards models to investigate TRAP exposure and dementia incidence using age as the time axis and further adjusting for sex, self-reported race, calendar year, education, socioeconomic status, PM2.5, and APOE genotype. We ran sensitivity analyses where we did not adjust for PM2.5 and other sensitivity and secondary analyses where we adjusted for multiple pollutants, applied alternative exposure models (including total and size-specific UFP), modified the adjustment covariates, used calendar year as the time axis, assessed different exposure periods, dementia subtypes, and others.

RESULTS

We identified 1,041 incident all-cause dementia cases in 4,283 participants over 37,102 person-years of follow-up. We did not find evidence of a greater hazard of late-life dementia incidence with elevated levels of long-term TRAP exposures. The estimated hazard ratio of all-cause dementia was 0.98 (95 % CI: 0.92-1.05) for every 2000 pt/cm3 increment in UFP, 0.95 (0.89-1.01) for every 100 ng/m3 increment in BC, and 0.96 (0.91-1.02) for every 2 ppb increment in NO2. These findings were consistent across sensitivity and secondary analyses.

DISCUSSION

We did not find evidence of a greater hazard of late-life dementia risk with elevated long-term TRAP exposures in this population-based prospective cohort study.

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.

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

Exposure to particulate matter (PM) has been associated with a range of health impacts, including neurological abnormalities that affect neurodevelopment, neuroplasticity, and behavior. Recently, there has been growing interest in investigating the possible relationship between PM exposure and the onset and progression of neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, Huntington's disease, and multiple sclerosis. However, the precise mechanism by which PM affects neurodegeneration is still unclear, even though several epidemiological and animal model studies have provided mechanistic insights. This article presents a review of the current research on the neurotoxicity of PM and its impact on neurodegenerative diseases. This review summarizes findings from epidemiological and animal model studies collected through searches in Google Scholar, PubMed, Web of Science, and Scopus. This review paper also discusses the reported effects of PM exposure on the central nervous system and highlights research gaps and future directions. The information presented in this review may inform public health policies aimed at reducing PM exposure and may contribute to the development of new treatments for neurodegenerative diseases. Further mechanistic and therapeutic research will be needed to fully understand the relationship between PM exposure and neurodegenerative diseases.

Acoustic stimulation during sleep improves cognition and ameliorates Alzheimer's disease pathology in APP/PS1 mice

Nonpharmacological therapies for Alzheimer's disease (AD) have become a popular research topic, and acoustic stimulation during sleep is one such promising strategy for the clinical treatment of AD. Some animal experiments have illustrated that acoustic stimulation at a specific frequency can ameliorate AD-related pathology or improve cognition in mice, but these studies did not explore the effective time window of auditory stimulation. Here, we explored the effects of acoustic stimulation during wakefulness and acoustic stimulation during sleep on cognition and AD-related pathology in APP/PS1 mice and the underlying mechanisms. In this study, forty APP/PS1 mice were equally divided into the following 4 groups and treated for 28 days: the chronic sleep deprivation (CSD) group (exposed to sleep deprivation from zeitgeber time [ZT] 0 to ZT 12 each day), the normal sleep and stress exposure (NSS) group (exposed to a stressor from ZT 0 to ZT 12 each day), the acoustic stimulation during wakefulness (ASW) group (exposed to sleep deprivation and 40 Hz acoustic stimulation from ZT 0 to ZT 12 each day) and the acoustic stimulation during sleep (ASS) group (exposed to sleep deprivation from ZT 0 to ZT 12 and 40 Hz acoustic stimulation from ZT 12 to ZT 24 each day). After the intervention, cognition was assessed by behavioural experiments. The amyloid-β burden was analysed by Western blotting, immunofluorescence and enzyme-linked immunosorbent assay. Tau pathology was assessed by Western blotting. Mitochondrial function was evaluated by transmission electron microscopy, Western blotting and fluorescence intensity measurement. We found that the NSS and ASS groups had better cognitive functions than the CSD and ASW groups. The Aβ burden and tau phosphorylation were lower in the NSS and ASS groups than in the CSD and ASW groups. Mitochondrial function was better in the NSS and ASS groups than in the CSD and ASW groups. However, the differences in these parameters between the NSS and ASS groups and between the CSD and ASW groups were not significant. Our findings suggest that acoustic stimulation at a specific frequency during sleep, but not during wakefulness, reduces the amyloid-β burden by inhibiting amyloid beta precursor protein-binding protein 2, hinders tau phosphorylation by blocking glycogen synthase kinase 3 beta, and restores mitochondrial function by elevating mitophagy and promoting mitochondrial biogenesis.

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.

Impact of Particulate Matter Exposure and Aerobic Exercise on Circulating Biomarkers of Oxidative Stress, Antioxidant Status, and Inflammation in Young and Aged Mice

Exposure to particulate matter (PM) and exercise training can have antagonistic effects on inflammatory responses and the balance between pro-oxidants and antioxidants in the body. However, the underlying mechanisms of these effects remain unclear. This study aimed to investigate the effects of PM exposure and aerobic exercise training on oxidative stress, antioxidant status, and inflammation in mice of different ages. Two groups of male C57BL/6 mice, comprising forty 1-month-old and forty 12-month-old mice, were exposed to either PM or exercise training or both for 8 weeks. PM exposure led to significantly higher 8-hydroxydeoxyguanosine (8-OHdG), malondialdehyde (MDA), interleukin-1β (IL-1β), interleukin-6 (IL-6), and tumor necrosis factor α (TNF-α) levels (p < 0.05) and significantly lower superoxide dismutase (SOD) and catalase (CAT) activities (p < 0.05) in both age groups exposed to PM compared to the control groups. Conversely, aerobic exercise training led to significantly lower 8-OHdG, MDA, IL-1β, IL-6, and TNF-α levels (p < 0.05) and significantly higher SOD and CAT activities (p < 0.05) in both age groups receiving exercise training, compared to those exposed to PM. Moreover, young mice in the exercise training and PM group showed significantly lower 8-OHdG, MDA, and IL-1β levels (p < 0.05) and significantly higher SOD and CAT activities (p < 0.05) than young mice in the PM exposure group. However, these levels did not vary significantly between the group of old mice that either received exercise training or exposure to PM. Our results suggest that while PM exposure could cause pro-oxidant/antioxidant imbalances and inflammatory responses, regular aerobic exercise could ameliorate these negative effects, although these vary with age. Nevertheless, the antioxidant and anti-inflammatory effects of exercise were countered by PM exposure, especially in older mice.

Korean Red Ginseng Prevents the Deterioration of Lung and Brain Function in Chronic PM2.5-Exposed Mice by Regulating Systemic Inflammation

This study was conducted to confirm the effects of Korean red ginseng on lung and brain dysfunction in a BALB/c mice model exposed to particulate matter (PM)2.5 for 12 weeks. Learning and cognitive abilities were assessed with Y-maze, passive avoidance, and Morris water maze tests. To evaluate the ameliorating effect of red ginseng extract (RGE), the antioxidant system and mitochondrial function were investigated. The administration of RGE protected lung and brain impairment by regulating the antioxidant system and mitochondrial functions damaged by PM2.5-induced toxicity. Moreover, RGE prevented pulmonary fibrosis by regulating the transforming growth factor beta 1 (TGF-β1) pathway. RGE attenuated PM2.5-induced pulmonary and cognitive dysfunction by regulating systemic inflammation and apoptosis via the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB)/c-Jun N-terminal kinases (JNK) pathway. In conclusion, RGE might be a potential material that can regulate chronic PM2.5-induced lung and brain cognitive dysfunction.

Neurotoxicity of the air-borne particles: From molecular events to human diseases

Exposure to PM_2.5 is associated with an increased incidence of CNS diseases in humans, as confirmed by numerous epidemiological studies. Animal models have demonstrated that PM_2.5 exposure can damage brain tissue, neurodevelopmental issues and neurodegenerative diseases. Both animal and human cell models have identified oxidative stress and inflammation as the primary toxic effects of PM_2.5 exposure. However, understanding how PM_2.5 modulates neurotoxicity has proven challenging due to its complex and variable composition. This review aims to summarize the detrimental effects of inhaled PM_2.5 on the CNS and the limited understanding of its underlying mechanism. It also highlights new frontiers in addressing these issues, such as modern laboratory and computational techniques and chemical reductionism tactics. By utilizing these approaches, we aim to fully elucidate the mechanism of PM_2.5-induced neurotoxicity, treat associated diseases, and ultimately eliminate pollution.

Air Pollutant impacts on the brain and neuroendocrine system with implications for peripheral organs: a perspective

Air pollutants are being increasingly linked to extrapulmonary multi-organ effects. Specifically, recent studies associate air pollutants with brain disorders including psychiatric conditions, neuroinflammation and chronic diseases. Current evidence of the linkages between neuropsychiatric conditions and chronic peripheral immune and metabolic diseases provides insights on the potential role of the neuroendocrine system in mediating neural and systemic effects of inhaled pollutants (reactive particulates and gases). Autonomically-driven stress responses, involving sympathetic-adrenal-medullary and hypothalamus-pituitary-adrenal axes regulate cellular physiological processes through adrenal-derived hormones and diverse receptor systems. Recent experimental evidence demonstrates the contribution of the very stress system responding to non-chemical stressors, in mediating systemic and neural effects of reactive air pollutants. The assessment of how respiratory encounter of air pollutants induce lung and peripheral responses through brain and neuroendocrine system, and how the impairment of these stress pathways could be linked to chronic diseases will improve understanding of the causes of individual variations in susceptibility and the contribution of habituation/learning and resiliency. This review highlights effects of air pollution in the respiratory tract that impact the brain and neuroendocrine system, including the role of autonomic sensory nervous system in triggering neural stress response, the likely contribution of translocated nano particles or metal components, and biological mediators released systemically in causing effects remote to the respiratory tract. The perspective on the use of systems approaches that incorporate multiple chemical and non-chemical stressors, including environmental, physiological and psychosocial, with the assessment of interactive neural mechanisms and peripheral networks are emphasized.

Disturbance of REM sleep exacerbates microglial activation in APP/PS1 mice

Although both nonrapid eye movement (NREM) sleep loss and rapid eye movement (REM) sleep loss exacerbate Alzheimer's disease (AD) progression, they exert different effects. Microglial activation can be beneficial or detrimental to AD patients under different conditions. However, few studies have investigated which sleep stage is the main regulator of microglial activation or the downstream effects of this activation. We aimed to explore the roles of different sleep phases in microglial activation and to investigate the possible effect of microglial activation on AD pathology. In this study, thirty-six 6-month-old APP/PS1 mice were equally divided into 3 groups: the stress control (SC), total sleep deprivation (TSD), and REM deprivation (RD) groups. All mice underwent a 48-hour intervention before their spatial memory was assessed using a Morris water maze (MWM). Then, microglial morphology, activation- and synapse-related protein expression, and inflammatory cytokine and amyloid β (Aβ) levels in hippocampal tissues were measured. We found that the RD and TSD groups exhibited worse spatial memory in the MWM tests. In addition, the RD and TSD groups showed greater microglial activation, higher inflammatory cytokine levels, lower synapse-related protein expression and more severe Aβ accumulation than the SC group, but there were no significant differences between the RD and TSD groups. This study demonstrates that disturbance of REM sleep may activate microglia in APP/PS1 mice. These activated microglia may promote neuroinflammation and engulf synapses but show a weakened ability to clear plaques.

Air pollution and plasma amyloid beta in a cohort of older adults: Evidence from the Ginkgo Evaluation of Memory study

Air pollution has been linked to Alzheimer's disease and related dementias (ADRD), but the mechanisms connecting air pollution to ADRD have not been firmly established. Air pollution may cause oxidative stress and neuroinflammation and contribute to the deposition of amyloid beta (Aβ) in the brain. We examined the association between fine particulate matter<2.5 μm in diameter (PM2.5), particulate matter<10 μm in diameter (PM10), nitrogen dioxide (NO2), and plasma based measures of Aβ1-40, Aβ1-42 and Aβ1-42/Aβ1-40 using data from 3044 dementia-free participants of the Ginkgo Evaluation of Memory Study (GEMS). Air pollution exposures were estimated at residential addresses that incorporated address histories dating back to 1980, resulting in one-, five-, 10- and 20- year exposure averages. Aβ was measured at baseline (2000-2002) and then again at the end of the study (2007-2008) allowing for linear regression models to assess cross-sectional associations and linear random effects models to evaluate repeated measures. After adjustment for socio-demographic and behavioral covariates, we found small positive associations between each air pollutant and Aβ1-40 but no association with Aβ1-42 or the ratio measures in cross sectional analysis. In repeat measures analysis, we found larger positive associations between each air pollutant and all three outcomes. We observed a 4.43% (95% CI 3.26%, 5.60%) higher Aβ1-40 level, 9.73% (6.20%, 13.38%) higher Aβ1-42 and 1.57% (95% CI: 0.94%, 2.20%) higher Aβ1-42/Aβ1-40 ratio associated with a 2 µg/m3 higher 20-year average PM2.5. Associations with other air pollutants were similar. Our study contributes to the broader evidence base on air pollution and ADRD biomarkers by evaluating longer air pollution exposure averaging periods to better mimic disease progression and provides a modifiable target for ADRD prevention.

Air Pollution-Related Neurotoxicity Across the Life Span

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

Effects of Qi-Fu-Yin on aging of APP/PS1 transgenic mice by regulating the intestinal microbiome

Introduction

Alzheimer's disease is the most common form of dementia and closely related to aging. Qi-Fu-Yin is widely used to treat dementia, but its anti-aging effects is unknown.

Methods

We used 11-month-old APP/PS1 transgenic mice for behavioral tests to observe the changes in cognitive function and age-related symptoms after Qi-Fu-Yin treatment. Fecal samples were collected for 16sRNA sequencing and metagenomic sequencing. Differences among the groups of intestinal microbiota and the associations with aging and intestinal microbiota were analyzed based on the results.

Results

Here we found that Qi-Fu-Yin improved the ability of motor coordination, raised survival rate and prolonged the survival days under cold stress stimulation in aged APP/ PS1 transgenic mice. Our data from 16sRNA and metagenomic sequencing showed that at the Family level, the intestinal microbiota was significantly different among wild-type mice, APP/PS1 transgenic mice and the Qi-Fu-Yin group by PCA analysis. Importantly, Qi-Fu-Yin improved the functional diversity of the major KEGG pathways, carbohydrate-active enzymes, and major virulence factors in the intestinal flora of APP/PS1 transgenic mice. Among them, the functions of eight carbohydrate-active enzymes (GT2_Glycos_transf_2, GT4, GT41, GH2, CE1, CE10, CE3, and GH24) and the functions of top three virulence factors (defensive virulence factors, offensive virulence factors and nonspecific virulence factors) were significantly and positively correlated with the level of grasping ability. We further indicated that the Qi-Fu-Yin significantly reduced the plasma levels of IL-6.

Conclusion

Our results indicated that the effects of Qi-Fu-Yin anti-aging of APP/PS1 transgenic mice might be through the regulation of intestinal flora diversity, species richness and the function of major active enzymes.

Neurodevelopmental toxicity induced by PM2.5 Exposure and its possible role in Neurodegenerative and mental disorders

Recent extensive evidence suggests that ambient fine particulate matter (PM2.5, with an aerodynamic diameter ≤2.5 μm) may be neurotoxic to the brain and cause central nervous system damage, contributing to neurodevelopmental disorders, such as autism spectrum disorders, neurodegenerative diseases, such as Alzheimer's disease and Parkinson's disease, and mental disorders, such as schizophrenia, depression, and bipolar disorder. PM2.5 can enter the brain via various pathways, including the blood-brain barrier, olfactory system, and gut-brain axis, leading to adverse effects on the CNS. Studies in humans and animals have revealed that PM2.5-mediated mechanisms, including neuroinflammation, oxidative stress, systemic inflammation, and gut flora dysbiosis, play a crucial role in CNS damage. Additionally, PM2.5 exposure can induce epigenetic alterations, such as hypomethylation of DNA, which may contribute to the pathogenesis of some CNS damage. Through literature analysis, we suggest that promising therapeutic targets for alleviating PM2.5-induced neurological damage include inhibiting microglia overactivation, regulating gut microbiota with antibiotics, and targeting signaling pathways, such as PKA/CREB/BDNF and WNT/β-catenin. Additionally, several studies have observed an association between PM2.5 exposure and epigenetic changes in neuropsychiatric disorders. This review summarizes and discusses the association between PM2.5 exposure and CNS damage, including the possible mechanisms by which PM2.5 causes neurotoxicity.

Ambient particulate matter exposure causes visual dysfunction and retinal neuronal degeneration

PM_2.5 pollution is related to neurotoxic and vascular effects in eye diseases such as glaucoma. This study investigates the adverse effects of PM_2.5 exposure on visual function and retinal neurons. A versatile aerosol concentration enrichment system was used to expose mice to either control air or PM_2.5 polluted air. Six months after PM_2.5 exposure, visual function was measured by electroretinography (ERG). Hematoxylin and eosin staining and immunofluorescence staining were used for histopathological analysis. Protein markers of apoptosis, astrocytic reactivity, inflammatory cytokines, lipid peroxidation, protein nitration and DNA damage response were quantified with ELISA, western blot or detected using immunofluorescence and immunohistochemistry. After six months of exposure, PM_2.5-exposed mice responded poorly to light stimuli compared with those exposed to the control air. PM_2.5 exposure caused retinal thinning and reduction in the expression of retinal ganglion cell-selective marker RNA-binding protein with multiple splicing (RBPMS). Further, positive TUNEL staining was observed in the inner nucleus and outer nuclear layers of the retinae after exposure to PM_2.5, which was accompanied by the activation of apoptosis signaling molecules p53, caspase-3 and Bax. PM_2.5 induced the release of inflammatory cytokines including tumor necrosis factor-α and cleaved interleukin-1β. Furthermore, increased levels of 8-OHdG and γ-H2AX in the mouse retinea were indicative of DNA single and double strand breaks by PM_2.5 exposure, which activated PARP-1 mediated DNA damage and repair. In conclusion, this study demonstrates sub-chronic systemic exposure to concentrated PM_2.5 causes visual dysfunction and retinal neuronal degeneration. DATA AVAILABILITY: The datasets during and/or analyzed during the current study available from the corresponding author on reasonable request.

Air pollution, depressive and anxiety disorders, and brain effects: A systematic review

Accumulating data suggest that air pollution increases the risk of internalizing psychopathology, including anxiety and depressive disorders. Moreover, the link between air pollution and poor mental health may relate to neurostructural and neurofunctional changes. We systematically reviewed the MEDLINE database in September 2021 for original articles reporting effects of air pollution on 1) internalizing symptoms and behaviors (anxiety or depression) and 2) frontolimbic brain regions (i.e., hippocampus, amygdala, prefrontal cortex). One hundred and eleven articles on mental health (76% human, 24% animals) and 92 on brain structure and function (11% human, 86% animals) were identified. For literature search 1, the most common pollutants examined were PM2.5 (64.9%), NO2 (37.8%), and PM10 (33.3%). For literature search 2, the most common pollutants examined were PM2.5 (32.6%), O3 (26.1%) and Diesel Exhaust Particles (DEP) (26.1%). The majority of studies (73%) reported higher internalizing symptoms and behaviors with higher air pollution exposure. Air pollution was consistently associated (95% of articles reported significant findings) with neurostructural and neurofunctional effects (e.g., increased inflammation and oxidative stress, changes to neurotransmitters and neuromodulators and their metabolites) within multiple brain regions (24% of articles), or within the hippocampus (66%), PFC (7%), and amygdala (1%). For both literature searches, the most studied exposure time frames were adulthood (48% and 59% for literature searches 1 and 2, respectively) and the prenatal period (26% and 27% for literature searches 1 and 2, respectively). Forty-three percent and 29% of studies assessed more than one exposure window in literature search 1 and 2, respectively. The extant literature suggests that air pollution is associated with increased depressive and anxiety symptoms and behaviors, and alterations in brain regions implicated in risk of psychopathology. However, there are several gaps in the literature, including: limited studies examining the neural consequences of air pollution in humans. Further, a comprehensive developmental approach is needed to examine windows of susceptibility to exposure and track the emergence of psychopathology following air pollution exposure.

Acoustic Stimulation Improves Memory and Reverses the Contribution of Chronic Sleep Deprivation to Pathology in 3xTgAD Mice

Acoustic stimulation during sleep is believed to enhance slow waves, which are critical to memory consolidation. However, clinical trials of acoustic stimulation have yielded mixed results concerning its effectiveness in improving human memory. A few studies have implied that acoustic stimulation ameliorates the pathology of Alzheimer's disease (AD) in mice with normal sleep. Here, we explored the effect of acoustic stimulation on 3xTgAD mice suffering from chronic sleep deprivation, as these data may shed light on the potential use of acoustic stimulation in AD patients with insomnia. Methods: Twenty-four 8-month-old 3xTgAD mice were randomly and equally divided into three groups: the normal sleep group (S group), the sleep deprivation group (SD group), and the acoustic stimulation group (AS group). During a 14-day sleep intervention, the SD and AS groups received 6 h of sleep deprivation per day, and the AS group also received acoustic stimulation in the dark phase. Then, the mice underwent Morris water maze (MWM) tests and arterial spin labelling (ASL) magnetic resonance imaging (MRI) scans and were sacrificed for pathological evaluation. Results: The three groups showed similar stress levels. The S and AS groups exhibited better spatial memory, better brain perfusion, and milder amyloid β (Aβ) and tau pathology than the SD group, although no significant discrepancies were found between the S and AS groups. Conclusion: Acoustic stimulation may exert a protective effect in 3xTgAD mice by improving spatial memory, enhancing the blood supply of the brain, and reversing the contribution of chronic sleep deprivation to Aβ and tau pathology to mimic the effect of normal sleep patterns.

Particulate matter and Alzheimer's disease: an intimate connection

The environmental role in disease progression has been appreciated for decades; however, understanding how airborne toxicant exposure can affect organs beyond the lungs is an underappreciated area of scientific inquiry. Particulate matter (PM) includes various gases, liquids, and particles in suspension and is produced by industrial activities such as fossil fuel combustion and natural events including wildfires and volcanic eruptions. Although agencies have attempted to reduce acceptable airborne particulate levels, with urbanization and population growth, these policies have been only moderately effective in mitigating disease progression. A growing area of research is focused on the role of PM exposure in the progression of Alzheimer's disease (AD). This review will summarize the knowns and unknowns of this expanding field.

The Physiological Effects of Air Pollution: Particulate Matter, Physiology and Disease

Nine out of 10 people breathe air that does not meet World Health Organization pollution limits. Air pollutants include gasses and particulate matter and collectively are responsible for ~8 million annual deaths. Particulate matter is the most dangerous form of air pollution, causing inflammatory and oxidative tissue damage. A deeper understanding of the physiological effects of particulate matter is needed for effective disease prevention and treatment. This review will summarize the impact of particulate matter on physiological systems, and where possible will refer to apposite epidemiological and toxicological studies. By discussing a broad cross-section of available data, we hope this review appeals to a wide readership and provides some insight on the impacts of particulate matter on human health.

White matter pathology in alzheimer's transgenic mice with chronic exposure to low-level ambient fine particulate matter

BACKGROUND

Air pollution, especially fine particulate matter (PM), can cause brain damage, cognitive decline, and an increased risk of neurodegenerative disease, especially alzheimer's disease (AD). Typical pathological findings of amyloid and tau protein accumulation have been detected in the brain after exposure in animal studies. However, these observations were based on high levels of PM exposure, which were far from the WHO guidelines and those present in our environment. In addition, white matter involvement by air pollution has been less reported. Thus, this experiment was designed to simulate the true human world and to discuss the possible white matter pathology caused by air pollution.

RESULTS

6 month-old female 3xTg-AD mice were divided into exposure and control groups and housed in the Taipei Air Pollutant Exposure System (TAPES) for 5 months. The mice were subjected to the Morris water maze test after exposure and were then sacrificed with brain dissection for further analyses. The mean mass concentration of PM2.5 during the exposure period was 13.85 μg/m3. After exposure, there was no difference in spatial learning function between the two groups, but there was significant decay of memory in the exposure group. Significantly decreased total brain volume and more neuronal death in the cerebral and entorhinal cortex and demyelination of the corpus callosum were noted by histopathological staining after exposure. However, there was no difference in the accumulation of amyloid or tau on immunohistochemistry staining. For the protein analysis, amyloid was detected at significantly higher levels in the cerebral cortex, with lower expression of myelin basic protein in the white matter. A diffuse tensor image study also revealed insults in multiple white matter tracts, including the optic tract.

CONCLUSIONS

In conclusion, this pilot study showed that even chronic exposure to low PM2.5 concentrations still caused brain damage, such as gross brain atrophy, cortical neuron damage, and multiple white matter tract damage. Typical amyloid cascade pathology did not appear prominently in the vulnerable brain region after exposure. These findings imply that multiple pathogenic pathways induce brain injury by air pollution, and the optic nerve may be another direct invasion route in addition to olfactory nerve.

Recent Insights into Particulate Matter (PM2.5)-Mediated Toxicity in Humans: An Overview

Several epidemiologic and toxicological studies have commonly viewed ambient fine particulate matter (PM_2.5), defined as particles having an aerodynamic diameter of less than 2.5 µm, as a significant potential danger to human health. PM_2.5 is mostly absorbed through the respiratory system, where it can infiltrate the lung alveoli and reach the bloodstream. In the respiratory system, reactive oxygen or nitrogen species (ROS, RNS) and oxidative stress stimulate the generation of mediators of pulmonary inflammation and begin or promote numerous illnesses. According to the most recent data, fine particulate matter, or PM_2.5, is responsible for nearly 4 million deaths globally from cardiopulmonary illnesses such as heart disease, respiratory infections, chronic lung disease, cancers, preterm births, and other illnesses. There has been increased worry in recent years about the negative impacts of this worldwide danger. The causal associations between PM_2.5 and human health, the toxic effects and potential mechanisms of PM_2.5, and molecular pathways have been described in this review.

Biochanin A alleviates cognitive impairment and hippocampal mitochondrial damage in ovariectomized APP/PS1 mice

BACKGROUND

Estrogen deficiency leads to mitochondrial defects that precede Alzheimer's disease (AD)-associated pathological changes in a postmenopausal mouse model. Biochanin A (BCA) is a phytoestrogen isolated from Trifolium pratense L. used to relieve postmenopausal problems in women. In previous work, we observed that oral BCA treatment led to neuroprotection in an ovariectomized rat model. The objective of this study was to investigate whether and how BCA protects against hippocampal mitochondrial damage in a postmenopausal model of AD.

METHOD

APP/PS1 mice underwent bilateral ovariectomy and then, seven days later, received oral BCA at 20 or 40 mg/kg, or oral estradiol at 0.5 mg/kg, daily for 90 days. Sham animals were not ovariectomized and received no additional treatments. Cognitive function was examined using the passive avoidance task, novel object recognition test, and Morris water maze test. The level of circulating estrogen in vivo was assessed indirectly by measuring the wet weight of the uterus. We detected Aβ deposition and PGC-1α in brain by immunohistochemistry; p62, by immunofluorescence; and ERα, ERβ, PGC-1α, NRF1, mtTFA, Drp1, OPA1, Mfn2, Beclin1, LC3B, Pink1, and Parkin by immunoblotting.

RESULTS

BCA treatment rescued cognitive decline and reduced Aβ deposition and BACE1 expression in the hippocampus of ovariectomized APP/PS1 mice. BCA reversed the imbalance of mitochondrial dynamics caused by ovariectomy by increasing the expression of phospho-Drp1 (ser637), OPA1, and Mfn2. BCA reversed abnormal mitophagy induced by ovariectomy by increasing the expression of Beclin1, LC3B, Pink1, and Parkin, as well as by reducing the expression of p62.

CONCLUSIONS

BCA treatment enhances learning and memory abilities and alleviates AD symptoms in a postmenopausal model of AD. A possible mechanism is that BCA rescues the reduction of mitochondrial biogenesis, imbalance of mitochondrial dynamics, and abnormal mitophagy caused by ovariectomy. This study supports further research on BCA to develop treatments for postmenopausal women with AD.

Transcranial Direct Current Stimulation Alleviates Neurovascular Unit Dysfunction in Mice With Preclinical Alzheimer’s Disease

Neurons, glial cells and blood vessels are collectively referred to as the neurovascular unit (NVU). In the Alzheimer’s disease (AD) brain, the main components of the NVU undergo pathological changes. Transcranial direct current stimulation (tDCS) can protect neurons, induce changes in glial cells, regulate cerebral blood flow, and exert long-term neuroprotection. However, the mechanism by which tDCS improves NVU function is unclear. In this study, we explored the effect of tDCS on the NVU in mice with preclinical AD and the related mechanisms. 10 sessions of tDCS were given to six-month-old male APP/PS1 mice in the preclinical stage. The model group, sham stimulation group, and control group were made up of APP/PS1 mice and C57 mice of the same age. All mice were histologically evaluated two months after receiving tDCS. Protein content was measured using Western blotting and an enzyme-linked immunosorbent assay (ELISA). The link between glial cells and blood vessels was studied using immunofluorescence staining and lectin staining. The results showed that tDCS affected the metabolism of Aβ; the levels of Aβ, amyloid precursor protein (APP) and BACE1 were significantly reduced, and the levels of ADAM10 were significantly increased in the frontal cortex and hippocampus in the stimulation group. In the stimulation group, tDCS reduced the protein levels of Iba1 and GFAP and increased the protein levels of NeuN, LRP1 and PDGRFβ. This suggests that tDCS can improve NVU function in APP/PS1 mice in the preclinical stage. Increased blood vessel density and blood vessel length, decreased IgG extravasation, and increased the protein levels of occludin and coverage of astrocyte foot processes with blood vessels suggested that tDCS had a protective effect on the blood-brain barrier. Furthermore, the increased numbers of Vimentin, S100 expression and blood vessels (lectin-positive) around Aβ indicated that the effect of tDCS was mediated by astrocytes and blood vessels. There was no significant difference in these parameters between the model group and the sham stimulation group. In conclusion, our results show that tDCS can improve NVU function in APP/PS1 mice in the preclinical stage, providing further support for the use of tDCS as a treatment for AD.

An Air Particulate Pollutant Induces Neuroinflammation and Neurodegeneration in Human Brain Models

Fine particulate matter (PM2.5), a major component among air pollutants, highlights as a global health concern. Several epidemiological studies show the correlation between chronical PM2.5 exposure and incidents of neurological disorders including Alzheimer's disease. However, the mechanisms have not been well understood, partly due to the lack of model systems that reflect the physiologically relevant innate immunity in human brains. Here, PM2.5-polluted human brain models (PMBs) are created in a 3D microfluidic platform reconstituting key aspects of human brain immunity under the PM2.5 exposure. PM2.5 penetration across a blood-brain barrier (BBB) model and accumulation in the brain tissue side of the model are first validated. Second, the PMB model shows that the BBB-penetrating PM2.5 initiates astrogliosis, resulting in slight neuronal loss and microglial infiltration. Third, it is demonstrated that the infiltrating microglia obtain M1 phenotype induced by interleukin-1β and interferon-γ from neurons and reactive astrocytes under the PM2.5 exposure. Finally, it is observed that additional proinflammatory mediators and nitric oxide released from the M1 microglia exacerbate neuronal damages, such as synaptic impairment, phosphoric tau accumulation, and neuronal death. This study suggests that PM2.5 can be a potential environmental risk factor for dementia mediated by the detrimental neuroinflammation.

Inflammatory Chemokines Expression Variations and Their Receptors in APP/PS1 Mice

BACKGROUND

In Alzheimer's disease (AD), an increase in inflammation is distinctive. Amyloid precursor protein plus presenilin-1 (APP/PS1 mice) is a model for this illness. Chemokines secreted by central nervous system (CNS) cells could play multiple important roles in AD. Data looking for the chemokines involved in inflammatory mechanisms are lacking. To understand the changes that occur in the inflammation process in AD, it is necessary to improve strategies to act on specific inflammatory targets.

OBJECTIVE

Chemokines and their receptors involved in phagocytosis, demyelination, chemotaxis, and coagulation were the objective of our study.

METHODS

Female APPswe/PS1 double-transgenic mice (B6C3-Tg) were used and cortex brain from 20-22-month-old mice obtained and used to quantify chemokines and chemokine receptors expression using RT-PCR technique.

RESULTS

Significant inflammatory changes were detected in APP/PS1 compared to wild type mice. CCR1, CCR3, CCR4, and CCR9 were elevated, and CCR2 were decreased compared with wild type mice. Their ligands CCL7, CCL11, CCL17, CCL22, CCL25, and CXCL4 showed an increase expression; however, changes were not observed in CCL2 in APP/PS1 compared to wild type mice.

CONCLUSION

This change in expression could explain the differences between AD patients and elderly people without this illness. This would provide a new strategy for the treatment of AD, with the possibility to act in specific inflammatory targets.

Racial/Ethnic Disparities in Alzheimer's Disease Risk: Role of Exposure to Ambient Fine Particles

BACKGROUND

Whether racial/ethnic disparities in Alzheimer's disease (AD) risk may be explained by ambient fine particles (PM2.5) has not been studied.

METHOD

We conducted a prospective, population-based study on a cohort of Black (n = 481) and White (n = 6 004) older women (aged 65-79) without dementia at enrollment (1995-1998). Cox models accounting for competing risk were used to estimate the hazard ratio (HR) for racial/ethnic disparities in AD (1996-2010) defined by Diagnostic and Statistical Manual of Mental Disorders, 4th edition and the association with time-varying annual average PM2.5 (1999-2010) estimated by spatiotemporal model.

RESULTS

Over an average follow-up of 8.3 (±3.5) years with 158 incident cases (21 in Black women), the racial disparities in AD risk (range of adjusted HRBlack women = 1.85-2.41) observed in various models could not be explained by geographic region, age, socioeconomic characteristics, lifestyle factors, cardiovascular risk factors, and hormone therapy assignment. Estimated PM2.5 exposure was higher in Black (14.38 ± 2.21 µg/m3) than in White (12.55 ± 2.76 µg/m3) women, and further adjustment for the association between PM2.5 and AD (adjusted HRPM2.5 = 1.18-1.28) slightly reduced the racial disparities by 2%-6% (HRBlack women = 1.81-2.26). The observed association between PM2.5 and AD risk was ~2 times greater in Black (HRPM2.5 = 2.10-2.60) than in White (HRPM2.5 = 1.07-1.15) women (range of interaction ps: <.01-.01). We found similar results after further adjusting for social engagement (social strain, social support, social activity, living alone), stressful life events, Women's Health Initiative's clinic sites, and neighborhood socioeconomic characteristics.

CONCLUSIONS

PM2.5 may contribute to racial/ethnic disparities in AD risk and its associated increase in AD risk was stronger among Black women.

Activation of Endogenous Retrovirus, Brain Infections and Environmental Insults in Neurodegeneration and Alzheimer's Disease

Chronic neurodegenerative diseases are complex, and their pathogenesis is uncertain. Alzheimer’s disease (AD) is a neurodegenerative brain alteration that is responsible for most dementia cases in the elderly. AD etiology is still uncertain; however, chronic neuroinflammation is a constant component of brain pathology. Infections have been associated with several neurological diseases and viruses of the Herpes family appear to be a probable cause of AD neurodegenerative alterations. Several different factors may contribute to the AD clinical progression. Exogeneous viruses or other microbes and environmental pollutants may directly induce neurodegeneration by activating brain inflammation. In this paper, we suggest that exogeneous brain insults may also activate retrotransposons and silent human endogenous retroviruses (HERVs). The initial inflammation of small brain areas induced by virus infections or other brain insults may activate HERV dis-regulation that contributes to neurodegenerative mechanisms. Chronic HERV activation in turn may cause progressive neurodegeneration that thereafter merges in cognitive impairment and dementia in genetically susceptible people. Specific treatment for exogenous end endogenous pathogens and decreasing pollutant exposure may show beneficial effect in early intervention protocol to prevent the progression of cognitive deterioration in the elderly.