Toxic Environmental Risk Factors for Alzheimer’s Disease: A Systematic Review

Long-Term Neurotoxic Effects and Alzheimer's Disease Risk of Early EHDPP Exposure in Zebrafish: Insights from Molecular Mechanisms to Adult Pathology

2-Ethylhexyl diphenyl phosphate (EHDPP), ubiquitously monitored in environmental media, is highly bioaccumulative and may pose long-term risks, even after short-term exposure. In this investigation, larval zebrafish were exposed to 0.05, 0.5, and 5.0 μg/L EHDPP from 4 to 120 h postfertilization (hpf) to examine the long-term neurotoxicity effects of early exposure. Exposure to 5.0 μg/L EHDPP yielded hyperactive locomotor behavior, which was characterized by increased swimming speed, larger turning angles, and heightened sensitivity to light-dark stimulation. The predicted targets of EHDPP (top 100 potential macromolecules) were primarily associated with brain diseases like Alzheimer's disease (AD). Comparisons of differentially expressed genes (DEGs) from AD patients (GSE48350) and RNA-seq data from EHDPP-exposed zebrafish confirmed consistently abnormal regulatory pathways. EHDPP's interaction with M1 and M5 muscarinic acetylcholine receptors likely disrupted calcium homeostasis, leading to mitochondrial dysfunction and neurotransmitter imbalance as well as abnormal locomotor behavior. Especially, 5.0 μg/L EHDPP exposure during early development (4-120 hpf) triggered early- and midstage AD-like symptoms in adulthood (180 dpf), characterized by cognitive confusion, aggression, blood-brain barrier disruption, and mitochondrial damage in brains. These findings provide deep insights into the long-term neurotoxicity effects and Alzheimer's disease risks of early EHDPP exposure at extremely low dosages.

Metals in Alzheimer's Disease

The role of metals in the pathogenesis of Alzheimer's disease (AD) is still debated. Although previous research has linked changes in essential metal homeostasis and exposure to environmental heavy metals to the pathogenesis of AD, more research is needed to determine the relationship between metals and AD. In this review, we included human studies that (1) compared the metal concentrations between AD patients and healthy controls, (2) correlated concentrations of AD cerebrospinal fluid (CSF) biomarkers with metal concentrations, and (3) used Mendelian randomization (MR) to assess the potential metal contributions to AD risk. Although many studies have examined various metals in dementia patients, understanding the dynamics of metals in these patients remains difficult due to considerable inconsistencies among the results of individual studies. The most consistent findings were for Zn and Cu, with most studies observing a decrease in Zn levels and an increase in Cu levels in AD patients. However, several studies found no such relation. Because few studies have compared metal levels with biomarker levels in the CSF of AD patients, more research of this type is required. Given that MR is revolutionizing epidemiologic research, additional MR studies that include participants from diverse ethnic backgrounds to assess the causal relationship between metals and AD risk are critical.

Early-Life Environment Influence on Late-Onset Alzheimer's Disease

With the expand of the population's average age, the incidence of neurodegenerative disorders has dramatically increased over the last decades. Alzheimer disease (AD) which is the most prevalent neurodegenerative disease is mostly sporadic and primarily characterized by cognitive deficits and neuropathological lesions such as amyloid -β (Aβ) plaques and neurofibrillary tangles composed of hyper- and/or abnormally phosphorylated Tau protein. AD is considered a complex disease that arises from the interaction between environmental and genetic factors, modulated by epigenetic mechanisms. Besides the well-described cognitive decline, AD patients also exhibit metabolic impairments. Metabolic and cognitive perturbations are indeed frequently observed in the Developmental Origin of Health and Diseases (DOHaD) field of research which proposes that environmental perturbations during the perinatal period determine the susceptibility to pathological conditions later in life. In this review, we explored the potential influence of early environmental exposure to risk factors (maternal stress, malnutrition, xenobiotics, chemical factors … ) and the involvement of epigenetic mechanisms on the programming of late-onset AD. Animal models indicate that offspring exposed to early-life stress during gestation and/or lactation increase both AD lesions, lead to defects in synaptic plasticity and finally to cognitive impairments. This long-lasting epigenetic programming could be modulated by factors such as nutriceuticals, epigenetic modifiers or psychosocial behaviour, offering thus future therapeutic opportunity to protect from AD development.

Association of Insulin Receptor Substrate-1 Gene Polymorphism (rs1801278) with Alzheimer’s Disease

Background: Alzheimer’s disease (AD) is the most common form of dementia. AD is also the leading cause of morbidity and mortality due to dementia worldwide. It has been shown that AD is associated with type 2 diabetes mellitus (T2DM) and brain insulin resistance. Rs1801278 is a polymorphism in insulin receptor substrate-1 (IRS-1) gene which changes the amino acid Arg972. This polymorphism has been found to be associated with susceptibility to AD in some populations. Objective: In the present study, our aim was to investigate the association of Arg972 IRS-1 (rs1801278) gene polymorphism and late-onset Alzheimer’s disease (LOAD) in an Iranian population. Methods: In this case-control study, 150 patients with LOAD and 150 unrelated healthy controls were recruited. Polymerase chain reaction (PCR) was performed to amplify a DNA segment of 263 base-pair (bp) length containing the single nucleotide polymorphism (SNP). The PCR product was then incubated with MvaI restriction enzyme to undergo enzymatic cleavage. Electrophoresis was thereafter carried out using agarose gel and DNA safe stain. The gel was ultimately visualized under a UV trans-illuminator. Allelic and genotypic frequencies were then compared. Results: A allele (mutant) of the gene was significantly associated with the risk of AD after adjustment for sex and age (p = 0.04, adjusted OR:1.77, 95% CI:1.00–3.11). Only AA genotype (mutant homozygote) was significantly associated with the risk of AD after adjustment for sex and age (p = 0.01, adjusted OR:2.39, 95% CI:1.22–4.66). Conclusion: SNP rs1801278 is significantly associated with the risk of developing AD in the studied Iranian population.

Environmental Substances Associated with Alzheimer's Disease-A Scoping Review

Alzheimer’s disease (AD) is the most common form of dementia, prevalent in approximately 50–70% of the dementia cases. AD affects memory, and it is a progressive disease interfering with cognitive abilities, behaviour and functioning of the person affected. In 2015, there were 47 million people affected by dementia worldwide, and the figure was estimated to increase to 75 million in 2030 and to 132 million by 2050. In the framework of European Human Biomonitoring Initiative (HBM4EU), 18 substances or substance groups were prioritized for investigation. For each of the priority substances, a scoping document was prepared. Based on these scoping documents and complementary review of the recent literature, a scoping review of HBM4EU-priority substances which might be associated with AD was conducted. A possible association between risk of AD and pesticides was detected. For mercury (Hg), association is possible but inconsistent. Regarding cadmium (Cd) and arsenic (As), the results are inconsistent but inclined towards possible associations between the substances and the risk of disease. The evidence regarding lead (Pb) was weaker than for the other substances; however, possible associations exist. Although there is evidence of adverse neurological effects of environmental substances, more research is needed. Environmental chemical exposure and the related hazards are essential concerns for public health, and they could be preventable.

The association between toxic pesticide environmental exposure and Alzheimer's disease: A scientometric and visualization analysis

Alzheimer's disease (AD) is one of the most common neurodegenerative diseases. The association between environmental factors (e.g., pesticide) and AD has attracted considerable attention. However, no systematic analysis has been performed and make it difficult to provide deeper insights of AD correlated with pesticide exposure. Hence, this study utilized a bibliometric and visual approach that included map collaborations, co-citations, and keywords, to identifying the knowledge structure, hot topics and the research trends based on 372 publications from the Web of Science Core Collection and PubMed databases. The results showed that 116 institutions from 52 countries published articles in this field. The United States and Israel played a leading role with numerous publications in related journals, as well as prolific institutions and authors, respectively. Three hot topics in pesticide-induced AD were recognized based on co-occurrence keywords detection, including acetylcholinesterase (AChE) inhibitor, oxidative stress, and AChE. Moreover, analysis of keywords burst suggests that some potential molecular mechanisms and therapy targets of pesticide-induced AD, especially for mitochondrial dysfunction and monoamine oxidase-B (MAO-B) that catalyzes the oxidative deamination and causes oxidative stress, are emerging trends. In addition, the study of various pesticides and the assessment method of pesticide exposure will step forward as well. To the best of our knowledge, this study is the first to specifically visualize the relationship between AD and pesticide exposure and to predict potential future research directions.

PM2.5 air pollution contributes to the burden of frailty

Frailty is common among older people and results in adverse health outcomes. We investigated whether exposure to PM_2.5 is associated with frailty. This cross-sectional study involved 20,606 community-dwelling participants aged ≥ 65 years, residing in New Taipei City, Taiwan. Analytic data included phenotypic frailty, disease burden by Charlson Comorbidity Index (CCI), urban or rural residence, and household income. PM_2.5 exposure was calculated from air quality monitoring records, with low exposure defined as the lowest quartile of the study population. 1,080 frail participants (5.2%) were older, predominantly female, had more comorbidities, lived rurally, and had low PM_2.5 exposure (all p < 0.001). In multinomial logistic regression analyses, the likelihood of high PM_2.5 exposure was higher in prefrail (OR 1.4, 95% CI 1.3–1.5) and frail adults (OR 1.5, 95% CI 1.2–1.9) than in robust individuals, with stronger associations in those who were male (frail: OR 2.1, 95% CI 1.5–3.1; prefrail: OR 2.2, 95% CI 1.9–2.6), ≥ 75 years old (frail: OR 1.8, 95% CI 1.3–2.4; prefrail: OR 1.5, 95% CI 1.3–1.8), non-smokers (frail: OR 1.6, 95% CI 1.3–2.0; prefrail: OR 1.4, 95% CI 1.2–1.5), had CCI ≥ 2 (frail: OR 5.1, 95% CI 2.1–12.6; prefrail: OR 2.1, 95% CI 1.2–3.8), and with low household income (frail: OR 4.0, 95% CI 2.8–5.8; prefrail: OR 2.7, 95% CI 2.2–3.3). This study revealed a significant association between PM_2.5 exposure and frailty, with a stronger effect in vulnerable groups.