Alzheimer's disease and environmental exposure to lead: the epidemiologic evidence and potential role of epigenetics

Exposure to Lead in Drinking Water Causes Cognitive Impairment via an Alzheimer's Disease Gene-Dependent Mechanism in Adult Mice

Background

Exposure to lead (Pb) is a major public health problem that could occur through contaminated soil, air, food, or water, either during the course of everyday life, or while working in hazardous occupations. Although Pb has long been known as a neurodevelopmental toxicant in children, a recent and growing body of epidemiological research indicates that cumulative, low-level Pb exposure likely drives age-related neurologic dysfunction in adults. Environmental Pb exposure in adulthood has been linked to risk of late-onset Alzheimer's disease (AD) and dementia.

Objective

Although the biological mechanism underlying this link is unknown, it has been proposed that Pb exposure may increase the risk of AD via altering the expression of AD-related genes and, possibly, by activating the molecular pathways underlying AD-related pathology.

Methods

We investigated Pb exposure using a line of genetically modified mice with AD-causing knock-in mutations in the amyloid precursor protein and presenilin 1 (APPΔNL/ΔNL x PS1P264L/P264L) that had been crossed with Leprdb/db mice to impart vulnerability to vascular pathology.

Results

Our data show that although Pb exposure in adult mice impairs cognitive function, this effect is not related to either an increase in amyloid pathology or to changes in the expression of common AD-related genes. Pb exposure also caused a significant increase in blood pressure, a well known effect of Pb. Interestingly, although the increase in blood pressure was unrelated to genotype, only mice that carried AD-related mutations developed cognitive dysfunction, in spite of showing no significant change in cerebrovascular pathology.

Conclusions

These results raise the possibility that the increased risk of dementia associated with Pb exposure in adults may be tied to its subsequent interaction with either pre-existing or developing AD-related neuropathology.

Metabolic and Environmental Biomarkers in Mild Cognitive Impairment and Dementia: An Exploratory Study

Objective: To determine the frequency with which suspected pathogenic factors, including metals and metabolites that might contribute to Alzheimer's disease (AD), may be found in patients with cognitive impairment through commonly available blood tests. Methods: A variety of serum studies, including metals, ammonia, homocysteine, vitamin B12, folate, thyroid tests, metabolic products, and inflammatory markers, were measured in two cohorts: one meeting mild cognitive impairment (MCI) criteria and the other meeting mild-to-moderate dementia (DE) criteria. Medications these patients received were reviewed. Results: Metal abnormalities were detected in over half the subjects, including evidence of mercury, lead, and arsenic elevation as well as instances of excessive essential metals, iron (Fe), and copper. Some metal aberration was detected in 64% of the DE group and 66% of the MCI group. Females were more likely to have elevated copper, consistent with hormonal effects on copper excretion. Homocysteinemia was the most common abnormality, detected in 71% with DE and 67% with MCI, while methylmalonic acid was not elevated. Slight hyperammonemia was moderately common (38%) suggesting a hepatic factor in this subset. Findings of moderate insulin resistance were present in nearly half (44% DE, 52% MCI). Sixty of 65 (92%) had at least one abnormal biomarker and 60% had two or more. The most common drug taken by the total cohort was proton pump inhibitors at 22% DE and 38% MCI. Conclusions: This study suggests that both toxic metals and excessive vital metals such as copper and iron, as well as common metabolic and hepatic factors are detectable at both stages of MCI and DE. There appears to be a multiplicity of provocative factors leading to DE. Individualized interventions based on these parameters may be a means to reduce cognitive decline leading to DE. A more comprehensive prospective study of these environmental and metabolic factors with corrective early interventions appears warranted.

The bioaccessibility of adsorped heavy metals on biofilm-coated microplastics and their implication for the progression of neurodegenerative diseases

Microplastic (MP) tiny fragments (< 5 mm) of conventional and specialized industrial polymers are persistent and ubiquitous in both aquatic and terrestrial ecosystem. Breathing, ingestion, consumption of food stuffs, potable water, and skin are possible routes of MP exposure that pose potential human health risk. Various microorganisms including bacteria, cyanobacteria, and microalgae rapidly colonized on MP surfaces which initiate biofilm formation. It gradually changed the MP surface chemistry and polymer properties that attract environmental metals. Physicochemical and environmental parameters like polymer type, dissolved organic matter (DOM), pH, salinity, ion concentrations, and microbial community compositions regulate metal adsorption on MP biofilm surface. A set of highly conserved proteins tightly regulates metal uptake, subcellular distribution, storage, and transport to maintain cellular homeostasis. Exposure of metal-MP biofilm can disrupt that cellular homeostasis to induce toxicities. Imbalances in metal concentrations therefore led to neuronal network dysfunction, ROS, mitochondrial damage in diseases like Alzheimer's disease (AD), Parkinson's disease (PD), and Prion disorder. This review focuses on the biofilm development on MP surfaces, factors controlling the growth of MP biofilm which triggered metal accumulation to induce neurotoxicological consequences in human body and stategies to reestablish the homeostasis. Thus, the present study gives a new approach on the health risks of heavy metals associated with MP biofilm in which biofilms trigger metal accumulation and MPs serve as a vector for those accumulated metals causing metal dysbiosis in human body.

Model of neural development by differentiating human induced pluripotent stem cells into neural progenitor cells to study the neurodevelopmental toxicity of lead

Lead (Pb) exposure causes immeasurable damage to multiple human systems, particularly the central nervous system (CNS). In this study, human induced pluripotent stem cells (hiPSCs) were differentiated into neural progenitor cells (NPCs) to investigate the neurotoxic effects of Pb. The hiPSCs were treated with 0, 0.5, 1.0, 2.5, 5.0 and 10.0 μmol/L Pb for 7 days, whereas embryoid bodies (EBs) and NPCs were treated with 0, 0.1, 0.5, and 1.0 μmol/L Pb for 7 days. Pb exposure disrupted the cell cycle and caused apoptosis in hiPSCs, EBs, and NPCs. Besides, Pb inhibited the differentiation of NPCs and EBs. Whole exome sequencing revealed 2509, 2413, and 1984 single nucleotide variants (SNVs) caused by Pb in hiPSCs, EBs, and NPCs, respectively. The common mutation sites in the exon region were mostly nonsynonymous mutations. We identified 18, 19, and 18 common deleterious mutations in hiPSCs, EBs, and NPCs, respectively. Additionally, Online Mendelian Inheritance in Man database analysis revealed 30, 20, and 13 genes related to CNS disorders in hiPSCs, EBs, and NPCs, respectively. Our findings suggest that this in vitro model may supplement animal models and be applied to the study of neurodevelopmental toxicity in the future.

Targeting epigenetics: A novel promise for Alzheimer's disease treatment

So far, the search for a cure for Alzheimer Disease (AD) has been unsuccessful. The only approved drugs attenuate some symptoms, but do not halt the progress of this disease, which affects 50 million people worldwide and will increase its incidence in the coming decades. Such scenario demands new therapeutic approaches to fight against this devastating dementia. In recent years, multi-omics research and the analysis of differential epigenetic marks in AD subjects have contributed to our understanding of AD; however, the impact of epigenetic research is yet to be seen. This review integrates the most recent data on pathological processes and epigenetic changes relevant for aging and AD, as well as current therapies targeting epigenetic machinery in clinical trials. Evidence shows that epigenetic modifications play a key role in gene expression, which could provide multi-target preventative and therapeutic approaches in AD. Both novel and repurposed drugs are employed in AD clinical trials due to their epigenetic effects, as well as increasing number of natural compounds. Given the reversible nature of epigenetic modifications and the complexity of gene-environment interactions, the combination of epigenetic-based therapies with environmental strategies and drugs with multiple targets might be needed to properly help AD patients.

Developmental Pb exposure increases AD risk via altered intracellular Ca2+ homeostasis in hiPSC-derived cortical neurons

Exposure to environmental chemicals such as lead (Pb) during vulnerable developmental periods can result in adverse health outcomes later in life. Human cohort studies have demonstrated associations between developmental Pb exposure and Alzheimer's disease (AD) onset in later life which were further corroborated by findings from animal studies. The molecular pathway linking developmental Pb exposure and increased AD risk, however, remains elusive. In this work, we used human iPSC-derived cortical neurons as a model system to study the effects of Pb exposure on AD-like pathogenesis in human cortical neurons. We exposed neural progenitor cells derived from human iPSC to 0, 15, and 50 ppb Pb for 48 h, removed Pb-containing medium, and further differentiated them into cortical neurons. Immunofluorescence, Western blotting, RNA-sequencing, ELISA, and FRET reporter cell lines were used to determine changes in AD-like pathogenesis in differentiated cortical neurons. Exposing neural progenitor cells to low-dose Pb, mimicking a developmental exposure, can result in altered neurite morphology. Differentiated neurons exhibit altered calcium homeostasis, synaptic plasticity, and epigenetic landscape along with elevated AD-like pathogenesis markers, including phosphorylated tau, tau aggregates, and Aβ42/40. Collectively, our findings provide an evidence base for Ca dysregulation caused by developmental Pb exposure as a plausible molecular mechanism accounting for increased AD risk in populations with developmental Pb exposure.

High affinity of β-amyloid proteins to cerebral capillaries: implications in chronic lead exposure-induced neurotoxicity in rats

Lead (Pb) is a known environmental risk factor in the etiology of Alzheimer's disease (AD). The existing reports suggest that Pb exposure increases beta-amyloid (Aβ) levels in brain tissues and cerebrospinal fluid (CSF) and facilitates the formation of amyloid plaques, which is a pathological hallmark for AD. Pb exposure has long been associated with cerebral vasculature injury. Yet it remained unclear if Pb exposure caused excessive Ab buildup in cerebral vasculature, which may damage the blood-brain barrier and cause abnormal Ab accumulation. This study was designed to investigate the impact of chronic Pb exposure on Aβ accumulation in cerebral capillary and the expression of low-density lipoprotein receptor protein-1 (LRP1), a critical Aβ transporter, in brain capillary and parenchyma. Sprague-Dawley rats received daily oral gavage at doses of 0, 14 (low-dose), and 27 (high-dose) mg Pb/kg as Pb acetate, 5 d/wk, for 4 or 8 wks. At the end of Pb exposure, a solution containing Aβ40 was infused into the brain via the cannulated internal carotid artery. Data by ELISA showed a strikingly high affinity of Ab to cerebral vasculature, which was approximately 7-14 times higher than that to the parenchymal fractions collected from control brains. Pb exposure further aggravated the Aβ accumulation in cerebral vasculature in a dose-dependent manner. Western blot analyses revealed that Pb exposure decreased LRP1 expression in cortical capillaries and hippocampal parenchyma. Immunohistochemistry (IHC) studies further revealed a disrupted distribution of LRP1 alongside hippocampal vasculature accompanied with a decreased expression in hippocampal neurons by Pb exposure. Taken together, the current study demonstrated that the cerebral vasculature naturally possessed a high affinity to Aβ present in circulating blood. Pb exposure significantly increased Aβ accumulation in cerebral vasculature; such an increased Aβ accumulation was due partly to the diminished expression of LRP1 in response to Pb in tested brain regions. Perceivably, Pb-facilitated Ab aggravation in cerebral vasculature may contribute to Pb-associated amyloid alterations.

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.

Association between Heavy Metal Exposure and Parkinson's Disease: A Review of the Mechanisms Related to Oxidative Stress

Parkinson's disease (PD) is a gradually progressing neurodegenerative condition that is marked by a loss of motor coordination along with non-motor features. Although the precise cause of PD has not been determined, the disease condition is mostly associated with the exposure to environmental toxins, such as metals, and their abnormal accumulation in the brain. Heavy metals, such as iron (Fe), mercury (Hg), manganese (Mn), copper (Cu), and lead (Pb), have been linked to PD and contribute to its progression. In addition, the interactions among the components of a metal mixture may result in synergistic toxicity. Numerous epidemiological studies have demonstrated a connection between PD and either single or mixed exposure to these heavy metals, which increase the prevalence of PD. Chronic exposure to heavy metals is related to the activation of proinflammatory cytokines resulting in neuronal loss through neuroinflammation. Similarly, metals disrupt redox homeostasis while inducing free radical production and decreasing antioxidant levels in the substantia nigra. Furthermore, these metals alter molecular processes and result in oxidative stress, DNA damage, mitochondrial dysfunction, and apoptosis, which can potentially trigger dopaminergic neurodegenerative disorders. This review focuses on the roles of Hg, Pb, Mn, Cu, and Fe in the development and progression of PD. Moreover, it explores the plausible roles of heavy metals in neurodegenerative mechanisms that facilitate the development of PD. A better understanding of the mechanisms underlying metal toxicities will enable the establishment of novel therapeutic approaches to prevent or cure PD.

Epigenetic Biomarkers of Lead Exposure and Cardiovascular Disease: Prospective Evidence in the Strong Heart Study

Background Lead is a cardiotoxic metal with a variety of adverse health effects. In the absence of data on bone lead exposure, epigenetic biomarkers can serve as indicators of cumulative lead exposure and body burden. Herein, we leveraged novel epigenetic biomarkers of lead exposure to investigate their association with cardiovascular disease (CVD) incidence and mortality. Methods and Results Blood DNA methylation was measured using the Illumina MethylationEPIC BeadChip among 2231 participants of the Strong Heart Study (SHS) at baseline (1989-1991). Epigenetic biomarkers of lead levels in blood, patella, and tibia were estimated using previously identified cytosine-guanine dinucleotide (CpG) sites. CVD incidence and mortality data were available through 2017. Median concentrations of lead epigenetic biomarkers were 13.8 μg/g, 21.3 μg/g, and 2.9 μg/dL in tibia, patella, and blood, respectively. In adjusted models, the hazard ratio (HR) (95% CI) of CVD mortality per doubling increase in lead epigenetic biomarkers were 1.42 (1.07-1.87) for tibia lead, 1.22 (0.93-1.60) for patella lead, and 1.57 (1.16-2.11) for blood lead. The corresponding HRs for incident CVD were 0.99 (0.83-1.19), 1.07 (0.89-1.29), and 1.06 (0.87-1.30). The association between the tibia lead epigenetic biomarker and CVD mortality was modified by sex (interaction P value: 0.014), with men at increased risk (HR, 1.42 [95% CI, 1.17-1.72]) compared with women (HR, 1.04 [95% CI, 0.89-1.22]). Conclusions Tibia and blood epigenetic biomarkers were associated with increased risk of CVD mortality, potentially reflecting the cardiovascular impact of cumulative and recent lead exposures. These findings support that epigenetic biomarkers of lead exposure may capture some of the disease risk associated with lead exposure.

Lead-induced neurodevelopmental lesion and epigenetic landscape: Implication in neurological disorders

Lead (Pb) was implicated in multiple genotoxic, neuroepigenotoxic, and chromosomal-toxic mechanisms and interacted with varying synaptic plasticity pathways, likely underpinning previous reports of links between Pb and cognitive impairment. Epigenetic changes have emerged as a promising biomarker for neurological disorders, including cognitive disorders, Alzheimer's disease (AD), and Parkinson's disease (PD). In the present review, special attention is paid to neural epigenetic features and mechanisms that can alter gene expression patterns upon environmental Pb exposure in rodents, primates, and zebrafish. Epigenetic modifications have also been discussed in population studies and cell experiment. Further, we explore growing evidence of potential linkage between Pb-induced disruption of regulatory pathway and neurodevelopmental and neurological disorders both in vivo and in vitro. These findings uncover how epigenome in neurons facilitates the development and function of the brain in response to Pb insult.

Biomarkers of maternal lead exposure during pregnancy using micro-spatial child deciduous dentine measurements

BACKGROUND

Lead is a toxic chemical of public health concern, however limited biomarkers are able to reconstruct prior lead exposures in early-life when biospecimens are not collected and stored. Although child tooth dentine measurements accurately assess past child perinatal lead exposure, it has not been established if they reflect maternal exposure in pregnancy.

AIM

To assess the prenatal relationship between child tooth dentine and maternal blood lead measurements and to estimate maternal lead exposure during the 2nd and 3rd trimesters of pregnancy from weekly child dentine profiles.

METHODS

We measured early-life lead exposure in child tooth dentine and maternal blood from 419 child-mother dyads enrolled in the Programming Research in Obesity, Growth, Environment and Social Stress (PROGRESS) cohort. We employed the Super-Learner algorithm to determine the relationship of dentine lead data with maternal blood lead concentrations and to predict maternal lead from child dentine lead data in blinded analyses. We validated and quantified the bias of our results internally.

RESULTS

Mothers had moderate blood lead levels (trimesters: 2nd = 29.45 ug/L, 3rd = 31.78 ug/L). Trimester-averaged and weekly child dentine lead measurements were highly correlated with maternal blood levels in the corresponding trimesters. The predicted trimester-specific maternal lead levels were significantly correlated with actual measured blood values (trimesters: 2nd = 0.83; 3rd = 0.88). Biomarkers of maternal lead exposure discriminated women highly exposed to lead (>mean) with 85 % and 96 % specificity in the 2nd and 3rd trimesters, respectively, with 80 % sensitivity.

DISCUSSION

Weekly child dentine lead levels can serve as biomarkers of past child and maternal lead exposures during pregnancy.

Gene-environment interactions in Alzheimer disease: the emerging role of epigenetics

With the exception of a few monogenic forms, Alzheimer disease (AD) has a complex aetiology that is likely to involve multiple susceptibility genes and environmental factors. The role of environmental factors is difficult to determine and, until a few years ago, the molecular mechanisms underlying gene-environment (G × E) interactions in AD were largely unknown. Here, we review evidence that has emerged over the past two decades to explain how environmental factors, such as diet, lifestyle, alcohol, smoking and pollutants, might interact with the human genome. In particular, we discuss how various environmental AD risk factors can induce epigenetic modifications of key AD-related genes and pathways and consider how epigenetic mechanisms could contribute to the effects of oxidative stress on AD onset. Studies on early-life exposures are helping to uncover critical time windows of sensitivity to epigenetic influences from environmental factors, thereby laying the foundations for future primary preventative approaches. We conclude that epigenetic modifications need to be considered when assessing G × E interactions in AD.

Lead-exposure associated miRNAs in humans and Alzheimer’s disease as potential biomarkers of the disease and disease processes

Alzheimer’s disease (AD) is a neurodegenerative disease that eventually affects memory and behavior. The identification of biomarkers based on risk factors for AD provides insight into the disease since the exact cause of AD remains unknown. Several studies have proposed microRNAs (miRNAs) in blood as potential biomarkers for AD. Exposure to heavy metals is a potential risk factor for onset and development of AD. Blood cells of subjects that are exposed to lead detected in the circulatory system, potentially reflect molecular responses to this exposure that are similar to the response of neurons. In this study we analyzed blood cell-derived miRNAs derived from a general population as proxies of potentially AD-related mechanisms triggered by lead exposure. Subsequently, we analyzed these mechanisms in the brain tissue of AD subjects and controls. A total of four miRNAs were identified as lead exposure-associated with hsa-miR-3651, hsa-miR-150-5p and hsa-miR-664b-3p being negatively and hsa-miR-627 positively associated. In human brain derived from AD and AD control subjects all four miRNAs were detected. Moreover, two miRNAs (miR-3651, miR-664b-3p) showed significant differential expression in AD brains versus controls, in accordance with the change direction of lead exposure. The miRNAs’ gene targets were validated for expression in the human brain and were found enriched in AD-relevant pathways such as axon guidance. Moreover, we identified several AD relevant transcription factors such as CREB1 associated with the identified miRNAs. These findings suggest that the identified miRNAs are involved in the development of AD and might be useful in the development of new, less invasive biomarkers for monitoring of novel therapies or of processes involved in AD development.

Mitochondria-Mediated Moderation of Apoptosis by EGCG in Cytotoxic Neuronal Cells Induced by Lead (Pb) and Amyloid Peptides

The developmental, epigenetic, and epidemiological studies on lead (Pb) toxicity have reported a strong connection between lead exposure and the progression of Alzheimer's disease (AD). The amyloid peptides were the main triggering elements, in the generation of extracellular plaques through which multiple cellular signaling events such as apoptosis and primarily oxidant-antioxidant balancing system will be affected, which leads to neuronal cell death. Our previous studies indicated that epigallocatechin gallate (EGCG), abundantly present in green tea, was found to be effective in alleviating the metal-induced neurotoxicity at the cellular level in terms of cell viability and apoptosis The aim of this study was to explore the protective mechanism of EGCG on the markers of oxidant-antioxidant system and mitochondria, which are involved in metal-induced neuronal cell death. Initially, the IC₅₀ values for lead(Pb-5 µM), amyloid peptides (AP(1-40)-60 µM; AP(1-40)-8 µM), and EC₅₀ value for EGCG(50 µM) were determined by both time- (12 h, 24 h, 48 h) and concentration-dependent manner and analyzed by MTT assay. The experimental groups were designed initially by treating with Pb and APs individually and in different combinations along with the presence of EGCG and are compared to the Pb and AP treated group without EGCG exposure. The cell lysates were used for analyzing oxidative stress markers by standardized laboratory protocol and the expression of mitochondrial markers such as VDAC and cytochrome C which were analyzed by both western blot and real-time PCR. Our results indicate that the EGCG-treated group has shown a significant increase in antioxidant marker expression levels (GSH, SOD, catalase, vitamin C) and a decrease in oxidative stress marker (NOS, MDA) levels when compared to the group without EGCG treatment (p < 0.05). Similarly, a significant decrease in expression levels of VDAC and cytochrome c were observed in the EGCG-treated group when compared to the group without EGCG treatment (p < 0.05). Our approach revealed that EGCG protects SH-SY5Y cells from Pb- and AP-induced cytotoxicity by regulating voltage-dependent anion channel (VDAC) expression and oxidant-antioxidant system and inhibits neuronal cell death.

Exploring the Involvement of the Amyloid Precursor Protein A673T Mutation against Amyloid Pathology and Alzheimer's Disease in Relation to Therapeutic Editing Tools

Alzheimer's disease (AD) is biologically defined as a complex neurodegenerative condition with a multilayered nature that leads to a progressive decline in cognitive function and irreversible neuronal loss. It is one of the primary diseases among elderly individuals. With an increasing incidence and a high failure rate for pharmaceutical options that are merely symptom-targeting and supportive with many side effects, there is an urgent need for alternative strategies. Despite extensive knowledge on the molecular basis of AD, progress concerning effective disease-modifying therapies has proven to be a challenge. The ability of the CRISPR-Cas9 gene editing system to help identify target molecules or to generate new preclinical disease models could shed light on the pathogenesis of AD and provide promising therapeutic possibilities. Here, we sought to highlight the current understanding of the involvement of the A673T mutation in amyloid pathology, focusing on its roles in protective mechanisms against AD, in relation to the recent status of available therapeutic editing tools.

Lead acetate induces hippocampal pyramidal neuron degeneration in mice via up-regulation of executioner caspase-3, oxido-inflammatory stress expression and decreased BDNF and cholinergic activity: Reversal effects of Gingko biloba supplement

PURPOSE

It has been hypothesized that compounds with strong anti-oxidant activity might mitigate lead-induced neurotoxicity that resulted to neuronal degeneration.Ginkgo biloba supplement (GB-S) is a neuroactive supplement which has been reported to demonstrate neuroprotective effects. In this study, we investigated the reversal effect and the underlying mechanism of GB-S following lead-induced neurotoxicity in mice.

METHODS

Male Swiss mice (n = 8) were pre-treated with lead acetate (100 mg/kg) for 30 min before GB-S (10 mg/kg and 20 mg/kg) or Ethylenediaminetetraacetic acid (EDTA) (50 mg/kg) intraperitoneally for 14 consecutive days. Memory impairment symptoms were evaluated on day 13 and 14 using Y-maze and Novel object recognition test (NORT) respectively. Thereafter, spectrophotometry, ELISA, immunohistochemistry and histomorphormetry were used to estimate the degree and expression of biomarkers of neuronal inflammation: oxido-inflammatory stress, apoptosis and degeneration in the hippocampus (HC).

RESULTS

Lead acetate treatment significantly (p < 0.05) induced neurobehavioral impairment which was reversed by GB-S as evident in increased percentage alternation and discrimination index. GB-S significantly (p < 0.05) reduced lipid peroxidation and nitrite level, inhibited TNF-α and acetylcholinesterase activity and improved glutathione, catalase and superoxide dismutase activity in the HC. Moreover, GB-S inhibited hippocampal apoptosis via elevated expression of caspase-3 with marked increase level of brain derived neurotrophic factor (BDNF). Also, the histomorphormetric study showed that GB-S rescued death of pyramidal neurons (CA3) in the HC.

CONCLUSION

Our findings however suggest that GB-S decreased memory impairment progression induced by lead acetate via mechanisms connected to inhibition of oxido-inflammatory stress mediators, restrained acetylcholinesterase activity, up-regulated BDNF/Caspase-3 expression and suppression of hippocampal pyramidal neuron degeneration in mice.

Evaluation of Chelating Agents Used in Phytoextraction by Switchgrass of Lead Contaminated Soil

Soil lead (Pb) contamination is a recognized environmental and global health problem. Phytoextraction of Pb using switchgrass (Panicum virgatum L.), a second-generation biofuel crop, is typically enhanced by soil chelation. The effectiveness of four different chelating agents, phytic acid (inositol hexaphosphate), citric acid, NTA (nitrilotriacetic acid), and EDTA (ethylenediaminetetraacetic acid) was examined in pot culture. Plants treated with EDTA (1 mM) showed significantly higher shoot Pb concentrations compared to control plants and plants treated with other chelates. Lead-solubility following phytoextraction was examined by soil washing using 0.01 and 0.05 M acetic acid as an extractant solution revealed no significant differences in Pb concentrations in soil among different chelate treatments and control. Furthermore, the effects of different concentrations (1, 2, 5 and 10 mM) of NTA on Pb phytoextraction of switchgrass were examined. Plants receiving 5 mM and 10 mM NTA had significantly higher foliage concentrations of Pb compared to plants treated with lower levels (1 and 2 mM) of NTA. Moreover, the effect of NTA application alone was significantly improved by a combined application of Triton X-100, an alkyl polyglucoside (APG); the Pb concentration in the foliage of switchgrass was more than doubled when treated with NTA combined with APG. The use of NTA combined with APG has great potential in improving phytoextraction efficiencies of switchgrass on Pb-contaminated soils.

Pb Induces MCP-1 in the Choroid Plexus

Lead (Pb) is an environmental element that has been implicated in the development of dementia and Alzheimer's disease (AD). Additionally, innate immune activation contributes to AD pathophysiology. However, the mechanisms involved remain poorly understood. The choroid plexus (CP) is not only the site of cerebrospinal fluid (CSF) production, but also an important location for communication between the circulation and the CSF. In this study, we investigated the involvement of the CP during Pb exposure by evaluating the expression of the monocyte chemoattractant protein-1 (MCP-1). MCP-1 is highly expressed in the CP compared to other CNS tissues. MCP-1 regulates macrophage infiltration and is upregulated in AD brains. Our study revealed that Pb exposure stimulated MCP-1 expression, along with a significantly increased macrophage infiltration into the CP. By using cultured Z310 rat CP cells, Pb exposure stimulated MCP-1 expression in a dose-related fashion and markedly activated both NF-κB and p38 MAP kinase. Interestingly, both SB 203580, a p38 inhibitor, and BAY 11-7082, an NF-κB p65 inhibitor, significantly blocked Pb-induced MCP-1 expression. However, SB203580 did not directly inhibit NF-κB p65 phosphorylation. In conclusion, Pb exposure stimulates MCP-1 expression via the p38 and NF-κB p65 pathways along with macrophage infiltration into the CP.

Nutrition and cognition across the lifetime: an overview on epigenetic mechanisms

The functioning of our brain depends on both genes and their interactions with environmental factors. The close link between genetics and environmental factors produces structural and functional cerebral changes early on in life. Understanding the weight of environmental factors in modulating neuroplasticity phenomena and cognitive functioning is relevant for potential interventions. Among these, nutrition plays a key role. In fact, the link between gut and brain (the gut-brain axis) is very close and begins in utero, since the Central Nervous System (CNS) and the Enteric Nervous System (ENS) originate from the same germ layer during the embryogenesis. Here, we investigate the epigenetic mechanisms induced by some nutrients on the cognitive functioning, which affect the cellular and molecular processes governing our cognitive functions. Furthermore, epigenetic phenomena can be positively affected by specific healthy nutrients from diet, with the possibility of preventing or modulating cognitive impairments. Specifically, we described the effects of several nutrients on diet-dependent epigenetic processes, in particular DNA methylation and histones post-translational modifications, and their potential role as therapeutic target, to describe how some forms of cognitive decline could be prevented or modulated from the early stages of life.

Lab-on-a-ZnO-Submicron-Particle Sensor Array for Monitoring AD upon Cd2+ Exposure with CSF Tau441% as an Effective Hallmark

In this study, based on the posttreatment strategy, blue-color-emissive ZnO submicron particles (B-ZnO SMPs) and red-color-emissive ZnO submicron particles (R-ZnO SMPs) were obtained from rationally designed Zn-infinite coordination polymer (ICP) precursors. After modification of thiol-containing aptamers, diverse spectral changes in the ultraviolet and visible regions of B- and R-ZnO SMPs toward different tau species were explored to construct a lab-on-a-ZnO-submicron-particle sensor array. Assisted by principal component analysis (PCA), the unique fingerprints of the sensor array enabled the simultaneous differentiation and quantitative detection of different tau species (tau381, tau410, and tau441) for the first time. Furthermore, the dynamic changes of tau441% (the ratio of the two most reported representative 4R isoform (full-length tau441) and 3R isoform (tau381)) in cerebrospinal fluid (CSF) during the Alzheimer's disease (AD) onset of Cd²⁺-exposed rats could also be monitored by the lab-on-a-ZnO-submicron-particle sensor array, which was supposed to be an effective hallmark and highly correlated with the formation of neurofibrillary tangles (NFTs). This study not only provides a further insight into the involvement of subchronic Cd²⁺ exposure in the tau etiology of AD but also offers more comprehensive and effective information about the asymptomatic stage of AD upon environmental risk, which has potential applications in the early diagnosis and therapy.

Blood lead levels in Peruvian adults are associated with proximity to mining and DNA methylation

BACKGROUND

Inorganic lead (Pb) is common in the environment, and is toxic to neurological, renal, and cardiovascular systems. Pb exposure influences the epigenome with documented effects on DNA methylation (DNAm). We assessed the impact of low levels of Pb exposure on DNAm among non-miner individuals from two locations in Peru: Lima, the capital, and Cerro de Pasco, a highland mining town, to study the effects of Pb exposure on physiological outcomes and DNAm.

METHODS

Pb levels were measured in whole blood (n = 305). Blood leukocyte DNAm was determined for 90 DNA samples using the Illumina MethylationEPIC chip. An epigenome-wide association study was performed to assess the relationship between Pb and DNAm.

RESULTS

Individuals from Cerro de Pasco had higher Pb than individuals from Lima (p-value = 2.00E-16). Males had higher Pb than females (p-value = 2.36E-04). Pb was positively associated with hemoglobin (p-value = 8.60E-04). In Cerro de Pasco, blood Pb decreased with the distance from the mine (p-value = 0.04), and association with soil Pb was approaching significance (p-value = 0.08). We identified differentially methylated positions (DMPs) associated with genes SOX18, ZMIZ1, and KDM1A linked to neurological function. We also found 45 differentially methylated regions (DMRs), seven of which were associated with genes involved in metal ion binding and nine to neurological function and development.

CONCLUSIONS

Our results demonstrate that even low levels of Pb can have a significant impact on the body including changes to DNAm. We report associations between Pb and hemoglobin, Pb and distance from mining, and between blood and soil Pb. We also report associations between loci- and region-specific DNAm and Pb.

Associations of Community Water Lead Concentrations with Hemoglobin Concentrations and Erythropoietin-Stimulating Agent Use among Patients with Advanced CKD

BACKGROUND

Although patients with kidney disease may be particularly susceptible to the adverse health effects associated with lead exposure, whether levels of lead found commonly in drinking water are associated with adverse outcomes in patients with ESKD is not known.

METHODS

To investigate associations of lead in community water systems with hemoglobin concentrations and erythropoietin stimulating agent (ESA) use among incident patients with ESKD, we merged data from the Environmental Protection Agency (EPA) Safe Drinking Water Information System (documenting average 90^th percentile lead concentrations in community water systems during 5 years before dialysis initiation, according to city of residence) with patient-level data from the United States Renal Data System.

RESULTS

Among 597,968 patients initiating dialysis in the United States in 2005 through 2017, those in cities with detectable lead levels in community water had significantly lower pre-ESKD hemoglobin concentrations and more ESA use per 0.01 mg/L increase in 90^th percentile water lead. Findings were similar for the 208,912 patients with data from the first month of ESKD therapy, with lower hemoglobin and higher ESA use per 0.01 mg/L higher lead concentration. These associations were observed at lead levels below the EPA threshold (0.015 mg/L) that mandates regulatory action. We also observed environmental inequities, finding significantly higher water lead levels and slower declines over time among Black versus White patients.

CONCLUSIONS

This first nationwide analysis linking EPA water supply records to patient data shows that even low levels of lead that are commonly encountered in community water systems throughout the United States are associated with lower hemoglobin levels and higher ESA use among patients with advanced kidney disease.

Effects of Exogenous Application of Plant Growth Regulators (SNP and GA3) on Phytoextraction by Switchgrass (Panicum virgatum L.) Grown in Lead (Pb) Contaminated Soil

Soil lead (Pb) contamination is a major environmental and public health risk. Switchgrass (Panicum virgatum), a second-generation biofuel crop, is potentially useful for the long-term phytoremediation and phytoextraction of Pb contaminated soils. We evaluated the efficacy of a coordinated foliar application of plant growth regulators and soil fungicide and a chelator in order to optimize phytoextraction. Plants were grown in soil culture under controlled conditions. First, three exogenous nitric oxide (NO) donors were evaluated at multiple concentrations: (1) S-nitroso-N-acetylpenicillamine (SNAP); (2) sodium nitroprusside (SNP); and (3) S-nitrosoglutathione (GSNO). Second, the effect of SNP (0.5 μM) was examined further with the model chelate EDTA and the soil fungicide propicanazole. Third, a combined foliar application of SNP and gibberellic acid (GA3) was examined with EDTA and propicanazole. The soil application of propiconazole (a broad-spectrum fungicides) reduced AMF colonization and allowed greater Pb phytoextraction. The foliar application of SNP resulted in similar concentrations of Pb (roots and foliage) to plants that were challenged with chelates and soil fungicides. The combined foliar application of SNP and GA3 resulted in significantly greater average Pb concentration (243 mg kg−1) in plant foliage in comparison to control plants (182 mg kg−1) and plants treated with GA3 alone (202 mg kg−1). The combined foliar application of SNP and GA3 resulted in the greatest phytoextraction efficiency and could therefore potentially improve phytoextraction by switchgrass grown in Pb contaminated soils.

Extracellular Vesicles in Premature Aging and Diseases in Adulthood Due to Developmental Exposures

The developmental origins of health and disease (DOHaD) is a paradigm that links prenatal and early life exposures that occur during crucial periods of development to health outcome and risk of disease later in life. Maternal exposures to stress, some psychoactive drugs and alcohol, and environmental chemicals, among others, may result in functional changes in developing fetal tissues, creating a predisposition for disease in the individual as they age. Extracellular vesicles (EVs) may be mediators of both the immediate effects of exposure during development and early childhood as well as the long-term consequences of exposure that lead to increased risk and disease severity later in life. Given the prevalence of diseases with developmental origins, such as cardiovascular disease, neurodegenerative disorders, osteoporosis, metabolic dysfunction, and cancer, it is important to identify persistent mediators of disease risk. In this review, we take this approach, viewing diseases typically associated with aging in light of early life exposures and discuss the potential role of EVs as mediators of lasting consequences.

Mechanisms of Metal-Induced Mitochondrial Dysfunction in Neurological Disorders

Metals are actively involved in multiple catalytic physiological activities. However, metal overload may result in neurotoxicity as it increases formation of reactive oxygen species (ROS) and elevates oxidative stress in the nervous system. Mitochondria are a key target of metal-induced toxicity, given their role in energy production. As the brain consumes a large amount of energy, mitochondrial dysfunction and the subsequent decrease in levels of ATP may significantly disrupt brain function, resulting in neuronal cell death and ensuing neurological disorders. Here, we address contemporary studies on metal-induced mitochondrial dysfunction and its impact on the nervous system.

DNA methylation at birth potentially mediates the association between prenatal lead (Pb) exposure and infant neurodevelopmental outcomes

Early-life lead (Pb) exposure has been linked to adverse neurodevelopmental outcomes. Recent evidence has indicated a critical role of DNA methylation (DNAm) in cognition, and Pb exposure has also been shown to alter DNAm. However, it is unknown whether DNAm is part of the mechanism of Pb neurotoxicity. This longitudinal study investigated the associations between trimester-specific (T1, T2, and T3) maternal blood Pb concentrations, gene-specific DNAm in umbilical cord blood, and infant neurodevelopmental outcomes at 12 and 24 months of age (mental development index, psychomotor development index, and behavioral rating scale of orientation/engagement and emotional regulation) among 85 mother-infant pairs from the Early Life Exposure in Mexico to Environmental Toxicants (ELEMENT) study. In the mediation analysis for this pilot study, P < 0.1 was considered significant. DNAm at a locus in CCSER1 (probe ID cg02901723) mediated the association between T2 Pb on 24-month orientation/engagement [indirect effect estimate 4.44, 95% confidence interval (-0.09, 10.68), P = 0.06] and emotional regulation [3.62 (-0.05, 8.69), P = 0.05]. Cg18515027 (GCNT1) DNAm mediated the association of T1 Pb [-4.94 (-10.6, -0.77), P = 0.01] and T2 Pb [-3.52 (-8.09, -0.36), P = 0.02] with 24-month EMOCI, but there was a positive indirect effect estimate between T2 Pb and 24-month psychomotor development index [1.25 (-0.11, 3.32), P = 0.09]. The indirect effect was significant for cg19703494 (TRAPPC6A) DNAm in the association between T2 Pb and 24-month mental development index [1.54 (0, 3.87), P = 0.05]. There was also an indirect effect of cg23280166 (VPS11) DNAm on T3 Pb and 24-month EMOCI [2.43 (-0.16, 6.38), P = 0.08]. These associations provide preliminary evidence for gene-specific DNAm as mediators between prenatal Pb and adverse cognitive outcomes in offspring.

Prenatal Lead (Pb) Exposure and Peripheral Blood DNA Methylation (5mC) and Hydroxymethylation (5hmC) in Mexican Adolescents from the ELEMENT Birth Cohort

BACKGROUND

Gestational lead (Pb) exposure can adversely affect offspring health through multiple mechanisms, including epigenomic alterations via DNA methylation (5mC) and hydroxymethylation (5hmC), an intermediate in oxidative demethylation. Most current methods do not distinguish between 5mC and 5hmC, limiting insights into their individual roles.

OBJECTIVE

Our study sought to identify the association of trimester-specific (T1, T2, T3) prenatal Pb exposure with 5mC and 5hmC levels at multiple cytosine-phosphate-guanine sites within gene regions previously associated with prenatal Pb (HCN2, NINJ2, RAB5A, TPPP) in whole blood leukocytes of children ages 11-18 years of age.

METHODS

Participants from the Early Life Exposure in Mexico to Environmental Toxicants (ELEMENT) birth cohorts were selected (n=144) for pyrosequencing analysis following oxidative or standard sodium bisulfite treatment. This workflow directly quantifies total methylation (5mC+5hmC) and 5mC only; 5hmC is estimated by subtraction.

RESULTS

Participants were 51% male, and mean maternal blood lead levels (BLL) were 6.43±5.16μg/dL in Trimester 1 (T1), 5.66±5.21μg/dL in Trimester 2 (T2), and 5.86±4.34μg/dL in Trimester 3 (T3). In addition, 5hmC levels were calculated for HCN2 (mean±standard deviation(SD), 2.08±4.18%), NINJ2 (G/C: 2.01±5.95; GG: 0.90±3.97), RAB5A (0.66±0.80%), and TPPP (1.11±6.67%). Furthermore, 5mC levels were measured in HCN2 (81.3±9.63%), NINJ2 (heterozygotes: 38.6±7.39%; GG homozygotes: 67.3±9.83%), RAB5A (1.41±1.21%), and TPPP (92.5±8.03%). Several significant associations between BLLs and 5mC/5hmC were identified: T1 BLLs with 5mC in HCN2 (β=-0.37, p=0.03) and 5hmC in NINJ2 (β=0.49, p=0.003); T2 BLLs with 5mC in HCN2 (β=0.37, p=0.03) and 5hmC in NINJ2 (β=0.27, p=0.008); and T3 BLLs with 5mC in HCN2 (β=0.50, p=0.01) and NINJ2 (β=-0.35, p=0.004) and 5hmC in NINJ2 (β=0.45, p<0.001). NINJ2 5mC was negatively correlated with gene expression (Pearson r=-0.5, p-value=0.005), whereas 5hmC was positively correlated (r=0.4, p-value=0.04).

DISCUSSION

These findings suggest there is variable 5hmC in human whole blood and that prenatal Pb exposure is associated with gene-specific 5mC and 5hmC levels at adolescence, providing evidence to consider 5hmC as a regulatory mechanism that is responsive to environmental exposures. https://doi.org/10.1289/EHP8507.

Metals toxicity and its correlation with the gene expression in Alzheimer's disease

Alzheimer's disease is a common neurodegenerative disease in the elderly population and a leading cause of dementia. Genetics and environmental risk factors were considered to play a major role in the onset of the disease. This study aimed to examine the correlation between different metals levels and the gene expression in Alzheimer's patients with age-matched control subjects. Non- essential metals were measured in the whole blood due to its higher concentration in red blood corpuscles (RBCs) and essential biometals in the serum samples of Alzheimer's disease (AD) by using Inductively coupled plasma optical emission spectroscopy (ICP-OES) that allows the analysis and detection of the different elements at low levels. Gene expression level was performed by quantitative real-time PCR (qRT-PCR). In this study, the levels of Lead and Arsenic metals were not detected in the AD patient samples. Cadmium, Mercury, and Aluminum were found higher in cases as compared to controls with 0.009240 ± 0.0007707 (P =  < 0.0001), 0.02332 ± 0.001041 (P =  < 0.0001), and 0.09222 ± 0.02804 (P = 0.0087) respectively. Essential biometal like copper was higher 0.1274 ± 0.02453 (P = 0.0254) in cases, while iron 0.1117 ± 0.009599 (P = 0.0304) and zinc 0.03800 ± 0.003462 mg/L were found significantly lower as compared to controls. All targeted genes such as APP, PSEN1, PSEN2, and APOE4 were found up-regulated in AD patients. We concluded that there was no significant correlation between metals dyshomeostasis and gene expressions in this study.

Phosphorylated tau targeted small-molecule PROTACs for the treatment of Alzheimer's disease and tauopathies

Tau is a microtubule-stabilizing protein that plays an important role in the formation of axonal microtubules in neurons. Phosphorylated tau (p-Tau) has received great attention in the field of Alzheimer's disease (AD) as a potential therapeutic target due to its involvement with synaptic damage and neuronal dysfunction. Mounting evidence suggests that amyloid beta (Aβ)-targeted clinical trials continuously failed; therefore, it is important to consider alternative therapeutic strategies such as p-tau-PROTACs targeted small molecules for AD and other tauopathies. The present article describes the characteristics of tau biology, structure, and function in both healthy and pathological states in AD. It also explains data from studies that have identified the involvement of p-tau in neuronal damage and synaptic and cognitive functions in AD. Current article also covers several aspects, including small molecule inhibitors, and the development of p-tau-PROTACs targeted drug molecules to treat patients with AD and other tauopathies.

Lead and zinc interactions - An influence of zinc over lead related toxic manifestations

BACKGROUND

Interaction between metals is known from earlier studies, in which one metal influences the absorption and functional role of other. Lead is known to cause debilitating effects in living organisms and also prevents several essential trace metals from functioning normally.

METHODS

The relevant literature using the key words lead toxicity, lead zinc interaction, zinc nutrition and the ability of zinc to act against lead has been reviewed.

RESULTS

Role of several nutrients in reducing the manifestations of toxic metals have been elucidated recently. Lead damages bio-membranes, causes cognitive disabilities and disturbs the normal process of DNA replication and transcription. Zinc on the other hand helps in proper maintenance of the cellular membranes and plays an important role as a metal cofactor in most of the proteins vital for membrane integrity. Zinc has essential role in cognitive functioning, zinc finger proteins and significantly neutralizes most toxic effects of lead.

CONCLUSION

Increased lead exposure and limited resources for tackling lead poisoning may cause an increased possibility of future environmental emergencies. Interactions between essential nutrient metals and non-essential toxic metals may act as important factor which can be used to target the metal toxicities. An assumption is made that the lead toxicity can be reduced by maintaining the status of essential trace metals like zinc.

A critical review of the epidemiological evidence of effects of air pollution on dementia, cognitive function and cognitive decline in adult population

Dementia is arguably the most pressing public health challenge of our age. Since dementia does not have a cure, identifying risk factors that can be controlled has become paramount to reduce the personal, societal and economic burden of dementia. The relationship between exposure to air pollution and effects on cognitive function, cognitive decline and dementia has stimulated increasing scientific interest in the past few years. This review of the literature critically examines the available epidemiological evidence of associations between exposure to ambient air pollutants, cognitive performance, acceleration of cognitive decline, risk of developing dementia, neuroimaging and neurological biomarker studies, following Bradford Hill guidelines for causality. The evidence reviewed has been consistent in reporting associations between chronic exposure to air pollution and reduced global cognition, as well as impairment in specific cognitive domains including visuo-spatial abilities. Cognitive decline and dementia incidence have also been consistently associated with exposure to air pollution. The neuro-imaging studies reviewed report associations between exposure to air pollution and white matter volume reduction. Other reported effects include reduction in gray matter, larger ventricular volume, and smaller corpus callosum. Findings relating to ischemic (white matter hyperintensities/silent cerebral infarcts) and hemorrhagic (cerebral microbleeds) markers of cerebral small vessel disease have been heterogeneous, as have observations on hippocampal volume and air pollution. The few studies available on neuro-inflammation tend to report associations with exposure to air pollution. Several effect modifiers have been suggested in the literature, but more replication studies are required. Traditional confounding factors have been controlled or adjusted for in most of the reviewed studies. Additional confounding factors have also been considered, but the inclusion of these has varied among the different studies. Despite all the efforts to adjust for confounding factors, residual confounding cannot be completely ruled out, especially since the factors affecting cognition and dementia are not yet fully understood. The available evidence meets many of the Bradford Hill guidelines for causality. The reported associations between a range of air pollutants and effects on cognitive function in older people, including the acceleration of cognitive decline and the induction of dementia, are likely to be causal in nature. However, the diversity of study designs, air pollutants and endpoints examined precludes the attribution of these adverse effects to a single class of pollutant and makes meta-analysis inappropriate.

Blood DNA methylation biomarkers of cumulative lead exposure in adults

BACKGROUND

Lead is a ubiquitous toxicant following three compartment kinetics with the longest half-life found in bones. Patella and tibia lead levels-validated measures of cumulative exposure-require specialized X-ray-fluorescence-spectroscopy available only in a few centers worldwide. We developed minimally invasive biomarkers reflecting individual cumulative lead exposure using blood DNA methylation profiles-obtainable via Illumina 450K or IlluminaEPIC bead-chip assays.

METHODS

We developed and tested two methylation-based biomarkers from 348 Normative Aging Study (NAS) elderly men. We selected methylation sites with strong associations with bone lead levels via robust regressions analysis and constructed the biomarkers using elastic nets. Results were validated in a NAS subset, reporting specificity, and sensitivity.

FINDINGS

Participants were 73 years old on average (standard deviation, SD = 6), with moderate lead levels of (mean ± SD patella: 27 ± 18 µg/g; tibia:21 ± 13 µg/g). Methylation-based biomarkers for lead in patella and tibia included 59 and 138 DNA methylation sites, respectively. Estimated lead levels were significantly correlated with actual measured values, (r = 0.62 patella, r = 0.59 tibia) and had low mean square error (MSE) (MSE = 0.68 patella, MSE = 0.53 tibia). Means and distributions of the estimated and actual lead levels were not significantly different across patella and tibia bones (p > 0.05). Methylation-based biomarkers discriminated participants highly exposed (>median) to lead with a specificity of 74 and 73% for patella and tibia lead levels, respectively, with 70% sensitivity.

INTERPRETATION

DNA methylation-based lead biomarkers are novel tools that can be used to reconstruct decades' worth of individual cumulative lead exposure using only blood DNA methylation profiles and may help identify the consequences of cumulative exposure.

DNA Methylation-Based Biomarkers of Environmental Exposures for Human Population Studies

PURPOSE OF REVIEW

This manuscript orients the reader to the underlying motivations of environmental biomarker development for human population studies and provides the foundation for applying these novel biomarkers in future research. In this review, we focus our attention on the DNA methylation-based biomarkers of (i) smoking, among adults and pregnant women, (ii) lifetime cannabis use, (iii) alcohol consumption, and (iv) cumulative exposure to lead.

RECENT FINDINGS

Prior environmental exposures and lifestyle modulate DNA methylation levels. Exposure-related DNA methylation changes can either be persistent or reversible once the exposure is no longer present, and this combination of both persistent and reversible changes has essential value for biomarker development. Here, we present available biomarkers representing past and cumulative exposures using individual DNA methylation profiles. In the present work, we describe how the field of environmental epigenetics can leverage machine learning algorithms to develop exposure biomarkers and reduce problems of misreporting exposures or limited access technology. We emphasize the crucial role of the individual DNA methylation profiles in those predictions, providing a summary of each biomarker, and highlighting their advantages, and limitations. Future research can cautiously leverage these DNA methylation-based biomarkers to understand the onset and progression of diseases.

(Ascorb)ing Pb Neurotoxicity in the Developing Brain

Lead (Pb) neurotoxicity is a major concern, particularly in children. Developmental exposure to Pb can alter neurodevelopmental trajectory and has permanent neuropathological consequences, including an increased vulnerability to further stressors. Ascorbic acid is among most researched antioxidant nutrients and has a special role in maintaining redox homeostasis in physiological and physio-pathological brain states. Furthermore, because of its capacity to chelate metal ions, ascorbic acid may particularly serve as a potent therapeutic agent in Pb poisoning. The present review first discusses the major consequences of Pb exposure in children and then proceeds to present evidence from human and animal studies for ascorbic acid as an efficient ameliorative supplemental nutrient in Pb poisoning, with a particular focus on developmental Pb neurotoxicity. In doing so, it is hoped that there is a revitalization for further research on understanding the brain functions of this essential, safe, and readily available vitamin in physiological states, as well to justify and establish it as an effective neuroprotective and modulatory factor in the pathologies of the nervous system, including developmental neuropathologies.

Emerging risk of environmental factors: insight mechanisms of Alzheimer's diseases

Neurodegenerative disorders are typically sporadic in nature in addition to usually influenced through an extensive range of environmental factors, lifestyle, and genetic elements. Latest observations have hypothesized that exposure of environmental factors may increase the prospective risk of Alzheimer's diseases (AD). However, the role of environmental factors as a possible dangerous issue has extended importance concerned in AD pathology, although actual etiology of the disorder is still not yet clear. Thus, the aim of this review is to highlight the possible correlation between environmental factors and AD, based on the present literature view. Environmental risk factors might play an important role in decelerating or accelerating AD progression. Among well-known environmental risk factors, prolonged exposure to several heavy metals, for example, aluminum, arsenic, cadmium, lead, and mercury; particulate air, and some pesticides as well as metal-containing nanoparticles have been participated to cause AD. These heavy metals have the capacity to enhance amyloid β (Aβ) peptide along with tau phosphorylation, initiating amyloid/senile plaques, as well as neurofibrillary tangle formation; therefore, neuronal cell death has been observed. Furthermore, particulate air, pesticides, and heavy metal exposure have been recommended to lead AD susceptibility and phenotypic diversity though epigenetic mechanisms. Therefore, this review deliberates recent findings detailing the mechanisms for a better understanding the relationship between AD and environmental risk factors along with their mechanisms of action on the brain functions.

Selective loss of 5hmC promotes neurodegeneration in the mouse model of Alzheimer's disease

5-hydroxymethylcytosine (5hmC) is an intermediate stage of DNA de-methylation. Its location in the genome also serves as an important regulatory signal for many biological processes and its levels change significantly with the etiology of Alzheimer's disease (AD). In keeping with this relationship, the TET family of enzymes which convert 5-methylcytosine (5mC) to 5hmC are responsive to the presence of Aβ. Using hMeDIP-seq, we show that there is a genome-wide reduction of 5hmC that is found in neurons but not in astrocytes from 3xTg mice (an AD mouse model). Decreased TET enzymatic activities in the brains of persons who died with AD suggest that this reduction is the main cause for the loss of 5hmC. Overexpression of human TET catalytic domains (hTETCDs) from the TET family members, especially for hTET3CD, significantly attenuates the neurodegenerative process, including reduced Aβ accumulation as well as tau hyperphosphorylation, and improve synaptic dysfunction in 3xTg mouse brain. Our findings define a crucial role of deregulated 5hmC epigenetics in the events leading to AD neurodegeneration.

Role of environmental pollutants in Alzheimer's disease: a review

Neurodegenerative disorders are commonly erratic influenced by various factors including lifestyle, environmental, and genetic factors. In recent observations, it has been hypothesized that exposure to various environmental factors enhances the risk of Alzheimer's disease (AD). The exact etiology of Alzheimer's disease is still unclear; however, the contribution of environmental factors in the pathology of AD is widely acknowledged. Based on the available literature, the review aims to culminate in the prospective correlation between the various environmental factors and AD. The prolonged exposure to the various well-known environmental factors including heavy metals, air pollutants (particulate matter), pesticides, nanoparticles containing metals, industrial chemicals results in accelerating the progression of AD. Common mechanisms have been documented in the field of environmental contaminants for enhancing amyloid-β (Aβ) peptide along with tau phosphorylation, resulting in the initiation of senile plaques and neurofibrillary tangles, which results in the death of neurons. This review offers a compilation of available data to support the long-suspected correlation between environmental risk factors and AD pathology. Graphical abstract .

Toxic Environmental Factors and their Association with the Development of Dementia: a Mini Review on Heavy Metals and Ambient Particulate Matter

INTRODUCTION

More and more studies are trying to establish a connection between dementia and environmental pollution. Dementia, most commonly associated with Alzheimer's disease, is a chronic, progressive, neurodegenerative disorder that is directly associated to aging. Although the etiology of the disease is not fully understood, it is recognized as a multifactorial one. Genetic and environmental factors contribute to the development of various forms of dementia. Both predisposing genes and environmental pollution have been shown to affect brain function through a variety of mechanisms.

AIM

The purpose of this bibliographic work is «ecological consciousness» of modern societies to be awaken, to identify the harmful environmental factors and to highlight their involvement in the causal pathogenesis of the most debated disease, dementia.

METHODS

Trying to achieve this aim, the available bibliography was reviewed and selected for further study. In particular, recent bibliographic data and scientific papers were selected, mainly from the last five years. The information was collected using the keywords "environmental pollution", " toxic agents" and "etiology of dementia", with particular emphasis on "Alzheimer's disease". The data were selected mainly from medical research databases. In particular, they were selected by PubMed, BioMed Central and Science Direct.

CONCLUSION

According to the results of this study, long-term exposure of individuals to pollutants may be associated with an increased risk of dementia. However, we must be cautious in our conclusions, as further reliable studies are needed to confirm the stated evidence. Among other things, health professionals are responsible for promoting health, preventing and encouraging lifestyle change, so that the progressively growing elderly population remains autonomous, healthy and active.

A New Discovery of MicroRNA-455-3p in Alzheimer's Disease

MicroRNA-455-3p (miR-455-3p) is identify as a member of broadly conserved miRNA family expressed in most of the phylum and species. In humans, miR-455 is present on the human chromosome 9 at locus 9q32 and encoded by the human COL27A1 gene (collagen type XXVII alpha 1 chain). The role of miR-455 has been implicated in various human diseases such as cartilage development, adipogenesis, preeclampsia, and cancers, e.g., colon cancer, prostate cancer, hepatocellular carcinoma, renal cancer, oral squamous cancer, skin cancer, and non-small cell lung cancer. Recently, our laboratory discovered the biomarker and therapeutic relevance of miR-455-3p in Alzheimer's disease (AD). Our global microarray analysis of serum samples from AD patients, mild cognitive individuals (MCI), and healthy subjects unveiled the high level of miR-455-3p in AD patients relative to MCI and healthy controls. Further, validation analysis using different kinds of AD samples such as serum, postmortem brains, AD fibroblasts, AD B-lymphocytes, AD cell lines, AD mouse models, and AD cerebrospinal fluid confirmed the biomarker potential of miR-455-3p. The mechanistic link of miR-455-3p in AD was determined via modulation of amyloid-β protein precursor (AβPP) and amyloid-β (Aβ) levels. Luciferase reporter assay confirmed AβPP as validated target of miR-455-3p. Our study on mouse neuroblastoma cells revealed the protective role of miR-455-3p against Aβ-induced toxicities. We also noticed that miR-455-3p enhances cell survival and lifespan extension. High level of miR-455-3p reduces Aβ toxicity, enhances mitochondrial biogenesis and synaptic activity, and maintains healthy mitochondrial dynamics. Based on these evidences, we cautiously conclude that miR-455-3p is a promising peripheral biomarker and therapeutic candidate for AD.

Reduction of Lead Levels in Patients Following a Long-Term, Intermittent Calcium Ethylenediaminetetraacetic Acid (EDTA)-Based Intravenous Chelation Infusions: A Prospective Experimental Cohort

Chronic exposure to and the accumulation of lead has been associated with cardiovascular and all-cause morbidity and mortality. It has also been associated with accelerated declines in cognitive function and has been theorized as a contributor to essential hypertension. This study demonstrates the capacity of intermittent infusions of calcium ethylenediaminetetraacetic acid (EDTA) to reduce the amount of lead measured by provocative urinary testing, which is considered a marker for total body lead stores. Since lead is a known toxic substance with no safe levels, reducing the amount of accumulated lead in an individual has the possibility of decreasing the risk of heart disease, dementia, and other chronic illnesses associated with lead exposure. This study population was 15 healthy, asymptomatic patients who were evaluated for accumulated total body lead stores as part of a routine health screening. Total body lead was estimated by measuring urinary output after the patients had received intravenous (IV) calcium EDTA as a chelating agent. After establishing their baseline stored lead levels, patients received a series of intravenous chelation infusions to reduce body lead. The average number of infusions given was 14, over an average period of 24 months. After the series of chelations, there was an average reduction in the lead of 39.16% (range of 16% to 40%). All 15 subjects had a reduction in the amount of excreted lead after the series of chelation infusions.

Environmental toxins and Alzheimer's disease progression

Alzheimer's disease (AD) is the most common form of dementia, which causes progressive memory loss and cognitive decline. Effective strategies to treat or prevent remains one of the most challenging undertakings in the medical field. AD is a complex and multifactorial disease that involves several risk factors. Aging and genetic factors both play important roles in the onset of the AD, however; certain environmental factors have been reported to increase the risk of AD. Chronic exposure to toxins has been seen as an environmental factor that may increase the risk of developing a neurodegenerative disease such as AD. Exposure to metals and biotoxins produced by bacteria, molds, and viruses may contribute to the cognitive decline and pathophysiology associated with AD. Toxins may contribute to the pathology of the disease through various mechanisms such as deposition of amyloid-beta (Aβ) plaques and tangles in the brain, induction of apoptosis, inflammation, or oxidative damage. Here, we will review how toxins affect brain physiology with a focus on mechanisms by which toxins may contribute to the development and progression of AD. A better understanding of these mechanisms may help contribute towards the development of an effective strategy to slow the progression of AD.

Antenatal Hypoxia Accelerates the Onset of Alzheimer's Disease Pathology in 5xFAD Mouse Model

Alzheimer’s disease (AD) is a chronic neurodegenerative disorder associated with cognitive impairment and later dementia among the elderly. Mounting evidence shows that adverse maternal environments during the fetal development increase the risk of diseases later in life including neurological disorders, and suggests an early origin in the development of AD-related dementia (ADRD) in utero. In the present study, we investigated the impact of antenatal hypoxia and fetal stress on the initiation of AD-related pathology in offspring of 5xFAD mice. We showed that fetal hypoxia significantly reduced brain and body weight in the fetal and the early postnatal period, which recovered in young adult mice. Using spontaneous Y-maze, novel object recognition (NOR), and open field (OF) tasks, we found that antenatal hypoxia exacerbated cognitive decline in offspring of 5xFAD compared with normoxia control. Of interest, fetal hypoxia did not alter intraneuronal soluble amyloid-β (Aβ) oligomer accumulation in the cortex and hippocampus in 5xFAD mouse offspring, indicating that antenatal hypoxia increased the vulnerability of the brain to synaptotoxic Aβ in the disease onset later in life. Consistent with the early occurrence of cognitive decline, we found synapse loss but not neuronal death in the cerebral cortex in 5xFAD but not wild-type (WT) offspring exposed to antenatal hypoxia. Furthermore, we also demonstrated that antenatal hypoxia significantly increased microglial number and activation, and reactive astrogliosis in the cerebral cortex in WT offspring. Moreover, antenatal hypoxia resulted in an exacerbated increase of microgliosis and astrogliosis in the early stage of AD in 5xFAD offspring. Together, our study reveals a causative link between fetal stress and the accelerated onset of AD-related pathology, and provides mechanistic insights into the developmental origin of aging-related neurodegenerative disorders.

Iron-responsive-like elements and neurodegenerative ferroptosis

A set of common-acting iron-responsive 5′untranslated region (5′UTR) motifs can fold into RNA stem loops that appear significant to the biology of cognitive declines of Parkinson's disease dementia (PDD), Lewy body dementia (LDD), and Alzheimer's disease (AD). Neurodegenerative diseases exhibit perturbations of iron homeostasis in defined brain subregions over characteristic time intervals of progression. While misfolding of Aβ from the amyloid-precursor-protein (APP), alpha-synuclein, prion protein (PrP) each cause neuropathic protein inclusions in the brain subregions, iron-responsive-like element (IRE-like) RNA stem–loops reside in their transcripts. APP and αsyn have a role in iron transport while gene duplications elevate the expression of their products to cause rare familial cases of AD and PDD. Of note, IRE-like sequences are responsive to excesses of brain iron in a potential feedback loop to accelerate neuronal ferroptosis and cognitive declines as well as amyloidosis. This pathogenic feedback is consistent with the translational control of the iron storage protein ferritin. We discuss how the IRE-like RNA motifs in the 5′UTRs of APP, alpha-synuclein and PrP mRNAs represent uniquely folded drug targets for therapies to prevent perturbed iron homeostasis that accelerates AD, PD, PD dementia (PDD) and Lewy body dementia, thus preventing cognitive deficits. Inhibition of alpha-synuclein translation is an option to block manganese toxicity associated with early childhood cognitive problems and manganism while Pb toxicity is epigenetically associated with attention deficit and later-stage AD. Pathologies of heavy metal toxicity centered on an embargo of iron export may be treated with activators of APP and ferritin and inhibitors of alpha-synuclein translation.

The potential role of nanoyttria in alleviating oxidative stress biomarkers: Implications for Alzheimer's disease therapy

Alzheimer's disease (AD) is a fatal neurodegenerative disease that requires immediate attention. Oxidative stress that leads to the generation of reactive oxygen species is a contributing factor to the disease progression by promoting synthesis and deposition of amyloid-β, the main hallmark protein in AD. It has been previously demonstrated that nanoyttria possesses antioxidant properties and can alleviate cellular oxidative injury in various toxicity and disease models. This review proposed that nanoyttria could be used for the treatment of AD. In this paper, the evidence on the antioxidant potential of nanoyttria is presented and its prospects on AD therapy are discussed.

Epigenetic Basis of Lead-Induced Neurological Disorders

Environmental lead (Pb) exposure is closely associated with pathogenesis of a range of neurological disorders, including Alzheimer’s disease (AD), Parkinson’s disease (PD), amyotrophic lateral sclerosis (ALS), attention deficit/hyperactivity disorder (ADHD), etc. Epigenetic machinery modulates neural development and activities, while faulty epigenetic regulation contributes to the diverse forms of CNS (central nervous system) abnormalities and diseases. As a potent epigenetic modifier, lead is thought to cause neurological disorders through modulating epigenetic mechanisms. Specifically, increasing evidence linked aberrant DNA methylations, histone modifications as well as ncRNAs (non-coding RNAs) with AD cases, among which circRNA (circular RNA) stands out as a new and promising field for association studies. In 23-year-old primates with developmental lead treatment, Zawia group discovered a variety of epigenetic changes relating to AD pathogenesis. This is a direct evidence implicating epigenetic basis in lead-induced AD animals with an entire lifespan. Additionally, some epigenetic molecules associated with AD etiology were also known to respond to chronic lead exposure in comparable disease models, indicating potentially interlaced mechanisms with respect to the studied neurotoxic and pathological events. Of note, epigenetic molecules acted via globally or selectively influencing the expression of disease-related genes. Compared to AD, the association of lead exposure with other neurological disorders were primarily supported by epidemiological survey, with fewer reports connecting epigenetic regulators with lead-induced pathogenesis. Some pharmaceuticals, such as HDAC (histone deacetylase) inhibitors and DNA methylation inhibitors, were developed to deal with CNS disease by targeting epigenetic components. Still, understandings are insufficient regarding the cause–consequence relations of epigenetic factors and neurological illness. Therefore, clear evidence should be provided in future investigations to address detailed roles of novel epigenetic factors in lead-induced neurological disorders, and efforts of developing specific epigenetic therapeutics should be appraised.

Docosahexaenoic Acid (DHA, C22:6, ω-3) Composition of Milk and Mammary Gland Tissues of Lactating Mother Rats Is Severely Affected by Lead (Pb) Exposure

Docosahexaenoic acid (DHA, C22:6, ω-3), an ω-3 polyunsaturated fatty acid (PUFA), is critical for brain growth, development, and cognitive ability. It is consumed by offspring via milk during lactation. However, the toxic heavy metal lead (Pb) readily passes into the mammary glands of mother animals and then to offspring through milk. Here, we investigated whether DHA composition of milk and mammary gland tissues is affected by Pb exposure. Mother rats were exposed to Pb via drinking water (0.1%). The fatty acid profile and levels of reduced glutathione (GSH), lipid peroxide (LPO), and pro-inflammatory TNF-α in milk and mammary tissues were measured. Levels of DHA and antioxidant GSH decreased (P < 0.05), while LPO and TNF-α levels increased (P < 0.05) both in milk and mammary tissues. Our results suggest that toxic Pb exposure can upset the level of milk DHA, which may affect brain growth and development, and hence cognitive ability in adulthood and later life.

Frailty syndrome, biomarkers and environmental factors - A pilot study

Frailty is an age-related syndrome expected to increase over the next decades. This syndrome has been identified to be the most common condition leading to disability, institutionalisation and death in the elderly. The aim of this pilot study is to investigate a possible link between frailty status, biomarkers and environmental exposures. A group of 71 older adults (≥65 years old) was engaged in this study. The study population was classified as 45.1% robust, 45.1% pre-frail and 9.8% frail. A significant higher prevalence of second-hand smokers was found in the pre-frail group when compared to robust. Furthermore, a higher prevalence of robust individuals was found among those consuming home-produced vegetables and water from well/springs. Significant differences were found between data collected in a lifetime exposure questionnaire (LTEQ) and the levels of genotoxicity endpoints and the mercury levels analysed regarding some exposure-related parameters, namely, smoking habits, intake of home-produced vegetables and the use of pesticides in agriculture. Understanding if the way we live(d) or worked can impact the way we age are important questions to be explored. Data obtained in this pilot study encourage further studies on this matter, exploring the role of exposures history and its impact on health.