Infantile exposure to lead and late-age cognitive decline: relevance to AD

Sex-specific characterization and evaluation of the Alzheimer's disease genetic risk factor sorl1 in zebrafish during aging and in the adult brain following a 100 ppb embryonic lead exposure

Developmental lead (Pb) exposure is suggested in laboratory studies to be a trigger for neurodegenerative diseases such as Alzheimer's disease (AD). Sortilin-related receptor, L (DLR class) A repeats-containing (SORL1) is a recently identified AD genetic risk factor. SORL1 has limited characterization in vertebrate models in comparison to other AD genetic risk factors. To characterize SORL1 further, protein sequence homology between humans, mice and zebrafish was analyzed and showed conservation of functional repeats and domain orientation. Next, spatial expression of sorl1 in zebrafish larvae was completed and diffuse expression in neural tissue that was not restricted to the brain was observed. Influences of sex and age on quantitative expression of sorl1 in the brain of adult zebrafish were then assessed. Sex-specific alteration of sorl1 expression transpired during the aging process in females. The zebrafish was then utilized to investigate the impacts of a 100 ppb embryonic Pb exposure on sorl1 expression and other known AD genetic risk factors. Sex-specific quantitative gene expression analysis was completed with adult zebrafish brain to compare those developmentally exposed to Pb or a control treatment, but no significant difference in sorl1 expression or other AD genetic risk factors was observed. Overall, this study provided characterization of sorl1 with changes in brain expression during aging being female-specific. This finding is in agreement with females being more prone to the onset of AD, but analysis of additional AD genetic risk factors is needed to facilitate our understanding of the impact of a 100 ppb embryonic Pb exposure. Copyright © 2016 John Wiley & Sons, Ltd.

A role for amyloid precursor protein translation to restore iron homeostasis and ameliorate lead (Pb) neurotoxicity

Iron supplementation ameliorates the neurotoxicity of the environmental contaminant lead (Pb); however, the mechanism remains undefined. Iron is an essential nutrient but high levels are toxic due to the catalytic generation of destructive hydroxyl radicals. Using human neuroblastoma SH-SY5Y cells to model human neurons, we investigated the effect of Pb on proteins of iron homeostasis: the Alzheimer's amyloid precursor protein (APP), which stabilizes the iron exporter ferroportin 1; and, the heavy subunit of the iron-storage protein, ferritin (FTH). Lead (Pb(II) and Pb(IV) inhibited APP translation and raised cytosolic iron(II). Lead also increased iron regulatory protein-1 binding to the cognate 5'untranslated region-specific iron-responsive element (IRE) of APP and FTH mRNAs. Concurrent iron treatment rescued cells from Pb toxicity by specifically restoring APP synthesis, i.e. levels of the APP-related protein, APLP-2, were unchanged. Significantly, iron/IRE-independent over-expression of APP695  protected SH-SY5Y cells from Pb toxicity, demonstrating that APP plays a key role in maintaining safe levels of intracellular iron. Overall, our data support a model of neurotoxicity where Pb enhances iron regulatory protein/IRE-mediated repression of APP and FTH translation. We propose novel treatment options for Pb poisoning to include chelators and the use of small molecules to maintain APP and FTH translation. We propose the following cascade for Lead (Pb) toxicity to neurons; by targeting the interaction between Iron regulatory protein-1 and Iron-responsive elements, Pb caused translational repression of proteins that control intracellular iron homeostasis, including the Alzheimer's amyloid precursor protein (APP) that stabilizes the iron exporter ferroportin, and the ferroxidase heavy subunit of the iron-storage protein, ferritin. When unregulated, IRE-independent over-expression of APP695 protected SH-SY5Y neurons from Pb toxicity. There is a novel and key role for APP in maintaining safe levels of intracellular iron pertinent to lead toxicity.

Perinatal exposure to lead (Pb) promotes Tau phosphorylation in the rat brain in a GSK-3β and CDK5 dependent manner: Relevance to neurological disorders

Hyperphosphorylation of Tau is involved in the pathomechanism of neurological disorders such as Alzheimer's, Parkinson's diseases as well as Autism. Epidemiological data suggest the significance of early life exposure to lead (Pb) in etiology of disorders affecting brain function. However, the precise mechanisms by which Pb exerts neurotoxic effects are not fully elucidated. The purpose of this study was to evaluate the effect of perinatal exposure to low dose of Pb on the Tau pathology in the developing rat brain. Furthermore, the involvement of two major Tau-kinases: glycogen synthase kinase-3 beta (GSK-3β) and cyclin-dependent kinase 5 (CDK5) in Pb-induced Tau modification was evaluated. Pregnant female rats were divided into control and Pb-treated group. The control animals were maintained on drinking water while females from the Pb-treated group received 0.1% lead acetate (PbAc) in drinking water, starting from the first day of gestation until weaning of the offspring. During the feeding of pups, mothers from the Pb-treated group were still receiving PbAc. Pups of both groups were weaned at postnatal day 21 and then until postnatal day 28 received only drinking water. 28-day old pups were sacrificed and Tau mRNA and protein level as well as Tau phosphorylation were analyzed in forebrain cortex (FC), cerebellum (C) and hippocampus (H). Concomitantly, we examined the effect of Pb exposure on GSK-3β and CDK5 activation. Our data revealed that pre- and neonatal exposure to Pb (concentration of Pb in whole blood below 10μg/dL, considered safe for humans) caused significant increase in the phosphorylation of Tau at Ser396 and Ser199/202 with parallel rise in the level of total Tau protein in FC and C. Tau hyperphosphorylation in Pb-treated animals was accompanied by elevated activity of GSK-3β and CDK5. Western blot analysis revealed activation of GSK-3β in FC and C as well as CDK5 in C, via increased phosphorylation of Tyr-216 and calpain-dependent p25 formation, respectively. In conclusion, perinatal exposure to Pb up-regulates Tau protein level and induces Tau hyperphosphorylation in the rat brain cortex and cerebellum. We suggest that neurotoxic effect of Pb might be mediated, at least in part, by GSK-3β and CDK5-dependent Tau hyperphosphorylation, which may lead to the impairment of cytoskeleton stability and neuronal dysfunction.

Developmental lead exposure and lifespan alterations in epigenetic regulators and their correspondence to biomarkers of Alzheimer's disease

INTRODUCTION

Early life lead (Pb) exposure results in a latent increase in Alzheimer's disease (AD)-related proteins, and cognitive deficits late in life in both rodents and primates. This study was conducted to investigate if these late life changes were accompanied by epigenetic alterations.

METHODS

Western blot analysis and RT-PCR were used to measure Deoxyribonucleic acid methylation regulators (DNMT1, DNMT3a, MeCP2, MAT2A) and histone proteins (H3K9Ac, H3K4me2, H3K27me3).

RESULTS

Cerebral levels of DNMT1 and MeCP2 were significantly reduced in mice exposed to Pb early in life, whereas the expression of DNMT3a was not altered. Levels of MAT2a were increased in the Pb-exposed mice across the lifespan. H3K9Ac and H3K4me2, involved in gene activation, were decreased, whereas the repressive mark H3K27me3 was elevated.

DISCUSSION

Epigenetic modifiers are affected by the developmental exposure to Pb and may play a role in mediating the latent increases in AD-related proteins in the brain.

Lead neurotoxicity: exploring the potential impact of lead substitution in zinc-finger proteins on mental health

This critical review focuses on one possible link between the cellular biology of lead and its neurotoxic effects: the link between Pb²⁺substitution for Zn²⁺in zinc-finger proteins and mental illness in adulthood.

Long-term changes in brain cholinergic system and behavior in rats following gestational exposure to lead: protective effect of calcium supplement

Our earlier studies showed that lactational exposure to lead (Pb) caused irreversible neurochemical alterations in rats. The present study was carried out to examine whether gestational exposure to Pb can cause long-term changes in the brain cholinergic system and behavior of rats. The protective effect of calcium (Ca) supplementation against Pb toxicity was also examined. Pregnant rats were exposed to 0.2% Pb (Pb acetate in drinking water) from gestational day (GD) 6 to GD 21. The results showed decrease in body weight gain (GD 6-21) of dams, whereas no changes were observed in offspring body weight at different postnatal days following Pb exposure. Male offspring treated with Pb showed marginal alterations in developmental landmarks such as unfolding of pinnae, lower and upper incisor eruption, fur development, eye slit formation and eye opening on postnatal day (PND) 1, whereas significant alterations were found in the righting reflex (PNDs 4-7), slant board behavior (PNDs 8-10) and forelimb hang performance (PNDs 12-16). Biochemical analysis showed decrease in synaptosomal acetylcholinesterase (AChE) activity and an increase in acetylcholine (ACh) levels in the cortex, cerebellum and hippocampus on PND 14, PND 21, PND 28 and in the four-month age group of rats following Pb exposure. Significant deficits were also observed in total locomotor activity, exploratory behavior and open field behavior in selected age groups of Pb-exposed rats. These alterations were found to be maximal on PND 28, corresponding with the greater blood lead levels observed on PND 28. Addition of 0.02% Ca to Pb reversed the Pb-induced impairments in the cholinergic system as well as in behavioral parameters of rats. In conclusion, these data suggest that gestational exposure to Pb is able to induce long-term changes in neurological functions of offspring. Maternal Ca administration reversed these neurological effects of Pb later in life, suggesting a protective effect of calcium in Pb-exposed animals.

Lactational exposure of mice to low levels of non-dioxin-like polychlorinated biphenyls increases susceptibility to neuronal stress at a mature age

Lactational exposure to low levels of the sum of the six indicator polychlorinated biphenyls (Σ6 NDL-PCBs, 10ng/kg/day) is known to lead to persistent anxious behavior in young and adult offspring mice at postnatal days 40 and 160, respectively. At more advanced life stages, we evaluated the effects on the mouse brain of neuronal stress induced by the synaptotoxic amyloid-beta (Aβ) peptide. Perinatal exposure of lactating mice to Σ6 NDL-PCBs did not affect short-term memory performances of their offspring male mice aged 14 months as compared to control PCB-naive mice. However, following intracerebroventricular injection of soluble Aβ oligomers, significant impairments in long-term memory were detected in the mice that had been lactationally treated with Σ6 NDL-PCBs. In addition, immunoblot analyses of the synaptosomal fraction of hippocampal tissues from treated mice revealed a lower expression of the synaptic proteins synaptophysin and PSD-95. Though preliminary, our findings suggest for the first time that early exposure to low levels of NDL-PCBs induce late neuronal vulnerability to amyloid stress. Additional experiments are needed to confirm whether early environmental influences are involved in the etiology of brain aging and cognitive decline.

Lead decreases cell survival, proliferation, and neuronal differentiation of primary cultured adult neural precursor cells through activation of the JNK and p38 MAP kinases

Adult hippocampal neurogenesis is the process whereby adult neural precursor cells (aNPCs) in the subgranular zone (SGZ) of the dentate gyrus (DG) generate adult-born, functional neurons in the hippocampus. This process is modulated by various extracellular and intracellular stimuli, and the adult-born neurons have been implicated in hippocampus-dependent learning and memory. However, studies on how neurotoxic agents affect this process and the underlying mechanisms are limited. The goal of this study was to determine whether lead, a heavy metal, directly impairs critical processes in adult neurogenesis and to characterize the underlying signaling pathways using primary cultured SGZ-aNPCs isolated from adult mice. We report here that lead significantly increases apoptosis and inhibits proliferation in SGZ-aNPCs. In addition, lead significantly impairs spontaneous neuronal differentiation and maturation. Furthermore, we found that activation of the c-Jun NH2-terminal kinase (JNK) and p38 mitogen activated protein (MAP) kinase signaling pathways are important for lead cytotoxicity. Our data suggest that lead can directly act on adult neural stem cells and impair critical processes in adult hippocampal neurogenesis, which may contribute to its neurotoxicity and adverse effects on cognition in adults.

Prenatal lead exposure is associated with decreased cord blood DNA methylation of the glycoprotein VI gene involved in platelet activation and thrombus formation

Early-life lead exposure impairs neurodevelopment and later exposure affects the cardiovascular system. Lead has been associated with reduced global 5-methylcytosine DNA methylation, suggesting that lead toxicity acts through epigenetic mechanisms. The objective of this study is to clarify how early-life lead exposure alters DNA methylation of specific genes, using an epigenomic approach. We measured lead concentrations in urine [gestational week (GW), 8] and erythrocytes (GW 14), using inductively coupled plasma mass spectrometry, for 127 pregnant mothers recruited in the MINIMat food and supplementation cohort in rural Bangladesh. Cord blood DNA methylation was analyzed with the Infinium HumanMethylation450K BeadChip, and top sites were validated by methylation-sensitive high-resolution melt curve analysis. Maternal urinary lead concentrations (divided into quartiles) showed significant (after adjustment for false discovery rate) inverse associations with methylation at nine CpGs. Three of these sites were in the 5'-end, including the promoter, of glycoprotein IV (GP6); cg18355337 (q = 0.029, β = -0.30), cg25818583 (q = 0.041, β = -0.18), and cg23796967 (q = 0.047, β = -0.17). The methylation in another CpG site in GP6 was close to significant (cg05374025, q = 0.057, β = - 0.23). The erythrocyte lead concentrations (divided into quartiles) were also inversely associated with CpG methylation in GP6, although this was not statistically significant after false discovery rate adjustments. Eight CpG sites in GP6 constituted a differentially methylated region in relation to urinary lead (P = 0.005, q = 0.48) and erythrocyte lead (P = 0.007, q = 0.46). In conclusion, we found that moderate prenatal lead exposure appears to epigenetically affect GP6, a key component of platelet aggregation and thrombus formation, suggesting a novel link between early lead exposure and cardiovascular disease later in life.

Early-Life Toxic Insults and Onset of Sporadic Neurodegenerative Diseases-an Overview of Experimental Studies

The developmental origin of health and disease hypothesis states that adverse fetal and early childhood exposures can predispose to obesity, cardiovascular, and neurodegenerative diseases (NDDs) in adult life. Early exposure to environmental chemicals interferes with developmental programming and induces subclinical alterations that may hesitate in pathophysiology and behavioral deficits at a later life stage. The mechanisms by which perinatal insults lead to altered programming and to disease later in life are still undefined. The long latency between exposure and onset of disease, the difficulty of reconstructing early exposures, and the wealth of factors which the individual is exposed to during the life course make extremely difficult to prove the developmental origin of NDDs in clinical and epidemiological studies. An overview of animal studies assessing the long-term effects of perinatal exposure to different chemicals (heavy metals and pesticides) supports the link between exposure and hallmarks of neurodegeneration at the adult stage. Furthermore, models of maternal immune activation show that brain inflammation in early life may enhance adult vulnerability to environmental toxins, thus supporting the multiple hit hypothesis for NDDs' etiology. The study of prospective animal cohorts may help to unraveling the complex pathophysiology of sporadic NDDs. In vivo models could be a powerful tool to clarify the mechanisms through which different kinds of insults predispose to cell loss in the adult age, to establish a cause-effect relationship between "omic" signatures and disease/dysfunction later in life, and to identify peripheral biomarkers of exposure, effects, and susceptibility, for translation to prospective epidemiological studies.

Exposure to As-, Cd-, and Pb-mixture induces Aβ, amyloidogenic APP processing and cognitive impairments via oxidative stress-dependent neuroinflammation in young rats

Environmental pollutants act as risk factors for Alzheimer's disease (AD), mainly affecting the aging population. We investigated early manifestations of AD-like pathology by a mixture of arsenic (As), cadmium (Cd), and lead (Pb), reported to impair neurodevelopment. We treated rats with As+Cd+Pb at their concentrations detected in groundwater of India, ie, 0.38, 0.098, and 0.22 ppm or 10 times of each, respectively, from gestation-05 to postnatal day-180. We identified dose-dependent increase in amyloid-beta (Aβ) in frontal cortex and hippocampus as early as post-weaning. The effect was strongly significant during early-adulthood, reaching levels comparable to an Aβ-infused AD-like rat model. The metals activated the proamyloidogenic pathway, mediated by increase in amyloid precursor protein (APP), and subsequent beta secretase (BACE) and presenilin (PS)-mediated APP-processing. Investigating the mechanism of Aβ-induction revealed an augmentation in oxidative stress-dependent neuroinflammation that stimulated APP expression through interleukin-responsive-APP-mRNA 5'-untranslated region. We then examined the effects of individual metals and binary mixtures in comparison with the tertiary. Among individual metals, Pb triggered maximum induction of Aβ, whereas individual As or Cd had a relatively non-significant effect on Aβ despite enhanced APP, owing to reduced induction of BACE and PS. Interestingly, when combined the metals demonstrated synergism, with a major contribution by As. The synergistic effect was significant and consistent in tertiary mixture, resulting in the augmentation of Aβ. Eventually, increase in Aβ culminated in cognitive impairments in the young rats. Together, our data demonstrate that exposure to As+Cd+Pb induces premature manifestation of AD-like pathology that is synergistic, and oxidative stress and inflammation dependent.

Infantile postnatal exposure to lead (Pb) enhances tau expression in the cerebral cortex of aged mice: relevance to AD

The sporadic nature in over 90% of Alzheimer's disease (AD) cases, the differential susceptibility and course of illness, and latent onset of the disease suggest involvement of an environmental component in the etiology of late onset AD (LOAD). Recent reports from our lab have demonstrated that molecular alterations favor abundant tau phosphorylation and immunoreactivity in the frontal cortex of aged primates with infantile lead (Pb) exposure (Bihaqi and Zawia, 2013). Here we report that developmental Pb exposure results in elevation of protein and mRNA levels of tau in aged mice. Western blot analysis revealed aberrant site-specific tau hyperphosphorylation accompanied by elevated cyclin dependent kinase 5 (CDK5) levels in aged mice with prior Pb exposure. Mice with developmental Pb exposure also displayed altered protein ratio of p35/p25 with more Serine/Threonine phosphatase activity at old age. These changes favored increase in tau phosphorylation, thus providing evidence that neurodegenerative diseases may be in part due to environmental influences that occur during development.

Infantile postnatal exposure to lead (Pb) enhances tau expression in the cerebral cortex of aged mice: relevance to AD

The sporadic nature in over 90% of Alzheimer's disease (AD) cases, the differential susceptibility and course of illness, and latent onset of the disease suggest involvement of an environmental component in the etiology of late onset AD (LOAD). Recent reports from our lab have demonstrated that molecular alterations favor abundant tau phosphorylation and immunoreactivity in the frontal cortex of aged primates with infantile lead (Pb) exposure (Bihaqi and Zawia, 2013). Here we report that developmental Pb exposure results in elevation of protein and mRNA levels of tau in aged mice. Western blot analysis revealed aberrant site-specific tau hyperphosphorylation accompanied by elevated cyclin dependent kinase 5 (CDK5) levels in aged mice with prior Pb exposure. Mice with developmental Pb exposure also displayed altered protein ratio of p35/p25 with more Serine/Threonine phosphatase activity at old age. These changes favored increase in tau phosphorylation, thus providing evidence that neurodegenerative diseases may be in part due to environmental influences that occur during development.

Evolving from reactive to proactive medicine: community lead (Pb) and clinical disparities in pre- and post-Katrina New Orleans

In 2012 the U.S. Centers for Disease Control (CDC) set the blood Pb reference value at ≥5 µg/dL. Clinical analysis of children's blood Pb levels is the common way to diagnose environmental Pb contamination, and intervention ensues with education and household dust cleanup. Recent review indicates that education and household dust cleanup are not effective at reducing children's Pb exposure. Here we review mapping environmental Pb and children's blood Pb response as an alternative approach for proactive Pb dust intervention. New Orleans was divided into a high (≥100 mg/kg) and low (<100 mg/kg) soil Pb communities. The children's blood Pb prevalence ≥5 µg/dL for the high and low Pb domains were 58.5% and 24.8% respectively pre-Katrina vs. 29.6% and 7.5% post-Katrina. Elevated soil Pb (mg/kg) and consequently Pb loading (µg/square area) permeates the high Pb domain and outdoor locations lack Pb dust safe play areas. The U.S. EPA 400 mg/kg soil Pb standard poses an outside Pb dust loading burden >37 times larger than allowed on interior residential floor environments. Environmental Pb dust is decreasing because of the transfer of large quantities of low Pb soil into selected communities. City-scale soil Pb mapping is an alternative diagnostic tool that provides information for planning proactive medicine to prevent clinical Pb exposure in the first place.

Lead exposure disrupts global DNA methylation in human embryonic stem cells and alters their neuronal differentiation

Exposure to lead (Pb) during childhood can result in learning disabilities and behavioral problems. Although described in animal models, whether Pb exposure also alters neuronal differentiation in the developing brains of exposed children is unknown. Here, we investigated the effects of physiologically relevant concentrations of Pb (from 0.4 to 1.9μM) on the capacity of human embryonic stem cells (hESCs) to progress to a neuronal fate. We found that neither acute nor chronic exposure to Pb prevented hESCs from generating neural progenitor cells (NPCs). NPCs derived from hESCs chronically exposed to 1.9μM Pb throughout the neural differentiation process generated 2.5 times more TUJ1-positive neurons than those derived from control hESCs. Pb exposure of hESCs during the stage of neural rosette formation resulted in a significant decrease in the expression levels of the neural marker genes PAX6 and MSI1. Furthermore, the resulting NPCs differentiated into neurons with shorter neurites and less branching than control neurons, as assessed by Sholl analysis. DNA methylation studies of control, acutely treated hESCs and NPCs derived from chronically exposed hESCs using the Illumina HumanMethylation450 BeadChip demonstrated that Pb exposure induced changes in the methylation status of genes involved in neurogenetic signaling pathways. In summary, our study shows that exposure to Pb subtly alters the neuronal differentiation of exposed hESCs and that these changes could be partly mediated by modifications in the DNA methylation status of genes crucial to brain development.

Tolfenamic acid downregulates BACE1 and protects against lead-induced upregulation of Alzheimer's disease related biomarkers

Environmental exposure to lead (Pb) early in life results in a latent upregulation of genes and products associated with Alzheimer's disease (AD), particularly the plaque forming protein amyloid beta (Aβ). Furthermore, animals exposed to Pb as infants develop cognitive decline and memory impairments in old age. Studies from our lab demonstrated that tolfenamic acid lowers the levels of the amyloid β precursor protein (APP) and its aggregative cleavage product Aβ by inducing the degradation of the transcription factor specificity protein 1 (Sp1). These changes were accompanied by cognitive improvement in transgenic APP knock-in mice. In this study, we examined the effects of tolfenamic acid on beta site APP cleaving enzyme 1 (BACE1) which is responsible for Aβ production and tested its ability to reverse Pb-induced upregulation in the amyloidogenic pathway. Mice were administered tolfenamic acid for one month and BACE1 gene expression as well as its enzymatic activity were analyzed in the cerebral cortex. Tolfenamic acid was also tested for its ability to reverse changes in Sp1, APP and Aβ that were upregulated by Pb in vitro. Differentiated SH-SY5Y neuroblastoma cells were either left unexposed, or sequentially exposed to Pb followed by tolfenamic acid. Our results show that tolfenamic acid reduced BACE1 gene expression and enzyme activity in mice. In neuroblastoma cells, Pb upregulated Sp1, APP and Aβ, while tolfenamic acid lowered their expression. These results along with previous data from our lab provide evidence that tolfenamic acid, a drug that has been used for decades for migraine, represents a candidate which can reduce the pathology of AD and may mitigate the damage of environmental risk factors associated with this disease.

Enhanced taupathy and AD-like pathology in aged primate brains decades after infantile exposure to lead (Pb)

Late Onset Alzheimer Disease (LOAD) constitutes the majority of AD cases (∼90%). Amyloidosis and tau pathology, which are present in AD brains, appear to be sporadic in nature. We have previously shown that infantile lead (Pb) exposure is associated with a change in the expression and regulation of the amyloid precursor protein (APP) and its beta amyloid (Aβ) products in old age. Here we report that infantile Pb exposure elevated the mRNA and protein levels of tau as well as its transcriptional regulators namely specificity protein 1 and 3 (Sp1 and Sp3) in aged primates. These changes were also accompanied by an enhancement in site-specific tau phosphorylation as well as an increase in the mRNA and protein levels of cyclin dependent kinase 5 (cdk5). There was also a change in the protein ratio of p35/p25 with more Serine/Threonine phosphatase activity present in aged primates exposed to Pb as infants. These molecular alterations favored abundant tau phosphorylation and immunoreactivity in the frontal cortex of aged primates with prior Pb exposure. These findings provide more evidence that neurodegenerative diseases may be products of environmental influences that occur during the development.

Epigenetics: a novel therapeutic approach for the treatment of Alzheimer's disease

Alzheimer's disease (AD) is the most common type of dementia in the elderly. It is characterized by the deposition of two forms of aggregates within the brain, the amyloid β plaques and tau neurofibrillary tangles. Currently, no disease-modifying agent is approved for the treatment of AD. Approved pharmacotherapies target the peripheral symptoms but they do not prevent or slow down the progression of the disease. Although several disease-modifying immunotherapeutic agents are in clinical development, many have failed due to the lack of efficacy or serious adverse events. Epigenetic changes including DNA methylation and histone modifications are involved in learning and memory and have been recently highlighted for holding promise as potential targets for AD therapeutics. Dynamic and latent epigenetic alterations are incorporated in AD pathological pathways and present valuable reversible targets for AD and other neurological disorders. The approval of epigenetic drugs for cancer treatment has opened the door for the development of epigenetic drugs for other disorders including neurodegenerative diseases. In particular, methyl donors and histone deacetylase inhibitors are being investigated for possible therapeutic effects to rescue memory and cognitive decline found in such disorders. This review explores the area of epigenetics for potential AD interventions and presents the most recent findings in this field.