Alzheimer’s Disease and Environmental Exposure to Lead: The Epidemiologic Evidence and Potential Role of Epigenetics

University of Michigan, School of Public Health, Department of Environmental Health Sciences, MI, USA.
Current Alzheimer research (Impact Factor: 3.89). 01/2012; 9(5):563-73. DOI: 10.2174/156720512800617991
Source: PubMed


Several lines of evidence indicate that the etiology of late-onset Alzheimer's disease (LOAD) is complex, with significant contributions from both genes and environmental factors. Recent research suggests the importance of epigenetic mechanisms in defining the relationship between environmental exposures and LOAD. In epidemiologic studies of adults, cumulative lifetime lead (Pb) exposure has been associated with accelerated declines in cognition. In addition, research in animal models suggests a causal association between Pb exposure during early life, epigenetics, and LOAD. There are multiple challenges to human epidemiologic research evaluating the relationship between epigenetics, LOAD, and Pb exposure. Epidemiologic studies are not well-suited to accommodate the long latency period between exposures during early life and onset of Alzheimer's disease. There is also a lack of validated circulating epigenetics biomarkers and retrospective biomarkers of Pb exposure. Members of our research group have shown bone Pb is an accurate measurement of historical Pb exposure in adults, offering an avenue for future epidemiologic studies. However, this would not address the risk of LOAD attributable to early-life Pb exposures. Future studies that use a cohort design to measure both Pb exposure and validated epigenetic biomarkers of LOAD will be useful to clarify this important relationship.

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    • "Next-generation sequencing will be the next step to identify additional variants with less frequency (rare variants) but large effects [236]. Besides DNA variation, there is accumulating evidence of epigenetic effect contributing to AD, which implies the complex interplay between genetic and environmental factors [237] [238] [239]. However, most epigenetic studies so far in AD are limited by the sample size and the genome coverage. "
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    • "of transposable element and repeat sequences (Hou et al. 2014). To circle back to early life for a moment, environmental lead exposure in early life has been suggested as a contributing factor to rates of epigenetic drift in later life, and to risk of Alzheimer's disease caused by ensuing destabilization of cellular regulation (Bakulski et al. 2012). This work is correlational: it takes a measure of exposure in the past or in the present through whatever proxy is available, and it measures some aspect of methylation in the genome, and it looks for a relation between the two. "
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    ABSTRACT: In the space of little more than a decade, ideas of the human genome have shifted significantly, with the emergence of the notion that the genome of an individual changes with development, age, disease, environmental inputs, and time. This paper examines the emergence of the genome with a life span, one that experiences drift, instability, and mutability, and a host of other temporal changes. We argue that developments in chromatin biology have provided the basis for this genomic embodiment of experience and exposure. We analyze how time has come to matter for the genome through chromatin, providing analysis of examples in which the human life course is being explored as a set of material changes to chromatin. A genome with a life span aligns the molecular and the experiential in new ways, shifting ideas of life stages, their interrelation, and the temporality of health and disease.
    New Genetics and Society 04/2015; 34(2). DOI:10.1080/14636778.2015.1034851 · 0.86 Impact Factor
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    • "Substantial evidence had demonstrated that Pb exposure is associated with both peripheral and central neurological effects including memory deficits and Alzheimer's disease-like pathology (Gu et al., 2011; Bakulski et al., 2012; Chander et al., 2014). Many researches also suggested that increase of immunoactivity for interleukin-1beta (IL-1b), tumor necrosis factor-alpha (TNF-a), beta-amyloid (Ab) and tau proteins may contribute to the progression of memory decline in animals with maternal Pb exposure (Bakulski et al., 2012; Zhang et al., 2012; Li et al., 2014). The endoplasmic reticulum (ER) is an organelle present in all eukaryotic cells, which is also a multifunctional signaling organelle that controls a wide range of cellular processes (Hu et al., 2006; Liu et al., 2013b). "
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    ABSTRACT: Proanthocyanidins (PCs), a class of naturally occurring flavonoids, had been reported to possess a variety of biological activities, including anti-oxidant, anti-tumor and anti-inflammatory. In this study, we examined the protective effect of PCs against lead-induced inflammatory response in the rat brain and explored the potential mechanism of its action. The results showed that PCs administration significantly improved behavioral performance of lead-exposed rats. One of the potential mechanisms was that PCs decreased reactive oxygen species production and increased the total antioxidant capacity in the brains of lead-exposed rats. Furthermore, the results also showed that PCs significantly decreased the levels of tumor necrosis factor-α, interleukin 1β and cyclooxygenase-2 in the brains of lead-exposed rats. Moreover, PCs significantly decreased the levels of beta amyloid and phosphorylated tau in the brains of lead-treated rats, which in turn inhibited endoplasmic reticulum(ER) stress. PCs also decreased the phosphorylation of protein kinase RNA-like ER kinase, eukaryotic translation initiation factor-2, inositol-requiring protein-1, c-Jun N-terminal kinase, p38 and inhibited nuclear factor-κB nuclear translocation in the brains of lead-exposed rats. In conclusion, these results suggested that PCs could improve cognitive impairments by inhibiting brain oxidative stress and inflammatory response.
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