showed malignant transformation associated with depressed SAM levels and global DNA hypomethylation (Zhao et al., 1997). An in vitro study on mammalian cells directly demonstrated that arsenic induces DNA hypomethylation that was associated with chromosomal instability (Sciandrello et al., 2004). In addition, arsenite has been shown to increase both the levels of the repressive histone mark dimethylated

H3K9 and the activating mark trimethylated H3K4, and decreases the repressive mark trimethylated H3K27 in human lung carcinoma A549 cells (Zhou et al., 2008). An unexpected finding was recently reported in vivo, as a global dose-dependent hypermethylation of blood DNA was observed in learn more Bangladeshi adults with chronic arsenic exposure (Pilsner et al., 2007). This effect was modified by folate, suggesting that arsenic-induced increases Lumacaftor nmr in DNA methylation were dependent from methyl availability (Pilsner et al., 2007). The same group, however, reported that lower blood DNA methylation was a risk factor for arsenic-induced skin lesions in a related Bangladeshi population (Pilsner et al., 2009). In a human study from India, significant DNA hypermethylation of p53 and p16 promoter regions was observed in blood DNA of subjects exposed to toxic level of arsenic compared to controls

(Chanda et al., 2006). In this study, hypermethylation showed a dose–response relationship with arsenic measured in drinking water. Environmental factors can alter gene expression by epigenetic mechanisms and lead to late-onset neurodegenerative diseases. Exposure to environmental neurotoxic metals, pesticides and other chemicals is increasingly recognized as a key risk factor in the pathogenesis of chronic neurodegenerative disorders such as Parkinson’s and Alzheimer’s

diseases (Kanthasamy et al., 2012, Kwok, 2010 and Migliore and Coppede, 2009). Kanthasamy et al. (2012) described the role of acetylation of histones and non-histone proteins in neurotoxicant-induced neurodegenerative processes in the nigral dopaminergic neuronal system. Paraquat, a widely used herbicide, and the organochlorine insecticide Dieldrin, are Alanine-glyoxylate transaminase among the environmental chemicals potentially linked with Parkinson’s disease. Histone acetylation may represent the key epigenetic change in dopaminergic neuronal cells during neurotoxic insults. Experimental evidence comes from the research conducted by Song et al. on N27 dopaminergic cells. Exposure to Paraquat induced histone H3 acetylation in a time-dependent manner and decreased total histone deacetylase (HDAC) activity (Song et al., 2010 and Song et al., 2011). In mesencephalic dopaminergic neuronal cells, Dieldrin lead to a time-dependent increase in the acetylation of core histones H3 and H4 by a Dieldrin-induced proteasomal dysfunction, resulting in accumulation of a key histone acetyltransferase (HAT).