Important findings using the human placenta have revealed associations between maternal cigarette smoking during pregnancy and DNA methylation in a gene-specific and even global fashion. Suter and colleagues observed that maternal tobacco use is associated with aberrant placental epigenome-wide DNA methylation and gene expression (Suter et al., 2011). Their work also suggested that maternal smoking during pregnancy is associated with altered site-specific CpG methylation which further correlates with important changes in gene expression in pathways crucial for ensuring proper growth and development. In a separate study, Suter and colleagues also noted that maternal tobacco smoking may modify placental CYP1A1 expression by altering methylation at CpG sites proximal to the 5′-xenobiotic response element transcription factor binding site (Suter et al., 2010). CYP1A1 is involved in Phase I of the metabolism of carcinogenic compounds such as polycyclic aromatic hydrocarbons (PAH), which are present in cigarette smoke. Specifically, CYP1A1 converts such compounds in a way that can eventually be excreted in Phase II metabolism, a process modulated in part by other genes (Suter, et al., 2010). Suter and colleagues found that methylation at
