a decreasing trendP = 0.06
As shown in Table 1 although the average methylation rates of the Fas promoter were not changed after nicotine treatment, among those CpG sites, nt +295, −2394, and −2441 showed significantly decreased frequency of single CpG methylation after nicotine treatment ( P < 0.05), and the methylation level on nt +456 also showed a decreasing trend ( P = 0.06).