Hossain et al. after adjustments for age and coca chewing or after additional adjustment for urinary arsenic concentration (Table 2). Further adjustments for urinary boron, lithium, or cesium also had little influence on effect esti- mates (data not shown). When the analysis for LINE-1 included an interaction term between cadmium and dichotomized arsenic in urine (median split), no significant inter- action was detected (p = 0.37). Excluding the four smokers (which left n = 198) did not change the estimated association between uri- nary cadmium and LINE methylation (in fully adjusted model: β = –0.44; 95% CI: –0.85, –0.034). There was no association between ln- transformed urinary or blood cadmium con- centrations and p16 or MLH1 methylation (Table 2). The association of urinary cadmium with LINE-1 methylation showed statistically significant interactions in unadjusted models with the genotypes DNMT1 rs10854076 and rs2228611 (Table 3). The association between urinary cadmium and LINE-1 methylation was significantly stronger in carriers of the CC and CG genotypes of DNMT1 rs10854076 than in common GG carriers, and in carriers of the rare GG DNMT1 rs2228611 genotype than in GA and AA carriers. DNMT3B geno- types did not significantly modify the asso- ciation between urinary cadmium and LINE-1 methylation, although associations were stron- ger among women with the variant genotypes of both DNMT3B polymorphisms. Characteristics of the 90 women included in the analyses of DNMT gene expression [see Table 3. Effect modification of DNMT1 and DNMT3B genotypes on the association between ln-transformed cadmium concentrations in urine and for LINE1 methylation levels (n = 172 in all analyses). Unadjusted analysis Adjusted analysis βa (95% CI) p-Valueb βc (95% CI) p-Valued Genotype DNMT1 rs10854076 CC (n = 25) CG (n = 69) GG (n = 78) rs2228611 GG (n = 35) GA (n = 68) AA (n = 69) DNMT3B rs2424913 CC + CT (n = 15) TT (n = 155) rs2424932 AA + GA (n = 18) GG (n = 152) Genotype DNMT1 rs10854076 CC (n = 8) CG (n = 30) GG (n = 37) rs2228611 GG (n = 12) GA (n = 31) AA (n = 32) DNMT3B rs2424913 CC + CT (n = 7) TT (n = 67) rs2424932 AA + GA (n = 8) GG (n = 66) 882 –0.99 (–2.03, 0.059) –1.04 (–1.91, –0.17) –0.053 (–0.61, 0.51) –1.04 (–1.96, –0.12) –0.38 (–1.14, 0.38) –0.13 (–0.75, 0.48) –1.04 (–3.36, 1.27) –0.39 (–0.81, 0.024) –1.43 (–3.39, 0.53) –0.39 (–0.81, 0.037) 92.2 90.0 87.3 91.0 89.2 87.8 85.1 89.2 86.4 89.1 0.027 0.23 0.068 0.19 0.045 0.064 0.38 0.25 0.040 0.26 0.036 0.11 Supplemental Material, Table 1 (http://dx.doi. org/10.1289/ehp.1104600)] were similar to those of all participants (Table 1), except that the subset was slightly younger (median, 32 vs. 34 years; p = 0.019). DNMT1 expression in blood was much higher than DNMT3B expression (Table 4). DNMT3B _1733929 [Illumina HT-12 transcripts are named ILMN_(number)] expression was significantly higher in DNMT1 rs10854076 CC and CG carriers than in GG carriers, and in DNMT3B rs2424913 TT carriers than in rare C allele carriers (Table 4). Urinary cadmium concentration was inversely correlated with expression of one DNMT3B transcript (ILMN_1733929; rS = –0.28, p = 0.0086) but not with the other four transcripts (rS = –0.12 to 0.20; p = 0.062–0.78) or with DNMT1 expression (rS = –0.075, p = 0.48). Urinary cadmium also was not associated with DNMT1 expression when stratified by DNMT1 rs10854076 genotype (CC + CG carriers: β = –19; 95% CI: –88, 50; GG carriers: β = 6.0; 95% CI: –63, 75) or by DNMT1 rs2228611 genotype (GG + GA carriers: β = –17.6; 95% CI: –80, 45; AA allele carriers: β = –0.60; 95% CI: –75, 74). There were no correlations between DNMT1 or DNMT3B (ILMN_1733929) expression and LINE-1 methylation (rS = 0.050 and –0.16, respectively; p-values = 0.64 and 0.14). Discussion We found that low-level urinary cadmium in women, which represents life-long cad- mium exposure, was inversely associated with LINE-1 methylation, a marker of global DNA methylation. Urinary cadmium exposure was also inversely associated with the expression of DNMT3B, which is involved in de novo CpG methylation, but not with expression of DNMT1, which is primarily involved in maintaining CpG methylation patterns in the genome. The inverse association between uri- nary cadmium and LINE-1 methylation var- ied according to DNMT1 polymorphisms; the inverse association was stronger among carriers of the rare alleles of DNMT1 rs10854076 and rs2228611. The gene expression data from blood show associations between polymor- phisms DNMT1 rs10854076 and DNMT3B rs2424913 and DNMT3B gene expression. Most likely, diet was the main source of cadmium for the study subjects. Only a few of the women smoked cigarettes, another major source of cadmium exposure, and judging from their blood cadmium concentrations (0.18–0.52 µg/L), it can be assumed they did not smoke much. Furthermore, the study area has minimal industrial pollution and little vehicle traffic. The urine cadmium concentrations in our study population (median, 0.23 µg/L; range, 0.013–1.5 µg/L; or a median of 0.26 µg/g creatinine) were ovlume 120 | number 6 | June 2012 • Environmental Health Perspectives –1.09 (–2.02, –0.15) –0.96 (–1.68, –0.24) –0.052 (–0.58, 0.47) –1.19 (–1.99, –0.40) –0.38 (–1.07, 0.31) –0.10 (–0.67, 0.47) –1.22 (–3.20, 0.77) –0.45 (–0.84, –0.064) –1.36 (–3.12, 0.40) –0.46 (–0.85, –0.065) 654.9 640.3 629.6 653.6 639.6 591.4 583.0 640.0 559.0 640.3 0.14 0.18 0.83 0.68 0.041 0.050 0.39 0.28 0.18 0.18 0.67 0.38 aPercent LINE1 methylation (stratified for each genotype) = α1 + β1 cadmium. bp-Value interaction from term β3 in the model: percent LINE1 methylation = α1 + β1 genotype + β2 cadmium + β3 (genotype × cadmium). cPercent LINE1 methyla- tion (stratified for each genotype) = α1 + β1 cadmium + β2 age + β3 coca chewing. dp-Value interaction from term β3 in the model: percent LINE1 methylation = α1 + β1 genotype + β2 cadmium + β3 (genotype × cadmium) + β4 age + β5 coca chewing. Table 4. DNMT1 and DNMT3B gene expression according to DNMT1 and DNMT3B genotypes.a DNMT1 DNMT3B Gene expressionb p-Valuec p-Valued Gene expressionb p-Valuec p-Valued aDNMT1 is represented by one transcript (ILMN_1760201), whereas DNMT3B is represented by five transcripts (values from ILMN_1733929 presented here). DNMT genotypes were not associated with the expression of other DNMT3B transcripts (p > 0.1). bMedian, expressed as an arbitrary unit. cp-Value from model gene expression = α1 + β1 × genotype. dp-Value from model gene expression = α1 + β1 × genotype + β2 × age + β3 × coca chewing.