Cadmium, Smoking, and Human Blood DNA Methylation Profiles in Adults from the Strong Heart Study

B ACKGROUND : The epigenetic e ff ects of individual environmental toxicants in tobacco remain largely unexplored. Cadmium (Cd) has been associated with smoking -related health e ff ects, and its concentration in tobacco smoke is higher in comparison with other metals. O BJECTIVES : We studied the association of Cd and smoking exposures with human blood DNA methylation (DNAm) pro fi les. We also evaluated the implication of fi ndings to relevant methylation pathways and the potential contribution of Cd exposure from smoking to explain the association between smoking and site -speci fi c DNAm. M ETHODS : We conducted an epigenome-wide association study of urine Cd and self -reported smoking (current and former vs. never, and cumulative smoking dose) with blood DNAm in 790,026 CpGs (methylation sites) measured with the Illumina In fi nium Human MethylationEPIC (Illumina Inc.) platform in 2,325 adults 45 - 74 years of age who participated in the Strong Heart Study in 1989 - 1991. In a mediation analysis, we estimated the amount of change in DNAm associated with smoking that can be independently attributed to increases in urine Cd concentrations from smoking. We also conducted enrichment analyses and in silico protein - protein interaction networks to explore the biological relevance of the fi ndings. R ESULTS : At a false discovery rate (FDR)-corrected level of 0.05, we found 6 di ff erentially methylated positions (DMPs) for Cd; 288 and 17, respec- tively, for current and former smoking status; and 77 for cigarette pack -years. Enrichment analyses of these DMPs displayed enrichment of 58 and 6 Gene Ontology and Kyoto Encyclopedia of Genes and Genomes gene sets, respectively, including biological pathways for cancer and cardiovascular disease. In in silico protein -to -protein networks, we observed key proteins in DNAm pathways directly and indirectly connected to Cd- and smoking- DMPs. Among DMPs that were signi fi cant for both Cd and current smoking (annotated to PRSS23, AHRR, F2RL3, RARA, and 2q37.1), we found statistically signi fi cant contributions of Cd to smoking -related DNAm. C ONCLUSIONS : Beyond replicating well-known smoking epigenetic signatures, we found novel DMPs related to smoking. Moreover, increases in smoking -related Cd exposure were associated with di ff erential DNAm. Our integrative analysis supports a biological link for Cd and smoking -associated health e ff ects, including the possibility that Cd is partly responsible for smoking toxicity through epigenetic changes. https://doi.org/10.1289/EHP6345