We previously found that cigarette sidestream smoke particulate matter (CSSP) could activate estrogen receptor ER alpha to generate estrogen-like tumor-promoting effects. This study sought to identify the compounds responsible for CSSP estrogenicity. We first identified the component compounds using a combination of GC-MS and mass spectral matching. Based on computational estrogenicity prediction, nine potential estrogenic compounds were selected for second GC-MS identification and quantification. Their estrogenic activities at levels detected in the CSSP were verified using an estrogen-responsive reporter assay. Only catechol, a possible human carcinogen, showed significant estrogenic activity, but the activity was too low to justify CSSP estrogenicity. Even so, the mixture of these compounds reconstituted according to their contents in CSSP produced almost one third of the estrogenic activity of CSSP. These compounds acted synergistically to induce greater estrogenic effects at levels without apparent estrogenic activities. Nicotine accounted for approximately 16% of the total CSSP mass. The high abundance raises concerns about nicotine toxicity, including potentially working together with estrogenic chemicals to promote tumor growth. In summary, this study presents a tiered testing approach to identify estrogenic chemicals. Although no individual components are accountable for CSSP estrogenicity, the low-dose mixture effects of CSSP components warrant public health concerns.
