Evaluation of estrogenic activity of phthalate esters by gene expression profiling using a focused microarray...

Phthalates are used industrially as plasticizers and are known to contaminate natural environments, mostly as di-ester or mono-ester complexes. Because they are structurally similar to natural estrogens, they could act as endocrine disruptors. Here, we used a DNA microarray containing estrogen responsive genes (EstrArray) to examine gene expression profiles in MCF-7 cells treated with 10 microM butylbenzyl phthalate (BBP), dibutyl phthalate (DBP), diethyl phthalate (DEP), and diisopropyl phthalate (DIP) along with the natural estrogen 17beta-estradiol ([E(2)], 10 nM). The profiles for phthalate esters and E(2) were examined by correlation analysis using correlation coefficients (r-values) and cluster analysis. We found that BBP showed the highest correlation with E(2) (r = 0.85), and DEP and DIP showed moderate r-values (r = 0.52 and r = 0.49, respectively). Dibutyl phthalate exhibited the lowest (but still significant) correlation with E(2) (r = 0.36). Furthermore, among the pairs of chemicals, DEP-DIP and DIP-DBP showed very high correlations (r = 0.90 and r = 0.80, respectively), and the other pairs showed moderate relationships, which reflected how structurally close they are to each other. The analysis of six functional groups of genes (enzymes, signaling, proliferation, transcription, transport, and others) indicated that the genes belonging to the enzyme, transcription, and other functional groups showed common responses to phthalate esters and E(2). Although the effect of BBP was similar to that of E(2), the other phthalate esters showed different types of effects. These results indicate that the structure of estrogenic chemicals is strongly related to their estrogenic activity and can be evaluated by appropriate grouping of the responsive genes by focused microarray analysis.