Measurement of copper(I) formation as a test for the stability of catecholestrogens and methoxyestrogens in solution

The biological effects of estrogens seem to be divided into three mechanisms of action: (1) the transcriptional action by the estrogen-estrogen receptor (ER) complex, (2) the non-genomic mechanism through ERs in cell membranes, and (3) the ER-independent mechanism. The latter mechanism has been attributed to be mediated by the basic chemical properties of estradiol (E2) metabolites, which seems to include their pro- and anti-oxidant properties. Therefore, in order to study the ER-independent actions of the E2 metabolites, their redox properties must be conserved. In this study, we have developed a test to measure the electron-donating properties of E2 and its metabolites based on the reduction of Cu(II) ion into Cu(I). Our results show that the catechol- and methoxy-metabolites of E2 lose their capability to reduce Cu(II) into Cu(I) after 3 months of storage at -20 degrees C. Thus, we propose this inexpensive and reliable test to verify the electron-donating properties of E2 metabolites in order to study their ER-independent biological effects in vitro.