Binding of oxygenated cholesterol metabolites to antiestrogen binding sites from chicken liver.

High affinity (KD 2-4 nM) binding sites (AEBS) for the triphenylethylene antiestrogen, tamoxifen, are found in chicken liver cytosol preparations. These sites exhibit affinity for triphenylethylene derivatives typical of those reported for AEBS in other systems. Although steroids and cholesterol do not compete for the sites, certain oxygenated cholesterol metabolites, particularly 7-ketocholesterol, do so. Hot ethanol extracts of chicken and human serum contain AEBS inhibitory activity. This activity is chromatographically heterogeneous, but a sterol-containing fraction has been isolated in which the 7-ketocholesterol concentration can account for the AEBS inhibitory activity of the fraction.