Potentiation of estradiol binding to human tissue proteins by unsaturated nonesterified fatty acids.

Nonesterified fatty acids (NEFAs) have been recently shown in the rat to be involved in steroid hormone expression, having effects on plasma transport and intracellular activity. This study examines the influence of saturated and unsaturated NEFAs on estradiol (E2) binding to cytosol from human uterus, breast, and melanoma. Binding was analyzed after separation with dextran-coated charcoal or hydroxylapatite and by sucrose density gradient centrifugation. Unsaturated NEFAs induced a 2- to 10-fold increase (P less than 0.001) in E2 binding to cytosol from normal, fibromatous, and neoplastic uteri, while saturated NEFAs had a slight inhibitory effect (P less than 0.05). Similar effects were seen with cytosol from metastatic melanoma lymph nodes and neoplastic breast tissues. By contrast, unsaturated NEFAs did not increase E2 binding to serum from these patients. Density gradient centrifugation indicated that the increased binding was associated with the proteins present in the 2- to 4 S region. Analysis of E2 metabolites in the presence of unsaturated NEFAs showed the formation of water-soluble derivatives. Seventy percent of these E2 derivatives were trichloracetic acid precipitable, suggesting a covalent link between the steroid and a protein. The existence of such water-soluble metabolites could be erroneously interpreted as a true binding to soluble cytoplasmic receptors.