Effect of tamoxifen and raloxifene on cholesterol transformation to bile acids in ovariectomized rats

Abstract

Tamoxifen is used as adjuvant therapy for prevention and treatment of metastatic breast cancer, whereas raloxoifene is approved for osteoporosis and is being investigated for breast cancer prevention. The most important aspects of these therapies are focused on their influence on bone and lipid metabolism. Several studies have reported the effect of tamoxifen and raloxifene on plasma lipids. Approximately 40% of total cholesterol removal occurs by conversion to bile acids, a process that takes place in the liver. The aim of the present study was to evaluate the influence of tamoxifen and raloxifene on the conversion of cholesterol to bile acids in estrogen-deficient in rats. The study included 40 female Wistar rats, divided into four groups: sham-operated controls, ovariectomized controls, ovariectomized rats treated with tamoxifen and ovariectomized rats treated with raloxifene. After 42 days of drug administration, bile was collected under anesthesia following administration of radioactive [4-14C]cholesterol and assayed for total 14C radioactivity; 14C-labeled bile acids were determined by the use of isotopic techniques after initial separation by thin-layer chromatography. Ovariectomy caused decreased excretion of bile and bile acids. Administration of tamoxifen and raloxifene significantly reduced the excretion of 14C-labeled bile and bile acids compared with ovariectomized controls. Tamoxifen therapy significantly reduced the excretion of taurocholic acid and glycochenodeoxycholic plus glycodeoxycholic acids, and excretion of cholic, litocholic and chenodeoxycholic plus deoxycholic acids was increased. Raloxifene significantly reduced the excretion of taurocholic, glycocholic and litocholic acids, taurochenodeoxycholic plus taurodeoxycholic acids, as well as chenodeoxycholic plus deoxycholic acids. The results of the present study suggest that tamoxifen and raloxifene did not reverse the changes in bile composition induced by estrogen deficiency. The decreased concentration of trihydroxy bile acids during therapy with raloxifene might decrease the risk of gallstone formation, although this hypothesis requires further investigation.