Sulfation of tibolone metabolites by human postmenopausal liver and small intestinal sulfotransferases (SULTs)

Sulfation is a major pathway in humans for the biotransformation of steroid hormones and structurally related therapeutic agents. Tibolone is a synthetic steroid used for the treatment for climacteric symptoms and postmenopausal osteoporosis. Sulfation inactivates the hydroxylated metabolites, 3α-hydroxytibolone (3α-OH-tibolone) and 3β-hydroxytibolone (3β-OH-tibolone), and contributes to the regulation of tissue responses to tibolone. We detected SULT1A1, SULT1A3, SULT1E1 and SULT2A1 mRNA expression by RT-PCR in postmenopausal liver and small intestine. Liver pool ( n = 5) SULT activities measured with tibolone substrates reflected COS-1 expressed SULT2A1 and SULT1E1 activities. Liver SULT2A1 activity (1.8 ± 0.3 units/mg protein, n = 8, mean ± SEM), and activities with 3α-OH-tibolone (0.6 ± 0.1, n = 8) and 3β-OH-tibolone (0.9 ± 0.2, n = 8) were higher than SULT1E1 activities (