Estrone sulfate is a major source of local estrogen formation in human bone.

Estrone sulfate (E1S) is the most abundant estrogen in the circulation of adults. The present study was undertaken to assess estrone (E1) and estradiol formation from E1S in freshly resected bone [bone fragments (BFs)] and osteoblast-like cells (hOB) cultured from BFs. Furthermore, we compared estrogen formation from E1S in rat and human osteosarcoma (OS) cell lines and that of estrogen formation from E1S with that of aromatization of androstenedione and testosterone in BFs and those from E1S and androstenedione in hOB cells.

Human osteoblast-like cells express predominantly steroid 5alpha-reductase type 1.

In previous studies we established that human bone and human osteoblast-like cells (hOB cells) cultured from bone express 5alpha-reductase (5alpha-R) activity, as demonstrated by the conversion of testosterone and androstenedione to their corresponding 5alpha-reduced metabolites, 5alpha-dihydrotestosterone (DHT) and 5alpha-androstanedione. Two 5alpha-R isozymes (types 1 and 2) have been identified in various tissues. As their nature in bone is unknown, we investigated which isozymes were expressed in first passage hOB cells cultured from bone specimens obtained from six donors (five women and one man).