Comparison of the action of 17β-estradiol and progestins with insulin-like growth factors-I/-II and transforming growth factor-β1 on the growth of normal adult human bone-forming cells

Endogenous growth factors may be involved in the prevention of bone loss by estrogen and progestins in postmenopausal women. The present study was performed to compare the action of estrogen/progestins on bone-derived cells with the effects of exogenously added purified growth factors. Human osteoblast-like (HOB) cells were incubated with 17β-estradiol (E₂), progesterone (P), dydrogesterone (DD), 20α-dihydroxydydrogesterone (DHD), with and without the growth factors, insulin-like growth factors-I/-II ( IGF-I -II) or transforming growth factor-β type 1 (TGF-β1) for 24 h under serum-free conditions. Cell growth and DNA synthesis were assessed by spectophotometrical analysis of total cell number and immunochemical detection of BrdU incorporation, respectively. Compared with the sex steroids, incubation of the cells with IGF-I or TGF-β1 resulted in at least a two-fold increase of total HOB cell numbers. No difference in stimulating HOB growth was observed between IGF-II and the female sex steroids E₂ and P. Combining IGF-I -II or TGF-β1 with either E₂ or P did not result in a significantly further increase in the human osteoblast-like cell growth. In conclusion, the bone anabolic growth factors, IGF-I and TGF-β1, may be more important regulators of osteoblast proliferation than the female sex steroids. An interaction of estrogen/gestagens with the growth factors IGF-I -II or TGF-β1 was not evident from the growth of human bone-forming cells in short-term cultures.