Selective toxic effects of tamoxifen on osteoclasts: comparison with the effects of oestrogen.
We investigated the actions of the trans- and cis-isomers of tamoxifen on the function of neonatal rat osteoclasts in vitro. Both compounds inhibited resorption pit formation by osteoclast-containing mixed bone cell cultures incubated for 24 h on cortical bone slices. Cell counts revealed that the inhibition was closely related to a cytotoxic effect, to which osteoclasts appeared particularly sensitive. Partial inhibition of resorption was seen in the presence of 2 microM trans-tamoxifen, whereas complete abolition of resorption and osteoclast viability occurred with 10 microM trans-tamoxifen; survival of mononuclear cells was unimpaired at either concentration. Cis-tamoxifen appeared to be slightly more toxic, with significant inhibitions of osteoclast viability and thus resorption pit formation at a concentration of 2 microM, and also of mononuclear cell numbers at 10 microM. Time-lapse video observations indicated that osteoclast death occurred rapidly (within 2-3 h) following exposure to 10 microM of either trans-tamoxifen or cis-tamoxifen. The morphological appearance of the dying cells was consistent with apoptosis. These results may help to explain the anti-resorptive action of tamoxifen seen in vivo in rats and humans. In contrast, oestradiol-17 beta consistently exerted no significant effects on resorption pit formation by rat osteoclasts over 24 h, even at grossly supraphysiological concentrations (up to 10 microM).
Arnett
T R
TR
Helen Hayes Hospital, New York State Department of Health, West Haverstraw 10993, USA.
Lindsay
R
R
Kilb
J M
JM
Moonga
B S
BS
Spowage
M
M
Dempster
D W
DW
D000818:Animals; D017209:Apoptosis; D001862:Bone Resorption; D002452:Cell Count; D018929:Cell Culture Techniques; D004958:Estradiol / Q000633:toxicity*; D004965:Estrogen Antagonists / Q000633:toxicity*; D018715:Microscopy, Video; D010010:Osteoclasts / Q000187:drug effects*; D051381:Rats; D013237:Stereoisomerism; D013629:Tamoxifen / Q000633:toxicity*
D004965:Estrogen Antagonists; D013629:Tamoxifen; D004958:Estradiol