Prevention of osteocyte and osteoblast apoptosis by bisphosphonates and calcitonin
Lilian I. Plotkin, … , Stavros C. Manolagas, Teresita Bellido
Lilian I. Plotkin, … , Stavros C. Manolagas, Teresita Bellido
Published November 15, 1999
Citation Information: J Clin Invest. 1999;104(10):1363-1374. https://doi.org/10.1172/JCI6800.
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Article

Prevention of osteocyte and osteoblast apoptosis by bisphosphonates and calcitonin

Abstract

Glucocorticoid-induced osteoporosis may be due, in part, to increased apoptosis of osteocytes and osteoblasts, and bisphosphonates (BPs) are effective in the management of this condition. We have tested the hypothesis that BPs suppress apoptosis in these cell types. Etidronate, alendronate, pamidronate, olpadronate, or amino-olpadronate (IG9402, a bisphosphonate that lacks antiresorptive activity) at 10–9 to 10–6 M prevented apoptosis of murine osteocytic MLO-Y4 cells, whether it was induced by etoposide, TNF-α, or the synthetic glucocorticoid dexamethasone. BPs also inhibited apoptosis of primary murine osteoblastic cells isolated from calvaria. Similar antiapoptotic effects on MLO-Y4 and osteoblastic cells were seen with nanomolar concentrations of the peptide hormone calcitonin. The antiapoptotic effect of BPs and calcitonin was associated with a rapid increase in the phosphorylated fraction of extracellular signal regulated kinases (ERKs) and was blocked by specific inhibitors of ERK activation. Consistent with these in vitro results, alendronate abolished the increased prevalence of apoptosis in vertebral cancellous bone osteocytes and osteoblasts that follows prednisolone administration to mice. These results suggest that the therapeutic efficacy of BPs or calcitonin in diseases such as glucocorticoid-induced osteoporosis may be due, in part, to their ability to prevent osteocyte and osteoblast apoptosis.

Authors

Lilian I. Plotkin, Robert S. Weinstein, A. Michael Parfitt, Paula K. Roberson, Stavros C. Manolagas, Teresita Bellido

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Bisphosphonates inhibit glucocorticoid-induced apoptosis of MLO-Y4 osteo...
Bisphosphonates inhibit glucocorticoid-induced apoptosis of MLO-Y4 osteocytic cells. MLO-Y4 cells stably transduced with GFP were treated for 1 hour with 10–7 M concentration of the indicated bisphosphonates, followed by addition of 10–6 M dexamethasone. After 6 hours, cells were fixed. Numbers indicate the percentage of cells undergoing apoptosis as determined by evaluating the nuclear morphology of more than 500 cells in fields selected by systematic random in at least 3 different experiments (mean ± SD). Original magnification: ×400. Data were analyzed by 1-way ANOVA. *P < 0.05 versus control (Student Newman-Keuls method). The effect of bisphosphonates on the proportion of MLO-Y4 cells exhibiting chromatin condensation and/or nuclear fragmentation in the absence of dexamethasone was also analyzed using exact χ2 tests in 3 experiments with pamidronate, olpadronate, or IG9402, and in 6 experiments with alendronate. Bonferroni adjusted pairwise comparisons between untreated groups and groups treated with bisphosphonates yielded no significant differences when the experiments were analyzed individually; however, differences were significant when all experiments for given treatment condition were combined in a stratified χ2 analysis (see the text).