Calcitonin increases the concentration of insulin-like growth factors in serum-free cultures of human osteoblast-line cells

The current studies were intended to determine whether the anabolic effects of calcitonin (CT) on human osteoblast-line cells were (1) unique to osteo sarcoma cells or also evident in osteoblast-line cells derived from normal human bone; and/or (2) associated with effects on several insulin-like grow th factor (IGF) system components. Preliminary studies identified several o steoblastic cell lines, derived from normal human bone, which showed calcit onin-dependent increases in cell proliferation, alkaline phosphatase activi ty, and/or Ca-45 uptake (P < 0.05-P < 0.001). Two of these cell lines-(huma n vertebrae) HBV-155 and HBV-163-were included with the human osteosarcoma cell line, SaOS-2, in most of our subsequent studies of calcitonin effects on selected IGF system components: IGF-II, IGF-I, and IGF binding proteins -3, -4, and -5, The results of those studies revealed that a 48 hour exposu re to salmon CT caused a dose-dependent (0.03-3 mU/ml) increase in the net extracellular level of IGF-II (r = 0.96, P < 0.01) in serum-free cultures o f SaOS-2 cells, with a maximal 60% increase at the highest tested dose (P < 0.02). Similar effects were seen with HBV-163 cells (r = 0.90, P < 0.01) a nd HBV-155 cells (r = 0.55, P < 0.02). The effect of calcitonin on the extr acellular level of IGF-II was biphasic with respect to time: it decreased a t 6 hours (P < 0.005 and P < 0.001, for SaOS-2 cells and HBV-163 cells, res pectively) and increased at 2 24 hours (P < 0.02 and P < 0.05). These calci tonin-dependent increases in the extracellular level of IGF-I were associat ed with parallel increases in IGF-I (P < 0.005 for SaOS-2 cells and P < 0.0 3 for HBV-163 cells), but calcitonin did not affect the extracellular level of transforming growth. factor (TGF)-beta. The calcitonin-dependent change s in IGF-II were not associated with changes in the extracellular levels of IGF binding proteins -3, -4, or -5. Finally, our studies showed that two o ther members of the CT superfamily-CT gene-related peptide and amylin-did n ot mimic the effect of CT to increase the extracellular level of IGF-IT. To gether, these data demonstrate that human osteoblast-line cells derived fro m normal human bone can respond to CT, and that those responses can include CT dose- and time-dependent increases in the extracellular levels of IGF-I and IGF-II.