We investigated the effect of endothelin-1 on bone formation in vitro and in vivo, and the effect of YM598, a novel selective endothelin ETA receptor antagonist, on endothelin-1-induced responses.
In in vitro studies, the effect of endothelin-1 on cellular responses was investigated by measuring intracellular Ca2+ levels, cell growth and alkaline phosphatase activity in the mouse osteoblast-like cell line MC3T3-E1. In in vivo studies, the effect of endothelin-1 on bone morphogenetic protein-2-induced ectopic bone formation in rats was investigated. A carrier containing bone morphogenetic protein-2 with or without endothelin-1 was subcutaneously implanted over the thorax, and the tissue (carrier) calcium content 3 weeks after implantation was evaluated. The inhibitory effect of YM598 on these responses was also investigated.
In the in vitro studies, endothelin-1 (10−13 to 10−6 M) significantly increased intracellular Ca2+ concentration, DNA synthesis and cell number in a concentration-dependent manner, while significantly decreasing alkaline phosphatase activity. YM598 (10−12 to 10−4 M) significantly inhibited these increases, as well as the decrease in alkaline phosphatase activity, in a concentration-dependent manner.
In the in vivo studies, the tissue calcium content 3 weeks after carrier implantation was significantly higher in the group that received both bone morphogenetic protein-2 and endothelin-1 than in the group receiving bone morphogenetic protein-2 alone. Chronically administered YM598 (1 mg/kg/day) marginally inhibited this endothelin-1-potentiated ectopic bone formation.
These results suggest that endothelin-1 may induce bone formation via endothelin ETA receptors in vitro and in vivo.