[Congenital angular deformity of the tibia in chick embryo induced by ethane-1-hydroxy-1, 1-diphosphonate (EHDP)]

Congenital angular deformity of the tibia (CADT) is one of the classic inborn errors. The treatment of the disease is very difficult because of insufficient clinical and experimental data and lack of complete experimental model of the disease. The present study is designed to establish a new experimental model of CADT. In vivo experiment: Only one injection of ethane-1-hydroxy-1,1-diphosphonate (EHDP) (4 X 10(-2)-4 X 10(-1) mumol/g egg wt.) was given into the yolk sac of fertile white leghorn egg at 8 days of incubation. The skeletal deformities of the chick embryos were examined during the period of EHDP-administration until hatching. Furthermore, the effect of EHDP was compared with that of its analogs (dichloromethylene diphosphonate: Cl2MDP and inorganic pyrophosphate: PPi) in a similar manner. In vitro experiment: Tibiae from 9-day-old chick embryos were cultured at 37 degrees C for 6 days by roller-tube method in the medium containing EHDP, Cl2MDP or PPi at concentrations of 4-400 microM to measure dry weight and calcium content of the tibiae. The results are summarized as follows. Angular deformity of the tibia in chick embryo was produced in vivo specifically by EHDP-administration compared to its analogs. There existed the critical stage of bone development and the critical dose of EHDP-administration to induce angular deformity of the tibia. The incidence and the severity of the tibial bowing depended on the dose of EHDP-administration. The thinning of periosteal bone collar and retardation of primary bone marrow formation were observed in EHDP-administered tibia. According to 3H-thymidine autoradiographic study, EHDP inhibited DNA synthesis of osteoblast by about 58% after 2 days of administration. The DNA synthesis of chondrocyte was also inhibited by about 20% after 2 days of EHDP-administration. EHDP had a more inhibitory effect on calcification of chick embryonic tibiae than Cl2MDP and PPi at concentration of 40 microM without influencing the dry weight of tibiae in vitro. This new experimental model of CADT offers a significant possibility to elucidate the etiology of this disease.