Bone cell transfection in tissue culture using hydroxyapatite microparticles

Coprecipitates of calcium phosphate and DNA have been used in vitro for several decades for cell transfection. We evaluated the efficiency of calcium phosphate ceramics associated to plasmid DNA in the transfection of bone cells in vitro when they are grown in tissue culture. Newborn rat calvariae and tibia epiphyses were grown on an agar surface for a period of 48 h to 30 days. The hydroxyapatite (HA)-particles were loaded with a plasmid bearing a galactosidase reporter gene by incubation of the plasmid solution in PBS with the particles. One milligram of HA-particles was then placed in contact with the bone explants for 8 and 30 days. Histological sections were then performed and the galactosidase activity was revealed using an X-gal solution. At eight days, very few cells expressing the galactosidase activity were detected. By 30 days, however, the explants appeared uniformly stained blue. The staining of sections showed that the osteoblasts, chondroblasts, perichondroblasts, and perisoteal cells all expressed the lacZ gene while the number of cells stained in the control was negligible. The time dependence of the transfection suggests that transfection using ceramics is linked to the degradation of the ceramic by the cells. Furthermore, the cells are stained remote from the particles suggesting that the particles induce a coprecipitate of DNA in the explant.