High radiosensitivity of the mineralization capacity of adult murine bone marrow in vitro to continuous alpha-irradiation compared to acute X-irradiation

Effects of in vitro alpha-particle irradiation on osteogenic bone marrow cultures

Murine bone marrow contains osteogenic precursor cells that undergo differentiation during in vitro cultivation. In vitro these cells are potential target cells for alpha-irradiation-induced bone tumour formation. Under defined tissue culture conditions these differentiating cells were directly exposed to alpha-particle irradiation from the radon daughter 210Po. Po deposits in soft tissue and it was shown to be associated with marrow cells and with the extracellular marrow tissue formed in vitro. These differentiating marrow cultures showed high sensitivity to alpha-irradiation. Cell death was observed at 210Po concentrations in tissue culture medium (TCM) > 7 Bq 210Po/ml. At lower concentrations (between 1 and 5 Bq 210Po per ml TCM) proliferation was enhanced as measured by uptake of 3H-thymidine, also differentiation was stimulated as measured by alkaline phosphatase activity and incorporation of 3H-proline in newly synthesized collagen. At several times of culture, the association of 210Po with the extracellular matrix and cells was measured. These retention data enabled us to calculate the daily alpha-particle fluence. At 1 Bq 210Po present per ml tissue culture, a daily alpha-particle fluence as low as 3-6 per 1000 cells seemed very efficient in changing the expression of osteogenic differentiation of marrow cells.

Osteosarcomagenic doses of radium (224Ra) and infectious endogenous retroviruses enhance proliferation and osteogenic differentiation of skeletal tissue differentiating in vitro

Cartilage tissue from embryonic mice which undergoes osteogenic differentiation during in vitro cultivation was used to study the effect of osteosarcomagenic doses of alpha-irradiation and bone-tumor-inducing retroviruses on proliferation and phenotypic differentiation of skeletal cells in a defined tissue culture model. Irradiated mandibular condyles showed dose-dependent enhancement of cell proliferation at day 7 of the culture and increased osteogenic differentiation at day 14. Maximal effects were found with 7.4 Bq/ml of 224Ra-labeled medium. Doses of 740 and 7400 Bq/ml of 224Ra-labeled medium induced increasing cell death. Retrovirus infection enhanced osteogenic differentiation and extended the viability of irradiated cells. After transplantation none of the treated tissues developed tumors in syngeneic mice.