Effect of irradiation on intramembranous ossification

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Proliferation and changes in the phenotypic expressions of osteoblasts after X-irradiation were investigated. Osteoblast-like cells, MC3T3-E1, at actively proliferating, confluent, and post-proliferation stages were subjected to 10Gy-X-irradiation. One to 10Gy dose of Irradiation decreased the DNA content of cells. On the other hand, irradiation enhanced type I collagen accumulation and Ca content normalized to DNA contents. The expression of osteocalcin mRNA was downregulated by irradiation at all stages, but that of osteopontin and osteonectin mRNAs was unchanged. The time-dependent increase in alkaline phophatase activity per cell exceeded that of the control after irradiation at later stages. The localization of alkaline phophatase positive cells was concordant with that of calcification. In addition, the quality of the calcium deposits was found to be similar to the control by energy dispersive spectrometry and calcium to phosphorus ratio determination, even if they were not exactly the same morphologically. taken together, changes in phenotypic expressions were closely related to calcification enhancement.