Effects of X-Ray Irradiation on Differentiation and Calcification of Growth Plate Chondrocytes

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Irradiation often causes retardation of skeletal growth, and this may be explained by injury of growth-plate cartilage. However there are no appropriate models in vitro. In the present study, we investigated the effects of X-ray irradiation on proliferation, proteoglycan (PG) synthesis, alkaline phosphatase activity and calcium content, and effects of insulin like growth factor-I (IGF-I) or parathyroid hormone (PTH) on recovery from irradiation damage of growth-plate chondrocytes. Chondrocytes were isolated from growth-plate of the ribs of 4-week old rabbits and cultivated as a packed mass in a 15-ml plastic centrifuge tube.1) The cells were exposed to single doses of X-ray between 0.3 and 10Gy on day 7 or day 14. Irradiation at 3-10Gy on day 7 caused significant decreases in DNA synthesis, alkaline phosphatase activity and Ca deposition without inhibition of PG shnthesis. Irradiation at 10Gy on day 14 caused 30% decreases in alkaline phosphatase and calcification, although it had little effect on DNA and PG synthesis.2) The cells were irradiated at 10Gy of a single dose on day 7. The addition of IGF-I from day 14 stimulated proliferation of chondrocytes and PTH addition from day 14 stimulated alkaline phosphatase activity. These results suggest that chondrocytes in pelleted cultures are a useful model for studies on the mechanisms involved in radiation damage of chondrocytes and their recovery from the damage.