Research for effect of irradiation on growth plate chondrocytes

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The retardation of bone growth caused by irradiation suggested to be closely related to the impairment of endochondral ossification in growth plate, but its mechanism remains unclear. In this study the direct effect of X-ray irradiation cytodifferentiation of the growth plate chondrocytes was examined using a rabbit growth plate chondrocyte culture system.1.One to 10Gy doses of X-ray to the chondrocytes in premature stage inhibited proteoglycan (PG) synthesis, and induced degradation of PG.A 10Gy dose of X-ray suppressed type X collagen synthesis and content without changing type II collagen expression, and decreased alkaline phosphatase (ALPase) activity. Calcium deposition in the extracellular matrix of 10Gy dose irradiated culture was 40% of the control. 2.A 10Gy dose of X-ray to the mature chondrocytes did not change PG synthesis. PG degradation, however, was enhanced after irradiation. Although 1 to 10Gy doses of X-ray did not affect type X collagen synthesis, suppressed ALPase activity and calcium deposition. 3.In the hypertrophic stage, 1 to 10Gy doses of irradiation had marginal effect on PG,type X collagen, and ALPase activity. However, [^<45>Ca] incorporation into the cell layr and calcium deposition were decreased. 4.The sensitivity of the cytodifferentiation of the chondrocytes to irradiation became less as their differentiation advanced.In this study we clarified that 1 to 10Gy doses of irradiation inhibited matrix formation, terminal differentiation and induction of extracellular matrix calcification of growth plate chondrocytes. However, once the chondrocytes were irradiated, they could not express the further differentiated phenotypes and the inhibitory effects of irradiation were never restored. These findings indicate that the disturbance of endochondral ossification by irradiation originate in the direct inhibitory effects of irradiation on the matrix synthesis and matrix calcification in growth plate chondrocytes.