EFFECTS OF X-IRRADIATION ON METABOLISM OF PROTEOGLYCANS

The effects of X irradiation on matrix formation by growth-plate and a rticular chondrocytes, as reflected by metabolism of proteoglycans and type II collagen, were examined in a rabbit chondrocyte culture syste m, Irradiation with 1 to 10 Gy selectively inhibited synthesis of prot eoglycans (incorporation of [S-35]sulfate) depending on the stage of d ifferentiation of the irradiated cells; however, synthesis of type II collagen was not affected, Irradiation of an immature culture, in whic h chondrocytes had just reached confluence, suppressed incorporation o f [S-35]sulfate into the glycosaminoglycan, 10 Gy inducing approximate ly 45-50% inhibition. In contrast, the irradiation of mature cultures, in which chondrocytes had already secreted extensive cartilage matrix , did not affect the rate of synthesis of proteoglycans (incorporation of [S-35]sulfate). We also found that here irradiation stimulated the degradation of proteoglycans, but with the effect differing in growth -plate chondrocytes and articular chondrocytes. In growth-plate chondr ocytes, cleavage from a site close to the G1 globular domain induced b y 10 Gy enhanced the release of S-35-labeled proteoglycans into the me dium, whereas in articular chondrocytes, irradiation had only marginal effects on the release of S-35-labeled proteoglycans. Our results sho w that irradiation with 1-10 Gy impaired proteoglycan metabolism in ca rtilage, with differing effects according to the stage of cell differe ntiation and the type of chondrocyte. (C) 1996 by Radiation Research S ociety