Effect of cadmium on the bone collagen metabolism of rat

Abstract

Effects of various metals on the chick bone lysyl oxidase activity have been studied. Cadmium and zinc at 5 × 10 −4 m in vitro inhibited the oxidase activity by approximately 62 and 69%, respectively. Iron, magnesium, and copper did not affect the lysyl oxidase activity, whereas manganese and mercury slightly enhanced the activity. When young rats were fed a diet containing 50 ppm cadmium for 6 weeks or 100 ppm for 8 weeks, the bone lysyl oxidase activity was inhibited by approximately 40 and 89%, respectively. The ratio of the amount of soluble bone collagen to that of the total collagen in cadmium-treated rats (50 ppm for 52 weeks) significantly increased compared with that of the control group. These results indicate an inhibitory effect of cadmium on the crosslinking of collagen. However, the lysyl oxidase activity remained unchanged when 50 ppm zinc was administered for 6 weeks to the rats. Cadmium accumulated in small amounts but significantly in the bones of cadmium-treated rats, particularly in the epiphyses rather than diaphyses. Cadmium was also found in the bone extracts prepared from epiphyses of the cadmium-treated rats. A remarkable decrease in the serum copper level was observed in the cadmium-treated rats but the copper contents of both bone and its extract did not change. Histological studies of the bone of cadmium-treated rats (100 ppm for 8 weeks) revealed thin cortices in the tibiae and unusual proliferation, irregular arrangements of resting cartilage cells, and shortening of cartilage cell columns in the epiphyseal plates of the bones.