Influence of tetracycline on the calcification of epiphyseal rat cartilage. Transmission and scanning electron-microscopic studies

Abstract

Tetracyclines are known to interfere with bone calcification. We therefore studied their effects on matrix vesicle production and initial calcification of cartilage. 15-day-old rats were injected intraperitoneally with oxytetracycline 100 mg/kg, 6 consecutive injections every 12 h. Epiphyseal plates were examined by scanning and transmission electron microscopy and compared to light microscopy findings. It was found that high doses of tetracyclines cause degeneration of the chondrocytes in the proliferating and hypertrophic zones. Chondrocytes had short processes with only few matrix vesicles covering their surface. In the chondrocytic lacunae of the longitudinal septa of hypertrophic and calcifying cartilage there were fewer matrix vesicles as compared to controls, and their ability to aggregate and form mineralized calcospherites was impaired. This was further proven when bones were immersed in 7% NaOCl or ashed, as minerals containing calcospherites were hardly seen. It is therefore presumed that interference with intracellular and probably extracellular accumulation of calcium by tetracycline might inhibit matrix vesicle production and aggregation, thus inhibiting calcification.

Calcospherulites11Calcospherulites (calco: calcium salt+spherulite: spherical crystalline body); calcium-containing, spherical bodies have also been referred to as calcified microspheres, mineral clusters, crystal ghost aggregates, calcification nodules, calcospherites, and small calcified spheres. isolated from the mineralization front of bone induce the mineralization of type I collagen

“…Based on a conventional approach to dynamically label newly forming bone tissue, there is a high confidence that these isolated calcospherulites were associated with the newly formed bone tissue at the mineralization front. In contrast to a previous report that used repeated, high-dose tetracycline labeling in vivo to severely inhibit growth plate mineralization (6 injections of 100 mg/kg each) [34], our in vivo labeling method used a single, low-dose (10 mg/kg) injection of calcein. Proof that this calcein injection did not overtly inhibit mineralization was revealed when some of the original calcein labeling line became incorporated into the underlying bone tissue within a few days of subsequent growth.…”