COMPARATIVE-EVALUATION OF ULTRASTRUCTURAL-CHANGES IN ARTICULAR-CARTILAGE OF OFLOXACIN-TREATED AND MAGNESIUM-DEFICIENT IMMATURE RATS

Ultrastructural changes in immature articular cartilage were studied a fter treatment of 5-wk-old rats with ofloxacin-a fluoroquinolone-and i n magnesium deficiency. Magnesium deficiency was induced by feeding a magnesium-deficient diet for 9 days; the condition was confirmed by me asuring the concentrations of the mineral in plasma, bone, and cartila ge samples of the animals by atomic absorption spectrophotometry. Oral administration of single doses of 600 or 1,200 mg ofloxacin/kg body w eight and magnesium deficiency were sufficient to induce gross structu ral cartilage defects. Alterations observed on the ultrastructural lev el showed striking similarities in magnesium-deficient rats and in rat s treated with single doses of 600 mg ofloxacin/kg body weight. Typica l observations were (a) bundle-shaped, electron-dense aggregates on th e surface and in the cytoplasm of chondrocytes, (b) detachment of the cell membrane from the matrix and necrotic chondrocytes, (c) reduction of the extracellular matrix, and (d) swelling of cell organelles such as mitochondria. These findings further substantiate the histological finding that quinolone treatment and a dietarily induced magnesium-de ficiency induce indistinguishable pathological conditions in immature joint cartilage, and they suggest that quinolone-induced arthropathy i s probably caused by a reduction of functionally available magnesium ( ionized Mg2+) in cartilage (42). Furthermore, they provide a basis for aimed studies with human cartilage samples from quinolone-treated pat ients that might be available postmortally or after hip replacement su rgery.