In vitro evidence for effects of magnesium supplementation on quinolone-treated horse and dog chondrocytes

Quinolones and magnesium deficiency cause similar lesions in joint cartilag e of young animals. Chondrocytes cultivated in the presence of quinolones a nd in Mg-free medium show severe alterations in cytoskeleton and decreased ability to adhere to the culture dish. We investigated whether Mg2+ supplem entation can prevent quinolone-mediated effects on chondrocytes in vitro. C hondrocytes cultivated in Dulbecco's modified Eagle's medium/HAM's F-12 med ium were treated with ciprofloxacin (80 and 160 mug/ml) and enrofloxacin (1 00 and 150 mug/ml). Mg2+ was added at a concentration of 0.0612 mg/ml (MgCl ) and 0.0488 mg/ml (MgSO4) or a triple dose. In addition, cells were cultiv ated in Mg-free medium and accordingly treated with Mg2+ supplementation. A fter 5 days in culture, the number of adherent cells per milliliter was det ermined. The number of chondrocytes in quinolone-treated groups decreased t o 12-36% that of the control group within the culture period. With Mg2+ sup plementation, the number of attached cells increased to 40-70% that of cont rol cells. The threefold dose of Mg2+ led to better results than did the si ngle dose. Cell proliferation tested by immunohistochemical staining with K i67 (clone MIB5) decreased from 70% in control groups to 55%, 48%, and 30% in enrofloxacin-treated groups in a concentration dependent manner (50, 100 , and 150 mug/ml). Addition of Mg2+ did not increase the rate of cell proli feration. These results suggest that a great part of quinolone-induced dama ge is due to magnesium complex formation, as Mg2+ supplementation is able t o reduce the effects in vitro. However, quinolone effects on cell prolifera tion seem to be an independent process that is not influenced by magnesium supplementation.