EFFECTS OF FLUOROQUINOLONES AND MAGNESIUM-DEFICIENCY IN MURINE LIMB BUD CULTURES

Quinolone-induced arthropathy is probably caused by a lack of function ally available magnesium in immature joint cartilage. We used an in vi tro assay to study the effects of fluoroquinolones on cartilage format ion in mouse limb buds from 12-day-old mouse embryos in regular and in magnesium-deficient medium. Omission of magnesium from the medium had no adverse effect on the outcome of the culture: limb buds grew and d ifferentiated well in regular and in magnesium-deficient Bigger's medi um. Lack of calcium, however, severely impaired the development of the explants; this result was even more enhanced when both minerals (magn esium and calcium) were omitted. Electron microscopy revealed cell nec rosis and deposition of electron-dense material in the vicinity of cho ndrocytes from limb buds after 6 days in a magnesium-free medium. A se ries of seven fluoroquinolones was tested at 30, 60, and 100 mg/l medi um. At a concentration of 30 mg/l sparfloxacin only had a slight effec t on limb development. At concentrations of 60 and 100 mg/l sparfloxac in, temafloxacin and ciprofloxacin impaired limb development in vitro concentration-dependently. The effects were enhanced in a magnesium-de ficient medium (concentration of magnesium <10 mu mol/l). Fleroxacin, lomefloxacin and ofloxacin impaired limb development only slightly; no significant differences were recognizable between the outcome in regu lar and in magnesium-deficient medium. Pefloxacin did not show any eff ect on limb development in both media. Using electron microscopy, very similar alterations as described above for the limbs cultured in magn esium-deficient medium were observed with ofloxacin at a concentration of 30 mg/l, which had no effect on the growth of the explants when ev aluated macroscopically. The affinity of six fluoroquinolones to magne sium was determined by the use of a fluorescence assay. The affinity t o magnesium correlated with the activity of the drugs in the limb bud assay. We conclude that fluoroquinolones have no effect on murine limb development in vitro at concentrations that are achieved under therap eutic conditions (peak concentrations approx. 1-5 mg/l in plasma). Eff ects at higher concentrations (60 and 100 mg/l) are slightly enhanced (factor 2) if the magnesium concentration in the medium is low. Macros copically, limbs develop regularly in a magnesium-free medium, but ult rastructurally typical alterations are exhibited (e.g. cell necrosis a nd pericellular deposition of electron-dense material).