Articular cartilage, epiphyseal growth plate and tendons have been recognized as targets of fluoroquinolone-induced connective tissue toxicity. The effects of fluoroquinolones on ligament tissues are still unknown. The aim of this study was to investigate the effects of levofloxacin, a typical fluoroquinolone antibiotic drug, on rabbit anterior cruciate ligament (ACL) cells in vitro. Rabbit ACL cells were treated with levofloxacin at different concentrations (0, 14, 28, 56, 112 and 224 μM) and were assessed to determine the possible cytotoxic effects of levofloxacin on ACL cells. Levofloxacin, with concentrations ranging from 28 to 224 μM, induced dose-dependent ACL cell apoptosis. Characteristic markers of programmed cell death and degenerative changes were identified by electron microscopy in the ACL cells treated with 28 μM of levofloxacin. Moreover, levofloxacin significantly increased the mRNA expression of matrix metalloproteinase 3 (MMP-3) and MMP-13 and decreased the expression of tissue inhibitors of metalloproteinase 1 (TIMP-1) in a concentration-dependent manner; TIMP-3 and collagen type I alpha 1 (Col1A1) mRNA expression was not affected. Immunocytochemical analysis indicated that levofloxacin markedly increased the expression of active caspase-3 within a concentration range of 28 to 224 μM, whereas a clear-cut decrease in Col1A1 expression was found with levofloxacin treatment concentrations of 112 and 224 μM, compared to controls. Our data suggest that levofloxacin has cytotoxic effects on ACL cells characterized by enhanced apoptosis and decreased extracellular matrix, which suggest a potential adverse effect of fluoroquinolones.
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