Ciprofloxacin-mediated cell proliferation inhibition and G₂/M cell cycle arrest in rat tendon cells

Objective. To investigate the effect of ciprofloxacin on the proliferation and cell cycle progression of tendon cells, and to explore the potential molecular mechanism of ciprofloxacin-associated tendinopathy by analyzing the expression of cell cycle-related cyclin and cyclin-dependent kinase (CDK). Methods. Rat Achilles tendon cells were treated with ciprofloxacin and then assessed by MTT assay, flow cytometric analysis, and fluorescence confocal microscopy. Levels of messenger RNA (mRNA) for CDK-1 and cyclin B were determined by reverse transcriptase-polymerase chain reaction. Protein expression of CDK-1, cyclin B, checkpoint kinase 1 (CHK-1), and polo-like kinase 1 (PLK-1) was determined by Western blot analysis. Results. Ciprofloxacin inhibited tendon cell proliferation and caused cell cycle arrest at the G ₂/M phase. Confocal microscopy revealed that chromosomes in ciprofloxacin-treated cells neither properly aligned along the equatorial planes nor segregated successfully during metaphase. Mitotic arrest, misaligned chromosomes, and poor bipolar spindle formation were observed in ciprofloxacin-treated cells. CDK-1 and cyclin B protein and mRNA were both down-regulated. CHK-1 protein expression was also suppressed, but PLK-1 protein expression was up-regulated by ciprofloxacin. Conclusion. Our findings suggest a possible mechanism of ciprofloxacin-associated tendinopathy. Down-regulation of CHK-1 and up-regulation of PLK-1 may account for mitotic arrest observed in ciprofloxacin-treated cells.