Apoptosis in Microencapsulated Juvenile Rabbit Chondrocytes Induced by Ofloxacin: Role Played by β₁-Integrin Receptor

Abstract

Quinolone(s) (QNs) is widely used in infection therapy due to its good antimicrobial characteristics. However, QNs-induced arthropathy of immature animals has led to restrictions on the therapeutic use of these antimicrobial agents. The exact mechanism(s) of QNs-induced chondrotoxicity remain unknown. In the present study, we investigated the possible mechanism of ofloxacin (one typical QNs)-induced injuries of chondrocytes. Juvenile rabbit joint chondrocytes cultured in alginate microspheres were incubated with ofloxacin at concentrations of 0, 2, 5, 10, 20, and 40 μg/ml for up to 96 h. Concentration of 10 μg/ml ofloxacin induced apoptosis of chondrocyte with visible apoptotic signs, including degradation of poly(ADP-ribose) polymerase, caspase-3 activation, and DNA ladder formation. Furthermore, extracellular signal-regulated kinase 1/2 (phospho-ERK1/2) and growth factor receptor-bound protein 2 (Grb2) were significantly reduced, and similar changes were also observed in the β₁-integrin receptor as assessed by immunoblotting. However, the mRNA level of β₁-integrin obtained from reverse transcription-polymerase chain reaction remained unchanged. Results of β₁-integrin immunoprecipitation have also shown that β₁-integrin did not interact with activated intracellular signaling proteins. In addition, ofloxacin did not induce apoptosis and decrease β₁-integrin expression in chondrocytes supplemented with Mg²⁺, and the ofloxacin-induced apoptosis was caspase-8-dependent, inhibition of which did not affect the expression mode of phospho-ERK1/2 and β₁-integrin. Our results demonstrate that ofloxacin affects β₁-integrin receptor functions and the ERK mitogen-activated protein kinase signaling pathway, causing caspase-8-dependent apoptosis after exposure of 48 h.