Effects of xylazine and dexmedetomidine on equine articular chondrocytes in vitro.

OBJECTIVE: To assess the effects of xylazine and dexmedetomidine on equine chondrocytes, in vitro.

STUDY DESIGN: Prospective, experimental study.

STUDY MATERIAL: Equine articular chondrocytes from five male horses.

METHODS: Chondrocytes were isolated from healthy equine articular cartilage of the metacarpo/metatarsophalangeal joints. Cell viability was assessed using the WST-8 assay by exposing chondrocytes to xylazine (0.5, 1, 2, 4, 8, 16.6, 25, 50 mg mL-1 ) or dexmedetomidine (0.001, 0.005, 0.01, 0.05, 0.175, 0.25 mg mL-1 ) for 15, 30 and 60 minutes. Based on the results of these tests, cells were treated with xylazine (1, 4, 25 mg mL-1 ) or dexmedetomidine (0.05, 0.175, 0.25 mg mL-1 ) for 15 minutes to further evaluate: cell viability by neutral red uptake; cell membrane integrity by lactate dehydrogenase release and by fluorescence microscopy with Hoechst 33342 and propidium iodide (PI), and apoptosis by flow cytometry using double staining with annexin V-fluorescein isothiocyanate/PI and by cell morphology.

RESULTS: Both drugs reduced cell viability in a dose-dependent manner. Specifically, all xylazine concentrations, except 0.5 mg mL-1 and 1 mg mL-1 , significantly reduced cell viability, whereas the effects of dexmedetomidine were evident only at 0.175 mg mL-1 and 0.25 mg mL-1 . The highest concentrations of xylazine (25 mg mL-1 ) and dexmedetomidine (0.25 mg mL-1 ) caused loss of membrane integrity. Cell morphology and flow cytometry analyses demonstrated signs of late apoptosis in xylazine-treated cells, and signs of late apoptosis and necrosis in dexmedetomidine-treated cells.

CONCLUSIONS AND CLINICAL RELEVANCE: This study offers new insights into the potential chondrotoxicity induced by dexmedetomidine and xylazine. Therefore, the intra-articular administration of α2 -agonists should be conducted with care, especially for doses of ≥ 4 mg mL-1 of xylazine and 0.175 mg mL-1 and 0.25 mg mL-1 of dexmedetomidine.