LAUSR

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.