Local anaesthetics or their combination with morphine and/or magnesium sulphate are toxic for equine chondrocytes and synoviocytes in vitro

BACKGROUND Chondrotoxic effects of local anaesthetics are well reported in humans and some animal species but knowledge on their toxic effects on synoviocytes or equine chondrocytes or the effects on cellular production of inflammatory cytokines is limited. The purpose of this study was to evaluate the in vitro effects of local anaesthetics, morphine, magnesium sulphate (MgSO4) or their combinations on cell viability and pro-inflammatory cytokine gene expression of equine synoviocytes and chondrocytes. Equine synoviocytes and cartilage explants harvested from normal joints in a co-culture system were exposed to mepivacaine (4.4 mg/ml), bupivacaine (2.2 mg/ml), morphine (2.85 mg/ml) and MgSO4 (37 mg/ml) alone or each local anaesthetic plus morphine or MgSO4 or both together. Chondrocyte and synoviocyte cell viability was assessed by CellTiter-Glo Luminescent Cell Viability Assay. Synoviocyte gene expression of IL-1β, IL-6 or TNF-α was measured and compared using the ∆∆CT method. RESULTS Morphine alone, MgSO4 alone or their combination did not alter cell viability or the expression of IL-1β, IL-6 or TNF-α. However, local anaesthetics alone or in combination with morphine and/or MgSO4 reduced cell viability and increased the gene expression of IL-1β, IL-6 or TNF-α. Single short exposure to local anaesthetics is toxic to both chondrocytes and synoviocytes and their combination with morphine and/or MgSO4 enhanced the cytotoxic effects. CONCLUSIONS This in vitro study gives further evidence of the absence of cytotoxic effects of morphine alone, MgSO4 alone or their combination on normal articular tissues. However, local anaesthetics alone or in combination with morphine and/or MgSO4 have cytotoxic effects on equine articular tissues.