In Vitro Cytotoxicity and Inflammatory Response of Local Anaesthetics and Corticosteroids in Canine Fibroblast-Like Synoviocytes.

ObjectiveThis study investigated the dose-dependent cytotoxicity and immunomodulatory effects of intra-articular local anaesthetics (lidocaine, mepivacaine, levobupivacaine) and corticosteroids (dexamethasone, methylprednisolone, methylprednisolone acetate) on canine fibroblast-like synoviocytes (FLS) in vitro. We evaluated cell viability and the expression of IL-6 and MMP-9.MethodsCanine FLS were exposed to increasing concentrations of intra-articular agents. Cell viability was determined via MTT assays. Immunomodulatory effects were assessed via ELISA for IL-6 and gelatin zymography for MMP-9 activity after TNF-α stimulation with IC50 concentrations.ResultsAll agents exhibited dose-dependent cytotoxicity. Dexamethasone was most cytotoxic (IC50 ≈ 3.4×10-4 mg/mL) but selectively inhibited TNF-α-induced MMP-9 activity without affecting IL-6 or inducing cytotoxicity at its IC50. Mepivacaine significantly inhibited MMP-9 activity by 40% at 1 mg/mL and uniquely induced IL-6 in unstimulated cells. Lidocaine, methylprednisolone, and methylprednisolone acetate suppressed TNF-α-induced IL-6 expression.ConclusionsCommonly used intra-articular agents induce dose-dependent cytotoxic effects on canine FLS at clinically relevant concentrations. This study provides the first evidence of species-specific responses for mepivacaine, levobupivacaine, and dexamethasone in canine FLS, highlighting mediator-specific and concentration-dependent effects crucial for optimizing intra-articular therapies in veterinary and translational medicine.