Ex Vivo Toxicity of Corticosteroids on Equine Deep Digital Flexor and Navicular Fibrocartilage Cells

Introduction: Navicular disease is a common cause of forelimb lameness in horses. Despite the common use of corticosteroids in the clinical practice, their toxic effects on deep digital flexor, and navicular fibrocartilage cells are unknown. Our objective was to investigate the effects of triamcinolone and methylprednisolone on metabolic activity and viability of resident cells present in dorsal fibrocartilaginous zone of “deep digital flexor tendon” (FC-DDFT) and “fibrocartilage on the flexor surface of the navicular bone” (FC-NB).

Materials and Methods: FC-DDFT and FC-NB explants were harvested from forelimbs of horses (n = 5) free of gross pathology. Explants were incubated with medium (control) or triamcinolone acetonide (TA at 0.6 and 6 mg/mL) or methylprednisolone acetate (MPA at 0.5 and 5 mg/mL) for 6 and 24 hours. Explant metabolic activity was measured using the Alamar Blue assay. Explant cell viability was assessed using Calcein–Sytox stained live-dead assay.

Results: TA (at both concentrations) did not significantly change the metabolic activity and cell viability of FC-DDFT and FC-NB explants compared with control. However, MPA at 5 mg/mL significantly reduced the metabolic activity and cell viability of FC-DDFT and FC-NB. MPA at 0.5 mg/mL did not significantly change the metabolic activity of FC-DDFT and FC-NB and resulted in approximately 20 to 40% reduction in cell viability at 6 and 24 hours of incubation, respectively.

Discussion/Conclusion: Triamcinolone is less cytotoxic to deep digital flexor and navicular fibrocartilage cells compared with methylprednisolone. This explant model is viable for evaluating effects of commonly used medications on deep digital flexor and navicular fibrocartilage, for which currently no information exists.

Acknowledgment: OSU CVM Equine Intramural Funds.