Ex vivo effects of corticosteroids on equine deep digital flexor and navicular fibrocartilage explant cell viability

OBJECTIVE To investigate the effects of triamcinolone acetonide (TA) and methylpredniso-lone acetate (MPA) on the viability of resident cells within the fibrocartilage on the dorsal surface of the deep digital flexor tendon (FC-DDFT) and fibrocarti-lage on the flexor surface of the navicular bone (FC-NB) of horses. SAMPLE 12 to 14 explants of FC-DDFT and of FC-NB from grossly normal forelimbs of 5 cadavers of horses aged 9 to 15 years without evidence of musculo-skeletal disease. PROCEDURES Explants were incubated with culture medium (control) or TA-supplement-ed (0.6 or 6 mg/mL) or MPA-supplemented (0.5 or 5 mg/mL) medium for 6 or 24 hours. Explant metabolic activity and percentage of dead cells were assessed with a resazurin-based assay and live-dead cell staining, respec-tively, at each time point. Drug effects were assessed relative to findings for the respective control group. RESULTS Application of TA (at both concentrations) did not significantly change the cell viability of FC-DDFT explants. For FC-NB explants, TA at 6 mg/mL significantly reduced the metabolic activity and increased the percentage of dead cells at both time points. With either MPA concentration, FC-DDFT and FC-NB explants had reduced metabolic activity and an increased percentage of dead cells at 24 hours, whereas only MPA at 5 mg/mL was cyto-toxic at the 6-hour time point. CONCLUSIONS AND CLINICAL RELEVANCE In ex vivo explants, TA was less cytotoxic to equine FC-DDFT and FC-NB cells, compared with MPA. Further work is warranted to characterize the drugs’ transcriptional and translational effects as well as investigate their cytotoxicity at lower concentrations.