Effects of cyclooxygenase and soluble epoxide hydrolase inhibitors on apoptosis of cultured primary equine chondrocytes

BACKGROUND: Apoptosis is an important mechanism underlying chondrocyte loss in osteoarthritis that could be affected by modulation of lipid signaling via inhibition of cyclooxygenases (COX) and soluble epoxide hydrolase (sEH).

OBJECTIVE: To determine the impact of inhibiting COX and sEH alone or in combination on apoptosis of equine chondrocytes.

METHODS: Cultured primary equine chondrocytes were subjected to serum deprivation or incubation with 1 μg/ml tunicamycin for 24 h to induce apoptosis via caspase activation and endoplasmic reticulum (ER) stress, respectively. Cells were treated with the non-selective COX inhibitor phenylbutazone, the COX-2 selective inhibitor firocoxib and the sEH inhibitor t-TUCB alone or in combination. The inhibitors were used at half-maximal (IC 50), 80% of maximal (IC 80) and 10-fold the 80% inhibitory concentration (10xIC 80) for the equine enzymes. Apoptosis was quantified via ELISA technique. Data were analyzed with unpaired two-tailed t-test or one-way ANOVA followed by Bonferroni's post-hoc while correcting for multiple comparisons via statistical hypothesis testing. P < 0.05 was considered significant.

RESULTS: In the caspase model, 10xIC 80t-TUCB significantly decreased whereas 10xIC 80 phenylbutazone significantly enhanced apoptosis. Apoptosis enhancement by phenylbutazone was significantly attenuated by concurrent 10xIC 80t-TUCB. The remaining treatments and concentrations had no effect on apoptosis development. In the ER stress model, IC 50 and IC 80 phenylbutazone and firocoxib significantly enhanced apoptosis, which was fully prevented by concurrent 10xIC 80t-TUCB.

MAIN LIMITATIONS: In vitro findings that will need to be verified in vivo.

CONCLUSIONS: Chondrocyte apoptosis caused by ER stress can be enhanced by COX inhibition but prevented by concurrent inhibition of sEH.