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

Abstract

BackgroundApoptosis 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). ObjectiveTo determine the impact of inhibiting COX and sEH alone or in combination on apoptosis of equine chondrocytes. MethodsCultured 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 (IC50), 80% of maximal (IC80) and 10-fold the 80% inhibitory concentration (10xIC80) 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. ResultsIn the caspase model, 10xIC80t-TUCB significantly decreased whereas 10xIC80 phenylbutazone significantly enhanced apoptosis. Apoptosis enhancement by phenylbutazone was significantly attenuated by concurrent 10xIC80t-TUCB. The remaining treatments and concentrations had no effect on apoptosis development. In the ER stress model, IC50 and IC80 phenylbutazone and firocoxib significantly enhanced apoptosis, which was fully prevented by concurrent 10xIC80t-TUCB. Main limitationsIn vitro findings that will need to be verified in vivo. ConclusionsChondrocyte apoptosis caused by ER stress can be enhanced by COX inhibition but prevented by concurrent inhibition of sEH.