Death Effects of Reveromycin A in Normal and Diseased Synoviocytes

Abstract

Reveromycin A (Rev A) is a natural compound that specifically causes apoptosis in osteoclasts and hence may have potential as an osteoporosis therapeutic. Earlier work in our laboratory demonstrated that Rev A did not cause significant cell death in chondrocytes. To date no studies have been conducted on Rev A activity in synoviocytes or the disease‐causing cells of rheumatoid arthritis, human fibroblast‐like synoviocytes (HFLS‐RA). LDH release assays were used to measure necrosis levels and caspase 3 was quantitated from cell extracts. Rev A‐induced cell death in both cell lines was characterized under the more acidic pH of 6.8, which mimics the pH of an inflamed joint and provides a pH believed to be important for Rev A action.10 microM Rev A‐treated normal synoviocytes showed distinct apoptotic changes with a 2‐fold increase in caspase 3 activity compared to untreated. At 0.1 and 1.0 microM Rev A, caspase 3 activity did not increase. Significant necrosis was not observed at any of the concentrations. These preliminary results suggest that 10 microM Rev A may have undesirable apoptotic effects in normal synoviocytes of the joint under acidic conditions. However at lower, potentially relevant therapeutic doses, apoptotic events do not appear to occur. Untreated and 10 microM Rev A‐treated HFLS‐RA at both 7.4 and 6.8 pH's demonstrated normal morphology under the phase contrast microscope and did not demonstrate significantly different levels of apoptosis or necrosis compared to untreated, suggesting that the typically apoptosis‐resistant HFLS‐RA behave in a similar fashion when exposed to Rev A. Funding provided by an Indiana Academy of Science senior research grant, the Hodson Summer Research Institute, and the Indiana Wesleyan University Division of Natural Sciences.