Death effects of reveromycin A in normal and disease-associated cells of the joint

Earlier work in our laboratory demonstrated that naturally occurring reveromycin A (Rev A) causes apoptosis in osteoclasts without accompanying necrosis. Rev A death effects in both normal and diseased joint cells were investigated in this study. A dose of 10 μM Rev A did not cause apoptosis nor necrosis in monolayer chondrocytes, even at pH 6.8, a pH mimicking that of an inflamed joint. In contrast, at the acidic pH Rev A did induce significant apoptosis (fourfold increase at 48 h of treatment, P < 0.005) in normal synoviocytes without accompanying necrosis. Western blot of the normal synoviocyte proteins revealed that cytochrome c levels were not significantly changed over the time course of treatment nor did caspase 8 activity increase; therefore, Rev A appears to exert this apoptotic effect through a mechanism independent of the classical intrinsic and extrinsic pathways. Fibroblast-like synoviocytes isolated from rheumatoid arthritis patients (RAFLS) as well as normal human fibroblast-like synoviocytes (NHFLS), cells known to play key roles in arthritic joint pathology, were also subjected to Rev A treatment at both physiologic and acidic pH's. Neither apoptosis nor necrosis was induced in either RAFLS or NHFLS. Parallel mitomycin C treatment of NHFLS induced both apoptosis and necrosis. Comparative structure-activity analyses of Rev A and mitomycin C revealed that Rev A is less likely to cross the cell membrane at near neutral pH. Collectively the data reveal that a physiological dose of Rev A under acidic conditions induces normal synoviocytes to undergo apoptosis while pathologic fibroblast-like synoviocytes are resistant to apoptosis and necrosis.