Nonsteroidal Anti-Inflammatory Drugs Induce Apoptosis in Association with Activation of Peroxisome Proliferator- Activated Receptor in Rheumatoid Synovial Cells

Nonsteroidal anti-inflammatory drugs (NSAIDs) have been reported to induce apoptosis in a variety of cell lines. In this study, we examined the effect of NSAIDs on the growth and apoptosis of synovial cells from patients with rheumatoid arthritis and analyzed the activation of peroxisome proliferator-activated receptor (PPAR ) as a possible mechanism of action of NSAIDs. Cell proliferation and viability were assessed from 5-bromo-2 deoxyuridine incorporation and by 4-[3-(4-iodophenyl)-2-(4-nitrophenyl)-2H-5-tetrazolio]-1,3-benzene disulfonate (WST-1) assay, respectively. The apoptosis of synovial cells was identified by DNA fragmentation assay and terminal deoxynucleotidyl transferasemediated dUTP nick-end labeling assay. Indometacin, diclofenac, oxaprozin, and zaltoprofen reduced cell proliferation and induced apoptotic cell death in synovial cells, whereas ketoprofen and acetaminophen did not. N-[2-(cyclohexyloxyl)-4-nitrophenyl]methanesulfonamide (NS-398), a selective cyclooxygenase-2 inhibitor, also inhibited cell proliferation, whereas it did not cause apoptosis. Rheumatoid synovial cells expressed PPAR mRNA, and the PPAR ligands 15-deoxyprostaglandin J2 and troglitazone reduced the proliferation and induced apoptosis in synovial cells. Luciferase reporter assay demonstrated that not only PPAR ligands but also NSAIDs, which could induce apoptosis, increased the activation of PPAR in synovial cells. Furthermore, the ability of NSAIDs and PPAR ligands to stimulate the activation of PPAR correlated with their ability to decrease cell viability(r 0.92, p 0.01) and ability to induce DNA fragmentation (r 0.97, p 0.001) in synovial cells. These results suggest that PPAR is an attractive target for induction of apoptosis in rheumatoid synovial cells and that the activation of the PPAR pathway is associated with the apoptotic action of NSAIDs. Nonsteroidal anti-inflammatory drugs (NSAIDs) are frequently used in the treatment of rheumatoid arthritis because of their analgesic and anti-inflammatory activities. A major mechanism of the action of NSAIDs is generally thought to be inhibition of cyclooxygenase (COX) (Vane, 1971). COX is a key enzyme in catalyzing the conversion of arachidonic acid, which is released from the cell membrane, to prostaglandin (PG) G2 and H2. There are two isoforms of COX, COX-1 and COX-2 (Kujubu et al., 1991; Xie et al., 1991). COX-1 is constitutively expressed in a number of cell types and tissues and plays an important role in maintaining homeostasis. In contrast, COX-2 is induced in inflammatory cells by a variety of stimuli, including cytokines. These observations suggest that COX-2 plays a key role in controlling inflammation. In addition, studies have found that COX-2, but not COX-1, is markedly elevated in most colorectal adenocarcinoma tumors (Eberhart et al., 1994), indicating that COX-2 expression may play a central role in colorectal car-