Regulation of cyclooxygenase-2 expression in human osteoblastic cells by N-acetylcysteine

Cyclooxygenase (COX) plays a pivotal role in the inflammatory process of inflammatory arthropathies, Inflammatory cytokines induce COX-2 expression in osteoblasts of inflamed joints, followed by osteoclast activation. The inhibition of COX-2 expression could help prevent prostaglandin E-2 secretion, followed by osteoclast activation for bone destruction and resorption. We examined whether the antioxidant N-acetylcysteine (NAC) inhibited COX-2 expression induced in the human osteoblastic cell line MG63 by interleukin-1 beta (IL-1 beta). According to Western blot and reverse transcription-polymerase chain reaction (RT-PCR) test results, NAC inhibited IL-1 beta -induced COX-2 expression in protein and messenger RNA. We also demonstrated immunohistochemically that NAC inhibited NF kappaB nuclear translocation. These results suggested that NAC inhibited both COX-2 expression and NF kappaB nuclear translocation in MG63, which in turn indicated that NAC could inhibit the inflammatory process involved in bone resorption by regulating COX-2 expression at the level of transcription.