Cyclooxygenase (COX) plays a pivotal role in the inflammatory process of in
flammatory arthropathies, Inflammatory cytokines induce COX-2 expression in
osteoblasts of inflamed joints, followed by osteoclast activation. The inh
ibition 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 exp
ression induced in the human osteoblastic cell line MG63 by interleukin-1 b
eta (IL-1 beta). According to Western blot and reverse transcription-polyme
rase chain reaction (RT-PCR) test results, NAC inhibited IL-1 beta -induced
COX-2 expression in protein and messenger RNA. We also demonstrated immuno
histochemically that NAC inhibited NF kappaB nuclear translocation. These r
esults suggested that NAC inhibited both COX-2 expression and NF kappaB nuc
lear translocation in MG63, which in turn indicated that NAC could inhibit
the inflammatory process involved in bone resorption by regulating COX-2 ex
pression at the level of transcription.