Peroxynitrite production by TNF-a and IL-1b: implication for suppression of osteoblastic differentiation

Hikiji, Hisako, Wee Soo Shin, Toshiyuki Koizumi, Tsuyoshi Takato, Takafumi Susami, Yoko Koizumi, Yoko Okai-Matsuo, and Teruhiko Toyo-oka. Peroxynitrite production by TNF-a and IL-1b: implication for suppression of osteoblastic differentiation. Am J Physiol Endocrinol Metab 278: E1031–E1037, 2000.—To determine the roles of nitric oxide (NO) and its metabolite, peroxynitrite (ONOO2), on osteoblastic activation, we investigated the effects of a NO donor [ethanamine, 2,28-(hydroxynitrosohydrazono)bis(dNO)], an O2 2 donor (pyrogallol), and an ONOO2 scavenger (urate) on alkaline phosphatase (ALPase) activity and osteocalcin gene expression, which are indexes of osteoblastic differentiation. dNO elevated ALPase activity in the osteogenic MC3T3-E1 cell line. The combination of dNO and pyrogallol reduced both ALPase activity and osteocalcin gene expression. Because both indexes were recovered by urate, ONOO2, unlike NO itself, inhibited the osteoblastic differentiation. Furthermore, treatment with a combination of the proinflammatory cytokines tumor necrosis factor-a (TNF-a) and interleukin-1b (IL-1b) was found to yield ONOO2 as well as NO and O2 . The reductions in ALPase activity and osteocalcin gene expression were also restored by urate. We conclude that ONOO2 produced by TNF-a and IL-1b, but not NO per se, would overcome the stimulatory effect of NO on osteoblastic activity and inhibit osteoblastic differentiation.