Cultured osteoblast synthesize nitric oxide in response to cytokines and lipopolysaccharide.

Nitric oxide (NO) is generated from L-arginine by NO synthase. NO has been reported to be produced by a variety of cell types such as vascular endothelial cells, macrophages, neutrophils and articular chondrocytes. A recent report demonstrated that NO inhibits osteoclast (OC) function and, in this way, is critically associated with bone metabolism. In the present study we have studied NO synthesis by osteoblasts (OBs). OB cell line, MC3T3-E1, was cultured with the various cytokines for 72 hrs. Nitrite, a stable endproduct of cell-generated NO, in the culture supernatant was then determined by using a spectrophotometric method based on Griess reaction. IL-1 alpha increased nitrite release in a dose-dependent fashion and a significant enhancement (p < 0.01) was attained at 10 U/ml. OBs released 14.2 nmol/4.0 x 10(4) cells of nitrite after 72 hrs stimulation by 100 U/ml IL-1 alpha. In contrast IL-1 beta, TNF-alpha and INF-gamma failed to affect NO synthesis by MC3T3-E1. The results suggest that OBs produce NO in response to IL-1 alpha and OB-induced NO may play a role in OB-OC interaction in the inflammatory process.