Effect of nitric oxide on mouse clonal osteogenic cell, MC3T3-E1, proliferation in vitro.

Nitric oxide (NO) is a very small lipophilic molecule which rapidly diffuses and reaches the cytoplasmic components, and results in the activation of diverse biological function. It has been already reported that cultured osteoblasts synthesize NO in response to proinflammatory cytokines and lipopolysaccaride. In terms of the action of NO on bone metabolism, cytokine-induced NO by osteoblast inhibits bone resorption through inducing the apoptosis of osteoclast progenitor cells and suppressing the osteoclast activity. Also, NO synthase (NOS) inhibitor, NG-monomethyl-L-arginine is reported to induce a dose-dependent inhibitory effect on the proliferation of osteoblast-like cell lines MG63 and ROS 17/2.8, which indicate that NO may stimulate cell proliferation. On the other hand, cytokine-induced NO is reported to reduce osteoblast activity significantly in high concentration, as was evidenced by inhibition of DNA synthesis, cell proliferation, alkaline phosphatase activity, and osteocalcin production. Thus, the effect of NO on osteoblast activities is still controversial. In the present study, S-nitroso-N-acetyl-dl-penicillamine(SNAP), NO donor enhanced DNA synthesis of MC3T3-E1 in vitro. This activation seems to be mediated by NO directly because specific NO scavenger, 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (carboxy-PTIO) partially attenuated the osteoblast proliferation induced by SNAP. On the other hand, the guanylate cyclase inhibitor, LY83583, failed to abolish the effect of SNAP on DNA synthesis of osteoblasts and 8-bromo cyclic guanosine 3',5'-monophosphate(cGMP), substituting for the accumulation of intracellular cGMP in osteoblasts, did not enhance the incorporation of 3H-thymidine(3H-TdR). It is, then, suggested that osteoblast proliferation might be enhanced by NO independently apart from the activation of cytoplasmic guanylate cyclase and cGMP-dependent mechanisms.