iNOS‐Derived Nitric Oxide Stimulates Osteoclast Activity and Alveolar Bone Loss in Ligature‐Induced Periodontitis in Rats

Abstract

Background Inflammatory stimuli activate inducible nitric oxide synthase (iNOS) in a variety of cell types, including osteoclasts (OC) and osteoblasts, resulting in sustained NO production. In this study, we evaluate the alveolar bone loss in rats with periodontitis under long-term iNOS inhibition, and the differentiation and activity of OC from iNOS-knockout (KO) mice in vitro. Methods Oral aminoguanidine (an iNOS inhibitor) or water treatment was started 2 weeks before induction of periodontitis. Rats were sacrificed 3, 7, or 14 days after ligature placement, and alveolar bone loss was evaluated. In vitro OC culture experiments were also performed to study the differentiation of freshly isolated bone marrow cells from both iNOS KO and wild-type C57BL/6 mice. OC were counted 6 days later after tartrate-resistant acid phosphatase staining (a marker of osteoclast identity), and bone resorption activity was assessed by counting the number of resorption pits on dentin disks. Results Rats with ligature showed progressive and significant alveolar bone loss compared to sham animals, and aminoguanidine treatment significantly inhibited ligature-induced bone loss at 7 and 14 days after the induction. In comparison to bone marrow cells from wild-type mice, cells from iNOS KO mice showed decreased OC growth and the resulting OC covered a smaller culture dish area and generated fewer resorption pit counts. Conclusion Our results demonstrate that iNOS inhibition prevents alveolar bone loss in a rat model of ligature-induced periodontitis, thus confirming that iNOS-derived NO plays a crucial role in the pathogenesis of periodontitis, probably by stimulating OC differentiation and activity.

R848, a toll-like receptor 7 agonist, inhibits osteoclast differentiation but not survival or bone-resorbing function of mature osteoclasts

“…Indeed, the expression levels of IL-6, IL-12, IFN-c, and iNOS were upregulated in mouse BMMs by R848 treatment, while the expression of IFN-b mRNA was not upregulated, but consistently expressed in the BMMs. Among these genes, IL-6 has been shown to promote osteoclast differentiation (Herrera et al 2011;Lee et al 2004;O'Brien et al 2005;Udagawa et al 1995), while iNOS, IL-12, IFN-b, and IFN-c inhibit it (Zheng et al 2006, Horwood et al 2001Takayanagi et al 2002;Takayanagi et al 2000). Therefore, we added neutralizing antibodies against these molecules and found that neutralization of IFN-b by the antibody partially recovered osteoclast differentiation inhibited by R848.…”

Myeloid-Derived Suppressor Cells Function as Novel Osteoclast Progenitors Enhancing Bone Loss in Breast Cancer

“…Nitric oxide is known to induce osteoclast differentiation of macrophages (32, 33). In the present study, very high levels of NO were observed as macrophages differentiated into osteoclasts (data not shown).…”

microRNA Expression in Rat Apical Periodontitis Bone Lesion

“…Inducible nitric oxide synthase (iNOS) is well known for the contribution to osteoclast activity and alveolar bone loss. Nitric oxide (NO) mediates adaptive bone formation, protects osteocytes against apoptosis and mediates osteoclastic activity (49)(50)(51). GO results enlightened the role of miRNA in regulating nitrogen compound related genes and furthermore, in regulating bone destruction and remolding.…”