title: 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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Physiology and Pathology, Araraquara Dental School, State University of São Paulo, Araraquara, SP, Brazil. brunoherreras@gmail.com
authors.forename: Bruno S
authors.initials: BS
authors.lastname: Herrera
authors.forename: Rodrigo
authors.initials: R
authors.lastname: Martins-Porto
authors.forename: Aline
authors.initials: A
authors.lastname: Maia-Dantas
authors.forename: Paula
authors.initials: P
authors.lastname: Campi
authors.forename: Luis C
authors.initials: LC
authors.lastname: Spolidorio
authors.forename: Soraia K P
authors.initials: SK
authors.lastname: Costa
authors.forename: Thomas E
authors.initials: TE
authors.lastname: Van Dyke
authors.forename: Robert
authors.initials: R
authors.lastname: Gyurko
authors.forename: Marcelo N
authors.initials: MN
authors.lastname: Muscara
mesh_terms: D016301:Alveolar Bone Loss / Q000150:complications / Q000201:enzymology*; D000818:Animals; D001862:Bone Resorption / Q000150:complications / Q000201:enzymology; D002478:Cells, Cultured; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006146:Guanidines / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D009569:Nitric Oxide / Q000378:metabolism*; D052247:Nitric Oxide Synthase Type II / Q000187:drug effects / Q000378:metabolism*; D010010:Osteoclasts / Q000166:cytology / Q000378:metabolism*; D010518:Periodontitis / Q000150:complications* / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar
chemical_list: D004791:Enzyme Inhibitors; D006146:Guanidines; D009569:Nitric Oxide; D052247:Nitric Oxide Synthase Type II; C004479:pimagedine