Immunocytohistochemical study of RANKL in experimental periapical lesions in SD rats

Objectives: Bone resorption is one of the hallmarks of inflammatory periapical lesions and is potently mediated by a series of cytokines, hormones and growth factors. Receptor activator of NF Kappa B ligand (RANKL), also called ODF/TRANCE/OPGL, has been recently identified as a membrane protein that is essential for osteoclastogenesis. The aim of this study was to observe the kinetics of RANKL and osteoclast expression in the experimental periapical lesions in rats. Materials & Methods: Twenty-five SD rats were randomly divided into 5 groups and sacrificed at day 0, 7, 14, 21, 28 respectively after the mandibular first molar pulps were exposed. The jaws that contain the first molar were obtained and tissue slices were routinely prepared for histological observations. Immunocytohistochemistry and enzymehistochemistry techniques were applied to detect the expression of RANKL and osteoclasts in the periapical lesions. The number of RANKL-positive cells and osteoclasts were counted single-blindly under the light microscope and then the statistic analysis was carried out to test the significance(¦Á=0.01). Results: The expression of RANKL and osteoclasts were observed at day 7. The expression and number of RANKL-positive cells and osteoclasts were climaxed at day 14. In the same period, inflammatory cell infiltration and alveolar bone resorption were abserved in the periapical lesions and deteriorated. In the 21 and 28-day-samples, the expression of RANKL decreased and fewer osteoclasts could be observed. Conclusion: RANKL can be observed in the periapical lesions. This protein may be involved in the differentiation of preosteoclasts into osteoclasts and then be responsible to the following periapical alveolar bone resorption.