Methods: AP was experimentally induced in C57BL/6, 129 and 5-LO-/-mice due to contamination of the root canals left open to the oral environment. MK-886 was used as a systemic inhibitor of 5-LO (5 mg/kg, daily). After 7, 14, 21 and 28 days the animals were euthanized and tissues were removed for gene evaluation by qRT-PCR, histological analysis and tartrate-resistant acid phosphatase (TRAP) staining. Statistical analysis was performed using one-way ANOVA followed by Dunnett's test (alpha= 0.05).
Results: In vivo contamination of root canals induced 5-LO, RANK, RANKL and OPG gene expression, which resulted in apical inflammation and bone resorption by TRAP positive osteoclasts. Treatment with 5-LO inhibitor reduced early RANKL and OPG expression at 7 and 14 days, differently from late treatment for 21 and 28 days, which resulted in increased expression, with higher ratio for RANKL (p < 0.05). Interestingly, late treatment induced TRAP positive osteoclast formation differently from early treatment (p < 0.05). AP induced in 5-LO-/- mice showed higher levels of RANK, RANKL and OPG with higher ratio of RANKL compared to wild type mice (p < 0.05). Inflammatory genes induced in early AP development were Il1b, Il11, Il17b, Il20, Mif, Lta, Spp, Ccl3, Ccl7, Cxcl9, Cxcl13, Cxcl15, Ccr8, and Ccr10. A shift in gene expression was observed in late stage of AP development characterized by downregulation of Il1b, Il11, Il20, Spp, Ccl3, Ccl7, Cxcl9, Cxcl13, Cxcl15, Ccr8, and Ccr10.
Conclusion: 5-lipoxygenase present a dual role in osteoclastogenesis signaling during AP development preventing osteoclast formation in early periods but inducing osteoclastogenesis later on. These data further indicate that in vivo5-LO inhibition might regulate bone metabolism in AP.
Financial support: FAPESP (2010/17611-4 and 2012/01292-2).