Expression of NET markers in experimental apical periodontitis induced in mice

This study aimed to evaluate the expression of neutrophil extracellular trap (NET) markers in experimental apical periodontitis (AP) induced in mice, focusing on protein arginine deiminase 4 (PAD4), cathepsin G (CatG), myeloperoxidase (MPO), and citrullinated histone 3 (CitH3).

AP was induced in 55 wild-type mice, randomly divided into a negative control (n = 5) and five experimental groups (n = 10) analyzed at 2, 5, 7, 21, and 42 days after pulp exposure of first lower molars to the oral environment. Histopathological and histomorphometric analyses included neutrophil counting and periapical lesion size measurement. NET marker expression was assessed by quantitative real-time polymerase chain reaction (qRT-PCR) and immunostaining using the immunoperoxidase technique. Comparative analyses were performed with a significance level of 5 %.

AP development was confirmed by tissue inflammation progression, pulp necrosis, and periapical bone resorption. Periapical lesion size significantly increased at 7, 21, and 42 days (p < 0.001). Neutrophil counts peaked significantly at 5, 7, 21, and 42 days (p < 0.001). Gene expression of all NET markers was significantly higher after 5 days (p < 0.001). Immunostaining scores indicated higher MPO/CitH3 co-localization at 5, 21, and 42 days (p < 0.001), PAD4 expression at 5, 7, 21, and 42 days (p < 0.001), and CatG expression at 2, 7, 21, and 42 days (p < 0.001).

Experimental AP induction increased the expression of NET markers in periapical tissues in mice, suggesting a dynamic involvement in acute and chronic inflammation stages.