Mitochondrial biogenesis disorder and oxidative damage promote refractory apical periodontitis in rat and human

Aim To elucidate whether mitochondrial biogenesis disorder and damage from oxidative stress promote refractory apical periodontitis (RAP) in rat and human. Methodology Twenty Enterococcus faecalis‐induced RAPs were established in the maxillary first molars of male Wistar rats. Concurrently, 12 periapical lesion specimens from patients presenting with RAP were obtained by apicoectomy. Radiographic examination and histologic analysis were conducted to evaluate periapical bone tissue destruction and morphological changes. The expression of key regulators of mitochondrial biogenesis, PGC‐1α and Nrf2, were detected by immunohistochemistry and double immunofluorescence staining, Western blot and real‐time PCR were also assayed. Mitochondrial ROS (mtROS) was identified by MitoSOX staining. Mitochondrial function was detected by the quantification of ATP production, mitochondrial DNA (mtDNA) copy number and activities of mitochondrial respiratory chain complexes. Furthermore, mitochondrial oxidative stress was evaluated by the determination of 3‐nitrotyrosine (3‐NT), 4‐hydroxy‐2‐nonenal (4‐HNE) and 8‐hydroxy‐deoxyguanosine (8‐OHdG) expression levels, as well as malondialdehyde (MDA) expression and antioxidant capacity. Student's t‐test was performed to determine significance between the groups; p