Immunohistochemical localization of heme oxygenase-1 expression in radicular cyst

Objectives: Radicular cysts are believed to result from inflammatory process in the periapical tissue associated with bacterial infection and necrosis of the dental pulp in carious teeth. Heme oxygenase-1 (HO-1) is known as a stress-inducible protein and functions as an antioxidant enzyme. It has been shown that HO-1 is induced rapidly by a variety of chemical and physical stimuli. In addition, HO-1 induction itself confers protection to tissues from further oxidative injuries. Little is known about the HO-1 expression in radicular cyst. The aim of this study was to investigate the in situ location of HO-1 in radicular cyst. Methods: Thirty formalin-fixed, paraffin-embedded biopsy specimens of radicular cysts were examined using immunohistochemistry. In addition, another section from each radicular cyst specimen was stained with hematoxylin and eosin to assess the presence of inflammatory infiltrates. Differences in HO-1 expression between tissue with low and high levels of inflammation were subsequently analyzed by Fisher's exact test. Results: HO-1 stain was detected in the lining epithelium, connective tissue, inflammatory infiltrates, and endothelium. Moreover, significantly greater HO-1 expression was noted in radicular cysts with high levels of inflammation as compared to tissue with low levels of inflammatory cell infiltrates (p<0.05). Conclusions: HO-1 expression is significantly higher in radicular cysts. HO-1 demonstrates a positive relationship with the grade of inflammation in the radicular cysts.