Gene profiles during root canal treatment in experimental rat periapical lesions

The purpose of this study was to profile gene expression in periapical lesions during root canal treatment (RCT). Periapical lesions were induced experimentally by exposing the pulp in Sprague-Dawley rats. After 3 wk, the animals received root canal filling (RCF) and were sacrificed 1 or 4 wk later. From the periapical tissues, total RNA was extracted and processed for cDNA-microarray analysis. The lesions were histologically and radiographically confirmed to expand 4 wk after pulp exposure (inflammation phase) and to stabilize 4 wk after RCF (healing phase). In approximately 30,000 genes on the microarray, 203 genes were up-regulated to more than 5-fold (e.g., IL-1 beta), and 864 genes were down-regulated to less than 20% of baseline level (e.g., caspase 8) in inflammation phase. Compared with inflammation phase, we found that 133 genes were up-regulated (e.g., IL-1 alpha) and 50 genes were down-regulated (e.g., defensin alpha 5) in healing phase. Corresponding to the gene expression profiles, accumulation of IL-1 alpha and IL-1 beta was observed in the periapical lesions by immunohistochemistry. These gene profiles might be useful in diagnosing the healing process of periapical lesions.