Phenytoin-induced gingival overgrowth caused by death receptor pathway malfunction

ObjectiveIn this study, we investigated the role of phenytoin (PHT) in death receptor-induced apoptosis of gingival fibroblasts to clarify the mechanism of PHT-induced gingival overgrowth. MethodsHuman gingival fibroblasts were cultured to semiconfluence and treated with PHT (0.025, 0.1, 0.25, and 1.0M) for 48h, and then, the apoptotic cell numbers were relatively determined by absorptiometry. After 24h of 0.25M PHT treatment, caspase activity was measured by absorptiometry, apoptotic and cell cycle phase distribution was analyzed by flow cytometry, expression levels of apoptotic genes were quantified by real-time qPCR, and expression of apoptotic proteins was detected by Western blot analysis. After 48h of 0.25M PHT treatment, appearance of apoptotic cells was detected by TUNEL assay. ResultsPHT treatment decreased the proportion of apoptotic cells in gingival fibroblasts compared to a serum-free control culture in response to the protein changes as follows: PHT upregulated c-FLIP and, in turn, downregulated FADD, caspase-8, and caspase-3; PHT upregulated c-IAP2 and downregulated TRAF2; PHT downregulated caspase-9 and caspase-3 via decreased RIPK1 activity and increased Bcl-2 activity. ConclusionPHT-induced gingival overgrowth may result from the above-mentioned mechanisms involving apoptosis inhibition in gingival fibroblasts.