Phenytoin‐induced gingival overgrowth caused by death receptor pathway malfunction

<jats:sec><jats:title>Objective</jats:title><jats:p>In this study, we investigated the role of phenytoin (<jats:styled-content style="fixed-case">PHT</jats:styled-content>) in death receptor‐induced apoptosis of gingival fibroblasts to clarify the mechanism of <jats:styled-content style="fixed-case">PHT</jats:styled-content>‐induced gingival overgrowth.</jats:p></jats:sec><jats:sec><jats:title>Methods</jats:title><jats:p>Human gingival fibroblasts were cultured to semiconfluence and treated with <jats:styled-content style="fixed-case">PHT</jats:styled-content> (0.025, 0.1, 0.25, and 1.0 <jats:italic>μ</jats:italic>M) for 48 h, and then, the apoptotic cell numbers were relatively determined by absorptiometry. After 24 h of 0.25 <jats:italic>μ</jats:italic>M <jats:styled-content style="fixed-case">PHT</jats:styled-content> 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 <jats:styled-content style="fixed-case">qPCR</jats:styled-content>, and expression of apoptotic proteins was detected by Western blot analysis. After 48 h of 0.25 <jats:italic>μ</jats:italic>M <jats:styled-content style="fixed-case">PHT</jats:styled-content> treatment, appearance of apoptotic cells was detected by <jats:styled-content style="fixed-case">TUNEL</jats:styled-content> assay.</jats:p></jats:sec><jats:sec><jats:title>Results</jats:title><jats:p><jats:styled-content style="fixed-case">PHT</jats:styled-content> 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: <jats:styled-content style="fixed-case">PHT</jats:styled-content> upregulated c‐<jats:styled-content style="fixed-case">FLIP</jats:styled-content> and, in turn, downregulated <jats:styled-content style="fixed-case">FADD</jats:styled-content>, caspase‐8, and caspase‐3; <jats:styled-content style="fixed-case">PHT</jats:styled-content> upregulated c‐<jats:styled-content style="fixed-case">IAP</jats:styled-content>2 and downregulated <jats:styled-content style="fixed-case">TRAF</jats:styled-content>2; <jats:styled-content style="fixed-case">PHT</jats:styled-content> downregulated caspase‐9 and caspase‐3 via decreased <jats:styled-content style="fixed-case">RIPK</jats:styled-content>1 activity and increased Bcl‐2 activity.</jats:p></jats:sec><jats:sec><jats:title>Conclusion</jats:title><jats:p><jats:styled-content style="fixed-case">PHT</jats:styled-content>‐induced gingival overgrowth may result from the above‐mentioned mechanisms involving apoptosis inhibition in gingival fibroblasts.</jats:p></jats:sec>