Effect of phenytoin on collagen accumulation by human gingival fibroblasts exposed to TNF-α in vitro

OBJECTIVE: Tumor necrosis factor (TNF)-alpha is associated with chronic gingival inflammation and reported to induce gingival overgrowth (GO), while phenytoin (PHT) is also known to be a causative agent of GO. We examined the synergistic effect of PHT and TNF-alpha on collagen metabolism in human gingival fibroblasts (HGFs). MATERIALS AND METHODS: HGFs were cultured with TNF-alpha and PHT. Quantitative real-time RT-PCR was employed to determine the mRNA levels for collagen, matrix metalloproteinases (MMPs), tissue inhibitors of metalloproteinases (TIMPs) and integrin subunits. Cellular collagen endocytosis was determined using a flow-cytometry. RESULTS: The proliferation of HGFs was not affected by TNF-alpha or PHT individually, whereas both synergistically increased collagen accumulation in HGFs. Further, collagen mRNA expression was not increased by TNF-alpha or PHT, although together they markedly prevented cellular collagen endocytosis, associated with the suppression of alpha 2 beta 1-integrin mRNA expression. The mRNA expression of MMP-1 and-2 was suppressed by PHT, while TIMP-1 mRNA expression was enhanced by both TNF-alpha and PHT. CONCLUSION: Our results suggest that TNF-alpha and PHT together cause impaired collagen metabolism by suppression of enzymatic degradation with MMPs/TIMP-1 and integrin-mediated endocytosis. These synergistic effects may also be involved in TNF-alpha- and PHT-induced collagen accumulation, leading to GO.