Effects of the exposition to dental alloys in human fibroblasts

Purpose: Cast alloys used in dentistry are common source of metal ions released into the gingival and oralmucosa, which in turn often cause gingival and periodontal inflammation. The aim of this study was to evaluate effects of exposure to orthodontic materials on transglutaminases in cultured human gingival fibroblasts. Methods and materials: The human gingival fibroblast cell line, HGF-1 (CRL 2014), was obtained from American Type Culture Collections. The incubation with Ni–Ti heat-activated (T3) or Ni–Ti super-elastic (T4), and with Ni–Cr–Co (T2) alloys produced respectively 2.5-fold and 8-fold increases in IL-6 release compared with control cultures. The biocompatibility of the five orthodontic samples after 24–48h of incubation with the release medium from cast alloys was tested by MTT reduction assay. IL-6 release from treated and untreated cultures was measured using an ELISA test and confocal laser scanning microscopy and western blot analysis was performed to evaluate transglutaminases activity. Results: A not significant loss of cell viability was observed in fibroblast cultures exposed for 24–48h to the medium containing the release products of ceramics (Ce) and Ni–Ti (T1, T3, T4) orthodontic alloys compared to control cultures, as monitored by MTT reduction assay. The Ni–Cr–Co (T2) alloy was the most toxic material tested. Transglutaminases activity was significantly increased in cells exposed to T3 and T4 alloys (about 170% of control; p < 0.05), where it was mainly localized close to inner part of cell membrane. The exposure to T3 and T4 specimens significantly up-regulated also tTG expression compared with control cultures. Conclusion: This study demonstrated that transglutaminases activity is significantly elevated in fibroblasts exposed to Ni–Ti alloys. These effects were associated with IL-6 release and were dependent on the presence of different elements in the cast alloy. It was shown an association between IL- 6 release and tissue transglutaminases increases, suggesting that TGase-mediated reactions may play a major role in periodontal inflammation.