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An early and late cytotoxicity evaluation of lidocaine on human oral mucosa fibroblasts

Local anesthetic drugs are extensively used in dentistry. However, the cytotoxic effects of these pharmaceutical compounds remain unclear. In this work, we have evaluated the cell viability and cell function of human oral mucosa fibroblasts exposed to different concentrations of lidocaine for increasing incubation times, using a global screening methods including structural, metabolic and microanalytical analyses. Our results demonstrate that lidocaine is able to alter cell viability and function even at low concentrations and times, although the effect of lidocaine concentration was more important than the incubation time. First, the structural analysis methods revealed that ≥5% concentrations of lidocaine are able to significantly reduce cell viability. Then, the metabolic 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and water-soluble tetrazolium salt (WST-1) assays suggest that concentrations starting from 1% were able to significantly hinder cell physiology. Finally, electron-probe X-ray microanalysis confirmed the deleterious effects of lidocaine and allowed us to demonstrate that these effects are associated to an apoptosis process of cell death. Therefore, care should be taken when lidocaine is clinically used, and the lowest efficient concentrations should always be used. Furthermore, these results suggest that the comprehensive evaluation method used in this work is accurate and efficient for screening of local anesthetics.