Production of TNF-α by macrophages stimulated with endodontic pathogens and its effect on the biological properties of stem cells of the apical papilla

Objectives: The first objective of the present study was to investigate TNF-α secretion by macrophages stimulated with endodontic pathogens and bacterial cell surface components. The second objective was to assess the in vitro effects of TNF-α on periostin, cytokine, and matrix metalloproteinase (MMP) secretion by and the viability, proliferation rate, and mineralization potential of stem cells of the apical papilla (SCAP). Methods: TNF-α secretion by macrophages stimulated with either endodontic pathogens or bacterial surface components was assessed using an enzyme-linked immunosorbent assay (ELISA). The viability and proliferation rate of SCAP treated with TNF-α were assessed using a colorimetric MTT assay. The mineralization potential of TNF-α-treated SCAP was determined by Alizarin Red staining. Periostin secretion by SCAP was determined by ELISA while cytokine and MMP secretion were assessed using a multiplexing laser bead assay. Results: TNF-α secretion by macrophages increased following a stimulation with Gram-negative and Gram-positive endodontic pathogens. Lipopolysaccharide and lipoteichoic acid also dose-dependently increased the secretion of TNF-α by macrophages. The viability, proliferation rate, and mineralization activity of SCAP were negatively affected by a TNF-α treatment. Treating SCAP with TNF-α attenuated the secretion of periostin and upregulated the secretion of several cytokines and MMPs. Conclusions: TNF-α exerts deleterious effects on SCAP by affecting their viability, proliferation rate, and mineralization potential. By its ability to induce the secretion of pro-inflammatory cytokines and MMPs by SCAP, TNF-α can contribute to creating an inflammatory environment, promoting tissue destruction, and consequently interfering with the success of regenerative endodontic therapy. Clinical relevance: TNF-α has deleterious impacts on stem cells of the apical papilla and may compromise the outcome of regenerative endodontic therapy.