Oral malodorous compound causes caspase-8 and-9 mediated programmed cell death in osteoblasts

Background and Objective: Hydrogen sulfide (H2S) is one of two volatile sulfur compounds that are known to be the main cause of oral malodor; the other is methyl mercaptan. Other known volatiles existing in mouth air do not contribute significantly to oral malodor originating in the oral cavity. Hydrogen sulfide is also known to be an etiological factor in periodontal disease. However, the effects of H2S on alveolar bone remain unclear. The objectives of this study were to determine the apoptotic effects of H2S on osteoblasts and to verify the apoptotic molecular pathways. Material and Methods: A clonal murine calvaria cell line was incubated with 50 ng/ mL of H2S. To detect apoptosis, the cells were analysed by flow cytometry and ELISA. Mitochondrial membrane depolarization was assessed using flow cytometry as well. ELISA was used to evaluate the release of cytochrome c into the cytosol and to assess Fas ligand, p53, tumor necrosis factor a, interleukin IL1-a IL-b, IL-2, IL-4, IL-10, interferon-c, granulocyte-colony stimulating factor and granulocyte-macrophage colony stimulating factor. Caspase-3, -8 and -9 activities were estimated. Expression of BAX and Bcl-2 was assessed by real-time quantitative RT-PCR. DNA fragmentation was detected by single-cell gel electrophoresis. Fas receptors were evaluated by western blotting. Results: After H2S incubation, apoptotic levels increased significantly in a time-dependent manner. Mitochondrial membrane depolarization, the release of cytochrome c, p53 and caspase-3, -8 and -9 and DNA fragmentation were all significantly greater. BAX gene activity was upregulated, whereas Bcl-2 remained low. Fas ligand/ Fas receptor, tumor necrosis factor a and other cytokines were not increased to a significant degree. Conclusion: At less-than-pathological concentrations in gingival crevicular fluid, H2S induces apoptosis in osteoblasts. The molecular mechanisms underlying the apoptotic process include p53, a mitochondrial pathway and caspase-8 activation.