Exposure of Periodontal Ligament Cells to Methyl Mercaptan Reduces Intracellular pH and Inhibits Cell Migration

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Abstract
Volatile sulfur compounds such as hydrogen sulfide and methyl mercaptan have been associated with adult periodontitis as well as with healing surgical wounds. To examine the effects of these compounds on the periodontium, we assayed periodontal ligament (PDL) cells for changes in intracellular pH, total protein, and cell migration following chronic exposure to CH3SH. Intracellular pH was quantitated by fluorescence measurements of cells loaded with BCECF, a pH-sensitive dye. Data show that 48-hour exposure to mercaptan lowered resting intracellular pH but did not consistently alter activity of the Na/H exchanger. This effect was seen in PDL cells from three different patients. Lowered pH was accompanied by decreases in both total protein and mature α1 and α2 chains of type I collagen. Since reductions in intracellular pH and total protein have been associated with inhibition of cell motility, migration was quantitated by sequential computer imaging, which measured the increase in size of plated cell circles at different times of migration. Incubation of PDL cells in pH 7.4 and 6.6 buffers reversibly altered intracellular pH. Migration was reversibly inhibited in pH 6.8 buffer. Exposure to CH3SH reduced intracellular pH in pH 7.4 buffer and in three independent assays inhibited enlargement of cell circles in pH 7.4 medium. These effects were therefore not related to alterations of extracellular pH, which remained at 7.4. The results support the hypothesis that gases such as methyl mercaptan may play a role in both surgical wound healing and periodontal disease by adversely affecting cell function and suggest that alterations in intracellular pH may be part of the mechanism for these changes.