Modulation of human gingival fibroblast cell metabolism by methyl mercaptan

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Abstract
Methyl mercaptan (CH3SH) is a malodorous compound whose levels are elevated in mouth and crevicular air of individuals with active periodontal disease. Since it may play a role in the disease process, its effects were evaluated using human gingival fibroblast cultures and viable porcine unkeratinized oral mucosal tissue sections. Results showed that the protein content of CH3SH‐exposed cell cultures pulsed with [14C]‐labelled glycine and proline was decreased by approximately 25%. Furthermore, this deleterious effect was irreversible in test cultures subsequently incubated for 24 h in a control 95% air/5% CO2mercaptan‐free environment. The supporting slab‐gel electrophoresis profiles yielded evidence that exposure to CH3SH caused an alteration in collagen metabolism and a pooling of Type I procollagens. In addition, DNA synthesis was suppressed in CH3SH‐exposed cultures by 44.1% at the 24 to 26 h peak of DNA synthesis. This is a true inhibition and not a shift in peak of maximum DNA synthesis as the shape and location of time‐course curves of control and test systems is very similar. Proline transport study using [14C]‐proline indicated a reduction in proline transport in the range of 40 to 50% in cultures exposed for 24 to 30 h to CH3SH. Significantly even 15 min exposure to 6.7 ng CH3SH/ml of incubating atmosphere suppressed proline transport by approximately 24%). This indicates that even brief exposure to low concentrations of CH3SH has a significant adverse effect on proline transport. Fluorescent staining of tissue sections exposed to mercaptan indicated that the agent elevated the number of cells stained with vital dye. The results demonstrate that CH3SH at concentrations employed in this study significantly decreased total protein content, collagen content, DNA synthesis and proline transport in fibroblast cell cultures, as well as exerting an adverse effect on the cellular integrity of intact oral mucosal tissues.