EFFECT OF VOLATILE THIOL COMPOUNDS ON PROTEIN-METABOLISM BY HUMAN GINGIVAL FIBROBLASTS

The levels of volatile sulphur compounds (VSC) in periodontal pockets and mouth air have been found to correlate with severity of the disease process. The purpose of this study was to examine the influence of hydrogen sulphide and methyl mercaptan on protein metabolism of human gingival fibroblasts. The incorporation of labelled amino acids into protein was used to evaluate effects on total protein content. Changes in collagenous protein concentration were monitored by release of radioactivity following collagenase digestion as well as direct analysis of hydroxyproline. Both thiols were found to reduce total protein synthesis, with mercaptan exerting a greater adverse effect. In cultures exposed to mercaptan, total protein was reduced by 35%. The changes in total protein were accompanied by a corresponding decrease in collagenase-digestible protein. Hydroxyproline analysis of CH3SH-exposed cultures confirmed the changes associated with collagenous proteins. It indicated that in comparison to the controls the CH3SH-exposed cultures had a 70% reduction in collagen which resulted from a combined effect of suppressed synthesis and increased rate of collagen degradation. The possibility of thiol reaction with collagen was determined using in vitro systems in which type I collagen was reacted with varying concentrations of [S-35]-H2S. The carboxymethyl (CM) cellulose assays of resulting reaction mixtures indicate that [S-35]-radioactivity was incorporated directly into alpha1, alpha2, beta11, beta12 peptide chains. Furthermore, upon exposure of collagen to elevated H2S concentrations, the H2S converted some of the acid-soluble collagen to a more soluble product which could be extracted in neutral salt and analyzed by CM-cellulose chromatography. This effect on collagen solubility may make it more susceptible to enzymatic degradation and contribute to the increased destruction of collagen observed in the thiol-treated fibroblast cultures.