The protective effect of peroxidase and thiocyanate against hydrogen peroxide toxicity assessed by the uptake of [3H]-thymidine by human gingival fibroblasts cultured in vitro.
The hypothiocyanite ion (OSCN-) is the principal oxidation product of the salivary peroxidase-thiocyanate (SCN-)-hydrogen peroxide antimicrobial system. Supplementation of human saliva in vitro and in vivo with low amounts (less than 1.0 mM) of hydrogen peroxide increase the concentration of salivary OSCN- (in vivo up to 0.3 mM). Elevated concentrations of OSCN- are strongly antimicrobial and may therefore be protective against dental caries. However, as OSCN- is a highly-reactive oxidizing agent, its possible toxic effect on human cells was studied using gingival fibroblasts as target cells. Concentrations of OSCN- (up to 300 microM) had no effect on [3H]-thymidine incorporation into the cells. However, fibroblasts were sensitive to peroxide so that 100 microM of H2O2 caused over 80 per cent reduction in [3H]-thymidine incorporation. The toxicity of H2O2 could be entirely prevented by adding lactoperoxidase and SCN- to the cell culture before the addition of peroxide. Thus, conversion of toxic H2O2 to non-toxic OSCN- in fibroblast culture by lactoperoxidase and SCN- suggests a dual role for the salivary peroxidase system: protection of human cells from H2O2 toxicity and antimicrobial action against oral pathogens. Furthermore, the elevated concentrations of OSCN- which produce inhibition of bacterial metabolism did not damage human cells.
D000328:Adult; D002478:Cells, Cultured; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism; D005881:Gingiva / Q000166:cytology / Q000187:drug effects*; D006801:Humans; D006861:Hydrogen Peroxide / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D007784:Lactoperoxidase / Q000494:pharmacology*; D008297:Male; D010544:Peroxidases / Q000494:pharmacology*; D013861:Thiocyanates / Q000378:metabolism / Q000494:pharmacology*; D013936:Thymidine / Q000378:metabolism
D013861:Thiocyanates; C014607:hypothiocyanite ion; D006861:Hydrogen Peroxide; D007784:Lactoperoxidase; D010544:Peroxidases; C009941:potassium thiocyanate; D013936:Thymidine