Peroxidase-Thiocyanate-Peroxide Antibacterial System Does Not Damage DNA

Abstract

The hypothiocyanite ion (OSCN - ) is a normal component of human saliva. It is a highly reactive oxidizing agent, and at concentrations above the values normally found in human saliva, it inhibits the growth and metabolism of oral bacteria. This finding has led to the suggestion that antibacterial properties of human saliva might be enhanced in vivo by appropriate supplements which elevate OSCN - concentrations. Since DNA is sensitive to oxidizing agents (hydrogen peroxide attacks nucleosides), high concentrations of OSCN - in human saliva might damage DNA and produce deleterious effects on the oral mucosa. In the present study, the effect of high OSCN - concentrations on several mutagen-sensitive Salmonella typhimurium strains was determined. These strains are used to detect base-pair substitutions and frameshift mutations. We also studied the effects of OSCN - on a Saccharomyces cerevisiae (yeast) strain commonly employed as a test cell for evaluating the potential of a compound to produce gene conversion, mitotic crossing-over, or reverse mutation. By recording the UV spectra of mixtures of calf thymus DNA and OSCN - , we explored the possible in vitro reactions of this oxidizing agent with eucaryotic genetic material. Our results show that, at concentrations above 10 μM, OSCN - is toxic for the tested Salmonella typhimurium strains. The mutant strains with defects in cell wall lipopolysaccharides are killed more readily by OSCN - than is the strain lacking these defects. However, OSCN - was not mutagenic for any of the tested strains. Saccharomyces cerevisiae was not affected by OSCN - even at concentrations above 800 μM. Calf thymus DNA was not oxidized by OSCN - . We conclude that the elevated concentrations of OSCN - required to produce antibacterial effects in the human mouth pose no threat to the genetic material of host tissues.