Toxicity of Metal Ions Used in Dental Alloys: A Study in the YeastSaccharomyces cerevisiae

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Abstract
Metal ions are released from dental alloys into the oral environment, which can cause biological responses over short and extended periods. Since most toxic metal ions are capable of inducing oxidative stress on cells through the mitochondrial respiratory chain, mitochondria may contribute to and be a target of metal toxicity. In this study, we investigated the effect of metal ions on growth of the budding yeast, Saccharomyces cerevisiae, and on the morphology and function of yeast mitochondria. Moreover, we tested whether mitochondrial respiratory activity contributes to metal toxicity. Metal ions affected yeast cell growth. The toxicity of metal ions to yeast cells, ranked in decreasing order are as follows: Hg>Ag>Au>Cu, Ni, Co, Zn. This result mostly correlates with the degree of toxicity of those metal ions to growth of human cells. The MIC90 of Hg, Ag and Au ions in synthetic complete media are 0.325, 5 and 320 µM, respectively. None of the toxic metal ions resulted in loss of mitochondrial respiratory activity. However, respiration-deficient rho0 cells appeared to be resistant to Ag ion, but not to Hg and Au ions. Furthermore, at high concentrations, Ag ion caused morphological changes in mitochondria. These studies indicate that yeast may be used as a model system to screen for toxic effect of metals ions from dental alloys, and that oxidation activity in mitochondria may play a role in acute toxicity of silver ion.