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. 2020 Oct 27;21(21):7993.
doi: 10.3390/ijms21217993.

Are Metal Ions That Make up Orthodontic Alloys Cytotoxic, and Do They Induce Oxidative Stress in a Yeast Cell Model?

Vito Kovač  1 , Borut Poljšak  1 , Jasmina Primožič  2 , Polona Jamnik  3
Affiliations

Are Metal Ions That Make up Orthodontic Alloys Cytotoxic, and Do They Induce Oxidative Stress in a Yeast Cell Model?

Vito Kovač et al. Int J Mol Sci. .

Abstract

Compositions of stainless steel, nickel-titanium, cobalt-chromium and β-titanium orthodontic alloys were simulated with mixtures of Fe, Ni, Cr, Co, Ti and Mo metal ions as potential oxidative stress-triggering agents. Wild-type yeast Saccharomyces cerevisiae and two mutants ΔSod1 and ΔCtt1 were used as model organisms to assess the cytotoxicity and oxidative stress occurrence. Metal mixtures at concentrations of 1, 10, 100 and 1000 µM were prepared out of metal chlorides and used to treat yeast cells for 24 h. Every simulated orthodontic alloy at 1000 µM was cytotoxic, and, in the case of cobalt-chromium alloy, even 100 µM was cytotoxic. Reactive oxygen species and oxidative damage were detected for stainless steel and both cobalt-chromium alloys at 1000 µM in wild-type yeast and 100 µM in the ΔSod1 and ΔCtt1 mutants. Simulated nickel-titanium and β-titanium alloy did not induce oxidative stress in any of the tested strains.

Keywords: cytotoxicity; lipid oxidation; metal ion; orthodontic appliances; oxidative stress; yeast.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Cell culturability, expressed as CFU/mL, of yeast cells treated with different compositions and concentrations of metal ions. Wild-type yeast and two yeast mutants ΔSod1 and ΔCtt1 were subjected to metal ions simulating (A) stainless steel, (B,C) cobalt-chromium Elgiloy and Remaloy, (D) nickel-titanium, and (E) β-titanium alloys. The box-plots (A1–E1) show an absolute values of CFU/mL, while the grouped columns (A2–E2) present relative values according to the untreated control group. The untreated control group is set at 100%, and the dotted line represents 100% culturability. Significant differences (p < 0.05 are indicated with * (* p < 0.05, ** p < 0.01, *** p < 0.001, and **** p < 0.0001).
Figure 2
Figure 2
Metabolic activity of wild-type yeast and two yeast mutants ΔSod1 and ΔCtt1 treated with different combinations of metal ions: stainless steel (A), cobalt-chromium Elgiloy (B), Remaloy (C), nickel-titanium (D), and β-titanium (E). For each yeast strain, the untreated control group represents 100% (dotted line). A comparison among untreated control groups of each yeast strain is shown in the graph (F).
Figure 3
Figure 3
Intracellular oxidation performed with two different methods for wild-type yeast and two yeast mutants ΔSod1 and ΔCtt1, and metal treatment: stainless steel (A), cobalt-chromium Elgiloy (B) and Remaloy (C), nickel-titanium (D) and β-titanium (E). Grouped columns represent either absolute values (A1–E1) or relative values according to the untreated control group (A2–E2). For each yeast strain, the untreated control group represents 100% (dotted line). Significant differences (p < 0.05) are indicated with * (* p < 0.05, ** p < 0.01, *** p < 0.001, and **** p < 0.0001).
Figure 4
Figure 4
Influence of 24-h metal treatment on the formation of oxidative lipid damage. Wild-type, ΔSod1, and ΔCtt1 yeast strains were treated with different concentrations of stainless steel (A), cobalt-chromium Elgiloy (B) and Remaloy (C), nickel-titanium (D), and β-titanium (E). Graph (F) compares untreated control groups of different yeast strains relative to the wild type. Significant differences (p < 0.05) are indicated with * (* p < 0.05, ** p < 0.01 and **** p < 0.0001).
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