| Summary: | The massive production of nanomaterials has created new pollutants whose interaction with living organisms is unclear. Recent studies have revealed that these materials generate reactive oxygen species, causing cell damage, when antioxidant systems fail, fact which justifies its inclusion in toxicological studies. Thus, the aim of this study was to test if early exposure of Saccharomyces cerevisiae to 5 μg/mL of titanium dioxide nanoparticles (TiO2-NP, size < 100 nm), with heat shock, does not disturb its antioxidant response mediated by superoxide dismutase and catalase activity. S. cerevisiae UE-ME3, a wild-type strain belonging to Oenology Laboratory of the University of Évora were grown in YEPG medium (3% glycerol) at 28 °C. At middle-exponential phase 2% glucose (YEPGD) and/or 5 μg/mL TiO2-NP stock solution were added and cells were grown for 200 min at 28 °C or 40 °C (heat-shock, ST). Culture medium lacking glucose or NPs served as control samples. At the end of the experiment, the dry weight was determined and remaining cells were disintegrated in 10 mM phosphate buffer pH 7.0 by ultra-sonication. The post-12,000 × g supernatant was used for determination of MDA content and catalase (CTT1) and superoxide dismutase (SOD1) activity. The pellet was used for determination of activities catalase (CTA1) and superoxide dismutase (SOD2). The results showed that the presence of glucose in the medium caused an increase of biomass, a decrease in the MDA content and CTT1 activity without change CTA1, SOD1 and SOD2 activity. Additionally, it was determined an increase in CTA1, SOD1 and SOD2 activity in the cells grown in YEPGD-ST medium. The NP-TiO2 exposure with ST, decreased CTT1 activity for similar levels to those estimated in the cells grown in YEPGD medium with nanoparticles, did not affect the CTA1 and SOD1 activity, increased the MDA level and kept the SOD2 activity in similar levels to those detected in cells grown in YEPGD-ST medium. The decrease in the CTT1 activity caused by NPs may justify, in part, the increase in MDA level.
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