PROOXIDANT-ANTIOXIDANT BALANCE IN THE METHYLOTROPHIC YEAST OGATAEA POLYMORPHA EXPOSED TO SPERMIDINE

Abstract

Background. Many molecular compounds used by eukaryotic cells as antioxidant agents can directly interact with reactive oxygen/nitrogen species. Among them are polyamines – natural substances with pronounced antioxidant properties. The main polyamines are putrescine, spermidine, spermine. Spermidine is a positively charged polyamine that is synthesized from putrescine and serves a precursor of spermine. In particular, spermidine is distinguished by its anti-aging properties. When administered to several model organisms, it prolonged their lifespan and provided resistance to stress. Spermidine also limits overproduction of reactive oxigene species and reduces age-related oxidative protein damage, which accounts for its antioxidant activity.
The aim of our study was to investigate the effects of exogenous spermidine in different concentrations on the prooxidant-antioxidant balance in the methylotrophic yeast Ogataea polymorpha naturally adapted to stressful conditions such as growth on toxic methanol-containing medium and cultivation at high temperatures (42–45 °C).
Materials and Methods. In this work, O. polymorpha wild-type strain was used. Yeast cells were cultivated in the mineral medium with 0.1 % glucose for creating stressful conditions. Spermidine was added in 1 and 2 mM concentrations immediately before the start of yeast cultivation. Reactive oxygen species, the level of oxidative modifications of proteins and lipids, the concentration of reduced gluthatione, superoxide dismutase and catalase activities were assayed to examine the prooxidant-antioxidant state of the yeast cells.
Results. In this study, we analyzed the effects of exogenous spermidine in different concentrations on the enzymatic (superoxide dismutase and catalase activity) and non-enzymatic (reduced glutathione) antioxidant defense systems and markers of oxidative injury (products of proteins and lipids oxidation) in the methylotrophic yeast O. polymorpha starved for glucose. It was revealed that 1 mM spermidine had a protective effect on O. polymorpha cells and decreased the content of products of the oxidative modification of proteins. At the same time, the superoxide dismutase and catalase activities and content of the reduced glutathione remained almost unchanged in the cells cultivated in the glucose-depleted medium with 1 mM spermidine compared to the medium without spermidine. Adverse effects of 2 mM spermidine (increased levels of carbonyl groups of proteins, lipid peroxidation products, disregulated superoxide dismutase and catalase activities, reduced glutathione levels, growth inhibition and cells vacuolization) were observed in the exponential growth phase of the yeast culture. During a long-term cultivation, these effects diminished, and the corresponding values approximated those of the cells grown in the control medium with the low concentration of glucose without spermidine.
Conclusions. The data suggest a concentration-dependent effect of spermidine on the physiology of O. polymorpha that can be used in further studies on compounds able to mitigate negative effects of the oxidative stress in this yeast and other model organisms. At 1 mM concentration, spermidine had an apparent protective effect, whereas at the elevated 2 mM concentration this polyamine exacerbated stress load in this yeast.