An Approach to Determine the Efficacy of Functional foods on Oxidative Stress Using Yeast as a Model System

Abstract

Faculty of Applied Sciences and Biotechnology newlineAbstract Cellular metabolism generates different reactive species of oxygen, sulfur and nitrogen which are highly unstable and reactive towards biomolecules like DNA, protein and lipids. Interaction between reactive species and biomolecules can cause physiological changes and pathological defects in concentration dependent manner. Antioxidant defence system of the cells mitigates the defects of free radicals by scavenging them. Peroxiredoxins (Prxs), counteract cellular peroxides by forming recyclable disulfides but under oxidative stress, hyperoxidation of their active-site Cys residue result in loss of their peroxidase activity. Saccharomyces cerevisiae deficient in human Prx (hPrx) ortholog TSA1 can be complemented with hPRXI but not by hPRXII, but it is not clear how the disulfide and hyperoxidation states of the hPrx vary under oxidative stress. To understand this, herein we used oxidative stress sensitive tsa1tsa2and#916; yeast strain to express hPRXI or hPRXII. We found that hPrxI in yeast exists as a mixture of disulfide linked dimer and reduced monomer but becomes hyperoxidized upon elevated oxidative stress. In contrast, hPrxII was predominantly dimeric in unstressed cells and was converted to a non hyperoxidized, peroxidase inactive monomer even with mild oxidative stress. Interestingly, we found that plant extracts containing antioxidants provided further protection against the growth defects of the tsa1tsa2and#916; strain expressing hPrx and preserved the peroxidase active forms of the Prxs. Antioxidants in extracts also helped to protect against hyperoxidation of hPrxs in HeLa cells. Based on these findings we hypothesize that protection by the hPrxs requires them to be maintained in a redox state that permits redox cycling and peroxidase activity. newline