Characterization of oxidative stress and antioxidant’s potency: Pay attention to time and location

Most of the commonly used assays of oxidative stress (OS) are based on the level of the studied biomarker, as measured at one time-point. OS, as evaluated with different assays do not correlate with each other, so that OS cannot be defined in universal terms. Furthermore, some biomarkers are not very stable in withdrawn blood and their level may depend on whether their level is measured immediately after being withdrawn or a half an hour later, particularly if the assay involves a stage of pretreatment. Most assays of antioxidants are conducted in solutions, whereas in biological systems amphiphilic phospholipids reside either in membranes or in emulsion micro-emulsion particles (lipoproteins) and peroxidation therefore occurs at the lipid-water interface. This, in turn, means that the relative activities of different antioxidants should be assayed in the medium of interest. Hence, an assay utilized to compare antioxidants in the search for improved inhibitors of peroxidation used as stabilizers of food-stuff, may have to be considerably different from the assay to be used in the search for antioxidants that will maximize the shelf life of a given drug. We propose evaluating oxidative status based on the length of the lag preceding copper-induced peroxidation of serum lipids and ranking antioxidants on the basis of the concentration of antioxidant required to double the lag.