Anti- and pro-oxidative activity measured directly as the extent of 8-oxoguanine production

An electrochemical method was developed for the evaluation of antioxidant activity based on the ability to inhibit 8‐oxoguanine production. It consists of a sequence of successive potential hold and scan steps, in which superoxide anion radical is generated by the reduction of dioxygen in a potential hold step in a buffer solution containing guanine and antioxidant, immediately followed by a potential scan step, in which 8-oxoguanine is detected and its amount determined. The effect of 11 antioxidants, among them simple alcohols for comparison, was investigated in pH 7 and pH 9 phosphate buffers saturated with guanine. The plots of 8-oxoguanine peak height, expressed as percent of the peak current in the absence of antioxidants, versus antioxidant concentration showed an exponential decay character. The decay parameter may be used as a measure of antioxidant activity. It is directly related to the IC50 coefficient used in other methods Only simple alcohols displayed single decay character. Other studied substances showed multi-exponential decay at pH 7, most investigated antioxidants were unable to entirely inhibit the generation of 8-oxoguanine, but led to a steady state of 8-oxoguanine level. At pH 9, many antioxidants, particularly polyphenolics and ascorbyl phosphate, showed pure pro-oxidant activity.

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