Prevention of a systematic underestimation of antioxidant activity in competition assays. The impact of unspecific reactions of the reactive species |
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| Authors: | Christiaan P. Beljaars |
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| Affiliation: | Department of Pharmacology and Toxicology, Faculty of Health, Medicine and Life Sciences, Maastricht University, 6200 MD Maastricht, The Netherlands |
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| Abstract: | In antioxidant competition assays, an antioxidant (A) and a detector compound (D) compete for a reactive species (R). In the evaluation of these assays, it is tacitly assumed that all of R is captured by either D or A. Due to the - by definition - high reactivity of R, unspecific reactions of R are likely to occur and neglecting these reactions will result in a systematic underestimation of antioxidant activity. It was shown that in the standard hydroxyl radical scavenging assay this was indeed the case; the inaccurate mathematical evaluation resulted in an underestimation of antioxidant activity of 25% in this competition assay. The systematic underestimation of antioxidant activity can be prevented by using an adjusted Stern-Volmer equation that takes into account that only part of R is captured by D or A. |
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| Keywords: | A, antioxidant D, detector compound R, reactive species S, signal measured in the competition assay derived from the reaction of the reactive species with the detector SA=0, baseline signal obtained in the competition assay without the antioxidant Smax, signal obtained when all of R is captured by the detector ka, the second order reaction rate constant of the antioxidant with the reactive species kd, the second order reaction rate constant of the detector molecule with the reactive species kx, the pseudo first order reaction rate constant of the parallel reactions of the reactive species EC50, concentration of antioxidant that reduces the signal in the competition assay by 50% MDA, malondialdehyde |
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