Abstract
The effects of several well-known natural and synthetic antioxidants on free radical production and oxygen uptake in rat liver mitochondria were measured. Ample concentration ranges (10−7 to 10−3 M) were explored in the search for stimulatory or inhibitory effects on both free radical production and oxygen uptake. The selected antioxidants are frequently present in foods, therapeutic formulations and supplements. Of the sixteen antioxidants, six of them increased free radical production in mitochondria at least over a certain concentration range, namely ascorbic acid, BHA, BHT, vanillic acid, caffeic acid and gallic acid. The last three inhibited free radical generation in the high concentration range. Several of the selected antioxidants behaved as inhibitors of energy metabolism at the concentrations causing 50% diminution of free radical production. The best inhibitors of free radical production in mitochondria were: resveratrol ≈ chlorogenic acid > epicatechin > rutin > ferulic acid. No significant correlations were found between the antioxidant strength in mitochondria and chemical systems nor was there any correlation between the antioxidant strength and the number of aromatic hydroxyls. Quantification of the free radical scavenging activity of a given compound or extract in chemical systems only exceptionally allows to infer its strength in mitochondria. It is proposed that the mitochondrial antioxidant assay should be used in addition to chemical assays when testing antioxidant preparations.
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