Pro-oxidant activity of vitamin C in drinking water ... - Ã bo Akademi

568P.J. Jansson et al.Figure 2. HPLC analysis of ascorbic acid induced hydroxylation of coumarin (100 mM) in the presence of copper or iron. 2 mM ascorbicacid was added to Milli-Q water buffered with 100 mg/l bicarbonate containing (A) 0.1 mg/l copper (B) 0.2 mg/l ferric iron. (C) Both 0.1 mg/lcopper and 0.2 mg/l ferric iron present. (D) Ascorbic acid standard (2 mM), 7-hydroxycoumarin standard (7 mM) and coumarin standard(100 mM) in Milli-Q water. Reaction time was 3 h.[27,28]. Here we show, by using coumarin-3-carboxylicacid as a fluorescent probe for detection of hydroxylradical formation, that even very low concentrations ofcopper (#0.1 mg/l) are sufficient to give a significanthydroxyl radical signal. However, when copper wassubstituted by iron, ascorbic acid was not capable tostimulate hydroxyl radical formation (Figure 1). Thiswas also demonstrated by using HPLC analysis. TheHPLC data clearly showed that coumarin, in Milli-Qwater supplemented with 100 mg/l bicarbonate, wasstrongly hydroxylated by ascorbic acid in the presence ofcopper ions but not in the presence of 0.2 mg/l iron alone(Figure 2A and B).Our results demonstrate that iron partly can inhibitthe ascorbic acid/copper driven hydroxyl radicalformation in a drinking water environment. When0.2 mg/l iron was added to the Milli-Q water that hadbeen supplemented with 100 mg/l bicarbonate and0.1 mg/l copper, the ascorbic acid induced formationof 7-hydroxycoumarin was inhibited by 47.5%(Figure 2C). Our results are in agreement with therecent report by White et al., demonstrating that ironcan impair reductant-mediated copper and H 2 O 2generation and neurotoxicity [29]. Moreover, ourresults are in line with the recent findings by Mundayet al. showing that copper-catalyzed cysteine oxidation