| Summary: | Ascorbic acid (AA) has antioxidant properties. However, in the presence of Fe<sup>2+</sup>/Fe<sup>3+</sup> ions and H<sub>2</sub>O<sub>2</sub>, it may behave as a pro-oxidant by accelerating and enhancing the formation of hydroxyl radicals (<sup>•</sup>OH). Therefore, in this study we evaluated the effect of AA at concentrations of 1 to 200 µmol/L on <sup>•</sup>OH-induced light emission (at a pH of 7.4 and temperature of 37 °C) from 92.6 µmol/L Fe<sup>2+</sup>—185.2 µmol/L EGTA (ethylene glycol-bis (β-aminoethyl ether)-N,N,N′,N′-tetraacetic acid)—2.6 mmol/L H<sub>2</sub>O<sub>2</sub>, and 92.6 µmol/L Fe<sup>3+</sup>—185.2 µmol/L EGTA—2.6 mmol/L H<sub>2</sub>O<sub>2</sub> systems. Dehydroascorbic acid (DHAA) at the same range of concentrations served as the reference compound. Light emission was measured with multitube luminometer (AutoLumat Plus LB 953) for 120 s after automatic injection of H<sub>2</sub>O<sub>2</sub>. AA at concentrations of 1 to 50 µmol/L and of 1 to 75 µmol/L completely inhibited light emission from Fe<sup>2+</sup>-EGTA-H<sub>2</sub>O<sub>2</sub> and Fe<sup>3+</sup>-EGTA-H<sub>2</sub>O<sub>2</sub>, respectively. Concentrations of 100 and 200 µmol/L did not affect chemiluminescence of Fe<sup>3+</sup>-EGTA-H<sub>2</sub>O<sub>2</sub> but tended to increase light emission from Fe<sup>2+</sup>-EGTA-H<sub>2</sub>O<sub>2</sub>. DHAA at concentrations of 1 to 100 µmol/L had no effect on chemiluminescence of both systems. These results indicate that AA at physiological concentrations exhibits strong antioxidant activity in the presence of chelated iron and H<sub>2</sub>O<sub>2</sub>.
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