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

Discussionperoxide might have an impact on the urinary tract. 152, 220-222 Interestingly, there have beensuggestions that urinary hydrogen peroxide can be a marker of oxidative stress inmalignancies. 152, 217, 218, 223, 224 In particular, in the absence of Fe 3+ ions, ascorbic acid/Cu 2+ -induced hydrogen peroxide formation in drinking water as demonstrated in our study inpaper V, might enhance the total hydrogen peroxide load and hydrogen peroxide inducedoxidative stress in some individuals.4. Rapid decomposition of vitamin C (ascorbic acid) in bicarbonatebuffered copper-contaminated drinking waterIn paper III we wanted to see how rapidly and to what extent ascorbic acid can be oxidizedin a copper-contaminated drinking water sample. In line with paper II, the presence ofboth copper ions and bicarbonate was required for the degradation of ascorbic acid.Ascorbic acid degradation by copper as a catalyst has been well documented in parenteralmixtures and cooking of vegetables in copper-contaminated water. 225 In our study,approximately one-third of the ascorbic acid added (2 mM) to a sample that contained 150mg/l bicarbonate and 0.5 mg/l copper had been oxidized after 15 minutes and the vitaminwas almost completely (93%) oxidized within 3 hours. On the contrary, in another samplethat contained 26 mg/l bicarbonate and 0.2 mg/l copper, only 39% of the added ascorbicacid had been oxidized during the 3 h incubation.Low concentrations of vitamin C in gastric juice have been associated with Helicobacter pyloriinfection. The Helicobacter pylori infection is the main cause of chronic gastritis and increasesthe risk of gastric cancer. 226-228 Inflammation in the stomach induced by H. pylori causessignificantly enhanced depletion of vitamin C, but also reduces secretion of the vitamininto the gastric lumen. 229-231 On the other hand, it has not been studied whether vitamin Cconsumed with a copper/bicarbonate-rich water could be linked to low gastricconcentration of vitamin C, and increased susceptibility to H. pylori infection.When ascorbic acid was oxidized in the presence of copper ions, DHA was formed. Toverify that DHA was formed in our drinking water samples, we used dithiothreitol as areducing agent. 183, 184 Dithiothreitol turned DHA in the samples back into ascorbic acid.DHA has previously been shown to be spontaneously decomposed into L-diketogulonate(2,3-DKG) or erythroascorbate. 72, 232, 233 Our results indicated that DHA, and notdiketogulonate, was present in the sample. The DHA formation in the bicarbonate-richwater sample contaminated with copper was very rapid, as up to 650 µM DHA was formedwithin 15 min. The amount of DHA formed within 15 minutes in the various tap water45