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

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ResultsRESULTS1. Vitamin C induces hydroxyl radicals in household drinking water[Paper I]Vitamin C induced hydroxyl radical generation was studied in drinking water samples bymeasuring the formation of 7-OHCCA from coumarin-3-carboxylic acid. A markeddifference in hydroxyl radical formation was observed over time in the drinking watersamples supplemented with 2 mM vitamin C. The highest value, observed among the 22household tap waters that were screened for hydroxyl radical formation, was around 920nM of 7-OHCCA as compared to 20 nM of 7-OHCCA in the water sample that gave thelowest signal after a 3 h incubation period with vitamin C. In general, hydroxyl radicalformation was lower in waters obtained from private wells as compared to wateroriginating from public water systems. The lowest hydroxyl radical formation was found indomestic sold bottled water.The hydroxyl radical formation in household drinking water supplemented with vitamin Ccould also be demonstrated using a DNA nicking assay. The hydroxylation observed invitamin C supplemented drinking water demonstrated by the coumarin-3-carboxylic acidmicroplate assay was in good agreement with the DNA nicking assay.The hydroxyl radical formation in the tap-water samples was strongly dependent on theflushing time before the samples were taken. The formation of 7-OHCCA within 3 h wasremarkably decreased when the faucet was flushed for 5 min (from 710 nM to 70 nM). Inthis water sample the copper concentration decreased from 1.85 mg/l measured in the firstdrawn to 0.07 mg/l by flushing the faucet for 5 min. On the other hand, flushing did notdecrease the formation of 7-OHCCA to the same extent in another sample originatingfrom a different public water system (from around 760 nM to close to 500 nM). In thissample, the copper concentration decreased from 1.24 mg/l to 0.18 mg/l.2. Ascorbic acid induced hydroxyl radical formation in drinking water isdependent on copper ions and bicarbonate [Paper II]In paper I we observed that addition of ascorbic acid to some tap water samplescontaminated with copper ions could induce hydroxyl radical formation. In paper II it wasobserved that the amount of copper ions present in the water samples did not alwayscorrelate with the amount of hydroxyl radicals generated after ascorbic acid addition.33
ResultsTherefore, in paper II we wanted to identify the compounds that might be involved in theascorbic acid induced hydroxyl radical generating reaction observed earlier in drinkingwater.To achieve this, we continued our work on two water samples. These samples had beentaken in the same way, directly drawn from the tap, but originating from two differentmunicipal water suppliers. Ascorbic acid supplementation led to high amounts ofhydroxylated coumarin-3-carboxylic acid in the first sample (above 800 nM) within 3 h. Inthe other sample, however, hardly any hydroxyl radical formation could be detected afterascorbic acid addition (around 10 nM). When 2 mM ascorbic acid and 200 µM coumarin-3-carboxylic acid were added, the pH in the first drinking water sample decreased rapidlyfrom 7.6 to 5.8 and stabilized at a new pH value close to 6.4. In contrast, when ascorbicacid and coumarin-3-carboxylic acid were added to the other drinking water sample, amuch deeper drop in the pH value could be seen. Here, the pH decreased rapidly from 7.2to 3.8 and remained under pH 4.0.Anion analysis by HPLC revealed that the drinking water sample generating higheramounts of hydroxyl radicals contained around 90 mg/l of both bicarbonate and chloride.In contrast, the other drinking water sample showed much lower concentrations ofbicarbonate and chloride, 30 mg/l and 10 mg/l respectively. No other anions could bedetected in the water samples tested (fluoride, nitrite, nitrate, bromide, phosphate orsulphate ions).The ascorbic acid induced hydroxyl radical formation was highly dependent on thebicarbonate concentration (buffer capacity) in the water samples. This could bedemonstrated using Milli-Q water supplemented with 2 mM ascorbic acid, 0.5 mg/l copperand increasing concentrations of bicarbonate. At 50 mg/l bicarbonate a prompt increase inthe hydroxyl radical formation was observed. The highest amount of 7-OHCCA wasobtained when 100 mg/l bicarbonate was added to the copper supplemented Milli-Q watersample. In the samples that contained 50 mg/l bicarbonate or more, a higher pH valuecould be measured. In contrast to ascorbic acid, the sodium-, calcium-, and magnesiumsalts of ascorbic acid could readily trigger hydroxyl radical formation in copper containingMilli-Q water even in the absence of bicarbonate. In the presence of bicarbonate, sodiumascorbate triggered the highest yield of hydroxylated coumarin-3-carboxylic acid at pH 5.0.At higher pH values the signal was lower.34
Page 1 and 2: Pro-oxidant activity of vitamin C i
Page 3 and 4: Supervised byDocent Tommy Nordströ
Page 5 and 6: ContentsCONTENTSLIST OF ORIGINAL PU
Page 8 and 9: List of original publicationsLIST O
Page 10 and 11: AcknowledgementsACKNOWLEDGEMENTSThi
Page 12 and 13: AbbreviationsABBREVIATIONSAsc …
Page 14 and 15: Review of the literatureREVIEW OF T
Page 16 and 17: Review of the literatureSince vitam
Page 18 and 19: Review of the literaturestill added
Page 20 and 21: Review of the literatureantioxidant
Page 22 and 23: Review of the literatureThe α-toco
Page 24 and 25: Review of the literatureCopper, wil
Page 26 and 27: Review of the literatureOH • + H
Page 28 and 29: Review of the literatureFormation o
Page 30 and 31: Review of the literature3.2. The ro
Page 32 and 33: Review of the literaturecopper conc
Page 34 and 35: Experimental proceduresEXPERIMENTAL
Page 36 and 37: Experimental procedures2.2. Measure
Page 38 and 39: Experimental procedurestetrahydrate
Page 42 and 43: Results3. Oxidative decomposition o
Page 44 and 45: Resultsdifferent water samples vari
Page 46 and 47: DiscussionDISCUSSIONNowadays, ascor
Page 48 and 49: DiscussionCu 2+ + Asc → Cu + + As
Page 50 and 51: Discussion3. Iron inhibits vitamin
Page 52 and 53: Discussionperoxide might have an im
Page 54 and 55: ConclusionsCONCLUSIONSThe main focu
Page 56 and 57: ReferencesREFERENCES1. Arrigoni O,
Page 58 and 59: References34. Padayatty SJ, Katz A,
Page 60 and 61: References66. Sies H, Stahl W, Sund
Page 62 and 63: References95. Halliwell B. Role of
Page 64 and 65: References127. Park S, Han SS, Park
Page 66 and 67: References157. Critchley MM, Cromar
Page 68 and 69: References185. Liao CH, Kang SF, Wu
Page 70 and 71: References214. Orr CW. Studies on a
Page 72: References243. Miller C, Kennington
Page 88 and 89: Free Radical Research, Volume 38 Nu
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VITAMIN C OXIDATION IN DRINKING WAT
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VITAMIN C OXIDATION IN DRINKING WAT
Page 94 and 95:
Free Radical Research, May 2005; 39
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Iron inhibits Vitamin C/copper-indu
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Iron inhibits Vitamin C/copper-indu
Page 100 and 101:
Free Radical Research, November 200
Page 102 and 103:
Hydrogen peroxide formation in drin
Page 104 and 105:
Page 106 and 107:
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