Dietary Protection Against Free Radicals: A Case for Multiple Testing to Establish Structure-activity Relationships for Antioxidant Potential of Anthocyanic Plant Species

Abstract

DNA damage by reactive species is associated with susceptibility to chronic human degenerative disorders. Anthocyanins are naturally occurring antioxidants, that may prevent or reverse such damage. There is considerable interest in anthocyanic food plants as good dietary sources, with the potential for reducing susceptibility to chronic disease. While structure-activity relationships have provided guidelines on molecular structure in relation to free hydroxyl-radical scavenging, this may not cover the situation in food plants where the anthocyanins are part of a complex mixture, and may be part of complex structures, including anthocyanic vacuolar inclusions (AVIs). Additionally, new analytical methods have revealed new structures in previously-studied materials. We have compared the antioxidant activities of extracts from six anthocyanin-rich edible plants (red cabbage, red lettuce, blueberries, pansies, purple sweetpotato skin, purple sweetpotato flesh and Maori potato flesh) using three chemical assays (DPPH, TRAP and ORAC), and the in vitro Comet assay. Extracts from the flowering plant, lisianthus, were used for comparison. The extracts showed differential effects in the chemical assays, suggesting that closely related structures have different affinities to scavenge different reactive species. Integration of anthocyanins to an AVI led to more sustained radical scavenging activity as compared with the free anthocyanin. All but the red lettuce extract could reduce endogenous DNA damage in HT-29 colon cancer cells. However, while extracts from purple sweetpotato OPEN ACCESSInt. J. Mol. Sci. 2009, 10 1082 skin and flesh, Maori potato and pansies, protected cells against subsequent challenge by hydrogen peroxide at 0 o C, red cabbage extracts were pro-oxidant, while other extracts had no effect. When the peroxide challenge was at 37 o C, all of the extracts appeared prooxidant. Maori potato extract, consistently the weakest antioxidant in all the chemical assays, was more effective in the Comet assays. These results highlight the dangers of generalising to potential health benefits, based solely on identification of high anthocyanic content in plants, results of a single antioxidant assay and traditional approaches to structure activity relationships. Subsequent studies might usefully consider complex mixtures and a battery of assays.

Red cabbage anthocyanins may protect blood plasma proteins and lipids

“…Their observations indicated that the red cabbage extracts might not engage in antioxidative protection against H 2 O 2 action, and might instead behave as pro-oxidants. Contrary to the results of Philpott et al [46], we found the ATH extract from red cabbage demonstrated antioxidative properties and partly protected blood plasma proteins, as well as lipids, against H 2 O 2 -induced damage. To exclude the possibility of direct interactions between ATH extract and plasma components, control experiments using blood plasma and the tested extract only (no addition of ONOO -or H 2 O 2 ) were performed; no pro-oxidative effects of the tested ATH were found (data not presented).…”

“…Philpott et al [46] underlined the dangers of generalizing to potential health benefits based solely on identification of high ATH content in plants, or other similar approaches. Their observations indicated that the red cabbage extracts might not engage in antioxidative protection against H 2 O 2 action, and might instead behave as pro-oxidants.…”

Inhibition or Enhancement by 4 Pacific Island Food Plants Against Cancers Induced by 2 Amino–3-Methylimidazo[4,5-f]Quinoline in Male Fischer 344 Rats

“…Kumara was by far the most important vegetable in the Maori diet in early New Zealand and is still widely eaten today. There are a number of chemical constituents of the tubers that could be protective (20,25,26). Although only 1% of the chemical constituents are protein, nevertheless these proteins may have some important properties.…”

Antimutagenesis Studies: Where Have They Been and Where Are They Heading?

“…Exogenous dietary antioxidants interact with endogenous antioxidants to form a cooperative network of cellular antioxidants, including free radical scavengers. A range of cell types also contain enzymatic cellular defence mechanisms to eliminate free radicals, including inhibitors of pro-oxidant enzymes, and inducers of endogenous defences (14,48,49). All of these classes of agents may be considered anti-mutagens.…”

“…For example, we considered a range of diŠerent red-purple coloured vegetables in the New Zealand diet, to show very potent antioxidant properties, occurring through various mechanisms (49,59). Some of these pigments are contained in the vacuole of a cell, where they will be readily available when the food plat is masticated.…”