Absorption and DNA protective effects of flavonoid glycosides from an onion meal |
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Authors: | SP Boyle VL Dobson SJ Duthie JAM Kyle AR Collins |
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Institution: | (1) present address: School of Pharmacy, The Robert Gordon University, Schoolhill, Aberdeen, AB10 1FR, GB;(2) Rowett Research Institute, Greenburn Road, Bucksburn, Aberdeen, AB21 9SB, Scotland, GB |
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Abstract: | Summary
Background. It is widely believed that antioxidant micronutrients obtained from fruit and vegetables afford significant protection against
cancer and heart disease, as well as ageing. Flavonoids are potential antioxidants found in food such as onions; information
on their effectiveness in vivo is so far lacking. Aims. To determine uptake as well as in vivo antioxidant effects of flavonoids from foods. Methods. Six healthy non-obese normocholesterolaemic female volunteers in the age range 20–44 years participated in a randomised two-phase
crossover supplementation trial to compare the antioxidant effects associated with (a) a meal of fried onions and (b) a meal
of fried onions and fresh cherry tomatoes. Plasma flavonoids, lymphocyte DNA damage, plasma ascorbic acid, tocopherols and
carotenoids, urinary malondialdehyde and 8-hydroxy-2’-deoxyguanosine were determined to assess flavonoid absorption and antioxidant
efficacy. Results. Flavonoid glucosides (quercetin-3-glucoside and isorhamnetin-4-glucoside) were significantly elevated in plasma following
ingestion of the onion meal and the increases were associated with an increased resistance of lymphocyte DNA to DNA strand
breakage. A significant decrease in the level of urinary 8-hydroxy-2’-deoxyguanosine was evident at 4 h following ingestion
of the onion meal. After the combined tomato and onion meal, only quercetin was detected in plasma. Endogenous base oxidation
was decreased but resistance to strand breakage was unchanged. There was no significant change in the excretion of urinary
malondialdehyde following either meal. Conclusion. Both meals – onions, and onions together with tomatoes – led to transient decreases in biomarkers of oxidative stress, although
the particular biomarkers affected differ. It is possible that the differences in patterns of response reflect the different
uptakes of flavonoids but the underlying mechanism is not understood.
Received: 1 April 2000, Accepted: 1 August 2000 |
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Keywords: | Flavonoids – lycopene – DNA damage – plasma lipid peroxidation |
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