ABSTRACT
This study aimed to characterize the antioxidant properties of Rama Forte persimmon, a tannin-rich fruit variety produced in Brazil. Extracts prepared with lyophilized pulps from fruits obtained in local markets were analyzed individually to evaluate the extent of antioxidant protection and investigate the antioxidant mechanism. Iron-mediated hydroxylation of 5,5-dimethyl-1-pirrolidine-N-oxide, determined by electron paramagnetic resonance (EPR), and oxidative degradation of 2-deoxyribose (2-DR) were inhibited by fruit extracts in a dose-dependent manner. There was a considerable individual variability in inhibition of 2-DR degradation by individual fruits. Higher protection of 2-DR degradation (by the extracts) was observed in Fe(III)-citrate/ascorbate in comparison with Fe(III)-EDTA/ascorbate system; however, antioxidant effectiveness of fruit extracts was not diminished by increasing EDTA concentration by 10-fold. Other competition experiments using the 2-DR assay (varying pre-incubation time and 2-DR concentration) indicated that protection comes mainly from free radical scavenging, rather that metal chelation antioxidant activity. Persimmon extracts prevented iron-mediated lipid peroxidation in rat liver homogenates, which correlated significantly with the inhibition of 2-DR oxidation. Finally, sugar content of individual fruits correlated inversely with inhibition of 2-DR degradation, which could indicate that maturation decreases soluble antioxidant concentration or efficiency. In conclusion, lipid peroxidation, 2-DR and EPR experiments indicated that extracts from commercial fruits showed mainly radical-scavenger activity and relevant antioxidant activity.
ABSTRACT
It is widely believed that the iron chelator 1,10-phenanthroline (phen) is able to fully block the Fenton reaction by forming a complex (Fe(phen)3(2+), also known as ferroin) that cannot react with H2O2. We observed that phen cannot fully prevent 2-deoxyribose (5 mM) degradation induced by Fenton reagents (30 microM Fe(II) plus 100-500 microM H2O2); protection varied from 55% to 66% when the phen/Fe(II) ratio was 3:1 to 20:1. Inhibition of 2-deoxyribose damage was nearly unchanged if phen was pre-incubated with Fe(II). Moreover, preformed Fe(phen)3(2+) complex added to the solution containing H2O2 was able to induce 2-deoxyribose degradation and methane sulfinic acid formation from the oxidation of 5% DMSO. The partially protective effect of phen was unchanged with the use of either phosphate or HEPES as buffers (5 mM, pH 7.2), or in unbuffered media (pH 5.1). Both DMSO oxidation and 2-deoxyribose degradation correlated with the increase in Fe(phen)3(2+) concentration. Strand breaks in plasmid pTARGETtrade mark DNA induced by Fenton reagents (1 microM Fe(II) plus 25 microM H2O2) in HEPES buffer could only be partially prevented by phen, even when the chelator was 16 times more concentrated than Fe(II). In these experiments, Fe(phen)3(2+) and DNA were pre-incubated from 1 to 10 min before addition of H2O2. Moreover, a high level of DNA strand breakage was observed when iron and phen are added to the reaction immediately before H2O2. On the other hand, phen fully prevented 2-deoxyribose degradation induced by the autoxidation of 30 microM Fe(II) in phosphate-buffered (3 to 30 mM) media. Our data provide evidence that the Fe(phen)3(2+) complex induces in vitro oxidative damage in the presence of H2O2 (possibly by means of Fe(phen)3(2+) dissociation into Fe(phen)2(2+)), but they show that the complex cannot undergo autoxidation.
