Binding of Iron (II) Ions by Aqueous Extractions from Yerba Mate (Ilex paraguariensis).

We studied the ability of an aqueous extract from yerba mate and a dry extract obtained on the basis of this aqueous extract to remove Fe(II) ions from an aqueous medium. Aqueous extracts from mate dose-dependently reduced the concentration of free Fe(II) ions assayed by the reaction with 1,10-phenanthroline. This can be attributed to polyphenolic compounds with iron-chelating properties present in aqueous extracts from mate, namely quercetin, rutin, caffeic and chlorogenic acids. These substances effectively removed Fe(II) ions from the medium (the initial concentration of these ions was 15 µM) in the concentration range of 20-30 µM. Binding of Fe(II) ions by aqueous mate extracts (due to the formation of chelate complexes with the participation of polyphenolic compounds) modified their absorption spectra in the visible region. Binding of Fe(II) ions can be a mechanism of the antioxidant action of yerba mate.

Effect of the combined action of flavonoids, ascorbate and alpha-tocopherol on peroxidation of phospholipid liposomes induced by Fe2+ ions.

The effect of alpha-tocopherol, ascorbate, rutin and dihydroquercetin on chemiluminescence (CL) accompanying the Fe2+-induced peroxidation of unsaturated fatty acids in phospholipid liposomes has been investigated. The amplitude of CL decreased and the latent period increased in the presence of alpha-tocopherol, rutin and dihydroquercetin which is typical of peroxide radical traps. Ascorbate also reduced the CL amplitude but only at small concentrations up to about 4 microM. A further increase of ascorbate concentration had a negligible effect on the amplitude. At the same time, the latent period in CL development increased with the growth of ascorbate concentration, apparently, as a result of recycling of divalent iron oxidized in the course of lipid peroxidation. The effects of rutin and dihydroquercetin on the liposomal CL in the presence of alpha-tocopherol and ascorbate in all experiments were almost the same as when these compounds were added individually. The antioxidant effects were merely summed up without any mutual enhancement or inhibition of each other's action.

Effect of carnosine and its components on free-radical reactions.

The antioxidant properties of carnosine and its components histidine and beta-alanine were compared using several model systems: glutathione-horseradish peroxidase-luminol (GSH-HRP-luminol), xanthine-xanthine oxidase (X-XO), stimulated human blood polymorphonuclear leukocytes (PML), and egg yolk phospholipid liposomes in the presence of Fe2+ ions. Carnosine and histidine (30-40 mM) were shown to cause 50% suppression of free radical reactions in the GSH-HRP-luminol system, whereas beta-alanine displayed no activity. The O(2-)-scavenging activity of carnosine in the X-XO system was demonstrated; 50% inhibition was achieved at 7.1 x 10(-5) M. Suppression of the luminol-dependent PML chemiluminescence by carnosine and reduction of the latent period of the Fe(2+)-induced chemiluminescence of the liposome suspension was suggested to demonstrate its ability to interact with Ca2+ and Fe2+ ions. This was confirmed by the o-phenanthroline test. The results obtained demonstrate that carnosine is capable of scavenging different radicals and binding divalent metal ions. The antioxidant activity of carnosine was observed in all the systems studied, and carnosine effective concentrations corresponded to those found in the brain and muscles. The universal effects of carnosine and its high concentration in excitable tissues suggest this dipeptide to be an inhibitor of free radical reactions in vivo.

Effect of antioxidants on the kinetics of chain lipid peroxidation in liposomes.

To elucidate the mechanism of action of various antioxidants, we studied the kinetics of chemiluminescence which accompanies the peroxidation of phospholipid liposomes as induced by divalent iron ions in the presence of C-525, a chemiluminescence activator. EDTA and desferal reduced the chemiluminescence latent period, probably, due to the chelation of Fe2+ ions which, thus, dropped out of chain oxidation reactions in the lipid phase. In contrast, ascorbate increased the chemiluminescence latent period, apparently, as a result of regeneration of divalent iron oxidized during lipid peroxidation. alpha-Tocopherol and rutin reduced the amplitude of the chemiluminescence slow flash and increased the duration of the latent period. beta-Carotene displayed its effect only at rather high concentrations, when the decrease in chemiluminescence intensity could be due (at least partially) to the reabsorption of chemiluminescence by this compound. The latent period remained invariable in this case.

The antioxidant properties of lycopene.

The antioxidant properties of the carotenoid lycopene were compared in three different model oxidative systems. In egg yolk liposomes, in the presence of 2.5 mM FeSO4 and 200 mM ascorbate, lycopene, alpha-tocopherol, and beta-carotene inhibited the accumulation of lipid peroxidation products reacting with 2-thiobarbituric acid (TBARS) in a dose-dependent mode, with the concentration of half-inhibition being 80, 30 and 130 mM, respectively. In the liposomes subjected to illumination with a He-Ne laser (632.8 nm) at a dose of 10.5 J/cm2, in the presence of 32.5 micrograms/ml hematoporphyrin derivatives (Fotogem, NIOPIC, Russia) TBARS accumulated, and this effect was inhibited by lycopene, alpha-tocopherol, and dihydroquercetin with approximately equal efficiencies (the half-inhibition concentrations were 10(-5) mM). In both systems studied, sodium azide at a concentration of 10 mM inhibited the TBARS accumulation by no more than 20%. Apparently, the inhibitory action of not only alpha-tocopherol, but also beta-carotene and lycopene was the result of their antiradical action, rather than quenching of the singlet oxygen in an aqueous medium. The introduction of lycopene, as well as beta-carotene in liposomes subjected to Fe(2+)-induced lipid peroxidation decreased the chemiluminescence (CL) intensity at the stage of CL slow flash, with no essential influence on the lag period. These data suggest that the effect of lycopene on lipid peroxidation was the result of its interaction with free radicals rather than chelating ferrous ions. The antiradical activity of lycopene was also confirmed by the method of luminol photochemiluminescence (PCL). Lycopene increased the PCL lag period (L) and decreased the PCL amplitude (A), which implies its antiradical and SOD-like activity in this system.