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Abstract
Silibinin dihemisuccinate (SDH) is a flavonoid of plant origin with hepatoprotective
effects which have been partially attributed to its ability to scavenge oxygen free
radicals. In the present paper the antioxidant properties of SDH were evaluated by
studying the ability of this drug to react with relevant biological oxidants such
as superoxide anion radical (O2-), hydrogen peroxide (H2O2), hydroxyl radical (HO.)
and hypochlorous acid (HOCl). In addition, its effect on lipid peroxidation was investigated.
SDH is not a good scavenger of O2- and no reaction with H2O2 was detected within the
sensitivity limit of our assay. However, it reacts rapidly with HO. radicals in free
solution at approximately diffusion-controlled rate (K = (1.0-1.2) x 10(10)/M/sec)
and appears to be a weak iron ion chelator. SDH at concentrations in the micromolar
range protected alpha 1-antiproteinase against inactivation by HOCl, showing that
it is a potent scavenger of this oxidizing species. Luminol-dependent chemiluminescence
induced by HOCl was also inhibited by SDH. The reaction of SDH with HOCl was monitored
by the modification of the UV-visible spectrum of SDH. The studies on rat liver microsome
lipid peroxidation induced by Fe(III)/ascorbate showed that SDH has an inhibitory
effect, which is dependent on its concentration and the magnitude of lipid peroxidation.
This work supports the reactive oxygen species scavenger action ascribed to SDH.