An in vitro study of the protective effect of the flavonoid silydianin against reactive oxygen species.

The inhibitory effect of silydianin, an active constituent of Silybium marianum, on the in vitro production and release of oxidative products has been examined. Polymorphonuclear neutrophils (PMNs) play a primary role in the initiation and propagation of inflammatory responses. Their apoptosis is a major mechanism associated with the resolution of inflammatory reactions. Neutrophils were assessed for caspase-3 activity, the rst step in the execution phase of apoptosis. When cells were cultured with 100 microM silydianin for 24 h, caspase-3 was activated. Induction of apoptosis by silydianin was accompanied by a decrease in luminol-enhanced chemiluminescence as well as superoxide radical (O2*-) release in freshly isolated cells and lipid peroxidation in mouse spleen microsomes. No significant effect of silydianin on PMN hydrogen peroxide production evaluated by a flow cytometric dichlorofluorescin oxidation assay was found. Such results indicate a possible antiinflammatory activity for silydianin, which regulates caspase-3 activation, affects cell membranes and acts as a free radical scavenger. Copyright 2006 John Wiley & Sons, Ltd.