Cucurbitacin glucosides: Antioxidant and free-radical scavenging activities

The cucurbitacins are of great interest because of the wide range of biological activities they exhibit in plants and animals. We studied the antioxidant properties of cucurbitacin B + E glucosides (cucurbitacin glucoside combination, CGC) and their direct free-radical scavenging properties, using ESR spectroscopy. Antioxidant activity was measured by the ability of the CGC to reduce preformed ABTS•+ into its native form and to inhibit MDA formation during the oxidation of linoleic acid. In both methods, the CGC exhibited antioxidant activity in a dose-dependent manner as expected from antioxidants. Using ESR spectroscopy, we found that the CGC inhibited •OH-dependent DEPMPO–OH adduct formation, O2--dependent DEPMPO–OOH adduct formation, and the 1O2-dependent TEMPO adduct generated in the photoradiation–porphin system. The IC50 values were 0.38, 8, and 11 mM, respectively. Together, these data demonstrate that the CGC exhibits antioxidant properties, probably through the involvement of a direct scavenging effect on several free radicals.