Cytotoxic effect of glycoprotein isolated from Solanum nigrum L. through the inhibition of hydroxyl radical-induced DNA-binding activities of NF-kappa B in HT-29 cells.

Solanum nigrum L. (SNL) has been traditionally used as an herbal plant for a long time. In the present study, SNL glycoprotein showed a dose-dependent radical scavenging activity on radicals, including 1,1-diphenyl-2-picrylhydrazyl (DPPH) radicals, hydroxyl radical (OH), and superoxide anion (O(2)(-)). When the HT-29 cells were treated with 60μg/ml SNL glycoprotein, the cytotoxic effect was induced in a time-dependent manner. More specifically, it was more than 60% (P<0.01) after 4h, compared to the control. On the other hand, the cells treated with 100mU/ml glucose oxidase (GO) to generate the OH radical showed a cancer resistance up to 12h. Furthermore, the addition of GO to the SNL glycoprotein caused a strong cytotoxic effect, rather than a radical scavenging effect. Interestingly, when the cells were exposed to 100mU/ml GO for 4h, the DNA-binding activity of nuclear factor-kappa B (NF-κB) was increased 4.15-fold (P<0.01) compared to the control, whereas 40μg/ml SNL glycoprotein completely blocked the DNA-binding activity of OH radical-induced NF-κB by electrophoretic mobility shift assays (EMSAs). Apoptosis, according to the apoptosis assay, increased as a result of treatment with 40μg/ml SNL glycoprotein in a time-dependent manner, whereas they were weakly induced by GO in the cells. Consequently, the SNL glycoprotein may induce apoptosis through the inhibition of NF-κB activation, induced by oxidative stress in HT-29 cells.