150 kDa glycoprotein isolated from Solanum nigrum Linne stimulates caspase-3 activation and reduces inducible nitric oxide production in HCT-116 cells

This study was carried out to investigate the apoptotic effects of glycoprotein (SNL glycoprotein, 150-kDa) isolated from Solanum nigrum Linne, which has been used as an antipyretic and anticancer agent in folk medicine. We found that SNL glycoprotein consists of carbohydrate content (69.74%) and protein content (30.26%), which contains more than 50% hydrophobic amino acids such as glycine and proline. SNL glycoprotein showed remarkable cytotoxic and apoptotic effects at 40 μg/ml of SNL glycoprotein for 4 h in HCT-116 cells. In the activity of the apoptotic related proteins [caspase-3 and poly(ADP-ribose)polymerase (PARP)], the results showed that SNL glycoprotein (40 μg/ml) has a stimulatory effect on caspase-3 activation and PARP cleavage in HCT-116 cells. Moreover, SNL glycoprotein blocked nuclear factor-kappa B (NF-κB) activation and reduced inducible nitric oxide (iNO) production. Interestingly, pyrrolidine dithiocarbamate (PDTC, for NF-κB inhibitor) and Nω-Nitro-l-arginine methylester hydrochloride (L-NAME, for NO inhibitor) effectively stimulated the caspase-3 activation in HCT-116 cells. The results in this experiment indicated that SNL glycoprotein induces apoptosis through the NF-κB activation and inducible nitric oxide (iNO) production in HCT-116 cells. Here, we speculate that SNL glycoprotein is one of the chemotherapeutic agents and of the modulators for apoptotic signals in HCT-116 cells.