Induction of non-apoptotic cell death by sodium 5,6-benzylidene-L-ascorbate in a human salivary gland tumor cell line.

We investigated whether sodium 5,6-benzylidene-L-ascorbate (SBA) induces apoptotic cell death in a human salivary gland tumor cell line HSG, using two different cytochemical methods. Millimolar concentrations of SBA dose-dependently reduced the viable cell number of HSG cells, accompanied by the detachment of dying cells from the culture plates. The nuclei of the dying cells were not stained with TUNEL reagent, indicating the lack of DNA nicks or fragments. On the other hand, the nuclei of epigallocatechin gallate (EGCG)-treated cells (positive control) were TUNEL-positive, demonstrating the production of DNA nicks or fragments. Furthermore, the cytoplasms of SBA-treated cells were not stained with M30 monoclonal antibody, which reacts with the degradation products of cytokeratin 18 by the activated caspases, in contrast to those of EGCG-treated cells. These results suggest that SBA induces non-apoptotic cell death, possibly necrosis, in HSG cells.