Protection of Ewing's sarcoma family tumor (ESFT) cell line SK-N-MC from betulinic acid induced apoptosis by alpha-DL-tocopherol.

Betulinic acid (BA) is known to induce apoptosis in melanoma neuroectodermal and malignant brain cancer cell lines. Present report describes the role of antioxidants on the BA-induced toxicity to human cell line SK-N-MC. Hydrophilic antioxidants viz., L-ascorbic acid (VitC) and N-acetyl-L-cysteine (l-NAC) had no protective effect on BA-induced apoptosis at the maximal concentrations tested. The lipophilic antioxidant, alpha-DL-tocopherol (VitE) showed a concentration and a time dependent effect on the protection of SK-N-MC cells from BA-induced apoptosis. The apoptotic parameters were analyzed using FACS analysis of propidium iodide (PI) stained nuclei, PS externalization using Annexin-V assay and changes in mitochondrial membrane potential. Generation of superoxide radical was monitored by the fluorescent dye hydroethidium (HE). Cells showed Annexin-V positivity and an increase in the propidium iodide (PI) uptake in the early hours of treatment with BA, which was concomitant with the loss of mitochondrial membrane potential. Addition of alpha-DL-tocopherol to the cell cultures 1-h prior to the treatment with BA abolished all the effects of BA-induced apoptosis. These observations suggest that BA initiates events at membrane level leading to induction of apoptosis. The observed ineffectiveness of hydrophilic antioxidants and substantial protection by lipophilic antioxidants indicate involvement of membrane-associated damages that form the basis of BA-induced cytotoxicity.