Abstract: Objective: To investigate the pro-apoptotic mechanism of soy isoflavones on transplanted H22 hepatoma cells in mice. Methods: Kunming mice were subcutaneously inoculated with mouse hepatoma H22 cells and then divided into model, soy isoflavone-treated and 5-fuorouracil-treated groups. The apoptosis of transplanted tumor tissue was detected by DNA ladder assay, and the expressions of cysteinyl aspartate specific proteinase (caspase)-3, caspase-8, caspase-9, B cell lymphoma/lewkmia-2 (Bcl-2), Bcl-2-associated X protein (Bax), cytochrome c (Cyt c), apoptosis-inducing factor (AIF), p53, survivin and signal transducer and activator of transcription (STAT)3 proteins were detected by Western blotting. Results: Compared with the model group, the growth of transplanted tumor was suppressed, and the intensity of DNA ladder was increased; the active fragments of caspase-3, caspase-8 and caspase-9 were increased; the expression of Bcl-2 protein was decreased, while the expression of Bax was increased; and the cytoplasmic levels of Cyt c and AIF in transplanted tumor tissue were elevated in the soy isoflavone group. In addition, soy isoflavone treatment elevated p53 protein expression, and reduced STAT3 activation and survivin protein expression in transplanted tumor tissue. Conclusion: Soy isoflavones can induce the apoptosis of H22 transplanted tumor cells, and the pro-apoptotic mechanism may be related to the regulation of p53 and STAT3.

Key words: soy isoflavone, transplanted hepatoma H22 cells, apoptosis, p53, signal transducer and activator of transcription