OBJECTIVE:

To investigate the effect of culture supernatant of Toxoplasma gondii on the proliferation and Toxoplasma gondii tachyzoites with seed counts of 2 x 10(7)/ml, apoptosis of human gastric cancer BGC-823 cells.

METHODS:

4 x 10(7)/ml, and 8 x 10(7)/ml harvested from infected mice were cultured for 24 h, and then the culture supernatant was collected. BGC-823 cells (5 x 10(4)/ml) at mid-exponential phase were incubated with different concentrations of culture supernatants of Toxoplasma gondii tachyzoites. While in control group, the same volume of DMEM was given. At 24, 48 and 72 h after incubation, the measurement of tumor cell growth inhibition rate was performed by using CCK-8 kit. Cell apoptosis was observed under a fluorescence microscope after 24 h incubation. The DNA ladder zone of apoptosis cells was analyzed with the method of agarose gel electrophoresis. Flow cytometric analysis was used to analyze cell cycle for cell proliferation index and the expression of p53 and Bcl-2.

RESULTS:

The culture supernatant of Toxoplasma tachyzoites inhibited the proliferation of BGC-823 cells and the growth inhibition rates increased with the time and the concentration. The highest rate reached at the 72nd hour when the concentration of Toxoplasma tachyzoites was 8 x 10(7)/ml. Apoptotic bodies were found in experimental group. The amount of apoptotic body was positively associated with the tachyzoite concentration. DNA fragment in the treated cells after 24 h incubation was revealed by agarose electrophoresis. When the proportion of BGC-823 cells in G0/G1 phase increased, the proportion of cells in S phase decreased. Cell proliferation index decreased with the increase of the concentration of tachyzoites. The proliferation index (0.36) of the cells cultured with culture supernatant of 8 x 10(7)/ml tachyzoites was significantly lower than that of control group (0.6, P < 0.05). p53 protein expression was higher in experiment group than that of the control, whereas Bcl-2 protein expression in experiment group was lower than that of the control (P < 0.05).

CONCLUSION:

The culture supernatant of Toxoplasma gondii can inhibit the proliferation of BGC-823 cells and cause apoptosis of BGC-823 cells, which may be related with up-regulating p53 expression and down-regulating Bcl-2 expression.