Bifidobacteria inhibit growth and influence apoptosis in HT-29 colon cancer cells

Probiotics, such as bifidobacteria, and prebiotics, such as fructooligosaccharide (FOS) are purported to improve the health of the colonic ecosystem (including the epithelium) by altering the colonic microflora. The objective of this study was to determine if bifidobacteria (Bif) and/or FOS could affect the growth of human colon carcinoma cells (HT-29). Treatments were: control (bacterial culture medium), FOS, Bif, or Bif + FOS (FBif). Bifidobacteria were grown in the presence or absence of 2% FOS for 24 h, followed by centrifugation to collect supernatants (Sn) and pellets (Pt). The Pt were resuspended in fresh bacterial culture medium. Fetal calf serum and penicillin/streptomycin were added to the Sn and Pt. The Sn and Pt were added to the HT-29 cells and the cells incubated for 24-36 h at 37° C in 95%air:5%CO₂. Supernatants and Pt from Bif and FBif resulted in a 10-15 fold decrease (p<0.05) in growth of HT-29 cells when compared to control or FOS. Supematants from Bif and FBif induced the greatest (p<0.05) amount of apoptosis and the least (p<0.05) amount of LDH release (cytotoxicity). HT-29 cells incubated with Bif and FBif (Sn and Pt) did not exhibit metabolic recovery 3 wk after removal of test media, suggesting a long-term effect. These data indicate that bifidobacteria can alter growth and apoptosis in human colon cancer cells. Because these are cancer cells, the effects on the normal colonocyte population also need to be determined.