Polyamines in human and rat milk influence intestinal cell growth in vitro

Background: Polyamines are required for intestinal growth and development. In this study, we examined whether milk can supply the polyamines needed for growth of LEC-6 cells, a line on non-transformed rat intestinal crypt cells. Methods: Human, bovine, and rat milk, and cow's milk-based infant formula were studied. Human, bovine, and rat milk were defatted and sterilized by filtration. IEC-6 cells were stabilized in Dulbecco's modified Eagle's medium (DMEM) containing 0.5% fetal bovine serum, 5 mM L-glutamine, 100 U/mL penicillin and 100 mu g/mL streptomycin for 24 h at 37 degrees C. Thereafter, to initiate active growth, cells were placed in fresh DMEM containing 5% FBS (plus the other ingredients) supplemented with 5% (vol/vol) milk or infant formula. In some experiments, cells were also treated with difluoromethylornithine (2.5 mM) (DFMO), an inhibitor of polyamine synthesis, or dialyzed milk plus DFMO. After 44 hours of culture, cells were pulsed with H-3-thymidine (H-3-TdR) for 4 hours, harvested and the radioactivity incorporated into DNA was measured. Results: Human and rat milk stimulated proliferation of IEC-6 cells (p < 0.05 compared to controls); addition of DEMO did not reverse the stimulatory effect. Bovine milk and the infant formula did not stimulate proliferation or prevent the growth inhibition induced by DEMO. After dialysis, human milk had less ability to reverse the DFMO inhibition (p < 0.05). Conclusions: These experiments suggest that both human and rat milk, but neither bovine milk nor the infant formula, contain sufficient bioactive polyamines to sustain cell growth during inhibition of polyamine synthesis.