Growth-inhibiting activity of casein and its hydrolysate to tumor cells

To investigate the anti-tumor properties of casein and its hydrolysate in vitro, Jurkat cell, SP20, and YAC-1 were exposed to bovine casein or its proteolytic hydrolysate directly, or mediated by murine peritoneal macrophages and Natural Killer (NK) cells. The results showed that casein hydrolysate alone (even at high concentration of 50 mg/ml) did not have inhibitory effect to Jurkat cell, SP20, and YAC-1, but it could significantly improve the cytotoxicity of both LPS-stimulated peritoneal macrophages and NK cell against these tested tumor cells, which means that the tumor-killing activity of casein hydrolysate must be mediated by peritoneal macrophages or NK cells. The effect of casein hydrolysate on the activity of NK cell and lipopolysaccharide (LPS)-mediated peritoneal macrophage changed with the type of tested cells, and the effect on SP20 and YAC-1 was higher than on that on Jurkat cell. It also demonstrated that the tumor-killing activity of casein hydrolysate showed a dose-dependent manner, and its effect on the cytotoxicity of NK cell and LIPS-mediated peritoneal macrophage increased with the increase of peptide concentration, while too high concentrations of casein hydrolysate induced a significant decrease in NK cell activity and LPS-mediated peritoneal macrophage activity.