Health Promoting Effects of Bioactive Peptides in Milk - Studies on Cultured Normal Cells and Cancer Cells

Abstract: This thesis concerns the bioactive peptides lactoferricin and ubiquitin and findings suggesting that they have ability to modify the risk of cancer. It is known that components in bovine milk may improve human health and modify the risk of diseases. Examples of such compounds are bioactive peptides, i.e. peptides with an effect on the body beyond the purely nutritional. Using cell culture as a model system possible cancer preventing effects were investigated with focus on cell proliferation, cell death and DNA repair. In one study, the effect of lactoferricin on CaCo-2 human colon cancer cells was investigated. Low concentrations of the peptide, equivalent to the amount released in the gut of a milk consumer, were used to study the effects during several weeks. A decreased proliferation rate was observed in cancer cells, raising the hypothesis that a prolongation of the cell cycle may be beneficial for the DNA repair system in normal cells. To test this, the effect of lactoferricin treatment was studied in a normal colon cell line. Lactoferricin treatment resulted in decreased proliferation and decreased levels of G1 and S phase proteins. In another study we induced DNA damage in CaCo-2 cells by exposure to UV-light and allowing them to grow in the absence or presence of lactoferricin. The measurement of DNA damage, as detected by the alkaline Comet assay, showed that cells treated with lactoferricin had less DNA damage than the control cells. Another part of the work was to identify new bioactive peptides in milk. Using quantitative Western blot and peptide mass fingerprinting techniques we found that the peptide ubiquitin is present in milk in low concentrations. The effect of ubiquitin on cell proliferation and protein expression was examined both in CaCo-2 cells and in two neuroblastoma cell lines, SH-SY5Y and LA-N-1. Ubiquitin treatment decreased the cell proliferation rate in CaCo-2 and SH-SY5Y cells. LA-N-1 cells initially responded to the ubiquitin treatment with a decreased proliferation rate but after almost three weeks of treatment an alteration in the growth pattern took place and the treated cells grew faster than the control cells. The cell proliferative effects correlated with the level of ubiquitination of intracellular proteins observed in respective cell line. The results showed that the effects of lactoferricin and ubiquitin on cell proliferation may contribute to the health promoting effects of milk.