Casein phosphopeptide-induced calcium uptake in intestinal cells is related to cell differentiation degree

Introduction: Casein phosphopeptides (CPPs) are known to bind minerals and prevent the precipitation of calcium ions. In a human intestinal tumor cell line, HT-29, they elicit a marked and transient rise of intracellular free calcium concentration. The aim of the present study is to understand if this CPP induced calcium uptake is correlated to cell differentiation degree. Moreover, stated the vitamin D role on intestinal cell differentiation, to explore a possible interplay between the two nutrients. Methods: Synthetic and natural CPPs were employed. Cytosolic calcium changes were measured on single cells by video-microscopy. Intestinal cell differentiation was studied by Transmission Electron Microscopy and enzyme activities. Results: CPP administration in HT-29 cells induces a calcium increase in 10% of the undifferentiated cells and in 75% of the differentiated cells, while the amount of the intracellular calcium reached does not vary. The same results were obtained using Caco2 cell line, even if in this case the percentage of responsive cells at a full differentiation degree never exceeds the 30%. Pretreatment of undifferentiated HT-29 and Caco2 cells with vitamin D induces a well differentiated cell phenotype. In these vitamin D-pretreated cells CPP administration evokes a calcium increments in all the analyzed cells, with sustained oscillations and calcium rises. The same vitamin D pretreatment on the two differentiated cell lines neither modifies their phenotype, nor affects the CPP influence on calcium uptake. Conclusion: The ability of CPP to increase calcium uptake is strictly related to the differentiation degree of the intestinal cells.