Casein phosphopeptides : from mineral carriers to potential nutraceutical/functional food for human enterocite-like cell lines

Introduction. Casein phosphopeptides (CPPs) are known to bind minerals and prevent the precipitation of calcium ions. It was demonstrated that they elicit a marked and transient rise of intracellular calcium concentration in human intestinal tumor cells differentiated in vitro toward an enterocityc phenotype. The CPP composition in terms of their origin from b, as1 and as2 casein and their supramolecular structure are known to be responsible for their bioactivity (1). Here recent data are presented about the correlation of CPP biological activity with the degree of cell differentiation (2), together with the possibility for CPPs to modulate intestinal human cell activity, tracing the basis for their use as possible dietary supplements in functional foods. Materials and methods. A commercial CPP preparations containing peptides from b, as1 and as2 bovine casein was used. The CPP bioactivity was evaluated on Caco-2 human intestinal cell lines, differentiated following an appropriate protocol (3), including treatment with vitamin D3. Cytosolic calcium changes induced by CPPs were monitored with the Fura-2 fluorescent method on single cells by video-microscopy. Gene expression of VDR and TRPV6 was evaluated on undifferentiated and differentiated Caco-2 cells, following vitamin D3 and CPP treatments. Total RNA was extracted, reverse transcribed and cDNA was used as template for real time PCR, performed with Sybr Green. The fold change in expression of the different genes compared with control cells was normalized to the expression of GAPDH gene. Results. The human intestinal-like cell line Caco2 was used as an in vitro model of intestine, for the features of absorptive enterocytes, characterized by the expression of VDR receptors and TRPV6 calcium channels on their apical membranes. The exposure of differentiated Caco2 cells to CPPs determines an increase in the intracellular calcium concentration. The pre-treatment with vitamin D3 of undifferentiated Caco2 cells results in a higher cellular response to CPPs, while the same pre-treatment in differentiated Caco2 cells results in lack of cellular response to CPPs. This latter result is probably due to the activation of apoptosis by vitamin D3 in differentiated Caco2 cells. CPPs does not affect the rate of cell proliferation and apoptosis in undifferentiated and differentiated Caco2 cells. Since the intracellular calcium is known to be an important cell biology and function modulator, the intracellular calcium changes elicited by CPPs were correlated to the possible activation of pathways of calcium uptake by the cells. The expression of VDR genes was never affected by CPPs or CPPs and vitamin D3 treatments. The expression of TRPV6 gene was increased by vitamin D3, as expected, but was unaffected by CPPs. Interestingly, the co-treatment with CPPs and vitamin D3 enhance the expression of TRPV6 gene in differentiated Caco2 cells. Taken together these results open the way for a use of CPPs as nutraceutical/functional food in all the physiological or pathological situations where a deficit of calcium occurs, since the over expression of the TRPV6 gene, found after CPP and vitamin D3 co-treatment, is necessary for an augment of calcium absorption at intestinal level.