INTERACTION OF CASEIN PHOSPHOPEPTIDES WITH CHANNELS INVOLVED IN CALCIUM ABSORPTION AND MODULATION OF PROLIFERATION RATE AND APOPTOSIS OF HUMAN INTESTINAL CELL LINES

Recent studies have evidenced that dietary calcium is able to exert a chemoprotective role on normal differentiated intestinal cells, while it behaves as a carcinogenesis promoter on aberrant colonocytes and adenomatous crypts. These different functions can be achieved through the modulation of proliferation and/or differentiation processes, triggered by the increase of the calcium ion concentrations in the intestinal lumen after a meal. Milk represents the major source of calcium in the diet, due to the high availability of the mineral bound to casein and casein phosphopeptides (CPPs). CPPs, derived by in vitro or in vivo casein hydrolysis, are able to bind calcium, blocking the mineral precipitation in the presence of phosphate and /or sulphate salts and to induce a calcium uptake in human intestinal tumor cell lines HT-29 and Caco2 differentiated in vitro toward an enterocityc phenotype. Thus the hypothesis that CPPs could differently affect proliferation and apoptosis in undifferentiated and differentiated HT-29 and Caco2 cells through their binding with calcium ions was here investigated. Results showed that in HT-29 cells CPPs protect differentiated cells from calcium overload toxicity, prevent their apoptosis, favoring proliferation, while in undifferentiated, tumor like, cells they induce apoptosis. The mechanism by which CPPs act in HT-29 cells is mainly the modulation of the voltage operated L-type calcium channels, known to activate calcium entry into the cells under depolarization, a situation occurring after a meal, and to exert a mitogenic effect. The L-type calcium channels have been now recognized to represent one of the two transcellular calcium absorption ways, characterized by the location in the distal ileum and the independence of vitamin D control. In Caco2 cells, CPPs did not significantly affect proliferation, while increase apoptosis in undifferentiated, tumor like, cells. The mechanism by which CPPs act in Caco2 cells is mainly through the TRPV6 channel, known as the main epithelial channel responsible for the transcellular calcium absorption at duodenum level, subject to vitamin D control and with a saturation kinetic for calcium. Taken together these results demonstrate the ability for CPPs, to modulate the two principal transcellular calcium absorption mechanisms. Moreover, through the binding with calcium ions and the stimulated ingression of this mineral in intestinal cells, CPPs can directly modulate the biological activity strictly related to the expression of a normal or cancer phenotype, thus opening the way for a use of CPPs as nutraceutical/functional food.