New methodological approach to induce a differentiation phenotype in Caco-2 cells prior to post-confluence stage

BACKGROUND: Various differentiation-inducing agents or harvesting of spontaneously late post-confluence cultures have been used to differentiate the human colon carcinoma Caco-2 cell line. We report a new procedure to generate pre-confluent subcultures of Caco-2 population at various stages of differentiation without altering culture conditions. MATERIALS AND METHODS: Ultrastructural analysis, cell proliferation activity and biochemical markers of differentiation were evaluated at different passages. RESULTS: Subcultures of Caco-2 cells at pre-confluence, exhibiting progressive acquisition of a more benign differentiation phenotype, were generated. Early passages of Caco-2 cells showed a well-developed brush border and incomplete junctional apparatus; subsequent subcultures yielded cell populations with well-developed junctions similar to those of small intestinal cells. CONCLUSION: These culture conditions represent a new versatile model not only to progressively induce the differentiation program in Caco-2 cells at pre-confluence without changes of culture media, but also to explore mechanistic modes of drug transport and tumor development

The influence of caseinphosphopeptides on intracellular calcium changes in primary human osteoblasts : a nutrient dependent modulation of bone cell metabolism

Caseinphosphopeptides (CPPs) are a family of peptides originating from in vivo and in vitro hydrolysis of casein. They possess a sequence of three phosphorylated serines followed by two glutamic acids, the acidic motif, able to bind minerals such as calcium. These nutritional compounds display the ability to increase calcium solubility in the digestive tract. Thus, CPPs were hypothesized to increase the calcium absorption and retention in vivo, with potential effects on bone mineralization. Notwithstanding, there are controversial reports on CPP action. The methodological approach used by different laboratories to study calcium absorption and bone mineralization resulted unable to out light whether the peptides have a specific effect on bone metabolism besides the enhancement of calcium availability. We have therefore designed the following study to evaluate a possible direct role of CPPs in bone cell metabolism. Primary human osteoblasts were established in culture using trabecular bone samples obtained from waste materials during orthopedic surgery of patients without metabolic or malignant bone disease. Cytosolic calcium changes were measured by video-microscopy using the fura-2 method on single cells. A mixture of CPPs of commercial origin as well as pure synthetic CPPs were used. The administration of CPPs to human osteoblasts caused an immediate but transient intracellular calcium change in a dose dependent manner. This CPP-induced effect, analogous to that reported for human intestinal cells, is not cytotoxic and is triggered by an influx of the extracellular ions through the cell plasma membrane. The osteoblast pre-treatment with the active form of vitamin D, known to differentiate human osteoblast, does not affect the cell responsiveness to CPP administration. The 24 hours cell incubation with CPPs induced the increase of the activity of alkaline phosphatase, a marker of osteoblast differentiation, reaching a level similar to that produced by vitamin D. The same CPP treatment caused a small but significative reduction in cell rate proliferation and a slight increase in apoptosis activity. Taken together these results indicate that CPPs are endowed of a bone specific effect which underlying mechanism requires further evaluation. CPPs may act not only as a mere carrier for improving calcium absorption and utilization, but also as a trophyc compound for bone health by enhancing osteoblast differentiation and activity

Casein-derived bioactive phosphopeptides : role of phosphorylation and primary structure in promoting calcium uptake by HT-29 tumor cells

Casein phosphopeptides beta-CN(1-25)4P and alpha(s1)-CN(59-79)5P, from beta- and alpha(s1)-casein, respectively, both carrying the characteristic 'acidic motif' Ser(P)-Ser(P)-Ser(P)-Glu-Glu, were chemically synthesized and administered to HT-29 cells differentiated in culture, which are a used model of intestinal epithelium for absorption studies. Both casein phosphopeptides caused an increase of [Ca(2+)](i) due to influx of extracellular Ca(2+). The response was quantitatively higher with beta-CN(1-25)4P than alpha(s1)-CN(59-79)5P. The synthetic peptide corresponding to the 'acidic motif' was ineffective and the dephosphorylated form of beta-CN(1-25)4P almost inactive. The lack of the N-terminally located five amino acids, or sequence modifications within the N-terminal segment of beta-CN(1-25)4P, caused a total loss of activity, whereas the lack of the C-terminal segment preserved activity. In conclusion, the influx of calcium into HT-29 cells caused by beta-CN(1-25)4P appears to depend on the phosphorylated 'acidic motif' and the preceding N-terminal region

Casein phosphopeptides influence calcium uptake by cultured human intestinal HT-29 tumor cells

We investigated the direct effects of casein phosphopeptides (CPP), which are formed by the proteolytic degradation of - and ß-caseins, on calcium uptake by human HT-29 intestinal tumor cells, which undergo an enterocytically oriented differentiation in culture. A commercial preparation containing a mixture of purified CPP and an individual CPP of 25 amino acids, both containing the characteristic Ca2+ binding motif, ser(P)-ser(P)-ser(P)-glu-glu, were employed. The study was performed at the single-cell level and on a cell population and measured the changes in cytosolic calcium concentration before and after CPP addition. In the presence of 2 mmol/L extracellular calcium, both CPP preparations induced a transient rise of free intracellular calcium ions, which did not influence ATP-induced release of calcium from intracellular stores, and which disappeared completely in the absence of extracellular calcium. Pretreatment of these cells with thapsigargin, which completely empties the intracellular calcium stores, did not abolish the cell responses to CPP. Repetitive stimulation of HT-29 cells with CPP always elicited a transient calcium rise, suggesting a lack of desensitization. The CPP-stimulated cytosolic calcium rise was dependent on CPP dose, in a seemingly nonsaturating mode, and on cell numbers. All of this is consistent with the hypothesis that CPP do not influence membrane-bound receptors or ion channels, but may act as calcium ionophores or calcium carriers across the membrane. The reported findings provide a new basis on which to assess the possibility that CPP enhance calcium absorption and bioavailability in animal

Casein-derived phosphopeptides differently promote calcium uptake in HT-29 intestinal tumor cells depending on their primary structure and extracellular calcium concentration

Preventing oxidative damage in the heart is subject of considerable investigation and studies developing nutritional intervention methods to attenuate or prevent the resulting pathological state of free radical damage are now emerging. In this light, a dietary intervention directed to increase the daily intake of antioxidant molecules represents a fundamental step to achieve a beneficial result. In this minireview the attention is focused on the damage induced in cultured cardiac cells by the antitumoral doxorubicin, known for its cardiotoxicity, and by hypoxia/reoxygenation that occur in a wide variety of important clinical conditions. The identification of antioxidant molecules having specific effectiveness in a particular cell type may be useful for the development of a prevention strategy specific for free radical induced-diseases related to that cell type. Although the connection between consumption of foods rich in polyphenolic compounds and the decreased risk of cardiovascular disease has been reported, the role of different antioxidant molecules contained in foods is still to be elucidated. The protective effect of the polyphenolic components of green tea in the prevention/counteraction of cell damage induced in the heart by doxorubicin or hypoxia/reoxygenation has been discussed