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In vitro evaluation of caseinophosphopeptides from different genetic variants on bone mineralization

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In vitro evaluation of

caseinophosphopeptides from different

genetic variants on bone mineralization

Anna Caroli

1

, Omar Bulgari

1

, Stefania Chessa

2

,

Daniela Cocchi

1

, Giovanni Tulipano

1

1Dipartimento di Scienze Biomediche e Biotecnologie, Università di Brescia, Italy 2Dipartimento di Scienze e Tecnologie Veterinarie per la Sicurezza Alimentare,

Università di Milano, Italy

Corresponding author: Anna Caroli. Dipartimento di Scienze Biomediche e Biotecnologie, sezione di Biologia

e Genetica, Facoltà di Medicina e Chirurgia, Università di Brescia. Viale Europa 11, 2�12� Brescia, Italy - Tel. ���� 0�0 �717���8 - Fa��� ���� 0�0 �717241 - Email������ 0�0 �717���8 - Fa��� ���� 0�0 �717241 - Email�� caroli@med.unibs.it

AbstrAct - Casein phosphopeptides (CPPs) have been shown to enhance calcium solubility and toCasein phosphopeptides (CPPs) have been shown to enhance calcium solubility and to increase the calcification by in vitro analyses. The aim of our study was to investigate the effects of four selected casein peptides, which differ in the number of phosphorylated serines, on osteoblast mineraliza-tion in vitro. The chosen peptides, related to different casein genetic variants, were obtained by chemical synthesis and tested on murine osteoblast cell line (MC�T�-E1). Our results suggest that the distinct peptides in protein hydrolysates may differentially affect calcium deposition in the e�tracellular matri� and that the genetic variation within the considered peptides is involved in their differential effect.

Key words: Caseinophosphopeptide, Milk protein, Biological effect, Bone.

Introduction - Milk contains different protein components, many of which showing biological

activities in addition to their nutritional value, and produced in their active form, i.e. lysozyme, lac-toferrin, growth factors, hormones (Lorenzini et al., 2007). Among the biologically active molecules, the caseinophosphopeptides (CPPs) are strongly phosphorylated peptides known to e�ert an effect on calcium metabolism but also on other minerals (Bouhallab and Bouglé, 2004). The CPPs have aThe CPPs have a strong capacity to fi� nutritionally interesting divalent cations such as calcium, iron or zinc, thus mak-ing them stable and soluble in different physico-chemical conditions in particular of pH (Brulé and Fauquant, 1��82; Meisel and Schlimme, 1�����). The CPPs obtained by enzymatic, 1��82; Meisel and Schlimme, 1�����). The CPPs obtained by enzymatic in vitro hydrolysis of caseins have been shown to enhance calcium solubility and to increase the calcification of embryonic rat femora and tibiae in vitro (Gerber and Jost, 1��8��).Gerber and Jost, 1��8��).).

From the genetic point of view, the biological activity of peptides released from milk protein diges-tion may be affected by amino acid e�changes or delediges-tions resulting from gene mutadiges-tions. The aimThe aim of our study was to investigate the effects of four selected peptides, which differ in the number of phosphorylated serine, on osteoblast in vitro mineralization. The peptides considered were related to different casein genetic variants.

Material and methods - We used a murine osteoblast cell line (MC�T�-E1) that has the potency

to differentiate during culture in the presence of ascorbic acid and glycerol-2-phosphate forming a mineralized e�tracellular matri�. The two copies of peptides were obtained by chemical synthesis (Table 1). Peptides were synthesised by CRIBI (Padova, Italy) (peptide-1 and -2), and PE & Elephants (Germany) (Peptide-� and -4). The main difference between peptide-1 and -2 is the occurrence of oneThe main difference between peptide-1 and -2 is the occurrence of one phosphorylated serine at position �� of the mature β-casein in the latter peptide. Moreover, Glu (E) at in the latter peptide. Moreover, Glu (E) at position �7 is substituted with Lys (K) in variant C. Both peptide-� and -4 carry two phosphorylated serines separated by one amino acid which differs in the two sequences (Ile vs. Thr). From a geneticFrom a genetic Ital.J.anIm.ScI. vol. 8 (Suppl. 2), 42-44, 2009

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point of view, it is to highlight that β-casein C variant is not common in cattle, and is mainly found in local breeds, whereas αs2-casein C was found in Bos grunniens (Formaggioni et al., 1������). Peptide-2

and -4 also occur in the known genetic variants of β-casein and αs2-casein in Capra hircus and Ovis

aries (Chessa et al., 200��). Calcium content of the cell monolayer lysates was determined as previously described by van Driel et al. (200��) after a �-week long treatment.(200��) after a �-week long treatment.

results and conclusions - Calcium concentration of the culture medium (alfa-MEM) was

inad-equate to support detectable mineralization of cell monolayer, based on the sensitivity of our calcium assay. When calcium lactate (0.� mM) was added to the culture medium, increased calcium deposition was observed (Figure 1). Hence, in order to study the effects of the four selected peptides on in vitro mineralization, cells were grown in the presence of calcium lactate supplement.

1 did not affect significantly final calcium content as compared with control wells. Peptide-2, which contains one phosphorylated serine, increased moderately calcium content (128±8% vs. con-trol, N=4, P<0.0�) at the higher dose tested (40 µM). Lower doses (1-10 µM) were ineffective. Pep-tide-� and -4, containing 2 phos-phorylated serines, reduced final calcium content to 42±10% and �4±8% vs. control, respectively (N=�, P<0.01 and P<0.001) at 40 µM concentration (Figure 2). Lower doses (0.4-4 µM) did not af-fect significantly mineralization.

The only peptide showing a significant positive effect on bone mineralization (peptide-2) carried carried one phosphorylated serine, and occurs in most bovine β-casein variants as well as in sheep and goat β-casein. As for αs2-casein,

the negative effect on bone miner-alization was less evident for the

Bos grunniens C variant.

Our preliminary results sug-gest that the distinct casein peptides in protein hydrolysates Figure 1. Effects of calcium lactate addition to culture

medium on cell mineralization. A, not diffe-rentiated cells. B, cells growing in differen-tiating medium (alpha-MEM supplemented with 100 µg/ml ascorbic acid, 5 mM glyce-rol-2-phosphate). C, not differentiated cells growing in medium supplemented with 0.5 mM calcium lactate. D, cells growing in dif-ferentiating medium supplemented with cal-cium lactate. 0 0.1 0.2 0.3 0.4 0.5 0.6 A B C D Free calcium concentration in cell lysates (mM)

Table 1. Peptides obtained by chemical synthesis and genetic variation involved. Phosphorylated serines are sub lined. Amino acid exchanges between the two peptide couples are bolded.

Sequence Bovine casein variant

Peptide-1 KIEKFQSEKQQQT β-casein C

Peptide-2 KIEKFQSEEQQQT β-casein AA1, 2, 3, 4, B, F, G, H1, 2, I

Peptide-3 EQLSISEENS αs2-casein C

Peptide-4 EQLSTSEENS αs2-casein A, B, D

Ital.J.anIm.ScI. vol. 8 (Suppl. 2), 42-44, 2009 43

proc. 18th nat. congr. aSpa, palermo, Italy

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may differentially affect calcium deposition in the e�tracellular matri�. The higher content of phos-phorylated serines in the peptide might compete with calcium deposition, probably subtracting Ca�� from the culture medium. Moreover, the genetic variation within the considered peptides may influ-ence their differential effect on osteoblast in vitro mineralization.

Research supported by SELMOL contract (MIPAAF) and PRIN 2007 - 2007XT947K.

references - bouhallab, S., Bouglé, D., 2004. Biopeptides of milk�� caseinophosphopeptides and

min-eral bioavailability. Reprod. Nutr. Dev. 44��4���-4��8.Reprod. Nutr. Dev. 44��4���-4��8. brulé, G., Fauquant, J., 1��82. Interactions des proteins du lait et des oligoéléments. Lait. ��2���2�-��1.Lait. ��2���2�-��1. chessa, S., Bulgari, O., Rignanese, D., Tulipano, G., Caroli, A., 200��. In silico analysis of caseinophosphopeptides in ruminants. XVIII Congresso Nazionale ASPA, Palermo, ��-12 giugno 200��. formaggioni, P., Summer, A., Malacarne, M., Mariani, P., 1999. Milk protein polymor-phism�� detection and diffusion of the genetic variants in Bos Genus. Ann. Fac. Med. Vet. Un. Parma, pp. 127-1���. Gerber, H.W., Jost, R., 1��8��. Casein phosphopeptides�� their effect on calcification of in vitro cultured embryonic rat bone. Calcif. Tissue Int. �8����0-��7.Calcif. Tissue Int. �8����0-��7. Lorenzini, E.C., Chessa, S., Chiatti, F., Caroli, A., Pag-nacco, G., 2007. Peptidi bioattivi di latte e derivati. Sci. Tecn. Latt. Cas. �8��11�-1���. Meisel, H., Schlimme, E., 1�����. Calcium and iron binding capacity of different fractions from in vitro proteolysis of casein. Kiels from in vitro proteolysis of casein. KielKiel Milchwirtsch Forschungsber. 4���2��-24�. van Driel, M., Koedam, M., Buurman, C.J., Roelse, M., Weyts, F., Chiba, H., Uitterlinden, A.G., Pols, H.A.P., van Leeuwen, J.P.T.M., 200��. Evidence that both 1alpha, 2�-dihy-Evidence that both 1alpha, 2�-dihy-dro�yvitamin D� and 24-hydro�ylated D� enhance human osteoblast differentiation and mineralization. J. Cell. Biochem. ��������22-����.

Figure 2. Mineralization trial results. Control=differentiated cells growing in medium supplemented with 100 µg/ml ascorbic acid, 5 mM glycerol-2-phosphate, 0.5 mM calcium lactate. Peptide concentrations=40 µM. Vit D=1alpha, 25-dihydroxyvitamin D3 (positive control). Results are the mean±SD of 4 to 5 replicate wells. *, P<0.05. **, P<0.01. ***, P<0.001 (one-way ANO-VA, Dunnett’ t test).

Ital.J.anIm.ScI. vol. 8 (Suppl. 2), 42-44, 2009

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