Effect of the phosphorylation structure in casein phosphopeptides on the proliferation, differentiation, and mineralization of osteoblasts and its mechanism

Our previous studies have shown that highly phosphorylated casein phosphopeptides (residues 1-25) P5 could efficiently bind calcium and promote intestinal calcium absorption, and enhanced bone development in rats. The purpose of this study was to investigate the effect of the phosphorylation structure in P5 on the proliferation, differentiation, and mineralization of osteoblasts (MC3T3-E1) and its mechanism. P5 was obtained by high-performance liquid chromatography (HPLC) and non-phosphorylated peptide P5-0 was obtained by chemical synthesis. Compared with the control group, the proliferation rate of MC3T3-E1 cells treated by P5 was 1.10 times that of P5-0 at 200 μg mL-1. P5 caused the cell cycle retention of MC3T3-E1 cells in the G2/M phase, while P5-0 had no significant difference in the G2/M phase. MC3T3-E1 cells incubated with P5 showed stronger alkaline phosphatase (ALP) activity than with P5-0, suggesting a tendency to promote cellular differentiation. Compared to the P5-0 treatment group, the P5 treatment group at concentrations of 10 μg mL-1 showed significant differences in the mineralization rates (p < 0.05). P5 significantly upregulated the expressions of Runx2, ALP, ColIα1, and OCN compared with the control group (p < 0.05). In addition, in silico molecular docking showed that the binding force of the P5-EGFR complex was stronger than that of the P5-0-EGFR complex, which was significantly related to the phosphorylation structure in P5 and might be an important reason for osteoblast proliferation. In conclusion, the phosphorylation structure and amino acid composition in P5 stimulated the osteogenic activity of MC3T3-E1 cells, and could be expected to be a functional food for the prevention of osteoporosis.

Osteopontin phosphopeptide mitigates calcium oxalate stone formation in a Drosophila melanogaster model

Kidney stone disease affects nearly one in ten individuals and places a significant economic strain on global healthcare systems. Despite the high frequency of stones within the population, effective preventative strategies are lacking and disease prevalence continues to rise. Osteopontin (OPN) is a urinary protein that can inhibit the formation of renal calculi in vitro. However, the efficacy of OPN in vivo has yet to be determined. Using an established Drosophila melanogaster model of calcium oxalate urolithiasis, we demonstrated that a 16-residue synthetic OPN phosphopeptide effectively reduced stone burden in vivo. Oral supplementation with this peptide altered crystal morphology of calcium oxalate monohydrate (COM) in a similar manner to previous in vitro studies, and the presence of the OPN phosphopeptide during COM formation and adhesion significantly reduced crystal attachment to mammalian kidney cells. Altogether, this study is the first to show that an OPN phosphopeptide can directly mitigate calcium oxalate urolithiasis formation in vivo by modulating crystal morphology. These findings suggest that OPN supplementation is a promising therapeutic approach and may be clinically useful in the management of urolithiasis in humans.

Effect of different surface treatments on the microhardness and colour change of artificial enamel lesions

BACKGROUND

To investigate the effect of three different surface treatments on the microhardness and colour change of artificial enamel lesions.

MATERIALS AND METHODS

One hundred bovine teeth were randomly assigned into four groups. Artificial enamel lesions were created using demineralizing solution for all groups except the sound enamel group. Different surface treatments were then performed G1: resin-infiltrant; G2: Casein phosphopeptide-amorphous calcium phosphate (CPP-ACP); G3: artificial saliva; G4: Sound Enamel. Each group was subdivided into three subgroups, where each subgroup was subjected to a different testing method. Subgroup 1: surface microhardness; subgroup 2: cross-sectional microhardness; subgroup 3: colour measurement. Statistical analysis was performed by ANOVA, followed by Tukey's post hoc test.

RESULTS

Sound enamel group recorded the highest surface and cross-sectional microhardness results. No significant difference was found between the resin-infiltrant group and CPP-ACP regarding surface and cross-sectional microhardness at different lesion depths. Resin-infiltrant group showed the least colour change (∆E) results compared to the other groups.

CONCLUSION

Resin-infiltrant can effectively enhance surface microhardness and enamel resistance to demineralization, additionally, reduces the staining susceptibility of white spot lesions (WSLs) after treatment. CPP-ACP application for 4 weeks seems to improve surface microhardness; however, has a limited effect in resisting staining of WSLs after treatment. © 2022 Australian Dental Association.

MHC Phosphopeptides: Promising Targets for Immunotherapy of Cancer and Other Chronic Diseases

Major histocompatibility complex-associated peptides have been considered as potential immunotherapeutic targets for many years. MHC class I phosphopeptides result from dysregulated cell signaling pathways that are common across cancers and both viral and bacterial infections. These antigens are recognized by central memory T cells from healthy donors, indicating that they are considered antigenic by the immune system and that they are presented across different individuals and diseases. Based on these responses and the similar dysregulation, phosphorylated antigens are promising candidates for prevention or treatment of different cancers as well as a number of other chronic diseases.

Enhanced Anti-Allergic Activity of Milk Casein Phosphopeptide by Additional Phosphorylation in Ovalbumin-Sensitized Mice

The proteolytic digest of milk casein, known as casein phosphopeptide (CPP-III), exhibits diverse biological activities, including calcium absorption and antioxidant activities. We hypothesized that the additional phosphorylation of this peptide can enhance its immunomodulatory activity such as suppression of allergy-associated cytokine and antigen-specific immune response. This study was conducted to assess whether oral intake of additionally phosphorylated CPP-III (P-CPP) attenuates ovalbumin (OVA)-induced IgE-mediated allergic reactions because of the additional phosphate groups. Female BALB/c mice were intraperitoneally sensitized with OVA twice at intervals of 14 days and then orally fed native CPP-III (N-CPP), P-CPP, and dephosphorylated CPP-III (D-CPP) for 6 weeks. Next, the mice were orally challenged with 50 mg of OVA. Oral administration of P-CPP suppressed total and specific IgE levels in the serum. Mice fed P-CPP exhibited low levels of OVA-specific IgG1 and increased OVA-specific IgG2a. P-CPP also suppressed IL-4 production, while D-CPP showed similar a level compared to that of the control. Further, P-CPP increased the population of the T follicular helper (Tfh) cell in the spleen. These results suggest that additional phosphorylation of CPP can enhance the attenuation of allergen-specific IgE-modulated allergic reactions in a murine food allergy model.

Enzymatic Assemblies Disrupt the Membrane and Target Endoplasmic Reticulum for Selective Cancer Cell Death

The endoplasmic reticulum (ER) is responsible for the synthesis and folding of a large number of proteins, as well as intracellular calcium regulation, lipid synthesis, and lipid transfer to other organelles, and is emerging as a target for cancer therapy. However, strategies for selectively targeting the ER of cancer cells are limited. Here we show that enzymatically generated crescent-shaped supramolecular assemblies of short peptides disrupt cell membranes and target ER for selective cancer cell death. As revealed by sedimentation assay, the assemblies interact with synthetic lipid membranes. Live cell imaging confirms that the assemblies impair membrane integrity, which is further supported by lactate dehydrogenase (LDH) assays. According to transmission electron microscopy (TEM), static light scattering (SLS), and critical micelle concentration (CMC), attaching an l-amino acid at the C-terminal of a d-tripeptide results in the crescent-shaped supramolecular assemblies. Structure-activity relationship suggests that the crescent-shaped morphology is critical for interacting with membranes and for controlling cell fate. Moreover, fluorescent imaging indicates that the assemblies accumulate on the ER. Time-dependent Western blot and ELISA indicate that the accumulation causes ER stress and subsequently activates the caspase signaling cascade for cell death. As an approach for in situ generating membrane binding scaffolds (i.e., the crescent-shaped supramolecular assemblies), this work promises a new way to disrupt the membrane and to target the ER for developing anticancer therapeutics.

Design, synthesis and biological evaluation of phosphopeptides as Polo-like kinase 1 Polo-box domain inhibitors

Polo-like kinase 1 (Plk1) is an anti-cancer target due to its critical role in mitotic progression. A growing body of evidence has documented that Peptide-Plk1 inhibitors showed high Plk1 binding affinity. However, phosphopeptides-Plk1 inhibitors showed poor cell membranes permeability, which limits their clinical applications. In current study, nine candidate phosphopeptides consisting of non-natural amino acids were rationally designed and then successfully synthesized using an Fmoc-solid phase peptide synthesis (SPPS) strategy. Moreover, the binding affinities and selectivity were evaluated via fluorescence polarization (FP) assay. The results confirmed that the most promising phosphopeptide 6 bound to Plk1 PBD with the IC50 of 38.99 nM, which was approximately 600-fold selectivity over Plk3 PBD (IC50 = 25.44 μM) and nearly no binding to Plk2 PBD. Furthermore the intracellular activities and the cell membrane permeability of phosphopeptide 6 were evalutated. Phosphopeptide 6 demonstrated appropriate cell membrane permeability and arrested HeLa cells cycle in G2/M phase by regulating CyclinB1-CDK1. Further, phosphopeptide 6 showed typical apoptotic morphology and induced caspase-dependent apoptosis. In conclusion, we expect our discovery can provide new insights into the further optimization of Plk1 PBD inhibitors.

Role of phosphate groups on antiviral activity of casein phosphopeptide against feline calicivirus as a surrogate for norovirus

BACKGROUND

Current research on the gastrointestinal digestion of milk-casein strongly suggests the existence of novel bioactive peptides with antiviral activities that are attributable to their immunostimulatory effects. In the present study, we investigated the antiviral activity of casein peptides rich in phosphate groups, such as casein phosphopeptide (CPP-III).

RESULTS

We prepared two types of CPP with different phosphorylation levels to clarify the role of the phosphate group. Further phosphorylation of CPP-III was conducted by dry heating with sodium pyrophosphate, whereas dephosphorylation was performed enzymatically using alkaline phosphatase and alkaline treatment. Feline calicivirus (FCV) strain F9, a typical norovirus surrogate, and Crandell Rees feline kidney cells were used as the target virus and host cells, respectively. Antiviral activity was determined based on the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and quantitative polymerase chain reaction quantification of antiviral cytokine mRNA expression. Higher cell viability was observed in the host cells treated with phosphorylated CPP-III, and a significant up-regulation of type 1 interferon expression was induced compared to that treated with native CPP-III. However, dephosphorylation of CPP-III resulted in a decrease in the anti-FCV effect.

CONCLUSION

The CPP effect was enhanced by the introduction of additional phosphates and conversely weakened by their elimination. Therefore, CPP-III phosphorylation represents an emerging approach for the production of food-grade antiviral agents. © 2016 Society of Chemical Industry.

Preparation and anti-osteoporotic activities in vivo of phosphorylated peptides from Antarctic krill (Euphausia superba)

Antarctic krill (Euphausia superba) protein serves as a novel sustainable protein source for human. Krill protein isolate was phosphorylated by the dry-heating method with sodium pyrophosphate. Phosphorylated peptides from Antarctic krill (PP-AKP) were obtained from phosphorylated protein through tryptic hydrolysis. Two types of phosphate bonds were introduced by phosphorylation, i.e. PO and PO bonds. The anti-osteoporotic activities of PP-AKP at two doses (400 and 800mg/kg body weight) were investigated with an osteoporotic rat model, which was established with bilateral ovariectomy surgery. Different doses of PP-AKP were given intraperitoneal injections to rats once a day with alendronate as a positive control. Phosphorylated peptides from Antarctic krill dose-dependently preserved bone mineral density in osteoporotic rats by increasing the degree of bone mineralization. Both trabecular and cortical bone strength in osteoporotic rats was significantly improved with PP-AKP treatment. The mechanism by which PP-AKP augmented bone mineral density and bone strength was relation to the reduction in osteoclast-mediated bone remodeling, as was supported by the decrease in bone resorption markers. Phosphorylated peptides from Antarctic krill could be developed as functional food or nutritional supplements.

Mono-anionic phosphopeptides produced by unexpected histidine alkylation exhibit high Plk1 polo-box domain-binding affinities and enhanced antiproliferative effects in HeLa cells

Binding of polo-like kinase 1 (Plk1) polo-box domains (PBDs) to phosphothreonine (pThr)/phosphoserine (pSer)-containing sequences is critical for the proper function of Plk1. Although high-affinity synthetic pThr-containing peptides provide starting points for developing PBD-directed inhibitors, to date the efficacy of such peptides in whole cell assays has been poor. This potentially reflects limited cell membrane permeability arising, in part, from the di-anionic nature of the phosphoryl group or its mimetics. In our current article we report the unanticipated on-resin N(τ)-alkylation of histidine residues already bearing a N(π)- alkyl group. This resulted in cationic imidazolium-containing pThr peptides, several of which exhibit single-digit nanomolar PBD-binding affinities in extracellular assays and improved antimitotic efficacies in intact cells. We enhanced the cellular efficacies of these peptides further by applying bio-reversible pivaloyloxymethyl (POM) phosphoryl protection. New structural insights presented in our current study, including the potential utility of intramolecular charge masking, may be useful for the further development of PBD-binding peptides and peptide mimetics.

Stimulatory Effects of Casein Phosphopeptide (CPP-III) on mRNA Expression of Cytokines in Caco-2 Cells

The effect of CPP-III, a commercially available casein phosphopeptide, on the mRNA expression of cytokines in Caco-2 cells was investigated. CPP-III enhanced the mRNAs of interleukin (IL)-6 and tumor necrosis factor-alpha while IL-1beta was not affected. The mRNA expression of IL-6 was stronger in the presence of both CPP-III and bacterial components such as peptidoglycan from Lactobacillus acidophilus and lipopolysaccharide from Salmonella typhimurium. These results suggest that CPP-III influences the expression of cytokines in intestinal epithelial cells.

Targeted delivery of a phosphopeptide prodrug inhibits the proliferation of a human glioma cell line

Peptides are ideal candidates for developing therapeutics. Polo-like kinase 1 is an important regulatory protein in the cell cycle and contains a C-terminal polo-box domain, which is the hallmark of this protein family. We developed a peptide inhibitor of polo-like kinase 1 that targets its polo-box domain. This new phosphopeptide, cRGDyK-S-S-CPLHSpT, preferentially penetrates the cancer cell membrane mediated by the integrin receptor, which is expressed at high levels by cancer cells. In the present study, using high performance liquid chromatography and mass spectroscopy, we determined the stability of cRGDyK-S-S-CPLHSpT and its cleavage by glutathione under typical conditions for cell culture. We further assessed the ability of the peptide to inhibit the proliferation of the U87MG glioma cell line. The phosphorylated peptide was stable, and the disulfide bond of cRGDyK-S-S-CPLHSpT was cleaved in 50 mM glutathione. This peptide inhibited the growth of cancer cells and changed their morphology. Therefore, we conclude that the phosphopeptide shows promise as a prodrug and has a high potential to act as an anticancer agent by inhibiting polo-like kinase 1 by binding its polo-box domain. These findings indicate the therapeutic potential of PLHSpT and peptides similarly targeted to surface receptors of cancer cells and to the functional domains of regulatory proteins.

Reversible inhibition of calcium oxalate monohydrate growth by an osteopontin phosphopeptide

Calcium oxalate, primarily as calcium oxalate monohydrate (COM), is the primary constituent of most kidney stones. Certain proteins, such as osteopontin (OPN), inhibit stone formation. The complexity of stone formation and the effects of urinary proteins at various stages of the process make it hard to predict the exact physiological roles of these proteins in growth inhibition. The inhibition of crystallization due to adsorbed impurities is usually explained in terms of a model proposed in 1958 by Cabrera and Vermilyea. In this model, impurities adsorb to growth faces and pin growth steps, forcing them to curve, thus impeding their progress via the Gibbs-Thomson effect. To determine the role of OPN in the biomineralization of kidney stones, crystal growth on the {010} face of COM was examined in real time with atomic force microscopy in the presence of a synthetic peptide corresponding to amino acids 65-80 (hereafter referred to as pOPAR) of rat bone OPN. We observed clear changes in the morphology of the growth-step structure and a decrease in step velocity upon addition of pOPAR, which suggest adsorption of inhibitors on the {010} growth hillocks. Experiments in which pOPAR was replaced in the growth cell by a supersaturated solution showed that COM hillocks are able to fully recover to their preinhibited state. Our results suggest that recovery occurs through incorporation of the peptide into the growing crystal, rather than by, e.g., desorption from the growth face. This work provides new insights into the mechanism by which crystal growth is inhibited by adsorbants, with important implications for the design of therapeutic agents for kidney stone disease and other forms of pathological calcification.

[Targeting the substrate binding domain of polo-like kinase 1: advances in the study of PBD1 inhibitors]

Polo-box domain 1 (PBD1) is a characteristic domain of polo-like kinase 1 (PLK1), which locates in C-terminal and can influence the catalytic activity and specific subcellular locations of PLK1. At present, most PLK1 inhibitors are developed to occupy the ATP pocket or its close sites. However, this kind of PLK1 inhibitors is difficult to pursue target selectivity and may encounter cross drug resistance with other kinase inhibitors due to the conserved sequence of ATP pocket. Recently, PBD1, with aberrant specificity in sequence and structure, has attracted enormous interests as the alternative target to the discovery of corresponding inhibitors for anti-tumor drugs. The structure and function of PBD1 as well as the advances of its inhibitors are reviewed in this paper.

A phosphopeptide mimetic prodrug targeting the SH2 domain of Stat3 inhibits tumor growth and angiogenesis

Signal transducer and activator of transcription 3 (Stat3) is constitutively activated in a number of human cancers and cancer cell lines. Via its Src homology 2 (SH2) domain, Stat3 is recruited to phosphotyrosine residues on intracellular domains of cytokine and growth factor receptors, whereupon it is phosphorylated on Tyr705, dimerizes, translocates to the nucleus and is reported to participate in the expression of genes related to angiogenesis, metastasis, growth and survival. To block this process, we are developing cell-permeable, phosphatase-stable phosphopeptide mimics, targeted to the SH2 domain of Stat3, that inhibit the phosphorylation of Tyr705 of Stat3 in cultured tumor cells (Mandal et al., J. Med. Chem. 54, 3549-5463, 2011). At concentrations that inhibit tyrosine phosphorylation, these materials were not cytotoxic, similar to recent reports on JAK inhibitors. At higher concentrations, cytotoxicity was accompanied by off-target effects. We report that treatment of MDA-MB-468 human breast cancer xenografts in mice with peptidomimetic PM-73G significantly inhibited tumor growth, which was accompanied by reduction in VEGF production and microvessel density. No evidence of apoptosis or changes in the expression of the canonical genes cyclin D1 or survivin were observed. Thus selective inhibition of Stat3 Tyr705 phosphorylation may be a novel anti-angiogenesis strategy for the treatment of cancer.

Identification of hen egg yolk-derived phosvitin phosphopeptides and their effects on gene expression profiling against oxidative stress-induced Caco-2 cells

Oxidative stress is involved in the initiation and propagation of chronic intestinal pathologies. Bioactive peptides such as egg yolk-derived phosvitin phosphopeptides (PPP3) have been previously shown to reduce in vitro oxidative stress by up-regulating glutathione synthesis and antioxidant enzyme activities. Peptide and gene expression profile analysis of the PPP3 peptides can provide insight into structures involved in signal transduction mechanisms in the antioxidative stress response. The objectives of this research were to identify the PPP3 amino acid sequences before and after simulated gastrointestinal digestion and to assess the genes influenced by PPP3. Peptide sequences were analyzed using ESI Q-TOF-MS/MS, and the expression profile of 84 human oxidative stress and antioxidant defense genes were analyzed. Undigested PPP3 was composed of three main peptides: GTEPDAKTSSSSSSASSTATSSSSSSASSPNRKKPMDE (phosvitin-PV residues 4-41), NSKSSSSSSKSSSSSSRSRSSSKSSSSSSSSSSSSSSKSSSSR (PV residues 155-197), and EDDSSSSSSSSVLSKIWGRHEIYQ (PV residues 244-257) and their fragments. There was limited degradation of PPP3 after gastrointestinal digestion as deduced from the fragment sizes of digested PPP3, which ranged from 5 to 32 amino acids. These fragments were rich in contiguous serines and, in some cases, monoesterified with phosphate. Both undigested and digested PPP3 significantly reduced IL-8 secretion in H(2)O(2)-induced Caco-2 cells, indicating that antioxidative stress bioactivity is retained upon digestion. After PPP3 pretreatment, antioxidant genes associated with oxygen and reactive oxygen species (ROS) metabolism and cellular responses to chemical stimulus, oxidative stress, and ROS are up-regulated in the presence and absence of oxidative stress, thereby contributing to the prevention of intestinal oxidative stress and the promotion of gut health.

Phosphopeptides with improved cellular uptake properties as ligands for the polo-box domain of polo-like kinase 1

Human polo-like kinase 1 (Plk1) is involved in cell proliferation and overexpressed in a broad variety of different cancer types. Due to its crucial role in cancerogenesis Plk1 is a potential target for diagnostic and therapeutic applications. Peptidic ligands can specifically interact with the polo-box domain (PBD) of Plk1, a C-terminal located phosphoepitope binding motif. Recently, phosphopeptide MQSpTPL has been identified as ligand with high binding affinity. However, a radiolabeled version of this peptide showed only insufficient cellular uptake. The present study investigated peptide dimers consisting of PBD-targeting phosphopeptide MQSpTPL and a cell-penetrating peptide (CPP) moiety. The new constructs demonstrate superior uptake in different cancer cell-lines compared to the phosphopeptide alone. Furthermore, we could demonstrate binding of phosphopeptide-CPP dimers to PBD of Plk1 making the compounds interesting leads for the development of molecular probes for imaging Plk1 in cancer.

[The interferon-induced and antiviral activities of dipeptides]

Five phosphodipeptides were synthesized; two of them (H-Lys-Ala(P) and H-Pro-Ala(P) had interferon-induced activity. These dipeptides at millimolar concentrations (10(-4)) and 10(-5) M) induced the synthesis of late (40-hour) interferon in human peripheral blood lymphocytes. The dipeptides H-Lys-Ala(P) and H-Pro-Ala(P) showed a protective antiviral activity in in vivo studies when singly intraperitoneally administered to mice 2 hours before inoculation with murine encephalomyocarditis virus.

Casein phosphopeptides promote calcium uptake and modulate the differentiation pathway in human primary osteoblast-like cells

Casein phosphopeptides (CPPs), originating by in vitro and/or in vivo casein digestion, are characterized by the ability to complex and solubilize calcium ions preventing their precipitation. Previous works demonstrated that CPPs improve calcium uptake by human differentiated intestinal tumor cell lines, are able to re-mineralize carious lesions in a dental enamel, and, as components of a diet, affect bone weight and calcium content in rats. The aim of the present study was to evaluate if CPPs can directly modulate bone cells activity and mineralization. Primary human osteoblast-like cells were established in culture from trabecular bone samples obtained from waste materials during orthopedic surgery. Commercial mixtures of bovine casein phosphopeptides were used. The CPP dependent intracellular calcium rises were monitored at the single cell level through fura2-fluorescence assays. Results show that CPPs: (i) stimulate calcium uptake by primary human osteoblast-like cells; (ii) increase the expression and activity of alkaline phosphatase, a marker of human osteoblast differentiation; (iii) affect the cell proliferation rate and the apoptotic level; (iv) enhance nodule formation by human SaOS-2. Taken together these results confirm the possibility that CPPs play a role as modulator of bone cell activity, probably sustained by their ability as calcium carriers. Although the exact mechanism by which CPPs act remains not completely clarified, they can be considered as potential anabolic factors for bone tissue engineering.

A new role of phosphopeptides as bioactive peptides released during milk casein digestion in the young mammal: regulation of gastric secretion

The aim of this work was to study in vivo the effect of ingestion of phosphopeptides (PP) alone or associated with caseinomacropeptide (CMP) on gastric secretion and to elucidate some possible mechanisms involved. Seven calves fitted with a gastric pouch received either a diet based on whey proteins without PP and CMP (C diet) or C diet in which PP or PP+CMP was introduced at concentrations similar to that of PP or PP+CMP in cow milk (PP diet and PP+CMP diet, respectively). Gastric juice secretion was measured during successive periods throughout the day. Twenty-four calves were fitted with a catheter introduced in one external jugular vein for blood sample collections. The daily secretion of electrolytes decreased with the presence of PP or PP+CMP in the diet. During the day, peptide supplementation in the diet resulted in (1) short term (1st-2nd postprandial h), a decrease of secreted quantities of gastric juice, enzymes and electrolytes, (2) long term (7-24h after the morning meal), a decrease of electrolyte secretions. Intervention of gastrin, CCK, somatostatin and BPP could be probable. Globally, inhibition of gastric secretions seemed more important when PP was given in association with CMP in the diet rather than alone. CMP and PP may have short and long term action respectively over the 24h day. To our knowledge, it is the first time that phosphopeptides coming from milk casein digestion are demonstrated to inhibit gastric secretion. Therapeutic uses are suggested.

New strategies in dental caries prevention: experimental study on casein phosphopeptides

AIM

Casein phosphopeptides (CPPs) are phosphorylated casein-derived peptides produced by proteolytic digestion of alphas 1-, betas 2- and beta-casein in vitro or in the digestive tract. CPPs exhibit anti-caries activity relates to their capability to localise high levels of amorphous Ca2+ phosphate on tooth surface. Aim of this study is in vitro testing of the capability of CPPs to prevent demineralisation and promote remineralization of early enamel lesions.

MATERIALS AND METHODS

159 samples of dental enamel were divided into 3 groups, which subsequently underwent 3 different chemical treatments: the samples from group I (control group) were preserved in distilled water; the samples from group II were treated with a demineralizing solution for producing artificial caries; the samples from group III underwent the same treatment as group II, but with the addition of CPPs. The effects of these procedures were evaluated by quantitative analysis (change in weight and calcium titration) and qualitative analysis (SEM).

STATISTICS

Statistical analysis of the results was performed using ANOVA. RESULTS In presence of CPPs, acid dissolution of human enamel is reduced by over 50% in vitro. CONCLUSION Our results demonstrate that CPPs could be a valid preventive system against demineralisation of early enamel lesions.

Influence of bovine and caprine casein phosphopeptides differing in αs1-casein content in determining the absorption of calcium from bovine and caprine calcium-fortified milks in rats

Bovine and caprine milks have a similar overall gross composition, but vary considerably in the ratios of their casein components. These differences cause significant changes in the ability of caseins to bind and stabilize calcium (Ca). It might be expected that these in vitro variations, which are thought to be due to differences in casein phosphopeptides (CPP) content, could lead to in vivo differences in the digestion and absorption of Ca. To test this hypothesis three milks with different casein ratios [bovine (B), caprine high in αs1-casein (CH) and caprine low in αs1-casein (CL)] were compared with regard to Ca absorption and deposition in growing male rats. For comparison, each milk was Ca-fortified (BCa-milk, CHCa-milk, and CLCa-milk) and CPP, prepared by enzymatic hydrolysis from the respective caseins (extrinsic CPP), were added to both native and Ca-milks. The effects of added CPP (extrinsic) could then be compared with intrinsic CPP released from the gastrointestinal digestion of caseins. Total gastric Ca was sampled at 15, 30 and 60 min after ingestion. No differences were found among the native milks with or without CPP, but the Ca from all Ca-milks (regardless of casein type) appeared to clear the stomach more rapidly and this was enhanced by the extrinsic CPP. The total intestinal Ca was not different among the native milks±CPP, however, it rose more rapidly with Ca fortification, and was higher at 30 min for all CPP-Ca-milks. At 60 min the total intestinal Ca level fell for the CPP-Ca-milks while all others continued to rise. These observations suggest that the CPP in Ca-milks enhance gastric clearance and uptake from the intestine. Ca availability from BCa-milk, CHCa-milk, and CLCa-milk with and without CPP was estimated by both plasma and femur uptake of 45Ca. Ca availability was enhanced at 5 h in the plasma in each case by added CPP. In all cases CPP stimulated Ca availability in the femur, but the CL-CPP was higher (P<0·05) than that of either CH-CPP or B-CPP (extrinsic CPP). Based on the results of this study we can conclude that the addition of CPP will have beneficial effect on the absorption of Ca in growing rats from CaCO3 added to bovine and caprine milks.

Oligophosphopeptides derived from egg yolk phosvitin up-regulate gamma-glutamylcysteine synthetase and antioxidant enzymes against oxidative stress in Caco-2 cells

Previously, we have found phosphopeptides (PPPs) from hen egg yolk phosvitin possess a potent antioxidative activity against oxidative stress in human intestinal epithelial cells, Caco-2. However, their biological activity at the cellular level has not yet fully understood. The objective of this study is to evaluate the regulation of glutathione (GSH) biosynthesis-associated and antioxidant enzymes against oxidative stress in Caco-2 cells using an in vitro model. Treatment of 1 mM H2O2-induced Caco-2 cells with PPPs increased cellular GSH levels, concomitant with a significant increase in gamma-glutamylcysteine synthetase (gamma-GCS) activity and the expression of gamma-GCS heavy subunit mRNA. Furthermore, intracellular glutathione reductase, glutathione S-transferase, and catalase activities were elevated by PPPs. In addition, PPPs with high content of phosphorus showed higher induction of these enzyme activities than PPPs without phosphorus. These data indicate that oligophosphopeptides from hen egg yolk phosvitin can up-regulate cellular GSH biosynthesis-associated enzymes activity and antioxidative activities, which play key roles against tissue oxidative stress in the human intestinal epithelial cells.

Fish-bone peptide increases calcium solubility and bioavailability in ovariectomised rats

Fish-bone peptides (FBP) with a high affinity to Ca were isolated using hydroxyapatite affinity chromatography, and FBP II with a high ratio of phosphopeptide was fractionated in the range of molecular weight 5·0–1·0kDa by ultramembrane filtration.In vitrostudy elucidated that FBP II could inhibit the formation of insoluble Ca salts in neutral pH.In vivoeffects of FBP II on Ca bioavailability were further examined in the ovariectomised rat. During the experimental period, Ca retention was increased and loss of bone mineral was decreased by FBP II supplementation in ovariectomised rats. After the low-Ca diet, the FBP II diet, including both normal level of Ca and vitamin D, significantly decreased Ca loss in faeces and increased Ca retention compared with the control diet. The levels of femoral total Ca, bone mineral density, and strength were also significantly increased by the FBP II diet to levels similar to those of the casein phosphopeptide diet group (no difference;P>0·05). In the present study, the results proved the beneficial effects of fish-meal in preventing Ca deficiency due to increased Ca bioavailability by FBP intake

Casein Phosphopeptides in Oral Health - Chemistry and Clinical Applications

The casein phosphopeptides (CPP) are derived from the milk protein casein by tryptic digestion. The CPP, containing the sequence -Pse-Pse-Pse-Glu-Glu- where Pse is a phosphoseryl residue, stabilize calcium and phosphate ions in aqueous solution and make these essential nutrients bioavailable. Under alkaline conditions the calcium phosphate is present as an alkaline amorphous phase complexed by the CPP, referred to as casein phosphopeptide-amorphous calcium phosphate (CPP-ACP). The CPP-ACP complexes readily incorporate fluoride ions forming casein phosphopeptide-amorphous calcium fluoride phosphate (CPP-ACFP). A mechanism is discussed which provides a rationale for the ability of the CPP-ACP to remineralize carious lesions in dental enamel. Clinical applications of the CPP-ACP as agents in the treatment of dental caries and other hypomineralized conditions are reviewed. It is concluded that the CPP are a safe and novel carrier for calcium, phosphate and hydroxide (fluoride) ions to promote enamel remineralization with application in oral care products, dental professional products and foodstuffs.

Optimization of the cellular import of functionally active SH2-domain-interacting phosphopeptides

Phosphopeptides interacting with src homology 2 (SH2) domains can activate essential signaling enzymes in vitro. When delivered to cells, they may disrupt protein-protein interactions, thereby influencing intracellular signaling. We showed earlier that phosphopeptides corresponding to the inhibitory motif of Fcgamma receptor IIb and a motif of the Grb2-associated binder 1 adaptor protein activate SH2-containing tyrosine phosphatase 2 in vitro. To study the ex vivo effects of these peptides, we have now compared different methods for peptide delivery: (i) permeabilization of the target cells and (ii) the use of cell-permeable vectors, which are potentially able to transport biologically active compounds into B cells. We found octanoyl-Arg(8) to be an optimal carrier for the delivery of phosphopeptides to the cells. With this strategy, the function of cell-permeable SHP-2-binding phosphopeptides was analyzed. These peptides modulated the protein phosphorylation in B cells in a dose- and time-dependent manner.

Development of a substrate-based cyclic phosphopeptide inhibitor of protein phosphatase 2Cdelta, Wip1

The wild-type p53-induced phosphatase, Wip1 (PP2Cdelta or PPM1D) is a member of the protein phosphatase 2C (PP2C) family and functions as a negative regulator of the p38 MAP kinase-p53 signaling pathway. PPM1D is amplified or Wip1 is overexpressed in several human cancers, and it acts as a weak oncogene. Although inhibition of Wip1 may have therapeutic value, no specific inhibitors are available. In this study, we designed phosphopeptide inhibitors for Wip1 on the basis of its optimal substrate sequence. We found that phosphoserine-containing diphosphorylated peptides with the sequence pSXpY inhibited Wip1 phosphatase activity, whereas phosphothreonine-containing peptides with the sequence pTXpY were physiological substrates. Moreover, the X residue in the pSXpY sequence modulated inhibitor activity, and beta-branched amino acid-substituted (Ile or Val) phosphopeptides showed high inhibitory potencies. A thioether cyclic phosphopeptide c(MpSIpYVA) had a K(i) <1.0 microM. Two serine/threonine phosphatases, PP2Calpha and PP2A, were not significantly inhibited by the cyclic phosphopeptide with a nonhydrolyzable phosphoserine mimetic. A homology model of Wip1 bound to a cyclic phosphopeptide and site-directed mutagenesis helped to identify residues important for Wip1 inhibitor selectivity among the PP2C family. These results provide the first proof of concept of a specific inhibitor of the catalytic site of Wip1 and should be useful for developing potential anti-cancer drugs.

Allosteric activation of the protein kinase PDK1 with low molecular weight compounds

Organisms rely heavily on protein phosphorylation to transduce intracellular signals. The phosphorylation of a protein often induces conformational changes, which are responsible for triggering downstream cellular events. Protein kinases are themselves frequently regulated by phosphorylation. Recently, we and others proposed the molecular mechanism by which phosphorylation at a hydrophobic motif (HM) regulates the conformation and activity of many members of the AGC group of protein kinases. Here we have developed specific, low molecular weight compounds, which target the HM/PIF-pocket and have the ability to allosterically activate phosphoinositide-dependent protein kinase 1 (PDK1) by modulating the phosphorylation-dependent conformational transition. The mechanism of action of these compounds was characterized by mutagenesis of PDK1, synthesis of compound analogs, interaction-displacement studies and isothermal titration calorimetry experiments. Our results raise the possibility of developing drugs that target the AGC kinases via a novel mode of action and may inspire future rational development of compounds with the ability to modulate phosphorylation-dependent conformational transitions in other proteins.

Phosphopeptide ligands of the SHP-1 N-SH2 domain: effects on binding and stimulation of phosphatase activity

Src homology 2 (SH2)-domain-mediated interactions with phosphotyrosine (pY)-containing ligands are critical for the regulation of SHP-1 phosphatase activity. Peptides based on a binding site from receptor tyrosine kinase Ros (EGLN-pY2267-MVL, 1) have recently been shown to bind to the SHP-1 N-terminal SH2 domain (N-SH2) with considerably high affinity. In addition, two peptides cyclized between positions -1 and +2 relative to pY (EGLc[K(COCH(2)NH)pYMX]L-NH(2), 2: X=D, 3: X=E) bound to the N-SH2 domain, but did not activate the enzyme and even partially prevented stimulation of SHP-1 activity by the physiological ligand 1. These findings prompted us to further examine the determinants for optimal binding to the N-SH2 domain and for the stimulation and inhibition of SHP-1 activity. Herein we demonstrate that combining the preferred residues in both pY+1 (such as Phe or norleucine, Nle) and pY+3 (such as homophenylalanine, Hfe) leads to highly efficient activating ligands of SHP-1. Particularly in the context of the cyclic peptides 7 (EGLc[K(COCH(2)NH)pYFD]Hfe-NH(2)) and 8 (EGLc[K(COCH(2)NH)pYNleD]HfeL-NH(2)), the incorporation of these residues resulted in high-affinity ligands with a significantly increased ability to stimulate SHP-1 activity. We suggest that different binding modes (according to consensus sequences class I and II) are responsible for obtaining either activating (7 and 8) or nonactivating (2 and 3) ligands. Peptides such as 7 and 8 that bind in the extended fashion of the type II mode activate the phosphatase through complete filling of the cavity for pY+3. In contrast, peptides such as 2 and 3 that bind in the class I mode do not activate the enzyme because they allow more conformational space at pY+3. Therefore, their binding does not force the conformational transition necessary to trigger the dissociation of N-SH2 and the catalytic domain.

Targeting Stat3 in cancer therapy

Stat3 is constitutively activated in many human cancers where it functions as a critical mediator of oncogenic signaling through transcriptional activation of genes encoding apoptosis inhibitors (e.g. Bcl-x(L), Mcl-1 and survivin), cell-cycle regulators (e.g. cyclin D1 and c-Myc) and inducers of angiogenesis (e.g. vascular endothelial growth factor). This article reviews several approaches that have been pursued for targeting Stat3 in cancer therapy including antisense strategies, tyrosine kinase inhibition, decoy phosphopeptides, decoy duplex oligonucleotides and G-quartet oligodeoxynucleotides (GQ-ODN). The GQ-ODN strategy is reviewed in somewhat greater detail than the others because it includes a novel system that effectively delivers drug into cells and tissues, addresses successfully the issue of specificity of targeting Stat3 versus Stat1, and has demonstrated efficacy in vivo.

Calcium absorption is not increased by caseinophosphopeptides

BACKGROUND

One of the suggested health benefits of caseinophosphopeptides (CPPs) is their ability to enhance calcium absorption. This possibility is based on the assumption that they resist proteolysis in the upper gastrointestinal tract and maintain calcium in a soluble form at alkaline pH in the distal ileum.

OBJECTIVE

The effects of CPP-enriched preparations (containing candidate functional food ingredients) on calcium absorption from a calcium lactate drink were tested.

DESIGN

A randomized crossover trial was undertaken in 15 adults in whom we measured the absorption of calcium from a calcium lactate drink (drink A: 400 mg Ca as lactate) and 2 preparations enriched with forms of CPP (1.7 g each; drinks B and C). Both drinks B and C contained 400 mg Ca as calcium lactate plus approximately 100 mg CPP-derived calcium). Each volunteer received the 3 drinks in random order. Absorption was measured by the dual-label calcium stable-isotope technique.

RESULTS

The quantity of calcium absorbed was significantly lower from drink A (103 mg) than from drink B (117 mg; P = 0.012) or drink C (121 mg; P = 0.002), which indicated a positive effect of the CPPs. However, because the CPP preparations contributed additional calcium besides that found in the calcium lactate (drink A), fractional absorption of calcium from drink B (23%) was slightly but significantly (P = 0.015) lower than that from drink A (26%).

CONCLUSIONS

The differences in calcium absorption are unlikely to have any biological significance. CPPs are unsuitable as candidate ingredients for functional foods that are designed to deliver improved calcium nutrition.

Calcium-enriched casein phosphopeptide stimulates release of IL-6 cytokine in human epithelial intestinal cell line

Phosphopeptides derived from digests of milk casein possess bioactive properties with gastrointestinal, immunological, vasoregulatory and nutritional activities (Clare & Swaisgood, 2000; Kitts & Weiler, 2003). Products of tryptic digestion of casein, yielding caseinphosphopeptides (CPP), bind to divalent minerals such as iron and calcium by ionic interactions that involve phosphoseryl residues (Kitts & Yuan, 1992; Aìt-Oukhartar, 2000). Distribution of phosphoserine moieties varies with the individual native caseinates, and the extent of phosphorylation directly influences CPP mineral binding affinity (e.g. αs2>, αs1>β-caseins). The anionic pentapeptide (SerP-SerP-SerP-Glu-Glu) is the distinctive feature for the major fractions of casein phosphopeptides (CPP) characterized both in vitro and in vivo. Common CPP derived from tryptic digests of whole bovine casein in vitro include, β-casein-4P (1–25), αs1-casein-5P (59–79), αs2-casein-4P (1–21) and αs2-casein-4P (46–70) (Kitts & Kwong, 2004).

Antioxidative stress activity of oligophosphopeptides derived from hen egg yolk phosvitin in Caco-2 cells

The protective effects of hen egg yolk phosvitin phosphopeptides (PPPs) against hydrogen peroxide (H2O2)-induced oxidative stress were evaluated in an in vitro assay using human intestinal epithelial cells. Caco-2 cells were stimulated with 1 mM H2O2 for 6 h, and the secretion of IL-8, a proinflammatory mediator, was determined by ELISA as a biomarker of oxidative stress. The inhibition of H2O2-induced IL-8 secretion from Caco-2 cells was observed by pretreatment for 2 h with PPPs, but not with phosvitin. PPPs also suppressed the formation of malondialdehyde in H2O2-treated Caco-2 cells. Furthermore, intracellular glutathione levels and glutathione reductase activity were elevated by the addition of PPPs. The protective effects of PPPs against H2O2-induced oxidative stress were almost the same as that of glutathione, and PPPs with a high content of phosphorus exhibited higher protective activity than PPPs without phosphorus; however, phosphoserine itself did not show any significant antioxidative stress activity. These findings suggest that oligophosphopeptides from hen egg yolk phosvitin possess novel antioxidative activity against oxidative stress in intestinal epithelial cells and that phosphorus and peptide structure seem to have a key role in the activity.

Absorption of calcium from milks enriched with fructo-oligosaccharides, caseinophosphopeptides, tricalcium phosphate, and milk solids

BACKGROUND

Adequate intakes of calcium are required for optimal bone health and protection against chronic disease. Dairy products are an excellent source of calcium.

OBJECTIVE

The absorption of calcium from a range of fortified milks was measured in humans with the use of stable isotopes.

DESIGN

Fifteen volunteers participated in a randomized, controlled, double-blind crossover study. Five types of semi-skimmed (1.9% fat) milk drinks were administered with a light breakfast: standard milk (control milk); milk enriched with calcium from milk solids and tricalcium phosphate [(TCP) MSS milk]; milk enriched with calcium from concentrated milk (CON milk); milk with added fructo-oligosaccharides [(FOSs) FOS milk]; and milk with added caseinophosphopeptides [(CPPs) CPP milk]. All the milks were labeled with 42Ca as CaCl2. The MSS milk was also labeled with 44Ca as TCP. The quantity of calcium in each drink was kept the same by varying the volume given.

RESULTS

Calcium absorption did not differ significantly between the control milk and the calcium-fortified milks (MSS and CON milk) or the FOS and CPP milks. However, calcium absorption from the TCP added to the MSS milk was significantly higher than that from the control milk (27.5 +/- 7.6% and 24.5 +/- 7.3%, respectively; P = 0.003).

CONCLUSIONS

Calcium-enriched milks are a valuable source of well-absorbed calcium. Absorption of added calcium as TCP was higher than that of calcium from the control milk, but the addition of FOSs or CPPs did not significantly increase calcium absorption. Further research is needed to ascertain the cost-effectiveness and public health benefits of consuming fortified milks.

Biopeptides of milk: caseinophosphopeptides and mineral bioavailability

The biological and physiological activities of milk proteins are partially attributed to several peptides encrypted in the protein molecules. These peptides can be liberated by enzymatic digestion in vitro and in vivo. Among the biologically active molecules, phosphorylated peptides (caseinophosphopeptides, CPP) are known to exert an effect on calcium metabolism but also on other minerals. While the existing discrepancy on the potential role of CPP on calcium availability has not been clarified, the results of our previous studies showed that a purified phosphopeptide (beta(1-25)) exhibits a positive effect on iron bioavailability in vivo. Here we report the main results on the efficiency of beta(1-25) in the absorption and availability of iron as well as on the mechanism involved.

Expression and bioactivity analysis of recombinant beta-CPP dimer

Beta-casein phosphopeptide (beta-CPP) is a bioactive peptide that carries different minerals, especially calcium. To investigate more effects of beta-CPP, eukaryotic expression vector of beta-CPP dimer was constructed and transfected into Chinese hamster ovary (CHO) cells. After selection, the cell lines stably expressing beta-CPP dimer were obtained, and the recombinant product was identified and purified. Activity assay of recombinant protein indicated that the recombinant beta-CPP dimer could improve Ca(2+) uptake of sperm, stimulate the proliferation of spleen cells, and induce apoptosis of some malignant tumor cells.

Phosphorylation of peptides derived from isolated soybean protein: effects on calcium binding, solubility and influx into Caco-2 cells

Calcium homeostasis in the human body is maintained primarily via the absorption of calcium through the intestine. In order to maintain an efficient absorption of calcium with minimal calcium loss due to the formation of calcium phosphate precipitates in the small intestinal lumen, we developed a calcium-binding mediator using peptides derived from isolated soybean protein (ISP). ISP was modified via tryptic digestion and chemical phosphorylation using sodium trimetaphosphate, thereby generating soybean phosphopeptides (SPP), and this was followed by conducting a binding reaction with calcium chloride. We have established an optimized procedure and reaction conditions for maximal phosphorylation and calcium binding. Consequently, the phosphorylation of soybean peptides resulted in considerable improvement in their calcium binding activities. Next, we demonstrated that SPP was able to render calcium ions resistant to precipitate formation with inorganic phosphates, which suggested the enhancement of calcium bioavailability. Finally, we noted that the addition of calcium-bound SPP induced an increase in cytosolic calcium concentration in the intestinal Caco-2 cells, due to an influx of calcium. These findings provide a new basis by which we may assess the possibility that SPP, as a potent calcium carrier, can be utilized in the prevention of poor absorption of dietary calcium in animals.

Characterization of Casein Phosphopeptides from Fermented Milk Products

This study dealt with the potential of fermented milk products as a source of functional casein phosphopeptides (CPPs) using plain yogurts and Camembert cheeses. The CPPs were prepared by tryptic digestion from four commercially available plain yogurts (P1-P4), five Camembert cheeses (C1-C5), and raw milk. From portions with a 1-g protein content of the plain yogurts, the Camembert cheeses, and the raw milk, 171 mg, 139 mg, and 146 mg of CPPs were obtained, respectively. The Camembert cheeses retained high amounts of organic phosphorus (32 microg) per 1 mg CPPs compared to the raw milk (15 microg) and plain yogurts (16 microg). Reverse-phase high-performance liquid chromatographic analysis showed that the elution patterns and retention times of the three major peaks of CPPs from P1 and C1 were similar to those from raw milk. Moreover, CPPs from P1 and C1 showed a mitogenic effect, while CPPs from C1 showed an IgA-enhancing effect in mouse spleen cell cultures. These results suggest that fermented milk products such as plain yogurts and Camembert cheeses generate functional CPPs in the body and exert beneficial effects on the immune system.

Antioxidant mechanisms of caseinophosphopeptides and casein hydrolysates and their application in ground beef

Caseinophosphopeptides (CPP) and casein hydrolysates have been shown to bind prooxidant metals such as iron, but their effectiveness as metal chelators to inhibit lipid oxidation in foods has still not been fully investigated. Thus, the antioxidant activity of CPP and casein hydrolysates was studied in phosphatidylcholine liposome model systems. CPP (< 1.0 mg/mL) and casein hydrolysates (0.3-1.7 mg/mL) were effective inhibitors of TBARS development when oxidation was promoted by ferric/ascorbate. High amounts of CPP (> 1.0 mg/mL) were prooxidant, whereas casein hydrolysates were observed to be only antioxidative. In the presence of peroxyl radicals, casein hydrolysates were more effective scavengers than enriched CPP (3-15 mM). In cooked ground beef, TBARS formation was inhibited 75, 39, and 17% by 0.5% enriched CPP, casein hydrolysates, and low molecular weight casein hydrolysates, respectively, after 4 days of storage. The results show that CPP and casein hydrolysates are promising sources of natural antioxidants for foods.

Inhibition of the Staphylococcus aureus sortase transpeptidase SrtA by phosphinic peptidomimetics

During pathogenesis, Gram-positive bacteria utilize surface protein virulence factors such as the MSCRAMMs (microbial surface components recognizing adhesive matrix molecules) to aid the initiation and propagation of infection through adherence to host endothelial tissue and immune system evasion. These virulence-associated proteins generally contain a C-terminal LPXTG motif that becomes covalently anchored to the peptidoglycan biosynthesis intermediate lipid II. In Staphylococcus aureus, deletion of the sortase isoform SrtA results in marked reduction in virulence and infection potential, making it an important antivirulence target. Here we describe the chemical synthesis and kinetic characterization of a nonhydrolyzable phosphinic peptidomimetic inhibitor of SrtA derived from the LPXTG substrate sequence.

Inhibition of hydroxyapatite formation by osteopontin phosphopeptides

Osteopontin (OPN) is an acidic phosphoglycoprotein that is believed to function in the prevention of soft tissue calcification. In vitro studies have shown that OPN can inhibit the formation of hydroxyapatite (HA) and other biologically relevant crystal phases, and that this inhibitory activity requires phosphorylation of the protein; however, it is not known which phosphorylated residues are involved. We have synthesized peptides corresponding to four phosphoserine-containing sequences in rat OPN: OPN7-17, containing phosphoserines 10 and 11; OPN41-52, containing phosphoserines 46 and 47; OPN248-264, containing phosphoserines 250, 257 and 262; and OPN290-301, containing phosphoserines 295-297. The abilities of these peptides to inhibit de novo HA formation were determined using a constant-composition autotitration assay. All four OPN phosphopeptides caused a dose-dependent increase in nucleation lag time, but did not significantly affect subsequent formation of the crystals. However, OPN41-52 (inhibitory constant 73.5 min/microM) and OPN290-301 (72.2 min/microM) were approx. 4 times more potent inhibitors than OPN7-17 (19.7 min/microM) and OPN247-264 (16.3 min/microM). 'Scrambling' the amino acid sequence of OPN290-301 resulted in decreased potency (45.6 min/microM), whereas omission of the phosphate groups from this peptide caused a greater decrease (5.20 min/microM). These findings have identified phosphorylated sequences that are important for the ability of rat bone OPN to inhibit HA crystal formation, and suggest that negative-charge density is an important factor in this activity.

Structure-activity relationships of small phosphopeptides, inhibitors of Grb2 SH2 domain, and their prodrugs

To develop potential antitumor agents directed toward HER2/ErbB2 overexpression in cancer, we have designed inhibitors of the recognition between the phosphotyrosine of the receptor and the SH2 domain of the adaptor protein Grb2. In the first part of the paper, we report the synthesis of mimetics of the constrained (alpha-Me)phosphotyrosine residue such as (alpha-Me)-4-phosphonomethylphenylalanine (-CH2PO3H2), (alpha-Me) 4-phosphonodifluoromethylphenylalanine (-CF2PO3H2), and (alpha-Me)-4-phosphonophenylalanine (-PO3H2). The incorporation of these residues in the mAZ-pTyr-Xaa-Asn-NH2 series provided compounds with very high affinity for the Grb2 SH2 domain, in the 10(-8)-10(-9) range of Kd values. These compounds behave as potent antagonists of the Grb2-Shc interaction. Our results highlight the importance of the doubly negative charge borne by the pY + 1 amino acid in accordance with the interactions observed in the complex crystallized between mAZ-pTyr-(alphaMe)pTyr-Asn-NH2 and the Grb2 SH2 domain. mAZ-pTyr-(alphaMe)pTyr-Asn-NH2 was derivatized as the S-acetyl thioester (SATE) of the phosphotyrosine residues, and its surrogates provided prodrugs with very potent antiproliferative activity on cells overexpressing HER2/ErbB2, with ED50 values amounting to 0.1 microM. Finally a new prodrug is put forth under the form of a monobenzyl ester of phosphate group that is as active as and much easier to synthesize than SATE prodrugs. These compounds show promising activity for further testing on in vivo models.

Caseinophosphopeptides and their cell modulating potential

In the context of the EU research project FAIR-CT 98-3077, studies were carried out to investigate caseinophosphopeptides (CPP) as potential ingredients for functional food and pharmaceutical applications. CPP preparations were produced by enrichment of CPP from hydrolytic casein digests. Enzyme preparations used for hydrolysis were PTN 3.0 S, Alcalase, Bioprotease P conc, Proteinase DS. Cytochemical studies were carried out to examine the cytotoxic potential or cell modulating activities of CPP using human cancer cell lines (HL-60, Caco-2) and non-malignant polymorphonuclear leukocytes (PML) from oral cavity. PML cells isolated by magnetic cell sorting using CD-15-antibody-labelled paramagnetic beads were used for the first time for testing food-derived peptides. Cell activity was measured by formazan dye formation. Effects on enterocytic differentiation properties of Caco-2 cells were examined by transepithelial membrane resistance of Caco-2 cell monolayers and brush border associated alkaline phosphatase activity. In conclusion, (1) no deleterious cytochemical consequences (apoptotic, antiproliferative or general cytotoxic effects) were observed on presenting a range of CPP preparations to various human cell systems, indicating that these compounds can be rated harmless at a cellular level, (2) stimulation of IgG-secretion into culture supernatant of PBL points to possible immunoenhancing properties of CPP preparations.

Development of Protacs to target cancer-promoting proteins for ubiquitination and degradation

The proteome contains hundreds of proteins that in theory could be excellent therapeutic targets for the treatment of human diseases. However, many of these proteins are from functional classes that have never been validated as viable candidates for the development of small molecule inhibitors. Thus, to exploit fully the potential of the Human Genome Project to advance human medicine, there is a need to develop generic methods of inhibiting protein activity that do not rely on the target protein's function. We previously demonstrated that a normally stable protein, methionine aminopeptidase-2 or MetAP-2, could be artificially targeted to an Skp1-Cullin-F-box (SCF) ubiquitin ligase complex for ubiquitination and degradation through a chimeric bridging molecule or Protac (proteolysis targeting chimeric molecule). This Protac consisted of an SCF(beta-TRCP)-binding phosphopeptide derived from IkappaBalpha linked to ovalicin, which covalently binds MetAP-2. In this study, we employed this approach to target two different proteins, the estrogen (ER) and androgen (AR) receptors, which have been implicated in the progression of breast and prostate cancer, respectively. We show here that an estradiol-based Protac can enforce the ubiquitination and degradation of the alpha isoform of ER in vitro, and a dihydroxytestosterone-based Protac introduced into cells promotes the rapid disappearance of AR in a proteasome-dependent manner. Future improvements to this technology may yield a general approach to treat a number of human diseases, including cancer.

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.

Biofunctional peptides from milk proteins: mineral binding and cytomodulatory effects

The protein fraction of milk contains many valuable components and biologically active substances. Moreover, milk proteins are precursors of many different biologically active peptides which are inactive within the sequence of the precursor protein but can be released by enzymatic proteolysis. Many milk protein-derived peptides, such as caseinophosphopeptides, reveal multi-functional bioactivities. Caseinophosphopeptides can form soluble organophosphate salts and may function as carriers for different minerals, especially calcium. Furthermore, they have been shown to exert cytomodulatory effects. Cytomodulatory peptides inhibit cancer cell growth or they stimulate the activity of immunocompetent cells and neonatal intestinal cells, respectively. Several bioactive peptides derived from milk proteins are potential modulators of various regulatory processes in the body and thus may exert beneficial physiological effects. Caseinophosphopeptides are already produced on an industrial-scale and as a consequence these peptides have been considered for application as ingredients in both 'functional foods' and pharmaceutical preparations. Although the physiological significance as exogenous regulatory substances is not yet fully understood, both mineral binding and cytomodulatory peptides derived from bovine milk proteins are claimed to be health enhancing components that can be used to reduce the risk of disease or to enhance a certain physiological function.

Use of caseinophosphopeptides as natural antioxidants in oil-in-water emulsions

Chelators are valuable ingredients used to improve the oxidative stability of food emulsions. Caseins and casein peptides have phosphoseryl residues capable of binding transition metals. Thus, the ability of enriched caseinophosphopeptides to inhibit lipid oxidation in corn oil-in-water emulsions was investigated. Enriched caseinophosphopeptides (25 microM) inhibited the formation of lipid oxidation at both pH 3.0 and 7.0 as determined by lipid hydroperoxides and hexanal. Calcium (0-100 mM) had no influence on the antioxidant activity of the enriched caseinophosphopeptides. Casein hydrolysates were more effective inhibitors of lipid oxidation than the enriched caseinophosphopeptides at equal phosphorus content. Thus, antioxidant properties might not be uniquely attributed to chelating metals by phosphoseryl residues but also by scavenging free radicals. Overall, the observed antioxidant activity of casein hydrolysates means they could be utilized to decrease oxidative rancidity in foods.

Identification of a high-affinity phosphopeptide inhibitor of Stat3

Stat3 is a latent transcription factor that exhibits elevated activity in a variety of human cancers. To find a lead peptide for peptidomimetic drug development we synthesized and tested phosphopeptides derived from known receptor docking sites and found Y(p)LPQTV as the optimal sequence. SAR studies showed that each residue from pY to pY+3 provided binding energy.

Caseinphosphopeptides in milk and fermented milk do not affect calcium metabolism acutely in postmenopausal women

BACKGROUND

Caseinphosphopeptides (CPPs) are formed in food processing or during digestion in the gastrointestinal tract. CPPs prevent the formation of insoluble calcium salts; thus, the hypothesis is that CPPs increase the absorption of calcium.

OBJECTIVE

We examined the effect of additional caseinphosphopeptides in milk and fermented milk on acute calcium metabolism by measuring intact PTH (iPTH), ionized calcium (iCa), total calcium (Ca) and phosphate (P) from serum, and 24-hour calcium from urine (U-Ca).

METHODS

The study consisted of two separate parts, both applying a double-blind randomized crossover study with two interventions, in nine postmenopausal women. The acute effect on calcium metabolism was analysed by measuring iPTH, iCa, Ca and P from serum during the first six hours after the administration of the study milks. U-Ca was analysed 24 hours prior to the study and 0, 2, 4, 6, 12 and 24 hours after the administration of the study milks. The study included two parts, both consisting of two study days with a one-week washout period in between. In the first part the effect of control milk and CPP-enriched milk was measured. The second part evaluated the effect of fermentation by giving subjects milk or fermented milk, both enriched with CPPs.

RESULTS

In the first part of the study there were no statistically significant differences in iPTH, iCa, Ca, P or U-Ca between the groups receiving control milk compared to CPP-containing milk. There was no difference in the AUC((0-6)) of iCa and iPTH. In the second part, fermentation did not affect calcium metabolism, when results from the CPP-enriched milk and CPP-enriched fermented milk groups were compared.

CONCLUSION

One gram of caseinphosphopeptides does not affect calcium metabolism acutely in postmenopausal women.

Localization, macromolecular associations, and function of the small heat shock-related protein HSP20 in rat heart

BACKGROUND

The small heat shock proteins HSP20, HSP25, alphaB-crystallin, and myotonic dystrophy kinase binding protein (MKBP) may regulate dynamic changes in the cytoskeleton. For example, the phosphorylation of HSP20 has been associated with relaxation of vascular smooth muscle. This study examined the function of HSP20 in heart muscle.

METHODS AND RESULTS

Western blotting identified immunoreactive HSP20, alphaB-crystallin, and MKBP in rat heart homogenates. Subcellular fractionation demonstrated that HSP20, alphaB-crystallin, and MKBP were predominantly in cytosolic fractions. Chromatography with molecular sieving columns revealed that HSP20 and alphaB-crystallin were associated in an aggregate of approximately 200 kDa, and alphaB-crystallin coimmunoprecipitated with HSP20. Immunofluorescence microscopy demonstrated that the pattern of HSP20, alphaB-crystallin, and actin staining was predominantly in transverse bands. Treatment with sodium nitroprusside led to increases in the phosphorylation of HSP20, as determined with 2-dimensional immunoblots. Incubation of transiently permeabilized myocytes with phosphopeptide analogues of HSP20 led to an increase in the rate of shortening. The increased shortening rate was associated with an increase in the rate of lengthening and a more rapid decay of the calcium transient.

CONCLUSIONS

HSP20 is associated with alphaB-crystallin, possibly at the level of the actin sarcomere. Phosphorylated HSP20 increases myocyte shortening rate through increases in calcium uptake and more rapid lengthening.