Purification and characterization of positive allosteric regulatory peptides of calcium sensing receptor (CaSR) from desalted duck egg white.

HPLC-ESI-MS/MS, molecular docking simulation and in situ single-pass intestinal perfusion (SPIP) study were used to identify, select, and confirm the binding affinities between peptides identified from desalted duck egg white peptides (DPs) and calcium sensing receptor (CaSR), respectively. F3 fraction from DPs possessed superior calcium binding activity (P < 0.05), and 16 peptides enriched aromatic amino acids and other 33 peptides were identified. FAE, FNE, INSW, FDPE and NFE presented well binding affinities with CaSR in molecular docking. Additionally, SPIP results showed that NFE and INSW significantly reduced the increased PTH levels by 45.8% and 48.8%, respectively (P < 0.05), and increased calcium percent absorption, calcium absorption rate constant (Ka) and calcium effective permeability (Peff) (P < 0.05), as well as up-regulated mRNA levels of CaSR (P < 0.05). Moreover, NFE and INSW could interact with the VFT domain of CaSR, which exhibited the potential activities in regulation of CaSR.

Desalted duck egg white peptides-chitosan oligosaccharide copolymers as calcium delivery systems: Preparation, characterization and calcium release evaluation in vitro and vivo.

Two novel calcium delivery systems with high calcium-binding ability were prepared with desalted duck egg white peptides (DPs) and chitosan oligosaccharide (COS) by Amadori-type linkage and transglutaminase (TGase) induced reaction. Fourier transform infrared spectroscopy (FTIR), Zeta potential and particle size analyses were used to characterize the copolymers. These two copolymers reversed the inhibition of phytic acid (PA) in calcium transport in Caco-2 cell monolayers. PA-induced calcium deficiency mice model indicated that copolymers could reverse the side effect of PA, promote calcium bioavailability, and improve gut health. Overall, these results confirmed the potentialities of DPs-COS copolymers as nutraceuticals/functional food for oral calcium delivery to promote calcium absorption and improve gut health.

Desalted duck egg white peptides promoted osteogenesis via wnt/ß-catenin signal pathway.

Osteoporosis is a degenerative disease that threatens bone health of the elderly (especially postmenopausal women). Since osteoporosis is important to prevent, the aim of this study was to investigate the regulation of desalted duck egg white peptides (DPs) on osteoporosis. In this study, the effects of DPs on bone formation were evaluated using MC3T3-E1 cells and ovariectomized (OVX) rats. DPs significantly enhanced the preosteoblasts proliferation, differentiation, and matrix mineralization via the upregulation of wnt3a expression, low-density lipoprotein receptor-related protein-5 (LRP-5), ß-catenin, runt-related transcription factor 2 (Runx2), and osteoprotegerin (OPG) (P < 0.05). The intracellular calcium concentration was significantly elevated by DPs (P < 0.05), which is attributed to calcium influx and L-type calcium channels. Additionally, OVX rat model experiment indicated that DPs (600 mg/kg bw) had a superior effect against bone loss induced by estrogen deficiency, as it significantly declined bone turnover markers, and significantly increased biomechanical parameters (P < 0.05). Mineralized bone surfaces and bone microstructure were also obviously improved by DPs treatment. Immunohistochemical analysis showed that receptor activator of nuclear factor κ B (RANK) expression of tibia in DPs group was significantly reduced compared with the model group (P < 0.05). Our results demonstrated that DPs could enhance preosteoblasts differentiation and antiosteoporosis via wnt/ß-catenin signal pathway and several key osteogenic transcription factors such as Runx2 and OPG. PRACTICAL APPLICATION: High-value utilization of salted duck egg white, a byproduct of food industry, is worthy of in-depth study. Desalted duck egg white peptides (DPs) were proved to promote bone formation, which suggests the potentials of DPs as cofactors in osteoporosis prevention.

Desalted Duck Egg White Peptides Promote Calcium Uptake and Modulate Bone Formation in the Retinoic Acid-Induced Bone Loss Rat and Caco-2 Cell Model.

Desalted duck egg white peptides (DPs) have been proven to promote calcium uptake in Caco-2 cells and rats treated with a calcium-deficient diet. The retinoic acid-induced bone loss model was used to evaluate the effect of DPs on calcium absorption and bone formation. Three-month-old Wistar female rats were treated with 0.9% saline, DPs (800 mg/kg), or alendronate (5 mg/kg) for three weeks immediately after retinoic acid treatment (80 mg/kg) once daily for two weeks. The model group was significantly higher in serum bone alkaline phosphatase than the other three groups (p < 0.05), but lower in calcium absorption rate, serum osteocalcin, bone weight index, bone calcium content, bone mineral density, and bone max load. After treatment with DPs or alendronate, the absorption rate increased and some serum and bone indices recovered. The morphology results indicated bone tissue form were ameliorated and numbers of osteoclasts decreased after supplementation with DPs or alendronate. The in vitro study showed that the transient receptor potential vanilloid 6 (TRPV6) calcium channel was the main transport pathway of both DPs and Val-Ser-Glu-Glu peptitde (VSEE), which was identified from DPs. Our results indicated that DPs could be a promising alternative to current therapeutic agents for bone loss because of the promotion of calcium uptake and regulation of bone formation.

Desalted Duck Egg White Peptides: Promotion of Calcium Uptake and Structure Characterization.

The effects of desalted duck egg white peptides (DPs) on calcium absorption were investigated in three models: Caco-2 cell monolayer model, Caco-2 cell population model, and everted intestinal sac model. DPs were found to enhance calcium transport and may do so by acting as calcium carriers and interacting with the cell membrane to open a special Ca(2+) channel, whereas the paracellular pathway may make only a minor contribution. Structure characterization demonstrated the important roles of seven crucial peptides, such as VSEE and LYAEE, in binding calcium and promoting calcium uptake. Three synthetic peptides (VHSS, VSEE, and VHS(p)S(p)) potently induced calcium transport in Caco-2 monolayers, with VHS(p)S(p) being the most effective. This research expands the understanding of the mechanism of cellular calcium uptake by DPs as well as highlights an opportunity for recycling an otherwise discarded processing byproduct.